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While I am reading a paper, I came across this paragraph, and I am not sure what it means:
Once the channel is equalized in the frequency domain, the signal is transformed back to the time domain, and the receiver decisions are based on the signal energy transmitted over the entire channel bandwidth. In other words, the SNR value that dictates performance (assuming that residual IS1 is negligible) corresponds to the average SNR of the channel. Consequently, the performance degradation due to a deep notch in the signal spectrum remains small with respect to that suffered by OFDM.
I am not able to put it in an exact context of what sort of communication system your dealing with:
Here is what I got: Since the system takes decision in time domain the impact of a notch in the frequency spectrum has little impact, which is not the case for OFDM.
I am not able to put it in an exact context of what sort of communication system your dealing with:
Here is what I got: Since the system takes decision in time domain the impact of a notch in the frequency spectrum has little impact, which is not the case for OFDM.
The justification for OFDM channel where the processing is done typically in the frequency domain, which is one of the advantages wherein it avoid timing sync errors, pretty much resistant to ISI. But since operations are in the frequency domain it is sensitive to frequency shift ie. doppler, frequency synchronization problems occur...which is why a deep notch in the frequency spectrum would affect OFDM.
I cannot comment on the channel of the "the comm system" that it is being compared to.
The other communication system is as follows: the received signal is converted to frequency domain and equalized at that domain, and then converted back to the time domain where the detection takes place. I hope this makes the paragraph at the first post clearer.
I think, that the sense of that paragraph is:
At the receiver after demodulator and before detector a matched filter is usually used (a linear filter, designed to provide the maximum signal-to-noise power ratio at it's output for a given transmitted signal waveform). The main property of the match filter is that the maximum output S/N or Eb/No (for detection period of time T) depends on the input signal energy and the power spectral density of the noise, not on the particular shape of the waveform that is used.
So, I think if due to a deep notch in the signal spectrum the waveform of the signal will be distorted, it can be equalized in the frequency domain and, as result, the quantity of the energy of the waveform will be recovered (to process further by matched filter in the time domain) and performance of the signal will not be affected.
In COFDM signal we have many sub carriers where each of them is processed separately. As result, distortion in the COFDM spectrum is more affected.
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