JP2023034981A - Receiving device, communication system, and frame synchronization recovery method - Google Patents

Abstract

To provide a receiving device, a communication system, and a frame synchronization recovery method capable of recovering frame synchronization even when data loss occurs.SOLUTION: A receiving device includes a receiving unit that receives a frame containing data and a synchronization word, a frame extraction unit that synchronizes the frame on the basis of the synchronization word, a data loss detection unit that determines whether data loss has occurred in the frame, a frame correction unit that generates a pseudo frame when the data loss detection unit determines that data loss has occurred in the frame, and an output unit that outputs the pseudo frame.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a receiver, a communication system equipped with the receiver, and a frame synchronization recovery method.

2. Description of the Related Art Conventionally, a communication system is known that includes a transmitting device that multiplexes and frames data of a plurality of channels and transmits it, and a receiving device that receives frames and identifies and extracts data for each channel. In such a communication system, a transmitting device generates a frame containing audio data for a plurality of channels generated from, for example, a microphone, and transmits the frame to a receiving device. The receiving device also synchronizes the received frames to identify and extract the data for each channel and provides the audio data to the application program. As a method for synchronizing frames in a receiving device, it is known to transmit a frame including a synchronization word from the transmitting device and detect the synchronization word in the receiving device to synchronize the frames (for example, Patent Document 1).

JP 2008-283550 A

In conventional communication systems, frames generated by a transmitting device are written into a buffer and read by a receiving device. The cycle in which frames are written to the buffer and the cycle in which frames are read out are asynchronous, and the cycle in which frames are read out by the receiving device is not constant. Therefore, if there is a delay in reading a frame by the receiving device, the buffer may overflow and some data in the read frame may be lost. Also, when a new frame is written while the buffer is full, the data of that frame is lost because the new frame cannot be written into the buffer.

In addition, when the receiving device cannot receive the frame transmitted by the transmitting device due to a communication error or a temporary processing delay of the software in the receiving device, the data in the frame may be lost.

When data loss occurs as described above, the receiving device cannot properly synchronize the frames, and the data position from the beginning to the end of the frame is deviated from the original data position, and processing continues. It will be. As a result, in the audio data provided to the application program, bits of adjacent channels are mixed according to the number of lost data, resulting in incorrect audio data.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a receiving apparatus, a communication system, and a frame synchronization recovery method capable of recovering frame synchronization even when data loss occurs. and

A receiver according to the present invention includes a receiver for receiving a frame including data and a synchronization word, a frame extractor for synchronizing the frame based on the synchronization word, and determining whether data loss has occurred in the frame. A data loss detection unit, a frame correction unit that generates a pseudo frame when the data loss detection unit determines that data loss has occurred in a frame, and an output unit that outputs the pseudo frame.

A communication system according to the present invention includes the receiving device and the transmitting device described above, and the transmitting device includes an input section for generating data, a synchronization word generation section for generating a synchronization word, and data and the synchronization word. A frame generator for generating a frame and a transmitter for transmitting the frame to a receiver are provided.

A frame synchronization recovery method according to the present invention comprises the steps of receiving a frame containing data and a synchronization word, synchronizing the frame based on the synchronization word, and determining whether a loss of data has occurred in the frame. and generating a pseudo frame if it is determined that data loss has occurred in the frame; and outputting the pseudo frame.

According to the present invention, when it is determined that data loss has occurred in a frame, a pseudo frame is generated and the pseudo frame is output. It is possible to output frames without

1 is a schematic configuration diagram of a communication system according to Embodiment 1; FIG. 4 is a diagram showing an example of a synchronization word generated by a synchronization word generator according to Embodiment 1; FIG. 4 is a diagram showing the structure of a frame generated by a frame generator according to Embodiment 1; FIG. 4 is a flow chart showing the operation of the transmitting device according to Embodiment 1; 4 is a flowchart showing the operation of the receiving device according to Embodiment 1; 5 is a flowchart of frame extraction processing according to Embodiment 1; 4 is a flowchart of data loss detection processing according to the first embodiment; FIG. 7 is a diagram for explaining data loss detection processing according to the first embodiment; FIG. 10 is a diagram illustrating an example of a case where synchronization word data is lost in the data loss detection process according to the first embodiment; 4 is a flowchart of frame correction processing according to Embodiment 1; FIG. 4 is a diagram showing an example of pseudo frames generated by a frame correction unit according to Embodiment 1; FIG. It is a figure explaining the data loss detection process which concerns on a modification.

Embodiment 1.
FIG. 1 is a schematic configuration diagram of a communication system 100 according to Embodiment 1. As shown in FIG. A communication system 100 includes a transmitter 1 and a receiver 2 . The transmitting device 1 and the receiving device 2 are composed of dedicated hardware, a general PC having a CPU and memory, or a combination thereof. In this embodiment, it is assumed that the transmitting device 1 is composed of dedicated hardware, and the receiving device 2 is composed of a general PC. Further, the solid line arrows in FIG. 1 indicate the movement of data, and the broken line arrows indicate the movement of control signals.

The transmission device 1 includes an input section 11 , a synchronization word generation section 12 , a frame generation section 13 , a transmission buffer section 14 and a transmission section 15 . Each part of the transmission device 1 is implemented by a dedicated device or a dedicated circuit. Alternatively, the transmitting device 1 may include a processor such as a CPU and a memory, and each unit of the transmitting device 1 may be realized by the processor executing a program stored in the memory. Alternatively, each part of the transmission device 1 may be realized by a combination of dedicated equipment or dedicated circuits and software.

The input unit 11 includes multiple microphones 111 . The input unit 11 generates audio data from audio input to each microphone 111 based on the sampling frequency signal from the frame generation unit 13 and outputs the audio data to the frame generation unit 13 . In this embodiment, the input unit 11 is provided with 31 microphones 111 and outputs audio data for 31 channels to the frame generation unit 13 . Also, the audio data generated by the input unit 11 is assumed to be 16 bits for each microphone 111 . Note that the number of microphones 111 provided in the input unit 11 and the number of bits of audio data are not limited to these.

The synchronization word generator 12 generates a synchronization word for frame synchronization based on the sampling frequency signal from the frame generator 13 and outputs it to the frame generator 13 . FIG. 2 is a diagram showing an example of a sync word generated by the sync word generator 12 according to the first embodiment. As shown in FIG. 2, the synchronization word of the present embodiment consists of a repetition part of upper 8 bits and a sequence number of lower 8 bits. The repeating portion of the synchronization word repeats two fixed values, '0x7F' and '0x80', in sequence for each frame. The sequence number of the sync word is a value that starts from "0x00" and is incremented by 1 for each frame, and repeats in the range from "0x00" to "0xFF".

When the audio data is 16 bits, "0x7F" and "0x80" are audio data with the maximum volume and the minimum volume, so it is an abnormal state for these to occur in each sampling cycle. Therefore, by using "0x7F" and "0x80" in the repetition part of the sync word, it can be handled as a value different from the voice data. Note that the synchronization word shown in FIG. 2 is an example defined to avoid erroneous synchronization, and does not necessarily have to be this value.

The frame generation unit 13 multiplexes the audio data generated by the input unit 11 and the synchronization word generated by the synchronization word generation unit 12 to generate a frame. FIG. 3 is a diagram showing the structure of a frame generated by the frame generator 13 according to Embodiment 1. As shown in FIG. In this embodiment, the sampling frequency is 15 kHz, and one frame generated by the frame generator 13 consists of 64 bytes (fixed length). The grounds for the sampling frequency and the number of data are obtained as follows. First, in the input unit 11, 16-bit (2-byte) audio data is generated for each microphone 111 in each sampling period. As a result, the number of data generated in each sampling period in the input unit 11 is 2 bytes×32 (31 channels+synchronization word)=64 bytes. FIG. 3 shows a state in which one frame of 64-byte data is divided into d0 to d7 every 8 bytes.

The frame generation section 13 also generates a sampling frequency signal and outputs it to the input section 11 and the synchronization word generation section 12 . The sampling frequency signal is specifically a sampling frequency clock. Furthermore, the frame generation unit 13 generates a write signal for writing frames at the sampling period, and outputs the write signal to the transmission buffer unit 14 .

The transmission buffer unit 14 has a transmission buffer 141 that stores data, and a buffer control unit 142 that controls writing data to and reading data from the transmission buffer 141 . Writing data to the transmission buffer 141 and reading data from the transmission buffer 141 are performed asynchronously. The transmission buffer 141 is a memory such as RAM, ROM, or flash memory provided in the transmission device 1 . The buffer control unit 142 writes the frame generated by the frame generation unit 13 to the transmission buffer 141 byte by byte based on the write signal from the frame generation unit 13 . Further, the buffer control unit 142 reads the data constituting the frame stored in the transmission buffer 141 one byte at a time based on the read signal from the transmission unit 15 and outputs the data to the transmission unit 15 .

The transmitting unit 15 communicates with the receiving device 2 according to a procedure based on the communication standard. In this embodiment, the transmitter 15 communicates with the receiver 2 based on the USB interface standard. The transmitting unit 15 responds to an inquiry about the presence or absence of data in the transmission buffer 141 received from the receiving device 2 via the USB interface. In addition, based on the readout instruction from the receiving device 2 , the transmission section 15 outputs a read signal for reading the frame from the transmission buffer 141 to the transmission buffer section 14 . Then, the transmission unit 15 converts the data constituting the frame read from the transmission buffer 141 into a USB packet suitable for the USB interface, and transmits the USB packet to the reception device 2 .

The receiving device 2 includes a processor such as a CPU, and includes a receiving unit 21, a frame extracting unit 22, a data loss detecting unit 23, and a frame correcting unit 24 as functional units realized by executing a program by the processor. , and an output unit 25 . The receiving device 2 also includes a memory such as a RAM, ROM, or flash memory, which includes a receive buffer 211 , a synchronization buffer 221 and an output buffer 241 .

The receiving unit 21 communicates with the transmitting device 1 according to a procedure based on the USB interface standard, and receives USB packets including audio data from the transmitting device 1 . The receiving unit 21 checks whether data is stored in the transmission buffer 141 of the transmission device 1 , and if data is stored in the transmission buffer 141 , instructs the transmission unit 15 to read the data. Further, the receiving unit 21 extracts the data body forming the frame from the USB packet received from the transmitting device 1 and outputs the extracted data to the receiving buffer 211 . The reception buffer 211 stores data output from the reception unit 21 .

The frame extraction unit 22 reads data from the reception buffer 211, detects the synchronization word, and acquires frame synchronization. Specifically, the frame extractor 22 searches for a synchronization word in continuous data in a frame, recognizes the position of the detected synchronization word as a frame break, and extracts the frame. If "0x7F" or "0x80" exists in the continuous data, the frame extraction unit 22 determines that the synchronization word is detected, and recognizes "0x7F" or "0x80" and the lower 8 bits as the synchronization word. do. In this embodiment, since the synchronization word is inserted in the last 16 bits of the frame, the frame extraction unit 22 treats the bit following the last bit of the synchronization word to the last bit of the synchronization word as one frame. Extract. The frame extraction unit 22 then stores the extracted frames in the synchronization buffer 221 .

The frame extraction unit 22 also generates a synchronization word expected value for the next frame based on the synchronization word at the time of synchronization capture, and stores it in the synchronization buffer 221 . Specifically, if the repetition part of the synchronization word of the frame whose synchronization is captured is "0x7F", the repetition part of the synchronization word expected value is set to "0x80", and 1 is added to the sequence number of the synchronization word of the frame whose synchronization is captured. The resulting value is used as the sequence number of the synchronization word expected value. Since the frame extractor 22 cannot generate the synchronization word expected value of the first frame, the initial value of the synchronization word is stored in advance in the synchronization buffer 221 as the synchronization word expected value of the first frame.

The data loss detector 23 reads the frame stored in the synchronization buffer 221 and determines whether or not data loss has occurred in the frame. Specifically, the data loss detection unit 23 determines that data loss has occurred when there is no bit string matching the synchronization word expected value at a predetermined position in the frame. Further, the data loss detection unit 23 obtains the number of data losses, and identifies frames in which data loss occurs according to the number of data losses.

The frame corrector 24 corrects the frame stored in the synchronization buffer 221 according to the detection result of the data loss detector 23 and stores it in the output buffer 241 . Specifically, when the data loss detection unit 23 determines that there is no data loss in the frame read from the synchronization buffer 221, the frame correction unit 24 directly transfers the frame stored in the synchronization buffer 221 to the output buffer. 241. Further, when the data loss detection unit 23 determines that data loss has occurred in the frame read from the synchronization buffer 221, the frame correction unit 24 generates a pseudo frame corresponding to the frame in which data loss has occurred, Store in the output buffer 241 .

The output unit 25 reads the frames stored in the output buffer 241, identifies and extracts data for each channel in the frames, and outputs them for use in application programs and the like. Specific contents such as the format of output data or interface conditions shall depend on the software design.

The operation of the transmission device 1 of this embodiment will be described below. FIG. 4 is a flow chart showing the operation of the transmitting device 1 according to the first embodiment. First, the input unit 11 generates audio data from the audio input to the multiple microphones 111 based on the sampling frequency signal from the frame generation unit 13 (S11). Also, the synchronization word generator 12 generates a synchronization word for each frame based on the sampling frequency signal from the frame generator 13 (S12). The generated audio data and synchronization word are output to the frame generator 13 .

Based on the sampling frequency signal, the frame generator 13 then multiplexes the audio data output from the input unit 11 and the sync word output from the sync word generator 12 to generate a frame (S13). . The generated frame is written to the transmission buffer 141 by the buffer controller 142 based on the write signal from the frame generator 13 (S14).

Then, when the transmission unit 15 receives a readout instruction from the reception device 2 (S15: YES), the data is read from the transmission buffer 141 by the buffer control unit 142 based on the readout signal from the transmission unit 15 (S16). . The read data is output to the transmitter 15, converted into a USB packet by the transmitter 15, and transmitted to the receiver 2 (S17).

Next, the operation of the receiving device 2 of this embodiment will be described below. FIG. 5 is a flow chart showing the operation of the receiver 2 according to the first embodiment. First, the receiving unit 21 inquires whether or not data is stored in the transmission buffer 141 of the transmission device 1. If data is stored in the transmission buffer 141 (S21: YES), the transmission device 1 A data read instruction is issued (S22). Then, when the receiving unit 21 receives the USB packet from the transmitting device 1, the data forming the frame is extracted from the received packet and stored in the receiving buffer 211 (S23).

Subsequently, frame extraction processing is performed by the frame extraction unit 22 (S24). FIG. 6 is a flowchart of frame extraction processing according to the first embodiment. In the frame extraction process, first, data is read from the reception buffer 211 (S241). Synchronization words are searched for in the read data, and frame synchronization capture is performed (S242). Then, the synchronous captured frame is extracted and stored in the synchronous buffer 221 (S243). Then, a synchronous word expected value is generated from the synchronous word detected by the synchronous capture (S244). After that, the frame extraction process is terminated, and the process returns to the flowchart of FIG.

When the frame extraction process ends, the data loss detection process is performed by the data loss detection unit 23 (S25). FIG. 7 is a flowchart of data loss detection processing according to the first embodiment. In the data loss detection process, first, the frame stored in the synchronization buffer 221 and the synchronization word expected value corresponding to the frame are read, and whether or not the bit string at the synchronization word confirmation position matches the synchronization word expected value is determined. is determined (S251).

FIG. 8 is a diagram for explaining data loss detection processing according to the first embodiment. The sync word confirmation position is the position of the sync word when the frame is normal (when there is no data loss). Become. If there is no data loss in the frame, that is, if the frame contains 64 bytes of data, the bit string at the sync word confirmation position is a sync word and matches the sync word expected value, as shown in FIG. 8(a). do. On the other hand, if there is data loss in the frame, i.e., if the frame contains less than 64 bytes of data, the bit string at the sync word confirmation position is changed to the sync word as shown in FIGS. 8(b) and 8(c). Word does not match expected value.

Returning to FIG. 7, when the bit string of the synchronization word confirmation position and the synchronization word expected value match (S251: YES), it is determined that there is no data loss in the frame extracted by the frame extractor 22 (S252). On the other hand, if the bit string of the synchronization word confirmation position and the synchronization word expected value do not match (S251: NO), the number of lost data in the current frame is acquired (S253). The “current frame” is data corresponding to the fixed length of the frame (1st to 64th byte data) among the data contained in the frame read from the synchronization buffer 221 . The data loss count is obtained by shifting the synchronization word confirmation position forward by one bit and searching for a bit string (synchronization word) that matches the synchronization word expected value. For example, in FIG. 8B, the number of lost data is 1 bit because the synchronization word expected value is matched by shifting it forward by 1 bit. In FIG. 8(c), the number of lost data is 2 bits because the synchronization word expected value is matched by shifting it forward by 2 bits.

Then, it is determined whether or not the number of lost data is greater than 62 bytes (S254). If the number of lost data is 62 bytes or less (S254: NO), it is determined that data is lost in the current frame (S255). In this case, data other than the sync word of the current frame is considered lost. On the other hand, if the number of lost data is more than 62 bytes (S254: YES), it is considered that the data of the synchronization word of the current frame is lost, so the number of lost data of the next frame is acquired (S256).

FIG. 9 is a diagram for explaining an example of a case where synchronization word data is lost in the data loss detection process according to the first embodiment. As shown in FIG. 9, if there is no bit string matching the sync word expected value in the current frame (bytes 1 to 64), at least the sync word data is considered lost. Therefore, in this case, the data of the 65th to 128th bytes of the frame extracted by the frame extraction unit 22 is used as the data of the 1st to 64th bytes of the next frame, and the number of lost data in the next frame is obtained. In this case, the 63rd to 64th bytes of the next frame are used as the synchronization word confirmation position, and the synchronization word confirmation position is shifted forward by one bit to search for a bit string (synchronization word) that matches the synchronization word expected value.

Then, it is determined whether or not the number of lost data in the next frame is greater than 63 bytes (S257). Here, if the number of data lost in the next frame is 63 bytes or less (S257: NO), it is determined that data is lost in the current frame and the next frame (S258). In the example of FIG. 9, the number of lost data in the next frame is 2 bits. In this case, 2 bits are lost in the data of the sync word of the current frame, 1 bit is lost in each of the data of the sync word and data other than the sync word of the current frame, or 1 bit of the data of the sync word of the current frame is lost. Either one bit of data other than the sync word of the next frame is lost. After that, the data loss detection process is terminated, and the process returns to the flowchart of FIG.

On the other hand, if the number of data lost in the next frame is greater than 63 bytes (S257: YES), the process proceeds to step S24 and performs the frame extraction process again. If there is no bit string (synchronization word) that matches the synchronization word expected value in either the current frame or the next frame, the number of lost data in the next frame is greater than 63 bytes. In this case, it is considered that at least the sync word data of the current frame and the next frame has been lost. Therefore, if the synchronization word cannot be detected in the next frame as well, the frame extraction process is performed again to redo the synchronization capture. Here, the search is performed up to the synchronization word of the next frame, but the same search may be performed at the synchronization word confirmation position of the next frame. The number of frames to be retrieved may be determined according to system specifications.

When the data loss detection process ends, the frame correction process is performed by the frame correction unit 24 (S26). 10 is a flowchart of frame correction processing according to Embodiment 1. FIG. In the frame correction process, if the data loss detection unit 23 determines that the frame read from the synchronization buffer 221 has no data loss (S261: NO), the frame read from the synchronization buffer 221 is transferred to the output buffer 241 as it is. (S262).

On the other hand, if the data loss detection unit 23 determines that the frame read from the synchronization buffer 221 has data loss (S261: YES), the frame correction unit 24 uses the pseudo data and the synchronization word expected value to create a pseudo frame. Generate a frame. Specifically, when the data loss detection unit 23 determines that data is lost in the current frame and the next frame (S263: YES), the current frame and the next frame are handled using the pseudo data and the synchronization word expected value. Two pseudo frames are generated (S264). On the other hand, if the data loss detector 23 determines that data is lost only in the current frame (S263: NO), one pseudo frame corresponding to the current frame is generated using the pseudo data and the synchronization word expected value. (S265).

FIG. 11 is a diagram showing an example of pseudo frames generated by the frame correction unit 24 according to the first embodiment. FIG. 11 shows a case where two pseudo frames are generated. As shown in FIG. 11, the pseudo frame generated by the frame corrector 24 consists of 62 bytes of pseudo data and a sync word expected value corresponding to the frame. The values of the pseudo data are determined in consideration of the usage or characteristics of the communication system 100. FIG. For example, in the case of audio data, a silent value, the same value as in the previous frame, or the average value of the values in the previous and next frames are used as pseudo data. Further, as described above, the data loss detector 23 can obtain the number of lost data, but cannot determine which data in the frame has been lost. Therefore, the frame correction unit 24 replaces the entire frame in which data may have been lost with a pseudo frame.

Then, the pseudo frame generated in step S264 or S265 is stored in the output buffer 241 (S266). As a result, all frames stored in the output buffer 241 contain fixed-length 64-byte data, and frame synchronization is maintained. After that, the frame correction processing is terminated, and the flow returns to the flowchart of FIG.

When the frame correction process is completed, the output unit 25 reads out the frames stored in the output buffer 241, extracts 31 channels of audio data from the read frames, and outputs them to an application program or the like ( S27).

According to this embodiment, the following effects can be expected. First, since the synchronization word generated by the transmitter 1 includes a repeating portion of repeating two fixed values and a sequence number, frame synchronization acquisition in the receiver 2 is easier than when the synchronization word consists of one fixed value. False synchronization of time can be suppressed. In addition, since the synchronization word includes the repeating part and the sequence number, the detection accuracy is higher than when the synchronization word is a single fixed value. This improves the accuracy of determination when searching for bit strings.

Also, since the sync word includes a sequence number, the value of the sync word can be different for each frame. Therefore, in the data loss detection process in the receiving device 2, when searching for a bit string that matches the expected value of the synchronization word, if the number of lost data reaches the size of the frame, that is, if a frame-by-frame loss occurs, synchronization It can be determined that a word of data has been lost.

In addition, since the receiving device 2 is provided with the data loss detection unit 23, it is possible to obtain data loss information such as the presence or absence of data loss, the number of data lost when data loss occurs, and the identification of frames in which data loss occurs. can. Furthermore, by providing the frame correcting unit 24 in the receiving device 2, it is possible to delete a frame in which data has been lost using the data loss information and replace it with a pseudo frame generated from pseudo data and a synchronization word expected value. As a result, the frame synchronization can be recovered, so that the data in the frame does not deviate, and the mixture of adjacent channel bits can be suppressed. As a result, it is possible to reliably provide the subsequent applications with correct data other than frames in which data has been lost.

Further, when frame synchronization is re-established when data loss occurs, the data remains out of sync until frame synchronization is established. Since pseudo frames are generated and output, there is no data deviation. Also, since there is no need to discard data until frame synchronization is established, continuity of data supply to applications can be maintained.

Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations of the above embodiments, and various modifications and combinations are possible within the scope of the technical idea thereof. . For example, in Embodiment 1, the case of transmitting audio data from the transmitting device 1 to the receiving device 2 has been described as an example, but the present invention is not limited to this. The same problem exists in a system in which the overflow occurrence factor of the transmission buffer 141 of the transmission device 1 depends on the read operation from the reception device 2 . In particular, it is effective to apply the present invention to a device in which, due to the simplification and price reduction of the transmitting device 1, there is no mechanism for notifying the receiving device 2 of the occurrence of overflow.

In addition, the output buffer 241 of the receiving device 2 may store frames containing correct audio data and pseudo frames in a identifiable manner, and may output information regarding whether or not the frames are pseudo frames when outputting data from the output unit 25 . . As a result, information regarding whether or not the frame is a pseudo frame can be used in a subsequent application. For example, when the number of pseudo frames exceeds a threshold, it can be determined that a problem such as an overflow of the transmission buffer 141 or a communication failure has occurred, and the user can be warned.

Further, the data loss detection unit 23 may perform processing for suppressing erroneous detection of the synchronization word. FIG. 12 is a diagram for explaining data loss detection processing according to the modification. In a modified example, the data loss detector 23 shifts forward by one bit from the synchronization word confirmation position, and determines whether all bits of the frame match the synchronization word expected value. Then, bit strings that match the expected value of the synchronization word are extracted as synchronization word candidates. In the example of FIG. 12, the bit string of the 62nd and 63rd bytes is the sync word candidate C1, and the bit string of the 40th and 41st bytes is the sync word candidate C2.

Then, the data loss detector 23 determines whether or not there is a bit string matching the expected value of the sync word at the positions of the sync word candidates C1 and C2 in the next frame, and verifies whether each candidate is a sync word. do. Here, in the present embodiment, data with an extremely low occurrence rate are used as synchronization words. Therefore, if the same bit string as the sync word exists at the same position in two frames, it can be determined that the sync word is correct. In the case of the example of FIG. 12, the position of the sync word candidate C2 in the next frame, that is, the 40th to 41st bytes does not have a bit string that matches the sync word expected value, so it is determined that the sync word candidate C2 is not a sync word. be done. On the other hand, since there is a bit string matching the expected value of the sync word at the position of the sync word candidate C1, that is, the 62nd to 63rd bytes, it is determined to be the sync word. Since the position of the synchronization word may shift due to data loss or the like, a range may be provided for the position of the synchronization word candidates.

For example, when one synchronization word candidate is detected in the current frame and it is determined that it is not a synchronization word as a result of performing the erroneous detection suppression process, the data loss detection unit 23 detects the current frame. Proceed as if no sync word was detected in the frame. Specifically, the processing after step S256 in FIG. 7 is performed. This makes it possible to improve the accuracy of frame synchronization recovery. By increasing the number of frames for confirming the position of the synchronization word, it is possible to improve the accuracy of avoiding erroneous detection.

1 transmitter, 2 receiver, 11 input unit, 12 synchronization word generator, 13 frame generator, 14 transmission buffer unit, 15 transmitter, 21 receiver, 22 frame extractor, 23 data loss detector, 24 frame correction Section 25 Output Section 100 Communication System 111 Microphone 141 Transmission Buffer 142 Buffer Control Section 211 Reception Buffer 221 Synchronization Buffer 241 Output Buffer.

Claims (8)

a receiver for receiving frames containing data and synchronization words;
a frame extraction unit for synchronizing the frame based on the synchronization word;
a data loss detection unit that determines whether data loss has occurred in the frame;
a frame correction unit that generates a pseudo frame when the data loss detection unit determines that data loss has occurred in the frame;
and an output unit that outputs the pseudo frame. 2. The receiving apparatus according to claim 1, wherein the synchronization word includes a repeat part repeating two fixed values and a sequence number. The frame extraction unit generates a synchronization word expected value based on the synchronization word,
3. The receiving apparatus according to claim 1, wherein the frame correction section generates the pseudo frame using pseudo data and the synchronization word expected value. 4. The receiving apparatus according to claim 3, wherein said data loss detector determines that data loss has occurred in said frame when there is no bit string matching said synchronization word expected value at a synchronization word confirmation position of said frame. 5. The data loss detector according to claim 4, wherein, when determining that data loss has occurred in the frame, the data loss detection unit acquires the number of data losses in the frame, and identifies the frame in which the data loss occurred based on the data loss number. Receiving device as described. 6. The receiving apparatus according to claim 5, wherein the frame correction unit generates pseudo frames according to the number of frames in which the data loss has occurred, which is specified by the data loss detection unit. a receiving device according to any one of claims 1 to 6;
a transmission device, wherein the transmission device is
an input unit that generates the data;
a synchronization word generator that generates the synchronization word;
a frame generator for generating the frame containing the data and the synchronization word;
and a transmitting unit configured to transmit the frame to the receiving device. receiving a frame containing data and a synchronization word;
synchronizing the frame based on the synchronization word;
determining whether a loss of data has occurred in the frame;
generating a pseudo frame if it is determined that data loss has occurred in the frame;
and outputting the pseudo frame.

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