JP5707926B2 - Wireless audio transmission method - Google Patents

Description

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

  In the audio field, it is practical to transmit audio signals by radio waves because it is complicated to connect a plurality of devices with cables or because the cables are not visually beautiful (for example, Patent Documents). 1). The frequency band that can be used relatively freely in consumer devices such as audio signal transmission is limited, and many devices including a wireless LAN use the 2.4 GHz band.

JP 2006-074374 A

  By the way, since the transmission of the audio signal continues for a long time without interruption, if the transmission of the audio signal occupies the communication channel, communication of another wireless device such as a wireless LAN cannot be performed at all. . On the other hand, if the transmission priority of the audio signal is lowered and the wireless LAN communication is prioritized, the transmission of the audio signal tends to be interrupted, and noise is generated in the audio signal reproduced on the receiving side. was there.

  An object of the present invention is to provide a wireless audio transmission method in which both wireless audio signal transmission and communication by other wireless devices are compatible.

The invention of claim 1 is a method of transmitting audio packets between a transmitter and a receiver using a plurality of communication channels used in combination with other wireless communication,
(1) the transmitter and the receiver select the same one channel;
(2) After the transmitter performs carrier sense of the selected channel and detects that the channel is idle,
(3) Wait for a waiting time T1 shorter than the shortest packet interval defined by the other wireless communication procedure, and transmit an audio packet;
(4) After the receiver completes reception of the audio packet, it waits for a waiting time T2 shorter than the shortest packet interval, and returns a response signal.
(5) When the transmitter does not receive a response signal from the receiver even after waiting for a waiting time T3 longer than the waiting time T2 and shorter than the shortest packet interval after completing transmission of the audio packet, the audio Resend the packet,
(6) When the transmitter has not received or transmitted a predetermined number of audio packets after receiving the response signal, the process returns to the procedure of (3) to transmit the next audio packet.
(7) The transmitter and the receiver switch back to the procedure of (2) by switching the selected channel when transmission / reception of the predetermined number of audio packets is completed.

The invention of claim 2 is a method for transmitting audio packets between a transmitter and a receiver using a plurality of communication channels used in combination with other wireless communication,
(1) the transmitter and the receiver select the same one channel;
(2) After the transmitter performs carrier sense of the selected channel and detects that the channel is idle,
(3) A standby time longer than SIFS, which is a packet interval of an acknowledgment response defined by the other wireless communication procedure, and shorter than DIFS, which is the shortest time of a normal packet interval defined by the other wireless communication procedure Just wait, send audio packets,
(4) After the receiver completes the reception of the audio packet, it waits for a waiting time T2 shorter than the SIFS and returns a response signal;
(5) When the transmitter completes transmission of the audio packet and does not receive a response signal from the receiver even when waiting for a waiting time T3 longer than the waiting time T2 and shorter than the SIFS, Resubmit,
(6) When the transmitter has not received or transmitted a predetermined number of audio packets after receiving the response signal, the transmitter waits for a waiting time T1 shorter than the SIFS, and then transmits the audio packet (4 )
(7) The transmitter and the receiver switch back to the procedure of (2) by switching the selected channel when transmission / reception of the predetermined number of audio packets is completed.

  According to a third aspect of the present invention, the plurality of communication channels used in combination with the other wireless communication are a plurality of communication channels defined by IEEE 802.11, and the switching of the selected channel in (7) It is characterized in that it is performed between channels that can be used simultaneously without overlapping communication frequency bands among communication channels.

  According to the present invention, audio packets are transmitted and received with priority over other wireless communication such as a wireless LAN while moving through a plurality of channels, so that audio packets can be transmitted without interruption and each channel can be transmitted. It is possible to minimize the influence on the wireless communication system being used.

Configuration diagram of a wireless audio system according to an embodiment of the present invention The figure explaining the transmission procedure of the audio packet in the same wireless audio system A diagram for explaining a plurality of communication channels defined in IEEE802.11b and channels used by the 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 for explaining an audio packet transmission procedure of the wireless audio system.

  This wireless audio system includes a transmitter 1, a receiver 2, a portable audio player 3 connected to the transmitter 1, and a stationary speaker 4 with an amplifier connected to the receiver 2. The transmitter 1 digitizes the audio signal reproduced / input from the portable audio player 3 and transmits it on the 2.4 GHz band quasi-microwave. The receiver 2 receives the high-frequency signal transmitted from the transmitter 1, D / A converts the audio signal superimposed on the high-frequency signal, and inputs the audio signal to the speaker 4 with amplifier. The digitized audio signal is transmitted from the transmitter 1 to the receiver 2 in one direction at a high speed, and the control signal such as a command is bidirectionally communicated between the transmitter 1 and the receiver 2 at a low speed.

  Communication between the transmitter 1 and the receiver 2 is performed while moving on 13 channels defined in IEEE802.11b. When transmission / reception (transmission) of a predetermined number of audio packets is completed on any channel, the channel is moved, and the next predetermined number of audio packets are transmitted on the moved channel. By repeating this, the audio packet is transmitted without interruption, and communication in a specific channel is completely impossible even if the wireless LAN system of IEEE802.11 (b) exists in the radio wave reachable range. There is no such thing.

  First, an audio packet transmission procedure in this wireless audio system will be described with reference to FIG. The transmitter 1 and the receiver 2 start transmission of audio packets on the same channel (Ch.A) that is negotiated or determined by a preset schedule. Thereafter, as described above, the transmitter 1 and the receiver 2 transmit audio packets while sequentially moving a plurality of channels (Ch. A, B, C) as shown in FIG.

  An audio packet transmission procedure in each channel will be described with reference to FIG. When the transmitter 1 starts transmitting an audio packet on a certain channel, it first performs carrier sense, the state in which another communication device is transmitting a signal (busy: BUSY) ends, and the state changes to idle. To monitor. When the channel state changes to idle, transmission of an audio packet is started after waiting for a waiting time T1 (for example, 3 μs). A wireless LAN terminal compliant with IEEE802.11b waits for at least 10 μs (SIFS: Short Inter Frame Space (see FIG. 2D)) after the channel state changes to idle, and is usually 50 μs or more (DIFS: (DCF Inter Frame Space + backoff time) After waiting, the transmission of the packet can be started without delay from the terminal of the wireless LAN. This audio packet is received by the receiver 2.

  When the transmission of the audio packet is completed, an acknowledgment ACK is transmitted from the receiver 2. The waiting time T2 from the completion of packet reception at the receiver 2 to the transmission of the acknowledgment ACK is, for example, 2 μs. Also in this case, it is possible to transmit an acknowledgment response ACK prior to the wireless LAN terminal in the same manner as described above.

  Further, as shown in FIG. 2C, the transmitter 1 retransmits the same audio packet when the acknowledgment response ACK is not received even after waiting for T3 (for example, 5 μs) after transmitting the audio packet. Since this waiting time T3 is also shorter than the shortest packet interval (SIFS) of the wireless LAN, the audio packet can be retransmitted without being interrupted by the terminal of the wireless LAN. The size of one audio packet is about 500 μs, and audio data for about 1 ms can be transmitted with this size. Therefore, even if retransmission occurs once every few times, the buffer does not underflow on the receiver 2 side.

  The wireless audio system is not intended for long-distance communication such as a wireless LAN, and is intended for packet transmission over a short distance of about 10 meters. Because it is a system. Of course, if the standby time is lengthened, the distance margin between devices of the wireless audio system and the throughput margin of the high-frequency circuit and the processing unit can be increased.

  In the description of this figure, the waiting times T1, T2, and T3 are all shorter than SIFS (10 μs). However, even if the waiting times T1, T2, and T3 are longer than SIFS, the shortest time of DIFS (50 μs). If shorter, communication is possible without being interrupted by the wireless LAN. In this case, transmission of the acknowledgment response ACK (10 μs standby) of the wireless LAN (IEEE802.11b) has priority over the start of audio packet transmission (T1> 10 μs) of this wireless audio system. The wireless audio system waits for completion of a series of packet transmission procedures for wireless LAN packet transmission and acknowledgment response, and starts transmission of audio packets. This delays the start of audio packet transmission slightly, but it can be said that this is more efficient in view of the efficiency of the entire wireless communication environment. Further, only T1 immediately after Busy in FIG. 2B is made longer than SIFS (10 μs) to give priority to the transmission of the wireless LAN confirmation response, and the subsequent waiting times T1, T2, and T3 are made shorter than SIFS and transmitted. The efficiency may be improved. As the shortest packet interval of the present invention, when “another wireless communication procedure” is IEEE802.11b, the shortest time of SIFS or DIFS can be applied.

  In this procedure, when the transmitter 1 and the receiver 2 transmit the audio packet, the audio packet is always transmitted with priority over the packet of the wireless LAN and the sound is not cut off. However, if this is continued for a long time, this channel (for example, Ch. In A), the wireless LAN system cannot communicate at all. Therefore, when transmission of a predetermined number (for example, four) of audio packets is completed, the transmission is moved to another channel (for example, Ch. B) and the transmission of audio packets is continued in the same procedure. Similarly, when transmission of a predetermined number of audio packets is completed on this channel, the transmission is further moved to another channel (for example, Ch. C), and audio packet transmission is continued in a similar procedure. This minimizes the influence on the wireless LAN while continuing the transmission of audio packets without interruption.

  Here, with reference to FIG. 3, 13 channels defined in IEEE802.11b and channels (Ch. A, B, C) used by this wireless audio system will be described. Thirteen channels are set at intervals of 5 MHz from 2412 MHz to 2472 MHz. When the communication bandwidth is 20 MHz, four channels Ch1, Ch5, Ch9, and Ch13 can be used simultaneously, as shown by the solid line in FIG. Therefore, when the transmission bandwidth of the wireless audio system (transmitter 1) is 20 MHz, by moving Ch1, Ch5, Ch9 and Ch13 sequentially, only one channel can be used while the other three channels can be used simultaneously. Audio packets can be transmitted for private use.

Further, when the transmission bandwidth is 22 MHz, three channels can be used simultaneously. There are various combinations of the three channels such as Ch1, Ch6, and Ch11 in addition to Ch1, Ch7, and Ch13 shown by the solid lines in FIG. Therefore, when the transmission bandwidth of the wireless audio system (transmitter 1) is 22 MHz, only one channel is occupied while the other two channels can be used simultaneously by sequentially moving the channels of the above combination. Audio packets can be transmitted.
However, the channel movement pattern in the present invention is not limited to these.

  Returning to FIG. 1, the configuration of the transmitter 1 and the receiver 2 will be described. 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, A communication circuit 13 and an antenna 14 for performing communication through a communication channel are provided. The communication circuit 13 transmits an audio signal and receives an acknowledgment ACK from the receiver 2. In addition, communication for switching the communication channel is performed in synchronization with the receiver 2. The controller 12 performs channel switching based on the negotiation or schedule with the receiver 2.

  The receiver 2 includes a built-in antenna 24, a communication circuit 20 that performs communication on each communication channel, a controller 21 that controls the operation of the receiver 2, a D / A converter 22 that converts a received digital audio signal into an analog signal, and An audio output unit 23 is provided for outputting an audio signal to the speaker 4 with amplifier. The communication circuit 20 receives the high frequency signal transmitted from the transmitter 1 and demodulates the audio signal and the control signal, and transmits a signal such as an acknowledgment ACK input from the controller 21 to the transmitter 1. The audio signal demodulated into the baseband digital signal by the communication circuit 20 is input to the D / A converter 22. The control signal demodulated by the communication circuit 20 is input to the controller 21. The D / A converter 22 converts the input digital audio signal into an analog audio signal and outputs the analog audio signal from the audio output unit 23 to the speaker with amplifier 4.

  FIG. 4 is a flowchart showing the operation of the controller 12 of the transmitter 1. When communication with the receiver 2 is established through a certain communication channel (S1), the following processing is started. First, a counter i for the number of packets transmitted through this channel is set to 1 (S2). Then, it is determined whether the channel is busy based on carrier sense (S3). It waits in S3 until the busy state of the channel is completed, and when the state shifts to idle (NO in S3), it waits for the waiting time T1 (S4) and transmits the i-th audio packet (S5). It is assumed that the carrier sense of the communication channel is also performed during the standby time T1.

  When the transmission of the audio packet is completed, it waits for T3 until it receives an acknowledgment ACK from the receiver 2 (S6, S7). If an acknowledgment ACK is received before T3 elapses (YES in S6), it is determined whether the packet number counter i is 4 (S8). If the packet number counter i is less than 4 (NO in S8), 1 is added to i (S9), and the process returns to S4 to transmit the next audio packet.

  On the other hand, in S6 and S7, if no acknowledgment response ACK is received from the receiver 2 even after the waiting time T3 has elapsed (YES in S7), the process returns to S5 to retransmit the i-th audio packet.

  If the packet number counter i is 4 in S8 (YES in S8), it is determined that the transmission of the audio packet on this channel is completed, and the communication channel is switched in synchronization with the receiver 2 (S10), and then the process goes to S2. Return and start transmitting audio packets on this channel.

  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

Claims (3)

A method of transmitting audio packets between a transmitter and a receiver using a plurality of communication channels used in combination with other wireless communication,
(1) the transmitter and the receiver select the same one channel;
(2) After the transmitter performs carrier sense of the selected channel and detects that the channel is idle,
(3) Wait for a waiting time T1 shorter than the shortest packet interval defined by the other wireless communication procedure, and transmit an audio packet;
(4) After the receiver completes reception of the audio packet, it waits for a waiting time T2 shorter than the shortest packet interval, and returns a response signal.
(5) When the transmitter does not receive a response signal from the receiver even after waiting for a waiting time T3 longer than the waiting time T2 and shorter than the shortest packet interval after completing transmission of the audio packet, the audio Resend the packet,
(6) When the transmitter has not received or transmitted a predetermined number of audio packets after receiving the response signal, the process returns to the procedure of (3) to transmit the next audio packet.
(7) The wireless audio transmission method according to (2), wherein the transmitter and the receiver switch back to the selected channel when the transmission / reception of the predetermined number of audio packets is completed. A method of transmitting audio packets between a transmitter and a receiver using a plurality of communication channels used in combination with other wireless communication,
(1) the transmitter and the receiver select the same one channel;
(2) After the transmitter performs carrier sense of the selected channel and detects that the channel is idle,
(3) A standby time longer than SIFS, which is a packet interval of an acknowledgment response defined by the other wireless communication procedure, and shorter than DIFS, which is the shortest time of a normal packet interval defined by the other wireless communication procedure Just wait, send audio packets,
(4) After the receiver completes the reception of the audio packet, it waits for a waiting time T2 shorter than the SIFS and returns a response signal;
(5) When the transmitter completes transmission of the audio packet and does not receive a response signal from the receiver even when waiting for a waiting time T3 longer than the waiting time T2 and shorter than the SIFS, Resubmit,
(6) When the transmitter has not received or transmitted a predetermined number of audio packets after receiving the response signal, the transmitter waits for a waiting time T1 shorter than the SIFS, and then transmits the audio packet (4 )
(7) The wireless audio transmission method according to (2), wherein the transmitter and the receiver switch back to the selected channel when the transmission / reception of the predetermined number of audio packets is completed. The plurality of communication channels used in combination with the other wireless communication are a plurality of communication channels defined by IEEE 802.11,
3. The wireless audio transmission method according to claim 1, wherein the switching of the selected channel in (7) is performed between channels that can be used simultaneously without overlapping communication frequency bands among the plurality of communication channels.

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