Limited Feedback Over Temporally Correlated Channels for the Downlink of a Femtocell Network

TL;DR

This paper investigates limited feedback beamforming in femtocell-enhanced macrocell networks, analyzing how feedback delay, interference, and spatial distribution affect outage probability and proposing rate backoff to optimize network performance.

Contribution

It models the impact of feedback delay and interference in femtocell networks and introduces rate backoff to enhance macrocell throughput under these conditions.

Findings

Limited feedback beamforming is feasible despite CSI inaccuracies.

Proper rate backoff significantly improves macrocell achievable rate.

Interference and feedback delay critically affect outage probability.

Abstract

Heterogeneous networks are a flexible deployment model that rely on low power nodes to improve the user broadband experience in a cost effective manner. Femtocells are an integral part of heterogeneous networks, whose main purpose is to improve the indoor capacity. When restricting access to home users, femtocells cause a substantial interference problem that cannot be mitigated through coordination with the macrocell base station. In this paper, we analyze multiple antenna communication on the downlink of a macrocell network, with femtocell overlay. We evaluate the feasibility of limited feedback beamforming given delay on the feedback channel, quantization error and uncoordinated interference from the femtocells. We model the femtocell spatial distribution as a Poisson point process and the temporal correlation of the channel according to a Gauss-Markov model. We derive the probability of outage at the macrocell users as a function of the temporal correlation, the femtocell density, and the feedback rate. We propose rate backoff to maximize the average achievable rate in the network. Simulation results show that limited feedback beamforming is a viable solution for femtocell networks despite the CSI inaccuracy and the interference. They illustrate how properly designed rate backoff improves the achievable rate of the macrocell system.