Multi-channel real-time communication in wireless sensor networks

Abstract

There are diverse applications in Wireless Sensor Networks (WSN) which require real-time communication. Factory automation, process automation, intelligent traffic system, and real-time location tracing system are representative real-time WSN applications. Messages in such applications need to be communicated in given deadlines or periods. To implement these applications, real-time communication protocols and real-time message scheduling algorithms are inevitable. In order to support real-time communication, MAC (Medium Access Control) layer is relying on TDMA scheme which avoids packet collision and provides a deterministic packet transmission time. For TDMA scheme allocates a time slot to each node, and only the owners of a time slot are communicate at the time slot. Most research on TDMA are focusing on fairly distribution of time slots and minimization of the length of TDMA schedule. However, this dissertation proposes a real-time message scheduling algorithm which is allocating time slots to each message to meet the deadline constraints. This dissertation studies a real-time communication scheme based on IEEE 802.15.4 beacon enabled mode, first. IEEE 802.15.4 standard defines a superframe structure in beacon enabled mode. The superframe structure is specified by a beacon frame transmitted by a network controller called PAN (Personal Area Network) Coordinator. The duration of superframe is determined by BO (beacon order) and divided into an active region and an inactive region. The active region consists of CAP and CFP and is divided into 16 equally sized slots. IEEE 802.15.4 allows allocations of GTS (Guaranteed Time Slot) in CFP, and the owner of GTS is allowed to access the wireless channel. We extend our previous study on a real-time message scheduling for IEEE 802.15.4. The proposed off-line scheduling algorithm is evaluated extensively and the limitations of the standard are analyzed. In addition, a guaranteed time service is implemented in a wirele...