Multiuser cooperative relay communication employing hierarchical modulation

We develop a scheme to improve data throughput for multiuser cooperative relay communications operating in half-duplex mode. Cooperative relay, while effective in mitigating fading effects, might reduce the overall throughput of the network since it requires additional resources for relay. In order to overcome this limitation, we develop a multiuser cooperative communication scheme that employs hierarchical modulation. This scheme exploits the different fading conditions for each user and allows the system to transmit two independent data streams simultaneously. Since the bit-error rate of the proposed system is a function of the distance parameters of hierarchical modulation, transmission reliability can be controlled flexibly by varying the distance parameter. We derive the error-rate expressions of the proposed scheme and compare its symbol-error rate performance for specific distance parameters with that of conventional relay schemes.