Codebook design and selection for multi-cell cooperative transmission limited feedback systems

Coherent multi-cell cooperative transmission, also referred to as coordinated multi-point transmission (CoMP), is a promising way to provide high spectral efficiency for universal frequency reuse cellular systems. To report the required channel information to the transmitter in frequency division duplexing systems, limited feedback techniques are often applied. Considering that the large scale fading gains of channels from multiple base stations (BSs) to one mobile station are different and the number of cooperative BSs may be dynamic, it is not flexible nor compatible to employ a large codebook for directly quantizing the CoMP channel. In this paper, per-cell codebook for separately quantizing local and cross channels are studied. We first optimize the bit allocation among per-cell codebooks, aiming at minimizing the average quantization error of the aggregated CoMP channel. A closed-form codebook size allocation method is proposed, which only depends on the large scale fading gains of per-cell channels. Considering that the optimal per-cell codeword selection for CoMP channel is of high complexity, we propose a serial codeword selection method, whose complexity is quite low but the performance approaches that of the optimal codeword selection. Simulation results validate our analysis and demonstrate an evident performance gain of our methods.