Swarmalators, entities that combine the properties of swarming particles with synchronized oscillations, represent a novel and growing area of research in the study of collective behavior. This review provides a comprehensive overview of the current state of swarmalator research, focusing on the interplay between spatial organization and temporal synchronization. After a brief introduction to synchronization and swarming as separate phenomena, we discuss the various mathematical models that have been developed to describe swarmalator systems, highlighting the key parameters that govern their dynamics. The review also discusses the emergence of complex patterns, such as clustering, phase waves, and synchronized states, and how these patterns are influenced by factors such as interaction range, coupling strength, and frequency distribution. Recently, some minimal models were proposed that are solvable and mimic real-world phenomena. The effect of predators in the swarmalator dynamics is also discussed. Finally, we explore potential applications in fields ranging from robotics to biological systems, where understanding the dual nature of swarming and synchronization could lead to innovative solutions. By synthesizing recent advances and identifying open challenges, this review aims to provide a foundation for future research in this interdisciplinary field.

This paper studies the suitability of 5G links for command and control of drones. Using system-level simulations, we evaluate link availability, latency, and block error rate in an urban scenario with drones flying above ground users. The results show that the requirements set by aviation safety authorities for beyond-visual-line-of-sight operations are only partially satisfied: link availability is adequate for basic operations but insufficient for demanding ones such as control-over-camera missions, latency meets most needs but remains too high for direct stick control, and the block error rate is generally too high. These findings suggest that network configurations tailored to aviation safety requirements are needed.

Implementing swarmalator behavior on mobile robots requires discretizing calculations and interactions. This is accomplished through numerical methods for differential equations, which involve selecting a step size for the density of supporting points. Large steps prevent convergence; small ones increase computational effort and interaction rate. We discuss how to choose an appropriate step size by deriving bounds for divergence, oscillatory behavior, and monotonic convergence, particularly for circular patterns. Our main result is a bound that ensures non-oscillatory convergence, enabling researchers to perform real-world system parameterization.

We analyze spatial patterns emerging in self-organized systems of swarmalators, focusing on constellations where all entities arrange in a sorted manner along one or more concentric circles. Key properties of these patterns are explored by computing their radii and examining stability criteria based on the number of entities and a coupling parameter. The findings can be applied to swarm robotics and other collective motion systems.

Coupled oscillator systems can lead to states in which synchrony and chaos coexist. These states are called "chimera states." The mechanism that explains the occurrence of chimera states is not well understood, especially in pulse-coupled oscillators. We study a variation of a pulse-coupled oscillator model that has been shown to produce chimera states, demonstrate that it reproduces several of the expected chimera properties, like the formation of multiple heads and the ability to control the natural drift that Kuramoto's chimera states experience in a ring, and explain how chimera states emerge. Our contribution is defining the model, analyzing the mechanism leading to chimera states, and comparing it with examples from the field of Kuramoto oscillators.

For randomly distributed nodes sending packets to a central gateway using slotted Aloha with a constrained number of retransmissions over a wireless fading channel, we take an iterative approach to compute the total traffic density of packet transmissions and collision-induced retransmissions as a function of the node-gateway distance. From this, we compute the outage probability, throughput, and energy consumption. This method can be used to analyze and dimension Low-Power Wide-Area Networks (LPWANs). Applying it in LoRa illustrates design tradeoffs concerning outage probability, spreading factors, energy consumption, and cell size. It notably shows that permitting more retransmissions helps the nodes near the gateway but hurts distant ones.

Swarm algorithms promise to solve certain problems in large multi-robot systems. The evaluation of large swarms is however challenging as simulations alone often lack some properties of real systems whereas real-world experiments are costly and complex. We present a mixed reality (MR) system that connects simulated and physical robots though a 5G network, facilitating MR experiments to evaluate communication-based swarm algorithms. The effectiveness of the system is demonstrated through extensive experiments with unmanned aerial vehicles. Measurements show that the communication requirements of swarm coordination are well met by 5G but the computing power of the simulation server can be a bottleneck. However, even when the simulation slows down, communication and coordination take place in real time. In conclusion, 5G-enabled MR experiments are a feasible tool for bridging the reality gap in the development and evaluation of robot swarms.

For a system of swarmalators converging to different types of circular patterns, we provide expressions for the outer and inner radii of these patterns and examine their dependence on the model parameters. Derivations are made for three static patterns with an infinite number of entities and a generalized swarmalator model with parameterized attraction and repulsion kernels. Simulations of finite systems show good agreement with the asymptotic expressions.

The temporal dynamics of interference in wireless networks affects their performance but has only been studied for some cases. This article addresses this gap by analyzing high-interference events, called pikes, concluding that they arrive in bursts in many cases. Specifically, we show that in Poisson networks with random access and multipath fading, the pike interarrival time increases with the interference correlation, irrespective of the source of correlation and burstiness of pikes. To demonstrate the applicability of this theory, we conduct a measurement campaign with an automotive user in different commercial 4G cellular networks. The experimental results indicate that interference pikes are bursty in the real world as well.

The concept of pulse-coupled oscillators for self-organized synchronization has been applied to wireless systems. Putting theory into practice, however, faces certain obstacles, particularly in radio technologies that cannot implement pulses but use common messages for interactions between nodes. This raises the question of how to deal with interference between messages. We show that interference can disturb the synchronization process and propose low-complex, randomization-based techniques to address this issue. First, we demonstrate that randomly switching between two transmit power levels (without increasing the average power) can expedite synchronization. The high-power transmissions temporarily boost network connectivity with negligible impact on the average interference. Second, we reduce interference by blindly distributing the messages over the entire oscillator cycle. Instead of using a fixed oscillator phase at which the pulses are sent, each node chooses its own, randomly selected phase to send a synchronization message. This node-specific “fire phase” is contained in the message to permit others to compute the timing. Third, we suggest that such interference management can also be beneficial for other synchronization techniques and validate this claim using Glossy as an example. Our insights may contribute to feasible solutions for self-organized wireless synchronization. Further work is needed to gain a comprehensive understanding of the effects of randomization and to develop algorithms for the adaptability of local parameters.

We propose a radio-based approach for height classification of mobile devices in cellular networks for the purpose of enabling the network infrastructure to distinguish between ground users and aerial devices like drones. The classifier is based on learning the properties of the reference signal received power (RSRP) values that each device obtains from base stations. Scenario-based simulations using the Vienna 5G System Level Simulator with adopted base station antenna patterns demonstrate the feasibility of decision tree classifiers with an average misclassification rate at about one percent with three height levels. It is shown that decision trees outperform other classification algorithms in this context.

The IEEE International Conference on Autonomic Computing and Self-Organizing Systems (ACSOS) is a reference venue for scientists and practitioners whose research interests focus on self-organization, autonomic computing, resilience, decentralized behavior, and self-adaptation. ACSOS is the merger of two well-established IEEE conferences: the International Conference on Autonomic Computing (ICAC), which counted 16 editions before the merge, and the International Conference on Self-adaptive and Self-Organising Systems (SASO), which had 13 editions. It provides a forum to share and present their experiences, discuss challenges, and report state-of-theart research in all areas related to autonomic computing, self-adaptation, and self-organization. ACSOS unified the two communities and continued along the path traced by its successful predecessors. The 2nd IEEE International Conference on Autonomic Computing and Self-Organizing Systems (ACSOS 2021), originally planned to be held in Washington, D.C., was held online due to the COVID-19 pandemic. Nevertheless, the conference received 56 high-quality paper submissions from around the globe, of which 14 were accepted as full papers, resulting in an acceptance rate of 25%, akin to previous editions of SASO and ICAC and similar to the first edition of ACSOS. This special issue contains extended versions of the four best papers presented at ACSOS 2021, selected based on the score obtained by at least four reviewers, the quality of their presentation, and the involvement and discussion they generated during the conference.

This work studies the issue of inter-cell interference that arises when drones are integrated into cellular networks. Using the Vienna 5G System Level Simulator, augmented with a drone-specific 3GPP path loss model, we demonstrate that uplink transmissions from regular ground users may experience significant degradation of signal-to-interference ratio and achievable throughput. Transmit power control in drones could alleviate this degradation while maintaining an acceptable link quality for the drones themselves.

Not all systems of pulse-coupled oscillators converge to synchrony from any initial configuration. The probability of synchronization depends on the network topology and the phase response function. It is often assumed that all oscillators are governed by the same phase response function. We exemplify that the synchronization probability can be significantly increased by using node-individual (local) values for the phase response parameter-rather than a single, global value. This insight motivates research into algorithms for parameter adjustment in self-organized network synchronization.

HiPR+ is an approach for centimeter-accurate indoor localization. It combines distance estimation between ultra-wideband (UWB) transceivers and location estimation using an extended Kalman filter (EKF). The performance is tested with experiments on hardware platforms from Decawave. The distance estimation of HiPR+ achieves an order of magnitude better precision and a multiple improvement in accuracy compared to the company's native solution while it only takes only a fraction the time needed for range computation. We evaluate the 3D localization capabilities with two least-squares approaches and an EKF. A median accuracy below one centimeter can be attained using the proposed ranging error compensations in combination with the EKF-based~positioning.

This work investigates by real-world experiments the throughput and latency of drone-to-drone communications using different wireless technologies. Direct air-to-air links via Wi-Fi 802.11ac are compared to communication via LTE-A and 5G systems on the ground. The following can be observed: Wi-Fi provides a significantly lower drone-to-drone latency than the detour via cellular infrastructure; LTE-A and 5G provide a moderate but reliable throughput of about 50 Mbit/s; and Wi-Fi offers a better throughput only when drones are close to each other. We envision that this work will provide relevant experimental insights for the design of communication protocols in the context of multi-drone systems.

Wireless solutions for on-board communications are gaining momentum in the aerospace industry with the aim to further improve flight safety, reduce aircraft costs, and lower environmental impact. Also passenger infotainment services are increasingly realized in a wireless way and call for high-rate connectivity to the Internet. There are many issues though, including security, coexistence, and power sustainability. We argue that ultra-wideband (UWB) technology is a promising implementation path for such intra-aircaft communications. From a power sustainability perspective, UWB attains a unique trade-off between power consumption and data rate that can become a key enabler. Experimental results from a proof-of-concept deployment of off-the-shelf UWB transceivers in an Airbus A319 support our discussion and shed light on the challenges ahead.

We report on multi-month experiments of a LoRa network deployed in a chemical plant. Using measurement data of nodes distributed (i) inside a building and (ii) over multiple buildings, all sending to a gateway, we estimate the path loss and fading characteristics of the links. Although we operate the system in a harsh environment according to these measurements-with a path loss exponent up to 5.1 and Nakagami fading with m as low as 0.7-the packet loss rate is low for in-building links (2.5% on the average), demonstrating LoRa's suitability for certain industrial applications.

Now that drones have evolved from bulky platforms to agile devices, a challenge is to combine multiple drones into an integrated autonomous system, offering functionality that individual drones cannot achieve. Such multidrone systems require connectivity, communication, and coordination. We discuss these building blocks along with case studies and lessons learned.