Research On The Construction Of Rate-Compatible Low-Density Parity-Check Codes

With the increasing requirement of high throughput in modern communication system, rate compatible technic rises in response to the proper time and condition. Compared with traditional fixed coding scheme, HARQ system with rate compatible error correction codes is able to improve transmission efficiency significantly. Among several existed error correction codes, LDPC codes have been drawing more and more attention due to their Shannon limit approaching performance under various channel conditions. Considering several advantages of LDPC codes, the research, including the construction of rate compatible LDPC codes with high structuring and low complexity, and its application in HARQ system, has significant meaning. This thesis investigates on the construction of rate compatible LDPC codes, explores the design of mother code, extending algorithm and puncturing algorithm deeply, and finally realize a kind of rate compatible LDPC codes with ideal performance. The main work and innovative points are summarized as follows:1. Based on the analysis of factors influencing the performance of LDPC codes, a construction method of IRA-like codes based on ACE optimization is proposed. It realizes a kind of LDPC codes with good structuring, low complexity and low storage, and provides good foundation for the realization of rate compatible algorithm.2. Based on the structure characters of parity check matrix of IRA-like codes, do the research on the extension of information nodes and parity nodes respectively. As for the extension of parity nodes, the effect of degree 1 nodes is analyzed with Gaussian Approximation, and finally degree 1 nodes are selected as extended parity nodes. As for the extension of information nodes, an extending method based on M-PEG algorithm is presented, which maximizes the girth in Tanner Graph as well as enhances the dependency between newly added and original matrix.3. Based on the zigzag pattern of IRA-like codes, an efficient puncturing algorithm is put forward. Following the principle of minimizing the recovery step of punctured nodes, the algorithm adopts a kind of reverse thinking that the order of punctured nodes is determined by way of assuming that all parity nodes are punctured firstly and then recovered one by one. The puncturing algorithm is able to reduce the impact on code performance efficiently.4. According to the analysis of factors influencing the performance of LDPC codes and the principles for extending and puncturing, the reason why the rate compatible LDPC codes in this thesis outperforms existed rate compatible LDPC codes is explored. Using the simulation data, together with the trait of data transmission, the throughput performance of type Ⅱ HARQ system is compared and analyzed.