| Author: | Zhan, Jia |
| Title: | Design of joint source-channel coding systems based on double P-LDPC codes |
| Advisors: | Lau, C. M. Francis (EEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Department: | Department of Electrical and Electronic Engineering |
| Pages: | xv, 125 pages : color illustrations |
| Language: | English |
| Abstract: | In a traditional joint source-channel coding system based on double protograph-based LDPC (DP-LDPC) codes, two P-LDPC codes are employed as the source code and the channel code, respectively. They are connected by a source-check-channel-variable (SCCV) linking matrix, which consists of an identity matrix and a zero matrix. This linking matrix connects check nodes (CNs) in the source P-LDPC code and variable nodes (VNs) in the channel P-LDPC code. A joint source-channel decoder that facilitates message exchange between the source decoder and the channel decoder is used to decode the source. Based on this traditional structure, this thesis proposes several novel joint source-channel coding systems, aiming at improving error performance further. Firstly, a novel class of DP-LDPC codes is proposed for the joint source-channel coding, where the identity matrix in the SCCV linking matrix of traditional DP-LDPC codes is replaced with a lower or upper triangular matrix with “1”s on its diagonal. By doing this, the flexibility of code design is increased and the linear source compression is preserved. Theoretical and simulation results have shown the superior performance of the proposed DP-LDPC codes compared to the traditional ones. Secondly, we propose a novel joint source-channel coding scheme based on spatially coupled DP-LDPC (SC-DP-LDPC) codes. It has been proved that a concatenated spatially coupled protograph-based LDPC (SC-P-LDPC) code can have better error performance than a traditional DP-LDPC block code. Motivated by this point, SC-DP-LDPC codes are proposed, where the source spatially coupled P-LDPC (SC-P-LDPC) code and the channel SC-P-LDPC code are linked by spatially coupled SCCV (SC-SCCV) connections. By doing this, source SC-P-LDPC and channel SC-P-LDPC are not in a simple concatenated relationship. Like decoding the concatenated SC-P-LDPC code, we use a sliding window joint belief propagation (BP) decoding algorithm to decode the SC-DP-LDPC code. Theoretical and simulation results show that the proposed codes are superior to the concatenated SC-LDPC codes and state-of-the-art DP-LDPC block codes. Thirdly, we propose two new types of joint source-channel coding systems for both low-entropy and high-entropy sources. Studies done by others have shown that for the traditional DP-LDPC codes, the source threshold can be improved by adding connections between VNs in source P-LDPC code and CNs in channel P-LDPC code, which is represented by a source-variable-channel-check (SVCC) linking (base) matrix. According to this finding and our first proposal, we propose a novel joint source-channel block code (JSC-BC) based on double P-LDPC block codes. Two P-LDPC block codes are connected not only by a source-variable-channel-check (SVCC) linking (base) matrix but also by a source-check-channel-variable (SCCV) linking (base) matrix, which consists of a zero matrix and a lower or upper triangular (base) matrix with “1”s on its diagonal. Also, we modify the traditional joint protograph-based extrinsic information transfer (JP-EXIT) algorithm to calculate the source threshold of a JSC-BC. The JP-EXIT algorithm uses the whole joint protomatrix to calculate the source threshold of a code. The new technique is called the untransmitted protograph-based EXIT (UP-EXIT) algorithm. Compared to the JP-EXIT algorithm, the proposed UP-EXIT algorithm is more efficient because a smaller protograph consisting of only the untransmitted VNs (i.e., the source VNs and the punctured channel VNs) and their connected check nodes need to be considered. We first search for the candidate codes with the proposed code structure and high source thresholds by using the UP-EXIT algorithm. Then we select those also with low channel thresholds among the candidate codes by using the JP-EXIT algorithm. Moreover, we construct new JSC-BCs whose decoding complexities are controlled by limiting their maximum row weights. Theoretical and simulation results show that the codes newly constructed outperform state-of-the-art DP-LDPC block codes. Next, we spatially couple the joint source-channel block code and obtain a spatially coupled joint source-channel code (SC-JSCC) for further error performance improvement. Theoretical analyses and simulation results show that even with a smaller window size and lower decoding complexity, the SC-JSCC with the spatially coupled structure for each sub-block (source protomatrix, channel protomatrix, SCCV linking matrix, and SVCC linking matrix) can have better error performance than existing spatially-coupled DP-LDPC codes. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/13242