Low iatency transmission protocols for IEEE 802.15.4 multi-hop networks over unreliable wireless links

Abstract

For many years, IEEE 802.15.4 standard has been used for various multi-hop networks such as wireless sensor networks (WSNs) and internet of things (IoT). Recently, many applications in IEEE 802.15.4 multi-hop networks have required supporting low delivery latency, and then low latency transmission protocols have been also proposed. In these transmission protocols, nodes synchronize time slots to forward data packets sequentially over multiple hos, so the data packets can be transmitted with low delay. However, they have shown limited performance over unreliable wireless links. Since the nodes tightly synchronize the time slot for the sequential transmissions, drooped packets cannot be retransmitted immediately. It will lead to not only delayed retransmissions but also the additional delay caused by end-to-end retransmissions. Furthermore, this limitation has become serious over multi-hop transmission because packets are dropped more frequently. To maintain lower delivery latency with unreliable and multihoptransmissions, this dissertation proposes the enhanced low latency transmission protocols. In the proposed protocols, nodes adjust the synchronized time slots by considering unreliable wireless links and channels. Then, nodes can retransmit dropped data packets immediately, and thus they can avoid the delayed retransmissions. Moreover, it helps to improve the transmission reliability, so additional delay caused by end-to-end retransmissions can be also prevented. The enhancements are veried through theoretical and simulation-based analysis. The analysis shows that that the proposed protocols can maintain much lower delivery latency regardless of various channel/link conditions and other network environments.