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How does OFDM receiver know the OFDM symbol start time using pilot aided estimation?

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engineer_eda

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Hello,

I am trying to understand how the receiver decides the length of OFDM symbol in time domain before it goes into DFT process at the receiver. The complete OFDM symbol (with Cyclic Prefix added) is propagated by the transceiver through the channel and it is received at the receiver with a time delay. This delay is caused by the propagation channel due to the objects or channel characteristics. And now lets say we have received the signal and first need to know what the symbol start time so that receiver can start the OFDM symbol and cut it at the end of the symbol. Then start for the consecutive symbol...

Is this performed by the correlation operator which compares the received OFDM signal with the pilot data which is already known by the receiver?

Could you please help me in understanding the logic behind this?

Thanks in advance!
 

engineer_eda

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I would appreciate if someone help me understanding this!

Thanks!
 

engineer_eda

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I have made some searches and have below questions on this.

So far I understand that there two methods for time synchronization which
are data-aided and non-data aided methods, and in the data-aided methods
the training subcarriers are included in OFDM symbol and they are
correlated with the known training subcarriers at the receiver and the
time of the peak of the auto-correlation is the time delay (tao)of the
channel and this means the OFDM symbol reaches the receiver after this tao
delay.

My questions here are;

1-For time synchronization, if the data-aided method is used, should the
one complete OFDM symbol contain all training subcarriers and then all are
correlated with the known trainings one by one at the receiver?

2-Or the OFDM symbol contains a few training subcarriers and when they are
received by the receiver each of the trainings is correlated by the known
pilots?

Thanks!
 

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