| With the continuous development of digital communication technology Direct sequence spread spectrum technology for anti-jamming and anti-multipath capability, confidentiality, and easy networking and other characteristics have been widely used.Particularly.In wartime,using spreadspectrum communication is an effective way to improve the security and survivabilitySpread spectrum communication is to be sent information and data is spread spectrum PN code to achieve spread spectrum, and then transmitted by the mod ulation process. The receiver is used to extract the extended phase encoding and judgments and other related treatment,to restore the original information data.Spr ead-spectrum communications with the anti-jamming,anti-noise,anti-multipathfading, confidentiality, high-power spectral density is low, cover and strong, low intercept ion rate and multi-site re-use, any location, etc., but these advantages for the mil itary communications is important, so its application to actual combat is particula rly pressing.At frist,on the frist chapter,we discussd the theory.on the one chapter ex patiated on the Spread spectrum communication Spread spectrum modulation and demodulation techniques.the third chapter describe how to design the SAW devi ces.based on .we begin to design the spread-spectrum transmitter and despread demodulation part, the key of spread spectrum communication techniques spread-spectrum modulation and demodulation techniques in the spread-spectrum commu nication system plays an important role. This paper describes a spread-spectrum modulation and demodulation techniques. based on the surface acoustic wave dev ices.SAW-based spread-spectrum devices spread-spectrum modulation and demodulation techniques, as opposed to digital technology, with high processing speed, large handle broadband and strong processing capabilities, especially in real-time processing has an absolute advantage, which are all at home and abroad their special attention and put a lot of manpower and resources development. SAW based on this technology has been widely used SS letter to machine ground, aircraft load, and spaceborne radar.This paper describes a spread-spectrum modulation and demodulation of spread-spectrum technology based on the surface acoustic wave devices, and the base of this developed a high sensitivity, large dynamic SAW despreading demodulation components. The component breaks through the traditional despread PSK demodulator will be designed to be applied to SAW devices despread demodulator, the main with the following features.1) To despread demodulation receiver structure greatly simplified. As the data rate spread-spectrum modulation process does not change, you can achieve the same piezoelectric substrate surface acoustic wave tapped delay line (be short for SAWTDL) SAW delay line (be short for SAWDL) the integration of design, SAW matched filter length as compared with the traditional design, reduced by half. This greatly simplifies the structure of spread-spectrum receiver.2) High sensitivity, large dynamic.3) As the "self-synchronization" feature of SAW matched filter in the design of circuits, ignore the synchronization circuit, simplifying the circuit, reducing the size of component.On this basis, this paper studied the idea of the spread-spectrum modulation to achieve the above in mind despread demodulation hardware, which includes PSK spread-spectrum transmitter and despread demodulation part of the PSK. PSK which launched in part by the spread-spectrum base-band spread spectrum signal generation part, the transmitter local oscillator signal source, as well as PSK signal modulation components.baseband spread spectrum signal generation in part by the PC machine and HP81110A pulse generator produces; transmitter local oscillator signal source is agilent signal source produces; PSK signal modulation in part by the BPSK modulator-based modulation circuit modules,it is complete function is generated by the PSK spread-spectrum transmitter of the base-band spread spectrum signal modulation letter code for a given frequency of the BPSK modulated signal; PSK despread demodulation function is performed by surface acoustic wave despread demodulation component to complete, the main principles of are: the PSK spread spectrum modulation signal into the low-noise put in place by the low-noise amplified, and then by limiting amplifier control range, the output of the BPSK signal more stable. By the SAW matched filter differential coherent matched filter correlation peak resulting from two-way, after a phase detector to extract the phase information, and then zoom through the op amp, the output video correlation peak, finally, by the decision, stretcher output TTL level of non-zero data signals.The project's main technical difficulties are:1) Input dynamic range, required dynamic range 70dB. After testing, the measured data is 80dB.2) High sensitivity, using logarithmic amplifier. The amplifier's small signal gain of 30dB, sensitivity of-65dBm, to meet the target requirements.3) SAW fixed tapped delay line was used to despreading data signals.By design, we use a fixed 127 SAW fixed tapped delay line with a fixed delay line, that is in the same piezoelectric substrate to achieve a SAWTDL and a SAWDL, the integration of design, not only to meet practical requirements, but also greatly simplify the despreading demodulation component structure.The SAW delay line matched filter integration of the design application in the system, greatly simplifies the size of the SAW despreading demodulation component have great significance to the design of SAW-related components. but also on the development of PSK spread spectrum communications systems have a major impact.Finally, on the last chapter,the paper gives the results of this program. Test results show that the program to achieve test requirements, Spread-spectrum radio can basically meet the vehicle performance and functional requirements and functional requirements, and the structure size and circuits such as superior to traditional programs, which confirmed the despread PSK spread-spectrum modulation and demodulation technology, the feasibility of ideas。... |
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