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In the next-generation communication systems, multiple access (MA) will play a crucial role in achieving high throughput to support future-oriented services. Recently, rate-splitting multiple access (RSMA) has received much attention from both academia and industry due to its ability to flexibly mitigate inter-user interference in a broad range of interference regimes. Further, with the growing emphasis on spectrum resource utilization, integrated sensing and communication (ISAC) technology, which improves spectrum efficiency by merging communication and radar signals, is expected to be one of the key candidate technologies for the sixth-generation (6G) wireless networks. In this paper, we first investigate the evolution of existing MA techniques and basic principles of RSMA-assisted ISAC systems. Moreover, to make the future RSMA-assisted ISAC systems, we highlight prime technologies of 6G such as non-terrestrial networks (NTN), reconfigurable intelligent surfaces (RIS), millimeter wave (mmWave) and terahertz (THz) technologies, and vehicular-to-everything (V2X), along with the main technical challenges and potential benefits to pave the way for RSMA-assisted ISAC systems. [ABSTRACT FROM AUTHOR]

In optical networks, designing optical orthogonal codes (OOCs) with appropriate parameters is essential for enhancing the overall system performance. They are divided into two categories, constant-weight OOCs (CW-OOCs) and variable-weight OOCs (VW-OOCs), based on the number of distinct Hamming weights present in their codewords. This paper introduces a method for constructing VW-OOCs of length k p by using the structure of an integer ring and the Chinese Remainder Theorem. In particular, we present some specific VW-OOCs with weights of 3, 4, or 5. The results demonstrate that certain optimal VW-OOCs can be obtained with parameters that are not covered in the existing literature. [ABSTRACT FROM AUTHOR]

The advent of groundbreaking nanomaterials like graphene, renowned for their exceptional electrical properties, has ignited significant interest in nanocommunication. The potential to develop graphene-based plasmonic nanoantenna arrays and transceivers, combined with the capability of transmitting nanocommunication pulses at terahertz (THz) frequencies—bridging the THz gap in the electromagnetic spectrum—has been particularly compelling. Over the past decade, research in nanocommunication has led to remarkable advancements, particularly in the physical and link layers. These developments have paved the way for integrating fully operational nanonetworks into beyond 6G (B6G) wireless systems. Given the anticipated data rates in the terabits per second range for nanonetwork applications, continuous efforts are being made to develop new modulation and multiple access (MA) schemes. This survey paper explores the most advanced modulation and MA strategies tailored for B6G nanosystems operating in the THz band. Unlike previous surveys, our focus is on the physical layer, emphasizing rate-division and time-hopping strategies, including pulse position and pulse amplitude modulation techniques. We begin with an introduction to the foundational aspects of nanocommunication as an integral part of B6G nanosystems, followed by a detailed examination of various modulation schemes and their applicability to MA in nanonetworks. The paper concludes with a comparative analysis of these approaches regarding link capacity and a discussion of key open issues and future research directions for the design of electromagnetic nanocommunication systems.

To address the limitations of half-space coverage, low information transmission efficiency of RIS assisted batteryless IoT, a STAR-RIS assisted transmission scheme was proposed. Specifically, a STAR-RIS was deployed between the batteryless device (BD) and the access point, facilitating the uplink information transmission from the BD to the access point, thereby achieving full-space network coverage of the BD. To further enhance energy transmission efficiency, energy beamforming was designed at the power station. To this end, the system sum-rate maximization problems for both space division multiple access (SDMA) and non-orthogonal multiple access (NOMA) scenarios were investigated, with jointly optimization of the relection coefficients of the BD, the energy beamforming vector at the base station and the coefficient matrices of the STAR-RIS. For the SDMA scenario, an iterative algorithm based on the block coordinate descent (BCD) framework was proposed to solve the optimization problem. Similarly, to address the non-convexity of the optimization problem in the NOMA scenario, the objective function was transformed to simplify its solution, and another iterative algorithm based on the BCD framework was proposed. Numerical results show the superiorities of the proposed schemes over the benchmark schemes. Moreover, the utilization of the NOMA achieves better performance than the SDMA.

Because the modulation bandwidth of the light emitting diode is narrow, the capacity of the visible light communication system is limited, the spectral efficiency and number of endpoint user can be improved by the multiple access technique. However, there is strong inter-user interference among multiple access users in the visible light communication system. In view of this problem, by utilizing the correlation among received signals of the visible communication system, a multiple user detection and signal recovery method of multiple users for multiple access based on deep neural network was proposed. The transmitter model and the receiver model of the visible light communication system were presented based on sparse code multiple access, the temporal convolutional network was adopted to learn the inter-signal temporal correlation of the long sequence, the output sequence was delivered to dense layer to learn the spatial mapping relationship of the signal sequence, in the end, signals of all users were recovered in the receiver of the visible light communication system. Experimental results indicate that the proposed signal recovery method improves the communication performance of the visible light communication system multiple access effectively, and the proposed method can play an active role under the condition of different communication distances, different signal noise ratios and transmit speeds.

The development of space-based Internet of Things is limited by insufficient allocable frequency resources and low spectrum utilization. To meet the demand for massive access users under the condition of restricted frequency resources, a multi-dimensional hybrid multiple-access method for space-time-frequency-code division based on user distribution (MHSTFC-UD) is established. It divides the beam cell of a low orbit satellite into the central and edge area and dynamically adjusts the radius of the central area and the allocation of frequency resources according to the distribution of users. The optimization model for the radius of the central area and the allocation of frequency resources is established and solved by the genetic algorithm. Also, it takes the edge area as the protection interval to realize the full-frequency multiplexing between the beam cells in the time domain, space domain and code domain. The simulation results show that compared with the traditional method of frequency reuse in two or three dimensions, the multi-dimensional hybrid multiple-access method can improve the maximum access capacity of a single satellite user by one to three orders of magnitude. Moreover, the MHSTFC-UD can increase users by an additional 11.5% to 33.1% compared to fixed area division and frequency resource allocation. [ABSTRACT FROM AUTHOR]

Molecular communication (MC) represents a paradigm shift in communication technologies, extending beyond traditional electromagnetic methods by incorporating advances in nanotechnology, biotechnology, and communication theory. This innovative approach holds promise for groundbreaking applications in diverse fields such as medicine, military operations, and environmental monitoring. MC employs molecules to carry and transmit data. In concentration-encoded molecular communication (CEMC), information is represented through the concentration levels of the transmitted molecules. In this study, we introduce a novel method named time-hopping concentration-position shift keying (TH-CPSK), designed to facilitate multiple access within MC networks. The TH-CPSK method encodes information based on the position of the transmitted molecular concentration, significantly enhancing the accuracy of data transmission by reducing interference in MC channels. Numerical simulations reveal that an increase in the number of users adversely affects communication performance. Furthermore, our findings indicate that augmenting the number of hops improves communication performance at transmitter-receiver distances of 1 cm and 2 cm. Conversely, at a distance of 3 cm, performance degradation is observed, attributed to the increased complexity. Therefore, it is important to carefully select the number of hops considering the molecular channel's characteristics. Overall, TH-CPSK can enhance the efficiency and reliability of CEMC systems, offering a significant step forward in the realization of MC's potential applications. [ABSTRACT FROM AUTHOR]

The increasing usage of the Internet of Things (IoT) and other modern massive machine-type communication applications has led to a growing demand for more efficient utilization of available communication bandwidth. These applications necessitate the concurrent operation of multiple communication channels. The classical approach is Orthogonal Multiple Access (OMA), such as Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA). However, an emerging alternative is Non-Orthogonal Multiple Access (NOMA), where communicating parties share one or more resources. The power domain NOMA scheme employs superposition coding (SC) and successive interference cancellation (SIC) to mitigate the effects of interference caused by overlapping frequency bands. Our proposal presents a partial NOMA solution: we retain the bandwidth division from the FDMA scheme but allow for partial overlap between neighboring channels. In this approach, we do not apply SIC; instead, we treat the interference caused by the overlap as part of the noise. This scheme enables the use of a wider bandwidth for individual channels. By carefully controlling the extent of overlap, we achieve a capacity increase resulting from the wider bandwidth that outweighs the capacity loss due to increased noise. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunications Science is the property of Beijing Xintong Media Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The increasing usage of the Internet of Things (IoT) and other modern massive machine-type communication applications has led to a growing demand for more efficient u tilization o f a vailable c ommunication bandwidth. These applications necessitate the concurrent operation of multiple communication channels. The classical approach is Orthogonal Multiple Access (OMA), such as Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA). However, an emerging alternative is Non-Orthogonal Multiple Access (NOMA), where communicating parties share one or more resources. The power domain NOMA scheme employs superposition coding (SC) and successive interference cancellation (SIC) to mitigate the effects of interference caused by overlapping frequency bands. Our proposal presents a partial NOMA solution: we retain the bandwidth division from the FDMA scheme but allow for partial overlap between neighboring channels. In this approach, we do not apply SIC; instead, we treat the interference caused by the overlap as part of the noise. This scheme enables the use of a wider bandwidth for individual channels. By carefully controlling the extent of overlap, we achieve a capacity increase resulting from the wider bandwidth that outweighs the capacity loss due to increased noise.

Sixth-generation (6G) wireless networks demand a more efficient implementation of non-orthogonal multiple access (NOMA) schemes for severe multipath fading environments to serve multiple users. Using non-orthogonal multiple access (NOMA) schemes in IoT 6G networks is a promising solution to allow multiple users to share the same spectral and temporal resource, increasing spectral efficiency and improving the network's capacity. In this work, we have evaluated the performance of a novel progressive pattern interleaver (PPI) employed to distinguish the users in interleaved division multiple access (IDMA) schemes, suggested by 3GPP guidelines as a NOMA scheme, with two multi-carrier modulation schemes known as single-carrier frequency-division multiple access (SC-FDMA) and orthogonal frequency-division multiplexing (OFDM), resulting in SC-FDMA-IDMA and OFDM-IDMA schemes. Both schemes are multi-carrier schemes with orthogonal sub-carriers to deal against inter-symbol interference (ISI) and orthogonal interleavers for the simultaneous access of multiple users. It has been suggested through simulation outcomes that PPI performance is adequate with SC-FDMA-IDMA and OFDM-IDMA schemes in terms of bit error rate (BER) under multipath channel conditions. Moreover, regarding bandwidth requirement and the implementation complexity of the transmitted interleaver structure, PPI is superior to the conventional random interleaver (RI). [ABSTRACT FROM AUTHOR]

The diverse applications of Machine-Type Communication (MTC) lead to exponential growth in Machine to Machine traffic. In connection with MTC deployment, a large number of devices are expected to access the wireless network simultaneously, resulting in network congestion. The conventional Random Access mechanism lacks the capability to handle the large number of access attempts expected from massive MTC (mMTC). Additionally, mMTC transceivers often operate by generating short data packets in a sporadic and sometimes unpredictable manner. To address the growing need for efficient communication in massive machine-type communication scenarios we propose an innovative solution, called Deep Reinforcement Learning-Based Multi-Access (DRLMA). Our model considers the Base Station (BS) as an agent navigating the landscape of machine-type communication devices. This agent dynamically switches between grant-based and grant-free access to leverage their strengths. We address the multi-access problem, formulating it as a Partially Observable Markov Decision Process (POMDP), to better understand and tackle challenges associated with dynamic access policies. Leveraging Deep Reinforcement Learning techniques, our approach optimizes sporadic traffic patterns, crafting an adaptable access policy to maximize both network throughput and energy efficiency under the battery constraint. Simulation results show that proposed DRLMA scheme outperforms traditional access schemes and existing access protocols in sporadic traffic in terms of the energy efficiency, throughput and network life time.

In recent times, a fluid antenna system (FAS) has gained attention as a potential contender for 6G wireless networks. Fluid antenna multiple access (FAMA) is a new technology that allows each user to constantly move to the position with the strongest signal-to-interference ratio (SIR) by means of a single RF-chain port fluid antenna. Research works in FAMA mainly focus on propose models and solutions linked to the enhancement of FAMA from several aspects, including FAS system, enhancing orthogonal and non-orthogonal multiple access, channel modeling, diversity gain, artificial intelligence (AI) techniques, FAMA with other emerging technologies for 6G such as intelligent reflecting surface (IRS), multiple-input multiple-output (MIMO), terahertz (THz) communication, etc. There is no survey which covers all these important aspects of FAMA. Based on several concerns, a comprehensive taxonomy of FAMA has been presented in this study. First, FAS system is discussed. Then, FAMA mechanism is presented with its channel modeling and diversity gain. After that, FAMA is investigated with other emerging technologies such as IRS, MIMO, THz communication, etc. AI approaches to enhance FAMA are provided. In the end, we cover the potential research directions for further study in all areas. When designing and enhancing the FAS system, facilitating communication via FAMA, and integrating it with other cutting-edge technologies for 6G, this article may serve as a reference or guidance.

Chromatic dispersion (CD) is one of the key limitations of increasing the transmission performance for short-reach transmission. The available optical dispersion-compensation techniques are not favored due to their high complexity and other expenses such as power. Reservoir computing is reviewed as a promising technique to provide equalization with memory in an easily trainable fashion, and the properties of the reservoir network are directly linked to system performance. In this article, the digital reservoir computing (RC) based CD-compensation technique is investigated to enhance the transmission performance for digital filter multiple access passive optical network (PON). Numerical results show within 50-km single mode fiber transmission distance for 16 GHz signal bandwidth, the RC-based technique is effective for CD compensation to improve the capacity by 25%.

An experimental study is conducted on several retro-reflective beamforming schemes for wireless power transmission to multiple wireless power receivers (referred to herein as “targets”). The experimental results demonstrate that, when multiple targets broadcast continuous-wave pilot signals at respective frequencies, a retro-reflective wireless power transmitter is capable of generating multiple wireless power beams aiming at the respective targets as long as the multiple pilot signals are explicitly separated from one another by the wireless power transmitter. However, various practical complications are identified when the pilot signals of multiple targets are not appropriately differentiated from each other by the wireless power transmitter. Specifically, when multiple pilot signals are considered to be carried by the same frequency, the wireless power transmission performance becomes heavily dependent on the interaction among the pilot signals, which is highly undesirable in practice. In conclusion, it is essential for a retro-reflective wireless power transmitter to explicitly discriminate multiple targets’ pilot signals among each other.

Molecular communication (MC) represents a paradigm shift in communication technologies, extending beyond traditional electromagnetic methods by incorporating advances in nanotechnology, biotechnology, and communication theory. This innovative approach holds promise for groundbreaking applications in diverse fields such as medicine, military operations, and environmental monitoring. MC employs molecules to carry and transmit data. In concentration-encoded molecular communication (CEMC), information is represented through the concentration levels of the transmitted molecules. In this study, we introduce a novel method named time-hopping concentration-position shift keying (TH-CPSK), designed to facilitate multiple access within MC networks. The TH-CPSK method encodes information based on the position of the transmitted molecular concentration, significantly enhancing the accuracy of data transmission by reducing interference in MC channels. Numerical simulations reveal that an increase in the number of users adversely affects communication performance. Furthermore, our findings indicate that augmenting the number of hops improves communication performance at transmitter-receiver distances of 1 cm and 2 cm. Conversely, at a distance of 3 cm, performance degradation is observed, attributed to the increased complexity. Therefore, it is important to carefully select the number of hops considering the molecular channel’s characteristics. Overall, TH-CPSK can enhance the efficiency and reliability of CEMC systems, offering a significant step forward in the realization of MC’s potential applications.

For satellite internet of things (IoT) scenarios with high propagation delay and the need to serve a larger number of users, firstly the shortcomings of IoT NTN in terms of technical solutions were analyzed, and then a new type of multi access solution called uncoordinated random access and NOMA transmission (URAT) was proposed.“Uncoordinated” refers to the process where a terminal does not require specialized network coordination signaling; “NOMA transmission” refers to the sharing of base station time-frequency resources by all terminals; URAT also achieves the integration of multiple access and NOMA transmission.Theoretical analysis and numerical simulation results indicated that the proposed scheme could reduce multi access latency, improve system efficiency, and increase the number of devices that could be served.It will be a potential solution for the 6G satellite IoT scenarios.

The widespread adoption of wireless body area network (WBAN) in healthcare presents opportunities to meet the increasing demand for medical services. WBAN enables continuous real-time (RT) monitoring through biomedical sensor nodes positioned in or around a patient's body, collecting vital physiological data. In addition, WBAN imposes stringent criteria for energy efficiency and reliability throughout data collection and transmission. This review paper places significant emphasis on the fundamental concept and essential characteristics of WBAN technology. First, the WBAN features, including architecture, sensor nodes types and network topology is presented. Then, the study explores a wide variety of communication standards and multiple access (MA) mechanism deployed in this technology. Moreover, it discusses open research and challenging issues such as heterogeneous traffic, quality of services (QoS), energy consumption, reliability, interference management, and human body movements effect. Finally, the paper is concluded, and future directions are identified in this evolving field of human health monitoring technology. [ABSTRACT FROM AUTHOR]

Remote lab systems are one of the essential requirements for an increased academic productivity in the modern digital world. These systems support and facilitate effective migration from face-to-face classroom education to online education. Digital technology applications and processes are required to easily build a remote lab system. With the availability of multiple access techniques, users can comfortably share laboratory equipment among themselves. The sharing of resources using the remote lab system is highly required for a smooth deployment and implementation of online education. This paper therefore proposed and tested some techniques that combine Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) in remote lab systems. The tested techniques are Multi-Carrier Direct Sequence CDMA (MC-DS-CDMA), Multi-Tone CDMA (MT-CDMA), Multi-Carrier CDMA (MC-CDMA), and Spread Spectrum Multi-Carrier Multiple Access (SS-MC-MA). The first step proposed in this work had to do with the setting of the comparison criteria. At the second step, the solutions cited previously in the real equipment was tested and the best option that met the criteria was selected for the eLab system since the performance technique varies with the laboratory equipment characteristic. The four techniques that were tested demonstrated high performance in telecommunications and online laboratory systems. The implementation of these techniques will benefit universities in several ways, which include reduction of remote lab cost and optimization of sharing of online resources among users. This will further provide students with conducive learning environment by addressing the challenges of reservation and time slot limit. It is therefore recommended that MC-CDMA should be integrated into remote lab system. [ABSTRACT FROM AUTHOR]

In Wi-Fi standards, a relatively narrow range of frequency spectrums is declared as working, on the operation of which additional restrictions are imposed in different countries. When creating dense wireless network ecosystems focused on massive information traffic, this circumstance causes significant interference even in the case of using Wi-Fi 6/6E-compatible equipment. An effective solution to this problem is the implementation of a centralized management mechanism for the relevant parameters of the target network ecosystem. The growing attention to ecology and rational use of electricity makes the problem of maximizing energy consumption for useful information traffic in a dense Wi-Fi 6/6E ecosystem an urgent task. Only the addressed information traffic between the transmitter and the target subscriber, which are subjects of the OFDMA technology and the MU-MIMO multiple access system (with an emphasis on the latter), is considered useful. To solve the problem, the authors formalized the Wi-Fi 6/6E ecosystem's energy consumption model, which takes into account the specifics of OFDMA and MU-MIMO, the influence of the communication channel characteristics on the speed of target information transfer, and detailed energy consumption for maintaining the network infrastructure in a functional state. Based on the created model, the research problem is represented by the difference between two monotonic functions, relative to which the problem of optimization with restrictions is set. The process of solving this problem is presented in the form of information technology with a branch-and-bound hierarchy and a nested unconditional optimization problem. The results of simulated modelling in the MATLAB-NS3 environment showed a significant advantage of the authors' approach. The energy power consumption by the Wi-Fi 6/6E ecosystem, the parameters of which were adjusted with the help of the authors' information technology, decreased by more than four times. [ABSTRACT FROM AUTHOR]

Copyright of Space-Integrated-Ground Information Networks is the property of Beijing Xintong Media Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An Internet of things (IoT) network is a distributed set of "smart" sensors, interconnected via a radio channel. The basic method of accessing the radio channels for these networks is Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA), in which access is carried out on the basis of contention, and confirmation of the correct reception of the packet is achieved using a receipt. If the sizes of information packets are small and comparable to the sizes of receipts, then the transmission of receipts requires a significant bandwidth of the channel, which reduces the efficiency of the network. This problem exists not only for IoT networks but also for monitoring systems, operational management of fast processes, telemetry, short messaging and many other applications. Therefore, an urgent task is to develop effective methods of multiple random access in the transmission of short information packets, the size of which is comparable to the size of receipts. To solve this problem, the authors proposed modifications of CSMA/CA random access in which, when packet collisions are detected, a diagnostic message (DM) is generated and transmitted in the broadcast mode. Based on simulation modeling, it is shown that in a wide range of network loads, the proposed random access options provide an increase in network capacity (the number of connected subscribers) of 1.5–2 times compared to the basic CSMA/CA access method when the size of the information packet is an order of magnitude larger than the size of receipts. The variant of access without acknowledgment is also considered, in which, as shown by the simulation results, at sufficiently large loads, the network can go into an unstable state. [ABSTRACT FROM AUTHOR]

This study explores a composite space-time and frequency-domain spreading strategy, designed to augment the capacity of multicarrier 5G systems operating over frequencyselective Rayleigh fading channels. The focus is directed towards a comprehensive analysis of the Bit Error Rate (BER) performance of the proposed system, with adjustments made to various parametric values. In tandem, receiver optimization techniques are meticulously studied, and their outcomes are positioned against existing literature. Within this context, the Parallel Interference Canceller (PIC) emerges as a viable alternative to the De-correlating Detector (DD), a shift primarily driven by the latter's heightened complexity and noise amplification. Additionally, this study demonstrates the acquisition of a larger number of users exclusively employing transmission diversity, thereby eliminating the need for receiving diversity and additional code sets. This approach incrementally augments hardware complexity at both ends of the transmission link, a minor trade-off for the benefits garnered. The efficacy of this scheme is substantiated through MATLAB simulations, indicating a promising avenue for improving the capacity of multicarrier 5G systems. The findings pave the way for significant advancements in the development of efficient and robust communication systems for the 5G era and beyond. [ABSTRACT FROM AUTHOR]

Time Reversal (TR) has been proposed as a competitive precoding strategy for low-complexity devices, relying on ultra-wideband waveforms. This transmit processing paradigm can address the need for low power and low complexity receivers, which is particularly important for the Internet of Things, since it shifts most of the communications signal processing complexity to the transmitter side. Due to its spatio-temporal focusing property, TR has also been used to design multiple access schemes for multi-user communications scenarios. However, in wideband time-division multiple access schemes, the signals received by users suffer from significant levels of inter-symbol interference as well as interference from uncoordinated users, which often require additional processing at the receiver side. This paper proposes an iterative TR scheme that aims to reduce the level of interference in wideband multi-user settings, while keeping the processing complexity only at the transmitter side. The performance of the proposed TR-based protocol is evaluated using analytical derivations. In addition, its superiority over the conventional Time Reversal Division Multiple Access (TRDMA) scheme is demonstrated through simulations as well as experimental measurements at 2.5 GHz carrier frequency with variable bandwidth values.

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.

Traditional multiple access schemes, as well as more recent preamble-based schemes, cannot achieve the extremely low latency, complexity, and collision probability required by the next-generation Internet-of-Things (IoT) networks to operate. To address such issues and further reduce the latency and packet loss, we introduce a novel semi-grant-free multiple access protocol for short packet transmission, the partial-information multiple access (PIMA) scheme. PIMA transmissions are organized in frames, and in the partial information acquisition (PIA) sub-frame of each frame, the base station (BS) estimates the number of active devices, i.e., the devices having packets waiting for transmission in their queue. Based on this estimate, the BS chooses both the total number of slots to be allocated in the data transmission (DT) sub-frame and the respective user-to-slot assignment. Although collisions may still occur due to multiple users assigned to the same slot, they are drastically reduced with respect to slotted ALOHA-based schemes, while achieving lower latency than both time-division multiple-access (TDMA) and preamble-based protocols, due to the extremely reduced overhead of the PIA sub-frame. We assess the performance of PIMA under various activation statistics, proving the robustness of the proposed solution to the traffic intensity, also with traffic bursts.

The TT＆amp;C and data transmission of spacecraft are divided into two methods: space-based and ground-based.Among them, space-based method has the advantages of global coverage, access at any time, and real-time information return, and have a wide range of application prospects.But it also puts forward certain requirements for the dynamic bandwidth allocation of its multi-spacecraft.Based on the studied of medium-orbit TT＆amp;C, data transmission constellation network architecture and multiple access protocols, a dynamic bandwidth allocation algorithm for on-doard multi-beam, multi-spacecraft users, and multi-task priorities for data transmission tasks was proposed.It was very suitable for the on-demand and real-time resource allocation of data transmission requests of multiple spacecraft in the mid-orbit constellation, and could be used as a multiple access protocol model for space-based measurement and control and data transmission access networks.

Considering the progress of the Flora Vascular de la República Argentina project, we introduce the first interactive, multi-access key to the angiosperm families of the Argentinian Flora. The key is an open resource, built under Lucid ™ software, and available through the Flora Argentina site (https://clave.floraargentina.edu.ar/), with an on-line form for the user's suggestions. We explain the advantages of multi-access keys versus dichotomous keys, briefly describe how the key was built, and how Lucid tools can be applied (Spanish version) for a better use of the key. [ABSTRACT FROM AUTHOR]

Copyright of Frontiers of Information Technology & Electronic Engineering is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using reconfigurable fluid antennas, it is possible to have a software‐controlled position‐tuneable antenna to realize spatial diversity and multiplexing gains that are previously only possible using multiple antennas. Recent results illustrated that fast fluid antenna multiple access (f‐FAMA) which always tunes the antenna to the position for maximum signal‐to‐interference ratio (SIR) on a symbol‐by‐symbol basis, could support hundreds of users on the same radio channel, all by a single fluid antenna at each user without complex coordination and optimization. The network outage rate, nevertheless, depends on the SIR threshold chosen for each user. Motivated by this, this paper adopts a first‐order approximation to obtain the outage probability expression from which a closed‐form solution is derived for optimizing the SIR threshold in maximizing the network outage rate. Moreover, a closed‐form expression is provided to estimate the number of users in the f‐FAMA network in which the outage rate begins to plateau. Numerical results show that the proposed SIR threshold achieves near‐maximal outage rate performance. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) technology is a significant topic of the present 5G investigation. A possible NOMA approach is Sparse Code Multiple Access (SCMA), increasing next-generation communication's ability to handle multiple users. In SCMA, codebook designing and optimization are crucial components that define the performance of multiple access systems. In this work, the complete design procedure of the SCMA codebook based on interleaving is explained and simulated. Furthermore, a chaotic interleaving based onArnold’sCat map is proposed to reduce the computational complexity. The performance of the SCMA codebook based on interleaving is evaluated through comparison with selected codebooks for SCMA multiplexing. The measures used for performance evaluation include Bit Error rate (BER), Peak to Average Power Ratio(PAPR), and minimum EuclidianDistance(MED). The results show that the proposed codebook with chaotic interleaving achieves comparable performance to the traditional codebook based on interleaving and less MED and higher BER compared to computer-generated and 16-star QAM codebook design methods but with reduced complexity.

With the wide application of the energy harvesting wireless sensor network (WSN) in many real-time communication scenarios, such as environmental monitoring, industrial automation and battlefield surveillance, the multiple access of such WSN needs to take into account both the delivery deadline constraint of data packets and the energy harvesting dynamics of sensor nodes.Due to the inherent decoupling of interference, delivery urgency and remaining energy, the design and optimization of such multiple access are more challenging than that of traditional multiple access that only needs to take into account the packet traffic pattern.A centralized access scheme was designed with the access actions relying on the global knowledge of current delivery urgency and remaining energy.And then, to avoid the costly overhead in the centralized access, a decentralized access scheme was designed with the access probabilities merely relying on the local knowledge of delivery urgency and remaining energy.Under the objective of maximizing the network throughput, the centralized access schemes were formulated with complete and simplified knowledge as two Markov decision processes (MDPs), respectively, and the backward induction algorithm was used to obtain optimal centralized policies for these MDPs.Furthermore, the decentralized access was formulated with simplified knowledge as a decentralized MDP, and the Markov policy search was used to propose an ε-optimal decentralized policy.Simulations under a wide range of network configurations were provided to verify the effectiveness of the simplified modeling and demonstrate the performance advantage of the proposed polices.

Sparse code multiple access (SCMA) is a multi-dimensional codebook based on a class of non-orthogonal multiple access (NOMA) technologies enabling the delivery of non-orthogonal resource elements to numerous users in 5G wireless communications without increasing complexity. This paper proposes a computer-generated sparse code multiple access (CG-SCMA) technique, where the minimum Euclidian distance (MED) of a star 16-point quadrature amplitude modulation is maximized by CG-SCMA, thus creating a complex SCMA codebook based on optimizing the difference between the first and other radiuses over rotated constellations. To specify the most suitable values for this constellation, it is divided into four sub-constellations using trellis coded modulation (TCM) in an effort to optimize MED. The new codebook has four sub-constellations with MED values of 3.85, 2.26, 2.26, and 3.85, respectively. Application of the message passing algorithm (MPA) ensures low complexity of the decoding process

Sparse code multiple access (SCMA) is a multidimensional codebook based on a class of non-orthogonal multiple access (NOMA) technologies enabling the delivery of nonorthogonal resource elements to numerous users in 5G wireless communications without increasing complexity. This paper proposes a computer-generated sparse code multiple access (CG-SCMA) technique, where the minimum Euclidian distance (MED) of a star 16-point quadrature amplitude modulation is maximized by CG-SCMA, thus creating a complex SCMA codebook based on optimizing the difference between the first and other radiuses over rotated constellations. To specify the most suitable values for this constellation, it is divided into four subconstellations using trellis coded modulation (TCM) in an effort to optimize MED. The new codebook has four sub-constellations with MED values of 3.85, 2.26, 2.26, and 3.85, respectively. Application of the message passing algorithm (MPA) ensures low complexity of the decoding process. [ABSTRACT FROM AUTHOR]

Emerging wireless technologies are envisioned to support a variety of applications that require simultaneously maintaining low latency and high reliability. Non-orthogonal multiple access techniques constitute one candidate for grant-free transmission alleviating the signaling requirements for uplink transmissions. In open-loop transmissions over fading channels, in which the transmitters do not have access to the channel state information, the existing approaches are prone to facing frequent outage events. Such outage events lead to repeated re-transmissions of the duplicate information packets, penalizing the latency. This paper proposes a multi-access broadcast approach in which each user splits its information stream into several information layers, each adapted to one possible channel state. This approach facilitates preventing outage events and improves the overall transmission latency. Based on the proposed approach, the average queuing delay of each user is analyzed for different arrival processes at each transmitter. First, for deterministic arrivals, closed-form lower and upper bounds on the average delay are characterized analytically. Secondly, for Poisson arrivals, a closed-form expression for the average delay is delineated using the Pollaczek-Khinchin formula. Based on the established bounds, the proposed approach achieves less average delay than single-layer outage approaches. Under optimal power allocation among the encoded layers, numerical evaluations demonstrate that the proposed approach significantly minimizes average sum delays compared to traditional outage approaches, especially under high arrival rates. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Current generation mobile communications require high-quality services. Adopting multiple access (MA) and multi-carrier waveforms potentially enhances the quality of services offered to end-users. However, in the majority of literature, the integration of multi-carrier and multiple-access approaches have not been extensively examined. One possible solution is to review multiple access and multi-carrier waveforms simultaneously to create a favorable foundation for the integration of these schemes. Thus, we consider a comprehensive review of multiple-access systems and multi-carrier waveforms jointly from $1^{st}$ to $5^{th}$ -generation (1G-5G) cellular networks. Initially, we present orthogonal MA (OMA) schemes called: frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and orthogonal frequency division multiple access (OFDMA) that have been utilized in 1G, 2G, 3G, and 4G, respectively. In addition, 5G wireless non-orthogonal multiple access (NOMA) techniques such as power domain NOMA (PD-NOMA), code domain NOMA (CD-NOMA), and other NOMA multiplexing methods are addressed in detail. On the other hand, we glanced at 5G cellular multi-carrier waveforms such as filter bank multi-carrier (FBMC), universal filtered multi-carrier (UFMC), generalized frequency division multiplexing (GFDM), and filtered orthogonal frequency division multiplexing (f-OFDM) waveforms. The assessment and comparison between different OMA, NOMA, and multi-carrier waveforms are carried out with the parameters: modulation schemes, bit error rate (BER), signal to noise ration (SNR), sum rate, peak-to-average power ratio (PAPR), latency, out of band emission (OOBE), and complexity. The analytical formulas of OMA, NOMA, and multi-carrier waveform schemes are also derived and verified using simulation data. Each multiple access strategy’s merits, shortcomings, applications, and factors influencing its performance are also addressed. Eventually, possible recommendations for the integration of multiple-access and modulation technologies for next-generation mobile networks are also included.

Increasing number of devices connected to the networks, applications and demands of new generation wireless communications cause very high energy consumption resulting in large amount of carbon emission. Thus, energy harvesting solutions together with accomplishing information transmission are required for energy efficient communications of new wireless communications generations such as 5G and 6G (i.e., 5G+). As such, due to the promise of energy efficient green communications, simultaneous wireless information and power transfer (SWIPT) techniques are expected to be indispensable component of 5G+. In this survey, the literature of multiuser SWIPT communications is reviewed for 5G+. Different multiuser SWIPT scenarios including multi-antenna communications, cooperative communications, network coding, communications security, and unmanned aerial vehicle (UAV)-enabled communication systems based on multiuser diversity and multiple access methods are thoroughly reviewed. The experimental studies are also discussed.

Visible light communication (VLC) has been introduced as a key enabler for high-data rate wireless services in future wireless communication networks. In addition to this, it was also demonstrated recently that non-orthogonal multiple access (NOMA) can further improve the spectral efficiency of multi-user VLC systems. In this context and owing to the significantly promising potential of artificial intelligence in wireless communications, the present contribution proposes a deep Q-learning (DQL) framework that aims to optimize the performance of an indoor NOMA-VLC downlink network. In particular, we formulate a joint power allocation and LED transmission angle tuning optimization problem, in order to maximize the average sum rate and the average energy efficiency. The obtained results demonstrate that our algorithm offers a noticeable performance enhancement into the NOMA-VLC systems in terms of average sum rate and average energy efficiency, while maintaining the minimum convergence time, particularly for higher number of users. Furthermore, considering a realistic downlink VLC network setup, the simulation results have shown that our algorithm outperforms the genetic algorithm (GA) and the differential evolution (DE) algorithm in terms of average sum rate, and offers considerably less run-time complexity.

We propose a novel indoor optical wireless communications (OWC) system using few-mode based beam shaping integrating time-slot coding (TSC) scheme to serve multiple users simultaneously. We simulated an indoor OWC system incorporating single-sideband (SSB) 16 quadrature amplitude modulation (16-QAM) modulated signals in a multi-user environment employing few-mode based beam shaping with single-photodetector (PD) and multi-PD reception with maximum ratio combining (MRC), respectively. The results show that for both single-PD and multi-PD receptions, the bit-error-rate (BER) performance can be significantly improved at different positions within the cell and the size of the effective coverage (BER−3) can be increased by 4 times by employing few-mode based beam shaping scheme at 1:1.79 power ratio between LP01 mode and LP11 mode, compared to conventional OWC systems without few-mode based beam shaping scheme. In addition, the system tolerance to signal overlapping can also be enhanced with the proposed few-mode based beam shaping. The optimal power ratios of LP01 mode and LP11 mode when achieving the maximum effective coverage under 7% and 20% HD-FEC thresholds for single-PD and multi-PD reception have also been investigated. Furthermore, the tolerance to the interval delay with 0.23 and 0.28 symbols can be achieved in single-PD and multi-PD reception, respectively.

An Internet of things (IoT) network is a distributed set of “smart” sensors, interconnected via a radio channel. The basic method of accessing the radio channels for these networks is Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA), in which access is carried out on the basis of contention, and confirmation of the correct reception of the packet is achieved using a receipt. If the sizes of information packets are small and comparable to the sizes of receipts, then the transmission of receipts requires a significant bandwidth of the channel, which reduces the efficiency of the network. This problem exists not only for IoT networks but also for monitoring systems, operational management of fast processes, telemetry, short messaging and many other applications. Therefore, an urgent task is to develop effective methods of multiple random access in the transmission of short information packets, the size of which is comparable to the size of receipts. To solve this problem, the authors proposed modifications of CSMA/CA random access in which, when packet collisions are detected, a diagnostic message (DM) is generated and transmitted in the broadcast mode. Based on simulation modeling, it is shown that in a wide range of network loads, the proposed random access options provide an increase in network capacity (the number of connected subscribers) of 1.5–2 times compared to the basic CSMA/CA access method when the size of the information packet is an order of magnitude larger than the size of receipts. The variant of access without acknowledgment is also considered, in which, as shown by the simulation results, at sufficiently large loads, the network can go into an unstable state.

We propose a data transmission model in a special topology network in which two players (network nodes) seek to send as many randomly appearing data packets as possible through a common node. It is assumed that the players do not have complete information about whether the other player has a data packet for possible transfer. For the solution, it is proposed to use cooperative and noncooperative approaches in accordance with which a cooperative solution and Nash equilibrium are found. The price of anarchy is calculated to compare the total payoffs of the players in the cooperative solution and the Nash equilibrium. [ABSTRACT FROM AUTHOR]

This study investigated relay-assisted mode 1 sidelink (SL) multicast transmission, which encounters interference from mode 2 SL transmission, for use in low-latency vehicle-to-everything communications. To accommodate mode 1–mode 2 SL traffic, we use the hybrid multiple access (MA) approach, which combines orthogonal MA (OMA) and nonorthogonal MA (NOMA) schemes. We introduce a low-complexity location-based hybrid MA algorithm and its associated relay selection that can be used when SL channel state information is unavailable. [ABSTRACT FROM AUTHOR]

In this correspondence, we propose a closed-form resource allocation called partition-based multiple access (MA), which simultaneously utilizes both a reconfigurable intelligent surface (RIS) and non-orthogonal multiple access (NOMA) to reduce processing overhead and transmit power. The RIS can tune the mmWave signal and reduce the downlink transmit power, and NOMA achieves a relatively higher spectral efficiency than other MA methods. The integration of the RIS and NOMA, thus, can be a powerful solution. Previous studies have yet to obtain a closed-form solution for both the beam tuning settings and the decoding order in low complexity in the conventional RIS-NOMA. The proposed partition-based MA method, however, divides and arranges the array elements of the RIS to generate a fine beam for NOMA communications. We compare the transmit power reduction of the proposed method with the transmit power reduction of time-sharing and decode-and-forward relay. To confirm the feasibility of the integration, we also derive the criteria for MA mode selection. [ABSTRACT FROM AUTHOR]

Vehicle to everything (V2X) faces several challenges including high data rate, low latency and stable connectivity requirements. Due to increased number of connected vehicles, Interference too appears to be a serious issue in V2X systems. Consequently, careful selection of multiple access techniques can lead to improved interference mitigation together with higher spectral efficiency and data rate. Vehicle mobility with growing traffic density is a demanding task that affects probability of vehicle connectivity, thereby resulting into requirement of sustained vehicle linkage for ongoing traffic safety. In this regard, our paper employs Rate Splitting Multiple Access (RSMA) technique, which considers change of both channel strength and direction for improved interference mitigation leading towards enhanced spectral efficiency. RSMA is optimized for weighted sum rate, further; it is integrated with mobility management to demonstrate sustained connectivity in the presence of increased traffic density. Presented results have been found promising, both in terms of spectral efficiency and stable connectivity. RSMA 5G V2X outperformed at higher Signal to noise ratio (SNR) values and on average achieved 25% better spectral efficiency compared to Non Orthogonal Multiple Access (NOMA) technique.

Today, steganographic systems with multiple access are of considerable importance. In such sys-tems, the orthogonal Walsh-Hadamard transform is most often used for multiplexing and divid-ing channels, which leads to the need for efficient coding of the Walsh-Hadamard transform coefficients for the convenience of their subsequent embedding. The purpose of the research is to develop a theoretical basis for efficient coding of the embedded signal in steganographic sys-tems with multiple access with an arbitrary number of users N, based on MC-CDMA technology. This purpose was fulfilled by forming the theoretical basis for constructing effective codes de-signed to encode the embedded signal in steganographic systems with multiple access. The most important results obtained are the proposed and proven relations that determine both the possible values of the Walsh-Hadamard transform coefficients, for a given value of the number of divid-ed channels, and the probability of occurrence of the given values of the Walsh-Hadamard transform coefficients, which allow the construction of effective codes to represent the embed-ded signal. In the case of the number of divided channels N=4, we propose to use a constant amplitude code that provides a smaller value of the average codeword length in comparison with the Huffman code, while the constructed code has correcting capabilities. The significance of the obtained results is determined by the possibility of using the developed theoretical basis when constructing effective codes for encoding the embedded signal in steganographic systems with multiple access at an arbitrary value of the number of divided channels N.