Cyclic prefix (CP) detection and removal in a wireless communications system (WCS)

1. A radio access network (RAN) communications system, comprising:

a remote radio circuit comprising at least one antenna port coupled to at least one antenna to receive at least one random-access symbol comprising a cyclic prefix (CP) followed by a random-access sequence; and

an open fronthaul gateway (OFG) circuit coupled to the remote radio circuit and comprising:

a networking port coupled to a distribution unit (DU); and

a processing circuit configured to:

determine a group delay between the at least one antenna port and the networking port;

determine a start of the CP in the at least one random-access symbol based on the determined group delay; and

remove the CP from the at least one random-access symbol based on the determined start of the CP.

2. The RAN communications system of claim 1 , wherein the processing circuit is further configured to communicate the random-access sequence in the at least one random-access symbol to the DU via the networking port.

3. The RAN communications system of claim 2 , wherein the processing circuit is further configured to:

convert the random-access sequence from a time domain data to a frequency domain data; and

communicate the frequency domain data to the DU via the networking port.

4. The RAN communications system of claim 3 , wherein the processing circuit is further configured to perform a Fast Fourier Transform (FFT) to convert the random-access sequence from the time domain data into the frequency domain data.

5. The RAN communications system of claim 3 , wherein:

the networking port comprises an Ethernet port; and

the processing circuit is further configured to encode the frequency domain data based on common public radio interface (CPRI) protocol for communication via the Ethernet port.

6. The RAN communications system of claim 1 , further comprising a digital routing circuit coupled between the remote radio circuit and the OFG circuit, wherein the group delay between the at least one antenna port and the networking port comprises:

a first processing delay in the remote radio circuit;

a first propagation delay from the remote radio circuit to the digital routing circuit;

a second processing delay in the digital routing circuit;

a second propagation delay from the digital routing circuit to the OFG circuit; and

a third processing delay in the OFG circuit.

7. The RAN communications system of claim 6 , wherein the processing circuit is further configured to:

send a test packet with a known pattern toward the remote radio circuit;

measure a round-trip delay upon receiving the test packet returned by the remote radio circuit; and

determine the first propagation delay, the second processing delay, and the second propagation delay as being equal to one-half of the measured round-trip delay.

8. The RAN communications system of claim 7 , wherein the OFG circuit further comprises a memory circuit configured to pre-store the first processing delay and the third processing delay.

9. The RAN communications system of claim 6 , further comprising:

an O-RAN DU (O-DU) comprising the DU; and

an O-RAN RU (O-RU) comprising the remote radio circuit, the digital routing circuit, and the OFG circuit.

10. A method for detecting and removing a cyclic prefix (CP) in a wireless communications system (WCS), comprising:

receiving at least one random-access symbol comprising the CP followed by a random-access sequence;

determining a group delay associated with at least one random-access symbol;

determining a start of the CP in the at least one random-access symbol based on the determined group delay; and

removing the CP from the at least one random-access symbol based on the determined start of the CP.

11. The method of claim 10 , further comprising communicating the random-access sequence in the at least one random-access symbol.

12. The method of claim 11 , further comprising:

converting the random-access sequence from a time domain data to a frequency domain data; and

communicating the frequency domain data.

13. The method of claim 12 , further comprising performing a Fast Fourier Transform (FFT) to convert the random-access sequence from the time domain data into the frequency domain data.

14. The method of claim 12 , further comprising encoding the frequency domain data based on a common public radio interface (CPRI) protocol.

15. The method of claim 10 , further comprising determining the group delay that comprises:

a first processing delay in a remote radio circuit;

a first propagation delay from the remote radio circuit to a digital routing circuit;

a second processing delay in the digital routing circuit;

a second propagation delay from the digital routing circuit to an open fronthaul gateway (OFG) circuit; and

a third processing delay in the OFG circuit.

16. The method of claim 15 , further comprising:

sending a test packet with a known pattern from the OFG circuit toward the remote radio circuit;

measuring a round-trip delay upon receiving the test packet returned by the remote radio circuit; and

determining the first propagation delay, the second processing delay, and the second propagation delay as being equal to one-half of the measured round-trip delay.

17. The method of claim 16 , further comprising pre-storing the first processing delay and the third processing delay.

18. A wireless communications system (WCS), comprising:

a radio access network (RAN) communications system, comprising:

a distribution unit (DU);

a remote radio circuit comprising at least one antenna port coupled to at least one antenna to receive at least one random-access symbol comprising a cyclic prefix (CP) followed by a random-access sequence; and

an open fronthaul gateway (OFG) circuit coupled to the remote radio circuit and comprising:

a networking port coupled to the DU; and

a processing circuit configured to:

determine a group delay between the at least one antenna port and the networking port;

determine a start of the CP in the at least one random-access symbol based on the determined group delay;

remove the CP from the at least one random-access symbol based on the determined start of the CP; and

communicate the random-access sequence in the at least one random-access symbol to the DU via the networking port.

19. The WCS of claim 18 , wherein the RAN communications system further comprises a digital routing circuit coupled between the remote radio circuit and the OFG circuit, wherein the group delay between the at least one antenna port and the networking port comprises:

a first processing delay in the remote radio circuit;

a first propagation delay from the remote radio circuit to the digital routing circuit;

a second processing delay in the digital routing circuit;

a second propagation delay from the digital routing circuit to the OFG circuit; and

a third processing delay in the OFG circuit.

20. The WCS of claim 18 , further comprising a distributed communications system (DCS), the DCS comprising:

a digital routing unit (DRU) coupled to a centralized services node via a baseband unit (BBU); and

a plurality of remote units each coupled to the DRU via a plurality of optical fiber-based communications mediums, respectively;

wherein:

the DRU comprises:

an electrical-to-optical (E/O) converter configured to convert a plurality of downlink communications signals into a plurality of downlink optical communications signals, respectively; and

an optical-to-electrical (O/E) converter configured to convert a plurality of uplink optical communications signals into a plurality of uplink communications signals, respectively; and

the plurality of remote units each comprises:

a respective O/E converter configured to convert a respective one of the plurality of downlink optical communications signals into a respective one of the plurality of downlink communications signals; and

a respective E/O converter configured to convert a respective one of the plurality of uplink communications signals into a respective one of the plurality of uplink optical communications signals.