Packet Collision Alleviation in IEEE 802.15.4 Networks

Abstract

Recently, IEEE 802.15.4 has been considered as an efficient candidate for wireless sensor networks that require low-complexity and low-power features. Child devices transmit packets to the coordinator by means of carrier sense multiple access with collision avoidance (CSMA/CA) with low message overhead. However, they may experience severe packet collision when a number of child devices transmit large number of data packets, yielding low transmission performance. Therefore, it may be desirable to alleviate packet collision to enhance the transmission performance. The CSMA/CA mechanism may suffer from two types of packet collision

contention collision and hidden node collision. The contention collision problem may occur in CSMA/CA-based packet transmission. When devices perform channel sensing at the same time, they may have opportunities of transmitting data packets simultaneously. In a CSMA/CA-based multi-user communication system, the contention collision problem is unavoidable and can be worse as the number of contending devices increases. The hidden node collision problem may occur when a device cannot detect the packet transmission of other devices. As a consequence, the device determines that channel is idle and initiates its own packet transmission, causing packet collision. It is experimentally known that a pair of devices may be in a hidden node relationship at a probability of up to approximately 41%. Although IEEE 802.15.4 networks may severely suffer from these packet collisions, it does not provide a mechanism to alleviate these collision problems. In this thesis, we consider the design of a novel scheme that can reduce packet collisions without high message signaling overhead. To this end, we partition the transmission period (e.g., the active period in IEEE 802.15.4 networks) into a number of periods each of which is allocated to a small number of child devices, reducing the contention collision. We can alleviate the hidden node problem by making child devices in a hidden node relationship use different transmission periods. Finally, the performance of the proposed scheme is verified by computer simulation in terms of the aggregated throughput and energy efficiency in contention-based transmission environments.