Research On Rate-Compatible LDPC Codes For Ieee 802.11 Ac Stardard

Future broadband wireless communication systems need highly reliable transmission in limited spectrum resource, and the channel coding schemes of high reliability are crucial. As a channel coding scheme which is approaching the channel capacity very closely, QC-LDPC codes with low complexity encoding, self-interleaving, low error floor, and many other advantages, become an optional channel coding scheme of the latest WLAN standard (IEEE802.11ac).In this thesis, a systematic research on the basic principle and encoding and decoding algorithms of LDPC codes has been conducted. In order to find the optimal decoding algorithms for IEEE 802.11ac standard LDPC codes, we have studied the improved decoding algorithms of LDPC codes in recent years, especially the newly proposed two-dimensional normalized min-sum (2D-NMS) decoding algorithm and adaptive normalized min-sum (AN-MS) decoding algorithm. The superior performance of the improved decoding algorithms through simulations has been verified. We also establish the IEEE 802.11ac standard codec simulation platform, and present the simulation performance of IEEE 802.11ac standard LDPC codes.Over time-varying channels, error-correction codes with adaptive rates and lengths according to the channel conditions can improve the transmission efficiency and the reliability of the system significantly. In such a case, a plurality of encoders and decoders obviously have high complexity to be realized, so a rate-compatible channel coding scheme of a single encoder and decoder is more realizable. Rate-compatible codes are effective to achieve adaptive coding rate and length. And these codes can use the same pair of encoder and decoder, so it has been widely applied in the practical communication system. Shortening, puncturing and repetition are combined to realize the rate-compatible in the WLAN. However, the WLAN shortening and puncturing algorithms are too simple to obtain optimal performance.In this thesis, two novel pruning schemes of quasi-cyclic (QC) Low-Density Parity-Check (LDPC) codes for wireless local area networks (WLAN) are proposed. They can be effectively applied to individual shortening and joint shortening and puncturing. By taking consideration of different shortening or puncturing impact on individual variable nodes, the proposed schemes are performed based on sequential criteria and destruction force. The pruning scheme based on sequential criteria select the optimal pruning patterns according to approximate cycle extrinsic message degree of variable nodes, and the pruning scheme based on destruction force selects the optimal pruning patterns according to the total destruction force of variable nodes. Simulation results demonstrate that the two proposed schemes can significantly improve the performance compared with the existing methods.