0 Preface
Power line communication technology (PLC) is a communication method that uses power lines to transmit information. The technology loads the high frequency signal carrying the information onto the power line, uses the power line for data transmission, separates the high frequency signal from the power line through a dedicated power line modem, and transmits it to the terminal device.
From the perspective of occupied frequency bandwidth, power line communication can be divided into narrowband PLC (NB-PLC) and broadband PLC (BB-PLC). The carrier frequency range of narrowband PLC is different in different countries and regions, 50~450kHz in the US and 3~149.5kHz in Europe (access to Access communication below 95kHz and In-Housee communication above 95kHz) ), China is 40~500kHz.
Narrowband power line communication is the first choice for smart grids. Establishing a two-way, integrated, real-time communication system is the basis for realizing a smart grid. Without such a communication system, the characteristics of any smart grid cannot be realized. Since the data acquisition, protection and control of the smart grid require such communication system support, establishing such a communication system is the first step toward the smart grid. At the same time, the communication system and the power grid are as deep as the tens of thousands of households, thus forming two closely connected networks - the power grid and the communication network. Only in this way can the goal of the smart grid be achieved.
The power line network is a network with a wide coverage and many transmission nodes, which means that any live terminal can be the starting point and the end point of information transmission.
However, power line communication networks also have limitations. Despite having the widest wiring infrastructure, power line communication networks can rely on power networks to transmit data. However, different filtering characteristics of the same facilities in power networks such as air switches and transformers can cause attenuation or even blockage of power line communication networks. In addition, power lines communication networks cannot communicate via the power network outdoors, or other special areas where power line wiring is inconvenient. The ZigBee-based narrowband power line communication repeater designed in this paper can effectively connect the power network in the separated state, and utilize ZigBee technology to extend the coverage of the power line communication network.
1 ZigBee technology
Zigbee is a low-power personal area network protocol based on the IEEE 802.15.4 standard. The ZigBee name is derived from the communication method used by the bee colony to survive and develop. The bee calls the Zigzag-shaped dance to inform the location, distance and direction of the new food source as the name of the new generation wireless communication technology. . ZigBee's predecessor was "HomeRFLite" which was launched in 1998 by industry giants such as INTEL and IBM.
The underlying technology of ZigBee is based on the IEEE 802.15.4 protocol. The physical layer and MAC layer of ZigBee directly reference the physical layer and MAC layer of the IEEE 802.15.4 protocol.
The advantages of ZigBee are as follows:
1 low power consumption. In the low-power standby mode, two No. 5 dry batteries can support one node for 6 to 24 months, or even longer. This is the outstanding advantage of ZigBee-, under the same conditions, Bluetooth can work for several weeks, WiFi can only work for hours.
2 low cost. By greatly simplifying the protocol (less than 1/10 of Bluetooth), the requirements for communication controllers are reduced. According to the prediction analysis, with the 8051 8-bit microcontroller, the full-featured master node needs 32KB code, the sub-function node is as small as 4KB code, and the ZigBee is free of protocol patent fees. The price per chip is about $2.
3 low rate. ZigBee operates at a lower rate of 20 to 250 kbps, providing raw data throughput rates of 250 kbps (2.4 GHz), 40 kbps (915 MHz), and 20 kbps (868 MHz), respectively, to meet the needs of low-speed data transmission applications.
4 close range. The transmission range is generally between 10 and 100 m. After increasing the RF transmission power, it can also be increased to 1~3 km. This refers to the distance between adjacent nodes. If the relay is transmitted through routing and inter-node communication, the transmission is transmitted. The distance will be further.
5 short delays. ZigBee's response speed is relatively fast, generally only 15ms from sleep to working state, node connection into the network only 30ms, further saving energy. In comparison, Bluetooth requires 3~10s and WiFi requires 3s.
6 high capacity. ZigBee can adopt a star-shaped, patch-like and mesh network structure. A master node manages several child nodes, and at most one layer of network nodes manages, and can form a large network of up to 65,000 nodes.
7 high security. ZigBee provides a three-level security model that includes no security settings, the use of access control lists (ACLs) to prevent unauthorized access to data, and symmetric passwords using the Advanced Encryption Standard (AES128).
8 license-free bands. The direct sequence spread spectrum is used to store the Industrial Scientific Medical (ISM) band, 2.4 GHz (global), 915 MHz (US) and 868 MHz (Europe).
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