Channel-coded time-hopping and direct-sequence ultrawideband systems

This thesis is aimed at providing detailed transceiver structures employing novel channel coding schemes for enhancing the achievable performance of UltraWideBand (UWB) systems. We commence by a rudimentary introduction to UWB systems, including a brief historical perspective of the field. Chapters 2 to 4 will then provide the designs of channel coded UWB systems with the aid of EXtrinsic Information Transfer (EXIT) charts in order to achieve near-capacity performances. Each chapter constitutes an evolutionary improvement of the previous chapter. Chapter 2 deals with the UWB channel, which is one of the major factors differentiating UWB system from their narrow-band counterparts. This chapter starts with a brief review of the last two decades’ advances in UWB channel estimation. Then the z-domain Discrete Time Transfer Function (DTTF) of UWB channels is derived based on the specifications presented in the preceding sections. This transfer function forms the basis of the proposed memory-efficient implementation of the equalizer advocated. Furthermore, the stability analysis and Mean Convergence Bound (MCB) of the UWB channel transfer function is presented. The UWB channel model is then used by all the following chapters, when developing enhanced UWB systems. Chapter 3 starts with the implications of appropriate diversity order selection. Since it is possible to resolve the closely spaced multipath components of the channel, the system benefits from a high number of independent fading paths, which results in a high multipath diversity gain. Then we propose an EXIT chart aided iteratively detected Direct-Sequence (DS) Code Division Multiple Access (CDMA) system, which uses 2-stage concatenation of an inner and outer encoders, with their corresponding decoders exchanging extrinsic information for the sake of enhancing the attainable system performance. This system model constitutes the foundation for the following chapters, which will be further developed using different coding schemes with the aid of EXIT charts. A DS and a Time-Hopping (TH) Pulse Position Modulated (PPM) UWB systems are studied using EXIT charts and it is demonstrated that classic regular Forward Error Correction (FEC) encoders are unable to arbitrarily approach the system’s capacity. Hence Chapter 4 provides a solution for this problem by replacing the regular FEC codes with more sophisticated irregular FEC codes that are capable of approaching the system’s capacity more closely. More specifically, we have used Irregular Variable Length Codes (IrVLC) in our design of a two-stage concatenated UWB TH Spread-Spectrum (SS) Impulse Radio (IR) system. We then progressed from the two-stage design philosophy to three-stage irregular concatenated UWB systems. Naturally, an improved performance is only achievable at the cost of an increased complexity and interleaver length. Hence, the second half of Chapter 4 addresses the above-mentioned complexity and interleaver delay problem by invoking sophisticated binary Self-Concatenated Convolutional Codes (SeCCC) using different puncturing rates. We commence with a rudimentary introduction of the binary SeCCC design, which is then used for developing a near-capacity TH UWB system. Finally, the achievable performance gains of different puncturing and coding rates are detailed.