CEENET Workshop 2001 Satellite communications Krzysztof Muchorowski NetSat Express muchor@ids.pl

1. CEENET Workshop 2001Satellite communicationsKrzysztof MuchorowskiNetSat Expressmuchor@ids.pl

2. Introductory remarks • The purpose of this lecture is to give you a very general overview of satellite communication, it is not meant to be a complete description of the world of satellite communication… • I will often mention applications and business services… • I will try not to deviate from the main course, but please stop me if I do.

3. A few reasons of satellite revolution: • A single satellite can provide coverage to over 30% of Earth’s surface. • It is often the only solution for developing areas. • It is ideal for broadcast applications. • It can be rapidly deployed. • It is scalable. • Depending on application, there is no need for the local loop. • Transmission cost is independent on distance. • One hop from the backbone, wherever you are. • Wide bandwidths (155 Mbps) are available now.

4. What is a satellite? • Isaac Newton noticed first, that if we throw an object on Earth horizontally with big enough velocity, it will not fall down, but will circulate around Earth indefinitely.

5. R=6400 km T=84 minutes • R=7100 km T=99 minutes (LEO) • R=11400 km T=201 minutes (MEO) • R=42350 km T=24 hrs (GEO) • So, an object placed at the orbit approx. 36 000 km above the equator will be seen at the same position in the sky from Earth. • But roundtrip time will be more than half a second! • Is this position actually stable?

6. a few remarks about LEO and MEO satellites(Teledesic, Iridium)

7. but ... • omnidirectional antenna vs directional one • what does it mean in terms of available frequency spectrum? There are (in general) three bands of spectrum available for GEO satellite communication: C, Ku, Ka. C - 4-7 GHz (5 cm wavelength) Ku - 10-14 GHz (2.3 cm wavelength) Ka - 18-30 GHz (1 cm wavelength)

8. Properties of spectrum bands • C band: • large beams • The actual footprint of Intersputnik Express 3A • little rain fade (but sand storms affect it as well!) • large antennas • expensive amplifiers • lots of noise on the ground! • also circular polarization • Rx: 3625 to 4200 MHz • Tx: 5850 to 6435 MHz

9. Properties of spectrum bands (contd) • Ku-band • most widely used today • smaller beams (even spot beams) • smaller antennas • stronger rain fade • cheaper amplifiers • suitable for home users as well • noise on the ground is already often a problem • steerable spot beams • Rx: 10.95 to 12.75 GHz • Tx: 14 to 14.5 GHz • Ka band (still at development phase)

10. OK, so now let’s take a look at how a satellite is built and launched.

12. India's GSAT Hits Problems Following its successful launch last week, ISRO's GSAT experimental satellite a series of in orbit manoeuvres have used most, if not all, of the available fuel on the spacecraft. Unfortunately, the GSLV launcher did not place GSAT in exactly the right orbit - the apogee achieved was 32,051 km instead of the 35,975 km expected. Also, the inclination of the orbit was 19.2° instead of the intended 19°. The reason for this slight difference has not yet been determined. It was originally believed that the intended orbit could be achieved by a series of short thruster burns using the satellite's attitude control thrusters at the expense of the on board fuel and hence satellite lifetime. Unfortunately, the satellite carries two different propellant tanks, which resulted in an unequal flow of fuel. The resulting imbalance created an impulse that made the spacecraft tilt. All the remaining fuel was then used in order to stabilise the satellite. Two different tanks were used because they were available. The designers were aware of the imbalance in flow rates but did not adequately compensate for its effects. GSAT is now in a 23 hour 2 minute orbit and is reported to be out of fuel. It is not yet known what, if any use can be made of the spacecraft. [press release, excerpts, April 2001]

13. Ariane 5 Satellites in Wrong Orbit Following a perfect lift off from its launch site at Kourou, French Guiana, on Thursday Ariane 5 failed to put two comsats in the correct transfer orbit. Initial indications are that the second stage of the rocket shut down prematurely. The two satellites were intended to be placed in a 35,853 km x 858 km transfer orbit with an inclination of 2.0°. They were actually left in a 17,528 km x 592 km orbit with an inclination of 2.9°. Early reports are that the second stage, the Astrium manufactured Storable Propellant Stage (EPS), only generated 80% of the intended thrust and cut out 80 seconds early. It should have fired for 16 minutes 20 seconds, but this should have automatically been extended to compensate for the reduced thrust. Telemetry indicated that an anomaly occurred three seconds after ignition. Speculation is that the problem was caused by a propellant leak. The upper stage uses monomethyl hydrazine fuel and nitrogen tetroxide oxidiser, which are fed from pressurised tanks to a single Aestus motor. In spite of these problems the second stage managed to orient itself correctly and successfully deployed the two satellites, leaving at least the possibility of recovery. The satellites left in limbo by Ariane 510 are Artemis, an experimental European Space Agency telecommunications satellite, and BSAT-2b, a Japanese TV broadcast satellite. Artemis, with a price tag of US$ 850 million, is ESA's most expensive satellite ever. It may carry enough fuel to allow it to reach geostationary orbit where it should be able to use ion propulsion thrusters for station keeping. Japanese Broadcasting Satellite System's BSAT-2b may be a different story - it probably has enough fuel to reach geostationary orbit, but would be left without fuel for station keeping. This was the tenth launch of an Ariane 5 and the third failure. Ariane 4, by comparison, which is due to be replaced by Ariane 5 in 2003 when the remaining stock of 12 launchers is used up, has had a series of 62 consecutive successful launches. Before Thursday's launch failure, Arianespace was expecting to have three further Ariane 5 launches and three more Ariane 4 launches before the end of the year. The next Ariane 5 was scheduled to launch Atlantic Bird 2 and Insat 3C in September and the next Ariane 4 was to launch Intelsat 902 on 23 August. An inquiry board has been appointed to investigate the cause of the launch failure. Preliminary conclusions are due at the beginning of August. [press release from July 2001]

14. How much does a satellite cost? • How much does it cost to launch it? • How many transponders does it carry? • How long does it work? • What happens at the end of life? • Inclined orbit satellites.

15. Business Models

16. Does Size Matter?

17. Canada Venezuela United States Colombia Ecuador Bahamas Dominican Republic Puerto Rico Brazil Peru Mexico Belize Jamaica Bolivia Honduras Guatemala Nicaragua Paraguay El Salvador Costa Rica Panama Argentina Chile Uruguay SATMEX PROPRIETARY INFORMATION Other satellite issues (to close the topic) • Rights to orbital slots, landing rights.

18. Other satellite issues (contd) • EIRP, G/T • Effective Isotropic Radiation Power - EIRP - often expressed in decibels relative to 1W - dBW. Ku-band satellites typically about 50 dBW, C-band satellites typically about 35 dbW • G/T - gain by temperature - parameter of satellite antennas and position on Earth.

19. Other satellite issues (contd) • spring and autumn equinox • twice a year, around March 21 and September 23, satellite, earth station and sun are positioned along one line… • C band signal are affected more than Ku band signals • Stronger carriers are obviously less affected • Smaller antennas are less affected because their beamwidth is wider relative to the perceived radiation beamwidth of the sun (there are fewer days of outage, with shorter durations each day). • In the Fall, the farther north from the equator the station is, the later the effect occurs (in the Northern Hemisphere, the fall effect occurs after the Equinox). In the Southern Hemisphere, the reverse is true; the Fall effect occurs before the Equinox, and the further south a station is located the earlier it occurs. Satellites in locations east of the ground station have sun outage periods in the morning, and conversely, satellites located west of the station experience sun outages in the afternoon.

20. (contd from previous page) • No action usually required unless: • You have an antenna tracking system, which should be put in standby or manual mode. • You want to reroute traffic for the several minutes of outage each day (worst case). • For those customers with duplex service, it is important to remember that the outage for your inbound and outbound links may occur at different days and at different times during the day. • http://www.ips.gov.au/papers/richard/calc_inter.html

21. Pro-s and con-s of inclined orbit satellites • Con-s: • One probably only has about a year of service left before the satellite finally dies. • One will suffer a large Doppler shift • One will need to add tracking to the antenna (typically +$20k for a 2.4m) • Pro-s: • Price!!!

22. Hardware: ground segment • Antenna • Receiving/transmitting chain • Types of connection • Link budget

23. Antenna • Parabolic or offset • diameter - gain (as a function of frequency) • noise - temperature (as a function of elevation) • cross-polarisation isolation • de-icing (if required) • wind resistance • temperature variations tolerance • tracking...

24. Antenna (contd)

25. Antenna (contd) • Various kinds of antennas… • (what if we used two to transmit…)

26. Antenna (contd) • Flat antennas (e.g. for Inmarsat phones) (A short break from the main course of the lecture :)

27. High Performance Outdoor UnitAntenna & RF • Flat panel antenna • RF Unit on rear • Single cable - no rf • All digital & DC • Self leveling tripod • Fixed mount available • Audio tone for antenna pointing

28. Compact Indoor Unit • 5 phone / fax jacks • 9.6 Kb. Data • 56 / 64 Kb HSD • Plug in Interfaces forRS-232,-449, V.35,X.21, and S0 ISDN • Menu in 5 languages • Speakerphone

29. “Go Anywhere” Package • Entire system packs in a soft carry case • Case contains: • Antenna • RF Unit • Indoor Unit • Power Unit • Cables • Manual

30. Great Accessories for a Great Product • The VIDEO EXPLORER • Briefcase video conferencing • TOKO BROADCAST VIDEO • Store & forward video at up to 2 Mb anywhere • STU-III Secure Phones at 9.6 Kb. • Datacom Accessories & Routers • Muxes, PBXs, Cordless Phones

31. The Video ExplorerH.320 Video Conferencing in a Briefcase • 2 way, live video • Camera with 12X zoom & autofocus • 6” color display • supports 56-384Kb.ISDN Network • weighs approx 18 lbs. • Internal Phone End of break - back to main course

32. LNA (Low Noise Amplifier) or LNB (Low Noise Block) LNA - amplifies RF signal from the antenna and feeds it into frequency converter (typically IF of 70/140 MHz) LNB - amplifies RF signal from the antenna and converts it to an L-band signal (950-2100 MHz) LNA is more precise and stable but more expensive than LNB (LO stability). Transmit power amplifiers provide amplification of signals to be transmitted to the satellite Transceiver takes 70/140 MHz signal and amplifies it to either C or Ku-band final frequency. Block UpConverter takes L-band signal and amplifies it to either C or Ku-band final frequency. What is better? Receiving/transmitting devices

33. LNB properties (example)

34. Ku-band transceiver (example)

35. Amplifiers • How much power is necessary? • Answer requires link budget… • typically, a few Watts for Ku-band, a few tens of Watts for C-band. • SSPA (Solid State Power Amplifiers) will be enough in almost every case.

36. Modems • Satellite modem: • modulates input digital signal into analog signal and vice versa: demodulates input analog signal to digital data. • Typical parameters • supported modulations • FEC, Reed-Solomon • maximum speed • interfaces (on both sides) • compatibility… (this you never know until you try)

37. Modem parameters • Modulations/coding • How many bits per symbol (cycle, 1 Hz)? • 1 - BPSK • 2 - QPSK • 3 - 8PSK • 4 - 16QAM • (cable modems have typically 64QAM or perhaps even better now…) • FEC - forward error correction • QPSK 3/4, 7/8 • 8PSK 2/3, 5/6 • 16QAM 3/4, 7/8 • Turbo coding • Reed-Solomon - additional performance improvement, but extra 188/204 factor

38. Modem parameters (contd) • Interfaces: • on IDU side: • V.35 (up to a few Mbps) • EIA-422, 449, 530 (up to 8 and 18 Mbps) • HSSI (up to 52 Mbps) • G.703 (as above) • OC-3c (exactly 155.52 Mbps) • on ODU side: • 70/140 MHz (to transceiver) • L-band (to BUC)

39. Modem parameters (example)

40. IRD instead of a modem • Integrated receiver decoder (IRD) performs same functions as demodulator except that it typically provides as its interfaces: • Ethernet • Video/audio outputs • Audio outputs • Don’t assume any compatibility between IRDs until you experimentally verify it. • IRDs are children of DVB era, direct-to-home and broadcast applications.

41. Redundancy • What is redundancy? • When is it required? • How is it done? • What remains a single point of failure?

42. Bit Error Rate • A demod’s BER performance is specified as a function of (signal energy per bit)-to-(noise power density per hertz) ratio - Eb/N0 • The Eb/N0 ratio is so important because the bit error rate for digital data is a decreasing function of this ratio. • To ensure that a specified BER is met, a link budget analysis must be performed in order to ensure that the required Eb/N0 ratio is provided to the demodulator.

43. Bit Error Rate

44. Link budget • Satellite transponders have two resources: bandwidth (Hz) and power (dbW). A proportional amount of transponder power is allocated across the transponder BW. • Power Equivalent Bandwidth (PEB) is the greater of two variables: • allocated bandwidth (a function of the data rate, modulation/coding scheme, carrier spacing) • allocated power (minimal power assignment which is sufficient to produce desired Eb/N0 ratio at the demodulator in the receiving station).

45. Link budget (contd) • What is needed as an input to link budget? • Satellite, its performance (EIRP, G/T) • location of both ground stations (elevation, rain zone) • data rate • required Eb/N0 ratio • any other limitations (e.g. maximum antenna diameter)

46. Link Budget (example)

47. Link budget (contd) • Therefore, link budget calculations tell us what is the optimum modulation/coding scheme used to maximize bandwidth utilisation, how much power we need to transmit certain amount of bandwidth (i.e. how powerful BUC should we buy), how big our antenna should be etc. etc. • Example calculation of allocated bandwidth: • 2 Mbps data stream, QPSK 3/4, Reed-Solomon coding, standard carrier spacing: BW = 2048*10^3 /2 *4/3 *204/188 *1.5 = 2.2 MHz

48. Link budget (final) • Transponder efficiency usage: • an example: two SCPC carriers per transponder, each receivable with 4.5m antenna or one MCPC carrier per transponder, receivable with 2.4m antenna. • Single/Multiple Channel Per Carrier - SCPC or MCPC • Same applies to transmitting: • if two carriers need to be transmitted through the same BUC, it is necessary to reserve more power i.e. two carriers each requiring 2W will need at least 8W BUC if sent through the same transmitting system. Multiplexer makes sense in such case… • Reed-Solomon is so useful as it allows to decrease antenna size (Eb/N0 ratio) while still maintaining very low BER.

49. Moving up one layer to layer 2... • OK, so we have a connection, both modems are locked to their carriers, the same stream of 0’s and 1’s is received as it is transmitted, what next? • Clear channel or link encapsulation: • HDLC • PPP • ATM • Frame Relay or • DVB

50. To DVB or not to DVB? What is Digital Video Broadcast? • World-wide standard for transmission of digital TV via satellite (S), cable (C) or terrestrial (T). • Utilizes MPEG-2 compression and packet standard • Supports data as well as video transmissions. • Supports multiple program streams, each of which can be encrypted • Supports sub-multiplexing within a program stream • Provides for high degree of forward error correction