JP4282399B2 - Wireless master unit and wireless slave unit - Google Patents

Description

  The present invention relates to a wireless transmission device (wireless master device and wireless slave device) that transmits video signals, audio signals, and the like via a wireless line, and in particular, transmits between a transmitting side and a receiving side via an asynchronous wireless transmission line. The present invention relates to a method for ensuring signal synchronization.

  In recent years, a wireless local area network (hereinafter referred to as “LAN”) represented by IEEE 802.11 (Institute of Electrical and Electronics Engineers) has been installed in place of a conventional wired LAN such as Ethernet (registered trademark). It has become popular due to its advantages such as high degree of freedom in places. In addition, wireless transmission devices that transmit video signals, audio signals, and the like using a wireless LAN have become widespread.

A conventional radio transmission apparatus will be described. FIG. 5 is a block diagram showing a configuration of a conventional radio transmission apparatus. In FIG. 5, 10A is a wireless master unit that encodes and modulates an input video signal and transmits it as a radio wave of a predetermined format, and 10B is a wireless slave unit that receives the radio wave, demodulates and decodes it, and outputs a video signal.
The wireless master device 10A includes a video signal encoding unit 400A, a time information generation unit 900A, a communication protocol processing unit 600A, a MAC (Media Access Control) processing unit 700A, an RF unit (Radio Frequency) 800A, and an antenna 30A. The wireless master device 10A is connected to the wireless slave device 10B via a wireless line.
The wireless slave device 10B includes a video signal decoding unit 500B, a time information generation unit 900B, a communication protocol processing unit 600B, a MAC processing unit 700B, an RF unit 800B, and an antenna 30B.
Both the wireless master device 10A and the wireless slave device 10B can perform bidirectional communication, but only a one-way transmission path is shown for the sake of simplicity of explanation.

An operation of the wireless master device 10A in FIG. 5 will be described. The wireless master device 10A inputs an external video signal. The input video signal is compressed and encoded in a predetermined format by the video signal encoding unit 400A. Normally, when a video signal is transmitted, it is encoded using the MPEG2-TS format (Moving Picture Experts Group 2-Transport Stream) for the purpose of reducing the amount of data transmission and transmitting clock information. The encoded video signal is packetized in the MPEG2-TS packet format.
The MPEG2-TS packet is input to the time information generation unit 900A and given a predetermined time stamp. The MPEG2-TS packet to which the time stamp is added is input to the communication protocol processing unit 600A, further packetized based on a predetermined communication protocol, and a header necessary for transmission is added. The communication protocols here include TCP / IP (Transmission Control Protocol / Internet Protocol) for realizing reliable data transmission, UDP / IP (User Datagram Protocol / Internet Protocol) suitable for transmission of stream data, and the like. Used, the MPEG2-TS packet is packetized into an IP packet (Internet Protocol) format.

The IP packet is input to the MAC processing unit 700A and assembled as a MAC packet based on a predetermined wireless communication method. For the configuration of the MAC packet, a method defined by a wireless LAN standard such as IEEE 802.11 is used.
Data assembled in the MAC packet format is input to the RF unit 800A. The RF unit 800A performs predetermined modulation and transmits data as a radio wave having a predetermined frequency via the antenna 30A. As the modulation method, quadrature modulation and spread spectrum or OFDM are used. The frequency uses a 2.4 GHz band, a 5 GHz band, or the like. The video signal input in this way is sent out on the wireless communication line by a predetermined method.

The operation of the wireless slave device 10B in FIG. 5 will be described. In the wireless slave device 10B, the radio wave (data) received by the antenna 30B is input to the RF unit 800B.
The RF unit 800B selects a desired frequency, demodulates received data, converts the received data into a baseband signal, that is, data in the MAC packet format, and outputs the data to the MAC processing unit 700B.
The MAC processing unit 700B analyzes the input data in the MAC packet format, converts it into an IP packet, and outputs it to the communication protocol processing unit 600B.
The communication protocol processing unit 600B extracts the MPEG2-TS packet to which the time stamp is added from the input IP packet, and outputs it to the time information generation unit 900B. The time information generation unit 900B outputs the MPEG2-TS packet to the video signal decoding unit 500B at a predetermined timing according to the added time stamp.
The video signal decoding unit 500B decodes the input MPEG2-TS packet, decompresses it, and outputs it as a video signal. The video signal input from the wireless master device 10A in this way is transmitted to the wireless slave device 10B via the wireless communication line, and is decoded, decompressed and externally output in the wireless slave device 10B.

FIG. 6 is a timing diagram showing the timing of signals transmitted on the wireless line. In FIG. 6, a beacon is a control signal transmitted from the wireless master device 10 </ b> A and is transmitted at a constant interval (cycle) of several ms to 1 s. The beacon includes control information such as an identification number for identifying the wireless master device 10A and a timer value provided in the wireless master device 10A.
The purpose of using this beacon is that the wireless slave device 10B can identify the wireless master device 10A based on the identification number included in the beacon, and the transmission / reception timing between the wireless master device 10A and the wireless slave device 10B with reference to the output timing of the beacon. When it is not necessary to transmit / receive video data between the wireless master device 10A and the wireless slave device 10B by adjusting the internal timer of the wireless slave device 10B to the timer value of the wireless master device 10A included in the beacon The power saving operation is performed by intermittently operating the reception operation of the wireless slave device 10B by the beacon reception timing.

Video data is sent at the timing between two adjacent beacons. IEEE802.11 employs the CSMA / CA method (Carrier Sense Multiple Access with Collision Avoidance). When transmitting data, first, reception is performed to determine whether or not a wireless line is available, that is, another wireless transmission device. In this case, control is performed such that data is transmitted after confirming that transmission by another wireless transmission device is completed.
Therefore, when there are a plurality of wireless slave units 10B, when the wireless line is in use for other communication, the transmission of the signal is completed and the transmission of the wireless line is awaited. A transmission delay may occur depending on the usage situation.

FIG. 7 is a block diagram illustrating an internal configuration of the wireless master device 10A and the wireless slave device 10B.
7, the MAC processing unit 700A includes a frame assembly unit 704A, a clock generation unit 701A, a beacon timer unit 702A, a beacon generation unit 703A, a frame analysis unit 705A, and a received data processing unit 706A. The time information generation unit 900A includes a time stamp timer unit 903A, a PLL processing unit 904A, and a time stamp addition unit 905A.
7, the MAC processing unit 700B includes a frame assembling unit 704B, a clock generation unit 701B, a beacon timer unit 702B, a beacon generation unit 703B, a frame analysis unit 705B, and a reception data processing unit 706B. The time information generation unit 900B includes a time stamp extraction unit 901B, a time stamp comparison unit 902B, a time stamp timer unit 903B, a PLL processing unit 904B, a reception data buffer unit 907B, and an initial value setting unit 910B. In FIG. 7, the same parts as those in FIG.

The operation when the wireless master device 10A transmits a beacon, the wireless slave device 10B receives the beacon, and synchronizes the internal timer of the wireless master device 10A and the internal timer of the wireless slave device 10B will be described with reference to FIG. . Beacon transmission / reception is performed by the MAC processing unit 700A of the wireless master device 10A and the MAC processing unit 700B of the wireless slave device 10B.
An operation when the wireless master device 10A transmits a beacon will be described. The clock generation unit 701A generates a clock signal for generating the timing for transmitting a beacon and outputs it to the beacon timer unit 702A.
The beacon timer unit 702A counts a clock signal, and includes, for example, a counter of about 64 bits.

  The beacon generation unit 703A refers to the count value (timer value) output from the beacon timer unit 702A, and detects that the timer value has changed to a predetermined value. And the timer value output from the beacon timer unit 702A are output to the frame assembling unit 704A. The predetermined value here is a value determined by the relationship with the clock signal of the clock generation unit 701A, and a desired beacon transmission cycle is set by this value. The frame assembling unit 704A stores the control information in a predetermined MAC frame and outputs it to the RF unit 800A. Thus, a beacon signal storing control information is transmitted at a predetermined cycle.

An operation when the wireless slave device 10B receives a beacon will be described. In the wireless slave device 10B, the received signal output from the RF unit 800B is analyzed by the frame analysis unit 705B to determine whether or not the signal is addressed to the own device. If the signal is not addressed to the own device, the signal is discarded. If the signal is addressed to the own device, the received data is output to the received data processing unit 706B.
When the received data is a beacon, the received data processing unit 706B extracts control information included in the received data, extracts timer value information (time information) from the control information, and outputs it to the beacon timer unit 702B. To do. This timer value is the timer value of the wireless master device 10A stored in the beacon by the wireless master device 10A.

  The beacon timer unit 702B of the wireless slave device 10B counts the clock signal output from the clock generation unit 701B in the same manner as the beacon timer unit 702A of the wireless master device 10A. The difference from the wireless master device 10A is that the count value of the beacon timer unit 702B of the wireless slave device 10B is rewritten by the timer value output from the received data processing unit 706B. By this rewriting, the count values of the beacon timer unit 702A of the wireless master device 10A and the beacon timer unit 702B of the wireless slave device 10B match.

The wireless slave device 10B rewrites the beacon timer unit 702B with the timer value of the wireless master device 10A included in the received beacon each time a beacon is received, thereby reusing the internal timer of the wireless master device 10A and the wireless slave device 10B. The timer can be synchronized.
When it is not necessary to transmit / receive video data between the wireless master device 10A and the wireless slave device 10B, the internal timer of the wireless master device 10A and the internal timer of the wireless slave device 10B are synchronized with each other. The device 10B can perform the reception operation of the wireless slave device 10B only at the timing when the wireless master device 10A transmits a beacon, and can stop the operation at other timings. Accordingly, the wireless slave device 10B can perform operation control such as reducing power consumption.

The operation of the time information generation units 900A and 900B will be described with reference to FIG.
First, an operation when generating time information for time stamp with higher accuracy (having time resolution) from time information output by the beacon timer unit 702A in the wireless master device 10A will be described. In a wireless transmission device compliant with IEEE 802.11, the accuracy (time resolution) of time information output by the beacon timer unit 702A is 1 μs. On the other hand, the clock used in MPEG2-TS is 27 MHz (one clock period is 0.037 μs), and the accuracy difference is large. In the wireless master device 10A, the PLL processing unit (Phase Lock Loop) 904A generates a clock having a higher frequency than the time information output from the beacon timer unit 702A. The PLL processing unit 904A generates a 27 MHz clock that is phase-synchronized with the timing of the time information output by the beacon timer unit 702A (the clock output by the clock generation unit 701A). The time stamp timer unit 903A outputs time information (time information having an accuracy (time resolution) of 27 MHz) that is advanced by the clock output from the PLL processing unit 904A to the time stamp adding unit 905A.

The time stamp adding unit 905A adds the time information output from the time stamp timer unit 903A to the MPEG2-TS packet output from the video signal encoding unit 400A, and outputs it to the communication protocol processing unit 600A.
In this way, time information generated from the 27 MHz clock following the clock generated by the clock generation unit 701A is added to the MPEG2-TS packet and transmitted.

An operation when the MPEG2-TS packet received by the wireless slave device 10B is output to the video signal decoding unit 500B in synchronization with the output timing of the video signal encoding unit 400A of the wireless master device 10A will be described.
The clock generation unit 701B outputs the same clock as the clock generation unit 701A. The beacon timer unit 702B outputs a beacon timer value that is set by a timer value included in the beacon extracted by the reception data processing unit 706B and that is incremented by a clock output from the clock generation unit 701B. The beacon timer unit 702B counts clock signals, and is configured with, for example, a counter of about 64 bits.
The PLL processing unit 904B generates a 27 MHz clock that is phase-synchronized with the timing of the timer value output by the beacon timer unit 702B (the clock output by the clock generation unit 701B). The time stamp timer unit 903B outputs time information (time information having an accuracy (time resolution) of 27 MHz) that advances according to the clock output from the PLL processing unit 904B to the time stamp comparison unit 902B.

The data output from the communication protocol processing unit 600B is input to the reception data buffer unit 907B. The reception data buffer unit 907B outputs the received data to the time stamp extraction unit 901B.
The time stamp extraction unit 901B extracts a time stamp from the received data and outputs it to the time stamp comparison unit 902B.
The time stamp comparison unit 902B compares the time stamp of the received data with the time information output from the time stamp timer unit 903B, and outputs a control signal permitting the output to the reception data buffer unit 907B only when they match. .
When the control signal is input, reception data buffer unit 907B outputs an MPEG2-TS packet obtained by removing the time stamp from the reception data to video signal decoding unit 500B.

The resetting of the time stamp of the wireless slave device 10B (time information generated by the time stamp timer unit 903B of the wireless slave device 10B) will be described.
The time stamp comparison unit 902B compares the time stamp extracted by the time stamp extraction unit 901B with the time information output by the time stamp timer unit 903B, and if they are different, the time extracted by the time stamp extraction unit 901B The stamp is output to the initial value setting unit 910B. The initial value setting unit 910B resets the time information output from the time stamp timer unit 903B using the time stamp.
That is, the initial value setting unit 910B resets the time information generated by the time stamp timer unit 903B (the count value incremented by the clock output from the PLL processing unit 904B) using the time stamp of the current wireless master device 10A. To do. This makes it possible to synchronize the time stamps of the wireless master device 10A and the wireless slave device 10B. The time stamp timer unit 903B is not reset with the timer value output by the beacon timer unit 702B.

  The timing of each part will be described with reference to FIG. In the case of MPEG2-TS, packet data of 188 bytes is output from the video signal encoding unit 400A. A time stamp is added by the time stamp adding unit 905A, and the time stamp adding unit output in FIG. 8 is obtained. The communication protocol processing unit 600A combines a plurality of (three in the figure) time stamped packets into one, adds a radio header, and outputs the packet as a radio packet. This is because if a radio header is added to each packet, the redundancy increases and the use of the radio band is wasted.

JP 2002-290295 A

  The wireless transmission device of the conventional example is configured as described above, and is a convenient device that can transmit a video signal from the wireless master device 10A to the wireless slave device 10B without laying a new wired transmission line. there were. However, the synchronization of the time stamp timers of the wireless master device 10A and the wireless slave device 10B is performed based on the time stamp added to the video packet data transmitted by the wireless master device 10A. As shown in FIG. The timing at which the stamp is added and the timing at which the wireless protocol is generated and transmitted to the wireless slave device 10B in the communication protocol processing unit 600A are deviated.

The time of the wireless packet reaching the wireless slave device 10B varies due to the influence of a change in communication state unique to the wireless line, propagation delay, communication protocol processing delay, and the like. Further, when the quality deteriorates due to interference or interference from other wireless communication devices, complementary processing such as detecting an error in the data to be transmitted and resending the data again is performed by the MAC processing unit. In this case, a large delay time occurs because the data once transmitted is sent again later.
Therefore, in such a case, there is a problem that synchronization between the wireless master device 10A and the wireless slave device 10B cannot be accurately guaranteed.

  The present invention has been made in order to solve the above-described problems. Data re-transmission is caused by a change in delay time due to communication protocol processing, a change in transmission delay time due to a propagation delay in a wireless line, or a change in propagation state. An object of the present invention is to provide a wireless transmission device (wireless master device and wireless slave device) that can correctly reproduce a video signal even when transmission occurs and a transmission delay time greatly changes.

In order to solve the above problems, a wireless transmission device (wireless master and wireless slave) of the present invention has the following configuration.
The invention according to claim 1 is a wireless master device of a wireless transmission device that transmits a video signal and / or an audio signal as packet data between a wireless master device and a wireless slave device connected by a wireless line, A time information generating unit that generates first time information; a first PLL unit that generates second time information having a higher time resolution than the first time information based on the first time information; A video signal having a video signal and / or an audio signal and generating a video signal and / or an audio signal packet to which the second time information or time information derived based on the second time information is added And / or an audio signal packet generation unit and a time information packet that includes the second time information or time information derived based on the second time information and does not include a video signal and / or an audio signal. Time information And Tsu DOO generating unit, the first time information intermittently transmitted at a predetermined period, the video signal and / or wireless communication unit for transmitting said time information packet and the audio signal packet, the radio personal station A time information request detector for detecting a time information request from the time information packet generator , the time information packet generator generates the time information packet based on the detected time information request, and the video signal and When the audio signal packet and the time information packet compete with each other, the wireless communication unit transmits the time information packet with priority or simultaneously with the video signal and / or audio signal packet. It is a wireless master unit.

The invention according to claim 6 is a method of controlling a wireless master of a wireless transmission device that transmits video signals and / or audio signals as packet data between a wireless master and a wireless slave connected via a wireless line. A first time information generating step for generating first time information; and second time information having a time resolution higher than that of the first time information in phase synchronization with the first time information. A second time information generation step, a video signal and / or an audio signal, and a video signal to which the second time information or time information derived based on the second time information is added and / or Or a video signal and / or audio signal packet generating step for generating an audio signal packet, and the second time information or time information derived based on the second time information, and the video signal and / or audio Including signal A time information packet generating step for generating no time information packet, and a radio for intermittently transmitting the first time information at a predetermined period and transmitting the video signal and / or audio signal packet and the time information packet A time information request detecting step for detecting a time information request from the wireless slave unit, and the time information packet is generated based on the time information request detected in the time information packet generating step. generates, the case where the video signal and / or in which the said time information packet and the audio signal packets conflict in the wireless communication step, the time information packet, and preferentially or the video signal and / or audio signal packet At the same time, it is a method of controlling a wireless master device characterized by transmitting.

The present invention enables the wireless slave unit to perform the correct timing even when the delay time due to processing of the data packet of the video signal or the like, or when the transmission delay time greatly changes due to the retransmission of data caused by the propagation state change or the like. It has an effect that it is possible to realize a wireless master device and a control method thereof that can reproduce a video signal or the like (it is difficult for frame dropping or freezing of a video signal or the like output from a wireless slave device).
When the time information is required, the wireless slave device can send a time information request to the wireless master device and acquire time information of the wireless master device.

The invention according to claim 2 is a wireless slave device of a wireless transmission device that transmits a video signal and / or an audio signal as packet data between a wireless master device and a wireless slave device connected by a wireless line, The first time information transmitted intermittently at a predetermined cycle is received from the wireless master unit, the video signal and / or the audio signal are included, and the first time information is generated in phase synchronization with the first time information. Receiving a video signal and / or an audio signal packet to which second time information having a time resolution higher than the first time information or time information derived based on the second time information is added; and A wireless communication unit having time information derived based on time information derived from the second time information or the second time information and receiving a time information packet not including a video signal and / or an audio signal; and the first time information Based on the first time A second PLL unit that generates second time information having higher time resolution than the information, the second time information generated by the second PLL unit, and the video signal and / or audio signal packet Time information added to the time information packet, and a first time information comparison unit that controls the output timing of the video signal and / or audio signal packet according to the comparison result. A time information setting unit for setting the second time information generated by the second PLL unit, and a time information requesting unit for requesting the wireless master device to transmit the time information packet. It is a wireless cordless handset.

The invention according to claim 7 is a method of controlling a wireless slave unit of a wireless transmission device that transmits video signals and / or audio signals as packet data between a wireless master unit and a wireless slave unit connected by a wireless line. Then, the first time information transmitted intermittently at a predetermined cycle is received from the wireless master unit, and has a video signal and / or an audio signal, and is generated in phase synchronization with the first time information. Receiving video signal and / or audio signal packet to which second time information having a higher time resolution than the first time information or time information derived based on the second time information is added; And a wireless communication step for receiving a time information packet having time information derived based on the second time information or the second time information and not including a video signal and / or an audio signal; Time information and phase synchronization A second time information generating step for generating second time information having a higher time resolution than the first time information; the second time information generated by the second time information generating step; A first time information comparing step of comparing time information added to the video signal and / or audio signal packet and controlling an output timing of the video signal and / or audio signal packet according to the comparison result; A time information setting step for setting the second time information generated in the second time information generation step based on the time information added to the time information packet; and transmission of the time information packet to the wireless master unit. And a time information requesting step for requesting the wireless slave device.

The present invention enables the wireless slave unit to perform the correct timing even when the delay time due to processing of the data packet of the video signal or the like, or when the transmission delay time greatly changes due to the retransmission of data caused by the propagation state change or the like. It has an effect that it is possible to realize a wireless slave unit and a control method thereof that can reproduce a video signal or the like (it is difficult for frame dropping or freezing of a video signal or the like output from the wireless slave unit).
When the time information is required, the wireless slave device can send a time information request to the wireless master device and acquire time information of the wireless master device.

According to a third aspect of the present invention, the time information included in the time information packet is compared with the second time information generated by the second PLL unit, and the difference may exceed a predetermined range. For example, a second time information comparison unit that allows the time information setting unit to set the second time information generated by the second PLL unit based on the time information added to the time information packet. The wireless slave device according to claim 2 , further comprising:

The invention according to claim 8 compares the time information included in the time information packet with the second time information generated by the second time information generation step, and the difference exceeds a predetermined range. If so, the second time information setting step allows the setting of the second time information generated by the second time information generation step based on the time information added to the time information packet. The wireless slave device control method according to claim 7 , further comprising a time information comparison step.
Since the wireless slave unit does not set (change) the second time information unless a time error of a certain level or more occurs, it does not generate unnecessary jitter and outputs a video signal and / or an audio signal at a stable timing. .

In the invention according to claim 4, when the time information packet is received, the time information setting unit generates the second PLL unit based on time information added to the time information packet. When the second time information is set and the time information packet is not received, the time information setting unit uses the time information added to the video signal and / or audio signal packet to determine the second PLL. The wireless slave unit according to claim 2 , wherein the second time information generated by a unit is set.

According to the ninth aspect of the present invention, when the time information packet is received, the second time information generation step generates the time information in the time information setting step based on the time information added to the time information packet. If the second time information is set and the time information packet is not received, the second time information is set based on the time information added to the video signal and / or audio signal packet in the time information setting step. The wireless slave device control method according to claim 7 , wherein the second time information generated by the time information generation step is set.

  The present invention realizes a wireless slave unit and a control method thereof capable of adaptively reproducing video signals and the like at the correct timing (the video signal output from the wireless slave unit is less likely to drop or freeze) Has the effect of being able to.

In the invention according to claim 5 , when the received video signal and / or audio signal packet includes an error, the wireless master unit is requested to retransmit the video signal and / or audio signal packet, 3. The wireless slave device according to claim 2 , wherein when the received time information packet includes an error, the wireless slave device does not request the wireless master device to retransmit the time information packet.
In the invention according to claim 10 , when the received video signal and / or audio signal packet includes an error, the wireless master unit is requested to retransmit the video signal and / or audio signal packet, 8. The wireless slave device control method according to claim 7 , wherein when the received time information packet includes an error, the wireless master device is not requested to retransmit the time information packet.
In the present invention, since the time information packet does not include a video signal and / or an audio signal, if the received time information packet includes an error, the wireless slave device retransmits the time information packet. The time information packet can be discarded. Due to the retransmitted time information, it is possible to prevent the time information from being reset incorrectly in the wireless slave unit.

According to the present invention, the transmission side and the reception side can be reliably synchronized in the continuous stream transmission of the video signal or the like on the time axis. For example, it is possible to obtain an advantageous effect of realizing a wireless transmission device that can prevent a frame drop or freeze (insufficiency) of a video and reproduce a video signal accurately.
According to the present invention, it is possible to detect a synchronization error between a wireless master device and a wireless slave device and perform resynchronization. There is an advantageous effect that it is possible to realize a wireless transmission apparatus that is less affected by a change in processing time of video packets or a delay due to retransmission and that can reproduce a video signal or the like at an accurate timing.
According to the present invention, resynchronization can be performed based on a request from a wireless slave unit. An advantageous effect is obtained that it is possible to realize a wireless transmission apparatus that can suppress transmission of an extra packet on a wireless line and can efficiently use the wireless line.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments that specifically show the best mode for carrying out the present invention will be described below with reference to the drawings.

Embodiment 1
A radio transmission apparatus according to Embodiment 1 of the present invention will be described using FIG. 1 and FIG. FIG. 1 is a block diagram illustrating a configuration of a wireless transmission device according to the first embodiment. In FIG. 1, 10A is a wireless master device, and 10B is a wireless slave device.
In the wireless master device 10A, the clock generation unit 701A and the beacon timer unit 702A constitute a time information generation unit that generates first time information. The PLL processing unit 904A and the time stamp timer unit 903A constitute a first PLL unit. The time stamp adding unit 905A and the communication protocol processing unit 600A constitute a video signal packet generating unit and a time information packet generating unit. The RF unit 800A constitutes a wireless communication unit.

In the wireless slave device 10B, the RF unit 800B constitutes a wireless communication unit. The PLL processing unit 904B and the time stamp timer unit 903B constitute a second PLL unit. The time stamp comparison unit 902B constitutes a first time information comparison unit. The initial value setting unit 910B constitutes a time information setting unit.
A video packet (a packet including a video signal, which is an MPEG2-TS packet in the first embodiment) and a beacon are transmitted between the wireless master device 10A and the wireless slave device 10B (as compared with the conventional example). Similarly, a time stamp packet is transmitted.
In FIG. 1, the same reference numerals are given to the same or corresponding parts as those of the conventional wireless transmission apparatus (FIGS. 5 and 7). In the following, the difference between the wireless transmission device of the first embodiment and the conventional example will be described. In the wireless transmission device of the first embodiment, the same points as in the conventional wireless transmission device will not be described.
In the wireless transmission device according to the first embodiment, compared to the conventional example (FIG. 7), a time stamp packet sending unit 911A is newly added to the wireless master device 10A, and the time stamp packet is extracted to the wireless slave device 10B. A part 912B is newly added. In the first embodiment, the processing in communication protocol processing unit 600A may be different from the conventional example. In other respects, the first embodiment is the same as the conventional example (FIG. 7).

The radio transmission apparatus according to the first embodiment configured as described above transmits time stamp transmission independently of the video signal on the transmission side, and uses the time stamp on the reception side to obtain time information at the time of transmission. The operation is different from the conventional example of synchronizing. Hereinafter, operations different from those of the conventional example and operations related to the operations of the radio transmission apparatus according to the first embodiment will be described.
First, in the wireless master device 10A, the beacon timer unit 702A outputs a timer value (first time information generation step). Similarly to the conventional example, the RF unit 800A transmits a beacon (a wireless communication step in which first time information is intermittently transmitted at a predetermined period). The PLL processing unit 904A outputs a clock having a higher frequency (27 MHz) in phase with the timer value (clock) output from the beacon timer unit 702A. The time stamp timer unit 903A outputs time information that advances according to the clock output from the beacon timer unit 702A (second time information generation step).
The time stamp packet sending unit 911A (outputs time information having higher time resolution than the beacon timer) is used to send the time stamp output by the time stamp timer unit 903A as one packet at a predetermined period. The timing signal is output to the time stamp adding unit 905A. The time stamp adding unit 905A outputs the time stamp output from the time stamp timer unit 903A as one time stamp packet (not including a video signal) to the communication protocol processing unit 600A when the timing signal is input. .

The communication protocol processing unit 600A adds a header necessary for transmission to the time stamp packet based on a predetermined communication protocol, further packetizes the time stamp packet, and outputs the packet as a wireless packet (in the first embodiment, the IP packet Packetized in the form of The communication protocol processing unit 600A of the first embodiment normally collects video packets to which a plurality of time stamps are added as one wireless packet (by the same processing as in the conventional example) (video signal packet generation step). . When the communication protocol processing unit 600A according to the first embodiment receives a time stamp packet, the communication protocol processing unit 600A postpones processing of the video packet (one or a plurality of video packets) stored in the communication protocol processing unit 600A at that time ( A radio packet including only the time stamp packet is generated with priority being given to the time stamp packet, and output immediately (time information packet generation step). Thereafter, the processing returns to the processing of the video packet (one or a plurality of video packets) stored in the communication protocol processing unit 600A.
As a result, the time from when the time stamp packet is generated to when the wireless packet including only the time stamp packet is output is shortened and substantially constant (time does not vary).

The wireless packet (the wireless packet including the time stamp packet and the wireless packet including the video packet) is transmitted to the MAC processing unit 700A and the wireless slave device 10B via the RF unit 800A (the video signal packet and the time information packet are transmitted). Transmitting wireless communication step). The timing at this time is shown in FIG. The time stamp packet (not including the video signal) is transmitted at a timing independent of the video packet and the beacon. The wireless master device 10A transmits a normal video packet and a time stamp packet during a period other than the beacon transmission timing.
The interval at which the time stamp packet is transmitted is arbitrary. Preferably, the wireless master device 10A transmits a plurality of time stamp packets in a period between two adjacent beacons.

The wireless slave device 10B includes a beacon that the wireless master device 10A intermittently transmits at a predetermined cycle, a wireless packet that includes the time stamp and the video packet that the wireless parent device 10A transmits, and a wireless packet that includes the time stamp packet. Receive (wireless communication step).
In the wireless slave device 10B, the radio wave (data) received by the antenna 30B is input to the RF unit 800B.
The RF unit 800B selects a desired frequency, demodulates received data, converts the received data into a baseband signal, that is, data in the MAC packet format, and outputs the data to the MAC processing unit 700B.
The MAC processing unit 700B analyzes the input data in the MAC packet format, converts it into an IP packet, and outputs it to the communication protocol processing unit 600B.
The communication protocol processing unit 600B extracts the MPEG2-TS packet to which the time stamp is added from the input IP packet, and outputs it to the time information generation unit 900B. The time information generation unit 900B outputs the MPEG2-TS packet to the video signal decoding unit 500B at a predetermined timing according to the added time stamp.
The video signal decoding unit 500B decodes the input MPEG2-TS packet, decompresses it, and outputs it as a video signal.

The clock generation unit 701B outputs the same clock as the clock generation unit 701A. The beacon timer unit 702B outputs a beacon timer value that is set by a timer value included in the beacon extracted by the reception data processing unit 706B and that is incremented by a clock output from the clock generation unit 701B. The beacon timer unit 702B counts clock signals, and is configured with, for example, a counter of about 64 bits.
The PLL processing unit 904B generates a 27 MHz clock that is phase-synchronized with the timing of the time information output by the beacon timer unit 702B (the clock output by the clock generation unit 701B). The time stamp timer unit 903B outputs time information (time information having an accuracy (time resolution) of 27 MHz) based on the clock output from the PLL processing unit 904B to the time stamp comparison unit 902B (second time information). Generation step).

The data output from the communication protocol processing unit 600B is input to the reception data buffer unit 907B. The reception data buffer unit 907B outputs the received data to the time stamp extraction unit 901B.
The time stamp extraction unit 901B extracts a time stamp from the received data and outputs it to the time stamp comparison unit 902B.
The time stamp comparison unit 902B compares the time stamp of the received data with the time information output from the time stamp timer unit 903B, and outputs a control signal permitting the output to the reception data buffer unit 907B only when they match. (First time information comparison step).
When the control signal is input, reception data buffer unit 907B outputs an MPEG2-TS packet obtained by removing the time stamp from the reception data to video signal decoding unit 500B.

The time stamp timer unit 903B of the wireless slave device 10B receives a time stamp with higher accuracy (having a higher time resolution) than the time information included in the beacon at a timing with higher accuracy. The time information (time stamp) that is synchronized with the time information (output of the time stamp timer unit 903A) output by 10A with high accuracy is output.
When the wireless slave device 10B receives the time stamp packet transmitted from the wireless master device 10A, the timer value output from the time stamp timer unit 903B becomes the timer value of the time stamp timer unit 903A of the wireless master device 10A. Synchronize. This operation will be described.

  The reception data buffer unit 907B of the wireless slave device 10B stores the packet transmitted by the wireless master device 10A. The time stamp packet extracting unit 912B extracts only the time stamp packet (not including the video signal) from the received packet, and outputs the time stamp included in the packet to the initial value setting unit 910B. The initial value setting unit 910B outputs the time stamp value to the time stamp timer unit 903B. Time information generated by the time stamp timer unit 903B (a count value that is incremented by a clock output from the PLL processing unit 904B) is reset (time information setting step). The time stamp timer unit 903B is not reset by the timer value output by the beacon timer unit 702B during the period in which the time stamp packet or video packet is received. If neither the time stamp packet nor the video packet is received, the time stamp timer unit 903B is reset with the timer value output from the beacon timer unit 702B.

In the first embodiment, the initial value setting unit 910B is not reset by the time stamp added to the video packet while inputting the time stamp packet at least at a predetermined interval.
In the first embodiment, if the received video packet includes an error (or if the error cannot be corrected), the wireless slave device 10B is in a communication mode that requests the wireless master device 10A to retransmit the video packet. Suppose there is. When the received time stamp packet includes an error (or when the error cannot be corrected), the wireless slave device 10B does not request the wireless master device 10A to retransmit the time stamp packet. When the received time stamp packet includes an error (or when the error cannot be corrected), the wireless slave device 10B discards the time stamp packet. Since the time stamp packet does not include a video signal, there is no problem even if it is discarded.
With the configuration of the first embodiment, it is possible to synchronize the time stamps of the wireless master device 10A and the wireless slave device 10B more accurately than the conventional example.

In another embodiment, the following processing is performed. When a time stamp packet is input, the communication protocol processing unit 600A collects all video packets (one or a plurality of video packets) stored in the communication protocol processing unit 600A at that time (or communication protocol at that time). The processing unit 600A combines all the video packets that have been processed into a single wireless packet and immediately outputs it. Thereafter, the communication protocol processing unit 600A generates a radio packet including only the time stamp packet and immediately outputs it. The synchronization accuracy of the time information (time stamp) output from the time stamp timer unit 903B of the wireless slave device 10B is inferior to that of the first embodiment, but better than the conventional example.
In still another embodiment, when a time stamp packet is input, the communication protocol processing unit 600A receives all video packets stored in the communication protocol processing unit 600A at that time (or the communication protocol processing unit at that time). All video packets that 600A has completed processing) and the input time stamp packets are combined into one radio packet and output immediately.
If the wireless packet has to have a constant data length, the communication protocol processing unit 600A adds null data to the time stamp packet to generate a wireless packet with a constant data length. In other embodiments and still other embodiments, null data is added to one or a plurality of video packets to generate a wireless packet having a fixed data length.

  In the first embodiment, the time stamp packet sending unit 911A outputs a timing signal for sending the time stamp output from the time stamp timer unit 903A as a single packet to the time stamp adding unit 905A at regular intervals. Instead, before the next video packet is generated after the wireless communication protocol processing unit 600A outputs a wireless packet including a plurality of video packets (normal wireless packet) (typically, the wireless communication protocol Immediately after the processing unit 600A outputs a wireless packet including a plurality of video packets, the time stamp packet sending unit 911A sends a timing signal for sending the time stamp output from the time stamp timer unit 903A as one packet. You may output to the time stamp addition part 905A.

In the wireless slave device 10B of the first embodiment, the initial value setting unit 910B sets the time information output from the time stamp timer unit 903B only by the time stamp output from the time stamp packet extraction unit 912B.
The initial value setting unit 910B may have both the function of the first embodiment and the function of the conventional example. That is, when the wireless slave device 10B receives the time stamp packet, the initial value setting unit 910B sets the time information output from the time stamp timer unit 903B by the time stamp added to the time stamp packet. For example, when a time stamp packet is not received for a predetermined time or more, the initial value setting unit 910B sets time information output from the time stamp timer unit 903B based on the time stamp added to the video packet.

<< Embodiment 2 >>
A radio transmission apparatus according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 3 is a block diagram illustrating a configuration of the wireless transmission device according to the second embodiment. In the wireless transmission device of the second embodiment, in addition to the configuration of the first embodiment, the wireless slave device 10B includes a second time stamp comparison unit 913B. In FIG. 3, the second time stamp comparison unit 913B of the wireless slave device 10B constitutes a second time information comparison unit. In other respects, the second embodiment has the same configuration as the first embodiment.
In FIG. 3, the same or corresponding parts as those of the wireless transmission apparatus (FIG. 1) of the first embodiment are denoted by the same reference numerals.

The operation of the radio transmission apparatus according to the second embodiment configured as described above will be described below with respect to operations different from those of the first embodiment.
First, in the wireless slave device 10B, the time stamp packet extraction unit 912B outputs the time stamp of the extracted time stamp packet to the second time stamp comparison unit 913B.
The second time stamp comparison unit 913B compares the time stamp extracted by the time stamp packet extraction unit 912B with the count value output from the time stamp timer unit 903B. If the difference between the time stamp input from the time stamp packet extraction unit 912B and the count value output from the time stamp timer unit 903B is larger than a predetermined value set as a result of the comparison, the time stamp packet extraction unit 912B The input time stamp is output to the initial value setting unit 910B (second time information comparison step). When the difference between the time stamp input from the time stamp packet extracting unit 912B and the count value output from the time stamp timer unit 903B is equal to or smaller than a predetermined value set in advance, the time stamp input from the time stamp packet extracting unit 912B is It is not output to the initial value setting unit 910B.

  The initial value setting unit 910B outputs the time stamp value to the time stamp timer unit 903B, and resets time information generated by the time stamp timer unit 903B (clock count value output from the PLL processing unit 904B). By comparing the count value with the second time stamp comparison unit 913B, it is possible to reset only when the error exceeds a predetermined value.

<< Embodiment 3 >>
A radio transmission apparatus according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 4 is a block diagram illustrating a configuration of the wireless transmission device according to the third embodiment. In the wireless transmission apparatus according to the third embodiment, in addition to the configuration of the first embodiment, the wireless master device 10A includes a time stamp packet request detection unit 914A, and the wireless slave device 10B includes a time stamp packet request unit 915B. In other respects, the third embodiment has the same configuration as the first embodiment.
4, the time stamp packet request unit 915B of the wireless slave device 10B constitutes a time information request unit, and the time stamp packet request detection unit 914A of the wireless master device 10A constitutes a time information request detection unit.
In FIG. 4, the same reference numerals are given to the same or corresponding parts as those of the wireless transmission apparatus (FIG. 1) of the first embodiment.
The wireless transmission device of the third embodiment configured as described above is characterized in that the wireless master device 10A transmits time information based on a request from the wireless slave device 10B.

Hereinafter, the operation of the radio transmission apparatus according to the third embodiment will be described.
First, in the wireless slave device 10B, the time stamp packet request unit 915B outputs a time stamp packet request to the communication protocol processing unit 600B, for example, every predetermined time. The time stamp packet request is transmitted as a radio packet to the radio base unit 10A via the communication protocol processing unit 600B, the MAC processing unit 700B, and the RF unit 800B (time information requesting step).
The wireless master device 10A receives the time stamp packet request packet transmitted from the wireless slave device 10B, and the communication protocol processing unit 600A outputs it to the time stamp packet request detection unit 914A.

  The time stamp packet request detection unit 914A detects a time stamp packet request packet from the received packets and outputs the detection signal to the time stamp packet transmission unit 911A (time information request detection step). Upon receiving the detection signal, the time stamp packet sending unit 911A outputs a timing signal for sending the time stamp output from the time stamp timer unit 903A as one packet to the time stamp adding unit 905A. When the timing signal is input, the time stamp adding unit 905A outputs the time stamp output by the time stamp timer unit 903A as one time stamp packet (not including a video signal) to the communication protocol processing unit 600A.

When the communication protocol processing unit 600A receives a time stamp packet, the communication protocol processing unit 600A postpones processing of the video packet (one or a plurality of video packets) stored in the communication protocol processing unit 600A at that time, and only the time stamp packet is received. A wireless packet including the same is generated and immediately output (the same processing as in the first embodiment). Thereafter, the processing returns to the processing of the video packet (one or a plurality of video packets) stored in the communication protocol processing unit 600A.
As a result, the time from when the time stamp packet is generated to when the wireless packet including only the time stamp packet is output is shortened and substantially constant (time does not vary).
The wireless packet is transmitted to the wireless slave device 10B to the MAC processing unit 700A and the RF unit 800A. Thus, the time stamp packet is transmitted based on the request from the wireless slave device 10B.

  In the above embodiment, the wireless transmission device that transmits a video signal has been described. The present invention can be applied to a wireless transmission device that transmits an arbitrary stream signal continuous on a time axis. For example, the present invention is applied to a wireless transmission device that transmits audio signals and a wireless transmission device that transmits video signals and audio signals by replacing the video signals in the embodiments with audio signals, video signals, and audio signals, respectively. I can do it.

  The wireless master device and the wireless slave device of the present invention are useful as a wireless transmission device that transmits video and audio signals, audio signals, and the like via an asynchronous wireless line.

1 is a block diagram showing a configuration of a wireless transmission device according to a first embodiment of the present invention. Timing chart showing the operation timing of each part in the radio transmission apparatus according to the first to third embodiments of the present invention. FIG. 2 is a block diagram showing a configuration of a wireless transmission device according to a second embodiment of the present invention. Block diagram showing a configuration of a wireless transmission device according to a third embodiment of the present invention The block diagram which shows schematic structure of the radio transmission apparatus of a prior art example Timing diagram showing the timing of signals sent over a wireless link The block diagram which shows the structure of the radio transmission apparatus of a prior art example Timing chart showing the operation timing of each part in the conventional wireless transmission device

Explanation of symbols

10A wireless master unit 10B wireless slave unit 30A, 30B antenna 400A video signal encoding unit 500B video signal decoding unit 600A, 600B communication protocol processing unit 700A, 700B MAC processing unit 701A, 701B clock generation unit 702A, 702B beacon timer unit 703A, 703B Beacon generation unit 704A, 704B Frame assembly unit 705A, 705B Frame analysis unit 706A, 706B Reception data processing unit 800A, 800B RF unit 900A, 900B Time information generation unit 901B Time stamp extraction unit 902B Time stamp comparison unit 903A, 903B Time stamp Timer unit 904A, 904B PLL processing unit 905A Time stamp adding unit 907B Reception data buffer unit 910B Initial value setting unit 911 Time stamp packet transmitting unit 912B time stamp packet extraction unit 913B second timestamp comparison unit 914A time stamp packet request detecting unit 915B time stamp packet request unit

Claims (10)

A wireless master device of a wireless transmission device that transmits video signals and / or audio signals as packet data between a wireless master device and a wireless slave device connected by a wireless line,
A time information generation unit for generating first time information;
A first PLL unit that generates second time information having higher time resolution than the first time information based on the first time information;
A video signal having a video signal and / or an audio signal, and generating a video signal and / or an audio signal packet to which the second time information or time information derived based on the second time information is added; / Or voice signal packet generator,
A time information packet generation unit for generating a time information packet having the second time information or time information derived based on the second time information and not including a video signal and / or an audio signal;
A wireless communication unit that intermittently transmits the first time information at a predetermined period, and transmits the video signal and / or audio signal packet and the time information packet;
A time information request detection unit for detecting a time information request from the wireless slave unit;
Have
The time information packet generation unit generates the time information packet based on the detected time information request,
When the video signal and / or audio signal packet and the time information packet compete, the wireless communication unit transmits the time information packet with priority or simultaneously with the video signal and / or audio signal packet. ,
A wireless master unit characterized by that.   A wireless slave device of a wireless transmission device that transmits video signals and / or audio signals as packet data between a wireless master device and a wireless slave device connected by a wireless line,
  The first time information transmitted intermittently at a predetermined cycle is received from the wireless master unit, the video signal and / or the audio signal are included, and the first time information is generated in phase synchronization with the first time information. Receiving a video signal and / or an audio signal packet to which second time information having a time resolution higher than the first time information or time information derived based on the second time information is added; and A wireless communication unit having time information derived based on the second time information or the second time information and receiving a time information packet not including a video signal and / or an audio signal;
  A second PLL unit that generates second time information having higher time resolution than the first time information based on the first time information;
  The second time information generated by the second PLL unit is compared with the time information added to the video signal and / or audio signal packet, and the video signal and / or audio is determined according to the comparison result. A first time information comparison unit for controlling the output timing of the signal packet;
  A time information setting unit for setting the second time information generated by the second PLL unit based on the time information added to the time information packet;
  A time information requesting unit that requests the wireless master device to transmit the time information packet;
  A wireless handset characterized by comprising:   The time information included in the time information packet is compared with the second time information generated by the second PLL unit, and if the difference exceeds a predetermined range, the time information setting unit is The apparatus further comprises a second time information comparison unit that permits setting of the second time information generated by the second PLL unit based on time information added to the time information packet. Item 3. The wireless slave device according to item 2.   When the time information packet is received, the time information setting unit sets the second time information generated by the second PLL unit according to the time information added to the time information packet, When the time information packet is not received, the time information setting unit generates the second time generated by the second PLL unit based on time information added to the video signal and / or audio signal packet. Information is set, The wireless subunit | mobile_unit of Claim 2 characterized by the above-mentioned.   If the received video signal and / or audio signal packet contains an error, the wireless master unit is requested to retransmit the video signal and / or audio signal packet, and the received time information packet contains an error. 3. The wireless slave device according to claim 2, wherein the wireless slave device does not request the wireless parent device to retransmit the time information packet.   A method of controlling a wireless master device of a wireless transmission device that transmits video signals and / or audio signals as packet data between a wireless master device and a wireless slave device connected by a wireless line,
  A first time information generating step for generating first time information;
  A second time information generating step for generating second time information that is phase-synchronized with the first time information and has a higher time resolution than the first time information;
  A video signal having a video signal and / or an audio signal, and generating a video signal and / or an audio signal packet to which the second time information or time information derived based on the second time information is added; A voice signal packet generation step;
  A time information packet generating step for generating a time information packet having the second time information or time information derived based on the second time information and not including a video signal and / or an audio signal;
  A wireless communication step of intermittently transmitting the first time information at a predetermined period, and transmitting the video signal and / or audio signal packet and the time information packet;
  A time information request detection step for detecting a time information request from the wireless slave unit;
  Have
  In the time information packet generation step, based on the detected time information request, the time information packet is generated,
  When the video signal and / or audio signal packet competes with the time information packet, in the wireless communication step, the time information packet is transmitted with priority or simultaneously with the video signal and / or audio signal packet. ,
A control method for a wireless master device, characterized in that:   A wireless slave device control method for a wireless transmission device that transmits video signals and / or audio signals as packet data between a wireless master device and a wireless slave device connected by a wireless line,
  The first time information transmitted intermittently at a predetermined cycle is received from the wireless master unit, the video signal and / or the audio signal are included, and the first time information is generated in phase synchronization with the first time information. Receiving a video signal and / or an audio signal packet to which second time information having a time resolution higher than the first time information or time information derived based on the second time information is added; and Wireless communication step of receiving a time information packet having time information derived from the time information of 2 or the second time information and not including a video signal and / or an audio signal;
  A second time information generating step for generating second time information that is phase-synchronized with the first time information and has a higher time resolution than the first time information;
  The second time information generated by the second time information generation step is compared with the time information added to the video signal and / or audio signal packet, and the video signal and / or according to the comparison result. Or a first time information comparison step for controlling the output timing of the voice signal packet;
  A time information setting step for setting the second time information generated in the second time information generation step based on the time information added to the time information packet;
  A time information requesting step for requesting the wireless master device to transmit the time information packet;
  A method of controlling a wireless slave unit, comprising:   The time information included in the time information packet is compared with the second time information generated by the second time information generation step, and if the difference exceeds a predetermined range, the time information setting step The method further comprises a second time information comparison step for permitting setting of the second time information generated by the second time information generation step according to the time information added to the time information packet. The method of controlling a wireless slave device according to claim 7, wherein:   If the time information packet is received, the second time information generated by the second time information generation step is set by the time information added to the time information packet in the time information setting step. If the time information packet is not received, the second time information generation step generates the second time information generation step based on the time information added to the video signal and / or audio signal packet in the time information setting step. The method of controlling a wireless slave device according to claim 7, wherein second time information is set.   If the received video signal and / or audio signal packet contains an error, the wireless master unit is requested to retransmit the video signal and / or audio signal packet, and the received time information packet contains an error. 8. The method of controlling a wireless slave device according to claim 7, wherein if it is included, the wireless master device is not requested to retransmit the time information packet.

Images