| Low-rate Wireless Personal Area Network(LR-WPAN) is a low-cost, efficient, low-data rate wireless technology, which operates on the band 2.4GHz and 868/915MHz. Based on LR-WPAN standard, ZigBee is a new short-range wireless technology which is optimized for low-complexity, low power consumption and low-cost. The intended market space of applications using the ZigBee standard is intelligent home, building automation, consumer electronics, industrial controls and medical sensors. For its special feature, ZigBee is the best choice for wireless sensor network. Along with ZigBee filled the vacancy of low-rate,low-cost and low power consumption wireless communication field, researchers pay more attention to the ZigBee technology wireless sensor network research day by day. However, the routing roles of ZigBee make the new challenge in control overhead and overall life expectancy of the ZigBee network when using ZigBee technology to form LR-WPAN.LR-WPAN standard provides the definition for physical layer(PHY) and medium access layer(MAC). Upon the PHY and MAC, ZigBee protocol providing the definition for network layer(NWK), which providing API function interface for the application layer. As be the core of ZigBee protocol, the network layer provides some functions such as join or leave the network, receive or discard the other nodes, seach routing and transmission of data, it also supports for routing algorithm such as Cluster-Tree, AODVjr, ZBR, and network topology such as star, tree and mesh.In ZigBee network, nodes are divided into two categories: RN+ and RN-. RN+ nodes are refer to have sufficient storage space and capacity to implement AODVjr routing protocol. However, RN- nodes are refers to have limited storage space and do not have the capacity to implement AODVjr routing, but can only use Cluster-Tree routing algorithm to processing packets. ZigBee specification defines a hybrid routing algorithm based on Cluster-Tree with AODVjr, which can be select routing by the type of transmission data and network situation. For example, ZigBee node could select Cluster-Tree routing for short-term, unexpected data streams or nodes move frequently and network topology changes rapidly. Otherwise,the node could select AODVjr routing for long-term transmission,which can achieve optimal routing efficiency.This article has first carried on the brief introduction to the ZigBee technology, including the development background, research status quo, network topology and the forms of ZigBee network. Then summarized ZigBee protocol stack based on LR-WPAN standard and ZigBee specification,including the functions of PHY layer, MAC layer, NWK layer, application layer, the interfaces between all levels and some service primitives. Through ZigBee technology with other wireless communication comparisons, the author point out that it is one of most potential technologies in the wireless sensor network.Second, the types and study status quo of the Ad Hoc network routing algorithms were introduced, then detailed analyzed the basic principles, existence of advantages and disadvantages of three typical Ad Hoc network routing algorithms: DSDV, DSR and AODV. Then summarized the disadvantages of AODV used in ZigBee network, and analyzed the routing algorithms defined in ZigBee specification such as Cluster-Tree, AODVjr and ZBR. Focused on the basic operations and flow charts of initiation of routing discovery, receiving a RREQ command frame as well as RREP.As the kernel of this paper, after detailed analyzed deficiencies of ZBR, a improved algorithm named C-ZBR was designed to reduce control overheads and extend the overall life of network. ZBR defined that when a souce node has no effective routing entry to destination node, it should broadcast a routing request packet. Although some packets with the trip against the destination node participated in routing discovery process, they cannot help to find a optimal path from the source to the destination. Therefore, C-ZBR defined a direction flag which added to routing request packets to enable nodes to discard out packets which were not suitable for them to forward, and that could avoid forwarding packets in the opposite direction of the destination as well as reduce flooding of routing control packets to save the overall energy consumption of network. C-ZBR also demanded nodes to make a tree-traversal operation before broadcasting a routing request packet as well as after receiving a request packet. A tree-traversal operation is that the current node could calculate the number of necessary hops to the destination with its address. When the number was within the scope of system, the current node should forward the packet directly rather than flood the packet. Thereby, it will reduce the number of routing control packets and take from the load of system. This algorithm also defines a minimum residual energy value to select different operations by comparing their current energy and the minimum value of the residual energy, that is, to take care of the low energy node without implementing a high energy consumption operation in order to avoid a number of energy consumption as a failure node, thereby affecting the operation of the entire network. This paper focused on the processes of broadcasting and receiving routing request packets in the improved routing algorithm, and a detailed analyzed of data structure and energy model.Finally, the author adopted LR-WPAN network simulation software platform based on NS2 in Cygwin environment to built a ZigBee routing simulation platform and simulate the routing algorithm of this paper, and analyzed the performance of the network. The result proves that the improved algorithm can be easily implemented, to reduce the control overheads and energy consumpion. Therefore, the algorithm can extend the overall life of network and it's a energy-efficient routing algorithm for ZigBee. |
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