Research On OTFS Signal Detection Algorithm In LEO Satellite Communication

The Low Earth Orbit(LEO)satellite communication system is listed as one of the important components in the development of 6G to promote the integration of the space-air-sea integrated network due to its advantages such as low power consumption,wide coverage,strong single-satellite replaceability,and not affected by extreme conditions on the ground,which has very broad application prospects.However,LEO satellite communication systems also have problems such as high moving speed of LEO satellites relative to the ground,large Doppler frequency shift,and complex channel characteristics.Orthogonal Frequency Division Multiplexing(OFDM)is widely used in ground communication systems,but it has poor bit error performance under the condition of high Doppler frequency shift channel,so it is not suitable for LEO satellite communication system.Orthogonal Time Frequency Space(OTFS)modulation is a new modulation technology proposed in recent years.Unlike OFDM,which processes signals in the time-frequency domain,OTFS introduces the concept of delay-Doppler domain.The time-frequency dual-selection channel in the high-dynamic scenario is transformed into a time-independent channel that is sparse and slow-varying in the delayDoppler domain,and all symbols experience approximately the same complex channel gain,so it has stronger robustness in high-dynamic scenarios.The OTFS signal detection algorithm is one of the key technologies that affect the bit error performance.How to achieve the trade-off between complexity and bit error rate in the LEO satellite mobile communication system with tight computing resources and high reliability requirements is a current hot issue.Therefore,this paper studies the low-complexity,high-performance OTFS signal detection algorithm under LEO satellite communication.The main contents of the paper are as follows:First,the characteristics of LEO satellite mobile communication and common satellite communication channel models are studied,and the applicability of the channel model is analyzed according to the characteristics of LEO satellite mobile communication.The basic principles of OTFS technology and common signal detection algorithms are also studied.Compare and analyze the advantages,disadvantages and bit error performance of different detection algorithms in LEO satellite communication.Then,in view of the problem that the OTFS signal detection algorithm under LEO satellite communication is difficult to achieve a trade-off between complexity and bit error rate,this paper proposed an improved Gaussian Approximate Message Passing(GA-MP)detection algorithms,by replacing the external information with the marginal posterior probability in the GA-MP algorithm to reduce the calculation amount.At the same time,the probability threshold is introduced to set the iteration stop criterion to effectively reduce the calculation complexity.The simulation results show that the improved GA-MP algorithm has better bit error performance and has certain advantages in complexity under LEO satellite channel conditions,realized a trade-off between complexity and bit error rate.Finally,in order to further improve the bit error performance,a joint detection decoding iterative detector is studied in this paper.Consider a single-input single-output OTFS system encoded with low density parity check code(LDPC),and introduce the turbo detection algorithm framework based on maximum ratio combination(MRC)into the turbo detection algorithm proposed in this paper.The complex log-likelihood ratio calculation is transformed into a mapping between symbol tables.The simulation results show that the performance of Turbo detection based on the improved GA-MP algorithm is better than the other two common algorithms in different modulation schemes.