Parallel Concatenated Gallager Codes Research Articles

A comprehensive review of parallel concatenation of LDPC code techniques

Objective: In the code theory, parallel concatenation of codes becomes more popular after the introduction of turbo codes. In recent years, the Low Density Parity Check (LDPC) code has found remarkable advancement and has seen them outshine turbo codes in terms of performance especially in the error floor and higher code rate. The main objective of this paper is to address the various techniques of a parallel concatenation of LDPC code in code theory. Method/Finding: To reduce the complexity of encoding and decoding for longer codes various parallel concatenation of LDPC coding methods were introduced and the performance was compared with other work. Novelty: When a longer block length is used, the parallel LDPC decoder is suffered from the complexity of prohibitive implementation. To overcome this issue and to achieve the best performance for longer codes, the different methods for parallel concatenation of LDPC codes were introduced with reduced complexity. This will helps to break the long and complex LDPC code into less complex and smaller LDPC to distribute the decoding and encoding load. Also, this will provides scalability and scope for improving the performance of LDPC codes in practical delay-sensitive and energy-aware applications. Keywords: Parallel concatenation; LowDensity ParityCheck (LDPC); turbo codes; Parallel Concatenated Gallager Codes (PCGC)

Joint sub-Nyquist wideband spectrum sensing and reliable data transmission for cognitive radio networks over white space

The emerging cognitive radio technology resolves the spectrum scarcity problem by exploiting the unutilised licenced spectrum on an opportunistic basis. Meanwhile, future cognitive devices require advanced sensing techniques for rapid and active identification of spectrum holes over a wideband. Incorporation of prior information from the geolocation database enhances the sensing performance, reduces the computation complexity and maximizes the spectrum utilisation by white space devices. However, unlike the TV white space database, other wideband spectrum databases are not yet available. Therefore for dynamic and fragile cognitive networks, the geolocation database cannot assist the spectrum sensing process, which necessitated database-independent real-time spectrum sensing. Constant interference from primary users is yet another major challenge with cognitive radio networks which makes reliable communication extremely difficult for secondary users. Forward error correction codes ensure the reliability of transmitted data, among which low-density parity check codes are the most appropriate. Lengthy low-density parity check codes, however, have certain drawbacks specifically high encoding and decoding complexity. Parallel concatenated Gallager code addresses these issues. This paper presents a reliable data transmission scheme for secondary users using the proposed non-zero syndrome parallel concatenated Gallager codes with interleaver for cognitive radio networks performing real-time spectrum sensing over white space. The joint sensing scheme along with prior knowledge from the geolocation database improves the spectrum sensing performance with reduced complexity and is more suitable for low-power cognitive devices. Further, simulation results affirm that proposed PCGC outperform a dedicated LDPC in terms of coding gain and bit-error rate.

Parallel concatenated Gallager codes for reliable data transmission in cognitive radio networks

Cognitive radio technology addresses the problem of spectrum scarcity by providing an opportunity for secondary users to exploit the unutilised licenced spectrum. However, constant interference from primary users makes reliable communication extremely challenging for secondary users in cognitive radio networks. Forward error correction codes ensure the reliability of transmitted data, among which low-density parity check codes are the most appropriate. Lengthy low-density parity check codes, however, have certain drawbacks specifically high encoding and decoding complexity. Parallel concatenated Gallager code addresses these issues. This paper evaluates the performance of various parallel concatenated Gallager codes in a dynamic and fragile cognitive radio network environment where the secondary users are prone to constant interference from the primary users. Simulation results affirms that proposed parallel concatenated Gallager codes outperform a dedicated low density parity check code of same frame length and code rate.

Modification of extrinsic information for parallel concatenated Gallager/Convolutional code to improve performance/complexity trade-offs

To benefit the properties of both Low-Density Parity-Check (LDPC) and Turbo Convolutional Codes (TCC), we propose a practical concatenated Gallager/Convolutional code in a turbo coding way. The modified code creates a balance between the advantages and the disadvantages of LDPC and TCC in terms of the overall complexity and latency. This will be done through two different component SISO decoders; LDPC and convolutional code of the same rate 1/2 without interleaver. Since the two SISO decoders are different in nature, they exchange extrinsic information that will be easily adapted to each other. The study of computation complexity and decoding performance over an AWGN channel indicates that such approach leads to excellent performance because of several factors. The proposed approach achieves a trade-off between waterfall and error floor regions. It reduces complexity decoding compared to TCC and 3D - TCC. It provides a better coding gain over LDPC and PCGC (Parallel Concatenated Gallager Codes). These features will ensure optimal outcomes and cost-performance ratio, and thus, this trend can be the best choice for today's communication systems.

Multiple Parallel Concatenated Gallager Codes: Code Design and Decoding Techniques

A novel technique to concatenate multiple component low density parity check (LDPC) codes in parallel is presented. Multiple Parallel Concatenated Gallager Codes leverage the advantage of breaking an equivalently long LDPC code into multiple small (lower-complexity) LDPC codes to offer scalability and scope for improving performance in practical implementation for delay-sensitive and resource-constrained applications. The construction as well as two proposed decoding techniques for MPCGCs is evaluated. It is shown that by optimizing the construction of the component LDPC codes and the number of decoding iterations at various channel conditions, the performance of MPCGCs can be significantly improved and their complexity reduced.

Analysis and design of parallel concatenated Gallager codes

The convergence characteristics of parallel concatenated Gallager codes using the Gaussian approximation of extrinsic information are analysed. A design strategy is introduced to select the component low-density parity-check codes effectively.

Parallel concatenated Gallager codes

A class of concatenated codes called parallel concatenated Gallager codes (PCGCs) in which low density parity check (LDPC) codes are used as the component codes is presented. Simulation results for PCGCs that outperform comparable LDPC codes in an AWGN channel are also presented.