Research On Puncture Algorithm For Rate-Compatible Low-Density Parity-Check Codes And Its Applicitions

With the high development of wireless communication technologies, people have the requirements for better quality and higher capacity of communication. In the growing shortage of band resources, how to maximize the spectral efficiency and guarantee reliability of system is widely concerned and studied in wireless communication field.Channel coding is an important way to improve system efficiency. As a kind of channel coding with high encoding gain, LDPC codes has become a hot topic in the area of channel coding, due to its excellent performance such as approaching to Shannon limit and low implementation complexity. Adaptive modulation and coding is one of link adaptive technologies which can improve the spectrum efficiency, and has become one of essential methods. Therefore, if we combine rate compatible LDPC codes with adaptive coding and modulation, high resistance to noise and spectral efficiency can be gained. First, this paper summarizes foundational theories of LDPC codes, including the history, the developing situation, the methods of Tanner representation and constructing parity check matrix and the encoding and decoding algorithms. The regular and irregular LDPC codes are compared through simulation. We choose the irregular LDPC codes with a good performance as a study object.Second, on the basis of the existing studies, we introduce rate-compatible LDPC codes and design a new puncturing algorithm——the Maximum Girth Puncturing Scheme. Based on the simulation results, we can see that the new algorithm has a better performance than the random puncture algorithm and is easily implemented. Compared with progressive edge-growth (PEG) method, the maximum girth puncturing scheme has a low complexity with the similar bit error rate, and can be used in adaptive modulation and coding system.Finally, the new algorithm is used in AMC system. A simulation module is built on AWGN channel. Fixed threshold MCS algorithm is adopted to optimize the threshold of SNR. We adopt HSDPA standard level 7 as MCS options. Through the curves of bit error rate and spectral efficiency, we get the optimum switching thresholds. The simulation results also show that the AMC system based on RC-LDPC codes performs better than that based on Turbo codes.