Patent Publication Number: US-2022225162-A1

Title: Switching Scheme for Opting In and Out of Multi-User Orthogonal Frequency-Division Multiple Access

Description:
RELATED APPLICATION(S) 
     This application is a divisional of and claims priority to U.S. patent application Ser. No. 16/713,956, filed on Dec. 13, 2019, the disclosure of which is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     The Wi-Fi Alliance (WFA) has developed a new standard called 802.11ax, which boosts Wi-Fi performance by implementing several schemes including multi-user orthogonal frequency-division multiple access (MU-OFDMA). In MU-OFDMA, channel bandwidth is shared among multiple users in both uplink and downlink transmissions. To achieve a target high efficiency, an 802.11ax access point aims to maximize the time used by devices in MU-OFDMA over the time used by the devices in a single-user (SU) mode. This target high efficiency is achieved by the access point forcing the devices to be less competitive in the medium contention window and wait for triggers sent by the access point by using a more-relaxed set of Enhanced Multimedia Distributed Control Access (EDCA) parameters relative to those used by the access point. 
     For example, the access point sends to an flax device (e.g., a device configured for 802.11ax), a MU-EDCA Parameter Set information element in management frames including beacon, probe response, associate response, and re-associate response. This information element includes a new set of values of EDCA (e.g., Arbitration Inter-Frame Spacing Number (AIFSN), Exponent form of Minimum Contention Window (ECWmin), and Exponent form of Maximum Contention Window (ECWmax)) for each access category. Those values are more relaxed than the initial set passed in the EDCA Parameter Set element. The MU-EDCA Parameter Set information element also includes a timer value for how long these parameters take effect (e.g., MU-EDCA Timer). 
     The 11ax device participating in MU-OFDMA would have to wait for triggers from the access point and abide by a scheduling algorithm in the access point for transmitting uplink traffic (e.g., uplink data and control signals). However, a legacy device would contend more aggressively to obtain the channel and would get full access to the bandwidth of the channel for its transmission. This makes the 11ax device participating in MU-OFDMA more inferior to legacy devices in high-traffic load scenarios. 
     SUMMARY 
     This summary is provided to introduce simplified concepts of a switching scheme for opting in and out of multi-user orthogonal frequency-division multiple access (MU-OFDMA). In one example, an electronic device can opt out of an MU-OFDMA mode (“multi-user mode”) when uplink traffic is high (e.g., above a threshold), which allows the electronic device to enter a single-user mode to maximize throughput by transmitting its uplink data without sharing channel bandwidth with other devices and without access restrictions mandated by the access point. In another example, the electronic device can opt out of the MU-OFDMA mode if low-latency requirements are critical, such as for an online gaming application, and if the access point is not responsive enough to meet those requirements. In yet another example, the electronic device can opt out of the MU-OFDMA mode based on Basic Service Set (BSS) metrics, such as if the electronic device estimates, based on a signal-strength measurement of a transmit channel, that the transmit channel can handle more data than the access point is allowing the electronic device to transmit under the multi-user mode. Opting out of the multi-user mode enables the electronic device to enter the single-user mode and contend for the transmit channel without any restrictions mandated by the access point. 
     The simplified concepts are further described below in the Detailed Description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The details of one or more aspects of a switching scheme for opting in and out of MU-OFDMA are described below. The use of the same reference numbers in different instances in the description and the figures indicate similar elements: 
         FIG. 1  illustrates an example environment, which includes one or more electronic devices and a Wi-Fi access point. 
         FIG. 2  illustrates an example device diagram of an access point and an electronic device in more detail. 
         FIG. 3  depicts an example method for opting in and out of MU-OFDMA when uplink traffic is high. 
         FIG. 4  depicts an example method for opting out of MU-OFDMA to honor low-latency Quality-of-Service (QoS) requirements. 
         FIG. 5  depicts an example method for opting out of MU-OFDMA based on Basic Service Set (BSS) metrics. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     This document describes methods, devices, systems, and means for a switching scheme for opting in and out of multi-user orthogonal frequency-division multiple access (MU-OFDMA). Conventional techniques used to achieve high efficiency and utilization of MU-OFDMA cause 11ax electronic devices (e.g., devices configured for 802.11ax) participating in MU-OFDMA to be inferior to legacy devices in heavy-traffic load scenarios because the 11ax devices are forced to be less competitive in the medium contention window and wait for triggers sent by the access point(s). Techniques are described to balance between preserving high efficiency in low-traffic (non-critical latency) scenarios for overall Basic Service Set (BSS) efficiency and being as aggressive in contention when data load or latency requirements are critical. Thus, the techniques described herein are directed to a switching scheme for opting in and out of MU-OFDMA. 
     In one aspect, a method for opting in or out of an MU-OFDMA mode is disclosed. The method includes an electronic device entering the MU-OFDMA mode to communicate via a wireless network over a shared-channel bandwidth. In addition, the method includes, during the MU-OFDMA mode, determining that an uplink-queue size is greater than a first threshold size. The method also includes, responsive to the determining, opting out of the MU-OFDMA mode and entering a single-user mode to contend for a transmit channel for transmitting uplink data. 
     In another aspect, an electronic device is disclosed. The electronic device includes a memory and processor system configured to execute instructions stored in the memory to implement an access-mode manager application configured to manage transmission and reception of signals over a wireless network according to an MU-OFDMA mode. The access-mode manager application is also configured to enter a low-latency mode for transmission of uplink data for an application. In addition, the access-mode manager application is configured to, during the MU-OFDMA mode and the low-latency mode of the electronic device, monitor a frequency at which triggers are received from an access point on the wireless network to determine whether to continue using the MU-OFDMA mode or to opt out of the MU-OFDMA mode. 
     In another aspect, a method for opting out of an MU-OFDMA mode is disclosed. The method is performed by an electronic device and includes, when connected to a wireless network using the MU-OFDMA mode, indicating to an access point of the wireless network that the electronic device has uplink data to transmit. The method also includes receiving one or more triggers from the access point for transmitting the uplink data, the one or more triggers including a mandated modulation and coding scheme (MCS). In addition, the method includes performing a clear channel assessment (CCA) of a transmit channel, measuring a signal strength of the transmit channel, estimating an MCS based on the measured signal strength, and comparing a first data rate associated with the estimated MCS to a second data rate associated with the mandated MCS to determine whether to opt out of the MU-OFDMA mode. 
     Example Environment 
       FIG. 1  illustrates an example environment  100 , which includes one or more electronic devices  110  and a Wi-Fi access point  120 . Each of these devices may be wireless-network-enabled and capable of communicating data, packets, and/or frames over a wireless link  130 . The wireless link  130  may include any suitable type of wireless communication link or wireless network connection. For example, the wireless link  130  may be implemented in whole or in part as a wireless local-area-network (WLAN), ad-hoc WLAN (e.g., a direct wireless link), wireless mesh network, near-field communication (NFC) link, wireless personal-area-network (WPAN), wireless wide-area-network (WWAN), or short-range wireless network. The wireless link  130  may be implemented in accordance with any suitable communication protocol or Institute of Electrical and Electronics Engineers (IEEE) standard, such as IEEE 802.11-2012, IEEE 802.11-2016, IEEE 802.11ac, IEEE 802.11ad, IEEE 802.11ah, IEEE 802.11ax, and the like. By using IEEE 802.11ax, the electronic device  110  can operate in radio bands between, and including, 1 and 6 GHz, such as 2.4 GHz, 5 GHz, and 6 GHz radio bands. 
     In this example, the access point  120  is implemented to provide and manage a wireless network that includes the wireless link  130 . The wireless links  130  may be implemented with any suitable modulation and coding scheme (MCS), such as orthogonal frequency division multiplexing access (OFDMA). In other cases, the access point  120  may include or be embodied as a host device, enhanced node base station, wireless router, broadband router, modem device, drone controller, vehicle-based network device, or other network administration node or device. Using IEEE 802.11ax, the access point  120  may provide multiple Wi-Fi networks, a 2.4 GHz Wi-Fi network (“AP2G”), a 5 GHz Wi-Fi network (“AP5G”), and/or a 6 GHz Wi-Fi network (“AP6G”). The electronic device  110  may detect both Wi-Fi networks using a multi-user (MU) OFDMA mode. The electronic device may also have Multiple Input Multiple Output (MIMO) capabilities. 
     The electronic device(s)  110  operate as stations in the wireless network provided by the access point  120 . The electronic device  110  may include a smart-phone, set-top box, tablet computer, a wireless speaker, a wireless smart-speaker, a camera, a wearable device, a wireless printer, a mobile station, a laptop computer, a medical device, a security system, a drone, an Internet-of-Things (IoT) device, a gaming device, a smart appliance, an Internet-protocol enabled television (IP TV), a personal media device, a navigation device, a mobile-internet device (MID), a network-attached-storage (NAS) drive, a mobile gaming console, and so on. 
     Generally, the access point  120  provides connectivity to the Internet, other networks, or network-resources through a backhaul link (not shown), which may be either wired or wireless (e.g., a T1 line, fiber optic link, broadband cable network, intranet, a wireless-wide-area network). The backhaul link may include or connect with data networks operated by an internet service provider, such as a digital subscriber line or broadband cable provider, and may interface with the access point  120  via an appropriately configured modem (not shown). While associated with the wireless network provided by the access point  120  (e.g., via the wireless links  130 ), the electronic device(s)  110  may access the Internet, exchange data with each other, or access other networks for which the access point  120  acts as a gateway. 
     Example Devices 
       FIG. 2  illustrates an example device diagram  200  of an access point and an electronic device in more detail. In aspects, the device diagram  200  describes devices that can implement various aspects of a switching scheme for opting in and out of MU-OFDMA. The electronic device(s)  110  operates as a station (STA) in the wireless network provided by the access point  120 . As a station, the electronic device  110  includes one or more antennas  202  and one or more transceivers  204  for communicating with the access point  120  or other wirelessly-enabled devices. The transceivers  204  may include any suitable number of respective communication paths (e.g., transmit or receive chains) to support transmission or reception of multiple spatial streams of data. Front-end circuitry (not shown) of the electronic device(s)  110  may couple or connect the transceiver  204  to the antennas  202  to facilitate various types of wireless communication. The antennas  202  may include an array of multiple antennas that are configured similar to or differently from each other. 
     The electronic device(s)  110  also includes processor(s)  206  and memory  208  (computer-readable storage media  208 , CRM  208 ). The processor(s)  206  may be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. The computer-readable storage media described herein excludes propagating signals. CRM  208  may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data  210  of the electronic device(s)  110 . The device data  210  includes user data, multimedia data, applications, and/or an operating system of the electronic device(s)  110  that are executable by processor(s)  206  to enable wireless communication and user interaction with the electronic device(s)  110 . In the context of the disclosure, the CRM  208  is implemented as storage media, and thus does not include transitory signals or carrier waves. 
     CRM  208  also includes an access-mode manager  212  (e.g., access-mode manager application  212 ). Alternately or additionally, the access-mode manager  212  may be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the electronic device(s)  110 . In at least some aspects, the access-mode manager  212  configures the transceiver(s)  204  to implement the techniques described herein for a switching scheme for opting in and out of MU-OFDMA. 
     The access point  120  includes one or more antennas  252  and one or more transceivers  254  for communicating with the electronic device(s)  110  or other wirelessly-enabled devices. The transceivers  254  may include any suitable number of respective communication paths (e.g., transmit or receive chains) to support transmission or reception of multiple spatial streams of data. Front-end circuitry (not shown) of the access point  120  may couple or connect the transceiver  254  to the antennas  252  to facilitate various types of wireless communication. The antennas  252  may include an array of multiple antennas that are configured similar to or different from each other. 
     The access point  120  also includes processor(s)  256  and memory  258  (computer-readable storage media  258 , CRM  258 ). The processor(s)  256  may be a single-core processor or a multiple-core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. The computer-readable storage media described herein excludes propagating signals. CRM  258  may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data  260  of the access point  120 . The device data  260  includes applications, and/or an operating system of the access point  120  that are executable by processor(s)  256  to enable wireless communication with the electronic device(s)  110 . In the context of the disclosure, the CRM  258  is implemented as storage media, and thus does not include transitory signals or carrier waves. 
     CRM  258  also includes an access point manager  262  (access point manager application  262 ). Alternately or additionally, the access point manager  262  may be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the access point  120 . In at least some aspects, the access point manager  262  configures the transceiver(s)  254  to implement the techniques described herein for a switching scheme for opting in and out of MU-OFDMA. The access point manager  262  also configures a network interface  264  to relay communications between the electronic device(s)  110 , the access point  120 , and an external network. 
     Example Methods 
     Example methods  300 ,  400 , and  500  are described with reference to  FIGS. 3-5 , respectively, in accordance with one or more aspects of a switching scheme for opting in and out of MU-OFDMA. The order in which the method blocks of methods  300 ,  400 , and  500  are described is not intended to be construed as a limitation, and any number of the described method blocks can be skipped, repeated, or combined in any order to implement a method or an alternate method. Generally, any of the components, modules, methods, and operations described herein can be implemented using software, firmware, hardware (e.g., fixed logic circuitry), manual processing, or any combination thereof. Some operations of the example methods may be described in the general context of executable instructions stored on computer-readable storage memory that is local and/or remote to a computer processing system, and implementations can include software applications, programs, functions, and the like. Alternatively or in addition, any of the functionality described herein can be performed, at least in part, by one or more hardware logic components, such as, and without limitation, Field-programmable Gate Arrays (FPGAs), Application-specific Integrated Circuits (ASICs), Application-specific Standard Products (ASSPs), System-on-a-chip systems (SoCs), Complex Programmable Logic Devices (CPLDs), and the like. 
       FIG. 3  depicts an example method  300  for opting in and out of MU-OFDMA when uplink traffic is high. During periods of high uplink traffic, it may be more efficient for the electronic device  110  to opt out of MU-OFDMA rather than sharing the bandwidth of a transmit channel with other devices. At  302 , an electronic device enters an MU-OFDMA mode for communicating with an access point via a wireless network over a shared-channel bandwidth. For example, an electronic device (e.g., the electronic device  110 ) transmits an Operation Mode Indication (OMI) to an access point (e.g., the access point  120 ) to request initiation of the MU-OFDMA mode. The access point controls and synchronizes uplink transmissions of multiple electronic devices in the MU-OFDMA mode to enable simultaneous multiple-user transmissions to occur. 
     At  304 , the electronic device initiates a timer T 1  (e.g., a first timer T 1 ). The timer T 1  may be any suitable timing mechanism and may be set to any suitable length of time, such as approximately 500 milliseconds (ms). The timer T 1  is used to provide a minimum amount of time in which the electronic device  110  remains in the MU-OFDMA mode before switching to a different mode, such as the single-user mode. 
     At  306 , the electronic device  110  determines if an uplink (UL) queue size is greater than a first threshold size TH- 1  for the uplink queue. The uplink-queue size may provide an indication of high or low uplink traffic. An example threshold size may include a threshold size substantially equal to a size of a transmit channel, approximately two megabytes (MB) of data, or any other suitable size. In one implementation, the electronic device  110  uses the first threshold size TH- 1  to determine if the uplink data is sufficient to fill the entire transmit channel. If the channel can be filled by the uplink data, then no efficiency is lost by not sharing bandwidth of the transmit channel according to the multi-user mode. 
     If the uplink-queue size is not greater than the first threshold size TH- 1  (e.g., “NO” at  306 ), then the electronic device  110  continues to monitor the size of the uplink queue. If the uplink-queue size is greater than the first threshold size TH- 1  (“YES” at  306 ), then at  308  the electronic device determines if the timer T 1  is expired. If the timer T 1  is not yet expired (“NO” at  308 ), then the electronic device  110  continues to monitor the uplink-queue size relative to the first threshold size TH- 1  at  306 . The timer T 1  prevents the electronic device  110  from opting out of the MU-OFDMA mode too quickly after entering the MU-OFDMA mode. 
     If the timer T 1  is expired (“YES” at  308 ), then at  310  the electronic device  110  opts out of the MU-OFDMA mode. Opting out of the multi-user mode enables the electronic device  110  to not be limited to requirements of the access point under the multi-user mode. In an example, the electronic device  110  can send an OMI signal to the access point  120  to indicate that the electronic device is selecting to exit the MU-OFDMA mode and contend for the transmit channel in a single-user mode. In particular, the electronic device  110  can send a frame with an OM Control subfield having an uplink MU Disable subfield set to one (1), or having the uplink MU Disable subfield set to zero (0) and an uplink MU Data Disable subfield set to one (1). The electronic device  110  can receive an acknowledgment signal (e.g., ACK) from the access point  120  indicating that the MU-OFDMA mode is disabled for the electronic device  110 . When this frame is acknowledged by the access point, the electronic device can ignore the MU-OFDMA EDCA parameter set, which is mandated by the access point and may have relaxed values in comparison to standard EDCA parameters included in an initial EDCA parameter set information element used by the access point. The electronic device  110  may then apply the standard EDCA parameters included in the initial EDCA parameter set information element, which do not have relaxed values. 
     At  312 , the electronic device  110  enters the single user (SU) mode to contend for the transmit channel. The single-user mode enables the electronic device to contend for the transmit channel using different parameters than the parameters mandated by the access point as part of the multi-user mode, enabling the electronic device  110  to contend for the transmit channel as aggressively as a legacy device and/or the access point  120 . 
     At  314 , the electronic device  110  initiates a timer T 2  (e.g., a second timer T 2 ) in response to entering the single-user mode. The timer T 2  may be set for any suitable duration of time, such as approximately 500 ms. The timer T 2  may prevent the electronic device  110  from exiting the single-user mode too quickly, essentially ping-ponging back and forth between the multi-user mode and the single-user mode. Accordingly, the timer T 2  provides a minimum amount of time for the electronic device  110  to operate in the single-user mode before it can attempt to re-enter the multi-user mode. 
     At  316 , the electronic device  110  determines if the uplink-queue size is below a second threshold size TH- 2 . An example of the second threshold size TH- 2  may include a threshold size substantially equal to half the size of a transmit channel, approximately one MB of data, or any other suitable size. The first threshold size TH- 1  and the second threshold size TH- 2  may be based on an access category (e.g., voice, video, best effort, and background access categories) of the uplink data, such that each threshold may differ for different access categories. For example, the first and second threshold sizes TH- 1  and TH- 2  can differ based on whether the uplink data is for Voice-over-Internet Protocol (VoIP), online gaming, audio data, video data, etc. In addition, in each access category, the first and second threshold sizes TH- 1  and TH- 2  can differ. An example implementation includes, for the voice access category, the first threshold size TH- 1  set to one kilobyte (KB) and the second threshold size TH- 2  set to 0.2 KB. In another implementation, for the video access category, the first threshold size TH- 1  may be set to 10 KB and the second threshold size TH- 2  may be set to 2 KB. An example implementation for the best effort and background access categories may include the first threshold size TH- 1  set to 2 MB and the second threshold size TH- 2  set to 1 MB. In another example, the first and second thresholds TH- 1  and TH- 2  may be dependent on the maximum latency in an uplink queue, such that each threshold may differ for different maximum latencies in uplink queues. Although several examples are described herein, any suitable threshold size may be used for the first and second threshold sizes TH- 1  and TH- 2 , and the sizes may depend on the implementation. These examples are not intended to be limiting. 
     If the uplink-queue size is equal to, or greater than, the second threshold size TH- 2  (“NO” at  316 ), then the electronic device  110  remains in the single-user mode for transmitting uplink data. However, if the uplink-queue size drops below the second threshold size TH- 2 , then it is likely that the uplink traffic is sufficiently low to allow the multi-user mode to be more efficient for the electronic device  110  than the single-user mode. Accordingly, if the electronic device  110  determines that the uplink-queue size has decreased to a size that is less than the second threshold size TH- 2  (“YES” at  316 ), then at  318 , the electronic device  110  determines if the timer T 2  is expired, which indicates that a sufficient amount of time has passed since entering the single-user mode. Alternatively, the electronic device  110  can wait until the timer T 2  expires before determining whether the uplink-queue size is equal to, or greater than, the second threshold size TH- 2 . 
     If the timer T 2  is not expired (“NO” at  318 ), then the electronic device  110  remains in the single-user mode for transmitting uplink data. Accordingly, the electronic device  110  delays opting back into the MU-OFDMA mode until expiration of the timer T 2 . If the timer T 2  is expired (“YES” at  318 ), then it is determined that the electronic device  110  has spent a sufficient amount of time in the single-user mode, and the electronic device  110  may proceed to opt in to the multi-user mode. 
     Other forms of hysteresis can be implemented between the two threshold sizes TH- 1  and TH- 2  to reduce or prevent ping-ponging between the multi-user and single-user modes. For example, instead of using the timer T 2  (or in addition to using the timer T 2 ), the electronic device  110  can wait for the uplink-queue size to fall below the second threshold size TH- 2  by a predefined amount (e.g., value or percentage) before determining whether to opt in to the multi-user mode. A third threshold size can be used that is less than the second threshold size TH- 2  by the predefined amount. This additional condition may further reduce the likelihood of the electronic device  110  bouncing back and forth between single-user and multi-user modes. 
     At  320 , the electronic device  110  opts into the MU-OFDMA mode. This can be achieved by the electronic device  110  transmitting an OMI signal, to the access point  120 , requesting to participate in the multi-user mode. The electronic device  110  receives an acknowledgment signal, from the access point  120 , providing permission and information to enter the multi-user mode. The electronic device  110  can then re-enter the MU-OFDMA mode at  302 . 
       FIG. 4  illustrates an example method  400  for opting out of MU-OFDMA to honor low-latency Quality-of-Service (QoS) requirements. The method  400  may be performed by the electronic device  110  when implementing a low-latency application that requires quick access to uplink and downlink channels. At  402 , an electronic device (e.g., the electronic device  110 ) connects to a wireless network using an MU-OFDMA mode. 
     At  404 , the electronic device  110  enters a low-latency mode for uplink traffic. The electronic device  110  may enter the low-latency mode when performing functions or executing an application having data load or latency requirements that are critical, such as online gaming. 
     At  406 , the electronic device  110  receives a plurality of triggers from an access point (e.g., the access point  120 ). Triggers (e.g., trigger frames) are used by the access point  120  to schedule multi-user transmissions in both uplink and downlink directions. The access point  120  acts as a central coordinating entity and assigns time-frequency resource units (RUs) for reception or transmission to associated stations, which avoids RU contention overhead and increases efficiency in scenarios of dense deployments. For example, the access point  120  (Wifi AP) sends a downlink trigger frame to inform particular stations to send their data. The trigger frame includes information identifying a transmission interval, a bit rate of transmission, and a transmit power for the station (the electronic device(s)  110 ) to use for the uplink transmission. The information in the trigger is defined in the 802.11ax specification. 
     At  408 , the electronic device  110  monitors a frequency at which the triggers are received from the access point  120 . In particular, the electronic device  110  monitors an average interarrival time of the triggers received from the access point  120 . 
     At  410 , the electronic device  110  determines if the frequency is greater than a threshold frequency TH 4 . Any suitable threshold frequency TH-f can be used as a measure for an acceptable frequency for the triggers. In some aspects, the threshold frequency TH-f can be based on a type of application being used (e.g., VoIP application, online gaming application, etc.), a type of data (e.g., voice traffic, video data, audio data, etc.), or a particular access category of the uplink data. If the frequency is greater than the threshold frequency TH-f (“YES” at  410 ), then the electronic device  110  maintains the MU-OFDMA mode and continues to monitor the frequency at  408 . The threshold frequency TH-f may represent a maximum queuing delay. When the frequency of the triggers is greater than the threshold frequency TH-f, then the triggers are being sent by the access point  120  fast enough to retain high efficiency in the multi-user mode. 
     If the frequency is less than the threshold frequency TH-f (“NO” at  410 ), then at  412 , the electronic device  110  opts out of the MU-OFDMA mode. When the frequency of the triggers drops below the threshold frequency TH-f, the electronic device  110  can determine that, for some reason, the access point  120  is not responsive enough for the low-latency requirements. Delayed triggers result in more transmission delay. Accordingly, to improve efficiency, the electronic device  110  can select to opt out of the MU-OFDMA mode. 
     At  414 , the electronic device  110  enters a single-user mode to contend for a transmit channel on the wireless network without restrictions mandated by the access point. As above, the single-user mode (after opting out of the multi-user mode) enables the electronic device  110  to avoid scheduling and shared-channel bandwidth requirements set by the access point for the multi-user mode. Further, by opting out of the multi-user mode and switching to the single-user mode, the electronic device  110  avoids being penalized on latency, which would occur if the electronic device  110  did not opt out of the multi-user mode and simply used a relaxed set of contention parameters provided by the access point  120 . 
     In some scenarios, after entering the low-latency mode at  404 , the electronic device  110  may, at  416 , receive no triggers from the access point over a predefined duration of time, or may receive only a single trigger over the duration of time. In such scenarios, the method  400  proceeds directly from  416  to  412  to opt out of the MU-OFDMA mode. 
     As latency requirements are relaxed, or after a predefined period of time, the electronic device  110  can optionally, at  418 , opt back into the MU-OFDMA mode. Then the method  400  may proceed to receiving triggers (at  406 ), or not receiving triggers (at  416 ), and monitoring (at  408 ) the frequency at which the triggers are received from the access point  120 . 
       FIG. 5  illustrates an example method  500  for opting out of MU-OFDMA based on Basic Service Set (BSS) metrics. At  502 , when connected to a wireless network using an MU-OFDMA mode, the electronic device  110  indicates to an access point of the wireless network uplink data to transmit. 
     At  504 , the electronic device  110  receives one or more triggers from the access point for transmitting the uplink data. In an example, the triggers include a mandated modulation and coding scheme (MC S) provided by the access point. 
     At  506 , the electronic device  110  performs a BSS clear channel assessment (CCA) of a transmit channel. A BSS CCA Busy is a Wi-Fi metric indicating how busy or clear the airtime of a channel is. The electronic device  110  can monitor the channel busy time over a duration of time to obtain this metric. For example, the electronic device  110  listens for radio frequency (RF) transmissions at a physical layer of an air interface. The electronic device  110  uses a signal-detect threshold to identify a preamble transmission from another transmitting radio (e.g., the access point  120 ) for synchronization between devices. In addition, the electronic device  110  uses an energy-detect threshold to detect other types of RF transmissions during the CCA. 
     At  508 , the electronic device  110  measures a received signal strength indicator (RSSI) of the transmit channel if the transmit channel is clear. This measurement provides an indication as to the quality of the signal on the transmit channel, which is in turn an indication of how fast the electronic device  110  can transmit data. 
     At  510 , the electronic device  110  estimates an MCS based on the measured RSSI. The estimated MCS indicates how many bits the electronic device  110  can transmit per symbol on the transmit channel. 
     At  512 , the electronic device  110  determines if a data rate associated the estimated MCS is greater than a data rate associated with the mandated MCS. In some aspects, the electronic device  110  can determine if the data rate associated with the estimated MCS is greater than the data rate associated with the mandated MCS by a threshold amount T The MCS is an index to an array of rates, such that a higher MCS corresponds to a higher rate, and a lower MCS corresponds to a lower rate. 
     If the data rate associated with the estimated MCS is less than the data rate associated with the mandated MCS (“NO” at  512 ), then at  514 , the electronic device  110  remains in the MU-OFDMA mode and transmits the uplink data using the MU-OFDMA mode according to the mandated MCS. In some aspects, the method  500  may proceed to  514  if the electronic device  110  determines that the data rate associated with the estimated MCS is greater than the data rate associated with the mandated MCS, but the difference between the data rates is less than the threshold amount T. 
     If the data rate associated with the estimated MCS is greater than the data rate associated with the mandated MCS (“YES” at  512 ), then at  516 , the electronic device  110  opts out of the MU-OFDMA mode. Alternatively, the electronic device  110  opts out of the MU-OFDMA mode at  516  if the data rate associated with the estimated MCS is greater than the data rate associated with the mandated MCS by at least the threshold amount T. 
     At  518 , the electronic device  110  enters a single-user mode to contend for the transmit channel on the wireless network for transmission of the uplink data without restrictions mandated by the access point  120 . 
     CONCLUSION 
     Although aspects of a switching scheme for opting in and out of MU-OFDMA have been described in language specific to features and/or methods, the subject of the appended claims is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as example implementations of the switching scheme for opting in and out of MU-OFDMA, and other equivalent features and methods are intended to be within the scope of the appended claims. Further, various different aspects are described, and it is to be appreciated that each described aspect can be implemented independently or in connection with one or more other described aspects.