Diversity combining with LDPC codes over fading channels

• Main Author: Tan, Beng Soon.
• Other Authors: Li Kwok Hung
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/51169
• Institution: Nanyang Technological University

Diversity-combining techniques have been used to combat the effects of multipath fading. The objective of these techniques is to make use of diversity branches to improve the signal-to-noise ratio (SNR) of the received signal, leading to better system performance. Some of the traditional diversity-combining techniques include maximum-ratio combining (MRC), equal-gain combining (EGC), selection combining (SC), and switch combining. MRC is an optimum diversity-combining technique in the absence of interference. However, its complexity is high as knowledge of the channel fading amplitude and phase are required. In order to reduce complexity for MRC, hybrid forms of diversity combining such as generalized selection combining (GSC) have been proposed. However, the trade-off is a slight degradation in system performance. Space-time block coding (STBC) is often used to provide transmit diversity over fading channels. More recently, a single transmit antenna selection (TAS) system, which selects the branch with the largest channel gain for transmission, has been proposed. It has been shown that the TAS is able to outperform the STBC with the same number of transmit and receive antennas. However, it comes with the additional complexity of a feedback channel. Low-density parity-check (LDPC) codes, which make use of the sum-product algorithm for decoding, have been shown to give excellent performance that can approach the Shannon limit. The sum-product algorithm is an iterative scheme that improves the reliability of the log-likelihood ratios passing between the bit and check nodes through each iteration. Generally, the analysis of LDPC codes has been restricted to simulations and density evolution (DE) due to the com- plex iterative decoding process.