The variability in estimating the noise variance can considerably diminish the effectiveness of the energy detection (ED). This study analyzes the performance of a newly introduced goodness-of-fit test called the modified Anderson-Darling (MAD) test, which shows improved statistical power when noise uncertainty is present. We derive and empirically validate the analytical formulations for the theoretical performance of the MAD regarding false alarm and detection probabilities. Additionally, we compare our developed method with existing techniques to assess its performance, including ED, generalized ED (GED), and a two-sample likelihood ratio statistic test. The MAD surpasses the investigated methods without the need for prior knowledge of a particular set of noise samples. Our findings indicate that the proposed spectrum sensing technique also results in reduced computational complexity. Moreover, we propose the idea of spectrum sensing based on channel bandwidth rather than detecting by frequency bin, which is more appropriate for enhancing the efficiency of tactical radio band detection in tactical radio communications.

This article proposes a nonlinear known-interference (KI) cancellation algorithm that allows a receiver to suppress the interference from a high-power cooperative jammer given that the transmitted interference is known in advance to the receiver. The proposed algorithm achieves this by estimating and compensating for the nonlinear power amplifier distortions, wireless channel effects, and frequency offsets that alter the transmitted interference as it propagates to the receiver. Measurements with commercial off-the-shelf radio platforms in both laboratory and outdoor conditions are presented. Their results demonstrate that the proposed method is able to cancel KI with moderate residuals for a wide range of received signal-to-interference-plus-noise ratio. This facilitates processing a signal of interest that is otherwise masked by the interference signal.

In this article, we study the advantages and disadvantages that full-duplex (FD) radio technology brings to remote-controlled drone and counter-drone systems in comparison to classical half-duplex (HD) radio technology. We consider especially the physical-layer reliability perspective that has not yet been comprehensively studied. For establishing a solid analytical background, we first derive original closed-form expressions to evaluate demodulation and detection performance of frequency-hopped and frequency-shift keyed drone remote control signals under external or self-inflicted interference. The developed analytical tools are verified by comparison to simulated results and then used to study the impact that the operation mode has on the operable area of drones and effectiveness of counter-drone systems in different scenarios, linking the physical layer performance to practical safety. Analysis of the scenarios shows that FD operation compared to HD can improve the effectiveness of a counter-drone system and that in FD mode a drone can detect the attacks from the counter-drone system from a greater distance than in HD mode. However, two-way communication between the remote controller and drone in FD mode compared to HD significantly reduces the drone’s operable area when targeted by a smart counter-drone system.

The electromagnetic spectrum’s scarcity, the tactical edge’s dynamic nature, and the variety of tactical operations impose challenges to military cognitive radio networks. Multi-radio dynamic spectrum management (DSM) and routing promise to increase the spectral efficiency and robustness of tactical ad hoc networks by adding key control plane tools that adapt the network to the varying harsh tactical environments. This paper describes a novel concept where implicit spectrum sensing, a distributed DSM architecture with ontology-based spectrum access policies, modified routing and network time synchronization capabilities interplay to address those challenges. The simulation results verify the designed functionality in harsh electromagnetic environments in a multitude of scenario sizes, in terms of number of radio terminals and number of networks. In particular, the simulation of a large operational scenario shows solid scaling capabilities and that ongoing jamming in several networks are efficiently mitigated and low-loss performance are re-established.

Secure and reliable communications are vital to defense forces in achieving operational goals. Likewise, limiting the opponents’ capabilities to communicate further advances the host forces’ chances of operational success. In this work, we propose a method to fortify the host forces’ wireless communications against adversarial attacks while at the same time restricting the opponents’ capabilities to wirelessly communicate. That is, we propose a band-limited known-interference cancellation (KIC) method that enables the host forces to cover a large portion of the electromagnetic spectrum with wideband jamming, yet lets the host force communication nodes cancel that jamming signal upon reception even if the nodes only receive a narrowband portion of it. We study how the proposed KIC method works based on measurements with commercial off-the-shelf software-defined radios. The results demonstrate that the band-limited KIC method achieves performance that is comparable to non-band-limited methods and, in doing so, leads the way for practical applications of cooperative jamming in scenarios where narrowband communication links span over a wide bandwidth.

Secure and reliable tactical communications within allied defense forces across a battlefield are often fundamental for achieving the forces' operational targets against an adversary. Likewise, limiting the adversary's capability to communicate securely and reliably promotes the host forces' chances for operational success. As such, armed conflicts typically involve an underlying battle in the electromagnetic (EM) spectrum to facilitate one's own communications and limit the opposition's. In this work, we propose the use of distributed cooperative jamming for augmenting tactical communications and gaining a technological advantage in that underlying battle. Specifically, we propose a multi-reference known-interference cancellation (KIC) method that allows the host force tactical communication nodes to cancel known interference (KI) from multiple cooperative jammers simultaneously. Relying on simulations, we then study how cooperative jamming affects the opposing forces' capabilities to use the EM spectrum in a simplified battlefield. Results show that cooperative jamming gives an advantage to those controlling the jammers, as the opposition's use of the EM spectrum is obstructed for both communications and signals intelligence.

In scenarios where Relay Nodes (RNs) need to be deployed to restore the connectivity of a partitioned wireless network, a positioning method limiting the number of RNs required is necessary. Optimally, the method must take into account the differences of transmission ranges between the different nodes - or the heterogeneity in range of the network. In particular, Unmanned Aerial Vehicles (UAVs) are considered to be great candidates as RNs with their high mobility and ability to be quickly deployed. However, their radio parameters will be different from the Initial Nodes (INs) of the network and there will be a diversity in propagation channel. Plus, even the network might be heterogeneous. With a mobile initial network, the placement method also have to be stable in terms of RN positions and number with respect to IN displacements. This paper introduces an approach to modify an effective RN placement algorithm for homogeneous networks to create a new algorithm capable of managing heterogeneity in the networks. The new algorithm is the Barycenter-focused Relay Positioning for Heterogeneous Wireless Networks (BRHEN) algorithm. In addition to lower the number of RNs compared to the initial algorithm, it also enhances its stability with respect to small IN displacements.

Physical layer security is a sought-after concept to complement the established upper layer security techniques in wireless communications. An appealing approach to achieve physical layer security is to use cooperative jamming with interference that is known to and suppressible by the legitimate receiver but unknown to, and hence not suppressible by, the eavesdropper. Suppressing known interference (KI), however, is challenging due to the numerous unknowns, including carrier and sampling frequency offsets, that impact its reception. This letter presents a measurement campaign that captures this challenge and then demonstrates the feasibility of solving that challenge by cancelling the KI using the frequency offsets least mean squares (FO-LMS) algorithm. Results show that KI suppression directly improves processing the signal-of-interest and that cooperative jamming effectively provides security at the physical layer.

This paper provides insights into the ongoing research work of NATO IST-175-RTG that aims to demonstrate the benefits of full-duplex radios in military applications. Full-duplex radios in general allow to simultaneously transmit and receive RF signals in the same frequency band but require solving technical challenges that are not present in conventional half-duplex systems. Mainly this means suppressing the self-interference which is caused by the transmitted signal reaching the receiver path. This can result because of, e.g., circulator leakage, antenna mismatch, or reflections from the environment. Several techniques, both digital and analog, have been proposed in literature to cope with such strong interference in the receiver path after the point from which the interference has reached there. However, an additional challenge can arise in transceivers with improper internal isolation such as, e.g., low-cost software-defined radios, where the leaking, or crosstalk, takes place inside the radio. In such cases, the analog cancellation cannot be positioned after the leakage point but must be implemented pre-emptively. This paper quantifies the crosstalk for one such commercial-off-the-self transceiver plus presents and compares solutions for managing both, the crosstalk, and the self-interference either separately or jointly. This paper was originally presented at the NATO Science and Technology Organization Symposium (ICMCIS) organized by the Information Systems Technology (IST) Panel, IST-200 RSY — the ICMCIS, held in Skopje, North Macedonia, 16–17 May 2023.

This article addresses the challenge of estimating and tracking wireless channels under carrier and sampling frequency offsets, which also incorporate phase noise and sampling time jitter. We propose a novel adaptive filter that explicitly estimates the channel impulse response, carrier frequency offset, and sampling frequency offset by minimizing the mean-square error (MSE) and, when the estimated parameters are time-varying, inherently performs tracking. The proposed filter does not have any requirements for the structure of the waveform, but the digital transmitted waveform must be known to the receiver in advance. To aid practical implementation, we derive upper bounds for the filter's step sizes. We also derive expressions for the filter's steady-state MSE performance, by extending the well-known energy conservation relation method to account for the self-induced nonstationarity and coupling of update equations that are inherent in the proposed filter. Theoretical findings are verified by comparison to simulated results. Proof-of-concept measurement results are also provided, which demonstrate that the proposed filter is able to estimate and track a practical wireless channel under carrier and sampling frequency offsets.

HF remains an essential military operational technology for BLOS communications when SATCOM is not available. 2G and 3G HF standards have been developped for 3 kHz narrowband channels. The latest wideband 4G HF standards enable higher data rates by increasing the bandwidth available for transmission. The two main solutions aggregate either contiguous or non-contiguous 3 kHz narrowband channels up to 24/48 kHz. This paper describes a low complexity generic receiver with channel estimation, time and frequency synchronization for 2G, 3G, 4G and HF-XL standards and a performance evaluation in terms of BER or PDR vs SNR on narrowband and wideband HF channel models. The narrowband and wideband HF standards have been implemented on a GPP-based SDR platform with open-source libraries and run in real-time. This paper was originally presented at the NATO Science and Technology Organization Symposium (ICMCIS) organized by the Information Systems Technology (IST) Panel, IST-200RSY — the ICMCIS, held in Skopje, North Macedonia, 16–17 May 2023.

Military radio, EW and RF sensor systems operate in a congested and contested electromagnetic environment. The NATO Science and Technology Organization established the Research Task Group 069 in order to take charge of the IST-146 project on Electromagnetic Environment Situational Awareness. The project was aimed at evaluating the operational benefits for NATO in line with the Electromagnetic Spectrum Strategy and at evaluating the Radio Environmental Map (REM) technology. The paper describes the military scenario considered for the study. Its operational analysis establishes the importance of Electromagnetic Spectrum Command and Control integrated with other C2 processes. The description of the data sources, models, and representation is done. Key user benefits are highlighted. Then proposals for possible evolution of electromagnetic operations and spectrum management within NATO are made. The paper further describes the proposed reference architecture based on the Internet of Things (IoT). It establishes how the relationships between the REM elements have been validated through the project scenario. Tests and simulations, carried out for the construction of measurement-based REMs and transmitter localization, are presented. The paper finally describes the proposed demonstration, which enables understanding through visualization of an interference situation and de-confliction by dynamically re-assigning frequencies.

Electromagnetic spectrum is a scarce resource becoming increasingly congested as information technologies advance. This is particularly concerning in the military domain, where frequencies are contested for by both CIS and EW systems. The success of NATO activities necessitates mission-critical communications with increasing throughput, hidden from enemy signals intelligence, robust against electronic attacks, and compatible with host EW tasks. In response, the NATO STO IST-175 research task group is working on the disruptive concept of FD radio technology to address those challenges. Military FD radios promise to increase the spectral efficiency and robustness of CIS and improve the performance of EW tasks through simultaneous operation and multifunctionality.

This paper summarizes the results of the NATO STO IST Panel’s Exploratory Team IST-ET-101. The team studied the full-duplex radio technology as an innovative solution to deal with the scarce and congested electromagnetic frequency spectrum, especially in the VHF and UHF bands. This scarcity is in strong contrast to the growing bandwidth requirements generally and particularly in the military domain. The success of future NATO operations relies more than ever on new real-time services going hand in hand with increased data throughputs as well as with robustness against and compatibility with electronic warfare. Therefore, future tactical communication and electronic warfare technologies must aim at exploiting the spectral resources to the maximum while at the same time providing NATO with an advantage in the tactical environment.

This paper deals with the jamming attack which may hinder the cognitive radio from efficiently exploiting the spectrum. We model the problem of channel selection as a Markov decision process. We propose a real-time reinforcement learning algorithm based on Q-learning to pro-actively avoid jammed channels. The proposed algorithm is based on wideband spectrum sensing and a greedy policy to learn an efficient real-time strategy. The learning approach is enhanced through cooperation with the receiving CR node based on its sensing results. The algorithm is evaluated through simulations and real measurements with software defined radio equipment. Both simulations and radio measurements reveal that the presented solution achieves a higher packet success rate compared to the classical fixed channel selection and best channel selection without learning. Results are given for various scenarios and diverse jamming strategies.

Since the jamming attack is one of the most severe threats in cognitive radio networks, we study how Q-learning can be used to pro-actively avoid jammed channels. However, Q-learning needs a long training period to learn the behaviour of the jammer. We take advantage of wideband spectrum sensing to speed up the learning process and we take advantage of the already learned information to minimise the number of collisions with the jammer. The learned anti-jamming strategy depends on the elected reward strategy which reflects the preferences of the cognitive radio. We start with a reward strategy based on the avoidance of the jammed channels, then we propose an amelioration to minimise the number of frequency switches The effectiveness of our proposal is evaluated in the presence of different jamming strategies and compared to the original Q-learning algorithm. We compare also the anti-jamming strategies related to the two proposed reward strategies.

The problem of jammer localization is an important problem in a tactical context. This paper describes a method for multiple jammer localization and transmission power estimation using only received signal strength (RSS) from spectrum sensing devices for radio environment map (REM). This method is able to localize multiple jammers and to estimate their transmission powers in the presence of known transmitters. Simulations show the efficiency of the method compared to existing methods in the literature such as inverse distance weighting (IDW), kriging, or LiveREM.

In cognitive radio, spectrum sensing is one of the most important tasks. In this article, a blind spectrum sensing method based on goodness-of-fit (GoF) test using likelihood ratio (LLR) is studied. In the proposed method, a chi-square distribution is used for GoF testing. The performance of the method is evaluated through Monte Carlo simulations. It is shown that the proposed spectrum sensing method outperforms the GoF test using Anderson Darling (AD) and the conventional energy detection (ED) in case of a limited number of received samples and low signal to noise ratio (SNR). We also evaluate the proposed method in case of a non-Gaussian noise and in case of noise uncertainty. It is shown that the GoF based spectrum sensing methods are less sensitive to both impairments, than the conventional ED. Finally, this paper investigates the influence of the number of samples on the detection performance. The performance difference between the GoF based sensing (LLR and AD) and ED increases with decreasing number of samples for sensing, which makes the proposed method very effective in CR systems with short sensing periods. Keywords—Cognitive Radio; Spectrum Sensing; Goodness of Fit test; Likelihood Ratio; Mixture Gaussian Noise.

Cognitive Radios are able to dynamically use free spectrum in their vicinity, avoiding interference and congestion and thus providing robust communication links. Cognitive Radio Networks go one step further, as they do not only consider the link to the next node but focus on end-to-end optimization. Dynamic adaptations of the whole protocol stack are required, especially on the network layer. This paper analyzes networking technologies regarding their support for end-to-end optimization in tactical environments and proposes enhancements. Based on the findings, an architecture framework for Cognitive Radio Networks is proposed.

In the absence of real-life implementations, this paper attempts to conceptually capture potential benefits and improvements that Cognitive Radio Networks (CRN) could introduce to a military environment. Functional business capability areas, as well as a system model, are used to frame analysis. Military CRNs improve reliability and availability of information flows. These may lead to improved information sharing and situation awareness and eventually to wider adoption of mission command and self-synchronization. However, fundamental capacity benefits of the CRNs remain a research topic. The requirement of computer-aided planning, preparation and simulation environment in support of deployed CRNs could also serve as a research and development platform for a Cognitive Radio System development activity as a collaborative international effort.