Wideband Modem Design Using FPGAs

1. ABSTRACT New waveform requirements are pushing the limits of traditional modem design techniques. Fortunately, modern Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) can achieve sampling rates in the GHz range. These new DACs and ADCs allow designers to directly synthesize channels that have bandwidths of more than 500 MHz+; allowing either wideband or multi-channel modems to be implemented entirely in the digital domain. This eases the requirements on the Radio Frequency (RF) portion of the radio design. To fully utilize the available bandwidth of the DACs and ADCs, new techniques in modem design must be considered. Using a combination of polyphase decomposition and sub-sampling, the FPGAbased modem can provide waveform processing for the entire Nyquist bandwidth of the DAC/ADC. This paper outlines the concepts involved in implementing a wideband digital modem.