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Coexistence Issues for Passive Earth Sensing from 57-64 GHz

Coexistence Issues for Passive Earth Sensing from 57-64 GHz. Authors:. Date: 2008-04-23.

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Coexistence Issues for Passive Earth Sensing from 57-64 GHz

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  1. Coexistence Issues for Passive Earth Sensing from 57-64 GHz Authors: Date: 2008-04-23 Notice:This document has been prepared to assist IEEE 802.19. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Joel Johnson, IEEE GRSS

  2. Abstract Important meteorological observations are conducted in the 57-64 GHz band by passive microwave systems on Earth observing satellites. The Earth Observing Satellite Service (EESS) has a shared primary international frequency allocation from 57-59.3 GHz, other frequencies have been used opportunistically Apparently no detailed co-existence analyses have been performed for currently proposed 802.15 or 802.11 standards. Here an initial co-existence analysis is provided to show that co-existence may be an issue and more detailed analyses should be performed Joel Johnson, IEEE GRSS

  3. Passive Microwave Observations • Passive microwave systems (microwave radiometers) have a long history of providing vital meteorological measurements • Systems are receive-only, and observe naturally emitted thermal noise from the Earth’s environment • Frequencies near the 60 GHz oxygen absorption line are critical for obtaining atmospheric temperature profiles; this is done by using several radiometer frequencies at varying locations along the line • Current and future US and international satellites are using these frequencies, including the AMSU and SSMI/S sensors on-board several defense meteorological satellites • ITU regulations recognize the importance of these frequencies for the Earth observations by providing the EESS (passive) service with a shared primary allocation from 57-59.3 GHz Joel Johnson, IEEE GRSS

  4. ITU Frequency Allocations 57-64 GHz • 57.000 - 58.200 EARTH EXPLORATION-SATELLITE (passive) FIXED INTER-SATELLITE MOBILE SPACE RESEARCH (passive) 5.5475.556A5.5575.558 • 58.200 - 59.000 EARTH EXPLORATION-SATELLITE (passive) FIXED MOBILE SPACE RESEARCH (passive) 5.5475.556 • 59.000 - 59.300 EARTH EXPLORATION-SATELLITE (passive) FIXED INTER-SATELLITE MOBILE RADIOLOCATION SPACE RESEARCH (passive) 5.556A5.5585.559 • 59.300 - 64.000 FIXED INTER-SATELLITE MOBILE RADIOLOCATION 5.1385.5585.559▲ Joel Johnson, IEEE GRSS

  5. ITU Footnotes (None for EESS) • 5.547 The bands 31.8-33.4 GHz, 37-40 GHz, 40.5-43.5 GHz, 51.4-52.6 GHz, 55.78-59 GHz and 64-66 GHz are available for high-density applications in the fixed service (see Resolutions 75 (WRC-2000) and 79 (WRC-2000)). Administrations should take this into account when considering regulatory provisions in relation to these bands. Because of the potential deployment of high-density applications in the fixed-satellite service in the bands 39.5-40 GHz and 40.5-42 GHz (see No. 5.516B), administrations should further take into account potential constraints to high-density applications in the fixed service, as appropriate. (WRC-03) • 5.556 In the bands 51.4-54.25 GHz, 58.2-59 GHz and 64-65 GHz, radio astronomy observations may be carried out under national arrangements. (WRC-2000) • 5.556A Use of the bands 54.25-56.9 GHz, 57-58.2 GHz and 59-59.3 GHz by the inter-satellite service is limited to satellites in the geostationary-satellite orbit. The single-entry power flux-density at all altitudes from 0 km to 1 000 km above the Earth's surface produced by a station in the inter-satellite service, for all conditions and for all methods of modulation, shall not exceed -147 dB(W/(m² × 100 MHz)) for all angles of arrival. (WRC-97) • 5.557 Additional allocation: in Japan, the band 55.78-58.2 GHz is also allocated to the radiolocation service on a primary basis. (WRC-97) • 5.558 In the bands 55.78-58.2 GHz, 59-64 GHz, 66-71 GHz, 122.25-123 GHz, 130-134 GHz, 167-174.8 GHz and 191.8-200 GHz, stations in the aeronautical mobile service may be operated subject to not causing harmful interference to the inter-satellite service (see No. 5.43). • 5.559 In the band 59-64 GHz, airborne radars in the radiolocation service may be operated subject to not causing harmful interference to the inter-satellite service (see No. 5.43). Joel Johnson, IEEE GRSS

  6. ITU RS.1029-2 • ITU recommendation RS.1029-2 also addresses the EESS service from 57-59.3 GHz • Sets a received power limit of -169 dBw not to be exceeded either 0.01% of the time or area • this is 0.01K in a 100 MHz radiometer bandwidth Joel Johnson, IEEE GRSS

  7. Initial Co-Existence Analysis • Radiometer is just a receiver with given antenna properties • Concern is the impact on the observed noise power • Convert non-thermal received powers into an increase in observed antenna temperature given radiometer channel bandwidth • Use Friis formula as starting point for received power Pr: • Requires knowledge of: • transmitted power (Pt) • antenna gain of transmitter in direction of radiometer (Gt) • radiometer antenna effective area (Aeff) in direction of transmitter • Range to radiometer (R) • atmospheric attenuation (exp(-tau)) Joel Johnson, IEEE GRSS

  8. Co-Existence Analysis (2) • EIRP (PtGt) assumed to add for N sources within radiometer antenna footprint • Some sort of antenna pattern averaging would be included in this • Transmit antenna pattern issues not clear at present • Also need to account for any scattering effects into radiometer beam • Relating the radiometer effective aperture to gain, then beamwidth, we get (assuming transmitter in radiometer main beam) where A is the radiometer footprint area on the ground • Now relate this to a change in brightness temperature through where B=radiometer bandwidth and k=Boltzmann’s const Joel Johnson, IEEE GRSS

  9. Co-Existence Analysis (3) • This gives the EIRP/(footprint area) (a “density of interferers”) to produce a given change in temperature: • Using the 57 GHz wavelength and simplifying gives where TdB is the atmospheric attenuation (positive dB) • We can use this equation to examine interference for current and future spaceborne radiometers Joel Johnson, IEEE GRSS

  10. What are reasonable numbers in this equation? • An antenna temperature perturbation of 0.01 to 0.001 K is justifiable • ITU RS 1029-2 uses 0.01K in 100 MHz • Such small changes are important for climate studies • Current systems can achieve these accuracies when averaged over time or space • Spot area: Footprint area of 2000 square kilometers assumed (AMSU instrument) • Bandwidth: Use the 100 MHz specified in RS 1029.2 Joel Johnson, IEEE GRSS

  11. Zenith Atmospheric Attenuation • Compute using ITU P676-7 algorithms: Joel Johnson, IEEE GRSS

  12. Comments on Zenith Attenuation • For sea level transmitters, minimum is around 95 dB @ 57.3 GHz (even lower at 64 GHz) • Transmitters at higher elevations (e.g. Denver) have minimum around 80 dB • No accounting here for through wall attenuation etc. • Is there any possibility of transmitters at higher altitudes (i.e. airborne?) • Results also depend weakly on atmospheric conditions, ITU separates into different climate regions Joel Johnson, IEEE GRSS

  13. Final result • Putting this all together (80 dB attenuation) yields or in Watts • Can also be re-written as where N’ is the number of transmitters per square km • EIRP needs to include the fact that the radiometer main beam is likely in a sidelobe of the transmit antenna, as well as any scattering issues Joel Johnson, IEEE GRSS

  14. Conclusion • Preliminary analysis performed here suggests that there is a potential for future 57-64 GHz systems to impact passive EESS service • However analysis presented here needs refinement • Improve antenna, scattering, and ground propagation analysis • Expected density of transmitters an issue • Suggest that more careful analysis should be performed • Should problem be shown to be definite, next steps need to be considered • More information at: • http://esl.eng.ohio-state.edu/~rstheory/57ghz/57ghz.html Joel Johnson, IEEE GRSS

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