Number Of Random Access Slots Research Articles

Hybrid ORA and NORA schemes for machine‐to‐machine communication in long‐term evolution networks

Massive machine-type communication (MTC) devices will be deployed in the fifth-generation wireless communication networks, which will inevitably result in access collision problems. To alleviate this issue, the authors propose a hybrid orthogonal random access (ORA) and non-orthogonal random access (NORA) scheme to improve the throughput. In the proposed scheme, an expanded physical random access channel is employed to transmit preambles and MTC devices identity information simultaneously, which can help the base station (BS) to determine whether the MTC device can successfully transmit preamble. Subsequently, the MTC devices whose transmitted preambles are detected successfully by BS are statistically grouped, and then the devices in the same group transmit their data messages in a non-orthogonal multiple access manner. Meanwhile, to further improve the access throughput, the MTC devices that did not pass access class barring check are permitted to compete for the remained unscheduled resources with orthogonal multiple access manner. They also analyse the access throughput of the proposed scheme. Simulation results show that to serve all MTC devices distributed in a cell, their proposed scheme outperforms the traditional multichannel ALOHA and two-stage random access scheme in terms of access throughput and required number of random access slots.

An Efficient Contention Resolution Scheme for Massive IoT Devices in Random Access to LTE-A Networks

Long-Term Evolution-Advanced (LTE-A) networks have been regarded as having great potential to support the Internet of Things (IoT). However, the high probability of preamble collisions when massive numbers of IoT devices try to access the network within a short period has become a significant problem. In this paper, we propose a new scheme to efficiently handle the initial access contention for massive numbers of IoT devices in LTE-A networks. The proposed scheme divides an entire preamble set into $k$ subgroups; then, contention resolution is performed in each subgroup independently in a parallel and pipelined manner. Simulation results show that our scheme leads to considerable improvement in terms of average access delay and standard deviation of access delays without increasing blocking probability. Moreover, utilization of preamble resources is greatly improved by reducing the number of random access slots, where only a few devices participate in preamble selection.

Optimal Access Class Barring for Stationary Machine Type Communication Devices With Timing Advance Information

The current wireless cellular networks can be used to provide machine-to-machine (M2M) communication services. However, the Long Term Evolution (LTE) networks, which are designed for human users, may not be able to handle a large number of bursty random access requests from machine-type communication (MTC) devices. In this paper, we propose a scheme that uses both access class barring (ACB) and timing advance information to prevent random access overload in M2M systems. We formulate an optimization problem to determine the optimal ACB parameter, which maximizes the expected number of MTC devices successfully served in each random access slot. Hence, the number of random access slots required to serve all MTC devices can be minimized. To reduce the computational complexity and improve the practicability of the proposed scheme, we propose a closed-form approximate solution to the optimization problem and present an algorithm to estimate the number of active MTC devices requiring access in each random access slot. The correctness of the analytical model and the accuracy of the estimation algorithm are validated via simulations. Results show that both numerical and approximate solutions provide the same performance. Our proposed scheme can reduce nearly half of the random access slots required to serve all MTC devices compared to the existing schemes, which use timing advance information only, ACB only, or cooperative ACB.

Optimizing the Use of Random Access Channels in GSM-GPRS

The random access channels and traffic channels are utilized, respectively, for call establishment and information transmission in the uplink direction (from mobile to base station) of the Global System for Mobile communications (GSM) networks. A call is either rejected or blocked depending on its inability to succeed either in the random access channels or in the traffic channels. The optimum number of random access slots is directly proportional to the average call arrival rate, being independent of the average channel holding time and the number of traffic channels. The number of slots occupied by a given call can be changed dynamically in the newly developed General Packet Radio Service (GPRS) systems. A complete analysis is executed for the traffic channel utilization and call blocking probability with the exact number of random access slots that provide almost zero call rejection probability. The overall call success probability is derived considering call rejection and call blocking probabilities.

Single channel occupied voice and multi-channel occupied HSCSD over GSM

Random access and traffic channel parts are utilized, respectively, for call establishment and information transmission in the uplink direction, comprising mobile to base station of the Global System for Mobile Communication (GSM) networks. Voice (V) and High Speed Circuit Switched Data (HSCSD) calls use two parallel random access parts and a common traffic channel part where a V call occupies a single traffic channel and a HSCSD call occupies a multiple number of traffic channels. A call is either rejected or blocked if it is unsuccessful either in the random access part or in the traffic channel part. The optimum number of random access slots is directly proportional to the average access arrival rate. According to the specification, four types of retransmission cut-off policies can be executed in the random access part wherein only one type can provide almost zero call rejection probability, pertaining to a limited amount of traffic arrival rate per random access slot. A complete analysis for the traffic channel utilization and call blocking probability for V and HSCSD calls with an exact number of random access slots in collaboration with four different types of retransmission cut-off schemes is introduced. The overall call success probability is devised resorting to call rejection and call blocking probabilities. Results demonstrate that the overall call success probability can be independent of random access part up to a certain call arrival rate if a special type of retransmission cut-off is utilized.