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 wai.h.fong@.nasa.gov

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

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

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 Diagram

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

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