JP2004297536A - Adaptive equalization method - Google Patents

Abstract

[Purpose] In a conventional equalization method, a training signal at the head of transmission data is performed. However, since training of the training signal is not sufficient, the convergence time of an equalization error increases and the data is not completely converged. There has been a problem that equalization of a signal is performed and an erroneously determined equalization result is output. However, the present invention provides a method that realizes an adaptive equalization method and can sufficiently follow a change in the transmission environment even in wireless communication in a fast-changing environment.
An adaptive equalization method according to the present invention improves transmission quality because an equalization error can be reduced more reliably and a determination of an equalization result can be made more reliably by a method of repeatedly performing equalization for training. Can be. Further, by repeatedly performing the training, it is possible to reduce the training signal length in one frame and increase the information signal length, so that the information signal transmission amount per frame can be increased.
[Selection] Fig. 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an adaptive equalization method used for land communication and the like, and particularly to an adaptive equalization method for compensating for multipath fading that occurs when performing high-speed data transmission.
[0002]
[Prior art]
Conventionally, it is generally known that a decision feedback equalizer (DFE: Decision Feedback Equalizer) is effective as an adaptive equalization method for preventing multipath fading. The DFE can be realized on a relatively small scale, and can be equalized even when the delay time is large.
[0003]
The DFE will be described with reference to FIG. FIG. 3 is a configuration block diagram of a conventional DFE. As shown in FIG. 3, the conventional DFE includes an FF filter (Feed Forward Filter) 150, an FB filter (Feed Back Filter) 160, a complex adder 112, a data determiner 113, a switch 115, and a training signal. It comprises a generator 114 and a tap coefficient updating unit 121.
[0004]
When an input signal (reception baseband signal) is input to the FF filter 150, the FF filter 150 executes a matching process for obtaining a diversity effect that captures a direct wave and a delayed wave. The delay registers 101 to 105 store the transmission data signal at half symbol intervals, and the complex multipliers 107 to 111 output the output of the corresponding delay registers 101 to 105, respectively, to the corresponding output of the delay registers 101 to 105 for equalization. A complex multiplication is performed with a complex tap coefficient ww (n).
[0005]
Further, the FB filter 160 receives a determination output of a previous symbol or a reference training signal from the training signal generator 120, which is switched by the SW 115 depending on whether the input signal to be equalized is a training signal or a data signal.
[0006]
The FB filter 160 feeds back the judgment output or the reference training signal, and performs an arithmetic process in the complex adder 112, thereby removing the residual delay wave. The delay registers 116 and 117 delay the number of symbols corresponding to the maximum delay time of the multipath delay wave generated on the propagation path, and the complex multipliers 118 and 119 apply the outputs of the corresponding delay registers 116 and 117 respectively. Perform complex multiplication with the corresponding complex tap coefficients ww (n) for equalization.
[0007]
The output signal of the FF filter 150 and the output signal of the FB filter 160 are input to the complex adder 112, the addition processing of the two signals is performed in the complex adder 112, and the resulting output signal is input to the data determination unit 113. You. The data determination unit 113 selects one mapping value corresponding to a signal point (mapping value) from which the signal from the complex adder 112 is pulled in. This output signal is a result of the symbol equalization processing. , And is used as a decision feedback value to the FB filter 160.
[0008]
The complex adder 120 obtains a difference between the output of the SW 115 and the equalized output that is the output of the complex adder 112, and outputs the difference as an equalization error. The tap coefficient update unit 121 updates the complex tap coefficient for equalization ww (n) by an MMSE (Minimum Mean Square Error) algorithm such as RLS or LMS to minimize the equalization error.
[0009]
In this way, by performing complex multiplication with the complex tap coefficient ww (n) for equalization that is updated as appropriate, diversity combining and cancellation operations of multiple wave components are performed, thereby realizing an equalization function.
[0010]
[Problems to be solved by the invention]
In the conventional equalization method as described above, the training is performed on the training signal at the head of the transmission data. However, since the training of the training signal is not sufficient, the convergence time of the equalization error increases, and before the convergence is complete, There is a problem in that the equalization of the data signal is performed and an erroneously determined equalization result is output.
[0011]
An object of the present invention is to provide an adaptive equalization scheme that can improve transmission quality while realizing adaptive equalization.
[0012]
[Means for Solving the Problems]
In the conventional adaptive equalization method, the training equalization process is performed only once from the beginning of the transmission data. However, in the present invention, the training equalization process is performed a plurality of times to perform training equalization. The transmission quality is improved by reducing the equalization error.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described with reference to the drawings.
[0014]
FIG. 1 shows a frame structure of transmission data provided for the multi-training adaptive equalization method according to the present invention. In the frame structure according to the present invention, data is arranged after the training signal.
[0015]
FIG. 2 shows a configuration of a multi-training adaptive equalization scheme according to an embodiment of the present invention.
[0016]
When an input signal (reception baseband signal) is input, the frame detection unit 10 captures a reception timing by detecting a training signal (synchronization word) in a frame. The frame detection unit 10 outputs the training signal to the training signal memory 11 and the data signal to the data memory 13 based on the captured reception timing, and stores them.
[0017]
The training signal stored in the training signal memory 11 is input to the FF filter 14 during training. The FF filter 14 performs a filter operation using the tap coefficient wwFF. As the tap coefficient wwFF, a value stored in the tap coefficient update unit 18 is used.
[0018]
The FB filter 15 receives the reference training signal output from the training signal generator 19. The FF filter 15 performs a filter operation using the tap coefficient wwFB. As the tap coefficient wwFB, a value stored in the tap coefficient update unit 18 is used.
[0019]
The complex adder 16 adds the filter outputs of the FF filter 14 and the FB filter 15 to obtain an equalized output. The complex adder 17 adds the equalized output of the complex adder 16 and the reference training signal, and calculates the sum of the equalized error powers.
[0020]
The tap coefficient updating unit 18 calculates the optimum tap coefficients (the tap coefficient wwFF and the tap coefficient wwFB) such that the calculated value is the minimum in the equalized error power sum calculated by the complex adder 17. When calculating the optimum tap coefficient, the tap coefficient update unit 18 updates and stores a new tap coefficient in place of the old tap coefficient. With the new tap coefficient, the FF filter 14 and the FB filter 15 perform respective filter operations.
[0021]
The equalization error threshold value determination unit 22 receives the sum of the equalization error powers calculated by the complex adder 17. The equalization error threshold value determination unit 22 calculates the training equalization error by cumulatively adding the training symbols to the equalization error power sum.
[0022]
The equalization error threshold value determination unit 22 has a predetermined value as a threshold value such that the training equalization error sufficiently converges, and determines the magnitude of the calculated training equalization error power sum and the threshold value. A comparison is made, and switching control between training equalization and data equalization is performed based on the comparison result.
[0023]
The training / data equalization switching control unit 23 controls switching of the FF filter input signal selector 12 and the FB filter input signal selector 20 based on the comparison result. The training equalization process is repeated a plurality of times until the calculated training equalization error becomes equal to or less than a predetermined threshold, and the optimum tap coefficient for data equalization is calculated.
[0024]
When the training equalization error is determined to be equal to or less than a predetermined threshold, the FF filter input signal selector 12 selects and outputs data stored in the data memory 13. When the determination is made, the FB filter input signal selector 20 selects the equalization result determination value output from the data determination unit 21 and outputs it as demodulated data.
[0025]
【The invention's effect】
As described above, the adaptive equalization method of the present invention can reduce the equalization error more reliably and reliably determine the equalization result by the method of repeating the equalization for training, so that the transmission quality can be improved. Can be improved. Further, by repeatedly performing the training, it is possible to reduce the training signal length in one frame and increase the information signal length, so that it is possible to increase the information signal transmission amount per frame. Furthermore, by reducing the training signal length, in wireless communication in a fast-changing environment, it becomes possible to sufficiently follow a change in the transmission environment, so that the transmission quality can be improved.
[Brief description of the drawings]
FIG. 1 shows a frame configuration provided for a multi-training adaptive equalization scheme according to the present invention.
FIG. 2 shows a configuration of a multi-training adaptive equalization scheme according to an embodiment of the present invention.
FIG. 3 shows a configuration of a DFE (Decision Feedback Equalizer) according to an embodiment of the related art.
[Explanation of symbols]
10: frame detection unit, 11: training signal memory, 12: FF filter input signal selector, 13: data memory, 14: FF filter, 15: FB filter, 16, 17: complex adder, 18: tap coefficient update unit , 19: training signal generator, 20: FB filter input signal selector, 21: data decision unit, 22: equalization error threshold decision unit, 23: training / data equalization switching control unit 101, 102, 103, 104: 1/2 symbol delay element, 107, 108, 109, 110, 111: complex multiplier, 112: complex adder, 113: data decision unit, 114: training signal generator, 115: FB filter input signal selector, 116 , 117: 1 symbol delay element, 118, 119: complex multiplier, 120: complex adder, 121: tap coefficient update , 150: FF filter, 160: FB filter

Claims (3)

In a system for adaptively equalizing transmission data using an adaptive equalizer,
The transmission data is a modulation scheme having a frame configuration in which a training signal having a predetermined pattern predetermined for each predetermined length is added,
When performing the receiving training process,
Means for performing equalizer tap coefficient training using the training signal portion in the frame and calculating filter tap coefficients,
At the end of training, a means for comparing a sum of equalization error power and an equalization error of the training signal unit with a predetermined equalization error threshold so as to converge to a predetermined value,
Based on the comparison result, the tap coefficients calculated until the equalization error becomes equal to or less than the threshold value are used as initial tap coefficient values for the second and subsequent equalizer tap coefficient trainings. Means for converging
An adaptive equalization method characterized by having: 2. A means for converging tap coefficients according to claim 1,
A frame detection unit that detects a frame of transmission data and separates a training signal part and a data part in the frame,
A training signal memory unit that stores the training signal unit;
A data memory unit for storing the data unit;
An FF filter unit that performs FF (Feed Forward) filter processing in the reception training signal processing;
An FB filter unit that performs FB (Feed Back) filter processing in the reception training signal processing;
An adding unit that adds the result of the FF filter processing and the result of the FB filter processing;
A training signal generator for generating a training signal;
A data determination unit that performs symbol determination on the equalization result;
An addition unit that adds the result of the equalization process and the result of the data determination to calculate an equalization error,
A tap coefficient updating unit that calculates an FF tap coefficient and an FB tap coefficient from the calculated equalization error;
An equalization error threshold determination unit that determines by comparing the calculated equalization error with a predetermined threshold,
A process switching unit that switches a reception training process or a data equalization process based on a determination result in the equalization error threshold value determination unit,
An adaptive equalizer characterized by having: 3. An adaptive equalization method, wherein a decision feedback equalizer is used as an equalizer in the equalization processing unit according to claim 1.

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