JPH0659045B2 - Common modem circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention converts a time division multiplex signal into a frequency division multiplex signal, modulates the signal with a common digital modulation circuit, and transmits the frequency division multiplex signal. The present invention relates to a common modulation / demodulation circuit that restores a time-division signal and then demodulates with a common digital demodulation circuit.

[Technical background of the invention and its problems]

A transmultiplexer is known as a device that performs mutual conversion between a frequency division multiplexed signal (FDM signal) and a time division multiplexed signal (TDM signal). The transmultiplexer has been conventionally used for a voice signal in a telephone line, but due to the recent progress of digital technology, its application to a data transmission channel has been considered.
If a digital transmultiplexer is applied to the data transmission channel, modulation can be performed using the digital modulation circuit common to all channels on the transmission side, and the digital demodulation circuit common to all channels can be used on the reception side. Since it is possible to demodulate,
Effective reduction of hardware scale can be achieved.

Due to its nature, the transmultiplexer having a digital circuit configuration used for such a data transmission channel needs to operate at an integer multiple of the frequency interval between channels of the FDM signal that constitutes the transmission signal. A digital demodulation circuit that extracts timing information and reproduces the original data needs to operate at a clock frequency that is an integral multiple of the data rate.

Generally, there is no special relationship between the data rate and the frequency bandwidth per channel of the FDM signal. For this reason,
Conventionally, it is practically difficult to use a common modulation / demodulation circuit using such a digital transformer multiplexer in the above data transmission channel, and its application is F
There has been a problem that the frequency bandwidth per channel of the DM signal is limited to a very special case where the frequency bandwidth is an integral multiple of the data rate.

[Object of the Invention]

The object of the present invention can be applied to a data transmission channel having no special relation such that the data rate and the frequency bandwidth per channel of the frequency-multiplexed signal forming the transmission signal are integral multiples. It is to provide a common modulation / demodulation circuit using a digital transformer multiplexer.

[Outline of Invention]

The present invention is provided between a first digital transmultiplexer for converting a time division multiplexed signal on a transmitting side into a frequency multiplexed signal and a digital modulation circuit for modulating the frequency multiplexed signal from the first digital transmultiplexer, and for receiving. Sampling on at least one of a second digital transmultiplexer for converting the received frequency-division-multiplexed signal into a time-division-multiplexed signal and a digital demodulation circuit for demodulating the time-division-multiplexed signal from the second digital transmultiplexer. It is characterized in that a conversion circuit for converting the frequency is inserted.

The conversion circuit inserted between the first digital transformer multiplexer for converting the time division multiplexed signal into the frequency multiplexed signal and the digital modulation circuit is one channel of the frequency multiplexed signal for transmitting the time division multiplexed signal from the digital modulation circuit. The sampling frequency is converted into a sampling frequency that is an integral multiple of the per-frequency band width and is supplied to the first digital transmultiplexer. Further, the conversion circuit inserted between the second digital transmultiplexer and the digital demodulation circuit converts the frequency multiplexed signal from the first digital transmultiplexer into a sampling frequency which is an integral multiple of the data rate of this frequency multiplexed signal. And supplies it to the digital demodulation circuit. Such a conversion circuit can be realized by, for example, an interpolation orthogonalization filter provided between a digital transmultiplexer including a reduction or bandpass filter operating at a predetermined clock and a digital demodulation circuit.

〔The invention's effect〕

According to the present invention, by inserting the conversion circuit for converting the sampling frequency as described above, between the digital modulation circuit and the first digital transmultiplexer on the transmission side or the second digital transmultiplexer on the reception side. Since it can be matched with the digital demodulation circuit, the digital transmultiplexer is used even when the frequency bandwidth per channel of the frequency-multiplexed signal forming the transmission signal and the data rate are other than integer multiples. By applying the common modulation / demodulation circuit described above, the hardware can be reduced, and the practical effect is extremely large.

Example of Invention

FIG. 1 shows an embodiment in which the present invention is applied to the transmission side of a data transmission system using a common modulation / demodulation circuit, that is, a common demodulation circuit, and FIG. 2 shows a frequency spectrum showing the operation of the circuit of FIG. It is a figure.

In FIG. 1, the input terminal 1 has a frequency bandwidth of, for example, 25 KHz of 8 kHz as shown in FIG. 2 (a).
An FDM signal obtained by frequency-multiplexing a channel data signal (data rate is 16 kbit / s) at 25 KHz intervals is input. This FDM signal is sampled by the A / D converter 2 at 400 KHz, for example, and converted into a digital signal. The FDM signal converted into a digital signal is input to the digital transformer multiplexer 3, and the time division multiplexed signal (TDM signal) as shown in FIG.
Is converted to.

The digital transformer multiplexer 3 receives the input FD
A circuit that separates the M signal into channels and further converts it into a baseband signal, and then extracts the signal of each channel as a TDM signal by sampling at, for example, 50 KHz. Volume "Applications of Digital Signal Processing" p.121-p134, Showa 5
Published May 20, 1994, in detail. That is, as shown in FIG. 2 (a), the input signals of the transmultiplexer 3 are the signals of 8 channels of ch # 0 to ch # 7 arranged on the frequency axis, and each channel ch #
The signal i (i = 0, 1, 2, ... 7) appears as a signal having a spectrum as shown in FIG. 2 (b) at the output of the digital transformer multiplexer 3. In FIG. 2B, the spectrum of the channel ch # i repeatedly appears at intervals of 50 KHz because the signal of each channel is output as a signal having a sampling frequency of 50 KHz.

The output signal of the digital transformer multiplexer 3 is input to the interpolation orthogonalization filter 4, and the interpolation orthogonalization filter 4 extracts only the signal component of 0 to 25 KHz as shown in FIG. And further orthogonalization is performed. That is, as shown in FIG. 2D, an integral multiple of the data rate (16 kbit / s), for example, 2
It is converted into a signal with a frequency of 32 KHz, which is doubled, and taken out. The interpolation orthogonalization filter 4 is specifically realized by a reduction filter or a bandpass filter that operates with a clock having a frequency of 800 KHz per channel. in this case,
Since the output signal from the digital transmultiplexer 3 is actually an 8-channel FDM signal, the interpolation orthogonalization filter 4 also processes these signals by time division multiplexing,
It operates at 00 KHz x 8 (ch) = 6.4 MHz, but functionally it is 80 for each signal of each channel ch # i.
Equivalent to processing a reduction or bandpass filter operating at 0 KHz. Then, the output signal of the interpolation orthogonalization filter 4 is guided to the demodulation circuit 5, where the original data signals of a plurality of channels are demodulated and reproduced.

FIG. 3 shows a specific example of the interpolation orthogonalization filter 4,
It is composed of a transversal filter. The input is, for example, a 50 KHz TDM signal X, which is input from the terminal 11 to the M-stage shift register 13 via the switch 12. The output of each stage of the shift register 13 is a coefficient ROM
After being multiplied by a predetermined coefficient by 14, it is added by an adder 15 and is taken out to an output terminal 17 via a switch 16 as a TDM signal y of 32 KHz which is twice the data rate. In this example, the switches 12 and 16 divide the clock signal ω of 800 KHz by the 1/16 frequency divider 18 and the 1/25 frequency divider 19 to obtain 50 KHz and 32 K, respectively.
Each operates by the signal of Hz. Shift register 1
4 is 800KH which is the least common multiple of 50KHz and 32KHz
It is shifted by the signal ω of z, but the input TDM signal X
Is 50 KHz, so M / (800/50) = M of M stages
The data exists only in the / 16th stage, and is O in the other stages.

In the above-described embodiment, the output signal of the digital transmultiplexer 3 is the signal of each channel output from the same output terminal, and the interpolation orthogonalization filter 4 also performs time division processing. The output signal may be output from different output terminals for each channel, and a plurality of interpolation orthogonalization filters may be placed in parallel corresponding to the channels.

FIG. 4 shows another embodiment of the present invention, which is an example in which the present invention is applied to a transmitting side, that is, a common modulation / demodulation circuit.

In FIG. 4, a time division multiplexed signal (T
A data signal of, for example, 8 channels that constitutes a DM signal) is input. This TDM signal is sent to the digital modulation circuit 22.
Is modulated by digital processing in, for example, PSK
Become a signal. For example, when the data rate is 16 kbit / s, the digital conversion circuit 22 operates at 32 KHz, which is twice the frequency of the data rate. The output signal from the digital conversion circuit 22 having a sampling frequency of 32 KHz is converted into a sampling frequency of, for example, 50 KHz by the interpolation filter 23. The interpolation filter 23 is, for example, a reduction filter or a bandpass filter that operates at a clock of 800 KHz, and its output signal is guided to the digital transformer multiplexer 24. The digital transmultiplexer 24 converts the TDM signal into the FDM signal, contrary to the previous embodiment. In this case, the output signal of the digital transmultiplexer 14 is an FDM signal having a bandwidth per channel of 25 KHz and 8 channels, which is converted into an analog signal by the D / A converter 25 and sent to the output terminal 26. In this way, by using a sampling frequency conversion circuit, for example, an interpolation filter also in the common modulation circuit, the TDM signal is converted from the TDM signal when the data rate of the original data signal and the frequency interval between channels of the FDM signal are different. It becomes possible to convert to an FDM signal.

In the embodiment shown in FIG. 4, the output signal of the digital conversion circuit 22 is the signal of each channel output from the same output terminal, and the interpolation filter also performs time division processing. Therefore, the signals of the respective channels may be output from different output terminals, and a plurality of interpolation filters may be provided corresponding to the channels.

The present invention can be variously modified without departing from the scope of the invention. For example, the characteristics of the interpolation filter do not necessarily have to be the same for each channel, and may be different for each channel. Further, although the interpolation filter is exemplified as the sampling frequency conversion circuit, it can be realized by other configurations such as using a memory and converting the sampling frequency by changing the writing and reading frequencies.

[Brief description of drawings]

FIG. 1 is a block diagram of the receiving side of a data transmission system according to an embodiment of the present invention, FIG. 2 is a frequency spectrum diagram of each signal for explaining the operation of the embodiment, and FIG. 3 is an interpolation filter. FIG. 4 is a block diagram of the transmitting side of a data transmission system according to another embodiment of the present invention. 1 ... FDM signal input terminal, 2 ... A / D converter, 3 ...
... Digital transformer multiplexer, 4 ... Interpolation filter (sampling frequency conversion circuit), 5 ... Digital demodulation circuit, 6 ... Demodulation data output terminal, 11 ... 50
KHz sampling TDM signal input terminal, 12, 16 ...
Switch, 13 ... Shift register, 14 ... Coefficient RO
M, 15 ... Adder, 17 ... 32KHz sampling T
DM signal output terminal, 18 …… 1/16 frequency divider, 19 …… 1
/ 25 frequency divider, 21 ... TDM signal input terminal, 22 ... digital modulation circuit, 23 ... interpolation filter (sampling frequency conversion circuit), 24 ... digital transmultiplexer, 25 ... D / A converter, 26 ... FDM signal output terminal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Nakamura 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research Institute, Inc. (72) Inventor Hideo Suzuki Komukai-Toshiba, Kawasaki-shi, Kanagawa No. 1 Incorporated company Toshiba Research Institute

Claims (2)

[Claims] 1. A first digital transmultiplexer for converting a time division multiplexed signal into a frequency multiplexed signal, a digital modulation circuit for modulating the frequency multiplexed signal from the first digital transmultiplexer, and a digital modulation circuit from the digital modulation circuit. A means for transmitting a signal, a second digital transmultiplexer for converting the received frequency-multiplexed signal into a time-division multiplexed signal, and a digital demodulation circuit for demodulating the time-division multiplexed signal from the second digital transmultiplexer. In the common modulation / demodulation circuit, a conversion circuit for converting a sampling frequency is inserted between at least one of the digital modulation circuit and the first digital transmultiplexer and between the second digital transmultiplexer and the digital demodulation circuit. That Common modulation and demodulation circuit to butterflies. 2. The conversion circuit is an interpolation orthogonalization filter provided between a digital transformer multiplexer and a digital demodulation circuit.
A common modulation / demodulation circuit according to the item.