Spectral efficiency and energy efficiency of distributed space-time relaying models

Cooperative relay techniques are exploited to reduce the transmission energy consumption which is very important for average and long range transmission in wireless sensor networks (WSNs). In this paper, the system having a two-antenna source, two one-antenna relays and a one-antenna destination is considered. Using distributed space-time code at relays, MIMO simple cooperative relay model (MSCR) and MIMO full cooperative relay model (MFCR) are proposed in comparison with MIMO normal cooperative relay model (MNCR) where the relays forward signals consecutively to destination. The outage probability analysis derives that all the models have the diversity order of 4. However, the analytic and simulation results show that MFCR has better performance than MNCR, whereas MSCR provides better spectral efficiency than MNCR. Moreover, the energy efficiency of these models is also considered by using a realistic power consumption model where the parameters are extracted from the characteristics of CC2420, a wireless sensor transceiver widely used and commercially available. For each transmission ranges, the optimal cooperative scheme in terms of energy efficiency is provided by simulation results.