Abstract
Sensor networks require a simple and efficient medium access control policy achieving high system throughput with no or limited control overhead in order to increase the network lifetime by minimizing the energy consumed during transmission attempts. Time-spread multiple-access (TSMA) policies that have been proposed for ad hoc network environments, can also be employed in sensor networks, since no control overhead is introduced. However, they do not take advantage of any cross-layer information in order to exploit the idiosyncrasies of the particular sensor network environment such as the presence of typically static nodes and a common destination for the forwarded data. An adaptive probabilistic TSMA-based policy, that is proposed and analyzed in this paper, exploits these idiosyncrasies and achieves higher system throughput than the existing TSMA-based policies without any need for extra control overhead. As it is analytically shown in this paper, the proposed policy always outperforms the existing TSMA-based policies, if certain parameter values are properly set; the analysis also provides for these proper values. It is also shown that the proposed policy is characterized by a certain convergence period and that high system throughput is achieved for long convergence periods. The claims and expectations of the provided analysis are supported by simulation results presented in this paper.
Highlights
Sensor networks have emerged in recent years offering a wide range of possible applications by the combination of sensing, computation, and communication capabilities in a single device
Sensor networks may be seen as a special case of ad hoc networks and share many of the principles in the design of, for example, the routing protocol, the medium access control (MAC), the physical layer, and so forth
There is a number of differences among the two environments: (a) in sensor networks the network topology is typically considered to be stationary while in ad hoc networks nodes’ movement is the default case; (b) in sensor networks data are forwarded towards a certain destination in the network, while in ad hoc networks the destination of the data can be any node
Summary
Sensor networks have emerged in recent years offering a wide range of possible applications by the combination of sensing, computation, and communication capabilities in a single device. Allocationbased MAC protocols have been proposed (e.g., [7]) and it has been shown that the derivation of an optimal scheduling (i.e., time slots during which a node is allowed to transmit during a frame) is an NP-complete problem, similar to the n-coloring problem in graph theory, [8, 9] These policies introduce a certain (and possibly large) control overhead for the scheduling derivation, which is not desirable especially in sensor network environments due to the aforementioned energy limitations. A new adaptive probabilistic policy, the A-Policy, based on the P-Policy and proposed in this paper (initially mentioned in [19]), is capable of achieving even higher throughput by exploiting the idiosyncrasies of the sensor network environment This particular policy makes better use of the unallocated time slots than the P-Policy (or the D-Policy that fails to utilize them at all).
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