JP2006042250A - Radio video transmission apparatus, radio video receiving apparatus and radio video transmitting/receiving system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio video transmission apparatus and a radio video receiving apparatus capable of excellently transmitting/receiving video images even when transmitting a video signal having a vertical frequency out of regular vertical frequencies. <P>SOLUTION: In a radio video transmission apparatus 1, video signals for four field period are encoded as a unit, a transmission interval of leading data of the encoded unit frame is equal to four field period but if a vertical frequency gets out of regular vertical frequencies, a pulse is generated which has a double period for four field period. During one period of the pulse, video signals for four field period after latest encoding are sent out only once. In a radio video receiving apparatus 2, a pulse of an encoding frame period is generated and a PLL is configured based on phase comparison with leading data of the encoding frame for clock synchronism. Only when arrival of leading data can be detected, phase comparison is performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless video transmission device, a wireless video reception device, and a wireless video transmission / reception system, and is used, for example, for video wireless transmission from a main TV device (parent TV device) to a child TV device.

  In a digital broadcasting system, video and audio are compressed, and a transport stream (TS) multiplexed by, for example, MPEG (Moving Picture Experts Group) is digitally modulated and transmitted. On the receiving device side, the received digital modulation signal is demodulated to generate a transport stream, which is separated into video, audio, and other information and analyzed to present video such as a program on the display.

By the way, in such a digital broadcasting system, error correction processing is performed in order to reduce transmission errors of video data (see Patent Document 1).
JP 2002-64759 A

  In recent years, there has been proposed a receiving system including a main body receiving device (parent television) that receives digital broadcasting and a child television that receives and displays video and audio data wirelessly transmitted from the main body receiving device. In such a receiving system as well, it is conceivable to correct transmission errors by adding parity bits or the like, as in the digital broadcasting described above.

  However, the conventional error correction process has a problem that the circuit becomes complicated. Therefore, the applicant of the present application has previously proposed the following wireless video transmission device and wireless video reception device. That is, the wireless video transmission apparatus performs encoding in units of video signals for a certain number of vertical periods, and sets the start data transmission interval of video signals for a fixed number of vertical periods after encoding for the predetermined number of vertical periods. Matches to and sends. Then, the wireless video reception device generates a periodic signal having a certain number of vertical periods based on the outputs of the horizontal period counter and the vertical period counter, and the arrival period of the head data of the received encoded video signal By comparing the phase with the periodic signal, a phase-locked loop is formed to control the counter, and the encoded video signal is decoded based on the output of the counter to output the video signal.

  However, in the wireless transmission of video with the above configuration, for example, when transmitting a video signal whose vertical frequency deviates from the normal vertical frequency, such as special playback of a video tape recorder, the operation of the phase locked loop in the wireless video receiver Malfunctions.

  In view of the above circumstances, the present invention provides a wireless video transmission apparatus, a wireless video reception apparatus, and a wireless video transmission / reception system that can perform satisfactory video transmission / reception even when transmitting a video signal whose vertical frequency deviates from the normal vertical frequency. For the purpose.

  The wireless video transmission apparatus according to the present invention performs encoding in units of video signals for a fixed number of vertical periods, and sets a first data transmission interval of video signals for a fixed number of vertical periods after encoding to the fixed number of vertical periods. A wireless video transmission device that transmits data in accordance with the minutes, and a buffer that temporarily holds the encoded video signal, and whether a vertical period of the input video signal is deviated by a predetermined value or more with respect to an assumed vertical period Means for determining whether or not a signal having a normal vertical period is generated, and a pulse having a period that is an integral multiple of the predetermined number of vertical periods is generated based on the signal; Means for reading out and sending out a video signal for a fixed number of vertical periods after the latest encoding from the buffer only once.

  Further, the wireless video receiving apparatus of the present invention generates a periodic signal having a period corresponding to a certain number of vertical periods based on the output of the counter, and the arrival period of the head data of the received encoded video signal and the periodic signal A wireless video receiver configured to control the counter by forming a phase-locked loop by performing a phase comparison of the output and to decode the encoded video signal based on the output of the counter and output the video signal, The phase comparison is performed only when the arrival of data is detected. Further, in the wireless video receiving apparatus having such a configuration, means for detecting a transmission drop of the encoded video signal, a buffer holding video data after video decoding for at least one field, and received video data that has been successfully received Preferably means for sequentially updating and recording in the buffer, and means for outputting video data held in the buffer when the transmission drop is detected.

  According to another aspect of the present invention, there is provided a wireless video transmission / reception system comprising the above-described wireless video transmission device and wireless video reception device.

  With such a configuration, even if the input video signal deviates from the assumed vertical period in the wireless video transmission apparatus, the encoded video signal is temporarily stored in the buffer, and a single encoded video is collected once in one period of the pulse. A signal is output. In the wireless video receiving apparatus, since the start data arrival time of the encoded video signal is an integral multiple of the vertical period of the video signal, the phase comparison is performed only when the arrival of the start data is detected. The PLL can be applied in the same manner as (when the input video signal is not deviated from the assumed vertical period). Also, if the decoded video signal is stored in a buffer and output when the encoded video signal to be decoded is not transmitted, there is no interruption in the video display, and the image disturbance due to transmission omission is inconspicuous can do.

  As described above, according to the present invention, there is an effect that good video transmission / reception can be performed even when a video signal whose vertical frequency is out of the normal vertical frequency is transmitted.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing a wireless video transmission / reception system 3 including a wireless video transmission device 1 and a wireless video reception device 2, and FIG. 2 is a time chart.

[Basic outline of this embodiment]
In this embodiment, a wireless video transmission / reception system in which the length of an encoded frame is 4 fields is described as an example. The wireless video transmission apparatus 1 of this embodiment encodes a video signal for a certain number of vertical periods as a unit, and encodes a “video signal for a certain number of vertical periods” which is a unit of this coding. This is referred to as a frame. The wireless video transmission apparatus 1 sets the transmission interval of the head data of the encoded frame obtained by encoding the video signal as a certain number of vertical cycle intervals. If the length of the encoded frame is 4 fields, the transmission interval of the head data of the encoded frame is 4 fields. The wireless video receiver 2 generates a pulse of an encoded frame period from a built-in counter and constructs a PLL (phase locked loop) based on the phase difference from the head data of the encoded frame, thereby synchronizing the clock. Take. Accordingly, the clock synchronization between the wireless video transmission device 1 and the wireless video reception device 2 can be achieved with a simple circuit configuration without requiring PCR.

[Outline of features of this embodiment]
In addition, the wireless video transmission device 1 holds the encoded video signal in a buffer, and when the input video signal has a vertical cycle that is out of the assumed vertical cycle, the wireless video transmission device 1 is based on a signal having a normal vertical cycle. A pulse having an integer multiple of a fixed vertical period is generated, and a video signal (encoded frame) for a fixed vertical period after the latest encoding from the buffer only once during the period of this pulse. Is read and sent out. In this case, the wireless video reception device 2 determines that transmission loss has occurred, does not perform the phase comparison operation, and outputs the stored video.

[Wireless video transmission device]
The NTSC decoder 11 of the wireless video transmission apparatus 1 inputs a composite video signal, and extracts a Y (luminance) signal, a color difference signal, H (horizontal synchronization signal), and V (vertical synchronization signal) from the composite video signal. The encoding circuit 14 receives the Y signal and color difference signal of the previous frame that has passed through the 1 frame delay circuit 12 and the current Y signal and color difference signal. In FIG. 2, the first encoded frame, which is encoded data, is composed of F1, F2, F3, and F4 (F is a field) of the input video signal. The encoding circuit 14 outputs the first encoded frame, which is encoded data, to the transmission buffer 15 in one frame period. The one frame period which is an encoding timing signal is generated by the timing generation circuit 13 and supplied to the transmission buffer 15. The timing generation circuit 13 generates the timing signal based on H and V supplied from the NTSC decoder 11.

  The timing generation circuit 13 generates an encoded frame start flag and supplies it to the read start control circuit 103. When the signal indicating “standard” is supplied from the vertical cycle determination circuit 101, the read start control circuit 103 supplies the encoded frame start flag to the transmission buffer 15 and the TS generation circuit 16 as a transmission start flag. On the other hand, when the signal indicating “non-standard” is supplied from the vertical cycle determination circuit 101, the read start control circuit 103 uses the output trigger output from the internal V counter 102 as a transmission start flag to generate the transmission buffer 15 and TS. Supply to circuit 16. The internal V counter 102 counts with a normal vertical period. In this embodiment, the internal V counter 102 outputs an output trigger with a period twice as long as an encoded frame (8 vertical (V) periods). The vertical period determination circuit 101 includes a counter, and determines whether the vertical period of the input video signal is shifted by a predetermined value or more with respect to the assumed vertical period (which may be the same as the normal vertical period). Specifically, for example, 225225 (858 × 262.5) count is performed during the assumed vertical period, and a signal indicating “non-standard” is generated when a deviation of ± 1000 counts or more occurs. Output. The non-standard time operation will be described in detail later.

  The TS generation circuit 16 converts the output of the transmission buffer 15 into a TS (transport stream) based on, for example, MPEG. At this time, the encoded frame start flag supplied from the timing generation circuit 13 is added to the header portion of the TS packet. Append. In this case, the encoded frame start flag is present on the TS with a period of 4 fields. The RF modulation circuit 17 subjects the TS to high frequency digital modulation processing, and this RF modulation signal (transmission wave) is transmitted from the transmission antenna unit 18 to the space.

[Non-standard time operation]
As described above, the timing generation circuit 13 outputs an encoded frame start flag indicating the output timing of the head data of the encoded frame output from the encoding circuit 14. In this embodiment, since the encoded frame has 4 fields, the encoded frame start flag is generated every 4 fields of the input signal. In the vertical cycle determination circuit 101, if the cycle of the encoded frame start flag is within the assumed cycle, it is determined as standard, and if it is outside the assumed cycle, it is determined as non-standard. In the case of the standard, the transmission start is performed by the encoded frame start flag, and in the case of the non-standard, it is performed by the output trigger of the 8V cycle output from the internal counter.

  When the vertical period of the input signal deviates greatly (for example, caused by special reproduction of a video tape recorder (VTR)), the interval of the encoded frame start flag varies from the standard period. In the wireless video reception device 2 described later, the voltage control oscillator 204 is controlled by comparing the phase of the reception timing of the head data of the encoded frame with the internal counter. Therefore, if the interval between the start flags of the encoded frame varies from the standard period, the voltage-controlled oscillator 204 is outside the variable range, causing a malfunction.

  Therefore, when it is determined as non-standard, the internal video counter 102 has a cycle twice that of the encoded frame in order to set the reception timing of the head data of the encoded frame at a constant interval on the wireless video reception device 2 side. Start transmission by output trigger. Upon receiving the transmission start flag, the transmission buffer 15 outputs the latest encoded frame inside. Since the interval between the output triggers is twice that of the encoded frame, the encoded frames always accumulate until the next output trigger is issued. For this reason, underflow does not occur. However, if the encoded frame is stored in the transmission buffer 15 and the next encoded frame is input to the transmission buffer 15 before the output trigger arrives, only the latest encoded buffer is left and the previous encoded frame data is stored. Discard.

[Wireless video receiver]
The wireless video receiver 2 receives the RF modulated signal (transmitted wave) by the receiving antenna 21, digitally demodulates the received signal by the RF demodulation circuit 22, and outputs a demodulated TS. The demodulated TS is temporarily stored in the reception buffer 26, sequentially read out according to the timing required for decoding, and input to the decoding circuit 27. The timing is determined by a horizontal / vertical timing generation circuit (not shown).

  The start flag extraction circuit 24 extracts an encoded frame start flag from the header of the demodulated TS, and supplies the encoded frame start flag to the phase comparison circuit 202 as a reference signal. The internal V counter 201 outputs a signal having a 4-field period (corresponding to the period of the encoded frame start flag) that is the read start timing of the start of the encoded frame. The phase comparison circuit 202 receives the signal of the four-field period, which is the output of the internal V counter 201, as the other signal, and outputs the phase comparison output through a low-pass filter (LPF) 203 as a voltage controlled oscillator (VCXO). oscillator) 204. As a result, a PLL (phase locked loop) for matching a signal having a 4-field period, which is the timing for reading the head of the encoded frame, with the arrival timing of the encoded frame start flag is configured.

  In other words, the encoded frame start flag is present in the transmitted TS in a 4-field cycle, and the receiving side generates a signal in a 4-field cycle that is the timing for reading the head of the encoded frame. Therefore, the difference between the former (transmission side) and the latter (reception side) in the four field periods is output as a phase comparison result, and this deviation is corrected by the PLL, and the transmission side and the reception side are corrected. Clock synchronization with the side is realized without PCR (program clock reference). As will be described in detail later, when performing “non-standard” processing on the transmission side, the reception side cannot extract the encoded frame start flag in a four-field period, and determines that a transmission loss has occurred. become. Since the phase comparison circuit 202 performs phase comparison with the internal V counter 201 only when the encoded frame start flag can be extracted, the operation of the voltage controlled oscillation becomes stable. As will be described below, the wireless video receiver 2 stores the decoded video signal in a one-frame delay (buffer) 28 and outputs the data in the buffer when the encoded video signal to be decoded is not transmitted. As a result, the video display is not interrupted, and the disturbance of the image due to transmission loss can be made inconspicuous.

  The decoding circuit 27 inputs the decoded first frame (F1, F2) to the switch SW2, and inputs the decoded second frame (F3, F4) to the switch SW1. The switch SW1 selects either the decoded second frame or the delayed second frame from the 1-frame delay circuit (buffer) 28 based on the “delay input selection” signal, and inputs it to the 1-frame delay circuit 28. The switch SW2 selects and outputs either the decoded first frame or the delayed second frame from the 1-frame delay circuit 28 based on the “final output selection” signal.

  For example, the transmission loss detection circuit 23 detects the extraction period of the encoded frame start flag, and determines that a transmission loss has occurred when this period deviates from the specified period. Transmission loss information and detection information of the encoded frame start flag are given to the signal switching control circuit 25.

  When the signal switching control circuit 25 receives the information indicating that the encoded frame start flag has been detected, the signal switching control circuit 25 switches the switch SW2 to the decoding first frame side, and after that one frame period, the delayed second frame (1-frame delay circuit 28) Command to select). That is, the selection state of the decoded first frame and the selection state of the delayed second frame are alternately switched at intervals of one frame. However, when information indicating a transmission drop is received, the switch SW2 is not switched to the decoding first frame side. When the signal switching control circuit 25 receives the information indicating that the encoded frame start flag has been detected, the signal switching control circuit 25 switches the switch SW1 to the decoded second frame side, and after that one frame period, the delayed second frame (one frame delay) A command for selecting the output of the circuit 28 is given. That is, the selection state of the decoded second frame and the selection state of the delayed second frame are alternately switched at intervals of one frame. Therefore, when the delayed second frame is output from the switch SW2, the delayed second frame is returned to the 1-frame delay circuit 28 again. When the decoded first frame is output from the switch SW2, the decoded second frame is output. The frame is supplied to the one-frame delay circuit 28. However, when the information indicating the transmission failure is received, the switch SW1 is not switched to the decoding second frame side.

  By the switching control of the switches SW1 and SW2, the decoded first frame from the decoding circuit 27 is output via the switch SW2 (final output), and the decoded second frame from the decoding circuit 27 is 1 through the switch SW1. The signal is stored in the frame delay circuit 28 and delayed by one frame to become a delayed second frame, which is output via the switch SW2. If there is no transmission drop, the selection state of the switch SW2 is as follows: Decoded first frame (F1, F2) → Delayed second frame (F3, F4) → Decoded first frame (F5, F6) → Delayed second frame (F7, F8), and so on.

  On the other hand, as shown in FIG. 2, when a transmission drop is detected, both the switches SW1 and SW2 are in the selected state of the delayed second frame, and the delayed second frame (F3, F4) from the 1-frame delay circuit 28 is selected. This is the final output, and the delayed second frame is returned to the 1-frame delay circuit 28 again. If there is no transmission drop thereafter, the normal switch control of the switches SW1 and SW2 is restored. Accordingly, while the decoded first frame (F9, F10) is output as the final output from the switch SW2 at the time of return, the delayed second frame (F3, F4) is output from the 1-frame delay circuit 28. The switch SW1 is in a state of selecting the decoded second frame (F11, F12), and the decoded second frame (F11, F12) is stored in the 1-frame delay circuit 28.

  In the above example, the fixed number of vertical synchronization units is four fields, and compression (encoding) based on the difference between the two frames is performed. However, the present invention is not limited to this. Note that as the number of fields serving as a fixed number of vertical synchronization units increases, the difference (time width) between the output video at the time of transmission failure and the output video at the time of return increases. Also, the determination of “non-standard” is not limited to the specific example described above. Since it is determined as “non-standard” in order to prevent the interval of the start flag of the encoded frame from changing from the standard to be outside the variable range of the voltage controlled oscillator 204, the balance with the variable range of the voltage controlled oscillator 204 is considered. Therefore, it is sufficient to determine “non-standard”. Such a wireless video transmission / reception system can be configured using a wireless LAN, but is not limited to using a wireless LAN.

1 is a block diagram illustrating a wireless video transmission / reception system according to an embodiment of the present invention. It is a timing chart which showed the timing of each signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wireless video transmission apparatus 11 NTSC decoder 13 Timing generation circuit 14 Coding circuit 16 TS generation circuit 101 Vertical period determination circuit 102 Internal V counter 103 Reading start control circuit 2 Wireless video reception apparatus 23 Packet missing detection circuit 25 Signal switching control circuit 28 1 frame delay circuit 201 internal V counter 202 phase comparison circuit

Claims (4)

A wireless video that is encoded in units of video signals for a certain number of vertical periods, and that is transmitted with the start data transmission interval of the video signals for a certain number of vertical periods after encoding matched to the predetermined number of vertical periods A transmission device for temporarily holding the encoded video signal; means for determining whether a vertical period of the input video signal is deviated by a predetermined value or more from an assumed vertical period; Means for generating a signal having a vertical period and generating a pulse having an integer multiple of the predetermined number of vertical periods based on the signal; and a latest code from the buffer only once in one period of the pulse. Means for reading out and transmitting video signals for a fixed number of vertical periods after conversion. Based on the output of the counter, a periodic signal having a period of a certain number of vertical periods is generated, and a phase locked loop is formed by comparing the phase of the arrival period of the head data of the received encoded video signal with the period signal. The wireless video receiving apparatus configured to control the counter, decode the encoded video signal based on the output of the counter and output the video signal, and only when the arrival of the head data can be detected A wireless video receiving apparatus configured to perform phase comparison. 3. The wireless video receiving apparatus according to claim 2, wherein means for detecting a transmission drop of the encoded video signal, a buffer holding video data after video decoding for at least one field, and a received video that has been successfully received. A wireless video receiving apparatus comprising: means for sequentially updating and recording data in the buffer; and means for outputting video data held in the buffer when the transmission drop is detected. A wireless video transmission / reception system comprising the wireless video transmission device according to claim 1 and the wireless video reception device according to claim 2 or 3.

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