Half-Symbol-Rate-Carrier Offset QPSK Transmitter for Bandwidth-Efficient High-Speed Data Communications

This letter proposes a half-symbol-rate-carrier (HSRC) offset quadrature phase shift keying (OQPSK) modulation for high-speed data communications. A prototype transmitter generating the HSRC-OQPSK signal was designed and built. Measurement results confirm the theory that the proposed HSRC-OQPSK modulation improves spectral efficiency by reducing the second lobe of the signal spectrum by 10 dB. Furthermore, HSRC-OQPSK modulation reduces the first null bandwidth by 25% compared to standard non-return-to-zero (NRZ) modulation. Like NRZ, HSRC-OQPSK uses two-level data decision which enables a simpler transceiver architecture than multilevel pulse amplitude modulations (PAMs), such as 4-PAM and duobinary