Detecting leakage of OFDM signals from an HFC network

A system for detecting a leak in a hybrid fiber-coax (HFC) network, the HFC network transmitting a plurality of orthogonal frequency division multiplexing (OFDM) signals to a plurality of services areas, respectively, each of the OFDM signals being characterized by a signal period that is synchronized to a standard reference clock, each of the service areas being defined by geographic coordinates, the leak being located in one of the service areas and emitting one of the OFDM signals over-the-air as an OFDM leakage signal, said system comprising:

• (a) a leakage data server containing a plurality of signatures associated with the plurality of OFDM signals, respectively, each signature including
• the signal period of the associated OFDM signal, and
• signal samples representing the associated OFDM signal and generated at a first sample rate;
• and
• (b) a leakage detector to be moved through the service areas of the HFC network, said leakage detector including—
• (i) a wireless modem for receiving, via a wireless network, the plurality of signatures from said leakage data server,
• (ii) a leakage signal receiver for receiving the OFDM leakage signal over the air,
• (iii) an analog-to-digital converter, coupled to the leakage signal receiver, for generating signal samples of the received OFDM leakage signal at the first sample rate, using a clock signal substantially synchronized to the standard reference clock,
• (iv) a global positioning system (GPS) receiver for determining a geographic position of said leakage detector,
• (v) a digital controller coupled to the GPS receiver and the wireless modem and configured to determine in which of the service areas said leakage detector is located based on the geographic position of said leakage detector and on the geographic coordinates of the service areas, the digital controller being further configured to select one of the signatures based at least on the service area in which said leakage detector is located,
• (vi) a local timer, coupled to the GPS receiver and the digital controller, for generating a series of triggering pulses having a period substantially synchronized to the signal period of the OFDM signal associated with the selected signature, and
• (vii) a cross-correlation processor, coupled to the analog-to-digital converter, to the digital controller, and to the local timer, for cross-correlating the signal samples of the selected signature with the signal samples of the received OFDM leakage signal, to produce a cross-correlation function having a peak, the cross-correlation processor being triggered by the series of triggering pulses generated by the local timer and performing the cross-correlation using a clock signal substantially synchronized to the standard reference clock and having a frequency equal to the first sample rate,
• whereby the OFDM leakage signal is detected from the peak of the cross-correlation function.

A leakage detector for detecting a leak in a hybrid fiber-coax (HFC) network, the HFC network transmitting a plurality of orthogonal frequency division multiplexing (OFDM) signals to a plurality of services areas, respectively, each of the OFDM signals being characterized by a signal period synchronized to a standard reference clock and being represented by a pre-constructed signature including signal samples created at a first sample rate, each of the service areas being defined by geographic coordinates, the leak being located in one of the service areas and emitting one of the OFDM signals over-the-air as an OFDM leakage signal, said leakage detector comprising:

• (a) a leakage signal receiver for receiving the OFDM leakage signal over-the-air at a detection point in one of the service areas of the HFC network;
• (b) an analog-to-digital converter, coupled to said leakage signal receiver, for generating signal samples of the received OFDM leakage signal at the first sample rate, using a clock signal substantially synchronized to the standard reference clock;
• (c) a global positioning system (GPS) receiver for determining a geographic position of the detection point;
• (d) a digital controller coupled to said GPS receiver and configured to determine in which of the service areas the detection point is located based on the geographic position of the detection point and the geographic coordinates of the service areas, the digital controller being further configured to select one of the signatures based at least on the service area in which the detection point is located;
• (e) a local timer, coupled to said GPS receiver and said digital controller, for creating a series of triggering pulses having a period substantially synchronized to the signal period of the OFDM signal represented by the selected signature;
• and
• (g) a cross-correlation processor, coupled to said analog-to-digital converter, to said digital controller, and to said local timer, for cross-correlating the signal samples of the selected signature with the signal samples of the received OFDM leakage signal, to produce a cross-correlation function having a peak, the cross-correlation processor being triggered by the series of triggering pulses created by the local timer and performing the cross-correlation using a clock signal substantially synchronized to the standard reference clock and having a frequency equal to the first sample rate,
• whereby the OFDM leakage signal is detected from the peak of the cross-correlation function.