JPH0766844A - High efficiency multi-value modulated wave demodulator - Google Patents

Abstract

PURPOSE:To reduce the hardware for A/D conversion and the quantity of arithmetic operation by enhancing the speed and accuracy of AGC control for compensating fading distortion in the demodulator for a high efficiency multi-value modulated wave such as a QAM signal. CONSTITUTION:A QAM modulation wave subjected to fading distortion is received by a radio section 210 and the level is adjusted to a level corresponding to a gain control signal and the result is outputted. Before a frame symbol is detected, the amplitude component in the unit of time around a fading period of the output is detected by a signal amplitude detection circuit 241 to obtain the gain control signal. After the frame symbol is detected from I, Q outputs of a QAM demodulation section 220, the gain control signal is decided based on an error between the amplitude data and a predetermined reference value. Since the frame symbol period is much shorter than the fading period, the speed of AGC control is improved and quantization accuracy and range of A/D converters 227,228 is reduced and precision for arithmetic operation of bit stream decoding and its arithmetic operation quantity for a data decoding control section 230 are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-efficiency multi-level modulation wave demodulator, and more particularly to a fading that is modulated by a high-efficiency multi-level modulation system that carries digital information not only for phase shifts of radio carriers but also for amplitude shifts. The present invention relates to a demodulator that receives a modulated wave in which a frame symbol for compensating for distortion is received, automatically controls the amplitude level, and demodulates the digital data.

[0002]

2. Description of the Related Art Conventionally, in land mobile communication, since the envelope (amplitude) of a received signal fluctuates greatly due to fading of a propagation path, QAM (Quadrature Amplitude) is used.
It has been impossible to apply a high-efficiency multilevel modulation method that carries information to the amplitude deviation other than the phase deviation (such as quadrature amplitude modulation), but fading by inserting frame symbols for channel characteristics measurement Distortion Compensation Method (Seihei Sampei's paper "16QAM for Land Mobile Communication"
"Fading distortion compensation method": IEICE Transactions (B-II), VOL. J72-B-II, NO. 1,
pp. 7-15 (January 1989)).

An example of time division multiplexing digital radio communication transmission using 16QAM modulation in land mobile communication will be described below with reference to the drawings.

FIG. 1 is a block diagram of a digital land mobile communication system. A radio base station 10 each having a radio transmitter and a receiver, and three mobile stations a20 to c2
2 and 1 are connected by a one-wave time division multiplex digital radio line. Downlink (link from wireless base station to mobile stations)
Is time-divided into three communication slots,
It is dedicatedly allocated to the mobile station a20, mobile station b21, and mobile station c22. In addition, the uplink (the line from the mobile station group to the radio base station) is synchronized with the downlink, and the mobile stations a22 to c22 communicate with each other through dedicated communication slots.

FIG. 2 shows the state of fluctuation of the received wave in which the FM analog modulation (constant envelope modulated wave) is fading by the propagation path of land mobile communication. In the received wave of the mobile station, the received voltage C (t) fluctuates drastically with time t as shown in (A) of the figure, so that the envelope R (t) of the signal fluctuates as shown in (B) of the figure. Resulting in. This fluctuating frequency is such that the carrier frequency is 800 MHz and the moving speed of the mobile station is 100.
It is said to be about 80 Hz (12.5 ms) in the case of Km / s.

FIG. 3 shows the configuration of downlink and uplink communication slots. A synchronization symbol (SW) indicating the start position of the communication slot is added to the beginning of the data symbol group,
The frame symbol (P) for performing the frame symbol insertion type fading distortion compensation has a fixed time (for example, 1).
It is inserted by interrupting each data symbol group (data 1 to 3) every ms).

FIG. 7 is a block diagram showing an example of a 16QAM demodulator used in a receiver of a mobile station and a fixed station. 16 by radio signal transmitted from the opposite transmitter
The QAM signal is input to the wireless unit 310 through the antenna,
It is amplified by a built-in gain controllable signal amplifier. AG
The C control circuit 340 receives the 16QAM signal R from the radio section 310 due to the fluctuation of the reception input due to the fading of the radio wave propagation path.
When the amplitude level of S changes, in order to keep the input signal amplitude level of the QAM demodulation unit 320 within a certain range,
An automatic gain control signal (AGC) for detecting the voltage level of the QAM signal RS and controlling the gain of the signal amplifier of the radio unit 310.
Voltage) is fed back. The 16QAM signal RS adjusted to a certain range by the AGC control circuit 340 is
The M demodulator 320 separates into two frequencies orthogonal to each other.
Digital (A / D) converted to parallel signal (ICH
And QCH) and is input to the control unit 330. The control unit 330 performs arithmetic processing on the input signal, detects synchronization symbols and frame symbols, estimates the amount of fading distortion received by the data symbols, corrects the received data, and reproduces the transmitted data.

[0008]

In this conventional demodulator, in order to keep the signal amplitude level to the QAM demodulator within a certain range, the amplitude component of the 16QAM signal output from the radio section is detected by a semiconductor such as a diode, and Controls the gain of the signal amplifier in the preceding radio unit so that the voltage is constant (AGC control)
By doing so, a method of suppressing the fluctuation of the 16QAM signal has been taken.

However, in the high-efficiency multilevel modulation system such as 16QAM, the information symbol amplitude component is not constant as shown in FIG. 4, so that there is information data in which, for example, S0 continues for several symbols and then S5 continues for several symbols. Since the amplitude component of the 16QAM signal and 16QAM signal changes, there is a possibility that incorrect AGC control may be performed, and a long time (1 fading cycle (12.5 ms or more)) that does not respond to changes in the amplitude component due to the arrangement of information symbols. A for fading fluctuation
Only GC control was possible. Therefore, it is necessary to widen the compensation range (variation width) of distortion compensation by frame symbols in order to compensate for fading fluctuations that occur in a short time (12.5 ms or less) in the propagation path of land mobile communication. This results in increasing the quantization range (dynamic range) and accuracy of the A / D conversion performed by the QAM demodulation unit and increasing the calculation accuracy and amount of calculation performed by the control unit.
In addition, semiconductors and A / A used for amplitude component detection of the QAM signal
An error in the AGC control due to the temperature characteristic of the D converter also increases the calculation accuracy and the calculation amount in the control unit.

Therefore, an object of the present invention is to perform accurate fading distortion compensation without increasing the quantization range and accuracy of the A / D converter, thereby increasing the operation accuracy and operation amount of digital data demodulation. It is to provide a high-efficiency multilevel modulation wave demodulation device that enables

[0011]

According to the present invention, a symbol corresponding to a digital data string of a plurality of bits on the transmitting side is modulated by a high-efficiency multi-value modulation system that carries information on amplitude deviation as well as carrier deviation. In a high-efficiency multilevel modulation wave demodulation device for receiving a modulated wave that has been generated through a propagation path in which fading distortion occurs, demodulating the symbol and restoring to the digital data string.

Amplitude gain control means for receiving the modulated wave subjected to fading distortion due to the propagation path, performing amplitude gain control according to the value of the gain control signal, and outputting as an amplitude controlled modulated wave, and the amplitude controlled Demodulation for synchronously detecting the modulated waves corresponding to mutually orthogonal phases, quantizing the amplitude of the analog signal of the symbol at a predetermined quantization level, and outputting as the first and second digital demodulation signals indicating the corresponding amplitude level values, respectively. Means, restoration control means for performing a predetermined arithmetic processing based on the values of both the first and second digital demodulated signals to judge the type of the symbol, and restore the digital data string of a plurality of bits; By the side, the frame symbol of a predetermined amplitude deviation inserted into the modulated wave at a constant period shorter than the period of the fading distortion, A frame symbol detection means for detecting, based on the serial restoration control unit symbol type determination result of,
The value of the gain control signal is set in accordance with the amplitude level value indicated by the first and second digital demodulation signals from the demodulation unit corresponding to the frame symbol detected by the frame symbol detection unit at every fixed period. First gain control means for determining, and envelope detection of the amplitude-controlled modulated wave from the amplitude gain control means, and the amplitude level value within a time range longer than the fixed period of the frame symbol Second for determining the value of the gain control signal
Of the gain control means and the output of the second gain control means at the start of reception of the modulated wave from the propagation path, and the first gain after the start of detection of the frame symbol by the frame symbol detection means. Selecting means for selecting the output of the control means as the gain control signal and inputting it to the amplitude gain control means.

In the above structure, the first gain control means detects the frame symbol by the first memory in which the reference value of the amplitude level of the frame symbol is stored in advance, and the frame symbol detection means detects the frame symbol. Means for comparing the amplitude level values indicated by the corresponding first and second digital demodulated signals with the reference value in the first memory to detect an error; and the second means at the time of starting the detection of the frame symbol. Second memory for storing the value of the gain control signal with the output value of the gain control means as an initial value, and the stored value in the second memory is adjusted according to the value of the error as the gain control signal. And a third memory for storing the value of the error from the means for detecting the error. Each time the frame symbol is detected, the value stored in the second memory may be adjusted according to the value of the error detected this time and the value of the error detected the previous time, and the value may be output as the gain control signal. .

[0014]

The present invention will be described below with reference to the drawings.

FIG. 5 is a block diagram showing an embodiment of the present invention. This embodiment is an example applied to each receiver of the radio base station 10 and the mobile stations a20 to c22 of the digital mobile communication system shown in FIG. 1, like the conventional example. A 16QAM signal, which is a radio signal having a communication slot configuration and a symbol configuration as shown, is received and demodulated to restore transmission data. In FIG. 5, the demodulator according to the present embodiment is 16Q which controls a communication slot on a wireless line and receives a fading distortion through an antenna 21.
A radio unit 210 which receives an AM radio wave signal, converts it to an intermediate frequency, amplifies it by a signal amplifier 212 capable of gain control by an AGC voltage from the outside, and outputs it as an amplitude level-adjusted 16QAM signal RS; multipliers 223, 224; The low pass filter (LPF) 225, 226, the carrier wave synchronizing circuit 221, the 90 ° (π / 2) phase shifter 222 and the analog / digital (A / D) converters 227, 228 are provided, and the The 16QAM signal RS is synchronously detected using two demodulated carriers whose phases are orthogonal to each other, and I is detected according to the phase and amplitude of the analog signal of each symbol.
Two systems of digital data of CH and QCH (12 for each)
QAM demodulation section 220 for demodulating (bits); sync symbol detection circuit 231 and frame symbol detection circuit 23
2, a data restoration control unit 230 that compares and calculates ICH and QCH data with reference data, detects synchronization symbols, recognizes frame symbols and data symbol positions, and restores transmission data; and a radio unit. 210 voltage level of 16QAM signal RS or QAM demodulator 2
An AGC control unit 240 for compensating for the amount of fading distortion by controlling the gain of the radio unit 210 according to the amplitude levels of 20 frame symbols on the ICH and DCH is provided.

Next, the operation will be described.

The radio base station 10 and each of the mobile stations a20 to c22 are provided with a transmitter as shown in FIG. Bit string of information data to be transmitted (a ₁ , a ₂ , a
_3, a _4, ...), the two systems in the serial / parallel converter 110 (ICH, parallel signal 2 bits of _{QCH) (a 1 a 2 →} Ai 1, a 5 a 6 → Ai 2, ... a a ₃
a ₄ → Aq ₁ , a ₇ a ₈ → Aq ₂ , ...), and the QAM modulator 13 via the selectors 120 and 121, respectively.
Quadrature modulation is performed with 0. At this time, selectors 120 and 1
In 21, a predefined synchronization symbol (for example, a combination of S0, S2, and Sa in FIG. 4) is added to the beginning of the communication slot, and the maximum amplitude of a predefined frame symbol, usually an information symbol, is set at fixed time intervals (for example, 1 ms). A 16QAM signal SS having the configuration shown in FIG. 3 is generated by inserting a fixed symbol having a component (for example, S8 in FIG. 4) into the transmission information data by interruption. The radio unit 140 controls the communication slot of the radio line, converts the 16QAM signal SS into a radio carrier frequency, and transmits the radio wave signal through the antenna 141. This radio wave signal is subject to fading as shown in FIG. 2 while receiving the antenna 2 of the receiver of the opposite station.
11, the radio unit 210 of the high-efficiency multilevel modulation wave demodulation device
Is input to.

When the demodulator starts reception, no frame symbol has been detected yet, and the AGC controller 240
Since the AGC timing control circuit 251 does not output the AGC system switching signal, the input of the switch 242 is connected to the signal amplitude detection circuit 241 side, and the signal amplitude detection circuit for the output 16QAM signal RS of the radio section 210 is detected. In 241 the voltage component (envelope detection) of the amplitude component is detected, and it is set as the AGC voltage to the signal amplitude unit 212 of the radio section 210 through the switch 242. The accuracy of AGC control at this time is determined by the QAM demodulation unit 2
The control may be as simple as 20 to receive the frame symbol. The frame symbol is one information symbol (S
8), the QAM demodulation unit 220 can limit the compensation range (variation width) of the distortion amount when extracting the frame symbol, and therefore the analog-digital converter 2
It is not necessary to increase the quantization range (dynamic range) of 27 and 228 and accuracy. In addition, the signal amplitude detection circuit 2
The output of 41 is an analog / digital (D / A) converter 2
At 43, the numerical data of the signal amplitude, that is, the numerical data of the AGC voltage is stored in the AGC data storage circuit 245. The AGC data storage circuit 245 allows the data storage from the A / D converter 243 and prohibits the data storage from the AGC data operation circuit 246 while the AGC system switching signal is not received. Data stored in the AGC data storage circuit 245 becomes an AGC voltage in the digital / analog (D / A) converter 244. Although this AGC voltage is slightly delayed from the output AGC voltage of the signal amplitude detection circuit 241, it has the same level. However, at this point, the wireless unit 210 is still
The output of the signal amplitude detection circuit 241 is selected as the AGC voltage to the.

Next, the frame symbol detection circuit 232 after the synchronization symbol detection circuit 231 detects the synchronization symbol from the I and Q data output from the QAM demodulation section 220.
When the frame symbol is detected at, a trigger signal is sent to the AGC timing control circuit 251. When the AGC timing control circuit 251 receives the trigger signal, the AGC timing control circuit 251 outputs an AGC system switching signal, outputs a clock synchronized with the frame symbol reception timing, and outputs the amplitude error detection circuit 253, the amplitude error estimation circuit 255, and the AGC data operation circuit 246. To operate in synchronization with the clock. The amplitude error detection circuit 253 compares the amplitude level value of the I and Q data of the frame symbol from the QAM demodulator 220 with the reference value stored in the frame symbol reference value circuit 252 in advance to calculate the error. For example, in FIG. 4, the reference value of the amplitude of the frame symbol S8 is "3" for both I and Q.
However, if the gain of the radio unit 210 is too large, the amplitude value of the output of the QAM demodulation unit 220 is “4”, and if it is too small, it is “2”, and the difference “1” or “−1” is an error. . This error data is extrapolated by the amplitude error estimation circuit 255 with the amplitude error data of the immediately preceding frame symbol stored in the amplitude error storage circuit 254, and the fading that the data signal receives before the reception of the next frame symbol is performed. Estimate the amount of strain. AGC data operation circuit 2
Reference numeral 46 is the estimated distortion amount and the AGC data storage circuit 245.
The ideal numerical value data of the AGC voltage is calculated from the current numerical value data of the AGC voltage stored therein.

On the other hand, the AGC system switching signal sent from the AGC timing control circuit 251 when the frame symbol is first detected causes the input of the switch 242 to be D /
While being switched to the A converter 244 side, data storage from the A / D converter 243 to the AGC data storage circuit 245 is prohibited, and data storage from the AGC data operation circuit 246 is permitted. As a result, the numerical data of the AGC voltage stored in the AGC data storage circuit 245 is based on the numerical data detected by the signal amplitude detection circuit 241 at the time when the frame symbol is first detected. Is adjusted according to the amplitude error. As mentioned above, this AG
The A / D converter 244 generates an AGC voltage in accordance with the numerical data stored in the C data storage circuit 245, and the switching device 2
It is supplied to the wireless unit 210 through 42. This AGC voltage is held for a fixed period (one frame symbol interval (1 ms)) until the next frame symbol can be received.

In the AGC control unit 240, the switch 242 is not provided, and the AGC voltage of the radio unit 210 is set to D.
The output of the / A converter 244 may be directly input. In this case, the voltage value itself of the amplitude component of the 16QAM signal RS detected by the signal amplitude detection circuit 241 is A
It is not necessary to use the GC voltage value, and by appropriately setting the conversion characteristics of the A / D converter 243 and the D / A converter 244, the flexibility of the AGC control characteristics of the wireless unit 210 is increased.

Further, the data restoration control unit 230 uses the QAM
Level determination calculation is performed on the ICH and QCH data from the demodulation unit 220 to make a 2-bit parallel signal, and a 16-bit serial signal is converted according to the value of the combination, and this is repeated to transmit the transmission information data. The bit string is restored and output.

In the state where the output of the radio section 210 is AGC controlled by the error signal by the frame symbol, the fading cycle (1/80 Hz) by the propagation path of the land mobile communication.
= 12.5 ms), the frame symbol is about 1/1
Since they are inserted at intervals of 0 (about 1 m), it is shown in FIG. 2 (B).
As described above, one fading of the propagation path is divided into 10 equal parts on the time axis, and the fading distortion amount input to the 16QAM demodulation unit is one fading amount (R (12.5 m
(s)) is divided into 10 (R (1 ms)), the A / D converters 227 and 228 of the QAM demodulation unit 220 are obtained.
Dynamic range (quantization range) is reduced to about the amount of amplitude fluctuation of the 16QAM signal, and the data restoration control unit 230
Also, the amount of calculation for the output bit reproduction processing can be suppressed. According to the experiment, for example, the number of quantization bits of the A / D converters 227 and 228 required 16 bits in the conventional technique, but the amplitude variation amount is 1/1 by using the present invention.
It was confirmed that it can be suppressed to 0 or less and that it is completed with 8 to 12 bits.

[0024]

The highly efficient multilevel modulation wave demodulator of the present invention is
A gain control signal of an amplitude gain control means for adjusting an input level to a demodulation means of a modulated wave of a highly efficient multi-level modulation method such as a QAM signal having a fading distortion due to a propagation path of mobile communication etc. within a predetermined range is created. The feedback path is automatically switched before and after the detection of the frame symbol, and the value of the gain control signal is determined according to the amplitude level of the envelope detection of the modulated wave before the detection of the frame symbol. The frame symbol can be detected by compensation, and after detecting the frame symbol, the value of the gain control signal is determined according to the amplitude level of the frame symbol, so fading distortion can be compensated in a time unit that is extremely shorter than the period. , The quantization range of the A / D converter of the demodulation means for converting the information symbol into a digital demodulation signal, and Suppressing the accuracy, it is possible to reduce the bit string calculation accuracy and calculation amount of digital data restoration control section, the cost can be reduced. Further, the output value of the semiconductor used for the envelope detection of the modulated wave is apt to change due to the temperature change, but since this output is not used after the detection of the frame symbol, the high precision amplitude gain control which is not influenced by the temperature becomes possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a digital mobile communication system to which the present invention is applied.

2A and 2B are diagrams showing a state of fading due to a radio wave propagation path in the system of FIG. 1, where a diagram (A) shows a variation of a reception voltage and a diagram (B) shows a variation of an envelope thereof.

3 is a diagram showing a configuration of a communication slot on a wireless line of the system of FIG.

FIG. 4 is a diagram showing an example of a signal space arrangement of 16QAM information symbols.

FIG. 5 is a block diagram showing an embodiment of the present invention.

FIG. 6 is a block diagram illustrating an example of a 16QAM transmitter.

FIG. 7 is a block diagram showing an example of a conventional 16QAM demodulation device.

[Explanation of Codes] 210 Radio Unit 212 Signal Amplifier 220 QAM Demodulation Unit 227, 228 Analog / Digital Converter 230 Data Restoration Control Unit 232 Frame Symbol Detection Circuit 240 AGC Control Circuit 241 Signal Amplitude Detection Circuit 242 Switcher 243 Analog / Digital Conversion 244 Digital / analog converter 245 AGC data storage circuit 246 AGC data operation circuit 251 AGC timing control circuit 252 Frame symbol reference value circuit 253 Amplitude error detection circuit 254 Amplitude error storage circuit 255 Amplitude error estimation circuit

Claims (3)

[Claims] 1. A modulation wave in which a symbol corresponding to a digital data string of a plurality of bits on the transmission side is modulated by a high-efficiency multi-value modulation system which carries information on amplitude deviation as well as carrier deviation, and fading distortion. In a high-efficiency multilevel modulation wave demodulation device which receives through a propagation path in which the signal is generated, demodulates the symbol and restores the digital data sequence. Amplitude gain control means for receiving the modulated wave that has undergone fading distortion due to the propagation path, performing amplitude gain control according to the value of the gain control signal, and outputting as an amplitude controlled modulated wave, the amplitude controlled modulated wave Demodulating means for synchronously detecting the signals corresponding to mutually orthogonal phases, quantizing the amplitude of the analog signal of the symbol at a predetermined quantization level, and outputting the first and second digital demodulated signals indicating the corresponding amplitude level values, respectively. Restoration control means for performing a predetermined calculation process based on the values of both the first and second digital demodulated signals to determine the type of the symbol and restore the digital data string of a plurality of bits; The frame symbol with a predetermined amplitude deviation inserted in the modulated wave at a constant period shorter than the period of fading distortion is subjected to the restoration control. Frame symbol detecting means for detecting based on the symbol type determination result of the means, and the first and second digital signals from the demodulating means corresponding to the frame symbols detected by the frame symbol detecting means at the constant period. First gain control means for determining the value of the gain control signal in accordance with the amplitude level value indicated by the demodulated signal, and envelope detection of the amplitude-controlled modulated wave from the amplitude gain control means for detecting the frame symbol Second gain control means for determining a value of the gain control signal according to an amplitude level value within a time range longer than the fixed cycle; and the second gain control means at the time of starting reception of the modulated wave from the propagation path. The output of the gain control means is changed to the first gain control means after the start of detection of the frame symbols by the frame symbol detection means. High-efficiency multi-level modulation wave demodulation device characterized by selecting the output as the gain control signal and a selection means for input to the amplitude gain control means. 2. The first gain control means stores the reference value of the amplitude level of the frame symbol in advance, and the first gain control means responds each time the frame symbol detection means detects the frame symbol. Means for comparing the amplitude level values indicated by the first and second digital demodulated signals with the reference value in the first memory to detect an error, and the second gain control at the time of starting the detection of the frame symbol. A second memory for storing the value of the gain control signal with the output value of the means as an initial value, and a means for adjusting the stored value in the second memory according to the value of the error and outputting the gain control signal. The high-efficiency multilevel modulation wave demodulation device according to claim 1, further comprising: 3. The first gain control means has a third memory for storing the value of the error from the means for detecting the error, and the error of the current detection is detected each time the frame symbol is detected. 3. The high-efficiency multilevel modulation wave demodulation device according to claim 2, wherein the value stored in the second memory is adjusted according to the value and the value of the error of the previous detection, and is output as the gain control signal.