A minimum physical distance delivery protocol based on ZigBee in smart grid

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 advanced measuring infrastructures. However, the current routing algorithms cannot fully satisfy the requirements of the application, and the characteristics of the node deployment and the data flows should be more considered. In this paper, we propose a minimum physical distance (MPD) delivery protocol based on the ZigBee specification in the smart grid to optimize the transmission of the monitoring and command packets which are from or to the ZigBee coordinator (ZC). The physical depth, which is introduced to indicate the least hops to the ZC, and the transmission paths are decided based on the neighbour table information. The simulation results show that the MPD could improve the performance of the monitoring and controlling packet transmission, it provided high reliability and short paths, the bits sent by the devices except the coordinator were reduced and the end-to-end delay was also shortened. 1 Introduction Smart grid is characterized by two-way flow of power in electrical network, and information in communication network to increase energy efficiency, transition to renewable energy sources, reduce greenhouse gas emissions, and build a sustainable economy that ensures prosperity for current and future generations [1-3]. The real-time communication ability of the smart grid will enable utilities to optimize and modernize the power grid in order to realize its full potential [4]. The communication network takes charge of the collection and analysis of real-time data, along with the control of electrical loads for energy reduction and demand response [5]. Advanced metering infrastructure (AMI) is the technology of automatically collecting data from energy metering devices and transferring that data to a central database by communication technology for remote control and analyzing. It is the totality of systems and networks for measuring, collecting, storing, analyzing, and using energy usage data. AMI will link consumers and power utilities together and provide foundation for future distribution automation and other smart grid functionalities [6]. Based on these functions, the nodes in AMI are always irregularly distributed and the communication is low data rate and short range. In the recent report on National Institute of Standard and Technology (NIST) framework and roadmap for smart grid interoperability standards, several wireless communication technologies are identified for smart grid. For examples, ZigBee and the ZigBee Smart Energy Profile (SEP) have been defined as the one of the communication standards for use in the customer premise network domain (including AMI) of the smart grid [7]. ZigBee technology is characterized by low cost, low power, low data rate, and simplicity [8]. These features, along with its operating over unlicensed spectrum and being a standardized protocol based on IEEE 802.15.4 standards, facilitate easy network deployment and implementation, and make it the most suitable wireless technology for smart grid applications [9]. It has also been selected by a large number of utilities as the communications platform of choice for their smart metering devices as it provides a standardized platform for exchanging data between utilities and smart metering devices and appliances located on customer premises [10]. ZigBee uses a mixed routing mechanism combined with HRP (hierarchical tree routing) and Z-AODV (ZigBee ad-hoc on demand distance vector) [11]. HRP is based on the address distribution and provides a simple and reliable measure for data transmission, though it is not always efficient and robust. For 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, since the HRP and Z-AODV are designed for different topologies, their benefits are alternative. Moreover, 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 in different environments [12]. For that reason, current network formation and routing protocols described in the ZigBee specification cannot fully address power consumption issues [13,14]. The deployment in smart grid is newly presented and the characteristics of application need to be more considered [15,16]. The diagram of AODV is shown in Figure 1. One can see at least two separate modes: route discovery/maintenance (phases I and II) and the actual forwarding of application packets (phase III), with the first mode involving special traffic that does not directly originate at the network's application [17]. The routing request is always flooding by rebroadcasting while the data is unicast transmitted. The prevailing wisdom regarding the organization of wireless networks assumes point-to-point communication, whereby each node forwarding the packet on its way to the destination sends it to a specific neighbour [18].Note that the benefits of unicast mechanism tend to be questionable [19] and much more so in sensor networks, where packets tend to be very short [20]. Firstly, the action of announcing the transmission with the handshake may take more bandwidth than the actual transmission; so the probability of damage to an unannounced transmission is in fact lower than that to the announcement [21]. Secondly, the neighbour identifier requires room in the packet header and thus incurs extra framing, which significantly inflates the otherwise short packet. Therefore, the mechanism in Figure 1 has two major disadvantages: one is the higher latency caused by routing discovery; the other one is that the bandwidth cost in the first two phases and the unicast in phase III have no more gains for short data packet delivery. Owing to the open nature in the wireless channel, the unicast is essentially a broadcasting that only a specified device would respond by identifying address information. If other parameters which are able to control the data flow and restraint the flooding can be found, we can design a proper delivery protocol to overcome the mentioned defects and achieve better performance in data transmission. Considering the regular data flows in AMI, they can be classified into two categories. One is the monitoring and controlling frames from or to the sink node, which is the ZigBee coordinator (ZC) in the ZigBee network. The other is the general communication between any other devices except the ZC. For the monitoring and controlling communication, as the ZC is the root of tree structure, these packets are transmitted along the hierarchical paths, where th (...truncated)