BACKGROUND

[0001] Smartphones and other types of mobile devices commonly wirelessly communicate with auxiliary devices to improve the smartphones' usefulness and extend their capabilities. For example, watch-type devices, such as smart watches and fitness and health trackers that have wrist-wrappable bands, can track different vital statistics of their wearers, as well as their wearers' physical activities, and report this information to smartphones to which they are connected. Such devices can also display limited amounts of information so that their wearers can simply turn their wrists to view the information instead of having to retrieve their smartphones, which may be tucked away in a pocket or a handbag. The devices can permit their wearers to perform functionality associated with their wirelessly connected smartphones, including answering and dismissing phone calls, and displaying and sending short messages like text messages. Other types of devices that can wirelessly communicate with smartphones and similar mobile devices include headphones, microphones, and wearable devices such as other types of fitness and health trackers that may be worn like necklaces or clipped to belts or clothing. BRIEF DESCRIPTON OF THE DRAWINGS

[0002] FIG. 1 is a flowchart of an example method for establishing a wireless communication channel between a host computing device and a target device.

[0003] FIG. 2 is a diagram of an example target device positioned against an example host computing device.

[0004] FIG. 3 is a diagram of a graph depicting an example manner by which the brightness of a displayed color can be temporally modulated to yield a temporal light pattern that encodes a passkey.

[0005] FIG. 4 is a flowchart of an example method of use for a user to establish a wireless communication channel between a host computing device and a target device.

DETAILED DESCRIPTION

[0006] As noted in the background section, mobile devices like

smartphones commonly wirelessly communicate with auxiliary devices. Such wireless communication can be achieved in a variety of different ways, including in various versions of the Bluetooth wireless communication protocol. In the Bluetooth as well as other protocols, a wireless communication channel between a smartphone or other mobile device and an auxiliary or target device like a smart watch is established prior to information being communicated between the two devices. The establishing of a wireless communication channel is sometimes referred to as pairing a target device to a smartphone (or other device), or vice-versa. [0007] The pairing process generally begins by placing the target device in a pairing mode, in which the target device broadcasts its availability to establish a wireless communication channel with a host device like a smartphone or other mobile device. The mobile device is placed in a discovery mode, in which it actively looks for target devices that are broadcasting such availability. The smartphone or other mobile device may display a list of target devices that it has discovered, from which the user of the smartphone can select the desired target device with which to establish a wireless communication channel.

[0008] To provide for better authentication and security in the pairing process, the mobile device may display a passkey, such as a four or five digit code, on its display, and request that the user enter this passkey on the target device. However, many types of target devices, including many types of smart watches and health and fitness trackers, lack the capability for users to easily enter passkeys. To improve the user experience, then, the pairing process may simply involve sending the passkey to the target device and the target device correspondingly displaying the passkey as well. The user is requested to confirm that the same passkey is displayed on both the mobile device (i.e., a

smartphone) and the target device. However, while this is more convenient from the user's perspective, it can imperil security; for instance, a user may mistakenly confirm that the same passkey is being displayed on both devices, even if it is not.

[0009] Furthermore, some types of target devices, like headphones and microphones, do not even have displays. Therefore, even this reduced security pairing process, in which the user provides visual confirmation of the same passkey being displayed on both the smartphone and the target device, is unworkable. In such instances, there may be no security at all in the pairing process. For example, the user may place the target device in a pairing mode in which it broadcasts its availability, and correspondingly place the smartphone or other host device in a discovery mode in which it looks for devices broadcasting their availability. A wireless communication channel is established after a user simply selects a target device listed by the smartphone, which increases the susceptibility of the user incorrectly establishing a wireless communication channel with an imposter device or a "spoofing" device.

[0010] Techniques described herein ameliorate these difficulties

associated with pairing smartphones and other mobile or host devices with target devices, even if the target devices lack user input or display capabilities. The smartphone displays, via its display hardware, a temporal light pattern encoding a passkey. For example, the temporal light pattern may be the increasing and decreasing of the brightness of a particular color in modulation with the bits of the passkey over a short period of time. The target device is placed against the display hardware of the smartphone so that a photosensor, like a photodiode, of the target device is adjacent to the display hardware. The target device's photosensor detects the temporal light pattern, and the target device

responsively decodes the passkey from the detected pattern. The target device wirelessly transmits the decoded passkey back to the smartphone, via a wireless radio such as in accordance with the Bluetooth protocol. Upon receipt of the passkey from the target device, and upon confirming that the passkey matches the passkey that the smartphone encoded in the displayed temporal light pattern, the smartphone establishes a wireless communication channel with the target device, such as a Bluetooth wireless communication channel.

[0011] These techniques can leverage existing hardware of target devices that are used for purposes other than wireless communication channel establishment and authentication. For example, many smart watches and fitness and health trackers have pulse oximeters. Such pulse oximeters noninvasively measure the oxygen saturation in their wearers' blood, by using a light source like a light-emitting diode (LED) to output light against and through the users (such as fingers thereof), and correspondingly measuring via photosensors the amount of certain wavelengths of light that are transmitted. Based on the oxygen saturation of the blood in a user's blood vessels, the amount of green light that the blood absorbs changes, for instance. The photosensor of an oximeter can be used to precisely detect such changes, and correlate them with the volumetric oxygen saturation of the user's bloodstream.

[0012] The techniques described herein can thus leverage this

photosensor of an oximeter of a target device for an entirely different and non- obvious usage, to authenticate the target device to a smartphone or other mobile or host device during the pairing process that is performed to establish a wireless communication channel between the two devices. Improved security in the pairing process is achieved without having to add any other hardware to a target device. Furthermore, existing target devices that have pulse oximeters can be reprogrammed to use the more secure pairing process. Target devices that normally do not have user input hardware or display hardware, such as headphones and microphones, can be designed to include low-cost and physically small photosensors to provide for heightened security in wireless communication channel establishment.

[0013] FIG. 1 shows an example method 100 for establishing a wireless communication channel between a host computing device and a target device. The host device can be a computing device like a smartphone or other type of mobile computing device. The host device includes at least display hardware, such as a liquid crystal display (LCD), and a wireless radio, such as a wireless radio that can transmit and receive data over a wireless frequency associated with the Bluetooth protocol. The host device may further include a user input device, such as a touch sensor like a touchscreen.

[0014] The target device can be a wearable device, such as a watch-type device like a smart watch or a fitness or health tracker that has a wrist-wrappable band. The target device can be another type of wearable device, such as a fitness or health tracker that is worn around a user's neck like a necklace, placed around a user's finger like a ring, or clipped to clothing or a belt of the user. The target device can be an input or output device, such as wireless headphones and/or a microphone. The target device includes at least a photosensor, which may be part of a pulse oximeter of the target device, and a wireless radio that can transmit and receive data over the same wireless frequency as the wireless radio of the host device, such as that associated with the Bluetooth protocol. [0015] Parts of the method 100 in the left column of FIG. 1 are performed by the host device. For example, a non-transitory computer-readable data storage medium of the host device may store computer-executable code that a processor of the host device executes to perform these parts of the method 100. Parts of the method 100 in the right column of FIG. 1 are performed by the target device. Similarly, for example, a non-transitory computer-readable data storage medium of the target device may store computer-executable code that a processor of the target device executes to perform these parts of the method 100. Parts of the method 100 between the right and left columns (i.e., parts 134 and 136) are performed by each of the host device and the target device.

[0016] The target device broadcasts its availability to establish a wireless communication channel (102), via the wireless radio of the target device. For example, a user may operate the target device to place it in a mode in which it performs this availability broadcast. In the context of the Bluetooth protocol, the target device may be placed in a pairing mode.

[0017] The host device, via the wireless radio of the host device, detects the target device's broadcast of the availability of the target device to establish a wireless communication channel (104). For example, a user may operate the host device to discover any devices, including the target device, within radio range of the host device's wireless radio that are broadcasting availability to establish wireless communication channels. In the context of the Bluetooth protocol, the target may be placed in a discovery mode. [0018] The host device learns a communication address of the target device from the detected broadcast, and transmits a request via the wireless radio of the host device to establish the communication channel (106). In the context of the Bluetooth protocol, this process can be referred to as the host device subscribing to the target device. The target device responsively receives the request via the target device's wireless radio (108).

[0019] The host device generates a passkey (1 10). The passkey may be a random series of bits of data of a prespecified length, such 32 bits, 64 bits, 128 bits, and so on. The host device generates a temporal light pattern that encodes the passkey (1 12). An example technique to encode (and correspondingly decode) the passkey is described later in the detailed description. In general, however, the temporal light pattern is a light pattern that can be displayed by the display hardware of the host device. The light pattern is a temporal light pattern in that transmission thereof occurs over a period of time in which the light changes in accordance with the passkey. Stated another way, the light pattern may not be a static image that is displayed, but rather light that changes according to a pattern encoding the passkey, such as by changing the brightness of a color corresponding to the photosensor (i.e., changing the brightness of a color of light that the photosensor is able to detect, such as green).

[0020] The host device can display via the display hardware an instruction to the user to place the target device against this display hardware such that the photosensor is adjacent to the display hardware (1 14). The host device can determine that the target device has been placed against its display hardware (1 16). For instance, the host device may receive confirmation from the user via the input hardware of the host device that the target device has been placed against the display hardware. As part of the instruction display in part 1 14, the host device may have instructed the user to press a particular displayed user interface element once the target device has been placed against the display hardware. As another example, the host device may have sensor hardware, such as the touchscreen of the host device, which can detect that the target device has been placed against the host device. For instance, the host device may have information regarding the approximate size, shape, and/or weight of the target device, and may utilize this information to conclude that input detected by the sensor hardware corresponds to the target device having been placed against the display hardware of the host device.

[0021] The host device displays via its display hardware the temporal light pattern that encodes the passkey (1 18). The host device may repeat display of the temporal light pattern a number of times to provide the target device adequate opportunity to correct detect the light pattern. The host device therefore displays the temporal light pattern while the photosensor of the target device is adjacent to the display hardware of the host device, which permits the target device, via the photosensor, to detect the displayed temporal light pattern (120). The target device may turn on its photosensor to determine if a temporal light pattern is being detected after it has received the host device's request in part 108. As another example, the target device may begin this detection process upon a user providing corresponding input to the target device. [0022] The target device decodes the passkey encoded within the temporal light pattern from the detected light pattern (122), and transmits via its wireless radio the decoded passkey to the host device (124). The host device receives the decoded passkey via the wireless radio of the host device (126). The host device determines that the decoded passkey received from the target device matches the displayed passkey that the host device previously displayed via its display hardware (128). The host device sends a confirmation, via the wireless radio of the host device, to the target device that the decoded passkey the target device sent to the host device is correct (130), and the target device receives this confirmation via its wireless radio (132).

[0023] The host device and the target device can thus establish a wireless communication channel with one another, via their corresponding wireless radios, and such as in accordance with the Bluetooth protocol (134). The host device in particular has authenticated the target device, in that the host device can be certain that the target device with which it is establishing the wireless

communication is the target device that has been placed against the display hardware of the host device. This authentication is performed out-of-band from the wireless communication channel itself, since the wireless communication channel is achieved via the wireless radios of the devices, whereas the passkey is communicated as a temporal light pattern using the host device's display hardware and detected using the target device's photosensor.

[0024] The authentication further does not require a user to manually input the passkey, which can be difficult if not impossible to achieve with some types of target devices. The authentication is more secure than requesting that the user visually confirm that a displayed passkey on the host device is the same displayed passkey on the target device, because such a visual confirmation can require trusting the user that the confirmation has been correctly performed, which cannot be otherwise verified by the host device. Rather, the host device has knowledge that the passkey it displayed is the passkey decoded by the target device, because the target device has communicate the passkey back to the host device. Once the wireless communication channel has been

established, the host device and the target device can communicate with one another over the channel (136), with the target device sending data over the channel that the host device receives, and vice-versa.

[0025] FIG. 2 shows how an example target device 202 is placed against an example host computing device 204 so that a photosensor 206 of the target device 202 is adjacent to and against display hardware 208 of the host device 204. In the example of FIG. 2, the target device 202 includes a pulse oximeter 210 having light-emitting diodes (LEDs) 212 as well as the photosensor 206, which may be a photodiode. As such, the photosensor 206 in this case is used for a purpose in the method 100 that has been described other than that its intended purpose. Rather than being used to detect the light output by the LEDs 212 as reflected by the bloodstream of a person for the pulse oximeter 210 to determine the person's oxygen saturation, the photosensor 206 is used to detect a temporal light pattern encoding a passkey that the host computing device 204 displays on its display hardware 208. [0026] Both the target device 202 and the host computing device 204 include wireless radios 214 and 216, respectively, by which they can transmit and receive RF signals over a frequency, such as in accordance with a standard protocol like the Bluetooth protocol. The target device 202 and the host device 204 both can include logic 218 and 220, respectively, which may each be implemented as a processor and a memory or other non-transitory computer- readable data storage medium storing computer-executable code that the processor executes. The logic 218 of the target device 202 can perform the parts of the method 100 ascribed to the target device 202, whereas the logic 220 of the host device 204 can perform the parts of the method 100 ascribed to the host device 204. Each of the target device 202 and the host device 204 can include additional hardware components, such as input hardware, sensor hardware, and so on.

[0027] The host computing device 204 generally can display a color on the display hardware 208 that the photosensor 206 of the target device 202 can detect. The host device 204 temporally can modulate the brightness of the display color according to the passkey, such as in accordance with bits of the passkey, as the temporal light pattern. The logic 218 of the target device 202 decodes the passkey from the detected temporal light pattern by associating brightness changes with bits of the passkey, for instance.

[0028] FIG. 3 shows a graph 300 depicting an example manner by which the brightness of the displayed color can be temporally modulated to yield the temporal light pattern that is detected for decoding of the passkey. In the example of the graph 300, the passkey is a series of eights bits 101 10001 . More generally, though, the passkey can be any number of bits, and may be 32, 64, 128, 192, 256, or more bits in length, for instance. The graph 300 includes an x- axis 302 denoting time, and a y-axis 304 denoting brightness.

[0029] The encoding approach used in the example of FIG. 3 is known a priori by the target device 202, so that the logic 218 of the target device 202 is able to properly decode the passkey from the detected temporal light pattern. The example encoding approach of FIG. 3 can be considered a digital temporal modulation approach. A maximum brightness of 100% of the displayed color is output on the display hardware 100 to denote a 1 bit, whereas a middle

brightness of 50% is output to denote a 0 bit. The brightness corresponding to the currently transmitted bit is output for a length of time t. Between adjacent bits, the display hardware does not display the color for the length of time t; that is, the color is displayed at a brightness of 0%.

[0030] An initial length of time Xt, where X is a relatively large multiple of the time t, such as ten, precedes the transmission of the first bit of the passkey. This ensures that the target device 202 does not mistakenly detect a subsequent bit of the passkey as the first bit, if detection by the target device 202 begins after the host computing device 204 has begun displaying the temporal light pattern. The temporal light pattern may be repeated a number of times, where prior to each repetition of the initial length of time Xt in which the color in question is not displayed again occurs. Therefore, if the target device 202 immediately begins detecting the color output by the host device 204, the target device 202 can discern that it has started detecting the temporal light pattern after the host device 204 began displaying the pattern, and thus can wait for a length of time Xt in which the color is not displayed for the next output of the temporal light pattern.

[0031] Other techniques can be employed to temporally modulate a displayed color of light in accordance with a passkey to encode the passkey within a temporal light pattern. For example, in an analog modulation approach, the brightness of the displayed color may be modulated at levels corresponding to bytes or half-bytes (i.e., nibbles). If the displayed color can be displayed by the displayed hardware 208 at 256 different brightness levels, and if the photosensor 206 can discern each of the 256 brightness levels, then the host device 204 may in a given time t display the color at a brightness level

corresponding to one byte (i.e., eight bits) of the passkey.

[0032] By comparison, if the displayed color can be displayed at just sixteen different brightness levels, or if the photosensor 206 can discern each of just sixteen different brightness levels, then the host device 204 may in a given time t display the color a brightness level corresponding to one nibble (i.e., four bits) of the passkey. In both these cases, transmission of a passkey of a particular length will occur more quickly than if each given time t in which the color is output corresponds to just one bit of the passkey. In other techniques, the time between which the color in question is not output (i.e., the color is output at a brightness of 0%) may be different than the time in which the color is output at any brightness. Furthermore, modulating the brightness of the displayed color can include turning the brightness on and off, where off corresponds to a zero bit and on corresponds to a one bit.

[0033] FIG. 4 shows an example method 400 of use that a user can perform to establish a wireless communication channel between the host computing device 204 and the target device 202. The user operates the target device 202 so that the target device 202 wirelessly broadcasts via the wireless radio 214 its availability to establish a wireless communication channel (402). For example, the user may press an associated pairing button on the target device 202.

[0034] The user operates the host computing device 204 to detect the wireless broadcasting by the target device 202 indicating the availability of the target device 202 to establish a wireless communication channel (404). For example, the user may causing a settings app or other computer program of the host device 204 to run, and then select a setting in which the wireless radio 216 of the host device 204 detects any such wireless availability broadcasts by devices like the target device 202. The user then places the target device 202 against the host device 204 so that the photosensor 206 is adjacent to the display hardware 208 of the host device (406).

[0035] If the host computing device 204 cannot itself detect placement of the target device 202 against the host device 204, the user may further operate the host device 204 to confirm or indicate that the target device 202 has been placed against the host device 204 (408). For example, the user may press a user interface control on a touchscreen of the host device 204 corresponding to this confirmation. Upon receiving confirmation from the host device 204 and/or the target device 202 that a wireless communication channel has been established between the devices 204 and 202 - i.e., that the target device 202 has been successfully paired with the host device 204 - the user can then remove the target device 202 so that it is no longer positioned against the host device 204 (410).