AG Kommunikationstheorie

Thema:

Algorithms for Interference Mitigation with Bidirectional Relay Stations

Abstract:

Cooperative relay systems play a significant role in coverage extension in the mobile networks. We consider two-way relay systems in which a multiple antenna relay receives data symbols coincidentally from different users, and maybe from a base station. Before the relay broadcasts the received signal towards all users, it performs appropriate signal processing (amplify-and-forward) in order to minimize total interference in the network. We first consider a multi-pair relay system where a multiple antenna relay station assists two groups of single antenna users. Relay is subject to a power constraint. We aim at maximizing minimum achievable rate of all users. The resulting optimization problem is nonconvex and NP-hard, in general. We first, solve this problem using semidefinite programming with bisection over SINR (signal-to-interference-plus-noise ratio) to have a reference model. Afterwards, we find the so-called minimax bound of minimum SINR in the network using which the original problem turns into an overdetermined system of quadratic equations. This unconstrained least-square problem will be solved using Levenberg-Marquardt method. Then, bisect over SINR in order to not violate power constraint. The convergence of this method is proven and complexity analysis is also given. We will observe that in addition to low-complexity the result is near-optimal. Later, we consider an asymmetric network and replace one of the groups of users with a multiple antenna base station. We first design a precoder for the base station, independently from the choice relay precoder. The proposed algorithm is closed-form and is succeeded with a fast iterative method for power allocation. Later, after the base station precoder is known the previous Levenberg-Marquardt method is applied to design the relay precoder. The main contribution of the proposed algorithm for joint relay-base stations design is imposing no alternating iteration, unlike most related works, and having a sub-optimal result in one and only one iteration.



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