Research On CS-Based Non-Orthogonal Multiple Access Technologies

The introduction of fifth generation(5G)and beyond mobile communi-cation brings new challenges for efficiently supporting the random access of massive users with ultra-reliable low latency requirements for machine type communication(MTC).To address these challenges,we propose a novel com-pressed sensing(CS)-based non-orthogonal multiple access(NOMA)scheme for uplink and downlink of MTC.We not only theoretically verifies the effec-tiveness of the proposed schemes,but also theoretically analyzes the design principles of the user signatures.At the same time,based on the proposed the-ories,we give the corresponding user signatures.In order to further reduce la-tency,a novel CS-based packet structure is proposed for the proposed scheme.In addition,we also analyze the performance of the proposed systems in both cases that the channel state information is perfect and imperfect.In details,we make the following specific contributions and achievements.Firstly,a novel compressed sensing(CS)-based non-orthogonal multiple access(NOMA)scheme,called CS-NOMA,is proposed for uplink of massive machine type communication(mMTC).The propose scheme can be applied in a CDMA or an OFDM system,and allows a joint detection of both the data and the user activity with low control signaling overhead and transmission la-tency.Then,by applying a novel CS-based multi-user detection(CS-MUD)in base station(BS),we can perform joint activity and data detection without the activity state information of users in the BS.In the CDMA-based CS-NOMA shceme,we introduce low coherence spreading(LCS)signatures to enable joint activity and data detection without requiring the activity information of users in advance.We present a sufficient condition for the construction of the LCS signatures to ensure that CS-MUD can be effectively deployed in base station.Furthermore,we study the CS-NOMA scheme with imperfect channel state in-formation(CSI)and present a bound for the performance of the CS-NOMA scheme.Simulation results show that the proposed scheme achieves a rela-tively high system overload(up to 4)when the active users are relatively sparse with an activity ratio of 1%,which implies that the CS-NOMA scheme can sig-nificantly improve the spectral efficiency,avoid the control signaling overhead,and reduce the transmission latency.Secondly,a novel grant-free CS-NOMA massive multiple input multiple output(MaMIMO)scheme,called CS-NOMA MaMIMO scheme,is proposed for the uplink of massive mission-critical machine type communication(mm-cMTC).MaMIMO techniques are adopted in NOMA to enhance the reliability and reduce latency in the proposed scheme.We present a sufficient condition for the construction of the CS signatures that ensure effective deployment of CS-MUD in BS without the activity state information of users,resulting in lower latency.In order to further reduce the latency,by taking the advantages of CS techniques to exploit two-dimensional(2D)sparsity,a novel CS-based packet(CSP)structure is proposed for the CS-NOMA MaMIMO scheme.In the CSP structure,the CS signatures are assigned to not only different users but also to different time slots of a packet,which achieves a user and time slot overload system.In addition,by considering the case of imperfect channel state infor-mation(CSI),we present an upper bound for the performance of the proposed scheme.Finally,simulation results show that the proposed scheme achieves a high system overload(up to 6)and low block error rate(BLER)(less than 10-6)when the activity ratio of the users is 1%.Furthermore,when the time slot overload is 3,the proposed scheme with CSP structure can shorten time slots by 2/3 times compared to conventional packet structure.At last,a novel CS-NOMA MaMIMO scheme is proposed for the down-link of mmcMTC.By taking the advantages of tensor CS techniques,a novel tensor CS-based packet(frame)structure,called TCS packet(frame),is pro-posed for the CS-NOMA MaMIMO scheme to further reduce the transmit time intervals(TTIs),resulting in smaller latency than that using conventional packet(frame)structure.In the TCS packet(frame)structure,the CS signatures are as-signed to not only different users but also to different time slots and different symbols of a time slot,then achieve a user,time slot,and symbol overload sys-tem.We present a sufficient condition for the construction of the CS signatures that ensures effective deployment of tensor CS-MUD in user receivers.Fur-thermore,we consider the case of imperfect channel state information(CSI)and present an upper bound for the performance of the proposed scheme.Fi-nally,simulation results show that the proposed scheme can achieve high user overload(up to 5)and time slot overload(up to 3)when the activity ratio of users is 1%.When the time slot overload is 3,the proposed scheme with TCS packet(frame)shortens time slots by at least 2/3 times compared to the typical grant-based NOMA schemes.In addition,the block error rate(BLER)of the proposed scheme with TCS packet(frame)is much lower than that with con-ventional packet(frame),even less than 10-9 by repeat transmission when the time slot overload is 3.