User Coded Cooperative Communication Based On OFDM System

In current communication field, mobile communication is the most dynamic mean of communication. In order to offer high-speed multimedia services, it is in compelling needs to improve performance and capacity of communication systems. Signal transported in mobile communication channels suffers from serious fading attenuation. As a result, a variety of technologies are proposed to overcome fading in mobile communication channels, for an example, MIMO (multiple-input multiple-output) technology has been proved to be able to effectively overcome signal fading. However, wireless ad hoc networks do not usually have a fixed infrastructure, so it is difficult to apply MIMO technology in ad hoc networks. Additionally, the small size and cost constraints of manufacturing mobile devices sometimes make the use of multiple antennas problematic. Coded user cooperative communication technology is capable of provide transmit diversity gain through combining channel coding and cooperation. In a cooperative network, two or more mobiles share their information and transmit jointly as a virtual antenna array. The technology provides higher data rates and spatial diversity and decreased sensitivity to channel variations.This paper mainly studies on user coded cooperative communication technology utilizing OFDM (Orthogonal Frequency Division Multiplexing) technology, which is one of the predominant technologies of 4G. Rsearch of this paper develops based on two methods, re-encoding and RCPC (rate-compatible punctured convolutiona) code.For the method of en-coding coded cooperative communication, we study its FEP (frame error probability) performance, through which we can find that diversity gain is achieved which depends on the number of non-zero taps in inter-user channel and user-destination channels. Moreover, we argue that for good inter-user channel, coded cooperation indeed achieves full diversity; when the inter-user channel is very noisy, even though cooperation does not provide diversity gain, there is still some coding gain compared with traditional communication. In a cooperative network, the partner overhears a noisy version form inter-user channel, so code used in cooperation have to be carefully designed to offer optimal performance.For coded cooperation based on RCPC code, traditional coded cooperation is introduced; FEP and code selection is discussed as well. In addition, we analyze the impact of cooperative ratio on diversity gain. Moreover, two improved schemes of adaptive coded cooperation and ARQ-based coded cooperation are introduced.The paper is organized as follows. The first chapter presents mobile communication environment and user cooperative communication. In the second chapter, user coded cooperative communication based on OFDM system is introduced. Two coded cooperation schemes, re-encoding-based coded cooperative communication and RCPC-based coded cooperative communication are discussed in detail in the third and fourth chapters respectively. Finally, we conclude in the fifth chapter; the application of network coding in user cooperative communication is mentioned as well.