Patent Publication Number: US-2022232475-A1

Title: Open loop wake-up radio based on transmitter fingerprinting

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/858,119, filed Apr. 24, 2020, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     One challenge in a wireless network that includes battery-operated devices is battery life. One type of wireless device is an Internet-of-Things (IoT) device. IoT devices often have a sensor usable to monitor an environmental condition (e.g., temperature), the operating state of a machine, or other type of condition. IoT devices generally are “headless” meaning that they have no direct user input/output capability (e.g., no keyboard, no display, etc.). IoT devices are often battery-operated and are installed within an environment or machine and are not intended to be directly accessed by a user. Many applications for the use of IoT devices benefit from the IoT devices&#39; batteries lasting a long time (e.g., years). 
     SUMMARY 
     In at least one example, a device includes a first radio, and a memory device accessible to the first radio. The memory device is configured to store a feature for a specific transmitter device. A second radio and a processor are also included. The process is coupled to the first and second radios. The first radio is configured to extract a feature of a first received wireless signal, determine that the extracted feature matches the feature stored in the storage device, and responsive to the determination that the extracted feature matches the feature stored in the storage device, cause the second radio to transition from a lower power state to a higher power state of operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of various examples, reference will now be made to the accompanying drawings in which: 
         FIG. 1  illustrates a wireless network including IoT devices in accordance with an example. 
         FIG. 2  shows an example implementation of an IoT having a wake-up radio. 
         FIG. 3  shows an example of a method for an IoT device to validate an access point based on a feature extracted from a wireless signal. 
     
    
    
     DETAILED DESCRIPTION 
     Some battery-powered wireless devices include a “main” radio and a “wake-up” radio. The main radio is used to transmit and/or receive data in accordance with the device&#39;s runtime operation. The main radio can enter a low power state (e.g., a sleep state, hibernation state, etc.) during periods of non-use. The wake-up radio receives wireless signals from transmitters in the wireless network to determine when to wake-up the main radio. Wake-up radios may operate in an “open loop” configuration or a “closed loop” configuration. A closed-loop wake-up radio is preconfigured to recognize, for example, a certain sequence of symbols from a transmitter, or negotiates with the transmitter for the transmitter-specific sequence of symbols. Closed-loop wake-up radios and transmitters may follow a particular wireless protocol that determine and/or negotiate a wake-up signal. The negotiation of the wake-up signal is in addition to the data and message signaling. 
     Although wireless devices operate according to applicable standard protocols (e.g., IEEE 802.11, Bluetooth Low Energy, etc.), a wireless transmitter within a given wireless network can be distinguished from other wireless transmitters due to imperfections in the analog components of the transmitter. Such imperfections may result from randomness introduced during the manufacturing of the components of the transmitters (e.g., digital-to-analog converters, filters, frequency mixers, power amplifiers, etc.). For example, the threshold voltage or on-resistance of metal oxide semiconductor field effect transistors (MOSFETs) may vary slightly from transistor to transistor even though the transistors are made in accordance with the same process steps. Such non-linear effects result in each transmitter having a unique “fingerprint.” Thus, radio frequency (RF) fingerprinting can be used by a receiver to identify a specific transmitter from among other possible transmitters to thereby wake-up the main radio. Waking up the main radio based on an RF fingerprint is an “open-loop” process in that a negotiation of a particular set of symbols between transmitter and receiver is not required. That is, a wake-up signal (generated internal to the wireless device) to wake a main radio in response to an aspect of a specific transmitter (an extracted “feature”) is generated based on the transmitter&#39;s standard transmission without adding any specific/integrated wake-up signal to the normal data transmission protocol. The receiver determines the RF fingerprint of a transmission that uniquely identifies a particular transmitter with which the receiver is to associate, and then uses that extracted feature to only wake-up the main radio when the valid feature is detected, for example, the extracted feature matches a feature stored in the radio&#39;s memory). The transmission being fingerprinted may also include an identifier of the IoT device(s) that the transmitter wants to wake. Fingerprinting a transmission with the IoT device-specific identifier will cause only that particular IoT device to wake its main radio when a future transmission with the relevant fingerprint is detected. 
     The disclosed examples are directed to a battery-powered, Internet-of-Things (IoT) devices that include a main radio and a wake-up radio. The main radio is used by the IoT device to transmit and/or receive data in accordance with its runtime operation. In one example, the battery-powered IoT device may have one or more integrated or external sensors, and the IoT device&#39;s main radio is used to transmit sensor data or event information to the wireless network. To save battery power, the main radio transitions to a lower power state (e.g., a sleep or hibernation state). While in the lower power state, the main radio is not usable to send or receive wireless signals. Instead, the main radio must be woken up for that purpose. The wake-up radio employs RF fingerprinting (i.e., a temporary “feature”) to detect when a valid transmitter (e.g., an access point) is attempting to communicate with the IoT device containing the wake-up radio. In this context, a valid transmitter is a transmitter to which the IoT device is paired and with which the IoT device should communicate. When the wake-up radio detects a valid fingerprint, the wake-up radio causes the main radio to wake up (i.e., transition from the lower power state to the higher power state) and to continue decoding the received wireless signal to thereby be capable of runtime operations such as transmitting sensor data, receiving wireless communications from the transmitter, etc. The wake-up radio described herein thus employs RF fingerprinting (e.g., comparing a newly extracted feature to one or more features stored in memory) to wake up the main radio. Because the wake-up event is generated while also receiving data in the course of normal operations (i.e., there is no dedicated wake-up signal), a negotiation of a specific set of dedicated wake-up symbols between transmitter and receiver according to a specific protocol is not needed for the open-loop wake-up radio described herein. 
       FIG. 1  shows an example of a wireless network  100  including access points  110  and  111  and IoT devices  120  and  130 . Any number of IoT devices (one or more) can be included within the wireless network  100 . In this example, each IoT device includes a battery, a main radio and a fingerprinting wake-up radio (WUR). IoT device  120  includes a battery  121 , a main radio  122 , and a fingerprinting wake-up radio  126 . Similarly, IoT device  130  includes a battery  131 , a main radio  132 , and a fingerprinting wake-up radio  136 . During extended periods of non-use, the main radios  122 ,  132  of the IoT devices  120 ,  130  are turned off to save battery power. However, the fingerprinting wake-up radios  122 ,  132  remain continuously powered on. In the configuration of  FIG. 1 , main radio  132  in IoT device  130  is turned off. The wake-up radio  126  in IoT device  120  has detected a valid fingerprint from a wireless signal transmitted by access point  110  (e.g., has extracted a feature from the wireless signal and determined that the feature matches a feature stored in the radio&#39;s memory). In response to detection of a valid fingerprint, the wake-up radio  126  causes the main radio  122  in IoT device  120  to wake to complete the reception on the arriving wireless signal (e.g., powered on or otherwise transitioned to a higher power, fully operational state). The wake-up radio  136  in IoT device  130  is not configured to recognize the same RF fingerprint as wake-up radio  126  (e.g., the feature extracted by wake-up radio  136  does not match any features stored in that radio&#39;s memory), and thus the main radio  132  in IoT device  130  remains in a low power state (e.g., sleep, hibernation, etc.). Instead, the wake-up radio  136  of IoT device  130  may be configured to recognize an RF fingerprint derived from access point  111 . 
       FIG. 2  shows additional detail regarding the implementation of IoT device  120 , but the same architecture may apply to IoT device  130  and/or other IoT devices in the wireless network  100 . In this example, IoT device  120  includes battery  121 , main radio  122 , fingerprinting wake-up radio  126 , a processor  210 , a sensor  220 , and a memory device  227 . The main and fingerprinting wake-up radios  122  and  126  as well as sensor  220  are coupled to processor  210 . The battery  121  provides operating power for some or all of the active components with in the IoT device  120 . While one processor  210  is shown in this example, more than one processor can be provided in other implementations. Similarly, more than one sensor  220  can be provided as well. The sensor  220  is application-specific. Examples of sensor  220  include a temperature sensor, a current sensor, a voltage sensor, etc. 
     Each radio  122 ,  126  is coupled to an antenna. Main radio  122  is coupled to antenna  225 , and wake-up radio  126  is coupled to antenna  235 . Each radio thus may be connected to its own antenna. In other example, one antenna or antenna array is shared between the two radios  122 ,  126 . As noted above, the main radio  122  is used for a different purpose than the fingerprinting wake-up radio. The main radio  122  is used to exchange (send and/or receive) wireless signals with an access point during device run-time. For example, the main radio  122  may be used to receive a request from an access point (e.g., access point  110 ) for a sensor reading, send data and/or signals from sensor  220  to the access point (e.g., access point  110 ), etc. In an implementation in which IoT device  120  responds to requests received from an access point, the main radio  122  in the IoT device may be powered off following transmission/reception of information to the access point as the IoT device awaits another request from the access point. Alternatively, the main radio  122  may be powered down following a predefined period of time of non-use (e.g., 30 second, 2 minutes, etc.). 
     The fingerprinting wake-up radio  126  remains continuously powered on and operational in at least some implementations and is used to detect a valid fingerprint from an access point&#39;s standard wireless signals. In response to detection of a valid RF fingerprint, the main radio  122  is caused to be transitioned from the lower power state to the higher power state in order to receive the incoming signal. 
     RF fingerprinting can be performed based on the following illustrative categories: transient-based RF fingerprinting and steady-state based RF fingerprinting generation. In transient-based RF fingerprinting generation, a transmitter transmitting from its off to on states triggers a unique transient feature within the transmitted wireless signal which appears before the transmission of the actual packet of data. In steady-state based RF fingerprinting generation, unique features are present in the transmitter&#39;s wireless signal during the modulation phase. In this case, the fingerprinting wake-up radio generates the fingerprint from at least one received symbol. Any of numerous different types of RF fingerprinting techniques can be implemented by an IoT device to validate a transmitter. Validating the transmitter means that the IoT device confirms whether a wireless signal the IoT device receives is from a transmitter with which the IoT device is associated (e.g., paired) and the extracted feature matches a feature already stored in the device&#39;s memory). 
     One example of transient-based RF fingerprinting includes the determination of the power spectral density (PSD) of the preamble in, for example, an IEEE 802.11a preamble. In this particular RF fingerprinting technique, the PSD is characterized by PSD coefficients, which can be calculated as: 
     
       
         
           
             
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     The PSD of a wireless signal received from a transmitter can be used to uniquely identify the transmitter. That is, the PSD varies between transmitters and is generally repeatable for a given transmitter. The fingerprinting wake-up radio described herein is usable to determine the PSD for an incoming wireless signal. The PSD for one or more transmitters to which an IoT device is associated is stored in memory  227  within the IoT device as fingerprint(s)  229 . The PSD determined for a given wireless signal can be compared to the PSD(s) stored in memory within the IoT device to determine whether a valid transmitter is attempting to communicate with the IoT device. If the PSD computed by the IoT device matches a PSD stored in the IoT device&#39;s memory, then the main radio is caused to be transitioned from its lower power state to its higher power state (i.e., awakened). 
     The fingerprint(s)  229  stored in memory  227  may be provided to or otherwise determined by the IoT device  120  in accordance with any suitable technique. In on example, a user device  211  is coupled to the processor  210  and can be used to indicate to the processor  210  that the processor  210  is to enter a training mode in which the processor  210  determines a fingerprint of a wireless signal it receives and store the fingerprint in memory  227  for subsequent use to enable the main radio  122 . In another example, a user can program one or more fingerprints  229  via a graphical user interface implemented on a computer system external to the IoT device  120  and cause the external computer system to transmit the fingerprint to the IoT device for storage in memory  227 . 
       FIG. 3  illustrates an example of a method performed by an IoT device (e.g., IoT device  120 ) to validate a transmitter by way of RF fingerprinting. At  306 , the IoT device communicates with the other transmitter and, at  308 , determines and stores a fingerprint of the transmitter. Fingerprint techniques such as those described above can be employed. The main radio  122  of the IoT device may be awake during steps  306  and  308  and may be used to provide signals from the transmitter to the IoT device&#39;s processor  210  for determination of the fingerprint. The processor  210  may store the fingerprint in memory  227 . 
     At  310 , the main radio  122  is transitioned to a low power state (e.g., sleep, hibernation). In one example, the processor  210  sends a signal to the main radio  122  to transition to the low power state following the main radio&#39;s use to reply to a request received from a transmitter. In another example, the processor  210  sends a signal to the main radio  122  to transition to the low power state upon timeout of a timer during a period of non-use of the main radio  122 . 
     At  320 , the fingerprinting wake-up radio (which remains on and operational) begins to receive a wireless signal. The wireless signal received may be from a valid or invalid transmitter. If the wireless signal is from a valid transmitter, the main radio  122  should be transitioned to its higher power (operational) state, but if the wireless signal is not from a valid transmitter, the main radio  122  should not be transitioned to its higher power state and thus remain in its low power state. As explained above, a valid transmitter is a transmitter to which the IoT device is paired and with which the IoT device should communicate. The wireless signal received at  320  may include reception of a preamble of an IEEE 802.11 message. Transitioning the main radio  122  to the higher power state may include one or more of: turning power on to the main radio, increasing the operational voltage to the main radio, clocking the main radio at a higher frequency, etc. 
     At  330 , the method includes extracting a feature from the received wireless signal. In one example, the extracted feature includes a computation of the PSD of the received wireless signal as described above. The fingerprinting wake-up radio  126  may compute the PSD of the received wireless signal. 
     At  340 , the method includes determining whether the extracted feature matches any features stored in memory  229  within the IoT device  120 . In one implementation, the fingerprinting wake-up radio  126  makes this determination. In another example, the fingerprinting wake-up radio  126  provides the extracted feature to the processor  210 , and the processor  210  compares the extracted feature to the feature(s) stored in memory  227 . In either case, a comparison is made of the newly extracted feature to any features previously stored in memory  227 . The extracted feature and the feature(s) stored in memory  227  may comprise PSDs of, for example, a preamble of wireless packet. 
     At  350 , if the extracted feature does not match any feature(s) stored in memory  227 , then the power state of the main radio  122  remains in the low power state, that is, the main radio  122  is not awakened. 
     At  360 , if the extracted feature does match at least one feature stored in memory  227 , the main radio is awakened and continues to decode the received signal. In one example, the fingerprinting wake-up radio  126  determines the match and sends a signal to processor  210  to awaken the main radio  122 . In another example, the fingerprinting wake-up radio extracts the feature from the wireless signal at  330  and provides the feature to the processor  210 , and the processor  210  determines a match exists and commands the main radio  122  to be transitioned to its higher power state (e.g., by providing an enable signal to the main radio  122 ). Once the main radio  122  is transitioned to its higher power state, the main radio continues receiving the incoming wireless signals and provides such signals to the processor  210  for further processing. While in the higher power state, the main radio  122  also can be used to transmit data (e.g., sensor data). 
     The term “couple” is used throughout the specification. The term may cover connections, communications, or signal paths that enable a functional relationship consistent with the description of the present disclosure. For example, if device A generates a signal to control device B to perform an action, in a first example device A is coupled to device B, or in a second example device A is coupled to device B through intervening component C if intervening component C does not substantially alter the functional relationship between device A and device B such that device B is controlled by device A via the control signal generated by device A. 
     Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.