Signal Detection And Performance Analysis Of Non-orthogonal Multiple Access Transmission Systems

In order to meet the requirements of transmission rate,delay and connection density in future Internet of Things(Io T)and wireless mobile communication systems,power domain or code domain non-orthogonal multiple access(No MA)and grant-free uplink No MA are considered candidates transmission schemes.In this paper,the reliable transmission performance of PD-No MA,sparse code multiple access(SCMA)and uplink grant-free No MA schemes are studied,respectively.For SCMA system,the design scheme of high dimensional sparse codebook is proposed,and the performance bound of SCMA system based on message passing algorithm(MPA)is analyzed.For PD-No MA system,we focus on the scheme based on power domain superposition coding and successive interference cancellation(SIC)reception.The influence of PD-No MA on channel state information(CSI)in the actual system is analyzed,and a solution to ensure PD-No MA's reliable transmission is given.For uplink grant-free No MA,we design multi-user joint detection.An algorithm of active user detection and channel estimation with low complexity and good performance is proposed,and the results obtained can be used to guide the transmission design and optimization of No MA system.Firstly,a simple design scheme of high dimensional sparse code is proposed for SCMA system,and the performance bounds based on MPA detection is analyzed.The reliable transmission performance of PD-No MA under chase combining hybrid automatic re-transmission(HARQ-CC)is analyzed in the case of only known the statistics of CSI.The closed expressions of individual probability and diversity gain for each user are derived.Based on the obtained expression of interrupt probability,the effects of power allocation,target rate selection,the minimum number of retransmissions and transmission times on the performance of the system are studied.The simulation results are presented to verify the correctness of the results of the analysis.In addition,the obtained results show that 1)the outage performance and diversity gain of the PD-No MA user can be reduced when only the statistic CSI is known.2)the HARQCC can improve the performance of the PD-No MA for the case with statistical CSI.3)With a given target rate,the power allocation and the number of retransmission have a trade-off relationship,especially for the users with good statistical channel,it needs to sacrifice the delay to relax the power requirements,so as to make up for the performance loss caused by another user with poor channel.Secondly,we investigate the outage performance and optimize the power allocation scheme of PD-No MA systems over time-correlated Rayleigh fading channels.In particular,according to the quality of service(Qo S)requirements of users,e.g.,a latency-critical user with a low target rate and a delay-tolerant user with a large target rate,two partial hybrid automatic repeat request(HARQ)transmission schemes,including partial HARQ with chase combining(HARQ-CC)and HARQ with incremental redundancy(HARQ-IR),are proposed.The closedform expressions of outage probabilities for PD-No MA with and without re-transmission are derived.With the developed outage probabilities,a condition on the superiority of PD-No MA to orthogonal multiple access(OMA)is obtained.In particular,the condition is characterized by the transmit powers for PD-No MA without re-transmission and is obtained by using the bisection method in the case with re-transmission.To further improve the performance of the HARQ enabled PD-No MA schemes,we consider an average transmit power minimization problem by optimizing the transmit power among different transmission rounds with outage constraints.However,due to the complexity of the developed outage probabilities,the formulated problem is non-convex and challenging to solve.Then we approximate the original problem by deriving the upper-bound approximations of the outage probabilities and solve it by using the geometric programming method.Simulation results demonstrate the accuracy of the developed analytical results.It is shown that the performance of PD-No MA is superior to OMA,only when the obtained condition is satisfied.HARQ-CC and HARQ-IR can enhance the outage performance of PD-No MA over time-correlated fading channels and the HARQ-IR has excellent performance in terms of energy efficiency.Thirdly,two short-packet transmission schemes are proposed to uplink and downlink nonorthogonal multiple access(NOMA)in large scale internet of things.The bit error rate(BER)and the block error rate(BLER)are investigated as well.In particular,a low-complexity algorithm based on generalized expectation consistent signal recovery(GEC-SR)is first proposed to detect the active devices and estimate their channel state information(CSI)for uplink grant-free NOMA.The BER of uplink non-orthogonal transmission data with the imperfect estimated CSI is then obtained by linear Minimum Mean Square Error(LMMSE)detector.The obtained results show the impact of the error propagation caused by the device detection on uplink data transmission.Meanwhile,we derive the closed-form expressions of BLERs of dwonlink data with finite block-length coding under imperfect CSI for each pair of active devices.In addition,a messages bits selection strategy in each pair of devices is proposed to guarantee the NOMA performance comparing with orthogonal multiple access(OMA).Both simulation and analytical results are provided to demonstrate the performance of the active device detection,the channel estimation and the data detection error.More importantly,the obtained results show that the BLER performance of downlink NOMA is superior to that of OMA,when the messages bits of one pair of devices are selected according to the proposed strategy.Finally,for large-scale No MA signal detection based on reliable information passing,the active user detection and channel estimation problem is characterized as an iteratively weighted LASSO problem.In single-carrier No MA system,the information of each iteration is solved by ADMM algorithm,and by making full use of the fast fading characteristics of the non-zero elements of the sparse signal and the known partial prior information of user activity at the base station,the active user detection and channel estimation algorithms with higher accuracy are obtained.For multi-user data detection,a low complexity detection algorithm based on alternating minimization is proposed according to the characteristics of received signal structure.The simulation results show that: 1)for short pilot sequence,the proposed algorithm has better performance in terms of false alarm rate and missing alarm rate;2)the AUD performance is improved at the cost of negligible computational complexity;3)for multi-user data detection,the alternative minimization method can avoid the matrix inverse computation and reduce the computational complexity.In addition,in multi-carrier No MA system,AUD and CE can be characterized as a signal recovery problem with block-sparse structure.Then the proposed algorithm is further extended and improved by using the block-sparse structure of the signal,and even achieves perfect AUD performance.