A FPGA based generalized parametrizable modulator

The present paper deals with design and development of a generalized parametrizable modulator (GPM) that can perform Gaussian minimum shift keying (GMSK) modulation and Quadrature Phase Shift Keying (QPSK) modulation in a reconfigurable baseband modulator for software defined radio (SDR) architecture. GMSK is the underlying modulation scheme for the Global System for mobile (GSM) standard, while QPSK technique is the basic modulation scheme for Code Division Multiple Access (CDMA) standard. Although GMSK is an inherently nonlinear modulation technique, the present work uses a linearly approximated GMSK technique to take the advantage of the simplicity of the filter structure. The normalised error in amplitude as a function of modulation index and bandwidth time product has been simulated thus capable of working at a data rate that satisfies the requirements of almost all 2G and 3G air interface standards.