Scan synchronous directional antennas for time division multiple access in multi-hop ad hoc wireless networks
Abstract
Directional antennas deployed in wireless ad hoc networks must be steered, and the steering control algorithm must know both the spatial location and antenna orientation of each neighbor. Contention-based channel access algorithms acquire neighbor position and antenna orientation through a handshaking protocol that must be performed prior to every message transmission. Each handshake wastes network capacity and forces each node to transition from a quiescent omnidirectional antenna pattern to a fully formed directional beam. This research shows how to solve the directional orientation problem by imposing a slotted time structure on each node, then rotating each node's directional pattern through a discrete angular step on each slot boundary. Synchronizing the rotation across all nodes enables each node to maintain global knowledge of instantaneous directional antenna orientation. Furthermore, the underlying slotted time structure supports a contention-free TDMA channel access protocol that improves end-to-end message throughput with conflict-free message transmissions. Directional gain enables each node to attenuate its radio frequency (RF) transmit power, relative to an omnidirectional antenna. The amount of attenuation is a function of beamwidth, and functions as an RF power reserve. Reducing the discrete rotation step size also reduces slot widths, while exploiting the RF reserve to maintain constant receive signal energy. For a given directional antenna beamwidth, there is a minimum slot width each node can accommodate before exhausting the RF reserve.
Degree
Ph.D.
Advisors
Zoltowski, Purdue University.
Subject Area
Electrical engineering
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