A Collaborative Cooperation Scheme using Hierarchical Modulation

In this paper, a novel forward link collaborative cooperation scheme using hierarchical modulation is proposed. Relay stations in a cell are assumed to operate in half-duplex mode. This leads to the degradation of throughput [bits/sec/Hz] performance due to the effect of additionally required resource for relaying. To overcome this limitation, we define a cooperative unit cell as a unit which includes base-station (BS), fixed relay- station (FRS) and two types of mobile-station (MS) being the relay-assisted mobile-station (RAMS) and the non-relay-assisted mobile-station (NRAMS). For collaboration between BS-FRS- RAMS link and BS-NRAMS link in the cooperative unit cell, hierarchical modulation is exploited. By using hierarchical modulation which enables simultaneous transmission of two data streams and provides multi-level protections, the proposed strategy yields an improved throughput reducing total transmission time in the cooperative unit cell. From the exact BER (bit error rate) performance of hierarchical modulation, throughput performance of the proposed strategy is deduced. It is shown that the proposed strategy recovers the throughput performance loss of half-duplex relay and outperforms the conventional cooperative and non-cooperative communication strategies with respect to the throughput performance.