Time-division duplexing (TDD) in distributed communications systems, including distributed antenna systems (DASs)
Time-division duplexing (TDD) in distributed communications systems, including distributed antenna systems (DASs) is disclosed. In one embodiment, a control circuit is provided and configured to control the TDD transmit mode of a DAS to control the allocation of time slots for uplink and downlink communications signal distribution in respective uplink path(s) and downlink path(s). The control circuit includes separate power detectors configured to detect either a transmit power level in a downlink path or a receive power level in an uplink path. If the transmit power detected in the downlink path is greater than receive power detected in the uplink path, the control circuit switches the TDD transmit mode to the downlink direction. In this manner, the control circuit does not have to control the TDD transmit mode based solely on detected power in the downlink path, where a directional coupler may leak uplink power in the downlink path.
1. A control circuit for controlling switching between a time-division duplexing (TDD) transmit mode and a TDD receive mode in a wireless communications system supporting TDD, the control circuit comprising:
a first power detector configured to determine a first power level in a downlink direction on a downlink optical path;
a second power detector configured to determine a second power level in an uplink direction on an uplink optical path;
a receive/transmit comparator coupled to the first power detector and to the second power detector, wherein the receive/transmit comparator compares the first power level to the second power level to provide a first indication that the system should be switched to TDD transmit mode when the first power level exceeds the second power level;
a second power comparator configured to determine a second indication indicative of whether the first power level exceeds a value of a transmit power reference; and
a logic circuit configured to determine if the system should be switched to TDD transmit mode or TDD receive mode based at least in part on a received first indication from the receive/transmit comparator and a received second indication from the second power comparator, wherein
the logic circuit has a first state in which the second power level exceeds the first power level to indicate TDD receive mode, and
the logic circuit has a second state in which the first power level exceeds the second power level.
2. The control circuit of claim 1 , wherein the logic circuit has a third state in which the first power level exceeds the second power level and the value of the transmit power reference to indicate TDD transmit mode.
3. The control circuit of claim 2 , wherein the receive/transmit comparator and the second power comparator have as an input an output of the first power detector.
4. The control circuit of claim 1 , wherein the receive/transmit comparator and the second power comparator have as an input an output of the first power detector.
5. The control circuit of claim 1 , further comprising a TDD switching circuit configured to effect the TDD transmit mode and the TDD receive mode for the system, and a directional coupler configured to receive and transmit communications between the TDD switching circuit and a radio source.
6. A control circuit for controlling switching between a time-division duplexing (TDD) transmit mode and a TDD receive mode in a wireless communications system, the control circuit comprising:
a first power detector configured to determine a first power level in a downlink direction on a downlink optical path;
a second power detector configured to determine a second power level in an uplink direction on an uplink optical path;
a receive/transmit comparator coupled to the first power detector and to the second power detector, wherein the receive/transmit comparator compares the first power level to the second power level to provide a first indication that the system should be switched to TDD transmit mode when the first power level exceeds the second power level;
a second power comparator configured to determine a second indication indicative of whether the first power level exceeds a value of a transmit power reference;
a logic circuit coupled to the receive/transmit comparator for receiving the first indication and configured to receive the second indication, wherein the logic circuit is configured to determine if the system should be switched to TDD transmit mode or TDD receive mode based at least in part on the received first indication from the receive/transmit comparator and the received second indication from the second power comparator; and
a TDD switching circuit configured to effect the TDD transmit mode and the TDD receive mode.
7. The control circuit of claim 6 , further comprising a saturation comparator configured to provide a third indication of saturation of the first power detector by comparing the first power level with a saturation level reference, the logic circuit coupled to the saturation comparator for receiving the third indication, wherein the logic circuit is configured to determine if the system should be switched to TDD transmit mode or TDD receive mode based at least in part on the received third indication of saturation from the saturation comparator.
8. The control circuit of claim 6 , wherein the logic circuit has a first state in which the second power level exceeds the first power level to indicate TDD receive mode.
9. The control circuit of claim 8 , wherein the logic circuit has a second state in which the first power level exceeds the second power level and the first power level does not exceed the value of the transmit power reference to indicate TDD receive mode.
10. The control circuit of claim 9 , wherein the logic circuit has a third state in which the first power level exceeds the second power level and the value of the transmit power reference to indicate TDD transmit mode.
11. The control circuit of claim 8 , further comprising a saturation comparator configured to provide a third indication of saturation of the first power detector by comparing the first power level with a saturation level reference, the logic circuit configured to receive the third indication, wherein the logic circuit is configured to determine if the system should be switched to TDD transmit mode or TDD receive mode.
12. A control circuit for controlling switching between a time-division duplexing (TDD) transmit mode and a TDD receive mode in a system supporting TDD in a wireless communications system, the control circuit comprising:
a first power detector configured to determine a first power level in a downlink direction on a downlink optical path;
a second power detector configured to determine a second power level in an uplink direction on an uplink optical path;
a receive/transmit comparator configured to compare the first power level to the second power level to provide a first indication that the system should be switched to TDD transmit mode when the first power level exceeds the second power level;
a second power comparator configured to determine a second indication indicative of whether the first power level exceeds a value of a transmit power reference;
a logic circuit coupled to receive the first indication, the logic circuit coupled to the second power comparator for receiving the second indication, wherein the logic circuit is configured to determine if the system should be switched to TDD transmit mode or TDD receive mode based at least in part on the received first indication from the receive/transmit comparator and the received second indication from the second power comparator; and
a saturation comparator configured to provide a third indication of saturation of the first power detector.
13. The control circuit of claim 12 , wherein the logic circuit is coupled to the saturation comparator for receiving the third indication, wherein the logic circuit is configured to determine if the system should be switched to TDD transmit mode or TDD receive mode based at least in part on the received third indication of saturation from the saturation comparator.
14. The control circuit of claim 12 , wherein the receive/transmit comparator and the second power comparator have as an input an output of the first power detector.
15. The control circuit of claim 12 , wherein the logic circuit has a first state in which the second power level exceeds the first power level to indicate TDD receive mode.
16. The control circuit of claim 13 , wherein the receive/transmit comparator and the second power comparator have as an input an output of the first power detector, and the logic circuit has a first state in which the second power level exceeds the first power level to indicate TDD receive mode.
17. A control circuit for controlling switching between a time-division duplexing (TDD) transmit mode and a TDD receive mode in a wireless communications system, the control circuit comprising:
a first power detector configured to determine a first power level in a downlink direction on a downlink optical path;
a second power detector configured to determine a second power level in an uplink direction on an uplink optical path;
a receive/transmit comparator coupled to the first power detector to compare the first power level to the second power level to provide a first indication that the system should be switched to TDD transmit mode when the first power level exceeds the second power level;
a second power comparator configured to determine a second indication indicative of whether the first power level exceeds a value of a transmit power reference; and
a logic circuit coupled to the receive/transmit comparator for receiving the first indication, the logic circuit coupled to the second power comparator for receiving the second indication, wherein the logic circuit is configured to determine if the system should be switched to TDD transmit mode or TDD receive mode based at least in part on the received first indication from the receive/transmit comparator and the received second indication from the second power comparator, wherein
the receive/transmit comparator and the second power comparator have as an input an output of the first power detector.
18. The control circuit of claim 17 , further comprising a TDD switching circuit configured to effect the TDD transmit mode and the TDD receive mode for the system.
19. The control circuit of claim 18 , wherein the TDD switching circuit comprises an input switch and an antenna switch located upstream and downstream the downlink optical path, respectively.
20. The control circuit of claim 19 , wherein the TDD switching circuit comprises a transmit amplifier and a receive amplifier located between the input switch and the antenna switch.