Method for reconstructing system time clock (STC) without carrying PCR

• US 20070242678A1
• Filed: 09/29/2006
• Published: 10/18/2007
• Est. Priority Date: 04/17/2006
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Chen, Xuemin, Fu, Jiang, Yang, Zhijie, Heng, Brian A.
• Granted Patent: US 9,544,638 B2
• Time in Patent Office: Days
• US Class Current: 370/395.620
• CPC Class Codes: H04L 25/49 using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems spectral shaping H04L25/03828
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
• CPC Class Codes: H04N 21/234318 by decomposing into objects, e.g. MPEG-4 objects
• CPC Class Codes: H04N 21/235 Processing of additional data, e.g. scrambling of additional data or processing content descriptors
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04N 21/43072 of multiple content streams on the same device
• CPC Class Codes: H04N 21/4348 Demultiplexing of additional data and video streams
• CPC Class Codes: H04N 21/435 Processing of additional data, e.g. decrypting of additional data, reconstructing software from modules extracted from the transport stream

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.

Claims

1. 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 transport rate information 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 the frequency of the 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 the difference between the frequency of the local system time clock and the frequency of the representative encoder clock; and

a low-pass filter circuit adapted to filter the error signal for input to the voltage controlled oscillator.

2. The clock recovery apparatus of claim 1,

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 information;

and

wherein the feedback loop further comprises a counter to output local timestamp data whose value increments with the system time clock cycles, the counter having an input that initializes its output value, and a jitter calculator to output the error signal equal to the difference between the timestamp data from the counter and the timestamp data from the receiver.

3. The clock recovery apparatus of claim 1, wherein the packets received are MPEG-2 type packets.

4. The clock recovery apparatus of claim 1, wherein the frequency of the system time clock is in the range of 26.999199 MHz to 27.000810 MHz.

5. The clock recovery apparatus of claim 1, wherein the counter is a digital counter.

6. The clock recovery apparatus of claim 1, wherein the packet receiver retrieves the packet count information and the transport rate information from a header portion of one or more of said received packets.

7. The clock recovery apparatus of claim 6, wherein the received packets are MPEG packets, and the packet count information and transport data rate are located in an adaptation field of a header portion of the MPEG header.

8. A method for reconstructing a system clock, comprising:

receiving digitized packets containing packet count information and transport rate information from a sending clock;

determining timestamps from the packet count information and the transport rate information;

generating a local system clock based on a control signal, and generating local timestamps based on the local system clock;

generating an error signal based on the difference between the local timestamps and the timestamps determined from the received packet count information and transport rate information; and

filtering the error signal to produce the control signal.

9. The method of claim 8, wherein the digitized packets are MPEG-2 packets.

10. The method of claim 9, wherein the step of determining timestamps from the packet count information and the transport rate information includes the steps of retrieving the packet count information and the transport rate information from a header of the MPEG-2 packet.

11. The method of claim 9, wherein the step of retrieving includes the step of retrieving the packet count information and the transport rate information from the adaptation field of the header of the MPEG-2 packet.

12. A method for encoding a plurality of data packets with timestamp information for transmission over a communications system, comprising:

receiving a plurality of data packets;

determining packet count information and transport rate information for the plurality of data packets; and

loading the packet count information and transport rate information in header portions of one or more of the plurality of data packets.

13. The method of claim 12, wherein the data packets are MPEG-2 data packets, and wherein the step of loading includes the step of inserting packet count information and transport rate information in an adaptation field of the header portions of the data packets.

14. The method of claim 12, wherein the packet count information and the transport rate information represent the timestamp information.