Waveform Designs And Applications In Sensing And Communications Systems

With the development of radar sensing and wireless communication,it is recognized that there are many similarities and commonalities between them in terms of operating frequency bands,waveform types,signal processing,hardware architectures,etc.In order to improve spectral efficiency,reduce hardware costs and meet new business requirements,academia and industry have proposed integrated sensing and communication(ISAC)systems that share the transmitted signal waveform.Focusing on the poor Doppler resilience of the sensing waveform in the sensing systems,the high peak-to-average power ratio(PAPR)of the sounding reference signal(SRS)in communications,and the limited moving targets’ detection performance of the ISAC waveform,this thesis mainly studies waveform designs and their applications in sensing,communications,and ISAC systems.Firstly,in fully polarimetric radar systems,the conventional complementary waveforms are sensitive to Doppler shift,which causes the complementary waveform to lose its perfect pulse compression characteristic.Thus,a novel class of sequence pairs,called “quasi-orthogonal Z-complementary pairs(QOZCPs)” are proposed.The properties of a QOZCP are that its aperiodic auto-correlation sum has the Z-complementary property,and its aperiodic cross-correlation has a low correlation zone.Accordingly,the successively distributed algorithm under majoriza-tion minimization(SDAMM)is proposed to construct the QOZCPs.Doppler resilient QOZCP waveforms applied for fully polarimetric radar systems can be constructed by using PTM se-quences and Alamouti space-time codes.Numerical results verify the effectiveness of the pro-posed algorithm and that the QOZCP waveforms have better Doppler resilience than the con-ventional Golay complementary waveforms.Secondly,to further improve the Doppler resilience of complementary waveforms in sens-ing systems,a new singular value decomposition(SVD)-based Doppler resilient complementary waveform(DRCW)construction is proposed.The character of this waveform is that it can sup-press range sidelobes in the Doppler interval of interest by jointly considering the transmitted pulse train(made up of complementary pairs)and the weights of the receiver filter.Also,for the proposed SVD-based DRCW,a theoretical bound of the range sidelobes of the ambiguity function is derived within the Doppler interval of interest.Moreover,to improve the system’s signal-to-noise ratio(SNR),a challenging non-convex optimization problem is formulated to maximize the SNR with the constraint of low range sidelobes.Basis selection(BS)method and modified coordinate descent(MCD)method are proposed to construct BS-SVD DRCW and MCD-SVD DRCW,respectively.It is shown that,compared with the existing DRCWs,the proposed SVD-based DRCW has better Doppler resilience.Furthermore,compared with the original SVD-based DRCWs,the BS-SVD DRCW and MCD-SVD DRCW have higher SNR while maintaining the same Doppler resilience.Thirdly,in 5G NR,as the conventional SRSs based on Zadoff-Chu(ZC)sequences have a high peak-to-average-power ratio(PAPR),the low-PAPR SRS is designed in this thesis.A multi-variables optimization problem is formulated,in which the frequency SRS sequence is unimodular,and its time-domain PAPR is controlled by a threshold.Then,the alternating di-rection method of multipliers(ADMM)-based method is introduced to tackle the formulated problem by breaking the two variables into two subproblems that can be solved separately in closed forms.A large number of SRSs with low PAPR can be efficiently obtained by using the proposed method.Furthermore,for each length,from the obtained SRSs,60 SRSs with low cross-correlation can be selected when interferences among multiple SRSs are considered.Numerical results verify the effectiveness of the proposed SRS.In addition,based on the com-munication frame structure of IEEE 802.11ad/802.11 ay,this thesis also designs a min-point SC-OFDM GCC preamble waveform in the channel estimation field(CEF).Compared with the traditional preamble waveform of IEEE 802.11 ad,the designed waveform has better perfor-mance in terms of ranging and speed measurement.Finally,since the Doppler resilience is limited in the existing joint design of ISAC wave-forms,a new Doppler resilient ISAC waveform design is proposed based on joint design.First,with the pulse train ambiguity function,a construction of the Doppler-resilient pulse train is deduced,which is equivalent to designing a waveform with a very low integral sidelobe level(ISL)in a correlation zone.Accordingly,to achieve the construction of a Doppler resilient ISAC pulse train,an optimization problem is proposed,which takes minimizing the weighted integral sidelobe level(WISL)of the ISAC waveform as the objective function,and takes the energy of the transmitted waveform,the PAPR,and the phase difference between the transmit-ted ISAC waveform and the communication data modulated waveform as constraints.Since the optimization problem is nonconvex,an iterative optimization algorithm based on the MM framework is proposed to solve it.Simulation results show that,compared with the existing ISAC waveform design method,the ISAC waveform proposed in this thesis has higher Doppler resilience and lower symbol error rate,and the detection performance of the ISAC system for moving targets is significantly improved without loss of the communication quality.