Non-coherent cooperative jammer for multi-platform applications

In the unmanned aerial vehicle (UAV) based localization of slow-moving radio frequency (RF) sources with unknown transmitted strength of signal, such as a person with a cell phone in a search and rescue mission, the UAV navigation errors are significant sources of localization error. Although the use of a global positioning system (GPS) can reduce the UAV’s localization error significantly resulting in more accurate RF source localization, if the GPS signal is lost temporarily or permanently, the accuracy of the UAV-based localization decreases rapidly. In this paper, a simultaneous localization and mapping (SLAM)-inspired approach for simultaneous localization of UAV and RF sources (SLUS) is proposed. The proposed approach solves these two connected problems, i.e. the UAV localization and RF source localization, simultaneously to decrease the error of the UAV position estimation and the error of the RF source localization. In the proposed approach, beside the UAV position prediction, the RF source position prediction is also performed. Then the predicted states are augmented and the augmented predicted state information is corrected using range-ratio and bearing observations, i.e. RF source features, considering the unknown transmitted power. The proposed approach is simulated and the results show that the normal divergence of a target localization and the divergence of the UAV navigation in latitude and longitude channels have been eliminated using this approach. In other words, simultaneous localization of the UAV and RF sources uses the RF sources, as features in the environment, to aid the navigation system. Although the approach is similar to the mapping of RF sources in the environment, the created map would be useless after finding the RF sources. That is why SLUS has been used instead of SLAM. The main contributions of this work are: 1) performing simultaneous localization of a UAV and targets using RF signals, especially in a non-line of sight (NLOS) condition; 2) using difference of signal strength, i.e. differential received strength signal indicator (DRSSI), to eliminate the impact of unknown target signal power; and 3) simultaneous multi-target localization and tracking.

Hybrid radio frequency (RF)/free space optical (FSO) systems are among the candidate enabling technologies for the next generation of wireless networks since they benefit from the advantages of both the FSO subsystem, e.g. high data rates, and the RF subsystem, e.g. high reliability in terms of link connectivity. In this paper, we focus on the problem of throughput maximization in the parallel hybrid RF/FSO relay channel. In the parallel hybrid RF/FSO relay channel, a source node sends its data to a destination node with the help of multiple relay nodes. Thereby, the source-relay and the relay-destination FSO links are orthogonal with respect to each other due to the narrow beam employed for FSO transmission whereas the RF links are half duplex with respect to each other due to the broadcast nature of RF signals. We derive the optimal relay selection policies for transmission and reception for the RF and FSO links and the optimal time allocation policy to the RF relay reception and transmission links. Simulation results demonstrate that a considerable gain can be achieved by the proposed adaptive protocol in comparison with benchmark schemes from the literature.

Free-space optical (FSO) communication offers advantages such as high bandwidth and high transmission rates, making it suitable for 6G backhaul networks. However, FSO systems have drawbacks like sensitivity to fog, atmospheric turbulence, and pointing errors. Radio frequency (RF) links are incorporated to achieve more reliable and wider-range communication. RF links are susceptible to rain and have limited bandwidth but are not sensitive to fog or atmospheric turbulence. The complementary characteristics of RF and FSO systems make hybrid RF-FSO systems highly effective in mitigating environmental impairments. Reconfigurable intelligent surfaces (RISs) can also further extend the coverage and enhance the system bit error rate (BER) performance of RF-FSO. The state-of-the-art link selection schemes in RIS-assisted hybrid RF-FSO are normally based on channel state information (CSI). However, there is a chance that the CSI is inaccurate or even unavailable to the receiver. This paper investigates a hybrid RF-FSO communication system where CSI is unknown. In our system, the RF link is modeled using the Nakagami-m distribution, and the FSO link accounts for attenuation, Gamma-Gamma distributed turbulence, and pointing errors. The key concept of our system is the adoption of index modulation (IM) for link switching so that CSI is not needed at both transmitter and receiver, and we call it RIS-IM. Exact closed-form expressions for the signal-to-noise ratio (SNR) of the RIS-RF and RIS-FSO links are derived using multivariate Fox’s H-function without using central limit theorem, including the probability density function (PDF) and cumulative distribution function (CDF). We derive the closed-form expressions for the average BER (ABER) for RIS-IM using the SNR statistics. Furthermore, numerical analyses of RIS-IM are conducted. The numerical results of RIS-IM are given comparing with pure-IM, RIS-FSO, and hard switching as benchmarks. Mont-Carlo simulation results demonstrate the superiority of RIS-IM in terms of ABER. In the future, more analysis including outage probability (OP) and ergodic capacity (EC) await further explorations.

This chapter first introduces the fundamental elements of the communications satellite Radio Frequency (RF) or free space link. It then introduces basic transmission parameters, such as antenna gain, beamwidth, free‐space path loss, and the basic link power equation. In this chapter, the authors develop procedures to determine the equivalent noise temperature for specific elements of interest in the communications circuit. The chapter discusses three types of devices, including active devices, passive devices, and the receiver antenna system. The chapter deals with a description of a) parameters of interest describing the desired signal power levels on the satellite communications RF link, and, b) parameters of interest describing the noise power levels on the link. It brings together these concepts to define overall RF link performance in the presence of system noise. These results will be essential for defining satellite system design and link performance for a wide range of applications and implementations.

Modern observation systems can be composed by heterogeneous entities (e.g., buoys, USVs, UAVs, on-shore sensors, etc.) that rely on dependable communications for coordination and data collection, often provided by over-water radio-frequency (RF) links. In tide-affected water bodies, RF links at a fixed height from the shore can experience the so-called tidal fading, a cyclic time-varying tide-induced interference. To mitigate it, the classical space-diversity reception technique (i.e., the use of two or more receiver antennas positioned at different heights) is often applied, commonly combined with the consideration of having one of the antennas at the largest possible height. Yet, this approach does not always ensure the best performance. In this work, we focus on static over-water links of short-to-medium-range distances that use antennas installed at a few meters above surface. We leverage the geometrical basis of the two-ray propagation model to investigate the optimal single-antenna height design that minimizes overall average path losses over a given tidal range. We then extend this analysis to incorporate a second receiver antenna and identify its optimal antenna height. Analytical results show that our method considerably outperforms the more classical approach, thus enabling superior (average) link capacities.

In this paper, the physical layer security (PLS) analysis for a decode-and-forward (DF) protocol based multi-hop hybrid radio frequency (RF)/ free space optics (FSO) is presented. Herein, two different scenarios are considered for detecting the secured information at the destination. In the first scenario, at each hop, the received signals with higher secrecy capacity are selected. However, in the second scenario, the RF and FSO signals are simply decoded and forwarded to the next hop and selection is done at the last hop only. Each node in the system is connected to its subsequent node through parallel RF and FSO links. The FSO links and RF links are characterized by Málaga ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {M}$</tex-math></inline-formula> ) and Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> composite distributions respectively. For both scenarios, the secrecy outage probability (SOP), strictly positive secrecy capacity (SPSC), intercept probability (IP), and effective secrecy throughput (EST) are obtained as performance metrics. These performance metrics are obtained by considering pointing error, different optical signal detection methods, turbulence effect, and the RF link fading parameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> ). Using the results, the security and reliability trade-off analysis is discussed for two scenarios. In addition, the asymptotic results are also obtained to study the system in depth. Further, the secrecy diversity order (SDO) and secrecy coding gain (SCG) are obtained to analyse the system in depth. Finally, Monte-Carlo Simulation is performed to verify the obtained results. The results manifest that the scenario with selection at each hop provides better secrecy performance than the scenario with selection at the last hop.

On the maximal-ratio combining of FSO and RF links over generalized distributions and its applications in hybrid FSO/RF systems

Due to its low implementation cost, the combination of the Received Signal Strength (RSS) with the Angle of Arrival (AOA) measurements is one of the solutions for Radio Frequency (RF) source localization, especially in a Non-Line of Sight (NLOS) environment. It is critical to determine the search space for a person who is lost in rural areas where the mobile network is unavailable due to a lack of Base Tower Stations (BTS) in order to reduce search time. In this paper, we introduce a new beacon-based approach for RF source localization, where the RF signal is received in NLOS after 1-bounce reflection, by combining the information coming from both the RSS-AOA sensors and the beacons, which are used as helpers- that move along a determined path. The proposed approach relies on determining the reflector’s pose first, after which the RF source is localized. The work has been verified in simulation and the Root Mean Square Error (RMSE) is used as a performance metric for RF source localization. Results show that our proposed approach has the lowest RMSE among localization methods mentioned in the literature under the same conditions.&#x0D; HIGHLIGHTS&#x0D; &#x0D; A new beacon-based approach for RF source localization in Non-Line Of Sight (NLOS) condition&#x0D; A reflector’s pose is determined based on the signal received from beacons&#x0D; The reflector’s pose is used to determine the location of the RF source&#x0D; One bounce reflection is considered since the chance of receiving RF signal with more reflections is very low&#x0D; &#x0D; GRAPHICAL ABSTRACT

The ion cyclotron radio frequency (RF) source for the ITER tokamak will employ two amplifier chains combined at the end stage using a wideband quadrature hybrid combiner. The combiner response has been simulated for the matched &amp; mismatched load condition (3MW/VSWR 1.5/ all reflection phases) of the RF source. The fabricated prototype combiner has been validated for the RF performance in combiner mode up to ~5 kW level and up to 1.5 MW in power splitter mode. This work discusses the study performed to validate the voltage handling capability of the prototype combiner, which, further provided inputs to improve the combiner design for the RF source operating conditions. The voltage handling test setup for the combiner was prepared by shorting two diagonally opposite ports through variable short circuit coaxial stubs. The RF simulations of the test setup provided a return loss better than -26dB at 60MHz with peak voltage ~18 kV (E-field 2.26 kV/mm) near the target voltage probes with the input power of 1.7MW. During the high-power test, the input power was increased up to 2.26 MW which provided a measured voltage level up to ~21.4 kV where the voltage breakdown occurred inside the combiner. Investigation through simulation suggested an E-field level of 2.61 kV/mm for the given breakdown condition. Finally, based on these experimental findings, the design of the combiner was updated to limit the E-field level below 1.45 kV/mm for the load power of 3MW at VSWR 1.5 thus providing a two-fold margin from the breakdown limit.

Patients who are suffering from conductive hearing loss and single sided deafness cannot sometimes be rehabilitated by conventional air conduction hearing aids. Today, percutaneous Bone Anchored Hearing Aid (BAHA) is an important alternative for such patients. BAHA uses a titanium implant which penetrates the skin and can cause skin infection, skin redness and requires life-long commitment of care every day. A novel Bone Conduction Implant (BCI) is designed as an alternative to the percutaneous BAHA, because it leaves the skin intact. It comprises an external audio processor and an implanted unit called the BCI Bone Bridge. Sound is transmitted to the implant via an inductive radio frequency (RF) link through the intact skin using amplitude modulation. This paper presents an analog RF data and power link design as a first implementation for the BCI. The RF link is designed to operate in critical coupling to transmit maximum power to the implant. Maximum Power Output of the BCI was measured at 2 mm skin thickness and was found to be 105 dB relative to 1 µN at the transducer resonance frequency. This output force is fairly robust in 2 mm to 6 mm skin thickness range.

A three-hop long range communication system with mixed fading for smart grid (SG) wide area network (WAN) is proposed. The three hops proposed here are power line communication (PLC), radio frequency (RF) and free space optical (FSO) in cascade. The smart meter (SM) transfers the data to the access point (AP) through a PLC link. The AP is acting as a decode-and-forward (DF) relay. It retransmits the data to data aggregator unit (DAU) through RF link. The DAU also acts as a DF relay and retransmits the information to meter data management system (MDMS) through FSO link. The PLC, RF, and FSO links are distributed with Log-Normal, Nakagami-m, and Gamma-Gamma distribution, respectively. The modulation scheme considered here is binary phase shift keying (BPSK). A closed form expression for average bit error probability (ABEP) is obtained. Numerical and Monte-Carlo simulation results demonstrate the effect of impulsive noise scenario in the PLC channel, fading severity in Nakagami-m channel, and different FSO parameters in SG communication system.

The expression ‘linear accelerator technology’ usually addresses all technological topics related to linear accelerators’ (linac) realization. These topics comprise, for instance, accelerating structures, Radio Frequency (RF) sources, magnets, diagnostics systems, controllers, power supplies, vacuum systems, particle sources, etc. Obviously, the extent of all these subjects is too wide to be covered in a single one-hour lecture and, therefore, this paper will only present an verview of the RF structures (including their fabrication technology) with a few examples of particle sources, RF sources and waveguide components. Moreover, the focus will be on linac technology for Free-Electron Lasers (FELs) and Energy Recovery Lasers (ERLs), which are electron accelerators. Electrons, in fact, even at very low energies (a few MeV) travel very close to the speed of light, and this fact has a direct consequence in the accelerating structures design, since they can be identical all along the linac.

This paper presents a new approach to estimate the location and height of the obstacle located between two unmanned aerial vehicles (UAVs) using Received Signal Strength Indication (RSSI) observations. The goal of developing this approach is to improve the localization of a radio frequency (RF) source by estimating the effect of obstacles on the signal attenuation. The effect of an obstacle on signal strength attenuation is the most important source of error in distance estimation based on general or empirical path loss model. Therefore, mapping the primary obstacle, which has the greatest effect on the signal attenuation, can improve the distance estimation. The main idea of the proposed approach is in the distinction between the effects of obstacle(s) on the signal attenuation, i.e. the diffraction loss, and the path loss. The proposed approach uses a model of diffraction loss to estimate the height and position of the primary knife-edge obstacle. The observations include the diffraction losses which are collected on the UAV's paths. Due to the Gaussian distribution of the diffraction loss observations and nonlinearity of the observation function, extended Kalman filter (EKF), unscented Kalman filter (UKF), and particle filter are implemented and compared with each other. The results of the simulations show that the proposed approach is able to map an obstacle between two RF sources. Furthermore, the detected and estimated obstacle can be used for better RF source localization.

Device-Free Localization (DFL) based on the Radio Frequency (RF) is an emerging wireless sensing technology to perceive the position information of the target. To realize the real-time DFL with lower power, Back-projection Radio Tomographic Imaging (BRTI) has been used as a lightweight method to achieve the goal. However, the multipath noise in the RF sensing network may interfere with the measurement and the BRTI reconstruction performance. To resist the multipath interference in the observed data, it is necessary to recognize the informative RF link measurements that are truly affected by the target appearance. However, the existing methods based on the RF link state analysis are limited by the complex distribution of the RF link state and the high time complexity. In this paper, to enhance the performance of RF link state analysis, the RF link state analysis is transformed into a decomposition problem of the RF link state matrix, and an efficient RF link recognition method based on the low-rank and sparse decomposition is proposed to sense the spatiotemporal variation of the RF link state and accurately figure out the target-affected RF links. From the experimental results, the RF links recognized by the proposed method effectively reflect the target-induced RSS measurement variation with less time. Besides, the proposed method by recognizing the informative measurement is helpful to improve the accuracy of BRTI and enhance the efficiency in actual DFL applications.

With the advent of the new decade, unmanned aerial vehicles (UAVs) will increasingly play an active role mainly as broadband transmission relays for broadcast applications. In the present study, we consider a feasible network where a transmitter, mounted on a hill, is connected through an optical wireless link with a UAV, hovering at a certain height above the earth. The UAV provides coverage over a circular geographic area and communicates through a radio frequency (RF) link with a ground user who is randomly located inside the circular region. In this context, a mixed optical/RF link is established where the performance is thoroughly investigated in terms of the outage probability. We assume that the optical wireless link is affected by a plethora of deteriorating factors, including the presence of fog, or the atmospheric scintillation, while the RF link is subject to small‐scale fading. Depending on the appearance of fog or turbulence, two different problems occur with a different mathematical formulation. For both cases, we extract closed‐form expressions for the signal‐to‐noise ratio statistics, which are the critical component towards determining the outage probability. Then, the impact of the impairments for some typical parameter values is properly depicted in appropriate graphs.