Evolution of Satellite Communication Systems

Transcription

1 Mathieu DERVIN Brussels, 6th May 2015 Brussels, May 2015

2 Agenda I. From Sputnik to wideband satellite services: The key technological evolutions II. Increase the satellite system capacity: A global system optimization III.Towards the future: High throughput satellite systems 2

4 From Sputnik to wideband satellite access 4 th October 1957: Sputnik First artificial satellite Elliptical low earth orbit: 223 km 950 km Simple radio transmitter (1W, 3.5 Kg) 0.3s pulses at MHz and MHz Emission during 21 days 4 months in orbit 4

5 From Sputnik to wideband satellite access 1960: ECHO 1 First communication satellite First transcontinental communications (point to point) Passive reflector 30-meter balloon inflated in space, 70 Kg Low earth orbit (~ 1600 km) 8 years in orbit 5

6 From Sputnik to wideband satellite access 1960: ECHO 1 Passive satellite very low received signal power! Moving satellite Antenna tracking is necessary Sparse service delivery: ~10 minutes every 2 hours (typically) High cost of the ground stations Service limited to institutional use 6

7 From Sputnik to wideband satellite access 1962: TELSTAR 1 First active communication satellite Elliptical, low earth orbit ( km) 14W of electrical power delivered by solar cells, 80 Kg Transparent transponders based on travelling wave tube amplifiers Amplification + retransmission of the received signals Visibility: 20 min every 2.5 hours Out of service in February 1963, due to space radiations 7

8 From Sputnik to wideband satellite access 1963: SYNCOM 2 First Geostationary satellite: km 28W initial power, 70 Kg at launch, 35 Kg in orbit Two 500 khz transponders (2W power) handling: 1 two-way telephone channel or 16 one-way teletype channels One additional 5 MHz transponder (2W) First successful TV transmission through a geosynchronous satellite Satellite used as a relay between ground stations Low quality video no sound! Fixed ground antennas, but still not accessible to the consumer First Direct-to-Home TV broadcast per satellite: only in 1974 Final turn-off in

9 From Sputnik to wideband satellite access 1965: INTELSAT 1 (Early Bird) First commercial satellite for telecommunications Geostationary ( km) 68 Kg at launch, 40 W power, 1 transponder Services: television, telephone, telegraph In service for 4 years 9

10 From Sputnik to wideband satellite access 2015: Fifty years later Inmarsat / Hellas-sat satellite order Launch: end of years lifetime Multi-mission Payload: Multi-beam coverage in S-band for mobile communications in Europe Powerful Ku-band Payload for telecommunications and TV broadcast services in Europe, Middle-East and Southern Africa 10 Based on Thales Alenia Space Spacebus 4000 C4 platform Kg at launch 12.3 kw power delivered by 2 deployable solar arrays

11 From Sputnik to wideband satellite access Commercial services have been enabled by The increase of the satellite power (solar array technology, high power amplifiers) Alleviates the user terminal performance requirements Lower cost for the consumer Market development The increase of the satellite mass (launcher) Greater payload complexity Higher satellite throughputs Increased profitability Besides Wider frequency bands are now available for satellite communications Digital communications have replaced Analog transmissions Still, satellite systems are power and spectrum limited. the competitiveness of satellite systems strongly relies on the power and spectral efficiency 11

13 Increase the satellite system capacity From global coverage to multiple beam satellites The satellite is power limited How to focus the signal power where it is useful? The satellite is band-limited How to maximize the use of the available spectrum? global coverage Suited to broadcast applications Multispot coverage High antenna directivity Spatial isolation between beams Suited to unicast transmissions 13

14 Increase the satellite system capacity From global coverage to multiple beam satellites Antenna gain : the narrower the antenna beam, the larger the antenna gain More focused signal power Spatial isolation of the RF signals allows the frequency re-use across the coverage High impact on the capacity (well known in cellular networks) Well suited to broadband access systems with specific user contents (unicast) 14 High frequency bands are required to allow the design of narrow beam antennas with reasonable size Example: 10 beams on France : ~ 0.5 beam size >10m satellite GHz (C band) 3.7m satellite GHz (Ku band) 2.2m satellite GHz (Ka band) Satellite multi-beam technology enabled thanks to Ku and Ka-band equipments

15 Increase the satellite system capacity Capacity of a multiple beam satellite C = B F C is the satellite transmission throughput in bit/s if the waveform spectral efficiency in bit/s/hz B is the total RF bandwidth allocated to the satellite in Hz F is the frequency reuse factor in the coverage To improve the satellite throughput, there are three main options : Option 1: Improve the spectral efficiency ( ) Option 2: Enlarge the RF frequency bands (B) Option 3: Increase the frequency reuse across the coverage (F) Note 1 : Parameters, B and F are not independent : they are notably linked through the average signal to noise and interference ratio (SNIR) in the coverage Note 2 : The satellite capacity increase is obtained at the cost of extra consumed power and equipment the capacity remains limited by the platform power / mass capability! 15

16 Increase the satellite system capacity Improve the spectral efficiency? Increase the modulation order Requires higher signal to noise and interference ratio at the receiver input First digital TV broadcast in the 90 s Current broadband solutions 16

17 Increase the satellite system capacity Improve the spectral efficiency in a non-linear channel? The non-linear response of the satellite amplifier induces intermodulation noise High order modulations are more sensitive to the non-linear channel distortions Improving the channel linearity induces poor energy efficiency The spectral efficiency increase is limited in practice by the channel non linearity Achievable spectral efficiency Linear (Gaussian) channel Non-linear channel Consumed energy per useful transmitted bit 17

18 Increase the satellite system capacity Enlarge the RF frequency bands? User Throughput Increase of the transmission rate Increase of the spectral efficiency Signal Power when RF bandwidth is available, increasing the transmission rate is the most efficient way to use extra power to increase the throughput 18

19 Increase the satellite system capacity Enlarge the RF frequency bands? Available resources for fixed satellite services C band (4/6 GHz) 1100 MHz (planned + unplanned links) Ku band (12/14 GHz) 2000 MHz (planned + unplanned) Ka band (20/30 GHz) 2900 MHz (partly shared bands) Indicative values for earth-to-space links (variable regulatory constraints depending on the covered areas) Possible impact on the link budgets and the spectral efficiency for very large signal bandwidths due to the satellite power limitation! 19

20 Increase the satellite system capacity Maximize the frequency reuse? The narrower the beam size, the higher the frequency reuse factor Tighter frequency reuse patterns? f 4 channels f 3 channels 1 channel f 20 More intense frequency re-use induces more intra-system interference impact on the link budget and the spectral efficiency!

21 Increase the satellite system capacity The most efficient approach to increase the total satellite throughput is: To increase the RF bandwidth dedicated to the users To maximize the frequency reuse by increasing the number of user beams Consequences on the average link budget : The useful signal power is spread over larger bandwidths Degraded signal to noise ratio due to power limitations Lower antenna isolation among the beams Degraded signal to interference ratio The satellite transponders are shared among several beams Degraded signal-to-intermodulation noise ratio 21

22 Increase the satellite system capacity In other words The capacity increase is obtained thanks to a more intensive use of the frequency resource, despite a spectral efficiency reduction C ( ) = ( ) B( ) F( ) 22

24 Towards High throughput satellite systems Current solutions in Ka-band The most capacitive satellite broadband access solutions rely on the Ka band Beam size : 0.4 to 0.5 obtained with ~2m satellite antennas Ka band shared among the satellite / gateway links and the satellite / user links forward return Earth to space (uplink) gateways users 27.5 GHz 30 GHz Space to earth (downlink) gateways users 17.7 GHz 20.2 GHz 24

25 Towards High throughput satellite systems Current solutions in Ka-band The band allocated to the users is divided into channels depending on the frequency reuse pattern A gateway addresses several user beams The more bandwidth allocated to a gateway link, the less the number of gateways in the system Ka-band sharing with the users If the gateways are located in the user coverage, the band must be shared between the user and the feeder links trade-off capacity v.s number of gateways 25

26 Towards High throughput satellite systems The wider the band allocated to the users, the greater the capacity Move the feeder link to higher frequency bands allows to dedicate the full Kaband to the user links Q/V bands V band Earth to space (uplink) users 27.5 GHz 30 GHz gateways 47.2 GHz 51.4 GHz forward return Ka band Space to earth (downlink) users 17.3 GHz 20.2 GHz 2.9 GHz gateways 37.5 GHz 42.5 GHz Q band 26

27 Towards High throughput satellite systems BATS project Broadband Access via Integrated Terrestrial and Satellite Systems : an example of HTS system over Europe (2020) Ka User Project funded by the European Commission Tx+Rx European Partners Ka User Tx+Rx Ka User Tx/Rx Ka User Tx/Rx Ka User Rx Ka User Tx+Rx 300 user beams on EU28 + Turkey with 0.21º beamwidth. Two satellites QV GWs Tx+Rx SFPB architecture (Ka and QV bands) Each satellite involves 2 Ka-band antennas with 4.8m reflectors and a Q/V-band antenna with 2m reflector West satellite QV GWs Tx/Rx MFPB architecture for Ka-band and SFPB for QV-band East satellite 27

28 Towards High throughput satellite systems BATS project: an example of HTS system over Europe (2020) System performance : Throughput (with two satellites) Forward link: 750 Gbps Return link: 250 Gbps Payload supported by evolved NEOSAT satellite platform mass: ~1600 Kg (payload only) power: ~18 kw 25 gateways per satellite 50 gateways in the system + redundant sites for diversity 28

29 Towards High throughput satellite systems Conclusion The increase of the satellite capacity is the key to competitiveness The evolution towards high throughput satellite systems is mainly supported by: Narrower user beams More intensive frequency reuse Wider RF bandwidth A greater number of highly capacitive gateways Main technical challenges for the future : Antenna design : large reflectors, beamforming networks, Wideband payload equipments : filters, frequency converters, amplifiers,. High data rate ground processing: interference cancellation, non linear equalization, Frequency band sharing : cognitive radio, Backbone design : high data rate interconnection, network optimisation, site diversity management. 29

30 End of the presentation Thank you 30