Abstract
This paper addresses the filter design issues for multiuser cooperative nonregenerative MIMO relay systems in both downlink and uplink scenarios. Based on the formulated signal model, the filter matrix optimization is first performed for direct path and relay path respectively, aiming to minimize the mean squared error (MSE). To be more specific, for the relay path, we derive the local optimal filter scheme at the base station and the relay station jointly in the downlink scenario along with a more practical suboptimal scheme, and then a closed-form joint local optimal solution in the uplink scenario is exploited. Furthermore, the optimal filter for the direct path is also presented by using the exiting results of conventional MIMO link. After that, several schemes are proposed for cooperative scenario to combine the signals from both paths. Numerical results show that the proposed schemes can reduce the bit error rate (BER) significantly.
Highlights
Wireless relays are essential to provide reliable transmission, high-throughput, and broad coverage for next-generation wireless networks [1]
It is clear that the cooperative system can be divided into two paths, that is, the direct path and the relay path
As the optimal filter for the direct path can be obtained by using the exiting results of conventional MIMO link, we focus on the optimization for the relay path first
Summary
Wireless relays are essential to provide reliable transmission, high-throughput, and broad coverage for next-generation wireless networks [1]. In [16], the optimal design of nonregenerative relays for multiuser MIMO-relay systems based on sum rate is investigated. We consider the problem of joint linear optimization for both downlink and uplink in multiuser cooperative nonregenerative MIMO-relay systems based on MSE criterion, which is different from the sum rate criterion in [16]. (i) We derive the optimal joint design of the BS and RS filter matrices that achieves the minimum mean squared error (MMSE) for both downlink and uplink of the multiuser MIMO relay systems at the absence of direct path. E(·) and tr(·) denote the expectation and trace operation, respectively, and, I is the identity matrix
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