Design and Implementation of II/4 Shift D-QPSK Baseband Modem Using DSP Techniques

The performance of a digital baseband signal processing system and data transmission rate depends on the modulation technique. One of the famous modulation techniques is II/4 shift Differential-Quadrature Phase Shift Keying (II/4 shift D-QPSK). II/4 D-QPSK is a four level modulation scheme first proposed by Baker in 1962 [1] and is currently the focus of intensive research. The aim of this paper is to design and implement the II/4 D-QPSK baseband modem on the Texas Instruments TMS320C6711 digital signal processor (DSP) with DSP-BIOS technique. The implementation included II/4 D-QPSK signal mapping using a look-up table and raised cosine filtering to reduce Inter-Symbol Interference (ISI), and spectral spreading. This paper also describes the differential detection and data recovery design theory in the demodulator and the theory behind the symbol timing recovery module is introduced.