Research On Key Technologies In Wireless Relay Cooperative Systems

The aspiration of communicating anywhere at any time boosts the evolution of wireless networks. The relay based wireless networks have solved many problems that exist in the traditional wireless networks, e.g. the covergence and capacity, thus the concept of relaying is a promising solution for the challenging throughput and high data rate coverage requirements of future wireless cellular networks. The dissertation focuses on the key techniques in wireless relay systems, and gives a thorough and comprehensive study on the distributed space-time cooperative system design, timing synchronization scheme and admission control(CAC) mechanism.Firstly, focused on the normal cooperative relay system, the bit error rate(BER) and capacity performance of amplify-and-forward (AF) and decode-and-forward (DF) relaying method are respectively studied. We further derive the closed form expression of outage probability for DF under Rayleigh fading channel. Then, we study the BER performance of AF and DF distributed space-time cooperative relay system under block-fading Rayleigh channel.The extension to distributed space-time cooperative diversity networks with frequency-selective fading channels is investigated. We present a new scheme of joint equalization and interference cancellation by single carrier frequency domain equalization (SC-FDE) for Alamouti-like space-time block-coded (STBC) transmissions. Furthermore, the problem of lacking of perfect timing synchronization in the distributed space-time cooperative relay system is studied, including the research of orthogonal frequency division multiplexing (OFDM) based system. We propose a timing synchronization scheme to improve the performance of the receiver.The dissertation makes further investigation on the admission control(CAC) problem in multi-service cellular relay system with orthogonal frequency division multiplexing access (OFDMA).Subjected to constraints of the quality-of-service (QoS) requirements and the capability of relay, the admission control problem could be formulated to maximize the amount of subcarriers decreased by relaying transmission. With further consideration of the user's selection of relays and the competence among users, several new algorithms are proposed. Meanwhile, the effect caused by the ratio of services with different transmission rates is studied by simulation.