Design of lowpass filter for digital down converter in OFDM receivers

Orthogonal frequency-division multiplexing (OFDM) is a favored technique in digital broadband wireless communications due to its easiness to combat highly dispersive transmission. The feasible implementation of an OFDM receiver relies on fully digital technique. In this paper, we discuss the issue regarding to the design of an efficient lowpass filter specifically for the digital down converter (DDC) in OFDM receivers with digital intermediate frequency (IF) input. The lowpass filter in the DDC possesses the function to suppress both the image band signal due to frequency mixing and the noise residing in aliasing bands resulted from decimation. The lowpass filter designed with a newly proposed criterion exhibits performance improvement comparing to those designed with traditional specification.