Enhanced Schemes For Tandem Spreading Mutiple Access

With the rapid development of the Internet of Things industry,academia and industry have proposed massive machine-type communication as one of the three core scenarios of the fifth-generation mobile communication technology.As a new type of non-orthogonal multiple access technology,tandem spreading multiple access is expected to be applied to massive machine-type communications because it takes into account the high connectivity and high reliability of multi-user access.However,the existing tandem spreading multiple access has limitations in its anti-multiple access interference ability and anti-asynchronous delay ability,which makes it difficult to introduce into practical application.This paper is based on the tandem spreading multiple access,in view of the limitations of its application in the current Internet of Things communication scenarios,taking into account the requirements of massive machine-type communication for user access and reliable transmission,and interference cancellation theory,pseudo-random sequence expansion based on the spreading theory,combining system improvement,algorithm design and simulation evaluation methods.Two enhanced schemes for tandem spreading multiple access for massive machine-type communication are proposed.They are the successive interference cancellation-based tandem spreading multiple access and Gold sequence-based asynchronous tandem spreading multiple access.This thesis is mainly composed of the following two researchs:1)In view of the limitations of the multi-slot tandem spreading multiple access scheme in user collision resolution,this paper deepens the successive interference cancellation of the coded-slot-ALOHA scheme and applies it to the physical layer,proposes successive interference cancellation-based tandem spreading multiple access enhanced scheme.This scheme uses successive interference cancellation algorithms in the user identification module of the tandem spreading multiple access receiver to combat multiple access interference to achieve more reliable user access.This paper then uses numerical simulation to verify the performance of the enhanced scheme.The simulation results indicate that the proposed enhanced scheme can improve user access reliability under the premise of appropriately increasing the complexity of the receiver.2)In view of the limitation of the anti-asynchronous delay ability of the asynchronous tandem spreading multiple access scheme,which is limited by the length of cyclic prefix,this paper proposes Gold sequence-based asynchronous tandem spreading multiple access enhanced scheme by designing a new type of spreading sequence based on the Gold pseudo-random sequence.This scheme uses Gold sequence for tandem spreading,user identification and channel estimation,so as to combat high asynchronous delay to achieve multi-user highly reliable communication.This paper then uses numerical simulation to verify the performance of the enhanced scheme.The simulation results indicate that the proposed asynchronous enhanced scheme can take into account the high connectivity and high reliability of user access in high asynchronous delay communication scenarios.