Base Station Cooperation with Feedback Optimization: A Large System Analysis

TL;DR

This paper analyzes feedback optimization for two-cell MIMO broadcast channels, comparing analog and digital feedback schemes, and derives optimal strategies for maximizing SINR in large system limits with cooperative base stations.

Contribution

It provides a large system analysis of feedback optimization for cooperative base stations, including optimal power and bit allocation for analog and digital feedback schemes.

Findings

Optimal power allocation for feedback in analog schemes.

Optimal bit partitioning for direct and cross links in digital schemes.

Performance insights for MCP and CBf cooperation strategies.

Abstract

In this paper, we study feedback optimization problems that maximize the users' signal to interference plus noise ratio (SINR) in a two-cell MIMO broadcast channel. Assuming the users learn their direct and interfering channels perfectly, they can feed back this information to the base stations (BSs) over the uplink channels. The BSs then use the channel information to design their transmission scheme. Two types of feedback are considered: analog and digital. In the analog feedback case, the users send their unquantized and uncoded CSI over the uplink channels. In this context, given a user's fixed transmit power, we investigate how he/she should optimally allocate it to feed back the direct and interfering (or cross) CSI for two types of base station cooperation schemes, namely, Multi-Cell Processing (MCP) and Coordinated Beamforming (CBf). In the digital feedback case, the direct and cross link channel vectors of each user are quantized separately, each using RVQ, with different size codebooks. The users then send the index of the quantization vector in the corresponding codebook to the BSs. Similar to the feedback optimization problem in the analog feedback, we investigate the optimal bit partitioning for the direct and interfering link for both types of cooperation. We focus on regularized channel inversion precoding structures and perform our analysis in the large system limit in which the number of users per cell ($K$) and the number of antennas per BS ($N$) tend to infinity with their ratio $\beta=\frac{K}{N}$ held fixed.