MMSE Precoding for Downlink Coordinated Base Station Transmission

In a Coordinated Base Station Transmission scenario for the downlink, we propose a precoding scheme based on a MMSE criterion to manage the inter-user interference. In order to allocate the transmitted power to each user´s signal, we set up an iterative procedure based on a modified waterfllling distribution, which approaches the optimal performance with a viable complexity with respect to the numerical optimization. A further simplification may be introduced, giving a simple iterative waterfilling scheme, at the expense of some performance loss. The performance is illustrated obtaining the achievable rates for different antenna configurations and different kinds of power constraints. A comparison with a Block-Diagonalization approach shows the advantage of MMSE, in particular at low SNR.