Article
To read the full-text of this research, you can request a copy directly from the author.

Abstract

A class of aeronautical wide-band channel models is proposed, featuring parking and taxi environments, takeoff and landing situations, and en-route scenarios for ground-air and air-air links. Typical and worst case parameter sets are suggested, based on published measurement results and empirical data. The models are suitable for channel emulators that can be easily implemented on digital computers or in hardware and thus are useful for the validation of digital aeronautical links. A time-domain and frequency-domain implementation of such a channel emulator are derived, and results for a typical multicarrier system are presented. It is shown that the scenarios have distinguishable performance results depending on the underlying maximum ranges and shapes of the Doppler and delay spectra and the presence of a line-of-sight path. Finally, the degrading effects of intersymbol interference and intersubcarrier interference on the multicarrier signal are explained

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the author.

... There are numerous studies available in the literature on the characteristics of aeronautical channels [7], [10]- [13]. Aeronautical communications can be broadly classified into communications between the pilot or crew with the ground controller and wireless data communication for passengers. ...
... Both of these types of communication are dependent on the flight route characteristics. In [10] the propagation channel is divided into three main phases of flight, termed as parking and taxiing, en-route, and take off and landing. Each phase of flight was described by different channel characteristics (type of fading, Doppler spread, and delay), but this relatively early paper was not comprehensive nor fully supported by measurements. ...
... Doppler shifts can introduce carrier frequency offset (CFO) and inter carrier interference, especially for orthogonal frequency division multiplexing (OFDM) implementations. There are several studies that consider modeling of Doppler spread [10], [22], [23], [30], [43]- [46]. Some channel access algorithms e.g., multi carrier code division multiple access, have been shown to be robust against Doppler spread in AG propagation [47]. ...
Preprint
Full-text available
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, ease of availability, and 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 when compared 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.
... Rician fading aeronautical communications channels in an en route scenario is assumed to provide a realistic evaluation of the HBD-ACS [33], [34], [35]. Following the work in [33] and [35], the link between AS-1 and AS-2 is also modeled as a Rician fading channel. ...
... Rician fading aeronautical communications channels in an en route scenario is assumed to provide a realistic evaluation of the HBD-ACS [33], [34], [35]. Following the work in [33] and [35], the link between AS-1 and AS-2 is also modeled as a Rician fading channel. Accordingly, we assume that the ASs are communicating with the GS at cruising altitude, with the signal model of this work based on [11]. ...
... From [44], f X gs (x) = j ≥0 α( j, Ω X α g,2 , K X gs , 1)x j . Thus, (33) can be rewritten as: ...
Preprint
A hybrid-duplex aeronautical communication system (HBD-ACS) consisting of a full-duplex (FD) enabled ground station (GS), and two half-duplex (HD) air-stations (ASs) is proposed as a direct solution to the spectrum crunch faced by the aviation industry. Closed-form outage probability and finite signal-to-noise ratio (SNR) diversity gain expressions in aeronautical communications over Rician fading channels are derived for a successive interference cancellation (SIC) detector. Similar expressions are also presented for an interference ignorant (II) detector and HD-equivalent modes at GS and ASs. Through outage and finite SNR diversity gain analysis conducted at the nodes, and system level, residual SI and inter-AS interference are found to be the primary limiting factors in the proposed HBD-ACS. Additional analysis also revealed that the II and SIC detectors in the proposed HBD-ACS are suitable for weak and strong interference scenarios, respectively. When compared to HD-ACS, the proposed HBD-ACS achieves lower outage probability and higher diversity gains at higher multiplexing gains when operating at low SNRs. Finite SNR analysis also showed the possibility of the proposed HBD-ACS being able to attain interference-free diversity gains through proper management of residual SI. Hence, the proposed HBD-ACS is more reliable and can provide better throughput compared to existing HD-ACS at low-to-moderate SNRs.
... Specifically, it has been shown that the favorable line-of-sight (LoS) propagation conditions for UAVs flying in the sky can compensate for the reduced gain of antenna side lobes of the BSs, provided that UAVs fly below 120 − 200 m. A first consequence of flying at lower altitudes is that the AU-to-BS channel exhibits multipath components (MPCs) consisting of an LoS link with high probability and a cluster of reflected, delayed paths [9]. Severe Doppler shifts are caused by the high carrier frequency and high velocity of the UAV, and they are influenced by the angular distribution of the scattered components. ...
... Indeed, it is tacitly assumed that large Doppler shifts have been previously compensated for or, as in [31], that the AU transmits its data to the BS by maintaining a fixed position over selected points along a given trajectory (i.e., transmission during hovering flight). However, compensation of Doppler shifts is a challenging task in multipath channels, except for the case when the MPCs of the AU-to-BS channel have a very similar Doppler shift, which is a situation that may not be fulfilled in the lowaltitude airspace [9]. Moreover, allowing the UAV to transmit only in the hovering-flight state along its trajectory entails a waste of both communication and power resources. ...
... For A2C link, we assume a two-ray channel model, 5 which includes the LoS path and a scattered (i.e., non-LoS) component [9] (see also Fig. 1). The non-LoS (NLoS) component is physically due to many rays reflected or scattered from closely-spaced terrestrial obstacles within the vicinity of the BS, which are characterized by a very narrow beamwidth [9] and appear grouped or "clustered" in delay for sufficiently high elevation angles [54]. ...
Article
Full-text available
Integration of unmanned aerial vehicles (UAVs) for surveillance or monitoring applications into fifth generation (5G) New Radio (NR) cellular networks is an intriguing problem that has recently tackled a lot of interest in both academia and industry. For an efficient spectrum usage, we consider a recently-proposed sky-ground nonorthogonal multiple access (NOMA) scheme, where a cellular-connected UAV acting as aerial user (AU) and a static terrestrial user (TU) are paired to simultaneously transmit their uplink signals to a base station (BS) in the same time-frequency resource blocks. In such a case, due to the highly dynamic nature of the UAV, the signal transmitted by the AU experiences both time dispersion due to multi-path propagation effects and frequency dispersion caused by Doppler shifts. On the other hand, for a static ground network, frequency dispersion of the signal transmitted by the TU is negligible and only multipath effects have to be taken into account. To decode the superposed signals at the BS through successive interference cancellation, accurate estimates of both the AU and TU channels are needed. In this paper, we propose channel estimation procedures that suitably exploit the different circular/noncircular modulation formats ( modulation diversity) and the different almost-cyclostationarity features ( Doppler diversity) of the AU and TU by means of widely-linear time-varying processing. Our estimation approach is semi-blind since Doppler shifts and time delays of the AU are estimated based on the received data only, whereas the remaining relevant parameters of the AU and TU channels are acquired relying also on the available training symbols, which are transmitted by the AU and TU in a nonorthogonal manner. Monte Carlo numerical results demonstrate that the proposed channel estimation algorithms can satisfactorily acquire all the relevant parameters in different operative conditions.
... al. [6] present many papers that address aeronautical and UAV channels. Haas [8] presents channel models for aeronautical channels in different scenarios. Measurement campaigns are given in [9][10][11]. ...
... In [8], a channel model is presented for aeronautical links in different scenarios. The first scenario discusses the communication links in en-route scenarios when the airplane is airborne. ...
... is assumed to be 1μs in order to generate Riciandistributed samples. In [8], it is shown how to generate as in equation 2. ( ) is a random uniformly distributed variable ( ) (0,1) and ( ) is the inverse of the desired cumulative distribution function. ...
Article
Full-text available
Drones have greatly enhanced search and rescue missions. They help improve the response time of the rescue team. They can cover vast challenging terrains quickly. Drones used in rescue missions are expensive. Because of the challenging terrains, if any drone crashes, it cannot be retrieved. This paper presents two contributions. The first contribution is a cruising scheme for a swarm of drones heading to a dangerous area to rescue victims. The proposed scheme guarantees the safety of the drones during the mission. It guarantees that no drone is lost; whenever a drone’s controller fails, another drone will guide it home. Basically, each pair of drones should monitor the control system of one another. In case no watchdog signal is sent, an error is perceived and the operational drone begins to control the malfunctioning one (the drone with a failed controller). Every drone sends all its sensor data to the other drone every 1msec. When a fault occurs, the operational drone sends back the control signals to the malfunctioning one to control its actuators. A robust air-to-air communication channel between pairs of drones, is needed in order to realize the proposed navigation scheme and to achieve a safe cruise and a successful mission to every single drone in the whole swarm. Therefore, the second contribution is a channel model for the air-to-air links between pairs of drones. It is assumed that drones’ transceivers use the 802.11n protocol. Simulations are conducted to test the proposed channel model in two scenarios. The first one is fault- free and the other one is when one of the controllers in a pair of drones, fails. The separating distance between every two drones in each pair and their relative velocity with respect to one another, differ in both scenarios. The proposed channel is robust as it achieves approximately zero BER in both scenarios.
... A seguir são propostos vários cenários aeronáuticos de forma a abranger as principais fases de um vôo típico como rota, pouso, decolagem, táxi e estacionamento. Resultados de medidas publicadas e valores empíricos foram utilizados para a especificação de cada cenário [12], [10], [15]. A seguir serão apresentadas as principais características de cada cenário simulado. ...
... Tipicamente, este cenário consiste em um caminho em visada direta e um grupo de caminhos refletidos e com atrasos. De acordo com [10] e [15], o caminho direto pode ser modelado como um processo constante e a componente difusa do canal como um processo Rayleigh. O fator Rice tem uma grande variação de 2 a 20 dB onde 2 dB é o pior caso e 15 dB é o valor típico encontrado. ...
... Em [15], uma largura do feixe da ordem de c) Atraso O pior caso de atraso é de aproximadamente 200 µs para enlaces terra-ar e até 1 ms para enlaces ar-ar. Em [10], os valores típicos para o atraso são de 33 µs para enlaces terra-ar e 66 µs para enlaces ar-ar. ...
... As an essential part of the performance evaluation of the aerial communication systems, channel modeling of the aerial communication system is a very hot topic [1,2]. In the past years, aeronautical channel models, including air-to-ground (A2G) channel models [3][4][5][6][7], airto-air (A2A) channel models [8][9][10][11], and satellite-toaircraft (S2A) channel models [12][13][14], have been widely discussed and developed. As emerging applications of unmanned aerial vehicle (UAV) communications, precise low-altitude A2A channel modeling attracts interests from the researchers, as in [8][9][10][15][16][17][18]; measurements were also performed in [19,20]. ...
... us, in most of the situations, the channel is highly nonstationary. According to the general method of developing aeronautical channel models, such as presented in [5,21], three paths, including the line-of-sight path, the reflection path, and the diffuse scattering paths, are considered in this paper and are assumed to be uncorrelated to each other. ...
... Area. e ground scatterers are assumed to be randomly distributed in the elliptic area determined by the maximum time-delay ellipsoid truncated by the XOY plane. e maximum timedelay ellipsoid is determined by (4) with T and R as its foci; thus, the boundary of this elliptic area is determined by (5): ...
Article
Full-text available
Aerial communication is very flexible due to almost no restrictions on geographical conditions. In recent years, with the development and application of the unmanned aerial vehicle, the air-to-air communication attracts dense interests from the researchers. More accurate and precise channel modeling for air-to-air communication is a new hot topic because of its essential role in the performance evaluation of the systems. This paper presents an analytical nonstationary regular-shaped geometry-based statistical model for low-altitude air-to-air communication over an open area with considerations on ground scattering. Analytical expressions of the channel impulse response and the autocorrelation functions based on the three-ray model are derived. Based on the assumption of uniform distribution of the ground scatterers, the distributions of the channel coefficients such as time delay and path attenuation are derived, simulated, compared, and fitted. The nonstationary characteristics of the channel are observed through the time-variant distributions of the channel coefficients as well as the time-variant autocorrelated functions and time-variant Doppler power spectrum density.
... In Fig. 3 we have plotted NMSE vs 1/ǫ for the proposed M-MLE algorithm. We have considered a channel model for the aircraft arrival scenario based on the model in [25]. The details of this channel model is described in the third paragraph of Section IV. ...
... After the estimation of the delay of the strongest channel path we estimate the Doppler shift of this strongest channel path from the (l ′′ + 1)-th row of the received M × N pilot matrix X p . Let c l ′′ ∈ C N ×1 denote the (l ′′ + 1)-th column of X T p where l ′′ (given by (25)) is the delay domain index of the DDRE where the highest energy is received. Then from (14) we have ...
... For the numerical studies we consider the wireless channel between an aircraft and the ground station during the aircraft's arrival. The channel model for this aircraft arrival scenario is based on the model in [25]. We consider P = 5 paths, where the delay of the first path i.e., direct line-of-sight path (LOS) path is τ 1 = 0 and the delay of all other paths is distributed uniformly in (0 , 7µs]. ...
Preprint
We consider the problem of accurate channel estimation for OTFS based systems with few transmit/receive antennas, where additional sparsity due to large number of antennas is not a possibility. For such systems the sparsity of the effective delay-Doppler (DD) domain channel is adversely affected in the presence of channel path delay and Doppler shifts which are non-integer multiples of the delay and Doppler domain resolution. The sparsity is also adversely affected when practical transmit and receive pulses are used. In this paper we propose a Modified Maximum Likelihood Channel Estimation (M-MLE) method for OTFS based systems which exploits the fine delay and Doppler domain resolution of the OTFS modulated signal to decouple the joint estimation of the channel parameters (i.e., channel gain, delay and Doppler shift) of all channel paths into separate estimation of the channel parameters for each path. We further observe that with fine delay and Doppler domain resolution, the received DD domain signal along a particular channel path can be written as a product of a delay domain term and a Doppler domain term where the delay domain term is primarily dependent on the delay of this path and the Doppler domain term is primarily dependent on the Doppler shift of this path. This allows us to propose another method termed as the two-step method (TSE), where the joint two-dimensional estimation of the delay and Doppler shift of a particular path in the M-MLE method is further decoupled into two separate one-dimensional estimation for the delay and for the Doppler shift of that path. Simulations reveal that the proposed methods (M-MLE and TSE) achieve better channel estimation accuracy at lower complexity when compared to other known methods for accurate OTFS channel estimation.
... In mesh networks of aircraft, the ground stations (GSs) are typically located at the airport, which allows the aircraft to directly communicate with Air traffic control for delivering vital control messages. Apart from being either the source or destination, the aircraft also provide relaying services during their landing/take-off, taxiing and holding patterns [1], [27], where these phases are associated with rather diverse channel characteristics, especially the air-to-ground (A2G) or air-toair (A2A) links [28]. The A2G communications and A2A communications rely on the same channel model for their data transmission, but they have different maximum delay. ...
... Intuitively, there is a line-of-sight (LOS) path in A2A communications, where the power ratio between the LOS path and the diffuse components is given by [27] ...
... where α ∈ R is the amplitude of the LOS path and β ∈ R is the variance of the diffuse component having zero-mean quadrature components. Hence, given the Rician factor K Rice , we have [27], [29] ...
Article
Full-text available
Terrestrial Internet access is gradually becoming the norm across the globe. However, there is a growing demand for Internet access of passenger airplanes. Hence, it is essential to develop aeronautical networks above the clouds. Therefore the conception of an aircraft mobility model is one of the prerequisite for aeronautical network design and optimization. However, there is a paucity of realistic aircraft mobility models capable of generating large-scale flight data. To fill this knowledge-gap, we develop a semi-stochastic aircraft mobility model based on large-scale real historical Australian flights acquired both on June 29th, 2018 and December 25th, 2018, which represent the busiest day and the quietest day of 2018, respectively. The semi-stochastic aircraft mobility model is capable of generating an arbitrary number of flights, which can emulate the specific features of aircraft mobility. The semi-stochastic aircraft mobility model was then analysed and validated both by the physical layer performance and network layer performance in the case study of Australian aeronautical networks, demonstrating that it is capable of reflecting the statistical characteristics of the real historical flights.
... (22) In the offline training phase, the covariance matrices realizations can be generated by simulating the A2G channels following some realistic models, such as the model given in [36], and constructing the random impulse interference based on the commonly known statistical models, such as the Gaussian mixture model [37]. ...
... The number of past IPN observations fed into the 3DConvTransformer is set to P = 25, while the temporal prediction range is set to L = 5. The past IPN observations are obtained by generating a simulated dataset based on the A2G multi-path channel model provided in [36] as well as the DME interference model. Specifically, the dataset consists of 100000 samples with the AC velocities generated uniformly following the distribution of U[300km/h, 600km/h]. ...
Preprint
A novel time-efficient framework is proposed for improving the robustness of a broadband multiple-input multiple-output (MIMO) system against unknown interference under rapidly-varying channels. A mean-squared error (MSE) minimization problem is formulated by optimizing the beamformers employed. Since the unknown interference statistics are the premise for solving the formulated problem, an interference statistics tracking (IST) module is first designed. The IST module exploits both the time- and spatial-domain correlations of the interference-plus-noise (IPN) covariance for the future predictions with data training. Compared to the conventional signal-free space sampling approach, the IST module can realize zero-pilot and low-latency estimation. Subsequently, an interference-resistant hybrid beamforming (IR-HBF) module is presented, which incorporates both the prior knowledge of the theoretical optimization method as well as the data-fed training. Taking advantage of the interpretable network structure, the IR-HBF module enables the simplified mapping from the interference statistics to the beamforming weights. The simulations are executed in high-mobility scenarios, where the numerical results unveil that: 1) the proposed IST module attains promising prediction accuracy compared to the conventional counterparts under different snapshot sampling errors; and 2) the proposed IR-HBF module achieves lower MSE with significantly reduced computational complexity.
... • Doppler effects: Considering the geometric relationship between _ errestrial user and a satellite, a normalized maximum Doppler frequency has been derived in [19] along with its distribution in [20]. Given the normalized maximum Doppler frequency, the Doppler shift distribution has been modelled as a dubbed Jakes distribution in [21]. Further mitigation of the Doppler effects has been achieved by non-coherent detection [22], Doppler frequency shift estimation [23], and orthogonal time frequency space (OTFS) modulation [24], [25]. ...
... It obeys the Shadowed-Rician distribution, whose probability density function (PDF) and cumulative distribution function (CDF) are expressed as (9) and (10), respectively. The path loss P P L is formulated in (21). The attenuation of molecular absorption, denoted as P abs , is presented as (23). ...
Preprint
Full-text available
Given their extensive geographic coverage, low Earth orbit (LEO) satellites are envisioned to find their way into next-generation (6G) wireless communications. This paper explores space-air-ground integrated networks (SAGINs) leveraging LEOs to support terrestrial and non-terrestrial users. We first propose a practical satellite-ground channel model that incorporates five key aspects: 1) the small-scale fading characterized by the Shadowed-Rician distribution in terms of the Rician factor K, 2) the path loss effect of bending rays due to atmospheric refraction, 3) the molecular absorption modelled by the Beer-Lambert law, 4) the Doppler effects including the Earth's rotation, and 5) the impact of weather conditions according to the International Telecommunication Union Recommendations (ITU-R). Harnessing the proposed model, we analyze the long-term performance of the SAGIN considered. Explicitly, the closed-form expressions of both the outage probability and of the ergodic rates are derived. Additionally, the upper bounds of bit-error rates and of the Goodput are investigated. The numerical results yield the following insights: 1) The shadowing effect and the ratio between the line-of-sight and scattering components can be conveniently modeled by the factors of K and m in the proposed Shadowed-Rician small-scale fading model. 2) The atmospheric refraction has a modest effect on the path loss. 3) When calculating the transmission distance of waves, Earth's curvature and its geometric relationship with the satellites must be considered, particularly at small elevation angles. 3) High-frequency carriers suffer from substantial path loss, and 4) the Goodput metric is eminently suitable for characterizing the performance of different coding as well as modulation methods and of the estimation error of the Doppler effects.
... In [8], [9], the application of simple tap-delay line models on aeronautical channel modeling has been discussed. The authors have already stated, that the different phases of a flight require different models or at least an individual parametrization. ...
... is generated using the delay and Doppler shifts of the MPCs given in the current (hypothetical) set of MPCsM (b) i similar to (9). Then, an equation similar to (10)Ỹ ...
Article
Full-text available
The operation of unmanned aircraft is unthinkable without reliable wireless communication links: Despite a comparatively high expected level of autonomy of unmanned aircraft, monitoring and remote controlling are required to some degree. As the design of every communication link requires good knowledge on the characteristics of the communication channel, we have performed a measurement campaign to collect channel sounding data for the wireless air-ground channel at C-band. While we have focused on the campaign description and the analysis of the dominant signal component in previous publications, we now concentrate on the detection and tracking of multipath components. In this paper, we present our data processing chain that allows a fast parallel processing of the measurement data, as data dependencies are reduced as much as possible. We furthermore introduce a path-based multipath component tracking approach and apply it to our measurement data. This tracking allows us to estimate the location of reflectors causing multipath component signals. We apply our processing chain to data recorded during take-off at a small airport and compare the results of the reflector localization to a satellite image of the airport to successfully verify our approach.
... The elements of A L = [A 1 , ..., A L ] depend on the channel model. For air-to-air channels (A2A), the signal typically has a strong LoS and a small number of weak reflected components, and thus, such channels can be modeled using the Rician fading [65]- [71]. According to the general Rician channel model, the instantaneous channel coefficient can be represented as ...
... where c is the speed of light, d t-r is the distance between the transmitter and receiver, and is the pathloss exponent. However, as the measurements indicate, the Rice factor K for A2A channel is about 20 dB, and the received signal power may remain constant for long time periods [65]- [71]. Consequently, the channel coefficients h i 's are not suffering from small scale fading, and the large scale fading is dominated by the free space path loss. ...
Article
Full-text available
This work presents the symbol error rate (SER) and outage probability analysis of multi-layer unmanned aerial vehicles (UAVs) wireless communications assisted by intelligent reflecting surfaces (IRS). In such systems, the UAVs may experience high jitter, making the estimation and compensation of the end-to-end phase for each propagation path prone to errors. Consequently, the imperfect phase knowledge at the IRS should be considered. The phase error is modeled using the von Mises distribution and the analysis is performed using the Sinusoidal Addition Theorem (SAT) to provide accurate results when the number of reflectors L ≤ 3, and the Central Limit Theorem (CLT) when L ≥ 4. The achieved results show that accurate phase estimation is critical for IRS based systems, particularly for a small number of reflecting elements. For example, the SER at 10-3 degrades by about 5 dB when the von Mises concentration parameter κ = 2 and L = 30, but the degradation for the same κ surges to 25 dB when L = 2. The air-to-air (A2A) channel for each propagation path is modeled as a single dominant line-of-sight (LoS) component, and the results are compared to the Rician channel. The obtained results reveal that the considered A2A model can be used to accurately represent the A2A channel with Rician fading.
... For A2G link, we assume a two-ray channel model, which includes the line-of-sight (LoS) path and the multipath with scattering components [38]. The LoS component accounts for the coherent sum of a very small number of stronger rays, while the multipath (scattered) component physically represents many weaker rays reflected or scattered from surrounding obstacles within the vicinity of the BS. ...
... The Rician factor of the AU channel is K A = 6 dB. The delays τ TX,k are randomly generated according to the onesided exponentially decreasing delay power spectrum [38], i.e., ...
Preprint
Full-text available
Integration of unmanned aerial vehicles (UAVs) into fifth generation (5G) and beyond 5G (B5G) cellular networks is an intriguing problem that has recently tackled a lot of interest in both academia and industry. An effective solution is represented by cellular-connected UAVs, where traditional terrestrial users coexist with flying UAVs acting as additional aerial users, which access the 5G/B5G cellular network infrastructure from the sky. In this scenario, we study the challenging application in which an UAV acting as aerial user (AU) and a static (i.e., fixed) terrestrial user (TU) are paired to simultaneously transmit their uplink signals to a ground base station (BS) in the same time-frequency resource blocks. In such a case, due to the highly dynamic nature of the UAV, the signal transmitted by the AU experiences both time dispersion due to multipath propagation effects and frequency dispersion caused by Doppler shifts. On the other hand, for a static ground network, frequency dispersion of the signal transmitted by TU is negligible and only multipath effects have to be taken into account. To decode the superposed signals at the BS by using finite-length data record, we propose a novel sky-ground (SG) nonorthogonal multiple access (NOMA) receiving structure that additionally exploits the different circularity/noncircularity and almost-cyclostationarity properties of the AU and TU by means of improved channel estimation and time-varying successive interference cancellation. Numerical results demonstrate the usefulness of the proposed SG uplink NOMA reception scheme in future 5G/B5G networks.
... For airplanes, typically lower frequency bands are used for longrange aeronautical communications, where the coverage may reach over 200 nautical miles [2], [3], [54], [55]. Due to the altitude of the airplane, often a LoS is observed [56], but the DRAFT 9 TABLE III: Summary of CSI estimation for the OFDM-based OTFS system with symbol-wise CP. ...
Article
Full-text available
The recently-developed orthogonal time frequency space (OTFS) modulation is capable of transforming the time-varying fading of the time-frequency (TF) domain into the time-invariant fading representations of the delay-Doppler (DD) domain. The OTFS system using orthogonal frequency-division multiplexing (OFDM) as inner core naturally requires the subcarrier spacing (SCS) Δ f to be larger than the maximum Doppler frequency ϑ max , i.e. Δ f > ϑ max , when perfect channel state information (CSI) knowledge is assumed. However, for the first time in literature, we explicitly demonstrate that the practical OFDM-based OTFS systems have to double their SCS in order to facilitate CSI estimation, requiring Δ f ′ = 2Δ f > 2ϑ max . In order to mitigate this loss, we propose a novel noncoherent OTFS system, which is capable of operating at Δ f > ϑ max . The major challenge in this context is the mitigation of the DD-domain interference without CSI. Against this background, we draw an analogy between the input-output model of OTFS and that of V-BLAST, where V-BLAST’s blind inter-antenna interference mitigation technique is invoked. Moreover, we propose to partition the DD-domain modulated symbols into groups, where space-time block coding is invoked in order to eliminate the DD-domain interference within each group. Our simulation results demonstrate that the proposed noncoherent OTFS is capable of substantially outperforming its coherent counterparts relying on CSI estimation.
... is the deterministic part of the Rician channel and H (d/r) a,r is the scattered component of the Rician channel. Typically, the Rician factor is affected by the altitude of the UAV [5], [28], [34], where a higher UAV is more likely experience a higher Rician factor, namely a stronger LoS component. Owing to the minimum safety separation distance, the transmit antennas on different drones experience uncorrelated fading, whilst the receive antennas deployed on URAVs are located at the same site. ...
Preprint
Full-text available
The emerging drone swarms are capable of carrying out sophisticated tasks in support of demanding Internet-of-Things (IoT) applications by synergistically working together. However, the target area may be out of the coverage of the ground station and it may be impractical to deploy a large number of drones in the target area due to cost, electromagnetic interference and flight-safety regulations. By exploiting the innate \emph{agility} and \emph{mobility} of unmanned aerial vehicles (UAVs), we conceive a mobile relaying-assisted drone swarm network architecture, which is capable of extending the coverage of the ground station and enhancing the effective end-to-end throughput. Explicitly, a swarm of drones forms a data-collecting drone swarm (DCDS) designed for sensing and collecting data with the aid of their mounted cameras and/or sensors, and a powerful relay-UAV (RUAV) acts as a mobile relay for conveying data between the DCDS and a ground station (GS). Given a time period, in order to maximize the data delivered whilst minimizing the delay imposed, we harness an ϵ\epsilon-multiple objective genetic algorithm (ϵ\epsilon-MOGA) assisted Pareto-optimization scheme. Our simulation results demonstrate that the proposed mobile relaying is capable of delivering more data. As specific examples investigated in our simulations, our mobile relaying-assisted drone swarm network is capable of delivering 45.38%45.38\% more data than the benchmark solutions, when a stationary relay is available, and it is capable of delivering 26.86%26.86\% more data than the benchmark solutions when no stationary relay is available.
... is the deterministic part of the Rician channel and H (d/r) a,r is the scattered component of the Rician channel. Typically, the Rician factor is affected by the altitude of the UAV [5], [28], [34], where a higher UAV is more likely experience a higher Rician factor, namely a stronger LoS component. Owing to the minimum safety separation distance, the transmit antennas on different drones experience uncorrelated fading, whilst the receive antennas deployed on URAVs are located at the same site. ...
Article
Full-text available
The emerging drone swarms are capable of carrying out sophisticated tasks in support of demanding Internet-of-Things (IoT) applications by synergistically working together. However, the target area may be out of the coverage of the ground station and it may be impractical to deploy a large number of drones in the target area due to cost, electromagnetic interference and flight-safety regulations. By exploiting the innate agility and mobility of unmanned aerial vehicles (UAVs), we conceive a mobile relaying-assisted drone swarm network architecture, which is capable of extending the coverage of the ground station and enhancing the effective end-to-end throughput. Explicitly, a swarm of drones forms a data-collecting drone swarm (DCDS) designed for sensing and collecting data with the aid of their mounted cameras and/or sensors, and a powerful relay-UAV (RUAV) acts as a mobile relay for conveying data between the DCDS and a ground station (GS). Given a time period, in order to maximize the data delivered whilst minimizing the delay imposed, we harness an-multiple objective genetic algorithm (-MOGA) assisted Pareto-optimization scheme. Our simulation results demonstrate that the proposed mobile relaying is capable of delivering more data. As specific examples investigated in our simulations, our mobile relaying-assisted drone swarm network is capable of delivering 45.38% more data than the benchmark solutions, when a stationary relay is available, and it is capable of delivering 26.86% more data than the benchmark solutions when no stationary relay is available.
... During the en-route phase, the A2G scattered components are typically not isotropically distributed. For example, in [8], the scatters were assumed to be uniformly distributed within a beamwidth of β = 3.5 • . ...
Article
Full-text available
To provide seamless coverage during all flight phases, aeronautical communications systems (ACS) have to integrate space-based, air-based, as well as ground-based platforms to formulate aviation-oriented space-air-ground integrated networks (SAGINs). In continental areas, L-band aeronautical broadband communications (ABC) are gaining popularity for supporting air traffic management (ATM) modernization. However, L-band ABC faces the challenges of spectrum congestion and severe interference due to the legacy systems. To circumvent these, we propose a novel multiple-antenna aided L-band ABC paradigm to tackle the key issues of reliable and high-rate air-to-ground (A2G) transmissions. Specifically, we first introduce the development roadmap of the ABC. Furthermore, we discuss the peculiarities of the L-band ABC propagation environment and the distinctive challenges of the associated multiple-antenna techniques. To overcome these challenges, we propose an advanced multiple-antenna assisted L-band ABC paradigm from the perspective of channel estimation, reliable transmission, and multiple access. Finally, we shed light on the compelling research directions of the aviation component of SAGINs.
... During the en-route phase, the A2G scattered components are typically not isotropically distributed. For example, in [8], the scatters were assumed to be uniformly distributed within a beamwidth of β = 3.5 • . ...
Preprint
Full-text available
To provide seamless coverage during all flight phases, aeronautical communications systems (ACS) have to integrate space-based, air-based, as well as ground-based platforms to formulate aviation-oriented space-air-ground integrated networks (SAGINs). In continental areas, L-band aeronautical broadband communications (ABC) are gaining popularity for supporting air traffic management (ATM) modernization. However , L-band ABC faces the challenges of spectrum congestion and severe interference due to the legacy systems. To circumvent these, we propose a novel multiple-antenna aided L-band ABC paradigm to tackle the key issues of reliable and high-rate air-to-ground (A2G) transmissions. Specifically, we first introduce the development roadmap of the ABC. Furthermore, we discuss the peculiarities of the L-band ABC propagation environment and the distinctive challenges of the associated multiple-antenna techniques. To overcome these challenges, we propose an advanced multiple-antenna assisted L-band ABC paradigm from the perspective of channel estimation, reliable transmission, and multiple access. Finally, we shed light on the compelling research directions of the aviation component of SAGINs.
... From the literature review, it is manifested that evolutionary approaches have been applied to optimise the route of an AV [10,13,40]. Furthermore, references [23,33] and [48] prove that effort is being made to improve link performance. Our previous work [18] proposes a novel EA that maximises A2G channel performance based on a channel model's output. ...
Article
Full-text available
The urban air mobility market is expected to grow constantly due to the increased interest in new forms of transportation. Managing aerial vehicles fleets, dependent on rising technologies such as artificial intelligence and automated ground control stations, will require a solid and uninterrupted connection to complete their trajectories. A path planner based on evolutionary algorithms to find the most suitable route has been previously proposed by the authors. Herein, we propose using particle swarm and hybrid optimisation algorithms instead of evolutionary algorithms in this work. The goal of speeding the route planning process and reducing computational costs is achieved using particle swarm and direct search algorithms. This improved path planner efficiently explores the search space and proposes a trajectory according to its predetermined goals: maximum air-to-ground quality, availability, and flight time. The proposal is tested in different situations, including diverse terrain conditions for various channel behaviours and no-fly zones.
... The SNR saving of joint OBEPPA and joint OBEPPL at 10 −1 is around 3 dB. In the future, this work can be extended for en-route channel to address the issues discussed in [49] with suitable equalization techniques [50]. The performance of these methods in LDACS RL can be analyzed. ...
Article
Full-text available
Interference mitigation in L-band digital aeronautic communication systems from legacy users is vital due to stringent safety requirements and steady-state increase in air traffic. This paper proposes an L-band digital aeronautic communication systems receiver prototype that employs nonlinear operations to reduce the interference from the prime interference contributor distance measuring equipment. The knowledge of genie-aided estimator and optimum Bayesian estimator is utilized to propose improved and low complexity nonlinear devices, such as a genie-aided estimator enhanced pulse peak attenuator, genie-aided estimator enhanced pulse peak limiter, joint genie-aided estimator enhanced pulse peak attenuator, joint genie-aided estimator enhanced pulse peak limiter, optimum Bayesian estimator enhanced pulse peak attenuator, optimum Bayesian estimator enhanced pulse peak limiter, joint optimum Bayesian estimator enhanced pulse peak attenuator and joint optimum Bayesian estimator enhanced pulse peak limiter. The performance of the proposed methods is compared with the classical pulse blanking in terms of the received bit error rate for different signal-to-noise ratios. The proposed genie-aided estimator enhanced methods exhibited SNR saving in the range of 2 to 2.5 dB at a bit error rate of 10−1. At the same BER, the proposed optimum Bayesian estimator enhanced methods achieved SNR saving in the range of 2.5 to 3 dB.
... where λ 0 = c 0 /f 0 is the wavelength, c 0 = 3 · 10 8 m/s denotes the light speed, and d TX is the distance between TX and the CU, whereas the delays τ TX,k are randomly generated according to the one-sided exponentially decreasing delay power spectrum [64], i.e., ...
Preprint
Full-text available
Unmanned aerial vehicles (UAVs) can be integrated into wireless sensor networks (WSNs) for smart city applications in several ways. Among them, a UAV can be employed as a relay in a “store-carry and forward” fashion by uploading data from ground sensors and metering devices and, then, downloading it to a central unit. However, both the uploading and downloading phases can be prone to potential threats and attacks. As a legacy from traditional wireless networks, the jamming attack is still one of the major and serious threats to UAV-aided communications, especially when also the jammer is mobile, e.g., it is mounted on a UAV or inside a terrestrial vehicle. In this paper, we investigate anti-jamming communications for UAV-aided WSNs operating over doubly-selective channels in the downloading phase. In such a scenario, the signals transmitted by the UAV and the malicious mobile jammer undergo both time dispersion due to multipath propagation effects and frequency dispersion caused by their mobility. To suppress high-power jamming signals, we propose a blind physical-layer technique that jointly detects the UAV and jammer symbols through serial disturbance cancellation based on symbol-level post-sorting of the detector output. Amplitudes, phases, time delays, and Doppler shifts – required to implement the proposed detection strategy – are blindly estimated from data through the use of algorithms that exploit the almost-cyclostationarity properties of the received signal and the detailed structure of multicarrier modulation format. Simulation results corroborate the anti-jamming capabilities of the proposed method, for different mobility scenarios of the jammer.
... where λ 0 = c 0 /f 0 is the wavelength, c 0 = 3 · 10 8 m/s denotes the light speed, and d TX is the distance between TX and the CU, whereas the delays τ TX,k are randomly generated according to the one-sided exponentially decreasing delay power spectrum [64], i.e., ...
Article
Unmanned aerial vehicles (UAVs) can be integrated into wireless sensor networks (WSNs) for smart city applications in several ways. Among them, a UAV can be employed as a relay in a “store-carry and forward” fashion by uploading data from ground sensors and metering devices and, then, downloading it to a central unit. However, both the uploading and downloading phases can be prone to potential threats and attacks. As a legacy from traditional wireless networks, the jamming attack is still one of the major and serious threats to UAV-aided communications, especially when also the jammer is mobile, e.g., it is mounted on a UAV or inside a terrestrial vehicle. In this paper, we investigate anti-jamming communications for UAV-aided WSNs operating over doubly-selective channels in the downloading phase. In such a scenario, the signals transmitted by the UAV and the malicious mobile jammer undergo both time dispersion due to multipath propagation effects and frequency dispersion caused by their mobility. To suppress high-power jamming signals, we propose a blind physical-layer technique that jointly detects the UAV and jammer symbols through serial disturbance cancellation based on symbol-level post-sorting of the detector output. Amplitudes, phases, time delays, and Doppler shifts – required to implement the proposed detection strategy – are blindly estimated from data through the use of algorithms that exploit the almost-cyclostationarity properties of the received signal and the detailed structure of multicarrier modulation format. Simulation results corroborate the anti-jamming capabilities of the proposed method, for different mobility scenarios of the jammer.
... Finally, we can observe that OTFS is indeed insensitive to the magnitude of the Doppler shifts, while the performance of OFDM degrades significantly even under small-to-moderate Doppler values if the number of subcarriers increases. Therefore, OTFS is effectively a good candidate for high-mobility systems in rural environments (e.g., high speed trains [48]) or aerial environments (e.g., UAVs [49]), where Doppler shifts may be large, and the propagation channel contains typically the line-of-sight and a few other reflection components (e.g., ground reflection, hills, large buildings), and it is therefore sparse in the Doppler-delay domain. ...
Article
Full-text available
Many recent works in the literature declare that Orthogonal Time-Frequency-Space (OTFS) modulation is a promising candidate technology for high mobility communication scenarios. However, a truly fair comparison with its direct concurrent and widely used Orthogonal Frequency-Division Multiplexing (OFDM) modulation has not yet been provided. In this paper, we present such a fair comparison between the two digital modulation formats in terms of achievable communication rate. In this context, we explicitly address the problem of channel estimation by considering, for each modulation, a pilot scheme and the associated channel estimation algorithm specifically adapted to sparse channels in the Doppler-delay domain, targeting the optimization of the pilot overhead to maximize the overall achievable rate. In our achievable rate analysis we consider also the presence of a guard interval or cyclic prefix. The results are supported by numerical simulations, for different time-frequency selective channels including multiple scattering components and under non-perfect channel state information resulting from the considered pilot schemes. This work does not claim to establish in a fully definitive way which is the best modulation format, since such choice depends on many other features which are outside the scope of this work (e.g., legacy, intellectual property, ease and know-how for implementation, and many other criteria). Nevertheless, we provide the foundations to properly compare multi-carrier communication systems in terms of their information theoretic achievable rate potential, within meaningful and sensible assumptions on the channel models and on the receiver complexity (both in terms of channel estimation and in terms of soft-output symbol detection).
... where λ 0 = c 0 /f 0 is the wavelength, c 0 = 3 · 10 8 m/s denotes the light speed, and d TX is the distance between TX and the CU, whereas the delays τ TX,k are randomly generated according to the one-sided exponentially decreasing delay power spectrum [64], i.e., ...
Preprint
Full-text available
Unmanned aerial vehicles (UAVs) can be integrated into wireless sensor networks (WSNs) for smart city applications in several ways. Among them, a UAV can be employed as a relay in a “store-carry and forward” fashion by uploading data from ground sensors and metering devices and, then, downloading it to a central unit. However, both the uploading and downloading phases can be prone to potential threats and attacks. As a legacy from traditional wireless networks, the jamming attack is still one of the major and serious threats to UAV-aided communications, especially when also the jammer is mobile, e.g., it is mounted on a UAV or inside a terrestrial vehicle. In this paper, we investigate anti-jamming communications for UAV-aided WSNs operating over doubly-selective channels in the downloading phase. In such a scenario, the signals transmitted by the UAV and the malicious mobile jammer undergo both time dispersion due to multipath propagation effects and frequency dispersion caused by their mobility. To suppress high-power jamming signals, we propose a blind physical-layer technique that jointly detects the UAV and jammer symbols through serial disturbance cancellation based on symbol-level post-sorting of the detector output. Amplitudes, phases, time delays, and Doppler shifts – required to implement the proposed detection strategy – are blindly estimated from data through the use of algorithms that exploit the almost-cyclostationarity properties of the received signal and the detailed structure of multicarrier modulation format. Simulation results corroborate the anti-jamming capabilities of the proposed method, for different mobility scenarios of the jammer.
... By contrast, in our case, the channel between the airliner and the user is dominated by the LoS component due to the airliner's altitude. Typically the aeronautical model for such a scenario has a strong LoS path and a much weaker NLoS ground-reflected path [54]. Hence using a TPC vector relying on the estimated channel matrix is counterproductive. ...
Article
Full-text available
A high-rate yet low-cost air-to-ground (A2G) communication backbone is conceived for integrating the space and terrestrial network by harnessing the opportunistic assistance of the passenger planes or high altitude platforms (HAPs) as mobile base stations (BSs) and millimetre wave communication. The airliners act as the network-provider for the terrestrial users while relying on satellite backhaul. A null-steered beamforming technique relying on a large-scale planar array is used for transmission by the airliner/HAP for achieving a high directional gain, hence minimizing the interference between the users. Furthermore, approximate spectral efficiency (SE) and area spectral efficiency (ASE) expressions are derived and quantified for diverse system parameters.
... A good A2G channel model should reflect the latter mentioned channel characteristics in a realistic manner. In general, high altitude SISO-A2G propagations are mainly represented on the basis of a two-ray model [24], [25] or stochastic model [19], [26], [27], [28], [29], [30]. Furthermore, among the accepted MIMO channel modeling options, Geometry-Based Stochastic Channel Model (GBSCM) have gained much attention due to their capability of providing an angular response in a direct way enabling a straightforward computation of spatial and temporal correlation properties [31]. ...
Article
Full-text available
Increasing the availability of Unmanned Aerial Vehicles (UAV’s) platforms leads to a variety of applications for aerial exploration, surveillance, and transport. Many of these applications rely on the communication between the UAV and the ground receiver which is subjected to high mobility that may lead to restrictions on link connectivity and throughput. In order to design high throughput and efficient communication schemes for these scenarios, a deep understanding of the communication channel behavior is required, especially taking into account measurement data from flight experiments. Channel propagation in urban environments involves diffraction effects which modify the Line-of-Sight (LoS) contribution of the total received signal, especially when the receiver is located on the ground. This process leads to scenarios where Multiple-Input Multiple-Output (MIMO) signal processing can take advantage from this situation. In this context, the goal of this paper is to study the diffraction effects of the LoS component through spatial correlation metrics of the signal. To accomplish this, we propose the use of a geometric stochastic technique to model the channel behavior which lies between High Altitude Platforms (HAP) and terrestrial link communications.
... Initially, four test models were implemented based on the results of [4,5]. These simplified models did not take the various possible scenarios and flight conditions into account, as well as the angular characteristics of the multipath communication channel and the radiation patterns of the used antenna systems. ...
Article
Full-text available
The development and the main technical characteristics of a software-hardware complex (SHC) intended for the design and field-model testing of broadband radio electronic systems (RES) for radio communication, radar, and navigation of high-speed objects are presented. The software-hardware complex provides generation and processing of signals with a carrier frequency of up to 6 GHz and a bandwidth of up to 200 MHz, a refresh rate of the channel impulse response up to 60 kHz, and a maximum rays delay in channel models up to 10 μs. The complex allows one to study radio communication systems with objects that move with a relative speed difference of up to 5 M. The software part of the complex includes models of the signal formation and processing in the receiving and transmitting equipment of the radio electronic device, as well as models of radio channels for target scenarios of using the developed RES. The hardware part of the SHC is a set of digital, digital-to-analog, and analog-to-digital modules that allow full-scale and model testing of RES and their blocks in real time. Examples of studying the characteristics of a modern broadband aviation radio communication system with high-speed objects under conditions of signal multipath propagation are given. The application of the SHC may decrease the time of full-scale and model testing of RES by approximately 65 times compared to direct computer simulation.
Preprint
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 4 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 Mbps data rate when the communication distance is less than 25\,km.
Article
The high Doppler effect and severe multipath delay are among the major challenges in air-to-ground (A2G) communication scenarios, where the maximum multipath delay may exceed the duration of one or more orthogonal frequency division multiplexing (OFDM) symbols, resulting in severe inter-symbol interference (ISI). In this letter, we propose a new frame structure constituted by grouped training sequences (GTSs), OFDM symbols and guard interval (GI). Specifically, two GTSs are respectively prefixed and postfixed to several cyclic-prefix-free OFDM symbols for Doppler frequency offset (DFO) and multipath delay estimation. Moreover, a two-path serial ISI cancellation (TSIC) algorithm is designed to recover the transmitted signal. Compared with existing algorithms, the new scheme can reduce errors and increase the spectral efficiency of the system.
Article
У цій статті проаналізовано різні класи і типи існуючих безпілотних літальних апаратів. Обговорюються численні переваги безпілотних літальних апаратів. Безпілотні літальні апарати (БПЛА) все частіше використовуються в різних секторах, включаючи військову сферу, логістику. Навігація є однією з найважливіших систем БПЛА, що забезпечує автономне пересування та виконання завдань. Актуальність теми полягає в тому, що вона спрямована на вирішення важливої проблеми при проектуванні та експлуатації БПЛА: підвищення точності визначення навігаційних параметрів навігаційним обладнанням БПЛА за рахунок комплексної обробки навігаційної інформації від інерціальної навігації та супутникових навігаційних систем.
Article
This article is the second part of a two-part manuscript addressing the DME/TACAN multipath impact on the future airborne GNSS L5/E5a receivers. Part I developed the analytical carrier-to-noise-ratio degradation model due to DME/TACAN considering multipath, in the presence of a temporal blanker. Part II introduces an air-ground channel model, that is wide band, geometry based and combines deterministic and statistical parts. The model includes an Okumura-Hata path loss for computing the scatterer illumination, an analytical formula for the additional delay and the mathematical expression of the scattered power. Given the very large number of illuminated scatterers to be considered for an Air-Ground scenario, a statistical simplification of the Physical Optics approach is introduced to simplify the derivation of the scattered powers. The propagation channel model and the mathematical model of the carrier-to-noise-ratio degradation are applied to two low-altitude operational hot-spots, JALTO (Pennsylvania, United-States) and TIXAK (Frankfurt, Germany). It is shown that only a few illuminated scatterers generate a scattered power above the blanking threshold and that the additional carrier-to-noise-ratio degradation generated by the DME/TACAN multipath only is smaller than 0.52 dB.
Article
The family of aeronautical communication systems is considered as one of the core technologies for the beyond-the-fifth-generation (B5G) networks, thus attracting rapidly increasing attention from both industry and academia. In this paper, a new multiple-input multiple-output (MIMO) precoding scheme is proposed for aeronautical communication systems, where the transmit power for the aerial user equipment (UE) approaching the target cell is maximized based on the direction information. Specifically, we first transform the precoding optimization problem into a linear programming problem, and then develop two algorithms to derive the precoders for two transmission modes, namely the multi-stream and single-stream transmissions. For the multi-stream case, an algorithm based on manifold optimization is proposed, which guarantees the equal power allocation for each antenna. For the single-stream case, we derive a precoder by a numerically stable algorithm that extends the Newton-Raphson method. Simulation results show that the proposed precoding schemes can improve the link performance of the UEs with known directions, while ensuring that the performance of the UEs with unknown directions can still be close to that achievable by conventional schemes.
Article
We propose a low-complexity channel estimation method for Orthogonal Time Frequency Space (OTFS) modulation based systems. Two important aspects of OTFS modulation, namely, (i) fine delay-Doppler (DD) resolution which results in path separation and, (ii) the separability of the effective DD domain channel gain expression into delay domain and Doppler domain terms, are used to propose an iterative channel estimation method which separately estimates the delay, Doppler shift and the channel gain for each channel path. The proposed estimation does not require matrix inversion and therefore has lower complexity when compared to other known methods. The proposed method is shown to achieve a normalized mean square estimation error (NMSE) performance better than other methods.
Article
The recent progress in unmanned aerial vehicles (UAV) technology has significantly advanced UAV-based applications for military, civil, and commercial domains. Nevertheless, the challenges of establishing high-speed communication links, flexible control strategies, and developing efficient collaborative decision-making algorithms for a swarm of UAVs limit their autonomy, robustness, and reliability. Thus, a growing focus has been witnessed on collaborative communication to allow a swarm of UAVs to coordinate and communicate autonomously for the cooperative completion of tasks in a short time with improved efficiency and reliability. This work presents a comprehensive review of collaborative communication in a multi-UAV system. We thoroughly discuss the characteristics of intelligent UAVs and their communication and control requirements for autonomous collaboration and coordination. Moreover, we review various UAV collaboration tasks, summarize the applications of UAV swarm networks for dense urban environments and present the use case scenarios to highlight the current developments of UAV-based applications in various domains. Finally, we identify several exciting future research direction that needs attention for advancing the research in collaborative UAVs.
Preprint
Full-text available
The recent progress in unmanned aerial vehicles (UAV) technology has significantly advanced UAV-based applications for military, civil, and commercial domains. Nevertheless, the challenges of establishing high-speed communication links, flexible control strategies, and developing efficient collaborative decision-making algorithms for a swarm of UAVs limit their autonomy, robustness, and reliability. Thus, a growing focus has been witnessed on collaborative communication to allow a swarm of UAVs to coordinate and communicate autonomously for the cooperative completion of tasks in a short time with improved efficiency and reliability. This work presents a comprehensive review of collaborative communication in a multi-UAV system. We thoroughly discuss the characteristics of intelligent UAVs and their communication and control requirements for autonomous collaboration and coordination. Moreover, we review various UAV collaboration tasks, summarize the applications of UAV swarm networks for dense urban environments and present the use case scenarios to highlight the current developments of UAV-based applications in various domains. Finally, we identify several exciting future research direction that needs attention for advancing the research in collaborative UAVs.
Article
This paper aims to address the problem of providing internet connectivity to aircraft flying above the ocean without using satellite connectivity given that there is no ground network infrastructure in the ocean. Is it possible to guarantee a minimum flow rate to each aircraft flying over an ocean by forming an aeronautical ad hoc network and connecting that network to internet via a set of limited number of ground base stations at the coast as anchor points? We formulated the problem as mixed-integer-linear programming (MILP) to maximize the number of aircraft with flow data rate above a certain threshold. Since this is a multi-commodity flow problem and at least NP-complete, we propose a two-phase heuristic algorithm to efficiently form topology and assign flows to each aircraft by maximizing the minimum flow. The performance of the heuristic algorithm is evaluated over the North Atlantic Corridor, heuristic performs only 8% less than the optimal result with low densities. In high network densities, the connectivity percentage changes from 70% to 40% under 75 Mbps data rate threshold. Furthermore, the connectivity percentage is investigated for different network parameters such as altitude and compared with upper and lower bounds and a baseline algorithm.
Article
Modulation classification is a classical topic in the field of signal classification, and is of great significance in various applications including aeronautical communications. However, changes in the features of the signals transmitted through the Rician time-varying channels deteriorate the performance of modulation classification. In this study, a robust moment-based algorithm is proposed to counter the influence of the channels. The statistical correlation of the received samples are utilized for the estimation on the Rician factor. According to the derivation of the relationship between the moments of the transmitted samples and the received samples, the features utilized for classification are compensated mathematically. Finally, decision tree and random forest classifier are presented for classification. The estimation and classification performance of the proposed algorithm are analyzed for aeronautical en-route (EN) and arrival/takeoff (AT) channels through simulations. Meanwhile, real world signals of L-band digital aeronautical communication system (L-DACS1) are utilized for verification. The results show that our algorithm has high classification accuracy and low computational complexity.
Chapter
Unmanned aerial vehicles (UAVs) have stroked great interested both by the academic community and the industrial community due to their diverse military applications and civilian applications. Furthermore, UAVs are also envisioned to be part of future airspace traffic. The application functions delivery relies on information exchange among UAVs as well as between UAVs and ground stations (GSs), which further closely depends on aeronautical channels. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
Article
Full-text available
In this paper, a mathematical model of a communication channel with an unmanned aerial vehicle and taking into account the specifics of the locations of a ground communication point when determining the effects of refraction, diffraction and interference of electromagnetic waves is proposed. A meaningful statement of the problem based on the mathematical relationship between the energy parameters of the first transmission equation and the quality indicators (BER) of the second transmission equation has been formed. The main features of calculating the parameters of the first equation are to determine the rules for calculating the level of attenuation due to the influence of the earths surface. The calculation of attenuations for cases of removal of an unmanned aerial vehicle from a ground communication point within the areas of line of sight, partial shade and shadow has been clarified. The second transmission equation is based on the mathematical model of the Rice communication channel. With respect to the energy parameters and the selected communication quality indicator for the formed mathematical model, examples of graphical dependencies are given in the study of typical computational problems. With respect to the energy parameters and the selected communication quality indicator for the formed mathematical model, examples of graphical dependencies in the study of typical computational problems are given.
Article
A detailed assessment of the radiofrequency interference from terrestrial fixed service into aeronautical earth stations operating with geostationary satellite orbit networks in the fixed-satellite service is performed. We analyze the impact of the major physical, technical, operational, and regulatory parameters in the interference environment having multiple degrees of freedom to be considered. By performing exhaustive geometric computer simulations, we determine the statistical characteristics of the time-variant radiofrequency interference caused by multiple terrestrial fixed service transmitters using information of existing/registered fixed service stations in France. Subsequently, a stochastic channel model to predict the impact of the terrestrial interference using a higher order finite-state Markov process is developed. Balancing model accuracy and complexity, a reasonable vector quantization clustering algorithm is applied for the partitioning of the interference into representative channel states. For these channel states, we provide a method for scaling this model to different antenna sizes and flight velocities, to be used for development of interference mitigation measures and system design of aeronautical earth stations in motion operating in the 17.7–19.7 GHz frequency range.
Article
Full-text available
Establishing an instantaneous channel propagation model in aircraft engineering simulators is important for aircraft systems development. This paper investigates an instantaneous channel propagation modeling scheme with Compressive Sensing (CS) recovery and Electro-Magnetic (EM) interpolation for aeronautical communications systems to reduce the cost of flight experiments. Specifically, the system architecture introduces the proposed modeling process of the instantaneous aeronautical channel. The mathematical models are analyzed to show the sparsity of the aeronautical channel with a limited scattering environment. The channel modeling algorithm is detailed by explaining the CS algorithm and the EM interpolation scheme. The experimental results show the effectiveness of the proposed method. Most recovery relative errors between the recovering channel model and the real sampled channel responses are lower than 0.1, i.e., -10 dB. More than 75% of the sampling points can be reduced by the proposed method compared with the real flight experiments. Moreover, the proposed single-input single-output approach can also be applied in the potential aeronautical communications systems with multiple-input multiple-output transmission.
Article
A delay-Doppler robust spectrum sharing method is proposed for the unmanned aerial vehicle (UAV) and terrestrial systems by actively introducing the assistive slots (AS) in this work. With the aids of AS, the receiver in the UAV/terrestrial link can extract the delay-Doppler parameter of the signal, and hence further recover the desired signal. Inserting AS in frames introduces different possibilities of signals sampled at AS and non-AS points, and the UAV/terrestrial signal samples are differentiated from the compound signals by focusing on the energy gap among the samples. Since the signal sample differentiation and the delay-Doppler parameter extraction are receiver oriented, the effects of multipath and node mobility are included, and the signal recovery is free from the adverse impacts of delay and Doppler shifts. Analysis shows that although introducing AS is beneficial to recovering the UAV/terrestrial signal, the signal transmission efficiency suffers degradation. Therefore, the optimal AS ratio regarding the tradeoff between delay-Doppler parameter extraction accuracy and transmission efficiency is investigated. For the optimal AS ratio, the signal-to-interference ratio of the spectrum sharing system plays a key role under Rician/Rayleigh distributed terrestrial fading channels. The numerical results validate the effectiveness of the proposed scheme in comparison to the traditional methods.
Article
With the growing interest in providing internet access and cellular connectivity in the commercial aircraft, the compatibility between Air-to-Air (A2A) communications and current Air-to-Ground (A2G) macro-cellular communications is necessary to form an Aeronautical Ad hoc Network (AANet). Due to the typical features of airborne communications, such as high mobility, long transmission range and three-dimensional macro-cells, AANet is affected by intermittent links, which results in variant delayed data transmissions. To this end, we exploit a dynamic graph approach to model such an AANet with rapidly changing topology under a realistic airborne scenario. Targeting the problem of intermittent transmissions, by employing A2A, an AANet can bear three transmission modes: direct transmission, connected relay transmission and opportunistic transmission. To investigate the potential gain of A2A transmissions in terms of the end-to-end data flow transmission delay and the data traffic amount, we formulate an integer non-linear programming problem that minimizes the average end-to-end delay from Internet Gateways (IGWs) on shore to the aircraft receivers through multiple options of the transmission modes. Through solving this minimization problem based on the realistic dynamic graph model, the tradeoffs between the end-to-end transmission delay and other key network factors related to AANet formation and resource allocation can be obtained without much compromise on the transmission delay. The results show that the average end-to-end delay of the AANet is comparable to the direct transmission delay when having a tradeoff with the data traffic amount, buffer size and the spectrum sharing.
Article
The statistical characteristics of the fields and signals in the reception of radio frequencies by a moving vehicle are deduced from a scattering propagation model. The model assumes that the field incident on the receiver antenna is composed of randomly phased azimuthal plane waves of arbitrary azimuth angles. Amplitude and phase distributions and spatial correlations of fields and signals are deduced, and a simple direct relationship is established between the signal amplitude spectrum and the product of the incident plane waves' angular distribution and the azimuthal antenna gain. The coherence of two mobile-radio signals of different frequencies is shown to depend on the statistical distribution of the relative time delays in the arrival of the component waves, and the coherent bandwidth is shown to be the inverse of the spread in time delays. Wherever possible theoretical predictions are compared with the experimental results. There is sufficient agreement to indicate the validity of the approach. Agreement improves if allowance is made for the nonstationary character of mobile-radio signals.
Article
The computation of the tap gains of the discrete-time representation of a slowly time-varying multipath channel is investigated. Assuming the channel is wide-sense stationary with uncorrelated scattering (WSSUS), a known Monte Carlo based method approximating the given scattering function (which fully determines the WSSUS channel) is extended by including filtering and sampling. The result is a closed-form solution for the tap gains. This allows the efficient simulation of the continuous-time channel with, e.g., only one sample per symbol, and without explicit digital filtering
Article
This paper is concerned with characterizing the link between an airplane and a satellite. Attention is focused on the effect of indirect paths scattered from the surface of the earth. Applicable propagation-theoretic and system function-theoretic work is reviewed and integrated. Some new and some known expressions for channel correlation functions are presented for the "steepest descent" channel model.
Article
One of the fundamental technical problems in aeronautical digital communications is that of multipath propagation between aircraft and ground terminal. This paper examines in detail a model of the received multipath signal that is useful for application of modern detection and estimation theories. The model treats arbitrary modulation and covers the selective and nonselective cases. The necessarily nonstationary statistics of the received signal are determined from the link geometry and the surface roughness parameters via a Kirchhoff solution. Use of the model in solving detection and estimation problems is outlined. Results of a flight experiment are presented and compared to a digital simulation for verification of the model.
Article
This paper is concerned with various aspects of the characterization of randomly time-variant linear channels. At the outset it is demonstrated that time-varying linear channels (or filters) may be characterized in an interesting symmetrical manner in time and frequency variables by arranging system functions in (timefrequency) dual pairs. Following this a statistical characterization of randomly time-variant linear channels is carried out in terms of correlation functions for the various system functions. These results are specialized by considering three classes of practically interesting channels. These are the wide-sense stationary (WSS) channel, the uncorrelated scattering (US) channel, and the wide-sense stationary uncorrelated scattering (WSSUS) channel. The WSS and US channels are shown to be (time-frequency) duals. Previous discussions of channel correlation functions and their relationships have dealt exclusively with the WSSUS channel. The point of view presented here of dealing with the dually related system functions and starting with the unrestricted linear channels is considerably more general and places in proper perspective previous results on the WSSUS channel. Some attention is given to the problem of characterizing radio channels. A model called the Quasi-WSSUS channel is presented to model the behavior of such channels. All real-life channels and signals have an essentially finite number of degrees of freedom due to restrictions on time duration and bandwidth. This fact may be used to derive useful canonical channel models with the aid of sampling theorems and power series expansions. Several new canonical channel models are derived in this paper, some of which are dual to those of Kailath.
Conference Paper
Although there is a variety of system design proposals for aeronautical satellite communications, only a few field trials have been accomplished to investigate the behaviour of the aeronautical satellite transmission channel. The German Aerospace Research Establishment (DFVLR) finished in May 86 an extensive test program to provide necessary information for a system design. Over one thousand minutes of useable test signals could be recorded. With these recordings a detailed statistical evaluation had been performed.
Conference Paper
The aeronautical mobile radio channel is analyzed. A stochastic model for the channel is proposed in terms of the transmission coefficient. The power spectrum and the correlation functions are derived for cases of practical interest. The model is useful for predicting the error rate performance of digital modulation techniques. The results from a flight test showed the validity of the proposed model
Article
The statistical properties of radio propagation between a mobile unit and a base-station terminal are derived. The power spectrum of the transmission coefficient in the multipath medium is used to determine probability distributions of amplitude and phase, correlations of fields versus time and space at mobile and base stations, level-crossing rates and durations of fades, and random frequency modulation. Duality between the power spectrum and density of time delays is shown. The correlations versus frequency and the coherence bandwidth then follow from the density of time delays. The performance of standard diversity systems is then predicted. There is a review of results previously presented by Clarke [1], however, the derivations given herein utilize expressions of the power spectrum rather than expressions of the component waves. The power-spectral approach, used throughout, allows direct application of previous statistical analyses, particularly those of Rice [2].
Experimental and theoretical field strength evaluation on VHF channel for aeronautical mobiles AMCP Doc
  • B Roturier
B. Roturier et al., " Experimental and theoretical field strength evaluation on VHF channel for aeronautical mobiles, " AMCP Doc. AMCP/WG-D/7-WP/58, Madrid, Spain, Apr. 1997.
Mod-eling of multipath and ducting effects in VHF propagation channel for aeronautical mobiles, " AMCP doc
  • B Chateau
  • B Roturier
  • B Souny
  • P Combes
  • H Chevalier
B. Chateau, B. Roturier, B. Souny, P. Combes, and H. Chevalier, " Mod-eling of multipath and ducting effects in VHF propagation channel for aeronautical mobiles, " AMCP doc. AMCP/WG-D/7-WP/27, Madrid, Spain, Apr. 1997.
Channel sounding measurements in the VHF A/G radio communications channel AMCP doc
  • G Dyer
  • T G Gilbert
G. Dyer and T. G. Gilbert, " Channel sounding measurements in the VHF A/G radio communications channel, " AMCP doc. AMCP/WG-D/8-WP/19, Oberpfaffenhofen, Germany, Dec. 1997.
Modeling of multipath and ducting effects in VHF propagation channel for aeronautical mobiles
  • B Chateau
  • B Roturier
  • B Souny
  • P Combes
  • H Chevalier
B. Chateau, B. Roturier, B. Souny, P. Combes, and H. Chevalier, "Modeling of multipath and ducting effects in VHF propagation channel for aeronautical mobiles," AMCP doc. AMCP/WG-D/7-WP/27, Madrid, Spain, Apr. 1997.
Aviation System Performance Standards for Advanced VHF Digital Data Communications Incl. Compatibility with Digital Voice Techniques
  • Signal-In-Space Min
Microwave Mobile Communications
  • W C Jakes
W. C. Jakes, Ed., Microwave Mobile Communications. New York: Wiley, 1974.
Channel sounding measurements in the VHF A/G radio communications channel
  • G Dyer
  • T G Gilbert
G. Dyer and T. G. Gilbert, "Channel sounding measurements in the VHF A/G radio communications channel," AMCP doc. AMCP/WG-D/8-WP/19, Oberpfaffenhofen, Germany, Dec. 1997.