Analysis of Capacity Improvement by Directional Antennas in Wireless Sensor Networks

In this article we analyze capacity improvement by directional antennas over omni antennas in wireless sensor networks. The capacity in our analysis is the end-to-end per-node throughput. We analyze the typical traffic pattern for sensor networks, where traffics are destined to or originated from the sink. The main results of our analysis are summarized as follows. (1) The network capacity is O(1/N) for both omni and directional antennas, where N is the number of sensor nodes in the network. (2) In the case of line deployment, the capacity ratio of directional antennas over omni antennas is bounded by (2q+3)/(2q-1), where q is the ratio of the interference radius to the transmission radius. (3) In the case of two-dimensional deployment, the capacity for using directional antennas is O(1/theta) for m = 2, and O(lg m/theta(2) lg(1/theta)) for m > 2, where m is the number of radios (antennas) on each node and theta is the beamwidth of antennas. (4) When there are n > 1 sinks, the capacity has a non-monotonic relationship with the transmission radius. The optimal transmission radius depends on the ratio of n/q. (5) The capacity ratio of directional antennas over omni antennas in multi-channel networks decreases as the channel number/radio number ratio c/m increases.