JPH08321856A - Qam demodulation device - Google Patents

Abstract

PURPOSE: To enable to demodulate a modulation wave signal with simple configuration by storing the amplitude value of the high-order specifying one in the amplitude values per one frame and adjusting gain so as to permit difference between the average value or the integrated value of the amplitude value and the value to be judged as a max. amplitude at a demodulation side to be close to zero. CONSTITUTION: An amplitude value pick-up equipment 12 picks-up the amplitude value by receiving the output of a variable gain amplifier 11. When a QAM signal with a synchronizing symbol and a pilot symbol which are decided to be the max. amplitude during a prescribed period is received, a difference pick-up part 13 receives amplitude information from the amplitude value pick-up part 12 so as to store M- number of high-order amplitude value of the amplitudes per one frame. Then, the average value or the integrated value of the amplitude value is adopted. A signal for adjusting the gain of the amplifier 11 is generated so as to permit difference between the average value or the integrated value and the value to be judged as the max. value at the demodulation side to be close to zero. An integrater 14 integrates the signal of the difference pick-up equipment 13 and multiplies a time constant for stably operating the control system of an AGC circuit.

Description

Detailed Description of the Invention

[0001]

This invention relates to quadrature amplitude modulation (QA
The present invention relates to a QAM demodulator that demodulates a modulated wave signal according to M), and particularly to a QAM demodulator that can generate a synchronization symbol and a pilot symbol with a simple configuration and arithmetic processing.

[0002]

2. Description of the Related Art An MCA (Multi Channel Access) system is a system in which different users jointly use a plurality of channels and is widely used for business purposes. Further, in this MCA system, in addition to voice wireless communication, it is also used as various data communication.

The number of users in this MCA system has been increasing rapidly in recent years, and there is also a great demand for a system suitable for data transfer. Therefore, digital MC
The specifications of the A system were decided and put to practical use.

In such a system, multilevel QAM (Qu
adrature Amplitude Modulation) is used, for example, multi-valued quadrature amplitude modulation in which 4-valued amplitude modulation is performed by carrier signals having 90-degree different phases to have a 16-valued state.

Further, as a modulation method of a digital MCA system, RCR (Research & Development Center fo
The STD-32 digital MCA system defined as the standard of the Radio Systems: Development Center (Radio Systems Foundation) uses the M16QAM system and uses four subcarriers.

By the way, in wireless communication, the signal strength on the receiving side may change greatly due to changes in the propagation state, and automatic gain adjustment (automatic gain c) may occur in the processing of the received signal.
ontrol: AGC) is indispensable.

For example, the AGC circuit 1 for realizing AGC of a signal by frequency modulation or phase modulation is realized by a circuit as shown in FIG. That is, the variable gain amplifier 2 is processed after the integration result of the integrator 3 is processed by the low-pass filter 4 so that the integrated value of the output of the variable gain amplifier 2 becomes constant.
It was input to the gain control terminal of to adjust the gain. In this case, since the amplitude of the signal by frequency modulation or phase modulation is always constant, such processing can be realized.

By the way, since the QAM signal also has information on the amplitude value, the integrated value of the amplitude value is not always a stable value. Therefore, AGC cannot be realized by using the value obtained by integrating the amplitude value of the signal as shown in FIG.

Here, the multilevel QAM modulated signal can be expressed by the following equation. I (t) = Acosφ (t) Q (t) = Asinφ (t) That is, this multi-level QAM modulated signal is modulated so as to have information on the phase and the amplitude.

As described above, the AGC and the phase correction for the multi-level QAM modulated signal having information on the amplitude component are as shown in FIG.
It was general to carry out as follows using a circuit as shown in FIG.

First, the demodulation circuit 4 performs quadrature demodulation to separate the in-phase component I (T) and the quadrature component Q (T).
Then, the synchronization detector 5 detects a synchronization symbol from I (T) and Q (T), and the timing extractor 6 obtains the timing of the synchronization symbol from this synchronization symbol. Then, the phase / amplitude corrector 7 uses I (T) and Q using the amplitude value and the phase value of the synchronization symbol which are known in advance.
The amplitude correction (AGC) and the phase correction of (T) are performed.

In this case, the synchronization detector 5 has to perform the synchronization detection in a state where the amplitude value before the AGC is indefinite, which is a very difficult process. That is, the synchronization symbol is detected by utilizing the fact that it is defined by both the amplitude value and the phase angle, but the detection in the indefinite state depends on the hardware and processing of the processing circuit. There was a problem that complicated things were required in terms of algorithms.

That is, the synchronization detector 5 detects a synchronization symbol having a predetermined phase as follows. Here, assuming that the amplitude is A (T) and the phase is φ (T), tanφ (T) = (A (T) sinφ (t) / A (T) cosφ (t) = (Q (T) / I (T)).

Therefore, φ (T) = Arctan (Q (T) / I (T)).

Thus, regardless of the amplitude A (T), I
Φ (T) can be obtained from (T) and Q (T), and the process of detecting this phase φ (T) is performed by the phase detection unit 5a in FIG. Further, the phase φ (T) thus detected is compared with the phase of the sync symbol read from the phase table 5c by the phase comparator 5b, and the position of the sync symbol is detected.

[0016]

The synchronization detection process as described above has a problem that division is required to remove the amplitude value A (T). A circuit for realizing this division is generally complicated as compared with the processing such as integration. Furthermore,
Since the calculation of Arctan is required to obtain the phase φ (T), the processing is complicated. Also, a lot of processing time is required for processing such as table reference.

Further, in addition to the above-described phase synchronization detection,
Detection from the amplitude may also be performed incidentally. In this case, the sync detector 5 detects the sync symbol having the maximum amplitude value.
It is necessary to detect the amplitude value information for at least one frame and search the stored contents. Therefore, synchronization detection from this amplitude also has a problem that the circuit becomes large-scale.

Therefore, even when it is realized by a DSP, the arithmetic processing becomes troublesome and there is a problem that high-speed arithmetic is required.

The present invention has been made in view of the above points, and its purpose is to provide an accurate AGC with a simple configuration and calculation.
To realize a QAM demodulator capable of demodulating a modulated wave signal.

[0020]

The inventor of the present application has conducted earnest research to improve the disadvantage of the complexity of the arithmetic and processing circuit in AGC in the conventional QAM demodulator, and as a result,
The present invention has been completed by finding a new method for performing accurate AGC by paying attention to the amplitude of the synchronization symbol.

Therefore, the present invention, which is a means for solving the above-mentioned problems, is configured as described below.

That is, according to the present invention, which is a means for solving the problem, a frame constituted by an arbitrary number of consecutive symbols at a predetermined phase angle on a circle passing through a symbol of maximum amplitude in signal space coordinates. In a QAM demodulation device for demodulating a QAM signal including a synchronization symbol of 1 and a pilot symbol inserted in the middle of a frame for facilitating phase correction, a symbol timing reproduction signal almost synchronized with the symbol timing on the transmission side is used. , A reproducing circuit for reproducing a symbol signal composed of orthogonal components I (T) and Q (T), and M synchronization symbols and pilot symbols which are determined to have the maximum amplitude within a predetermined period. In this case, the upper M values of the amplitude value of the symbol signal within a predetermined period are extracted, and the extracted M values are extracted.
It is characterized in that it is provided with an AGC circuit for performing gain adjustment using the average value or integrated value of the amplitude values of the individual symbol signals.

[0023]

In the QAM demodulator which is a means for solving the problem, when receiving a QAM signal having a predetermined M number of synchronization symbols and pilot symbols which are determined to have the maximum amplitude within a predetermined period, Focusing on the upper M amplitude values of the amplitude value per frame, storing this,
The variable gain is adjusted so that the error between the average value or integrated value of the stored amplitude values and the value determined as the maximum amplitude on the demodulation side approaches zero.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a principle configuration of a main part of a QAM demodulator of the present invention, and FIG. 2 is a QAM of the present invention.
It is a block diagram which shows the whole structure of a demodulator. 1 and 2, the same parts are designated by the same reference numerals. In this embodiment, the case where the number of subcarriers is 4 will be described as an example.

First, the overall structure of the QAM demodulator and the outline of its operation and processing procedure will be described with reference to FIG. 2. After that, AGC, which is a characteristic part of the present invention, will be described with reference to FIG.

The QAM demodulator shown in FIG. 2 is roughly divided into a quadrature demodulator 8 for performing subcarrier separation and quadrature demodulation.
And a symbol extraction unit 9 for extracting symbol data,
It is divided into an AGC circuit 10 that performs AGC on the amplitude value, a phase correction unit 20 that performs phase correction, and a data demodulation unit 30 that performs data demodulation. The reproduction circuit is composed of a quadrature demodulation unit 8 and a symbol extraction unit 9. Hereinafter, description will be given separately for each part.

[Subcarrier Separation] In FIG. 2, the reception signal received by an antenna (not shown) and converted into an electric signal is frequency-converted into a modulated wave signal having an intermediate frequency fR ′, and the orthogonal demodulation unit 8 Is supplied to. And
In the quadrature modulation section 8, in-phase components (I signals: I1 (t), I2 (t), I3) are output as demodulated signals in the same number as the subcarriers.
(T), I4 (t)) and the orthogonal component (Q signal: Q1
(T), Q2 (t), Q3 (t), Q4 (t)) are obtained.

FIG. 3 is an explanatory view schematically showing the arrangement of the subcarriers, in which four subcarriers (Sub1 to Sub4) are arranged around the frequency f0 of the carrier. Here, the subcarriers are arranged at intervals of 4.5 kHz, and the center frequency of each tip is f0-6.75.
kHz, f0 -2.25 kHz, f0 +2.25 kHz
z, f0 +6.75 kHz.

In order to demodulate a modulated wave signal having such subcarriers, in a conventional general apparatus, the same number of subcarriers as four orthogonal demodulators are supplied. Each of the four quadrature demodulators has a frequency f of the intermediate frequency signal.
The frequency fL of the difference between R ′ and the frequency of the desired subcarrier
Quadrature signals (1) to fL (4)
A local oscillator signal from a local oscillator that produces signals (sin and cos components) is also provided. In this way, quadrature demodulation and subcarrier separation are performed.

However, in such a conventional general demodulation (subcarrier separation) system, the same number of local oscillators as the subcarriers are required to separate the subcarriers,
There is also a problem that the circuit configuration becomes complicated.

For this reason, the inventor of the present application has already proposed a method of separating subcarriers by a local oscillator smaller than the number of subcarriers as of April 21, 1995, and uses this technique. It is possible to

That is, in a QAM demodulator for quadrature demodulating a modulated wave signal using a plurality of subcarriers, first quadrature demodulation is performed on the modulated wave signal before separating the subcarriers to obtain an in-phase component and a quadrature component. For the in-phase component and the quadrature component for extracting the in-phase component, the second quadrature demodulation by the frequency of the difference between the center frequency of the modulated wave signal and the sub-carrier is performed to obtain the signal from the local oscillator whose number of sub-carriers is smaller than A quadrature demodulator using
An arithmetic processing circuit for arithmetically processing the result obtained by the second quadrature demodulation and an LPF for filtering the arithmetic processing result by the bandwidth of the subcarrier are provided, and the subcarrier separation and the target in-phase component are performed. The demodulation with the orthogonal component is performed.

By doing so, it becomes possible to separate the subcarriers with respect to the modulated wave signal using a plurality of subcarriers by the number of oscillators smaller than the number of subcarriers. From the above, the number of oscillators can be reduced, and the circuit configuration and scale can be reduced. It is also advantageous when processing with a DSP. Moreover, each frequency of the local oscillator used to separate the subcarriers is a simple integer ratio. This is because the frequency intervals of normal subcarriers are even. As a result, the original frequency used for frequency division and frequency multiplication can be shared. This point also works advantageously when processed by the DSP.

[Symbol Extraction] On the transmitting side, FIG.
As shown in, both the in-phase component I (T) and the quadrature component Q (T) of the orthogonal code are generated as signals having a plurality of stepwise levels. Here, four levels are shown. At the time when this is demodulated by the quadrature demodulator 8, FIG.
As shown in (b), the analog signal has a gentle slope. Therefore, the symbol extraction unit 9 performs symbol timing reproduction to reproduce the symbol clock (FIG. 4 (c)). Then, using the regenerated symbol clock, symbols are extracted from the orthogonal code of the analog signal (FIG. 4 (d)). In this way, the symbols are extracted and the orthogonal codes (I1 (T), I2 (T),
I3 (T), I4 (T), Q1 (T), Q2 (T), Q
3 (T) and Q4 (T)) are obtained.

[AGC] The AGC, which is a characteristic part of the present invention, will be described with reference to FIG.

A variable gain amplifier 11 for amplifying with a variable gain is arranged in the AGC circuit 10, and the gain is adjusted by a control signal to be described later supplied to a gain control terminal so that the AGC is realized. It has become. 2 shows only one of the signal processing systems for four subcarriers for the sake of explanation.
In a considerable overall circuit configuration, the number of processes equal to the number of subcarriers is performed.

First, the amplitude value extractor 12 receives the output signal of the variable gain amplifier 12 and extracts the amplitude value. In this case, the amplitude value is extracted by I ² (T) + Q ² (T) or (I
² (T) + Q ² (T)) ^1/2 .

Then, when receiving a QAM signal having M synchronization symbols and pilot symbols which are determined to have the maximum amplitude within a predetermined period, the error extraction unit 1
In 3, the amplitude information from the amplitude value extraction unit 12 is received and the upper M amplitude values of the amplitude value per frame are stored. Then, the average value or integrated value of the stored amplitude values is taken. A control signal for adjusting the gain of the variable gain amplifier 11 is generated so that the error between the average value or integrated value and the value determined as the maximum amplitude on the demodulation side approaches zero.

Further, the integrator 14 integrates the control signal generated by the error extractor 13 to multiply the time constant by which the control system of this AGC circuit operates stably.

Therefore, the variable gain amplifier 11 receives the control signal thus adjusted and adjusts the gain to generate the orthogonal code with the corrected amplitude value. That is, such processing is performed for each subcarrier to obtain an orthogonal code (I
1 (T), I2 (T), I3 (T), I4 (T), Q1
(T), Q2 (T), Q3 (T), Q4 (T)) are obtained.

According to such an AGC process, the process can be performed without going through the synchronization detection procedure which has been conventionally required, and moreover, the optimum amplitude correction can be performed on the QAM signal. Further, since the accurate amplitude correction is performed here, the subsequent synchronization detection and phase correction processing becomes easy.

[Phase Correction] The phase correction unit 20 corrects the phase of the orthogonal code whose amplitude is corrected by the AGC circuit 10.

Here, let the carrier angular frequency on the transmitter side be ω
c is the difference from the demodulation angular frequency on the receiver side, θ (t)
In this case, if the frequencies on the transmitter side and the receiver side are both stable, the above-mentioned θ (t) is proportional to the time t.

In the normal case, when the value of the nominal vector is known in advance, that is, the pilot symbols Ip, Q
This correction of θ (t) is performed when p is transmitted. In this case, in the conventional general phase correction unit, the phase difference between the data actually received in the pilot symbol period and the pilot symbol is obtained, and the correction (phase estimation) is performed based on the phase difference data. ing.

However, in order to make such a correction, the trigonometric function must always be calculated. For this, it is necessary to always perform series expansion or table reference.
There was a problem that the processing became complicated. Therefore, even when it is realized by a DSP, the calculation process becomes troublesome and high-speed calculation is required.

For this reason, the inventor of the present application has already obtained a fixed coefficient as of April 12, 1995,
We have proposed a method to perform phase correction according to this coefficient,
It is possible to use this technique.

That is, in the case of demodulating a multilevel QAM modulated signal in which pilot symbols Ip and Qp having predetermined predetermined phases and amplitudes are inserted, when the pilot symbols Ip and Qp of the multilevel QAM modulated signal are received. Sin β and cos β corresponding to the phase difference β between the pilot symbols Ip and Qp and the true values Io and Qo are obtained as phase difference coefficients having fixed values, and the phase difference coefficients sin β and c
It is possible to obtain true values Io and Qo by performing phase correction by integration and addition / subtraction using osβ and the in-phase component Ir and quadrature component Qr in each symbol of the received data. As a result, a simple calculation of addition and addition
It becomes possible to perform highly accurate phase correction.

Even if any of the above-mentioned methods is used for phase correction, since the amplitude has already been corrected, the configuration and processing contents of the processing circuit are simplified, and accurate phase correction can be performed. It will be possible.

[Data Demodulation] Then, the orthogonal code whose amplitude and phase are corrected as described above is demodulated by the data demodulator 30 according to a predetermined algorithm to obtain digital data of the bit stream output.

[Effect: Comparison with the conventional example] As described above, in the case of receiving a QAM signal having M synchronization symbols and pilot symbols which are determined to have the maximum amplitude within a predetermined period. In addition, the error extraction unit 13 receives the amplitude information from the amplitude value extraction unit 12, pays attention to the upper M amplitude values of the amplitude value per frame, stores them, and stores the stored amplitude values. The gain of the variable gain amplifier 11 is adjusted so that the error between the average value or integrated value and the value determined as the maximum amplitude on the demodulation side approaches zero.

As a result, the AGC process itself can be performed easily and appropriately. Further, since the synchronization detection can be performed in the state where the amplitude value is corrected by the AGC, the synchronization detection process becomes easy. Therefore, as compared with the conventional device, a simpler configuration can be used in terms of the hardware of the processing circuit and the processing algorithm.

[0053]

As described in detail above, according to the present invention,
When receiving a QAM signal in which the number of synchronization symbols and pilot symbols determined to have the maximum amplitude within a predetermined period is M, pay attention to the upper M amplitude values of the amplitude value in one frame. Then, this is stored, and the gain of the variable gain amplifier is adjusted so that the error between the average value or integrated value of the stored amplitude values and the value determined as the maximum amplitude on the demodulation side approaches 0. .

As a result, the AGC processing itself can be performed easily and accurately, and further, the synchronization detection can be performed with the amplitude value corrected by the AGC, and the synchronization detection processing can be facilitated. . Therefore, as compared with the conventional device, a simpler configuration can be used in terms of the hardware of the processing circuit and the processing algorithm. Therefore, it is an object to realize a QAM demodulation device capable of performing accurate AGC and demodulating a modulated wave signal with a simple configuration and calculation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a main part of a QAM demodulation device of the present invention.

FIG. 2 is a configuration diagram showing an overall configuration of a QAM demodulation device of the present invention.

FIG. 3 is an explanatory diagram showing an arrangement of four subcarriers.

FIG. 4 is an explanatory diagram showing a state of symbol extraction.

FIG. 5 is a configuration diagram showing a configuration of a conventional AGC circuit.

FIG. 6 is a configuration diagram showing a configuration of a circuit that executes conventional amplitude correction and AGC.

FIG. 7 is a configuration diagram showing a conventional phase detection circuit.

[Explanation of symbols]

 8 Quadrature demodulator 9 Symbol extractor 10 AGC circuit 20 Phase corrector 30 Data demodulator

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 7, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

Here, the multilevel QAM modulated signal can be expressed by the following equation. I (t) = A (t) cos φ (t) Q (t) = a (t) sin φ (t) That is, this multi-level QAM modulated signal is modulated so as to have information of phase and amplitude. ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 25, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

Here, the multilevel QAM modulated signal can be expressed by the following equation. I (t) = A (t) cosφ (t) Q (t) = A (t) sinφ (t) That is, this multi-level QAM modulated signal is modulated so as to have information on the phase and the amplitude.

Claims (1)

[Claims] 1. A synchronization symbol of a frame composed of an arbitrary number of consecutive symbols each having a predetermined phase angle on a circumference passing through a symbol of maximum amplitude in signal space coordinates,
In a QAM demodulator for demodulating a QAM signal including pilot symbols inserted in the middle of a frame for facilitating phase correction, an orthogonal component I is generated by a symbol timing reproduction signal substantially synchronized with the symbol timing on the transmission side. (T) and Q
A reproducing circuit for reproducing a symbol signal consisting of (T) and the amplitude value of the symbol signal when there are M synchronization symbols and pilot symbols which are determined to have the maximum amplitude within a predetermined period. An AGC circuit for extracting the upper M values in a predetermined period and adjusting the gain by using the average value or the integrated value of the amplitude values of the extracted M symbol signals is provided. QAM demodulator.