On Scheduling Guaranteed Time Slots for Time Sensitive Transactions in IEEE 802.15.4 Networks

IEEE 802.15.4 is a new enabling standard for low-rate wireless personal area networks and has been widely accepted as a de facto standard for wireless sensor networking. While primary motivations behind 802.15.4 are low power and low cost wireless communication, the data throughput and QoS being secondary, the standard does have provisions for supporting time and rate sensitive applications because of its ability to operate in pure CSMA/CA or TDMA access modes. The TDMA mode of operation is supported via the Guaranteed Time Slot (GTS) feature of the standard. In a beacon-enabled network topology, the PAN coordinator plays a role in reserving and assigning the GTS to applications on a first-come-first-served (FCFS) basis in response to requests from devices. This fixed FCFS scheduling service offered by the standard may not satisfy the time constraints of time-sensitive transactions having delay deadlines. Such operating scenarios arise when one considers wireless video surveillance and target detection applications running on sensor networks. In this paper we provide a scheduling model that tries to meet the delay constraints of time-sensitive transactions and show that the proposed model outperforms the existing scheduling model specified in IEEE 802.15.4.