| Summary: | 碩士 === 國立中央大學 === 通訊工程研究所 === 95 === Wireless routing algorithm is an important issue in last decade. Many research results about such topic have been proposed. However, most of proposed routing protocols are not able to actually work well. This is because that these approaches need to revise standard specifications and/or make some ideal assumptions. It’s important to find out an efficient routing protocol that is compatible with the contemporary wireless network technologies. The main goal of this thesis is to analyze the behavior of IEEE 802.15.4 ZigBee routing algorithm [2] and then find out all the improvable parts in standard.
ZigBee routing algorithm may generate a lot of route request (RREQ) commands and route reply (RREP) commands when network starts the route discovery procedure. From our simulation results, we found that ZigBee routing algorithm really generates a lot of RREQ and RREP commands and it will make ZigBee devices consume more power sources and it will downgrade the network throughput. The reason is that as more packets are transmitted, more contentions will be resulted. Based on the carrier sense multiple access with collision avoidance (CSMA-CA) algorithm, if the channel becomes busy, ZigBee devices need take a longer time for sending packets successfully. Consequently, ZigBee devices will consume much more power and obtain lower throughput.
ZigBee routing algorithm adopts the RREQ jitter to reduce the amount of RREQ and RREP commands. It is very helpful to reduce the network overhead. Unfortunately, ZigBee specification doesn’t specifically indicate how to set the RREQ jitter. In this dissertation, we observe the relationship between system performance and the RREQ jitter parameter via simulations. From observation, we found that there is a disadvantage of using the RREQ jitter. A larger of RREQ jitter is applied, a longer time of route establishment will be. In other words, ZigBee device takes a long time before data transmissions. In order to resolve this problem, we will propose the listen-before-transmit (LBT) algorithm, which is compatible with ZigBee routing algorithm and it is very easy to be implemented.
There is still a lot of command frames during the route discovery procedure, even if ZigBee routing algorithm uses the RREQ jitter. We analyze the protocol behavior and conclude that there are four cases the device can stop sending the useless command frames. By stopping sending useless command frames, the latency of routes establishment is shortened. The most important thing is that using such case detection strategy is fully compatible with standard ZigBee routing algorithm. In addition, we will highlight the observed features of ZigBee routing algorithm in this dissertation.
There are six chapters in this dissertation. Chapter 1 will introduce the ZigBee routing algorithm. Chapter 2 illustrates the procedure of the listen-before-transmit (LBT) algorithm. Chapter 3 discusses the ways that can reduce the command frames during the route discovery procedure and the unique features of ZigBee routing algorithm. Chapter 4 shows the simulation results. Chapter 5 compares the ZigBee with the other related wireless technologies. Chapter 6 concludes this dissertation.
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