Orthogonal Resources Research Articles

Non-orthogonal resource scheduling with enhanced preamble detection method for cellular random access networks

In this article, we propose a non-orthogonal resource scheduling (NORS) scheme with an enhanced preamble detection (PD) method for cellular random access (RA) systems. The enhanced PD method is designed based on a deep learning technique that can classify three PD statuses: idle, collision-free, and collision. Because of this collision resolution capability, the base station (BS) can exploit radio resources non-orthogonally in contention-based RA protocols. In addition, we mathematically analyze the performance of our proposed NORS scheme in terms of RA success probability and resource utilization efficiency and conduct a comparison with the baseline orthogonal resource scheduling (ORS) scheme. Through simulations, we verify the validity of our mathematical analysis. As a result, our results will be a useful guideline for resource scheduling and provide support for massive connectivity.

Precoding-Based Downlink OAM-MIMO Communications With Rate Splitting

Orbital angular momentum (OAM) and rate splitting (RS) are the potential key techniques for the future wireless communications. As a new orthogonal resource, OAM can achieve the multifold increase of spectrum efficiency to relieve the scarcity of the spectrum resource, but how to enhance the privacy performance imposes crucial challenge for OAM communications. RS technique divides the information into private and common parts, which can guarantee the privacies for all users. In this paper, we integrate the RS technique into downlink OAM-MIMO communications, and study the precoding optimization to maximize the sum capacity. First, the concentric uniform circular arrays (UCAs) are utilized to construct the downlink transmission framework of OAM-MIMO communications with RS. Particularly, users in the same user pair utilize RS technique to obtain the information and different user pairs use different OAM modes. Then, we derive the OAM-MIMO channel model, and formulate the sum capacity maximization problem. Finally, based on the fractional programming, the optimal precoding matrix is obtained to maximize the sum capacity by using quadratic transformation. Extensive simulation results show that by using the proposed precoding optimization algorithm, OAM-MIMO communications with RS can achieve higher sum capacity than the traditional communication schemes.

NR Sidelink Performance Evaluation for Enhanced 5G-V2X Services

The Third Generation Partnership Project (3GPP) has specified Cellular Vehicle-to-Everything (C-V2X) radio access technology in Releases 15–17, with an emphasis on facilitating direct communication between vehicles through the interface, sidelink PC5. This interface provides end-to-end network slicing functionality together with a stable cloud-native core network. The performance of direct vehicle-to-vehicle (V2V) communications has been improved by using the sidelink interface, which allows for a network infrastructure bypass. Sidelink transmissions make use of orthogonal resources that are either centrally allocated (Mode 1, Release 14) or chosen by the vehicles themselves (Mode 2, Release 14). With growing interest in connected and autonomous vehicles, the advancement in radio access technologies that facilitate dependable and low-latency vehicular communications is becoming more significant. This is especially necessary when there are heavy traffic conditions and patterns. We thoroughly examined the New Radio (NR) sidelink’s performance based on 3GPP Releases 15–17 under various vehicle densities, speeds, and distance settings. Thus, by evaluating sidelink’s strengths and drawbacks, we are able to optimize resource allocation to obtain maximum coverage in urban areas. The performance evaluation was conducted on Network Simulator 3 (NS3.34/5G-LENA) utilizing various network metrics such as average packet reception rate, throughput, and latency.

Distributed Learning Over a Wireless Network With Non-Coherent Majority Vote Computation

In this study, we propose an over-the-air computation (OAC) scheme to calculate the majority vote (MV) for federated edge learning (FEEL). With the proposed approach, edge devices (EDs) transmit the signs of local stochastic gradients, i.e., votes, by activating one of two orthogonal resources. The MVs at the edge server (ES) are obtained with non-coherent detectors by exploiting the accumulations on the resources. Hence, the proposed scheme eliminates the need for channel state information (CSI) at the EDs and ES. In this study, we analyze various gradient-encoding strategies through the weight functions and waveform configurations over orthogonal frequency division multiplexing (OFDM). We show that specific weight functions that enable absentee EDs (i.e., hard-coded participation with absentees (HPA)) or weighted votes (i.e., soft-coded participation (SP)) can substantially reduce the probability of detecting the incorrect MV. By taking path loss, power control, cell size, and fading channel into account, we prove the convergence of the distributed learning for a non-convex function for HPA. Through simulations, we show that the proposed scheme with HPA and SP can provide high test accuracy even when the time-synchronization and the power control are not ideal under heterogeneous data distribution scenarios.

Evolutionary Games for Dynamic Network Resource Selection in RSMA-Enabled 6G Networks

In this paper, we address a dynamic network resource selection problem for mobile users in a rate-splitting multiple access (RSMA)-enabled network by leveraging evolutionary games. Particularly, mobile users are able to locally and dynamically make their selection on orthogonal resource blocks (RBs), which are also considered as network resources (NRs), over time to achieve their desired utilities. Then, RSMA is used for each group of users selecting the same NR. With the use of RSMA, the main goal is to optimize the beamformers of the common and private messages for users in the same group to maximize their sum rate. The resulting problem is generally non-convex, and thus we develop a successive convex approximation (SCA)-based algorithm to efficiently solve it in an iterative fashion. To model the NR adaptation of users, we propose to use two evolutionary games, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e</i> . a traditional evolutionary game (TEG) and fractional evolutionary game (FEG). The FEG approach enables users to incorporate memory effects ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e</i> . their past experiences) for their decision-making, which is more realistic than the TEG approach. We then theoretically verify the existence of the equilibrium of the proposed game approaches. Simulation results are provided to validate their consistency with the theoretical analysis and merits of the proposed approaches. They also reveal that, compared with TEG, FEG enables users to leverage past information for their decision-making, resulting in less communication overhead, while still guaranteeing convergence.

Deep Spread Multiplexing and Study of Training Methods for DNN-Based Encoder and Decoder.

We propose a deep spread multiplexing (DSM) scheme using a DNN-based encoder and decoder and we investigate training procedures for a DNN-based encoder and decoder system. Multiplexing for multiple orthogonal resources is designed with an autoencoder structure, which originates from the deep learning technique. Furthermore, we investigate training methods that can leverage the performance in terms of various aspects such as channel models, training signal-to-noise (SNR) level and noise types. The performance of these factors is evaluated by training the DNN-based encoder and decoder and verified with simulation results.

Caching in Cellular Networks Based on Multipoint Multicast Transmissions

We consider cellular network caching with network-wide Orthogonal Multipoint Multicast (OMPMC) delivery. We apply a probabilistic model for content placement at the Base Stations (BSs). Content is delivered with multipoint multicast operating in file-specific orthogonal resources: all BSs caching a distinct file synchronously multicast it to requesting users in a dedicated resource. For a network modeled as a Poisson Point Process (PPP), an expression for the outage probability is derived. The outage-minimizing cache policy is found from a joint constrained optimization problem over cache placement and resource allocation. We devise principles by which the solution in one propagation environment can be generalized to another. To reduce computational complexity, we obtain a sub-optimal solution based on convex relaxation. We obtain an upper bound of the gap between the optimal and sub-optimal solutions. We compare the outage performance of OMPMC with delivery polices from the literature. Simulation results show that exploiting OMPMC with optimal cache placement and resource allocation outperforms single point cache delivery policies with a wide margin.

A Cluster-Based UE-Scheduling Scheme for NR-V2X

The New Radio Vehicle-to-Everything (NR-V2X) technology investigated by the Third Generation Partnership Project (3GPP) explores the high reliability requirement to support message dissemination by vehicle-to-vehicle (V2V) distributed communications for safety applications via a direct communication interface. However, the natural commonality of distributed resource selection may lead to severe resource collisions in a dense high mobility environment. In this paper, we propose a UE-scheduling resource allocation scheme to reduce distributed resource contentions, where vehicles are clustered autonomously based on orthogonal resource sets detection and the cluster size is determined by the cluster-joining threshold. In addition, the algorithms of clustering maintenance are designed to improve the stability of clusters by periodically checking the status of the resource sets and the movement of vehicles. Furthermore, a detailed frame structure design is described, and theoretical performance analysis models of the proposed scheme in different traffic scenarios are investigated. Finally, simulations and numerical results demonstrate that the proposed scheme can reduce packet collisions and increase the packet delivery ratio compared to the conventional distributed scheme, and outperforms some existing schemes in cluster stability.

Deep Learning-Based Activity Detection for Grant-Free Random Access

The cellular Internet of Things wireless network is a promising solution to provide massive connectivity for machine-type devices. However, designing grant-free random access (GF-RA) protocols to manage such connections is challenging, since they must operate in interference-aware scenarios with sporadic device activation patterns and a shortage of mutually orthogonal resources. Supervised machine learning models have provided efficient solutions for activity detection, noncoherent data detection, and nonorthogonal preamble design in scenarios with massive connectivity. In this article, we develop two deep learning (DL) sparse support recovery algorithms to detect active devices in massive machine-type communication random access. The DL algorithms, developed to deploy GF-RA protocols, are based on the deep multilayer perceptron and the convolutional neural network models. Unlike previous works, we investigate the impact of the type of sequences for preamble design on the activity detection accuracy. Our results reveal that preambles based on the Zadoff–Chu sequences, which present good correlation properties, achieve better activity detection accuracy with the proposed algorithms than random sequences. Besides, we demonstrate that our DL algorithms achieve activity detection accuracy comparable to state-of-the-art techniques with extremely low computational complexity.

Integration of Cognitive Radio Technology in NOMA-Based B5G Networks: State of the Art, Challenges, and Enabling Technologies

The integration of cognitive radio (CR) technology and non-orthogonal multiple access (NOMA) techniques, referred to as CR-based NOMA system, has been recently configured as a promising solution to meet the requirements of beyond fifth generation (B5G) networks, especially those related to Internet-of-Things (IoT) applications. With such integration, power domain NOMA allows multiple users to share the same orthogonal resource blocks, while CR technology enables opportunistic bandwidth utilization by permitting secondary users (SUs) to access the licensed spectrum frequency without interrupting the primary users’ (PUs) activities. To support the massive connectivity requirements of IoT-based networks, several multiple-access techniques have been recently combined with CR-based NOMA systems, including orthogonal multiple access (OMA) and multiple-antenna techniques. For example, in CR-based OMA-NOMA systems, the licensed frequency band is split into several channels, and a set of SUs is served on each channel using the NOMA technique. This paper provides an overview and analysis of the state-of-the-art CR-based NOMA network architecture. It summarizes the main design challenges related to the practical implementation of such systems. Furthermore, this paper presents the advances of combining CR-based NOMA with recent multiple-access techniques, where the potential capabilities and the design challenges of such integrated systems are also investigated and discussed. On the other hand, this paper demonstrates the potential capabilities of deploying recent technologies in CR-based NOMA networks. The technologies include intelligent reflecting surfaces, terahertz communications, machine learning, unmanned aerial vehicles, and hybrid NOMA systems. Finally, future research directions and open issues are provided and discussed.

Outage Probability analysis of Power Domain MISO-NOMA in Rayleigh Fading Channel

The multiple access technique of the current wireless communication system depends on the orthogonal multiple access (OMA) technique. The availability of orthogonal resources is limited in OMA and cannot support the increasing demand for a large number of users and efficient use of the spectrum in the coming years. The Non-orthogonal multiple access (NOMA) is considered in the future release of 5G and beyond 5G. In NOMA, multiple users can be dealt with in the same resource block at the same time, which allows NOMA to provide large connectivity, low latency, and high spectral efficiency. In this paper, the outage probability expression for the MISO-NOMA downlink system is derived by employing an indefinite quadratic form (IQF) approach. Analytical results are compared with the Monte Carlo simulations which validate our theoretical derivations. Further, the performance of the MISO-NOMA system is assessed with different numbers of users in the system and different SNR values.

Outage Probability and Ergodic Capacity Analysis of MIMO-NOMA Heterogeneous Network for 5G System

Based on the orthogonal multiple access (OMA) paradigm, multiple access techniques are now used in wireless networks. The capacity of OMA for orthogonal resources, which is already constrained, will be exceeded in the coming years by the demand for a significant number of users and efficient spectrum usage. Non-orthogonal multiple access (NOMA) is being considered for next 5G and beyond releases. NOMA can offer high connection, low latency, and excellent spectral efficiency because several users can be handled in the same resource block at once. This work presents a thorough literature evaluation of the MIMO-NOMA and identifies several research gaps. Additionally, using Monte Carlo simulations, For the MIMO-NOMA heterogeneous network, simulation was performed to analyze the outage probability and ergodic capacity. The MIMO-NOMA HetNets system’s performance is further evaluated using various SNR levels, number of clusters, user counts per cluster, and antenna count ratios.

High-security SCMA-OFDM multi-core fiber transmission system based on a regular hexagon chaotic codebook.

Sparse code multiple access (SCMA), a new code-domain non-orthogonal technology in the fifth-generation mobile communication (5G), can be modulated by orthogonal frequency division multiplexing (OFDM) to improve the link quality of a single user. In this paper, a high-security SCMA-OFDM multi-core fiber transmission system based on a regular hexagonal chaotic codebook is proposed for next-generation passive optical network (PON). The whole encryption process consists of a regular hexagon chaotic codebook design and frequency domain block scrambling. In designing the regular hexagon chaotic codebook, the optimization of constellation points on orthogonal resources are considered as the starting point. Firstly, the chaos factor generated by the four-dimensional Rossler chaos model is deployed to disturb the mother constellation, and then the corresponding chaotic book is formed by rotating the mother constellation and multiplying the sparse matrix. The designed codebook logically avoids the degradation of transmission performance caused by the rough scrambling of codebook constellation, to find a balance between codebook disturbance and bit error rate (BER). The security and reliability of the transmission system have been verified by performing 42 Gb/s encrypted SCMA-OFDM data transmission experiments in a 2km multi-core fiber. The key space of the encryption scheme can reach 10178, which effectively ensures the security of the transmission system. Furthermore, the performance of the transmission system with a regular hexagon chaotic codebook is improved by 2.5 dB compared with the traditional codebook when the BER is 1 × 10-3. Moreover, the SCMA-OFDM-based transmission architecture and the detection effects of different multi-user detection algorithms in the SCMA-OFDM multi-core fiber transmission system are also studied.

Performance Analysis of Rate Splitting Multiple Access Based Vortex Wave Communications

The vortex wave mode provides wireless communications with a new orthogonal resource for the multifold increase of spectrum efficiency. The rate splitting multiple access (RSMA) technique realizes the flexible decoding at the user equipment (UE) by dividing the information into private and common parts. This letter proposes the RSMA based vortex wave (RBVW) communications, which can enhance the access capability and privacy performance of vortex wave communications. By using the uniform circular array, we design the transmission framework of RBVW communications, where different user groups use different vortex wave modes and users in the same user group utilize RSMA to obtain the information. The UE channel model and achievable rate are derived for RBVW communications. Simulation results demonstrate that compared with the traditional schemes, RBVW communications can obtain higher achievable rate, especially for long distance transmission.

Modeling and Performance Analysis of Statistical Priority-Based Multiple Access: A Stochastic Geometry Approach

Statistical priority-based multiple access (SPMA) protocol has attracted much attention in virtue of its support for multi-priority traffic, and the guarantee of low-latency and high-reliability transmissions for high-priority. In this work, we propose an analytical framework to study the performance of SPMA from spatial perspective with tools from the stochastic geometry. We consider two kinds of priority traffic, including high-priority traffic and low-priority traffic. In SPMA, a packet is split into multiple bursts to reduce the collision probability, and the turbo coding, frequency hopping, and time hopping are employed to further decrease the packet loss rate. We first derive the analytical expressions for the medium access probability (MAP) and burst success probability of two priority users in closed form, taking into account the potential transmitters (PTs) density, ratio of different traffic users, amount of orthogonal resources, channel occupancy statistics (COS) threshold, and statistical sliding window (SSW). Based on the derived MAP and burst success probability, we further obtain the packet success probability and spatial throughput. After evaluating the effect of key parameters on the above performance metrics, we provide guidelines on optimal design of several key system parameters, such as the COS threshold and PTs density, to guarantee the high-priority user a 99% packet success probability.

Error Performance Analysis of Multiuser Detection in Uplink-NOMA With Adaptive M-QAM

This letter provides a generalized performance analysis for the multi-user uplink-NOMA system with adaptive square quadrature amplitude modulation (QAM) over Rayleigh fading channels. Motivated by the massive IoT connections and unavailability of orthogonal resources for each node, we consider a multi-access scheme where multi-users with single-antenna transmit data to a multiple-antenna base station through the same resource block. By taking advantage of combining diversity paths with the proposed joint maximum-likelihood detector (JMLD), a closed form expression for the upper bound of bit error rate (BER) is obtained. Despite the number of users or the order of modulation, the analytical results endorsed via computer simulations reveal the ability of the MRC-JMLD detector to discard the error floor completely. Moreover, the simulation results show that the MRC-JMLD surpasses its counterparts significantly and ensures a full diversity order.

Power-Time Channel Diversity (PTCD): A Novel Resource-Efficient Diversity Technique for 6G and Beyond

Diversity techniques have been applied for decades to overcome the effects of fading, which is one of the most challenging problems in wireless communications due to the randomness of the wireless channel. However, existing diversity techniques are resource-inefficient due to orthogonal resource usage, or they have high-power consumption due to multiple antennas and RF-chains which present an insurmountable constraint for small devices. To address this, this letter proposes a novel resource-efficient diversity technique called power-time channel diversity (PTCD). In PTCD, interleaved copies of the baseband symbols are transmitted simultaneously with weighted power coefficients. The PTCD provides a diversity order of the number of copies by implementing successive interference canceler at the receiver. To achieve this diversity, no additional resources are needed; hence, spectral efficient communication is guaranteed. Additionally, the power consumption at the transceivers is limited since the PTCD requires only one RF-chain. We provide an information-theoretic proof that the PTCD could have any diversity order. Based on extensive simulations, we reveal that PTCD can also outperform benchmarks without any additional cost.

Mathematical Model of Short Circuit Fault Diagnosis in management and collaborative System Based On Improved SOM Neural Network

The existing mathematical model for short-circuit fault diagnosis of management and collaborative system has the problem that the session characteristics of communication link are not clear, resulting in the slow upload speed of fault data. In order to solve this problem, a short-circuit fault diagnosis mathematical model of communication system based on improved SOM neural network and the innovative strategies also management and collaborative system is describe in this paper. Firstly, the early warning information of the system is collected, combined with the repeated information, the session characteristics of the communication link are extracted by using the quasi Newton algorithm, the mutually orthogonal physical resource blocks are transformed, the short-circuit fault diagnosis mode is optimized, the parameters of the components to be detected are estimated, the feature space vector is truncated, and the mathematical model is established by using the improved SOM neural network. Experimental results: the average value of the management and collaborative system short-circuit fault diagnosis mathematical model designed in this paper is 8.244 Mbps, and the average values of the other two management and collaborative system short-circuit fault diagnosis mathematical models are 5.756 Mbps and 5.863 Mbps respectively. The results show that the designed mathematical model for short circuit fault diagnosis of management and collaborative system has high application value.

Medium access control protocol design for wireless communications and networks review

&lt;p&gt;&lt;span&gt;Medium access control (MAC) protocol design plays a crucial role to increase the performance of wireless communications and networks. The channel access mechanism is provided by MAC layer to share the medium by multiple stations. Different types of wireless networks have different design requirements such as throughput, delay, power consumption, fairness, reliability, and network density, therefore, MAC protocol for these networks must satisfy their requirements. In this work, we proposed two multiplexing methods for modern wireless networks: Massive multiple-input-multiple-output (MIMO) and power domain non-orthogonal multiple access (PD-NOMA). The first research method namely Massive MIMO uses a massive number of antenna elements to improve both spectral efficiency and energy efficiency. On the other hand, the second research method (PD-NOMA) allows multiple non-orthogonal signals to share the same orthogonal resources by allocating different power level for each station. PD-NOMA has a better spectral efficiency over the orthogonal multiple access methods. A review of previous works regarding the MAC design for different wireless networks is classified based on different categories. The main contribution of this research work is to show the importance of the MAC design with added optimal functionalities to improve the spectral and energy efficiencies of the wireless networks.&lt;/span&gt;&lt;/p&gt;

Regular Sparse NOMA: Ultimate Performance in Closed Form

Understanding the fundamental limits of technologies enabling future wireless communication systems is essential for their efficient state-of-the-art design. A prominent technology of major interest in this framework is non-orthogonal multiple access (NOMA). In this paper, we derive an explicit rigorous <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">closed-form</i> analytical expression for the optimum spectral efficiency, in the large-system limit, of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">regular</i> sparse (code-domain) NOMA, along with a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">closed-form</i> formulation for the limiting spectral density of the underlying input covariance matrix. Sparse NOMA is an attractive and popular instantiation of NOMA, and its ‘regular’ variant corresponds to the case where only a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fixed and finite</i> number of orthogonal multiple-access resources are allocated to any designated user, and vice versa. Interestingly, the well-known Verdú-Shamai formula for (dense) randomly-spread code-division multiple access (RS-CDMA) turns out to coincide with the limit of the derived expression, when the number of orthogonal resources per user grows large. Furthermore, regular sparse NOMA is rigorously shown to be spectrally more efficient than RS-CDMA (viz. dense NOMA) across the entire system load range. Therefore, regular sparse NOMA may serve as an appealing means for reducing the throughput gap to orthogonal transmission in the underloaded regime, and to the ultimate Cover-Wyner bound for massive access overloaded systems. The spectral efficiency is also derived in closed form for the sub-optimal linear minimum-mean-square-error (LMMSE) receiver, which again extends the corresponding Verdú-Shamai LMMSE formula to the case of regular sparse NOMA.