Adaptive BIT allocation scheme for comp system with delayed limited feedback

Per-cell codebook based limited feedback technique in coordinated multi-point transmission (CoMP) system has received more and more attention due to its flexibility and scalability. In a practical system, as the capacity of backhaul links and the bandwidth of the feedback channels are finite, there exists channel state information (CSI) delay. In this paper, we study the bit allocation problem considering CSI delay in multi-cell joint transmission system based on Gauss-Markov temporal correlation channel model. We first analyze the global channel direction information (CDI) quantization accuracy of the users and give the approximate closed-form expression of the normalized global CDI quantization gain, we then propose an adaptive bit allocation scheme to allocate bits between quantizing the per-cell CDIs and the per-cell PAs (phase ambiguity) under the total number of feedback bits constraint, aiming at maximizing the normalized average global CDI quantization gain. Simulation results show that the proposed bit allocation scheme significantly improves the average sum-rate of the CoMP system compared with the conventional equal bit allocation scheme.