Clock frequency determining method and apparatus

A clock frequency determining method at a radio over fiber (RoF) device, wherein the method comprises:

• generating a combined optical signal, by coupling an optical signal of a first frequency and an optical signal of a second frequency;
• and
• sending the combined optical signal to access network devices in a positioning system in which the RoF device is located, to synchronize the access network devices to a clock frequency determined based on an absolute value of a frequency difference between the first frequency and the second frequency,
• wherein the access network devices further synchronize local clock times of the access network devices with each other, by exchanging messages including timestamp information with each other.

A communication apparatus, wherein the communication apparatus is an access network device, and the apparatus comprises:

• a transceiver configured to receive a combined optical signal from a radio over fiber (RoF) device, wherein the combined optical signal comprises an optical signal of a first frequency coupled with an optical signal of a second frequency;
• an optical-to-electrical converter configured to convert the combined optical signal into an electrical signal;
• and
• a processor configured to set a local clock frequency based on a signal frequency of the electrical signal and a first preset rule, wherein the signal frequency of the electrical signal is equal to an absolute value of a frequency difference between the first frequency and the second frequency,
• wherein
• the processor is further configured to perform synchronizing local clock time of the access network device with clock time of a further access network device in a positioning system in which the access network device is located, and
• in the synchronizing the local clock time of the access network device with the clock time of the further access network device, the transceiver is further configured to exchange a message including timestamp information with the further access network device.