Fronthaul network units and methods therein for synchronization over a single optical fiber in a frontahul network

A second fronthaul network unit for enabling synchronization with a first fronthaul network unit over a first single optical fiber in a fronthaul network, the second fronthaul network unit being configured to:

• receive a first optical signal on the first single optical fiber,
• separate the received first optical signal into a second optical signal carrying downlink (DL) radio data traffic having a first optical wavelength and a third optical signal carrying packet-based synchronization messages having a second optical wavelength, wherein the second optical wavelength is different from the first optical wavelength,
• output the separated second optical signal towards a first optical port in the second fronthaul network unit,
• split the separated third optical signal towards a second optical port in the second fronthaul network unit,
• receive DL radio data traffic in the separated second optical signal via the first optical port, and packet-based synchronization messages in the separated third optical signal via the second optical port,
• transmit DL radio data traffic not intended for the second fronthaul network unit using a third optical port that outputs a fourth optical signal having a third optical wavelength, and
• multiplex the fourth optical signal from the third optical port and the separated third optical signal onto a second single optical fiber.

A method performed by a first fronthaul network unit for enabling synchronization with at least two second fronthaul network units over a first single optical fiber in a fronthaul network, the method comprising:

• transmitting downlink (DL) radio data traffic intended for one or more of the at least two second fronthaul network units using a first optical port that outputs a first optical signal having a first optical wavelength;
• transmitting packet-based synchronization messages to the at least two second fronthaul network units using a second optical port that outputs a second optical signal having a second optical wavelength, wherein the second optical wavelength is different from the first optical wavelength;
• multiplexing the first optical signal from the first optical port and the second optical signal from the second optical port onto the same single optical fiber towards the at least two second fronthaul network units;
• and
• allocating a respective uplink time slot to each of the at least two second fronthaul network units for transmitting uplink synchronization messages on the second optical wavelength.