The present disclosure provides, for example, methods for measuring interference to a cable modem (CM), and corresponding example apparatuses and systems. One example method includes sending, by a cable modem termination system (CMTS), a broadcast message to all CMs connected to the CMTS, where the broadcast message includes information designating one of the CMs to send a probing signal by using a spectrum S in a timeslot T. The CMTS can then broadcast a pseudo random binary sequence (PRBS) by using the spectrum S in a downlink direction in the timeslot T, and can obtaining modulation error ratio (MER) information recorded in the timeslot T by other CMs. A difference between MER information in the timeslot T and MER information in a normal data timeslot can be used, for each of the other CMs, as intensity of interference to the corresponding CM.