Probabilistic based TX-beamformer design under partial CSIT using optimized SINR estimate

A long-standing problem in CoMP is that existing methods either require perfect and instantaneous CSIT which implies the need of excessive piloting and backhauling, so as to acquire and distribute CSIT accurately and timely. Thus, it is required to formulate a robust beamforming method to circumvent this drawbacks and has been the focus of many research papers recently. In this paper, a solution to the problem, which follows a relaxation-restriction (RAR) approach and emerges from the observation that the crux of the robustness problem is the construction of the SINR estimates themselves, subject to partial CSIT. Specifically, it is shown considering SINR-constrained transmit-power minimization that CoMP algorithms built using the biased estimator significantly outperform the best recent alternative method, namely the outage based probabilistic approach with Bernstein-type inequality relaxation of [1]. Our proposed alternative is also less relaxed as compared to existing literature. The level of conservatism can be further reduced through incorporating bisection method on top of the robust SINR-constrained optimization problem so that the required outage probability in this case is satisfied as per the user requirement and transmit power efficient solutions is obtained.