Non-orthogonal Random Access 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.

Nonorthogonal Random Access for 5G Mobile Communication Systems

This correspondence paper proposes two nonorthogonal random access (NORA) techniques for 5G mobile communication networks, where user equipments (UEs) make use of the channel inversion technique such that their received power at the base station (BS) can be one of the two target values. It enables the BS to decode two packets simultaneously with the successive interference cancellation (SIC) technique if a different power level is chosen. We propose two NORA systems; that is, UEs choose one of the two target power levels based on the channel gain or the region where they are. The performance of the proposed systems is analyzed in terms of access delay, throughput, and energy efficiency. Through analysis and extensive computer simulations, we show that the maximum throughput of the proposed NORA techniques can exceed 0.7, which is a significant improvement compared to the maximum throughput of conventional random access 0.368.

Layered Non-Orthogonal Random Access With SIC and Transmit Diversity for Reliable Transmissions

In this paper, we study a layered random access scheme based on non-orthogonal multiple access to improve the throughput of multichannel ALOHA. At a receiver, successive interference cancellation is carried out across layers to remove the signals that are already decoded. A closed-form expression for the total throughput is derived under certain assumptions. It is shown that the transmission rates of layers can be optimized to maximize the total throughput and the proposed scheme can improve the throughput with multiple layers. Furthermore, it is shown that the optimal rates can be recursively found using multiple individual 1-D optimizations. We also modify the proposed layered random access scheme with contention resolution repetition diversity for reliable transmissions with a delay constraint. It is shown to be possible to have a low outage probability if the number of copies can be optimized, which is desirable for high reliability low latency communications.

Non-Orthogonal Random Access for 5G Networks

The massive amounts of machine-type user equipments (UEs) will be supported in the future fifth generation (5G) networks. However, the potential large random access (RA) delay calls for a new RA scheme and for a detailed assessment of its performance. Motivated by the key idea of non-orthogonal multiple access, the non-orthogonal RA (NORA) scheme based on successive interference cancellation (SIC) is proposed in this paper to alleviate the access congestion problem. Specifically, NORA utilizes the difference of time of arrival to identify multiple UEs with the identical preamble, and enables power domain multiplexing of collided UEs in the following access process, while the base station performs SIC based on the channel conditions obtained through preamble detection. Our analysis shows that the performance of the NORA is superior to the conventional orthogonal RA (ORA) scheme in terms of the preamble collision probability, access success probability, and the throughput of RA. Simulation results verify our analysis and further show that our NORA scheme can improve the number of the supported UEs by more than 30%. Moreover, the number of preamble transmissions and the access delay for successfully accessed UEs are also reduced significantly by using the proposed RA scheme.

Non-Orthogonal Random Access in MIMO Cognitive Radio Networks: Beamforming, Power Allocation, and Opportunistic Transmission.

We study secondary random access in multi-input multi-output cognitive radio networks, where a slotted ALOHA-type protocol and successive interference cancellation are used. We first introduce three types of transmit beamforming performed by secondary users, where multiple antennas are used to suppress the interference at the primary base station and/or to increase the received signal power at the secondary base station. Then, we show a simple decentralized power allocation along with the equivalent single-antenna conversion. To exploit the multiuser diversity gain, an opportunistic transmission protocol is proposed, where the secondary users generating less interference are opportunistically selected, resulting in a further reduction of the interference temperature. The proposed methods are validated via computer simulations. Numerical results show that increasing the number of transmit antennas can greatly reduce the interference temperature, while increasing the number of receive antennas leads to a reduction of the total transmit power. Optimal parameter values of the opportunistic transmission protocol are examined according to three types of beamforming and different antenna configurations, in terms of maximizing the cognitive transmission capacity. All the beamforming, decentralized power allocation, and opportunistic transmission protocol are performed by the secondary users in a decentralized manner, thus resulting in an easy implementation in practice.