Multiple Access Communication Systems Research Articles

Effective capacity analysis of configurable intelligent surface-assisted NOMA communications systems

This paper investigates the integration of configurable intelligent surfaces (CIS) into relay radio networks, focusing on communication system enhancement. Towards this end, we propose CIS-assisted non-orthogonal multiple access (NOMA) communication systems to improve direct connections between a base station and two destination nodes. Our primary objective is to assess the net-work’s overall capacity, considering critical factors like signal-to-noise ratio, the number and placement of CIS components, quality of service exponent, and power distribution coefficients. Analytical equations developed in this research closely align with simulation results, validating our theoretical analysis. This study underscores the growing significance of CISs in modern communication systems, introducing adaptability and optimization to wireless networks. By exploring CIS-assisted NOMA communication systems, we contribute to dis-cussions about the evolving landscape of wireless communication technologies, poised to revolutionize information transmission and reception in the digital age.

A new construction of asymptotically optimal codebooks

<abstract><p>Codebooks with small cross-correlation amplitude have extensive applications in many fields including code division multiple access (CDMA) communications systems, space-time codes, and compressed sensing. In this paper, a class of asymptotically optimal codebooks was constructed, and the maximum inner-product of these presented codebooks was determined by using properties of character sums over finite fields. Furthermore, these codebooks provided new parameters.</p></abstract>

Outage analysis of aerial semi-grant-free NOMA systems

In this paper, we analyze the outage performance of Unmanned Aerial Vehicles (UAVs)-enabled downlink Non-Orthogonal Multiple Access (NOMA) communication systems with the Semi-Grant-Free (SGF) transmission scheme. A UAV provides coverage services for a Grant-Based (GB) user and one Grant-Free (GF) user is allowed to utilize the same channel resource opportunistically. The analytical expressions for the exact and asymptotic Outage Probability (OP) of the GF user are derived. The results demonstrate that no-zero diversity order can be achieved only under stringent conditions on users' quality of service requirements. Subsequently, an efficient Dynamic Power Allocation (DPA) scheme is proposed to relax such data rate constraints. The analytical expressions for the exact and asymptotic OP of the GF user with the DPA scheme are derived. Finally, Monte Carlo simulation results are presented to validate the correctness of the derived analytical expressions and demonstrate the effects of the UAV's location and altitude on the OP of the GF user.

Performance Analysis of the STAR-RIS-Assisted Downlink NOMA Communication System With MRC

We discuss a simultaneously transmitting and reflecting-reconfigurable intelligent surface (STAR-RIS)-assisted downlink non-orthogonal multiple access (NOMA) communication system. STAR-RIS employs the energy splitting protocol for transmitting and reflecting the incident signals to users located on different sides of the surface. To study the impact of multiple antennas on the system performance, we perform maximum ratio combining (MRC) at NOMA users and beamforming towards STAR-RIS at the base station (BS). We model the distribution of cascaded Rician fading channels for the proposed system. Closed-form expressions of outage probability, asymptotic outage probability, and system throughput are derived. All theoretically derived results are verified via Monte Carlo simulation.

Joint Location and Beamforming Design for STAR-RIS Assisted NOMA Systems

Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted non-orthogonal multiple access (NOMA) communication systems are investigated in its vicinity, where a STAR-RIS is deployed within a predefined region for establishing communication links for users. Both beamformer-based NOMA and cluster-based NOMA schemes are employed at the multi-antenna base station (BS). For each scheme, the STAR-RIS deployment location, the passive transmitting and reflecting beamforming (BF) of the STAR-RIS, and the active BF at the BS are jointly optimized for maximizing the weighted sum-rate (WSR) of users. To solve the resultant non-convex problems, an alternating optimization (AO) algorithm is proposed, where successive convex approximation (SCA) and semi-definite programming (SDP) methods are invoked for iteratively addressing the non-convexity of each sub-problem. Numerical results reveal that 1) the WSR performance can be significantly enhanced by optimizing the specific deployment location of the STAR-RIS; 2) both beamformer-based and cluster-based NOMA prefer asymmetric STAR-RIS deployment.

Quantum wavelength-division-multiplexing and multiple-access communication systems and networks: Global and unified approach

The march towards successful global quantum internet requires introducing all-quantum networks and signal processing techniques. In this paper, we develop and discuss methods for various wavelength-division-multiplexing and multiple-access (WDM) communication systems and networks in fully quantum mechanical terms to obtain all-quantum WDM (QWDM) systems and networks. We begin the paper with a detailed discussion on various possible narrow-band and wideband sources of light signals used in typical WDM systems, such as coherent, number, and Poissonian mixed states. After introducing a generic and fully quantum mechanical WDM network, we develop methodologies for obtaining the necessary mathematical evolutions through wavelength distributors such as arrayed-waveguide-grating multiplexers and demultiplexers, and wavelength-sensitive and -insensitive broadcasting star couplers. In particular, using the methodologies introduced, one can use the results to obtain a complete and exact expression for any evolved pure quantum light signal through a typical WDM network using the aforementioned optical components. To test the validity and robustness of our mathematical expression for the evolved QWDM light signals, we use two opposing and extreme signals, namely, coherent state and number state, as inputs to various WDM communication and network systems and architecture. The methodologies and the required mathematical QWDM models introduced here can be extended to any fully quantum network architecture deemed necessary in a future global quantum internet, e.g., fiber to the home, Lambdanet-based broadcast WDM networks, and quantum routers based on a waveguide grating router.

Simultaneously Transmitting and Reflecting Reconfigurable Intelligent Surface Assisted NOMA Networks

Simultaneously transmitting/refracting and reflecting reconfigurable intelligent surface (STAR-RIS) has been introduced to achieve full coverage area. This paper investigate the performance of STAR-RIS assisted non-orthogonal multiple access (NOMA) networks over Rician fading channels, where the incidence signals sent by base station are reflected and transmitted to the nearby user and distant user, respectively. To evaluate the performance of STAR-RIS-NOMA networks, we derive new approximate expressions of outage probability and ergodic rate for a pair of users, in which the imperfect successive interference cancellation (ipSIC) and perfect SIC (pSIC) schemes are taken into consideration. Based on the asymptotic expressions, the diversity orders of the nearby user with ipSIC/pSIC and distant user are achieved carefully.The high signal-to-noise ratio slopes of ergodic rates for nearby user with pSIC and distant user are equal to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$one$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$zero$ </tex-math></inline-formula> , respectively. In addition, the system throughput of STAR-RIS-NOMA is discussed in delay-limited and delay-tolerant modes. Simulation results are provided to verify the accuracy of the theoretical analyses and demonstrate that: 1) The outage probability of STAR-RIS-NOMA outperforms that of STAR-RIS assisted orthogonal multiple access (OMA) and conventional cooperative communication systems; 2) With the increasing of reflecting elements <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> and Rician factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $ </tex-math></inline-formula> , the STAR-RIS-NOMA networks are capable of attaining the enhanced performance; and 3) The ergodic rates of STAR-RIS-NOMA are superior to that of STAR-RIS-OMA.

Multi-antenna relay assisted NOMA network with multiple imperfect factors

In this paper, a 5G downlink multi-antenna relay assisted non-orthogonal multiple access (NOMA) communication system is investigated. The relay can work in half-duplex (HD) or full-duplex (FD) mode with maximum-ratio-combining/transmission antenna selection (MRC/TAS) scheme, and the direct links between the source and destinations are also considered. The exact expressions for the outage probability are derived when considering the effects of hardware impairment (HDI), imperfect successive interference cancellation (ipSIC), channel estimation error(CEE), antenna number and loop-interference (LI) for FD mode. Then, based on the accurate outage probability, the approximate low bound and asymptotic results are derived. From the derived formulas, we find that the maximum diversity order of the considered system is min{(1−μ)N+1,M+1} when CEE does not appear, where μ is the LI cancellation grade, N and M are the receiving and transmitting antenna number equipped at the relay. Otherwise the diversity decreases to one or zero regardless of multi-antenna when CEE appears, but multiple antennas still improve system performance by promoting the array gain. The FD mode may outperform the HD mode with less LI which is decided by μ. Monte Carlo simulations are also done to validate the correctness of theoretical analysis.

Energy-Efficient Resource Allocation for Short Packet Transmission in MISO Multicarrier NOMA

In this article, we investigate energy efficiency (EE) maximization of short packet transmission (SPT) in a downlink multiple-input single-output (MISO) multi-carrier non-orthogonal multiple access (MC-NOMA) communication system. We use the ratio of the effective throughput to the power as a performance metric to formulate a non-convex mixed-integer nonlinear programming (MINLP) problem. Then, a low-complexity three-step optimization framework is proposed for MINLP optimization. Under a given maximum transmit power and channel blocklength of each subcarrier, a block coordinate descent (BCD) based method is proposed to jointly optimize the power allocation coefficient, transmission rate, and transmit power within a single subcarrier. Then, we transform the subcarrier allocation problem into a weighted bipartite graph matching problem and obtain the optimal subcarrier allocation scheme using the Kuhn-Munkres (KM) algorithm. Finally, a dynamic programming (DP) method is proposed to obtain the optimal channel blocklength allocation scheme. The simulation results validate the effectiveness of the proposed three-step optimization framework and indicate that the MC-NOMA system achieves higher EE and higher effective throughput than the orthogonal frequency-division multiple access (OFDMA) system in SPT.

Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic Channels.

The objective of this study is to evaluate Grassmannian constellations combined with a spread spectrum multiple access scheme for underwater acoustic mobile multiple access communication systems. These communication systems enable the coordination of a fleet of Autonomous Underwater Vehicles (AUVs) from a surface or bottom control unit, e.g., a boat. Due to its robustness against phase rotation, the demodulator of Grassmannian constellations uses non-coherent detection, and the main advantage of such modulation lies in the spectrum efficiency gain with respect to conventional differential modulation. The communication system under study in this paper consists of (i), at the transmitter side, a Grassmannian modulation used in an orthogonal spread spectrum multiple access scheme called Multiuser Hyperbolic Frequency Modulation (MU-HFM) and (ii), at the receiver side, a non-coherent array decoder. The modulation and demodulation are presented as well as the considered spreading sequences. Finally, performances of the proposed transmission scheme are evaluated over replayed underwater acoustic channel responses collected at sea by a multi-sensor acoustic acquisition system.

Dispersion-division multiple access: A temporal holography-based method

Multiple access methods are the backbone of today’s most communication systems. Increasing the efficiency of these schemes is a challenging engineering task. This paper introduces dispersion-division multiple access, a novel multiple-access technique that can improve the efficiency of multiple-access communication systems. When two (or more) pulses experience different Group Delay Dispersion (GDD) values on a propagation medium, they can be synchronized to overlap in time for combining the phase and amplitude of those pulses. This paper suggests the recoverability of these pulses while being mixed in the transmitter by propagating the combined pulse in a negative Group Velocity Dispersion (GVD)medium with GDD values corresponding to the minus of the corresponding GDD values in the input. This method shares similarities with coherent holography, with the only difference being that in spatial coherent holography, the combined wave-fronts are recorded in a plate, encoding the phase information of a three-dimensional object into intensity. However, the proposed method does not record the combined pulse and immediately sends it through the channel. In addition to the excellent simplicity provided by this method, the performed simulations also validate its notable performance in increasing the number of channels under low Bit Error Rates (BER).

MMW-NOMA: An Uplink NOMA Communication System Based on the Node Pairing Algorithm of Maximum and Minimum Weight in Underwater Acoustic Networks

In orthogonal multiple access (OMA) communication systems, resources are allocated to numerous users based on time, frequency, or code domains. The low bandwidth of the underwater acoustic network limits the number of nodes that can be supported by the OMA system, due to limited resources. The innovative concept of nonorthogonal multiple access (NOMA) provides a solution that offers more nodes and increases spectral efficiency. As a promising technique, it optimizes power allocation through channel characteristics and adopts serial interference cancellation algorithms to decode the signal at the receiver. This paper introduces an underwater communication system based on the node pairing algorithm of maximum and minimum weight (MMW-NOMA). First, we build the system model in a UAN scenario. Second, we present the node pairing strategy. Third, we design a node replacement mechanism. Furthermore, we offer a power allocation algorithm. Finally, we compare the performance of MMW-NOMA with randomly paired NOMA (RP-NOMA) and orthogonal frequency division multiplexing (OFDM). Numerical results show that MMW-NOMA outperforms RP-NOMA and OFDM in throughput, mean square error, and energy efficiency. However, the complexity of MMW-NOMA is slightly higher than that of RP-NOMA but significantly lower than OFDM. These results show that MMW-NOMA achieves a reasonable trade-off between performance and complexity.

Exploiting Incremental Virtual Full Duplex Non-Orthogonal Multiple Access Systems

This paper investigates the throughput performance of an incremental virtual full-duplex non-orthogonal multiple access (I-VFD-NOMA) communication system, where two energy harvesting (EH) enabled near users are willing to forward message for far user using decode-and-forward (DF) protocol. If the direct link between the source and the far user exists, I-VFD-NOMA scheme is used to save the channel resources. If the direct link between the source and the far user does not exist, I-VFD-NOMA can not be used and only VFD-NOMA can be used. With this structure, The analytical expressions of the system throughput considering imperfect successive interference cancellation (I-SIC) and selection combining (SC) are derived when the direct link exists or not. With the aim of maximizing the throughput, the expression for the optimal power splitting factor at near users is also derived when the direct link does not exist. All theoretical results are validated by numerical simulations which demonstrate that the proposed I-VFD-NOMA scheme is superior to existing NOMA systems.

On Secure NOMA-Based Terrestrial and Aerial IoT Systems

In this paper, we study the secure communication performance of non-orthogonal multiple access (NOMA) communication systems with aerial eavesdroppers. Firstly, the ground-to-ground NOMA communications systems are considered wherein the near user is uniformly distributed in an inner disc and the far user is uniformly distributed in an outer ring within cell coverage of a base station at the center. A single eavesdropper is uniformly distributed outside the protected zone or multiple eavesdroppers are randomly dispersed and modeled as a three-dimensional (3D) homogeneous Poisson point process. Subsequently, the secrecy performance of the ground-to-air NOMA communications systems are investigated wherein the near user is uniformly distributed in an internal 3D spherical cap and the far user is uniformly distributed in an external 3D spherical cap. To enhance secrecy performance, a protected zone is introduced around the ground base station. Novel exact expressions for the secrecy outage probability (SOP) for both scenarios are derived. Finally, Monte Carlo simulation results are presented to validate the correctness of the derived analytical expressions and demonstrate the effects of system parameters on SOP of the considered system.

QoS-Aware Secrecy Rate Maximization in Untrusted NOMA With Trusted Relay

This letter considers a trusted decode-and-forward relay-assisted two-user non-orthogonal multiple access (NOMA) communication system, and tackles the secure rate maximization problem at the near user. The problem is solved optimally using KKT conditions, while satisfying the quality of service (QoS) requirements of the far user. Particularly, closed-form expressions for the power sharing between the source and the relay, and the power allocation coefficients corresponding to power-domain NOMA for both users are obtained. An upper-bound on the threshold rate of the far user is also derived, which indicates the best QoS that can be ensured. Numerical results showed that the relay-user link acts as the bottleneck and provide design insights on optimal power allocation satisfying the tradeoff between the rate secrecy at the near user and the QoS requirements of the far user.

Design of Polyphase Sequences With Low Integrated Sidelobe Level for Radars With Spectral Distortion via Majorization-Minimization Framework

Polyphase sequences with low aperiodic autocorrelation levels, assessed in terms of the integrated sidelobe level (ISL), can be applied in many engineering fields, such as radars, sonars, and code-division multiple access communication systems. In practice, a polyphase sequence that is optimal in some sense (for example, minimum ISL) could be significantly distorted, thus reducing the detection performance of the radar system. Hence in this article, we focus on designing ISL minimization-based polyphase sequences with spectral distortion taken into consideration, where we first derive an expression for the ISL under spectral distortion, i.e., distorted ISL (DISL), and then we propose an iterative algorithm based on majorization-minimization framework to solve the DISL minimization problem. The proposed algorithm is proved to be nonincreasing and is guaranteed to converge to a stationary point. A variety of design results utilizing the proposed algorithm in different scenarios are presented and compared with those by other methods or some known sequences. The proposed algorithm is proved to be effective to design polyphase sequences with low DISL.

Performance of Uplink NOMA with User Mobility Under Short Packet Transmission

The scenario of an uplink two-user non-orthogonal multiple access (NOMA) communication system is analytically studied when it operates in the short packet transmission regime. The considered users support mobility and each is equipped with a single antenna, while they directly communicate with a multi-antenna base station. Power-domain NOMA is adopted for the signal transmission as well as the successive interference cancellation approach is performed at the receiver for decoding. The packet error rate (PER) is obtained in simple closed formulae under independent Rayleigh faded channels and for arbitrary user mobility profiles. The practical time variation and correlation of the channels is also considered. Moreover, useful engineering insights are manifested in short transmission time intervals, which define a suitable setup for the forthcoming ultra-reliable and low latency communication systems. Finally, it turns out that the optimal NOMA power allocation can be computed in a straightforward cost-effective basis, capitalizing on the derived PER expressions.

Quantum CDMA Communication Systems

Barcoding photons can provide a host of functionalities that could benefit future quantum communication systems and networks beyond today's imagination. As a significant application of barcoding photons, we introduce code division multiple-access (CDMA) communication systems for various applications. In this context, we introduce and discuss the fundamental principles of a novel quantum CDMA (QCDMA) technique based on spectrally encoding and decoding of continuous-mode quantum light pulses. In particular, we present the mathematical models of various QCDMA modules that are fundamental in describing an ideal and typical QCDMA system, such as quantum signal sources, quantum spectral encoding phase operators, M$\times$M quantum broadcasting star-coupler, quantum spectral phase decoding operators, and the quantum receivers. In describing a QCDMA system, this paper considers a unified approach where the input continuous-mode quantum light pulses can take on any form of pure states such as Glauber states and quantum number states. For input number states, one can observe features like entanglement and quantum interference. More interestingly, due to Heisenberg's uncertainty principle, the quantum signals sent by photon number states obtain complete phase uncertainty at the time of measurement. Therefore, at the receiver output, the multiaccess inter-signal interference vanishes. Due to Heisenberg's uncertainty principle, the received signal intensity at the photodetector's output changes from a coherent detection scheme for input Glauber states to an incoherent detection scheme for input number states. Our mathematical model is valuable in the signal design and data modulations of point-to-point quantum communications, quantum pulse shaping, and quantum radar signals and systems where the inputs are continuous mode quantum signals.

On the performance of physical layer security in virtual full-duplex non-orthogonal multiple access system

This paper investigates physical layer security analysis of cooperative non-orthogonal multiple access (NOMA) communication system. A virtual full-duplex (VFD) relaying scheme with an untrusted amplify-and-forward (AF) half-duplex (HD) relay and a trusted decode-and-forward (DF) HD relay is used in this system to improve the spectral efficiency. In order to prevent the untrusted relay from eavesdropping, a simple and practical cooperative jamming scheme is designed to confuse the untrusted relay. The exact expressions of effective secrecy throughput (EST) for NOMA users and approximate expression of EST for non-NOMA user are derived. All theoretical results are validated by numerical simulations which demonstrate that the proposed VFD-NOMA scheme is superior to existing HD-NOMA scheme in cooperative system and jamming plays an important role for obtaining acceptable EST. In addition, simulation results shows that the best secrecy performance highly depends on the system parameters such as transmit powers and jamming signal power.

Design of Eight-Phase Sequences using Modified Particle Swarm Optimization for Spread Spectrum and Radar Applications

For a multiple access communication system and radar system, it is desirable to have a set of sequences such that each sequence has a peaky autocorrelation and each pair of sequence has a negligible cross-correlation as possible. Peakyness of the auto-correlation of a sequence is measured in terms of its discrimination, which is to be maximized. The negligibility of a cross-correlation is judged based on the energy in the cross-correlation which is to be minimized. Obtaining such sequences is a combinatorial problem for which many global optimization algorithms like genetic algorithm, particle swarm optimization algorithm, simulated annealing algorithm were reported in the literature. In this paper a Modified Particle Swarm Optimization (MPSO) Algorithm is being designed to achieve these sequences. The MPSO Algorithm is a combination of the Hamming Scan Algorithm (HAS) and Particle Swarm Optimization (PSO) and has the fast convergence rate of Hamming Scan and global minima convergence of Particle Swarm Optimization. Eight-phase sequences of lengths varying from 40 to 300 have been synthesized using MPSO and synthesized sequence sets achieved have better values of the above two properties compared with the literature.