- 170 Dbm Key Techniques Of The Two-dimensional Spread Spectrum Signal Detection

Two Dimensional Spread Spectrum (2DSS) is a new spread spectrum communicationtechnology which has been proposed in recent years. It is the promotion of thetraditional methods because of spreading spectrum both in time domain and frequencydomain. By using two sets of spreading codes,2DSS has a stronger capability formultiple accesses, a larger processing gain, and a better anti-fading performance, whichtakes full advantage of the one-dimensional spread spectrum only in time domain orfrequency domain.The existing methods of2DSS signal detection are mainly concentrated on the pilotsymbol assisted with coherent demodulation and the chip-level differential detectionwith no-coherent demodulation. On one hand, pilot matrix and data matrix arecode-divided, between which the orthogonality cannot be maintain in fading channel.On the other hand, traditional coherent detection method assumes that thetwo-dimensional area should smaller than the correlative area in fading channel, whichoften does not hold in time-selective and frequency-selective environment.Thus, a two-dimensional pilot symbol assisted method is proposed by distributingpilot chips and data chips both in time domain and frequency domain, which avoids theinterference between the pilot symbol and data symbol. By analysis and simulation, it isshown that if the two-dimensional area is smaller than the correlative area in richscattering multipath fading channel, the difference between the theoretical andsimulation curve of processing gain and bit error rate (BER) is less than0.5dB, with theBPSK modulation and the signal noise ratio (SNR)0~30dB.Secondly, we propose a joint algorithm of coherent detection and non-coherentdetection based on dividing correlative area, which gets rid of the limit of the correlativearea. In this method, coherent detection is achieved through channel compensation in acorrelative area, while no-coherent detection is achieved through accumulation of allareas. By analysis and simulation, it is shown that in rich scattering8-path fadingchannel, the difference between the theoretical and simulation curve of processing gainand BER is less than3dB, while joint detection has10dB improvement for processinggain and8dB improvement for BER better than coherent detection, with the BPSKmodulation, the SNR0~30dB, the maximum Doppler shift10kHz.Finally, a FPGA software outline design, detailed design and coding implementationare proposed for the engineering requirements, which base on the topic of-170dBmtwo-dimensional spread spectrum signal detection and verification. By test and analysis,it is shown that the results have met required specifications, including intermediatefrequency70MHz, bandwidth19.52MHz, receiver sensitivity-170.45dBm, and SNR-77.5dB.The research in this thesis design and implement a signal detection method in very low spectral density supported by optimizing2DSS. On one hand, the experimentaltransceiver can be used for weak signal identification, Low Probability of Interception(LPI), etc. On the other hand, the key technologies such as joint algorithm of coherentdetection and non-coherent detection can be used for time-selective andfrequency-selective communication scenes.