PATENT DOCUMENT

Publication Number: US-10104615-B2
Application Number: US-201715444043-A
Country: US
Kind Code: B2

Title: Synchronized low-energy detection technique

Abstract:
In order to reduce the power consumption after a transmitting electronic device in a wireless network has been detected, a receiving electronic device calculates transmit times of subsequent beacons from the transmitting electronic device based on a clock drift of the transmitting electronic device and the beacon period. Then, the receiving electronic device receives the subsequent beacon by opening scan windows that encompass the calculated transmit times. However, because the transmit times are more predictable after the transmitting electronic device has been detected (and the clock drift of the transmitting electronic device is known to the receiving electronic device), the receiving electronic device can reduce the width of the scan windows. In addition, the transmitting electronic device can further reduce the power consumption by increasing the beacon period.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 an interface circuit configured to: 
 periodically scan for beacons in a high power-consumption mode using a plurality of high-power scan windows; 
 receive a first beacon during a first scan window of the plurality of high-power scan windows; 
 establish a connection based at least in part on the received first beacon; and 
 subsequent to establishing the connection, periodically scan for beacons in a low power-consumption mode using a plurality of low-power scan windows. 
 
     
     
       2. The electronic device of  claim 1 , wherein each scan window in the plurality of low-power scan windows has a smaller width than each scan window in the plurality of high-power scan windows. 
     
     
       3. The electronic device of  claim 1 , wherein the interface circuit is further configured to calculate and transmit a revised beacon period subsequent to establishing the connection. 
     
     
       4. The electronic device of  claim 1 ,
 wherein to periodically scan for beacons in the high power-consumption mode, the interface circuit is configured to scan using high-power scan windows separated by a high-power window period; 
 wherein to periodically scan for beacons in the low power-consumption mode, the interface circuit is configured to scan using low-power scan windows separated by a low-power window period; and 
 wherein the high-power window period is shorter than the low-power window period. 
 
     
     
       5. The electronic device of  claim 1 , wherein the interface circuit is further configured to periodically scan for beacons, subsequent to a predetermined time duration after establishing the connection, in a high power-consumption mode using a plurality of high-power scan windows. 
     
     
       6. The electronic device of  claim 1 , wherein the interface circuit is further configured to:
 receive a network clock; 
 calculate a transmit time of a second beacon in a set of future beacons based at least in part on the network clock; 
 receive the second beacon at an actual transmit time; 
 compare the actual transmit time of the second beacon with the calculated transmit time of the second beacon; and 
 in response to a determination that a difference between the actual transmit time of the second beacon and the calculated transmit time of the second beacon exceeds a threshold value, determine and transmit a synchronization correction. 
 
     
     
       7. A method comprising:
 receiving, using an interface circuit of an electronic device operating in a high power-consumption mode, a first beacon; 
 establishing a connection based at least in part on the received first beacon; 
 after establishing the connection, periodically scanning for beacons in a low power-consumption mode using a plurality of low-power scan windows and receiving, using the interface circuit operating in the low power-consumption mode, a second beacon; and 
 prior to receiving the first beacon, periodically scanning for beacons using a plurality of high-power scan windows. 
 
     
     
       8. The method of  claim 7 , further comprising receiving, prior to establishing the connection, clock information. 
     
     
       9. The method of  claim 8 , wherein receiving the clock information comprises performing one of:
 receiving information that specifies an initial beacon period and a clock drift; receiving a set of beacons and determining the initial beacon period and the clock drift using the set of beacons; accessing, via a network, information specifying the initial beacon period and the clock drift; or accessing information, stored in the electronic device, specifying the initial beacon period and the clock drift. 
 
     
     
       10. The method of  claim 7 , further comprising:
 receiving a network clock; 
 calculating a transmit time of a second beacon in a set of future beacons based at least in part on the network clock; 
 receiving the second beacon at an actual transmit time; 
 comparing the actual transmit time of the second beacon with the calculated transmit time of the second beacon; and 
 in response to a determination that a difference between the actual transmit time of the second beacon and the calculated transmit time of the second beacon exceeds a threshold value, determining and transmitting a synchronization correction. 
 
     
     
       11. The method of  claim 7 ,
 wherein high-power scan windows are separated in time by a high-power window period; 
 wherein low-power scan windows are separated in time by a low-power window period; and 
 wherein the high-power window period is less than the low-power window period. 
 
     
     
       12. The method of  claim 7 ,
 wherein each scan window in the plurality of low-power scan windows has a smaller width than each scan window in the plurality of high-power scan windows. 
 
     
     
       13. The method of  claim 7 , further comprising calculating and transmitting a revised beacon period subsequent to establishing the connection. 
     
     
       14. An electronic device, comprising:
 an interface circuit configured to: 
 periodically transmit a first set of beacons while operating in a high power-consumption mode; 
 establish a connection based at least in part on a beacon in the first set of beacons transmitted while operating in the high power-consumption mode; 
 subsequent to establishing the connection, periodically transmit a second set of beacons while operating in a low power-consumption mode. 
 
     
     
       15. The electronic device of  claim 14 ,
 wherein, in the high power-consumption mode, the interface circuit is configured to transmit beacons at a first beacon periodicity; 
 wherein, in the low power-consumption mode, the interface circuit is configured to transmit beacons at a second beacon periodicity; and 
 wherein the first periodicity is shorter than the second beacon periodicity. 
 
     
     
       16. The electronic device of  claim 15 , wherein, to establish the connection, the interface circuit is configured to receive the second beacon periodicity. 
     
     
       17. The electronic device of  claim 15 , wherein the interface circuit is further configured to transmit, while transmitting the beacons, information that indicates the first beacon periodicity. 
     
     
       18. The electronic device of  claim 14 ,
 further comprising a clock circuit configured to output a clock signal; 
 wherein the interface circuit is further configured to: 
 receive a network clock, wherein the clock circuit outputs the clock signal using the network clock; 
 receive a synchronization correction; and 
 adjust the clock circuit based at least in part on the synchronization correction. 
 
     
     
       19. The electronic device of  claim 14 ,
 further comprising a clock circuit configured to output a clock signal; 
 wherein the interface circuit is further configured to transmit, while transmitting the beacons, information that specifies a clock drift of the clock signal. 
 
     
     
       20. The electronic device of  claim 1 , wherein the interface circuit is configured to transmit a synchronization correction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/222,264, titled “SYNCHRONIZED LOW-ENERGY DETECTION TECHNIQUE,” which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The described embodiments relate to techniques for reducing power consumption by synchronizing the detection of electronic devices in a wireless network. 
     Related Art 
     Many modern electronic devices include a networking subsystem that is used to wirelessly communicate with other electronic devices. For example, these electronic devices can include a networking subsystem with a cellular network interface (UMTS, LTE, etc.), a wireless local area network interface (e.g., a wireless network such as described in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard or Bluetooth™ from the Bluetooth Special Interests Group of Kirkland, Wash.), and/or another type of wireless interface. 
     In many wireless-communication protocols, electronic devices detect each other by regularly broadcasting beacons and scanning for the beacons from other electronic devices. For example, an electronic device that communicates with another electronic device in a wireless network using a communication protocol that is compatible with an IEEE 802.11 standard (which is sometimes referred to as ‘Wi-Fi’) may wake up its radio periodically to receive a beacon frame at beacon transmission times. 
     However, regularly transmitting and receiving these beacons typically results in significant power consumption by the networking subsystems. Therefore, the existing detection techniques in wireless networks may reduce the operating time of the electronic device, which can degrade the user experience. 
     SUMMARY 
     The described embodiments include a receiving electronic device. This receiving electronic device includes: an antenna; and an interface circuit, coupled to the antenna, that communicates with a transmitting electronic device in a wireless network. The interface circuit detects the transmitting electronic device by receiving, during a scan window, a beacon in a set of beacons having an initial beacon period, where the interface circuit uses scan windows having an initial window width and an initial window period. Then, the interface circuit calculates transmit times of subsequent beacons from the transmitting electronic device based on clock drift of the transmitting electronic device and/or the initial beacon period. Next, the interface circuit receives the subsequent beacons from the transmitting electronic device during subsequent scan windows that encompass the calculated transmit times of the subsequent beacons, where the subsequent scan windows have widths that are less than the initial width. 
     In some embodiments, after detecting the transmitting electronic device, the interface circuit provides a revised beacon period to the transmitting electronic device, where the revised beacon period is greater than the initial beacon period, and the calculated transmit times of the subsequent beacons are further calculated based on the revised beacon period. 
     Moreover, for subsequent times greater than a synchronization time between the transmitting electronic device and the receiving electronic device, the interface circuit may receive the subsequent beacons from the transmitting electronic device by opening scan windows having the initial width at the initial window period. Thus, after the synchronization time, the receiving electronic device may revert to an initial detection technique. 
     Furthermore, for the subsequent times, the subsequent scan windows may increase in size as a function of time, and the increase in size may be proportionate to the clock drift. 
     The receiving electronic device may obtain or determine the clock drift of the transmitting electronic device in a variety of ways. In particular, after detecting the transmitting electronic device, the interface circuit may: receive information from the transmitting electronic device that specifies the initial beacon period and the clock drift; receive transmitted beacons and determine the initial beacon period and the clock drift based on the transmitted beacons; access, via a network, information specifying the initial beacon period and the clock drift; and access information, stored in the receiving electronic device, specifying the initial beacon period and the clock drift. 
     In some embodiments, the interface circuit: receives a network clock via a network, where the calculated transmit times are also based on the network clock. Then, the interface circuit compares the transmit times of the subsequent beacons with the network clock. When a difference between the transmit times and the calculated transmit times exceeds a threshold value, the interface circuit provides a synchronization correction to the transmitting electronic device. 
     Note that in some embodiments at least some of the preceding operations performed by the interface circuit are performed by a processor executing a program module that includes instructions for at least some of the preceding operations. 
     Another embodiment provides a computer-program product for use with the receiving electronic device. This computer-program product includes instructions for at least some of the operations performed by the receiving electronic device. 
     Another embodiment provides a method for communicating between the transmitting electronic device and the receiving electronic device. This method includes at least some of the operations performed by the receiving electronic device. 
     Another embodiment provides the transmitting electronic device. The transmitting electronic device includes: an antenna; and an interface circuit, coupled to the antenna, that communicates with the receiving electronic device in the wireless network. Moreover, the interface circuit transmits beacons based on the initial beacon period. Then, the interface circuit receives the revised beacon period from the receiving electronic device, where the revised beacon period is greater than the initial beacon period. Next, the interface circuit transmits beacons based on the revised beacon period. 
     Note that the transmitting electronic device may include a clock circuit having a clock drift, and the beacons may be transmitted at transmit times based on a clock output by the clock circuit. Moreover, the interface circuit may receive the network clock via the network, where the clock circuit outputs the clock based on the network clock. Then, the interface circuit may receive, from the receiving electronic device, the synchronization correction. Next, the interface circuit may adjust the clock circuit based on the synchronization correction so that a difference between the network clock and a multiple of the clock is less than a threshold value. 
     In some embodiments, while transmitting the beacons, the interface circuit provides information to the receiving electronic device that specifies the initial beacon period and the clock drift. 
     Another embodiment provides a computer-program product for use with the transmitting electronic device. This computer-program product includes instructions for at least some of the operations performed by the transmitting electronic device. 
     Another embodiment provides a method for communicating between the transmitting electronic device and the receiving electronic device. This method includes at least some of the operations performed by the transmitting electronic device. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a block diagram illustrating electronic devices wirelessly communicating in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a timing diagram illustrating communication between the electronic devices of  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 3  is a timing diagram illustrating communication between the electronic devices of  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 4  is a timing diagram illustrating communication between the electronic devices of  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 5  is a flow diagram illustrating a method for communicating between the electronic devices in  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 6  is a flow diagram illustrating a method for communicating between the electronic devices of  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 7  is a drawing illustrating communication between the electronic devices of  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 8  is a block diagram illustrating one of the electronic devices of  FIG. 1  in accordance with an embodiment of the present disclosure. 
     
    
    
     Note that like reference numerals refer to corresponding parts throughout the drawings. Moreover, multiple instances of the same part are designated by a common prefix separated from an instance number by a dash. 
     DETAILED DESCRIPTION 
     In order to reduce the power consumption after a transmitting electronic device (such as a sensor) in a wireless network has been detected, a receiving electronic device (such as a smartphone) calculates transmit times of subsequent beacons from the transmitting electronic device based on a clock drift of the transmitting electronic device and the beacon period. Then, the receiving electronic device receives the subsequent beacon by opening scan windows that encompass the calculated transmit times. However, because the transmit times are more predictable after the transmitting electronic device has been detected (and the clock drift of the transmitting electronic device is known to the receiving electronic device), the receiving electronic device can reduce the width of the scan windows. In addition, the transmitting electronic device can further reduce the power consumption by increasing the beacon period. The receiving electronic device may also monitor synchronization with the transmitting electronic device based on actual beacon transmit times, and may provide a synchronization correction to the transmitting electronic device to maintain the synchronization, thereby allowing continued use of the smaller scan windows and/or the increased beacon period. 
     For example, the beacons, information specifying the clock drift, and the synchronization correction may be conveyed in packets that are transmitted and received by radios in the receiving electronic devices in accordance with a communication protocol, such as an Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, Bluetooth™ (from the Bluetooth Special Interests Group of Kirkland, Wash.), and/or another type of wireless interface. In the discussion that follows, Bluetooth™ is used as an illustrative example. 
     The communication between the electronic devices is shown in  FIG. 1 , which presents a block diagram illustrating electronic devices  110  and  112  wirelessly communicating. In particular, these electronic devices may wirelessly communicate while: detecting one another by scanning wireless channels, transmitting and receiving beacons or beacon frames on wireless channels, establishing connections (for example, by transmitting connect requests), and/or transmitting and receiving packets (which may include the request and/or additional information as payloads). 
     As described further below with reference to  FIG. 8 , electronic devices  110  and  112  may include subsystems, such as a networking subsystem, a memory subsystem and a processor subsystem. In addition, electronic devices  110  and  112  may include radios  114  in the networking subsystems. More generally, electronic devices  110  and  112  can include (or can be included within) any electronic devices with the networking subsystems that enable electronic devices  110  and  112  to wirelessly communicate with another electronic device. This can comprise transmitting beacons on wireless channels to enable electronic devices to make initial contact with or detect each other, followed by exchanging subsequent data/management frames (such as connect requests) to establish a connection, configure security options (e.g., IPSec), transmit and receive packets or frames via the connection, etc. 
     As can be seen in  FIG. 1 , wireless signals  116  (represented by a jagged line) are transmitted from a radio  114 - 1  in electronic device  110 . These wireless signals  116  are received by radio  114 - 2  in electronic device  112 . In particular, electronic device  110  (such as a sensor, e.g., a heart-rate monitor or a computer mouse) may broadcast or transmit beacons at transmit times. In turn, electronic device  112  (such as a smartphone) may receive one or more beacons, thereby detecting the presence of electronic device  110 , by opening scan windows during the transmit times. This may allow electronic devices  110  and  112  to optionally establish a connection and communicate with each other. 
     However, because electronic devices  110  and  112  are not synchronized, electronic device  110  may need to transit beacons more often and/or electronic device  112  may need to use a wide scan-window width in order to ensure that the beacons are received. In turn, this may require the networking subsystems (such as interface circuits) in electronic devices  110  and  112  to be in active or a high power-consumption mode more often and/or for a longer duration, which may increase the power consumption and decrease the operating time of electronic devices  110  and  112 . 
     In the detection technique described below, electronic device  112  may receive or determine a clock drift of electronic device  110  after or while electronic device  110  is discovered. For example, electronic device  112  may receive, via wireless communication, information specifying the clock drift from electronic device  110 . Alternatively or additionally, electronic device  112  may determine the clock drift by measuring the transmit times, accessing, via network  118 , the information stored in computer  120  and/or accessing information, stored in electronic device  112 , specifying the clock drift (e.g., the information may have been preloaded into electronic device  112 ). 
     Using the clock drift of electronic device  110 , electronic device  112  may calculate the subsequent transmit times of beacons from electronic device  110 . This may allow electronic device  112  to use smaller scan-window widths. In addition, electronic device  112  may provide instructions to electronic device  110  to increase the time interval between beacon transmit times (which is sometimes referred to as the ‘beacon period’). In this way, the detection technique may allow the networking subsystems in electronic devices  110  and/or  112  to spend less time in the high power-consumption mode, thereby reducing the power consumption and increasing the operating time between battery charging of electronic devices  110  and/or  112 . 
     Over time, the uncertainty in the transmit times will grow. Eventually, after a synchronization time, the uncertainty is large enough that electronic device  112  would have to revert to the initial scan-window width and/or electronic device  110  would have to revert to the initial beacon period. For example, electronic devices  110  and  112  may connect and communicate briefly. If there is no communication between electronic devices  110  and  112  for a time interval and then electronic devices  110  and  112  attempt to communicate again, electronic device  112  may ‘remember’ electronic device  110  and may use the reduced scan-window width so long as this subsequent communication occurs for times less than the synchronization time after the initial connection between electronic devices  110  and  112  or the initial detection of electronic device  110 . Otherwise, electronic devices  110  and  112  may use the initial beacon period and/or the reduced scan-window width. 
     In an alternative approach, electronic device  112  may monitor the transmit times of the subsequent beacons from electronic device  110  and may provide a synchronization correction to electronic device  110  so that the synchronization between electronic devices  110  and  112  is maintained (i.e., the uncertainty in the transmit times may remain bounded). This re-synchronization approach may be facilitated by a network clock, such as one provided by: computer  120 , a cellular-telephone network and/or a global positioning system such as GPS (thus the network clock may be a GPS clock). In particular, electronic device  112  can use its own clock and/or the network clock to assess the drift in the transmit times and can provide, via wireless communication, the synchronization correction (as needed) to electronic device  110  to maintain the synchronization between electronic devices  110  and  112 . This may allow the continued use of the smaller scan-window width and/or the increased beacon period and, thus, the continued reduction in the power consumption of electronic devices  110  and/or  112 . 
     Note that in some embodiments the synchronization occurs between electronic devices  110  and  112  after or while electronic device  110  is detected without a connection being established between electronic devices  110  and  112 . Thus, in the context of Bluetooth™, there may not be bidirectional packet exchange between electronic devices  110  and  112  in the detection technique. 
     In the described embodiments, processing a packet or frame in either of electronic devices  110  and  112  includes: receiving wireless signals  116  with the packet or frame; decoding/extracting the packet or frame from received wireless signals  116  to acquire the packet or frame; and processing the packet or frame to determine information contained in the packet or frame (such as the request or the additional information in the payload, e.g., information specifying clock drift of electronic device  110  and/or a synchronization correction). 
     Although we describe the network environment shown in  FIG. 1  as an example, in alternative embodiments, different numbers or types of electronic devices may be present. For example, some embodiments comprise more or fewer electronic devices. As another example, in another embodiment, different electronic devices are transmitting and/or receiving packets or frames. 
       FIG. 2  presents a timing diagram illustrating communication between electronic devices  110  and  112  in  FIG. 1 . During the communication, electronic device  110  transmits beacons  210  at transmit times  212  that are separated by a nominal or target initial beacon period  214 . Because of clock drift in electronic device  110 , transmit times  212  have uncertainty  216 . Consequently, electronic device  112  may open scan windows (such as scan window  218 ) having initial width  222  at initial window period  220  in order to receive one or more of beacons  210  and, thus, to detect electronic device  110 . In particular, window period  220  may be short and width  222  may be wide. 
     After electronic device  110  has been detected, electronic device  112  may optionally establish a connection or pairing with electronic device  110 . (However, as noted previously, in some embodiments a connection is not established.) Then, electronic device  112  may receive, access or determine the clock drift and/or beacon period  214 . For example, electronic device  112  may: receive information specifying the clock drift and/or beacon period  214  from electronic device  110 ; determine the clock drift and/or beacon period  214  from transmit times  212 ; access stored information specifying the clock drift and/or beacon period  214  in computer  120  ( FIG. 1 ) based on an identifier of electronic device  110  (such as a media access control address or MAC address of electronic device  110 , or a model type of electronic device  110 ); and/or access information, stored in electronic device  112 , specifying the initial beacon period and the clock drift based on the identifier of electronic device  110 . Using this information, electronic device  112  may calculate transmit times  226  for subsequent beacons  224 . These beacons may be received by electronic device  112  by opening subsequent scan windows (such as scan window  232 ) having revised width(s) (such as width  236 ) at revised window period  234 . The revised window period  234  may be less than initial window period  220 , and revised width  236  may be less than width  222 . As noted previously, this may significantly reduce the power consumption of electronic device  112 . 
     Furthermore, after electronic device  110  is detected, electronic device  112  may provide a revised beacon period  228  to electronic device  110 . This revised beacon period may be greater than initial beacon period  214 , which may significantly reduce the power consumption of electronic device  110 . In these embodiments, electronic device  112  may also calculate transmit times  226  for subsequent beacons  224  based on revised beacon period  228 . 
     Because of the clock drift in electronic device  110 , there is a growing uncertainty  230  in transmit times  226 . In particular, the uncertainty in transmit times  226  may increase as a function of time. For example, for a clock drift of 2 ppm, two hours after electronic device  110  is detected the cumulative uncertainty may be 28 ms. Electronic device  112  may address this increasing uncertainty by proportionately increasing the width of the subsequent scan windows as a function of time. 
     Eventually, for times greater than a synchronization time between electronic devices  110  and  112 , electronic device  112  may need to revert to the initial detection technique. This is shown in  FIG. 3 , which presents a timing diagram illustrating communication between electronic devices  110  and  112  in  FIG. 1 . In particular, after the synchronization time (which may be hours or days after electronic device  110  is first detected), electronic device  112  may open the scan windows having initial width  222  at initial window period  220 . Similarly, electronic device  110  may revert to initial beacon period  214  when transmitting beacons. 
     In some embodiments, electronic devices  110  and/or  112  receive a high-precision network clock, e.g., via a network (such as network  118  in  FIG. 1 ). (In some embodiments, the network clock is provided during normal operation of the network and, thus, is not a special signal.) Electronic device  112  may calculate transmit times  226  based on the network clock. Furthermore, electronic device  112  may compare the actual transmit times  226  with a time determined based on the network clock (such as an M/N multiple of the network clock, where M and N are integers). When a difference between the actual transmit times and the calculated transmit times exceeds a threshold value, electronic device  112  may provide a synchronization correction to electronic device  110 . In this way, the uncertainty in the transmit times may be bounded by maintaining the synchronization between electronic devices  110  and  112 , which may allow the power savings to be continued. In these embodiments, the widths of the subsequent scan windows may be held constant (as opposed to increasing as a function of time). 
     This approach (which is sometimes referred to as ‘calibrated detection’) is shown in  FIG. 4 , which presents a timing diagram illustrating communication between electronic devices  110  and  112  in  FIG. 1 . In particular, when uncertainty  410  in one of transmit times  226  exceeds a threshold value (such as a fraction of width  236 ), electronic device  112  may provide synchronization correction  412  to electronic device  110 , thereby allowing electronic device  110  to adjust subsequent transmit times and to reset or eliminate the uncertainty (at least for a time). 
     For example, electronic device  110  may include a clock circuit (such as clock circuit  828  in  FIG. 8 ) having the clock drift, and beacons  224  may be transmitted at transmit times  226  based on a clock output by the clock circuit. If electronic device  110  receives the network clock, then the clock circuit may also output the clock based on the network clock. 
     When electronic device  110  receives synchronization correction  412 , electronic device  110  may adjust the clock circuit based on synchronization correction  412  so that a difference between the network clock and a multiple of the clock (such as M/N times the clock) is less than a threshold value. In this way, uncertainty  410  in transmit times  226  may be bounded, thereby allowing the continued use of window period  234 , width  236 , and/or revised beacon period  228 . 
     Note that the synchronization correction may be shared with multiple electronic devices (such as other ‘scanners’), so that these other electronic devices can use the detection technique (including the reduced scan-window width and/or increased window period) the first time they interact with electronic device  110 . In addition, the use of a global or network clock may allow a replay-resistant encryption technique to be used during the communication between electronic devices  110  and  112 . 
     While the preceding examples illustrated the use of a fixed initial beacon period  214  and a fixed initial window period  220  ( FIGS. 2 and 3 ), in some embodiments the initial beacon period and the initial window period may be selected randomly (thus, the initial values may be mean values). For example, during a beaconing mode, Bluetooth™ may use a random beacon and scan-window technique where electronic device  110  ( FIG. 1 ) sends beacons and electronic device  112  ( FIG. 1 ) scans for the beacons. Because these activities are not synchronized, the likelihood that the scanner (electronic device  112 ) will meet the advertiser (electronic device  110 ) is low. This statistical approach may require the use of either a very wide scan-window width (with a commensurate negative impact on the power consumption) or a very long detection time (up to tens of seconds). In contrast, after detection and optionally establishing the connection, the disclosed detection technique allows electronic devices  110  and  112  to exchange a shared clock that allows them to synchronize subsequent advertising and scanning to reduce the power consumption and the detection time (which is now deterministic). 
     In an exemplary embodiment, the initial beacon period may be 181 ms, the initial window period may be 900 ms and the initial scan-window width may be 30 ms. These values may result in an average detection time of 3.5 s and a power consumption of 500 mW. After electronic device  110  is detected and electronic devices  110  and  112  ( FIG. 1 ) are synchronized, the revised beacon period may be 1.8 s, the revised window period may be 1.8 s and the revised scan-window width may be 100 μs. The revised values may result in an average detection time of 1.8 s (more generally, the detection time may be selected to be 0.5-2 s) and a power consumption of 300 mW. 
       FIG. 5  presents a flow diagram illustrating method  500  for communicating between the electronic devices in  FIG. 1 , such as electronic device  112  communicating with electronic device  110 . During operation, the electronic device detects another electronic device by receiving beacons (operation  510 ) that are broadcast or transmitted at an initial beacon period. For example, the electronic device may open scan windows having an initial width at an initial window period. Then, the electronic device optionally establishes a connection (operation  512 ) with the other electronic device. Moreover, the electronic device receives information specifying a clock drift of the other electronic device or determines the clock drift (operation  514 ). The electronic device may also optionally provide a revised beacon period (operation  516 ) to the other electronic device. This revised beacon period may be greater than the initial beacon period. 
     Next, the electronic device may calculate transmit times of subsequent beacons (operation  518 ) from the other electronic device. Furthermore, the electronic device may receive the subsequent beacons at the calculated transmit times (operation  520 ) from the other electronic device. For example, the electronic device may open scan windows having a revised width at a revised window period. Note that the revised width may be less than the initial width, and the revised window period may be greater than the initial window period. 
     In some embodiments, the communication between the electronic devices is calibrated. In particular, the electronic device may provide a synchronization correction to the other electronic device based on a clock (such as a network clock or a clock in the electronic device) and the actual transmit times (operation  522 ). The synchronization correction may allow the other electronic device to bound an uncertainty in the transmit times, which is associated with the clock drift. 
       FIG. 6  presents a flow diagram illustrating a method for communicating between the electronic devices of  FIG. 1 , such as electronic device  110  communicating with electronic device  112 . During operation, the other electronic device transmits beacons based on an initial beacon period (operation  610 ). Then, the other electronic device optionally establishes the connection (operation  612 ) with the electronic device. Moreover, the other electronic device may optionally provide information (operation  614 ) specifying the clock drift of the other electronic device and/or the initial beacon period. Note that the other electronic device may optionally receive information specifying a revised beacon period (operation  616 ) from the electronic device. 
     Subsequently, the other electronic device transmits subsequent beacons at transmit times that are based on the revised beacon period (operation  618 ). 
     In embodiments where the communication between the electronic devices is calibrated, the other electronic device may receive the synchronization correction from the electronic device (operation  620 ). The synchronization correction may allow the other electronic device to bound an uncertainty in the transmit times, which is associated with the clock drift. 
     In these ways, the electronic devices (for example, interface circuits and/or drivers in the electronic devices) may facilitate communication between the electronic devices with reduced power consumption and reduced detection times. In particular, advertising or broadcast and detection may be deterministic (instead of statistical), which may allow interface circuits in the electronic devices to spend less time in a high power-consumption mode. In addition, because the beacons communicated among the electronic devices in the wireless network can be at known or deterministic times, competition for scarce network resources can be avoided. This may reduce the probability of contention, which may allow the amount of time the electronic devices spend in the active (high power-consumption) mode to be reduced. 
     In some embodiments of methods  500  ( FIG. 5 ) and  600 , there may be additional or fewer operations. Moreover, the order of the operations may be changed, and/or two or more operations may be combined into a single operation. 
     The detection technique is further illustrated in  FIG. 7 , which presents a drawing illustrating communication between electronic devices  110  and  112  ( FIG. 1 ). In particular, electronic device  110  may transmit beacons  710  to electronic device  112  at transmit times having an initial beacon period. In turn, electronic device  112  may receive one or more of beacons  710  by opening scan windows having initial widths at an initial window period. 
     When a beacon (such as beacon  710 - 2 ) is received, a connection  712  between electronic devices  110  and  112  is optionally established. Then, electronic device  110  may optionally provide information  714  specifying a clock drift and/or the initial beacon period to electronic device  112 . Alternatively or additionally, electronic device  112  may optionally determine the clock drift and/or the initial beacon period based on the transmit times. In some embodiments, electronic device  112  optionally accesses stored information in electronic device  112  and/or computer  120  that specifies the clock drift and/or the initial beacon period associated with electronic device  110 . For example, electronic device  112  may request  716  the information and, in response, computer  120  may provide information  718 . 
     After connection  712  is optionally established, electronic device  112  may also optionally provide a revised beacon period  720  to electronic device  110 . 
     Moreover, electronic device  112  may calculate the transmit times of subsequent beacons from electronic device  110  based on the clock drift, the initial beacon period and/or the revised beacon period. 
     Subsequently, electronic device  110  may transmit beacons (such as beacons  710 - 3  and  710 - 4 ) to electronic device  112  at transmit times having the revised beacon period. In turn, electronic device  112  may receive one or more of beacons  710 - 3  and  710 - 4  by opening scan windows having revised widths at a revised window period. Because the revised beacon period is greater than the initial beacon period, the revised width is less than the initial width and/or the revised window period is greater than the initial window period, there may be significant power savings from electronic devices  110  and/or  112 . 
     In some embodiments, computer  120  provides a network clock  722  to electronic devices  110  and/or  112 . Electronic device  112  may use network clock  722  and the actual transmit times of subsequent beacons  710 - 3  and  710 - 4  provided by electronic device  110  to determine when the uncertainty or variation in the transmit times exceeds a threshold value. When this occurs, electronic device  112  may provide a synchronization correction  724  to electronic device  110 , which allows electronic device  110  to keep the uncertainty bounded and, thus, which allows electronic devices  110  and  112  to continue to advertise and detect each other in a deterministic manner. 
     We now describe embodiments of the electronic device.  FIG. 8  presents a block diagram illustrating an electronic device  800 , such as one of electronic devices  110  and  112  in  FIG. 1 . This electronic device includes processing subsystem  810 , memory subsystem  812 , and networking subsystem  814 . Processing subsystem  810  includes one or more devices configured to perform computational operations. For example, processing subsystem  810  can include one or more microprocessors, application-specific integrated circuits (ASICs), microcontrollers, programmable-logic devices, and/or one or more digital signal processors (DSPs). 
     Memory subsystem  812  includes one or more devices for storing data and/or instructions for processing subsystem  810  and networking subsystem  814 . For example, memory subsystem  812  can include dynamic random access memory (DRAM), static random access memory (SRAM), and/or other types of memory. In some embodiments, instructions for processing subsystem  810  in memory subsystem  812  include: one or more program modules or sets of instructions (such as program module  822  or operating system  824 ), which may be executed by processing subsystem  810 . Note that the one or more computer programs may constitute a computer-program mechanism. Moreover, instructions in the various modules in memory subsystem  812  may be implemented in: a high-level procedural language, an object-oriented programming language, and/or in an assembly or machine language. Furthermore, the programming language may be compiled or interpreted, e.g., configurable or configured (which may be used interchangeably in this discussion), to be executed by processing subsystem  810 . 
     In addition, memory subsystem  812  can include mechanisms for controlling access to the memory. In some embodiments, memory subsystem  812  includes a memory hierarchy that comprises one or more caches coupled to a memory in electronic device  800 . In some of these embodiments, one or more of the caches is located in processing subsystem  810 . 
     In some embodiments, memory subsystem  812  is coupled to one or more high-capacity mass-storage devices (not shown). For example, memory subsystem  812  can be coupled to a magnetic or optical drive, a solid-state drive, or another type of mass-storage device. In these embodiments, memory subsystem  812  can be used by electronic device  800  as fast-access storage for often-used data, while the mass-storage device is used to store less frequently used data. 
     Networking subsystem  814  includes one or more devices configured to couple to and communicate on a wired and/or wireless network (i.e., to perform network operations), including: control logic  816 , an interface circuit  818  and an antenna  820 . For example, networking subsystem  814  can include a Bluetooth™ networking system, a cellular networking system (e.g., an 3G/4G network such as UMTS, LTE, etc.), a universal serial bus (USB) networking system, a networking system based on the standards described in IEEE 802.11 (e.g., a Wi-Fi networking system), an Ethernet networking system, and/or another networking system. 
     Networking subsystem  814  includes processors, controllers, radios/antennas, sockets/plugs, and/or other devices used for coupling to, communicating on, and handling data and events for each supported networking system. Note that mechanisms used for coupling to, communicating on, and handling data and events on the network for each network system are sometimes collectively referred to as a ‘network interface’ for the network system. Moreover, in some embodiments a ‘network’ between the electronic devices does not yet exist. Therefore, electronic device  800  may use the mechanisms in networking subsystem  814  for performing simple wireless communication between the electronic devices, e.g., transmitting advertising or beacon frames and/or scanning for advertising frames transmitted by other electronic devices as described previously. 
     Within electronic device  800 , processing subsystem  810 , memory subsystem  812 , and networking subsystem  814  are coupled together using bus  830 . Bus  830  may include an electrical, optical, and/or electro-optical connection that the subsystems can use to communicate commands and data among one another. Although only one bus  830  is shown for clarity, different embodiments can include a different number or configuration of electrical, optical, and/or electro-optical connections between the subsystems. 
     In some embodiments, electronic device  800  includes a display subsystem  826  for displaying information on a display, which may include a display driver and the display, such as a liquid-crystal display, a multi-touch touchscreen, etc. In addition, electronic device  800  may include clock circuit  828  that outputs a clock. Note that clock circuit  828  may be included in a GPS circuit. 
     Electronic device  800  can be (or can be included in) any electronic device with at least one network interface. For example, electronic device  800  can be (or can be included in): a desktop computer, a laptop computer, a server, a media player (such as an MP3 player), an appliance, a subnotebook/netbook, a tablet computer, a smartphone, a cellular telephone, a piece of testing equipment, a network appliance, a set-top box, a personal digital assistant (PDA), a toy, a controller, a digital signal processor, a game console, a computational engine within an appliance, a consumer-electronic device, a portable computing device, a personal organizer, a sensor, a user-interface device and/or another electronic device. 
     Although specific components are used to describe electronic device  800 , in alternative embodiments, different components and/or subsystems may be present in electronic device  800 . For example, electronic device  800  may include one or more additional processing subsystems  810 , memory subsystems  812 , networking subsystems  814 , and/or display subsystems  826 . Additionally, one or more of the subsystems may not be present in electronic device  800 . Moreover, in some embodiments, electronic device  800  may include one or more additional subsystems that are not shown in  FIG. 8 . For example, electronic device  800  can include, but is not limited to, a data collection subsystem, an audio and/or video subsystem, an alarm subsystem, a media processing subsystem, and/or an input/output (I/O) subsystem. Also, although separate subsystems are shown in  FIG. 8 , in some embodiments, some or all of a given subsystem or component can be integrated into one or more of the other subsystems or component(s) in electronic device  800 . For example, in some embodiments program module  822  is included in operating system  824 . 
     Moreover, the circuits and components in electronic device  800  may be implemented using any combination of analog and/or digital circuitry, including: bipolar, PMOS and/or NMOS gates or transistors. Furthermore, signals in these embodiments may include digital signals that have approximately discrete values and/or analog signals that have continuous values. Additionally, components and circuits may be single-ended or differential, and power supplies may be unipolar or bipolar. 
     An integrated circuit may implement some or all of the functionality of networking subsystem  814 , such as a radio. Moreover, the integrated circuit may include hardware and/or software mechanisms that are used for transmitting wireless signals from electronic device  800  and receiving signals at electronic device  800  from other electronic devices. Aside from the mechanisms herein described, radios are generally known in the art and hence are not described in detail. In general, networking subsystem  814  and/or the integrated circuit can include any number of radios. Note that the radios in multiple-radio embodiments function in a similar way to the described single-radio embodiments. 
     In some embodiments, networking subsystem  814  and/or the integrated circuit include a configuration mechanism (such as one or more hardware and/or software mechanisms) that configures the radio(s) to transmit and/or receive on a given communication channel (e.g., a given carrier frequency). For example, in some embodiments, the configuration mechanism can be used to switch the radio from monitoring and/or transmitting on a given communication channel to monitoring and/or transmitting on a different communication channel. (Note that ‘monitoring’ as used herein comprises receiving signals from other electronic devices and possibly performing one or more processing operations on the received signals, e.g., determining if the received signal comprises an advertising frame, etc.) 
     While a communication protocol compatible with the Bluetooth™ standard was used as an illustrative example, the described embodiments of the communication techniques may be used in a variety of network interfaces. Furthermore, while some of the operations in the preceding embodiments were implemented in hardware or software, in general the operations in the preceding embodiments can be implemented in a wide variety of configurations and architectures. Therefore, some or all of the operations in the preceding embodiments may be performed in hardware, in software or both. For example, at least some of the operations in the detection technique may be implemented using program module  822 , operating system  824  (such as a driver for interface circuit  818 ) or in firmware in interface circuit  818 . Alternatively or additionally, at least some of the operations in the detection technique may be implemented in a physical layer, such as hardware in interface circuit  818 . 
     In the preceding description, we refer to ‘some embodiments.’ Note that ‘some embodiments’ describes a subset of all of the possible embodiments, but does not always specify the same subset of embodiments. 
     The foregoing description is intended to enable any person skilled in the art to make and use the disclosure, and is provided in the context of a particular application and its requirements. Moreover, the foregoing descriptions of embodiments of the present disclosure have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present disclosure to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Additionally, the discussion of the preceding embodiments is not intended to limit the present disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Metadata:
Filing Date: 20170227
Publication Date: 20181016
Grant Date: 20181016
Priority Date: 20140321
Inventors: IRONY, RAN
KATZ, RAN
PAYCHER, ALON
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W76/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W56/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0229", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W52/0229", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W52/0229", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W56/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W56/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W56/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0229", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 54053852