Research On OTFS Technology Based On Spread Hopping Spectrum

Low orbit satellites have the advantages of low launch cost,low transmission loss,and low latency,making them an important part of building future global communication networks.With the rapid development of mobile internet,the low orbit satellite Internet of Things has become a hot research topic,and the integration of satellites and mobile internet is the future development trend of mobile communication.Orthogonal Time Frequency Space(OTFS)modulation,as an emerging modulation technique,converts high-speed time-varying channels into quasi time invariant channels based on time delay Doppler domain,demonstrating strong advantages in high-speed mobile scenarios.Spread hopping is a classic mobile communication technology.This thesis combines OTFS with it and proposes a reference scheme for channel estimation and multiple access reception in multi user OTFS,as well as for frequency hopping communication scenarios to combat interference.In this thesis,a spread spectrum multiple access model based on Doppler domain is proposed,and corresponding channel estimation and signal detection schemes are designed.In order to achieve multi-user channel estimation,a pilot sequence including intervals is designed,including embedded pulse pilots and two-dimensional Gaussian block pilots based on compression sensing algorithms.Aiming at the problem of poor performance of embedded pilots at low signal-to-noise ratios,a method of using spread spectrum communication to improve the received signal-to-noise ratio is proposed to improve the accuracy of pilot sequence estimation results.For the design of multiple access and reception schemes,based on the analysis of the shortcomings of existing OTFS multiple access schemes,a Doppler domain based OTFS-CDMA multiple access scheme is proposed.This scheme uses cyclic orthogonal sequences as user address codes,which can achieve the separation of multiple user signals through despreading operations,and convert the target user signal into a reduced dimensional delay tap model.After that,linear schemes such as Zero Forcing(ZF)equalization and Minimum Mean Square Error(MMSE)equalization can be used for equalization detection.At the same time,diversity combining technology can be used to implement a Rake reception scheme based on OTFS-CDMA.Secondly,for the communication anti-interference issues of OTFS in high-speed mobile scenarios,usually including single/multi tone interference and partial band interference,this article analyzes their impact on OTFS reception.An anti interference communication scheme combining OTFS and frequency hopping communication technology is proposed.This scheme is a frequency hopping communication scheme based on Doppler domain,which converts the frequency domain hopping of traditional digital frequency hopping communication to Doppler domain for hopping,thereby realizing the expansion of Doppler domain to counter interference.