prototype lrpt receiver noaa satellite direct readout conference for the americas december 9-13,...
TRANSCRIPT
Prototype LRPT Receiver
NOAA Satellite Direct Readout Conference for the Americas
December 9-13, 2002
Miami, FL
Wai Fong
NASA/GSFC
Code 567
Microwave and Communications System Branch
Background
• Low-Resolution Picture Transmission (LRPT) is a proposed standard for direct broadcast transmission of satellite weather images for METOP
• LRPT definition is a joint effort by EUMETSAT and NOAA
• Goddard Space Flight Center was tasked to build an LRPT Demonstration System (LDS) and study the protocol performance
Objective
• To develop and demonstrate the feasibility of a low-cost receiver utilizing as much Commercial-off-the-shelf (COTS) equipment as possible.
• Determine the performance of the protocol in a
simulated Radio Frequency (RF) environment.
Approach
• Utilize Personal Computers as the primary processing component.
• Develop all software elements to process and control data flow.• Identify and procure COTS RF modulator/demodulator
(MODEM).• Utilize the Institute for Telecommunications Sciences (ITS)
study for modeling two noise environments: Residential (Lakewood, CO) and Business (Downtown Denver, CO).
• Perform BER analysis of protocol and simulate a satellite pass.• Use Modulated Lapped Transform (MLT) instead of current
JPEG variant.
Top-level Diagram
SPACECRAFT SIMULATOR/TRANSMITTER
GROUND STATION/RECEIVER
RF Signal
ENVIRONMENT SIMULATOR
RF Signal + Noise, Scintillation
Transmitter Description
• Compress, channel code and CCSDS format AVHRR data off-line and store in the Transmitter buffer
• RF Modem performs QPSK modulation
Transmitter Block Diagram
ANT.
137.1 MHz
AMP
UPCONVERT
QPSKMOD
UWINSERT
CONVOL.INTER-LEAVER
CONVOL.ENCODER
SOFTWARE ELEMENTS
AVHRR Data2K pixel/stripeimage files
CCSDSPACKETIZER
M_PDUGENERATOR
Source files for all AP IDs inMETOP Spec.
CCSDSPACKETIZER
M_PDUGENERATOR
CADUGENERATOR/PN ENCODER/SM INSERT
MLTCOMPRESSOR
XMITBUFFER
DATASTOR.DEVICE
70 MHz
REAL-TIME ELEMENTS
Key Features of the Receiver• Hardware elements:
– Modem performs QPSK demodulation– Bit synchronization producing 3-bit soft-decision samples
• Real-time Software elements:– Unique Word (UW) synchronization– Convolutional de-interleaving– Viterbi decoding– CCSDS Frame Synchronization– CCSDS Block de-interleaving– Reed-Solomon decoding– CCSDS Virtual-Channel processing – CCSDS Packet processing – Modulated Lapped Transform (MLT) decompression – Image Display – Status/Statistical analysis and display
Receiver Block DiagramANT.
137 MHz
PRE-AMP
DOWNCONVERT
QPSKDEMOD
BITSYNC
DE-INTERLEAVER
VITERBIDECODER
FRAMESYNC
RSDECODER
VIRTUALCHANNELSORTER
PACKETEXTRACTION
DECOM-PRESSION
DISPLAY
STORE ALLOTHERVCDU'S
SOFTWARE ELEMENTS
DATASTOR.DEVICE
UWSYNC
Noise and Scintillation Generation
• Noise and Scintillation patterns are generated by ITS models.
• Use Pattern Generators to drive programmable attenuators and phase shifters.
Testing Block Diagram
High Speed 2 ChannelPattern Generator
DigitalAttenuator
DigitalPhase Shifter
137 MhzSignalGenerator
Pattern
Man-made/Gausian Noise
DigitalAttenuator
DigitalPhase Shifter
Pattern Pattern
Scintillation Simulator
SPACECRAFT SIMULATOR/TRANSMITTER
GROUND STATION/RECEIVER
RF Signal
Scintillated RF Signal
Noise Controller
Control
Man-made/Gaussian Noise Generator
ENVIRONMENT SIMULATOR
Pattern
Scintillation Controller
Summary of Results• 40% of the CPU bandwidth required for Receiver processing.• 7 dB of coding gain at the output of the Viterbi decoder @ 10-4 BER in
a residential environment with Man-made/Gaussian noise and Scintillation.
• Coding gain decrease to 5.2 dB as the Man-made noise increased for the urban environment.
• Use of convolutional interleaving can provide as much as 2 dB of gain.• The output of the R-S decoder was virtually error-free as long as the
receiver maintained solid lock.• For residential (low noise) environments e.g. Lakewood, nearly 100%
coverage for either Yagi or Omni antenna.• In high noise urban environments like Downtown Denver, 65%
coverage using an Omni antenna.
Conclusion
• Protocol mitigates scintillation and man-noise effects.
• In larger more populated metropolitan areas, use a tracking Yagi antenna and/or a better receiver due to the noisier environment.
• Inexpensive LRPT receivers can be made by using software to perform most of the receiving functions.
Demonstration
• Pass simulation of Downtown Denver with Omni Antenna in Man-made noise/Gaussian noise and Scintillation
• Pass simulation of Lakewood with Yagi Antenna in Man-made noise/Gaussian noise and Scintillation