Advanced Channel Coding for 5G Wireless System

Abstract

Channel coding may be viewed as the best-informed and most potent component of cellular communication systems, which is used for correcting the transmission errors inflicted by noise, interference and fading. The powerful turbo code was selected to provide channel coding for Mobile Broad Band (MBB) data in the 3G UMTS and 4G LTE cellular systems. However, the 3GPP standardization group has recently determined to replace it by Low Density Parity Check (LDPC) and polar codes in 5G New Radio (NR), which adopted the LDPC code family for enhanced Mobile Broad Band (eMBB) data and polar codes for eMBB control. Against this background, this thesis has deeply researched and reviewed the three main type of channel coding system, including turbo, LDPC and polar codes. We exploit these three channel coding systems from their encoding characterisations to the decoding performance. By the time of publishing of the 5G NR standardisation from the 3RD Generation Partnership Project (3GPP) group, we summarised the factors that influenced this standardisation, with a particular focus on the Application specific integrated circuit (ASIC) implementation of the decoders of these three codes. As presented in this thesis, we show that the overall implementation complexity of turbo, LDPC and polar decoders depend on numerous other factors beyond their computational complexity. More specifically, we compare the throughput, error correction capability, flexibility, area efficiency and energy efficiency of ASIC implementations drawn from 110 papers and use the results for characterising the advantages and disadvantages of these three codes as well as for avoiding pitfalls and for providing design guidelines. We then focus on one of the main channel coding systems in the 5G NR standard, namely the NR LDPC code. In this thesis, the full standard about the 5G NR LDPC code that is specified in TS38.212 [1] is presented with straight-forward context and corresponding illustrations. By contrast to the LDPC codes adopted in the previous standards, the NR LDPC code can be considered to be a concatenation of a LDPC code and a Low Density Generator Matrix (LDGM) code. This particular character has the advantage of offering a flexible coding rate, which actually effects the correctness of the conventional 2D Extrinsic Information Transfer (EXIT) chart analysis. In the thesis, we commence with the conventional 2D EXIT chart analysis for regular LDPC code as the background. Then, we characterise the incorrect 2D EXIT chart’s analysis and addresses it using a novel reinterpretation of the NR LDPC factor graph. Based on this factor graph, a novel 3D EXIT chart technique is conceived for our three-stage scheme, which facilities the visual characterisation of the NR LDPC decoder’s iterative decoding convergence process for the first time. We also introduce a novel 2D projection of the EXIT chart for NR LDPC decoder, which directly solve the problem that resulted by the conventional 2D EXIT chart. Since our novel EXIT chart analysis is able to describe the exchange of mutual information (MI) in NR LDPC decoder correctly, we research implementations relying-on our v novel EXIT charts. We demonstrate this technique by using it to design a novel iterative decoding activation order for the NR LDPC decoder, which reduces the decoding complexity by approximately 17% compared to a conventional flooding based decoder without any degrading of its error correction capability. We conclude by discussing several other opportunities for exploiting the proposed 3D EXIT chart technique to improve the design of concatenated LDPC and LDGM codes. We also use this novel EXIT chart analysis to improve the NR Hybrid Automatic Repeat reQuests (HARQ) system for LDPC coded data transmission that is specified in the NR standard by attaching two proposed scheme, namely the Deferred Iteration (DI) and the Early Abandon (EA). The proposed HARQ scheme significantly reduce the complexity of the conventional HARQ system without any degrading on the performance of effective throughput and error-correction.

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Identifiers

ORCID for Shuai Shao: orcid.org/0000-0003-4135-7973

ORCID for Robert Maunder: orcid.org/0000-0002-7944-2615

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