This paper investigates a co-design framework for wireless networked control systems (WNCSs) that integrates multi-hop IEEE 802.15.4-based links under Wi-Fi interference, addressing the challenges of signal-to-interference-plus-noise ratio (SINR) degradation in adverse industrial environments. Multihop configurations are essential for extending the operational range and improving SINR in harsh propagation conditions, but they introduce trade-offs in control stability, latency, and computational complexity. We investigate the impact of multi-hop communication on system performance, comparing Bernoulli and Markovian control strategies. Our results demonstrate that multihop links effectively extend the operational range and mitigate SINR degradation, but at the cost of increased latency and computational cost. We analyze the spectral radius of the system stability verification matrix and control costs for Bernoulli and Markovian control strategies, illustrating that network latency and hop counts can be balanced while maintaining the stability of the multi-hop WNCS. Markovian strategy, although more computationally intensive, outperforms Bernoulli strategy under high interference, offering a robust solution for industrial WNCSs. The proposed framework provides a practical approach for deploying reliable WNCSs in interference-prone environments.

Time-domain macromodeling represents an effective technique for generating compact models of the linear time-invariant portion of complex electromagnetic systems. Among the various techniques, a well-known one involves the computation of the port impulse response at the system’s ports, which is then used for calculating convolution integrals. Such computation is typically slow. Recently, a method has been proposed to accelerate such computation by exploiting a piecewise constant approximation of the impulse responses, leading to the so-called segment fast convolution approach. The contribution of the present work is twofold: i) to extend the aforementioned method to the case of piecewise linear approximation of the port impulse responses in the case of linear time-invariant circuits; ii) to define a highly efficient quasi-recursive convolution computation algorithm for both constant and linear piecewise approximations. Moreover, vectorization is exploited to further improve computational efficiency. The proposed convolution schemes are validated in the case of a simple two-port network and then applied to relevant case studies of large-scale electromagnetic systems. Specifically, Reconfigurable Intelligent Surfaces (RISs) and neuromorphic circuits are modeled and validated. The numerical evaluation shows that the proposed schemes are able to guarantee high accuracy together with significant computational speed-ups.

Intelligent Reflective Surfaces (IRSs) enable controlling the radio propagation environment to enhance wireless communications and are particularly relevant for vehicle-to-everything (V2X) applications. This paper explores the integration of IRSs for virtual line-of-sight (VLOS) propagation in urban vehicle platoons that operate with New Radio (NR)-V2X mode 2 sidelink communications and proposes a semi-analytical framework to assess the performance of such systems. The framework considers the availability of resources, the number of interference vehicles, and their relative positions. A Nakagami-Lognormal composite channel model is assumed to describe the propagation environment. This approach provides a cost-effective and accurate estimate of packet success rates, facilitating optimal configuration and parameter adjustments for vehicle platoons. We demonstrate that under typical inter-vehicle distances and with large numbers of vehicles, VLOS communication via IRS can even surpass the performance of conventional Line-of-Sight (LOS) scenarios.

While data quality and quantity directly affect the estimation accuracy of deep learning-based localization techniques, obtaining empirical position data is often costly due to time-consuming experiments, especially for large-scale indoor environments. This paper proposes a novel data collection method to build deep learning-based localization models for indoor vehicle navigation services using multi-directional beacons. By defining the directed graph of the model applicability, we show that high-resolution position labeling data of a limited number of beacons is sufficient to train the localization model for the whole indoor scenario. However, obtaining the ideal directed graph of the model applicability still requires costly high-resolution empirical data from all beacons. We thus propose an autoencoder-based predicted graph method using only cost-effective low-resolution proximity data. We derive the minimum set of beacons needed to collect high-resolution empirical data to train the localization model. We evaluate the proposed beacon selection method in terms of the estimation accuracy and the data collection cost to the beacon-specific model and the ideal directed graph-based method through the extensive set of experimental measurements. The evaluation results show that the proposed localization model using the autoencoder-based predicted graph provides good estimation accuracy while considerably reducing the required training beacons.

While indoor vehicle navigation is an essential component in large-scale parking garages of major cities, technical limitations and challenging propagation environments considerably affect the accuracy of existing localization techniques. We propose practical and robust proximity and direction detection schemes of vehicles for indoor navigation services using low-cost beacons. Specifically, the proposed solution allows a handheld mobile device within a moving vehicle to autonomously detect its approximate position and moving direction by only observing received signal strength (RSS) values of beacon signals. The proposed approach essentially exploits the differential RSS technique over perpendicularly oriented directional beams to reduce the impact of uncontrolled factors, including the vehicle and the mobile device. A low-cost multidirectional beacon prototype is developed using Bluetooth technology. The localization performance is evaluated using 96 beacons in an underground parking garage within an area of$394.8 \mathrm {m} \times 304.3 \mathrm {m}$. Experimental results show that the 90th percentiles of the average proximity and direction detection errors are 0.8 and 1.64 m, respectively. Furthermore, our proposed scheme provides robust proximity and direction detection performance with various vehicles and mobile devices’ orientations.

In the aeronautics industry, wireless avionics intracommunications (WAICs) have a tremendous potential to improve efficiency and flexibility while reducing weight, fuel consumption, and maintenance costs over traditional wired avionics systems. This survey starts with an overview of the major benefits and opportunities in the deployment of wireless technologies for critical applications in an aircraft. The current state of the art is presented in terms of system classifications based on data rate demands and transceiver installation locations. We then discuss major technical challenges in the design and realization of the envisioned aircraft applications. Although WAIC has aspects and requirements similar to mission-critical applications of industrial automation, it also has specific issues, such as wireless channels, complex structures, operations, and safety of the aircraft that make this area of research self-standing and challenging. Existing wireless techniques are discussed to investigate the applicability of the current solutions for the critical operations of an aircraft. Specifically, IEEE 802.15.4-based and Bluetooth-based solutions are discussed for low data rate applications, whereas IEEE 802.11-based and UWB-based solutions are considered for high data rate applications. We conclude the survey by highlighting major research directions in this emerging area.

In this paper, we propose a framework for cross-layer analysis of multi-static passive RFID systems. The model takes into account details of the shared wireless channel, including fading and capture effect, whereas, at the medium access control (MAC) layer, the anti-collision mechanism proposed in the EPC Generation 2 standard is taken as a reference. To address the complexity of the system model, we rely on a semi-analytical approach, that combines a moment matching approximation method to abstract the physical layer and Monte-Carlo simulations to describe the MAC dynamics. Furthermore, based on the space diversity feature offered by the multi-static settings, we introduce the concept ofcapture diversityand propose a modification to the standard to fully support this form of diversity. Numerical results show the impact of deployment conditions and the relative positions of interrogator, tags, and detection points on the performance of tags’ identification. We show how the number of detection points impacts the system performance under various channel conditions and MAC parameters’ settings. Finally, we validate the proposed update of the MAC protocol, showing substantial performance improvement with respect to the standard collision resolution policy.

In this paper, we propose a model for the analysis of distributed passive backscattering systems for Radio Frequency Identification with physically separated illuminator and reader. The model takes into account the physical channel characteristics including shadow fading components and thresholds for powering and detection. The dynamic framed ALOHA medium access mechanism defined by the EPC Global Generation 2 standard is considered to evaluate the performance. To address the complexity of the system model, our framework is based on a semi-analytical approach that combines moment matching approximation method at channel level and Monte-Carlo approach for the medium access control dynamics. Results show the impact of deployment conditions and the relative positions among illuminator, tags, and reader on the identification performance. Interestingly, the detection of the back-scattered signal at a remote reader can improve the performance with a higher probability of capture. However, as the distance increases, the impact of shadow fading counterpoises the capture effect. The resulting trade-off is accurately described by our model.

This paper focuses on the impact of intelligent topology formation and routing on resilient mesh topologies consisting of heterogeneous devices in Internet of Things (IoT) networks. We consider a Bluetooth network comprising of low-power short-range devices that are heterogeneous in terms of energy source (e.g. the mains or coin-cell). In the first step, a resilient mesh topology is created by taking into account device characteristics such as energy sources and parameters related to neighbors. The Bluetooth devices negotiate master and slave roles, and form piconets which are then connected through multiple bridge nodes thus forming a scatternet. An energy aware algorithm is proposed to select the routing paths for packet forwarding between connected devices. The performance of topology and routing is evaluated through simulations in a large indoor office scenario based on realistic channel models and propagation characteristics. Results show that intelligent topology formation, in conjunction with the proposed energy aware routing algorithm leads to a significant gain (more than 100%) in terms of network lifetime, when compared to the baseline approaches.

IEEE 802.11ah and Bluetooth Low Energy (BLE) are candidates to become key technologies for many Internet of Things (IoT) applications. In this paper, 802.11ah and BLE technologies are evaluated and compared in a home automation scenario. The selected use case includes battery powered sensors, which generate traffic, and mains powered actuators, which consume traffic, connected through a central gateway. The performance is assessed in terms of service ratio, delay and activity factor of the transceivers. Results show that both technologies are suitable for the reference use case scenario. 802.11ah benefits from a higher throughput and lower delay jitter, whereas BLE sensors show lower activity factors and a longer battery lifetime is expected. The analysis is conducted for both fixed and variable traffic load. The performance of BLE results to be more sensitive to an increase of the traffic load with respect to 802.11ah. Eventually, the limitations of the current scenario are illustrated and alternative setups are discussed.

In systems employing pilot-symbol aided channel estimation, the pilot-to-data power ratio is known to have a large impact on performance. Therefore, previous works proposed methods setting the pilot power such that either the weighted sum of the mean squared error (MSE) of the estimated data symbols is minimized or the overall spectral efficiency (SE) is maximized. However, previous works did not take into account the impact of correlated antennas and channel state information (CSI) errors on the optimal pilot power setting. In this paper, we consider the uplink of a multiuser multiple-input multiple-output (MU MIMO) system employing a receiver that minimizes the MSE of the received data symbols in the presence of CSI errors and derive closed-form expressions for the MSE and the achievable SE. These expressions take into account the impact of antenna correlation and CSI errors, and are a function of pilot power and the number of receive antennas. The analytical and numerical results can help set the pilot power, minimizing the MSE in multiple antenna systems.

We consider the uplink of a single cell single input multiple output (SIMO) system, in which the mobile stations use intra-cell orthogonal pilots to facilitate uplink channel estimation. In such systems, the problem of transmission power balancing between pilot and data is known to have a large impact on the mean square error (MSE) for the received signal and, consequently, on the achievable uplink data rate. In this paper, we derive a closed form expression of the MSE for the received signal as a function of the pilot and data power levels under a per-user sum pilot-data power constraint. As a major contribution, our model is developed for arbitrary channel covariance matrices and it enables us to study the impact of the number of antennas and antenna correlation structures, including the popular 3GPP spatial channel model. Numerical results suggest that the effect of the antenna spacing is limited, but the angle of arrival and angular spread have a strong and articulated impact on the MSE performance. Moreover, as the number of antennas at the base station grows large, we show that a higher percentage of the power budget should be allocated to pilot signals than with a lower number of antennas.

In this paper, a coverage analysis of Bluetooth Low Energy (BLE) and IEEE 802.11ah technologies for indoor scenarios is performed. This is of particular relevance when these technologies are deployed as part of capillary networks. The physical layer parameters of BLE and IEEE 802.11ah are modeled, together with a detailed and accurate indoor propagation scenario that accounts for wall losses, ray tracing multi-path, and diffractions. A real case office building scenario is considered for practical evaluation. The minimum density of BLE central devices and IEEE 802.11ah access points that guarantees a predetermined coverage level is derived and compared between the two technologies. It is shown that BLE requires five times the number of central devices than IEEE 802.11ah access points to guarantee 95% coverage. IEEE 802.11ah benefits from the use of lower frequency band, higher transmit power and better receiver sensitivity than BLE, which permits a low cost and effective deployment of Internet of Things applications. Mesh capabilities and range extension for BLE are therefore essential for the success of BLE within the Internet of Things framework.

Passive tags based on backscattered signals yield low energy consumption and enable a rich set of applications. In this paper, the performance of the dynamic framed ALOHA of the ISO/IEC 18000-6C standard is investigated. A Markov chain model of the protocol is developed by including the effects of the channel under different propagation scenarios. Depending on the air interface parameters and the fading components, it is shown that multiple access interference determines complex and unexpected effects on the system performance. An explicit analysis of the successful interrogation probability is obtained with respect to the number of tags, number of interrogation rounds and fading severity. It is shown that channel statistics may induce significant degradation, although a moderate spread of the fading can be beneficial especially for those contexts that include time-varying conditions.

Although the performance of the medium access control (MAC) of the IEEE 802.15.4 has been investigated under the assumption of ideal wireless channel, the understanding of the cross-layer dynamics between MAC and physical layer is an open problem when the wireless channel exhibits path loss, multi-path fading, and shadowing. The analysis of MAC and wireless channel interaction is essential for consistent performance prediction, correct design and optimization of the protocols. In this paper, a novel approach to analytical modeling of these interactions is proposed. The analysis considers simultaneously a composite channel fading, interference generated by multiple terminals, the effects induced by hidden terminals, and the MAC reduced carrier sensing capabilities. Depending on the MAC parameters and physical layer thresholds, it is shown that the MAC performance indicators over fading channels can be far from those derived under ideal channel assumptions. As novel results, we show to what extent the presence of fading may be beneficial for the overall network performance by reducing the multiple access interference, and how this information can be used for joint selection of MAC and physical layer parameters.

Medium access control (MAC) and routing protocols are fundamental blocks in the design of low power and lossy networks (LLNs). As new networking standards are being proposed and different existing research solutions patched, evaluating the performance of the network becomes challenging. Specific solutions that can be individually efficient, when stacked together may have unexpected effects on the overall network behavior. In this paper, we provide an analysis of the fundamental MAC and routing protocols for LLNs: IEEE 802.15.4 MAC and IETF RPL. Moreover, a characterization of their cross-layer interactions is presented by a mathematical description, which is essential to truly understand the protocols mutual effects and their dynamics. Novel metrics that guide the interaction between MAC and routing are compared to existing metrics. Furthermore, a protocol selection mechanism is implemented to select the appropriate routing metric and MAC parameters given specific performance constraints. Analytical and experimental results show that the behavior of the MAC protocol can hurt the performance of the routing protocol and vice versa, unless these two are carefully optimized together.

The IEEE 802.15.4 communication protocol is a de-facto standard for wireless applications in industrial and home automation. Although the performance of the medium access control (MAC) of the IEEE 802.15.4 has been thoroughly investigated under the assumption of ideal wireless channel, there is still a lack of understanding of the cross-layer interactions between MAC and physical layer in the presence of realistic wireless channel models that include path loss, multi-path fading and shadowing. In this paper, an analytical model of these dynamics is proposed. The analysis considers simultaneously a composite Rayleigh-lognormal channel fading, interference generated by multiple terminals, the effects induced by hidden terminals, and the MAC reduced carrier sensing capabilities. It is shown that the reliability of the contention-based MAC over fading channels is often far from that derived under ideal channel assumptions. Moreover, it is established to what extent fading may be beneficial for the overall network performance.

In this paper, routing metrics for low power and lossy networks are designed and evaluated. The cross-layer interactions between routing and medium access control (MAC) are explored, by considering the specifications of IETF RPL over the IEEE 802.15.4 MAC. In particular, the experimental study of a reliability metric that extends the expected transmission count (ETX) to include the effects of the level of contention and the parameters at MAC layer is presented. Moreover, a novel metric that guarantees load balancing and increased network lifetime by fulfilling reliability constraints is introduced. The aforementioned metrics are compared to a routing approach based on backpressure mechanism.

Distributed processing through ad hoc and sensor networks is having a major impact on scale and applications of computing. The creation of new cyber-physical services based on wireless sensor devices relies heavily on how well communication protocols can be adapted and optimized to meet quality constraints under limited energy resources. The IEEE 802.15.4 medium access control protocol for wireless sensor networks can support energy efficient, reliable, and timely packet transmission by a parallel and distributed tuning of the medium access control parameters. Such a tuning is difficult, because simple and accurate models of the influence of these parameters on the probability of successful packet transmission, packet delay, and energy consumption are not available. Moreover, it is not clear how to adapt the parameters to the changes of the network and traffic regimes by algorithms that can run on resource-constrained devices. In this paper, a Markov chain is proposed to model these relations by simple expressions without giving up the accuracy. In contrast to previous work, the presence of limited number of retransmissions, acknowledgments, unsaturated traffic, packet size, and packet copying delay due to hardware limitations is accounted for. The model is then used to derive a distributed adaptive algorithm for minimizing the power consumption while guaranteeing a given successful packet reception probability and delay constraints in the packet transmission. The algorithm does not require any modification of the IEEE 802.15.4 medium access control and can be easily implemented on network devices. The algorithm has been experimentally implemented and evaluated on a testbed with off-the-shelf wireless sensor devices. Experimental results show that the analysis is accurate, that the proposed algorithm satisfies reliability and delay constraints, and that the approach reduces the energy consumption of the network under both stationary and transient conditions. Specifically, even if the number of devices and traffic configuration change sharply, the proposed parallel and distributed algorithm allows the system to operate close to its optimal state by estimating the busy channel and channel access probabilities. Furthermore, results indicate that the protocol reacts promptly to errors in the estimation of the number of devices and in the traffic load that can appear due to device mobility. It is also shown that the effect of imperfect channel and carrier sensing on system performance heavily depends on the traffic load and limited range of the protocol parameters.

IEEE 802.15.4 multi-hop wireless networks are an important communication infrastructure for many applications, including industrial control, home automation, and smart grids. Existing analysis of the IEEE 802.15.4 medium access control (MAC) protocol are often based on assumptions of homogeneous traffic and ideal carrier sensing, which are far from the reality when predicting performance for multi-hop networks. In this paper, a generalized analysis of the unslotted IEEE 802.15.4 MAC is presented. The model considers heterogeneous traffic and hidden terminals due to limited carrier sensing capabilities, and allows us to investigate jointly IEEE 802.15.4 MAC and routing algorithms. The analysis is validated via Monte Carlo simulations, which show that routing over multi-hop networks is significantly influenced by the IEEE 802.15.4 MAC performance. Routing decisions based on packet loss probability may lead to an unbalanced distribution of the traffic load across paths, thus motivating the need of a joint optimization of routing and MAC.

Control applications over wireless sensor networks (WSNs) require timely, reliable, and energy efficient communications. Cross-layer interaction is an essential design paradigm to exploit the complex interaction among the layers of the protocol stack and reach a maximum efficiency. Such a design approach is challenging because reliability and latency of delivered packets and energy are at odds, and resource constrained nodes support only simple algorithms. In this paper, the TREnD protocol is introduced for control applications over WSNs in industrial environments. It is a cross-layer protocol that embraces efficiently routing algorithm, MAC, data aggregation, duty cycling, and radio power control. The protocol parameters are adapted by an optimization problem, whose objective function is the network energy consumption, and the constraints are the reliability and latency of the packets. TREnD uses a simple algorithm that allows the network to meet the reliability and latency required by the control application while minimizing for energy consumption. TREnD is implemented on a test-bed and compared to some existing protocols. Experimental results show good performance in terms of reliability, latency, low duty cycle, and load balancing for both static and time-varying scenarios.

We present a novel approach for Medium Access Control (MAC) protocol design based on protocol engine. Current way of designing MAC protocols for a specific application is based on two steps: First the application specifications (such as network topology and packet generation rate), the requirements for energy consumption, delay and reliability, and the resource constraints from the underlying physical layer (such as energy consumption and data rate) are specified, and then the protocol that satisfies all these constraints is designed. Main drawback of this procedure is that we have to restart the design process for each possible application, which may be a waste of time and efforts. The goal of a MAC protocol engine is to provide a library of protocols together with their analysis such that for each new application the optimal protocol is chosen automatically among its library with optimal parameters. We illustrate the MAC engine idea by including an original analysis of IEEE 802.15.4 unslotted random access and Time Division Multiple Access (TDMA) protocols, and implementing these protocols in the software framework called SPINE, which runs on top of TinyOS and is designed for health care applications. Then we validate the analysis and demonstrate how the protocol engine chooses the optimal protocol under different application scenarios via an experimental implementation.

A generalized analysis of the IEEE 802.15.4 medium access control (MAC) protocol in terms of reliability, delay and energy consumption is presented. The IEEE 802.15.4 exponential backoff process is modeled through a Markov chain taking into account retry limits, acknowledgements, and unsaturated traffic. Simple and effective approximations of the reliability, delay and energy consumption under low traffic regime are proposed. It is demonstrated that the delay distribution of IEEE 802.15.4 depends mainly on MAC parameters and collision probability. In addition, the impact of MAC parameters on the performance metrics is analyzed. The analysis is more general and gives more accurate results than existing methods in the literature. Monte Carlo simulations confirm that the proposed approximations offer a satisfactory accuracy.

This paper proposes an analytical framework for performance evaluation of TCP (transport control protocol) over adaptive wireless links. Specifically, we include adaptation of power, modulation format and error recovery strategy, and incorporate some features of wireless fading channels. This framework is then used to pursue joint optimization through maximization of an objective functional, that expresses a trade-off between achievable throughput and energy costs. A set of numerical results is reported, and it is seen that hybrid ARQ schemes may provide significant benefits in the optimization framework