Control And Non-payload Communication Research Articles

Communication Manager for Hyper-Connected RPAS Environments

The revolution of Remotely Piloted Aircraft Systems (RPASs), both in the commercial and the research field, has accelerated the arrival of innovative and complex services to the civilian environment within non-segregated airspace. The extensive deployment of these services will still require solving relevant challenges in several topics, such as regulation, security, or diverse technical defiance. In particular, the services to be provided increasingly demand network resources and performance improvements. This scenario will be strongly exacerbated by the upcoming resources provided by the 5G/6G architectures, where Remotely Piloted Aircrafts (RPAs) will likely support multiple communication interfaces and will be able to establish multi-hop network connectivity with numerous devices leading to an unprecedented hyper-connected RPA environment. In addition, future RPASs will have to enhance the management of their connectivity capabilities to comply with the latest regulations, which demand an uninterrupted link for the Control and Non-Payload Communications (CNPC). This article presents a flexible Communication Infrastructure Manager (CIM) based on Software-Defined Networking (SDN) and virtualization technologies capable of handling the complexity inherent to this ecosystem and being adapted to different operation requirements to cope with all these communication challenges. Finally, the article shows several validation experiences to demonstrate the potential of the CIM versus the standard approach.

Modeling Control Delays for Edge-Enabled UAVs in Cellular Networks

Real-time control solutions for unmanned aerial vehicles (UAVs) have attracted great interest in recent years. Most existing control methods use Wi-Fi technology. While Wi-Fi is inexpensive and easy to use, it has only a limited transmission range. Thus, 4G/5G cellular networks have been proposed as an alternative enabling technology. This study focuses on the problem of improving the appropriateness of the control commands sent by the ground control station (GCS) to the UAV over the control and nonpayload communication (CNPC) link of the UAV through the cellular network. To satisfy the low-latency requirement of the CNPC link, multiaccess edge computing (MEC) technology is leveraged to collocate the GCS and base station. The effectiveness of the proposed edge-based approach is demonstrated by conducting experiments on two LTE platforms with different MEC deployment methods. An edge-enabled UAV control solution is proposed in which each end-to-end control delay in the UAV-GCS system is estimated based on the preceding delay such that the location of the UAV at the moment it receives the control command from the GCS can be predicted in advance and taken into consideration by the GCS when formulating an appropriate control decision. To this end, an analytical modeling method is proposed for estimating the expected error range of each control delay based on a bimodal distribution approximation of the empirical control delays observed at the UAV. Finally, an event-driven simulator is developed to confirm the accuracy of the analytical predictions of the control delay based on the expected error between consecutive delays.

Learning to Optimize User Association and Spectrum Allocation With Partial Observation in mmWave-Enabled UAV Networks

To support large-scale unmanned aerial vehicle (UAV) networks with both payload communication (PC) packets and control and non-payload communication (CNPC) packets, millimeter wave (mmWave) communication is convinced to be a promising solution. However, efficient user association and spectrum allocation are still challenging in mmWave-enabled UAV networks considering that the network state is dynamic and the status information of each UAV is incomplete. In this paper, we investigate a joint UAV association and spectrum allocation problem under a hybrid mmWave sharing paradigm, where PC packets are transmitted over both licensed and pooled bands in a shared manner to achieve high throughput and CNPC packets are transmitted over licensed band in an exclusive manner to guarantee high reliability. To this end, we introduce a strategic form game that can characterize network stochastic states and individual partial observations to reformulate the problem, and then propose a counterfactual regret minimization scheme to achieve its correlated equilibrium (CE). Benefited from the updating mechanism on random <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">observation-action</i> pairs, the designed scheme can converge to the corresponding CE solutions for the two types of packets with partial observation. Finally, our simulation results demonstrate the superior performance of the proposed scheme over the baseline schemes.

Predictive decision and reliable accessing for UAV communication in space-air-ground integrated networks

The cooperation of multiple Unmanned Aerial Vehicles (UAVs) has become a promising scenario in Space-Air-Ground Integrated Networks (SA-GINs) recently due to their widespread applications, where wireless communication is a basic necessity and is normally categorized into control and non-payload communication (CNPC) as well as payload communication. In this paper, we attempt to tackle two challenges of UAV communication respectively on establishing reliable CNPC links against the high mobility of UAVs as well as changeable communication conditions, and on offering dynamic resource optimization for Quality-of-Service (QoS) guaranteed payload communication with variable link connectivity. Firstly, we propose the concept of air controlling center (ACC), a virtual application equipped on the infrastructure in SAGINs, which can collect global information for estimating UAV trajectory and communication channels. We then introduce the knapsack problem for modelling resource optimization of UAV communication in order to provide optimal access points for both CNPC and payload communication. Meanwhile, using the air controlling information, predictive decision algorithm and handover strategy are introduced for the reliable connection with multiple access points. Simulation results demonstrate that our proposal ensures an approximate always-on reliable accessing of communication links and outperforms the existing methods against high mobility, sparse distribution, and physical obstacles.

Time-Domain to Delay-Doppler Domain Conversion of OTFS Signals in Very High Mobility Scenarios

In Orthogonal Time Frequency Space (OTFS) modulation, information symbols are embedded in the delay-Doppler (DD) domain instead of the time-frequency (TF) domain. In order to ensure compatibility with existing OFDM systems, most prior work on OTFS receivers consider a two-step conversion, where the received time-domain (TD) signal is firstly converted to a time-frequency (TF) signal (using an OFDM demodulator) followed by post-processing of this TF signal into a DD domain signal. In this paper, we show that the spectral efficiency (SE) performance of a two-step conversion based receiver degrades in very high mobility scenarios where the Doppler shift is a significant fraction of the communication bandwidth (e.g., control and non-payload communication (CNPC) in Unmanned Aircraft Systems (UAS)). We therefore consider an alternate conversion, where the received TD signal is directly converted to the DD domain. The resulting received DD domain signal is shown to be not the same as that obtained in the two-step conversion considered in prior works. The alternate conversion does not require an OFDM demodulator and is shown to have lower complexity than the two-step conversion. Simulations reveal that even in very high mobility scenarios, the SE and symbol error rate performance of the alternate conversion is invariant of Doppler shift and is significantly better than the performance achieved with two-step conversion (which degrades with increasing Doppler shift).

Widely linear FRESH receivers for cancellation of data-like rectilinear and quasi-rectilinear interference with frequency offsets

Widely linear (WL) receivers have been developed in the past for single antenna interference cancellation (SAIC) of one rectilinear (R) or quasi-rectilinear (QR) data-like multi-user interference (MUI) or co-channel interference (CCI) in particular. The SAIC technology has been implemented in global system for mobile communications (GSM) handsets in particular and has been further analyzed for voice services over adaptive multi-user channels on one slot (VAMOS) standard. It remains of great interest for several current and future applications using R or QR signals, such as anti-collisions processing in radio frequency identification (RFID) or in satellite-AIS systems and to densify 5G and Beyond 5G (B5G) networks through one dimensional signaling or over-loaded large MU-MIMO systems. It may be required to cancel the inter-symbol interference (ISI) of control and non-payload communications (CNPC) links of unmanned aerial vehicles (UAV) and the inter-carrier interference (ICI) of filter bank multi-carrier offset quadrature amplitude modulation (FBMC-OQAM), which are now candidate for B5G mobile networks. For these challenging applications, the development of enhanced WL filtering based SAIC or Multiple Antenna Interference Cancellation (MAIC) receivers for R and QR signals may be of great interest. Such a receiver, corresponding to a three-input WL frequency shift (FRESH) receiver, has been introduced recently for QR signals. However this WL receiver is not robust to a data-like MUI having a residual frequency offset (FO), which occurs for most of the previous applications. In this context, the paper first extends, for arbitrary propagation channels, the standards (for R and QR MUI) and the enhanced (for QR MUI) SAIC/MAIC WL receivers to MUI with a non-zero FO. Then, it shows the less efficiency of the two-input WL receiver for QR MUI with a non-zero FO and the performance improvement obtained with the three-input WL receiver. Finally, it analyzes, both analytically and by simulations, for R and QR MUI, the impact of the MUI FO on the performance of the proposed receivers. The results of the paper should allow the development of new powerful WL receivers for UAV CNPC links, anti-collisions AIS systems and for FBMC-OQAM networks in particular.

Aircraft to Ground-Station C-Band Channel—Small Airport Scenario

Channel effects can severely degrade performance and reliability of a wireless communication system if they are not taken into account. An accurate characterization is indispensable for the proper design and parametrization of such data links. In this paper, the focus is on aircraft to ground station channel sounding and characterization to lay the foundation for unmanned aerial vehicle (UAV) control and non-payload communication (CNPC) link designs. After a comprehensive review of related work, an introduction into the implemented channel sounding principle with the aid of a custom-made sounder is given, followed by a detailed description of the two measurement campaigns at Ingolstadt/Manching airport, Germany. The obtained large-scale fading results are presented, including shadowing and antenna misalignment effects. Then, small-scale fading is discussed by means of K-factors, delay, and Doppler spread statistics. For all evaluations, the recorded data set has been classified to work out and compare the characteristics of typical phases of UAV operation. Implications of the presented analyses on the parametrization of CNPC links are mentioned as well.

Ultra-Reliable and Low-Latency Communications in Unmanned Aerial Vehicle Communication Systems

In this paper, we establish a framework for enabling ultra-reliable and low-latency communications in the control and non-payload communications (CNPC) links of the unmanned aerial vehicle (UAV) communication systems. We first derive the available range of the CNPC links between UAVs and a ground control station. The available range is defined as the maximal horizontal communication distance within which the round-trip delay and the overall packet loss probability can be ensured with a required probability. To exploit the macro-diversity gain of the distributed multi-antenna systems (DAS) and the array gain of the centralized multi-antenna systems (CAS), we consider a modified DAS (M-DAS), where the ground control station is equipped with the distributed access points (APs), and each AP can have multiple antennas. We then show that the available range can be maximized by judiciously optimizing the altitude of UAVs, the duration of the uplink and downlink phases, and the antenna configuration. To solve the non-convex problem, we propose an algorithm that can converge to the optimal solution in DAS and CAS, and then extend it into more general M-DAS. The simulation and numerical results validate our analysis and show that the available range of M-DAS can be significantly larger than those of the DAS and CAS.

Equalization Techniques of Control and Non-Payload Communication Links for Unmanned Aerial Vehicles

In the next years, several new applications involving unmanned aerial vehicles (UAVs) for public and commercial uses are envisaged. In such developments, since UAVs are expected to operate within the public airspace, a key issue is the design of reliable control and non-payload communication (CNPC) links connecting the ground control station to the UAV. At the physical layer, CNPC design must cope with timeand frequency-selectivity (so-called double selectivity) of the wireless channel, due to lowaltitude operation and flight dynamics of the UAV. In this paper, we consider the transmission of continuous phase modulated (CPM) signals for UAV CNPC links operating over doubly-selective channels. Leveraging on the Laurent representation for a CPM signal, we design a two-stage receiver: the first one is a linear time-varying (LTV) equalizer, synthesized under either the zero-forcing (ZF) or minimum mean-square error (MMSE) criterion; the second one recovers the transmitted symbols from the pseudo-symbols of the Laurent representation in a simple recursive manner. In addition to LTV-ZF and LTV-MMSE equalizers, their widely-linear versions are also developed, to take into account the possible noncircular features of the CPM signal. Moreover, relying on a basis expansion model of the doubly-selective channel, we derive frequencyshift versions of the proposed equalizers, by discussing their complexity issues and proposing simplified implementations. Monte Carlo numerical simulations show that the proposed receiving structures are able to satisfactorily equalize the doubly-selective channel in typical UAV scenarios.

Air–Ground Channel Characterization for Unmanned Aircraft Systems—Part III: The Suburban and Near-Urban Environments

Applications for unmanned aircraft systems (UAS), or “drones,” are increasing rapidly. In order to provide safe and reliable links to integrate UAS into the National Airspace System (NAS), control and nonpayload communication (CNPC) system requirements are being specified. A comprehensive knowledge of the air-to-ground (AG) channels in the bands of interest (C-band and L-band) plays an essential role. The NASA Glenn Research Center has sponsored an AG channel measurement campaign for most of the typical ground site (GS) local environments, including over water [8] , hilly/mountainous [9] , suburban, and near-urban. As a continuation of our prior study, this paper addresses the suburban and near-urban scenarios. Our developed AG channel models include path loss, small-scale fading Ricean K factors, spatial and interfrequency correlations for multiple aircraft antennas, root-mean-square (RMS) delay spread, and wideband tapped delay line (TDL) models. The path loss is described by either log-distance or two-ray models, with small corrections for flight direction. The K factors were 12 (14) dB in L-band and 27.4 (28.5) dB in C-band in near-urban (suburban) environments. The interband signals were uncorrelated, but the intra-band signals were highly correlated, with the median correlation coefficient greater than 0.85. The C-band RMS delay spread was on average 10 to 60 ns, with maximum of approximately 4 μs. The TDL models are composed of the line-of-sight (LOS) component, a ground reflection, and up to seven intermittent multipath components (MPCs). Relative power, phase, occurrence probability, duration, and excess delays for these intermittent MPCs are quantified. An algorithm to simulate the AG channel impulse response (CIR) via the TDL models is provided.

Air–Ground Channel Characterization for Unmanned Aircraft Systems Part II: Hilly and Mountainous Settings

The use of unmanned aircraft systems (UAS) is expanding rapidly. For safe and reliable integration of UAS into the National Airspace System (NAS), control and nonpayload communication (CNPC) system requirements are being developed. The air-to-ground (AG) channel characteristics essentially determine CNPC link performance. The National Aeronautics and Space Administration (NASA) Glenn Research Center has sponsored a comprehensive AG channel measurement campaign in 2013 in both the Land C-bands recently allocated for UAS. These measurements covered nearly all typical ground site (GS) local environments, including over water, hilly, mountainous, suburb, and near urban. As a continuation of results reported for the over-water scenarios, a description of the measurement campaign, measured results, and complete AG channel models for hilly and mountainous terrains are provided in this paper. The path loss is modeled by a modified log-distance path loss model with a correction for flight direction; path loss results are close to those of free space. A strong ground reflection was observed only for some small portions of some of the flight paths. The small-scale fading is well modeled by the Ricean distribution with a K-factor of 29.4 dB in the C-band and 12.8 dB in the L-band. The interband signals are uncorrelated. The spatial correlation for the two intraband channels with an aircraft antenna separation of 1.8 m is greater than 0.85. The C-band root-mean-square delay spread (RMS-DS) is 10 ns most of the time, with a maximum of 1 μs in hilly terrain and 180 ns in mountainous terrain. Tapped delay line (TDL) models accounting for the line of sight (LOS) and up to seven intermittent multipath components (MPCs) were developed, including the MPCs' probability of occurrence, relative power, phase, duration, and excess delay.

Air–Ground Channel Characterization for Unmanned Aircraft Systems—Part I: Methods, Measurements, and Models for Over-Water Settings

The use of unmanned aerial systems (UASs), which are also known as unmanned aerial vehicles, and by the term “drones” in the popular press, is growing rapidly. To ensure safety, UAS control and nonpayload communication (CNPC) links must operate very reliably in a variety of conditions. This requires an accurate quantitative characterization of the air–ground (AG) channel, and this channel characterization is the focus of this paper. After providing motivation and background, we describe our methods and modeling approach, followed by a description of our simultaneous dual-band (L-band ∼970 MHz, C-band ∼5 GHz) measurement campaign and the over-water (OW) measurement sites. Example results for path loss and root-mean-square delay spread are provided, as well as the results for channel stationarity distance (SD), used in calculating small-scale Rician $K$ - factor and correlations between the two receiver antennas that we employed in each frequency band. Two distinct SD measures—the power delay profile (PDP) correlation coefficient and the spatial autocorrelation matrix collinearity—were used and found to be of the same order. Path-loss exponents are near that of free space, but significant two-ray cancelation effects for these OW settings warrant more accurate models, which we provide. Delay spreads in the OW channels are also dominated by the two-ray components and are hence typically very small (∼10 ns) but can exceed 350 ns. A third intermittent multipath component (MPC) is also present a nonnegligible fraction of time; hence, we provide statistical wideband AG channel models to represent this. Future papers in this series will report results for the AG channel with ground sites in other types of environments.

무인 항공 시스템 데이터링크 기술 동향 및 성능 분석

무인 항공 시스템 (UAS)은 무인 항공기 운용에 필요한 장비, 네트워크 및 운용 인원을 포함하는 시스템을 통칭한다. 이러한 무인 항공 시스템은 과거 군사적인 목적으로 주로 이용되었으나, 최근 기술 발전에 힘입어 점차 민간용 시장으로 확대되고 있으며, 국가 공역내 통합되어 시장 규모가 급격히 성장할 것으로 예상된다. 따라서, 공역내 안정적인 통합을 위해 표준화된 무인기 제어 및 비임무용 (CNPC; control and non-payload communication) 통신시스템의 구축 필요성이 증대되고 있으며, 미국, 유럽을 비롯한 선진국에서는 높은 신뢰성을 제공 가능한 제어용 통신 기술 개발을 진행하고 있다. 본 논문에서는 무인 항공 시스템의 CNPC 데이터링크의 기술개발 동향을 기술하고, IEEE 802.15.4 ZigBee 시스템을 개량한 CNPC 시스템의 성능 분석 결과를 제시한다. Unmanned aircraft systems (UAS) are defined as the system whose components include the necessary equipment, network, and personnel to control an unmanned aircraft. In the past, UAS were predominately operated for military operations. However, nowadays, the applications of UAS to commercial area are explosively augmented and UAS are being expected to be integrated in national airspace. Therefore, the need for the standardized datalink systems rapidly and the development of control and non-payload communication (CNPC) system are being processed for integration in national airspace in United States and Europe. In this paper, the technology trends for UAS CNPC datalink are explained and presented the performance evaluation results for CNPC system, which is the modified version of IEEE 802.15.4 ZigBee system.

Air-ground channel measurements and modeling for UAS

Unmanned aircraft systems (UAS) are expected to be used in greatly increasing numbers in the near future. To safely integrate them into the National Airspace System (NAS) [1] requires highly reliable communication links for control and nonpayload communications (CNPC) [2]. Although spectrum allocations for UAS appear to be in place, UAS missions can differ markedly from those of conventional piloted aircraft, and new challenges will appear. One of these challenges is the potential detrimental effects of the air-ground (AG) channel [3]. For past systems that used elevated ground site (GS) antennas in open areas, multipath propagation was minimal. Data rates and bandwidths of past systems were also small, rendering the multipath issue either inconsequential or easily overcome by (sometimes large) transmit power increases or longer latencies. Legacy voice communication systems are also comparatively low rate and forgiving of delay and can usually resort to repetition to improve reliability.

Radio Spectrum Requirements of Control and Non-Payload Communications Links for Future Unmanned Aircraft Systems

The planned introduction of unmanned aircraft (UA) systems (UAS) into non-segregated civil airspace will require highly reliable radio links to enable remote pilots to maintain operational control and ensure safe operation. The safety-critical functions of those control and non-payload communications (CNPC) links distinguishes them from “payload” links (e.g., area-surveillance data downlinks) that, although essential to UAS missions, are not needed for piloting. Enough spectrum must be allocated to meet the individual and aggregate bandwidth requirements of the CNPC links. Obtaining all the spectrum needed is a major challenge, since competing uses already exist for every usable frequency band of significant size. In this paper we describe our work in preparing for the 2012 World Radiocommunication Conference (WRC-12) to support the quest for protected UAS CNPC spectrum. We analyze the bandwidth requirements of the CNPC system, identify suitable frequency bands, describe a potential system architecture, and demonstrate that such a system can coexist with other radio systems using the same bands.