hello,
i'm trying to implement an ofdm transmitter
(and afterwards a receiver) for demonstration.
the parameters should match the drm standard.
so my first try was to implement the
transmitter with the following main
parameters:
ofdm transmitter block
fft length = 256 (--> fft length >=
occupied carriers)
cyclic prefix = 64 (--> 256/4)
occupied carriers = 228 (--> (-114,
-113, ..., 113, 114))
for this try no pilot carriers and symbols
and no sync words. everything works fine but
there is a problem with the spectrum of this
ofdm signal. from older posts i have the
following equation to set the bandwidth (bw)
of my ofdm output signal:
bw = sampling_rate * occupied_carriers /
fft_length
with the parameters above and the wish of a
bandwidth of 10khz (to match the drm standard)
i will get the following sampling rate:
sampling_rate = bw * fft_length /
occupied_carriers = 10khz * 256 / 228 =
11.228khz
now i have two questions:
1) if there is an input source with a
sampling rate higher than 11.228khz (maybe
from my sound card (44.1khz) or a wav file (48
khz)) should i use a resampler block because
there is a problem with nyquist? how can i
handle this problem?
2) the same problem goes with the output.
if i mix up the ofdm signal to a carrier
frequency (for example 12khz) how can i handle
this? there is also a problem with nyquist.
thanks in advance!
alphonso