LDPC CODING FOR FREQUENCY DIVERSITY IN MULTI-CHANNEL AIR-TO-GROUND TELEMETRY

Abstract

We consider the application of LDPC codes for improving performance in multi-channel (spectrum aggregation) for air-to-ground telemetry, by virtue of frequency diversity available on a wideband frequency-selective multipath channel. Our particular interest is in use of multi-channel OFDM transmission on “white spots” in the microwave spectrum. Each such channel is subject to frequency-selective fading over its bandwidth (typically a few MHz) due to multipath, for which typical OFDM equalization is standard. However, some subcarriers within this OFDM channel may experience deep fading at the output of the equalizer, rendering the symbol error probability poor relative to that on an AWGN channel at the same average SNR. We study simulated performance on a multipath channel described by the ETU fading model. Specific performance reported includes error rate of LDPC coding constrained to a single channel (effective diversity order roughly 2) and error rate of coding across eight channels (diversity order roughly 5). Further, performance on this dispersive fading channel is only about 3 dB worse than that on a no-multipath channel, at block error probability 0:01.