JP2007306235A - Modem - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DSP modem which is prevented from generating a false bit to have an improved error rate by using a quadratic curve as calculation expression by a carrier level adjustment processing section to generate a sent-out waveform approximating a conventional analog system. <P>SOLUTION: The DSP modem 6 comprises a modulation processing section 3 which sends out or stops a carrier based upon an RS of a terminal device 1 and modulates the carrier based upon an SD; the carrier level adjustment processing section 4 which adjusts rise and fall characteristics of the carrier when the carrier is sent out and stopped; a transmitting filter processing section 5 which removes an unnecessary signal included in the output signal from the carrier level adjustment processing section 4; a receiving filter processing section 9 which removes an unnecessary signal included in a reception signal; an AGC processing section 10 which adjusts the reception signal level output from the receiving filter processing section 9 to a predetermined level; and a demodulation processing section 11 which demodulates the carrier to regenerate a digital signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a modem, and more particularly to a DSP (digital signal processor) modem that improves the reception characteristics of a modem by using transmission wave control.

  A modem is a device used when a digital signal is converted into a carrier wave of a voice band signal and transmitted, and data transmission is performed using a telephone line. As a modem modulation / demodulation method, a low-speed modem of 1200 Bit / S or less uses a narrow band, so that different carrier waves are used for transmission / reception, and full-duplex or half-duplex communication is performed on a two-wire or four-wire line. May be configured. However, since conventional modems use passive components such as coils and capacitors as filters for removing unwanted wave components from transmitted and received carrier wave signals, it is difficult to reduce the size and cost. A modem using a DSP that does not use a capacitor or a capacitor has been developed.

  However, the modem using the conventional DSP as described above has the following problems when transmitting / stopping the carrier wave under the control of the RS signal from the terminal device. That is, when the modem is realized by DSP processing, the output waveform has a characteristic that it instantaneously rises to a level of 100% and instantaneously falls to a level of 0% when a carrier wave is transmitted / stopped. On the other hand, when the transmission-side carrier wave is transmitted via the line transformer, there is a considerable mismatch between the impedance of the line transformer and each terminal impedance, and therefore, a certain level of the carrier wave wraps around the reception side. A considerable part of the transmission signal that wraps around to the reception side is removed by the filter processing unit on the reception side, but the frequency of the carrier on the transmission side and the carrier on the reception side are used close to each other like a low-speed modem. If the received signal is received, the received signal and the transmitted transmission signal are input from the filter processing unit to the AGC processing unit. At this time, if the amount of leakage that wraps around from the transmission side changes instantaneously as described above, and if the reception signal changes instantaneously, the AGC processing unit and reception filter of the DSP and further the demodulation processing unit cannot follow. As a result, the reception characteristics deteriorated.

In order to improve the degradation of the reception characteristics, Patent Document 1 includes a carrier level adjustment processing unit that adjusts the rising and falling characteristics of the carrier wave when the carrier wave modulated by the modulation processing unit is transmitted and stopped. There has been disclosed a DSP modem that reduces the influence of a transmission signal on a reception side AGC processing unit at the time of transmission and stop and improves reception characteristics.
FIG. 5 is a diagram illustrating a rising waveform (a), a falling waveform (b), and a waveform envelope (C) adjusted by the carrier wave level adjustment processing unit in the DSP modem of Patent Document 1. As shown in FIG. 5A, the calculation formula used when the carrier level adjustment processing unit of Patent Document 1 transmits a carrier by a transmission request signal is Vr as the carrier level and E as the output level when the carrier level is not adjusted. , Where M is the number of processes for stepwise adjustment of the carrier level Vr at time tr, and A is the inverse 1 / M of the number of processes M, V is changed from 0 to M, and Vr = E × A × I was seeking as M. Further, as shown in FIG. 5B, the calculation formula when the conventional carrier level adjustment processing unit stops the carrier by the transmission request signal is similarly obtained as Vf = E × A × M.
JP 2001-24716 A

However, in the prior art disclosed in Patent Document 1, since the calculation formula for adjusting the rising and falling characteristics of the carrier wave is obtained as Vr = Vf = E × A × M, the carrier wave levels Vr and Vf are processed. It changes linearly in proportion to the number M (the increase / decrease value of the carrier level per unit time is constant), and the transmission waveform is different from the conventional analog system. It was a factor that worsened the error rate.
In view of such problems, the present invention prevents the generation of pseudo bits by, for example, using a quadratic curve as a calculation formula by the carrier level adjustment processing unit in order to generate a transmission waveform that approximates the conventional analog method. An object is to provide a modem with improved error rate.

In order to solve this problem, the present invention provides a modulation processing unit that transmits or stops a carrier wave based on a transmission request signal and modulates the carrier wave based on a transmission data signal, and the modulation processing unit. A carrier wave level adjustment processing unit that inputs the modulation signal output from the carrier wave and adjusts the rising and falling characteristics of the carrier wave when the carrier wave is transmitted and stopped, and an unnecessary signal included in the output signal from the carrier wave level adjustment processing unit A transmission filter processing unit for removing signals, a reception filter processing unit for removing unnecessary signals included in the received signal, an AGC processing unit for adjusting the received signal level output from the reception filter processing unit to a predetermined level, A demodulation processing unit that demodulates the carrier wave output from the AGC processing unit and reproduces a digital signal, and the carrier level adjustment processing unit comprises: Level adjustment so that the increase value of the carrier level per unit time gradually increases with time at the rising edge of the transmission, and the decrease value of the carrier level per unit time gradually decreases with time at the fall of the carrier wave It is characterized by doing.
The DSP modem of the present invention is similar in configuration to a conventional DSP modem, but is an improved internal calculation formula of a carrier level adjustment processing unit provided therein. That is, in the conventional calculation formula, the calculation formula for adjusting the rising and falling characteristics of the carrier wave changes linearly, so that the transmission waveform is different from the conventional analog method, and there is a possibility that a pseudo bit is generated. Therefore, in the present invention, this calculation formula is changed to a quadratic curve formula to prevent the generation of pseudo bits and improve the error rate.

According to a second aspect of the present invention, the carrier level adjustment processing unit sets the carrier level Vr when the carrier is transmitted according to the transmission request signal, the output level when the carrier level is not adjusted, E, and the carrier level Vr. , Where M is the number of processes for stepwise adjustment to a predetermined time, and A is the inverse 1 / M of the number of processes M, Vr = E × (A × M) ² while changing M from 0 to M It is characterized by obtaining as.
The calculation formula when the conventional carrier level adjustment processing unit transmits the carrier wave by the transmission request signal is stepwise by setting the carrier level to Vr, the carrier level unadjusted output level to E, and the carrier level to Vr at a predetermined time. When the number of processes to be adjusted to M is M and the reciprocal 1 / M of the number of processes M is A, M is changed from 0 to M, and Vr = E × A × M. On the other hand, in the present invention, by obtaining Vr = E × (A × M) ² , the rising level of the carrier wave changes two-dimensionally and can be approximated to the conventional analog method.

According to a third aspect of the present invention, the carrier level adjustment processing unit sets the carrier level Vf when the carrier is stopped by the transmission request signal, the output level when the carrier level is not adjusted, E, and the carrier level Vf. , Where M is the number of processes to be adjusted stepwise in a predetermined time, and A is the inverse 1 / M of the number of processes M, Vf = E × [1− (A × M) ² ].
The calculation formula used when the conventional carrier level adjustment processing unit stops the carrier wave in response to the transmission request signal is as follows. The carrier level is Vf, the output level when the carrier level is not adjusted is E, and the carrier level Vf is stepped in a predetermined time. When the number of processes to be adjusted to M is M and the inverse 1 / M of the number of processes M is A, M is changed from 0 to M, and Vf = E × A × M. On the other hand, in the present invention, by calculating as Vf = E × [1− (A × M) ² ], the falling level of the carrier wave changes two-dimensionally and approximates to the conventional analog method. it can.

  According to the present invention, the internal calculation formula is made to be a quadratic curve formula by the carrier level adjustment processing section that adjusts the rising and falling characteristics of the carrier at the time of sending and stopping the carrier, so that the pseudo bit The error rate can be improved by preventing the occurrence.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
FIG. 1 is a block diagram of a modem according to the present invention. The modem 2 includes a DSP modem 6 and a line transformer 7. The DSP modem 6 transmits or stops a carrier based on a transmission request signal (RS) of the terminal device 1, and also based on a transmission data signal (SD). A modulation processing unit 3 that modulates the carrier wave; a carrier wave level adjustment processing unit 4 that receives the modulation signal output from the modulation processing unit 3 and adjusts the rising and falling characteristics of the carrier wave when the carrier wave is transmitted and stopped; A transmission filter processing unit 5 that removes unnecessary signals included in the output signal from the level adjustment processing unit 4, a reception filter processing unit 9 that removes unnecessary signals included in the reception signal, and a signal output from the reception filter processing unit 9 An AGC processing unit 10 that adjusts the received signal level to a predetermined level, and a carrier wave output from the AGC processing unit 10 is demodulated to reproduce a digital signal Configured to include a demodulation processing unit 11.

  Next, the operation of the modem 2 will be described. For example, the modulation method is an FS modulation method, the transmission speed is 200 bits / sec or less, the center frequency is set to 1200 Hz on the low frequency side and 1600 Hz on the high frequency side as the carrier frequency, 1200 Hz is assigned to the transmission side, and 1600 Hz is assigned to the reception side. As for the shift width, the space signal “0” is set to +100 Hz, and the mark signal “1” is set to −100 Hz. The operation of starting the modem and performing data transmission will be described. First, when the terminal device 1 sets the RS signal to “1” as a transmission request, the modem 2 instantaneously outputs a carrier level of 1300 Hz, which is a space signal in response to the modulation processing unit 3, to 100%, and then according to the SD signal. The carrier wave is modulated to 1200 Hz ± 100 Hz. At this time, since the above-described problem occurs due to the instantaneous rise of the level of the carrier wave, the carrier wave is input to the carrier wave level adjustment processing unit 4 so that the rise of the carrier wave is moderated.

  2A and 2B show output waveforms of the carrier level adjustment processing unit. FIG. 2A shows a rising waveform when the carrier wave is transmitted, FIG. 2B shows a falling waveform when the carrier wave is stopped, and FIG. Indicates a helix. In the present embodiment, the processing times tr and tf of the DSP modem 6 are set to change the carrier level from 0% to 100% and from 100% to 0% to 20 ms. Note that the frequency of the carrier wave waveform shown in FIG. 2 is used to indicate the function of the carrier wave level adjustment processing unit 4 and is different from the actual frequency. Next, the level-adjusted carrier wave having a center frequency of 1200 Hz is input to the transmission filter processing unit 5 and passes only 1200 Hz ± 100 Hz, which is a use band on the transmission side, so that unnecessary waves are not output to the two-wire line 8. Filter. The filtered carrier wave is input to the line transformer 7 that performs 2-wire / 4-wire conversion, and is output to the 2-wire line 8.

  On the other hand, the carrier wave from the opposite station received from the two-wire line 8 is converted into a two-wire / four-wire type by the line transformer 7 and taken into the receiving circuit. The received carrier wave modulated to the center frequency of 1600 Hz ± 100 Hz is allowed to pass only 1600 Hz ± 100 Hz, which is the reception side use band, by the reception filter processing unit 9 to remove noise components. Subsequently, the filtered carrier wave is automatically adjusted by the AGC processing unit 10 to a predetermined level necessary for demodulation. At this time, when a carrier wave having a center frequency of 1600 Hz on the transmitting side of the opposite station is transmitted / stopped, the carrier level on the receiving side changes accordingly. However, as described above, the level change is a gentle change. The operating time of the DSP modem 6 that processes the AGC processing unit 10 can sufficiently follow, and the reception level is automatically adjusted. The carrier wave automatically adjusted to a predetermined level is input to the demodulation processing unit 11, and the carrier wave of 1700 Hz is demodulated to the space signal “0” and 1500 Hz to the mark signal “1”, and is output to the terminal device 1 as the RD signal.

As described above, the DSP modem 6 of the present embodiment is similar in configuration to the conventional DSP modem, but is an improved internal calculation formula of the carrier level adjustment processing unit 4 provided therein. That is, in the conventional calculation formula, the calculation formula for adjusting the rising and falling characteristics of the carrier wave changes linearly, so that the transmission waveform is different from the conventional analog method, and there is a possibility that a pseudo bit is generated. Therefore, in this embodiment, this calculation formula is changed to a quadratic curve formula to prevent the generation of pseudo bits and improve the error rate.
That is, the calculation formula when the carrier level adjustment processing unit 4 of the present embodiment transmits the carrier by the transmission request signal (RS) is Vr for the carrier level, E for the carrier level without adjustment, and E for the carrier level. When the number of processes for adjusting the level Vr stepwise to the predetermined time tr is M and the inverse 1 / M of the process number M is A, M is changed from 0 to M, and Vr = E × (A × M ) By calculating as ² , the rising level of the carrier wave changes two-dimensionally and can be approximated to the conventional analog method. Further, the calculation formula when the conventional carrier level adjustment processing unit stops the carrier by the transmission request signal is as follows: the carrier level is Vf, the carrier level is not adjusted, the output level is E, and the carrier level Vf is the predetermined time tf. Where M is the number of processes to be adjusted step by step, and A is the reciprocal 1 / M of the number of processes M, V is changed from 0 to M, and Vf = E × [1− (A × M) ² ] As a result, the falling level of the carrier wave changes two-dimensionally and can be approximated to a conventional analog method.

FIG. 3 is a flowchart showing the level adjustment operation at the rising edge of the carrier wave of the modem according to the present invention. As described with reference to FIG. 2, the time to the steady state at the rise and fall of the carrier wave level is 20 ms, the sampling frequency is 8 kHz, and the level adjustment process is 100 steps. The constant A is set to 0.01 (the value of A is set so that A × M = 1 after 100 rounds of the program) so that the carrier level adjustment is executed in 100 steps over 20 ms. First, the presence / absence of the transmission request signal RS from the terminal device 1 is detected. When the RS signal is not detected (NO route in S1), the standby state is maintained (S1). On the other hand, when the RS signal is detected (YES route in S1), the process proceeds to step S2, and it is determined whether or not there is a transmission request signal (RS) in the previous routine (S2). Immediately after the RS signal is detected in step S1, there is no transmission request signal in the previous routine, so the previous round RS signal (BRS) is 0 (NO route in S2), and the process proceeds to step S3. That is, the rising edge of the RS signal is detected, and the level adjustment process at the time of rising is started (S3). In the level adjustment process, the positive number M is set to 0 (S4), and the calculation of Vr = E × (A × M) ² is executed (S5). Thereafter, the positive number M is incremented by “+1” (S6), the previous round RS signal (BRS) is set to 1 (S7), and the process returns to step S1.

In the second routine, if there is a transmission request signal RS (YES route in S1), the process proceeds to step S2, and at that time, BRS is set to 1 in step S7 of the previous routine, so the process proceeds to step S8. (YES route in S2), the value of the positive number M is determined (S8). When the positive number M is not “0” (NO route in S8), the process proceeds to step S9, and it is determined again whether the value of the positive number M is 100 (S9). If not reached M = 100 (route NO at S9), Vr = E × ( A × M) 2 calculations are performed in step S5. That is, the output E when the carrier level is not adjusted is multiplied by M = 1 and A = 0.01, the level is adjusted, and the positive number M is counted up (S6), and S1 → S2 → The process of S8 → S9 → S5 → S6 → S7 → S1 is performed.

  On the other hand, since M = 100 in the 100th routine, the determination in step S9 is “Yes”, the process proceeds to step S10, M = 0 is set (S10), and the output Vr becomes the unadjusted carrier level E ( S11) As long as the transmission request signal RS continues to be input, the process of steps S7 → S1 → S2 → S8 → S11 → S7 is performed. With the above processing, the rising characteristic of the carrier wave becomes a quadratic curve that changes with the square of the number M of processing, and can be approximated to a conventional analog system.

4 is a flowchart showing the level adjustment operation at the time of falling of the carrier wave of the modem according to the present invention. As in the embodiment of FIG. 3, the carrier level change time is 20 ms, the sampling frequency is 8 kHz, the adjustment stage 100, The constant A is set to 0.01. First, the presence / absence of a transmission request signal (RS) is confirmed (S21). If the carrier request signal RS is present, it waits because data transmission is in progress. When the transmission request signal RS is not detected (YES route in step S21), it is confirmed whether or not there is no transmission request signal in the previous routine (S22), and when it is not “BRS = 0” (NO routine in S22) ), The falling of the transmission request signal is detected, and the process is started (S23). Next, the positive number M is set to 100 (S24), and Vf = E × [1- (A × M) ² ] is calculated (S25). Thereafter, the positive number M is set to “−1” (S26), the one-round previous carrier request signal (BRS) is set to 0 (S27), and the processing is performed again from step S21. In the processing after the detection of the fall of the transmission request signal, “BRS = 0” is set in step S22, so that the process proceeds to step S28 and the value of the positive number M is determined. When the positive number M is not equal to “0”, the processing of S25 → S26 → S27 → S21 → S22 → S28 → S25 is performed, and the positive number M is decreased by 1 so that the output is the value when the carrier level is not adjusted. The level gradually decreases from E. On the other hand, when the positive number M becomes equal to “0” (YES route in S28), the process proceeds to step S29, where the output Vf is set to 0 and the process is terminated. By executing the carrier level adjustment process as described above, the carrier level can be gradually changed even when the modem is configured by using the DSP modem, whereby the line transformer and the reception side filter and the AGC are changed. Unnecessary signals that wrap around the processing unit can be reduced. By the above processing, the falling characteristic of the carrier wave becomes a quadratic curve that changes with the square of the number M of processing, and can be approximated to the conventional analog method.

As described above, according to the present invention, since the carrier level adjustment processing unit 4 that adjusts the rising and falling characteristics of the carrier wave at the time of sending and stopping the carrier wave, the internal calculation formula becomes a quadratic curve formula. It is possible to improve the error rate by preventing the generation of pseudo bits.
Further, when the carrier wave level adjustment processing unit 4 transmits the carrier wave by the transmission request signal (RS), the carrier wave level is set to Vr, the carrier wave level unadjusted output level is set to E, and the carrier wave level Vr is set to a predetermined time. Assuming that the number of processes to be adjusted is M and the reciprocal 1 / M of the number of processes M is A, V is obtained as Vr = E × (A × M) ² while changing M from 0 to M. The rising characteristic is a quadratic curve that changes with the square of the number of processes M, and can be approximated to a conventional analog method.

Further, when the carrier level is stopped by the transmission request signal (RS), the carrier level adjustment processing unit 4 sets the carrier level to Vf, the carrier level unadjusted output level to E, and the carrier level Vf to a predetermined time. Assuming that the number of processes to be adjusted is M and the reciprocal 1 / M of the number M is A, A is obtained as Vf = E × [1− (A × M) ² ] while changing M from 0 to M. Therefore, the falling characteristic of the carrier wave becomes a quadratic curve that changes with the square of the number of processes M, and can be approximated to the conventional analog method.

It is a block diagram of a modem according to the present invention. An output waveform of the carrier level adjustment processing unit is shown, (a) is a diagram showing a rising waveform when the carrier is transmitted, (b) is a diagram showing a falling waveform when the carrier is stopped, (c) is a diagram It is a figure which shows an envelope. It is a flowchart which shows the operation | movement of level adjustment at the time of the carrier wave rising of the modem which concerns on this invention. It is a flowchart which shows the operation | movement of level adjustment at the time of the carrier wave fall of the modem which concerns on this invention. It is a waveform adjusted by a carrier level adjustment processing unit in a conventional DSP modem, (a) is a diagram showing a rising waveform, (b) is a diagram showing a falling waveform, and (c) is a waveform envelope. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Terminal device, 2 Modem, 3 Modulation process part, 4 Carrier-wave level preparation part, 5 Transmission filter process part, 6 DSP modem, 7 Line transformer, 8 2-wire type line, 9 Reception filter process part, 10 AGC process part, 11 Demodulation processor

Claims (3)

A modulation processing unit that transmits or stops a carrier wave based on a transmission request signal and modulates the carrier wave based on a transmission data signal;
A carrier wave level adjustment processing unit that inputs a modulation signal output from the modulation processing unit and adjusts rising and falling characteristics of the carrier wave when the carrier wave is transmitted and stopped; and
A transmission filter processing unit for removing unnecessary signals included in the output signal from the carrier wave level adjustment processing unit;
A reception filter processing unit for removing unnecessary signals included in the reception signal;
An AGC processing unit that adjusts the received signal level output from the reception filter processing unit to a predetermined level;
A demodulation processing unit that demodulates the carrier wave output from the AGC processing unit and reproduces a digital signal,
The carrier level adjustment processing unit adjusts the level so that an increase value of the carrier level per unit time gradually increases with time at the rising edge of the carrier wave, and a decrease value per unit time of the carrier level at the falling edge of the carrier wave. A modem characterized in that the level is adjusted to gradually decrease with time. The carrier level adjustment processing unit sets the carrier level Vr when the carrier is transmitted by the transmission request signal, the output level when the carrier level is not adjusted to E, and the carrier level Vr to a predetermined time. When the number of processes to be adjusted is M and the reciprocal 1 / M of the number of processes M is A, A is obtained as Vr = E × (A × M) ² while changing M from 0 to M. The modem according to claim 1. The carrier level adjustment processing unit sets the carrier level Vf when the carrier is stopped by the transmission request signal, the output level when the carrier level is not adjusted to E, and the carrier level Vf to a predetermined time. Assuming that the number of processes to be adjusted is M and the reciprocal 1 / M of the number M is A, Vf = E × [1− (A × M) ² ] while changing the M from 0 to M 3. The modem according to claim 1, wherein the modem is obtained.

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