Method and apparatus for performing timing synchronization in a wireless communication system
A method and apparatus for performing time synchronization is provided. The method/apparatus includes, at a radio subsystem: receiving, from a digital subsystem, a first signal via the link, where the link not dedicated to timing synchronization; determining a time difference between the first signal and a second signal; converting the time difference to a time error, sending, via the link, the time error or time difference to the digital subsystem. The method further includes, at the digital subsystem, inputting the time error, received from the radio subsystem, to a phased locked loop (PLL) in order to adjust an oscillator frequency so as to reduce the amount of the time error and thus synchronizing the radio access network with the second signal received at the radio subsystem, without the need for an additional connection between the digital and radio subsystems.
1. A method for timing synchronization in a base station comprising a radio subsystem that is coupled to a plurality of digital subsystems via a link not dedicated to timing synchronization, the method comprising:
at the radio subsystem:
receiving, from a first digital subsystem of the plurality of digital subsystems, a first signal via the link;
determining a time difference between the first signal and a second signal sourced by a second digital subsystem of the plurality of digital subsystems;
sending, via the link, an indication of the time difference to at least one of the plurality of digital subsystems;
at the at least one of the plurality of digital subsystem:
inputting the indication of the time difference received from the radio subsystem to a phase locked loop (PLL); and
synchronizing the base station with the second signal based on an output from the PLL.
2. The method of claim 1 wherein the indication of the time difference is a time error signal and wherein the method further comprises:
determining a delay associated with conveying the first signal over the link;
adjusting the time error signal based on the link delay and prior to an application of the time error signal to the phase locked loop.
3. The method of claim 1 , wherein the first signal is a clock signal received from the digital subsystem.
4. The method of claim 1 , wherein the radio subsystem and the digital subsystem are located remotely from each other.
5. The method of claim 1 , wherein the radio subsystem and the digital subsystem each resides in a remote radio head.
6. The method of claim 1 , further comprising synchronizing, by the digital subsystem, an another radio subsystem with the second signal.
7. The method of claim 6 , wherein the another radio subsystem resides inside a location without an ability to receive Global Navigation Satellite System signals.
8. The method of claim 1 , wherein the link is a control signal link used to exchange non-timing synchronization related control signals.
9. An apparatus for providing timing synchronization in a communication system, the apparatus comprising a base station having:
a radio subsystem comprising:
a first radio interface that is configured to receive a first signal from a first digital subsystem of a plurality of digital subsystems;
a second radio interface that is configured to receive a second signal from a second digital subsystem of the plurality of digital subsystems;
a comparator that is configured to determine a time difference between the first signal and the second signal; and
an interface to a link to the at least one of the plurality of digital subsystems, wherein the link is not dedicated to timing synchronization and wherein the interface is configured to send, via the link, an indication of the time difference to at least one of the plurality of digital subsystems;
the at least one of the plurality of digital subsystems, comprising:
a phase locked loop (PLL) that is configured to process the indication of the time difference received from the radio subsystem; and
an oscillator that is configured to synchronize the base station with the second signal based on the output from the PLL.
10. The apparatus of claim 9 , wherein the first signal is a clock signal received from the digital subsystem.
11. The apparatus of claim 9 , wherein the radio subsystem and the digital subsystem are located remotely from each other.
12. The apparatus of claim 9 , wherein the digital subsystem synchronizes an another radio subsystem with the second signal.
13. The apparatus of claim 12 , wherein the another radio subsystem resides inside a location without an ability to receive Global Navigation Satellite System signals.
14. The apparatus of claim 9 , wherein the link is a control signal link used to exchange non-timing synchronization related control signals.
15. The apparatus of claim 9 , where the first signal is adjusted based on a determined link delay prior to determining a time error between the first signal and the second signal.
16. A remote radio head comprising the apparatus of claim 9 .