Autocorrelation of OFDM Signal ?..

Started by alexsunny123 2 years ago3 replieslatest reply 2 years ago194 views


I have captured OFDM I-Q data at IF. I have down-converted to it to base-band and then simply performed autocorrleation. I was trying to find a clear peak that would be show me OFDM useful time duration. Although I see the peak where it should be due to cyclic prefix, I also find other peaks and harmonic like peaks. I was wondering -

1) What could be the reason for such peak?

2) How to suppress other peaks to get my desired peak?

3) How to identify the harmonics and rejects them?



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Reply by dgshaw6December 20, 2020

One source of other correlation components is pilot signals.

Almost every OFDM system has pilot symbols to assist with certain timing acquisition.
Depending on your system of interest, most of these pilots are very well defined in standards documents.

Once you identify the pilot elements, you may be able to cancel or nullify their contribution

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Reply by kazDecember 21, 2020

As dgshaw6 replied. The ofdm being a long 2D signal is used like a bucket of salad where they put any useful signals, called reference signals (pilots) on top of or hidden in the payload. If your post is about LTE then expect at least:

uplink: srs, dm-rs, prach

downlink: pss, sss, pbch, dm-rs, cs_rs

Some are optional, some omitted depending on standards, some are triggered, some are semi persistent and some are continuous. Most are waveforms but few are just coded strings.

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Reply by Mannai_MuraliDecember 21, 2020

I think in any ofdm if the channel is not AWGN any dispersive channel may cause multiple peaks.You may take the first peak.