(An) efficient TDMA scheduling scheme for wireless sensor and actor networks

Abstract

This thesis presents an efficient time slot assignment algorithm for a wireless sensor and actor network (WSAN), which consists of stationary sensors for detecting events and mobile actors for performing tasks. The stationary sensors are typically characterized by low-cost, low-power and tiny devices with limited sensing, computation, and wireless communication capabilities. On the other hands, the mobile actors have better processing capabilities, higher transmission powers and longer battery life. WSANs are expected to be an integral part of systems such as military application, environmental application, health application, and home application. These systems usually need to complete timely missions without human interventions. For example, intrusion detection system alarms the event to the police so that thieves are captured before they run away. Similarly, in a fire extinguishment system, actions should be initiated on the detected area as soon as possible. Due to timely tasks, sensors in WSANs relay the event to actors within given delay bounds. Therefore, the consideration of real-time communication is really necessary in WSANs. In wireless multi-hop network, MAC protocols have a major influence on the latency of packet delivery. Classical contention-based protocols are not suitable for real-time communication, since contention-based channel access requires random backoffs and handshakes (exchange of RTS, CTS and ACK) due to collisions and hidden terminals. Random backoffs and handshakes increase the latency of the data; moreover, it is difficult to estimate how long their duration is. In comparison, TDMA protocols are suitable for WSANs, because they can potentially reduce the delay and provide real-time guarantees by eliminating collisions and solving hidden terminal problems. Traditional TDMA protocols are based on centralized algorithms and their main concern is to reduce the number of assigned slots. Note that the problem of assigning...