Research On Pilot Random Access For Massive Access In Massive MIMO Systems

The massive multiple-input multiple-output(MIMO)technology can theoretically achieve extraordinary improvements in spectral efficiency,data rate,and energy efficiency by employing a large number of antennas at the base station(BS)and serving multiple user equipments(UEs)over the same time-frequency resource,which is regarded as a key technology for the fifth-generation(5G)communication system.The future 5G communication system will make great efforts to the Internet of Things(IoT)application,such as machineto-machine(M2M)communication or the communications centered on machines,making a huge number of UEs access the network.Due to the limit of channel delay spread and coherence time,the number of UEs accessing the network is much smaller than the number of available pilots.The traditional dedicated pilot allocation is not enough to support such massive access scenario.Alternatively,pilot random access(RPA)allows all of the active UEs to randomly select their pilots from the pilot pool to address the pilot shortage problem,such that more UEs can access the network.Under this pilot random access mechanism,the pilot collision becomes unavoidable,which degenerates the performance of massive MIMO system.So,research on the pilot random access scheme is critical to achieve the excellent performance for the massive MIMO system.For the massive access scenarios in massive MIMO system,this dissertation is to design effective pilot random access schemes by utilizing linear and nonlinear optimization theory and methods,stochastic analysis theory,probability theory,coding and detection theory,which provides theoretical support and technical guidance for the related standardization of5 G.The detailed contents are presented as follows.Firstly,in order to improve the pilot resource utilization of strongest user collision resolution(SUCR)scheme for M2 M communication,a SUCR combined idle pilot access(SUCR-IPA)scheme is proposed.SUCR,proposed in recent years,is a scheme with high probability of resolving pilot collision,which only considers pilots selected by UEs and ignores idle pilots not selected by any UEs.This proposed SUCR-IPA scheme allows the failed UEs judged by SUCR to contend for the idle pilots to improve the pilot resource utilization.To make full use of the idle pilots,the access class barring(ACB)mechanism is proposed to perform the congestion control for UEs selecting the idle pilots.Simulation results show that,compared to SUCR,the SUCR-IPA increases the number of successful UEs significantly and decreases the number of access attempts dramatically by utilizing the idle pilots.Secondly,to recover channel state information(CSI)of collision UEs of the SUCR scheme,this dissertation proposes a new pilot random access scheme,called as SUCR combined graph-based pilots access(SUCR-GBPA).By exploiting the characteristic that the channel responses between UEs and BS are invariant within the coherence time,a bipartite graph is established.Based on this bipartite graph,the successive interference cancellation(SIC)algorithm is designed to estimate the channel state information of each UE to improve the throughput.Simulation results demonstrate that,compared to SUCR,the proposed SUCRGBPA significantly increases throughput and provides accurate estimation on the channel information at the same time.Thirdly,an identity-aided pilot access(IDPA)scheme is proposed to address the massive access in massive multiple-input multiple-output with interleave-division multiple-access(MIMO-IDMA)system.To our best knowledge,there is no effective pilot random access scheme to support massive access in massive MIMO-IDMA system.The proposed scheme make each UE transmit its identify number(ID)to the BS,which makes its interleaver available at the BS.Then,the BS obtains the uplink message of the contenders selecting the same pilot by performing the multi-user detection(MUD),which is an effective pilot random access scheme for the massive MIMO-IDMA system.BS only needs to estimate the sum of contenders' channel state information instead of each UE's channel state information to reduce the computational complexity at the BS.Furthermore,to mitigate the pilot collision by performing the ACB mechanism,a method of estimating the number of active UEs is proposed.Numerical results show that the IDPA scheme achieves high throughput,and provide accurate estimation on the number of active UEs.Finally,for the high data processing delay in the Grant-Free pilot random access mechanism,this dissertation proposes an ensemble independent-component-analysis based pilot access scheme(EICA-PA).An EICA detection algorithm is designed to perform the joint activation and data detection without the CSI detection procedure by utilizing ICA classifier and ensemble classifier,to reduce the data processing delay.To solve the issue of ICA phase ambiguity,one symbol interpolation method is proposed.To identify the decoded UE,we propose to insert the ID information into the uplink message.Numerical results show that,the EICA-PA scheme significantly improves the throughput,provides low missed detection probability and frame error rate(FER).