Low - Rate Information Transmission (LRIT) Downlink and Reception

1
Low - Rate Information Transmission (LRIT)
Downlink and Reception

• Satellite Direct Readout Conference for the
  Americas
• Frank Eng, Computer Sciences Corp.
• December 10, 2002

2
Introduction

• This session and presentation will address
• The space to ground link budget for broadcasting
  and receiving GOES LRIT signals.
• Link budget calculations, based on spacecraft and
  ground system characteristics, and their
  relationship to LRIT user station design.
• Description of the spacecraft parameters that
  impact the link budget.
• Conclusions, with a description of the relevant
  receiver characteristics resulting from the link
  budget analysis.

3
GOES LRIT System Parameters

• Frequency L-band
• GOES spacecraft transponder power
• GOES I-M 12 Watts
• GOES N-P 7 Watts
• Data Rate 128 kbps
• Forward Error Correction
• Reed Solomon, 1/2 rate Convolutional

4
Propagation Parameters

• Propagation Distance 35,000 to 42,000 km
• Atmospheric Absorption 0.04 to 0.4 dB
• Free Space Loss 188 to 190 dB
• Polarization Loss 0.2 dB
• Pointing Loss 0.3 dB
• Rain Attenuation 0.01 to 0.1 dB

5
Receiver Parameters

• 1 Meter Antenna Gain 22.5 dB
• System Temperature 190.50 Kelvin
• G/T -0.3 dB
• Filter Insertion Loss 1 dB
• Turn around (uplink) loss 0.17 dB
• Modulation Loss 2.30 dB
• Coding Gain 7 to 9.4 dB

6
System Performance Considerations

• Conservative assumptions 3 dB link margin
• Highly Reliable Link BER objective of 10-8
• Scintillation Losses 5 dB at specific times and
  places
• Potential RFI from cellular systems
• Relatively low cost less then 5000

7
Propagation Link Performance 1-meter dish
8
Receiver Link Performance 1-meter dish
9
Link Summary

• Performance objectives satisfied down to 150
  elevation angle
• Existing 1 meter WEFAX antenna is sufficient in
  most cases
• Low cost objective should be readily achieved
  with availability of NOAA S/W
• Preliminary link testing completed
• Final link testing in early 2003