Time Division Multiple Access Technique Research Articles

Improved tag estimation method for TDMA anticollision protocols using CA-CFAR technique

Abstract Radio Frequency Identification (RFID) is considered a key element of the Internet of Things (IoT). It enables objects to be identified and tracked using radio waves. In RFID systems, several tags may be present within the range of the reader, leading to collisions and interference between signals that reduce system performance. Several anti-collision solutions have been proposed to solve this problem based on TDMA (Time-Division Multiple Access) technique, such as the ALOHA, Slotted ALOHA and Dynamic Framed Slotted ALOHA (DFSA) protocols. In this paper, we propose to improve TDMA anti-collision protocols based on the Cell Averaging Constant False Alarm Rate (CA-CFAR) scheme. The CA-CFAR technique is introduced to estimate the number of tags in the physical layer so that the reader can adjust its transmission parameters accordingly and avoid collisions. The obtained results show that this technique achieves good results in terms of system efficiency and the number of required slots to identify all the tags of the system.

Resource Allocation in Multi-Cluster Cognitive Radio Networks With Energy Harvesting for Hybrid Multi-Channel Access

Cognitive radio and energy harvesting techniques have been able to provide insight for solutions to the inefficiency in spectrum utilization and the effects of the limited storage capacity of energy batteries. Nevertheless, the requirement for interference constraint for primary user (PU) protection, the quality of service (QoS) requirements of the SUs, and the low power density of the ambient electromagnetic waves have restricted the performance of the radio frequency powered cognitive radio networks (RF-CRNs) in terms of the achievable data rate for specific energy budget or sufficient energy budget for target data rate. We are therefore motivated to investigate a radio frequency powered cognitive radio (RF-CR) with the capacity for improved achievable throughput and energy harvesting. Our model consists of multiple PUs and SUs coexisting in a practical overlapping clustered network. In each time frame for the adopted time division multiple access (TDMA) technique, SUs can exploit the multi-user benefit to harvest energy from both the PU and SUs transmissions for improved active probability. Therefore, taken into consideration the heterogeneity of each SUs in terms of their signal-to-noise (SNR), the energy harvesting rates and the inter- and intra-cluster interference, the problem is formulated into a fractional nonlinear optimization to determine the sensing duration, and power allocations that maximize the average energy efficiency of the RF-CRN subject, to constraints on energy causality, and PU protection. The performance of the proposed hybrid multi-channel access scheme is studied in terms of the trade-off between the total achievable throughput by the secondary users and the interference generated among others. Simulation results show that a trade-off exists between achieving optimal spectral efficiency and energy efficiency and, the optimal transmit power therefore depends on the primary design objective. Results equally show that the proposed hybrid multi-channel access scheme outperforms the existing scheme in literature.

Joint Resource Allocation on Slot, Space and Power Towards Concurrent Transmissions in UAV Ad Hoc Networks

With innovative applications of unmanned aerial vehicle (UAV) ad hoc networks in various areas, their demands on broad bandwidth, large capacity and low latency become prominent. The combination of millimeter wave, directional antenna and time division multiple access techniques, which enables concurrent transmissions, is promising to deal with it. In this paper, we study the resource allocation problem in UAV ad hoc networks. Specifically, the slot assignment, antenna boresight and transmit power are jointly optimized to promote the network capacity. First, we formulate the optimization problem as the maximization of the fairness-weighted network capacity, subject to the constraint on priority guarantee. Then, because the formulated problem is a mixed integer non-linear programming problem (MINLP), which is NP-hard, two algorithms called dual-based iterative search algorithm (DISA) and sequential exhausted allocation algorithm (SEAA) are respectively proposed to efficiently solve it with acceptable complexity. DISA slacks the MINLP into a continuous-variable optimization problem and solves it with the Lagrangian dual method in an iterative manner. As a heuristic method, SEAA schedules links sequentially, i.e., from high-priority to low-priority ones. Numerical results demonstrate that both DISA and SEAA can efficiently allocate resources for UAVs, while guaranteeing the fairness and priority of links.

Transmit Beamspace DDMA Based Automotive MIMO Radar

The time division multiple access (TDMA) technique has been applied in automotive multiple-input multiple-output (MIMO) radar. However, it suffers from the transmit energy loss, and as a result the parameter estimation performance degradation when the number of transmit elements increases. To tackle these problems, a transmit beamspace (TB) Doppler division multiple access (DDMA) approach is proposed. First, a phase modulation matrix with empty Doppler spectrum is introduced. By exploiting the empty Doppler spectrum, a test function based on sequential detection is developed to mitigate the Doppler ambiguity in DDMA waveform. Then, a discrete Fourier transform (DFT)-based TB in slow-time is formed. The proposed method can achieve waveform diversity in Doppler domain and generate a TB in slow-time that concentrates the transmitted power in a fixed spatial region to improve the transmit energy distribution for automotive MIMO radar, which is favored by medium/long range radar (MRR/LRR) applications. As compared to the conventional TDMA technique, the proposed TB DDMA approach can fully exploit the transmission capabilities of all transmit elements to ensure that the emitted power is efficiently used and inherits easy implementation.Moreover, the proposed TB DDMA method avoids the trade-off between the active time for each transmit antenna element and the frame time due to Doppler ambiguity mitigation. Simulation results verify the effectiveness of the proposed TB DDMA approach for automotive MIMO radar.

Cross Layer MAC Protocol for a Peer Conscious Opportunistic Network Coded Cooperation System

This paper presents a peer conscious opportunistic network coded cooperation (PC-O-NCC) system that exploits multi-user diversity (MUD) gain in a simple network coded cooperation (NCC) based network. It prioritizes sources with better channel conditions by granting them earlier access than the other competing nodes unlike the prevalent time division multiple access (TDMA) technique used widely in any NCC network. This improves the outage performance of the overall system. To prioritise sources with better channel conditions, a novel timer-based MAC protocol is proposed. The proposed protocol is designed such that it aims to reduce collisions by taking the network load into account along with channel conditions while generating the timer values. It also minimizes the power consumption in performing clear channel assessment (CCA) by sources which is a costly affair for battery-operated devices. The simulation results show that the proposed algorithm improves the outage performance while keeping the latency to a minimum value. The improvement in the outage performance can prove to be important in taking key decisions which becomes crucial in disaster management, drone assisted scenarios or intelligent transportation systems.

Cognitive Radio and Dynamic TDMA for efficient UAVs swarm communications

In the last decades, under technological progress in electronic and avionics systems, Unmanned Aerial Vehicles (UAVs) have known an increasing use in several military and civilian missions. Multiple UAVs can cooperatively carry out dangerous applications for human operators or missions where human intervention is not needed, such as surveillance and monitoring of areas of interest and physical infrastructures. Due to the lack of proper communication rules and standards, communication remains one of the most crucial design issues for UAVs swarm. Furthermore, UAVs generally operate in frequency bands shared with other users. Hence, these spectral bands become overcrowded and UAVs may face a spectrum scarcity issue. To address the above challenges, it is essential to define a reliable communication architecture for multiple UAVs coordination and efficient bandwidth sharing. A promising technology that can satisfy the spectrum requirements of the emerging UAVs Networks is Cognitive Radio Network (CRN). The goal is to opportunistically use spectral bands with minimum interference to other users or applications, i.e., primary users. In this paper, we consider the problem of spectrum scarcity encountered by UAVs. We present a centralized CRN-based communication approach for UAVs-Ground Control Station (GCS) communication. The GCS is used as a central coordinator to handle bandwidth usage for the UAVs swarm in its coverage zone. It selects, allocates, and shares available frequencies using CRN and Software Defined Radio (SDR). To share the available CRN-frequency between the different UAVs in its scope, the GCS uses dynamic Time Division Multiple Access (TDMA) technique. The performance of the proposed communication approach is evaluated in a surveillance context in terms of the total time required to transfer UAVs data, the total number of packets sent, and the achieved throughput.

Distribution of Safety Messages Using Mobility-Aware Multi-Hop Clustering in Vehicular Ad Hoc Network

Reliability and security when distributing safety messages among vehicles in an extremely mobile environment are prominent issues in Vehicular Ad-Hoc Networks (VANETs). In VANET, data transfer becomes challenging because of inherent features such as excessive speed, geographically constrained topologies, unsteady communication links, diversity in the capacity of the channel, etc. A major challenge in the multi-hop framework is maintaining and building a path under such a rigid environment. With VANET, potency in the traffic safety applications has performed well because of the proper design of medium access control (MAC) protocols. In this article, a protocol is proposed pertaining to the distribution of safety messages named mobility-aware multi-hop clustering-based MAC (MAMC-MAC) to accomplish minimum communication overhead, high reliability, and delivery of safety messages in real-time environments. MAMC-MAC has the ability to establish clustering-based multi-hop sequence using the time-division multiple access (TDMA) technique. The protocol was specially developed for highway outlines to achieve network enhancement and efficient channel usage and guarantees integrity among the vehicles. The performance of the proposed protocol is evaluated using Network Simulator (NS-2), and it demonstrates its superiority over various standard protocols in terms of a number of quality-of-service (QoS)-based parameters. The criteria to select and assess these parameters are their sensitivity and importance to the safety-based applications they provide.

Deep Q-learning-based resource allocation for solar-powered users in cognitive radio networks

Abstract This paper considers uplink solar-powered cognitive radio networks (CRNs) where multiple secondary users (SUs) transmit data to a secondary base station (SBS) by sharing a licensed channel of a primary system. A deep Q-learning (DQL) algorithm, which combines non-orthogonal multiple access (NOMA) and time division multiple access (TDMA) techniques, is proposed to maximize the long-term throughput of the system. By using our scheme, the agent (i.e. the SBS) can obtain the optimal decision by interacting with the environment to learn about system dynamics. Simulation results validate the superiority of the performance under the proposed scheme, compared with traditional schemes.

Energy Optimization in Wireless Sensor Networks Under Dynamic Spectrum Access Using Adaptive Listening

The efficient use of energy consumption in WSNETs is one of the most promising areas for researchers. In such networks, a considerable amount of bandwidth and energy is wasted for sensing the communication over the common channels. To recognise these complications, WSNETs offers dynamic allocation of the spectrum to optimise the bandwidth utilization. The S-MAC protocol which is based upon Time Division Multiple Access technique has already been proven as a better protocol for the efficient use of energy at MAC Layer. We revised all the patents related to the energy issues in Wireless Sensor Networks. The Hidden terminal problem is a well-known issue in wireless networks due to which the performance of the single-channel medium access protocols is affected. An adaptive listening technique at the MAC Layer was exploited under Dynamic Spectrum Access to address the issue. Adaptive listening proposes a dynamic sleep/idle period based on the data transmission pattern. Thus, the S-MAC protocol further improves the performance in terms of energy consumption and bandwidth utilization at the MAC Layer. The performance of this proposed model is compared with other protocols like IEEE 802.11 and SMAC with periodic sleep. The proposed model offers better network throughput and better energy consumption as seen in these simulation results under various parameters.

An Optimal Policy for Hybrid Channel Access in Cognitive Radio Networks With Energy Harvesting

In this aticle, an optimal policy is presented to maximize the secondary user's (SU's) throughput in an energy harvesting cognitive radio network with multiple SUs and single primary user (PU). The SU can access the PU's channel in a hybrid interweave/underlay channel access mode using time division multiple access (TDMA) technique. This hybrid access mode combines the benefits of interweave channel access mode of accessing the PU's channel opportunistically with high transmission power to gain high throughput and that of the underlay channel access mode of transmission at any time regardless of the PU's activity with controlled power. Moreover, energy harvesting from ambient sources promotes the SU's device to be portable and self sustainable. To deal with the random environment, the system is modeled as a mixed (full/partial) observable Markov decision process (MOMDP). Moreover, to reduce the solution complexity, the point-based value iteration (PBVI) algorithm is used to solve the proposed model. The simulation results show the superiority of the proposed model compared to other related models in terms of throughput. Based on an insight on the optimal policy of the proposed model and the time complexity comparison with the related models, a couple of suboptimal policies are proposed, namely, a myopic policy, an interweave only policy, and a combined-policy approach.

Employing sensor network based opportunistic spectrum utilization for agricultural monitoring

In this work, a cognitive Wireless Regional Area Network (WRAN) technology-based sensor network for agricultural monitoring is proposed. In WRAN technology, a Consumer Premise Equipment (CPE) and a base station communicate through incumbent channels opportunistically without causing any harmful interference to incumbent operations. Because CPE in IEEE 802.22 WRAN is considered as a fixed device, CPE with sensing capability is suitable for wireless sensor network environment in agriculture monitoring where there is no need for node mobility. The proposed network model consists of terrestrial and underground networks. In terrestrial network, CPEs employ Time Division Multiple Access (TDMA) technique with the purpose of sensing environmental data such as temperature, pressure, etc. and transmitting them to the base station. In the underground network, underground sensor nodes use Carrier Sense Multiple Access (CSMA) technique with the aim of sensing underground data such as humidity, soil mineral, etc. and transmitting them to the base station via cluster heads. After obtaining the analytical model of the proposed network, the simulation model of the network is carried out using Riverbed Modeler. The graphical results prove the validity and applicability of the proposed network in terms of throughput and energy consumption without any spectrum cost for agricultural monitoring in rural areas.

A Collision-Free Hybrid MAC Protocol Based on Pipeline Parallel Transmission for Distributed Multi-Channel Underwater Acoustic Networks

The transmission rate between two nodes is usually very low in underwater acoustic networks due to the low available bandwidth of underwater acoustic channels. Therefore, increasing the transmission parallelism among network nodes is one of the most effective ways to improve the performance of underwater acoustic networks. In this paper, we propose a new collision-free hybrid medium access control (MAC) protocol for distributed multi-channel underwater acoustic networks. In the proposed protocol, handshaking and data transmission are implemented as a pipeline on multiple acoustic channels. Handshaking is implemented using the time division multiple access (TDMA) technique in a dedicated control channel, which can support multiple successful handshakes in a transmission cycle and avoid collision in the cost of additional delay. Data packets are transmitted in one or multiple data channels, where an algorithm for optimizing the transmission schedule according to the inter-nodal propagation delays is proposed to achieve collision-free parallel data transmission. Replication computation technique, which is usually used in parallel computation to reduce the requirement of communication or execution time, is used in the data packet scheduling to reduce communication overhead in distributed environments. Simulation results show that the proposed protocol outperforms the slotted floor acquisition multiple access (SFAMA), reverse opportunistic packet appending (ROPA), and distributed scheduling based concurrent transmission (DSCT) protocols in throughput, packet delivery rate, and average energy consumption in the price of larger end-to-end delay introduced by TDMA based handshaking.

Interference Mitigation Using Angular Diversity Receiver With Efficient Channel Estimation in MIMO VLC

Visible Light Communication (VLC) is a promising solution to meet the ever increasing demand for indoor data connectivity with high bit rates. VLC uses the license-free bands and provides high-speed connections unlike RF wireless communication. However; indoor VLC suffers from performance degradation due to either co-channel interference (CCI) or inter-symbol interference (ISI). In this paper, an interference management scheme is proposed for VLC Multi-Input Multi-Output (MIMO) based systems. The scheme reduces the number of interfered signals by using a constrained field-of-view angular diversity receiver CFOV-ADR and then uses least-square (LS) channel estimation with maximum-likelihood (ML) equalizer to resolve the interfered signals. The proposed interference mitigation scheme using constrained-FOV-ADR with channel estimation IM-CFOV-CE enables frequency reuse of one. The bit-error-rate (BER) is calculated at various room positions with different receiver’s heights and rotation angles. The performance evaluation results reveal that the proposed system can achieve a higher number of downlink channels and superior BER performance than that of without CCI management. Also, the proposed scheme has been compared with Time Division Multiple Access (TDMA) technique, and achieves enhanced performance at all positions and orientations of the ADR.

Experimental demonstration of a real-time multi-channel uplink VLC system

We propose and experimentally demonstrate a multi-channel uplink visible light communication (VLC) system for the first time, which is based on three commercially available white light emitting diodes (LED) and only one photo-diode (PD). By employing independent Xilinx field programmable gate arrays (FPGA), we realize the real-time data transmission. The on–off keying (OOK) modulation and time division multiple access (TDMA) techniques are combined together to offer a reliable multiple uplink access for three users. The electrical idle signal is designed to deal with serious inter-symbol interference (ISI) caused by the overlap of different LED signals at the receiver side, as well as to provide a stable illuminating environment. The experiment results indicate that our scheme has a great potential for the indoor practical VLC system implementation.

Microfluidic Time-Division Multiplexing Accessing Resistive Pulse Sensor for Particle Analysis.

Due to its simplicity and robustness, pore-based resistive pulse sensors have been widely used to detect, measure, and analyze particles at length scales ranging from nanometers to micrometers. While multiple pore-based resistive pulse sensors are preferred to increase the analysis throughput and to overcome the clogging issues, the scalability is often limited. In response, by combining the time-division multiple access technique in the telecommunication field with the microfluidics, we reported a microfluidic time-division multiplexing accessing (TDMA) single-end resistive pulse sensor, in which particles can be analyzed through a scalable number of microfluidic channels. With an eight-channel microfluidic device and polystyrene particles as proof-of-principle, we successfully demonstrated this multiplexed technology is effective in measuring the particle size and concentration, in analyzing the particle arriving dynamics, and in discriminating mixed populations. Importantly, the availability of multiple sensing pores provides a robust mechanism to overcome the clogging issue, allowing the analysis to continue even when some of the pores are clogged. We anticipate this TDMA approach could find wide applications and facilitate future development of multiplexed resistive pulse sensing from the microscale to nanoscale.

Analysis of 5G New Radio Uplink Signals on an Analogue-RoF System Based on DSP-Assisted Channel Aggregation

The 3rd Generation Partnership Project (3GPP) is in the process of developing 5th generation (5G) radio access technology, the so-called new radio (NR). The aim is to achieve the performance requirements forIMT-2020 radio interface technology. In this paper, we focus on the analysis of the transmission of 5G NR uplink physical channels, such as physical uplink shared channel (PUSCH) and physical uplink control channel (PUCCH), dedicated for data and control channels, respectively, as specified in the 3GPP standard, using digital signal processing (DSP)-assisted frequency division multiple access (FDMA) and time division multiple access (TDMA) channel aggregation techniques on an analogue radio-over-fiber (A-RoF) architecture. We verified that there is ~34% spectral efficiency gain and lower error vector magnitude (EVM) achieved using the TDMA technique.

A Robust Approach to TDMA Synchronization in Aerial Networks.

Unmanned Aerial Vehicles (UAVs) can be a powerful tool for live (interactive) remote inspection of large-scale structures or areas of interest. Instead of manual, local, and labor-intensive inspections, we envision human operators working together with networks of semi-autonomous UAVs. The current state-of-the-art for low-delay high-throughput inter-vehicle networking relies on Time-Division Multiple Access (TDMA) techniques that require accurate synchronization among all network nodes. In this paper, we propose a delay-tolerant synchronization approach that converges to the correct order of the TDMA slots implemented over COTS WiFi in a fully-distributed way and without resorting to a global clock. This highly flexible solution allows building an ad-hoc aerial network based on a backbone of relaying UAVs. We show several alternatives to achieve this synchronization in a concrete aerial network and compare them in terms of slots’ overlap, throughput, and packet delivery. The results show that these alternatives lead to trade-offs in the referenced metrics. The results also provide insight into the delays caused by buffering in the protocol stack and especially in the WiFi interface.

Comparison of DSP-based TDMA and FDMA channel aggregation techniques in mobile fronthauling

Abstract Cloud Radio Access Network (C-RAN) is perceived as a future essential technology to satisfy the ever-increasing demand of mobile data traffic. Considerable research efforts are expending in the optimization of C-RAN architecture. In this paper, we perform a comparison of two DSP-based fronthauling techniques for aggregation of radio waveforms: time division multiple access (TDMA) and frequency division multiple access (FDMA), in terms of error vector magnitude (EVM), spectral bandwidth efficiency and digital signal processing (DSP) complexity as a performance metrics. The two techniques are compared by means of simulation and validated experimentally on an intensity modulation and direct detection (IM-DD) optical fronthaul link capable of aggregating 48 and 96 LTE-A (20 MHz) channels. Moreover, we made simulation comparison on 24 (100 MHz) new radio (NR) waveforms which will be used in the upcoming 5G applications. We reveal that there is ∼50% and ∼20% spectral efficiency gain by TDMA aggregation on LTE-A and NR waveforms respectively. Hence TDMA gives slightly better performance in the case of 96 LTE-A channels which is attributed to slightly better linearity over the optical channel frequency response for larger number of channel. In addition, we show that TDMA is more efficient in terms of complexity than FDMA system that requires an additional pre-emphasis technique to equalize the overall per channel performance.

Reliability and Energy Efficiency Enhancement for Emergency-Aware Wireless Body Area Networks (WBANs)

Medium access control protocols based on time division multiple access (TDMA) can improve the reliability and efficiency of wireless body area network (WBAN). However, traditional static TDMA techniques adopted by IEEE 802.15.4 and IEEE 802.15.6 do not sufficiently consider the channel status or the buffer requirements of the nodes within heterogeneous contexts. Although there are some solutions that have been proposed to alleviate the effect of the deep fade in WBAN channel by adopting dynamic slot allocation, these solutions still suffer from some reliability and energy efficiency issues and they do not avoid channel deep fading. This paper presents two novel and generic TDMA based techniques to improve WBAN reliability and energy efficiency. Both techniques synchronize nodes adaptively while tackling their channel and buffer status in normal and emergency contexts. Extensive simulation experiments using various traffic rates and time slot lengths demonstrate that the proposed techniques improve the reliability and the energy efficiency compared to IEEE 802.15.4 and IEEE 802.15.6 in both situations, the normal and emergency contexts. This improvement has been achieved in terms of packet loss, up to 90%, and energy consumption, up to 13%, confirming the significant enhancements made by the developed scheduling techniques.

A power allocation method for $$2 \times 2$$ 2 × 2 VLC-MIMO indoor communication

Visible light communication (VLC) has been a promising field of optical communications which focuses on visible light spectrum that humans can see. Unlike existing studies which mainly discuss point-to-point communication, in this paper, we consider a VLC network, in particular a \(2 \times 2\) system. Our focus is on dealing with interference in this network. The objective is to maximize the signal to interference plus noise ratio (SINR) of one receiver for a given SINR of another receiver. We formulate a power allocation optimization problem to deal with such interference, and introduce dichotomy to solve this optimization problem. Simulation results have twofold meaning: First, \(\mathrm{SINR}_1\) increases with the growth of \(\mathrm{SINR}_2\), which are the SINR of the two receivers, respectively. Second, our proposed scheme outperforms the classical time-division multiple access technique in terms of transmit powers of both light sources when the data rate for these two schemes are set to be identical for each user, respectively.