Broadband multimedia services and wireless services are becoming very popular. Broadband multimedia dan layanan nirkabel menjadi sangat populer. They are presently the Mereka saat ini adalah
two major drivers in the telecommunication industry. dua driver utama dalam industri telekomunikasi. It is expected that wireless mobile users' demands for Diharapkan bahwa pengguna ponsel nirkabel 'permintaan
multimedia mobile services will rapidly increase in the future. multimedia layanan mobile akan meningkat pesat di masa depan. The paper starts by presenting the evolution Makalah ini dimulai dengan menghadirkan evolusi
of wireless networks to support future integrated multimedia wireless personal services and highlight the need jaringan nirkabel untuk mendukung layanan multimedia terpadu masa depan pribadi nirkabel dan menyoroti kebutuhan
for efficient resource management. untuk pengelolaan sumber daya yang efisien. The limited resources in wireless systems, such as spectrum resource and Yang terbatas sumber daya dalam sistem nirkabel, seperti sumber daya spektrum dan
transmitter power also stress the need for efficient resource management. kekuatan pemancar juga menekankan perlunya pengelolaan sumber daya yang efisien.
Emphasis is given in the paper to the Penekanan diberikan dalam kertas ke
discussion of the channel allocation, mobility management, and bandwidth distribution problems. diskusi tentang alokasi saluran, manajemen mobilitas, dan distribusi masalah bandwidth. A review of Sebuah tinjauan
some approaches proposed in the literature to solve these problems is presented. beberapa pendekatan yang diusulkan dalam literatur untuk memecahkan masalah ini adalah disajikan. Finally, the paper discusses Akhirnya, makalah ini membahas
some of the key resource management issues that need to be addressed in the context of future wireless mobile beberapa isu pengelolaan sumber daya kunci yang perlu dibahas dalam konteks masa depan mobile wireless
networks that support multimedia communications while ensuring quality of service guarantees. jaringan yang mendukung komunikasi multimedia sambil memastikan jaminan kualitas layanan.
1. 1.
Introduction Pengantar
The confluence of users demand for personal communication systems and technological advances in Pertemuan permintaan pengguna untuk sistem komunikasi pribadi dan kemajuan teknologi di
hardware design, RF circuitry, rechargeable batteries, and spread spectrum communications has led desain hardware, RF sirkuit, baterai isi ulang, dan komunikasi spektrum tersebar telah menyebabkan
world-wide to a phenomenal explosion and deployment of mobile wireless communications. komunikasi di seluruh dunia untuk fenomenal ledakan dan penyebaran nirkabel mobile. Compared Dibandingkan
to traditional wired telecommunication networks, wireless communications have evolved at a rapid pace untuk tradisional jaringan telekomunikasi kabel, komunikasi nirkabel telah berevolusi dengan pesat
from simple first-generation analogue to second-generation digital networks. dari analog generasi pertama sederhana untuk jaringan digital generasi kedua. The last decade has par- Dekade terakhir telah par-
ticularly witnessed the preparation for future wireless personnel communication. ticularly menyaksikan persiapan personil komunikasi nirkabel masa depan. The latter aims at Yang terakhir ini bertujuan
providing communication services from any person to any person in any place at any time without any menyediakan jasa komunikasi dari orang apapun kepada orang di mana saja setiap saat tanpa
delay in any form through any medium by using one pocket-sized unit at minimum cost with acceptable keterlambatan dalam bentuk apapun melalui media apapun dengan menggunakan satu unit berukuran saku dengan biaya minimum yang dapat diterima
quality and security [1]. mutu dan keamanan [1]. The deployment of third-generation mobile wireless networks is expected for Penyebaran generasi ketiga jaringan mobile wireless diharapkan untuk
year 2001 via Universal Personal Communications systems to provide universal speech and local mul- tahun 2001 melalui sistem Universal Pribadi Komunikasi untuk memberikan pidato universal dan lokal mul-
timedia services. timedia jasa. Moreover, fourth-generation mobile wireless networks are emerging to offer capacities Selain itu, generasi keempat jaringan nirkabel bergerak yang muncul untuk menawarkan kapasitas
up to 150 Mb/s to fully mobile users in various environments [2]. hingga 150 Mb / s untuk sepenuhnya pengguna ponsel di berbagai lingkungan [2]. In such rapidly evolving environment, Dalam lingkungan yang berkembang pesat,
resource management remains an important issue in the near and distant future. pengelolaan sumber daya tetap menjadi isu penting dalam dan jauh waktu dekat.
Efficient resource management is of paramount importance due to: the rapid increase in size of the pengelolaan sumber daya yang efisien adalah sangat penting karena: peningkatan pesat dalam ukuran
wireless mobile community; its demand for high-speed multimedia communications; and the limited re- mobile wireless masyarakat; permintaan untuk komunikasi multimedia kecepatan tinggi dan keterbatasan kembali
sources. sumber. This survey article outlines some of the crucial resource management problems in wireless and Artikel survei menguraikan beberapa masalah pengelolaan sumber daya penting dalam nirkabel dan
mobile networks. selular jaringan. In particular, the paper reviews channel allocation, mobility management, and band- Secara khusus, makalah ini tinjauan alokasi saluran, manajemen mobilitas, dan band-
width distribution mechanisms. lebar mekanisme distribusi. Approaches proposed in the literature are summarized and discussed. Pendekatan yang diusulkan dalam literatur diringkas dan dibahas.
Furthermore, the requirements of multimedia applications on the surveyed resource management issues Selanjutnya, persyaratan dari aplikasi multimedia pada isu pengelolaan sumber daya yang disurvei
are highlighted. yang disorot.
The most common resource management issue faced by wireless operators is channel allocation en- Yang umum sumber daya yang paling manajemen isu yang dihadapi oleh operator nirkabel alokasi kanal en-
compassing frequency planning and channel reuse methods, as well as the optimization of network compassing perencanaan frekuensi dan penggunaan kembali metode saluran, serta optimalisasi jaringan
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capacity. kapasitas. Channel allocation is crucial as it influences the network performance. Alokasi Channel adalah penting karena mempengaruhi kinerja jaringan. Several techniques Beberapa teknik
have been proposed to improve the network capacity through efficient utilization of channel resources. telah diusulkan untuk meningkatkan kapasitas jaringan melalui penggunaan sumberdaya yang efisien saluran.
However, most of these techniques involved compromises in terms of service quality. Namun, sebagian besar teknik-teknik yang terlibat kompromi dalam hal kualitas layanan. Channel allocation Channel alokasi
techniques can typically be classified into fixed, dynamic and hybrid. teknik biasanya dapat diklasifikasikan ke dalam tetap, dinamis dan hibrida. Fixed cellular allocation strategies Tetap strategi alokasi selular
permanently assigns specific channels to specific cells. permanen memberikan saluran khusus untuk sel-sel spesifik. On the other hand, dynamic channel allocation Di sisi lain, saluran alokasi dinamis
schemes have been developed to use the channel resource more efficiently by dynamically assigning skema telah dikembangkan untuk menggunakan sumber daya kanal lebih efisien dengan dinamis menugaskan
channels to cells, on demand basis, to satisfy call requests. saluran untuk sel, atas dasar permintaan, untuk memenuhi permintaan panggilan. Hybrid channel allocation strategies com- Hybrid saluran strategi alokasi com-
bine fixed and dynamic approaches by supporting both permanent and dynamic channel allocations. tunas tetap dan dinamis pendekatan dengan mendukung kedua saluran alokasi dinamis dan permanen.
Also, variations of the fixed channel allocation technique that exploit the overlapping of adjacent cells Selain itu, variasi teknik alokasi kanal tetap yang mengeksploitasi tumpang tindih sel yang berdekatan
are used to improve the wireless system performance. digunakan untuk meningkatkan kinerja sistem nirkabel. Directed retry and selective handoff schemes are Sutradara coba dan skema handoff selektif
examples of such variations. contoh variasi tersebut.
The previous techniques are used to assign frequency channels to the wireless network cells, which Teknik yang sebelumnya digunakan untuk menentukan saluran frekuensi ke dalam sel-sel jaringan nirkabel, yang
use these channels to set up mobile calls. menggunakan saluran untuk membuat panggilan mobile. The cells have also to deal with handoffs to ensure call con- Sel-sel juga berurusan dengan handoffs untuk memastikan con panggilan
tinuity, while the allocated radio channel changes either within one cell, intra-cell handoff, or during tinuity, sedangkan saluran radio yang dialokasikan perubahan baik di dalam satu sel, sel handoff intra, atau selama
cell crossing, inter-cell handoff. sel persimpangan, handoff antar-sel. Therefore, channel allocation strategies in the event of a handoff are Oleh karena itu, strategi alokasi saluran dalam hal handoff adalah
highly desirable. sangat diinginkan. Such strategies have to be reliable in order for wireless mobile networks to provide strategi tersebut harus dapat diandalkan dalam rangka untuk jaringan mobile nirkabel untuk menyediakan
seamless communications under fluctuating radio channel behavior, and unpredictable radio resource mulus saluran komunikasi menurut fluktuasi perilaku radio, dan sumber daya radio tak terduga
conditions. kondisi. They have a significant impact on both system capacity and performance. Mereka memiliki dampak yang signifikan pada kedua kapasitas sistem dan kinerja. For example, Misalnya,
channel assignment schemes are developed for macrocell/microcell overlays in such a way to increase saluran skema tugas yang dikembangkan untuk macrocell / mikro lapisan sedemikian rupa untuk meningkatkan
overall system capacity and to reduce the number of handoffs. kapasitas sistem secara keseluruhan dan untuk mengurangi jumlah handoffs. Power control is another important issue Power control merupakan isu penting
that is strongly related to the channel assignment problem and which is used to increase the overall yang sangat terkait dengan masalah tugas dan saluran yang digunakan untuk meningkatkan keseluruhan
system capacity by reducing carrier-to-interference ratio. kapasitas sistem dengan mengurangi carrier-to interferensi rasio.
Another key issue in mobile wireless networks is mobility management, which can be categorized into Isu penting lainnya dalam jaringan nirkabel mobile adalah manajemen mobilitas, yang dapat dikategorikan
two areas: Location management procedures that enable the network to track the current location of dua daerah: prosedur manajemen Lokasi yang memungkinkan jaringan untuk melacak lokasi saat ini
every user and deliver incoming calls; Handoff processes that ensure the continuity of a mobile user setiap pengguna dan menyampaikan panggilan masuk; handoff proses yang menjamin kelangsungan pengguna mobile
connection. koneksi.
Location management schemes are essentially based on both users' mobility and incoming call rate skema manajemen Lokasi pada dasarnya didasarkan pada data user 'mobilitas baik dan tingkat panggilan masuk
characteristics. karakteristik. It involves two basic procedures: location and paging. Ini melibatkan dua prosedur dasar: lokasi dan paging. The paging process consists of Proses paging terdiri dari
sending paging messages in all cells where the mobile terminal could be located. mengirim pesan paging di semua sel di mana terminal mobile bisa ditemukan. The location pro- Lokasi pro-
cedure implements mobile terminal registration and tracking. cedure menerapkan pendaftaran terminal mobile dan pelacakan. It allows the system to keep the user’s Hal ini memungkinkan sistem untuk menjaga pengguna
location knowledge up to date and to bring the user's service profile near its location. lokasi pengetahuan up to date dan untuk membawa's layanan profil pengguna dekat lokasi. In case of an Dalam kasus
incoming call, the system is then capable to locate the users and to provide them rapidly with their panggilan masuk, sistem ini kemudian mampu untuk mencari pengguna dan untuk menyediakan mereka dengan cepat dengan mereka
customized services. disesuaikan jasa. Several location updating procedures have been proposed which can be either as Beberapa lokasi memperbarui prosedur telah diajukan yang dapat baik sebagai
manual, performed by the user when requested, or automatic, eg, geographic when the mobile enters manual, dilakukan oleh user ketika diminta, atau otomatis, misalnya, geografis saat mobile masuk
a new location area, periodic every average time period, etc. Although the previous basic procedures lokasi daerah baru, periodik setiap periode waktu rata-rata, dll Meskipun prosedur dasar sebelumnya
of network mobility, ie, location and paging, are antagonist, it is highly desirable to select location mobilitas jaringan, yaitu, lokasi dan paging, yang antagonis, sangat diinginkan untuk memilih lokasi
updating and terminal-paging policies that minimize the total cost in terms of wireless bandwidth and memperbarui dan-paging terminal kebijakan yang meminimalkan total biaya dalam hal bandwidth nirkabel dan
terminal power. terminal daya. The previous basic procedures of mobility management become more complex when Prosedur dasar sebelumnya manajemen mobilitas menjadi lebih kompleks ketika
dealing with inter-systems mobility. berurusan dengan-sistem mobilitas antar. The requirement for inter-systems mobility refers to the ability of Persyaratan untuk-sistem mobilitas antar mengacu pada kemampuan
a mobile user to make and receive calls in places other than the home system. pengguna mobile untuk membuat dan menerima panggilan di tempat lain daripada sistem rumah. Roaming between differ- Roaming antar berbeda-
ent systems may not be possible unless many critical issues are solved like location-awareness services, ent sistem mungkin tidak dapat dilakukan kecuali masalah penting banyak yang diselesaikan seperti kesadaran layanan lokasi,
roaming between similar and dissimilar systems, call detail recording, privacy and authentication. roaming antar dan berbeda sistem serupa, detail merekam panggilan, privasi dan otentikasi.
The handoff process is related to access, radio resources, and network control. Proses handoff terkait dengan akses, sumber daya radio, dan kontrol jaringan. It successively involves Hal ini berturut-turut melibatkan
a measurement phase, a handoff initiation/control phase, a channel assignment phase and a change in fase pengukuran, inisiasi handoff / kontrol fase, fase tugas saluran dan perubahan dalam
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the connection within the network involving possibly rerouting and buffering. sambungan dalam jaringan yang melibatkan kemungkinan rerouting dan buffering. Several handoff schemes Beberapa skema handoff
have been proposed, which can be classified as hard, seamless or soft according to the way the new path telah diusulkan, yang dapat digolongkan sebagai keras, mulus atau lunak menurut jalan jalan baru
is set up and the connection shifted from the actual to the new path. sudah disiapkan dan sambungan bergeser dari yang sebenarnya ke jalan baru. The handoff is already a key handoff ini sudah kunci
process in current systems and it is foreseen to gain increasing importance in third and fourth generation proses dalam sistem saat ini dan adalah diramalkan untuk mendapatkan pentingnya peningkatan dan keempat generasi ketiga
cellular systems as cells radius is decreasing, while the number of users is expected to grow dramati- sistem selular sebagai radius sel mengalami penurunan, sedangkan jumlah pengguna diperkirakan akan tumbuh secara dramatis
cally. Cally. In particular, appropriate multimedia handoff schemes are essential to overcome the additional Secara khusus, sesuai multimedia skema handoff sangat penting untuk mengatasi tambahan
complexity due to the nature of multimedia applications involving many mobile users and distributed didistribusikan kompleksitas karena sifat multimedia aplikasi mobile yang melibatkan pengguna dan
media sources/sinks. sumber media / tenggelam. The wireless mobile system has to support the reestablishment and the rerouting Sistem mobile wireless harus mendukung pembentukan kembali dan rerouting
of distributed multimedia streams in the event of a handoff. multimedia didistribusikan aliran pada saat terjadi handoff.
Broadband multimedia services and wireless services are presently the two major drivers in the Broadband multimedia dan layanan nirkabel saat ini dua pembalap utama dalam
telecommunication industry. industri telekomunikasi. Considering the explosion of the World Wide Web and multimedia-based Mengingat ledakan dari World Wide Web dan berbasis multimedia
applications, it is expected that wireless mobile user demands for integrated multimedia mobile services aplikasi, diharapkan bahwa tuntutan pengguna mobile nirkabel untuk layanan mobile multimedia terintegrasi
will continue increasing for the foreseeable future. akan terus meningkat di masa mendatang. This trend will raise the requirement for mecha- Tren ini akan meningkatkan kebutuhan untuk mekanisme-
nisms to control the access to the wireless network to avoid congestion and to ensure user quality of nal untuk mengontrol akses ke jaringan nirkabel untuk menghindari kemacetan dan untuk memastikan kualitas pengguna
service (QoS). layanan (QoS). QoS provisioning in wireless mobile networks is more challenging than in fixed networks. QoS Provisioning dalam jaringan nirkabel bergerak lebih menantang daripada di jaringan tetap.
Indeed, characteristics of wireless mobile networks such as channel fading, mobility and handoff lead Memang, karakteristik jaringan mobile nirkabel seperti fading, mobilitas saluran dan memimpin handoff
to fluctuations in network resources availability, and hence, bring more complexity to the QoS provi- terhadap fluktuasi ketersediaan sumber daya jaringan, dan karenanya, membawa kompleksitas lebih QoS penyediaan in-
sioning problem. menugaskan masalah. Issues such as traffic characterization, bandwidth partitioning, call admission control, Isu-isu seperti karakterisasi lalu lintas, partisi bandwidth, masuk kontrol panggilan,
and resource reservation are posing new challenges, and little work has been done, so far, to address dan reservasi resource yang berpose tantangan baru, dan bekerja sedikit yang telah dilakukan, sejauh ini, ke alamat
these issues in wireless mobile networks. isu-isu ini dalam jaringan mobile nirkabel. For instance, call admission control (CAC) has to be provided Sebagai contoh, kontrol panggilan masuk (CAC) harus disediakan
when the mobile station initially enters the network, but also whenever the mobile station roams in ketika stasiun bergerak awalnya memasuki jaringan, tetapi juga setiap kali menjelajah stasiun bergerak dalam
the wireless network and hands off from one cell to another. jaringan nirkabel dan tangan lepas dari satu sel yang lain. This imposes temporal constraints on the Hal ini menyebabkan kendala temporal pada
CAC mechanism as it necessitates a continuous control due to users' mobility and the dynamic nature CAC karena membutuhkan mekanisme kontrol yang terus menerus karena 'mobilitas pengguna dan sifat dinamis
and fluctuations of resources availability at a wireless network access point, typically the base station dan fluktuasi ketersediaan sumber daya pada suatu titik akses jaringan nirkabel, biasanya base station
within a cell. dalam sel. Bandwidth in a wireless network is the most precious and scarce resource of the entire Bandwidth dalam jaringan nirkabel adalah berharga dan sumber daya yang paling langka dari seluruh
communication system. sistem komunikasi. Base stations must find the best compromise between maintaining maximum Base stasiun harus menemukan kompromi terbaik antara menjaga maksimum
bandwidth utilization and reserve enough bandwidth resources so that to reduce the rate of unsuccessful pemanfaatan bandwidth dan cukup sumber daya bandwidth cadangan sehingga untuk mengurangi tingkat gagal
incoming handoffs due to insufficient available resources. tersedia sumber daya yang masuk handoffs cukup untuk jatuh tempo. Yet the requirement for QoS end-to-end in Namun persyaratan untuk QoS untuk mengakhiri-end-in
wireless mobile networks still need to be addressed. jaringan mobile nirkabel ini masih perlu diatasi.
This paper is organized into 5 main sections. Tulisan ini disusun dalam 5 bagian utama. Section 2 introduces a typical wireless mobile network Bagian 2 memperkenalkan mobile jaringan nirkabel khas
architecture, and discusses the evolution of wireless personal communications. arsitektur, dan membahas evolusi komunikasi pribadi nirkabel. Section 3 gives a brief Bagian 3 memberikan singkat
overview of existing multiple access and allocation strategies. gambaran yang ada akses jamak dan strategi alokasi. Performances of the basic channel alloca- Kinerja dari alloca saluran dasar-
tion strategies are discussed together with a number of variations of these strategies and related issues tion strategi dibahas bersama-sama dengan beberapa variasi strategi dan isu-isu terkait
such as handoff handling and power control. seperti penanganan handoff dan kontrol daya. Section 4 is dedicated to the mobility management issue Bagian 4 didedikasikan untuk masalah manajemen mobilitas
in wireless networks. dalam jaringan nirkabel. It discusses two major problems related to mobility management: location; and Ini membahas dua masalah utama yang berhubungan dengan manajemen mobilitas: lokasi; dan
handoff procedures. handoff prosedur. It also presents a survey of existing approaches to solve these problems. Hal ini juga menyajikan survei yang ada pendekatan untuk mengatasi masalah ini. Section 5 Bagian 5
addresses the requirement for bandwidth partitioning and allocation mechanisms for the provisioning alamat kebutuhan partisi bandwidth dan mekanisme alokasi untuk provisioning
of QoS in future integrated multimedia mobile communications. QoS di multimedia terintegrasi masa depan komunikasi bergerak. Section 6 concludes this survey paper. Bagian 6 menyimpulkan makalah ini survei.
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2. 2.
Wireless Mobile Networks Mobile Wireless Networks
2.1. 2.1. Architecture and Evolution Arsitektur dan Evolusi
Wireless mobile networks consist of a fixed network and a large number of mobile terminals. Jaringan nirkabel seluler terdiri dari jaringan tetap dan sejumlah besar terminal mobile. These Ini
terminals include telephones, portable computers, and other devices that exchange information with terminal termasuk telepon, komputer portabel, dan perangkat lain yang bertukar informasi dengan
remote terminals through the fixed network. remote terminal melalui jaringan tetap. The wireline network can be the telephone network in Jaringan wireline dapat jaringan telepon di
use today or the ATM network in the future. digunakan saat ini atau jaringan ATM di masa depan. In order to effectively utilize the very limited wireless Agar dapat secara efektif memanfaatkan sangat terbatas nirkabel
bandwidth to support an increasing number of mobile subscribers, current wireless mobile networks are bandwidth untuk mendukung peningkatan jumlah pelanggan mobile, saat ini jaringan mobile nirkabel
designed based on a cellular architecture. dirancang berdasarkan arsitektur selular. The network coverage area is divided into a large number of Area cakupan jaringan dibagi menjadi sejumlah besar
smaller areas called cells. daerah lebih kecil yang disebut sel. Terminals within a cell communicate with the wireline network through a base Terminal dalam sel berkomunikasi dengan jaringan wireline melalui basis
station (BS) that is installed inside the cell. stasiun (BS) yang diinstal di dalam sel. This base station serves as the network access point for all Ini base station berfungsi sebagai titik akses jaringan untuk semua
the terminals within the cell. terminal dalam sel. When a terminal enters another cell, if the new base station has enough Ketika terminal masuk sel lain, jika stasiun basis baru telah cukup
resources to accept the mobile, this later will switch to the new base station. sumber daya untuk menerima ponsel, ini nanti akan beralih ke stasiun pangkalan baru. In the other case, many Dalam kasus lain, banyak
mechanisms can be used to accommodate the user (like load balancing strategies, directed retry, power mekanisme yang dapat digunakan untuk mengakomodasi pengguna (seperti strategi load balancing, coba diarahkan, kekuasaan
assignment, auxiliary pilot...) if no other solution is possible the call is dropped. tugas, pilot bantu ...) jika tidak ada solusi lain yang mungkin panggilan dijatuhkan. A number of adjacent Sejumlah berdekatan
cells grouped together form an area and the corresponding BSs communicate through a so-called Mobile sel dikelompokkan bersama-sama membentuk suatu area dan BSS berkomunikasi yang sesuai melalui disebut Mobile sehingga
Switching Center (MSC). Switching Center (MSC). The MSC may be connected to other MSCs on the same network or to the MSC dapat dihubungkan ke MSC lainnya pada jaringan yang sama atau ke
wireline network. wireline jaringan.
A typical architecture of a cellular mobile network contains mainly the following components (see Sebuah arsitektur khas jaringan bergerak selular terutama berisi komponen-komponen berikut (lihat
Figure 1): Mobile Switching Center (MSC), Base Stations (BSs), and Mobile Stations (MSs). Gambar 1): Mobile Switching Center (MSC), base station (BSS), dan Stasiun Mobile (MSS). These Ini
components interact via wired links and air interfaces. komponen yang berinteraksi melalui link kabel dan interface udara. The MS is the physical communication equipment MS adalah peralatan komunikasi fisik
of the user (mobile service subscriber). dari pengguna (pelanggan layanan mobile). As part of the MSC also the HLR (Home Location Register) and Sebagai bagian dari MSC juga HLR (Home Location Register) dan
the VLR (Visitor Location Register) are the support databases where information on the subscribers VLR (Visitor Location Register) adalah mendukung database mana informasi mengenai pelanggan
are stored (eg, their home and current locations). disimpan (misalnya, rumah mereka dan lokasi saat ini). Two other databases are also used within the MSC: Dua database lainnya juga digunakan dalam MSC:
the Equipment Identity Register (EIR) and the Authentication Center (AuC). Identitas Peralatan Register (EIR) dan Authentication Center (AUC). The BS handles radio BS menangani radio
traffic within its cell (from and to a MS). lalu lintas di dalam sel (dari dan ke MS). A Base Station Controller (BSC), which controls a number of Sebuah Base Station Controller (BSC), yang menguasai sejumlah
BSs continually collect statistics on the number of calls, successful or unsuccessful handoffs, traffic per BSS terus mengumpulkan statistik tentang jumlah panggilan, atau tidak berhasil handoffs sukses, lalu lintas per
cell, etc. sel, dll
The future wireless personnel communications, defined as being the ultimate goal of today's com- Para personel komunikasi nirkabel masa depan, yang didefinisikan sebagai tujuan akhir dari's com hari ini-
munication engineers, will provide communication services from any person to any person in any place munication insinyur, akan menyediakan layanan komunikasi dari orang apapun kepada orang di mana saja
at any time without any delay in any form through any medium by using one pocket-sized unit at sewaktu-waktu tanpa keterlambatan dalam bentuk apapun melalui media apapun dengan menggunakan satu unit berukuran saku di
minimum cost with acceptable quality and security through the use of a personal telecommunication biaya minimum dengan kualitas yang dapat diterima dan keamanan melalui penggunaan penyelenggara telekomunikasi pribadi
reference number [1]. nomor referensi [1]. The objectives of the research and development of these systems are focused in Tujuan dari penelitian dan pengembangan sistem ini difokuskan di
three technological platforms [3]: universal mobile telecommunication system (UMTSs), mobile broad- tiga platform teknologi [3]: sistem telekomunikasi selular universal (UMTSs), mobile luas
band systems (MBSs), and wireless customer premises networks (WCPNs). band sistem (MBSs), dan) tempat pelanggan jaringan nirkabel (WCPNs.
Third-generation systems are expected to be deployed by the year 2001 via Universal Personal Com- Generasi ketiga sistem tersebut diharapkan akan digunakan pada tahun 2001 melalui Universal Personal Com-
munications systems, which will provide universal speech and local multimedia services. munications sistem, yang akan memberikan pidato universal dan lokal layanan multimedia. They are in the Mereka berada di
process of development world-wide by the ITU (International Telecommunications Union) within the proses pembangunan di seluruh dunia oleh ITU (International Telecommunication Union) dalam
framework of the International Mobile Telecommunications 2000 (IMT-2000). rangka Telekomunikasi Bergerak Internasional 2000 (IMT-2000). The European Telecom- Telecom Eropa
munications Standards Institute (ETSI) has started with Universal Mobile Telecommunication System munications Standards Institute (ETSI) telah dimulai dengan Universal Mobile Sistem Telekomunikasi
(UMTS), which will be a member of the IMT-2000 ”family of systems” within the responsibility of the (UMTS), yang akan menjadi anggota dari "sistem IMT-2000" keluarga dalam tanggung jawab
ITU. ITU.
With the emergence of unlimited networks in places of congregation such as airports, conferences and Dengan munculnya jaringan tak terbatas di tempat-tempat jemaat seperti bandara, konferensi dan
hotels, and with the increase reliance on the easy availability of multimedia information on the Internet, hotel, dan dengan peningkatan ketergantungan pada ketersediaan informasi yang mudah multimedia di Internet,
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5 5
SS7 SS7
EIR EIR
AUC AUC
HLR HLR
VLR VLR
VLR VLR
Cell Sel
BS BS
MSC MSC
MSC MSC
CO CO
CO CO
BS : Base Station BS: Base Station
BSC : Base Station Controller BSC: Base Station Controller
MSC : Mobile Switching Center MSC: Mobile Switching Center
CO : Central Office CO: Kantor Pusat
HLR : Home Location Register HLR: Home Location Register
VLR : Visitor Location Register VLR: Visitor Location Register
EIR : Equipment Identity Register EIR: Equipment Identity Register
AUC : Authentication Center AUC: Authentication Center
PSTN : Public Switched Telephone Network Jaringan Telepon: Public Switched PSTN
SS7 : Signaling System 7 Network SS7: Signalling System 7 Jaringan
BSC BSC
BSC BSC
BSC BSC
PSTN PSTN
Figure 1. Gambar 1. A typical architecture of a cellular network Sebuah arsitektur khas jaringan selular
we are surely moving toward widespread use of handheld wireless multimedia communications. kita pasti bergerak menuju meluasnya penggunaan komunikasi multimedia genggam nirkabel.
UMTS is intended to provide a wide range of mobile services to users via a range of mobile terminals UMTS adalah dimaksudkan untuk menyediakan berbagai layanan mobile pengguna melalui berbagai terminal mobile
that enable the use of the pocket telephone in almost any location, indoor or outdoor, in home, office, yang memungkinkan penggunaan telepon saku di hampir setiap lokasi, indoor atau outdoor, di rumah, kantor,
or street. atau jalan. The future access scheme will be either CDMA or one of the hybrid multiple access schemes Skema akses masa mendatang akan baik CDMA atau salah satu dari beberapa skema akses hibrida
based mainly on the combination of CDMA and TDMA/FDMA [1,4,5]. terutama berdasarkan kombinasi dari CDMA dan / TDMA FDMA [1,4,5]. Figure 2 shows three wireless Gambar 2 menunjukkan tiga nirkabel
environments; PCS/Cellular, Third generation and Wireless LANs. lingkungan; PCS / Cellular, generasi ketiga dan Wireless LAN. They are classified according to Mereka diklasifikasikan menurut
cell size and data rates supported. ukuran sel dan laju data didukung. Readers interested in a recent discussion of the evolution of wireless Pembaca yang tertarik dalam diskusi baru-baru ini dari evolusi nirkabel
communications can refer to [6]. komunikasi dapat merujuk pada [6].
Market studies show that multimedia services will have in the year 2001 a penetration of more than Pasar studi menunjukkan bahwa layanan multimedia akan memiliki pada tahun 2001 penetrasi lebih dari
60 percent in most industrialized countries. 60 persen di negara-negara industri paling. Emerging fourth generation mobile wireless systems will Emerging generasi keempat sistem nirkabel seluler akan
allow the provision of seamless services over an increasing number of distinct and heterogeneous fixed memungkinkan penyediaan jasa mulus melalui peningkatan jumlah yang berbeda dan heterogen tetap
and wireless networks operating across different frequency bands. dan jaringan nirkabel yang beroperasi di band frekuensi yang berbeda.
2.2. 2.2. Resource Management : An overall view Manajemen Sumberdaya: Suatu pandangan keseluruhan
The evolution of wireless mobile networks is tributary of the availability of more sophisticated re- Evolusi jaringan nirkabel bergerak adalah anak sungai ketersediaan lebih canggih re-
source management mechanisms capable to handle the growing number of mobile users; multimedia manajemen sumber mekanisme yang mampu untuk menangani pertumbuhan jumlah pengguna ponsel; multimedia
applications; and the limited wireless resources, eg, spectrum resource and transmitter power. aplikasi, dan sumber daya nirkabel terbatas, misalnya, sumber daya spektrum dan kekuatan pemancar. Figure Gambar
3 illustrates the most common resource management problems encountered in the wireless mobile envi- 3 menggambarkan pengelolaan sumber daya umum masalah yang paling dihadapi dalam suasana yang mobile wireless-
ronment. ronment.
Figure 3 also shows where the enumerated resource management problems must be dealt with in Gambar 3 juga menunjukkan di mana masalah-masalah pengelolaan sumber daya disebutkan harus ditangani dalam
the network. jaringan.
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Cell Size Ukuran Cell
Data rates Data tingkat
144 kbps 144 kbps
384 kbps 384 kbps
2 Mbps 2 Mbps
Vehicular Yg berkenaan dgn kendaraan
Pedestrian Pejalan kaki
Indoor Dalam
Indoor Dalam
Outdoor Outdoor
P P
C C
S S
/ /
C C
e e
ll akan
u u
l l
a sebuah
r r
10 Mbps 10 Mbps
Wireless Wireless
LAN LAN
Third generation Generasi ketiga
Figure 2. Gambar 2. Wireless environments Wireless lingkungan
Figure 3. Gambar 3. An overall view Pandangan keseluruhan
Supporting multimedia communications and advanced services, such as bit-hungry high-resolution Mendukung multimedia dan jasa komunikasi canggih, seperti bit-lapar-resolusi tinggi
multimedia ones, over wireless networks is a hard problem because of several factors: scarcity of band- multimedia yang, melalui jaringan nirkabel merupakan masalah yang sulit karena beberapa faktor: kelangkaan band-
width, time-varying error characteristics of the transmission channel, power limitations of the wireless lebar, waktu bervariasi kesalahan karakteristik saluran transmisi, keterbatasan kekuatan nirkabel
devices, and mobility of the users. perangkat, dan mobilitas dari pengguna. The provision of wireless multimedia services to mobile users with a Penyediaan layanan multimedia nirkabel untuk pengguna ponsel dengan
certain quality of service imposes stringent requirements on the design of resource management mecha- kualitas tertentu pelayanan memberlakukan persyaratan ketat pada desain mekanisme pengelolaan sumber daya
nisms. nal. Multimedia applications are often of a bursty nature and require a dynamic amount of bandwidth. aplikasi Multimedia sering bersifat bursty dan memerlukan jumlah dinamis bandwidth.
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Guaranteeing quality of service for such multimedia applications while optimizing resource utilization Menjamin kualitas pelayanan untuk aplikasi multimedia seperti saat mengoptimalkan pemanfaatan sumberdaya
necessitates specific resource management mechanisms. membutuhkan mekanisme pengelolaan sumber daya yang spesifik. Figure 4 zoom on the left area circled in Figure Gambar 4 zoom pada bagian kiri dilingkari pada Gambar
3. 3. It illustrates some of the resource management problems that may occur while the user roam the Ini menggambarkan beberapa masalah pengelolaan sumber daya yang mungkin terjadi ketika pengguna menjelajah
network. jaringan.
Figure 4. Gambar 4. Some resource management issues Beberapa isu-isu pengelolaan sumber daya
The next section reviews resource allocation schemes that encompass frequency planning, power con- Sumber daya next section review alokasi skema yang mencakup perencanaan frekuensi, con power-
trol, and channel reuse methods, as well as the optimization of network capacity. trol, dan penggunaan kembali metode saluran, serta optimalisasi kapasitas jaringan.
3. 3.
Multiple access and Channel allocation schemes Multiple akses dan skema alokasi Channel
FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA FDMA (Frekuensi Division Multiple Access), TDMA (Multiple Access Time Division) dan CDMA
(Code Division Multiple Access) are the three multiple access schemes commonly used. (Code Division Multiple Access) adalah tiga skema akses jamak umum digunakan. These tech- Ini tech-
niques are used to divide a given radio spectrum into a set of disjoint or non-interfering radio channels. tehnik yang digunakan untuk membagi suatu spektrum radio yang diberikan ke dalam satu set menguraikan atau non-mengganggu saluran radio.
FDMA divides radio channels into a range of radio frequencies and is used in the traditional analog FDMA membagi saluran radio ke berbagai frekuensi radio dan digunakan di analog tradisional
cellular system. sistem selular. With FDMA, only one subscriber is assigned to a channel at a time. Dengan FDMA, hanya satu pelanggan ditugaskan ke saluran pada suatu waktu. Other users can Lainnya pengguna dapat
access this channel only after the subscriber's call has terminated or after the original call is handed off akses saluran ini hanya setelah pelanggan telah mengakhiri panggilan atau setelah panggilan asli diserahkan
to a different channel by the system. ke saluran yang berbeda oleh sistem. TDMA is a common multiple access technique employed in digital TDMA adalah akses beberapa teknik umum yang digunakan dalam digital
cellular systems. sistem selular. It divides conventional radio channels into time slots to increase the capacity. Ini membagi saluran radio konvensional dalam slot waktu untuk meningkatkan kapasitas. As with Seperti
FDMA, no other users can access an occupied TDMA channel until the channel is vacated. FDMA, tidak ada pengguna lain dapat mengakses channel TDMA yang diduduki sampai saluran tersebut dikosongkan. CDMA CDMA
uses a radically deferent approach. menggunakan pendekatan relatif kecil radikal. It assigns each subscriber a unique code to put multiple users on Hal ini memberikan pelanggan masing-masing kode unik untuk menempatkan beberapa pengguna pada
the same wideband channel at the same time. dengan pita lebar saluran yang sama pada waktu yang sama. The codes, called ”pseudo-random code sequences”, are Kode, yang disebut "random kode urutan-pseudo", adalah
used by both the mobile station and the base station to distinguish between connections. digunakan oleh kedua stasiun bergerak dan stasiun pangkalan untuk membedakan antara koneksi. The FDMA, FDMA ini,
TDMA, and CDMA techniques can be combined in various ways to design more elaborated schemes. TDMA, dan CDMA teknik dapat dikombinasikan dalam berbagai cara untuk merancang skema diuraikan lebih lanjut.
A system such as GSM is a combination of TDMA/FDMA system achieved by dividing each frequency Sebuah sistem seperti GSM adalah kombinasi dari TDMA / FDMA sistem dicapai dengan membagi frekuensi masing-masing
band of an FDMA system into time slots. band sistem FDMA dalam slot waktu.
Both channel derivation and allocation methods will influence the network performance. Baik derivasi dan alokasi metode saluran akan mempengaruhi kinerja jaringan. In FDMA Dalam FDMA
or TDMA the resource usage is based on the channel reuse concept applied throughout the cells and atau TDMA penggunaan sumber daya yang didasarkan pada konsep penggunaan kembali saluran diterapkan di seluruh sel dan
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microcells. microcell. Channel reuse implies that distinct terminals use the same channel in different cells, with Channel kembali menyiratkan bahwa terminal yang berbeda menggunakan saluran yang sama dalam sel yang berbeda, dengan
the only constraint of meeting a given interference threshold. kendala hanya pertemuan ambang batas gangguan diberikan.
The basic prohibiting factor in radio spectrum reuse is interference caused by the environment or Faktor melarang dasar dalam menggunakan kembali spektrum radio gangguan disebabkan oleh lingkungan atau
other mobiles. ponsel lainnya. Co-channel interference caused by channel reuse is the most restraining factor on the Co-channel interferensi yang disebabkan oleh penggunaan kembali kanal merupakan faktor yang menahan paling di
overall system capacity in the wireless network. sistem secara keseluruhan kapasitas dalam jaringan nirkabel. There are a number of other problems related to the Ada sejumlah masalah lainnya yang berhubungan dengan
operation of the cellular network in a real world. pengoperasian jaringan selular di dunia nyata. Adjacent channel interference is one problem that gangguan saluran Berdekatan adalah salah satu masalah yang
occurs when there is a strong signal being emitted from a channel adjacent to the channel of concern. terjadi ketika ada sinyal kuat yang dipancarkan dari saluran berdekatan dengan saluran perhatian.
The environment in which the cellular network operates is another source of problems. Lingkungan di mana jaringan selular beroperasi adalah sumber masalah. Mountains, hills, Pegunungan, bukit,
and valleys act like huge reflectors, causing multipath problems. dan lembah-lembah bertindak seperti reflektor besar, menyebabkan masalah multipath. The atmosphere can cause propaga- Suasana dapat menyebabkan propagasi-
tion loss. tion rugi. The buildings can cause reception problems as well as logistic problems like impeding the Bangunan-bangunan dapat menyebabkan masalah penerimaan serta masalah logistik seperti menghambat
placement of base stations. penempatan BTS.
The main idea behind channel allocation algorithms is to make use of radio propagation path loss Gagasan utama di balik algoritma alokasi kanal adalah untuk menggunakan path loss propagasi radio
([7,8]) characteristics in order to minimize the carrier-to-interference ratio (CIR). ([7,8]) karakteristik untuk meminimalkan gangguan-untuk-rasio carrier (CIR). The major driving Mengemudi utama
factor in determining the number of channels with certain quality that can be used for a given wireless faktor dalam menentukan jumlah saluran dengan kualitas tertentu yang dapat digunakan untuk diberikan nirkabel
spectrum is the level of received signal quality that can be achieved in each channel. spektrum adalah tingkat kualitas sinyal yang diterima yang dapat dicapai dalam setiap saluran.
The channel allocation scheme is an essential feature in personal communications systems and im- Skema alokasi kanal merupakan fitur penting dalam sistem komunikasi pribadi dan im-
pacts the network performance. pakta kinerja jaringan.
Channel allocation schemes can be implemented in centralized or distributed fashion. skema alokasi Channel dapat diimplementasikan dalam atau didistribusikan mode terpusat. Channel al- Channel al-
location schemes can be divided into a number of different categories depending on the comparison skema lokasi dapat dibagi menjadi beberapa kategori yang berbeda tergantung pada perbandingan
basis. dasar. For example, when channel allocation algorithms are compared based on the manner in which Sebagai contoh, bila saluran algoritma alokasi dibandingkan berdasarkan cara yang
co-channels are separated, they can be divided into fixed channel allocation (FCA), dynamic channel co-saluran yang terpisah, mereka dapat dibagi menjadi alokasi saluran tetap (FCA), saluran dinamis
allocation (DCA), and hybrid channel allocation (HCA). Alokasi (DCA), dan alokasi kanal hibrida (HCA).
The diagram below shows the sub-strategies existing within the three major allocation strategies Diagram di bawah menunjukkan sub-strategi yang ada dalam tiga strategi alokasi utama
stated above. dinyatakan di atas.
Fixed Tetap
Dynamic Dinamis
Hybrid Hibrida
Simple FCA Sederhana FCA
Traffic-adaptive FCA Traffic-adaptif FCA
Scheduled Terjadwal
Predictive Prediktif
Channel Borrowing (Simple / Hybrid) Channel Pinjaman (Wikipedia / Hybrid)
Interference-adaptive DCA Interferensi-adaptif DCA
Traffic-adaptive DCA Traffic-adaptif DCA
C C
h h
a sebuah
nn nn
e e
l l
A A
ll akan
o o
ca ca
ti ti
o o
n n
S S
c c
h h
e e
m m
e e
s s
C C
e e
n n
t t
r r
a sebuah
l l
i i
z z
e e
d d
/ /
D D
i i
s s
t t
r r
i i
b b
u u
t t
e e
d d
Figure 5. Gambar 5. Variants of channel allocation strategies Varian strategi alokasi kanal
3.1. 3.1. Fixed allocation strategies Tetap strategi alokasi
In fixed channel allocation schemes [9–11] a number of channels are assigned to each cell according to Dalam skema alokasi kanal tetap [9-11] sejumlah saluran yang ditugaskan untuk setiap sel menurut
some reuse pattern, depending on the desired signal quality. beberapa pola menggunakan kembali, tergantung pada kualitas sinyal yang diinginkan. The common underlying theme in all fixed Tema pokok umum pada semua tetap
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allocation strategies is the permanent allocation of a set of channels to each cell. strategi alokasi alokasi permanen dari satu set saluran untuk setiap sel. The same set of radio Set yang sama radio
frequencies is reused by another cell at some distance away. frekuensi digunakan kembali oleh sel lain di agak jauh. Here a definite relationship is assumed Berikut hubungan pasti diasumsikan
between each channel and each cell, in accordance to co-channel reuse constraints. antara masing-masing saluran dan setiap sel, sesuai untuk menyalurkan kembali kendala-co.
Fixed allocation strategies can be classified into simple fixed, traffic-adaptive and borrowing schemes. strategi alokasi tetap dapat dikelompokkan menjadi tetap, lalu lintas-adaptif dan pinjaman skema sederhana.
3.1.1. 3.1.1. Simple fixed channel allocation Wikipedia saluran alokasi tetap
In the simple fixed channel allocation strategy, the same number of nominal channels is allocated Dalam alokasi strategi tetap saluran sederhana, jumlah nominal yang sama saluran dialokasikan
to each cell. ke sel masing-masing. So a call attempt at a cell site can only be served by unoccupied channels from the Jadi upaya panggilan di sebuah situs sel hanya dapat dilayani oleh saluran kosong dari
predetermined set of channels at that cell site (see an example in Figure 6). ditentukan set saluran di lokasi tersebut sel (lihat contoh pada Gambar 6).
C C
A A
B B
C C
E E
B B
D D
F F
G G
D D
A A
G G
B B
C C
E E
B B
G G
D D
A A
G G
F F
C C
E E
D D
A A
E E
B B
A A
G G
F F
C C
E E
D D
A A
F F
B B
G G
F F
C C
Figure 6. Gambar 6. Basic fixed allocation strategy. Dasar strategi alokasi tetap. AG denote different sorts of channels permanently assigned to cells menunjukkan jenis berbeda AG saluran permanen ditugaskan untuk sel
3.1.2. 3.1.2. Traffic-adaptive fixed channel allocation -Adaptif tetap alokasi kanal Lalu Lintas
Because traffic in cellular systems can be nonuniform with temporal and spatial fluctuations, simple Karena lalu lintas dalam sistem selular dapat seragam dengan fluktuasi temporal dan spasial, sederhana
fixed channel allocation scheme may result in poor channel utilization. skema alokasi kanal tetap dapat menyebabkan saluran pemanfaatan miskin. Non-uniform channel allocation Non-seragam alokasi channel
[12,13], static borrowing [14,15] or flexible channel allocation strategy [16] were proposed to solve this [12,13], pinjaman statis [14,15] atau strategi yang fleksibel alokasi channel [16] yang diusulkan untuk memecahkan ini
problem. masalah.
In non-uniform channel allocation the number of nominal channels allocated to each cell depends Dalam seragam saluran non-alokasi jumlah saluran nominal yang dialokasikan untuk setiap sel tergantung
on the expected traffic profile in that cell. pada profil lalu lintas yang diharapkan dalam sel itu. Thus heavily loaded cells are assigned more channels than Jadi dimuat sel sangat ditugaskan saluran lebih dari
lightly loaded ones. yang ringan dimuat. In [12] an algorithm, namely nonuniform compact pattern allocation, is proposed Dalam [12] suatu algoritma, yaitu pola alokasi kompak seragam, diusulkan
for allocating channels to cells according to the traffic distribution in each of them. untuk mengalokasikan saluran untuk sel sesuai dengan distribusi lalu lintas di masing-masing. Simulation results Hasil simulasi
in [12] show that the blocking probability using nonuniform compact pattern is always lower than the dalam [12] menunjukkan bahwa probabilitas blocking menggunakan pola seragam kompak selalu lebih rendah dari
blocking probability of uniform channel allocation. probabilitas blocking alokasi kanal seragam.
In the static borrowing schemes, unused channels from lightly loaded cells are reassigned to heavily Dalam skema pinjaman statis, saluran yang tidak terpakai dari sel dimuat ringan yang dipindahkan ke berat
loaded ones at distances higher than the minimum reuse distance. yang dimuat pada jarak yang lebih tinggi dari jarak minimum reuse. The number of nominal channels Jumlah saluran nominal
assigned in each cell may be reassigned periodically on a scheduled or predictive manner. ditugaskan di setiap sel dapat dipindahkan secara berkala atas atau prediksi secara terjadwal.
In the flexible channel allocation schemes, the set of available channels is divided into fixed and Dalam skema alokasi kanal yang fleksibel, set saluran yang tersedia dibagi menjadi tetap dan
flexible sets. fleksibel set. Each cell is assigned a set of fixed channels that typically suffices under a light traffic Setiap sel diberi satu set saluran tetap yang biasanya cukuplah bawah lampu lalu lintas
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load. beban. The flexible channels are assigned to those cells whose channels have become inadequate under Saluran fleksibel ditugaskan untuk sel-sel yang telah menjadi tidak memadai saluran bawah
increasing traffic loads. peningkatan beban lalu lintas. The assignment of these emergency channels among the cells is done in either a Penugasan ini saluran darurat di antara sel-sel dilakukan di baik
scheduled or predictive manner. dijadwalkan atau prediksi cara. In the literature proposed fixed allocation techniques differ according Dalam literatur yang diusulkan teknik alokasi tetap berbeda sesuai
to the time at which and the basis on which additional channels are assigned. ke waktu di mana dan dasar saluran tambahan yang ditugaskan.
In the predictive strategy, the traffic intensity or, equivalently, the blocking probability is constantly Dalam strategi prediksi, intensitas lalu lintas atau, sama, probabilitas blocking terus
measured at every cell site so that the reallocation of the flexible channels can be carried at any point diukur pada setiap situs sel sehingga realokasi saluran fleksibel dapat dilakukan di setiap titik
in time. pada waktunya.
If the flexible channels are assigned on a scheduled basis, it is assumed that the variations of traffic Jika saluran fleksibel ditugaskan secara dijadwalkan, diasumsikan bahwa variasi lalu lintas
are estimated a priori. diperkirakan a priori. The change in assignment of flexible channels is then made at the predetermined Perubahan tugas saluran fleksibel ini kemudian dibuat pada yang telah ditentukan
peaks of traffic change [17]. puncak perubahan lalu lintas [17].
3.1.3. 3.1.3. Channel borrowing Channel pinjaman
In channel borrowing schemes, if all permanent channels of a cell are busy, a channel is borrowed Dalam skema pinjaman saluran, jika semua saluran permanen dari sel yang sibuk, saluran radio sudah dipinjam
from a neighboring cell, only if this channel does not interfere with the ongoing calls. dari sel tetangga, hanya jika saluran ini tidak mengganggu dengan panggilan yang sedang berlangsung. When a channel is Jika saluran radio sudah
borrowed, additional cells are prohibited from using it. dipinjam, sel-sel tambahan dilarang menggunakannya. The MSC supervises the borrowing procedure, MSC mengawasi prosedur peminjaman,
favoring channels of cells with the most unoccupied channels to be borrowed. mendukung saluran sel dengan saluran kosong paling yang akan dipinjam. It keeps track of free, Ia mencatat bebas,
serving and borrowed channels and informs all the base stations (BSs) about locked channels. melayani dan meminjam saluran dan memberitahu semua stasiun dasar (BSS) tentang saluran terkunci.
The proposed channel borrowing schemes differ in the way a free channel is selected from a cell to be Peminjaman saluran skema yang diusulkan berbeda dalam cara saluran bebas dipilih dari sel yang akan
borrowed by another cell. dipinjam oleh sel lain. They can be categorized into simple and hybrid schemes. Mereka dapat dikategorikan ke dalam dan hibrida skema sederhana.
In simple channel borrowing schemes, any nominal channel in a cell can be borrowed by a neighboring Dalam skema pinjaman saluran sederhana, setiap saluran nominal dalam sel yang bisa dipinjam oleh tetangga
cell for temporary use. sel untuk digunakan sementara. Examples of these schemes are Simple Channel Borrowing [14,15,18,19], Borrow Contoh dari skema ini adalah Wikipedia Channel Pinjaman [14,15,18,19], Pinjam
from the Richest [14], Basic Algorithm [14,15], Basic Algorithm with Reassignment [15] and Borrow First dari Terkaya [14], Dasar Algoritma [14,15], Dasar Algoritma dengan pergantian [15] dan Pinjam Pertama
Available [14]. Tersedia [14]. A general conclusion reached by most performance studies of simple channel borrowing Kesimpulan umum yang dicapai oleh studi kinerja sebagian besar pinjaman saluran sederhana
schemes is that adopting a simple test for borrowing yields performance results quite comparable to skema adalah bahwa mengadopsi tes sederhana untuk menghasilkan kinerja pinjaman hasil yang cukup sebanding dengan
systems which perform an exhaustive and complex search method to find a candidate channel. sistem yang melakukan pencarian kompleks metode dan lengkap untuk menemukan saluran kandidat.
In hybrid channel borrowing strategies, the set of channels assigned to each cell is divided into Dalam strategi pinjaman saluran hibrida, set saluran ditugaskan untuk setiap sel dibagi menjadi
two groups, local channels and borrowable channels. dua kelompok, saluran lokal dan saluran borrowable. The first group is for use only in the nominally Kelompok pertama adalah untuk digunakan hanya dalam nominal
assigned cell, while the second group is allowed to be lent to neighboring cells. ditugaskan sel, sedangkan kelompok kedua adalah boleh dipinjamkan kepada sel tetangga. The ratio of the numbers Rasio jumlah
of channels in the two groups is pre-determined, depending on the estimation of the traffic conditions. saluran dalam dua kelompok adalah pra-ditentukan, tergantung pada perkiraan kondisi lalu lintas.
Examples of hybrid channel allocation schemes are: Simple Hybrid Channel Borrowing strategy [20], Contoh skema alokasi kanal hibrida: Wikipedia Hybrid Pinjaman strategi Channel [20],
Borrowing with Channel Ordering [12,18,19] and Borrowing with Directional Channel Locking [12]. Pinjaman dengan Channel Pengurutan [12,18,19] Meminjam dengan Directional Mengunci Channel [12].
Borrowing with ordering strategy elaborates on the idea of hybrid allocation by dynamically varying Pinjaman dengan memesan menguraikan strategi pada gagasan alokasi hibrida oleh berbagai dinamis
the local-to-borrowable channel ratio according to the changing traffic conditions. ke-borrowable saluran rasio-lokal sesuai dengan kondisi lalu lintas berubah. Each channel has a Setiap saluran memiliki
different adjustable probability of being borrowed and is ranked with respect to this probability. adjustable probabilitas yang berbeda yang dipinjam dan menempati peringkat sehubungan dengan probabilitas ini. This Ini
way, channels with high probability are more likely to be borrowed. jalan, saluran dengan probabilitas tinggi lebih cenderung akan dipinjam. The MSC determines and updates MSC menentukan dan update
each channel's probability of being borrowed based on the traffic conditions, by using an adaptive saluran setiap probabilitas yang dipinjam berdasarkan kondisi lalu lintas, dengan menggunakan adaptif
algorithm. algoritma.
In [18], directional channel locking is used to increase the number of channels available for borrowing. Dalam [18], mengunci saluran directional digunakan untuk meningkatkan jumlah saluran yang tersedia untuk pinjaman.
In [19], rearrangements are used when a local channel becomes available. Dalam [19], penyusunan ulang digunakan ketika saluran lokal yang tersedia.
In [21], a channel sharing method for cellular communications, called Channel Borrowing Without Dalam [21], metode berbagi saluran untuk komunikasi seluler, yang disebut Channel Pinjaman Tanpa
Locking (CBWL), is presented. Mengunci (CBWL), disajikan. In CBWL, a channel can be borrowed only from an adjacent cell. Dalam CBWL, saluran bisa dipinjam hanya dari sebuah sel yang berdekatan. The The
Borrowed channel is used with reduced transmitted power such that co-channel interference caused by saluran dipinjam digunakan dengan daya yang ditransmisikan dikurangi sehingga co-channel interferensi yang disebabkan oleh
channel borrowing is no worse than that of a non-borrowing scheme. pinjaman kanal tidak lebih buruk dari itu dari non-pinjaman skema. Borrowed channels can be accessed saluran dipinjam dapat diakses
only in part of the cell. hanya di bagian sel. The authors in [22] present CBWL with cut-off priority for calls that arise in the Para penulis di [22] CBWL hadir dengan cut-off prioritas untuk panggilan yang timbul dalam
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cell. sel. This scheme discourages excessive channel lending and borrowing at high traffic load and promotes Skema ini menghambat saluran kredit yang berlebihan dan pinjaman pada beban lalu lintas tinggi dan mempromosikan
a more uniform grade of service throughout the service area. seragam kelas lebih dari layanan di seluruh wilayah layanan.
3.2. 3.2. Dynamic allocation strategies Dynamic strategi alokasi
Fixed Channel Allocation schemes are simple, however they do not adapt to traffic conditions and Tetap Channel Alokasi skema yang sederhana, namun mereka tidak menyesuaikan diri dengan kondisi lalu lintas dan
user distribution. pengguna distribusi. In order to overcome these deficiencies, Dynamic Channel Allocation (DCA) strategies Untuk mengatasi kekurangan ini, Dynamic Channel Alokasi (DCA) strategi
[23] have been introduced. [23] telah diperkenalkan.
Dynamic channel allocation policies provide system operators with flexible planning procedure capable kebijakan saluran alokasi Dinamis menyediakan operator sistem dengan prosedur perencanaan yang fleksibel yang mampu
of adapting the allocation of resources available at base stations according to environmental conditions. beradaptasi alokasi sumber daya yang tersedia di BTS sesuai dengan kondisi lingkungan.
In DCA, cells have no channels themselves but refer all call attempts to the MSC, which manages all Dalam DCA, sel-sel tidak punya saluran sendiri, tetapi merujuk semua upaya panggilan ke MSC, yang mengelola semua
channel allocation in its region. saluran alokasi di wilayahnya. All channels are kept in a central pool and are assigned dynamically Semua saluran disimpan dalam kolam pusat dan ditugaskan secara dinamis
to radio cells as new calls arrive in the system. untuk sel radio sebagai panggilan baru tiba di sistem. After a call is completed, its channel is returned to the Setelah panggilan selesai, saluran tersebut dikembalikan ke
central pool. tengah kolam.
In general, more than one channel might be available to be assigned to a cell that requires a channel, Secara umum, lebih dari satu saluran mungkin tersedia untuk ditugaskan ke sel yang membutuhkan saluran,
the MSC must apply some strategy to select the assigned channel. MSC harus menerapkan strategi tertentu untuk memilih saluran yang ditetapkan. The MSC evaluates the cost of using MSC mengevaluasi biaya menggunakan
each candidate channel and the channel with the minimum cost, provided that certain interference setiap saluran kandidat dan saluran dengan biaya minimum, dengan ketentuan bahwa gangguan tertentu
constraints are satisfied, is selected. kendala puas, dipilih. The selection of the cost function is what differentiates dynamic Pemilihan fungsi biaya adalah apa yang membedakan dinamis
channel allocation schemes. alokasi saluran skema. The cost function depends on several criteria such as: Fungsi biaya tergantung pada beberapa kriteria seperti:
1. 1. the future blocking probability in the vicinity of the cell, masa depan probabilitas blocking di sekitar sel,
2. 2. the usage frequency of the candidate channel, frekuensi penggunaan saluran calon,
3. 3. the reuse distance, jarak kembali,
4. 4. channel occupancy distribution under current traffic conditions, hunian saluran distribusi dalam kondisi arus lalu lintas,
5. 5. radio channel measurements of individual mobile users, or saluran radio pengukuran pengguna ponsel individu, atau
6. 6. the average blocking probability of the system.
In the literature numerous adaptive resource allocation schemes have been proposed [24–26] which can
be classified into two broad categories, namely traffic-adaptive and interference-adaptive algorithms,
according to their adaptability to either traffic or interference.
The basic principle of dynamic channel allocation algorithms, both traffic and interference adaptive, is
to make radio channels available everywhere for every call by means of smart rules capable of minimizing
mutual interference among all different active calls.
Traffic-adaptive schemes are based on the a-priori knowledge of the mutual interference among cells;
so an off line process to evaluate the statistics of carrier to interference ratio is necessary. This process is Proses ini
feasible only in macrocellular environment whereas with small cells it is difficult due to deep and rapid
changes in the propagation conditions. Furthermore this off line process must be repeated if a new cell
has to be added due to network development.
DCA can be classified either as call-by-call DCA or adaptive DCA schemes. In the call-by-call DCA,
the channel assignment is based only on current channel usage conditions in the service area, while
in adaptive DCA the channel assignment is adaptively carried out using information on the previous
as well as present channel usage conditions. DCA schemes can be also divided into centralized and
distributed schemes with respect to the type of control they employ. Examples of centralized DCA are
First Available [27] and Locally Optimized Dynamic Assignment [12,18].
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In [28] a dynamic channel assignment algorithm with rearrangement for cellular mobile communication
systems is suggested. They claim that their DCA algorithm is both traffic and interference adaptive.
Simulation and analysis results show that under low traffic intensity, DCA strategies performs better
[20,27,29]. However, FCA schemes become superior at high offered traffic, especially in the case of
uniform traffic.
3.3. 3.3. Hybrid allocation strategies
DCA schemes provide flexibility and traffic adaptability. However, DCA strategies are less efficient
than FCA under high load conditions. To overcome this drawback, hybrid allocation [20] techniques
were designed by combining FCA and DCA schemes.
In HCA, the total number of channels available for service is divided into fixed and dynamic sets.
The fixed set contains a number of nominal channels that are assigned to cells as in the FCA schemes
and, in all cases, are to be preferred for use in their respective cells. The second set of channels is
shared by all users in the system to increase flexibility. When a call requires service from a cell and all
of its nominal channels are busy, a channel from the dynamic set is assigned to the call. The channel Saluran
assignment procedure from the dynamic set follows any of the DCA strategies presented in the previous
subsection. Huruf.
The ratio of fixed to dynamic channels is a significant parameter that defines the performance of the
system. sistem. In general, the ratio of fixed to dynamic channels is a function of the traffic load and would
vary over time according to offered load distribution estimations.
Another hybrid scheme is the ”fixed and dynamic channel assignment”. It is a combination of FCA
and DCA that tries to achieve the lowest blocking rate of each technique depending on traffic intensity.
In low traffic intensity the DCA scheme is used; in heavy traffic situations the FCA strategy is used.
3.4. 3.4. Exploiting overlapping cells
In a real wireless cellular network, cells are not disjoined. There is an inevitable overlap among
neighboring cells due to their non-regular shapes. The schemes presented so far do not exploit this fact.
In this section, we present schemes that take advantage of cells' overlapping.
Theoretical shape
Ideal shape
Example of actual shape
Figure 7. Gambar 7. Theoretical, ideal and actual cell coverage shapes
Eklundh [30] proposed a variation of FCA called directed retry (DR). It is a channel-sharing scheme
that exploits the overlap that exists among cells. In directed retry if a user is in an overlapping area,
and finds its first-attempt cell has no free channels, it can look for free radio channels in more than one
base if the BS can provide sufficient signal quality.
Directed retry preserves the merits of FCA and at the same time, reduces the blocking probability
of a cell by increasing its channel utilization. The improvement is accomplished at the expense of an
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increased number of handoffs and an increased level of co-channel interference. [31] stated that the use
of directed retry, is expected to cause only a minimum amount of additional load in handoff processing
and has only a minimal effect on the probability of handoff failure.
In [32], the authors present a hybrid scheme (CBWL-DR) that has the advantages of CBWL (see
section 3.1.3) and directed retry such as high channel capacity and simple channel management. The The
scheme also overcomes their disadvantages such as high system processing loads and intracell handoff.
The simulation results presented in [32] show that in comparison with FCA, the proposed scheme can
significantly improve system performance.
In [33], the authors propose a dynamic load-balancing scheme for the channel allocation problem in a
cellular mobile environment. Their load-balancing scheme migrates unused channels from underloaded
cells to an overloaded one. Detailed simulation experiments are carried out and the performance of
the proposed load balancing scheme is compared with the fixed channel assignment, simple borrowing,
and two existing strategies with load balancing (eg directed retry and CBWL), and a significant
improvement of the system behavior is noted.
Another selective handoff scheme for traffic balancing, called directed handoff (DH), based on the
concept of FCA and overlapping cells is proposed in [34]. If the traffic of a cell increases temporarily
such that all or almost all of its channels are in use, those schemes may direct some of the calls currently
in progress in the cell to attempt handoff to the appropriate adjacent cells. The schemes attempt to
redistribute calls in heavily loaded cells to lighter loaded cells. Therefore, in the case of a temporarily
traffic increase calls can be distributed to adjacent cells which share the overlapping area.
Simulation results in [34] show that selective handoff scheme improves traffic performance under the
condition of uniformly distributed traffic, and enhances the spectrum utilization in the time domain
through the handoff of mobiles in the overlapped areas of the cell. In [35] the performance of both the
DR and DH schemes was compared with the MP dynamic scheme that provides an upper bound in the
performance of DCA schemes. The conclusions reached by simulations in [35] were that both schemes
improve the efficiency of the system.
The above schemes are expected to improve system performance. This improvement depends on
the percentage of overlapping between adjacent cells. The wider the cell overlapping, the more traffic
performance is expected to improve.
3.5. 3.5. Channel Allocation in the Event of Handoff
In a cellular radio network, a cell must deal with two types of calls, new calls and handoff calls.
New calls refer to calls that originate within the cell, while handoff calls refer to ongoing calls that are
transferred from one cell to another due to the mobility of the portables. The handoff procedure has
an important effect on the performance of the system.
From the point of view of a mobile user forced termination of an ongoing call is less desirable than
blocking a new call. Consequently, it is important to limit the probability of forced call termination.
For this purpose, the system must reduce the chances of unsuccessful handoffs by reserving some chan-
nels explicitly for handoff calls. Many channel assignment strategies that allocate channels to handoff
requests more readily than new calls have been proposed in previous works [13,36–39]. Those schemes
provide improved performance at the expense of a reduction in the total admitted traffic and an increase
in the blocking probability of new calls.
It is important to study the new call and handoff blocking probabilities because these two quantities
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affect the QoS in cellular networks. The first determines the fraction of new calls that are blocked,
while the second is closely related to the fraction of admitted calls that terminate prematurely due to
dropout. A good evaluation of the measures of performance can help a system designer to make its
strategic decisions concerning cell size and frequency planing.
In [40] the authors present a model that captures the differences between new call blocking and
handoff blocking. They demonstrated that the usual assumptions made in the literature which do not
differentiate between the new call blocking probability and the handoff blocking probability may be
incorrect. salah. They found that the difference between the two kinds of blocking is particularly significant
when the users move fast or when the cells are very small.
Under Complete Sharing Policy (CSP), no distinction is made between new calls and handoff calls
for channel assignment. However, from a subscriber's perspective, abrupt termination of an ongoing
call is more disruptive than getting a busy signal. Therefore, several policies with priority to handoff
calls have been proposed [13,36,38,39,41].
One of the priority-oriented policies that is quite well known is the Cut-off Priority Policy (CPP)
[13,38,42,43] or the guard channel scheme [39]. Reserving a certain number of channels, also known as
guard channels ensures priority to handoff calls. Under CPP, a new call is accepted only if the total
number of calls in progress, regardless of their type, is below a cut-off value and a free channel is avail-
able. mampu.
While the effectiveness of a fixed number of guard channels has been demonstrated under stationary
traffic conditions, with non stationary call arrival rates in a practical system, the achieved handoff call
blocking probability may deviate significantly from the desired objective. The authors in [44] propose
a dynamic guard channel scheme, which adapts the number of guard channels in each cell according to
the current estimate of the handoff call arrival rate. The latter is derived from the current number of
ongoing calls in neighboring cells and the mobility pattern. The pursued goal is to keep the handoff call
blocking probability close to a given target while constraining the new call blocking probability under
given level.
Another policy that gives priority to handoff calls is the Threshold Priority Policy (TPP) [45]. Under Bawah
both TPP and CPP, a handoff call is accepted as long as a channel is free. However, under TPP, a new
call is accepted only if the number of new calls in progress is below a threshold value and a free channel
is available. tersedia. [46] compares TPP with CSP and CPP using major performance measures including new
call blocking probability, handoff call blocking probability, forced termination probability, and the call
non-completion probability. Several numerical experiments are done for various values of offered load
and portable mobility. The results are compared using performance metrics which mainly take into
account the trade-off between new call blocking probability and the forced termination probability. The The
numerical results show that when the offered load is high, TPP may be better alternative to CPP with
respect to the considered performance metrics.
Other prioritizing schemes allow either the handoff to be queued or new calls to be queued until new
channels are obtained in the cell. Several variations of the basic cutoff priority scheme, with queuing of
handoff requests or of new call requests, have also been discussed in the literature [39,44]. The guard
channel concept can be used in FCA or DCA schemes.
The basic queuing discipline in queuing handoff requests is first-in-first-out (FIFO). Other researchers Para peneliti lain
tried to improve the performance of the handoff queuing scheme by modifying the queuing discipline.
In [43], a non-preemptive priority queuing discipline based on a mobile's subscriber measurement was
used for queuing handoffs. A handoff request is ranked according to how close the mobile stands to,
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and possibly how fast it is approaching, the receiver level. The simulation and analysis results in [43]
indicate that the proposed scheme offers a better performance in terms of quality of service and spec-
trum efficiency.
In [47] the authors use a fuzzy logic controller to generate proper guard channels according to the
fluctuating handoff traffic pattern so as not to waste or not to lack the valuable resources.
The limited availability of radio frequency spectrum will require future wireless systems to use more
efficient and sophisticated resource allocation methods to increase network capacity and support multi-
media users. A way to achieve this goal is to combine channel assignment with power assignment and
base station assignment. The next subsections will deal with those aspects.
3.6. 3.6. Macrocell/Microcell overlays
In microcellular systems, frequent handoffs are very common. In overlaying macrocellular scheme a
cluster of microcells are grouped together and covered by a macrocell. The total wireless resource is
divided between the macrocell and all the microcells in its domain.
Figure 8. Gambar 8. An example of macrocells and microcells
Fast moving users are generally encouraged to join macrocells whereas slow users typically join mi-
crocells. This jointly reduces the number of handoffs and increases the total system capacity. Also, in Selain itu, dalam
case of congestion, if there are not enough microcell channels for handoff calls, then macrocell channels
can be used. dapat digunakan. Later, if an appropriate channel becomes available in a microcell, the macrocell channel
is released and the call is handed off to the microcell channel. Several channel assignment schemes for
macrocell/microcell overlays system have been proposed [48,49]. The macro and micro cells can use
either the same or different channel access schemes [50]. For instance, the macro cells can use CDMA
while the micro cells are using TDMA. Combining Macrocells and microcells increases the capacity of
the system without increasing the handoff rates. It is, however, achieved at the expense of an increased
complexity of the channel allocation and assignment schemes.
3.7. 3.7. Power Management and Control
The radio connection comprises three dimensions: the allocated channel (channel allocation), allo-
cated power (power assignment procedure), and allocated location (base-station assignment procedure).
The three problems are interrelated, and can be considered jointly.
Power control schemes play an important role in spectrum and resource allocation in cellular net-
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works. bekerja. Since the CIR (Carrier-to-Interference Ratio) at a wireless terminal is directly proportional to
the power level of the desired signal and inversely proportional to the sum of the power of co-channel
interferers, one can use power control schemes to achieve the required CIR level. By increasing the
transmitted power of the desired signal and/or decreasing the power level of interfering signals the CIR
level can be accommodated.
Power control schemes try to reduce the overall CIR in the system by measuring the received power
and increasing (or decreasing) the transmitted power in order to maximize the minimum CIR in a given
channel allocation of the system. This can result in a dramatic increase of overall system capacity
measured in terms of the number of mobiles that can be supported.
Power control can be done in either centralized or distributed fashion. Centralized power control
schemes require a central controller that has complete knowledge of all radio links and their power
levels in the system [51,52]. In the distributed approach [53,54], each wireless terminal adjusts its trans-
mitter's power level based on local measurements.
In [55] the authors propose a joint resource allocation algorithm that makes the channel, base station
and power assignment attempting to minimize the number of channels needed to provide each user in
the system with an acceptable radio connection. The algorithm operates in a wireless network with
an arbitrary number of base stations and mobiles. It is compared, in terms of the achievable traffic
capacity, with some bounds on the performance of the maximum packing, clique packing, and reuse
partitioning techniques. The latter bounds are usually used as benchmarks on the capacity that can be
achieved by any traffic-adaptive dynamic channel assignment strategy, where the quality is guaranteed
by the reuse distance. The performance results confirm the improvement expected from the integration
of the channel, base station and power assignments.
The channel assignment problem in cellular networks (when the powers and base stations are pre-
assigned and fixed) has been shown to be equivalent to a generalized graph-coloring problem [17,27],
which is known to be NP complete. Since no efficient algorithm that solves this problem exists, many
heuristic channel assignment algorithms with varying complexity have been proposed and evaluated in
the literature. literatur.
Existing studies on the channel assignment problem mostly focus on developing efficient heuristic
algorithms [56,57], owing to its NP-completeness [58]. The solutions thereby generated are often less
than satisfactory and usually there is no way of determining how far they are from the optimum [59].
Studies, as [60], on deriving lower bounds on the numbers of frequencies required for frequency assign-
ment problem's have thus arisen out of their capacity of indirectly checking the quality of the assignment
solutions at hand.
Power management is a more general problem than power control. One objective of current research
is to develop efficient and low power consumption algorithms and protocols. Power management in
wireless mobile networks is expected to gain more importance when multimedia applications will be
deployed due to the extra processing needed such as data encoding/decoding and transcoding.
3.8. 3.8. Code assignment
As wireless communications evolve towards third generation, wideband CDMA (W-CDMA) appears
to be the de facto network access scheme. This sub-section overviews code spreading and code assign-
ment schemes adopted within UMTS/IMT-2000 framework.
CDMA techniques allow many users to transmit simultaneously in the same band without sub-
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stantial interference by using approximately orthogonal spread-spectrum waveforms. A CDMA spread
spectrum signal is created by modulating the radio frequency signal with a spreading sequence known as
a pseudo-noise digital signal. The receiver uses a locally generated replica pseudo noise code to separate
the desired coded information from all possible signals.
If the spreading signals are orthogonal then the interference of any other signal on the wanted signal
is theoretically zero after despreadings. Some good examples of orthogonal codes are Hamadard/Walsh
codes [61,62]. However, when these codes are misaligned, the cross-correlation of these codes will be
non-zero, that is, they are no longer orthogonal.
For CDMA to eliminate the other channels' interference, the local despreading code is required to
be accurately aligned with the arriving wanted code. This is a costly requirement for practical systems
where the communication terminals are constantly moving.
For this reason non-orthogonal codes are used. However, to reduce the interference from other chan-
nels to a minimum, the cross-correlation between any pair of codes of the code set at any time shift
should be small. Examples of non-orthogonal codes are Gold codes and Kasami codes [62–64].
UMTS/IMT-2000 adopts multiple spreading or two-layered spreading in such a way that whenever
synchronization between channels can be easily maintained orthogonal codes are used, and when asyn-
chronous transmission is favored in terms of system implementation and deployment, non-orthogonal
codes are used.
Multiple spreading is realized in the following way: all the channels originated from a single transmit-
ter can be readily synchronized; therefore orthogonal codes are used to separate these channels. These Ini
channels are then linearly combined and multiplied by a transmitter-specific non-orthogonal code.
Since CDMA uses codes instead of frequency bands or time slots to distinguish between multiple
wireless conversations, code assignment is an important issue.
Almost all the channel allocation schemes presented in the above sub-sections can be applied to do
code allocation taking into consideration that two users can not use the same code, at least in the same
cell, and that the codes are not infinite, so spatial reuse of codes is utilized.
The provision of wireless multimedia applications to mobile users has an impact on channel access
and allocation schemes. Indeed, multimedia applications such as a video application often require a dy-
namic amount of bandwidth. For example, compressed video sources produce a variable bit rate (VBR)
traffic with a high degree of burstiness. Also a multimedia user can ask for more than one channel,
which further complicates the channel assignment problem. Guaranteeing quality of service for such
VBR applications over wireless links necessitates specific resource management mechanisms.
4. 4.
Mobility Management
Mobility Management is a key issue in wireless mobile networks. It encompasses the functionalities
that enable the network to track the current location of every user and deliver incoming calls. Another Lain
key functionality that is closely related to mobility management is the handling of handoffs in order to
ensure the continuity of a mobile user connection.
4.1. 4.1. Location Management
When an incoming call is received for a mobile station, the call has to be routed to the cell in which
the mobile is located so it can be set-up. One way to locate the mobile would be to transmit a calling
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message (page) for the mobile on every cell site in the network (as was the case for the first generation
wireless networks such as the North American Advanced Mobile Phone Service (AMPS) [9]). Clearly Jelas
with several hundreds of cells and many thousands of mobiles, the required signaling capacity would
be too high. terlalu tinggi. Because of the radio bandwidth inefficiency of such a policy, second generation networks,
such as Pan-European Digital Cellular (GSM) [65] and North American Digital Cellular [66], employ
a different approach. For example, the GSM [67] and IS-41 [68] cellular standards use Home Location
Registers (HLR) and Visitor Location Registers (VLR) to implement mobile registration and tracking.
Moreover, the cellular network is usually split up into a number of location areas in order to further
reduce the signaling traffic.
The network location areas are either fixed or dynamically determined. In fixed-location area schemes,
the mapping between location areas and cells is fixed (based on traffic and mobility patterns). In dy-
namic or adaptive location tracking schemes, the mapping of location areas to cells is adjusted according
to terminal movement, as well as in response to other events such as call pattern changes or system
failures. kegagalan.
It is desirable to select location-updating and terminal-paging policies that can minimize the total
cost (wireless bandwidth and terminal power). Registrations are only performed in the border cells of
a location area. When location areas are large the location update traffic is reduced but the paging
message load is increased. Inversely small location areas save on paging cost at the expense of increased
location update traffic. A method for computing the optimal location area size given the respective
costs for location update and terminal paging is introduced in [69].
The following subsection enumerates different mobile users location update methods. Since the geo-
graphic location update method is used in most evolving second-generation cellular systems, it will be
studied in section 4.1.2.
4.1.1. 4.1.1. Mobile users location update methods
There are four basic location update methods:
1. 1. Geographic: A user updates the system when it enters a new location area.
2. 2. Timer: The user updates the location periodically every given average time period.
3. 3. Stimulus: The user performs a location update only when requested.
4. 4. ON/OFF: A location update occurs only after the mobile powers on and before it powers down.
Three other sophisticated location update schemes are studied in [70]: Time-based, movement-based
and distance-based. Under these three schemes, location updates are performed based respectively,
on the time elapsed, the number of movements performed, and the distance traveled, since the last
location update. A distance based location update scheme is introduced in [71] where an iterative
algorithm generates the optimal threshold distance resulting in a minimum cost. However, the number
of iterations required for the algorithm to converge varies widely depending on the considered mobility
and call arrival probabilities. The time required to locate a mobile terminal is directly proportional
to the distance traveled by the mobile terminal since its last location update. A dynamic location
update mechanism is introduced in [72] where the location update time based on data obtained on-line
is dynamically determined. In [73], paging subject to delay constraints is considered. In [74], a location
management scheme that combines a distance based location update mechanism with a paging scheme
that guarantees a pre-defined maximum delay requirement is presented.
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4.1.2. 4.1.2. Geographic-based location update of mobile users
In this type of location update methods, the cellular network is split up into a number of location
areas, each with its own area identity number. This number is then transmitted regularly from all base
stations in the area as part of the system's control information. A mobile station when not engaged in
a call, will lock onto the control channel of the nearest base station upon switching on and, as it moves
in the network, will from time to time select a new base station to lock onto. The mobile will check the
area identity number transmitted by the base station, and when it detects a change indicating that it
has moved to a new location area, it will automatically inform the network of its new location by means
of a signaling exchange with the base station. This way, the network can keep a record (registration) of
the current location area of each mobile, and hence will call the mobile (find) within that area only.
Several studies [75–77] indicated that the signaling traffic due to find and registration operations is
significant. signifikan. When the frequency of incoming calls is high compared to terminal mobility (ie, the rate
that a terminal moves to new registration areas), a location cache scheme [78,79] has been proposed to
reduce the traffic (ie, to reduce the number of find operations). When the call frequency is low compared
to terminal mobility, the number of registration operations increase, which significantly degrades the
performance of the location cache scheme. Several algorithms such as the pointer forwarding algorithm
[77,80] and the alternative location algorithm [81] have been proposed to reduce the registration cost.
Xie and Goodman [82] propose the use of a gateway VLR to limit mobility management traffic to the
metropolitan area where a mobile currently resides.
While the HLR/VLR concept reduces the signaling traffic on the radio link over first generation
approaches, numerous studies [75,76] indicate that it incurs a tremendous increase of signaling traffic in
the fixed network. [76] estimates that around 50% of the time people don't have their phones on. Since Sejak
at least 50% of all mobile-terminated call attempts fail there is inefficiency in the HLR/VLR based
approach. pendekatan. As an alternative, the reverse virtual call set-up (RVC) algorithm is proposed in [83]. In this Dalam hal ini
algorithm a mobile-terminated call is routed from the fixed phone to a switch with the capability to
query the HLR. However, the switch does not set-up the call in the usual manner, but instead, waits
for a signal to arrive from the called party and then bridges the two connections. Bridging functionality
has already been implemented in a public cordless telephone system trial [84]. But it is necessary to
consider the billing implications of such a strategy. The authors claimed that the fixed network signaling
load and the call set-up delay under RVC are reduced except when the location area is smaller than
a VLR area, which is unlikely to happen as they propose the use of an overlaid paging in conjunction
with RVC.
The locality of reference patterns is exploited in [85]. The notion of working set for mobile hosts is
introduced. diperkenalkan. Nodes in a mobile host's working set communicate with the mobile host more frequently
than nodes that are not in the working set. A location management scheme has been described in [85]
in which a mobile host can dynamically determine its working set depending on the call-to-mobility
ratio between network node and mobile host pairs. Nodes in the working set are informed about the
location update when a mobile host moves, while other nodes have to search for the mobile host when
they wish to communicate with it.
In [86], some base stations are designated as reporting centers (similar to location servers). Location Lokasi
update is done when a mobile host moves into the cells corresponding to the reporting centers. When Ketika
a mobile host has to be located, it is searched for in vicinity of the reporting center at which the last
update was made. However, an issue that needs to be addressed is how such a reporting center is
determined. One simple solution would be to probe all reporting centers to determine the one with the
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latest update. However, this imposes high communication overhead on the fixed network.
4.2. 4.2. Multimedia handoff schemes
With the spectacular growth of mobile telephony and the success of second-generation mobile cellular
systems paralleled by the staggering growth of the Internet, mobile multimedia services are expected to
be in high demand by mobile wireless users on a global scale. It is anticipated that the traffic in next
generation high-speed wireless networks will be mostly generated by personal multimedia applications.
Examples of such applications are: fax, video-on-demand, news-on-demand, WWW browsing, and trav-
eler information systems. Therefore, next generation wireless networks are expected to provide adequate
support for multimedia services and support user mobility with extended geographical coverage.
Multimedia applications can require a dynamic amount of bandwidth. To guarantee quality of service
for such bandwidth-greedy applications when used over a wireless link, some of the traditional schemes
used for supporting voice services should be reviewed and specific resource management solutions must
be proposed. Handoff is a time-critical feature in wireless mobile communications that has to be ad-
dressed to provide seamless multimedia communications under changing radio resource conditions.
Handoff ensures the continuity of a call, or any relationship between the mobile terminal and the
network, while the dedicated radio resource changes within one cell (intra-cell handoff) or during cell
crossing (inter-cell handoff), within or outside of a switch control area. Handoff is related to access,
radio resources, and network control. It has a significant impact on system capacity and performance.
Effective and reliable handoff is highly desirable from the subscriber's point of view. The handoff
is already a key process in current systems and it is foreseen to gain increasing importance in third
and fourth generation cellular systems as cells radius is going to decrease and the number of users is
expected to grow dramatically.
A prevalent underlying theme is the techniques used to control the handoff of users as they move
between shrinking cells, at greater speeds, and with stricter requirements on both the QoS delivered to
the user and the operational costs associated with a connection. Minimizing the expected number of
handoffs minimizes the switching load. Another concern is delay. If handoff does not occur quickly, the
QoS may degenerate below an acceptable level. Combining macrocells and microcells further compli-
cates the control of a handoff.
A handoff process is either mobile station-triggered or network-triggered. Basically, it involves four
successive phases:
1. 1. measurement;
2. 2. handoff initiation/control;
3. 3. channel assignment; and
4. 4. network connection reconfiguration possibly involving rerouting and buffering.
Measurements concern mainly the signal strength and allow deciding the initiation of a handoff. Among Antara
the handoff initiation approaches analyzed in the literature, there are:
1. 1. Relative signal strength: chooses the strongest received base station at all times.
2. 2. Relative signal strength with threshold: initiates a handoff only if the current signal is sufficiently
weak (less than a threshold) and the other is the stronger of the two.
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3. 3. Relative signal strength with hysteresis: initiates a handoff only if the new base station is sufficiently
stronger (by a hysteresis margin) than the current one.
4. 4. Relative signal strength with hysteresis and threshold: initiates a handoff only if the current signal
level drops below a threshold and the target BS is stronger than the current one by a given hysteresis
margin. margin.
5. 5. Prediction techniques that base the handoff decision on the expected future value of the received
signal strength.
Huang [87] introduces a factor called glue-point, in the design of a handoff protocol in order to keep
data dependency and presentation continuity. The glue-point delimits the boundary of two consecutive
media units. Using the concept of glue-point, handoff can occur at glue-points but no where else.
Tabbane [88] proposes three target cell decision algorithms for handoffs, which are based on the com-
bination of three criteria. The first criterion is the path loss criterion [89] that is used in GSM to choose
the target BS. The second criterion is the capacity criterion, which allows to take into account resource
availability. ketersediaan. The last criterion used when selecting the target cell is the cell type criterion. Both the Baik
type of the current cell and the type of target cell (pico, micro or macro cell) are taken into account
during the decision making process.
Channel assignment in the event of a handoff has been introduced in section 3 as part of the review
of existing channel allocation schemes.
The last phase of the handoff process dealing with network connection reconfiguration is described
in the following together with a classification of handoff schemes with respect to connection reconfigu-
ration in both connection-oriented and connectionless networks. Wireless Asynchronous Transfer Mode
(WATM) based networks are particularly emphasized for the potential they offer to support future mo-
bile multimedia communications.
The handoff process can be classified according to the way the new path is set up and the connection
shifted from the actual to the new path. Figure 9, Figure 10 and Figure 11 illustrate the three main
classes of handoff, namely hard handoff, seamless handoff, and soft handoff.
Before Sebelum
During Selama
After Setelah
Figure 9. Gambar 9. Hard handoff
In hard handoff, the mobile terminal has to change radio channel (frequency) to the new path with
possibly a short interruption of the connection in progress. The new path is constructed in advance
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through the network in such a way that interruption is as short as possible. Switching to the new path
and rerouting of the carried information are performed simultaneously.
Before Sebelum
During Selama
After Setelah
Figure 10. Gambar 10. Seamless Handoff
In a seamless handoff process, the new path is established in parallel with the old one and the mobile
terminal transmits the information flow on both paths. The active path remains the old one for a while.
Then, the new stream is activated (through a switching action in the network), the old one is stopped
and the old links are released.
Before Sebelum
During Selama
After Setelah
Figure 11. Gambar 11. Soft handoff
In a soft handoff there are two active paths and two corresponding streams, at least for a while. The The
asynchronous behavior of the handoff process makes time a non-critical element. The mobile terminal
is simultaneously connected with two (or more) base stations and both streams are considered on the
mobile and network side to recover a single information flow. CDMA based wireless networks are ex-
amples of systems using soft handoff.
Hierarchical and low-latency handoff schemes have been proposed for connection-oriented networks
such as WATM networks. One of the main objectives of WATM is to support multimedia communica-
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23 23
tions characterized by varying connection bandwidth and Quality of Service (QoS) requirements. Some Beberapa
connections mainly require low delay and delay variation (eg, video traffic) while others require very
low cell loss (eg, data traffic). The 'goodness' of a handoff impacts on the end-to-end QoS that can be
provided to mobile users.
Handoff in a Wireless ATM network requires changes in virtual connections. Several handoff schemes
have been proposed, such as connection extension [90], full establishment [91], partial re-establishment
[91] and multicast establishment [91,92].
The full establishment approach requires the setup of a completely new connection between the end
users. pengguna. Figure 12 represents the path evolution for a mobile terminal that moves within three cells in a
network adopting the full establishment approach.
BS1
BS2
BS3
Remote terminal
Original path
New connection for BS2
New connection for BS3
Figure 12. Gambar 12. path evolution example adopting full establishment approach
When the handoff occurs, the connection extension scheme extends the path between the users by
adding one hop that provides the connection from the old base station to the new base station through
the fixed network. Figure 13 shows the path modifications needed to follow the roaming terminal.
The multicast establishment approach preallocates resources in the network portion surrounding the
cell where the user is located. When a new mobile connection is established, a set of virtual connections,
named a virtual connection tree, is created. The latter reaches all BSs managing the cells toward which
the mobile terminal might move in the future. Thus, the mobile user can freely roam in the area covered
by the tree without invoking the network call admission control during handoff. The allocation of the
virtual connection tree may be static [93] or dynamic [94] during the connection lifetime. Figure 14 Gambar 14
shows a multicast establishment, assuming that the mobile terminal roams through three cells.
Acampora et al. [93] propose building a virtual connection tree covering base stations in a local
area, with virtual circuits pre-established from the root of the tree to each base station. In this case, a Dalam kasus ini,
handoff only involves the switching to an already established virtual circuit.
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BS1
BS2
BS3
Remote terminal
Original path
Path extension 1
Path extension 2
Figure 13. Gambar 13. path evolution example adopting connection extension approach
BS1
BS2
BS3
Remote terminal
Virtual connection tree
Figure 14. Gambar 14. path evolution example adopting multicast establishment approach
In the partial re-establishment handoff scheme (see Figure 15), a new path is established from the
new base station to a node in the original connection path. Hence this method requires the discovery
of the crossover switch (COS), the setting up of the new partial path and the tearing down of the old
partial path. The purpose of crossover switch discovery is to locate a suitable COS so that a new partial
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path can be established from the new base station (BS) to the COS.
Five COS discovery schemes (loose select, prior path knowledge, prior path resultant optimal, dis-
tributed hunt and backward tracking) have been presented and evaluated in [95]. Another COS discovery
scheme is presented in [96].
BS1
BS2
BS3
Remote terminal
Original path
First reestablishment
Second reestablishment
Figure 15. Gambar 15. path evolution example adopting partial reestablishment approach
In loose select discovery, the new BS establishes a new path towards the destination node with no
regard to existing path nodes. If the new path 'intersects' with the old path, the intersecting node is the
crossover node. In prior path knowledge discovery, information about existing path nodes (ie possible
COS) is obtained by querying the connection server. With this information, the new BS derives all
possible partial paths and selects the partial path that fulfills QoS requirements.
The prior path resultant COS discovery is derived from prior path knowledge discovery with the
exception that the considered nodes are only those supporting new paths either shorter or equal to the
existing path prior to handoff. In distributed hunt COS discovery, the new BS initiates a broadcast
to locate all possible COSs within the network. Again, among all possible partial paths, the partial
path that fulfills QoS requirements is selected. Finally, in backward tracking discovery, each node in
the existing path will progressively verify if it can reach both old and new BSs. Backtracking starts at
the closest node to the old BS and continues along the existing path until a crossover node is found.
A route chaining technique is used in [97] to extend virtual circuits to the mobile's new location.
To obtain a more efficient route, the previous chains are collapsed into a new virtual circuit. Another Lain
scheme based on extending and collapsing virtual circuits is proposed by Agrawal et al. in [98].
Several works used clustering to structure the wireless environment and hence to facilitate the han-
dling of handoffs. For instance, Toh [95] groups into clusters adjacent cells in a wireless network.
Movement within a cluster is handled in a single ATM switch that is connected to all the BSs in the
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cluster, while movement between clusters is handled by rerouting virtual circuits at the last switch on
the route common to both clusters.
Akyol [99] proposes a procedure called ”Nearest Common Node Rerouting (NCNR)” to perform the
rerouting of user connections due to handoff event. The NCNR attempts to perform the rerouting for a
handoff at the closest ATM network node that is common to both base stations involved in the handoff
transaction. transaksi. The rerouting is then performed starting from this common node.
Hierarchical and low-latency handoffs have been also proposed for connectionless networks. For in- Untuk di-
stance, DeSimone and Nanda describe in [100] the scheme used in Cellular Digital Packet Data (CDPD).
In this scheme, base stations are grouped and connected to a single Mobile Data Intermediate Station
(MDIS), which handles the roaming between base stations within the corresponding group.
A scheme involving a mobile's home agent and multicasting is proposed by Seshan in [101]. The The
mobile's home agent encapsulates data destined for the mobile in multicast packets, and sends these
packets to multiple BSs in close vicinity of the mobile. Among the previous BSs, only one actively
forwards packets to the mobile. The other BSs buffer recent packets and quickly forward them to the
mobile should a handoff occur. This scheme allows reducing handoff latency and packet losses at the
expense of increased use of buffer space in the BSs. The use of multicast relieves the home agent of
detailed knowledge of the mobile's current location, but incurs the complexity of managing multicast
groups as mobiles move.
Subir Kumar et al. [102] propose a concept of per mobile software entity, known as mobile rep-
resentative. A representative acts as an intermediate agent between its client mobile unit and other
remote peer entities. Representatives can dynamically migrate themselves, following their client mobile
users. pengguna. A connection handoff is dealt with by a caching scheme where a bank of connection segments
are dynamically created and destroyed, following the mobility pattern of an end user. During a handoff
those segments are appropriately switched in and out to maintain the desired connectivity.
Some of the above schemes attempt to anticipate handoffs by using measurements of signal strength
and knowledge of previous mobility patterns. The performance metrics usually used to evaluate handoff
schemes are: Call blocking probability, Handoff blocking probability, Handoff probability, Call dropping
probability, Probability of an unnecessary handoff, Rate of handoff, Duration of interruption and Delay.
Jiang et al. Jiang et al. [103] propose a handoff support approach which uses message between the user and the
network to handle handoff. By classifying the user's requirements of mobility support according to user
states, this scheme asks the user to declare the type of mobility support in the call request and requires
the network to inform the user in advance if a handoff fails. Simulation results presented in [103] show
that this approach accepts more calls and reduces call-dropping probability thus improving resource
utilization in comparison with the traditional approach.
Iraqi et al. [104] propose a configurable multi-agents architecture for QoS control in WATM. The The
agents dynamically manage the buffer space at the level of a switch and interact to reduce the cell loss
ratio while guaranteeing a bounded transit delay. A dynamic reconfiguration of the agents is performed
during partial reestablishment handoffs in order to continue meeting user QoS requirements end-to-end.
5. 5.
QoS-sensitive resource management
Following the enormous trend in wireless communication, there is a growing interest in how to deploy
the system network infrastructure to achieve maximum capacity, coverage and flexibility in the most
cost-efficient manner. To maximize the number of subscribers within a cellular network while main-
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taining overall quality of service, one can apply a range of techniques, each smoothly boosting the total
network capacity a little further to meet the market demand.
Creating a multi-layered network by adding micro- and picocells is one such technique that allows for
capacity optimization. Methods such as power control, efficient channel allocation, and traffic control
between the layers are also employed to exploit the full potential of the network. In [105], the authors
discuss some important aspects of creating high-capacity cellular networks that operate with a limited
amount of frequency spectrum. Macrocells are initially used to build a network with cost-effective wide-
area coverage. By decreasing site-to-site distance and tightening frequency reuse, the capacity of the
macro network can be increased substantially. Subsequently, micro- and picocells are added, creating a
multi-layered cellular network. Picocells are introduced to efficiently handle even higher traffic in indoor
environments such as offices.
For QoS-sensitive communications such as multimedia communications, the goal of an efficient re-
source management technique is to guarantee the QoS of ongoing connections, while at the same time
the available radio spectrum is used efficiently. This goal addressed by network operators and service
providers into two main steps: firstly by partitioning the resources; and secondly by controlling the
access and usage of these resources.
The bandwidth in a wireless network is perhaps the most precious and scarce resource of the entire
communication system. This resource should be used in the most efficient manner. Several bandwidth
partitioning strategies that allocate bandwidth ”fairly” for different traffic classes while attempting to
achieve maximum network throughput have been proposed in the literature [106,4,107]. Previous stud-
ies of these techniques in wireless networks have focused on the co-existence of data and voice traffic,
while video traffic has generally been ignored.
At the two extremes of resource partitioning strategies are the Complete Sharing (CS) and Complete
Partitioning (CP) (also called Mutually Restricted Access or MRA) strategies, and in between are the
rest, generally referred as hybrid strategies.
In CS, all traffic classes share the entire bandwidth. Although trivial to enforce, the main drawback of
this strategy is that a temporary overload of one traffic class results in degrading the connection quality
of all other classes. In CP, bandwidth is divided into distinct portions with each portion corresponding
to a particular traffic class. CP is wasteful of bandwidth if the predicted bandwidth demand for a
particular traffic class is greater than the actual bandwidth demand. A compromise between CS and
CP is a strategy in which bandwidth is allocated dynamically to match the varying traffic load. One Salah satu
such technique is called Priority Borrowing (PB). A moving boundary exists between the bandwidth
allocated for the various traffic classes and priority users (usually voice traffic) are allowed to borrow
bandwidth from non-priority users (data traffic). It has been shown that this hybrid scheme provides
better performance than both CS and CP, over a range of offered loads both in micro-cellular and
macro-cellular environments [4]. The reader is referred to [106,108] for a survey of such schemes.
In [109], the authors have extended Priority Borrowing to include static bandwidth reservation with a
moving boundary. They call it Priority Sharing with Restrictions (PSR). In this scheme only real-time
video connections are allowed to make lifetime (or static) reservations; voice and data connections make
reservations dynamically. The amount of bandwidth reserved for static reservations is determined by
their ”Smart Allocate Algorithm”.
Finding the optimal partitioning point is a very difficult task since it can be directly modeled by an
NP-complete graph-coloring problem. Because of the algorithmic intractability of finding the exact opti-
mum, various sub-optimal solutions have been proposed in the literature [108]. In fact, the intractability
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of finding the optimum is present already in the simplest situation, when the traffic consists of voice
calls only and the statistics of the offered traffic class are completely known. The problem becomes
even more difficult when the wireless network carries integrated non-homogeneous traffic, a situation
occurring naturally in wireless multimedia networks.
Wireless mobile networks are characterized by user/terminal mobility. Therefore, access control to
resources (referred to as call admission control) must be implemented both at the initial call set-up and
during handoffs. Hence, a base station may need to reserve resources, even if this means denying access
to a mobile terminal requesting admission to the network, in order to keep enough resources to support
active users currently outside of its coverage area, but who may soon emigrate to its cell. Base stations
must maintain a balance between the two conflicting requirements:
1. 1. Maintain maximum resource (bandwidth) utilization.
2. 2. Reserve enough bandwidth resources so that the maximum rate of unsuccessful incoming handoffs
(due to insufficient resources) is kept below an acceptable level.
The probability of unsuccessful handoffs can be established in terms of a quality-of-service (QoS) metric,
eg, call dropping probability that the network agrees to maintain.
A method for a base station to maintain a certain call dropping probability is to reserve some re-
sources. sumber. An accurate determination of the amount of resources that a base station must reserve is likely
to become an issue of extreme importance in future wireless networks. In contrast to current wireless
mobile systems, future ones will support a wide range of applications with diverse bandwidth require-
ments. KASIH. Also, in future systems the demand on wireless bandwidth within a cell may change abruptly
in a short period of time, as for example, when several video or high data rate users enter or leave a
cell at the same time. In contrast, in current systems the bandwidth demand usually varies gradually,
and hence it is much easier to handle. Moreover, future wireless networks may provide customized QoS
parameters on a per call and/or on a service base, enabling users to select a level of service according
to the pricing plan.
In order to maintain an acceptable call dropping probability, several schemes [17,110–112] have been
proposed to dynamically organize the allocation of bandwidth resources. These schemes consider only
limited information from neighboring cells, and do not specifically consider admission control policies as
means to prevent congestion. Issues and relationships between resource reservation, channel allocation,
call admission, and traffic intensity have been studied previously [16,113]. Admission control policies,
which determine the number of new voice or data users for acceptance in a packet radio network, are
given in [113]. For these policies, voice users are accepted only if a long-term blocking probability is not
exceeded, while data users are accepted only if the mean packet delay and the packet loss probability
are maintained below certain levels. In [16], a flexible channel allocation scheme is proposed based on
the analysis of offered traffic distributions or blocking probabilities. A distributed call admission control
procedure is proposed in [114]. It takes into consideration the number of calls in adjacent cells as well
as in the cell where a new call request is being made, in addition to the knowledge of the mean call
arrival, call departure, and call handoff rates. None of these schemes consider the individual trends of
the users in the wireless network, eg, position, speed, direction, and bandwidth demands.
David A. Levine et al. [115] use the shadow cluster concept [116] to estimate future resource re-
quirements and to perform call admission decisions in wireless networks. The framework of a shadow
cluster system can be viewed as a message system where mobile terminals inform the base stations in
their neighborhood about their requirements, position, and movement parameters. With this informa-
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tion, base stations predict future demands, reserve resources accordingly, and admit only those mobile
terminals which can be supported adequately. Base stations determine the probabilities that a mobile
terminal will be active in other cells at future times, define and maintain shadow clusters by using
probabilistic information on the future position of their mobile terminals with active calls, and predict
resource demands based on shadow cluster information.
The shadow cluster approach is an important work step towards a compromise between maintaining
maximum resource utilization and satisfying user QoS requirements. However, the prediction capability
assumes that mobile terminals use a fixed number of bandwidth units for all the call duration. This al-
lows guaranteeing the desired QoS at the expense of non-optimal resources utilization in case of variable
bit rate traffic. Also, as recognized by the authors, the proposed approach lacks fairness as it highly
prioritarizes ongoing calls over new calls in the system.
In ATM networks, calls are accepted according to some call admission policy, but due to the bursty
nature of non-voice traffic, the bursts from different traffic streams may coincide, and temporarily require
bit rates higher than the network capability. Effective bandwidth [117–123] is one popular approach to
this problem, where each type of call is assigned an effective bandwidth lying somewhere between the
mean rate and the peak rate.
In [124], the authors investigate how effective bandwidth can be utilized in the modeling of CDMA
cellular mobile networks. They allocate an effective bandwidth to each mobile depending on its class
and its location relative to a target cell. The important contribution of this work is that the resultant
network model is of similar form to a circuit-switched network and the traffic analysis for the latter can
be directly applied to the CDMA cellular model.
In general existing call admission control approaches defined for wireless mobile networks have not
addressed the quality of service requirement end-to-end. This will necessitate interoperability between
different QoS management mechanisms supported by the heterogeneous fixed and wireless intercon-
nected networks.
6. 6.
Conclusion Kesimpulan
The last decade has witnessed a fantastic growth of mobile personal communications systems. This Ini
growth encompasses several telecommunication applications, particularly at the access network level,
such as cordless phones for residential lines, wireless PBX for corporate networks, paging systems and
cellular systems. For example, it is easy to predict that cellular systems will continue growing to accom-
modate the increasing number of mobile subscribers and the volume of traffic generated by each mobile
user. pengguna. The traffic will grow significantly with the arrival of Internet accesses and multimedia services
requiring, consequently, higher capacity network infrastructures and more sophisticated resource alloca-
tion and management mechanisms. In this article we have discussed some of the issues and approaches
related to resource management in wireless and mobile multimedia networks. The discussed issues in-
clude Access and allocation strategies; their influence on network performance; mobility management
aspects including location and handoff procedures; bandwidth allocation; and network access control.
The transport of multimedia traffic over wireless mobile networks introduces specific resource manage-
ment requirements, some of which have been discussed throughout the paper such as channel access and
assignment, call admission control, and handoff. There are many challenging and open research issues,
and we do not claim to have addressed them all. One key issue in supporting future multimedia mobile
networking and QoS provisioning end-to-end is the design of resource management mechanisms capable
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to adapt to the network state changes and to the nature of multimedia traffic. This is a research area
currently attracting a lot of attention [44,125–128]. Another key issue is the trade-off between maximiz-
ing resource utilization and reserving enough resources so as to reduce the rate of unsuccessful incoming
handoffs. This is an area where research is just in its infant stages. We have tried in the following
table to assess the resource management issues on which multimedia applications have an impact and
to identify for each of these issues the features suitable for supporting multimedia applications
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