Dynamic Feedback Allocation Algorithms for Interference Management in MIMO Uplink

This paper investigates the impact of limited feedback on the uplink of a wireless network with multiple access points. The network adopts universal frequency re-use with each access point serving a set of users using orthogonal signalling. All wireless nodes are multiple-input-multiple-output-capable. Block Diagonalization, a popular technique for interference cancellation, is performed at each transmitter. Interference cancellation on the cell boundary is being considered in future wireless standards such as IEEE 802.16m and 3GPP Long Term Evolution Advanced. In such systems, the precoder is fed back to the mobile by its home base station. It follows that the rate achieved at the home as well as neighbouring access points is a function of the bandwidth of this feedback channel. We study the problem of minimizing the network-wide feedback budget subject to guaranteeing a minimum rate at each access point. We compute the optimal network-wide allocation using dynamic programming on junction trees with complexity that depends on the structure of the underlying interference graph. Unfortunately, when the interference graph forms a grid such as the traditional arrangement of base stations, this complexity becomes exponential in the number of users, N. We propose a greedy allocation algorithm with significantly-reduced complexity and with an approximation guarantee that, provably, scales as N. The constant of proportionality is shown to be a function of the precoder quantizer distortion, cost per feedback bit (for reliable delivery) and the size of the largest neighbourhood of the network.