| With the rapid development of mobile communication technology,the related technical standards are also evolving.It has experienced the conversion from analog to digital modulation,and a dramatic increase in data rate.The 5G standard is being developed to pursue higher transmission rate and spectrum efficiency,so as to achieve the requirements of low delay,high reliability and low power consumption.Orthogonal Frequency Division Multiple Access(OFDMA)technology is widely applied in 4G,and can satisfy the requirements of broadband mobile communications in the short future.However,with the popularization and application of smart terminals and the growing demand for new mobile services,the demand for wireless transmission data rate increases exponentially,and it will still be difficult to meet the needs of future mobile communications.IMT-2020(5G)propulsion group proposed that 5G aims at higher spectrum efficiency,faster rate and larger capacity,and spectrum efficiency needs to be improved by 5?15 times compared with 4G.In order to maintain a good system throughput and low cost of receiver,Orthogonal Multiple Access(OMA)technology is adopted in 4G.In OMA,One single wireless resource can only be assigned to one user,such as frequency,time or space.Therefore,new multiple access technology were proposed to maintain the requirements of 5G,which was incorporated into the 3GPP research project,and termed as Multi-User Superposition Transmission(MUST)technology.By superimposing the power domain,code domain or constellation domain,data of multiple users can be transmitted in the same resource block,which improves the spectrum efficiency and the number of access users.However,the superposition of users' signals introduces interference,so the interference cancellation algorithm is needed at the receiver.In the MUST scenario,the receiver can acquire interference signal parameters in two ways,one is signaling,the other is signal detection.The advantage of the former way is that the receiver does not need to add detection algorithm,but it increases the cost of signaling;the latter one can reduce the signaling overhead,but it needs to sacrifice the complexity of the receiver.This thesis studies MUST in 3GPP's discussions,and designs interference detection algorithms.The detection of interference signal consists of two parts,one is the existence of interference,and the other is the modulation order of interference.For the first one,a detection algorithm is proposed based on the idea of threshold estimation.The detection rate(DR)of this algorithm increases with the Signal to Noise Ratio(SNR)increases,and can reach 100%with higher SNR,but low DR will not have a serious impact on the throughput performance of target UE.For the second one,there are a considerable amount of literature about this problem,including algorithms based on likelihood ratio,recognition and feature extraction,Constellation Clustering,and etc.This thesis puts forward three interference detection algorithms,which are based on minimum average Euclidean distance,minimum relative average Euclidean distance and maximum likelihood criterion separately.The detection results of the first algorithm are mostly high order modulation,while the second is mostly low order modulation,which means none of the first two algorithms can meet the detection requirements in all cases.The modulation detection algorithm based on maximum likelihood criterion can achieve 100%DR in QPSK(Quadrature Phase Shift Keying)modulation,while in other high order modulation,when the channel condition is good enough,the detection rate can reach 100%.To detect the interference signal in MUST,it is necessary to add detection algorithm at the receiver.And after the interference is detected,the nonlinear receiver algorithm is needed to cancel the interference.The interference detection and cancellation algorithms need a lot of calculation,so it is necessary to discuss whether valuable to sacrifice the complexity of the receiver to save signaling overhead. |
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