Downlink multicell processing employing QAM quantization under a constrained backhaul

Multicell processing has been recognized as a solution to improve spectral efficiency in future wireless networks. However, the sharing of channel information and data among base stations (BSs) requires an higher backhaul throughput, which is not provided by current cellular systems. In this paper we consider a downlink multicell scenario with constraints on the backhaul throughput and BSs employing beamforming and QAM constellations. As for each mobile terminal (MT) the auxiliary BSs know only a partial version of data, we propose a transmission scheme where a quantized QAM symbol is transmitted cooperatively by all the BSs in the network, while the serving BS transmits an additional signal in order to allow the detection of the full QAM symbol at the receiver. We formulate the problem of maximizing the network spectral efficiency optimizing for each MT a) the QAM constellation size and b) the quantization rate. Numerical results provided for typical cellular scenarios show that the proposed practical approach outperforms in terms of network spectral efficiency both the case of single cell transmission and the case of full network coordination due to the backhaul constraints.