A directional broadcasting algorithm for routing discovery in ZigBee networks

Jiasong Mu 0 0 College of Electronic and Communication Engineering, Tianjin Normal University , Tianjin 300387, China ZigBee provides a simple and reliable solution for the low-cost networks. The ZigBee ad hoc on-demand distance vector (Z-AODV) could use the global shortest path for data transmission by flooding the routing quest when necessary. However, the current routing algorithms cannot fully address the energy consumption issue. In this paper, we propose a directional broadcasting algorithm in routing discovery (DBRD) to reduce the routing overhead. Based on the network addresses, the network is divided into several continuous 'clusters'. The node relative positioning and direction information are represented by the sequence of the clusters, and the devices which are not in the clusters covering the shortest path may not take part in the routing request rebroadcasting. The simulation results show that the DBRD could improve the performances of routing discovery, the routing overhead was effectively reduced and the end-to-end delay was also shortened since the algorithm occupied less finding time. 1 Introduction ZigBee uses a mixed routing mechanism combined with hierarchical routing protocol (HRP) and ZigBee ad hoc on-demand distance vector (Z-AODV) [1]. For the Z-AODV, each node may initiate routing discovery when necessary; a global shortest path between the source and destination is obtained during the process and the data frame was sent along the route. However, ZigBee devices have limited processing capabilities, storage, power supplies and communication bandwidth. They may also move about randomly, which results in topology changes of the network. These constraints make it very difficult to find proper routing mechanisms that ensure high network throughput [2,3]. The routing protocols described in the specification still need more improvement [4,5]. In this paper, we focus on the improvement of the performance in routing discovery. In the original Z-AODV, an intermediate node may rebroadcast a certain routing request only once and abandon the other duplications. By this method, the routing request can arrive every device in the network. Nevertheless, this mechanism is not efficient since not all the devices have to take part in this procedure [6]. The coverage of the routing request broadcasting should be the whole network theoretically to ensure that the global shortest path can be found. However, this range can be reduced if some prior knowledge is available. The path length and direction are two common parameters to optimize the routing discovery if they are predictable in some level. Some improved broadcasting strategies based on the length control have been proposed in the ZigBee networks, e.g. the rebroadcasting times of the routing request can be limited to no more than the hierarchical hop counts [7]. By contrast, the path direction is more difficult to forecast because of the lack of the nodes spatial information and the high cost of operation and maintenance [8]. In this paper, a simple directional rebroadcasting algorithm in routing discovery which follows the ZigBee specification is proposed. In our method, the two difficulties mentioned above are solved as follows. In the ZigBee networks, the recommended distributed address allocation mechanism (DAAM) guarantees a hierarchical topology, in which each subtree and its root can be regarded as the cluster and the cluster head. The transmission link between the nodes in different clusters can be described by a sequence of clusters. If the clusters are organized based on the location information, this sequence may also contain the directional information. Due to the limited resources and power supply in the ZigBee devices, it is impossible to realize positioning by itself or external devices. However, the relative position information would be enough to indicate the direction, and it can be easily obtained from the neighbour table, which is specified in the ZigBee specification. We propose an address reassignment algorithm based on relative position to ensure that the hierarchical structure is formed according to the nodes spatial deployment. To address the energy cost issue, all the needed information are sent to the ZC, which has sufficient computing and storage capabilities. The ZC is responsible to calculate the cluster sequence to represent the direction and announce it to all the other devices. The rest of this paper is organized as follows: The related works are reviewed in Section 2. Section 3 briefly introduces the ZigBee specification, and the directional broadcasting algorithm in routing discovery is proposed in Section 4. In Section 5, simulation results are presented. Finally, the conclusion is drawn in Section 6. 2 Related works Considering the improvement of the routing discovery broadcasting, some progress has been made [9]. In [10], a hybrid routing algorithm without flooding is proposed. The hierarchical topology information is utilized to optimize the routing request broadcasting to reduce the overhead, and the residential energy of nodes is considered as one routing metric to balance the energy consumption. Because the link may follow the hierarchical path when a corresponding entry is found in the neighbour table of a certain intermediate node, the path it found is not proved the global shortest. In [11], an improved architecture for the combined routing mechanism is studied. The subtree parameter of the ZigBee network and network addresses of destination nodes are used to control the transmission range and restrict its transmission direction in Z-AODV. The algorithm could significantly improve the routing performance, but the routing cost and routing selection is not considered. It requires the accurate location information which is from external positioning devices. Sahinoglu et al. [12] propose self-pruning and forward node selection algorithms that exploit the hierarchical address space in ZigBee networks. The simulation results show that it improves the performance in terms of the number of rebroadcast nodes, number of duplicates received, coverage time and communication overhead. Nevertheless, this method is designed for data transmission, and it only excludes some high-depth nodes from the ones which rebroadcast a certain frame. The retransmission range is not well controlled. In [13], an effective broadcast algorithm called ZigBee broadcasting algorithm on route discovery (ZBARD) is proposed. As a known path, the HRP hop counts, which can be obtained when the network addresses of the source and destination devices are given, must be no less than the shortest path, and it can be used as the maximum retransmission times of the routing request. The ZBARD sets the broadcast radius to this value to reduce the control packets issued by the route discovery. This work effectively limits the retransmission range of routing requests, yet the direction of the coverage is n (...truncated)