Smooth roaming with transmission of duplicate frames

Abstract

Joint Transmission (JTX) techniques for seamless roaming in next-generation Wi-Fi networks. There is a challenge in maintaining low-latency, high-reliability connections while roaming in advanced Wi-Fi networks. The techniques encompass a JTX-based roaming mechanism where multiple Access Points (APs) collaborate to transmit data simultaneously to a roaming station during handover. This creates a "make-before-break" scenario, eliminating connection interruptions typical in conventional "break-before-make" roaming procedures. The technique involves coordinated transmission between the current and target APs, utilizing methods such as coordinated beamforming, time and frequency synchronization, and potentially MU-MIMO technology. By maintaining a continuous data path during transitions, the techniques reduce roaming delay, prevent packet loss, and ensure consistent throughput. This JTX approach supports the requirements of emerging low-latency, high-reliability applications in dense Wi-Fi deployments, enhancing user experience in mobile scenarios across various demanding use cases.

Description

SMOOTH ROAMING WITH TRANSMISSION OF DUPLICATE FRAMESCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of United States Provisional Application No. 63 / 580,692 filed September 5, 2023, the entire contents of which is hereby incorporated by reference.TECHNICAL FIELD

[0002] The present disclosure generally relates to wireless communications, and more specifically, relates to smooth roaming with transmission of duplicate frames in wireless networks such as wireless local area networks (WLANs) that operate according to nextgeneration Institute of Electrical and Electronics Engineers (IEEE) 802.11 local area network technical standards.BACKGROUND

[0003] Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of standards for implementing wireless local area network (WLAN) communication in various frequencies, including but not limited to the 2.4 gigahertz (GHz), 5 GHz, 6 GHz, and 60 GHz bands. These standards define the protocols that enable Wi-Fi devices to communicate with each other.The 802.11 family of standards has evolved over time to accommodate higher data rates, improved security, and better performance in different environments. Some of the most widely used standards include 802.11a, 802.11b, 802.11g, 802.1 In, 802.1 lac, and 802.1 lax (also known as “Wi-Fi 6”). These standards specify the modulation techniques, channel bandwidths, and other technical aspects that facilitate interoperability between devices from various manufacturers. IEEE 802.11 has played an important role in the widespread adoption of wireless networking in homes, offices, and public spaces, enabling users to connect their devices to the internet and each other without the need for wired connections.

[0004] IEEE 802.1 Ibe, also known as “Wi-Fi 7”, is currently under development. 802.1 Ibe aims to significantly improve upon the capabilities of its predecessor, 802.1 lax / Wi-Fi 6, by offering even higher data rates, lower latency, and increased reliability. The standard is expected to leverage advanced technologies such as multi-link operation (MLO), which allows devices to simultaneously use multiple frequency bands and channels for enhanced performance andreliability. Additionally, 802. l lbe will introduce 4096-QAM (Quadrature Amplitude Modulation), enabling higher data rates by encoding more bits per symbol. The standard will also feature improved medium access control (MAC) efficiency, enhanced power saving capabilities, and better support for high-density environments. With these advancements, 802.1 Ibe is expected to deliver theoretical maximum data rates of up to 46 gigabits per second (Gbps), making it suitable for bandwidth-intensive applications such as virtual and augmented reality, 8K video streaming, and high-performance gaming. The IEEE 802.1 Ibe standard is projected to be finalized by the end of 2024, paving the way for the next generation of Wi-Fi devices and networks such as IEEE 802.1 Ibn (also known as “Ultra High Reliability” or “UHR”).BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The disclosure will be more fully understood from the detailed description provided below and the accompanying drawings that depict various embodiments of the disclosure. However, these drawings should not be interpreted as limiting the disclosure to the specific embodiments shown; they are provided for explanation and understanding only.

[0006] FIG. 1 illustrates an example of a wireless local area network (WLAN) with a basic service set (BSS) that includes multiple wireless devices, in accordance with some embodiments of the present disclosure.

[0007] FIG. 2 is a schematic diagram of a wireless device, in accordance with some embodiments of the present disclosure.

[0008] FIG. 3 A illustrates components of a wireless device configured to transmit data, in accordance with some embodiments of the present disclosure.

[0009] FIG. 3B illustrates components of a wireless device configured to receive data, in accordance with some embodiments of the present disclosure.

[0010] FIG. 4 illustrates interframe space (IFS) relationships, in accordance with some embodiments of the present disclosure.

[0011] FIG. 5 illustrates a carrier sense multiple access with collision avoidance (CSMA / CA)- based frame transmission procedure, in accordance with some embodiments of the present disclosure.

[0012] FIG. 6 illustrates maximum physical layer (PHY) rates for Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, in accordance with some embodiments of the present disclosure.

[0013] FIG. 7 provides a detailed description of fields in extremely high throughput physical layer protocol data unit (EHT PPDU) frames, including their purposes and characteristics, in accordance with some embodiments of the present disclosure.

[0014] FIG. 8 illustrates an example of multi-user orthogonal frequency division multiple access (MU-OFDMA) transmission where multiple frames are transmitted to or from multiple stations (STAs) simultaneously using different frequency resources, in accordance with some embodiments of the present disclosure.

[0015] FIG. 9 illustrates an example of an access point sending a trigger frame to multiple associated STAs and receiving uplink orthogonal frequency division multiple access triggerbased physical layer protocol data units (UL OFDMA TB PPDUs) in response, according to some embodiments of the present disclosure.

[0016] FIG. 10 illustrates an overview of a smooth roaming architecture, according to some embodiments of the present disclosure.

[0017] FIG. 11 illustrates transition steps of smooth roaming, according to some embodiments of the present disclosure.

[0018] FIG. 12 illustrates a scenario where a non-access point multi-link device (non-AP MLD) moves toward a target AP MLD, according to some embodiments of the present disclosure.

[0019] FIG. 13 illustrates an example of a process for smooth roaming where a non-AP MLD moves toward a target AP MLD, according to some embodiments of the present disclosure.

[0020] FIG. 14 illustrates a first example of the joint sounding sequence, according to some embodiments of the present disclosure.

[0021] FIG. 15 illustrates a second example of the joint sounding sequence, according to some embodiments of the present disclosure.

[0022] FIG. 16 illustrates a method for smooth roaming with transmission of duplicate frames performed at a wireless device capable of multi-link operation (MLO) and operating as a non- access point multi-link device (non-AP MLD) in a wireless network, according to some embodiments of the present disclosure.

[0023] FIG. 17 illustrates a method for smooth roaming with transmission of duplicate frames performed at a wireless device capable of MLO and operating as a current AP MLD in a wireless network, according to some embodiments of the present disclosure.

[0024] FIG. 18 illustrates a method for smooth roaming with transmission of duplicate frames performed at a wireless device capable of multi-link operation (MLO) and operating as a target AP MLD in a wireless network, according to some embodiments of the present disclosure.

[0025] FIG. 19 illustrates a method for smooth roaming with transmission of duplicate frames performed at a wireless device capable of multi-link operation (MLO) and operating as a roaming AP MLD in a wireless network, according to some embodiments of the present disclosure.DETAILED DESCRIPTION

[0026] The present disclosure generally relates to wireless communications, and more specifically, relates to smooth roaming with transmission of duplicate frames in wireless networks such as wireless local area networks (WLANs) that operate according to nextgeneration Institute of Electrical and Electronics Engineers (IEEE) 802.11 local area network technical standards.OVERVIEW

[0027] The are technical challenges associated with maintaining low-latency and high- reliability connections in next-generation Wi-Fi networks, particularly in scenarios involving mobile stations (STAs). The IEEE 802.1 Ibe standard and beyond aims to address these issues, but the mobility of STAs presents a significant technical hurdle.

[0028] When a STA roams between multiple Access Points (APs), it may disconnect from its current AP and reconnect to the target AP. This process, known as handover or roaming, typically follows a "break-before-make" approach. In this method, the network may switch the data path after the STA disconnects from the original AP and before it fully associates with the new AP. This transition may introduce a delay in the connection, which can be detrimental to applications requiring low latency and high reliability.

[0029] The delay during roaming can lead to packet loss, increased latency, and potential disruption of services, especially for time-sensitive applications. This issue becomes more pronounced in environments with frequent handovers, such as large enterprise networks or public spaces with dense AP deployments. The problem is further exacerbated by the increasing demands of modem applications for seamless connectivity and the growing expectations for uninterrupted service in mobile scenarios.

[0030] Addressing this roaming delay may be crucial for maintaining the quality of service and meeting the stringent requirements of emerging applications in areas such as augmented reality, virtual reality, and industrial loT, which require not only high throughput but also consistent, low-latency connections even as users move through the network coverage area.

[0031] These and other issues are addressed by techniques disclosed herein. The techniques address the roaming delay problem by implementing Joint Transmission (JTX) of roaming data.The techniques aim to reduce the delay time associated with the traditional "break-before-make" handover approach by allowing seamless data transmission during the transition period between Access Points (APs).

[0032] In the disclosed JTX-based roaming mechanism, multiple APs collaborate to transmit data to the roaming Station (STA) simultaneously during the handover process. This approach enables the STA to receive data from both the current AP and the target AP during the transition period, effectively creating a "make-before-break" scenario. By doing so, the techniques maintain a continuous data path, eliminating the interruption typically experienced during conventional roaming procedures.

[0033] The implementation of the disclosed JTX techniques for roaming involves coordination between the APs to synchronize their transmissions and may help to ensure that the roaming STA can successfully decode the jointly transmitted data. This may require techniques such as coordinated beamforming, time and frequency synchronization, and possibly the use of MultiUser Multiple-Input Multiple-Output (MU-MIMO) technology to effectively deliver the data to the moving STA.

[0034] By enabling this smooth transition between APs, the disclosed techniques not only reduce the roaming delay but also prevent packet loss and maintain a consistent throughput during the handover process. The disclosed techniques comport with the goals of nextgeneration Wi-Fi standards to support low-latency, high-reliability applications, particularly in scenarios involving mobile users or devices. The disclosed JTX approach for roaming can improve the user experience in dense Wi-Fi deployments and support more demanding applications that require seamless mobility.

[0035] The disclosed techniques can be implemented in a method for smooth roaming in a multi-link operation (MLO) capable wireless network. This method, executed by a non-access point multi-link device (non-AP MLD), encompasses several steps to facilitate seamless transition between access points. Initially, the non-AP MLD communicates with a first AP MLD via a wireless link. When roaming is necessary, the non-AP MLD initiates the process by transmitting a roaming request frame to both the current (first) and target (second) AP MLDs simultaneously. Upon receiving a roaming confirm frame from the second AP MLD, the non-AP MLD proceeds to transmit a roaming initiation frame to both AP MLDs. This triggers the joint transmission (JTX) phase, where the non-AP MLD simultaneously receives identical data from both AP MLDs, leveraging the coordinated transmission techniques described earlier. This JTX phase effectively creates the "make-before-break" scenario, maintaining continuous connectivity during the transition. Finally, the roaming process concludes with the non-AP MLD establishinga new wireless link with the second AP MLD for subsequent communications. This method embodies the core principles of the JTX-based roaming mechanism, providing low-latency, high-reliability handovers in next-generation Wi-Fi networks.

[0036] In an embodiment, the non-AP MLD remains in State 4 of the IEEE 802.11 state machine for STAs (stations) during and after the roaming process. In State 4, the non-AP MLD is authenticated and associated with an AP and can send and receive data frames. The techniques disclose a mechanism where the non-AP MLD maintains its fully connected and operational state (State 4) throughout the roaming process, thereby enabling seamless transition between AP MLDs, without the need for re-authentication or re-association, which is typically required in conventional Wi-Fi roaming. By allowing the non-AP MLD to maintain State 4 during and after roaming, the disclosed techniques reduce roaming time and prevent data loss during transitions, addressing technical challenges in mobile scenarios in next-generation Wi-Fi networks.

[0037] According to an embodiment, the method further extends to the operations of the first AP MLD, highlighting the coordination required for successful joint transmission. In this phase, the first AP MLD receives a JTX sounding trigger frame from a roaming AP MLD, which serves as a central coordinator in the network. This trigger frame initiates the synchronization process for effective JTX. Upon reception, the first AP MLD calculates pre-corrected values based on the information contained in the trigger frame. These pre-corrected values are for synchronizing transmissions between multiple APs, addressing factors such as timing offsets and carrier frequency differences. The first AP MLD then transmits a JTX data frame to the non- AP MLD, which includes both the shared JTX data and the calculated pre-corrected values. This step helps ensure that the jointly transmitted data from multiple APs can be coherently combined at the non-AP MLD, maintaining signal quality and data integrity during the roaming process. By incorporating these pre-correction mechanisms, the method extension enhances the reliability and effectiveness of the JTX-based roaming technique, reducing or minimizing potential disruptions during handovers in MLO-capable networks.

[0038] In an embodiment, complementing the operations of the first AP MLD, the method also encompasses the role of the second AP MLD in the JTX-based roaming process. Similar to the first AP MLD, the second AP MLD receives the JTX sounding trigger frame from the roaming AP MLD. This uniform trigger distribution helps ensure synchronization across all participating APs. Upon receiving this frame, the second AP MLD performs its own calculations to derive pre-corrected values, which may differ from those of the first AP MLD due to its unique spatial relationship with the non-AP MLD. These calculations are for addressing potential timing and frequency offsets specific to the second AP MLD's transmission path. Subsequently, the secondAP MLD transmits its JTX data frame to the non-AP MLD, containing both the shared JTX data and its uniquely calculated pre-corrected values. This parallel operation of both AP MLDs, each applying its own pre-corrections while transmitting identical data, may be part of the JTX mechanism. It allows the non-AP MLD to receive coherent signals from both APs simultaneously, effectively achieving the "make-before-break" transition.

[0039] In an embodiment, the method further delineates the role of the roaming AP MLD in facilitating the smooth transition between the first and second AP MLDs. Acting as a central coordinator, the roaming AP MLD receives specific data from the first AP MLD, which is currently serving the non-AP MLD. This data transfer occurs over a high-speed backhaul network connecting the APs. Upon receiving this data, the roaming AP MLD then transmits it to the second AP MLD, which is the target AP for the roaming process. This data forwarding mechanism helps ensure that both the first and second AP MLDs have access to the same information, which becomes the content of the joint transmission (JTX) data. By synchronizing the data across both APs, the roaming AP MLD enables them to perform coordinated joint transmission to the non-AP MLD.

[0040] Embodiments also encompass a wireless device comprising a radio frequency transceiver, a memory device, a set of one or more processors coupled to the memory device, and a set of instructions stored in the memory device and configured to cause the wireless device to perform any of the foregoing methods.WIRELESS COMMUNICATIONS

[0041] In this detailed description, only certain embodiments are shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various ways, all without departing from the spirit or scope of the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

[0042] Turning now to FIG. 10, it illustrates example wireless local area network (WLAN) 100. WLAN 100 encompasses example basic service set (BSS) 102. BSS 102 may be composed of multiple WLAN devices 104. Each WLAN device 104 within BSS 102 may be equipped with a medium access control (MAC) layer and a physical layer (PHY), which adhere to one or more IEEE 802.11 standards.

[0043] Among WLAN devices 104 in BSS 102, at least one device serves as an access point station (AP STA) 104 A, while the remaining devices function as non-AP stations (non-AP STAs) 104B. In an ad-hoc networking environment, all WLAN devices 104 may be non-AP STAs. Generally, both the AP STAs and the non-AP STAs can be referred to individually as astation (STA) or collectively as stations (STAs). However, for the sake of providing clear examples in this description, only the non-AP STAs are referred to as STAs.

[0044] FIG. 2 is a schematic block diagram that represents a WLAN device, labeled as WLAN device 104, which comprises several components. Baseband processor 210 may be responsible for performing baseband signal processing and includes two sub-components: MAC processor 212 and PHY processor 222. MAC processor 212 may be further divided into MAC software processing unit 214 and MAC hardware processing unit 216. Memory 232, which can be a non-transitory computer-readable medium, stores MAC software that implements some functions of the MAC layer. MAC software processing unit 214 executes this software, while MAC hardware processing unit 216 implements the remaining MAC layer functions in hardware.

[0045] PHY processor 222 comprises transmitting (TX) signal processing unit 224 and receiving (RX) signal processing unit 226, which handle the PHY processing of the transmitted and received signals, respectively.

[0046] Other components of WLAN device 104 include RF transceiver 240, which facilitates wireless communication, antenna unit 250 for transmitting and receiving signals, input interface unit 234 for receiving user input, and output interface unit 236 for providing output to the user. All these components, along with baseband processor 210 and memory 232, communicate with each other through bus 260, which serves as a communication pathway within the device.

[0047] RF transceiver 240 may be a component of WLAN device 104 that encompasses two sub-components: RF transmitter 242 and RF receiver 244. These sub-components are responsible for transmitting and receiving RF signals, respectively.

[0048] In addition to storing the MAC software, memory 232 may also store an operating system and various applications necessary for the functioning of the WLAN device.

[0049] Input interface unit 234 may be responsible for receiving information from the user, such as commands or data input. On the other hand, output interface unit 236 may be tasked with outputting information to the user, which could include status updates, processed data, or any other relevant information.

[0050] Antenna unit 250 comprises one or more antennas that facilitate wireless communication between the WLAN device and other devices in the network. In cases where a multiple-input multiple-output (MIMO) or a multiuser multiple-input multiple-output (MU- MIMO) system may be employed, antenna unit 250 may include multiple antennas to support these advanced communication techniques, which enhance the capacity and performance of the wireless network.

[0051] FIG. 3 A illustrates transmitting signal processing unit 224 in WLAN device 104. Unit 224 encompasses several components that process the input data before transmission. Encoder 300 encodes the input data using forward error correction (FEC) techniques, such as binary convolutional code (BCC) or low-density parity-check (LDPC) encoding. A scrambler may be used to scramble the input data before encoding to reduce the occurrence of long sequences of 0s or Is. If BCC encoding is used, an encoder parser may be employed to demultiplex the scrambled bits among multiple BCC encoders.

[0052] Interleaver 302 changes the order of bits in each stream output from the encoder, which may be applicable only when BCC encoding is used. Mapper 304 then maps the interleaved bits to constellation points. If LDPC encoding is used, mapper 304 may also perform LDPC tone mapping.

[0053] When MIMO or MU-MIMO is used, multiple interleavers 302 and mappers 304 may be employed, corresponding to the number of spatial streams (NSS). A stream parser divides the outputs of the BCC encoders or the LDPC encoder into blocks sent to different interleavers 302 or mappers 304. A space-time block code (STBC) encoder spreads the constellation points from the spatial streams into space-time streams, and a spatial mapper maps the space-time streams to transmit chains using direct mapping, spatial expansion, or beamforming.

[0054] Inverse Fourier transformer (IFT) 306 converts the constellation points from the mapper or spatial mapper to a time-domain symbol using an inverse discrete Fourier transform (IDFT) or an inverse fast Fourier transform (IFFT). When MIMO or MU-MIMO is used, cyclic shift diversities (CSDs) may be inserted to prevent unintentional beamforming, either before or after the IFT, per transmit chain, per space-time stream, or as part of the spatial mapper.

[0055] Guard interval (GI) inserter 308 prepends a GI to each symbol, and optional windowing may be applied to smooth the symbol edges. Finally, RF transmitter 242 converts the symbols into an RF signal and transmits it via antenna unit 250. In MIMO or MU-MIMO systems, the GI inserter and RF transmitter may be provided for each transmit chain.

[0056] As illustrated in FIG. 3B, receiving signal processing unit 226 in WLAN device 104 encompasses several components that process the received RF signal. RF receiver 244 receives the RF signal via antenna unit 250 and converts it into one or more symbols. GI remover 318 removes the GI from the symbol. In MIMO or MU-MIMO systems, RF receiver 244 and GI remover 318 may be provided for each receive chain.

[0057] Fourier transformer (FT) 316 converts the time-domain symbol into a block of constellation points using a discrete Fourier transform (DFT) or a fast Fourier transform (FFT). In MIMO or MU-MIMO systems, a spatial demapper may be used to convert the Fouriertransformed receiver chains to constellation points of the space-time streams, and an STBC decoder may despread the constellation points from the space-time streams into the spatial streams.

[0058] Demapper 314 demaps the constellation points from FT 316 or STBC decoder to bit streams. If LDPC encoding is used, the demapper may also perform LDPC tone demapping before constellation demapping. Deinterleaver 312 deinterleaves the bits of each stream from the demapper, which may be applicable only when BCC encoding is used.

[0059] In MIMO or MU-MIMO systems, multiple demappers 314 and deinterleavers 312 may be used, corresponding to the number of spatial streams. A stream deparser may be employed to combine the streams from the deinterleavers.

[0060] Decoder 310 decodes the streams from deinterleaver 312 or stream deparser. The decoder may be an FEC decoder, such as a BCC decoder or an LDPC decoder. A descrambler may be used to descramble the decoded data. If BCC decoding is used, an encoder deparser may multiplex the data decoded by multiple BCC decoders. If LDPC decoding is used, the encoder deparser may not be necessary.

[0061] FIG. 4 illustrates the relationships between different types of interframe spaces (IFSs) in a WLAN system. WLAN devices can exchange data frames, control frames, or management frames. Data frames are used to transmit data to higher layers, and a WLAN device transmits a data frame after performing backoff if a distributed coordination function interframe space (DIFS) has elapsed from the time the medium has been idle.

[0062] Management frames are used to exchange management information that is not forwarded to higher layers. Subtype frames of management frames include beacon frames, association request / response frames, probe request / response frames, and authentication request / response frames. Control frames are used to control access to the medium and include subtypes such as request-to-send (RTS) frames, clear-to-send (CTS) frames, and acknowledgement (ACK) frames.

[0063] If a control frame is not a response frame to a previous frame, the WLAN device transmits the control frame after performing backoff if the DIFS has elapsed. However, if the control frame is a response frame to a previous frame, the WLAN device transmits the control frame without performing backoff if a short interframe space (SIFS) has elapsed. The type and subtype of a frame can be identified by the type field and subtype field in the frame control field.

[0064] Quality of Service stations (QoS STAs) may transmit frames after performing backoff if an arbitration interframe space (AIFS) for an associated access category (AC) (e.g.,AIFSfAC]) has elapsed. In this case, data frames, management frames, or control frames that are not response frames may use the AIFS[AC].

[0065] FIG. 5 illustrates a carrier sense multiple access with collision avoidance (CSMA / CA)- based frame transmission procedure for avoiding collisions between frames in a channel. In this scenario, STA1 may be the transmit WLAN device, STA2 may be the receive WLAN device, and STA3 may be a WLAN device located in an area where it can receive frames transmitted from both STA1 and STA2.

[0066] STA1 determines channel availability by carrier sensing, which can be based on the energy level on the channel, correlation of signals in the channel, or by using a network allocation vector (NAV) timer. After determining that the channel is idle for a duration of DIFS, STA1 transmits an RTS frame to STA2 after performing backoff. Upon receiving the RTS frame, STA2 responds with a CTS frame after SIFS.

[0067] When STA3 receives the RTS frame, it sets its NAV timer for the transmission duration of subsequent frames using the duration information included in the RTS frame. This duration may include SIFS + CTS frame duration + SIFS + data frame duration + SIFS + ACK frame duration. Similarly, when STA3 receives the CTS frame, it sets its NAV timer for the transmission duration of subsequent frames using the duration information included in the CTS frame. If STA3 receives a new frame before the NAV timer expires, it updates the NAV timer using the duration information in the new frame. STA3 does not attempt to access the channel until the NAV timer expires.

[0068] After receiving the CTS frame from STA2, STA1 transmits a data frame to STA2 after SIFS elapses from the time the CTS frame was completely received. Upon successfully receiving the data frame, STA2 responds with an ACK frame after SIFS elapses.

[0069] When the NAV timer expires, STA3 determines if the channel is busy using carrier sensing techniques. If the channel is not in use by other devices during DIFS and after the NAV timer has expired, STA3 may attempt channel access after a random backoff within a contention window has elapsed.

[0070] The IEEE 802.1 Ibn (sometimes referred to as “Ultra High Reliability” or just “UHR”) working group has been established to address the growing demand for higher peak throughput and reliability in Wi-Fi. As shown in FIG. 6, the peak PHY rate has significantly increased from IEEE 802.1 lb to IEEE 802.1 Ibe (Wi-Fi 7), with the latter focusing on further improving peak throughput. The UHR study group aims to enhance the tail of the latency distribution and jitter to support applications that require low latency, such as video-over- WLAN, gaming, AR, and VR.

[0071] IEEE 802.1 Ibe focuses on WLAN indoor and outdoor operation in the 2.4, 5, and 6 GHz frequency bands, with various candidate features being considered, such as 320MHz bandwidth, enhanced multi -band / multi-channel aggregation, 16 spatial streams, enhanced multi - AP coordination, and enhanced link adaptation and retransmission protocols.

[0072] The focus of IEEE 802.1 Ibn (UHR) is still under discussion, with candidate features including MLO enhancements, latency and reliability improvements, bandwidth expansion, aggregated PPDU, enhanced multi-link single-radio extensions to access point (AP), roaming improvements, and power-saving schemes.

[0073] Some of these features, such as increasing bandwidth and the number of spatial streams, have proven effective in previous projects aimed at increasing link throughput and are considered feasible.

[0074] With the availability of the wide 6 GHz unlicensed band (5.925 - 7.125 GHz), Wi-Fi devices can access wider bandwidths, enabling larger than 160MHz data transmissions (e.g., 320MHz / 640MHz) to increase the maximum PHY rate. This can be achieved by transmitting data in the 6 GHz band or across both the 5 and 6 GHz bands.

[0075] In the process of wireless communication, a transmitting station (transmitting STA) creates a physical layer protocol data unit (PPDU) frame and sends it to a receiving station (receiving STA). The receiving STA then receives, detects, and processes the PPDU.

[0076] The extremely high throughput physical layer protocol data unit (EHT PPDU) frame encompasses several components. It includes a legacy part, which comprises fields such as the Legacy Short Training Field (L-STF), Legacy Long Training Field (L-LTF), Legacy Signal Field (L-SIG), and Repeated Legacy Signal Field (RL-SIG). These fields are used to maintain compatibility with older Wi-Fi standards.

[0077] In addition to the legacy part, the EHT PPDU frame also contains the Universal Signal Field (U-SIG), EHT Signal Field (EHT-SIG), EHT Short Training Field (EHT-STF), and EHT Long Training Field (EHT-LTF). These fields are specific to the EHT standard and are used for various purposes, such as signaling, synchronization, and channel estimation.

[0078] FIG. 7 provides a more detailed description of each field in the EHT PPDU frame, including their purposes and characteristics.

[0079] Regarding the Ultra High Reliability physical layer protocol data unit (UHR PPDU), its frame structure is currently undefined and will be determined through further discussions within the relevant working group or study group. This indicates that the specifics of the UHR PPDU are still under development and will be finalized based on the outcomes of future deliberations.

[0080] The distributed nature of channel access networks, such as IEEE 802.11 WLANs, makes the carrier sense mechanism useful for ensuring collision-free operation. Each station (STA) uses its physical carrier sense to detect transmissions from other STAs. However, in certain situations, it may not be possible for a STA to detect every transmission. For instance, when one STA is located far away from another STA, it might perceive the medium as idle and start transmitting a frame, leading to collisions. To mitigate this hidden node problem, the network allocation vector (NAV) has been introduced.

[0081] As the IEEE 802.11 standard continues to evolve, it now includes scenarios where multiple users can simultaneously transmit or receive data within a BSS, such as uplink (UL) and downlink (DL) multi-user (MU) transmissions in a cascaded manner. In these cases, the existing carrier sense and NAV mechanisms may not be sufficient, and modifications or newly defined mechanisms may be required to facilitate efficient and collision-free operation.

[0082] For the purpose of this disclosure, MU transmission refers to situations where multiple frames are transmitted to or from multiple STAs simultaneously using different resources. Examples of these resources include different frequency resources in Orthogonal Frequency Division Multiple Access (OFDMA) transmission (e.g., as depicted in FIG. 8) and different spatial streams in Multi-User Multiple Input Multiple Output (MU-MIMO) transmission. Consequently, downlink OFDMA (DL-OFDMA), downlink MU-MIMO (DL-MU-MIMO), uplink OFDMA (UL-OFDMA), uplink MU-MIMO (UL-MU-MIMO), and OFDMA with MU- MIMO are all considered examples of MU transmission.

[0083] In the IEEE 802.1 lax and 802.1 Ibe specifications, the trigger frame plays a useful role in facilitating uplink multi-user (MU) transmissions. The purpose of the trigger frame may be to allocate resources and solicit one or more trigger-based (TB) physical layer protocol data unit (PPDU) transmissions from the associated STAs.

[0084] The trigger frame contains information required by the responding STAs to send their uplink TB PPDUs. This information includes the trigger type, which specifies the type of TB PPDU expected, and the uplink length (UL Length), which indicates the duration of the uplink transmission.

[0085] FIG. 9 illustrates an example scenario where an AP operating in an 80MHz bandwidth environment sends a trigger frame to multiple associated STAs. Upon receiving the trigger frame, the STAs respond by sending their respective uplink orthogonal frequency division multiple access (UL OFDMA) TB PPDUs, utilizing the allocated resources within the specified 80MHz bandwidth.

[0086] After successfully receiving the UL OFDMA TB PPDUs, the access point (AP) acknowledges the stations (STAs) by sending an acknowledgement frame. This acknowledgement can be in the form of an 80MHz width multi-STA block acknowledgement (Block Ack or BA) or a block acknowledgement with a direct feedback (DF) OFDMA method. The multi-STA block ack allows the AP to acknowledge multiple STAs simultaneously, while the block ack with DF OFDMA enables the AP to provide feedback to the STAs using the same OFDMA technique employed in the uplink transmission.

[0087] The trigger frame may be a useful component in enabling efficient uplink MU transmissions in IEEE 802.1 lax and 802.1 Ibe networks, by allocating resources and coordinating the uplink transmissions from multiple STAs within the same bandwidth.

[0088] WLAN systems rely on the retransmission of MAC protocol data units (MPDUs) when the transmitter (TX) does not receive an acknowledgement from the receiver (RX) or when the MPDUs are not successfully decoded at the RX. In the traditional automatic repeat request (ARQ) approach, the receiver discards the last failed MPDU before receiving the new retransmitted one. To meet the requirements of enhanced reliability and reduced latency, the 1 Ibe working group decided to evolve this approach toward hybrid ARQ (HARQ).

[0089] HARQ processing can be done using two methods: Type 1 HARQ, also known as chase combining (CC), and Type 2 HARQ, also known as incremental redundancy (IR).

[0090] In Type 1 HARQ (CC), the retransmitted signals are the same as the previously failed signal because all retransmitted subpackets use the same puncturing pattern. Puncturing removes some parity bits after encoding with an error-correction code. Using the same puncturing pattern in CC-HARQ generates a coded data sequence with forward error correction (FEC) and enables the receiver to use maximum-ratio combining (MRC) to combine the received bits with the same bits from previous transmissions. In WLAN systems, one HARQ packet may be divided into four subpackets. The information sequences are usually transmitted in fixed-length packets, and error correction and detection are performed on the entire packet at the receiver. If the packet is found to be in error, the conventional ARQ scheme may be inefficient when burst errors occur. Applying subpackets can improve this situation more efficiently, as only the subpackets containing errors need to be retransmitted.

[0091] The receiver uses both the current and previously received subpackets to decode the packet, reducing the error probability as more subpackets are used. The decoding process passes the CRC check and ends when the packet is decoded without error or when the maximum number of subpackets is reached. Because HARQ operates in a stop-and-wait protocol, the terminal sends an ACK to the transmitter if it can decode the packet, and the transmitterterminates the HARQ transmission upon receiving the ACK correctly. If the terminal cannot decode the packet, it sends a NAK to the transmitter, triggering the retransmission process.

[0092] In Type 2 HARQ (IR), different puncturing patterns are used for each subpacket, causing the signal to change for each subpacket. IR uses two puncturing patterns alternately for odd-numbered and even-numbered transmissions, resulting in a coded data sequence with the coding rate used in IR HARQ. The redundancy scheme of IR improves the log likelihood ratio (LLR) of the parity bit by combining information sent across different transmissions and lowers the code rate as additional subpackets are used, leading to a lower error rate compared to CC. The puncturing pattern used in HARQ may be indicated by the subpacket identity (SPID). The first subpacket's SPID may be always set to 0 and may contain all the systematic bits and punctured parity bits, allowing self-decoding when the receiving SNR environment is good. Generally, subpacket SPIDs may be transmitted in increasing order but can be exchanged, except for the first SPID.

[0093] Advanced techniques for improving wireless local area network (WLAN) system throughput, specifically focusing on Access Point (AP) coordination, has been a topic of discussion in IEEE 802.1 Ibe (Wi-Fi 7) and continues to be explored in 802.1 Ibn (Wi-Fi 8). There is a need for predefined mechanisms at the AP level to support various coordination schemes. These schemes may encompass coordinated beamforming, Orthogonal Frequency- Division Multiple Access (OFDMA), Time Division Multiple Access (TDMA), spatial reuse, and joint transmission. These techniques aim to optimize spectrum utilization and enhance overall network performance.

[0094] As a specific example of Coordinated TDMA (C-TDMA), an AP that obtains a transmit opportunity (TXOP) may initiate a coordination process. This AP, referred to as the "sharing AP," may broadcast its coordination capabilities through frames such as beacon frames or probe response frames. This broadcast may serve to determine the set of candidate APs for coordination. The APs that receive this frame and choose to participate in the coordination scheme are termed "shared APs." In some contexts, the sharing AP may additional or alternatively be referred to as the "master AP" or "coordinating AP," while the shared APs may be referred to as "slave APs" or "coordinated APs." This hierarchical structure and coordination mechanism aim to enhance the efficiency of spectrum usage and improve overall WLAN performance by allowing multiple APs to work in concert, potentially reducing interference and optimizing resource allocation across the network.SMOOTH ROAMING WITH TRANSMISSION OF DUPLICATE FRAMES

[0095] The disclosed techniques encompass an advanced roaming mechanism for future Wi-Fi standards beyond IEEE 802.1 Ibe that address the challenge of connection delays during handovers between Access Points (APs). The disclosed techniques encompass a novel architecture to facilitate smooth roaming in multi-AP environments.

[0096] FIG. 10 illustrates an overview of a smooth roaming architecture, according to some embodiments of the present disclosure. Central to this architecture is the concept of a Roaming AP Multi-Link Device (MLD). This Roaming AP MLD leverages Multi-Link Operation (MLO), a feature that allows devices to operate simultaneously on multiple frequency bands or channels. The Roaming AP MLD serves as an overarching entity that can affiliate with multiple AP MLDs, such as AP MLD1 and AP MLD2. These affiliated AP MLDs may be physically collocated or logically grouped to support seamless roaming.

[0097] In this framework, AP MLD1, AP MLD2, and the non-AP MLD (representing the client device) are logical entities that can encompass one or more physical APs or stations (STAs), respectively. The roaming process involves the non-AP MLD transitioning its connection from the current AP MLD (e.g., AP MLD1) to the target AP MLD (e.g., AP MLD2). The disclosed techniques provide the ability to maintain connectivity through the Roaming AP MLD during the transition. As the non-AP MLD moves from one AP MLD's coverage area to another, it can potentially maintain multiple simultaneous connections, leveraging the MLO capability. This approach aims to minimize or eliminate the delay associated with conventional roaming methods. By enabling a more fluid transition between AP MLDs, the disclosed techniques seek to provide a smoother roaming experience, potentially reducing latency, minimizing packet loss, and maintaining consistent throughput during handovers. The disclosed techniques may be particularly relevant for scenarios requiring high mobility support, low- latency applications, and seamless connectivity in dense Wi-Fi deployments.

[0098] FIG. 11 illustrates transition steps of smooth roaming, according to some embodiments of the present disclosure. The transition steps occur in a multi-link device (MLD) enabled Wi-Fi network. The process is divided into three main phases: before transition, during transition, and after transition.

[0099] Initially, before the transition, a non-AP MLD (client device) is actively associated with the current AP MLD (e.g., AP MLD1). This represents the standard connection state where the client is communicating through a single access point.

[0100] As the roaming process begins, the non-AP MLD initiates an association with the target AP MLD (e.g., AP MLD2) while maintaining its connection with the current AP MLD.This intermediate step, depicted by the circle in FIG. 11, represents an aspect of the smooth roaming mechanism. During this phase, the non-AP MLD is simultaneously active with both the current and target AP MLDs. This dual association allows the client device to be logically activated with both AP MLDs concurrently. The significance of this dual activation lies in the non-AP MLD's ability to send and receive frames through both AP MLDs simultaneously. This is possible because the client device is within the transmission range of both AP MLDs. This overlap in coverage is useful for the smooth transition, as it eliminates the traditional "break- before-make" approach in conventional roaming.

[0101] Once the transition is complete, the non-AP MLD terminates its active connection with the current AP MLD (e.g., AP MLD1) and fully transitions to sending and receiving frames exclusively through the target AP MLD (e.g., AP MLD2). This final state represents the completion of the roaming process, with the client now fully associated with the new access point.

[0102] This smooth roaming mechanism leverages the multi-link capabilities of the MLDs to provide a seamless transition between access points, potentially reducing or eliminating connection interruptions, packet loss, and latency spikes typically associated with traditional roaming methods. Such an approach is useful for, among other applications, applications requiring consistent, low-latency connectivity in environments with multiple overlapping Wi-Fi access points.

[0103] FIG. 12 illustrates a scenario where the non-AP MLD (e.g., STA1) moves to the target AP MLD (e.g., AP2), according to some embodiments of the present disclosure. The scenario focuses on the non-AP MLD, referred to as STA1, as it moves from the coverage area of one AP MLD (e.g., API) to another (e.g., AP2). Initially, STA1 is associated with the current AP MLD (e.g., API) via Link 1.

[0104] As STA1 moves, it enters an area where the Basic Service Sets (BSSs) of API and AP2 overlap. In this intermediate position, represented by a circle in FIG. 12, STA1 faces a challenge: it is now at a considerable distance from both API and AP2. Consequently, if STA1 were to receive frames from only one AP (either API or AP2), it would likely experience poor signal quality, resulting in lower data rates. This situation could lead to performance degradation during the transition period.

[0105] To address this issue, the disclosed techniques propose implement Joint Transmission (JTX) during the transition period. JTX is an advanced technique where multiple APs collaborate to transmit data to a single client simultaneously. By leveraging JTX, both API and AP2 can transmit frames to STA1 concurrently, potentially combining their signals to providebetter reception quality at STAl's location. The implementation of JTX during the transition is expected to increase throughput and overall network performance for STA1. This approach aims to maintain high-quality connectivity even when the client would otherwise experience suboptimal signal conditions from either AP individually. After completing the transition, STA1 becomes fully associated with AP2. The benefit of this approach is that the transition occurs smoothly, without the performance degradation typically associated with traditional roaming methods.

[0106] FIG. 13 illustrates an example of a process for smooth roaming where the non-AP MLD moves to the target AP MLD (e.g., AP2), according to some embodiments of the present disclosure. This process leverages Joint Transmission (JTX) to maintain optimal performance during the transition.

[0107] Joint Transmission (JTX) is an advanced wireless networking technique used according to techniques disclosed herein to improve the performance and reliability of a client device (STA1) during the roaming process between two Access Point Multi-Link Devices (AP MLDs). Specifically, JTX is employed when STA1 is in an area where the coverage of the current AP (API) and the target AP (AP2) overlap, but the signal from either AP alone may be insufficient to maintain high data rates.

[0108] In the scenario of FIG. 13, both API and AP2 transmit the same data to STA1 concurrently at Step 5 of the process. The JTX process requires coordination between API and AP2, facilitated by the Roaming AP MLD. This includes sharing information about the duration and size of the JTX data. To help ensure effective JTX, the APs perform a joint sounding sequence (represented by the oval in FIG. 13). This allows for pre-correction of the data frames to synchronize the transmissions from API and AP2. By combining signals from both APs, JTX aims to provide better reception quality and higher data rates for STA1 when STA1 would otherwise experience suboptimal signal conditions. JTX serves as a bridge during the roaming process, allowing STA1 to maintain high-quality connectivity as it moves from API's primary coverage area to AP2's. The JTX phase is temporary, designed to cover the transition period of the roaming process. Once STA1 is closer to AP2, normal single-AP transmission resumes. The implementation of JTX in this roaming mechanism represents an innovative approach to maintaining consistent high performance in mobile Wi-Fi scenarios, particularly in environments with overlapping AP coverage.

[0109] Initially, at Step 1, STA1 is associated with API, communicating via Link 1 as depicted in FIG .3. Link 1 refers to the initial wireless connection between the client device (STA1) and the first Access Point Multi-Link Device (AP MLD), specifically API. Link 1 is theprimary communication channel established between STA1 and API before the roaming process begins.

[0110] Link 1 is one of the possible links in the Multi-Link Device (MLD) architecture. In this example, it represents a specific frequency band or channel used for communication between the non-AP MLD (STA1) and the AP MLD (API). Link 1 is the active connection used for data transmission and reception between STA1 and API before STA1 begins moving towards AP2's coverage area. As STA1 moves and initiates the roaming process, Link 1 serves as the starting point from which the transition to AP2 begins. During the Joint Transmission (JTX) phase of roaming, Link 1 may continue to be used alongside the new connection to AP2, allowing for simultaneous data reception from both APs. As STA1 moves closer to AP2, the significance of Link 1 diminishes. Eventually, when the roaming process is complete, Link 1 is no longer used, and STA1 communicates exclusively with AP2.

[0111] Multi-Link Device (MLD) refers to a device capable of operating simultaneously on multiple frequency bands or links within a Wi-Fi network. There are different types of MLDs. An Access Point MLD (AP MLD) is an access point capable of multi-link operations. AP MLD1 and AP MLD2 represent the current and target access points in the roaming scenario examples. A non-AP MLD refers to a client device such as STA1 in the examples. As a non-AP MLD, STA1 can maintain connections with multiple AP MLDs simultaneously during the roaming process. A Roaming AP MLD is a central entity that facilitates the roaming process. A Roaming AP MLD uses Multi Link Operation (MLO). The AP MLDs (e g., AP MLD1 and AP MLD2) are allowed to be affiliated with the Roaming AP MLD for smooth roaming.

[0112] The MLD architecture of the disclosed techniques allows for more flexible and efficient use of the available spectrum. In the roaming context, it enables simultaneous association with multiple APs. The non-AP MLD (STA1) can be active with both the current and target AP MLDs during the transition phase. It also enables coordinated data transmission. The AP MLDs can coordinate to provide joint transmission (JTX) to the non-AP MLD during roaming. It further enables efficient backhaul communication. The Roaming AP MLD serves as a central point for coordinating the roaming process and sharing data between AP MLDs. By leveraging MLD capabilities, the disclosed roaming mechanism can provide a smoother transition between access points, maintaining connectivity and performance throughout the process.

[0113] At Step 2, as STA1 moves towards AP2's coverage area, it initiates the roaming process by transmitting a Roaming Request (R-req) frame to both API and AP2. This R-req frame contains information for smooth roaming, including a solicitation for AP2 to respond witha Roaming Confirm (R-con) frame, and instructions for API to duplicate data intended for STA1 and deliver it to the Roaming AP MLD (e.g., via Link 2 as shown in FIG. 12). Additional roaming information, such as reassociation details, security parameters, and Block Acknowledgment (BA) session data, can be communicated through the backhaul network (e.g., the Roaming AP MLD of FIG. 12).

[0114] The Roaming Request (R-req) frame is an initial frame that triggers the roaming process. The R-req frame is transmitted by STA1 when it detects the need to roam from API to AP2. Notably, the R-req frame is sent to both the current AP (API) and the target AP (AP2). This dual transmission helps ensure that both APs are informed of the impending roaming process simultaneously. The R-req frame may contain information to facilitate smooth roaming including information to solicit a response from AP2 in the form of a Roaming Confirm (R-con) frame and information to instruct API to begin duplicating data intended for STA1 and deliver it to the Roaming AP MLD. Specifically, the information may include a request for AP2 to respond with an R-con frame. The information may also include instructions for API regarding data duplication and delivery to the Roaming AP MLD. The information may include additional roaming information such as details about reassociation, security parameters, Block Acknowledgment (BA) sessions, etc. The R-req frame initiates processes that involve backhaul communication through the Roaming AP MLD, allowing for efficient transfer of roaming- related information between API and AP2. By informing both APs of the roaming intent, the R- req frame facilitates the subsequent Joint Transmission (JTX) phase of the roaming process. The information contained in the R-req frame allows both APs to prepare for the transition, thereby enabling a smoother roaming experience with minimal interruption to the client's connectivity.

[0115] Link 2 refers to the communication channel between the current Access Point MultiLink Device (API) and the Roaming AP MLD. Link 2 facilitates the smooth roaming process, particularly in the data duplication and transfer phase. When STA1 initiates the roaming process by sending the Roaming Request (R-req) frame, it instructs API to begin duplicating data intended for STA1. This duplicated data is then delivered to the Roaming AP MLD through Link 2. Link 2 may also serve as a backhaul connection, allowing for efficient transfer of data and roaming-related information between API and the Roaming AP MLD. This link enables the system to maintain data continuity during the transition period, ensuring that no packets are lost as STA1 moves from API's coverage area to AP2's. The use of Link 2 for data duplication and transfer contributes to the seamless handover process and minimizing potential disruptions in service for STA1. By leveraging Link 2, the smooth transition mechanism can prepare for JointTransmission (JTX) and helps ensure that both API and AP2 have access to the same data for simultaneous transmission to STA1 during the transition phase.

[0116] At Step 3, upon receiving the R-req, AP2 responds with an R-con frame and requests the duplicated data from the Roaming AP MLD (e.g., via Link 3 as shown in FIG. 12). The Roaming Confirm (R-con) frame, referred to as "R-con," is an element in the smooth roaming mechanism described. This frame is sent by the target Access Point Multi-Link Device (AP2) in response to the Roaming Request (R-req) frame initiated by the client device (STA1).

[0117] At Step 3, AP2 transmits a R-con frame. This action occurs after AP2 receives the R- req frame from STA1. The R-con frame may serve multiple purposes in the roaming process. Firstly, it may acknowledge AP2's readiness to participate in the roaming procedure. Secondly, it may contain information necessary for establishing the new connection between STA1 and AP2. Upon sending the R-con frame, AP2 requests the duplicated data to roaming AP MLD as shown in FIG. 12 (e.g., via Link 3). The R-con frame not only confirms AP2's participation in the roaming process but also triggers a request for the duplicated data that API has been sending to the Roaming AP MLD. This helps ensure that AP2 has access to the same data as API, enabling seamless Joint Transmission (JTX) during the transition period. Link 3 refers to the communication channel between the target Access Point Multi-Link Device (AP2) and the Roaming AP MLD. This link facilitates the transfer of duplicated data to AP2. AP2 requests the duplicated data to roaming AP MLD as shown in FIG. 12 (e.g., via Link 3). This action occurs after AP2 transmits the Roaming Confirm (R-con) frame in response to the client device's (STA1) roaming request.

[0118] Link 3 may serve as a backhaul connection, allowing AP2 to retrieve the duplicated data that the current AP (API) has been sending to the Roaming AP MLD. This data retrieval is useful for enabling the Joint Transmission (JTX) phase of the roaming process, where both API and AP2 simultaneously transmit the same data to STA1. By leveraging Link 3, the roaming mechanism helps ensure that AP2 has access to the same up-to-date information as API, thus maintaining data continuity during the transition period.

[0119] At Step 4, STA1 then transmits a Roaming Initiation (R-init) frame to both APs, triggering the Joint Transmission phase. The Roaming Initiation (R-init) frame is a component in the smooth roaming mechanism. This frame is transmitted by the client device (STA1) to both the current Access Point Multi -Link Device (API) and the target Access Point Multi -Link Device (AP2) after receiving the Roaming Confirm (R-con) frame from AP2.

[0120] At Step 4, STA1 transmits a R-init frame to both API and AP2. This action effectively triggers the actual transition phase. By sending the R-init frame to both APssimultaneously, STA1 signals its readiness to begin the Joint Transmission (JTX) phase of the roaming process. The R-init frame may contain information necessary for both APs to synchronize their actions and prepare for the JTX. This frame may include parameters such as timing information, channel specifications, or other technical details required for coordinated transmission. The transmission of the R-init frame serves as the immediate precursor to the JTX phase, where both API and AP2 begin transmitting the same data to STA1 concurrently.

[0121] At Step 5, during JTX, API and AP2 simultaneously transmit identical data to STAl. The duration and size of the JTX data are predefined and shared between the APs through the Roaming AP MLD. To help ensure synchronization, a joint sounding sequence (depicted by the circle in FIG. 13) is performed, allowing for pre-correction of the data frames. The joint sounding sequence, represented by the circle in FIG. 13, facilitates the Joint Transmission (JTX) phase. This sequence is designed to synchronize and optimize the transmission between API and AP2 to STAl during the roaming process. The data frame can be pre-corrected through the joint sounding sequence for JTX in FIG. 13 in order to synchronize between API and AP2. The joint sounding sequence serves as a preparatory step for the JTX phase, allowing both APs to adjust their transmission parameters for optimal performance.

[0122] A purpose of the joint sounding sequence may be to enable the APs to gather information about the channel conditions between each AP and STAl. This may involve the exchange of specialized frames that allow the APs to measure various channel characteristics such as signal strength, interference levels, and timing offsets. By performing this joint sounding, API and AP2 can coordinate their transmissions more effectively, adjusting factors like transmit power, beamforming parameters, and timing to combine their signals constructively at STAl's location. This synchronization and pre-correction are useful for the JTX phase, as they help to maximize the signal quality at STAl when it receives simultaneous transmissions from both APs. By optimizing the joint transmission in this way, the roaming mechanism can provide seamless connectivity and maintain high performance for STAl throughout the transition process, even when the client device is at a point from both APs where individual signals might be weak.

[0123] At Step 6, STAl acknowledges the received JTX data by transmitting a multidestination Acknowledgment (ACK) frame (e.g., Multi -AP Block ACK) to both API and AP2. The JTX (Joint Transmission) data refers to the information transmitted simultaneously by both API and AP2 to STAl during the transition phase of the smooth roaming process. API and AP2 transmit the same data. In particular, both access points send identical information to STAl concurrently, allowing the client device to receive a stronger combined signal even when theclient device is in an area where individual signals from either AP might be weak. The duration of JTX and the size of the JTX data can be predefined and shared between API and AP2 through Roaming AP MLD. In particular, the JTX phase may be a carefully coordinated process, with both APs agreeing on the specifics of the data transmission beforehand. The involvement of the Roaming AP MLD in sharing this information is part of backend coordination in facilitating smooth roaming. The data frame can be pre-corrected through the joint sounding sequence for JTX in order to synchronize between API and AP2. This pre-correction and synchronization can ensure that the JTX data from both APs arrives at STA1 in a coherent manner, maximizing the effectiveness of the joint transmission. The JTX data transmission continues until STA1 moves closer to AP2, at which point the roaming process completes, and normal single- AP transmission resumes. This coordinated JTX data transmission can provide uninterrupted, high- quality connectivity throughout the transition between access points.

[0124] The multi-destination acknowledgement frame is a specialized acknowledgement mechanism used by STA1 during the Joint Transmission (JTX) phase of the smooth roaming process. After receiving the jointly transmitted data from both access points, STA1 may need to confirm successful reception to both APs simultaneously. This multi-destination capability is useful in the context of JTX, where data is being received from two sources concurrently. By using a single ACK frame that can be interpreted by both API and AP2, the system reduces overhead and improves efficiency in the acknowledgement process. This is useful during the roaming transition, where maintaining low latency and high throughput is useful. This acknowledgement frame may be capable of confirming the receipt of multiple data blocks in a single transmission. This may be useful in a scenario where large amounts of data are being transmitted during the JTX phase.

[0125] At Step 7, as STA1 moves closer to AP2, it eventually disassociates from API and becomes fully associated with AP2. At this point, normal data transmission resumes between STA1 and AP2, with standard ACK procedures as in Step 8.

[0126] This mechanism demonstrates an advanced approach to Wi-Fi roaming, utilizing MLD capabilities, JTX, and coordinated AP communication to provide a seamless transition between access points. By maintaining connectivity through both APs during the transition, this method aims to minimize latency, reduce packet loss, and help ensure consistent high performance throughout the roaming process.

[0127] FIG. 14 illustrates a first example of the joint sounding sequence, according to some embodiments of the present disclosure. FIG. 14 depicts a process for initiating and synchronizing Joint Transmission (JTX) in a multi-link device (MLD) enabled Wi-Fi networkduring a roaming scenario. The process begins with the Roaming AP MLD broadcasting a JTX sounding trigger frame simultaneously to both API and AP2. This trigger frame serves multiple functions in the JTX process.

[0128] Upon receiving the JTX sounding trigger frame, API and AP2 use it as a reference signal to estimate pre-correction values, specifically the residual Carrier Frequency Offset (CFO) and timing. These pre-correction values are useful for synchronizing the transmissions from both APs during the JTX phase. The calculation of these values occurs after the reception of the trigger frame, allowing the APs to apply the corrections to their subsequent data transmissions, as indicated in Step 5 of the process (corresponding to Step 5 of the process of FIG. 13).

[0129] The JTX sounding trigger frame also acts as a timing reference, soliciting JTX transmissions after a Short Interframe Space (SIFS) interval. This helps ensure that both APs initiate their JTX transmissions simultaneously and in a coordinated manner. The SIFS interval is a standard Wi-Fi timing parameter that allows for precise synchronization between the trigger frame and the start of the JTX.

[0130] Furthermore, the trigger frame can contain additional information pertinent to the JTX process, such as length alignment parameters. This information helps in further optimizing the joint transmission, ensuring that both APs transmit data of the same length and format.

[0131] This synchronization process enables API and AP2 to transmit identical data simultaneously as part of the JTX, providing robust and uninterrupted connectivity to the roaming client device. By leveraging precise timing, pre-correction techniques, and coordinated transmission, this method aims to minimize interference, maximize signal quality, and help ensure seamless connectivity during the critical roaming transition phase in a multi-AP environment.

[0132] FIG. 15 illustrates a second example of the joint sounding sequence, according to some embodiments of the present disclosure. FIG. 15 presents an alternative approach to initiating and synchronizing Joint Transmission (JTX) in a multi-link device (MLD) enabled Wi-Fi network during a roaming scenario. In this case, the process introduces a hierarchical structure between the participating Access Points (APs), designating one as the "main AP" and the other as the "assist AP".

[0133] The process begins with the main AP (which could be either API or AP2) transmitting a JTX sounding trigger frame to the assist AP the other of API or AP2. This trigger frame serves as both a synchronization signal and a command to initiate the JTX process.

[0134] Upon receiving the JTX sounding trigger frame, the assist AP uses it as a reference to calculate pre-correction values. These values, which can include parameters such as residual Carrier Frequency Offset (CFO) and timing adjustments, are useful for synchronizing the assist AP's transmission with that of the main AP during the JTX phase. The assist AP computes these pre-correction values immediately after receiving the trigger frame and applies them to its subsequent data transmission, as indicated in Step 5 of the process (corresponding to Step 5 of the process of FIG. 13).

[0135] The JTX sounding trigger frame also acts as a timing reference, soliciting JTX transmissions from both the main AP and the assist AP after a Short Interframe Space (SIFS) interval. This helps ensure that both APs begin their JTX transmissions simultaneously and in a coordinated manner, despite the hierarchical structure. The SIFS interval, a standard Wi-Fi timing parameter, allows for precise synchronization between the trigger frame and the start of the JTX.

[0136] Additionally, the trigger frame can contain supplementary information relevant to the JTX process, such as length alignment parameters. This information helps in further optimizing the joint transmission, ensuring that both APs transmit data of the same length and format.

[0137] This synchronization method enables the main AP and assist AP to transmit identical data simultaneously as part of the JTX, providing robust and uninterrupted connectivity to the roaming client device. By employing a main AP-assist AP structure, precise timing, precorrection techniques, and coordinated transmission, this approach aims to minimize interference, maximize signal quality, and help ensure seamless connectivity during the roaming transition phase in a multi-AP environment.EXAMPLE METHODS

[0138] FIG. 16 illustrates a method 1600 for smooth roaming with transmission of duplicate frames performed at a wireless device capable of multi-link operation (MLO) and operating as a non-access point multi-link device (non-AP MLD) in a wireless network, according to some embodiments of the present disclosure.

[0139] This method 1600 encompasses a roaming process for a wireless device capable of multi-link operation (MLO) in a next-generation Wi-Fi network. The device, operating as a non- access point multi-link device (non-AP MLD), executes a series of steps to achieve seamless transition between two access point multi-link devices (AP MLDs).

[0140] Initially, the non-AP MLD communicates 1605 with a current AP MLD through standard frame exchanges. When roaming becomes necessary (e.g., the non-AP MLD physically moves away from the current AP MLD and towards a target AP MLD), the non-AP MLDinitiates the process by simultaneously transmitting 1610 a roaming request frame to both its current AP MLD and the target AP MLD. This dual transmission ensures both APs are synchronously informed of the impending roaming event.

[0141] Upon receiving 1615 a roaming confirm frame from the target AP MLD, indicating its readiness to accept the roaming device, the non-AP MLD proceeds to transmit 1620 a roaming initiation frame to both the current and target AP MLDs. This step triggers preparatory actions in both APs for the impending joint transmission.

[0142] The roaming process involves the simultaneous reception 1625 of identical joint transmission (JTX) data from both the current and target AP MLDs. This JTX mechanism allows the non-AP MLD to maintain continuous data reception during the transition, effectively implementing a "make-before-break" approach to roaming.

[0143] The roaming process includes the non-AP MLD establishing 1630 a new communication link with the target AP MLD, as evidenced by the exchange of frames between them. This method aims to minimize disconnection time and maintain high performance during the roaming process in MLO-capable networks.

[0144] In the context of this multi-link operation (MLO) roaming method 1600, the step 1605 establishes the baseline communication between the non-access point multi-link device (non-AP MLD) and its current associated access point. This step 1605 involves the wireless exchange of one or more frames over a designated link between these two devices. These frames could encompass a variety of 802.11 frame types, potentially including data frames, management frames (such as beacon frames, probe requests / responses), or control frames (like acknowledgments). This communication represents the normal operation state before the roaming process is initiated. The link may be bidirectional, allowing for both uplink and downlink traffic. This step 1605 establishes the initial connection that the non-AP MLD will transition away from during the roaming process. It also serves as a reference point for comparing the performance and connectivity before and after the roaming event, helping to evaluate the seamlessness of the transition. Furthermore, this initial communication may involve the exchange of information that could trigger the decision to initiate roaming, such as signal strength measurements or quality of service metrics.

[0145] Multi -Link Operation (MLO) in the context of method 1600 refers to a Wi-Fi networking capability that allows devices to operate simultaneously on multiple frequency bands or channels. In this roaming method 1600, MLO facilitates a seamless transition between access points. Specifically, MLO enables the non-AP MLD and the current and target AP MLDs toutilize multiple links concurrently. These links could be on different frequency bands (e.g., 2.4 GHz, 5 GHz, 6 GHz) or different channels within the same band.

[0146] This multi-link capability provides several advantages in the roaming context. The non-AP MLD can communicate with both the first and second AP MLDs concurrently during the roaming process, as evidenced by the ability to send the roaming request and initiation frames to both APs. MLO allows for a "make-before-break" approach, where the new connection is established before the old one is terminated, reducing the likelihood of disconnection during roaming. MLO enables the simultaneous reception of the same data from both AP MLDs, which is an aspect of the roaming method 1600. The ability to use multiple links provides more options for managing network resources during the roaming process. By leveraging multiple links, the roaming process 1600 becomes more robust against interference or poor performance on any single link.

[0147] Multi -Link Operation (MLO) in the context of this roaming method 1600 can be implemented in several ways, each offering distinct advantages for the smooth transition between access points. One approach is simultaneous multi-band operation, where the non-AP MLD and AP MLDs communicate across different frequency bands concurrently. For instance, the initial connection with the first AP MLD might be on a 5 GHz link, while the roaming request to the second AP MLD is sent on a 6 GHz link, allowing for efficient use of available spectrum and potentially reducing congestion.

[0148] Another implementation could involve channel aggregation within the same band. Here, the non-AP MLD might use multiple 80 MHz or 160 MHz channels simultaneously, distributing the roaming-related frames and data across these channels to increase throughput and reliability during the transition. This approach could be particularly beneficial for the joint transmission (JTX) phase, where high bandwidth is useful for maintaining seamless connectivity.

[0149] A load balancing implementation of MLO could dynamically allocate traffic across available links based on real-time conditions. During the roaming process, less time-sensitive data might be transmitted on one link while prioritizing roaming-related frames on another, ensuring critical handover information is delivered promptly.

[0150] MLO could also be implemented with a primary-secondary link structure. The non- AP MLD might maintain a primary high-bandwidth link for data transmission while using a secondary, more reliable but lower-bandwidth link for roaming signaling. This could help ensure that roaming control frames are delivered successfully even in challenging RF environments.

[0151] Lastly, an adaptive MLO implementation could dynamically adjust the number and characteristics of active links based on the roaming stage. It might start with a single link to the first AP MLD, transition to using multiple links during the JTX phase for maximum reliability, and then optimize for performance with the second AP MLD post-transition. This flexible approach could offer an optimal balance of reliability, performance, and power efficiency throughout the roaming process.

[0152] In the context of this roaming method 1600, a multi-link device (MLD) refers to a WiFi enabled device capable of operating simultaneously on multiple frequency bands or channels. There are at least two types of MLDs: the non-access point MLD (non-AP MLD) and the access point MLDs (AP MLDs). The non-AP MLD may be a client device such as a smartphone, laptop, or loT device or other portable or moveable Wi-Fi enable device capable of multi-link operation (ML), while the AP MLDs are the network access points.

[0153] These MLDs may be equipped with multiple radio chains and MAC layer entities, allowing them to establish and maintain concurrent connections on different links. Each link can operate on a distinct frequency band (e.g., 2.4 GHz, 5 GHz, 6 GHz) or separate channels within the same band. This multi-link capability enables more flexible and efficient use of the available spectrum.

[0154] In the roaming scenario of the method 1600, the MLD architecture allows the non-AP MLD to communicate with both the first and second AP MLDs simultaneously during the transition phase. This is evident in the ability to send roaming request and initiation frames to both APs and to receive joint transmission data from both APs concurrently. The MLD functionality thus facilitates a seamless "make-before-break" roaming approach, where the connection to the new AP is established before disconnecting from the current AP, thereby minimizing interruption in connectivity.

[0155] Furthermore, the MLD capability enables more sophisticated roaming decisions and executions. The device can assess link quality across multiple bands, potentially choosing the optimal link for each phase of the roaming process. This multi-link awareness and utilization contribute to a more robust and efficient roaming mechanism, addressing the challenges of maintaining low-latency, high-reliability connections in next-generation Wi-Fi networks.

[0156] In the context of the multi-link operation (MLO) roaming method 1600, the step 1610 of wirelessly transmitting a roaming request frame to both the first and second AP MLDs represents an initiation of the roaming process. This step 1610 leverages the MLO capability of the non-AP MLD to simultaneously communicate with multiple access points across different links or frequency bands.

[0157] The roaming request frame is a specialized management frame that signals the non- AP MLD's intent to transition its connection from the first AP MLD (current association) to the second AP MLD (target association). By transmitting this frame to both AP MLDs concurrently, the non-AP MLD efficiently informs both the current and target APs of the impending roaming event.

[0158] This simultaneous transmission reduces the overall time required to initiate the roaming process, as both APs receive the request simultaneously rather than sequentially. Secondly, it allows the current AP (first AP MLD) to begin preparing for the handover, potentially by starting to buffer data or adjusting its transmission parameters. Thirdly, it prompts the target AP (second AP MLD) to assess its readiness to accept the roaming device and prepare necessary resources.

[0159] The roaming request frame may contain information such as the non-AP MLD's capabilities, current connection parameters, and possibly the reason for initiating the roaming process. This information helps both AP MLDs to optimize their responses and prepare for the subsequent steps in the roaming procedure, ultimately contributing to a more seamless and efficient transition between access points.

[0160] The roaming request frame in the MLO-capable roaming method 1600 is a management frame that initiates the transition process between access points. The roaming request frame may be implemented as a single logical frame, designed to efficiently communicate with both the current and target AP MLDs simultaneously.

[0161] The roaming request frame's structure may be tailored to support this dual-AP communication. It may include a Transmitter Address (TA) field set to the non-AP MLD's address, identifying the roaming device. The roaming request frame can contain multiple AP MLD information fields, allowing it to include the addresses of both the current and target AP MLDs. This multi-address capability enables the frame to be processed by both APs, despite being a single transmission.

[0162] Two potential mechanisms for ensuring the frame reaches both APs are suggested. In the first approach, the roaming request frame directly includes both AP MLD addresses, allowing each AP to recognize and process the request. Alternatively, if the current and target AP MLDs are associated with the same distribution system, the current AP MLD may already know the target AP MLD's address. In this scenario, when the current AP MLD transmits roaming control frames to the non-AP MLD, it can include the address of the target AP MLD. This inclusion allows the target AP MLD to implicitly anticipate and prepare for the incoming roaming request from the non-AP MLD.

[0163] This implementation leverages the MLO capability to its fullest, allowing for efficient, simultaneous communication with multiple APs. It reduces overhead by using a single frame transmission to initiate the roaming process with both the current and target APs, potentially speeding up the overall roaming procedure and contributing to a more seamless transition between access points.

[0164] In the context of the MLO-capable roaming method 1600, the step 1615 of wirelessly receiving a roaming confirm frame from the target AP MLD occurs after the non-AP MLD has transmitted its roaming request frame to both the current and target AP MLDs and represents the target AP MLD's response to that request.

[0165] The roaming confirm frame is a specialized management frame that serves multiple purposes. Primarily, it indicates the target AP MLD's willingness and readiness to accept the roaming non-AP MLD. This frame may contain important information such as the target AP MLD's capabilities, available resources, and potentially, specific parameters for the impending connection.

[0166] The roaming confirm frame may include details such as any of all of: supported data rates and modulation schemes, available bandwidth and channel information, security parameters and authentication methods, quality of Service (QoS) capabilities, any specific MLO-related information such as which links or bands are available for the roaming device, or any other suitable information.

[0167] The reception of this frame by the non-AP MLD confirms that the target AP MLD is prepared for the handover, allowing the non-AP MLD to proceed with the next steps in the roaming sequence. Information contained in the roaming confirm frame may inform the non-AP MLD's subsequent actions, particularly in preparing for the joint transmission (JTX) phase that follows. It may help the non-AP MLD optimize its settings for the upcoming transition, potentially configuring its multi-link capabilities to best utilize the resources offered by the target AP MLD.

[0168] In the context of this MLO-capable roaming method 1600, the step 1620 of wirelessly transmitting a roaming initiation frame to both the current AP MLD and the target AP MLD occurs after the non-AP MLD has received confirmation from the target AP MLD and signals the imminent transition of the connection.

[0169] The roaming initiation frame is a specialized management frame. By transmitting this frame to both AP MLDs simultaneously, the non-AP MLD leverages its multi-link capabilities to efficiently coordinate the roaming process across multiple network nodes.

[0170] This frame may contain several pieces of information include any or all of: timing information for the impending transition, specific parameters for the joint transmission (JTX) phase, resource allocation requests for both APs, any necessary updates to the initially requested roaming parameters, confirmation of the non-AP MLD's readiness to receive JTX data, or any other suitable information.

[0171] For the current AP MLD, the roaming initiation frame may trigger the initiation of data buffering or forwarding mechanisms to ensure no packets are lost during the transition. It may also signal the current AP to prepare for the upcoming JTX phase. For the target AP MLD, the roaming initiation frame could serve as the final confirmation to allocate resources and prepare for the imminent connection. It may trigger the target AP to synchronize with the current AP for the JTX phase.

[0172] In the context of this MLO-capable roaming method 1600, the roaming initiation frame coordinates the handover process between the current and target AP MLDs. This frame may be implemented as a single logical frame at higher layers, though its physical layer transmission might involve broadcast or multicast mechanisms to reach both AP MLDs simultaneously.

[0173] In a broadcast approach, the non-AP MLD may construct the roaming initiation frame with a broadcast address in the Receiver Address (RA) field. The frame's body then contains multiple AP MLD info fields, each specifying the address and other relevant details for the current and target AP MLDs. This structure allows a single frame to carry specific instructions for both APs while being transmitted as a broadcast message.

[0174] In this case, the roaming initiation frame's structure could include any or all of the following information:

[0175] Transmitter Address (TA): Set to the non-AP MLD's address.

[0176] Receiver Address (RA): Set to broadcast address.

[0177] AP MLD info fields: Separate fields for each AP MLD, containing: Individual RA for each AP MLD and additional parameters specific to each AP.

[0178] This structure enables the roaming initiation frame to efficiently communicate with both AP MLDs in a single transmission, reducing overhead and supporting synchronization in the roaming process. The frame may contain critical information to coordinate the imminent joint transmission (JTX) phase, such as timing parameters, resource allocation details, and any final adjustments to the roaming parameters.

[0179] Alternatively, the roaming initiation frame may be transmitted in a way that allows AP MLDs to implicitly identify that the message is intended for them, for example, byleveraging their awareness of the ongoing roaming process and their association with the same distribution system.

[0180] By leveraging either broadcast transmission or implicit identification mechanisms, this approach ensures that both the current and target AP MLDs receive the necessary information simultaneously.

[0181] The step 1625 of wirelessly and simultaneously receiving the same joint transmission (JTX) data from both the current and target AP MLDs bridges the transition between the two access points. JTX involves the synchronized transmission of identical data packets from multiple sources (in this case, the current and target AP MLDs) to a single recipient (the non-AP MLD). This simultaneous transmission leverages the multi-link capabilities of the devices involved, allowing the non-AP MLD to receive and process data from multiple sources concurrently. The "same" JTX data means that both AP MLDs are transmitting identical information, which leverages coordination between the APs. This coordination may involve precise timing synchronization and the use of techniques such as coordinated beamforming or MU-MIMO (Multi-User Multiple-Input Multiple-Output) to ensure the signals combine constructively at the receiver.

[0182] From the non-AP MLD's perspective, this step 1625 may involve utilizing its multiple radio chains and advanced signal processing capabilities to coherently combine the signals from both AP MLDs. This may involve techniques such as maximal ratio combining (MRC) or other diversity combining methods to optimize the received signal quality.

[0183] The simultaneous reception of JTX data serves ensures continuity of data flow during the handover, implementing a true "make-before-break" transition. It also may improve signal quality and reliability by leveraging spatial diversity. It may allow for a gradual transition of the data path from the current AP MLD to the target AP MLD without interruption.

[0184] In the context of this MLO-capable roaming method 1600, the same JTX data refers to identical information packets transmitted simultaneously by both the current and target AP MLDs to the roaming non-AP MLD. Transmitting the same JTX data may involve both AP MLDs transmitting bit-for-bit identical data frames or packets. This may require a high degree of coordination between the two AP MLDs, facilitated by a fast, low latency backhaul connection. The current AP MLD, which is actively serving the non-AP MLD, needs to share its outgoing data stream with the target AP MLD in real-time. This shared data is then simultaneously broadcast by both AP MLDs.

[0185] The implementation of transmitting the same JTX data may involve several technical considerations. Both AP MLDs may have access to the same data buffer, ensuring that they aretransmitting identical information at the same time. Precise timing mechanisms are useful to ensure that the data transmissions from both AP MLDs arrive at the non-AP MLD simultaneously or with minimal offset. The AP MLDs may need to adjust their carrier frequencies to account for any differences, ensuring that the signals can be coherently combined at the receiver. Transmission power levels may be coordinated to optimize the combined signal strength at the non-AP MLD's location. Both AP MLDs may use identical encoding and modulation schemes for the JTX data to ensure compatibility.

[0186] The transmission of the same JTX data allows the non-AP MLD to receive a single, coherent data stream from two sources simultaneously. This approach can potentially improve signal quality through constructive interference and provides redundancy, ensuring that data packets are more likely to be received correctly even if the signal from one AP is momentarily degraded.

[0187] By transmitting the same data, this method 1600 creates a virtual overlap period where the non-AP MLD is effectively connected to both AP MLDs, enabling a seamless transition without any interruption in the data flow. This provides a "make-before-break" roaming approach, which is useful for maintaining high performance and low latency in advanced Wi-Fi applications.

[0188] In the context of this MLO-capable roaming method 1600, while simultaneously receiving in the step 1625 of receiving joint transmission (JTX) data may aim for perfect synchronization between the current and target AP MLDs, a particular implementation may involve a more flexible and robust approach to implementing this simultaneity.

[0189] There are practical challenges in achieving perfect synchronization between two separate AP MLDs. An implementation may leverage the multi-link capabilities of the devices to create a system that is resilient to slight timing discrepancies. Thus, simultaneously does not necessarily mean exact temporal alignment of the signals from both AP MLDs, but rather a coordinated transmission over different links that the non-AP MLD can process as a unified data stream.

[0190] For example, a simultaneously approach could work as follows:

[0191] The current AP MLD transmits the JTX data over one link.

[0192] The target AP MLD transmits the same JTX data over a different link.

[0193] The non-AP MLD receives these transmissions over its multiple links, which may arrive at slightly different times.

[0194] The non-AP MLD stores the data frame that arrives first, regardless of which link it came through.

[0195] It then waits for the duplicate data frame to arrive on the other link.

[0196] Then, the non-AP MLD combines or "muxes" these frames, potentially gaining performance benefits from this diversity.

[0197] This approach turns the potential issue of slight desynchronization into an advantage. By using different links for each AP MLD's transmission, the system becomes more robust to timing issues. If there's a delay on one link, the data can still be successfully received on the other, ensuring continuity of the data stream.

[0198] The acknowledgment (ACK) mechanism adapts to this flexible approach. The non-AP MLD can send ACKs over the respective links to each AP MLD independently, accommodating any timing differences in the received data.

[0199] In essence, simultaneously in the JTX context prioritizes the end result - the successful and continuous reception of data during the roaming process - over the strict temporal alignment of the transmissions. This approach aligns with the goals of MLO to provide seamless connectivity and improved performance, even in challenging network conditions during the roaming process.

[0200] The MLO-capable roaming method 1600 involves the non-AP MLD wirelessly transmitting or receiving 1630 one or more frames via a wireless link with the target AP MLD. This step 1630 signifies the completion of the roaming process 1600 and the establishment of a new primary connection. The step 1630 represents the transition to normal operation with the target AP MLD after the joint transmission (JTX) phase. Bidirectional communication is possible, encompassing both uplink and downlink traffic. These frames could include various types of 802.11 frames such as data frames for actual user traffic, management frames for ongoing network maintenance, or control frames for link quality management.

[0201] By establishing a functional link with the target AP MLD, this step 1630 confirms that the roaming process has completed successfully. It may involve the finalization of resource allocation, such as assigning specific channels or spatial streams for continued communication. Initial frames exchanged may include measurements to assess the quality of the new connection, potentially triggering further optimizations. If not completed earlier, this step 1630 may involve finalizing security associations, such as key exchanges or authentication processes. Given the MLO capabilities, this new link may be part of a multi-link setup, potentially utilizing multiple frequency bands or channels simultaneously. The initial frame exchanges may be used to finetune parameters like transmission power, modulation and coding schemes, and MIMO configurations.

[0202] This step 1630 essentially marks the transition from the carefully orchestrated roaming process 1600 to standard Wi-Fi operation, with the advanced capabilities provided by MLO. It represents the culmination of the seamless handover, where the non-AP MLD is now fully operational with its new association to the target AP MLD, ready to continue high- performance, low-latency communication in the Wi-Fi network.

[0203] FIG. 17 illustrates a method 1700 for smooth roaming with transmission of duplicate frames performed at the wireless device capable of MLO and operating as the current AP MLD in the wireless network, according to some embodiments of the present disclosure.

[0204] The method 1700 expands on the roaming process 1600 outlined in FIG. 16 by detailing the operations performed by the current AP MLD during the Joint Transmission (JTX) phase of the roaming procedure. This method 1700 leverages advanced Multi -Link Operation (MLO) capabilities to ensure a smooth and synchronized handover.

[0205] The process 1700 begins with the current AP MLD wirelessly receiving 1705 a JTX sounding trigger frame. This frame is transmitted by a roaming AP MLD, which acts as a central coordinator in the network, orchestrating the roaming process. The JTX sounding trigger frame initiates the synchronization process necessary for effective joint transmission.

[0206] Upon receiving this trigger frame, the current AP MLD performs calculations 1710 to derive one or more pre-corrected values. These pre-corrected values are useful for synchronizing transmissions between multiple APs and ensuring that the signals from different APs can be coherently combined at the non-AP MLD (the roaming client device). The pre-corrected values address factors such as timing offsets, frequency differences, and phase alignments between the APs.

[0207] Following these calculations, the current AP MLD wirelessly transmits 1715 a JTX data frame to the non-AP MLD. This frame is a specialized construct that contains the actual JTX data (which is identical to the data being transmitted by the target AP MLD) and the calculated pre-corrected values.

[0208] The inclusion of pre-corrected values in the JTX data frame allows the non-AP MLD to adjust and align the received signals from multiple sources. This approach enables the non-AP MLD to effectively combine the signals from both the current and target AP MLDs, potentially improving signal quality and ensuring data integrity during the critical handover phase.

[0209] The JTX sounding trigger frame is a specialized management frame that initiates and coordinates the Joint Transmission (JTX) phase of the MLO-capable roaming process. This frame, transmitted by the roaming AP MLD (a central coordinating entity in the network), synchronizes the actions of multiple AP MLDs involved in the roaming procedure.

[0210] The JTX sounding trigger frame may contain any or all of the following elements: Precise timestamps or synchronization markers to align the transmission timing of participating AP MLDs. Instructions for AP MLDs to measure and report on their current channel conditions. Specifications for power levels, frequency bands, and spatial streams to be used in the upcoming JTX. Information to uniquely identify the roaming session and involved devices. Directives on how AP MLDs should allocate their resources for the JTX phase.

[0211] The JTX sounding frame's reception triggers the current AP MLD to enter a preparatory phase for JTX. It prompts the AP to assess current channel conditions, calculate necessary adjustments (e.g., the pre-corrected values), and prepare for synchronized transmission with other AP MLDs.

[0212] This sounding process may be analogous to techniques used in beamforming or MU- MIMO (Multi-User Multiple-Input Multiple-Output) systems, where precise channel knowledge is useful for coordinated transmission. However, in this context, it is extended to synchronize multiple APs for a seamless client handover.

[0213] By providing a common reference point and instructional set for all participating AP MLDs, the JTX sounding trigger frame ensures that the subsequent JTX phase can occur with the high degree of synchronization necessary for effective signal combination at the roaming client device.

[0214] The roaming access point multi-link device (roaming AP MLD) represents a specialized network entity that coordinates the advanced MLO-capable roaming process. This device acts as a central orchestrator, facilitating the seamless transition of a client device (non- AP MLD) between different access points in the network.

[0215] The roaming AP MLD may be a high-performance network node encompass any or all of the following elements. As an MLD, it can operate simultaneously on multiple frequency bands or channels, allowing for efficient communication with various network elements. It may be capable of a comprehensive view of the network topology, including the status and capabilities of all AP MLDs involved in potential roaming scenarios. It may have the computational resources necessary to make real-time decisions about roaming processes and to generate complex coordination frames like the JTX sounding trigger frame. It may connect to other AP MLDs via a high-bandwidth, low-latency backhaul network, enabling rapid information exchange and coordination. It may maintain precise timing synchronization across the network, useful for coordinating simultaneous transmissions from multiple APs.

[0216] In the roaming process, the roaming AP MLD may perform any or all of the following functions. It may transmit the JTX sounding trigger frame to involved AP MLDs, signaling thestart of the coordinated roaming procedure. It may determine how network resources should be allocated among APs during the roaming process. It may facilitate the transfer of data between the current and target AP MLDs to ensure continuity during the handover. It may monitor the quality of connections and makes decisions about when to initiate roaming procedures.

[0217] By centralizing these functions in a dedicated device, the network can achieve a higher level of coordination in roaming processes, leading to more seamless transitions for client devices.

[0218] The pre-corrected values refer to a set of one or more calculated parameters that the current AP MLD derives based on the information received in the JTX sounding trigger frame. These values are useful for ensuring synchronized and coherent joint transmission from multiple AP MLDs to the roaming non-AP MLD.

[0219] The pre-corrected values are adjustments applied to the transmission parameters of the AP MLD to compensate for various physical and environmental factors that could affect the synchronization and quality of the joint transmission. These values are calculated to optimize the reception of signals at the non-AP MLD, ensuring that transmissions from multiple sources can be effectively combined.

[0220] Examples of possible pre-corrected values include any or all of the following values. Timing Offset Correction: This value adjusts the transmission timing to ensure that signals from different AP MLDs arrive at the non-AP MLD simultaneously. It might be expressed in nanoseconds or as a number of symbol periods. Carrier Frequency Offset (CFO) Compensation: This corrects for slight differences in the carrier frequencies between AP MLDs, for example, measured in Hz or parts per million (ppm) of the carrier frequency. Phase Adjustment: This value aligns the phase of the transmitted signals from different AP MLDs, for example, expressed in radians or degrees. Power Level Adjustment: This parameter fine-tunes the transmission power to balance the received signal strengths from different AP MLDs, for example, measured in dB. Beamforming Coefficients: These are complex numbers applied to multiple antenna elements to shape the transmission beam towards the non-AP MLD. Doppler Shift Compensation: For scenarios involving significant movement, this value corrects for the Doppler effect, typically expressed as a frequency shift in Hz. Channel Estimation Corrections: These values adjust for the estimated channel conditions between the AP MLD and the non-AP MLD, for example, represented as complex numbers for amplitude and phase adjustments across different subcarriers in OFDM systems.

[0221] By calculating and applying these pre-corrected values, the AP MLD can improve the likelihood of successful signal combination at the non-AP MLD, enhancing the overall performance and reliability of the joint transmission during the critical roaming phase.

[0222] The JTX (Joint Transmission) data frame is a specialized frame structure used during the MLO-capable roaming process. This frame, transmitted by the current AP MLD to the non- AP MLD (roaming client device), is designed to facilitate seamless transition and maintain data continuity during the handover.

[0223] The JTX data frame is a composite structure that integrates two components. The same JTX data refers to the actual payload data that is being jointly transmitted by both the current and target AP MLDs. It ensures that the non-AP MLD receives identical information from multiple sources, allowing for potential signal combining and improved reliability. The pre-corrected values are the one or more calculated parameters that enable synchronized and coherent reception of signals from multiple AP MLDs.

[0224] The JTX data frame structure may include any or all of the following. A standard 802.11 MAC header, potentially with modifications to indicate its JTX nature. A specialized JTX header or information element containing the pre-corrected values. The payload data. And a frame check sequence for error detection.

[0225] The inclusion of pre-corrected values within the data frame allows for frame-by-frame adjustment of transmission parameters, enabling highly dynamic and responsive joint transmission. This is particularly valuable in mobile scenarios where channel conditions can change rapidly.

[0226] The JTX data frame ensures uninterrupted data flow to the non-AP MLD during the roaming process. It carries the necessary information for the non-AP MLD to coherently combine signals from multiple sources. By including pre-corrected values, it allows for continual fine-tuning of the joint transmission process.

[0227] FIG. 18 illustrates a method 1800 for smooth roaming with transmission of duplicate frames performed at the wireless device capable of multi-link operation (MLO) and operating as the target AP MLD in a wireless network, according to some embodiments of the present disclosure.

[0228] Method 1800 delineates the role and actions of the target AP MLD in the MLO- capable roaming process 1600 of FIG. 16, complementing the operations described for the current AP MLD method 1700 of FIG. 17. This method 1800 illustrates the sophisticated coordination required for seamless roaming in advanced Wi-Fi networks.

[0229] The processl800 begins with the target AP MLD wirelessly receiving 1805 the Joint Transmission (JTX) sounding trigger frame. This frame, transmitted by the roaming AP MLD, serves as a synchronization initiator and coordinator for the JTX phase of the roaming process. The roaming AP MLD, acting as a central orchestrator, ensures that both the current and target AP MLDs receive the same trigger, enabling coordinated action.

[0230] Upon receiving the JTX sounding trigger frame, the target AP MLD performs calculations 1810 to derive one or more pre-corrected values. These values are useful for synchronizing the target AP MLD's transmissions with those of the current AP MLD. The precorrected values address various parameters such as timing offsets, frequency adjustments, and phase alignments, which are useful for ensuring that the signals from both AP MLDs can be coherently combined at the non-AP MLD (the roaming client device).

[0231] Following these calculations, the target AP MLD wirelessly transmits 1815 a JTX data frame to the non-AP MLD. This specialized frame contains the actual JTX data (identical to the data being transmitted by the current AP MLD) and the one or more calculated pre-corrected values.

[0232] The inclusion of pre-corrected values in the JTX data frame allows the non-AP MLD to adjust and align the received signals from both the current and target AP MLDs. This technique is useful for effective signal combination at the receiver, potentially enhancing signal quality and maintaining data integrity during the critical handover phase.

[0233] FIG. 19 illustrates a method 1900 for smooth roaming with transmission of duplicate frames performed at the wireless device capable of multi-link operation (MLO) and operating as the roaming AP MLD in a wireless network, according to some embodiments of the present disclosure.

[0234] The method 1900 focuses on the roaming access point multi -link device (AP MLD) in facilitating seamless data transfer during the transition between access points. In this process 1900, the roaming AP MLD acts as a central coordinator and data relay point. It begins by wirelessly receiving 1905 particular data from the current AP MLD. This data represents the ongoing communication stream that the non-AP MLD (client device) is currently receiving. The transmission of this data to the roaming AP MLD could occur over a dedicated high-speed wireless backhaul link, utilizing one of the multiple links available in the MLO-capable network.

[0235] Upon receiving this data, the roaming AP MLD then wirelessly transmits 1910 the same particular data to the target AP MLD. This step 1910 ensures that both the current and target AP MLDs have access to identical data for the joint transmission phase. The transmissionto the target AP MLD might also occur over a separate high-speed wireless link, leveraging the multi-link capabilities of the network.

[0236] This particular data becomes the content of the joint transmission (JTX) data. This means that during the handover phase, both the current and target AP MLDs will simultaneously transmit this identical data to the roaming non-AP MLD.

[0237] This method 1900 ensures uninterrupted data flow to the non-AP MLD during the roaming process. By providing both AP MLDs with the same data, it enables precise synchronization of the joint transmission. It allows the non-AP MLD to receive consistent data from both AP MLDs, facilitating a smooth transition between them.

[0238] This approach may require high-speed, low-latency communication between all involved MLDs, precise timing mechanisms to ensure data consistency, and scheduling algorithms to manage the data flow across multiple network nodes. The roaming AP MLD's role as a data relay point is useful in achieving the "make-before-break" roaming mechanism, effectively eliminating data gaps or duplications that might occur during traditional roaming procedures.

[0239] This method exemplifies the advanced coordination capabilities of MLO-enabled networks, showcasing how multiple network elements can work in concert to provide seamless, high-performance connectivity for mobile devices.

[0240] In an embodiment of method 1600, method 1700, method 1800, or method 1900, the non-AP MLD remains in State 4 of the IEEE 802.11 state machine for STAs (stations) during and after the roaming process. In State 4, the non-AP MLD is authenticated and associated with an AP and can send and receive data frames. The method supports a mechanism where the non- AP MLD maintains its fully connected and operational state (State 4) throughout the roaming process, thereby enabling seamless transition between AP MLDs, without the need for reauthentication or re-association, which is typically required in conventional Wi-Fi roaming. By allowing the non-AP MLD to maintain State 4 during and after roaming, the method reduces roaming time and prevents data loss during transitions, addressing technical challenges in mobile scenarios in next-generation Wi-Fi networks.

[0241] In an embodiment of method 1600, method 1700, method 1800, or method 1900, the method encompasses a procedure for seamless roaming in a multi-link device (MLD) environment. The procedure is designed to maintain connectivity as a non-AP MLD transitions from one AP MLD to another. The procedure may encompass a distributed system (DS) mapping change where the network is notified of the change in the non-AP MLD’s association from the current AP MLD to the target AP MLD. During roaming, the current AP MLD maydeliver buffered downlink (DL) data frames for a period of time and may forward downlink data to the target AP MLD. During roaming, the non-AP MLD can retrieve buffered download data from the current AP MLD and can send uplink (UL) data to the target AP MLD. The target AP MLD can deliver data frames to the non-AP MLD after the DS mapping change. By allowing the current AP MLD to continue delivering buffered data, it reduces the chance of data loss during transition. The non-AP MLD can both receive data from the current AP and send data to the target AP during transition, ensuring continuous connectivity. The option for the current AP to forward data to the target AP ensures that data is not left behind in the transition.EXTENSIONS AND ALTERNATIVES

[0242] A smooth roaming mechanism designed for multi-link device (MLD) enabled Wi-Fi networks has been disclosed. This mechanism facilitates the transition of a non-AP MLD (typically a client device) from its current AP MLD to a target AP MLD, addressing the challenges associated with maintaining connectivity and performance during the roaming process.

[0243] The mechanism provides uninterrupted high-throughput connectivity during the transition phase. This is achieved through a coordinated approach involving techniques such as Joint Transmission (JTX), where both the current and target AP MLDs simultaneously transmit data to the roaming device. By enabling the non-AP MLD to receive signals from both APs during the transition, the mechanism helps to ensure that the client device can maintain a strong, high-quality connection even as it moves between coverage areas.

[0244] The mechanism may employ advanced signal processing techniques, including beamforming or other methods to optimize signal quality. This, combined with the simultaneous transmission from multiple APs, allows the client device to achieve high throughput without experiencing the interruptions or performance degradations typically associated with traditional roaming processes.

[0245] By eliminating or minimizing these interruptions, the proposed mechanism addresses a challenge in wireless networking: maintaining seamless connectivity for mobile devices in environments with multiple access points. This approach is useful in scenarios requiring consistent high-performance connectivity, such as in enterprise environments, public spaces with dense Wi-Fi deployments, or applications demanding low-latency and high-reliability wireless connections.

[0246] The solutions presented in this document have been described in the context of a wireless LAN system. However, it is important to note that these solutions are not limited towireless LANs and can be applied to other network environments, such as cellular telecommunication networks and wired networks.

[0247] An embodiment of the present disclosure may take the form of an article of manufacture, where a non-transitory machine-readable medium, such as microelectronic memory, stores instructions that program one or more data processing components, referred to as a "processor" or "processing unit," to perform the operations described earlier. In other embodiments, some of these operations might be carried out by specific hardware components containing hardwired logic, such as dedicated digital filter blocks and state machines. Alternatively, these operations could be performed by a combination of programmed data processing components and fixed hardwired circuit components.

[0248] In some cases, an embodiment of the invention may be an apparatus, such as an access point station (AP STA), a non-AP station (non-AP STA), or another network or computing device, that includes one or more hardware and software logic structures for performing one or more of the described operations. For example, as previously mentioned, the apparatus may include a memory unit that stores instructions executable by a hardware processor installed in the apparatus. The apparatus may also incorporate additional hardware or software elements, such as a network interface or a display device.

[0249] Some portions of the preceding detailed descriptions have been presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the ways used by those skilled in the data processing arts to convey the substance of their work most effectively to others skilled in the art.

[0250] An algorithm is here, and generally, conceived to be a self-consi stent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

[0251] It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. The present disclosure can refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage systems.

[0252] The present disclosure also relates to an apparatus for performing the operations herein. This apparatus can be specially constructed for the intended purposes, or it can include a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. For example, a computer system or other data processing system may carry out the computer-implemented methods described herein in response to its processor executing a computer program (e.g., a sequence of instructions) contained in a memory or other non- transitory machine-readable storage medium. Such a computer program can be stored in a computer readable storage medium, such as, but not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, each coupled to a computer system bus.

[0253] The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general -purpose systems can be used with programs in accordance with the teachings herein, or it can prove convenient to construct a more specialized apparatus to perform the method. The structure for a variety of these systems will appear as set forth in the description below. In addition, the present disclosure is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages can be used to implement the teachings of the disclosure as described herein.

[0254] The present disclosure can be provided as a computer program product, or software, that can include a machine-readable medium having stored thereon instructions, which can be used to program a computer system (or other electronic devices) to perform a process according to the present disclosure. A machine-readable medium includes any mechanism for storing information in a form readable by a machine (e.g., a computer). In some embodiments, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium such as a read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory components, etc.

[0255] In the foregoing specification, embodiments of the disclosure have been described with reference to specific example embodiments thereof. It will be evident that various modifications can be made thereto without departing from the broader spirit and scope of embodiments of the disclosure as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Claims

CLAIMSWhat is claimed is:

1. A method compri sing : at a wireless device capable of multi-link operation (MLO) and operating as a non-access point multi-link device (non-AP MLD) in a wireless network: wirelessly transmitting or receiving one or more frames via a wireless link between the non-AP MLD and a first access point multi-link device (AP MLD) in the wireless network; wirelessly transmitting a roaming request frame to both the first AP MLD and a second access point multi-link device (AP MLD) in the wireless network; wirelessly receiving a roaming confirm frame from the second AP MLD; wirelessly transmitting a roaming initiation frame to both the first AP MLD and the second AP MLD; wirelessly and simultaneously receiving a same joint transmission (JTX) data from both the first AP MLD and the second AP MLD; and wirelessly transmitting or receiving one or more frames via a wireless link between the non-AP MLD and the second AP MLD.

2. The method of claim 1, wherein the roaming request frame comprises: a solicitation of the second access point multi-link device (AP MLD) to respond with a roaming confirm frame, and an indication to the first AP MLD to deliver data intended for transmission to the non- AP MLD to a roaming AP MLD in the wireless network.

3. The method of claim 1, further comprising: at the wireless device capable of multi-link operation (MLO) and operating as the non- access point multi-link device (non-AP MLD) in the wireless network: in response to wirelessly and simultaneously receiving the same joint transmission (JTX) data from both the first access point multi-link device (AP MLD) and the second AP MLD, wirelessly transmitting a multiaccess point block acknowledgement frame to both the first AP MLD and the second AP MLD.

4. The method of claim 1, further comprising: at a wireless device capable of multi-link operation (MLO) and operating as the first access point multi-link device (AP MLD) in the wireless network: wirelessly receiving a joint transmission (JTX) sounding trigger frame, wherein the JTX sounding trigger frame is wirelessly transmitted by a roaming access point multi-link device (AP MLD) in the wireless network; calculating one or more pre-corrected values based on the JTX sounding trigger frame; and wirelessly transmitting a JTX data frame to the non-AP MLD, the JTX data frame comprising the same JTX data and the one or more pre-corrected values.

5. The method of claim 1, further comprising: at a wireless device capable of multi-link operation (MLO) and operating as the second access point multi-link device (AP MLD) in the wireless network: wirelessly receiving a joint transmission (JTX) sounding trigger frame, wherein the JTX sounding trigger frame is wirelessly transmitted by a roaming access point multi-link device (AP MLD) in the wireless network; calculating one or more pre-corrected values based on the JTX sounding trigger frame; and wirelessly transmitting a JTX data frame to the non-AP MLD, the JTX data frame comprising the same JTX data and the one or more pre-corrected values.

6. The method of claim 5, further comprising: at a wireless device capable of multi-link operation (MLO) and operating as the second access point multi-link device (AP MLD) in the wireless network: wirelessly transmitting the JTX data frame to the non-AP MLD after a short interframe space (SIFS) interval that follows the second AP MLD wirelessly receiving the JTX sounding trigger frame.

7. The method of claim 1, wherein one of the first access point multi -link device (AP MLD) or the second AP MLD operates as a main access point (AP) and the other of the first APMLD and the second AP MLD operates as an assist AP; and wherein the method further comprises: the main AP wirelessly transmitting a joint transmission (JTX) sounding trigger frame to the assist AP; the assist AP calculating one or more pre-corrected values based on the JTX sounding trigger frame; and the assist AP wirelessly transmitting a JTX data frame to the non-access point multi-link device (non-AP MLD), the JTX data frame comprising the same JTX data and the one or more pre-corrected values.

8. The method of claim 1, further comprising: at a wireless device capable of multi-link operation (MLO) and operating as a roaming access point multi-link device (AP MLD) in the wireless network: wirelessly receiving particular data from the first AP MLD; wirelessly transmitting the particular data to the second AP MLD; and wherein the same joint transmission (JTX) data comprises the particular data.

9. The method of claim 8, further comprising: at the wireless device capable of multi-link operation (MLO) and operating as the roaming access point multi-link device (AP MLD) in the wireless network: wirelessly transmitting a joint transmission (JTX) sounding trigger frame to the first AP MLD; and wireless transmitting the JTX sounding trigger frame to the second AP MLD.

10. The method of claim 1, wherein: the first access point multi-link device (AP MLD) belongs to a first basic service set (BSS) in the wireless network; the second AP MLD belongs to a second BSS in the wireless network; the wireless device capable of multi-link operation (MLO) and operating as the non-AP MLD is located in a coverage area of the first BSS when wirelessly transmitting or receiving one or more frames via a wireless link between the non-AP MLD and first AP MLD; the wireless device capable of multi-link operation (MLO) and operating as the non-AP MLD has moved to an area where coverage of the first BSS and the second BSS overlap when wirelessly and simultaneously receiving the same jointtransmission (JTX) data from both the first AP MLD and the second AP MLD; and the wireless device capable of multi-link operation (MLO) and operating as the non-AP MLD has moved to within a coverage of the second BSS when wirelessly transmitting or receiving one or more frames via a wireless link between the non- AP MLD and the second AP MLD.

11. The method of claim 1, further comprising: at the wireless device capable of multi-link operation (MLO) and operating as the non- access point multi-link device (non-AP MLD) in the wireless network: wirelessly and simultaneously receiving a first joint transmission (JTX) data frame from the first AP MLD and a second JTX data frame from the second AP MLD, the first JTX data frame and the second JTX data frame both comprising the same JTX data.

12. A system comprising: a first wireless device capable of multi-link operation (MLO) and capable of operating as a non-access point multi-link device (non-AP MLD) in a wireless network, the first wireless device comprising a radio frequency transceiver and a set of one or more processors coupled to a memory device storing a set of instructions configured to cause the non-AP MLD to perform: wirelessly transmitting or receiving one or more frames via a wireless link between the non-AP MLD and a first access point multi-link device (AP MLD) in the wireless network; wirelessly transmitting a roaming request frame to both the first AP MLD and a second access point multi-link device (AP MLD) in the wireless network; wirelessly receiving a roaming confirm frame from the second AP MLD; wirelessly transmitting a roaming initiation frame to both the first AP MLD and the second AP MLD; wirelessly and simultaneously receiving a same joint transmission (JTX) data from both the first AP MLD and the second AP MLD; and wirelessly transmitting or receiving one or more frames via a wireless link between the non-AP MLD and the second AP MLD.

13. The system of claim 12, wherein the roaming request frame comprises: a solicitation of the second access point multi-link device (AP MLD) to respond with a roaming confirm frame, and an indication to the first AP MLD to deliver data intended for transmission to the non- AP MLD to a roaming AP MLD in the wireless network.

14. The system of claim 12, wherein the set of instructions stored in the memory device of the first wireless device are further configured to cause the non-AP MLD to perform: in response to wirelessly and simultaneously receiving the same joint transmission (JTX) data from both the first access point multi-link device (AP MLD) and the second AP MLD, wirelessly transmitting a multi-access point block acknowledgement frame to both the first AP MLD and the second AP MLD.

15. The system of claim 12, further comprising: a second wireless device capable of multi-link operation (MLO) and capable of operating as the first access point multi-link device (AP MLD) in the wireless network, the second wireless device comprising a radio frequency transceiver and a set of one or more processors coupled to a memory device storing a set of instructions configured to cause the first access point multi-link device (AP MLD) to perform: wirelessly receiving a joint transmission (JTX) sounding trigger frame, wherein the JTX sounding trigger frame is wirelessly transmitted by a roaming access point multi-link device (AP MLD) in the wireless network; calculating one or more pre-corrected values based on the JTX sounding trigger frame; and wirelessly transmitting a JTX data frame to the non-AP MLD, the JTX data frame comprising the same JTX data and the one or more pre-corrected values.

16. The system of claim 12, further comprising: a second wireless device capable of multi-link operation (MLO) and capable of operating as the second access point multi-link device (AP MLD) in the wireless network, the second wireless device comprising a radio frequency transceiver and a set of one or more processors coupled to a memory device storing a set of instructionsconfigured to cause the second access point multi-link device (AP MLD) to perform: wirelessly receiving a joint transmission (JTX) sounding trigger frame, wherein the JTX sounding trigger frame is wirelessly transmitted by a roaming access point multi-link device (AP MLD) in the wireless network; calculating one or more pre-corrected values based on the JTX sounding trigger frame; and wirelessly transmitting a JTX data frame to the non-AP MLD, the JTX data frame comprising the same JTX data and the one or more pre-corrected values.

17. The system of claim 16, wherein the set of instructions stored in the memory device of the second wireless device are further configured to cause the second access point multi-link device (AP MLD) to perform: wirelessly transmitting the JTX data frame to the non-AP MLD after a short interframe space (SIFS) interval that follows the second AP MLD wirelessly receiving the JTX sounding trigger frame.

18. The system of claim 12, further comprising: a second wireless device capable of multi-link operation (MLO) and capable of operating as the first access point multi-link device (AP MLD) in the wireless network, the second wireless device comprising a radio frequency transceiver and a set of one or more processors coupled to a memory device storing a set of instructions configured to cause the first AP MLD to perform wirelessly transmitting a joint transmission (JTX) sounding trigger frame to the second AP MLD; and a third wireless device capable of multi-link operation (MLO) and capable of operating as the second AP MLD in the wireless network, the third wireless device comprising a radio frequency transceiver and a set of one or more processors coupled to a memory device storing a set of instructions configured to cause the second access point multi-link device (AP MLD) to perform: calculating one or more pre-corrected values based on the JTX sounding trigger frame; and wirelessly transmitting a JTX data frame to the non-access point multi-link device (non-AP MLD), the JTX data frame comprising the same JTX data and the one or more pre-corrected values.

19. The system of claim 12, further comprising: a second wireless device capable of multi-link operation (MLO) and capable of operating as a roaming access point multi-link device (AP MLD) in the wireless network, the second wireless device comprising a radio frequency transceiver and a set of one or more processors coupled to a memory device storing a set of instructions configured to cause the roaming AP MLD to perform: wirelessly receiving particular data from the first AP MLD; wirelessly transmitting the particular data to the second AP MLD; and wherein the same joint transmission (JTX) data comprises the particular data.

20. The system of claim 19, wherein the set of instructions stored in the memory device of the second wireless device are further configured to cause the roaming access point multi-link device (AP MLD) to perform: wirelessly transmitting a joint transmission (JTX) sounding trigger frame to the first AP MLD; and wireless transmitting the JTX sounding trigger frame to the second AP MLD.

21. The system of claim 12, wherein the set of instructions stored in the memory device of the first wireless device are further configured to cause the non-access point multi-link device (non-AP MLD) to perform: wirelessly and simultaneously receiving a first joint transmission (JTX) data frame from the first AP MLD and a second JTX data frame from the second AP MLD, the first JTX data frame and the second JTX data frame both comprising the same JTX data.

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