Radio access networks
Among other things, a communication system comprising remote units, a reference timing source, a controller, a controller clock, and a remote unit clock. The remote units exchange radio frequency (RF) signals with mobile devices. The reference timing source is synchronized with a coordinated universal time (UTC) or a Global Positioning System (GPS). The controller clock is synchronized with the reference timing source and provides timing information to the controller. The remote unit clock is synchronized with the controller clock and provides timing information to a remote unit. The controller and the remote unit are configured to transmit time stamp messages to synchronize the controller clock and the remote unit clock, by avoiding contention between time stamp transmissions and baseband data transmissions or between time stamp transmissions of different remote units to the controller.
1. A communication system comprising:
remote units to exchange radio frequency signals with mobile devices, at least some of the radio frequency signals comprising information destined for, or originating from, the mobile devices;
a controller connected to an external network, the controller being separated from the remote units by an intermediate switched network, over which data corresponding to the information is transmitted in frames between the controller and the remote units;
a reference timing source that is synchronized to a stable reference clock;
a controller clock synchronized with the reference timing source, the controller clock for providing first timing information to the controller; and
a remote unit clock to be synchronized with the controller clock, the remote unit clock for providing second timing information to a remote unit;
wherein at least one of the controller or the remote unit is configured to transmit time stamp messages to synchronize the remote unit clock to the controller clock; and
wherein at least one of the controller or the remote unit is configured to transmit the time stamp messages to affect a frequency of contention in switches of the intermediate switched network.
2. The communication system of claim 1 , wherein the controller and the remote unit are configured to transmit the time stamp messages to affect the frequency of contention in the switches of the intermediate switched network between time stamp transmissions of different remote units to the controller.
3. The communication system of claim 1 , wherein the controller is configured to time transmissions of the time stamp messages and data to reduce the frequency of contention in the switches of the intermediate switched network.
4. The communication system of claim 1 , wherein the remote unit is configured to time transmission of the time stamp messages to affect the frequency of contention in the switches of the intermediate switched network.
5. The communication system of claim 1 , wherein the remote unit is configured to time transmission of the time stamp messages to reduce the frequency of contention in the switches of the intermediate switched network.
6. The communication system of claim 1 , wherein the controller is configured to time transmissions of the time stamp messages and data to affect the frequency of contention in the switches of the intermediate switched network; and
wherein the remote unit is configured to delay transmission of time stamp messages by a configurable time interval.
7. The communication system of claim 6 , wherein the remote unit is configured to determine transmission times of the time stamp messages based on transmission of data from the remote unit.
8. The communication system of claim 1 , wherein the controller is configured to time transmissions of time stamp messages and data to affect the frequency of contention in the switches of the intermediate switched network; and
wherein the remote unit is configured to delay transmission of the time stamp messages by a pseudo-randomly chosen time interval.
9. The communication system of claim 8 , wherein the remote unit is configured to determine transmission time of the time stamp messages based on transmission of data from the remote unit.
10. The communication system of claim 1 , wherein the reference timing source is a global positioning system (GPS), and wherein a GPS receiver synchronizes the controller clock to the reference timing source.
11. The communication system of claim 10 , wherein the GPS receiver is located in the controller.
12. The communication system of claim 1 , wherein the controller and the remote unit are configured to exchange the time stamp messages using IEEE 1588 protocol.
13. The communication system of claim 1 , wherein the controller and the remote unit each comprise a system-on-chip to generate and to process the time stamp messages.
14. The communication system of claim 1 , wherein the intermediate switched network is a switched Ethernet network.
15. The communication system of claim 1 , wherein the remote unit is configured to use the time stamp messages to estimate, and to correct, an error of the remote unit clock; and
wherein the estimate is based on knowledge about downlink and uplink time stamp message delays.
16. The communication system of claim 15 , wherein the knowledge about the downlink and uplink time stamp message delays comprises a ratio of downlink time stamp message delay to uplink time stamp message delay.
17. The communication system of claim 15 , wherein the knowledge about the downlink and uplink time stamp message delays comprises a ratio of an average downlink time stamp message delay to an average uplink time stamp message delay.
18. The communication system of claim 15 , wherein the error comprises a timing phase error; and
wherein the remote unit is configured to estimate the timing phase error by at least one of weighting or offsetting measured time stamp messages in an uplink and a downlink based on the knowledge about the downlink and uplink time stamp message delays.
19. The communication system of claim 1 , wherein the at least one of the controller or the remote unit is configured to transmit the time stamp messages at a high priority according to an IEEE 802.1q protocol.
20. The communication system of claim 1 , wherein the at least one of the controller or the remote unit is configured to transmit the time stamp messages and data on different virtual local area networks (VLANs).
21. The communication system of claim 1 , wherein the at least one of the controller or the remote unit is configured to transmit the time stamp messages and data on a same virtual local area network (VLAN) using different IEEE 802.1q protocol priority markings.
22. The communication system of claim 1 , wherein the intermediate switched network is a switched Ethernet network; and
wherein the data and the time stamp messages are transmitted over dedicated Ethernet ports and dedicated Ethernet links of the switched Ethernet network.
23. The communication system of claim 1 , comprising:
a plurality of controllers, of which the controller is one of the plurality of controllers;
wherein one of the plurality of controllers is configured to operate as a master controller, the master controller being configured to transmit the time stamp messages with remote units associated with the master controller and with remote units associated with other controllers of the plurality of controllers.
24. The communication system of claim 1 , wherein at least some of the data is baseband data; and
wherein the controller is configured to advance, in time, a subframe of the baseband data to be delivered to the remote unit in order to compensate for a time delay between the remote unit clock and the controller clock.
25. The communication system of claim 24 , wherein the controller is configured to advance, in time, the subframe of the baseband data by a predetermined amount.
26. The communication system of claim 25 , wherein the predetermined amount is based on a time delay associated with transmitting the baseband data over the intermediate switched network.
27. The communication system of claim 1 , wherein the controller is configured to output data representing information that is destined for one or more of the mobile devices, the information being usable by the one or more of the mobile devices to advance a timing phase of the radio frequency signals transmitted to one or more of the remote units relative to the radio frequency signals received by the one or more mobile devices from the one or more remote units.