Spectral efficiency comparison between MC-CDMA two-hop relay systems with different channel information

The knowledge of channel state information (CSI) is crucial for improving the performance of cooperative communication systems. In multiuser two-hop relay systems, the global CSI between a relay and multiple source-and-destination nodes can be estimated at the relay, and the local CSI between each node and the relay can be estimated at each node. In this paper, we analyze the spectral efficiency of multicarrier code-division multiple-access (MC-CDMA) two-hop relay systems, either with global CSI only at the relay or with local CSI only at every node. We resort to asymptotical analysis with random-matrix theory to derive the average spectral efficiency of decode-and-forward (DF) and amplify-and-forward (AF) two-hop relay systems. We then analyze the impact of spreading sequences, fading channel statistics, and low-complexity transceivers. Analytical and simulation results show that when an orthogonal spreading sequence is used, the relay system with local CSI only at every node is spectrally more efficient than that with global CSI only at the relay. Moreover, an artificially constructed one-tap spreading sequence can achieve a good tradeoff between the performance and the complexity.