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Effect of sampling frequency change in OFDM

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thavamaran

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Hi guys, I have this question, I know in OFDM system, when you upconvert the signal with certain carrier frequency with certain sampling frequency and when you downconvert it, if the carrier frequency is same, but the sampling is not, then you will have a sampling frequency offset and that will cause unsyncronized problem, like you will get a phase rotation or shifted constellation.

But how actually this sampling difference causes the intermixing in subcarrier or even changes the phase of the signal? In theoretical perspective, I dont really get it. Please someone explain it to me, I went through books, and still I dont get the idea. thank you very much!
 

hi ,
frequency offsets are due to channel delay spread (coz of channel impairments ) and Doppler spread ( movin vehicles)

suppose ur upconvertin RF frquency is @ 2 Ghz and IF :100 MHZ , ur transmitting frequency will be 2100 MHZ
so if ur channel delay spread is say 10 HZ
ur recieved signal at RX will be 2100. 000 010 hz , ur receiver downcoverts the signal by 2GHZ
so If would be 100.000 010 (IF ) which is frequency shifted by 10 HZ (freq offset )

if u process with this IF and demodulate it .. it will shift your bits by (2*pi)/F offset

hope it helps
 

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