Research On Detection Algorithm Of Grant-Free Multi-User Transmission System

With the continuous development of mobile communications,the ever-increasing demand for wireless networks has put forward higher requirements for communication technology.Massive connectivity,high reliability,and low latency have become the key words for a new generation of communications.To realize massive machine-type communication(mMTC),it is required to transmit information on timefrequency resources in a non-orthogonal multiple access(NOMA)for multiple users.In order to adapt to the transmission characteristics of sporadic communication of short data packets in mMTC,the grant-free NOMA transmission technology has gradually become a more concerned field.In this thesis,a blind detection receiver scheme is investigated and designed for grant-free NOMA scenario,which can achieve reliable and effective multi-user detection while achieving system overload.First of all,a grant-free multi-user transmission system model is build,so that users can randomly send information at any time,and a fully blind multi-user detection scheme is designed at the receiving end.The effective distinction of user information is realized through two modules of activity detection and data detection.In this thesis,the block error rate is used as the performance indicator,and the sequence selection in activity detection and the channel equalization in data detection are optimized to improve the detection performance.Secondly,aiming at the phase ambiguity caused by the use of geometric features in data detection,differential modulation is introduced into the grant-free transmission system,and the channel equalization method is improved.The amount of data that each module of the receiver needs to process is reduced by about 50%.In addition,a receiver improvement scheme combined with soft information iteration is proposed.In the process of interference cancellation,the soft information output by the decoder is utilized to realize the message passing between the decoder and the detector,improving the bit error performance of the receiver.The simulation results show that the blind detection receiver designed in this thesis can realize the effective distinction and recovery of multi-user signals;the introduction of differential modulation greatly reduces the receiver complexity on the premise of ensuring the bit error performance.