Communication apparatus and communication method for coordinated time division multiple access (c-TDMA)

Abstract

Communication apparatuses and methods for Coordinated Time Division Multiple Access (C- TDMA) are provided. One exemplary embodiment provides a first communication apparatus comprising: circuitry, which in operation, generates a frame comprising information indicating the frame is a last transmission within a portion of transmission opportunity (TXOP), the portion of TXOP being shared by an access point (AP); and a transmitter, which in operation, transmits the frame to the AP or a second communication apparatus.

Description

DescriptionCOMMUNICATION APPARATUS AND COMMUNICATION METHOD FOR COORDINATED TIME DIVISION MULTIPLE ACCESS (C-TDMA)TECHNICAL FIELD

[0001] The present disclosure relates to communication methods and apparatuses, and more particularly relates to methods and apparatuses for Coordinated Time Division Multiple Access (C-TDMA) transmission.BACKGROUND

[0002] Multiple Access Point (Multi-AP) coordination is considered as a new feature for IEEE 802.1 1 . Currently, the Multi-AP coordination schemes can be summarized as coordinated Time Division Multiple Access (C-TDMA), coordinated Orthogonal Frequency-Division Multiple Access (C-OFDMA), coordinated Spatial Reuse (C-SR), coordinated beamforming (C-BF), and other similar schemes.

[0003] Among the discussed Multi-AP coordination schemes mentioned above, C-TDMA mainly considers a sharing AP allocating time resources to shared AP(s) within its obtained transmission opportunity (TXOP) using Triggered TXOP Sharing (TXS), which was introduced in Extremely High Throughput (EHT).

[0004] However, there has not been adequate discussion on the implementation of C-TDMA.

[0005] There is thus a need for communication apparatuses and methods that can solve the above-mentioned issue. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.SUMMARY

[0006] Non-limiting and exemplary embodiments facilitate providing communication apparatuses and communication methods for C-TDMA.

[0007] According to an aspect of the present disclosure, there is provided a first communication apparatus comprising: circuitry, which in operation, generates a frame comprising information indicating the frame is a last transmission within a portion of transmission opportunity (TXOP), the portion of TXOP being shared by an access point (AP); and a transmitter, which in operation, transmits the frame to the AP or a second communication apparatus.

[0008] According to another aspect of the present disclosure, there is provided an access point comprising: circuitry, which in operation, generates a multi-user request to send transmission opportunity sharing (MU-RTS TXS) Trigger frame indicating an order and a duration for sharing a TXOP with a first communication apparatus; and a transmitter, which in operation, transmits the MU-RTS TXS Trigger frame to the first communication apparatus.

[0009] According to another aspect of the present disclosure, there is provided a communication method implemented by a first communication apparatus comprising: generating a frame comprising information indicating a portion of transmission opportunity (TXOP) that remains after a transmission from the first communication apparatus using the TXOP, the TXOP being shared from an access point (AP); and transmitting the frame to the AP or a second communication apparatus.

[0010] According to another aspect of the present disclosure, there is provided a communication method implemented by an access point (AP) comprising: generating a multi-user request to send transmission opportunity sharing (MU-RTS TXS) T rigger frame indicating an order and a duration for sharing a TXOP with a first communication apparatus; and transmitting the MU-RTS TXS Trigger frame to the first communication apparatus.

[0011] It should be noted that general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any selective combination thereof. Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and / or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and / or advantages.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying figures where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to illustrate various embodiments and to explain various principles and advantages in accordance with present embodiments.

[0013] FIG. 1 A depicts an exemplary illustration of a shared AP returning a remaining portion of a TXOP to a sharing AP by sending a TXOP Return (TR) frame according to various embodiments of the present disclosure.

[0014] FIG. 1 B depicts an exemplary illustration of a shared AP indicating a remaining portion of a TXOP to another shared AP by sending a TR frame according to various embodiments of the present disclosure.

[0015] FIG. 2 depicts an exemplary illustration of a TXOP return process using a Contention Free-End (CF-End) frame as the TR frame according to various embodiments of the present disclosure.

[0016] FIG. 3 depicts an exemplary illustration of a CF-End frame according to various embodiments of the present disclosure.

[0017] FIG. 4 depicts an exemplary illustration of a Common Info field in a multi-user request to send TXOP sharing (MU-RTS TXS) Trigger frame according to various embodiments of the present disclosure.

[0018] FIG. 5 depicts an exemplary illustration of a User Info field in an MU-RTS TXS Trigger frame according to various embodiments of the present disclosure.

[0019] FIG. 6 depicts an exemplary illustration of a TXOP return to a sharing AP by sending a TR frame to the sharing AP according to various embodiments of the present disclosure.

[0020] FIG. 7 depicts an exemplary illustration of a Public Action frame used as a TR frame according to various embodiments of the present disclosure.

[0021] FIG. 8A depicts an exemplary illustration of a TR frame Action field format according to various embodiments of the present disclosure.

[0022] FIG. 8B depicts an exemplary illustration of another TR frame Action field format according to various embodiments of the present disclosure.

[0023] FIG. 9A depicts an exemplary illustration of Public Action field values used in a frame for TXOP return according to various embodiments of the present disclosure.

[0024] FIG. 9B depicts an exemplary illustration of Public Action field values used in a frame for multi-AP setup according to various embodiments of the present disclosure.

[0025] FIG. 10 depicts an exemplary illustration of a Quality of Service (QoS) Null frame used as a TR frame according to various embodiments of the present disclosure.

[0026] FIG. 1 1 depicts an exemplary illustration of Control ID values for an A-Control subfield used in a TR frame according to various embodiments of the present disclosure.

[0027] FIG. 12 depicts an exemplary illustration of Control ID values for a command and status (CAS) Control field according to various embodiments of the present disclosure.

[0028] FIG. 13 depicts an exemplary illustration of a Control Information subfield in a CAS Control field according to various embodiments of the present disclosure.

[0029] FIG. 14 depicts an exemplary illustration of a TXOP return process by including TR in a QoS Data frame according to various embodiments of the present disclosure.

[0030] FIG. 15 depicts an exemplary illustration of a signal (SIG) field format of a data frame physical layer protocol data unit (PPDU) for TXOP return according to various embodiments of the present disclosure.

[0031] FIG. 16 depicts an exemplary illustration of a TXOP return process in which a shared AP uses a remaining portion of TXOP according to various embodiments of the present disclosure.

[0032] FIG. 17 depicts an exemplary illustration of a TXOP return process in which a sharing AP uses a remaining portion of TXOP according to various embodiments of the present disclosure

[0033] FIG. 18 depicts an exemplary illustration of a Common Info field in an MU-RTS TXS Trigger frame according to various embodiments of the present disclosure.

[0034] FIG. 19 depicts an exemplary illustration of User Info fields in an MU-RTS TXS Trigger frame according to various embodiments of the present disclosure.

[0035] FIG. 20 depicts an exemplary illustration of a TXOP return process in which a shared AP fails to receive a TR frame according to various embodiments of the present disclosure.

[0036] FIG. 21 depicts an exemplary illustration of a TXOP return process in which a sharing AP uses a remaining portion of TXOP after no signal is detected according to various embodiments of the present disclosure.

[0037] FIG. 22 depicts an exemplary illustration of a TXOP return process with more than two shared APs according to various embodiments of the present disclosure.

[0038] FIG. 23 depicts an exemplary illustration of a TXOP return process in which sharing of a TXOP is looped among a plurality of shared APs according to various embodiments of the present disclosure.

[0039] FIG. 24 depicts an exemplary illustration of a TXOP return process in which a last shared AP returns a remaining TXOP to a sharing AP according to various embodiments of the present disclosure.

[0040] FIG. 25 depicts an exemplary illustration of a TXOP return process in which a last shared AP releases a remaining TXOP according to various embodiments of the present disclosure.

[0041] FIG. 26 depicts an exemplary illustration of a TXOP return process in which the TR frame is an MU-RTS TXS Trigger frame according to various embodiments of the present disclosure.

[0042] FIG. 27 depicts an exemplary illustration of a Common Info field of an MU-RTS TXS Trigger frame according to various embodiments of the present disclosure.

[0043] FIG. 28 depicts an exemplary illustration of a User Info field in an MU-RTS TXS Trigger frame according to various embodiments of the present disclosure.

[0044] Fig. 29 shows an exemplary flowchart illustrating a communication method according to various embodiments of the present disclosure.

[0045] FIG. 30 shows an exemplary flowchart illustrating another communication method according to various embodiments of the present disclosure.

[0046] FIG. 31 shows an exemplary schematic view of a communication apparatus that can be implemented for C-TDMA according to various embodiments of the present disclosure.

[0047] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale.DETAILED DESCRIPTION

[0048] The following detailed description is merely exemplary in nature and is not intended to limit the embodiments or the application and uses of the embodiments. There is no intention to be bound by any theory presented in the preceding background or this detailed description. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

[0049] Some embodiments of the present disclosure will be described, by way of example only, with reference to the drawings. Like reference numerals and characters in the drawings refer to like elements or equivalents.

[0050] In the following paragraphs, certain exemplifying embodiments are explained with reference to one or more mobile terminals (also referred to herein as devices, peer devices, communication apparatuses, STAs (stations) or other similar terms) which may operate as an access point (AP) or a non-AP STA.

[0051] In the context of IEEE 802.1 1 (Wi-Fi) technologies, a mobile terminal is a communication apparatus that has the capability to use the IEEE 802.1 1 protocol. Based on the IEEE 802.11 - 2020 definition, a mobile terminal can be any device that contains an IEEE 802.1 1 -conformant media access control (MAC) and physical layer (PHY) interface to the wireless medium (WM).

[0052] For example, a mobile terminal may be any device such as a laptop, a desktop personal computer (PC), a personal digital assistant (PDA), an access point or a mobile phone in a wireless local area network (WLAN) environment. The mobile terminal here may be fixed or mobile.

[0053] Likewise, an AP, which may be interchangeably referred to as a wireless access point (WAP) or AP multi-link device (AP MLD) in the context of IEEE 802.11 (Wi-Fi) technologies, is a communication apparatus that allows mobile terminals in a WLAN to connect to a wired or another wireless network. The AP may be connected to a router (e.g., via a wired network) as a standalone device, but it can also be integrated with or employed in the router.

[0054] A mobile terminal in a WLAN may operate as an AP at different occasions, and vice versa. This is because communication apparatuses in the context of IEEE 802.11 (Wi-Fi) technologies may include both non-AP hardware components and AP hardware components. In this manner, the communication apparatuses may switch between a non-AP mode and an AP mode, based on actual WLAN conditions and / or requirements.

[0055] Unless explicitly indicated otherwise, it will be appreciated that, the disclosure should be applicable to various generations of IEEE 802.1 1 protocols and other standards and / or technologies in wireless communication involving similar features.

[0056] Using an MU-RTS TXS Trigger frame to allocate a portion of TXOP in C-TDMA is discussed in IEEE 802.11 -23 / 1085r0 (Thoughts on Coordinated TDMA). For example, a sharing AP may use an MU-RTS TXS Trigger frame to allocate TXOP to single or multiple shared AP(s).Further, using TXOP return to return an allocated TXOP to a shared AP is discussed in IEEE 802.1 1 -24 / 41 1 rO (TXOP Return in C-TDMA). TXOP return is helpful to improve medium utilization by enabling a sharing AP to use the remaining TXOP. However, in a scenario when a part of a time duration in a TXOP is allocated to shared APs, resource wastage may occur when the allocated time is more than required.

[0057] FIG. 1A depicts an exemplary illustration 100 of a shared AP returning a remaining portion of a TXOP to a sharing AP using a TXOP Return (TR) frame according to various embodiments of the present disclosure. Further, FIG. 1 B depicts an exemplary illustration 1 16 of a shared AP indicating a remaining portion of a TXOP to another shared AP using a TR frame according to various embodiments of the present disclosure. An AP intending to share a TXOP 1 10 (e.g., sharing AP 102), which is referred to as a sharing AP, may announce TXOP Sharing information 108 to one or more other APs (e.g., shared AP1 104 and shared AP2 106), to schedule an order and a time duration allocated to the one or more APs, which are referred to as shared APs. Frequency resources, allocated time duration for each shared AP, an order of allocated time durations, and other similar information may be indicated. The sharing AP 102 may obtain the TXOP 1 10 by contending to transmit a frame for the TXOP Sharing information 108, or it may already obtain the TXOP 1 10 before transmitting the frame (e.g., by a preceding clear to send (CTS)-to-self). Within the allocated TXOP, as shown in FIG. 1A, a first shared AP (e.g., shared AP1 104) may return a remaining portion of TXOP by sending a TXOP Return (TR) frame 1 12 to the sharing AP 102. The sharing AP 102 may use the returned time for its own data transmission, or allocate time resource to another shared AP (e.g., shared AP2 106). In another example as shown in FIG. 1 B, the shared AP1 104 may indicate a remaining portion of TXOP by sending a TR frame 1 18 to another shared AP (e.g., shared AP2 106). The shared AP2 106 may start data transmission after receiving the TR frame 1 18 (e.g., using returned TXOP 1 14). Otherwise, shared AP1 104 may send the TR frame 1 18 to the sharing AP 102 instead (e.g., as shown in FIG. 1 A). Advantageously, it is possible to have flexibility to allow a shared AP to either return TXOP to a sharing AP, or to share TXOP to another shared AP efficiently without signaling overhead by the sharing AP. It will be appreciated that C-TDMA TXOP return may also be referred to herein as TXOP return.

[0058] In an implementation, a Contention Free-End (CF-End) frame may be used as a TXOP return frame to return the remaining TXOP between APs. For example, referring to illustration 200of FIG. 2, a CF-End frame 208 is transmitted by shared AP1 204 to sharing AP 202 to return a remaining portion of TXOP to sharing AP 202. Sharing AP 202 sends an MU-RTS TXS Trigger frame 210 to shared AP2 206 after a priority interframe space (PIFS) or less time after the receiving CF-End frame 208. Advantageously, it is possible for the sharing AP to allocate time resources to multiple APs without being interrupted by other ST As.

[0059] FIG. 3 depicts an exemplary illustration of a CF-End frame 300 according to various embodiments of the present disclosure. In the CF-End frame 300, a Duration field 302 may be set to 0, a Receiver Address (RA) field 304 may be set to broadcast address, and a Transmitter Address (TA) may be set to the MAC address of a shared AP that transmits the CF-End frame 300.

[0060] FIG. 4 depicts an exemplary illustration of a Common Info field 402 in an MU-RTS TXS Trigger frame 400 according to various embodiments of the present disclosure. In the Common Info field 402, TXS Mode subfield value may be set to 3 (see row 408 of table 404), which was Reserved in IEEE 802.1 1 be Standard, to indicate MU-RTS that initiates a TXS procedure wherein a scheduled AP can transmit one or more Medium Access Control Protocol Data Unit(s) (MPDU(s)) addressed to one or more of its associated STAs or another AP. Another option may be to change TXS Mode value 2 (see row 406 of table 404) description to: MU-RTS that initiates TXS procedure wherein a scheduled STA can transmit MPDU(s) addressed to its associated AP or addressed to another STA, or a scheduled AP can transmit MPDU(s) addressed to its associated STAs or another APs.

[0061] FIG. 5 depicts an exemplary illustration of a User Info field 502 in an MU-RTS TXS Trigger frame 500 according to various embodiments of the present disclosure. The User Info field 502 may comprise an AID12 field 504. An AP identifier (APID) to uniquely identify an AP among multiple APs (e.g., to identify a shared AP among a plurality of shared APs) may be indicated in the AID12 field 504.

[0062] FIG. 6 depicts an exemplary illustration 600 of a TXOP return to a sharing AP by sending a TR frame to the sharing AP according to various embodiments of the present disclosure. For example, shared AP1 604 may be configured to transmit a TR frame 608 to sharing AP 602 toreturn a remaining portion of TXOP to the sharing AP 602, and / or shared AP2 606 may transmit a TR frame 610 to return a remaining portion of TXOP to the sharing AP 602.

[0063] A TR frame is a MAC frame to indicate an AP, that received a time portion of a TXOP from a sharing AP, returning the remainder of the allocated time (if any) back to the sharing AP. FIG. 7 depicts an example of a frame format of a TR frame 700. The TR frame 700 is defined as one type of Management frame, for example, a Public Action frame according to various embodiments of the present disclosure. For example, the TR frame 700 may comprise an Address 1 field 702 that may indicate a sharing AP’s address, an Address 2 field 704 that may indicate a shared AP’s address that transmits the frame 700, an Address 3 field 706 that may indicate the sharing AP’s Basic Service Set Identifier (BSSID), and a Frame Body field 708 that may comprise an Action field. FIG. 8A depicts an exemplary illustration of a TR frame Action field 800 according to various embodiments of the present disclosure. The TR frame Action field 800 may comprise a Reserved field 806 that may contain information related to TXOP return, for example, a remaining portion of TXOP that is to be returned, or other similar information. The TR frame Action field 800 may also comprise a Category field 802 that may indicate that the TR frame is a Public frame, and a Public Action field 804. that may indicate a value of 54 (see row 904 of table 902 in FIG. 9A) which may represent TXOP Return (TR). An Action No Ack frame (e.g., an Action frame for which no acknowledgement is required from a recipient of the frame) may be used.

[0064] FIG. 9A depicts an exemplary illustration 900 of a Public Action field value for use in a TR frame according to various embodiments of the present disclosure. A new Management frame (e.g., Public Action frame) may be defined for TXOP Return. For example, Public Action field value 54 (see row 904 of table 902), which was Reserved, may be assigned to TXOP Return (TR).

[0065] Further, TR frame 700 may also be defined as one type of Management frame for Multi- AP setup (e.g., a frame which may be used in the setup of a variety of multi-AP coordination schemes). For example, FIG. 8B depicts an exemplary illustration of a multi-AP setup frame Action field 808 according to various embodiments of the present disclosure. The TR frame Action field 808 may comprise a Type field 814 that may indicate ‘TXOP return' as one of the types, or other similar information. The TR frame Action field 808 may also comprise a Category field 810 that may indicate that the TR frame is a Public frame, and a Public Action field 812. that may indicate a value of 54 (see row 910 of table 908 in illustration 906 of FIG. 9B) which may representMulti-AP setup. An Action No Ack frame (e.g., an Action frame for which no acknowledgement is required from a recipient of the frame) may be used.

[0066] Alternatively, a TR frame is a Quality of Service (QoS) Null frame, QoS Data frame or Management frame to which a control subfield (e.g., an A-Control subfield) is included to indicate an intent of TXOP return. FIG. 10 depicts an exemplary illustration of a QoS Null frame 1000 for use as a TR frame according to various embodiments of the present disclosure. For example, the QoS Null frame 1000 may comprise a High Throughput (HT) Control subfield 1002 in which there may be three variants: HT (see row 1004), Very High Throughput (VHT, see row 1006), and High Efficiency (HE, see row 1008) that are differentiated by the value of B0 (see column 1010) and B1 (see column 1012). In an implementation, TXOP return may be indicated in an aggregated (A)-Control subfield 1014 of the HE variant HT Control under row 1008. No ACK may be indicated in QoS Control field 1024. Further, Address 1 field 1016 may contain a Receiver Address (RA, for example a sharing AP’s address), Address 2 field 1018 may contain a Transmitter Address (TA, for example a shared AP’s address that is transmitting the frame), and Address 3 field 1020 may contain a BSSID. Further, Address 4 field 1022 may not be present in the QoS Null frame 1000.

[0067] In a variation, a new A-Control subfield may be defined for TR Control. FIG. 1 1 depicts an exemplary illustration of a Control ID value for an A-Control subfield for use in a TR frame according to various embodiments of the present disclosure. The Control ID subfield (e.g., Control ID subfield 1026 in the A-Control subfield 1014) indicates the type of information carried in the Control Information subfield (e.g., Control Information subfield 1028 in the A-Control subfield 1014). The values of the Control ID subfield are defined in table 1 100 of FIG. 1 1 . For Control ID with value 10, which was Reserved, the meaning may be changed to indicate TXOP Return (TR, see row 1102 of table 1100). Further, the Control Information subfield of the TR Control subfield (e.g., an A-Control subfield indicating a Control ID value of 10) was Reserved.

[0068] In another variation, a command and status (CAS) Control field of a QoS Null frame may be reused to indicate TR control. FIG. 1 depicts an exemplary illustration of a Control ID value of 6 (e.g., see row 1 02 in table 1 00) being allocated for a CAS Control field to indicate TXOP return according to various embodiments of the present disclosure. For example, further referring to a Control Information subfield 1300 (e.g., of a CAS Control field) in FIG. 13, RDG / More PPDU subfield 1302 in the CAS control (e.g., the CAS Control field indicating ID with a value 6 as shown in row 1202 of table 1200) may be used for TXOP return in TXS mode 2 according to the IEEE802.1 1 be draft 7.0 specification. CAS control may also be reused for returning a TXOP between sharing and shared APs in C-TDMA operation.

[0069] In an implementation, TR may be included in QoS Data 1410 for TXOP return process. For example, referring to illustration 1400 in FIG. 14, TXOP Return may be indicated in a last data frame (e.g., QoS data frame 1408) sent from shared AP1 1404 to sharing AP 1402 (e.g., indicate TXOP Return in HT Control or reuse CAS Control), wherein TR is included in the QoS Data frame 1408 sent from shared AP1 1404 to sharing AP 1402 for the TXOP return process. Further, TXOP Return may also be indicated in a last data frame (e.g., QoS Data frame 1410) sent from shared AP2 1406 to sharing AP 1402 (e.g., indicate TXOP Return in HT Control or reuse CAS Control), wherein TR is included in the QoS Data frame 1410 sent from shared AP2 1406 to sharing AP 1402 for the TXOP return process.

[0070] FIG. 15 depicts an exemplary illustration of a data frame PPDU SIG field format 1500 for TXOP return according to various embodiments of the present disclosure. The data frame PPDU SIG field format 1500 may comprise a User Specific field 1502 comprising one or more User fields (e.g., 1 to n User fields). For example, User field n 1504 (e.g., a last User field of a plurality of User fields) is for an intended receiver AP of TR (and thus comprises an AP-ID field), and User fields 1 - (n-1 ) are for in-BSS ST As (and thus each of these User Fields comprises a STA-ID field). AP-ID is an identifier to uniquely identify an AP among multiple APs. In this example, AP-ID is changed from STA-ID for User field n 1504. AP-ID field 1506 in User field n 1504 is set to an AP- ID of an intended receiver AP of TR.

[0071] FIG. 16 depicts an exemplary illustration 1600 of a TXOP return process in which a first shared AP uses a remaining portion of TXOP according to various embodiments of the present disclosure. Sharing AP 1602 shares TXOP to both shared APs (e.g., shared AP1 1604 and shared AP2 1606) through a modified MU-RTS TXS Trigger frame 1608. The order and durations of sharing are indicated in the MU-RTS TXS Trigger frame 1608. After data transmission 1610 in its allocated TXOP, shared AP (e.g., shared AP1 1604) sends a TR frame 1612 to the other shared AP (e.g., shared AP2 1606). Shared AP2 1606, upon receiving the TR frame 1612, starts data transmission 1614 in its BSS. Prior to the data transmission 1614, other non-data frames such as Control frame may be sent. After data transmission, shared AP2 1606 may send a TR frame 1616 to shared AP1 1604. After shared AP2 1606 returns the remaining TXOP, shared AP1 1604 may use the returned TXOP for data transmission 1618. Advantageously, MU-RTS TXS may bereused to contain TXOP Sharing information. Shared AP1 uses the returned TXOP if there is data to transmit.

[0072] Further referring to illustration 1700 of FIG. 17, the shared AP2 1606 may send another TR frame 1702 to sharing AP 1602 after some predetermined interframe space (XIFS) time (e.g., priority interframe space (PIFS) or Short interframe space (SIFS) + aps)) if no signal is detected in a primary channel. It will be appreciated that the addressing of TR may be modified accordingly based on which AP transmits and which AP receives the TR (e.g., for a TR frame, RA is an address of an AP that receives the TR frame, and TA is an address of an AP that transmits the TR frame). Advantageously, a sharing AP can transmit data after taking back control of the TXOP to reduce resource wastage.

[0073] FIG. 18 depicts another exemplary illustration of a Common Info field 1802 in an MU- RTS TXS Trigger frame 1800 according to various embodiments of the present disclosure. In the Common Info field 1802, a TXS Mode subfield value may be set to 3 (see row 1806 of table 1804), which was Reserved, to indicate MU-RTS that initiates TXS procedure wherein a scheduled AP can transmit MPDU(s) addressed to its associated STAs or another APs. Another option is changing the TXS Mode value 2 description to: MU-RTS that initiates TXS procedure wherein a scheduled STA can transmit MPDU(s) addressed to its associated AP or addressed to another STA, or a scheduled AP can transmit MPDU(s) addressed to its associated STAs or another APs.

[0074] FIG. 19 depicts an exemplary illustration of User Info fields 1902 and 1902 (as an example of a plurality of User Info fields) in MU-RTS TXS Trigger frame 1900 according to various embodiments of the present disclosure. Each User Info field may indicate an allocated TXOP duration, and an order of allocation for each associated shared AP. For example, User Info field 1902 may be allocated to a first shared AP, and User Info field 2 1904 may be allocated to a second shared AP. The order of User Info field may be related to allocated time durations. Further, APID is an identifier to uniquely identify an AP among multiple APs. For example, APID may be indicated in an AID12 field 1906 of User Info field 1902. An allocated duration in User Info field 1902 may be same as defined in IEEE 802.1 1 be draft 7.0 specification, while an allocated duration in user Info field 1904 may be based on one or more options. In a first option, a time allocated to each shared AP may be calculated according to all preceding User Info fields (e.g., the starting time of the allocated duration is the end of the consolidated duration indicated in all preceding User Info fields). If there is a TXOP return, a next shared AP may obtain the remaining durationplus an originally allocated duration. In this manner, an end of each duration is fixed regardless of TR (e.g., the TXOP duration is calculated in advance), although the second (and each successive) shared AP must be configured to parse all preceding User Info fields. In a second option, an allocated duration may be truncated by TR. A starting time of an allocated duration of a successive shared AP may be the end of the previous allocation duration (e.g., this starting time is variable due to TR). Allocation Duration field of the associated TR frame may indicate the time duration from the starting time. For this option, it is possible for every shared AP to acquire the time duration indicated in a corresponding User Info field of the TR frame. However, shared APs must parse all preceding User Info fields, receive all TRs correctly and recalculate the end of the allocated duration.

[0075] FIG. 20 depicts an exemplary illustration of a TXOP return process 2000 in which a second shared AP fails to receive a TR frame according to various embodiments of the present disclosure. For example, sharing AP 2002 may share TXOP to both shared APs (e.g., shared AP1 2004 and shared AP22006) through a modified MU-RTS TXS Trigger frame 2008. The order and durations of sharing may be indicated in the MU-RTS TXS Trigger frame 2008. After finishing data transmission 2010 in its allocated TXOP, shared AP1 2004 may send a TR frame 2012 to the other shared AP (e.g., shared AP2 2006). If no signal is detected in a primary channel after a period of time, for example an XIFS time (e.g., shared AP2 2006 fails to receive TXOP Return), shared AP1 2004 may send a TR frame 2014 to sharing AP 2002. Sharing AP 2002 may use the TXOP for its own data transmission (e.g., as shown in data transmission 2102 in illustration 2100 of FIG. 21 ) or send an MU-RTS TXS Trigger frame 2016 to shared AP2 2006 to allocate the remaining portion of TXOP. Shared AP2 2006 may return the TXOP to sharing AP 2002 through a transmission of a TR frame 2018.

[0076] FIG. 22 depicts an exemplary illustration 2200 of a TXOP return process with more than two shared APs according to various embodiments of the present disclosure. A sequence of TXOP sharing may be indicated in MU-RTS TXS Trigger frame 2210 (e.g. using an order of User Info fields). After finishing data transmission in its allocated TXOP, a current shared AP may return the TXOP by sending a TR frame to a next shared AP (e.g., shared AP1 2204 transmitting a TR frame 2212 to shared AP2 2206 after data transmission 2212). A last shared AP (e.g., shared APn 2208) may either return a remaining portion of TXOP to shared AP1 2204 or return to sharing AP 2202 via transmission of TR frame 2214 to the shared AP1 2204 or sharing AP 2202 respectively. Advantageously, in a more than 2 shared APs scenario, the orderof TXOP sharing may be controlled by the sharing AP through transmission of an MU-RTS TXS Trigger frame.

[0077] In an option, a last shared AP (e.g., a shared APn) may send a TR frame to a shared AP1 , and the shared AP1 may use the returned TXOP for data transmission, or send a TXOP Return frame to a next shared AP (e.g., a shared AP2). The process is repeated until the end of total shared TXOP, e.g., sharing of the TXOP is looped within shared APs as shown in table 2300 of FIG. 23. Each column in table 2300 is for a sequence of TXOP allocation, and each row in table 2300 indicates an allocation of a portion of TXOP for each respective sharing AP and shared AP. In general, the table 2300 shows the sequence of AP that is allocated a portion of TXOP.

[0078] In another option, a last shared AP (e.g., a shared APn as represented by row 2404 in table 2400 of FIG. 24) may return a remaining portion of TXOP to a sharing AP (e.g., a sharing AP as represented by row 2402 in table 2400 of FIG. 24) by sending a TR frame to the sharing AP, e.g., sharing AP takes back control of TXOP as shown in row 2402, column 2406 of table 2400.

[0079] In another option, a last shared AP (e.g., a shared APn as represented by row 2502 in table 2500 of FIG. 25) may release a remaining portion of TXOP, for example in a case where a sharing AP has no intention to reclaim the remaining TXOP. In this case, sharing AP may go to a power save mode after sharing to the first shared AP.

[0080] In another option, an MU-RTS TXS Trigger frame may be used as a TR frame, and a receiver AP may be configured to transmit a clear to send (CTS) frame upon receiving the TR frame. For example, referring to illustration 2600 of FIG. 26 in which sharing AP 2602 allocates TXOP to a shared AP1 2604 and a shared AP2 2606. The shared AP1 2604 may transmit an MU-RTS TXS Trigger frame as a TR frame 2608 to the shared AP2 2606, and the shared AP2 2606 may transmit a CTS frame 2610 to the shared AP1 2604 upon receiving the TR frame 2608. Likewise, the shared AP2 2606 may transmit an MU-RTS TXS Trigger frame as a TR frame 2612 to the shared AP1 2604, and the shared AP1 2604 may transmit a CTS frame 2614 to the shared AP2 2606 upon receiving the TR frame 2612. Advantageously, an MU-RTS TXS Trigger frame may be reused to contain TXOP Sharing information. Further, the shared AP1 2604 may beconfigured to use the remaining portion of TXOP if it has data to transmit e.g., data 2616 as shown in illustration 2600.

[0081] The allowed options may be determined by a shared AP (e.g., shared AP 104 and / or shared AP 106 as shown in FIG. 1 ) based on information signaled before or during the announcement of TXOP Sharing information (e.g., TXOP Sharing information 108 in FIG. 1) by the sharing AP (e.g., sharing AP 102 in FIG. 1 ).

[0082] FIG. 27 depicts an exemplary illustration of a Common Info field 2702 in an MU-RTS TXS Trigger frame 2700 (e.g., for use as a TR frame) according to various embodiments of the present disclosure. The Common Info field 2702 may comprise a Guard Interval (Gl) And HE / EHT-long training field (LTF) Type / TXS Mode field 2704 in which a TXS Mode subfield value of 3 (see row 2708 of table 2706) may be used to indicate MU-RTS that initiates TXS procedure wherein a scheduled AP can transmit MPDU(s) addressed to its associated STAs or another APs. Further, FIG. 28 depicts an exemplary illustration of a User Info field 2802 of an MU-RTS TXS Trigger frame 2800 according to various embodiments of the present disclosure. The User Info field 2802 may comprise an AID12 field 2804. An AP identifier (APID) to uniquely identify an AP among multiple APs (e.g., to identify a shared AP among a plurality of shared APs) may be indicated in the AID12 field 2804. Further, Allocation Duration field 2806 may be set to indicate a remaining duration of a current TXOP. For example, the Allocation Duration field 2806 may be set to the remaining duration of the current TXOP. The AP that receives the frame can get the information of the remaining duration from the Allocation Duration field 2806.

[0083] FIG. 29 shows an exemplary flow diagram 2900 illustrating a communication method according to various embodiments. At step 2902, a frame is generated by a first communication apparatus, the frame comprising information indicating a portion of transmission opportunity (TXOP) that remains after a transmission from the first communication apparatus using the TXOP, the TXOP being shared from an access point (AP). At step 2904, the frame is transmitted to the AP or a second communication apparatus.

[0084] FIG. 30 shows an exemplary flow diagram 3000 illustrating another communication method according to various embodiments of the present disclosure. At step 3002, a multi-user request to send transmission opportunity sharing (MU-RTS TXS) Trigger frame is generated byan access point, the MU-RTS TXS Trigger frame indicating an order and a duration for sharing a TXOP with a first communication apparatus. At step 3004, the MU-RTS TXS Trigger frame is transmitted to the first communication apparatus.

[0085] FIG. 31 shows an exemplary schematic view of a communication apparatus 3100 that can be implemented for C-TDMA in accordance with the various embodiments. The communication apparatus 3100 may be implemented as a mobile terminal, application host, router, server, non-AP or AP according to various embodiments.

[0086] Various functions and operations of the communication apparatus 3100 are arranged into layers in accordance with a hierarchical model. In the model, lower layers report to higher layers and receive instructions therefrom in accordance with IEEE specifications. For the sake of simplicity, details of the hierarchical model are not discussed in the present disclosure.

[0087] As shown in FIG. 31 , the communication apparatus 3100 may include circuitry 3114, at least one radio transmitter 3102, at least one radio receiver 3104 and at least one antenna 31 12 (for the sake of simplicity, only one radio receiver and only one antenna is depicted in FIG. 31 for illustration purposes). The circuitry may include at least one controller 3106 for use in software and / or hardware aided execution of tasks it is designed to perform, including control of communications with one or more other devices in a wireless network. The at least one controller 3106 may control at least one transmission signal generator 3108 for generating frames to be sent through the at least one radio transmitter 3102 to one or more other non-APs or APs and at least one receive signal processor 31 10 for processing frames received through the at least one radio receiver 3104 from the one or more other non-APs or APs. The at least one transmission signal generator 3108 and the at least one receive signal processor 3110 may be stand-alone modules of the communication apparatus 3100 that communicate with the at least one controller 3106 for the above-mentioned functions. Alternatively, the at least one transmission signal generator 3108 and the at least one receive signal processor 31 10 may be included in the at least one controller 3106. It is appreciable to those skilled in the art that the arrangement of these functional modules is flexible and may vary depending on the practical needs and / or requirements. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and / or in chipsets.

[0088] In various embodiments, when in operation, the at least one radio transmitter 3102, at least one radio receiver 3104, and at least one antenna 31 12 may be controlled by the at least one controller 3106. Furthermore, while only one radio transmitter 3102 is shown, it will be appreciated that there can be more than one of such transmitters.

[0089] In various embodiments, when in operation, the at least one radio receiver 3104, together with the at least one receive signal processor 3110, forms a receiver of the communication apparatus 3100. The receiver of the communication apparatus 3100, when in operation, provides functions required for receiving data, a signal, a frame such as a TR frame or other similar frame, or other similar transmission. While only one radio receiver 3104 is shown, it will be appreciated that there can be more than one of such receivers.

[0090] The communication apparatus 3100, when in operation, provides functions required for C-TDMA TXOP return. For example, the communication apparatus 3100 may be a first communication apparatus, and the circuitry 31 14 may, in operation, generate a frame comprising information indicating a portion of transmission opportunity (TXOP) that remains after a transmission from the first communication apparatus using the TXOP, the TXOP being shared from an access point (AP). The transmitter 3102 may, in operation, transmit the frame to the AP or a second communication apparatus.

[0091] The circuitry 31 14 may be further configured to generate a further frame based on whether or not a signal is detected on a primary channel within a predetermined duration, the further frame indicating a remaining portion of the TXOP; and the transmitter 3102 may be further configured to transmit the further frame to the AP. The frame may be a Contention Free-End (CF- End) frame or a Public Action frame. The receiver 3104 may, in operation, receive a multi-user request to send TXOP sharing (MU-RTS TXS) Trigger frame from the AP prior to the transmission from the first communication apparatus using the TXOP, the MU-RTS TXS Trigger frame indicating an order and a duration for sharing the TXOP with a plurality of communication apparatuses comprising the first and the second communication apparatuses. The receiver 3104 may, in operation, receive a frame indicating a remaining portion of the TXOP from a last communication apparatus of a plurality of communication apparatus, and the transmitter 3102 may be further configured to transmit a further frame indicating the remaining portion of TXOP to the AP, or perform a data transmission utilizing the remaining portion of TXOP.

[0092] The frame may be a Quality of Service (QoS) Null frame or a data frame comprising a TR Control subfield or a command and status (CAS) Control field indicating that the frame is for TXOP Return. The frame may be transmitted with a PPDU comprising a user field indicating an identifier of the AP.

[0093] The frame may be a multi-user request to send TXOP sharing (MU-RTS TXS) Trigger frame, and the receiver 3104 may, in operation, receive a clear to send (CTS) in response to the transmitted MU-RTS TXS Trigger frame. The MU-RTS TXS Trigger frame may indicate in a TXS Mode subfield that the first and second communication apparatuses can transmit one or more Medium Access Control Protocol Data Unit(s) (MPDU(s)) addressed to an associated station (STA) or AP. The MU-RTS TXS Trigger frame may indicate, in a corresponding User Info field associated with each of the first and the second communication apparatuses, the duration of an allocated TXOP for each of the first and the second communication apparatuses, and the order is based on an order of the User Info fields in the MU-RTS trigger frame.

[0094] The communication apparatus 3100 may be an access point. The circuitry 3114 may, in operation, generate a multi-user request to send transmission opportunity sharing (MU-RTS TXS) Trigger frame indicating an order and a duration for sharing a TXOP with a first communication apparatus. The transmitter 3102 may, in operation, transmit the MU-RTS TXS Trigger frame to the first communication apparatus.

[0095] The MU-RTS TXS Trigger frame may further indicate the order and the duration for sharing the TXOP with a plurality of communication apparatuses comprising the first communication apparatus and a second communication apparatus; and the receiver 3104 may, in operation, receive, from the first or the second communication apparatus, a frame comprising information indicating a portion of the TXOP that remains after a transmission from at least one of the first communication apparatus and the second communication apparatus using the TXOP. The transmitter 3102 may be further configured to perform a data transmission using the portion of TXOP based on whether a signal is detected in a channel for data transmission from the first or second communication apparatus after a period of time.

[0096] 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 integrated circuit (IC) such as LSI (Large Scale Integration), and each process described in each embodiment may be controlled partly or entirely by a 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, an ultra-LSI, a very-large-scale integration (VLSI), or a system on a chip (SoC) depending on the integration scales. 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 and / or analogue processing. The functional blocks could be integrated with various integrated circuit technologies which are not limited to those mainly used at present. Biotechnology can also be applied.

[0097] The present disclosure can be realized by any kind of apparatus, device or system having a function of communication, which is referred to as a communication apparatus.

[0098] Some non-limiting examples of such communication apparatus may include a phone (e.g., cellular (cell) phone, smart phone), a tablet, a personal computer (PC) (e.g., laptop, desktop, netbook), a camera (e.g., digital still / video camera), a digital player (digital audio / video player), a wearable device (e.g., wearable camera, smart watch, tracking device, head mounted display (HMD), smart glasses), a game console, a digital book reader, a telehealth / telemedicine (remote health and medicine) device, and a vehicle providing communication functionality (e.g., automotive, airplane, ship), and various combinations thereof.

[0099] The communication apparatus is not limited to be portable or movable, and may also include any kind of apparatus, device or system being non-portable or stationary, such as a smart home device (e.g., an appliance, lighting, smart meter, control panel), a vending machine, and any other “things” in a network of an “Internet of Things (loT)”.

[0100] The communication may include exchanging data through, for example, a cellular system, a wireless LAN system, a satellite system, etc., and various combinations thereof.

[0101] The communication apparatus may comprise a device such as a controller or a sensor which is coupled to a communication apparatus performing a function of communication described in the present disclosure. For example, the communication apparatus may comprise a controller or a sensor that generates control signals or data signals which are used by a communication apparatus performing a communication function of the communication apparatus.

[0102] The communication apparatus also may include an infrastructure facility, such as a base station, an access point, and any other apparatus, device or system that communicates with or controls apparatuses such as those in the above non-limiting examples.

[0103] According to the present disclosure, various examples below have been described:Example 1 . A first communication apparatus comprising: circuitry, which in operation, generates a frame comprising information indicating the frame is a last transmission within a portion of transmission opportunity (TXOP), the portion of TXOP being shared by an access point (AP); and a transmitter, which in operation, transmits the frame to the AP or a second communication apparatus.Example 2.The first communication apparatus of example 1 , wherein the circuitry is further configured to generate a further frame based on whether or not a signal is detected on a primary channel within a predetermined duration, the further frame indicating a remaining portion of the TXOP; and the transmitter is further configured to transmit the further frame to the AP.Example 3.The first communication apparatus of example 1 or 2, wherein the frame is a Contention Free-End (CF-End) frame.Example 4.The first communication apparatus of example 1 or 2, wherein the frame is a Public Action frame.Example 5.The first communication apparatus of example 1 or 2, wherein the frame is a Quality of Service (QoS) Null frame or a data frame comprising a TR Control subfield or a command and status (CAS) Control field indicating that the frame is for TXOP Return.Example 6.The first communication apparatus of example 5, wherein the frame is transmitted with a PPDU comprising a user field indicating an identifier of the AP.Example 7.The first communication apparatus of example 1 or 2, wherein the frame is a multiuser request to send TXOP sharing (MU-RTS TXS) Trigger frame, and the first communication apparatus comprises a receiver which, in operation, receives a clear to send (CTS) in response to the transmitted MU-RTS TXS Trigger frame.Example 8.The first communication apparatus of any one of examples 1 to 7, further comprising a receiver which, in operation, receives a multi-user request to send TXOP sharing (MU-RTS TXS) Trigger frame from the AP prior to the transmission from the first communication apparatus using the TXOP, the MU-RTS TXS Trigger frame indicating an order and a duration for sharing the TXOP with a plurality of communication apparatuses comprising the first and the second communication apparatuses.Example 9.The first communication apparatus of example 7, wherein the MU-RTS TXS Trigger frame indicates in a TXS Mode subfield that the first and second communication apparatuses can transmit one or more Medium Access Control Protocol Data Unit(s) (MPDU(s)) addressed to an associated station (ST A) or AP.Example 1 O.The first communication apparatus of example 7, wherein the MU-RTS TXS Trigger frame indicates, in a corresponding User Info field associated with each of the first and the second communication apparatuses, the duration of an allocated TXOP for each of the first and the second communication apparatuses, and the order is based on an order of the User Info fields in the MU-RTS frame.Example 1 1 .The first communication apparatus of any one of example 1 to 7, further comprising a receiver which, in operation, receives a frame indicating a remaining portion of the TXOP from a last communication apparatus of a plurality of communication apparatus, and the transmitter isfurther configured to transmit a further frame indicating the remaining portion of TXOP to the AP, or perform a data transmission utilizing the remaining portion of TXOP.Example 12. An access point (AP) comprising: circuitry, which in operation, generates a multi-user request to send transmission opportunity sharing (MU-RTS TXS) Trigger frame indicating an order and a duration for sharing a TXOP with a first communication apparatus; and a transmitter, which in operation, transmits the MU-RTS TXS Trigger frame to the first communication apparatus.Example 13. The AP of example 12, wherein the MU-RTS TXS Trigger frame further indicates the order and the duration for sharing the TXOP with a plurality of communication apparatuses comprising the first communication apparatus and a second communication apparatus; and the AP further comprises a receiver which, in operation, receives, from the first or the second communication apparatus, a frame comprising information indicating a portion of the TXOP that remains after a transmission from at least one of the first communication apparatus and the second communication apparatus using the TXOP.Example 14. The AP of example 12 or 13, wherein the transmitter is further configured to perform a data transmission using the portion of TXOP based on whether a signal is detected in a channel for data transmission from the first or second communication apparatus after a period of time.Example 15. A communication method performed by a first communication apparatus comprising: generating a frame comprising information indicating a portion of transmission opportunity (TXOP) that remains after a transmission from the first communication apparatus using the TXOP, the TXOP being shared from an access point (AP); and transmitting the frame to the AP or a second communication apparatus.Example 16. A communication method performed by an access point (AP) comprising: generating a multi-user request to send transmission opportunity sharing (MU-RTS TXS) Trigger frame indicating an order and a duration for sharing a TXOP with a first communication apparatus; and transmitting the MU-RTS TXS Trigger frame to the first communication apparatus.

[0104] Thus, it can be seen that the present embodiments provide communication apparatuses and methods for C-TDMA.

[0105] While exemplary embodiments have been presented in the foregoing detailed description of the present embodiments, it should be appreciated that a vast number of variations exist. It should further be appreciated that the exemplary embodiments are examples, and are not intended to limit the scope, applicability, operation, or configuration of this disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing exemplary embodiments, it being understood that various changes may be made in the function and arrangement of steps and method of operation described in the exemplary embodiments and modules and structures of devices described in the exemplary embodiments without departing from the scope of the subject matter as set forth in the appended claims.

Claims

CLAIMS1 . A first communication apparatus comprising: circuitry, which in operation, generates a frame comprising information indicating return of time allocated by an access point (AP); and a transmitter, which in operation, transmits the frame to the AP or a second communication apparatus.

2. The first communication apparatus of claim 1 , wherein the circuitry is further configured to generate a further frame based on whether or not a signal is detected on a primary channel within a predetermined duration, the further frame indicating a remaining portion of a transmission opportunity (TXOP); and the transmitter is further configured to transmit the further frame to the AP.

3. The first communication apparatus of claim 1 , wherein the frame is a Contention Free-End (CF-End) frame.

4. The first communication apparatus of claim 1 , wherein the frame is a Public Action frame.

5. The first communication apparatus of claim 4, wherein a Public Action field value of the Public Action frame is a value indicating the return.

6. The first communication apparatus of claim 1 , wherein the frame comprises a TR Control subfield or a command and status (CAS) Control field indicating that the frame is for TXOP Return.

7. The first communication apparatus of claim 6, wherein the frame is transmitted with a PPDU comprising a user field indicating an identifier of the AP.

8. The first communication apparatus of claim 1 , wherein the frame is a multi-user request to send TXOP sharing (MU-RTS TXS) Trigger frame, and the first communication apparatus comprises a receiver which, in operation, receives a clear to send (CTS) in response to the transmitted MU-RTS TXS Trigger frame.

9. The first communication apparatus of claim 1 , further comprising a receiver which, in operation, receives a multi-user request to send TXOP sharing (MU-RTS TXS) Trigger frame from the AP prior to the transmission from the first communication apparatus using a TXOP, the MU-RTS TXS Trigger frame indicating an order and a duration for sharing the TXOP with a plurality of communication apparatuses comprising the first and the second communication apparatuses.

10. The first communication apparatus of claim 8, wherein the MU-RTS TXS Trigger frame indicates in a TXS Mode subfield that the first and second communication apparatuses can transmit one or more Medium Access Control Protocol Data Unit(s) (MPDU(s)) addressed to an associated station (ST A) or AP.1 1. The first communication apparatus of claim 8, wherein the MU-RTS TXS Trigger frame indicates, in a corresponding User Info field associated with each of the first and the second communication apparatuses, the duration of an allocated TXOP for each of the first and the second communication apparatuses, and the order is based on an order of the User Info fields in the MU-RTS TXS Trigger frame.

12. The first communication apparatus of claim 1 , further comprising a receiver which, in operation, receives a frame indicating a remaining portion of a TXOP from a last communication apparatus of a plurality of communication apparatus, and the transmitter is further configured to transmit a further frame indicating the remaining portion of the TXOP to the AP, or perform a data transmission utilizing the remaining portion of the TXOP.

13. The first communication apparatus of claim 1 , wherein the first communication apparatus returns the time allocated by the AP based on information in announcement information indicated by the AP.

14. The first communication apparatus of claim 1 , wherein the transmitter, which in operation, transmits the frame only to the AP.

15. An access point (AP) comprising:circuitry, which in operation, generates a multi-user request to send transmission opportunity sharing (MU-RTS TXS) Trigger frame indicating time allocated to a first communication apparatus; and a transmitter, which in operation, transmits the MU-RTS TXS Trigger frame to the first communication apparatus.

16. The AP of claim 15, wherein the MU-RTS TXS Trigger frame further indicates a duration for sharing a TXOP with a plurality of communication apparatuses comprising the first communication apparatus and a second communication apparatus; and the AP further comprises a receiver which, in operation, receives, from the first or the second communication apparatus, a frame comprising information indicating a portion of the TXOP that remains after a transmission from at least one of the first communication apparatus and the second communication apparatus using the TXOP.

17. The AP of claim 16, wherein the transmitter is further configured to perform a data transmission using the portion of the TXOP based on whether a signal is detected in a channel for data transmission from the first or second communication apparatus after a period of time.

18. The AP of claim 15, wherein the MU-RTS TXS Trigger frame includes information for the first communication apparatus to return the time.

19. A communication method performed by a first communication apparatus comprising: generating a frame comprising information indicating return of time allocated by an access point (AP); and transmitting the frame to the AP or a second communication apparatus.

20. A communication method performed by an access point (AP) comprising: generating a multi-user request to send transmission opportunity sharing (MU-RTS TXS) Trigger frame indicating time allocated to a first communication apparatus; and transmitting the MU-RTS TXS Trigger frame to the first communication apparatus.

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