Application of Zigbee Technology in Personnel Positioning System

Establishing a positioning network:

1. According to the actual needs of the site, a Zigbee network module (which can be battery-driven or use other power sources) is set at an appropriate position in the tunnel (such as the top) every 200 meters along the tunnel (consistent with the position of the underground power interface), and the working face distance can be reduced to 50 meters. At the same time, corresponding Zigbee network modules are also placed in other places where positioning and network connection are required; in order to avoid interference of the underground environment on the wireless signal, all wireless network modules use the anti-interference direct sequence spread spectrum communication method, and each module has a received signal strength indication function (RSSI)

2. The installed network modules will automatically form a Zigbee communication network. When arranging the positions of the network modules, it is important to ensure that each module can communicate with at least two or more modules, that is, to avoid "single-line communication" to ensure the reliability of Zigbee network communication. This communication network is actually a positioning network, and each network node is a positioning point. However, compared with the method of using RFID for positioning, our network nodes can also determine the location information of the moving target by reading the signal strength of the moving target. In addition, Zigbee network nodes are much smaller, and the communication between network nodes does not necessarily require the use of additional optical fibers or communication cables for connection.

Wireless ID card module for mobile targets:

1. Each mobile target that needs to be located (such as miners) needs to carry a wireless ID card module, or a button battery-driven fully enclosed module fixed on a safety helmet. The size is about (50 x 40 x 8 mm), and the transmission power of each module is less than 1/1000 watt. It is recommended to use our simplified SC8836A or low-cost SC8836A module.

2. In order to increase battery life, the wireless identity module transmits an identity code signal every 5-30 seconds. In order to avoid interference with wireless signals in the underground environment, all wireless identity card modules use anti-interference direct sequence spread spectrum communication; at the same time, in an emergency, you can also send emergency messages at any time through the button on the card.

3. The wireless identity module can also be connected to sensors such as gas detection. In this way, it can not only collect various information required for safe production (such as gas concentration, wind pressure and wind speed, etc.) at different locations (especially mining faces) according to needs, but also automatically transmit the location information and related information of the collection point to the monitoring center. This gas collection point can be placed at a fixed position on the mining face and move with the movement of the mining face. It can also be carried by gas security personnel, which is very convenient. When the gas concentration exceeds the standard, the wireless module can immediately transmit the concentration information, location information and alarm signal to the monitoring center through the Zigbee network. If necessary, other linked emergency equipment will be started at the same time;

4. Adjust the transmission power of the wireless positioning identity card module so that it can communicate with at least one positioning node module.

Determination of the position of the mobile target:

1. When only one positioning node receives the signal of a mobile identity card, the position of this positioning point is the position of the mobile target; 2. When two

positioning nodes receive the signal of a mobile identity card at the same time, the middle position between the two positioning points is the position of the mobile target;

3. When using signal strength to improve positioning accuracy, the signal strength of a mobile identity card received by a positioning node can also be used to determine the distance of the mobile target from the positioning node. The stronger the signal, the closer it is to the positioning node. The functional relationship between signal strength and distance to the positioning point can be obtained through simple actual measurements in advance. When two positioning nodes receive the signal of a mobile target at the same time, we can determine that the mobile target must be somewhere between the two positioning nodes. Its specific location can be obtained by simple calculation and on-site measurement correction using the specific value of the signal strength of the mobile target received by the two positioning points.

It is worth noting that in places with more complex environments, especially where the positioning area is not linear, such as some work surfaces, we need to increase the number of positioning nodes to improve positioning accuracy.