Improved Error Performance in SOQPSK Modulation Using a Ternary Symbol Encoder

Abstract

Telemetry transmissions have been evolving over the recent years from PCM/FM to other constant envelope modulation schemes such as SOQPSK and multi-h CPM. These newer modulations schemes have better spectral efficiency but tend to have worse error performance than optimally detected PCM/FM. We present a new ternary symbol encoder to replace the existing differential encoder and pre-coder for SOQPSK. This improves error performance while minimally affecting the spectral properties. The "reach" of the new ternary code length is not much longer than current symbol encoder, so there will not be a significant increase in synchronization time in the receiver. We provide simulation results showing the increased performance. Along the way, we also provide a simplified view of the current SOQPSK differential encoder and pre-coder.