An adaptive routing optimization and energy-balancing algorithm in ZigBee hierarchical networks

Jiasong Mu 0 Wei Wang 0 Baoju Zhang 0 Wei Song 0 0 College of Electronic and Communication Engineering, Tianjin Normal University , Tianjin 300387, China ZigBee hierarchical tree routing protocol (HRP; ZigBee Alliance, San Ramon, CA, USA) provides a simple but reliable topology. However, the transmission routes are not always efficient, and the links are fixed after they were determined during the network initialization. In this paper, we propose an adaptive routing optimization and energy-balancing algorithm in ZigBee hierarchical networks. In our routing algorithm, the parent node could adaptively maintain its child's links for lower network load, and all the information needed can be obtained from a neighbour table to avoid introducing extra communication overhead. Such algorithm makes ZigBee's hierarchical topology to adaptively maintain and optimize the routing paths during its lifetime, and an address reassignment mechanism is also introduced to ensure that our algorithm follows ZigBee specification. In addition, an energy-balancing algorithm is also proposed to reduce the power cost of low-battery device. Simulation results show that our routing scheme has better performance with lower average transmission hops and network load, and our energy-balancing algorithm could reduce the power consumption of low-battery device. 1 Introduction Since the ZigBee (ZigBee Alliance, San Ramon, CA, USA) specification was first released in 2004, the study on the protocol stack and application continuously emerged due to its attractive identities of low power and low cost [1]. ZigBee aims at low power consumption and therefore long-living networks. As the energy cost of transmitter in data transmission process is the primary cost in wireless application, the routing efficiency mostly decides the power and lifetime of wireless networks. 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]. ZigBee uses a mixed routing mechanism combined with hierarchical tree routing protocol (HRP) and ZigBee ad hoc on-demand distance vector (Z-AODV) [3]. Nevertheless, current network formation and routing protocols described in the ZigBee specification do not fully address power consumption issues [4]. HRP is an active routing method whose routing information is established when the network is deployed and keeps invariable unless the network structure changes. HRP provides a simple and reliable topology for wireless networks [5]. To each node, if the destination of a data frame is the descendant of itself, it will send the packet to the corresponding child. Otherwise, it will transmit the message to its parent. HRP is efficient from the view of routing acquisition and memory use, but the routing paths in HRP are always inefficient, because the data frames are limited in parent-child link. Moreover, the changeless topology requires it to rebuild the hierarchical structure when nodes move and limits its performance in network extension. Finally, due to the fact that the tree is not dynamically balanced, the possibility that certain installation scenarios, such as long lines of devices, may exhaust the address capacity of the network long before the real capacity is reached exists [6]. Another problem of energy cost in wireless network is the uneven consumption of the nodes. Overall, routing methods only guarantee the better average performance [7]. Due to the network structure and node location, some devices may be overused (e.g. the node at the centre of the network is more likely to receive data and join a routing path). This may lead to potential network segmentation and shorten the lifetime of the whole network [8]. To avoid some node exhausting their power too soon, an energybalancing algorithm is also investigated in this paper. The rest of this paper is organized as follows. In Section 2, we review the related work. Section 3 briefly introduces the related contents in the ZigBee specification, and the adaptive routing optimization and energybalancing algorithm are proposed in Section 4. And, Section 5 presents the simulation results. Finally, the conclusion is shown in Section 6. 2 Related works So far, although most researches on ZigBee routing have focused on the Z-AODV [9], some progress on routing performance optimization in hierarchical networks has also been made in the field of protocol improvement, beacon slot distribution, hybrid routing algorithm and so on. A modified tree routing mechanism with the introduction of neighbour table is given in [10]. The transmission cost (e.g. hops) via each neighbour device is estimated and compared to improve the routing path. It has a better performance with less power consumption per packet transfer and a long life cycle. But, this algorithm is based on the two-hop neighbour information; it may lead to severe energy and memory overhead in ZigBee networks. In [11], the reuse pattern of beacon slots in ZigBee hierarchical networks is investigated. It is concluded that beacon slots can be reused judiciously, especially when the risk of beacon collision caused by such reuse is low. On that basis, ZigBee-compatible, distributed and risk-aware probabilistic beacon scheduling algorithm is proposed. By the algorithm, one can easily assess the risk of slot reuse to decide whether the reuse is allowed and thus reduce the transmission latency. However, one key parameter in the algorithm is the estimated range of node transmission which may rapidly change in wireless channel. This may degrade the performance and cause collision in beacon slot reuse. In [12], 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. Nevertheless, the optimized links are based on hierarchical topology, the coverage of routing request; thus, the routing efficiency remains questionable. The authors in [13-15] propose several similar routing algorithms for hierarchical topology; the information in neighbour table was used to get shorter paths. However, the links in their methods were still invariable. HRP in ZigBee does not need nor allow any communication to maintain the routing path for the purpose of low power consumption. In ZigBee specification, all ZigBee devices are required to maintain neighbour tables, which record the information of the nodes in their one-hop neighbourhood. The contents in the table include each neighbour's address, device type, status of receiver and link quality [16]. This information in the tables reflects the topology of the network and can be used to improve (...truncated)