Research On M2M Random Access Technology In LTE-A Networks

Machine-to-Machine(M2M)communication refers to the autonomous transfer of data be-tween machines through a communication network without human intervention.As the main connection method of the fifth-generation(5G)mobile communication to realize the internet of everything,it is gradually applied to the internet of things industries such as s-mart transportation,smart home,electronic medical and remote monitoring,which makes the connection demand of machine type communication(MTC)device increase dramati-cally.When the massive MTC devices are simultaneously connected to the existing mobile communication network designed for human-to-human(H2H)communication,the radio ac-cess network(RAN)overload happens,which will reduce the successful accesses,increase the access delay and energy consumption,and even lead to suspension of M2M communica-tions service.Therefore,in the existing LTE-A network architecture,it is extremely urgent to study a random access scheme suitable for M2M communication.For the access congestion problem of M2M communication,this dissertation utilizes lin-ear and nonlinear optimization theory,stochastic theory,probability theory and statistics to design effective random access schemes suitable for M2M communication.The main contributions of this dissertation are presented as follows.1.In order to reduce the access collision probability of joint access class barring and tim-ing advance(ACB-T_A)scheme for M2M communication,a preamble placement method is designed,and based on this,an alleviating-collision based timing-advance(ACT_AS)orthog-onal random access scheme is proposed.For each preamble,the base station can select the T_Ainformation with the minimum collision probability by utilizing the designed preamble placement method and the orthogonality of the preamble.Using the selected T_Ainformation for random access can reduce the collision probability of the random access process.Fur-thermore,combined with the spatial distribution of MTC devices,this dissertation further proposes an joint enhance ACB and ACT_AS(EACB-ACT_AS)random access scheme.This solution introduces EACB parameters so that MTC devices in different locations have the same probability of successful access.Simulation results show that,compared to ACB-T_A,the two mentioned schemes have higher successful access throughput.2.To improve the time-frequency resource utilization of orthogonal random access schemes,this dissertation proposes a joint orthogonal random access and non-orthogonal random ac-cess scheme based on control surface data transmission.This scheme allows a MTC device to attach its own ID information when sending the preamble,which can help the base sta-tion determine whether the MTC device can successfully transmit preamble.Combining the principle of hybrid random access and data transmission(HRA-DT),the MTC devices that successfully transmit the preamble transmit their data messages in a non-orthogonal man-ner.Meanwhile,the MTC devices that fail to transmit the preamble are permitted to compete for the unscheduled resources with orthogonal manner,thus realizing the reuse of idle time frequency resources.Simulation results show that the proposed scheme can significantly improve the probability of successful access and system resource utilization.3.For the problem that the transmission power of MTC devices in the power domain non-orthogonal random access scheme violates the random selection,a T_Ainformation aided power domain non-orthogonal random access scheme is designed.This scheme presents multiple available power levels.The MTC device that has passed the ACB detection and successfully matched the T_Ainformation randomly selects an available power level as the target received power for data transmission.At the receiver,the base station uses the succes-sive interference cancellation(SIC)technology to recover the superimposed data signal.In order to analyze the performance of this scheme,the theoretical lower bound expression of access throughput is derived,and a regional power selection strategy is designed to reduce the average transmission power of MTC devices.Numerical results show that the proposed scheme can obtain higher access throughput,and the average power consumption can be significantly reduced by using the regional power selection strategy.4.Considering the massive MTC(m MTC)scenario with multiple delay constraints coexist,an adaptive non-orthogonal random access scheme oriented to multiple delay constraints is proposed.This scheme can adaptively adjust the ACB parameter according to the service load and the delay requirements of different delay-constrained device groups.The MTC devices that pass ACB detection can share the same resource in a power domain multiplexing manner.In order to satisfy the delay constraint requirements of delay-sensitive devices,an ACB parameter matrix calculation algorithm for different device groups in each access slot is presented.In order to make the access of delay-tolerance device more efficient,combined with ACB parameter matrix,an analytical expression of maximal throughput about delay-tolerance devices is given.Numerical results show that the proposed scheme can ensure the delay-tolerance devices can complete random access within the restricted,and the delay-tolerant devices can obtain the maximal throughput in each slot.