JPH0273504A - Digital signal magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To lower a bit error rate by the distortion of an electromagnetic conversion system by setting the threshold value of a decoder at a level where the distances from adjacent signal points on a signal arrangement drawing are substantially equal. CONSTITUTION:In a decoder 18 to convert the quaternary signals of the two systems of LPFs 16 and 17 into a digital signal, its threshold value is not fixed as before and a threshold value table is stored beforehand in a prescribed ROM so that the threshold value can be adjusted. The decoder 18 sets the threshold value at the level where the distances from the adjacent signal points on the signal arrangement drawing are substantially equal. Therefore, since the threshold value fit for the distortion can be set for the distortion of the electromagnetic conversion system, the bit error rate can be made lower than the decoding of a fixed threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital videotape recorder (DVT).
The present invention relates to a digital signal magnetic recording/reproducing device for recording and reproducing digital signals such as R) on a magnetic recording medium.

2. Description of the Related Art In general, when multilevel amplitude quadrature modulation (QAM) is used as a modulation method for digital signals, the method for converting two systems of multilevel signals into digital signals in decoding is as follows.
Hard decisions are often used to identify signals using a certain threshold level set between each signal point in the signal constellation map after modulation (for example, "Digital Wireless Communication", Masayoshi Murotani, Sangyo Tosho (1985 37-). page 55).

Problems to be Solved by the Invention However, when QAM is used for magnetic recording and reproduction of digital signals, nonlinear distortion caused by the electromagnetic conversion system causes distortion in signals corresponding to large power components, as shown in Figure 3 (a).
), the signal arrangement that should exist may become as shown in FIG. 3(b).

In this case, if the reproduced signal is decoded and converted into a digital chill signal using a hard decision, there is a drawback that the bit error rate after identification increases.

The present invention was made in view of the problems with conventional QAM decoding, and takes into account nonlinear distortion of the electromagnetic conversion system.
The purpose of this invention is to obtain a digital signal magnetic recording and reproducing device that reduces the bit error rate by increasing the precision of the decoder.

Means for Solving the Problems In order to achieve the above object, the digital signal magnetic recording and reproducing apparatus of the present invention includes a multi-value converting circuit that converts an input digital signal into two systems of multi-value signals, and a multi-value converting circuit that converts the multi-value signal into two systems of multi-value signals. A modulator that performs two-phase modulation, a magnetic recording and reproducing unit that records the modulated signal on a magnetic recording medium and reproduces it from the recorded medium, and a reproduced signal from the modulated magnetic recording and reproducing unit. The threshold level is defined as the level at which the distance from the demodulator that demodulates two systems of multi-level signals and the adjacent signal points on the signal constellation diagram, which changes due to the distortion received by the demodulated multi-level signal, is substantially equal. and a decoder that decodes the signal.

Effect of the present invention With the above-described configuration, the threshold value of the decoder is set so that the distance from the signal point after demodulation is equal, taking into account the nonlinear distortion generated in the electromagnetic conversion system. The signal is accurately decoded in a certain state, and the bit error rate can be reduced.

Embodiment Hereinafter, a digital signal magnetic recording and reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the main configuration of an embodiment of the present invention. An n-bit digital signal is input to a multi-value conversion circuit 2 from an input terminal 1. Although the number of input bits can be any value, the case of 4 bits (16 values) will be explained below. The input 4-bit digital signal is output by the multi-value converting circuit 2 as two systems of 4-value signals for each of the upper and lower two pits. The outputs of the multilevel conversion circuit 2 are each input to a low pass filter (hereinafter referred to as LPF) 3.4.

LPF3.4 has root cosine roll-off characteristics. The output of the LPF 3.4 is given to the modulator 5.

The modulator 5 performs quadrature two-phase modulation by combining the amplitude modulated waves of two systems of four-level signals using the carrier wave output from the carrier wave generator 6 and a carrier wave whose phase is shifted by π/2 from this carrier wave. Yes, 16-level quadrature amplitude modulation (16QAM)
Output a signal. The 18QAM signal output from the modulator 5 is input to an adder 7, where it is added to a bias signal output from a bias signal generator 8, and input to a recording amplifier 9. The output signal of the recording amplifier 9 is sent to the recording head 10.
Bias recording is performed on the magnetic recording medium 11 via the magnetic recording medium 11.

A signal recorded on the magnetic recording medium 11 is reproduced by a reproduction head 12 and input to a reproduction amplifier 13. The reproduced signal amplified by the regenerative amplifier 13 is input to an equalization circuit 14, where frequency deterioration occurring in the electromagnetic conversion system is corrected. The output of the equalization circuit 14 is input to a demodulator 15. The reproduced 18QAM signal input to the demodulator 15 is synchronously detected by the reproduced carrier wave output from the carrier wave regeneration circuit 20, and is detected by the LPF 16. 17. LPF18. 1
7 has a root cosine φ roll-off characteristic. LPF16. The output of 17 is input to a decoder 18 as two systems of four-level signals. The two systems of multilevel signals input to the decoder 18 are outputted from the output terminal 19 as 4-bit (16-value) digital signals. Also, LPF16
．． The output of 17 is input to a carrier wave recovery circuit 20 and used for carrier wave recovery.

FIG. 2 shows the configuration of the decoder 18. The demodulated multilevel signals inputted from terminals 31 and 32 are respectively quantized into N bits by analog-to-digital converters (hereinafter referred to as A/D converters) 33 and 34. Here, it is assumed that N>n/2. For a conventional hard-decision decoder with a fixed threshold, the A/D
The number of quantization pits in the converter is n/2 bits, and the A/D
The converter is the only component of the decoder. On the other hand, in the present invention, the threshold value can be adjusted by setting N>n/2. For example, let N=8 bits.

The outputs of the A/D converters 33 and 34 are input to a lead fist only memory (hereinafter referred to as RO&1) 35. R.O.
M35 is each 8-bit A/D of A/D converter 33 and 34.
The conversion output is converted into 16-bit address information, converted into a 4-bit (16-value) digital signal on the ROM table, and outputted from output terminals 36, 37, 38, and 39. The ROM 35 stores in advance a table of threshold values for converting from 2N bits to n bits.

In other words, the decoder 18 considers nonlinear distortion in two dimensions on the signal arrangement, as shown in FIG. This is a decoder that has equal threshold values and determines the output signal using the values of the ■ axis and Q axis as address information.

As described above, according to this embodiment, due to the nonlinearity of the electromagnetic conversion system, the signal arrangement originally shown in FIG. 3(a) becomes distorted as shown in FIG. 3(b). By setting a threshold according to the distortion, the bit error rate can be reduced compared to decoding using a fixed threshold.

In addition, in the embodiment of the present invention, the LPF before modulation
Although the LPF and the demodulated LPF each have a root cosine roll-off characteristic, they may also have a cosine roll-off characteristic as a characteristic throughout the device including the magnetic conversion system.

Furthermore, although 16QAM modulation has been described in this embodiment, it goes without saying that it is also applicable to 84QAM and the like. In that case, if the signals shown in the demodulated signal constellation diagram shown in FIG. 4(a) are reproduced after magnetic recording, the reproduced signal constellation diagram will be as shown in FIG. 4(b). At this time as well, the threshold level shown by the broken line in the figure is used so that the distances from adjacent signal points are equal.

Effects of the Invention As described above, according to the present invention, the threshold value of the decoder is considered two-dimensionally on the signal constellation diagram, and the adjacent Since the threshold value is set so that the distances from the two signal points are substantially equal, the bit error rate due to distortion can be reduced, which is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of main parts showing one embodiment of the present invention, and FIG.
Figure 3 is a block diagram of a decoder in an embodiment of the present invention.
Figure (a) shows how the digital signal is converted into one in the embodiment of the present invention.
Signal arrangement diagram after modulation to 8QAM signal, Figure 3(b)
4(a) is a signal arrangement diagram of a 16QAM signal reproduced after recording on a magnetic recording medium, FIG. 4(a) is a signal arrangement diagram after modulating a digital signal into a 64QAM signal in an embodiment of the present invention, and FIG. 4(b) is a signal arrangement diagram of a 64QAM signal reproduced after recording on a magnetic recording medium. 2φ...Multi-value circuit, 3, 4...L P F. 5...Modulator, 6...Carrier wave generator, 7.
...Adder, 8...Bias signal generator, 9...
・Recording amplifier, 13. Life Φ reproduction amplifier, 14. Φ.
Equalization circuit, 15Φ・Program adjustment, 16, 17・
Skewer φLPF1 18...Decoder, 20Φ...Carrier regenerator, 33, 34...A/D converter, 35
-・-ROM. Figure Figure

Claims (1)

[Claims] A device for recording and reproducing digital signals on a magnetic recording medium, which includes a multi-value circuit that converts an input digital signal into two systems of multi-value signals, and a modulator that modulates the multi-value signal into two-phase orthogonal signals. , a magnetic recording and reproducing unit that records the modulated signal on a magnetic recording medium and reproduces it from the recorded medium, and a two-system multi-value system that outputs the reproduced signal from the magnetic recording and reproducing unit that has undergone the modulation. A demodulator that demodulates the signal, and a decoder that decodes the signal using a threshold level at which the distances from adjacent signal points on the signal constellation diagram, which change due to distortion due to nonlinearity of the electromagnetic conversion system, are substantially equal. What is claimed is: 1. A digital signal magnetic recording and reproducing device comprising: