We propose two novel clustered linear precoding schemes applicable to network multi-input multi-output systems using only partial channel state information to enhance the sum-rate of the system. Using a channel model that decomposes a multi-input multi-output channel matrix into transmit and receive steering vectors and assuming that only transmit steering vectors are available at the base transmit stations, we, first, propose a regularized channel inversion precoding scheme to enhance the sum-rate assuming only single-antenna users are available in the system. Next, because of the limitation of regularized channel inversion to handle users with multiple receive antennas, a novel block diagonalization method is proposed. We construct the precoding matrices that jointly eliminate inter-cell interference and maximize the sumrate for a given input covariance matrix. Assuming total power constraint and per-base-station power constraints, optimal power allocation schemes are further developed to optimize the sum-rate. We analytically show that the sum-rate increases linearly with the number of users when only single-antenna users are present in the system. Numerical results show that at low signal-to-noise ratios, the block diagonalization precoding outperforms the regularized channel inversion in terms of the bit error rate; while at high signal-to-noise ratios, the regularized channel inversion provides a better performance.Clustered linear precoding for downlink network MIMO systems or a part of the channel matrix (e.g., [27,28]). In this paper, however, we use a special multiplicative model that decomposes the channel matrix into a known and an unknown. We then use this model to derive the proposed partial CSI-based precoders.
Related WorkAmong precoding techniques for downlink multiuser systems, regularized channel inversion and block diagonalization (BD) with full CSI have received lots of attention. The recent attempts on the design of regularized channel inversion precoding have mainly focused on maximizing the sum-rate of single-cell and multi-cell systems [29][30][31][32].In [29], optimal power allocation for the case of multiuser multi-input single-output is proposed, and it is shown that, for large number of transmit antennas, the power allocation converges to a waterfilling scheme. In [30], the throughput of a multi-cell downlink network with imperfect CSI is investigated and in [31] and [32], secrecy sum-rate and ergodic secrecy sum-rate of the multiuser MIMO have been studied. In [5] and [9], the BD technique with full CSI, originally proposed for single-cell multi-user MIMO systems [10][11][12], is deployed to design precoder matrices for network MIMO to mitigate the ICI between user equipments (UEs). More recently, the complexity reduction of BD techniques have been investigated in [33][34][35]. In [33] and [34], the authors propose the complexity reduction of BD using a common channel inversion method, QR decomposition, and lattice reduction, while in [35], a generalized zero-forcing precoder is prop...