JPH0648789B2 - Demodulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a demodulator in a digital carrier transmission system, and more particularly to a demodulator including an IF type transversal equalizer and a digital type transversal equalizer. Regarding

[Prior Art] In a conventional demodulation device, in order to overcome multipath fading of a propagation path in a digital carrier transmission system,
An IF type transversal equalizer was used.

FIG. 2 is a block diagram of a conventional demodulation device using an IF type transversal equalizer.

In the figure, 1 is an IF type analog transversal filter, 2 is a control signal generating circuit, 3 and 4 are multipliers, 5 is a π / 2 phase shifter, 6 and 7 are low-pass filters, and 8 and 9 are. amplifier,
Reference numerals 10 and 11 are A / D converters, 15 is a carrier control signal generation circuit, 16 is a voltage controlled oscillator, and 17 and 18 are control signal generation circuits which serve both as an automatic gain control circuit and an automatic drift control circuit.

In the demodulator having the above-mentioned configuration, 1 is input to the modulation that has been subjected to waveform distortion due to multipath fading or the like, and outputs are obtained from the A / D converters 10 and 11.

At this time, the output signals r ₁ and r _{2 of} the A / D converters 10 and 11
Controls the control signal generating circuit 2, and controls the transversal filter 1 in a negative feedback manner by the output signal r ₃ . Then, after obtaining the modulated wave m from which the waveform distortion is removed, the carrier waves T ₄ and T ₅ having a phase difference of π / 2 from each other and the modulated wave m are synchronously detected by the multipliers 3 and 4, and the baseband is obtained. The signals n ₁ and n ₂ are obtained.

The baseband signals n ₁ and n ₂ are low-pass filters 6 and 7, respectively.
After being waveform-shaped by, it is input to the amplifiers 8 and 9. The amplifiers 8 and 9 are automatically controlled in gain and DC drift by the control signals s _{5 to} s ₈ generated by the control signal generation circuits 17 and 18 which also function as an automatic gain control circuit and an automatic drift control circuit. Circuit 17, 1
8 is controlled by the output signals s _{1 to} s ₄ of the A / D converters 10 and 11. As a result, the A / D converter 10,
At the input of 11, the baseband signals g ₁ and g ₂ are such that a correct determination is always made.

On the other hand, the output signals T ₁ and T of the A / D converters 10 and 11
₂ is input to the carrier wave control signal generation circuit (CARR) 15 and becomes the carrier phase control signal T ₃ . The control signal T ₃ is input to the voltage controlled oscillator (VCO) 16 to control the carrier oscillation frequency, and the reproduction carrier is synchronized with the input signal under normal conditions.

By the way, in recent years, in order to increase frequency utilization efficiency and enable highly efficient information transmission, multi-valued quadrature amplitude modulation such as 256QAM has been attempted. Therefore, in order to realize such a system, it is an important issue to improve the accuracy of the technique for overcoming the multipath fading occurring in the propagation path more than ever before.

However, since the IF-type transversal equalizer in the demodulator described above is composed of analog circuits, there are problems such as delay line frequency characteristics, distortion due to analog multipliers, and noise addition, and there are also a few adjustment points. It was difficult to achieve high precision in 10 places.

Therefore, recently, all-digitalization has been proposed as a means of achieving higher accuracy (the 1986 National Conference of the Institute of Electronics and Communication Engineers 419 "Configuration and characteristics of digitizing transversal equalizer").

FIG. 3 is a block diagram of a demodulator using such a digital transversal equalizer.

In the figure, 12 and 14 are digital type transversal equalizers, and 13 is a control signal generating circuit.

In the demodulator having the above configuration, first, the carriers d ₂ and d ₃ having a phase difference of π / 2 with each other and the modulated wave input μ having waveform distortion are synchronously detected by the multipliers 3 and 4, and the bases are detected. Band signals n ₁ and n ₂ are obtained. Then, the baseband signals n ₁ and n ₂ are waveform-shaped by the low-pass filters 6 and 7 and then input to the amplifiers 8 and 9. Here, the gain and the DC drift in the amplifiers 8 and 9 are automatically controlled by the control signals b _{1 to} b _{4 of} the control signal generation circuit 13 that also functions as the carrier wave control signal generation circuit, the automatic gain control circuit, and the automatic drift control circuit. ing. Further, the control signal generating circuit 13 includes a digital transversal equalizer 12, 1
4 is controlled by the force signals a ₁ and a ₂ , but the digital transversal equalizers 12 and 14 here are used.
Is the signal y identified by the A / D converters 10, 11.
_The waveform distortion is equalized by logically operating ₁ and y ₂ .

By going through such a loop, the A / D converters 10, 1
With the input of ₁ , the baseband signals x ₁ and x ₂ are such that a correct determination is always made. The control signal d ₁ is input to the voltage controlled oscillator (VCO) 16 to control the carrier oscillation frequency, and the reproduction carrier is synchronized with the input signal under normal conditions.

However, a demodulator using such a digital transversal equalizer also has the following two drawbacks.

First, the carrier recovery circuit produces a control signal from the output of the digital transversal equalizer, which causes a delay of several tens of bits in the circuit.

Secondly, since the signal before the waveform distortion is equalized is used as the input signal for A / D conversion, if a normal level diagram is used, a large amplitude portion of the signal is likely to be interfered with and out of range, This is a drawback of causing non-linear distortion.

Therefore, conventionally, in order to make up for these drawbacks, the loop band of the carrier recovery circuit is narrowed for the first drawback, and the analog input of the A / D converter for the second drawback. This has been dealt with by compressing the signal to expand the identification range equivalently and providing a post-processing circuit in the final stage to obtain the original signal from the output signal of the digital transversal equalizer.

[Problems to be Solved] The above-described conventional demodulator has a problem that a sufficient loop band of the carrier recovery circuit cannot be obtained and that the S / N is deteriorated by compressing the analog input signal.

The present invention has been made in view of the above problems. It is possible to obtain a sufficient loop band in a carrier recovery circuit, and demodulation that can be identified by a normal level diagram in an A / D converter. The purpose is to provide a device.

[Means for Solving the Problems] In order to achieve the above object, the demodulation device of the present invention includes an IF type analog transversal equalizer for compensating waveform distortion to the extent that carrier synchronization can be sufficiently performed, and a carrier reproducing for reproducing a carrier. Means, a multiplication means for obtaining a baseband signal by synchronously detecting an output of the IF type analog transversal equalization means with a carrier wave reproduced by the carrier wave reproduction means, and a waveform of the baseband signal output from the multiplication means. After the shaping, the amplifying means for amplifying, the A / D conversion identifying means for identifying the output of the amplifying means by A / D conversion, and the output signal of the A / D conversion identifying means are equalized to obtain the IF type. Digital transversal equalizer for compensating waveform distortion that could not be compensated by analog transversal equalizer, and control of gain and drift of the amplifier Automatic gain drift control means for controlling the automatic gain drift control means by the output signal of the digital transversal equalization means, and the carrier recovery means for the output signal of the A / D conversion identification means. It is configured to be controlled by.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a demodulation device according to an embodiment of the present invention. The parts common to or corresponding to the conventional example are denoted by the same reference numerals.

In the demodulator having the configuration shown in the figure, an input modulation signal a, which has undergone waveform distortion due to multipath fading in the propagation path, becomes a modulated wave b from which the waveform distortion has been removed via the IF type analog transversal filter 1. here,
The IF type analog transversal filter 1 has a capability of inputting input levels of A / D converters 10 and 11 described later in a normal dynamic range and capable of compensating for waveform distortion to the extent that carrier synchronization can be sufficiently performed. All you have to do is do it. The transversal filter 1 is controlled by the output control signal k ₃ of the control signal generation circuit 2,
Further, the control signal generation circuit 2 is provided with the A / D converter 1
It is controlled by the output signals k ₁ and k _{2 of} 0 and 11.

Next, a carrier wave j having a phase difference of π / 2 from each other
_{4, j 5} and after obtaining a baseband signal _c 1, _{c 2} by synchronous detection of the modulation wave b in a multiplier 3,4, the baseband signal _c 1, _{c 2} a low-pass wave filter 6 , 7 and the waveform is shaped and input to the amplifiers 8 and 9. The gain and DC drift in the amplifiers 8 and 9 are automatically controlled by the control signals i _{1 to} i ₄ generated by the control signal generation circuit 13. In addition, the control signal generation circuit 13 includes the A / D converters 10 and 11
Controlled by the output signals k ₁ and k _{2 of} the digital transversal equalizers 12 and 14 that equalize the waveform distortion by logically operating the signals f ₁ and f ₂ identified in step ₁ .

As a result, at the inputs of the A / D converters 10 and 11, the baseband signals e ₁ and e ₂ having normal levels are provided so that a correct determination is always made.

In addition, digital type transversal equalizers 12, 14
Compensates for waveform distortion (intersymbol interference due to fading or the like) that cannot be compensated for by the IF type analog transversal filter 1 described above.

On the other hand, the carrier recovery circuit is different from the demodulator using the conventional digital transversal equalizer. That is, first, the output signals j ₁ , j of the A / D converters 10, 11 are
₂ is input to the carrier control signal generation circuit (CARR) 15 to obtain the carrier phase control signal j _3, and the voltage controlled oscillator (VCO) 16 is controlled by the control signal j ₃ to reproduce the carrier synchronized with the input signal. ing.

As described above, in this embodiment, the IF type transversal equalizer is placed at the first stage of the demodulation device using the conventional digital type transversal equalizer.

As a result, the input signal of the A / D converter becomes a signal from which waveform distortion has been removed due to fading, etc., and there is no need to compress the analog input signal, which is the second problem described above. A signal can be input.

Further, since the waveform distortion is removed from the input signal of the A / D converter, the control signal of the carrier recovery circuit can be generated from the output signal of the A / D converter. Therefore, it is not necessary to make the loop band in consideration of the bit delay, which is the first problem described above, and it is possible to make the loop band of a necessary and sufficient width.

The equalization capability of the IF-type transversal equalizer placed in the first stage may be such that the input of the A / D converter does not fall outside the discrimination range and nonlinear distortion occurs. Therefore, this IF type transversal equalizer may be of a small scale. For this reason, the digital transversal equalizer, which does not need to take the bit delay into consideration, can increase the number of taps in order to increase the equalization capability.

On the other hand, the IF type analog transversal filter has a small equalization capability and is not sufficient as a capability for compensating for intersymbol interference due to fading or the like. On the other hand, since the digital transversal equalizer can be integrated into an LSI, the circuit scale can be reduced and a sufficient equalization capability can be realized. The circuit scale for realizing this with an IF type analog transversal equalizer becomes large and the cost also increases. That is, the digital transversal equalizer in the demodulator can perform waveform distortion compensation, which would be a large-scale circuit and costly if the IF-type analog transversal equalizer is used, in a small-scale circuit and at low cost. I am trying.

[Effects of the Invention] As described above, the present invention has the following features by placing the IF type transversal equalizer in the first stage of the demodulator using the conventional digital type transversal equalizer. It is possible to provide a demodulating device.

The input signal of the A / D converter used as the discriminator is a signal from which waveform distortion due to fading or the like is removed, and an analog signal based on a normal level diagram can be input.

Since the output signal of the A / D converter is also a signal from which waveform distortion has been removed to some extent, the output signal can be used in the carrier recovery circuit, and it is not necessary to form a loop band in consideration of bit delay. A loop band of sufficient width can be obtained.

Further, since the present invention does not need to take the bit delay into consideration, it is possible to increase the number of taps of the digital transversal equalizer in order to increase the equalization capability of the digital transversal equalizer. There is also an effect.

[Brief description of drawings]

1 is a block diagram of a demodulator according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional demodulator using an IF type transversal equalizer, and FIG. 3 is a digital type transversal equalizer. FIG. 10 is a block diagram of a conventional demodulation device using a power supply. 1: IF type analog transversal filter 2: Control signal generation circuit 3, 4: Multiplier 5: π / 2 phaser 6, 7: Low-pass filter 8, 9: Amplifier 10, 11: A / D converter 12, 14: Digital type transversal equalizer 13: Control signal generation circuit 15: Carrier control signal generation circuit 16: Voltage controlled oscillator

Claims (1)

[Claims] 1. An IF type analog transversal equalizing means for compensating for waveform distortion to the extent that carrier synchronization can be sufficiently performed, a carrier wave reproducing means for reproducing a carrier wave, and an output of the IF type analog transversal equalizing means. The multiplication means for obtaining a baseband signal by synchronously detecting the carrier wave reproduced by the carrier wave reproduction means, the amplification means for waveform-shaping the baseband signal which is the output of the multiplication means, and the amplification means, and the output of this amplification means. A / D conversion identification means for A / D conversion and identification, and an output signal of the A / D conversion identification means are equalized, and the above I
The F-type analog transversal equalizer comprises a digital transversal equalizer for compensating for waveform distortion that could not be compensated, and an automatic gain drift controller for controlling the gain and drift of the amplifier. A demodulator characterized in that the drift control means is controlled by an output signal of the digital type transversal equalization means, and the carrier recovery means is controlled by an output signal of the A / D conversion identifying means.