Successive Interference Cancellation Decoding Research Articles

Energy-Efficient Resource Allocation for 6G Backscatter-Enabled NOMA IoV Networks

The integration of Ambient Backscatter Communication (AmBC) with Non-Orthogonal Multiple Access (NOMA) is expected to support connectivity of low-powered Internet-of-Vehicles (IoVs) in the upcoming Sixth-Generation (6G) transportation systems. This paper proposes an energy-efficient resource allocation framework for the AmBC-enabled NOMA IoV network under imperfect Successive Interference Cancellation (SIC) decoding. In particular, multiple Road-Side Units (RSUs) transmit superimposed signals to their associated IoVs utilizing downlink NOMA transmission. Meanwhile, the Backscatter Tags (BackTags) also transmit data symbols towards nearby IoVs by reflecting the superimposed signals of RSUs. Thus, the objective is to maximize the total energy efficiency of the NOMA IoV network subject to the minimum data rate of all IoVs. A joint problem that simultaneously optimizes the total power budget of each RSU, power allocation coefficient of IoVs and reflection power of BackTags under imperfect SIC decoding is formulated. A Dinkelbach approach is first adopted to transform the optimization problem and then the transformed problem is decoupled into two subproblems for optimal transmit power at RSUs and efficient reflection power at BackTags, respectively. To solve the problems efficiently, dual theory and Karush-Kuhn-Tucker conditions are exploited, where the Lagrangian dual variables are iteratively calculated using the subgradient method. To check the performance of the proposed framework, a benchmark optimization without AmBC is also provided. Numerical results demonstrate the superiority of the proposed AmBC-enabled NOMA IoV framework over the benchmark conventional IoV framework.

Full-duplex cooperative uplink NOMA with adaptive decoding order

In this paper, a full-duplex (FD) cooperative uplink (UL) non-orthogonal multiple access (NOMA) network is studied, where a far user communicates with a base station via a direct link and user relaying. It is assumed that there exist randomly located M users in the vicinity wishing to share the same spectrum, one of which is selected and paired with far user by maxmin selection. The analytical derivations are performed for the outage probabilities of both users when three successive interference cancellation (SIC) schemes are adopted: channel state information (CSI)-based, quality of service (QoS)-based and hybrid SIC. The main issue in UL-NOMA networks is the inevitable error floor in the selected user's performance curves at high signal-to-noise ratio region. The hybrid SIC eliminates the error floor by adaptively changing the SIC decoding order and provides robustness to self-interference due to FD, in terms of selected user's outage performance, unlike the CSI-based and QoS-based SIC. It is shown that the selected user's performance can be further improved by power allocation besides the improved performance of far user by cooperation. The superiority of the hybrid SIC protocol for UL-FD-NOMA over reference half-duplex (HD) NOMA and OMA is demonstrated. Moreover, the results show that the performance of both users improves with increasing M.

Joint Beamforming Design and Power Splitting Optimization in IRS-Assisted SWIPT NOMA Networks

This paper proposes a novel network framework of intelligent reflecting surface (IRS)-assisted simultaneous wireless information and power transfer (SWIPT) non-orthogonal multiple access (NOMA) networks, where IRS is used to enhance the NOMA performance and the wireless power transfer (WPT) efficiency of SWIPT. We formulate a problem of minimizing base station (BS) transmit power by jointly optimizing successive interference cancellation (SIC) decoding order, BS transmit beamforming vector, power splitting (PS) ratio and IRS phase shift while taking into account the quality-of-service (QoS) requirement and energy harvested threshold of each user. The formulated problem is non-convex optimization problem, which is difficult to solve it directly. Hence, a two-stage algorithm is proposed to solve the above-mentioned problem by applying semidefinite relaxation (SDR), Gaussian randomization and successive convex approximation (SCA). Specifically, after determining SIC decoding order by designing IRS phase shift in the first stage, we alternately optimize BS transmit beamforming vector, PS ratio, and IRS phase shift to minimize the BS transmit power. Numerical results validate the effectiveness of our proposed optimization algorithm in reducing BS transmit power compared to other baseline algorithms. Meanwhile, compared with non-IRS-assisted network, the IRS-assisted SWIPT NOMA network can decrease BS transmit power by 51.13%.

Successive Interference Cancellation Decoding With Adaptable Decision Regions for NOMA Schemes

In this work, we propose adaptable decision regions in the successive interference cancellation (SIC) decoder for the three-user uplink/downlink non-orthogonal multiple access (NOMA) scheme by exploiting the knowledge of the channel gains. We present scenarios in which the modified SIC decoder outperforms the traditional one and is able to replicate the performance achieved by a deep learning-based decoder. We present analytical symbol error rate (SER) expressions for the three users, compare them to simulation results, and discuss possible consequences of our analysis, such as the optimal power allocation. We also employ heatmaps to analyze the joint influence on the SER of some system parameters, such as signal-to-noise ratio and channel gains.

Efficient Resource Allocation for Wireless-Powered MIMO-NOMA Communications

Wireless-powered communication (WPC) is a promising technology for varied smart network applications in the industrial, commercial, and security sectors. It employs a large number of connected low-powered user equipments (UEs) in which the harvested energy from electromagnetic radiations is used for signal transmission. However, efficient resource allocation schemes are still required to optimize the performance of WPC networks over limited power and spectrum environments. In this paper, a new approach of wireless-powered multiple-input multiple-output non-orthogonal multiple access (WP-MIMO-NOMA) is designed by employing harvest-then-transmit protocol with joint time-split and power control (TS-PC) techniques to optimize the network performance and lifetime with affordable complexity. We derive the sum rate, UEs’ rates, and rate region expressions based on power-domain NOMA and successive interference cancellation (SIC) decoding. An optimal joint TS-PC (OJTS-PC) scheme is proposed to maximize the network sum rate with enhanced user-fairness under constrained harvested energy level, uplink transmit power, and minimum UE’s rate. Besides, a near-optimal greedy TS-PC (GTS-PC) algorithm is designed to reduce computational efforts significantly. For comparison, we derive the rate expressions for the reference WP-MIMO-OMA system based on orthogonal frequency-division multiple access (OFDMA) and time-division multiple access (TDMA). Numerical results validate the effectiveness of proposed resource allocation schemes in terms of realized sum rate, UE’s rate, and user-fairness without scarifying the limited power of far UEs. This will prolong the lifetime of WPC networks operating over constrained power and bandwidth resources.

Joint Multi-User Decoding for Polar-Coded Uplink Non-Orthogonal Multiple Access Systems

Polar-coded non-orthogonal multiple access (NOMA) is a competitive candidate for future wireless physical layer access techniques. The conventional NOMA system employs successive interference cancellation (SIC) for signal decoding. The SIC decoding procedure is optimal only when the code length is sufficiently long. Transmissions with long codes may undergo channel fluctuations. Considering the channel fluctuations, we propose a joint multi-user successive cancellation decoding algorithm for the polar-coded uplink NOMA system. It is shown by simulation results that the proposed joint multi-user decoding algorithm is robust to channel fluctuations.

QoS-Aware User Grouping Strategy for Downlink Multi-Cell NOMA Systems

In multi-cell non-orthogonal multiple access (NOMA) systems, designing an appropriate user grouping strategy is an open problem due to diverse quality of service (QoS) requirements and inter-cell interference. In this paper, we exploit both game theory and graph theory to study QoS-aware user grouping strategies, aiming at minimizing power consumption in downlink multi-cell NOMA systems. Under different QoS requirements, we derive the optimal successive interference cancellation (SIC) decoding order with inter-cell interference, which is different from existing SIC decoding order of increasing channel gains, and obtain the corresponding power allocation strategy. Based on this, the exact potential game model of the user grouping strategies adopted by multiple cells is formulated. We prove that, in this game, the problem for each player to find a grouping strategy can be converted into the problem of searching for specific negative loops in the graph composed of users. Bellman-Ford algorithm is expanded to find these negative loops. Furthermore, we design a greedy based suboptimal strategy to approach the optimal solution with polynomial time. Extensive simulations confirm the effectiveness of grouping users with consideration of QoS and inter-cell interference, and show that the proposed strategies can considerably reduce total power consumption comparing with reference strategies.

Switching Signal Decoding Order in Uplink NOMA System With Imperfect SIC

The decoding order of successive interference cancelation (SIC) is a key issue in SIC implementation for non-orthogonal multiple access (NOMA) systems. This letter focuses on the dynamic SIC decoding order and proposes a switching SIC scheme, which dynamically determines the SIC order according to the ratio of the instantaneous received power to target data rate of each user. The outage performance is theoretically analyzed for our proposed scheme under the imperfect SIC conditions. Both the analysis and simulation demonstrate the effectiveness of our proposed scheme. It avoids searching possible SIC orders but achieves almost the same outage performance as the ideal exhaustive-search-SIC that considers all possible SIC orders to decode a signal.

Optimal SIC Decoding Order and WPT Time Length for WPCN With Imperfect SIC

Wireless Power Transfer (WPT) and Non-Orthogonal Multiple Access (NOMA) are two emerging technologies towards next generation wireless networks. In this letter we assume the integration of those two technologies in Wireless Powered Communication Network (WPCN). We evaluate the impact of WPT time length and Successive Interference Cancellation (SIC) decoding order for an arbitrary number of terminals by assuming imperfect SIC. The optimal solution can be obtained by optimization solvers whereas a suboptimal solution is conceived based on analytical insights. Numerical results show that the decoding order is relevant for spectral efficiency maximization when imperfect SIC is assumed. Also, the proposed low-complexity solution shows a quasi-optimal performance.

Correlated Superposition Coding: Lossless Two-User NOMA Implementation Without SIC Under User-Fairness

Non-orthogonal multiple access (NOMA) has a larger achievable sum rate than orthogonal multiple access (OMA). This superiority is achieved via superposition coding (SC) and successive interference cancellation (SIC). In this letter, the authors propose a lossless NOMA implementation without SIC. This implementation is achieved via correlated SC (CSC), in contrast to conventional independent SC (ISC). In addition, correlated non-SIC decoding is performed, in contrast to conventional SIC decoding. Using the random channel coding theorem, we prove that the conditional achievable sum rate given channel gain realizations in the conventional ISC/SIC NOMA scheme can be achieved without SIC, without loss, over the power allocation range of user-fairness.

BER analysis of NOMA with max-min relay selection

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.

DRL-Assisted Resource Allocation for NOMA-MEC Offloading with Hybrid SIC.

Multi-access edge computing (MEC) and non-orthogonal multiple access (NOMA) are regarded as promising technologies to improve the computation capability and offloading efficiency of mobile devices in the sixth-generation (6G) mobile system. This paper mainly focused on the hybrid NOMA-MEC system, where multiple users were first grouped into pairs, and users in each pair offloaded their tasks simultaneously by NOMA, then a dedicated time duration was scheduled to the more delay-tolerant user for uploading the remaining data by orthogonal multiple access (OMA). For the conventional NOMA uplink transmission, successive interference cancellation (SIC) was applied to decode the superposed signals successively according to the channel state information (CSI) or the quality of service (QoS) requirement. In this work, we integrated the hybrid SIC scheme, which dynamically adapts the SIC decoding order among all NOMA groups. To solve the user grouping problem, a deep reinforcement learning (DRL)-based algorithm was proposed to obtain a close-to-optimal user grouping policy. Moreover, we optimally minimized the offloading energy consumption by obtaining the closed-form solution to the resource allocation problem. Simulation results showed that the proposed algorithm converged fast, and the NOMA-MEC scheme outperformed the existing orthogonal multiple access (OMA) scheme.

Backscatter-Enabled NOMA for Future 6G Systems: A New Optimization Framework Under Imperfect SIC

This letter proposes a new optimization framework for power-domain non-orthogonal multiple access (PD-NOMA) ambient backscatter communication (AmBC) system with imperfect successive interference cancellation (SIC) decoding. In particular, we jointly optimize the transmit power of the source and the reflection coefficient of the backscatter tag to enhance the sum-rate of the system. Closed-form solutions are derived for the considered joint optimization problem via iteratively computing the Lagrange multipliers by the sub-gradient method. Simulation results validate the superiority of the proposed joint optimization framework over other benchmark frameworks, namely suboptimal PD-NOMA AmBC, optimal pure PD-NOMA, and orthogonal multiple access.

Asynchronous Transmission for Multiple Access Channels: Rate-Region Analysis and System Design for Uplink NOMA

In this work, we thoroughly analyze the rate-region provided by the asynchronous transmission in multiple access channels (MACs). We derive the corresponding capacity-regions, applicable to a wide range of pulse shaping methods. We analytically prove that asynchronous transmission enlarges the capacity-region of MACs. Although successive interference cancellation (SIC) can achieve the optimal sum-rate for the conventional uplink non-orthogonal multiple access (NOMA) methods, it is unable to achieve the boundary of the capacity-region for the asynchronous transmission. We demonstrate that for the asynchronous transmission, the optimal SIC decoding order to achieve the maximum sum-rate is based on the users' channel strengths. This optimal ordering is in contrast to the conventional uplink NOMA, where various decoding orders can result in the maximum sum-rate. Furthermore, we provide practical transceiver designs to approach the capacity-region. The memory induced by asynchronous transmission enables the use of the trellis-based detection methods which improves the performance. In addition, we propose a transceiver design, based on channel diagonalization to exploit the frequency-selectivity introduced by timing offsets. The proposed transceiver design, joint with the turbo principle, enables us to achieve a rate pair that is not achievable by the synchronous transmission.

NOMA for Multiple Access Channel and Broadcast Channel in Indoor VLC

Orthogonal frequency division multiplexing (OFDM) based non-orthogonal multiple access (NOMA) has increased complexity and reduced spectral efficiency in visible light communications (VLC) NOMA compared to radio-frequency NOMA due to non-negative real value constraint on transmit symbols. To address this issue, we propose a generalized non-OFDM based scheme for two scenarios of indoor VLC; i) Multiple access channel (MAC), ii) Broadcast channel (BC). We evaluate the performance of the proposed scheme for MAC using successive interference cancellation (SIC) based decoding, joint maximum likelihood (JML) decoding, and a combination of SIC and JML decoding. For BC, we evaluate the performance using SIC based decoding. It is observed that, for MAC, the proposed scheme with JML decoding performs better than the state-of-the-art orthogonal multiple access both in terms of bit error rate (BER) and computations. For BC, the proposed scheme is computationally efficient with trade-off on BER.

A Note on Decoding Order in User Grouping and Power Optimization for Multi-Cell NOMA With Load Coupling

In this technical note, we present a new theoretical result for multi-cell non-orthogonal multiple access (NOMA). For multi-cell scenarios, a so-called load-coupling model has been proposed earlier to characterize the presence of mutual interference for NOMA, and the optimization process relies on the use of fixed-point iterations across cells. One difficulty here is that the order of decoding for successive interference cancellation (SIC) in NOMA is generally not known a priori. This is because the decoding order in one cell depends on interference, which, in turn, is governed by resource usage in other cells, and vice versa. To achieve convergence, previous works have used workarounds that pose restrictions to NOMA, such that the SIC decoding order remains throughout the fixed-point iterations. As a comment to the previous works, we derive and prove the following result: The convergence is guaranteed, even if the order changes over the iterations. The result not only waives the need of previous workarounds, but also implies that a wide class of optimization problems for multi-cell NOMA is tractable, as long as that for single cell is.

Proactive Eavesdropping of Suspicious Non-Orthogonal Multiple Access Networks

In this correspondence, legitimate surveillance of a downlink suspicious non-orthogonal multiple access (NOMA) network with multiple groups of suspicious users (SUs), in the presence of a full-duplex monitor equipped with a successive interference cancellation (SIC) decoder, is investigated. Proactive eavesdropping is adopted, i.e., the monitor simultaneously eavesdrops the suspicious communications, and sends jamming signals. The problem of maximizing the number of successfully eavesdropped SUs by jointly optimizing the jamming power allocation and the decoding order at the monitor is investigated considering both imperfect full-duplex self-interference cancellation, and imperfect SIC. By exploring the particular problem structure, a heuristic iterative algorithm is proposed, where the optimal decoding at the monitor is proved to be equal to that at the SUs. Extensive simulations confirm that the proposed algorithm achieves performance very close to the optimal one but with significantly lower complexity, and outperforms various benchmark algorithms.

Partial Non-Orthogonal Multiple Access (NOMA) in Downlink Poisson Networks

Non-orthogonal multiple access (NOMA) allows users sharing a resource-block to efficiently reuse spectrum and improve cell sum rate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {R}_{\mathrm{ tot}}$ </tex-math></inline-formula> at the expense of increased interference. Orthogonal multiple access (OMA), on the other hand, guarantees higher coverage. We introduce partial-NOMA in a large two-user downlink network to provide both throughput and reliability. The associated partial overlap controls interference while still offering spectrum reuse. The nature of the partial overlap also allows us to employ receive-filtering to further suppress interference. For signal decoding in our partial-NOMA setup, we propose a new technique called flexible successive interference cancellation (FSIC) decoding. We plot the rate region abstraction and compare with OMA and NOMA. We formulate a problem to maximize <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {R}_{\mathrm{ tot}}$ </tex-math></inline-formula> constrained to a minimum throughput requirement for each user and propose an algorithm to find a feasible resource allocation efficiently. Our results show that partial-NOMA allows greater flexibility in terms of performance. Partial-NOMA can also serve users that NOMA cannot. We also show that with appropriate parameter selection and resource allocation, partial-NOMA can outperform NOMA.

Unveiling the Importance of SIC in NOMA Systems—Part 1: State of the Art and Recent Findings

The key idea of non-orthogonal multiple access (NOMA) is to serve multiple users simultaneously at the same time and frequency, which can result in excessive multiple-access interference. As a crucial component of NOMA systems, successive interference cancelation (SIC) is key to combating this multiple-access interference, and is the focus of this letter, where an overview of SIC decoding order selection schemes is provided. In particular, selecting the SIC decoding order based on the users' channel state information (CSI) and the users' quality of service (QoS), respectively, is discussed. The limitations of these two approaches are illustrated, and then a recently proposed scheme, termed hybrid SIC, which dynamically adapts the SIC decoding order is presented and shown to achieve a surprising performance improvement that cannot be realized by the conventional SIC decoding order selection schemes individually.

Sum-rate maximization and data delivery for wireless seismic acquisition

Traditional seismic acquisition systems suffer from a number of difficulties related to telemetry cables that are used as a means of data transmission. Transforming the traditional seismic acquisition system to a wireless system has been considered as a potential solution to most of these difficulties. The wireless seismic acquisition system has to serve a huge aggregate data rate requirement as is usually the case in a large wireless sensor network. This paper considers the wireless acquisition system, and studies the maximum achievable transmission data rates from the geophones to the wireless gateways. Successive interference cancellation decoding is assumed to be used at the gateway nodes. We consider the problem of sum-rate maximization by optimizing the decoding process at each gateway node. The optimization searches for optimal decoding set at each gateway, i.e. which group of geophones will be decoded at each gateway. Various integer programming algorithms are proposed for solving the maximization problem. These optimization algorithms are simulated and compared among each other, where it is shown that the ant system algorithm achieves the highest sum-rate with lower computational complexity compared to other algorithms. Furthermore, the data delivery from the gateways to the data center is also considered. In this stage, two gateways with different buffer sizes are studied. For small-size buffers, two optimization problems are identified and solved. The first problem considers the minimization of the total power of the gateways, and the second problem considers power fairness between the gateways. For large-size buffers, the problem of maximizing the weighted sum rate of the gateways is solved.