Performance evaluation of CoMP for downlink 60-GHz radio-over-fiber fronthaul

We propose and experimentally demonstrate a downlink 60-GHz millimeter-wave radio-over-fiber fronthaul incorporating coordinated multipoint (CoMP) transmission scheme. CoMP function is implemented in the centralized baseband unit to obtain the transmission diversity. Space-time diversity gain is exploited to improve the data rate of cell-edge users as well as the coverage of 60-GHz small cells. To serve a cell-edge user, Alamouti space-time block code (STBC) is used between two coordinated remote radio heads (RRHs). 2 Gbps 4-QAM signal was transmitted over 3 km fronthaul link. Experimental results show that receiver sensitivity of CoMP system can be improved by 1.8 dB compared with two RRHs transmission without STBC at BER=1e-4. The impact of time synchronization errors between two cooperative channels is also analyzed. The coordinated fronthaul scheme employing STBC can be tolerable to much higher delays than would be possible for two channels transmission without STBC.