JPH05284063A - Automatic equalizer - Google Patents

Abstract

PURPOSE:To provide an over sampling type automatic equalizer which can be applied when a multi-level digital modulation/demodulation system is used for the field of mobile communication. CONSTITUTION:At the judge feedback type automatic equalizer provided with a sampler to sample received signals at sampling intervals shorter than a repeating cycle T of a data symbol, and front and rear taps to be supplied the output of this sampler, transversal filters (30-33 and 130-133) are provided with two antenna diversity inputs or more as front taps, and taps just for the number of dividing the repeating cycle T are provided as rear taps.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system using a digital modulation / demodulation system and, more particularly, to an automatic equalizer for mobile communication in an applicable area having a delay time range of a short symbol period. ..

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Examined Patent Publication No. 4-6132, in an automatic equalizer, in order to eliminate variations in the timing phase of the received signal and to stably perform clock extraction, the received signal is converted into data symbols. Sampling is performed at a sampling interval shorter than the repetition cycle T of, and this is called an oversampling type automatic equalizer, which is known as an equalizer capable of absorbing a timing phase shift of a received signal.

FIG. 2 shows an example of the block configuration of a conventional oversampling type automatic equalizer. The received signal is input from the receiving antenna 10 and the Automatic Gain Con
After the average level is adjusted by the troll (AGC) 20, it is converted into a baseband band by the detection unit 21 and input to the automatic equalizer unit. In this equalizer unit, the delay element 3 is sampled at a timing when the input signal is sampled by oversampling by n times.
The data is input to the transversal filter unit composed of 0 to 33 and transferred while sequentially shifting (T / n). These shifted data are multiplied by tap coefficients in multipliers 70 to 73 and then added in adder 40. Further, the addition result is identified by the identifier 41 as digital data and output to the output terminal 42.

The difference value between the data before and after the discriminator 41 is sent to the next tap coefficient control unit 60 as a discrimination error. The tap coefficient control unit 60 uses an algorithm (Least Mean) that minimizes the discrimination error in a root mean square manner.
Square algorithm: LMS) or recursive Lesat Square algorithm (RLS)
Is used to control the tap coefficient to be multiplied by the multipliers 70 to 73.

[0005]

However, with this equalizer configuration, when it is used in an application area such as mobile communication, delayed waves due to reflection / scattering due to buildings or terrain (mountains, hills), etc. are dealt with. Therefore, there is a problem that the identification error of the equalizer does not converge, the identification error increases, and the received signal does not exactly match the transmitted signal. In addition, a large number of training symbols are required during the training operation for initializing the tap coefficient of the equalizer, and thus there is a drawback that the number of information symbols in the transmission data cannot be increased.

[0006]

The present invention eliminates the above-mentioned problems and provides an oversampling type automatic equalizer applicable when a multilevel digital modulation / demodulation system is used in the field of mobile communication. The purpose is to do. The present invention relates to an oversampling type automatic equalizer,
As a front tap, a transversal filter having two or more antenna diversity inputs is provided, and as the rear tap, the number of taps equal to the number obtained by dividing the repetition cycle T is provided.

[0007]

1 is a block diagram of an oversampling type automatic equalizer according to the present invention. In FIG. 1, FIG.
The same number is used for the same function.

The operation of FIG. 1 has two antennas 10 and 11.
The received input signals from 0 are corrected in average levels by the AGCs 20 and 120, converted into baseband bands by the detection units 21 and 121, and input to the automatic equalizer unit, respectively. In the automatic equalizer unit, these two inputs are input to the transversal filter units (30 to 33, 130 to 133) which form the two front tap filters. FIG. 1 shows an example where n = 2.

The input data is branched from the delay element which is each component, multiplied by the tap coefficient data, and input to the adder 40. The output of the adder 40 is input to the discriminator 41, and the difference value of the data before and after the discriminator 41 (the output of the subtractor 50) is input to the tap coefficient control unit 60.

Further, the output of the discriminator 41 is input to delay elements 81 and 82 (here, n = 2, so there are two) which form a backward tap, and a multiplier 90 multiplies the tap coefficients. Then, it is input to the adder 40.

On the other hand, the tap coefficient control unit 60 controls the tap coefficients of the front filter and the rear filter by using the above-described LMS and RLS algorithms.

An example in which the automatic equalizer operates normally due to the presence of this rear filter is shown in FIGS. 3 and 4. In FIG. 3, the horizontal axis represents the number of training symbols, and the vertical axis represents the characteristic in which the output power of the subtractor 50 is normalized by the input power of the automatic equalizer. The condition of FIG. 3 is that the received signal of 16QAM to which Rayleigh fading of two waves is added is input to the automatic equalizer having the configuration of FIG. The characteristic of the automatic equalizer of FIG. 1 of the present invention converges at 20 to 30 symbols, whereas the characteristic of the conventional example FIG. 2 does not converge even at 150 symbols.

Further, FIG. 4 is a bit error rate characteristic (BER) showing the result of bit-by-bit comparison between the transmission data and the reception data in the information data section after the training state of FIG. 3 is completed. The vertical axis represents the bit error rate, and the horizontal axis represents the power Eb per bit from the total power of the direct wave and the delayed wave. Similar to FIG. 3, compared with the characteristics of the conventional example, Eb in the practical range (BER = 10 ⁻² to 10 ⁻³ )
Since / N ₀ is improved by ₈ to 10 dB, it can be seen that it has a great effect on the improvement of communication quality.

[0014]

As described above, the present invention can deal with delayed waves due to reflection / scattering due to buildings or terrain (mountains, hills) or the like in an application area such as mobile communication. Can be reduced, and a great effect can be expected in improving reliability. Further, since the number of training symbols in the training operation for initializing the tap coefficient of the equalizer can be reduced as compared with the conventional method, there is an advantage that it helps improve the information transmission efficiency.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an automatic equalizer of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional automatic equalizer.

FIG. 3 is a characteristic example 1 of the automatic equalizer (normalized identification error power).
Graph showing

FIG. 4 is a graph showing a characteristic example 2 (bit error rate characteristic) of the automatic equalizer.

[Explanation of symbols]

10,110 Reception antenna 20,120 AGC 21,121 Detection part 30-33 Delay element of transversal filter part 130-133 Delay element for transversal filter 40 Adder 41 Discriminator 50 Subtractor 60 Tap coefficient control part 70- 73 multiplier 170-173 multiplier 81,82 delay element 90 multiplier

Claims (1)

[Claims] 1. A sample feedback circuit for sampling a received signal at a sampling interval shorter than a repetition period T of a data symbol, and a decision feedback type automatic equalizer having a front tap and a rear tap to which an output of this sampler is supplied. An automatic equalizer having a transversal filter having two or more antenna diversity inputs as front taps, and providing as many taps as rear taps by a number obtained by dividing the repetition period T.