SINR Estimation in Limited Feedback Coordinated Multipoint Systems

Coordinated multipoint (CoMP) transmission can provide high spectral efficiency for cellular systems if perfect channels are available. In limited feedback systems, except for channel direction, signal-to-noise-plus-interference ratio (SINR) is necessary to assist in user scheduling and adaptive transmission. When the methods to estimate SINR in single-cell systems is applied to CoMP systems, the performance will significantly degrade. In this paper, we estimate the SINR for downlink CoMP systems. We start by showing that the quantization error vector is no longer isotropic when quantizing CoMP channels. This implies that the vector has an inherent structure. We proceed to formulate an optimization problem to find the quantization error vector that maximizes the multiuser interference power under the structure constraint. This way, we can exploit the nonisotropic nature of the quantization error vector and avoid overestimating the SINR. Simulation results show that the proposed method provides high throughput and low outage probability with negligible extra feedback overhead.