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  2. 2. DIVISION OF COMPUTER ENGINEERING SCHOOL OF ENGINEERING COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY KOCHI-682022 Certificate Certified that this is a bonafide record of the seminar entitled “HALO NETWORK” done by the following student NIKHIL DEV.B thof the VII semester,Computer Science and Engineering in the year 2008 inpartial fulfillment of the requirements to the award of Degree of Bachelor ofTechnology in Computer Science and Engineering of Cochin University ofScience and Technology.Mrs.Dhanya K Sudheesh Dr.David Peter SSeminar Guide Head of the DepartmentDate:
  3. 3. ACKNOWLEDGEMENT Although a single sentence hardly suffices, I would like to thankalmighty god for blessing me with his grace and taking my endeavor to asuccessful culmination. I also express my gratitude to Dr. David Peter,HOD and myseminar guide for providing me with adequate facilities, ways and meansby which I was able to complete this seminar. I express my sinceregratitude to him for his constant support and valuable suggestions withoutwhich the successful completion of this seminar would not have beenpossible. I thank Mrs.Dhanya K Sudheesh my seminar guide for herboundless cooperation and helps extended for this seminar. I would liketo extend my gratitude to all staff of Department Of Computer Sciencefor the help and support rendered to me. I have benefited a lot from thefeedback, suggestions and blessings given by them. I would like to extend my gratitude to all of my friends for theirhelp and support rendered to me in the various phases of this seminar. NIKHIL DEV.B
  4. 4. ABSTRACT The High Altitude Long Operation NetworkTM is a broadbandwireless metropolitan area network, with a star topology, whose solitaryhub is located in the atmosphere above the service area at an altitudehigher than commercial airline traffic. The HALO/Proteus airplane is thecentral node of this network. It will fly at altitudes higher than 51,000 ft.The signal footprint of the network, its "Cone of Commerce," will have adiameter on the scale of 100 km. The initial capacity of the network willbe on the scale of 10 Gb/s, with growth beyond 100 Gb/s. The networkwill serve the communications needs of each subscriber with bit rates inthe multimegabit per second range. A variety of spectrum bands licensedby the FCC for commercial wireless services could provide the neededmillimeter wavelength carrier bandwidth. An attractive choice for thesubscriber links is the LMDS band. The airplanes fuselage can house switching circuitry and fastdigital network functions. An MMW antenna array and its relatedcomponents will be located in a pod suspended below the aircraftfuselage. The antenna array will produce many beams, typically morethan 100. Adjacent beams will be separated in frequency. Electronicbeamforming techniques can be used to stabilize the beams on theground, as the airplane flies within its station keeping volume. For thealternative of aircraft-fixed beams, the beams will traverse over a userlocation, while the airplane maintains station overhead, and the virtualpath will be changed to accomplish the beam-to-beam handoff. For eachisolated city to be served, a fleet of three aircraft will be operated in shiftsto achieve around-the-clock service. In deployments where multiple citieswill be served from a common primary flight base, the fleet will be sizedfor allocating, on average, two aircraft per city to be served. Flight
  5. 5. operational tactics will be steadily evolved and refined to achievecontinuous presence of the node above each city. Many services will beprovided, including but not limited to T1 access, ISDN access, Webbrowsing, high-resolution videoconferencing, large file transfers, andEthernet LAN bridging.
  6. 6. Chapter-1 Introduction1.1 Introduction Passage of the 1996 Telecommunications Act and the slow growth of infra-structure for transacting multimedia messages (those integrating voice, text, sound,images, and video) have stimulated an intense race to deploy non-traditional infra-structure to serve businesses and consumers at affordable prices. The game is new andthe playing field is more level than ever before. Opportunities exist for entrepreneursto challenge the market dominance enjoyed for years by incumbents. New types ofservice providers will emerge. An electronic "information fabric" of a quilted character—including space, at-mospheric, and terrestrial data communications layers—will emerge that promises tosomeday link every digital information device on the planet. Packet-switched datanetworks will meld with connection-oriented telephony networks. Communicationsinfrastructures will be shared more efficiently among users to offer dramatic reduc-tions in cost and large increases of effective data rates. An era of inexpensive band-width has begun which will transform the nature of commerce. The convergence of innovative technologies and manufacturing capabilities af-fecting aviation, millimeter wave wireless, and multi-media communications indus-tries enables Angel Technologies Corporation and its partners to pursue new wirelessbroadband communications services. The HALO™ Network will offer ubiquitous ac-cess to any subscriber within a "super metropolitan area" from an aircraft operating athigh altitude. The aircraft will serve as the hub of the HALO™ Network serving tensto hundreds of thousands of subscribers. Each subscriber will be able to communicateat multi-megabit per second data rates through a simple-to-install subscriber unit. TheHALO™ Network will be steadily evolved at a pace with the emergence of data com-munications technology world-wide. The HALO™ Network will be a universal wire-less communications network solution. It will be deployed globally on a city-by-citybasis. The equipment needed to perform the functions of this broadband wireless ser-vice will be evolutionary in nature, not revolutionary. Most of the technology already
  7. 7. exists. The engineering effort will be focused primarily at adapting and integrating theexisting components and subsystems from terrestrial markets into a complete networksolution. Proven technology will be used to the maximum extent. Since the HALO™Aircraft are operated from regional airports, the equipment will be routinely main-tained and calibrated. This also allows for equipment upgrades as technology ad-vances yield lower cost and weight and provide increased performance.1.2 Wireless Broadband Communications Market There are various facts that show the strong interest in wireless communica-tions in the United States: • 50 million subscribers to wireless telephone service • 28 million dollars annual revenue for wireless services • 38,000 cell sites with 37 billion dollars cumulative capital investment • 40% annual growth in customers • 25 million personal computers sold each year • 50 million PC users with Internet access "The demand for Internet services is exploding and this creates a strong de-mand for broadband, high data rate service. It is expected that there will soon be aworldwide demand for Internet service in the hundreds of millions". (Lou Gerstner,IBM, April 1997) The growth in use of the World Wide Web and electronic commercewill stimulate demand for broadband services.
  8. 8. 1.3 A Broadband Wireless Metropolitan Area Network HALO™ Aircraft Provides Wireless Broadband Services over Metropolitan Centers An airplane specially designed for high altitude flight with a payload capacityof approximately one ton is being developed for commercial wireless services. It willcircle at high altitudes for extended periods of time and it will serve as a stable plat-form from which broadband communications services will be offered. The High Alti-tude Long Operation (HALO™) Aircraft will maintain station at an altitude of 52 to60 thousand feet by flying in a circle with a diameter of about 5 to 8 nautical miles.Three successive shifts on station of 8 hours each can provide continuous coverage ofan area for 24 hours per day, 7 days per week. Such a system can provide broadbandmultimedia communications to the general public. One such platform will cover an area of approximately 2800 square miles en-compassing a typical metropolitan area. A viewing angle of 20 degrees or higher willbe chosen to facilitate good line-of-sight coverage at millimeter wave (MMW) fre-quencies (20 GHz or higher). Operation at MMW frequencies enables broadband sys-
  9. 9. tems to be realized, i.e., from spectrum bandwidths of 1 to 6 GHz. MMW systemsalso permit very narrow beam widths to be realized with small aperture antennas. Fur-thermore, since the aircraft is above most of the earths oxygen, links to satellite con-stellations can be implemented using the frequencies overlapping the 60 GHz absorp-tion band for good immunity from ground-based interference and good isolation frominter-satellite links. The HALO™ Network can utilize a cellular pattern on the ground so that eachcell uses one of four frequency sub-bands, each having a bandwidth up to 60 MHzeach way. A fifth sub-band can be used for gateways (connections to the public net-work or dedicated users). Each cell will cover an area of a few square miles. The en-tire bandwidth will be reused many times to achieve total coverage throughout the2800 square mile area served by the airborne platform. The total capacity of the net-work supported by a single airborne platform can be greater than 100 Gbps. This iscomparable to terrestrial fiber-optic (FO) networks and can provide two-way broad-band multimedia services normally available only via FO networks. The HALO™ Network provides an alternative to satellite- and ground-basedsystems. Unlike satellite systems, however, the airborne system concentrates all of thespectrum usage in certain geographic areas, which minimizes frequency coordinationproblems and permits sharing of frequency with ground-based systems. Enoughpower is available from the aircraft power generator to allow broadband data accessfrom small user terminals.1.4 A New Layer in the Wireless Infrastructure Raytheon TI Systems and Angel Technologies Corporation have the opportun-ity to serve the growing wireless communications market by using a HALO™ Air-craft that transmits high-speed data traffic throughout a metropolitan region. The goalis to interconnect more than 100,000 subscribers within a metropolitan center and itssurrounding communities through a star topology network. This HALO™ Networkhas the benefits of low cost, high flexibility, and high quality of service.
  10. 10. HALO™ Aircraft provide a new layer in the traditional hierarchy of wirelesscommunications. The HALO™ Network can be thought of as a "tall tower" approachthat provides better line of sight to customers without the high cost of deploying andoperating a satellite constellation. Terrestrial Towers <200 feet HALO™ Aircraft 10 miles Low Earth Orbit (LEO) Satellites 400 miles Geostationary Earth Orbit (GEO) Satellites 22,300 miles This paper will describe the architecture and the concept of operations of theHALO™ Network. It will also describe key characteristics of the HALO™ Aircraftand the communications payload and subscriber units. A companion paper1 entitled"The Cone of Commerce™" covers the business and market aspects of the HALO™Network. The paper by Djuknic2 provides an overview of the various options andhighlights the unique advantages of stratospheric platforms for providing wirelesscommunications services.
  11. 11. Chapter-2 THE HALO NETWORK CONCEPT2.1 Overall Concept The attributes of the HALO™ Network are illustrated in the figure below. Manytypes of subscribers will benefit from the low price of HALO™ Network broadbandservices—schools, families, hospitals, doctors offices, and small to medium size busi-nesses. The equipment will connect to existing networks and telecommunicationsequipment using standard broadband protocols such as ATM and SONET. TheHALO™ Gateway provides access to the Public Switched Telephone Network(PSTN) and to the Internet backbone for such services as the World Wide Web andelectronic commerce.
  12. 12. High-Speed Data Links Transmitted Over Millimeter Wave Frequencies ProvideBroadband Data Services to Various End-Users2.2 Key FeaturesThe 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 transactions • Bandwidth on demand provides efficient use of available spectrum2.3 Service Area Most metropolitan areas will fit within a signal "footprint" of 40-60 milesdiameter. The following figure shows the coverage of a 50-mile HALO™ Networkservice-area footprint for the New York City metropolitan area. Notice that "doublecoverage" of certain areas occurs due to overlapping adjacent footprints. Thisprovides higher reliability links and reduces blocking factors on requests for service.The footprint over Manhattan covers 4.8 million households or 12.5 million people.2.4 Service Attributes There are various classes of service to be provided. A consumer service wouldprovide 1-5 Mbps communication links. A business service would provide 5-12.5Mbps links. Since the links would be "bandwidth-on-demand," the total availablespectrum would be time-shared between the various active sessions. The nominal data
  13. 13. rates would be low while the peak rates would expand to a specified level. A gatewayservice can be provided for "dedicated" links of 25-155 Mbps. Based on the LMDS spectrum and 5-fold reuse, the service capacity would be10,000 to 75,000 simultaneous, symmetrical T1 circuits (1.5 Mbps) per Communica-tions Payload. The HALO™ Aircraft would provide urban and rural coverage from asingle platform to provide service to: a. 100-750,000 subscribers b. 40-60 mile diameter service area (1,250 to 2,800 square miles) Coverage of the New York City Metropolitan Area by HALO™ Aircraft2.4.1 Spectrum Options There are various options for spectrum utilization, the main options being
  14. 14. spectrum at 28 GHz for the Local Multipoint Distribution Service (LMDS) and themicrowave point-to-point allocations at 38 GHz. The FCC is expected to allocate 850MHz of spectrum between 27.5 and 28.35 GHz for the LMDS service. The systemcharacteristics described in this paper are for the LMDS frequency.2.4.2 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 an-tenna serves a single "cell" on the ground in a frequency-division multiplex fashionwith 5 to 1 frequency reuse, four for subscriber units and the fifth for gateways to thepublic network and to high-rate subscribers. Other reuse factors such as 7:1 and 9:1are possible. Various network access approaches are being explored.
  15. 15. Cell Coverage by Frequency Division Multiplexing using Spot Beams2.4.3 Network Services The HALO™ node provides a multitude of connectivity options as shown be-low. It can be used to connect physically separated Local Area Networks (LANs)within a corporate intranet through frame relay adaptation or directly through LANbridges and routers. Or it can provide videoconference links through standard ISDNor T1 interface hardware. The HALO™ Network may use standard SONET and ATMprotocols and equipment to minimize the cost of the equipment and to take advantageof the wide availability of these components.
  16. 16. The HALO™ Network Accommodates a Variety of Interfaces
  17. 17. Chapter-3 HALO NETWORK ARCHITECTURE3.1 Network Elements The major elements of the HALO™ Network are shown below. The HALO™Network interfaces to the Public Switched Telephone Network (PSTN) and to the In-ternet backbone through the HALO™ Gateway. On the subscriber side, the HALO™Network provides connectivity to local networks of various kinds. The HALO™ Network Architecture
  18. 18. 3.2 Network Architecture 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 betweenany two subscribers possessing premise equipment within the service coverage area. Asingle hop with only two links is required, each link connecting the payload to a sub-scriber. The links are wireless, broadband and line of sight. Information created outside the service area is delivered to the subscribersconsumer premise equipment ("CPE") through business premise equipment ("BPE")operated by Internet Service Providers ("ISPs") or content providers within that re-gion, and through the HALO™ Gateway ("HG") equipment directly connected to dis-tant metropolitan areas via leased trunks. The HG is a portal serving the entire net-work. It avails system-wide access to content providers and it allows any subscriber toextend their communications beyond the HALO™ Network service area by connect-ing them to dedicated long-3.3 Field of View Angel assumes the "minimum look angle" (i.e., the elevation angle above thelocal horizon to the furthest point on the orbit as seen by the antenna of the premiseequipment) is generally higher than 20 degrees. This value corresponds to subscribersat the perimeter of the service footprint. In contrast, cellular telephone designers as-sume that the line of sight from a customer to the antenna on the nearest base stationis less than 1 degree. Angel chose such a high look angle to ensure that the antenna ofeach subscribers premise equipment will very likely have access to a solid angleswept by the circling HALO™ Aircraft free of dense objects, and to ensure highavailability of the service during heavy rainfall to all subscribers. The high look angle also allows the sharing of this spectrum with ground-based wireless networks since usually high-gain, narrow beams are used and the an-tenna beams of the HALO™ and ground-based networks will be separated in angle
  19. 19. far enough to ensure a high degree of signal isolation. Service area
  20. 20. Chapter-4 HALO AIRCRAFT The HALO™ Aircraft is under development and flight testing is expected tooccur by mid-1998. The aircraft has been specially designed for the HALO™ Net-work with the Communications Payload Pod suspended from the underbelly of its fu-selage. HALO™ Aircraft with Suspended Communications Payload The HALO™ Aircraft will fly above the metropolitan center in a circular orbitof five to eight nautical miles diameter. The Communications Payload Pod is mountedto a pylon under the fuselage. As the aircraft varies its roll angle to fly in the circularorbit, the Communications Payload Pod will pivot on the pylon to remain level withthe ground. Other details on the aircraft can be found in the Cone of Commerce™ pa-per.
  21. 21. Chapter-5 COMMUNICATIONS PAYLOAD The HALO™ Network will use an array of narrow beam antennas on theHALO™ Aircraft to form multiple cells on the ground. Each cell covers a small geo-graphic area, e.g., 4 to 8 square miles. The wide bandwidths and narrow beam widthswithin each beam or cell are achieved by using MMW frequencies. Small aperture an-tennas can be used to achieve small cells. For example, an antenna having a diameterof only one foot can provide a beam width of less than three degrees. One hundreddish antennas can be easily carried by the HALO™ Aircraft to create one hundred ormore cells throughout the service area. If lenses antennas are utilized, wider beamscan be created by combining beams through each lens aperture, and with multiplefeeds behind each lens multiple beams can be formed by each compound lens. If 850 MHz of spectrum is assumed, then a minimum capacity of one full-du-plex OC-1 (51.84 Mbps) channel is available per cell. For example, a single platform reusing 850 MHz of spectrum in 100 cells would provide the equivalent of two, OC-48 fiber optic rings. Higher capacities are possible by increasing the number ofcells. By using Asynchronous Transfer Mode (ATM) technology with over-the-air dy- namic bandwidth allocation, this capacity can be shared by multiple users in an effi- cient manner. An ATM-like packet switch on the HALO™ Aircraft provides the net-work switching capability to cross-connect all users within the coverage area as wellas connections to other users through gateways. The elements in the communications payload are shown below. It consists of MMW transceivers, pilot tone transmitter,high-speed modems, SONET multiplexers, packet switch hardware and software, and associated ancillary hardware such as power supplies, processors, etc.
  22. 22. Functional Block Diagram of the Communications Payload The major design options for antennas in the Communications Payload are toutilize either platform-fixed beams or earth-fixed beams. For the case of platform-fixed beams, each antenna would have a fixed field of view. The total field of view forthe entire HALO™ Network would be the sum of these fields of view of the individu-al antennas. The network could initially have a small footprint and as demands on theHALO™ services increase, additional antennas could be added to the Communica-tions Payload. This results in a modular design, readily adaptable for growth. Platform-fixed beams are simpler to construct generally, but require the "han-doffs" between beams to be accomplished by the packet switching equipment as thebeams "sweep" across the ground with the movement of the aircraft. However, thecost and performance penalties for frequently changing the virtual path through thepacket switch may be appreciable. An alternative is to electronically steer the beams so they remain "fixed" onthe ground as the aircraft moves. These results in more electronic and physical com-plexity for the antennas, but this may be a good trade-off to make since the burden on
  23. 23. the packet switch and its network management software would be greatly reduced.These trade-offs are still being assessed. For the case of earth-fixed beams, each antenna would have a wider field ofview than the sum of the beams in that antenna since each beam can be steered in alldirections. Each beam could be capable of steering throughout the HALO™ footprint,or could be assigned a smaller portion. If there are "gaps" in the required coveragedue to such things as rivers, hills, or forests, then the earth-fixed beams can be steeredaway from these undesirable coverage zones and more efficient usage of the antennasmight result compared to the case of platform-fixed beams..
  24. 24. Chapter-6 SUBSCRIBER UNITS A block diagram describing the CPE (and BPE) is shown below. It entailsthree major sub-groups of hardware: The RF Unit (RU) which contains the MMWAntenna and MMW Transceiver; the Network Interface Unit (NIU); and the applica-tion terminals such as PCs, telephones, video servers, video terminals, etc. The RUconsist of a small dual-feed antenna and MMW transmitter and receiver which ismounted to the antenna. An antenna tracking unit uses a pilot tone transmitted fromthe Communications Payload to point the antenna toward the airborne platform. The MMW transmitter accepts an L-band (950 - 1950 MHz) IF input signalfrom the NIU, translates it to MMW frequencies, amplifies the signal using a poweramplifier 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 NoiseAmplifier (LNA), down converts the signal to an L-band IF and provides subsequentamplification and processing before outputting the signal to the NIU. Although theMMW transceiver is broadband, it typically will only process a single 40 MHz chan-nel at any one time. The particular channel and frequency is determined by the NIU.
  25. 25. Functional Block Diagram of the Subscriber Equipment The NIU interfaces to the RU via a coax pair which transmits the L-band TXand RX signals between the NIU and the RU. The NIU comprises an L-band tunerand down converter, a high-speed (up to 60 Mbps) demodulator, a high-speed modu-lator, multiplexers and de multiplexers, and data, telephony and video interface elec-tronics. Each user terminal will provide access to data at rates up to 51.84 Mbps eachway. In some applications, some of this bandwidth may be used to incorporate spreadspectrum coding to improve performance against interference (in this case, the userinformation rate would be reduced). The NIU equipment can be identical to that already developed for LMDS andother broadband services. This reduces the cost of the HALO™ Network services tothe consumer since there would be minimal cost to adapt the LMDS equipment to thisapplication and we could take advantage of the high volume expected in the other ser-vices. Also, the HALO™ RU can be very close in functionality to the RU in the otherservices (like LMDS) since the primary difference is the need for a tracking functionfor the antenna
  26. 26. Chapter-7 SUMMARY The HALO™ Network is capable of providing high rate communications tousers of multimedia and broadband services. The feasibility of this approach is reas-onably assured due to the convergence of technological advancements. The key en-abling technologies at hand include: • GaAs 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 commer-cial markets. The HALO™ Network seeks to integrate these various technologies intoa service of high utility to small and medium businesses and other multimedia con-sumers at a reasonable cost.
  27. 27. REFERENCE• N. Colella and J. Martin, ” The cone of Commerce ” ,Proc. Of the SPIE Inter- national Symposium on Voice, Video, and Data Communications : Broadband Engineering for Multimedia Markets,1997.• G. Djuknic , J. Freidenfelds, et al. “Establishing Wireless Communications Services via High Altitude Aeronautical Platforms: A concept Whose Time Has Come? “ IEEE Communications Magazine , September 1997.• www.angeltechnologies.com/techpapers