Abstract
This paper considers coordinated transmission for interference mitigation and power allocation in a correlated two-user two-hop multi-input multioutput (MIMO) relay system. The proposed transmission scheme utilizes statistical channel state information (CSI) (e.g., transmit correlation) to minimize the cochannel interference (CCI) caused by the relay. To this end, it is shown that the CCI can be represented in terms of the eigenvalues and the angle difference between the eigenvectors of the transmit correlation matrix of the intended and CCI channel, and that the condition minimizing the CCI can be characterized by the correlation amplitude and the phase difference between the transmit correlation coefficients of these channels. Then, a coordinated user-scheduling strategy is designed with the use of eigen-beamforming to minimize the CCI in an average sense. The transmit power of the base station and relay is optimized under separate power constraint. Analytic and numerical results show that the proposed scheme can maximize the achievable sum rate when the principal eigenvectors of the transmit correlation matrix of the intended and the CCI channel are orthogonal to each other, yielding a sum rate performance comparable to that of the minimum mean-square error-based coordinated beamforming which uses instantaneous CSI.
Highlights
The use of wireless relays with multiple antennas, so-called multi-input multioutput (MIMO) relay, has received a great attention due to its potential for significant improvement of link capacity and cell coverage in cellular networks [1,2,3,4,5,6,7,8]
When relay users and direct-link users coexist in multiuser MIMO relay channels, it is of an important concern to develop a MIMO relay transmission strategy that mitigates cochannel interference (CCI) caused by the relay [4]
We have considered the use of coordinated transmission for the interference mitigation and power allocation in a correlated two-user two-hop MIMO relay system
Summary
The use of wireless relays with multiple antennas, so-called multi-input multioutput (MIMO) relay, has received a great attention due to its potential for significant improvement of link capacity and cell coverage in cellular networks [1,2,3,4,5,6,7,8]. In a multiuser MIMO cellular system, recent works have shown that the CCI caused by adjacent base stations (BSs) can be mitigated with the use of coordinated beamforming (CBF) [15,16,17] They derived a closed-form expression for the minimum mean square error (MMSE) and zero-forcing (ZF)-based CBF [15] in terms of maximizing the signalto-interference plus noise ratio (SINR) [18, 19]. We consider coordinated transmission for the CCI mitigation and power allocation in a correlated two-user two-hop MIMO relay system, where one is served through a relay and the other is served directly from the BS. Throughout this paper, lower- and uppercase boldface are used to denote a column vector a and matrix A, respectively; AT and A∗, respectively, indicate the transpose and conjugate transpose of A; a denotes the Euclidean norm of a; tr(A) and det(A), respectively, denote the trace and the determinant of A; IM is an (M × M) identity matrix; E{·} stands for the expectation operator
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