Efficient optimal power allocation for MIMO MAC in cognitive radio networks

This paper considers a cognitive radio (CR) network, in which the unlicensed (secondary) users (SUs) are allowed to concurrently access the spectrum allocated to the licensed (primary) users provided that their interference to the primary users (PUs) satisfies certain constraints. Under ensuring the quality of service (QoS) of the PUs, the precious spectrum resource can be utilized by maximizing the sum-rate and optimizing power allocation of the SUs. On the other hand, the multiple-antenna mobile user case needs further investigating for the problem mentioned above. Thus, we simply term this setting as multiple input multiple output multiple access channels (MIMO-MAC) in the CR Networks. To effectively and efficiently optimize the power allocation of the SUs, a tight pair of upper and lower bounds, as an interval, of the optimal Lagrange multiplier is proposed. Furthermore, a novel water-filling is proposed for the inner loop computation of the proposed problem. It is shown that the new water-filling can obtain the exact solution with a few finite computations. Therefore, not only is convergence of the proposed algorithm guaranteed, but efficient computation is also provided by the proposed algorithm.