High Altitude Aeronautical Platform Stations (HAAPS) is the name of a technology for providing wireless narrowband and broadband telecommunication services as well as broadcasting services with either airships or aircraft's. The HAAPS are operating at altitudes between 3 to 22 km. A HAAPS shall be able to cover a service area of up to 1000 km diameter, depending on the minimum elevation angle accepted from the user's location. The platforms may be airplanes or airships (essentially balloons) and may be manned or un-manned with autonomous operation coupled with remote control from the ground. HAAPS mean a solar-powered and unmanned airplane or airship, capable of long endurance on-station possibly several years.
A high altitude telecommunication system comprises an airborne platform typically at high atmospheric or stratospheric altitudes with a telecommunications payload, and associated ground station telecommunications equipment. The combination of altitude, payload capability, and power supply capability makes it ideal to serve new and metropolitan areas with advanced telecommunications services such as broadband access and regional broadcasting. The opportunities for applications are virtually unlimited. The possibilities range from narrowband services such as paging and mobile voice to interactive broadband services such as multimedia and video conferencing.
For future telecommunications operators such a platform could provide blanket coverage from day one with the added advantage of not being limited to a single service. Where little or unreliable infrastructure exists, traffic could be switched through air via the HAAPS platform. Technically, the concept offers a solution to the propagation and rollout problems of terrestrial infrastructure and capacity and cost problems of satellite networks. Recent developments in digital array antenna technology make it possible to construct 100+ cells from one platform. Linking and switching of traffic between multiple high altitude platforms, satellite networks and terrestrial gateways are also possible. Economically it provides the opportunity for developing countries to have satellite-like infrastructure without the funds flowing out of the country due to gateways and control stations located outside of these countries.
A typical HAAP-based communications systems structure is shown .
The platform is positioned above the coverage area. There are basically two types of HAAPS. Lighter-than air HAAPS are kept stationary, while airplane based HAAPS are flown in a tight circle. For broadcast applications, a simple antenna beams signals to terminals on the ground. For individualized communication, such as telephony, "cells" are created on the ground by some beam forming technique in order to reuse channels for spatially separated users, as is done in cellular service. Beam forming can be as sophisticated as the use of phased-array antennas, or as straightforward as the use of lightweight, possible inflatable parabolic dishes with mechanical steering. In the case of a moving HAAP it would also be necessary to compensate motion by electronic or mechanical means in order to keep the cells stationary or to "hand off" connections between cells as is done in cellular telephony.
HALO Network Concepts
High-Altitude Long Operation (HALO) aircraft present a new layer in the hierarchy of wireless communications -- a 10-mile tall tower in the stratosphere above rain showers and below meteor showers (i.e., high above terrestrial towers and well below satellite constellations).
HALO airplane will be the central node of a wireless broadband communications network. The HALO Network, whose initial capacity will be on the scale of 10 Gbps, with a growth potential beyond 100 Gbps. The packet-switched network will be designed to offer bit rates to each subscriber in the multimegabit-per-second range.
The airplane's fuselage can house switching circuitry and fast digital network functions. A MMW antenna array and its related components will be located in a pod suspended below the aircraft fuselage. The antenna array will produce many beams -- typically, more than 100. Broadband channels to subscribers in adjacent beams will be separated in frequency. For the case of aircraft-fixed beams, the beams will traverse over a user location, while the airplane maintains stationary overhead, and the virtual path will be changed to accomplish the beam-to-beam handoff. The aircraft will fly above commercial airline traffic, at altitudes higher than 51,000 feet. For each city to be served, a fleet of three aircraft will be operated in shifts to achieve around-the-clock service. Flight operational tactics will be steadily evolved to achieve high availability of the node in the stratosphere.
The High Altitude Long Operation (HALO) Network is a broadband wireless metropolitan area network (MAN) consisting of HALO aircraft operating at high altitude and carrying an airborne communications network hub and network elements on the ground.
The HALO Network combines the advantages of two well-established wireless communication services: satellite networks and terrestrial wireless networks like cellular and personal communication systems. Satellite networks was deployed at low earth orbit (LEO), medium earth orbit (MEO), high elliptic orbit (HEO), and geosynchronous earth orbit (GEO) . Their disadvantages include expensive high-power user terminals, long propagation delays. Also, system capacity will be practically fixed and can be increased incrementally only by adding satellites. In contrast, terrestrial wireless networks have advantages such as low-cost, low-power user terminals, short propagation delays, and good scalability of system capacity. However, their disadvantages include low look angles and complex infrastructures. They require many base stations that must be interlinked over cables or microwave links. They often require significant re-engineering to increase capacity when using cell-splitting techniques.
The HALO network will be located in the atmosphere, at an altitude of 15 miles above terrestrial wireless, but hundreds to thousands of miles below satellite networks. It will provide broadband services to businesses and small offices/home offices in an area containing a typical large city and its neighbouring towns. To each end user it will offer an unobstructed line of sight and a free-space-like channel with short propagation delay, and it will allow the use of low-power low-cost user terminals.
The HALO network infrastructure is simple, with a single central hub. Consequently, the deployment of service to the entire metropolitan area can occur on the first day the network is deployed; and the subsequent maintenance cost is expected to be low. The system capacity can be increased by decreasing the size of beam spots on the ground while increasing the number of beams within the signal footprint, or by increasing the signal bandwidth per beam. The HALO network can interface to existing networks. It can operate as a backbone to connect physically separated LANs through frame relay adaptation or directly through LAN bridges and routers.
The HALO Network will be able to offer wireless broadband communications services to a "super metropolitan area," an area encompassing a typical large city and its surrounding communities. The aircraft will carry the "hub" of the network from which we will serve tens to hundreds of thousands of subscribers on the ground. Each subscriber will be able to communicate at multi-megabit per second bit rates through a simple-to-install user terminal. The HALO Network will be evolved at a pace with the emergence globally of key technologies from the data communications, millimeter wave RF, and network equipment fields.
The HALO aircraft will be operated in shifts from regional airports. While on the ground, the network equipment aboard the aircraft will be assessed, maintained and upgraded on a routine basis to ensure optimal performance. The HALO/Proteus airplane has been specially designed to carry the hub of the HALO Network. In the stratosphere, the airplane can carry a weight of approximately one ton. The airplane is essentially an equipment bus from which commercial wireless services will be offered. A fleet of three aircraft will be cycled in shifts to achieve continuous service. Each shift on station will have an average duration of approximately eight hours. The HALO/Proteus airplane will maintain station at an altitude above 51 Kft in a volume of airspace.
The look angle, defined to be the angle subtended between the local horizon and the airplane with the user terminal at the vertex; will be greater than a minimum value of 20 degrees. (The minimum look angle (MLA) for a given user terminal along the perimeter of the service footprint is defined to occur whenever the airplane achieves the longest slant range from that terminal while flying within the designated airspace.) Under these assumptions, the Many types of organizations schools, hospitals, doctors' offices, and small to medium-size businesses around the world will benefit from the low pricing of broadband services provided by the HALO Network. Standard broadband protocols such as ATM and SONET will be adopted to interface the HALO Network as seamlessly as possible. The gateway to the HALO Network will provide access to the Public Switched Telephone Network (PSTN) and to the Internet backbone for such services as the World Wide Web and electronic commerce. The gateway will provide to information content providers a network-wide access to a large population of subscribers
Some desirable features of the HALO Network include the following:
- Seamless ubiquitous multimedia services
- Adaptation to end-user environments
- Rapidly deployable to sites of opportunity
- Bandwidth on demand for efficient use of available spectrum
Signal footprint will cover an area of approximately 2,000 to 3,000 square miles, large enough to encompass a typical city and its neighbouring communities. Such a high value for the MLA was chosen to ensure a line-of-sight connection to nearly every rooftop in the signal footprint and to ensure high availability during heavy rainfall.
By selecting MMW frequencies, a broadband network of high capacity can be realized. The airborne antenna array can be configured to project a pattern of many cells numbering from 100 to more than 1,000. Each cell on the ground will cover an area of a few square miles to several tens of square miles.
The HALO network will provide wireless broadband communication services. The HALO network has several advantages over terrestrial wireless networks. The latter have complex geometries involving many base stations interlinked by cabling or microwaves. Moreover, each time cell splitting is used to increase system capacity, the network can demand significant reengineering. On the other hand, satellite networks require more expensive terminals with high power to achieve the same data rates possible through the HALO Network. Also, the longer propagation delays demand more complex algorithms to achieve interactivity. The capacity of a satellite network can be increased, but at higher expense than the HALO Network, typically only by adding more satellites. And, like terrestrial networks, reengineering of the entire satellite network may be required. The HALO Network has striking advantages over proposed large LEO(LOWER EARTH ORBIT) constellations, including ease of repair and rapidly evolving performance.