Research On Collision Detection And Resolution Methods For LTE-based M2M Random Access

As one of the key technologies of the Internet of Things(Io T),machine-to-machine(M2M)systems are deemed to create a revolution in our future world.However,the existing LTE communication system is mainly designed and optimized for human-to-human(H2H)communications,and obviously cannot meet the requirements for large-scale M2 M communications.When massive M2 M devices request access to the network,it will inevitably lead to a large number of collisions of preamble sequences and network congestion,which will seriously affect the communication performance of M2 M devices.Therefore,the research of this paper concentrate on LTE-based M2 M random access collision detection and resolution methods:(1)This paper studies the problem of collision detection for large-scale M2 M random access.Firstly,the generation and detection methods of LTE preamble sequences are introduced,as well as the existing early preamble collision detection(e-PACD)method for detection of preamble collisions,and the disadvantages of existing algorithms are analyzed.Secondly,to overcome the shortcomings of the e-PACD method that uses a large number of root sequences,and taking the low/no mobility characteristics of M2 M users into account,an improved e-PACD method is proposed.The method uses position information to compensate the arrival time uncertainty of each user in advance,and adopts several cyclic shift sequences of different root sequences to determine preamble collisions,which effectively reduces the number of non-orthogonal root sequences required for multiple access.Simulation results show that,compared with the existing methods,the improved method significantly reduces the multiple access interference caused by the non-orthogonality of different root sequences,and achieves better detection performance of preamble detection and collision detection at the same signal-to-noise ratio,and also reduces the error probability of conflict detection.(2)Based on distributed queuing(DQ)random access protocol,this paper further studies the M2 M random access conflict resolution method.Firstly,this paper introduces the traditional DQ protocol and its application in the LTE random access process,and points out the disadvantages of the existing DQ LTE method.Secondly,aiming at the shortcomings of the existing methods with low access efficiency,a dynamic DQ random access conflict resolution method is proposed.The proposed method dynamically merges several subgroups of the queue head according to the utilization of the preambles,and consequently improves the access efficiency.Simulation results demonstrate that,in comparison with standard LTE and existing DQ LTE methods,the proposed method is able to efficiently resolve collisions and avoid network congestion.Under the premise of ensuring successful access for all users,the dynamic DQ solution can obviously reduce the average access delay,and the improvement is more significant with the increment of the number of concurrent users and the available preambles.