Overload control of massive random access for machine-type communications

Abstract

We show that random access retransmissions can lead to performance degradation.A Markov model is proposed to evaluate the performance of LTE random access.There is an optimal number of retransmissions for massive random access.Random access resources are separated into two subsets for MTC overload control.Conventional and proposed schemes can be used adaptively depending on traffic load. Traditional cellular systems may not be appropriate to support machine-type communications (MTC) due to a large number of devices and relatively small, infrequent data transmissions. The 3GPP has identified the MTC as an important area of the LTE system and has discussed several mechanisms that control random access (RA) overload caused by massive MTC devices. In this paper, we show that a retransmission mechanism of RA may lead to performance degradation in an overload situation, and propose two RA solutions that relieve the RA overload. Since the RA success probability is closely related with the number of simultaneous RA attempts, the first solution adjusts the maximum number of RA retransmissions to control the amount of RA attempts. The second solution separates the RA resources into two subsets that MTC devices can access according to the number of consecutive RA failures and distributes the RA traffic over the two subsets. The two proposed solutions are analyzed by a mathematical model assuming a simplified operation, and a more realistic environment is considered by protocol-level simulations. Since the performance of the proposed solutions depends on the system configurations and parameters, the base station may adaptively adjust them for an optimal operation.