LDPC Codes for IRIG-106 Waveforms: Part II – Receiver Design

Abstract

Low density parity check (LDPC) codes allow a communications link to operate reliably at signal to noise ratios that are very close to the Shannon limit. Because of this, in the early 2000s they were studied in connection with SOQPSK-TG and were eventually adopted into the IRIG-106. The deployment for SOQPSK-TG has proved to be very successful, which has motivated interest in finding an LDPC solution for PCM/FM and ARTM CPM. Such a solution, however, has proved to be elusive for reasons that were not entirely clear in the past. In our companion paper, we reveal these reasons, which also allows us to develop an LDPC design procedure for all IRIG-106 modulations and we apply this procedure to PCM/FM and ARTM CPM. In this paper, our focus is on developing high-speed, parallelizable decoders/demodulators that are suitable for highthroughput applications. We present the performance characteristics of our fixed-point software prototype system. We demonstrate that the coded LDPC system performs around one dB from the respective channel capacities of these modulations. As such, these codes can be considered to fill in the LDPC options that are currently absent in the IRIG-106 standard for PCM/FM and ARTM CPM.