Clock synchronization for a wireless communications system
View Patent ↗A method of clock synchronization for a wireless communications system includes receiving a radio frequency (RF) signal at a base station and at a network reference server (NRS). The NRS is also coupled to receive a reference clock signal. A clock offset value is then calculated in response to the RF signal received at the base station, the RF signal received at the NRS, and the reference clock signal. A local clock signal at the base station is then synchronized with the reference clock signal in response to the calculated clock offset value.
1. A method, comprising:
receiving a radio frequency (RF) signal at a base station and at a network reference server (NRS);
calculating a location of the base station in response to the received RF signal;
receiving a reference clock signal at the NRS;
calculating a clock offset value in response to the RF signal received at the base station, the RF signal received at the NRS, and the reference clock signal, wherein calculating the clock offset value comprises calculating a time T 0 when the RF signal was transmitted by an RF transmitter, and wherein the clock offset value is based on the location of the base station, a location of the NRS and the time T 0 ; and
synchronizing a local clock signal at the base station with the reference clock signal in response to the clock offset value.
2. The method of claim 1 , wherein receiving the RF signal at the base station and the NRS comprises receiving a first plurality of RF signals at the base station and receiving a second plurality of RF signals at the NRS, the method further comprising:
calculating a location of the NRS in response to the received second plurality of RF signals.
3. The method of claim 1 , wherein calculating the clock offset value further comprises:
determining a time T 1 when the RF signal was received at the NRS; and
calculating the time T 0 in response to the time T 1 and in response to a distance between the RF transmitter and the NRS;
determining a time T 2 when the RF signal was received at the base station; and
calculating the clock offset value in response to time T 2 and the delay between time T 0 and the reference clock signal.
4. The method of claim 1 , wherein the RF signal comprises a broadcast television signal.
5. The method of claim 1 , wherein the RF signal comprises a timestamp, the method further comprising:
determining a time T 1 when the timestamp of the RF signal was received at the NRS;
determining a time T 2 when the timestamp of the RF signal was received at the base station; and
calculating the clock offset value in response to the times T 1 and T 2 .
6. A base station, comprising:
a radio receiver to receive a radio frequency (RF) signal;
a local clock to generate a local clock signal; and
a wireless interface coupled to receive the local clock signal and configured to wirelessly communicate with a mobile device in response to the local clock signal; and
a processing device coupled to the radio receiver and the wireless interface, wherein the processing device is configured to determine when the RF signal was transmitted and a location of the base station, and wherein the processing device is configured to calculate a clock offset value based on a time delay between when the RF signal was transmitted, the location of the base station, and a reference clock signal, wherein the local clock signal is synchronized with the reference clock signal in response to the clock offset value.
7. The base station of claim 6 , wherein the RF signal is one of a plurality of RF signals and the radio receiver is coupled to receive the plurality of RF signals, wherein the processing devices is configured to calculate a distance between the base station and an RF transmitter in response to the received plurality of RF signals, wherein the RF transmitter transmitted at least one of the plurality of RF signals.
8. The base station of claim 6 , further comprising a network interface coupled to the radio receiver and to be coupled to a network reference server (NRS) via a computer network, wherein the network interface transmits data representative of a time T 2 to the NRS via the computer network, wherein the time T 2 represents a time when the RF signal was received at the radio receiver of the base station.
9. The base station of claim 8 , wherein the network interface receives the time delay from the NRS via the computer network, wherein the processing device is configured to calculate the clock offset value in response to the received time delay.
10. The base station of claim 8 , wherein the network interface comprises a Digital Subscriber Line (DSL) modem.
11. The base station of claim 10 , wherein the network interface comprises a discrete multi-tone (DMT) communication device.
12. The base station of claim 11 , wherein the DMT communication device is a digital subscriber line (DSL) modem.
13. The base station of claim 6 , wherein the RF signal comprises a broadcast television signal that includes a synchronization signal.
14. The base station of claim 13 , wherein the broadcast television signal comprises a National Television Standards Committee (NTSC) signal.
15. The base station of claim 13 , wherein the broadcast television signal comprises an American Television Standards Committee (ATSC) Digital Video Television (DTV) signal.
16. The base station of claim 6 , wherein the base station is a first base station of a communications system extending over a wireless region, the communications system formed of a plurality of base stations, where each base station provides wireless communications coverage for a mobile device within a respective portion of the wireless region, the wireless interface further configured to negotiate a hand off of the mobile device from one of the plurality of base stations to the first base station after the local clock signal is synchronized with the reference clock signal.
17. The base station of claim 6 , wherein the wireless interface wirelessly communicates with a mobile device via a Universal Mobile Telecommunications System (UMTS) standard.