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VSAT

VSAT. Agenda. Introduction to Gilat Satellite Networks What is a VSAT ? Typical VSAT Applications Satellite Communication Fundamentals VSAT Network Architectures Access Schemes Network Components Network Management VSATs Applications in Amateur Radio Demonstration of Equipment Summary.

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VSAT

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  1. VSAT

  2. Agenda • Introduction to Gilat Satellite Networks • What is a VSAT ? • Typical VSAT Applications • Satellite Communication Fundamentals • VSAT Network Architectures • Access Schemes • Network Components • Network Management • VSATs Applications in Amateur Radio • Demonstration of Equipment • Summary

  3. Gilat Satellite Networks Ltd. • Founded in 1987 • Over 950 employees worldwide • Core technology: End-to-end two-way satellite broadband platform • Sales, service and support offices worldwide • Traded on NASDAQ (GILTF) since 1993 • Revenues in 2001: $389M • Headquartered in Petech Tikva, Israel • Three Regional Headquarters: • Spacenet (North America) Mclean, VA • Gilat Latin America – Sunrise, FL • Gilat Asia, Pacific Rim and Africa – Petach Tikva, Israel

  4. What is a VSAT ? • VSAT = Very Small Aperture Terminal • Satellite-based Wide Area Network (WAN), with centrally managed hub • Remote site: less than 1.2m dish antenna • Multi-service platform: Data, telephony and multimedia communications • Optimal for continent-wide networks of hundreds or thousands of units • Small networks integrated in shared hub service • Large networks, in the tens of thousands, for Internet access

  5. VSAT Advantages • Full or partial independence from terrestrial infrastructure • Cost savings over terrestrial lines • Nationwide reach, distance-independent • Network management from a single point • Quick deployment, network flexibility • Consistent and rapid response time • Increased network availability and reliability • Inherent broadcast / multicast platform

  6. Unicast, Multicast, Broadcast • Each Unicast Packet is Numbered and Acknowledged

  7. Unicast, Multicast, Broadcast • Multicasts Packets are Not Acknowledged • Different Data Steams can be sent simultaneously to many users

  8. Unicast, Multicast,Broadcast • Broadcast Packets are sent to all users in the Network Simultaneously • Broadcasts are Not Acknowledged • VSAT Networks can use Reliable BroadcastProtocols and applications that are based on NACK’s, not ACK’s

  9. VSAT SpeedsCompared to Dialup Modem • The name of the game is THROUGHPUT ! • A 56K Modem will typically connect at speeds of only 43Kbps

  10. VSAT Markets • Enterprise • Retail; Oil & Gas; Banking; Government • POS; Back Office; Browsing; Telemetry • Telephony • Public: Public Call Offices, small businesses, farmers, private lines • Corporate: Telephony/Data infrastructure • Internet (IP) • High-speed, always-on, Internet-access for consumers, small businesses and schools • Intranet and IP infrastructure for the enterprise • IP multicast-based services • BTV • Content delivery

  11. Characteristics of GEO Satellites • 35,680 Km above the Earth • ~24 Hour Period • Average 14-17 Year Lifespan • Single Satellite theoretically can provide up to 42% Earth Coverage • Large, expensive, difficult to launch • Located approximately every 2oabove the equator • Several Satellites may operate at the same azimuth on different frequencies/polarization

  12. The Clarke Belt • xx

  13. GEO/LEO Comparison

  14. Geosynchronous Orbit Fleet

  15. LEO Orbit ConstellationGlobalstar • Loral initiative • Subsidiary of Airtouch (Cellular) • Aimed at global cellular phone coverage • Qualcomm based CDMA • 48 satellite constellation (8 planes x 6 ea. + 4 spares) • 52 now in orbit ! • 8 orbital planes of 6 satellites each • 80% Earth coverage (+/- 68 degrees) • LEO orbit (1414 km) • Ground Operations Control Centers (GOCCs) and Satellite Operations Control Centers (SOCCs) control gateway and control functions Qualcomm GSP1600

  16. Obtaining Satellite Detailshttp://www.lyngsat.com

  17. Obtaining Satellite Detailshttp://www.lyngsat.com

  18. Satellite Details – Amos 1http://www.spacecom.co.il/ Middle East Beam

  19. Satellite Details – Amos 1http://www.spacecom.co.il/ European Beam

  20. VSAT Network ArchitecturesOne Way Satellite DVB Modulator LAN RFT VSAT TVRO Antenna IP Encapsulator Router Internet • One-Way – Receive Only • High Bit-Rate DVB Compliant Outbound • Inbound Return Channel via Dial-Up Modem • Can be used with existing infrastructure • Example: Harmonic’s CyberStreamTM Baseband Equipment DVB Receiver Modem/ISDN Return TCP/IP ACK’s NACK’s

  21. VSAT Network ArchitecturesTwo-Way Star Topology • All VSATs Communicate via a Single Hub • Network is Independent of Existing Infrastructure • VSAT Antenna Size dependent upon Power and Gain of Hub Antenna • Also Upon Inbound Bitrate, ODU Power and Satellite Footprint • Contention Based Access – Usually TDMA or FTDMA • Typical Ping Times Approximately 650-700ms VSAT VSAT VSAT Hub VSAT VSAT VSAT VSAT VSAT

  22. VSAT Network ArchitecturesTwo-Way Star Topology – Double Hop

  23. VSAT Network ArchitecturesTwo-Way Mesh Topology • VSATs communicate directly with each other • Some systems require initial signaling via the Hub • Larger Antennas, Higher Power required at the VSAT • Smaller Antenna, Lower Power required at the Hub • Used extensively in Telephony Networks • Delay minimized on VSAT to VSAT Calls VSAT VSAT VSAT VSAT VSAT VSAT

  24. Network Components Skystar 360E

  25. Typical Hub Configuration

  26. Network Management • Entire Network Controlled, Configured and Monitored from a Single Location called the NOC (Network Operations Center)

  27. Typical VSAT Indoor Unit(Skystar 360E) (Front) (Rear)

  28. Typical VSAT Outdoor Unit/Antenna Reflector Feed-Assembly LNB-F (Optional) LNB-F (Optional) LNB LNB SSPA(HPC) (Front) (Rear)

  29. VSAT Communication Bands • VSAT Networks use Geostationary Satellites (GEO) • All located directly above the equator, at an altitude of ~36,000 km and spaced approximately every 2 degrees

  30. Space Segment • VSAT Networks lease space segment from the Fixed Satellite Service (FSS) Provider • Price is mainly determined by Bandwidth and Power • Geosynchronous Satellites frequencies consist of an Uplink and Dowlink, each covering a 500 MHz bandwidth • The many transponders operating within this range typically extend from 36-72 MHz each • Each Transponder has a finite power level that is shared amongst the users • Excessive Power levels can cause distortion to all users on the transponder

  31. Bit Rate/Symbol Rate • If more bits can be sent with each symbol, then the same amount of data can be sent in a narrower spectrum • For example, for a bitstream of 80 kbps using BPSK (1 bit per symbol), the symbol rate is the same. For QPSK (2 bits per symbols), the symbol rate is ½ the bit rate or, 40 kbps. For 8PSK (3 bits per symbol) is would be 1/3 the bit rate, or 26.66 kbps Bit Rate Symbol Rate= # of bits transmitted with each symbol

  32. Modulation Types Q 0 State 1 State I • BPSK – Binary Phase Shift Keying • Use alternative sine wave phase to encode bits • Simple to implement • Inefficient use of Bandwidth • Very Robust • One bit per symbol (2 States) • QPSK – Quadrature (Quarternary) Phase Shift Keying • Efficient use of Bandwidth • Requires more complex receiver for demodulation • Two bits per symbol (4 States) • MSK – Minimal Shift Keying • Easy to Generate – More Complex Receiver • Special form of FSK • Spectrally efficient, better noise performance at receiver 45o11 State Q 45deg “00” 315deg “01” 315o00 State I 225deg “11” 135deg “10” 135o10 State 225o00 State Q I

  33. Forward Error Correction (FEC) BER 10E-1 Un coded 10E-2 Coded 10E-3 10E-4 10E-5 Coding Gain 10E-6 Eb/N0 3 4 5 6 7 8 9 • FEC provides the ability for transmitted data to be ‘self-correcting’ without the need for re-transmission (As in ARQ) • Thus, we can transmit with LESS POWER - The price is Overhead and Bandwidth ! • FEC ½ means that for every bit sent, an additional bit of overhead is sent; ¾ means for every 3 bits, one bit of overhead, and so on…

  34. Forward Error Correction (FEC) • Two classes of Forward Error Correction codes • Convolutional Codes and Block Codes • Convolutional Coding (Viterbi Decoding) • Based on minimum hamming distance “code words” feed through a shift register • Reed Solomon Code (RS) is a form of Block Code that breaks the data stream up into fixed size blocks and adds redundancy symbols • On the other side of the link, the data is decoded using linear algebraic algorithms . This type of code adds considerable overhead • Concatenated Viterbi – refers to an error correction technique which uses Viterbi in conjunction with Reed Solomon coding. Adds approximately 2dB to the link budget • Turbo Codes with an even stronger coding gain will eventually replace Convolutional and RS coding

  35. Bit Error Rate (BER) & Eb/N0 • Bit error rate is Directly Proportional to the Eb/N0 Threshold • Typical BER in some VSAT Systems can be <1.00E -08 (Less than one error in every 100,000,000 bits) for an Eb/No of only 4.8dB • “Robust” in the digital worlds describes a system that can be (near) error-free in a noisy signal path C  Place Picture of C/N Here Place MSK Signal Here N DPSK Modulation CW

  36. Link Budget (Margin) • The process of correctly sizing uplink and downlink paths for: • Satellite • Hub • Remotes • Takes into account: • Satellite performance • Path Loss • Atmospheric effects • Frequency bands • Uplink antenna and amplifier performance • Download antenna size and receiver noise figure • Path Loss at 12 GHz over 36,000 km can exceed –205 dB !

  37. Access SchemesThe Need for Bandwidth Efficiency OB IB F1 F2 F3 F4 F5 F6 F7 Fn • Bandwidth (and power) = $ • Better bandwidth efficiency translates into Cost Savings • Outbound and Inbound BW proportional to: • Number of Users • Bit Rate • Power/Modulation & Error Correction Coding • Type of traffic • QoS (Quality of Service) • Outbound Transmission: Constant, Single Frequency • Inbound Transmission: Bursty, Frequency Hopping • All VSATs must share the allocated inbound BW

  38. Access SchemesTime Division Multiple Access (TDMA) 17 17 17 11 11 11 19 Frequency 1 • Transmissions occur on the same frequency from multiple sources • When a collision occurs, each source waits a random amount of time before re-transmitting • Time slots are allowed to pass unused • In a loaded network, more collisions will occur, increasing the random wait time 12 Time 17 CollisionOccurs 18 Collision Recognized Retransmits after 3 slots delay time Retransmits after 5 slots delay time

  39. Access SchemesTime Division Multiple Access (TDMA) 17 17 17 11 11 11 19 Frequency 1 • Transmissions occur on the same frequency from multiple sources • When a collision occurs, each source waits a random amount of time before re-transmitting • Time slots are allowed to pass unused • In a loaded network, more collisions will occur, increasing the random wait time 12 Time 17 CollisionOccurs 18 Collision Recognized Retransmits after 3 slots delay time Retransmits after 5 slots delay time

  40. Access SchemesFrequency/Time Division Multiple Access – Random Access (RA) 102 053 021 102 021 053 102 021 Collision 006 006 102 Retransmission 102 006 006 006 Allocated Bandwidth Inbound Frequencies 1.2MHz F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 Frequency 120kHz Time Slots Time VSAT 006 VSAT 021 VSAT 053 VSAT 102

  41. Access SchemesAutomatic Dedicated Access • A “private” frequency is allocated to a single VSAT • Collision free, high throughput channel for batch applications and file transfer • When a DA is required by a VSAT, initiate request is sent in RA mode, triggered • According to IP-socket or IP address • According X.25 destination address • Throughput based • Then, a DA frequency is allocated f RA DA DA 11 31 17 34 14 17 34 21 17 34 21 14 17 t 34 25 17 34 17 34 25 14 17 17 34

  42. Access SchemesAutomatic Partial Dedicated Access • Partial allocation for better utilization of DA channel • Optimal for Constant Bit Rate (CBR) applications, such as voice • Guarantees fixed response time • DA can be flexibly divide into PDAs f RA 11 31 17 15 14 17 32 21 17 21 14 17 15 25 17 32 17 25 14 17 15 17 32 t

  43. Access SchemesDual Bit Rate • Support of dual bit rate improves space segments utilization • Any 2 bit rates can be supported • Each VSAT supports two bit rates with multiple access modes • Lower bit rate for RA and higher bit rate for DA • Each Receiver Cage at the hub can handle two bit rates f RA DA PDA 11 17 15 14 17 32 21 17 21 14 17 15 17 32 17 36 25 14 17 15 17 32 76.8 153.6 76.8 t

  44. Acknowledgments over SatelliteSpoofing • The Problem: TCP/IP requires acknowledgment of each and every packet • The Satellite delay [(36,000/300000)2]2 in addition to all the routers along the way adds significant latency • Spoofing Concept: • Acknowledge TCP packets locally at the VSAT/Hub – Send ‘Acknowledge Summary’ periodically No Spoofing With Spoofing

  45. Acknowledgments over SatelliteInternet Page Acceleration (IPA) • On Terrestrial Based Networks, each HTML object is requested and acknowledged • IPA requests all the objects on a specific URL • All objects on an HTML Page are sent to the VSATs at once

  46. Amateur Radio ApplicationsInternet-to-Radio Link • Typical Node VSAT Antenna PC + Sound Card + VoIP Application VHF or UHF Omni VSAT Radio/PC Interface VHF/UHF Conventional or Trunked Repeater

  47. Amateur Radio ApplicationsInternet-to-Radio Link New York Repeater/VSAT Hub VoIP Servers Boston Repeater/VSAT VoIP Internet Direct Internet London Repeater/Direct

  48. Amateur Radio ApplicationsInternet-to-Radio Link - eQSO • xx

  49. Amateur Radio ApplicationsInternet-to-Radio Link - Echolink

  50. Amateur Radio ApplicationsHF Remote Base/Diversity Reception

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