Application of hybrid communication network in remote street lamp monitoring

Dong Jianping, Shen Xiaobo, Zhou Xunsheng, Zhejiang Lighting Association (310020) 1 Overview Since 2000, many large and medium-sized cities in China have launched remote streetlight monitoring projects. In the project establishment and program demonstration stage, it is often the most difficult for decision makers to start communication. The choice of the network...

According to statistics, there are no fewer than ten kinds of communication technologies used in China's current street lamp monitoring system. At the same time, with the continuous development of China's communication industry, new products and new technologies are constantly being introduced and new. There are often countless communication solutions in front of people. In terms of performance, price, engineering installation, maintenance, etc., they each have their own advantages and disadvantages, and have different applicability for different applications.

Comprehensive evaluation and selection of an optimal communication scheme is currently widely used, but the choice of a scheme often means giving up the advantages of other schemes, but also means closing the door to new developments in communication technology in the future. Is it possible to have a technology that is compatible with various communication networks and to continuously integrate new technologies? This paper proposes a street lighting monitoring technology based on hybrid communication networks, which can be simultaneously on the same monitoring system platform. It accommodates a variety of communication networks and maintains openness to new technologies and products.

2 The existing communication schemes currently have many communication schemes adopted in the streetlight communication monitoring in China. The mainstream technologies mainly include analog radio stations, digital radio stations, telephone networks, CDPD wireless systems, GSM short messages, GPRS networks, and CDMA networks. , USSD, professional digital wireless communication network, 802.11 wireless local area network, cable broadband network, power line carrier and so on.

These schemes can be divided into wireless networks and wired networks according to different communication media; they can be divided into private networks and public networks according to different owners of communication networks; they can be divided into analog networks and digital networks according to different modem technologies; Whether to establish and maintain connection can be divided into connected communication mode and connectionless communication mode. According to different initiators of the communication process, it can be divided into center initiation communication and terminal initiation communication. According to whether communication can access multiple terminals, it can be divided into strings. Line and parallel mode. According to the number of communication solutions owned at the same time, it can be divided into a single communication network and a hybrid communication network.

Table 1 is a breakdown of these mainstream communication schemes. Table 2 is a comparison of these communication schemes. Table 1 Communication scheme classification Communication scheme Communication medium public/private network analog/digital connection status communication initiator serial/parallel analog radio station wireless private network simulation without center/terminal serial digital radio Taiwan wireless private network digital no center / terminal serial wireless public network digital no center / terminal serial telephone network cable public network analog center / terminal serial GSM short message especially public network digital no center / terminal serial GPKS network wireless Public network digital terminal parallel CDMA network wireless public network digital terminal parallel wireless public network digital terminalless parallel professional digital wireless communication network wireless public network digital no center / terminal parallel 802. 丨 1 wireless LAN wireless public network digital center / terminal Parallel Cable Broadband Network Cable Public Network Digital Center/Terminal Parallel Power Line Carrier Cable Private Network Digital Centerless/Terminal Serial Communication Scheme Communication Rate Stability Reliability Safety Timely Response Construction and Maintenance Convenience Mature Advanced Analog Radio Low Highly complex mature digital radio stations are higher without complex maturity | higher than no convenience has been scoured ftj telephone network low Higher complex E elimination 丨 GSM short message low higher no convenient GPRS network higher low higher convenience is not mature enough CDMA network higher convenience is not mature enough higher no convenience not mature enough professional digital wireless communication network higher high no convenient mature Advanced 11 wireless LAN high and high, convenient, not mature enough, wired broadband network, high, convenient, mature, advanced power line carrier, low, high, no convenient, not mature enough. From Table 1 and Table 2, we can see that each of these programs has its own characteristics, each with its own advantages and disadvantages. . They are suitable for different occasions, such as near the center, and analog radio stations and digital stations are suitable for flat terrain. In areas with long distances, complex terrain (such as under viaducts, high-rise buildings) or where antennas cannot be installed, GPRS, CDMA, GSM, USSD, and professional digital wireless communication networks are more suitable. It is more appropriate to use wired broadband networks in urban communities.

3 Solution The hybrid communication network must be designed to improve the system, mainly through the abstraction and layering of hardware, communication protocols and software to achieve a hybrid communication network.

For connectionless communication solutions, the hardware does not need to be specially designed, and the general hardware can be used.

For the connected communication scheme initiated by the terminal, the function of automatically establishing the connection and maintaining the connection must be completed on the terminal communication device, and the function of detecting the validity and reconnection of the connection should be also provided.

For a connected communication scheme initiated by the center, the terminal communication device must be able to automatically accept the connection and maintain the connection function. In addition, it should also check the validity of the connection and re-accept the connection.

In order to protect the investment of the RTU equipment of the street lamp monitoring terminal, the RTU should provide at least one RS232 standard interface to be connected with the communication device. If possible, the interface can be set to RS485 or TTL communication interface through the hardware jumper. Since different communication devices use different communication rates and communication configurations (baud rate, data bits, stop bits, parity bits), the RTU should be able to set different communication parameters through software, and also because some communication devices have to pass hardware. The handshake line is used to convert the receive/transmit status. The RTU should provide at least one RTS hardware handshake line. In addition, the conversion time of the communication device status can be set.

Communication equipment must be modular in design, providing functions such as RS232-wireless, RS232-802.11, RS232-802.3 and other communication interface converters. In order to be able to seamlessly modify the communication devices, the power supply parts of these communication devices should be unified, such as 12V DC power supply.

2 protocol due to the use of a mixed communication network, in the communication protocol requires a key design of the system addressing problem, each device in the system should have a device address, this device address can be a serial number or other number, this is a logic Address, the device address of each device in the whole system should be unique. In different communication networks, each device may or may not have a corresponding physical address. In some networks, there must be a unique physical address. The mapping between device addresses and physical addresses must be established.

The system generally has the following methods: The first one is broadcast mode, all communication data can be received by each site, and the central point and the terminal point have no fixed physical address: this is usually a connectionless communication method, such as Analog radio and digital radio mode. It is judged whether it is the data that should be responded by comparing the target device address of the data with the own device address. Therefore, the device address of the target end must be included in the communication protocol.

The second way is to supplement the first one, and it is also a connectionless communication method, if the data is to be transmitted to the target terminal through relay communication of other terminals. The protocol should include a routing table for the communication, telling the order of the data routes and the device address of the corresponding routing terminal.

The third type is a connectionless communication method in which both the center and the terminal have a unique fixed physical address. The center knows the physical address of the terminal, but the terminal does not know the physical address of the center. For example, the network of professional wireless digital networks, their physical address is the pulse number of the corresponding device. When the center sends a data packet to the terminal, the center queries the physical address of the target device through the mapping between the device address and the physical address, and the protocol intermediate address.

The fourth type is a connectionless communication method in which both the center and the terminal have a unique physical address, the center can know the communication address of the terminal, and the terminal can also know the communication address of the center. For example, GSM short message mode, their address is the phone number of their respective CIM card. In order to avoid configuring the central address on the terminal, you need to modify the central address configuration of each terminal one by one when modifying the central address in the future. You can use the third communication method to process, that is, the mapping table between the device address and the physical address is maintained by the center.

The fifth type is that the center has a fixed physical address, and each time the physical address of the terminal changes, a connected communication method initiated by the terminal, such as a GPRS network and a CDMA network, whose physical address is the other party IP address and port number. The central IP address and service port are always fixed, and the terminal will assign a changed IP address and port number each time the terminal initiates a connection. In this case, the terminal must be configured with the physical address of the center. When the system starts running, the center enters the state of waiting for the connection, and the terminal initiates the connection. Once the connection is successful, the center should be able to query the terminal for the target terminal through the corresponding data communication protocol. The device address, and then the center maintains a dynamic mapping table of device addresses and physical addresses, so the protocol design must include the device address query protocol. In addition, since the communication connection may be a terminal, a connection status detection protocol, such as a heartbeat message, should be included in the design of the communication protocol. Therefore, the protocol design should include both status and maintenance messages.

The sixth type is a connected communication method in which the center and the terminal have fixed physical addresses. This method can adopt a center-initiated communication method or a terminal-initiated communication method. For example, the broadband wired network VPN mode, their physical address is their assigned IP address and port number; the telephone network dialing mode, their physical address is their own phone number, in order to simplify the processing, usually also adopt the fifth way.

Since the communication scheme has different serial and parallel modes, it is also designed separately in the protocol processing. The serial mode is a blocking mode, that is, after the center sends a message command to a terminal, unless it receives a response or waits from the terminal. After the response times out, the communication processing for the next terminal is performed. The parallel mode is a non-blocking mode. After the center sends a message command to a terminal, it can perform communication processing for the next terminal without receiving a response from the terminal or waiting for the response timeout. Serial communication is relatively intuitive and easy to handle, but the system efficiency is low, the system of parallel communication is highly efficient, but the communication status with each terminal must be monitored, and the complex C 3 software is processed in order to integrate multiple communication schemes and technologies. On a system platform, the communication part of the system software must be carefully designed, and various mature software design patterns are used to design the system software to realize the abstraction of the communication layer and maintain the flexibility, maintainability and robustness of the system. Sex: The software design here can adopt the Factory factory mode, which is realized by inheritance and polymorphism. The specific design is introduced separately due to the space relationship, and will not be described here.

4 Advantages and characteristics of hybrid communication networks Compared with previous single communication networks, hybrid communication networks have unparalleled advantages.

First, the hybrid communication network can greatly reduce the query speed and response speed of the system by the parallel processing of the system by distributing the various endpoints of the system on each communication channel. The processing time of the four communication channels is better than the processing of one communication channel. Time is at least four times faster.

Second, the hybrid communication network can adopt different communication methods for different monitoring points, and it can greatly improve the flexibility of the system according to local conditions. For example, sometimes the monitoring is interrupted and installed in the basement, the antenna cannot be installed through the tube, or the antenna is too long. A few points change the entire communication scheme, and we can use wired broadband at these points or install GPRS or CDMA systems where there is indoor wireless coverage. For example, some buildings have CDMA wireless coverage installed, and some buildings have GPRS wireless coverage. We can't ask which wireless coverage system to use. With a hybrid communication network, we can have CDMA coverage. The CD-MA communication module is installed in the place where the GPRS communication module is installed in the place where GPRS is covered. For example, in some scenic areas, it is impossible to establish a high antenna to influence the landscape. We can use a professional digital network with small antennas or a wired broadband network without antennas.

Third, the use of hybrid communication networks can adapt to the continuous development of technology. Nowadays, existing communication technologies are not mature enough or the facilities are not enough. With the development of society, one day will develop and mature, and the supporting will keep up. New technologies will continue to emerge, using a hybrid communication network to seamlessly integrate human systems in the future when new technologies emerge, without having to reinvent the original investment and protect the original investment. You can also enjoy new technological achievements and ensure the advanced nature of the system.

Fourth, the use of hybrid communication networks can reduce the dependence on products and improve the system's risk resistance, such as the suspension of the original equipment (such as Motorola's 998 radio), the price of equipment caused by tariffs (such as the Japanese number in 2002) Radio) and other risks.

Fifth, these communication methods and products not only compete continuously in similar products, but also have fierce competition for quality and service in different types of products. The use of hybrid communication networks can avoid market monopoly, maintain a benign and orderly competition in the market, and urge communication equipment suppliers and communication service providers to continuously improve product quality, reduce product prices, and improve service quality and quality.

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