Synchronization process in optical frequency division multiplexing transmission systems

A symbol synchronization method in the receiving part of an optical orthogonal frequency division multiplexing (OOFDM) transceiver that comprises the steps of:

• a) converting the incoming real-valued samples from serial to parallel into two orthogonal frequency division multiplexing (OFDM) symbol groups wherein one group contains an original copy of the symbols and the other group contains a time-delayed copy of the symbols;
• b) performing a first subtraction operation between sample at position x of the original symbol copy and sample at position x+N−L of the time-delayed copy wherein N is the total number of samples and L is the length of a cyclic prefix;
• c) storing the absolute value of the subtraction in position x of a synchronization register;
• d) performing a next subtraction operation between sample at position x+1 x of the original symbol copy and sample at position x+1+N-L of its time-delayed copy counterpart;
• e) storing the absolute value of the subtraction in position x+1 of the synchronization register;
• f) repeating the subtraction operation until x=N and selecting the subsequent sample as x=1;
• g) when the synchronization register is full, reallocating each slot of the synchronization register with subsequent round of subtractions wherein random noise and inter-symbol interference is minimized by averaging each new value with the value stored previously using equation y(n)=α.x(n)+(1−α).y(n−1) wherein α is a coefficient controlling the growth of the calculated value, y(n−1) is the synchronization vector previously stored in the synchronization register and x(n) is the new synchronization vector;
• h) repeating the operation over at most 500 blocks of symbols as needed to generate a synchronization profile;
• i) inverting the synchronization profile in order to generate a window;
• j) calculating the centre of gravity of the window in order to determine the synchronization signal position;
• k) convolving the window of step j) with a Gaussian window having its centre positioned at the position of the synchronization signal.