Patent Publication Number: US-10321297-B2

Title: Systems and methods for reducing connection latency

Description:
RELATED APPLICATION 
     This patent application is a continuation of U.S. patent application Ser. No. 15/807,097 filed Nov. 8, 2017 (now U.S. Pat. No. 10,091,638), which is a continuation of U.S. patent application Ser. No. 14/978,077 filed Dec. 22, 2015 (now U.S. Pat. No. 9,820,135), which claims priority to U.S. Provisional Patent Application No. 62/095,628, filed Dec. 22, 2014. Each of the above-referenced patent applications is incorporated by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This patent specification relates to systems and methods for reducing connection latency. More particularly, this specification relates to shortening connection latency between devices operating according to a Bluetooth protocol. 
     BACKGROUND 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Bluetooth Low Energy (BLE) is a wireless radio technology, aimed at new, principally low-power and low-latency applications for wireless devices within a short range (up to about 160 feet). BLE networks are particularly well-suited for a wide range of applications and smaller form factor devices in the healthcare, fitness, security and home entertainment industries. As its name implies, BLE is intended for such energy-constrained applications as a sensor or a disposable device, particularly those that transmit relatively little data and do so infrequently. BLE was designed to enable wireless connectivity with small devices running for extended periods of time on, for example, a coin cell battery. While an objective of networks that utilize BLE technologies is robust and secure delivery of information, saving battery power is also a concern. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     Systems and methods for reducing connection latency are described herein. More particularly, this specification relates to shortening connection latency between devices operating according to a Bluetooth protocol. Connection latency can be reduced by using the receipt of a wireless packet as a trigger for selectively accelerating a transmission rate of advertising packets. By selectively accelerating the transmission rate advertising packets, a connection interval between two devices can be shortened. For example, in one embodiment, a method is provided for operating a device according to a first advertising mode that transmits adverting packets according to a first frequency. The method further includes receiving a scan request packet in response to the transmission of one of the adverting packets, and operating the device according to a second advertising mode in response to the received scan request packet, wherein in the second advertising mode the adverting packets are transmitted according to a second frequency that is greater than the first frequency. 
     In another embodiment, an apparatus is provide the includes a wireless transceiver and control circuitry coupled to the wireless transceiver and operative to cause the wireless transceiver to send and receive wireless packets. The control circuitry can be operative to transmit advertising packets at an advertising frequency having a first period, monitor for receipt of a scan request packet within a listening window, determine if a scan request packet is monitored, adjust the advertising frequency to have a second period in response to a determination that a scan request packet is monitored, wherein the second period is less than the first period, and transmit at least one subsequent advertising packet at the advertising frequency having the second period. 
     In yet another embodiment, a method for establishing low latency connection between central and peripheral devices is provided. The method can be implemented by the peripheral device and can include wirelessly transmitting advertising packets to alert the presence of the peripheral device to the central device, and adjusting an advertising rate for transmitting the advertising packets based on whether a scan request packet is received in response to a transmitted advertisement package, wherein the advertising rate is temporarily accelerated in response to a received scan request packet to reduce latency in establishing a connection between the central and peripheral devices. 
     Various refinements of the features noted above may be used in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may be used individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. The brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter. 
     A further understanding of the nature and advantages of the embodiments discussed herein may be realized by reference to the remaining portions of the specification and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows two wireless devices, according to an embodiment; 
         FIG. 2  illustrates a block diagram of a peripheral device, according to an embodiment; 
         FIG. 3  shows an illustrative timing diagram of wireless communications between central and peripheral devices, where the central is passively listening; 
         FIG. 4  shows an illustrative timing diagram of wireless communications between central and peripheral devices, where the central is actively listening; 
         FIG. 5  shows an illustrative flowchart of a process that may be implemented by a peripheral device according to an embodiment; 
         FIG. 6  shows an illustrative timing diagram of wireless communications between central and peripheral devices, performed according to the process of  FIG. 5 , according to an embodiment; and 
         FIG. 7  shows illustrative additional steps may be performed by the process of  FIG. 5 , according to an embodiment; 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the various embodiments. Those of ordinary skill in the art will realize that these various embodiments are illustrative only and are not intended to be limiting in any way. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. 
     In addition, for clarity purposes, not all of the routine features of the embodiments described herein are shown or described. One of ordinary skill in the art would readily appreciate that in the development of any such actual embodiment, numerous embodiment-specific decisions may be required to achieve specific design objectives. These design objectives will vary from one embodiment to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine engineering undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     In some wireless networks, wireless devices set up connections with each other to facilitate data transfer. This disclosure focuses on BLE networks, but the scope of the disclosure and the claims applies to other network types as well. The problem with the connection setup process is that a BLE slave device spends a great deal of time in the connection setup phase. In general, a BLE device may operate in different modes depending on required functionality. The main modes of operation include the advertising mode, the scanning mode, central device mode, and peripheral device mode. In advertising mode, the BLE device periodically transmits advertising packets and may respond with more information upon request from other devices. In the scanning mode, a BLE device listens for and receives advertising packets transmitted by other devices and may request additional information from the originator of an advertising packet. A central device may passively scan or actively scan. A peripheral device can connect to a single central, but a central may connect to multiple peripheral devices simultaneously. 
     To establish a connection, a first BLE device transmits an advertising packet. A second BLE device responds to the advertising packet and may request additional information. If additional information is requested, the first device transmits the requested information. The connection can then be established with the first device being the peripheral device and the second device being the central device. In this disclosure, references to “peripheral device” refer to the BLE device that sends out the advertising packets, and the “central device” is the BLE device that receives and responds to the advertising packets. 
       FIG. 1  shows two wireless devices  100  and  200 . Wireless device  100  is a central device and wireless device  200  is a peripheral device. As noted above, to establish a connection between the central device  100  and peripheral device  200 , peripheral device  200  transmits an advertising packet which, if received by central  100 , indicates the presence of peripheral device  200  to central device  100 . Central device  100  may respond with a scan request (SCAN_REQ) packet. Peripheral device  200  responds to the SCAN_REQ with a scan response (SCAN_RSP) packet to provide additional data if necessary before establishing the connection. Central device  100  and peripheral device  200  thus engage in information exchange before establishing a connection. By way of example, central device  100  may be a line powered device or a device with substantial power reserves, and peripheral device  200  may be a battery powered device with limited power reserves. As a specific example, central device  100  may be a locking mechanism of a door that can control access to a home, and peripheral device  200  may be a portable fob that a user can use to gain access to the home via central device  100 . That is, when a user is within close proximity of the home, peripheral device  200  may alert its presence to central device  100 , which may attempt to connect to device  200 . After a connection is made, the user may lock or unlock the door using the portable fob. 
       FIG. 2  illustrates a block diagram of peripheral device  200 . As shown, device  200  includes control circuitry  220 , BLE timing module  222 , transceiver  240 , antenna  260 , and power source  280 . Power source  280  provides electrical power to circuitry  220 , module  222 , and transceiver  240 . Transceiver  240  can accept signals from circuitry  220  to transmit wirelessly via antenna  260 . Similarly, wireless signals received by antenna  260  are provided by transceiver  240  to controller  220  for processing. Transceiver  240  may be capable of bi-directional data communications with another wireless device such as central device  100 . Control circuitry  220  may include a processor that executes software. Control circuitry  220  may access BLE timing module  222  to adjust an advertising frequency according to various embodiments. Control circuitry  220  can perform some or all of the functionality described herein as attributed to peripheral device  200 . The architecture depicted in  FIG. 2  may be used as well to implement central device  100 . 
     In the BLE protocol, channels 37, 38, and 39 are dedicated for use in transmitting advertising packets and the associated responses. Central device  100  can listen on each advertising channel for an advertising packet being transmitted by peripheral device  200 . Central device  100  can passively listen or actively listen for advertising packets. During passive listening, central device  100  may not transmit scan requests responsive to a received advertising packet. During active scanning, however, central device  100  may transmit scan requests responsive to a received advertising packet. 
     Peripheral device  200  may transmit advertising packets according to an advertising frequency. The advertising frequency can characterized as having an advertising period. Thus, device  200  can transmit an advertising packet at the end of each advertising period. Within each period, device  200  can listen for wireless packets during a listen window. The listen window may have a start point that coincides with the start of a period, and an end point that defines the end of the listen window. The listen window may be a fixed parameter set, for example, by a Bluetooth Low Energy (BLE) protocol. The listen window may define the only time during an advertising period during which device  200  can listen for wireless packets. For example, device  200  may listen for scan request packets or connection request packets being transmitted by central device  100  during the listen window. 
       FIG. 3  shows an illustrative timing diagram of wireless communications between central and peripheral devices, where the central is passively listening. An advertisement packet (shown as “advert_n”) is transmitted at an advertising frequency having a period of X. The listen window is shown to exist within each period. In this timing diagram, the peripheral device transmits advert_ 1  to alert the presence of the peripheral to the central device. After the central receives advert_ 1 , it must wait until it receives advert_ 2  before it attempts to send, for example, a connection request packet (shown as “Conn_Req) to the peripheral. The central may have to wait for a subsequent advertising packet to be received before attempting to send a packet because of the limited listen window of the peripheral. That is, the central may have to immediately transmit a packet after receiving an advertisement packet to ensure the peripheral receives it during its listen window. This packet exchange may occur more than once to ensure packets are adequately transmitted and received. 
       FIG. 4  shows an illustrative timing diagram of wireless communications between central and peripheral devices, where the central is actively listening. As with the timing diagram of  FIG. 3 , the advertising packets are transmitted according to an advertising frequency having a period of X. In response to receiving advert_ 1 , the central may immediately transmit a scan request packet (shown as “Scan_Req”) to the peripheral so that it is received during the listen window. The peripheral may respond to the scan request packet by transmitting a scan response packet (shown as “Scan_Res”). The scan request and scan response packets may be handled by a different level of the software stack for implementing BLE communications than the level that handles advertising packets. Thus, the scan response packets may not be constrained by the advertising frequency. The can request packet may be transmitted by the central to request additional information from the peripheral. The central may evaluate the scan response packet received in response to its scan request packet to determine whether it wishes to establish a connection with the peripheral. If the central decides to establish a connection, it will wait until it receives another advertisement packet from the peripheral and immediately transmit a connection request packet. This is illustrated in the timing diagram, where Conn_Req is transmitted in response to receiving Advert_ 2 . 
     The timing diagrams of both  FIGS. 3 and 4  both illustrate that a connection sequence requires a minimum of two advertising packets in order to establish a connection. Thus, the advertising frequency is shown to be a limiting factor establishing a connection. The advertising period is X, thus a connection interval can range from X to 2X. The X−2X interval may be perceived as too long a time to establish a connection. For example, users may become frustrated with the slow connection experience. Peripheral devices may operate at the advertising frequency having the X period to strike an appropriate balance between power consumption and connectively. Shorter X periods may provide a faster connection interval, but at the expense of increased power consumption. Since peripheral devices typically operate using a relatively limited power source, increasing power consumption is not a viable option. 
     Embodiments herein strive to decrease the connection interval with minimal increase in power consumption by leveraging the scan request packet to selectively adjust the advertising frequency to temporarily operate at a faster advertising frequency. Assuming that the advertising frequency normally operates with a first period, the peripheral device can change the advertising frequency to operate with a second period in response to a received scan request packet, where the second period is less than the first period, thereby resulting in a faster transmission of advertising packets. This enables the central device to establish a connection faster with the peripheral device. The scan request packet can be used as a trigger for selectively adjusting the advertising frequency. This additional use of the scan request packet does not conflict with the provisions of the BLE protocol, but advantageously is additionally purposed to enable the peripheral device to throttle its advertising rate. 
       FIG. 5  shows an illustrative flowchart of process  500  that may be implemented by a peripheral device according to an embodiment.  FIG. 6  shows an illustrative timing diagram of wireless communications between central and peripheral devices, performed according to process  500 .  FIGS. 5 and 6  will be collectively reference in the following discussion. Starting at step  510 , the peripheral device may be operating in a normal (first) advertising mode, where adverting packets are transmitted every X period, as indicated by step  520 . Advert_ 1  and Advert_ 2  are transmitted while the peripheral device is operating in the normal advertising mode. The normal advertising mode may represent the mode where the peripheral device spends the majority of its operational life. This is in contrast to a fast (second) advertising mode, discussed below, which is a temporary operational mode of the peripheral device. 
     At step  530 , a determination is made as to whether a scan request packet is received. As discussed above, the peripheral may only be capable of receiving packets during its listen window, shown as LW in  FIG. 6 . If no scan request packet is received, process  500  may return to step  510 . For example, because no scan request packet is received after advert_ 1  was transmitted at step  530 , process  500  returns to step  510 . If a scan request packet is received at step  530 , process  500  may proceed to step  540 . For example, a scan request packet is received after transmission of advert_ 2 . The peripheral device may transmit a scan response packet in response (shown as “Scan_Resp”). 
     At step  540 , the peripheral device may operate in a fast advertising mode where advertising packets are transmitted every Y period, where Y is less than X. The timing diagram illustrates the change in the advertising period to period Y. In addition, the timing diagrams shows that Adverts_ 3 - 5  are transmitted when the peripheral device is operating in the fast advertising mode. At step  550 , an advertising packet is transmitted at time Y. For example, Advert_ 3  is transmitted at time Y as opposed to time X. 
     At step  560 , a determination is made whether the fast advertising mode has timed out. The fast advertising mode may time out after a fixed period of time or transmission of a fixed number of advertising packets. If the determination is YES, process  500  may proceed to step  510 . If the determination is NO, process  500  may proceed to step  570 , which determines whether a connection request is received. If the determination at step  570  is NO, process  500  may loop back to step  540 , otherwise, if YES, process  500  may end at step  580 . 
     Referring to  FIG. 6 , a connection request packet is transmitted after Advert_ 3  is transmitted. According to process  500 , process  500  would end and the standard connection process may ensue. Assume, for example, that no connection request packet is transmitted. Based on process  500 , process  500  may continue to transmit advertising packets at period Y until it time outs. After it times out, the peripheral may return to operating in the normal advertising mode, during which it transmits advertisements every X period. 
     It should be appreciated that the steps of  FIG. 5  are merely illustrative and that additional steps may be added, steps may be omitted, or the steps may be re-ordered. For example, the peripheral device may perform additional steps upon receipt of a scan request packet. These additional steps are discussed in  FIG. 7 . 
       FIG. 7  shows illustrative additional steps may be performed by process  500  in response to a determination that a scan request packet is received at step  530 . At step  531 , a determination is made whether the peripheral device is operating in the fast operating mode. If the determination at step  531  is YES, process  500  may proceed to step  540 , where process  500  continues to operate in the fast operating mode. If the determination is NO, process  500  may proceed to step  532 . At step  532 , the peripheral device may evaluate the received scan packet to determine whether to enter into the fast advertising mode (step  533 ). The evaluation criteria can include, for example, verification of a source of the packet and verification of an intention of the source. For example, if the source does not have permission to communicate with the peripheral, then the peripheral may not enter into the fast advertising mode. If the determination at step  533  is NO, process  500  may return to step  510 . If the determination is YES, process may proceed to step  540 . 
     Any processes described with respect to  FIGS. 1-7 , as well as any other aspects of the invention, may each be implemented by software, but may also be implemented in hardware, firmware, or any combination of software, hardware, and firmware. They each may also be embodied as machine- or computer-readable code recorded on a machine- or computer-readable medium. The computer-readable medium may be any data storage device that can store data or instructions that can thereafter be read by a computer system. Examples of the computer-readable medium may include, but are not limited to, read-only memory, random-access memory, flash memory, CD-ROMs, DVDs, magnetic tape, and optical data storage devices. The computer-readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. For example, the computer-readable medium may be communicated from one electronic subsystem or device to another electronic subsystem or device using any suitable communications protocol. The computer-readable medium may embody computer-readable code, instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave or other transport mechanism, and may include any information delivery media. A modulated data signal may be a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. 
     It is to be understood that any or each module or state machine discussed herein may be provided as a software construct, firmware construct, one or more hardware components, or a combination thereof. For example, any one or more of the state machines or modules may be described in the general context of computer-executable instructions, such as program modules, that may be executed by one or more computers or other devices. Generally, a program module may include one or more routines, programs, objects, components, and/or data structures that may perform one or more particular tasks or that may implement one or more particular abstract data types. It is also to be understood that the number, configuration, functionality, and interconnection of the modules or state machines are merely illustrative, and that the number, configuration, functionality, and interconnection of existing modules may be modified or omitted, additional modules may be added, and the interconnection of certain modules may be altered. 
     Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that the particular embodiments shown and described by way of illustration are in no way intended to be considered limiting. Therefore, reference to the details of the preferred embodiments is not intended to limit their scope.