WI-FI DEVICE AND ASSOCIATED TRANSMISSION CONTROL METHOD

A Wi-Fi (Wi-Fi) device and a transmission control method are provided. The Wi-Fi device selectively transmits at least a data division of a transmission data on a low performance link based on several parameters. The parameters include a start time point of a backoff procedure of the low performance link, a duration information associated with another Wi-Fi device on a high performance link, and some predefined exception conditions. By overhearing status of another Wi-Fi device on the high performance link, the Wi-Fi device attempts to acquire the duration information. If the duration information can be acquired, the Wi-Fi device calculates a coherent remnant-duration accordingly. Then, the Wi-Fi device determines whether the transmission data should be transmitted immediately on the low performance link, transmitted later on the high performance link, or partially transmitted on the low performance link.

TECHNICAL FIELD

The disclosure relates in general to a Wi-Fi device and an associated transmission control method, and more particularly to a Wi-Fi device and an associated transmission control method capable of enhancing throughput with a multi-link coherent operation.

BACKGROUND

In a Wi-Fi multi-link operation (MLO), there may exist several links between two MLDs, including one access point (AP) and one non-AP station (STA), that occupy different radio-frequency (RF) bands. These links can operate independently to increase the overall throughput and/or to improve the connection stability. However, each link has its own capacity that is based on several parameters, including bandwidth (BW), number of spatial streams (NSS), modulation and coding mechanism (MCS), etc. In addition, each link has its own condition that is based on several parameters, including loading, interference, etc. Capacities and conditions of links can be very different. Hence, it is desirable to optimally utilize these asymmetric links to maximize the overall system performance.

SUMMARY

The disclosure is directed to a Wi-Fi device and an associated transmission control method capable of enhancing throughput with a multi-link coherent operation.

According to one embodiment, a Wi-Fi device is provided. The Wi-Fi device and another Wi-Fi device are in an overlapping basic service set (BSS). The another Wi-Fi device transmits a first physical layer protocol data unit (PPDU) frame on a first link between a first-first time point and a third-first time point. The Wi-Fi device includes a MAC module, and the media access control address (MAC) module includes a receiving circuit, a first transmission circuit corresponding to the first link, a second transmission circuit, and a link selection module. The receiving circuit acquires duration information associated with a first payload portion of the first PPDU frame at a second-first time point, wherein the second-first time point is between the first-first time point and the third-first time point. The second transmission circuit selectively transmits a second PPDU frame on a second link between a first-second time point and a second-second time point, wherein the performance of the second link is lower than the performance of the first link. The link selection module is electrically connected to the receiving circuit, the first transmission circuit, and the second transmission circuit. The link selection module selectively controls the first transmission circuit and the second transmission circuit to perform transmission according to the statuses of the first link and the second link.

According to another embodiment, a transmission control method employed by the Wi-Fi device is provided. The Wi-Fi device and another Wi-Fi device are in an overlapping basic service set (BSS), and the another Wi-Fi device transmits a first PPDU frame on a first link between a first-first time point and a third-first time point. The transmission control method includes the following steps. Firstly, duration information associated with a first payload portion of the first PPDU frame is acquired at a second-first time point. The second-first time point is between the first-first time point and the third-first time point. Then, a second PPDU frame is selectively transmitted on a second link between a first-second time point and a second-second time point. The performance of the second link is lower than the performance of the first link.

DETAILED DESCRIPTION

The frame exchange process between a station device (STA) and an access point (STA) in an environment having asymmetric multi-links is concerned. To enhance transmission efficiency, EMLSR is an approach proposed in 802.11 specifications. However, the conventional EMLSR proposed in 802.11 specifications is not suitable for environments having unbalanced links, so an EMLXR-based txOnRx alignment was proposed in the US patent application (application Ser. No. 17/964,045). In short, the EMLXR-based txOnRx alignment intends to acquire the duration information reported by the header portion and simultaneously make use of the low performance link L_LO before the PPDU frame exchange process of other Wi-Fi devices access L_HI completes. Nevertheless, the EMLXR-based txOnRx alignment has limitations for low to medium overlapping basic service sets (OBSS) load, and further improvement is required. In the specification, EMLXR may present enhanced multi-link single-radio (EMLSR) and/or enhanced multi-link multi-radio (EMLMR).

For better comprehension of the technical features of the proposed multi-link coherent operation, the following embodiments assume that the asymmetric multi-links include a high performance link L_HI with higher throughput and a low performance link L_LO with lower throughput. The two links do not interfere with each other. The core concept of the multi-link coherent transmission is that the STA transmits data to its corresponding AP on the low performance link L_LO only while the high performance link L_HI is utilized by another pair of AP and STA.

The performance of a link is comprehensively determined by different link capabilities (for example, bandwidth (BW), modulation coding scheme (MCS), and/or number of spatial streams (NSS)) and conditions (for example, loading and/or interference). The high performance link L_HI and the low performance link L_LO might represent two channels at the same band (one of the 2.4 GHz, 5 GHz, and 6 GHz bands) or at different bands (two of the 2.4 GHz, 5 GHz, and 6 GHz bands).

FIG.1is a schematic diagram illustrating an occasion when multiple access points and multiple stations coincidently select the same links for the frame exchange process. InFIG.1, the frame exchange process between Wi-Fi (Wi-Fi) multi-link devices (MLD)151,171, and the frame exchange process between MLDs153and173are performed. For illustration purposes, the MLD151is considered as an access point (AP1), the MLD153is considered as an access point (AP2), the MLD171is considered as a station device (STA1), and the MLD173is considered as a station device (STA2).

The MLD (AP1)151and the MLD (STA1) perform a frame exchange process on the high performance link L_H11and the low performance link L_LO1. The MLD (AP2)153and the MLD (STA2)173perform a frame exchange process on the high performance link L_H12and the low performance link L_LO2. As channel (link) contentions are concerned in the specification, it is assumed L_H11=L_H12=L_HI and L_LO1=L_LO2=L_LO.

As the OBSS distribution in the environment changes from time to time, a flexible transmission control method applied to an MLD (for example, STA2) is provided. According to the embodiments of the present disclosure, the Wi-Fi MLD concerns several parameters, including the link status and attributes of its transmission data. Various transmission configurations are provided to make the Wi-Fi MLD adaptively select the appropriate and efficient configuration for data transmission.

According to the embodiments of the present disclosure, the Wi-Fi MLD may transmit the packets on one of the high performance link L_HI and the low performance link L_LO, suspend packet transmission, or transmit part of the packets on the low performance link L_LO and leave the other part of the packets for transmission later. Different embodiments are illustrated below to demonstrate how the transmission control method selects the suitable transmission configuration.

FIG.2is a schematic diagram illustrating a Wi-Fi (Wi-Fi) system according to an embodiment of the present disclosure. For brevity and simplicity, it is assumed that the Wi-Fi system2includes MLDs21and23. The MLD21is a station device (STA), and the MLD23is an access point (AP).

The MLD21includes a function circuit217, a wireless control circuit, a media access control address (MAC) module211, a physical layer (PHY) module24, and multiple antennas. The wireless control circuit215is electrically connected to the MAC module211and the function circuit217. The wireless control circuit215executes Wi-Fi-related programs at the upper layer. Moreover, the wireless control circuit215communicates and cooperates with the function circuit217. The PHY module24is electrically connected to the MAC module211and the antennas.

The MAC module211includes control registers (CR)218, a link selection module211a, and plural link-specific MACs. Depending on the number of coherent links utilized by the MLD21, the control registers (CR) are configured, and the number of link-specific MACs may vary. For the sake of illustrations, the following embodiments are demonstrated on a two-link basis. Therefore, a link-specific MAC (HI)26corresponding to the high performance link L_HI and a link-specific MAC (LO)28corresponding to the low performance link L_LO are shown inFIG.2.

The link-specific MAC (HI)26includes a collision avoidance module (HI)261, a TxMAC(HI)263, and a RxMAC(HI)265, and all are electrically connected to the link selection module211a. The collision avoidance module (HI)261is electrically connected to the TxMAC(HI)263. The TxMAC(HI)263and the RxMAC(HI)265are electrically connected to the PHY module24.

The link-specific MAC (HI)28includes a collision avoidance module (LO)281, a TxMAC(LO)283, and a RxMAC(LO)285, and all are electrically connected to the link selection module211a. The collision avoidance module (LO)281is electrically connected to the TxMAC(LO)283. The TxMAC(LO)283and the RxMAC(LO)285are electrically connected to the PHY module24.

It is assumed in the embodiments that the collision avoidance module (HI)261includes a backoff counter corresponding to the high performance link L_HI (that is, backoff counter CNT_HI) and the collision avoidance module (LO)281includes a backoff counter corresponding to the low performance link L_LO (that is, backoff counter CNT_LO). The counting values of the backoff counters CNT_HI and CNT_LO are referred to by the link selection module211ato determine how the TxMAC(HI)263and TxMAC(LO)283are controlled.

The MLD21utilizes carrier-sense mechanisms to determine if any channel activity exists/occurs at its corresponding links. If there is no medium activity in its corresponding links, the backoff counter corresponding to the link (CNT_HI or CNT_LO) is decreased by the unit of time slot. On the other hand, if any of the medium activity exists/occurs in one of the other links, the backoff counter (CNT_HI or CNT_LO) holds its counting value. The counting value held by the backoff counter (CNT_HI or CNT_LO) (that is, the residual backoff counting value) will be decreased later once there is no medium activity in the links corresponding to the MLD21. The link corresponding to the backoff counter (CNT_HI or CNT_LO) being counted to zero will start transmitting data. In short, the backoff counter CNT_HI is utilized to determine whether the high performance link L_HI can be accessed by the MLD21, and the backoff counter CNT_LO is utilized to determine whether the low performance link L_HI can be accessed by the MLD21.

In some embodiments, the MLD21,23may own x links L1-Lx and may communicate with each other via y links L1-Ly. The variables x and y are positive integers, wherein y is not smaller than 2, and x is greater than or equivalent to y. In this embodiment, each of the links L1-Ly may be defined by a channel of a band. For example, the links L1-Ly may include different channels of the same band (for example, 2.4 GHz, 5 GHz, or 6 GHz band) and/or channels of different bands (for example, 2.4 GHz, 5 GHz, and/or 6 GHz band).

FIG.3is a schematic diagram illustrating the classification of data transmission modes being selected by the link selection module according to the embodiment of the present disclosure. For the sake of illustration, the frame exchange processes described below are mainly based on a viewpoint of STA2. The following mentioned operations and components belong to STA2unless otherwise specified.

InFIG.3, different types of OBSS distribution and combinations of the unbalanced links are concerned. As a station device, STA2dynamically adjusts its transmission configuration to effectively respond to the asymmetric link's real-time status. Details about the classification inFIG.3are illustrated together with other figures, as noted in the brackets.

FIG.4is a flow diagram illustrating the transmission control method capable of adaptively selecting the transmission mode in response to the satisfaction of the predefined quality condition according to the embodiment of the present disclosure. Please refer toFIGS.2,3, and4together. Firstly, the link selection module211achecks if a predefined quality condition is satisfied (step S41). Please note that the predefined quality condition is not limited but freely defined in practical applications.

An exemplary predefined quality condition is related to the OBSS load. For example, the predefined quality condition is considered satisfied if the OBSS load in the environment is lower than or equivalent to a predefined OBSS threshold, and vice versa. The predefined OBSS threshold can be, for example, between 40%˜50%.

If the determination result of step S41is negative, the link selection module211acontrols one of the TxMAC(HI)263and TxMAC(LO)283to perform the frame exchange process with the conventional EMLXR, depending on which of the backoff procedures corresponding to collision avoidance module (LO) and collision avoidance module (HI) ends first (step S43). In step S43, the link selection module211ainforms the link-specific MAC (LO)28to perform the EMLXR frame exchange process on the low performance link L_LO if the backoff procedure of the low performance link BOL ends prior to the backoff procedure of the high performance link BOH ends and vice versa.

If the determination result of step S41is positive, the link selection module211adynamically changes its transmission configuration based on comprehensive consideration (step S45). The factors affecting the decision made by the link selection module211ainclude the overhearing result, the backoff procedures of the low performance link BOL and the high performance link BOH, and inherent features of the transmission data txDAT_STA2. The dotted frame FM1inFIG.3covers the classifications of the transmission configurations related to step S45.

Step S45further includes the following steps. The link selection module211achecks the backoff counter CNT_HI in the collision avoidance module (HI)261to clarify if the link-specific MAC (HI)26can get access right on high performance link L_HI (step S451). If the counting value of the backoff counter CNT_HI reaches “0”, the determination result of step S451is positive, and the link selection module211acontrols the link-specific MAC (HI)26to perform the frame exchange process on the high performance link L_HI (situation shown inFIG.5) (step S453). In step S453, the duration length of the frame exchange process performed by the link-specific MAC (HI)26is directly dominated by the data length of the transmission data txDAT_STA2.

If the determination result of step S451is negative, the link selection module211aknows that the link-specific MAC (HI)26cannot perform the frame exchange process yet. Despite this, the link selection module211adoes not control the link-specific MAC (LO)28to perform the frame exchange process immediately. Instead, the link selection module211aneeds to consider more factors (step S455). In step S455, the link selection module211amay control the link-specific MAC (LO)28to perform the frame exchange process on the low performance link L_LO (situations shown inFIGS.11A and11B), controls the link-specific MAC (LO)28not to perform the frame exchange process (situations shown inFIGS.12A˜12B and14), or controls the link-specific MAC (LO)28to perform the frame exchange process in a coherent manner (situations shown inFIGS.17and19). The dotted frame FM2inFIG.3covers the classifications of the transmission configurations related to step S455.

In the specification, the frame exchange processes representing different situations are illustrated. Each of the frame exchange processes includes multiple timing axes to represent the procedures of the frame exchange processes on the high performance link L_HI and the low performance link L_LO. The rectangles above the timing axes represent the frames sent from an STA to an AP (for example, STA1to AP1, or STA2to AP2), and the rectangles underneath the timing axes represent the frames sent from an AP to an STA (for example, AP1to STA1, or AP2to STA2).

In these frame exchange processes, the rectangles use different screen tones to represent their source devices and their destination devices. The horizontal screen tones represent the frame exchange process between the MLDs whose reactions and operations are described by the specification (for example, AP2and STA2), and the dotted screen tones represent the frame exchange process between other MLDs (for example, AP1and STA1) whose reactions are not described in the present specification.

Moreover, a relatively dense screen tone (above a timing axis) is used to represent the signal transmitted from an STA to its corresponding AP, and the relatively loose screen tones (below a timing axis) are used to represent the signal transmitted from an AP to its corresponding STA. For example, the horizontal screentone representing the frame exchange process from STA2to AP2is relatively dense, and the horizontal screen tone representing the frame exchange process from AP2to STA2is relatively loose.

The backoff procedure of the low performance link BOL represents the procedure that the backoff counter CNT_LO counts from a random value down to 0. The backoff procedure of the high performance link BOH represents the procedure that the backoff counter CNT_HI counts from a random value down to 0. In the frame exchange processes, acknowledgment frames (ACK), distributed inter-frame spacings (DIFS), and short interframe spaces (SIFS) are shown. Generation and duration control related to the backoff procedures (BOH, BOL), the distributed inter-frame spacing (DIFS), the short interframe space (SIFS), and the acknowledgment frame (ACK) can be referred to 802.11 specifications.

In the frame exchange processes, data frames are labeled with a physical layer protocol data unit (PPDU), with numbers representing the origin and the destination of the PPDU frame. For example, the PPDU_11frame represents the data frame to be transmitted by STA1to AP1, and the PPDU_22frame represents the data frame to be transmitted by STA2to AP2.

FIG.5is a schematic diagram illustrating an exemplary construction of the PPDU_22frame. InFIG.5, the PPDU_22frame includes a header portion HD_22and a payload portion PL_22, and the duration of the PPDU_22frame is equivalent to the duration of the header portion HD_22(Thd) and the duration of the payload portion PL_22(TPL_22). In some applications, the PPDU_22frame may further include one or more padding bits.

In the disclosure, the payload portion PL_22of the PPDU_22frame is assumed to be an aggregate-MAC protocol data unit (A-MPDU) in most cases. Thus, the payload portion PL_22of the PPDU_22frame can be represented as A-MPDU_22(PL_22=A-MPDU_22), and the A-MPDU_22includes M A-MPDU subframes subF[1]˜subF[M]. In practical applications, the internal constructions of the header portion HD_22and the payload portion PL_22of the PPDU_22frame may vary with different versions of 802.11 specifications. With adequate modifications, the concepts of the disclosure can be applied to other types of PPDU_22frames having various constructions of the header portion HD_22and the payload portion PL_22.

Each of the A-MPDU subframes subF[1]˜subF[M] carries one of the N data subsets subDAT[n], wherein n=1˜N, and 1≤M≤N. For example, the A-MPDU subframe subF[m] (m=1˜M) carries the data subset subDAT[n].

As the format of the header portion HD_22is specified in the 802.11 specification, the duration of the header portion HD_22(Thd) is known. On the other hand, the duration of the payload portion PL_22changes with the number of A-MPDU subframes (that is, M). According to 802.11 specifications, the duration information durINFOPL_22(reporting TPL_22=TA-MPDU_22) associated with the payload portion PL_22of the PPDU_22frame is reported in the header portion HD_22of the PPDU_22frame.

FIGS.6A and6Bare schematic diagrams illustrating the exemplary construction of an A-MPDU subframe subF[m]. InFIGS.6A and6B, the A-MPDU subframe subF[m] includes an MPDU subframe header (MPDUhd[m]) and an MPDU subframe payload (MPDUpI[m]), wherein the MPDU subframe payload (MPDUpI[m]) carries an n-th data subset subDAT[n].

InFIG.6A, the MPDU subframe payload MPDUpI[m] includes a data subset subDAT[n]. Thus, the duration of A-MPDU subframe subF[m](that is, TsubF[m]) inFIG.6Ais equivalent to the summation of the duration of the MPDU subframe header (MPDUhd[m]) (TMPDUhd[m]) and the duration of data subset subDAT[n] (TsubDAT[n]). That is, TsubF[m]=TMPDUhd[m]+TsubDAT[n].

InFIG.6B, the MPDU subframe payload MPDUpI[m] includes a data subset subDAT[n] and MPDU paddings MPDUpad[m]. Thus, the duration of A-MPDU subframe subF[m] (TsubF[m]) inFIG.6Bis equivalent to the summation of the duration of MPDU subframe header MPDUhd[m](TMPDUhd[m]), the duration of data subset subDAT[n] (TsubDAT[n]), and the duration of MPDU paddings (TMPDUpad[m]). That is, TsubF[m]=TMPDUhd[m]+TsubDAT[n]+TMPDUpad[m].

According toFIGS.6A and6B, the MPDU paddings MPDUpad[m] are selectively appended. In practical applications, the MPDU paddings MPDUpad[m] are added at the end of the MPDU subframe payload MPDUpI[m] whenever necessary, and the exact format and length of the MPDU paddings MPDUpad[m] is not limited. Basically, the MPDU paddings MPDUpad[m] are utilized for dynamically adjusting the duration of the payload portion TPL_22.

Before an STA initiates the frame exchange process, it senses (listens) the medium status to determine if the link is free (if the medium is occupied by others). If the link is free, the STA (for example, STA2) starts the backoff procedure (BOH or BOL) to wait for a duration. Thus, an STA can listen to the header portions of the PPDU frames sent by other MLDs and be aware of the medium status in the environment. Based on the overhearing result, STA2knows how to dynamically configure its data transmission.

To be more specific, by sharing the header portions of PPDU frames, the MLD is able to know whether a link is ongoing. Alternatively speaking, the MLD knows how long the link will be occupied by another MLD and manages its frame exchange process better. With the overhear mechanism, the opportunities for collisions can be reduced, and the throughput can be increased.

FIGS.7,11A,11B,12A,12B,14,17, and19are examples showing how the link selection module211areacts and adjusts its transmission configuration according to different overhearing results.

FIG.7is a schematic diagram illustrating that the Wi-Fi device STA2performs the frame exchange process on the high performance link L_HI. Please refer toFIGS.4and7together.FIG.7corresponds to step S453inFIG.4. In this embodiment, the high performance link L_HI is not occupied by MLDs other than STA2and AP2.

As shown inFIG.7, the counting value of the backoff counter CNT_HI of STA2reaches 0 at the time point t1. Therefore, STA2gains access to the high performance link L_HI, and transmits the PPDU_22frame on the high performance link L_HI between the time points t1 and t3, that is, DURPPDU_22=(t3−t1). As summarized inFIG.3, the link selection module211aselects the high performance link L_HI for data transmission when the high performance link L_HI is not accessed by other MLDs (for example, AP1and STA1). InFIG.7, all the transmission data txDAT_STA2are transmitted with a single PPDU_22frame, and the data subsets subDAT[1]˜subDAT[N] are respectively carried by A-MPDU subframes subF[1]˜subF[M] in the payload PL_22, wherein M=N. Consequentially, the duration of the PPDU_22frame (DURPPDU_22) is equivalent to the summation of the duration of the header portion HD_22(Thd) and the durations of the A-MPDU subframes subF[1]˜subF[M] (TsubF[1]+ . . . TsubF[M]). That is, DURPPDU_22=Thd+TPL_22=Thd+TA-MPDU_22=Thd+(TsubF[1]+ . . . TsubF[M]).

FIG.7represents an ideal occasion that the high performance link L_HI is free to access. Whereas the situation inFIG.7is unlikely to happen all the time, and STA2needs to share or compete the usage of the high performance link L_HI and the low performance link L_LO with other Wi-Fi devices. Thus, an overhearing function has been provided in 802.11 specifications. In practical applications, the links' status changes constantly, and the overhearing result could dynamically reflect it. According to the embodiments of the present disclosure, different transmission configurations are provided to suit the various statuses of the links.

In general, the link selection module211a, according to the embodiments of the present disclosure, prefers to perform the frame exchange process on the high performance link L_HI. However, as shown in the classification inFIG.3, there are some occasions when the link selection module211aneeds to adjust its transmission configuration. The embodiments, according to the present disclosure, clarify how the transmission configuration should be adjusted in response to status changes of the unbalanced links.

FIG.8is a block diagram illustrating a MAC module according to an embodiment of the present disclosure. The MAC module81is electrically connected to the wireless control circuit85and the PHY module24.

The PHY module24includes a TxPHY module243and an RxPHY module241. The RxPHY module241includes a receiving PHY corresponding to the high performance link L_HI (RxPHY(HI)2411and a receiving PHY corresponding to the low performance link L_LO (RxPHY(LO))2413. The TxPHY module243includes a transmission PHY corresponding to the high performance link L_HI (TxPHY(HI))2431and a transmission PHY corresponding to the low performance link L_LO (TxPHY(LO))2433.

The MAC module81includes a link selection module89, control registers (CR), a link-specific MAC (HI)86corresponding to the high performance link L_HI, and a link-specific MAC (LO)88corresponding to the low performance link L_LO. The control registers CR are electrically connected to the link selection module89. The internal components and the interconnections of the link-specific MAC (HI)86are briefly described below.

The link-specific MAC (HI)86includes a collision avoidance module861, a TxMAC(HI)863, and an RxMAC(HI)865. The internal components of the collision avoidance module861, the TxMAC(HI)863, and the RxMAC(HI)865are respectively described.

The collision avoidance module861further includes a SIFS timer8611, a backoff counter8613, and a DIFS timer8615corresponding to the high performance link L_HI. The SIFS timer8611, the backoff counter (CNT_HI)8613, and the DIFS timer8615are electrically connected to the TxMAC(HI)863and the link selection module89.

The TxMAC(HI)863further includes a Tx buffer (HI)8633and a frame constructor (HI)8631. The Tx buffer (HI)8633is electrically connected to the TxPHY(HI)2431and the frame constructor (HI)8631. The frame constructor (HI)8631is electrically connected to the link selection module89and the collision avoidance module86.

The SIFS timer8611, the backoff counter (CNT_HI)8613, and the DIFS timer8615transmit their statuses to the frame constructor8631. The frame constructor8631organizes and constructs frames in the Tx packets based on the statuses of the SIFS timer8611, the backoff counter (CNT_HI)8613, and the DIFS timer8615, the transmission data TxDAT received from the wireless control circuit85and the transmission configurations sent from the link selection module89. After the frame constructor8631constructs the Tx packets, the Tx packets are temporarily stored at the Tx buffer (HI)8633. Then, the Tx buffer (HI)8633transmits the Tx packets to the TxPHY(HI)2431at appropriate time points.

The RxMAC(HI)865further includes a frame detector (HI)8653and a frame parser (HI)8651. The frame detector (HI)8653is electrically connected to the RxPHY(HI)241and the frame parser (HI)8651. The frame parser (HI)8651is electrically connected to the link selection module89. The frame detector (HI)8653receives Rx data from the RxPHY(HI)2411and passes Rx packets to the frame parser (HI)8651. Then, the frame parser (HI)8651parses the fields in the Rx packets.

Similarly, the link-specific MAC (LO)88includes a collision avoidance module881, a TxMAC(LO)883, and a RxMAC(LO)885. The TxMAC(LO)883is electrically connected to the TxPHY(LO)2433, and the RxMAC(LO)885is electrically connected to the RxPHY(LO)2413. As the internal components in the link-specific MAC (LO)88are similar to those in the link-specific MAC (HI)86, detailed descriptions of the internal components in the link-specific MAC (LO)88and their interconnections are omitted.

The link selection module89further includes a boundary analysis circuit891and an EMLXR Tx configuration circuit893. The boundary analysis circuit891is electrically connected to the link-specific MAC (HI)86, the link-specific MAC (LO)88, the EMLXR Tx configuration circuit893, and the wireless control circuit85. The Tx configuration circuit893is electrically connected to the wireless control circuit85and the frame constructor853. The EMLXR Tx configuration circuit893informs the TxMAC(HI)863and TxMAC(LO)883whether they should both wait for the next transmission chance or one of them should perform the frame exchange process immediately.

FIG.9is a flow diagram illustrating an exemplary implementation of step S455inFIG.4. The EMLXR Tx configuration circuit893checks if the transmission data (txDAT) satisfies any of the predefined exception conditions (step S4551). Step S4551corresponds to the flow diagram inFIG.10. If the determination result of step S4551is positive, the EMLXR Tx configuration circuit893informs the link-specific MAC (LO)88to perform the frame exchange process on the low performance link L_LO (step S4553), as illustrated inFIGS.11A and11B.

In some applications, it is possible to skip steps S4451and S4553. Or, in some applications, it is possible to execute step S4451after step S4555ewith some modifications. Details about such alternative designs are omitted. In practical applications, the order of the steps might be adjusted with appropriate modifications.

If the determination result of step S4551is negative, the EMLXR Tx configuration circuit893controls the link-specific MAC (LO)88to temporarily ignore the transmission data txDAT_STA2(see counterexamples inFIGS.12A˜12B and14); transmit the complete transmission data txDAT_STA2with the PPDU_22frame (seeFIG.17); or transmit part of the transmission data txDAT_STA2with the PPDU_22frame (seeFIG.19) (step S4555). Step S4555further includes the following steps.

Firstly, the frame detector (HI)8653overhears the high performance link L_HI and the frame parser (HI)8651attempts to acquire the fields in the header of the frames transmitted on the high performance link L_HI (step S4555a). Then, the frame parser (HI)8651parses the fields in the header portion of the PPDU_11frame and successfully acquires the duration information durINFOPL_11associated with the payload portion PL_11of the PPDU_11frame being transmitted by STA1(step S4555c).

If the determination result of step S4555cis negative, the EMLXR Tx configuration circuit893does not control the link-specific MAC (LO)88to perform the PPSU_22frame exchange process.FIGS.12A and12Bdemonstrate problems caused by the conventional EMLXR when the determination result of step S4555cis negative.

FIGS.14,17, and19correspond to scenarios when the determination result of step S4555cis positive. If the determination result of step S4555cis positive, the boundary analysis circuit891further verifies whether there is sufficient duration for transmitting at least part of the transmission data txDAT_STA2with the PPDU_22frame (step S4555e). In step S4555e, the boundary analysis circuit calculates the coherent remnant-duration Trmn based on the duration information durINFOPL_11associated with the payload portion PL_11and verifies if the coherent remnant-duration Trmn is greater than the minimum PPDU duration min_DURPPDU(Trmn>min_DURPPDU).

If the determination result of step S4555eis negative, the EMLXR Tx configuration circuit893controls the link-specific MAC (LO)88not to perform the PPSU_22frame exchange process.FIG.14is an exemplary scenario when the determination result of step S4555eis negative.

If the determination result of step S4555eis positive, the EMLXR Tx configuration circuit893informs the link-specific MAC (LO)88to proceed with the PPDU_22frame exchange process in a coherent transmission manner (seeFIGS.17and19) (step S4555g).

Please refer toFIG.5. The transmission data txDAT_STA2are split into N data subsets subDAT[1]˜subDAT[N]. The difference betweenFIGS.17and19is whether the coherent remnant-duration Trmn is sufficient for transmitting the N data subsets subDAT[1]˜subDAT[N] with M A-MPDU subframes subF[1]˜subF[M]. If the coherent remnant-duration Trmn is sufficient for transmitting the N data subsets subDAT[1]˜subDAT[N] with the M A-MPDU subframes subF[1]˜subF[M] (M=N), the link-specific MAC (LO)88transmits the whole transmission data txDAT_STA2with the PPDU_22frame (seeFIG.17). Instead, if the coherent remnant-duration Trmn is not sufficient for transmitting the N data subsets subDAT[1]˜subDAT[N] with the M A-MPDU subframes subF[1]˜subF[M] (M<N), the link-specific MAC (LO)88merely transmits part of the transmission data txDAT_STA2(p of the N data subsets subDAT[1]˜subDAT[N]) with the PPDU_22frame (seeFIG.19).

FIG.10is a flow diagram illustrating that STA2performs a frame exchange process on the low performance link L_LO when any predefined exception conditions are satisfied.FIG.10corresponds to step S4551inFIG.9. Please refer toFIGS.8and10together.

If the determination result of step S61is negative, the link selection module89verifies if the transmission data txDAT_STA2requires short latency (step S65). If the determination result of step S65is positive, step S63is performed. Otherwise, the link selection module89verifies if the transmission data txDAT_STA2is inappropriate for aggregation or padding (step S67). If the determination result of step S67is positive, step S63is performed. Steps S61, S65, and S67are examples of predefined exception conditions. In practical applications, the types of predefined exception conditions are not limited.

To summarize, the predefined exception conditions may include, for example, whether the transmission data txDAT_STA2has high priority, whether the transmission data txDAT_STA2requires short latency, and/or whether the transmission data txDAT_STA2is inappropriate for aggregation/padding. In practical applications, the predefined exception conditions are not limited to the examples mentioned herein.

Exemplary procedures of the PPDU_22frame exchange processes related to step S63are shown inFIGS.11A and11B. In short,FIGS.11A and11Bcorrespond to the occasions that the low performance link L_LO is directly selected for the frame exchange process when the PPDU_22meets any of the predefined exception conditions. These predefined exception conditions represent situations where the transmission data txDAT_STA2needs to be transmitted as soon as possible. Therefore, in step S63, STA2chooses to perform the frame exchange process on the low performance link L_LO immediately, without waiting for the access chance on the high performance link L_HI. In step S63, the duration length of the frame exchange process performed on the low performance link L_LO is dominated by the data length of the transmission data txDAT_STA2.

On the other hand, if the determination result of step S67is negative, the link selection module89needs to further analyze the overhearing result of the high performance channel L_HI, the time point when the counting value of the backoff counter CNT_L of STA2reaches 0, and the duration of the PPDU_22frame (DURPPDU_22) (step S69). Step S69corresponds to step S4555inFIG.9, and more details about scenarios related to step S69are described inFIGS.12A,12B,14, and16˜19.

FIGS.11A and11Bare schematic diagrams illustrating that the high performance channel L_HI is already accessed by STA1, and STA2determines to perform the frame exchange process on the low performance link L_LO. InFIGS.11A and11B, it is assumed that the data to be transmitted by STA2(that is, txDAT_STA2) meets at least one of the predefined exception conditions, and STA2needs to perform the frame exchange process immediately.

InFIGS.11A and11B, the backoff procedure of the high performance link BOH ends at the time point t1 (defined as a first-first time point tp11), and STA1transmits the PPDU_11frame on the high performance channel L_HI between the time points t1 and t4 (defined as a first-first time point tp31 inFIG.11A) or between the time points t1 and t5 (defined as a first-first time point tp31 inFIG.11B). The duration information durINFOPL_11, which reports the duration of the payload portion PL_11of the PPDU_11frame, is transmitted from STA1to AP1at the time point t2 (defined as a second-first time point tp21).

As STA2is not busy at the time point t2, STA2can overhear the duration information durINFOPL_11on the high performance link L_HI. Alternatively speaking, before the backoff procedure of the low performance link BOL ends at the time point t3, STA2is aware of the time point when the PPDU_11frame is scheduled to end (that is, the third-first time point tp31). For example, the PPDU_11frame ends at the time point t4 (tp31=t4) inFIG.11Aand it ends at the time point t5 (tp31=t5) inFIG.11B.

InFIGS.11A and11B, the backoff procedures of the low performance link BOL end at the time point t3 (defined as a first-second time point tp12). Then, STA2starts to transmit the PPDU_22frame immediately. The duration length of the PPDU_22frame (DURPPDU_22) is related to the data length of the payload portion PL22, which is directly determined by the data length of the transmission data txDAT_STA2.FIGS.11A and11Bare similar, except for the duration of the payload portion PL_22inFIG.11Ais longer than that inFIG.11B.

InFIG.11A, the PPDU_22frame on the low performance link L_LO starts at the time point t3 and ends at the time point t5 (defined as a second-second time point tp22). That is, DURPPDU_22=t5−t3. InFIG.11B, the PPDU_22frame on the low performance link L_LO starts at the time point t3 and ends at the time point t4 (defined as a second-second time point tp22). That is, DURPPDU_22=t4-t3=tp22-tp12.

According toFIGS.11A and11B, if its transmission data (txDAT_STA2) meets at least one of the predefined exception conditions, STA2starts to transmit the PPDU_22frame without considering the end time point of the PPDU_11frame (time point tp31=t4 inFIG.11A, and time point tp31=t5 inFIG.11B). Examples of the predefined exception conditions can be referred to steps S61, S65, and S67inFIG.10.

As the transmission data txDAT_STA2is encapsulated in the PPDU_22frame, the duration of the PPDU_22frame (DURPPDU_22) is changed with the data length of the transmission data txDAT_STA2. The longer the transmission data txDAT_STA2is, the longer the duration of the PPDU_22frame (DURPPDU_22) is required. InFIG.11A, the PPDU_22frame (between time points t3 and t5) ends later than the PPDU_11frame (between time points t1 and t4) because the data length of the transmission data txDAT_STA2is longer. InFIG.11B, the PPDU_22frame (between time points t3 and t4) ends earlier than the PPDU_11frame (between time points t1 and t5) because the data length of the transmission data txDAT_STA2is shorter.

When the predefined quality condition is not satisfied, the link selection module211aselects the conventional EMLXR for data transmission (step S43inFIG.4). When the predefined quality condition is satisfied, the link selection module211adynamically switches its transmission configuration based on considering different timing combinations (that is, relationships between the time points tp11, tp21, tp31, tp12, and tp22) (step S45inFIG.4). Various transmission configurations are illustrated below.

Based on the illustrations inFIGS.4,9,10,11A, and11B, the link selection module89provides transmission configurations as follows. When the predefined quality condition is satisfied, STA2first checks if it can gain access right on the high performance link L_HI. Suppose the predefined quality condition is satisfied and link selection module89learns from the backoff counter CNT_HI that the link-specific MAC (HI) could gain access right on the high performance link L_HI, STA2directly chooses the high performance link L_HI for data transmission (step S453inFIG.4). On the other hand, when the predefined quality condition is satisfied, and the link selection module89learns from the backoff counter CNT_LO that the link-specific MAC (LO) could gain the access right on the low performance link L_LO, STA2does not directly choose the low performance link L_HO for data transmission. Instead, STA2must consider more issues before selecting its transmission configuration (step S455inFIG.4).

FIG.12Ais a schematic diagram illustrating an exemplary situation in which STA2cannot estimate the end time point of the PPDU_11frame on the high performance link L_HI. InFIG.12A, when STA1transmits the duration information durINFOPL_11on the high performance link L_HI at the time point t5 (defined as a second-first time point tp21), STA2cannot acquire the duration information durINFOPL_11on the high performance link L_HI because STA2is busy at proceeding the PPDU_22frame exchange process on the low performance link L_LO. Consequentially, STA2is incapable of estimating/calculating the end time point of the PPDU_11frame (that is, the third-first time point tp31) based on the duration information durINFOPL_11.

The DIFS duration of the high performance link L_HI of STA1starts at the time point t1 and ends at the time point t3. Thus, STA2cannot take advantage of the high performance link L_HI until the time point t3. At the time point t2 (defined as a first-second time point tp12), the backoff procedure of the low performance link BOL of STA2ends. Then, the PPDU_22frame starts at the time point t2 and ends at the time point t6 (defined as a second-second time point tp22). That is, DURPPDU_22=t6-t2=tp22-tp12.

The backoff procedure of the high performance link L_HI (BOH) of STA1starts at the time point t3 and ends at the time point t4 (defined as a first-first time point tp11). Then, the PPDU_11frame is transmitted between the time points t4 and t7 (defined as a third-first time point tp31). That is, DURPPDU_11=(t7-t4)=tp31-tp11. During the PPDU_11frame (DURPPDU_11), the duration information durINFOPL_11is transmitted at the time point t5 (defined as a second-first time point tp21).

By the time (time point t5=tp21) that STA1transmits the duration information durINFOPL_11, STA2is already transmitting the PPDU_22frame (DURPPDU_22=(t6−t2)). Therefore, STA2cannot overhear the status of the high performance link L_HI at the time point tp21. Without the duration information durINFOPL_11, STA2cannot estimate the end time point (that is, the time point t7=tp31) of the PPDU_11frame.

FIG.12Bis a schematic diagram illustrating another example situation in that STA2cannot estimate the end time point of the PPDU_11frame on the high performance link L_HI. InFIG.12B, STA2cannot estimate the end time point of the PPDU_11frame on the high performance link L_HI because STA2is already in transmitting the PPDU_22frame (DURPPDU_22=(t6−t3)) when STA1transmits the duration information durINFOPL_11on the high performance link L_HI at the time point t4 (defined as a second-first time point tp21).

At the time point t2 (defined as a first-first time point tp11), the backoff procedure of the high performance link BOH of STA1ends, and AP1starts to transmit the PPDU_11frame. The PPDU_11frame (DURPPDU_11) is transmitted between the time points t2 and t5 (defined as a third-first time point tp31), and the header portion having the duration information durINFOPL_11is transmitted at the time point t4 (defined as a second-first time point tp21).

The backoff counter CNT_LO of STA2starts to count down at the time point t1 and ends at 0 at the time point t3 (defined as a first-second time point tp12). Therefore, at the moment (time point t4) that AP1transmits the duration information durINFOPL_11, STA2is already transmitting the PPDU_22frame (DURPPDU_22=(t6−t3)). Accordingly, STA2cannot listen to the status of the high performance link L_HI at the time point t4=tp21 when STA1sends the duration information durINFOPL_11.

Please refer toFIGS.3and12A˜12B together. According to the classification inFIG.3,FIGS.12A and12Brepresent the situations in which the duration information durINFOPL_11aand durINFOPL_11bcannot be successfully detected by STA2.FIGS.12A and12Bdemonstrate that, if the time point tp21 (time point t3 inFIG.12A, or time point t4 inFIG.12B) that STA1transmits the duration information durINFOPL_11is within the duration of the PPDU_22frame (for example, between time points t2˜t6 inFIG.12A, or between time points t3˜t6 inFIG.12B), STA2is incapable of overhearing the duration information durINFOPL_11, nor calculating the end time point of the PPDU_11frame (that is, the time point tp31).

In contrast toFIGS.12A and12B, there are situations that STA2can successfully acquire the duration information durINFOPL_11. For these situations, the link selection module89calculates a coherent remnant-duration Trmn based on the acquired duration information durINFOPL_11. Then, the acquired duration information durINFOPL_11is utilized to calculate the coherent remnant-duration Trmn, and the coherent remnant-duration Trmn is compared with a minimum PPDU duration min_DURPPDU. More details about the minimum PPDU duration min_DURPPDUcan be referred toFIG.13.

The coherent remnant-duration Trmn is the time difference between the end time point of the PPDU frame performed by STA1on the high performance link L_HI and the end time point of the backoff procedure of the low performance link BOL of STA2(that is, Trmn=(tp31−tp12)). As the transmission operations of STA1and STA2are independent, the actual duration length of the coherent remnant-duration Trmn is not a constant value.

Based on the definition of the coherent remnant-duration Trmn (that is, Trmn=tp31−tp12), the length of the coherent remnant-duration Trmn is varied with the end time point of the PPDU frame on the high performance link L_HI (that is, the third-first time point tp31) and the end time point of the backoff procedure of the low performance link BOL (that is, the first-second time point tp12). Therefore, STA2needs to know the end time point of the PPDU_11frame (that is, the third-first time point tp31) in advance to calculate the coherent remnant-duration Trmn. Moreover, STA2needs to acquire the duration information durINFOPL_11on the high performance link L_HI to know the end time point of the PPDU_11frame (that is, the third-first time point tp31).

For the situations shown inFIGS.12A and12B, the coherent remnant-duration Trmn is unavailable for STA2because STA2does not have the chance to overhear the duration information durINFOPL_11on the high performance link L_HI. Consequentially, the end time point of the PPDU frame on the high performance link L_HI (that is, the third-first time point tp31) cannot be successfully estimated, nor the coherent remnant-duration Trmn can be calculated.

In some applications, the STA2can overhear the duration information durINFOPL_11on the high performance link L_HI at the second-first time point tp21 and estimate the end time point of the PPDU_11frame (that is, the third-first time point tp31) accordingly. When the end time point of the PPDU_11frame can be successfully calculated/estimated, the coherent remnant-duration Trmn can be calculated. Later, the boundary analysis circuit891compares the coherent remnant-duration Trmn with the minimum PPDU duration (min_DURPPDU).

After comparison, the comparison result is transmitted to the EMLXR Tx configuration circuit893. The EMLXR Tx configuration circuit893refers to the comparing result (Trmn≥min_DURPPDU, or Trmn<min_DURPPDU) to determine which transmission configuration suits the PPDU_22frame and the link status better.

The payload portion of the PPDU_22frame is preferred to be constructed by aggregating one or multiple A-MPDU subframes subF[1]˜subF[M] to enhance the transmission throughput. The duration of the first A-MPDU subframe subF[1], qualified for the transmission, defines the minimum PPDU duration min_DURPPDU. In other words, the minimum PPDU duration min_DURPPDUrefers to the duration of a PPDU that contains only the first A-MPDU subframe that is qualified for transmission.

FIG.13is a schematic diagram illustrating different results reflecting comparisons between the minimum PPDU duration min_DURPPDUand the coherent remnant-duration Trmn. The minimum PPDU duration min_DURPPDUis time period between the time points t1 and t3 (min_DURPPDU=t3-t1).

In the first situation (case1), the coherent remnant-duration Trmn is assumed to be between the time points t1 and t4 (Trmn=t4−t1), and the coherent remnant-duration Trmn is longer than the minimum PPDU duration min_DURPPDU(that is, Trmn=t4−t1>min_DURPPDU=t3−t1). In the second situation (case2), the coherent remnant-duration Trmn is assumed to be between the time points t1 and t3 (Trmn=t3-t1), and the coherent remnant-duration Trmn is equivalent to the minimum PPDU duration (that is, Trmn=min_DURPPDU=t3−t1).

According to the embodiments of the present disclosure, STA2selects to perform the coherent transmission for the first and the second situations. Please refer toFIGS.15,16A,16B,17,18A,18B, and19for further classification of the scenarios of the first and the second situations.

For the third situation (case3), the coherent remnant-duration Trmn is assumed to be between the time points t1 and t2 (Trmn=t2−t1), and the coherent remnant-duration Trmn is shorter than the minimum PPDU duration min_DURPPDU(that is, Trmn=t2−t1<min_DURPPDU=t3−t1). Under such circumstances, the link selection module89knows that the coherent remnant-duration Trmn is too short for the link-specific MAC (LO)88to transmit any of the A-MPDU subframes qualified for being transmitted first. Accordingly, the TxMAC(LO)883does not transmit any part of the transmission data txDAT_STA2for the third situation (case3).

FIG.14is a schematic diagram illustrating that the coherent remnant-duration Trmn is shorter than the minimum PPDU duration min_DURPPDU(Trmn<min_DURPPDU). For such a situation, STA2pauses the transmission of the transmission data txDAT_STA2on the low performance link L_LO.

The backoff procedure of the high performance link BOH ends at the time point t1 (defined as a first-first time point tp11), and the PPDU_11frame lasts between the time points t1 and t4 (defined as a third-first time point tp31). That is, DURPPDU_11=(t4−t1). The header portion HD_11of the PPDU_11frame reports the duration information durINFOPL_11at time point t2 (defined as a second-first time point tp21).

As STA2is not occupied at the time point t2, STA2can overhear the status of the high performance link L_HI and successfully acquire the duration information durINFOPL_11. With the duration information durINFOPL_11, STA2can calculate/estimate that the PPDU_11frame will end at t4 (defined as a third-first time point tp31).

On the low performance link L_LO, the counting value of the backoff counter CNT_LO of STA2reaches 0 at the time point t3. Thus, STA2can calculate the coherent remnant-duration Trmn based on the end time point of the backoff procedure of the low performance link BOL (time point t3, that is, the second-first time point tp21) and the estimated end time point of the PPDU_11frame (time point t4, that is, the third-first time point tp31). That is, Trmn=t4−t3=tp31−tp12.

InFIG.14, the BOL ends at the time point t3 (defined as a first-second time point tp12), and STA2gets access right on the low performance link L_HO. On the other hand, the high performance link L_HI is still used by STA1. Therefore, the conventional STA2transmits the PPDU_22frame between the time points t3 and t5 (defined as a second-second time point tp22).

FIG.14represents that the available coherent remnant-duration Trmn=(t4−t3) is not sufficient for STA2to complete the transmission of a minimum PPDU duration (min_DURPPDU) on the low performance link L_LO. InFIG.14, a dotted circle CR2is shown. The frame exchange processes circulated in dotted circle CR2are performed in the conventional approach but removed according to the embodiments of the present disclosure. When STA2encounters a situation in which the coherent remnant-duration Trmn is too short, likeFIG.14, the EMLXR Tx configuration circuit893should control the link-specific MAC (LO)88to skip the PPDU_22frame exchange process.

Please refer toFIGS.9,12A,12B, and14together.FIG.12Aand12B represent the situation when the determination result of step S4555cis negative, andFIG.14represents the situation when the determination result of step S4555eis negative. For situations likeFIGS.12A,12B, and14, STA2assumes that the direct access on the low performance link L_LO is inefficient and prefers to wait for the next access chance of the high performance link L_HI. Thus, the transmission is paused, and the situations described inFIGS.12A,12B, and14will not happen when the embodiments of the present disclosure are adopted.

When the coherent remnant-duration Trmn is sufficient for a PPDU frame with the minimum PPDU duration min_DURPPDU, STA2needs to further compare the length of the coherent remnant-duration Trmn with the duration of the PPDU_22frame (DURPPDU_22) to know whether the transmission data txDAT_STA2can be transmitted with one PPDU frame or not.FIGS.15,16A,16B,17,18A,18B, and19further analyze how the link selection module89determines that the link-specific MAC (LO)88should transmit the whole or only part of the transmission data txDAT_STA2.

When the coherent remnant-duration Trmn is longer than or equivalent to the minimum PPDU duration (min_DURPPDU), the EMLXR Tx configuration circuit893can inform the link-specific MAC (LO)88to transmit the PPDU_22coherently. Then,FIG.15is executed.

FIG.15is a flow diagram illustrating an exemplary implementation of step S4555ginFIG.9.FIG.15corresponds to the situations that the link selection module89selects to perform coherent transmission. When the coherent transmission proceeds, STA1and STA2respectively precede their corresponding frames on the high performance link L_HI and the low performance link L_LO parallelly during the coherent remnant-duration Trmn. That is, during the coherent remnant-duration Trmn, STA2transmits the PPDU_22frame on the low performance link L_LO, and STA1transmits the PPDU_11frame on the high performance link L_HI.

Firstly, the EMLXR Tx configuration circuit893verifies if the coherent remnant-duration Trmn is longer than or equivalent to the duration required to transmit the whole transmission data txDAT_STA2with one PPDU_22frame (Trmn≥DURPPDU_22?) (step S71). Accordingly, the EMLXR Tx configuration circuit893knows whether more than one PPDU_22frame is required to transmit the transmission data txDAT_STA2.

If the determination result of step S71is positive, the EMLXR Tx configuration circuit893informs the link-specific MAC (LO)88to directly perform the PPDU_22frame exchange process on the low performance link L_LO (step S73). Thus, the transmission data txDAT_STA2is transmitted by a single PPDU_22frame. Details about step S73can be referred toFIGS.16A,16B, and17.

If the determination result of step S71is negative, the boundary analysis circuit891reports to the EMLXR Tx configuration circuit893that the duration required to transmit the whole transmission data txDAT_STA2is too long for the coherent remnant-duration Trmn, and the EMLXR Tx configuration circuit893informs the link-specific MAC (LO)88to perform the EMLXR-based txOnRx alignment (step S75). Then, the transmission data txDAT_STA2is transmitted by more than one PPDU_22frame. Details about step S75can be referred toFIGS.18A,18B, and19.

In practical applications, instead of transmitting the boundary analysis result to the EMLXR Tx configuration circuit893, the boundary analysis circuit891might directly inform the link-specific MAC (LO)88to proceed with step S75. Alternative designs can be implemented in practical applications.

FIGS.16A and16Bare schematic diagrams illustrating that the M A-MPDU subframes subF[1]˜subF[M] of the payload portion of the PPDU_22frame are capable of carrying all the N data subsets subDAT[n]˜subDAT[N](M=N) when the coherent remnant-duration Trmn is longer than the duration of the PPDU_22frame (DURPPDU_22).FIGS.16A and16Bare generally similar, except that padding bits (dummy bits) are further added inFIG.16B.

InFIG.16A, the coherent remnant-duration Trmn is equivalent to the summation of the duration of the header portion HD_22and the durations of all M A-MPDU subframes subF[1]˜subF[M]. That is, Trmn=Thd+(TsubF[1]+ . . . TsubF[M])=(t3−t1). Thus, the PPDU_22frame is constructed with the header portion HD_22and A-MPDU subframes subF[1]˜subF[M].

InFIG.16B, the coherent remnant-duration Trmn is longer than the summation of the duration of the header portion HD_22(Thd), and the duration of all M A-MPDU subframes subF[1]˜subF[M] (TsubF[1]+ . . . +TsubF[M]). That is, Trmn=(t4−t1)>Thd+(TsubF[1]+ . . . TsubF[M])=(t3−t1). Thus, one or more padding bits are added to an extended padding duration TPad22=(t4−t3) to extend the duration of the PPDU_22frame (DURPPDU_22). Consequentially, the PPDU_22frame is constructed with the header portion HD_22, the payload portion including A-MPDU subframes subF[1]˜subF[M], and one or more padding bits PAD_22.

In bothFIGS.16A and16B, the number of the A-MPDU subframes (M) is equivalent to the number of data subsets subDAT[1]˜subDAT[N] (M=N). Therefore, each of the data subset subDAT[1]˜subDAT[N] is carried by one of the A-MPDU subframes subF[1]˜subF[M].

FIG.17is a schematic diagram illustrating that the link selection module controls the link-specific MAC (LO) to perform the coherent transmission when the coherent remnant-duration Trmn is longer than the duration of the PPDU_22frame (DURPPDU_22).

When the duration of the PPDU_22frame (DURPPDU_22) is shorter than or equivalent to the coherent remnant-duration Trmn (DURPPDU_22Trmn), the TxMAC(LO)883can finish transmitting the PPDU_22frame by the end time point of the PPDU_11frame (defined as a third-first time point tp31). In other words, the end time point of the PPDU_22frame may be earlier than or aligned with the time point t5.

The counting value of the backoff counter CNT_HI of STA1reaches 0 at the time point t1, and the PPDU_11frame is transmitted between the time points t1 (defined as a first-first time point tp11) and t5 (defined as a third-first time point tp31). That is, DURPPDU_11=(t5−t1). The header portion HD_11of the PPDU_11frame carrying the duration information durINFOPL_11is transmitted at the time point t2 (defined as a second-first time point tp21).

As the duration information durINFOPL_11is overheard by STA2at the time point t2, the boundary analysis circuit891knows that the PPDU_11frame will end at the time point t5. Therefore, the boundary analysis circuit891calculates the coherent remnant-duration Trmn based on the difference between the end time point of the PPDU_11frame (time point t5) and the end time point of the backoff procedure of the low performance link BOL (time point t3, as a first-second time point tp12). That is, Trmn=(t5−t3) inFIG.17.

Meanwhile, the boundary analysis circuit891receives the transmission data txDAT_STA2from the wireless control circuit85and knows the duration required to transmit the transmission data txDAT_STA2(DURPPDU_22). InFIG.17, as the duration of the PPDU_22frame for transmitting the whole transmission data txDAT_STA2is shorter than the coherent remnant-duration Trmn (DURPPDU_22<Trmn=(t5−t3)), the boundary analysis circuit891knows that the PPDU_22frame will end at the time point t4 (that is, before the time point t5). InFIG.17, one or more padding bits are added in the extended padding duration TPad22between the time points t4 and t5. The boundary analysis circuit891informs the duration comparison result to the EMLXR Tx configuration circuit893. Then, the (EMLXR Tx configuration circuit893controls the frame constructor (LO) to add the padding bits to the PPDU_22frame accordingly.

Therefore, once the counting value of the backoff counter CNT_LO of STA2reaches 0 at the time point t3, the EMLXR Tx configuration circuit893controls the TxMAC(LO)883to transmit the PPDU_22frame immediately. Then, the header portion HD_22and the payload portion PL_22of the PPDU_22frame are transmitted between the time points t3 and t4, and one or more padding bits are transmitted between the time points t4 and t5.

InFIG.17, the PPDU_11frame ends at the time point t5, and the payload portion PL_22of the PPDU_22frame ends at the time point t4. The duration between the time points t4 and t5 is an extended padding duration TPad22(TPad22=(t5−t4)), during which one or more padding bits are added to make the end time point of the PPDU_22frame (that is, the time point tp22) be aligned with the end time point of the PPDU_11frame (that is, the time point tp31).

FIGS.18A and18Bare schematic diagrams illustrating that the A-MPDU subframes subF[1]˜subF[N] of the payload portion of the PPDU_22frame are incapable of carrying all N data subsets subDAT[n]˜subDAT[N](M<N) when the coherent remnant-duration Trmn is shorter than the duration of the PPDU_22frame (DURPPDU_22).FIGS.18A and18Bare generally similar, except that padding bits (dummy bits) are excluded inFIG.18Abut included inFIG.18B.

InFIG.18A, the coherent remnant-duration Trmn=t3−t1 is equivalent to the summation of the duration of the header portion HD_22(Thd) and durations of p A-MPDU subframes subF[1]˜subF[p] (TsubF[1]˜TsubF[p]), wherein p is a positive number, and 1≤p<N. That is, Trmn=Thd+(TsubF[1]+ . . . +TsubF[p]). Details about constructing the p A-MPDU subframes subF[1]˜subF[p] are omitted. In short, the p A-MPDU subframes subF[1]˜subF[p] are constructed by selecting p of the N data subsets subDAT[1]˜subDAT[N]. Please note that the ordering sequence (1˜p) of the A-MPDU subframes subF[1]˜subF[p] is not required to be identical to the ordering sequence (1˜N) of the data subsets subDAT[1]˜subDAT[N].

InFIG.18B, the coherent remnant-duration Trmn=t4−t1 is longer than the summation of the duration of the header portion HD_22(Thd) and durations of A-MPDU subframes subF[1]˜subF[p] (TsubF[1]˜TsubF[p]) and shorter than the summation of the duration of the header portion HD_22(Thd) and durations of A-MPDU subframes subF[1]˜subF[p+1] (TsubF[1]˜TsubF[p+1]). That is, Thd+(TsubF[1]+ . . . +TsubF[p])<Trmn<Thd+(TsubF[1]+ . . . +TsubF[p]+TsubF[p+1]). In other words, the TxMAC(LO)883cannot transmit more than p A-MPDU subframes subF[1]˜subF[p] within the coherent remnant-duration Trmn. Accordingly, the A-MPDU subframes subF[1]˜subF[M] in the payload portion PL_22carry only M=p of the N data subsets subDAT[1]˜subDAT[N].

InFIGS.18A and18B, the number of A-MPDU subframes (M) is set to be equivalent to p (set M=p), and p is smaller than N (p<N). This implies that the payload portion of the PPDU_22frame (PL_22=A-MPDU_22) is incapable of transmitting all the data subsets subDAT[1]˜subDAT[N] with the A-MPDU subframes subF[1]˜subF[M]. If the payload portion PL_22=A-MPDU_22further carries any of the remaining data subsets subDAT [M+1]˜subDAT[N], the duration of the PPDU_22frame DURPPDU_22will exceed the coherent remnant-duration Trmn, such a situation is not desired in the coherent transmission.

InFIG.18A, it is assumed that the summation of the duration of header portion Thdand the durations of A-MPDU subframes (TsubF[1]+ . . . TsubF[p]) is equivalent to the coherent remnant-duration Trmn. Thus, the PPDU_22frame includes a header portion HD_22and a payload portion PL_22having A-MPDU subframes subF[1]˜subF[p].

InFIG.18B, the PPDU_22frame includes a header portion HD_22, a payload portion PL_22having A-MPDU subframes subF[1]˜subF[p], and one or more padding bits PAD_22. The padding bits PAD_22are inserted in an extended padding duration TPad22=(t4−t3) to extend the duration of the PPDU_22frame (DURPPDU_22). By doing so, the end time point of the PPDU_22frame (that is, the second-second time point tp22) is aligned with the end time point of the coherent remnant-duration Trmn (that is, the third-first time point tp31).

In comparison with the payload portion PL_22frame inFIGS.16A and16B, the payload portion PL_22inFIGS.18A and18Binclude fewer A-MPDU subframes because not all the transmission data txDAT_STA2are carried. By not transmitting all the transmission data txDAT_STA2, the EMLXR Tx configuration circuit893knows that the link-specific MAC(HI)86can get a better chance to transmit the remaining data subsets subDAT[p+1]˜subDAT[N] on the high performance link L_HI soon after the PPDU_11frame and PPDU_22frame end.

FIG.19is a schematic diagram illustrating that the link selection module controls the link-specific MAC (LO) to perform the coherent transmission when the coherent remnant-duration Trmn is shorter than the duration of the PPDU_22frame (DURPPDU_22).

Please refer toFIGS.15,18B, and19together. When the duration required by the PPDU_22frame to transmit all the data subsets subDAT[1]˜subDAT[M] is longer than the coherent remnant-duration Trmn (DURPPDU_22>Trmn), the TxMAC(LO)883cannot finish transmitting the whole transmission data txDAT_STA2with a single PPDU_22frame before the PPDU_11frame ends at the third-first time point tp31. That is, the duration of the PPDU_22frame (DURPPDU_22) is too long for the coherent remnant-duration Trmn if N is greater than M (N>M). Thus, the EMLXR Tx configuration circuit informs the frame constructor (LO) that only part of the transmission data txDAT_STA2(subDAT[1]˜subDAT[p]) are carried by the A-MPDU subframes subF[1]˜subF[M] in the PPDU_22frame (Step S751inFIG.15).

After the backoff procedure of the high performance link BOH ends at the time point t1 (defined as a first-first time point tp11), STA1transmits the PPDU_11frame between the time points t1 and t4 (defined as a third-first time point tp31). That is, DURPPDU_11=(t4−t1). At the time point t2 (defined as a second-first time point tp21), the frame detector (HI)8653detects the status of the high performance link L_HI, and the frame parser (HI)8651parses the overheard result to acquire the duration information durINFOPL_11. Then, the frame parser (HI)8651passes the duration information durINFOPL_11to the boundary analysis circuit891. Based on the duration information durINFOPL_11, the boundary analysis circuit891can estimate the end time point of the PPDU_11frame (defined as a third-first time point tp31), for example, the time point t4 inFIG.19.

On the other hand, from the backoff counter CNT_LO8813, the boundary analysis circuit891knows that the backoff procedure of the low performance link BOL ends at the time point t3 (defined as a first-second time point tp12). Thus, the boundary analysis circuit891can calculate the coherent remnant-duration Trmn as the duration between time points t3 and t4. That is, Trmn=t4−t3=tp31−tp12.

Moreover, the boundary analysis circuit891receives the transmission data txDAT_STA2from the wireless control circuit85. Based on the data length of the transmission data txDAT_STA2, the boundary analysis circuit891knows that the transmission data txDAT_STA2cannot be completely transmitted within the coherent remnant-duration Trmn (between the time points t3 and t4). Thus, the EMLXR Tx configuration circuit893should configure the link-specific MAC (LO)88to perform the PPDU_22frame exchange process with EMLXR-based txOnRx alignment (step S753inFIG.15).

According to the embodiments of the present disclosure, the EMLXR Tx configuration circuit893notifies the link-specific MAC (LO)88that the transmission data txDAT_STA2cannot be fully transmitted by the end of the coherent remnant-duration Trmn, so the link selection module89controls the link-specific MAC (LO)88to perform the PPDU frame exchange process in which not all of the transmission data txDAT_STA2are transmitted.

To be more specific, the duration of the PPDU_22frame (DURPPDU_22) is specially arranged to be equivalent to the coherent remnant-duration Trmn to ensure that the end time point of the PPDU_22frame (defined as a second-second time point tp22) aligns with the end time point of the PPDU_11frame (defined as a third-first time point tp31), for example, the time point t4 inFIG.19.

Step S753inFIG.15corresponds to the PPDU_22frame described inFIGS.18A,18B, and19. InFIG.19, the PPDU_22frame is constructed based onFIG.18B. The EMLXR Tx configuration circuit893controls the TxMAC(LO)883to transmit the PPDU_22frame during the time points t3 and t4. That is, DURPPDU_22=(t4−t3)=tp22−tp12. As shown inFIG.19, t4 is the end time point of both the PPDU_11frame (t4=tp31) and the PPDU_22frame (t4=tp22). In other words, the PPDU_11and PPDU_22frames end synchronously (tp31=tp22).

Furthermore, the link-specific MAC(HI)86may take advantage of the high performance link L_HI to transmit the remaining transmission data (that is, data subsets subDAT[p+1]˜subDAT[N]) after the PPDU_11and PPDU_22frame exchange processes finish. The remaining transmission data is the difference between the complete transmission data txDAT_STA2and the transmission data carried by the payload portion PL_22(that is, data subsets subDAT[1]˜subDAT[p]). The transmission procedure of the remaining transmission data requires another execution round ofFIG.4, and the details are omitted.

As illustrated above,FIGS.17and19show that STA2performs the PPDU_22frame exchange process when the coherent remnant-duration Trmn is longer than or equivalent to the minimum PPDU duration min_DURPPDU. That is, Trmn min_DURPPDU.

The embodiments shown inFIGS.17and19represent that STA1and STA2respectively perform their corresponding PPDU_11and PPDU_22frame exchange processes on the high performance link L_HI and the low performance link L_LO parallelly and simultaneously. Thus, such an approach is called coherent transmission in the present disclosure. The difference betweenFIGS.17and19is that the PPDU_22frame inFIG.17carries all the transmission data txDAT_STA2(data subsets subDAT[1]˜subDAT[N]), and the PPDU_22frame inFIG.19carries only part of the transmission data txDAT_STA2(data subsets subDAT[1]˜subDAT[p]).

If DURPPDU_22≤Trmn (seeFIGS.16A,16B, and17), both STA1and STA2complete their data transmission by the time point that the coherent remnant-duration Trmn ends. On the other hand, if DURPPDU_22>Trmn (seeFIGS.18A,18B, and19), STA1and ST2coherently transmit their transmission data to their corresponding APs (AP1and AP2, respectively) during the coherent remnant-duration Trmn, and some of the transmission data txDAT_STA2(that is, data subsets subDAT[p+1]˜subDAT[N]) are not transmitted yet.

In some applications, the functions, operations, and connections related to the boundary analysis circuit891and EMLXR Tx configuration circuit893can be modified, switched, or integrated together. The alternative implementations of the components in the link selection module89are not limited.

By way of example, the link selection module performs a transmission control method for transmitting data with the proposed multi-link coherent operation. STA1transmits the PPDU_11frame between the first-first time point tp11 and the third-first time point tp31, and the duration information associated with the payload portion PL_11of the PPDU_11frame is transmitted at the second-first time point tp21. STA2tries to acquire the duration information durINFOPL_11by overhearing the status on the high preperformance link L_HI when it can do so. Besides, STA2selectively transmits the PPDU_22frame on the low performance link L_LO between the first-second time point tp12 and the second-second time point tp22.

As demonstrated in the embodiments above, the relative relationships between the time points (tp11, tp21, tp31, tp12, and tp22) may change with the real-time status in the environment, and the transmission control method adaptively selects suitable transmission configurations in response. The transmission configurations, their corresponding suitable situations, and related figures illustrated above are summarized in Table 1.

The Wi-Fi device dynamically switches its transmission configuration for uplink usage, depending on the OBSS traffic. Please note that the transmission configurations, according to the embodiments of the present application, need only adjustment at the local side MLD (for example, STA2itself). No handshaking with other MLD (for example, AP2) is required. Thus, the MLD can freely and efficiently react to the status changes in the asymmetric links.

When the predefined quality condition is unsatisfied, the MAC module81performs the frame exchange process based on the conventional EMLXR. According to the embodiments of the present disclosure, the MAC module81freely changes its transmission configuration when the predefined quality condition is satisfied.

As illustrated above, the MAC module81may perform the PPDU_22frame exchange process on the high performance link L_HI (FIG.7) or on the low performance link L_LO (FIGS.11A,11B, and17), wherein the payload portion PL_22includes all transmission data txDAT_STA2. Or, the MAC module81may temporarily ignore or skip the transmission operation (FIGS.12A,12B, and14). Alternatively, the MAC module81may perform the PPDU_22frame exchange process on the low performance link L_LO, wherein the payload portion PL_22does not include all transmission data txDAT_STA2(FIG.19). According to simulation results, the proposed Wi-Fi device and its associated transmission control method can achieve higher throughput and reduce the latency, regardless changes of environment quality.