Impact of Channel Asymmetry on Base Station Cooperative Transmission with Limited Feedback

TL;DR

This paper investigates how channel asymmetry affects the performance of coordinated multi-point transmission in cellular systems with limited feedback, highlighting the importance of user locations and quantization accuracy.

Contribution

It provides an analytical and simulation-based analysis of rate loss due to quantization in CoMP systems, emphasizing the impact of user locations on feedback requirements.

Findings

Per-user rate loss depends on user locations and quantization errors.

Quantization accuracy varies with user and paired user positions.

Performance loss is influenced by channel asymmetry and feedback limitations.

Abstract

Base station (BS) cooperative transmission, also known as coordinated multi-point transmission (CoMP), is an effective way to avoid inter-cell interference in universal frequency reuse cellular systems. To gain the promised benefit, however, huge feedback overhead is in demand to gather the channel information. In this paper, we analyze the impact of channel asymmetry, which is inherent in CoMP systems, on downlink BS cooperative transmission with limited feedback. We analyze the per-user rate loss of a multi-user CoMP system led by quantization. Per-cell quantization of multicell channels is considered, which quantizes the local channel and cross channel separately and is more feasible in practice. From both the analytical and simulation results, we provide a whole picture on various critical factors that lead to the performance loss. Specifically, we show that the per user rate loss led by limited feedback depends on the location of its paired users, except for relying on its own signal to noise ratio and the quantization errors as in single cell multi-user multiple antenna systems. This implies that the quantization accuracy required for local and cross channel of each user depends on the locations of its own as well as its paired users.