HALO                 HALO Network

Broadband.com Data Services from a HALO Aircraft

Peter H. Diamandis and Nicholas J. Colella

Angel Technologies Corporation - 314-918-1700/phone 314-918-1710/fax

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Scaled Composites Incorporated, a partner of Angel Technologies Corporation (www.broadband.com), has recently built and will soon flight test a High Altitude Long Operation (HALO) airplane specially engineered for providing wireless communications networks. The HALO airplane has a fixed-wing airframe with twin turbofan propulsion. It will be FAA certified for piloted operation. Its high altitude flight regime was pioneered in the 1950’s and its components will benefit from decades of aerospace industry experience and innovation.


The HALO Network will serve tens of thousands of subscribers within a super-metropolitan area, by offering ubiquitous access throughout the network’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 DS1-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 Network’s ubiquitous multi-gigabit per second "bit cloud" upon demand.



Keywords: HALO Aircraft, HALO Network, Cone of Commerce™, broadband wireless services, metropolitan area network, bit cloud.




An electronic "information fabric", a weave of space-based, atmospheric, and terrestrial data communications infrastructure, is emerging hat will link digital information devices anywhere on the Earth. Packet-switched data networks will meld with or replace connection-oriented telephony networks. An era of inexpensive, ubiquitous bandwidth has already begun.

The convergence of market demand, regulatory reform, innovative technologies and manufacturing capabilities affecting aviation, millimeter wave wireless, and multi-media communications industries enables Angel to pursue new wireless broadband communications services. The HALO Network will offer ubiquitous access to any subscriber within a "super metropolitan area" from an aircraft operating at high altitude. The aircraft will serve as the hub of the HALO Network serving tens of thousands of customers. Each customer will be able to communicate at multi-megabit per second data rates through a simple-to-install subscriber unit. The HALO Network will be steadily evolved at a rapid pace defined by the emergence of advanced technology world-wide. The HALO Network will be a wireless communications network solution. It will be an evolving template to be deployed globally on a city-by-city basis.


2. The HALO Network

Subscribers in homes, businesses, schools and health-care facilities will be able to communicate with each other and with producers/distributors of information, special content, and entertainment services. The subscriber’s premise equipment will be standards-based and will require a level of understanding by the subscriber no higher than an ordinary modem for today’s personal computers. A small dome mounted on the outside of the premise will house a high-gain antenna with a small aperture that will automatically track the HALO aircraft circling miles away at high altitude.


Figure 1: Premise Equipment for The HALO™ Network


At the apex of a wireless Cone of Commerce™, the payload of the HALO aircraft will serve as 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.


Information created outside the service area is delivered to the subscriber’s consumer premise equipment ("CPE") through business premise equipment ("BPE") operated by Internet Service Providers ("ISPs") or content providers within that region, and through the HALO Gateway ("HG") directly connected to distant metropolitan areas. The HG is a portal serving the entire network. It avails system-wide access to content providers 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.





Figure #2: The HALO™ Network


The CPE, BPE and HG have functions in common. They use a high-gain antenna that automatically tracks the HALO aircraft; extract modulated signals conveyed through the air by millimeter waves; convert the extracted signals to digital data; provide standards-based data communications interfaces; and route the digital data to information appliances, personal computers, workstations and servers connected to the premise equipment. Thus, some of the technologies and components, both hardware and software, will be common to the designs of these three basic network elements. All of these elements are being demonstrated in related forms by terrestrial 38 GHz and 28 GHz (LMDS) vendors.


As with all wireless millimeter wave links, rainfall will reduce the strength of the signal received by a given subscriber. For customers at the perimeter of the signal footprint who own CPEs, Angel plans to ensure maximum data rates more than 99.7% of the time, provide 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. Customers at shorter slant ranges will have higher availability. Angel plans 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 the length of the signal path through heavy rainfall.


Angel assumes the minimum look angle ("MLA") will be higher than 20 degrees typically, perhaps as low as 10 degrees for regions with low rainfall attenuation. The MLA corresponds to subscribers at the perimeter of the service footprint and is defined to be the elevation angle above the local horizon to the furthest point on the orbit as measured from the antenna of the premise equipment. Angel chose such a high look angle to ensure that the antenna of each subscriber’s premise equipment will very likely have access to a solid angle swept by the circling HALO aircraft free of dense objects, and to ensure high availability of service to all subscribers even during heavy rainfall.


A frequency reuse approach similar to traditional cellular mobile networks can be employed in the HALO™ Network. The available spectrum would be divided into frequency sub-bands that are projected from the communications pod as separate "beams". Details on this approach are also described in prior papers, "Broadband Wireless Services from a HALO™ Aircraft" and "The Cone of Commerce".1


Suppose the frequency bands providing the up and down links to the HALO™ aircraft are divided into five (5) equal sub-bands {A, B, C, D, and E}. A subset of four (4) sub-bands {A, B, C, and D} can then be arranged to form a square tile which, in turn, is tessellated to cover the service area. Each sub-band within a tile, whether labeled A, B, C, or D, will serve many subscribers who share the capacity available in the beam spot corresponding to that sub-band.


On the other hand, sub-band {E} is "orthogonal" in frequency to the other four (i.e., its spectrum is disjoint of the other four sub-bands). It offers frequencies not used in any tiles. Consequently, it can be located anywhere within the signal area to serve premiere customers on a dedicated basis. (This assertion requires the separation between neighboring {E} beam spots be not less than the minimum distance linking the centers of neighboring tiles within the service area, assuming all sub-bands involve similar size antenna apertures on the HALO™ aircraft.)


Each frequency tile repeated on the ground corresponds to a single airborne antenna "cell" in the pod suspended beneath the HALO™ aircraft. The antenna cells are arranged somewhat like the photo-receptors forming the eye of a common household fly to cover the service area. Each cell creates many beams, i.e., multiples of the four sub-bands {A,B,C,D}, through a common refractive optical train specifically optimized for millimeter wave throughput. Whereas, the {E} beam spots are created by conventional, high-gain antennas that are pointed and stabilized by electro-mechanical or electronic steering means.




The HALO aircraft fuselage contains the Airborne Switching Node ("ASN"), the primary coolant loop, and power conditioning. Packing switching and network management functions are performed by the ASN. The communications pod suspended beneath the aircraft fuselage contains the millimeter wave antenna array with amplifiers and transceivers. It converts millimeter waves to and from digital signals and is composed of an array of antennas that beam signals to subscribers and to the HG. Power and coolant flow between the platform and the payload through a pylon mount which, in turn, can maintain the payload pod level relative to the ground about the aircraft roll axis if required. A standard optical interface conveys digital communications data across the pylon interface that connects the ASN to the Mux/Demux circuitry in the Pod, which, in turn, impresses the modulated signal upon or extracts it from the millimeter wave carrier.




Figure #3: HALO™ Aircraft with Its Communications Pod

From a payload perspective, the HALO™ aircraft is a "flying antenna". It is being prepared for flight testing by Burt Rutan and his team at Scaled Composites during the Summer 1998.


The aircraft configuration is fixed wing with carbon composite materials. Propulsion will be provided by FAA-certified twin fan jets. The platform will be operated by a pilot and co-pilot. The crew cabin will be pressurized to provide a comfortable "shirt sleeve" work environment. Station keeping will be performed by an auto-pilot utilizing coordinates provided by the Global Position Satellite constellation. The two pilots will alternate the duty of flying the airplane. The pilot who is relieved of flight responsibility can be made available to perform routine status checks of the communications payload, including the operations of the components of the ASN in the fuselage section, as well as those in the suspended Pod. Smart diagnostics data regarding health, status, and operation of the communications equipment will be graphically displayed to the pilot to enable early detecting and forecasting of problems. Similar but wider data streams will be sent to the local operations center on the ground through the Gateway to enable technicians to monitor the status, health, and performance of the airborne communications node.


The payload bearing attributes of the HALO aircraft include:

2300 lb. for the airborne elements of the HALO Network distributed as 1800 lb. for the suspended communications Pod, and 500 lb. for the fuselage section with the pylon and the ASN;

18 ft diameter communications Pod housing the antennas and their interfaces;

40 KVA power for the ASN and Pod elements with matched thermal management; and

If required, bank angle compensation of the Pod.



4. Concept of operations

The HALO aircraft will execute a circular orbit of roughly 5 to 8 nautical miles in diameter at an altitude above 51,000 feet. From that vantage, broadband services can be offered to users over an area of several thousand square miles or larger encompassing a typical major city and its surrounding towns and communities.



Piloted Aircraft. In order to streamline the aircraft development and FAA certification processes, the HALO aircraft will be manned with two pilots. Over time, Angel may decide to transition to single pilot operation, to be followed by unmanned operations, if the regulatory climate becomes more favorable.



Number of Aircraft per Site. Angel will maintain a continual HALO aircraft presence on-station above each market served. Angel has planned for 8-hour mission times on station, although the airplane is capable of longer endurance. Three aircraft will be assigned to each isolated site: one on-station, one ascending or descending or being prepared for flight at the local or regional airport facility, and one spare.



Rapid Ground Turnaround Time. An emphasis on "line replaceable unit" maintenance will allow Angel’s dedicated personnel to perform regular and unscheduled maintenance actions between missions.



Weather Diversions. Angel will pursue a certificate under FAR23 regulations and will be authorized to operate in the full range of normal instrument flight conditions. Angel’s operational plan will be conservative for it will allows the HALO aircraft to avoid significant weather by diverting to alternate municipal airports with current and forecast conditions approaching visual flight rules. Even the largest storm systems, a few hundred miles across, can be avoided, since such a distance will be readily traversed with the flight speed and fuel margin offered by the airplane.


The following factors contribute to Angel’s expectation of achieving high operating reliability with HALO aircraft:


Lessons over decades with airborne military transport and express freight aircraft operations will be applied.

Angel will utilize fleet redundancy to ensure continuity of service in anticipation of worst case failure scenarios.

HALO aircraft fleet operations will be steadily improved as the aircraft design is refined and as operating behaviors and performance are logged, analyzed, and utilized to upgrade choices of components and maintenance activities.

HALO aircraft incorporate redundant mission critical systems.

The pilots will provide real-time awareness of aircraft and communications systems through highly-responsive graphical user interfaces.



5. Markets & services

Angel is implementing a two-part domestic marketing strategy coupled with an international Joint Venture strategy to rapidly deploy HALO Networks worldwide.



5.1 Domestic- Phase 1

Angel is pursuing relationships with those customers who desire a ubiquitous network offering a first-mile/last-mile broadband solution independent of the legacy networks, an agile, routinely upgraded, service mix, and a wireless solution which can be quickly installed with minimum fixed capital expenditures. Angel’s near-term customers are likely to be the "carriers". As a "Carrier’s Carrier", Angel may serve two types of customers: (1) those who need first mile/last mile services to highspeed "backbones" or long-line carriers to better serve their customers; and (2) millimeter-wave licensed spectrum holders who want to increase their subscriber base.



5.2 Domestic- Phase 2

Angel will continue as a "Carriers Carrier", and will begin to directly serve diverse businesses. As new cities are opened by Angel, the Company may wholesale a large fraction of its capacity to Carriers and reserve the remainder for Angel-branded broadband services. Angel anticipates offering a mix of digital information services to business customers. Angel plans to reach its customers through a variety of sales channels, including strategic marketing relationships, reciprocal resale agreements, and direct and indirect sales efforts. Examples of Angel’s customers include the following:


County & City Government: Angel can provide County and City Governments with an agile broadband network to provide Fire, Police, Emergency Management, and Public Works departments with backup communications to the terrestrial networks, offering a "disaster resistant" solution. The HALO Network gives "portable" broadband connectivity to these departments.

Internet Service Providers: Regional ISPs wanting to provide business customers high speed connections independent of RBOCs and Cable companies.

Healthcare Industry: Hospitals who wish to extend their network to multiple buildings, physician’s offices, Human Relations offices, and to convalescing patients at home.

Manufacturing Industry: Large corporations wishing to interconnect their office buildings, manufacturing plants, sub-contractors, customers, executives and consultants.


5.3 International

Outside the United States, Angel plans to establish regional joint ventures, involving partners working in concert to market, deploy, and operate HALO Networks at the major cities within their region. Deployments will be accomplished with the cooperation of national PTTs and/or the local wireless operators as required.



5.4 First Market – Los Angeles

Los Angeles is a strong candidate to be Angel’s first marketplace. Beta testing may commence midyear-2000 and, if market and regulatory conditions are right, Angel may enter full commercial operation soon thereafter. LA is an attractive candidate because it has fair weather, a large population, and mandates for increased telecommuting. After a successful deployment in LA, Angel and its partners will select other cities. The first 3 or 4 domestic HALO sites may be on the west coast, from San Diego to as far north as Seattle.



5.5 Competitive Service Pricing

Broadband connection prices vary extensively depending upon the distance of the business from the Central Office (CO) and the number of competitive access providers in the region. Typical pricing for a T1 Connection is $300 to $700 per month, and for 10 Megabit (10 Based-T) at $4,000 to $8,000 per month. Angel has evaluated how to price its services based upon today’s market and the competitive playing field in the year 2000 and beyond. The Company has assumed rapidly falling prices of these services. The HALO Network throughput is expected to be increased from its initial 16 Gbps capacity to over 100 Gbps during the first five years.


6. HALO Aircraft as satellite concentrators

The HALO Network can serve as a valuable adjunct to a broadband satellite network. Compared to HALO Networks, satellite-based broadband systems suffer four limitations, namely: they are power limited; they require costly premise equipment; transmission frequencies are regulated by the ITU; and satellites do not serve high density population centers effectively because of their inherent power and distance limitations. The HALO Network can increase the throughput and the competitiveness of satellite systems.


HALOs can compensate for the limitations:

They have ample power. The baseline power buss of the HALO airplane can deliver more than 40 KVA or greater, typically 10 times higher than available on satellites.

Because of the relatively short range between the HALO airplane and the user (10 to 50 miles), low-cost, low-power premise equipment can be used. Only a single antenna with slow tracking is required.

The HALO Network does not require ITU coordination. Frequencies assigned to the HALO Network are within the control of the local PTT. In the U.S., for example, the HALO Network can utilize 28 GHz and 38 GHz frequency bands licensed to terrestrial services. Since the HALO Network is a "frequency agnostic", frequencies in the 3 to 20 GHz range can be used for broadband services in other countries.

The HALO Network can serve hundreds-of-thousands of broadband subscribers on a metropolitan distance scale. As such, a HALO can serve as a "concentrator" for satellite systems, through which connections to destinations outside the Cone of Commerce can be made through HALO-to-satellite links.


Figure #4: HALO/Satellite Hybrid Networks

HALOs offer three benefits to an integrated HALO-satellite global network:

Since HALOs are positioned high above most of the atmosphere, they can easily "see" numerous satellites, even those over oceans and deserts.

The HALO-to-satellite link can use very high carrier frequencies, e.g., those above 60 GHz offering ultra-wide bandwidths.

The HALO is the front end of the integrated system. The airplane and its communications systems can be accessed each day. The integrated network can thus be steadily evolved (even radically changed, if necessary).


7. Attractive Attributes of the HALO™ Network

Given the lack of infrastructure to support the current and projected demands for broadband data communications, an intense race has begun to deploy broadband networks to satisfy businesses and consumers. These networks include satellite constellations, atmospheric alternatives to HALO aircraft, and terrestrial wired and wireless networks. The space layer includes satellites operating at geo-synchronous orbit ("GEO") and low-Earth orbit ("LEO"). The atmospheric layer includes high-altitude autonomous airships (i.e., dirigibles) and the HALO aircraft. The terrestrial layer includes wireless data transport at millimeter wave carrier frequencies, wireless local loop at the PCS frequency band, data transport over coaxial cable installed for cable television, and an assortment of digital subscriber line services ("xDSL") over twisted wire pairs installed for telephone networks.


According to multiple interviews with prospective customers, the HALO Network offers the following attractive attributes:

Ubiquity. Perhaps the most compelling attribute of the HALO Network is the ubiquitous nature of its services within the 75 mile diameter footprint. Once the HALO is flying overhead – on Day 1 of service -- anyone within the "Cone of Commerce" can access service and communicate with anyone else within that footprint.

Upgradeability. The total capacity (throughput) of the HALO Network can be increased by swapping out the "Hub" or payload with an upgraded version.

Network Reliability/Maintenance. After each landing of the HALO aircraft, the network operations team will be able to conduct a complete and thorough "check-out" of the entire network, thus making sure that the network is operating at an optimal level of performance at the beginning of each shift.

Independence from traditional carriers. The HALO Network will offer to Internet Service Providers a means of directly connecting to their customers without having to utilize Cable or Copper services, which are now beginning to compete with ISPs.

Rapid provisioning. The HALO Network can turn-on a new customer within one day, an attribute desirable to ISPs. This is best exemplified by a quote from a LA-based ISP, who said, "The Local Loop carrier everywhere is a big pain and very slow … If we can bypass them all together that would be a great advantage. Right now if your customer asks you to install a ISDN or T1 connection, it’ll really test your relationship with that customer because of the delays and difficulties involved in working with that unknown Telco."

Portable broadband services. HALO broadband services can be provided to stationary cars and trucks, for example police cars, fire trucks, and emergency management vans. Angel refers to this as "portable" broadband, of potentially high value to municipal services and to businesses such as real-estate, building/construction and transportation companies.

Easily movable/re-deployable. Because the HALO broadband connection can be so quickly provisioned, it can also be rapidly removed and reinstalled. This is of particular value to companies/organizations who wish to install temporary connections, e.g., consultants for companies, hospitals wishing to set up a connection at the home of the recovering patient, and rapidly growing businesses who are constantly juggling offices and buildings.

Disaster-Proof Infrastructure. By virtue of the airborne nature of the HALO Network, Angel is able to offer a system that is disaster-resistant to earthquakes, tornadoes, and hurricanes.

Angel has several parameters to vary in order to enhance the performance and to increase the capacity of the HALO Network. For example, enhancements of network capacity can be realized by increasing the number of cells in the communications pod, or the number of beam feeds per cell, or both, along with appropriate scaling of electronics. Alternatively, the bandwidth per beam spot can be widened or the encoding order increased. Performance enhancements practical at the system level, however, will be determined by trades and balances. Increasing the system capacity more than ten-fold within several years after the introduction of the first network may be realizable.



Angel and its partners are creating a wireless broadband "super-metropolitan" area network to interconnect tens to hundreds of thousands of subscribers 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. Angel will serve two distinct market segments: ‘first-mile/last-mile’ connections for current carriers; and broadband connections to selected businesses. The HALO Network can serve as a valuable adjunct to proposed satellite networks by serving as a "concentrator." Due to the high altitude of the HALO airplane, the HALO Network can greatly increase access to potential subscribers of terrestrial millimeter-wave services obscured by natural and man-made objects relative to towers. Angel plans to cultivate partnerships with strategic vendors, to hire engineers of superb talent, and to foster "win-win" opportunities with satellite-based and terrestrial service providers. The HALO aircraft will commence flight testing during the summer of 1998.




J. Martin and N. Colella, "Broadband Wireless Services from a HALO™ Aircraft," Proc. of the SPIE International Symposium on Voice, Video, and Data Communications: Broadband Engineering for Multimedia Markets, 1997.

Also refer to "The Cone of Commerce," by N. Colella and J. Martin at the same conference.

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