This letter proposes a relay selection scheme in order to improve a performance in the wireless cooperative communication system. The cooperative communication uses the relays in order to obtain a improved performance. The relay selection scheme has a great influence on the performance of the wireless cooperative communication. Because the diversity gain is affected by the superposition of the channels, a superposition of the channels is important in the wireless cooperative communication. The constructive superposition of the channels can improve the performance of the wireless cooperative communication. Because the conventional schemes do not consider the superposition of the channels, the conventional schemes are not suitable for the cooperative communication using the multiple relays. The new scheme considers the superposition of channels and selects the relays that can achieve the constructive superposition. Therefore, the new scheme can provide the improved performance by using the phase information between channels. The simulation results show that the bit error performance of the proposed scheme is better than the conventional schemes.

This letter proposes a cooperative communication scheme with pre-coding in order to improve a performance in a wireless communication system. In a conventional scheme, a performance of the system is degraded due to the signal attenuation by the path loss and inter-cell interference (ICI). The proposed scheme uses two relays in order to obtain a diversity gain. Additionally, the proposed scheme uses a constructive spatial phase coding (SPC) using the phase relation of the channels in order to obtain an improved diversity gain. Therefore, the proposed scheme can prevent the performance degradation caused by the path loss. When a mobile is located in the cell edge, the signal suffers from the ICI by the other signals transmitted from a neighboring base station. In the proposed scheme, the other signals broadcast from neighboring base station are destructively superimposed by using the destructive SPC scheme. And then the power of the destructively superimposed signal is reduced. Therefore, the proposed scheme can reduce the ICI effect in the cell edge. Also, the destructively superimposed signal does not cause the performance degradation of other mobiles in the neighboring cell. The simulation results show that the bit error performance of the proposed scheme is better than the conventional scheme.