Aeronautical Communication System Research Articles

Feasibility of Cell Planning for the <italic>L</italic>-Band Digital Aeronautical Communications System Under the Constraint of Secondary Spectrum Usage

The L -band digital aeronautical communications system (LDACS) is a cellular air-ground data link for air traffic control. It is a cornerstone of the future aeronautical communications infrastructure. LDACS shall operate in the frequency band 960–1164 MHz under the constraint of secondary spectrum usage. This implies strict spectral, power, and spatial separation toward current legacy systems operating in this frequency band. It has been proposed to fulfil these restrictions using cell planning for LDACS without changing frequency allocations of the legacy systems. However, the feasibility of such a cell planning is yet to be demonstrated. In this paper, we demonstrate the feasibility of LDACS cell planning under these constraints. For this purpose, we introduce the theoretical limits for such a separation enabling the coexistence of LDACS and distance measuring equipment (DME: the primary user) system in the same frequency band. Closed-form expressions are obtained such that the proper operation of DME is not harmfully affected by LDACS. These expressions are utilized in the first step to find DME-compliant locations for LDACS ground stations. In the second step, interference constraints within LDACS itself are defined and applied. This approach yields DME-compliant locations of LDACS ground stations with channel assignments fulfilling the interference constraints. The application of our method shows that LDACS cell planning in Europe is possible without disturbing the proper operation of the DME system.

M-pulse amplitude modulation of a flat-topped beam for aeronautical laser communications.

Using the Rytov method, bit error rate (BER) performances of M-pulse amplitude modulation (M-PAM) are investigated for a flat-topped beam when such a beam is employed in an aeronautical laser communication system operating in vertical paths having weak atmospheric turbulence. By using the on-axis scintillation index and the log-normal distributed intensity, the average BER (⟨BER⟩) is evaluated for M-PAM when M=2,4,8. The scintillation indices of collimated flat-topped beams of various flatness orders N are compared against propagation lengths, source sizes, and zenith angle for laser communication vertical paths, including uplink and downlink. Also, the ⟨BER⟩ versus the average signal to noise ratio (⟨SNR⟩) is examined for various beam flatness orders. It is shown that as the flatness order increases, the scintillation index decreases. Taking one of the best flatness order values, N=15, for reducing the scintillations, ⟨BER⟩ versus propagation lengths, source sizes, zenith angle, and ⟨SNR⟩ are found for various values of M. When M is increased, the ⟨BER⟩ is found to deteriorate.

Efficient Spectrum Sensing for Aeronautical LDACS Using Low-Power Correlators

Air traffic has seen tremendous growth over the past decade pushing the need for enhanced air traffic management schemes. The $L$ -band digital aeronautical communication system (LDACS) is gaining traction as a scheme of choice, and aims to exploit the capabilities of modern digital communication techniques and computing architectures. Cognitive radio-based approaches have also been proposed for LDACS to improve spectrum efficiency and communication capacity; however, these require intelligent compute capability in aircrafts that enforce limited space and power budgets. This paper proposes the use of multiplierless correlation to enable spectrum sensing in LDACS air-to-ground links, and its integration into the on-board LDACS system. The proposed architecture offers improved performance over traditional energy detection (ED) even at low signal-to-noise ratio (SNR) with lower energy consumption than a multiplier-based correlator, while also assisting in receiver synchronization. We evaluate the proposed architecture on a Xilinx Zynq field-programmable gate array and show that our approach results in 28.3% reduction in energy consumption over the multiplier-based approach. Our results also show that the proposed architecture offers 100% accuracy in detection even at −12-dB SNR without requiring additional circuitry for noise estimation, which are an integral part of ED-based approaches.

Ambiguity Function Analysis for OFDM-Based LDACS Passive Multistatic Radar

The ambiguity function analysis is central to investigating the resolution capabilities of a radar system. It is particularly important for passive radar scenarios, where the signals of opportunity have not been originally designed for radar purposes. This paper focuses on studying the achievable resolution capabilities for a noncoherent orthogonal frequency division-multiplexing (OFDM)-based passive multistatic radar for L-band digital aeronautical communication system (LDACS) signals. For this purpose, the ambiguity function obtained when employing the OFDM-based LDACS communications signals as signals of opportunity is studied. A generic bistatic link is considered and closed-form expressions for the expectation of the corresponding ambiguity function when accounting for the different signal contributions are derived. The resulting expressions are then used to evaluate and analyze the overall multistatic radar ambiguity function for two sample radar scenarios. The results highlight the impact of the geometry on the shape of the ambiguity function, allowing therefore for a better understanding of the effect that the geometry has on the range and velocity resolution capabilities of the studied system.

A Hardware-Efficient Synchronization in L-DACS1 for Aeronautical Communications

L-band digital aeronautical communication system type-1 (L-DACS1) is an emerging standard that aims at enhancing air traffic management by transitioning the traditional analog aeronautical communication systems to the superior and highly efficient digital domain. L-DACS1 employs modern and efficient orthogonal frequency-division multiplexing (OFDM) modulation technique to achieve more efficient and higher data rate in comparison to the existing aeronautical communication systems. However, the performance of OFDM systems is very sensitive to synchronization errors such as symbol timing offset (STO) and carrier frequency offset (CFO). STO and CFO estimations are extremely important for maintaining orthogonality among the subcarriers for the retrieval of information. This paper proposes a novel efficient hardware synchronizer for L-DACS1 systems that offers robust performance at low power and low hardware resource usage. Monte Carlo simulations show that the proposed synchronization algorithm provides accurate STO estimation as well as fractional CFO estimation. Implementation of the proposed synchronizer on a widely used field-programmable gate array (FPGA) (Xilinx xc7z020clg484-1) results in a very low hardware usage which consumed 6.5%, 3.7%, and 6.4% of the total number of lookup tables, flip-flops, and digital signal processing blocks, respectively. The dynamic power of the proposed synchronizer is below 1 mW.

Mitigation of DME interference in LDACS1-based future air-to-ground (A/G) communications

In this article, an algorithm for mitigating distance measuring equipment (DME) interference in L-band digital aeronautical communication system type 1 (LDACS1)-based aeronautical communication sys...

Cancelation of Distance Measuring Equipment Interference for Aeronautical Communications

The L-band digital aeronautical communications system (L-DACS1) is subject to strong interference caused by distance measuring equipment (DME). For efficient statistical processing of interference, we adopt a Gaussian mixture (GM) distribution to model the impulsive nature of DME signals. Hence, we drive the parameters of the GM model in terms of properties of DME signals. This allows us to redesign the optimum receiver for mitigating DME interference. We also provide a simple pulse detector to estimate the presence of DME signals utilizing the null subcarriers of the L-DACS1.

Datalink security in the L-band digital aeronautical communications system (LDACS) for air traffic management

Today's very high-frequency (VHF) voice-based air–ground communication system for tactical aircraft guidance is suffering from the VHF band's increasing saturation in high-density areas [1]. The air–ground1 communication infrastructure is therefore undergoing modernization to ensure the sustainable growth of the European air transportation system in the coming decades [2], [3]. One major goal of this effort is the introduction of computerized air traffic management applications and new digital communication links between aircraft and ground systems.

Application of cognitive radio and interference cancellation in the L-Band based on future air-to-ground communication systems

The Very High Frequency band (VHF) currently used for aeronautical communications is becoming congested, and future Air-to-Ground (A/G) communication will require much greater use of data communications. For meeting future capacity requirements in aeronautical communications, we propose two new approaches one of which is a cognitive radio based A/G communication network that provides dynamic spectrum access to airplanes to overcome the spectrum scarcity problem in the VHF band. Another approach involves use of a new spectrum in the Ultra-High Frequency band (UHF) to create a new A/G link. In this paper, we propose and investigate the possibilities for developing a spectrum sensing approach to detect idle band in the VHF spectrum and analyze the possible interference between future L-band Digital Aeronautical Communication System (L-DACS) and legacy aeronautical systems.

Pulse-Pair Interference Automatic Detection and Mitigation for L-Band Aeronautical Communication System

Pulse-pairs (PP) generated by distance measuring equipment (DME) cause severe interference to the L-band digital aeronautical communication systems. Unlike previous works that mainly improved receiver structure for mitigating the DME interference, this paper proposes a novel and practical time domain PP mitigation method without changing the existing receiver structure. Our method is composed of three parts and utilizes a specific property, i.e., a relatively fixed waveform of DME PP. First, the complex-valued waveform of PP is automatically detected through an iterative weighted average method. Then, on the basis of the detected PP waveform, each PP is reconstructed according to its amplitude, position, and initial phase, which are estimated through a sparse representation algorithm. Finally, the reconstructed PPs are subtracted from the contaminated signal. Numerical experiments show that compared with recently published methods the bit error rate obtained by our method is approximately 5 dB better, while the complexity is maintained at the same level.

FBMC and L-DACS Performance for Future Air-to-Ground Communication Systems

Recently, two different L-band digital aeronautical communication systems (L-DACS), i.e., L-DACS1 and L-DACS2, have been proposed as two future communication infrastructure candidates for air-to-ground (AG) communication systems, with L-DACS1 selected as the best candidate. In this paper, we describe a filter bank multicarrier (FBMC)-based communication system and show its advantages over the L-DACS systems. We provide simulation results for all three communication systems to fairly compare their power spectral density, peak-to-average power ratio (PAPR), and bit error ratio (BER) performance. We show that in a measurement-based AG communication channel model, FBMC has better performance (and spectral containment) than the L-DACS schemes, and this is particularly true in the presence of actual interfering signals from distance measuring equipment (DME). Simulation results show that FBMC can substantially reduce the out-of-band power and can suppress DME interference by at least 19.5 dB, due to its well-localized subcarrier prototype filters. FBMC can also increase throughput and spectral efficiency by reducing the number of guard-band subcarriers and removal of the cyclic prefix, postfix, as well as windowing techniques used in L-DACS1. These results show that an FBMC-based communication system can be an appealing candidate for future AG communication systems.

Modified Cramér‐Rao lower bounds for joint position and velocity estimation of a Rician target in OFDM‐based passive radar networks

AbstractOwing to the increased deployment and the favorable range and Doppler resolutions, orthogonal frequency‐division multiplexing (OFDM)‐based L band digital aeronautical communication system type 1 (LDACS1) stations have become attractive systems for target surveillance in passive radar applications. This paper investigates the problem of joint parameter (position and velocity) estimation of a Rician target in OFDM‐based passive radar network systems with multichannel receivers placed on moving platforms, which are composed of multiple OFDM‐based LDACS1 transmitters of opportunity and multiple radar receivers. The modified Cramér‐Rao lower bounds (MCRLBs) on the Cartesian coordinates of target position and velocity are computed, where the received signal from the target is composed of dominant scatterer (DS) component and weak isotropic scatterers (WIS) component. Simulation results are provided to demonstrate that the target parameter estimation accuracy can be improved by exploiting the DS component. It also shows that the joint MCRLB is not only a function of the transmitted waveform parameters, target radar cross section, and signal‐to‐noise ratio but also a function of the relative geometry between the target and the passive radar networks. The analytical expressions of MCRLB can be utilized as a performance metric to access the target parameter estimation in OFDM‐based passive radar networks in that they enable the selection of optimal transmitter‐receiver pairs for target estimation.

OFDM Receiver Structure for a Subband-Selective Mitigation of Time-Variant Interference

System performance of orthogonal frequency-division multiplexing (OFDM) degrades in the presence of time-variant frequency-selective interference. In the literature, several pulse-blanking concepts have been introduced over the past few years, which are promising ways to mitigate impulsive interference for OFDM reception. However, blanking yields an attenuation of the signal and intercarrier interference (ICI). In this paper, a receiver structure is proposed, which consists of a frequency-selective pulse-blanking unit, a blanking mitigation unit, and an iterative ICI cancelation unit. The L-band Digital Aeronautical Communication System 1 (L-DACS 1) is regarded as an application that suffers from interference from the impulsive Distance Measuring Equipment (DME) system whose frequency bands partly overlap. It is shown that, by using the proposed mitigation scheme for impulsive interference, a reliable reception is possible, even in strong interference situations.

Cramér–Rao bounds for L‐band digital aeronautical communication system type 1 based passive multiple‐input multiple‐output radar

In this study, of concern is the achievable estimation accuracy for a non-coherent passive multiple-input multiple-output (MIMO) radar employing orthogonal frequency-division multiplexing (OFDM) based signals of opportunity. The motivation behind this investigation is the surveillance aspect of the air trac management modernisation process currently taking place in civil aviation. To this end, the surveillance capability of the OFDM-based L-band digital aeronautical communication system type 1 (LDACS1) is analysed. The extension of the LDACS1 communication system towards surveillance is of great importance since it would enable an alternative, non-cooperative surveillance application, and, together with the already validated navigation extension, establish a fully integrated LDACS1-based communication, navigation, and surveillance technology. The modied Cramer-Rao bound on the joint estimation of target location and velocity for a non-coherent passive MIMO radar, employing the OFDM-based LDACS1 signals as signals of opportunity, is investigated. The analysis is carried out assuming one target, multiple and widely separated transmit and receive antennas, orthogonal waveforms, independent reection coecients, and zero-mean white Gaussian noise. Closed-form expressions for the relevant elements of the modied Fisher information matrix are obtained. The results can be used to assess the estimation accuracy of a multiple antenna passive radar system employing any OFDM-based signals of opportunity.

Erratum: Cramér–Rao bounds for L‐band digital aeronautical communication system type 1 based passive multiple‐input multiple‐output radar

Erratum: Cramér–Rao bounds for L‐band digital aeronautical communication system type 1 based passive multiple‐input multiple‐output radar

A Tool for Beamforming and Real-Time Link Budget Analysis in Aeronautical Communications Using Kinematics

Aeronautical Communication (AC) systems are likely to be a part of future tiered communication network structures. Therefore maintaining a robust AC link with a minimum power burden on the host platform has a critical importance. In this paper, we analyze the AC systems from a link budget analysis point of view and define the requirements for the parameters of link budget with an emphasize on antenna gains. First, we study the link budget analysis in an AC system. Then, we present a mathematical framework to provide an end-to-end link budget analysis utilizing the platform kinematics. Finally, we present the numerical results for typical AC scenarios and discuss that these results can be used for calculating the real-time link budget and electronic beamforming to provide a robust link.

Cognitive Radio for Aeronautical Communications: A Survey

Novel air traffic management (ATM) strategies are proposed through the Next Generation Air Transportation and Single European Sky for ATM Research projects to improve the capacity of the airspace and to meet the demands of the future air traffic. The implementation of the proposed solutions leads to increasing use of wireless data for aeronautical communications. Another emerging trend is the unmanned aerial vehicles. The unmanned aerial systems (UASs) need reliable wireless data link and dedicated spectrum allocation for its operation. On-board broadband connectivity also needs dedicated spectrum to satisfy the quality of service requirements of the users. With the growing demand, the aeronautical spectrum is expected to be congested. However, the studies revealed that the aeronautical spectrum is underutilized due to the static spectrum allocation strategy. The aeronautical communication systems, such as air-air and air-ground communication systems, inflight infotainment systems, wireless avionics intra-communications, and UAS, can benefit significantly from the introduction of cognitive radio-based transmission schemes. This paper summarizes the current trends in aeronautical spectrum management followed by the major applications and contributions of cognitive radio in solving the spectrum scarcity crisis in the aeronautical domain. Also, to cope with the evolving technological advancement, researchers have prioritized the issues in the case of cognitive radio that needs to be addressed depending on the domain of operation. The proposed cognitive aeronautical communication systems should also be compliant with the Aeronautical Radio Incorporated and Aerospace Recommended Practice standards. An overview of these standards and the challenges that need immediate attention to make the solution feasible for a large-scale operation, along with the future avenues of research is also furnished.

航空激光通信系统的特性分析及机载激光通信实验

航空激光通信系统的特性分析及机载激光通信实验

Impulse interference mitigation method based on joint compressed sensing and whitening of interference

To mitigate the deleterious influence of distance measure equipment( DME) interference on orthogonal frequency division multiplexing( OFDM) receiver of L-band digital aeronautical communications system 1( L-DACS1) operating as an inlay system,a new DME interference suppression method was proposed based on joint compressed sensing and whitening of residual interference. Firstly,the DME impulse interference was observed via null subcarriers channel of the OFDM receiver and reconstructed with convex optimization constrained l1 norm minimization method based on the sparse property of the DME impulse interference in time domain. Then the reconstructed DME impulse interference was transformed to frequency domain and eliminated from the received signal. Finally,to avoid burst errors of demodulator,the residual impulse interference was converted to white Gaussian noise by using the de-interleaver and inverse orthogonal transformer.The computer simulation indicates that the proposed method can reduce the impact of DME interference effectively,and improve the reliability of OFDM receiver of the L-DACS1 system significantly.

Improving the safety, capacity and efficiency of airport traffic management with AeroMACS

For the past 50 years, the aviation industry has set an unparalleled standard for transportation safety and efficiency. In spite of a few notable headlines, there remains a higher safety rate in aviation than in most other methods of travel. With the support of a broad range of international stakeholders, the industry is in the midst of a global adoption of ‘next-gen’ wireless technologies designed to enhance the safety, capacity and efficiency of fixed and mobile ground communications. AeroMACS, the aeronautical mobile aircraft communication system, provides the broadband connectivity needed to support the growing bandwidth demands of aircraft and ground infrastructure and air traffic management applications. This paper examines the past, present and future of AeroMACS, including: limitations to the current approach to airport communications; an overview of the WiMAX 802.16 standard and its advantages for aviation; potential barriers to AeroMACS adoption; and use models that will drive future implementations.