JP3983119B2 - MODEM DEVICE, COMMUNICATION DEVICE, AND COMMUNICATION METHOD - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to ITU-T Recommendation V.3. The present invention relates to a modem device, a communication device, and a communication method used in a communication system conforming to 90.
[0002]
[Prior art]
ITU-T Recommendation V. 90, a communication system for performing data communication between the digital modem 101 and the analog modem 102 is defined as shown in FIG. 7. Here, the digital modem 101 provided in an ISP (Internet Service Provider) or the like is defined. A communication speed of 56 kbps is realized in the downstream direction to the analog modem 102 on the user side connected to a digital line such as ISDN and connected to the analog line via the digital exchange 103.
[0003]
In such a communication system, data communication by the PCM (Pulse Code Modulation) method using the μ-law is performed on a digital transmission path between the digital modem 101 and the digital switch 103, and the digital switch 103 and the analog modem 102 are connected to 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. Processing for extracting the corresponding code from the level value of the received signal is performed in accordance with the characteristic curve indicating the corresponding relationship with the corresponding U code (level number).
[0004]
[Problems to be solved by the invention]
However, as shown in FIG. 7, the digital line network may be provided with a digital PAD 104 having a function of performing attenuation processing on the digital signal in order to optimize the speech voice. In this case, the characteristic curve changes as shown in FIG. 8 due to the influence of the attenuation process of the digital PAD 104 (in this case, attenuation of 4 dB). As a result, it becomes difficult to identify the level values originally assigned to different codes, and the codes finally obtained through the demodulation process of the analog modem are made identical, resulting in inconvenience that accurate data transmission cannot be performed.
[0005]
The present invention has been devised to solve such problems of the prior art, and the main purpose thereof is ITU-T Recommendation V.3. The present invention provides 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 line network in a communication system conforming to 90. .
[0006]
[Means for Solving the Problems]
In order to achieve such an object, in the present invention, the amount of attenuation of the attenuation processing device in the communication network is determined based on the survey signal received from the transmission side device via the communication network. Decay amount determination means, constellation information generation means for obtaining corrected constellation information obtained by correcting the level value of constellation information used in demodulation processing downward according to the attenuation amount, and constellation points used for communication based on the corrected constellation information and constellation point selection means for selecting said information constellation points have a notification means for notifying the transmitting device, the transmitting-side apparatus and performs a transmission operation using a constellation point selected. According to this, by performing communication using the constellation points set based on the modified constellation information, it is possible to avoid the problem that different data becomes identical due to the influence of attenuation processing, and accurate data transmission is possible Become.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The modem device according to the first embodiment of the present invention determines the attenuation amount of the attenuation processing device in the communication network based on the survey signal received from the transmitting device via the communication network. A constellation information generating means for obtaining corrected constellation information obtained by downwardly correcting the level value of constellation information used for demodulation processing according to the attenuation amount, and a constellation used for communication based on the corrected constellation information and constellation point selection means for selecting points, the information of constellation points have a notification means for notifying the transmitting device, the transmitting device performs a transmission operation using a constellation point selected. According to this, by performing communication using the constellation points set based on the modified constellation information, it is possible to avoid the problem that different data becomes identical due to the influence of attenuation processing, and accurate data transmission is possible 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 selection means has a constellation point according to a level interval set based on the SN ratio of the survey signal. Is to select. According to this, it is possible to avoid the inconvenience that different data becomes the same as the SN ratio decreases, and it is possible to improve the data transmission quality.
[0009]
In the modem device according to the third embodiment of the present invention, in the configuration according to the first or second embodiment, the constellation point selecting means limits the signal power according to the level value in the corrected constellation information. The constellation point to be satisfied is selected. According to this, by performing communication according to the original constellation information at 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 restricts the receiving level. Without exceeding, the transmission signal power of the transmission side apparatus is compensated by the amount corresponding to the digital PAD, and the influence of the analog digital PAD can be excluded.
[0010]
A communication apparatus according to a fourth embodiment of the present invention includes the modem apparatus according to any one of the first to third aspects. According to this, it is possible to avoid the inconvenience that different data is made identical due to the influence of attenuation processing, and accurate data transmission becomes possible.
[0011]
In the communication method according to the fifth embodiment of the present invention, a survey signal is transmitted from a transmitting device to a receiving communication terminal via a communication network, and the receiving communication terminal is based on the survey signal. Determines the amount of attenuation of the attenuation processing device in the communication network, generates corrected constellation information in which the level value of the constellation information used for demodulation processing is corrected downward based on the attenuation amount, and based on the corrected constellation information A constellation point to be used for communication is selected, information on the constellation point is notified to the transmission side device, and the transmission side device performs a transmission operation using the selected constellation point . According to this, it is possible to avoid the problem that different data is made identical due to the influence of attenuation processing, and accurate data transmission becomes possible.
[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 is an ITU-T recommendation V.30. Data communication between the digital modem 2 and the digital modem 2 is performed in accordance with 90, and the digital transmission path between the digital modem 2 and the digital exchange 3 is data by the PCM (pulse code modulation) method using the μ-law. Communication is performed, and data communication by the PAM (pulse amplitude modulation) method is performed on the 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 attenuation processing on a digital signal in order to optimize speech voice. . The conversion rule used in the PCM method may be the a-law used mainly in Europe. In this case, an a-law linear value is used instead of the μ-law linear value. .
[0014]
The analog modem 1 includes a DPAD detection unit (attenuation amount judging means) 11 for judging the presence / absence of the digital PAD 4 in the communication network and the attenuation amount based on the investigation signal received from the digital modem 2 on the transmission side via the communication network. A table creating unit (constellation information generating means) 13 for obtaining a modified constellation table (corrected constellation information) obtained by downwardly correcting the level value of the constellation table (constellation information) used for the demodulation processing in the demodulation unit 12 according to the attenuation amount; A constellation selection section (constellation point selection means) 14 for selecting a constellation point to be used for communication based on the modified constellation table, and a constellation notification section (notification) for generating a signal for notifying information on the constellation point to the communication device on the transmission side Means) 15 and a notification signal of the constellation to be used is sent to the line via the modulation section 16 and sent to the digital modem 2.
[0015]
The analog modem 1 also includes an SN measuring unit 17 for obtaining the SN ratio of the survey signal from the digital modem 2, and an interval determining unit 18 for determining the level interval (level value difference) of the constellation points based on the SN ratio of the survey signal. The constellation point is selected in the constellation selection unit 14 according to the level interval obtained here.
[0016]
FIG. 2 shows the constellation table correction status in the table creation unit shown in FIG. As described above, the table creation unit (constellation information generating means) generates a corrected constellation table (corrected constellation information) by correcting the level value of the original constellation table (constellation information) downward according to the attenuation amount of the digital PAD. To do. The constellation table shows the correspondence between the μ-law linear value (level value) and the U code (level number) corresponding to the 8-bit code, and has a gain corresponding to the attenuation amount (for example, 4 dB or 8 dB) of the digital PAD. 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 unit shown in FIG. The interval determination unit determines the level interval of the constellation points from the SN ratio of the survey signal based on this correspondence table. For example, if the SN ratio is 60, the level interval is 64, and the level interval increases as the SN ratio decreases.
[0018]
FIG. 4 shows how to select a constellation point in the constellation selection unit shown in FIG. As described above, the constellation selection unit (constellation point selection means) selects constellation points to be used for communication based on the modified constellation table. At this time, the constellation points are arranged at uniform intervals in linear values (level values). A constellation point is selected. The level interval D of the constellation points is determined based on the SN ratio of the survey signal from the digital modem. Here, an example in which the level interval D = 64 is shown, and the linear value (level value) is initially D / 2 = 32 so that the constellation points have the same interval even in the region of positive and negative linear values (level values). A constellation point (constellation selection start point) is determined, and thereafter, 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 for 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 points is obtained from the S / N of the received signal. 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. This constellation point setting process is repeated until it is determined in step 5 that the end of the corrected constellation table has been reached. This completes the selection process of usable constellation points, and then shifts to the selection process of constellation points to be actually used.
[0020]
In selecting the constellation point to be used, the first constellation point that can be used in step 6 (the one with the lowest level value) is selected (provisionally determined) as the constellation point to be used. The power of the point is calculated, and it is further determined in step 8 whether the power limit is satisfied. If the power limit is satisfied, the process returns to step 6, the next constellation point (the next highest level value) is selected as the use constellation point, and the processes of steps 7 and 8 are performed. The use constellation points are selected in descending order of the level value until it is determined that the power limit is not satisfied in this way, and if it is determined that the power limit is not satisfied, the process proceeds to step 9 and the selected constellation point is selected. Cancel one (the one with the highest level value) and exit.
[0021]
FIG. 6 shows an attenuation state of a signal transmitted from the digital modem shown in FIG. 1 to the analog modem. In the analog modem 1, as described above, a constellation point is selected based on the modified constellation table created corresponding to the digital PAD 4, and the U code (level number) of the selected constellation point is notified to the digital modem 2. The 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 transmission stage in the digital modem 2 is -16 dBm, which is -12 dBm in the past, and is transmitted from the digital exchange 3 to the analog modem 1 after 4 dB attenuation in the digital PAD. Then, what was -8 dBm in the past is -12 dBm, and the signal power is compensated by the 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 the 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. And a center device connected to a digital line such as ISDN may be used for data communication.
[0023]
【The invention's effect】
As described above, according to the present invention, by performing communication using the constellation points set based on the modified constellation information, it is possible to avoid the inconvenience that different data becomes identical due to the influence of attenuation processing in the digital PAD. Therefore, even when a digital PAD is provided in the digital network, accurate data transmission is possible.
[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 correction status of a constellation table in the table creation unit shown in FIG. 1. FIG. 3 is an interval determination unit shown in FIG. FIG. 4 is a diagram showing a correspondence table between SN ratio and level interval used in FIG. 4. FIG. 4 is a diagram showing a point of constellation point selection in the constellation selection unit shown in FIG. 1. FIG. Fig. 6 is a flowchart showing the processing procedure of constellation selection. Fig. 6 is a diagram showing the attenuation state of a signal transmitted from the digital modem shown in Fig. 1 to the analog modem. Fig. 7 is a schematic configuration of a communication system to which the present invention is applied. Block diagram shown [Fig. 8] Diagram showing signal attenuation by digital PAD [Explanation of symbols]
1 Analog modem (modem device according to the present invention)
2 Digital modem (transmission side device)
3 Digital exchange 4 Digital PAD (Attenuation processor)
11 DPAD detector (attenuation amount determination means)
12 demodulation unit 13 table creation unit (constellation information generation means)
14 Constellation selection part (constellation point selection means)
15 Constellation notification unit (notification means)
16 Modulating unit 17 SN measuring unit 18 Interval determining unit

Claims (5)

Attenuation amount determining means for determining the attenuation amount of the attenuation processing device in the communication network based on the survey signal received from the transmission side device via the communication network, and the level value of the constellation information used for the demodulation process Constellation information generating means for obtaining corrected constellation information downwardly corrected according to the above, constellation point selection means for selecting a constellation point used for communication based on the corrected constellation information, and information on the constellation point to the transmitting side device modem apparatus characterized by have a notification means for notifying that performs a transmission operation using said constellation point said sender device selected.   The modem device according to claim 1, wherein the constellation point selection unit selects a constellation point according to a level interval set based on an S / N ratio of the survey 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 any one of claims 1 to 3. 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 in the receiving communication terminal based on the survey signal. Based on this attenuation, it generates corrected constellation information by downwardly correcting the level value of constellation information used for demodulation processing, selects a constellation point to be used for communication based on this corrected constellation information, and information on this constellation point Is transmitted to the transmission side device, and the transmission side device performs a transmission operation using the selected constellation point .

Images