Joint Space-time Coding and Power Domain Non-orthogonal Multiple Access for Future Wireless System

NOMA (Non- orthogonal Multiple Access) is an early candidate for 5G that concentrates on networks capacity expansion. It can be broadly classified into two major categories; Power-Domain NOMA (PD-NOMA) and Code-Domain NOMA (CD-NOMA). This research focuses on PD-NOMA. The significance of PD- NOMA is that concurrent transmission and reception can be accomplished on the same frequency and with this spectral efficiency can be enhanced. The objective of this research is to investigate the impact of error propagation caused due to AWGN (Additive White Gaussian Noise) channel in PD-NOMA 5G system. A 2 × 2 PD-NOMA system is simulated in Matlab version 2019a. In the Uplink, the raw data is BPSK modulated and transmitted to the Base Station (BS). In the downlink, from the BS, User 1 data is transmitted with a power level of 0.25 watts and User 2 with 0.75 watts based on their placement. In the Reception section, Successive Interference Cancellation (SIC) is executed to segregate the data which is further recovered through decoding process. To analyze the performance, AWGN channel is introduced in the proposed simulated system model. The Signal to Noise Ratio is varied from 5 to 25 dB. From the results obtained, it is inferred that, Bit Error Rate experienced by the users varies from 0.1 to 1.

This study introduces a low-complexity, short-code-based strategy that combines energy harvesting for power domain non-orthogonal multiple access (PD-NOMA) techniques. Due to its non-orthogonal nature, PD-NOMA is relatively more exposed to security vulnerabilities, rapid battery depletion in users due to multi-level SIC, and significant outage probability in congested environments. The presented work uses coded cooperation and short block-length codes to make it harder for unlicensed users to manipulate or steal the data of licensed users. This makes it less likely that unlicensed users will be able to find and decode data belonging to licensed users in the NOMA system. To optimize performance and reduce the frequent outage probability in the NOMA system, we developed a novel user clustering technique. Due to multi-level successive interference cancellation (SIC) at the cell center, users’ batteries quickly drain out in congested NOMA networks, leading to their declaration as energy-constrained. To overcome this issue, we use simultaneous wireless information and power transfer (SWIPT) at user-located cell centers based on the received radio frequency signals. Furthermore, it allows cell-center users to assist cell-edge users through the coded multi-user cooperation (coded Cop-PD-NOMA) technique, thereby enhancing the base station’s (gNodeB) network coverage. During the validation process, the proposed design offers secure NOMA communication, a novel user-clustering technique, and the application of SWIPT to cooperation in the PD-NOMA infrastructure. Bit-error rate (BER) and outage probability (OP) tests show that novel user-clustering and multiuser-coded Cop-PD-NOMA outperform single-user cooperation. Simulation results show that the proposed approach significantly reduces the outage probability (OP) and improves bit-error-rate (BER) performance by approximately 6.5 dB, which is only 2.5 dB in single-user cooperation.

The fifth generation (5G) of wireless communication accompanied by the advancement of mobile internet and the Internet of Things (IoT) will create stormy data traffic. The 5G challenges like higher spectral efficiency, massive connectivity, and low latency are addressed by the Non-Orthogonal Multiple Access (NOMA) in recent years. NOMA is proven to be a promising technique from its capability to accommodate a larger number of users in contrast to the conventional orthogonal multiple access (OMA) schemes. NOMA comprises two distinct techniques such as Power-Domain NOMA and Code-Domain NOMA. The non-orthogonal resource allocation in Power-Domain NOMA is practically realized by the Superposition Coding (SC) at the Base Station (BS) and an advanced Successive Interference Cancellation at the User Equipment (UE). In this manuscript, the basic concepts of NOMA, on comparing its channel gain with OMA are discussed first. Specifically, a comprehensive survey of various SIC techniques applied under perfect and imperfect Channel State Information (CSI) uncertainties are summarized in terms of outage probability, ergodic capacity, and system performance. In addition, the sophisticated SIC techniques, when NOMA is integrated with modern wireless communication technologies such as multiple-input multiple-output (MIMO-NOMA) and Cooperative (C-NOMA) communications are investigated. Furthermore, the challenges to be solved with their corresponding opportunities and future research directions of NOMA are explored.

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.

Non-orthogonal multiple access (NOMA) on shared resources has been identified as a promising technology in 5G to improve resource efficiency and support massive access in all kinds of transmission modes. Power domain and code domain NOMA have been extensively studied and evaluated in both literatures and 3GPP standardization, especially for the uplink where large number of users would like to send their messages to the base station. Though different in the transmitter side design, power domain NOMA and code domain NOMA share the same need of the advanced multi-user detection (MUD) design at the receiver side. Various multi-user detection algorithms have been proposed, balancing performance and complexity in different ways, which is important for the implementation of NOMA in practical networks. In this paper, we introduce a unified variational inference (VI) perspective on various universal NOMA MUD algorithms such as belief propagation (BP), expectation propagation (EP), vector EP (VEP), approximate message passing (AMP) and vector AMP (VAMP), demonstrating how they could be derived from and adapted to each other within the VI framework. Moreover, we unveil and prove that conventional elementary signal estimator (ESE) and linear minimum mean square error (LMMSE) receivers are special cases of EP and VEP, respectively, thus bridging the gap between classic linear receivers and message passing based nonlinear receivers. Such a unified perspective would not only help the design and adaptation of NOMA receivers, but also open a door for the systematic design of joint active user detection and multi-user decoding for sporadic grant-free transmission.

In this paper, a unified framework of non-orthogonal multiple access (NOMA) networks is proposed, which can be applied to code-domain NOMA (CD-NOMA) and power-domain NOMA (PD-NOMA). Since the detection of NOMA users mainly depend on efficient successive interference cancellation (SIC) schemes, both imperfect SIC (ipSIC) and perfect SIC (pSIC) are taken into considered. To characterize the performance of this unified framework, the exact and asymptotic expressions of outage probabilities as well as delay-limited throughput for CD/PD-NOMA with ipSIC/pSIC are derived. Based on the asymptotic analysis, the diversity orders of CD/PD-NOMA are provided. It is confirmed that due to the impact of residual interference (RI), the outage probability of the n-th user with ipSIC for CD/PD-NOMA converges to an error floor in the high signal-to-noise ratio (SNR) region. Numerical simulations demonstrate that the outage behavior of CD-NOMA is superior to that of PD-NOMA.

This study shows how the channel estimation based Deep Learning (DL) and a power allocation method are together employed for multi-user detection in a Power domain Non-Orthogonal Multiple Access (PD-NOMA) network. Successive interference cancellation (SIC) procedure is typically employed at receiver side, where numerous users are decoded in a successive approach. Fading channels may scatter transferred signal and initiate dependencies between scattered components, this might influence the channel estimation technique and therefore impact the SIC procedure and signal recognition precision. In our proposed scheme, the influence of Deep Neural Network (DNN) in clearly approximating the channel parameters for users in NOMA cell is inspected. In our scenario, we incorporate the Long Short Term Memory (LSTM) layer with NOMA cell where the LSTM is employed for complex data management to perform training and predication. The DNN is trained online on basis of random channel models and then the trained network is used to approximate the channel taps that will be utilized by the receiver in recovering the desired symbols. Additionally, power factors for user’s devices are optimized to maximize the sum-rate of users where whole power and Quality of service (QoS) restrictions are considered. Simulation outcomes in terms of Bit Error Rate (BER), Outage probability, and sum rate have shown the dominance of the suggested channel estimation using DL over standard estimation approach. Moreover, both fixed power and optimized power schemes are also assessed when DNN is applied.

The fourth Industrial Revolution is expected to lead to an era of technological innovation and digitization that would require connectivity by the users, anywhere and anytime. The fifth generation of wireless communication systems and the technologies therein are being explored to cater to high connectivity needs that encompass high data rates, very low latencies, energy‐efficient systems, etc. A multiuser environment is anticipated that would require multiple access techniques, such as Nonorthogonal Multiple Access (NOMA). The user data in the power domain NOMA is superimposed, at the transmitter base station, which is in turn subjected to Successive Interference Cancellation at the user end. In the multiuser downlink, the desired user’s signal is subjected to imperfect SIC due to incomplete cancellation of the undesired user’s signal. Pulse‐shaping of NOMA symbols using wavelet transform is proposed to mitigate the multiuser interference due to imperfect SIC. Closed‐form symbol error rate (SER) expression is derived for the wavelet NOMA system for a three‐user scenario. Analytical results show that wavelet transform pulse‐shaped NOMA performs better compared to Fourier transform pulse‐shaped NOMA symbols in mitigating SIC and thereby minimize the residual error due to imperfect SIC.

In a heterogeneous cellular network (HetNet), consider that a base station in the HetNet is able to simultaneously schedule and serve $K$ users in the downlink by performing the power-domain non-orthogonal multiple access (NOMA) scheme. This paper aims at the preliminary study on the downlink coverage and throughput performances of the HetNet with the non-coordinated NOMA and the proposed coordinated joint transmission NOMA (JT-NOMA) schemes. First, the coverage probability and link throughput of $K$ users in each cell are studied and their accurate expressions are derived for the non-coordinated NOMA scheme in which no BSs are coordinated to jointly transmit the NOMA signals for a particular user. We show that the coverage and link throughput can be largely reduced if transmit power allocations among the $K$ users do not satisfy the constraint derived. Next, we analyze the coverage and link throughput of $K$ users for the coordinated JT-NOMA scheme in which the void BSs without users are coordinated to enhance the farthest NOMA user in a cell. The derived accurate results show that coordinated JT-NOMA can significantly improve the coverage and link throughput of all users. Finally, we show that there exist optimal power allocation schemes that maximize the average cell coverage and throughput under some derived power allocation constraints and numerical results validate our analytical findings.

Non-orthogonal multiple access (NOMA) is a rapidly emerging paradigm with the capability to improve the spectral efficiency of data-driven, intelligence inspired, and highly digitized sixth-generation (6G) wireless networks. In the backdrop of ever-evolving NOMA techniques, this article presents a novel resource optimization framework for maximizing the spectral efficiency (SE) of the Internet-of-things (IoT) networks using power domain NOMA. The proposed framework considers a limited number of frequency blocks in the IoT network and provides an optimal power and frequency block allocation method. Different practical constraints like successive interference cancellation (SIC) complexity, ensuring the minimum gap of received power among different IoT equipment over the same frequency block for successful SIC operation, quality of services requirements, and IoT equipment's transmit powers have also been taken into account. Accordingly, a non-convex optimization problem has been formulated for resource management where the objective of spectral efficiency is coupled by both frequency block and power allocation. To effectively solve this problem, the resource optimization problem is decoupled into two subproblems for frequency block assignment and power allocation. A suboptimal algorithm has been designed for frequency block assignment and a new optimal sequential quadratic programming (SQP) approach is employed to solve the non-convex power control subproblem. For the sake of fair comparison, a low complexity suboptimal NOMA power allocation scheme, based on Karush-Kuhn-Tucker (KKT) conditions, and conventional orthogonal multiple access (OMA) scheme are also provided. The results demonstrate that the proposed optimal resource management scheme significantly improves the system performance compared to other schemes.

A novel power-domain non-orthogonal multiple access (NOMA) scheme with high-dimensional modulation is proposed. Signals for two users, each of which selected from a high-dimensional modulation constellation matrix, are superimposed on the same time-frequency resource for transmissions. While inter-user interference is treated as noise at the receiver of the far user, successive interference cancellation is used at the receiver of the near user. By analyzing the upper bounds of the detection errors, the power allocation factor is derived, which depends only on the relative power gain of the two users, i.e., the ratio between the squared of the two channel gains, but not on the operating signal-to-noise ratio. This nice feature allows us to perform user pairing easily for a system with more than two users. The optimal user pairing strategy that minimizes the total power consumption is analytically derived. Simulation results show that our proposed design outperforms some benchmark scheme.

In the current passive optical networks (PONs), we address the challenge of dealing with asymmetric channel conditions and asymmetric data rates in order to meet the traffic demand of optical network unit (ONU) to ONU (O2O) communications. A joint network-coding (NC) and power domain non-orthogonal multiple access (NOMA) approach (NC-NOMA) is discussed. The novelty of this NC-NOMA scheme lies in the way the inter-ONUs communicates with an optical line terminal (OLT) at different modulation formats. Specifically, in the uplink communications, at each ONU side, multiple data streams from different ONUs are superimposed into one single symbol. Meanwhile, NOMA is considered by adjusting the optical transmission power of ONUs such that the OLT can decode the signals from different ONUs based on successive interference cancellation (SIC). At the OLT side, the adding zeros approach at the specific positions of the shorter bit sequence is introduced. In the downlink communications, the ONUs obtain their own data by decoding the received messages. By applying NC-NOMA, the ONU with better channel condition only needs to demodulate the fictitious symbols with a low order modulation format instead of demodulating the symbols with a high order modulation format. The simulation results show NC-NOMA with hierarchical adding zeros approach outperforms NC-NOMA with traditional zero padding approach in terms of having lower average end-to-end BER of ONUs without having additional complexity.

In the fifth generation (5G) and beyond 5G (B5G) mobile communication, non-orthogonal multiple access (NOMA) has attracted great attention due to higher spectral efficiency and massive connectivity. We investigate the impacts of the channel estimation errors on the bit-error rate (BER) of NOMA, especially with the single-user decoding (SUD) receiver, which does not perform successive interference cancellation (SIC), in contrast to the conventional SIC NOMA scheme. First, an analytical expression of the BER for SUD NOMA with channel estimation errors is derived. Then, it is demonstrated that the BER performance degrades severely up to the power allocation less than about 20%. Additionally, we show that for the fixed power allocation of 10% in such power allocation range, the signal-to-noise (SNR) loss owing to channel estimation errors is about 5 dB. As a consequence, the channel estimation error should be considered for the design of the SUD NOMA scheme

ABSTRACTTo address the exploding traffic demands for mobile data, non-orthogonal multiple access (NOMA) schemes for resource allocation are considered as one of the potential candidates for future radio access. To this date, NOMA is implemented via orthogonal frequency division multiplexing (OFDM) for waveform shaping, which employs redundancy in the form of cyclic prefix (CP) and induces peak-to-average power ratio () problem. In this paper, wavelet OFDM (WOFDM) is proposed as a waveform shaping scheme for transceivers employing power domain NOMA for resource allocation. Since WOFDM-based systems do not use CP, they can reduce and increase spectral efficiency (SE). Link level performance of power domain NOMA with OFDM and WOFDM as waveform shaping techniques is evaluated in terms of , SE, and computational complexity (CC). In addition, power spectral densities of both transceivers are also analyzed. Simulation results show that NOMA with WOFDM outperforms NOMA with OFD in terms of reduction, out of band emissions reduction, SE, and CC.

In this paper, we investigate the impact of channel coding on two kinds of non-orthogonal multiple access (NOMA) schemes, either with a successive interference cancellation (SIC) receiver or with a joint decoding (JD) receiver. Firstly, the information-theoretic individual achievable signal-to-noise ratio (SNR) regions of SIC and JD are analyzed. Then single-user-oriented (SU) code and multi-users-oriented (MU) code are considered for SIC and JD, and the practical individual achievable SNR regions of SIC and JD with these two kinds of channel codes are obtained, which provides an intuitive way to evaluate system performance under different channel conditions and transmission rates. Simulation results show that, the practical boundaries of individual achievable SNR region of SIC generally lie inside the boundaries of JD, as predicted by the theoretical analysis. Moreover, SU code, which is capacity-approaching over point-to-point channel, performs better than MU code for SIC, while the choice of channel codes for JD depends on transmission rates and channel conditions.