JPH05252078A - Discrimination feedback type adaptive equalizer and communication equipment having the equalizer - Google Patents

Abstract

PURPOSE:To reduce number of symbols required for a training operation by decreasing a converging time of a tap coefficient at the training operation. CONSTITUTION:k-Sets of taps 10 connected in series at an interval of a fractional number are arranged to 1st-m-th branches and taps 20 connected in series at an interval of one symbol are disposed to 1st-(mXn)th branches respectively in cascade. The 1st-m-th branches and the 1st-(mXn)th branches are respectively connected to an input signal terminal 100 and a training signal input terminal 102 via a switch S1 and a switch S4. Each of the branches 1-m(1-(mXn)) is connected respectively to a multiplier 30 via a switch S2 (S3). The tap coefficient is adjusted at a speed of 1/(T/(n*m)) of an over-rate in the training by using the switches S1-S4 so as to apply changeover processing to the 1st-m-th branches and the 1st-(mXn)th branches.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a decision feedback type adaptive equalizer,
In particular, the present invention relates to a decision feedback type adaptive equalizer which is advantageously applied to a digital communication system in which the delay characteristic of a transmission line varies.

[0002]

2. Description of the Related Art In a communication system, signal distortion, such as amplitude distortion and phase distortion, is generated depending on the state of the transmission path between the other station and the local station. When the signal transmitted from the partner station has such distortion, if the signal is reproduced as it is, the transmission signal cannot be reproduced accurately. Therefore, for example, in the conventional technique disclosed in Japanese Patent Laid-Open No. 1-194622, an automatic equalizer for waveform equalization is provided in the terminal device,
Prior to data transmission, a training operation is performed to perform signal equalization according to the line status.

On the other hand, in the case of a mobile communication system, the delay characteristic of the transmission line varies in addition to the amplitude distortion and the phase distortion. For this reason, a training operation is performed on such a transmission line whose delay characteristics fluctuate with a known reference signal (hereinafter, this signal is referred to as a training signal to distinguish it from the reference signal sent from the partner station). Each tap coefficient is converged by using the feedback signal as a reference signal at the time of data to adjust the tap coefficient.

FIG. 3 is a functional block diagram of a prior art decision feedback equalizer applied to a transmission line whose delay characteristics thus fluctuate. In the figure, the input signal terminal 100 is
It is connected to an A / D converter (not shown) and inputs the reference signal or data sent from the partner station as a digital signal. To the input signal terminal 100, serially connected fractionally spaced taps 10-1 to 10-k are connected. The signal input from the input signal terminal 100 is applied to each tap 10
The signals are delayed by a predetermined time by -1 to 10-k and then sent to the multipliers 30-11 to 30-1k.

The training signal input terminal 102 is an input terminal for inputting a training signal during a training operation, and is connected to the tap coefficient calculator 60 via the switch S5 and the symbols connected in series via the switch S6. It is connected to the taps 20-1 to 20-1 of the interval.

The switch S5 is connected to the terminal 104 side to send a training signal to the tap coefficient calculator 60 at the time of training, and is connected to the terminal 106 side to send the output of the determiner 50 to the tap coefficient calculator 60 at the time of data. Also,
The switch S6 is connected to the terminal 110 side to send a training signal to the tap 20 during training, and is connected to the terminal 108 side to send the output of the determiner 50 to each tap 20 at the time of data. The signal input through the switch S6 is delayed by each tap 20 for a predetermined time and then sent to the multipliers 30-21 to 30-2l. The switches S5 and S6 are switching-controlled by a control circuit (not shown).

Multipliers 30-10 to 30-1k and 30
-21 to 30-21 input the tap coefficient calculated by the tap coefficient calculator 60, multiply the input signal by this value, and output the multiplied signal to the adder 40. The adder 40 adds the outputs from the multipliers 30 and 40 and sends the result to the determiner 50 and the tap coefficient calculator 60.

The determiner 50 detects a signal that is not on the complex plane, that is, noise, removes it, and outputs it. The tap coefficient calculator 60 calculates the tap coefficient from the signal input from the adder 40 and the signal input via the switch S5, and outputs the calculated value to each of the multipliers 30 and 40. After the training is completed, when the data from the partner station is sent, the terminal 108 is connected to a decoding circuit (not shown), and the waveform-equalized signal is sent inside the device.

Next, the operation of the prior art will be described with reference to FIG. During the training operation, the tap 10 inputs a signal sampled at every T / n (T: symbol period, n: positive integer) through the input signal terminal 100, and the tap 20 receives the training signal through the switch S6. input. The signal held at each tap 10 and 20 is
The multiplier 30 multiplies the tap coefficient and outputs the result to the adder 40. The tap coefficient calculator 60 inputs the training signal via the output of the adder 40 and the switch S5,
The tap coefficient is adjusted by these signals.

Next, the signal held in each tap 10 and 20 is shifted by the T interval. At this time, the signals held in taps 10-k and 20-l are discarded. A new signal is input to the tap 10 having no shift input, and a training signal is input to the rear tap 20-1. The above operation is repeated for the number of training symbols.

When the training operation is completed, the switches S5 and S6 are switched by a control circuit (not shown), and the tap 20 and the tap coefficient calculator 60 are determined by the determiner 5.
The output of 0 is fed back. That is, unlike the case of the training operation, the output of the determiner 50 and the adder 4 at the time of data are
With the output of 0, the tap coefficient calculator 60 adjusts the tap coefficient.

The operation of the decision feedback equalizer is described in, for example, Shahid UH Qureshi, "Adaptive Equali".
zation ”, PROCEEDING OF THE IEEE, Volume 73. Issue 9 (1
(September 985) 1356-1359.

[0013]

In mobile communication, for example, if a long time is used for the training operation, the time for exchanging data is substantially reduced, so that the tap coefficient can be converged in a short time with high accuracy. It is particularly desirable to be done. However, in the related art, since the tap coefficient is adjusted at the speed of the symbol rate 1 / T even during the training operation, the convergence rate of the tap coefficient depends on the symbol rate. Therefore, in order to reduce the equalization error, a large number of symbols are required for the training operation, and there is a problem that the convergence time is extended by the number of symbols.

The present invention eliminates the drawbacks of the prior art and adjusts the tap coefficient at the rate of overrate, thereby shortening the tap coefficient convergence time and reducing the symbol required for the training operation. An object of the present invention is to provide a decision feedback adaptive equalizer capable of reducing the number and a communication device having the same.

[0015]

In order to solve the above-mentioned problems, the present invention adopts a decision feedback type adaptive equalization for equalizing waveform distortion in a transmission line by performing a training operation prior to data transmission. The container includes a first tap group in which a plurality of branches in which a plurality of first taps are connected in series are arranged in a cascade, and a second group in which a plurality of branches in which a plurality of second taps are connected in series are arranged in a row. Of taps, tap coefficient calculating means for calculating a tap coefficient for equalizing waveform distortion, a plurality of multiplying means for multiplying the input signal by the tap coefficient calculated by the tap coefficient calculating means, Inputting the values multiplied by the multiplying means, adding them, and sending them to the tap coefficient calculating means.

Further, according to the present invention, a communication apparatus having a decision feedback adaptive equalizer as described above for equalizing waveform distortion in a transmission line by performing a training operation prior to data transmission, The synchronous detection circuit that receives the signal sent via this and performs synchronous detection from this signal, the synchronous circuit that detects the position of the reference signal in the training operation from the signal output from the synchronous detection circuit, and the synchronous detection circuit A timing generation circuit that generates a sampling clock from the output signal, a reference signal memory that stores the training signal during the training operation, the position of the reference signal from the synchronization circuit, and the sampling clock from the timing generation circuit, From these, the control of the first switch and the second switch in the decision feedback adaptive equalizer Cormorants and a equalization control circuit.

According to the present invention, during the training operation,
Each branch of the first tap group inputs the reference signal via the first switch, and each branch of the second tap group receives the second signal.
The training signal stored in advance is input via the switch. Then, by performing the switching process of the first switch and the second switch at a predetermined speed,
The adjustment process of the tap coefficient during the training operation is performed at the overrate speed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a decision feedback adaptive equalizer according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a functional block diagram showing an embodiment of a communication apparatus having a decision feedback type adaptive equalizer according to the present invention. In the figure, a functional block diagram of the communication device until decoding the signal received from the partner station is shown.

The synchronous detection circuit 1 is a circuit for extracting the in-phase component and the quadrature component of the signal from the received signal from the partner station.
The synchronous detection circuit 1 includes a synchronous circuit 2 and a timing generation circuit 3.
And A / D converter 6, and sends a signal after detection to them.

The synchronization circuit 2 detects the position of the reference signal from the signal output from the synchronous detection circuit 1 and sends it to the equalization control circuit 4. The timing generation circuit 3 also generates a sampling clock of the received signal from the signal output from the synchronous detection circuit 1 and outputs this clock to the equalization control circuit 4 and the A / D converter 6.

The equalization control circuit 4 uses the signal for notifying the position of the reference signal input from the synchronizing circuit 2 and the signal for notifying the sampling timing input from the timing generating circuit 3 and the equalizing circuit 7 and the reference. Signal memory 5
Control.

The A / D converter 6 samples the signal from the synchronous detection circuit 1 by the sampling clock of the timing generation circuit 3 and outputs a digital signal to the equalization circuit 7. The reference signal memory 5 is a memory in which a training signal during the training operation is stored in advance, and sends the training signal to the equalization circuit 7 during the training operation.

The equalization circuit 7 is a decision feedback type adaptive equalizer that equalizes the waveform of the digital signal input from the A / D converter 6 and outputs it to the decoding circuit 8. The equalizer 7 also uses a control signal from the equalization control circuit 4 to switch S, which will be described later.
The control of 1 to S6 is performed, and the training signal is input from the reference signal memory 5 during the training operation. The decoding circuit 8 is a circuit which receives the signal equalized in waveform from the equalization circuit 7 and decodes the signal.

FIG. 1 is a functional block diagram showing the inside of the equalization circuit 7. An embodiment of a decision feedback type adaptive equalizer according to the present invention will be described with reference to FIG. In addition, in FIG.
The same components as those of the prior art shown in FIG. In this embodiment, as is apparent from the figure, taps 1 (k: positive integer) with a fractional interval are connected in series.
0 is connected to the first to m-th branches, and l (l: positive integer) taps 20 having symbol intervals are serially connected to the first to (m × n) branches.

That is, the taps 10-11 to 10-11 each having a fractional interval.
10-1k is on the first branch, taps 10-21 to 1
0-2k is on the second branch ,. ． ． , Tap 10-
m1 to 10-mk are connected in series to the m-th branch. These first to m-th branches are T / (m
It is connected to the input signal terminal 100 through the switch S1 which switches every xn). Each of the branches 1 to m is also connected to the multiplier 30-1 by the switches S2-0 to S2-k.
0-30-1k is connected.

Similarly, taps 20-11 with symbol intervals are provided.
~ 20-1l is in the first branch, taps 20-21 ~
2l to the second branch ,. ． ． , Tap 20- (mx
n) 1 to 20- (m × n) l are connected in series to the (m × n) th branch, respectively. These first to the first (mx
The branch n) has a training signal input terminal 10 via a switch S4 that switches every T / (m × n).
Connected to 2. Each of the branches 1 to (m × n) is also connected to the multipliers 30-21 to 30-21 by the switches S3-1 to S3-1.
0-2l.

These switches S1 to S4 are switches that operate in synchronization with each other during training under the control of the equalization control circuit 4 (FIG. 2). For example, when the switch S1 is connected to the first branch, the switches S2 to S4. Is also connected to the first branch. Therefore, in this embodiment,
1 / (T / (n
The tap coefficient is adjusted at the speed of * m)).

Next, the operation of this embodiment will be described. First, the operation during training (overrate) will be described. In this case, the switch S5 is connected to the terminal 104 side and the switch S6 is connected to the terminal 110 side. (1) As an initial setting, T / (n * is set for each tap 10 and 20.
The signal sampled every m) (m: positive integer) is input, and the tap coefficient calculator 50 is initialized. (2) The first to the mth operations are performed by the switching process of the switch S1
Any one of the first to (m × n) branches is connected to the training signal input terminal 102 by the switching processing of the input signal terminal 100 and S4, and is switched so as to match each tap interval. The input signal is input. (3) The signals of the taps of the branches designated by the switches S1 to S4 for each T / (n * m) are multiplied by the multipliers 30-10 to 30-3.
After being multiplied by 0-1k, 30-21 to 30-21, the adder 40 adds them. (4) When the addition result of the adder 40 is output to the tap coefficient calculator 60, the tap coefficient calculator 60 uses the result and the previously stored training signal input from the training signal input terminal 102 to calculate the tap coefficient. Is calculated. Then, the calculated tap coefficient is multiplied by the multiplier 30-10.
To 30-1k and 30-21 to 30-21. (5) The signal of each tap of the current branch connected by the switches S1 to S4 is shifted to the next tap. At this time, the signals of the last taps of taps 10 and 20 are discarded. That is, in the case of the first branch, the signals of the taps 10-1k and 20-11 are discarded. (6) An input signal, which is a reference signal, is input to the front tap that is not shift-inputted via the switch S1, and a training signal is input to the rear tap via the switch S4. That is, if it is the first branch, tap 10-
An input signal is input to 11 and a reference signal is input to taps 20-11. (7) The switches S1 to S4 are switched to the next branch. (8) The processes shown in (2) to (7) above are repeated to converge the tap coefficients during the training operation.

When the training operation is completed, the adjustment of the tap coefficient shifts from the over rate to the symbol rate. Therefore, the switches S1 and S4 are fixed to the branch whose training signal has the same value as the determination value. Also,
The switch S5 is at the terminal 106, and the switch S6 is at the terminal 10.
The signal which is connected to No. 8 and has the noise removed by the determiner 50 is fed back to the tap coefficient calculator 60 and the tap 20 on the rear side, and is output from the terminal 108 to the decoding circuit 8 (FIG. 2). This shifts from the training operation to the data input operation.

Next, the operation at the time of data (symbol rate) will be described. (1) The signal at each tap 10 and 20 for each T is multiplied by the multiplier 3
After being multiplied by 0-10 to 30-1k and 30-21 to 30-21, they are added by the adder 40. (2) The tap coefficient calculator 60 inputs the result added by the adder 40 and the signal from which the addition result has been removed to remove noise, and calculates the tap coefficient. The calculated tap coefficient is applied to each of the multipliers 30-10 to 30-1k, 3
0-21 to 30-2l. (3) The signals held in the taps 10 and 20 are shifted by the T interval. At this time, tap 10 and tap 2
The signal held at the last tap of 0 is discarded. (4) The input signal from the switch S1 is input to the tap 10 having no shift input, and the output of the determiner 50 is input to the tap 20 on the rear side of the shift input via the switch S6. (5) While data is being input, the operations (1) to (4) are repeatedly performed, and the adaptation operation is performed at the symbol rate.

As described above, in this embodiment, waveform equalization can be performed while adjusting the tap coefficient at the overrate speed during the training operation and at the symbol rate during the data operation. Therefore, as shown in FIG. 4, it is possible to converge with a smaller number of training symbols than in the conventional technique, and the convergence time can be shortened.
Therefore, the decision feedback adaptive equalizer shown in the present embodiment is effective in a wired communication system, but the interference waveform of the interference waveform in the transmission line in which the delay characteristic varies such as mobile radio communication in the digital communication system. Especially effective for equalization.

Further, in the present embodiment, the adaptation operation is performed at the symbol rate at the time of data, so that the tap coefficient can be adjusted according to the fluctuation of the transmission line even when the data is being received.

The tap adjustment is performed using an algorithm such as the LMS algorithm or the RLS algorithm.

[0035]

As described above, according to the decision feedback type adaptive equalizer of the present invention, a plurality of branches in which a plurality of taps are connected in series are arranged in series, and these branches are switched at a predetermined interval during a training operation. Thus, the tap coefficient can be adjusted at an overrate speed. For this reason,
It is possible to shorten the tap coefficient convergence time during training and reduce the number of symbols in the training operation.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of a decision feedback type adaptive equalizer according to the present invention,

2 is a functional block diagram of a communication device to which the embodiment of FIG. 1 is applied;

FIG. 3 is a functional block diagram showing a decision feedback adaptive equalizer in the prior art;

FIG. 4 is an explanatory diagram showing a comparative example of the convergence characteristics of the related art and the present embodiment.

[Explanation of symbols]

1 Synchronous detection circuit 2 Synchronous circuit 3 Timing generation circuit 4 Equalization control circuit 5 Reference signal memory 6 A / D converter 7 Decision feedback type adaptive equalizer 8 Decoding circuit 10-11 to 10-1k, 10-21 to 10 -2
k ,. ． ． , 10-m1 to 10-mk
Fractionally spaced taps 20-11 to 20-11, 20-21 to 20-2
l ,. ． ． , 20- (m × n) 1 to 20- (m × n) l
Symbol interval taps 30-10 to 30-1k, 30-21 to 30-2l multiplier 40 adder 50 determiner 60 tap coefficient calculator

Claims (2)

[Claims] 1. A decision feedback type adaptive equalizer for equalizing waveform distortion in a transmission line by performing a training operation prior to data transmission, wherein a plurality of branches in which a plurality of first taps are connected in series are connected. A first tap group provided, a second tap group in which a plurality of branches in which a plurality of second taps are connected in series are arranged in series, and a tap coefficient for equalizing the waveform distortion are A tap coefficient calculating means for calculating, a plurality of multiplying means for multiplying the input signal by the tap coefficient calculated by the tap coefficient calculating means, and a value multiplied by the plurality of multiplying means are input and added. And adding means for sending to the tap coefficient calculation means, each branch of the first tap group outputs a reference signal in the training operation via a first switch during the training operation. Each branch of the second tap group inputs a training signal stored in advance via a second switch, and performs switching processing of the first switch and the second switch at a predetermined speed. As a result, the decision feedback type adaptive equalizer is characterized in that the tap coefficient is adjusted at an overrate speed. 2. A communication apparatus having a decision feedback type adaptive equalizer according to claim 1, wherein the waveform distortion is equalized in the transmission line by performing a training operation prior to data transmission. A synchronous detection circuit that receives a signal sent from the synchronous detection circuit and performs a synchronous detection from this signal; a synchronous circuit that detects the position of the reference signal in the training operation from the signal output from the synchronous detection circuit; A timing generation circuit that generates a sampling clock from the signal output from the circuit, a reference signal memory that stores a training signal during the training operation, a position of the reference signal from the synchronization circuit, and a timing generation circuit from the timing generation circuit. The sampling clock is input and the first clock in the decision feedback adaptive equalizer is input from them. Communication device; and a equalization control circuit for controlling the switch and the second switch.