JP3865287B2 - Judgment feedback type equalization method and transmitter / receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a decision feedback type equalization method and a transmission / reception apparatus, and more particularly to a decision feedback type equalization method suitable for equalizing a waveform of a digital signal wirelessly transmitted using a radio for analog audio transmission, and The present invention relates to a transmission / reception device.
[0002]
[Prior art]
In a radio that transmits and receives audio signals as analog signals on radio carrier waves, an AGC circuit for coping with fluctuations in the received electric field, a limiter circuit for suppressing input exceeding the dynamic range of the transmission amplifier, etc. are used. It has been. On the other hand, in order to perform higher-quality audio transmission using such a radio device or to configure a plurality of audio channels by multiplexing the channels between the radio devices, the audio signal is digitized and, for example, 16QAM is used. May be generated in a voice band and transmitted / received by a conventional analog radio. In this way, the radio channel can be used effectively, and it becomes easy to improve transmission quality, make the audio signal secret, multiplex the audio channel, and the like. Further, it is easy to transmit a data signal from a data terminal such as a personal computer in place of a digitized audio signal, and the same effect as that of an audio signal is obtained.
[0003]
FIG. 2 is a block diagram illustrating a configuration example of a transmission side of a system that generates a modulated wave of an audio signal using the 16QAM modulation method and transmits / receives the modulated wave using an analog wireless device. An analog audio signal input from the microphone 201 is converted into a digital signal by the A / D converter 202, data is encoded by the audio encoder 203, and stored in the buffer memory 204. When a PTT control signal is output from a PTT (Press Talk Timing) controller 205 by a caller's operation, the frame generator 206 stores the encoded data DT having a predetermined length and the training signal memory 207 from the buffer memory 204. A transmission frame is formed from the training signal TS. FIG. 4 shows this frame configuration. Here, the training signal TS is a fixed pattern signal, and usually includes a synchronization signal for frame synchronization or the like. The framed signal is input to the data mapper 208 and converted to 16-value data with 4-bit data as one symbol, and the converted 16-value data is mapped onto the signal space for encoding and modulation. It is output as a modulation side I / Q signal. The modulation-side I / Q signal is subjected to phase modulation for each of two carriers having a phase difference of π / 2 by a quadrature modulator 209, and a 16QAM digital modulation signal is generated. This digital modulation signal is converted to an analog signal in the voice band by the D / A converter 210, and the analog radio 211 converts the analog signal from the D / A converter 210 into a radio signal and transmits it.
[0004]
FIG. 3 is a block diagram illustrating a configuration example on the receiving side of a 16QAM-modulated radio signal. A radio signal transmitted from the radio 211 of the partner station is received by the analog radio 301 and converted into a voice band signal. The voice band signal is converted into a digital reception signal by the A / D converter 302. This digital received signal is subjected to quadrature detection by the quadrature detector 303 to extract the demodulated I / Q signal, which is input to the synchronization processor 304, where the head of the data is detected by frame synchronization / symbol synchronization processing and reconstructed. Frame data is output. The equalizer 305 is a decision feedback equalizer that performs equalization processing to remove waveform distortion caused by multiple wave components generated in the wireless transmission path. The equalized I / Q signal is input to the data mapper 306, where one symbol is converted into a 4-bit signal and stored in the buffer memory 307. The signal in the buffer memory 307 is subjected to voice decoding processing by the voice decoder 308 and output as a reproduced voice signal. The reproduced audio signal is converted into an analog audio signal by the D / A converter 309 and output from the speaker 310.
[0005]
FIG. 5 is a block diagram showing the configuration of the decision feedback equalizer 305. The I and Q phase signals after quadrature detection are input to a transversal FF filter (Feed Forward Filter) 501 and the output thereof is the same. A difference from the output of the transversal type FB filter (Feed Back Filter) 502 is obtained by a (complex) adder 503. The output is determined by the equalization error determination unit 504 and input as an equalization I / Q signal and is input to one input terminal of the switch 505. A training signal 506 is input to the other input terminal of the switch 505, and a selection output of the switch 505 is input to the FB filter 502. The difference between the input and output of the equalization error determination unit 504 is obtained by the adder 507, and the tap coefficient control unit 508 minimizes the output of the adder 507 in accordance with the output value of the FF filter 501 and the FB filter 502. Control the tap factor. However, the training signal 506 has the same fixed pattern as that inserted in the frame on the transmission side.
[0006]
In the equalizer of FIG. 5 described above, the FF filter 501 executes a matching process for obtaining a diversity effect that removes an interference component generated when a delayed wave generated in multiple propagation paths is superimposed on a direct wave, and the FB filter 502 is The residual delayed wave is removed by using the determination output of the equalization error determination unit 504 or the training signal 506. In this case, when the input I / Q signal is a training signal, the switch 505 selects the training signal 506, and when the input I / Q signal is a data signal, the determination output of the equalization error determination unit 504 is selected and input to the FB filter 502. , At least during the training signal, a signal having a determination result without error is input to the FB filter. Therefore, the convergence of the tap coefficient of each filter to the optimum value can be realized more reliably and in a short time.
[0007]
[Problems to be solved by the invention]
According to the systems shown in FIG. 2 and FIG. 3, it is possible to realize a diversity effect and the like that could not be obtained when communicating only with the analog wireless devices 211 and 301, and improve transmission quality, channel multiplexing, and the like. realizable. These effects are brought about by effective use of the frequency by the 16QAM system and the action of the equalizer. However, the modulated wave by the 16QAM system includes information in both the phase and the amplitude of the carrier wave. Therefore, it is necessary to transmit so that neither the amplitude nor the phase is distorted. However, since the analog wireless devices shown in FIGS. 2 and 3 are provided with the AGC and limiter functions as described above, distortion with respect to the amplitude component is inevitable. In particular, the analog radios 211 and 301 and other circuit components (modem parts) are not necessarily designed as a fixed pair, and the available analog radios and modem parts are used in appropriate combinations. In some cases, amplitude distortion due to the AGC operation and limiter operation of the radio device and distortion due to input exceeding the dynamic range of the transmission amplifier of the radio device may increase, leading to deterioration in transmission quality. Such a distortion generated in an analog radio cannot be sufficiently compensated for by the decision feedback equalizer shown in FIG.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a decision feedback type equalization method capable of receiving a digital signal more reliably by equalizing them even when distortion due to an AGC or a limiter of an analog radio device occurs, as well as a diversity effect. An object of the present invention is to provide a transmission / reception apparatus having the method.
[0009]
[Means for Solving the Problems]
The present invention is a decision feedback type equalization method for equalizing a reception signal received via a wireless transmission system, a digital transmission signal in which each frame is composed of a digital data signal and a training signal having a fixed pattern. There,
The transversal type first, second, and third filters whose tap coefficients can be variably controlled, and an error signal that is a difference between the equalized signal and a digital signal obtained by judging the signal as an input A tap controller for controlling the tap coefficients of the first, second, and third filters;
In a period in which the received signal is a training signal, the difference between the output of the first filter when the received signal is input and the output of the third filter when the fixed pattern of the training signal is input is The tap controller controls the tap coefficient of the first filter so that the error signal at that time is minimized.
In a period in which the received signal is a data signal, the received signal is input to the first filter, the output when the output is input to the second filter, and the digital signal after determining the equalized signal The tap coefficient controller uses the difference between the output of the third filter and the tap coefficient of the second and third filters so that the error signal at that time is minimized. A decision feedback type equalization method characterized in that is controlled.
[0010]
Furthermore, the present invention provides a transmitting apparatus for converting a digital transmission signal, each frame of which is a digital data signal and a training signal having a fixed pattern, into a radio signal and transmitting the radio signal, and a waveform equalizing means for receiving the radio signal. In the transmitting / receiving apparatus comprising the receiving apparatus that demodulates and extracts the data signal after performing waveform equalization by the waveform equalization signal, the waveform equalization signal is a transversal type first, second, second, And a third filter;
A tap controller that controls the tap coefficients of the first, second, and third filters by using an error signal that is a difference between the equalized signal and the digital signal that is digitized by determining the signal;
The difference between the output of the first filter when the received signal is input and the output of the third filter when the fixed pattern of the training signal is input during the period when the received signal of the receiving device is the training signal. And the tap controller controls the tap coefficient of the first filter so that the error signal at that time is minimized, and the received signal is a data signal during a period in which the received signal is a data signal. Is input to the first filter and the output is input to the second filter, and the output of the third filter is input to the digital signal after determining the equalization signal. Switch means for controlling the tap coefficients of the second and third filters so that the difference is the equalized signal and the error signal at that time is minimized. It discloses a transmitting and receiving apparatus, characterized in that it comprises an.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a configuration example of a decision feedback equalizer according to the present invention, which is used as the equalizer 305 in FIG. The equalizer FB filter 102, adder 103, equalization error determination unit 104, switch 105, training signal buffer 106, and adder 107 correspond to the components 502 to 507 of the same name shown in FIG. The second FF filter 101 corresponds to the FF filter 501 in FIG. These parts have the same function as that of FIG. 5 together with a part of the function of the tap coefficient controller 115, that is, a diversity effect for compensating for propagation path distortion. Further, in the present invention, the first FF filter 111 and the switches 112 and 114 are provided in order to compensate for the distortion generated in the analog wireless device, and the tap coefficient controller 115 also calculates the optimum tap coefficient of the first FF filter 111. Has function. The operation will be described in detail below.
[0012]
The operation of the equalizer of FIG. 1 is divided into two intervals, and the control is performed by the synchronization signal SYC. This synchronization signal SYC is a signal synchronized with the received frame detected by the synchronization processor 304 of FIG. 3, and is, for example, “ON” during the training signal starting from the beginning of the received frame, and “ОFF” between the subsequent data signals. Is a signal. Such a training signal can be easily generated from the frame synchronization signal because the length of the training signal is determined. The switches 105, 112, 113, and 114 are connected to the a-side contact when the synchronization signal SYC is “ON”, and are connected to the b-side contact when “SYNC”, so that processing in each interval is executed.
[0013]
First, when the synchronization signal SYC is “ON” is called a training process, the training signal is being received in this interval, and the input I / Q signal is processed by the first FF filter 111 and its output is switched. The data is input to the adder 103 via 112 and 114. This first FF filter is also a transversal type filter like the other filters, and its tap coefficient can be variably controlled. On the other hand, the training signal from the training signal buffer 106 is input to the FB filter 102 via the switch 105, and the difference between the output and the output processed by the first FF filter 111 is calculated by the adder 103, and the output Is determined by the equalization error determination unit 104 and output as an equalization I / Q signal. The difference between the input and output of the equalization error determiner 104 is calculated as an error signal by the adder 107, and the tap coefficient of the first FF filter 111 that minimizes this error signal is calculated by the tap coefficient controller 115. Thus, the tap coefficient of the first FF filter 111 is controlled via the switch 113. In the above training process, the initial value of the tap coefficient of the first FF filter 111 is a value that compensates for a fixed waveform distortion (independent of the propagation path state) generated due to an AGC or a limiter of the analog radio. Is determined in advance and set. Then, the tap coefficient of the first FF filter 111 converges to a value that compensates for the fixed waveform distortion, and the training signal is input to the FB filter 102, so that high-speed convergence is performed without being affected by transmission errors. Is called.
[0014]
Next, when the synchronization signal SYC is “OFF” is called a tracking process, the data signal DT is being received in this interval, and the input I / Q signal is also input to the first FF filter. In this tracking process, the switches 104 and 112 to 114 are all connected to the b-side contact. Therefore, the tap coefficient control of the first FF filter 111 is not performed, and is fixed to the value updated in the immediately preceding training process. Therefore, the fixed distortion component generated in the radio device in the input data signal DT is the first FF filter 111. Is equalized and removed. The equalized data signal is input to the adder 103 via the switch 112, the second FF filter 101, and the switch 114. At this time, the signal of the specific result from the equalization error determination unit 104 is input to the FB filter 102, and the tap coefficient controller 115 determines the second FF filter based on the error signal that is the input / output difference of the equalization error determination unit 104. 101, the tap coefficients of the FB filter 102 are calculated, and the tap coefficients of these filters are controlled via the switch 113. This state has the same circuit configuration as that of the tracking process in the circuit of FIG. That is, an operation of removing interference waves derived from multiple waves generated in the wireless transmission path is performed.
[0015]
In the above embodiment, the digital signal to be transmitted has been described as a 16QAM modulation signal. However, the present invention is effective as long as it is a modulation system in which information corresponds to an amplitude change other than the 16QAM system. It is clear.
[0016]
【The invention's effect】
According to the present invention, a diversity effect for removing multi-wave distortion generated in a radio transmission line and a decision feedback type capable of removing waveform distortion fixedly generated due to AGC and limiter operations of an analog radio. There is an effect that the equalizer can be realized by a compact integrated configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of a decision feedback equalizer according to the present invention.
FIG. 2 is a block diagram showing a configuration example of a system for transmitting a 16QAM modulated digital signal by an analog wireless device.
FIG. 3 is a block diagram illustrating a configuration example of a system for demodulating a 16QAM digital signal received by an analog wireless device.
FIG. 4 is a diagram illustrating a frame configuration of transmission digital data.
FIG. 5 is a block diagram showing a configuration example of a conventional decision feedback equalizer.
[Explanation of symbols]
101 Second FF filter 102 FB filter 103, 107 Adder 104 Equalization error determiner 105, 112, 113, 114 Switch 106 Training signal buffer 111 First FF filter 115 Tap coefficient controller 211, 301 Radio

Claims (2)

A decision feedback type equalization method for equalizing a reception signal received via a wireless transmission system, a digital transmission signal each frame comprising a digital data signal and a training signal having a fixed pattern,
The transversal type first, second, and third filters whose tap coefficients can be variably controlled, and an error signal that is a difference between the equalized signal and a digital signal obtained by judging the signal as an input A tap controller for controlling the tap coefficients of the first, second, and third filters;
In a period in which the received signal is a training signal, the difference between the output of the first filter when the received signal is input and the output of the third filter when the fixed pattern of the training signal is input is The tap controller controls the tap coefficient of the first filter so that the error signal at that time is minimized.
In a period in which the received signal is a data signal, the received signal is input to the first filter, the output when the output is input to the second filter, and the digital signal after determining the equalized signal The tap coefficient controller uses the difference between the output of the third filter and the tap coefficient of the second and third filters so that the error signal at that time is minimized. A decision feedback type equalization method characterized in that control is performed. Each frame converts a digital transmission signal composed of a digital data signal and a training signal having a fixed pattern into a radio signal and transmits the radio signal, and receives the radio signal and performs waveform equalization by waveform equalization means. In a transmitting / receiving device comprising a receiving device that demodulates and extracts the data signal after performing
The waveform equalization signal includes first, second, and third filters of transversal type capable of variably controlling the tap coefficients;
A tap controller that controls the tap coefficients of the first, second, and third filters by using an error signal that is a difference between the equalized signal and the digital signal that is digitized by determining the signal;
The difference between the output of the first filter when the received signal is input and the output of the third filter when the fixed pattern of the training signal is input during the period when the received signal of the receiving device is the training signal. And the tap controller controls the tap coefficient of the first filter so that the error signal at that time is minimized, and the received signal is a data signal during a period in which the received signal is a data signal. Is input to the first filter and the output is input to the second filter, and the output of the third filter is input to the digital signal after determining the equalization signal. Switch means for controlling the tap coefficients of the second and third filters so that the difference is the equalized signal and the error signal at that time is minimized. ,
A transmission / reception apparatus comprising:

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