Frequency Selection Design Of Radio Frequency In Receiving Traffic Information

How to efficiently and reliably gain dynamical traffic information is one of the most important problems in ITS (Intelligent Transportation Systems). Recently, Dr. Mu Fenghao and others put forward a new Intelligent Transportation System which is entirely different from the systems using image processing or induction coil. It can receive information by wireless communication between electronic identification plate and base station which is used to monitor traffic, when vehicles are installed electronic identification plate. According the information, it can manage, query vehicles and find lost vehicles. The system works at 2.4GHz~2.5GHz. Though it does not need to apply dedicated channel, the system must has great ability in interference immunity, because there are too many other wireless signals.According this problem, firstly this paper delves into radio circumstance of the band, frequency selecting rule and spectral density estimation. Basing on this research, this paper puts forward a frequency selection scheme basing on estimating spectral density of channels in 2.4GHz~2.5GHz. Basing on spectral density of channels, the scheme makes use of self-adaptation frequency hopping, network monitor, and receiving signal strength indicator to assure the system communicating normally. Basing on characteristics of wireless signal of the system, this paper design and implement the frequency selection sheme major by MAX2822 which is used as radio frequency module and TMS320F2812 used as core processor.The major work of this paper is:(1) This paper researches deeply in many kinds of spectral density estimation algorithms, takes characteristics of algorithms into count and selects fit algorithms to the scheme according to characteristics of scheme.(2) This paper makes use of TMS320F2812 to implement sampling signal, filtering mirror-image interference, spectral density estimation, and communication between parts of the system. In course of sampling signal, the wireless signal of the system is sample by the Analog-to-Digital Converter in TMS320F2812 after lowered frequency by MAX2822. In course of filtering mirror-image interference, the method of quadrature demodulation which is used to filter mirror-image interference can prevent the system from hopping frequency in working order. In the course of spectral density estimation, this paper analyses the influence of fixed-point with spectral density estimation algorithms. According to the spectral densities estimatedby algorithms of spectral density estimation, the system can judge whether the system is working in abnormal circumstance, find the reason why the system can not wok in order and how to hand the exceptions. The major kinds of communication in the system include the communication between the frequency selection module and control center, the communication between TMS320F2812 and MAX2822, between TMS320F2812 and wireless communication module.(3) The method is processed simulation experiments. The results indicate the frequency selection schedule putted forward in this paper can assure the system communicating normally.