Method for reconstructing system time clock (STC) without carrying PCR
AssigneeBroadcom Corporation
InventorsJiang Fu, Zhijie Yang, Brian A. Heng, Xuemin Chen
Life of this patent
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Abstract
In conventional packet communications systems, such as MPEG-2, the data stream includes a program clock reference (PCR) so that the receiver decoder can lock on to the data stream. The invention eliminates the need to send the PCR by transferring a data transport rate explicitly in the header of the data packets so that the decoder can use the transport rate as a locking reference and adjust its phase lock loop. The transport rate is carried in the adaptation field as user private data.
Claims20
In a communications system, a clock recovery apparatus to recover an encoder clock for received packets, comprising:
- a packet receiver configured to detect packet count information and a transport rate value embedded in the received packets and that is representative of the encoder clock for the received packets;
- a voltage controlled oscillator for generating a local system time clock, the voltage controlled oscillator having an input that allows a frequency of the local system time clock to be adjusted in proportion to a control signal received on the input;
- a feedback loop adapted to output an error signal that represents a difference between the frequency of the local system time clock and a frequency of the encoder clock;
- and
- a low-pass filter circuit adapted to filter the error signal for input to the voltage controlled oscillator,
- wherein the packet receiver includes a packet timing extractor for outputting timestamp data that is representative of the encoder clock based on the packet count information and the transport rate value, and
- wherein the feedback loop further comprises a counter to output local timestamp data whose value increments with cycles of the local system time clock, the counter having an input that initializes its output value, and a jitter calculator to output the error signal equal to a difference between the local timestamp data from the counter and the timestamp data from the packet receiver.
In a communications system, a clock recovery apparatus to recover an encoder clock for received packets, comprising:
- a packet receiver configured to detect packet count information and a transport rate value embedded in the received packets and that is representative of the encoder clock for the received packets;
- a voltage controlled oscillator for generating a local system time clock, the voltage controlled oscillator having an input that allows a frequency of the local system time clock to be adjusted in proportion to a control signal received on the input;
- a feedback loop adapted to output an error signal that represents a difference between the frequency of the local system time clock and a frequency of the encoder clock;
- and
- a low-pass filter circuit adapted to filter the error signal for input to the voltage controlled oscillator,
- wherein the feedback loop further comprises:
- a counter to output local timestamp data whose value increments with cycles of the local system time clock, the counter having an input that initializes its output value, and
- a jitter calculator to output the error signal equal to a difference between the local timestamp data from the counter and timestamp data representative of the encoder clock, wherein the timestamp data is determined based on the packet count information and the transport rate value.
Dependencies are inferred from the claim text.