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In this paper, we introduce a novel CSMA/CA-based reservation scheme that improves the multiple access throughput of wireless ad-hoc networks using switched beam antennas. First, we show the performance limitations of the omni-directional and directional reservation paradigms investigated in the literature. This is done via emphasizing the trade-off between minimizing the number of control/data packet collisions and minimizing the number of neighbors that back-off unnecessarily. Next, we propose a novel concept that balances this trade-off via sending reservation messages, that carry information about the intended direction of transmission, on all unblocked beams. The innovation in this approach is to send directional information to as many neighbors as possible in order to better assist them in deciding whether to transmit or refrain from transmission on a specific beam. Finally, the algorithm is examined via simulations and compared to the omni-directional and directional reservation approaches.

Using directional antennas in wireless ad hoc networks can greatly improve the spatial reuse and the transmission range. However, it will cause the deafness problem, which greatly impairs the network performance. This paper proposes a new MAC protocol SDMAC (Selectively Directional MAC) that can effectively address the deafness problem and significantly improve the network throughput. Simulation results show that our protocol can achieve a better performance than the existing MAC protocols using directional antennas. I.

Abstract—The free space time domain coupled electric and magnetic field integral equation solution for Maxwell’s differential equations is derived. The coupled field integral equation solution is expressed as a vector containing the electric and magnetic fields found in terms of a surface integral over the equivalent surface currents on a boundary, an integral over the electric and magnetic current sources in the region enclosed by the boundary, and a volume integral over the initial field in the bounded region. Because of the irreversibility of the vector differential equation and the lack of spatial symmetry in the corresponding free space dyadic Green function, as a starting point the Green differential equation is replaced by the reciprocal (adjoint) equation and the dyadic Green function is replaced by its transpose. These replacements plus identities that relate the components of the Green function to its transpose lead in a straightforward way to the coupled field solution. The general dyadic expression derived here provides a framework for developing source current, boundary integral, and propagator methods that are based on the interaction between the electric and magnetic vector field components in the time domain. Index Terms—Coupled field, dyadic Green function, dyadic Green’s function, integral equations, Maxwell equations, propagator.