Non-orthogonal Multiple Access Signal Research Articles

Performance analysis of partial NOMA-based layered D2D communications

Conventionally, non-orthogonal multiple access (NOMA) has traditionally been implemented separately from orthogonal multiple access (OMA), aiming to improve the capacity of multi-user systems. However, a recent study has ventured beyond this conventional approach by integrating OMA and NOMA proportionally within the same system. In spite of these advancements, the consideration towards optimizing multi-user systems remains incomplete especially when user service requirements vary significantly. Therefore, this paper explores a novel layered device-to-device (D2D) partial NOMA (P-NOMA) scheme, which introduces a hybrid power-domain access method into multi-user systems. The analysis primarily focuses on evaluating both the system performance and the impact of various parameters on it. In contrast to conventional fully overlapped NOMA signals, P-NOMA signals are partially overlapped with an overlap rate that can be determined based on quality-of-service (QoS) requirements. Simulation results demonstrate that judicious utilization of P-NOMA can effectively enhance overall system performance, particularly in terms of sum rate (SR) metrics, while also flexibly accommodating diverse QoS requirements for multiple users.

Secrecy outage analysis for RIS-assisted hybrid FSO-RF systems with NOMA

In this paper, we investigate the physical-layer security performance for a reconfigurable intelligent surface (RIS) assisted free-space optical (FSO) communication-radio frequency (RF) system with non-orthogonal multiple access (NOMA). In particular, the source (S) transmits an optical NOMA signal to the relay (R), which forwards the optical-to-electrical converted signal to both users in the presence of an eavesdropper (E). Furthermore, for the far user, the scenario that there is no direct path from R and it can only receive the signal from R via the RIS is considered. While for the near user, three signal transmission scenarios are taken into account: 1) only the direct path from R exists; 2) only the reflected paths from RIS exist; 3) both the direct and the reflected paths exist and superimpose together. In addition, for the first hop of information transmission, E may or may not locate in the region of laser beam divergences of S. Therefore, both scenarios that the first hop may or may not be overheard by E are taken into consideration. Considering the FSO link is with a Gamma-Gamma distribution and the RF channels experience the Nakagami-m fading, the analytic and asymptotic expressions of secrecy outage probability for both users are presented. Monte-Carlo simulations are also conducted to validate the accuracy of the derived expressions.

Performance evaluation for multi-antenna UWOC-RF NOMA systems with imperfect CSI and SIC

Information transmission is easily affected by obstacles or other factors, which makes it challenging to achieve perfect channel state information (CSI) and successive interference cancellation (SIC) in practical applications. Therefore, in this paper, a dual-hop underwater wireless optical communication-radio frequency (UWOC-RF) system with non-orthogonal multiple access (NOMA) in the presence of both imprecise CSI and imperfect SIC is investigated. In particular, the underwater source sends a superimposed optical NOMA signal to a pair of land-based users via a decode-and-forward relay on the surface, which decodes the received signal and encodes it into the RF one before broadcasting it to the terrestrial users. Considering a scenario that both the land-based users are equipped with multiple antennas and adopt a maximal-ratio combining technique to deal with those multiple copies of received signals, we first format the expressions of probability density function, cumulative distribution function, and the p-th moment of the imperfect channel gain in the UWOC link. And then the analytical and asymptotic expressions for outage probability as well as the closed-form expression for average achievable rate of each user are obtained by utilizing the Meijer's-G and the Fox's-H functions. Finally, Monte-Carlo simulations are performed to validate the accuracy of those analytical expressions.

Sensing-Efficient NOMA-Aided Integrated Sensing and Communication: A Joint Sensing Scheduling and Beamforming Optimization

Integrated sensing and communication (ISAC) system has been expected to play a vital role in future wireless networks and services. In this paper, we investigate a non-orthogonal multiple access (NOMA)-aided ISAC system in which the ISAC base station utilizes NOMA to serve multiple NOMA-users while performing radar sensing towards a group of sensing targets by leveraging the superimposed NOMA signals for NOMA-users. To investigate this problem, we formulate a joint optimization of the beamforming, the NOMA transmission duration and the sensing scheduling of sensing targets, with the objective of maximizing the sensing efficiency (i.e., the number of sensed targets within a time-interval) of ISAC system, while satisfying both the communication quality requirement of each NOMA-user and the sensing quality requirement of each selected targets. Despite that the formulated joint optimization problem is strictly non-convex, we propose a decomposition-based algorithm for solving the problem. Specifically, we exploit the successive convex approximation and penalty function method to equivalently transform the problem of optimizing the beamforming into a convex problem which can be addressed efficiently. Furthermore, with the optimal beamforming, we leverage the monotonic feature and adopt a bisection-search method to determine the NOMA transmission duration. Finally, we utilize an algorithm based on the cross-entropy learning to compute the optimal sensing scheduling. Numerical results verify the effectiveness of our proposed algorithms and show the performance advantage of our NOMA-aided ISAC system. Compared with some benchmark schemes, our NOMA-aided ISAC sensing scheduling scheme can achieve better performance in communication and sensing.

A CA and ML approach for M-MIMO optical non-orthogonal multiple access power efficiency

Abstract The non-orthogonal multiple access (NOMA) multiple access approach can be used in future wireless communication systems to support massive connections and increase spectrum efficiency. Because user signal intensities and interference levels vary, precise channel assessment is essential in NOMA. Optimal power allocation and decoding order are made possible by precise algorithms, increasing system effectiveness and performance. However, NOMA can be adversely impacted by high peak-to-average power ratio (PAPR) values, leading to worsened system performance and more complex power amplifiers. In order to solve this issue, this paper recommends PAPR reduction in NOMA using companding methods for 512, 256, and 64 sub-carriers. Nonlinear companding techniques, such as MA and A-law companding, can efficiently reduce the high peak power of NOMA signals while reducing distortion and enhancing overall system dependability. The effectiveness of the proposed companding methods is evaluated using simulations, and the results demonstrate a significant decrease in PAPR, ensuring higher bit error rate (BER) effectiveness and transmission resilience in NOMA-based communication systems. The proposed approach is compared to the traditional Ml (C- Ml) and A-Law (C- A-Law).

Performance Analysis for Dual-Hop UWOC-RF Systems With NOMA

In this study, we investigate a non-orthogonal multiple access (NOMA)-assisted dual-hop underwater wireless optical communication-radio frequency (UWOC-RF) network. Specifically, an optical source forwards a NOMA signal to a marine relay, which first deploys either the heterodyne detection or intensity modulation direct detection to process the received signal, and then encodes and re-transmits a superimposed signal to two terrestrial destinations. Assuming the UWOC channel is subject to a unified mixture Exponential-Generalized Gamma distribution and the RF channels experience Nakagami-m fading, the analytical as well as asymptotic expression for outage probability is obtained in the form of the Meijer’s G-function. Moreover, the average achievable rate is also investigated by utilizing the bivariate Fox’s H-function. In addition, the accuracy of those expressions is verified with Monte-Carlo simulations.

Performance Enhancement of Cooperative MIMO-NOMA Systems Over Sub-6 GHz and mmWave Bands

In this paper, two radio links with different frequency bands are considered for base stations (BS) serving users via decode-and-forward (DF) cooperative relays. Backhaul and access links are proposed with sub-6 GHz and millimeter wave (mmWave) bands, respectively. Non-orthogonal multiple access (NOMA) is employed in the backhaul link to simultaneously transmit a superposed signal in the power domain, using the same band. The superposed signals, containing two signals that differ in terms of power allocation factors (PAFs), are designed for two selected DF relays in the BS. The two relays are chosen from several relays to be serviced by the BS based on a pairing algorithm that depends on different users’ circumstances. The furthest DF relay detects the incoming NOMA signal directly, while the nearest one applies successive interference cancellation (SIC) before extracting its signal. Each DF relay forwards the detected signals toward their intended users over mmWave channels. Three performance metrics are utilized to evaluate the system’s performance: outage probability, achievable throughput, and bit error rate. Comparisons between two mmWave bands in the access link (28 and 73 GHz) are made to demonstrate the superiority of the 28 GHz band in terms of the three performance-related metrics.

Зменшення відношення пікової до середньої потужності за допомогою алгоритму компандування для NOMA сигналу

Майбутні системи бездротового зв’язку можуть підтримувати величезну кількість з’єднань і підвищити ефективність використання спектра завдяки використанню підходу неортогонального множинного доступу NOMA (non-orthogonal multiple access). Однак високі рівні відношення пікової до середньої потужності PAPR (Peak-to-Average Power Ratio) можуть негативно впливати на NOMA, що призводить до зниження продуктивності системи та ускладнення підсилювачів потужності. У цьому дослідженні пропонується зменшити PAPR в NOMA, використовуючи методи компандування для 512, 256 і 64 піднесучих з метою вирішення цієї проблеми. Висока пікова потужність сигналів NOMA може бути ефективно стиснута за допомогою нелінійних методів компандування, таких як ущільнення за μ-законом і A-законом, що зменшує спотворення і покращує загальну надійність системи. Для оцінки ефективності запропонованих методів компандування використано моделювання, результати якого свідчать про значне зменшення PAPR, що забезпечує підвищення ефективності коефіцієнта бітових помилок BER (Bit Error Rate) та стійкості передачі в системах зв’язку на основі NOMA. Запропонований метод порівнюється з традиційними A-законом (C-A-law) та μ-законом (C-μ-law).

Підвищення ефективності максимальної потужності сигналів NOMA покоління 5G і вище з використанням SLM алгоритму

В роботі представлено новий підхід для послаблення шкідливих впливів великого значення відношення пікового рівня потужності до середнього PAPR (Peak-to-Average Power Ratio), притаманних сигналам неортогональної системи множинного доступу NOMA (Non-Orthogonal Multiple Access), при застосуванні техніки вибіркового відображення SLM (Selective Mapping). NOMA — добре відома схема множинного доступу в сучасних системах безпроводового зв’язку, яка сприяє одночасній передачі сигналів багатьох користувачів за допомогою одного частотно-часового ресурсу. Однак система NOMA чутлива до підвищених рівнів PAPR, що викликає погіршення ккд та міжсимвольні перешкоди. Пропонований метод використовує SLM для подолання піків PAPR в сигналах NOMA. Шляхом формування набору різноманітних послідовностей фаз, SLM створю альтернативні варіанти оригінального сигналу NOMA. Тоді фазова послідовність, яка призводить до найнижчого значення PAPR, вибирається для передачі. Ця динамічна адаптація суттєво зменшує піки переданого сигналу і таким чином підвищує ккд, мінімізує спотворення, та зменшу ризик нелінійного підсилення. Проведено моделювання для оцінки ккд процедури, що розробляється. Результати показали значне зниження PAPR в сигналах NOMA у порівнянні з традиційними методами передачі. Крім того, цей метод зберігає якість сигналу та зменшує рівень бітових помилок BER (bit error rate), покращу спектральну густину потужності PSD (power spectral density) та підвищу загальну надійність структури радіомовлення. Ця стаття приводить до висновку про реалістичність інтегрування SLM в існуючі системи на основі NOMA, пропонуючи перспективний шлях для оптимізації ефективності сучасних радіомереж.

Performance improvement of non-orthogonal multiple access with a 3D constellation and a 2D IFFT modulator.

In this paper, we propose a performance improvement of non-orthogonal multiple access (NOMA) with a three-dimensional (3D) constellation and a two-dimensional Inverse Fast Fourier Transform IFFT modulator (2D-IFFT) for the passive optical network (PON). Two kinds of 3D constellation mapping are designed for the generation of a three-dimensional NOMA (3D-NOMA) signal. Higher-order 3D modulation signals can be obtained by superimposing signals of different power levels by pair mapping. Successive interference cancellation (SIC) algorithm is implemented at the receiver to remove interference from different users. Compared with the traditional two-dimensional NOMA (2D-NOMA), the proposed 3D-NOMA can increase the minimum Euclidean distance (MED) of constellation points by 15.48%, which enhances the bit error rate (BER) performance of the NOMA. The peak-to-average power ratio (PAPR) of NOMA can be reduced by 2 dB. A 12.17 Gb/s 3D-NOMA transmission over 25 km single-mode fiber (SMF) is experimentally demonstrated. The results show that at the bit error rate (BER) of 3.8 × 10-3, the sensitivity gain of the high-power signals of the two proposed 3D-NOMA schemes is 0.7 dB and 1 dB compared with that of 2D-NOMA under the condition of the same rate. Low-power level signal also has 0.3 dB and 1 dB performance improvement. Compared with 3D orthogonal frequency-division multiplexing (3D-OFDM), the proposed 3D-NOMA scheme could potentially expand the number of users without obvious performance degradation. Due to its good performance, 3D-NOMA is a potential method for future optical access systems.

Outage performance for full-duplex relaying satellite-terrestrial multi-antenna NOMA systems with imperfect SIC

Due to the masking effect, a reliable line-of-sight transmission between a satellite and terrestrial nodes is not always guaranteed, and a half-duplex (HD) relaying is commonly performed in literature to assist such transmission. However, the system efficiency could be seriously degraded with the HD relaying as a two-time slot is required for a dual-hop information transmission. Therefore, in this paper, a full-duplex (FD) relaying, which can enable signal receiving and transmitting simultaneously, is considered for a satellite-terrestrial non-orthogonal multiple access (NOMA) system consisting of a multi-antenna satellite source, a FD relay, and two multi-antenna destination nodes. Specifically, the satellite source adopts a maximum ratio transmission scheme to transmit a NOMA signal to the relay, and the relay deploys a decode-and-forward protocol to forward the information to two destination nodes simultaneously, which employ the maximal ratio combining strategy to process the received signals. Assuming the satellite link experiences Shadowed-Rician fading and the terrestrial links undergo Nakagami-m fading distribution, both analytical and asymptotic expressions of outage probability (OP) for two destination nodes are presented in the presence of residual self-interference and imperfect successive interference cancellation. In addition, an adaptive power allocation (APA) scheme is performed, and the system throughput under the delay-limited transmission mode is also analyzed. Finally, Monte-Carlo simulations are adopted to verify the accuracy of those derived analytical expressions. Numerical results show that the OP performance with the FD mode outperforms that with the HD one, and adopting the APA scheme can result in the best OP performance.

Deep Learning-Based Joint NOMA Signal Detection and Power Allocation in Cognitive Radio Networks

Presently, Non-Orthogonal Multiple Access (NOMA) frequently uses Successive Interference Cancellation (SIC) with channel estimation to detect the receivers’ signal successfully. However, it’s a slow and sophisticated process. Consequently, the decoding precision of previous Primary Users (PUs) / Secondary Users (SUs) is degraded due to error propagation. These shortcomings are mitigated by the proposed Deep Learning (DL) schemes for signal detection and Power Allocation (PA) in NOMA-based futuristic Cognitive Radio Networks (CRNs). Hence, proposed technique is optimized jointly and determines the desired solution in one step without channel estimation through skilled Deep Neural Network (DNN) approach. It can understands the things because it is the core (so-called heart) of DL, which integrates user detection with channel estimation and PA. The optimization problem for fair PA is planned by combining proposed technique for optimizing systems threshold throughput. In addition, DNN training algorithms is also analyzed, and used to retrieve users’ information from the aired signal directly during the testing stage. The real-time experimental results and analytic outcomes are investigated and validate the supremacy of the proposed scheme over prevailing techniques, respectively. Furthermore, the robustness of the DL technique is additionally evaluated for its dominance over existing approaches.

STBC-Assisted MDC-NOMA Image Transmission Scheme for Multi-Antenna Systems

As an efficient and interference-resistant coding technique, multiple description coding (MDC) is proposed with the aim to solve the transmission unreliability problem caused by packet errors, loss or blocking delays. The integration of MDC with non-orthogonal multiple access (NOMA) scheme (MDC-NOMA) can effectively boost the robustness and throughput of the underlying system. Additionally, space-time block coding (STBC) can further enhance the system reliability with increased diversity gain, as well as reduced decoding complexity. In this paper, we propose a novel framework referred to as MDC-NOMA-STBC, in which we apply Alamouti STBC integrated with MDC and NOMA to implement more reliable transmission. Specifically, NOMA signals are constructed by superimposing the descriptions from different users, then transmitted by the base station (BS) using Alamouti STBC. In order to substantiate the performance of the proposed framework, first, we derive closed-form expressions of both the outage probability and ergodic rate for each user in a two-antenna BS scenario. Second, for multi-antenna BS, we investigate different antenna selection strategies to further enhance the outage performance under the considered framework, whose analytical expression is provided wherever possible. Third, Monte Carlo simulation results are presented to validate our theoretical framework and to corroborate the superiority of the proposed MDC-NOMA-STBC over state-of-the-art MDC-NOMA scheme. Moreover, under realistic contexts with image transmission, it is confirmed that MDC-NOMA-STBC outperforms its counterpart MDC-NOMA in terms of the peak signal-to-noise ratio and the bit error rate.

Development of CNN-LSTM Hybrid Deep Learning Network for the Joint Detection of Non-Orthogonal Multiple Access Signals in 5G Uplink Receivers

Development of CNN-LSTM Hybrid Deep Learning Network for the Joint Detection of Non-Orthogonal Multiple Access Signals in 5G Uplink Receivers

Active User Detection and Channel Estimation for Massive Machine-Type Communication: Deep Learning Approach

Recently, massive machine-type communications (mMTCs) have become one of key use cases for 5G. In order to support massive users transmitting small data packets at low rates, grant-free (GF) access and nonorthogonal multiple access (NOMA) have been suggested. Since each device transmits information without scheduling in the GF-NOMA systems, the device identification process, called active user detection (AUD), is required at the base station (BS). For the NOMA-based systems, the channel estimation (CE), an operation after the AUD, is a challenging task since multiple devices’ transmit signals and channels are superimposed in the same wireless resources. In this article, we propose a deep learning (DL)-based AUD and CE in the GF-NOMA systems. In our work, DL figures out the direct mapping between the received NOMA signal and the indices of active devices and associated channels using the long short-term memory (LSTM). From numerical experiments, we show that the proposed scheme is effective in handling the AUD and CE in the mMTC environments.

Secrecy performance analysis for a NOMA based FSO-RF system with imperfect CSI

In this paper, we consider a non-orthogonal multiple access (NOMA) based mixed free space optical–radio frequency (FSO-RF) system with imperfect channel state information (CSI) and evaluate the secrecy performance in terms of secrecy outage probability (SOP). Specifically, a source ( S ) first forwards an optical NOMA signal to a relay ( R ) via an FSO link, and then R performs an optical–electrical conversion and broadcasts the converted signal to users over the RF links. Both the FSO and RF links are incorporated with the NOMA technique, and the CSI imperfection in both links is considered. Assuming both users have multiple antennas, and adopting the maximal ratio combining diversity schemes, we derive the analytical and asymptotic expressions for SOP when the FSO link undergoes gamma–gamma fading with pointing error and the RF links are subject to Rayleigh fading. In addition, both decode-and-forward and amplify-and-forward protocols are taken into account and compared. Monte Carlo simulations are also used to verify the accuracy of the derived results.

Beamforming and Jamming Optimization for IRS-Aided Secure NOMA Networks

The integration of intelligent reflecting surface (IRS) and multiple access provides a promising solution to improved coverage and massive connections at low cost. However, securing IRS-aided networks remains a challenge since the potential eavesdropper also has access to an additional IRS reflection link, especially when the eavesdropping channel state information is unknown. In this paper, we propose an IRS-assisted non-orthogonal multiple access (NOMA) scheme to achieve secure communication via artificial jamming, where the multi-antenna base station sends the NOMA and jamming signals together to the legitimate users with the assistance of IRS, in the presence of a passive eavesdropper. The sum rate of legitimate users is maximized by optimizing the transmit beamforming, the jamming vector and the IRS reflecting vector, satisfying the quality of service requirement, the IRS reflecting constraint and the successive interference cancellation (SIC) decoding condition. In addition, the received jamming power is adapted at the highest level at all legitimate users for successful cancellation via SIC. To tackle this non-convex optimization problem, we first decompose it into two subproblems, and then each subproblem is converted into a convex one using successive convex approximation. An alternate optimization algorithm is proposed to solve them iteratively. Numerical results show that the secure transmission in the proposed IRS-NOMA scheme can be effectively guaranteed with the assistance of artificial jamming.

PAPR Reduction of NOMA Using Vandermonde Matrix-Particle Transmission Sequence

Non-Orthogonal Multiple Access (NOMA) is an ideal choice for 5G waveforms due to their characteristics such as high data rate, massive device connectivity, high spectral access, and effective frequency selective fading. Thus, it permits gigantic connectivity. The spectrum overlaps with NOMA, which consents several operators to segment the spectrum at the same frequency. These features make NOMA more suitable for use beyond 5G. Peak to Average Power (PAPR) is a major problem in Multi-Carrier Techniques (MCT) like NOMA and it also degrades the performance of the amplifier. The Partial Transmission Sequence (PTS) is a superior algorithm for moderating the PAPR. However, it also increases the complexity of the structure. The PAPR is reduced in NOMA by multiplying the NOMA signal with optimised phase vectors (P). The phase vectors are generated by using the Vandermonde Matrix (VM). In this work, we proposed a VM-PTS algorithm for the NOMA system, and the number of computations to search the optimal phase vectors for NOMA high PAPR signal is less as compared with existing PTS. The outcomes demonstrate that the performance of the recommended PTS in terms of PAPR, Bit Error Rate (BER), and complexity is better than the conventional PTS (C-PTS).

Multi-Threshold Detector With Fair Power Allocation Coefficients for NOMA Signals With Statistical CSI

In this letter, we modify the multi-threshold detector (MTD) for detection of downlink non-orthogonal multiple access (NOMA) signals in the Rician fading channel with statistical knowledge of channel state information (CSI). First, the error probability (Pe) for both MTD and successive interference cancellation (SIC) with statistical CSI is calculated. Then, we use the obtained Pe expression to fairly allocate power to different users in the sense that the maximum Pe of the users is minimized. Finally, computer simulations are performed, which show that MTD outperforms the SIC in the case that error propagation happens in the noise-free SIC.

Improved Closed-Form Bounds on Interference Distribution and Applications for Tractable Analysis in Cellular Networks

It has been a challenging task to derive the complementary cumulative distribution function (CCDF) of aggregate interference as closed-form in Poisson point process (PPP). In this paper, we consider wireless communication networks where transmitters are all distributed according to homogeneous PPP and study the CCDF of the interference. Mainly, we derive generalized bounds on the CCDF of aggregate interference from whole homogeneous PPP based on discretization of interference, which considerably enhance tightness compared to the previous bounds. These bounds can be used to the analysis requiring the distribution for aggregate interference, such as deployment and activation of BSs, massive MIMO, and millimeter wave communication networks. As examples of utilizing the derived bounds, we derive tractable coverage probabilities of uplink non-orthogonal multiple access (NOMA) users and downlink users in cellular networks under line-of-sight(LoS)/non-line-of-signt (NLOS) channels, respectively. In NOMA, we derive the closed-form bounds on coverage probability when successive interference cancellation is adopted for NOMA signal demodulation. Using the proposed bounds, we also obtain the bounds on coverage probability of a cellular system with LoS/NLOS channels. The tightness of bounds in this work is shown via numerical comparison. Moreover, we mathematically prove the convergence of bounds to exact CCDF.