Questions about synchronization in OFDM

OFDM: Synchronization

Hello Friends,
First of all very very thanx to dear friend MAOMUN.I m really very encouraged by his response.Thank u Maomun.
Now i want 2 ask something about synchronization in OFDM.
Synchronization means (1) symbol timing (2) Frequency offset.After cyclic extension my data on TX is in the form of array(using Matlab)...
[2+0.5j 1-2j -1.3+2j .............]
Now my question z that on the RX side wat this symbol timing and frequency offset means.What shud i do.
If i use Pilot.Where shud i insert these pilots on TX side.
thanx once again.
I m very happy with this community.[/b]

Re: OFDM: Synchronization

Hi,QMA

From the Rx side, assume perfect operation

(1) is the position of time index start for DFT window process of N point (only useful data length) mean as find the first edge of each symbol or some point between channel length <offset≤ max GI length in estimation case(first point of data index is optimum).

(2) is the position of frequency index detected (at the top peak of sinc signal) mean as dection of signal's ampli at every subcarrier.

In real situation and practical those offset are sensitive error from several reason Ex. differ in tx rx 's oscillator or Doppler shift ....other that affect ISI ICI and then loss in SNR.

About pilot trianing it's could place as first known symbol of each frame or scatter in some or every symbol as the way to derive channel estimation. Of course only cyclic extension can use to find timing and frequency offset too.

By the way, solution to derive and identical sync algorithm in OFDM is so complicated and have many way. I purpose u a good OFDM text (read there synch chapter) by follow this link below for drive your inspiration and understand.

1. OFDM for Wireless Communication



2.Multi-carrier Digital Communications: Theory And Applications Of OFDM (2nd Edition)