Patent Description:
The IEEE (Institute of Electrical and Electronics Enigneers) <NUM> Working Group is developing <NUM>1ax HE (High Efficiency) WLAN (Wireless Local Area Network) air interface in order to achieve a very substantial increase in the real-world throughput achieved by users in high density scenarios. OFDMA (Orthogonal Frequency Division Multiple Access) multiuser transmission has been envisioned as one of the most important features in <NUM>. OFDMA is a multiple access scheme that performs multiple operations of data streams to and from the plurality of users over the time and frequency resources of the OFDM (Orthogonal Frequency Division Multiplexing) system.

Studies are underway to perform frequency scheduling for OFDMA multiuser transmission in <NUM>1ax. Frequency scheduling is generally performed based on an RU (Resource Unit). An RU comprises a plurality of consecutive subcarriers. According to frequency scheduling, a radio communication access point apparatus (hereinafter simply "access point" or "AP") adaptively assigns RUs to a plurality of radio communication station apparatuses (hereinafter simply "terminal stations" or "STAs") based on reception qualities of frequency bands of the STAs. This makes it possible to obtain a maximum multiuser diversity effect and to perform communication quite efficiently.

However, certain conditions have been imposed on uplink (UL) multi-user OFDMA transmissions. For example, all STAs taking part in an UL multi-user OFDMA transmission need to synchronize their transmissions to start at the same time point and to end at the same time point as well. 11ax, this is achieved by an AP that transmits a special control frame called a Trigger frame. The Trigger frame carries information such as the identity information of each of the STAs that may take part in the UL multi-user transmission, the transmission duration, the RU allocation for each STA and other useful information. STAs that are indicated in the Trigger frame transmit their respective frames on their respectively allocated RU after a fixed interval of time, e.g., SIFS (Short Interframe Spacing, since the end of the Trigger frame). This arrangment works well when the AP has enough information regarding the STAs taking part in the UL multi-user transmission such as buffer status and STA operating state, etc. But, there are cases where the AP may not have adequete information about the STAs to perform the RU allocation in an efficient manner. In such cases, it is beneficial to allocate RUs to STAs and let the STAs contend for the RUs based on their actual needs. To meet such needs, UL OFDMA-based random access (UORA) mechanism has been introduced in <NUM>.

<CIT> describes a trigger frame for random access (TF-R), which is used by an AP to notify one or more user devices that resource units are available for contention-based access, e.g. for random access. The TF-R may include a cascade indication indicating whether the AP is scheduling another TF-R right after the end of a current interval of a current TF-R. If a user device does not win channel access via contention on a TF-R, the cascade indication may assist the user device to wake up at the time of the next TF-R to contend for channel access.

<CIT> relates to triggered target wake time (TWT) operation. Based on the TWT schedule, an AP may transmit a trigger frame indicating uplink resources to multiple STAs. The trigger message may include a cascaded indicator indicating whether the AP will transmit an additional trigger message in the TWT service period. Trigger frames may contain resource unit(s) for random access.

<NPL>, relates to power saving when performing random access. A signalling mechanism to indicate whether a scheduled TF-R is cascaded or not is proposed.

11ax, some RUs in <NUM>, <NUM>, <NUM>+<NUM> or <NUM> OFDMA operation are restricted from being used for <NUM> operating STAs. There is currently no rule regarding how RUs are assigned for random access in a Trigger frame by an AP. In some cases, no RUs assigned for random access in a Trigger frame are available to <NUM> operating STAs and thus a <NUM> operating STA cannot get an opportunity to reach the AP with the UORA mechanism when receiving the Trigger frame for random access.

The present disclosure can be better understood with the aid of following figures and embodiments. The embodiments described here are merely exemplary in nature and are used to describe some of the possible applications and uses of the present disclosure and should not be taken as limiting the present disclosure with regard to alternative embodiments that are not explicitely described herein.

In any wireless communication system, a wide variety of devices may be a part of the wireless network, each device differing in terms of traffic needs, device capabilities, power supply types and so on. Some class of devices may have high bandwidth requirements, high QoS (Quality of Service) requirements in terms of latency or transmission success rate etc. But they may not be very concerned about power consumption since they may be main-powered or have large batteries (e.g., laptop computers). While another class of devices may have less bandwidth requirements and also less stringent QoS requirements but may be relatively more concerned about power consumption (e.g., mobile phones). Yet another class of devices may have low bandwidth requirements as well as very low duty cycles but may be very sensitive to power consumption due to extremely small batteries or extremely long life expectancy (e.g., sensors for remote sensing).

In many wireless communication systems, there will be one or more central controllers which will determine the wireless network coverage area, the wireless frequency channels, the device admission policy, coordination with other neighboring wireless networks etc. and usually also act as a gateway to the backend infrastructure network. Examples of the central controllers are base stations or eNBs in cellular wireless networks or APs in WLANs.

Even though the techniques described in the present disclosure may apply to many wireless communication systems, for the sake of example, the rest of the descriptions in this disclosure are described in terms of an IEEE <NUM> WLAN system and its associated terminologies. This should not be taken as limiting the present disclosure with regard to alternative wireless communication systems. In IEEE <NUM> based WLANs, majority of networks operate in infrastructure mode, i.e., all or most of the traffic in the network need to go through the AP. As such, any STA wishing to join the WLAN must first negotiate the network membership with the AP through a process called association and authentication.

<FIG> illustrates an example wireless network <NUM> including an AP <NUM> and a plurality of STAs. STA2 <NUM> and STA6 <NUM> represent a device class with high bandwidth and possibly high QoS requirements and relatively low requirement for power saving, which may be able to operate with <NUM>, <NUM>, <NUM>, <NUM>+<NUM> or <NUM> channel width. STA1 <NUM> and STA4 <NUM> represent another device class that may also have high bandwidth and possibly high QoS requirements but are relatively more concerned about power consumptions, which may be able to operate <NUM>, <NUM> or <NUM> channel width. On the other extreme, STA3 <NUM> and STA5 <NUM> represent another class of devices that may have low bandwidth requirements but may be very sensitive to power consumption, which may be able to operate with <NUM> channel width only. STAs of this device class may be called "<NUM> operating STAs" or "<NUM> only STAs. " Notice that <NUM> operating STAs (e.g., STA3 <NUM> and STA5 <NUM>) operate in the primary <NUM> channel only. In other words, RUs which are not located in the primary <NUM> channel cannot be used by <NUM> operarting STAs. In addition, non-<NUM> operating STAs (e.g., STA1 <NUM>, STA2 <NUM>, STA4 <NUM> and STA6 <NUM>) may reduce their operating channel width to <NUM> by the so-called operating mode indication procedure for power saving purpose.

RU tone mapping in <NUM> bandwidth is not aligned with RU tone mapping in <NUM>, <NUM>, <NUM>+<NUM> or <NUM> bandwidth. Due to misalignment of RU locations, some of RUs may cause significant performance penalty or interference to neighbor RUs when a <NUM> operating STA engages in <NUM>, <NUM>, <NUM>+<NUM> or <NUM> downlink (DL) or UL OFDMA operation. To improve throughput and interoperability, some RUs in <NUM>, <NUM>, <NUM>+<NUM> or <NUM> OFDMA operation are restricted from being used for <NUM> operating STAs. In more details, in terms of <NUM> DL or UL OFDMA operation, <NUM> out of <NUM> (i.e., <NUM>%) <NUM>-tone RUs shall be restricted from being used for <NUM> operating STAs. In terms of <NUM> DL or UL OFDMA operation, <NUM> out of <NUM> (i.e., <NUM>%) <NUM>-tone RUs, <NUM> out of <NUM> (i.e., <NUM>%) <NUM>-tone RUs, <NUM> out of <NUM> (i.e., <NUM>%) <NUM>-tone RUs shall not be allocated to <NUM> operating STAs. In terms of <NUM>+<NUM> or <NUM> DL or UL OFDMA operation, <NUM> out of <NUM> (i.e., <NUM>%) <NUM>-tone RUs, <NUM> out of <NUM> (i.e., <NUM>%) <NUM>-tone RUs, <NUM> out of <NUM> (i.e., <NUM>%) <NUM>-tone RUs shall not be allocated to <NUM> operating STAs. Furthermore, a <NUM>-tone RU shall not be allocated to <NUM> operating STAs in <NUM>, <NUM>, <NUM>+<NUM> or <NUM> UL OFDMA operation. Apparently, the number of RUs that are restricted from being used for <NUM> operating STAs in <NUM>, <NUM>, <NUM>+<NUM> or <NUM> OFDMA operation is not insignificant.

UORA is a mechanism for STAs to randomly select RUs assigned for random access by the AP <NUM> in a soliciting Trigger frame. An STA that uses the UORA mechanism maintains an internal counter termed as OFDMA Backoff (OBO) counter. The OFDMA Contention Window (OCW) is an integer with an initial value of OCWmin and an upper limit of OCWmax. The AP <NUM> reports to STAs the values of OCWmin and OCWmax for the UORA operation.

<FIG> illustrates an example UORA method <NUM> operated by an STA. The UORA method <NUM> starts when the STA receives a Trigger frame for random access from the AP <NUM>. Details of the example UORA method will be described later.

<FIG> illustrates an example format of the Trigger frame <NUM>, which comprises a Common Info field <NUM> and one or more User Info field <NUM>. The Common Info field <NUM> comprises a Trigger Type subfield <NUM>, a Cascade Indication subfield <NUM> and an optional Trigger Dependent Common Info subfield <NUM>. The Trigger Type subfield <NUM> indicates the type of the Trigger frame <NUM>, e.g., basic Trigger, beamforming report poll Trigger, BSRP (Buffer Status Report Poll) Trigger or random access Trigger. Notice that the random access Trigger frame contains a single User Info field <NUM>. The AP <NUM> may transmit a basic Trigger frame, a random access Trigger frame or a BSRP Trigger frame that contains one or more RUs for random access. If the Cascade Indication subfield <NUM> is <NUM>, then a subsequent Trigger frame follows the Trigger frame <NUM>. Otherwise the Cascade Indication subfield <NUM> is <NUM>. The User Info field <NUM> comprises an AID12 subfield <NUM>,an RU Allocation subfield <NUM> and a SS Allocation subfield <NUM>. The AID12 subfield <NUM> carries the least significant <NUM> bits of the AID (Association Identifier) of the STA for which the User Info field <NUM> is intended. The AID12 subfield <NUM> that is <NUM> indicates that the User Info field <NUM> identifies an RU for random access. The RU Allocation subfield <NUM> indicates the RU allocated to the STA identified by the AID12 subfield <NUM> to transmit a Trigger based PPDU (Physical Layer Protocol Data Unit). Except for the random access Trigger frame, the the SS Allocation subfield <NUM> of the User Info field <NUM> indicates the spatial streams of the Trigger based PPDU response of the STA identified by the AID12 subfield <NUM>. For the random access Trigger frame, the SS Allocation subfield <NUM> of the User Info field <NUM> indicates the number of contigious RUs used for random access starting from the RU indicated in the RU Allocation subfield <NUM>, and each RU has the same size as the size of the RU indicated in RU Allocation subfield <NUM>.

Going back to <FIG>, at step <NUM>, the STA determines if its UL transmission is an initial trigger based PPDU transmission or follows a successful trigger based PPDU transmission. If its UL transmission is an initial trigger based PPDU transmission or follows a successful trigger based PPDU transmission, the STA sets the value of OCW to OCWmin at step <NUM>. Otherwise the STA continues to check if its UL transmission is retransmission of an unsuccessful trigger based PPDU transmission at step <NUM>. If its UL transmission is retransmission of an unsuccessful trigger based PPDU transmission, the UORA method <NUM> proceeds to step <NUM>. Otherwise the UORA method <NUM> jumps to step <NUM>.

At step <NUM>, the STA initializes its OBO counter to a random value in the range of zero and OCW and the UORA method <NUM> goes to step <NUM>. At step <NUM>, the STA determines if its OBO counter is equal to zero. If its OBO counter is equal to zero, this implies the STA won the contention and selected one of the RUs for random access in the previously received Trigger frame and but did not transmit a trigger-based PPDU in the previously selected RU which was considered busy, and the UORA method <NUM> goes to step <NUM>. If its OBO counter is not equal to zero, this implies that the STA did not win the contention to access the RUs for random access in the previously received Trigger frame and the UORA method <NUM> goes to step <NUM>.

At step <NUM>, the STA checks if its OBO counter is smaller than the number of RUs for random access in the received Trigger frame. If its OBO counter is smaller than the number of RUs for random access in the received Trigger frame, the STA decrements its OBO counter to zero at step <NUM>, i.e., it wins the random access contention, and the UORA method <NUM> jumps to step <NUM>. Otherwise the STA decrements its OBO counter by the number of RUs for random access in the received Trigger frame at step <NUM>. Notice that when its OBO counter is the same as the number of RUs for random access in the received Trigger frame, the STA actually decrements its OBO counter to zero. At step <NUM>, the STA determines if its OBO counter is equal to zero. If its OBO counter is equal to zero, it wins the random access contention and the UORA method <NUM> goes to step <NUM>. Otherwise the UORA method <NUM> just stops.

At step <NUM>, the STA randomly selects one of the RUs for random access in the received Trigger frame. At step <NUM>, the STA checks if the selected RU is idle as a result of both physical and virtual carrier sensing. If the selected RU is idle, the STA transmits a trigger based PPDU at the selected RU at step <NUM>. Othewise the UORA method <NUM> just stops.

At step <NUM>, the STA determines if the trigger-based PPDU is successfully transmitted at the selected RU. If the trigger-based PPDU transmitted at the selected RU solicits an immediate response and the expected response is not received, the transmission is considered unsuccessful and the UORA method <NUM> goes to step <NUM>. Otherwise, the transmission is considered successful and the UORA method <NUM> just stops. If the trigger-based PPDU transmitted at the selected RU does not solicit an immediate response, the transmission is also considered successful. At step <NUM>, the STA sets the value of OCW to the minimum of {a sum of double the current value of OCW and one} and {a value of OCWmax} and then the UORA method <NUM> just stops.

<FIG> illustrates example multi-user frame exchange involving STAs using the example UORA method <NUM> as illustrated in <FIG>. Three STAs (e.g., STA1 <NUM>, STA2 <NUM> and STA3 <NUM> in <FIG>) contend for UL transmission using the UORA method <NUM>. STA1 <NUM>, STA2 <NUM> and STA3 <NUM> start the UORA method <NUM> when receiving the Trigger frame <NUM> from the AP <NUM>. The Trigger frame <NUM> contains three RUs for random access (i.e., RU1, RU2 and RU3 with AID set to zero) which are available to all STAs. Assume that UL transmission for each of STA1 <NUM>, STA2 <NUM> and STA3 <NUM> is an intial Trigger based PPDU transmission or follows a successful Trigger based PPDU transmission, and the OBO counters for STA1 <NUM>, STA2 <NUM> and STA3 <NUM> are initilized to <NUM>, <NUM> and <NUM>, respectively. Since the number of RUs for random access in the received Trigger frame <NUM> is three, the OBO counters for STA1 <NUM>, STA2 <NUM> and STA3 <NUM> becomes <NUM>, <NUM> and <NUM>, respectively. Eventually STA3 <NUM> with its OBO counter being <NUM> wins the contention, randomly selects RU3 which is considered idle and transmits a trigger based PPDU <NUM> at RU3 SIFS after receving the Trigger frame <NUM>. If STA3 <NUM> receives an acknowledge frame <NUM> from the AP <NUM> within a determined time period after transmitting the Trigger based PPDU <NUM>, the transmission of the Trigger based PPDU <NUM> is successful. Otherwise the transmission of the Trigger based PPDU <NUM> is unsuccessful.

Although UORA may be scheduled at any time point at the discretion of the AP <NUM>, a most likely usage scenario is at times when the AP <NUM> has no knowledge on the presence of unassociated STAs that are not able to communicate with the AP <NUM>. Specifically, the AP <NUM> may not know the presence of unassociated <NUM> operating STAs. Notice that there is currently no rule regarding how RUs are assigned by the AP <NUM> for random access in a Trigger frame. In some cases, no RUs assigned by the AP <NUM> for random access in a Trigger frame are available to <NUM> operating STAs. In other words, no RUs assgined for random access in a Trigger frame are in the primary <NUM> channel and unrestricted to be used for <NUM> operating STAs. In this case, a <NUM> operating STA cannot get an opportunity to reach the AP <NUM> with the UORA method <NUM> when receiving the Trigger frame for random access.

Next, according to the present disclosure, various embodiments of an apparatus and a method for UORA will be explained in further details.

According to a first embodiment of the present disclosure, a first example UORA method operated by the AP <NUM> is that every N-th Trigger frame for random access transmitted by the AP <NUM> includes at least one RU for random access which is available to <NUM> operating STAs, where N is a positive integer. In other words, every N-th Trigger frame for random access contains at least one RU for random access which is in the primary <NUM> channel and unrestricted from being used for <NUM> operating STAs.

According to the first embodiment of the present disclosure, a second example UORA method operated by the AP <NUM> is that in a determined period of time (e.g., one Beacon interval), the AP <NUM> transmits one or more Trigger frame for random access, each including at least one RU for random access which is available to <NUM> operating STAs.

According to the first embodiment of the present disclosure, a <NUM> operating STA is given an opportunity to reach the AP <NUM> with the UORA mechanism when receiving Trigger frames for random access.

<FIG> illustrates a first example UORA method <NUM> operated by a <NUM> operating STA according to the first embodiment of the present disclosure. The UORA method <NUM> starts when the <NUM> operating STA receives a Trigger frame for random access from the AP <NUM>. At step <NUM>, the <NUM> operating STA determines if its UL transmission is an initial trigger based PPDU transmission, or follows a successful trigger based PPDU transmission, or follows an unsuccessful triggered based PPDU transmission for which there is no more retransmission attempt. If its UL transmission is an initial trigger based PPDU transmission, or follows a successful trigger based PPDU transmission, or follows an unsuccessful triggered based PPDU transmission for which there is no more retransmission attempt, the <NUM> operating STA sets the value of OCW to OCWmin and sets the RAR (Random Access Retry) counter to zero at step <NUM> where the RAR counter is an internal counter maintained by the STA, which is purposed to keep track of the retransmission attempt of a failed trigger-based PPDU transmission. Otherwise the <NUM> operating STA continues to check if its UL transmission is retransmission of an unsuccessful trigger based PPDU transmission at step <NUM>. If its UL transmission is retransmission of an unsuccessful trigger based PPDU transmission, the UORA method <NUM> proceeds to step <NUM>. Otherwise the UORA method <NUM> jumps to step <NUM>.

At step <NUM>, the <NUM> operating STA initializes its OBO counter to a random value in the range of zero and OCW and the UORA method <NUM> goes to step <NUM>. At step <NUM>, the <NUM> operating STA determines if its OBO counter is equal to zero. If its OBO counter is equal to zero, this implies the <NUM> operating STA won the contention and selected one of the RUs for random access in the previously received Trigger frame and but did not transmit a trigger-based PPDU in the previously selected RU since one or more <NUM> channels containing the previously selected RU are considered busy, and the UORA method <NUM> goes to step <NUM>. If its OBO counter is not equal to zero, this implies that the <NUM> operating STA did not win the contention to access the RUs for random access in the previously received Trigger frame and the UORA method <NUM> goes to step <NUM>.

At step <NUM>, the <NUM> operating STA checks if its OBO counter is not larger than the number of RUs for random access in the received Trigger frame. If its OBO counter is not larger than the number of RUs for random access in the received Trigger frame, the <NUM> operating STA decrements its OBO counter to zero at step <NUM>, which implies it wins the random access contention, and the UORA method <NUM> jumps to step <NUM>. Otherwise the <NUM> operating STA decrements its OBO counter by the number of RUs for random access in the received Trigger frame at step <NUM>, and then the UORA method <NUM> just stops. Notice that step <NUM> to step <NUM> of the UORA method <NUM> perform random access contention in an more efficient manner than step <NUM> to step <NUM> of the UORA method <NUM> since one less step is required for the UORA method <NUM> than the UORA method <NUM>.

At step <NUM>, the <NUM> operating STA determines if at least one RU for random access which is available to <NUM> operating STAs exists in the received Trigger frame. Step <NUM> can be skipped if every Trigger frame for random access contains at least one RU for random access which is available to <NUM> operating STAs. If at least one RU for random access which is available to <NUM> operating STAs exists in the received Trigger frame, the UORA method <NUM> goes to step <NUM>. Otherwise the UORA method <NUM> just stops.

At step <NUM>, the <NUM> operating STA randomly selects one of the RU(s) for random access which is available to <NUM> operating STAs in the received Trigger frame. At step <NUM>, the <NUM> operating STA checks if each of one or more <NUM> channels including the selected RU is idle as a result of both physical and virtual carrier sensing. If each of one or more <NUM> channels including the selected RU is idle, the <NUM> operating STA transmits a trigger based PPDU at the selected RU at step <NUM>. Otherwise the UORA method <NUM> just stops. Notice that step <NUM> of the UORA method <NUM> is different from step <NUM> of the UORA method <NUM> since it is more practical for the <NUM> operating STA to check the CCA (Clear Channel Assessment) of one or more <NUM> channels than an RU.

At step <NUM>, the <NUM> operating STA determines if the trigger-based PPDU is successfully transmitted at the selected RU. If the trigger-based PPDU transmitted at the selected RU solicits an immediate response and the expected response is not received, the transmission is considered unsuccessful and the UORA method <NUM> goes to step <NUM>. Otherwise the transmission is considered successful and the UORA method <NUM> just stops. If the trigger-based PPDU transmitted at the selected RU does not solicit an immediate response, the transmission is also considered successful. At step <NUM>, the <NUM> operating STA increments the RAR counter by one and sets the value of OCW to the minimum of the current value of OCW multiplied by two plus one and OCWmax. At step <NUM>, the <NUM> operating STA determines if the RAR counter is larger than a threshold termed as RARetryLimit, which indicates the maximum number of random access retransmission attempts. If the the RAR counter is not larger than the threshold RARetryLimit, the UORA method <NUM> just stops. Otherwise the <NUM> operating STA determines there is no more restransmission attempt at step <NUM> and then the UORA method <NUM> just stops.

Notice that the first example UORA method <NUM> differs from the example UORA method <NUM> in that the former requires a <NUM> operating STA to maintain a RAR counter, which enables the <NUM> operating STA to reset the OCW to OCWmin if its UL transmisison follows an unsuccessful trigger-based PPDU transmission for which there is no more retransmission attempt. This may increase its probability of winning the random access contention and transmitting a trigger-based PPDU successfully in a randomly selected RU when receiving the Trigger frame for random access following a couple of failed consecutive retransmission attempts.

<FIG> illustrates an example UORA method <NUM> operated by a non-<NUM> operating STA according to the first embodiment of the present disclosure. The UORA method <NUM> starts when the non-<NUM> operating STA receives a Trigger frame for random access from the AP <NUM>. Step <NUM> to step <NUM> are the same as step <NUM> to step <NUM> in the UORA method <NUM> as shown in <FIG>, respectively.

At step <NUM>, the non-<NUM> operating STA randomly selects one of the RU(s) for random access in the received Trigger frame. Step <NUM> to step <NUM> are the same as step <NUM> to step <NUM> in the UORA method <NUM> as shown in <FIG>, respectively.

Notice that similar to the example UORA method <NUM> of <FIG>, the example UORA method <NUM> differs from the example UORA method <NUM> in that the former requires a non-<NUM> operating STA to maintain a RAR counter, which enables the non-<NUM> operating STA to reset the OCW to OCWmin if its UL transmisison follows an unsuccessful trigger-based PPDU transmission for which there is no more retransmission attempt. This may increase its probability of winning the random access contention and transmitting a trigger-based PPDU successfully in a randomly selected RU when receiving the Trigger frame for random access following a couple of failed consecutive retransmission attempts.

<FIG> illustrates first example multi-user frame exchange related to UORA according to the first embodiment of the present disclosure. STA1 and STA2 are non-<NUM> operating STAs and content for UL transmission using the UORA method <NUM>, while STA3 is a <NUM> operating STA and contents for UL transmission using the UORA method <NUM>. STA1 and STA2 start the UORA method <NUM> and STA3 starts the UORA method <NUM> when receiving the Trigger frame <NUM> that contains three RUs for random access (i.e., RU1, RU2 and RU3 with AID set to zero) from the AP where RU1 is unavailable to <NUM> operating STAs. Assume that UL transmission for each of STA1, STA2 and STA3 is an intial Trigger-based PPDU transmission or follows a successful Trigger based PPDU transmission, and the OBO counters for STA1, STA2 and STA3 are initilized to <NUM>, <NUM> and <NUM>, respectively. Since the number of RUs for random access in the received Trigger frame <NUM> is three, the OBO counters for STA1, STA2 and STA3 becomes <NUM>, <NUM> and <NUM>, respectively. Eventually STA3 with its OBO counter being <NUM> wins the random access contention and randomly selects RU3 which is available to <NUM> operating STAs. If each of one or more <NUM> channels including RU3 is considered idle, STA3 transmits a Trigger-based PPDU <NUM> at RU3 SIFS after receving the Trigger frame <NUM>. If STA3 receives an acknowledge frame <NUM> from the AP within a determined time period after transmitting the Trigger based PPDU <NUM>, the transmission of the Trigger based PPDU <NUM> is successful. Otherwise the transmission of the Trigger based PPDU <NUM> is unsuccessful.

<FIG> illustrates a second example UORA method <NUM> operated by a <NUM> operating STA according to the first embodiment of the present disclosure. The UORA method <NUM> starts when the <NUM> operating STA receives a Trigger frame for random access from the AP.

At step <NUM>, the <NUM> operating STA determines if at least one RU for random access which is available to <NUM> operating STAs exists in the received Trigger frame. Step <NUM> can be skpped if every Trigger frame for random access contains at least one RU for random access which is available to <NUM> operating STAs. If at least one RU for random access which is available to <NUM> operating STAs exists in the received Trigger frame, the UORA method <NUM> goes to step <NUM>. Otherwise the UORA method <NUM> just stops.

Step <NUM> to step <NUM> are the same as step <NUM> to step <NUM> in the UORA method <NUM> as shown in <FIG>, respectively.

At step <NUM>, the <NUM> operating STA checks if its OBO counter is not larger than the number of RUs for random access which are available to <NUM> operating STAs in the received Trigger frame. If its OBO counter is not larger than the number of RUs for random access which are available to <NUM> operating STAs in the received Trigger frame, the <NUM> operating STA decrements its OBO counter to zero at step <NUM>, which implies it wins the random access contention, and the UORA method <NUM> jumps to step <NUM>. Otherwise the <NUM> operating STA decrements its OBO counter by the number of RUs for random access which are available to <NUM> operating STAs in the received Trigger frame at step <NUM> and then the UORA method <NUM> just stops.

Notice that the second example UORA method <NUM> in <FIG> differs from the first example UORA method <NUM> in <FIG> in that for the former method, a <NUM> operating STA only takes into account the RUs for random access which are available to <NUM> operating STAs in the random access contention. As a result, the former method enables a <NUM> operating STA to decrement its OBO counter more slowly and thus its opportunity of winning the random access contention is reduced.

Step <NUM> to step <NUM> in <FIG> is the same as step <NUM> to step <NUM> in <FIG> in the UORA method <NUM> as shown in <FIG>, respectively.

<FIG> illustrates second example multi-user frame exchange related to UORA according to the first embodiment of the present disclosure. STA1 and STA2 are non-<NUM> operating STAs and content for UL transmission using the UORA method <NUM> of <FIG>, while STA3 is a <NUM> operating STA and contents for UL transmission using the UORA method <NUM> of <FIG>. STA1 and STA2 start the UORA method <NUM> and STA3 starts the UORA method <NUM> when receiving the Trigger frame <NUM> that contains three RUs for random access (i.e., RU1, RU2 and RU3 with AID set to zero) from the AP where RU1 is unavailable to <NUM> operating STAs. Assume that UL transmission for each of STA1, STA2 and STA3 is an intial Trigger-based PPDU transmission or follows a successful Trigger based PPDU transmission, and the OBO counters for STA1, STA2 and STA3 are initilized to <NUM>, <NUM> and <NUM>, respectively. Since the number of RUs for random access in the received Trigger frame <NUM> is three and the number of RUs for random access which is available to <NUM> operating STAs in the received Trigger frame <NUM> is two, the OBO counters for STA1, STA2 and STA3 becomes <NUM>, <NUM> and <NUM>, respectively. Eventually no any STA wins the random access contention.

<FIG> illustrates an example format of the Trigger frame <NUM> according to the first embodiment of the present disclosure. The Trigger frame <NUM> comprises a Common Info field <NUM> and one or more User Info field <NUM>. The Common Info field <NUM> comprises a Trigger Type subfield <NUM>, a Cascade Indication subfield <NUM> and a Trigger Dependent Common Info subfield <NUM>. The Trigger Type subfield <NUM> and the Cascade Indication subfield <NUM> are the same as their respective counterparts <NUM> and <NUM> in the Trigger frame <NUM> as illustrated in Figure <NUM>. The Trigger Dependent Common Info subfield <NUM> further comprises a Priority subfield <NUM>, which indicates the priority of <NUM> operating STAs. For example,.

Alternatively, priority signaling can be broadcasted in the Beacon frame or a Probe Response frame. <FIG> illustrates an example format of a UORA Parameter element <NUM> included in the Beacon frame or the Probe Response frame according to the first embodiment of the present disclosure. The UORA element <NUM> comprises a Priority field <NUM> which indicates the priority of <NUM> operating STAs in the same manner as the Priority subfield <NUM> of <FIG>.

According to the first embodiment of the present disclosure, whether a <NUM> operating STA uses the first example UORA method <NUM> or the second example UORA method <NUM> depends on the priority signaling broadcasted in the Trigger frame for random access or in the UORA parameter element included in the Beacon frame or the Probe Response frame. For example, if <NUM> operating STAs have lower priority than non-<NUM> operating STAs, the second UORA method <NUM> is used by a <NUM> operating STA. Otherwise the first example UORA method <NUM> is used by a <NUM> operating STA. As a result, a <NUM> operating STA is able to optimize its UORA operation according to its priority.

According to the first embodiment of the present disclosure, in the Trigger frame for random access or in the UORA parameter element included in the Beacon frame or the Probe Response frame, the AP may broadcast multiple value pairs of OCWmin and OCWmax, each of which is assigned to STAs with a specific priority. For example, the AP may broadcast two value pairs of OCWmin and OCWmax. A first value pair of OCWmin and OCWmax is assigned to STAs with higher priority and a second value pair of OCWmin and OCWmax is assigned to STAs with lower priority. If <NUM> operating STAs have higher priority than non-<NUM> operating STAs, the first value pair of OCWmin and OCWmax is assigned to <NUM> operating STAs and the second value pair of OCWmin and OCWmax is assigned to non-<NUM> operating STAs, vice versa. An STA is able to know its values of OCWmin and OCWmax based on its priority indicated in the Trigger frame for random access or in the UORA parameter element included in the Beacon frame or the Probe Response frame. Basically STAs with higher priority have smaller values of OCWmin and OCWmax than STAs with lower priority. As a result, STAs with higher priority may have higher probability of winning the random access contention with the UORA method <NUM>, the UORA method <NUM> or the UORA method <NUM>.

Alternatively, in the Trigger frame for random access or in the UORA parameter element included in the Beacon frame or the Probe Response frame, the AP may broadcast a single value pair of OCWmin and OCWmax, which is assigned to STAs with a specific priority, e.g., the OCWmin subfield <NUM> and the OCWmax subfield <NUM> in the Trigger Dependent Common Info subfield <NUM> of the Trigger frame <NUM> as illustrated in <FIG> or the OCWmin field <NUM> and the OCWmax field <NUM> in the UORA parameter element <NUM> as illustrated in <FIG>. The values of OCWmin and OCWmax for STAs with another priority can be derived from the broadcasted value of OCWmin and OCWmax. For example, the AP may broadcast a single value pair of OCWmin and OCWmax for STAs with higher priority. If <NUM> operating STAs have higher priority than non-<NUM> operating STAs, the broadcasted value pair of OCWmin and OCWmax is assigned to <NUM> operating STAs and the value pair of OCWmin and OCWmax for non-<NUM> operating STAs is equal to the value pair of OCWmin and OCWmax for <NUM> operating STAs plus a determined positive integer.

According to a second embodiment of the present disclosure, a first example UORA method operated by the AP is that every N-th Trigger frame for random access transmitted by the AP includes at least one RU for random access which is available to <NUM> operating STAs, where N is a positive integer. A Trigger frame may include at least one RU for random access which is available to <NUM> operating STAs and may also include at least one RU for random access which is unavailable to <NUM> operating STAs. In this Trigger frame, the at least one RU for random access which is available to <NUM> operating STAs is restricted from being used for non-<NUM> operating STAs. And the number of RUs for random access which are restricted from being used for non-<NUM> operating STAs is the same as the number of RUs for random access which is unavailable to <NUM> operating STAs.

According to the second embodiment of the present disclosure, a second example UORA method operated by the AP is that in a determined period of time (e.g., one Beacon interval), the AP transmits one or more Trigger frame for random access, each including at least one RU for random access which is available to <NUM> operating STAs. In a Trigger frame including at least one RU for random access which is available to <NUM> operating STAs and at least one RU for random access which is unavailable to <NUM> operating STAs, the at least one RU for random access which is available to <NUM> operating STAs is restricted from being used for non-<NUM> operating STAs and the number of RUs for random access which are restricted from being used for non-<NUM> operating STAs is the same as the number of RUs for random access which is unavailable to <NUM> operating STAs.

According to the second embodiment of the present disclosure, a <NUM> operating STA is given an opportunity to reach the AP with the UORA mechanism when receiving Trigger frames for random access. Furthermore, after winning the random access contention, probability of successful transmission in a selected RU for a <NUM> operating STA can be similar to that of a non-<NUM> operating STA.

<FIG> illustrates a first example UORA method <NUM> operated by a non-<NUM> operating STA according to the second embodiment of the present disclosure. The UORA method operated by a <NUM> operating STA is the same as the UORA method <NUM> as shown in <FIG> or the UORA method <NUM> as shown in <FIG>. The UORA method <NUM> of <FIG> starts when the non-<NUM> operating STA receives a Trigger frame for random access from the AP.

At step <NUM>, the non-<NUM> operating STA randomly selects one of the RUs for random access which is available to non-<NUM> operating STAs in the received Trigger frame.

<FIG> illustrates first example multi-user frame exchange related to UORA according to the second embodiment of the present disclosure. STA1 and STA2 are non-<NUM> operating STAs and contend for UL transmission using the UORA method <NUM>, while STA3 is a <NUM> operating STA and contends for UL transmission using the UORA method <NUM>. STA1 and STA2 start the UORA method <NUM> and STA3 starts the UORA method <NUM> when receiving the Trigger frame <NUM> that contains three RUs for random access (i.e., RU1, RU2 and RU3 with AID set to zero) from the AP where RU1 is unavailable to <NUM> operating STAs and RU3 is unavailable to non-<NUM> operating STAs. Assume that UL transmission for each of STA1, STA2 and STA3 is an intial Trigger-based PPDU transmission or follows a successful Trigger based PPDU transmission, and the OBO counters for STA1, STA2 and STA3 are initilized to <NUM>, <NUM> and <NUM>, respectively. Since the number of RUs for random access in the received Trigger frame <NUM> is three, the OBO counters for STA1, STA2 and STA3 becomes <NUM>, <NUM> and <NUM>, respectively. Eventually STA1 with its OBO counter being <NUM> wins the random access contention and randomly selects RU2 which is available to non-<NUM> operating STAs. If each of one or more <NUM> channels including the RU2 is considered idle, STA1 transmits a Trigger-based PPDU <NUM> at RU2 SIFS after receving the Trigger frame <NUM>. If STA1 receives an acknowledge frame <NUM> from the AP within a determined time period after transmitting the Trigger based PPDU <NUM>, the transmission of the Trigger based PPDU <NUM> is successful. Otherwise the transmission of the Trigger based PPDU <NUM> is unsuccessful.

<FIG> illustrates a second example UORA method <NUM> operated by a non-<NUM> operating STA according to the second embodiment of the present disclosure. The UORA method <NUM> starts when the non-<NUM> operating STA receives a Trigger frame for random access from the AP.

Step <NUM> to step <NUM> in <FIG> are the same as step <NUM> to step <NUM> in the UORA method <NUM> as shown in <FIG>, respectively.

At step <NUM>, the non-<NUM> operating STA checks if its OBO counter is not larger than the number of RUs for random access which is available to non-<NUM> operating STAs in the received Trigger frame. If its OBO counter is not larger than the number of RUs for random access which is available to non-<NUM> operating STAs in the received Trigger frame, the non-<NUM> operating STA decrements its OBO counter to zero at step <NUM>, which implies it wins the random access contention, and the UORA method <NUM> jumps to step <NUM>. Otherwise the non-<NUM> operating STA decrements its OBO counter by the number of RUs for random access which is available to non-<NUM> operating STAs in the received Trigger frame at step <NUM> and then the UORA method <NUM> just stops.

Notice that the second example UORA method <NUM> in <FIG> differs from the first example UORA method <NUM> in <FIG> in that for the former method, a non-<NUM> operating STA only takes into account the RUs for random access which are available to non-<NUM> operating STAs in the random access contention. As a result, the former method enables a non-<NUM> operating STA to decrement its OBO counter more slowly and thus its opportunity of winning the random access contention is reduced.

<FIG> illustrates second example multi-user frame exchange related to UORA according to the second embodiment of the present disclosure. STA1 and STA2 are non-<NUM> operating STAs and content for UL transmission using the UORA method <NUM> in <FIG>, while STA3 is a <NUM> operating STA and contents for UL transmission using the UORA method <NUM> in <FIG>. STA1 and STA2 start the UORA method <NUM> and STA3 starts the UORA method <NUM> when receiving the Trigger frame <NUM> that contains three RUs for random access (i.e., RU1, RU2 and RU3 with AID set to zero) from the AP where RU1 is unavailable to <NUM> operating STAs and RU3 is unavailable to non-<NUM> operating STAs. Assume that UL transmission for each of STA1, STA2 and STA3 is an intial Trigger-based PPDU transmission or follows a successful Trigger based PPDU transmission, and the OBO counters for STA1, STA2 and STA3 are initilized to <NUM>, <NUM> and <NUM>, respectively. Since the number of RUs for random access in the received Trigger frame <NUM> is three, the OBO counters for STA1, STA2 and STA3 becomes <NUM>, <NUM> and <NUM>, respectively. Eventually no any STA wins the random access contention.

<FIG> illustrates an example format of the Trigger frame <NUM> according to the second embodiment of the present disclosure. The Trigger frame <NUM> comprises a Common Info field <NUM> and one or more User Info field <NUM>. The User Info field <NUM> comprises an AID12 subfield <NUM>, an RU Allocation subfield <NUM>, a SS Allocation subfield <NUM> and a Restriction Indication subfield <NUM>. The AID12 subfield <NUM>, the RU Allocation subfield <NUM> and the SS Allocation subfield <NUM> are the same as their respective counterparts <NUM>, <NUM> and <NUM> in the Trigger frame <NUM> as illustrated in <FIG>. The Restriction Indication subfield <NUM> indicates if an RU for random access is restricted to be used for non-<NUM> operating STAs. For example,.

TWT (Target Wake Time) is a <NUM> function that permits the AP to define a specific time or a set of times for STAs to access the medium. The STA and the AP exchange information that includes an expected activity duration to allow the AP to control the amount of contention and overlap among competing STAs. TWT may be used to reduce network energy consumption, as STAs that use it can enter a doze state until their TWT arrives.

<FIG> illustrates an example format of an TWT element <NUM>. The TWT element <NUM> comprises a Control field <NUM>, a Request Type field <NUM>, a Target Wake Time field <NUM> and a TWT Wake Interval Mantissa field <NUM>. The Control field <NUM> comprises a Broadcast subfield <NUM>, which indicates if the TWT SP (Service Period) defined by the TWT element <NUM> is a broadcast TWT SP. The Broadcast subfield <NUM> is <NUM> to indicate that the TWT SP defined by the TWT element <NUM> is a broadcast TWT SP. The Broadcast subfield <NUM> is <NUM>, otherwise. The Request Type field <NUM> comprises a Trigger subfield <NUM>, a TWT Flow Identifier subfield <NUM> and a TWT Wake Interval Exponent subfield <NUM>. The Trigger subfield <NUM> indicates if the TWT SP defined by the TWT element <NUM> includes Trigger frames. The Trigger subfield <NUM> is set to <NUM> to indicate a trigger enabled TWT, namely, at least one Trigger frame is transmitted during the TWT SP. The Trigger subfield <NUM> is set to <NUM> otherwise. For a broadcast TWT SP, the TWT Flow Identifier subfield <NUM> contains a value that indicates recommendations on the types of frames that are transmitted by scheduled STAs during the broadcast TWT SP. The TWT Flow Identifier subfield <NUM> is set to <NUM> to indicate no constraints on the frames transmitted during the broadcast TWT SP and a Trigger frame transmitted during the broadcast TWT SP may contain zero or more RU for random access. The TWT Flow Identifier subfield <NUM> is set to <NUM> to indicate that i) there is no constraints on the frames transmitted by the scheduling STA during the broadcast TWT SP, ii) frames transmitted during the broadcast TWT SP by a scheduled STA are recommended to be limited to some specific types of frames (e.g., frames that are sent as part of a sounding feedback exchange; and iii) a Trigger frame transmitted by the AP during the broadcast TWT SP will not contain RUs for random access. The TWT Flow Identifier subfield <NUM> is set to <NUM> to indicate that i) there is no constraints on the frames transmitted by the scheduling STA during the broadcast TWT SP, ii) frames transmitted during the broadcast TWT SP by a scheduled STA are recommended to be limited to some specific types of frames (e.g., frames that are sent as part of a sounding feedback exchange; and iii) a Trigger frame transmitted by the AP during the broadcast TWT SP will contain at least one RU for random access. The TWT wake time of the scheduled STA is determined by the Target Wake Time field <NUM> while the TWT wake interval of the scheduled STA is determined by the TWT Wake Interval Mantissa field <NUM> and the TWT Wake Interval Exponent subfield <NUM>.

According to a first example power save mechanism with UORA, an STA that receives a Beacon frame or a management frame containing a TWT element <NUM> may enter the doze state until the start of the TWT SP defined by the TWT element <NUM>. This TWT element <NUM> includes the Broadcast subfield <NUM> set to <NUM> and the TWT Flow Identifier subfield <NUM> set to <NUM>.

According to a second example power save mechanism with UORA, if random access allocations are made in a sequence of Trigger frames within a trigger enabled TWT SP, then all the Trigger frames in the sequence shall have the Cascade Indication field set to <NUM>, except for the last Trigger frame in the sequence, which shall have the Cascade Indication field set to <NUM>. An STA may use the value indicated in the Cascade Indication field in a Trigger frame to enter the doze state. If its OBO counter decrements to a non-zero value with the random access procedure in a Trigger frame with Cascade Indication field set to <NUM>, it may enter the doze state immediately. If its OBO counter decrements to a non-zero value with the random access procedure in a Trigger frame with Cascade Indication field set to <NUM>, it may remain awake for random access in the cascaded Trigger frame.

<FIG> illustrates an example format of an TWT element <NUM> according to a third embodiment of the present disclosure. The TWT element <NUM> comprises a Control field <NUM>, a Request Type field <NUM>, a Target Wake Time field <NUM> and a TWT Wake Interval Mantissa field <NUM>. The Control field <NUM> comprises a Broadcast subfield <NUM>. The Request Type field <NUM> comprises a Trigger subfield <NUM>, a TWT Flow Identifier subfield <NUM> and a TWT Wake Interval Exponent subfield <NUM>. The Request Type field <NUM>, the Target Wake Time field <NUM> and the TWT Wake Interval Mantissa field <NUM> are exactly the same as their counterparts <NUM>, <NUM> and <NUM>. The Control field <NUM> differs from its counterpart <NUM> in that the former comprises an additional RA (Random Access) Restriction subfield <NUM>. The RA Restriction subfield <NUM> indicates if at least one RU for random access in the Trigger frames transmitted within the broadcast TWT SP defined by the TWT element <NUM> is available to <NUM> operating STAs. The RA Restriction subfield <NUM> is set to <NUM> to indicate that at least one RU for random access in the Trigger frames transmitted within the broadcast TWT SP is available to <NUM> operating STAs. The RA Restriction subfield <NUM> is set to <NUM> otherwise.

According to the third embodiment of the present disclosure, when a <NUM> operating STA receives a Beacon frame or a management frame containing the TWT element <NUM>, it may enter the doze state until the start of the TWT SP defined by the TWT element <NUM>. This TWT element <NUM> includes the Broadcast subfield <NUM> set to <NUM>, the Trigger subfield <NUM> set to <NUM>, the RA Restriction field <NUM> set to <NUM> and the TWT Flow Identifier subfield <NUM> set to either <NUM> or <NUM>. And the trigger-based TWT SP defined by the TWT element <NUM> contains one or more Trigger frames for random access in which at least one RU for random access is available to <NUM> operating STAs. When a <NUM> operating STA receives a Beacon frame or a management frame containing the TWT element <NUM> with the Broadcast subfield <NUM> set to <NUM>, the Trigger subfield <NUM> set to <NUM> and the RA Restriction subfield <NUM> set to <NUM>, namely, the trigger-based TWT SP defined by the TWT element <NUM> contains one or more Trigger frames for random access in which no any RU for random access is available to <NUM> operating STAs, it may enter the doze state at least until the end of the TWT SP defined by the TWT element <NUM>. As a result, according to the third embodiment of the present disclosure , using the RA Restriction subfield <NUM> in the TWT element <NUM>, a <NUM> operating STA may be able to save even more power, compared with the first example power save mechanism with UORA.

According to the third embodiment of the present disclosure, it is possible for a <NUM> operating STA or a non-<NUM> operating STA to make use of values of signaling fields in the TWT element <NUM> to save more power in various ways. For a first example, when a non-<NUM> operating STA receives a Beacon frame or a management frame containing the TWT element <NUM> with the Broadcast subfield <NUM> set to <NUM>, the Trigger subfield <NUM> set to <NUM> and the TWT Flow Identifier subfield <NUM> set to either <NUM> or <NUM>, namely the trigger-based TWT SP defined by the TWT element <NUM> contains zero or more RUs for random access, it may enter the doze state until the start of the TWT SP defined by the TWT element <NUM>. For a second example, when a non-<NUM> operating STA or a <NUM> operating STA receives a Beacon frame or a management frame containing the TWT element <NUM> with the Broadcast subfield <NUM> set to <NUM>, the Trigger subfield <NUM> set to <NUM> and the TWT Flow Identifier subfield <NUM> set to <NUM>, namely, the trigger-based TWT SP defined by the TWT element <NUM> contains no RUs for random access, it may enter the doze state at least until the end of the TWT SP defined by the TWT element <NUM>. For a third example, when a non-<NUM> operating STA or a <NUM> operating STA receives a Beacon frame or a management frame containing the TWT element <NUM> with the Broadcast subfield <NUM> set to <NUM> and the Trigger subfield <NUM> set to <NUM>, namely, the TWT SP defined by the TWT element <NUM> contains no any Trigger frame, it may enter the doze state at least until the end of the TWT SP defined by the TWT element <NUM>.

According to a fourth embodiment of the present disclosure, which is according to the invention, the Common Info field <NUM> of the Trigger frame <NUM> as illustrated in <FIG> includes a Subsequent TF-R Indication subfield <NUM>. This Subsequent TF-R Indication subfield <NUM> contains information to indicate if any subsequent Trigger frame includes at least one RU for random access which is available to <NUM> operating STAs. The Subsequent TF-R Indication subfield <NUM> is set to <NUM> to indicate that subsequent Trigger frames include at least one RU for random access which is available to <NUM> operating STAs. The Subsequent TF-R Indication subfield <NUM> is set to <NUM> otherwise.

According to the fourth embodiment of the present disclosure, random access allocations are made in a sequence of Trigger frames within a Trigger enabled TWT SP, and all the Trigger frames in the sequence shall have the Cascade Indication field set to <NUM>, except for the last Trigger frame in the sequence, which shall have the Cascade Indication field set to <NUM>.

According to the fourth embodiment of the present disclosure, if random access allocations are made in a sequence of Trigger frames within a Trigger enabled TWT SP, a Trigger frame in the sequence shall have the Subequent TF-R Indication subfield set to <NUM> if the following Trigger frames in the sequence do not contain any RU for random access which is available to <NUM> operating STAs.

According to the fourth embodiment of the present disclosure, it is possible for a <NUM> operating STA or a non-<NUM> operating STA to make use of the value indicated in the Cascade Indication field in a Trigger frame for power saving purpose in various ways. For a first example, if the OBO counter decrements to a non-zero value with a UORA method (e.g., the UORA method <NUM>, the UORA method <NUM>, the UORA method <NUM>, the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM> or if the OBO counter decrements to zero and but each of one or more <NUM> channels including the selected RU is considered busy with a UORA method (e.g., the UORA method <NUM>, the UORA method <NUM>, the UORA method <NUM>, the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM>, namely, there is no more cascaded Trigger frame, a <NUM> operating STA or a non-<NUM> operating STA may enter the doze state immediately. If the OBO counter decrements to a non-zero value with a UORA method (e.g., the UORA method <NUM>, the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM> or if the OBO counter decrements to zero and but each of one or more <NUM> channels including the selected RU is considered busy with a UORA method (e.g., the UORA method <NUM>, the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM>, namely, there is at least one more cascaded Trigger frame, a non-<NUM> operating STA may remain awake for random access in the cascaded Trigger frame.

According to the fourth embodiment of the present disclosure, a <NUM> operating STA may use the value indicated in the Cascade Indication field and the value indicated in the Subsequent TF-R Indication subfield in a Trigger frame to enter the doze state. For example, if the OBO counter decrements to a non-zero value with a UORA method (e.g., the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM> and the Subsequent TF-R Indication field set to <NUM>, no any RU for random access in the cascaded Trigger frame is available to <NUM> operating STAs. And the <NUM> operating STA may enter the doze state immediately. For another exampler, if the OBO counter decrements to zero but each of one or more <NUM> channels including the selected RU is considered busy with a UORA method (e.g., the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM> and the Subsequent TF-R Indication field set to <NUM>, namely, no any RU for random access in the cascaded Trigger frame is available to <NUM> operating STAs. And the <NUM> operating STA may enter the doze state immediately.

As a result, according to the fourth embodiment of the present disclosure, using the Subsequent TF-R Indication subfield in the Trigger frame, a <NUM> operating STA may be able to save even more power, compared with the second example power save mechanism with UORA. If the OBO counter decrements to a non-zero value with a UORA method (e.g., the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM> and the Subsequent TF-R Indication field set to <NUM>, at least one RU for random access in the cascaded Trigger frame is available to <NUM> operating STAs. And the <NUM> operating STA may remain awake for random access in the cascaded Trigger frame. Or if the OBO counter decrements to zero but each of one or more <NUM> channels including the selected RU is considered busy with a UORA method (e.g., the UORA method <NUM> or the UORA method <NUM>) in a Trigger frame with Cascade Indication field set to <NUM> and the Subsequent TF-R Indication field set to <NUM>, namely, at least one RU for random access in the cascaded Trigger frame is available to <NUM> operating STAs. And the <NUM> operating STA may remain awake for random access in the cascaded Trigger frame.

<FIG> is a simple block diagram of an example STA 1900A, which may be any one of the STAs in <FIG>. The STA 1900A comprises a receive signal processing circuitry <NUM> and a receiver <NUM>. The receiver <NUM> receives a plurality of signals transmitted by an AP. Each of the received signals may carry a Trigger frame for random access, a Beacon frame including the TWT element, or a management frame including the TWT element. The trigger frame is configured according to the first embodiment, the second embodiment and/or the fourth embodiment of the present disclosure. The TWT element is configured according to the third embodiment of the present disclosure. The The receive signal processing circuitry <NUM> processes the received signals.

<FIG> is a detailed block diagram of an example STA 1900B, which may be any one of the STAs in <FIG>. The STA 1900B comprises a CPU (Central Processing Unit) <NUM> coupled to a memory <NUM>, a secondary storage <NUM> and to one or more wireless communication interfaces <NUM>. The secondary storage <NUM> may be a non-volatile computer readable storage medium that is used to permanently store pertinent instruction codes and data, etc. At the time of start up, the CPU <NUM> may copy the instruction codes as well as related data to the volatile memory <NUM> for execution. The instruction code may be an operating system, user applications, device drivers and execution codes, etc, which are required for the operation of the STA 1900B. The STA 1900B may also comprise a power source <NUM>, for example, a lithium ion battery or a coin cell battery, etc. The wireless communication interface <NUM> may comprise an interface for cellular communication or an interface for short range communication protocols such as Zigbee or it may be a WLAN interface. The wireless communication interface <NUM> may further comprise a MAC (Medium Access Control Layer) module <NUM> and a PHY (Physical Layer) module <NUM>. The MAC module <NUM> may comprise a UORA circuitry <NUM> which is responsible for operating UORA method according to the first or second embodiments of the present disclosure. The MAC module <NUM> may also comprise a power save circuitry <NUM> which is responsible for configuring the STA 1900B to enter the doze state according to the third and fourth embodiments of the present disclosure. The MAC module <NUM> may also comprise a message processing circuitry <NUM> which is responsible for generating MAC frames to be transmitted and processing received MAC frames (e.g., Trigger frame, Beacon frame, etc.). The PHY module <NUM> is responsible for converting data of the MAC module <NUM> to/from the transmission/reception signals. The wireless communication interface <NUM> may also be coupled, via the PHY module <NUM>, to one or more antennas <NUM> that are responsible for the actual transmission/reception of the wireless communication signals on/from the wireless medium.

STA 1900B may comprise many other components that are not illustrated, for sake of clarity, in <FIG>. Only those components that are most pertinent to the present disclosure are illustrated.

<FIG> is a simple block diagram of an example AP 2000A, which may be the AP <NUM> in <FIG>. The AP 2000A comprises a transmission signal generating circuitry <NUM> and a transmitter <NUM>. The transmission signal generating circuitry <NUM> generates a plurality of transmission signals. Each of the transmission signals may carry a Trigger frame for random access, a Beacon frame including the TWT element, or a management frame including the TWT element. The trigger frame is configured according to the first embodiment, the second embodiment and/or the fourth embodiment of the present disclosure. The TWT element is configured according to the third embodiment of the present disclosure. The transmitter <NUM> transmits the generated transmission signals.

<FIG> is a detailed block diagram of an example AP 2000B, which may be the AP <NUM> in <FIG>. The AP 2000B comprises a CPU <NUM> coupled to a memory <NUM>, a secondary storage <NUM>, to one or more wireless communication interfaces <NUM>, as well as to other wired communication interfaces <NUM>. The secondary storage <NUM> may be a non-volatile computer readable storage medium that is used to permanently store pertinent instruction codes and data, etc. At the time of start up, the CPU <NUM> may copy the instruction codes as well as related data to the volatile memory <NUM> for execution. The instruction code may be an operating system, user applications, device drivers and execution codes, etc, which are required for the operation of the AP 2000B. The size of the instruction code and hence the storage capacity of both the secondary storage <NUM> as well as the memory <NUM> may be substantially bigger than that of the STA 1900B.

The AP 2000B may also comprise a power source <NUM> which in most cases may be a power mains but in some cases may also be some kind of high capacity battery, for example, a car battery. The wired communication interface <NUM> may be an ethernet interface, or a powerline interface, or a telephone line interface, etc. The wireless communication interface <NUM> may comprise an interface for cellular communication, or an interface for short range communication protocols such as Zigbee, or it may be a WLAN interface.

The wireless communication interface <NUM> may further comprise a MAC module <NUM> and a PHY module <NUM>. The MAC module <NUM> may comprise an RU allocation scheduling circuitry <NUM> which is responsible for allocate RUs for DL or UL OFDMA transmission. In particular, the RU allocation scheduling circuitry <NUM> allocates RUs for random access in Trigger frames according to the first or second embodiments of the present disclosure. The MAC module <NUM> may also comprise a message processing circuitry <NUM> which is responsible for generating MAC messages to be transmitted and processing received MAC messages. In particular, the message processing circuitry <NUM> generates a Trigger frame, a TWT element included in a Beacon frame or a management frame, or a UORA parameter element included in a Beacon frame or a Probe Response frame according to the first, second, third or fourth embodiment of the present disclosure.

The PHY module <NUM> is responsible for converting data of the MAC module <NUM> to/from the transmission/reception signals. The wireless communication interface <NUM> may also be coupled, via the PHY module <NUM>, to one or more antennas <NUM> that are responsible for the actual transmission/reception of the wireless communication signals on/from the wireless medium.

AP 2000B may comprise many other components that are not illustrated, for sake of clarity, in <FIG>. Only those components that are most pertinent to the present disclosure are illustrated.

The present disclosure can be realized by software, hardware, or software in cooperation with hardware. Each functional block used in the description of each embodiment described above can be partly or entirely realized by an LSI such as an integrated circuit, and each process described in the each embodiment may be controlled partly or entirely by the same LSI or a combination of LSIs. The LSI may be individually formed as chips, or one chip may be formed so as to include a part or all of the functional blocks. The LSI may include a data input and output coupled thereto. The LSI here may be referred to as an IC, a system LSI, a super LSI, or an ultra LSI depending on a difference in the degree of integration. However, the technique of implementing an integrated circuit is not limited to the LSI and may be realized by using a dedicated circuit, a general-purpose processor, or a special-purpose processor. In addition, a FPGA (Field Programmable Gate Array) that can be programmed after the manufacture of the LSI or a reconfigurable processor in which the connections and the settings of circuit cells disposed inside the LSI can be reconfigured may be used. The present disclosure can be realized as digital processing or analogue processing, as a result of the advancement of semiconductor technology or other derivative technology,.

Should a circuit integration technology replacing LSI appear as a result of advancements in semiconductor technology or other technologies derived from the technology, the functional blocks could be integrated using the future integrated circuit technology. Another possibility is the application of biotechnology and/or the like.

Claim 1:
A station (1900A) comprising:
a receiver (<NUM>) adapted to receive a trigger frame (<NUM>) for allocating a resource unit for random access, TF-R; and
receive signal processing circuitry (<NUM>) adapted to process the received trigger frame;
wherein
random access allocations are made in a sequence of trigger frames within a trigger enabled Target Wake Time Service Period, TWT SP, and
all the trigger frames in the sequence have a Cascade Indication field set to <NUM>, except for a last trigger frame in the sequence, which has a Cascade Indication field set to <NUM>;
characterized in that
the TF-R includes a Subsequent TF-R Indication subfield (<NUM>) containing information to indicate if any subsequent trigger frame includes at least one resource unit for random access which is available for <NUM> operating stations, wherein
the Subsequent TF-R Indication subfield is set to <NUM> if following trigger frames in the sequence do not contain any resource unit for random access which is available for <NUM> operating stations;
a trigger frame in the sequence having the Cascade Indication field set to <NUM> and the Subsequent TF-R Indication subfield set to <NUM> indicates that one or more following trigger frames allocating no resource unit for random access are transmitted within the trigger enabled TWT SP; and
the receive signal processing circuitry adapted to process the subsequent trigger frame based on the information and the Cascade Indication field.