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