introduction
In the modernization of the city, the management and scheduling of public transportation is a very important aspect. The management center can dispatch vehicles at any time according to road conditions and passenger needs; on the other hand, through the display of the bus station, the passengers are notified how far away the waiting vehicle is from the station, so that in the case of traffic jams, passengers can choose to travel by themselves the way. This paper designs a positioning system based on the ZigBee wireless sensor network. In this system, buses are regarded as positioning nodes. Reference nodes are widely distributed along urban roads. The positioning nodes are calculated through the reference nodes. The positioning information is reported to the gateway. The gateway passes to the backbone network and finally to the control center.
1 Network principle and implementation of wireless positioning system
The principle of the network positioning is shown in Figure 1. It can be seen from the figure that almost all of the network positioning can use wireless transmission, which can solve the problem of road wiring and save a lot of hardware costs.
Figure 1 Principle of positioning system
â‘ Host computer: The computer of the management center is equipped with relevant interface software, which is convenient for observing the bus position of each bus line, which is also convenient for management and scheduling.
â‘¡Gateway: Designed with CC2430, it can set up a ZigBee network. In each area, that is, on each bus line, the gateway acts as a coordinator and reports the location node, that is, the location information of each bus to the management center.
â‘¢Reference node: The reference node is also designed with CC2430. It acts as a router in the network. It is placed on the bus line during the positioning process of the system. The user specifies fixed coordinates and provides the coordinates and RSSI average value for the designated node. In addition, the reference node can also be expanded, through the video function, you can obtain traffic information, and further provide data for the management center.
â‘£Positioning node: The positioning node is designed with CC2431, which has a positioning engine inside, which can calculate its own precise coordinate position based on the fixed coordinates and RSSI average value provided by the reference node, and coordinate this coordinate as the node identification number and send it to the gateway.
2 The specific design of each node of the system
2.1 Positioning node
The positioning node is designed with CC2431, uses the internal engine to calculate its own position, and then passes it to the gateway. The design principle is shown in Figure 2. It can be seen from the figure that only the CC2431 and the necessary external wireless devices are used, and there are no other peripherals. On the one hand, the design is simplified, on the other hand, it is conducive to energy saving.
Figure 2 Design principle of positioning node
After receiving the RSSI value of all reference nodes in the positioning area, the positioning node calculates its coordinate value through a positioning algorithm. The positioning node includes the following functions:
â‘ Join the network and send and receive data wirelessly.
â‘¡ The function of controlling the reference node to collect the signal strength value when communicating with the positioning node multiple times.
â‘¢ Control the reference node to calculate the average value of the signal strength value of multiple mobile phone positioning nodes and send it as the node function.
â‘£The function of standard parameters that can be dynamically configured by the coordinator in the air.
⑤ The function of not losing the standard parameter information after the drop.
â‘¥Calculate and send XY coordinates.
⑦The function of sending the positioning node number.
The basic function of the positioning node includes the function of sending and receiving data wirelessly, controlling the reference node to collect the signal strength value during communication with the positioning node multiple times, and controlling the reference node to calculate the average value of the signal strength value of the positioning node for multiple collections and sending to the positioning node . The positioning node also needs to accept the gateway to perform air dynamic configuration of standard parameters, and ensure that the standard parameter information will not be lost after power failure.
After the positioning node is powered on, the system will give it a default standard parameter, including A value, N value, mode, collection wait time, cycle in automatic mode, minimum reference node number and other information, if it is the first time to join the reference network , The system writes these data to flash; otherwise, if it already exists in the network, it will read the standard parameters stored in flash.
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