Ldpc Codes And Its Application In Research And Application Of Coded Modulation Systems

Nowadays, with mobile communication's development in broadband in a high-speed, spectrum resource has become increasingly valuable, how to transmit more information with the limited bandwidth becomes a very practical problem. Coded Modulation scheme is an effective way to address this issue. Coded Modulation integrate coding and modulation together, it enhances the effectiveness of the bandwidth, meanwhile it keeps the effectiveness of the power efficiency. Trellis coded modulation (TCM) and block coded modulation (BCM) are two main kinds of Coded modulation.LDPC codes have high-performance which is close to the Shannon Limit, and its coding schemes could be achieved. this paper do some research on the efficient coded modulation scheme of LDPC code.The main contribution of this paper is constituted of three parts as following:(1) Based on the research on Bit-interleaved code modulation (BICM). We introduce a new method that combines LDPC with BICM, due to the randomness of LDPC coding, LDPC-BICM coded modulation scheme could omit the interleaver. On Rayleigh channel, this paper investigates and analyzes the channel state information's influence on the performance of the LDPC-BICM system scheme.(2) In this paper, according to the bits' different protection capability in QAM constellation points, we propose to use an inner-interleaved LDPC coding method, it can arrange information bits with a specific way. We design a simulation of 16 QAM modulation, simulation results prove that the new coding scheme is better than random coding schemes.(3) In order to alleviate the contradiction between power effectiveness and spectrum effectiveness, this paper proposes a system scheme that combines LDPC codes and trellis coded modulation (TCM). In order to use soft decoding method (SOVA algorithm) based on log-likelihood ratio of bits, we make use of recursive system convolutional Code as component code of TCM. We Analyzes the system's performance in additive white Gaussian noise channel and in Rayleigh channel. The simulation results show that the system can use spectrum resource moreeffectively and have better performance than normal LDPC schemes.These results show that LDPC-BICM and LDPC-TCM systems have good performance and have good application Prospects in the future's communication.