Study of various TDMA schemes for wireless networks in the presenceof deadlines and overhead

The objective of this paper is to determine the minimum system dropping rate (or, equivalently, dropping probability) induced by time division multiple access (TDMA) schemes supporting time-constrained applications with common maximum cell delay tolerance. Expressions are derived for the induced system dropping rate for various TDMA schemes with different overhead and the maximum number of users than can be admitted in the network without violating the maximum dropping rate constraint is determined. The system dropping rate achieved by suboptimal TDMA schemes is compared against the optimal (although ideal) TDMA scheme performance. The performance limiting factors associated with the suboptimal schemes are identified, and the magnitude of their (negative) impact is evaluated. Based on this information it is possible to point to performance improving modifications which should be pursued to the extent permitted by technological constraints. Finally, based on this derivations a network designer may choose the best TDMA scheme-among realizable variations of those considered here-to use in a particular situation     

Ad hoc networking with directional antennas: a complete system solution

Directional antennas offer tremendous potential for improving the performance of ad hoc networks. Harnessing this potential, however, requires new mechanisms at the medium access and network layers for intelligently and adaptively exploiting the antenna system. While recent years have seen a surge of research into such mechanisms, the problem of developing a complete ad hoc networking system, including the unique challenge of real-life prototype development and experimentation has not been addressed. In this paper, we present utilizing directional antennas for ad hoc networking (UDAAN). UDAAN is an interacting suite of modular network- and medium access control (MAC)-layer mechanisms for adaptive control of steered or switched antenna systems in an ad hoc network. UDAAN consists of several new mechanisms-a directional power-controlled MAC, neighbor discovery with beamforming, link characterization for directional antennas, proactive routing and forwarding-all working cohesively to provide the first complete systems solution. We also describe the development of a real-life ad hoc network testbed using UDAAN with switched directional antennas, and we discuss the lessons learned during field trials. High fidelity simulation results, using the same networking code as in the prototype, are also presented both for a specific scenario and using random mobility models. For the range of parameters studied, our results show that UDAAN can produce a very significant improvement in throughput over omnidirectional communications.