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 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.

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 In developing the feasibility study presented here, the following hypotheses have been Made: Feasibility study For the design of a BTS placed on a HAP called Aerial BTS for a GSM/GPRS and a UMTS.

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.

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