How does the OFDM system receiver decide the OFDM symbol length? 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...

Could anyone please explain how to visualize this?

Thanks in advance!
First of all, the timing, phase and frequency offsets of the channel are removed. After synchronization, the cyclic prefix is removed, to avoid ISI between OFDM symbols. Now because the transmitter and receiver agree upon a common standard before the communication begins, the receiver knows how many samples to consider as a symbol.

Generally, the the number of samples in an OFDM symbol depend upon the bandwidth.