High reliability wireless communications for mission-critical applications often necessitates path diversity through redundant channels. In this context, we explore the combination of the IEC 62439 High-availability Seamless Redundancy (HSR) architecture with IEEE 802.1CB Frame Replication and Elimination for Reliability (FRER) features. While HSR is well-established for wired networks, both HSR and FRER aim to enhance network reliability through redundancy. However, the HSR algorithm assumes frame ordering, which is impractical in wireless networks due to packet ordering and time-based elimination challenges. To address this, we propose integrating the IEEE 802.1CB vector recovery algorithm within the HSR framework. We focus on Wireless Local Area Networks (WLANs), where we modify an existing HSR implementation in Linux to operate over wireless channels. Our experimental analysis demonstrates significant improvements in latency metrics compared to non-redundant communications subject to interfering traffic. The proposed implementation targets industrial applications, such as robotic feedback control with stringent two-millisecond latency deadlines. By considering latency and out-of-order delivery—features not well-supported by the current HSR standard, we demonstrate improved reliability and latency characteristics required for demanding real-time control applications utilizing wireless as a principal communications medium.

Time-sensitive networking (TSN) is emerging as a viable means to achieving deterministic quality of service (QoS) communications within mission critical industrial applications such as feedback control systems, robotics, and precision sensing and actuation. Originally developed for Ethernet-based audio-video applications using the User Datagram Protocol (UDP). TSN assume unidirectional flows from source (talked) to destination(listener) and it is most easily implemented using UDP in which packets are transmitted without an acknowledgment from the recipient. However, most existing industrial protocols are implemented using the reliable Transport Control Protocol (TCP) in which each transmission is explicitly acknowledged. In this work, a bandwidth efficient TSN schedule is developed to accommodate the TCP traffic flow between two synchronized robots collaboratively moving an object. We then demonstrate an IEEE 802.1Qbv TSN schedule over an IEEE 802.11 wireless medium that guarantees robot performance requirements are maintained while accommodating concurrent best-effort traffic flows. The process for schedule selection and experimental data collection is discussed, and TSN configuration parameter tuning and experimental results are provided.

Time-sensitive networking (TSN) is an emerging topic for the advancement of wireless networking for industrial applications. TSN, as defined under the umbrella of IEEE 802.1 working group standards, addresses issues related to providing deterministic communications over IEEE 802-based Local Area Networks (LANs). TSN was originally designed to support real-time audio/video applications over Ethernet providing better reliability and lower, more deterministic latency with traffic shaping capabilities. TSN has since expanded its scope and applicability to other applications such as those in industrial environments and automotive applications. Industrial examples include machine-machine communications for robot control, end-effector actuation, real-time sensing, and safety integrated systems. Applications utilizing a wireless local area network (WLAN) can also benefit from scheduling and traffic shaping as defined in the 802.1Qbv standard; however, factors such as clock stability, synchronization, resource requirements and protocol options come into play when selecting a schedule to support multiple application types on the same network. In this article, we present a scenario for a collaborative robot heavy lift operation, in which, two robots communicate over an IEEE 802.11 WLAN with TSN capabilities to lift a rigid body in three dimensions. Scheduling is performed using 802.1Qbv over WLAN with the robot operating system (ROS) used as the software middleware utilizing the transport control protocol (TCP). As a part of the research, we describe our process for schedule selection to accommodate the time-sensitive traffic of the robotic scenario while allowing an industrial internet of things (IIoT) high data rate traffic to coexist. We then provide an analysis of the impacts of TSN schedule selection on the operational performance of the collaborative robot application.

In this article, we describe a methodology and associated models to evaluate a time sensitive collaborative robotics application enabled by wireless time sensitive networking (WTSN) capabilities. We also present a method to configure WTSN scheduling to meet the application time budget and validate it in a realistic industrial use case. We detail the methodologies for implementing and characterizing the performance of key WTSN capabilities, namely time synchronization and time-aware scheduling, over an IEEE 802.11 based network. We deploy the WTSN capabilities with a collaborative robotic workcell consisting of two robotic arms, which emulate a material handling application, known as machine tending. We further explore configurations and measurement methodologies to characterize application performance of this use case and correlate it to the performance of the wireless network.

Industrial wireless plays a crucial role in cyber-physical system (CPS) advances for the future vision of smart manufacturing. However, industrial wireless environments are different from each other and are different from home and office environments. Hence, industrial wireless channel modeling is essential for the development of industrial wireless systems. Moreover, millimeter-wave (mmWave) wireless bands have a high potential to be used for the high data-rates required for industrial automation reliability, with multiple antennas envisioned to mitigate the high path loss. As a result, in this work, we introduce a machine learning (ML) based exemplar extraction approach on mmWave wireless spatial-channel measurements. The proposed approach processes the measured power-angle-delay-profiles to cluster them into a number of groups with respect to the angle of arrival. Then, an exemplar power-delay-profile (PDP) is extracted to represent each group. The resulting set of exemplars provide a tractable way to conduct mmWave industrial wireless systems testing and evaluation by compactly representing various feature groups. This allows the assessment of wireless equipment over the exemplars without the need to test over all of the different instances of wireless channel paths.

For accurate characterization and evaluation of wireless mechatronic systems, effective modeling of wireless communication channels is of paramount importance, especially to simulation-oriented methods. Conventional simulation methods employ mathematical models to abstract details of prototype channels. Although such mathematical models often have rigorous theoretical underpinnings, they can be weak in capturing complex environmental characteristics and complex forms of diversity that are exhibited in industrial communication environments. To address this problem, we develop, in this paper, a new approach to deriving effective simulation models for industrial communication channels. Our approach involves field measurements from actual wireless mechatronic environments together with feature extraction from the measurements, and data-driven classification based on the extracted features. Our approach leads to a general framework for simulating wireless mechatronic systems in a way that realistically incorporates the complex channel characteristics of these systems.

In this paper, we describe a collaborative robotic workcell testbed enabled by Wireless Time Sensitive Networking (WTSN) technologies and discuss deployment, performance measurement and management guidelines challenges. We detail the methodologies for implementing and characterizing the performance of key WTSN capabilities (time synchronization and time-aware scheduling) over IEEE 802.11/Wi-Fi. We deployed WTSN capabilities on the National Institute of Standards and Technology (NIST) collaborative robotic workcell testbed consisting of two robotic arms that emulates a material handling application, known as machine tending. We further explore configurations and measurement methodologies to characterize Quality of Experience (QoE) of this use case and correlate it to the performance of the wireless network.

Efficient and accurate simulation methods are of increasing importance in the design and evaluation of factory communication systems. Model-based simulation methods are based on formal models that govern the interactions between components and subsystems in the systems that are being simulated. The formal models facilitate systematic integration across the system, and enable powerful methods for analysis and optimization of system performance. However conventional simulation approaches utilize communication channel models that do not fully reflect the characteristics and diversity of industrial communication channels. To help bridge this gap, we develop in this paper new methods for channel model construction for link-layer simulation that systematically incorporate field measurements of wireless communication channels from industrial networks, and derive corresponding channel modeling library components. The generated library components capture channel characteristics in the form of lookup tables, which can be flexibly integrated into system-level simulators or co-simulation tools. We integrate our new table-generation methods into a model-based co-simulator that jointly simulates the interactions among process flows, physical layouts of workcells, and communication channels in factory systems that are integrated with wireless networks. Experimental results using our lookup-table-augmented co-simulator demonstrate the utility of the proposed methods for flexibly and accurately integrating realistic industrial network channel conditions into simulation processes.

The wireless devices in cyber-physical systems (CPS) play a primary role in transporting the information flows within such systems. Deploying wireless systems in industry has many advantages due to lower cost, ease of scale, and flexibility due to the absence of cabling. However, industrial wireless deployments in various industrial environments require having the proper models for industrial wireless channels. In this work, we propose and assess an algorithm for characterizing measured channel impulse response (CIR) of time-varying wireless industrial channels. The proposed algorithm performs data processing, clustering, and averaging for measured CIRs. We have deployed a dynamic time warping (DTW) distance metric to measure the similarity among CIRs. Then, an affinity propagation (AP) machine learning clustering algorithm is deployed for CIR grouping. Finally, we obtain the average CIR of various data clusters as a representation for the cluster. The algorithm is then assessed over industrial wireless channel measurements in various types of industrial environments. The goal of this work is to have a better industrial wireless channels representation that results in a better recognition to the nature of industrial wireless communications and allows for building more effective wireless devices and systems.

Industrial Internet of Things (IIoT) applications, featured with data-centric innovations, are leveraging the observability, control, and analytics, as well as the safety of industrial operations. In IIoT deployments, wireless links are increasingly used in improving the operational connectivity for industrial data services, such as collecting massive process data, communicating with industrial robots, and tracking machines/parts/products on the factory floor and beyond. The wireless system design for IIoT applications is inherently a joint effort between operational technology (OT) engineers, information technology (IT) system architects, and wireless network planners. In this paper, we propose a new reference framework for the wireless system design in IIoT use cases. The framework presents a generic design process and identifies the key questions and tools of individual procedures. Specifically, we extract impact factors from distinct domains including industrial operations and environments, data service dynamics, and the IT infrastructure. We then map these factors into function clusters and discuss their respective impact on performance metrics and resource utilization strategies. Finally, discussions take place in four exemplary IIoT applications where we use the framework to identify the wireless network issues and deployment features in the continuous process monitoring, discrete system control, mobile applications, and spectrum harmonization, respectively. The goals of this work are twofold: 1) to assist OT engineers to better recognize wireless communication demands and challenges in their plants, 2) to help industrial IT specialists to come up with operative and efficient end-to-end wireless solutions to meet demanding needs in factory environments.

Visible light communication (VLC) has emerged as a promising candidate to complement and enhance the performance of the existing radio frequency (RF) networks in indoor environments. Due to the broadcast nature of both RF and VLC channels, improving the transmission confidentiality is a requirement in practical wireless networks. Physical-layer security has emerged to provide a first line of defense against eavesdropping attacks. In this paper, we study the physical layer security problem of a hybrid RF/VLC system. First, we formulate the minimization problem of the consumed electrical power in the hybrid RF/VLC network while satisfying the user's required secrecy rate. Then, we propose a zero forcing beamforming strategy and a minimum power allocation algorithm. Simulations results show that the proposed power allocation and beamforming algorithms outperform the benchmark algorithms in terms of the average consumed electrical power in various indoor scenarios.

Visible light communications (VLC) technology has recently emerged as a complementary technology to the indoor radio frequency (RF) networks. While the backhauling of the indoor RF networks has been supported by fiber optics, the backhauling of the VLC network is still an open research problem. Power line communications (PLC) has been considered as a possible solution for the VLC networks due to its ubiquity. However, given the noisy behaviour of the channels, the use of PLC backhauling requires further study to investigate the maximum rate which can be supported for VLC networks. In this paper, we continue our work on a single-user hybrid PLC/VLC/RF system [1] to study the effect of PLC backhauling in multi-user hybrid VLC/RF networks. To this end, we adopt an orthogonal frequency division multiplexing (OFDM)- based PLC backhaul system where we find the optimal power and subcarrier allocation algorithm that maximizes the multi-user rate utility function for the cascaded PLC and VLC links in parallel with the RF network. Moreover, we study numerically the impact of various parameters on the system performance including the PLC transmission power, the RF and VLC maximum allowable rates, and the numbers of mobile terminals and access points.

In literature, dynamic planning (base station (BS) on-off switching) is proposed as an efficient approach for energy saving at a low call traffic load condition. All related research efforts aim to employ dynamic planning to save energy for the network operators while satisfying the quality-of-service (QoS) for downlink mobile users. On the other hand, although switching off a BS can save energy for network operators and satisfy the downlink QoS, it may lead to associating uplink mobile users with a faraway BS, and hence, degrade the uplink QoS. Such an impact of dynamic planning on uplink service quality is not well investigated in literature. In this paper, we aim to quantify this impact by considering two QoS metrics, namely, user required throughput and call dropping probability due to mobile terminal battery depletion for uplink data calls. Simulation results demonstrate that BS switching off decisions that do not account for the uplink QoS requirements can result in severe service quality degradation.

In this work, bit error rate (BER) measurements of visible light communications (VLC) systems are introduced as an effective possible replacement of reflectivity measurements in a conventional optical plasmonic sensing procedure. In particular, we investigate a procedure where we exploit the phenomenon of the variations of BER values of the VLC systems with the sensed concentration of contaminations in the sensing medium. We consider a system composed of a VLC white LED source that transmits data through the sensing medium, which is then detected by a receiver and the BER values are computed. Our analysis proves that the information extracted from the BER measurements is sufficient to learn about the sensing medium and hence can replace conventional measurement techniques used in optical sensing. Thus, a simpler procedure of optical sensing is proposed due to the low cost of the proposed system and its flexibility in sensing medium in different environment scenarios. In this work, the proposed idea is verified for optical SPR sensors for their high impact state-of-art performance over other conventional optical sensors. Moreover, the VLC-based system is shown to have no negative effect on the performance of the designed optical SPR sensor in a way that undermines its operation.

Developing energy efficient wireless communication networks has become crucial due to the associated environmental and financial benefits. Visible light communication (VLC) has emerged as a promising candidate for achieving energy efficient wireless communications. Integrating VLC with radio frequency (RF)-based wireless networks has improved the achievable data rates of mobile users. In this paper, we investigate the energy efficiency benefits of integrating VLC with RF-based networks in a heterogeneous wireless environment. We formulate and solve the problem of power and bandwidth allocation for energy efficiency maximization of a heterogeneous network composed of a VLC system and an RF communication system. Then, we investigate the impact of the system parameters on the energy efficiency of the mixed RF/VLC heterogeneous network. Numerical results are conducted to corroborate the superiority in performance of the proposed hybrid system. The impact of hybrid system parameters on the overall energy efficiency is also quantified.

Dynamic planning has been used by network operators for energy saving by switching ON-OFF base stations (BSs) according to the traffic load condition while providing quality-of-service (QoS) guarantee for mobile users. In the literature, research efforts focus mainly on satisfying the QoS of downlink mobile users. However, the impact of dynamic planning on the QoS of uplink mobile users is overlooked. A dynamic planning approach that relies only on the downlink performance of mobile users to determine the BS switching decision can result in deactivating nearby small cells and associating uplink mobile users to a faraway macro BS. Consequently, uplink mobile users may suffer from QoS degradation due to the longer transmission distance. Hence, while saving energy for the network operators and satisfying the downlink QoS, the uplink QoS could be violated. In this paper, we propose a balanced dynamic planning approach that accounts for QoS requirements both in the uplink and downlink to specify the BS switching decision. The switching decision is formulated as a two-timescale average reward Markov decision process with finite horizon. Due to computational complexity, sub-optimal algorithms are proposed. Simulation results demonstrate the trade-off between energy saving and QoS guarantee.

In this paper, we asses the benefits of using partial relaying in energy-harvesting networks. We consider a system composed of a source, a relay, and a destination. Each of the source and the relay has energy-harvesting capability and generates its own traffic. The source is helped by the relay through a partial relaying network-level cooperation protocol. The relay regulates the arrivals from the source by accepting only a proportion of the successfully received packets at the relay. The relaying parameter, which determines the proportion of packets to be accepted, is selected based on the parameters of the network to ensure the stability of the source and the relay data queues. In this work, we provide an exact characterization of the stability region of the network. We derive the optimal value of the relaying parameter to maximize the stable throughput of the source for a given data arrival rate to the relay. Also, we compare the stability region of the proposed strategy with partial relaying to the stability regions of simple transmission strategies. Finally, we consider the problem of network utility optimization in which we optimize over the value of the relaying parameter for a given pair of data arrival rates for the source and the relay.

The increased demands for indoor wireless data services with the limited available radio frequency (RF) spectrum are motivating researchers to investigate alternative technologies to augment the existing RF networks. Utilizing the visible light spectrum by exploiting visible light communication (VLC) has shown strong potential to augment RF networks in indoor scenarios. The ubiquity of the power-line network makes it an attractive choice as a communication medium between the data sources and the VLC transmitters through power line communication (PLC). Hence, integrating VLC and PLC systems can be a strong complementary hybrid wireline/wireless technology for indoor data networks. In this paper, we investigate the power allocation problem for a communication scenario in which data is transferred through a cascaded PLC/VLC channel in parallel to an RF wireless channel. We develop an algorithm for allocating the transmission powers among the communication nodes to maximize the achievable rate. Our results show that the proposed system provides appreciable rate gains compared to conventional RF communication systems for the same amount of total transmission power.

In this paper, the performance of a visible light communication (VLC) network exploiting power control is considered. The achievable rate region of two VLC communication pairs is characterized. The system employs optical orthogonal frequency division multiplexing (O-OFDM) with power control performed at the transmitters. The optical signal clipping effect is taken into consideration which results from the physical limitations at the transmitters. Also, the system is constrained by the desired illumination power for each transmitter. We prove that the achievable rate region is defined as the union of two regions where the boundary of each of these regions can be obtained by a single variable optimization problem. Our numerical results show the effects of the system parameters including direct current (DC) bias, the desired illumination power, clipping noise and the relative positions of the receivers relative to the LED transmitters on the achievable rate region of the two users. We show the enhancement in the performance resulted from using power control compared to orthogonal resource allocation techniques.

Wireless systems of rechargeable nodes have extended lifetime and are self-sufficient. The transmission policies in these systems need to adapt to the harvested energy availability. In this work, we investigate the interaction between relaying, energy harvesting, and stability. We introduce the problem of general relaying cost minimization for cooperative energy harvesting networks. We consider a simple network in which a source transmits to a destination through network-level cooperation with a number of relay nodes. The source and the relays have energy harvesting capability. To adapt the relaying process to the available harvested energy, we exploit partial relay cooperation in which the flows through the relays are controlled. The relaying cost minimization problem is feasible when the data queues of the source and the relays are stable. The stability conditions of the data queues are derived. Then, we introduce the energy consumption as a cost criterion for the optimization problem to find an energy-efficient partial relaying protocol. We assess the effect of partial relay cooperation compared to the cases of no cooperation and full relay cooperation.

We propose a secondary CDMA network that operates as an underlay for a primary CDMA network where the code assignment for the secondary network is done cognitively. A code assignment criterion that minimizes interference from primary users and existing secondary users is formulated. The primary user codes as well as bit boundaries are unknown to the secondary network. The problem is initially formulated as a constrained optimization problem. Exhaustive search has complexity that is exponential in the spreading factor. The constraints are therefore relaxed to obtain a near-optimal solution with a complexity that is linear in the spreading factor and performance very close to the exhaustive search method. We consider the different cases where the primary users are bit- and chip-synchronous, chip-synchronous but bit-asynchronous, and chip-asynchronous over multi-path fading channels. We propose a method for blind epoch acquisition by processing the covariance matrix of the received signal. In all cases the performance improvement of the interference-minimizing code assignment over random code assignment is significant reaching over 3 dB for coded systems.

Abstract In this paper, we propose a code‐division multiple‐access (CDMA) secondary network to operate cognitively as an underlay for a primary network. A novel interference‐minimizing code assignment (IMCA) for secondary users is proposed such that the interference from existing primary and secondary users is minimized. This is accomplished by minimizing the mean square cross‐correlations between the candidate codes and the received signal. Since the codes of the primary CDMA network are unknown to the secondary network the scheme operates blindly and the problem is formulated as a constrained optimization of a Boolean quadratic form. The solution is obtained exhaustively and we demonstrate significant performance gains compared to random code assignment (RCA). We then slightly relax the constraint on the user code space and obtain a near‐optimal solution with complexity that is linear in the spreading factor. For the secondary network, we propose a slightly modified minimum‐output energy receiver that operates semi‐blindly as a first stage followed by parallel interference cancellation. For this receiver structure, we derive improved log‐likelihood ratios for the single‐user decoders based on partial knowledge of the user codes and channel coefficients. Significant error probability performance improvements of 2 dB or more are obtained due to IMCA in the coded case. Copyright © 2008 John Wiley & Sons, Ltd.