Design And Implementation Of Transmitter In Spread Spectrum Radio Succor System

The radio rescue system, as the timely and effective relief means in distress important means, has already obtained the world's attention. The major developed countries have developed and carried out their own radio rescue systems in the world. Though we have studied the subject of emergency radio indicating position, we don't carry out the whole product; we even rely on importing the similar products in China.The chief content of this paper that studied is the design and implementation of transmitter in radio rescue system. Spread spectrum technology is adopted for it has better performance in many aspects, such as frequency spectrum utilization, privacy and anti-jamming of communication. This scheme sets DSP as control core and adopts direct digital frequency synthesis (DDS) technology to design and implement the transmitter, which has a simple structure and good performance. This transmitter has many characteristics, including accurate output frequency high frequency stability, high frequency resolution, high frequency conversion speed and well spurious reduction. The main contents of this paper are as follows:First of all, we introduce the basic theory of the transmitter in the spread spectrum radio rescue system, which including the principle of GPS, the technology of spread spectrum communications, the pseudo noise code theory, the convolution code theory, the phase locked loop technology, the direct digital frequency synthesis technology, and other basic theories and technologies. They all lay the foundation for the coming design.Secondly, according to the technique target request of the system, we propose the whole design scheme of the transmitter. We plot the small functional module of the whole module, and then design the corresponding hardware and software of the transmitter, and show the idiographic realization methods of every small functional module. The hardware of the transmitter includes the control circuit of DSP, the interface circuit of GPS and DSP, the DDS and clock circuit, the filter circuit, and the power amplifier circuit. The implementation of every circuit in the hardware is given too. Accordingly, in software design, this paper introduces the overall process of software and implementation methods of each module. The software includes DSP and CPLD two parts:in the DSP section, we introduce the GPS output data format, the asynchronous communication module, the clock signal and the BPSK waveform signal software design and so on. In the CPLD section, we introduce the dividing-frequency module, pseudo-noise code generation, synthesis of data code module and the processing of glitches signals.Finally, according to the design principle of PCB, we designed and made the circuit board. The feasibility of this scheme is verified by testing the waveform of the transmitter.The testing results indicate that the design of the transmitter in the spread spectrum radio rescue system fully integrate the advantages of hardware and software and is capable of matching the design demand, and realizing the anticipating functions.