Chirp-Based Physical-layer Secure Communication Signal Design And Processing

Satellite communication has many advantages,such as high coverage,long transmission distance,and flexible networking.It has been widely used in the field of space tracking and control,mobile communications,and digital broadcasting and television.Since the satellite channel is an open medium,any receiver within the radiation range is able to receive the transmitting signals and even intercept the confidential information.As a result,the security of satellite communication is an important issue.Physical-layer security,which achieves secure transmission in the physical-layer by the means of waveform design,encoding,and modulation,can satisfy the requirements of both communication security and reliability.However,due to the restriction of signal dimension,the traditional single frequency physicallayer secure communication signal often suffers high processing complexity and low power efficiency.To achieve a better balance between security and reliability,this dissertation uses Chirp signal to design physical-layer secure communication signal.The main contributions of this work can be summarized as follows:1.In the Ka-band telemetry,track,and command(TT&C)system,the received TT&C signal will suffer from more than 800 kHz of Doppler shift.Even with code phase-Doppler parallel search algorithm based on FFT,the mean acquisition time(MAT)will be more than several seconds.To solve this problem,a novel chirp noise waveform(CNW)based spread spectrum signal and its fast acquisition algorithm are proposed.We derive the close-form expression of the generalized ambiguity function of CNW,and exploit the ambiguity function to theoretically analyze the Doppler tolerance,time-frequency resolution,and physical layer security of the CNW.By exploiting the Doppler tolerance of CNW,a fast acquisition method based on dual match filters is proposed.Due to the delay-Doppler coupling feature,the receiver can achieve both code synchronization and Doppler shift estimation through only 1-Dimensional delay search,and then MAT can be reduced significantly.2.Ka-band multibeam satellite communication system may suffer large Dopper shift,multi-access interference(MAI)within each beam,and inter-beam interference(IBI).To achive multi-access communication in each beam,a novel CNW based multi-access communication signal is presented,which assigns to each user a unique signal consisting of two CNWs at baseband.Each user will occupy the same bandwidth and time duration,and the MAI can be eliminated by assigning different chirp-rates and pseudorandom phases for each user.Physical-layer secure beamforming is also studied.With perfect eavesdropping channel state information(CSI),an artificial noise aided optimal beamforming solution is proposed to minimize the total transmit power and the number of antenna feeds while satisfying individual intended users' secrecy rate constraints.When the eavesdropping CSI is unavailable,an artificial noise aided zero-forcing solution is provided.In this solution,the eavesdropping channel is modelled as a fading channel combining rain attenuation and ?-? shadow fading,the close-form expression of the secrecy outage probability is derived,and an optimized power allocation approach for each beam is proposed to maximize average secrecy outage capacity.3.To satisfy the requirement of high-rate transmission in satellite communication,we utilize the fractional Fourier transform(FrFT)to design a physical-layer secure communication system called coded orthogonal frequency division multiplexing based on multiorder FrFT(MFrFT-COFDM).When all the TOs are correct,the MFrFT-COFDM system can provide almost the same reliable performance as the traditional OFDM system.However,as long as any one TO is wrong,the final decoding bit error rate will be 0.5.In order to retrieve desired data,the eavesdropper has to test a huge number of TO combinations,which is usually an impractical task for the current computing power.Physical-layer secure transform order sharing approach is also discussed.Furthermore,a time-varying spreadspectrum orthogonal frequency division multiplexing subsystem is provided to realize confidential transform order transmission in multipath channel.Compared with typical physical-layer secure OFDM system,the MFrFT-COFDM system is more suited to satellite communication with strong light of sight path,and the transmitting power can be used more efficiently because the data symbol is not transmitted along with additional interference.