In the communication of multimedia content, certain dependency structure often exists among the source-coded messages by different source coding techniques, where by "dependency" we mean the dependent contributions of the messages to the overall reconstruction quality. Motivated by such notion of dependency, this thesis considers the problem of communicating dependent source-coded messages over compound channels, which include the attractive wireless channels and packet-loss channels. In this thesis we propose a novel framework to model arbitrary dependency structure among source-coded messages from the source-reconstruction perspectives, and formulate the problem of communicating such messages over compound channels as the problem of maximizing the average utility at the receiver. Over discrete memoryless channels (DMC), we derive the expression of maximal achievable utility, which appears to be governed by the channel coding theorem. Over degraded compound channels, we study analytically the maximal achievable utility by superposition codes. To achieve the maximal utility, the encoder chooses the best sub-chain in the utility graph and encodes it using the best superposition code. For the case of two source-coded messages, we show that the maximal utility achieved by superposition codes is the maximum among all coding schemes. Since in practice layered codes (LC) and multiple description codes (MDC) are two most attracted source coding schemes which induce different dependency structures among coded messages, we numerically evaluate the maximal achievable utility for sources coded with those two source coding schemes communicated over DMC and degraded compound channels respectively, and show the impact of communication delay and channel condition on their respective achievable utilities. In addition, for communicating a Gaussian N(0,1) independent identically distributed (i.i.d.) sequence over degraded compound channels, the joint source channel coding schemes are considered and the minimal achievable distortion is derived and compared for different combinations of source and channel codes. It is shown that the combination of LC and superposition codes outperforms other coding schemes. The comparative behaviour among those techniques is further demonstrated by the experimental results. Practically, we study the performances of various coding schemes for communicating two dependent messages over quasi-static Rayleigh fading channels, which include conventional channel codes, time sharing codes, and a low-density parity-check (LDPC) based coding scheme, termed Bi-LDPC codes. The success rates and the throughput of the considered coding schemes are compared. For communicating a Gaussian N(0,1) source sequence encoded by LC and MDC respectively over quasi-static Rayleigh fading channels, the average distortion is also compared among different channel coding schemes. It appears that Bi-LDPC codes, conventional channel codes encoding both messages, and time sharing type-2 (TS-2) codes, each has their advantage over different region of signal-to-noise ratio (SNR), compared with each other.

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This dissertation considers three different aspects of modern digital communication systems and is therefore divided in three parts. The first part is distributed coding. This part deals with source and source- channel code design issues for digital communication systems with many transmitters and one receiver or with one transmitter and one receiver but with side information at the receiver, which is not available at the transmitter. Such problems are attracting attention lately, as they constitute a way of extending the classical point-to-point communication theory to networks. In this first part of this dissertation, novel source and source-channel codes are designed by converting each of the considered distributed coding problems into an equivalent classical channel coding or classical source-channel coding problem. The proposed schemes come very close to the theoretical limits and thus, are able to exhibit some of the gains predicted by network information theory. In the other two parts of this dissertation classical point-to-point digital com- munication systems are considered. The second part is quantization of coded chan- nel measurements at the receiver. Quantization is a way to limit the accuracy of continuous-valued measurements so that they can be processed in the digital domain. Depending on the desired type of processing of the quantized data, different quantizer design criteria should be used. In this second part of this dissertation, the quantized received values from the channel are processed by the receiver, which tries to recover the transmitted information. An exhaustive comparison of several quantization cri- teria for this case are studied providing illuminating insight for this quantizer design problem. The third part of this dissertation is faster-than-Nyquist signaling. The Nyquist rate in classical point-to-point bandwidth-limited digital communication systems is considered as the maximum transmission rate or signaling rate and is equal to twice the bandwidth of the channel. In this last part of the dissertation, we question this Nyquist rate limitation by transmitting at higher signaling rates through the same bandwidth. By mitigating the incurred interference due to the faster-than-Nyquist rates, gains over Nyquist rate systems are obtained.

Polar codes were invented as the first error-correcting codes to achieve the capacity for the discrete channels with relatively low-complexity for encoding and decoding. However, this is only possible with significantly large code lengths which are not practical for many systems. Meanwhile, the performance of the finite-lengths polar codes is not competitive with other modern error-correcting codes. This can be attributed to the suboptimality of the decoding process and the relatively poor minimum Hamming distances. This thesis aims to improve the performance of polar codes. The contributions include improving the performance of the conventional successive cancellation decoder. This is based on a novel technique, namely one-step decision delay, which incorporates some extra computational nodes to the code tree. Also, this thesis presents two methods for increasing the Hamming distances of polar codes; in the first, the code rate remains unchanged, while in the second, that produces superior performance, a modest reduction in the code rate occurs. Both methods enhance the performance with using belief propagation decoder. In addition, the latency of the decoding process is reduced by applying the fast Hadamard transform decoder on polar codes for the first time. In this regard, a method to modify the encoder is presented for some lengths that are not normally compatible with the proposed decoder. Interestingly, this modification method has another advantage that in the sense that it increases the minimum Hamming distances of the codes. Furthermore, this thesis presents the utilisation of polar codes in some practical communication systems. Firstly, polar codes are examined over power line communication systems. In this respect, the construction of polar codes is analysed by using three different methods. Additionally, the practical performance of polar codes is illustrated for both single-carrier and multi-carrier channels. Secondly, this thesis explores polar codes for unequal error protection by partitioning the information sets into a number of subsets with different reliabilities. JPEG2000, which is an image compression method, is used for validating the advantages of the proposed technique. Moreover, a new joint source channel decoding is proposed from the combination of the polar decoder and JPEG2000 decoder in order to enhance the quality of the compressed images. Finally, polar codes are investigated for the energy transfer by presenting new subcodes that are chosen according to the weights of the produced codewords. In this context, two modes of energy transfer are presented. The proposed modes can successfully extend the lifetime of the receiver's battery.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / This paper considers the joint selection of the source code rate and channel code rate in an image telemetry system. Specifically considered is the JPEG2000 image coder and an LDPC code family. The goal is to determine the optimum apportioning of bits between the source and channel codes for a given channel signal-to-noise ratio and total bit rate, R(total). Optimality is in the sense of maximum peak image SNR and the tradeoff is between the JPEG2000 bit rate R(source) and the LDPC code rate R(channel). For comparison, results are included for the industry standard rate-1/2, memory-6 convolutional code.

Tα σύγχρονα τηλεπικοινωνιακά συστήματα έχουν υιοθετήσει κώδικες διόρθωσης λαθών με στόχο να αυξήσουν της αξιοπιστία των συστημάτων κατά τη μετάδοση πληροφορίας. Οι LDPC (Low-Density-Parity-Check codes) κώδικες είναι μία κατηγορία κωδίκων που πρόσφατα άρχισαν να απασχολούν την επιστημονική κοινότητα κι αυτό γιατί διαθέτουν εξαιρετικές επιδόσεις. Οι κώδικες αυτοί είναι γραμμικοί block κώδικες με απόδοση πολύ κοντά στο όριο του Shannon. Επιπλέον, ο εύκολος παραλληλισμός της διαδικασίας αποκωδικοποίησής τους, τους καθιστά κατάλληλους για υλοποίηση σε υλικό. Στην παρούσα διπλωματική μελετήθηκαν αρχικά τα ιδιαίτερα χαρακτηριστικά και οι παράμετροι των κωδίκων αυτών. Ο στόχος ήταν να σχεδιαστεί ένας αποκωδικοποιητής που να υποστηρίζει τα χαρακτηριστικά των LDPC κωδίκων που έχουν υιοθετηθεί από το DVB-S2. Με αυτό το στόχο υλοποιήθηκε στο System Generator(εργαλείο του Xilinx) ένας ημιπαράλληλος αποκωδικοποιητής. Η ημιπαράλληλη αρχιτεκτονική επιτρέπει καταλαμβάνοντας μικρή περιοχή του υλικού να δημιουργηθεί ένας αποκωδικοποιητής που να είναι εφικτό να χρησιμοποιείται από οποιοδήποτε κώδικα με χρήση των ίδιων λειτουργικών μονάδων και διαφορετικών μονάδων ελέγχου. Στην αποκωδικοποίηση χρησιμοποιήθηκε ο Min-Sum αλγόριθμος καθώς αυτός προσφέρει χαμηλή πολυπλοκότητα χωρίς να θυσιάζει αρκετά σε επίπεδο απόδοσης. Η σωστή λειτουργία ολόκληρου του σχεδιασμού επιβεβαιώθηκε με εξομοιώσεις στη Matlab. / Modern telecommunication systems have adopted error correction codes in order tor improve the reliability during information transmission. LDPC (Low-Density-Parity-Check codes) are a special group of codes with extremely good performance. These codes are linear block codes with performance near to the theoretical Shannon limit. Furthermore, the fact that the procedure of the decoding is easily parallelism makes them suitable for implementation on hardware. At the beginning of this thesis, the special characteristics and the parameters of these codes were stated. The main aim was to design a decoder that can be used for the DVB-S2 system. So, it was designed at System Generator a semi parallel decoder. The implementation of this architecture allows every code (block size, code rate) to be decoded, using the same functional units and different control units. Moreover this implementation requires small area but it is not possible to succeed high throughput. For the decoding process, Min-Sum Algorithm has been used, as it is the less complex algorithm for hardware implementations.The design has been successfully verified with simulations using Matlab.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / A practical joint source/channel coding algorithm is proposed for the transmission of multiple images and videos to reduce the overall reconstructed source distortion at the receiver within a given total bit rate. It is demonstrated that by joint coding of multiple sources with such an objective, both improved distortion performance as well as reduced quality variation can be achieved at the same time. Experimental results based on multiple images and video sequences justify our conclusion.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper presents a joint source-channel decoding scheme based on a JPEG2000 source coder and an LDPC channel coder. At the encoder, JPEG2000 is used to perform source coding with certain error resilience (ER) modes, and LDPC codes are used to perform channel coding. At the decoder, after one iteration of LDPC decoding, the output codestream is then decoded by JPEG2000. With the error resilience mode switches on, the source decoder detects the position of the first error within each codeblock of the JPEG2000 codestream. This information is fed back to the channel decoder, and incorporated into the calculation of likelihood values of variable nodes for the next iteration of LDPC decoding. Our results indicate that the proposed method has significant gains over conventional separate channel and source decoding.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Telemetry for Earth-Observation missions is characterized by very high data rates and stringent requirements. Channel codes both power and bandwidth efficient must be used to improve downlink performance and to achieve the very low values of error rates needed at the received side. In this paper, we review and analyzed three codes of possible interest for these applications: turbo codes, serial turbo codes and product codes. These schemes are evaluated and compared both by simulation and analytical techniques. A particular attention is devoted to complexity, a key issue for practical implementation at high data rates.

International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / This paper presents the method of real time telemetry data synthesis for multi-beams and multi-receivers system in theory. For the practical implementation, we introduce a TMS320C25-based data synthesis board. Through a large number of simulating experiments, the satisfactory results are obtained, which obviously improve the performance of telemetry system. Therefore, all those technigues and results have the value of practical applications.