Cooperative relaying has played an important role in rapid evolution of wireless communications.The cooperative performance strongly depends on the selected relays.In this paper,we concentrate on relay selection in amplify-and-forward(AF)cooperative communication system,and an optimal multi-relay selection scheme is put forward to minimize the average symbol error rate(SER)of the system.Firstly,for the minimum average SER,on the basis of the statistic channel information,we define a parameter named equivalent channel gain which describes the channel status of two phases in the cooperative process.Then,under the constraint of equal power allocation,an optimal relay selection scheme is proposed in ascending order of equivalent channel gain(ECG).The scheme implies that the suitable number of relay nodes should be selected under the different signal-to-noise ratio(SNR)ranges to minimize the average SER.Computer simulation results show that the average SER rate of the proposed scheme is lower than these of the other schemes.
Considering the joint channel estimation and data detection in time-varying orthogonal frequency division multiplexing （OFDM） and addressing transmission performance degradation induced by the severe inter-carrier interference （ICI） at very high speed, a new progressive iterative channel estimation scheme is proposed. To alleviate the error propagation of the inaccurate data due to ICI, the measurement subcarriers in the Kalman filter is designed to be extended from pilots subcarriers to all the subcarriers progressively through the iterations. Furthermore, in iteration process, the interference of the non-pilot data to the measurement subcarriers is considered to be part of noise in the modified Kalman filter, which improves the estimation accuracy. Simulation indicates that the proposed scheme improves the performance in fast time-varying situation.
YANG Rui-zheYE Si-yangZHANG Yan-huaSUN Yan-huaYU Richard
The intersubcarrier interference(ICI) degrades the performance of the pilot-aided channel estimation in fast time-varying orthogonal frequency division multiplexing(OFDM) systems.To solve the error propagation in joint channel estimation and data detection due to this ICI,a scheme of error propagation determined iterative estimation is proposed,where in the first iteration,Kalman filter based on signal to interference and noise is designed with ICI transformed to be part of the noise,and for the later iterations,a determined iterative estimation algorithm obtains an optimal output from all iterations using the iterative updating strategy.Simulation results present the significant improvement in the performance of the proposed scheme in high-mobility situation in comparison with the existing ones.
