关键词: 低密度奇偶校验码, 缩短码, IEEE802.16e, 短环, 编码算法

Abstract: The shortened LDPC codes based on the current IEEE802.16e Standard, has plenty of small girth. In order to resolve this problem, this paper presents a new scheme of designing the shortened LDPC codes. In the proposed scheme, the design has modified the sub-parity check matrix under the frame of the IEEE802.16e Standard. The proposed check matrix with the spreading factor (zf=48) is constructed with quasi-cyclic matrix method and finite geometry method. Moreover, parity check points was searched the node degree in the way of synchronous sequential, the proposed sub- parity check matrix has minor girth-6 and no girth-4. The results of simulation in the AWGN channels show that the improved short code with the code rate approaching to 0.5, can fast encode as excellent as the IEEE802.16e protocol contains，moreover, a good BER performance of the proposed code is 1.1dB more than the Shannon limit of this channel.

Key words: （Low Density Parity Check Code）LDPC, shortened code, IEEE802.16e, Short Cycles, encoding algorithm