Transcript https://mentor.ieee.org/802.19/file/08/19-08-0013-01-0000-coexistence-issues-for-passive-earch-sensing.ppt

May 2008
doc.: IEEE 802.19-08/0013r1
Coexistence Issues for Passive Earth
Sensing from 57-64 GHz: Update
Date: 2008-05-08
Authors:
Name
Company
Address
Phone
email
Joel T. Johnson
IEEE
Geoscience and
Remote Sensing
Society (FARS
committee)
The Ohio State
University
205 Dreese Labs
2015 Neil Ave
Columbus, OH
43210
614-292-1606
or 614-2921593
[email protected]
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.
Submission
Slide 1
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
Abstract
Previous slides IEEE 802.19-08/0013r0 documented the
potential for co-existence issues between 802 plans 5764 GHz and Earth Observing Passive Microwave
sensors
Analysis updated here to correct an error, to reflect
comments on previous presentation, and to provide
more information on specific sensors currently in orbit
Submission
Slide 2
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
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 as well as the future ATMS
• 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
Submission
Slide 3
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
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
Frequency
band(s)(1)
(GHz)
52.6-54.25P,
54.25-59.3p
Total
bandwidth
required
(MHz)
6 700(5)
Reference
bandwidth
(MHz)
Maximum
interference
level
(dBW)
Percentage of area
or time permissible
interference level
may be exceeded(2)
(%)
Scan mode
(N, L)(3)
100
161/169(4)
0.01
N
• Scan mode: N=Nadiral, L=Limb
Submission
Slide 4
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
Previous Co-Existence Analysis
• Used Friis formula as starting point for received power Pr:
PR 
PT GT
4R 2
Aeff e 
• 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))
• Recast in terms of an EIRP density equation for brightness
perturbation given radiometer bandwidth B and number of
sources N in footprint of area A; k is Boltzmann’s constant
PT GT kBTe  64 
N

 
2
A
  
Submission
Slide 5
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
Equation in more convenient units
•
Rewrite in terms of the number of sources per square kilometer N’ and
get rid of constants:
BMHzTmK  N ' ( EIRP )W (Q)( F )(108 e  )
- Q<1 is a scale factor to account for the fact that the satellite is in a
transmitter antenna sidelobe
- F<1 is a scale factor to account for the portion of the transmitter EIRP
that lies within the radiometer bandwidth
•
CORRECT ERROR: previous final equation gave left hand side as 1 for
100 MHz and 10 mK, should be 1000
•
CLARIFY: For systems observing at oblique angles, attenuation in dB is
multiplied by the secant of the incidence angles, e.g. at 45 degrees
attenuation in dB increases 41%
Submission
Slide 6
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
Zenith Atmospheric Attenuation
• Compute using ITU P676-7 algorithms:
Submission
Slide 7
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
What are Q and F?
• Information on expected transmit antenna properties as well as
through wall-attenuation, scattering, etc. is required to model Q
– Learned that transmit antennas are expected to be around 10 dBi gain last
time, suggests that zenith sidelobes may not be extremely small
– Presence of transmitters at higher altitudes (i.e. airborne) is a concern due
to reduction in atmospheric attenuation
• Information on radiometer bandwidths and transmitter
modulation properties required to model F
– Nominally would be B/(Bt) where Bt is the transmitter bandwidth if the
transmitter produces a flat power spectral density (psd)
– Will transmit psd be flat? What are expected variations in time?
Radiometer integration times are ~msec scales so average up to ~msec is
of interest
Submission
Slide 8
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
Current state of analysis
• If we go ahead and assume a flat psd for transmitters we can get
rid of F by using the transmit bandwidth on the RHS
B

TmK  N ' ( EIRP )W (Q)(10 e )
trans
MHz
8
• If the transmit bandwidth is 2000 MHz and we use 10 mK, the left
hand side is (2000)(10).
• 42 dBm EIRP=16 Watts, 82 dBm EIRP=160 kW
• Zenith atmospheric attenuation ~80 dB @ 57.3 GHz in Denver;
about a factor of 30 times more at sea level
• Need some guesses as to what Q and N’ are!
Submission
Slide 9
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
AMSU
• The Advanced Microwave Sounding Unit-A (AMSU-A) is a 15channel cross- track, stepped-line scanning, total power microwave
radiometer
– The instrument has an instantaneous field-of-view of 3.3° at the halfpower points providing a nominal spatial resolution at nadir of 48 km
(29.8 mi)
– The antenna provides a cross-track scan, scanning ±48.3° from nadir with
a total of 30 Earth fields-of-view per scan line
– This instrument completes one scan every 8 seconds.
• AMSU measures thermal noise in 26 frequency bands from 56.9 to
57.7 GHz, bandwidths from 3 to 330 MHz
• Multiple AMSU’s currently in orbit, more planned for the future
Submission
Slide 10
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
SSMI/S
• SSMI/S is a conical scanning multi-frequency
radiometer observing at 53.1 degrees incidence angle
– Main beam attenuation in dB 66.6% larger than nadiral
– However any nadiral antenna sidelobes could be a concern
•
Includes channels from 57.1-57.5 and 63-63.6 GHz, as
well as several near 60 GHz
– Lower overall attenuation @ 63 GHz could be an issue (no
allocation for EESS observations here)
Submission
Slide 11
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
Future instruments
• The NPOESS system is slated to combine DoD and
NOAA weather satellites into a single system in the next
decade
• ATMS: Similar to AMSU in most aspects
• MIS: still under definition but likely somewhat similar
to SSMI/S
Submission
Slide 12
Joel Johnson, IEEE GRSS
May 2008
doc.: IEEE 802.19-08/0013r1
Conclusion
• Correction of error shows there is more lee-way than
previously derived
• However it is still not clear that interference will not
occur
• Need guesses regarding N’ and Q
– Probably 42 dBm systems will have larger values of Q than 82
dBm systems
– Properties of 82 dBm system antennas +scattering are important
• More information at:
– http://esl.eng.ohio-state.edu/~rstheory/57ghz/57ghz.html
Submission
Slide 13
Joel Johnson, IEEE GRSS