PATENT DOCUMENT

Publication Number: US-10129165-B2
Application Number: US-201715445853-A
Country: US
Kind Code: B2

Title: Electronics devices having antenna diversity capabilities

Abstract:
An electronic device may include first and second antennas and a Bluetooth transceiver. Control circuitry may perform Bluetooth antenna diversity operations by coupling the Bluetooth transceiver to a selected one of the first and second antennas at a given time. The Bluetooth transceiver may transmit a first Bluetooth data packet and may determine whether a scheduled response packet associated with the first packet has been received over the first antenna during a predetermined time period. In response to determining that the Bluetooth transceiver has failed to receive the scheduled response packet during the first predetermined time period, the Bluetooth transceiver may re-transmit the first packet using the second antenna. This may serve to reduce the error rate of the transmitted Bluetooth data over time relative to scenarios where a single antenna is used, without requiring resource-intensive sensor circuitry to actively monitor the performance of the antennas.

Claims:
What is claimed is: 
     
       1. A method of operating an electronic device having a Wireless Personal Area Network (WPAN) transceiver, control circuitry, and first and second antennas, the method comprising:
 with the WPAN transceiver, transmitting a first WPAN packet from a sequence of WPAN packets over the first antenna; 
 with the control circuitry, determining whether the WPAN transceiver has received a second WPAN packet over the first antenna during a predetermined time period following transmission of the first WPAN packet; and 
 with the WPAN transceiver, in response to determining that the WPAN transceiver has failed to receive the second WPAN packet during the predetermined time period, transmitting the first WPAN packet over the second antenna. 
 
     
     
       2. The method defined in  claim 1 , wherein the sequence of WPAN packets comprises a third WPAN packet subsequent to the first WPAN packet in the sequence, the method further comprising:
 with the WPAN transceiver, in response to determining that the WPAN transceiver has received the second WPAN packet during the predetermined time period, transmitting the third WPAN packet over the first antenna. 
 
     
     
       3. The method defined in  claim 2 , wherein the WPAN transceiver comprises a Bluetooth transceiver, the first WPAN packet comprises a first Bluetooth data packet, the third WPAN packet comprises a third Bluetooth data packet, and the second WPAN packet comprises an acknowledge (ACK) packet generated by an external device in response to receiving the first Bluetooth data packet transmitted by the first antenna. 
     
     
       4. The method defined in  claim 1 , further comprising:
 with the control circuitry, subsequent to transmitting the first WPAN packet over the second antenna, determining whether the WPAN transceiver has received the second WPAN packet over the second antenna during an additional predetermined time period following transmission of the first WPAN packet over the second antenna. 
 
     
     
       5. The method defined in  claim 4  wherein the sequence of WPAN packets comprises a third WPAN packet subsequent to the first WPAN data packet in the sequence, the method further comprising:
 with the WPAN transceiver, in response to determining that the WPAN transceiver has received the second WPAN packet during the additional predetermined time period, transmitting the third WPAN packet over the second antenna. 
 
     
     
       6. The method defined in  claim 4 , wherein the sequence of WPAN packets comprises a third WPAN packet subsequent to the first WPAN packet in the sequence, the method further comprising:
 with the WPAN transceiver, in response to determining that the WPAN transceiver has received the second WPAN packet during the additional predetermined time period, transmitting the third WPAN packet over the first antenna. 
 
     
     
       7. The method defined in  claim 4 , wherein the sequence of WPAN packets comprises a third WPAN packet subsequent to the first WPAN packet in the sequence, the method further comprising:
 with the control circuitry, in response to determining that the WPAN transceiver has failed to receive the second WPAN packet during the additional time period, comparing a number of re-transmission attempts for the first WPAN packet to a threshold value; 
 with the WPAN transceiver, in response to determining that the number of re-transmission attempts is less than the threshold value, re-transmitting the first WPAN packet using the first antenna; and 
 with the WPAN transceiver, in response to determining that the number of re-transmission attempts is greater than or equal to the threshold value, transmitting the third WPAN data packet using a selected one of the first and second antennas. 
 
     
     
       8. The method defined in  claim 1 , wherein the WPAN transceiver comprises a Bluetooth transceiver, transmitting the first WPAN packet over the first antenna comprises transmitting a first Bluetooth data packet over the first antenna during a first set of consecutive Bluetooth protocol timeslots, and the predetermined time period comprises a second set of consecutive Bluetooth protocol timeslots subsequent to the first set of consecutive Bluetooth protocol timeslots. 
     
     
       9. An electronic device, comprising:
 first and second antennas; 
 Wireless Personal Area Network (WPAN) transceiver circuitry; 
 a switch having a first switch port coupled to the first antenna, a second switch port coupled to the second antenna, and a third switch port coupled to the WPAN transceiver circuitry, wherein the WPAN transceiver circuitry is configured to transmit a WPAN data packet over the second antenna while the second switch port is shorted to the third switch port; and 
 control circuitry, wherein the control circuitry is configured to control the switch to short the first switch port to the third switch port and the WPAN transceiver circuitry is configured to re-transmit the WPAN data packet over the first antenna in response to reception of a non-acknowledge (NACK) packet corresponding to the WPAN data packet over the second antenna while the second switch port is shorted to the third switch port. 
 
     
     
       10. The electronic device defined in  claim 9 , further comprising:
 Wireless Local Area Network (WLAN) transceiver circuitry, wherein the WLAN transceiver circuitry is configured to transmit WLAN signals over the first and second antennas. 
 
     
     
       11. The electronic device defined in  claim 10 , wherein the WLAN transceiver circuitry comprises a first WLAN transceiver that is configured to transmit the WLAN signals over the first antenna and a second WLAN transceiver that is configured to transmit the WLAN signals over the second antenna, the electronic device further comprising:
 an additional switch having a fourth switch port coupled to the second WLAN transceiver, a fifth switch port coupled to the WPAN transceiver, and a sixth switch port coupled to third switch port of the switch. 
 
     
     
       12. The electronic device defined in  claim 11 , wherein the control circuitry is configured to control the switch to short the second switch port to the third switch port and is configured to control the additional switch to short the fourth switch port to the sixth switch port while the second WLAN transceiver transmits the WLAN signals over the second antenna. 
     
     
       13. The electronic device defined in  claim 12 , wherein the WPAN transceiver circuitry comprises a Bluetooth transceiver and the WPAN data packet comprises a Bluetooth data packet. 
     
     
       14. The electronic device defined in  claim 13 , wherein the first WLAN transceiver, the second WLAN transceiver, the Bluetooth transceiver, and the additional switch are formed on a shared integrated circuit having first and second ports, the first port couples the first WLAN transceiver to the first antenna, and the second port couples the additional switch to the second antenna through the switch. 
     
     
       15. The electronic device defined in  claim 13 , further comprising:
 a conductive electronic device housing having opposing first and second ends; 
 an ear speaker at the first end; and 
 a microphone at the second end, wherein the first antenna is formed at the first end and the second antenna is formed at the second end. 
 
     
     
       16. A method of operating an electronic device having a Bluetooth transceiver and first and second antennas coupled to the Bluetooth transceiver, the method comprising:
 with the Bluetooth transceiver, transmitting a first Bluetooth data packet from a sequence of Bluetooth data packets over the first antenna during a first transmit period; 
 with the Bluetooth transceiver, in response to reception of an acknowledge (ACK) packet corresponding to the first Bluetooth data packet over the first antenna during a first receive period, transmitting a second Bluetooth data packet from the sequence over the first antenna during a second transmit period, wherein the first receive period is subsequent to the first transmit period and the second transmit period is subsequent to the first receive period; and 
 with the Bluetooth transceiver, in response to failing to receive the ACK packet over the first antenna during the first receive period, transmitting the first Bluetooth data packet over the second antenna during the second transmit period. 
 
     
     
       17. The method defined in  claim 16 , further comprising:
 with the Bluetooth transceiver, in response to reception of the ACK packet over the second antenna during a second receive period subsequent to the second transmit period, transmitting the second Bluetooth data packet over a selected one of the first and second antennas during a third transmit period subsequent to the second receive period; and 
 with the Bluetooth transceiver, in response to reception of an additional ACK packet corresponding to the second Bluetooth data packet over the selected one of the first and second antennas during a third receive period, transmitting a third Bluetooth data packet from the sequence of Bluetooth data packets over the selected one of the first and second antennas during a fourth transmit period subsequent to the third receive period, wherein the third receive period is subsequent to the third transmit period. 
 
     
     
       18. The method defined in  claim 17 , further comprising:
 with the Bluetooth transceiver, in response to failing to receive the ACK packet over the second antenna during the second receive period, transmitting the third Bluetooth data packet during the third transmit period. 
 
     
     
       19. The method defined in  claim 17 , further comprising:
 with the Bluetooth transceiver, in response to failing to receive the ACK packet over the second antenna during the second receive period, re-transmitting the second Bluetooth data packet using the first antenna during the third transmit period and waiting for reception of the additional ACK packet by the first antenna during the third receive period. 
 
     
     
       20. The method defined in  claim 16 , wherein the electronic device further comprises Wireless Local Area Network (WLAN) transceiver circuitry and switching circuitry, the method further comprising:
 with the WLAN transceiver circuitry, transmitting WLAN signals over the first and second antennas during a set of time periods that are different from the first and second transmit periods and the first receive period; and 
 with the switching circuitry, decoupling the Bluetooth transceiver from the first and second antennas during the set of time periods.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with wireless communications circuitry. 
     Electronic devices often include wireless communications circuitry. For example, cellular telephones, computers, and other devices often contain antennas and wireless transceivers for supporting wireless communications. 
     It can be challenging to ensure that wireless communications circuitry in an electronic device will perform satisfactorily in all operating conditions. For example, the operating environment of an electronic device such as the presence or absence of an external object in the vicinity of an electronic device may affect antenna tuning and wireless performance. Unless care is taken, the wireless performance of an electronic device may not be satisfactory in certain operating environments. 
     It would therefore be desirable to be able to provide improved wireless circuitry for operating electronic devices in various operating environments. 
     SUMMARY 
     An electronic device may be provided with wireless circuitry and control circuitry. The wireless circuitry may include first and second antennas, Wireless Local Area Network (WLAN) transceiver circuitry (e.g., first and second WLAN transceivers), and a Wireless Personal Area Network (WPAN) transceiver such as a Bluetooth transceiver. A switch may be coupled between the first and second antennas and the Bluetooth transceiver. The control circuitry perform Bluetooth antenna diversity operations by controlling the switch to couple the Bluetooth transceiver to a selected one of the first and second antennas at a given time. The Bluetooth transceiver may perform Bluetooth communications during alternating transmit and receive time periods (e.g., as dictated by the Bluetooth protocol). The transmit and receive time periods may each include, for example, one or more consecutive 625 μs Bluetooth protocol timeslots. 
     The Bluetooth transceiver may obtain a sequence of Bluetooth data packets for transmission to external communications equipment such as a peripheral Bluetooth device. The Bluetooth transceiver may transmit a first Bluetooth data packet from the sequence over the first antenna during a first transmit period. The control circuitry may determine whether the Bluetooth transceiver has received an expected or scheduled response packet (e.g., an Acknowledge (ACK) packet corresponding to the first Bluetooth data packet) over the first antenna during a first receive period. The ACK packet may be generated by the external equipment in response to successfully receiving the transmitted first Bluetooth data packet, for example. 
     In response to determining that the Bluetooth transceiver has failed to receive the ACK packet or that the Bluetooth transceiver has received a non-acknowledge (NACK) packet signaling that the external equipment has not received correctly a scheduled transmission over the first antenna during the first receive period, the control circuitry may control the switch to couple the second antenna to the Bluetooth transceiver. The Bluetooth transceiver may subsequently re-transmit the first Bluetooth data packet using the second antenna during a second transmit period. In response to reception of the ACK packet during the first receive period, the Bluetooth transceiver may transmit the second Bluetooth data packet from the sequence over the first antenna during the second transmit period. 
     In scenarios where the second antenna re-transmits the first Bluetooth data packet during the second transmit period, the control circuitry may determine whether the second antenna has received the ACK packet during a second receive period. In response to determining that the second antenna has received the ACK packet during the second receive period, the second antenna may be used to transmit the second Bluetooth data packet during a third transmit period. If the second antenna fails to receive the ACK packet or receives a NACK packet during the second receive period, the number of re-transmit attempts for the first Bluetooth data packet may be compared to a threshold value. If the number of re-transmit attempts is less than the threshold value, the first antenna may be switched into use for re-transmitting the first Bluetooth data packet during the third transmit period. If the number of re-transmit attempts is greater than or equal to the threshold value, a selected one of the first and second antennas may be used to transmit the second Bluetooth data packet in the sequence during the third transmit period. 
     The first WLAN transceiver may transmit WLAN signals over the first antenna. The second WLAN transceiver may transmit WLAN signals over the second antenna. An additional switch may be used to couple a selected one of the Bluetooth transceiver and the second WLAN transceiver to the second antenna. The first and second WLAN transceivers, the additional switch, and the Bluetooth transceiver may be formed on a shared integrated circuit or chip. Performing Bluetooth antenna diversity operations in this way may, for example, allow a different antenna to be used for conveying Bluetooth signals in the event that the default antenna in the device is blocked by external objects (e.g., without requiring processing intensive sensor circuitry to actively monitor the performance of the antennas). This may serve to reduce the error rate of the Bluetooth data received at the external device over time relative to scenarios where a single antenna is used for performing Bluetooth communications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry for communicating with external equipment in accordance with an embodiment. 
         FIG. 3  is a circuit diagram of illustrative wireless communications circuitry having short range antenna diversity capabilities in accordance with an embodiment. 
         FIGS. 4 and 5  are timing diagrams that illustrate wireless activity associated with using communications circuitry such as illustrative wireless communications circuitry of the type shown in  FIG. 3  in accordance with an embodiment. 
         FIG. 6  is a flow chart of illustrative steps involved in performing short range antenna diversity operations using wireless communications circuitry in accordance with an embodiment. 
         FIG. 7  is an illustrative timing diagram that shows how short range data packets may be transmitted and received by multiple antennas in performing short range antenna diversity operations in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may contain wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. 
     The wireless communications circuitry of device  10  may include a Global Position System (GPS) receiver that handles GPS satellite navigation system signals at 1575 MHz or a GLONASS receiver that handles GLONASS signals at 1609 MHz. Device  10  may also contain wireless communications circuitry that operates in communications bands such as cellular telephone bands and wireless circuitry that operates in communications bands such as the 2.4 GHz Bluetooth) band and the 2.4 GHz and 5 GHz WiFi, wireless local area network bands (sometimes referred to as IEEE 802.11 bands or wireless local area network communications bands). If desired, device  10  may also contain wireless communications circuitry for implementing near-field communications, light-based wireless communications, or other wireless communications (e.g., millimeter wave communications at 60 GHz or other extremely high frequencies, etc.). 
     The wireless communications circuitry may include one more antennas. The antennas of the wireless communications circuitry can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, monopole antennas, dipole antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures. 
     The conductive electronic device structures may include conductive housing structures. The housing structures may include peripheral structures such as peripheral conductive structures that run around the periphery of an electronic device. The peripheral conductive structures may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, may have portions that extend upwards from an integral planar rear housing (e.g., to form vertical planar sidewalls or curved sidewalls), and/or may form other housing structures. 
     Gaps may be formed in the peripheral conductive structures that divide the peripheral conductive structures into peripheral segments. One or more of the segments may be used in forming one or more antennas for electronic device  10 . Antennas may also be formed using an antenna ground plane formed from conductive housing structures such as metal housing midplate structures and other internal device structures. Rear housing wall structures may be used in forming antenna structures such as an antenna ground. 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device (e.g., wireless earbuds or a wireless headset), earpiece device, or other wearable or miniature device, a handheld device such as a cellular telephone, a media player, or other small portable device. Device  10  may also be a set-top box, a desktop computer, a keyboard, mouse, joystick, trackpad device, remote control, microphone, computer workstation, docking device, a display into which a computer or other processing circuitry has been integrated, a display without an integrated computer, or other suitable electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may be mounted on the front face of device  10 . Display  14  may be a touch screen that incorporates capacitive touch electrodes or may be insensitive to touch. The rear face of housing  12  (i.e., the face of device  10  opposing the front face of device  10 ) may have a planar housing wall. The rear housing wall may have slots that pass entirely through the rear housing wall and that therefore separate housing wall portions (and/or sidewall portions) of housing  12  from each other. The slots may separate portions of the rear housing wall from portions of the sidewalls of housing  12  if desired. Housing  12  (e.g., the rear housing wall, sidewalls, etc.) may also have shallow grooves that do not pass entirely through housing  12 . The slots and grooves may be filled with plastic or other dielectric. If desired, portions of housing  12  that have been separated from each other (e.g., by a through slot) may be joined by internal conductive structures (e.g., sheet metal or other metal members that bridge the slot). 
     Display  14  may include pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable pixel structures. A display cover layer such as a layer of clear glass or plastic may cover the surface of display  14  or the outermost layer of display  14  may be formed from a color filter layer, thin-film transistor layer, or other display layer. Buttons such as button  24  may pass through openings in the cover layer. The cover layer may also have other openings such as an opening for speaker port  26 . Speaker port  26  may allow audio signals (sound) to be heard by a user of device  10  (e.g., while the user holds device  10  and speaker port  26  to their ear). Speaker port  26  may therefore sometimes be referred to herein as ear speaker port  26  or ear speaker  26 . 
     Housing  12  may include peripheral housing structures such as structures  16 . Structures  16  may run around the periphery of device  10  and display  14 . In configurations in which device  10  and display  14  have a rectangular shape with four edges, structures  16  may be implemented using peripheral housing structures that have a rectangular ring shape with four corresponding edges (as an example). Peripheral structures  16  or part of peripheral structures  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or that helps hold display  14  to device  10 ). Peripheral structures  16  may also, if desired, form sidewall structures for device  10  (e.g., by forming a metal band with vertical sidewalls, curved sidewalls, etc.). 
     Peripheral housing structures  16  may be formed of a conductive material such as metal and may therefore sometimes be referred to as peripheral conductive housing structures, conductive housing structures, peripheral metal structures, or a peripheral conductive housing member (as examples). Peripheral housing structures  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming peripheral housing structures  16 . If desired, holes such as holes  8  may be provided in peripheral structures  16  or in a rear surface of housing  12 . Speakers within device  10  may transmit sound to the exterior of device  10  through holes  8  and/or through ear speaker  26 . If desired, microphones may be placed adjacent to holes  8  or any other desired locations within device  10  to generate audio signals from sound received by device  10 . 
     It is not necessary for peripheral housing structures  16  to have a uniform cross-section. For example, the top portion of peripheral housing structures  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. The bottom portion of peripheral housing structures  16  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). Peripheral housing structures  16  may have substantially straight vertical sidewalls, may have sidewalls that are curved, or may have other suitable shapes. In some configurations (e.g., when peripheral housing structures  16  serve as a bezel for display  14 ), peripheral housing structures  16  may run around the lip of housing  12  (i.e., peripheral housing structures  16  may cover only the edge of housing  12  that surrounds display  14  and not the rest of the sidewalls of housing  12 ). 
     If desired, housing  12  may have a conductive rear surface. For example, housing  12  may be formed from a metal such as stainless steel or aluminum. The rear surface of housing  12  may lie in a plane that is parallel to display  14 . In configurations for device  10  in which the rear surface of housing  12  is formed from metal, it may be desirable to form parts of peripheral conductive housing structures  16  as integral portions of the housing structures forming the rear surface of housing  12 . For example, a rear housing wall of device  10  may be formed from a planar metal structure and portions of peripheral housing structures  16  on the sides of housing  12  may be formed as flat or curved vertically extending integral metal portions of the planar metal structure. Housing structures such as these may, if desired, be machined from a block of metal and/or may include multiple metal pieces that are assembled together to form housing  12 . The planar rear wall of housing  12  may have one or more, two or more, or three or more portions. 
     Housing  12  may include internal conductive structures such as metal frame members and a planar conductive housing member (sometimes referred to as a midplate) that spans the walls of housing  12  (i.e., a substantially rectangular sheet formed from one or more parts that is welded or otherwise connected between opposing sides of member  16 ). Device  10  may also include conductive structures such as printed circuit boards, components mounted on printed circuit boards, and other internal conductive structures. These conductive structures, which may be used in forming a ground plane in device  10 , may be located in the center of housing  12 . 
     In regions  22  and  20 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive housing structures  16  and opposing conductive ground structures such as conductive housing midplate or rear housing wall structures, a printed circuit board, and conductive electrical components in display  14  and device  10 ). These openings, which may sometimes be referred to as gaps, may be filled with air, plastic, and other dielectrics and may be used in forming slot antenna resonating elements for one or more antennas in device  10 . 
     Conductive housing structures and other conductive structures in device  10  such as a midplate, traces on a printed circuit board, display  14 , and conductive electronic components may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, may contribute to the performance of a parasitic antenna resonating element, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . 
     In general, device  10  may include any suitable number of antennas (e.g., one or more, two or more, three or more, four or more, etc.). In the example of  FIG. 1 , device  10  includes a first antenna  40 L and a second antenna  40 U formed on opposing sides of device  10 . For example, antenna  40 L may be formed within region  20  at the lower end of device  10  (e.g., the end of device  10  adjacent to microphone holes  8 ) and may therefore sometimes be referred to herein as lower antenna  40 L. Similarly, antenna  40 U may be formed within region  22  at the upper end of device  10  (e.g., the end of device  10  adjacent to ear speaker  26 ) and may therefore sometimes be referred to herein as upper antenna  40 U. Antennas  40 L and  40 U may, if desired, be used separately to cover identical communications bands, overlapping communications bands, or separate communications bands. The antennas may be used to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. Antennas  40 L and  40 U may each include antenna resonating elements that are coupled to corresponding antenna signal feed terminals and antenna ground elements that are coupled to corresponding antenna ground feed terminals. Transmission line structures may be coupled between wireless transceiver circuitry in device  10  and the antenna feed terminals. The antenna resonating elements may be formed using portions of conductive housing wall  16  and/or using separate conductive elements located within regions  20  and  22 . 
     The arrangement of  FIG. 1  is merely illustrative. In general, the antennas in device  10  may be located at opposing first and second ends of an elongated device housing (e.g., at ends  20  and  22  of device  10  of  FIG. 1 ), along one or more edges of device housing  12 , in the center of device housing  12 , in other suitable locations, or in one or more of these locations. 
     Portions of peripheral housing structures  16  may be provided with peripheral gap structures. For example, peripheral conductive housing structures  16  may be provided with one or more gaps such as gaps  18 , as shown in  FIG. 1 . The gaps in peripheral housing structures  16  may be filled with dielectric such as polymer, ceramic, glass, air, other dielectric materials, or combinations of these materials. Gaps  18  may divide peripheral housing structures  16  into one or more peripheral conductive segments. There may be, for example, two peripheral conductive segments in peripheral housing structures  16  (e.g., in an arrangement with two of gaps  18 ), three peripheral conductive segments (e.g., in an arrangement with three of gaps  18 ), four peripheral conductive segments (e.g., in an arrangement with four gaps  18 ), etc. 
     The segments of peripheral conductive housing structures  16  that are formed in this way may form parts of antennas in device  10 . For example, the segment of peripheral conductive housing structures  16  that is located between the two gaps  18  in region  20  may form some or all of an antenna resonating element for lower antenna  40 L (e.g., one or more resonating element arms of an inverted-F antenna resonating element in scenarios where lower antenna  40 L is an inverted-F antenna, a portion of a loop antenna resonating element in scenarios where lower antenna  40 L is a loop antenna, a conductive portion that defines an edge of a slot antenna resonating element in scenarios where lower antenna  40 L is a slot antenna, combinations of these, or any other desired antenna resonating element structures). Similarly, the segment of peripheral conductive housing structures  16  that is located between the two gaps  18  in region  22  may form some or all of an antenna resonating element for upper antenna  40 U. This example is merely illustrative. If desired, antennas  40 L and  40 U may not include any portion of peripheral conductive housing structures  16  or segments of structures  16  may form part of an antenna ground plane for antennas  40 L and  40 U. 
     Antennas in device  10  may be used to support any communications bands of interest. For example, device  10  may include antenna structures for supporting local area network communications, voice and data cellular telephone communications, global positioning system (GPS) communications or other satellite navigation system communications, Bluetooth® communications, etc. 
     A schematic diagram showing illustrative components that may be used in device  10  of  FIG. 1  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may include control circuitry such as storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol or other Wireless Personal Area Network (WPAN) protocols, cellular telephone protocols, multiple-input and multiple-output (MIMO) protocols, antenna diversity protocols, etc. If desired, circuitry  28  may be used in tuning antennas, adjusting wireless transmit powers for transceivers in device  10  (e.g., transmit powers may be adjusted up and down in response to transmit power commands from wireless base stations while observing an established overall maximum allowed transmit power), and/or in otherwise controlling the wireless operation of device  10 . 
     Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices  32  may include touch screens, displays without touch sensor capabilities, buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, position and orientation sensors (e.g., sensors such as accelerometers, gyroscopes, and compasses), capacitance sensors, proximity sensors (e.g., capacitive proximity sensors, light-based proximity sensors, etc.), fingerprint sensors (e.g., a fingerprint sensor integrated with a button such as button  24  of  FIG. 1  or a fingerprint sensor that takes the place of button  24 ), etc. 
     Input-output circuitry  30  may include wireless communications circuitry  34  for communicating wirelessly with external equipment. Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, transmission lines, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include radio-frequency transceiver circuitry  35  for handling various radio-frequency communications bands. For example, circuitry  34  may include transceiver circuitry  36 ,  38 , and  42 . Short range (local) transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in frequency ranges such as a low communications band from 700 to 960 MHz, a low-midband from 960-1710 MHz, a midband from 1710 to 2170 MHz, and a high band from 2300 to 2700 MHz or other communications bands between 700 MHz and 2700 MHz or other suitable frequencies (as examples). Circuitry  38  may handle voice data and non-voice data. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include 60 GHz transceiver circuitry, circuitry for receiving television and radio signals, paging system transceivers, near field communications (NFC) circuitry, etc. Wireless communications circuitry  34  may include global positioning system (GPS) receiver equipment such as GPS receiver circuitry  42  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. In WiFi and Bluetooth links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, monopole antenna structures, dipole antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. Dedicated antennas may be used for transmitting and/or receiving signals in a particular band or, if desired, antennas  40  can be configured to receive signals for multiple communications bands. 
     Wireless communications circuitry  34  may use antennas  40  to communicate with one or more external devices such as external equipment  41  over wireless link  42 . Wireless link  42  may, for example, be a short range (local) wireless link. Local wireless transceiver circuitry  36  may transmit radio-frequency signals to external equipment  41  over short range wireless link  42  and may receive radio-frequency signals from external equipment  41  over short range wireless link  42 . In one illustrative scenario, short range wireless link  42  includes a WPAN path such as a Bluetooth path that is used to support communications between external equipment  41  and device  10 . In this scenario, wireless signals that are conveyed over link  42  may include WPAN signals (e.g., Bluetooth signals) formatted according to the Bluetooth protocol. Bluetooth signals conveyed over link  42  may be transmitted in a Bluetooth frequency band at 2.4 GHz, for example. 
     External equipment  41  may have corresponding wireless communications circuitry. For example, external equipment  41  may be an accessory or peripheral device such as a wireless headset, wireless headphones, earpiece device, wireless microphone, wireless speakers, wireless monitor or display, a game controller, other equipment that receives and plays audio and/or video content, or other equipment that receives a user input and conveys the user input to device  10  over Bluetooth link  42 . External equipment  41  may therefore sometimes be referred to herein as peripheral device  41 , peripheral electronic device  41 , accessory  41 , or accessory device  41 . These examples are merely illustrative. If desired, external equipment  41  may include a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device (e.g., wireless earbuds or a wireless headset), earpiece device, or other wearable or miniature device, a handheld device such as a cellular telephone, a media player, remote control, or other small portable device. External equipment  41  may also include a set-top box, a desktop computer, a keyboard, mouse, joystick, trackpad device, remote control, microphone, computer workstation, docking device, a display into which a computer or other processing circuitry has been integrated, a display without an integrated computer, or other suitable electronic equipment. In general, external equipment  41  may be any desired electronic device or system that wirelessly communicates with electronic device  10  over Bluetooth link  42 . 
     If desired, device  10  may perform communications over other local wireless links in addition to Bluetooth link  42 . For example, antennas  40  on device  10  may also establish a local wireless links such as a WiFi link. Because WiFi links are typically used to establish data links with local area networks, links such as WiFi links are sometimes referred to as WLAN links. WLAN links may operate at 2.4 GHz or 5.6 GHz (as examples), whereas Bluetooth link  42  operates at 2.4 GHz. The frequencies that are used to support these local links in device  10  may depend on the country in which device  10  is being deployed (e.g., to comply with local regulations), the available hardware of the transceiver circuitry  36  or other equipment with which device  10  is connecting, and other factors. 
     If desired, device  10  may communicate using both the popular 2.4 GHz WiFi bands (802.11(b) and/or 802.11(g)) and the 2.4 GHz Bluetooth band using the same antenna  40 . In this type of configuration, the antenna is designed to operate at a frequency of 2.4 GHz, so the antenna is suitable for use with the 2.4 GHz radio-frequency signals that are used in connection with both the WiFi and Bluetooth communications protocols (e.g., the antenna may have a resonating length, perimeter, or volume such that the antenna has satisfactory antenna efficiency at 2.4 GHz). Circuitry  36  may include switching circuits and other suitable circuitry that allows WiFi and Bluetooth signals to both be conveyed over a single antenna  40 . 
     In typical scenarios, wireless communications circuitry  34  conveys Bluetooth signals using only a single antenna  40  (e.g., circuitry  34  uses the same antenna  40  whenever Bluetooth signals are conveyed). However, in practice, the radio-frequency performance of the antenna that is used to convey Bluetooth signals may become degraded (e.g., due to the presence of external objects such as a user&#39;s body or other objects). This may degrade the quality of Bluetooth link  42 , may cause communications errors, may cause link  42  to be dropped, etc. 
     To help mitigate these risks, wireless communications circuitry  34  may implement a short range (local) antenna diversity scheme such as a Bluetooth antenna diversity scheme in which multiple antennas  40  are used to convey Bluetooth signals with external equipment  41 . For example, an upper antenna  40 U located in upper device region  22  of  FIG. 1  and a lower antenna  40 L located in lower device region  20  may both be used to convey Bluetooth signals under a Bluetooth antenna diversity scheme. 
       FIG. 3  is a circuit diagram showing how wireless communications circuitry  34  may include circuitry for performing Bluetooth antenna diversity operations using two antennas  40 U and  40 L. As shown in  FIG. 3 , wireless communications circuitry  34  may include upper antenna  40 U, lower antenna  40 L, and local wireless transceiver circuitry  36 . Upper antenna  40 U may be located within device region  22  whereas lower antenna  40 L is located within device region  20  ( FIG. 1 ). This is merely illustrative and, in general, antennas  40 U and  40 L may be formed at any desired locations within device  10 . 
     In practice, one of antennas  40 U and  40 L may typically be favored over the other for conveying Bluetooth signals over Bluetooth link  42 . For example, it may be preferable more often to use upper antenna  40 U rather than lower antenna  40 L due to considerations such as superior efficiency, superior band coverage, superior radiation patterns, etc. As another example, upper antenna  40 U may be statistically more likely to be located closer to or facing external equipment  41  during normal operations of device  10  by a user (e.g., while device  10  is being held in the user&#39;s hand, while device  10  is placed on a surface, while device  10  is located within the user&#39;s pocket, etc.). In other words, upper antenna  40 U may be statistically more likely to support a higher quality Bluetooth link with external equipment  41  than lower antenna  40 L at any given moment. Upper antenna  40 U may therefore sometimes be referred to herein as the primary antenna, primary Bluetooth antenna, default antenna, or default Bluetooth antenna for device  10 , whereas lower antenna  40 L may sometimes be referred to herein as the secondary antenna or secondary Bluetooth antenna for device  10 . This example is merely illustrative. In general, any desired antenna  40  in device  10  may be the primary antenna (e.g., an antenna physically located closest to transceiver  36 , an antenna having the highest average efficiency, etc.). 
     Device  10  may attempt to use the primary antenna as much as possible for conveying Bluetooth signals but may switch to using the secondary antenna for conveying Bluetooth signals when operation of the primary antenna becomes disrupted. Antenna operation can be disrupted when the antenna is blocked by an external object such as a user&#39;s hand, when device  10  is placed near objects that interfere with proper antenna operation, or due to other factors (e.g., device orientation relative to its surroundings, etc.). 
     Antenna diversity systems in which device  10  has a primary antenna and a secondary antenna are sometimes described herein as an example. This is, however, merely illustrative. Device  10  may use an antenna diversity arrangement that is based on three or more antennas or may use other types of antenna configurations. 
     Local wireless transceiver circuitry  36  may include multiple radio-frequency transceivers. As shown in  FIG. 3 , local wireless transceiver circuitry  36  may include a first WLAN transceiver (“WIFI1”)  80 , a second WLAN transceiver (“WIFI2”)  62 , and a Bluetooth transceiver (“BT”)  64 . WLAN transceivers  80  and  62  may handle signals formatted according to a WLAN (e.g., WiFi) protocol (sometimes referred to herein as WLAN signals or WiFi signals). Bluetooth transceiver  64  may handle Bluetooth signals formatted according to the Bluetooth protocol. 
     In one suitable arrangement, each of the components of local wireless communications transceiver circuitry  36  (e.g., WLAN transceiver  80 , WLAN transceiver  62 , and Bluetooth transceiver  64 ) are formed on a single shared integrated circuit, chip, or substrate (e.g., a single shared printed circuit board substrate, a single application specific integrated circuit, etc.). Local wireless communications transceiver circuitry  36  may therefore sometimes be referred to herein as radio-frequency module  36 . WLAN/Bluetooth module  36 , local wireless communications chip  36 , or local wireless communications module  36 . This example is merely illustrative. If desired, transceivers  80 ,  62 , and/or  64  may be formed on one or more different integrated circuits, chips, or substrates. Some or all of transceiver circuits  42  and  38  ( FIG. 2 ) may be formed on the same integrated circuit, chip, or substrate as module  36  if desired. 
     Radio-frequency module  36  may include a first port  50  coupled to the secondary antenna (e.g., antenna  40 L) via radio-frequency transmission line  54 . Module  36  may include a second port  52  coupled to the primary antenna (e.g., upper antenna  40 U) via radio-frequency transmission line  56 . Lines  54  and  56  may include coaxial cable structures, stripline transmission line structures, and/or a microstrip transmission line structures (as examples). Ports  52  and  50  may each include any desired radio-frequency connector structures such as conductive pins, contact pads, conductive sockets, conductive spring structures, conductive screws, conductive clips, solder balls, micro bumps, conductive adhesive or tape, welds, coaxial connectors, micro-coaxial connectors, U.FL connectors, or other conductive structures. 
     WLAN transceiver circuitry  80  may be coupled to applications processor circuitry  44  over path  74 . WLAN transceiver circuitry  62  may be coupled to applications processor  44  over path  72 . Bluetooth transceiver circuitry  64  may be coupled to applications processor  44  over path  70 . Paths  72 ,  74 , and  70  may each be implemented using a corresponding serial data path (e.g., a universal asynchronous receiver/transmit (UART) path) or using any other desired data paths. Applications processor  44  may include a portion of storage and processing circuitry  28  or other processing circuitry on device  10 . Applications processor  44  may be formed on a different integrated circuit, chip, or substrate than radio-frequency module  36 , as an example. 
     Applications processor  44  may generate data for transmission to external equipment  41  and may pass the generated data to WLAN transceiver circuitry  80  via path  74 , to WLAN transceiver circuitry  62  via path  72 , and/or to Bluetooth transceiver circuitry  64  via path  70  (e.g., based on which communications protocol is to be used). Similarly, applications processor  44  may receive data from WLAN transceiver  80  over path  74 , may receive data from WLAN transceiver  62  over path  72 , and/or may receive data from Bluetooth transceiver  64  over path  70 . 
     Module  36  may, if desired, include baseband circuitry (not shown) that formats transmit data received from applications processor  44  according to the desired communications protocol (e.g., at a baseband frequency). In another suitable arrangement, some or all of the baseband circuitry may be formed as a part of applications processor  44 . WLAN transceivers  80  and  62  may receive baseband data that has been formatted according to a WLAN protocol from the baseband processor circuitry. WLAN transceivers  80  and  62  may each include mixer circuitry that generates radio-frequency WLAN signals by up-converting the baseband data to a radio-frequency (e.g., a 2.4 GHz WLAN frequency). Mixer circuitry in transceivers  80  and  62  may also down-convert radio-frequency signals received by antennas  40  to baseband frequencies. If desired, WLAN transceivers  80  and  62  may each include converter circuitry (e.g., analog-to-digital converter circuitry and/or digital-to-analog converter circuitry), amplifier circuitry (e.g., power amplifier and/or low noise amplifier circuitry), switching circuitry, filtering circuitry, phase shifting circuitry, or any other desired circuitry for handling radio-frequency signals. 
     WLAN transceiver circuitry  80  may transmit radio-frequency WLAN signals to antenna  40 L over port  50  and radio-frequency transmission line  54 . Antenna  40 L may subsequently transmit the radio-frequency WLAN signals to external equipment  41 . Similarly, antenna  40 L may receive radio-frequency WLAN signals from external equipment  41  and may convey the received signals to WLAN transceiver circuitry  80  via port  50  and transmission line  54 . 
     Bluetooth transceiver  64  may receive baseband data that has been formatted according to the Bluetooth protocol from the baseband processor circuitry. Bluetooth transceiver circuitry  64  may include mixer circuitry that generates radio-frequency Bluetooth signals by up-converting the baseband data to a radio-frequency (e.g., a 2.4 GHz Bluetooth frequency). Mixer circuitry in transceiver  64  may also down-convert radio-frequency signals received by antennas  40  to baseband frequencies. If desired, Bluetooth transceiver  64  may include converter circuitry (e.g., analog-to-digital converter circuitry and/or digital-to-analog converter circuitry), amplifier circuitry (e.g., power amplifier and/or low noise amplifier circuitry), switching circuitry, filtering circuitry, phase shifting circuitry, or any other desired circuitry for handling radio-frequency signals. 
     Bluetooth transceiver  64  may transmit the radio-frequency Bluetooth signals (sometimes referred to herein as radio-frequency Bluetooth data, Bluetooth data, or Bluetooth signals) over port  52  of module  36 . A first radio-frequency switch  66  (“SW1”) on module  36  may be coupled between WLAN transceiver  62 , Bluetooth transceiver  64 , and port  52  (e.g., switch  66  may have a first switch port coupled to WLAN transceiver  62 , a second switch port coupled to Bluetooth transceiver  64 , and a third switch port coupled to port  52 ). The switch ports may sometimes be referred to herein as switch terminals. Switch  66  may selectively connect one of transceivers  62  and  64  to module port  52  at a given time. Switch  66  may include, for example, a single-pole double-throw (SPDT) switch or any other desired switching circuitry. Switch  66  may have a first state in which WLAN transceiver  62  is coupled to port  52  and Bluetooth transceiver  64  is decoupled from port  52  (e.g., a first state in which the first switch port is shorted to the third switch port). Switch  66  may have a second state in which WLAN transceiver  62  is decoupled from port  52  and Bluetooth transceiver  64  is coupled to port  52  (e.g., a second state in which the second switch port is shorted to the third switch port). 
     Control circuitry on module  36  and/or storage and processing circuitry  28  ( FIG. 1 ) may control the state of switch  66  using a corresponding control path (not shown). When it is desired to convey WLAN data over upper antenna  40 U, switch  66  is placed in the first state to couple port  52  to WLAN transceiver  62 , so that data can be transmitted from WLAN transceiver  62  to antenna  40 U or from antenna  40 U to WLAN transceiver  62  over path  56 . Switch  66  is placed in the second state to couple port  52  to Bluetooth transceiver  64  when it is desired to convey Bluetooth signals over antennas  40 . Control paths between WLAN transceiver  80  and WLAN transceiver  62  (e.g., intra-chip control paths) may allow WLAN transceivers  80  and  62  to coordinate WLAN communications over antennas  40 L and  40 U, if desired. 
     A second radio-frequency switch  60  (“SW2”) may be interposed on transmission line  56  and  54 . Switch  60  may have a first switch port coupled to upper antenna  40 U, a second switch port coupled to port  52 , a third switch port coupled to lower antenna  40 L, and a fourth switch port coupled to port  50 . Switch  60  may selectively couple port  52  to antenna  40 L and port  50  to  40 U or may alternatively couple port  52  to antenna  40 U and port  50  to antenna  40 L. Switch  60  may include, for example, a double-pole double-throw (DPDT) switch or any other desired switching circuitry. Switch  60  may be formed external to module  36  (e.g., switch  60  may not be formed on the integrated circuit, substrate, or chip on which circuitry  36  is formed), as an example. Switch  60  may have a first state in which port  52  is coupled to upper antenna  40 U and port  50  is coupled to lower antenna  40 L. Switch  60  may have a second state in which port  52  is coupled to lower antenna  40 L and port  50  is coupled to upper antenna  40 U. Switch  60  may be toggled to selectively route Bluetooth signals transmitted at port  52  to a given one of antennas  40 U and  40 L or to selectively route Bluetooth signals from a given one of antennas  40 U and  40 L to port  52  while performing Bluetooth antenna diversity operations. 
     Control circuitry on Bluetooth transceiver circuitry  64  may control the state of switch  60  using Bluetooth antenna diversity control signals CTRL provided over control path  68 . When it is desired to convey Bluetooth data over upper antenna  40 U, switch  66  is placed in the second state to couple port  52  to Bluetooth transceiver  64  and switch  60  is placed in the first state, so that Bluetooth signals can be transmitted from Bluetooth transceiver  64  to upper antenna  40 U or from antenna  40 U to Bluetooth transceiver  64  over port  52  and path  56 . When it is desired to convey Bluetooth data over lower antenna  40 L, switch  66  is placed in the second state and switch  60  is placed in the second state, so that Bluetooth signals can be transmitted from Bluetooth transceiver  64  to lower antenna  40 L or from antenna  40 L to Bluetooth transceiver  64  over port  52 . Switch  60  may be placed in the first state to couple port  52  to upper antenna  40 U whenever WLAN transceiver  62  is in use (e.g., whenever switch  66  is placed in the first state to couple WLAN transceiver  62  to port  52 ). 
     When Bluetooth transceiver  64  is coupled to upper antenna  40 U, WLAN communications may be simultaneously maintained over lower antenna  40 L if desired (e.g., WLAN transceiver  80  may continue to transmit and receive WLAN signals over antenna  40 L and path  54  while Bluetooth transceiver  64  conveys Bluetooth signals using upper antenna  40 U). When Bluetooth transceiver  64  is coupled to lower antenna  40 L, WLAN communications may be temporarily halted. In another suitable arrangement. Bluetooth communications may be performed by Bluetooth transceiver  64  on a sub band using lower antenna  40 L while lower antenna  40 L also conveys WLAN signals. If desired, WLAN communications may be time multiplexed with Bluetooth communications using lower antenna  40 L (e.g., WLAN signals may be conveyed between antenna  40 L and WLAN transceiver  80  during time periods in which Bluetooth signals are not actively being transmitted or received over lower antenna  40 L). 
     By toggling switch  60 . Bluetooth transceiver  64  may change which antenna is being used for performing wireless communications over Bluetooth link  42  in real time. This may allow an antenna that exhibits greater radio-frequency performance to be used for Bluetooth signal transmission or reception whenever the other antenna exhibits deteriorated radio-frequency performance (e.g., due to being blocked by an external object). 
     The example of  FIG. 3  is merely illustrative. In general, any desired radio-frequency circuitry may be interposed on conductive paths  54 ,  56  (e.g., radio-frequency matching circuitry, filtering circuitry, amplifier circuitry, switching circuitry, duplexer circuitry, diplexer circuitry, passive components, active components, etc.). More than two antennas may be used if desired. More than two WLAN transceivers may be used if desired. 
     The example sometimes described herein in which link  42  is a Bluetooth link and transceiver  64  is a Bluetooth transceiver is merely illustrative. In general, link  42  may be any desired Wireless Personal Area Network (WPAN) link (e.g., a wireless link operated using an IEEE 802.15 protocol) and transceiver  64  may be any desired WPAN transceiver (e.g., a transceiver that performs transmission and/or reception according to an IEEE 802.15 protocol). Transceiver  64  may therefore sometimes be referred to herein as WPAN transceiver  64 . Packets conveyed over link  42  may sometimes be referred to herein as WPAN packets (e.g., Bluetooth packets) or WPAN data packets. The WPAN link may support wireless communications over a personal area network (e.g., a wireless network governed by an IEEE 802.15 WPAN protocol such as a network of local wirelessly connected devices within a user&#39;s vicinity or workspace or on a user&#39;s body). Two devices in the WPAN network may communicate over wireless link  42  as if they were plugged in using a physical wire, as an example. This may involve protocol that prevents other nearby devices from interfering with the two linked devices. As an example, data may be symmetrically conveyed over link  42  such that wireless WPAN data packets (e.g., audio packets) conveyed from a first device to a second device are each acknowledged by a corresponding response packet sent from the second device to the first device. WPAN protocols that may be supported by transceiver  64  for communicating over link  42  may include, but are not limited to, Bluetooth protocols (e.g., a Bluetooth 4.0, Bluetooth 4.1, Bluetooth 4.2, Bluetooth 5, or other Bluetooth protocols), Z-Wave® protocols, ZigBee® protocols, Wireless USB protocols. Body Area Network protocols, Infrared Data Association®, protocols, or other IEEE 802.15 protocols, as examples. 
     In some scenarios, sensor circuitry or other circuitry on device  10  may actively monitor the radio-frequency performance of each antenna  40 L and  40 U to determine which antenna to use for Bluetooth communications at a given time. If the sensor circuitry (e.g., a capacitive proximity sensor, impedance measurement circuitry, an ambient light sensor, etc.) determines that antenna  40 U will likely exhibit superior radio-frequency performance relative to antenna  40 L (e.g., if the sensor circuitry determines that an external object is blocking antenna  40 L), antenna  40 U may be switched into use for handling Bluetooth communications. Likewise, if the sensor circuitry determines that antenna  40 L will exhibit superior radio-frequency performance relative to antenna  40 U, antenna  40 L may be switched into use for handling Bluetooth communications. However, performing Bluetooth diversity operations in this manner may consume excessive time and result in one or more packets of the Bluetooth data stream being lost or dropped. This may result in excessively high data error rates for the Bluetooth data received at external equipment  41 . If desired, device  10  may perform Bluetooth antenna diversity operations without using sensor circuitry to actively monitor the radio-frequency performance of each antenna. 
       FIG. 4  is a timing diagram that illustrates how Bluetooth transceiver  64  may alternate between transmitting and receiving Bluetooth signals over time. As shown in  FIG. 4 , time is plotted on the horizontal axis. During Bluetooth operations. Bluetooth transceiver  64  alternates between transmitting data and receiving data according to a schedule that is determined by the Bluetooth protocol specifications. Bluetooth transceiver  64  transmits Bluetooth signals during transmit periods (timeslots)  80  (“BT TX”). Bluetooth transceiver  64  receives Bluetooth signals during receive periods (timeslots)  82  (“BT RX”). If desired, each transmit period  80  and each receive period  82  may include one, two, three, four, five, or more than five consecutive 625 μs Bluetooth protocol timeslots, as examples (e.g., each time period  80  and  82  may be greater than or equal to 625 μs in duration). 
     Bluetooth data that is transmitted or received using the Bluetooth protocol is formatted into a sequence (series) of Bluetooth data packets. For example, applications processor  44  may generate data for transmission to Bluetooth transceiver  64  (e.g., audio data or video data to be played on a peripheral device  41 , control data for controlling the operation of device  41 , etc.). Baseband circuitry may format (encode) the data received from applications processor  44  into data packets according to the Bluetooth protocol. Transceiver  64  may generate the sequence of Bluetooth data packets (e.g., the radio-frequency Bluetooth signals) by up-converting the data packets to a Bluetooth frequency. The Bluetooth frequency may be, for example, a frequency in one of the 79, 1 MHz bandwidth, designated Bluetooth frequency channels or in one of the 40, 2 MHz bandwidth, designated Bluetooth low energy channels. Transceiver  64  may perform frequency hopping operations in which each Bluetooth data packet in the sequence is generated in a respective one of the designated Bluetooth or Bluetooth low energy channels (e.g., the first Bluetooth data packet in the series may be generated in Bluetooth channel 4, the second Bluetooth data packet in the series may be generated in Bluetooth channel 50, the third Bluetooth data packet in the series may be generated in Bluetooth channel 33, etc.). The particular channel that is used for each packet may be determined by transceiver  64  based on the standards of the Bluetooth protocol, for example. 
     Transceiver  64  may schedule each Bluetooth data packet in the sequence for transmission during a corresponding transmit period  80  (e.g., each Bluetooth data packet in the sequence may be transmitted during the one to five 625 μs Bluetooth protocol timeslots associated with the corresponding transmit period  80 ). The Bluetooth protocol dictates that each transmit period  80  is followed by a corresponding receive period  82  during which transceiver  64  waits to receive a scheduled Bluetooth data packet from external equipment  41  (e.g., without transmitting any Bluetooth data). 
     In order to ensure that each of the Bluetooth data packets are being successfully received at external equipment  41 , external equipment  41  generates a respective scheduled Bluetooth data packet in response to successfully receiving each Bluetooth data packet that is transmitted by transceiver  64 . The scheduled Bluetooth data packets generated by external equipment  41  may be Bluetooth response or acknowledge (ACK) packets (sometimes referred to as acknowledgement packets), as examples. Each ACK packet generated by external equipment  41  thereby corresponds to a respective one of the Bluetooth data packets transmitted by device  10  (e.g., equipment  41  may generate a first ACK packet in response to receiving the first Bluetooth data packet transmitted by device  10 , may generate a second ACK packet in response to receiving the second Bluetooth data packet transmitted by device  10 , etc.). Each ACK packet may, for example, have a header field that includes information that identifies the packet as an ACK packet and/or that identifies the particular received data packet that the ACK packet is acknowledging successful receipt of by external equipment  41 . 
     If desired, external equipment  41  may signal to transceiver  64  over Bluetooth link  42  that a scheduled Bluetooth data packet has not been received or decoded correctly during a predetermined time slot using a non-acknowledge (NACK) packet. External equipment  41  may transmit the NACK packet to device  10  in response to failing to receive or correctly decode the scheduled Bluetooth data packet. The NACK packet may, for example, have a header field that includes information identifying the NACK packet as a NACK packet and/or that identifies the corresponding scheduled Bluetooth data packet that has not been successfully received at equipment  41 . Transceiver  64  may identify that each Bluetooth data packet transmitted by device  10  has been successfully received by external equipment  41  when a corresponding ACK packet has been received from external equipment  41 . Once transceiver  64  has received an ACK packet identifying that a corresponding transmitted Bluetooth data packet has been successfully received by external equipment  41 , transceiver  64  may transmit the next Bluetooth data packet in the sequence of Bluetooth data packets to external equipment  41 . 
     In a scenario in which only a single antenna is used for Bluetooth communications, if an ACK packet has not been received or a NACK packet has been received within a scheduled receive period  82  (e.g., within the receive period  82  immediately following the transmit period  80  in which the corresponding Bluetooth data packet was transmitted by device  10 ), transceiver  64  re-transmits the corresponding Bluetooth data packet using the same antenna  40 . After a threshold number of un-acknowledged re-transmit attempts (e.g., two un-acknowledged re-transmit attempts), the corresponding Bluetooth data packet may be considered to have been dropped or lost and transceiver  64  proceeds to transmit the next Bluetooth data packet in the sequence. 
     Consider an example of this scenario in which transceiver  64  transmits a first Bluetooth data packet in the sequence using a given antenna and during a first scheduled transmit period  80  ( FIG. 4 ). Transceiver  64  may wait for the duration of the first scheduled receive period  82  to receive the ACK packet corresponding to the first Bluetooth data packet from external equipment  41 . If transceiver  64  receives the ACK packet, transceiver  64  transmits the second Bluetooth data packet in the sequence during the second scheduled transmit period  80  using the same antenna. If transceiver  64  does not receive the ACK packet, transceiver  64  re-transmits the first Bluetooth data packet during the scheduled second transmit period  80  using the same antenna. Transceiver  64  then waits for the duration of the second scheduled receive period  82  to receive the ACK packet. If transceiver  64  receives the ACK packet, transceiver  64  transmits the second Bluetooth data packet in the sequence during the scheduled third transmit period  80  using the same antenna. If transceiver  64  does not receive the ACK packet, transceiver  64  performs one more re-transmit attempt for the first Bluetooth data packet over the same antenna. If the ACK packet is still not received after the second re-transmission attempt, transceiver  64  then moves on to the second Bluetooth data packet in the sequence for transmission. Performing Bluetooth communications in this way using a single antenna can result in one or more packets in the sequence being dropped (e.g., because that single antenna is being blocked by an external object), thereby introducing undesirable errors in the data that is received at external equipment  41 . 
     The example of  FIG. 4  is merely illustrative. If desired, other time periods may be interposed between scheduled transmit periods  80  and receive periods  82 .  FIG. 5  is a timing diagram that shows how additional time periods may be interposed between periods  80  and  82 . As shown in  FIG. 5 , periods  84  (“BTOFF”) may be interposed between transmit time periods  80  and receive time periods  82 . Periods  84  may be time periods during which no Bluetooth data packets are transmitted or received by transceiver  64 . As an example, the timing diagram of  FIG. 5  may correspond to how signals are conveyed over lower antenna  40 L. In this scenario, WLAN signals handled by WLAN transceiver  80  may be conveyed using lower antenna  40 L during time periods  84  (e.g., WLAN signals may be time-multiplexed with the Bluetooth signals on a given antenna if desired). This example is merely illustrative and, in general, any desired timing that accommodates or conforms to the Bluetooth protocol may be used. 
     If desired, Bluetooth transceiver  64  may perform Bluetooth antenna diversity operations in order to help mitigate the risk of dropping packets and introducing errors over Bluetooth link  42 . The Bluetooth antenna diversity operations may involve switching between different antennas  40  while transmitting a sequence of Bluetooth data packets. Bluetooth transceiver  64  may select which antenna  40  (e.g., a selected one of antennas  40 L and  40 U) to use at a given time based on scheduling associated with the Bluetooth protocol (e.g., without relying on sensors or other processing-intensive circuitry). 
       FIG. 6  is a flow chart of illustrative steps that may be performed by Bluetooth circuitry  64  and/or processing circuitry  28  in performing Bluetooth antenna diversity operations based on the scheduling associated with the Bluetooth protocol. 
     At step  100 , Bluetooth circuitry  64  may select a default antenna for transmitting Bluetooth data packets to external equipment  41 . Bluetooth circuitry  64  may provide control signals CTRL over control path  68  to place switch  60  in a state that couples the selected antenna to port  52 . In the example of  FIG. 3 , upper antenna  40 U is the default antenna and circuitry  64  may control switch  60  to couple upper antenna  40 U to port  52 . Upper antenna  40 U may be selected as the default (primary) antenna because antenna  40 U is statistically more likely to have a high link quality with external equipment  41  (e.g., because upper antenna  40 U is more likely to be facing external equipment  41  at a given time than lower antenna  40 L), because antenna  40 U is located closer to module  36  in device  10  than lower antenna  40 L (e.g., so less loss is incurred in conveying signals to antenna  40 U than to antenna  40 L from module  36 ), or because upper antenna  40 U has superior radiation characteristics than lower antenna  40 L, as examples. In general, any desired antenna  40  may be selected as the default antenna. 
     Bluetooth transceiver  64  may receive a stream of data packets from baseband circuitry for transmission over Bluetooth link  42 . The stream of data packets may, for example, include a stream of audio packets, video packets, or any other desired data. Transceiver  64  may convert the stream of data packets into a sequence of Bluetooth data packets according to the Bluetooth protocol. The sequence of Bluetooth data packets may be arranged in a chronological order (e.g., the sequence may begin with a first Bluetooth data packet and end in a last Bluetooth data packet). 
     At step  102 , transceiver circuitry  64  may transmit the next Bluetooth data packet in the sequence using the selected antenna (e.g., antenna  40 U). When transmission of a given sequence of Bluetooth packets has just commenced, the next Bluetooth data packet may be the first Bluetooth data packet in the sequence. Transceiver circuitry  64  may transmit the first Bluetooth data packet during a corresponding scheduled transmit period  80  ( FIG. 4 ). Once the first Bluetooth data packet has been transmitted, transceiver circuitry  64  may wait for reception of one or more scheduled packets from external equipment  41  over the selected antenna. The one or more scheduled packets may include the Bluetooth ACK packet associated with the first Bluetooth data packet transmitted by device  10 . Transceiver circuitry  64  may wait an expected amount of time (e.g., for the duration of the scheduled receive time period  82  immediately following the time period  80  during which the first Bluetooth packet was transmitted) to receive the scheduled packet(s). This example is merely illustrative and, in general, transceiver  64  may wait for reception of two or more ACK packets or other scheduled packets if desired. 
     If the one or more scheduled packets (e.g., the scheduled ACK packet generated by external equipment  41  in response to successfully receiving the first Bluetooth data packet transmitted by device  10 ) are received within the expected amount of time (e.g., during the scheduled receive period  82 ), processing may loop back to step  102  as shown by path  104 . Transceiver  64  may subsequently transmit the second Bluetooth data packet in the sequence of Bluetooth data packets using selected antenna  40 U. Transceiver  64  may continue to transmit the remaining Bluetooth data packets in the sequence using selected antenna  40 U as long as the corresponding ACK packets are received in the expected (scheduled) receive time periods  82 . 
     If the one or more scheduled packets (e.g., the ACK packet corresponding to the transmitted first Bluetooth data packet) are not received within the expected amount of time or a NACK packet is received, processing may proceed to step  108  as shown by path  106 . Failure to receive the ACK packet within the scheduled period may, for example, be indicative of the selected antenna  40 U being blocked or otherwise hindered from properly communicating with external equipment  41  over link  42 . If transceiver  64  attempts to re-transmit the first Bluetooth data packet using the selected antenna  40 U, there may be a relatively high likelihood that the re-transmitted packet will also fail to be successfully received by external equipment  41  (e.g., because it may be unlikely that antenna  40 U has moved so as to become unblocked between re-transmissions of the first packet). 
     At step  108 , transceiver circuitry  64  may select the other (e.g., secondary) antenna for transmitting Bluetooth data packets to external equipment  41  (e.g., without attempting to re-transmit the first Bluetooth data packet using the primary antenna). Bluetooth circuitry  64  may provide control signals CTRL over control path  68  to place switch  60  in a state that couples the newly selected antenna to port  52 . In the example of  FIG. 3 , switch  60  may be controlled to couple lower antenna  40 L to port  52 . 
     At step  110 , transceiver  64  may re-transmit the current (e.g., first) Bluetooth data packet using the selected secondary antenna  40 L. Once the first Bluetooth data packet has been re-transmitted using secondary antenna  40 L, transceiver circuitry  64  may wait for reception of the one or more scheduled packets (e.g., the ACK packet associated with the transmitted first Bluetooth data packet). Transceiver circuitry  64  may wait an expected amount of time (e.g., for the duration of the scheduled Bluetooth receive time period  82  immediately following the transmit time period  80  during which the first packet was re-transmitted) to receive the one or more scheduled packets. 
     If the one or more scheduled packets (e.g., the ACK packet) is received within the expected amount of time, processing may proceed to optional step  114 . At optional step  114 , transceiver circuitry  64  may select the other antenna (e.g., primary antenna  40 U) to transmit any subsequent Bluetooth data packets in the stream. Processing may then loop back to step  102  as shown by path  116  to transmit the second Bluetooth data packet in the sequence using primary antenna  40 U. Primary antenna  40 U may continue to transmit the remaining Bluetooth data packets in the sequence until transceiver  64  fails to receive a scheduled ACK packet. 
     In another suitable arrangement, step  114  may be omitted and processing may loop back to step  102  as shown by path  116  so that secondary antenna  40 L is used to transmit the second Bluetooth data packet in the stream. Secondary antenna  40 L may continue to transmit the remaining Bluetooth data packets in the sequence until transceiver  64  fails to receive a scheduled ACK packet. Omitting step  114  may, for example, allow transceiver  64  to continue Bluetooth communications using the antenna that is known to have most recently performed a successful transmission to external equipment  41 . 
     If desired, optional step  114  may be performed whenever the secondary antenna is used to re-transmit a given Bluetooth packet at step  110  and may be omitted whenever the default antenna is used to perform step  110 . Such operations may, for example, be performed if external equipment  41  is statistically more likely to successfully receive the second Bluetooth data packet from the default antenna than the secondary antenna at any given time (e.g., due to the default antenna more often being oriented towards external equipment  41 , having a higher maximum antenna efficiency than the secondary antenna, etc.). 
     If the one or more scheduled packets (e.g., the ACK packet) are not received within the expected amount of time while processing step  110 , processing may proceed to step  120  as shown by path  118 . At step  120 , transceiver circuitry  64  may determine whether the number of re-transmit attempts performed for the current Bluetooth data packet is less than a re-transmit threshold. The re-transmit threshold may dictate the number of allowable re-transmit attempts before the packet is dropped in favor of transmitting the next Bluetooth data packet in the stream. If the number of re-transmit attempts for the current Bluetooth data packet is less than the threshold, processing may loop back to step  108  as shown by path  122  to attempt another re-transmission of the packet using the other antenna (e.g., upper antenna  40 U). If the number of re-transmit attempts for the current Bluetooth data packet is greater than or equal to the threshold, processing may loop back to step  102  as shown by paths  124  and  116  or may proceed to optional step  114  as shown by path  124  (e.g., so that the next Bluetooth data packet in the stream may be transmitted by upper antenna  40 U or lower antenna  40 L). 
     By blindly and proactively switching antennas when a corresponding ACK packet is not received or a NACK packet is received, Bluetooth transceiver  64  may increase the overall probability that a given Bluetooth data packet will be successfully received by external equipment  41  relative to scenarios where only a single antenna is used to re-transmit the Bluetooth data packets. In this way, Bluetooth transceiver  64  may decrease the overall probability of packet loss over time for Bluetooth link  42  regardless of the environmental conditions (e.g., orientation) of device  10  and without using other sensor circuitry that would otherwise require an excessive amount of time to determine a desired antenna for use. Performing Bluetooth antenna diversity operations in this way may, as an example, decrease the average error rate in the Bluetooth data received at external equipment  41  by as much as 10-50% relative to scenarios in which only a single antenna is used to re-transmit each Bluetooth data packet. 
       FIG. 7  shows a timing diagram  150  illustrating one example of how Bluetooth transceiver  64  may perform Bluetooth antenna diversity operations using antennas  40 L and  40 U for a corresponding stream of Bluetooth data packets. As shown in  FIG. 7 , time is plotted on the horizontal axis and is divided into a number of alternating transmit and receive time periods T (e.g., a first time period T0, a second time period T1, a third time period T2, etc.). The duration of time periods T may be dictated by the Bluetooth protocol. Each time period T may include, for example, one or more consecutive 625 μs Bluetooth protocol timeslots. Even-numbered time periods (e.g., periods T0, T2, T4, etc.) may be transmit time periods such as time periods  80  of  FIG. 4 , whereas odd-numbered time periods (e.g., periods T1, T3, T5, etc.) may be receive time periods such as time periods  82  of  FIG. 4 . Each time period T may have the same duration or two or more time periods T may have different durations. In general, the durations of each time period T may be dictated by transceiver  64  based on the specifications of the Bluetooth protocol. 
     Bluetooth transceiver circuitry  64  may generate a stream or sequence of Bluetooth data packets P for transmission to external equipment  41  (e.g., a sequence of audio packets formatted according to the Bluetooth protocol for playback on external audio speakers, etc.). The sequence of Bluetooth data packets may be generated for transmission in a corresponding chronological order (e.g., a first Bluetooth data packet P1, a second Bluetooth data packet P2 subsequent to first packet P1, a third Bluetooth data packet P3 subsequent to second packet P2, etc.). 
     As shown in  FIG. 7 , row  152  of timing diagram  150  illustrates radio-frequency Bluetooth data that is transmitted using a first (default) antenna (“ANT 1 TX”). Row  154  of timing diagram  150  illustrates radio-frequency Bluetooth data that is received using the first antenna (“ANT 1 RX”). For example, row  152  may illustrate Bluetooth data that is transmitted using upper antenna  40 U of  FIG. 3  whereas row  154  illustrates Bluetooth data that is received using upper antenna  40 U. Row  156  of timing diagram  150  illustrates radio-frequency Bluetooth data that is transmitted using a secondary antenna (“ANT 2 TX”). Row  158  of timing diagram  150  illustrates radio-frequency Bluetooth data that is received using the secondary antenna (“ANT 2 RX”). For example, row  156  may illustrate Bluetooth data that is transmitted using lower antenna  40 L of  FIG. 3  whereas row  158  illustrates Bluetooth data that is received using lower antenna  40 L. 
     Prior to period T0, Bluetooth transceiver  64  may control switch  60  to couple default upper antenna  40 U to port  52  for transmission (e.g., while processing step  100  of  FIG. 6 ). Bluetooth transceiver  64  may transmit the first Bluetooth data packet P1 from the sequence using upper antenna  40 U during transmit period T0. Bluetooth transceiver  64  may wait for a predetermined (scheduled) amount of time (e.g., for the duration of scheduled receive time period T1) to receive an ACK packet corresponding to transmitted data packet P1 from external equipment  41  over upper antenna  40 U (e.g., while processing step  102  of  FIG. 6 ). 
     Each time period T may include a corresponding guard or buffer time  160  to allow time for Bluetooth transceiver  64  to perform any necessary frequency hopping or switching operations. For example, guard times  160  may allow time for transceiver circuitry  64  to perform changes in frequency for each packet. Similarly, guard times  160  may allow time for Bluetooth transceiver  64  to adjust switching circuitry  60  whenever it is desired to change the antenna that is coupled to port  52 . Each guard time  160  may be on the order of 0-1 μs, as an example. Each guard time  160  may have the same duration or different guard times  160  may have different durations. The example of  FIG. 7  in which guard times  160  occur at the beginning of each time period T is merely illustrative and, in general, guard times  160  may occur at the end of each time period T or at any other desired time in each time period T. 
     In the example of  FIG. 7 , upper antenna  40 U receives a scheduled first ACK packet “ACK P1” from external equipment  41  during receive time period T1. This may be indicative of external equipment  41  successfully receiving packet P1 during transmit time period T0. Transceiver circuitry  64  and upper antenna  40 U may subsequently transmit the second Bluetooth data packet P2 from the sequence during transmit time period T2 (e.g., while looping back to step  102  over path  104  of  FIG. 6 ). Transceiver circuitry  64  may wait to receive a scheduled ACK packet “ACK P2” corresponding to packet P2 from external equipment  41  during receive time period T3. 
     In the example of  FIG. 7 , upper antenna  40 U does not receive any ACK packets during receive time period T3. This may be indicative of an external object blocking upper antenna  40 U, changes in orientation of upper antenna  40 U with respect to external equipment  41 , or other antenna performance deteriorations. Because the scheduled ACK packet is not received during the expected amount of time (e.g., because ACK P2 is not received during the scheduled receive time period T3), transceiver circuitry  64  may subsequently adjust switch  60  to couple lower antenna  40 L to port  52  (e.g., while processing step  108  of  FIG. 6 ). Transceiver circuitry  64  may subsequently re-transmit second packet P2 using lower antenna  40 L during transmit time period T4 and wait to receive scheduled ACK packet ACK P2 from external equipment  41  during receive time period T5. In the example of  FIG. 7 , lower antenna  40 L receives scheduled ACK packet ACK P2 from external equipment  41  during receive time period T5. This may be indicative of external equipment  41  successfully receiving packet P2 during time period T4 (e.g., because lower antenna  40 L is not blocked by external objects and is able to successfully communicate with external equipment  41 ). 
     In one suitable arrangement, optional step  114  of  FIG. 6  may be performed whenever the secondary antenna is used to re-transmit a given Bluetooth packet while performing step  110  of  FIG. 6  (e.g., optional step  114  may be omitted whenever the default antenna is used to perform step  110 ). In the example of  FIG. 7 , lower antenna  40 L is the secondary antenna so transceiver circuitry  64  subsequently switches the default antenna (e.g., upper antenna  40 U) back into use (e.g., by adjusting switch  60  to couple antenna  40 U to port  52 ). Transceiver circuitry  64  may then transmit the third Bluetooth data packet P3 using selected upper antenna  40 U during scheduled transmit time period T6 (e.g., while processing step  102  after looping back through path  116  from step  114  of  FIG. 6 ). This example is merely illustrative. If desired, transceiver  64  may perform or omit optional step  114  every time processing loops back to step  102  via path  116  of  FIG. 6  for a given sequence of Bluetooth data packets. In another suitable arrangement, transceiver  64  may perform step  114  of  FIG. 6  for any desired first subset of Bluetooth data packets and may omit step  114  for any desired second subset of Bluetooth data packets from a given sequence of Bluetooth data packets. 
     Transceiver circuitry  64  may wait for the duration of receive time period T7 to receive scheduled ACK packet “ACK P3” corresponding to packet P3 from external equipment  41 . In the example of  FIG. 7 , upper antenna  40 U does not receive any ACK packets during receive time period T7. Because the scheduled ACK packet is not received in the expected amount of time (e.g., because scheduled ACK packet ACK P3 is not received during receive time period T7), transceiver circuitry  64  may subsequently adjust switch  60  to couple lower antenna  40 L to port  52  (e.g., while processing step  108  of  FIG. 6 ). Transceiver circuitry  64  may then re-transmit third packet P3 using lower antenna  40 L during transmit time period T8 and wait to receive scheduled ACK packet ACK P3 during receive time period T9 (e.g., while processing step  110  of  FIG. 6 ). 
     In the example of  FIG. 7 , lower antenna  40 L does not receive any ACK packets during receive time period T9. Because the expected ACK packet is not received in scheduled receive time period T9, transceiver circuitry  64  may proceed to determine whether the threshold number of re-transmit attempts for packet P3 has been exceeded (e.g., while processing step  120  of  FIG. 6 ). In this example, the threshold is three or greater and transceiver  64  subsequently switches upper antenna  40 U back into use (e.g., while processing steps  120  and  108  after looping back over path  122  of  FIG. 6 ). Transceiver  64  may re-transmit third packet P3 using upper antenna  40 U during transmit time period T10 and may wait to receive scheduled ACK packet ACK P3 using upper antenna  40 U during the corresponding receive time period T11 (e.g., while processing step  110  after looping back to step  108  over path  122  of  FIG. 6 ). 
     In the example of  FIG. 7 , transceiver circuitry  64  receives the expected ACK packet ACK P3 during receive period T11 using upper antenna  40 U. Because upper antenna  40 U is the default antenna in this scenario, transceiver  64  of  FIG. 7  omits optional step  114  of  FIG. 6  and transmits the next (fourth) Bluetooth data packet P4 in the sequence using upper antenna  40 U during transmit time period T12 (e.g., while looping back to step  102  over path  116  and omitting step  114  of  FIG. 6 ). In another suitable arrangement, transceiver  64  may perform optional step  114  of  FIG. 6  so that lower antenna  40 L transmits packet P4. 
     Transceiver circuitry  64  may wait to receive a scheduled ACK packet “ACK P4” from external equipment  41  over antenna  40 U during the subsequent receive time period T13. Because no ACK packets are received by antenna  40 U during receive time period T13, transceiver circuitry  64  may control switch  60  to couple lower antenna  40 L to port  52  (e.g., while processing step  108  of  FIG. 6 ). Transceiver  64  may re-transmit fourth packet P4 during transmit time period T14 and may wait to receive scheduled ACK packet ACK P4 during receive time period T15 (e.g., while processing step  110  of  FIG. 6 ). Because the scheduled ACK packet is not received in receive time period T15, transceiver circuitry  64  may proceed to determine whether the threshold number of re-transmit attempts for packet P4 has been exceeded (e.g., while processing step  120  of  FIG. 6 ). The threshold may be the same as or different from the threshold used when processing packet P3. For the sake of illustrating the different possible steps of  FIG. 6 , in the example of  FIG. 7 , the threshold for packet P4 is two re-transmits. Because packet P4 has only been re-transmitted once (which is less than the re-transmit threshold of two), transceiver circuitry  64  may control switch  60  to couple upper antenna  40 U to port  52  (e.g., while looping back to step  108  over path  122 ). 
     Transceiver circuitry  64  may re-transmit fourth packet P4 over upper antenna  40 U during transmit time period T16 and may wait to receive scheduled ACK packet ACK P4 over antenna  40 U during subsequent receive time period T17. Because scheduled ACK packet ACK P4 is not received over antenna  40 U during receive time period T17, transceiver  64  may compare the number of re-transmits for packet P4 to the re-transmit threshold. Because the re-transmit threshold for packet P4 is two in this example, transceiver  64  may move on to the next (fifth) Bluetooth data packet P5 in the stream and may control upper antenna  40 U to transmit the fifth Bluetooth data packet P5 during transmit time period T18 (e.g., while looping back to step  102  via paths  124  and  116  and omitting optional step  114  of  FIG. 6 ). In scenarios were optional step  114  is performed, lower antenna  40 L may be controlled to transmit packet P5. 
     In this way. Bluetooth transceiver  64  may utilize the scheduling of the Bluetooth protocol in addition to information about whether or not expected packets (e.g., scheduled ACK packets) are received in performing Bluetooth antenna diversity operations. In other words, transceiver  64  may determine whether a scheduled ACK packet has been received within a predetermined receive time period and may use that determination in deciding when to switch antennas. Such operations may be performed without input from other sensor circuitry that would otherwise identify the presence of environmental factors affecting antenna performance. This may, for example, reduce the amount of time and processing resources required to select which antenna to use for Bluetooth link  42  relative to scenarios where other sensor circuitry is used to select the antennas. In addition, these operations may be performed without transmitting the same Bluetooth data packet during two consecutive transmit time periods  80 , which may optimize the likelihood of successful reception of the Bluetooth data packets at external equipment  41 . This may, for example, allow for Bluetooth transceiver  64  to achieve improved data accuracy (e.g., reduced error rates) relative to scenarios in which a single antenna is used to perform Bluetooth communications. 
     The example of  FIG. 7  is merely illustrative of how Bluetooth data packets from a sequence of Bluetooth data may be transmitted and received by two different antennas while performing the Bluetooth diversity operations of  FIG. 6 . The performance of wireless communications circuitry  34  may vary in practice. For example, transceiver  64  may wait to receive more than one ACK packet or other scheduled packets during the odd numbered periods T. In the example of  FIG. 7 , each packet P and each ACK packet is shown as being conveyed over antennas  40  for the entirety of the corresponding time period T (minus buffer periods  160 ). This is merely illustrative and, in practice, each packet P and each ACK packet may be conveyed over antennas  40  for a subset of the corresponding time period T (excluding buffer periods  160 ). In general, other time periods may be interposed among the time periods T shown in  FIG. 7 , more than two antennas may be used, WLAN signals may be multiplexed onto antenna  40 L and/or antenna  40 U, each period may involve the transmission or reception of more than one data packet, etc. The examples above describe antenna diversity operations that are performed using the Bluetooth protocol. In general, similar antenna selection and diversity operations may be performed for communications using any desired short range or long range communications protocols. 
     The operations of devices  10  (e.g., the operations of  FIG. 6 ) may be performed by control circuitry  28 , applications processor  44 , and/or control circuitry on module  36 . During operation, this control circuitry (which may sometimes be referred to as processing circuitry, processing and storage, computing equipment, a computer, etc.) may be configured to perform the methods of  FIG. 6  and/or other operations (e.g., using dedicated hardware and/or using software code running on hardware such as control circuitry  28  and/or control circuitry on module  36 ). Software code for performing these operations may be stored on non-transitory (tangible) computer readable storage media. The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, other computer readable media, or combinations of these computer readable media. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  16  and/or  18 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20170228
Publication Date: 20181113
Grant Date: 20181113
Priority Date: 20170228
Inventors: DI NALLO, CARLO
PASCOLINI, MATTIA
GUTERMAN, Jerzy S.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04L5/006", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W72/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0404", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B1/401", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/006", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B7/0404", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L5/0023", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L1/1816", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L47/564", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B7/061", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0087", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/1887", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W84/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/0087", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/006", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L47/564", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B7/0404", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/1816", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/061", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L1/1887", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0023", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L1/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0604", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B7/0404", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/0064", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/006", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 63112540