05-09-2014, 11:37 AM
MOBILE COMMUNICATION VIA STRATOSPHERE
[attachment=67661]
INTRODUCTION
The HAPS, known also as HALE (High Altitude Long Endurance) stations or SPR (Stratospheric Platform Radio) are reusable unmanned aeronautical vehicles (UAV) at stratospheric altitudes that offer an alternative to the terrestrial and satellite telecommunication systems. They promise access to modern telecommunication services in many situations at lower costs and shorter deployment times. The HAPS can equally well be used in both, mobile and fixed services, but detailed discussion of fixed applications goes beyond the scope of this article. Locating radio stations at higher altitudes to obtain better services over greater areas is not a new idea. High antenna masts have been used since the beginning of radio, and satellite technology has put the antennas at altitudes of hundreds or even thousands kilometres. The HAPS aim at exploiting potential benefits of intermediate altitudes between those used by the terrestrial and satellite technologies.
Studies on HAPS have started at a few universities since the late 1950s. As the work was progressing, numerous potential applications of high altitude platforms have been identified. The technology has been recognized as a critical future technology and several governments decided to invest capital and intellect in its development. Consequently, systematic studies have been undertaken in China, Germany, Hungary, Italy, Japan, Korea, Slovenia, Spain, Switzerland, UK, and USA. The European Space Agency (ESA) and International Telecommunication Union (ITU) have been involved in this area since the late 1990s. The Wireless World Research Forum (WWRF), created to formulate visions on strategic future research directions and to generate, identify, and promote research
STRATOSPHERE
The stratosphere is a part of the Earth’s atmosphere, which consists of several distinct layers. The lowest one is the troposphere. It extends from the Earth’s surface to the tropopause about 10 to 18 km in altitude, depending on the season and geographical position. In the troposphere, the air temperature generally decreases with height. The air pressure decreases from about 1000 hPa at the sea level to about 100 hPa at the tropopause altitude. Approximately 80% of the total air mass resides here, and almost all weather phenomena.
The stratosphere is the next layer, extending from the tropopause to the stratopause at about 50 km. The ozone layer resides here and more than 99% of the total air mass is concentrated in the first 40 km from the Earth’s surface. The stratosphere is characterized by a high static stability associated with increase of temperature with height. The pressure decreases further to reach about 1 hPa at the stratopause.
The mesosphere extends from the stratopause to the mesopause at about 90 km, where the pressure is 0.01 to 0.001 hPa. Most of meteors burn up in the mesosphere as a result of collisions with gas particles there. Higher, up to 300 km, the thermosphere is located. Here, aurora phenomena occur.
PLATFORMRANGE
The communication range of high altitude platform station depends on the platform altitude, signal arrival elevation angle, and the Earth’s dimensions. Figure 2 shows the maximum diameter of the line-of sight (LOS) coverage area for station altitudes from 10 m up to the geostationary satellite orbit. The diagram was created exploiting the fact that microwaves employed by the HAPS propagate along almost straight lines, like the visible light. In the first approximation, the higher is the antenna located, the greater is the station range, but there is a limit. The maximal diameter of the coverage area is somewhat less than the Earth's diameter
HAP:AEROSTATS&AERODYNES
There are two families of high altitude platforms that operate under different physical laws: aerodynes, which are heavier-than-air, and aerostats (balloons or dirigibles), which are lighter-than-air
AEROSTATS
The aerostats exploit the buoyancy force discovered by Archimedes more than 200 years BC. The Archimedes Principle states that a static object submerged in the air is subject to a buoyancy force that is equal to the weight of the air displaced by that object. Modern aerostats are usually filled with helium. They float in the air in the same way that a ship floats in water, and can stay in a fixed place in the air without movement. If no movement is needed, their energy needs are defined solely by the mission equipment they carry.
AERODYNES
The aerodynes exploit aerodynamic forces, discovered by Daniel Bernoulli (1700-1782). He found out that the total energy in a steadily flowing fluid system is constant along the flow path: when flow speed increases, pressure decreases and vice versa. For instance, an airplane wing is designed so that the air speed is higher over the upper surface than on the lower one. Thus, the pressure on the top surface is lower than the pressure on the bottom surface. This difference in pressures provides the lift force that keeps the airplane in the air. For lifting force to compensate the craft weight, an adequate forward thrust must be provided by propellers, jet engines, or other thrusters (gliders with no engines gain their thrust from gravity).
COMBUSTIONENGINES
A number of stratospheric aerodynes carrying fuel reserves on the board have been developed for military purposes. One of first such platforms was famous U-2 spying plane shot down in the Soviet Union 1 May 1960. In 1986, an experimental plane (Rutan Voyager) with a crew of two, proved an endurance of 216 fly hours without interruption (however at moderate altitudes). A more recent stratospheric airplane, Proteus (Figure 5), is capable to lift 1000 kg payload to an altitude of 20 km and circulate there for 14 hours or so
MICROWAVE-POWEREDPLATFORMS
The mission endurance of microwave-powered platforms can be unlimited. Moreover, such platforms do not produce any polluting gases. For these reasons, the possible use of microwave beam to power stratospheric stations has been explored early. The first public demonstration of microwave-powered HAP (1/8 scale demonstrator model) took place in Canada in 1987. It was a 4.5-metre wing span pilot-less, radio-controlled aircraft powered by microwave beam at 2.45 GHz from ground-based antenna. The microwaves were captured by a disc-shaped collector located on the aircraft just behind the wings. The collector consisted of a number of rectennas (rectifier antennas) that converted microwaves to direct current powering the payload, control system, and two motor-driven propellers. Later, also laser beam as power transmission medium was examined. Experiments with microwave-powered and laser-beam powered platforms were undertaken in Japan, USA, and Israel. However, microwave-powered and laser-powered platforms involve irradiation risks and are not considered as 100% safe and environmental friendly
SOLAR-POWEREDPLATFORMS:
The Sun is the most natural energy source for stratospheric platforms located above clouds. The efficiency of photovoltaic cells has been significantly improved, making solar energy an attractive alternative to power high altitude platforms. As quasi-stationary stations experience the same day-night cycle as any point on the Earth surface, solar cells can produce electricity only 12-hours a day. Energy drawn from solar radiation during the daytime must thus be stored for use at night to assure continuous operation of station. The regenerative fuel cells (RFC) which use water as fuel are to be used for that purpose. During the day, the water is decomposed into hydrogen and oxygen in the electrolytic process. At night, the chemical reactions run backwards producing electricity and water with no pollution. Based on electrochemical processes, they are not limited by the efficiency of thermodynamically reversible engines (Carnot cycle).
BROADBANDACCESS:
The need for fast broadband communications can probably never be fully satisfied, as the needs grow faster than the current technology can offer. There are two obstacles in making it the broadband access popular. The first one results from the different treatment of audio, video, and data and separate standards used in wireless and wired telecommunication networks. That obstacle will eventually be overcome by the new integrating standards and new version of Internet protocol IPv6. The second obstacle is the very high cost of cabling at the user’s premises. It is known as the “last-mile problem” as seen from the service provider’s perspective or “first-mile problem” from the user’s perspective. The HAPS can offer a cost effective solution to that problem. This is appealing to small-medium enterprise (SME) and small office/ home office (SOHO) users. In future, when wideband services such as high-definition digital interactive television or video telephony are more popular, it may be a major market
MOBILEINTERNET
Progress in electronics and telecommunications makes it possible to process reliably more information, in shorter time, and at low cost. Based on wireless communications, laptop-computers and their pocket and palm equivalents are becoming more and more popular. Combined with cell phones, they create a new brand of portable “personal assistants”, with merged functions of information processing, storing, displaying, as well as information receiving and transmitting via microwaves. The speed of processing information by these devices exceeds greatly the transmission capabilities of most radiocommunication systems presently in operation. Here, wideband HAPS could replace or complement wireless terrestrial access points
EMERGENCYCOMMUNICATIONS
Martin Griffiths, then Director of UN Department of Humanitarian Affairs described the problem as follows: “In all emergency operations, high-risk decisions must be taken early on often based on unverifiable [...] estimations. Facts change wildly from day to day. Search and rescue, medical relief, food aid, shelter and rehabilitation issues all [have] to be accessed and prioritised almost simultaneously. Tight time limits, combined with surrounding post-disaster chaos and the lacking resources in situ, impose the highest demands on the management, logistics, coordination, and communication efficiency
NAVIGATION
The location precision offered by the present global navigation/ positioning systems such as GPS of the USA, Russian GLONASS, is insufficient for a number of critical applications. The future European Galileo system will have similar limitations. The differential or augmented positioning systems can increase substantially that precision. However, an additional signal is required for that purpose. Such a signal is now disseminated by terrestrial and satellite stations. The HAPS can be a cost-effective alternative in distributing that augmentation signal over large areas
SKYSTATION
Sky Station is the name of a solar-powered aerostatic HAP system planned by Sky Station International.Initially, ion engines were envisaged. A single platform will provide mobile and fixed telecommunication services to an area of 150...1000 km diameter using spot-bam antennas. The planned data rates are 2 Mbps uplink and 10 Mbps downlink in fixed services. For mobile applications, 16 kbps for voice and 384 for data are planned. The cost of a worldwide broadband infrastructure is estimated at $2.5 billion
SKYTOWER
SkyTower is a solar-powered radio-controlled aerodyne platform planned by SkyTower Telecommunications. It is based on Helios airplane (mentioned earlier). The interactive network systems are being designed for the total throughput of 10...20 Gbps per platform (125 Mbps per user), with an average transmission speed of 1.5 Mbps. The company claims that the system, applied to solve the last-mile problem, will have over 1000 times the broadband local access capacity of a satellite (as measured in bit-per-second- per-square kilometre), a fraction of the cost of cable and DSL to deploy (as measured in dollars-per-subscriber) and to be capable of set up in days. In June-July 2002, the first HDTV and IMT-2000 transmission capabilities were successfully demonstrated, including video telephony using an off-the shelf handsets and Internet wireless modem at a speed of 384 kbps.
CONCLUSION
The High Altitude Platform Stations are expected to provide, in a cost-effective manner, a multitude of telecommunication and other services over large areas. Known also as stratospheric repeaters, they may operate individually or be interconnected with other similar HAPS and/or terrestrial and satellite-based stations. Compared to terrestrial
[attachment=67661]
INTRODUCTION
The HAPS, known also as HALE (High Altitude Long Endurance) stations or SPR (Stratospheric Platform Radio) are reusable unmanned aeronautical vehicles (UAV) at stratospheric altitudes that offer an alternative to the terrestrial and satellite telecommunication systems. They promise access to modern telecommunication services in many situations at lower costs and shorter deployment times. The HAPS can equally well be used in both, mobile and fixed services, but detailed discussion of fixed applications goes beyond the scope of this article. Locating radio stations at higher altitudes to obtain better services over greater areas is not a new idea. High antenna masts have been used since the beginning of radio, and satellite technology has put the antennas at altitudes of hundreds or even thousands kilometres. The HAPS aim at exploiting potential benefits of intermediate altitudes between those used by the terrestrial and satellite technologies.
Studies on HAPS have started at a few universities since the late 1950s. As the work was progressing, numerous potential applications of high altitude platforms have been identified. The technology has been recognized as a critical future technology and several governments decided to invest capital and intellect in its development. Consequently, systematic studies have been undertaken in China, Germany, Hungary, Italy, Japan, Korea, Slovenia, Spain, Switzerland, UK, and USA. The European Space Agency (ESA) and International Telecommunication Union (ITU) have been involved in this area since the late 1990s. The Wireless World Research Forum (WWRF), created to formulate visions on strategic future research directions and to generate, identify, and promote research
STRATOSPHERE
The stratosphere is a part of the Earth’s atmosphere, which consists of several distinct layers. The lowest one is the troposphere. It extends from the Earth’s surface to the tropopause about 10 to 18 km in altitude, depending on the season and geographical position. In the troposphere, the air temperature generally decreases with height. The air pressure decreases from about 1000 hPa at the sea level to about 100 hPa at the tropopause altitude. Approximately 80% of the total air mass resides here, and almost all weather phenomena.
The stratosphere is the next layer, extending from the tropopause to the stratopause at about 50 km. The ozone layer resides here and more than 99% of the total air mass is concentrated in the first 40 km from the Earth’s surface. The stratosphere is characterized by a high static stability associated with increase of temperature with height. The pressure decreases further to reach about 1 hPa at the stratopause.
The mesosphere extends from the stratopause to the mesopause at about 90 km, where the pressure is 0.01 to 0.001 hPa. Most of meteors burn up in the mesosphere as a result of collisions with gas particles there. Higher, up to 300 km, the thermosphere is located. Here, aurora phenomena occur.
PLATFORMRANGE
The communication range of high altitude platform station depends on the platform altitude, signal arrival elevation angle, and the Earth’s dimensions. Figure 2 shows the maximum diameter of the line-of sight (LOS) coverage area for station altitudes from 10 m up to the geostationary satellite orbit. The diagram was created exploiting the fact that microwaves employed by the HAPS propagate along almost straight lines, like the visible light. In the first approximation, the higher is the antenna located, the greater is the station range, but there is a limit. The maximal diameter of the coverage area is somewhat less than the Earth's diameter
HAP:AEROSTATS&AERODYNES
There are two families of high altitude platforms that operate under different physical laws: aerodynes, which are heavier-than-air, and aerostats (balloons or dirigibles), which are lighter-than-air
AEROSTATS
The aerostats exploit the buoyancy force discovered by Archimedes more than 200 years BC. The Archimedes Principle states that a static object submerged in the air is subject to a buoyancy force that is equal to the weight of the air displaced by that object. Modern aerostats are usually filled with helium. They float in the air in the same way that a ship floats in water, and can stay in a fixed place in the air without movement. If no movement is needed, their energy needs are defined solely by the mission equipment they carry.
AERODYNES
The aerodynes exploit aerodynamic forces, discovered by Daniel Bernoulli (1700-1782). He found out that the total energy in a steadily flowing fluid system is constant along the flow path: when flow speed increases, pressure decreases and vice versa. For instance, an airplane wing is designed so that the air speed is higher over the upper surface than on the lower one. Thus, the pressure on the top surface is lower than the pressure on the bottom surface. This difference in pressures provides the lift force that keeps the airplane in the air. For lifting force to compensate the craft weight, an adequate forward thrust must be provided by propellers, jet engines, or other thrusters (gliders with no engines gain their thrust from gravity).
COMBUSTIONENGINES
A number of stratospheric aerodynes carrying fuel reserves on the board have been developed for military purposes. One of first such platforms was famous U-2 spying plane shot down in the Soviet Union 1 May 1960. In 1986, an experimental plane (Rutan Voyager) with a crew of two, proved an endurance of 216 fly hours without interruption (however at moderate altitudes). A more recent stratospheric airplane, Proteus (Figure 5), is capable to lift 1000 kg payload to an altitude of 20 km and circulate there for 14 hours or so
MICROWAVE-POWEREDPLATFORMS
The mission endurance of microwave-powered platforms can be unlimited. Moreover, such platforms do not produce any polluting gases. For these reasons, the possible use of microwave beam to power stratospheric stations has been explored early. The first public demonstration of microwave-powered HAP (1/8 scale demonstrator model) took place in Canada in 1987. It was a 4.5-metre wing span pilot-less, radio-controlled aircraft powered by microwave beam at 2.45 GHz from ground-based antenna. The microwaves were captured by a disc-shaped collector located on the aircraft just behind the wings. The collector consisted of a number of rectennas (rectifier antennas) that converted microwaves to direct current powering the payload, control system, and two motor-driven propellers. Later, also laser beam as power transmission medium was examined. Experiments with microwave-powered and laser-beam powered platforms were undertaken in Japan, USA, and Israel. However, microwave-powered and laser-powered platforms involve irradiation risks and are not considered as 100% safe and environmental friendly
SOLAR-POWEREDPLATFORMS:
The Sun is the most natural energy source for stratospheric platforms located above clouds. The efficiency of photovoltaic cells has been significantly improved, making solar energy an attractive alternative to power high altitude platforms. As quasi-stationary stations experience the same day-night cycle as any point on the Earth surface, solar cells can produce electricity only 12-hours a day. Energy drawn from solar radiation during the daytime must thus be stored for use at night to assure continuous operation of station. The regenerative fuel cells (RFC) which use water as fuel are to be used for that purpose. During the day, the water is decomposed into hydrogen and oxygen in the electrolytic process. At night, the chemical reactions run backwards producing electricity and water with no pollution. Based on electrochemical processes, they are not limited by the efficiency of thermodynamically reversible engines (Carnot cycle).
BROADBANDACCESS:
The need for fast broadband communications can probably never be fully satisfied, as the needs grow faster than the current technology can offer. There are two obstacles in making it the broadband access popular. The first one results from the different treatment of audio, video, and data and separate standards used in wireless and wired telecommunication networks. That obstacle will eventually be overcome by the new integrating standards and new version of Internet protocol IPv6. The second obstacle is the very high cost of cabling at the user’s premises. It is known as the “last-mile problem” as seen from the service provider’s perspective or “first-mile problem” from the user’s perspective. The HAPS can offer a cost effective solution to that problem. This is appealing to small-medium enterprise (SME) and small office/ home office (SOHO) users. In future, when wideband services such as high-definition digital interactive television or video telephony are more popular, it may be a major market
MOBILEINTERNET
Progress in electronics and telecommunications makes it possible to process reliably more information, in shorter time, and at low cost. Based on wireless communications, laptop-computers and their pocket and palm equivalents are becoming more and more popular. Combined with cell phones, they create a new brand of portable “personal assistants”, with merged functions of information processing, storing, displaying, as well as information receiving and transmitting via microwaves. The speed of processing information by these devices exceeds greatly the transmission capabilities of most radiocommunication systems presently in operation. Here, wideband HAPS could replace or complement wireless terrestrial access points
EMERGENCYCOMMUNICATIONS
Martin Griffiths, then Director of UN Department of Humanitarian Affairs described the problem as follows: “In all emergency operations, high-risk decisions must be taken early on often based on unverifiable [...] estimations. Facts change wildly from day to day. Search and rescue, medical relief, food aid, shelter and rehabilitation issues all [have] to be accessed and prioritised almost simultaneously. Tight time limits, combined with surrounding post-disaster chaos and the lacking resources in situ, impose the highest demands on the management, logistics, coordination, and communication efficiency
NAVIGATION
The location precision offered by the present global navigation/ positioning systems such as GPS of the USA, Russian GLONASS, is insufficient for a number of critical applications. The future European Galileo system will have similar limitations. The differential or augmented positioning systems can increase substantially that precision. However, an additional signal is required for that purpose. Such a signal is now disseminated by terrestrial and satellite stations. The HAPS can be a cost-effective alternative in distributing that augmentation signal over large areas
SKYSTATION
Sky Station is the name of a solar-powered aerostatic HAP system planned by Sky Station International.Initially, ion engines were envisaged. A single platform will provide mobile and fixed telecommunication services to an area of 150...1000 km diameter using spot-bam antennas. The planned data rates are 2 Mbps uplink and 10 Mbps downlink in fixed services. For mobile applications, 16 kbps for voice and 384 for data are planned. The cost of a worldwide broadband infrastructure is estimated at $2.5 billion
SKYTOWER
SkyTower is a solar-powered radio-controlled aerodyne platform planned by SkyTower Telecommunications. It is based on Helios airplane (mentioned earlier). The interactive network systems are being designed for the total throughput of 10...20 Gbps per platform (125 Mbps per user), with an average transmission speed of 1.5 Mbps. The company claims that the system, applied to solve the last-mile problem, will have over 1000 times the broadband local access capacity of a satellite (as measured in bit-per-second- per-square kilometre), a fraction of the cost of cable and DSL to deploy (as measured in dollars-per-subscriber) and to be capable of set up in days. In June-July 2002, the first HDTV and IMT-2000 transmission capabilities were successfully demonstrated, including video telephony using an off-the shelf handsets and Internet wireless modem at a speed of 384 kbps.
CONCLUSION
The High Altitude Platform Stations are expected to provide, in a cost-effective manner, a multitude of telecommunication and other services over large areas. Known also as stratospheric repeaters, they may operate individually or be interconnected with other similar HAPS and/or terrestrial and satellite-based stations. Compared to terrestrial