An Innovative Scheme for Increasing Connectivity in Zigbee Networks

An Innovative Sch Z Chia-Ming Wu Dept. of Computer Science and Information Engineering National Dong Hwa University Hualien, Taiwan, R. O. C. cmwu@mail.ndhu.edu.tw Abstract—ZigBee networks based on the IEEE are designed for wireless sensor and control cost, low power consumption, and low data ZigBee network with the tree topology requirement of a device is simple and low thre device may become an isolated node due configuration parameters in the ZigBee netw isolated nodes, we propose an approach Connectivity Scheme for the ZigBee network efficiently reconstruct parts of the network t join and hence increase the join ratio. Our met improve the connectivity of ZigBee networks. results show that Enhanced Connectivity performance. We provide an innovative so connectivity of ZigBee networks. Keywords-ZigBee; wireless sensor networ connectivity I. INTRODUCTION A wireless sensor network is a network sensors with limited hardware capabilities [2 15, 16] based on the IEEE 802.15.4 standard low-cost, low-rate, and low-power wireless networks. Because the hardware requiremen joining in ZigBee is low, ZigBee is widely fields such as home automation, building auto automation [14]. Three types of devices, ZigBee Coordin Router (ZR), and ZigBee End Device (ZE ZigBee networks. The ZigBee network is f and multiple ZRs. Only ZC can initiate a After initiating, ZC accepts the join request fr extend the ZigBee network. A joined ZR c join request to connect to ZED or other ZR. to one ZC or ZR at most. ZigBee suppor network topologies, star, mesh, and tree. In a star topology, all devices have to connect to mesh topologies, devices use a multi communicate with each other. Only ZC and packets. Figure 1 shows a ZigBee netwo topology. Many research papers about ZigBee ne published in recent years. Most of them fo heme for Increasing Co ZigBee Networks Ruay-Shiung Chang Dept. of Computer Science and Information Engineering National Dong Hwa University Hualien, Taiwan, R. O. C. rschang@mail.ndhu.edu.tw De Na m E 802.15.4 standard networks with low rate. To join in a y, the hardware eshold. However, a to constraints of work. To decrease called Enhanced k. This scheme can to let more devices thod can efficiently . The experimental Scheme has high olution to increase rks; isolated node; k used to connect 2, 9]. ZigBee [10, [6] is designed for sensor and control nt of a device for applied in various omation, industrial nator (ZC), ZigBee ED) are defined in formed by one ZC ZigBee network. from ZR or ZED to an also accept the A device can join rts three kinds of a network with the o ZC. For tree and -hop manner to d ZR can forward ork with the tree etworks have been ocus on the power consumption [1, 13], the sensor broadcast approach [3, 4], and such researches, they assume th connectivity. When devices are system, a device may become a to any ZC or ZR in a Zig communication range can reach that causes isolated nodes is the ZR or ZC is limited [5]. Figure 1. A ZigBee netw The connectivity of ZigBee communication performance. method to reconnect the joine this joined node and its nei method cannot let more isolated [12], the authors propose a met of ZigBee network. They app method to decrease the numb joined node that cannot join m from isolated nodes, it can d which can change their connec However, while multiple isolat to a joined node, the method i isolated node will be disconnec In this paper, we propose Connectivity Scheme to improv Our method can select a no potentially increase more experimental results show that ratio compared with the me onnectivity in Pu-I Lee ept. of Computer Science and Information Engineering ational Dong Hwa University Hualien, Taiwan, R. O. C. m9721024@ems.ndhu.edu.tw r network coverage [2], the data the routing algorithm [7, 8]. In hat ZigBee networks have good e randomly deployed in a ZigBee an isolated node that cannot join gBee network even though its h other joined node. The reason e number of nodes connecting to work with the tree topology. networks profoundly affects the In [11], the authors present a ed node while the link between ghbor node is breakage. This d devices join to the network. In thod to improve the connectivity roach uses the connection shift er of isolated devices. While a more nodes receives join requests disjoin connecting nodes those ctions to accept the join request. ted nodes send the join requests in [12] cannot determine which cted to gain the best connectivity. e an approach called Enhanced ve the method proposed in [12]. de from all isolated nodes to isolated nodes joining. The t our method has a higher join thod in [12]. We provide an 2011 International Conference on Parallel Processing 0190-3918/11 $26.00 © 2011 IEEE DOI 10.1109/ICPP.2011.20 99 efficient solution for improving the conne networks. The rest of the paper is organized a 2 describes the background knowledge of Section 3 illustrates our Enhanced Connecti experimental results are shown in Sec conclusions are given in Section 5. II. ZIGBEE NETWORKS ZeeBee-2007 is the latest specification of ZigBee adopts IEEE 802.15.4 as its phy medium access control (MAC) layers. The MAC beacon is shown in Figure 2. Only ZC periodically send beacon frames to inform whether it has capacity to accept the isolated node. If it has capacity to accept ZR or ZE Capacity or End Device Capacity is set as TR While a ZR or ZED knows that a joinab communication range, it sends the join re joining process, this ZR or ZED is joining becomes a child of the node. Figure 2. The format of ZigBee MAC b A distributed address assignment mechan is designed to allocate network addresses for ZigBee networks. Each device has an addres their child nodes. There are 65536 devices in since the size of ZigBee network address i also defines three configuration paramete network. They are nwkMaxChildren, nw nwkMaxRouters. nwkMaxChildren is defined as the ma children that a device can have. nwkMaxDept depth that a device can have and nwkMaxRo the maximal number of child routers that a Even though an unconnected node communication ranges of other joined nodes, due to the limitation of configuration para randomly deployment under constrains parameters, many devices may be isolated. In [12], the authors present a method isolated nodes under constrains of configurat their method, joined devices can inform thei are shiftable because in their communicatio node that still has capacity to accept child n owns shiftable children is a potential parent In [12], the potential parent can run an procedure to disjoin its shiftable child no isolated node. In such manner, they can decre nodes to improve the connectivity of the net there are many isolated nodes that want t parent, their method cannot select the best is the best connectivity. ectivity of ZigBee as follows. Section ZigBee networks. ivity Scheme. The ction 4. Finally, S f ZigBee networks. ysical (PHY) and format of ZigBee C or joined ZR can m other nodes that device as its child ED, fields, Router RUE, respectively. ble node is in its equest to it. After g to the node and beacon. nism, called Cskip, the joined node in ss space to allocate n a network at most is 16 bits. ZigBee rs to control the wkMaxDepth, and aximal number of th is defined as the outers is defined as a device can have. can reach the it may be rejected ameters. Thus, in of configuration d to accept more tion parameters. In ir parents that they on range there is a nodes. A node that for isolated nodes. extended joining ode and join the ease many isolated twork. However, if o join a potential solated node to get III. ENHANCED CO In this section, we describ ZigBee networks. Our approac Scheme is illustrated in detail nodes in ZigBee networks as method can increase the join r device in a ZigBee system. A. Problem Description The connectivity problem shows an example of this pro Figure 3, nodes, B, I, J, and K constraint of the netw nwkMaxChildren is 3, node G Nodes C and M are shiftable si their parents from nodes A and receive the join requests fro respectively, at the same time, t M, respectively, to accept the jo node (B or I) can join in this Ze Figure 3. An example of the conne If node I successfully join requests from nodes K and J s node B joins to node A, successfully join in this ZigBee cannot choose the best isolate The best isolated node means th the number of isolated nodes choose the isolated nodes to nodes as many as possible is an B. Shiftable Information Anno If we want to reconstruct ZigBee network to improv information has to be announ beacon shown in Figure 2, a n However, how a shiftable nod shiftable. We adopt the announc If the shiftable node is a ZR parent. We use one bit of the re payload as a shiftable flag. Fig payload with the shiftable flag ONNECTIVITY SCHEME be the connectivity problem of ch called Enhanced Connectivity l. We can decrease the isolated much as possible. Hence, our ratio of the randomly deployed is described in [12]. Figure 3 oblem in a ZigBee network. In K, are isolated nodes due to the work parameters. Because G can receive one more child. ince they can potentially change d L to node G. If nodes A and L om isolated nodes B and I, they can disconnect nodes C and oin requests. However, only one eeBee network. ectivity problem in a ZigBee network. ns to node L, it can accept join ince node I is ZR. Contrarily, if only one isolated node can e network. In [12], their method ed node to extend the network. hat while it joins to the network, will decrease at most. How to reduce the number of isolated n important issue. uncement the part of connections in the ve connectivity, the shiftable nced. According to the ZigBee node can realize if it is shiftable. de can notify its parent that it is cing method presented in [12]. R, it uses the beacon to notify its eserved field in the MAC beacon gure 4 shows the MAC beacon g. While a parent node receives 100 beacons from its children, it records the sh children into the neighbor table. Because ZE beacon frame, it uses the short message to the shiftable information. The format of the shown in Figure 5. For reducing the commun ZED sends the short notification message when its status is changed. Figure 4. The MAC beacon payload with the Figure 5. The format of the short mes A potential parent can use fields, Router Device Capacity, to announce that it can acc If an isolated node sends the join request to th the potential parent has to run an extended j We have to add a mechanism into the information base (NIB) to run the shif announcement process. We also use the me in [12] that add a new item nwkUseShiftin nwkUseShifting is set as TRUE, the node can joining and extended joining procedures. Ou procedure is described as the following subse C. Algorithm of Enhanced Connectivity Sche Our extended joining procedure for ZigB following. Step 1. If nwkUseShifting = TRUE, the periodically announces that it has c more children. Otherwise, it announ accept more children. Step 2. While the potential parent receives from isolated nodes, the poten Enhanced Connectivity Scheme (E best isolated node. Step 3. While the potential parent succes shiftable child, it accepts the isolated Step 2. Step 4. If the potential parent still has shifta Step 1. Otherwise, it announces tha more children. hiftable statuses of ED cannot send the notify their parent e short message is nication overhead, to its parent only shiftable flag. ssage. Capacity and End cept more children. he potential parent, joining procedure. ZigBee network ftable information echanism proposed ng in NIB. While n run both original ur extended joining ection. eme Bee is shown as the potential parent capacity to accept nces that it cannot s joining requests ntial parent runs ECS) to select the ssfully disjoins a d node selected by able children, go to at it cannot accept The most important part of joining procedure is to selec algorithm for selecting the Enhanced Connectivity Schem either ZR or ZED in ZeeBee multiple isolated nodes tha connecting to a potential parent best isolated node in the three c Case 1: All isolated nodes cannot accept the other isolated communication range, it does n the network. If all isolated nod the one with the smallest d consumption of transferring dat Case 2: All isolated nodes nodes are ZR, we have to ch within its communication rang wants to join the network, it h nodes are within its communic potential parent this message potential parent receives the jo device that has the most nodes w Case 3: Isolated nodes cons case, the ZR device is selected other isolated devices and pote the network. If the isolated nod potential parent has capacity to method in Case 2 is used to cho parent only has capacity to a method in Case 1 is used to cho The algorithm of Enhanced as the following. /*ca_capacity: the capacity of the p pp_isolated_ZR: the number of iso range of the potential parent. */ pp_isolated_ZED: the number of i communication range of the poten Num_of_pp_isolated: the number communication range of the poten ZR[i].count: the array of isolated Z nodes within communication rang ZED[j].depth: the array of isolated While (ca_capacity != 0 && Num_ { If (pp_isolated_ZR != 0) { temp.count = 0; k = 0; For (i=0; i<= pp_isolat { If (ZR[i].count >= { temp.count=ZR k=i; } } Return ZR[k]; // r } Else f the algorithm of our extended ct the best isolated node. The best isolated node is called me (ECS). An isolated node is a e. We illustrate three cases of at simultaneously request for t and how our method selects the cases as the following. s are ZED devices. Since ZED d nodes as its children within its not improve the connectivity of des are ZED devices, we choose epth due to the lower power ta to ZC. s are ZR devices. If all isolated heck how many isolated nodes ge for each isolated ZR. If a ZR has to scan how many isolated cation range. Then it notifies the with a join request. When the oin requests, it chooses the ZR within its communication range. sist of both ZR and ZED. In this d since it has capacity to accept entially improve connectivity of des contain multiple ZRs and the o accept ZR as its children, the oose the best ZR. If the potential accept ZED as its children, the oose the best ZED. d Connectivity Scheme is shown otential parent. olated ZRs within communication isolated ZEDs within ntial parent. r of isolated nodes within ntial parent. ZRs and the number of isolated ge of ZR i. d ZEDs and the depth of ZED j. */ _of_pp_isolated != 0) ted_ZR;i++) temp.count) R[i].count; return node k 101 { temp.depth =0; q =0; For (j=0; j<= pp_isolated_ZED; j++) { If (ZED[j].depth <= temp.depth) { temp.depth=ZED[j].depth; q = j; } } Return ZED[q]; //return node q } } Figure 6 shows an example of the extende There are five isolated nodes that contain tw and three ZEDs, R, J, and K, in the ZigBee n 6, nodes A and L are potential parents sinc and M can connect to node G that has cap child. In the extended join process, nodes A a to announce that they can accept more childr I want to join to their potential parents that a respectively. They have to scan how many is their communication range. In this example one and node I has two. Because node G on accept one child due to network parameters, M as its child due to following our method in Figure 6. An example of the extended joini After node M successfully joining to accepts node I as its child. Subsequently, th and K can join in the network by node I un of network parameters. In this example, w isolated nodes. Figure 7 shows the ZigBee ne after our extended joining process. ) ed joining process. wo ZRs, B and I, network. In Figure ce their children C pacity to accept a and L use beacons ren. If nodes B and are nodes A and L, solate nodes within , node B only has nly has capacity to it will accept node n Case 3. ing process. node G, node L he isolated nodes J der the constraints we decrease three etwork of Figure 6 Figure 7. The ZigBee network in Fig IV. EXPERIM We design a simulator for method. Two simulation enviro join ratio. Both environments a the transmission range for each parameters, nwkMaxChildre nwkMaxDepth are set as 5, 2 environments. The location of Z area, and ZRs and ZEDs are environments, we assume that shows the environment par implement methods presented i to compare with our method. TABLE I. PARAMETERS SETTI Parameters Network size Number of sensors ZC ZR ZED Transmission range nwkMaxChildren (Cm) nwkMaxRouters (Rm) nwkMaxDepth (Lm) Figure 8 shows the experim Scennario1. The join ration is d Join Ratio ＝ ZRsjoined where ZRsjoined is the number the number of joined ZEDs. ZC joined ZCs in the network. Z current ZeeBee specification. T of devices which are deployed i gure 6 after our extended joining process. MENTAL RESULTS r simulating and examining our onments are used to evaluate the are in a 100m x 100m area and h node is 20m. The configuration en, nwkMaxRouters, and 2, and 4, respectively, in both ZC device is in the center of the e deployed randomly. In both t all devices are static. Table 1 rameters in detail. We also in [12] and the ZigBee standard ING OF SIMULATION ENVIRONMENT. Scenario 1 Scenario 2 100 x 100 m2 = 1 = 10~60 D = 40 ZC = 1 ZR = 50 ZED = 0~50 20 m 5 2 4 mental results of the join ratio in defined as: d+ZEDsjoined+ZCjoined Total nodes of joined ZRs and ZEDsjoined is Cjoined represents the number of ZCjoined is equal to one in the Total nodes represent the number in the network. 102 Figure 8. The experimental results of the join rat In Figure 8, ZigBee is the abbreviation of ZigBee standard and ZCIM is the abbreviatio [12]. The join ratio of our proposed joining an 8% to 13% improvement of that of ZigBe 5% improvement of that of ZCIM. Figu experimental results of the join ratio in Scenn the join ratio of our proposed joining schem to 11% improvement of that of ZigBee, and improvement of that of ZCIM. In Figure 8 number of ZRs becomes large, the impro obvious since ZR can accept more children. Figure 9. The experimental results of the join rat We examine our method in the environ ZigBee network parameters. In this simula the number of ZEDs is 40 and the number Figure 10 shows the join ratios in the environ Cm, and the join ratio in the environment w shown in Figure 11. The two figures show th direct proportion with Cm and Lm. From th also observe that when the connectivity is ratio decreases slowly. The two experimenta that while the density of deployed devices i the value of Cm can improve the connectivi If the density of deployed devices is low, in of Lm can improve the connectivity of the net V. CONCLUSIONS The ZigBee network system is a commu for low power consumption, low data ra tio in Scennario1. f the method of the on of the method in scheme (ESC) has ee, and has a 2% to ure 9 shows the nario2. In Figure 9, me (ESC) has a 4% d has a 1% to 4% 8 and 9, while the ovement becomes tio in Scennario2. nment with varied ation environment, of ZRs is varied. nment with various with various Lm is hat the join ratio is he two figures, we saturated, the join l re