PATENT DOCUMENT

Publication Number: US-10681632-B2
Application Number: US-201816012969-A
Country: US
Kind Code: B2

Title: System and method for low power signaling in a wireless local area network

Abstract:
A station, a method performed by a station and a corresponding method performed by an access point (AP) of a network to allow the station to operate a wireless local area network (WLAN) radio in a sleep state until the WLAN radio is ready to receive a beacon from the AP. The station includes a low power (LP) radio configured to receive a wake up signal from an AP of a network to which the station is connected. The station further includes a WLAN radio configured to operate in a sleep state until the WLAN radio receives an indication from the LP radio that the wakeup signal has been received, wherein WLAN radio is further configured to operate in a fully awake state after receipt of the indication to receive a beacon from the AP indicating a data transmission is pending for the station.

Claims:
What is claimed is: 
     
       1. An access point (AP), comprising:
 a transmitter; and 
 a processor configured to perform operations, including:
 transmitting a poll to a station associated with the AP, the poll configured to be received by a low power (LP) radio of the station and indicate a request for a power mode status of a wireless local area network (WLAN) radio of the station; 
 receiving, from the LP radio of the station, a signal indicating the power mode status of the WLAN radio; 
 determining that data is to be transmitted to the station associated with the AP; 
 in response to determining that the data is to be transmitted to the station, transmitting a wake up signal to the station, wherein the wake up signal is configured to be received by the (LP) radio of the station and indicates that the WLAN radio of the station is to transition to a higher-power state; and 
 transmitting a message to the station, wherein the message is configured to be received by the WLAN radio of the station and indicates that the data is to be transmitted to the station. 
 
 
     
     
       2. The AP of  claim 1 , wherein the wake up signal is transmitted at a first time and the message is transmitted at a second time subsequent to the first time. 
     
     
       3. The AP of  claim 2 , wherein the operations further include receiving an indication that indicates when a physical layer (PHY) of the WLAN radio of the station is to transition to the higher-power state, wherein a duration between the first time and the second time is based on the indication. 
     
     
       4. The AP of  claim 2 , wherein the data is transmitted at a third time that is subsequent to the first time and the second time. 
     
     
       5. The AP of  claim 1 , wherein the message is included in a management frame. 
     
     
       6. The AP of  claim 1 , wherein the wake up signal is broadcast to the station and at least one further station associated with the AP. 
     
     
       7. The AP of  claim 1 , wherein the wake up signal is formatted as a first type of signal that corresponds to the LP radio of the station and the message is formatted as a second type of signal that corresponds to the WLAN radio of the station. 
     
     
       8. The AP of  claim 1 , wherein the wake up signal and the message are transmitted on a same band. 
     
     
       9. The AP of  claim 1 , wherein the wake up signal is transmitted on a narrow band. 
     
     
       10. A method, comprising:
 at an access point (AP):
 determining that data is available to be transmitted to a station associated with the AP; 
 transmitting a poll to a station, the poll configured to be received by a low power (LP) radio of the station and indicate a request for a power mode status of a wireless local area network (WLAN) radio of the station; 
 receiving, from the LP radio of the station, a station indication signal indicating the power mode status of the WLAN radio; 
 transmitting to the station a first signal configured to be received by the LP radio of the station and to initiate a transition of the WLAN radio of the station from a lower-power state to a higher-power state; and 
 transmitting to the station a second signal indicating that data is to be transmitted to the station. 
 
 
     
     
       11. The method of  claim 10 , wherein:
 the first signal is transmitted at a first time; 
 the second signal is transmitted at a second time subsequent to the first time; and the data is transmitted at a third time subsequent to the first time and the second time. 
 
     
     
       12. The method of  claim 10 , wherein the second signal and the data are transmitted to the WLAN radio of the station. 
     
     
       13. The method of  claim 10 , wherein the first signal and the second signal are transmitted on different bands. 
     
     
       14. The method of  claim 10 , wherein the LP radio of the station is activated for the entirety of the association between the AP and the station. 
     
     
       15. The method of  claim 10 , wherein the first signal includes an AP identifier. 
     
     
       16. The method of  claim 15 , wherein the first signal includes a station identifier. 
     
     
       17. A method, comprising:
 at an access point (AP):
 determining that a station associated with the AP is configured to operate during a first duration with a low power (LP) radio of the station activated; 
 determining that data is to be transmitted to the station; 
 transmitting, to the station, a poll configured to be received by the LP radio of the station and indicate a request for a power mode status of a wireless local area network (WLAN) radio of the station; 
 receiving, from the LP radio of the station, a station indication signal indicating the power mode status of the WLAN radio; 
 transmitting, to the station, a first signal during the first duration, wherein the first signal is configured to be received by the LP radio of the station and to initiate a transition of a wireless local area network (WLAN) radio of the station to a higher-power state; and 
 transmitting to the station a second signal to be received by the WLAN radio of the station, wherein the second signal indicates that data is to be transmitted to the station. 
 
 
     
     
       18. The method of  claim 17 , wherein:
 the first signal is transmitted at a first time; 
 the second signal is transmitted at a second time subsequent to the first time; and the data is transmitted at a third time subsequent to the first time and the second time. 
 
     
     
       19. The method of  claim 17 , wherein the station is configured to operate during a second duration with the LP radio of the station deactivated. 
     
     
       20. The method of  claim 17 , wherein the signal is formatted as a first type of signal that corresponds to the LP radio of the station and the second signal is formatted as a second type of signal that corresponds to the WLAN radio of the station.

Description:
PRIORITY CLAIM/INCORPORATION BY REFERENCE 
     This application claims priority to U.S. Provisional Application 61/928,914 entitled “System and Method for Low Power Signaling in a Wireless Local Area Network,” filed on Jan. 17, 2014, the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND INFORMATION 
     A wireless local area network (WLAN) may be used to exchange data from one station to another station. The station that receives the data may be configured using a duty cycle. The duty cycle may indicate a schedule indicating a time duration in which the WLAN radio of the receiving station is to be activated at select time periods to listen for beacons transmitted from a network component such as an access point of the WLAN. The WLAN radio may be activated for a first predetermined time period within the duty cycle and deactivated or placed to sleep (e.g., hibernate) if no beacon is received in this time period. The WLAN radio may sleep for a second predetermined time period after which the WLAN radio is again activated for the first predetermined time period. This may repeat until a beacon is received by the WLAN radio while activated. The power required to activate and deactivate the WLAN radio is relatively high and may be wasted, particularly when no beacon is received. 
     SUMMARY 
     In one exemplary embodiment, a station connected to a network performs a method. The method includes receiving, by a low power (LP) radio of a station, a wake up signal from an access point (AP) of a network the station is connected, the wake up signal configured to fully wake a wireless local area network (WLAN) radio of the station and receiving, by the WLAN radio of the station, a beacon indicating a data transmission is pending for the station. 
     In another exemplary embodiment, an access point (AP) of a network performs a method. The method includes determining at least one station of the network to receive a data transmission, transmitting a wake up signal to a low power (LP) radio of the at least one station, the wake up signal configured to wake a wireless local area network (WLAN) radio of the at least one station and transmitting, by the AP, a beacon to the WLAN radio of the at least station, the beacon indicating the data transmission is pending for the at least one station. 
     In a further exemplary embodiment, a station includes a low power (LP) radio and a wireless local area network (WLAN) radio. The LP radio is configured to receive a wake up signal from an access point (AP) of a network to which the station is connected. The WLAN radio is configured to operate in a sleep state until the WLAN radio receives an indication from the LP radio that the wakeup signal has been received, wherein WLAN radio is further configured to operate in a fully awake state after receipt of the indication to receive a beacon from the AP indicating a data transmission is pending for the station. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary network arrangement to transmit an indication prior to transmitting a beacon indicating a subsequent data transmission. 
         FIG. 2  shows an exemplary station configured to receive the indication, the beacon, and the subsequent data transmission. 
         FIG. 3  shows a first exemplary signaling diagram utilizing the wake up signal. 
         FIG. 4  shows a second exemplary signaling diagram utilizing the wake up signal. 
         FIG. 5  shows an exemplary block diagram of receiving the wake up signal and subsequent operations. 
         FIG. 6A  shows an exemplary wake up signal format. 
         FIG. 6B  shows an exemplary station indication signal format. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments may be further understood with reference to the following description and the related appended drawings, wherein like elements are provided with the same reference numerals. The exemplary embodiments are related to systems and methods for low power signaling in a WLAN. Specifically, an access point (AP) of the WLAN may transmit an indication (e.g., a wake up signal) to a station scheduled to receive a data transmission prior to transmitting a beacon to the receiving station. The receiving station may receive the indication using a first radio to activate a second radio such that the second radio is configured to receive the beacon. The first radio may utilize a low power consumption for operation that is lower than the second radio. Therefore, the receiving station may conserve power by not using the higher power second radio to continuously listen for the beacon. The low power signaling, the indication, the beacon, the AP of the WLAN, the receiving station, the first and second radios, and the power conservation will be described in further detail below. 
     Initially, it should be noted that the description below relates to using the first and second radios as well as the wake up signal in a WLAN. However, the use of the WLAN is only exemplary. The exemplary embodiments may also be used in various other network types including, for example, a peer-to-peer (P2P) network. 
     When a station is mobile, it is often restricted to using a portable power supply, which is limited. Therefore, an important design constraint for mobile stations is that a minimal amount of power be used for any given operation to allow the station to be used for a longer duration without being connected to a fixed power source. One particular application in for which lower power consumption is desirable is low data throughput and low duty cycle applications relating to data transmissions. The station may be configured with a duty cycle that indicates time intervals within a given time duration that a radio is to be activated to listen for beacons. The beacon may represent, for example, a management frame in the 802.11 specifications provided by the Institute of Electrical Engineers (IEEE). Specifically, the beacon may include information regarding a pending data transmission to be received by the station. 
     With a radio used in the 802.11 specifications, the power consumed during the receiving functionality is relatively high. For example, in a 5 GHz network, the power consumption could be 30% more than in a 2.4 GHz network. Those skilled in the art will understand that the power consumption to receive a data transmission is substantially similar to the power consumption to look for a received signal. Accordingly, the radio utilizes a relatively large amount of power each time it is activated and used to receive the beacon. 
     One manner of reducing this power consumption is maintaining a low duty cycle. For example, the radio consumes the large amount of power for a smaller amount of time, thereby reducing an overall power consumption of the station. For example, a duty cycle at 50% requires that the radio be activated for half the time of the duration of the cycle. By decreasing the duty cycle to a smaller amount such as 10%, the radio is activated for 40% less time within the duration of the cycle. Nevertheless, the large amount of power is still required each time the radio is activated. 
     Furthermore, the low duty cycle only applies to when the radio is allowed to sleep during times it is not activated or being used. However, this is substantially impossible to achieve on a busy WLAN. For example, the radio must stay awake and activated to receive even undesired packets. In another example, the WLAN may be congested to a degree that a beacon that is scheduled to be received according to a Target Beacon Transmission Time (TBTT) known to the station is delayed. The station may therefore be required to maintain the radio in the full power activated state from the indicated time of the TBTT until the delayed beacon is received. 
     In addition, the AP of the WLAN may have successfully indicated that there is a packet (i.e., data to be transmitted thereto as indicated in the beacon) pending for the station. However, with a busy WLAN or for other reasons, the station must contend for the medium to send out a power save (PS)-Poll frame to solicit the frame since the radio has been woken from the sleep or power-saving mode. This may further worsen the power consumption, as the radio must be maintained in the activated state until the PS-Poll frame is successfully transmitted to the AP. 
     The exemplary embodiments provide a mechanism to utilize low power signaling as well as a mechanism to reduce a total time required for the high power consuming radio to be activated. That is, the high power consuming radio is allowed to sleep for an overall longer duration to decrease the power consumption. As used herein, the high power consuming radio will be referred to as a WLAN radio. The exemplary embodiments utilize the WLAN radio and a further low power (LP) radio. The LP radio may utilize a substantially smaller amount of power to operate than the WLAN radio. The LP radio may be configured to receive an indication or wake up signal from the AP of the WLAN. Accordingly, the AP of the WLAN may be configured to provide this wake up signal. The activated LP radio may use a relatively low amount of power and receive the wake up signal, which is used to wake a sleeping WLAN radio (e.g., wake a PHY of the station). In this manner, the WLAN radio is only woken when it is known that subsequent transmissions are destined for the station. Specifically, the WLAN radio is awake to receive a beacon that indicates a subsequent data transmission of pending packets at the AP. As will also be described in further detail below, the exemplary embodiments may provide further mechanisms that substantially prevent the station from contending for a medium as well as enable the LP radio to be used for uplink operations such as providing the PS-Poll frame. 
       FIG. 1  shows an exemplary network arrangement  100  to transmit an indication prior to transmitting a beacon indicating a subsequent data transmission. The network arrangement  100  may include a network  105  and an AP  110  that is used by a plurality of stations  115 - 125  to connect to the network. The network  105  may be, for example, a WLAN using a 802.11 specification as defined by the IEEE. However, those skilled in the art will understand that the network  105  may be any type of communications network in which data is exchanged between at least one first electronic device and at least one second electronic device of the network itself. Accordingly, the network arrangement  100  may include further network components (not shown) such as servers, routers, network management arrangements, network databases, etc. 
     The stations  115 - 125  may each be connected to the network  105  via the AP  110 . Specifically, the stations  115 - 125  may be associated with the AP  110  using, for example, a handshake functionality. However, the exemplary embodiments also relate to and may be used for stations that are non-AP stations. It should be noted that the number of the stations  115 - 125  in the network arrangement  100  is only exemplary. Those skilled in the art will understand that any number of stations  115 - 125  may be present. It should also be noted that the network  105  may have any number of APs that may be used by the stations  115 - 125  to connect to the network. In addition, there may be other types of devices that allow network access that are not APs. These other types of network access devices may also implement the functionality described herein for the AP  110 . 
     The AP  110  may be configured to transmit data indicated as having a destination to at least one of the stations  115 - 125 . The data that is to be transmitted by the AP  110  to one of the stations  115 - 125  may be received from the stations  115 - 125  or from the network  105 . For example, the station  115  may transmit data destined for the station  125  via the AP  110 . As will be described in further detail below, the AP  110  may initially transmit a wake up signal to the stations that are to receive the data before transmitting a beacon that provides information as to the transmission of the data. After the beacon has been transmitted, the AP  110  may then transmit the data to the stations. 
       FIG. 2  shows an exemplary station  200  configured to receive the indication, the beacon, and the subsequent data transmission. Specifically, the station  200  may represent an electronic device such as the stations  115 - 125 . More specifically, the station  200  may be any portable device configured to exchange data with the network  105  such as a cellular phone, a smartphone, a tablet, a phablet, a laptop, etc. The station  200  may include a processor  205 , a memory arrangement  210 , a display device  215 , an input/output (I/O) device  220 , a WLAN radio  225 , a LP radio  230 , and other components  235 . 
     The processor  205  may be configured to execute a plurality of applications of the station  200 . For example, the applications may include a text message application to receive a text from a further station when connected to the network  105 . In another example, the applications may include a radio activation application that transmits signals to the WLAN radio  225  to wake it (based upon signals from the LP radio  230 ) or to place the WLAN radio into a sleep state (e.g., based upon expected transmission inactivity). It should be noted that the applications being a program executed by the processor  205  is only exemplary. The applications may also be represented as a separate incorporated component of the station  200  or may be a modular component coupled to the station  200 . It should also be noted that the use of the radio activation application is only exemplary. In another example, a direct signaling path may be established between the WLAN radio  225  and the LP radio  230  in which the LP radio  230  performs the functionalities of the radio activation application. In another exemplary embodiment, the functionalities described for the radio activation application may be implemented in a separate integrated circuit with or without firmware. 
     The memory arrangement  210  may be a hardware component configured to store data related to operations performed by the station  200 . For example, the memory arrangement  210  may store the information received from the AP  110  relating to data transmissions. The display device  215  may be a hardware component configured to show data to a user while I/O device  220  may be a hardware component configured to receive inputs from the user and output corresponding data. The other components  235  may include a portable power supply (e.g., battery), a data acquisition device, ports to electrically connect the station  200  to other electronic devices, an audio I/O device, etc. 
     The WLAN radio  225  may be a hardware component configured to transmit and/or receive data (e.g., a transceiver) with the network  105 . As discussed above, the WLAN radio  225  may be the high power consuming radio used in a 802.11 WLAN. Thus, when activated, the WLAN radio  225  may consume, for example, 180 mW of power when the WLAN operates at 2.4 GHz or 240 mW of power when the WLAN operates at 5 GHz. As will be described in further detail below, the WLAN radio  225  may be in one of two states: awake/activated or asleep/deactivated. When awake, the WLAN radio  225  may be configured to receive a beacon from the AP  110  as well as data scheduled for transmission to the station  200 . 
     Because the WLAN radio  225  operates using wireless signals, these signals are propagated using various frequencies. These frequencies may be attained using, for example, a crystal oscillator. A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material (e.g., quartz crystal) to create an electrical signal with a very precise frequency. As will be described in further detail below, the time required to activate the crystals of the WLAN radio  225  may impact a manner in which the exemplary embodiments utilize the wake up signal. Specifically, the crystals may require 3-5 ms to activate whereas other aspects of the WLAN radio  225  (e.g., PHY) may only require a fraction of that time. For example, for the WLAN radio  225  to be fully awake after the crystals are ON, the PHY may be turned ON. The turning ON of the PHY requires approximately 500 μs to first be placed in a standby mode and approximately another 50 μs to be placed ON. However, it should be noted that the operation to place the PHY from standby to ON may be between 25-100 μs. 
     It should be noted that the use of crystals in the WLAN radio  225  is only exemplary. For example, non-crystal components may be used. The crystals may represent any oscillator that enables a selection of a frequency. Furthermore, the WLAN radio  225  may use other manners of generating the signals at selected frequencies. For example, non-oscillator components may also be used. Therefore, the crystals described herein may represent any component of the WLAN radio  225  that enables signals to be generated at a known frequency. Those skilled in the art will understand that depending on these other manners, the exemplary embodiments may be modified to accommodate the timing issues with using components in these other manners. 
     The LP radio  230  may be a hardware component configured to transmit and/or receive signals with the AP  110 . Specifically, the LP radio  230  may provide a specified data exchange functionality. As discussed above, the LP radio  230  may receive the wake up signal from the AP  110 . In a first example, the LP radio  230  may forward a corresponding signal to the processor  205  such that the radio activation application may wake the WLAN radio  225 . For example, the processor may send an activation signal to the WLAN radio  225  to activate the PHY to ON and the crystals may also be activated. In a second example, the activation signal for the WLAN radio  225  may be generated by the LP radio  230  and this activation signal may be sent to the WLAN radio  225  via a direct pathway between the LP radio  230  and the WLAN radio  225 . Furthermore, after the activation operation of the WLAN radio  225 , the LP radio  230  may be configured to transmit a station indication signal that indicates to the AP  110  the current power state of the WLAN radio  225 . That is, the low power signaling may also be used for subsequent signal transmissions that the AP  110  would normally require for the data transmission to be performed. Accordingly, the WLAN radio  225  may not be required to perform this functionality. 
     As discussed above, the LP radio  230  may use a significantly smaller amount of power when activated as compared to the WLAN radio  225 . For example, the LP radio  230  may use 400 μW of power when activated. In comparison to the milli-Watts of power used by the WLAN  225 , one skilled in the art will appreciate the amount of power conservation that may be realized. As such, it should be noted that the LP radio  230  may be manufactured with components that are different or less complex than the components used to manufacture the WLAN radio  225  but still configured to perform the functionalities described herein. 
     It should be noted that the LP radio  230  having a lower power consumption by drawing 400 μW of power in comparison to the 180-240 mW of power drawn by the WLAN radio  225  is only exemplary. Specifically, this smaller amount of power used by the LP radio  230  relates to any further radio that requires less power from being activated than the WLAN radio  225 . That is, the overall amount of power used by the LP radio  230  to listen for a beacon is less than the overall amount of power used by the WLAN radio  225  to listen for the beacon. 
     According to the exemplary embodiments, the AP  110  may be configured to receive or generate data to be transmitted to one or more of the stations  115 ,  120 ,  125 . Prior to transmitting this data to the selected stations  115 - 125 , the AP  110  may notify the stations  115 - 125  that there is an incoming data transmission. This notification provides information to the selected stations  115 - 125  so that the WLAN radio  225  is to be awake and prepared to receive the data transmissions. As discussed above, the WLAN radio  225  may be activated at select time intervals within a duty cycle to receive a beacon. However, according to the exemplary embodiments, the stations  115 - 125  may utilize the duty cycle to determine when the LP radio  230  is activated. Specifically, the LP radio  230  is activated for the duration of the duty cycle. It is noted that the low power consumption of the LP radio  230  still results in an overall decreased power usage than the standard waking/sleeping of the WLAN radio  225 . 
     While the LP radio  230  is activated, it may listen for an incoming wake up signal that is generated and transmitted by the AP  110 . That is, part of the notification performed by the AP  110  includes an initial wake up signal that is received by the LP radio  230 . In a first example, the AP  110  may generate the wake up signal for each of the stations  115 - 125  that is scheduled for a subsequent beacon and data transmission. For example, if all the stations  115 - 125  are to receive a subsequent beacon and data transmission, the AP  110  may generate a respective wake up signal for each of the stations  115 - 125 . In another example, if the stations  115 ,  120  are to receive a subsequent beacon and data transmission, the AP  110  may generate a respective wake up signal for only these stations while no wake up signal is generated for the station  125 . In a second example, the AP  110  may also generate the wake up signal in a broadcast manner for all the stations  115 - 125  to check the subsequent beacon (e.g., instead of individual wakeup signals being generated). In a third example, the AP  110  may group the stations and send a wakeup signal in a group manner where one wakeup signal may be transmitted to all the stations in the group. 
     When the LP radio  230  of the select stations receive the wake up signal, the LP radio  230  may forward an activation signal to the WLAN radio  225  (e.g., as described above, the activation signal may be directly forwarded to the WLAN radio  225  or the LP radio may forward the wake up signal to the processor  205  that generates the activation signal to send the WLAN radio  225 ). The activation signal may indicate that the WLAN radio  225  is to wake from its sleeping state such as turning the PHY ON and possibly activating the crystals. As discussed above, the activation of the crystals in the WLAN radio  225  may affect the timing of the signal transmissions with the AP  110 . Accordingly, the exemplary embodiments provide two mechanisms to use the wake up signal received by the LP radio  230 . 
     In a first exemplary embodiment, the stations  115 - 125  may be configured to activate the crystal of the WLAN radio  225  for the duration of the duty cycle. That is, the LP radio  230  and the crystal of the WLAN radio  225  may both be activated during the duration of the duty cycle. However, the PHY of the WLAN radio  225  may remain asleep. More specifically, the PHY of the WLAN radio  225  may be on standby (i.e., an intermediary setting between sleep and wake). By activating the crystal of the WLAN radio  225  for the duty cycle prior to a subsequent beacon transmission and placing the PHY on standby, a relatively fast wake up procedure may be provided. Specifically, only the PRY of the WLAN radio  225  is required to be turned ON since the crystal is already activated. As discussed above, the process to place the PHY from standby to ON may need less than 50 μs. Thus, the wake up signal from the AP  110  may be transmitted to the stations  115 - 125  about 50 μs before a beacon is transmitted. In this way, a sufficient amount of time is provided for the stations  115 - 125  to be prepared to receive the beacon. Subsequently, a NOW signal may be transmitted from the AP  110  to the stations  115 - 125  immediately prior to the beacon being transmitted. The NOW signal may allow the stations  115 - 125  to save further power until an actual beacon transmission. 
     In a second exemplary embodiment, the stations  115 - 125  may be configured for the multi-stage wake up procedure. Specifically, the WLAN radio  225  may be asleep in which the crystal is deactivated and the PHY is turned OFF. Thus, to wake the WLAN radio  225 , the crystal should be activated (using 3-5 ms) and the PHY should be placed on standby/ON (using 50-550 μs). In view of this extended period of time that is required, the AP  110  may transmit the wake up signal at least 4 ms before the transmission of the beacon to allow sufficient time for the WLAN radio  225  to be fully awake. After the wake up signal is transmitted, the AP  110  may wait this predetermined time period and subsequently transmit the NOW signal immediately prior to the beacon being transmitted. It should be noted the use of 4 ms is only exemplary and different wait times may be used. However, it should also be noted that a delay greater than 4 ms may not be desired due to potential additional power loss. 
     Those skilled in the art will understand that the wake up signals may cause further stations that are not scheduled to receive a data transmission to also wake. There may be a variety of reasons for such a scenario to arise. Thus, the exemplary embodiments provide a mechanism for the wake up signal to be received only by the intended station. Specifically, the wake up signals are prevented from colliding with other network traffic. In a first example, the specifications defined under 802.11 may be used. Specifically, the 802.11 protection frame may be used prior to sending the wake up signal. In a second example, the wake up signals may be generated in such a way that it is impervious to 802.11 traffic such as using a dedicated channel only for the transmission of wake up signals. 
     It should be noted that other traffic may be on the air before the beacon is transmitted. In view of this possibility of different transmissions occupying the medium being used for the wake up procedure and beacon transmission, the exemplary embodiments provide the timing feature described above. For the first example, just enough time is set between the transmission of the wake up signal and the transmission of the beacon for the WLAN radio  225  to wake. The NOW signal may immediately be transmitted after transmitting the wake up signal with no gap therebetween. The NOW signal may initially provide the feature of indicating that the beacon is being transmitted immediately after the NOW signal. The NOW signal may also provide a placeholder for the medium such that the medium is still available for the beacon to be transmitted. For the second example, just enough time is set between the transmission of the wake up signal and the transmission of the beacon for the WLAN radio  225  to wake. However, there may be a gap between the transmission of the wake up signal and the transmission of the NOW signal. The NOW signal may therefore be used as described above to hold the medium for the transmission of the beacon immediately following the NOW signal. The NOW signal may also be used to activate a medium access control (MAC) of the station to prepare to receive the beacon. 
     When viewing the transmission of data from the perspective of the AP  110 , the AP  110  may initially transmit a network packet. For example, the network packet may include a request for a medium for the subsequent data transmissions. After the network packet is sent, the Network Allocation Vector (NAV) protection scheme may be used. As discussed above, this may entail using the wake up signal that does not collide with other network traffic. This wake up signal may be transmitted to the select stations  115 - 125  that will also receive a beacon and subsequent data transmission. The optional filler packet such as the NOW signal may be transmitted immediately prior to the beacon being transmitted. Those skilled in the art will understand the use of an acknowledgement (ACK) signal when a signal has been transmitted. However, the exemplary embodiments may not utilize the ACK when the wake up signal is transmitted. For example, the impervious nature of the wake up signal may negate the need for the ACK. 
     The wake up signal may be formatted in a variety of manners. However, the wake up signal is designed to be transmitted by the AP  110  and to be received by the LP radio  230  of the selected stations. In an exemplary embodiment, the wake up signal has a predetermined number of bits that are relatively small. For example, only mandatory parameters may be included in the wake up signal. The parameters may include those related to addressing. Since a false positive may cause a redundant wake up, the wake up signal is not required to identify the transmitter and receiver of the radio fully. Thus, a reduced source address may be used (e.g., last 6 bits of MAC address) and a reduced destination address may be used (e.g., last 6 bits of unicast or multicast or partial TIM bitmap). Optional parameters may also be included such as a frame type (e.g., type and sub-type restricted to 6 bits) and an awake/sleep indicator (using 1 bit). 
     In a specific exemplary format and as illustrated in  FIG. 6A , the wake up signal  600  may include three fields. A first field may be a short source address. Examples of a short source address may be the partial source MAC address or a hash of source MAC address. A second field may be a beacon update. For example, whenever the AP  110  updates any beacon parameter, this field may be increased by one. The station may quickly determine whether a check is to be performed for a following beacon for the updated parameter. In a third field may be a downlink data indication. The downlink data indication may be an indication of which station or stations have pending downlink data (i.e., subsequent data transmission after beacon). This may be a station AID bitmap (similar to TIM in the 802.11 specifications) or an address list. As shown in the  FIG. 6A , the fields of the wake up signal may also have a specified order so the stations will understand the data that is being received in the wake up signal. However, it is not a requirement that the order be the same as shown in  FIG. 6A . 
     As discussed above, after the WLAN radio  225  has been awoken based on the wake up signal received by the LP radio  230  and the WLAN radio  225  has received the beacon, the LP radio  230  may again be used to indicate the status of the WLAN radio  225  to the AP  110 . That is, select ones of the stations  115 - 125  with the WLAN radio  225  awake may wish to indicate to the AP  110  the wake up status of the WLAN radio  225  and/or solicit a packet, namely the pending data transmission which prompted the wake up procedure. Therefore, the low power signaling may be used in a reverse direction. 
     When conventional response signals are transmitted, the WLAN radio  225  is used and must contend with other stations to send the PS-Poll frame or NULL or QoS NULL to the AP  110 , This may waste a substantial amount of medium time for only a few bits of information (e.g., backoff, 802.11 frame, etc.). The exemplary embodiments provide a mechanism that utilizes the LP radio  230  to transmit the response. 
     Specifically, the station uses a station indication signal, which is substantially similar to the wake up signal. The station indication signal informs the AP  110  about the current status of the WLAN  125  (e.g., power mode) and whether it has packets to transmit/receive. The station indication signal may be sent as a response to an optional poll transmitted by the AP  110  immediately after the beacon is transmitted. However, even with no poll, the LP radio  230  may be used to transmit the station indication signal. It should be noted that the poll may be transmitted as a separate signal, may be implicit, or may be included with the beacon. In this manner, the low power signaling may again be used to transmit the station indication signal from the stations  115 - 125  to the AP  110 . The station indication signal will not collide with other network traffic. It should be noted that it may be assumed that multiple indication frames may be sent concurrently such as by utilizing different tones. 
     The station indication signal may also be formatted in a variety of manners substantially similar to the wake up signal. In a specific exemplary format and as illustrated in  FIG. 6B , the station indication signal  650  may include three fields. A first field may be a short source address. This field may be substantially similar to the short source address of the wake up signal but may also be a partial AID or similar (non-strictly) unique identifier. A second field may be a short destination address. For example, the short destination address may be a partial destination MAC address, a hash of destination MAC address, or similar (non-strictly) unique identifier. A third field may be a power mode. The power mode may be an indication of the state of the WLAN radio  225 . For example, a power mode (PM) of 0 may indicate that the WLAN radio  225  is awake; a PM of 1 may indicate that the WLAN radio  225  is asleep; a PM of 3 may indicate that the WLAN radio  225  is asleep but may be woken up with a wake up signal trigger; etc. 
       FIG. 3  shows a first exemplary signaling diagram  300  utilizing the wake up signal. Specifically, the signaling diagram  300  relates to the first exemplary embodiment described above in which the crystal is activated for the duration of the duty cycle. The signaling diagram  300  will describe an exchange of signals between the AP  110  and the station  115 . However, it should be clear that the same type of signaling may occur between the AP and the other stations  120  and  125 . An initial step may be to determine a beginning of the duty cycle. When the duty cycle starts, the crystal of the WLAN radio  225  may be activated  305 . The LP radio  230  may also be activated at the beginning of the duty cycle. 
     The AP  110  may determine that the station  115  is to receive a beacon and a subsequent data transmission. Thus, the AP  110  generates a wake up signal  310  for the station  115 . The wake up signal  310  is transmitted from the AP  110  to the LP radio  130  of the station  115 . It should be noted that the wake up signal transmitted to the LP radio  230  may be transmitted in the same band as the signals that will be transmitted to the WLAN radio  225  or may also be transmitted on any other band that is available for transmission. That is, the band on which the wake up signal is transmitted is not important to the exemplary embodiments, merely that the wake up signal is transmitted and received. The LP radio  230  forwards an activation signal  315  to the WLAN radio  225  such that the PHY of the WLAN radio  225  is turned ON  320 . As described above, the activation signal  315  may be sent directly from the LP radio  230  to the WLAN radio  225  or via the processor  225 . The AP  110  may also activate a timer  325  upon transmitting the wake up signal  310 . In the first exemplary embodiment, this timer  325  may be set to 50 μs. The duration of the timer is set based upon a time required for the WLAN radio  125  to be fully awake. 
     The expiration of the timer  325  indicates when the beacon is to be transmitted by the AP  110 . Immediately before the timer  325  expires, the AP  110  may transmit the NOW signal  330  to the WLAN radio  225  which is now awake. The receipt of the NOW signal  330  may also cause the station  115  to activate the MAC  340  to prepare to receive the beacon. The NOW signal  330  may occupy the medium used for the beacon transmission. Thus, when the timer  325  expires, the beacon  335  is transmitted over the known medium without other network traffic commandeering this medium. 
     After the beacon  335  is transmitted, the AP  110  may optionally transmit a poll  345  for a response. The WLAN radio  225  may determine its status  350  and provide this information via a status signal  355  to the LP radio  230 . The LP radio  230  may transmit the station indication signal  360  (e.g., PS-Poll frame) back to the AP  110 . As described above, the status indication signal  360  may provide information concerning the station  115  to the AP  110 , e.g., the activation state of the WLAN radio  225 . 
       FIG. 4  shows a second exemplary signaling diagram  400  utilizing the wake up signal. Specifically, the signaling diagram  400  relates to the second exemplary embodiment described above in which the multi-stage wake up procedure is used and the crystal is activated after receiving the wake up signal. The signaling diagram  400  will also be used to describe signals that are exchanged between the AP  110  and the station  115 . Again, an initial step may be to determine a beginning of the duty cycle. When the duty cycle starts, the LP radio  230  may be activated. 
     Again, the AP  110  may determine that the station  115  is to receive a beacon and a subsequent data transmission. Thus, the AP  110  generates a wake up signal  405  for the station  115 . The wake up signal  405  is transmitted from the AP  110  to the LP radio  230  of the station  115 . The LP radio  230  forwards a activation signal  410  to the WLAN radio  225  such that the crystal is activated  415  and the PHY of the WLAN radio  125  is turned ON  420 . Upon transmitting the wake up signal  405 , the AP  110  may activate a timer  425 . In the second exemplary embodiment, this timer  425  may be set to 4 ms. Again, the duration of the timer  425  is set based upon a time required for the WLAN radio  125  to be fully awake. Since, in this embodiment, the activation signal  410  signals that the crystal should be turned on, the time  425  is set to a longer duration than the time  325  of the previous embodiment where the crystal was turned on at the beginning of the duty cycle. 
     Subsequent steps including the transmission of the NOW signal  430  to the WLAN radio  225 , the activation  440  of the MAC of the station  115 , the transmission of the beacon  435  to the WLAN radio  225 , the optional transmission of the poll  445 , the status determination  450 , the status signal  455  and the station indication signal  460  may be substantially similar to the first exemplary embodiment described above with regard to the signaling diagram  300 . 
       FIG. 5  shows an exemplary block diagram  500  of an exemplary station receiving the wake up signal and subsequent operations. Specifically, the block diagram  500  illustrates components of the LP radio  230  and the WLAN radio  225  used in the wake up procedure including the use of the wake up signal. As illustrated, the top half of the block diagram  500  may represent the LP radio  230  while the bottom half of the block diagram  500  may represent the WLAN radio  225 . Since both the WLAN radio  225  and the LP radio  230  are part of a common station, the MAC address disposed between the WLAN radio  225  and the LP radio  230  may represent a high level layer. 
     Initially, as discussed above, the LP radio  230  may receive a wake up signal using its antenna. The wake up signal may be processed using a variety of components whose functionality is known to those skilled in the art. For example, the LP radio  130  may include an amplifier module, a mixer, a filter, an analog/digital module, an AGC module, an offset estimation module, a channel estimation module, an equalizer, a decoder, and an identifier. The identifier may generate the activation signal. The activation signal include power on signals that are forwarded to sub-components of the WLAN radio  125  such as the analog RF portion, the digital front end portion, and the digital block portion. 
     With the power on signals being received, each portion may be activated. Specifically, the crystals may be activated and the PHY may be turned on. The WLAN radio  125  may also include a variety of components whose functionality is known to those skilled in the art. For example, the WLAN radio  125  may include a RF module, a filter, an analog/digital module, a AGC module, a CRS module, an offset estimation module, a channel estimation module, a FFT module, a demodulator, a decoder, and a MAC module. Thus, when the beacon is received by the WLAN radio  125  using its antenna, the beacon may be processed. 
     The exemplary embodiments provide a system and method for a low power signaling that conserves power. The stations may include a first radio (i.e., WLAN radio) used for receiving a beacon and a subsequent data transmission indicated in the beacon. The stations may further include a second radio (i.e., LP radio) used for receiving a wake up signal that wakes the WLAN radio from a sleep state. Using the LP radio that does not use a high power, the station may conserve a limited power supply by keeping the high power using WLAN radio asleep for longer periods of time and only activating the WLAN radio for pending packets to be received. 
     It should be noted that the wake up PHY design may relate to minimizing a receiving power and using a transmission power no larger than other 802.11 PHY parameters. That is, the receiving bandwidth, the noise figure, the dynamic range, and LO phase noise requirements are reduced. Since the wake up signal does not include a data payload, the LP radio may be configured with low power consuming components. The wake up signal may have a sensitivity matching a lowest data rate (e.g., 6 Mbps). Furthermore, false alarms are minimized from AWGN and 802.11 traffic. It should also be noted that parameters of 2 or 4-FSK may be with a simple block code. Furthermore, the frequency of operation for the wake up signal may be on an existing channel or a new narrow bandwidth channel (e.g., between channel 6 and 11). In addition, simultaneous wake up signal transmissions may be performed using different tones for each wake up signal with some repetition and/or use a spread spectrum. 
     Those skilled in the art will understand that the above-described exemplary embodiments may be implemented in any suitable software or hardware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Mac platform, MAC OS, iOS, Android OS, etc. In a further example, the exemplary embodiments of the above described method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor. 
     It will be apparent to those skilled in the art that various modifications may be made in the present invention, without departing from the spirit or the scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalent.

Metadata:
Filing Date: 20180620
Publication Date: 20200609
Grant Date: 20200609
Priority Date: 20140117
Inventors: RAMAMURTHY, HARISH
KIM, JOONSUK
LIU, YONG
HANSEN, CHRISTOPHER
Assignee: APPLE INC
CPC Classifications: [{"code": "Y02D70/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0212", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W88/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/028", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0235", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02D70/22", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0229", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02D70/142", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0235", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0229", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0212", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W52/0229", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W88/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/028", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0212", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W88/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0235", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/028", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 53546015