E-SOQPSK Modulation Waveforms for Aeronautical Mobile Telemetry Comms
May 05, 2021
Published in Microwaves & RF
Since the introduction of multi-carrier (MC) orthogonal frequency-division multiplexing (OFDM) in 1966 by Chang, Bell Laboratory, the MC modulation waveform has demonstrated its robust link performance with high modulation bandwidth efficiency in wireless-communication applications. They include today’s Wi-Fi and Long-Term Evolution (LTE) technology.
Traditional single-carrier (SC) modulation-based wireless systems, such as quadrature amplitude modulation (QAM), shaped-offset quadrature phase-shift keying (SOQPSK), and the like, have shown a higher transmitter power efficiency when compared to OFDM-based systems, while having a comparably good modulation bandwidth efficiency. However, it’s known that the link quality of a SC-based system such as SOQPSK-TG (Telemetry Group) deteriorates noticeably in a wireless channel with multipath, especially in time-varying multipath channels.
Over decades of research efforts, various channel-equalization algorithms for QAM and other SC modulations have been proposed and utilized. For example, frequency-domain adaptive equalization algorithms were proposed and experimented on.
Sparse adaptive-channel equalization algorithms were invented to combat wireless link degradation in terrestrial multipath environments,6 as was sparse equalization of SOQPSK-TG for aeronautical telemetry applications. Those equalization algorithms have mostly been in the experimental stage, not being widely implemented in wireless-communication applications for their limited capacity to deal with rapidly time-varying wireless channels.
For example, it may occur in an aeronautical telemetry communications link when a test article (TA, i.e., an aircraft serving as a test platform) is flying at low altitudes, or during take-off, landing, or taxiing. These typical time-varying multipath cases remain a major challenge for link integrity in aeronautical telemetry wireless communications.