Study Of Carrier Recovery And Spread Spectrum Transceiver Adopting DSSS And HFSS Technologies

Due to the unique advantages about Anti-Jamming and Low Probability Detecting and Low Probability Intercept, spread spectrum technology, as one of the high technologies in modern military domain, has been applied in military communication system widely. Therefore, spread spectrum transceiver has been the key equipment in the military communication system. The spectrum of the signal code is spreaded by both Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) technologies in the transmitter section. The wide band spreaded spectrum signal is despreaded and demodulated with surface acoustic wave devices in real-time in the receiver section. The carrier recovery of the wide spread spectrum signal is implemented with improved squaring loop. Almost all main modules in the spread spectrum transceiver are studied in this paper. Meanwhile, research domain extends from device lever to system lever. Because of its military purpose, the technological parameters of this project are high. By tested jointly, the whole system works stably and reliably and fully meet the design requirement.The main original work and valuable results in this paper are as follows:1. Beginning from the most important SAW devices, a whole spread spectrum transceiver based on the SAW and PLL technologies are designed and accomplished. The theoretic design method and hard-ware implement means on all key point of the signal link are formulated clearly.2. In order to despreading and demodulating the wide band spreaded spectrum signal in real time, the longest PN code (255bit) mono-chip SAW matched filter with Gp=23.5dB, only lower 0.5dB than the theoretic value, center frequency offset≤±3kHz, was developed inland. The long delay time and wide band SAW stable delay line with delay time τ=25μs, IL≤－55dB, Δf－3dB≥21.7MHz, was made on the ST-SiO2 substrate.3. In the jointed frequency synthesizer module, 70MHz frequency synthesizing section with SSB phase noise≤-112dBc/Hz@1kHz, suppress to spur≥80dB and the hopping frequency synthesizing section with SSB phase noise≤-102dBc/Hz@1kHz, suppress to spur≥65dB are successfully integrated on one PCB by solving the serious EMI (increasing the spur suppressing from 56dB to 69dB) on the board so as to reduce the bulk and simplify the assembling flow. This kind of jointed frequency synthesizer structure and the method to suppress spur are reported firstly.4. In the carrier recovery module, the ordinary squaring loop was improved by increasing two frequency dividers, taking advantage of the particular effect of the frequency divider about suppressing spur. This improvement makes the rapid tracking (4kHz/s) and low SSB phase noise (≤-114dBc/Hz@1kHz) of recovered carrier in a large Doppler frequency shift range (±150kHz) fulfilled together. The spur which only has a ±39.4kHz frequency offset to the recovered carrier was suppressed more deeply, increasing from 56dB to 69dB. 5. The thesis about carrier recovery in the spreading spectrum receiver based on the matched filter technology is studied in detailed. Moreover, two meaningful conclusions are come to. At last, a structure of spreading spectrum receiver based on the conclusion mentioned above, is put forward, by which the receiver can work stably even the large Doppler frequency shift exits and the long PN code sensitive to Doppler frequency shift is adopted, as long as the rate of the information code is high enough.