JP2000059344A - Digital signal transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To start reproduction of a signal immediately without a wait even in the case that reception is started on the way of a signal stream. SOLUTION: A signal transmitter 200 at a receiver side reproduces and outputs a left channel signal frame delayed by a transmitter side in both left right channel signal frames for a period equivalent to a transmission time difference that is given between both the left right channels from a reception start point of time in the case of starting reception reproduction of the signal on the way of a multiplexed stream attended with a program switching operation or the like as a monaural signal, and reproduces and outputs both the left right channel signal frames after the time difference is eliminated after the end of the monaural reproduction period as a stereo signal respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital stereo broadcasting and multimedia information transmission.
The present invention relates to a digital signal transmission device used as a receiving station in a digital signal transmission system for transmitting information signals of a plurality of channels having correlation with each other via different channels.

[0002]

2. Description of the Related Art In recent years, in the field of radio broadcasting and communication, various systems have been developed in which a transmission signal is converted into a digital signal for each channel, and the digital signal is wirelessly transmitted using a code decoding technique and a digital modulation / demodulation technique. Or has been proposed.

When transmitting a transmission signal by digital radio,
It is necessary to protect a transmission signal from code errors due to fading or the like, and various error control techniques are used for that purpose. For example, in a mobile communication system such as a mobile phone system, a transmitting station voice-encodes a speech signal, then performs error correction coding using an error correction code, digitally modulates a carrier signal with the coded signal, and transmits the signal. Then, the receiving station digitally demodulates the received signal, performs error correction decoding processing on the demodulated signal to correct a code error, and then reproduces the speech signal by voice decoding. However, the method using the error correction code is generally effective for a small number of code errors, but may not be effective for a burst error.

Accordingly, the present inventors have disclosed in Japanese Patent Application No. 10-048.
371 and Japanese Patent Application No. 10-199538, for example, in a system for transmitting signals of a plurality of channels having correlation with each other, such as a stereo signal, from a transmission side to a reception side, the transmission side determines the transmission timing of each channel signal. The transmission is made different from each other by a time corresponding to the maximum time length of the burst error. And on the receiving side,
Monitor the reception quality of each of the signals of each channel transmitted from the transmission side, if it is detected that the reception quality of any channel has dropped below a predetermined level, the reception quality reduction section of the signal, A method of reproducing a signal based on a corresponding section of a signal of another channel arriving with the time difference has been proposed.

[0005] When such a method is used, signals of a plurality of channels are transmitted with a time difference from each other. Therefore, even if burst errors occur simultaneously in the plurality of channels due to, for example, fading, the received signal of one of the channels is transmitted. Reproduction can be performed based on a sound reception signal of the other channel.

[0006]

However, in this type of system, when a received signal is reproduced on the receiving side, a time difference given between signals of a plurality of channels is eliminated by a delay unit. Error detection is performed for each channel to reproduce a signal of each channel. Therefore, when the reception is started in the middle of the signal stream, the time interval is eliminated by the above-described delay control from the time when the reception is started, and a silent section is formed until the signal is actually reproduced. At this time, the time difference between the channels is set to correspond to the maximum time of the burst error as described above, and may be as long as several seconds, for example. For this reason, the receiver may feel confused or uneasy due to the silent section, which is not preferable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. It is an object of the present invention to enable instantaneous signal reproduction without having to wait even when reception is started in the middle of a signal stream. An object of the present invention is to provide a digital signal transmission device in which a user's anxiety is reduced.

[0008]

In order to achieve the above object, the present invention transmits a plurality of signals having a correlation with each other from a transmitting station to a receiving station with their transmission timings being different from each other by a predetermined time. In the digital signal transmission system, the digital signal transmission device used as the receiving station further includes a time difference recovery unit and a signal output control unit. In the time difference recovery means, for each of the plurality of signals transmitted from the transmitting station, a process of restoring the time difference formed by the transmitting station is performed. In the signal output control means, in a period from the time when the reception / playback instruction is input to the time when each signal whose time difference is restored by the time difference recovery means is obtained, of the signals received in the time period, The signal that is delayed the most is reproduced and output, and after the end of the period, each signal whose time difference is restored by the time difference recovery means is reproduced and output.

Therefore, according to the present invention, one of the plurality of received signals is maintained even during a period from when the reception / reproduction instruction is input to when each signal whose time difference is restored by the time difference recovery means is obtained. It is selectively reproduced and output. For this reason, when the reception / reproduction instruction is input, at least one signal, although not all signals, is reproduced and output from that point in time, so that there is no silence section and the user of the receiving station does not feel anxious. Disappears.

Further, according to the present invention, in the signal output control means, in a period until each signal whose time difference has been restored by the time difference recovery means is obtained, a time delay of each signal received in the period is most delayed. The selected signal is reproduced and output, and another signal is reproduced and output based on the selected signal. With this configuration, it is possible to perform signal reproduction of higher quality without loss of the reproduced signal.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention is as follows.
In a system that delays one of the left and right channel signals constituting a stereo audio signal and transmits the delayed signal, thereby giving a time difference to the transmission timing of the left and right channel signal frames on the wireless transmission path, When the device starts receiving and reproducing a signal from the middle of the multiplexed stream, the signal frame of the channel delayed on the transmitting side among the signal frames of the left and right channels during a period corresponding to the time difference from the start of reception. Is reproduced and output as a monaural signal, and after the end of the period, the signal frames of both the left and right channels after the time difference is eliminated are reproduced and output as stereo signals.

FIG. 1 is a circuit block diagram showing a main part of a digital stereo transmission system and a signal transmission device of the digital stereo transmission system according to this embodiment, wherein 100 is a transmission signal transmission device, and 200 is a reception signal transmission device. Are respectively shown.

First, the signal transmitting apparatus 100 on the transmitting side multiplexes audio encoders 11L and 11R provided for the left and right channels R and R of the stereo signal with error detecting code adders 12L and 12R. A section 13 and a delay unit 14 are provided.

The audio encoders 11L and 11R encode the input audio signals ASLin and ASRin divided into a predetermined frame length by a frame division unit (not shown) for each frame. As an encoding method, for example, an MPEG / Audio algorithm is used. The details are described in Hiroshi Yasuda, "International Standard for MPEG / Multimedia Coding".

The error detection code adders 12L and 12R add an error detection code for detecting a transmission error to each frame of the encoded signal output from the audio encoders 11L and 11R.

The multiplexing unit 13 includes the error detection code adder 1
The left channel transmission signal and the right channel transmission signal output from the 2L and 12R are time-division multiplexed in frame units, and the multiplexed transmission signal is supplied to a radio modulation unit (not shown).

On the other hand, the signal transmission device 200 on the receiving side includes a demultiplexer 21, error detectors 22L and 22R, audio decoders 23L and 23R, a reproduction channel controller 24, a delay controller 25, and a delay unit 27. And

The separation unit 21 separates the multiplexed reception signal received and demodulated by a radio demodulation unit (not shown) into a left channel reception signal and a right channel reception signal in frame units. The signal and the received signal of the right channel are input to error detectors 22L and 22R, respectively.

The error detectors 22L and 22R detect the presence or absence of a code error using an error detection code added to the left channel received signal and the right channel received signal.
Then, a switching control signal corresponding to the detection result is provided to the signal selection switches 24L and 24R.

The audio decoders 23L and 23R decode the left channel and right channel received signals output from the error detectors 22L and 22R, and output the decoded frame signals.

The reproduction channel controller 24 operates according to the switching control signal output from the error detectors 22L and 22R, and decodes the left channel decoded frame signal and the right channel decoded output from the audio decoders 23L and 23R. The frame signal is selectively selected and output.

A delay unit 14 is interposed between the left channel error detection code adder 12L and the multiplexing unit 13 in the transmission-side signal transmission device 100. The delay unit 14 delays the transmission signal of the left channel output from the error detection code adder 12L by a predetermined time. This delay time is set to the maximum time of a burst error assumed on the wireless transmission path.

On the other hand, a delay unit 27 is interposed between the separation unit 21 and the right channel error detector 22R in the signal transmission device 200 on the receiving side. This delay device 27
The right channel reception signal output from the separation unit 21 is delayed by a predetermined time. This delay time is set to the same time as the time set in the delay unit 14 provided in the signal transmission device 100 on the transmission side, that is, the maximum time of a burst error assumed on the radio transmission path.

The signal transmission device 200 on the receiving side is provided with a delay controller 25. The delay controller 25 operates in response to a program switching signal supplied from a main control unit (not shown), and has a period corresponding to a delay time difference provided between the left and right channels from the input of the program switching signal. , A switching control signal is supplied to the reproduction channel controller 24 to output the left channel signal as decoded frame signals ASLout and ASRout of both the left and right channels. After the elapse of the period, a switching instruction is given to the reproduction channel controller 24 to convert the signals of both the left and right channels into the decoded frame signal ASLout.
, ASRout.

Next, the operation of the apparatus configured as described above will be described. In the signal transmission device 100 on the transmission side, audio signals ASLin and ASRin output from left (L) and right (R) microphones (not shown) are first converted to digital signals and divided into frames of a fixed length. Subsequently, the audio is coded for each frame in the audio encoders 11L and 11R. The coded signals of the left and right channels are added with an error detection code for each frame by error detection code adders 12L and 12R, and the transmission signal of the left channel is transmitted to the delay unit 14 on the radio transmission path. Is delayed by a time corresponding to the maximum time of the burst error assumed in the above. FIG.
(A) shows an example of the correspondence between the right channel signal and the left channel signal after the delay processing. The delayed signals of both the left and right channels are time-division multiplexed on a multiplexed stream after frame synchronization in the multiplexing unit 13.

That is, on the time-division multiplexed stream, the transmission signal frame of the left channel and the transmission signal frame of the right channel are longer than the maximum time length of the burst error assumed on the radio transmission path as shown in FIG. Time difference T
D is placed.

On the other hand, in the signal transmission device 200 on the receiving side,
A radio transmission signal transmitted from the signal transmission device 100 on the transmission side via a radio line is received by an antenna and then demodulated by a radio demodulation unit (not shown).
Is separated into a left channel received signal and a right channel received signal for each frame. Then, the reception signal of the right channel is delayed by a time TD corresponding to the maximum time length of the burst error assumed by the delay unit 27, and after the frame synchronization with the reception signal of the left channel is obtained. , Are input to the error detectors 22L and 22R. The error detectors 22L and 22R detect the presence or absence of a code error for each frame, and then are decoded by the audio decoders 23L and 23R.

By the way, it is assumed that the user performs a switching selection operation to another program while listening to an arbitrary program. Then, the main controller (not shown) sends the delay controller 25
Is supplied with a program switching signal. Upon receiving this program switching signal, the delay controller 25 gives the delay time TD to the delay unit 27, and starts the delay processing of the channel signal corresponding to the newly selected program.
At the same time, the delay controller 25 supplies a switching control signal to the reproduction channel controller 24, whereby only the period from the input of the program switching signal to the elapse of the delay time TD set in the delay unit 27 has elapsed. Then, the reproduction channel controller 24 is switched and set to a state in which the decoded signal frame of the left channel is selected for both the left and right channels as shown in FIG.

For this reason, in the period from the input of the program switching signal to the elapse of the delay time TD,
As shown in FIG. 3C, the left channel decoded signals L2 and L
3 is the decoded signal frames ASLout, A of both the left and right channels
It is output as SRout as it is. That is, the left channel signals L2 and L3 are reproduced and output as monaural signals. Therefore, a decrease in sound quality is inevitable as compared with the case where a stereo signal is reproduced and output. Then, the user can start listening to the program after switching without feeling uneasy. Moreover, the left channel signal L
2 and L3 are not only reproduced and output as left channel signals, but also the left channel signals L2 and L3 are reproduced and output as right channel signals, so that signal reproduction with less discomfort is achieved. It becomes possible.

When the monaural reproduction section ends and the stereo reproduction section starts, a switching control signal is given from the delay controller 25 to the reproduction channel controller 24, whereby the reproduction channel controller 24 is turned on as shown in FIG. It switches to the normal state shown in. Therefore, from the reproduction channel controller 24, the decoded signal frames L4, L5,... Of the left channel and the decoded signal frame L4 of the left channel delayed by the delay unit 27, for example, as shown in FIG. , L
, And the right-channel decoded signal frames R4, R5,. That is, a stereo signal is reproduced and output.

When the operation shifts to the stereo reproduction section, the signal transmission device 200 on the receiving side performs channel reproduction control according to the reception quality of each channel. For example, it is assumed that the quality of the wireless transmission path is now good and no code error has occurred in the received signals of both the left and right channels. In this case, no error is detected by the error detectors 22L and 22R, and therefore, the reproduction channel controller 24 maintains the normal state shown in FIG. Therefore, in this case, the signals output from the audio decoders 23L and 23R are output as they are as the left channel decoded signal frame ASLout and the right channel decoded signal frame ASRout.

On the other hand, it is now assumed that fading or the like has occurred on the radio transmission path, and the signal of both the left and right channels has caused a burst error simultaneously in an arbitrary transmission frame section due to the influence. However, the transmission signals of both the left and right channels are multiplexed after being shifted in advance by the maximum time of the burst error in the signal transmission device 100 on the transmission side. For this reason, as described above, even if the signal frames of the left and right channels simultaneously cause a burst error in an arbitrary transmission frame section, the signal frames of the right and left channels that are originally temporally corresponding to these left and right channels are Is transmitted in another transmission frame section, there is a high possibility that it will be correctly received without being affected by the burst error.

Therefore, the signal transmission device 200 on the receiving side
In the above, after the time difference between the left and right channels is eliminated by the delay unit 27, error detection is performed, and the signal of the left and right channels is selected by the reproduction channel controller 24 in accordance with the result. Can be replaced with a signal of the other channel having a strong correlation corresponding to the signal in time. Therefore, even if both left and right channel signals multiplexed and transmitted on the same transmission frame on the wireless transmission path cause a burst error, it is possible to reproduce both of the left and right channel signals.

As described above, in this embodiment, when the signal transmission device 200 on the receiving side attempts to start reception and reproduction of a signal from the middle of a multiplexed stream due to a program switching operation, etc. During the period corresponding to the transmission time difference TD given between the left and right channels, the signal frame of the left channel delayed on the transmitting side among the signal frames of the left and right channels is reproduced and output as a monaural signal. After the end of the reproduction section, the signal frames of both the left and right channels after the elimination of the time difference are reproduced and output as stereo signals.

Therefore, according to this embodiment, in the period from when the program switching operation is performed to when the signals of both the left and right channels whose time differences are restored are obtained.
The decoded signal frame of the left channel is reproduced and output as a monaural signal. Therefore, immediately after performing the program switching operation, the user can start listening to the reproduced sound of the program immediately after the switching without waiting until the reproduction of the stereo signal is started.

Further, since the left channel signal is not only reproduced and output as the left channel signal but also the left channel signal is reproduced and output as the right channel signal, the sense of discomfort is further reduced. Signal reproduction becomes possible.

FIG. 4 is a timing chart showing the operation of the conventional apparatus which does not perform monaural reproduction. The period from the point when the program switching operation is performed until the delay time TD elapses is a silent section. The user may feel uneasy during the period, which is not preferable.

The present invention is not limited to the above embodiment. For example, when the device is provided with a liquid crystal display, a message indicating that monaural reproduction is being performed or a mark in place of the message may be displayed during the monaural reproduction period. Further, a monaural / stereo display light emitting diode may be provided, and the driving mode of the light emitting diode may be changed to display a monaural reproduction period and a stereo reproduction period. In addition, the type and configuration of the device can be variously modified and implemented without departing from the gist of the present invention.

[0039]

As described above in detail, according to the present invention, a time difference recovery means and a signal output control means are newly provided, and each of the plurality of signals transmitted from the transmission station is transmitted to the transmission station by the time difference recovery means. A process for restoring the formed time difference is performed, and in the signal output control means, during a period from when the reception / reproduction instruction is input to when each signal whose time difference is restored by the time difference recovery means is obtained. It is configured to reproduce and output the signal that is the most delayed in time among the signals received during the period, and to reproduce and output each signal whose time difference has been restored by the time difference recovery unit after the period. ing.

Therefore, according to the present invention, it is possible to provide a digital signal transmission apparatus capable of immediately starting signal reproduction without waiting, even when reception is started from the middle of a signal stream.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of a digital signal transmission device according to the present invention.

FIG. 2 is a circuit diagram showing a configuration of a reproduction channel controller of the apparatus shown in FIG.

FIG. 3 is a timing chart used to explain the operation of the device shown in FIG. 1;

FIG. 4 is a timing chart showing the operation of the conventional device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100: transmitting signal transmitting device 200: receiving signal transmitting device 11L, 11R: audio encoders 12L, 12R: error detection code adder 13: multiplexing unit 14: delay unit 21: separating unit 22L, 22R: error Detectors 23L, 23R: Audio decoder 24: Reproduction channel controller 25: Delay controller

 ────────────────────────────────────────────────── ─── Continued from the front page (72) Michiko Noguchi 70 Yanagicho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term in Toshiba Yanagicho Plant (reference) 5K021 AA01 AA06 BB04 CC04 CC14 DD07 EE04 GG01 5K059 BB01 CC03 DD35 DD39 EE02 EE03 5K068 AA08 AA22 BA01 BB01 BC02 BC04 CB01 CC16 DA01 DB01 DC03

Claims (2)

[Claims] 1. A digital signal transmission system used as a receiving station in a digital signal transmission system for transmitting a plurality of signals having a correlation with each other from a transmitting station to a receiving station with transmission timings different from each other by a predetermined time. In the apparatus, for each of a plurality of signals transmitted from the transmitting station,
Quality monitoring means for monitoring the reception quality; and when the quality monitoring means detects that the reception quality of an arbitrary signal has dropped below a predetermined level, the reception quality reduction section of the signal is set to another section. Quality compensation means for reproducing based on a temporally corresponding section before the time difference formation in the signal, and for each of the plurality of signals transmitted from the transmitting station,
A time difference restoring means for restoring the time difference formed by the transmitting station, and a period from when the reception / playback instruction is input to when each signal whose time difference is restored by the time difference restoring means is obtained. A signal output control for selecting and reproducing and outputting the signal with the longest delay among the received signals, and reproducing and outputting each signal whose time difference has been restored by the time difference recovery means after the end of the period. And a digital signal transmission device. 2. The signal output control means, in a period until each signal whose time difference is restored by the time difference recovery means is obtained, a signal which is the most delayed in time among signals received in the period. 2. The digital signal transmission apparatus according to claim 1, wherein the selected signal is reproduced and output, and another signal is reproduced and output based on the selected signal.