54 research outputs found
Multilevel structured low-density parity-check codes for AWGN and Rayleigh channels
No full textWe propose a novel class of protograph low-density parity-check (LDPC) codes having a combinatorial rather than a random structure, which are termed multilevel-structured (MLS) LDPC codes. It is demonstrated that they posses a strikingly simple structure and, thus, benefit from reduced storage requirements, hardware-friendly implementations, and low-complexity encoding. Our simulation results provided for both additive white Gaussian noise (AWGN) and uncorrelated Rayleigh (UR) channels demonstrate that these advantages accrue without compromising the attainable bit error ratio (BER) and block error ratio (BLER) performance, when compared with their previously proposed more complex random-construction-based counterparts, as well as with other structured codes of the same length
Generalized MIMO transmit preprocessing using pilot symbol assisted rateless codes
No full textIn this paper, we propose a generalized multiple-input multiple-output (MIMO) transmit preprocessing system, where both the channel coding and the linear MIMO transmit precoding components exploit the knowledge of the channel. Moreover, we also propose a novel technique, hereby referred to as pilot symbol assisted rateless (PSAR) coding, where a predetermined fraction of binary pilot symbols is interspersed with the channel-coded bits at the channel coding stage, instead of multiplexing the pilots with the data symbols at the modulation stage, as in classic pilot symbol assisted modulation (PSAM). We will subsequently demonstrate that the PSAR code-aided transmit preprocessing scheme succeeds in gleaning more beneficial knowledge from the inserted pilots, because the pilot bits are not only useful for estimating the channel at the receiver, but they are also beneficial in terms of significantly reducing the computational complexity of the rateless channel decoder
Myths and Realities of Rateless Coding
No full textFixed-rate and rateless channel codes are generally treated separately in the related research literature and so, a novice in the field inevitably gets the impression that these channel codes are unrelated. By contrast, in this treatise, we endeavor to further develop a link between the traditional fixed-rate codes and the recently developed rateless codes by delving into their underlying attributes. This joint treatment is beneficial for two principal reasons. First, it facilitates the task of researchers and practitioners, who might be familiar with fixed-rate codes and would like to jump-start their understanding of the recently developed concepts in the rateless reality. Second, it provides grounds for extending the use of the well-understood code design tools — originally contrived for fixed-rate codes — to the realm of rateless codes. Indeed, these versatile tools proved to be vital in the design of diverse fixed-rate-coded communications systems, and thus our hope is that they will further elucidate the associated performance ramifications of the rateless coded schemes
Channel code division multiple access and its multilevel structured LDPC based instantiation
No full textIn this paper, we introduce and outline the concept of Channel Code Division Multiple Access (CCDMA) using a design example based on the recently proposed Multilevel Structured (MLS) LDPC codes. We succeeded in making the memory requirements of the multi-user transceiver to become practically independent of the total number of users supported by the system as well as ascertain that each user benefits from the same Quality of Service (QoS). Finally, we will demonstrate that despite their beneficial compact structure, the proposed MLS LDPC codes do not suffer from any Bit Error Ratio (BER) or Block Error Ratio (BLER) performance degradation, when compared to an otherwise identical benchmarker scheme using significantly more complex LDPC codes having pseudo-random parity-check matrices
Design of low-density parity-check codes: An overview
No full textThis article provides an overview of the conflicting design tradeoffs of low-density parity-check (LDPC) codes and thus advocates a more holistic approach to their design for wireless channels. We reveal some of the intricate interdependencies of the LDPC code parameters and hence recommend designing codes that strike an attractive tradeoff concerning a number of desirable attributes, rather than simply designing codes that closely approach capacity but possess less-attractive hardware implementations
Near-capacity fixed-rate and rateless channel code constructions
No full textFixed-rate and rateless channel code constructions are designed for satisfying conflicting design tradeoffs, leading to codes that benefit from practical implementations, whilst offering a good bit error ratio (BER) and block error ratio (BLER) performance. More explicitly, two novel low-density parity-check code (LDPC) constructions are proposed; the first construction constitutes a family of quasi-cyclic protograph LDPC codes, which has a Vandermonde-like parity-check matrix (PCM). The second construction constitutes a specific class of protograph LDPC codes, which are termed as multilevel structured (MLS) LDPC codes. These codes possess a PCM construction that allows the coexistence of both pseudo-randomness as well as a structure requiring a reduced memory. More importantly, it is also demonstrated that these benefits accrue without any compromise in the attainable BER/BLER performance. We also present the novel concept of separating multiple users by means of user-specific channel codes, which is referred to as channel code division multiple access (CCDMA), and provide an example based on MLS LDPC codes. In particular, we circumvent the difficulty of having potentially high memory requirements, while ensuring that each user’s bits in the CCDMA system are equally protected. With regards to rateless channel coding, we propose a novel family of codes, which we refer to as reconfigurable rateless codes, that are capable of not only varying their code-rate but also to adaptively modify their encoding/decoding strategy according to the near-instantaneous channel conditions. We demonstrate that the proposed reconfigurable rateless codes are capable of shaping their own degree distribution according to the near-instantaneous requirements imposed by the channel, but without any explicit channel knowledge at the transmitter. Additionally, a generalised transmit preprocessing aided closed-loop downlink multiple-input multiple-output (MIMO) system is presented, in which both the channel coding components as well as the linear transmit precoder exploit the knowledge of the channel state information (CSI). More explicitly, we embed a rateless code in a MIMO transmit preprocessing scheme, in order to attain near-capacity performance across a wide range of channel signal-to-ratios (SNRs), rather than only at a specific SNR. The performance of our scheme is further enhanced with the aid of a technique, referred to as pilot symbol assisted rateless (PSAR) coding, whereby a predetermined fraction of pilot bits is appropriately interspersed with the original information bits at the channel coding stage, instead of multiplexing pilots at the modulation stage, as in classic pilot symbol assisted modulation (PSAM). We subsequently demonstrate that the PSAR code-aided transmit preprocessing scheme succeeds in gleaning more information from the inserted pilots than the classic PSAM technique, because the pilot bits are not only useful for sounding the channel at the receiver but also beneficial for significantly reducing the computational complexity of the rateless channel decoder
Reconfigurable rateless codes
No full textWe propose novel reconfigurable rateless codes, that are capable of not only varying the block length but also adaptively modify their encoding strategy by incrementally adjusting their degree distribution according to the prevalent channel conditions without the availability of the channel state information at the transmitter. In particular, we characterize a reconfigurable ratelesscode designed for the transmission of 9,500 information bits that achieves a performance, which is approximately 1 dB away from the discrete-input continuous-output memoryless channel’s (DCMC) capacity over a diverse range of channel signal-to-noise (SNR) ratios
Low-density parity-check codes and their rateless relatives
No full textThis survey guides the reader through the extensive open literature that is covering the family of low-density parity-check LDPC codes and their rateless relatives. In doing so, we will identify the most important milestones that have occurred since their conception until the current era and elucidate the related design problems and their respective solutions
Construction of regular quasi-cyclic protograph LDPC codes based on Vandermonde matrices
No full textIn this contribution, we investigate the attainable performance of quasi-cyclic (QC) protograph Low-Density Parity-Check (LDPC) codes for transmission over both Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh channels. The codes presented are constructed using the Vandermonde matrix and benefit from both low-complexity encoding and decoding, low memory requirements as well as hardware-friendly implementations. Our simulation results demonstrate that the advantages offered by this family of QC protograph LDPC codes accrue without any compromise in the attainable Bit Error Ratio (BER) and Block Error Ratio (BER) performance. In fact, it is also shown that despite their implementational benefits, the proposed codes exhibit slight BER/BLER gains when compared to some of their more complex counterparts of the same length
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