  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.
