The IEEE 802.11bn draft amendment to the 802.11 Wi-Fi standard introduces Non-Primary Channel Access (NPCA) to enhance spectrum efficiency and mitigate congestion in dense wireless environments. NPCA allows stations to transmit over non-primary channels when the primary channel is occupied, improving overall spectrum utilization and reducing transmission delays. This paper presents a detailed evaluation of NPCA, focusing on its effectiveness in scenarios involving hidden nodes—one of the key challenges limiting its performance. Our research models NPCA based on IEEE contributions and proposals, implementing realistic network topologies to analyze both its strengths and weaknesses. The findings provide critical insights into NPCA’s practical deployment, highlighting its potential benefits and identifying areas requiring further optimization to ensure fairness and adaptability in real-world networks.

The increasing demand for high-performance wireless communication, due to emerging applications such as augmented reality, virtual reality, and Internet-of-Things (IoT), has highlighted the need for enhanced Peer-to-Peer (P2P) communication in Wi-Fi networks. P2P communication, often implemented through technologies like Wi-Fi Direct and Wi-Fi Aware, plays a crucial role in enabling seamless device-to-device interaction. This paper explores two significant enhancements for improving P2P communication: enhancing base-channel P2P through the optimization of TXOP sharing for P2P groups, and improving off-channel P2P through multi-AP coordination for channel advertisement. First, we examine the enhancement of base-channel P2P communication by introducing a refined transmission opportunity (TXOP) sharing mechanism, where an AP allocates portions of its TXOP to P2P devices within a group. This allocation ensures that devices can transmit data within a controlled, synchronized framework, thereby reducing contention and improving overall throughput. Furthermore, the proposed improvements enable devices to efficiently share resources based on group-level needs, supporting latency-sensitive applications such as real-time media streaming. Second, we address the challenges of off-channel P2P communication in OBSS (Overlapping Basic Service Set) environments, where interference from neighboring networks can severely affect performance. Through multi-AP coordination, APs can advertise recommended P2P channels that minimize overlap with infrastructure operations, thereby providing cleaner and more reliable channels for P2P communication. In addition, this coordination also facilitates faster setup and more efficient operation of P2P links.

Today, Wi-Fi is over 25 years old. Yet, despite sharing the same branding name, today’s Wi-Fi boasts entirely new capabilities that were not even on the roadmap 25 years ago. This article aims to provide a holistic and comprehensive technical and historical tutorial on Wi-Fi, beginning with Institute of Electrical and Electronics Engineers 802.11b (Wi-Fi 1) and looking forward to IEEE 802.11bn (Wi-Fi 8). This is the first tutorial article to span these eight generations. Rather than a generation-by-generation exposition, we describe the key mechanisms that have advanced Wi-Fi. We begin by discussing spectrum allocation and coexistence, and detailing the IEEE 802.11 standardization cycle. Second, we provide an overview of the physical layer (PHY) and describe key elements that have enabled data rates to increase by over 1000×. Third, we describe how Wi-Fi medium access control (MAC) has been enhanced from the original distributed coordination function (DCF) to now include capabilities spanning from frame aggregation to wideband spectrum access. Fourth, we describe how Wi-Fi 5 first broke the one-user-at-a-time paradigm and introduced multi-user (MU) access. Fifth, given the increasing use of mobile, battery-powered devices, we describe Wi-Fi’s energy-saving mechanisms over the generations. Sixth, we discuss how Wi-Fi was enhanced to seamlessly aggregate spectrum across 2.4-, 5-, and 6-GHz bands to improve throughput, reliability, and latency. Finally, we describe how Wi-Fi enables nearby access points (APs) to coordinate in order to improve performance and efficiency. In the Appendix, we further discuss Wi-Fi developments beyond 802.11bn, including integrated millimeter-wave (IMMW) operations, sensing, security and privacy extensions, and the adoption of artificial intelligence (AI)/machine learning (ML).

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.

This paper presents a methodology to evaluate the safety performance in wideband wireless systems through frequency-selective channels. We propose a methodology based on the error distribution along an Orthognal Frequency Division Multiplexing (OFDM) symbol for a given channel situation. From there, a mathematical method that considers the benefits of channel coding is derived to characterize the performance of safety communication layer tools as defined by the regulatory framework. This process is illustrated using an example with industry-specific data. It is shown that the effect of fading variability benefits the safety performance of the wireless system. The analytical model shows that variability reduces the probability of events with many errored subcarriers. This reduction facilitates the identification of a higher number of situations that put the safety function at risk. The possibilities of reaching some SIL limits within the proposed scenario are also explored.

Presents corrections to the paper, On the Feasibility of Wireless Communications for Safety Applications in Industry.

Communication systems are a key element for the industry 4.0 revolution, where the remote access to the machinery is a fundamental part for the automation of tasks related to monitoring and control of the different industrial processes. There is an increasing interest in performing such communications using a wireless medium, as they offer several advantages as a lower cost, greater flexibility or the ability to operate in moving elements. However, existing works have showed that the achievable performance in the sub-6 GHz frequency bands is insufficient to cope with all the requirements, which motivated the analysis of the millimeter wave spectrum for these use cases. Industrial environments present a harsh condition for electromagnetic wave propagation, where the abundance of reflective surfaces can present difficulties to properly exchange information. Thus, a thorough analysis and characterization of the propagation through this kind of environment is necessary to develop protocols and standards accordingly. This work provides the results of measurements carried out in two industrial facilities, which are a university workshop and a pit oven building from a steel company. Metrics of the results are computed and discussed as well, where a significantly larger losses can be seen for the pit oven measurements compared to other industrial scenarios.

This article presents a methodology to characterize the reliability and safety capabilities of redundant wireless systems planned for an industrial application. The equations that describe the residual error are presented and studied in situations that model an industrial wireless scenario. We propose different voting systems and their performance is evaluated analytically and by simulations. Likewise, a voting system based on a combination of filtering and cross-checking techniques is proposed. This solution significantly reduces the probability of undetected dangerous events while maintaining availability under control. Moreover, an improved version with triple redundancy is also presented. The results demonstrate that it is possible to fulfill the requirements of standard IEC 61508 without compromising system availability statistics. The solutions have been implemented on hardware wireless prototypes to illustrate the effectiveness of the proposed voting systems.

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.

The millimeter-wave (mmWave) bands contain some properties that can be key enablers for future wireless communications in industrial scenarios, but, despite the potential this new medium presents, very few efforts have been carried out to characterize such environments. This paper presents a cost-effective and flexible channel sounder that aims to measure indoor industrial setups in order to develop models that will assist in the development of future protocols and standards. The complete design and selected hardware (HW) of the sounder are discussed, and three preliminary tests carried out in laboratory and machining workshop scenarios are also presented, where the performance of the sounder is validated.

This paper presents a method to evaluate the feasibility of using wireless links as part of functional safety systems. We present an analytical model to describe the wireless safety links' performance operating in fading industrial environments. The work considers integrity failures, wrong addressing, message sequence errors, and masquerade events. The contributions of each perturbation to the overall system residual error are modeled with equations. Moreover, a MAC scheme based on the tools suggested in IEC 61784–3 is proposed and validated under industry-recommended use case parameters. The results show that the variation of the frame structure and application-specific parameters impact the overall residual error. The work concludes that the residual error probability of the CRC dominates residual error performance, but it may be reduced using consistent countermeasures against other possible sources of error.

Standard wireless systems are rapidly evolving to support the strict requirements of industrial applications. In this research line, wireless time-sensitive networking (TSN) is gaining momentum, thanks to the interest of wired TSN among the industries. A critical aspect of the wireless TSN research is the integration of wired and wireless TSN to create large-scale hybrid TSN networks. This integration is currently being discussed for 5G, whereas the integration between wired TSN and IEEE 802.11 is a step behind. To address this gap in the state of the art, this article discusses the integration challenges of wired TSN and wireless local area network technologies and proposes a hybrid TSN device architecture. Based on the architecture, we have developed a hybrid TSN network proof-of-concept. The proof-of-concept demonstrates that the hybrid TSN architecture can maintain the essential TSN services, including providing guaranteed latency in the 100-microsecond level.

Industrial control systems present numerous challenges from the communication systems perspective: clock synchronization, deterministic behavior, low latency, high reliability, flexibility, and scalability. These challenges are mostly solved with standard technologies over Ethernet, e.g., time-sensitive networking (TSN). As a research trend, it is expected that TSN will converge with wireless, leading to the Wireless TSN paradigm. Also, Wireless TSN is expected to be integrated with Ethernet TSN to create large-scale wired–wireless (Hybrid) TSN networks. The first step toward Hybrid TSN is the distribution of the clock reference from the wired to the wireless domain. In this article, we leverage existing Ethernet TSN and wireless technologies implementations (Wi-Fi and w-SHARP) and present two hardware architectures specifically engineered to enable the clock synchronization distribution among the network domains. The hardware architectures have been implemented over a system-on-chip field-programmable gate array platform. We demonstrate through several experiments that the implementation is able to fulfill the synchronization performance required by TSN.

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.

Many Intelligent Transportation System (ITS) applications rely on communication between fixed ITS stations (roadside installations) and mobile ITS stations (vehicles) to provide traffic safety. In VANETs, the Control Channel (CCH) and Service Channels (SCHs) are applied to transmit the safetyrelated data. The CCH used in IEEE 802. 11p standard for exchanging high-priority safety messages and control information and it can be easily congested by high-frequency periodic beacons under high density scenarios. Also, employing the DedicatedShort Range Communication (DSRC) band of IEEE 802.11p standard can hardly satisfy the requirements of high-critical safety applications. Also, transmitting safety beacons at a constant rate regardless of considering the condition of the links leads to the lack of flexibility and medium resources to support meeting the reliability requirements of these applications. In this paper, we evaluate a beacon rate control method, which assigns a higher beacon rate to nodes based on link conditions, i.e. with more surrounding nodes and better conditions to disseminate beacons. On the other hand, as IEEE 802.11p Medium Access Control (MAC) layer does not perform well under high channel load, so in this paper, we use Self-organizing Time Division Multiple Access (STDMA) in our simulations as MAC layer protocol. The results of the simulations demonstrate the rate of beacon transmission/reception effectively improves, results in better resource utilization. Also, Packet Error Rate (PER) and Packet Inter-Reception time (PIR) decrease significantly which is crucial for safety applications.

The European Train Control System (ETCS) relies today on the 2nd generation cellular system GSM-R. GSM-R obsolescence has triggered the evolution of the current European Railway Traffic Management System (ERTMS) to the Future Railway Mobile Communication System (FRMCS), under development. FRMCS considers the use of several radio access technologies in parallel such as Wi-Fi, LTE, Satellite and 5G. Testing new communication systems along railway tracks is time and money consuming. Consequently, it is important to develop a zero-on-site-testing approach thanks to the development of emulation platforms. These platforms, combining hardware and software, are able to reproduce in laboratory real railway infrastructure behavior and scenarios. This paper presents the EMULRADIO4RAIL platforms, developed in the framework of Shift2Rail program and gives examples of results obtained.

This paper presents a methodology to characterize the impact of deep fading in wireless links related to safety functions for industrial applications. We analyze the different methods available to describe the residual error probability and discuss their application to practical wireless systems, where fading is a key propagation impairment. An analytical method to derive the residual error probability in fading channels is proposed, and calculated curves are compared to empirical results obtained by system simulations. The procedure is illustrated using two well known CRC polynomials with codeword lengths and appropriate safety data rates for industry cases. The system residual error probabilities are compared with those associated to SIL targets. Moreover, an erroneous packet filtering technique is proposed to approach IEC 61508 specifications. Results show that the choice of a proper CRC is critical in safety wireless and demonstrate that CRCs, combined with filtering techniques, can achieve performance values in the range of SIL targets.

This paper discusses an implementation of a wireless-wired TSN network, named SHARP, which delivers hard real-time capabilities with bounded latencies of hundreds of microseconds and clock synchronization with tens of nanosecond accuracy along both wired and wireless segments. It has been demonstrated that the network is able to maintain the most important TSN services in various situations of critical real-time and non-critical traffic in the context of a representative Industry 4.0 application. The communication solution presented here is expected to pave the way for massive digitization of future flexible smart factories, especially when combined with other technologies to be commercially available in the short-medium term like 5G.

Real-time Industrial applications in the scope of Industry 4.0. present significant challenges from the communication perspective: low latency, ultra-reliability, and determinism. Given that wireless networks provide a significant cost reduction, lower deployment time, and free movement of the wireless nodes, wireless solutions have attracted the industry attention. However, industrial networks are mostly built by wired means because state-of-the-art wireless networks cannot cope with the industrial applications requirements. In this article, we present the hardware implementation of wireless SHARP (w-SHARP), a promising wireless technology for real-time industrial applications. w-SHARP follows the principles of time-sensitive networking and provides time synchronization, time-aware scheduling with bounded latency and high reliability. The implementation has been carried out on a field-programmable gate array-based software-defined radio platform. We demonstrate, through a hardware testbed, that w-SHARP is able to provide ultra-low control cycles, low latency, and high reliability. This implementation may open new perspectives in the implementation of high-performance industrial wireless networks, as both PHY and MAC layers are now subject to be optimized for specific industrial applications.

Critical communication requirements included in Factory Automation applications are complex to implement due to the difficulties encountered in guaranteeing high reliability and ultra-low latencies at the same time. In this work-in-progress, a technical solution for the physical layer is proposed: the Quasi-Cyclic LDPC of the Progressive Edge Growth family (QC-PEGLDPC). This coding scheme is considered as a promising candidate due to two main factors: the good decoding performance for short packet transmissions and the low latency that can be obtained by using full parallel decoding architectures. The obtained results are compared with the 5G New Radio coding scheme, which includes LDPCs as part of the solution for Ultra Reliable Low Latency (URLLC) use cases. In these first results, QC-PEG-LDPC shows a performance improvement of 1 dB when compared with the 5G LDPC codes for a message length of 128 bits. Latency analysis indicate that QC-PEG-LDPC could allow decoding latencies of 0.13 μs providing that the full parallel decoding architecture is enabled.

Time Sensitive Networking (TSN) is becoming the standard Ethernet-based technology for converged networks of Industry 4.0 due to its capacity to support deterministic latency requirements. However, it cannot provide the required flexibility to support mobile industrial applications required for the factories of the future. This could be enabled through the integration of wireless technologies in factories, and in particular of 5G and Beyond networks since they have been designed to support ultra-reliable and low-latency communications. This has triggered significant interest to integrate 5G and TSN networks, and first frameworks for such integration have been defined. However, the work is at early stages and the solutions to effectively integrate the two networks so that 5G can support TSN QoS levels are yet to be designed. This paper discusses current research and standardization work on 5G-TSN integration, and quantifies for a closed loop control application the 5GS bridge delay. The paper uses an example based on 5G-ACIA [1] to discuss open technical and research challenges to effectively integrate 5G and TSN.

Wireless communications have attracted great interest from the industry due to its lower cost and the possibility of enabling new use cases. The new use cases are commonly related to mobile robotics, such as Unmanned Aerial Vehicles. The design of wireless systems for these use cases requires deep knowledge of the channel behavior. However, the weight and size of full channel sounders exceed the payload of most mobile robots. In addition, full channel sounders usually require wired time synchronization. Hence, channel measurements in these scenarios are constrained to use limited channel sounders, which can only measure some specific parameters (frame error rate, channel attenuation, etc.). In this paper, we present the design and implementation of a portable 802.11-based channel sounder combined with a sub-nanosecond wireless time synchronization algorithm. Thanks to the wireless time synchronization, the channel sounder can be used to periodically take complex baseband Channel Impulse Response samples synchronized to absolute time. From these samples, relevant channel parameters can be extracted, including the Power Delay Profile, Doppler spectrum, and channel delay. The verification of the channel sounder through a wireless channel emulator confirms its feasibility for mobile robotics applications.

Industrial applications in the industry 4.0 scope present significant requirements and challenges from the communication technologies perspective: low latency, reliability, and determinism. However, some use cases add requirements on mobility, scalability and openness, such as flexible and large automated warehouses and production lines. Combining these two kinds of requirements calls for wireless technologies that can provide an adequate trade-off. This paper compares two protocols that rate particularly well in such trade-off, namely Self-Organizing Time Division Multiple Access (STDMA) and Reconfigurable and Adaptive Time Division Multiple Access (RATDMA). The comparison was carried out through simulations under a multipath dispersed time-variant industrial channel while subject to a variable Doppler shift. To this end, we used OMNeT++ in combination with the VEINS framework to evaluate several relevant metrics such as packet losses and packet inter-arrival time. Overall, RA-TDMA shows longer disconnections caused by the hand-over between separate networks. Concerning packet losses, the protocols perform similarly, with RA-TDMA outperforming STDMA under overlapping networks or poor clock synchronization.

The time-sensitive network paradigm envisions the integration of operation technology and information technology in the same network. One of the requirements for building time-sensitive networks is sharing a global time along the network. This requirement is especially critical in wireless systems, where there are few robust methods to perform accurate time transfer. In this article, the problem of time transfer over realistic wireless channels is studied, and a time distribution scheme is proposed. The time distribution scheme has three components: Precision time protocol, a novel timestamping method (enhanced timestamps) and an algorithm to implement the enhanced timestamps. The performance of the proposed scheme has been evaluated in MATLAB using the IEEE 802.11n Standard under several standard wireless local area network channel models. The results show that the system can reach subnanosecond time transfer accuracy under non-line-of-sight and time-variant conditions, but its performance greatly depends on the signal-to-noise ratio and on the channel variation rate.

The reliability of a point-to-point link for Industrial Wireless Sensor and Actuator Networks (IWSANs) is evaluated in this paper. The point-to-point link is based on the physical layers (PHYs) 1M and 2M of Bluetooth Low Energy (BLE). Both PHYs are tested under different wireless channels: additive white Gaussian noise (AWGN), Rician, Rayleigh, and the IEEE 802.15.4a CM8 industrial channel. The packet error rate (PER) is the metric used to evaluate the reliability. Results are presented and compared with the requirements of typical industrial use cases.

Industrial automation systems that present strong real-time requirements have been traditionally implemented using wired networks. However, the prolific development of the wireless networks, and the important benefits derived from their use, have brought an increase in the introduction of the wireless networks as an extension of wired ones. Even so, the current wireless standards do not allow the coexistence with wired networks that present severe reliability and real-time requirements, such as those used in industrial control applications. In order to solve this problem, this paper presents a hybrid network with deterministic features, including a wired network with Time Sensitive Network (TSN) and a new Medium Access Control (MAC) wireless protocol for the wireless section. Moreover, this paper gives details about the bridge that has been developed for transmitting data between the two sections of the hybrid network in a deterministic way. The proposed approach has been implemented, and the measures in real hardware prove the fulfilment of the deterministic real-time requirements demanded by the hybrid network.

Press machine maintenance requires to incorporate cutting-edge technologies in the most critical elements for enhancing press and components robustness and functionality in order to facilitate proactive-predictive maintenance activities. In this work, a wireless torque sensor node has been designed, developed, tested and validated. This increases machines and components reliability reducing high costs caused by production downtimes with required maintenance repair operations. The development of this wireless torque sensor node improves maintenance strategies, monitoring and analysing non-intrusively the shaft status.

Wireless communication technologies play an important role in today's society and, for that reason, wireless systems are almost ubiquitous. The keys of the success of wireless communications are, among others: reduced cost of wiring, implementation and maintenance or greater flexibility. Given these advantages, there is a growing interest in expanding the wired networks used in the most critical industrial applications to a wireless domain, fulfilling the real-time requirements of these applications. In addition, the incorporation of mobile devices to hybrid networks allows to expand the application area and obtain even more benefits from using wireless solutions. Nevertheless, guaranteeing the robustness and determinism required by factory automation applications where several Access Points (AP) are necessary to cover the entire wireless area is not an easy task. Therefore, in this paper, a novel soft-handover algorithm is presented. This algorithm guarantees an uninterrupted communication during the handover process required by the wireless devices together with a dynamic management of the resources within the hybrid (wired/wireless) scheme. To make this possible, the handover algorithm is combined with a slotted Medium Access Control (MAC) based on a superframe structure with a contention-free phase and a contention phase, where the contention-free phase is divided into uplink and downlink slots. The performance of the algorithm has been evaluated through OMNeT++ simulations.

In industrial automation systems, the introduction of wireless networks as an extension of the existing wired networks is increasing. However, with the existing wireless technologies, it is impossible to guarantee this coexistence for those applications with strict real-time and reliability requirements such as Networked Control Systems (NCS) or Distributed Control Systems (DCS). The main problem lies in the design of the Medium Access Control (MAC) protocol, as this plays a key role in fulfilling real-time and deterministic requirements. Moreover, the integration of both networks is fundamental to provide a seamless coexistence guaranteeing the demanding requirements of these applications. So, in order to expand the wired network used in NCS to a wireless domain, a hybrid IEEE 802.3/IEEE 802.11 real-time TDMA-based MAC scheme is proposed in this paper. The proposed scheme can support the transmission of periodic real-time traffic and aperiodic real-time traffic in a deterministic way, together with best-effort (BE) traffic. Moreover, with the aim of increasing the reliability of the communication system, retransmission mechanisms are defined. The performance of these MAC schemes has been evaluated over Rayleigh fading channel through OMNeT++ simulator. Provided results show that the transmission of periodic real-time traffic is not affected by the transmission of aperiodic or BE traffic. Moreover, results show that the transmissions and retransmissions are adapted to tight control cycles.

Wireless communications enables introduction of Internet of Things (IoT) in industrial networks. Unfortunately, real-time guarantees required for many IoT applications, may be compromised in wireless networks due to an unreliable transmission medium. A key component in enabling real-time communications is the medium access control (MAC) layer and its ability to effectively avoid concurrent transmissions that causes deadline misses. Also, deploying the network in a harsh interference environment can lead to low reliability. Time diversity, based on transmitting several copies of the same data at different instants, increases reliability but at the expense of increased jitter and bandwidth. A more efficient resource utilization is expected from cognitive radio, which dynamically takes into account the status of the wireless environment before performing transmissions. This paper proposes a wireless MAC protocol based on scheduled timeslots to avoid concurrent transmissions, combined with two different mechanisms to increase reliability, one based on time diversity and another on cognitive radio. The protocol and its mechanisms to enhance reliability are compared in different interference scenarios, and show that cognitive radios achieves better performance than time diversity, especially when the interference is produced by a jammer.

This work presents measurements and characterizations of a 2.53 GHz wireless propagation channel for radio links in railway onboard applications. Wireless technologies have a great potential use in train control and structural health monitoring applications; however, in harsh propagation environments they suffer from severe signal degradation, including delay spread, deep fading and Doppler spread. The aim of this work is to analyze the signal propagation in railway environments by means of a measurement campaign at 2.53 GHz, taking into account antenna locations both inside and below the train car. Results from wideband and narrowband analysis are shown, focusing on delay spread, small-scale envelope fading distribution and Doppler spectrum.

A Medium Access Control (MAC) protocol for time-critical wireless applications called Enhanced Priority MAC (EPMAC) is proposed in this paper. The proposed scheme supports three traffic categories prioritizing emergency traffic over non critical one and beacons are emitted to announce that the channel will be occupied. EP-MAC is designed so that the highest priority traffic postpones lowest priority transmissions. The performance of this protocol has been evaluated over several industrial channels through OPNET simulator. Compared with PriorityMAC, provided results show that EP-MAC is able to reduce the latency of all the traffic categories supported, whilst fulfilling the stringent requirements of time-critical applications.

The evaluation of Cognitive Radio (CR) for Wireless Sensor and Actuator Networks (WSANs) in industrial wireless automation applications is presented in this contribution. Current wireless solutions do not ensure enough performance for hard real-time and reliability requirements, based on time-critical data traffic. These industrial applications are characterized by harsh environments, where the robustness of wireless communications plays an important role. In these kinds of environments, CR can increase the system's reliability and robustness. Thus, several cognitive and non-cognitive MACs which ensure mission-critical and time-critical data transmission have been evaluated through OPNET network simulator over several fading and interference channels. The provided results show that CR-based MACs are able to maintain the performance of the network in harsh channels and under interference.

In this work a time-synchronized Wireless Sensor Network (WSN) has been designed and implemented for a realtime Structural Health Monitoring (SHM) system for trains. Channel measurements have been done in the first place on a real operational scenario, and obtained results have been used as inputs for the design of the physical layer of the WSN. A specific Time Division Multiple Access (TDMA) MAC layer and a synchronization algorithm have also been developed for allowing a deterministic data collection and synchronized sampling, which are critical aspects in SHM applications. Performance measurements of the WSN have also been done, which have shown maximum sampling synchronization jitter values within 1 μs for sensor nodes belonging the same base station, and maximum jitter values within 2 μs for nodes of different base stations.

In this paper an FPGA-based wideband wireless channel emulator is presented which is suitable for early evaluation of Wireless Sensor and Actuator Networks in industrial environments. The emulator works in complex baseband and has a 100 MHz-wide RF interface which covers the full Industrial, Scientific and Medical (ISM) band of 2.45 GHz (2.4–2.5 GHz); this allows the direct connection of either custom or commercial WSN nodes to the emulator. The emulator has been deployed on a FPGA where a soft processor has been included, and is able to generate white Gaussian noise, and multipath and Doppler fading effects. In this paper the details of the platform are presented, and validation results are shown for its diverse functionalities. BER and PER values are also presented which have been obtained for AWGN and Rayleigh channels using real WSN nodes connected to the emulator.

This paper presents the implementation of several data coding functions used in Software Defined Radios, on R3TOS: a Reliable, Reconfigurable and Real-Time Operating System. The latter offers efficient high performance computing on FPGAs as well as protection against emerging faults, hence making it a perfect candidate for the implementation of SDRs. In particular, R3TOS' ICAP-based Inter-task Communication Infrastructure (I2CI) has been used for data feeding and collection from coding functions, while a task context saving and restoration procedure, and a fast function parameterization system have been developed in order to improve system performance. The design of the data coding functions has been carried out using Xilinx's rapid prototyping tool System Generator in order to ease their development.

In this study, the performance of two asynchronous multi-access direct sequence code division multiple access (DS-CDMA) and multicarrier code division multiple access (MC-CDMA) systems with binary and polyphase long sequences is compared. An indoor multipath powerline channel model generated from random impedance networks is used. The powerline background, narrowband and impulsive noise are modelled statistically, based on models and measurements done in previous works. A complete analytical performance study is done for asynchronous MC-CDMA employing an interval guard in the form of a cyclic prefix (CP) and periodic long sequences, which provides a better channel coding than short sequences. The analytical results are completed with Monte Carlo simulations for both, DS-CDMA and MC-CDMA systems. Under impulsive noise an upper bound in the bit error rate (BER) performance for DS-CDMA and MC-CDMA systems is obtained analytically, which is confirmed by the Monte Carlo simulations.