Design and Implementation of Reconfigurable Modulator Using FPGA for Cognitive Radio System

With the increase of smartphones and laptops, number of users using communication systems is increasing day by day exponentially. The frequency spectrum required for these systems is limited. Thus in order to increase the proper utilization of the spectrum, cognitive radio technology is being developed. In this system, spectrum is shared between the primary (licensed) users and secondary (unlicensed) users. Secondary user uses a channel only when it is not being used by the primary user. Also different channels require different modulation techniques based on the noise present in their respective channel. Thus, a secondary user transmitter should be able to cope up with this requirement. In this paper an assumption has been made on the channel selection by frequency reconfiguration, so the paper focuses on the reconfiguration in digital modulation scheme. A way of designing and implementing reconfigurable modulator system using FPGA is discussed in the paper. Different types of noise present in the channel are detected with the help of Fourier transform and decision is taken to dynamically switch between different digital modulators.