JP2551080B2 - Adaptive receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention automatically estimates transmission path characteristics in an adaptive receiver, particularly in digital signal transmission on a transmission path having selective fading, and The present invention relates to improvement of a receiver that adaptively configures optimum receiver characteristics.

[Prior Art] Conventionally, diversity reception is often performed as a measure against fading. However, if there is selective fading that causes a deep notch in the signal band, only minus and plus diversity of diversity can provide sufficient transmission quality. Often cannot be secured. On the other hand, it is known that by introducing decision feedback automation and combining it with diversity, a considerable improvement effect can be obtained.

For this reason, conventionally, an adaptive receiver including an adaptive matched filter, a decision feedback equalizer, etc. has been proposed (Japanese Patent Application No. 54-19367).

FIG. 2 shows a conventional example of an adaptive receiver.
In the figure, 2 and 2 are input terminals, 3 and 4 are a plurality of transversal filters provided in proportion to the diversity multiplicity, 5 is an adder, 6 is an automatic gain control amplifier, 7 is a forward equalizer, 9 is a demodulator, 10 is a subtractor, 11 is a determiner, 12 is a subtractor, 13 and 14 are correlators, 15 and 16 are modulators, 17 and 18 are correlators, and the first diversity transmission Road signal is terminal 2
To the transversal filter 3, and the second diversity transmission path signal is input from the terminal 2 to the transversal filter 4. The outputs of the two transversal filters are linearly combined by the adder 5 to perform optimum diversity combining.

The output of the adder 5 is gain-controlled by the automatic gain control amplifier 6.

Then, the output of the automatic gain control amplifier 6 is subjected to the inter-symbol interference at the leading edge of the pulse in the front equalizer 7.

The output signal of the front equalizer 7 is demodulated in the demodulator 9 and output to the subtractor 10. Also the subtractor
A feedback signal generated by the backward equalizer 8 is input to the input terminal 10.

Then, the subtractor 10 subtracts the feedback signal output from the backward equalizer 8 from the output signal of the demodulator 9, thereby removing intersymbol interference due to the trailing edge of the pulse, and outputting.

In this way, the signal output from the subtractor 10 is identified by the determiner 11, and a transmission data estimation value that is hardly affected by intersymbol interference due to selective fading is output from the terminal 19 as a receiver output.

At this time, the tap gain of the transversal filter 3 is adjusted by the correlator 13 to which the transmission data estimated value and the signal from the terminal position are input. Similarly, the tap gain of the transversal filter 4 is adjusted by the correlator 14.

Further, the subtractor 12 outputs the difference between the input and output signals of the determiner 11 as an error signal, and outputs it to the correlator 17 via the modulator 15.

The correlator 17 adjusts the tap gain of the front equalizer 7 based on the error signal input via the modulator 15 and the input signal of the front equalizer 7.

In this way, the adaptive receiver is provided with the transversal filters 3 and 4 in each of the diversity transmission lines, and the tap gains of the transversal filters 3 and 4 are not set so as to minimize the error signal. It is adjusted to estimate the sample value of the equivalent baseband impulse response of each diversity transmission line. That is, the transversal filters 3 and 4 form an adaptive matched filter for the corresponding diversity, and the outputs of the transversal filters 3 and 4 are combined to optimize the SN ratio.

Furthermore, the output that combines the output signals of each filter,
A decision feedback equalizer composed of a front equalizer 7 and a backward feedback equalizer 8 is connected in cascade, and intersymbol interference is removed by this equalizer.

[Problems to be solved] However, in such a conventional optimum receiver, when the input level to the transversal filters 3 and 4 is turned off or lowered, the output level of each of these filters 3 and 4 is lowered, As a result, the data cannot be demodulated, and the control signals from the correlators 13 and 14, which are the correlation values between the data signal and the input signal, to the filters 3 and 4 are zero voltage because they are uncorrelated.

Therefore, even if the input signals to the filters 3 and 4 are restored thereafter, the filter output level remains low because the control signals to the filters 3 and 4 are 0 voltage, and data demodulation can be restarted. There was a problem that I could not.

In particular, such a receiver is used in various environments, and the input level often drops due to severe facing, etc. It has been desired to develop an adaptive receiver capable of resuming data demodulation promptly when the signal returns.

The present invention has been made in view of such a conventional problem, and an object thereof is to adapt to the fact that even if the input level is lowered, the demodulation of data can be restarted at the same time as soon as the input level is restored. Type receiver.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides: a number of transversal filters proportional to diversity multiplicity; a means for linearly combining the outputs of the respective transversal filters; An automatic gain control amplifier that performs automatic gain control, a decision feedback equalizer that receives an output signal of the automatic gain control amplifier, and a tap gain of the transversal filter that receives a transmission data estimation value are provided to respective diversity transmission lines. A means for adjusting to form a matched filter, receiving the transmission data estimated value and the output signal of the decision feedback equalizer, and adjusting the tap gain of the decision feedback equalizer so that intersymbol interference is minimized. Adjusting means for obtaining a received output signal which is the transmitted data estimation value; and Based on the level detection signal of the amplifier,
When the level is lowered, the transversal filter provided in at least one diversity path is provided with a means for controlling the transversal filter to a forced pass state.

[Example] Next, a preferred example of the present invention will be described. Members corresponding to those of the conventional device shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 shows a preferred embodiment of the adaptive receiver according to the present invention.

According to the present invention, based on the level detection signal of the automatic gain control amplifier 6, a forced bias is applied to the tap signal of the transversal filter provided in at least one diversity path when the level is lowered, and the filter is controlled to the forced pass state. It is characterized in that a control circuit 21 is provided.

With the above configuration, the level of the input signal to the filters 3 and 4 is lowered due to, for example, severe fading, and as a result, the output level of the automatic gain amplifier 6 is lowered, data reproduction is erroneous, and the correlator 13, 14 control signals are 0
Even if the signal input is rejected, the control circuit 21
At least one of 3 and 4 is controlled to the forced passage state.

Therefore, when the input signals to these filters 3 and 4 are restored, appropriate tap signals are output from the correlators 13 and 14 to the corresponding filters 3 and 4, so that the adaptive receiver itself can be restored immediately. it can.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention.

For example, although double diversity is considered in the present embodiment, generally with N-fold diversity, exactly the same operation can be performed if the number of transversal filters and correlators is N.

Furthermore, the transversal filter and forward equalizer
It is also possible to operate after demodulation, ie in the band.

[Effects of the Invention] As described above, according to the present invention, when there is an error in data reproduction due to an input level or the like, 0 output of a correlation value, or a decrease in output level of an automatic gain control amplifier, a transversal filter is used. By forcibly applying a bias to the tap signal and controlling the filter to be forcedly passed, there is an effect that the adaptive receiver can be immediately restored.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a preferred embodiment of an adaptive receiver according to the present invention, and FIG. 2 is a block circuit diagram of a conventional adaptive receiver. 1,2 …… Input terminals 3,4 …… Transversal filter 5 …… Adder 6 …… Automatic gain control amplifier 7 …… Front equalizer 8 …… Back equalizer 9 …… Demodulator 10… Subtractor 11 …… Judger 12 …… Subtractor 13,14 …… Correlator 15,16 …… Modulator 17,18 …… Correlator 19 …… Output terminal 21 …… Control circuit

Claims (1)

(57) [Claims] 1. A transversal filter having a number proportional to diversity multiplicity, a means for linearly combining the outputs of the transversal filters, an automatic gain control amplifier for performing automatic gain control of a linearly combined signal, and A decision feedback equalizer for receiving the output signal of the gain control amplifier; a means for adjusting the tap gain of the transversal filter for receiving the transmission data estimation value so as to configure a matched filter for each diversity transmission path; Receives the transmission data estimation value and the output signal of the decision feedback equalizer, adjusts the tap gain of the decision feedback equalizer so that intersymbol interference is minimized, and outputs the reception output signal that is the transmission data estimated value. An adaptive receiver including: a means for obtaining a level when the level is lowered based on the level detection signal of the automatic gain control amplifier. An adaptive receiver characterized by further comprising means for controlling a transversal filter provided in at least one diversity path to a forced pass state.