How to Apply Wireless Communication Technology to Community Intelligent Construction

1. The current status of intelligent districts and main system control modes 1.1.1 The current status of intelligent districts
For a long time, intelligent community access control systems, one-card systems, perimeter protection systems, electronic patrol systems, three-meter remote reading systems, household alarm systems, and parking lot management systems have all been networked using the RS485 bus. Each system is independent. Each system must use a very large number of buses, and each system is not connected to each other, each using its own networking line. If the community is large, the networking line will be longer, and the network will be repetitively routed and cannot be shared. This will not only result in large investment, but also be affected by lightning, resulting in a high failure rate. In addition, this type of networking is limited by distance. The longest line length is only 1000 meters. For large and medium-sized communities, it is impossible to meet the demand, but some remedial measures have to be adopted. The direct result is excessive signal loss, instability, etc. Disadvantages. Due to the limitation of the topology structure of the network (star or network structure cannot be adopted), and because it is a wired connection, even if it is buried underground, the environmental impact and the impact of lightning are also very serious.

1.1.2 Main System Control Mode of the Current Intelligent Community
Here we take the access control system as an example to illustrate the main system control mode of the current intelligent community.

For a long time, for the modern residential smart community, the practice of the access control system is as follows:

Place a card reader (or place the reader on its own) in each of the unit doors in each building with a memory in the reader. The owner is given a card and authorizes the card to open the owner's home unit lock, and this card number has been saved to a computer placed in the monitoring room. The computer passes this authorization information to the reader and saves it in the reader. When the industry chair opens the door, the card reader can determine if the card is valid. And each time the door card is used to open the door, the card reader will transmit this door opening information to the computer placed in the monitoring room, and the computer may record the usage record of each door card. This system allows the metal key to be replaced by an authorized smart card, so that the mechanical door lock is replaced by a card reader and an electronically controlled lock, controlled by the unit control circuit, and the background permission setting and monitoring management are implemented through the networked communication method. The superiority of the access control system is obvious. It makes the control of the authority very flexible. The authorization of the smart card can realize multiple cards for the access control, and can also restrict the permission period of the card, or adjust or cancel the card in case of personnel change or card loss. Permissions, do not have to replace the door lock. China Card Network released. For example, the authority for property management personnel and security can be set higher, and multiple doors can be opened; for cleaning personnel, they can enter the building within a limited time. All district management departments implement centralized authorization management.

The RS485 bus networked all readers. The bus required a parallel connection of the devices to be connected. The star connection was generally not allowed. If a large-scale intelligent community is constructed, the length of the bus is too long, causing signal instability and excessive loss. The biggest drawback of traditional wiring methods and the problem that is difficult to solve is the problem of lightning strikes. Even if buried underground, it is difficult to avoid lightning damage. If it is destroyed, all reader modules on a line are burned and destroyed, and some cameras are also burned. The loss was huge and the schedule was delayed.

2. Implementation of line transmission in intelligent cell system 2.1.1 ZigBee wireless network technology
ZigBee is an internationally-accepted new generation wireless communication technology. The name comes from the bees that inform the discovery of food by dancing in the shape of a ZigZag dance. ZigBee technology is an emerging short-range, low-rate, low-power wireless network technology that is mainly used for short-range wireless connectivity. Adopt ZigBee technology, this is decided by its main technological advantage: The data transmission rate is low, concentrate on the low transmission application;

Low power consumption: The power consumption is only 1LW in the sleep state, and the power consumption in the working state is 30mW when the communication distance is short. In the low power standby mode, two regular 5th batteries can be used for 6 months to 2 hours. year. This is also a unique advantage of ZigBee technology; low cost: ZigBee data transmission rate is low, the protocol is simple, so the cost is greatly reduced, and royalty free; network capacity is large: Each ZigBee network can support up to 255 devices. Each ZigBee network can support up to 65000 nodes, which means that each ZigBee node can be connected to tens of thousands of nodes; the delay is short: usually the delay is between 15 milliseconds and 30 milliseconds; the effective range is small: effective coverage Between 10 and 75 meters, depending on the actual transmit power and various application modes. However, it can be extended to hundreds of meters, depending on the actual transmit power and various application modes, and can basically cover an ordinary home or office environment.

2.1.2 implement subsystem functions <br> <br> to access control systems to illustrate the implementation of intelligent wireless transmission cell. The access control system consists of a master control device, a wireless data transmission module (referred to as a wireless module), a management PC, a smart card, a card reader, and an electronic control door (lock). The system includes sensor nodes and gateway nodes. A large number of nodes (sensing nodes) are deployed in the cell to form a network. With ZigBee technology, a ZigBee module is placed in each building or unit, and a ZigBee module is placed in the monitoring room to form a star network and a mesh network. In this way, not only the cost of the bus is saved, but also the module itself has a routing function, which improves the stability of the signal, has good lightning protection performance, and avoids further losses.

The data monitored by the sensor node relays data from one sensor to another through radio waves in a relay mode, and then transmits to the gateway node after multiple levels of transmission. Finally, it can reach the monitoring through the Internet (IP/TCP) or other mobile network. center. Because there are many nodes, there are multiple redundant communication paths. If the path being used is interrupted, the network will automatically select another path to maintain normal communication. In the wireless mesh network, when the number of nodes is large, newly added nodes can communicate with neighboring nodes. After a node joins the network, these nodes will create a path with the destination node, and the node itself will be able to establish a route. After sending information and receiving information and forwarding it, the process will repeat from node to node between the nodes from the initial node to the destination node until the information reaches the destination node. The destination node returns a confirmation to the initial node indicating that the information has been received.

The distribution of the system network is shown in Figure 1. The master control device is the central component of the access control system. It communicates with the computer through the wireless transmission module, downloads the user's card number and uploads the card reading information. The system's wireless data transmission design is divided into two parts: the single chip end and the PC end in terms of hardware. The single-chip microcomputer mainly completes the data acquisition and processing, and receives the data transmitted by the PC. The system uses VisualC as a front-end development tool, which mainly consists of smart card management, owner management, and message management. The system's PC can realize real-time monitoring. The system back-end database uses SQL Server. After the owner swipes the card, the MCU receives the user information and stores the information in memory. The sending end sends the user information in the memory. After the receiving end receives the information, it does not receive the information immediately, but examines the state of the network, and stores the received information and the sending device information in the memory. If the network is idle and the sender is a valid sending device, the receiver receives the information and returns a message to the sender indicating successful reception. The information is sent again until it reaches the destination controller and the sender receives the message. After the message is returned, the corresponding information in its memory is erased. If the sender is an invalid sending device, the receiver does not receive the information.

3. Language

With the booming construction market and the emergence of smart communities, wherever smart buildings are needed, wireless communication technology will be needed. ZigBee is currently the most suitable wireless communication technology for wireless sensor networks. Our application is based on ZigBee's characteristics. Combining with the construction market, the smart building's reform and innovation in smart buildings will mainly save expenses, improve anti-jamming capability, and also reduce the impact of lightning on intelligent systems. It is believed that with its major technical advantages, wireless networks using ZigBee technology will become the main networking form of community intelligence.

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