Automated warehouses involve robots that move across the floor, avoiding obstacles while remaining connected via an access point (AP) to a central controller that instructs the robots. The complex propagation environment and presence of metallic surfaces results in spotty coverage, which changes over time as the location of stored products and machinery changes. Thus, maintaining an assured connectivity to APs while performing navigation is a challenge, although it is needed to relay local sensor data from the robots to the controller and receive directions from the latter.$\rm{DARWIN}$, involves creating a digital twin of the warehouse for training the robots by jointly optimizing the navigation and avoiding wireless dead-spots.$\rm{DARWIN}$has three key capabilities: First, it captures the features of both physical and RF environments in the digital world. Second, it allows real-time updating of the digital twin if significant disparity is detected compared to the physical environment. Finally, it includes a reinforcement learning algorithm that jointly optimizes navigation and network resource management, while accounting for handover and outage. We validate$\rm{DARWIN}$on an emulation environment consisting of Robot Operating System and Gazebo platforms along with real-world RF measurements. Results reveal that$\rm{DARWIN}$reduces the number of steps by 43% compared to choosing the closest AP, while detecting environmental changes with maximum 96% accuracy to maintain a high-fidelity digital twin.

In light of the evolving landscape of future converged networks, heightened demands for scalability and performance have become paramount, particularly in the industrial context where enhanced flexibility, adaptability, time synchronization and deterministic low latency are key features. Time-Sensitive Networking (TSN) has been introduced to provide converged networks with determinism. To mitigate the complexities associated with cabling requirements, Wireless Time-Sensitive Networking (WTSN) emerges as a more suited solution in industrial applications that need mobility. This study presents an application in smart manufacturing that incorporates WTSN technology. Specifically, it focuses on a scenario where an Unmanned Ground Vehicle (UGV), under the control of an edge controller connected through a wireless link, operates within a critical environment subject to constraints such as to avoid obstacles and to build a real-time map of the surrounding area. The mapping outcome performed by the edge controller demonstrates the effectiveness of the WTSN capabilities.

Guest Editorial: Co-Design of Communication, Computing, and Control in Industrial Cyber-Physical Systems—Part I

Autonomous Industrial Cyber-Physical Systems (ICPS) represent a future vision where industrial systems achieve full autonomy, integrating physical processes seamlessly with communication, computing and control technologies while holistically embedding intelligence. Cloud-Fog Automation is a new digitalized industrial automation reference architecture that has been recently proposed. This architecture is a fundamental paradigm shift from the traditional International Society of Automation (ISA)-95 model to accelerate the convergence and synergy of communication, computing, and control towards a fully autonomous ICPS. With the deployment of new wireless technologies to enable almost-deterministic ultra-reliable low-latency communications, a joint design of optimal control and computing has become increasingly important in modern ICPS. It is also imperative that system-wide cyber-physical security are critically enforced. Despite recent advancements in the field, there are still significant research gaps and open technical challenges. Therefore, a deliberate rethink in co-designing and synergizing communications, computing, and control (which we term “3C co-design”) is required. In this paper, we position Cloud-Fog Automation with 3C co-design as the new paradigm to realize the vision of autonomous ICPS. We articulate the state-of-the-art and future directions in the field, and specifically discuss how goal-oriented communication, virtualization-empowered computing, and Quality of Service (QoS)-aware control can drive Cloud-Fog Automation towards a fully autonomous ICPS, while accounting for system-wide cyber-physical security.

Guest Editorial: Co-Design of Communication, Computing, and Control in Industrial Cyber-Physical Systems—Part II

The demand for precise time synchronization is of great interest in contemporary networked systems, especially in the context of converged networks where seamless communication among devices, actuators, and sensors is imperative. This has led to the development and adoption of Time-Sensitive Networking (TSN) and Wireless TSN (WTSN) technologies, with a particular attention to the IEEE 802.1AS Generalized Precision Time Protocol (gPTP) standard. In this work, we explore the role of time synchronization in a wireless network scenario involving an Unmanned Ground Vehicle (UGV) that has to track a desired time dependent trajectory. The UGV receives trajectory waypoints from a secondary station, emphasizing the importance of precise timing in trajectory tracking. Utilizing the IEEE 802.1AS standard for wireless time synchronization, this study investigates the impact of clock synchronization errors and latency on trajectory tracking. Hence, it demonstrates the capability and benefits of IEEE 802.1AS in managing device clocks and facilitating time correction to ensure precise trajectory tracking despite synchronization errors and latency.

The ever more used and widespread Time-Sensitive Networking (TSN) has changed real-time networks, enabling reliable communication for time-critical applications. At the same time Software-Defined Networking (SDN) has emerged as a solution to ensure proper quality of service for managing dynamic network configurations even in evolving topologies. This paper investigates the integration between TSN and SDN to enable dynamic network re-configuration and improve performance for time-critical applications. We present an experimental setup designed to evaluate this approach. The setup focuses on scenarios where an SDN controller can dynamically reroute critical data flows across different TSN network devices to avoid interference and maintain consistent Quality-of-Service (QoS).

Emerging applications in the wireless domain such as factory automation or extended reality require high reliable and deterministic communications. New scheduling mechanisms introduced in current state-of-the-art Wi-Fi (i.e. 802.11ax, 802.11be) offer better performance, but in many cases not sufficient to meet the requirements of the aforementioned applications. In this paper, we present a hardware implementation of Scheduled Time-Sensitive Transmission Opportunity (S-TXOP) over Wi-Fi, S-TXOP provides accurate time synchronization and time-aware scheduling to enable highly efficient deterministic wireless communications. We describe a field-programmable gate array software-defined radio S-TXOP implementation, and show numerical and experimental results supporting low cycle time transmissions with determinism.

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.

Multi-Link Operation (MLO) in Wi-Fi 7 is expected to tangibly boost throughput while lowering transmission latency at the same time. This is very relevant in industrial scenarios and makes MLO suitable, e.g., to support seamless device mobility. Benefits depend on the ability of multi-link devices to select at run-time the best link, among the available ones, in order to maximize both communication performance and reliability.In this paper an experimental platform is proposed, with the aim of leveraging commercial hardware and open source software, and easing prototyping and evaluation of MLO techniques. The platform has been employed to analyze the transmission quality of two pairs of non-overlapping channels, and in particular to assess whether or not adequate diversity is provided, so that those channels can be exploited to improve reliability. Results point out that correlation between different links is, in most cases, limited, which makes MLO a valuable approach.

The next generation of Wi-Fi is meant to achieve ultra-high reliability for wireless communication. Several approaches are available to this extent, some of which are being considered for inclusion in standards specifications, including coordination of access points to reduce interference.In this paper, we propose a centralized architecture based on digital twins, called WiTwin, with the aim of supporting wireless stations in selecting the optimal association according to a set of parameters. Unlike prior works, we assume that Wi-Fi 7 features like multi-link operation (MLO) are available. Moreover, one of the main goals of this architecture is to preserve communication quality in the presence of mobility, by helping stations to perform reassociation at the right time and in the best way.

Managing Wireless networks, particularly in industrial and factory environments, to meet the escalating demands of time critical applications has become more complex and warrants proactive management strategies. This work introduces an innovative approach to wireless network management enabled by a Digital Twin (DT) designed and continuously enhanced by real-time device telemetry and user inputs through an Extended Reality interface. By collecting real telemetry data from network devices, our methodology defines and calibrates a DT representation of the network, enabling accurate prediction of wireless signal properties and network performance based on simulation models. The DT serves as an automation tool to analyze various scenarios, allowing for informed adjustments to user applications, devices and network configurations. The paper describes a real-life DT implementation of a wireless system in a real enterprise network scenario. Experimental results are provided demonstrating improved performance and user experience enabled by the proposed DT-based network management. The proposed methodology addresses the challenges of real-time network optimization and contributes to advance wireless network management based on device and network telemetry.

Robotic factory floors will revolutionize the future of manufacturing and the service industry by automating tasks. However, to fully supplement human effort, these robots will need low-latency, reliable connectivity throughout the work zone through links established by wireless access points (APs). This will allow the robot to assuredly respond to programming directives that rely on the real-time relaying of robot-generated sensor data to the Mobile Edge Computing (MEC) server. In this paper, we propose L-NORM, a multi-AP and multi-robot coordination framework, as a multi-tiered solution for such autonomous edge networks. First, multi-robot motion planning through reinforcement learning occurs at the MEC, using as input multi-modal robot sensor data. Second, multi-AP resource orchestration is performed using another reinforcement learning-based method that maps a subset of available APs to each robot toward meeting their sensor data delivery requirements. Furthermore, we suggest diversity combination of uplink channels with the 802.11ax scheduled access mode that will (i) support high reliability of multi-robot uplink sensor packets and (ii) enable multi-AP coordination, for optimized resource utilization. Through extensive simulation studies, we show that the probability of robot deviation to remain within 0.5 m from its optimal path, is 19% more in L-NORM compared to classical 802.11ax based edge network solution, considering$\sim$1 MB of sensor data per robot.

The introduction of Time-Sensitive Networking (TSN) is revolutionizing real-time networks and time-critical applications. Recent advancements in this field extended the TSN capabilities to wireless technologies, giving rise to the concept of wireless TSN (WTSN). This paper focuses on the integration of wireless TSN with Software-Defined Networking (SDN) to enable dynamic network configuration and improve the performance of time-sensitive applications. We present a practical test environment that uses a hybrid network configuration consisting of wireless and wired TSN links. The primary objective is to evaluate the effectiveness of combining a TSN-capable network with an SDN controller. This setup enables dynamic configuration and routing within the system, allowing for prompt actions to address network issues, such as seamlessly re-routing data paths between the two links due to an increase in latency or packet loss. A measurement setup using OpenVSwitch in the wireless TSN domain is presented, along with the evaluation of time synchronization and dynamic route selection capabilities.

Industrial Internet of Things (IIoT) use cases have stringent reliability and latency requirements to enable real-time wireless control systems, which are supported by the 5G ultra-reliable low-latency communications (URLLC). However, extremely high quality-of-service (QoS) requirements in 5G URLLC causes huge radio resource consumption and low spectral efficiency, thus limiting network capacity in terms of the number of supported devices. Industrial control applications typically incorporate redundancy in their design and may not always require extreme QoS to achieve the expected control performance. Therefore, we propose both communication-control co-design and dynamic QoS to address the capacity issue for robotic manipulation use cases in 5G-based IIoT. We have developed an advanced co-simulation framework that includes a network simulator, physics simulator, and compute emulator, for realistic performance evaluation of the proposed methods. Through simulations, we show significant improvements in network capacity (i.e., the number of supported URLLC devices), and about 2x gain for the robotic manipulation use case.

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.

By removing wire harness, Wi-Fi is becoming increasingly pervasive in every aspect of our lives, in both the consumer and industrial worlds. Besides flexibility, the recent high efficiency and extremely high throughput versions managed to close the performance gap with Ethernet. However, it still lags behind Ethernet for what concerns dependability. To this aim, the ultra high reliability study group has been recently formed. This paper reports on some preliminary ideas and proposals about the ways seamless redundancy can be exploited to make Wi-Fi more reliable, yet retaining a good degree of backward compatibility with existing network infrastructures.

Mobile and autonomous robots are among the most critical technology applications requiring wireless connectivity with deterministic performance, including bounded latency with high reliability, even under congested network conditions. Emerging Wireless Time-Sensitive Networking (WTSN) capabilities over Wi-Fi and 5G can enable time synchronization and bounded low latency through time-aware scheduling mechanisms. Such Wireless TSN capabilities have been demonstrated in several industrial/robotic use cases, but under static conditions. Mobility introduces new challenges due to the roaming events and associated network outages owing to signaling between client devices and network infrastructure during these events. In this paper, we show how we can take advantage of the TSN redundancy capability (as defined in the IEEE 802.1CB standard) to eliminate outages or delays due to events like roaming and interference in a mobile robot use case enabled by Wi-Fi 6 TSN. We demonstrate the roaming performance with no delay impact on the applications though simulations of a mobile robot in a factory scenario and experimental results with a mobile robot connected via multiple Wi-Fi 6 radios in a warehouse environment.

This work discusses Access Point Coordination techniques for future 802.11 communications in the context of industrial Wireless TSN scenarios. A Coordinated OFDMA setup is proposed with a frame exchange scheme based on implicit wireless channel sounding prior to transmission. The scheduler assigns resource units to the users, trying to maximize the probability of all the STAs in the network to successfully deliver their data. In order to evaluate the quality of the channels without introducing overhead in the network, we propose a virtual sounding mechanism. We present simulation results first to validate the virtual sounding mechanism and, second, to show the achievable reliability of a Multi-AP network for a set of representative scenarios. These results highlight that Multi-AP can be effectively used to enhance the reliability of the network though special attention must be taken for time-varying scenarios.

Industrial automation, Augmented Reality (AR), Virtual Reality (VR), Robotics, and many other applications need accurate time and data delivery with strict deadlines. The IEEE 802.1 Time-Sensitive Networking (TSN) group defines a set of tools for deterministic communication with high reliability. Although TSN has started from wired (Ethernet) networks, the newer generation wireless technologies, especially Wi-Fi 6/6E and 5G, offer capabilities to extend and enhance TSN operation over the wireless medium. The 3rd Generation Partnership Project (3GPP) Release 16 supports Ultra-Reliable Low-Latency Communications (URLLC) and introduces the capabilities for integrating 5G with TSN networks motivated by the requirements of time-critical industrial systems. This paper presents and evaluates an industrial control system enabled by 5G and TSN capabilities. We describe a TSN over 5G testbed developed with 3GPP Release 15 hardware and discuss the measurement methodology along with Key Performance Indicators (KPIs) required for meeting timing requirements for an industrial control application. We also explore the configuration of TSN over 5G systems and methodologies needed to characterize the Quality of Experience (QoE) for industrial use cases.

Time-sensitive applications, such as industrial automation and extended reality (XR), require packets to be delivered within tight latency bounds and with high reliability. Meeting those requirements over Wi-Fi links is challenging even considering the efficient scheduling techniques provided by the latest Wi-Fi generations (e.g., based on IEEE 802.11ax). In this paper we introduce the concept of Scheduled Transmission Opportunities (S-TXOP) where the network controller exploits the deterministic traffic pattern associated with most time-sensitive applications to minimize the control overhead and provide scheduled channel access that can meet very low latency cycles. Our results show that the S-TXOP meets those challenges with higher robustness and efficiency compared to existing scheduling techniques in 802.11

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.

We consider the problem of controlling a series of industrial systems, such as industrial robotics, in a factory environment over a shared wireless channel leveraging edge computing capabilities. The wireless control system model supports the offloading of computational intensive functions, such as perception workloads, to an edge server. However, wireless communications is prone to packet loss and latency and can lead to instability or task failure if the link is not kept sufficiently reliable. Because maintaining high reliability and low latency at all times prohibits scalability due to resource limitations, we propose a communication-control co-design paradigm that varies the network quality of service (QoS) and resulting control actions to the dynamic needs of each plant. We further propose a modular learning framework to solve the complex learning task without knowledge of plant or communication models in a series of learning steps and demonstrate its effectiveness in learning resource-efficient co-design policies in a robotic conveyor belt task.

Timeliness has become critical across industrial automation, AR/VR, robotics, and many other use cases. IEEE Time-sensitive networking (TSN) standards provide high-reliability & determinism across wired (Ethernet) networks. Time-critical hard/soft real-time applications typically run over these wired TSN links. However, TSN over-wired links lack the mobility and potential to meet all the needs of Industry 4.0. New generation wireless technologies such as Wi-Fi and 5G that are now introducing TSN supporting capabilities can fulfill this need. The 5G Release 16 from the 3rd Generation Partnership Project (3GPP) supports Ultra-Reliable Low-Latency Communications (URLLC), which brings the possibility of combining 5G with TSN to meet the stringent requirements of industry 4.0. 5G that comes with the support of both private and public networks is coupled with TSN to support the use cases with deterministic performance and required latency levels. The 5G-TSN networks must provide a low end-to-end (E2E) latency to support time-sensitive applications. The traffic steering delay within the User Equipment (UE) in edge compute devices is a critical component in addition to network latencies. This paper discusses the traffic steering aspects of UE and proposes a new use case of eXpress Data Path (XDP) programming over the 5G modem of UE to efficiently steer the traffic in 5G-TSN networks. Experiment results show that the proposed solution provides 100 times lower latency in traffic steering latency compared to a conventional Layer 2 (L2) software bridge.

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.

With the uprising of new fields such as robotics, IoT or Augmented Reality, one of the main objectives of industrial modernization is the incorporation of safe and secure wireless technologies in the factory floor. However, nowadays wireless protocols can not fulfill the communication requirements of industrial networks, among which reliability and bound guaranteed latency are probably the most stringent ones. The lack of guaranteed low latency and ultra-high reliability of wireless networks are mainly derived from the error-prone nature of wireless propagation. Multi-link techniques are expected to provide enhanced reliability, latency and also protection against external interference. In this work, we assess the reliability and latency enhancement of the Multi-Link technique proposed in 802.11be. The assessment is done through simulation means using realistic industrial propagation and interference models. The results shown in this paper prove that Multi-Link provides an enhancement in wireless reliability and latency.

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.

We consider the problem of allocating 5G radio resources over wireless communication links to control a series of independent low-latency wireless control systems common in industrial settings. Each control system sends state information to the base station to compute control signals under tight latency requirements. Such latency requirements can be met by restricting the uplink traffic to a single subframe in each 5G frame, thus ensuring a millisecond latency bound while leaving the remaining subframes available for scheduling overhead and coexisting broadband traffic. A linear assignment problem can be formulated to minimize the expected number of packet drops, but this alone is not sufficient to achieve good performance. We propose an optimal scheduling with respect to a control operation cost that allocates resources based on current control system needs. The resulting control-aware scheduling method is tested in simulation experiments that show drastically improved performance in 5G settings relative to control-agnostic scheduling under the proposed time-sliced frame structure.

The present work deals with diminishing the effects of wireless communication latency in time-sensitive networks. It takes advantage of modern approaches that offer bounded latency and it focuses on methods to cope with the nondeterministic delays introduced by communication latency.An observer-predictor scheme module is designed and added in the control loop to prevent the performance degradation when a wireless network is introduced. The goal is to allow the use of same controllers used in wired networks. This module may exploit information provided by the wireless communication devices, such as expected latency, timestamp, and time synchronization along the network.The proposed module allows the controller to have a performance similar as when in a wired network. This enables wireless networked control in systems with low time constants (i.e. timesensitive).Lab experiments are presented in real-time to illustrate the observer-predictor scheme module proposed. Finally, the conclusions and future work are presented.

We consider the problem of allocating radio resources over wireless communication links to control a series of independent low-latency wireless control systems common in industrial settings. Supporting wireless control in time sensitive settings requires fast data rates over wireless links, which comes at the cost of reliability. It is challenging to meet both latency and reliability requirements with an equal or arbitrary allocation of resources. We thus propose a novel control-aware approach to the low-latency scheduling problem in which we incorporate control and channel state information in allocating bandwidth and data rates across the wireless links. Control systems that are in desirable states are given modest requirements on error rates, while systems in undesirable states are given more priority. We derive control-aware packet error rate targets for each system to satisfy stability goals and make scheduling decisions to meet such targets while reducing total transmission time. The resulting control-aware based method is tested in simulation experiments that demonstrate its effectiveness in meeting control-based goals under tight latency constraints relative to control-agnostic scheduling.

We consider the problem of allocating radio resources over wireless communication links to control a series of independent wireless control systems. Low-latency transmissions are necessary in enabling time-sensitive control systems with high sampling rates to operate over wireless links. Enabling low-latency through fast data rates comes at the cost of reliability in the form of higher packet error rates due to channel noise. However, the impact of such communication link errors on the control system performance depends dynamically on the control system state. We propose a novel control-aware communication design to the low-latency resource allocation problem. In our proposed method, we incorporate both control and channel state information in scheduling transmissions across time slots, frequency bands, and data rates using the next-generation Wi-Fi scheduling architecture. Control systems that are closer to instability or further from a desired range in a given control cycle are given higher packet delivery rate targets to meet. Rather than a simple priority ranking, we derive precise adaptive packet error rate targets for each system needed to satisfy control-specific performance requirements. We use these adaptive rate targets to make scheduling decisions that reduce total transmission time. The resulting control-aware low-latency scheduling (CALLS) method is tested in numerous simulation experiments that demonstrate its effectiveness in meeting control-based goals under tight latency constraints relative to control-agnostic scheduling.

Many industrial automation systems rely on time-synchronized (and timely) communication among sensing, computing, and actuating devices. Advances in Ethernet enabled by time-sensitive networking (TSN) standards, being developed by the IEEE 802.1 TSN Task Group, are significantly improving time synchronization as well as worst case latencies. Next-generation industrial systems are expected to leverage advances in distributed time coordinated computing and wireless communications to enable greater levels of automation, efficiency, and flexibility. Significant progress has been made in extending accurate time synchronization over the air (e.g., 802.1AS profile for IEEE 802.11/Wi-Fi). Given the inherently unreliable, varying capacity and latency prone characteristics associated with wireless communications, proving the feasibility of worst case latency performance over the wireless medium is a major research challenge. More specifically, understanding what levels of capacity, reliability, and latency could be guaranteed over wireless links with high reliability are important research questions to guide the development of new radios, protocols, and time coordinated applications. This paper provides an overview of the potential applications, requirements, and unique research challenges to extend TSN capabilities over wireless. The paper also describes advances in wireless technologies (e.g., next-generation 802.11 and 5G standards) toward achieving reliable and accurate time distribution and timeliness capabilities. It also provides a classification of wireless applications and a reference architecture for enabling the integration of wired and wireless TSN capabilities in future industrial automation systems.

In recent years, we have seen tremendous growth in the applications of wireless sensor networks (WSNs) operating in unlicensed spectrum bands. However, there is evidence that existing unlicensed spectrum is becoming overcrowded. On the other hand, with recent advances in cognitive radio (CR) technology, it is possible to apply the dynamic spectrum access (DSA) model in WSNs to get access to less congested spectrum, possibly with better propagation characteristics. In this paper we present a conceptual design of CR-based WSNs, identify the main advantages and challenges of using CR technology, and suggest possible remedies to overcome the challenges. As an illustration, we study the performance of CR-based WSN used for the automation and control applications in residential and commercial premises. Our simulation results compare the performance of a CR-based WSN with a standard ZigBee/802.15.4 WSN.

This paper analyses the energy efficiency and QoS performance of 802.11e as a connectivity solution for low-rate applications, such as wireless automation and monitoring. The authors consider non-interference and co-existence scenarios and show through modeling and simulations that the power save operation mode and the EDCA QoS mechanisms in the 802.11e standard can be exploited to achieve the power consumption requirements of low-rate applications. The authors also provide a comparison of the energy efficiency between 802.11e and 802.15.4 under varying interference and traffic conditions. Our results suggest that in some specific scenarios, 802.11e can achieve higher energy efficiency and QoS than 802.15.4.

Abstract A growing need to have ubiquitous connectivity has motivated our research to provide continuous connection between various wireless platforms such as cellular networks, wireless local area networks (WLANs), and mobile ad hoc networks (MANETs). In this paper, we consider integration at the routing layer and propose two adaptable routing protocols (IRP‐RD and IRP‐PD) that exploit topology information stored at the fixed network components (cellular base stations and WLAN access points) for the route discovery and maintenance processes. Our proposed protocols can provide connectivity to the cellular network and/or WLAN hotspots through multihop routing, while differ in the gateway discovery approach used. In IRP‐RD, multihop routes to gateways to the cellular network or WLAN hot spots are discovered on demand, while in IRP‐PD out of coverage users proactively maintain routes to the gateways. Furthermore, proposed protocols can be used in any heterogeneous scenario, combining a cellular network and WLANs operating in infrastructure or ad hoc (MANET) mode. We provide simulation results that demonstrate the effectiveness of the proposed integrated routing protocols and show the advantages and drawbacks of each gateway discovery approach in different heterogeneous scenarios. Copyright © 2006 John Wiley & Sons, Ltd.

Wireless mesh networks exploit multi-hop wireless communications between access points to replace wired infrastructure. However, in multi-hop networks, effective bandwidth decreases with increasing number of hops, mainly due to increased spatial contention. Longer hop length flows suffer from extremely low throughputs which is highly undesirable in the envisioned scenarios for mesh networks. In this paper, we show that queue/buffer management, at intermediate relay mesh nodes, plays an important role in limiting the performance of longer hop length flows. We propose a novel queue management algorithm for IEEE 802.11s based mesh networks that improves the performance of multihop flows by fairly sharing the available buffer at each mesh point among all the active source nodes whose flows are being forwarded. Extensive simulations reveal that our proposed scheme substantially improves the performance of multihop flows. We also identify some important design issues that should be considered for the practical deployment of such mesh networks.

Tins paper presents CMAC, a fully desynchronized MAC protocol that is designed to exploit the existing multi-channel support in sensor nodes. The hardware requirements of our protocol are minimal, requiring a single half-duplex transceiver and a low-power wake-up radio. CMAC takes into account the fundamental energy constraint in sensor nodes by placing them in a default sleep mode and waking them up only when necessary. As a contrast to other dual radio wake-up schemes, our protocol focuses on how communication and its preceding control message exchange mechanism can be undertaken in a multi-channel scenario without assuming a separate control channel. CMAC enables spatial channel re-use, nearly collision free communication, and addresses the deafness problem without incurring a tradeoff in fairness or latency. When compared with a recent MAC protocol SMAC, results show that CMAC obtains nearly 200% reduction in energy consumption, significantly improved throughput, and end-to-end delay values that are 50-150% better than SMAC for our simulated topologies

Over the past few years, wireless local area networks (WLANs) have gained an increased attention and a large number of WLANs are being deployed in universities, companies, airports etc. Majority of the IEEE 802.11 based WLANs employ distributed coordination function (DCF) in wireless access points (AP) to arbitrate the wireless channel among Wireless Stations (STAs). However, DCF poses serious unfairness problem between uplink and downlink flows. To overcome this unfairness problem, we propose a simple enhancement to the IEEE 802.11 DCF which provides priority to the AP and thus enables it to acquire a larger share of the channel when required. We have demonstrated the unfairness problem through systematic measurements in an experimental test bed of WLAN using the legacy 802.11 DCF. We also developed analytical models to calculate the throughput of AP and the STAs and verify these results through thorough simulations in ns-2. We observe that our simulation results find in good agreement with our analytical models. Results show that our proposed enhancement achieves a fair distribution of bandwidth and improves the throughput (by nearly 300%) for the downlink flows as compared to the DCF, without severely affecting the performance of uplink flows

This paper proposes a new heterogeneous multi-hop cellular IP (MCIP) network that integrates multi-hop communication with cellular IP. MCIP increases the coverage of the wireless network and improves the network robustness against adverse propagation phenomena by supporting communication in dead zones and areas with poor radio coverage. MCIP includes three components: location management, connection management and route reconfiguration. Location management is responsible for maintaining the location information for mobile stations (MSs) in a local domain. Connection management establishes an initial path for data transmission and a route reconfiguration mechanism is proposed to take advantage of various multi-hop connection alternatives available based on terminal interfaces, network accessibility and topology. Our simulation results show that MCIP performs well in networks of various sizes.

A growing need for ubiquitous connectivity has motivated the integration of various wireless technologies such as cellular systems, WLANs and MANETs. In this paper we introduce the integrated routing protocol (IRP) that exploits topology information obtained by cellular base stations and WLAN access points in the route discovery and maintenance in a heterogeneous wireless access network. IRP also provides connectivity to the cellular network and/or WLAN hotspots through the multi-hop routing by allowing out of coverage users to maintain routes to Gateway Nodes (GN). We provide a simulation study of IRP with two different link quality metrics, number of hops and a new integrated metric based on the expected transmission time (ETT). Our results show that IRP improves the network coverage and capacity and allows connectivity alternatives that are not supported by other integrated solutions.

Future wireless networks are expected to integrate heterogeneous devices equipped with multiple radios and different characteristics. Therefore, it is important to understand how these heterogeneous radios can affect connectivity and overall multi-hop network performance. In this paper, we study the connectivity of a heterogeneous ad hoc network. We consider two types of nodes: nodes equipped with a single communication interface with communication range r, and dual-mode (DM) nodes, equipped with two communication interfaces with two different communication ranges r and r/sub f/, respectively, where r/sub f/>r. We assume the radios in the DM nodes operate in two different channels. We provide a theoretical analysis of connectivity in a linear network and we present simulation results for the two-dimensional case that show the impact of DM nodes on connectivity, broadcast latency and robustness in static scenarios.

This paper presents a simulation environment for mobile cellular networks called CELSA, which implements a mobility model based on users, regions and time period characteristics. This environment was used to obtain quality of service (QoS) parameters of a mobile cellular network and to evaluate the performance of a non-uniform channel allocation scheme called CA-STV compared to fixed and dynamic channel allocation.