RF signal transport over passive optical networks
View Patent ↗One embodiment provides an EPON for transporting RF signals. The system includes a reference clock, an ONU, and an OLT. The ONU includes a mechanism for receiving a frequency and phase-reference signal from the OLT, a mechanism for receiving an RF signal, an ADC for converting the RF signal into a digital signal using a sampling signal associated with the frequency and phase-reference signal, a mechanism for assembling at least a portion of the digital signal into a packet, a mechanism configured to timestamp the packet, and an optical transceiver. The OLT includes a mechanism for receiving the packet, a buffer, a delay mechanism configured to delay reading the received packet from the buffer for a predetermined amount of time, and a DAC for converting the digital signal included in the packet back to RF domain using a clock signal associated with the frequency and phase-reference signal.
1. An optical network unit (ONU) in an Ethernet passive optical network (EPON), comprising:
an analog-to-digital converter (ADC) configured to convert an analog signal into a digital signal using a sampling signal based upon a reference signal that is received from an optical line terminal (OLT);
a packet-assembling mechanism configured to assemble at least a portion of the digital signal into a packet; and
an optical transceiver configured to transmit the packet to the OLT.
2. The ONU of claim 1 , further comprising:
a counter configured to generate a timestamp based upon the reference signal.
3. The ONU of claim 2 , wherein the packet-assembling mechanism is further configured to include the timestamp within a header of the packet.
4. The ONU of claim 2 , wherein the timestamp is configured to indicate a start time of the ADC.
5. The ONU of claim 1 , further comprising:
a frequency multiplier configured to multiply the reference signal to generate the sampling signal.
6. The ONU of claim 1 , wherein the reference signal is substantially aligned with a reference clock within the OLT.
7. The ONU of claim 6 , wherein the reference clock is a pulse signal, the reference signal being substantially aligned with a rising edge of a pulse from among the pulse signal.
8. The ONU of claim 1 , further comprising:
a reference-clock receiving mechanism configured to receive a message from the OLT, the message indicating a time when a next pulse of a reference clock within the OLT is to occur,
wherein the reference-clock receiving mechanism is further configured to adjust the reference signal to be substantially aligned with the next pulse.
9. The ONU of claim 1 , wherein the analog signal is a radio frequency (RF) signal that is received from a set-top box.
10. An optical network unit (ONU) in an Ethernet passive optical network (EPON), comprising:
a reference-clock receiving mechanism configured to provide a reference signal in response to receiving a message from an optical line terminal (OLT), the message providing information relating to a reference clock within the OLT; and
an analog-to-digital converter (ADC) configured to convert an analog signal into a digital signal using a sampling signal that is based upon the reference signal.
11. The ONU of claim 10 , wherein the information indicates a time when a next pulse of the reference clock is to occur.
12. The ONU of claim 11 , wherein the reference-clock receiving mechanism is further configured to adjust the reference signal to be substantially aligned with the next pulse.
13. The ONU of claim 11 , further comprising:
a counter configured to generate a timestamp based upon the reference signal; and
a packet-assembling mechanism configured to assemble at least a portion of the digital signal into a packet and to include the timestamp within a header of the packet.
14. The ONU of claim 11 , further comprising:
a frequency multiplier configured to multiply the reference signal to generate the sampling signal.
15. A method for transporting radio frequency (RF) signals in an Ethernet passive optical network (EPON), comprising:
providing, by an optical network unit (ONU), a reference signal in response to receiving a message from an optical line terminal (OLT), the message providing information relating to a reference clock within the OLT;
converting, by the ONU, an analog signal into a digital signal using a sampling signal based upon the reference signal;
generating, by the ONU, a timestamp in response to the converting;
assembling, by the ONU, at least a portion of the digital signal into a packet that is received from an optical line terminal (OLT), the packet including a header that includes the timestamp; and
transmitting, by the ONU, the packet to the OLT.
16. The method of claim 15 , wherein the step of providing comprises:
providing the reference signal in response to receiving an indication of a time when a next pulse of the reference clock is to occur.
17. The method of claim 16 , wherein the step of providing comprises:
adjusting the reference signal to be substantially aligned with the next pulse.
18. The method of claim 15 , wherein the step of providing comprises:
providing the reference signal in response to receiving an indication of a time when an edge of the reference clock is to occur.
19. The method of claim 15 , wherein the step of generating comprises:
generating the timestamp upon starting the step of converting.
20. The method of claim 15 , further comprising:
multiplying the reference signal to generate the sampling signal.