QPSK, Staggered QPSK, and MSK - A Comparative Evaluation

Bandwidth- and power-efficient quadrature carrier modulation techniques are identified, evaluated, and compared. The modulation techniques include quadrature phase shift keying (QPSK), staggered QPSK (SQPSK), and minimum (frequency) shift keying (MSK). High quality QPSK, SQPSK, and MSK transmitters and receivers were used in the evaluation, along with a computer simulation program which modeled the hardware. Both linear and nonlinear channels were included in the comparative investigation. The agreement between simulated and measured results is shown to be excellent. In the comparison of modulation techniques, the effects of channel filtering (band limiting), nonlinearities, detection techniques, and phase equalization are addressed. The application-oriented results are intended to be an aid in selecting modulation and detection implementations, and in predicting the performance of linear and nonlinear communication systems. For systems with imperfections, data are presented for determination of passive detection filters which can outperform "matched" integrate and dump (I&D) filters.