1,720,983 research outputs found
Iterative decoding convergence and termination of serially concatenated codes
No full textIn this paper we demonstrate that previously proposed serially concatenated codes only facilitate iterative decoding convergence towards points that are near but not at the top-right hand corner of the EXIT chart, which typically results in an error floor. Furthermore, we propose a novel method for approaching the (1,1) point of the EXIT chart, where the Maximum Likelihood (ML) Bit Error Ratio (BER) performance is attained. Our method employs specifically designed termination sequences having a free distance of at least two to terminate an inner recursive code. Additionally, we provide optimal termination sequences for a range of inner code designs. Finally, we demonstrate that our novel approach facilitates useful BER reductions in the challenging application scenario when employing short frame lengths of the order of 100 bits, which are typical in wireless sensor networks, for example
Genetic algorithm aided design of component codes for irregular variable length coding
Full text linkIn this paper we propose a novel Real-Valued Free Distance Metric (RV-FDM) for comparing the error correction capabilities of Variable Length Error Correction (VLEC) codebooks that have the same integer-valued free distance lower bounds. We demonstrate that VLEC codebooks having higher RV-FDMs tend to have EXtrinsic Information Transfer (EXIT) functions with more pronounced 'S'-shapes. Furthermore, we show that higher-accuracy EXIT chart matching can be achieved if the component EXIT functions of an irregular code exhibit more variety. This motivates the employment of our novel genetic algorithm for designing the component VLEC codes of irregular variable length coding, that have particular EXIT functions, in addition to exhibiting desirable bit entropies and decoding complexities
Near-capacity irregular variable length coding and irregular unity rate coding
Full text linkIn this contribution we introduce an EXtrinsic Information Transfer (EXIT) chart matching technique for the design of two serially concatenated irregular codecs, each constituted by a variety of component codes. This approach facilitates a higher degree of design freedom than matching the EXIT function of an irregular codec to that of a regular codec, comprising only a single component code. As a result, a narrow EXIT chart tunnel can be created, facilitating operation at SNR values that are closer to the channel's capacity bound. This is demonstrated for a serial concatenation of iteratively decoded Irregular Variable Length Coding (IrVLC) and Irregular Unity Rate Coding (IrURC), which is favourably compared with an IrVLC and regular Unity Rate Coding (URC) based benchmarker. Finally, we show that the iterative decoding complexity of our IrVLC-IrURC scheme can be reduced by about 25% upon employing a method of jointly performing EXIT chart matching, while seeking a reduced iterative decoding complexit
Block-based precoding for serially concatenated codes
No full textPrecoders have been shown to facilitate iterative decoding convergence towards the Maximum Likelihood (ML) performance in serially concatenated schemes. In this letter, we propose a novel block-based precoder as an alternative to classic convolutional precoders. Furthermore, we demonstrate that the proposed block-based precoder facilitates operation at significantly reduced channel Signal to Noise Ratios (SNRs) in practical schemes, having limited latencies, as well as limited implementational and computational decoding complexities
Irregular Variable Length Coding
Full text linkIn 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
Concatenated Irregular Variable Length Coding and Irregular Unity Rate Coding
Full text linkIn this contribution we propose the novel serial concatenation of Irregular Variable Length Coding (IrVLC) and Irregular Unity Rate Coding (IrURC), where we matched the corresponding EXtrinsic Information Transfer (EXIT) functions to each other. This approach facilitates a higher degree of design freedom than matching the EXIT function of an irregular codec to that of a regular codec. As a result, a narrower EXIT chart tunnel can be created, facilitating operation at SNR values that are closer to the channel's capacity bound. The computational complexity and Bit Error Ratio (BER) performance of our IrVLC-IrURC scheme is favourable in comparison to the bench markers that replace either one or both of the irregular codecs by the equivalent-rate regular codec
Extrinsic Information Transfer Analysis and Design of Block-Based Intermediate Codes
Full text linkIntermediate codes have been shown to facilitate iterative decoding convergence to the maximum likelihood error ratio performance in serially concatenated schemes. In this paper, we propose a novel block-based intermediate code as an alternative to classic convolutional intermediate codes. Since it is block-based, our intermediate code facilitates practical implementations having reduced memory and processing requirements. Furthermore, we demonstrate that it is simpler to analyse and optimise the iterative decoding process, when our block-based intermediate code is employed instead of a convolutional intermediate code. Finally, we demonstrate that the proposed block-based intermediate code facilitates significantly reduced error ratios in practical schemes, when employing short transmission frames and a limited decoding complexity
Genetic Algorithm Aided Design of Near-Capacity Irregular Variable Length Codes
No full textIn this paper we demonstrate that our ability to match the EXtrinsic Information Transfer (EXIT) function of an Irregular Variable Length Code (IrVLC) to that of a serially-concatenated inner code depends on the availability of a suite of component Variable Length Error Correction (VLEC) codebooks having a wide variety of inverted EXIT function shapes. We also show that the inverted EXIT function shape of a VLEC codebook depends on its coding rate and Error Correction Capability (ECC). This motivates the design of a Genetic Algorithm (GA) that searches the large VLEC parameter space to find codebooks having specific coding rates, ECCs and, hence, EXIT function shapes. The employment of this GA therefore facilitates the design of component VLEC codebook suites without the manual trial-and-error that is required when employing the state-of-the-art Heuristic Algorithm (HA) used as our bench marker, which cannot design component VLEC codebooks having specific EXIT function shapes
Evolutionary Algorithm Aided Interleaver Design for Serially Concatenated Codes
Full text linkIn this paper, we propose an algorithm for designing the interleavers of Serially Concatenated Codes (SCCs), in order to increase the Minimum Hamming Distance (MHD) between the legitimate permutations of the encoded bit sequence and hence to improve the corresponding error floor. Unlike previous so-called Code Matched Interleaver (CMI) designs, our approach is capable of creating interleavers for serial concatenations of both irregular and non-linear codes, as well as achieving MHDs that are arbitrarily close to the maximum possible, provided that a sufficiently high off-line complexity is affordable. However, owing to the efficiency of the proposed approach, only a relatively low number of algorithm generations are required to achieve significant improvements to the error floor of low-delay wireless sensor network, speech and audio schemes, for example. Indeed, we demonstrate that our interleavers are capable of completely eradicating the error floors that would otherwise be apparent, if classic random or S-random interleavers were employed
Iterative Detection of Three-Stage Concatenated FFH-MFSK
No full textSerially concatenated and iteratively decoded Irregular Variable Length Coding (IrVLC) combined with precoded Fast Frequency Hopping (FFH) M-ary Frequency Shift Keying (MFSK) is considered. We employ EXtrinsic Information Transfer (EXIT) charts to investigate the 3-stage concatenation of the FFH-MFSK demodulator, the rate-1 decoder and the outer IrVLC decoder. The proposed joint source and channel coding scheme is capable of operating at low Signal-to-Noise Ratio (SNR) in Rayleigh fading channels contaminated by Partial Band Noise Jamming (PBNJ). The IrVLC scheme is comprised of a number of component Variable Length Coding (VLC) codebooks employing different coding rates for encoding particular fractions of the input source symbol stream. These fractions may be chosen with the aid of EXIT charts in order to shape the inverted EXIT curve of the IrVLC codec so that it can be matched with the EXIT curve of the inner decoder. We demonstrate that using the proposed scheme an infinitesimally low bit error ratio may be achieved at low SNR values
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