| Light detection and ranging（Lidar）communication integration technology can share resources such as spectrum,hardware platform and signal processing algorithm between Lidar and communication system to improve the spectrum efficiency,hardware resource utilization and signal processing efficiency of the system,so as to obtain integrated gain.In addition,the technology can further improve the performance of each other through the mutual cooperation of the dual functions of Lidar sensing and communication,so as to obtain the cooperative gain.Thanks to these two advantages,Lidar communication integration technology has been widely used in emerging fields such as intelligent transportation,intelligent industry,and the Internet of things.The key of Lidar communication integration technology is to design an integrated waveform suitable for simultaneous target detection and information transmission.At present,the concept of integrated waveform design is mainly based on the existing communication waveforms optimization,such as single carrier spread spectrum,orthogonal frequency division multiplexing（OFDM）,etc.Among them,the integrated waveform based on single carrier spread spectrum has the advantages of strong anti-interference ability and low interception rate,but there are problems such as low transmission rate.The integrated waveform based on OFDM has the advantages of high spectral efficiency and flexibility,but it faces the problems of high peak to average power ratio（PAPR）and poor communication error performance.These problems will directly affect the overall performance of the Lidar communication integrated system.In order to solve these problems,the specific research content of this paper is as follows:（1）To solve the integrated waveform based on single carrier spread spectrum have problem of the transmission rate is low.This paper combines phase modulation and spread spectrum technology to propose an integrated waveform design scheme based on quadrature phase shift keying（QPSK）-direct sequence spread spectrum（DSSS）.In this scheme,the digital baseband signal in the communication signal is spread spectrum to make it have good autocorrelation,to meet the needs of Lidar detection.At the same time,QPSK technology is used to achieve a higher transmission rate.Then,the average symbol error rate and average distance ambiguity function of the integrated QPSK-DSSS waveform are derived to verify the feasibility of the scheme.Finally,the effects of relevant parameters on the system communication performance and Lidar performance are analyzed by Monte-Carlo simulation.The results show when the spread factor is 511,the average signal-to-noise ratio threshold is 3.8×10-3,and the structure constant of atmospheric refractive index is 1.13×10-12m-2/3,the signal-to-noise ratio of the integrated system after spread spectrum is improved by about 8d B compared with that before spread spectrum.At the same time,when the distance measurement of 60 meters was performed,the Lidar ranging results were consistent with the set value.（2）To solve the integrated waveform based on OFDM has problems such as high PAPR and poor communication symbol error rate performance.In this paper,the scheme of integrated waveform design of coherent optical orthogonal frequency division multiplexing with index modulation（CO-OFDM-IM）is proposed,by combining coherent detection,OFDM and index modulation（IM）.This scheme reduces PAPR by activating a portion of the subcarriers in CO-OFDM and silencing the remaining subcarriers.At the same time,compressed sensing is combined with modulation symbol algorithm to improve Lidar performance for the side flap effect brought by the silent subcarrier in CO-OFDM-IM when performing Fourier transform.Finally,the communication performance and Lidar performance of the integrated waveform with CO-OFDM are compared by Monte-Carlo simulation.The results show when the threshold of average signal-to-noise ratio is 3.8×10-3 and the structure constant of atmospheric refractive index is 1×10-18m-2/3,the integrated waveform of CO-OFDM-IM in the 2-choice activation mode improves the signal-to-noise ratio by 2 d B and reduces the PAPR by 0.1 d B relative to the CO-OFDM waveform.At the same time,radar performance similar to that of CO-OFDM waveforms is maintained. |
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