JPH0454733A - Signal processing unit - Google Patents

Abstract

PURPOSE:To ensure the estimate and correction of deterioration in the S/N in real time by superimposing a consecutive known signal onto a consecutive transmission (recording) original signal and allowing a signal reception (reproduction) device to estimate the state of deterioration in the S/N in real time based on a known noise signal whose S/N is deteriorated through a transmission path and to use a reception signal based on the estimated value. CONSTITUTION:Since a signal transmitter superimposes a known signal from a known signal generating means 10 onto an original signal SS in real time to estimate the deterioration in the characteristic through a signal transmission system 3, the known signal included in the reception signal is also subjected to the effect of the signal transmission path 3 similarly to the case with the original signal. Since a signal receiver knows a form of the known signal already, the effect on the original signal due to the deterioration in the characteristic through the signal transmission path 3 is recognized by analyzing the reception state representing the deterioration in the known signal. Thus, an adaptive filtering means 50 estimate the effect, and a signal reproduction means 52 eliminates the estimated signal and the superimposed known signal to reproduce the original signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording/reproducing device such as a tape recorder, or a signal transmission method such as a communication method having a transmitting device and a receiving device.

A signal transmission device and this signal transmission device that improves the S/N deterioration of the signal from the recording system (or transmission system) whose characteristics have deteriorated in the intermediate signal transmission system and reproduces (demodulates) the signal accurately. The present invention relates to a signal transmission system having a corresponding signal receiving device.

[Prior Art and Problems to be Solved by the Invention] In signal recording/reproducing devices such as tape recorders, in order to improve S/N deterioration in high frequency regions, a recording/reproducing intermediate section having a head etc. is used during recording. Pre-emphasis processing is performed to suppress the influence of noise added during playback, and de-emphasis processing corresponding to the pre-emphasis is performed during playback to perform playback processing of the recorded signal. There are various other methods that perform such pre-emphasis processing and de-emphasis processing, such as one communication system. In the communication system as well, in order to improve S/N deterioration in a signal transmission intermediate system, for example, a wireless communication path, a transmitting device performs pre-emphasis processing and a receiving device performs de-emphasis processing.

Such emphasis processing is normally performed with a fixed time constant of 1. However, in a tape recorder, for example, the influence of hysteresis noise that occurs during recording on and reproducing from a magnetic tape (VL magnetic tape magnetic material) cannot be avoided. The ratio (S/N) of such hysteresis noise to the signal differs depending on the type of magnetic material, the characteristics of the recording head, etc. Furthermore, the spectral distribution of signals to be recorded also varies. therefore.

Such emphasis processing with a fixed time constant cannot optimally improve characteristic deterioration in the high frequency region.

If one attempts to make the time constant variable in order to improve the above-mentioned problem caused by the fixed time constant, it is necessary to inform the reproduction system of the time constant required at each time during reproduction. However, since such time constant information must normally be recorded on the magnetic tape,
This method cannot be easily adopted.

Furthermore, when a pre-emphasis circuit and its inverse de-emphasis circuit are constructed from analog circuits such as amplifiers, resistors, and capacitors, such analog circuits suffer from variations in component characteristics, large temperature dependence, and aging (deterioration). ) etc., it is difficult to obtain de-emphasis characteristics as accurate inverse characteristics to pre-emphasis.

As a result, a problem arises in that accurate signal reproduction cannot be performed.

The above-mentioned problem is not limited to recording and reproducing devices such as tape recorders, but is also a problem in communication systems that are subject to various signal deteriorations in the signal transmission system between the transmitting system and the receiving system.

For example, a ghost canceller is known as a solution to such a problem. However, since the ghost canceller is a method that grasps the deterioration characteristics of the signal transmission system by transmitting impulses etc. during the signal pause time when no transmitted signal is present, it is possible to detect the S/N degradation that is added to the actual transmitted signal in real time. The effects cannot be completely removed in real time. Additionally, a ghost canceller transmits a continuous signal with no pauses.

For example, it cannot be applied to tape recorders or communication systems that continuously transmit signals.

Therefore, the present invention provides a signal transmission system that optimally improves S/N deterioration in a signal transmission system for continuous signals and reproduces (or demodulates) accurate signals, as well as a signal transmission system that is applied to this signal transmission system. recording) equipment and signal reception (
The purpose is to provide a playback) device.

[Means to solve the problem]

In order to solve the above problems, 1 the signal transmission system of the present invention, as shown in FIG. 10. Adding means 12 for superimposing the known continuous signal on the continuous original signal. and.

A signal sending device is provided which includes pre-emphasis means 14 for performing pre-emphasis processing on the superimposed signal from the addition means. Furthermore, the signal transmission system of the present invention provides a signal receiving side 5 with a predetermined method for estimating the reception characteristics degraded in the signal transmission system 3 based on the known signal and estimating the emphasis characteristics added to the received signal. Adaptive filtering means 50 for performing adaptive filtering processing. Further, there is provided a signal reproducing device comprising a signal reproducing means 52 for subtracting a signal corresponding to the known signal added to the original signal on the signal sending side from the output signal of the adaptive filtering means.

Note that the signal sending device and the signal receiving device may be provided independently or may be provided integrally so as to cooperate with each other, provided that the signal receiving device is operated in correspondence with the signal transmitting device.

[Effect]

In the signal transmitting device, since the known signal for estimating characteristic deterioration in the signal transmission system 3 from the known signal generating means 10 is superimposed on the original signal S in real time, the known signal included in the received signal is also the original signal. It is affected by the same signal transmission path 3. Since this known signal form is known by the signal receiving device, by analyzing the degraded reception state of this known signal, the influence of characteristic degradation in the signal transmission path 3 of the original signal can also be determined. Therefore, the adaptive filtering means 50 estimates this influence, and the signal reproducing means 52 removes the estimated bone and the superimposed known signal to reproduce the original signal.

〔Example〕

FIG. 2 shows a signal processing circuit for a tape recorder as an embodiment of the signal transmission system of the present invention.

In FIG. 2, a magnetic tape recording/reproducing section 300 as a signal transmission system 3 is provided between the signal transmitting (recording) side 1 and the signal reproducing side 5 in FIG. teeth,
Known signal generation circuit 100 as known signal generation means lO in FIG. A pre-emphasis circuit 140 is provided as the addition means 12 and pre-emphasis means 14 shown in FIG. Further, on the signal receiving (reproducing) side 5, an LMS (least square method) adaptive filter circuit 500 as an adaptive filter means 50 is provided. De-emphasis reproducing circuit 520 as signal reproducing means 52. Then, the synchronization signal detection circuit 54
0 is set.

The magnetic tape recording/reproducing section 300 records the following information on the magnetic tape 310:
An amplifier 302, a recording head 304, and a magnetic tape 310 for recording continuous analog original signals such as audio.
a playback head 322 for playing back the original signal recorded on the
and an amplifier 324 are provided.

The known signal generation circuit 100 includes a known noise generation circuit 102 and a pilot signal generation circuit 104. The known noise generation circuit 102 generates a known noise that can be clearly distinguished from the original signal for recording and the noise applied by the magnetic tape recording/reproducing section 300 as a signal for estimating the emphasis characteristic on the recording side during signal reproduction. Generate a signal, for example 1M sequence noise. The known noise signal 5102 generated by the known noise generation circuit 102 is a continuous noise signal because it is continuously superimposed on the continuous recording original signal S. Further, the pilot signal generating circuit 104 generates a continuous pilot signal 5104 as a known synchronization signal for synchronizing the signal receiving side 5 with the signal transmitting side 1.

A circuit example of the known noise generation circuit 102 is shown in FIG. Delay type flip-flops (D-FF) 1021 to 1028 are connected as shown in the figure. The Q output of the previous stage is applied to the D input of the D-FF of the next stage, and the recording (signal sending) side clock CLK is applied to the clock terminal of each D-FF. In this example, the known noise signal 5102 is output from each D-FF 1021-1028 as 8-bit M-sequence noise signal data Q1-Q8. By appropriately changing the input signal to the EXOR game (EXOR game) 1029, the noise signal pattern can be changed. Further, the circuit configuration of the viroft signal generation circuit 104 is shown in FIG.

The pilot signal generation circuit 104 includes an address counter 1
04a! : Consists of ROM104b. The address counter 104a outputs an 8-bit address signal in response to the recording side clock CLK, and this 8-bit address signal is applied to the ROM 104b and the corresponding ROM 104 is
Read the data in b. In the ROM 104b, 8-bit sine wave pattern data is stored in advance as a pilot signal. Therefore, in this embodiment, the pilot signal generation circuit 104 outputs a sine wave pilot signal as a synchronization signal. The value of the frequency of this pilot signal is set to be an integral multiple, for example, 256 times, of the frequency f sampled by an analog/digital converter 502 on the receiving side 5, which will be described later.

Furthermore, the known signal generation circuit 100 generates an 8-bit known noise signal 5102 and an 8-bit sine wave pilot signal 5.
Adder 106° that overlaps 104 and adder 106
It has a D/A converter (DAC) 108 that converts the superimposed digital signal from the DAC into an analog signal.

therefore.

A 9M sequence noise signal 510 is generated from the known signal generation circuit 100.
2 and a sinusoidal pilot signal 5104 is generated in analog form.

The pre-emphasis circuit 140 shown in FIG. 2 is an analog circuit pre-emphasis circuit consisting of a bypass filter and a summing amplifier circuit.
A known noise signal from the known signal generation circuit 100 is added to (superimposed on) s, and the added signal is emphasized with characteristics as shown by the solid line in FIG. Figure 5 shows
The horizontal axis represents frequency, and the vertical axis represents frequency response (dB). Note that the broken line indicates a de-emphasis characteristic line corresponding to emphasis.

A pre-emphasis signal 5140 from the pre-emphasis circuit 140 that emphasizes the ti signal on which the recording original signal, known noise signal and pilot signal are superimposed is sent to the magnetic tape 3 via the amplifier 302 and the recording head 304.
recorded in 10.

Next, first, the entire circuit of the signal receiving side 5 will be described.

The LMS adaptive filter circuit 500 applies a least squares method (LMS) to an M-sequence noise signal for estimating the characteristics of the magnetic tape recording/reproducing section 300 and a synchronization pilot signal from the signals read through the reproducing head 322 and the amplifier 324. Extract by filtering. The de-emphasis reproducing circuit 520 estimates the inverse characteristic of pre-emphasis by performing adaptive filtering processing, and reproduces a signal corresponding to the original signal S. The synchronization signal detection circuit 540 receives a synchronization signal for operating the LMS adaptive filter circuit 500 and the de-emphasis regeneration circuit 520 in synchronization with the signal from the signal transmission side 1, and a regeneration (reception) side system clock CL K sv.
s, generates a sampling clock CLKsrL and a reset pulse RESET.

The LMS adaptive filter circuit 500 includes an analog/digital converter (ADC) 502. Delay circuit 504. FI
R filter 506. A subtraction circuit 50B is connected and configured as shown in the figure. The ADC 502 receives a sampling clock CLKS from the synchronization signal detection circuit 540, for example, with a sampling frequency f, = 48KH.
Based on the PL, the analog signal recorded on the magnetic tape 310 detected by the reproducing head 322 is converted into a 16-bit digital signal. , delay circuit 504 and FI
R filter 506 extracts a pilot signal from this regenerated ADC signal 5502. The delay circuit 504 may delay the recovered ADC signal 5502 for a predetermined period of time long enough such that there is no signal correlation.

It consists of a FIFO buffer memory that delays by 10,000 samples. This delayed signal is the FIR filter 5
06 to reproduce a sine waveform corresponding to the pilot signal 5104. The subtraction circuit 508 is a reproduction ADC.
The extracted pilot signal 5506 is subtracted from the signal 5502 to extract the component of the recording original signal S3 and the known noise signal 5102 component on the signal sending side superimposed on this signal component (this is called the re-outgoing signal 5508). do. This reproduction original signal 3508 has a degraded S/N due to the influence of the magnetic tape recording/reproducing section 300.

The FR filter 506 will be described with reference to FIG. This FIR filter 506 is composed of SPs whose tap coefficients can be updated, and each stage has a unit delay circuit Z-1. Coefficient multiplication circuit M= (i= 1.2...
. , n) and an adder circuit Σ are connected in n stages in series as shown. In this example, n is 65. That is, this FIR filter 506 is a 65-tap FIR filter. Coefficient multiplication circuit M1
multiplies the output and coefficient of the previous stage unit delay circuit Z-1 by 8. This multiplication result is added to the addition result of the adder circuit Σ1 at the previous stage. An S/N deterioration correction pilot signal 3506 is output from the final stage adder circuit Σ1. In order to appropriately perform S/N deterioration correction, the tap coefficient ki to be added to the coefficient multiplication circuit M is appropriately determined. For this reason, the FIR filter 506 is further provided with an adder circuit Σ and an LMS adaptive algorithm calculation circuit. The adder circuit Σ is the output y of the final stage adder circuit Σ7, (FIR output signal 5
506) to the expected signal d. , ie.

An error signal e(n) is calculated by eliminating a signal equivalent to the sine wave pilot signal generated from the pilot signal generation circuit 104 on the signal transmission side l, and the LMS adaptive algorithm calculation circuit calculates this error signal e(n). Based on this, the tap coefficient k is appropriately determined and outputted to the nine multiplication circuits M, so that the error is minimized. In this embodiment, a least squares algorithm is used as the adaptive algorithm. That is, the synchronization signal detection circuit 540 sequentially determines the tap coefficients so that the sum of the squares of the error signal e (n) is minimized, and the delay circuit 504 and the FIR
An inverting amplifier circuit 542 inverts the polarity of the pilot signal 5506 extracted by the filter 506, and a sampling clock CLKspL and a receiving system clock CLKs are synchronized in phase with the extracted pilot signal whose polarity has been inverted.
A PLL circuit 544 that generates ys. And D-FF546 and NA for generating reset pulse RESET
It is composed of an ND gate 548. PLL circuit 54
4 is an EXOR gate 54 that functions as a 1-phase comparison circuit.
4a, low-pass filter 544b, voltage-controlled oscillator (VCO) 544c, and frequency divider 544d
It consists of This frequency divider 544d outputs a reproduction side system clock CLKivs and a sampling clock CLK3te whose phases are synchronized. The reproduction side system clock CLK svs is used as an operation clock for the entire circuit on the signal receiving side 5. In addition, as mentioned above, the sampling clock CLKspL is the ADC50
It is used as the second sampling clock. VCO5
D-FF 54 which uses the output of 44c as a clock and the inverted extracted pilot signal from the 9 inverted amplifier circuit 542 as its D input.
By applying the Q output of No. 6 and the inverted extracted pilot signal from the inverting amplifier circuit 542 to the NAND gate 548, a reset pulse RESE synchronized with the sine wave pilot signal of the pilot signal generation circuit 104 on the signal sending side 1 is generated.
T is generated. This reset pulse RESET is used as a synchronization signal for a known noise generation circuit 524, which will be described later.

The de-emphasis regeneration circuit 520 includes an FIR filter 52
2. A known noise generating circuit 524 having the same circuit configuration as the known noise generating circuit 102 on the signal sending side l; subtracting circuit 526. The DAC 52B is configured as shown in the figure.

The circuit configuration of the FIR filter 522 itself is an LMS adaptive filter using a 65-tap DSP, similar to the FIR filter 506 shown in FIG. However, this FIR filter 522 performs a control operation to estimate the emphasis characteristics of the signal sending side 1 and the characteristics of the recording system, and the tap coefficients of the filter for this purpose are also determined by the LMS adaptive algorithm. The known noise generation circuit 524 has the same circuit configuration as the known noise generation circuit 102 on the signal transmission side 1, and generates the same reproduction side known noise signal 5524 as the signal transmission side known noise signal 3102. However, in order to synchronize with the application of the known noise signal by the known noise generation circuit 102.

The known noise generation circuit 524 is synchronized with the reset pulse RESET from the NAND gate 548.

A known noise signal 5524 is generated according to the reproduction side system clock CLKsvs. The subtraction circuit 526 subtracts the reproduction side known noise signal 5524 from the corrected output signal 3522 from the FIR filter 522 to extract a reproduction signal corresponding to the original signal S. DA0528 converts the digital signal from subtraction circuit 526 into analog reproduction signal SII.

With the circuit configuration described above, on the signal receiving side 5,
The S/N deterioration in the magnetic tape recording/reproducing unit 300 is estimated based on the characteristic estimation known noise signal 5102 added to the recording original signal S on the signal sending side 1, and a reproduced signal S is generated that compensates for it. be able to.

Furthermore, according to the second embodiment, the characteristics of the pre-emphasis circuit on the signal transmission side l are automatically estimated using the FIR filter 522, so that the characteristics of the pre-emphasis circuit on the signal transmission side l are automatically estimated. Appropriate time constants can be set on the recording and playback sides without standardizing pre-emphasis.

In the above embodiment, a circuit that generates the M-sequence noise signal shown in FIG. 3 is exemplified as the known noise generation circuit 102, but various other noise signals can be used as the known noise signal. For example, as shown in FIG. 7, as the known noise generation circuit 102, the address counter 102
The ROM 102b stores predetermined pseudo-noise pattern data, applies the recording side clock CLK to the address counter 102a, and uses the recording side clock CLK as an address signal to read the ROM 102b.
A predetermined pseudo-noise signal can be generated from 102b. Corresponding to the known noise generating circuit 102 on the signal sending side 1, the known noise generating circuit 524 on the signal receiving side 5 has a similar configuration.

Furthermore, the known noise generation circuit 102 and the corresponding known noise generation circuit 524 only need to generate a known continuous signal for estimating characteristic deterioration of the transmission system, and do not need to be circuits that generate noise signals. , the pilot signal generation circuit 104 has been described using a sine wave as a synchronization signal, but various other signals may be used as long as the signal pattern for synchronization, such as a 1M sequence noise signal, so analog format may be used. Although a case has been described in which a signal such as audio is recorded and reproduced, the present invention can also be applied to a case where the original signal for recording and the reproduction signal are in digital format. In this case, the pre-emphasis circuit 1) 140 on the signal sending side 1 is made into a digital pre-emphasis circuit. This digital pre-emphasis circuit, as shown in FIG.
Figure δBypass filter 14 that passes frequencies f1 and above
2, emphasis coefficient multiplier 144. and adder circuit 1
It consists of 46 pieces. According to this circuit configuration.

The DAC 108 and the ADC 502 on the signal receiving side 5 in FIG. 2 are unnecessary. Further, according to this digital pre-emphasis circuit, accurate inverse emphasis characteristics can be obtained without depending on characteristic changes that occur in analog pre-emphasis circuits.

The embodiments for the case of a tape recorder have been described above, but the present invention is also applicable to S
/N through a medium that degrades it.

The present invention is similarly applicable to signal processing systems provided with a signal sending device and a signal receiving device, for example, two various communication systems. In this case, the signal transmission path 3 in FIG. 1 is a wired communication path or a wireless communication path, a transmitting device is provided on the signal sending side 1, and a receiving device is provided on the signal receiving side 5.

Furthermore, the present invention is not limited to the case where the signal transmitting device and the signal receiving device are always integrally configured as described above.
For example, in a case like a VTR, where the recording side and the reproducing side are separate and independent in terms of distance and time. It can be applied to both a signal recording device and a corresponding playback device. In this case, there is no need for mutual standardization of emphasis.

〔Effect of the invention〕

As described above, according to the present invention, signal transmission (recording)
In the device, a continuous known signal is superimposed on the continuous original signal for transmission (recording), and in the signal receiving (reproducing) device, the S/N deterioration state of the transmission path is determined from the known noise signal that has been S/N degraded in the transmission path. By estimating in real time and correcting the received signal using the estimated value, it is possible to reproduce an accurate signal in which the S/N degradation estimation correction is performed on the transmission side original signal in real time.

Further, according to the present invention, appropriate time constants can be set on the recording side and the reproduction side without standardizing the pre-emphasis of analog signals, which is widely performed in radio broadcasting and the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a signal transmission system according to the present invention. FIG. 2 is a tape recorder signal processing circuit diagram as a specific example of the magnetic recording/reproducing system according to the first embodiment of the present invention. FIG. 3 is a diagram showing the pre-emphasis characteristics in FIG. 2. FIG. 4 is a diagram of the known noise generation circuit shown in FIG. FIG. 5 is a pilot signal generation circuit shown in FIG. 2, and FIG. 6 is a configuration diagram of the FIR filter shown in FIG. 2. FIG. 7 is another circuit diagram of the known noise generating circuit of FIG. 2. FIG. 8 is a pre-emphasis circuit diagram as another embodiment of the present invention. (Explanation of symbols) 1...Signal sending side 3...Signal transmission system. 5... Signal receiving side lO... Known signal generating means. 12... Addition means. 14...Pre-emphasis means. 50...Adaptive filter means. 52...Signal reproducing means. 100...Known signal generation circuit. 140...Pre-emphasis circuit. 300--Magnetic tape recording/reproducing section 500...LMS adaptive filter circuit. 520...De-emphasis reproduction circuit. 540...Synchronization signal detection circuit.

Claims (1)

[Claims] 1. Known signal generating means for generating a known continuous signal for estimating characteristic deterioration in a signal transmission system; Adding means for superimposing the known continuous signal on a continuous original signal;
and a signal sending device comprising preemphasis means for performing predetermined preemphasis processing on the superimposed signal from the addition means, and sending out the preemphasized signal. 2. Estimate the degradation state of the characteristics of the known signal to estimate the characteristics of the signal transmission system superimposed on the original signal, estimate the reception characteristics of the degraded original signal, and estimate the emphasis characteristics added to the received signal. In order to perform a predetermined adaptive filtering process, the signal reproducing means subtracts from the output signal of the adaptive filtering a signal corresponding to the known signal added to the original signal on the signal sending side, and the signal reproducing means is provided. A signal reproducing device that reproduces the original signal on the sending side. 3. A known signal generating means for generating a known continuous signal for estimating characteristic deterioration in the signal transmission system across the signal transmission system, an addition means for superimposing the known continuous signal on the continuous original signal, and , a signal transmitting device comprising a pre-emphasis means for performing pre-emphasis processing on the superimposed signal from the adding means, and a signal transmitting device comprising a pre-emphasis means for performing pre-emphasis processing on the superimposed signal from the addition means; Adaptive filtering means for estimating the reception characteristic of the degraded original signal and performing predetermined adaptive filtering processing to estimate the emphasis characteristic added to the received signal, and a signal sending side from the output signal of the adaptive filtering means. A signal transmission system comprising a signal reproducing device having a signal reproducing means for subtracting a signal corresponding to a known signal added to an original signal.