CSMA/CF Protocol for IEEE 802.15.4 WPANs

Different emerging IEEE 802.15.4 wireless personal area networks (WPANs) are one solution for wireless sensor networks (WSNs), where applications are restricted by low data rate, short transmission distance, and low power consumption. The frame transmission mechanism of the IEEE 802.15.4 standard, which adopts the blind random backoff mechanism, was designed to minimize power consumption. However, it cannot provide satisfactory performance in a realistic hidden-node environment, because it may incur a hidden-node collision chain situation and unexpectedly limit the overall network capacity. For each successful data transmission, any inefficient transmission mechanism will incur prolonged access delay and will consume too much power. Moreover, the current design becomes inefficient as the number of devices significantly increases. As a solution, we propose a new multiple access protocol with improved efficiency at the sublayer between the media access control layer and the physical layer, i.e., a carrier sense multiple access with collision freeze (CSMA/CF) protocol, which comprises a collision resolving scheme and a P-frozen contention strategy. The CSMA/CF protocol can quickly alleviate aggravated collision situations in a hidden-node environment. Such a particular collision phenomenon is denoted as a collision chain problem (CCP). The impact from CCP is thoroughly discussed and analyzed. As confirmed by the results of analysis and performance evaluations, the proposed CSMA/CF protocol can achieve significant performance improvement in energy conservation, access delay reduction, and transmission reliability enhancement.