Limited TWT with Enhanced Multi-Link Single Radio (EMLSR) Operation

Abstract

A method and apparatus for facilitating coexistence of Enhanced Multi-Link Single Radio (EMLSR) operation and Target Wake Time (TWT) operation in a wireless local area network. A non-Access Point (AP) MLD includes STAs, each including a transceiver forming a link with a corresponding AP of the AP MLD, and a processor. A Restricted-TWT (R-TWT) schedule is established on a first link, a first STA on the link is a member of an R-TWT Service Period (SP) on the link. A second STA on a second link is not a member of any R-TWT SP on the link that overlaps with an R-TWT SP on the first link. The processor transitions the non-AP MLD to EMLSR operation, the first link and the second link form an EMLSR link pair, and determines that a transmission opportunity (TXOP) has begun on the second link, and coordinates between the STAs such that a frame exchange sequence with the AP MLD on the second link during the TXOP does not overlap with an R-TWT SP on the first link.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates generally to power saving operation for latency sensitive traffic in wireless communication systems including multi-link devices. Embodiments of the present disclosure relate to methods and apparatus for facilitating the use of enhanced multi-link single radio operation with target wake time operation in multi-link devices in wireless local area network communication systems. [Background technology]

[0002] Wireless Local Area Network (WLAN) technology allows devices to access the Internet in the 2.4 GHz, 5 GHz, 6 GHz, or 60 GHz frequency bands. WLAN is based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. The IEEE 802.11 family of standards aims to increase the speed, reliability, and range of wireless networks.

[0003] Multi-Link Operation (MLO) is a key feature for next generation Extremely High Throughput (EHT) WI-FI systems, e.g., IEEE 802.11be. A WI-FI device that supports MLO is called a Multi-Link Device (MLD). With MLO, a non-access point (non-AP) MLD can discover, authenticate, associate, and set up multiple links with an AP MLD. Channel access and frame exchange are possible on each link set up between the AP MLD and the non-AP MLD.

[0004] Target Wake Time (TWT) is one of the key features of the IEEE 802.11ax amendment. TWT enables wake time negotiation between stations (STAs) associated with an access point (AP) to improve power efficiency. With TWT operation, a STA only needs to wake up at a pre-scheduled time negotiated with other STAs or APs in the network. The IEEE 802.11ax standard allows two types of TWT operation: individual TWT operation and broadcast TWT operation. An individual TWT agreement can be established between two STAs or between a STA and an AP. Meanwhile, with broadcast TWT (bTWT) operation, an AP can set up a shared TWT session for a group of STAs.

[0005] The negotiated parameters such as wake interval, wake duration, and initial wake time (offset) greatly affect the latency, throughput, and power efficiency, which are directly related to QoS (Quality of Service) or customer experience. Services with different traffic characteristics will have different TWT parameter configurations for better QoS. In addition, the TWT configuration should adapt to the changes of network and service conditions.

[0006] TWT allows non-AP STAs to wake up only at specified times, thereby reducing power consumption. Some applications (e.g., cloud gaming, AR glasses) may have periodic burst traffic with very strict latency requirements. At the time of TWT setup by a non-AP STA, the STA may not have traffic delay information (i.e., arrival time of downlink traffic) at the AP. This may lead to a large delay between DL traffic arrival time and TWT service period (SP) start time. This may significantly affect latency-sensitive applications. If a non-AP STA has information about traffic delay at the AP, it can adjust its TWT parameters accordingly and thus better support TWT traffic.

[0007] Based on the broadcast TWT operation, the restricted TWT (rTWT or R-TWT) operation is a feature introduced to provide better support for latency-sensitive applications. Restricted TWT provides a protected service period for other STAs in the BSS that are not members of the restricted TWT schedule by sending a quiet element to them, where the quiet interval corresponding to the quiet element overlaps with the initial part of the restricted TWT SP. Thus, restricted TWT gives more channel access opportunities to STAs scheduled as restricted TWT members, helping latency-sensitive traffic flows.

[0008] TWT operation may be essential for efficient power management for MLD. Broadcast TWT is a special type of TWT operation where multiple STAs can obtain membership in the same TWT schedule. A restricted TWT schedule, a variant of the broadcast TWT schedule, may be configured for multilink devices for efficient power management.

[0009] 802.11be non-AP MLD can have different capabilities for multi-link operation. Many 802.11be non-AP MLDs may only have a single radio. Enhanced Multi-Link Single Radio (EMLSR) allows multi-link operation with a single radio. With EMLSR operation, non-AP MLD can achieve increased throughput with reduced latency, i.e. performance approaching that of simultaneous dual-radio non-AP MLD. Summary of the Invention [Means for solving the problem]

[0010] DETAILED DESCRIPTION OF THE DRAWINGS Embodiments of the present disclosure provide methods and apparatus for facilitating coexistence of TWT and EMLSR operations for MLD in wireless local area networks.

[0011] In one embodiment, a non-AP MLD is provided, comprising a STA and a processor operably coupled to the STA. Each STA comprises a transceiver configured to form a link with a corresponding AP of the AP MLD. For communication on a first one of the links, an R-TWT schedule is established such that a first one of the STAs operating on the first link is a member of an R-TWT SP on the first link, and a second one of the STAs operating on a second link of the links is not a member of any other R-TWT SP on the second link that overlaps in time with the R-TWT SP on the first link. The processor is configured to transition the non-AP MLD to an EMLSR mode of operation, the first link and the second link form an EMLSR link pair, determine that a transmission opportunity (TXOP) has begun on the second link, and coordinate between the STAs such that a frame exchange sequence with the AP MLD on the second link during the TXOP does not overlap in time with the R-TWT SP on the first link.

[0012] In one embodiment, an AP MLD is provided, comprising an AP and a processor operably coupled to the AP. The APs each comprise a transceiver configured to form a link with a corresponding STA of the non-AP MLD. For communication on a first one of the links, an R-TWT schedule is established such that a first one of the STAs operating on the first link is a member of an R-TWT SP on the first link, and a second one of the STAs operating on a second link of the links is not a member of any other R-TWT SP on the second link that overlaps in time with the R-TWT SP on the first link. The processor is configured to determine that the non-AP MLD intends to transition to an EMLSR mode of operation, the first link and the second link form an EMLSR link pair, determine that a TXOP has begun on the second link, and coordinate between the APs such that a frame exchange sequence with the non-AP MLD on the second link during the TXOP does not overlap in time with the R-TWT SP on the first link.

[0013] In one embodiment, a method of wireless communication is provided, performed by non-AP MLD STAs each comprising a transceiver configured to form a link with a corresponding AP of the AP MLD, and an R-TWT schedule is established for communication on a first one of the links such that a first one of the STAs operating on the first link is a member of an R-TWT SP on the first link and a second one of the STAs operating on a second link of the links is not a member of any other R-TWT SP on the second link that overlaps in time with the R-TWT SP on the first link. The method includes transitioning the non-AP MLD to an EMLSR mode of operation, the first link and the second link forming an EMLSR link pair, determining that a TXOP has begun on the second link, and coordinating between the STAs such that a frame exchange sequence with the AP MLD on the second link during the TXOP does not overlap in time with the R-TWT SP on the first link.

[0014] Other technical features may be readily apparent to those skilled in the art from the following figures, descriptions, and claims.

[0015] Before proceeding with the detailed description below, it may be advantageous to provide definitions of some terms and phrases used throughout this patent specification. The term "couple" and its derivatives refer to any direct or indirect communication between two or more elements, regardless of whether they are in physical contact with one another. The terms "transmit", "receive", and "communicate" and their derivatives encompass both direct and indirect communication. The terms "include" and "comprise" and their derivatives mean including, but not limited to. The term "or" means and / or and is inclusive. The term "associated with" and its derivatives mean including, included in, interconnected, containing, contained in, connected, coupled, communicable, cooperating, interleaving, juxtaposing, adjacent, coupled, having, having a nature of, having a relationship, and the like. The term "controller" refers to any device, system, or part thereof that controls at least one operation. Such a controller may be implemented in hardware or a combination of hardware and software and / or firmware. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. When used in conjunction with a list of items, the phrase "at least one of" means that one or more different combinations of the listed items may be used, and only one item in the list may be required. For example, "at least one of A, B, and C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. As used herein, terms such as "first" and "second" or "first" and "second" may be used merely to distinguish corresponding components from others and do not limit the components in other aspects (e.g., importance or order).When an element (e.g., a first element) is described as being "coupled with," "coupled to," "connected to," or "connected to" another element (e.g., a second element), with or without the terms "operably" or "communicatively," it should be understood that this means that the element may be coupled to the other element directly (e.g., with a wire), wirelessly, or through a third element.

[0016] As used herein, the term "module" may include a unit implemented in hardware, software, or firmware, and may be used interchangeably with other terms, such as "logic," "logic block," "portion," or "circuit." A module may be a single integrated component or a minimum unit or portion thereof adapted to perform one or more functions. For example, according to one embodiment, a module may be implemented in the form of an application specific integrated circuit (ASIC).

[0017] Furthermore, various functions described below may be implemented or supported by one or more computer programs, each of which is formed from computer-readable program code and organized in a computer-readable medium. The terms "application" and "program" refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or portions thereof, adapted to be implemented in suitable computer-readable program code. The phrase "computer-readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer-readable medium" includes any type of medium that can be accessed by a computer, such as read-only memory (ROM), random access memory (RAM), hard disk drive, compact disc (CD), digital video disc (DVD), or any other type of memory. A "non-transitory" computer-readable medium excludes wired, wireless, optical, or other communication links that transmit transient electrical or other signals. Non-transitory computer-readable media includes media in which data may be permanently stored and media in which data may be stored and later overwritten, such as a rewritable optical disk or an erasable memory device.

[0018] Definitions of several other words or phrases are provided throughout this patent specification. Those of skill in the art will understand that in many, if not most, cases such definitions apply to previous and future uses of the words and phrases so defined.

[0019] For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts and in which: [Brief description of the drawings]

[0020] [Figure 1]FIG. 1 illustrates an exemplary wireless network according to one embodiment of the present disclosure. [Figure 2a] FIG. 2 illustrates an exemplary AP according to one embodiment of the present disclosure. [Figure 2b] FIG. 2 illustrates an exemplary STA according to one embodiment of the present disclosure. [Diagram 3] A diagram showing an example of non-AP MLD transitioning to EMLSR mode according to an embodiment of the present disclosure. [Figure 4] FIG. 1 illustrates an example conflict between a TWT doze state and a listening mode of EMLSR operation, according to an embodiment of the present disclosure. [Diagram 5] FIG. 1 illustrates an example of suspension of TWT operation on one link during EMLSR operation on another link according to an embodiment of the present disclosure. [Figure 6] FIG. 13 illustrates an example of exempting a link from EMLSR listening mode according to an embodiment of the present disclosure. [Figure 7] FIG. 1 illustrates an example process for determining whether to exempt a link from EMLSR listening mode, according to an embodiment of the present disclosure. [Figure 8] FIG. 1 illustrates an example of implementing EMLSR listening mode during TWT SP on a link according to an embodiment of the present disclosure. [Figure 9] FIG. 1 illustrates an example of avoiding initiating a frame exchange sequence during a TWT SP on a link based on the remaining duration of the TWT SP, according to an embodiment of the present disclosure. [Figure 10] FIG. 13 illustrates an example of terminating a TXOP early during EMLSR operation based on overlap with a TWT SP, according to an embodiment of the present disclosure. [Figure 11] FIG. 1 illustrates an example of continuing an ongoing EMLSR frame exchange during a period when a TWT SP is scheduled on a different link, according to an embodiment of the present disclosure. [Figure 12]FIG. 1 illustrates an example process for determining whether to continue or terminate an ongoing EMLSR TXOP on a link when the TXOP overlaps with a scheduled TWT SP on another link, in accordance with an embodiment of the present disclosure. [Figure 13] A diagram illustrating an example format of an R-TWT link selection frame, according to an embodiment of the present disclosure. [Figure 14] FIG. 2 illustrates an example process for facilitating coexistence of TWT and EMLSR operations for MLD in a WLAN in accordance with one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 1 through 14 described below and the various embodiments used in this patent specification to illustrate the principles of the present disclosure are merely illustrative and should not be construed as limiting the scope of the present disclosure in any way. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

[0022] Embodiments of the present disclosure recognize that a non-AP STA collaborating with a non-AP MLD may establish one or more restricted TWT schedules over one or more links between the AP MLD and the non-AP MLD. The present disclosure considers a scenario in which the non-AP MLD establishes one or more restricted TWT schedules over a single link between the AP MLD and the non-AP MLD.

[0023]

[0013] Embodiments of the present disclosure further recognize that EMLSR operation poses some conflicts with TWT operation in MLD due to the interaction between the TWT doze state and the EMLSR listening mode, which requires all STAs to be awake, as well as the possibility that EMLSR operation requires remaining silent on a link while latency-sensitive traffic is scheduled for transmission on that link using TWT operation. Thus, embodiments of the present disclosure provide an apparatus and method that facilitates coexistence of TWT and EMLSR operations for MLD in wireless local area networks.

[0024] It should be understood that R-TWT is a subset of TWT, so any of the procedures described herein below with respect to R-TWT will also work with unrestricted TWT. It should be understood that while the purpose of R-TWT (protecting latency sensitive traffic) is served by reducing signaling overhead, reducing signaling overhead is beneficial regardless of whether the traffic is latency sensitive, and thus embodiments of the present disclosure are desirable for TWT modes of operation that do not necessarily include latency sensitive traffic.

[0025] 1 illustrates an exemplary wireless network 100 according to one embodiment of the present disclosure. The embodiment of wireless network 100 illustrated in FIG. 1 is for illustration purposes only. Other embodiments of wireless network 100 may be used without departing from the scope of the present disclosure.

[0026] The wireless network 100 includes an AP 101 and an AP 103. The AP 101 and the AP 103 communicate with at least one network 130, such as the Internet, a proprietary Internet Protocol (IP) network, or other data network. The AP 101 provides wireless access to the network 130 for multiple STAs 111-114 within the coverage area 120 of the AP 101. The APs 101-103 may communicate with each other and with the STAs 111-114 using Wi-Fi or other WLAN communication techniques.

[0027] Depending on the network type, other well-known terms such as "router" or "gateway" may be used in place of "access point" or "AP". For convenience, the term "AP" is used in this disclosure to refer to a network infrastructure component that provides wireless access to remote terminals. Given that in a WLAN, APs may also be referred to as STAs (e.g., AP STAs), given that APs also contend for wireless channels. Also, depending on the network type, other well-known terms such as "mobile station", "subscriber station", "remote terminal", "user equipment", "wireless terminal", or "user device" may be used in place of "station" or "STA". For convenience, the terms "station" and "STA" are used in this disclosure to refer to remote wireless equipment that wirelessly accesses an AP or contends for wireless channels in a WLAN, regardless of whether the STA is a mobile device (such as a mobile phone or smartphone) or is typically considered a fixed device (such as a desktop computer, AP, media player, fixed sensor, television, etc.). This type of STA may also be referred to as a non-AP STA.

[0028] In one embodiment of the present disclosure, each of the AP 101 and the AP 103 and each of the STAs 111-114 may be an MLD. In such an embodiment, the AP 101 and the AP 103 may be an AP MLD, and the STAs 111-114 may be non-AP MLDs. Each MLD is associated with two or more STAs. For convenience of explanation, an AP MLD is described herein as being associated with two or more APs (e.g., two or more AP STAs), and a non-AP MLD is described herein as being associated with two or more STAs (e.g., two or more non-AP STAs).

[0029] The dotted lines indicate the approximate extent of coverage areas 120 and 125, which are shown as approximately circular for illustrative and explanation purposes only. It should be clearly understood that coverage areas associated with an AP, such as coverage areas 120 and 125, may have other shapes, including irregular shapes, depending on the configuration of the AP in the wireless environment and variations in associated natural and man-made obstacles.

[0030] As described in more detail below, one or more of the APs may include circuitry and / or programming to facilitate coexistence of TWT and EMLSR operations for MLD in a WLAN. Although FIG. 1 illustrates an example of a wireless network 100, various modifications may be made to FIG. 1. For example, the wireless network 100 may include any number of APs and any number of STAs in any suitable configuration. Also, the AP 101 may directly communicate with any number of STAs and provide those STAs with wireless broadband access to the network 130. Similarly, each of the APs 101-103 may directly communicate with the network 130 and provide the STAs with direct wireless broadband access to the network 130. Additionally, the AP 101 and / or AP 103 may provide access to other or additional external networks, such as an external telephone network or other type of data network.

[0031] FIG. 2A illustrates an exemplary AP 101 according to one embodiment of the present disclosure. The embodiment of AP 101 illustrated in FIG. 2A is for illustrative purposes only, and AP 103 in FIG. 1 may have the same or similar configuration. In the embodiment described herein below, AP 101 is an AP MLD. However, APs come in a wide variety of configurations, and FIG. 2A does not limit the scope of the present disclosure to any particular implementation of an AP.

[0032] The AP MLD 101 is associated with multiple APs 202a-202n (e.g., sometimes referred to as AP1-APn). Each of the associated APs 202a-202n includes multiple antennas 204a-204n, multiple RF transceivers 209a-209n, a transmit (TX) processing circuit 214, and a receive (RX) processing circuit 219. The AP MLD 101 also includes a controller / processor 224, a memory 229, and a backhaul or network interface 234.

[0033] The illustrated components of each cooperating AP 202a-202n may represent the physical (PHY) layer and the lower media access control (LMAC) layer in the Open Systems Interconnection (OSI) networking model. In such an embodiment, the illustrated components of the AP MLD 101 represent a single upper MAC (UMAC) layer and other higher layers in the OSI model that are shared by all of the cooperating APs 202a-202n.

[0034] For each associated AP 202a-202n, the RF transceivers 209a-209n receive input RF signals, such as signals transmitted by STAs in the network 100, from the antennas 204a-204n. In some embodiments, each associated AP 202a-202n operates at a different bandwidth, e.g., 2.4 GHz, 5 GHz, or 6 GHz, and accordingly, the input RF signals received by each associated AP may be RF at different frequencies. The RF transceivers 209a-209n downconvert the input RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuitry 219, which generates processed baseband signals by filtering, decoding, and / or digitizing the baseband or IF signals. The RX processing circuitry 219 sends the processed baseband signals to the controller / processor 224 for further processing.

[0035] For each associated AP 202a-202n, the TX processing circuitry 214 receives analog or digital data (such as voice data, web data, email, or interactive video game data) from the controller / processor 224. The TX processing circuitry 214 encodes, multiplexes, and / or digitizes the output baseband data to generate a processed baseband or IF signal. The RF transceivers 209a-209n receive the processed output baseband or IF signal from the TX processing circuitry 214 and upconvert the baseband or IF signal to an RF signal that is transmitted via the antennas 204a-204n. In an embodiment in which each associated AP 202a-202n operates at a different bandwidth, e.g., 2.4 GHz, 5 GHz, or 6 GHz, the output RF signal transmitted by each associated AP may be a different frequency of RF.

[0036] The controller / processor 224 may include one or more processors or other processing devices that control the overall operation of the AP MLD 101. For example, the controller / processor 224 may control the reception of forward channel signals and the transmission of reverse channel signals by the RF transceivers 209a-209n, the RX processing circuitry 219, and the TX processing circuitry 214 in accordance with well-known principles. The controller / processor 224 may also support additional functionality, such as more advanced wireless communication functions. For example, the controller / processor 224 may support beamforming or directional routing operations in which output signals from multiple antennas 204a-204n are weighted differently to effectively steer the output signals in a desired direction. The controller / processor 224 may also support OFDMA operations in which output signals are assigned to different subsets of subcarriers for different recipients (e.g., different STAs 111-114). Any of a wide variety of other functions may be supported by the controller / processor 224 in the AP MLD 101, including facilitating coexistence of TWT and EMLSR operations for MLD in a WLAN. In some embodiments, the controller / processor 224 includes at least one microprocessor or microcontroller. The controller / processor 224 may also execute programs and other processes that reside in the memory 229, such as an OS. The controller / processor 224 may move data in or out of the memory 229 as required by the running processes.

[0037] The controller / processor 224 is also coupled to a backhaul or network interface 234. The backhaul or network interface 234 allows the AP MLD 101 to communicate with other devices or systems through a backhaul connection or through a network. The interface 234 can support communication through any suitable wired or wireless connection. For example, the interface 234 can allow the AP MLD 101 to communicate through a wired or wireless local area network or through a wired or wireless connection to a larger network (such as the Internet). The interface 234 includes any suitable structure that supports communication through a wired or wireless connection, such as an Ethernet or RF transceiver. The memory 229 is coupled to the controller / processor 224. A portion of the memory 229 can include RAM, and another portion of the memory 229 can include flash memory or other ROM.

[0038] As described in more detail below, the AP MLD 101 may include circuitry and / or programming to facilitate coexistence of TWT and EMLSR operations for MLD in a WLAN. FIG. 2A illustrates an example of an AP MLD 101, although various modifications may be made to FIG. 2A. For example, the AP MLD 101 may include any number of each of the components illustrated in FIG. 2A. As a particular example, the AP MLD 101 may include several interfaces 234, and the controller / processor 224 may support a routing function to route data between different network addresses. As another particular example, although each associated AP 202a-202n is shown including a single instance of the TX processing circuitry 214 and a single instance of the RX processing circuitry 219, the AP MLD 101 may include multiple instances of each (e.g., one per RF transceiver) in one or more of the associated APs 202a-202n. Alternatively, only one antenna and RF transceiver path may be included in one or more of the cooperating APs 202a-202n, such as a legacy AP. Also, various components of FIG. 2a may be combined, further subdivided, or omitted, and additional components may be added according to particular needs.

[0039] FIG. 2b illustrates an exemplary STA 111 according to one embodiment of the present disclosure. The embodiment of the STA 111 illustrated in FIG. 2b is for illustrative purposes only, and the STAs 111-115 in FIG. 1 may have the same or similar configurations. In the embodiment illustrated herein below, the STA 111 is a non-AP MLD. However, STAs come in a wide variety of configurations, and FIG. 2b does not limit the scope of the present disclosure to any particular implementation of a STA.

[0040] The non-AP MLD 111 is associated with a number of STAs 203a-203n (e.g., sometimes referred to as STA1-STAn). Each of the associated STAs 203a-203n includes an antenna 205, a radio frequency (RF) transceiver 210, a TX processing circuit 215, and a receive (RX) processing circuit 225. The non-AP MLD 111 also includes a microphone 220, a speaker 230, a controller / processor 240, an input / output (I / O) interface (IF) 245, a touch screen 250, a display 255, and a memory 260. The memory 260 includes an operating system (OS) 261 and one or more applications 262.

[0041] The illustrated components of each associated STA 203a-203n may represent the PHY and LMAC layers in the OSI networking model. In such an embodiment, the illustrated components of the non-AP MLD 111 represent a single UMAC layer and other higher layers in the OSI model that are shared by all of the associated STAs 203a-203n.

[0042] For each associated STA 203a-203n, the RF transceiver 210 receives from the antenna 205 an input RF signal transmitted by an AP of the network 100. In some embodiments, each associated STA 203a-203n operates at a different bandwidth, e.g., 2.4 GHz, 5 GHz, or 6 GHz, and accordingly, the input RF signal received by each associated STA may be a different frequency RF. The RF transceiver 210 downconverts the input RF signal to generate an intermediate frequency (IF) or baseband signal. The IF or baseband signal is sent to the RX processing circuit 225, which generates a processed baseband signal by filtering, decoding, and / or digitizing the baseband or IF signal. The RX processing circuit 225 transmits the processed baseband signal to the speaker 230 (e.g., in the case of voice data) or to the controller / processor 240 for further processing (e.g., in the case of web browsing data).

[0043] For each associated STA 203a-203n, the TX processing circuitry 215 receives analog or digital voice data from the microphone 220 or other outgoing baseband data (such as web data, email, or interactive video game data) from the controller / processor 240. The TX processing circuitry 215 encodes, multiplexes, and / or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceiver 210 receives the processed outgoing baseband or IF signal from the TX processing circuitry 215 and upconverts the baseband or IF signal to an RF signal that is transmitted via the antenna 205. In embodiments where each associated STA 203a-203n operates at a different bandwidth, e.g., 2.4 GHz, 5 GHz, or 6 GHz, the outgoing RF signal transmitted by each associated STA may be a different frequency of RF.

[0044] The controller / processor 240 may include one or more processors and execute basic OS programs 261 stored in memory 260 to control the overall operation of the non-AP MLD 111. In one such operation, the main controller / processor 240 controls the reception of forward channel signals and the transmission of reverse channel signals by the RF transceiver 210, the RX processing circuitry 225, and the TX processing circuitry 215 in accordance with well-known principles. The main controller / processor 240 may also include processing circuitry configured to facilitate coexistence of TWT and EMLSR operations for MLD in a WLAN. In some embodiments, the controller / processor 240 includes at least one microprocessor or microcontroller.

[0045] The controller / processor 240 may also execute other processes and programs resident in the memory 260, such as operations for facilitating coexistence of TWT and EMLSR operations for MLD in a WLAN. The controller / processor 240 may move data into or out of the memory 260 as required by the processes being executed. In some embodiments, the controller / processor 240 is configured to execute multiple applications 262, such as an application for facilitating coexistence of TWT and EMLSR operations for MLD in a WLAN. The controller / processor 240 may operate the multiple applications 262 based on an OS program 261 or in response to signals received from an AP. The main controller / processor 240 is also coupled to an I / O interface 245, which provides the non-AP MLD 111 with the ability to connect to other devices, such as laptop computers and handheld computers. The I / O interface 245 is a communication path between these accessories and the main controller 240.

[0046] Controller / processor 240 is also coupled to touchscreen 250 and display 255. An operator of non-AP MLD 111 can use touchscreen 250 to input data into non-AP MLD 111. Display 255 may be a liquid crystal display, light emitting diode display, or other display capable of rendering text and / or at least limited graphics, such as from a website. Memory 260 is coupled to controller / processor 240. A portion of memory 260 may include random access memory (RAM) and another portion of memory 260 may include flash memory or other read-only memory (ROM).

[0047] FIG. 2b illustrates an example of a non-AP MLD 111, although various modifications may be made to FIG. 2b. For example, various components of FIG. 2b may be combined, further subdivided, or omitted, and additional components may be added according to particular needs. In a particular example, one or more of the associated STAs 203a-203n may include any number of antennas 205 for MIMO communication with the AP 101. In another example, the non-AP MLD 111 may not include voice communication, or the controller / processor 240 may be divided into multiple processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Also, although FIG. 2b illustrates the non-AP MLD 111 configured as a mobile phone or smartphone, the non-AP MLD may be configured to operate as other types of mobile or fixed devices.

[0048] EMLSR operation and the behavior of STAs associated with a non-AP MLD during EMLSR operation mode are defined in the 802.11be standard. When a non-AP MLD wishes to operate in EMLSR mode with its associated AP MLD, the STA associated with the non-AP MLD sends an EML Operating Mode Notification frame to its associated AP associated with the AP MLD, and the EMLSR mode subfield of the EML control field in the EML Operating Mode Notification frame is set to 1.

[0049] Upon receiving an EML operation mode notification frame from a non-AP MLD, the AP MLD may send another EML operation mode notification frame on any valid link between the AP MLD and the non-AP MLD, and the EMLSR mode subfield of the EML Control field in the EML operation mode notification frame is set to 1. The AP associated with the AP MLD is expected to send an EML operation mode notification frame in response to an EML operation mode notification frame sent by a STA associated with a non-AP MLD within the timeout interval indicated by the Transition Timeout subfield of the EML Capabilities subfield in the Basic Variant Multi-Link element most recently exchanged between the AP MLD and the non-AP MLD.

[0050] The non-AP MLD transitions to EMLSR mode immediately upon receiving an EML operation mode announcement frame from an AP associated with the AP MLD with the EMLSR mode subfield of the EML control field set to 1, or immediately after the timeout interval indicated in the Transition Timeout subfield of the EML Capabilities field of the Basic Variable Multilink Element has elapsed after the end of the last PPDU contained in the EML operation mode announcement frame sent by the non-AP MLD, whichever occurs first. Upon transition to EMLSR operation mode, all STAs associated with the non-AP MLD transition to active mode (listening mode).

[0051] 3 illustrates an example of a non-AP MLD transitioning to an EMLSR mode according to an embodiment of the present disclosure. The AP MLD may be an AP MLD 101, and the non-AP MLD may be a non-AP MLD 111. Although the AP MLD 101 is shown with two cooperating APs and the non-AP MLD 111 is shown with two cooperating non-AP STAs, it should be understood that this process may be applied in a suitable MLD having any number of cooperating APs or STAs. For ease of explanation, it should be understood that references to the AP MLD and the non-AP MLD in the following further embodiments refer to the AP MLD 101 and the non-AP MLD 111, respectively.

[0052] In this example, AP1 and AP2 are two APs associated with AP MLD, and STA1 and STA2 are two non-AP STAs associated with non-AP MLD. Two links are set up between AP MLD and non-AP MLD, namely, link 1 between AP1 and STA1, and link 2 between AP2 and STA2. In this example, both link 1 and link 2 are valid links.

[0053] The non-AP MLD attempts to transition to EMLSR mode, so STA2 sends an EML operation mode notification frame 302 to AP2 over link 2 with the EMLSR mode subfield of the EML control field set to 1. In response to the EML operation mode notification frame 302 sent by the non-AP MLD, AP2 sends another EML operation mode notification frame 304 to STA2 with the EMLSR mode subfield of the EML control field set to 1. After receiving the EML operation mode notification frame 304 from the AP MLD, the non-AP MLD transitions to EMLSR mode, and both STA1 and STA2 transition to listening mode.

[0054] As explained above, when a non-AP MLD transitions to EMLSR mode, all STAs associated with the non-AP MLD must transition to listening mode (i.e., awake or active state, hereafter referred to as awake state for simplicity). However, this command to transition all links to awake state does not contribute to power saving operations such as TWT operations (individual TWT, broadcast TWT, or restricted TWT) established on any of the enabled links between the AP MLD and the non-AP MLD.

[0055] For example, when one or more TWT agreements or TWT schedules are established on a link between an AP MLD and a non-AP MLD, if the non-AP MLD transitions to an EMLSR operation mode, which requires all links to transition to an awake state, TWT operation for a STA collaborating with the AP MLD on the link on which one or more TWT agreements or schedules are established may be suspended since the STA may be in a TWT doze state according to the TWT agreement or schedule, but the EMLSR operation requires the STA to be in an awake state, and these two actions are contradictory.

[0056] If an AP MLD sends an initial control frame for EMLSR operation on a link where a non-AP MLD is in TWT doze state based on a TWT agreement / schedule, the STAs operating on that link in conjunction with a non-AP MLD will not be able to receive the initial control frame, and therefore, subsequent frame exchange sequences on that link will not be possible.

[0057] FIG. 4 illustrates an example conflict between the TWT doze state and the listening mode of EMLSR operation according to an embodiment of the present disclosure. In this example, AP1 and AP2 are two APs associated with the AP MLD. And STA1 and STA2 are two non-AP STAs associated with the non-AP MLD. Two links are set up between the AP MLD and the non-AP MLD, namely, link 1 between AP1 and STA1, and link 2 between AP2 and STA2. In this example, both link 1 and link 2 are valid links. And, a TWT agreement / schedule is established on link 1.

[0058] The non-AP MLD in Figure 4 attempts to transition to EMLSR mode, so STA2 sends an EML operation mode notification frame to AP2 over link 2 with the EMLSR mode subfield of the EML control field set to 1. In response to the EML operation mode notification frame sent by the non-AP MLD, AP2 sends another EML operation mode notification frame to STA2 with the EMLSR mode subfield of the EML control field set to 1. After receiving the EML operation mode notification frame from the AP MLD, the non-AP MLD transitions to EMLSR mode, at which point both STA1 and STA2 should transition to listening mode (awake state), as in the example of Figure 3.

[0059] 4, based on the established TWT agreement / schedule, STA2 is also expected to be in TWT doze state on link 1, while EMLSR operation dictates that STA1 be in listening mode. If the AP MLD sends an EMLSR initial control frame 402 (such as MU-RTS or BSRP) on link 1, STA1 cannot receive it because it is in TWT doze state due to its TWT operation. This is also inconsistent with the current 802.11be standard, which dictates that a non-AP MLD must be able to listen (i.e., be awake) on all links in order to perform clear channel assessment (CCA) or to receive the initial control frame 402.

[0060] In another example, when a non-AP MLD operates in EMLSR mode and a frame exchange sequence is taking place on one of the enabled links (e.g., the second link) between the AP MLD and the non-AP MLD, if a TWT schedule or agreement is set up through another link between the same AP MLD and the same non-AP MLD, and if the TWT SP on the first link overlaps in time with the frame exchange sequence taking place on the second link, then since only one link can transmit or receive at any given time instant during EMLSR operation, a STA associated with the non-AP MLD operating on the first link cannot transmit or receive frames even if the STA is awake during the TWT SP. This may disrupt the TWT operation on the first link.

[0061] FIG. 5 illustrates an example of suspending TWT operation on one link during EMLSR operation on another link according to an embodiment of the present disclosure. In this example, AP1 and AP2 are two APs associated with AP MLD. And STA1 and STA2 are two non-AP STAs associated with non-AP MLD. Two links are set up between AP MLD and non-AP MLD, namely, link 1 between AP1 and STA1, and link 2 between AP2 and STA2. In this example, both link 1 and link 2 are valid links. Furthermore, a restricted TWT agreement / schedule is established on link 1.

[0062] 5 is already operating in EMLSR mode, and a frame exchange sequence begins on link 2 between AP2 and STA2 during TXOP 502. During the frame exchange sequence on link 2, a restricted TWT SP 504 begins on link 1. However, since STA1 is not supposed to transmit or receive frames on link 1 while the non-AP MLD is operating in EMLSR mode and exchanging frames on the other link (link 2), STA1's UL / DL latency sensitive traffic cannot be transmitted using the restricted TWT SP 504. This impacts the latency sensitive applications of the non-AP MLD.

[0063] An embodiment of the present disclosure herein below provides mechanisms and necessary rules to enable coexistence of TWT and EMLSR operation modes for scenarios such as those shown in FIG. 4 and FIG.

[0064] According to one embodiment for a scenario where a TWT agreement or TWT schedule is established on a link between an AP MLD and a non-AP MLD, when the non-AP MLD transitions to an EMLSR operation mode, the link on which the TWT agreement or schedule is established is exempted from the need to be in listening mode if the STAs associated with the non-AP MLD operating on that link are scheduled to be in a doze state according to the established TWT agreement or TWT schedule. According to this embodiment, since the AP MLD has knowledge of the TWT agreement or schedule established on that link, the AP MLD does not send EMLSR initial control frames (MU-RTS, BSRP, etc.) over a link on which the associated STAs should be in a doze state based on the existing TWT agreement or schedule established on that link. That is, the AP MLD does not initiate frame exchange over a link on which the associated STAs should be in a doze state.

[0065] FIG. 6 illustrates an example of exempting links from EMLSR listening mode according to an embodiment of the present disclosure. In this example, AP1, AP2, and AP3 are three APs associated with the AP MLD. And STA1, STA2, and STA3 are three non-AP STAs associated with the non-AP MLD. Three links are set up between the AP MLD and the non-AP MLD, namely, link 1 between AP1 and STA1, link 2 between AP2 and STA2, and link 3 between AP3 and STA3. In this example, link 1, link 2, and link 3 are valid links. A TWT agreement / schedule is established on link 1.

[0066] The non-AP MLD in Figure 6 attempts to transition to EMLSR mode, so STA2 sends an EML operation mode notification frame with the EMLSR mode subfield of the EML control field set to 1 to AP2 through link 2. In response to the EML operation mode notification frame sent by the non-AP MLD, AP2 sends another EML operation mode notification frame with the EMLSR mode subfield of the EML control field set to 1 to STA2. After receiving the EML operation mode notification frame from the AP MLD, the non-AP MLD transitions to EMLSR mode, and both STA2 and STA3 transition to listening mode. However, according to the established TWT agreement / schedule, STA1 remains in doze state on link 1. Therefore, in the EMLSR frame exchange, the AP MLD sends the initial control frame on either link 2 or link 3, but not on link 1.

[0067] 7 illustrates an example process for determining whether to exempt a link from EMLSR listening mode, according to an embodiment of the present disclosure. The process of FIG. 7 is an example of a process that may be used to determine whether to allow link 1 of FIG. 6 to be exempt from EMLSR listening mode.

[0068] According to one embodiment for a scenario where a TWT agreement or TWT schedule is established on a link between an AP MLD and a non-AP MLD, when the non-AP MLD transitions to the EMLSR operation mode, the link on which the TWT agreement or schedule was established can still transition to the EMLSR listening mode if the TWT SP for the STAs associated with the non-AP MLD operating on that link overlaps in time with either the end of an EML operation mode notification frame sent by the AP associated with the AP MLD in response to an EML operation mode notification frame sent by another STA associated with the same non-AP MLD, or the end of the timeout duration indicated in the transition timeout subfield of the EML capabilities subfield in the basic variable multilink element, whichever occurs first. In some embodiments, the STAs associated with the non-AP MLD operating on that link remain in the listening mode until the TWT SP for that STA ends.

[0069] FIG. 8 illustrates an example of implementing EMLSR listening mode during TWT SP on a link according to an embodiment of the present disclosure. In FIG. 8, AP1, AP2, and AP3 are three APs associated with the AP MLD. And STA1, STA2, and STA3 are three non-AP STAs associated with the non-AP MLD. Three links are set up between the AP MLD and the non-AP MLD, namely, link 1 between AP1 and STA1, link 2 between AP2 and STA2, and link 3 between AP3 and STA3. In this example, link 1, link 2, and link 3 are valid links. A TWT agreement / schedule is established on link 1.

[0070] The non-AP MLD in Figure 8 attempts to transition to EMLSR mode, so STA2 sends an EML operation mode notification frame to AP2 over link 2 with the EMLSR mode subfield of the EML control field set to 1. In response to the EML operation mode notification frame sent by the non-AP MLD, AP2 sends another EML operation mode notification frame to STA2 with the EMLSR mode subfield of the EML control field set to 1.

[0071] At the end of the EML operation mode announcement frame received from the AP MLD (at time 802), STA1 is in the awake state during TWT SP based on the TWT agreement or schedule established on that link. Thus, after receiving the EML operation mode announcement frame from the AP MLD, at time 802, the non-AP MLD transitions to EMLSR mode and STA1, STA2, and STA3 transition to listening mode. However, STA1 stays in listening mode only until its TWT SP end time (time 804), after which STA1 transitions to the TWT doze state.

[0072] According to one embodiment for a scenario where a TWT agreement or TWT schedule is established on a link between an AP MLD and a non-AP MLD, when the non-AP MLD transitions to an EMLSR operation mode, even if the link on which the TWT agreement or schedule is established is in listening mode because the corresponding STA operating on the link is awake during the TWT SP, if the AP MLD determines that the remaining time in the TWT SP on the link is not sufficient to complete the subsequent frame exchange sequence, the AP MLD will not send an EMLSR initial control frame on the link. Otherwise, the AP MLD may initiate a frame exchange sequence on the link.

[0073] FIG. 9 illustrates an example of avoiding initiating a frame exchange sequence during a TWT SP on a link based on the remaining duration of the TWT SP according to an embodiment of the present disclosure. In this example, AP1, AP2, and AP3 are three APs associated with the AP MLD. And STA1, STA2, and STA3 are three non-AP STAs associated with the non-AP MLD. Three links are set up between the AP MLD and the non-AP MLD, namely, link 1 between AP1 and STA1, link 2 between AP2 and STA2, and link 3 between AP3 and STA3. In this example, link 1, link 2, and link 3 are valid links. A TWT agreement / schedule is established on link 1.

[0074] The non-AP MLD in Figure 9 attempts to transition to EMLSR mode, so STA2 sends an EML operation mode notification frame to AP2 over link 2 with the EMLSR mode subfield of the EML control field set to 1. In response to the EML operation mode notification frame sent by the non-AP MLD, AP2 sends another EML operation mode notification frame to STA2 with the EMLSR mode subfield of the EML control field set to 1.

[0075] At the end of the EML operation mode notification frame received from the AP MLD, STA1 is in the awake state in the TWT SP based on the TWT agreement or schedule established on that link. After receiving the EML operation mode notification frame from the AP MLD, the non-AP MLD transitions to the EMLSR mode and STA1, STA2, and STA3 transition to the listening mode. However, the remaining time 902 in the TWT SP is too short and not enough to complete the intended frame exchange sequence with STA1 as determined by the AP MLD. Therefore, the AP MLD does not consider link 1 as a viable option for frame exchange under EMLSR operation and chooses either link 2 or link 3 for the EMLSR frame exchange sequence (link 3 is chosen in this example).

[0076] According to some embodiments, a subset of valid links may be defined, namely the EMLSR linkset, which indicates the set of valid links on which the EMLSR operation may proceed, i.e. the EMLSR frame exchange sequence may proceed only on one of the links listed in the EMLSR linkset.

[0077] According to one such embodiment, during EMLSR operation, valid links between AP MLDs and non-AP MLDs not listed in the EMLSR linkset can operate independently of EMLSR operation through links listed in the EMLSR linkset. According to this embodiment, at any given instant, there may be multiple transmit / receive possible links during EMLSR mode operation, i.e., one transmit / receive link selected from the EMLSR linkset, and one or more transmit / receive links from non-EMLSR links (i.e., valid links not listed in the EMLSR linkset).

[0078] According to another such embodiment, during EMLSR operation, the active links between the AP MLD and the non-AP MLDs not listed in the EMLSR link set remain in a doze state during the entire EMLSR operation. According to this embodiment, at any given moment, there is only one transmit / receive enabled link in the entire non-AP MLD in EMLSR mode, and the link for transmit / receive is chosen from the links listed in the EMLSR link set.

[0079] According to yet another such embodiment, for a scenario in which a TWT agreement or TWT schedule is established on a link between an AP MLD and a non-AP MLD, when the non-AP MLD transitions to an EMLSR operation mode, the link on which the TWT agreement or schedule is established is not included in the EMLSR link set.

[0080] According to another embodiment, for a scenario where a non-AP MLD is operating in EMLSR mode and a frame exchange sequence is taking place on one of the enabled links (e.g., the second link) between the AP MLD and the non-AP MLD, if a TWT schedule / agreement is set up through another link (e.g., the first link) between the same AP MLD and the non-AP MLD, the TWT SP on the first link overlaps in time with the frame exchange sequence taking place on the second link, and the AP MLD terminates the frame exchange sequence on the second link before the TWT SP starts on the first link. If a STA associated with the non-AP MLD is a TXOP holder, the non-AP MLD can also terminate the TXOP.

[0081] FIG. 10 illustrates an example of implementing EMLSR listening mode during EMLSR operation on the basis of overlap with TWT SP according to an embodiment of the present disclosure. In this example, AP1, AP2, and AP3 are three APs associated with AP MLD. And STA1, STA2, and STA3 are three non-AP STAs associated with non-AP MLD. Three links are set up between AP MLD and non-AP MLD, namely, link 1 between AP1 and STA1, link 2 between AP2 and STA2, and link 3 between AP3 and STA3. In this example, link 1, link 2, and link 3 are valid links. In other embodiments, link 3 may be an invalid link. TWT agreement / schedule is established on link 1.

[0082] The non-AP MLD in Figure 10 has transitioned to EMLSR mode and the AP MLD has begun a frame exchange sequence with the non-AP MLD. AP2, operating on link 2, is the TXOP holder for TXOP 1002 on link 2. The original end time 1004 of TXOP 1002 overlaps in time with TWT SP 1008 on link 1. Therefore, AP2 ends its TXOP 1002 on link 2 early (at time 1010) before TWT SP 1008 begins on link 1 (i.e., before start time 1006 of TWT SP 1008).

[0083] In this example, AP2 also ends its TXOP 1002 on link 2 a threshold amount of time 1012 before the start time 1006 of the TWT SP 1008. This threshold amount of time may be the time required to switch from one link to the other for frame exchange so that the non-AP MLD has enough time to switch the required radio Tx / Rx chain from the frame exchange link (link 2) to the TWT link (link 1). According to one embodiment, this threshold amount of time may be the amount of time indicated in the EMLSR Padding Delay subfield in the EML Capabilities subfield of the Basic Multilink Element. According to one embodiment, this threshold may be 0 μs, 32 μs, 64 μs, 128 μs, or 256 μs or 512 μs. According to one embodiment, this threshold amount may be the amount of time indicated in the EMLSR Transition Delay subfield in the EML Capabilities subfield of the Basic Multilink Element. Other thresholds are also possible.

[0084] According to one embodiment for a scenario where the non-AP MLD operates in EMLSR mode and a frame exchange sequence is taking place on one of the valid links between the AP MLD and the non-AP MLD (e.g., the second link), if the TWT schedule / agreement is set up through another link (e.g., the first link) between the same AP MLD and the non-AP MLD, the TWT SP on the first link overlaps in time with the frame exchange sequence taking place on the second link, and based on the previous embodiment, if the AP MLD or the non-AP MLD finishes the frame exchange sequence on the second link before the TWT SP starts on the first link, no initial control frame exchange (e.g., MU-RTS, CTS, etc.) is required before transmitting frames on the first link during the TWT SP. Instead, at the beginning of the TWT SP, a STA associated with the non-AP MLD operating on the first link can start a frame exchange with its associated AP associated with the AP MLD without an EMLSR initial control frame exchange for that link.

[0085] According to one embodiment for a scenario where the non-AP MLD operates in EMLSR mode and a frame exchange sequence is taking place on one of the valid links between the AP MLD and the non-AP MLD (e.g., the second link), if a TWT schedule / agreement is set up through another link (e.g., the first link) between the same AP MLD and the non-AP MLD, the TWT SP on the first link overlaps in time with the frame exchange sequence taking place on the second link, and if the set of TIDs mapped to the first link for TWT schedule is also mapped to the second link, the AP MLD can continue the frame exchange sequence on the second link. According to this embodiment, traffic (including latency sensitive traffic) destined for the non-AP MLD on link 1 can be transmitted on the second link, and the STAs operating on the first link can remain in the TWT doze state even during the TWT SP.

[0086] FIG. 11 illustrates an example of continuing ongoing EMLSR frame exchange during a period when TWT SP is scheduled on different links according to an embodiment of the present disclosure. In this example, AP1, AP2, and AP3 are three APs associated with AP MLD. And STA1, STA2, and STA3 are three non-AP STAs associated with non-AP MLD. Three links are set up between AP MLD and non-AP MLD, namely, link 1 between AP1 and STA1, link 2 between AP2 and STA2, and link 3 between AP3 and STA3. In this example, link 1, link 2, and link 3 are valid links. In other embodiments, link 3 may be an invalid link. TWT agreement / schedule is established on link 1.

[0087] The non-AP MLD in Figure 11 has transitioned to EMLSR mode and the AP MLD has started a frame exchange sequence with the non-AP MLD. AP2, operating on link 2, is the TXOP holder for TXOP 1102 on link 2. TXOP 1102 overlaps with TWT SP 1104 on link 1. However, the set of TIDs that are mapped to link 1 for the TWT schedule are also mapped to link 2. Thus, traffic for the non-AP MLD that is intended to be transmitted on link 1 during TWT SP can be transmitted on link 2 during TXOP 1102 as part of the ongoing frame exchange sequence. STA1 can therefore remain in TWT doze state during TWT SP 1104.

[0088] 12 illustrates an example process for determining whether to continue or terminate an ongoing EMLSR TXOP on a link when the TXOP overlaps with a scheduled TWT SP on another link, according to an embodiment of the present disclosure. The process of FIG. 12 is one example of a process that may be used to determine whether to terminate an ongoing EMLSR TXOP that overlaps with a scheduled TWT SP on another link, as shown in the example of FIG. 10, or to continue the ongoing EMLSR TXOP until it falls into the time scheduled for the TWT SP, as shown in the example of FIG. 11.

[0089] According to another embodiment, when a non-AP MLD is operating in EMLSR mode with its associated AP MLD, and an AP operating in association with the AP MLD on one of the EMLSR links (e.g., the second link) between the AP MLD and the non-AP MLD is a TXOP holder on that link, if an R-TWT schedule is established on the other EMLSR link (e.g., the first link) between the same AP MLD and the non-AP MLD, or on either link if the non-AP MLD is a single wireless device, the AP operating in association with the AP MLD on the second link will terminate its TXOP before the R-TWT SP begins on the first link.

[0090] According to one embodiment, in the above scenario, the AP ends its TXOP on the second link a threshold amount of time before the R-TWT SP starts on the first link. This threshold amount of time can be the amount of time required to switch the link from one link to the other for frame exchange so that the non-AP MLD has enough time to switch the required radio Tx / Rx chain from the first link to the R-TWT link (first link). According to one embodiment, this threshold amount of time can be the amount of time indicated in the EMLSR Padding Delay subfield in the EML Capability subfield of the Basic Multilink Element. According to this embodiment, this threshold can be 0 μs, 32 μs, 64 μs, 128 μs, or 256 μs or 512 μs. According to one embodiment, this threshold amount can be the amount of time indicated in the EMLSR Transition Delay subfield in the EML Capability subfield of the Basic Multilink Element. Other thresholds are also possible.

[0091] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with its associated AP MLD, and a STA operating in association with the non-AP MLD on one of the EMLSR links (e.g., the second link) between the AP MLD and the non-AP MLD is a TXOP holder on that link, if an R-TWT schedule is established on the other EMLSR link (e.g., the first link) between the same AP MLD and the non-AP MLD, or on either link if the non-AP MLD is a single wireless device, the STA operating in association with the non-AP MLD on the second link terminates its TXOP before the R-TWT SP begins on the first link.

[0092] According to one embodiment, in the above scenario, the STA ends its TXOP on the second link a threshold amount of time before the R-TWT SP starts on the first link. This threshold amount of time can be the time required to switch links from one link to the other for frame exchange so that non-AP MLD has enough time to switch the required radio Tx / Rx chain from the first link to the R-TWT link (first link). This threshold can be one of the values ​​shown in the previous embodiment.

[0093] According to one embodiment, when a non-AP MLD intends to operate in EMLSR mode with an AP MLD, if an R-TWT schedule is established on one of the EMLSR links between the AP MLD and the non-AP MLD, the STAs associated with the non-AP MLD and operating on the links on which the R-TWT schedule is established are exempted from the need to be in listening mode after the non-AP MLD successfully transmits an EML Operation Mode Notification frame on one of the EMLSR links and the transition delay indicated in the Transition Timeout subfield of the EML Capability subfield in the Basic Multilink Element expires, or after receiving an EML Operation Mode Notification frame from the AP MLD, or after the end of frame exchange on one of the EMLSR links, or after the duration indicated in the EMLSR Transition Delay subfield after the end of the TXOP if the STA associated with the non-AP MLD is the initiator of the TXOP.

[0094] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with an AP MLD and an R-TWT schedule is established on one of the EMLSR links between the AP MLD and the non-AP MLD, the AP associated with the AP MLD may initiate frame exchange on that link without sending an initial control frame to the R-TWT-scheduled STA associated with the non-AP MLD and operating on that link.

[0095] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with an AP MLD and multiple R-TWT schedules are established on multiple links between the AP MLD and the non-AP MLD, if those links are also included in the EMLSR links and if an R-TWT SP on one link (e.g., a first link) overlaps in time with an R-TWT SP on another link (e.g., a second link), the non-AP MLD disables the EMLSR mode before the overlapping TWT SP starts on any of the links.

[0096] According to one embodiment of the scenario described above, instead of disabling the EMLSR link before the overlap of the R-TWT SPs begins, the non-AP MLD may select one of the two R-TWT SPs on one of the two links for frame exchange on the selected link during the R-TWT SP on that link. According to one embodiment of this scenario, the non-AP MLD may send some signaling to the AP MLD through any of the valid links between the AP MLD and the non-AP MLD to indicate which R-TWT link of the two links has been selected for frame exchange. Such signaling may be implemented using a frame that may include link ID information of the selected R-TWT link, broadcast TWT ID of the selected R-TWT schedule, etc. For example, a control frame, R-TWT SP indicator, may be used for this purpose.

[0097] 13 illustrates an example format of an R-TWT link selection frame according to an embodiment of the present disclosure. The Broadcast TWT ID subfield of the R-TWT link selection frame indicates the Broadcast TWT ID of the R-TWT schedule of the selected link among the overlapping R-TWT SP links for the EMLSR frame exchange. The Selected Link ID subfield of the R-TWT link selection frame indicates the Link ID of the selected link among the overlapping R-TWT SP links for the EMLSR frame exchange.

[0098] According to one embodiment, a link corresponding to an R-TWT SP (among multiple overlapping R-TWT SPs) that starts earlier than the other R-TWT SPs is selected as the EMLSR link. According to one embodiment, a link corresponding to an R-TWT SP (among multiple overlapping R-TWT SPs) that has a longer SP duration than the other R-TWT SPs is selected as the EMLSR link.

[0099] According to one embodiment, the link corresponding to the R-TWT SP (among multiple overlapping R-TWT SPs) that has a higher priority TID negotiated during the R-TWT setup phase than the other R-TWT SPs is selected as the EMLSR link. If both links have the same set of negotiated TIDs, according to one embodiment, the SP with the higher (or lower) broadcast TWT ID value is selected. According to one embodiment, the first check is to look at the R-TWT SP with the higher priority. If all of the overlapping SPs have the same priority, the second check for selecting the SP can be based on any of the methods mentioned above.

[0100] According to other embodiments for the above scenario, the AP MLD may also perform the selection of the R-TWT SP and indicate the selected link to the non-AP MLD based on any of the methods described in the previous embodiments.

[0101] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with its associated AP MLD, and an AP operating in one of the EMLSR links (e.g., the second link) between the AP MLD and the non-AP MLD is a TXOP holder in that link, if an R-TWT schedule is established in another EMLSR link (e.g., the first link) between the same AP MLD and the same non-AP MLD, or in either link if the non-AP MLD is a single radio device, the AP operating in the second link in association with the AP MLD may continue its transmission in the second link regardless of the R-TWT SP start time in the first link. Upon observing that downlink transmission has not stopped on the second link, the STA operating in the first link in association with the non-AP MLD may remain in a doze state even during its scheduled R-TWT SP duration. According to one embodiment, in the above scenario, an AP associated with AP MLD and operating on the second link may continue its transmission on the second link if the AP has downlink latency sensitive traffic for a STA associated with non-AP MLD and operating on the second link.

[0102] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with its associated AP MLD, and a STA associated with the non-AP MLD and operating on one of the EMLSR links (e.g., the second link) between the AP MLD and the non-AP MLD is a TXOP holder on that link, if an R-TWT schedule is established on the other EMLSR link (e.g., the first link) between the same AP MLD and the same non-AP MLD, or on either link if the non-AP MLD is a single radio device, the STA associated with the non-AP MLD and operating on the second link may continue its transmission on the second link regardless of the R-TWT SP start time on the first link. According to this embodiment, due to ongoing transmission on the second link, the STA associated with the non-AP MLD and operating on the first link may remain in a doze state even during its scheduled R-TWT SP duration. According to one embodiment, in the above scenario, a STA associated with non-AP MLD and operating on the second link may continue its transmission on the second link if the STA has uplink latency sensitive traffic to an AP associated with AP MLD and operating on the second link.

[0103] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with the AP MLD, and an AP operating in one of the EMLSR links (e.g., the second link) between the AP MLD and the non-AP MLD is a TXOP holder on that link, if an R-TWT schedule is established on the other EMLSR link (e.g., the first link) between the same AP MLD and the same non-AP MLD, or on either link if the non-AP MLD is a single radio device, the AP operating in the second link in association with the AP MLD should end its TXOP at least the amount of time indicated in the EMLSR Padding Delay subfield of the EML Capability subfield of the Basic Multilink Element before the R-TWT SP starts on the first link, if the TID(s) negotiated for the R-TWT schedule on the first link are not mapped to the second link through a TID-to-Link mapping.

[0104] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with an AP MLD, and a STA associated with the non-AP MLD and operating on one of the EMLSR links (e.g., the second link) between the AP MLD and the non-AP MLD is a TXOP holder on that link, if an R-TWT schedule is established on the other EMLSR link (e.g., the first link) between the same AP MLD and the same non-AP MLD, or on either link if the non-AP MLD is a single radio device, the STA associated with the non-AP MLD and operating on the second link should end its TXOP at least the amount of time indicated in the EMLSR Padding Delay subfield of the EML Capability subfield of the Basic Multilink Element before the R-TWT SP starts on the first link, if the TID(s) negotiated for the R-TWT schedule on the first link are not mapped to the second link through a TID-to-link mapping.

[0105] According to one embodiment, when a non-AP MLD is operating in EMLSR mode with an AP MLD and an R-TWT schedule is established on one of the EMLSR links between the AP MLD and the non-AP MLD, the AP associated with the AP MLD may initiate frame exchange on that link during the R-TWT SP on that link without sending an initial control frame to the R-TWT-scheduled STAs associated with the non-AP MLD and operating on that link.

[0106] FIG. 14 illustrates an example process for facilitating coexistence of TWT and EMLSR operations for MLD in a WLAN according to one embodiment of the present disclosure. Although the process of FIG. 14 is described as being implemented by a non-AP MLD, it should be understood that a corresponding AP MLD implements the corresponding process. It should be further understood that these roles may be reversed, and that the process of FIG. 14 may be implemented with an AP MLD. In addition, for convenience, the process of FIG. 14 is described as being implemented by a WI-FI non-AP MLD including a plurality of STAs each equipped with a transceiver configured to form a link with a corresponding AP associated with the WI-FI AP MLD. Furthermore, for communication on a first one of the links, an R-TWT schedule is established such that a first one of the STAs operating on the first link is a member of an R-TWT SP on the first link, and a second one of the STAs operating on a second one of the links is not a member of any other R-TWT SP on the second link that overlaps in time with the R-TWT SP on the first link. However, it should be understood that any suitable wireless communication device may implement these processes.

[0107] 14, the process begins with the non-AP MLD determining to transition the non-AP MLD to an EMLSR operating mode (step 1405), where the first link and the second link form an EMLSR link pair. In some embodiments, after transitioning to the EMLSR mode, if the first link is in an R-TWT SP, the non-AP MLD transitions the first link to an EMLSR listening mode, allows the first link to enter a TWT doze state after the R-TWT SP ends, and transitions the remaining links to the EMLSR listening mode.

[0108] After transitioning to the EMLSR mode in step 1405, the non-AP MLD may, in some implementations, perform EMLSR operations with the AP MLD on a subset of links (e.g., an EMLSR linkset). In some such embodiments, if an R-TWT schedule is established on the first link, the first link is not included in the subset.

[0109] Next, the non-AP MLD determines that a TXOP has started on the second link (step 1410). The non-AP MLD then coordinates among STAs to ensure that the frame exchange sequence with the AP MLD on the second link during the TXOP does not overlap in time with the R-TWT SP on the first link (step 1415).

[0110] In some embodiments, if the second STA acts on the second link as a TXOP holder on the second link, the non-AP MLD coordinates between the STAs to have the second STA terminate the TXOP on the second link before the R-TWT SP begins on the first link in step 1415. If the TXOP on the second link is terminated, the non-AP MLD may begin a second frame exchange sequence during the R-TWT SP on the first link without an EMLSR initial control frame exchange being performed for the first link.

[0111] In some other embodiments where the second STA acts on the second link as a TXOP holder on the second link, in step 1415, the non-AP MLD coordinates between the STAs to ensure that the second STA terminates the TXOP on the second link at least a threshold amount of time before the R-TWT SP begins on the first link. This threshold amount may be equal to the EMLSR Transition Delay value indicated in the EMLSR Transition Delay subfield of the Basic Multilink element specified for the EMLSR link pair.

[0112] In some embodiments, if the set of TIDs mapped to the first link for the R-TWT schedule is also mapped to the second link, then in step 1415 the non-AP MLD allows the first link to remain in a TWT doze state during the R-TWT SP and enables at least one of the transceivers to transmit traffic corresponding to the set of TIDs to the AP MLD on the second link as part of a frame exchange sequence.

[0113] While the above flow charts illustrate example methods or processes that may be implemented in accordance with the principles of the present disclosure, various modifications may be made to the methods or processes illustrated in the flow charts. For example, although shown as a series of steps, various steps may overlap, occur in parallel, occur in a different order, or occur multiple times. In other examples, steps may be omitted or replaced with other steps.

[0114] Although the present disclosure has been described with exemplary embodiments, various changes and modifications may occur to those skilled in the art. The present disclosure is intended to encompass such changes and modifications that fall within the scope of the appended claims. Nothing in this application should be construed as implying that a particular element, step, or function is an essential element that must be included in the claims. The scope of the patented subject matter is defined by the claims. [Explanation of symbols]

[0115] 100 Wireless Network 101 Access Point (AP), AP MLD 102 AP 103 AP 111 Station (STA) / Non-AP MLD 112~114 STA 120 Coverage Area 125 Coverage Area 130 Network 202 AP 203 STA 204 Antenna 205 Antenna 209 Radio Frequency (RF) Transceivers 210 RF Transceiver 214 Transmit (TX) processing circuit 215 TX processing circuit 219 Receiver (RX) processing circuit 220 Microphone 224 Controller / Processor 225 RX processing circuit 229 Memory 230 Speakers 234 Backhaul / Network Interface 240 Main Controller / Processor 245 Input / Output (I / O) Interface (IF) 250 Touchscreen 255 Display 260 Memory 261 Operating System (OS) 262 Applications 302 EML operation mode notification frame 304 EML operation mode notification frame 402 EMLSR initial control frame 502 TXOP 504 Restricted TWT SP 802 hours 804 hours 902 Time Remaining 1002 TXOP 1004 Original end time 1006 Start time 1008 TWT SP 1010 hours 1012 Threshold Time Amount 1102 TXOP 1104 TWT SP

Claims

1. A non-access point (AP) multilink device (MLD) associated with a wireless network, comprising: a first non-AP station (STA) associated with the non-AP MLD, the first non-AP STA operating on a first link with a first AP associated with an AP MLD, wherein a Restricted Target Wake Time (R-TWT) schedule is established on the first link; a second non-AP STA associated with the non-AP MLD, the second non-AP STA operating on a second link with a second AP associated with the AP MLD, and wherein frames are exchanged on the second link during a transmission opportunity (TXOP); a processor coupled to the first non-AP STA and the second non-AP STA, operating with the AP MLD in an enhanced multi-link single radio (EMLSR) mode on the first link and the second link; coordinating between the second non-AP STA and the second AP so that the TXOP on the second link ends at least a threshold amount of time before an R-TWT service period (SP) begins on the first link; a processor configured to: Non-AP MLD with.

2. 2. The non-AP MLD of claim 1, wherein the first non-AP STA is a member of the R-TWT SP on the first link, and the second non-AP STA is not a member of any R-TWT SP on the second link that overlaps with the R-TWT SP on the first link.

3. 2. The non-AP MLD of claim 1, wherein the processor is configured to coordinate between the second non-AP STA and the second AP such that, if the second non-AP STA is a TXOP holder on the second link, the second non-AP STA terminates the TXOP on the second link at the latest the threshold amount of time before the R-TWT SP starts on the first link.

4. 2. The non-AP MLD of claim 1, wherein the processor is configured to coordinate between the second non-AP STA and the second AP such that, if the second AP is a TXOP holder on the second link, the second AP terminates the TXOP on the second link at the latest the threshold amount of time before the R-TWT SP starts on the first link.

5. The non-AP MLD of claim 1 , wherein the threshold amount of time is equal to an EMLSR transition delay indicated in an EMLSR transition delay subfield in an EML capability subfield of a basic multilink element.

6. 2. The non-AP MLD of claim 1, wherein the threshold amount of time is equal to the time required by the non-AP MLD to switch from exchanging frames on the second link to EMLSR listening mode on the first link.

7. The non-AP MLD of claim 1 , wherein the R-TWT SP on the first link overlaps in time with a frame exchange sequence occurring on the second link.

8. 2. The non-AP MLD of claim 1, wherein the processor is configured to coordinate between the second non-AP STA and the second AP such that if a set of traffic identifiers (TIDs) negotiated for the R-TWT SP on the first link is mapped to the second link for frame exchange, the frame exchange continues on the second link.

9. The non-AP MLD of claim 1 , wherein the first link and the second link form a pair of EMLSR links.

10. 1. An access point (AP) multilink device (MLD) associated with a wireless network, comprising: a first AP associated with the AP MLD, the first AP operating on a first link with a first non-AP station (STA) associated with a non-AP MLD, wherein a Restricted Target Wake Time (R-TWT) schedule is established on the first link; a second AP associated with the AP MLD, the second AP operating on a second link with a second non-AP STA associated with the non-AP MLD, wherein frames are exchanged on the second link during a transmission opportunity (TXOP); a processor coupled to the first AP and the second AP, operating in an enhanced multi-link single radio (EMLSR) mode on the first link and the second link with the non-AP MLD; coordinating between the second AP and the second non-AP STA so that the TXOP on the second link ends at least a threshold amount of time before an R-TWT service period (SP) begins on the first link; a processor configured to: AP MLD.

11. 11. The AP MLD of claim 10, wherein the first non-AP STA is a member of the R-TWT SP on the first link, and the second non-AP STA is not a member of any R-TWT SP on the second link that overlaps with the first SP.

12. 11. The AP MLD of claim 10, wherein the processor is configured to coordinate between the second AP and the second non-AP STA such that, if the second AP is a TXOP holder on the second link, the second AP terminates the TXOP on the second link at the latest a threshold amount of time before an R-TWT SP starts on the first link.

13. 11. The AP MLD of claim 10, wherein the threshold amount of time is equal to an EMLSR transition delay indicated in an EMLSR transition delay subfield in an EML capability subfield of a basic multilink element.

14. 11. The AP MLD of claim 10, wherein the threshold amount of time is equal to the time required by the non-AP MLD to switch from exchanging frames on the second link to EMLSR listening mode on the first link.

15. 11. The AP MLD of claim 10, wherein the processor is configured to coordinate between the second AP and the second non-AP STA such that if a set of traffic identifiers (TIDs) negotiated for the R-TWT SP on the first link is mapped to the second link for frame exchange, the frame exchange continues on the second link.

16. A method for a non-access point (AP) multi-link device (MLD) associated with a wireless network, the method comprising: operating with AP MLD in an Enhanced Multi-Link Single Radio (EMLSR) mode on a first link and a second link, the first link being established between a first non-AP station (STA) associated with the non-AP MLD and a first AP associated with the AP MLD, and the second link being established between a second non-AP STA associated with the non-AP MLD and a second AP associated with the AP MLD; coordinating between the second non-AP STA and the second AP such that a transmission opportunity (TXOP) on the second link ends at least a threshold amount of time before a restricted target wake time (R-TWT) service period (SP) begins on the first link, the first non-AP STA being a member of the R-TWT SP on the first link, and a frame exchange occurring on the second link during the TXOP; A method comprising:

17. The method described in claim 16, wherein if the second non-AP STA is a TXOP holder on the second link, the second non-AP STA terminates the TXOP on the second link at least the threshold amount of time before the R-TWT SP starts on the first link.

18. The method described in claim 16, wherein the threshold amount of time is equal to the time required by the non-AP MLD to switch from exchanging frames on the second link to EMLSR listening mode on the first link.

19. The method of claim 16, further comprising a step of coordinating between the second non-AP STA and the second AP so that if a set of traffic identifiers (TIDs) negotiated for the R-TWT SP on the first link is mapped to the second link for the frame exchange, the frame exchange continues on the second link.

20. The method of claim 16, wherein the R-TWT SP on the first link overlaps in time with a frame exchange sequence occurring on the second link.

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