Performance Improvement of Cooperative MB-OFDM System Based Coming Home Network

Since ultra wideband (UWB) system aims at low complexity, low cost, and low power consumption, employing multiple antennas seems not to be a good approach to improving error performance for UWB devices. On the contrary, recently developed cooperative diversity technique, which profits the transmit diversity only with the existing hardware by constituting a virtual antenna array, can be a solution. However, most of the introduced cooperative techniques have a common fault of decreased transmission rate because the destination should receive the decodable compositions of symbols from the source and the relay. In this paper, we propose an alternative use of hierarchical modulation and a suitable cooperative space-time block code (C-STBC). This technique is free from the rate-loss and allows seamless cooperative communication while similar diversity gain is benefited. The proposed technique is evaluated in terms of bit error rate (BER) for multi-band orthogonal frequency division multiplexing (MB-OFDM) system. Simulation results show that cooperative system based on our technique outperforms noncooperative one when relatively reliable source-to-relay link (S-R link) is guaranteed.