Multiuser Superposition Transmission Research Articles

An Advanced Non-Orthogonal Multiple Access Security Technique for Future Wireless Communication Networks

The future wireless communication systems demand much more enhanced security and reliability compared to currently deployed systems. In this work, we propose a much simpler yet more efficient physical layer security (PLS) technique for achieving reliable and secure communication in the multiple-input single-output non-orthogonal multiple access (MISO-NOMA) systems. This system is capable of providing enhanced confidential communication as well as inter-user interference cancellation without using the successive interference cancellation (SIC) method. The conventional NOMA was previously adopted under the name of multi-user superposition transmission (MUST) in release 13 of 3GPP but recently excluded from 3GPP-release 17 due to its performance degradation. In this work, we analyze the drawbacks in conventional NOMA and present a new kind of NOMA with more improved performance metrics. The proposed algorithm combines the benefit of pre-coder matrices with simultaneous transmission using antenna diversity to provide simple, reliable, and secure communication without complex processing at the receivers in downlink scenarios. The effectiveness of the proposed algorithm is verified and proven by extensive analysis and numerical simulations.

Enhanced Multiuser Superposition Transmission Through Structured Modulation

The fifth-generation (5G) air interface, namely, dynamic multiple access (MA) based on multiuser superposition transmission (MUST) and orthogonal MA (OMA), may require a complicated scheduling and heavy signaling overhead. To address these challenges, we propose a unified MA scheme for future cellular networks, which we refer to as structured MUST (S-MUST). In S-MUST, we apply complex power allocation coefficients (CPACs) over multiuser legacy constellations to generate a composite constellation. In particular, the in-phase ( $I$ ) and quadrature ( $Q$ ) components of the legacy constellation of each user are separately multiplied by those of the CPACs. As such, the CPACs offer an extra degree of freedom for multiplexing users and guarantee fairness in symmetric broadcast channels. This new paradigm of superposition coding allows us to design $IQ$ separation at the user side, which significantly reduces the decoding complexity without degrading performance. Hence, it supports low-complexity frequency-selective scheduling that does not entail dynamical switching between MUST and OMA. We further propose to quantize the CPACs into complex numbers where $I$ and $Q$ components of each quantized coefficient are primes, facilitating parallel interference cancellation at each user via modulo operations; last but not least, we generalize the design of S-MUST to exploit the capabilities of multiantenna base stations. The proposed S-MUST exhibits an improved user fairness with respect to conventional MUST (134% spectral efficiency enhancement) and a lower system complexity compared with dynamically alternating MUST and OMA.

Performance Analysis of Diversity-Controlled Multi-User Superposition Transmission for 5G Wireless Networks.

In this paper, we propose a novel low-complexity multi-user superposition transmission (MUST) technique for 5G downlink networks, which allows multiple cell-edge users to be multiplexed with a single cell-center user. We call the proposed technique diversity-controlled MUST technique since the cell-center user enjoys the frequency diversity effect via signal repetition over multiple orthogonal frequency division multiplexing (OFDM) sub-carriers. We assume that a base station is equipped with a single antenna but users are equipped with multiple antennas. In addition, we assume that the quadrature phase shift keying (QPSK) modulation is used for users. We mathematically analyze the bit error rate (BER) of both cell-edge users and cell-center users, which is the first theoretical result in the literature to the best of our knowledge. The mathematical analysis is validated through extensive link-level simulations.

On the Power Allocation for a Practical Multiuser Superposition Scheme in NOMA Systems

In this letter, we study nonorthogonal multiple access (NOMA) systems with a linear multiuser superposition transmission (MUST) scheme. To perform the power allocation or the determination of the transmission power ratio for linear MUST with practical modulation schemes of finite constellation sizes, we consider the mutual information. An approach based on Monte Carlo simulations is devised to obtain the mutual information. While the sum rate maximization (based on the capacity) has a trivial solution, numerical examples show that there is a nontrivial solution to the power allocation problem for maximizing total mutual information. Thus, for certain given conditions (e.g., the total transmission power and modulation schemes), we are able to decide the optimal power (and rate) allocation for the linear MUST scheme to maximize the total mutual information.

On Novel Access and Scheduling Schemes for IoT Communications

The Internet of Things (IoT) is expected to foster the development of 5G wireless networks and requires the efficient support for a large number of simultaneous short message communications. To address these challenges, some existing works utilize new waveform and multiuser superposition transmission schemes to improve the capacity of IoT communication. In this paper, we will investigate the spatial degree of freedom of IoT devices based on their distribution, then extend the multiuser shared access (MUSA) which is one of the typical MUST schemes to spatial domain, and propose two novel schemes, that is, the preconfigured access scheme and the joint spatial and code domain scheduling scheme, to enhance IoT communication. The results indicate that the proposed schemes can reduce the collision rate dramatically during the IoT random access procedure and improve the performance of IoT communication obviously. Based on the simulation results, it is also shown that the proposed scheduling scheme can achieve the similar performance to the corresponding brute-force scheduling but with lower complexity.