PATENT DOCUMENT

Publication Number: US-8768252-B2
Application Number: US-201113220224-A
Country: US
Kind Code: B2

Title: Un-tethered wireless audio system

Abstract:
A wireless audio system configured to receive audio information wirelessly transmitted by an audio source including first and second wireless transceivers. The first wireless transceiver establishes a bidirectional secondary wireless link with the audio source for receiving and acknowledging receipt of the audio information. The first and second wireless transceivers communicate with each other via a primary wireless link. A wireless audio system including an audio source and first and second wireless transceivers. The first and second wireless transceivers communicate via a primary wireless link. The audio source communicates audio information to the first wireless transceiver via a secondary wireless link which is configured according to a standard wireless protocol. The first wireless transceiver is configured to acknowledge successful reception of audio information via the secondary wireless link.

Claims:
The invention claimed is: 
     
       1. A wireless audio system configured to receive audio information wirelessly transmitted by an audio source, comprising:
 a first wireless transceiver, that is configured to establish a bidirectional secondary wireless link with the audio source for receiving and acknowledging receipt of the audio information; 
 a second wireless transceiver, wherein said first and second wireless transceivers are configured to communicate with each other via a primary wireless link; and 
 wherein said first wireless transceiver is configured to communicate at least one communication parameter to said second wireless transceiver via said primary wireless link, wherein the communication parameter is to enable said second wireless transceiver to establish unidirectional wireless communication with said audio source in order to receive the audio information transmitted by said audio source via said secondary wireless link. 
 
     
     
       2. The wireless audio system of  claim 1 , wherein said secondary wireless link is configured according to a standard wireless protocol. 
     
     
       3. The wireless audio system of  claim 1 , wherein said secondary wireless link is configured according to Bluetooth protocol. 
     
     
       4. The wireless audio system of  claim 1 , wherein said first and second wireless transceivers are configured to extract first and second audio channels, respectively, from the audio information. 
     
     
       5. The wireless audio system of  claim 1 , wherein the audio source transmits the audio information in audio packets, and wherein:
 said second wireless transceiver is configured to send an acknowledgement to said first wireless transceiver via said primary wireless link upon successful reception of an audio packet; and 
 wherein said first wireless transceiver is configured to send an acknowledgement to the audio source via said secondary wireless link upon successful reception of said audio packet and upon reception of an acknowledgement from said second wireless transceiver. 
 
     
     
       6. The wireless audio system of  claim 1 , wherein the audio source transmits the audio information in audio packets, and wherein:
 said second wireless transceiver is configured to send an acknowledgement to said first wireless transceiver via said primary wireless link upon successful reception of an audio packet; 
 wherein said first wireless transceiver is configured to send an acknowledgement to the audio source via said secondary wireless link upon successful reception of said audio packet; and 
 wherein said first wireless transceiver is configured to relay said audio packet to said second wireless transceiver when an acknowledgement from said second wireless transceiver is not received. 
 
     
     
       7. The wireless audio system of  claim 1 , wherein the audio information comprises stereo audio information. 
     
     
       8. The wireless audio system of  claim 7 , wherein said first wireless transceiver is coupled to a first loudspeaker and wherein said second wireless transceiver is coupled to a second loudspeaker. 
     
     
       9. The wireless audio system of  claim 1 , wherein said primary wireless link includes a unidirectional acknowledgement link from said second wireless transceiver to said first wireless transceiver. 
     
     
       10. The wireless audio system of  claim 1 , wherein said primary wireless link includes a bidirectional acknowledgement link. 
     
     
       11. The wireless audio system of  claim 1 , wherein said first and second wireless transceivers are programmed to be permanently paired with each other via said primary wireless link when powered up. 
     
     
       12. The wireless audio system of  claim 1 , wherein said first and second wireless transceivers employ at least one locked frequency reference of the audio source to synchronize audio playback between said first and second wireless transceivers. 
     
     
       13. The wireless audio system of  claim 1 , wherein said first and second wireless transceivers implement a control loop with the audio source to synchronize audio playback between said first and second wireless transceivers. 
     
     
       14. A wireless audio system, comprising:
 an audio source and first and second wireless transceivers; 
 wherein said first and second wireless transceivers are configured to communicate via a primary wireless link; 
 wherein said audio source communicates audio information to said first wireless transceiver via a secondary wireless link which is configured according to a standard wireless protocol; 
 wherein said first wireless transceiver is configured to communicate at least one communication parameter to said second wireless transceiver via said primary wireless link, and wherein said second wireless transceiver is configured to use said at least one communication parameter to operate as an observer of said secondary wireless link to receive said audio information; and 
 wherein said first wireless transceiver is configured to acknowledge successful reception of audio information via said secondary wireless link. 
 
     
     
       15. The wireless audio system of  claim 14 , wherein said standard wireless protocol is Bluetooth protocol. 
     
     
       16. The wireless audio system of  claim 14 , wherein said audio information comprises stereo audio information. 
     
     
       17. The wireless audio system of  claim 14 , wherein said first wireless transceiver extracts a first audio channel from said audio information and wherein said second wireless transceiver extracts a second audio channel from said audio information. 
     
     
       18. The wireless audio system of  claim 14 , wherein:
 said second wireless transceiver is configured to use said primary wireless link to acknowledge to said first wireless transceiver successful reception of said audio information; and 
 wherein said first wireless transceiver is configured to send unacknowledged audio information to said second wireless transceiver via said primary wireless link. 
 
     
     
       19. The wireless audio system of  claim 14 , wherein:
 said second wireless transceiver is configured to use said primary wireless link to acknowledge to said first wireless transceiver successful reception of said audio information; and 
 wherein said audio source re-sends said audio information when not successfully receive by either one or both of said first and second wireless transceivers. 
 
     
     
       20. The wireless audio system of  claim 14 , wherein said first wireless transceiver is coupled to a first loudspeaker, and wherein said second wireless transceiver is coupled to a second loudspeaker. 
     
     
       21. The wireless audio system of  claim 14 , wherein said first and second wireless transceivers employ at least one locked frequency reference of said audio source to synchronize audio playback between said first and second wireless transceivers. 
     
     
       22. A method performed by a first wireless transceiver to receive audio information wirelessly transmitted by an audio source, the method comprising:
 establishing a bidirectional secondary wireless link with the audio source for receiving and acknowledging receipt of the audio information; 
 establishing a primary wireless link with a second wireless transceiver; and 
 communicating a communication parameter to the second wireless transceiver via the primary wireless link, wherein the communication parameter is to enable the second wireless transceiver to snoop the secondary wireless link so as to receive the audio information transmitted by the audio source. 
 
     
     
       23. The method of  claim 22 , wherein the secondary wireless link is configured according to a standard wireless protocol. 
     
     
       24. The method of  claim 22 , wherein the first and second wireless transceivers are configured to extract first and second audio channels, respectively, from the audio information. 
     
     
       25. The method of  claim 22 , wherein the audio source transmits the audio information in audio packets,
 wherein the second wireless transceiver is configured to send an acknowledgement to the first wireless transceiver via the primary wireless link upon successful reception of an audio packet, 
 wherein the method further comprising sending an acknowledgement to the audio source via the secondary wireless link upon successful reception of the audio packet and upon reception of an acknowledgement from the second wireless transceiver. 
 
     
     
       26. The method of  claim 22 , wherein the audio source transmits the audio information in audio packets,
 wherein the second wireless transceiver is configured to send an acknowledgement to the first wireless transceiver via the primary wireless link upon successful reception of an audio packet, 
 wherein the method further comprising:
 sending an acknowledgement to the audio source via the secondary wireless link upon successful reception of the audio packet; and 
 relaying the audio packet to the second wireless transceiver when an acknowledgement from the second wireless transceiver is not received. 
 
 
     
     
       27. The method of  claim 22 , wherein the primary wireless link includes a unidirectional or bidirectional acknowledgement link from the second wireless transceiver to the first wireless transceiver.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/379,583, filed on Sep. 2, 2010 which is herein incorporated by reference in its entirety for all intents and purposes. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to un-tethered wireless transceivers that communicate with an audio source, and more particularly to an audio system which eliminates the need for a wired connection between the first and second wireless transceivers. 
     2. Description of the Related Art 
     The most common type of wireless stereo audio loudspeakers consists of a single radio frequency (RF) transceiver delivering audio to separate left and right loudspeakers via a wired connection. The term “loudspeaker” as used herein refers to any electro-acoustic transducer and includes, but is not limited to, home and professional audio speakers and headphones, earphones, ear buds, etc. The audio system may use a standard wireless protocol, such as Bluetooth or Wi-Fi® (based on the IEEE 802.11 family of standards of the Institute of Electrical and Electronics Engineers) or the like. The term “standard wireless protocol” or “standard protocol” as used herein refers to any open or publicly available wireless protocol or any wireless protocol that is a product of a standards body or special interest group, which includes but is not limited to Bluetooth and Wi-Fi®. The term “proprietary wireless protocol” or “proprietary protocol” as used herein refers to any wireless protocol other than a standard wireless protocol. Less common configurations are wireless loudspeakers that consist of separate RF receivers for the left and right audio channel. These loudspeakers use proprietary wireless protocols only. 
     A significant disadvantage of wireless stereo loudspeakers that use a proprietary wireless protocol is that a separate RF transmitter must be added to the audio source since the audio source does not otherwise support the proprietary protocol. These RF transmitters are typically in the form of a dongle, which plugs into the audio source. The dongle adds bulk to portable systems, and shortens battery life if it draws power from the audio source. If the dongle has its own power source, then it becomes one more item that requires a charger. 
     A significant disadvantage of wireless stereo loudspeakers that use standard protocols, such as Bluetooth or Wi-Fi® or the like, is that these protocols were not designed to reliably carry stereo audio traffic to separate left and right receivers. Therefore, current systems that use standard protocols use a wired connection between the left and right loudspeakers. This results in unsightly or otherwise inconvenient cables for traditional loudspeaker systems, or awkward form factors for small devices such as headphones. 
     Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The benefits, features, and advantages of the present invention will become better understood with regard to the following description, and accompanying drawings where: 
         FIG. 1  is a block diagram of a wireless audio system implemented according to an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram of a wireless audio system implemented according to one embodiment of the present invention including a participant and an observer of wireless communications; 
         FIG. 3  is a block diagram of a wireless audio system implemented according to one embodiment of the present invention including a bridge configuration for wireless communications; 
         FIG. 4  is a block diagram of a wireless audio system implemented according to a more specific embodiment using Bluetooth stereo audio transported via the Advanced Audio Distribution Profile (A2DP) for wireless communications; 
         FIG. 5  is a timing diagram illustrating operation of the wireless audio system of  FIG. 4 ; 
         FIG. 6  is a block diagram of a wireless audio system implemented in a substantially similar manner as the audio system of  FIG. 4  with a bidirectional acknowledge link for increased robustness; and 
         FIG. 7  is a timing diagram illustrating operation of the wireless audio system of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable one of ordinary skill in the art to make and use the present invention as provided within the context of a particular application and its requirements. Various modifications to the preferred embodiment will, however, be apparent to one skilled in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described herein, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed. 
     Various embodiments disclosed herein incorporate a primary RF wireless link between a pair of loudspeakers and a secondary RF wireless link between the audio source and one of the loudspeakers. The primary link may follow a standard wireless protocol, a proprietary wireless protocol, or a combination thereof. The secondary wireless link may follow a standard protocol, thus ensuring compatibility with the largest number of audio sources. 
       FIG. 1  is a block diagram of a wireless audio system  100  implemented according to an exemplary embodiment of the present invention. The wireless audio system  100  includes an audio source  101 , a first loudspeaker  103  (LOUDSPEAKER 1 ) and a second loudspeaker  105  (LOUDSPEAKER 2 ). The specific configuration of the audio source  101  and each of the loudspeakers  103  and  105  depends upon the particular application, which may have any one of several forms. The audio source  101  may be implemented as any one of a mobile phone (e.g., Blackberry, iPhone, etc.), a portable game player, a portable media player (e.g., MP3 player, iPod, etc.), a computer (e.g., PC, Apple computer, etc.), an audio/video (A/V) receiver as part of a home entertainment or home theater system, etc. An A/V receiver, for example, may have both wired and wireless loudspeakers, where the loudspeakers  103  and  105  may be wireless rear channel speakers or the like. The loudspeakers  103  and  105  are configured as any type of electro-acoustic transducers for converting audio information into sound, such as home or professional speakers, headphones, earphones, ear buds, etc. The present invention is not limited to any particular physical format or size of the audio source and speaker configuration. The loudspeaker  103  may be a left channel speaker and the loudspeaker  105  may be a right channel speaker, or vice-versa, in which either loudspeaker may be configured for either stereo channel. 
     The audio source  101  and the loudspeakers  103  and  105  each have a wireless transceiver for sending and receiving wireless communications. As shown, the audio source  101  includes a wireless transceiver (TXVR)  102 , the loudspeaker  103  includes a wireless transceiver  104 , and the loudspeaker  105  includes a wireless transceiver  106 . The transceivers  104  and  106  of the loudspeakers  103  and  105  establish a primary wireless link  107 . The transceiver of one of the loudspeakers, such as the transceiver  104 , establishes a secondary wireless link  109  with the transceiver  102  of the audio source  101 . 
     In one embodiment, the audio source  101  wirelessly transmits (via TXVR  102 ) a stream of audio stereo information in the form of one or more packets as understood by those of ordinary skill in the art of wireless communications. Each packet incorporates stereo audio information in the form of compressed or uncompressed stereo samples. The stereo audio information incorporates stereo samples for first and second audio channels, such as Left and Right channels or the like. As shown, for example, the audio source  101  wirelessly transmits a packet  111  incorporating audio information, which is conveyed to the loudspeaker  103  via the secondary wireless link  109 . The loudspeaker  103  wirelessly transmits (via TXVR  104 ) an acknowledgement packet  113  back to the audio source  101  upon successful reception of the packet  111 . 
     The primary wireless link  107  enables wireless communications between the loudspeakers  103  and  105 . The communication on the primary wireless link  107  depends upon the particular embodiment, as further described herein. In one embodiment, the loudspeaker  103  relays audio information for conversion by the loudspeaker  105  via the primary wireless link  107 . In another embodiment, communication information is provided by the loudspeaker  103  to the loudspeaker  105  to enable the transceiver  106  to “snoop” communications on the secondary wireless link  109 . 
       FIG. 2  is a block diagram of a wireless audio system  200  implemented according to one embodiment of the present invention including a participant and an observer of wireless communications. The wireless audio system  200  includes the audio source  101  and the loudspeakers  103  and  105  in a similar manner as shown for the wireless audio system  100 . The transceivers  102 ,  104  and  106  are included in the respective components, but are not shown for purposes of simplicity of illustration. The secondary wireless link  109  is established between the audio source  101  and the loudspeaker  103  and the primary wireless link  107  is established between the loudspeakers  103  and  105  in substantially the same manner. In this case, the loudspeaker  103  is configured as a participant in the wireless communications across the secondary wireless link  109 , whereas the loudspeaker  105  is configured only as an observer in wireless communications across the secondary wireless link  109 . As an observer the loudspeaker  105  only receives audio information from the audio source  101  as further described herein, but does not transmit information to the audio source  101 . 
     Once the primary and secondary wireless links  107  and  109  are established, the loudspeaker  103  sends one or more communication parameters  201  to the loudspeaker  105  via the secondary wireless link  109  in order to enable the loudspeaker  105  to receive packets transmitted by the audio source  101 . The loudspeaker  105  configures its transceiver  106  to receive communications from the audio source  101  in accordance with the communication parameters  201 , and establishes a unidirectional wireless communication path  203  from the audio source  101  to the loudspeaker  105 . The communication path  203  enables the loudspeaker  105  to snoop, listen or otherwise eavesdrop communications on the secondary wireless link  109  via the wireless path  203 . As understood by those of ordinary skill in the art, the wireless communications from the audio source  101  are typically omni-directional so that the loudspeakers  103  and  105  both receive wireless energy transmissions from the audio source  101 . As shown, the transceiver  106  is configured to snoop the secondary wireless link  109  (via path  203 ) to receive audio information from the audio source  101 , such as the packet  111 . 
     In this case, the primary wireless link  107  may be used by the transceiver  106  of the loudspeaker  105  to acknowledge successful reception of communications from the audio source  101 . As shown, the loudspeaker  105  transmits acknowledge information  205  to the loudspeaker  103  upon successful reception of a wireless communication from the audio source  101 , such as the packet  111 . 
     In this manner, both loudspeakers  103  and  105  receive audio information over the secondary wireless link  109 . As previously described, each wireless packet incorporates stereo audio information including first and second audio channels, such as the left audio channel and the right audio channel. One loudspeaker extracts the left audio channel from each packet of the stereo stream for playback, while the other extracts the right channel. When the observer loudspeaker  105  receives a packet from the audio source  101 , it provides an acknowledgement to the participant loudspeaker  103  over the primary wireless link  107 . 
     Acknowledgement to the audio source  101  and re-transmissions may be handled in any one of several manners. In a first embodiment, the participant loudspeaker  103  only sends an acknowledgement to the audio source  101  if it receives a packet and the observer loudspeaker  105  has indicated (over the primary wireless link  107 ) that it received the packet as well, such as by sending the acknowledge information  205 . The audio source  101  retransmits unacknowledged packets, such that the observer loudspeaker  105  and/or participant loudspeaker  103  may receive the missing data. In a second embodiment, the participant loudspeaker  103  acknowledges each packet it successfully receives from the audio source  101 , and relays to the observer loudspeaker  105  over the primary wireless link  107  any packets that the observer loudspeaker  105  did not acknowledge. 
       FIG. 3  is a block diagram of a wireless audio system  300  implemented according to one embodiment of the present invention including a bridge configuration for wireless communications. The wireless audio system  300  includes the audio source  101  and the loudspeakers  103  and  105  in a similar manner as shown for the wireless audio system  100 . The transceivers  102 ,  104  and  106  are included in the respective components, but are not shown for purposes of simplicity of illustration. The secondary wireless link  109  is established between the audio source  101  and the loudspeaker  103  and the primary wireless link  107  is established between the loudspeakers  103  and  105  in substantially the same manner as previously described. In this case, however, the loudspeaker  103  is configured as a bridge or relaying audio information to the loudspeaker  105 , and the loudspeaker  105  does not receive audio information directly from the audio source  101 . 
     In this case, only the bridge loudspeaker  103  receives audio traffic over the secondary wireless link  109 . As shown, for example, a packet  301  is wirelessly transmitted from the audio source  101  to the bridge loudspeaker  103 , and the loudspeaker  105  does not receive the packet  301 . The wireless packet  301  includes stereo audio information including a first audio channel CH 1  and a second audio channel CH 2 . Either channel may be the left or right audio channel according to stereo audio. The bridge loudspeaker  103  extracts both the first and second audio channels CH 1  and CH 2  from the stereo stream, sending the first channel data CH 1  to its local audio buffer for playback and the second channel data CH 2  as a separate packet  303  over the primary wireless link  107  to the loudspeaker  105 . The bridge loudspeaker  103  buffers the first channel audio data CH 1  until it receives acknowledgement, such as ACK  305 , from the loudspeaker  105  via the primary wireless link  107 . Unacknowledged packets from the loudspeaker  105  are retransmitted by the loudspeaker  103  to the loudspeaker  105 . It is noted that either loudspeaker  103  or  105  may be assigned the role of bridge, in which either one processes the left channel and the other processes the right channel. 
     The specific configurations of the primary and secondary wireless links  107  and  109  depend upon the implementation or mode of operation. In one embodiment, the primary wireless link  107  may be implemented using a combination of Bluetooth and a proprietary protocol, and the secondary wireless link  109  is implemented using Bluetooth. The combination of Bluetooth and a proprietary protocol is useful in configurations in which the loudspeaker  105  operates in a snoop mode, such as the wireless audio system  200 , and timing of the acknowledge from loudspeaker  105  to loudspeaker  103  is particularly significant. In another embodiment, the primary and secondary wireless links  107  and  109  may both be implemented using Bluetooth, such as the wireless audio system  300  in which loudspeaker  103  operates as a bridge. In another embodiment, the primary wireless link  107  is implemented with a non-Bluetooth protocol, and the secondary wireless link  109  is implemented using Bluetooth. The non-Bluetooth protocol may be Wi-Fi® (IEEE 802.11) in a peer-to-peer mode (such as ad-hoc, Wi-Fi Direct®, DLS, etc.) or any other standard or proprietary protocol. In yet another embodiment, a non-Bluetooth protocol is used for both the primary and secondary wireless links  107  and  109 . In this case, any standard wireless protocol may be used on the secondary wireless link  109  as long as the audio information is transmitted as a stereo stream, i.e., first and second (or left and right) channels are sent together in the same stream, rather than separate streams for each channel. Other embodiments are envisioned. 
       FIG. 4  is a block diagram of a wireless audio system  400  implemented according to a more specific embodiment using Bluetooth stereo audio transported via the Advanced Audio Distribution Profile (A2DP) for wireless communications. The wireless audio system  400  includes the audio source  101  and the loudspeakers  103  and  105 . The transceivers  102 ,  104  and  106  are included in the respective components, but are not shown for purposes of simplicity of illustration. Bluetooth technology is widely deployed in portable media players and mobile phones and the like. It uses various profiles to define the functions that a device provides. Bluetooth stereo audio is transported via the A2DP profile, though the present invention is not limited to this profile, nor are they limited to the Bluetooth protocol, and may be applied to any stereo stream in which the first and second (or left and right) channels are transported together. The A2DP profile refers to the source of the audio data as SRC and the sink of the audio data as SNK. The descriptions that follow use the same terminology, with the addition of suffixes for the SNK to differentiate between the first loudspeaker and channel (SNK- 1 ) and the second loudspeaker and channel (SNK- 2 ). 
     In the wireless audio system  400 , the audio source  101  is configured as the source of the audio data SRC according to the A2DP profile, and the loudspeakers  103  and  105  are configured as sinks of the audio data, shown as SNK- 1  and SNK- 2 , respectively. The primary wireless link  107  is implemented as a combination of a first Bluetooth piconet PICONET 1  and a proprietary link referred to as ACK LINK. The loudspeaker  103 , configured as SNK- 1 , is the master (M) of PICONET 1 , while the loudspeaker  105 , configured as SNK- 2 , is a slave (S) of PICONET 1 . The ACK LINK is shown as a unidirectional mode from SNK- 2  to SNK- 1 , although a bidirectional configuration is also contemplated as further described below. The secondary wireless link  109  is implemented as a second Bluetooth piconet PICONET 2  according to the A2DP profile in which SRC is the master of PICONET 2  and the loudspeaker SNK- 1  is a slave. Also, the loudspeaker SNK- 2  operates as an observer (O) of PICONET 2  or listen only mode, shown as the path  203 . Since SNK- 1  and SNK- 2  participate in two piconets simultaneously, they are able to support scatternet operation. 
     In one embodiment, pairing between SNK- 1  and SNK- 2  on PICONET 1  may be pre-programmed at manufacture, such that they may be permanently paired to one another and have a communication link while powered up. In one embodiment, such pairing means that the two loudspeakers are able to communicate using a common protocol on a common frequency or set of frequencies using predetermined or otherwise known endpoint addresses. The communication between the paired devices may be secure and each device may be authenticated. 
     After the SNK- 1  connects to SRC  101  via the PICONET 2  (secondary wireless link  109 ), it uses PICONET 1  to pass information to SNK- 2  so that SNK- 2  may listen to the communications between SNK- 1  and SRC in a “promiscuous” or “listen-only” mode as previously described. As previously described for the wireless audio system  200 , SNK- 1  sends communication parameters (e.g., communication parameters  201 ) to SNK- 2  to enable SNK- 2  to observe communications on PICONET 2 . For Bluetooth, this information includes, but is not limited to, the Bluetooth Device Address (BD_ADDR) and native clock (CLKN) of SRC, the logical transport address (LT_ADDR) and clock offset of SNK- 1 , and encryption parameters for the link between SNK- 1  and SRC, such as the link key. Note that security is not compromised because these parameters can be sent over PICONET 1  while encryption is enabled. 
     Stereo audio traffic is transported from SRC  101  to SNK- 1  and SNK- 2  over the PICONET 2 . An A2DP stream typically carries compressed stereo audio using subband codec (SBC), Moving Picture Experts Group (MPEG) Layer III (MP3), Advanced Audio Coding (AAC), Adaptive Transform Acoustic Coding (ATRAC), or other standard codecs. However, it may also carry proprietary formats, including uncompressed audio. Regardless of the codec, stereo A2DP traffic may be transported in a single stream, i.e., the first and second (or left and right) channels are transported together. SNK- 1  extracts the first channel from the stereo audio stream for playback, and SNK- 2  extracts the second channel. 
     The first and second channel audio data is synchronized because both SNK- 1  and SNK- 2  are listening to the same audio stream at the same time. Therefore, audio buffers in SNK- 1  and SNK- 2  fill at the same rate. However, SRC  101 , SNK- 1  and SNK- 2  may have different audio frequency references, which may affect the rate at which the audio buffers are emptied. Therefore, SNK- 1  and SNK- 2  may lock their frequency references to SRC  101  so they play the data back at the same rate. In one embodiment, this may be accomplished through a control loop implemented at each loudspeaker  103  and  105 . In addition, PICONET 1  may be used to establish a common point in time at which both SNK- 1  and SNK- 2  begin audio playback. 
     The ACK LINK provides a channel for SNK- 2  to indicate to SNK- 1  when it has received a packet. SNK- 2  sends one or more short acknowledgement packets with good auto-correlation properties to SNK- 1  whenever it receives a packet from SRC  101 . SNK- 1  only needs to detect one of the acknowledgement packets. Having good auto-correlation properties minimizes false detections, while repeating the packet more than once increases the likelihood of ACK packet detection, and thereby minimizes the number of unnecessary audio packet retransmissions. The acknowledgement packet may be transmitted on the same channel during the idle period that follows the packet transmitted by SRC  101 , but before the start of the next slot. Therefore, SNK- 1  and SNK- 2  do not need to re-tune their radios, but rather SNK- 2  merely changes its radio mode from receive to transmit. In an alternative embodiment, the ACK LINK may operate on a different channel other than PICONET 2 . However, this may require both SNK- 1  and SNK- 2  to re-tune their radios. For Bluetooth, the minimum idle period between the end of any packet and the start of the next slot is well over 200 microseconds. A radio with fast Rx/Tx turnaround time has ample time to transmit one or more acknowledgements during this idle period without running into the next slot time. 
       FIG. 5  is a timing diagram illustrating operation of the wireless audio system  400  for five different cases  501 - 505  between two consecutive timing slots N and N+1. In each case operation or function of the SRC  101 , SNK- 2  and SNK- 1  are listed as transmission (TX) or reception (RX). An idle period  506  is shown during slot N for SNK- 2  to acknowledge reception of a wireless packet by sending an acknowledge (ACK) packet to the SNK- 1 . 
     Bluetooth slaves that receive a packet during slot N acknowledge that packet during slot N+1. SNK- 1  only provides a positive acknowledgement to the SRC  101  if it has received a packet and if it receives an acknowledgement from SNK- 2  indicating that SNK- 2  also successfully received the packet. Therefore, SRC  101  re-transmits any packet missed by either SNK- 2  or SNK- 1 . The retransmit filtering mechanism in Bluetooth allows SNK- 2  and SNK- 1  to filter out duplicate packets due to re-transmission. 
     In the first case  501 , SNK- 2  and SNK- 1  both successfully receive an audio information packet transmitted by the SRC  101  during slot N. During the idle period  506  of slot N, SNK- 2  transmits an acknowledge packet (TX ACK) indicating successful reception of the packet, which is successfully received by SNK- 1  (RX ACK). In the next slot N+1, SRC  101  receives a positive acknowledge packet from SNK- 1  indicating successful transmission of the audio information packet. 
     Operation of the second case  502  is similar in which SNK- 1  and SNK- 2  both successfully receive the audio information packet from the SRC  101  during slot N. However, SNK- 1  does not successfully receive the acknowledge packet from SNK- 2  (missing RX ACK). In the next slot N+1, SNK- 1  transmits a negative acknowledge packet (NACK) to the SRC  101  (or provides no response at all) indicating failure of reception of the packet (even though both loudspeakers may have successfully received the audio information packet from the audio source). In this case, the SRC  101  may re-transmit the audio information packet in a subsequent slot. 
     For the next case  503 , SNK- 1  successfully receives the audio information packet from the SRC  101 , but SNK- 2  does not, so that it does not send an acknowledge packet during the idle period  506 . Thus, although SNK- 1  successfully received the audio information packet, it does not receive an acknowledge packet from SNK- 2 . In the next slot N+1, SNK- 1  transmits a negative acknowledge packet (NACK) to the SRC  101  (or provides no response at all) indicating failure of reception of the packet. In this case, the SRC  101  may re-transmit the audio information packet in a subsequent slot. 
     For the next case  504 , SNK- 2  successfully receives the audio information packet from the SRC  101 , but SNK- 1  does not. SNK- 2  sends the acknowledge packet to SNK- 1 , but SNK- 1  does not receive it. In this case, SNK- 1  does not respond and thus does not send an ACK in the next slot N+1, which indicates failure of reception of the packet. In this case, the SRC  101  may re-transmit the audio information packet in a subsequent slot. 
     For the next case  505 , both SNK- 1  and SNK- 2  do not successfully receive the audio information packet from the SRC  101 . Thus there are no further communications during the idle period  506  and slot N+1 indicating failure of reception of the packet. In this case, the SRC  101  may re-transmit the audio information packet in a subsequent slot. 
       FIG. 6  is a block diagram of a wireless audio system  600  implemented in a substantially similar manner as the audio system  400 , except that ACK LINK is configured as a bidirectional link for increased robustness. In this case, each ACK packet sent from SNK- 2  to SNK- 1  may receive a response (ACKr) from SNK- 1 . Whenever SNK- 2  fails to see the response acknowledge from SNK- 1  it re-transmits the acknowledgement packet. This protocol may be generalized to allow N retransmissions of the ACK. The bi-directional link provides an added level of robustness to minimize the number of audio packet re-transmissions. It may require a radio with very fast Rx/Tx and Tx/Rx turnaround times to provide enough time for the ACK exchange and any retransmissions. 
       FIG. 7  is a timing diagram similar to that of  FIG. 5  illustrating operation of the wireless audio system  600  for five different cases  701 - 705  between the two consecutive timing slots N and N+1. In each case operation of the SRC  101 , SNK- 2  and SNK- 1  are listed as transmission (TX) or reception (RX) for the audio information packets, or as T or R for the acknowledge packets. The same idle period  506  is shown during slot N for SNK- 2  to acknowledge reception of a wireless packet. In the bidirectional ACK LINK case, SNK- 2  sends an ACK to SNK- 1 , and SNK- 1  sends a response ACK back to SNK- 2  via ACK LINK. SNK- 2  sends a second ACK in the event SNK- 1  does not send a response ACK to the first ACK transmitted by SNK- 2 , or if SNK- 1  sent a response ACK but the response ACK was not received by SNK- 2 . 
     For case  701 , SNK- 1  and SNK- 2  both successfully receive an audio information packet from the SRC  101 . During the idle period  506 , SNK- 1  receives an ACK from SNK- 2  over the ACK LINK, and SNK- 2  receives a response ACK from SNK- 1  over the ACK LINK. SNK- 1  sends a positive ACK response to SRC  101  during the next slot N+1 to acknowledge successful transmission of the audio information packet. 
     For case  702 , SNK- 1  and SNK- 2  both successfully receive an audio information packet from the SRC  101 . During the idle period  506 , SNK- 1  receives an ACK from SNK- 2  over the ACK LINK, but SNK- 2  misses the response ACK from SNK- 1 . SNK- 2  thus sends a second ACK since the first was not acknowledged. Yet since the first ACK was received, SNK- 1  sends a positive ACK response to SRC  101  during the next slot N+1 to acknowledge successful transmission of the audio information packet. 
     For case  703 , SNK- 1  and SNK- 2  both successfully receive an audio information packet from the SRC  101 . During the idle period  506 , SNK- 1  misses the first ACK from SNK- 2  and thus does not respond. SNK- 2  sends a second ACK which is received by SNK- 1 . Since the second ACK was received, SNK- 1  sends a positive ACK response to SRC  101  during the next slot N+1 to acknowledge successful transmission of the audio information packet. 
     For case  704 , SNK- 1  and SNK- 2  both successfully receive an audio information packet from the SRC  101 . During the idle period  506 , SNK- 1  misses both the first and second ACK from SNK- 2 . In this case, SNK- 1  sends a negative ACK response to SRC  101  during the next slot N+1 to acknowledge failure of reception of the audio information packet. Alternatively, SNK- 1  may provide no response back to the SRC  101  also indicating failure. In this case, the SRC  101  may re-transmit the audio information packet in a subsequent slot. 
     For case  705 , only SNK- 2  receives the audio information packet from the SRC  101  and sends both ACK packets to SNK- 1 . SNK- 1  does not respond to SNK- 2  and does not respond to the SRC  101 , indicating failure of reception of the packet. In this case, the SRC  101  may re-transmit the audio information packet in a subsequent slot. 
     For either wireless audio system  400  or  600 , once SNK- 2  has synchronized to SRC  101 , the traffic on PICONET 1  may be significantly reduced by transitioning to one of the low power Bluetooth states such as sniff, hold, or park. The low power state has the advantage of reducing power consumption, thereby extending battery life, while also maximizing the amount of time that SNK- 1  and SNK- 2  may participate in PICONET 2 . SNK- 2  and SNK- 1  remain connected in this low power state so that PICONET 1  may be used for link maintenance in the event that either one loses its link to SRC  101 , or if SRC  101  modifies any of the link parameters (e.g., disables encryption, changes link key, etc.). 
     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions and variations are possible and contemplated. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of the present invention without departing from the spirit and scope of the invention as defined by the appended claims.

Metadata:
Filing Date: 20110829
Publication Date: 20140701
Grant Date: 20140701
Priority Date: 20100902
Inventors: WATSON CLARKE S.
COOK BENJAMIN W.
BERNY AXEL D.
TRACHEWSKY JASON A.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W4/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2420/05", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L2001/0097", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W4/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L2001/0092", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W4/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L2001/0097", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R3/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R3/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L2001/0092", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L1/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R5/02", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 46727566