JP2004040533A - Modem, communication system, and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modem which can realize accurate data transmission, even when a digital PAD is provided in a digital line network in a communication system, according to the V.90 Recommendations by the ITU-T. <P>SOLUTION: A modem includes a DPAD detector 11 for deciding attenuation of the digital PAD 4 in a communication network, on the basis of a inspection signal received from a digital modem 2 on a sender side via the communication network, a table creator 13 for downwardly correcting a corresponding level value of a constellation table for use in the demodulating operation of a demodulator 12 to obtain a corrected constellation table, a constellation selector 14 for selecting a constellation point for use in communication on the basis of the corrected constellation table, and a constellation notifier 15 for generating a signal, to inform the communication device on the sender side of information about the constellation point. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is based on ITU-T Recommendation V. TECHNICAL FIELD The present invention relates to a modem device, a communication device, and a communication method used in a communication system conforming to H.90.
[0002]
[Prior art]
ITU-T Recommendation V. 7, a communication system for performing data communication between a digital modem 101 and an analog modem 102 is defined as shown in FIG. 7, and here, a digital modem 101 provided in an ISP (Internet Service Provider) or the like is specified. It is connected to a digital line such as ISDN, and achieves a communication speed of 56 kbps in the downstream direction to the analog modem 102 on the user side connected to the analog line via the digital exchange 103.
[0003]
In such a communication system, data communication is performed by a PCM (Pulse Code Modulation) method using the μ-law on a digital transmission line between the digital modem 101 and the digital exchange 103, and the digital exchange 103 and the analog modem 102 communicate with each other. In the analog transmission line, data communication by the PAM (pulse amplitude modulation) method is performed. In the analog modem 102, as shown in FIG. 8, a μ-law linear value (level value) and an 8-bit code are used. A process of extracting a corresponding code from a level value of a received signal according to a characteristic curve indicating a correspondence relationship with a corresponding U code (level number) is performed.
[0004]
[Problems to be solved by the invention]
However, as shown in FIG. 7, the digital network may be provided with a digital PAD 104 having a function of performing an attenuating process on a digital signal in order to optimize a speech sound. In such a case, the characteristic curve changes as shown in FIG. 8 due to the influence of the attenuation processing of the digital PAD 104 (here, attenuation of 4 dB). As a result, it is difficult to identify the level values originally assigned to different codes, and the codes finally obtained through the demodulation processing of the analog modem become identical, which causes a problem that accurate data transmission cannot be performed.
[0005]
The present invention has been devised in order to solve such problems of the prior art, and its main object is to provide ITU-T Recommendation V.3. In a communication system conforming to H.90, there is provided a modem device, a communication device, and a communication method configured to enable accurate data transmission even when a digital PAD is provided in a digital network. .
[0006]
[Means for Solving the Problems]
In order to achieve such an object, according to the present invention, the configuration of a modem device is determined by determining an attenuation amount of an attenuation processing device in a communication network based on a survey signal received from a transmitting device via a communication network. Amount determining means, constellation information generating means for obtaining corrected constellation information in which the level value of constellation information used for demodulation processing is corrected downward according to the amount of attenuation, and selecting constellation points to be used for communication based on the corrected constellation information. Constellation point selecting means and notifying means for notifying the information of the constellation point to the transmitting apparatus are provided. According to this, by performing communication using constellation points set based on the corrected constellation information, it is possible to avoid the inconvenience of different data being equalized due to the effect of attenuation processing, enabling accurate data transmission Become.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The modem device according to the first embodiment of the present invention determines the amount of attenuation of the attenuation processing device in the communication network based on the investigation signal received from the transmitting device via the communication network. Attenuation amount determination means, constellation information generation means for obtaining corrected constellation information in which the level value of constellation information used for demodulation processing is corrected downward according to the attenuation amount, and a constellation point used for communication based on the corrected constellation information is selected. And a notifying means for notifying the transmitting apparatus of information on the constellation points. According to this, by performing communication using constellation points set based on the corrected constellation information, it is possible to avoid the inconvenience of different data being equalized due to the effect of attenuation processing, enabling accurate data transmission Become.
[0008]
In the modem device according to the second embodiment of the present invention, in the configuration according to the first embodiment, the constellation point selecting means may be configured such that the constellation point selecting means selects the constellation points according to the level interval set based on the S / N ratio of the investigation signal. Is to select. According to this, it is possible to avoid the inconvenience that different data becomes identical with a decrease in the SN ratio, and it is possible to improve data transmission quality.
[0009]
The modem device according to the third embodiment of the present invention, in the configuration according to the first or second embodiment, wherein the constellation point selecting means restricts the signal power in accordance with the level value in the modified constellation information. This is to select the constellation points to be filled. According to this, by performing communication in accordance with the original constellation information in the transmitting side device, a signal is transmitted at a level added by an amount corresponding to the attenuation amount, while the receiving side modem device limits the receiving level. Without exceeding, the transmission signal power of the transmission side device is compensated by an amount corresponding to the digital PAD, so that the influence of the analog digital PAD can be excluded.
[0010]
A communication device according to a fourth embodiment of the present invention includes the modem device according to any one of the first to third aspects. According to this, it is possible to avoid the inconvenience of different data being equalized due to the influence of the attenuation process, and it is possible to perform accurate data transmission.
[0011]
The communication method according to the fifth embodiment of the present invention transmits a survey signal from a transmitting device to a receiving communication terminal via a communication network, and in the receiving communication terminal based on the survey signal, It determines the amount of attenuation of the attenuation processing device in the communication network, generates corrected constellation information by lowering the level value of constellation information used for demodulation processing based on the amount of attenuation, and performs communication based on the corrected constellation information. The constellation point to be used is selected, and the information of the constellation point is notified to the transmitting apparatus. According to this, it is possible to avoid the inconvenience of different data being equalized due to the influence of the attenuation process, and it is possible to perform accurate data transmission.
[0012]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 is a block diagram showing a schematic configuration of an analog modem according to the present invention. This analog modem 1 conforms to ITU-T Recommendation V. Data communication is performed between the digital modem 2 and the digital exchange 3 in accordance with the PCM (pulse code modulation) method using the μ-law. Communication is performed, and data communication is performed in a PAM (pulse amplitude modulation) system on an analog transmission path between the digital exchange 3 and the analog modem 1. A digital line network connecting the digital modem 2 and the digital exchange 3 is provided with a digital PAD (attenuation processing device) 4 having a function of performing an attenuation process on a digital signal in order to optimize a call voice. . The conversion rule used in the PCM method may be an a-law that is mainly used in Europe. In this case, an a-law linear value is used instead of a μ-law linear value. .
[0014]
The analog modem 1 includes a DPAD detector (attenuation determining means) 11 for determining the presence / absence of the digital PAD 4 in the communication network and the amount of attenuation thereof based on the investigation signal received from the transmitting digital modem 2 via the communication network. A table creation unit (constellation information generating means) 13 for obtaining a modified constellation table (corrected constellation information) in which the level value of the constellation table (constellation information) used for the demodulation processing in the demodulation unit 12 is corrected downward according to the attenuation amount; A constellation selecting unit (constellation point selecting means) 14 for selecting a constellation point to be used for communication based on the corrected constellation table, and a constellation notifying unit (notification for generating a signal for notifying the communication device on the transmitting side of the information of the constellation point. 15), and the notification signal of the constellation to be used is sent out to the line via the modulator 16 and sent to the digital modem 2.
[0015]
In addition, the analog modem 1 includes an SN measuring unit 17 for obtaining an S / N ratio of the investigation signal from the digital modem 2 and an interval determination unit 18 for determining a level interval (difference in level value) between constellation points based on the S / N ratio of the investigation signal. The constellation point selection unit 14 selects constellation points according to the obtained level intervals.
[0016]
FIG. 2 shows a state of correction of the constellation table in the table creation unit shown in FIG. As described above, the table creating unit (constellation information generating means) corrects the level value of the original constellation table (constellation information) downward according to the attenuation of the digital PAD to generate a modified constellation table (corrected constellation information). I do. The constellation table indicates the correspondence between the μ-law linear value (level value) and the U code (level number) corresponding to the 8-bit code, and indicates the gain corresponding to the attenuation of digital PAD (for example, 4 dB or 8 dB). Based on this, a μ-law linear value (level value) for each U code (level number) is obtained.
[0017]
FIG. 3 shows a correspondence table between the SN ratio and the level interval used in the interval determining section shown in FIG. The interval determination unit determines the level interval of the constellation point from the S / N ratio of the investigation signal based on the correspondence table. For example, if the SN ratio is 60, the level interval becomes 64, and the level interval increases as the SN ratio decreases.
[0018]
FIG. 4 shows a point of constellation point selection in the constellation selecting unit shown in FIG. As described above, the constellation point selection unit (constellation point selection means) selects constellation points to be used for communication based on the corrected constellation table. At this time, the constellation points are arranged at uniform intervals in linear values (level values). The constellation point is selected. The level interval D between the constellation points is determined based on the S / N ratio of the investigation signal from the digital modem. Here, an example is shown in which the level interval D = 64, and the linear value (level value) is initially D / 2 = 32 so that the constellation points have the same interval even in the area of positive / negative linear values (level values). (Constellation selection start point) is determined, and constellation points satisfying the level interval D = 64 with respect to the constellation point selected immediately before are sequentially selected.
[0019]
FIG. 5 is a flowchart showing a processing procedure of constellation selection in the analog modem shown in FIG. First, in step 1, a modified constellation table corresponding to the digital PAD is created as shown in FIG. 2, and in step 2, the level interval D of the constellation point is obtained from the S / N of the received signal. Then, in step 3, the constellation selection start point is determined as shown in FIG. 4, and in step 4, the next constellation point is determined. The process of setting the constellation points is repeatedly performed until it is determined in step 5 that the corrected constellation table has reached the end. This completes the process of selecting usable constellation points, and then proceeds to the process of selecting a constellation point to be actually used.
[0020]
In the selection of the constellation point to be used, first, among the constellation points that can be used (the one with the lowest level value) among the constellation points that can be used, the constellation point is selected (provisionally determined) as the constellation point to be used. The power of the point is calculated, and it is determined in step 8 whether the power limit is satisfied. If the power limitation is satisfied, the process returns to step 6, where the next constellation point (the one with the next highest level value) is selected as the constellation point to be used, and the processing in steps 7 and 8 is performed. In this way, the constellation points to be used are sequentially selected from the one having the smaller level value until it is determined that the power restriction is not satisfied, and if it is determined that the power restriction is not satisfied, the process proceeds to step 9 to select the selected constellation point. Cancel one (the one with the largest level value) and end.
[0021]
FIG. 6 shows an attenuation state of a signal transmitted from the digital modem shown in FIG. 1 to the analog modem. As described above, the analog modem 1 selects a constellation point based on the corrected constellation table created for the digital PAD 4, and notifies the digital modem 2 of the U code (level number) of the selected constellation point. You. The digital modem 2 generates transmission data with reference to the original constellation table shown in FIG. As a result, the signal power at the stage of transmission by the digital modem 2 becomes -16 dBm, which was -12 dBm in the past, and is transmitted from the digital exchange 3 to the analog modem 1 through the attenuation of 4 dB in the digital PAD. In this case, what was conventionally -8 dBm is now -12 dBm, which means that the signal power has been compensated by an amount corresponding to the digital PAD. The analog modem 1 can extract an accurate code from the received signal using the modified constellation table shown in FIG. 2 and the constellation information shown in the constellation characteristic graph shown in FIG.
[0022]
Although FIG. 1 shows an example in which the PC 5 is connected to an analog modem, the present invention is not limited to this, and a user terminal device such as a set-top box having the same configuration as the analog modem described above. A data communication may be performed between the terminal device and a center device connected to a digital line such as ISDN.
[0023]
【The invention's effect】
As described above, according to the present invention, by performing communication using the constellation points set based on the corrected constellation information, it is possible to avoid the inconvenience of different data being equalized due to the influence of the attenuation process in the digital PAD. This allows accurate data transmission even when a digital PAD is provided in a digital network.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an analog modem according to the present invention; FIG. 2 is a diagram showing a state of correction of a constellation table in a table creating unit shown in FIG. 1; FIG. FIG. 4 is a diagram showing a correspondence table between the SN ratio and the level interval used in FIG. 4 FIG. 4 is a diagram showing a procedure for selecting constellation points in the constellation selecting unit shown in FIG. 1 FIG. FIG. 6 is a flowchart showing a constellation selection processing procedure. FIG. 6 is a diagram showing an attenuation state of a signal transmitted from the digital modem to the analog modem shown in FIG. 1. FIG. 7 is a schematic configuration of a communication system to which the present invention is applied. FIG. 8 is a diagram showing the state of signal attenuation by digital PAD.
1 Analog modem (modem device according to the present invention)
2 Digital modem (transmitting device)
3 Digital exchange 4 Digital PAD (Attenuation processing unit)
11 DPAD detection unit (attenuation determination means)
12 Demodulation unit 13 Table creation unit (constellation information generation means)
14 Constellation selection section (constellation point selection means)
15 Constellation notification unit (notification means)
16 Modulation unit 17 SN measurement unit 18 Interval determination unit

Claims (5)

Attenuation amount determining means for determining an attenuation amount of an attenuation processing device in the communication network based on a survey signal received from the transmitting side device via the communication network; and a level value of constellation information used for demodulation processing. Constellation information generating means for obtaining corrected constellation information corrected downward according to the above, constellation point selection means for selecting a constellation point to be used for communication based on the corrected constellation information, the constellation point information to the transmitting device A modem device, comprising: a notifying unit for notifying. The modem device according to claim 1, wherein the constellation point selecting means selects a constellation point according to a level interval set based on an S / N ratio of the investigation signal. The modem device according to claim 1, wherein the constellation point selection unit selects a constellation point that satisfies a restriction on signal power according to a level value in the corrected constellation information. A communication device comprising the modem device according to claim 1. A survey signal is transmitted from the transmitting device to the receiving communication terminal via the communication network, and the attenuation amount of the attenuation processing device in the communication network is determined at the receiving communication terminal based on the survey signal. Based on the amount of attenuation, generates corrected constellation information by lowering the level value of constellation information used for demodulation processing, selects constellation points to be used for communication based on the corrected constellation information, and generates information on the constellation points. Communication method to the transmitting apparatus.

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