Abstract-1 Shannon's channel capacity specifies the upper bound on the amount of bits per channel use. In this paper, we explicitly demonstrate that twin-component turbo codes suffer from a capacity loss, when the component code rate is less than unity, which is shown by exploiting the so-called area properties of Extrinsic Information Transfer (EXIT) charts. This capacity loss is unavoidable for twin-component turbo codes, when the overall turbo coding rate is less than 1/2, while multiple-component turbo codes are capable of overcoming it by using unity-rate component codes. In order to demonstrate that multiplecomponent turbo codes are capable of exhibiting a better asymptotic performance, the minimum Signal Noise Ratio (SNR) required for the EXIT charts to have open convergence tunnels is used as our metric, which is referred to as 'the open tunnel SNR threshold'. Furthermore, the employment of conventional two-dimensional EXIT charts is extended to facilitate the analysis of N -component turbo codes. Our results confirm that multiple-component turbo codes approach the Discrete-input Continuous-output Memoryless Channel's (DCMC) capacity more closely and achieve a lower Bit Error Ratio (BER) than twin-component turbo codes at the same coding rate and the same complexity.
Abstract-1 Hybrid Automatic Repeat reQuest (ARQ) plays an essential role in error control. Combining the incorrectly received packet replicas in hybrid ARQ has been shown to reduce the resultant error probability, while improving the achievable throughput. Hence, in this contribution, multi-level turbo codes have been amalgamated both with hybrid ARQ and efficient soft combining techniques for taking into account the LogLikelihood Ratios (LLRs) of retransmitted packet replicas. In this paper, we present a soft combining aided hybrid ARQ scheme based on multi-level turbo codes, which avoid the capacity loss of the twin-level turbo codes that are typically employed in hybrid ARQ schemes. More specifically, the proposed receiver dynamically appends an additional parallel concatenated Bahl, Cocke, Jelinek and Raviv (BCJR) algorithm based decoder in order to fully exploit each retransmission, thereby forming a multi-level turbo decoder. Therefore, all the extrinsic information acquired during the previous BCJR operations will be used as a priori information by the additional BCJR decoders, whilst their soft output iteratively enhances the a posteriori information generated by the previous decoding stages. We also present linklevel Packet Loss Ratio (PLR) and throughput results, which demonstrate that our scheme outperforms some of the previously proposed benchmarks.
Abstract-Fountain codes constitute novel erasure codes, which have been standardized for Forward Error Correction (FEC) in broadcast network protocols and by the Third-Generation Partnersonhip Project (3GPP). The basic operational units of Fountain codes are source packets, which have a particular fixed length. These codes are invoked here in an 802.11 Wireless Local Area Network (WLAN) scenario for protecting file transfers. More specifically, the optimal packet length is selected by considering the 802.11 Media Access Control (MAC) retransmission rate and the properties of the physical layer's modulation scheme. Naturally, owing to the limited memory of the encoders/decoders, large source files must be decomposed into shorter transport blocks. Therefore, methods for partitioning the file and acknowledging the successful transmission of each block are also proposed here. Compared to the file transfer regime operating without FEC over the classic TCP protocol, the proposed regime requires a lower threshold SNR for accomplishing a successful file transfer and hence enhances the transmission efficiency by about 50%.
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