Ultra-Wideband (UWB) is a key solution for wireless connectivity, characterized by ultralow power consumption and a good degree of robustness to interference. Evidence of its importance, is its recent use in the IEEE 802.15.4a standard. UWB technology with joint consideration of directional antennas can benefit when compared to classical omnidirectional antennas from the energy conservation viewpoint, which is of fundamental concern when it comes to wireless sensor networks (WSNs). However, exploiting directionality requires new approach in the design of a medium access control (MAC) protocol to be applied. In this work, idle nodes continuously rotate their receiving beams over 360 degrees until a predefined preamble trailer is detected. The resulting scheme is a directional ultra-wideband MAC protocol, named DU-MAC, which deals effectively with the problem of deafness and the problem of determination of neighbors' location. Simulation based studies would demonstrate the effectiveness of our protocol in many critical parameters.
I. INTRODUCTIONWireless communications based on UWB signals have attracted much attention both from standardization bodies and chip manufacturers. This air interface promises flexibility, increased data rate, an extended communication range, robustness against interference and the ability of providing sub-meter ranging accuracy. Moreover, UWB allows for ultralow power communications, typically under -10dBm, a property that is ideal for the energy-constraint sensor nodes. The recently released IEEE 802.15.4a standard [1], a spin-off to 802.15.4, adopted this alternate PHY, proving in that way its importance.While most of the existing research on UWB sensor networks typically assumes the use of omnidirectional antennas by all nodes, due to the omnidirectional nature of transmissions, several drawbacks exist. For example, the distribution of energy in all directions generates unnecessary interference to other nodes, while it decreases the opportunity to have simultaneous nearby transmissions. With directional communications instead, nodes' transmitted energy is concentrated only towards the destination's direction increasing the spatial reuse gains. Also, on the receiving side, these antennas enable a node to selectively receive signals only from desired directions.While traditional MAC protocols that have been designed under the omnidirectional assumption are no longer suitable for use over directional antennas, the proposed MAC should attempt to exploit both the benefits of directionality, namely spatial reuse and higher communication range. While spatial
