Multiplexing system for time division duplex communication systems
A method and system is disclosed for passing a transmit/receive control signal and a power signal through a coax cable from a base transceiver station to a tower top device in a time division duplex communication system. After generating the transmit/receive control signal and a radio frequency signal for communications, the transmit/receive control signal modulates a separate timing control operating on a separate control frequency. It is then multiplexed on at least one coax cable along with the radio frequency signal and DC power. At the tower top device, the modulated transmit/receive control signal is converted back to a DC level for providing a time division duplex control reference.
1. A system comprising:
a base transceiver station configured to:
generate a radio frequency communications signal;
generate a transmit/receive control signal based on an operational mode of the base transceiver station, wherein the transmit/receive control signal is a DC signal that is in a first state when the base transceiver station is in a transmit mode and the DC signal is in a second state when the base transceiver station is in a receive mode;
generate a timing control signal on a predetermined control frequency that is on a different frequency than the radio frequency communications signal, wherein the timing control signal is modulated by the transmit/receive control signal; and
multiplex the radio frequency communications signal with the timing control signal;
a coax cable having one end coupled to the base transceiver station and configured to carry the multiplexed radio frequency communications and timing control signals; and
a remote device coupled to another end of the coax cable and configured to convert the timing control signal back to a DC signal, and activate a transmit power amplifier of the remote device when the DC signal is in the first state.
2. The system of claim 1 , wherein the base transceiver station is configured to generate the timing control signal at the predetermined control frequency of about 10 MHz.
3. The system of claim 1 , wherein the base transceiver station further comprises:
an oscillator configured to generate a carrier signal at the predetermined control frequency; and
a switch coupled to the oscillator and configured to amplitude shift key modulate the carrier signal using the transmit/receive control signal as a modulating signal to generate the timing control signal.
4. The system of claim 1 , wherein the base transceiver station is configured to generate the transmit/receive control signal as a DC signal that is not present in the first state and that is present in the second state.
5. The system of claim 3 , wherein the base transceiver station further comprises at least one inductor and at least one capacitor coupled between the switch and the coax cable.
6. The system of claim 1 , wherein the remote device further comprises a filter configured to pass the timing control signal.
7. The system of claim 6 , wherein the remote device further comprises at least one inductor and at least one capacitor coupled between the filter and the coax cable.
8. The system of claim 1 , wherein the remote device further comprises a receive low noise amplifier that is activated when the DC signal is in the second state.
9. The system of claim 1 , wherein a shield of the coax cable is grounded.
10. A method comprising:
generating a radio frequency communications signal at a base transceiver station;
generating a transmit/receive control signal based on an operational mode of the base transceiver station, wherein the transmit/receive control signal is a DC signal that is in a first state when the base transceiver station is in a transmit mode and the DC signal is in a second state when the base transceiver station is in a receive mode;
generating a timing control signal on a predetermined control frequency that is on a different frequency than the radio frequency communications signal, wherein the timing control signal is modulated by the transmit/receive control signal;
transporting the timing control signal and the radio frequency communications signal to a remote device;
converting the timing control signal back to a DC signal; and,
activating a transmit power amplifier of the remote device when the DC signal is in the first state.
11. The method of claim 10 , wherein generating the timing control signal comprises generating the timing control signal at the predetermined control frequency of about 10 MHz.
12. The method of claim 10 , wherein generating the timing control signal further comprises:
operating an oscillator configured to generate a carrier signal at the predetermined control frequency; and
modulating the carrier signal using a switch coupled to the oscillator that amplitude shift key modulates the carrier signal using the transmit/receive control signal as a modulating signal to generate the timing control signal.
13. The method of claim 10 , further comprising isolating the radio frequency communications signal from the timing control signal.
14. The method of claim 10 , wherein converting further comprises converting the timing control signal to a DC signal using a detector.
15. The method of claim 10 , and further comprising at the remote device activating a receive low noise amplifier that is activated when the DC signal is in the second state.
16. The method of claim 10 , wherein generating the transmit/receive control signal comprises generating the DC signal that is not present in the first state and that is present in the second state.
17. A system comprising:
a base transceiver station configured to generate a transmit/receive control signal based on an operational mode of the base transceiver station, wherein the transmit/receive control signal is a DC signal that is in a first state when the base transceiver station is in a transmit mode and the DC signal is in a second state when the base transceiver station is in a receive mode;
an oscillator configured to generate a carrier signal;
a switch coupled to the oscillator and configured to amplitude shift key modulate the carrier signal using the transmit/receive control signal as a modulating signal to generate a timing control signal;
a coax cable having a first end that is configured to couple to the switch; and
a detector coupled to a second end of the coax cable and configured to convert the timing control signal to a DC signal.
18. The system of claim 17 , further comprising a first inductor and a first capacitor coupled in series between the switch and the first end of the coax cable and a second capacitor, a second inductor, and a filter coupled in series between the second end of the coax cable and the detector.
19. The system of claim 17 , wherein the base transceiver station is configured to generate the transmit/receive control signal as a DC signal that is not present in the first state and that is present in the second state.
20. The system of claim 17 , further comprising a transmit power amplifier and a receive low noise amplifier both coupled to the detector, wherein when the DC signal is in the first state the transmit power amplifier is activated and when the DC signal is in the second state the receive low noise amplifier is activated.