Performance of Half-Duplex Relays in Downlink Cellular Systems

For cellular systems, the performance improvements due to half- duplex low-power relays as compared to a no relay baseline are evaluated here via simulation. Each relay that has a better channel from the base station than the user can decode the message and then help the user so that the relay and base power add at the user's location. Comparisons are done in the context of a 19-cell, 57-sector set-up in which each of the served users must be delivered a message. The user messages are taken to have the same size and 90% of the users in the network must be served. The baseline has a fixed common rate requirement of 1 bit/sec/Hz. All simultaneous transmissions mutually interfere. Improvements due to relays are evaluated for the case of full power transmission from the base stations and relays and for the case of power controlled base stations and relays. In both of these cases, the ability of relays to reduce peak base transmit power while delivering the baseline rate or alternately to increase the user rate is computed. In the full power case, when users get their message they leave the system thus reducing the overall interference. The peak power saving is then 1.46 dB, alternately, the throughput improvement over the 1 bit/sec/Hz baseline rate is 21%. When power control is employed the peak power saving is 2.6 dB. Furthermore, the total power in the system is reduced so the total energy expended in the system can be reduced by 3 dB. We also observe a 34% improvement over the baseline rate in the common rate to the users in the system.