초록 ▼

A method and apparatus for time synchronization in a communications system such as a system including cable modems is provided. The synchronization method comprises the steps of receiving a first timestamp from a headend unit with the cable modem, and generating a first cable modem time reference wi

A method and apparatus for time synchronization in a communications system such as a system including cable modems is provided. The synchronization method comprises the steps of receiving a first timestamp from a headend unit with the cable modem, and generating a first cable modem time reference with the cable modem in response to the receipt of the first timestamp. The cable modem then receives a second timestamp from the headend unit and generates a second cable modem time reference in response to the receipt of the second timestamp. A headend difference time comprising the difference of the first and second timestamps is then generated as is a cable modem difference time comprising the difference of the first and second cable modem time references. A clock error time that comprises the difference of the headend difference time and the cable modem difference time is then generated as well as a correction factor in response to the clock error time. The local clock of the cable modem is then synchronized with the master clock of the headend unit through the adjusting of the output of the local clock output in response to the correction factor. The correction factor in one instance comprises an offset value representative of the amount of clock error per local clock pulse. This offset value is added to an accumulator on each local clock pulse, and the local clock output is adjusted when the accumulator rolls over. The synchronized clock signal can then be utilized to determine a time slot in which the cable modem can transmit an upstream signal to the headend without colliding the upstream signal with upstream signals from other modems in the system.

대표청구항 ▼

1. In a communications system comprising a control unit that includes a master clock and a plurality of transceiver devices coupled to the control unit wherein each transceiver device includes a local clock, a method for synchronizing the local clock of at least one of the transceiver devices with t

1. In a communications system comprising a control unit that includes a master clock and a plurality of transceiver devices coupled to the control unit wherein each transceiver device includes a local clock, a method for synchronizing the local clock of at least one of the transceiver devices with the master clock, the method comprising the steps of:receiving a first and second timestamp with the transceiver, wherein the first and second timestamp comprise signals generated by the control unit in response to the value of the master clock at the time the first and second timestamp signals are generated, respectively; generating a first and second transceiver time reference with the transceiver device in response to the receipt of the first and second timestamp signals, respectively; generating a correction factor in response to the first and second timestamp and the first and second transceiver time reference; providing the correction factor to an accumulator device; and generating a synchronized downstream reference signal by adjusting an output clock signal of the local clock in response to the accumulator device.