In this paper we study the threshold decode and forward (T-DF) fixed relays network with beamforming, which is more reliable than conventional decode and forward (DF) relaying. Deployment of a small number of antennas on fixed relays is easier than on mobile terminals, therefore, the impact of multiple antennas on the outage probability of cooperating fixed relays is considered. Under the total sum power constraint (TSPC) of all relays and also maximum per-relay power constraint (PRPC), the optimum beamforming weights have been found to maximize the received SNR at the destination. It is determined that increasing the number of relays and antennas at each relay increases capacity. The performance of threshold-maximal ratio combining (T-MRC) and threshold-selection combining (T-SC) of the multiple-antenna multiple fixed relays with beamforming is derived. It is observed that the performance of the network with selection combining (SC) configuration is close to the network in which maximal ratio combining (MRC) is used, in addition that it is less complex and less expensive to implement. The outage probability in Rayleigh fading channels is also analyzed.
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