JP2003298559A - Center control device and block code length control method for cable modem transmission system - Google Patents

Abstract

(57) [Problem] To provide a cable modem transmission system that provides efficient communication by monitoring an uplink noise level and changing an error correction block code length according to a noise generation situation. An uplink signal receiving unit of a center control device of the system monitors a noise level in an operating uplink frequency band and simultaneously calculates an uplink data error rate in a predetermined time section. When the noise level or the error rate indicates a predetermined amount of change, an error correction strength is calculated, and an optimum block code length is calculated based on the error correction strength. Next, it notifies the cable modem to perform encoding using the calculated block code length.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable modem transmission system, and more particularly to a cable modem transmission system having a block code length variable control method.

[0002]

2. Description of the Related Art Conventionally, an error correction coding method used in a cable modem transmission system improves communication quality in accordance with the quality of the transmission line to ensure stable communication, especially when deterioration of the transmission line quality is expected. It is provided.

The above-mentioned deterioration of transmission path quality is generally due to noise inflow or interference due to external factors. However, in recent years, high-speed data communication services and digital video and digital audio transmission systems have been rapidly developed, so that there is an increasing need to provide stable communication regardless of the quality of the transmission path. .

In order to provide such stable communication, Japanese Patent Laid-Open No. 9-116486 discloses a method of controlling the bit rate of an error correction code according to deterioration of the transmission line quality to improve the transmission line quality. Proposed.

In this system, some error correction means are prepared in advance in order to deal with independent transmission line quality between a relay station and a mobile station (or fixed station) in wireless communication, and the transmission line quality The optimum error correction means is selected from those error correction means according to the degree of deterioration.

[0006]

However, this method is
There is a problem that it is difficult to apply when the degree of noise generation is uncertain, as in the case of an upstream transmission line of a cable television.

Therefore, in the above method, the control is inevitably corresponding to the fixed noise generation pattern. Therefore,
Even if the above method can be applied to a specific cable television transmission line, there is a problem that the error correction means must be changed according to the condition in the cable television transmission line having different conditions.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to perform a flexible adaptive error correction control according to the situation of upstream noise in a cable modem transmission system using a cable television transmission line to ensure stable communication. To provide.

According to the first embodiment of the present invention, the means for monitoring the noise level of the upstream data and the first predetermined time interval when the monitored noise level changes by a predetermined range or more. A means for detecting the number of errors that could not be corrected in the upstream data; a means for calculating an error rate after the error correction of the upstream data in the second predetermined time interval from the detected number of errors; When an error rate is calculated, means for calculating an error correction strength using the noise level and the error rate, means for calculating a block code length based on the calculated error correction strength, and a block code A center control device for a cable modem transmission system is provided, which has means for notifying a cable modem installed in a subscriber's house so as to change the length to the calculated block code length.

According to the second embodiment of the present invention,
In the first embodiment, there is provided a center control device, wherein an integral multiple of the first predetermined time period is the second predetermined time period.

According to the third embodiment of the present invention,
In the first embodiment, the first predetermined time period includes a third time period and a fourth time period which are different from each other in consideration of a frame length of a data packet, The second predetermined time period is a time corresponding to the transmission time of the frame length of the data packet of the uplink data, and the means for calculating the error rate is the third predetermined time period and the fourth time period. There is provided a center control device configured to estimate an error rate in the second predetermined time interval from the number of errors in the predetermined time interval.

Furthermore, according to a fourth embodiment of the present invention, in the first embodiment, when the first predetermined time interval has a plurality of combinations of block code length and error correction strength. Further, a plurality of units are set according to the block code length and the error correction strength, and the error rate calculating means calculates an error rate in a combination of the unknown block code length and the error correction strength as the first error rate. There is provided a center controller configured to make an estimation based on the number of errors in a predetermined time interval of.

According to a fifth embodiment of the present invention,
In the first embodiment, the means for notifying the cable modem to change the block code length transmits the signal to the cable modem by multiplexing the control signal with downlink data, and the control signal is A center controller configured to include at least a block code length change notification is provided.

Further, according to a sixth embodiment of the present invention, in the first embodiment, a cable modem of a plurality of subscribers' houses is connected to a higher-order network forming a backbone through a router, A center control device is provided which is connected in parallel via optical nodes and constitutes a cable modem transmission system for distributing communication data between the backbone and the cable modem.

Further, according to a seventh embodiment of the present invention,
Monitoring the noise level of the upstream data, and when the monitored noise level changes by a predetermined range or more,
A step of detecting the number of errors in which the error of the uplink data could not be corrected in the first predetermined time section, and an error after the error correction of the uplink data in the second predetermined time section from the detected number of errors A rate, a step of calculating an error correction strength by using the noise level and the error rate when the error rate is calculated, and a block code length based on the calculated error correction strength. Block code length control used in a cable modem transmission system, which comprises: A method is provided.

Further, according to an eighth embodiment of the present invention,
A means for monitoring the noise level of the upstream data; and a first means when the monitored noise level changes by a predetermined range or more.
Means for detecting the number of errors that could not be error-corrected for the upstream data in the predetermined time interval, and an error rate after error correction of the upstream data in the second predetermined time interval from the detected error number. Calculating means, means for calculating an error correction strength by using the noise level and the error rate when the error rate is calculated, and a block code length based on the calculated error correction strength Means to do
A computer for functioning as a center control device used in a cable modem transmission system, comprising means for notifying a cable modem installed in a subscriber's house to change the block code length to the calculated block code length. The program is provided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION First, the configuration of a cable modem transmission system according to an embodiment of the present invention will be described. FIG. 1 shows a functional block diagram of a center control device of a cable modem transmission system. Such a center control device is often called a "cable modem control device". One is connected to a higher-level network that constitutes the backbone through a router, and the other is connected to a plurality of cable modems installed in the subscriber's home. , Are respectively connected in parallel via an optical node or the like.

In this embodiment, an error correction method using a block code is used. Further, among the methods, a method using Reed-Solomon code, which is often used in communication systems, will be described as a premise. However, the invention of the present application is not limited to such a system using the Reed-Solomon code.

The center control device of this embodiment comprises a variable block code length control unit 1, a downlink data multiplexing unit 2, a downlink error correction coding / modulation unit 3, an upstream data demodulation unit 4, an upstream error correction decoding unit 5, An upstream noise level measuring unit 6 is provided.

The variable block code length control unit 1 includes a terminal control message generation unit 11 and an error correction strength calculation unit 12.

Here, the downlink data signal 100 is supplied to the downlink data multiplexer 2 and the terminal control message generator 1
It is multiplexed with the control signal p from 1. The output of the downlink data multiplexing unit 2 is processed by the downlink error correction coding / modulation unit 3 and output as the downlink RF signal 101.

On the other hand, the upstream RF signal 200 is demodulated into an upstream reception signal by the upstream data demodulation section 4 and supplied to the upstream error correction decoding section 5. In the upstream error correction decoding unit 5, the block code length data k from the error correction strength calculation unit 12 is subjected to error correction processing and output as an upstream data signal 202.

The number of byte errors g that cannot be corrected after the error correction processing is supplied to the error correction strength calculation unit 12.

The upstream IF signal 201 frequency-converted after the frequency selection by the upstream data demodulation unit 4 is supplied to the upstream noise level measurement unit 6. The upstream noise level measurement unit 6 determines whether or not there is an upstream burst signal from the cable modem, and uses the interval between the burst signals to perform the noise level measurement process within the frequency band.

Variable block code length control unit 1 of this embodiment
Monitors the change of the noise level by the noise level data e read periodically from the upstream noise level measuring unit 6,
The error correction strength is calculated by receiving the number of byte errors g output from the upstream error correction decoding unit 5, and the block code length is changed by supplying the block code length data k to the upstream error correction decoding unit 5. .

Also, the terminal control message generation unit 11 processes the parameter data m related to the block code length change, and outputs the control signal p including the upstream error correction parameter change notification to the downlink data multiplexing unit 2 to the cable modem. Then, the uplink error correction processing on the cable modem side and the center control apparatus side are matched.

Upon receiving the control signal p, the cable modem stops the transmission of the uplink data, and then the block code length is changed based on the uplink error correction parameter change notification (block code length change notification) to the cable modem. It
After that, the transmission of uplink data is resumed. here,
The uplink error correction decoding unit 5 determines whether the cable modem stops transmitting the uplink data and restarts the transmission.
For example, it is necessary to change the block code length of the cable modem according to the same notification as the uplink error correction parameter change notification.

The block coding length of the upstream error correction decoding unit 5 may be changed at the time when the upstream error correction parameter change notification is transmitted to the cable modem.

The parameter data m includes, for example, the block length (original data + 2 × number of error correction bytes) and the number of error correction bytes.

On the other hand, the control signal p includes the upstream error correction parameter change notification (block code length change notification) to the cable modem, as described above, and the upstream data transmission stop notification or the upstream data restart notification. May be included.

The upstream noise level measuring section 6 shown in FIG.
Are well known to those skilled in the art and are not directly related to the present invention, and therefore detailed description thereof will be omitted.

Next, the processing of the center control device of the embodiment of the present invention will be described.

First, the operation of the variable block code length control unit 1 will be described with reference to the flowchart of FIG.
When the operation of the variable block code length control unit 1 is started, the noise level data e is read from the upstream noise level measurement unit 6 in step S10. This reading is repeated at predetermined intervals. Next, in step S11, it is determined whether the read noise level has changed. The determination is performed, for example, by storing the noise level read within a predetermined period immediately before and comparing the noise level with the noise level read this time. Also, a predetermined threshold can be set to determine whether or not it has changed. For example, the previous noise level is compared with the current noise level, and if there is a difference equal to or more than the threshold value, it is determined that the noise level has changed.

If no change in the noise level is found in step S11, the process returns to step S10 and the reading of the noise level is repeated. When it is determined that the noise level has changed (YES in step S11)
S), the process proceeds to step S12, where the error occurrence is detected for each time interval CWL according to the block code length by the byte error number g output from the upstream error correction decoding unit 5.

Further, in step S13, the time interval T
The error rate in (= CWL × n) is calculated. After this,
In step S14, the error correction strength is calculated based on the change amount of the error rate and the change amount of the noise level.

In order to calculate the error rate, it is necessary to perform calculation based on a specific time, and the time segment T is set for that purpose. Here, as a premise, the upstream direction is a burst signal, and it is impossible to measure whether or not the data is erroneous unless the signal comes from the terminal. Therefore, it is necessary to expect a certain amount of information of the burst signal that rises randomly, and a relatively long time T is provided.

For example, if a time interval of 1 ms is provided, it may be possible that some or no data exists. However, if a time interval of 1 second is provided, it is considered that at least data exists, and the data error rate can be calculated. .

To obtain the error correction strength, the following method is used, for example.

(1) The signal-to-noise ratio (S / N) consisting of the input level and the noise level and the error rate change amount at the error correction strength (in the block code, for example, the number of corrected bytes u = 2 to 8) The relationship is prepared as a theoretical value in advance and stored in a theoretical value table (array).

(2) The change amount of the S / N and the error rate is searched in the theoretical value table, and the error correction strength below the reference error rate, which does not pose a problem in operation, is obtained.

Here, the change amount is obtained, for example, by comparing the value in CWL × n (= time interval T) with the value in the immediately preceding time interval T for both the error rate and the noise level. Is. In this case, the time interval T needs to be as long as possible, as described above, in order to avoid unstable operation in the system due to tracking due to an instantaneous change.

Next, in step S15, a corresponding block code length is determined from the calculated error correction strength, in step S16, upstream communication to the cable modem is temporarily stopped, and in step S17, the block code length is changed. The message is notified, and the upstream communication is restarted in step S18. The processing from step S16 to step S18 is automatically performed by the terminal control message generation unit 11 transmitting the control signal p including the uplink error correction parameter change notification to the downlink data multiplexing unit 2. Further, the terminal control message generation unit 11 may transmit the control signal p to the downlink data multiplexing unit 2 so as to perform the respective processes.

Thereafter, the process proceeds to step S10, where the reading of the upstream noise level measurement value is repeated.

When the error rate change amount and the noise level change amount are small, it is not necessary to change the block code length. For this reason, each change amount is a predetermined value (threshold value)
It is also possible to judge whether or not the block code length is exceeded, and to control not to change the block code length when either or both of the change amounts do not exceed the threshold value.

In step S15, the block code length s is calculated by y + 2u, for example. Where u is
It represents the error correction strength (the number of corrected bytes), and y represents the original data length.

In this way, the block code length variable control unit 1
Repeats the above process after starting operation until it is stopped.

Next, referring to FIG. 3, the above step S1
A method of calculating the uplink error rate performed in 3 will be described. FIG. 3A shows the flow of data packets on the upstream transmission path from the cable modem to the center communication device, and shows a state in which the data packets are being transmitted in bursts. Corresponding to this figure, the left end portion of each of FIGS. 3B to 3D represents a center communication terminal,
The rightmost part represents the cable modem.

FIG. 3B shows a first method for calculating the error rate in the block code length variable control unit 1 of the center control device, in which the byte error number g is acquired in the time section CWL unit and the time is calculated. The error rate in the section T is estimated.

Here, the byte error number g is not normally acquired in all the time intervals CWL, and the error rate in the time interval T is estimated based on the byte error number g at a certain time. In addition, past data (for example, how the byte error rate changes when the code length is changed based on the byte error rate measured in a certain noise state) is effectively used to make the above estimation. Done.

FIG. 3C shows the second method for calculating the error rate. In consideration of the frame length of the data packet, the byte error number g is acquired for each of the sections CWL1 and CWL2 having different time lengths, and the error rate in the frame length is estimated.

The above CWL1 and CWL2 have different lengths, which means that the block code length differs depending on the combination of the error code correction strength and the original data length. CWL1 corresponds to the case where the original data length is short and the number of corrected bytes is small, and CWL2 corresponds to the case where the original data length is made longer than CWL1 and the number of corrected bytes is increased. The estimation is performed using the error rate in the case of using CWL2 from the error rate in CWL1 under the same noise condition.

FIG. 3D shows the third method for calculating the error rate. When there are multiple combinations of code length and the number of bytes that can be corrected, the time interval CWLn is set according to the code length and the number of corrected bytes, the number of byte errors g is obtained, and the combination of the unknown code length and the number of corrected bytes is acquired. Estimate the error rate at.

As described above, the block code length is s =
It can be determined by y + 2u. Various lengths of the block code length s are assumed depending on the combination of the original data length y and the error correction strength (correction byte number) u. Original data length y
If is fixed, the code length s is proportional to the error correction strength u, but if the original data length y is fixed, the efficiency becomes poor. Therefore, the original data length y needs to be variable. Therefore,
Code lengths CWL1 and CWL with the original data length y fixed
2. From the past error rate for each CWLn, the error rate when the original data length y is shortened or lengthened is interpolated and estimated.

In any of the above calculation methods, if no data packet is received, it is not included in the error. This is because, as described above, data is received in bursts in the upstream, so if you include it even when there is no data,
This is because there is no error during that time, and the error rate becomes small. There is no problem if the data flows randomly and uniformly, but this is not the case in reality, and there is a point in that the error only at the time of data reception can be effectively grasped.

In the above embodiment, the noise level is directly measured to determine the upstream transmission path quality condition, but since the center control device controls the upstream transmission, it is possible to receive the upstream data signal. Is known in advance.
Therefore, the situation determination may be performed by using the CRC error detection of the upstream data signal together. Further, the variable block code length control unit 1 may be implemented by software using a computer or the like instead of being incorporated in the center control device.

Further, the center control device of the present invention is connected to a higher-order network forming a backbone via a router, and is further connected in parallel to a plurality of cable modems installed in a subscriber's home via optical nodes. Connected,
The communication data may be distributed between the backbone and the cable modem.

[0057]

As described above, according to the cable modem transmission system of the present invention, since the upstream noise level is monitored and the block code length for error correction is changed according to the noise occurrence condition, it is possible to efficiently and favorably Can communicate.

It is also possible to divide the error rate and obtain it. Furthermore, the error rate that occurred in the past can be accumulated. Since the noise generation status is not constant, the present invention makes it possible to effectively estimate the error correction strength and the block code length by storing past noise generation patterns.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a cable modem transmission system according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the block code length variable control unit 1.

FIG. 3 is a diagram for explaining a method of calculating an uplink error rate.

[Explanation of symbols]

1 block code length variable control unit 2 Downlink data multiplexer 3 Downlink error correction coding / modulation section 4 Uplink data demodulator 5 Uplink error correction decoding unit 6 Upstream noise level measurement unit 11 Terminal control message generator 12 Error correction strength calculator 100 downlink data signal 101 Downlink RF signal 200 upstream RF signal 201 upstream IF signal 202 Upstream data signal

   ─────────────────────────────────────────────────── ─── Continued front page    (71) Applicant 000005821             Matsushita Electric Industrial Co., Ltd             1006 Kadoma, Kadoma-shi, Osaka (72) Inventor Yoshitaka Nakano             2-31-25 Shiba, Minato-ku, Tokyo             -Cable Media Co., Ltd. (72) Inventor Yoshinori Rokugo             2-31-19 Shiba, Minato-ku, Tokyo Communications and broadcasting             Within the mechanism (72) Inventor Takeo Matsuura             2-31-19 Shiba, Minato-ku, Tokyo Communications and broadcasting             Within the mechanism (72) Inventor Katsuro Osawa             2-31-25 Shiba, Minato-ku, Tokyo             -Cable Media Co., Ltd. F-term (reference) 5C059 MA27 RA01 RA08 RB02 RF07                       RF15 UA39                 5C064 BA02 BB05 BC10 BC16 BD05                       BD07 BD14                 5K014 AA01 DA01 FA13 GA02

Claims (12)

[Claims] 1. A center control device used in a cable modem transmission system, comprising: means for monitoring a noise level of upstream data; and a first means for monitoring the noise level of the upstream data when the monitored noise level changes by a predetermined range or more. Means for detecting the number of errors that could not be error-corrected for the upstream data in a predetermined time interval, and calculating the error rate after error correction of the upstream data in the second predetermined time interval from the detected number of errors Means for calculating an error correction strength by using the noise level and the error rate when the error rate is calculated, and a block code length based on the calculated error correction strength And a means for notifying the cable modem installed in the subscriber's house to change the block code length to the calculated block code length. Center control device. 2. The center control device according to claim 1, wherein an integer multiple of the first predetermined time period is the second predetermined time period. 3. The center control device according to claim 1, wherein the first predetermined time period and the third time period are different from each other in consideration of a frame length of a data packet. The second predetermined period section is a time corresponding to the transmission time of the frame length of the data packet of the upstream data, and the means for calculating the error rate is the third section. From the number of errors in the predetermined time period and the fourth predetermined time period,
A center control device for estimating an error rate in the second predetermined time period. 4. The center control device according to claim 1, wherein when there are a plurality of combinations of block code length and error correction strength, the first predetermined time period includes the block code length and the error. A plurality of units are set according to the correction strength, and the means for calculating the error rate calculates an error rate in a combination of the unknown block code length and the error correction strength based on the number of errors in the first predetermined time interval. A center control device which is characterized by: 5. The center control device according to claim 1, wherein the means for notifying the cable modem to change the block code length sends the signal to the cable modem by multiplexing a control signal with downlink data. The center control device which is transmitted, wherein the control signal includes at least a block code length change notification. 6. The center control device according to claim 1, wherein the center control device is connected to a higher-order network that constitutes a backbone via a router, and is connected in parallel to cable modems of a plurality of subscribers' homes via optical nodes. A center control device, which is connected to a cable modem transmission system for distributing communication data between the backbone and the cable modem. 7. A block code length control method used in a cable modem transmission system, comprising: a step of monitoring a noise level of uplink data; and a step of: when the monitored noise level changes by a predetermined range or more. A step of detecting the number of errors in which the error of the upstream data could not be corrected in one predetermined time period; and an error rate after the error correction of the upstream data in the second predetermined time period from the detected number of errors And a step of calculating an error correction strength by using the noise level and the error rate when the error rate is calculated, and a block code length based on the calculated error correction strength. The step of calculating and the step of notifying the cable modem installed in the subscriber's house to change the block code length to the calculated block code length And a block code length control method. 8. The block code length control method according to claim 7, wherein an integer multiple of the first predetermined time period is the second predetermined time period. Method. 9. The block code length control method according to claim 7, wherein the first predetermined time section is a third time section having different time lengths in consideration of a frame length of a data packet. And a fourth time interval, the second predetermined time interval is a time corresponding to the transmission time of the frame length of the data packet of the uplink data, and the step of calculating the error rate includes the 3. A block code length control method, comprising estimating an error rate in the second predetermined time section from the number of errors in the third predetermined time section and the fourth predetermined time section. 10. The block code length control method according to claim 7, wherein when there are a plurality of combinations of block code lengths and error correction intensities, the first predetermined time period includes: A plurality of values are set according to the error correction strength, and the step of calculating the error rate is performed by calculating an error rate in a combination of the unknown block code length and the error correction strength by the number of errors in the first predetermined time interval. A block code length control method, which is characterized by: 11. The block code length control method according to claim 7, wherein said notifying step transmits said signal to said cable modem by multiplexing a control signal with downlink data, and said control signal is at least A block code length control method including a block code length change notification. 12. A means for monitoring the noise level of upstream data, the computer being capable of correcting the error of the upstream data in a first predetermined time interval when the monitored noise level changes by a predetermined range or more. Means for detecting the number of errors that did not exist, means for calculating the error rate after error correction of the uplink data in the second predetermined time interval from the detected number of errors, and the case where the error rate is calculated A means for calculating an error correction strength using the noise level and the error rate; a means for calculating a block code length based on the calculated error correction strength; and a block code length for the calculated block As a center control device used in a cable modem transmission system, which comprises means for notifying a cable modem installed in a subscriber's house to change the code length A program to make it work.