Kafes kodlamalı hızlı frekans kaydırmalı anahtarlama tekniğinin otamatik yineleme istemli sistemlere uyarlanması
The Application of trellis coded fast frequency shift keying modulation to the automatic repeat request systems
- Tez No: 39112
- Danışmanlar: DOÇ.DR. H. ÜMİT AYGÖLÜ
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Anahtarlama, Frekans kayması, Kafes kodlama, Otomatik sistemler, Switching, Frequency shift, Trellis coding, Automatic systems
- Yıl: 1993
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
Bu tez çalışmasında, kodlama ve modülasyon işlemlerinin bir bütün olarak ele alındığı kafes kodlamalı Hızlı Frekans Kaydırmalı Anahtar lama (Fast Frequency Shift Keying, FFSK> modülasyonu, iletişim sistemlerinde hata kontrolü için kullanılan bir yöntem olan Otomatik Yineleme istemeli f. Automatic Repeat Request, ARQ> tekniğine uygulanmıştır. Tene! yapı oluşturulduktan sonra, alıcı tarafta bellek kullanılması ve kod sözcüğünün ilk iletiminde hata serildiğin de verici tarafından aynı sözcüğün“m”kez ard arda iletilmesi gibi iyileştirmeler sisteme ilave edilerek, başarımın arttırılması yoluna gidilmiştir. Oluşturulan sistemlerin Gauss gürültülü ve Rayleigh genlik sünümlemeli kanallardaki iş çıkarma yetenekleri ve bit hata olasılık üst sınırları analitik yöntemlerle incelendiği gibi oluşturulan bir benzetim modeli yardımıyla da değerlendirilmiştir.
Özet (Çeviri)
SUMMARY THE APPLICATION OF TRELLIS CODED FAST FREQUENCY SHIFT KEYING MODULATION TO THE AUTOMATIC REPEAT REQUEST SYSTEMS In this thesis, trellis coded fast frequency shift keying (FFSK) technique is introduced for modula tion operation in automatic-repeat-request (ARQ) schemes in order to improve their throughput performances. The performance of the proposed system is investigated in noisy and fading environment by both analytical and simulation approaches. On the other hand, some modifica tions like the m>l times retransmission of the codeword detected in error or the use of a memory in the receiver are also considered. There are two basic types of error-control schemes in data transmission systems: the forward-error control <FEC) scheme and the automatic-repeat-request <ARQ) scheme. In a FEC system, an error-correcting code is used. When the receiver detects the presence of errors in a received vector, it attempts to determine the error locations and then corrects the errors. After the error correction has been performed, the decoded word is then delivered to the user. If the receiver fails to determine the exact locations of errors, the received vector will be decoded incorrectly and eroneous data will be delivered to the user. In an ARQ error- control system, a code with good error - detecting capability, incorporated with a certain retransmission protocol is used. When a word is received, the receiver computes its syndrome. (a syndrome is a binary word computed by the decoder and used in making the decision as to which codeword was transmitted) If the syndrome is zero, the received word is a codeword in the code being used and is accepted by thereceiver and delivered to the user. At the same time, the receiver notifies the transmitter, via a return channel, that the transmitted code vector has been successfully received. If the syndrome is not zero, errors are detected in the received vector. Then, the receiver discards the erroneously received word, and requests a retransmission of the same codeword via a feedback channel. Retransmissions continue until the codeword is successfully received. The performance of the ARQ error - control system is normally measured by its reliability and throughput efficiency. Since the probability of a decoding error is much greater than the probability of an undetected error, it is harder to achieve high system reliability with FEC systems. In an ARQ error-control scheme, the receiver commits decoding error whenever it accepts a received word with undetected errors. Clearly, the probability of this error event can be made very small by using a good detecting - code, so that the reliability of the system will be high. The throughput of a FEC system is constant, and higher than the throughput of an ARQ system. There are 3 basic types of ARQ schemes a- Stop and Wait Autoniatic-Repeat-Request : In this type of error-control system, the transmitter sends a codeword to the receiver and waits for an acknowledgment. A positive acknowledgement <ACK) from the receiver indicates that the transmited codeword has been successfully received and the transmitter sends the next codeword. A negative acknowledgement (NAK) from the receiver indicates that the transmitted codeword has been detected in error, and the transmitter then resends the codeword and again waits for an acknow ledgement. Retransmissions continue until transmitter receives an ACK. b- Go-Back-N Automatic-Repeat-Request : In this scheme, the transmitter continuously transmits codewords in order and does not wait for an acknowledgement after sending a codeword. The acknow ledgement for a codeword arrives after round-trip-delay defined as the time interval between the transmission of codeword and the receipt of an acknowledgement for that codeword. During this interval, N-l other codewords are -vxxalso transmitted. When NAK is received, the transmitter backs up to the codeword that is negatively acknowledged and resends that codeword and N-l succeeding codewords which were transmitted during one round-trip-delay. Re transmission continues until that codeword is positively acknowledged. In each retransmission for that codeword, the transmitter resends the same sequence of codewords. As soon as the codeword is positively acknowledged, the transmitter proceeds to transmit new codewords. c- Select ive -Repeat Automatic-Repeat-Request: In this scheme, codewords are also transmitted transmitted continuously. However, the transmitter only resends those codewords that are negatively acknowledged Since ordinarily codewords must be delivered to the user in correct order, a buffer must be provided at the receiver to store the error-free received vectors following a received vector detected in error. When the first negatively acknowledged code word is successfully received, thhe receiver then releases the error-free received vectors in consecutive order until the next erroneously received vector is encountered. Sufficient receiver- buffer must be provided in a selective-repeat ARQ system, otherwise, buffer overflow may occur and codewords may be lost. All three basic ARQ schemes achieve the same system reliability, but they provide different throughput efficiencies. The selective-repeat ARQ is the most, efficient scheme, whereas the stop and wait ARQ scheme is the least efficient one. The throughput of the selective-repeat ARQ does not depend on the round-trip- delay of the system; however, the throughputs of the other two ARQ schemes depend on the round-trip-delay. Drawbacks of the ARQ and FEC schemes can be overcomed if the two basic error-control schemes are properly combined. Such a combination of the two basic error-control schemes is referred to as hybrid ARQ. A hybrid ARQ system consists of a FEC subsystem contained in an ARQ system. The function of the FEC system is to reduce the frequency of retransmission by correcting the error patterns which occur most frequently. This increases the system throughput performance. However, when less-frequent error pattern occurs and is detected, the receiver requests retransmission rather than passing than the unreliably decoded message to the user. This incieases the eyatem reliability. As a result, a proper combination of FEC and ARQ provides higher reliability -viii-than a FEC system alone and higher throughput than a system with ARQ alone. In this thesis, we use trellis coded fast frequency shift keying technique in order to achieve a higher throughput performance. Trellis coded modulation <TCM) can he described as a combination of coding and modulation techniques over band-limited channels. TCM allows the achievement of significant coding gains over conventional uncoded multilevel modulation without compromising bandwidth efficiency. TCM schemes use redundant nonbinary modulation in combination with a finite-state encoder which governs the selection of modulation signals to generate coded signal sequences. In the receiver, the noisy signals are decoded by a soft -decision maximum-likelihood sequence decoder. Simple four state TCM schemes can improve the robustness of digital transmission against additive noise by 3 dB, compared to conventional uncoded modulation. With more complex TCM schemes, the coding gain can reach 6 dB or more. These gains are obtained without bandwidth expansion or reduction of information rate. Signal waveforms representing information sequences are most impervious to noise-induced detection errors if they are very different from each other. Mathematically, this translates into the requirement that signal sequences should have large distance in Euclidean signal space. TCM use signal-set expansion to provide redundancy for coding, and to design coding and signal- mapping functions jointly so as to maximize directly the free distance (minimum Euclidean distance) between the coded signal sequences. This allowed the construction of modulation codes whose free distance significantly exceeded the minimum distance between uncoded modulation signals, at the same information rate, bandwidth, and signal power. TCM techniques are used in applications such as; satellite, terrestrial microwave, and mobile communications, in order to increase throughput rate or to permit satisfactory operation at lower signal-to-rate ratios. In this thesis, we use structure of combinations of binary trellis codes and FFSK modulation. Because of its constant envelope, continuous phase, spectral efficiency, error rate performance of binary PSK, and self -synchronizing capability we prefer FFSK technique for modulation operation in TCM. As a result of this combined structure, the free Euclidean distance of the -ix-FFSK codes is maximized for the rate k/1 and the number of states in the trellis code. FFSK modulation is an instance of continuous- phase frequency-shift keying (CPFSK) modulation with modulation index h=l/2. Studies in the literature show that, in order to optimize the combined coding-modulation system for FFSK modulation, the best combinations can be realized using convolutional encoders. The optimization criterion is the maximum free Euclidean distance for a given rate of the convolutional code and for a required number of states in the code trellis corresponding to the combined coding-modulation system. In this thesis, the behaviour of the proposed ARQ scheme with trellis coded FFSK modulation is analyzed in noisy and fading channels. This coded modulation structure permits to increase the Euclidean distances among the signal sequences which lead to better throughput performance compared to the classical ARQ schemes. It is assumed that, the source generates symbols from a binary alphabet A={0, i>. Each block of 3 information symbols coming out of the source is encoded in a codeword g of a code C(6,3). g is G symbols long. Code C is able to correct 2 = 26_3=8 errors and to detect 2n-2k=26 -23=56 errors. C<6, 3) is used only to detect errors in the receiver which sends a negative acknowledgement for each erroneously decoded codeword. R=l/2 trellis coded FFSK modulator is made up of a good combination of R=l/2 convolutional code and FFSK modulation. Each coming symbol from the block encoder, is translated into 2 FFSK signals. Each signal has a duration of T sec and this is referred as the modulation interval. As a result of FFSK modulation, there is a phase continuity at signal transitions. At the receiver part, we use soft-decision Viterbi decoder, so that demodulation and decoding operations are considered together. The Viterbi algorithm decides after each 12 T sec. long observation interval, and delivers the corresponding received binary sequence of 6 bits long to the (6,3) block decoder. Then, the received sequence is compared to the codewords of the linear block code C<6, 3) If the received sequence is a codeword of the code C(6, 3) then, the receiver sends a positive acknowledgement to the transmitter through a noiseless feedback channel and the information bits are delivered to the user. On the other hand, if the received vector is not a codeword of the code C(6, 3) then, the receiver sends a negative acknowledgement to the transmitter. The transmitter then stops sending new codewords and retransmits this codeword, detected in error. Retransmissions continue -x-until the transmitter receives positive acknowledgement for that codeword. Many modifications have been introduced in order to improve the performance of ARQ techniques. An interesting approach is the introduction of a memory in the decoding operation. In this case, the received vectors, also those detected in error, are retained in order to facilitate the correct decoding of the transmitted codeword. In some ARQ schemes, a codeword detected in error is retransmitted m times consecutively in order to increase the throughput under high error rate conditions. In the second section, the three basic ARQ techniques, stop and wait, go back-N, and selective- repeat, and their throughput analysis are presented. The third section is destinated to the FFSK modulation technique which is interesting especially for earth-satellite communications with its constant envelope continuous phase and spectral efficiency characteritics. The integration of coding and modulation operations for ARQ schemes are considered in section 4. Different approaches given in the literature are compared. In the fifth section, the ARQ scheme using trellis coded FFSK modulation is presented and its throughput and error performances over additive Gaussian noisy and amplitude fading channels are analyzed. The bit error probability upper bounds for 2 and 4 state FFSK encoders are obtained based on the transfer approach. On the other hand, a simulation model for the proposed ARQ scheme is used to obtain its throughput with respect to the signal-to-noise ratio in noisy and fading environment. The last section is destinated to a conclusion of the obtained results. -xx-
Benzer Tezler
- 14400 b/s hızlı bir modemin hata başarımının incelenmesi
Başlık çevirisi yok
HAKAN GÖKDAN
Yüksek Lisans
Türkçe
1993
Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve KontrolYıldız Teknik ÜniversitesiDOÇ. DR. H. ÜMİT AYGÖLÜ
- Different computational methods for distance spectra of trellis coded modulation (TCM)
Çit kodlamalı modülasyon için uzaklık görüngesinin farklı yöntemlerle hesaplanması
EMRE ALTUĞ YAVUZ
Yüksek Lisans
İngilizce
1998
Elektrik ve Elektronik MühendisliğiOrta Doğu Teknik ÜniversitesiElektrik-Elektronik Mühendisliği Ana Bilim Dalı
DOÇ. DR. MELEK YÜCEL
- Design and performance analysis of trellis coded system over rician fading channels with imperfect phase reference
Faz seyirmeli ve ricain sönümlemeli kanallar için kafes kodlamalı sistem tasarımı ve başarım analizi
MURAT UYSAL
Yüksek Lisans
İngilizce
1998
Elektrik ve Elektronik Mühendisliğiİstanbul Teknik ÜniversitesiElektrik-Elektronik Mühendisliği Ana Bilim Dalı
DOÇ. DR. ÜMİT AYGÖLÜ
- Desing and analysis of a multidimensional trellis coded modulation scheme
Çok boyutlu bir çit kodlamalı modülatör tasarımı ve analizi
FETİH ÇELİKSÖZ
Yüksek Lisans
İngilizce
1992
Elektrik ve Elektronik MühendisliğiOrta Doğu Teknik ÜniversitesiDOÇ. DR. MELEK YÜCEL
- Sayısal işaret işlemci ile V.32 modem tasarımı
Designing V.32 modem with digital signal processor
MUSTAFA ISNIK
Yüksek Lisans
Türkçe
2001
Elektrik ve Elektronik Mühendisliğiİstanbul Teknik ÜniversitesiDOÇ. DR. M. ERTUĞRUL ÇELEBİ