JPH11225167A - Digital signal receiver, its method and recording medium storing program concerning the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device which is easily mounted by simple constitution by estimating the hourly position of a leading sample by the time stamp of packet data, arranging samples excepting for the leading sample at each interval of a prescribed time from the hourly position of the leading sample so as to estimate the hourly position of each sample and correcting the value of a time interval so as to generate a sampling clock. SOLUTION: The estimated time local time of a sample 6 is changed to T2 of an accurate hourly position. In addition, as the estimated hourly position is more advanced at the time of comparing the position of a finishing point 6' estimated as the position of the sample 6 and the accurate position T2, a time interval for arranging samples 7 to 9 is corrected in the direction of reducing. To put it in the concrete, a prescribed value α is subtracted from a time interval Δt1 used at the time of obtaining the estimated time of samples 2 to 5 to obtain Δt2 and this is made the time interval between the samples 7 to 9. A line segment 604 shows the state of arranging the samples 7 to 9 at each time interval Δt2 from the position of T2 of the sample 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission system for packetizing and transferring a digital audio signal, and more particularly, to a digital signal receiving apparatus and method, and a storage medium storing a program according to the method.

[0002]

2. Description of the Related Art When transmitting digital audio signals, a method of transferring N audio signals (samples) generated in each service interval into one packet is conceivable. The sample number N of each packet is not constant even if the sampling frequency of the audio signal is constant and the service interval is an integral multiple of the sampling period, unless the two are completely synchronized.
Therefore, when such packetization is performed, for example, if the occurrence time of the first sample of the packet is added to the packet as a time stamp, the time stamp exists for every non-constant number of samples.

On the audio signal receiving side, for example, an analog PLL (Phase-Locked Loop) is used.
Is used to generate the same sampling clock as that on the transmitting side. Here, it is well known that when a sampling clock is generated from a sequence of time stamps, the time stamp interval is constant and a power of 2 simplifies the implementation. This is because the receiving side can predict the time at which the next time stamp will be sent, and the configuration may be adjusted to that.

[0004]

However, when a sampling clock is generated from a series of time stamps that exist for every inconsistent number of samples as described above, packetization becomes complicated and transmission / reception delay becomes long. And other problems occur.

The present invention relates to a system for transmitting a digital audio signal. In a system in which a time stamp is sent from the transmitting side for every fixed number of samples and a sampling clock is generated on the receiving side, the sampling clock on the transmitting side is accurately output. It is an object of the present invention to provide a digital signal receiving apparatus, a method, and a storage medium storing a program according to the digital signal receiving apparatus, which can generate a digital signal, and can be easily implemented with a simple configuration.

[0006]

In order to achieve the above object, a digital signal receiving apparatus according to the first aspect of the present invention comprises a packet data including a plurality of continuous samples and a time stamp indicating a temporal position of a leading sample of the samples. Means for estimating the temporal position of the first sample based on the time stamp of the received packet data, and arranging samples other than the first sample at predetermined time intervals from the temporal position of the first sample. Means for estimating the temporal position of each sample, and means for correcting the value of the time interval according to the difference between the estimated temporal position and the time stamp of the next packet data. Means for generating a sampling clock from the temporal position of each sample.

According to a second aspect of the present invention, there is provided a digital signal receiving method, comprising the steps of: receiving packet data including a plurality of continuous samples and a time stamp indicating a time position of a first sample of the sample; Estimating the temporal position of the first sample based on the above, and estimating the temporal position of each sample by arranging samples other than the first sample at predetermined time intervals from the temporal position of the first sample. Correcting the value of the time interval according to the difference between the estimated time position and the time stamp of the next packet data; and generating a sampling clock from the estimated time position of each sample. It is characterized by including.

In the storage medium storing the digital signal receiving program according to claim 3, the program receives packet data including a plurality of continuous samples and a time stamp indicating a time position of a leading sample of the sample. And estimating the temporal position of the first sample based on the time stamp of the received packet data, and arranging samples other than the first sample at predetermined time intervals from the temporal position of the first sample. Estimating the temporal position of
Modifying the value of the time interval according to the difference between the estimated time position and the time stamp of the next packet data; and generating a sampling clock from the estimated time position of each sample. It is characterized by including.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows a configuration example of a transmission system to which the present invention is applied. From transmission node 401, transmission line 404
, A digital audio signal is transmitted to the receiving node 402 at regular time intervals (referred to as service intervals). The digital audio signal to be transmitted and received is packet data including a plurality of samples and a time stamp. In the receiving node 402, a digital PLL 403 is provided.
And generates a sampling clock of the audio signal from the received packet data. The transmitting node 401 and the receiving node 402 each operate at a reference clock (GLOBAL) operating at a frequency sufficiently higher than the frequency of the sampling clock of the audio signal to be transferred.
_TIME), and these reference clocks are always adjusted to indicate the same time with constant accuracy.

FIG. 5 is a time chart showing packetization on the transmitting side. 502 is a time axis, 501
Indicates each sample of the digital audio signal arranged on the time axis at a period according to a predetermined sampling clock. At 501, the positions numbered as samples 1, 2, 3,... (Positions marked with *) are the temporal positions of the respective samples. These samples 1,
2, 3,... Are grouped together to create packet data.

The packet data is configured by setting a time stamp at the head of the data and the number of samples included in the packet, and then sequentially setting the samples. 511 to 513 are samples 1 to 1 shown in 501.
4 is an example in which the packet No. 4 is packetized. Packet data 511
Is a time stamp T1 set at the beginning, and is the number of samples included in this packet data, followed by "5"
Is set. Thereafter, samples 1 to 5 are set in order. The time stamp is a value indicating the temporal position of the first sample among the samples included in the packet. For example, the time stamp T1 of the packet data 511 indicates the temporal position of sample 1, which is the first sample in the packet. Similarly, packet data 512 and 513 also have time stamp T
2, T3, the number of samples, and the order of each sample.

The packet data 511 to 51 as described above
3 is transmitted from the transmission node 401 of FIG. In the receiving node 402, a sampling clock is generated by the digital PLL 403 based on the received packet data 511 to 513. At this time, it is desired to reproduce the sampling clock on the transmission side described in FIG. 5 as accurately as possible. Therefore, in the system of this embodiment, the sampling clock is estimated on the receiving side by the digital PLL 403 as shown in FIG. Hereinafter, this estimation method will be described.

FIG. 6 is a time chart for explaining a sampling clock estimation method on the receiving side. Here, a temporal position of each received sample is estimated, and a sampling clock is generated based on the position. Hereinafter, the temporal position of each sample is referred to as the estimated time Loca.
Called lTime. LocalTime is a variable that stores the value of the estimated time. A symbol representing a variable such as LocalTime represents the variable itself and a value stored in the variable (for example, LocalTime).
, The estimated time).

When the receiving node 402 (FIG. 4) receives the packet data 511 (FIG. 5), the receiving node 402 uses the time stamp T1 to estimate the estimated time LocalTime of the sample 1 which is the first sample of the packet data 511.
Let e be T1. On the other hand, at this point, it is not guaranteed whether or not the next packet data 512 has been received. Therefore, for samples 2 to 5 included in the packet data 511, the estimated time of sample 1 is LocalTime = T1
From a predetermined time interval Δt1. The line segment 603 in FIG.
5 is arranged at intervals of time Δt1. The estimated time LocalTime of each of the samples 2 to 5 is obtained by adding Δt1 to the value of the estimated time of the immediately preceding sample.

Further, the estimated time Loc of the next sample 6
alTime is similarly obtained. The position of the end point 6 ′ of the line segment 603 in FIG. 6 is the estimated time LocalTi of the sample 6.
It is the position of me. Below that, LocalTime = LocalTime + Δt1 * 5 is the estimated time LocalTime of sample 6.
Is the estimated time LocalTime (= T
1) shows that it is obtained by adding the product of Δt1 and 5 (there are five time intervals Δt1 from sample 1 to sample 6). Note that Local on the left side of the above equation is
Time indicates the estimated time of sample 6, and Loc on the right side
alTime indicates the estimated time of sample 1.

In the case of FIG. 6, at time T2, the packet data 512 including the time stamp T2 (samples 6 to
Assume that 9) is received. Here, the estimated time LocalTime of the sample 6 is estimated to be the position of the end point 6 ′ of the line segment 603 as described above, but since the packet data 512 is received and the time stamp T2 is obtained, the estimated time It can be seen that the proper temporal position is T2.
Therefore, the estimated time LocalTime of the sample 6 is changed to T2 which is an accurate temporal position. The position of the end point 6 'estimated as the position of the sample 6 and the accurate position T
In the case of 2, since the estimated temporal position is advanced,
The correction is made in such a way that the time interval at which the samples 7 to 9 are arranged is reduced. Specifically, a predetermined value α is subtracted from the time interval Δt1 used when obtaining the estimated times of the samples 2 to 5, and Δt2 (= Δt1−α) is calculated.
Nine time intervals. That is, the packet data 512
For the samples 7 to 9 included in the time interval Δt from the estimated time LocalTime = T2 of the sample 6,
Place every two. A line segment 604 in FIG. 6 shows a state in which samples 7 to 9 are arranged at time intervals Δt2 from the position of T2 of sample 6.

Further, the estimated time Lo of the next sample 10 is
calTime is similarly obtained. Line segment 604 in FIG.
Is the estimated time Loca of the sample 10
It becomes the position of lTime. Below that, LocalTime = LocalTime + Δt2 * 4 means that the estimated time of the sample 10 is LocalTime.
e is the estimated time LocalTime (= T
2) shows that the value is obtained by adding the product of Δt2 and 4 (four time intervals Δt2 exist from sample 6 to sample 10). Note that Loca on the left side of the above equation
lTime indicates the estimated time of sample 10, and LTime on the right side
ocalTime indicates the estimated time of sample 6.

In the case of FIG. 6, packet data 513 (samples 10 to 10) including a time stamp T3 at time T3.
14) is received. Here, the estimated time LocalTime of the sample 10 is estimated to be the position of the end point 10 ′ of the line segment 604 as described above.
Has been received and its time stamp T3 has been obtained, it can be seen that the exact temporal position of the sample 10 is T3. Therefore, the estimated time Local of the sample 10 is
Change Time to T3, which is the exact temporal position. In addition, since the estimated temporal position is delayed between the position of the end point 10 'estimated as the position of the sample 10 and the accurate position T3, the time interval for arranging the samples 11 to 14 is corrected to be increased. I do. Specifically, the time interval Δt2 used when obtaining the estimated times of the samples 7 to 9
Is added to a predetermined value β to obtain Δt3 (= Δt2 + β),
This is the time interval of samples 11 to 14. That is, the samples 11 to 1 included in the packet data 513
4, the estimated time LocalTi of the sample 10
It is arranged at every time interval Δt3 from me = T3. A line segment 605 in FIG. 6 shows a state where the samples 11 to 14 are arranged at time intervals Δt3 from the position of T3 of the sample 10.

Similarly, every time packet data is received, the first sample of the packet data is arranged based on the accurate time stamp, and the time interval Δt is determined based on the amount of deviation between the time stamp and the estimated time. Is corrected, and samples are arranged at each time interval Δt to obtain an estimated time of each sample. A sampling clock is generated based on the estimated time of each sample.

FIGS. 1 and 2 are flowcharts showing a processing procedure for obtaining an estimated time LocalTime of each sample on the receiving side, and a digital PLL on the receiving side.
Reference numeral 403 denotes a specific procedure for executing the processing described in FIG. FIG. 1 shows a sample with a time stamp (eg,
FIG. 2 shows the processing in the case of the samples 1, 6, and 10 described with reference to FIGS. 5 and 6, and FIG.
5, 7, 10 and 11 to 14).

In FIG. 1, in the case of a sample having a time stamp, first, at step 101, a time stamp is obtained from the received packet and set to timestamp (variable). Next, in step 102, the current estimated time L
ocalTime is the timestamp timestamp
, Ie, whether the estimated time is ahead of the time stamp.

If the estimated time is advanced in step 102, then in step 103, Work = LocalTime LocalTime = timestamp is set while the time is not reversed. “Work” is a work variable for saving the current estimated time. "To prevent time from reversing" means, for example, in the example of FIG. 6, when the estimated time of sample 5 is earlier than time stamp T2, the estimated time of sample 6 is set to T
If it is adjusted to 2, the sample 5 is placed after the sample 6 and the time is reversed, so that such a case is avoided.

When the time is reversed due to such advance, Loc of the processing in step 103 is used.
The processing of alTime = timestamp is not executed (that is, the time stamp value is not used), and the current estimated time LocalTime is used as it is. Reference numerals 606 and 607 in FIG. 6 show examples in which the estimated time is used without using the time stamp value. 606 is 6
Same as 03. 607 is not the position of the time stamp value T2, but samples 6 to 10 from the position of the estimated time 6 '.
Has been arranged.

Next, in step 104, Work (the estimated time before the processing in step 103 is saved) and t
the difference from the current stamp is a predetermined threshold THRESHOL
It is determined whether or not D_GAIN or more. If so, in step 105, the predetermined value S is calculated from the time interval Δt.
LOWER is subtracted, and the routine returns. Step 104
And the difference between Work and timestamps is equal to the threshold THR
If it is not equal to or greater than ESHOLD_GAIN, the process returns. Note that Δt is a variable for setting the time intervals Δt1, Δt2, or Δt3 described in FIG. The predetermined value SLOWER corresponds to the predetermined value α described in FIG.

If it is determined in step 102 that the estimated time is equal to or later than the time stamp, step 106
Then, Work = LocalTime LocalTime = timestamp is set. Next, in step 107, Work (the estimated time before the processing in step 106 is saved) and t
the difference from the current stamp is a predetermined threshold THRESHOL
It is determined whether or not D_LOSE or more. If so, at step 108, the time interval Δt is set to the predetermined value FA.
Add STER and return. In step 107,
The difference between Work and timestamps is the threshold THRES
If it is not equal to or larger than HOLD_LOSE, the process returns. The predetermined value FASTER corresponds to the predetermined value β described in FIG.

With reference to FIG. 2, a method of obtaining an estimated time in the case of a sample having no time stamp will be described. In this case, in step 201, the estimated time is obtained by LocalTime = LocalTime + Δt, and the process returns.

FIG. 3 shows the details of step 103 in FIG. Step 103 is replaced with steps 301 and 302 in FIG.
Can be replaced with In step 301, the estimated time Lo
time stamp timestamp from calTime
It is determined whether or not the difference obtained by subtracting is equal to or longer than the time interval Δt. When the difference is equal to or larger than Δt, LocalT
If "im = timestamp" is set, the time is reversed, so the current Local
In order to use Time, in step 302, the Work =
After setting only LocalTime, the process proceeds to step 104. If the difference is not equal to or larger than Δt in step 301, the time does not reverse, so that in step 303, Work = LocalTime and Loc
After setting alTime = timestamp, the process proceeds to step 104.

As described above, the receiving digital PLL 40
In step 3, the same sampling clock as the transmitting-side sampling clock can be generated.

The processing in steps 103 and 106 is as follows.
Various modifications may be made, including not doing anything. Also,
In the process of FIG. 1, THRESHOLD_GAI
Since the operation changes in accordance with the values of N, THRESHOLD_LOSE, FASTER, and SLOWER, by appropriately controlling these values, it is possible to adjust the manner in which each sample is temporally arranged. Also, FAS
The values of TER and SLOWER are the values of Work and timestamp evaluated in step 104 or 107, respectively.
If it is determined according to the magnitude of the difference from Δt, Δt can converge to an appropriate value more quickly.

In the above embodiment, the digital PLL 4
03, the sampling clock is generated, but an analog PLL may be used after the digital PLL 403.

[0032]

As described above, according to the present invention, on the receiving side, the temporal position of the first sample is estimated based on the time stamp of the received packet data, and samples other than the first sample are replaced with the first sample. The temporal position of each sample is estimated by arranging the temporal position of the first sample at predetermined time intervals from the temporal position of the first sample, and the time interval is determined according to the difference between the estimated temporal position and the time stamp of the next packet data. Since the value of is corrected, even in a system that sends a time stamp from the sending side for each inconsistent number of samples and generates a sampling clock on the receiving side, it is possible to accurately generate the sampling clock on the sending side. In addition to this, there is an effect that it can be easily mounted with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure for obtaining an estimated time of a sample having a time stamp.

FIG. 2 is a flowchart showing a processing procedure for obtaining an estimated time of a sample having no time stamp.

FIG. 3 is a detailed diagram of step 103;

FIG. 4 is a diagram showing a configuration example of a transmission system to which the present invention is applied;

FIG. 5 is a time chart showing packetization on the transmission side.

FIG. 6 is a time chart for explaining a sampling clock estimation method on the receiving side.

[Explanation of symbols]

Reference numeral 401: transmission node, 402: reception node, 403: digital PLL, 404: transmission line, 511 to 513: packet data.

Claims (3)

[Claims] And means for receiving packet data including a plurality of consecutive samples and a time stamp indicating a time position of a first sample of the sample, wherein a time of the first sample is determined based on a time stamp of the received packet data. Means for estimating the temporal position and estimating the temporal position of each sample by arranging samples other than the leading sample at predetermined time intervals from the temporal position of the leading sample; and Means for correcting the value of the time interval according to the difference between the time stamp of the next packet data and the time stamp of the next packet data, and means for generating a sampling clock from the estimated time position of each sample. Signal receiver. 2. A method for receiving packet data including a plurality of continuous samples and a time stamp indicating a time position of a first sample of the sample, the method comprising: detecting a time stamp of the first sample based on a time stamp of the received packet data; Estimating a temporal position of each sample by estimating a position and arranging samples other than the leading sample at predetermined time intervals from a temporal position of the leading sample; and A digital signal, comprising: correcting the value of the time interval according to a difference from the time stamp of the next packet data; and generating a sampling clock from the estimated temporal position of each sample. Receiving method. 3. A storage medium storing a digital signal receiving program, the program comprising: receiving packet data including a plurality of continuous samples and a time stamp indicating a temporal position of a leading sample of the samples. Estimating the temporal position of the first sample on the basis of the time stamp of the received packet data, and arranging samples other than the first sample at predetermined time intervals from the temporal position of the first sample so that Estimating a temporal position; correcting the value of the time interval according to a difference between the estimated temporal position and a time stamp of the next packet data; and a temporal position of each of the estimated samples. Generating a sampling clock from the digital signal. Storage medium storing a program for receiving a signal.