Time Division Multiple Access Research Articles

Over-the-Air Max-Consensus in Clustered Networks Adopting Half-Duplex Communication Technology

This work considers a network of autonomous agents that exploit the superposition property of the wireless channel for achieving max-consensus under communication constraints. In technical applications, superposition (or interference) is traditionally avoided by physically separating transmissions from different agents, e.g., by employing TDMA (Time Division Multiple Access) or FDMA (Frequency Division Multiple Access) protocols. In contrast, Over-the-Air Computation relies on simultaneous transmissions of signals in the same frequency band to boost performance. This paper extends the results presented in Molinari et al. [14] in a significant way: rather than requiring a new and hardly accessible technology that allows simultaneous receiving and transmission of signals (Full-Duplex), we present a solution based on cheap and ubiquitous Half-Duplex technology. However, Half-Duplex technology only allows agents to either receive or transmit at a given time, hence, requiring agents to be grouped into clusters. The proposed method, first, enables each cluster to achieve max-consensus within itself. Then, agents belonging to more than one cluster spread the information across different clusters that are, in general, not synchronized. The proposed max-consensus protocol can deal with asynchronism, and allows the network to achieve max-consensus within a finite number of steps. Simulations confirm our theoretical results.

Energy Constrained Sum-Rate Maximization in IRS-Assisted UAV Networks With Imperfect Channel Information

The focus of this work is maximizing the sum-rate of wireless unmanned aerial vehicle (UAV) networks with intelligent reflecting surfaces (IRS) in the presence of system practical limitations. More specifically, we consider that the phase compensation at the IRS is imperfect due to various factors such as device imperfections and channel estimation errors. Moreover, we consider that the IRS elements have limited switching frequency, which limits the possibility of being allocated to different UAVs over consecutive time slots when time-division multiple access (TDMA) is considered. To this end, we formulate an optimization problem where the objective is to maximize the network sum-rate subject to total energy and quality-of-service (QoS) constraints by optimizing the number of IRS elements and power allocated to each UAV. To solve the optimization problem, a low-complexity heuristic algorithm is proposed based on the quality of the estimated phase for each IRS element. The proposed approach is compared to benchmark techniques such as the uniform allocation process and genetic algorithm. The obtained results show that a significant sum-rate improvement of up to 45% can be gained using the proposed algorithm.

Research on onboard multistage digital demultiplexer for satellite communication based on MF-TDMA system

A new multicarrier multi-rate digital demultiplexer system structure based on MF-TDMA(Multi-Frequency Time Division Multiple Access) in a wideband satellite communication system is described. Compared with the traditional tree multicarrier demultiplexer method, the new structure uses a half-band filter instead of the quadrature mirror filter, which has three advantages: 1) It fully avoids the shortcomings of the traditional method, such as confusion distortion and amplitude distortion. 2) The computation to achieve filtering is reduced by nearly half. 3) It effectively improves the demodulation performance of the system. In this paper, the new structure performs the multistage digital demultiplexer and demodulation of the MF-TDMA signal. The results show no obvious signal distortion, which is demultiplexed by the new structure. The bit error rate of the demodulated signal is better than that of the traditional single carrier demodulator. The bit error rate is very close to the theoretical value of QPSK demodulation.

Ranging and multipath‐enhanced device‐free localisation with densely‐meshed ultra‐wideband devices

AbstractDevice‐free localisation (DFL) is a prominent example of radio sensing and radio frequency (RF)‐based passive localisation. RF‐based passive localisation approaches determine the position of a non‐cooperative user based on the user's impact on radio propagation. In this regard, DFL systems measure user‐induced changes in the properties of the received RF signals. With multipath‐enhanced device‐free localisation (MDFL), a novel passive localisation approach which is taking the advantage of user‐induced fading in the multipath signals, that is, reflected and scattered signals is introduced. In this work, the authors realise an MDFL system using low‐cost ultra‐wideband (UWB) devices. Specifically, the Qorvo (DecaWave) DW1000 module is used, for which how to access the channel impulse response is described in detail. Additionally, an overview of the required signal processing for MDFL is provided and a possible sequential Bayesian approach is introduced. Moreover, an efficient ranging scheme based on time‐division multiple access (TDMA) and message broadcasting is outlined, which allows the deployment of a large number of interconnected UWB devices. Using an exemplary network of interconnected UWB devices, the localisation performance of both DFL and MDFL for an indoor scenario is evaluated. Thereby, MDFL is shown to clearly outperform DFL in terms of robustness and accuracy. Furthermore, a TDMA‐based ranging scheme for active localisation is used, that is, for localising an UWB device carried by the user, allowing for a direct comparison between active and passive localisation. Achieving a sub‐decimetre accuracy, the active localisation outperforms both DFL and MDFL, and thus, shows the possibility of using an active localisation device to initialize MDFL.

Ultraviolet random access collaborative networking protocol based on time division multiple access

The ultraviolet network, with its advantages of high security, non-line-of-sight communication, and all-weather operation, has broad military application potential. This study proposes an ultraviolet random access collaborative networking protocol based on time division multiple access that combines the benefits of synchronous and asynchronous media access control protocols. Considering the physical layer characteristics, the frame structure of the protocol is constructed based on a cross-layer design. Compared with the time division multiple access protocol, the proposed protocol can achieve higher throughput with a lower delay and packet loss rate by the dynamic timeslot allocation mechanism. Then, the effects of maximum cache capacity and burst traffic on network performance are investigated. Finally, the conducted network experiments prove the cooperative forwarding and random access capabilities of the ultraviolet random access collaborative networking protocol. The proposed protocol provides a reliable and effective method for independent and flexible ultraviolet networks.

Optimization of LEACH Protocol for WSNs in Terms of Energy Efficient and Network Lifetime

Wireless Sensor Network (WSN) is a group of small, intelligent sensors with limited resources. WSN has limited energy restrictions, so, the network lifetime is the major challenge that directly affect the efficiency of the network. This work presents an energy-saving clustering hierarchical algorithm for WSNs; it is an improvement of Low-Energy adaptive Clustering Hierarchy (LEACH) algorithm. The aim of this algorithm is to minimize power consumption by the appropriate election of new cluster heads in every data transfer round and avoid network collisions. This goal achieved by using an efficient function to select the best cluster heads nodes in each round, which takes into account the current energy in the sensors. The proposed algorithm improves the cluster formation process by relying on the shorter distance to the base station. The Time Division Multiple Access (TDMA) mechanism also utilized to schedule the transmission of data packets to cluster heads nodes and to avoid data packet collisions at the base station. Experiments conducted in MATLAB R (2020a) software showed that the suggested algorithm extended the network lifetime by 14.5%, and improved the network throughput by 16.8% compared to the LEACH algorithm. That means, the proposed energy-saving clustering hierarchy algorithm has improved the performance of the LEACH algorithm in term of enhancing network lifetime and increasing network throughput.

Low-Latency Hybrid NOMA-TDMA: QoS-Driven Design Framework

Enabling ultra-reliable and low-latency communication services while providing massive connectivity is one of the major goals to be accomplished in future wireless communication networks. In this paper, we investigate the performance of a hybrid multi-access scheme in the finite blocklength (FBL) regime that combines the advantages of both non-orthogonal multiple access (NOMA) and time-division multiple access (TDMA) schemes. Two latency-sensitive application scenarios are studied, distinguished by whether the queuing behaviour has an influence on the transmission performance or not. In particular, for the latency-critical case with one-shot transmission, we aim at a certain physical-layer quality-of-service (QoS) performance, namely the optimization of the reliability. And for the case in which queuing behaviour plays a role, we focus on the link-layer QoS performance and provide a design that maximizes the effective capacity. For both designs, we leverage the characterizations in the FBL regime to provide the optimal framework by jointly allocating the blocklength and transmit power of each user. In particular, for the reliability-oriented design, the original problem is decomposed and the joint convexity of sub-problems is shown via a variable substitution method. For the effective-capacity-oriented design, we exploit the method of Lagrange multipliers to formulate a solvable dual problem with strong duality to the original problem. Via simulations, we validate our analytical results of convexity/concavity and show the advantage of our proposed approaches compared to other existing schemes.

A TDMA approach for OFDM-based multiuser RadCom systems

This paper is focused on the multiuser implementation of fusion of radar and communication (RadCom) in internet-of-vehicles (IoV) scenarios. Traditional time-division multiple access (TDMA) technology degrades the velocity detection performance of orthogonal frequency-division multiplexing (OFDM)-based RadCom systems. We propose a new TDMA approach for OFDM-based RadCom systems, where multiuser communication and radar detection are completed synchronously. We consider a continuous-wave TDMA OFDM structure in which random user data or Zadoff-Chu (ZC) sequences are transmitted in one symbol duration to ensure detection performance. As an application of interference cancellation method, user data demodulation and environment sensing can be simultaneously accomplished by our proposed approach. We carry out numerical evaluation and show wireless communication and radar detection performance over the continuous-wave TDMA OFDM-based RadCom approach.

A Just-in-Time Networking Framework for Minimizing Request-Response Latency of Wireless Time-Sensitive Applications

This article puts forth a networking paradigm, referred to as just-in-time (JIT) communication, to support client-server applications with stringent request-response latency requirement. Of interest is not just the round-trip delay of the network, but the actual request-response latency experienced by the application. The JIT framework contains two salient features. At the client side, the communication layer will “pull” a request from the client just when there is an upcoming transmission opportunity from the network. This ensures that the request contains information that is as fresh as possible (e.g., a sensor reading obtained just before the transmission opportunity). At the server side, the network ascertains that the server, after receiving and processing the request to generate a response (e.g., a control command to be sent to the client), will have a transmission opportunity at just this time. We realize the JIT system, including the protocol stack, over a time-division-multiple-access (TDMA) network implemented on a System-on-Chip (SoC) platform. We prove that a TDMA network with a power-of-2 time slots per superframe is optimal for realizing the server-side JIT function. Our experimental results validate that JIT networks can yield significantly lower request-response latency than networks without JIT support can.

Multilayer Joint Optimization of Packet Size and Adaptive Transmission Scheduling of Wireless Sensor Networks for Mechanical Vibration Monitoring

Limitations pertaining to the storage capacity and bandwidth of wireless sensor networks (WSNs) for mechanical vibration monitoring (MVM) pose difficulties in the realization of reliable and energy-efficient communication of big data. To prolong the lifetime of battery-limited WSNs, this paper proposes a multi-layer joint optimization of packet size and adaptive transmission scheduling (ATS) to jointly optimize the energy consumption of acquisition nodes from the storage and transmission layers. First, owing to the frequent storage and transmission of massive mechanical vibration data in WSNs, the packet size significantly affects the energy consumption during storage and transmission. The proposed packet size optimization based on the lowest energy consumption (PSO-LEC) model optimizes the energy consumption of acquisition nodes from three aspects: writing, reading, and transmission of data. Second, when transmitting massive vibration data frequently, the direct beacon frame conflict and indirect beacon frame conflict markedly induce data conflict and delay problems. Therefore, adaptive transmission scheduling based on the time division multiple access (TDMA/ATS) method is proposed to optimize the errors in data collision and transmission delay. Thus, the packet size and ATS are considered jointly to improve the network lifetime for MVM. Comprehensive experimental results indicate that the transmission reliability and energy-efficiency of the proposed scheme are significantly improved, and the network life is effectively prolonged for MVM.

IRS-Assisted Wireless Powered IoT Network With Multiple Resource Blocks

In this paper, we investigate an intelligent reflecting surface (IRS)-assisted wireless powered Internet of Things (WP-IoT) network that operates in multiple resource blocks (RBs). Particularly, the IRS helps in both downlink wireless energy transfer (WET) and uplink wireless information transfer (WIT), in a way that it improves energy reflection in WET from a power station (PS) to various IoT devices and boosts information delivery in WIT from the IoT devices to an access point (AP). Those IoT devices are capable of utilizing the collected energy, and adopting the time-division multiple access (TDMA) or non-orthogonal multiple access (NOMA) scheme in the uplink WIT. Aiming to maximize the average throughput as the overall performance indicator of the considered network, we jointly optimize the transmit power allocation of the PS, the time scheduling, and the IRS phase shifts. These coupled variables lead to the non-convexity of this optimization problem, which cannot be solved directly. To address this problem, we first design the optimal PS’s transmit power allocation for each RB. For the TDMA-based scheme, we design the closed-form IRS beam pattern of the uplink WIT. Then, the closed-form downlink and uplink time allocations are derived by the Lagrange dual method and the Karush-Kuhn-Tucker (KKT) conditions. In addition, the quadratic transformation (QT)-based Alternating Direction Method of Multipliers (ADMM) approach is proposed to iteratively derive the sub-optimal IRS beam pattern of the downlink WET in an alternated fashion. For the NOMA-based scheme, we propose to apply an alternating optimization (AO) algorithm to iteratively optimize the IRS phase shifts, where the uplink IRS beam pattern is iteratively designed by the Riemannian Manifold Optimization (RMO) approach, and the QT-based ADMM method is adopted to alternately derive the sub-optimal downlink IRS phase shifts. Finally, numerical results demonstrate the improved performance of the proposed solution approaches compared to the benchmark schemes, also highlight advantages of the application of IRS in multiple RB scenarios.

Enhancing energy efficiency of IEEE 802.15.4- based industrial wireless sensor networks

The IEEE 802.15.4 standard protocol has been widely used in many industrial wireless sensor networks (IWSN), due to its low energy, optimal data rate and relative long-distance characteristics. The protocol operation, however, should be optimized to maximize efficiency and minimize interference between wireless sensor network (WSN) nodes. The protocol supports two media access modes: carrier sense multiple access (CSMA) and time division multiple access (TDMA). In this paper, we use the enhancing energy efficiency of wireless sensor networks (EEE-WSN) protocol that alternates between these two modes. The objective is to accommodate for traffic load and to produce better efficiency. EEE-WSN utilizes CSMA in the case of having lightweight traffic, which is normally the case when having normal and non-critical events in the area of interest (AoI). It switches operation in case of heavy traffic load conditions, which often happen when a critical event is detected. Furthermore, a modified selective activation (SA) technique is used to minimize the energy consumption and to reduce the interference between redundant nodes. The protocol has been implemented using Qualnet simulator and its performance has been evaluated for different simulation time, packet rate ratios, and sent packets. The simulation results showed that the EEE-WSN outperformed the IEEE 802.15.4 while operated in either CSMA or TDMA by decreasing the energy consumption by around 1%. The amount of energy saving is exponentially increasing as a function of the simulation time. The EEE-WSN has lower end-to-end delay by 0.4, 0.1 s under light traffic conditions when compared with IEEE 802.15.4- TDMA, and IEEE 802.15.4-CSMA modes, respectively. At heavy traffic conditions, the EEE- WSN has similar end-to-end delay to IEEE 802.15.4- TDMA, and less end-to-end delay values by 0.3 s when compared to IEEE 802.15.4- CSMA. Although IEEE 802.15.4- TDAM has lower packet loss values by 5% when compared to EEE-WSN under light traffic conditions and similar loss at heavy traffic conditions, EEE-WSN still has lower packet loss values by 5% and 25% when compared to IEEE 802.15. 4- CSMA, under light and heavy traffic conditions, respectively.

A Biologically Inspired Self-Organizing Underwater Sensor Network

Wireless underwater sensor networks have various applications—such as ocean exploration and deep-sea disaster monitoring—making them a hot topic in the research field. To cover a larger area and gather more-precise information, building large-scale underwater sensor networks has become a trend. In such networks, acoustic signals are used to transmit messages in an underwater environment. Their features of low speed and narrow bandwidth make media access control (MAC) protocols unsuitable for radio communications. Furthermore, a network consists of a large number of randomly deployed nodes, making it impossible to pre-define an optimized routing table or assign a central controller to coordinate the message propagation process. Thus, optimized routing should emerge via interaction among individual nodes in the network. To address these challenges, in this paper we propose a communication coordinator under the time division multiple access (TDMA) framework. Each node in the network is equipped with such a coordinator so that messages in the network can be sent following the shortest path in a self-organized way. The coordinator consists of a slot distributor and a forwarding guide. With the slot distributor, nodes in the sensor network occupy proper communication slots and the network finally converges to the state without communication collision. This is achieved with a set of ecological niche- and pheromone-inspired laws, which encourage nodes to occupy slots that can decrease the waiting time for a node to send a message packet while weakening the enthusiasm for a node to occupy the slots that it fails to occupy several times. With the forwarding guide, a node can send the message packet to the best successor node so that the message packet can be sent to the base station along the shortest path. It has been proven that the laws in the forwarding guide are equivalent to the Dijkstra Algorithm. Simulation experiment results indicate that with our coordinator, the network can converge to the state without collision using fewer coordination messages. In addition, the time needed to send a message to the destination is shorter than that of the classical Aloha protocol.

Tackling Age of Information in Access Policies for Sensing Ecosystems.

Recent technological advancements such as the Internet of Things (IoT) and machine learning (ML) can lead to a massive data generation in smart environments, where multiple sensors can be used to monitor a large number of processes through a wireless sensor network (WSN). This poses new challenges for the extraction and interpretation of meaningful data. In this spirit, age of information (AoI) represents an important metric to quantify the freshness of the data monitored to check for anomalies and operate adaptive control. However, AoI typically assumes a binary representation of the information, which is actually multi-structured. Thus, deep semantic aspects may be lost. In addition, the ambient correlation of multiple sensors may not be taken into account and exploited. To analyze these issues, we study how correlation affects AoI for multiple sensors under two scenarios of (i) concurrent and (ii) time-division multiple access. We show that correlation among sensors improves AoI if concurrent transmissions are allowed, whereas the benefits are much more limited in a time-division scenario. Furthermore, we discuss how ML can be applied to extract relevant information from data and show how it can further optimize the transmission policy with savings of resources. Specifically, we demonstrate, through simulations, that ML techniques can be used to reduce the number of transmissions and that classification errors have no influence on the AoI of the system.

Detection of AIS messages falsifications and spoofing by checking messages compliance with TDMA protocol

Automatic identification system is a navigation aid system that allows vessels to exchange automatically positions, identity and other information. It improves the safety of the maritime traffic and helps to monitor it. However, this system can be manipulated to send falsified information and to mask illicit activities. While previous research has proposed strategies to detect these threats, none of them suggest a solution that considers the time-division multiple access (TDMA) communication protocol. In this work, the compliance of the sent messages with this protocol, specified by the system's standard, is checked for every ship to detect message falsifications. Furthermore, because the ships velocity affects TDMA protocol, a strategy based a Kalman filter is applied to track every ship and to assess the consistency of their velocity data sent. The proposed strategy was validated on real data and showed very promising results. Being computationally cheap, the method can be run in real time. Source codes of the method are open-source to foster research activities from both industry and academia in this field.

Low Complex Analog Beamforming Design in Multi-User mmWave Non-Orthogonal Multiple Access (NOMA)

In this paper, we investigate non-orthogonal multiple access (NOMA) scheme in millimeter wave (mmWave) communication to serve nonclustered multiple users. We explore a low complex design of an analog beamforming weight vector and the power requirement of users aiming to minimize the total power targeting to satisfy the spectral efficiency (SE) requirements of all users. We propose a low complex constant modulus analog beamforming (CMAB) algorithm, where we first reduce the number of signal to interference plus noise ratio (SINR) constraints, which is attained from the order of equivalent channel gain of users. Then, the nonconvex constraint of constant modulus (CM) is relaxed and semi-definite programming (SDP) is used to solve the problem. Obtained weight vector and power for all users are optimal since the rank of positive semi-definite (PSD) matrix is one. Later, CM constraint is included. Simulation results show that the proposed algorithm requires less power with minimum complexity compared to the existing research, digital beamforming NOMA and time division multiple access (TDMA) for the same SE requirements.

Active IRS Aided Multiple Access for Energy-Constrained IoT Systems

In this paper, we investigate the fundamental multiple access (MA) scheme in an active intelligent reflecting surface (IRS) aided energy-constrained Internet-of-Things (IoT) system, where an active IRS is deployed to assist the uplink transmission from multiple IoT devices to an access point (AP). Our goal is to maximize the sum throughput by optimizing the IRS beamforming vectors across time and resource allocation. To this end, we first study two typical active IRS aided MA schemes, namely time division multiple access (TDMA) and non-orthogonal multiple access (NOMA), by analytically comparing their achievable sum throughput and proposing corresponding algorithms. Interestingly, we prove that given only one available IRS beamforming vector, the NOMA-based scheme generally achieves a larger throughput than the TDMA-based scheme, whereas the latter can potentially outperform the former if multiple IRS beamforming vectors are available to harness the favorable time selectivity of the IRS. To strike a flexible balance between the system performance and the associated signaling overhead incurred by more IRS beamforming vectors, we then propose a general hybrid TDMA-NOMA scheme with device grouping, where the devices in the same group transmit simultaneously via NOMA while devices in different groups occupy orthogonal time slots. By controlling the number of groups, the hybrid TDMA-NOMA scheme is applicable for any given number of IRS beamforming vectors available. Despite of the non-convexity of the considered optimization problem, we propose an efficient algorithm based on alternating optimization, where each subproblem is solved optimally. Simulation results illustrate the practical superiorities of the active IRS over the passive IRS in terms of the coverage extension and supporting multiple energy-limited devices, and demonstrate the effectiveness of our proposed hybrid MA scheme for flexibly balancing the performance-cost tradeoff.

Empirical Study on Wireless Multimedia & Mesh Ad-Hoc Network

In this paper, we present about the construction of a wireless multimedia & mesh ad-hoc network needs to go across the mixed environment with the indoor, the wall-penetration, and the outdoor condition. This paper presents contribution to address the system design aspects of a multimedia enabled network based on IEEE 802.11g ad-hoc mode. There are distinct differences between indoor and outdoor environment and penetrating he walls stressed the system limit of the 802.11g ad-hoc mode. Therefore, routing decisions should be made intelligently with the environmental respect to maximize the bandwidth support on the end-to-end paths. One of the biggest issues in routing is providing adequate connectivity whiles calling the network. IEEE 802.16 employs TDMA (Time Division Multiple Access) as the access method and the policy for selecting scheduled links in a given time slot will definitely impact the system performance. We propose a collision-free centralized scheduling algorithm for IEEE 802.16 based Wireless Mesh Networks (WMN) to provide high-quality wireless multimedia services. We design a relay strategy for the mesh nodes in a transmission tree, taking special considerations on fairness, channel utilization and transmission delay

Exploring propagation delay and mobility in underwater acoustic networks

This work investigates the impact of mobility on underwater acoustic communication networks where the propagation delay is comparable to or larger than the packet duration. A new simulator is proposed to implement the acoustic communication timing model when the nodes are mobile or static. Synchronous and asynchronous Medium Access Control (MAC) protocols are employed with ALOHA, TDMA (Time-Division Multiple Access), and Artificial Intelligent (AI) agent nodes. Extensive simulations are conducted to study the throughput of a MAC network where a large number of source nodes transmit to a single sink node. A network of 2–15 source nodes are assumed to be randomly located in a 1500 m cubic space and some of the nodes are moving in random directions at 2–4 m/s speed. The simulation results show that the asynchronous MAC protocols achieve much higher throughput than the synchronous protocols by allowing time slots to be much shorter than the maximum propagation delay among nodes and allowing asynchronous transmission time. High mobility of a few mobile nodes also favors asynchronous protocols and improves the network throughput in a manner similar to an AI agent.

Achieving Multi-Beam Gain in Intelligent Reflecting Surface Assisted Wireless Energy Transfer

Intelligent reflecting surface (IRS) is a promising technology to boost the efficiency of wireless energy transfer (WET) systems. However, for a multiuser WET system, simultaneous multi-beam energy transmission is generally required to achieve the maximum performance, which may not be implemented by using the IRS having only a single set of coefficients. As a result, it remains unknown how to exploit the IRS to approach such a performance upper bound. To answer this question, we aim to maximize the total harvested energy of a multiuser WET system subject to the user fairness constraints and the non-linear energy harvesting model. We first consider the static IRS beamforming scheme, which shows that the optimal IRS reflection matrix obtained by applying semidefinite relaxation is indeed of high rank in general as the number of energy receivers (ERs) increases, due to which the resulting rank-one solution by applying Gaussian Randomization may lead to significant loss. To achieve the multi-beam gain, we then propose a general time-division based novel framework by exploiting the IRS's dynamic passive beamforming. Moreover, it is able to achieve a good balance between the system performance and complexity by controlling the number of IRS shift patterns. Finally, we also propose a time-division multiple access (TDMA) based passive beamforming design for performance comparison. Simulation results demonstrate the necessity of multi-beam transmission and the superiority of the proposed dynamic IRS beamforming scheme over existing schemes.