Time-Multiplexed Offset-Carrier QPSK for GNSS

A new method of time-multiplexing quadrature phase shift keying (QPSK) signals modulated by a complex subcarrier is proposed. In its simplest form the proposed time-multiplexed off-set carrier quadrature phase shift keying (TMOC-QPSK) can replace the constant-envelope alternate binary offset carrier (AltBOC) currently used for some Global Navigation Satellite System (GNSS) signals. The signal structure is described focusing on the signal generation methodology, power spectral density (PSD), and correlation function in comparison with the alternate binary offset carrier (AltBOC) modulation first used for the Galileo E5 signal. It is shown that the PSD and correlation functions match exactly to those of an AltBOC modulated signal. A method to realize the correlator for the proposed TMOC-QPSK signal is described, and the complexities compared with AltBOC are presented. A field-programmable gate array (FPGA)-based implementation shows that the core TMOC-QPSK correlator requires 32% less hardware resources and consumes 23% less power compared with an AltBOC correlator.