0 Preface
Power line communication technology (PLC) is a communication method that uses power lines to transfer information. This technology loads high-frequency signals carrying information on the power line, uses the power line for data transmission, and separates the high-frequency signals from the power line through a dedicated power line modem to transmit to the terminal equipment.
From the perspective of occupied frequency bandwidth, power line communication can be divided into narrow-band PLC (NB-PLC) and broadband PLC (BB-PLC). The carrier frequency range of the narrow-band PLC is different in different countries and regions, 50 ~ 450kHz in the United States, 3 ~ 149.5kHz in Europe (below 95kHz for access to Access communication, and above 95kHz for indoor In-Housee communication ), China is 40 ~ 500kHz.
Narrowband power line communication is the first choice for smart grids. The establishment of a two-way, integrated, real-time communication system is the basis for the realization of a smart grid. Without such a communication system, any feature of a smart grid cannot be realized. Because the data acquisition, protection and control of the smart grid all need the support of such a communication system, the establishment of such a communication system is the first step towards a smart grid. At the same time, the communication system, like the power grid, penetrates into 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 become the starting and ending point of information transmission.
However, power line communication networks also have limitations. Despite having the most extensive wiring infrastructure, the power line communication network can rely on the power network to transmit data. However, the different filtering characteristics of the same facilities in the power network such as air switches and transformers can attenuate or even block the power line communication network. In addition, for outdoor or other special areas where it is inconvenient for power line wiring, the power line communication network cannot communicate via the power network. The narrowband power line communication repeater based on ZigBee that we designed in this paper can effectively connect to the separated power network, and at the same time, the use of ZigBee technology also extends 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 name ZigBee comes from the communication method used by the bee colony for survival and development. The bee informs the location, distance and direction of the discovery of a new food source by dancing a Zigzag-shaped dance. . The predecessor of ZigBee was "HomeRFLite" initiated by industrial giants such as INTEL and IBM in 1998.
The underlying technology of ZigBee is based on IEEE 802.15.4 protocol. The physical layer and MAC layer of ZigBee directly refer to the physical layer and MAC layer of IEEE 802.15.4 protocol.
The advantages of ZigBee are the following:
â‘ Low power consumption. In the low power consumption standby mode, two No. 5 dry batteries can support one node to work for 6 ~ 24 months, or even longer. This is a prominent advantage of ZigBee-, and under the same conditions, Bluetooth can work for weeks and WiFi can only work for hours.
â‘¡ Low cost. By greatly simplifying the protocol (less than 1/10 of Bluetooth), the requirements for the communication controller are reduced. According to predictive analysis, with 8051 8-bit microcontroller, the full-featured master node requires 32KB code, the sub-function node is as little as 4KB code, and ZigBee is free of agreement patent fees. The price of each chip is about 2 dollars.
â‘¢ Low rate. ZigBee works at a lower rate of 20 ~ 250 kbps, providing raw data throughput rates of 250 kbps (2.4GHz), 40kbps (915MHz) and 20kbps (868 MHz), respectively, to meet the application requirements of low-rate transmission data.
â‘£ up close. The transmission range is generally between 10 and 100 m. After increasing the RF transmission power, it can also be increased to 1 to 3 km. This refers to the distance between adjacent nodes. If the relay is used to communicate with each other through routing, the transmission The distance will be farther.
⑤ Short delay. ZigBee's response speed is relatively fast, generally only 15ms to go from sleep to working state, only 30ms to connect the node to the network, further saving power. In comparison, Bluetooth needs 3 ~ 10s, WiFi needs 3s.
â‘¥High capacity. ZigBee can adopt star, sheet and mesh network structures. A master node manages several sub-nodes, and at most one layer of network nodes can manage up to 65,000 nodes.
⑦High security. ZigBee provides a three-level security model, including no security settings, the use of access control lists (ACL) to prevent illegal access to data, and the use of advanced encryption standards (AES128) symmetric passwords.
⑧Free license band. Direct sequence spread spectrum is used to store the Industrial Scientific Medical (ISM) frequency band, 2.4GHz (global), 915MHz (United States) and 868MHz (Europe).
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