Cooperative beamforming and relay selection in cognitive radio systems (original) (raw)
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ArXiv, 2014
In order to address the asynchronous interference issue for a generalized scenario with multiple primary and multiple secondary receivers, in this paper, we propose an innovative cooperative beamforming technique. In particular, the cooperative beamforming design is formulated as an optimization problem that maximizes the weighted sum achievable transmission rate of secondary destinations while it maintains the asynchronous interferences at the primary receivers below their target thresholds. In light of the intractability of the problem, we propose a two-phase suboptimal cooperative beamforming technique. First, it finds the beamforming directions corresponding to different secondary destinations. Second, it allocates the power among different beamforming directions. Due to the multiple interference constraints corresponding to multiple primary receivers, the power allocation scheme in the second phase is still complex. Therefore, we also propose a low complex power allocation algo...
This paper has investigated linear beamforming techniques in relay networks with one source and multiple relays and destinations with the goal to determine the beamforming matrix so that the signal to noise plus interference ratio at the destination is maximized subject to different power constraints. Two power constraints were considered here: 1-a total (source and relay) power constraint and 2-individual relay power constraints. The key point of this paperwas tha only the second order statistics of channel state information (CSI) was proposed for use which is a more realistic scenario than the case where instantaneous CSI is assumed to be perfectly known at the relay place. It was considered that the source is equipped with multiple transmit antennas and hence it transmits a vector of several symbols at each time. Based on a former work of (J. Li, A. P. Petropulu and H. V. Poor 2011), this new optimization problem was solved and it was shown that despite some losses when compared to the case of zero forcing (ZF) precoding with perfect channel state information (CSI), the obtained results clearly show that second order statistics based beamforming algorithms are good candidates to reliably support multiple parallel data streams with SINR requirements in multiuser multi-relay systems.