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Joint Source Power Allocation and Distributed Relay Beamforming Design in Cognitive TwoWay Relay Networks
Binyue LIU Guiguo FENG Wangmei GUO
Publication
IEICE TRANSACTIONS on Communications
Vol.E97B
No.8
pp.15561566 Publication Date: 2014/08/01 Online ISSN: 17451345
DOI: 10.1587/transcom.E97.B.1556 Type of Manuscript: Special Section PAPER (Special Section on EU's FP7 ICT R&D Project Activities on Future Broadband Access Technologies in Conjunction with Main Topics of 2013 IEICE ICT Forum) Category: Keyword: cognitive twoway relay networks (CTRN), power allocation and distributed beamforming (PADB), iterative algorithm,
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Summary:
This paper studies an underlaybased cognitive twoway relay network which consists of a primary network (PN) and a secondary network (SN). Two secondary users (SUs) exchange information with the aid of multiple singleantenna amplifyandforward relays while a primary transmitter communicates with a primary receiver in the same spectrum. Unlike the existing contributions, the transmit powers of the SUs and the distributed beamforming weights of the relays are jointly optimized to minimize the sum interference power from the SN to the PN under the qualityofservice (QoS) constraints of the SUs determined by their output signaltointerferenceplusnoise ratio (SINR) and the transmit power constraints of the SUs and relays. This approach leads to a nonconvex optimization problem which is computationally intractable in general. We first investigate two necessary conditions that optimal solutions should satisfy. Then, the nonconvex minimization problem is solved analytically based on the obtained conditions for singlerelay scenarios. For multirelay scenarios, an iterative numerical algorithm is proposed to find suboptimal solutions with low computational complexity. It is shown that starting with an arbitrarily initial feasible point, the limit point of the solution sequence derived from the iterative algorithm satisfies the two necessary conditions. To apply this algorithm, two approaches are developed to find an initial feasible point. Finally, simulation results show that on average, the proposed lowcomplexity solution considerably outperforms the scheme without source power control and performs close to the optimal solution obtained by a grid search technique which has prohibitively high computational complexity.

