JP2015128312A - Radio transmission method for audio signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio transmission method for an audio signal which uses radio communication and implements transmission of the audio signal with less possibility of a sound break.SOLUTION: A radio transmission method for an audio signal comprises the steps of: selecting a primary and secondary channels from communication channels of a communication channel group having 3 or more channels; performing transmission of the audio signal by using both channels reciprocally; measuring transmission error rates of both channels while performing transmission of the audio signal and comparing the error rates of both channels; and, when the comparison result shows that the error rate of the primary channel is larger than that of the secondary channel, selecting the current secondary channel as a new primary channel, selecting a new secondary channel from the communication channels of the communication channel group and continuing the transmission of the audio signal.

Description

  The present invention relates to a wireless transmission method for transmitting an audio signal using radio waves.

  In some cases, a speaker may be connected to a portable audio player to enjoy music at a high volume. In such a case, conventionally, a method of connecting a speaker cable to an earphone jack of a portable audio player and inputting an audio signal to a speaker (such as a speaker with an amplifier) has been common. However, when the speaker cable is connected to the portable audio player, the cable may be in the way, and the portable audio player may not be placed at the user's hand due to restrictions on the length of the cable and the routing location.

  Therefore, it is conceivable to transmit the musical sound reproduced by the portable audio player to the speaker using wireless communication. In this type of wireless communication, a frequency in the 2.4 GHz band that is generally open to consumer use is used. This frequency band is used by various consumer devices such as wireless LANs, microwave ovens, and cordless telephones. Therefore, it is necessary to select and use a frequency (channel) that is not occupied by other devices with good radio wave conditions. There is. A conventional method for detecting a radio wave condition has been scanning by received signal strength measurement (RSSI: Received Signal Strength Indicator). In the RSSI scan, each channel is received and the signal strength is measured, and the channel having the weakest signal strength is determined to be a free channel in good condition (see Patent Document 1).

JP 2010-258836 A

  However, in order to perform RSSI scanning, a circuit for measuring an accurate signal level is required, which is expensive.

  The 2.4 GHz band is frequently used by various devices, so that the radio wave state constantly fluctuates, and the channel suitable for audio signal transmission also fluctuates constantly. Therefore, if an audio signal with few errors is to be transmitted, it is necessary to review the selection of the communication channel at an appropriate interval. However, in order to perform the RSSI scan, it is necessary to stop the transmission of the audio signal, and there is a problem that the risk of sound interruption increases during this time.

  An object of the present invention is to provide an audio signal wireless transmission method that realizes transmission with a low possibility of sound interruption in audio signal transmission using a plurality of wireless communication channels.

The present invention is a method for transmitting an audio signal using a group of communication channels having three or more channels,
(1) Procedure for selecting a primary channel and a secondary channel from the communication channels of the communication channel group (2) Procedure for transmitting an audio signal using the primary channel and the secondary channel alternately (3) Procedure (2) (4) Procedure for comparing the error rate of the primary channel and the secondary channel at a predetermined timing (5) The result of the comparison in (4) When the error rate of the primary channel is less than or equal to the error rate of the secondary channel, the procedure of returning to (2) and continuing the transmission of the audio signal (6) As a result of the comparison of (4), the error rate of the primary channel is secondary If it is greater than the channel error rate After selecting the current secondary channel as a new primary channel and selecting a new secondary channel from the communication channels of the communication channel group, the procedure of returning to (2) and continuing the transmission of the audio signal is sequentially executed. Features.

  According to the present invention, it is possible to change the primary channel and the secondary channel to a channel having a good communication state while transmitting an audio signal, thereby realizing transmission of an audio signal with less possibility of sound interruption. It becomes possible.

Configuration diagram of a wireless audio system according to an embodiment of the present invention The figure which shows the structure of the communication channel group which the wireless audio system uses The figure explaining the switching procedure of the communication channel in the same wireless audio system Flow chart showing operation of transmitter of wireless audio system

  FIG. 1 is a configuration diagram of a wireless audio system according to an embodiment of the present invention. FIG. 2 is a diagram showing a communication channel group used in this wireless audio system. This wireless audio system includes a portable audio player 3 that reproduces an audio signal of music, a stationary amplifier-equipped speaker 4 that inputs the audio signal and emits sound as sound, and the portable audio player 3 to the amplified speaker 4. It consists of a transmitter 1 and a receiver 2 that transmit audio signals.

  The portable audio player 3 includes a storage unit that stores music data that has been compression-encoded in MP3, a playback unit that decodes and plays back the music data that has been compression-encoded, and a display unit that displays the name of the music being played And an operation unit such as a PLAY button and a STOP button for receiving a user operation. In addition, you may comprise an operation part with the touchscreen provided in the display part surface, and the icon image displayed on a display part. The portable audio player 3 selects music data according to the user's operation and reproduces the music data. The reproduced audio signal is output from the output terminal. The portable audio player 3 includes an earphone terminal such as a mini jack and a composite connector as audio output terminals. The composite connector is, for example, a dock connector (trademark) receptacle (female connector), and includes a stereo audio output terminal, a control signal input / output terminal, a power supply terminal, and the like. The composite connector is connected to the transmitter 1, and an audio signal is input to the transmitter 1 through the composite connector.

  The transmitter 1 transmits the audio signal reproduced by the portable audio player 3 to the receiver 2. The receiver 2 inputs the audio signal received from the transmitter 2 to the speaker 4 with amplifier. Communication between the transmitter 1 and the receiver 2 is performed using a communication channel group set in the 2.4 GHz band. The communication channel group includes eight communication channels that do not interfere with each other (see FIG. 2). Communication between the transmitter 1 and the receiver 2 is performed by digital packet transfer. Audio signals are transmitted by high-speed unidirectional communication, and control signals such as commands are transmitted and received by low-speed bidirectional communication.

  The transmitter 1 includes an audio input unit 10 to which the portable audio player 3 is connected, an A / D converter 11 that converts an audio signal input from the portable audio player 3 into a digital signal, a controller 12 that controls the operation of the transmitter 1, communication A communication circuit 13 for performing wireless communication using a channel and an antenna 14 are provided. The audio input unit 10 has the same composite connector as the portable audio player 3. This composite connector is a plug connector (male connector) connected to the receptacle of the portable audio player 3, and inputs an audio signal from the portable audio player 3 through this connector and charges the battery of the portable audio player 3. The A / D converter 11 converts the audio signal input from the audio input unit 10 into a digital signal. The communication circuit 13 transmits audio signals and transmits / receives control signals and the like to / from the receiver 2. The control signal is an acknowledgment ACK, a communication channel switching schedule, or the like. The controller 12 performs processing such as calculation of a communication error rate and selection of a communication channel. Details of the processing of the controller 12 will be described later.

  The receiver 2 is a device that receives a high-frequency signal transmitted from the transmitter 1, demodulates an audio signal superimposed on the high-frequency signal, and inputs the demodulated signal to the speaker 4 with amplifier. The receiver 2 includes a built-in antenna 24, a communication circuit 20 that performs communication through each communication channel, a controller 21 that controls the operation of the receiver 2, a buffer 22 that stores a predetermined amount of received digital audio signals, and a buffer 22 that stores digital audio signals. The D / A converter 23 for reading out the signal from the signal and converting it to an analog signal, and the audio output unit 24 for outputting the audio signal to the speaker 4 with amplifier. The communication circuit 20 receives the high frequency signal transmitted from the transmitter 1, demodulates the audio signal and the control signal, and transmits the control signal input from the controller 21 to the transmitter 1. The control signal demodulated by the communication circuit 20 is input to the controller 21. The audio signal demodulated into a baseband digital signal by the communication circuit 20 is stored in the buffer 22. The buffer 22 has a capacity of, for example, 50 milliseconds. The D / A converter 23 sequentially reads out audio signals stored in the buffer 22, converts them into analog signals, and inputs them to the audio output unit 24. The audio output unit 24 outputs the input audio signal to the speaker 4 with amplifier.

  The amplifier-equipped speaker 4 is a device having a built-in audio amplifier and a stereo speaker in the housing and having a connector connected to the audio output unit 24 of the receiver 2, and amplifies an audio signal input from the receiver 2 with the audio amplifier. Then, the sound is emitted from the speaker. The user may operate the amplifier-equipped speaker 4 from a panel switch, but may operate the portable audio player 3 connected to the transmitter 1 using a remote control device. That is, when the user operates the portable audio player 3, the operation information is sent to the speaker with amplifier 4 via the transmitter 1 and the receiver 2, and the function of the speaker with amplifier 4 is controlled based on this operation information.

  In this embodiment, the receiver 2 is provided separately from the speaker 4 with amplifier and is connected by a connector. However, the receiver 2 may be built in the speaker 4 with amplifier.

  FIG. 2 is a diagram illustrating a configuration of a communication channel group used for audio signal transmission. As a communication channel group, 8 channels with a bandwidth of 20 MHz are set in the 2.4 GHz band at intervals that do not interfere with each other. Since the channels are set at intervals that do not interfere with each other in this way, a plurality of systems can transmit audio signals using adjacent channels. Of these channels, the transmitter 1 and the receiver 2 select and use the channel with the best communication state as the primary channel, and then select and use the channel with the best communication state as the secondary channel. In the present invention, the communication channel group is not limited to eight channels. Further, the frequency band is not limited to the 2.4 GHz band.

  Hereinafter, the primary channel / secondary channel selection method by the controller 12 of the transmitter 1 will be described with reference to the time chart of FIG. 3 and the flowchart of FIG. 4. When the transmission of the audio signal from the transmitter 1 to the receiver 2 is interrupted and the audio data in the buffer 22 of the receiver 2 is emptied, sound interruption occurs in the sound emitted from the speaker 4 with amplifier. In this wireless audio system, in order to prevent such sound interruption, the channel having the best communication state among the eight communication channel groups as the channel used for audio signal transmission is the primary channel, and then the next communication. A channel in a good state is selected as a secondary channel, and audio signals are transmitted using these two channels alternately. Further, while transmitting the audio signal, the error rate of both channels is measured, and based on the measurement result, the primary channel and the secondary channel are switched, and the secondary channel is reselected (switched).

  FIG. 3A is a diagram for explaining a transmission procedure of an audio signal using a primary channel and a secondary channel. First, a primary channel and a secondary channel are selected. The primary channel and the secondary channel at the start of communication may be selected by any method. For example, the received signal strength of each channel is measured, that is, a RSSI (Received Signal Strength Indicator) scan is performed. As a result, the channel with the lowest received signal (noise) strength is set as the primary channel, and the next lowest channel is set as the secondary channel. That's fine. However, the selection of the primary channel and the secondary channel is not limited to this method. For example, the primary channel and the secondary channel may be selected at random.

  When the primary channel and the secondary channel are selected, an audio signal is transmitted by alternately using the primary channel and the secondary channel with weighting so that the primary channel has a large ratio. For example, the ratio of primary channel: 8 and secondary channel: 2 is used. The channel selection information indicating which channel is selected as the primary channel and the secondary channel, the switching timing of the primary channel / secondary channel at the time of audio signal transmission, and the like are notified in advance from the transmitter 1 to the receiver 2, and both transmission and reception are synchronized. Is made possible.

  Transmission of the audio signal using the primary channel and the secondary channel alternately is continued for a predetermined time (one set). This time is not limited, but a time of about the capacity of the buffer 22 of the receiver 2 (for example, 50 milliseconds) is appropriate. For example, if 50 ms is set as one set and the audio signal is alternately transmitted at a time of primary channel: 4 ms and secondary channel: 1 ms, one set of time is transmitted 10 times for each channel. Elapses. After that, while transmitting the next set, the error rate of the primary channel and the secondary channel in the completed set is determined. The error rate can be determined by the packet retransmission rate.

  If the error rate Ep of the primary channel and the error rate Es of the secondary channel are set to Ep ≦ Es, the primary channel is in a better communication state than the secondary channel, so the transmission is continued while maintaining the selection of the primary channel as it is. . That is, the process returns as indicated by the broken line arrow R in FIG.

  In this example, the primary channel and the secondary channel are weighted by the time ratio, but may be weighted by another ratio, for example, the ratio of the number of transmission packets.

  If Ep> Es, the process proceeds as shown by the solid line arrow S in FIGS. 3A and 3B, the current secondary channel is selected as a new primary channel, and a large ratio is set for this channel. (For example, 4 milliseconds) of audio signals are transmitted. Then, as shown in FIG. 3B, a new secondary channel is selected from 7 channels other than the new primary channel. The primary channel replacement and the secondary channel reselection schedule are notified from the transmitter 1 to the receiver 2.

  FIG. 3B is a diagram showing a procedure for selecting a secondary channel. While a large ratio is set for the new primary channel, the audio signals are transmitted sequentially using the seven channels (channels a to g in the figure) as temporary secondary channels. Since the channel with the good communication state is selected as the primary channel, even if the communication state of the temporary secondary channel is bad, the transmission of the audio signal is not completely interrupted, and the sound cut occurs at the receiver 2 side. There is nothing. In FIG. 3B, the channels a to g are selected as temporary secondary channels once, but may be selected multiple times. One set of transmissions as shown in FIG. 3A may be performed in a state where channels a to g are selected as temporary secondary channels.

  When the transmission of audio signals using channels a to g as temporary secondary channels is completed, the error rate of each channel is measured. Then, the channel with the lowest error rate is selected as a new secondary channel. In FIG. 3B, channel b is selected as a new secondary channel. This is performed during the transmission period of the primary channel, and the selection result is notified to the receiver 2. When a new secondary channel is selected, the transmission procedure shown in FIG. 3A is returned to as shown by a one-dot chain line arrow T by the combination of the new primary channel and the secondary channel.

  By transmitting the audio signal while updating the primary channel and secondary channel in this way, the audio signal is transmitted without interruption, and the best primary channel and secondary channel according to the situation at that time are transmitted. The combination can be maintained. In the above configuration, since the transmitter 1 does not require a high-frequency energy detection circuit (RSSI circuit), a high-quality analog circuit is not required, and a simple and inexpensive circuit configuration can be achieved. Moreover, since it is not necessary to frequently perform RSSI scans, the control load can be reduced.

  The new secondary channel selection procedure is not limited to the procedure shown in FIG. Any procedure may be used as long as the communication channel having the best communication state (radio wave state) is selected from the communication channels other than the new primary channel.

The operation of the controller 12 of the transmitter 1 will be described with reference to the flowchart of FIG. First, an RSSI scan is executed for all eight channels of the communication channel group (S1). Based on the scan result, the channel with the best radio wave condition, that is, the channel with the least noise is selected as the primary channel, and the channel with the second radio wave condition is selected as the secondary channel (S2). The primary channel and secondary channel selection information is notified to the receiver 2. Note that the RSSI scan of S1 is not essential, and the primary channel and the secondary channel may be selected by an appropriate method in S2.
Then, transmission of the audio signal is started using the primary channel and the secondary channel (S3). As described above, the audio signal is transmitted by alternately using the primary channel and the secondary channel, but is weighted so that the ratio of the primary channel is increased. When one set of transmission is completed, the transmission error rates of the primary channel and the secondary channel are compared (S4). If the error rate Ep of the primary channel is equal to or less than the error rate Es of the secondary channel (NO in S5), the process returns to S4 and continues to transmit the audio signal while maintaining the current selection of the primary channel and secondary channel.
If the error rate Ep of the primary channel is larger than the error rate Es of the secondary channel (YES in S5), the secondary channel is selected as a new primary channel (S6), and the 7 channels except for the new primary channel are selected. A new secondary channel is selected from among them (S7, S8). In this embodiment, the selection of a new secondary channel is performed according to the procedure shown in FIG. That is, the audio signal is transmitted using 7 channels other than the new primary channel as a temporary secondary channel (S7), and the error rates at the time of transmitting the audio signal are tabulated. Then, the channel having the smallest error rate is selected as a new secondary channel (S8), and the process returns to S4. The new primary channel selection information and the new secondary channel selection information are respectively notified to the receiver 2.

  In this embodiment, if the error rate Ep of the primary channel is equal to or lower than the error rate Es of the secondary channel in the process of S5, the combination of the primary channel and the secondary channel is maintained and the process returns to S4 to transmit the audio signal. However, when the error rate Es of the secondary channel is a certain value or more, the primary channel may be maintained as it is, and only the secondary channel may be reselected.

  In this embodiment, the device that reproduces the audio signal is the portable audio player 1, but the reproducing device is not limited to a portable device.

1 Transmitter 12 Controller 2 Receiver 21 Controller

The present invention transmits audio signals by alternately using a selected channel that is one communication channel selected from a plurality of communication channels and a non-selected channel that is the unselected channel among the plurality of communication channels. The communication state of the non-selected channel is tested by transmitting the audio signal through the non-selected channel .

According to the present invention, the audio signal is alternately transmitted between the selected channel and the non-selected channel, and the communication status of the channel is tested by transmitting the audio signal in the non-selected channel. It is not necessary to provide time separately, and it is possible to test the communication status of the non-selected channel while transmitting the audio signal.

Claims (1)

A method for transmitting an audio signal using a communication channel group having a channel number of 3 or more,
(1) Procedure for selecting a primary channel and a secondary channel from the communication channels of the communication channel group (2) Procedure for transmitting an audio signal using the primary channel and the secondary channel alternately (3) Procedure (2) (4) Procedure for comparing the error rate of the primary channel and the secondary channel at a predetermined timing (5) The result of the comparison in (4) When the error rate of the primary channel is less than or equal to the error rate of the secondary channel, the procedure of returning to (2) and continuing the transmission of the audio signal (6) As a result of the comparison of (4), the error rate of the primary channel is secondary If it is greater than the channel error rate After selecting the current secondary channel as a new primary channel and selecting a new secondary channel from the communication channels of the communication channel group, the procedure of returning to (2) and continuing the transmission of the audio signal is sequentially executed. A method for wireless transmission of an audio signal.

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