PATENT DOCUMENT

Publication Number: US-11290955-B2
Application Number: US-201916586297-A
Country: US
Kind Code: B2

Title: Low latency wireless protocol

Abstract:
This application relates to electronic devices configured to connect to a wireless local area network and communicate using a trigger-based access mechanism. An access point is configured to define a contention-free period associated with a communications medium utilized by the wireless local area network. During the contention-free period, the access point allocates transmission opportunities to each of a number of electronic devices by transmitting trigger frames to the electronic devices via the communications medium. Each trigger frame can be directed to a particular electronic device and indicates to that electronic device that the current transmission opportunity has been allocated to that electronic device to transmit data (e.g., frames) to the access point via the communications medium. The access point implements an algorithm for allocating two or more transmission opportunities within a contention-free period to two or more corresponding electronic devices.

Claims:
What is claimed is: 
     
       1. An access point, comprising:
 one or more nodes configured to communicatively couple to an antenna; 
 an interface circuit, communicatively coupled to the one or more nodes, configured to communicate with a set of electronic devices in a wireless local area network (WLAN), and configured to cause the access point to:
 transmit, via a communications medium associated with the WLAN, a trigger frame to the set of electronic devices, the trigger frame including information specifying an ordered list of electronic devices in the set of electronic devices that are allowed to transmit data within the WLAN via the communications medium, each electronic device triggered to transmit respective data sequentially and non-overlapping in time with data from other electronic devices based on the ordered list of electronic devices, and 
 receive a sequence of frames from at least two electronic devices in the ordered list of electronic devices via the communications medium during a contention-free period, each frame including a quality of service (QoS) control field indicating a QoS type and a priority value for data included in the frame; and 
 
 a processing subsystem, communicatively coupled to the interface circuit, and configured to cause the access point to:
 define the contention-free period associated with the communications medium; and 
 allocate at least two transmission opportunities within the contention-free period to the at least two electronic devices in the ordered list of electronic devices, wherein allocation of transmission opportunities to each of the at least two electronic devices is based at least in part on QoS types and priority values received from the at least two electronic devices in one or more previous contention-free periods. 
 
 
     
     
       2. The access point of  claim 1 , wherein a start of each transmission opportunity in the at least two transmission opportunities within the contention-free period is adjusted dynamically by the processing subsystem based on traffic transmitted via the communications medium. 
     
     
       3. The access point of  claim 2 , wherein a transmission opportunity is terminated in accordance with transmission of an acknowledgment frame that indicates the access point received at least one frame from a corresponding electronic device. 
     
     
       4. The access point of  claim 2 , wherein:
 each transmission opportunity is associated with a maximum duration, and 
 a duration of a particular transmission opportunity can be less than or equal to the maximum duration. 
 
     
     
       5. The access point of  claim 1 , wherein each electronic device is configured to enter a low power mode at an end of a corresponding transmission opportunity allocated to the electronic device and wake up to listen to the communications medium prior to a start of a next contention-free period. 
     
     
       6. The access point of  claim 5 , wherein a time associated with the start of the next contention-free period is indicated within the trigger frame. 
     
     
       7. The access point of  claim 1 , wherein a start of each transmission opportunity in the at least two transmission opportunities within the contention-free period is fixed by the processing subsystem according to a schedule based at least in part on the QoS types and priority values previously received from the at least two electronic devices. 
     
     
       8. The access point of  claim 7 , wherein a duration of each transmission opportunity within the contention-free period is equal to a duration of the contention-free period divided by a number of electronic devices in the ordered list of electronic devices. 
     
     
       9. The access point of  claim 7 , wherein each electronic device is configured to enter a low power mode at an end of a corresponding transmission opportunity allocated to the electronic device and wake up to listen to the communications medium prior to a start of a corresponding transmission opportunity allocated to the electronic device during a next contention-free period that is subsequent to a start of the next contention-free period. 
     
     
       10. The access point of  claim 1 , wherein the processing subsystem is configured to cause the interface circuit to re-transmit the trigger frame to a corresponding electronic device appearing first in the ordered list of electronic devices when the access point fails to receive a frame of data from the corresponding electronic device within a threshold time of an end of transmission of the trigger frame. 
     
     
       11. An electronic device, comprising:
 one or more nodes configured to communicatively couple to an antenna; and 
 an interface circuit, communicatively coupled to the one or more nodes, configured to communicate with an access point in a wireless local area network (WLAN), and configured to cause the electronic device to:
 receive, from the access point, a trigger frame that includes information specifying an ordered list of electronic devices in a set of electronic devices that are allowed to transmit data via a first communications medium during a contention-free period, each electronic device in the set of electronic devices triggered to transmit respective data sequentially and non-overlapping in time with data from other electronic devices based on the ordered list of electronic devices, and 
 transmit a frame at a temporal position in a sequence of frames based on the ordered list of electronic devices during the contention-free period, the frame including a quality of service (QoS) control field indicating a QoS type and a priority value for data included in the frame; and 
 
 a processing subsystem, communicatively coupled to the interface circuit, and configured to cause the electronic device to:
 read an identifier positioned first in the ordered list of electronic devices from the trigger frame, 
 determine that the identifier is associated with the electronic device, 
 transmit the frame at the temporal position subsequent to an end of the trigger frame and associated with the first communications medium being idle for a period of time, 
 identify a time associated with a subsequent contention-free period, and 
 enter a low power mode subsequent to transmission of the frame, 
 
 wherein the access point allocates transmission opportunities to the electronic devices in the set of electronic devices based at least in part on QoS types and priority values received from the set of electronic devices in one or more previous contention-free periods. 
 
     
     
       12. The electronic device of  claim 11 , wherein the interface circuit is configured to cause the electronic device to:
 transmit an advertising packet to the access point via a second communications medium associated with a wireless personal area network (WPAN); 
 receive, via the second communications medium, a packet of information associated with the WLAN, wherein the information includes a basic service set identifier (BSSID) for the WLAN, and 
 receive, via the first communications medium associated with the WLAN, the trigger frame. 
 
     
     
       13. The electronic device of  claim 12 , wherein:
 the first communications medium comprises one or more channels within a 5 GHz radio frequency (RF) spectrum, and 
 the second communications medium comprises one or more channels within a 2.4 GHz RF spectrum. 
 
     
     
       14. The electronic device of  claim 11 , wherein the period of time is approximately 16 microseconds. 
     
     
       15. The electronic device of  claim 11 , wherein a wake-up timer is set based on a time that corresponds to a start of the subsequent contention-free period. 
     
     
       16. The electronic device of  claim 11 , wherein a wake-up timer is set based on a time that corresponds to a start of a corresponding transmission opportunity allocated to the electronic device during the subsequent contention-free period as indicated by a timestamp included in the trigger frame. 
     
     
       17. A method for transmitting a frame from an electronic device configured to communicate with an access point in a wireless local area network (WLAN), the method comprising:
 by the electronic device:
 reading an identifier positioned first in an ordered list of electronic devices included in a trigger frame received, via an interface circuit of the electronic device, from the access point during a contention-free period, 
 determining that the identifier is associated with the electronic device, 
 transmitting, during the contention-free period subsequent to an end of the trigger frame and after a period of time during which a first communications medium associated with the WLAN is idle, a frame to the access point in response to receiving the trigger frame, the frame including a quality of service (QoS) control field indicating a QoS type and a priority value for data included in the frame, 
 receiving an acknowledgment frame from the access point, 
 identifying a time associated with a subsequent contention-free period as specified within the trigger frame, and 
 entering a low power mode subsequent to transmission of the frame, 
 wherein:
 each electronic device in the ordered list of electronic devices triggered to transmit respective data sequentially and non-overlapping in time with data from other electronic devices based on the ordered list of electronic devices, and 
 the access point allocates transmission opportunities to the electronic devices in the ordered list of electronic devices based at least in part on QoS types and priority values received from the set of electronic devices in one or more previous contention-free periods. 
 
 
 
     
     
       18. The method of  claim 17 , the method further comprising:
 by the electronic device:
 transmitting an advertising packet to the access point via a second communications medium associated with a wireless personal area network (WPAN); 
 receiving, via the first communications medium, a packet of information associated with the WLAN, wherein the information includes a basic service set identifier (BSSID) for the WLAN, and 
 receiving, via the first communications medium associated with the WLAN, the trigger frame. 
 
 
     
     
       19. The method of  claim 18 , wherein the WPAN is associated with a Bluetooth Low Energy communications protocol. 
     
     
       20. The method of  claim 17 , wherein a wake-up timer is set based on a time that corresponds with a start time of a transmission opportunity allocated to the electronic device during the subsequent contention-free period, the start time of the transmission opportunity indicated by a timestamp included in a field of the trigger frame.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/738,668, entitled “LOW LATENCY WIRELESS PROTOCOL,” filed Sep. 28, 2018, the content of which is incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD 
     The described embodiments relate, generally, to wireless communications among stations in a wireless local area network (WLAN), including wireless (electronic) devices and access points, and techniques for providing low latency wireless communications in a real-time environment. 
     BACKGROUND 
     Many wireless local area networks (WLANs), such as those based on a communication protocol that is compatible with a set of Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, also referred to as ‘Wi-Fi’, involve contention-based, distributed access systems. Typically, the WLANs are contention-based because they utilize unlicensed radio frequency (RF) bands or spectra, which are unpredictable and are often subject to interference. The unpredictability of the interference can make coordination across multiple electronic devices, also referred to as stations (STAs), challenging (especially for an unmanaged WLAN), and can result in failure of a contention-free period (CFP). 
     Legacy Wi-Fi can rely on contention-based, multi-user transmission in the uplink referred to as Carrier Sense Multiple Access, Collision Avoidance (CSMA/CA). Each station (STA) listens to one or more communication channels to determine whether the communications medium is busy. If the communications medium is idle, then a STA can attempt to transmit data to another STA during a time period that is divided into a number of backoff slots. Each STA selects a random backoff slot within a contention window, e.g., using a backoff timer, and can transmit during the selected backoff slot if the communications medium remains idle until expiration of the backoff timer. If another STA transmits on the communications medium before the backoff timer has expired, then the STA resets the backoff timer and waits until the next frame to re-attempt transmission over the communications medium. However, if the backoff timer expires before another STA attempts to transmit over the communications medium, the STA will attempt transmission over the communications medium. However, attempting the transmission does not ensure that another STA has not randomly selected the same backoff slot to attempt to transmit over the communications medium, thereby causing a collision to occur when both STAs attempt to transmit during the same backoff slot. Failure of the STA to receive an acknowledgment frame could indicate that a collision occurred, and the STA can attempt to retry transmission after doubling the size of the contention window to decrease the probability of another collision during the next transmission opportunity. 
     The contention-based access mechanism for legacy Wi-Fi, described above, leads to unbounded latency for transmission of data packets, where the expected latency is correlated with the number of STAs transmitting over the communications medium. Large number of STAs attempting to transmit on the same communication channel can result in a high probability of collisions, which can quickly lead to latencies in the hundreds of milliseconds (ms). While these latencies are tolerable for some applications, such as requesting a web page on a wireless device, latencies of hundreds of milliseconds are intolerable for real-time applications such as audio streaming, virtual reality, and gaming. 
     Contention-free, multi-user transmission in an uplink direction from a STA to an access point (AP) has been proposed for inclusion in the IEEE 802.11ax standard. This approach can dramatically change how a wireless device accesses the communications medium. In particular, a wireless device can transmit without contending for the communications medium. Instead, a primary STA (e.g., the AP) controls access to the communications medium for the STAs connected to the WLAN by granting transmission opportunities to each individual STA using a trigger frame (which may be referred to as ‘trigger-based access’ or ‘trigger-based channel access,’ for uplink multi-user transmission). In principle, the use of trigger-based access and multi-user transmission can significantly reduce contention for access to the communications medium by the wireless devices in the WLAN. Consequently, trigger-based access is expected to result in improved communication performance. However, this contention-free access mechanism does little to alleviate contention issues with multiple WLANs attempting to communicate over the same communications medium (e.g., where multiple access points in close proximity implement different WLANs on the same channels of the communications medium). 
     Furthermore, trigger-based access and multi-user transmission can significantly increase energy consumption of the wireless devices in the WLAN. In particular, for N wireless devices sharing a communication channel, the average data bandwidth can be reduced by a factor of N and, therefore, the energy required to transmit the data can be increased by a factor of N. Moreover, the access overhead in the WLAN typically increases with trigger-based access and multi-user transmission. Furthermore, this approach for allocating shared resources can be inefficient (including wasted or unused resource units and, more generally, suboptimal channel utilization) and inflexible (because the wireless devices can be required to transmit over the same duration time period using identical data rates). In addition, trigger-based access and multi-user transmission is not backwards compatible with existing or legacy wireless devices. 
     SUMMARY 
     Some embodiments regard an access point that controls access to a communications medium for a set of electronic devices connected to a WLAN. In particular, during operation, an interface circuit in the access point transmits a trigger frame that includes information specifying an ordered list of electronic devices that are allowed to transmit data via a communications medium during a contention-free period. Subsequently, the interface circuit of the access point sequentially receives one or more frames from the ordered list of electronic devices via the communications medium. A processing subsystem in the access point causes the access point to allocate at least two transmission opportunities within the contention-free period to at least two electronic devices in the ordered list of electronic devices. 
     In some embodiments, each transmission opportunity within the contention-free period is adjusted dynamically, as determined and controlled by an unscheduled access mechanism implemented within the processing subsystem of the access point. According to operation of the unscheduled access mechanism, a start of each transmission opportunity in the at least two transmission opportunities within the contention-free period is adjusted dynamically by the processing subsystem based on traffic transmitted via the communications medium. A transmission opportunity can be terminated by the access point in accordance with the transmission of an acknowledgment frame that indicates the access point received at least one frame from a corresponding electronic device. In some embodiments, the processing subsystem of the access point can limit a duration of each transmission opportunity to a maximum duration, where a duration of a particular transmission opportunity can be less than or equal to the maximum duration. In particular, where a first electronic device has responded to a trigger frame during a first transmission opportunity and the access point has transmitted an acknowledgment frame to the first electronic device, the access point can indicate a start to a second transmission opportunity allocated to a second electronic device by transmitting a second trigger frame prior to a duration of the first transmission opportunity reaching the maximum duration. 
     In some embodiments, when the access point is configured to utilize the unscheduled access mechanism, each electronic device is configured to enter a low power mode at an end of a corresponding transmission opportunity allocated to the electronic device and wake up to listen to the communications medium prior to a start of a next contention-free period. A time associated with the start of the next contention-free period is indicated within the trigger frame. 
     In some embodiments, each transmission opportunity within the contention-free period is fixed, as determined and controlled by a scheduled access mechanism implemented within the processing subsystem of the access point. According to operation of the scheduled access mechanism, a start of each transmission opportunity in the at least two transmission opportunities within the contention-free period is fixed by the processing subsystem according to a schedule. In some embodiments, the processing subsystem in the access point can implement a scheduling algorithm that defines a duration of each transmission opportunity within the contention-free period as equal to a duration of the contention-free period divided by a number of electronic devices in the ordered list of electronic devices. The duration of the contention-free period can be pre-defined, such as 2 milliseconds, and the access point can periodically define new contention-free periods after a particular time interval elapses, such as every 5 milliseconds. 
     In some embodiments, when the access point is configured to utilize a scheduled access mechanism, each electronic device is configured to enter a low power mode at an end of a corresponding transmission opportunity allocated to the electronic device and wake up to listen to the communications medium prior to a start of a corresponding transmission opportunity allocated to the electronic device during a next contention-free period. A time associated with the start of a transmission opportunity allocated to the electronic device during the next contention-free period can be indicated within the trigger frame received during a current contention-free period. 
     In some embodiments, the processing subsystem of the access point is configured to cause the interface circuit of the access point to re-transmit the trigger frame to a corresponding electronic device appearing first in the ordered list of electronic devices when the access point fails to receive a frame of data from the corresponding electronic device within a threshold time of an end of transmission of the trigger frame. In some embodiments, a determination of whether to re-transmit the trigger frame can be based on a comparison of a remaining duration of the current transmission opportunity with a minimum threshold time. 
     In some embodiments, an electronic device includes: one or more nodes configured to communicatively coupled to an antenna, an interface circuit communicatively coupled to the one or more nodes, and a processing subsystem communicatively coupled to the interface circuit. The interface circuit is configured to cause the electronic device to receive, from the access point, a trigger frame that includes information specifying an ordered list of electronic devices in a set of electronic devices that are allowed to transmit data via a first communications medium during a contention-free period and transmit a frame at a temporal position in a sequence of frames from the ordered list of electronic devices. The processing subsystem is configured to cause the electronic device to: read an identifier positioned first in the ordered list of electronic devices from the trigger frame; determine that the identifier is associated with the electronic device; transmit the frame at the temporal position subsequent to the end of the trigger frame and associated with the communications medium being idle for a period of time; identify a time associated with a subsequent contention-free period; and enter a low power mode subsequent to transmission of the frame. 
     In some embodiments, the interface circuit is further configured to cause the electronic device to: transmit an advertising packet to the access point via a second communications medium associated with a wireless personal area network (WPAN); receive, via the second communications medium, a packet of information associated with the WLAN; and receive the trigger frame via the first communications medium associated with the WLAN. In some embodiments, the information includes a basic service set identifier (BSSID) for the WLAN and/or information regarding one or more channels associated with the first communications medium and utilized by the WLAN. 
     In some embodiments, the first communications medium comprises one or more channels within a 5 GHz RF spectrum, and the second communications medium comprises one or more channels within a 2.4 GHz radio-frequency spectrum. 
     In some embodiments, the period of time that the communications medium is idle is referred to as a Short Interframe Space (SIFS) having a duration of at least 16 microseconds. 
     In some embodiments, a wake-up timer of the electronic device is set based on a time that corresponds to a start of the subsequent contention-free period. In other embodiments, the wake-up timer of the electronic device is set based on a time that corresponds to a start of a corresponding transmission opportunity allocated to the electronic device during the subsequent contention-free period as indicated by a timestamp included in the trigger frame. 
     In some embodiments, a method is described for transmitting a frame from an electronic device configured to communicate with an access point in a WLAN. The method includes, via a processing subsystem of the electronic device, reading an identifier positioned first in an ordered list of electronic devices included in a trigger frame received, via an interface circuit of the electronic device, from the access point during a contention-free period. The method also includes, via the processing subsystem of the electronic device, determining that the identifier is associated with the electronic device, and transmitting, subsequent to the end of the trigger frame and after a period of time during which a first communications medium associated with the WLAN is idle, a frame to the access point in response to receiving the trigger frame. The method also includes, via the processing subsystem of the electronic device, receiving an acknowledgment frame from the access point, and identifying a time associated with a subsequent contention-free period as specified within the trigger frame. The method further includes, via the processing subsystem of the electronic device, entering a low power mode subsequent to transmission of the frame. In some embodiments, a wake-up timer is set based on a time that corresponds with a start time of a transmission opportunity allocated to the electronic device during a subsequent contention-free period, the start time of the transmission opportunity indicated by a timestamp included in a field of the trigger frame. 
     In some embodiments, the method further includes transmitting, via the interface circuit, an advertising packet to the access point via a second communications medium associated with a WPAN. The method further includes receiving, via the second communications medium, a packet of information associated with the WLAN, wherein the information includes a basic service set identifier for the WLAN. The method also includes receiving the trigger frame via the first communications medium associated with the WLAN. In some embodiments, the WPAN is associated with a Bluetooth Low Energy communications protocol. 
     Other aspects and advantages of the embodiments described above will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the described embodiments. 
     This Summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the subject matter described herein. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The included drawings are for illustrative purposes and serve only to provide examples of possible structures and arrangements for the disclosed systems and techniques for intelligently and efficiently managing communication between multiple associated user devices. These drawings in no way limit any changes in form and detail that can be made to the embodiments by one skilled in the art without departing from the spirit and scope of the embodiments. The embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIG. 1  illustrates a block diagram of an exemplary set of electronic devices communicating wirelessly in a wireless local area network (WLAN), in accordance with some embodiments. 
         FIG. 2  illustrates an exemplary protocol for an electronic device to connect to the WLAN of  FIG. 1 , in accordance with some embodiments. 
         FIG. 3  illustrates a trigger frame communicated from the access point to an electronic device  110 , in accordance with some embodiments. 
         FIG. 4  illustrates a data frame communicated between stations of the WLAN, in accordance with some embodiments. 
         FIG. 5  illustrates an acknowledgment frame communicated between stations of the WLAN, in accordance with some embodiments. 
         FIG. 6  illustrates a contention-free end frame communicated from the access point to an electronic device, in accordance with some embodiments. 
         FIG. 7  illustrates an unscheduled access mechanism, in accordance with some embodiments. 
         FIG. 8  illustrates an unscheduled access mechanism with retries, in accordance with some embodiments. 
         FIG. 9  illustrates a sleep cycle for a number of electronic devices utilizing the unscheduled access mechanism to communicate via the WLAN, in accordance with some embodiments. 
         FIG. 10  illustrates a scheduled access mechanism, in accordance with some embodiments. 
         FIG. 11  illustrates a scheduled access mechanism with retries, in accordance with some embodiments. 
         FIG. 12  illustrates a sleep cycle for a number of electronic devices utilizing the scheduled access mechanism to communicate via the WLAN, in accordance with some embodiments. 
         FIG. 13  illustrates access to the communications medium by multiple WLANs, in accordance with some embodiments. 
         FIG. 14  presents a flow diagram illustrating an exemplary method for allocating transmission opportunities within a contention-free period defined by an access point, in accordance with some embodiments. 
         FIG. 15  presents a flow diagram illustrating an exemplary method for reducing a power consumption associated with a wireless station, in accordance with some embodiments. 
         FIG. 16  presents a flow diagram illustrating an exemplary method for connecting to a WLAN, in accordance with some embodiments. 
         FIG. 17  presents a block diagram of an electronic device in accordance with some embodiments. 
     
    
    
     Note that like reference numerals refer to corresponding parts throughout the drawings. Moreover, multiple instances of the same part are designated by a common prefix separated from an instance number by a dash. 
     DETAILED DESCRIPTION 
     In various embodiments, stations (STAs) connected to a WLAN, including electronic devices and/or access points (APs), are configured to communicate via a communications medium using a trigger-based access mechanism. An access point is configured to define a contention-free period associated with the communications medium for transmitting data between stations. During the contention-free period, the access point allocates transmission opportunities to each of a number of electronic devices by transmitting trigger frames to the electronic devices connected to the WLAN via the communications medium. Each trigger frame can be directed at a particular electronic device and indicates to that electronic device that the current transmission opportunity has been allocated to that electronic device to transmit data (e.g., frames) to the access point via the communications medium. A processing subsystem of the access point implements an algorithm, which can be referred to as an access mechanism, for allocating two or more transmission opportunities within a contention-free period to two or more corresponding electronic devices connected to the WLAN. 
     An unscheduled access mechanism is described where the access point dynamically adjusts a duration of each transmission opportunity within the contention-free period based on the traffic on the communications medium. A particular transmission opportunity is allocated to an electronic device by transmitting a trigger frame that identifies that electronic device as a first device in an ordered list of devices. The electronic device can respond to the trigger frame by transmitting one or more data frames to the access point via the communications medium. The access point can then acknowledge receipt of the one or more frames by transmitting an acknowledgment frame to the electronic device, thereby terminating the transmission opportunity allocated to the electronic device. If the electronic device does not respond to a trigger frame, then the access point can determine whether the trigger frame should be re-transmitted to the electronic device. The duration of the transmission opportunity varies according to a number and duration of frames transmitted via the communications medium during the transmission opportunity as well as delays between frames where the communications medium is idle. The access point, via the unscheduled access mechanism, can limit the duration of a particular transmission opportunity to ensure that a minimum number of electronic devices connected to the WLAN are allocated at least one transmission opportunity during the current contention-free period. Furthermore, once all frames associated with a given electronic device have been transmitted via the communications medium, the access point can create a new transmission opportunity by sending a trigger frame targeted to a different electronic device. 
     A low power mode can be implemented by stations that are connected to the WLAN. While utilizing the unscheduled access mechanism, a station can enter the low power mode after completion of a transmission opportunity allocated to the station. Stations can wake up at the start of a next contention-free period to listen to the communications medium for additional trigger frames targeted to that station. 
     A scheduled access mechanism is described where the access point pre-defines a duration of each transmission opportunity within the contention-free period. In some cases, the contention-free period is subdivided to provide at least one transmission opportunity to each of a number of electronic devices connected to the WLAN. Consequently, each electronic device is provided with a fixed schedule of time during a contention-free period during which that electronic device can transmit data via the communications medium. 
     In some embodiments, the stations can utilize a low power mode more efficiently when access to the communications medium is controlled according to the scheduled access mechanism. For example, electronic devices can be configured to wake up at a start of a corresponding transmission opportunity allocated to the electronic device rather than at the start of the contention-free period. This can allow for the electronic device to be in the low power mode during both a first portion of the contention-free period prior to the allocated transmission opportunity and a second portion of the contention-free period subsequent to the allocated transmission opportunity. 
     These and other embodiments are discussed below with reference to  FIGS. 1-17 ; however, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
     Note that the communication techniques described herein can be used during wireless communication between electronic devices in accordance with a communication protocol, such as an IEEE 802.11 standard (also referred to as Wi-Fi). For example, the communication technique can be used with IEEE 802.11ax, which is used as an illustrative example in the discussion that follows. However, this communication technique can also be used with a wide variety of other communication protocols, and in access points and electronic devices (such as portable electronic devices or mobile devices) that can incorporate multiple different radio access technologies (RATs) to provide connections through different wireless networks that offer different services and/or capabilities 
     In particular, an electronic device can include hardware and software to support a wireless personal area network (WPAN) according to a WPAN communication protocol, such as those standardized by the Bluetooth® Special Interest Group (in Kirkland, Wash.) and/or those developed by Apple® (in Cupertino, Calif.) that are referred to as an Apple Wireless Direct Link (AWDL). Moreover, the electronic device can communicate via: a wireless wide area network (WWAN), a wireless metro area network (WMAN), a WLAN, near-field communication (NFC), a cellular-telephone or data network (such as using a third generation (3G) communication protocol, a fourth generation (4G) communication protocol, e.g., Long Term Evolution (LTE), LTE Advanced (LTE-A), a fifth generation (5G) communication protocol, or other present or future developed advanced cellular communication protocol) and/or another communication protocol. In some embodiments, the communication protocol includes a peer-to-peer communication technique. 
     The electronic device, in some embodiments, can also operate as part of a wireless communication system, which can include a set of client devices, which can also be referred to as stations (STAs), client devices, or client electronic devices, interconnected to an access point, e.g., as part of a WLAN, and/or to each other, e.g., as part of a WPAN and/or an ‘ad hoc’ wireless network, such as a Wi-Fi direct connection. In some embodiments, the client device can be any electronic device that is capable of communicating via a WLAN technology, e.g., in accordance with a WLAN communication protocol. Furthermore, in some embodiments, the WLAN technology can include a Wi-Fi (or more generically a WLAN) wireless communication subsystem or radio, and the Wi-Fi radio can implement an IEEE 802.11 technology, such as one or more of: IEEE 802.11a; IEEE 802.11b; IEEE 802.11g; IEEE 802.11-2007; IEEE 802.11n; IEEE 802.11-2012; IEEE 802.11ac; IEEE 802.11ax, or other present or future developed IEEE 802.11 technologies. 
     In some embodiments, the electronic device can act as a communications hub that provides access to a WLAN and/or to a WWAN and, thus, to a wide variety of services that can be supported by various applications executing on the electronic device. Thus, the electronic device can include an ‘access point’ that communicates wirelessly with other electronic devices (such as using Wi-Fi), and that provides access to another network (such as the Internet) via IEEE 802.3 (which is sometimes referred to as ‘Ethernet’). 
     Additionally, it should be understood that the electronic devices described herein can be configured as multi-mode wireless communication devices that are also capable of communicating via different 3G and/or second generation (2G) RATs. In these scenarios, a multi-mode electronic device or user equipment (UE) can be configured to prefer attachment to LTE networks offering faster data rate throughput, as compared to other 3G legacy networks offering lower data rate throughputs. For example, in some implementations, a multi-mode electronic device is configured to fall back to a 3G legacy network, e.g., an Evolved High Speed Packet Access (HSPA+) network or a Code Division Multiple Access (CDMA) 2000 Evolution-Data Only (EV-DO) network, when LTE and LTE-A networks are otherwise unavailable. 
     In accordance with various embodiments described herein, the terms ‘wireless communication device,’ ‘wireless device,’ ‘electronic device,’ ‘mobile device,’ ‘mobile station,’ ‘wireless station,’ ‘wireless access point,’ ‘station,’ ‘access point’ and ‘user equipment’ (UE) can be used herein to describe one or more consumer electronic devices that can be capable of performing procedures associated with various embodiments of the disclosure. 
       FIG. 1  illustrates a block diagram  100  of an example of electronic devices communicating wirelessly, in accordance with some embodiments. In particular, one or more electronic devices  110  (such as a smartphone, a laptop computer, a notebook computer, a tablet, or another such electronic device) and access point  112  communicate wirelessly in a WLAN. Thus, electronic devices  110  are associated with access point  112 . For example, electronic devices  110  and access point  112  can wirelessly communicate while: detecting one another by scanning wireless channels in a communications medium such as a subset of the RF spectrum, transmitting and receiving beacons or beacon frames on wireless channels, establishing connections (for example, by transmitting connect requests), and/or transmitting and receiving packets or frames (which can include the request and/or additional information, such as data, as payloads). Note that access point  112  can provide access to a network, such as the Internet, via an Ethernet protocol, and can be a physical access point or a virtual or ‘software’ access point that is implemented by a host on a computer or an electronic device. In some embodiments, the access point  112  can be omitted and a primary electronic device  110  can function similar to the access point  112 , but without providing access via Ethernet or some other wired or wireless protocol to a separate external network such as the Internet. 
     As described further below with reference to  FIG. 17 , electronic devices  110  and access point  112  can include subsystems, such as a networking subsystem, a memory subsystem, and a processing subsystem. In addition, electronic devices  110  and access point  112  include radios  114  in the networking subsystems. More generally, electronic devices  110  and access point  112  can include (or can be included within) any electronic devices with networking subsystems that enable electronic devices  110  and access point  112  to wirelessly communicate with another electronic device via a communications medium, such as one or more channels of a radio frequency (RF) spectrum. This can include transmitting beacon frames on wireless channels to enable the electronic devices  110  to make initial contact with or to detect each other, followed by exchanging subsequent data/management frames (such as connect requests) to establish a connection, configure security options (e.g., IPSec), transmit and receive packets or frames via the connection, etc. 
     As depicted in  FIG. 1 , wireless signals  116  (represented by a bi-directional jagged line) are communicated by radios  114  in electronic device  110 - 1  and access point  112 , respectively. For example, as noted previously, electronic device  110 - 1  and access point  112  can exchange packets using a communication protocol in a WLAN. For example, access point  112  transmits trigger frames to the one or more electronic devices  110 . In response, one or more of electronic devices  110  (which are sometimes referred to as a ‘set of electronic devices’) transmit one or more frames to access point  112 . The trigger frame can include information specifying an ordered list of electronic devices in the one or more electronic devices  110  that are allowed to transmit over the communications medium. For example, the information specifying the ordered list of electronic devices (such as identifiers of the electronic devices in the ordered list of electronic devices) can be included in dedicated information bytes in a field following a MAC header of the trigger frame. 
     In response to the trigger frame, the one or more electronic devices  110  in the ordered list of electronic devices (such as electronic device  110 - 1 ) sequentially transmit one or more frames to access point  112  at temporal positions or transmission opportunities that correspond to or are based on the ordered list of electronic devices. For example, a given electronic device in the ordered list of electronic devices can transmit a frame in a sequence of one or more frames after another frame is transmitted by a preceding electronic device in the ordered list of electronic devices. Alternatively, the given electronic device can transmit a frame in the sequence of one or more frames during a time slot after an unused transmit opportunity of the preceding electronic device in the ordered list of electronic devices. 
     In this trigger-based channel-access technique, the given electronic device can select a data rate and a length of the frame that it transmits in response to the trigger frame. For example, the information in the trigger frame can specify a maximum frame duration, and the frame from or transmitted by the given electronic device can have a duration that is less than or equal to the maximum frame duration. Thus, the lengths and/or the data rates of two or more of the frames received from the ordered list of electronic devices can be different from each other. For example, each frame can specify data rates of 6 Mbps, 24 Mbps, or 54 Mbps depending on the amount of data that needs to be transmitted within a particular frame. 
     Furthermore, the information in the trigger frame can specify that each of the electronic devices in the ordered list of electronic devices responds to the trigger frame (e.g., by transmitting a frame). Therefore, access point  112  receives a frame from each of the electronic devices in the ordered list of electronic devices. In some cases, that frame can be a null frame (e.g., wherein the payload in the frame contains no data). However, in other embodiments, the electronic devices in the ordered list of electronic devices only transmit at their corresponding transmission opportunities (which are indirectly specified by the ordered list of electronic devices) if they have uplink or queued data. 
     After the last electronic device in the ordered list of electronic devices has transmitted a frame or been allocated a transmission opportunity, access point  112  can transmit a block acknowledgment to the ordered list of electronic devices. However, in other embodiments access point  112  transmits an acknowledgment to each of the electronic devices in the ordered list of electronic devices after each of the electronic devices transmits a corresponding frame of data. 
     Note that access point  112  and at least some of electronic devices  110  can be compatible with an IEEE 802.11 standard that includes trigger-based channel access (such as IEEE 802.11ax). However, access point  112  and at least this subset of electronic devices  110  can also communicate with one or more legacy electronic devices that are not compatible with the IEEE 802.11 standard (e.g., that do not use multi-user trigger-based channel access). As described further below, the communication technique can also be implemented using a legacy electronic device. 
     In addition, note that the transmit power of the electronic devices in the ordered list of electronic devices can be proportional to a transmit bandwidth of these electronic devices (as opposed to being proportional or scaling as a number of electronic devices N in the ordered list of electronic devices). 
     In these ways, the communication technique can allow electronic devices  110  and access point  112  to reduce contention in the WLAN and to improve communication performance (e.g., decrease latency with regard to frame transmission). These capabilities can improve the user experience when using electronic devices  110 , especially in the context of real-time applications. 
     In the described embodiments, processing a packet or frame in one of electronic devices  110  and access point  112  includes: receiving wireless signals  116  encoding a packet or a frame; decoding/extracting the packet or frame from received wireless signals  116  to acquire the packet or frame; and processing the packet or frame to determine information contained in the packet or frame (such as data in the payload). 
     In general, the communication via the WLAN in the communication technique can be characterized by a variety of communication-performance metrics. For example, the communication-performance metric can include: a received signal strength (RSS), a data rate, a data rate for successful communication (which can also referred to as a throughput), a latency, an error rate (such as a retry or resend rate), a mean-square error of equalized signals relative to an equalization target, inter-symbol interference, multipath interference, a signal-to-noise ratio (SNR), a width of an eye pattern, a ratio of number of bytes successfully communicated during a time interval (such as one to ten seconds) to an estimated maximum number of bytes that can be communicated in the time interval (the latter of which can also be referred to as the capacity of a communication channel or link), and/or a ratio of an actual data rate to an estimated data rate (which can also be referred to as utilization). 
     Although we describe the network environment shown in  FIG. 1  as an example, in alternative embodiments, different numbers and/or types of electronic devices can be present or otherwise included in the WLAN. For example, some embodiments can include more or fewer electronic devices  110  connected to the access point  112 . 
       FIG. 2  illustrates a protocol  200  for an electronic device  110  to connect to the WLAN of  FIG. 1 , in accordance with some embodiments. It will be appreciated that communication via the communications medium associated with the WLAN can consume significant energy. For example, operation of the radios  114  can consume energy as data is transmitted via or received over the wireless communications medium. Therefore, it can be beneficial to reduce energy consumption by disabling the radio  114  or other signal processing circuitry in the electronic device  110  for communicating via the WLAN when the electronic device  110  is not connected to the WLAN. The electronic device  110  can be disconnected from the WLAN when the electronic device  110  is out of range of the access point  112  or when the electronic device  110  is initially powered up. Alternatively, the electronic device  110  can automatically disconnect from the WLAN when the electronic device  110  remains idle for a timeout period (e.g., when the electronic device  110  does not transmit data to the access point  112  for a specified period of time) or under other disconnection criteria, including user input explicitly requesting the electronic device  110  disconnect from the WLAN. 
     In some embodiments, the electronic device  110  can be connected to a WPAN that is separate and distinct from the WLAN. For example, the electronic device  110  can communicate wirelessly with the access point  112  via a Bluetooth Low Energy (BLE) communications protocol that utilizes either the radio  114 , or a separate radio, configured to communicate via communication channels within the 2.4 GHz RF spectrum. The WPAN communication protocol is designed to reduce energy consumption of the device when compared to using, e.g., a standard Wi-Fi communication protocol specified by one or more of the IEEE 802.11 standards. The WPAN communication protocol saves energy by reducing the complexity of the communication protocol, thereby reducing the data throughput transmitted over the communication channel. However, this reduced data throughput can be insufficient for certain applications that require more data throughput or lower latency than the WPAN communication protocol can provide. Therefore, the electronic device  110  can be configured to use the WPAN to communicate with the access point  112  in order to connect to the WLAN for wireless communication between devices. 
     As depicted in  FIG. 2 , the protocol  200  begins at the electronic device  110 , which can also be referred to as a station, by advertising the presence of the electronic device  110  on one or more channels of a communications medium associated with a WPAN. In some embodiments, the electronic device  110  periodically transmits an advertising packet on one or more channels (e.g., three channels) in the 2.4 GHz RF spectrum. At  204 , the access point  112  begins to scan for devices by listening to the one or more channels for advertising packets. It will be appreciated that, in some embodiments, the access point  112  can begin scanning for devices prior to the electronic device  110  initiating the transmission of advertising packets at  202 . In such cases, the access point  112  can receive the initial advertising packet transmitted by the electronic device  110 . Otherwise, as shown in  FIG. 2 , one or more advertising packets is not be received by the access point  112  prior to a particular advertising packet being received at  206 , where the access point  112  identifies the electronic device  110  by the payload included in the advertising packet. 
     In some embodiments, the advertising packet includes a universally unique identifier (UUID) that identifies a WPAN interface for the electronic device  110 . The UUID is unique to the electronic device  110  and is used to distinguish a particular electronic device  110  from all other electronic devices  110  transmitting advertising packets via the one or more channels associated with the WPAN. In some embodiments, the UUID is a media access control (MAC) address associated with a WPAN interface implemented by the electronic device  110 . In some embodiments, the advertising packet can also include one or more advertising data structures. Each advertising data structure can include a UUID for one or more services implemented by the electronic device  110 . For example, the electronic device  110  can implement a service for connecting to a WLAN that provides low latency, such that the advertising packet indicates to the access point  112  that the electronic device  110  is requesting a connection with the WLAN. 
     At  208 , the access point  112  transmits connection data to the electronic device  110 . The connection data can include any data necessary for the electronic device  110  to connect to the WPAN. At  210 , the electronic device  110  receives the connection data, which is used to configure the electronic device  110  to connect to the WPAN. Subsequently, at  212 , the access point  112  transmits peer-to-peer (P2P) information to the electronic device  110  via the WPAN, and, at  214 , the electronic device  110  receives the P2P information. 
     In some embodiments, the P2P information includes information for establishing a connection with a WLAN configured to provide low latency Wi-Fi. For example, the P2P information can include a basic service set identifier (BSSID), a channel or channels associated with the WLAN, and any other parameters necessary to connect to and communicate with the access point  112  over the WLAN, such as parameters for implementing IPSec. In some embodiments, the WLAN is established utilizing one or more channels within a 5 GHz RF spectrum, which is separate and distinct from the RF spectrum utilized by the WPAN (e.g., the 2.4 GHz RF spectrum). 
     At  216 , the access point  112  initializes the WLAN. Initialization can include configuring the radio  114  to communicate on one or more channels of the RF spectrum. Initialization can also include adding an identifier for the electronic device  110  and/or a service implemented by the electronic device  110  to a data structure stored in a memory of the access point  112 . The identifier can be utilized by the access point  112  to target the electronic device  110 . In some embodiments, the identifier is an association identifier (AID) that can be included in the trigger frame to allocate a transmission opportunity over the communications medium to a particular electronic device  110 . 
     At  218 , the access point  112  can begin communicating with the electronic device  110  according to a trigger-based channel-access technique over the WLAN. In some embodiments, the trigger-based channel-access technique can be referred to as a Triggered Wi-Fi Access Protocol (TWAP), described in more detail in U.S. patent application Ser. No. 15/644,495, which is incorporated herein in its entirety. 
     At  220 , the electronic device  110  initializes the WLAN based on the P2P information received via the WPAN. Initialization can include configuring the radio  114  to communicate on one or more channels of the RF spectrum. Initialization can also include listening for the receipt of one or more trigger frames from the access point  112 . It will be appreciated that one or more trigger frames can be transmitted by the access point  112  prior to initialization of the WLAN by the electronic device  110  at  220 . In such cases, the access point  112  will retransmit the trigger frame until receiving a response from the electronic device  110 . Alternatively, the electronic device  110  can initialize the WLAN at  220  prior to the access point transmitting a trigger frame at  218 . 
     At  222 , the electronic device  110  receives the trigger frame. In some embodiments, the trigger frame includes an identifier associated with the electronic device  110 , such as the AID, which indicates that the access point  112  has allocated a transmission opportunity for the electronic device  110  to transmit data on an uplink of the WLAN. At  224 , the electronic device  110  transmits one or more frames of station data to the access point  112  via the WLAN. At  226 , the access point  112  receives the one or more frames of station data. At  228 , the access point  112  transmits an acknowledgment (ACK) frame to the electronic device  110  via the WLAN to acknowledge receipt of the one or more frames of station data, and, at  230 , the electronic device receives the ACK frame. In some embodiments, an ACK frame is transmitted for each frame of station data received from the electronic device  110 . In other embodiments, a single ACK frame is transmitted for multiple frames of station data received from the electronic device  110 . For example, a single ACK frame can be transmitted to the electronic device  110  in response to a burst of two or more sequential frames of station data to acknowledge receipt of the two or more sequential frames of station data. 
     It will be appreciated that although the WLAN is described as being implemented over one or more channels in the 5 GHz RF spectrum, nothing in the detailed description should be construed as limiting all embodiments of the WLAN to be implemented on a particular channel or frequency range of the RF spectrum. In other embodiments, the WLAN can be implemented on one or more communication channels in a different portion of the RF spectrum, such as the 2.4 GHz RF spectrum, a 6 GHz RF spectrum, and the like. 
       FIG. 3  illustrates a trigger frame  300  communicated from the access point  112  to an electronic device  110 , in accordance with some embodiments. In particular, the trigger frame  300  can include a number of fields. In some embodiments, the trigger frame  300  includes the following fields: a frame control field  302 , a duration field  304 , a receive address (RA) field  306 , a transmit address (TA) field  308 , a base timestamp field  310 , a slot end timestamp field  312 , a next slot timestamp field  314 , a trigger options field  316 , an AID list length field  318 , an AID list field  320 , an optional data field  322 , and a frame check sequence (FCS) field  324 . While example lengths in bytes are provided in  FIG. 3 , any/all of the lengths can be modified, and one or more fields can be added, removed, or modified in other implementations. 
     Trigger frame  300  can be referred to as a control frame. Note that the trigger frame  300  specifies an ordered list of electronic devices (e.g., in AID list field  320 ) that can use an uplink of the communications medium in the order specified in the AID list field  320 . The specific access mechanisms utilized to allocate specific transmission opportunities to each electronic device in the ordered list is described in more detail below. 
     In some embodiments, the frame control field  302  is fixed at two bytes. The frame control field  302  can be set to indicate the trigger frame  300  is a low latency Wi-Fi trigger frame. The frame control field  302  distinguishes a low latency Wi-Fi trigger frame from other types of frames, such as ACK frames or data frames. 
     In some embodiments, the duration field  304  is fixed at two bytes. The duration field  304  can be set to indicate a remaining time of a contention-free period associated with the WLAN. As used herein, a contention-free period refers to a set interval where the access point  112  is responsible for allocating resource units of the communications medium to various electronic devices  110  connected to the WLAN. In some embodiments, the value of the duration field  304  can be referred to as a network allocation vector (NAV) that indicates the remaining time in a contention-free period. 
     In some embodiments, the RA field  306  and the TA field  308  are fixed at six bytes. The RA field  306  can be set to a multicast or broadcast address of the WLAN such that all electronic devices  110  associated with the multicast or broadcast address receive the trigger frame  300 . The TA field  308  can be set to the BSSID for the WLAN. 
     In some embodiments, the base timestamp field  310  is fixed at four bytes, and the slot end timestamp field  312  and the next slot timestamp field  314  are fixed at two bytes. The base timestamp field  310  includes the lower 32-bits of the access point  112  timing synchronization function (TSF) at a point in time the trigger frame  300  was generated. The TSF is a timer with modulus 2 64  (e.g., 64-bit timer) counting in increments of microseconds (e.g., ticking on 1 MHz clock). Each electronic device  110  maintains a separate TSF that is synchronized with the access point  112  TSF utilizing a timestamp included in periodic beacon frames transmitted by the access point  112 . 
     In a scheduled access mechanism, as described in more detail below, the slot end timestamp field  312  includes the lower 16-bits of the access point  112  TSF corresponding to the scheduled end of the current uplink slot associated with the trigger frame  300 , and the next slot timestamp field  314  includes the lower 16-bits of the access point  112  TSF corresponding to the scheduled start of the next scheduled uplink slot for the first electronic device  110  in the AID list field  320  during the next contention-free period. In an unscheduled access mechanism, as described in more detail below, the slot end timestamp field  312  and the next slot timestamp field  314  can be ignored in favor of the duration field  304 , which indicates the end of the current contention-free period. 
     In some embodiments, the trigger options field  316  is fixed at one byte. The trigger options field  316  can include a number of flags. For example, a scheduled trigger flag can be set to one to indicate the trigger frame  300  is associated with a scheduled access mechanism where each electronic device  110  is allocated a fixed slot within the contention-free period, or the scheduled trigger flag can be set to zero to indicate the trigger frame  300  is associated with an unscheduled access mechanism where each electronic device  110  is triggered in order as listed in the AID list field  320 . The trigger options field  316  can also include an explicit trigger flag that can be set to one to indicate that each electronic device  110  included in the AID list field  320  will be triggered by a separate trigger frame or can be set to zero to indicate multiple electronic devices  110  are triggered, in an order as specified in the AID list field  320 , in response to a single trigger frame. The trigger options field  316  can also include an immediate ACK flag that can be set to one to indicate each uplink packet will be acknowledged by a separate ACK frame or can be set to zero to indicate that multiple uplink packets can be acknowledged by a single ACK frame. 
     In some embodiments, the AID list length field  318  is fixed at two bytes. The AID list length field  318  is set to indicate a number of electronic devices  110  that are allocated an uplink slot in the current contention-free period. It will be appreciated that the value of the AID list length field  318  indicates the number of separate and distinct electronic devices  110  referenced in the AID list field  320 . 
     In some embodiments, the AID list field  320  includes a list of AIDs for one or more electronic devices  110  allocated uplink slots within the current contention-free period. A size of the AID list field  320  is variable between two and 2N bytes, where N is the number of electronic devices  110  allocated uplink slots within the current contention-free period. 
     In some embodiments, an optional data field  322  can include any additional data transmitted from the access point  112  to the electronic device  110 . In some embodiments, the data field  322  can be utilized to transmit feedback information to an electronic device  110 . For example, the access point  112  can transmit haptic data to an electronic device  110  within the trigger frame  300 . The data field  322  can be used for various purposes but is typically limited in size, e.g., less than 20 bytes. More substantial information passed between the access point  112  and the electronic device  110  can be transmitted within a separate data frame, as discussed below. 
     In some embodiments, the FCS field  324  is fixed at four bytes. The FCS field  324  contains an error-detecting code that is added to the end of the trigger frame  300 . The value contained in the FCS field  324  is calculated based on the values in one or more other fields of the frame, such as the frame control field  302 , the duration field  304 , the RA field  306 , and so forth. Receiving stations can check the integrity of the received trigger frame  300  by checking the value in the FCS field  324  against a value calculated from the values in one or more other fields in the received trigger frame  300 . 
     It will be appreciated that, in other embodiments, the format of the trigger frame  300  can be different than the format set forth above. For example, the AID list length can be fixed at N devices and the AID list length field  318  can be omitted from the trigger frame  300 . As another example, the FCS field  324  can be omitted where the communications protocol does not implement error checking. In some embodiments, the order of the fields in the frame can be changed. For example, the trigger options field  316  can be ordered after the data field  322 . 
       FIG. 4  illustrates a data frame  400  communicated between stations of the WLAN, in accordance with some embodiments. In particular, the data frame  400  can include a number of fields. In some embodiments, the data frame  400  includes the following fields: a frame control field  402 , a duration field  404 , a first address (A1) field  406 , a second address (A2) field  408 , a third address (A3) field  410 , a sequence control field  412 , a Quality of Service (QoS) control field  414 , a data field  416 , and a frame check sequence (FCS) field  418 . While example lengths in bytes are provided in  FIG. 4 , any/all of the lengths can be modified, and one or more fields can be added, removed, or modified in other implementations. 
     In some embodiments, the frame control field  402  is fixed at two bytes. The frame control field  402  can be set to indicate the data frame  400  includes a data payload and to differentiate the data frame from other control and management frames such as RTS/CTS frames, ACK frames, and the like. 
     In some embodiments, the duration field  404  is fixed at two bytes. The duration field  404  can be set to a fixed value, e.g., 32767 when the data frame  400  is transmitted within a contention-free period. In other embodiments, the duration field  404  can be set to a value that indicates the length of the data frame  400 . 
     In some embodiments, the address fields, e.g., the A1 field  406 , the A2 field  408 , and the A3 field  410  are fixed at six bytes. The A1 field  406  can be set to destination address (DA), the A2 field  408  can be set to the source address (SA), and the A3 field  410  can be set to the BSSID for the WLAN. The address fields can take the form of conventional IEEE 802.11 MAC addresses. 
     In some embodiments, the sequence control field  412  is fixed at two bytes. The sequence control field  412  includes a sequence number and fragment number for a sequence of data frames. The sequence control field  412  can be used in a burst mode where multiple data frames are sent in order prior to receiving an ACK frame in response. 
     In some embodiments, the QoS control field  414  is fixed at two bytes. The QoS control field  414  includes parameters related to providing QoS for a data stream of one or more data frames. The parameters can include a QoS type (e.g., video, audio, etc.), a priority value, as well as other parameters for implementing a QoS algorithm. 
     In some embodiments, a data field  416  can include any data transmitted from one station to another station. The data field  416  is variable size, but can be limited at the upper end by a maximum size of a frame transmitted over the communications medium minus the number of bytes for the MAC header and MAC footer (e.g., FCS field  418 ). 
     In some embodiments, the FCS field  418  is fixed at four bytes. The FCS field  324  contains an error-detecting code that is added to the end of the data frame  400 . The value contained in the FCS field  324  is calculated based on the values in one or more other fields of the data frame, such as the frame control field  402 , the duration field  404 , the address fields  406 / 407 / 408 , and so forth. Receiving stations can check the integrity of the received data frame by checking the value in the FCS field  418  against a value calculated from the values in one or more other fields in the received data frame. 
       FIG. 5  illustrates an acknowledgment (ACK) frame  500  communicated between stations of the WLAN, in accordance with some embodiments. In particular, the ACK frame  500  can include a number of fields. In some embodiments, the ACK frame  500  includes the following fields: a frame control field  502 , a duration field  504 , a receive address (RA) field  506 , and a FCS field  508 . While example lengths in bytes are provided in  FIG. 5 , any/all of the lengths can be modified, and one or more fields can be added, removed, or modified in other implementations. 
     In some embodiments, the frame control field  502  is fixed at two bytes. The frame control field  502  can be set to indicate the ACK frame  500  is an acknowledgment of successful receipt of a previously transmitted frame transmitted over the communications medium by a station. 
     In some embodiments, the duration field  504  is fixed at two bytes. The duration field  504  can be set to a fixed value, e.g., 32767 when the ACK frame  500  is transmitted within a contention-free period. In other embodiments, the duration field  504  can be set to a value that indicates the length of the ACK frame  500 . 
     In some embodiments, the RA field  506  is fixed at six bytes. The RA field  506  includes an 802.11 MAC address for the station that sent the frame being acknowledged. 
     In some embodiments, the FCS field  508  is fixed at four bytes. The FCS field  508  contains an error-detecting code that is added to the end of the ACK frame  500 . The value contained in the FCS field  508  is calculated based on the values in one or more other fields of the ACK frame  500 , such as the frame control field  502 , the duration field  504 , and the RA field  506 . Receiving stations can check the integrity of the received ACK frame  500  by checking the value in the FCS field  508  against a value calculated from the values in one or more other fields in the received ACK frame  500 . 
     In some embodiments, the format of the ACK frame  500  can also be used as a clear-to-send (CTS) frame, where the frame control field  502  includes a different value that indicates the frame is a CTS frame instead of an ACK frame. 
       FIG. 6  illustrates a contention-free end (CF-END) frame  600  communicated from the access point  112  to an electronic device  110 , in accordance with some embodiments. In particular, the CF-END frame  600  can include a number of fields. In some embodiments, the CF-END frame  600  includes the following fields: a frame control field  602 , a duration field  604 , a receive address (RA) field  606 , a transmit address (TA) field  608 , and an FCS field  610 . While example lengths in bytes are provided in  FIG. 6 , any/all of the lengths can be modified, and one or more fields can be added, removed, or modified in other implementations. 
     In some embodiments, the frame control field  602  is fixed at two bytes. The frame control field  602  can be set to indicate the CF-END frame  600  identifies the end of the contention-free period. 
     In some embodiments, the duration field  604  is fixed at two bytes. The duration field  604  can be set to a fixed value, e.g., 32767 when the CF-END frame  600  is transmitted within a contention-free period. In other embodiments, the duration field  604  can be set to a value that indicates the length of the CF-END frame  600 . 
     In some embodiments, the RA field  606  and the TA field  608  are fixed at six bytes. The RA field  606  can be set to a multicast or broadcast address of the WLAN such that all electronic devices  110  associated with the multicast or broadcast address receive the CF-END frame  600 . The TA field  608  can be set to the BSSID for the WLAN. 
     In some embodiments, the FCS field  608  is fixed at four bytes. The FCS field  608  contains an error-detecting code that is added to the end of the CF-END frame  600 . The value contained in the FCS field  608  is calculated based on the values in one or more other fields of the CF-END frame  600 , such as the frame control field  602 , the duration field  604 , the RA field  606 , and the TA field  608 . Receiving stations can check the integrity of the received CF-END frame  600  by checking the value in the FCS field  608  against a value calculated from the values in one or more other fields in the received CF-END frame  600 . 
     In some embodiments, the format of the CF-END frame  600  can also be used as a request-to-send (RTS) frame, where the frame control field  602  includes a different value that indicates the frame is a RTS frame instead of a CF-END frame. 
     In some embodiments, each electronic device  110  can transmit an RTS frame to the access point  112  prior to transmitting a data frame via the communications medium. In such embodiments, the electronic device  110  will confirm receipt of a corresponding CTS frame from the access point  112  prior to sending the data frame. 
     Several contention-free access mechanisms utilized by the WLAN are now described. During the communication technique, the access point can transmit a trigger frame via the communications medium in order to allocate an uplink slot (e.g., a transmission opportunity) during a contention-free period to a particular electronic device. The electronic devices can transmit data via the communications medium during their allocated transmission opportunity if they have buffered or queued data. Otherwise, an electronic device can elect not to transmit on the uplink during the allocated transmission opportunity. When that occurs, the next electronic device in the ordered list of electronic devices can be allocated the next transmission opportunity. 
     The WLAN is managed by the access point  112 . Management of the WLAN can include allocating resource units of the communications medium, managing connections to the WLAN, monitoring the communications medium for interference from other signals, and so forth. The AP  112  specifically allocates resource units of the communications medium, via the transmission of trigger frames, to particular electronic devices  110  to transmit via the communications medium according to a contention-free access mechanism. 
       FIG. 7  illustrates a diagram  700  of an unscheduled access mechanism, in accordance with some embodiments. The unscheduled access mechanism refers to an algorithm, implemented by the processing subsystem of the access point, where the duration of a transmission opportunity is not pre-defined by the access point. Instead, a start of each transmission opportunity in at least two transmission opportunities within the contention-free period is adjusted dynamically by the processing subsystem based on traffic transmitted via the communications medium. 
     According to operation of the unscheduled access mechanism, the access point  112  determines an order of a number of transmission opportunities in a particular contention-free period allocated to one or more electronic devices  110  connected to the WLAN. The access point  112  then transmits trigger frames over the communications medium according to the order, allowing the various electronic devices  110  connected to the WLAN to transmit data to the access point  112  in one or more frames. 
     As depicted in  FIG. 7 , at the start of a contention-free period, the access point  112  transmits a first trigger frame  712  to a first electronic device  110 - 1 . In response to the first trigger frame  712 , the first electronic device  110 - 1  transmits a frame of station data  722  to the access point  112  after a specified delay. In some embodiments, the delay utilized by the unscheduled access medium has a duration of 16 microseconds (μs) and can be referred to as a Short Interframe Space (SIFS), which is utilized for high-priority transmissions in other contention-based protocols. In other embodiments, the delay can be increased or decreased (e.g., the delay can be 10 μs). Upon receiving the frame of station data  722  and after a delay (e.g., SIFS), the access point  112  transmits an ACK frame  732  to the first electronic device  110 - 1 . The ACK frame  732  indicates the end of the transmission opportunity allocated to the first electronic device  110 - 1 . 
     After a delay (e.g., SIFS) and at the start of a second transmission opportunity, the access point  112  transmits a second trigger frame  714  to a second electronic device  110 - 2 . In response to the second trigger frame  714 , the second electronic device  110 - 2  transmits a frame of station data  724  to the access point  112  after a specified delay. Upon receiving the frame of station data  724  and after a delay (e.g., SIFS), the access point  112  transmits an ACK frame  734  to the second electronic device  110 - 2 . The ACK frame  734  indicates the end of the second transmission opportunity allocated to the second electronic device  110 - 2 . 
     After a delay (e.g., SIFS) and at the start of a third transmission opportunity, the access point  112  transmits a third trigger frame  716  to a third electronic device  110 - 3 . In response to the third trigger frame  716 , the third electronic device  110 - 3  transmits a frame of station data  726  to the access point  112  after a specified delay. Upon receiving the frame of station data  726  and after a delay (e.g., SIFS), the access point  112  transmits an ACK frame  736  to the third electronic device  110 - 6 . The ACK frame  736  indicates the end of the third transmission opportunity allocated to the second electronic device  110 - 3 . 
     After a delay (e.g., SIFS) and at the start of a fourth transmission opportunity, the access point  112  transmits a fourth trigger frame  718  to a fourth electronic device  110 - 4 . In response to the fourth trigger frame  718 , the fourth electronic device  110 - 4  transmits a frame of station data  728  to the access point  112  after a specified delay. Upon receiving the frame of station data  728  and after a delay (e.g., SIFS), the access point  112  transmits an ACK frame  738  to the fourth electronic device  110 - 4 . The ACK frame  738  indicates the end of the fourth transmission opportunity allocated to the fourth electronic device  110 - 4 . 
     The access point  112  can continue sending trigger frames and receiving frames of station data for zero or more additional electronic devices  110  connected to the WLAN in accordance with the order determined by the access point  112 . Once all transmission opportunities have been allocated to the electronic devices  110  connected to the WLAN, the access point  112  transmits a CF-END frame  742  indicating the end of the contention-free period. The number of transmission opportunities that are available within a particular contention-free period depends on a duration of the contention-free period, the size and/or data rate associated with each of the frames transmitted during each transmission opportunity, a maximum size of a frame (e.g., maximum size of the frame of station data), and so forth. Consequently, in the unscheduled access mechanism, the total number of transmission opportunities within a fixed contention-free period is unknown at the start of the contention-free period. 
       FIG. 8  illustrates a diagram  800  of an unscheduled access mechanism with retries, in accordance with some embodiments. In some cases, a particular electronic device  110  can fail to send station data to the access point  112  in response to a trigger frame. In some cases, an electronic device  110  can fail to receive a trigger frame. This failure can be caused by, among other reasons, interference on the communications medium, inadequate signal strength, and the like. In other cases, the electronic device  110  can receive the trigger frame; however, the electronic device  110  can determine that there is no buffered or queued data to send to the access point  112 . In yet other cases, the electronic device  110  can attempt to transmit the station data to the access point  112 ; however, the access point  112  can fail to receive the station data due to, e.g., interference, inadequate signal strength, and the like. 
     In some cases, the access point  112  can be configured to perform a number of retries when a particular electronic device  110  fails to respond to a trigger frame. As depicted in  FIG. 8 , the access point  112  can wait for a specified time after transmission of the trigger frame to receive a response from the electronic device  110 . If a response (e.g., a frame of station data) is not received within the specified time, then the access point  112  can attempt to re-transmit the trigger frame. In some cases, re-transmitting the trigger frame will result in receipt of the frame of station data from the electronic device (as illustrated during the transmission opportunity allocated to the first electronic device  110 - 1 ), at which point an ACK frame is transmitted to the electronic device  110 . In other cases, re-transmitting the trigger frame will not result in the receipt of the frame of station data from the electronic device (as illustrated during the transmission opportunity allocated to the second electronic device  110 - 2 ), where no ACK frame is transmitted to the electronic device and, instead, a new trigger frame associated with a new transmission opportunity can be transmitted to a different electronic device  110 . 
     It will be appreciated that, in various embodiments, the number of retry attempts implemented by the access point  112  during each transmission opportunity can be dynamically set at zero or more. In some embodiments, the number of retries can be set based on the number of electronic devices connected to the WLAN. It will be appreciated that failures and subsequent retries can increase the duration of a particular transmission opportunity within the contention-free period. A large number of failures and subsequent retries can mean fewer transmission opportunities can be allocated within a particular contention-free period of fixed length. Consequently, an access point cannot guarantee that all electronic devices  110  are allocated a transmission opportunity within the contention-free period before the expiration of the contention-free period (e.g., before expiration of the NAV set in the duration field  304  of the trigger frame  300 ). In some embodiments, each transmission opportunity is associated with a maximum duration, and a duration of a particular transmission opportunity can be less than or equal to the maximum duration. Consequently, the access point can guarantee that a minimum number of electronic devices  110  are allocated a transmission opportunity within the contention-free period. 
     A major problem with contention-based access mechanisms implemented in legacy Wi-Fi is that Quality of Service (QoS) cannot be ensured due to the variable latency associated with the contention-based access mechanisms. In contrast, low latency Wi-Fi can be implemented by limiting the duration of the contention-free period and allocating transmission opportunities to electronic devices  110  according to a duty cycle associated with a series of contention-free periods. For example, in some embodiments, the access point  112  sets the contention-free period to have a duration of 2 ms. A number of transmission opportunities can be allocated to one or more electronic devices  110  within the contention-free period, followed by a number of additional transmission opportunities allocated to the one or more electronic devices  110  in a subsequent contention-free period. 
     In some embodiments, QoS can be provided to at least one electronic device  110  by prioritizing the at least one electronic device  110  within the order of electronic devices  110  listed in the AID list field  320  of a trigger frame  300 . In some cases, a maximum size of a frame along with knowledge of the number of allowed retries per transmission opportunity and an order and type of frames transmitted during a transmission opportunity as well as a duration of the contention-free period can determine a minimum number of transmission opportunities per contention-free period. The minimum number of transmission opportunities can represent a number of electronic devices  110  for which a particular QoS can be ensured utilizing the unscheduled access mechanism. In this manner, low latency Wi-Fi can be provided for real-time applications such as streaming video, audio, gaming, and the like. 
     In some embodiments, the individual stations might benefit from reduced power consumption when configured to communicate with the WLAN according to the aforementioned communication techniques. In such embodiments, the stations can advantageously enter a low-power mode during at least a portion of the contention-free period in order to reduce power consumption of the electronic device  110 . 
     In some embodiments, each trigger frame  300  transmitted by the access point  112  includes an AID list field  320  indicating the electronic devices  110  that will be allocated a transmission opportunity, if sufficient resource units are available, within the contention-free period. The trigger frames  300  transmitted by the access point  112  also include an indication of the end of the current contention-free period, relative to the base timestamp field  310 , in the duration field  304 . Consequently, each electronic device  110  can inspect the AID list field  320  to determine if an AID associated with that particular electronic device  110  is listed in the AID list field  320 . If the corresponding AID for that electronic device  110  is not included in the AID list field  320  of the trigger frame  300 , then the electronic device  110  can enter the low power mode until the end of the current contention-free period. In some embodiments, the low power mode includes disabling the radio  114  and/or signal processing circuitry associated with the physical layer of the WLAN. 
       FIG. 9  illustrates a diagram  900  of a sleep cycle for a number of electronic devices utilizing the unscheduled access mechanism to communicate via the WLAN, in accordance with some embodiments. All electronic devices  110  connected to the WLAN should wake up at the beginning of the contention-free period  910  and listen to the communications medium to receive trigger frames  300 . 
     As depicted in  FIG. 9 , at the beginning of the contention-free period  910 , a first trigger frame  712 , transmitted by the access point  112 , allocates a first transmission opportunity to a first electronic device  110 - 1 . The first electronic device  110 - 1  responds to the first trigger frame  712  by transmitting a frame of station data  722  to the access point  112 . The access point  112  then transmits an ACK frame  732  to the first electronic device  110 - 1 , ending the first transmission opportunity. Once the first transmission opportunity is concluded, the first electronic device  110 - 1  can enter a low power mode, sometimes referred to as a sleep mode. Prior to entering the low power mode, the first electronic device  110 - 1  can calculate a wake-up time, relative to a value of the TSF of the first electronic device  110 - 1 , corresponding to the start of the next contention-free period. The first electronic device  110 - 1  can be configured to exit the low power mode at or prior to the wake-up time. In some embodiments, an electronic device  110  can set a wake-up timer based on the wake-up time that corresponds to a start of the subsequent contention-free period. The expiration of the wake-up timer is configured to trigger an operation to exit the low power mode. 
     The other electronic devices  110  remains awake during the first transmission opportunity to await the next trigger frame  300 . At the beginning of the second transmission opportunity, a second trigger frame  714 , transmitted by the access point  112 , allocates a second transmission opportunity to a second electronic device  110 - 2 . The second electronic device  110 - 2  responds to the second trigger frame  714  by transmitting a frame of station data  724  to the access point  112 . The access point  112  then transmits an ACK frame  734  to the second electronic device  110 - 2 , ending the second transmission opportunity. Once the second transmission opportunity is concluded, the second electronic device  110 - 2  can enter the low power mode. Prior to entering the low power mode, the second electronic device  110 - 2  can calculate a wake-up time, relative to a value of the TSF of the second electronic device  110 - 2 , corresponding to the start of the next contention-free period. The second electronic device  110 - 2  can be configured to exit the low power mode at or prior to the wake-up time. 
     The third electronic device  110 - 3  and the fourth electronic device  110 - 4  similarly enter a low power mode subsequent to the conclusion of a corresponding transmission opportunity allocated to the third electronic device  110 - 3  or the fourth electronic device  110 - 4 , respectively. It will be appreciated that the ratio of an awake period to a sleep period for each electronic device  110  depends on a position of the transmission opportunity allocated to the corresponding electronic device  110  during the contention-free period  910 . For example, a ratio of the awake period to sleep period for the first electronic device  110 - 1  is lower than the ratio of the awake period to sleep period for the fourth electronic device  110 - 4 . Consequently, power consumption of the fourth electronic device  110 - 4  is typically greater than the power consumption of the first electronic device  110 - 1 , all other things being equal (e.g., the amount of data transmitted via the WLAN, transmission power, etc.). 
     In some embodiments, the access point  112  is configured to mitigate uneven power consumption effects by adjusting the order of the transmission opportunities allocated to the various electronic devices  110  during a number of contention-free periods according to a round-robin schedule. For example, during a first contention-free period, the order of electronic devices  110  can be selected as  110 - 1 ,  110 - 2 ,  110 - 3 , and  110 - 4 ; during a second contention-free period, the order of electronic devices  110  can be selected as  110 - 2 ,  110 - 3 ,  110 - 4 , and  110 - 1 ; during a third contention-free period, the order of electronic devices  110  can be selected as  110 - 3 ,  110 - 4 ,  110 - 1 , and  110 - 2 ; and during a fourth contention-free period, the order of electronic devices  110  can be selected as  110 - 4 ,  110 - 1 ,  110 - 2 , and  110 - 3 . Consequently, this round-robin scheduling ensures that, on average over a number of contention-free periods, the ratio of awake period to sleep period for all electronic devices is approximately similar. 
     The ability to sleep between transmission opportunities allocated to a particular electronic device  110  can be instrumental in saving power and extending the battery life of mobile devices. The unscheduled access mechanism described above is not conducive to absolute efficiency when determining when an electronic device  110  can enter the low power mode and when the electronic device  110  needs to wake up. Due to the nature of the unscheduled access mechanism, each electronic device is only aware, a priori, when the next contention-free period is scheduled to begin and whether the access point  112  will attempt to allocate a transmission opportunity to the electronic device  110  during the current transmission opportunity. This means that the electronic device  110  must remain awake and listen to the communications medium for a trigger frame targeted at that device, even during a duration of one or more other transmission opportunities allocated to different electronic devices  110 . 
       FIG. 10  illustrates a diagram  1000  of a scheduled access mechanism, in accordance with some embodiments. The scheduled access mechanism refers to an access mechanism where a start of each transmission opportunity in the at least two transmission opportunities within the contention-free period is fixed by the processing subsystem of the access point  112  according to a schedule. In some embodiments, the schedule is determined prior to the start of each contention-free period. In some embodiments, a duration of each transmission opportunity within the contention-free period is set equal to a duration of the contention-free period divided by a number of electronic devices in the ordered list of electronic devices. In other embodiments, a duration of each transmission opportunity within the contention-free period can be set based on a QoS type or priority value associated with each electronic device of a number of electronic devices. For example, a larger transmission opportunity can be granted to a video QoS type than an audio QoS type. Nevertheless, the duration of each transmission opportunity is fixed at the start of a contention-free period and is not adjusted dynamically based on the traffic transmitted via the communications medium. 
     According to the scheduled access mechanism, the access point  112  determines an order of a number of transmission opportunities in a particular contention-free period allocated to one or more electronic devices  110  connected to the WLAN. The access point  112  is configured to divide the contention-free period into a number of discrete transmission opportunities that are allocated to particular electronic devices  110  at specific times within the contention-free period. The access point  112  then transmits trigger frames over the communications medium according to the order and at the specific times, allowing the various electronic devices  110  connected to the WLAN to transmit station data to the access point  112  during a corresponding transmission opportunity. 
     In other words, as depicted in  FIG. 10 , at the start of a contention-free period, the access point  112  transmits a first trigger frame  1012  to a first electronic device  110 - 1  at the beginning of a first transmission opportunity  1052 . In response to the first trigger frame  1012 , the first electronic device  110 - 1  transmits a frame of station data  1022  to the access point  112  after a specified delay. Upon receiving the frame of station data  1022  and after the delay (e.g., SIFS), the access point  112  transmits an ACK frame  1032  to the first electronic device  110 - 1 . Unlike in the unscheduled access mechanism, described above, the ACK frame  1032  does not indicate the end of the first transmission opportunity  1052  allocated to the first electronic device  110 - 1 . Again, a duration of the first transmission opportunity  1052  is pre-defined by the access point  112  and, therefore, even though the first electronic device  110  has finished transmitting the station data and received an acknowledgment from the access point  112  at a first time during the first transmission opportunity  1052 , the access point  112  waits until the start of the second transmission opportunity  1054  to send then second trigger frame  1014  to the second electronic device  110 - 2 . 
     At the start of the second transmission opportunity  1054 , the access point  112  transmits a second trigger frame  1014  to a second electronic device  110 - 2 . In response to the second trigger frame  1014 , the second electronic device  110 - 2  transmits a frame of station data  1024  to the access point  112  after a specified delay. Upon receiving the frame of station data  1024  and after the delay (e.g., SIFS), the access point  112  transmits an ACK frame  1034  to the second electronic device  110 - 2 . Again, the access point  112  waits until subsequent transmission opportunities to send additional trigger frames to one or more additional electronic devices  110 . Following all scheduled transmission opportunities, the access point  112  transmits a CF-END frame  1042  to indicate the end of the contention-free period. 
     It will be appreciated that the information identifying the pre-defined duration of the transmission opportunities can be supplied to the electronic devices  110  within the trigger frame. In some embodiments, the access point  112  populates or generates the fields of the trigger frame, including: a NAV value in the duration field  304  indicating the time remaining in the contention-free period, a value (e.g., timestamp) corresponding to the start of the current transmission opportunity in the base timestamp field  310 , and a value (e.g., timestamp) corresponding to the end of the current transmission opportunity in the slot end timestamp field  312 . The electronic device  110  can read these fields from the trigger frame to determine how much time is available to send data during the currently allocated transmission opportunity. 
     In some embodiments, the electronic device  110  can adjust the payload included in the frame of station data based on the duration of the transmission opportunity. For example, the size of the payload can be adjusted to fit within the transmission opportunity and allow the access point  112  to send an ACK frame to the electronic device  110 . Any truncated data can be queued or buffered to be transmitted during the next transmission opportunity. Alternatively, in some embodiments, the header for the frame of station data can include a field that indicates the station has buffered data that needs to be sent such that the access point  112  can allocate an additional transmission opportunity to the electronic device  110  during the next contention-free period. For example, an additional transmission opportunity (e.g., two transmission opportunities) can be allocated to the same electronic device  110  during a subsequent contention-free period. 
     In other embodiments, the electronic device  110  can adjust a data rate associated with a fixed payload size to ensure that the frame of station data can be transmitted within the currently allocated transmission opportunity. For example, the electronic device  110 , can change the modulation and coding scheme (MCS) used to transmit the frame of station data based on the duration of the transmission opportunity. The selected MCS can be set in the preamble or header of the frame using a code in a field of the preamble or header. Higher data rates will enable more data to be transmitted in a shorter duration of the transmission opportunity, but at the cost of potential interference causing a failure at the access point  112  to receive the frame of station data. It will be appreciated that the algorithm for selecting the MCS based on the duration of the allocated transmission opportunity can take into consideration additional criteria such as: a size of the queued data to be encoded within the frame payload, whether one or more retries within the transmission opportunity are enabled or disabled, historical information related to the success or failure of previous frame transmissions, and the like. 
     It will also be appreciated that the delay between the ACK frame  1032  and the start of the second transmission opportunity  1054  represents an idle communications medium. Where the delay is significantly longer than the SIFS, stations of other WLANs using the same communications medium with a contention-based access mechanism such as CSMA/CA could transmit over the communications medium prior to the start of the next transmission opportunity allocated within the WLAN. In other words, there is no guarantee that the communications medium will be idle at the start of the second transmission opportunity when the delay between the ACK frame  1032  and the trigger frame  1014  is large. In such cases, the access point  112  delays the sending of the second trigger frame  1014  until the communications medium is idle for a minimum delay (e.g., the SIFS). In other words, the trigger frame  1014  can be delayed while waiting for traffic from other WLANs to finish transmission on the communications medium. 
     This delay is immaterial as long as the trigger frame is transmitted prior to the end of the current transmission opportunity and there is a sufficient amount of time left before the end of the transmission opportunity to transmit a frame of station data and receive an ACK frame from the access point  112 . In some embodiments, if the trigger frame is received by the electronic device  110  and the electronic device  110  determines that the time between the trigger frame and the end of the transmission opportunity is smaller than a minimum time threshold to send data and receive the ACK frame, then the electronic device  110  can ignore the trigger frame and wait for the next transmission opportunity to be allocated to the electronic device  110  by the access point  112 . 
       FIG. 11  illustrates a diagram  1100  of a scheduled access mechanism with retries, in accordance with some embodiments. In some embodiments, the access point  112  can be configured to perform a number of retries within a scheduled transmission opportunity when a particular electronic device  110  fails to respond to a trigger frame. As depicted in  FIG. 11 , the access point  112  can wait for a specified time after transmission of the trigger frame to receive a response from the electronic device  110 . If a response (e.g., a frame of station data) is not received within the specified time, then the access point  112  can attempt to re-transmit the trigger frame. In some cases, re-transmitting the trigger frame will result in receipt of the frame of station data from the electronic device (as illustrated as trigger frames  1012 - 1  and  1012 - 2  transmitted during the first transmission opportunity  1052  allocated to the first electronic device  110 - 1 ), at which point an ACK frame is transmitted to the electronic device  110 . In other cases, re-transmitting the trigger frame will not result in the receipt of the frame of station data from the electronic device (as illustrated during the transmission opportunity allocated to the second electronic device  110 - 2 ), where no ACK frame is transmitted to the electronic device and, instead, a new trigger frame associated with a new transmission opportunity can be transmitted to a different electronic device  110 . The trigger frame can be re-transmitted two or more times during a particular transmission opportunity (as illustrated as trigger frames  1012 - 1  and  1012 - 2  transmitted during the first transmission opportunity  1052  allocated to the first electronic device  110 - 1 ). 
     It will be appreciated that, in various embodiments, the number of retry attempts implemented by the access point  112  during each transmission opportunity can be dynamically adjusted based on the duration of the current transmission opportunity. In some embodiments, the number of retries can be set based on a minimum time that is required to receive station data from the electronic device  110  and also send an ACK frame to the electronic device  110 . The access point  112  can compare the time remaining in the current transmission opportunity with the minimum time in order to determine whether enough time is available to make another attempt to trigger the station. Thus, retries are enabled only if there is adequate time left within a transmission opportunity to attempt the retry. For example, if an ACK frame takes approximately 25 microseconds to transmit, a frame of station data takes approximately 50 microseconds to transmit, and each delay between frames is, e.g., 16 microseconds, then approximately 140 microseconds after the trigger frame is required to wait a delay, receive the station data, wait a delay, send the ACK frame and wait a delay before the start of the next transmission opportunity to send the next trigger frame. Consequently, a threshold time of, e.g., 200 microseconds can be required to remain within the current transmission opportunity in order to transmit a subsequent trigger frame as part of a retry attempt. 
     It will be appreciated that the duration of the transmission opportunities can be set based on the number of electronic devices  110  connected to the WLAN. For example, the contention-free period can be fixed at, e.g., 3 milliseconds. If there are eight electronic devices  110  connected to the WLAN, then each transmission opportunity can be set at 375 microseconds. Thus, whether retries are enabled within the scheduled access mechanism can be dependent on the number of electronic devices  110  connected to the WLAN because the duration of the transmission opportunity provided to each electronic device  110  can be shorter when more devices are connected to the WLAN. 
     In some embodiments, the duration of transmission opportunities can be fixed (e.g., 300 microseconds), which limits the number of transmission opportunities available within a contention-free period. However, if the contention-free period includes more transmission opportunities than the number of electronic devices  110  connected to the WLAN, then the access point can reserve one or more transmission opportunities within the contention-free period to allow for retry attempts to unresponsive electronic devices  110 . In such cases, the electronic devices  110  can be included in the AID list field  320  multiple times in the trigger frames at the start of the contention-free period in order to force the electronic devices  110  to stay away for the subsequent transmission opportunity. Then, when an unassigned transmission opportunity is reached, the access point  112  can re-assign that transmission opportunity dynamically on an as-needed basis. For example, the transmission opportunity can be assigned in response to a failure to receive station data from a particular electronic device  110  during a preceding transmission opportunity within the current contention-free period. As another example, the transmission opportunity can be assigned in response to a flag set in the station data received during a preceding transmission opportunity. For example, an electronic device  110  can indicate that there is additional queued or buffered station data that is waiting to be transmitted to the access point  112 . The access point  112  can then allocate one of the extra transmission opportunities within the contention-free period to that particular electronic device  110 . 
     In some embodiments, the individual stations can benefit from reduced power consumption when configured to communicate with the WLAN according to the aforementioned communication techniques. In such embodiments, the stations can advantageously enter a low-power mode during at least a portion of the contention-free period in order to save power. 
     In some embodiments, each trigger frame  300  transmitted by the access point  112  includes a base timestamp field  310  that indicates the current value of the TSF maintained by the access point  112  corresponding with a time matching the generation of the trigger frame  300 . The value in the base timestamp field  310  should be synchronized to a value of the TSF maintained by the electronic device  110 . The trigger frames  300  transmitted by the access point  112  also include an indication of the end of the current contention-free period, relative to the base timestamp field  310 , in the duration field  304 , an indication of the end of the current transmission opportunity in the slot end timestamp field  312 , and an indication of a start of the next transmission opportunity allocated to the electronic device  110  during the next contention-free period in the next slot timestamp field  314 . Consequently, each electronic device  110  can inspect these fields in a trigger frame  300  to determine when the electronic device  110  can enter a low power mode. 
     For example, when a particular electronic device  110  is targeted by a trigger frame  300 , such as by being listed first in the AID list field  320 , that electronic device  110  can determine a time corresponding to the end of the transmission opportunity allocated to that electronic device  110  by inspecting the slot end timestamp field  312 , relative to the base timestamp field  310 . The electronic device  110  can then enter the low power mode when the current transmission opportunity expires. In addition, the electronic device  110  can determine a time corresponding to a next scheduled transmission opportunity allocated to the electronic device  110  by inspecting the next slot timestamp field  314 , relative to the base timestamp field  310 . The electronic device  110  can then set a wake-up timer corresponding to the start of the next transmission opportunity allocated to the electronic device  110  during the next contention-free period. It will be appreciated that the scheduled access mechanism allows the electronic device  110  to spend more time in the low power mode than the unscheduled access mechanism because the access point  112  can indicate to the electronic device  110  during a current transmission opportunity when the next scheduled transmission opportunity in the next contention-free period is scheduled to occur. Thus, all electronic devices  110  do not need to wake at the start of the next contention-free period to listen for their trigger frame; instead, each electronic device  110  can wake at their expected transmission opportunity as previously scheduled by the access point  112 . Again, in some embodiments, the low power mode includes disabling the radio  114  and/or signal processing circuitry associated with the physical layer of the WLAN. 
       FIG. 12  illustrates a diagram  1200  of a sleep cycle for a number of electronic devices utilizing the scheduled access mechanism to communicate via the WLAN, in accordance with some embodiments. Each electronic device  110  connected to the WLAN can wake up at the beginning of a corresponding transmission opportunity and listen to the communications medium to receive a trigger frame  300  targeted to that electronic device  110 . It will be appreciated that, prior to the first contention-free period after the electronic device  110  connects to the WLAN, the electronic device  110  will be awake and is configured to listen for a trigger frame  300  targeted at the electronic device  110 . That trigger frame  300  includes information that specifies the next transmission opportunity for that electronic device  110 , enabling the electronic device  110  to enter the low power mode between transmission opportunities. 
     As depicted in  FIG. 12 , at the beginning of the contention-free period  1210 , a first trigger frame  1012 , transmitted by the access point  112 , allocates a first transmission opportunity to a first electronic device  110 - 1 . The first electronic device  110 - 1  responds to the first trigger frame  1012  by transmitting a frame of station data  1022  to the access point  112 . The access point  112  then transmits an ACK frame  1032  to the first electronic device  110 - 1 , ending the first transmission opportunity. Once the first transmission opportunity is concluded, the first electronic device  110 - 1  can enter a low power mode, sometimes referred to as a sleep mode. Prior to entering the low power mode, the first electronic device  110 - 1  can calculate a wake-up time, relative to a value of the TSF of the first electronic device  110 - 1 , corresponding to the start of the next transmission opportunity allocated to the first electronic device  110 - 1 . The first electronic device  110 - 1  can be configured to exit the low power mode at or prior to the wake-up time. In some embodiments, the electronic device  110  can set a wake-up timer based on the time that corresponds to a start of a corresponding transmission opportunity allocated to the electronic device during the subsequent contention-free period as indicated by the next slot timestamp field  314  included in the trigger frame  300 . 
     At some point between the end of the first transmission opportunity and prior to transmission of a second trigger frame  1014  during a second transmission opportunity, a second electronic device  110 - 2  wakes up and resumes listening to the communications medium. A second trigger frame  1014 , transmitted by the access point  112 , allocates a second transmission opportunity to the second electronic device  110 - 2 . The second electronic device  110 - 2  responds to the second trigger frame  1014  by transmitting a frame of station data  1024  to the access point  112 . The access point  112  then transmits an ACK frame  1034  to the second electronic device  110 - 2 , ending the second transmission opportunity. Once the second transmission opportunity is concluded, the second electronic device  110 - 1  can enter the low power mode. Prior to entering the low power mode, the second electronic device  110 - 2  can calculate a wake-up time, relative to a value of the TSF of the second electronic device  110 - 2 , corresponding to the start of the next transmission opportunity allocated to the second electronic device  110 - 2 . The second electronic device  110 - 2  can be configured to exit the low power mode at or prior to the wake-up time. 
     It will be appreciated that the first electronic device  110 - 1  and the second electronic device  110 - 2  are not configured to wake up at the same time, like in the sleep cycle for the unscheduled access mechanism as illustrated in  FIG. 9 . Consequently, the ratio of an awake period to a sleep period for each electronic device  110  can be reduced compared to the sleep cycle for the unscheduled access mechanism, thereby saving more power at the electronic device  110 . 
     In some embodiments, the electronic device  110  can be configured to enter the low power mode immediately after the ACK frame is received by the electronic device  110 , even if there is still time remaining during the current transmission opportunity. In some embodiments, the electronic device  110  can be configured to wake up prior to the start of the next allocated transmission opportunity to ensure that the electronic device  110  does not miss the start of the next trigger frame  300  targeted at the electronic device  110 . For example, the wake-up timer can be set to expire 50 microseconds ahead of the scheduled start of the next transmission opportunity. 
     In some embodiments, the slot end timestamp field  312  and the next slot timestamp field  314  include values relative to the beginning of the contention-free period  1210 . Thus, each electronic device  110  can only identify a wake-up time for a particular transmission opportunity within the current contention-free period once the start time for the contention-free period is identified. In such cases, all electronic devices  110  are configured to wake up and listen to the communications medium for a short time to identify the beginning of the contention-free period, and then all but one electronic device  110  allocated the first transmission opportunity can enter the low power mode and wait until a start of a corresponding transmission opportunity within the contention-free period. This type of operation can be important when the start of the contention-free period can be delayed while contending for access to the communications medium with other WLANs. 
       FIG. 13  illustrates a diagram  1300  of access to the communications medium by multiple WLANs, in accordance with some embodiments. As described above, at least some of the communications techniques can monopolize the communications medium over legacy contention-based access mechanisms where the delay between frames transmitted over the communications medium is too short for the contention-based access algorithms to acquire a transmission opportunity. This is an intentional choice by utilizing the SIFS (e.g., 16 microseconds) as the selected delay between frames and then immediately transmitting another frame, thereby not enabling, e.g., legacy Wi-Fi stations to reach a particular random back-off slot. However, where the communications medium is shared among multiple WLANs, some using the techniques described herein and others using legacy communications protocols, care should be taken to ensure shared access to the communications medium. 
     One technique for sharing access to the communications medium can be inherent simply based on the selection of the duration of the contention-free period and the number of transmission opportunities allocated therein. For example, if long duration contention-free periods are specified by the WLAN (e.g., 10 ms), and a small number of electronic devices  110  are connected to the WLAN (e.g., 4 devices), then each electronic device  110  can be allocated a long duration for a particular transmission opportunity (e.g., 2.5 ms). The natural effect of a long duration for each transmission opportunity is that the electronic device  110  can finish transmission very early in the transmission opportunity, allowing other WLAN stations in other WLANs to utilize the communications medium prior to the start of the next transmission opportunity within the contention-free period. For example, transmission of data between an electronic device  110  and the access point  112  could be complete in 200 microseconds, leaving 2.3 ms in the transmission opportunity to be utilized by other WLANs to transmit data over the communications medium. 
     Another technique for sharing access to the communications medium can be implemented by adjusting the duty cycle of contention-free periods associated with the WLAN to contention-based periods associated with other WLANs. As depicted in  FIG. 13 , the communications medium  1310  can be divided into time slices  1320  at a particular frequency. Each time slice  1320  can include a contention-free period  1330  that provides access to the communications medium  1310  for the WLAN. A duration of the contention-free period  1330  is less than a duration of the time slice  1320 , enabling other WLANs to access the communications medium  1310  outside of the contention-free period  1330 . 
     By way of example as depicted in  FIG. 13 , the access point  112  can be configured to divide the communications medium  1310  into time slices  1320  at a frequency of, e.g., 200 Hz. Each time slice  1320  is therefore 5 ms in duration. Within each time slice  1320 , the access point  112  can allocate resource units (e.g., transmission opportunities) to electronic devices  110  connected to the WLAN within a contention-free period  1330  having a duration of, e.g., 2 ms, leaving 3 ms of time in the time slice  1320  for other WLANs to contend for access to the communications medium. Three time slices  1320 - 1 ,  1320 - 2 , and  1320 - 3  are shown in  FIG. 13  as well as three corresponding contention-free periods  1330 - 1 ,  1330 - 2 , and  1330 - 3 . 
     In some embodiments, the access point  112  utilizes contention-based access mechanisms to get access to the communications medium  1310  from other WLANs. For example, the access point  112  can implement carrier sense techniques to determine when the communications medium  1310  is idle. The access point  112  can wait for the communications medium  1310  to be idle for a specified delay (e.g., SIFS) before beginning the contention-free period  1330 . However, once the access point  112  has acquired the communications medium  1310 , the contention-free period  1330  can allow unfettered access to the communications medium  1310  for the remainder of the contention-free period  1330  assuming transmissions continue unabated via the WLAN with minimal delays in between frames. 
       FIG. 14  presents a flow diagram  1400  illustrating an exemplary method for allocating transmission opportunities within a contention-free period defined by an access point, in accordance with some embodiments. This method can be performed by one or more components included in an access point (and, more generally, an electronic device), such as an interface circuit and/or a processing subsystem in access point  112  in  FIG. 1 . 
     At  1402 , a contention-free period is defined by the access point. In some embodiments, a processing subsystem included in the access point implements an algorithm to define a start time, an end time, and/or a duration of a contention-free period associated with a communications medium utilized for communication between a set of electronic devices connected to a WLAN. In some embodiments, the communications medium includes one or more channels associated with a 5 GHz RF spectrum. 
     At  1404 , a trigger frame is transmitted to the set of electronic devices via the communications medium. The trigger frame can be transmitted by, or in coordination with, an interface circuit included in the access point. In some embodiments, the trigger frame can be transmitted from the access point to a multicast or broadcast address associated with the WLAN. 
     At  1406 , a sequence of frames are received, via the communications medium, from at least one of the electronic devices in the ordered list of electronic devices. The sequence of frames can be transmitted by, or in coordination with, the interface circuit included in the access point. In some embodiments, the access point is configured to transmit acknowledgment frames to the electronic devices to acknowledge successful receipt of one or more frames in the sequence of frames. 
     At  1408 , at least two transmission opportunities are allocated within the contention-free period to electronic devices included in the ordered list of electronic devices. In some embodiments, the processing subsystem included in the access point is configured to implement an algorithm for determining which transmission opportunities are allocated to corresponding electronic devices. The transmission opportunities can be allocated according to an unscheduled access mechanism or, alternatively, according to a scheduled access mechanism. 
       FIG. 15  presents a flow diagram  1500  illustrating an exemplary method for reducing a power consumption associated with a wireless station, in accordance with some embodiments. This method can be performed by one or more components included in a station (and, more generally, an electronic device), such as an interface circuit and/or a processing subsystem in electronic device  110  in  FIG. 1 . 
     At  1502 , an identifier positioned first in an ordered list of electronic devices is read from a trigger frame. In some embodiments, the identifier is an AID located in an AID list field of the trigger frame. 
     At  1504 , the electronic device determines that the identifier is associated with the electronic device. In some embodiments, a processing subsystem compares the identifier to a stored identifier that uniquely identifies the device. In some embodiments, the identifier is an AID that is compatible with an 802.11 MAC address associated with the electronic device. 
     At  1506 , a frame is transmitted, via the communications medium, at a temporal position subsequent to an end of the trigger frame and associated with the first communications medium being idle for a period of time. In some embodiments, the electronic device is configured to transmit a data frame, via the interface circuit, over the communications medium after a delay period from the end of the trigger frame. The delay period can be set to a SIFS period of 16 microseconds. 
     At  1508 , a wake-up timer is set based on a time associated with a subsequent contention-free period. In some embodiments, the electronic device is configured to exit a low power mode and listen to the communications medium at the expiration of the wake-up timer. 
     At  1510 , a low power mode is entered subsequent to the transmission of the frame. In some embodiments, the low power mode can include disabling at least one of an antenna or an interface circuit communicatively coupled to the antenna. 
       FIG. 16  presents a flow diagram  1600  illustrating an exemplary method for connecting to a WLAN, in accordance with some embodiments. This method can be performed by one or more components included in a station (and, more generally, an electronic device), such as an interface circuit and/or a processing subsystem in electronic device  110  in  FIG. 1 . 
     At  1602 , an advertising packet is transmitted via a communications medium associated with a WPAN. In some embodiments, the advertising packet is transmitted over a communications medium associated with a Bluetooth Low Energy communications protocol. The communications medium can include one or more channels associated with a 2.4 GHz RF spectrum. 
     At  1604 , a packet of information associated with a WLAN is received via the communications medium associated with the WPAN. In some embodiments, the packet of information contains a BSSID as well as information identifying one or more channels associated with a separate communications medium utilized by the WLAN. The separate communications medium utilized by the WLAN can include one or more channels associated with a 5 GHz RF spectrum. 
     At  1606 , a trigger frame is received via the sepater communications medium associated with the WLAN. The trigger frame can be received after the electronic device has connected to the WLAN by at least configuring the interface circuit to listen to the one or more channels associated with the separate communications medium for any frames associated with the BSSID included in the packet of information. 
       FIG. 17  presents a block diagram of an electronic device  1700  (which can be an access point, another electronic device, such as a station or a legacy electronic device) in accordance with some embodiments. This electronic device includes processing subsystem  1710 , memory subsystem  1712 , and networking subsystem  1714 . Processing subsystem  1710  includes one or more devices configured to perform computational operations. For example, processing subsystem  1710  can include one or more microprocessors, application-specific integrated circuits (ASICs), microcontrollers, programmable-logic devices, and/or one or more digital signal processors (DSPs). 
     Memory subsystem  1712  includes one or more devices for storing data and/or instructions for processing subsystem  1710  and networking subsystem  1714 . For example, memory subsystem  1712  can include dynamic random access memory (DRAM), static random access memory (SRAM), a read-only memory (ROM), flash memory, and/or other types of memory. In some embodiments, instructions for processing subsystem  1710  in memory subsystem  1712  include: one or more program modules or sets of instructions (such as program module  1722  or operating system  1724 ), which can be executed by processing subsystem  1710 . For example, a ROM can store programs, utilities or processes to be executed in a non-volatile manner, and DRAM can provide volatile data storage, and can store instructions related to the operation of electronic device  1700 . Note that the one or more computer programs can constitute a computer-program mechanism, a computer-readable storage medium or software. Moreover, instructions in the various modules in memory subsystem  1712  can be implemented in: a high-level procedural language, an object-oriented programming language, and/or in an assembly or machine language. Furthermore, the programming language can be compiled or interpreted, e.g., configurable or configured (which can be used interchangeably in this discussion), to be executed by processing subsystem  1710 . In some embodiments, the one or more computer programs are distributed over a network-coupled computer system so that the one or more computer programs are stored and executed in a distributed manner. 
     In addition, memory subsystem  1712  can include mechanisms for controlling access to the memory. In some embodiments, memory subsystem  1712  includes a memory hierarchy that comprises one or more caches coupled to a memory in electronic device  1700 . In some of these embodiments, one or more of the caches is located in processing subsystem  1710 . 
     In some embodiments, memory subsystem  1712  is coupled to one or more high-capacity mass-storage devices (not shown). For example, memory subsystem  1712  can be coupled to a magnetic or optical drive, a solid-state drive, or another type of mass-storage device. In these embodiments, memory subsystem  1712  can be used by electronic device  1700  as fast-access storage for often-used data, while the mass-storage device is used to store less frequently used data. 
     Networking subsystem  1714  includes one or more devices configured to couple to and communicate on a wired and/or wireless network (i.e., to perform network operations), including: control logic  1716 , an interface circuit  1718  and a set of antennas  1720  (or antenna elements) in an adaptive array that can be selectively turned on and/or off by control logic  1716  to create a variety of optional antenna patterns or ‘beam patterns.’ (While  FIG. 17  includes set of antennas  1720 , in some embodiments electronic device  1700  includes one or more nodes, such as nodes  1708 , e.g., a pad, which can be coupled to set of antennas  1720 .) For example, networking subsystem  1714  can include a Bluetooth networking system, a cellular networking system (e.g., a 3G/4G/5G network such as UMTS, LTE, etc.), a universal serial bus (USB) networking system, a networking system based on the standards described in IEEE 802.11 (e.g., a WiFi® networking system), an Ethernet networking system, and/or another networking system. 
     Networking subsystem  1714  includes processors, controllers, radios/antennas, sockets/plugs, and/or other devices used for coupling to, communicating on, and handling data and events for each supported networking system. Note that mechanisms used for coupling to, communicating on, and handling data and events on the network for each network system are sometimes collectively referred to as a ‘network interface’ for the network system. Moreover, in some embodiments a ‘network’ or a ‘connection’ between the electronic devices does not yet exist. Therefore, electronic device  1700  can use the mechanisms in networking subsystem  1714  for performing simple wireless communication between the electronic devices, e.g., transmitting advertising or beacon frames and/or scanning for advertising frames transmitted by other electronic devices. 
     Within electronic device  1700 , processing subsystem  1710 , memory subsystem  1712 , and networking subsystem  1714  are coupled together using bus  1728  that facilitates data transfer between these components. Bus  1728  can include an electrical, optical, and/or electro-optical connection that the subsystems can use to communicate commands and data among one another. Although only one bus  1728  is shown for clarity, different embodiments can include a different number or configuration of electrical, optical, and/or electro-optical connections among the subsystems. 
     In some embodiments, electronic device  1700  includes a display subsystem  1726  for displaying information on a display, which can include a display driver and the display, such as a liquid-crystal display, a multi-touch touchscreen, etc. Display subsystem  1726  can be controlled by processing subsystem  1710  to display information to a user (e.g., information relating to incoming, outgoing, or an active communication session). 
     Electronic device  1700  can also include a user-input subsystem  1730  that allows a user of the electronic device  1700  to interact with electronic device  1700 . For example, user-input subsystem  1730  can take a variety of forms, such as: a button, keypad, dial, touch screen, audio input interface, visual/image capture input interface, input in the form of sensor data, etc. 
     Electronic device  1700  can be (or can be included in) any electronic device with at least one network interface. For example, electronic device  1700  can include: a cellular telephone or a smartphone, a tablet computer, a laptop computer, a notebook computer, a personal or desktop computer, a netbook computer, a media player device, an electronic book device, a MiFi® device, a smartwatch, a wearable computing device, a portable computing device, a consumer-electronic device, an access point, a router, a switch, communication equipment, test equipment, as well as any other type of electronic computing device having wireless communication capability that can include communication via one or more wireless communication protocols. 
     Although specific components are used to describe electronic device  1700 , in alternative embodiments, different components and/or subsystems can be present in electronic device  1700 . For example, electronic device  1700  can include one or more additional processing subsystems, memory subsystems, networking subsystems, and/or display subsystems. Additionally, one or more of the subsystems can be omitted in electronic device  1700 . Moreover, in some embodiments, electronic device  1700  can include one or more additional subsystems that are not shown in  FIG. 17 . Also, although separate subsystems are shown in  FIG. 17 , in some embodiments some or all of a given subsystem or component can be integrated into one or more of the other subsystems or component(s) in electronic device  1700 . For example, in some embodiments program module  1722  is included in operating system  1724  and/or control logic  1716  is included in interface circuit  1718 . 
     Moreover, the circuits and components in electronic device  1700  can be implemented using any combination of analog and/or digital circuitry, including: bipolar, PMOS and/or NMOS gates or transistors. Furthermore, signals in these embodiments can include digital signals that have approximately discrete values and/or analog signals that have continuous values. Additionally, components and circuits can be single-ended or differential, and power supplies can be unipolar or bipolar. 
     An integrated circuit (which is sometimes referred to as a ‘communication circuit’) can implement some or all of the functionality of networking subsystem  1714 . This integrated circuit can include hardware and/or software mechanisms that are used for transmitting wireless signals from electronic device  1700  and receiving signals at electronic device  1700  from other electronic devices. Aside from the mechanisms herein described, radios are generally known in the art and hence are not described in detail. In general, networking subsystem  1714  and/or the integrated circuit can include any number of radios. Note that the radios in multiple-radio embodiments function in a similar way to the described single-radio embodiments. 
     In some embodiments, networking subsystem  1714  and/or the integrated circuit include a configuration mechanism (such as one or more hardware and/or software mechanisms) that configures the radio(s) to transmit and/or receive on a given communication channel (e.g., a given carrier frequency). For example, in some embodiments, the configuration mechanism can be used to switch the radio from monitoring and/or transmitting on a given communication channel to monitoring and/or transmitting on a different communication channel. (Note that ‘monitoring’ as used herein comprises receiving signals from other electronic devices and possibly performing one or more processing operations on the received signals) 
     In some embodiments, an output of a process for designing the integrated circuit, or a portion of the integrated circuit, which includes one or more of the circuits described herein can be a computer-readable medium such as, for example, a magnetic tape or an optical or magnetic disk. The computer-readable medium can be encoded with data structures or other information describing circuitry that can be physically instantiated as the integrated circuit or the portion of the integrated circuit. Although various formats can be used for such encoding, these data structures are commonly written in: Caltech Intermediate Format (CIF), Calma GDS II Stream Format (GDSII) or Electronic Design Interchange Format (EDIF). Those of skill in the art of integrated circuit design can develop such data structures from schematic diagrams of the type detailed above and the corresponding descriptions and encode the data structures on the computer-readable medium. Those of skill in the art of integrated circuit fabrication can use such encoded data to fabricate integrated circuits that include one or more of the circuits described herein. 
     While the preceding discussion used a Wi-Fi communication protocol as an illustrative example, in other embodiments a wide variety of communication protocols and, more generally, wireless communication techniques can be used. Thus, the communication technique can be used in a variety of network interfaces. Furthermore, while some of the operations in the preceding embodiments were implemented in hardware or software, in general the operations in the preceding embodiments can be implemented in a wide variety of configurations and architectures. Therefore, some or all of the operations in the preceding embodiments can be performed in hardware, in software or both. For example, at least some of the operations in the communication technique can be implemented using program module  1722 , operating system  1724  (such as a driver for interface circuit  1718 ) or in firmware in interface circuit  1718 . Alternatively, or additionally, at least some of the operations in the communication technique can be implemented in a physical layer, such as hardware in interface circuit  1718 . In some embodiments, the communication technique is implemented, at least in part, in a MAC layer and/or in a physical layer in interface circuit  1718 . 
     Furthermore, in general, the communication technique can be used to facilitate scheduled channel access in time and/or frequency in conjunction with multi-user multiple input multiple output (MU-MIMO) and/or OFDMA. 
     It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20190927
Publication Date: 20220329
Grant Date: 20220329
Priority Date: 20180928
Inventors: BOGER, YOEL
DVORY, YANIV
BORGES, Daniel R.
SALMAN, DANNY
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W52/0219", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W74/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W74/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W76/11", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0219", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0219", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W76/11", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W74/02", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 69946753