Successive Interference Cancellation Decoding Order Research Articles

Secure wireless communications for STAR‐RIS‐assisted millimetre‐wave NOMA uplink networks

AbstractThis paper explores the potential application of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR‐RIS) in improving the physical layer security (PLS) of millimetre wave (mmWave) non‐orthogonal multiple access (NOMA) uplink communications. In particular, the legitimate users on both sides of STAR‐RIS send confidential information simultaneously to the base station (BS) while keeping it secret from the eavesdroppers near the BS by exploiting the STAR‐RIS to proactively regulate the electromagnetic propagation environment. By jointly designing the transmit power, the active beamforming at the BS, and the reflecting/transmitting coefficients at the STAR‐RIS, the authors' goal is to maximize the minimum secrecy capacity subject to the successive interference cancellation decoding order constraints. Due to the non‐convexity of the formulated problem, an efficient algorithm is proposed by capitalizing on alternating optimization, a penalty‐based approach, successive convex approximation, and semi‐definite relaxation. Firstly, a two‐layer iterative algorithm based on the penalty for the joint beamforming optimization sub‐problem is proposed. Then, the non‐convex problem is transformed into a convex positive semi‐definite programming problem for the transmit power sub‐problem. Numerical simulation results reveal that the STAR‐RIS‐aided system has more tremendous advantages and effectiveness in improving the PLS of mmWave NOMA uplink communication compared with the benchmark schemes.

Learning-Assisted Energy Minimization for MEC Systems With Noncompletely Overlapping NOMA

This article investigates the long-term energy minimization of mobile edge computing (MEC) systems with multiuser noncompletely overlapping nonorthogonal multiple access (NOMA) when time varying channel is considered. Different from the existing work with multiuser noncompletely overlapping NOMA that adopted the delay-based successive interference cancellation (SIC) decoding order, we adopt the channel gain-based SIC decoding order, which is widely used and has been proved to be more energy-efficient. We formulate the problem as a joint transmit power, transmission time, and computing resource optimization problem with multiple deeply coupled variables. To ensure the real-time decision-making, the considered problem is characterized as a deep reinforcement learning (DRL) problem by introducing penalty mechanism into the immediate reward function when the constraints are violated, and we propose a soft actor-critic (SAC) algorithm to solve it. Simulations show that the proposed algorithm can significantly improve the system's performance, and, compared with the noncompletely overlapping NOMA mechanism with delay-based SIC decoding order, the completely overlapping NOMA mechanism and time division multiple access (TDMA) mechanism, the noncompletely overlapping NOMA mechanism with channel gain-based SIC decoding order can achieve an average energy consumption reduction of 32.4%, 49.9%, and 74.4%, respectively.

Outage Performance Analysis of RSMA-Aided Semi-Grant-Free Transmission Systems

In this paper, we analyze the outage performance of a rate-splitting multiple access (RSMA)-aided semi-grant-free (SGF) transmission system, in which a grant-based user (GBU) and multiple grant-free users (GFUs) access the base station by sharing the same resource blocks. In the RSMA-aided SGF (RSMA-SGF) transmission system, the GBU and admitted GFU are respectively treated as the primary and secondary users by using the cognitive radio principle. With the aid of RSMA, the admitted GFU’s transmit power allocation, target rate allocation, and successive interference cancellation decoding order are jointly optimized to attain the maximum achievable rate for the admitted GFU, without deteriorating the GBU’s outage performance compared to orthogonal multiple access. Taking into account the extended non-outage zone achieved by rate-splitting, a closed-form expression is derived for the outage probability of the admitted GFU in the considered RSMA-SGF system. Asymptotic analysis for the admitted GFU’s outage probability is also provided. The superior outage performance and full multiuser diversity gain achieved by the RSMA-SGF transmission system are verified by the analytical and simulation results.

Performance comparison of successive interference cancellation decoding order for base station association and power control in small cell networks incorporating handoff optimization

The co-channel interference and frequent handoff are two important issues that have a great impact on the spectrum and energy efficiency in the non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC) in the small cell networks (SCN). This paper investigates the performance of SIC decoding order based on the users’ channel state information (CSI) and random SIC decoding order under the perfect and imperfect conditions for the handoff optimization in SCNs with NOMA. The effect of SIC decoding order in the joint base station association and power control problem is studied by considering the motion of mobile users (MUs). Two optimization problems are formulated using the number of associated MUs, the number of handoffs, and the transmit power of all MUs, under the maximum allowable transmit power and minimum average-rate constraints. Two objectives are combined into a single-stage optimization problem through the weighted sum method. The formulated problem is solved using a game theory-based algorithm and primal decomposition theory. The simulation results show that changing the SIC decoding order can lead to performance improvement in the uplink NOMA- based SCNs. Also, it is shown that the proposed algorithm can significantly reduce the frequent handoffs in small cell networks.

On the Secrecy Design of STAR-RIS Assisted Uplink NOMA Networks

This paper investigates the secure transmission in a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted uplink non-orthogonal multiple access system, where the legitimate users send confidential signals to the base station by exploiting STAR-RIS to reconfigure the electromagnetic propagation environment proactively. Depending on the availability of the eavesdropping channel state information (CSI), both the full CSI and statistical CSI of the eavesdropper are considered. For the full eavesdropping CSI scenario, we adopt the adaptive-rate wiretap code scheme with the aim of maximizing minimum secrecy capacity subject to the successive interference cancellation decoding order constraints. To proceed, we propose an alternating hybrid beamforming (AHB) algorithm to jointly optimize the receive beamforming, transmit power, and reflection/transmission coefficients. While for the statistical eavesdropping CSI scenario, the constant-rate wiretap code scheme is employed to minimize the maximum secrecy outage probability (SOP) subject to the quality-of-service requirements of legitimate users. Then, we derive the exact SOP expression under the constant-rate coding strategy and develop an extended AHB algorithm for the joint secrecy beamforming design. Simulation results demonstrate the effectiveness of the proposed scheme. Moreover, some useful guidance about the quantification of phase shift/amplitude and the deployment of STAR-RIS is provided.

Intelligent reflecting surface-assisted cognitive radio-inspired rate-splitting multiple access systems

Intelligent reflecting surface (IRS) has been widely regarded as a promising technology for configuring wireless propagation environments. In this paper, we utilize IRS to assist transmission of a secondary user (SU) in a cognitive radio-inspired rate-splitting multiple access (CR-RSMA) system in which a primary user's (PU's) quality of service (QoS) requirements must be guaranteed. Without introducing intolerable interference to deteriorate the PU's outage performance, the SU conducts rate-splitting to transmit its signal to the base-station through the direct link and IRS reflecting channels. For the IRS-assisted CR-RSMA (IRS-CR-RSMA) scheme, we derive the optimal transmit power allocation, target rate allocation, and successive interference cancellation decoding order to enhance the outage performance of the SU. The closed-form expression for the SU's outage probability achieved by the IRS-CR-RSMA scheme is derived. Various simulation results are presented to clarify the enhanced outage performance achieved by the proposed IRS-CR-RSMA scheme over the CR-RSMA scheme.

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%.

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.

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.

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.

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.

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.

User Clustering in mmWave-NOMA Systems With User Decoding Capability Constraints for B5G Networks

This article proposes a millimeter wave-NOMA (mmWave-NOMA) system that takes into account the end-user signal processing capabilities, an important practical consideration. The implementation of NOMA in the downlink (DL) direction requires successive interference cancellation (SIC) to be performed at the user terminals, which comes at the cost of additional complexity. In NOMA, the weakest user only has to decode its own signal, while the strongest user has to decode the signals of all other users in the SIC procedure. Hence, the additional implementation complexity required of the user to perform SIC for DL NOMA depends on its position in the SIC decoding order. Beyond fifth-generation (B5G) communication systems are expected to support a wide variety of end-user devices, each with their own processing capabilities. We envision a system where users report their SIC decoding capability to the base station (BS), i.e., the number of other users signals a user is capable of decoding in the SIC procedure. We investigate the rate maximization problem in such a system, by breaking it down into a user clustering and ordering problem (UCOP), followed by a power allocation problem. We propose a NOMA-minimum exact cover (NOMA-MEC) heuristic algorithm that converts the UCOP into a cluster minimization problem from a derived set of valid cluster combinations after factoring in the SIC decoding capability. The complexity of NOMA-MEC is analyzed for various algorithm and system parameters. For a homogeneous system of users that all have the same decoding capabilities, we show that this equates to a simple maximum number of users per cluster constraint and propose a lower complexity NOMA-best beam (NOMA-BB) algorithm. Simulation results demonstrate the performance superiority in terms of sum rate compared to orthogonal multiple access (OMA) and traditional NOMA clustering schemes that do not incorporate individual users’ SIC decoding capability constraints.

Jamming-Assisted Legitimate Surveillance of Suspicious Interference Networks With Successive Interference Cancellation

This letter investigates legitimate surveillance of a suspicious interference network in the presence of a full-duplex monitor. To improve the surveillance performance, jamming from the monitor is applied to interfere with the suspicious users and successive interference cancellation (SIC) decoder is equipped at the monitor to better decode signals from multiple suspicious users. To maximize the number of successfully eavesdropped suspicious users, the jamming power as well as the SIC decoding order at the monitor are optimized. By exploring the particular problem structure, high-complexity optimal and low-complexity suboptimal algorithms are proposed. It is shown that the suboptimal algorithm is practically optimal and the proposed algorithms outperform the benchmark algorithms with conventional SIC decoding order.

Design and Analysis of Probabilistic Shaping Scheme for Uplink Nonorthogonal Multiple Access Systems

Probabilistic shaping (PS) combined with bipolar amplitude shift keying modulation is a promising transmission scheme to increase spectral efficiency. Different from the existing design of the point to point communications, we propose a PS-based uplink nonorthogonal multiple access (NOMA) scheme for fading channels to support multiple connections simultaneously, where successive interference cancellation (SIC)-based maximum a posterior (MAP) detection is implemented at the receiver. To exploit the shaping gain for each user, we first theoretically analyze the ergodic channel capacity and the constellation constrained (CC) capacity with discrete-constellation inputs, respectively. And then, a multi-step optimization scheme for maximizing the ergodic CC capacity is proposed to obtain the optimal probability mass function (PMF) of these input signals. The order of optimization is inverse to the SIC decoding order so that for each specific user, the remaining multiuser interference is calculated based on the optimal PMF of the later decoded users. Furthermore, based on this non-equiprobable transmission scheme, the closed-form pairwise error probability expressions for each user are obtained for the first time. Finally, compared with the uniform scheme, the simulations show that the proposed PS NOMA strategies achieve more than 1 dB gain in terms of the error performance.

Resource Allocation for D2D Communications Underlaying a NOMA-Based Cellular Network

This letter investigates the power control and channel assignment problem in device-to-device (D2D) communications underlaying a non-orthogonal multiple access (NOMA) cellular network. With the successive interference cancellation decoding order constraints, our target is to maximize the sum rate of D2D pairs while guaranteeing the minimum rate requirements of NOMA-based cellular users. Specifically, the optimal conditions for power control of cellular users on each subchannel are derived first. Then, based on these results, we propose a dual-based iterative algorithm to solve the resource allocation problem. Simulation results validate the superiority of proposed resource allocation algorithm over the existing orthogonal multiple access scheme.

Individual secrecy of fading homogeneous multiple access wiretap channel with successive interference cancellation

We investigate individual secrecy performance in a K-user quasi-static Rayleigh fading homogeneous multiple access wiretap channel (MAC-WT), where a legitimate receiver employs successive interference cancellation (SIC) decoding. We first evaluate individual secrecy performance under an arbitrary SIC order by deriving closed-form expressions with respect to secrecy outage probability and effective secrecy throughput (EST) as main metrics. The resulting closed-form expressions disclose a significant impact on the secrecy performance from the order of SIC decoding. Therefore, we propose three SIC decoding order scheduling schemes: (1) round-robin scheme, absolutely fair and served as a benchmark; (2) suboptimal scheme, based on each user’s main channel condition; and (3) optimal scheme, based on each user’s achievable secrecy rate. Comparison results show that the last two schemes outperform the first one with regard to both the EST and the multi-user diversity gain, whereas the performance of the suboptimal scheme is highly close to that of the optimal scheme which is usually impractical due to a requirement for the eavesdropper’s channel state information (CSI).

The mine locomotive wireless network strategy based on successive interference cancellation with dynamic power control

Mine locomotives are widely used in mining industry for transporting. Usually, these locomotives need to move along the tunnels and communicate with access points which are equipped on the side of these tunnels. It is important to maintain high-quality communication services due to the unsafe underground working environment. In this article, we design the mine locomotive wireless network strategy based on successive interference cancellation with dynamical power control. We first divide the whole schedule time into time segments and build the problem model in each time segment. To maximize throughput for each time segment, we formulate a linear programming problem based on certain features of successive interference cancellation decoding order. However, this problem has lots of constraints which makes it hard to solve in polynomial time. Then, we propose a concept of the maximum successive interference cancellation set to reduce the problem size. Based on this concept, we propose a polynomial complexity algorithm named max-SIC-set algorithm. Simulation results show that our algorithm can increase throughput significantly compared with the algorithm using successive interference cancellation only (no power control) and with the algorithm without using successive interference cancellation and power control.