JPH021676A - Multiplex radio device with multilevel orthogonal amplitude modulation - Google Patents

Abstract

PURPOSE:To prevent the error rate of a demodulated digital signal from being deteriorated by adding a transmitting side AGC amplifier and an amplitude compensating means to send a difference output from the output of the amplifier to a transmitting side. CONSTITUTION:A transmitting side is provided with the amplitude compensating means 5 for compensating the amplitude compressed portion of a receiving side AGC amplifier 31. The output of a modulator 1 is divided into a first and a second parts, and the first part is amplified by an amplifier 51. The second part is amplified by the transmitting side AGC amplifier 52 which has the same time constant as the amplifier 31 and is set so as to send the output level of 1/n of the output level of the amplifier 51. Then, the difference output between the outputs of the amplifier 52 and the amplifier 51 is taken. Since an amplitude portion corresponding to the amplitude compressed portion in the amplifier 31 is added extra to the difference output, a correct QAM modulated wave is obtained at the output side of the amplifier 31. Thus, even it the follow-up speed of the amplifier 31 is made fast, the error rate of the demodulated digital signal is not deteriorated.

Description

[Detailed Description of the Invention] [Summary] For example, regarding a multilevel quadrature amplitude modulation multiplexing radio device used for a branch line from a long-distance trunk line, especially a narrowband multilevel quadrature amplitude modulation multiplexing radio device, the receiving side automatic gain In order to prevent the error rate of the demodulated digital signal from deteriorating even if the tracking speed of the control amplifier is increased, the transmitting side is equipped with a modulator that performs multilevel orthogonal amplitude modulation of the carrier wave using the input digital signal, and a modulator that modulates the carrier wave with the input digital signal. A transmitting section that converts the output of the modulator to a predetermined frequency and power and outputs it, and a receiving side that converts the received signal to a predetermined frequency and then compresses the amplitude change of the received signal with an automatic gain control amplifier on the receiving side. a receiving section to
In the multilevel orthogonal amplitude modulation multiplexing radio apparatus having a demodulating section that demodulates the output of the receiving section, the output of the modulator is transmitted to the first .
a second portion, amplifying the first portion with an amplifier;
The second portion is amplified by a transmitting automatic gain control amplifier that has the same time constant as the receiving automatic gain control amplifier and is set to output an output level that is 1/n of the output level of the amplifier. , an amplitude compensating means for sending out a difference output between the output of the automatic gain control amplifier on the transmitting side and the output of the amplifier is added to the transmitting side.

For example, the present invention relates to a multilevel orthogonal amplitude modulation multiplexing radio device used for a branch line from a long-distance trunk line, and particularly to a narrowband multilevel quadrature amplitude modulation multiplexing radio device.

Generally, when the state of the space in which radio waves propagate changes, the reception level fluctuates and line quality deteriorates.

Therefore, an automatic gain control circuit (hereinafter abbreviated as an AGC circuit) is installed on the receiving side of a wireless device to compress fluctuations in the receiving input level, but a multilevel quadrature amplitude modulation method (hereinafter referred to as an AGC circuit)
When information is also added to the amplitude component of the modulated signal, such as in a multi-level QAM system (abbreviated as multilevel QAM system), even if the tracking speed of the AGC amplifier on the receiving side is increased.

It is necessary to prevent the error rate of the demodulated digital signal from deteriorating.

[Conventional technology]

FIG. 4 shows a conventional process diagram.

First, the modulator 1 on the transmitting side generates a multilevel QAM wave from an internally generated carrier wave (for example, 70 MHz) and input digital signals of multiple series, and sends this to the transmitter 2.

In the transmitting section 2, the multilevel QAM wave inputted by the amplifier 21 is amplified to a predetermined level, and then the frequency converter 22 amplifies the input multilevel QAM wave to the oscillator 2.
Mixed with the output of 3, for example 2
'l wave, amplified to a predetermined level by the power amplifier 24, and sent to the receiving side.

Next, on the receiving side, after being amplified by the low-noise amplifier 31 in the receiving section 3, it is converted into a 7QMHz multilevel QAM wave by the first frequency converter 32 using the output of the oscillator 33. Frequency amplifier 34. A reception-side AGC amplifier 35 compresses fluctuations in the reception input level and amplitude changes in the modulated signal. Then, a demodulator 4 extracts a digital signal.

[Problem to be solved by the invention]

As mentioned above, the receiving side AGC amplifier 35 has the function of compressing fluctuations in the receiving input level and amplitude changes in the modulated signal, so when the amplitude component also carries information like a multilevel QAM wave, This amplitude change is compressed and the error rate deteriorates.

In particular, in the case of the narrowband QAM method used for branch lines from long-distance trunk lines, the influence of compression becomes large because the frequency components of digital signals are low.

Therefore, in order to reduce this effect, the time constant τ of the receiving side AGC amplifier 35 is increased (and the tracking speed is slowed down). There was a problem in that the line was disconnected, leading to a decrease in line reliability.

In the present invention, even if the tracking speed of the receiving side AGC amplifier is increased,
The purpose is to prevent the error rate of the demodulated digital signal from deteriorating.

[Means to solve problems]

FIG. 1 shows a block diagram of the principle of the present invention.

In the figure, 1 is a modulator that performs multilevel orthogonal amplitude modulation of a carrier wave using an input digital signal, 2 is a transmitter that converts the output of the modulator into a predetermined frequency and power, and outputs the received signal. After converting the received signal to a predetermined frequency, the reception side AGC amplifier compresses the amplitude change of the received signal.

Further, 4 is a demodulating section that demodulates the output of the receiving section, and 5 is a demodulating section that demodulates the output of the modulator. Distribute into the second portion.

The first part is amplified by an amplifier 51, and the second part is set to have the same time constant as the receiving AGC amplifier and output an output level that is 1/n of the output level of the amplifier. The transmitting side AGC amplifier 52 amplifies the transmitting side AGC amplifier 52.
This is an amplitude compensation means for sending out a difference output between the output of the amplifier 52 and the output of the amplifier 51.

[Effect]

The present invention deals with changes in the amplitude of the signal input to the receiving section.

This is a combination of changes caused by spatial propagation and changes due to modulation content, and cannot be separated. However, on the transmitting side, there are no changes caused by spatial propagation, but only changes due to the modulation content.

Therefore, an amplitude compensating means 5 is provided on the transmitting side to compensate for the amplitude compression of the AGC amplifier on the receiving side.

That is, the output of the modulator 1 is set to the first . The first portion is amplified by an amplifier 51. The second part has the same time constant τ as the receiving side AGC amplifier 31, and the amplifier 5
It is amplified by the transmission side AGC amplifier 52 which is set to send out an output level of 1/n of the output level of 1. and,
The difference output between the output of the transmitting side AGC amplifier 52 and the output of the amplifier 51 is obtained.

This difference output has an extra amplitude bone corresponding to the amplitude compression at the receiving side AGC amplifier, so the receiving side AGC amplifier
A correct QAM modulated wave is obtained at the output side of the C amplifier.

As a result, even if the tracking speed of the receiving side AGC amplifier is increased, the error rate of the demodulated digital signal does not deteriorate.

〔Example〕

FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of FIG. 2. Also, the symbols in Figure 3 indicate the waveforms of the parts with the same symbols in Figure 2, and the solid lines in Figure 3 - ○ and ■ are the waveforms in Figure 3 - ■, which are shown as a reference and the one-dot line indicates a waveform with compressed amplitude changes.

Here, the amplifier 51. Phase shifter 52. Transmission side AGC amplifier 53. The hybrids 54, 55 are components of the amplitude compensation means 5, and are variable attenuators 531. Amplifier 532. Operational amplifier 533. Detector 534. capacitor C1, resistor R,
is a component of the transmitting side AGC amplifier 53. Note that the same reference numerals indicate the same objects throughout the figures.

The operation of FIG. 2 will be described below with reference to FIG. 3, assuming that the ratio of the output level of the amplifier 51 to the output level of the transmitting side AGC amplifier 53 is 2:1, for example.

First, to set the output levels of the amplifier 51 and the transmitting side AGC amplifier 53, an unmodulated wave is added to the input side of the hybrid 54, and the unmodulated wave level is adjusted so that the former has a predetermined output level. After that, adjust the variable resistor Rv to
The output level of the C amplifier is set to 1/n.

Next, the multilevel QAM wave of, for example, 70 MHz as shown in FIG. The first part is amplified by an amplifier 51,
Added to Hybrid 55.

After the phase of the second part is reversed by 180 degrees by the phase shifter 52,
Variable attenuator 531. It is added to the hybrid 55 via an amplifier 532, but a portion is detected by a detector 534.
The detected voltage is applied to operational amplifier 533.

Therefore, the amount of attenuation of the variable attenuator 531 is controlled so that the detected voltage matches the reference voltage v0, and the rising and falling edges are compressed compared to the original waveform as shown by the dotted line in Figure 3-■. The amplitude change in the second portion is compressed by a delay equal to the time constant τ of the AGC amplifier.

Then, in the hybrid 55, the amplifier 51 and the transmitting side AGC
The difference in the output level of the amplifier 53 is taken, and an output is obtained as shown by the dotted line in FIG.

Here, this output level is 1 if there is no compression of amplitude changes.
should be output, but since it is compressed by the GC amplifier 53 to the transmitting side, the number of subtractions is reduced by that much, and an extra number than 1 is output. This extra part disappears when it is compressed by the AGC amplifier on the receiving side.

The correct original multilevel QAM wave is obtained and the demodulator (not shown)
added to.

That is, even if the tracking speed of the receiving AGC amplifier is increased, the error rate of the demodulated digital signal does not deteriorate.

〔Effect of the invention〕

As described in detail above, according to the present invention, even if the tracking speed of the receiving side AGC amplifier is increased, the error rate of the demodulated digital signal does not deteriorate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is an explanatory diagram of the operation of FIG. 2, and FIG. 4 is a block diagram of a conventional example. In the figure, (2) is a modulator, 2 is a transmitting section, 3 is a receiving section, 4 is a demodulator, and 5 is an amplitude compensation means. 2. The A-Dtsufu-no-ma of A-cho, the city of A-machi. 2. Figure 1000 3 Q

Claims (1)

[Claims] On the transmitting side, a modulator (1) that performs multilevel orthogonal amplitude modulation of a carrier wave using an input digital signal, and a transmitter (1) that converts the output of the modulator into a predetermined frequency and power and outputs the modulator (1). 2), on the receiving side, a receiving section (3) that converts the received signal to a predetermined frequency and then compresses the amplitude change of the received signal with a receiving side automatic gain control amplifier (31); and an output of the receiving section. In a multilevel orthogonal amplitude modulation multiplexing radio device having a demodulator (4) that demodulates the ), and the second part has the same time constant as the receiving automatic gain control amplifier (31), and has an output level of 1/n (n is a positive number) of the output level of the amplifier (51). A transmitting side automatic gain control amplifier (52) configured to transmit the amplitude is amplified by a transmitting side automatic gain control amplifier (52), and transmitting an amplitude compensation means (5) for transmitting a difference output between the output of the transmitting side automatic gain control amplifier and the output of the amplifier. A multilevel orthogonal amplitude modulation multiplexing radio device characterized by being added to the side.