| As a specific area within sensor networks, wireless in-home sensor networks are promising in improving residential environments and developing desirable home facilities. Nonetheless, this area has some dissimilar characteristics from previous research. First, much previous work deals with issues related to networks having homogeneous sensor nodes. In reality, sensors with different radio coverage, power capacity, and processing capabilities are deployed. In addition, not all of the sensors are mobile or have the same mobility freedom or mobility attributes (e.g. speed). The topology and routing protocol for this type of heterogeneous sensor networks must be based on the resources and characteristics of their member nodes. In this dissertation, a network topology that is a hub-spoke structure is proposed, which is adaptively formed according to the resources of its members. A protocol called the Resource Oriented Protocol (ROP) was developed to build the network topology. It is stressed that due to the existence of nodes with limitless resources, a top-down appointment process can build the hub-spoke structure with minimum consumption of resources in ordinary nodes. To avoid overhead of periodic route updates, a reactive strategy is used to maintain the route cache.; A traditional scheme to solve the hidden terminal problem is to use a four-way handshaking scheme, in which nodes first use short packets to reserve the channel and then send long data packets if reservation is successful. The risk and penalty of collision are now restricted to short packets. Unfortunately, in the hub-spoke structure built by ROP, nodes may not be able to reach each other directly to complete the scheme. Therefore, a multi-hop MAC method is proposed to implement it. The basic idea is to use routing information to obtain packet paths for each of the packets in the handshaking process. Packets are sent directly for any reachable sensor and relayed by intermediate sensors otherwise. Before the routing information is available, sensors broadcast their packets without requesting feedback from their peers. The same metric, system lifetime, is used to measure the performance of this design. Simulation results show that multi-hop MAC scheme can save much energy of ordinary sensors and thus achieve long system lifetime. |
