Hello, I have a question regarding the OFDM transmitter. In order to reduce the burden on the reconstruction filters, oversampling is used before feeding the data to the DAC. Oversampling, however, creates images of the baseband signal. To remove these images, low pass filters are placed after the rate up converter. These filters are FIR systems, and, when applied to the signal, "smudge" it in time domain, meaning that consecutive OFDM symbols are overlapping each other before the data is even sent to the DAC. In my understanding, this is exactly the problem created by the multipath channel, and the cyclic prefix is added to make the linear convolution of the signal with the channel impulse response analogous to a circular convolution. Why is it, then, that the convolution of the data with the interpolation filter does not pose the same problem for the receiver as the multipath channel? Thanks.
OFDM transmitter oversampling
Started by ●October 19, 2006