PATENT DOCUMENT

Publication Number: US-11451966-B2
Application Number: US-202016809432-A
Country: US
Kind Code: B2

Title: Wireless access protocol with collaborative spectrum monitoring

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 manage the wireless local area network. The access point includes a processing subsystem configured to select a channel associated with a communications medium for communicating with the set of electronic devices. The processing subsystem is also configured to monitor the channel to detect interference from radio frequency sources not connected to the wireless local area network, receive channel information for at least one additional channel associated with the communications medium from the electronic devices, and configure an interface circuit of the access point to communicate with the set of electronic devices on a new channel based, at least in part, on the channel information. Each electronic device can be configured to collect the channel information and transmit the channel information to the access point for analysis.

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 
 a processing subsystem, communicatively coupled to the interface circuit, configured to cause the access point to:
 select a channel associated with a communications medium for communicating with the set of electronic devices; 
 monitor the channel to detect interference from radio frequency (RF) sources not connected to the WLAN; 
 receive channel information for at least one additional channel associated with the communications medium from one or more electronic devices in the set of electronic devices; and 
 configure the interface circuit to communicate with the set of electronic devices on a new channel of the at least one additional channel, 
 
 wherein:
 the access point communicates with the one or more electronic devices via scheduled communication during contention-free periods separated by quiet periods to share the communications medium with other WLANs; and 
 the one or more electronic devices each select a modulation and coding scheme (MCS) to use to transmit uplink data to the access point during a respective allocated transmission opportunity based on a duration of the transmission opportunity and historical information related to success or failure of previous transmissions. 
 
 
     
     
       2. The access point of  claim 1 , wherein:
 the channel information comprises a signal metric measured by a particular electronic device in the one or more electronic devices for each channel in the at least one additional channel; 
 the new channel is selected based on a comparison of the signal metric for the new channel with a corresponding signal metric for the channel; and 
 the signal metric for a particular channel is weighted based on whether the particular channel is associated with a center frequency in a range of 5.250 gigahertz (GHz) to 5.710 GHz. 
 
     
     
       3. The access point of  claim 1 , wherein the one or more electronic devices each select the MCS further based on a size of queued data to be encoded with a frame payload. 
     
     
       4. The access point of  claim 1 , wherein the one or more electronic devices each select the MCS further based on whether one or more retries with the transmission opportunity are enabled or disabled. 
     
     
       5. The access point of  claim 1 , wherein the interface circuit is configured to transmit a wireless signal to the set of electronic devices that causes each electronic device to configure a radio to operate on the new channel. 
     
     
       6. The access point of  claim 5 , wherein the wireless signal is sent via a connection established via a wireless personal area network (WPAN). 
     
     
       7. The access point of  claim 1 , wherein the processing subsystem is further configured to cause the access point to:
 transmit a wireless signal to a particular electronic device in the set of electronic devices, the wireless signal causing the particular electronic device to adjust a transmitter power of a radio used to communicate with the access point. 
 
     
     
       8. The access point of  claim 7 , wherein the particular electronic device reduces the transmitter power to reduce interference with other stations connected to one or more additional WLANs. 
     
     
       9. The access point of  claim 1 , wherein the communications medium comprises a number of channels in a 5 GHz RF spectrum, each channel in the number of channels having a center frequency between 5.170 GHz and 5.835 GHz. 
     
     
       10. The access point of  claim 1 , wherein each electronic device in the one or more electronic devices is configured to collect the channel information during a period of time subsequent to an end of a first contention-free period and prior to a start of a second contention-free period, wherein the first contention-free period and the second contention-free periods are defined by the access point and associated with a trigger-based access mechanism. 
     
     
       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 over a channel of a communications medium associated with a wireless local area network (WLAN); and 
 a processing subsystem, communicatively coupled to the interface circuit, configured to cause the electronic device to:
 receive a request from the access point to collect channel information for at least one additional channel associated with the communications medium; 
 measure a signal metric associated with each additional channel in the at least one additional channel; 
 populate the signal metric for each additional channel in the at least one additional channel into a data structure to generate the channel information; 
 select a modulation and coding scheme (MCS) to use to transmit the channel information during an allocated transmission opportunity based on a duration of the transmission opportunity and historical information related to success of failure of previous transmissions; and 
 transmit the channel information to the access point during the allocated transmission opportunity. 
 
 
     
     
       12. The electronic device of  claim 11 , wherein the processing subsystem is further configured to:
 receive information that identifies a new channel in the at least one additional channel; and 
 configure the interface circuit to communicate with the access point over the new channel. 
 
     
     
       13. The electronic device of  claim 11 , wherein the processing subsystem is further configured to:
 receive a request from the access point to reduce a transmitter power of the electronic device; and 
 configure the interface circuit to reduce a power of wireless signals transmitted via the antenna. 
 
     
     
       14. The electronic device of  claim 11 , wherein the communications medium comprises a number of channels in a 5 gigahertz (GHz) radio frequency (RF) spectrum, each channel in the number of channels having a center frequency between 5.170 GHz and 5.835 GHz. 
     
     
       15. The electronic device of  claim 11 , wherein 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 the communications medium during a contention-free period, and 
 transmit a frame at a temporal position in a sequence of frames based on the ordered list of electronic devices. 
 
     
     
       16. A method for managing a wireless local area network (WLAN), the method comprising:
 via a processing subsystem of an access point:
 monitoring a portion of a radio frequency spectrum to detect a power associated with one or more channels associated with the WLAN while the one or more channels are inactive; 
 selecting an optimum channel within the radio frequency spectrum utilized to communicate with at least one electronic device connected to the WLAN; 
 configuring an interface circuit of the access point to communicate with the at least one electronic device via the optimum channel; 
 selecting a second channel in the radio frequency spectrum based, at least in part, on channel information collected by one or more electronic devices connected to WLAN; and 
 re-configuring the interface circuit of the access point to communicate with the at least one electronic device via the second channel, 
 
 wherein:
 the access point communicates with the one or more electronic devices via scheduled communication during contention-free periods separated by quiet periods to share the communications medium with other WLANs; and 
 the one or more electronic devices each select a modulation and coding scheme (MCS) to use to transmit uplink data to the access point during a respective allocated transmission opportunity based on a duration of the transmission opportunity and historical information related to success or failure of previous transmissions. 
 
 
     
     
       17. The method of  claim 16 , the method further comprising:
 via the processing subsystem of the access point:
 causing a wireless signal to be transmitted to the at least one electronic device via a wireless personal area network (WPAN), wherein the wireless signal causes each electronic device of the at least one electronic device to configure a respective interface circuit of the electronic device to communicate with the access point via the second channel. 
 
 
     
     
       18. The method of  claim 16 , wherein the radio frequency spectrum comprises a number of channels having a center frequency in a range of frequencies between 5.170 gigahertz (GHz) and 5.835 GHz. 
     
     
       19. The method of  claim 18 , wherein the center frequency of the second channel is in a range between 5.250 GHz to 5.710 GHz. 
     
     
       20. The method of  claim 16 , wherein the channel information comprises a signal metric measured by a particular electronic device in the one or more electronic devices for each channel in the radio frequency spectrum.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 62/813,520, entitled “WIRELESS ACCESS PROTOCOL WITH COLLABORATIVE SPECTRUM MONITORING,” filed Mar. 4, 2019, the content of which is incorporated herein by reference 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 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. Usually, the WLANs are contention based because they typically utilize unlicensed frequency 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 listens to one or more communication channels to determine whether the communications medium is busy. If the communications medium is idle, then a station can attempt to transmit data to another station during a period divided into a number of backoff slots. Each station selects a random backoff slot within a contention window, as embodied by a backoff timer, and can transmit during the selected backoff slot if the communications medium remains idle until the expiration of the backoff timer. If another station transmits on the communications medium before the backoff timer has expired, then the station 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 station attempts to transmit over the communications medium, the station will attempt transmission over the communications medium. However, attempting the transmission does not ensure that another station randomly selected the same backoff slot to attempt to transmit over the communications medium, thereby causing a collision to occur. Failure of the station to receive an acknowledgment frame could indicate that a collision likely occurred, and the station will 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 stations transmitting over the communications medium. Large number of stations 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 (msecs). While these latencies are tolerable for some applications, such as requesting a web page on a device, latencies of hundreds of msecs are intolerable for real-time applications such as audio streaming, virtual reality, and gaming. 
     Contention-free multi-user transmission in uplink has been proposed for inclusion in the IEEE 802.11ax standard. This approach can dramatically change how an electronic device accesses the communications medium. In particular, an electronic device can transmit without contending for the communications medium. Instead, a primary station (e.g., an access point) controls access to the communications medium for the stations connected to the WLAN by granting transmission opportunities to each individual station using a trigger frame (which is sometimes referred to as ‘trigger-based access’ or ‘trigger-based channel access,’ e.g., 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 electronic 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 electronic devices in the WLAN. In particular, for N electronic devices sharing a 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 electronic devices can need 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 electronic devices. 
     SUMMARY 
     Some embodiments are described that relate to 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 can transmit a trigger frame including 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 can sequentially receive one or more frames from the ordered list of electronic devices via the communications medium. A processing subsystem in the access point can manage the WLAN, controlling connections of electronic devices to the WLAN and selecting optimal channels for communications based on monitoring activities that assess traffic on the channels of the communications medium. 
     In some embodiments, an access point is disclosed that manages the WLAN. The access point includes one or more nodes configured to communicatively couple to an antenna. The access point further includes an interface circuit communicatively coupled to the one or more nodes and configured to communicate with a set of electronic devices in the WLAN. The access point further includes a processing subsystem communicatively coupled to the interface circuit and configured to cause the access point to: select a channel associated with a communications medium for communicating with the set of electronic devices, monitor the channel to detect interference from radio frequency (RF) sources not connected to the WLAN, receive channel information for at least one additional channel associated with the communications medium from one or more electronic devices in the set of electronic devices, and configure the interface circuit to communicate with the set of electronic devices on a new channel of the at least one additional channel. 
     In some embodiments, the processing subsystem is further configured to cause the access point to transmit a wireless signal to a particular electronic device in the set of electronic devices. The wireless signal causes the particular electronic device to adjust a transmitter power of a radio used by the particular electronic device to communicate with the access point. The particular electronic device reduces the transmitter power to reduce interference with other stations connected to one or more additional WLANs. 
     In some embodiments, each electronic device in the one or more electronic devices is configured to collect the channel information during a period of time subsequent to an end of a first contention-free period and prior to a start of a second contention-free period. The first contention-free period and the second contention-free periods are defined by the access point and associated with a trigger-based access mechanism included in a wireless access protocol. 
     In some embodiments, the communications medium comprises a number of channels in a 5 GHz radio frequency spectrum, each channel in the number of channels having a center frequency between 5.170 GHz and 5.835 GHz. 
     In some embodiments, the channel information comprises a signal metric for each channel in the at least one additional channel. The signal metric can be measured by a particular electronic device in the one or more electronic devices. The new channel can be selected based on a comparison of the signal metric for the new channel with a corresponding signal metric for the channel. In some embodiments, the signal metric for a particular channel is weighted based on whether the particular channel is associated with a center frequency in a range of 5.250 GHz to 5.710 GHz. 
     In some embodiments, the interface circuit is configured to transmit a wireless signal to the set of electronic devices that causes the electronic devices to configure a radio to operate on the new channel. In some embodiments, the wireless signal is transmitted via the WLAN. In other embodiments, the wireless signal is transmitted via a wireless personal area network. 
     In some embodiments, an electronic device is disclosed that includes one or more nodes configured to communicatively couple to an antenna. The electronic device also includes an interface circuit communicatively coupled to the one or more nodes and configured to communicate with an access point over a channel of a communications medium associated with WLAN. The electronic device further includes a processing subsystem communicatively coupled to the interface circuit and configured to cause the electronic device to: receive a request from the access point to collect channel information for at least one additional channel associated with the communications medium, measure a signal metric associated with each additional channel in the at least one additional channel, populate the signal metric for each additional channel in the at least one additional channel into a data structure to generate the channel information, and transmit the channel information to the access point. 
     In some embodiments, the processing subsystem of the electronic device is further configured to: receive information that identifies a new channel in the at least one additional channel, and configure the interface circuit to communicate with the access point over the new channel. 
     In some embodiments, the processing subsystem is further configured to: receive a request from the access point to reduce a transmitter power of the electronic device, and configure the interface circuit to reduce a power of wireless signals transmitted via the antenna. 
     In some embodiments, the interface circuit is configured to cause the electronic device to: receive 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 the communications medium during a contention-free period, and transmit a frame at a temporal position in a sequence of frames based on the ordered list of electronic devices. 
     In some embodiments, a method for managing a WLAN is described. The method can be performed, at least in part, by the processing subsystem of an access point. The method includes the steps of: monitoring a portion of a radio frequency spectrum to detect a power associated with one or more channels associated with the WLAN while the one or more channels are inactive; selecting an optimum channel within the radio frequency spectrum utilized to communicate with at least one electronic device connected to the WLAN; and configuring an interface circuit of the access point to communicate with the at least one electronic device via the optimum channel. The method further includes the steps of selecting a second channel in the radio frequency based, at least in part, on channel information collected by one or more electronic devices connected to the WLAN, and re-configuring the interface circuit of the access point to communicate with the at least one electronic device via the second channel. 
     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 or spirit 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  is a block diagram illustrating an example of electronic devices communicating wirelessly, in accordance with some embodiments. 
         FIG. 2  illustrates a 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, in accordance with some embodiments. 
         FIG. 4  illustrates a data frame communicated between stations in the WLAN, in accordance with some embodiments. 
         FIG. 5  illustrates an acknowledgment frame communicated between stations in 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. 7A  illustrates an unscheduled access mechanism, in accordance with some embodiments. 
         FIG. 7B  illustrates an unscheduled access mechanism, in accordance with other 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. 10A  illustrates a scheduled access mechanism, in accordance with some embodiments. 
         FIG. 10B  illustrates a scheduled access mechanism, in accordance with other 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  is a chart that depicts a portion of the 5 GHz RF spectrum, in accordance with some embodiments. 
         FIG. 15  presents a flow diagram illustrating an exemplary method for monitoring a radio frequency spectrum and adjusting a mode of communication of the WLAN, in accordance with some embodiments. 
         FIG. 16  presents a flow diagram illustrating an exemplary method for collecting channel information associated with a communications medium, 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 connected to a WLAN, including electronic devices and/or access points, 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. 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 thereby 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 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 access point manages the WLAN by monitoring the radio frequency spectrum utilized by the WLAN. The access point can detect interference on the channel of the communications medium utilized by the stations communicating via the WLAN. The access point can also monitor additional channels in the radio frequency spectrum to detect a better channel than the currently selected channel and, optionally, configure the WLAN to use the better channel. 
     In some embodiments, the access point utilizes a collaborative spectrum monitoring technique that utilizes the electronic devices connected to the WLAN to monitor the radio frequency spectrum. Each electronic device can generate channel information that includes signal metrics associated with each channel of a subset of channels in the radio frequency spectrum. The channel information can be transmitted to the access point, which then analyzes the channel information to select an optimum channel to utilize for communications via the WLAN. 
     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,’ ‘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  is a block diagram  100  illustrating 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, which is sometimes referred to as a ‘primary 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 station (e.g., a primary electronic device) 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 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 sequences 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 device 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 . 
     In some embodiments, the electronic devices  110  can be referred to as controllers. As used herein, a controller is any device that is configured as a human interface device (HID). For example, a controller can be implemented as a game pad for a gaming console, similar to an Xbox wireless controller as produced by Microsoft® Corporation (in Redmond, Wash.). As another example, a controller can be implemented as a wearable device such as a band or head-mounted device. The wearable device can be configured to track a movement or location of a part of a user&#39;s body. In some embodiments, the controller can provide HID data to the access point and receive haptic (HAP) data from the access point. The HAP data can be utilized by the controller to provide feedback to a user through a haptic feedback system such as a vibrating motor or an audio transducer. 
       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 can 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 HID data to the access point  112  via the WLAN. At  226 , the access point  112  receives the one or more frames of HID 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 HID data, and, at  230 , the electronic device  110  receives the ACK frame. At  232 , the access point  112  transmits a frame of HAP data to the electronic device  110  via the WLAN, and, at  234 , the electronic device  110  receives the frame of HAP data. At  236 , the electronic device  110  transmits an ACK frame to the access point  112  via the WLAN to acknowledge receipt of the HAP data, and, at  238 , the access point  112  receives the ACK frame. 
     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 in 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 in 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. 7A  illustrates 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. 
     In other words, 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 HID 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 HID 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 . In some embodiments, the ACK frame  732  indicates the end of the first transmission opportunity  752  allocated to the first electronic device  110 - 1 . 
     However, in other embodiments, the access point  112  can be configured to extend the first transmission opportunity  752  to provide feedback information to the first electronic device  110 - 1  by sending one or more data frames to the electronic device  110 - 1 . As depicted in  FIG. 7 , the access point  112  can transmit a frame of HAP data  762  to the first electronic device  110 - 1 . In some embodiments, the frame of HAP data  762  can include control signals for a haptic feedback system included in the controller, such as a vibration device or an audio transducer. In other embodiments, the frame of HAP data  762  can include other types of feedback information. It will be appreciated that the frame of HAP data  762  can be replaced by one or more data frames  400  including any generic information transmitted from the access point  112  to the electronic device  110 . After receiving the frame of HAP data  762 , the first electronic device  110 - 1  responds by transmitting an ACK frame  734  to the access point  112 , thereby indicating the end of the first transmission opportunity  752  allocated to the first electronic device  110 - 1 . 
     After a delay (e.g., SIFS) and at the start of a second transmission opportunity  754 , 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 HID data  724  to the access point  112  after a specified delay. Upon receiving the frame of HID data  724  and after a delay (e.g., SIFS), the access point  112  transmits an ACK frame  736  to the second electronic device  110 - 2 . In some embodiments, the ACK frame  736  indicates the end of the second transmission opportunity  754  allocated to the second electronic device  110 - 2 . In other embodiments, the access point  112  transmits a frame of HAP data  764  to the second electronic device  110 - 2 , and the second electronic device  110 - 2  transmits a corresponding ACK frame  738  to the access point  112 . The ACK frame  738  indicates the end of the second transmission opportunity  754  allocated to the second electronic device  110 - 2 . 
     The access point  112  can continue sending trigger frames and receiving frames of HID 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 HID 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. 7B  illustrates an unscheduled access mechanism, in accordance with other embodiments. Unlike in the unscheduled access mechanism of  FIG. 7A , the unscheduled access mechanism of  FIG. 7B  transmits a frame of bulk HAP data  772  to a number of electronic devices  110  at the end of the contention-free period. Consequently, the transmission opportunities are merely utilized for the electronic devices  110  to transmit frames of HID data  722 ,  724 , etc. to the access point  112 . The feedback information included in the various frames of HAP data  762 ,  764 , etc. transmitted to the corresponding electronic devices  110  can be queued and broadcast or multicast to a number of electronic devices  110  at the end of the contention-free period in the frame of bulk HAP data  772  rather than sending multiple frames of HAP data  762 ,  764 , etc. targeted to particular electronic devices  110  to each of the corresponding electronic devices  110 . It will be appreciated that each of the electronic devices  110  does not need to transmit an ACK frame to the access point  112  when bulk HAP data is transmitted in a broadcast or multicast data frame at the end of the contention-free period. 
     In other embodiments, bulk HAP data can be transmitted to a number of electronic devices  110  every M transmission opportunities. For example, the access point  112  allocates four transmission opportunities to four electronic devices  110  and multicasts or broadcasts a frame of HAP data associated with the four electronic devices  110 . Then, the access point  112  allocates four additional transmission opportunities to four additional electronic devices  110  and multicasts or broadcasts another frame of HAP data associated with the four additional electronic devices  110 . Consequently, multiple frames of bulk HAP data  772  can be transmitted by the access point  112  during a contention-free period, each frame of bulk HAP data directed to a different subset of electronic devices  110 . 
       FIG. 8  illustrates an unscheduled access mechanism with retries, in accordance with some embodiments. In some cases, a particular electronic device  110  can fail to send HID data to the access point  112  in response to a trigger frame. In other 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 HID data to the access point  112 ; however, the access point  112  can fail to receive the HID 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 HID 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 HID data from the electronic device (as illustrated during the first transmission opportunity  752  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 HID data from the electronic device (as illustrated during the second transmission opportunity  754  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 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 controllers 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 transmitted by the access point  112  includes an AID list field  320  indicating the electronic devices  110  that will be allocated a transmission opportunity during the contention-free period, if sufficient resource units are available. The trigger frames 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, 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 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. 
     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 HID data  722  to the access point  112 . The access point  112  then transmits an ACK frame  732  to the first electronic device  110 - 1  followed by a frame of HAP data  762 . The first electronic device  110 - 1  then sends a corresponding ACK frame  734  to the access point  112 , thereby 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  remain awake during the first transmission opportunity to await the next trigger frame. 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 HID data  724  to the access point  112 . The access point  112  then transmits an ACK frame  736  to the second electronic device  110 - 2  followed by a frame of HAP data  764 . The second electronic device  110 - 2  then sends a corresponding ACK frame  738  to the access point  112 , thereby 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  similarly enters a low power mode subsequent to the conclusion of a corresponding transmission opportunity allocated to the third electronic device  110 - 3 . 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 , and  110 - 3 ; during a second contention-free period, the order of electronic devices  110  can be selected as  110 - 2 ,  110 - 3 , and  110 - 1 ; and during a third contention-free period, the order of electronic devices  110  can be selected as  110 - 3 ,  110 - 1 , and  110 - 2 . 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 contention-free period. 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. 10A  illustrates 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 HID 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 HID data  1022  to the access point  112  after a specified delay. Upon receiving the frame of HID 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 . Following the ACK frame  1032  and after a delay, the access point  112  transmits a frame of HAP data  1062  to the first electronic device  110 - 1 . The first electronic device  110 - 1  then transmits an ACK frame  1034  to the access point  112 . Unlike in the unscheduled access mechanism, described above, the ACK frame  1034  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 communications between the first electronic device  110 - 1  and the access point  112  are complete, 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 HID data  1024  to the access point  112  after a specified delay. Upon receiving the frame of HID data  1024  and after the delay (e.g., SIFS), the access point  112  transmits an ACK frame  1036  to the second electronic device  110 - 2 . Following the ACK frame  1036  and after a delay, the access point  112  transmits a frame of HAP data  1064  to the second electronic device  110 - 2 . The second electronic device  110 - 2  then transmits an ACK frame  1038  to the access point  112 . Again, the access point  112  waits until the start of 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 frames. 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. 
       FIG. 10B  illustrates a scheduled access mechanism, in accordance with other embodiments. Unlike in the scheduled access mechanism of  FIG. 10A , the scheduled access mechanism of  FIG. 10B  transmits a frame of bulk HAP data  1072  to a number of electronic devices  110  at the end of the contention-free period. Consequently, the transmission opportunities are merely utilized for the electronic devices to transmit frames of HID data  1022 ,  1024 , etc. to the access point  112 . The feedback information included in the various frames of HAP data  1062 ,  1064 , etc. transmitted to the corresponding electronic devices  110  can be queued and broadcast or multicast to a number of electronic devices  110  at the end of the contention-free period in the frame of bulk HAP data  1072 . It will be appreciated that each of the electronic devices  110  does not need to transmit an ACK frame to the access point  112  when bulk HAP data is transmitted in a broadcast or multicast data frame at the end of the contention-free period. 
     In some embodiments, the electronic device  110  can adjust the payload included in the frame of HID 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 and a frame of HAP data 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 HID 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 HID 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 HID 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 HID 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  1034  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 the required data. 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/or receive data, 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 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 HID 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 HID data from the electronic device, 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 HID data from the electronic device, 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. 
     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 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. 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 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 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 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 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 targeted at the electronic device  110 . That trigger frame 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 HID data  1022  to the access point  112 . The access point  112  then transmits an ACK frame  1032  to the first electronic device  110 - 1  followed by a frame of HAP data  1062 . The first electronic device  110 - 1  then transmits an ACK frame  1034  to the access point  112 . Once all of the data has been transmitted and received during the transmission opportunity, 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. 
     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 HID data  1024  to the access point  112 . The access point  112  then transmits an ACK frame  1036  to the second electronic device  110 - 2  followed by a frame of HAP data  1064 . The second electronic device  110 - 2  then transmits an ACK frame  1038  to the access point  112  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 in response to the frame of HAP data is transmitted to the access point  112  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 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. 
     Nevertheless, it will be appreciated that utilization of these communications techniques can negatively affect other wireless communications protocols contending for the same channels. Therefore, in some embodiments, the access point  112  is configured to exhibit “good neighbor” behavior that attempts to reduce interference with other wireless communications. 
       FIG. 14  is a chart  1400  that depicts a portion of the 5 GHz RF spectrum, in accordance with some embodiments. The 5 GHz RF spectrum has been reserved for unlicensed use by, e.g., personal wireless communications systems such as wireless antennas associated with the stations of the WLAN. The 5 GHz RF spectrum is divided into a number of channels having center frequencies spaced 5 MHz apart. The WLAN can operate on one or more channels within the 5 GHz RF spectrum. 
     As depicted in  FIG. 14 , the 5 GHz RF spectrum is divided into a number of channels. Four distinct ranges of frequencies within the 5 GHz RF spectrum can be referred to as part of the Unlicensed National Information Infrastructure (U-NII) radio band. U-NII-1 operates on frequencies between 5.170 and 5.250 GHz; U-NII-2 operates on frequencies between 5.250 GHz and 5.330 GHz; U-NII-2-Extended operates on frequencies between 5.490 GHz and 5.710 GHz; and U-NII-3 operates on frequencies between 5.735 GHz and 5.815 GHz. Each of the channels is 20 MHz, 40 MHz, or 80 MHz wide and is centered on a center frequency associated with the channel number. For example, U-NII-1 includes four 20 MHz wide channels: Channel 36, Channel 40, Channel 44, and Channel 48. U-MI-1 also includes two 40 MHz wide channels: Channel 38 and Channel 46. Furthermore, U-NII-1 includes one 80 MHz wide channel: Channel 42. 
     In some embodiments, the access point  112  is configured to select an optimum channel for communication between stations connected to the WLAN. During setup, the access point  112  can monitor the RF spectrum in order to determine the optimum channel. For example, in some embodiments, the access point  112  configures a radio  114  for a particular channel. The access point  112  then measures a power associated with that channel over a period of time, generating a signal metric for the channel. In some embodiments, the signal metric is a received signal strength metric. In other embodiments, the signal metric is a noise metric. 
     The access point  112  can re-configure the radio  114  to receive signals on a different channel and to measure a power associated with that channel. After a period of time, the access point  112  collects the signal metric for a subset of channels within the 5 GHz RF spectrum and determines which channel is an optimum channel based on criteria. The criteria can be based, at least in part, on the collection of signal metrics collected for the one or more channels. In some embodiments, the access point  112  selects a channel with a minimum received signal strength metric value as the optimum channel. It will be appreciated that a low received signal strength metric value indicates that the channel is likely to exhibit less interference from RF sources external to the WLAN compared to other channels. 
     For example, the access point  112  can measure the power associated with each channel and determine that Channel  104  is the optimum channel. The access point  112  then configures the radio  114  to use Channel  104 . As the access point  112  receives requests to connect to the WLAN from one or more electronic devices  110 , the access point  112  transmits P2P information to the electronic devices  110  that includes information that indicates the WLAN is configured to use Channel  104 . 
     In some embodiments, the access point  112  selects the optimum channel based on a combination of multiple criteria. For example, the access point  112  can select an optimum channel based, at least in part, on a number of electronic devices  110  connected to the WLAN. The access point  112  can select a 40 MHz wide or an 80 MHz wide channel instead of a 20 MHz channel based on the number of electronic devices  110  connected to the WLAN. In some embodiments, a weight can be applied to the collection of signal metrics for the channels, where the weight applied to a particular signal metric is based on the number of electronic devices  110  connected to the WLAN and a width of the channel (e.g., 20 MHz, 40 MHz, 80 MHz, etc.). 
     In some embodiments, the access point  112  monitors the selected channel utilized by the WLAN periodically. For example, the access point  112  can be configured to scan the channels in the 5 GHz RF spectrum during the contention-period while the WLAN is idle in between contention-free periods. The access point  112  is configured to detect neighboring networks and other RF sources that interfere with the communications of the WLAN on the selected channel. In some embodiments, if the amount of interference on the selected channel is above a threshold value, as indicated by comparing the signal metric value to a threshold value, then the access point  112  determines if there is a better channel available and re-configures the WLAN to use the better channel. A better channel can be defined as a channel having a lower signal metric value that indicates that there is less interference on that channel compared to a signal metric value for the selected channel. 
     In some embodiments, the access point  112  is configured to utilize one or more electronic devices  110  connected to the WLAN to assist with the detection, which can be referred to as collaborative spectrum monitoring. It will be appreciated that the RF interference in one location will be different than the RF interference in another location. Even though RF interference on a particular channel is high as measured by the access point  112 , the RF interference on that particular channel can be lower for one or more of the electronic devices  110  located in a different location. Similarly, even though the RF interference on a different channel can be low as measured by the access point  112 , the RF interference on that different channel can be high at one or more electronic devices  110 . 
     The access point  112  can request each of one or more electronic devices  110  connected to the WLAN to collect channel information for a number of channels. The channel information can include signal metric values for a number of channels as measured by the electronic device  110 . The electronic devices  110  can transmit the collected channel information to the access point  112 , which aggregates the collected channel information from one or more electronic devices  110  as well as channel information collected by the access point  112 . In some embodiments, the access point  112  can calculate a mean signal metric value for each of a plurality of channels. In other words, the access point  112  can calculate a mean value measured by different devices for a particular signal metric for a channel as the aggregate signal metric value for the channel. The aggregate signal metric values can then be used when determining whether to switch channels. This collaborative spectrum monitoring algorithm attempts to select an optimum channel for all devices connected to the WLAN rather than simply the optimum channel for the access point  112 . 
     In other embodiments, the access point  112  can perform a statistical analysis of the channel information collected from multiple sources when selecting the new channel. For example, the access point  112  can determine the variance associated with a plurality of data points for a given signal metric from a plurality of electronic devices  110 . The statistical values can be utilized in a calculation to determine the optimum channel. 
     In some embodiments, the access point  112  is configured to prioritize the use of radar channels for the WLAN. The radar channels are those channels in the U-NII-2 and U-NII-2-Extended radio bands (e.g., 5.250 GHz-5.710 GHz). These channels can be referred to as Dynamic Frequency Selection (DFS) channels because regulations require transmitters on these channels to monitor the channel for interference and switch channels to avoid interference with radar systems that also use these channels. In some embodiments, the access point  112  can multiply the signal metric values by a weight in order to prioritize selection of the DFS channels over channels outside these radio bands. In other embodiments, the access point  112  can select a channel in the radar channels over another channel as the optimum channel when the difference between the signal metric values is below a threshold value. In other words, if the interference on a channel outside the radar channels is less than the interference on a radar channel, but only by a marginal amount less than a threshold value, then the access point  112  can select the radar channel over the non-radar channel. It will be appreciated that the radar channel may not be selected in certain cases in order to adhere to regulations that govern these channels. 
     In some embodiments, the access point  112  can also implement a closed loop transmission power control algorithm. In some cases, an electronic device  110  may be located in close proximity to the access point  112 . In such cases, the received signal strength of wireless signals transmitted from that electronic device  110  to the access point  112  can be very strong and be associated with a high signal-to-noise ratio (SNR). The power of the transmitter in the electronic device  110  can be reduced so that the transmitted signals do not interfere with other RF antennas within range of the electronic device  110 . 
     In some embodiments, the access point  112  is configured to periodically transmit a control frame to the electronic device  110  that causes the electronic device  110  to adjust a power associated with the transmitted signals generated by the radio  114  of the electronic device  110 . The access point  112  can measure the SNR of a wireless signal received from the electronic device  110 , and adjust a target transmitter power value associated with the electronic device  110  based on the measured SNR. The target transmitter power is adjusted using a closed loop control algorithm to make the measured SNR track a target SNR. In other embodiments, the access point  112  is configured to adjust the transmit power of the electronic device  110  using other control schemes, which can be based on other measured metrics. For example, the access point  112  can adjust the transmitter power of electronic devices  110  to attempt to normalize the received signal strength from two or more electronic devices  110  rather than track a target SNR. In some embodiments, the access point  112  only negotiates reduced transmitter power responsive to detecting interference above a threshold level (e.g., as measured by SNR or some other noise metric). In other words, the electronic devices  110  can transmit at full power while the channel is uncongested. However, once the access point  112  detects interference on the channel, the access point  112  can instruct one or more electronic devices  110  to decrease a power of their corresponding transmitters in order to attempt to reduce interference from those electronic devices  110  with other RF devices. 
     The above techniques are useful in reducing a disruption caused by the WLAN on other WLANs or other RF devices in proximity to the access point  112  and/or the electronic device  110 . 
       FIG. 15  presents a flow diagram  1500  illustrating an exemplary method for monitoring a radio frequency spectrum and adjusting a mode of communication of the WLAN, 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  1502 , a channel is selected for communicating with a set of electronic devices. In some embodiments, a processing subsystem of the access point is configured to cause the access point to select an optimum channel based on signal metrics measured for that channel as well as one or more additional channels. The processing subsystem can configure an interface circuit of the access point, which is communicatively coupled to one or more nodes coupled to an antenna, to communicate (e.g., transmit and/or receive) on the selected channel. In some embodiments, the channel is a channel in a 5 GHz RF spectrum having a center frequency between 5.170 GHz and 5.835 GHz. 
     At  1504 , the channel is monitored to detect interference from radio frequency sources not connected to the WLAN. In some embodiments, the access point monitors the channel by measuring a power associated with the channel during a contention period where the WLAN is idle. The processing subsystem can analyze wireless signals to calculate a signal metric for the channel. The signal metric can be compared against a threshold value to detect a level of the interference. 
     At  1506 , channel information for at least one additional channel associated with the communications medium is received from one or more electronic devices. Each electronic device in a set of electronic devices can perform monitoring operations to measure wireless signals on the additional channels and calculate signal metrics associated with those channels. The electronic devices then transmit the channel information to the access point. 
     At  1508 , the interface circuit of the access point is configured to communicate with the set of electronic devices on a new channel of the at least one additional channel. In some embodiments, the access point analyzes the channel information to select an optimum channel from the at least one additional channel that is better than the current channel used for communications within the WLAN. 
       FIG. 16  presents a flow diagram  1600  illustrating an exemplary method for collecting channel information associated with a communications medium, 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 , a request is received from the access point to collect channel information for at least one additional channel associated with the communications medium. In some embodiments, the request can be communicated via the WLAN in a control frame. For example, a flag can be set in a control frame, such as a trigger frame, that causes the electronic device to monitor the RF spectrum and report channel information to the access point. In other embodiments, the request can be received via a WPAN. 
     At  1604 , a signal metric is measured for each channel in the at least one additional channel. In some embodiments, the signal metric can be a received signal strength metric. In other embodiments, the signal metric can be a noise metric that measures a power of the wireless signal on the channel while the channel is idle during a contention period. 
     At  1606 , the signal metric for each additional channel is populated into a data structure to generate the channel information. The electronic device can store the data structure in a memory subsystem and update the data structure over a period of time for a number of channels in the at least one additional channel. 
     At  1608 , the channel information is transmitted to the access point. In some embodiments, the electronic device transmits the channel information to the access point in a data frame via the WLAN. In other embodiments, the channel information is transmitted to the access point via a WPAN. 
       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 orthogonal frequency-division multiple access (OFDMA). 
     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: 20200304
Publication Date: 20220920
Grant Date: 20220920
Priority Date: 20190304
Inventors: BORGES, Daniel R.
HAKIM, JOSEPH
Hariharan, Sriram
BOGER, YOEL
WANG, XIAOWEN
DVORY, YANIV
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W72/541", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/541", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/345", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W16/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/24", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W88/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/243", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W88/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W16/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W16/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W16/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W88/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/082", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W88/06", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 72335862