Spatial Interference Cancellation for Multi-Antenna Mobile Ad Hoc Networks

TL;DR

This paper analyzes how multiple antennas and zero-forcing beamforming can significantly improve the transmission capacity of mobile ad hoc networks by canceling interference, with mathematical modeling and numerical validation.

Contribution

It provides a stochastic geometry-based analysis of the impact of interference cancellation and CSI accuracy on transmission capacity scaling in MANETs.

Findings

Canceling one interferer increases capacity by over tenfold.

Transmission capacity scales with the number of canceled interferers as L^(1-2/α).

CSI inaccuracy has negligible effect when training sequences are properly designed.

Abstract

Interference between nodes is a critical impairment in mobile ad hoc networks (MANETs). This paper studies the role of multiple antennas in mitigating such interference. Specifically, a network is studied in which receivers apply zero-forcing beamforming to cancel the strongest interferers. Assuming a network with Poisson distributed transmitters and independent Rayleigh fading channels, the transmission capacity is derived, which gives the maximum number of successful transmissions per unit area. Mathematical tools from stochastic geometry are applied to obtain the asymptotic transmission capacity scaling and characterize the impact of inaccurate channel state information (CSI). It is shown that, if each node cancels L interferers, the transmission capacity decreases as the outage probability to the power of 1/(L+1) as the outage probability vanishes. For fixed outage probability, as L grows, the transmission capacity increases as L to the power of (1-2/alpha) where alpha is the path-loss exponent. Moreover, CSI inaccuracy is shown to have no effect on the transmission capacity scaling as the outage probability vanishes, provided that the CSI training sequence has an appropriate length, which we derived. Numerical results suggest that canceling merely one interferer by each node increases the transmission capacity by an order of magnitude or more, even when the CSI is imperfect.