Wireless Networks Based
on
High-Altitude Platforms for
the
Provision of Integrated
Navigation/Communication
Services
- By Amith P. Jayanthilal
HAP – High Altitude Platforms
• Airships or Planes
• Pilots, Self guided or Controlled remotely
• Stratosphere – 15 to 30 Kms above the earth surface
• Less Rain
• Solar powered
HAP – Advantages
· Relatively low cost upgrading of the platform
· Rapid deployment
· Large area coverage (compared with terrestrial) - long
range terrestrial links are severely affected by rain
attenuation and obstructions to the line-of-sight paths
· Low propagation delay, compared with satellites;
· Less ground-based infrastructure required than with
terrestrial;
· Lower launch costs than satellites.
HAP – Applications
• Telecommunication services
• Remote sensing
• Pollution monitoring
• Meteorological measurements
• Real time monitoring of sesmic or coastal regions and
terestrial structures
• Agriculture support
GSM
Global System for Mobile Communications. A standard for digital cellular
communications adopted by over 60 countries. The GSM standard is currently used in
the 900 MHz and 1800 MHz bands.
GPRS
General Packet Radio Service: a radio technology for GSM networks
• Packet-switching protocols
• Shorter set-up time for ISP connections
• Possibility to charge by amount of data sent rather than connect time
• Promises to support flexible data transmission rates typically up to 20 or 30 Kbps (with
a theoretical maximum of 171.2 Kbps), as well as continuous connection to the network.
BTS
A BTS contains the transmit and receive technology like antennas, signal processing,
amplifiers necessary for radio transmission, etc.
UMTS
UMTS is one of the major new third generation mobile communications systems being
developed within the framework defined by the ITU to offer broad band multimedia
services in addition to basic services such as voice telephony.
Carrier to Interference Ratio
The carrier-to-interference ratio is very important in cellular systems in order to
determine the maximum allowed interference level for which the system will still work.
Feasibility study
For the design of a BTS placed on a HAP called Aerial BTS for a GSM/GPRS and a
UMTS.
In developing the feasibility study presented here, the following hypotheses have been
Made:
• A BTS is placed on a HAP at an altitude
of 17 km, with a payload of 100 kg and
a total power available for
telecommunications applications of
800 W.
• The platform keeps a circular course of a
few kilometers in radius, and can
therefore be considered stationary in
the sky.
• A free-space propagation model between
the mobile handsets and the platform
is assumed, where the received power
is proportional to the squared distance.
• The aerial BTS is used to provide
services to the aerial macrocell
GSM/GPRS
If a system completely compliant to the terrestrial standard must be designed, then
according to the synchronization constraints of the GSM standard,
C/I ratio should be ≥ 9dB and the the maximum acceptable transmission delay should be
116 µs, a fact that limits the aerial cell radius to R=35 Km
UMTS
The system capacity can be evaluated, taking into account the minimum C/I that must
be guaranteed according to the UMTS standard.
It is well known that code-division multiple access (CDMA)-based systems like UMTS
are interference limited, and that the system capacity strongly depends on the C/I
experienced at the mobile receiver. The interference level is due to several contributions:
• The total traffic power transmitted by the home BTS
• The other users belonging to both the same cell and neighboring cells
• Thermal noise and other non-CDMA systems
Augmentation systems (AS)
The accuracy provided by the functional satellite navigation systems (GPS, GLONASS,
Galileo) for critical applications and harsh environments is improved by means of
support systems, denoted as augmentation systems (AS), which can be terrestrial (local
AS) or based on geostationary satellites (wide area AS) .
Feasibility study
HAP-based AS, able to provide services over larger regions with respect to ground AS,
but with better performance than satellite AS.
HAP-Based Augmentations
Using HAPs it is possible to broadcast the differential corrections evaluated by a
terrestrial reference station to a large region of about 120 km radius (accepting a
minimum grazing angle of 10°), which improves the differential service availability.
This system is defined as a satellite like signal transmitter, typically called a
pseudosatellite or pseudolite.
Investigation through simulations of the achievements given by the presence of the
stratolite (stratospheric pseudo-satellite) in GPS and Galileo yielded promising
results. The main advantages that can be achieved with respect to terrestrial pseudolites
are
• enlarged coverage
• a reduced near-far effect,
• improved quality of the received signal and
• mobility on demand yielding mitigation of the geometrical dilution of precision (GDOP)
problem
Halo-Proteus
Angel Technology Corporation (USA) is planning to offer broadband telecommunication
service using manned aircraft . A piloted, FAA-certified High Altitude Long Operation
(HALO) aircraft will provide the “hub” of the network. Operating continuously over each
market in three eight hours shifts. Consumers will be able to access video, data, and the
Internet at rates ranging from 1 to 5 Mbps.
Sky Tower
Through funding support from NASA, AeroVironment has developed an unmanned,
solar-electric airplane called Helios which will be capable of continuous flight for up to six
months or more at 60'000 feet in the stratosphere, above the weather and commercial
air traffic Helios will provide a telecommunications platform from this position in the
stratosphere, acting as an 11-mile tall tower—hence the name “SkyTower”. SkyTower’s
stratospheric communications networks are comprised of airborne segments (or
payloads) which communicate with user terminals and gateway stations on the ground.
Fixed wireless broadband total throughput is projected to be approximately 10 to 20
Gbps per platform with typical user transmission speeds of 1.5 Mbps or higher (125
Mbps is feasible for a single user).
Conclusions
• In this article, the use of high-altitude platforms has been proposed for a joint provision
of cellular communication services and support services for navigation satellite systems.
• Results obtained in the system design have shown that they are suitable to implement
macrocells of large radius.
• In some cases the number of sustainable physical channels is limited by the standard
constraints, but can be improved by information on user location. Communication
channels can then be used for the transmission of navigation messages to mobiles and
can be exploited by users to notify the network of their position.
Thank You