Wireless stereo audio system, wireless audio playback device and communication method

Abstract

The present application relates to a wireless stereo audio system, a wireless audio playback device, and a communication method. The present application describes a wireless system comprising: a first device in operative communication with a master device over a first link; and a second device that eavesdrops on transmissions from the master device to the first device. The wireless system adjusts at least one of a first clock signal for the first link and a second clock signal for a second link between the second device and the first device based on a reference clock signal.

Description

[0001] This application is a divisional application of the application with the application date of January 18, 2019, application number 201980008897.3, and invention name “A wireless stereo audio system, wireless audio playback device and communication method” (formerly known as “Dual Advanced Audio Distribution Framework (A2DP) Receiver”).

[0002] priority

[0003] This application is an international application of U.S. non-provisional patent application No. 16 / 250,855, filed on January 17, 2019, and claims priority to and the benefit of U.S. Provisional Application No. 62 / 619,578, filed on January 19, 2018, all of which are incorporated herein by reference in their entirety. Technical Field

[0004] The present disclosure relates to the field of wireless audio playback devices. background

[0005] The wireless speakers can be configured to play back stereo sound from a signal audio source. The audio information packets are shared with the wireless speakers via a wireless link. Each wireless speaker can receive the audio information separately, or the audio information can be received by one speaker and sent to another speaker. In the latter case, the delay between the audio source and the playback may be too large for acceptable performance experienced by the user. Therefore, it is preferred that both wireless devices have a mechanism to receive audio information from the source at the same time. If the audio source is in active communication with a single wireless speaker, the second speaker may need to receive the audio information with knowledge of the audio source. In this case, a mechanism for the second speaker to recover or otherwise receive lost or damaged audio information packets may be necessary. Summary of the Invention

[0006] This application provides the following:

[0007] 1) A wireless stereo audio system, comprising:

[0008] a primary audio playback device that is in effective communication with the audio source over a medium; and

[0009] a secondary audio playback device configured to eavesdrop on audio information transmitted from the audio device to the primary audio playback device,

[0010] The secondary audio playback device is configured to transmit a NACK signal on the medium, wherein the NACK is used to interfere with an ACK signal from the primary audio playback device on the medium.

[0011] 2) The wireless stereo audio system of clause 1), wherein the primary audio playback device is in operative communication with the secondary audio playback device.

[0012] 3) The wireless stereo audio system according to item 2), wherein the primary audio device is configured to transmit communication information for effective communication between the primary audio playback device and the audio source to the secondary audio playback device, the communication information being used to establish an eavesdropping connection between the audio source and the secondary audio playback device.

[0013] 4) The wireless stereo system according to item 1), wherein the primary audio playback device and the secondary audio playback device are configured as slave devices of the audio source.

[0014] 5) The wireless stereo system according to item 1), wherein the primary audio playback device is a master device of the secondary audio playback device.

[0015] 6) The wireless stereo audio system according to item 1), wherein the primary audio playback device is configured to transmit audio information not received by the secondary audio playback device from the audio source to the secondary audio playback device.

[0016] 7) The wireless stereo audio system according to item 6), wherein the audio information not received by the auxiliary audio playback device is identified by sharing data packet sequence information between the primary audio playback device and the auxiliary audio playback device.

[0017] 8) The wireless stereo audio system of clause 7), wherein the packet sequence information is shared by the primary audio playback device and the secondary audio playback device during a sniffing operation.

[0018] 9) The wireless stereo audio system according to item 6), wherein the audio information not received by the auxiliary audio playback device is recovered via a packet loss concealment scheme.

[0019] 10) The wireless stereo audio system according to item 1), wherein the primary audio playback device and the secondary audio playback device are configured to exchange roles based on system parameters.

[0020] 11) The wireless stereo audio system according to item 10), wherein the system parameter is the remaining battery power.

[0021] 12) The wireless stereo audio system according to item 10), wherein the system parameter is wireless signal strength between the audio source and the primary audio playback device and the secondary audio playback device.

[0022] 13) The wireless stereo audio system according to item 1), wherein the primary device is a left earbud and the secondary device is a right earbud.

[0023] 14) A method comprising:

[0024] The primary device receives data on the audio source-primary device (AP) link;

[0025] suspending data exchange on the AP link;

[0026] collecting protocol and timing information for the AP link;

[0027] The primary device sends protocol and timing information for the AP link to the secondary device;

[0028] applying, by the secondary device, protocol and timing information for the AP link to the secondary device; and

[0029] Resume data exchange on the AP link.

[0030] 15) The method according to item 14) further comprising:

[0031] Establishing an audio source-auxiliary device (AS) link; and

[0032] Information for the auxiliary device is received on the AS link, and the received information is simultaneously transmitted on the AP link.

[0033] 16) The method according to item 14), wherein the AS link is a wiretap link, which is transparent to the audio source.

[0034] 17) The method according to item 14) further comprising:

[0035] When audio information is successfully received over the AP link, the primary device transmits an ACK signal; and

[0036] A NACK signal is transmitted by the secondary device when audio information is not successfully received over the AS link, the NACK signal being configured to interfere with the ACK signal of the primary device.

[0037] 18) The method according to item 14), wherein the NACK signal is transmitted substantially before the ACK signal.

[0038] 19) A first wireless audio playback device, comprising:

[0039] An audio converter for playing audio information;

[0040] an antenna configured to receive audio information from an audio source on a medium; and

[0041] A controller is configured to execute instructions, wherein the controller is configured to send a NACK signal on the medium when no audio information is received from the audio source, the NACK signal being used to interrupt an ACK signal from a second wireless audio playback device.

[0042] 20) The first wireless audio playback device according to item 19), wherein the audio information received from the audio source on the medium is received via a wiretap link.

[0043] 21) The first wireless audio playback device of clause 19), wherein the wiretap link is transparent to the audio source. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 An example system for wireless audio playback is shown according to one embodiment.

[0045] Figure 2 is an example scatternet for wireless audio playback, according to one embodiment.

[0046] Figures 3A-3C This is a timing diagram about the communication between the audio source and the primary device, and between the primary device and the secondary device, where the communication timing between the primary device and the secondary device follows the communication timing between the audio source and the primary device.

[0047] Figure 4 is a flow chart illustrating an example method for establishing eavesdropping in a wireless audio system, according to some example embodiments.

[0048] Figure 5 is a communication scheme according to various embodiments, wherein the first data packet is NACKed by the primary device.

[0049] Figure 6 is a sampled communication between the audio source and the primary and secondary devices according to various embodiments, including lost or corrupted packets.

[0050] Figure 7 Sample communications between an audio source and primary and secondary devices, including lost or corrupted packets and sniffing operations, according to various embodiments.

[0051] Figure 8 is a flow chart of ACK interference by a secondary device according to one embodiment.

[0052] Figure 9 is a communication scheme including ACK interference by a secondary device according to various embodiments.

[0053] Figure 10 is a communication scheme including ACK interference by a secondary device according to various embodiments.

[0054] Figure 11 A communication scheme including ACK interference and loss of data packets communicated on a primary-secondary (PS) link by a secondary device according to various embodiments.

[0055] Figure 12 is a flow chart for role switching between a primary device and a secondary device according to one embodiment.

[0056] Figure 13A and 13B is an example of role switch decision making according to various embodiments.

[0057] Figure 14 is a software / firmware stack for wireless audio playback according to one embodiment. Detailed description

[0058] The following description sets forth many specific details of examples such as specific systems, components, methods, etc., in order to provide a good understanding of various embodiments of the communication schemes and technologies. However, it will be apparent to those skilled in the art that at least some embodiments can be implemented without these specific details. In other cases, well-known components or methods are not described in detail or are presented in simple block diagram form in order to avoid unnecessarily obscuring the technology described herein. Therefore, the specific details set forth below are merely exemplary. Specific implementations may vary based on these exemplary details and are still contemplated to be within the spirit and scope of the present invention.

[0059] References in the specification to "an embodiment," "one embodiment," "example embodiment," "some embodiments," and "various embodiments" mean that the particular feature, structure, or characteristic being referenced is included in at least one embodiment of the present invention. Furthermore, the appearances of the phrases "an embodiment," "one embodiment," "example embodiment," "some embodiments," and "various embodiments" in various places in the specification are not necessarily all referring to the same embodiment.

[0060] In various embodiments, the communication schemes and techniques described herein may include one or more methods performed by one or more devices and / or their controllers. Although the operation of such methods is shown and described below in a particular order, the operation of each method may be changed so that specific operations can be performed in a different order, or so that specific operations can be performed (at least in part) simultaneously and / or in parallel with other operations. In other embodiments, instructions or sub-operations of different operations may be performed in an intermittent and / or alternating manner. Therefore, the various method embodiments of the technology and the order of their operation are considered to be illustrative, not restrictive.

[0061] In an example embodiment of the communication scheme and technology described herein, the device includes a main audio playback device and a secondary audio playback device, the main audio playback device effectively communicating with the audio source on a wireless medium (frequency band), and the secondary audio playback device is configured to eavesdrop on the audio information transmitted from the audio device to the main audio playback device on the medium. The secondary audio device can be configured to transmit a NACK signal on the medium, which is used to interfere with the ACK signal that can be transmitted by the main device. The main device and the secondary device can also effectively communicate with each other through the medium, and the communication can be synchronized with the signal or clock from the audio source to ensure reliable communication on each link (i.e., to avoid conflicts). The main device and the secondary device can be configured as slave devices of the audio source, and the secondary device can be configured as a slave device of the main device. The main device and the secondary device can be configured to share audio information that is not received by each device to complete the audio information. The sharing of this audio information can be carried out on the link between the main device and the secondary device and can occur during a periodic sniffing operation. The sniffing operation can be synchronous or asynchronous. Lost packets can be identified by sharing a sequence of packets received by the primary and secondary devices on the medium through sniffing operations. The roles of the primary and secondary devices can also be switched or otherwise changed during development, manufacturing, startup, or during operation based on system parameters such as battery life and signal strength.

[0062] In an example embodiment of the communication scheme and technology described herein, a method includes: receiving data on an audio source-primary device (AP) link by a primary device; suspending data exchange on the AP link; collecting protocol and timing information for the AP link; sending the protocol and timing information for the AP link by the primary device to the secondary device; applying the protocol and timing information for the AP link to the secondary device by the secondary device; and resuming data exchange on the AP link. The method may also include establishing a link (AS link) between the audio source and the secondary device and receiving information for playback from the audio source on the AS link. In another embodiment, the secondary device may send a NACK signal to interfere with the ACK signal from the primary device to the audio source. When the ACK signal is interfered with, the audio source may retransmit the audio information on the medium so that it can be received by the primary device and the secondary device.

[0063] In the example embodiment of the communication scheme and technology described in this article, the wireless audio playback device may include an audio converter (e.g., a loudspeaker) for playing the audio information sent from an audio source. The antenna may be configured to receive audio information from an audio source on a medium. The wireless audio playback device may be configured to transmit a NACK signal on a medium when a data packet is damaged or otherwise unavailable for the wireless audio playback device. The NACK signal may be an ACK signal that causes the audio source to retransmit audio information to the wireless audio playback device (the first and second wireless audio playback devices). The audio information of the first wireless audio playback device can be received on the wiretap link between the first wireless audio playback device and the audio source. In one embodiment, the wiretap link can be transparent to the audio source.

[0064] Figure 1 A system 100 for wireless audio playback is shown, including a system configured with Wireless Audio Stereo Sync (WASS TM) wireless device. System 100 includes an audio source 110 that is configured to provide audio information (i.e., "data packets") to wireless devices 120 and 122. Wireless devices 120 and 122 may include a primary wireless device ("primary device") 120 and a secondary wireless device ("secondary device") 122. Primary device 120 may be a left earbud corresponding to left ear 130 of user 101, and secondary device 122 may be a right earbud corresponding to right ear 132 of user 101. The assignment of primary device 120 and secondary device 122 to the respective ears of user 101 may be arbitrary, may be based on system parameters, may be defined during manufacturing, or may be defined during device startup or operation. The assignment of primary device 120 and secondary device 122 to the left or right ear may change during operation in response to signals from the audio source, measurements of battery levels of the primary and secondary devices, signal strength, or other system parameters.

[0065] A link (AP link 140) can be established between audio source 110 and primary device 120 and is known to audio source 110. A link (AS link 142) can be established between audio source 110 and secondary device 122 and is unknown to audio source 110. Secondary device 122 can use AS link 142 to "eavesdrop" on signals (and packets) transmitted on AP link 140 without the knowledge or control of audio source 110. A link (PS link 124) can be established between primary device 120 and secondary device 122 to share timing and other information about communications from audio source 110 with secondary device 122, enabling eavesdropping via AS link 142. AP link 140, AS link 142, and PS link 124 can all share a common medium. In other words, they can share a wireless frequency band. The PS link can also be used to share lost or missing audio information (packets) between primary device 120 and secondary device 122, as well as information about communications with audio source 110.

[0066] Figure 2 Shown for a similar Figure 1The system 100 of the present invention is a scatternet 200 for wireless audio playback. The scatternet 200 includes a source 210, which can be configured as a master device ("M"). The scatternet 200 also includes a main device 220 capable of wirelessly communicating with the source 210 over a link 240. The link 240 can be used for synchronous audio with a hands-free profile (HFP) or asynchronous audio with an advanced audio distribution profile (A2DP). HFP can be used for communication of voice signals. A2DP can be used for music streaming or other similar audio output. The main device 220 can operate as a slave device ("S") of the source 210. The scatternet 200 also includes a secondary device 222 capable of receiving audio information from the audio source 210 via a wiretap link 242. The secondary device 222 can operate as a slave device of the source 210. A third interface (I / F) 224 can be formed between the main device 220 and the secondary device 222, wherein the main device 220 operates as a master device and the secondary device operates as a slave device. The PS I / F 224 may be used to communicate connection and timing information to the auxiliary device 222, or to share audio information (ie, data packets) between the primary device 220 and the auxiliary device 222 to ensure that users (eg, Figure 1 High-quality playback of user 101).

[0067] Figures 3A-3C The timing of communication on the AP link 140 and the PS link 124 is shown. Figure 3A In the embodiment, the clock 310 of the AP link 140 and the clock 312 of the PS link 124 are aligned so that there are no conflicts and the transmit / receive (TX / RX) operations on each link are not affected by the TX / RX operations on the other link.

[0068] Figure 3B It is shown that AP link 140 may have a different clock drift 320 than PS link 124 (drift 322). Over time, the difference in drift 320 and drift 322 may cause clock 310 to correspond to clock 330 and clock 312 to correspond to clock 332. Clocks 330 and 332 may have a collision 335, which may impair performance on each link as the signals interfere with each other.

[0069] A solution in Figure 3C, where the clock 312 of the PS link 124 follows the clock 310 of the AP link 140 by a certain interval 350. By binding clock 312 to clock 310 and following clock 310, there are no conflicts between clocks 310 and 312. Clock following can be established by using the Bluetooth clock of the audio source as the master clock or reference clock and adjusting the clocks used for communication between the primary device and the secondary device (for the PS link 124) to match (and follow) the clock of the audio source. In this embodiment, the audio source can send clock information at each TX. The primary device and the secondary device can then calculate the change in their clocks using the difference between their clocks and the master clock received on the AP link and PS link. This maintains alignment and prevents conflicts. In this way, the audio source can control the timing of the PS link 124.

[0070] Aligning the clocks on the AP link 140 and PS link 124 can also align the clock on the AS link 142, allowing for better alignment in audio playback. In addition, synchronization of music or voice through clock synchronization allows for synchronous injection of audio. In one embodiment, the primary device or the secondary device can determine that audio that is not sent from the audio source will be played through the corresponding speaker. Examples of such audio played through the respective speakers include remaining battery life, volume level, link status with the audio source, or other information related to the primary device and the secondary device but not broadcast from the audio source. By synchronizing the clocks of the primary device and the secondary device with the Bluetooth clock of the audio source, the primary device and the secondary device can arbitrate what needs to be played and when. For example, the primary device and the secondary device can determine that an audio clip will be played 75ms in the future. Having synchronized clocks on both devices makes this possible and provides the user with information that is superimposed on or in place of the audio information from the audio source.

[0071] Figure 4 shows the use of auxiliary equipment in Figure 1 AS Link 142 or Figure 2Method 400 for establishing eavesdropping on an AS link 242 of a primary device. A link (AP link) can be established between a primary device and an audio source, over which data (audio data or data packets) can be exchanged. The AP link can be established according to known methods, including methods described in the Bluetooth (BT) specification. When eavesdropping is established by a secondary device, data exchange on the AP link can be suspended in step 410. Then, in step 420, protocol and timing information can be collected by the primary device and sent to the secondary device in step 430. In step 440, the secondary device can apply the protocol and timing information provided by the primary device, enabling the secondary device to receive audio information on the AS link (or eavesdropping link) in step 440. Then, in step 450, the primary device can unpause the AP link. After the AP link is unpaused, audio information can be shared between the audio source and the primary device and further received by the secondary device via the AS link (or eavesdropping link).

[0072] Figure 5 Various embodiments of data packet transmission, reception, and acknowledgment are shown, wherein the first data packet transmitted by the source is always NACKed by the primary device, causing the source to retransmit the packet. A NACK by the primary device may result in a second transmission for each data packet from the audio source. This provides the primary and secondary devices with two opportunities to receive the same information (data packet). In some cases, such as if the primary device did not receive the data packet on the first transmission, this may occur regardless. However, in other cases, the second transmission of the data packet is repeated for either the primary or secondary device, or both. In still other cases, the second transmission of the data packet may not be received by either the primary or secondary device, but as long as the first transmission of the data packet is received, the information is provided to both the primary and secondary devices, and audio playback is provided.

[0073] In transmission 501, data packet 511 is transmitted by the source and received by both the primary and secondary devices as data packet 512. Since the primary device is the only device actively communicating with the source device, NACK 513 is transmitted only by the primary device and received at the source device as NACK 514. Since data packet 511 has already been NACKed, a second data packet 515, identical to data packet 511, is transmitted. Data packet 515 is received by both the primary and secondary devices as data packet 516. The primary device transmits ACK 517, which is received by the source device as ACK 518. In the embodiment of transmission 501, information is sent twice by the source device as data packets 511 and 515, but data packet 511 is redundant as a retransmission of data packet 515 because it is received by the secondary device.

[0074] In transmission 502, data packet 511 is transmitted by the source device and received by the primary device as data packet 512. The secondary device does not receive this information as data packet 512. Instead, the data packet is not received or is otherwise corrupted as data packet 522. Because the secondary device is not actively communicating with the source device, it has no mechanism to request the source device to retransmit data packet 511. However, due to NACK 513 provided by the primary device and received as NACK 514, data packet 515 is transmitted and received by the secondary device as data packet 516. Thus, information is provided to both the primary and secondary devices; a second transmission caused by NACK 513 is necessary.

[0075] In transmission 503, packet 511 is transmitted by the source device and received by the primary device as packet 512. The secondary device does receive the information as packet 512, but as with transmissions 501 and 502, the primary device transmits NACK 513, which is received as NACK 514. Then, packet 515 is sent and received by the primary device as packet 516, but is not received or is otherwise corrupted as packet 536. It is insignificant that the secondary device did not receive the retransmitted packet 515, as the original packet 511 was received by the secondary device as packet 512. As with transmission 501, the primary device's NACK is unnecessary because the original packet was received by both the primary and secondary devices.

[0076] In transmission 504, packet 511 is transmitted by the source device and received by the primary device as packet 512. Similar to transmission 502, the secondary device does not receive the information as packet 512. The primary device automatically sends NACK 513, which is received as NACK 514, and the source device sends packet 515, just as in transmissions 501-503 above. However, in transmission 504, packets 511 and 515 are either not received or are otherwise corrupted as packets 542 and 546, respectively. Because the secondary device has no mechanism to communicate the failure to the source device, the secondary device does not receive the information in packets 511 and 515 from the source device. To receive or recover the information, a different mechanism must be used.

[0077] In transmission 505, as in transmission 502, data packet 511 is transmitted by the source device and received by the primary device as data packet 512. The secondary device does not receive this information as data packet 512. Instead, the data packet is not received or is otherwise damaged as lost data packet 552. Because the secondary device is not actively communicating with the source device, it has no mechanism to request the source device to retransmit data packet 511. However, because NACK 513 is provided by the primary device and received as NACK 514, data packet 515 is transmitted and received by the secondary device as data packet 516. Thus, information is provided to both the primary and secondary devices; a second transmission caused by NACK 513 is necessary.

[0078] In transmission 506, as in transmission 504, data packet 511 is transmitted by the source device and received by the primary device as data packet 512. The secondary device does not receive this information as data packet 512. The primary device automatically sends NACK 513, which is received as NACK 514, and the source device sends data packet 515, just as in transmissions 501-505 above. However, in transmission 506, the secondary device does not receive data packets 511 and 515. Because the secondary device does not have a mechanism to communicate the failure to the source device, the secondary device does not receive the information in data packets 511 and 515 from the source device. If the information is to be received or recovered, a different mechanism must be used.

[0079] Figure 6 A sequence 600 of data packets transmitted by an audio source is shown, wherein the first data packet is as described with respect to Figure 5 shown and described are NACKed. Figure 5 6. Each transmission 501-506 of FIG. 600 shows and references packets received or not received by the secondary device. The transmissions where packets 511 and 515 are lost or otherwise damaged at the secondary device are shown as transmissions 504 / 506. This occurs twice in string 600.

[0080] Figure 7 Shows something like Figure 6 The data packets of the string 600 are transmitted by the audio source, wherein the first data packet is as shown in FIG. Figure 5 and Figure 6As shown and described, the primary and secondary devices may be NACKed. However, the primary and secondary devices may periodically sniff the medium. Periodic sniffing of the medium by the primary and secondary devices allows the primary and secondary devices to ensure that the packets received by each device are a complete list of packets transmitted by the audio source. Sniffing 710 may occur at certain time intervals. The primary device may transmit the packets it receives from the audio source. The secondary device may receive the information and transmit the packets it receives from the audio source. If a packet is missing from the list provided by the secondary device, the primary device may transmit the packet to the secondary device at a subsequent sniff interval or immediately after the transmit operation 720.

[0081] The sniffing 710 or transmitting 720 operation from the primary device to the secondary device may result in a collision with a packet from the audio source. In this case, no ACK or NACK is sent from the primary device and received by the audio source. Therefore, a replacement packet 750 is provided. The replacement packet may be like Figure 5 Data packets 512 and 516 are received as well.

[0082] Figure 7 The embodiment of FIG. 7 illustrates that a packet lost on a secondary device can be provided by the primary device. However, in another embodiment, sniffing 710 can identify that the packet was received by the secondary device rather than the primary device. In this embodiment, the secondary device can forward the lost or otherwise damaged packet to the primary device.

[0083] During a sniffing operation, the primary and secondary devices may first share the sequence numbers of received data packets without sharing the actual packet information. Since less information is shared on the PS link, they can save time and power. If the packet sequence numbers are different for the primary and secondary devices, a subsequent sniffing operation can be used to share lost packets between the primary and secondary devices. In one embodiment, a conventional sniffing operation may be used. In this embodiment, the data shared between the primary and secondary devices during a regularly scheduled sniff may include packet information that was identified as lost or otherwise damaged in the previous sniffing interval. In another embodiment, data transmission may be performed between the primary and secondary devices immediately after sharing the sequence numbers, or at a time that is not aligned with the conventional sniffing operation, to correct lost or damaged packets. Table 1 shows various embodiments of shared data based on sequence data exchanged between the primary and secondary devices on the PS link.

[0084] Table 1.

[0085]

[0086] For Sniff 1, both the primary and the secondary have the same packet in the exchanged sequence number. In this case, no audio information (packets) needs to be shared between the primary and secondary to correct for lost or damaged packets. For Sniff 2, the primary has a packet sequence of 5-6-7-8, while the secondary has a packet sequence of 5-7-8. This means that the secondary did not receive the packet [6]. The primary can share this packet with the secondary in a subsequent sniff operation, or it can be shared asynchronously by transmitting it out of phase on the PS link. For Sniff 3, the primary has a sequence of 9-10-12, while the secondary has a sequence of 9-10-11-12. This means that the primary did not receive the packet

[11] . The secondary can share this packet with the primary in a subsequent sniff operation, or it can be shared asynchronously by transmitting it out of phase on the PS link. For Sniff 4, the primary has a sequence of 13-14-16, while the secondary has a sequence of 14-15-16. This means that the primary device did not receive the packet

[15] , while the secondary device did not receive the packet

[13] . The primary and secondary devices can share the missing packet with each other in a subsequent sniffing operation, or they can share it asynchronously by transmitting out of phase on the PS link.

[0087] Table 1 shows a simplified exchange between the primary and secondary devices. However, longer (or shorter) sequences can be shared. In some cases, a significant number of packets may be lost or otherwise damaged. In these cases, it may be necessary to employ a packet loss concealment scheme. These packet loss concealment schemes can be based on isolating received packets on the primary and secondary devices, or they can use combined packet information. For example, if both the primary and secondary devices lose the same packet, it may be necessary to request the lost packet from the audio source again. In another embodiment, the primary and / or secondary devices can employ a packet loss concealment scheme to repair the audio information.

[0088] In yet another embodiment, there may be too many lost or damaged data packets to hide or share between the primary device and the secondary device. In this case, the primary device or the secondary device or both can play (or otherwise broadcast) silence to keep the audio information synchronized.

[0089] Figure 8A method 800 is shown for ACK jamming (or "ACK clobbering") by a secondary device when a data packet is erroneous or otherwise corrupted. In this embodiment, the secondary device jams the ACK of the primary device so that the audio source does not receive the ACK. Since the audio source does not receive the ACK, the data packet is retransmitted. First, in step 810, the audio source transmits a data packet. The data packet is only transmitted to the primary device, but the secondary device receives the data packet based on the primary device's ACK. Figure 4 The primary device is configured to eavesdrop on the signal and, therefore, receives data packets intended for the primary device. If the primary device does not receive the data packet in step 813, it may request the data packet from the secondary device via a sniffing operation in step 845 and receive the data packet from the secondary device in step 855. Once the primary device has the information from the audio source and the secondary device, it may play the audio information in step 880. If the data packet is received in step 813 but is determined to be corrupted in step 823, a NACK is sent to the audio source in step 820 to request transmission. If the data packet is received and is not corrupted, an ACK is sent to the audio source in step 830. Simultaneously with the primary device's determination, if the secondary device does not receive the data packet in step 817, it may request the data packet from the primary device in step 850 and receive the data packet from the primary device in step 860. This may occur synchronously (via a sniffing operation) or asynchronously. Once the secondary device receives the data packet, it may play the audio information in step 880. If the data packet is received in step 817 and is not corrupted in step 827, the audio information contained therein may be similarly played by each of the primary and secondary devices in step 880. If the data packet is received in step 817 but is corrupted in step 827, a NACK may be transmitted in step 840. The purpose of the NACK in step 840 is to interfere with or "collide" with the ACK from the primary device in step 830, thereby prompting the audio source to retransmit the data packet in step 810.

[0090] In some embodiments, a NACK from a secondary device to interfere with an ACK from the primary device may be transmitted slightly earlier and / or at a higher power than the ACK from the primary device. In some embodiments, a NACK from a secondary device may be transmitted 2-3 μs before an ACK from the primary device.

[0091] Figure 9 Various embodiments of transmitting audio information from an audio source to a primary device and being eavesdropped on by a secondary device are shown. In transmission 901, a data packet 511 is transmitted by the audio source and received by the primary and secondary devices as data packet 512. The primary device sends an ACK 513 which is received by the audio source as ACK 514.

[0092] In transmission 902, data packet 511 is not received or is otherwise corrupted as data packet 922. The primary device responds with a NACK 923, which is received by the audio source as a NACK 924. The secondary device receives this information as data packet 512, but does not provide an ACK because it is not actively communicating with the audio source. After receiving NACK 924, the audio source then retransmits the audio information as data packet 515, which is received by both the primary and secondary devices as data packet 516. The secondary device already has the audio information, but the primary device does not. The primary device responds with an ACK 517, which is received by the audio source as an ACK 518.

[0093] In transmission 903, data packet 511 is not received by the secondary device or is otherwise corrupted as data packet 932. Data packet 511 is received by the primary device as data packet 512. The primary device attempts to respond with an ACK 913, but the secondary device interferes with ACK 913 with a NACK 939, which may be transmitted slightly before ACK 913 and / or at a higher power than ACK 913. As a result, NACK 939 is received by the audio source as NACK 934. The audio source then retransmits the audio information as data packet 515, which is received by both the primary and secondary devices as data packet 516. The primary device responds with an ACK 517, which, when received intact by the secondary device, is not interfered with by the NACK from the secondary device.

[0094] In transmission 904, packet 511 is not received by the primary and secondary devices or is corrupted as packet 942. The primary device responds with NACK 943, and the secondary device responds with NACK 949, which are received by the audio source as NACK 944. Subsequently, the audio source sends packet 515, which is received by the secondary device as packet 516, but is not received by the primary device or is otherwise corrupted as packet 945. The primary device responds with NACK 946, causing the audio source to retransmit the packet a second time as packet 915, which is received by both the primary and secondary devices as packet 946. The secondary device now has the audio information as packet 516. The primary device responds with ACK 517, which is received by the audio source as ACK 518.

[0095] In transmission 905, the secondary device does not receive data packet 511 at all. The secondary device may not have enough information to respond with a NACK to interfere with the primary device's ACK. In this case, the secondary device can request information from the primary device, as described above with respect to Figure 7In other embodiments, other methods of error correction or packet loss concealment may be employed.

[0096] Figure 10 Various transfers between the audio source and the primary and secondary devices are shown. In transfer 1001, it may correspond to Figure 9 Transmitting 901, data packet 511 is sent from the audio source and received by the primary device and the secondary device as data packet 512. The primary device may respond with an ACK 513, which is received as an ACK 514.

[0097] In transmission 1002, it may correspond to Figure 9 In transmission 902, data packet 511 is sent from the audio source and received by the secondary device as data packet 512. Data packet 511 may not be received or may be otherwise corrupted at the primary device as data packet 922. The primary device may then respond with a NACK 923, which is received by the audio source as a NACK 924. The audio source may retransmit the audio information as data packet 515, which is received by both the primary and secondary devices as data packet 516. The primary device may respond with an ACK 517, which is received by the audio source as an ACK 518.

[0098] In transmission 1003, it may correspond to Figure 9 In transmission 903, data packet 511 is sent from the audio source and received by the primary device as data packet 512. The data packet may not be received by the secondary device. The primary device may respond to receipt of data packet 512 with an ACK 513. However, the secondary device may interfere with ACK 513 from the primary device with a NACK 939, which may be sent earlier and at a higher power than ACK 513. The amount of time 1010 by which NACK 939 is transmitted earlier than ACK 513 may be 2-3 μs. The audio source may respond to NACK 939 by retransmitting the audio information as data packet 515, which may be received by both the primary and secondary devices as data packet 516. The primary device may respond with an ACK 517, which is received by the audio source as ACK 518. When the secondary device successfully receives data packet 515, no NACK is used to interfere with ACK 517.

[0099] In transmission 1004, it may correspond to Figure 9In transmission 904, data packet 511 is sent from the audio source and received by the primary device as data packet 512. However, data packet 511 is not received at the secondary device or is otherwise corrupted as data packet 942. When the primary device attempts to respond with ACK 513, the secondary device interferes with ACK 513 with NACK 949, which is received by the audio source as NACK 944. Subsequently, the audio source transmits audio information as data packet 515, which is received by the secondary device as data packet 516, but is not received by the primary device or is otherwise corrupted as data packet 922. The primary device responds to the second attempt to transmit audio information with NACK 923, which is received by the audio source as NACK 924. The audio source attempts a third transmission of audio information as data packet 1015, which is received by both the primary and secondary devices as data packet 1016. The primary device acknowledges receipt of data packet 1016 with ACK 1017 , which is received as ACK 1018 by the audio source.

[0100] Figure 11 An embodiment of a transmission 1101 is shown in which the secondary device does not receive audio information from the audio source. However, in transmission 1101, the ACK from the primary device is not interfered with by a NACK from the secondary device. In this case, the secondary device can send a missing packet request 1110 to the primary device, and the primary device can respond with a packet 1115. The missing packet request can be synchronous and corresponds to the following: Figure 7 Sniffing as shown. Lost Packet Requests can also be asynchronous.

[0101] Figure 12 A method 1200 for switching the roles of a primary device and a secondary device in active communication with an audio source is shown. First, in step 1210, the primary device may suspend data exchange on the AP link. Then, in step 1220, the primary device may send a "switch start" message to the secondary device. In steps 1232 and 1234, the primary device and the secondary device may each collect status information of the other. In steps 1242 and 1244 of step 1240, the primary device may apply the status information of the secondary device, and the secondary device may apply the status information of the primary device. In this step, the previous secondary device may appear to the audio source as the primary device, while the previous primary device may no longer appear to the audio source. Then, in step 1250, the new primary device (the previous secondary device) may unpause the AP link and resume data exchange on the AP link.

[0102] Figure 13A and Figure 13BAn example of primary / auxiliary device role switching according to various embodiments is shown. The primary and auxiliary devices are not directly coupled to each other and may have different (or independent) batteries, such that the remaining charge in one battery may be different from or substantially the same as the remaining charge in the other battery. Figure 13A , a graph 1301 of the remaining battery life of the primary and secondary devices can be used to determine when / whether to switch the roles of the primary and secondary devices. In some embodiments, the primary device can consume more power. As the primary device consumes more and more power, the battery life of the primary device correspondingly decreases. It may be preferable to switch the roles of the primary and secondary devices to maintain the longest combined battery life of the combined wireless devices. The primary device power level 1312 may drop faster than the secondary device power level 1310. At some time, the ratio of the power levels of the primary and secondary devices may determine the role switch. The decision may be based on relative power levels. It may also be a fixed point (when the power level of the primary device is below 67% of capacity). In Figure 13A In the illustrated embodiment, a role switch 1320 occurs when the primary device's battery level is two-thirds that of the secondary device. When this occurs, the secondary device assumes the role of primary, and vice versa. This means that the secondary device, now operating as the primary, will lose battery power faster than the primary device (now the secondary). At some point, the secondary device's battery level will drop below that of the primary device. At another point, the secondary device's battery level may be two-thirds that of the primary device (now the secondary). When this occurs, a second role switch 1322 may occur, thereby extending the operating life of the wireless audio system. Those skilled in the art will appreciate that various battery voltage thresholds may be used. The two-thirds ratio is merely exemplary and not limiting. In other embodiments, a fixed voltage may be used. Furthermore, in still other embodiments, battery level hysteresis may be used to prevent rapid role transitions between primary and secondary devices, which could result in excessive pauses in the AP link and potentially degraded audio performance.

[0103] Figure 13BA graph 1302 shows the signal strength of wireless headphones over time and their respective roles as primary and secondary devices. Preferably, the device with the lowest signal strength is operated as the primary device. This ensures that the secondary device eavesdropping has access to the strongest signal. The signal level 1332 of the primary device may be lower because it is farther away from the audio source or because its environment is noisier or more attenuated than the wireless signal from the audio source. At some point in time, the signal level 1340 of the secondary device may begin to drop. This may be because of external signals interfering with the eavesdropping, because of some attenuating element near the secondary device, or because the secondary device may have moved away from the audio source while the position of the primary device relative to the audio source remained the same. There may also be other reasons for the reduction in signal strength. When the signal strength on the secondary device drops enough, a condition may occur according to Figure 12 The roles are switched (there may be some hysteresis). While the signal strength 1330 of the secondary device (the secondary device is actually operating as the primary device) is lower than the signal strength 1332 of the primary device, the roles remain switched. However, at some point 1342, when the signal strength on the secondary device (operating as the primary device) rises and exceeds the signal strength of the primary device (operating as the secondary device), the roles can be switched back again.

[0104] Figure 14 A software / firmware stack 1400 for an audio device configured to perform the audio playback functions described herein is shown. The stack 1400 may include a Wireless Audio Stereo Synchronization (WASS) application module 1410. The stack 1400 may also include a plurality of application programming interfaces (APIs), including Wireless Integrated Connectivity for Embedded Devices (WICED) and Wireless Audio Stereo Sync (WASS). TM ) API 1421 and audio library 1423. The stack 1400 may also include an embedded Bluetooth stack 1430, which may include a core, a framework support module 1431 and a Bluetooth low-level protocol 1433. The framework support module 1431 may include information for supporting frameworks such as the Advanced Audio Distribution Profile (A2DP) and the Hands-Free Profile (HFP). The stack 1400 may also include a core firmware module 1440, which includes a Bluetooth low-level protocol module 1441, a low-level WASS API 1443, high-level audio algorithms 1445, low-level scheduling information 1447 and device drivers 1449. The stack 1400 may also include firmware and software for interacting and communicating with device-specific hardware 1450.

[0105] Figure 14A single software / firmware stack is shown. Stack 1400 can be provided in each of the primary and secondary devices, and the specific audio information played according to stack 1400 can be determined in part by the device ID (e.g., left or right). Because both the primary and secondary devices include the same software / firmware, they can easily switch roles.

[0106] Various embodiments of the encryption / decryption techniques described herein can include various operations. These operations can be performed by hardware, firmware, or a combination thereof. As used herein, the term "coupling" means directly connecting as much as possible, or indirectly connecting through one or more intermediate components on a PCB wiring / pad, switch, bus, jack, trace, and / or programmable interconnect. Any signal provided by various PCB wiring / pads, switches, jacks, traces, and programmable interconnects can be time-division multiplexed with other signals and can be provided on one or more public or dedicated buses and / or signal traces. Each bus can alternatively include one or more single signal traces, and one or more signal traces can alternatively perform the function of a bus.

[0107] In the foregoing specification, the present invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.

Claims

1. A wireless system comprising: a first device in operative communication with the master device over a first link; and a second device configured to eavesdrop on transmissions from the master device to the first device, The wireless system is configured to adjust at least one of a first clock signal for the first link and a second clock signal for a second link based on a reference clock signal so that each of a plurality of periodic transmissions on the second link follows a corresponding transmission on the first link at a predetermined interval, wherein the second link is between the second device and the first device.

2. The wireless system according to claim 1, wherein: The first clock signal has a first clock drift; and The second clock signal has a second clock drift different from the first clock drift.

3. The wireless system of claim 1 , wherein: The master device indicates the reference clock signal in each of a plurality of transmissions to the first device and the second device.

4. The wireless system of claim 1 , wherein: The first device is configured to calculate a variation of the first clock signal based on a first difference between the first clock signal and the reference clock signal; as well as The second device is configured to calculate a variation of the second clock signal based on a second difference between the second clock signal and the reference clock signal.

5. The wireless system of claim 1 , wherein: The first device is configured to minimize a difference between the first clock signal and the reference clock signal.

6. The wireless system of claim 1 , wherein: The first device is further configured to periodically transmit and receive at times determined by the first clock signal; and The second device is further configured to periodically transmit and receive at times determined by the second clock signal.

7. The wireless system according to claim 1, wherein: The second device is configured to: adjusting the second clock signal based on a difference between the second clock signal and the reference clock signal; and An ACK signal transmitted by the first device is interfered with by transmitting a NACK signal at a time determined by the adjusted second clock signal.

8. The wireless system of claim 1 , wherein: Each of the first device and the second device is configured to play an audio clip at a predetermined time, wherein the first clock signal indicates the predetermined time for the first device and the second clock signal indicates the predetermined time for the second device.

9. A method comprising: At the first device, communicating with the master device over a first link; At a second device, eavesdropping on information transmitted from the master device to the first device; and Based on a reference clock signal, at least one of a first clock signal for the first link and a second clock signal for a second link between the second device and the first device is adjusted so that each of a plurality of periodic transmissions on the second link follows a corresponding transmission on the first link at a predetermined interval.

10. The method according to claim 9, further comprising: generating the first clock signal having a first clock drift; and The second clock signal is generated to have a second clock drift different from the first clock drift.

11. The method according to claim 9, further comprising: The reference clock signal from the master device is received at each of the first device and the second device.

12. The method according to claim 9, further comprising: calculating a variation of the first clock signal based on a first difference between the first clock signal and the reference clock signal; and A variation of the second clock signal is calculated based on a second difference between the second clock signal and the reference clock signal.

13. The method according to claim 9, further comprising: The first clock signal is adjusted to minimize a difference between the first clock signal and the reference clock signal.

14. The method according to claim 9, wherein: Communicating with the master device over the first link is performed at a time determined by the first clock signal; and Eavesdropping on transmissions from the master device to the first device is performed at a time determined by the second clock signal.

15. The method according to claim 9, further comprising, at the second device: adjusting the second clock signal based on a difference between the second clock signal and the reference clock signal; and An ACK signal transmitted by the first device is interfered with by transmitting a NACK signal at a time determined by the adjusted second clock signal.

16. The method according to claim 9, further comprising: At each of the first device and the second device, an audio clip is played at a predetermined time, wherein the first clock signal indicates the predetermined time for the first device and the second clock signal indicates the predetermined time for the second device.

17. A first device comprising: an antenna configured to eavesdrop on information transmitted from the master device to the second device over the first link; and A controller is configured to execute instructions for adjusting a first clock signal for a second link based on a reference clock signal so that each of a plurality of periodic transmissions on the second link follows a corresponding transmission on the first link at a predetermined interval, wherein the second link is between the first device and the second device.

18. The first device according to claim 17, wherein: The antenna is further configured to receive the reference clock signal from the master device; and The controller is further configured to: A variation of the first clock signal is calculated based on a difference between the first clock signal and the reference clock signal.

19. The first device according to claim 17, wherein: The first device is further configured to: adjusting the first clock signal based on a difference between the first clock signal and the reference clock signal; and An ACK signal transmitted by the second device is interfered with by transmitting a NACK signal at a time determined by the adjusted first clock signal.

20. The first device according to claim 17, wherein: The antenna is further configured to eavesdrop on the information at a time determined by the first clock signal.

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