The Research On Delay Elimination In Cooperative Communication Based On Frequency Domain Equalization

Cooperative communication system can be formulated as virtual MIMO (Multi-Input Multi-Output) systems. However, different from MIMO, one challenge for cooperative communication is that the relays are dispersed in space and the distances from relays to the destination are different. So, a major problem for cooperative communication is how to eliminate the propagation delay of each link. In this paper, frequency domain equalization (FDE) is proposed in order to eliminate the impact of these delays on system performance.Chapter 2 proposes the cooperative communication system model with propagation delay. Specially, instructions the damage to the space-time signal structure due to the presence of delay errors compared with the fully synchronized cooperative system.Chapter 3 studies how to overcome these different delays by the frequency domain equalization technology in cooperative communication system. Firstly, impact of delays on the parallel relay cooperative communication system is analyzed theoretically, as well as the block diagram of frequency domain equalization and several commonly used algorithms are introduced. Then this chapter analyses how to use a cyclic prefix to overcome different delays. It's proved that frequency domain equalization is able to guarantee system performance while the computational complexity is lower compared with the time domain equalization.Chapter 4 proposes a full-diversity time-space coding cooperative frequency domain equalization scheme based on AF (Amplify and Forward) and DF (Decode and Forward) cooperative transmission mechanisms in further. This scheme combines the time-space signal designing in the relay node and frequency-domain equalization in the destination node in which the relay node operates simple inversion, conjugate, etc, and the destination node takes full advantage of the FFT(Fast Fourier Transform) IFFT(Inverse Fast Fourier Transform) in computational complexity. By comparison of delay tolerant the STTC (space-time trellis code) and OFDM (Orthogonal Frequency Division Multiplexing) frequency domain equalization, simulation results show that the superiority of the proposed method in complexity and performance.