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GD SDR Automatic Gain Control
Characterization Testing
Jennifer Nappier
NASA Glenn Research Center, Cleveland, Ohio
Co-Author: Janette Briones
NASA Glenn Research Center, Cleveland, Ohio
SDR-WInnComm
January 2013
https://ntrs.nasa.gov/search.jsp?R=20130010499 2020-07-29T16:16:50+00:00Z
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Presentation Contents
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• SCaN Testbed Overview
• GD SDR Description
• AGC Characterization Test Objectives
• Test Setup
• Test Results
• Useful Applications of the AGC Characterization
Testing Data
• Recommendations
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SCaN Testbed Flight System Overview
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• 2 S-band SDRs
• 1 Ka-band SDR
• Ka-band TWTA
• S-band switch network
• Antennas
– 2 - low gain S-band
antennas
– 1 - L-band GPS antenna
– Medium gain S-band and
Ka-band antenna on
antenna pointing
subsystem.
• Antenna pointing system
• Flight Computer/Avionics
• Launched on Japanese HTV-3 on
July 20, 2012
• Installed on ISS August 7, 2012
• Checkout and Commissioning is in
progress
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• TDRSS S-band Transponder
– 8 Forward link receive waveform configurations
– 30 Return link transmit waveform configurations
• 1 Xilinx Virtex II QPro FPGA, 3 M gate
• ColdFire microprocessor with VxWorks RTOS running the Space
Telecommunications Radio System (STRS) Architecture
SCaN Testbed GD SDR Description
Waveform
Number
Center
Frequency
Data Rate
(kbps)
Forward
Error
Correction
1 SA 18 Coded
2 SA 18 Uncoded
3 SA 72 Coded
4 SA 72 Uncoded
5 MA 18 Coded
6 MA 18 Uncoded
7 MA 72 Coded
8 MA 72 Uncoded
• CRAM (Chalcogenide
RAM) Memory (4 Mb)
• Analog (10 MHz filter
bandwidth) and Digital
(6 MHz filter
bandwidth) automatic
gain controls (AGCs)
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Test Objective and Plan • Characterize the relationship
between:
– SDR input power
– SDR baseplate temperature
– Waveform configuration
– The digital and analog AGC
values
• Temperature range:
– -15 to +45 °C
• SDR input power range:
– -90 to -130 dBm
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• Results will be used to estimate SDR input power in future testing
• Testing phases included:
– GD verification testing
– GRC thermal vacuum (TVAC) testing
– GRC verification testing
SCaN Testbed during TVAC testing, March 2011
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GRC Test Setup
• S-Band TDRSS Simulator (TSIM) was
used to emulate the forward link
waveform
• TSIM was connected to the SCaN
Testbed using a test equipment
interface circuit and RF cable
• SDR input power was measured from
a coupled port in the interface circuit
using a power meter
• The RF subsystem inside the SCaN
Testbed was used to connect an
antenna port to the GD SDR
• During TVAC, the RF cable and SCaN
Testbed were located in the vacuum
chamber
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S-Band TDRSS Simulator
Forward Link
Waveform
Var Att.
Tx
Test Equipment Interface Circuit
80 dB
Attenuator
CouplerPower
Meter
SCAN Testbed
RF
Subsystem
GD SDR
RF Tx RF Rx
GRC Test Setup
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AGC Characterization Results at Ambient Temperature
Analog AGC at 26 °C Digital AGC at 26 °C
7
100
110
120
130
140
150
160
-130 -120 -110 -100 -90 -80
An
alo
g A
GC
Val
ue
SDR Input Power (dBm)
18k, Uncoded, SA
18k, Coded, SA
72k, Coded, SA
72k, Uncoded, SA
18k, Coded, MA
18k, Uncoded, MA
72k, Coded, MA
72k, Uncoded, MA
0
50
100
150
200
250
-130 -120 -110 -100 -90 -80D
igit
al A
GC
Val
ue
SDR Input Power (dBm)
18k, Uncoded, SA
18k, Uncoded, MA
18k, Coded, SA
18k, Coded, MA
72k, Coded, SA
72k, Coded, MA
72k, Uncoded, SA
72k, Uncoded, MA
• Analog AGC varies with center frequency (MA/SA)
• Digital AGC varies with symbol rate (coding + data rate)
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AGC Characterization Results over Temperature
Analog AGC Digital AGC
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60
80
100
120
140
160
180
200
-125 -120 -115 -110 -105 -100 -95 -90
An
alo
g A
GC
Val
ue
SDR Input Power (dBm)
60 deg C
48 deg C
39 deg C
33 deg C
26 deg C
21 deg C
-7 deg C
-8 deg C
-20 deg C
0
20
40
60
80
100
120
140
160
-125 -120 -115 -110 -105 -100 -95 -90
Dig
ital
AG
C V
alu
eSDR Input Power (dBm)
60 deg C
48 deg C
39 deg C
33 deg C
26 deg C
21 deg C
-7 deg C
-8 deg C
-20 deg C
• Both analog and digital AGCs vary over temperature.
The analog AGC variation is more significant.
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Sources of Error in Data Collection
• Differences in the
GD and GRC test
setup (+/-.5 dB)
• Compensation
method for the cable
loss over
temperature during
thermal vacuum
testing (+/-.5 dB)
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• Data interpolated for waveforms with incomplete
data sets (+/- 1 dB)
• System loss measurement error (+/-.3 dB)
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SDR Input Power Estimation using Digital AGC
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• The Digital AGC characterization
data was used estimate the SDR
input power during operations on
ISS (note: predicted power is
TBD)
• The Eb/No was
calculated from the
SDR input power and
used to create a BER
curve
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Estimation of Interferer Signal Strength using Digital AGC
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• Digital AGC shows received
power is higher than expected
due to an interferer
• The purple curve was plotted with
the Eb/No calculated from a
measured power.
• The green curve was plotted with
the Eb/No calculated from the
digital AGC
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Recommendations and Forward Work
Recommendations
• Plan test phases and
design a test setup that
can be kept constant
throughout each phase
• Balance SDR
reconfigurable
parameters with project
test time
Forward Work
• 3 SDR input power
estimation algorithms
have been developed
• Characterize the SDR
input power algorithms
during on-orbit operations
on ISS
• Utilize the engineering
model (EM)
characterization data to
create SDR input power
estimators for the EM 12
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Questions?
[email protected]
216-433-6521
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