High Altitude Platforms Communication Research Articles

A Wideband Non-Stationary 3D GBSM for HAP-MIMO Communication Systems at Millimeter-Wave Bands

High-altitude platforms (HAPs) are considered to be the most important equipment for next-generation wireless communication technologies. In this paper, we investigate the channel characteristics under the configurations of massive multiple-input multiple-output (MIMO) space and large bandwidth at millimeter-wave (mmWave) bands, along with the moving essence of the HAP and ground terminals. A non-stationary three-dimensional (3D) geometry-based stochastic model (GBSM) is proposed for a HAP communication system. We use a cylinder-based geometric modeling method to construct the channel and derive the channel impulse response (CIR). Additionally, the birth–death process of the scatterers is enclosed using the Markov process. Large-scale parameters such as free space loss and rainfall attenuation are also taken into consideration. Due to the relative motion between HAP and ground terminals, the massive MIMO space, and the wide bandwidth in the mmWave band, the channel characteristics of HAP exhibit non-stationarities in time, space, and frequency domains. By deriving the temporal auto-correlation function (ACF), we explore the non-stationarity in the time domain and the impact of various parameters on the correlations across the HAP-MIMO channels. The spatial cross-correlation function (CCF) for massive MIMO scenarios, and the frequency correlation function (FCF) in the mmWave bands are also considered. Moreover, we conduct simulation research using MATLAB. Simulation results show that the theoretical results align well with the simulation results, and this highlights the fact that the constructed 3D GBSM can characterize the non-stationary characteristics of HAP-MIMO channels across the time, space, and frequency domains.

Investigating the effect of High Altitude Platform Positioning on Latency and Coverage of 4G Cellular Systems

Wireless communication technologies are rapidly being adopted and developed by countries all over the world as a strategy for sustaining a digital economy. This has proven very useful for economic recovery from the crises brought about by the COVID-19 pandemic of the year 2020. The latency and coverage area of a wireless network are two major areas that are always seeking improvement. The High Altitude Platform communication technology can provide improvement in speed and coverage area for 4G cellular systems. This work investigated the effect of positioning High Altitude Platforms on the latency and coverage of 4G cellular Systems. A quantitative approach was used in the methodology of this paper. A HAP model showing a single platform flying in a circular trajectory over Base Transceiver Stations BTSs and serving as a relay mobile station was presented. A detailed simulation algorithm for the HAP and results for the simulation were given. Results showed that using the HAP as a relay mobile station in a network can give a latency reduction of up to 58.9%. Also, the altitude of the HAP directly affects the angle of reception which was found to improve the coverage.

An Efficient HAPS Cross-Layer Design to Mitigate COVID-19 Consequences

This paper proposes a new cross-layer communication system for the provision of Internet services and applications to mitigate the negative impacts of COVID-19, due to which the massive online demands are affecting the current communication systems’ infrastructures and capabilities. The system requirements and model are investigated where it utilizes high-altitude platform (HAP) for fast and efficient connectivity provision to bridge the communication infrastructure gap in the current pandemic. The HAP is linked to the main server or gateway station located on ground and can provide communication narrow beams towards isolated areas which suffer from poor terrestrial radio coverage or lack of communication infrastructure. The vital e-learning applications using Internet services provision from the proposed HAP system are described and modelled including system adaptation parameters such as the application and physical layers to control the data rates of different e-learning applications and the overall cell data rate. On the other hand, the provision of high-speed Internet services from the proposed system is supported by using adaptive antenna arrays onboard HAP which provides high-gain beams to achieve the required high-quality transmission data rates at the student premises and provides the capability of coverage cell area adaptation for load balancing. The concentric circular antenna arrays with tapered feeding are proposed in this adaptive antenna system to control the cell mainlobe gain and reduce the out-of-coverage radiation as well. In addition, the system feasibility has been proved in two coverage scenarios including single-beam and multibeam HAP communications.

Aerial RIS-Assisted High Altitude Platform Communications

We optimize the deployment of an aerial reconfigurable intelligent surface (ARIS) to assist the high altitude platform (HAP) downlink transmission when the direct link is blocked. Specifically, we maximize the received signal-to-noise ratio (SNR) of the ground users by jointly optimizing the trajectory and the phase-shift of the ARIS with the consideration of the unknown movement of HAP, which is caused by the changes in the stratospheric wind and air density. Due to the non-convex nature of the formulated optimization problem, we decouple the optimization problem and propose an alternative two-stage optimization. By proving that the movement of the HAP follows a finite state Markov stochastic process, we first learn the optimal ARIS trajectory via model-free reinforcement learning, and then adjust the optimal phase-shift of the ARIS, alternately. Next, the convergence of the proposed algorithm is analyzed based on the obtained upper bound of the accumulated reward. The numerical results show substantial performance gain of HAP communications with the optimized ARIS assistance.

Spatial-polarization diversity HAP-MIMO transmission system for emergency high-capacity mobile communications

The deployment of high-altitude platforms (HAPs) as an emergency communication system is a cost-effective method to deal with the decrease in channel capacity caused by shadows or multipath fading at low elevation angles. This study proposes a 4 × 4 multiple-input multiple-output (MIMO) scheme that employs spatial and polarization diversity to improve the channel capacity for HAP communication systems. This scheme utilizes the advantages of HAP size to install two pairs of dual-polarized antennas between HAP and mobile terminals to form a 4 × 4 spatial-polarized diversity MIMO system to counteract shadows and multipath fading. The polarization and spatial correlation matrices are obtained through the reasonable expansion of a 2 × 2 polarized parametric or spatial geometry MIMO channel model. Simulation results show that the proposed 4 × 4 MIMO transmission scheme can effectively improve the channel capacity by 1.5 times compared with the existing satellite 2 × 2 dual-polarization MIMO system at low elevation angles under typical scenarios.

A 3-D GBSM Based on Isotropic and Non-Isotropic Scattering for HAP-MIMO Channel

A 3-D geometry-based stochastic model (GBSM) based on two cylinders is proposed for high altitude platform (HAP) communication systems. The proposed 3-D GBSM uses the volume of inner cylinder to model isotropic scattering environment, and that between the inner cylinder and the outer cylinder to model non-isotropic scattering environment. In this letter, the time-variant parameters, including distances between the scatterers and receiver, azimuth angle of departure, and elevation angle of departure (EAOD), are investigated for HAP multiple-input multiple-output (MIMO) channel. The proposed model is validated by the spatial correlation function of measurement results, and the numerical results also demonstrate that the proposed 3-D GBSM with time-varying parameters is applicable to describe the 3-D HAP-MIMO channel.

High-speed and Long-reach Hybrid AMI–WDM–PI Inter-satellite Communication System

AbstractIn the current context of high-altitude platform communication system, inter-satellite communication is remarkable and highly effective. The present work aims to develop an integrated data transmission system incorporating alternate mark inversion, wavelength-division multiplexing, and polarization interleaving scheme for transmitting data of eight channels, each carrying 20 Gbps data over inter-satellite link of 5,000 km. The performance of the integrated data transmission of 160 Gbps data up to 5,000 km will be evaluated by means of signal-to-noise ratio, total received power, and eye diagram.

SC-FDMA LTE Performance Through High Altitude Platforms Communications Channel

It is known that HAPS is one of the promising wireless infrastructures in the years to come. HAPS exploit many advantages from cellular satellite system as well as from cellular terrestrial system. Therefore, HAPS is envisaged as a novel technology for communication. This paper aims at evaluating the performance of a pilot-based channel estimation for uplink LTE using SC-FDMA over Ricean HAPS communication channel. Pilot-based channel estimation is used to estimate an uplink channel of LTE users who transmit the data to HAPS as a base transceiver station (BTS). Analysis is performed to determine the effect of users elevation angle with respect to user position inside HAPS coverage, LTE channel bandwidth, modulation type, and the Doppler frequency shift effect. We found that user’s elevation angle contribute major effect to the pilot-based channel estimation of LTE SC-FDMA performance. System capability to overcome fading effect that users with low elevation angle would be needed to increase the performance. In particular to keep an acceptable performance, in this paper we compensate the channel bandwidth, changing modulation type, and limit the Doppler effect through vehicle speed limitation.

An Efficient 2D-DOA Estimation Technique for High-Altitude Platforms Mobile Communications

High-altitude platform (HAP) is promising for providing efficient wireless communications services. One of the critical issues in HAP communications is the difficulty to localize users through two-dimensional direction-of-arrival (2D-DOA) estimation due to the high computational complexity and the large covered area. Therefore, in this paper, an efficient technique is proposed to determine user location through 2D-DOA with a reduced processing time. The proposed technique estimates the 2D-DOA in two successive stages; the first will utilize a low-resolution 2D-DOA estimation technique such as Bartlett algorithm performed on a low-resolution distance, then applying a suitable threshold on the normalized Bartlett 2D-DOA spectrum to define ground windows over which the next high-resolution 2D-DOA stage will be performed such as MUSIC algorithm. Two scenarios are examined for the proposed technique to investigate the reduction in calculations time compared to the conventional 2D-DOA MUSIC algorithm without windowing. Simulation results show that at a resolution of 40 m, the required processing time is reduced to only 20 % of the conventional MUSIC algorithm and can be further reduced to 4 % at resolution of 100 meters at the same array size. In addition, the proposed technique is flexible and can be applied for any other efficient low-complexity 2D-DOA algorithms.

6 x 20Gbps Long Reach WDM-PI based High Altitude Platform Inter-Satellite Communication System

InterSatellite communication is one of the remarkable technologies in the era of high altitude platform (HAP) communication system. This work is focused on the transmission of six channels, each carrying 20Gbps non return to zero (NRZ) data over inter-satellite link of 3500Km by adopting wavelength division multiplexing (WDM) and polarization interleaving (PI) scheme. The results are reported in terms of signal to noise ratio (SNR), total received power and eye diagrams which show successful transmission of 20x6Gbps data up to 3500km.

A Novel Technique to improve the Performance of Wireless Sensor Network using Adaptive Antennas and High-Altitude Platform Communications

this paper, the performance of Wireless Sensor Networks (WSN) is improved using adaptive antenna technique and High-Altitude Platforms Systems (HAP). An adaptive concentric circular array (ACCA) is proposed to improve the communications link between sink and sensor nodes. The system is first demonstrated for several scenarios including different cell sizes at a HAP height of 20 km and the quality of link in terms of the ratio of bit energy to noise power is demonstrated where it shows the capability and reliability of building HAP-WSN despite of the long distance between ground sensors and HAP sink. The proposed ACCA technique provides a power gain profile that both increases the power to and from sensor nodes as well as it reduces the out-of cell radiation to other HAP-WSN areas.

Handoff Study of Ring Shaped Cellular Configuration Designed for High Altitude Platform Communications

In this paper, the concentric ring shaped cellular configuration is designed for High Altitude Platforms (HAPs). An one dimensional (1D) vertical linear antenna array is used to generate this configuration. The effect of different types of HAP mobility models, e.g. drift, random walk, and reflection has been examined. The possibility of reducing the need for mechanical stabilization via handoff techniques is demonstrated through the study of handoff, dropping, and blocking probabilities. General Terms Handoff probability, blocking probability, and dropping probability.

Complex Envelope Second-Order Statistics in High-Altitude Platforms Communication Channels

High-altitude platforms are one of the most promising alternative infrastructures for realizing next generation high data rate wireless networks. This paper presents a three-dimensional (3-D) scattering model for land mobile stratospheric multipath-fading channel with its complex faded envelope. From the scattering model and the complex envelope second-order statistics are derived for a 3-D non-isotropic scattering environment. When we discuss on the second-order statistics we refer to the level crossing rate and the average fade duration, whichare two main parameters in describing the fading severity over time and are very important in assess system characteristics such as hand off, velocities of the transmitter and receiver and fading rate. Numerical calculations have been carried out to demonstrate theoretical derivations and the utility of the proposed model.

Flat-Top Ring-Shaped Cell Design for High-Altitude Platform Communications

In this paper, a new design for ring-shaped cells is introduced where to improve the power distribution and carrier-to-interference ratio (CIR) over the cell area. The designed cell has flat-top radiation pattern with minimal ripples in the service area while the out-of-cell area has lower radiation levels. The new design utilizes two weighting functions applied to a vertical linear array; the first is responsible for the flat-top design and the second smoothes the pattern and reduces the sidelobe levels. The resulted power pattern has a uniform distribution over the cell stripe with as small as 0.25 dB ripples and a uniform CIR values greater than 43 dB within the cells which reduces the burden of power control and increases the immunity to propagation problems.

Smart cell design for high altitude platforms communication

This paper proposes a novel design technique for irregular shaped cells in the high altitude platforms (HAPs) cellular system. This technique is based on dividing the coverage area into a grid of small pixel spots and the desired cell is obtained by grouping some pixel spots to give the desired cell shape. These spots are formed with narrow and low sidelobe level beams using concentric ring array (CRA) to reduce the cochannel interference as well as improving the resolution of the design. The desired cell pattern is converted into a spatial mask that selects the desired pixel spots with a proper pre-weight smoothing function. The proposed cell design technique will optimize the cell shape according to the user distribution and behavior in the covered area and consequently is expected to reduce the frequent handoff and signaling traffic of location updating from moving users. Simulation results show that a cell with any irregular shape can be formed with as low as 40dB sidelobe level using Gaussian CRA.

Cooperative directional inter-cell handover scheme in high altitude platform communications systems

A novel Cooperative Directional inter-cell Handover Scheme (CDHS) for High Altitude Platform (HAP) communications systems is proposed, in which the handover target cell and the two cells adjacent to this handover target cell work cooperatively to exploit the traffic fluctuation to improve handover performance. Users in the overlap area of the overloaded handover target cell will be forced to handover directionally before their optimal handover boundary in order to free up resources for the handover calls which would otherwise be dropped due to the shortage of resources and queue time out. Simulation results show that the handover call dropping probability is greatly reduced (at least 60%) compared with the general queue handover scheme, with little performance reduction to the call blocking probability, and the Not in the Best Cell (NBC) average time is only increased moderately. Moreover, an optimal cell radius can be achieved for a specific platform speed by minimizing the unified system performance, which is the linear combination of the handover call dropping probability and the NBC average time.

Optical Communications for High-Altitude Platforms

This paper contains a review of technologies, theoretical studies, and experimental field trials for optical communications from and to high-altitude platforms (HAPs). We discuss the pointing, acquisition, and tracking of laser terminals and describe how laser beams with low divergence can be used to transmit data at multi-Gigabits per second. Investigating the influence of the atmosphere, background light, and flight qualification requirements on system design, we explain why the data rates in free-space optical communications are still significantly below those possible in today's terrestrial fiber-based systems. Techniques like forward-error correction, adaptive optics, and diversity reception are discussed. Such measures help to increase the data rate or link distance while keeping the bit error ratio and outage probability of the optical HAP communication system low.

The Effect of Mutual Coupling on a High Altitude Platform Diversity System Using Compact Antenna Arrays

We analyze the destructive effects of mutual coupling and spatial correlation between the separate antenna elements on a combined diversity system consisting of multiple HAPs (High-Altitude Platforms) employing various compact MIMO (Multiple-Input Multiple-Output) antenna array configurations, in order to enhance the mutual information in HAP communication links. In addition, we assess the influence of the separation angle between HAPs on system performance, and determine the optimal separation angles that maximize the total mutual information of the system for various compact MIMO antennas. Simulation results show that although the mutual information is degraded by mutual coupling and spatial correlation, the proposed HAP diversity system still provides better performance compared to a nondiversity system for all tested scenarios.

On the application of fuzzy-based flow control approach to High Altitude Platform communications

Most of the research effort in the field of HAP communications until now has been invested in the physical layer of the protocol stack, and in the radio related issues in particular. However, the o...

UMTS-HSDPA in High Altitude Platforms (HAPs) communications with finite transmitted power and unequal cell’s load

In this paper, the performance of HAPs (High Altitude Platforms) UMTS HSDPA (High Speed Downlink Packet Access) is studied for different scenarios and two directions (0° and 30°) within the cell where the network under study is assumed to have 61 cells. It is concluded that, for urban zone users, the effective range is lower than the effective range for users in rural zones. It is shown that in rural zones, the HSDPA mode can support the modulation 16QAM with 7/8 code rate when cells are not fully loaded. For fully loaded rural cells, the 16QAM modulation scheme with code rate of 7/8 cannot be supported. Also, it is noticed that, in urban zones, HSDPA mode can support 16QAM with code rate of 1/2 and QPSK modulation schemes when cells are not fully loaded. For fully loaded urban cells, only QPSK with code rate of 1/2 can be supported.