Abstract: This paper introduces a design scheme of a remote automatic meter reading system based on wireless sensor network from the aspects of system composition, network protocol stack and hardware platform. The system has the advantages of simple installation, reliability, high efficiency and low cost. Keywords: wireless sensor network; automatic meter reading system; network protocol Introduction With the advancement of the "one meter per household" project transformation and the requirements for automation by water supply, power supply and gas supply departments, remote automatic meter reading system has become an indispensable part of water, electricity and gas automation management and intelligent control[1]. In the process of power system informatization, the automatic transmission of household meter data is of great significance and is also an urgent problem for industry units to solve, because the accuracy and timeliness of meter data transmission directly affect the informatization level of power system, and even management decisions and economic benefits. Traditional manual meter reading is time-consuming and labor-intensive, and its accuracy and timeliness cannot be reliably guaranteed. This results in marketing and enterprise management software being unable to obtain sufficiently detailed and accurate raw data. While manual meter reading is generally done monthly, which is feasible for user metering, it is insufficient for deeper analysis and management decision-making by relevant supply departments. The actual needs of the industry are driving the continuous development of automatic meter reading systems. Currently, automatic meter reading systems on the market are mainly based on wireless communication and power line carrier communication. Wireless communication has advantages such as simple construction, flexible networking, and low cost. Addressing the market demand for ultra-low power consumption and ultra-long-range wireless technology in wireless meter reading, Shanghai Hualong Information Technology Development Center has launched the TrackRFID remote meter reading system. This system adopts industry-leading wireless technology and has unique advantages in ultra-low power consumption, ultra-long range, and anti-interference. Especially in terms of anti-interference, TrackRFID employs advanced processing mechanisms such as frequency hopping transmission, data interleaving, error correction coding, carrier sensing, and interference detection, giving it extremely strong anti-interference capabilities. The system's networking method is based on a self-organizing network routing protocol, offering advantages such as flexibility, reliability, simple construction, and low cost. The TrackRFID remote meter reading system operates in free frequency bands, currently primarily supporting 433MHz and 2.4GHz. For multi-unit residential buildings, a TrackNode is installed on each floor. Each TrackNode can directly connect to the electricity meters of multiple households via a 485 interface. Typically, one TrackNode can connect to multiple meters. During installation, a dedicated program within the wireless communication module is used to retrieve the ID number of each meter. The terminal directly records the usage information of each meter in real time and transmits it directly to the system concentrator installed in the property management center via the building's wireless self-organizing network. The concentrator can operate unattended, continuously in real time, automatically reading and storing meter data for all households in the community. The TrackCenter is equipped with wired and wireless modems, establishing direct communication with the power company's billing and management departments via the local telephone network. The power company can collect water, electricity, and gas usage information from each user at any time through the local telephone network, automatically settle accounts, print, and query data. Below, we will introduce the system in detail from several aspects, including system structure, networking protocol, and hardware structure. System Structure Depending on the actual construction environment, the TrackRFID remote wireless meter reading system consists of a series of optional products, including the system concentrator TrackCenter, local information concentrator TrackCollect, information repeater TrackRepeater, and meter reading terminal collector TrackNode. The system composition is shown in Figure 1. Figure 1: Composition of TrackRFID Wireless Automatic Meter Reading System Meter Reading Terminal Collector The meter reading terminal collector (TrackNode) is a device that collects and transmits the readings of each meter and monitors the operating status of the meters. It is generally installed in the meter box or inside the meter. This module consists of three parts: wireless data transceiver, signal acquisition, and control. The wireless data transceiver part uses the highly integrated dedicated short-range, low-power wireless data transmission chip CC1020, which has the advantages of simple connection with the control unit (direct serial port connection), stable and reliable performance, and has been widely used. The control unit uses the low-power, high-speed single-chip microcomputer MSP430, which boasts strong control capabilities and low power consumption, making the control unit simple, efficient, and highly reliable. The TrackNode connects to the data acquisition terminal via a 485 interface, allowing simultaneous collection of information from one or more electricity and water meters. The collected information is then transmitted to the TrackCollect via a multi-hop network. In addition to information collection, the TrackNode also has relay forwarding capabilities. Depending on the needs, the TrackNode is powered by a 3-6V battery or directly by the electricity meter. Local Information Concentrator To improve parallel transmission capabilities and shorten transmission time, the community is divided into several clusters. The local information concentrator (TrackCollect) collects the meter data uploaded by all TrackNodes in its managed clusters and finally aggregates and uploads it to the TrackCenter. TrackCollect is available in handheld and fixed versions, with large storage space, and is generally placed on the roof. It is powered by batteries or a power supply, depending on the situation. The handheld device adds a user-friendly human-machine interface. System Concentrator The system concentrator (TrackCenter) is typically installed in the community property management center. Its basic functions include timed calls to and reception of data from collection terminals; sending freeze commands to collection terminals to ensure data simultaneity; receiving commands from the central control station and sending relevant data to the central control station; storing hourly electricity consumption, monthly cumulative electricity consumption, and daily and monthly maximum average power consumption and occurrence time for each user. TrackCenter typically manages a single community, collecting meter data from all TrackCollect devices under its jurisdiction, and then uploading it to relevant equipment via serial or network port. This equipment then transmits the data to the power center via a wireless public network link such as GPRS/CDMA. TrackCenter has high transmission power and is not limited by power supply. Central Control Station Installed in the electricity management department of the power supply branch company and the business offices of gas and water companies, it consists of one or more microcomputers, printers, and modems. It receives and stores electricity, gas, and water data from each user, performing statistical analysis, summarization, billing, and report/billing printing. The property management center can also receive and display relevant data using a modem if it needs to query water, electricity, and gas data for a user, but cannot modify the data. Information repeater The main function of the information repeater (TrackRepeater) is to solve the problem of wireless signal coverage. It functions similarly to a GSM repeater. Information can be forwarded through the TrackRepeater, thereby effectively extending the distance between the TrackNode and the TrackCenter. Hardware platform The basic wireless data transmission module TrackNode adopts a hardware platform combining MSP430 and CC1020, as shown in Figure 2. Chipcon's CC1020 chip uses GFSK coding and modulation, currently supports two data rates of 9.6Kbps / 19.2Kbps, output power reaches 10dBm, and line-of-sight transmission distance can reach 1Km[5]. MSP430 is an ultra-low power processor chip from TI, which supports fast sleep and has the advantages of saving system energy. Due to storage space requirements, TrackCollect is built using ARM7 and CC1020. Due to cost and other application requirements, the RF chip can be replaced by, for example, CC1100, and its structure can be flexibly replaced according to specific application requirements. Figure 2 Hardware Platform Network Protocol Currently, we have not only independently developed hardware platforms such as TrackNode and TrackCollect/TrackCenter based on MSP430, ARM7, and CC1020/CC2240, but also independently designed and implemented a self-organizing network protocol stack for automatic meter reading, TrackRFID. Based on this, we have built a TrackRFID remote wireless meter reading experimental system. The network structure adopts a two-layer hybrid self-organizing network structure, as shown in Figure 3. Figure 3 Typical TrackRFID Remote Meter Reading Network Structure Currently, this system mainly supports two applications: centralized meter reading and individual meter reading. "Centralized meter reading" refers to the TrackCenter periodically collecting all meter information through polling or a single command, such as monthly meter reading and billing or electricity consumption statistical analysis. "Individual meter reading" refers to the TrackCenter needing to query and read/write specific meter data, such as real-time meter pre-charge services and node fault alarm functions. Each TrackCenter can manage multiple TrackCollect clusters, and can manage at least thousands of TrackNodes, as shown in Figure 2. Clusters can be divided according to location, such as nodes in the same building being grouped into the same cluster. Based on our experience, the cluster head node Trackcollect can usually be reached within three hops. TrackCollect is responsible for collecting the data collected by all TrackNodes in the cluster and passing it to TrackCenter. TrackCollet is usually installed on the top of the building. Each TrackCollect can collect information of nodes in the cluster and then send the information to TrackCenter, as shown in Figure 3. From the perspective of simplicity and practicality, we designed a TrackRFID protocol stack. First, the system nodes use the broadcast channel function of the wireless data link layer. One node sends a broadcast message, and a group of nodes that receive the broadcast message achieve time synchronization by comparing the local time of the messages they received [2]. In the multiple access problem, we use a multiple access algorithm that combines periodic slot scheduling and CSMA to solve the problem of avoiding data collisions in node data transmission [3]. Among them, the self-organizing network routing algorithm between the cluster head nodes TrackCollect is the core of this protocol stack. We use broadcast flooding for topology discovery. In this process, a tree-based network topology structure is established, thus laying the foundation for tree-based routing strategies [4]. To meet the requirement of fast single-point query, the maximum hop count between TrackCollect and TrackNode within a cluster does not exceed 3. Therefore, we use a simple broadcast flooding method for intra-cluster information transmission. In addition, we employ an addressing method that is completely transparent to the meters and collection center, using the meter address as the data packet source address; for physical link transmission, we use frequency hopping technology to enhance communication anti-interference performance. Currently, within a specified time, for a network of hundreds of nodes, this protocol stack can basically guarantee a 100% correct data packet collection rate. Conclusion This paper introduces a community automatic meter reading system based on a wireless sensor network. This system has been implemented on the TrackRFID remote meter reading system platform at the Shanghai Hualong Information Technology Development Center and has undergone repeated field tests, proving its stable operation and feasibility. Currently, the network scale is 150 nodes, and larger-scale network testing is still underway. 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