| In recent years, with the popularity of intelligent equipment and generalization of wireless network coverage, people become more urgent for market demand in Real-time information services and communication. However, call system, such as catering, entertainment, medical, industrial and so on, meets the needs of people in this area to some extent, so the system is applied to numbers of occasions. But most of traditional calling system is based on a wired network, the system has so many problems of complicated wiring, installation and high cost in the course of using. When these problems occurred, you need to wire the layout, add a lot of extra cost of materials and labor costs. With the comprehensive development of various wireless communication technology, people have more demands for technical applications. Zigbee technology as a means of wireless communications has developed rapidly in recent years, the technology is widely used for various fields because the advantages of its low power consumption, big network capacity, data transfer reliability, good expand property, low cost, high safety and so on. Therefore, it has a very broad development prospects to use Zigbee technology into wireless calling system.Based on in-depth research basis of Zigbee technology, the paper presented a designing project, which is based on Zigbee wireless call system, the project focuses mainly on its software design and its Positioning for wireless call system function. In the paper we select RSSI location method and triangular measurements as implementation of location algorithm. According to the problems of RSSI measurement which are susceptible to environmental impact, the paper uses the regional environmental factor real-time estimation methods to reduce error that RSSI measurement causes by environmental factor. However, in order to overcome the effects of trilateration method by range error, this paper presents a new method, which can handle all possible error caused by ranging. The main content of the article will be shown in the following.(1)The paper explains the background to study and introduce the development and application of wireless calling system, several wireless communication technologies are introduced and compared. We point out the advantage of Zigbee technology and introduce mainly the characteristics of Zigbee technology, Zigbee protocol architecture and specification, device types supported by the Zigbee are supported, network topology and so on.(2) Because you need to use positioning function in the call system and network wireless sensor network, there are several common positioning methods, and each method has been introduced and compared to others, finally the location method based on RSSI measurement will be used. Then we introduce detail the principles and process of positioning method in location and node positioning, and analysis the effects on the ranging accuracy of the algorithm from environmental factors by experiment data, and analysis the existing questions in trilateration method, finally proposed improvements to the algorithm method to improve positioning accuracy and stability and explained in detail of algorithm improvement principle.(3) According to the actual requirements of the system, we are given a detailed description of the system structure, introduce working process of all function modules in the call system, and achieve the function by Programming. Programming includes workflow of each node in Zigbee network, software realization of positioning algorithm and call control center computer program designing, while we design the Serial communication protocols between PC and Zigbee networks. Finally testing the improved positioning algorithm by experiment, and comparing the results between traditional method and the algorithms presented in this paper. Then we test the calling function in call systems to test the feasibility of the system. |
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