Tez Arşivi

Tez aramanızı kolaylaştıracak arama motoru. Yazar, danışman, başlık ve özete göre tezleri arayabilirsiniz.


İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü

2.ve 3. nesil CDMA temelli mobil haberleşme protokolleri

2.and 3. generation mobile communication protocols based on CDMA

Teze Git (tez.yok.gov.tr)

Bu tezin tam metni bu sitede bulunmamaktadır. Teze erişmek için tıklayın. Eğer tez bulunamazsa, YÖK Tez Merkezi tarama bölümünde 104153 tez numarasıyla arayabilirsiniz.

Özet:

2. ve 3. Nesil CDMA Temelli Haberleşme Protokolleri ÖZET Çalışmanın temel amacı, IS-95 ve IMT-2000 gibi mevcut veya gelecekte uygulanması düşünülen CDMA temelli mobil sistemleri incelemektir. Burada, IS-95 CDMA ve genişbantlı CDMA hava arabirimi detaylı biçimde tanıtılmış; genişbantlı CDMA hava arabirimi için, Avrupa ve Japonya'da kabul edilen WCDMA ile A.B.D'de kabul edilen cdma2000 standartları ele alınmıştır. Düşük chip hızı ve cdma2000'e göre dar bantgenişliğine sahip IS-95 ile, IMT-2000'nin veya Üçüncü Nesil Mobil sistemlerin veri hızı gerelcsinimlerinin karşılanması imkansızdır. cdma2000 standardı, geniş bantgenişliklerinde CDMA desteği sağlayarak ve IS-95 ile geri uyumluluk göstererek A.B.D'de Üçüncü Nesil mobil sistemi olarak seçilmiştir. Çalışmada bu sistemlerden WCDMA (UMTS) tanıtılmıştır. CDMA sistemlerinde konvolüsyon kodlama ile doğrudan yaymanın karşılaştırılıp avantaj larının değerlendirilmesi, bir IS-95 ileri-yön(DL) bağlantısının simülasyonu, mobil hızının BER'de etkisi, CDMA sisteminde aynı hücre kullamcılanmn girişimlerinin ve Yayma Faktörü'nün sistem performansına etkisinin tespiti simülasyonlar yardımıyla yapılmıştır. Bölüm 2'de, "Çoklu Erişim Teknikleri" adı altında günümüzde birçok alanda sıklıkla kullanılan FDMA, TDMA, CDMA ve OFDM hakkında bilgi sunulmuştur. Çalışmamızda odaklandığımız konu CDMA protokolü olduğundan, bundan sonraki bölümlerde CDMA ve bu teknolojinin kullanılldığı mobil haberleşme sistemleriyle ilgilenilmiştir. Bölüm 3'de ilk olarak, CDMA'in kullandığı yayılmış spektrum haberleşmesi anlatıldıktan sonra, CDMA protokolleri çeşitlerine geçilmiştir. FH- CDMA, TH-CDMA ve DS-CDMA, özellikle incelenen protokollerdir. Bunların içersinde, DS-CDMA hem ikinci hemde üçüncü nesil mobil haberleşme sistemlerinde kullamlmaktadır. CDMA sistemlerinde hücre kapasitesinin hesaplanmasına da bu bölümde yer verilmiştir. Dördüncü bölümde, IS-95 olarak bilinen ve A.B.D'de kullanılmakta olan CDMA temelli ikinci nesil mobil sistemi incelenmiştir. IS-95 'de UL ve DL bağlantıları için blok şemalar ve burada kullanılan herbir bloğun işlevleri verilip MATLAB kodu karşılıkları sunulmuştur. IS-95'in sağladığı bir diğer avantaj da kesintisiz aktarma (Soft Handover) olduğundan kesintisiz aktarma prosedürleri incelenmiştir. Hata- Okumura Modeli kullanılıp, mobil istasyonun bağlı olduğu iki baz istasyonun aldığı güçdeki değişim simüle edilerek aktarma kararının ne zaman verilebileceği gösterilmiştir. Beşinci bölümde, üçüncü nesil mobil haberleşme sistemlerinin neler olduğu, geçiş teknolojileri, getirdiği yenilikler, uygulamaları ve gerelcsinimleri ile spektrum tahsisi XVAvrupa'da kulanılması düşünülen ve genişbandlı CDMA teknolojisine dayanan UMTS sistemi ve bunun kullandığı UTRA olarak adlandırılan hava arabirimi protokolü detaylı biçimde altıncı bölümde incelenmiştir. UTRA protokolünde kullanılması düşünülen kodlama (FEC-Forward Error Correction) türleri, spektrum yayma metodlan, gizlilik için kullanılan karıştırma kodları, modülasyon, kanal çeşitleri ve fonksiyonları, UL ve DL için ayrı ayrı incelenmiştir. Bölüm 7'de IS-95 CDMA sistemi DL bağlantısında alıcı ve vericide kullanılan fonksiyonel blokların MATLAB programı ile karşılıkları verilerek bir DL bağlantısı simülasyonu yapılmıştır, ikinci olarak, konvolüsyon kodlamasının AWGN ve Rayleigh kanallar için BER değişimi çıkartılmış, kodlamanın yapılmadığı sadece direkt yaymanın kullanıldığı bir sistemle de kıyaslanmıştır. Sonuç olarak düşük Eb/No değerleri için konvolüsyon kodlama kullanılmadığı durumda dahi kabul edilebilir BER değerleri elde edilebildiği gösterilmiştir. Mobil kullanıcı hızının kanal modeline nasıl bir etki yaptığı gösterilerek 10 ve 100 km/saat mobil kullanıcı hızlan için BER'in değişimi çıkartılmıştır. Hız arttıkça Rayleigh kanalında zayıflama çukurlarının sayısı artacağından işaret bozulmaları daha fazla hissedilmiş buda BER'in kötüleşmesine neden olmuştur. Bir diğer performans değerlendirmesi de aynı hücre kullanıcılarından kaynaklanan girişimlerin DL için BER'deki etkisi ölçülmüş, girişim sayısı arttıkça sistemin kabul edilemez BER'lere sahip olabileceği tespit edilmiş ve böylece girişimlerin CDMA sistemlerinde en önemli sorun olduğu görülmüştür. XVI

Summary:

2. and 3. Generation Mobile Communication Protocols Based On CDMA SUMMARY The major objectives of this thesis is to review the CDMA based present and future mobile systems namely, IS-95 and EMT-2000. An overview of IS-95 CDMA and main wideband CDMA air interface are presented in detail. For wideband CDMA air interface WCDMA (UMTS) in Europe is described. The personal mobile wireless systems currently in use around world are first and second generation (2G) systems. The first generation cellular systems generally use analog Frequency Modulation techniques, so they are called analog mobile systems. They offered only voice communications and employ FDMA (Frequency Division Multiple Access) with each channel assigned to a unique frequency band within a cluster of cells. AMPS (Advanced Mobile Phone Services), NAMPS (Narrowband AMPS), TACS (Total Access Communication System) ve NMT-900 (Nordic Mobile Telephone) are the most notable of first generation systems. 2G systems take the advantage of compression and coding techniques associated with digital technology. All the 2G systems use digital modulation schemes. TDMA and CDMA are used along with FDMA as a multiple access techniques. 2G cellular systems are: USDC (U.S. Digital Cellular) standards IS-54 and IS-136, GSM (Global System of Mobile Communications), PDC (Pacific Digital Cellular) and cdmaOne. TDMA systems commonly start with a slice of spectrum referred to as one "carrier". Each carrier is the divided into time slots. Only one subscriber at a time is assigned to each time slot or channel. With CDMA, unique digital codes, rather than separate RF frequencies or channels, are used to differentiate subscribers. The codes are shared by both mobile and base station, and are called "pseudo-random code sequences". All users share the same range of radio spectrum. In addition, since CDMA is wideband in nature, several undesirable qualities of narrowband systems are mitigated, such as particular types of interface. Third Generation (3G) systems are currently in development, and will offer multimedia capabilities to 2G platforms like support for high bit rates (144 kbit/s to 2 Mbit/s) and extended capabilities over 2G systems. When 3G wireless systems begin launching worldwide, sometime after 2002, mobile subscribers will be able to notice a number of advantages over current wireless sytems.Data access rates will increase more than 20 times faster. 3G will also offer mulimedia capabilities and even location-enabled features such as 1 12. This means a user from New York will be able to use his/her phone in Istanbul to dial 112, and Istanbul emergency crews will pinpoint his/her location to send help. 3G technology will also allow subscribers to access several services at once. For instance, a user will be able to carry on voice conversation while surfing in Internet, or to participate in a video conference while sending a fax. In addition, 3G will offer a true global wireless system, permitting xvnsubscribers to roam all over the world and make connections with anyone, anywhere, anytime. International Telecommunications Union (ITU) is overseeing worldwide efforts to define 3G wireless standards. These standards, known as International Mobile Telecommunications-2000 (IMT-2000), will provide universal coverage and enable seamless roaming across multiple networks. IMT-2000 until recently was known as the Future Public Land Mobile Telephone System (FPLMTS). The original goal of IMT-2000 was to create a single system, common to all global regions. However, most of the world2s wireless service providers are heavily invested in their 2G cellular systems. Many of these carriers have demanded that 3G networks evolve gracefully from their existing digital systems, in order to protect their investments in 2G technology. As a result, IMT-2000 vision evolved into the idea of creating a "family of systems". The gola now is to upgrade all the world's 2G systems to comply with a common set of 3G requirements.The main technical objectives and requirements of IMT-2000 are:. Voice quality comparable to Public Switched Telephone Network (PSTN).. Support of high data rate.. Vehicular-» 144kbit/s. Outdoor to indoor and pedestrian -»384 kbit/s. Indoor Office -» 2 Mbit/s. High spectrum efficiency (more users) compared to existing systems.. Support of both packet-switched and circuit-switched data services.. Backward compatibility with pre-existing networks and high flexibility to introduce new services and technology.. Support of wide variety of mobile equipment.. An adaptive radio interface suited to the highly asymmetric nature of most Internet communications: a much greater bandwidth for the downlink than uplink. At the March 25, 1999 meeting of the IMT-2000 committee of the ITU, they reached some decisions regarding the air interface for IMT-2000. They essentially allow a single flexible standard with a choice of multiple access methods which consist of CDMA, TDMA and hybrid TDMA/CDMA. This thesis will focus on CDMA proposals, since it seems that CDMA will be the predominant air interface. The 3G evolution is taking place on three fronts: Japan, Europe and North America. Japanese telecommunications operators such as NTT DoCoMo and Japan Telecom are focusing on Wideband CDMA (W-CDMA) as their preferred technology for 3G services. ETSI is developing a uropean set of 3G standards, called the Universal Mobile Telecommunication System (UMTS). The current UMTS proposal, now called UMTS Terrestrial Radio Access (UTRA), focuses on ways that GSM technology can evolve into the 3G by taking avantage of wideband CDMA technology. In North America, major efforts are under way by the TIA to determine the evolution path of cdmaOne and TDMA (IS- 136) technology into the 3G. On CDMA side, wideband cdmaOne (cdma2000) is the technology of choice. It offers higher capacity and more advanced multimedia services than current 2G CDMA systems. The current CDMA standard, cdmaOne (IS-95B), uses an RF bandwidth of 1.25 MHz, while the wideband CDMA system uses 5 MHz. This wider bandwidth allows better performance in the presence of multipath since the receiver can separate the multipaths easier, to increase diversity and improve performance. The XVlllbandwidth also alloews support of high rate services, up to 2 Mbit/s peak rate. Third, this 5 MHz is a good fit in the tight-fitting spectrum allocations available. This wide bandwidth has given rise to the name Wideband CDMA or WCDMA. There are two different modes namely Time Division Duplex (TDD) and Frequency Division Duplex (FDD). Both duplex schemes are supported by WCDMA air interface. Some of key technical features of the WCDMA radio ineterface are:. Multiple Access Scheme -> DS-CDMA. Duplex Scheme -> FDD/TDD. Multirate/Variable rate scheme -> Variable spreading factor and multi-code. Chip rate -> 3.84 Mchip/s. Carrier Spacing -» 4.4 - 5.2 MHz (200 kHz carrier raster). Frame Length -> 10 ms. Channel Coding Scheme -» Convolutional Code, Turbo Code The chip rate may be exttended to two or three times the standard 3.84 Mchip/s to accommodate for data rates higher than 2 Mbit/s. The 200 kHz carrier raster has been chosen to facilitate coexistence and interoperabilitiy with GSM. The TLA TR45.5 committee has a subcommittee, TR45.5.4, which is responsible for the selection of cdma2000 concepts. Like for all the other wideband CDMA schemes, the goal has been to provide data rates that meet the IMT-2000 performance requirements of at least 144 kbit/s in a vehicular environment, 384 kbit/s in a pedestrian environment and 2048 kbit/s in a indoor office environment. The mani focus of standardization has been providing 144 kbit/s and 384 kbit/s with approximately 5 MHz bandwidth. There are two main alternatives for the downlink in cdma2000: multicarrier and direct spread. The multicarrier approach involves setting up three carrier frequency's with a spreading bandwidth of 1.25 MHz each, so that they span a total 4.75 MHz, non-overlapping, with a small guard band between them. Each carrier has a chip rate of 1.2288 Mchip/s, for a total of 3.6864 Mchip/s. This will allow easy evolution and co-existence with current IS-95B systems. The direct spread option involves a single carrier in the middle of the allocated spectrum, with a spreading bandwidth of 4.75 MHz. There is also the possibility of using 10, 15, 20 MHz channels, for very high bit rate applications. The main parameters of cdma2000 can be listed as follows:. Channel Bandwidth -> 1.25, 5, 10, 15, 29 MHz. Downlink RF Channel structure -> Direct spread or multicarrier. Chip Rate -+ DS: 1.2288, 3.6864, 7.3728, 11.0593, 14.7456 Mchip/sn MC: n x 1.2288 Mchip/sn (n= 1,3,6,9, 12). Frame Length -> 20 ms for data and control / 5 ms for control information on the fundamental and dedicated control channel. Data Modulation -> QPSK (Downlink), BPSK (Uplink). Spreading factors -> 4 - 256. Power control -» Open loop and fast closed loop. System Timing -> Network synchronous. Handover -> Soft Handover, Interfrequency handover. Multirate -> Variable spreading factor and multi-code In this thesis, I have studied the IS-95 standard that is one of the CDMA stanndards for wireless personal communication systems (PCS) as specified by TLA. It operates in the 800 MHz band and 1.9 GHz PCS band. One IS-95 channel occupies 1.25 MHz of spectrum on each link. Main parameters of the IS-95 air interface are: XIX. Bandwidth-» 1.25 MHz. Chip Rate -» 1.2288 Mchip/s. Frequency band uplink -> 869 - 894 MHz, 1930 - 1980 MHz. Frequency band downlink -> 824 - 849 MHz, 1850 - 1910 MHz. Frame Length -> 20 ms. Bit Rates -> Rate Set 1: 9.6 kbit/sn, Rate Set 2: 14.4 kbit/s, IS-95B : 1 15.2 kbit/s. Spreading Codes -» Walsh + Long M-sequence. Handover -» Soft Handover This thesis is organized as follows: Chapter 2 presents some multiple access techniques use in mobile communication; such as FDMA, TDMA, CDMA and OFDM. In Chapter 3, I have focused on and provide some technical background about CDMA protocol and Spread Spectrum communication that is necessary to understand how new generation CDMA mobile systems are designed. 2G CDMA sytem called IS-95 is introduced in Chapter 4 and functional blocks (convolutional encoder, interleaver, PN code generator) are simulated using MATLAB. IMT-2000 services and applications, 3G standadization activities, IMT-2000 frequency allocations identified at WARC92/WRC95 and WRC2000, licensing situation for 3G spectrum are introduced in Chapter 5. Chapter 6 reviews the main wideband CDMA air interface WCDMA for UMTS. In Chapter 7, CDMA system simulations are given. I have tried to to simulate a IS-95 forward link as accurately as possible. This thesis also gives knowledge about enhancements to be made to the present day IS-95B systems to meet the 3G standard. Coding is an integral part of communication since it greatly help us to decrease the BER. Convolutional codes are extensively used in the present IS-95B system which uses Viterbi decoding. With the next generation of cellular systems, data transmission will be nearly as important as voice, but data does not require constant connections and can support more errors since data can be retransmitted, so new handsets can be made which take advantage of this fact. One method for reducing complexity is to direct spread the data in a CDMA system, thus removing the costly Viterbi decoder and memory intensive interleaver/deinterleaver. In this thesis, I have investigated the performance of a direct spread version of IS-95 with the orginal IS-95, and show that under some certain conditions the direct spread version performs better than IS-95. Another CDMA performance evaluation was done by calculating BER against interfering signals; for that purpose I have used MATLAB codes and observed that the performance of the system decreases linearly as the number of interfering signals increase. Even though I have not used error correction capabilities of convolution coding, still get a sufficiently small BER. I have also used the same code for showing the advantage of increasing Spread Factor (SF). Finally simulation results show that BER performance is improved by increasing SF. Another performance evaluation was doen by figuring out the effect of same cell user interferences. Simulation results showed that interferences cause to decrease BER performance. Using Gold or Kasami codes instead of PN codes or more small cells; for example pico- or micro- cells, can mitigate the effects of interference problem. XX