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SpaceOps 2002 SPECTRUM USE IN THE XXI CENTURY Benito O. Guti é rrez-Luaces Houston, Texas, October 9 to 12, 2002 T5-48

SpaceOps 2002 SPECTRUM USE IN THE XXI CENTURY Benito O. Guti é rrez-Luaces Houston, Texas, October 9 to 12, 2002 T5-48 AGENDA Basic parameters to be considered to achieve optimum use of the electromagnetic spectrum (EM) among all its potential users

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SpaceOps 2002 SPECTRUM USE IN THE XXI CENTURY Benito O. Guti é rrez-Luaces Houston, Texas, October 9 to 12, 2002 T5-48

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  1. SpaceOps 2002 SPECTRUM USE IN THE XXI CENTURY Benito O. Gutiérrez-Luaces Houston, Texas, October 9 to 12, 2002 T5-48

  2. AGENDA • Basic parameters to be considered to achieve optimum use of the electromagnetic spectrum (EM) among all its potential users • Emphasizing the importance of passive observations of the Earth and the Universe • Suggestions of how to optimally assign the S-band space-to-Earth link of near-Earth satellite constellations randomly distributed in space • Results for the down-link studies of this presentation are verified by the use of actual satellite constellations models. These models to be used in future studies on the optimization of the Earth-to-space link

  3. INTRODUCTION • The use of the electromagnetic spectrum in “free-space” has been increasing since the demonstration of the EM energy transmission by Hertz (Germany) in 1887 • Today it is a very scarce, appreciated and therefore expensive global asset • Optimization of its use is therefore a priority to be pursued by all of its users

  4. Receiver Sensitivity Limitations • The evolution of radio-transmissions started at low frequencies where the high transmitted power was more important than the receiver sensitivity • Receiver sensitivity becomes important at frequencies in the Earth based window (0.5-10 GHz) because the antenna temperature may be as low as 3K • Another potential limitation that must always be taken into account is the natural radiation of the Sun. Antenna pattern is clearly an important factor when all these natural limitations are considered

  5. The Radio ReceiverNOISE TEMPERATURE of AMPLIFIERS(from: Cryogenic,HEMT, ...; S.Weinreb...,1988 IEEE MTT-S Digest)

  6. NATURAL LIMITS (summary)

  7. Typical Spectral Power Flux Density (SPFD)Sun, Radio Astronomy, Deep Space

  8. Passive Observations • Through the observation of the EM energy present in the Universe, Radio Astronomy has contributed, contributes today and will contribute in the future to increase our knowledge of the Universe • Radio Astronomy observations that may last several hours, are realized through the measurement of the variations in temperature of a usually very directive antenna • Same approach will allow the probing of a limited area of the Earth atmosphere • Also through the interaction of the EM waves with the Earth, surface parameters can be measured

  9. Passive Space Earth Exploration(the importance of the band 18.6-18.8 GHz) SALINITY WIND SPEED Antenna temperature relative sensitivity to different geophysical parameters (oceanic) v.s. observing frequency LIQUID CLOUDS WATER VAPOR Frequency (GHz) SEA SURFACETEMPERATURE

  10. Transmission of messages • The most popular use of the antenna/receiver combination is for the reception of messages from a distant transmitter • EM power from those transmitters are a man-made source of noise that should be limited as much as possible to allow an optimum use of the spectrum • It appears that digital transmissions because of the substantial power reduction over analog ones should take precedence in future (see next viewgraph)

  11. Analog or digital transmissions?

  12. Optimizing the space-to-Earth transmissions • As a result of the narrower bandwidth usually required in the Earth-to-space direction (uplink) in most of the Space Science applications, the space-to-Earth(downlink) studies of a two way-link for near-Earth satellites took precedence • Given a limited spectrum bandwidth the maximum number of satellites that may be allowed to operate above the Earth station horizon for a given link degradation is of importance • Results for the band 2200-2290 GHz (S-band) given in Fig. 6. have helped to propose the assignment of common bands for systems with similar characteristics, instead of the first-come first-serve approach

  13. Optimizing the Earth-to-space transmissions • Nowadays, the Space Science uplink S-band spectrum (2025-2110 GHz) is increasingly shared with new incoming near-Earth applications • Uplink bandwidth requirements for these new systems will most likely be as large as those of the downlink, therefore this will be the subject of further studies • Computer programs have been developed for simulations of these scenarios • Results of down-link simulations for near-Earth constellations have been included into Fig. 6 in the next viewgraph showing a very close agreement with previous models

  14. Near-Earth Total Number of Space Craftin-view at S-Band (2,3 GHz) 70 ssnr (dB) (4) 60 (9) 50 40 Constellation (1400km; 88deg.; 30 Max. Number of s/c in view for p<0.001 I/No=-6dB;p~0.001) 48x8 20 (14) 24x8 10 12x8 0 6x8 0 5 10 15 20 25 30 Antenna Diameter (m)

  15. CONCLUSIONS • Some of the limitations imposed by Nature in the use of free-space propagation of the EM energy have been introduced • Active users of free-space propagation should pay attention to limitations imposed by passive observations • Satellite-constellation computer models have been completed and verified with previous results for the space-to-Earth data transmissions • These models will be used to define requirements for the Earth-to-space scenario optimization

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