Abstract:
Apparatus configured to be implemented in a first wireless communication device, having corresponding non-transitory computer-readable media, comprise a memory configured to store a coexistence schedule, wherein the coexistence schedule defines WLAN intervals and non-WLAN intervals; a WLAN transceiver configured to transmit WLAN signals in an IBSS network; a non-WLAN transceiver configured to transmit wireless non-WLAN signals; and a coexistence circuit configured to allow the WLAN transceiver to transmit the WLAN signals in the IBSS network only during the WLAN intervals, wherein the coexistence circuit is further configured to allow the non-WLAN transceiver to transmit the wireless non-WLAN signals only during the non-WLAN intervals; and wherein the coexistence circuit is further configured to cause the WLAN transceiver to transmit one or more coexistence request messages, each indicating a duration of at least one of a respective one of the WLAN intervals, and a respective one of the non-WLAN intervals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This disclosure claims the benefit of U.S. Provisional Patent Application Ser. No. 61/481,079, filed on Apr. 29, 2011, entitled “WLAN/BT Coexistence Schemes for IBSS,” the disclosure thereof incorporated by reference herein in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to wireless communications. More particularly, the present disclosure relates to coexistence between wireless local-area networking (WLAN) signals and wireless non-WLAN signals. 
       BACKGROUND 
       [0003]    The popularity of various wireless networking technologies for handheld platforms has created a need to integrate multiple networking technologies on a single wireless communication device. Of these networking technologies, the two most widely used are wireless local-area networking (WLAN) and Bluetooth. Both of these technologies use the same un-licensed 2.4 GHz Industrial, Scientific and Medical (ISM) band. This situation poses a difficult problem for designing integrated circuits, external logic components, and wireless communication devices that allow these technologies to coexist. Because Bluetooth operates according to a known schedule, a multi-technology wireless communication device can schedule WLAN transmissions around the Bluetooth transmissions. However, because the Bluetooth schedule is not known to WLAN link partners, there are frequent collisions on the receive side. These collisions can reduce WLAN performance to one-half of baseline. 
       SUMMARY 
       [0004]    In general, in one aspect, an embodiment features an apparatus configured to be implemented in a first wireless communication device, wherein the apparatus comprises: a memory configured to store a coexistence schedule, wherein the coexistence schedule defines wireless local-area network (WLAN) intervals and non-WLAN intervals; a WLAN transceiver configured to transmit WLAN signals in an independent basic service set (IBSS) network; a non-WLAN transceiver configured to transmit wireless non-WLAN signals; and a coexistence circuit configured to allow the WLAN transceiver to transmit the WLAN signals in the IBSS network only during the WLAN intervals, wherein the coexistence circuit is further configured to allow the non-WLAN transceiver to transmit the wireless non-WLAN signals only during the non-WLAN intervals; and wherein the coexistence circuit is further configured to cause the WLAN transceiver to transmit one or more coexistence request messages, wherein each of the coexistence request messages indicates a duration of at least one of a respective one of the WLAN intervals, and a respective one of the non-WLAN intervals. 
         [0005]    Embodiments of the apparatus can include one or more of the following features. In some embodiments, the IBSS network comprises one or more second wireless communication devices; and responsive to the one or more coexistence request messages, the one or more second wireless communication devices transmit no WLAN signals during the respective non-WLAN intervals. In some embodiments, the non-WLAN signals comprise at least one of: Bluetooth signals; near field communication (NFC) signals; FM signals; and GPS signals. In some embodiments, at least one of the coexistence request messages comprises: a clear-to-send-to-self frame, wherein the clear-to-send-to-self frame includes a duration parameter, wherein the duration parameter indicates the duration of the respective one of the non-WLAN intervals. In some embodiments, at least one of the coexistence request messages comprises: a vendor-specific action frame, wherein the vendor-specific action frame includes a duration parameter, wherein the duration parameter indicates the duration of the respective one of the non-WLAN intervals. In some embodiments, at least one of the coexistence request messages comprises: a vendor-specific action frame, wherein the vendor-specific action frame includes a duration parameter, wherein the duration parameter indicates the duration of a period between a respective one of the non-WLAN intervals and another one of the non-WLAN intervals. Some embodiments comprise a wireless communication device comprising the apparatus. In some embodiments, the wireless communication device is implemented as one of: a mobile telephone; a personal digital assistant (PDA); a tablet computer; and a personal computer. In some embodiments, the wireless communication device is compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, 802.11w, 802.11aa, 802.11ac, 802.11ad, 802.11ae, 802.11af, 802.11ah, and 802.11ai. 
         [0006]    In general, in one aspect, an embodiment features non-transitory computer-readable media embodying instructions executable by a computer to perform functions comprising: storing a coexistence schedule, wherein the coexistence schedule defines wireless local-area network (WLAN) intervals and non-WLAN intervals; allowing a WLAN transceiver to transmit WLAN signals in an independent basic service set (IBSS) network only during the WLAN intervals; allowing a non-WLAN transceiver to transmit wireless non-WLAN signals only during the non-WLAN intervals; and causing the WLAN transceiver to transmit one or more coexistence request messages, wherein each of the coexistence request messages indicates a duration of at least one of a respective one of the WLAN intervals, and a respective one of the non-WLAN intervals. 
         [0007]    Embodiments of the non-transitory computer-readable media can include one or more of the following features. In some embodiments, the IBSS network comprises one or more second wireless communication devices; and responsive to the one or more coexistence request messages, the one or more second wireless communication devices transmit no WLAN signals during the respective non-WLAN intervals. In some embodiments, the non-WLAN signals comprise at least one of: Bluetooth signals; near field communication (NFC) signals; FM signals; and GPS signals. 
         [0008]    In general, in one aspect, an embodiment features an apparatus configured to be implemented in a first wireless communication device, wherein the apparatus comprises: a wireless local-area network (WLAN) transceiver configured to transmit WLAN signals in an independent basic service set (IBSS) network, wherein the IBSS network comprises one or more second wireless communication devices; and a coexistence circuit configured to allow the WLAN transceiver to transmit no WLAN signals during non-WLAN intervals responsive to the WLAN transceiver receiving coexistence request messages, wherein each coexistence request message indicates a duration of at least one of a respective one of the non-WLAN intervals, and a period between a respective one of the non-WLAN intervals and another one of the non-WLAN intervals. 
         [0009]    Embodiments of the apparatus can include one or more of the following features. In some embodiments, the non-WLAN signals comprise at least one of: Bluetooth signals; near field communication (NFC) signals; FM signals; and GPS signals. In some embodiments, at least one of the coexistence request messages comprises: a clear-to-send-to-self frame, wherein the clear-to-send-to-self frame includes a duration parameter, wherein the duration parameter indicates the duration of the respective one of the non-WLAN intervals. In some embodiments, at least one of the coexistence request messages comprises: a vendor-specific action frame, wherein the vendor-specific action frame includes a duration parameter, wherein the duration parameter indicates a duration of the respective one of the non-WLAN intervals. In some embodiments, at least one of the coexistence request messages comprises: a vendor-specific action frame, wherein the vendor-specific action frame includes a duration parameter, wherein the duration parameter indicates a duration of a period between a respective one of the non-WLAN intervals and another one of the non-WLAN intervals. Some embodiments comprise a wireless communication device comprising the apparatus. In some embodiments, the wireless communication device is implemented as one of: a mobile telephone; a personal digital assistant (PDA); a tablet computer; and a personal computer. In some embodiments, the wireless communication device is compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, 802.11w, 802.11aa, 802.11ac, 802.11ad, 802.11ae, 802.11af, 802.11ah, and 802.11ai. 
         [0010]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  shows elements of a multi-technology wireless communication system according to one embodiment. 
           [0012]      FIG. 2  shows detail of the multi-technology wireless communication device of  FIG. 1  according to one embodiment. 
           [0013]      FIG. 3  shows detail of a WLAN communication device of  FIG. 1  according to one embodiment. 
           [0014]      FIG. 4  illustrates a coexistence schedule according to one embodiment. 
           [0015]      FIG. 5  shows the format of the CTS-to-self frame according to the IEEE 802.11g standard. 
           [0016]      FIG. 6  shows the timing of the transmission of the CTS-to-self frames with reference to the coexistence schedule of  FIG. 4  according to one embodiment. 
           [0017]      FIG. 7  shows a process for the multi-technology wireless communication system of  FIG. 1  according to the embodiment of  FIG. 6 . 
           [0018]      FIG. 8  shows the format of the vendor-specific action frame according to the IEEE 802.11 standard. 
           [0019]      FIG. 9  shows the format of the vendor-specific information element according to the IEEE 802.11 standard. 
           [0020]      FIG. 10  shows the timing of the transmission of the vendor-specific action frames with reference to the coexistence schedule of  FIG. 4  according to an embodiment where the duration parameter indicates the duration of the following Bluetooth interval. 
           [0021]      FIG. 11  shows a process for the multi-technology wireless communication system of  FIG. 1  according to the embodiment of  FIG. 10 . 
           [0022]      FIG. 12  shows the timing of the transmission of the vendor-specific action frames with reference to the coexistence schedule of  FIG. 4  according to an embodiment where the duration parameter indicates the duration of the current WLAN interval. 
           [0023]      FIG. 13  shows the format of the Unscheduled Automatic Power Save Delivery (UAPSD) information element according to the IEEE 802.11 standard. 
           [0024]      FIG. 14  shows a process for the multi-technology wireless communication system of  FIG. 1  according to the embodiment of  FIG. 13 . 
       
    
    
       [0025]    The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
       DETAILED DESCRIPTION 
       [0026]    Embodiments of the present disclosure provide coexistence for multi-technology wireless communication devices in an IEEE 802.11 independent basic service set (IBSS) networks. In particular, in one aspect, the disclosed embodiments describe coexistence for wireless local-area networking (WLAN) and Bluetooth technologies. However, while the disclosed embodiments are described in terms of WLAN and Bluetooth technologies, the disclosed techniques are applicable to other wireless technologies as well. The wireless technologies can include wireless non-WLAN signals other than Bluetooth. For example, the wireless non-WLAN signals can include near field communication (NFC) signals, FM signals, GPS signals, other ISM band signals, and the like. 
         [0027]    According to the described embodiments, a multi-technology wireless communication device operates in an IBSS. The wireless technologies include wireless local-area network (WLAN) and wireless non-WLAN technologies. For example, the WLAN technology can be based on the IEEE 802.11 standard, and the non-WLAN technology can include Bluetooth signals, near field communication (NFC) signals, FM signals, GPS signals, other ISM band signals, and the like. The multi-technology wireless communication device includes a WLAN transceiver configured to transmit WLAN signals during WLAN intervals, and a non-WLAN transceiver configured to transmit wireless non-WLAN signals during non-WLAN intervals. 
         [0028]    In accordance with one embodiment, a WLAN transceiver transmits a coexistence request message for each of the non-WLAN intervals. As used herein, the term the term “message” generally refers to a wireless electronic signal representing a digital message. Each coexistence request message indicates a duration of a respective one of the WLAN intervals, or a duration of a respective one of the non-WLAN intervals. In response to each coexistence request message, the other WLAN devices in the IBSS transmit no WLAN signals during the respective non-WLAN interval. The result is reduction or elimination of interference between the WLAN signals and the wireless non-WLAN signals. 
         [0029]      FIG. 1  shows elements of a multi-technology wireless communication system  100  according to one embodiment. Although in the described embodiments the elements of multi-technology wireless communication system  100  are presented in one arrangement, other embodiments may feature other arrangements. For example, elements of multi-technology wireless communication system  100  can be implemented in hardware, software, or combinations thereof. 
         [0030]    Referring to  FIG. 1 , multi-technology wireless communication system  100  includes a multi-technology wireless communication device  102 , one or more WLAN communication devices  104 A-N, and a Bluetooth communication device  106 . Multi-technology wireless communication device  102  can be implemented as any wireless communication device capable of performing the functions described herein. For example, multi-technology wireless communication device  102  can be implemented as a mobile telephone such as a smartphone or feature phone, a personal digital assistant (PDA), a tablet computer, a personal computer, or the like. 
         [0031]    WLAN communication devices  104  can be implemented as any wireless communication devices capable of performing the functions described herein. For example, each WLAN communication device  104  can be implemented as a mobile telephone such as a smartphone or feature phone, a personal digital assistant (PDA), a tablet computer, a personal computer, or the like. In addition, each WLAN communication device  104  can be implemented as a multi-technology wireless communication device  102 , but this is not required. 
         [0032]    Multi-technology wireless communication device  102  and WLAN communication devices  104  form an independent basic service set (IBSS). That is, multi-technology wireless communication device  102  and WLAN communication devices  104  communicate over an ad hoc WLAN  108 . In some embodiments, ad hoc WLAN  108  is compliant with all or part of IEEE standard 802.11, including draft and approved amendments such as 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, 802.11k, 802.11n, 802.11v, 802.11w, 802.11aa, 802.11ac, 802.11ad, 802.11ae, 802.11af, 802.11ah, and 802.11ai. Multi-technology wireless communication device  102  communicates with Bluetooth communication device  106  over a wireless Bluetooth link  110 . 
         [0033]      FIG. 2  shows detail of multi-technology wireless communication device  102  of  FIG. 1  according to one embodiment. Although in the described embodiments the elements of multi-technology wireless communication device  102  are presented in one arrangement, other embodiments may feature other arrangements. For example, elements of multi-technology wireless communication device  102  can be implemented in hardware, software, or combinations thereof. 
         [0034]    Referring to  FIG. 2 , multi-technology wireless communication device  102  includes a WLAN transceiver  202 , a Bluetooth transceiver  204 , a coexistence circuit  206 , a memory  212 , and a timer  216 . Coexistence circuit  206  can be implemented as a processor. WLAN transceiver  202 , Bluetooth transceiver  204 , coexistence circuit  206 , memory  212 , and timer  216  can be fabricated as one or more integrated circuits. 
         [0035]    WLAN transceiver  202  transmits and receives (or transceives) WLAN signals  208  over ad hoc WLAN  108 . Bluetooth transceiver  204  transceives Bluetooth signals  210  over Bluetooth link  110 . Coexistence circuit  206  schedules WLAN transceiver  202  and Bluetooth transceiver  204  to prevent interference between WLAN signals  208  and Bluetooth signals  210  transmitted by multi-technology wireless communication device  102 . Coexistence circuit  206  also causes WLAN transceiver  202  to transmit coexistence request messages over ad hoc WLAN  108  to prevent interference between Bluetooth signals  210  and WLAN signals  208  transmitted by WLAN communication devices  104 . Memory  212  stores a coexistence schedule  214 . 
         [0036]      FIG. 3  shows detail of a WLAN communication device  104  of  FIG. 1  according to one embodiment. Although in the described embodiments the elements of WLAN communication device  104  are presented in one arrangement, other embodiments may feature other arrangements. For example, elements of WLAN communication device  104  can be implemented in hardware, software, or combinations thereof. 
         [0037]    Referring to  FIG. 3 , WLAN communication device  104  includes a wireless local-area network (WLAN) transceiver  302 , a coexistence circuit  306 , and a timer  316 . Coexistence circuit  306  can be implemented as a processor. WLAN transceiver  302 , coexistence circuit  306 , and timer  316  can be fabricated as one or more integrated circuits. 
         [0038]    WLAN transceiver  302  transceives WLAN signals  208  over ad hoc WLAN  108 . Coexistence circuit  306  schedules its WLAN transceiver  302  in accordance with the coexistence request messages transmitted by multi-technology wireless communication device  102  to prevent interference between WLAN signals  208  transmitted by WLAN communication devices  104  and Bluetooth signals  210 . 
         [0039]    Multi-technology wireless communication device  102  communicates with Bluetooth communication device  106  over wireless Bluetooth link  110  according to coexistence schedule  214  and timer  216 .  FIG. 4  illustrates a coexistence schedule  214  according to one embodiment. Coexistence schedule  214  consists of Bluetooth intervals  402  and WLAN intervals  404 . In general, the schedule is periodic, so that all Bluetooth intervals  402  have the same duration Tbt, and so that all WLAN intervals  404  have the same duration Twlan. However, this periodicity is not required. In general, the duration Twlan of WLAN intervals  404  is greater than the duration Tbt of Bluetooth intervals  402 , but this is not required. 
         [0040]    Coexistence schedule  214  is known to multi-technology wireless communication device  102 . Therefore coexistence circuit  206  can control the transmissions of WLAN transceiver  202  and Bluetooth transceiver  204  deterministically according to coexistence schedule  214  and timer  216  so as to avoid interference between the transmissions. In particular, coexistence circuit  206  allows WLAN transceiver  202  to transmit WLAN signals  208  only during WLAN intervals  404 , and allows Bluetooth transceiver  204  to transmit Bluetooth signals  210  only during Bluetooth intervals  402 . 
         [0041]    However, coexistence schedule  214  is not known to WLAN communication devices  104 . To prevent interference between the transmissions of WLAN communication devices  104  and Bluetooth signals  210 , coexistence circuit  206  of multi-technology wireless communication device  102  causes WLAN transceiver  202  to transmit coexistence request messages. Each coexistence request message indicates a duration of one of the WLAN intervals  404 , or a duration of one of the Bluetooth intervals  402 . At each WLAN communication device  104 , responsive to the WLAN transceiver  302  receiving a coexistence request message, coexistence circuit  306  allows the WLAN transceiver  302  to transmit no WLAN signals  208  during one of the Bluetooth intervals  402 . Bluetooth communication device  106  has knowledge of coexistence schedule  214 , and so transmits Bluetooth signals  210  only during Bluetooth intervals  402 . 
         [0042]    In some embodiments, the coexistence request message is implemented as a clear-to-send-to-self (CTS-to-self) frame.  FIG. 5  shows the format of the CTS-to-self frame according to the IEEE 802.11g standard. The CTS-to-self frame includes a two-octet Frame Control field, a two-octet Duration field, a six-octet Receiver Address (RA) field, and a four-octet Frame Check Sequence (FCS) field. The RA field contains the MAC address of multi-technology wireless communication device  102 . The duration field contains a duration parameter that indicates the duration of the next Bluetooth interval  402 . 
         [0043]      FIG. 6  shows the timing of the transmission of the CTS-to-self frames with reference to coexistence schedule  214  of  FIG. 4  according to one embodiment. Referring to  FIG. 6 , coexistence circuit  206  of multi-technology wireless communication device  102  causes WLAN transceiver  202  to transmit a CTS-to-self frame  602  just prior to the start of each Bluetooth interval  402 . The duration parameter of each CTS-to-self frame  602  indicates the duration of the subsequent Bluetooth interval  402 . WLAN transceivers  302  of WLAN communication devices  104  receive CTS-to-self frames  602 . 
         [0044]    At each WLAN communication device  104 , responsive to the WLAN transceiver  302  receiving a CTS-to-self frame  602 , coexistence circuit  306  allows the WLAN transceiver  302  to transmit no WLAN signals  208  for the interval specified by the duration parameter in that CTS-to-self frame  602 . That is, coexistence circuit  306  allows the WLAN transceiver  302  to transmit no WLAN signals  208  during the subsequent Bluetooth interval  402 . 
         [0045]      FIG. 7  shows a process  700  for multi-technology wireless communication system  100  of  FIG. 1  according to the embodiment of  FIG. 6 . Although in the described embodiments the elements of process  700  are presented in one arrangement, other embodiments may feature other arrangements. For example, in various embodiments, some or all of the elements of process  700  can be executed in a different order, concurrently, and the like. Also some elements of process  700  may not be performed, and may not be executed immediately after each other.  FIG. 7  is arranged in two columns, with processes of multi-technology wireless communication device  102  shown in the left-hand column, and with processes of a WLAN communication device  104  shown in the right-hand column. 
         [0046]    Referring to  FIG. 7 , at  702  and  704 , a WLAN interval  404  begins. During WLAN interval  404 , WLAN transmission is allowed for both multi-technology wireless communication device  102  and WLAN communication device  104 . At  706 , multi-technology wireless communication device  102  determines when the WLAN interval  404  is ending. In particular, coexistence circuit  206  of multi-technology wireless communication device  102  consults the coexistence schedule  214  stored in memory  212  and timer  216 . At  708 , just prior to the end of the WLAN interval  404 , multi-technology wireless communication device  102  transmits a CTS-to-self frame  602  that includes the duration of the following Bluetooth interval  402 . Then the Bluetooth interval  402  begins. Coexistence circuit  206  does not allow WLAN transmission by multi-technology wireless communication device  102  during Bluetooth interval  402 . 
         [0047]    At  710 , WLAN communication device  104  receives the CTS-to-self frame  602 , and gets the duration of the Bluetooth interval  402  from that frame  602 . Bluetooth interval  402  begins. Coexistence circuit  306  does not allow WLAN transmission by WLAN communication device  104  during Bluetooth interval  402 . 
         [0048]    At  712 , multi-technology wireless communication device  102  determines when the Bluetooth interval  402  has ended. In particular, coexistence circuit  206  of multi-technology wireless communication device  102  consults timer  216  and the coexistence schedule  214  stored in memory  212 . When the Bluetooth interval  402  ends, the next WLAN interval begins at  702 . Coexistence circuit  206  allows WLAN transmission by multi-technology wireless communication device  102  during WLAN interval  404 . 
         [0049]    At  714 , WLAN communication device  104  determines when the peer&#39;s Bluetooth interval  402  has ended (that is, when the Bluetooth interval  402  for multi-technology wireless communication device  102  has ended). In particular, coexistence circuit  306  of WLAN communication device  104  uses timer  316  and the duration from the CTS-to-self frame  602  to determine when the peer&#39;s Bluetooth interval  402  has ended. When the peer&#39;s Bluetooth interval  402  ends, the next WLAN interval begins at  704 . Coexistence circuit  306  allows WLAN transmission by WLAN communication device  104  during WLAN interval  404 . 
         [0050]    In some embodiments, the coexistence request message is implemented as a vendor-specific action frame, where the vendor-specific action frame includes a duration parameter. The coexistence request message can also be sent using beacons and probe request/response messages when possible. In some embodiments, the duration parameter indicates the duration of the following Bluetooth interval  402 . In other embodiments, the duration parameter indicates the duration of the current WLAN interval  404 . 
         [0051]      FIG. 8  shows the format of the vendor-specific action frame according to the IEEE 802.11 standard. Referring to  FIG. 8 , the vendor-specific action frame includes a one-octet Category field, a three-octet OUI field, and a variable-length Vendor-Specific Content field. The Category field is set to the value indicating the vendor-specific category. The OUI field contains a public OUI, assigned by the IEEE, of the entity that has defined the content of the particular vendor-specific action. The Vendor-Specific Content field contains one or more vendor-specific fields. In the described embodiment, the Vendor-Specific Content field contains the vendor-specific information element. 
         [0052]    In some embodiments, the vendor-specific action frame includes a vendor-specific information element that includes the duration parameter.  FIG. 9  shows the format of the vendor-specific information element according to the IEEE 802.11 standard. Referring to  FIG. 9 , the vendor-specific information element includes a one-octet Element ID field, a one-octet Length field, a three-octet OUI field, and a variable-length Vendor-Specific Content field. The Element ID field indicates the information element is a vendor-specific information element. The OUI field contains a public OUI assigned by the IEEE. The Vendor-Specific Content field contains one or more vendor-specific fields. In the described embodiment, the Vendor-Specific Content field contains the duration parameter. In other embodiments, the vendor-specific action frame includes a WiFi Direct Notice of Absence element that includes the duration parameter. 
         [0053]      FIG. 10  shows the timing of the transmission of the vendor-specific action frames with reference to coexistence schedule  214  of  FIG. 4  according to an embodiment where the duration parameter indicates the duration of the following Bluetooth interval  402 . Referring to  FIG. 10 , coexistence circuit  206  of multi-technology wireless communication device  102  causes WLAN transceiver  202  to transmit a vendor-specific action frame  1002  just prior to the start of each Bluetooth interval  402 . The duration parameter of each vendor-specific action frame  1002  indicates the duration of the subsequent Bluetooth interval  402 . WLAN transceivers  302  of WLAN communication devices  104  receive the vendor-specific action frames  1002 . 
         [0054]    At each WLAN communication device  104 , responsive to the WLAN transceiver  302  receiving a vendor-specific action frame  1002 , coexistence circuit  306  allows the WLAN transceiver  302  to transmit no WLAN signals  208  for the interval specified by the duration parameter in that vendor-specific action frame  1002 . That is, coexistence circuit  306  allows the WLAN transceiver  302  to transmit no WLAN signals  208  during the subsequent Bluetooth interval  402 . 
         [0055]      FIG. 11  shows a process  1100  for multi-technology wireless communication system  100  of  FIG. 1  according to the embodiment of  FIG. 10 . Although in the described embodiments the elements of process  1100  are presented in one arrangement, other embodiments may feature other arrangements. For example, in various embodiments, some or all of the elements of process  1100  can be executed in a different order, concurrently, and the like. Also some elements of process  1100  may not be performed, and may not be executed immediately after each other.  FIG. 11  is arranged in two columns, with processes of multi-technology wireless communication device  102  shown in the left-hand column, and with processes of a WLAN communication device  104  shown in the right-hand column. 
         [0056]    Referring to  FIG. 11 , at  1102  and  1104 , a WLAN interval  404  begins. During WLAN interval  404 , WLAN transmission is allowed for both multi-technology wireless communication device  102  and WLAN communication device  104 . At  1106 , multi-technology wireless communication device  102  determines when the WLAN interval  404  is ending. In particular, coexistence circuit  206  of multi-technology wireless communication device  102  consults the coexistence schedule  214  stored in memory  212  and timer  216 . At  1108 , prior to the end of the WLAN interval  404 , multi-technology wireless communication device  102  transmits a vendor-specific action frame  1002  that includes the duration of the following Bluetooth interval  402 . Then the Bluetooth interval  402  begins. Coexistence circuit  206  does not allow WLAN transmission by multi-technology wireless communication device  102  during Bluetooth interval  402 . 
         [0057]    At  1110 , WLAN communication device  104  receives the vendor-specific action frame  1002 , and gets the duration of the Bluetooth interval  402  from that frame  1002 . Bluetooth interval  402  begins. Coexistence circuit  306  does not allow WLAN transmission by WLAN communication device  104  during Bluetooth interval  402 . 
         [0058]    At  1112 , multi-technology wireless communication device  102  determines when the Bluetooth interval  402  has ended. In particular, coexistence circuit  206  of multi-technology wireless communication device  102  consults timer  216  and the coexistence schedule  214  stored in memory  212 . When the Bluetooth interval  402  ends, the next WLAN interval begins at  1102 . Coexistence circuit  206  allows WLAN transmission by multi-technology wireless communication device  102  during WLAN intervals  404 . 
         [0059]    At  1114 , WLAN communication device  104  determines when the peer&#39;s Bluetooth interval  402  has ended (that is, when the Bluetooth interval  402  for multi-technology wireless communication device  102  has ended). In particular, coexistence circuit  306  of WLAN communication device  104  uses timer  316  and the duration from the vendor-specific action frame  1002  to determine when the peer&#39;s Bluetooth interval  402  has ended. When the peer&#39;s Bluetooth interval  402  ends, the next WLAN interval  404  begins at  1104 . Coexistence circuit  306  allows WLAN transmission by WLAN communication device  104  during WLAN intervals  404 . 
         [0060]      FIG. 12  shows the timing of the transmission of the vendor-specific action frames with reference to coexistence schedule  214  of  FIG. 4  according to an embodiment where the duration parameter indicates the duration of the current WLAN interval  404 . Referring to  FIG. 12 , coexistence circuit  206  of multi-technology wireless communication device  102  causes WLAN transceiver  202  to transmit a vendor-specific action frame  1202  at the start of each WLAN interval  404 . The duration parameter of each vendor-specific action frame  1202  indicates the duration of that WLAN interval  404 . WLAN transceivers  302  of WLAN communication devices  104  receive vendor-specific action frames  1202 . 
         [0061]    At each WLAN communication device  104 , responsive to the WLAN transceiver  302  receiving a vendor-specific action frame  1202 , coexistence circuit  306  allows the WLAN transceiver  302  to transmit WLAN signals  208  only during the interval specified by the duration parameter in that vendor-specific action frame  1202 . That is, coexistence circuit  306  allows the WLAN transceiver  302  to transmit WLAN signals  208  only during that WLAN interval  404 . 
         [0062]    In some embodiments, the vendor-specific action frame includes an Unscheduled Automatic Power Save Delivery (UAPSD) information element that includes the duration parameter.  FIG. 13  shows the format of the UAPSD information element according to the IEEE 802.11 standard. Referring to  FIG. 13 , the UAPSD information element includes a one-octet Element ID field, a one-octet Length field, an eight-octet TSF 0 Offset field, a four-octet Interval/Duration field, and a variable-length Optional Subelements field. 
         [0063]    The Element ID field contains a predetermined value that identifies the information element as being the UAPSD information element. The value of the Length field is 12 plus the length of any additional subelements present. The TSF 0 Offset field is not required in this embodiment. The Interval/Duration field contains the duration parameter. The Optional Subelements field format contains zero or more subelements. 
         [0064]      FIG. 14  shows a process  1400  for multi-technology wireless communication system  100  of  FIG. 1  according to the embodiment of  FIG. 13 . Although in the described embodiments the elements of process  1400  are presented in one arrangement, other embodiments may feature other arrangements. For example, in various embodiments, some or all of the elements of process  1400  can be executed in a different order, concurrently, and the like. Also some elements of process  1400  may not be performed, and may not be executed immediately after each other.  FIG. 14  is arranged in two columns, with processes of multi-technology wireless communication device  102  shown in the left-hand column, and with processes of a WLAN communication device  104  shown in the right-hand column. 
         [0065]    Referring to  FIG. 14 , at  1402  and  1404 , a Bluetooth interval  402  begins for multi-technology wireless communication device  102 . During Bluetooth interval  402 , WLAN transmission is not allowed for either multi-technology wireless communication device  102  or WLAN communication device  104 . At  1406 , multi-technology wireless communication device  102  determines when the Bluetooth interval  402  has ended. In particular, coexistence circuit  206  of multi-technology wireless communication device  102  consults the coexistence schedule  214  stored in memory  212  and timer  216 . At  1408 , after the end of the Bluetooth interval  402 , multi-technology wireless communication device  102  transmits a vendor-specific action frame  1302  that includes the duration of the current WLAN interval  404 . Coexistence circuit  206  allows WLAN transmission by multi-technology wireless communication device  102  only during WLAN intervals  404 . 
         [0066]    At  1410 , WLAN communication device  104  receives the vendor-specific action frame  1302 , and gets the duration of the WLAN interval  404  from that frame  1302 . WLAN interval  404  has begun. Coexistence circuit  306  allows WLAN transmission by WLAN communication device  104  only during WLAN intervals  404 . 
         [0067]    At  1412 , multi-technology wireless communication device  102  determines when the WLAN interval  404  has ended. In particular, coexistence circuit  206  of multi-technology wireless communication device  102  consults timer  216  and the coexistence schedule  214  stored in memory  212 . When the WLAN interval  404  ends, the next Bluetooth interval begins at  1402 . Coexistence circuit  206  does not allow WLAN transmission by multi-technology wireless communication device  102  during Bluetooth intervals  402 . 
         [0068]    At  1414 , WLAN communication device  104  determines when the WLAN interval  404  has ended. In particular, coexistence circuit  306  of WLAN communication device  104  uses timer  316  and the duration from the vendor-specific action frame  1302  to determine when the WLAN interval  404  has ended. When the WLAN interval  404  ends, the next Bluetooth interval  402  begins at  1404 . Coexistence circuit  306  doe not allow WLAN transmission by WLAN communication device  104  during Bluetooth intervals  402 . 
         [0069]    Multiple embodiments have been described using CTS-to-self frames and vendor-specific action frames. In some devices, only one of these embodiments are implemented. In other devices, two or more of these embodiments are implemented, and are selected dynamically according to factors such as network conditions. For example, embodiments that employ CTS-to-self frames can be selected when the IBSS includes only one multi-technology wireless communication device  102  and one WLAN communication device  104  and no other IBSS is nearby. As another example, embodiments that employ vendor-specific action frames can be selected when the IBSS includes multiple WLAN communication devices  104 . 
         [0070]    Various embodiments of the present disclosure can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations thereof. Embodiments of the present disclosure can be implemented in a computer program product tangibly embodied in a computer-readable storage device for execution by a programmable processor. The described processes can be performed by a programmable processor executing a program of instructions to perform functions by operating on input data and generating output. Embodiments of the present disclosure can be implemented in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, processors receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer includes one or more mass storage devices for storing data files. Such devices include magnetic disks, such as internal hard disks and removable disks, magneto-optical disks; optical disks, and solid-state disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
         [0071]    A number of implementations have been described. Nevertheless, various modifications may be made without departing from the scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.