In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, wide availability, and relative ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail, relative to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios.

pdf/a-survey-of-air-to-ground-propagation-channel-modeling-for-n5gs0ku1n2.pdf

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

A major modernization process in air traffic management for civil aviation is currently taking place under the framework of SESAR and NextGen in Europe and the United States, respectively. Air traffic management modernization is required to meet the needs sustainable air traffic growth in Europe, the United States, and worldwide are posing. A key enabler for this modernization process is the introduction of improved communications, navigation, and surveillance technologies. In this article, new developments in aeronautical communications for air traffic management are presented, with special focus on the air/ground communications technology L-band Digital Aeronautical Communications System (LDACS). The most promising LDACS technology candidate, LDACS1, is described in detail, and possible extensions toward navigation and surveillance are discussed. With these extensions, LDACS1 is well placed to become the first integrated communications, navigation, and surveillance technology for civil aviation. Utilizing a common ground infrastructure, such an integrated approach simplifies deployment and reduces costs for both deployment and maintenance.

LDACS: future aeronautical communications for air-traffic management

This paper surveys the literature of opportunistic offloading. Opportunistic offloading refers to offloading traffic originally transmitted through the cellular network to opportunistic network, or offloading computing tasks originally executed locally to nearby devices with idle computing resources through opportunistic network. This research direction is recently emerged, and the relevant research covers the period from 2009 to date, with an explosive trend over the last four years. We provide a comprehensive review of the research field from a multi-dimensional view based on application goal, realizing approach, offloading direction, etc. In addition, we pinpoint the major classifications of opportunistic offloading, so as to form a hierarchical or graded classification of the existing works. Specifically, we divide opportunistic offloading into two main categories based on application goal: traffic offloading or computation offloading. Each category is further divided into two smaller categories: with and without offloading node selection, which bridges between subscriber node and the cellular network, or plays the role of computing task executor for other nodes. We elaborate, compare, and analyze the literatures in each classification from the perspectives of required information, objective, etc. We present a complete introductory guide to the researches relevant to opportunistic offloading. After summarizing the development of the research direction and offloading strategies of the current state-of-the-art, we further point out the important future research problems and directions.

A Survey of Opportunistic Offloading

The engineering vision of relying on the ``smart sky" for supporting air traffic and the ``Internet above the clouds" for in-flight entertainment has become imperative for the future aircraft industry. Aeronautical ad hoc Networking (AANET) constitutes a compelling concept for providing broadband communications above clouds by extending the coverage of Air-to-Ground (A2G) networks to oceanic and remote airspace via autonomous and self-configured wireless networking amongst commercial passenger airplanes. The AANET concept may be viewed as a new member of the family of Mobile ad hoc Networks (MANETs) in action above the clouds. However, AANETs have more dynamic topologies, larger and more variable geographical network size, stricter security requirements and more hostile transmission conditions. These specific characteristics lead to more grave challenges in aircraft mobility modeling, aeronautical channel modeling and interference mitigation as well as in network scheduling and routing. This paper provides an overview of AANET solutions by characterizing the associated scenarios, requirements and challenges. Explicitly, the research addressing the key techniques of AANETs, such as their mobility models, network scheduling and routing, security and interference are reviewed. Furthermore, we also identify the remaining challenges associated with developing AANETs and present their prospective solutions as well as open issues. The design framework of AANETs and the key technical issues are investigated along with some recent research results. Furthermore, a range of performance metrics optimized in designing AANETs and a number of representative multi-objective optimization algorithms are outlined.

Aeronautical Ad Hoc Networking for the Internet-Above-The-Clouds

In order to meet the demands of “Internet above the clouds,” we propose a multiple-antenna aided adaptive coding and modulation (ACM) for aeronautical communications. The proposed ACM scheme switches its coding and modulation mode according to the distance between the communicating aircraft, which is readily available with the aid of the airborne radar or the global positioning system. We derive an asymptotic closed-form expression of the signal-to-interference-plus-noise ratio (SINR) as the number of transmitting antennas tends to infinity, in the presence of realistic co-channel interference and channel estimation errors. The achievable transmission rates and the corresponding mode-switching distance-thresholds are readily obtained based on this closed-form SINR formula. Monte-Carlo simulation results are used to validate our theoretical analysis. For the specific example of 32 transmit antennas and four receive antennas communicating at a 5-GHz carrier frequency and using 6-MHz bandwidth, which are reused by multiple other pairs of communicating aircraft, the proposed distance-based ACM is capable of providing as high as 65.928-Mb/s data rate when the communication distance is less than 25 km.

/pdf/adaptive-coding-and-modulation-for-large-scale-antenna-array-bf1ag2kssk.pdf

Adaptive Coding and Modulation for Large-Scale Antenna Array-Based Aeronautical Communications in the Presence of Co-Channel Interference

L-DACS1 is the broadband candidate technology for the future L-band Digital Aeronautical Communications System (L-DACS) The flexible design of L-DACS1 allows the deployment as an inlay system in the spectral gaps between two adjacent channels used by the Distance Measuring Equipment (DME) as well as the non-inlay deployment in unused parts of the L-band In this paper, the specification of the L-DACS1 physical layer enabling the deployment as an inlay and as a non-inlay or as a mixed inlay and non-inlay system is presented Apart from the transmitter design, the design of the L-DACS1 receiver is addressed including methods for mitigating interference from other L-band systems Special emphasis is put on channel estimation which has to be robust towards interference The different proposed algorithms for channel estimation are evaluated in simulations of the overall L-DACS1 physical layer performance The results show that L-DACS1 is capable of operating even under severe interference conditions, hence confirming the feasibility of the inlay concept

https://www.ldacs.com/wp-content/uploads/2014/02/09_icns_brandes.pdf

Physical layer specification of the L-band Digital Aeronautical Communications System (L-DACS1)

LDACS1 is the broadband candidate technology for the future L-band digital aeronautical communications system. As unused spectrum is very scarce in the L-band, LDACS1 pursues the approach to make use of the gaps between adjacent channels used by the distance measuring equipment to meet the capacity requirements of a new aeronautical data link. This is a challenging approach as the power of DME signals is well above the LDACS1 received power in many scenarios. In addition, further legacy system, operating in the L-band might affect LDACS1. In this paper, we will characterize the different sources of interference and derive scenarios for their influence onto LDACS1. We will also distinguish between the situations in the forward, i.e. at an airborne receiver, and in the reverse link, corresponding to a ground station receiver. Next we will have a look onto detecting interference pulses which is a challenging task for LDACS1, as it uses orthogonal frequency division multiplexing modulation, which leads to remarkable fluctuations of the useful signal power itself. The efficiency of the proposed interference detection will be confirmed by realistic simulations. Based on the investigated detection capabilities, we will finally assess, by means of bit-error rate simulations, how the different types of interference influence the LDACS1 performance if a basic interference mitigation algorithm is applied.

https://elib.dlr.de/70867/1/dasc2011_epple.pdf

Overview of interference situation and mitigation techniques for LDACS1

When pulsed interference is mitigated by means of pulse blanking, interference is reduced significantly. However, at the same time certain fractions of the useful orthogonal frequency-division multiplexing (OFDM) signal are erased. Consequently, only moderate improvements are achieved with pulse blanking. When representing the pulse blanking operation as multiplication with a rectangular window exhibiting notches at the positions where blanks are inserted, it becomes obvious, that pulse blanking mainly leads to inter-carrier interference (ICI). In this paper, the compensation of the impact of pulse blanking is proposed by reconstructing and subtracting ICI. The required shape of the subcarrier spectra is derived from the pulse blanking window. For an estimation of the transmitted data symbols and the channel coefficients of each subcarrier an iterative receiver structure is proposed. Simulation results at hand of a realistic interference scenario show that with perfect channel estimation and known data symbols the impact of pulse blanking can be reduced to a small loss in signal-to-noise ratio resulting from the energy loss due to erasing a certain fraction of the OFDM signal. With real channel estimation and estimated data symbols, the ideal case with perfect channel estimation and known data symbols is approached by 1.2 dB after only three iterations.

/pdf/compensation-of-the-impact-of-interference-mitigation-by-1dd9ur72pk.pdf

Compensation of the Impact of Interference Mitigation by Pulse Blanking in OFDM Systems

LDACS1 is a candidate for the future digital aeronautical communications system in L-band. As unused spectrum is very scarce in the L-band, LDACS1 pursues the approach to make use of the gaps between adjacent channels used by the distance measuring equipment (DME). This DME signal has a severe influence on the performance of LDACS1. In this paper, an algorithm for modeling the DME impact on LDACS1 is presented. This enables to determine whether LDACS1 can cope with DME interference for a certain area and channel frequency. The performance evaluation is based only on the positions, pulse rates, and transmit frequencies of the DME stations, without carrying out extensive simulation. Results for Europe indicate that a reliable operation of LDACS1 can be achieved.

/pdf/modeling-dme-interference-impact-on-ldacs1-1g8d1u391f.pdf

Modeling DME interference impact on LDACS1

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