Design Of Cross-Layer System Combining ACM With HARQ Based On LDPC Codes

Along with the development of wireless communication, the main issue of future wireless communication is poor spectrum resources against the increasing demand of high-speed and high-quality communication. ACM and HARQ are two well used link adaptation techniques. Combining ACM with HARQ can increase the spectrum efficiency of the system greatly, for ACM of physical layer provides the coarse data rate selection based on channel conditions, while HARQ of data link layer provides fine adjustment of data rate. Based on the HARQ protocol in IEEE 802.16e systems, the dissertation proposed a cross-layer optimization algorithm, which efficiently combined the sub-packet transmission scheme at data link layer and the ACM at physical layer. Then, with a better PER, the number of sub-packets and the coding and modulation scheme were jointly optimized to maximize the spectral efficiency of the system. And a novel criterion on the SNR threshold of ACM was also given with taking the HARQ protocol into consideration.Firstly, the dissertation studied the fundamental theory of LDPC codes, including its foundational principle, coding and decoding technologies, and the generating of check matrix. And then, compared the BER of progressive edge-growth (PEG) method and random construction method.Secondly, the dissertation introduced the basic principal and characteristics of ACM, and focused on ACM based on the channel state information. About the adaptive algorithm, it researched three common method of selecting ACM scheme thresholds.Thirdly, I carried out simulation for three types of ARQ transfer mode, and compared their transmitting efficiency, so as to choose the best to formulate HARQ. At the next step, I compared the PER of three types of HARQ techniques, then confirmed the best one for cross-layer design.Finally, the complete model of cross-layer system combining ACM with HARQ based on LDPC codes was given. The dissertation also analyzed the system's working progress and confirmed the modulation and coding algorithm. Through computer simulation, PER and spectrum efficiency performances of the new algorithm and the conditional one were analyzed and contrasted under Rayleigh channel. The simulation results suggested that the new algorithm can enhance the spectrum efficiency of system obviously with an approximately equal PER.