Propagation modeling and characteristic analysis of terahertz waves via high altitude platforms

In this paper, propagation modeling and performance analysis on the HAPs are obtained. Elevation angle is the dominant parameter on the model. All possible propagation environments are divided into four groups: suburban (SU), urban (U), dense urban (DU) and urban high rise (UHR). These groups are modeled using well-known statistical models with a dependence on elevation angle. The main parameters are the elevation angle, Rayleigh and Ricean propagation factors, and percentage of time a given fade depth is exceeded. To observe the effects of the parameters on the model, the correlation coefficients between model parameters and the fade depth are calculated. This new HAP model contains two cases-line of sight (LOS) and non-line of sight (NLOS) between a HAP and a user. In a conclusion, obtained models are combined with free space path loss and full formulations of total path loss for the four possible HAPs propagation environments at three different frequencies (2, 3.5, and 5.5 GHz) are given.

This paper examines the behaviour of system capacity in High Altitude Platform (HAP) communications systems as a function of antenna directivity and HAP positioning. Antenna models for the user and the HAP are discussed, and it is shown that a flat sidelobe antenna pattern is suitable for modelling multiple HAP constellations when HAPs are located outside the coverage area. Using a single HAP scenario it is shown how narrowing the HAP antenna beamwidth may give better downlink Carrier-to-Noise Ratio (CNR) over the most of the coverage area. The roles of the HAP antenna beamwidth, HAP antenna pointing and HAP spacing radius are investigated. An equation is derived to determine the location of the peak CNR combined with these three parameters. A more complex multiple HAP scenario where all HAP's operate on the same channel and interfere with each other is also assessed in terms of the Carrier to Interference plus Noise Ratio (CINR) and spectral efficiency. It is shown that locating HAPs at a specific spacing radius that is outside the coverage area can improve performance. Using these techniques the combined bandwidth efficiency is shown to increase almost pro-rata when the number of HAPs is increased up to 16.

In this work, a mixed free-space optics (FSO)/radio-frequency (RF) based multiple serial high altitude platforms (HAPs) assisted multiuser multiantenna terrestrial communication system is considered. For the considered multi-hop system, earth station to HAP and HAP to HAP links are assumed as FSO links, and HAP to terrestrial mobile users (MUs) link is assumed as RF link. At the FSO detector both the heterodyne detection and intensity modulation direct detection techniques are considered. Atmospheric turbulence of the ES to HAP FSO link is modeled with Gamma-Gamma fading along with the pointing error impairments. As HAP situates in the stratosphere, negligible atmospheric turbulence exists at HAP altitude (20 km), hence, only pointing error is considered for the inter HAP links. Further, the HAP consists of multiantenna array to provide high data-rates to the terrestrial users via RF links, considered to be Nakagami-m distributed. The intermediate HAPs perform selective decode-and-forward relaying and opportunistic user scheduling is performed for the best user selection. For the performance analysis, analytical expression of overall outage probability is obtained and the impact of various selection parameters like pointing error, FSO detection type, MU selection, number of antennas, and RF fading severity are observed on the outage performance. Asymptotic outage probability is also derived to obtain the diversity order of the considered communication system. Further, considering various modulation schemes, a generalized average bit-error-rate expression is derived and the impact of pointing error, FSO detection type, MU selection, number of antennas, and RF fading severity are observed on its performance. Finally, derived results are validated through Monte-Carlo simulations.

One among the most recent configurations in satellite architectures, is enhanced with respect to the traditional ones, by the presence of HAPs (High Altitude Platforms). Those balloons are located at stratospheric altitudes, and make possible to separate the link from LEO to ground into two segments: the former crosses the highest levels of atmosphere and can be developed by optical technology, the latter is more sensitive to scattering and absorption, since it crosses lower atmosphere, so it must be carried out in RF domain where more consolidated technology can be used. The insertion of HAPs in the global architecture enhances the system performance in terms of LEO-Ground link capacity, connectivity and flexibility; in addition the wide band-width offered by optics makes more and more effective those improvements. Even better results can be obtained if a proper coding system is designed. 1 Scenario Description For a HAP-LEO link an optical communication system based on 1550 nm technology is proposed. This wavelength ensures a wide capacity and the consolidated technology used in terrestrial links. In addition EDFA (Erbium Doped Amplifiers) optical amplifiers work in that band, offering some important improvements in terms of system performance. The optical communication subsystem should be designed starting from the knowledge of the operative scenario. In the case we consider, data stream is mainly transmitted from LEO to HAP: LEO can collect information during its orbit, for example from high resolution Earth Observation imageries. Instead of transferring data to a Ground Station with a RF link in the visibility window, it is possible to increase the downloading effectiveness by locating a HAP just above the destination Ground Station [1,3,4]. As a matter of fact, the HAP location at 20 km allows to avoid the most limitative atmosphere layers making possible to carry out an optical link from LEO to HAP (Fig. 1). With a 10 Gbit/s link, even in a very short time window for download it is possible to transfer up to some Terabit per day. HAP can transmit stored data to Ground Station until the next time LEO becomes visible to HAP and it starts its downloading again. Between two consecutive accesses there is a time delay, that sometimes is some hours long, depending on the HAP latitude. That means HAP has a quite long time to empty its memory, so the link to Ground does not require a wide band [5]. During this silent delay, HAP 728 Satellite Communications and Navigation Systems can transmit data even to another HAP exploiting optical technology, as well. That can improve the downloading speed and the network connectivity.

Coverage analysis of aerial communication networks based on high altitude platforms (HAPs) and low altitude platforms (LAPs) is of great significance to understand the service provisioning capability of aerial base stations. This letter uses stochastic geometry to analyze network coverage of an integrated HAP and LAP (IHL) system with respect to backhaul constraints, where LAPs aim to provide services for ground user equipments in the malfunction area and a HAP is to provide backhaul connectivity for LAPs. Based on stochastic geometry theory, the analytical framework of the IHL system coverage is derived along with the analysis on the impact of some key parameters, such as aerial platform altitudes and LAP densities. The derived analytical framework can also provide insights for the backhaul design of LAP aerial base stations, which is also revealed in the numerical analyses part.

High Altitude Platform System (HAPS) is an exceptional technology in aerial communications systems. Some inimitable facets of HAPS compose it as a spectacular service provider. However, interference with other aerial or terrestrial communications systems is a significant issue. With regards to system interference as of other commercial products or systems which perform partially at the same frequency range as HAPS, escalating HAPS performance by bringing about in conjunction with these systems seems unavoidable. One of the most significant systems which operating at the same frequency of HAPS is Fixed Satellite Service (FSS). This article concentrates on tropical and subtropical areas' coexisting systems specifications Functioning in C-band. Foremost emphasis would be given to interference amount gauge churned out by FSS uplink (5925–6725 MHz) towards HAPS gateway links in commission at 5850–7075 MHz frequency range. The criteria are compatible to and derived out from the International Telecommunication Union (ITU) and World Radio-Communication Conferences (WRCs) publications.

A superimposed (arithmetically added) Pilot (SiP) sequence based channel estimation method for beamforming assisted multi-antenna High Altitude Platform (HAP) land mobile radio communication systems is proposed, which exploits the prior available information of users' spatial location, density of users, and beam-width of HAP directional antenna. A thorough characterization of HAP sparse multipath radio propagation channels' is presented in first part of the paper, where mathematical relationship of HAP antenna beam-width with channel's delay span and optimal length of SiP base sequence are presented. Further, a location information aided and low- power SiP sequence based Stage-wise Orthogonal Match Pursuit (StOMP) algorithm is proposed for estimation of channels from single-antenna user terminals to beamforming assisted large scale multiple-antenna HAP. A thorough analysis on the basis of Normalized Channel Mean Square Error (NCMSE) and Bit Error Rate (BER) performance of proposed method is presented; where the effect of channels' sparsity level, Pilot-to-Information power Ratio (PIR), beam-width of HAP's directional antenna, amount of HAP antenna elements, density of interfering users, and spatial location of active user terminal are thoroughly studied. A comparison of the proposed method with a notable reference technique available in the literature is also presented.

When high altitude platforms (HAPs) work as communication relay platforms, mobile terminals (MTs) generally make use of the handoff algorithm based on RSSI for handoff between HAPs. However, when several MTs send information to ground command center simultaneously, using the handoff algorithm based on RSSI will lead to HAPs with large received signal strength overload and HAPs with small received signal strength idle, putting HAPs network at risk of load imbalance and causing the phenomenon of congestion and packet loss, which thereby increases end-to-end delay and reduces packet delivery ratio. Aiming at the above problem and considering the limited energy of HAPs, a load balancing handoff algorithm based on RSSI and energy-aware in HAPs network is proposed. The simulation results obtained show that compared with the handoff algorithm based on RSSI, the proposed handoff algorithm can effectively balance network loads, reduce end-to-end delay and improve packet delivery ratio.

Third generation mobile systems are gradually being deployed in many developed countries in hotspot areas. However, owing to the amount of new infrastructures required, it will still be some time before 3G is ubiquitous, especially in developing countries. One possible cost effective solution for deployments in these areas is to use High Altitude Platforms (HAPs) (Collela et al., 2000; Djuknic et al., 1997; Grace et al., 2001; 2005; Miura & Oodo, 2002; Park et al., 2002; Steele, 1992; Thornton et al., 2001; Tozer & Grace, 2001) for delivering 3G (WCDMA) communications services over a wide coverage area (Dovis et al., 2002; Falletti & Sellone, 2005; Foo et al., 2000; Masumura & Nakagawa, 2002; Vazquez et al., 2002). HAPs are either airships or planes that will operate in the stratosphere, 17-22 km above the ground. This unique position offers a significant link budget advantage compared with satellites and much wider coverage area than conventional terrestrial cellular systems. Such platforms will have a rapid roll-out capability and the ability to serve a large number of users, using considerably less communications infrastructure than required by a terrestrial network (Steele, 1992). In order to aid the eventual deployment of HAPs the ITU has allocated spectrum in the 3G bands for HAPs (ITU, 2000a), as well as in the mm-wave bands for broadband services at around 48 GHzworldwide (ITU, 2000b) and 31/28 GHz for certain Asian countries (Oodo et al., 2002). Spectrum reuse is important in all wireless communications systems. Cellular solutions for HAPs have been examined in (El-Jabu, 2001; Thornton et al., 2003), specifically addressing the antenna beam characteristics required to produce an efficient cellular structure on the ground, and the effect of antenna sidelobe levels on channel reuse plans (Thornton et al., 2003). HAPs will have relatively loose station-keeping characteristics compared with satellites, and the effects of platform drift on a cellular structure and the resulting inter-cell handover requirements have been investigated (Thornton et al., 2005). Cellular resourcemanagement strategies have also been developed for HAP use (Grace et al., 2002). Configurations of multiple HAPs can also reuse the spectrum. They can be used to deliver contiguous coverage and must take into account coexistence requirements (Falletti & Sellone, 2005; Foo et al., 2000). A technique not widely known is their ability to serve the same

HAP(High Altitude Platform)은 지표면 17~22km위에 있는 성층권 영역에서 운행하는 정지 궤도 공중 플랫폼으로 공중에서의 MBS(Mobile Base Station)로서의 역할이 가능하다. HAP 기반 네트워크는 인공위성 시스템과 지상통신 시스템의 장점들을 가지고 있다. 본 논문에서는 HAP 기반망의 구성 및 그 유지를 위한 HAP MBS의 배치에 대해 연구한다. 이 연구를 위해 지상 이동 노드들을 클러스터링하기 위한 클러스터링 알고리즘이 사용되는데, 본 논문에서는 EM(Expectation Maximization) 클러스터링 알고리즘을 사용한다. 본 논문의 목표는 이동 통신 단말기들 간의 거리와, 각 단말기들의 이동속도를 고려하여 단말기들이 효율적으로 클러스터링 되어 HAP의 배치가 효율적일 수 있도록 EM 알고리즘을 적용 및 개선하고, 이 EM 알고리즘을 이용한 HAP MBS 배치기법을 인구밀도에 기반을 둔 RWP(Random Waypoint) 노드 모빌리티를 이용하여 그 성능을 평가한다. HAP(High Altitude Platform) is a stationary aerial platform positioned in the stratosphere between 17Km and 22Km height and it could act as an MBS (Mobile Base Station). HAP based Network has advantages of both satellite system and terrestrial communication system. In this paper we study the deploy of multiple HAP MBS that can provides efficient communication for users. For this study, EM(Expectation Maximization) clustering algorithm is used to cluster terrestrial mobile nodes. The object of this paper is improving EM algorithm into the clustering algorithm for efficiency in variety aspects considering distance between mobile terminal units and speed of mobile terminal units, and estimating performance of HAP MBS deploy technique with use of improved EM algorithm using RWP (Random Waypoint) node mobility.

In this paper, we investigate a cost-effective wireless broadband service provision from high altitude platforms (HAPs) and an economical business model design. Different deployment strategies of HAP system are illustrated in terms of a stand-alone HAP system and in collaboration with terrestrial or satellite systems. An IEEE 802.16 fixed broadband service from HAP is examined to show the effectiveness of providing the service delivery. We propose a partnership-based business model for HAP system, which can be adopted for a cost-effective service delivery, and applied in different application scenarios with collaboration partners, e.g. information service provider (ISP), equipment vendors, and mobile network operator (MNO). Key factors of successfully delivering HAP services and collaboration with partners are investigated in terms of coexistence capability with major wireless network operators and different approaches for a cost-effective HAP service delivery.

The aim of the paper is to prove the technical feasibility and the advantages of a joint RF and optical communication system. The reference scenario foresees the use of a HAP (high altitude platform) or multiple HAPs for data purposes. HAPs are based on airships or balloons placed at about 20 km height and they combine both the advantages of terrestrial networks (the highest mast in the town) and of satellites (a LEO in very low orbit). As earth observation (EO) satellites need the download of huge amount of data, HAPs could establish an optical link with a LEO EO satellite in order to exploit the high data rate. Optical space communications offer a wide bandwidth and low interference channel. By the use of this system, it is possible to increase the amount of information downloaded by a high altitude platform from a LEO satellite, reaching data rate up to 10 Gbit/s. There are some critical points to face in order to dimension this link. First of all, a fast pointing acquisition and tracking procedure must be implemented. Another point is related to the high relative speed between LEO satellite and HAP that leads to an important contribution of Doppler shift in the received signal spectrum, this phenomenon is not stochastic and it can be managed by a tunable filter. The third point to focus on, strictly related to the transmitter design, is the optical carrier choice. It is important to take into account the atmospheric layer from 20 to 100 km, in terms of absorption and scattering spectra, temperature and refractive index variations in altitude and time varying phenomena. The transmitter is designed choosing the best performing technology in different optical window frequencies in which the channel presents low absorption and scattering, this choice involves the modulation format, as well. Three optical windows are available: 850nm, 1064nm and 1550nm. The first one is the most affected by Doppler effect but offers high gain telescope and low cost components; devices that work in the second window can transmit high amount of power but the modulation constraints of laser source can make the design more complicated; the third window is the most used in terrestrial communication systems and many devices are available, the Doppler effect is lower than at other frequencies and for this carrier it is possible to carry out DPSK (differential phase shift keying) modulation schemes other than classical OOK (on off keying) techniques. Moreover, HAPs could use terrestrial electronics equipments in order to the data received by the optical link (e.g. hard disks). The link between HAP and ground can be exploited by the use of high data rate RF links in Ka-band or X-band (mainly used in EO satellites), V-band (allocated for HAPs) or W-Band (the new frontier). Despite the impact by weather and atmospherics, it was demonstrated that the availability of W-band satellite links is at least 95% (Fragale, 2004). This scenario overcomes the limits imposed by the short time window for EO satellites data download, using an advanced store and forward-data relay concept.

Space-air-ground networks play important roles in both fifth generation (5G) and sixth generation (6G) techniques. Low earth orbit (LEO) satellites and high altitude platforms (HAPs) are key components in space-air-ground networks to provide access services for the massive mobile and Internet of Things (IoT) users, especially in remote areas short of ground base station coverage. LEO satellite networks provide global coverage, while HAPs provide terrestrial users with closer, stable massive access service. In this work, we consider the cooperation of LEO satellites and HAPs for the massive access and data backhaul of remote area users. The problem is formulated to maximize the revenue in LEO satellites, which is in the form of mixed integer nonlinear programming. Since finding the optimal solution by exhaustive search is extremely complicated with a large scale of network, we propose a satellite-oriented restricted three-sided matching algorithm to deal with the matching among users, HAPs, and satellites. Furthermore, to tackle the dynamic connections between satellites and HAPs caused by the periodic motion of satellites, we present a two-tier matching algorithm, composed of the Gale-Shapley-based matching algorithm between users and HAPs, and the random path to pairwise-stable matching algorithm between HAPs and satellites. Numerical results show the effectiveness of the proposed algorithms.

In this paper, we investigate techniques for optimizing the coexistence performance of providing WiMAX (IEEE802.16a) from High Altitude Platforms (HAPs) and terrestrial deployments in shared 3.5 GHz frequency bands are presented. The paper will show that it is effective to provide WiMAX services from HAPs with optimized performance by appropriate choice of parameters, including varying the HAP deployment spacing radius and directive antenna beamwidth based on the adopted antenna models for HAPs and receivers. Illustrations and comparisons of changing the antenna pointing offset, narrowing the transmitting and receiving antenna beamwidth as well as keeping the accepted CINR performance across the HAP coverage area, will demonstrate that that efficiently utilizing these techniques are able to enhance the HAP system performance while effectively coexisting with the terrestrial WiMAX systems.

In this paper, performance of providing WiMAX from high altitude platforms (HAPs) with multiple antenna payload will be investigated as well as considering the coexistence capability with multiple-operator terrestrial deployments. A scenario of a HAP and terrestrial WiMAX base stations deployed inside a HAP coverage area with a radius at 30 km will be proposed. HAP cellular formation with different reuse patterns will be established. Coexistence performance will be assessed in terms of HAP downlink signal interfered by terrestrial WiMAX deployment. This paper will show it is effective to deliver WiMAX via HAPs and can efficiently share the spectrum with terrestrial WiMAX systems.