Limited feedback orthogonal beamforming in coordinated multi-point systems

Abstract

The performance of coordinated multi-point (CoMP) transmission systems will be severely degraded by channel quantization error when each user employs limited number of bits to quantize and feed back its channel information. This is especially true for multi-user multi-antenna CoMP with joint processing (CoMP-JP), where multi-user interference becomes dominant for high power region. As an alternative strategy, orthogonal beamforming (ORBF) based limited feedback strategy has the potential to improve the performance due to its robustness to the quantization error. In this paper, we consider limited feedback downlink CoMP-JP systems based on per-cell codebooks, which are scalable for large systems and compatible to existing systems. We propose an ORBF limited feedback strategy for CoMP-JP, where the coordinated base stations (BSs) schedule multiple users with mutually orthogonal codewords for their corresponding per-cell channels with the same BS. To facilitate spatial scheduling, we derive a method to estimate the signal to noise and interference ratio (SINR) at each user that will be fed back to the BSs. It is demonstrated by simulations that the proposed feedback scheme provides substantial performance gain over the channel quantization based limited feedback CoMP-JP and CoMP coordinate beamforming (CoMP-CB), as well as the ORBF based Non-CoMP systems, especially when the number of coordinated BSs is small and the number of antennas at each BS is large.