Analysis Of Relay Channel Capacity And LDPC-Coded Cooperations With The Applications For Satellite Communications

Information theory、Channel coding and Cooperative communication are the main theories of digital communication system. Based on the characteristics and laws of information, the main task of Information theory is to provide theoretical basis to design an effective and reliable communications system. Channel coding, developed under the guidance of information theory and gradually matured, provides effective ways to transmit information in the channel reliably. LDPC code, as one of the most outstanding and popular channel coding techniques, performs well near to the shannon limit and has been widely applied. Cooperative communication , as the key technology of future mobile communications, the basic idea of which is that the cooperative users can achieve the benefits from diversity through a signaling scheme that allows them to send their information using both of their antennas, just like a virtual MIMO system.This paper starts from the core principles of information theory, and it proposed modified chernoff bound innovatively, which is applied to get the tight upperbound of tail probability of n i.i.d random variables. Then, according to shnnon random code andε- typical sequence, it carried out the derivation and proof of capacity of single relay channel. Next, from LDPC code and cooperative communication analysis, a cooperative communication scheme based on regular LDPC codes is proposed. And they are also apply to improve the performance of satellite communications.The specific contents are as follows:1. After understanding chernoff bound、AEP and large deviation theory throughly, the problem was faced that the upper-boud of tail probability of n i.i.d random variables calculated by chernoff bound is too loose. So this paper proposed modified chernoff bound to qualify the tail probability more precise.2. After studying the shannon random code and channel coding theory, the paper analyzed the channel capacity. It includes some basic channels of communication system and the emphasis is the single relay channel. For single relay channel, an achieveable rate formula and a simple coding scheme to achieve it are presented. For degraded channel, this achievable rate is shown to be the exact capacity.3. Proposed a cooperative communication scheme based on regular LDPC codes and joint decoding over the relay channel. In the first stage of decoding, two decoders at the destination node decode their own received symbols, and then output the corresponding soft detection information separately. In the process of joint decoding, two sets of soft information from the respective different decoders, which are complementary with each other, are incorporated into one step of signal estimation. This joint decoding achieves the coding gains from the employed LDPC codes and the diversity gains from the cooperative strategy.4. Apply the LDPC code to the satellite communications. Rain attenuation is a dominant influence in satellite communication, which greatly affects the transmission quality and limits system’s availability. In order to overcome such difficulties, this paper used the LDPC code to get the high gains to compensate rain attenuation. Otherwise, we also used the aided channel in satellite communication system as the cooperative channel to get the diversity gains to improve the performance.