05-07-2010, 05:27 PM
Air Borne Internet.doc (Size: 303.5 KB / Downloads: 190)
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ABSTRACT
The word on just about every Internet user's lips these days is "broadband." We have so much more data to send and download today, including audio files, video files and photos, that it's clogging our wimpy modems. Many Internet users are switching to cable modems and digital subscriber lines (DSLâ„¢s) to increase their bandwidth. There's also a new type of service being developed that will take broadband into the air.
Our paper explains some of the drawbacks that exist in satellite Internet and introduces the airborne Internet, called High Altitude Long Operation (HALO), which would use lightweight planes to circle overhead and provide data delivery faster than a T1 line for businesses. Consumers would get a connection comparable to DSL. The HALO Network will serve tens of thousands of subscribers within a super-metropolitan area, by offering ubiquitous access throughout the networkâ„¢s signal "footprint". The HALO aircraft will carry the "hub" of a wireless network having a star topology. The initial HALO Network is expected to provide a raw bit capacity exceeding 16 Gbps.
The concept of basic network connectivity could be used to connect mobile vehicles, including automobiles, trucks, trains, and even aircraft. Network connectivity could be obtained between vehicles and a ground network infrastructure.
INTRODUCTION
High Altitude Long Operation (HALO) airplane is specially engineered for providing wireless communications networks, as a compliment to the existing system. The HALO airplane has a fixed-wing airframe with twin turbofan propulsion. The HALO Network will serve tens of thousands of subscribers within a super-metropolitan area, by offering ubiquitous access throughout the networkâ„¢s signal "footprint". The HALO aircraft will carry the "hub" of a wireless network having a star topology. The initial HALO Network is expected to provide a raw bit capacity exceeding 16 Gbps, which by utilizing packet-switching could, for example, serve 50,000 to 100,000 subscribers requiring links with DSL-equivalent peak data rates in both directions.
Three HALO aircraft will fly in shifts to provide continuous service, 24 hour per day by 7 days per week, with an overall system reliability of 99.9% or greater. The HALO airplane will fly above commercial airline traffic and adverse weather at altitudes higher than 51,000 and will provide a communications service footprint or "Cone of Commerce" of approximately 120 kilometers in diameter. Any subscriber within that region will be able to access the HALO Networkâ„¢s ubiquitous multi-gigabit per second "bit cloud" upon demand.
SATELLITE INTERNET
It takes weeks, sometimes months, to get a terrestrial broadband connection installed. Sometimes it takes that long before the provider admits that it cannot be delivered at all. Satellite Internet does not require the user to have any particular type of software, hardware or network. The system meshes with any combination of PCs, Macs, and UNIX or mainframe computers. It will plug into any network and performs well. Adding capacity can be handled remotely, meaning your satellite Internet can easily grow as your company grows. A temporary increase for a special situation can be handled without any difficulty.
WORKING
The data travels from the satellite equipment at the customers location to the satellite, and then to the teleport for routing to the Internet. The teleport is a secure facility where many large aperture satellite dishes are operated. The SES American operations center is located at the teleport and our equipment is located in a leased area inside the Network Operations Center (NOC).
At the NOC, routers are connected to the Internet using optical connections to a Internet backbone provider. Proprietary acceleration and advanced spoofing technology is employed to provide IP transparency and increase throughput speed.
Spoofing makes the service capable of very high speeds. The entire Internet is based on TCP/IP. TCP (Transmission Control Protocol) manages and controls transmissions using IP (Internet Protocol). TCP sends data and looks for acknowledgments (receipts) sent back from the receiving end to indicate that everything was received. If the acknowledgments are not received, TCP resends the packets and slows down its transmission speed for future data. TCP expects these acknowledgments to be received within a certain time frame. Because of the long round-trip (90,000+ miles) that the packets must travel over the satellite link and back, the acknowledgments are delayed by several hundred milliseconds. If uncorrected, this delay would cause TCP to throttle back its speed dramatically.
Spoofing is accomplished by special NOC equipment (Hybrid Gateway) that causes TCP acknowledgments to be returned to the sender very quickly. It does this by spoofing (pretending to be the remote site) and acknowledging the packets instantly, at the same time as it forwards the packets to the remote site.
DRAWBACKS
GEO satellites, when compared to terrestrial networks, are not as well suited to the tasks of connecting regional telecommuters to their corporate backbone and of transacting small information packets.
GEO satellites are less desirable than terrestrial networks for performing highly interactive collaborative work, now commonly occurring on modern corporate and campus networks.
Though GEOs offer a large amount of bandwidth downstream, they are challenged to offer a high enough upstream rate for truly interactive broadband services involving peer-to-peer active collaboration.
The cost to provide sufficient power in terrestrial end-user terminals in order to uplink the signals to the satellite at a high rate, especially through dense rain, are considered too high for the consumer, the small office/home office (SOHO), and even for most small- and medium-size businesses.
If you are located on the equator and are communicating with a satellite directly overhead then the total distance (up and down again) is nearly 72,000 km so the time delay is 240 ms. A satellite is visible from a little less than one third of the earth's surface and if you are located at the edge of this area the satellite appears to be just above the horizon. The distance to the satellite is greater and for earth stations at the extreme edge of the coverage area, the distance to the satellite is approx 41756 km. If you were to communicate with another similarly located site, the total distance is nearly 84,000 km so the end to end delay is almost 280 ms, which is a little over quarter of a second.
Extra delays occur due to the length of cable extensions at either end, and very much so if a signals is routed by more than one satellite hop. Significant delay can also be added in routers, switches and signal processing points along the route. The use of the TCP/IP protocol over satellite is not good and a number of companies have developed ways of temporarily changing the protocol to XTP over the satellite link to achieve IP acceleration.
AIRBORNE INTERNET
It was already shown that satellite Internet access can work. The airborne Internet will function much like satellite-based Internet access, but without the time delay. Bandwidth of satellite and airborne Internet access are typically the same, but it will take less time for the airborne Internet to relay data because it is not as high up. Satellites orbit at several hundreds of miles above Earth. The airborne-Internet aircraft will circle overhead at an altitude of 52,000 to 69,000 feet (15,849 to 21,031 meters). At this altitude, the aircraft will be undisturbed by inclement weather and flying well above commercial air traffic.
An airborne Internet network, called High Altitude Long Operation (HALO), which would use lightweight planes to circle overhead and provide data delivery faster than a T1 line for businesses. Consumers would get a connection comparable to DSL. The equipment will connect to existing networks and telecommunications equipment using standard broadband protocols such as ATM and SONET. The HALO Gateway provides access to the Public Switched Telephone Network (PSTN) and to the Internet backbone for such services as the World Wide Web and electronic commerce.
Key Features
The key features of the HALO Network are summarized below:
¢ Seamless ubiquitous multimedia services
¢ Adaptation to end user environments
¢ Enhanced user connectivity globally
¢ Rapidly deployable to sites of opportunity
¢ Secure and reliable information and data transactions
¢ Bandwidth on demand for efficient use of available spectrum
HALO - overview
There are various classes of service to be provided: (a) 1-5 Mbps communication links to consumers; and (b) 5-12.5 Mbps links for business users. Since the links would be bandwidth-on-demand, the total available spectrum would be shared between concurrent active sessions. The nominal data rates would be low while the peak rates would expand to a specified level. A gateway type service can be provided for dedicated links at 25-155 Mbps.
Network Access various methods for providing access to the users on the ground are feasible. The figure below shows one approach where each spot beam from the payload antenna serves a single cell on the ground in a frequency-division multiplex fashion with 5-to-1 frequency reuse, four for subscriber units and the fifth for gateways to the public network and to high-rate subscribers. Other reuse factors such as 7:1 and 9:1 are possible. Various network access approaches are being explored.
HALO Network Architecture
The HALO node provides a multitude of connectivity options as shown on the next page. It can be used to connect physically separated Local Area Networks (LANs) within a corporate intranet through frame relay adaptation or directly through LAN bridges and routers. Or it can provide videoconference links through standard ISDN or T1 interface hardware. The HALO Network may use standard SONET and ATM protocols and equipment to minimize the cost of the equipment and to take advantage of the wide availability of these components.
At the apex of a wireless Cone of Commerce, the payload of the HALO Aircraft becomes the hub of a star topology network for routing data packets between any two subscribers possessing premise equipment within the service coverage area. A single hop with only two links is required, each link connecting the payload to a subscriber. The links are wireless, broadband and line of sight.
HALO Network Architecture
Information created outside the service area is delivered to the subscriberâ„¢s consumer premise equipment (CPE) through business premise equipment (BPE) operated by businesses, Internet Service Providers (ISPs), or content providers within that region, and through the HALO Gateway ("HG") equipment directly connected to distant metropolitan areas via leased trunks. The HG is a portal serving the entire network. It avails system-wide access to content providers or advertisers, and it allows any subscriber to extend their communications beyond the HALO Network service area by connecting them to dedicated long-distance lines such as inter-metro optical fiber.
As with all wireless millimeter wave links, high rainfall rates can reduce the effective data throughput of the link to a given subscriber. It is planned to ensure maximum data rates more than 99.7% of the time, reduced data rates above an acceptable minimum more than 99.9% of the time, and to limit outages to small areas (due to the interception of the signal path by very dense rain columns) less than 0.1% of the time. It is planned to locate the HG close to the HALO orbit center to reduce the slant range from its high-gain antenna to the aircraft and hence its signal path length through heavy rainfall.
HALO Aircraft
The aircraft has been specially designed for the HALO Network with the Communications Payload Pod suspended from the underbelly of its fuselage. The HALO Aircraft will fly above the metropolitan center in a circular orbit of five to eight nautical miles diameter. The Communications Payload Pod is mounted to a pylon under the fuselage. As the aircraft varies its roll angle to fly in the circular orbit, the Communications Payload Pod will pivot on the pylon to remain level with the ground.
HALO Aircraft
Communications Payload
The HALO Network will use an array of narrow beam antennas on the HALO Aircraft to form multiple cells on the ground. Each cell covers a small geographic area, e.g., 4 to 8 square miles. The wide bandwidths and narrow beam widths within each beam or cell are achieved by using MMW frequencies. Small aperture antennas can be used to achieve small cells.
SUBSCRIBER UNITS
The block diagram entails three major sub-groups of hardware: the RF Unit (RU) which contains the MMW Antenna and MMW Transceiver; the Network Interface Unit (NIU); and the application terminals such as PCs, telephones, video servers, video terminals, etc. The RU consist of a small dual-feed antenna and MMW transmitter and receiver which is mounted to the antenna. An antenna tracking unit uses a pilot tone transmitted from the HALO Aircraft to point its antenna at the airplane.
The MMW transmitter accepts an L-band (950 - 1950 MHz) IF input signal from the NIU, translates it to MMW frequencies, amplifies the signal using a power amplifier to a transmit power level of 100 - 500 mW of power and feeds the antenna. The MMW receiver couples the received signal from the antenna to a Low Noise Amplifier (LNA), down converts the signal to an L-band IF and provides subsequent amplification and processing before outputting the signal to the NIU. Although the MMW transceiver is broadband, it typically will only process a single 40 MHz channel at any one time. The particular channel and frequency is determined by the NIU.
The NIU interfaces to the RU via a coax pair which transmits the L-band TX and RX signals between the NIU and the RU. The NIU comprises an L-band tuner and down converter, a high-speed (up to 60 Mbps) demodulator, a high-speed modulator, multiplexers and de-multiplexers, and data, telephony and video interface electronics. Each user terminal will provide access to data at rates up to 51.84 Mbps each way. In some applications, some of this bandwidth may be used to incorporate spread spectrum coding to improve performance against interference (in this case, the user information rate would be reduced).
The NIU equipment can be identical to that already developed for LMDS and other broadband services. This reduces the cost of the HALO Network services to the consumer since there would be minimal cost to adapt the LMDS equipment to this application and we could take advantage of the high volume expected in the other services.
Also, the HALO RU can be very close in functionality to the RU in the other services (like LMDS) since the primary difference is the need for a tracking function for the antenna. The electronics for the RF data signal would be identical if the same frequency band is utilized. The subscriber equipment can be readily developed by adapting from existing equipment for broadband services.
CONVERGING TECHNOLOGIES
The HALO Network is capable of providing high rate communications to users of multimedia and broadband services. The feasibility of this approach is reasonably assured due to the convergence of technological advancements.
The key enabling technologies at hand include:
 GaAs (Gallium Arsenide) RF devices which operate at MMW frequencies
 ATM/SONET Technology and Components
 Digital Signal Processing for Wideband Signals
 Video Compression
 Very Dense Memory Capacity
 Aircraft Technology
These technologies are individually available, to a great extent, from commercial markets. The HALO Network seeks to integrate these various technologies into a service of high utility to small and medium businesses and other multimedia consumers at a reasonable cost.
ADVANTAGES
Wireless Communications from High Altitude Aircraft
The HALO aircraft will operate above 52,000 feet, high above commercial airline traffic and adverse weather. Viewed as a very tall tower or an "atmospheric satellite," the HALO aircraft with its large antenna array and network components will serve customers throughout an area of thousands of square miles. The HALO aircraft has a fixed-wing airframe with twin turbofan propulsion.
Ubiquitous Access through the HALO Network
Prospective customers, irrespective of their location within the service area will be able to access the HALO Network unobstructed by foliage, buildings, and local terrain. This attribute, referred to as "ubiquitous access," results from the high operating altitude of the HALO aircraft.
The HALO Network Compared to Terrestrial Wireless Networks
The HALO Network utilizes a frequency re-use pattern to cover the service area with hundreds of contiguous virtual cells, each comparable to a terrestrial tower offering broadband service at millimeter-wave frequencies. The deployment of a terrestrial wireless network may be sporadic and local since it requires negotiations of roof rights, compliance with local zoning laws, and construction of many towers. In contrast, the HALO Network can offer ubiquitous access and a consistent quality of service to prospective subscribers throughout the entire super-metropolitan region on the first day of service. In addition, Angel can easily and immediately implement network-wide performance enhancements through scheduled upgrades of modular components.
The HALO Network Compared to Satellite Systems
The HALO Network can complement satellite systems by transmitting local or regional content, and by serving as a local concentrator of data traffic. The HALO aircraft is 10 to 1,000 times closer to the user than a satellite, with 10 times the available electrical power.
Consequently, the HALO Network can allocate significant capacity directly to densely populated regions. Unlike satellite systems, which are "all or nothing" multi-billion dollar investments, the HALO Network can be financed one market at a time. In addition, the central node of the HALO Network, the airborne hub, can be routinely serviced for optimal performance, and be steadily enhanced with emerging technologies resulting from world-wide competition.
Routine Operations and Maintenance
HALO aircraft will be certified by the Federal Aviation Administration (FAA) for piloted commercial operation and can operate from regional airports without special authorization. The aircraft can utilize alternate airports anywhere within a 300 mile radius of the city if required. Such operational flexibility ensures service availability. Prior to each flight, the aircraft and their HALO Network components undergo scheduled maintenance to guarantee high service quality. Each HALO site is serviced by a fleet of three HALO aircraft which operate in overlapping shifts around-the-clock.
Broadband Services for Businesses
Corporations with local area networks and intranets will use the HALO Network to extend their LANs outside the corporate firewall to their employeeâ„¢s homes, regional offices, field locations, key suppliers and customers. Corporations also will be able to utilize video conferencing and allow their employees to telecommute, saving both time and money. Entrepreneurs, consultants, and small companies will form virtual corporations interconnected within the Cone of Commerce." Business users will be offered connection speeds ranging from 5 to 12.5 Mbps. Initial high capacity users can enjoy links at 25 Mbps and higher.
Ease of Installation
It is designed the HALO Network and the consumer premise equipment (CPE) to ensure ease of installation by the consumer. The CPE, whether delivered or purchased through a retailer, is designed for rapid installation and ease of use. The antenna is self-pointing and is mounted on an outside area offering a clear view of the HALO aircraft.
CONCLUSION
Using this wireless broadband "super-metropolitan" area network, tens to hundreds of thousands of subscribers could be integrated each at multi-megabit per second data rates. A HALO aircraft will operate above commercial airline traffic to serve as the hub of the millimeter wave wireless broadband network providing ubiquitous coverage as well as dedicated point-to-point connections. Broadband wireless services will be delivered to diverse enterprises to promote new forms of dialogue and interaction.
REFERENCES
1. J. Martin and N. Colella , "Broadband Wireless Services from High Altitude Long Operation (HALO) Aircraft,"
2. N. Colella and J. Martin, "The Cone of Commerce".
3.G. Djuknic, J. Freidenfelds, et al., "Establishing Wireless Communications Services via High-Altitude Aeronautical Platforms: A Concept Whose Time Has Come.