Cooperative NOMA Based on OAM Transmission for Beyond 5G Applications

Buffer‐aided cooperative nonorthogonal multiple access (NOMA) improves the effectiveness of the spectral by allowing more than one user to share the same resources to realize massive connectivity. This is notably attractive in the fifth generation (5G) and beyond systems, where a massive number of connections are essential such as the Internet of Things (IoT). Wireless‐powered communication through energy harvesting is another 5G promising solution for the future massively dense networks. To sufficiently utilize energy harvesting in a buffer‐aided cooperative NOMA network, the relay selection rule must consider the energy level of the selected relay in addition to its data content to avoid an outage. This paper proposes a relay selection rule for energy‐harvesting buffer‐aided cooperative NOMA networks. The proposed relay selection scheme considers the state of both the data buffer and the energy buffer. The simulations show that the proposed selection rule has improved the network outage probability and throughput as well. This enhancement is kept with changing the number of relays. The results also show that the impact of changing the energy buffer size is crucial, and the larger, the better. Furthermore, making the source transmitting power larger than the relay transmitting power is beneficial, especially with large enough energy buffer sizes.

In this work, resource allocation of Cooperative Power Domain Non-Orthogonal Multiple Access (PD-NOMA) with energy harvesting technique using Multiple Input Single Output (MISO) is examined. This paper focuses on improvement of bit error rate (BER), spectral efficiency and capacity compared to conventional Non-Orthogonal Multiple Access (NOMA). Two users scenario is considered, where an user is near to the base station (BS) while the other one is far away from the base station. As both users with different power levels exist in the same spectrum, co-channel interference is inevitable. To alleviate this, an interference cancellation technique known as Successive Interference Cancellation (SIC) is used. The simulation results of cooperative NOMA with energy harvesting are compared with conventional NOMA and it can be inferred that cooperative NOMA performance is better than NOMA.

This paper investigates the impact of relay selection (RS) on the performance of cooperative non-orthogonal multiple access (NOMA), where relays are capable of working in either full-duplex (FD) or half-duplex (HD) mode. A number of relays (i.e., K relays) are uniformly distributed within the disc. A pair of RS schemes are considered insightfully: 1) single-stage RS (SRS) scheme; and 2) two-stage RS (TRS) scheme. In order to characterize the performance of these two RS schemes, new closed-form expressions for both exact and asymptotic outage probabilities are derived. Based on analytical results, the diversity orders achieved by the pair of RS schemes for FD/HD cooperative NOMA are obtained. Our analytical results reveal that: 1) the FD-based RS schemes obtain a zero diversity order, which is due to the influence of loop interference at the relay; and 2) the HD-based RS schemes are capable of achieving a diversity order of K , which is equal to the number of relays. Finally, simulation results demonstrate that: 1) the FD-based RS schemes have better outage performance than HD-based RS schemes in the low signal-to-noise ratio (SNR) region; 2) as the number of relays increases, the pair of RS schemes considered are capable of achieving the lower outage probability; and 3) the outage behaviors of FD/HD-based NOMA SRS/TRS schemes are superior to that of random RS and orthogonal multiple access based RS schemes.

The non‐orthogonal multiple access (NOMA) technique is a prospective solution to support the massive connectivity of an ever‐increasing number of wirelessly connected devices and address the spectrum scarcity issue. In this article, the outage probability and ergodic capacity of a two‐hop cooperative NOMA network with an energy‐limited relaying node are quantified over a generalizedstatistical model. The relay acts in an amplify‐and‐forward mode and performs energy harvesting (EH) using the time‐switching and power splitting relaying protocols. Moreover, the impact of hardware impairments (HIs) is incorporated into the performance evaluation. The obtained results prove the importance of HIs and allow one to evaluate the outage probability and ergodic capacity over various statistical models and system parameters. Finally, the results suggest that the optimal performance at a specific scenario depends on the combination of multiple factors, such as channel conditions, HI level, transmit power, and EH protocol.

Non-orthogonal multiple access (NOMA) is a promising spectrally-efficient technology to satisfy the massive data requirement of the next-generation wireless communication networks. In this paper, we consider cooperative non-orthogonal multiple access (CNOMA) networks with relaying user selection, where a two-stage user selection scheme is adopted to optimize the received signal-to-noise ratio (SNR) of the weak user. We derive analytical expressions of the outage probability of the CNOMA users under two different types of channel estimation errors. Afterwards, we investigate the asymptotic characteristics the outage probability of the CNOMA systems in the high SNR regimes. Our results show that for the case of constant variance of the channel estimation error, the outage probability of each user is saturated and cannot be improved by increasing the transmit power of the access point. In contrast, there is no performance bottleneck of the outage probability for all the users when the variance of the channel estimation errors decease with SNR, whilst fully diversity gain is achieved by the weak user.

The full-duplex (FD) cooperative nonorthogonal multiple access (NOMA) achieves a superior throughput over the conventional half-duplex (HD) cooperative NOMA, wherein the strong users (SUs) with good channel conditions can act as an FD relay node for the weak users with poor channel conditions. However, the energy efficiency (EE) of a cooperative NOMA may be degraded due to the additional power consumption incurred at the SUs. We are, therefore, motivated to investigate the EE maximization problem of an FD cooperative NOMA system. More importantly, we investigate the “signal-to-inference-noise ratio gap reversal” problem of cooperative NOMA systems, which imposes successive interference cancellation (SIC) performance degradation at the SUs. This problem has not been documented in the existing cooperative NOMA literature. A low-complexity algorithm is proposed for maximizing the system's EE while guaranteeing a successful SIC operation. Our numerical results show that the proposed algorithm achieves both a higher EE and throughput over the existing HD cooperative NOMA and nonadaptive FD cooperative NOMA. More importantly, the proposed scheme guarantees a successful SIC operation at the SUs.

A two-user downlink cooperative non-orthogonal multiple access (NOMA) short-packet communication network is investigated in flat Rayleigh fading channels, where a central user cooperatively relays the signals intended to a cell-edge user. To derive the average block error rate (BLER) of the central user, unlike the work in the literature where the product term is neglected, a new method that works well for the whole range of power allocation factor is proposed. Furthermore, the average BLER of the cell-edge user is theoretically derived. Numerical results demonstrate that while remaining almost the same average BLER for the central user, the cell-edge user in our proposed cooperative NOMA network achieves lower average BLER than those in the conventional NOMA network and the cooperative orthogonal multiple access network.

Envisioned as a promising component of the future wireless Internet-of-Things (IoT) networks, the non-orthogonal multiple access (NOMA) technique can support massive connectivity with a significantly increased spectral efficiency. Cooperative NOMA is able to further improve the communication reliability of users under poor channel conditions. However, the conventional system design suffers from several inherent limitations and is not optimized from the bit error rate (BER) perspective. In this article, we develop a novel deep cooperative NOMA scheme, drawing upon the recent advances in deep learning (DL). We develop a novel hybrid-cascaded deep neural network (DNN) architecture such that the entire system can be optimized in a holistic manner. On this basis, we construct multiple loss functions to quantify the BER performance and propose a novel multi-task oriented two-stage training method to solve the end-to-end training problem in a self-supervised manner. The learning mechanism of each DNN module is then analyzed based on information theory, offering insights into the explainable DNN architecture and its corresponding training method. We also adapt the proposed scheme to handle the power allocation (PA) mismatch between training and inference and incorporate it with channel coding to combat signal deterioration. Simulation results verify its advantages over orthogonal multiple access (OMA) and the conventional cooperative NOMA scheme in various scenarios.

In this paper, a novel cooperative non-orthogonal multiple access (NOMA) system is proposed, where one near user is employed as decode-and-forward relaying switching between full-duplex (FD) and half-duplex (HD) mode to help a far user. Two representative cooperative relaying scenarios are investigated insightfully. The first scenario is that no direct link exists between the base station (BS) and far user. The second scenario is that the direct link exists between the BS and far user. To characterize the performance of potential gains brought by the FD NOMA in two considered scenarios, three performance metrics outage probability, ergodic rate, and energy efficiency are discussed. More particularly, we derive new closed-form expressions for both exact and asymptotic outage probabilities as well as delay-limited throughput for two NOMA users. Based on the derived results, the diversity orders achieved by users are obtained. We confirm that the use of direct link overcomes zero diversity order of far NOMA user inherent to FD relaying. In addition, we derive new closed-form expressions for asymptotic ergodic rates. Based on these, the high signal-to-noise ratio (SNR) slopes of two users for FD NOMA are obtained. Simulation results demonstrate that: 1) the FD NOMA is superior to the HD NOMA in terms of outage probability and ergodic sum rate in the low SNR region; and 2) in delay-limited transmission mode, the FD NOMA has higher energy efficiency than the HD NOMA in the low SNR region; However, in delay-tolerant transmission mode, the system energy efficiency of the HD NOMA exceeds the FD NOMA in the high SNR region.

The outage performance of a reconfigurable intelligent surface‐ (RIS‐) aided full‐duplex cooperative nonorthogonal multiple access (NOMA) system is studied in this paper. Based on the statistical characteristics of the signal‐to‐noise ratio of the reflection channel from the access point via RIS to the near user, and the cooperative channel from the near user to the far NOMA user, the outage probability of both the near and far users is derived. Through the comparison with the outage performance of conventional cooperative NOMA without employing RIS, the superiority of the proposed scheme is demonstrated. Finally, the correctness of the analytical results is validated with simulation.

Geolocation of mobile nodes with non‐orthogonal multiple access (NOMA) is a crucial process for enabling advanced location‐based services (LBSs) in 5G networks. In this study, the authors investigate the theoretical limits of received‐signal‐strength (RSS)‐based positioning for uplink cooperative NOMA under different network conditions with special emphasis on the user fairness feature. In addition, they compare the performance of the RSS‐based positioning of cooperative NOMA with that of orthogonal multiple access (OMA). The Cramer‐Rao lower bounds are derived in order to show the fundamental limits of position estimation error by taking amplify‐and‐forward and decode‐and‐forward relaying into account. The numerical results for both schemes are presented and compared considering the effects of number of relays and user equipments, different relaying on the performance of RSS positioning. The effects of power allocation on the user fairness of cooperative NOMA are also investigated. The results show that the cooperative NOMA outperforms cooperative OMA in terms of positioning. It provides high precision position accuracy and user fairness under different network conditions. Hence, the results suggest that the RSS‐based positioning for uplink cooperative NOMA is a promising technique for achieving user fairness and supporting diversified low‐cost LBSs in 5G networks.

In this letter, a cooperative non-orthogonal multiple access (NOMA) method is utilized in millimeter wave (mmWave) communications to active non-line-of-sight (NLOS) users, where NOMA users are modeled with the aid of Poisson point process (PPP) and all users are severed by a central base station (BS). Closed-form expressions for outage probabilities of paired NOMA users are derived to characterize the performance of the proposed networks. Our numerical results show that the proposed system outperforms the traditional mmWave networks using non-cooperative NOMA.

In this paper, two energy harvesting policies deploying in cooperative non-orthogonal multiple access (NOMA) systems are considered. After period of wireless power transfer, the NOMA users including cell-edge and cell-center users simultaneously transmit the superposition coded symbols to the base station (BS). In the last time slot, the BS decodes to achieve its signal based on superposition coded symbol with corresponding power allocation factors. This paper provides exact expressions of outage probability in two schemes. Performance gap of two NOMA users can be raised by providing different power allocation factors. It is confirmed by numerical result. Distance and data rate are main factors affecting outage performance. Scheme I exhibit scenario where power beacon transmits energy signal to NOMA user while the BS feeds energy to NOMA user in Scheme II. It is shown that outage performance of Scheme I is better than that of Scheme II.

In contrast with orthogonal multiple access (OMA) technologies, non-orthogonal multiple access (NOMA) technology can achieve higher spectral efficiency and support more users simultaneously. Multiple relays can be deployed in NOMA networks, in order to combat fading and thus increase the transmission reliability. In the existing works on cooperative NOMA networks with multiple relays, the decoding error at the relays and the imperfect successive interference cancellation (SIC) are not taken into account simultaneously. In this work, we consider the bit error rate (BER) analysis of relay-aided NOMA networks, where max-min relay selection is employed. Particularly, closed-form BER expressions are derived for NOMA networks with Rayleigh fading, in the existence of the relay decoding error and imperfect SIC. The asymptotic BER performance is then obtained to provide some useful insights into the system design such as the diversity order. Finally, simulation results illustrate the correctness of the derived expressions. The presented results reveal the effects of imperfect SIC and relay decoding error on the performance of cooperative NOMA networks.

This letter studies the impact of network-coded multiple access (NCMA) on the outage performance of full-duplex cooperative non-orthogonal multiple access (NOMA). In particular, we propose a network-coded cooperative NOMA (NC-CNOMA) strategy, under which user devices utilize physical-layer network coding (PNC) to demodulate signals with greater probability. The exact analytical expression of the outage probability is derived to evaluate the performance of the proposed scheme. The provided simulation results validate our analysis and the proposed NC-CNOMA scheme outperforms the conventional cooperative NOMA with regard to outage performance.