Detection of CPD using leaked forward signal

A method of detecting common path distortion (CPD) in a hybrid-fiber coax (HFC) network that includes a headend or hub, a coaxial cable plant, and a fiber node coupled between the headend or hub and the coaxial cable plant,

• the headend or hub containing a return receiver having an adjustable capturing bandwidth,
• the fiber node including an optical transceiver, a diplexer having forward and return legs, a forward path defined between the optical transceiver and the forward leg, and a return path defined between the optical transceiver and the return leg,
• the optical transceiver of the fiber node receiving a return signal from the coaxial cable plant via the return leg of the diplexer and the return path, the optical transceiver providing a forward signal to the coaxial cable plant via the forward path and the forward leg of the diplexer, a portion of the forward signal leaking through the return leg of the diplexer and traveling to the optical transceiver via the return path, the optical transceiver transmitting the return signal and the leaked forward signal to the return receiver contained in the headend or hub,
• the return signal containing an actual CPD signal generated by an interaction between the forward signal and a CPD source in the coaxial cable plant, the forward signal propagating from the fiber node to the CPD source and the actual CPD signal propagating from the CPD source to the fiber node all within a round-trip interval,
• said method comprising the steps of:
• (a) adjusting the capturing bandwidth of the return receiver contained in the headend or hub to include the return signal and a range of frequencies of the leaked forward signal;
• (b) operating the return receiver contained in the headend or hub to synchronously capture the return signal and the range of frequencies of the leaked forward signal over a limited capture duration of at least the round-trip interval;
• and
• (c) detecting the actual CPD signal by processing the leaked forward and the return signals captured in step (b), and wherein step (c) includes:
• (i) generating from the captured leaked forward signal a reference CPD signal that substantially simulates the actual CPD signal;
• (ii) performing a cross-correlation of the reference CPD signal and the captured return signal to produce a correlation peak associated with the actual CPD signal;
• and
• (iii) detecting the actual CPD signal from the correlation peak.

A method of detecting common path distortion (CPD) in a hybrid-fiber coax (HFC) network that includes a headend or hub, a coaxial cable plant, and a fiber node coupled between the headend or hub and the coaxial cable plant,

• the headend or hub containing a return receiver having an adjustable capturing bandwidth,
• the fiber node including an optical receiver, an optical transmitter, a diplexer having forward and return legs, a forward path defined between the optical receiver and the forward leg, and a return path defined between the optical transmitter and the return leg,
• the optical transmitter of the fiber node receiving a return signal from the coaxial cable plant via the return leg of the diplexer and the return path, the optical receiver of the fiber node providing a forward signal to the coaxial cable plant via the forward path and the forward leg of the diplexer, a portion of the forward signal leaking through the return leg of the diplexer and traveling to the optical transmitter via the return path, the optical transmitter transmitting the return signal and the leaked forward signal to the return receiver contained in the headend or hub,
• the return signal containing an actual CPD signal generated by an interaction between the forward signal and a CPD source in the coaxial cable plant, the forward signal propagating from the fiber node to the CPD source and the actual CPD signal propagating from the CPD source to the fiber node all within a round-trip interval,
• said method comprising the steps of:
• (a) adjusting the capturing bandwidth of the return receiver contained in the headend or hub to include the return signal and a range of frequencies of the leaked forward signal;
• (b) operating the return receiver contained in the headend or hub to synchronously capture the return signal and the range of frequencies of the leaked forward signal over a limited capture duration of at least the round-trip interval;
• and
• (c) detecting the actual CPD signal by processing the leaked forward and the return signals captured in step (b), and wherein the capturing bandwidth of the return receiver is defined by a center frequency of a plurality of center frequencies, and wherein step (a) includes selecting one of the plurality of center frequencies as the center frequency of the capturing bandwidth.