JPH03268687A - Carrier and clock recovery system - Google Patents

Abstract

PURPOSE:To attain carrier recovery and clock recovery by forming an HD waveform and a frame pulse waveform to be waveforms similar to that of an original MUSE signal even after a modulation format is converted into a single phase in the case of converting the MUSE signal into a biphase for the orthogonal modulation. CONSTITUTION:A high frequency input signal is distributed by distributers 1, 2, they are subject to envelope detection (3), its output is A/D converted (4), a frame pulse is detected by a frame pulse detector 5 and the result is given to a HD detector 6. The HD signal is used to extract a carrier from the high frequency input signal by a gate circuit 7 and a continuous carrier is recovered by a PLL circuit 8 employing a local oscillator 9. On the other hand, a phase error of an HD wave being an envelope detection output is confirmed for each 1H similarly to the case of a base band signal of a MUSE signal and the clock is recovered at a clock recovery device 10 by using an integration value of the phase error. The output is given to a carrier recovery section 11 and then inputted to a signal multiplier 14. The output is fed to a multiplier 13, a carrier at a point E of the output of the multiplier 13 is completely coincident with the sender side carrier and coincident with the recovered clock of the base band system. Thus, the carrier and the clock are recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to carrier recovery and clock recovery on the demodulator side in a two-line parallel orthogonal modulation/demodulation transmission system for high-definition television signals.

(Summary of the Invention) The present invention relates to carrier recovery and clock recovery on the demodulator side in an orthogonal modulation/demodulation system for two-line parallel MUSE signals, and eliminates the loss of phase information between the baseband signal and the transmitted high-frequency signal on the transmitting side. , without transmitting the pilot carrier, using a local conversion frequency created from the clock of the baseband signal obtained by envelope detection of the received signal, and a receiving frequency extracted from the received signal and regenerated using PLL. The phase information is recovered by converting it to the same frequency as the transmitting side.

As a result, carrier recovery and clock recovery can be performed on the receiving side without adding a special pilot carrier.

(Prior technology) MUSE (Mu
ltiple 5ub-Nyquist Sample
There is a transmission method called ng encoding.
This is an excellent band compression transmission method that was developed by researchers at the NHK Broadcasting Technology Research Institute, and research is currently ongoing into various modified methods. The early MUSE transmission system was developed for satellite broadcasting, and the Hesshand bandwidth was approximately 8MHz analog transmission with FM modulation.Because of this FM modulation transmission, a system with subcarriers was not suitable. , a component method has been adopted for signal processing before band compression.

On the other hand, the MUSE signal requires not only satellite transmission but also terrestrial transmission. When it comes to terrestrial transmission, AM modulation is naturally selected as the modulation method, and if the baseband is 8 MHz, the transmission band is 161 in total on both sides.
'IHz, 12-3 M) 12 would be required as a residual sideband.

What can be considered here is a transmission method in which the signal for two horizontal scanning lines of the MUSE signal is time-expanded into two lines for each line, and each of these is orthogonally modulated and transmitted in parallel. , baseband 8 M)l
The z signal has a baseband of 4 MHz, and even with complete double-sideband transmission, the transmission band only needs to be 8 MHz, and the transmission band can be compressed without reducing the transmitted information. The inventors of the present application will call this method 2-line parallel orthogonal modulation/demodulation transmission method 2.

When the orthogonal modulation/demodulation method is adopted, it is necessary to regenerate the carrier wave for demodulation on the receiving side, and in the color subcarrier of the known NTSC transmission method in which this method is adopted, the carrier is suppressed on the modulation side. Although the color burst signal is modulated, a color burst signal is transmitted, and this is essentially a pilot carrier superimposed transmission.

For details of the above-mentioned AυSE, see Ninomiya et al.: MUS
Development of E method, NHK Technical Research, Vol. 39. No
, 2, pp.

18-53.1987.

(Problem to be solved by the invention) When the pilot carrier superimposition method is used for carrier recovery and clock recovery in orthogonal modulation and demodulation, the position at which the pilot carrier is superimposed is between adjacent channels at the edge of the transmission band. The problem of interference and influence on the received signal occurs within the transmission band.

Therefore, an object of the present invention is to solve the above-mentioned problems.
A transmission method that does not superimpose the pilot carrier is adopted, and the modulation format of the MUSE signal (high-definition television signal) is configured to facilitate carrier recovery and clock recovery on the receiving side, and the envelope detection output of the received signal is The purpose of this paper is to provide a reproduction method that performs carrier recovery and clock recovery using .

(Means for Solving the Problems) In order to achieve this object, the carrier recovery and clock recovery method of the present invention converts a set of two frame pulses, which are superimposed on adjacent horizontal lines and have opposite phases to each other, into a frame synchronization signal. A pilot carrier is transmitted from the transmitting side when transmitting a time-division multiplexed sub-sampled high-definition television signal in a 2-line parallel orthogonal modulation/demodulation range compressed transmission using drive pulses whose phase is inverted for each horizontal line as a line synchronization signal. In order to regenerate the carrier for demodulating the orthogonally modulated received signal and the clock for demodulating the subsampled received signal on the receiving side, the transmitting side uses the frame pulse for vertical synchronization and the frame pulse for horizontal synchronization. The drive pulse is limited to one of two types of pulses with inverted phases, and this is transmitted, and on the receiving side, a local pulse generated from the baseband signal clock obtained by envelope detection of the received signal is transmitted. It is characterized by demodulating the same frequency and phase information as on the transmitting side using the oscillation frequency and the receiving frequency extracted from the received signal and reproduced using a phase-locked loop.

(Examples) The present invention will be described in detail below by way of examples with reference to the accompanying drawings.

FIG. 2 shows a modulation format when the two-line parallel orthogonal modulation/demodulation transmission system according to the present invention is applied to the MUSE signal.

In the 2-line parallel method, odd-numbered lines are
The phase modulation signal and subsequent even lines are orthogonally modulated as Q phase modulation signals during transmission. However, in the 1125th line of the high-definition television signal, the first half of one line is an I-phase modulation signal, and the second half is a Q-phase modulation signal. In this case, if N is a positive integer, the horizontal drive waveform (HD waveform) of the 4N+1 line is the same as the HD waveform of the 1st line of the MUSE signal, and the HD waveform of the 4N+3 line is the same as the 2nd HD waveform of the MUSE signal. Make it the same as the HD waveform of the line. Further, the position corresponding to HD on the second N line is made to have no signal. However, the 112th
The second half of the 5th line will have no signal. The HD waveform of the MUSE signal is of a positive polarity synchronization type, and the waveforms of the odd-numbered lines and the even-numbered lines have opposite phases.

In addition, the MUSE signal has a frame pulse added to the first and second lines of each frame to identify whether the number of frames is odd or even. is reversed.

This part is naturally affected by the 2-line parallel system, so
In the method of the present invention, the frame pulse of the first line is MUS
The same pulse as E is inserted with a slightly additional pulse number than MUSE, and the position corresponding to the frame pulse of the second line is left with no signal. This result) 10, both frame pulse and I
It will be superimposed only on the phase modulation signal. By changing the formant in this way, orthogonal modulation and demodulation processing can be performed in a neat manner. Note that this conversion is performed on the modulator side.
Due to the phase conversion, the inverse conversion is performed as a one-phase conversion on the demodulator side.

Next, clock recovery and carrier recovery will be explained with reference to the system diagram shown in FIG.

Point A is a signal input section into which a high frequency signal of MUSE which has been orthogonally modulated is input. Point E is a signal output section that continues to the digital demodulation section.

Here, the I-phase carrier of the transmitting side modulator output is COS (
ωat+θC). θ. is uniquely determined by the baseband system clock phase. This carrier becomes cos ((ω.+ω,)1+(θ.+θI)) by a frequency converter inserted in the middle of the transmission path, and this is input to point A. Here, ω1 and θ are the frequency and phase of the local oscillator, respectively.

A high-frequency input signal is divided by distributors 1 and 2, and envelope-detected by an envelope detector 3. This detector output signal is a signal in which the odd lines and even lines shown in the second figure are superimposed, and the waveforms of the HD and frame pulses are almost similar to the MUSE signal. Therefore, this signal is converted into A/D converter 4.
The frame pulse detector 5 detects the frame pulse from the /D converted signal, and then the HD detector 6 detects the frame pulse.
Detection is performed.

With this HD, a high frequency input signal is gated by a gate circuit 7, carriers are extracted, and continuous carriers are reproduced by a PLL circuit 8 using a local oscillator (VCXO) 9.

This is the carrier at point B, (Os ((ω,
+ωI) t+ (θ0+θI)).

On the other hand, in the HD waveform of the envelope detection output, the phase error can be easily determined for each line (IH), similar to the MUSE baseband signal. In other words, the difference between the center of the rise or fall of the HD waveform and the average value of the values before and after it is the IH
This is a phase error that is determined once every time.

The VCXO is controlled using this integral value to configure a PLL, and the clock regenerating section 10 regenerates the clock. This clock is equal to the baseband system clock on the modulator side. The carrier recovery unit shown in the first figure uses the clock as a carrier, so the carrier becomes cos (ω, t+θC),
This is input to the signal multiplier 14 at the 0 point.

The signal at point D is the output of this multiplier 14 and becomes cos (ω1 is +θ1), and this signal becomes the carrier of the local oscillator that returns the high frequency input signal to the output frequency of the modulator on the transmitting side. Therefore, the carrier at point E, which is the output of the multiplier 13, is co
s (ωct + θC), which completely matches that of the transmitting side and also matches the reproduced baseband system clock.

As a result, the phases of the subsequent (digital system clock) and the carrier for demodulation match, and complete carrier recovery and clock recovery are performed.

(Effects of the Invention) As described above in detail, according to the method of the present invention, the modulation formant when converting the MUSE signal into two phases (■ modulation and Q modulation signal) for orthogonal modulation is changed to one phase. Even after combining the HD waveform and frame pulse waveform, the original MUS
The waveform was made to be similar to that of the E signal. As a result, carrier recovery and clock recovery have become possible by using the envelope detection output of the high-frequency received signal without adding a special pilot carrier.

[Brief explanation of drawings]

FIG. 1 shows a system block diagram of a reproduction method according to the present invention, and FIG. 2 is a diagram showing a modulation format when the method of the present invention is applied to a MUSE signal. 1.2...Distributor 3...Envelope line detector 4.
...A/D converter 5...Frame pulse detector 6...HD detector 7...Gate circuit 8...
... Phased lock loop circuit 9 ... Local frequency oscillation circuit

Claims (1)

[Claims] 1. A set of two frame pulses that are superimposed on adjacent horizontal lines and whose phases are inverted to each other is used as a frame synchronization signal, and a drive pulse whose phase is inverted for each horizontal line is used as a line synchronization signal. When transmitting time-division multiplexed sub-sampled high-definition television signals using 2-line parallel orthogonal modulation and demodulation band compression transmission, a carrier and In order to regenerate the clock for demodulating the subsampled received signal, on the transmitting side, the frame pulse for vertical synchronization and the drive pulse for horizontal synchronization are converted to one of two types of pulses with reversed phases. On the receiving side, the local oscillation frequency created from the baseband signal clock obtained by envelope detection of the received signal and the reception frequency extracted from the received signal and regenerated using a phase-locked loop are used. A carrier and clock recovery method characterized by demodulating the same frequency and phase information as on the transmitting side. 2. The reproduction method according to claim 1, wherein adjacent lines to be orthogonally modulated in the high-definition television signal to be subjected to two-line parallel orthogonal modulation are an I-phase modulation line signal and a Q-phase modulation line signal. and a carrier and clock regeneration method, characterized in that the drive pulse is limited to only an I-phase modulated line signal.