Reconfigurable intelligent surfaces (RISs) and nonorthogonal multiple access (NOMA) have been recognized as key enabling techniques for the envisioned sixth generation (6G) of mobile communication ...networks. The key feature of RISs is to intelligently reconfigure the wireless propagation environment, which was once considered to be fixed and untunable. The key idea of NOMA is to utilize users' dynamic channel conditions to improve spectral efficiency and user fairness. Naturally, the two communication techniques are complementary to each other and can be integrated to cope with the challenging requirements envisioned for 6G mobile networks. This survey provides a comprehensive overview of the recent progress on the synergistic integration of RISs and NOMA. In particular, the basics of both techniques are introduced first, and then, the fundamentals of RIS-NOMA are discussed for two communication scenarios with different transceiver capabilities. Resource allocation is of paramount importance for the success of RIS-assisted NOMA networks, and various approaches, including artificial intelligence (AI)-empowered designs, are introduced. Security provisioning in RIS-NOMA networks is also discussed as wireless networks are prone to security attacks due to the nature of the shared wireless medium. Finally, the survey is concluded with detailed discussions of the challenges arising in the practical implementation of RIS-NOMA, future research directions, and emerging applications.
This letter proposes a novel hybrid half-duplex (HD)/full-duplex (FD) relaying scheme to enhance the relay channel security. A source node (Alice) communicates with her destination node (Bob) in the ...presence of a buffer-aided FD relay node (Rooney) and a potential eavesdropper (Eve). Rooney adopts two different relaying strategies, namely, randomize-and-forward and decode-and-forward relaying, to improve the security of the legitimate system. In the first relaying strategy, Rooney uses a codebook different from that used at Alice. In the second relaying strategy, Rooney and Alice use the same codebooks. In addition, Rooney switches between the HD and FD modes to further enhance the security of the legitimate system. The numerical results demonstrate that our proposed scheme achieves a significant average secrecy end-to-end throughput improvement relative to the conventional bufferless FD relaying scheme.
Narrowband powerline communications (NB-PLC) and unlicensed wireless communications are two leading communications technologies for the emerging smart grid applications. The channel and noise ...statistics experienced by powerline and wireless transmissions are independent and of a non-identical nature. In this paper, we exploit the diversity provided by the simultaneous transmission of the same information signal over powerline and wireless links to enhance the overall system reliability. In particular, we propose efficient techniques to combine the received signals of the NB-PLC and wireless links for both coherent and differential modulation schemes while considering the impulsive nature of the noise on both links. In addition, we derive closed-form expressions for the average bit-error-rate of the proposed combining techniques. Furthermore, we present simulation results that quantify the performance gains achieved by our proposed receive diversity combining techniques compared with conventional combining techniques.
Investigating the physical layer security performance of full-duplex (FD) radio transceivers has been the subject of numerous research studies. However, self-interference cancellation that enables ...full exploitation of FD communications is a crucial aspect that deserves special attention. Hence, in this paper, we analyze the effect of a FD transceiver's in-phase and quadrature imbalance (IQI) on simultaneously jamming the receiver of an eavesdropper and detecting a signal of interest by deriving an expression for the secrecy outage probability (SOP) metric. Through further analysis for some special and limiting cases, performance insights are drawn by showing that the SOP is dependent on the image rejection capability of the FD transceiver and is approximately equal to <inline-formula><tex-math notation="LaTeX">\frac{3}{\text{IRR}}(\ln {(\text{IRR})} - 1.83)</tex-math></inline-formula>, where the IRR is the image-rejection ratio. The accuracy of the derived SOP expression is verified through Monte-Carlo simulations.
In this paper, we present a novel approach based on compressive sensing theory to estimate and mitigate asynchronous narrow-band interference (NBI) in orthogonal frequency division multiplexing ...systems with multiple transmit and/or multiple receive antennas. We consider the practical scenarios where one or multiple asynchronous NBI signals experience fast fading and/or frequency-selective fading channels. Furthermore, we propose a novel technique for estimating the desired signal's channel in the presence of unknown NBI. Our approach does not require any prior information about the NBI. Simulation results demonstrate the effectiveness of our proposed techniques in mitigating NBI and approaching the interference-free performance limit over practical ranges of NBI power levels, spectral widths, and mobility levels.
In recent years, radar emitter signal recognition has enjoyed a wide range of applications in electronic support measure systems and communication security. More and more deep learning algorithms ...have been used to improve the recognition accuracy of radar emitter signals. However, complex deep learning algorithms and data preprocessing operations have a huge demand for computing power, which cannot meet the requirements of low power consumption and high real-time processing scenarios. Therefore, many research works have remained in the experimental stage and cannot be actually implemented. To tackle this problem, this paper proposes a resource reuse computing acceleration platform based on field programmable gate arrays (FPGA), and implements a one-dimensional (1D) convolutional neural network (CNN) and long short-term memory (LSTM) neural network (NN) model for radar emitter signal recognition, directly targeting the intermediate frequency (IF) data of radar emitter signal for classification and recognition. The implementation of the 1D-CNN-LSTM neural network on FPGA is realized by multiplexing the same systolic array to accomplish the parallel acceleration of 1D convolution and matrix vector multiplication operations. We implemented our network on Xilinx XCKU040 to evaluate the effectiveness of our proposed solution. Our experiments show that the system can achieve 7.34 giga operations per second (GOPS) data throughput with only 5.022 W power consumption when the radar emitter signal recognition rate is 96.53%, which greatly improves the energy efficiency ratio and real-time performance of the radar emitter recognition system.
We consider a power constrained downlink communication scenario where energy efficiency, reliability, and latency take precedence over rate, as in some Internet of Things (IoT) applications. To ...reduce its receiver power consumption and complexity, we assume that the IoT device has a single RF chain and investigate the finite-resolution analog-to-digital converter (ADC) operation with differential Phase Shift Keying (PSK) modulation. A lower ADC resolution leads to an exponential decrease in power consumption, while adopting differential PSK enables the use of a low-cost detector with no channel state information (CSI) or carrier phase recovery circuitry. Our main goal in this article is to compare, both analytically and numerically using representative IoT system design parameters, the receiver energy efficiency of the proposed differential PSK system with a coherent PSK system that uses estimated CSI under reliability and latency constraints in Rayleigh slow-fading and ADC quantization distortion conditions. To mitigate the ADC finite-resolution effects without requiring CSI at the receiver or transmitter, we propose and analyze a PSK differentially-modulated Alamouti space-time block transmission scheme with only two RF chains at the transmitter while still restricting the IoT device to have a single RF chain. Our results demonstrate that in the considered low-rate, and outage and latency-constrained scenario with stringent power consumption requirements, differentially-modulated Alamouti transmissions to a single RF-chain IoT device with a low-resolution ADC is an attractive choice in terms of receiver energy efficiency, reliability, and transmission latency.
We investigate the problem of secure non-orthogonal multiple access (NOMA) against full-duplex proactive eavesdropping, where the eavesdropper performs passive eavesdropping and active jamming ...simultaneously to interrupt the NOMA transmissions. To avoid the transmission outage caused by the unknown jamming level from the eavesdropper, we propose a novel transmission outage constrained scheme to limit the transmission outage probabilities of the users to a maximum tolerable threshold, which is also helpful in reducing the secrecy outage. We derive analytical expressions for the secrecy outage probability and secrecy diversity order to characterize the secrecy performance. Simulation results are provided to demonstrate the accuracy of the derived analytical results and the efficiency of the proposed scheme.
The subcarrier signal-to-interference-plus-noise ratio (SINR) expression for orthogonal frequency-division multiplexing (OFDM) systems impaired by in-phase/quadrature (I/Q) imbalance is a ratio of ...correlated random variables. In its original form, a quadruple integral is required to evaluate the exact average subcarrier SINR, which is cumbersome to compute numerically. We show that the quadruple integral can be reduced to a single integral, which can be easily evaluated numerically. Furthermore, closed-form expressions are derived for several important special cases, including transmit (TX)-only I/Q imbalance, receive (RX)-only I/Q imbalance, and joint TX/RX I/Q imbalance with equal levels of I/Q imbalance at the transmitter and at the receiver. In addition, we derive high-input-SNR approximations that provide valuable insights on how the average SINR is affected by the I/Q imbalance levels at the transmitter and the receiver and by the channel correlation between the image OFDM subcarriers. For example, we show that at high input SNR, TX-only I/Q imbalance is more harmful, in terms of average subcarrier SINR, than RX-only I/Q imbalance. Furthermore, we show that an approximate OFDM subcarrier SINR expression, commonly used in the literature, is not accurate when RX I/Q imbalance is present.
This article investigates the downlink communications of intelligent reflecting surface (IRS) assisted non-orthogonal multiple access (NOMA) systems. To maximize the system throughput, we formulate a ...joint optimization problem over the channel assignment, decoding order of NOMA users, power allocation, and reflection coefficients. The formulated problem is proved to be NP-hard. To tackle this problem, a three-step novel resource allocation algorithm is proposed. Firstly, the channel assignment problem is solved by a many-to-one matching algorithm. Secondly, by considering the IRS reflection coefficients design, a low-complexity decoding order optimization algorithm is proposed. Thirdly, given a channel assignment and decoding order, a joint optimization algorithm is proposed for solving the joint power allocation and reflection coefficient design problem. Numerical results illustrate that: i) with the aid of IRS, the proposed IRS-NOMA system outperforms the conventional NOMA system without the IRS in terms of system throughput; ii) the proposed IRS-NOMA system achieves higher system throughput than the IRS assisted orthogonal multiple access (IRS-OMA) systems; iii) simulation results show that the performance gains of the IRS-NOMA and the IRS-OMA systems can be enhanced via carefully choosing the location of the IRS.
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