CN101388750B

CN101388750B - Random arrived CMTS time stamp correcting method

Info

Publication number: CN101388750B
Application number: CN2008102253748A
Authority: CN
Inventors: 李占才; 镇云锋; 王晨曦
Original assignee: BEIJING BM ELECTRONICS HIGH-TECHNOLOGY Co Ltd
Current assignee: BEIJING BM ELECTRONICS HIGH-TECHNOLOGY Co Ltd
Priority date: 2008-10-31
Filing date: 2008-10-31
Publication date: 2012-07-04
Anticipated expiration: 2028-10-31
Also published as: CN101388750A

Abstract

The invention relates to a method for checking CMTS timestamps which are arrived randomly, the structure which is realized by the method comprises an analog CMTS timing module, a data receiving delayed module, a time_err calculating module and a novel timing reference generating module. The method is characterized in that the value of the CMTS timestamps is changed through calculating the time difference time_err that corresponding data arrives between MPEG-2 data which is arrived with uniform speed in analog and MPEG-2 data which is actually received by the CM end and is arrived with non-uniform speed and, judging whether the data arrives through judging the analog data which is generated to the analog CMTS timing module by the time_err calculating module and has the same time reference with the CMTS end and MPEG-2 data which is arrived with the non-uniform speed and is actually received by the CM end, and then calculating the time_err, as shown in pictures, A is a symbol for finding the data arriving during generating the analog data in the analog CMTS timing module, and B is a symbol for finding the data arriving in the MPEG-2 data which is received by the CM end.

Description

A kind of to the bearing calibration of the CMTS timestamp of arrival at random

Technical field

The present invention relates to the cable TV network transmission field.

Technical background

The invention belongs to CMTS in the cable TV network transmission transmit alternately with CM in the content of DOCSIS physical layer descending hop.The structure of the J.83B cable television digital transmission system of middle regulation of ITU is as shown in Figure 1.

At the CMTS transmitting terminal; The data of MPEG-2 transport layer are at first carried out framing by the frame format of MPEG-2; Data are carried out error correction coding after the framing, and encoder comprises RS encoder, interleaver, scrambler, convolution coder (only in U.S.'s mark, adopting), gets into Channel Transmission through the QAM modulation at last.At the CM receiving terminal, CM at first carries out demodulation to the signal that receives, and deciphers then, from the MPEG-2 Frame, extracts needed data at last.

In order to realize CMTS and CM transmitted in both directions, CMTS must with fixed frequency in downstream the delivery time synchronously (SYNC-MAC management information) to set up an overall timing base.This MAC management information comprises that can be discerned the timestamp when CMTS transmits this information definitely.The CMTS timestamp is to be the count status of 32 binary counters that increase progressively of drive clock with CMTS 10.24MHz master clock.On behalf of first byte (or apart from first byte a regular time depart from) of MAC administrative messag, it regularly synchronously be transferred to the count status of the moment of Physical Media Dependent sublayer from transmission convergence sublayer.

At the CMTS transmitting terminal, timestamp is when to be the MPEG-2 data at the uniform velocity sent, and CMTS 10.24MHz master clock count status is sampled and generated and be embedded in the MPEG-2 data.Because the MPEG-2 data need pass through error correction coding, again after the QAM modulation again through Channel Transmission, when CM after demodulation, error correction, the byte stream right and wrong of the MPEG-2 Frame of being received at the uniform velocity arrive, and are as shown in Figure 2.This shows that time that the CMTS timestamp arrives is uncertain, the time that the value of timestamp can not correct representation arrives, directly sets up the difficulty that overall timing base can increase digital phase-locked loop greatly with the timestamp of receiving.

For the moment that lets timestamp ability correct representation arrive, the method below adopting usually.

At the CM receiving terminal; Deposit MPEG-2 data in a RAM earlier through error correction coding, QAM modulation, Channel Transmission, demodulation, decoding; Then the MPEG-2 data are at the uniform velocity read the time that the CMTS timestamp in the MPEG-2 data of reading this moment can be expressed data arrives.

What the present invention proposed is a kind of to the bearing calibration of the CMTS timestamp of arrival at random, is not adjustment MPEG-2 data speed, but changes the value of CMTS timestamp.

Summary of the invention

What the present invention proposed is a kind of to the bearing calibration of the CMTS timestamp of arrival at random; Its characteristics are the time difference through corresponding data arrival between the non-MPEG-2 data that at the uniform velocity arrive of calculating MPEG-2 data that simulation at the uniform velocity arrives and CM end actual reception, and change the value of CMTS timestamp.Wherein, the timing base of the MPEG-2 data sent of the timing base of the MPEG-2 data that at the uniform velocity arrive of simulation and CMTS transmitting terminal is identical.Whether it is the one group of analogue data that is produced by simulation CMTS time block, and this analogue data provides data to the sign that reaches in the fixed position, supply CM end judgment data to arrive, and promptly this analogue data is simulated reception with the speed that the CMTS transmitting terminal sends at the CM end.The time difference of corresponding data arrival, i.e. time_err between the MPEG-2 data that at the uniform velocity arrive that the focusing on of this method calculated simulation and the non-MPEG-2 data that at the uniform velocity arrive of CM end actual reception.

Calculate time_err and take following method.

Calculating the time_err module judges respectively with the non-at the uniform velocity MPEG-2 data of arrival of CM end actual reception the MPEG-2 data that simulation at the uniform velocity arrives.For the analogue data that simulation CMTS time block produces, judgment data arrives is masked as A, and for the MPEG-2 data in CM end actual reception, judgment data arrives is masked as B.

If the precision of reformed CMTS timestamp is d, time_err is the time difference of corresponding data arrival between the non-MPEG-2 data that at the uniform velocity arrive of the MPEG-2 data that at the uniform velocity arrive of simulation and CM end actual reception, and its initial value is 0.

Calculate the time_err module analogue data that simulation CMTS time block produces is judged, find the sign that data arrive, i.e. A=1, then time_err=time_err+d.To judging, find that data arrive, i.e. B=1, then time_err=time_err-d simultaneously in the non-MPEG-2 data that at the uniform velocity receive of CM end.If both found the sign that data in the analogue data arrive, find that data in the MPEG-2 data that the CM termination receives arrive simultaneously again, i.e. A=B=1, the time_err value is constant; Both do not found the sign that data in the analogue data arrive, do not found the sign of the data arrives in the MPEG-2 data that the CM termination receives again, i.e. A=B=0, the time_err value is also constant, and is as shown in Figure 4.

Like this, the MPEG-2 data and the CM that can obtain at the uniform velocity transmitting with the speed that the CMTS transmitting terminal sends hold the time difference time_err that corresponding data arrives between the non-MPEG-2 data that at the uniform velocity receive, thereby change the value of CMTS timestamp, set up new timing reference.

Description of drawings

Fig. 1 is the structure chart of cable television digital transmission system;

Fig. 2 is the sketch map of timestamp at transmitting terminal and receiving terminal;

The structure chart of a kind of bearing calibration to the CMTS timestamp that arrives at random that Fig. 3 proposes for the present invention;

Fig. 4 is for calculating the method sketch map of time_err.

Embodiment

To combine accompanying drawing below, the present invention further specified through concrete implementation process.

A kind of bearing calibration that the present invention proposes to the CMTS timestamp that arrives at random, its structure is as shown in Figure 3, and it comprises: simulation CMTS time block, Data Receiving Postponement module, calculate time_err module, new timing reference generation module.

Simulation CMTS time block is used to produce the MPEG-2 data that simulation at the uniform velocity arrives, and the speed of the MPEG-2 transfer of data of sending from the CMTS transmitting terminal of the speed of this analog data transmissions and reality is identical, has identical timing reference with the CMTS transmitting terminal.What it was different with actual MPEG-2 data of sending from the CMTS transmitting terminal is; This analogue data just provides the sign of data in the fixed position; Whether arrived to calculate time_err module judgment data, realize being simulated reception at the CM end with the speed of CMTS transmitting terminal transmission.The analogue data that simulation CMTS time block produces flows to calculates the time_err module.

Calculate the time_err module, be used to calculate the time difference time_err of corresponding data arrival between the non-MPEG-2 data that at the uniform velocity arrive of MPEG-2 data that simulation at the uniform velocity arrives and CM end actual reception.Method is as indicated above, and this module produces analogue data to simulation CMTS time block to be judged, finds the A that is masked as of data arrives; Find the sign of data arrives in the analogue data, i.e. A=1, then time_err=time_err+d; Whether the non-MPEG-2 data of simultaneously the CM termination being received that at the uniform velocity arrive arrive is judged, finds the B that is masked as of data arrives, finds that data arrive; Be B=1, time_err=time_err-d then.If find the MPEG-2 data arrives that sign and the CM termination of data arrives in the analogue data are received simultaneously, i.e. A=B=1, the time_err value is constant.Both do not found the sign of data arrives in the analogue data, do not found the MPEG-2 data arrives that the CM termination is received again, i.e. A=B=0, the time_err value is also constant, and is as shown in Figure 4.The initial value of time_err is 0, and d is the precision of reformed CMTS timestamp.Calculate the time_err module time_err that calculates is flowed to new timing reference generation module.

The Data Receiving Postponement module offers new timing reference generation module after making data delay again.Timing period calculates the value that the time_err module calculates time_err.Other that can the MPEG-2 data not changed data bulk and valid data position are handled and are realized postponing.

New timing reference generation module, the value CMTS_time of change CMTS timestamp, CMTS_time=CMTS_time+time_err.

A kind of new bearing calibration that the present invention proposes to the CMTS timestamp that arrives at random; Through the time difference between the corresponding data in the non-at the uniform velocity MPEG-2 data of calculating MPEG-2 data that the CMTS end at the uniform velocity sends and CM termination receipts, change the value of CMTS timestamp.

Claims

1. bearing calibration to the CMTS timestamp that arrives at random is characterized in that the structure that realizes comprises: simulation CMTS time block, Data Receiving Postponement module, calculate time_err module and new timing reference generation module;

Wherein, Described simulation CMTS time block; Produce one group and have the analogue data of identical timing base with MPEG-2 data that the CMTS transmitting terminal sends, the MPEG-2 data that this analogue data and actual CMTS transmitting terminal send are different, and it only produces a timing reference identical with the CMTS transmitting terminal; Position fixing provides data to the sign that reaches; Whether supply CM end judgment data to arrive, realize that this analogue data simulates reception by the speed that the CMTS transmitting terminal sends at the CM end, the analogue data that simulation CMTS time block produces is sent out the module to time_err;

Described calculating time_err module is judged the analogue data that simulation CMTS time block produces, and finds the sign that data arrive, i.e. A=1, then time_err=time_err+d; To judging, find that data arrive, i.e. B=1, then time_err=time_err-d simultaneously in the non-MPEG-2 data that at the uniform velocity receive of CM end; If both found the sign that data in the analogue data arrive, find that data in the MPEG-2 data that the CM termination receives arrive simultaneously again, i.e. A=B=1, the time_err value is constant; Both do not found the sign that data in the analogue data arrive, do not found the sign of the data arrives in the MPEG-2 data that the CM termination receives again, i.e. A=B=0, the time_err value is also constant; D is the precision of reformed CMTS timestamp; The time difference of corresponding data arrival between the MPEG-2 data that time_err at the uniform velocity arrives for simulation and the non-MPEG-2 data that at the uniform velocity arrive of CM end actual reception, initial value is 0; Calculate the time_err module time_err that calculates is flowed to new timing reference generation module;

Described Data Receiving Postponement module; Offer new timing reference generation module again after making data delay; Other that can the MPEG-2 data not changed data bulk and valid data position are handled and are realized postponing, and timing period calculates the value that the time_err module calculates time_err;

Described new timing reference generation module, the value CMTS_time of change CMTS timestamp, CMTS_time=CMTS_time+time_err.