Capacity Scaling of Ad Hoc Networks with Spatial Diversity
Andrew M. Hunter, Jeffrey G. Andrews, Steven P. Weber · 2007
This paper derives the exact outage probability and transmission capacity of ad hoc wireless networks with nodes employing multiple antenna diversity techniques. The analysis enables a direct comparison of the number of simultaneous transmissions achieving a certain data rate under different diversity techniques. Preliminary results derive the outage probability and transmission capacity for a general class of signal distributions which facilitates quantifying the gain for fading or non-fading environments. The transmission capacity is then given for uniformly random networks with path loss exponent alpha > 2 in which nodes: (1) perform maximal ratio transmission/combining on M antennas with Theta(M 2/alpha ) gains; (2) various antenna selection combining schemes which give appreciable but rapidly diminishing gains; and (3) orthogonal space-time block coding, for which there is only a small gain due to channel hardening. It is concluded that in ad hoc networks, beamforming performs best, selection combining performs well for smaller numbers of antennas, and that space-time block coding offers only marginal gains.