DC offset
Hi people,
This is a problem of AC coupling:
The baseband spectrum is low-pass, i.e. it has important components around zero frequency. AC coupling places a zero at frequency 0 that eliminates DC but also some of the spectral content of the signal, that ‘losses the baseline’, increasing the error probability. This loss can be mitigated placing the pole at very low frequency, that can work well in steady state, but is not suitable for burst mode because the time required for reaching steady state (i.e. to charge the capacitor) is inversely proportional to the frequency the pole.
This problem would be eliminated using a modulation scheme without spectral contents around the carrirer, e.g. using a baseband shaping like Manchester, but this would increase the bandwidth (e.g. roughly speaking Manchester needs a bandwidth twice that NRZ).
Cancelling DC is possible in burst mode after digitization if the ADC don´t saturate.
Regards
Z