Irregular Variable Length Coding

In this thesis, we introduce Irregular Variable Length Coding (IrVLC) and investigate its applications, characteristics and performance in the context of digital multimedia broadcast telecommunications. During IrVLC encoding, the multimedia signal is represented using a sequence of concatenated binary codewords. These are selected from a codebook, comprising a number of codewords, which, in turn, comprise various numbers of bits. However, during IrVLC encoding, the multimedia signal is decomposed into particular fractions, each of which is represented using a different codebook. This is in contrast to regular Variable Length Coding (VLC), in which the entire multimedia signal is encoded using the same codebook. The application of IrVLCs to joint source and channel coding is investigated in the context of a video transmission scheme. Our novel video codec represents the video signal using tessellations of Variable-Dimension Vector Quantisation (VDVQ) tiles. These are selected from a codebook, comprising a number of tiles having various dimensions. The selected tessellation of VDVQ tiles is signalled using a corresponding sequence of concatenated codewords from a Variable Length Error Correction (VLEC) codebook. This VLEC codebook represents a specific joint source and channel coding case of VLCs, which facilitates both compression and error correction. However, during video encoding, only particular combinations of the VDVQ tiles will perfectly tessellate, owing to their various dimensions. As a result, only particular sub-sets of the VDVQ codebook and, hence, of the VLEC codebook may be employed to convey particular fractions of the video signal. Therefore, our novel video codec can be said to employ IrVLCs. The employment of IrVLCs to facilitate Unequal Error Protection (UEP) is also demonstrated. This may be applied when various fractions of the source signal have different error sensitivities, as is typical in audio, speech, image and video signals, for example. Here, different VLEC codebooks having appropriately selected error correction capabilities may be employed to encode the particular fractions of the source signal. This approach may be expected to yield a higher reconstruction quality than equal protection in cases where the various fractions of the source signal have different error sensitivities. Finally, this thesis investigates the application of IrVLCs to near-capacity operation using EXtrinsic Information Transfer (EXIT) chart analysis. Here, a number of component VLEC codebooks having different inverted EXIT functions are employed to encode particular fractions of the source symbol frame. We show that the composite inverted IrVLC EXIT function may be obtained as a weighted average of the inverted component VLC EXIT functions. Additionally, EXIT chart matching is employed to shape the inverted IrVLC EXIT function to match the EXIT function of a serially concatenated inner channel code, creating a narrow but still open EXIT chart tunnel. In this way, iterative decoding convergence to an infinitesimally low probability of error is facilitated at near-capacity channel SNRs

EXIT-chart aided near-capacity irregular bit-interleaved coded modulation design

A near-capacity irregular Bit-Interleaved Coded Modulation based Iterative Decoding (Ir-BICM-ID) aided scheme is proposed. The irregular design of the scheme pervades the three basic components of BICM-ID, namely the encoder, the unity-rate precoder and the bit-to-symbol mapper. As a result, irregular BICM-ID schemes constituted by irregular components are created, which are capable of approaching the capacity of coded modulation. This is achieved by creating a marginally open EXtrinsic Information Transfer (EXIT) chart tunnel, and exploiting the theorem that the open tunnel’s area is characteristic of how closely the scheme operates to the channel’s capacity. The proposed Ir-BICM-ID scheme employs Irregular Convolutional Codes (IrCC), Irregular Unity-Rate Codes (IrURC) and Irregular Mappers (IrMapper)

Iterative decoding of multilevel and bit-interleaved coded modulation

A comparative study of various codeq. modulation schemes is carried out in terms of their different block length, number of iterations and complexity, quantified by the number of trellis states as well as the EXtrinsic Information Transfer (EXIT) charts are used for analysing their decoding convergence and Bit Error Ratio (BER). A threeDimensional (3-D) EXIT chart is introduced for MultiLevel Coding (MLC) invoking MultiStage Decoding (MSD). Based on this 3-D EXIT chart, we design a precodedMLC scheme employing both MSD and Parallel Independent Decoding (PID). In order to provide space diversity, we study the new arrangement of Bit-Interleaved Coded Modulation with Iterative Decoding (BICM-ID) and MLC combined with Space Time Block Codes (STBC) invoking a novel Sphere Packing (SP) modulation scheme. An equivalent-capacIty-based design of MLCs based on this SP modulation is proposed. We use the Binary Switching Algorithm (BSA) to optimise our cost function for the sake of obtaining appropriate bit-to-SP-symbol mapping schemes. A hybrid mapping scheme is introduced for achieving unequal error protection. Furthermore, bit-to-SP-symbol mapping to 256 constellation points is designed for a serially concatenated BICM-ID aided twin-antenna STBC arrangement for creating a system, which is capable of outperforming an identical-throughput 16-level Quadrature Amplitude Modulation (16QAM) scheme. Furthermore, the benefits of MLC PID designs employing Generalised Low Density Parity Check (GLDPC) codes are investigated, which results in a low-delay scheme useful for multimedia transmission. A stopping criterion is designed for this scheme for the sake of terminating the iterative decoding process, once the target BER is attained. We then contrive coding schemes for the wireless Internet by introducing a BICM-ID scheme combined with Luby Transform (LT) coding constructed for the AWGN-contaminated Binary Erasure Channel (BEC). An improved robust LT packetdegree distribution is introduced for determining the specific number of LT source packets combined with modulo-2 additions in order to create an LT-encoded packet. Furthermore, a Log-Likelihood Ratio (LLR) based reliability estimation scheme is invoked in order to achieve a performance improvement based on this amalgamated design. Finally, a near-capacity Irregular Bit-Interleaved Coded Modulation with Iterative Decoding (Ir-BICM-ID) scheme was designed with the aid of an EXIT chart. An Irregular Convolution Code (IrCC) is proposed for the sake of introducing a diverse range of outer code EXIT functions. By contrast, the inner code is based on the serially concatenated components constituted by an Irregular Unity-Rate Code (IrURC) and an Irregular Mapper (IrMapper). An EXIT chart matching algorithm is invoked for constructing an Ir-BICM-ID scheme, which exhibits a narrow but still open EXIT tunnel and hence approaches the theoretical capacity limit.EThOS - Electronic Theses Online ServiceGBUnited Kingdo