-In ad hoc networks, devices are required to selforganize themselves into a network without previously established infrastructure. The kind of ad hoc network we consider in this paper is made up of a multitude of relatively low mobility, short range, wireless devices, pervasively deployed throughout the environment. One of the most important design criteria for this type of network is energy efficiency. This paper looks at the energy efficiency aspect of the system design.Specifically, this paper looks at the optimum one-hop transmission distance that will minimize the total system energy. The analysis assumes that the individual devices do not have power control, but that the transmission range of all the devices as a group can be varied in the design stage. The results show that the optimum one-hop transmission distance is independent of the physical network topology, the number of transmission sources, and the total transmission distance. It only depends on the propagation environment and the device parameters.With this result, some system design trade offs can be made to minimize the total system energy. We discuss what these parameters are, how they interact with each other, and how they can be used to obtain an energy efficient wireless system. We also discuss the implications this result has for future developments of low bit rate, short range, and highly dense wireless devices for ad hoc networks.

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Abstract-An effective location algorithm, which considers nonline-of-sight (NLOS) propagation, is presented. By using a new variable to replace the square term, the problem becomes a mathematical programming problem, and then the NLOS propagation's effect can be evaluated. Compared with other methods, the proposed algorithm has high accuracy.Index Terms-Maximum-likelihood (ML) estimation, non-lineof-sight (NLOS) propagation, time difference of arrival (TDOA), time of arrival (TOA).

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