Patent Publication Number: US-2023164709-A1

Title: Time synchronization for coordinated restricted target wake time (r-twt) operation

Description:
TECHNICAL FIELD 
     This disclosure relates generally to wireless communication, and more specifically, to time synchronization for coordinated restricted target wake time (r-TWT) operation. 
     DESCRIPTION OF THE RELATED TECHNOLOGY 
     A wireless local area network (WLAN) may be formed by one or more access points (APs) that provide a shared wireless medium for use by a number of client devices or stations (STAs). Each AP, which may correspond to a Basic Service Set (BSS), may periodically broadcast beacon frames to enable any STAs within wireless range of the AP to establish and maintain a communication link with the WLAN. WLANs that operate in accordance with the IEEE 802.11 family of standards are commonly referred to as Wi-Fi networks. 
     Some wireless communication devices may be associated with low-latency applications having strict end-to-end latency, throughput, and timing requirements for data traffic. Example low-latency applications include, but are not limited to, real-time gaming applications, video communications, and augmented reality (AR) and virtual reality (VR) applications (collectively referred to as extended reality (XR) applications). Such low-latency applications may specify various latency, throughput, and timing requirements for wireless communication systems that provide connectivity for these applications. Thus, it is desirable to ensure that WLANs are able to meet the various latency, throughput, and timing requirements of such low-latency applications. 
     SUMMARY 
     The systems, methods and devices of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein. 
     One innovative aspect of the subject matter described in this disclosure can be implemented as a method of wireless communication. The method can be performed by a wireless communication device to coordinate service periods (SPs) with an overlapping basic service set (OBSS). In some implementations, the method can include receiving first timing information indicating a timing of a first SP associated with an OBSS; transmitting, to one or more wireless stations (STAs), second timing information indicating the timing of the first SP, where the second timing information is associated with a first timing synchronization function (TSF) timer associated with the wireless communication device; and communicating with the one or more STAs, via a first wireless channel, associated with the second timing information. 
     Another innovative aspect of the subject matter described in this disclosure can be implemented in a wireless communication device. The wireless communication device can include a processing system and an interface configured to receive first timing information indicating a timing of a first SP associated with an OBSS; transmit, to one or more STAs, second timing information indicating the timing of the first SP, where the second timing information is associated with a first TSF timer associated with the wireless communication device; and communicate with the one or more STAs associated with the second timing information. 
     Another innovative aspect of the subject matter described in this disclosure can be implemented as a method of wireless communication. The method can be performed by a wireless communication device to coordinate SPs with an OBSS. In some implementations, the method can include synchronizing a local TSF timer with a first TSF timer associated with a basic service set (BSS); receive timing information indicating a timing of a first SP associated with an OBSS, where the timing information is associated with the first TSF timer; and communicate with one or more devices associated with the BSS and the received timing information. 
     Another innovative aspect of the subject matter described in this disclosure can be implemented in a wireless communication device. The wireless communication device can include a processing system configured to synchronize a local TSF timer with a first TSF timer associated with a BSS; and an interface configured to receive timing information indicating a timing of an SP associated with an OBSS, where the timing information is associated with the first TSF timer, and communicate with the one or more devices associated with the BSS and the received timing information. 
     Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims. Note that the relative dimensions of the following figures may not be drawn to scale. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a block diagram of an example wireless system. 
         FIG.  2    shows a block diagram of an example wireless station (STA). 
         FIG.  3    shows a block diagram of an example access point (AP). 
         FIG.  4    shows a timing diagram depicting an example of wireless communication among devices belonging to a basic service set (BSS). 
         FIG.  5    shows an example communication environment that includes overlapping basic service sets (OBSSs). 
         FIG.  6    shows a timing diagram depicting an example of wireless communication among devices associated with OBSSs. 
         FIG.  7    shows a timing diagram depicting an example of wireless communication among devices associated with OBSSs. 
         FIG.  8 A  shows a sequence diagram depicting an example message exchange between devices associated with OBSSs. 
         FIG.  8 B  shows a sequence diagram depicting an example message exchange between devices associated with OBSSs. 
         FIG.  8 C  shows a sequence diagram depicting an example message exchange between devices associated with OBSSs. 
         FIG.  9    shows a sequence diagram depicting an example message exchange between devices associated with OBSSs. 
         FIG.  10    shows an illustrative flowchart depicting an example wireless communication operation. 
         FIG.  11    shows an illustrative flowchart depicting an example wireless communication operation. 
         FIG.  12    shows a block diagram of an example wireless communication device. 
         FIG.  13    shows a block diagram of an example wireless communication device. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The following description is directed to some particular implementations for the purposes of describing innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. The described implementations can be implemented in any device, system or network that is capable of transmitting and receiving radio frequency (RF) signals according to one or more of the Long Term Evolution (LTE), 3G, 4G or 5G (New Radio (NR)) standards promulgated by the 3rd Generation Partnership Project (3GPP), the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, the IEEE 802.15 standards, or the Bluetooth® standards as defined by the Bluetooth Special Interest Group (SIG), among others. The described implementations can be implemented in any device, system or network that is capable of transmitting and receiving RF signals according to one or more of the following technologies or techniques: code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), single-user (SU) multiple-input multiple-output (MIMO) and multi-user (MU) MIMO. The described implementations also can be implemented using other wireless communication protocols or RF signals suitable for use in one or more of a wireless wide area network (WWAN), a wireless personal area network (WPAN), a wireless local area network (WLAN), or an internet of things (IOT) network. 
     The IEEE 802.11be amendment of the IEEE 802.11 standard describes a restricted target wake time (r-TWT) service period (SP) that can be allocated for latency-sensitive traffic. As used herein, the term “non-legacy STA” refers to any wireless station (STA) that supports the IEEE 802.11be amendment, or future generations, of the IEEE 802.11 standard, while the term “low-latency STA” refers to any non-legacy STA that has latency-sensitive traffic to send or receive. In contrast, the term “legacy STA” may refer to any STA that only supports the IEEE 802.11ax, or earlier generations, of the IEEE 802.11 standard. Non-legacy STAs that support r-TWT operation and acquire transmit opportunities (TXOPs) outside of an r-TWT SP must terminate their respective TXOPs before the start of any r-TWT SP for which they are not a member. Further, an AP may suppress traffic from all legacy STAs during an r-TWT SP by scheduling a quiet interval to overlap with the r-TWT SP. As such, r-TWT SPs can provide more predictable latency, reduced worst case latency, or reduced jitter, with higher reliability for latency-sensitive traffic. 
     Aspects of the present disclosure recognize that overlapping basic service sets (OBSSs) exist in many wireless communication environments, particularly in dense or crowded environments. An OBSS is any basic service set (BSS) having an overlapping coverage area, and operating on the same wireless channel, as another BSS. As such, wireless communications in a given BSS may interfere or collide with wireless communications in an OBSS, resulting in increased latency of communications in the BSS, the OBSS, or both. Wireless communication devices (including access points (APs) and STAs) that operate in accordance with existing versions of the IEEE 802.11 standard (including an initial release (R1) of the IEEE 802.11be amendment) may not be aware of latency-sensitive traffic in an OBSS. Accordingly, new communication protocols and signaling are needed to prevent latency-sensitive traffic in a given BSS from interfering or colliding with latency sensitive-traffic in an OBSS. 
     Implementations of the subject matter described in this disclosure may be used to coordinate SPs among OBSSs. For example, an AP associated with a BSS may receive timing information indicating a scheduled SP (such as an r-TWT SP, a coordinated r-TWT SP, or a coordinated SP) associated with an OBSS. More specifically, the received timing information may indicate the timing of the SP in relation to a timing synchronization function (TSF) timer associated with the OBSS. In some aspects, the AP may transmit, to its associated STAs, coordinated timing information indicating the timing of the SP in relation to a TSF timer associated with the AP. In some implementations, the AP may adjust the timing information to account for an offset between the TSF timer associated with the AP and the TSF timer associated with the OBSS. In such implementations, the timing information received by the AP may be different than the coordinated timing information transmitted to its associated STAs. In some other implementations, the AP may synchronize its TSF timer with the TSF timer associated with the OBSS. In such implementations, the timing information received by the AP may be the same as the coordinated timing information transmitted to its associated STAs. In some aspects, the AP may communicate with its associated STAs based on the coordinated timing information. For example, the AP may schedule its communications with the STAs to be orthogonal (in time, frequency, or various other parameters) to communications in the OBSS during the SP. 
     Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. By coordinating SPs among OBSSs, aspects of the present disclosure may improve the latency gains achievable by latency-sensitive traffic through application of r-TWT SPs. As described herein, concurrent data transmissions in OBSSs may interfere or collide with one another, thereby increasing the latency of communications in such OBSSs. By scheduling communications between the AP and its associated STAs to be orthogonal to communications in the OBSSs during the SP, aspects of the present disclosure may prevent communications in the BSS from interfering or colliding with latency-sensitive communications in the OBSS. More specifically, aligning the coordinated timing information with the TSF timer of the AP allows the STAs associated with the AP to more accurately determine the timing of SPs associated with the OBSS. As a result, the STAs may avoid or otherwise honor any r-TWT SP schedules associated with the OBSS. Thus, with coordinated scheduling of SPs among OBSSs, r-TWT SP operation may provide even more predictable latency, reduced worst case latency, or reduced jitter, with higher reliability for latency-sensitive traffic in OBSSs. 
       FIG.  1    shows a block diagram of an example wireless system  100 . The wireless system  100  is shown to include a wireless access point (AP)  110  and a number of wireless stations (STAs)  120   a - 120   i . For simplicity, one AP  110  is shown in  FIG.  1   . The AP  110  may form a wireless local area network (WLAN) that allows the AP  110 , the STAs  120   a - 120   i , and other wireless devices (not shown for simplicity) to communicate with each other over a wireless medium. The wireless medium, which may be divided into a number of channels or into a number of resource units (RUs), may facilitate wireless communications between the AP  110 , the STAs  120   a - 120   i , and other wireless devices connected to the WLAN. In some implementations, the STAs  120   a - 120   i  can communicate with each other using peer-to-peer communications (such as without the presence or involvement of the AP  110 ). The AP  110  may be assigned a unique MAC address that is programmed therein by, for example, the manufacturer of the access point. Similarly, each of the STAs  120   a - 120   i  also may be assigned a unique MAC address. 
     In some implementations, the wireless system  100  may correspond to a multiple-input multiple-output (MIMO) wireless network and may support single-user MIMO (SU-MIMO) and multi-user (MU-MIMO) communications. In some implementations, the wireless system  100  may support orthogonal frequency-division multiple access (OFDMA) communications. Further, although the WLAN is depicted in  FIG.  1    as an infrastructure Basic Service Set (BSS), in some other implementations, the WLAN may be an Independent Basic Service Set (IBSS), an Extended Service Set (ESS), an ad-hoc network, or a peer-to-peer (P2P) network (such as operating according to one or more Wi-Fi Direct protocols). 
     The STAs  120   a - 120   i  may be any suitable Wi-Fi enabled wireless devices including, for example, cell phones, personal digital assistants (PDAs), tablet devices, laptop computers, or the like. The STAs  120   a - 120   i  also may be referred to as a user equipment (UE), a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. 
     The AP  110  may be any suitable device that allows one or more wireless devices (such as the STAs  120   a - 120   i ) to connect to another network (such as a local area network (LAN), wide area network (WAN), metropolitan area network (MAN), or the Internet). In some implementations, a system controller  130  may facilitate communications between the AP  110  and other networks or systems. In some implementations, the system controller  130  may facilitate communications between the AP  110  and one or more other APs (not shown for simplicity) that may be associated with other wireless networks. In addition, or in the alternative, the AP  110  may exchange signals and information with one or more other APs using wireless communications. 
     The AP  110  may periodically broadcast beacon frames to enable the STAs  120   a - 120   i  and other wireless devices within wireless range of the AP  110  to establish and maintain a communication link with the AP  110 . The beacon frames, which may indicate downlink (DL) data transmissions to the STAs  120   a - 120   i  and solicit or schedule uplink (UL) data transmissions from the STAs  120   a - 120   i , are typically broadcast according to a target beacon transmission time (TBTT) schedule. The broadcasted beacon frames may include a timing synchronization function (TSF) value of the AP  110 . The STAs  120   a - 120   i  may synchronize their own local TSF values with the broadcasted TSF value, for example, so that all of the STAs  120   a - 120   i  are synchronized with each other and with the AP  110 . 
     In some implementations, each of the stations STAs  120   a - 120   i  and the AP  110  may include one or more transceivers, one or more processing resources (such as processors or Application-Specific Integrated Circuits (ASICs)), one or more memory resources, and a power source (such as a battery). The one or more transceivers may include Wi-Fi transceivers, Bluetooth transceivers, cellular transceivers, or other suitable radio frequency (RF) transceivers (not shown for simplicity) to transmit and receive wireless communication signals. In some implementations, each transceiver may communicate with other wireless devices in distinct frequency bands or using distinct communication protocols. The memory resources may include a non-transitory computer-readable medium (such as one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, etc.) that stores instructions for performing one or more operations described with respect to  FIGS.  5 - 11   . 
       FIG.  2    shows an example wireless station (STA)  200 . The STA  200  may be one implementation of at least one of the STAs  120   a - 120   i  of  FIG.  1   . The STA  200  may include one or more transceivers  210 , a processor  220 , a user interface  230 , a memory  240 , and a number of antennas ANT1-ANTn. The transceivers  210  may be coupled to antennas ANT1-ANTn, either directly or through an antenna selection circuit (not shown for simplicity). The transceivers  210  may be used to transmit signals to and receive signals from other wireless devices including, for example, a number of APs and a number of other STAs. Although not shown in  FIG.  2    for simplicity, the transceivers  210  may include any number of transmit chains to process and transmit signals to other wireless devices via antennas ANT1-ANTn, and may include any number of receive chains to process signals received from antennas ANT1-ANTn. Thus, the STA  200  may be configured for MIMO communications and OFDMA communications. The MIMO communications may include SU-MIMO communications and MU-MIMO communications. In some implementations, the STA  200  may use multiple antennas ANT1-ANTn to provide antenna diversity. Antenna diversity may include polarization diversity, pattern diversity, and spatial diversity. 
     The processor  220  may be any suitable one or more processors capable of executing scripts or instructions of one or more software programs stored in the STA  200  (such as within the memory  240 ). In some implementations, the processor  220  may be or include one or more microprocessors providing the processor functionality and external memory providing at least a portion of machine-readable media. In other implementations, the processor  220  may be or include an Application Specific Integrated Circuit (ASIC) with the processor, the bus interface, the user interface, and at least a portion of the machine-readable media integrated into a single chip. In some other implementations, the processor  220  may be or include one or more Field Programmable Gate Arrays (FPGAs) or Programmable Logic Devices (PLDs). 
     In some implementations, the processor  220  may be a component of a processing system. A processing system may generally refer to a system or series of machines or components that receives inputs and processes the inputs to produce a set of outputs (which may be passed to other systems or components of, for example, the STA  200 ). For example, a processing system of the STA  200  may refer to a system including the various other components or subcomponents of the STA  200 . 
     The processing system of the STA  200  may interface with other components of the STA  200 , and may process information received from other components (such as inputs or signals), output information to other components, and the like. For example, a chip or modem of the STA  200  may be coupled to or include a processing system, a first interface to output information, and a second interface to obtain information. In some instances, the first interface may refer to an interface between the processing system of the chip or modem and a transmitter, such that the STA  200  may transmit information output from the chip or modem. In some instances, the second interface may refer to an interface between the processing system of the chip or modem and a receiver, such that the STA  200  may obtain information or signal inputs, and the information may be passed to the processing system. A person having ordinary skill in the art will readily recognize that the first interface also may obtain information or signal inputs, and the second interface also may output information or signal outputs. 
     The user interface  230 , which is coupled to the processor  220 , may be or represent a number of suitable user input devices such as, for example, a speaker, a microphone, a display device, a keyboard, a touch screen, and so on. In some implementations, the user interface  230  may allow a user to control a number of operations of the STA  200 , to interact with one or more applications executable by the STA  200 , and other suitable functions. 
     In some implementations, the STA  200  may include a satellite positioning system (SPS) receiver  250 . The SPS receiver  250 , which is coupled to the processor  220 , may be used to acquire and receive signals transmitted from one or more satellites or satellite systems via an antenna (not shown for simplicity). Signals received by the SPS receiver  250  may be used to determine (or at least assist with the determination of) a location of the STA  200 . 
     The memory  240  may include a device database  241  that may store location data, configuration information, data rates, a medium access control (MAC) address, timing information, modulation and coding schemes (MCSs), traffic indication (TID) queue sizes, ranging capabilities, and other suitable information about (or pertaining to) the STA  200 . The device database  241  also may store profile information for a number of other wireless devices. The profile information for a given wireless device may include, for example, a service set identification (SSID) for the wireless device, a Basic Service Set Identifier (BSSID), operating channels, TSF values, beacon intervals, ranging schedules, channel state information (CSI), received signal strength indicator (RSSI) values, goodput values, and connection history with the STA  200 . In some implementations, the profile information for a given wireless device also may include clock offset values, carrier frequency offset values, and ranging capabilities. 
     The memory  240  also may be or include a non-transitory computer-readable storage medium (such as one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, and so on) that may store computer-executable instructions  242  to perform all or a portion of one or more operations described in this disclosure. 
       FIG.  3    shows an example access point (AP)  300 . The AP  300  may be one implementation of the AP  110  of  FIG.  1   . The AP  300  may include one or more transceivers  310 , a processor  320 , a memory  330 , a network interface  340 , and a number of antennas ANT1-ANTn. The transceivers  310  may be coupled to the antennas ANT1-ANTn, either directly or through an antenna selection circuit (not shown for simplicity). The transceivers  310  may be used to transmit signals to and receive signals from other wireless devices including, for example, one or more of the STAs  120   a - 120   i  of  FIG.  1    and other APs. Although not shown in  FIG.  3    for simplicity, the transceivers  310  may include any number of transmit chains to process and transmit signals to other wireless devices via the antennas ANT1-ANTn, and may include any number of receive chains to process signals received from the antennas ANT1-ANTn. Thus, the AP  300  may be configured for MIMO communications and OFDMA communications. The MIMO communications may include SU-MIMO communications and MU-MIMO communications. In some implementations, the AP  300  may use multiple antennas ANT1-ANTn to provide antenna diversity. Antenna diversity may include polarization diversity, pattern diversity, and spatial diversity. 
     In high frequency (such as 60 GHz or millimeter wave (mmWave)) wireless communication systems (such as conforming to the IEEE 802.11ad or 802.11ay amendments of the IEEE 802.11 standard), communications may be beamformed using phased array antennas at the transmitter and the receiver. Beamforming generally refers to a wireless communication technique by which the transmitting device and the receiving device adjust transmit or receive antenna settings to achieve a desired link budget for subsequent communications. The procedure to adapt the transmit and receive antennas, referred to as beamforming training, may be performed initially to establish a link between the transmitting and receiving devices and also may be performed periodically to maintain a quality link using optimized transmit and receive beams. 
     The processor  320  may be any suitable one or more processors capable of executing scripts or instructions of one or more software programs stored in the AP  300  (such as within the memory  330 ). In some implementations, the processor  320  may be or include one or more microprocessors providing the processor functionality and external memory providing at least a portion of machine-readable media. In other implementations, the processor  320  may be or include an ASIC with the processor, the bus interface, the user interface, and at least a portion of the machine-readable media integrated into a single chip. In some other implementations, the processor  320  may be or include one or more FPGAs or PLDs. In some implementations, the processor  320  may be a component of a processing system. For example, a processing system of the AP  300  may refer to a system including the various other components or subcomponents of the AP  300 . 
     The processing system of the AP  300  may interface with other components of the AP  300 , and may process information received from other components (such as inputs or signals), output information to other components, and the like. For example, a chip or modem of the AP  300  may include a processing system, a first interface to output information, and a second interface to obtain information. In some instances, the first interface may refer to an interface between the processing system of the chip or modem and a transmitter, such that the AP  300  may transmit information output from the chip or modem. In some instances, the second interface may refer to an interface between the processing system of the chip or modem and a receiver, such that the AP  300  may obtain information or signal inputs, and the information may be passed to the processing system. A person having ordinary skill in the art will readily recognize that the first interface also may obtain information or signal inputs, and the second interface also may output information or signal outputs. 
     The network interface  340 , which is coupled to the processor  320 , may be used to communicate with the system controller  130  of  FIG.  1   . The network interface  340  also may allow the AP  300  to communicate, either directly or via one or more intervening networks, with other wireless systems, with other APs, with one or more back-haul networks, or any combination thereof. 
     The memory  330  may include a device database  331  that may store location data, configuration information, data rates, the MAC address, timing information, MCSs, ranging capabilities, and other suitable information about (or pertaining to) the AP  300 . The device database  331  also may store profile information for a number of other wireless devices (such as one or more of the stations  120   a - 120   i  of  FIG.  1   ). The profile information for a given wireless device may include, for example, an SSID for the wireless device, a BSSID, operating channels, CSI, received signal strength indicator (RSSI) values, goodput values, and connection history with the AP  300 . In some implementations, the profile information for a given wireless device also may include TID queue sizes, a preferred packet duration for trigger-based UL transmissions, and a maximum amount of queued UL data that the wireless device is able to insert into TB PPBUs. 
     The memory  330  also may be or include a non-transitory computer-readable storage medium (such as one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, and so on) that may store computer-executable instructions  332  to perform all or a portion of one or more operations described in this disclosure. 
       FIG.  4    shows a timing diagram  400  depicting an example of wireless communication among devices belonging to a BSS. In the example of  FIG.  4   , the BSS may include multiple non-legacy STAs  402  and  404  that support r-TWT operation. More specifically, the STA  402  may be a low-latency STA that is a member of an r-TWT SP, which spans a duration from times t 3  to t 8 , whereas the STA  404  may be a non-member STA. In some implementations, each of the STAs  402  and  404  may be one example of any of the STAs  120   a - 120   i  of  FIG.  1    or the STA  200  of  FIG.  2   . Although only two non-legacy STAs  402  and  404  are shown in the example of  FIG.  4   , in actual implementations the BSS may include any number of legacy or non-legacy STAs. 
     The non-member STA  404  attempts to access a shared wireless channel prior to the start of the r-TWT SP. More specifically, the non-member STA  404  senses that the channel is idle for a threshold duration, from times t 0  to t 1 , based on a channel sensing operation (such as clear channel assessment (CCA)) and further counts down a random backoff (RBO) duration, from times t 1  to t 2 , before attempting to acquire a TXOP. For example, the threshold duration (from times t 0  to t 1 ) may be an arbitration interframe spacing (AIFS) duration associated with a particular access category (AC) of data traffic. Accordingly, the RBO duration (from times t 1  to t 2 ) may be randomly selected from a range of RBOs spanning a contention window associated with the AC. At time t 2 , the non-member STA  404  senses that the wireless channel is still idle and proceeds to acquire a TXOP, for example, by initiating a transmission over the shared channel. In the example of  FIG.  4   , the desired TXOP may be longer than the duration remaining before the start of the r-TWT SP at time t 3 . However, because the existing rules regarding r-TWT operation require non-member STAs to terminate their TXOPs by the start of an r-TWT SP, the non-member STA  404  must truncate its TXOP between times t 2  to t 3 . 
     The low-latency STA  402  attempts to access the shared wireless channel at the start of the r-TWT SP. In the example of  FIG.  4   , the low-latency STA  402  senses that the channel is idle for an AIFS duration, from times t 3  to t 4 , and further counts down an RBO duration, from times t 4  to t 6 , before attempting to acquire a TXOP. As shown in  FIG.  4   , the non-member STA  404  also attempts to access the shared wireless channel at the start of the r-TWT SP. For example, the non-member STA  404  senses that the channel is idle for an AIFS duration, from times t 3  to t 5 , and further counts down an RBO duration beginning at time t 5 . In some implementations, the data traffic associated with the low-latency STA  402  may be assigned to a higher-priority AC than the data traffic associated with the non-member STA  404 . As such, the AIFS or RBO durations associated with the low-latency STA  402  may be shorter than the AIFS or RBO durations, respectively, associated with the non-member STA  404 . As a result, the low-latency STA  402  wins access to the wireless channel, at time t 6 , and acquires a TXOP, for example, by initiating a transmission over the shared channel. 
     The non-member STA  404  senses that the wireless channel is busy, at time t 6 , and refrains from accessing the shared channel for the duration of the TXOP (from times t 6  to t 7 ). After the TXOP has terminated, at time t 7 , the non-member STA  404  may once again attempt to access the wireless channel. In this manner, the r-TWT operation may prioritize latency-sensitive traffic in the BSS, for example, by requiring non-member STAs to terminate their TXOPs by the start of any r-TWT SPs of which they are not members. Additionally, an AP (not shown for simplicity) may suppress all traffic from legacy STAs associated with the BSS by scheduling a quiet interval to overlap with at least a portion of the r-TWT SP (such as one or more time-units (TUs) beginning at time t 3 ). For example, the duration of the quiet interval may be indicated by one or more quiet elements included in management frames (such as beacon frames or probe response frames) transmitted by the AP prior to the start of the r-TWT SP. 
       FIG.  5    shows an example communication environment  500  that includes OBSSs. More specifically, the example communication environment  500  includes a number of STAs  501 - 506  and a number of APs  511 - 513 . In some implementations, each of the STAs  501 - 506  may be one example of any of the STAs  120   a - 120   i  of  FIG.  1    or the STA  200  of  FIG.  2   . In some implementations, each of the APs  511 - 513  may be one example of any of the APs  110  or  300  of  FIGS.  1  and  3   , respectively. The APs  511 - 513  may represent BSSs (BSS1-BSS3) having coverage areas  521 - 523 , respectively. 
     As shown in  FIG.  5   , the STAs  501  and  502  are associated with the AP  511  (or BSS1) and located within the coverage area  521 , the STAs  503 - 505  are associated with the AP  512  (or BSS2) and located within the coverage area  522 , and the STA  506  is associated with the AP  513  (or BSS3) and located within the coverage area  523 . In the example of  FIG.  5   , each of the APs  511 - 513  may be configured to operate on the same wireless channel. Further, the APs  511  and  512  have overlapping coverage areas  521  and  522 , respectively. Thus, the APs  511  and  512  represent OBSSs. Similarly, the APs  512  and  513  have overlapping coverage areas  522  and  523 , respectively. Thus, the APs  512  and  513  represent OBSSs. 
     In some aspects, each of the STAs  501 - 506  and each of the APs  511 - 513  may support r-TWT operation. More specifically, the AP  511  may schedule one or more r-TWT SPs that can be used by its associated STAs  501  and  502  to communicate latency-sensitive traffic, the AP  512  may schedule one or more r-TWT SPs that can be used by its associated STAs  503 - 505  to communicate latency-sensitive traffic, and the AP  513  may schedule one or more r-TWT SPs that can be used by its associated STA  506  to communicate latency-sensitive traffic. Because BSS2 overlaps with BSS1 and BSS3, wireless communications in BSS2 can interfere or collide with wireless communications in any of BSS1 or BSS3. Similarly, wireless communications in any of BSS1 or BSS3 can interfere or collide with wireless communications in BSS2. 
     In some aspects, the APs  511  and  512  may coordinate the scheduling of their respective r-TWT SPs to avoid interference or collisions between latency-sensitive data traffic in BSS1 and latency-sensitive data traffic in BSS2. As such, the APs  511  and  512  may be referred to herein as “r-TWT coordinating APs.” In some implementations, the APs  511  and  512  may schedule their respective r-TWT SPs to be orthogonal in time. For example, the AP  511  may schedule one or more r-TWT SPs to occur during periods of time that do not overlap with any r-TWT SPs scheduled by the AP  512 . Similarly, the AP  512  may schedule one or more r-TWT SPs to occur during periods of time that do not overlap with any r-TWT SPs scheduled by the AP  511 . In some other implementations, the APs  511  and  512  may schedule their r-TWT SPs to overlap in time, while allocating coordinated resources to concurrent or overlapping latency-sensitive traffic in BSS1 and BSS2 (such as using one or more multi-AP coordination techniques). For example, within the same or overlapping r-TWT SPs, latency-sensitive traffic may be transmitted at a relatively low power or on different time or frequency resources across BSS1 and BSS2. 
     In some aspects, the coordinated r-TWT SPs may be scheduled by a central coordinator. For example, the central coordinator may schedule r-TWT SPs for each of the APs  511  and  512  and may communicate the r-TWT SP schedules to the APs  511  and  512  via coordinated r-TWT signaling. In some implementations, the central coordinator may be an AP such as, for example, one of the APs  511  or  512 . In some other implementations, the central coordinator may be a network controller that communicates with the APs  511  and  512  via a (wired or wireless) backhaul. In some other aspects, the coordinated r-TWT SPs may be scheduled in a distributed manner. For example, the AP  511  may communicate its r-TWT SP schedule to the AP  512 , and the AP  512  may schedule its r-TWT SPs based on the r-TWT SP schedule of the AP  511 . In some implementations, the AP  511  may “explicitly” signal its r-TWT SP schedule to the AP  512  via a wired backhaul or in one or more packets transmitted to (or intended for reception by) the AP  512 . In some other implementations, the AP  511  may “implicitly” signal its r-TWT SP schedule to the AP  512 . In such implementations, the AP  512  may acquire the r-TWT SP schedule of the AP  511  by intercepting one or more packets transmitted by the AP  511  to its associated STAs (such as the STAs  501  or  502 ). 
     In some implementations, each of the r-TWT coordinating APs  511  and  512  may transmit or broadcast coordinated r-TWT signaling information to other APs or STAs in its vicinity. For example, the AP  511  may broadcast its r-TWT SP schedule as well as the r-TWT SP schedule of the AP  512  to its associated STAs  501  and  502  and to any other APs within wireless communication range. Accordingly, the STAs  501  and  502  (and other APs) may schedule their latency-sensitive communications to coincide with the r-TWT SPs of the AP  511  while avoiding access to the wireless channel during the r-TWT SPs of the AP  512 . In some implementations, the AP  511  may further schedule quiet intervals to overlap with the r-TWT SPs of the AP  512 , for example, to prevent legacy STAs from interfering with latency-sensitive communications in BSS2. Similarly, the AP  512  may broadcast its r-TWT SP schedule as well as the r-TWT SP schedule of the AP  511  to its associated STAs  503 - 505  and to any other APs within wireless communication range. Accordingly, the STAs  503 - 505  may schedule their latency-sensitive communications to coincide with the r-TWT SPs of the AP  512  while avoiding access to the wireless channel during the r-TWT SPs of the AP  511 . In some implementations, the AP  512  may further schedule quiet intervals to overlap with the r-TWT SPs of the AP  511 , for example, to prevent legacy STAs from interfering with latency-sensitive communications in BSS1. 
     In some aspects, the AP  513  may not coordinate the scheduling of its r-TWT SPs with the AP  512  (or may not support coordinated r-TWT scheduling). As such, the AP  513  may be referred to herein as an “r-TWT non-coordinating AP.” In some implementations, the AP  512  may acquire the r-TWT SP schedule of the AP  513  by intercepting beacon frames, management frames, or other packets transmitted by the AP  513  to its associated STAs (such as the STA  506 ). Accordingly, the AP  512  may schedule its r-TWT SPs based on the r-TWT SP schedule of the AP  513 . In some implementations, the AP  512  may schedule its r-TWT SPs to be orthogonal in time to (or otherwise avoid) any r-TWT SPs scheduled by the AP  513 . In some other implementations, the AP  512  may utilize other information associated with the AP  513 , in addition to the r-TWT SP schedule of the AP  513 , in scheduling its own r-TWT SPs. For example, the AP  512  may assess a level of interference from the AP  513  based on a received signal strength indication (RSSI) of wireless signals received from the AP  513  and may adjust the transmit power or timing of latency-sensitive traffic in BSS2 to avoid interference or collisions with latency-sensitive traffic in BSS3. 
     In some other aspects, the AP  513  may be hidden from (or otherwise undetectable by) the AP  512 . In some implementations, the AP  512  may acquire the r-TWT SP schedule of the AP  513  from one or more associated STAs located within the coverage area  523  of the AP  513  (such as the STA  505 ). For example, the STA  505  may intercept one or more beacon frames, management frames, or other packets transmitted by the AP  513  to its associated STAs (such as the STA  506 ). The STA  505  may parse the intercepted packets for r-TWT schedule information indicating the r-TWT SP schedule of the AP  513  and relay the r-TWT SP schedule to the AP  512 . Accordingly, the AP  512  may schedule its r-TWT SPs based on the r-TWT SP schedule of the AP  513 . In some implementations, the AP  512  may schedule its r-TWT SPs to be orthogonal in time to (or otherwise avoid) any r-TWT SPs scheduled by the AP  513 . In some other implementations, the AP  512  may utilize other information associated with the AP  513  (such as an RSSI of wireless signals received from the AP  513 ), in addition to the r-TWT SP schedule of the AP  513 , in scheduling its own r-TWT SPs. For example, the AP  512  may adjust the transmit power or timing of latency-sensitive traffic in BSS2 to avoid interference or collisions with latency-sensitive traffic in BSS3. 
       FIG.  6    shows a timing diagram  600  depicting an example of wireless communication among devices associated with OBSSs (BSS1-BSS3). In the example of  FIG.  6   , BSS1, BSS2, and BSS3 are represented by access points AP 1 , AP 2 , and AP 3 , respectively. In some implementations, the access points AP 1 , AP 2 , and AP 3  may be examples of the APs  511 ,  512 , and  513 , respectively, of  FIG.  5   . As shown in  FIG.  6   , the access points AP 1  and AP 2  belong to a coordinated r-TWT scheduling group. As such, the access points AP 1  and AP 2  may schedule their r-TWT SPs in a coordinated manner so that latency-sensitive data traffic in BSS1 does not interfere or collide with latency-sensitive data traffic in BSS2. In contrast, the access point AP 3  does not belong to the coordinated r-TWT scheduling group. As such, the access point AP 3  does not schedule its r-TWT SPs in a coordinated manner with any of the access points AP 1  or AP 2 . 
     In some implementations, the access points AP 1  and AP 2  may schedule their r-TWT SPs to be orthogonal in time while avoiding any r-TWT SPs scheduled by the access point AP 3 . As shown in  FIG.  6   , the access point AP 3  schedules an r-TWT SP (r-TWT SP3) to occur from times t 3  to t 4 . Accordingly, the access points AP 1  and AP 2  may avoid scheduling any of their r-TWT SPs to occur between times t 3  and t 4 . In the example of  FIG.  6   , the access point AP 1  schedules an r-TWT SP (r-TWT SP1) to occur from times t 1  to t 2  and the access point AP 2  schedules an r-TWT SP (r-TWT SP2) to occur from times t 2  to t 3 . In some implementations, each of the service periods r-TWT SP1, r-TWT SP2, and r-TWT SP3 may be one example of the r-TWT SP shown in  FIG.  4    (from times t 3  to t 8 ). Accordingly, the first access point AP 1  may communicate latency-sensitive data with one or more low-latency STAs in BSS1 during r-TWT SP1, the second access point AP 2  may communicate latency-sensitive data with one or more low-latency STAs in BSS2 during r-TWT SP2, and the third access point AP 3  may communicate latency-sensitive data with one or more low-latency STAs in BSS3 during r-TWT SP3. 
     Aspects of the present disclosure recognize that STAs located at the edge of an AP&#39;s coverage area (such as the STAs  502 ,  503  and  505  of  FIG.  5   ) are more susceptible to interference from an OBSS than STAs located closer to the AP. Thus, allocating such STAs to r-TWT SPs that are orthogonal in time may significantly improve the quality of their latency-sensitive data communications compared to other means of coordinated r-TWT scheduling. In some aspects, each of the access points AP 1 , AP 2 , and AP 3  may assign or otherwise allocate low-latency STAs to the service periods r-TWT SP1, r-TWT SP2, and r-TWT SP3, respectively, based on r-TWT schedule information carried in beacon or other management frames transmitted prior to (or during) one or more r-TWT SPs. In some implementations, the r-TWT schedule information associated with a particular r-TWT SP may assign one or more STAs to that r-TWT SP. In some other implementations, a STA may request to join a particular r-TWT SP responsive to receiving r-TWT schedule information associated with that r-TWT SP. 
     As shown in  FIG.  6   , the access point AP 1  transmits a beacon frame  601 , at time t 0 , carrying r-TWT schedule information indicating the schedule associated with r-TWT SP1. With reference for example to  FIG.  5   , the beacon frame  601  may be transmitted by the AP  511  and may assign or otherwise allocate the STA  502  to r-TWT SP1. The access point AP 2  transmits a beacon frame  602 , at time t 0 , carrying r-TWT schedule information indicating the schedule associated with r-TWT SP2. With reference for example to  FIG.  5   , the beacon frame  602  may be transmitted by the AP  512  and may assign or otherwise allocate one or more of the STAs  503  or  505  to r-TWT SP2. The access point AP 3  transmits a beacon frame  603 , at time t 0 , carrying r-TWT schedule information indicating the schedule associated with r-TWT SP3. With reference for example to  FIG.  5   , the beacon frame  603  may assign or otherwise allocate the STA  506  to r-TWT SP3. Although  FIG.  6    shows the beacon frames  601 - 603  being transmitted at the same time (to), in some other implementations, one or more of the beacon frames  601 - 603  may be transmitted at a different time. 
     In some implementations, the beacon frames  601  and  602  broadcast by the coordinated access points AP 1  and AP 2 , respectively, may further carry coordinated r-TWT signaling information. As described herein, the coordinated r-TWT signaling information may indicate the r-TWT SP schedules associated with one or more OBSSs. For example, the beacon frame  601  may carry coordinated r-TWT signaling information indicating the schedules for one or more of the service periods r-TWT SP2 or r-TWT SP3 and the beacon frame  602  may carry coordinated r-TWT signaling information indicating the schedules for one or more of the service periods r-TWT SP1 or r-TWT SP3. As used herein, the term “schedule” may include timing information, resource allocation information, or various other communication parameters associated with an r-TWT SP. For example, the schedule for r-TWT SP1 may indicate that r-TWT SP1 is to occur from times t 1  to t 2 , the schedule for r-TWT SP2 may indicate that r-TWT SP2 is to occur from times t 2  to t 3 , and the schedule for r-TWT SP3 may indicate that r-TWT SP3 is to occur from times t 3  to t 4 . 
     In some implementations, STAs associated with the access point AP 1  (or BSS1) may avoid accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS2 and BSS3 during the service periods r-TWT SP2 and r-TWT SP3, respectively, based on the coordinated r-TWT signaling information received from the access point AP 1 . In some other implementations, the access point AP 1  may schedule one or more quiet intervals to overlap with the service periods r-TWT SP2 and r-TWT SP3, for example, to prevent legacy STAs associated with the access point AP 1  (or BSS1) from accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS2 and BSS3, respectively, during such times. In some implementations, STAs associated with the access point AP 2  (or BSS2) may avoid accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS1 and BSS3 during the service periods r-TWT SP1 and r-TWT SP3, respectively, based on the coordinated r-TWT signaling information received from the access point AP 2 . In some other implementations, the access point AP 2  may schedule one or more quiet intervals to overlap with the service periods r-TWT SP1 and r-TWT SP3, for example, to prevent legacy STAs associated with the access point AP 2  (or BSS2) from accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS1 and BSS3, respectively, during such times. 
       FIG.  7    shows a timing diagram  700  depicting an example of wireless communication among devices associated with OBSSs (BSS1-BSS3). In the example of  FIG.  7   , BSS1, BSS2, and BSS3 are represented by access points AP 1 , AP 2 , and AP 3 , respectively. In some implementations, the access points AP 1 , AP 2 , and AP 3  may be examples of the APs  511 ,  512 , and  513 , respectively, of  FIG.  5   . As shown in  FIG.  7   , the access points AP 1  and AP 2  belong to a coordinated r-TWT scheduling group. As such, the access points AP 1  and AP 2  may schedule their r-TWT SPs in a coordinated manner so that latency-sensitive data traffic in BSS1 does not interfere or collide with latency-sensitive data traffic in BSS2. In contrast, the access point AP 3  does not belong to the coordinated r-TWT scheduling group. As such, the access point AP 3  does not schedule its r-TWT SPs in a coordinated manner with any of the access points AP 1  or AP 2 . 
     In some implementations, the access points AP 1  and AP 2  may schedule their r-TWT SPs to overlap in time while avoiding any r-TWT SPs scheduled by the access point AP 3 . As shown in  FIG.  7   , the access point AP 3  schedules an r-TWT SP (r-TWT SP3) to occur from times t 2  to t 3 . Accordingly, the access points AP 1  and AP 2  may avoid scheduling any of their r-TWT SPs to occur between times t 2  and t 3 . In the example of  FIG.  7   , the access points AP 1  and AP 2  schedule respective r-TWT SPs (r-TWT SP1 and r-TWT SP2) to occur from times t 1  to t 2 . In some implementations, each of the service periods r-TWT SP1, r-TWT SP2, and r-TWT SP3 may be one example of the r-TWT SP shown in  FIG.  4    (from times t 3  to t 8 ). Accordingly, the first access point AP 1  may communicate latency-sensitive data with one or more low-latency STAs in BSS1 during r-TWT SP1, the second access point AP 2  may communicate latency-sensitive data with one or more low-latency STAs in BSS2 during r-TWT SP2, and the third access point AP 3  may communicate latency-sensitive data with one or more low-latency STAs in BSS3 during r-TWT 
     In some aspects, the access points AP 1  and AP 2  may coordinate their allocation of resources for wireless communications during the overlapping service periods r-TWT SP1 and r-TWT SP2 to prevent latency-sensitive traffic in BSS1 from interfering or colliding with latency-sensitive traffic in BSS2. Example suitable resources include, among other examples, transmit power, timing, or frequency allocations for latency-sensitive traffic. In some implementations, the access points AP 1  and AP 2  may coordinate the transmit times of wireless communications in BSS1 and BSS2 during the service periods r-TWT SP1 and r-TWT SP2. In such implementations, the timing of latency-sensitive traffic in BSS1 may be orthogonal to the timing of latency-sensitive traffic in BSS2. For example, each of the access points AP 1  and AP 2  may initiate a TXOP during the service periods r-TWT SP1 and r-TWT SP2 by transmitting a multi-user (MU) request-to-send (RTS) frame that solicits concurrent clear-to-send (CTS) frames from multiple STAs, thereby protecting the TXOP from interference by STAs in OBSSs. 
     In some other implementations, the access points AP 1  and AP 2  may coordinate the frequency resources (such as RUs) allocated for wireless communications in BSS1 and BSS2 during the service periods r-TWT SP1 and r-TWT SP2. In such implementations, the frequency resources allocated for latency-sensitive traffic in BSS1 may be orthogonal to the frequency resources allocated for latency-sensitive traffic in BSS2. For example, prior to (or during) the service periods r-TWT SP1 and r-TWT SP2, the access points AP 1  and AP 2  may exchange coordination information indicating an allocation of frequency resources for wireless communications in at least one of BSS1 or BSS2 (such as in accordance with coordinated OFDMA (C-OFDMA) operation). The access points AP 1  and AP 2  may utilize the coordination information exchange to propose, accept, or negotiate orthogonal frequency resources to be allocated for wireless communications in BSS1 and BSS2 during the overlapping service periods r-TWT SP1 and r-TWT SP2. 
     Still further, in some implementations, the access points AP 1  and AP 2  may coordinate the transmit powers of wireless communications in BSS1 and BSS2 during the service periods r-TWT SP1 and r-TWT SP2. In such implementations, the transmit power of latency-sensitive traffic in BSS1 may be suitably low so as not to interfere with latency-sensitive traffic in BSS2 and the transmit power of latency-sensitive traffic in BSS2 may be suitable low so as not to interfere with latency-sensitive traffic in BSS1. For example, prior to (or during) the service periods r-TWT SP1 and r-TWT SP2, the access points AP 1  and AP 2  may exchange coordination information indicating a transmit power to be used for wireless communications in at least one of BSS1 or BSS2 (such as in accordance with coordinated spatial reuse (C-SR) operation). The access points AP 1  and AP 2  may utilize the coordination information exchange to propose, accept, or negotiate transmit powers to be used for wireless communications in BSS1 and BSS2 during the overlapping service periods r-TWT SP1 and r-TWT SP2. 
     Aspects of the present disclosure recognize that STAs located close to an AP (such as STAs  501  and  504  of  FIG.  5   ) are less susceptible to interference from an OBSS than STAs located further from the AP. Thus, lowering the transmit power of wireless communications associated with such STAs may effectively suppress interference between OBSSs during overlapping r-TWT SPs. In some aspects, each of the access points AP 1 , AP 2 , and AP 3  may assign or otherwise allocate low-latency STAs to the service periods r-TWT SP1, r-TWT SP2, and r-TWT SP3, respectively, based on r-TWT schedule information carried in beacon or other management frames transmitted prior to (or during) one or more r-TWT SPs. In some implementations, the r-TWT schedule information associated with a particular r-TWT SP may assign one or more STAs to that r-TWT SP. In some other implementations, a STA may request to join a particular r-TWT SP responsive to receiving r-TWT schedule information associated with that r-TWT SP. 
     As shown in  FIG.  7   , the access point AP 1  transmits a beacon frame  701 , at time t 0 , carrying r-TWT schedule information indicating the schedule associated with r-TWT SP1. With reference for example to  FIG.  5   , the beacon frame  701  may be transmitted by the AP  511  and may assign or otherwise allocate the STA  501  to r-TWT SP1. The access point AP 2  transmits a beacon frame  702 , at time t 0 , carrying r-TWT schedule information indicating the schedule associated with r-TWT SP2. With reference for example to  FIG.  5   , the beacon frame  702  may be transmitted by the AP  512  and may assign or otherwise allocated the STA  504  to r-TWT SP2. The access point AP 3  transmits a beacon frame  703 , at time t 0 , carrying r-TWT schedule information indicating the schedule associated with r-TWT SP3. With reference for example to  FIG.  5   , the beacon frame  703  may assign or otherwise allocate the STA  506  to r-TWT SP3. Although  FIG.  7    shows the beacon frames  701 - 703  being transmitted at the same time (t 0 ), in some other implementations, one or more of the beacon frames  701 - 703  may be transmitted at a different time. 
     In some implementations, the beacon frames  701  and  702  broadcast by the coordinated access points AP 1  and AP 2 , respectively, may further carry coordinated r-TWT signaling information. As described herein, the coordinated r-TWT signaling information may indicate the r-TWT SP schedules associated with one or more OBSSs. For example, the beacon frame  701  may carry coordinated r-TWT signaling information indicating the schedules for one or more of the service periods r-TWT SP2 or r-TWT SP3 and the beacon frame  702  may carry coordinated r-TWT signaling information indicating the schedules for one or more of the service periods r-TWT SP1 or r-TWT SP3. More specifically, the schedule for r-TWT SP1 may indicate that r-TWT SP1 is to occur from times t 1  to t 2 , the schedule for r-TWT SP2 may indicate that r-TWT SP2 is also to occur from times t 1  to t 2 , and the schedule for r-TWT SP3 may indicate that r-TWT SP3 is to occur from times t 2  to t 3 . 
     In some implementations, STAs associated with the access point AP 1  (or BSS1) may avoid accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS3 during r-TWT SP3 based on the coordinated r-TWT signaling information received from the access point AP 1 . In some other implementations, the access point AP 1  may schedule a quiet interval to overlap with r-TWT SP3, for example, to prevent legacy STAs associated with the access point AP 1  (or BSS1) from accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS3 during r-TWT SP3. In some implementations, STAs associated with the access point AP 2  (or BSS2) may avoid accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS3 during r-TWT SP3 based on the coordinated r-TWT signaling information received from the access point AP 2 . In some other implementations, the access point AP 2  may schedule a quiet interval to overlap with r-TWT SP3, for example, to prevent legacy STAs associated with the access point AP 2  (or BSS2) from accessing the wireless channel or otherwise interfering with latency-sensitive communications in BSS3 during r-TWT SP3. 
     Aspects of the present disclosure recognize that the SP coordination techniques described with reference to  FIGS.  5 - 7    require accurate timing information to be conveyed to the devices associated with each of the OBSSs. For example, to avoid accessing a shared wireless channel during an r-TWT SP associated with a given BSS, a STA associated with an OBSS must know (with relative accuracy) the start time of the r-TWT SP. According to existing versions of the IEEE 802.11 standard, the starting time of an SP is defined as an integer value associated with a timing synchronization function (TSF) timer associated with the AP (or BSS) that schedules the SP. The current value of the TSF timer is included in beacons (and other frames) transmitted by the AP and used to synchronize local TSF timers maintained by other devices associated with the BSS. However, the TSF timer associated with a given BSS may be offset in relation to the TSF timer associated with an OBSS. Such offset between TSF timers can affect the accuracy or effectiveness of SP coordination among the OBSSs. 
     With reference for example to  FIG.  5   , the AP  511  may broadcast a beacon frame that includes a timestamp having a value equal to 185234501 μs (which corresponds to the value of the TSF timer associated with the AP  511  at the time the beacon is transmitted) and a TWT information element (IE) indicating an SP start time equal to 185236512 μs. In this example, STAs associated with BSS1 (such as the STAs  501  and  502 ) know that the SP will occur when their local TSF timers indicate 185236514 μs (or 2011 μs after the current beacon frame). However, the TSF timer associated with the AP  512  may be 5.21s ahead of the TSF timer associated with the AP  511 . As a result, the TSF timer associated with the AP  512  (as well as the local TSF timers associated with the STAs  503 - 505 ) will have a value equal to 190446514 μs at the start of the SP associated with the OBSS. In other words, the TSF timer value (185236512 μs) indicated in the TWT IE of the beacon frame broadcast by the AP  511  does not accurately reflect the start of the SP relative to the TSF timer associated with BSS2. 
     In some aspects, coordinated APs may correct the timing of SPs indicated by the coordinated r-TWT signaling information transmitted to their associated STAs to account for offsets between TSF timers associated with the coordinated APs. For example, an AP may receive timing information indicating a timing of an SP associated with an OBSS and may transmit, to its associated STAs, corrected (or “coordinated”) timing information indicating the timing of the SP relative to a TSF timer associated with the AP. In some implementations, the AP may adjust the received timing information by at least the amount of offset between its TSF timer and a TSF timer associated with the OBSS. For example, if the TSF timer associated with the AP is 5.21s ahead of the TSF timer associated with the OBSS, the AP may add 5.21s to the start time indicated by the received timing information. As a result, the timing information received by the AP may be different than the coordinated timing information transmitted to its associated STAs. In some other implementations, the AP may synchronize its TSF timer with the TSF timer associated with the OBSS. In such implementations, the timing information received by the AP may be the same as the coordinated timing information transmitted to its associated STAs. 
     Aspects of the present disclosure also recognize that the offset between a TSF timer associated with a BSS and a TSF timer associated with an OBSS may affect the scheduling of quiet intervals coinciding with SPs associated with the OBSS. As described herein, a quiet interval can be scheduled via a quiet element included in management frames (such as beacon frames or probe response frames). The quiet element includes a quiet count field and a quiet offset field. The value of the quiet count field indicates a number of TBTTs until the beacon interval during which the quiet interval begins and the value of the quiet offset field indicates an offset (in TUs) associated with the start of the quiet interval relative to the TBTT specified by the quiet count field. As such, the timing of a quiet interval is defined with respect to the TBTTs associated with the AP that schedules the quiet interval. Because TBTTs are further defined in relation to the TSF timer associated with a given AP, offsets between TSF timers associated with OBSSs may lead to offset TBTTs between the OBSSs. In some aspects, coordinated APs may use the coordinated timing information to schedule quiet intervals that overlap the SPs associated with OBSSs. For example, an AP may specify the start time of a quiet interval (overlapping an SP associated with an OBSS) relative to its own TBTTs. 
       FIG.  8 A  shows a sequence diagram  800  depicting an example message exchange between devices associated with OBSSs (BSS1 and BSS2). As shown in  FIG.  8 A , BSS1 includes an AP  802  and a STA  804 , and BSS2 includes an AP  806  and a STA  808 . In some implementations, each of the APs  802  and  806  may be one example of the APs  511  and  512 , respectively, of  FIG.  5   , the STA  804  may be one example of any of the STAs  501  or  502 , and the STA  808  may be one example of any of the STAs  503 - 505 . 
     In some aspects, the APs  802  and  806  may coordinate the scheduling of SPs so that communications in BSS2 do not interfere or collide with communications in BSS1 (such as described with reference to any of  FIGS.  5 - 7   ). In the example of  FIG.  8 A , the AP  802  schedules a first SP (SP1) and transmits or broadcasts timing information indicating a timing (or start time) of SP1 to the STA  804 . For example, SP1 may be an r-TWT SP, a coordinated r-TWT SP, or a coordinated SP, among other examples. As shown in  FIG.  8 A , the SP1 timing information may be carried in a first beacon frame (such as in a TWT IE) broadcast by the AP  802 . However, in some implementations, the SP1 timing information may be transmitted separately from the beacon frame. For example, the SP1 timing information may be carried in timing advertisement frames, other types of management frames, new frame types, or new fields or information elements in existing frame types. In some implementations, the STA  804  may join SP1 (as a member of an r-TWT SP) responsive to receiving the SP1 timing information from the AP  802 . 
     The AP  806  also receives the first beacon frame and the SP1 timing information from the AP  802  and calculates a TSF timer offset based on a timestamp included in the beacon frame. As described herein, the timestamp indicates the value of the TSF timer associated with the AP  802  at the time the beacon frame is transmitted. In some implementations, the offset between the TSF timers associated with the APs  802  and  806  can be determined as the difference between the timestamp included in the first beacon frame and the value of the TSF timer associated with the AP  806  at the time the first beacon frame is received (plus propagation delay). In some implementations, the amount of propagation delay can be estimated by the AP  806  (for example, based on frames or packets received from the AP  802 ). In some other implementations, the amount of propagation delay can be estimated by the AP  802  and provided to the AP  806  (for example, in the beacon frame or other frames transmitted to the AP  806 ). Still further, in some implementations, the AP  806  may assume the propagation delay to be negligible. In some aspects, the AP  806  may adjust the received SP1 timing information to account for the TSF timer offset between the APs  802  and  806 . For example, the AP  806  may add the TSF timer offset to the received SP1 timing information to obtain the adjusted SP1 timing information (where the TSF timer offset is a positive or negative value depending on whether the TSF timer associated with the AP  806  is ahead of, or behind, the TSF timer associated with the AP  802 ). 
     In some aspects, the AP  806  may schedule one or more SPs (associated with BSS2) based on the adjusted SP1 timing information. In some implementations, the AP  806  may schedule a second SP to be orthogonal in time to SP1 (such as described with reference to  FIG.  6   ). In some other implementations, the AP  806  may schedule a second SP to overlap in time with SP1 (such as described with reference to  FIG.  7   ). In such implementations, the access points AP  802  and  806  may further coordinate the allocation of resources (such as transmit power, timing, or frequency allocations) for wireless communications during the overlapping service periods. In some aspects, the AP  806  may further transmit or broadcast the adjusted SP1 timing information to the STA  808 . In some implementations, the adjusted SP1 timing information may be carried in beacons or other management frames (such as in a TWT IE or a timing advertisement element). In some other implementations, the adjusted SP1 timing information may be carried in a timing advertisement frame. Still further, in some implementations, the adjusted SP1 timing information may be carried in a new type of frame or in a new field or IEs of an existing frame. 
     In some aspects, the AP  806  may further schedule a quiet interval to at least partially overlap SP1. For example, the AP  806  transmit beacons or management frames including a quiet element indicating the timing of the quiet interval. In some implementations, the AP  806  may configure one or more fields of the quiet element to indicate the timing of the quiet interval based on the adjusted SP1 timing information. For example, the AP  806  may set the values of the quiet count field and the quiet offset field to indicate the start time of the quiet interval relative to the TBTTs associated with the AP  806 . As a result, non-legacy STAs (such as the STA  808 ) associated with the AP may schedule their communications to avoid interfering with communications in BSS1, during SP1, based on the adjusted SP1 timing information, while legacy STAs (not shown for simplicity) associated with the AP may avoid accessing the wireless channel during the scheduled quiet interval (which overlaps SP1). 
     After a TBTT, the AP  802  transmits or broadcasts a second beacon frame. Because the second beacon frame is transmitted prior to the start of SP1, the second beacon frame also may carry the SP1 timing information. In some implementations, the AP  806  may receive the second beacon frame from the AP  802  and may calculate another TSF timer offset based on a timestamp included in the second beacon frame. In some instances, the TSF timer offset associated with the second beacon frame may be different than the TSF timer offset associated with the first beacon frame as a result of clock drift between the TSF timers associated with the APs  802  and  806 . For example, the TSF timer associated with the AP  802  may be faster or slower than the TSF timer associated with the AP  806 . As a result, the AP  806  may receive the second beacon frame sooner or later than expected (in relation to the beacon interval indicated by the beacon frames). 
     In some aspects, the AP  806  may further adjust the SP1 timing information based on the most recent TSF timer offset. As such, the SP1 timing information may be periodically updated or adjusted to account for clock drift between the TSF timers associated with the APs  802  and  806 . In some implementations, the AP  806  may reschedule (or update the schedule for) one or more of the SP associated with BSS2 to account for changes in the relative timing of SP1 due to clock drift. In some aspects, the AP  806  may further transmit or broadcast the updated SP1 timing information to the STA  808 . In some implementations, the AP  806  also may update any quiet intervals scheduled to overlap SP1 based on the amount of clock drift. For example, the AP  806  may transmit beacons or management frames including a quiet element with updated timing information associated with the quiet interval. More specifically, the AP  806  may update the values of the quiet count field and the quiet offset field to account for the amount of clock drift between the TSF timers associated with the APs  802  and  806 . 
     Aspects of the present disclosure recognize that the TSF timers associated with OBSSs may continue to drift over time. However, frequently updating the SP1 timing information may consume significant resources and communications overhead among devices in BSS2 (such as the AP  806  and the STA  808 ). Thus, in some aspects, the AP  806  may factor clock drift into the timing information provided to the STA  808 . In some implementations, the AP  806  may determine an amount of clock drift between the TSF timers based on the timer offsets calculated with respect to successive beacon frames received from the AP  802 . More specifically, changes in the calculated timer offset between successive beacon frames may reflect the amount of clock drift between the TSF timers associated with the APs  802  and  806 . In some implementations, the AP  806  may transmit or broadcast clock drift information, indicating the amount of clock drift, to its associated STAs. In such implementations, the STAs may further adjust the received SP1 timing information to account for clock drift. In some other implementations, the AP  806  may add a buffer period to the SP1 timing information provided to its associated STAs. In such implementations, the buffer period may be long enough to at least account for clock drift or propagation delay. 
       FIG.  8 B  shows a sequence diagram  810  depicting an example message exchange between devices associated with OBSSs (BSS1 and BSS2). As shown in  FIG.  8 B , BSS1 includes an AP  812  and a STA  814 , and BSS2 includes an AP  816  and a STA  818 . In some implementations, each of the APs  812  and  816  may be one example of the APs  511  and  512 , respectively, of  FIG.  5   , the STA  814  may be one example of any of the STAs  501  or  502 , and the STA  818  may be one example of any of the STAs  503 - 505 . 
     In some aspects, the APs  812  and  816  may coordinate the scheduling of SPs so that communications in BSS2 do not interfere or collide with communications in BSS1 (such as described with reference to any of  FIGS.  5 - 7   ). In the example of  FIG.  8 B , the AP  812  schedules a first SP (SP1) and transmits or broadcasts timing information indicating a timing (or start time) of SP1 to the STA  814 . For example, SP1 may be an r-TWT SP, a coordinated r-TWT SP, or a coordinated SP, among other examples. As shown in  FIG.  8 B , the SP1 timing information may be carried in a first beacon frame (such as in a TWT IE) broadcast by the AP  812 . However, in some implementations, the SP1 timing information may be transmitted separately from the beacon frame. For example, the SP1 timing information may be carried in timing advertisement frames, other types of management frames, new frame types, or new fields or information elements in existing frame types. In some implementations, the STA  814  may join SP1 (as a member of an r-TWT SP) responsive to receiving the SP1 timing information from the AP  812 . 
     The AP  816  also receives the first beacon frame and the SP1 timing information from the AP  812  and calculates a TSF timer offset based on a timestamp included in the beacon frame. As described herein, the timestamp indicates the value of the TSF timer associated with the AP  812  at the time the beacon frame is transmitted. In some implementations, the offset between the TSF timers associated with the APs  812  and AP  816  can be determined as the difference between the timestamp included in the first beacon frame and the value of the TSF timer associated with the AP  816  at the time the first beacon frame is received (plus propagation delay). In some implementations, the amount of propagation delay can be estimated by the AP  816  (for example, based on frames or packets received from the AP  812 ). In some other implementations, the amount of propagation delay can be estimated by the AP  812  and provided to the AP  816  (for example, in the beacon frame or other frames transmitted to the AP  816 ). Still further, in some implementations, the AP  816  may assume the propagation delay to be negligible. In some aspects, the AP  816  may adjust the received SP1 timing information to account for the TSF timer offset between the APs  812  and  816 . For example, the AP  816  may add the TSF timer offset to the received SP1 timing information to obtain the adjusted SP1 timing information (where the TSF timer offset is a positive or negative value depending on whether the TSF timer associated with the AP  816  is ahead of, or behind, the TSF timer associated with the AP  812 ). 
     In some aspects, the AP  816  may schedule one or more SPs (associated with BSS2) based on the adjusted SP1 timing information. In some implementations, the AP  816  may schedule a second SP to be orthogonal in time to SP1 (such as described with reference to  FIG.  6   ). In some other implementations, the AP  816  may schedule a second SP to overlap in time with SP1 (such as described with reference to  FIG.  7   ). In such implementations, the access points AP  812  and  816  may further coordinate the allocation of resources (such as transmit power, timing, or frequency allocations) for wireless communications during the overlapping service periods. In some aspects, the AP  816  may further transmit or broadcast the adjusted SP1 timing information to the STA  818 . In some implementations, the adjusted SP1 timing information may be carried in beacons or other management frames (such as in a TWT IE or a timing advertisement element). In some other implementations, the adjusted SP1 timing information may be carried in a timing advertisement element of a timing advertisement frame. Still further, in some implementations, the adjusted SP1 timing information may be carried in a new type of frame or in a new field or IEs of an existing frame. 
     In some aspects, the AP  816  may further schedule a quiet interval to at least partially overlap SP1. For example, the AP  816  may transmit beacons or management frames including a quiet element indicating the timing of the quiet interval. In some implementations, the AP  816  may configure one or more fields of the quiet element to indicate the timing of the quiet interval based on the adjusted SP1 timing information. For example, the AP  816  may set the values of the quiet count field and the quiet offset field to indicate the start time of the quiet interval relative to the TBTTs associated with the AP  816 . As a result, non-legacy STAs (such as the STA  818 ) associated with the AP may schedule their communications to avoid interfering with communications in BSS1, during SP1, based on the adjusted SP1 timing information, while legacy STAs (not shown for simplicity) associated with the AP may avoid accessing the wireless channel during the scheduled quiet interval (which overlaps SP1). 
     After a TBTT, the AP  812  transmits or broadcasts a second beacon frame. Because the second beacon frame is transmitted prior to the start of SP1, the second beacon frame also may carry the SP1 timing information. In some implementations, the AP  816  may receive the second beacon frame from the AP  812  and may calculate an amount of clock drift between the TSF timers associated with the APs  812  and  816  based on a timestamp included in the second beacon frame. For example, the AP  816  may calculate an updated timer offset between the TSF timers associated with the APs  812  and  816  based on the timestamp included in the second beacon frame and may determine the amount of clock drift based on changes or differences in the timer offsets calculated with respect to the first beacon frame and the second beacon frame. In some implementations, the AP  816  may reschedule (or update the schedule for) one or more of the SPs associated with BSS2 to account for changes in the relative timing of SP1 due to clock drift. 
     In some aspects, the AP  816  may further transmit or broadcast clock drift information, indicating the amount of clock drift (plus propagation delay), to the STA  818 . In some implementations, the amount of propagation delay can be estimated by the AP  816  (for example, based on frames or packets received from the AP  812 ). In some other implementations, the amount of propagation delay can be estimated by the AP  812  and provided to the AP  816  (for example, in the beacon frame or other frames transmitted to the AP  816 ). Still further, in some implementations, the AP  816  may assume the propagation delay to be negligible. In some implementations, the clock drift information may indicate the exact amount of clock drift between the APs  812  and  816 . In some other implementations, the clock drift information may indicate a relative amount of clock drift (such as in relation to a reference timer or value). In some implementations, the clock drift information may indicate a timing error (such as a mean or standard deviation of the estimated error associated with the clock drift information). Still further, in some implementations, the clock drift information may include an estimated time difference between a reference time and a timestamp included with the clock drift information (such as in the same frame or packet). 
     In some implementations, the clock drift information may be carried in beacons or other management frames (such as in a new field or IE or a timing advertisement element). In some other implementations, the clock drift information may be carried in a timing advertisement frame. Still further, in some implementations, the clock drift information may be carried in a new type of frame or in a new field or IEs of an existing frame. As a result, the STA  818  may update the SP1 timing information previously received from the AP  816  to account for the clock drift. For example, the STA  818  may calculate how far apart the TSF timers associated with the APs  812  and  816  will drift by the start of SP1 and update the SP1 timing information to account for the amount of drift. Accordingly, the STA  818  may schedule its communications to avoid interfering with communications in BSS1, during SP1, based on the updated SP1 timing information. 
     Aspects of the present disclosure recognize that legacy STAs may not be able to interpret the clock drift information transmitted or broadcast by the AP  816 . Thus, in some implementations, the AP  816  may further update any quiet intervals scheduled to overlap SP1 based on the amount of clock drift. For example, the AP  816  may transmit beacons or management frames including a quiet element with updated timing information associated with the quiet interval. More specifically, the AP  816  may update the values of the quiet count field and the quiet offset field to account for the amount of clock drift between the TSF timers associated with the APs  802  and  806 . As a result, any legacy STAs associated with the AP also may update their channel access schedules to avoid accessing the wireless channel during the updated quiet intervals (which are corrected to overlap SP1 due to clock drift). 
       FIG.  8 C  shows a sequence diagram  820  depicting an example message exchange between devices associated with OBSSs (BSS1 and BSS2). As shown in  FIG.  8 C , BSS1 includes an AP  822  and a STA  824 , and BSS2 includes an AP  826  and a STA  828 . In some implementations, each of the APs  822  and  826  may be one example of the APs  511  and  512 , respectively, of  FIG.  5   , the STA  824  may be one example of any of the STAs  501  or  502 , and the STA  828  may be one example of any of the STAs  503 - 505 . 
     In some aspects, the APs  822  and  826  may coordinate the scheduling of SPs so that communications in BSS2 do not interfere or collide with communications in BSS1 (such as described with reference to any of  FIGS.  5 - 7   ). In the example of  FIG.  8 C , the AP  822  schedules a first SP (SP1) and transmits or broadcasts timing information indicating a timing (or start time) of SP1 to the STA  824 . For example, SP1 may be an r-TWT SP, a coordinated r-TWT SP, or a coordinated SP, among other examples. As shown in  FIG.  8 C , the SP1 timing information may be carried in a first beacon frame (such as in a TWT IE) broadcast by the AP  822 . However, in some implementations, the SP1 timing information may be transmitted separately from the beacon frame. For example, the SP1 timing information may be carried in timing advertisement frames, other types of management frames, new frame types, or new fields or information elements in existing frame types. In some implementations, the STA  824  may join SP1 (as a member of an r-TWT SP) responsive to receiving the SP1 timing information from the AP  822 . 
     The AP  826  also receives the first beacon frame and the SP1 timing information from the AP  822  and calculates a TSF timer offset based on a timestamp included in the beacon frame. As described herein, the timestamp indicates the value of the TSF timer associated with the AP  822  at the time the beacon frame is transmitted. In some implementations, the offset between the TSF timers associated with the APs  822  and AP  826  can be determined as the difference between the timestamp included in the first beacon frame and the value of the TSF timer associated with the AP  826  at the time the first beacon frame is received (plus propagation delay). In some implementations, the amount of propagation delay can be estimated by the AP  826  (for example, based on frames or packets received from the AP  822 ). In some other implementations, the amount of propagation delay can be estimated by the AP  822  and provided to the AP  826  (for example, in the beacon frame or other frames transmitted to the AP  826 ). Still further, in some implementations, the AP  826  may assume the propagation delay to be negligible. In some aspects, the AP  826  may adjust the received SP1 timing information to account for the TSF timer offset between the APs  822  and  826 . For example, the AP  826  may add the TSF timer offset to the received SP1 timing information to obtain the adjusted SP1 timing information (where the TSF timer offset is a positive or negative value depending on whether the TSF timer associated with the AP  826  is ahead of, or behind, the TSF timer associated with the AP  822 ). 
     In some aspects, the AP  826  may schedule one or more SPs (associated with BSS2) based on the adjusted SP1 timing information. In some implementations, the AP  826  may schedule a second SP to be orthogonal in time to SP1 (such as described with reference to  FIG.  6   ). In some other implementations, the AP  826  may schedule a second SP to overlap in time with SP1 (such as described with reference to  FIG.  7   ). In such implementations, the access points AP  822  and  826  may further coordinate the allocation of resources (such as transmit power, timing, or frequency allocations) for wireless communications during the overlapping service periods. In some aspects, the AP  826  may further transmit or broadcast the adjusted SP1 timing information to the STA  828 . In some implementations, the adjusted SP1 timing information may be carried in beacons or other management frames (such as in a TWT IE or a timing advertisement element). In some other implementations, the adjusted SP1 timing information may be carried in a timing advertisement frame. Still further, in some implementations, the adjusted SP1 timing information may be carried in a new type of frame or in a new field or IEs of an existing frame. 
     In some aspects, the AP  826  may further schedule a quiet interval to at least partially overlap SP1. For example, the AP  826  may transmit beacons or management frames including a quiet element indicating the timing of the quiet interval. In some implementations, the AP  826  may configure one or more fields of the quiet element to indicate the timing of the quiet interval based on the adjusted SP1 timing information. For example, the AP  826  may set the values of the quiet count field and the quiet offset field to indicate the start time of the quiet interval relative to the TBTTs associated with the AP  826 . As a result, non-legacy STAs (such as the STA  828 ) associated with the AP may schedule their communications to avoid interfering with communications in BSS1, during SP1, based on the adjusted SP1 timing information, while legacy STAs (not shown for simplicity) associated with the AP may avoid accessing the wireless channel during the scheduled quiet interval (which overlaps SP1). 
     After a TBTT, the AP  822  transmits or broadcasts a second beacon frame. Because the second beacon frame is transmitted prior to the start of SP1, the second beacon frame also may carry the SP1 timing information. In some implementations, the AP  826  may receive the second beacon frame from the AP  822  and may calculate an amount of clock drift between the TSF timers associated with the APs  822  and  826  based on a timestamp included in the second beacon frame. For example, the AP  826  may calculate an updated timer offset between the TSF timers associated with the APs  822  and  826  based on the timestamp included in the second beacon frame and may determine the amount of clock drift based on changes or differences in the timer offsets calculated with respect to the first beacon frame and the second beacon frame. In some implementations, the AP  826  may reschedule (or update the schedule for) one or more of the SPs associated with BSS2 to account for changes in the relative timing of SP1 due to clock drift. 
     In some aspects, the AP  826  may further update the SP1 timing information based on the clock drift. In some implementations, the AP  826  may add a buffer period to the adjusted SP1 timing information calculated with respect to the first beacon frame. The buffer period provides a margin of error for the adjusted SP1 timing information to ensure that devices associated with BSS2 do not interfere with communications in BSS1 at the start of SP1. Thus, the duration of the buffer period may be greater than or equal to the amount of clock drift expected to occur by the start of SP1. In some implementations, the AP  826  may add a buffer period to the adjusted SP1 timing information even if the amount of clock drift is unknown. For example, the buffer period may have a fixed duration (such as 100 μs) that is long enough to account for a threshold amount of clock drift (or propagation delay). In some aspects, the AP  826  may further transmit or broadcast the updated SP1 timing information to the STA  828 . In some implementations, the updated SP1 timing information may be carried in beacons or other management frames (such as in a TWT IE or a timing advertisement element). In some other implementations, the updated SP1 timing information may be carried in a timing advertisement frame. Still further, in some implementations, the updated SP1 timing information may be carried in a new type of frame or in a new field or IEs of an existing frame. 
     Aspects of the present disclosure recognize that legacy STAs may not be able to interpret the updated SP1 timing information transmitted or broadcast by the AP  826 . Thus, in some implementations, the AP  826  may further update any quiet intervals scheduled to overlap SP1 based on the amount of clock drift. For example, the AP  826  may transmit beacons or management frames including a quiet element with updated timing information associated with the quiet interval. More specifically, the AP  826  may update the values of the quiet count field and the quiet offset field to account for the amount of clock drift between the TSF timers associated with the APs  802  and  806 . As a result, any legacy STAs associated with the AP also may update their channel access schedules to avoid accessing the wireless channel during the updated quiet intervals (which are corrected to overlap SP1 due to clock drift). 
       FIG.  9    shows a sequence diagram  900  depicting an example message exchange between devices associated with OBSSs (BSS1 and BSS2). As shown in  FIG.  9   , BSS1 includes an AP  902  and a STA  904 , and BSS2 includes an AP  906  and a STA  908 . In some implementations, each of the APs  902  and  906  may be one example of the APs  511  and  512 , respectively, of  FIG.  5   , the STA  904  may be one example of any of the STAs  501  or  502 , and the STA  908  may be one example of any of the STAs  503 - 505 . 
     In some aspects, the APs  902  and  906  may synchronize their respective TSF timers. For example, each AP in a group of coordinated APs may synchronize its TSF timer to a master AP associated with the group. For example, the master AP may be selected as the AP with the fastest drifting TSF timer among the group of coordinated APs. Other suitable master AP selection criteria may include various capability and operation parameters (such as r-TWT SPs, r-TWT support, or BSS load, among other examples). In some implementations, the master AP may be negotiated or otherwise designated upon establishing the group of coordinated APs. In some other implementations, the master AP may be dynamically selected so that the most suitable AP is selected as the master AP at any given time (based on the selection criteria). In the example of  FIG.  9   , the AP  902  is selected as the master AP. Thus, the AP  906  may synchronize its TSF timer to the TSF timer associated with the AP  902 . 
     In some implementations, the AP  902  may transmit TSF synchronization information to the AP  906 . The TSF synchronization information may include any information that can be used by the AP  906  to synchronize its TSF timer to the TSF timer associated with the AP  902 . In some implementations, the TSF synchronization information may include a timestamp of a beacon frame transmitted or broadcast by the AP  902 . In some other implementations, the TSF synchronization information may be carried in a timing advertisement frame. Still further, in some implementations, the TSF synchronization information may be carried in a new type of frame or in a new field or IEs of an existing frame. 
     In some aspects, the AP  902  may transmit the TSF synchronization information separately from beacon frames transmitted to its associated STAs (such as the STA  904 ), for example, to ensure more reliable delivery of the TSF synchronization information. In some implementations, the TSF synchronization information may be transmitted on a different channel than the wireless channel on which intra-BSS communications (such as between the AP  902  and the STA  904 ) occur. In some other implementations, the TSF synchronization information may be transmitted during designated SPs (such as particular r-TWT SPs). In some implementations, one or more STAs may act as bridges or relays between coordinated APs. For example, if the STA  908  is within the coverage area of the AP  902 , the STA  908  may receive or intercept the TSF synchronization information from the AP  902  and forward the information to the AP  906 . 
     In some aspects, the AP  906  may synchronize its TSF timer to the TSF timer associated with the AP  902  based on the received TSF synchronization information. As described herein, the timestamp included in a beacon frame indicates the value of the TSF timer associated with the AP  902  at the time the beacon frame is transmitted. Thus, in some implementations, the AP  906  may synchronize its TSF timer to the TSF timer associated with the AP  902  by setting its TSF timer to the value indicated by the timestamp of a beacon frame received from the AP  902  (plus propagation delay). In some implementations, the amount of propagation delay can be estimated by the AP  826  (for example, based on frames or packets received from the AP  822 ). In some other implementations, the amount of propagation delay can be estimated by the AP  822  and provided to the AP  826  (for example, in the beacon frame or other frames transmitted to the AP  826 ). Still further, in some implementations, the AP  826  may assume the propagation delay to be negligible. Any STAs associated with the AP  906  (such as the STA  908 ) may synchronize their respective TSF timers to the TSF timer associated with the AP  906  based on beacon frames transmitted or broadcast by the AP  906  (in accordance with existing versions of the IEEE 802.11 standard). 
     In some aspects, the APs  902  and  906  may coordinate the scheduling of SPs so that communications in BSS2 do not interfere or collide with communications in BSS1 (such as described with reference to any of  FIGS.  5 - 7   ). In the example of  FIG.  9   , the AP  902  schedules a first SP (SP1) and transmits or broadcasts timing information indicating a timing (or start time) of SP1 to the STA  904 . For example, SP1 may be an r-TWT SP, a coordinated r-TWT SP, or a coordinated SP, among other examples. As shown in  FIG.  9   , the SP1 timing information may be carried in a first beacon frame (such as in a TWT IE) broadcast by the AP  902 . However, in some implementations, the SP1 timing information may be transmitted separately from the beacon frame. For example, the SP1 timing information may be carried in timing advertisement frames, other types of management frames, new frame types, or new fields or information elements in existing frame types. In some implementations, the STA  904  may join SP1 (as a member of an r-TWT SP) responsive to receiving the SP1 timing information from the AP  902 . 
     The AP  906  also receives the first beacon frame and the SP1 timing information from the AP  902 . In some aspects, the AP  906  may schedule one or more SPs (associated with BSS2) based on the received SP1 timing information. Because the TSF timers are synchronized among the APs  902  and  906  (and their associated STAs), the AP  906  does not need to adjust the SP1 timing information to account for timer offset. In some implementations, the AP  906  may schedule a second SP to be orthogonal in time to SP1 (such as described with reference to  FIG.  6   ). In some other implementations, the AP  906  may schedule a second SP to overlap in time with SP1 (such as described with reference to  FIG.  7   ). In such implementations, the access points AP  902  and  906  may further coordinate the allocation of resources (such as transmit power, timing, or frequency allocations) for wireless communications during the overlapping service periods. In some aspects, the AP  906  may further transmit or broadcast the SP1 timing information to the STA  908 . For example, the AP  906  may copy the received SP1 timing information directly into a packet or frame for transmission to the STA  908 . In some implementations, the SP1 timing information may be carried in beacons or other management frames (such as in a TWT IE or a timing advertisement element). In some other implementations, the SP1 timing information may be carried in a timing advertisement frame. Still further, in some implementations, the SP1 timing information may be carried in a new type of frame or in a new field or IEs of an existing frame. 
     In some aspects, the AP  906  may further schedule a quiet interval to at least partially overlap SP1. For example, the AP  906  may transmit beacons or management frames including a quiet element indicating the timing of the quiet interval. In some implementations, the AP  906  may set the values of the quiet count field and the quiet offset field to indicate the start time of the quiet interval relative to the TBTTs associated with the AP  906 . As a result, non-legacy STAs (such as the STA  908 ) associated with the AP may schedule their communications to avoid interfering with communications in BSS1, during SP1, based on the SP1 timing information, while legacy STAs (not shown for simplicity) associated with the AP may avoid accessing the wireless channel during the scheduled quiet interval (which overlaps SP1). 
     After a TBTT, the AP  902  transmits or broadcasts a second beacon frame. Because the second beacon frame is transmitted prior to the start of SP1, the second beacon frame also may carry the SP1 timing information. As described herein, the TSF timers associated with the APs  902  and  906  may drift apart over time. In some implementations, the AP  906  may resynchronize its TSF timer to the TSF timer associated with the AP  902  based on the timestamp included in the second beacon frame. Any STAs associated with the AP  906  (such as the STA  908 ) may synchronize their respective TSF timers to the TSF timer associated with the AP  906  based on beacon frames transmitted or broadcast by the AP  906  (in accordance with existing versions of the IEEE 802.11 standard). Because the TSF timers are synchronized among the APs  902  and  906  (and their associated STAs), the AP  906  does not need to update the SP1 timing information to correct for clock drift (such as described with reference to  FIG.  8 A ), transmit clock drift information to the STA  908  (such as described with reference to  FIG.  8 B ), or add a buffer period to the SP1 timing information (such as described with reference to  FIG.  8 C ). 
       FIG.  10    shows an illustrative flowchart  1000  depicting an example wireless communication operation. The example operation  1000  may be performed by a wireless communication device such as any of the APs  110  or  300  of  FIGS.  1  and  3   , respectively. 
     The wireless communication device receives first timing information indicating a timing of a first SP associated with an OBSS ( 1002 ). The wireless communication device transmits, to one or more STAs, second timing information indicating the timing of the first SP, where the second timing information is associated with a first TSF timer associated with the wireless communication device ( 1004 ). The wireless communication device further communicates with the one or more STAs, via a first wireless channel, associated with the second timing information ( 1006 ). 
     In some aspects, the first timing information may be different than the second timing information. In some implementations, the wireless communication device may further receive, from an AP associated with the OBSS, a second beacon frame that includes a first timestamp associated with a second TSF timer and perform a timer offset calculation operation that indicates an offset between the first TSF timer and the second TSF timer associated with the first timestamp. In some implementations, the difference between the first timing information and the second timing information may be equal to the offset indicated by the timer offset calculation operation. 
     In some implementations, the wireless communication device may further receive, from the AP, a third beacon frame that includes a second timestamp associated with a second TSF timer and perform a clock drift calculation operation that indicates an amount of drift between the first TSF timer and the second TSF timer associated with the first timestamp and the second timestamp. In some implementations, the difference between the first timing information and the second timing information may be equal to the offset indicated by the timer offset calculation operation plus a buffer duration that is greater than or equal to the amount of drift indicated by the clock drift calculation operation. In some other implementations, the wireless communication device may further transmit, to the one or more STAs, clock drift information indicating the amount of drift between the first TSF timer and the second TSF timer. 
     In some other aspects, the first timing information may be equal to the second timing information. In some implementations, the wireless communication device may further obtain, from an AP associated with the OBSS, TSF synchronization information associated with a second TSF timer and synchronize the first TSF timer to the second TSF timer associated with the TSF synchronization information. In some implementations, the TSF synchronization information may be received over a second wireless channel that is different than the first wireless channel. In some other implementations, the TSF synchronization information may be received during a second SP that is different than the first SP. Still further, in some implementations, a STA associated with the wireless communication device may intercept the TSF synchronization information from the AP and relay or retransmit the information to the wireless communication device. 
     In some aspects, the communications between the wireless communication device and the one or more STAs may be orthogonal to communications associated with the OBSS during the first SP. In some implementations, the wireless communication device may transmit scheduling information indicating a second SP associated with the wireless communication device, where the communications between the wireless communication device and the one or more STAs occurs during the second SP. Still further, in some aspects, the wireless communication device may transmit a quiet element associated with the first TSF timer, where the quiet element indicates a quiet interval that overlaps the first SP. 
       FIG.  11    shows an illustrative flowchart  1100  depicting an example wireless communication operation. The example operation  1100  may be performed by a wireless communication device such as any of the STAs  120   a - 120   i  of  FIG.  1    or the STA  200  of  FIG.  2   . 
     The wireless communication device synchronizes a local TSF timer with a first TSF timer associated with a BSS ( 1102 ). The wireless communication device receives timing information indicating a timing of a first SP associated with an OBSS, where the timing information is associated with the first TSF timer ( 1104 ). The wireless communication device further communicates with one or more devices associated with the BSS and the received timing information ( 1106 ). 
     In some implementations, the wireless communication device may further receive clock drift information indicating an amount of clock drift between the first TSF timer and a second TSF timer associated with the OBSS, where the communications between the wireless communication device and the one or more devices is further associated with the received clock drift information. In some implementations, the wireless communication device may further receive, from a first AP associated with the OBSS, TSF synchronization information associated with a second TSF timer and transmit the TSF synchronization information to a second AP associated with the BSS. 
     In some aspects, the wireless communications between the wireless communication device and the one or more devices may be orthogonal to communications associated with the OBSS during the first SP. In some implementations, the wireless communication device may further receive scheduling information indicating a second SP associated with the BSS, where the communications between the wireless communication device and the one or more devices occur during the second SP. 
       FIG.  12    shows a block diagram of an example wireless communication device  1200 . In some implementations, the wireless communication device  1200  may be configured to perform the operation  1000  described with reference to  FIG.  10   . The wireless communication device  1200  can be an example implementation of any of the APs  110  or  300  of  FIGS.  1  and  3   , respectively. More specifically, the wireless communication device  1200  can be a chip, SoC, chipset, package or device that includes at least one processor and at least one modem (for example, a Wi-Fi (IEEE 802.11) modem or a cellular modem). 
     The wireless communication device  1200  includes a reception component  1210 , a communication manager  1220 , and a transmission component  1230 . The communication manager  1220  further includes an SP signaling component  1222 . Portions of the SP signaling component  1222  may be implemented at least in part in hardware or firmware. In some implementations, the SP signaling component  1222  is implemented at least in part as software stored in a memory (such as the memory  240  of  FIG.  2    or the memory  330  of  FIG.  3   ). For example, portions of the SP signaling component  1222  can be implemented as non-transitory instructions (or “code”) executable by a processor (such as the processor  320  of  FIG.  3   ) to perform the functions or operations of the respective component. 
     The reception component  1210  is configured to receive RX signals from one or more other wireless communication devices. In some implementations, the reception component  1210  may receive first timing information indicating a timing of a first SP associated with an OBSS. The communication manager  1220  is configured to manage wireless communications with one or more other wireless communication devices. In some implementations, the SP signaling component  1222  may transmit, to one or more STAs, second timing information indicating the timing of the first SP, where the second timing information is associated with a first TSF timer associated with the wireless communication device. The transmission component  1230  is configured to transmit TX signals to one or more other wireless communication devices. In some implementations, the transmission component  1230  may communicate with the one or more STAs, via a wireless channel, associated with the second timing information. 
       FIG.  13    shows a block diagram of an example wireless communication device  1300 . In some implementations, the wireless communication device  1300  may be configured to perform the operation  1100  described with reference to  FIG.  11   . The wireless communication device  1300  can be an example implementation of any of the STAs  120   a - 120   i  of  FIG.  1    or the STA  200  of  FIG.  2   . More specifically, the wireless communication device  1300  can be a chip, SoC, chipset, package or device that includes at least one processor and at least one modem (for example, a Wi-Fi (IEEE 802.11) modem or a cellular modem). 
     The wireless communication device  1300  includes a reception component  1310 , a communication manager  1320 , and a transmission component  1330 . The communication manager  1320  further includes a TSF timer synchronization component  1322 . Portions of the TSF timer synchronization component  1322  may be implemented at least in part in hardware or firmware. In some implementations, the TSF timer synchronization component  1322  is implemented at least in part as software stored in a memory (such as the memory  240  of  FIG.  2    or the memory  330  of  FIG.  3   ). For example, portions of the TSF timer synchronization component  1322  can be implemented as non-transitory instructions (or “code”) executable by a processor (such as the processor  220  of  FIG.  2   ) to perform the functions or operations of the respective component. 
     The reception component  1310  is configured to receive RX signals from one or more other wireless communication devices. In some implementations, the reception component  1310  may receive timing information indicating a timing of a first SP associated with an OBSS, where the timing information is associated with the first TSF timer. The communication manager  1320  is configured to manage wireless communications with one or more other wireless communication devices. In some implementations, the TSF timer synchronization component  1322  may synchronize a local TSF timer with a first TSF timer associated with a BSS. The transmission component  1330  is configured to transmit TX signals to one or more other wireless communication devices. In some implementations, the transmission component  1330  may communicate with one or more devices associated with the BSS associated with the received timing information. 
     Implementation examples are described in the following numbered clauses:
         1. A method for wireless communication by a wireless communication device, including:   receiving first timing information indicating a timing of a first service period (SP) associated with an overlapping basic service set (OBSS);   transmitting, to one or more wireless stations (STAs), second timing information indicating the timing of the first SP, the second timing information being associated with a first timing synchronization function (TSF) timer associated with the wireless communication device; and   communicating with the one or more STAs, via a first wireless channel, associated with the second timing information.   2. The method of clause 1, where the first timing information is different than the second timing information.   3. The method of any of clauses 1 or 2, further including:   receiving, from an access point (AP) associated with the OBSS, a second beacon frame that includes a first timestamp associated with a second TSF timer; and   performing a timer offset calculation operation that indicates an offset between the first TSF timer and the second TSF timer associated with the first timestamp.   4. The method of any of clauses 1-3, where the difference between the first timing information and the second timing information is equal to the offset indicated by the timer offset calculation operation.   5. The method of any of clauses 1-3, further including:   receiving, from the AP, a third beacon frame that includes a second timestamp associated with a second TSF timer; and   performing a clock drift calculation operation that indicates an amount of drift between the first TSF timer and the second TSF timer associated with the first timestamp and the second timestamp.   6. The method of any of clauses 1-3 or 5, where the difference between the first timing information and the second timing information is equal to the offset indicated by the timer offset calculation operation plus a buffer duration that is greater than or equal to the amount of drift indicated by the clock drift calculation operation.   7. The method of any of clauses 1-3 or 5, further including:   transmitting, to the one or more STAs, clock drift information indicating the amount of drift between the first TSF timer and the second TSF timer.   8. The method of clause 1, where the first timing information is equal to the second timing information.   9. The method of any of clauses 1 or 8, further including:   obtaining, from an AP associated with the OBSS, TSF synchronization information associated with a second TSF timer; and   synchronizing the first TSF timer to the second TSF timer associated with the TSF synchronization information.   10. The method of any of clauses 1, 8, or 9, where the TSF synchronization information is received over a second wireless channel that is different than the first wireless channel.   11. The method of any of clauses 1 or 8-10, where the TSF synchronization information is received during a second SP that is different than the first SP.   12. The method of any of clauses 1 or 8-11, where the obtaining of the TSF synchronization information includes:   receiving the TSF synchronization information from a STA that intercepts the TSF synchronization information from the AP.   13. The method of any of clauses 1-12, where the communications with the one or more STAs are orthogonal to communications associated with the OBSS during the first SP.   14. The method of any of clauses 1-13, where the communicating with the one or more STAs includes:   transmitting scheduling information indicating a second SP associated with the wireless communication device, the communications with the one or more STAs occurring during the second SP.   15. The method of any of clauses 1-14, further including:   transmitting a quiet element associated with the first TSF timer, the quiet element indicating a quiet interval that overlaps the first SP.   16. A wireless communication device, including:   a processing system; and   an interface configured to:
           receive first timing information indicating a timing of a first service period (SP) associated with an overlapping basic service set (OBSS);   transmit, to one or more wireless stations (STAs), second timing information indicating the timing of the first SP, the second timing information being associated with a first timing synchronization function (TSF) timer associated with the wireless communication device; and   communicate with the one or more STAs associated with the second timing information.   
           17. The wireless communication device of clause 16, where the first timing information is different than the second timing information, and where:   the interface is further configured to receive, from an access point (AP) associated with the OBSS, a second beacon frame that includes a first timestamp associated with a second TSF timer; and   the processing system is further configured to perform a timer offset calculation operation that indicates an offset between the first TSF timer and the second TSF timer associated with the first timestamp.   18. The wireless communication device of any of clauses 16 or 17, where the difference between the first timing information and the second timing information is equal to the offset indicated by the timer offset calculation operation.   19. The wireless communication device of any of clauses 16 or 17, where:   the interface is further configured to receive, from the AP, a third beacon frame that includes a second timestamp associated with a second TSF timer; and   the processing system is further configured to perform a clock drift calculation operation that indicates an amount of drift between the first TSF timer and the second TSF timer associated with the first timestamp and the second timestamp.   20. The wireless communication device of any of clauses 16, 17, or 19, where the difference between the first timing information and the second timing information is equal to the offset indicated by the timer offset calculation operation plus a buffer duration that is greater than or equal to the amount of drift indicated by the clock drift calculation operation.   21. The wireless communication device of any of clauses 16, 17, or 19, where the interface is further configured to transmit, to the one or more STAs, clock drift information indicating the amount of drift between the first TSF timer and the second TSF timer.   22. The wireless communication device of clause 16, where the first timing information is equal to the second timing information, the processing system being further configured to:   obtain, from an access point (AP) associated with the OBSS, TSF synchronization information associated with a second TSF timer; and   synchronize the first TSF timer to the second TSF timer associated with the TSF synchronization information.   23. The wireless communication device of any of clauses 16-22, where the interface is further configured to transmit a quiet element associated with the first TSF timer, the quiet element indicating a quiet interval that overlaps the first SP.   24. A method performed by a wireless communication device, including:   synchronizing a local timing synchronization function (TSF) timer with a first TSF timer associated with a basic service set (BSS);   receiving timing information indicating a timing of a first service period (SP) associated with an overlapping basic service set (OBSS), the timing information being associated with the first TSF timer; and   communicating with one or more devices associated with the BSS and the received timing information.   25. The method of clause 24, where the communicating with the BSS includes:   receiving clock drift information indicating an amount of drift between the first TSF timer and a second TSF timer associated with the OBSS, the communications with the one or more devices being further associated with the received clock drift information.   26. The method of clause 24, further including:   receiving, from a first access point (AP) associated with the OBSS, TSF synchronization information associated with a second TSF timer; and   transmitting the TSF synchronization information to a second AP associated with the BSS.   27. The method of any of clauses 24-26, where the communications with the one or more devices are orthogonal to communications associated with the OBSS during the first SP.   28. The method of any of clauses 24-27, where the communicating with the one or more devices includes:   receiving scheduling information indicating a second SP associated with the BSS, the communications with the one or more devices occurring during the second SP.   29. A wireless communication device, including:   a processing system configured to synchronize a local timing synchronization function (TSF) timer with a first TSF timer associated with a basic service set (BSS); and   an interface configured to:
           receive timing information indicating a timing of a service period (SP) associated with an overlapping basic service set (OBSS), the timing information being associated with the first TSF timer; and   communicate with one or more devices associated with the BSS and the received timing information.   
           30. The wireless communication device of clause 29, where the interface is further configured to receive clock drift information indicating an amount of drift between the first TSF timer and a second TSF timer associated with the OBSS, the communications with the one or more devices being further associated with the received clock drift information.       

     As used herein, a phrase referring to “at least one of” or “one or more of” a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c. 
     The various illustrative components, logic, logical blocks, modules, circuits, operations and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware or software, including the structures disclosed in this specification and the structural equivalents thereof. The interchangeability of hardware, firmware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described herein. Whether such functionality is implemented in hardware, firmware or software depends upon the particular application and design constraints imposed on the overall system. 
     Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein. 
     Additionally, various features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described herein as acting in particular combinations, and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.