Research On DD Domain Grid Resource Allocation And Spectrum Efficiency For Uplink Of OTFS System

In order to solve the problems caused by inter-carrier interference and inter-symbol interference to communication systems in high mobility scenarios,a novel modulation scheme called orthogonal time frequency space(OTFS)is proposed by Hadani et al.Compared with orthogonal frequency division multiplexing(OFDM)carried in time frequency domain,OTFS carried in delay Doppler(DD)domain has the advantages of resisting time dispersion and frequency dispersion,and OTFS is more suitable for transmitting signals in high mobility scenarios.On the DD plane,the delay domain and Doppler domain are divided into several parts,then the DD plane will be divided into several grids,each of which is a resource block that can transmit information.The uplink transmitted signal in the OTFS system is composed of these resource blocks.After the transmitted signal undergoes a series of transformations such as two-dimensional twisted convolution,the uplink received signal will have a certain displacement in the delay domain and Doppler domain in the DD domain.Therefore,it is necessary to set an appropriate size of the guard interval to prevent interference between signals.However,this traditional resource allocation method faces a problem,that is,the maximum guard interval will cause a great waste of resources.Considering that the user’s delay and Doppler shift can be obtained by integrated sensing and communication(ISAC)technology,the guard interval can be designed according to the actual delay and Doppler shift,instead of using the maximum guard interval to avoid inter-user interference.Therefore,this thesis discusses the DD domain grid resource allocation method and spectral efficiency of the uplink in the OTFS system,and the main contributions are as follows:(1)In this thesis,a dynamic grid resource allocation method for uplink in the OTFS system is proposed.By rationally arranging the resource allocation of pilots,guard intervals and data symbols,the error performance is close to the traditional method achieved.However,the dynamic grid resource allocation method can send more data and improve resource utilization.In the dynamic resource allocation method,user matching needs to be performed for the consideration of saving resources.When the users need to access quickly,this method is not so applicable.Therefore,this thesis proposes a new resource allocation method based on the dynamic resource allocation method,which will sacrifice part of the grid resources,but improve the access speed.(2)From the current research status,there is also a multiple access-orthogonal time frequency space(MA-OTFS)system in the existing OTFS system uplink,in which the guard interval is not required,but the computational complexity is very high,so some people later proposed MA-OTFS with a guard band mode to reduce the calculation.In this thesis,the dynamic grid resource allocation method and the MA-OTFS with guard band mode are combined,and the dynamic Doppler domain guard band mode and the dynamic delay domain guard band mode are proposed.The calculation formula of spectral efficiency is presented,and the spectral efficiency under different guard interval modes is simulated and analyzed.