A multi rate CPFSK transmitter

This paper presents the design of an implemented prototype of a multi-rate Continuous Phase Frequency Shift Keying (CPFSK) transmitter. In case of a fixed rate CPFSK transmitter, the input symbol rate remains constant, thus the pulse shaping filter and frequency deviation are also fixed to a certain bandwidth. Contrary to this, for a multirate CPFSK design, the input symbol rate may vary and the pulse shaping filter and the frequency deviation must adapt accordingly. The main challenge of such a design is to detect the input symbol rate and then use it for the adjustments. Incorporating these, makes the CPFSK transmitter a true multirate system, capable enough to adapt to arbitrary input symbol rate. In this text the design of a working prototype of CPFSK transmitter is presented. Xilinx system generator is used in conjunction with Simulink for RTL code generation. The generated bit-stream is ported on a Virtex-2 based customized FPGA platform. The generated I/Q from the board was up-converted to ISM-band using the Agilent ESG series Vector Signal Generator and the results are observed and compiled on Agilent VSA 89600 using the Agilent ESA series Spectrum Analyzer. The paper concludes by presenting the parameters FSK-error, constellation and the spectrum of the implemented design.