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The target coverage optimisation is an important problem in directional sensor networks (DSNs). In this study, the authors present a novel algorithm, called cover critical target first (CCTF), for improving the coverage ratio in DSN. CCTF simultaneously maximises the number of covered targets, reduces the number of active sensors, and extends network lifetime. For a set of uncovered targets, CCTF always finds the highest priority target which has the minimum number of covering sensors. Among sensors that could cover this target, CCTF activates a sensor that covers more additional targets besides the found target. CCTF's performance is evaluated in terms of coverage ratio, the number of active sensors, and power consumption through extensive simulation. The simulation indicates that CCTF is robust against orientation and localisation errors. Nomenclature m number of sensors n number of targets p number of possible direction for each sensor θ working angle of a sensor α viewing angle of a sensor r sensing range of a sensor ŵ unit vector representing the working direction of a sensor G set of targets {g 1 , g 2 , … g m } S set of sensors {s 1 , s 2 , … s n } G CV list of covered targets G NC list of uncovered targets G θ s list of targets that could be covered by s in direction θ FL this list contains a triple value of the form s, θ, G θ s for each working angle of a sensor GS[g i ] list of sensors that could cover g i. It contains a pair of the form [s, θ] which means that s covers g i in direction θ S NA list of inactive sensors S o list of active sensors and their working angle M list of current critical targets

Abstract. The current multicast routing protocols require state maintenance in the on-tree routers in order to forward multicast packet properly. Therefore, the routers memory may be easily saturated when there are very !arge nurober of low to moderate size multicast groups. In contrast, the explicit multicast protocols offer a stateless design using header space of multicast data packets. In this paper, we introduce new stateless scheme called Linkcast that efficiently eliminates processing overhead of explicit multicast protocols like Xcast. The Linkcast represents the multicast tree by encoding its counterpart links. Simulation results show that Linkcast completely eradicates the required unicast Iookups in explicit multicast protocols with less header size overhead.

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