Abstract:
Electronic devices may have multiple wireless integrated circuits such as a pair of baseband processor integrated circuits and may have multiple antennas such as a pair of antennas. An electronic device may be operated in different modes depending on the operating environment of the electronic device. When both antennas are unblocked, both baseband processors and both antennas may be used in transmitting signals. When one antenna is not available, the device may be operated in a mode in which the available antenna is used and both baseband processors are used or in a mode in which the available antenna is used and only one of the baseband processors is used. Operating mode decisions may be made so as to minimize the potential for intermodulation distortion and absorbed radiation.

Description:
[0001]    This application claims the benefit of provisional patent application No. 61/433,160, filed Jan. 14, 2011, which is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    This relates to electronic devices such as cellular telephones and, more particularly, to methods for transmitting wireless traffic across antenna arrays. 
         [0003]    Electronic devices such as cellular telephones contain wireless circuitry such as radio-frequency transceiver integrated circuits and associated wireless baseband circuitry. These wireless circuits may be used in handling wireless voice and data communications. 
         [0004]    In some cellular telephones, multiple antennas are available. Configurable circuitry in this type of cellular telephone may be used to choose which of the antennas should receive incoming wireless traffic based on factors such as the measured quality of received signals on each of the antennas. 
         [0005]    Challenges can arise, however, in determining how to optimize wireless performance when transmitting signals though this type of antenna configuration. If care is not taken, voice calls may be dropped or data transmission operations may be disrupted. 
         [0006]    It would therefore be desirable to provide improved ways in which to support wireless communications in electronic devices. 
       SUMMARY 
       [0007]    An electronic device may transmit voice and data using multiple antennas. For example, a device may have first and second antennas that can be selectively connected to a voice source and a data source using switching circuitry. The mode in which the device transmits signals may be adjusted dynamically during operation. Priority may be given to voice signals. If the device is operating at a large distance from a cell tower in which there is insufficient transmit power margin available to accommodate both data and voice, the device may use the best available antenna to transmit voice only (a 1×1 operating mode). If the device is operating close to a cell tower and both antennas are available, the device may transmit voice through one antenna and data through the other antenna (a 2×2 operating mode). If the device is operating close to a cell tower and only one antenna is available, the device may operate in a mode in which the available antenna is shared by the voice and data sources (a 2×1 operating mode). 
         [0008]    Further features of the present invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
           [0010]      FIG. 2  is a schematic diagram of a wireless network including a base station and an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
           [0011]      FIG. 3  is a diagram of illustrative wireless communications circuitry that may be used in an electronic device having multiple antennas in accordance with an embodiment of the present invention. 
           [0012]      FIG. 4  is a diagram illustrating a transmit mode in which first and second transceiver circuits are each coupled to a respective one of the antennas in accordance with an embodiment of the present invention. 
           [0013]      FIG. 5  is a diagram illustrating a transmit mode in which only one of the antennas is switched into use and in which that antenna is coupled to a selected one of two transceiver circuits in accordance with an embodiment of the present invention. 
           [0014]      FIG. 6  is a diagram illustrating a transmit mode in which only one of the antennas is switched into use and in which that antenna is shared between two transceiver circuits in accordance with an embodiment of the present invention. 
           [0015]      FIG. 7  is a diagram showing illustrative transmit modes in which a wireless electronic device may be operated in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Electronic devices may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. The wireless communications circuitry may include multiple antennas arranged to implement an antenna diversity system. 
         [0017]    The antennas can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may be formed from conductive electronic device structures such as conductive housing structures (e.g., a ground plane and part of a peripheral conductive housing member or other housing structures), traces on substrates such as traces on plastic, glass, or ceramic substrates, traces on flexible printed circuit boards (“flex circuits”), traces on rigid printed circuit boards (e.g., fiberglass-filled epoxy boards), sections of patterned metal foil, wires, strips of conductor, other conductive structures, or conductive structures that are formed from a combination of these structures. 
         [0018]    An illustrative electronic device of the type that may be provided with one or more antennas (e.g., two antennas, three antennas, four antennas, five or more antennas, etc.) is shown in  FIG. 1 . 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 cellular telephone, a media player, a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, etc. 
         [0019]    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. 
         [0020]    Device  10  may, if desired, have a display such as display  14 . Display  14  may, for example, be a touch screen that incorporates capacitive touch electrodes. Display  14  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electronic ink elements, liquid crystal display (LCD) components, or other suitable image pixel structures. A cover glass layer may cover the surface of display  14 . Portions of display  14  such as peripheral regions  201  may be inactive and may be devoid of image pixel structures. Portions of display  14  such as rectangular central portion  20 A (bounded by dashed line  20 ) may correspond to the active part of display  14 . In active display region  20 A, an array of image pixels may be used to display images for a user. 
         [0021]    The cover glass layer that covers display  14  may have openings such as a circular opening for button  16  and a speaker port opening such as speaker port opening  18  (e.g., for an ear speaker for a user). Device  10  may also have other openings (e.g., openings in display  14  and/or housing  12  for accommodating volume buttons, ringer buttons, sleep buttons, and other buttons, openings for an audio jack, data port connectors, removable media slots, etc.). 
         [0022]    Housing  12  may include a peripheral conductive member such as a bezel or band of metal that runs around the rectangular outline of display  14  and device  10  (as an example). The peripheral conductive member may be used in forming the antennas of device  10  if desired. 
         [0023]    Antennas may be located along the edges of device  10 , on the rear or front of device  10 , as extending elements or attachable structures, or elsewhere in device  10 . With one suitable arrangement, which is sometimes described herein as an example, device  10  may be provided with one or more antennas at lower end  24  of housing  12  and one or more antennas at upper end  22  of housing  12 . Locating antennas at opposing ends of device  10  (i.e., at the narrower end regions of display  14  and device  10  when device  10  has an elongated rectangular shape of the type shown in  FIG. 1 ) may allow these antennas to be formed at an appropriate distance from ground structures that are associated with the conductive portions of display  14  (e.g., the pixel array and driver circuits in active region  20 A of display  14 ). 
         [0024]    If desired, a first cellular telephone antenna may be located in region  24  and a second cellular telephone antenna may be located in region  22 . Antenna structures for handling satellite navigation signals such as Global Positioning System signals or wireless local area network signals such as IEEE 802.11 (WiFi®) signals or Bluetooth® signals may also be provided in regions  22  and/or  24  (either as separate additional antennas or as parts of the first and second cellular telephone antennas). Antenna structures may also be provided in regions  22  and/or  24  to handle WiMax (IEEE 802.16) signals. 
         [0025]    In regions  22  and  24 , openings may be formed between conductive housing structures and printed circuit boards and other conductive electrical components that make up device  10 . These openings may be filled with air, plastic, or other dielectrics. Conductive housing structures and other conductive structures may serve as a ground plane for the antennas in device  10 . The openings in regions  22  and  24  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 such as an inverted-F antenna resonating element formed from part of a conductive peripheral housing structure in device  10  from the ground plane, or may otherwise serve as part of antenna structures formed in regions  22  and  24 . 
         [0026]    Antennas may be formed in regions  22  and  24  that are identical (i.e., antennas may be formed in regions  22  and  24  that each cover the same set of cellular telephone bands or other communications bands of interest). Due to layout constraints or other design constraints, it may not be desirable to use identical antennas. Rather, it may be desirable to implement the antennas in regions  22  and  24  using different designs. For example, the first antenna in region  24  may cover all cellular telephone bands of interest (e.g., four or five bands) and the second antenna in region  22  may cover a subset of the four or five bands handled by the first antenna. Arrangements in which the antenna in region  24  handles a subset of the bands handled by the antenna in region  22  (or vice versa) may also be used. Tuning circuitry may be used to tune this type of antenna in real time to cover either a first subset of bands or a second subset of bands and thereby cover all bands of interest. 
         [0027]    A schematic diagram of a system in which electronic device  10  may operate is shown in  FIG. 2 . As shown in  FIG. 2 , system  11  may include wireless network equipment such as base station  21  (sometimes referred to as a base transceiver station). Base stations such as base station  21  may be associated with a cellular telephone network or other wireless networking equipment. Device  10  may communicate with base station  21  over wireless link  23  (e.g., a cellular telephone link or other wireless communications link). 
         [0028]    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  and other control circuits such as control circuits in wireless communications circuitry  34  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, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
         [0029]    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 such as base station  21 , 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, IEEE 802.16 (WiMax) protocols, cellular telephone protocols such as the “2G” Global System for Mobile Communications (GSM) protocol, the “2G” Code Division Multiple Access (CDMA) protocol, the “3G” Universal Mobile Telecommunications System (UMTS) protocol, the “4G” Long Term Evolution (LTE) protocol, etc. 
         [0030]    Circuitry  28  may be configured to implement control algorithms that control the use of antennas in device  10 . For example, circuitry  28  may configure wireless circuitry  34  to switch a particular antenna into use for transmitting and/or receiving signals. In some scenarios, circuitry  28  may be used in gathering sensor signals and signals that reflect the quality of received signals (e.g., received paging signals, received voice call traffic, received control channel signals, received traffic channel signals, etc.). Examples of signal quality measurements that may be made in device  10  include bit error rate measurements, signal-to-noise ratio measurements, measurements on the amount of power associated with incoming wireless signals, channel quality measurements based on received signal strength indicator (RSSI) information (RSSI measurements), channel quality measurements based on received signal code power (RSCP) information (RSCP measurements), channel quality measurements based on signal-to-interference ratio (SINR) and signal-to-noise ratio (SNR) information (SINR and SNR measurements), channel quality measurements based on signal quality data such as Ec/lo or Ec/No data (Ec/lo and Ec/No measurements), etc. This information may be used in controlling which antenna is used. Antenna selections can also be made based on other criteria. 
         [0031]    Input-output circuitry  30  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 circuitry  30  may include input-output devices  32 . Input-output devices  32  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, accelerometers (motion sensors), ambient light sensors, and other sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  32  and may receive status information and other output from device  10  using the output resources of input-output devices  32 . 
         [0032]    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, and other circuitry for handling RF wireless signals. 
         [0033]    Wireless communications circuitry  34  may include satellite navigation system receiver circuitry such as Global Positioning System (GPS) receiver circuitry  35  (e.g., for receiving satellite positioning signals at 1575 MHz). 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 cellular telephone bands such as bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz or other cellular telephone bands of interest. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired (e.g., WiMax circuitry, etc.). Wireless communications circuitry  34  may, for example, include, wireless circuitry for receiving radio and television signals, paging circuits, etc. 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. 
         [0034]    Wireless communications circuitry  34  may include antennas  40 . Antennas  40  may be formed using any suitable types of antenna. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, closed and open slot antenna structures, planar inverted-F antenna structures, helical antenna structures, strip antennas, monopoles, dipoles, 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. As described in connection with  FIG. 1 , there may be multiple cellular telephone antennas in device  10 . For example, there may be one cellular telephone antenna in region  24  of device  10  and another cellular telephone antenna in region  22  of device  10 . These antennas may be fixed or may be tunable. 
         [0035]    In some embodiments of the present invention, device  10  may be described that supports the circuit switching technology and packet switching technology. Circuit switching involves establishing a dedicated/exclusive communications channel through a network before any user data is transmitted. A channel established using circuit switching guarantees the full bandwidth of the channel and remains connected for the entire duration of the session (e.g., the channel remains unavailable to other users until the session is terminated and the channel is released). 
         [0036]    Traditionally, the Public Switched Telephone Network (PTSN) is implemented using circuit switching. Device  10  may include a baseband processing circuit configured to support circuit switching technologies such as the “3G” CDMA2000 1xRTT (sometimes referred to herein as “1x”) cellular telephone communications technology, the “3G” Universal Mobile Telecommunications System (UMTS) cellular telephone communications technology, and the “2G” GSM cellular telephone communications technology (as examples). The baseband processing circuit that is being operated to support circuit switching cellular telephone communications protocols may therefore sometimes be referred to as a “voice” baseband processor integrated circuit. 
         [0037]    Packet switching involves organizing data to be transmitted into groups referred to as packets in accordance with the Internet Protocol (IP). Each packet may contain the IP address of the source node, the IP address of the destination node, user data (often referred to as data load or payload), and other control information. Unlike circuit switching, packet switching shares available network resources among multiple users. Each packet being sent may be routed independently to the desired destination, and as a result, each packet may experience varying packet transfer delays. Packets arriving at the destination node may be buffered until all the packets have arrived. Once a sufficient number of packets have reached their destination, the packets can be reassembled to recover the original transmitted data at the source. 
         [0038]    The Internet and most local area networks rely on packet switching. Device  10  may include a baseband processing circuit configured to support packet switching technologies such as the “3G” Evolution-Data Optimized (sometimes referred to herein as “EV-DO”) radio access technology, the “4G” LTE radio access technology, the “3G” High Speed Packet Access (HSPA) radio access technology, the “2G” Enhanced Data Rates for GSM Evolution (EDGE) radio access technology, and the “2G” General Packet Radio Service (GPRS) radio access technology (as examples). The baseband processing circuit that is being operated to support packet switching radio access technologies may therefore sometimes be referred to as a “data” baseband processor integrated circuit. 
         [0039]    In one suitable arrangement of the present invention, device  10  may include a first baseband processing circuit  102  that is used exclusively (or primarily) for handling packet switched “data” traffic and a second baseband processing circuit  104  that is used exclusively (or primarily) for handling circuit switched “voice” traffic (see, e.g.,  FIG. 3 ). First and second baseband processing circuits  102  and  104  may be separate integrated circuits that are mounted on a printed circuit board secured within housing  12  of device  10 . As an example, first baseband processor  102  may include memory and control circuitry for implementing the LTE protocol stack to handle LTE functions while the second baseband processor  104  may include memory and control circuitry for implementing the UMTS protocol stack to handle UMTS functions. The use of device  10  that supports two radio access technologies such as LTE and UMTS radio access technologies is merely illustrative. If desired, processors  102  and  104  and additional baseband processing circuits within device  10  may be configured to support other radio access technologies. 
         [0040]    Baseband processors  102  and  104  may be coupled to a common control circuit such as applications processor  100 . Applications processor  100  may be configured to store and execute control code for implementing control algorithms. Baseband processors  102  and  104  may be part of wireless circuitry  34 , whereas applications processor  100  may be part of storage and processing circuitry  28 . Baseband processors  102  and  104  may provide data traffic and voice traffic to applications processor  100  via respective paths. In addition to the transmitted user data, processors  102  and  104  may also provide applications processor  100  with information on whether responses (acknowledgements) are being received from a cellular telephone tower corresponding to requests from device  10 , information on whether a network access procedure has succeeded, information on how many re-transmissions are being requested over a cellular link between the electronic device and a cellular tower, information on whether a loss of signaling message has been received, information on whether paging signals have been successfully received, and other information that is reflective of the performance of wireless circuitry  34 . This information may be analyzed by applications processor  100  and/or processors  102  and  104  and, in response, baseband processors  102  and  104  (or, if desired, applications processor  100 ) may issue control commands for controlling wireless circuitry  34 . For example, baseband processors  102  and  104  may issue control signals Vc over path  116  to selectively switch desired antennas in and out of use. 
         [0041]    Wireless circuitry  34  may include radio-frequency transceiver circuitry such as radio-frequency transceiver circuitry (e.g., transceiver circuits  106  and  108 ) and radio-frequency front-end circuitry  62 . Some transceivers may include both a transmitter and a receiver. If desired, one or more transceivers may be provided with receiver circuitry, but no transmitter circuitry (e.g., to use in implementing receive diversity schemes). As shown in the illustrative configuration of  FIG. 3 , transceiver  106  that is associated with data baseband processor  102  may include a transmitter such as transmitter  106 T and a receiver such as receiver  106 R, whereas transceiver  108  that is associated with voice baseband processor  104  may include a transmitter such as transmitter  108 T and a receiver such as receiver  108 R. 
         [0042]    Wireless communications circuitry  34  may further include radio-frequency front end circuitry  110  coupled between the transceiver circuitry and antennas  40 . In particular, transceivers  106  and  108  may be coupled to front end circuitry  110  via paths  112  and  114 , respectively. Radio-frequency front end  110  may be used to convey the radio-frequency signals that are produced by the radio-frequency transceiver circuitry to antennas  40 . Radio-frequency front end  110  may include radio-frequency switches, impedance matching circuits, band-pass filters, duplexers, power amplifiers, low noise amplifiers, and other circuitry for forming an interface between antennas  40  and transceivers  106  and  108 . Antennas  40  may include at least first antenna  40 A and second antenna  40 B. First antenna  40 A may be formed in region  24  of device  10 , whereas second antenna  40 B may be formed in region  22  of device  10 . Antenna  40 A may serve as the default active antenna and may be switched into use more often than antenna  40 B. Antenna  40 A may therefore sometimes be referred to as the primary antenna while antenna  40 B may be referred to as the secondary antenna. If desired, antennas  40  may include more than two antennas, more than five antennas, etc. 
         [0043]    Incoming radio-frequency signals that are received by antennas  40  may be provided to baseband processors  102  and  104  via radio-frequency front end  110 , paths such as paths  112  and  114 , and receiver circuitry in transceivers  106  and  108 . Path  112  may, for example, be used in handling signals associated with transceiver  106 , whereas path  114  may be used in handling signals associated with transceiver  108 . Baseband processors  102  and  104  may be used to convert received signals into digital data that is provided to applications processor  100 . Baseband processors  102  and  104  may also extract information from received signals that is indicative of signal quality for the channel to which the associated transceivers are currently tuned. 
         [0044]    Radio-frequency front end  110  may include switching circuitry. The switching circuitry may be configured by control signals Vc received from applications processor  100  (e.g., control signals from storage and processing circuitry  28  via path  116 ). If desired, the state of radio-frequency front end  110  may also be controlled using control signals generated from at least one of baseband processors  102  and  104 . 
         [0045]    As an example, the switching circuitry in front end  110  may be capable of coupling transceiver  106  to antenna  40 B while coupling transceiver  108  to antenna  40 A so that each of baseband processors  102  and  104  is transmitting/receiving radio-frequency signals via a respective dedicated antenna (e.g., wireless circuitry  34  may be placed in dual antenna mode). As another example, the switching circuitry may be capable of switching one antenna into use (referred to as a currently active antenna) while switching the other antenna out of use (referred to as a currently inactive antenna). In this scenario, the currently active antenna may be coupled to either transceiver  106  for handling data traffic or transceiver  108  for handling voice traffic. As another example, the switching circuitry may be capable of coupling both antennas to a selected one of transceivers  106  and  108  for implementing receive diversity (e.g., both antennas  40  may feed received signals to the receiver in the selected transceiver). As another example, the switching circuitry may be capable of coupling both transceivers  106  and  108  to one active antenna so that transmit signals may be radiated using a common antenna. 
         [0046]    If desired, antenna selection may be made by selectively activating and deactivating transceivers without using a switch in front end  110 . For example, if it is desired to use antenna  40 A but not antenna  40 B, transceiver  108  (which may be coupled to antenna  40 A through circuitry  110 ) may be activated and transceiver  106  (which may be coupled to antenna  40 B through circuitry  110 ) may be deactivated. If it is desired to use antenna  40 B but not antenna  40 A, applications processor  100  may activate transceiver  106  and deactivate transceiver  108 . Combinations of these approaches may also be used to select which antennas are being used to transmit and/or receive signals. When it is desired to receive incoming signals such as paging signals using both antennas, transceiver  106  and transceiver  108  may be simultaneously activated to place device  10  in a dual antenna mode. The radio configuration of  FIG. 3  is merely illustrative and is not intended to limit the scope of the present invention. If desired wireless circuitry  34  may include any number of baseband processing integrated circuits and associated transceivers, any number of antennas, and any suitable circuitry for interfacing the antennas and the transceivers. 
         [0047]    Embodiments of the present invention relate to different ways of transmitting voice and data signals using antennas  40  on a device  10 . Antenna  40 A may, for example, exhibit a maximum free-space total radiated power (e.g., a measurement reflective of antenna efficiency) greater than that of antenna  40 B. Consider a scenario in which device  10  is used to simultaneously maintain a voice call and a data session (i.e., data baseband processor  102  and voice baseband processor  104  both needs to transmit radio-frequency signals via at least one of antennas  40 ). In this scenario, primary antenna  40 A may be used to handle the voice traffic while secondary antenna  40 B may be used to handle the data traffic (e.g., voice traffic may have priority over data traffic and may therefore be transmitted using the antenna with greater efficiency). 
         [0048]    The performance of antenna  40 A may, however, be degraded when a user of device  10  holds device  10  in a certain manner during wireless transmission. For example, the user gripping lower end  24  of housing  12  during a voice call may substantially attenuate the output power of lower antenna  40 A. Device  10  may be capable of detecting such attenuation and may reconfigure radio-frequency front end  110  to switch antenna  40 A out of use. Signals generated using voice baseband processor  104  may be rerouted to antenna  40 B for transmitting. Operations associated with data baseband processor  102  may continue using remaining active antenna  40 B or may be temporarily put on hold for at least the duration of the voice call. 
         [0049]    In one suitable arrangement of the present invention, device  10  may be placed in a first transmit mode (mode 2×2) in which each of the baseband processors transmits signals using a respective one of antennas  40  (see, e.g.,  FIG. 4 ).  FIG. 4  shows exemplary wireless circuitry in the transmit path between antennas  40  and the transceivers. Receive circuitry is not shown for clarity. As shown in  FIG. 4 , front end  110  may include radio-frequency switching circuitry such as radio-frequency switching circuitry  204 , power amplifying circuitry such as power amplifiers  206 - 1  and  206 - 2 , a radio-frequency combiner such as combiner  200 , and multiplexing circuit  202 . 
         [0050]    Switching circuitry  204  may be a crossover (double-pole-double-throw) switch. Switch  204  may have a first port P 1  that is coupled to data transmitter  106 T, a second port P 2  that is coupled to voice transmitter  108 T, a third port P 3  that is coupled to antenna  40 A via power amplifier  206 - 1 , and a fourth port P 4  that is coupled to antenna  40 B via power amplifier  206 - 2 . The state of switch  204  may be controlled by control signals received on path  116  from applications processor (sometimes referred to as control circuitry)  100 . 
         [0051]    In particular, data transmitter  106 T may have a first output that is coupled to port P 1  and a second output that is coupled to a first input of combiner  200 . Voice transmitter  108 T may have a first output and a second output that is coupled to a second input of combiner  200 . Radio-frequency combiner  200  may serve to combine the two radio-frequency signals received at its inputs and present the combined version of the input signals at its output. Multiplexer  202  may have a first input that is coupled to the first output of voice transmitter  108 T, a second input that is coupled to the output of combiner  200 , an output that is coupled to port P 2 , and a control input that receives controls signals from control circuitry  100  via path  116 . These control signals may configure multiplexer  202  to route radio-frequency signals from a selected one of its inputs to its output. 
         [0052]    In the 2×2 mode, multiplexer  202  may be configured to route radio-frequency signals from its first input to its output (e.g., the voice signals generated at it output of voice transmitter  108 T may be passed directly to port P 2  as indicated by dotted path  215 ). In this mode, switch  204  may be configured to couple P 1  to a selected one of the antennas and to couple P 2  to the other antenna. As an example, switch  204  may be configured to couple port P 1  to P 4  (e.g., to couple data transmitter  106 T to antenna  40 B, as shown by dotted line  212 ) and to couple port P 2  to P 3  (e.g., to couple voice transmitter  108 T to antenna  40 A, as shown by dotted line  210 ). As another example, switch  204  may be configured to couple port P 1  to P 3  (e.g., to couple data transmitter  106 T to antenna  40 A) and to couple port P 2  to P 4  (e.g., to couple voice transmitter  108 T to antenna  40 B). 
         [0053]    Antenna  40 A may not always exhibit better transmit performance than antenna  40 B. As described previously, device  10  may be capable of obtaining signal quality measurements such as bit error rate measurements, RSSI measurements, RSCP measurements, SINR and SNR measurements, channel quality measurements based on signal quality data, and other radio-frequency measurements. This information can be used to determine to which one of the multiple antennas each of the baseband processors is coupled. For example, in a data priority scheme (i.e., a scheme in which data traffic is given higher priority over voice traffic), data transmitter  106 T may be coupled to the antenna exhibiting higher performance levels while voice transmitter  108 T is coupled to the antenna exhibiting lower performance levels. In a voice priority scheme (i.e., a scheme in which voice traffic is given higher priority over data traffic), voice transmitter  108 T may be coupled to the antenna exhibiting greater signal strength while data transmitter  106 T is coupled to the antenna exhibiter lesser signal strength. 
         [0054]    In the 2×2 transmit mode, at least one of transmitters  106 T and  108 T may be momentarily throttled to help reduce wireless interference. For example, consider a scenario in which data baseband processor  102  is transmitting uplink signals in LTE band  15  at 1900 MHz while voice baseband processor  104  is transmitting uplink signals in the UMTS Personal Communications Service (PCS) band at 1850 MHz. Ideally, the transmit circuitry (e.g., the power amplifiers, switches, duplexers, and other front end circuitry) associated with the data and voice baseband processors is perfectly linear. In practice, however, the transmitter circuits exhibit nonlinearities, which can create undesired spurious emissions at sideband frequencies that are relatively close to the fundamental operating frequencies. This phenomenon in which spurious signals are generated at frequencies other than at harmonic frequencies is sometimes referred to as intermodulation distortion. In the above scenario, third order intermodulation distortion (IMD3) signals may be generated at 1800 MHz (i.e., 2*1850 minus 1900), at 1950 MHz (i.e., 2*1900 minus 1850), and at other intermodulation frequencies (as an example). Sideband signals generated in this way contribute to adjacent channel leakage, which can result in adjacent channel interference, a reduction in dynamic range, increased spectrum usage, and other unwanted effects. 
         [0055]    In scenarios where the intermodulation signals are unacceptably noisy, at least one of the baseband processors may be temporarily placed in idle mode to eliminate intermodulation distortion. For example, if the IMD3 spurious signals exceed a predetermined level, data baseband processor  102  may be temporarily throttled until voice baseband processor  104  is no longer transmitting any voice traffic (in a voice transmit priority scheme). If desired, voice baseband processor  104  may be temporarily throttled until data baseband processor  102  is no longer transmitting any data traffic (in a data transmit priority scheme). 
         [0056]    The example of  FIG. 4  is merely illustrative and is not intended to limit the scope of the present invention. In general, device  10  may have any number of baseband processing integrated circuits that can transmit in parallel radio-frequency uplink signals using any number of antennas, where at least one of the multiple baseband processing integrated circuits may be throttled during instances in which intermodulation distortion is creating exceedingly high adjacent channel leakage levels. 
         [0057]    In another suitable arrangement of the present invention, device  10  may be placed in a second transmit mode (mode 1×1) in which only one antenna is active and in which that active antenna is being used to serve only one of the baseband processors (see, e.g.,  FIG. 5 ). In the 1×1 mode, multiplexer  202  may be configured to route radio-frequency signals from its first input to its output (e.g., voice signals may be passed directly to port P 2  as indicated by dotted path  216 ). As shown in  FIG. 5 , switch  204  may be configured to couple P 2  to antenna  40 B if signals received at antenna  40 A are severely attenuated (e.g., if receive signal strength is reduced from nominal levels by at least 20 dBm), as shown by dotted line  214 . When antenna  40 B is transmitting voice traffic, data transmitter  106 T may be temporarily placed in idle mode (e.g., data transmitter  106 T may be decoupled from antennas  40 ). 
         [0058]    As another example, data transmitter  106 T may transmit data signals using only antenna  40 A while voice transmitter  108 T is placed in idle mode (when device  10  is not being used in a voice call). In particular, switch  204  may be configured to couple port P 1  to P 3  while port P 2  is decoupled from antennas  40 . If the reception at antenna  40 A falls below satisfactory levels, data transmitter  106 T may rely on antenna  40 B to handle data traffic (e.g., switch  204  may be reconfigured to couple port P 1  to P 4 ). In general, it may be desirable to switch the antenna that is currently exhibiting higher transmit efficiency into use to support the active baseband processor during the second transmit mode. Device  10  operating in the 1×1 mode may experience minimal interference and out-of-band emissions, because only one of the two baseband processing circuits is transmitting radio-frequency signals at any given point during the 1×1 operating mode, thereby eliminating any intermodulation distortion. 
         [0059]    In another suitable arrangement of the present invention, device  10  may be placed in a third transmit mode (mode 2×1) in which only one antenna is active and in which that active antenna is being shared between the multiple baseband processors (see, e.g.,  FIG. 6 ). In the 2×1 mode, multiplexer  202  may be configured to route radio-frequency signals from its second input to its output (e.g., voice and data signals may be passed to port P 2  as indicated by dotted path  218 ). As shown in  FIG. 5 , switch  204  may be configured to couple P 2  to antenna  40 B if signals received at antenna  40 A are severely attenuated, as shown by dotted line  220 . In the 2×1 transmit mode, both data transmitter  106 T and voice transmitter  108 T may be transmitting at relatively lower power levels because the maximum total radiated power of antenna  40 B is limited (i.e., a first portion of the maximum TRP is being used by voice transmitter  108 T, whereas a second portion of the maximum TRP is being used by data transmitter  106 T). 
         [0060]    Device  10  operating in the 2×1 transmit mode may also be configured to monitor the sidebands for intermodulation distortion. In scenarios in which the third order intermodulation distortion spurious signals (sometimes referred to as IMD3 products/terms) exceed acceptable threshold levels, at least one of the baseband processors may be forced to transmit at further reduced output power levels or may be throttled. Intermodulation distortion constraints associated with the 2×1 transmit mode are generally more stringent than the IMD requirements associated with the 2×2 transmit mode because using a single antenna to transmit in multiple frequency bands is inherently more prone to adjacent channel leakage compared to using multiple antennas to transmit in respective frequency bands. 
         [0061]      FIG. 7  is a state diagram showing different illustrative transmit modes in which device  10  may operate. In each of the modes of  FIG. 7 , assume that device  10  has to transmit voice traffic (e.g., device  10  is in a voice call). As shown in  FIG. 7 , device  10  may operate in first transmit mode 2×2. When operating in the first transmit mode, voice baseband processor  104  may be switchably coupled to a first of multiple antennas  40  in device  10 , whereas data baseband processor  102  may be switchably coupled a second of multiple antennas  40  in device  10 . If desired, voice baseband processor  104  may be coupled to the antenna that is currently exhibiting the highest wireless transmission performance. Data transmitter  106 T may be optionally throttled in response to detecting undesired IMD3 interference (as an example). 
         [0062]    If at least one of antennas  40  experiences high levels of signal attenuation (e.g., if signals received using antenna  40 A is attenuated below nominal power levels by 40 dB), device  10  may be placed in either the second transmit mode (mode 1×1) or the third transmit mode (mode 2×1). In mode 1×1, voice transmitter  108 T may be configured to transmit at maximum output power via antenna  40 B while data transmitter  106 T is throttled to suppress possible thermal noise or interference terms. 
         [0063]    In mode 2×1, voice transmitter  108 T may be configured to transmit at an output power level that is less than the maximum output power. Data transmitter  106 T may optionally be transmitted using shared antenna  40 B, as long as intermodulation distortion terms are kept under satisfactory levels. 
         [0064]    Device  10  may continuously monitor the radio-frequency performance levels associated with antennas  40 . In response to antenna  40 A exceeding satisfactory performance criteria, device  10  may be placed in mode 2×2, as indicated by path  304 . The modes of  FIG. 7  assume that voice baseband processor  104  is currently generating active voice traffic that needs to be transmitted. During times when voice baseband processor  104  is idle (or in a sleep state), device may operating in a 1×1 mode in which data transmitter  106 T transmits data traffic at maximum output power levels using any desired antenna (e.g., using the better antenna). 
         [0065]    The three different transmit configurations shown in  FIG. 7  are merely illustrative and do not serve to limit the scope of the present invention. If desired, device  10  may be operable in less than three transmit modes, more than three transmit modes, or may be operating in any suitable transmit mode that uses any desired number of physical antennas to transmit any number/types of wireless traffic signals. 
         [0066]    The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.