Optical OFDMA communication network and method for operating an optical OFDMA communication network

The invention relates to an optical OFDMA communication network, comprising: - - a plurality of optical network units (ONUs 2a-2n), wherein each one of the ONUs (2a-2n) is configured to generate a ranging sequence (20b - 20n) for upstream synchronization of the ONUs (2a-2n); - - a receiving unit (5) for receiving signals of the ONUs (2a-2n), the receiving unit (5) being also configured to receive the ranging sequences (20b - 20n) of the ONUs (2a-2n), - - wherein the receiving unit (5) comprises a correlator unit (61) in which a plurality of ranging sequences (611) is stored, - - and wherein the receiving unit (5) is configured to perform a ranging detection operation including performing a correlation operation with a plurality of the received ranging sequences (20b - 20n) using at least one of the stored ranging sequences (611) and to transmit a ranging response to the ONUs (2a-2n); depending on the result of the correlation operation. The ranging sequence consists in a four time repeated CAZAC sequence, multiplied by a ONU specific PN sequence and by a frequency shift.