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Design of a portable wireless search and rescue positioning system
Easy-Key / 2014-03-31
With the development of national economy, the dependence of mine and coal mine resources is increasing day by day. In the rescue of victims, convenient, fast, accurate positioning of search and rescue system is particularly important, this article is based on this idea, based on the characteristics of wireless ad hoc network through the RF chip, worn on the victims who constantly returns the data values to determine the location of the victims, and rapid rescue.
1 wireless search and rescue principle
The main working principle of wireless searcher system in 802.15.14/Zigbee network is called terminal RF card (worn on the person in trouble) at a fixed time and frequency to the coordinator (with the rescuer transmits the data frame), including a received signal strength value in the data frame (RSSI). Attenuation and distance between the exponential decay of the signal intensity, the relationship between the two is:
The relationship between attenuation of signal intensity and distance to exponential decay
Where D is the distance, N signal propagation constant, A per meter of received signal strength, according to the analysis of experimental data, n is the best range of 3.25-4.5, A is the optimum range is 45-49. (1) type of equivalent transformation can be obtained:
Then, according to the change of D, we can know the change of the distance between the search and rescue device and the terminal.
2 system overall design
The wireless searcher includes two parts, one is the radio frequency card terminal, usually doing the work for staff attendance card, disaster victims, has a positioning function of position, the main chip is CC2430. wireless searcher by Samsung Corp ARMS3C2440 and CC2430 constitute the main function for the collection of RF card sent to the terminal data processing and positioning.
2.1 radio frequency terminal
Radio frequency card terminal selects CC2430 company's TI as radio frequency chip, the chip is Chipcon company production of the first 802.15.14/Zigbee technology in the RF system single chip. Wireless network node, which is suitable for all kinds of ZigBee or similar ZigBee, including tuner, router and terminal equipment. It has the advantages of low cost, low power consumption, significant multi node network transmission distance and other advantages, has the following main features: RF transceiver integrated with IEEE802.15.4 standard; excellent wireless receiver sensitivity and strong anti-interference; hardware support CSMA/CA function; digital RSSI/LQI support.
The hardware circuit of the CC2430 application as shown below, due to the RF terminal of each employee are required to wear one, from the cost point of view, taking a typical simple design method of circuit using a non balanced antenna, non connected balance transformer can make the linear better days.
Circuit application diagram
Figure 1 CC2430 circuit applications
The unbalanced transformer in the circuit is composed of a capacitor C341 and an inductance L341, L321, L331 and a PCB microwave transmission line, and the whole structure meets the requirements of the RF input / output matching resistance (50). The internal T/R switch circuit completes the exchange between LNA and PA. The R221 and R261 bias resistors, resistor R221 is mainly used to provide a suitable working current of 32MHz crystal. In 1 a 32 MHz quartz resonator (XTAL1) and 2 capacitors (C191 and C211) constitute a 32MHz oscillator circuit. In 1 a 32.768 kHz quartz resonator (XTAL2) and 2 capacitors (C441 and C431) consisting of a 32.768 kHz oscillator circuit. Voltage regulators for all the requirements of the 1.8V pin and the internal power supply, C241 and C421 capacitors are to the coupling capacitor, used to power filter, to improve the stability of the work of the chip.
2.2 wireless search and rescue device
The wireless search and rescue device is composed of a control module, a receiving module, a power module, a display module and a memory module. The control module mainly consists of S3C2440 of Samsung Corp, which is mainly responsible for receiving the data transmitted by the radio frequency receiving module and processing it, providing the function of the real-time clock and watchdog. Indicating the status of the search and rescue operation by indicating lamp and buzzer. The receiving module is composed of CC2430, which is mainly responsible for the data of the wireless radio frequency terminal, 802.15.14/Zigbee protocol processing and the dynamic scheduling algorithm of SI and BI. The storage module stores all kinds of data related to the application, mainly through the external RAM and ROM expansion to achieve. The power supply module to reduce the power consumption of the system to meet the requirements of the battery power supply, used in hardware design of low power devices, such as RF chip, RS-232 chip, a memory chip can work normally under 3.3V. LCD display module in real time the total number of victims, the victims and the search and rescue distance between the victims, the victims of personal information such as the ID number and so on display in the LCD display. The hardware connection block diagram is shown below:
Hardware block diagram of the search and rescue device
Fig. 2 hardware block diagram of the search and rescue device
2.3 system software implementation
Wireless searcher system consists of wireless searcher and personnel terminal RF card two, terminal wireless searcher as network coordinator, responsible for the establishment of a beacon enabled network, allowing a join request terminal RF card added to the network, when added after the success, can carry out data transfer, the software flow chart is shown in figure 3. The terminal RF card is used as an examination card in the absence of disaster, when the disaster occurs as a location card, the process is shown in Figure 4.
 
Coordinator flow chart
Fig. 3 flow chart of Coordinator
Terminal flow chart
Fig. 4 flow chart of terminal
2.4 dynamic settings for SI and BI
Wireless search and rescue in the search for the victims of the need to collect a large number of RSSI values to be positioned, which means that the network is very busy communication.
The general network for the beacon interval (BI) and superframe interval (SD) activities are set as a fixed value, but the router or coordinator when communication busy it is possible because the transmission of large amount of data, and the activities of super frame interval and relatively small, may cause packet loss etc. thus, become the bottleneck of network data transmission. This system from the actual experiment, take a dynamic set BI and SI method, the flow chart as shown in figure 5.
algorithm flow chart
Fig. 5 flow chart of algorithm
3 experimental results analysis
In several Zigbee network topology, cluster tree topology network is rapid, nodes join the network routing approach to the characteristics of high success rate, and has a network self-healing function, and because the router has data forwarding capability, transmission can achieve a large amount of data, so in the experiment, we will type RF card all the settings for the router, the topology of cluster tree topology. Packet Sniffer CC2430IEEE802.15.14 software through the data frame tracking in every frame to calculate the number of bytes in each super frame activities within the range of terminal data transmission,
here is BO and SO as the set value is compared with the dynamic setting BO and SO value of the amount of data transmission under two kinds of situations of the:
Table 1 transmission data comparison table
Transmission data comparison table
Table 1 shows that the dynamic setting BO and SO value, can significantly increase the number of transfer, thus greatly increasing the accuracy of positioning and the sensitivity of the search and rescue.
In the dynamic setting BO, SO value method, the wireless search and rescue system of the precision and sensitivity of the experiments available: when the wireless searcher distance from the terminal RF card 45 meters can search to the signal terminal card, the positioning error of less than 3 meters, with close to the distance between the positioning error is reduced accordingly, in the 20 meter positioning error can be controlled within 1 meters, considering this is obtained in the experiment under the condition of the conclusion, in the practical application due to various environmental interference, sensitivity and positioning accuracy will decline, but the general mine in the Ningbo road length are mostly in the more than 10 meters or so, the positioning error in about 0.7 meters. Based on the above experimental data, the wireless search and rescue system can meet the practical engineering application.
4 Conclusion
By collecting various radio terminal card RSSI, realize the positioning and search functions, and the use of dynamic setting BO, SO method, using innovative wireless search field, optimization of the beacon interval, solves the data transmission bottleneck problem, thereby improve the positioning accuracy and sensitivity. On the basis of this design, the precision of positioning and the penetration ability of nodes need to be further improved and studied.
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