Current Journal of Applied Science and Technology

Aims: Joint Power control and beamforming in MIMO one way AF relay networks by obtaining beamforming weights on relay nodes through maximizing sum rate while the total power consumed in all relay nodes are not greater than the certain predefined threshold.
Study Design: Comparative study by simulation in MATLAB software.
Place and Duration of Study: Digital Communications Signal Processing Research Lab., Shahid Rajaee Teacher Training University, Since June 2012 to June 2014.
Methodology: We consider a wireless communication network consisting of d source-destination pairs communicating in a pairwise manner via R non regenerative one way relay nodes. Our objective is maximizing sum rate supposing that the total power consumed in all relay nodes is not greater than the certain predefined threshold. It is shown that finding beamforming matrix which satisfies our goal is a non-convex problem. So, we use semidefinite relaxation technique to turn this problem into a semidefinite programming (SDP) problem. We propose two new algorithms which maximize total signal to total leakage (interference plus noise) ratio (TSTLR).
Results: Simulation results show that our proposed algorithm is a low-complex algorithm and outperforms the existing total leakage minimization algorithm, named TL. In addition, the effect of the number of relays, the number of transmitter-receiver pairs, quality of uplink as well as downlink channels and imperfect channel state information (CSI) are investigated.
Conclusion: The proposed method maximizes the total signal to total leakage ratio by maximizing the difference between the numerator and the denominator. It is shown that when the number of relays increases or the quality of uplink and downlink channels improves, higher sum rate can be achieved. Moreover, by increasing the number of source – destination pairs the sum rate increases, too. Also, it is shown that when uncertainty of channels increases the achievable sum rate decreases.