Our contribution in this paper is a scalable, easily implemented, self-organizing, energy conserving intrusion-detection sensor system applying concepts from cellular automata theory. The system self-assembles periodic wake-sensor barriers (waves) that sweep the sensor field; it is highly effective even in the case of frequent communication failures, sensor failures, large obstacles, and when intruders know sensor locations.

Cyclic Cellular Automata (CCAs) have been found to provide a natural, beguilingly simple, and elegant infrastructure for the design of sensor systems with sleep-wake scheduling to maximize system lifetime. The Greenberg-Hastings model (GHMZ) [3, 2] defined on the integer lattice Z2 is particularly appropriate and is described as follows. Each grid square of the integer lattice is a cell with a set of k ≫ 1 states and a neighborhood N; the neighborhoods of interest here are the von Neumann neighborhood and the Moore neighborhood. The von Neumann neighborhood Nx of cell x consists of just those cells to thenorth, east, south, and west of x, whereas the Moore neighborhood expands to that 3 £ 3 array of cells with x at its center, i.e., all cells that touch x at a side or vertex. All cells change state synchronously step by step according to aclock cycle and transition function common to all. The local rule for state changes is little more than a counter: The state »t+1(x) of cell x at time t + 1 is a simple mod k increment: »t+1(x) = »t(x) + 1 if »t(x) ≫ 0. But if »t(x) = 0;the state is incremented to 1 if and only if it has at least one neighbor in Nx which is currently in state 1.

While most transmission schemes in OBS networks relegate retransmission to higher protocol layers, the scheme proposed in this paper reduces retransmission delays by exploiting fiber delay lines at the optical layer. We present an analysis of the scheme that focuses not only on individual components but also on the end-to-end properties of the network. We also propose a facility location model suitable for optimizing the locations of sites with fiber delay lines when the number of such sites is limited. Evaluation of our proposed scheme on a common test network shows that major improvements in performance are possible.

Delivering sufficient fidelity to sensor network applications is challenging because unpredictable wireless links, network dynamics, and the presence of transitional regions in sensor networks impact the delivery of packets (i.e., fidelity) to the sink. One of the major reasons for this problem is due to the non-responsive nature of forwarding mechanisms commonly implemented in experimental sensor networks. Existing routing protocols implemented in these networks typically base their forwarding decision-making on some form of statistical observations regarding past communications or the quality of past beacon signals received by communicating nodes. This approach fails, however, to capture the link conditions at the exact time of forwarding packets across the wireless link, limiting the aggregate forwarding capability of the network. In this paper, we argue that the forwarding decision of a sensor device should be based not on historical information but on the instantaneous link conditions at the exact time of packet communications, and propose, solicitation-based forwarding (SOFA), a highly-responsive hop-by-hop routing protocol that results in increased application fidelity. SOFA represents a cost-effective, on-demand scheme that makes use of simple solicitation-based handshakes between a sender and multiple potential receivers at each wireless hop to negotiate the best forwarding path to a target destination (i.e., sink) when events occur in the sensor field. We present the detailed design, implementation, and experimental evaluation of SOFA in a 36-node Mica2 testbed using TinyOS, and discuss its measured performance benefits in comparison to the TinyOS standard routing protocol widely used by the experimental sensor network community