Apparatus and method for downlink and uplink multi-user transmissions

Description

TECHNICAL FIELD

[0001] The present description relates in general to wireless communication systems and methods, and more particularly to devices and methods for multi-user transmission of response frames.BACKGROUND

[0002] Wireless local area network (WLAN) devices are deployed in diverse environments. These environments are generally characterized by the existence of access points and non-access point stations. In some systems, stations may utilize multi-user (MU) transmissions to more efficiently communicate data. In particular, an access point may transmit a single downlink (DL) Orthogonal Frequency Division Multiple Access (OFDMA) frame that assigns particular resource units (RUs) to separate stations in the wireless system. Each RU may include data and / or control information that is intended for a single station or a set of stations.

[0003] Although described in relation to OFDMA, MU transmissions may be implemented through the use of Multiple-Input and Multiple-Output (MIMO) techniques. MU-MIMO techniques utilize multiple transmit and receive antennas to exploit multipath propagation. MIMO may be used separately or jointly with OFDMA to transmit data and control information in both the downlink and uplink directions.

[0004] US 2010 / 310003 A1 relates to clustering of signaling within wireless communication systems. US 2014 / 307612 A1 relates to a system for backwards-compatible preamble formats for multiple access wireless communication.SUMMARY

[0005] The invention provides a method for transmitting a response frame in a wireless network and a wireless device for transmitting a response frame in a wireless network as recited in the independent claims. Advantageous embodiments are set out in the dependent claims.

[0006] A method helpful for understanding the invention, implemented by a network device in a wireless network, for coordinating an uplink multi-user response transmission to a downlink multi-user transmission is described herein. The method may comprise: generating, by the network device, a downlink multi-user frame addressed to a plurality of stations operating in the wireless network, the downlink multi-user frame including a plurality of resource units that are each assigned to a station in the plurality of stations, wherein generating the downlink multi-user frame comprises: including a set of MAC Protocol Data Units (MPDUs) in each resource unit of the plurality of resource units, wherein one or more MPDUs in each of the resource units in the downlink multi-user frame includes acknowledgement information for indicating properties of a multi-user acknowledgement transmission transmitted by each respective station in the plurality of stations to acknowledge the downlink multi-user frame; and transmitting the downlink multi-user frame to the plurality of stations over a wireless channel.

[0007] In one example, generating the downlink multi-user frame further comprises: including the acknowledgement information, for indicating properties of the multi-user acknowledgement transmission transmitted by each respective station in the plurality of stations to acknowledge the downlink multi-user frame, in a header of the one or more MPDUs. In one embodiment, the header is a MAC header of the one or more MPDUs.

[0008] In one example, one of the one or more MPDUs in each of the resource units in the downlink multi-user frame is a unicast trigger frame that contains the acknowledgement information for the respective station in the plurality of stations. In one embodiment, the trigger frame instigates each respective station in the plurality of stations to transmit the multi-user acknowledgement transmission after an interframe spacing period following receipt of the downlink multi-user frame.

[0009] In one example, the method further comprises: generating, by the network device, a multi-user block acknowledgement request frame to solicit acknowledgements from two or more stations of the plurality of stations; and transmitting the multi-user block acknowledgment request frame following transmission of the downlink multi-user frame.

[0010] In one example, the acknowledgement information includes one or more of: (1) whether the acknowledgement transmission is multi-user or single user, (2) whether the acknowledgment transmission is immediate or non-immediate, and (3) resource scheduling information for the multi-user acknowledgement transmission.

[0011] A method helpful for understanding the invention, implemented by a first station in a wireless network, for transmitting an uplink acknowledgment is also described here. The method comprises: receiving a downlink multi-user frame addressed to a plurality of stations, including the first station, and received from an access point in the wireless network; processing a first MAC Protocol Data Units (MPDU) in the downlink multi-user frame to determine acknowledgement information for indicating properties of a first multi-user acknowledgement frame to acknowledge the downlink multi-user frame by two or more stations; generating the first multi-user acknowledgment frame based on the acknowledgement information; and transmitting the first multi-user acknowledgement frame to the access point based on the acknowledgement information.

[0012] In one example, the first MPDU is located in a first resource unit of the downlink multi-user frame allocated to the first station, wherein the downlink multi-user frame includes a second resource unit that contains a second MPDU with acknowledgement information for a second station to transmit a second multi-user acknowledgement frame. In one embodiment, the first multi-user acknowledgement frame and the second multi-user acknowledgement frame together form a multi-user acknowledgement frame for acknowledging the downlink multi-user frame.

[0013] In one example, processing the first MPDU comprises: extracting the acknowledgement information, for indicating properties of the first multi-user acknowledgement frame, in a header of the first MPDU. In one embodiment, the header is a MAC header of the first MPDU.

[0014] In one example, processing the MPDU comprises: extracting the acknowledgement information, for indicating properties of the first multi-user acknowledgement frame transmission, from a payload of the first MPDU, wherein the first MPDU is a unicast trigger frame. In one embodiment, the method further comprises: processing a second MPDU in a same resource unit as the first MPDU, wherein the second MPDU includes data intended for the first station. In one embodiment, the trigger frame instigates the first station to transmit the first multi-user acknowledgement after an interframe spacing period following receipt of the downlink multi-user frame.

[0015] In one example, the method further comprises: receiving a multi-user block acknowledgement request frame that solicits acknowledgements from two or more stations, wherein the first multi-user acknowledgement frame is transmitted after receipt of and in response to the multi-user block acknowledgement request frame.

[0016] In one example, the acknowledgement information includes one or more of: (1) whether the first multi-user acknowledgement frame is part of multi-user or single user transmission, (2) whether the first multi-user acknowledgement frame is transmitted immediately following receipt of the downlink multi-user frame or upon receipt of a multi-user block acknowledgement request frame, and (3) resource scheduling information for an uplink multi-user acknowledgement transmission.

[0017] A method helpful for understanding the invention, implemented by a first station in a wireless network, for transmitting an uplink acknowledgment is described herein. In one embodiment, the method comprises: receiving a downlink multi-user frame addressed to a plurality of stations, including the first station, wherein the downlink multi-user frame is received from an access point in the wireless network; receiving a multi-user block acknowledgement request frame that solicits acknowledgements from two or more stations, wherein the multi-user block acknowledgement request frame includes acknowledgement information for indicating properties of a first multi-user acknowledgement frame that acknowledges receipt of the downlink multi-user frame by the first station; generating the first multi-user acknowledgment frame based on the acknowledgement information; and transmitting the first multi-user acknowledgement frame to the access point based on the acknowledgement information.

[0018] In one example, the acknowledgement information includes one or more of: (1) whether the first multi-user acknowledgement frame is part of a multi-user or single user transmission and (2) resource scheduling information for the first multi-user acknowledgement transmission. In one embodiment, the acknowledgment scheduling information includes properties of a second multi-user acknowledgement frame generated and transmitted by a second station, wherein the first multi-user acknowledgement frame and the second multi-user acknowledgement together form a multi-user transmission.DETAILED DESCRIPTION

[0019] The detailed description set forth below is intended as a description of various implementations and is not intended to represent the only implementations in which the subject technology may be practiced. As those skilled in the art would realize, the described implementations may be modified in various different ways, all without departing from the scope of the appended claims. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0020] During the standardization activities of the Institute of Electrical and Electronics Engineers (IEEE) 802.11, multi-user (MU) simultaneous transmission techniques such as Orthogonal Frequency Division Multiple Access (OFDMA) and Multi-User Multiple Input Multiple Output (MU-MIMO) are considered to improve network efficiency. For example, Figure 1A depicts an MU transmission that solicits an immediate acknowledgement from a station while Figure 1B depicts an MU transmission that does not solicit an immediate response from any of the participating / target stations.

[0021] In particular, as shown in Figure 1A , an access point (AP) transmits a downlink (DL) MU physical layer convergence procedure (PLCP) protocol data unit (PPDU) to a set of stations (STAs) (i.e., addressed, target, or receiving STAs) on a shared wireless channel. The PPDU may identify a particular STA in the set of addressed STAs to send back an immediate acknowledgement on the shared wireless channel or a portion of the shared wireless channel (i.e., an implicit block acknowledgment request (BAR)). As used herein, an "immediate" response or acknowledgement refers to a transmission that is the next transmission on the shared wireless channel or a portion of the shared wireless channel after the DL PPDU. Accordingly, the immediate acknowledgment / response and the preceding transmission may be separated by a period during which no activity / transmission is occurring on the shared channel or a designated portion of the shared channel. For examples, as shown in Figure 1A , the period between the DL PPDU / frame and the immediate acknowledgment may be a short interframe space (SIFS) period. However, in other embodiments, other IFS periods may be used. After receiving the acknowledgement frame from the specific STA for which an immediate response was requested, the AP polls acknowledgement frames from every other STA that the AP has sent the DL MU PPDU using a set of BAR frames (i.e., explicit BARs). Response to each corresponding BAR In one or more implementations, a guard interval is a cyclic prefix (CP), and a guard interval duration is a CP length. In one or more aspects, the term duration may be referred to as a length. In one aspect, no guard interval is used for symbols in the L-STF field and / or HE-STF field. Each guard interval may be associated with a symbol and may be present between symbols (or between consecutive symbols). In some aspects, each OFDM symbol is preceded (or followed) by a guard interval. In some aspects, the OFDM symbol may be referred to as including the guard interval that precedes (or follows) the OFDM symbol.

[0022] In one or more implementations of a transmitter, a GI inserter 385 illustrated in Figure 4A may prepend a guard interval to an OFDM symbol. For a receiver, a GI remover 391 of Figure 4B may remove the prepended guard interval.

[0023] Turning now to Figure 5A, a method 500 will be described for coordinating UL MU acknowledgement / response transmissions to a DL MU transmission according to one example. As will explained in further detail below, the proposed method 500 facilitates UL MU acknowledgement / response transmissions for more advanced STAs (e.g., HE STAs), which support UL MU capabilities (e.g., UL OFDMA or UL MU-MIMO), while still being backwards compatible with legacy devices (e.g., High Throughput (HT) STAs, Very High Throughput (VHT) STAs, or other devices that do not support UL MU transmissions).

[0024] The method 500 may be performed by one or more devices in the network 200. For example, one or more operations or sub-operations of the method 500 may be performed by the device 211, which is operating as an AP in the network 200, and / or the device 212-215. In particular, in the method 500 the AP 211 may be in communication with two or more of the device 212-215, which operate as separate STAs in the network 200. In this configuration, the AP 211 and the STAs 212-215 may jointly performed the method 500 to efficiently acknowledge receipt of a DL MU PPDU / frame.

[0025] Each operation of the method 500 will be described by way of example below in relation to the transmission diagram shown in Figure 5B. Although one or more operations or sub-operations are described or shown in a particular sequential order, in other examples the operations / sub-operations may be rearranged in a different order, which may include performance of multiple operations / sub-operations in at least partially overlapping time periods.

[0026] The method 500 may commence at operation 501 with the generation of a DL MU PPDU / frame by an AP. The DL MU frame may be addressed to a set of target STAs operating in a network. For example, as shown in Figure 5B , the DL MU frame may be addressed to STA1, STA2, and STA3. In this example, STA1 and STA2 are non-legacy devices that support UL MU transmissions and STA3 is a legacy device that does not support UL MU transmissions. For example, STA1 and STA2 may be HE devices (i.e., devices that operate according to the IEEE 802.11ax standard, which is currently in development) and STA3 may be a VHT STA (i.e., a device that operates according to the IEEE 802.11ac standard), a HT STA (i.e., a device that operates according to the IEEE 802.11n standard), or another device that operates according to a wireless standard that does not support UL MU transmissions. The generated DL MU frame may be a MU-MIMO frame and / or an OFDMA frame. The generation of the frame at operation 501 may include the sub-operations described below.

[0027] At sub-operation 501A the AP may generate one or more MAC Protocol Data Units (MPDUs) or aggregated-MPDUs (A-MPDUs) for each non-legacy STA. In the example, one or more MPDUs / A-MPDUs may be generated for STA1 and one or more MPDUs / A-MPDUs may be generated for STA2. Each MPDU may include data and / or control frames intended for each respective STA and may be placed in resource units within the DL MU frame assigned / allocated to each respective STA. The resource units may be particular spatial streams or sub-channels of a wireless channel upon which the DL MU frame will be transmitted.

[0028] In one example, one or more MPDUs may include acknowledgement information that is used for indicating to respective STAs a scheme / technique used to transmit acknowledgement messages to the AP. In one example, generation of one or more MPDUs addressed to each STA may include setting an acknowledgement policy subfield (ACK policy subfield) in a header of the one or more MPDUs (i.e., a MAC header) such that STA1 and STA2 can identify which technique / scheme is to be used by each non-legacy STA for acknowledging successful receipt of the MPDUs by each respective STA. In one example, the ACK policy subfield is two bits and is located in the Quality of Service (QoS) Control Field of the MAC header. However, in other embodiments, the ACK policy subfield may be located in different portions of the MAC header and may be of a different length (e.g., 1bit, 3bits, etc.).

[0029] In examples in which the ACK Policy subfield is two bits in length, the interpretation of these two bits may be given by Table 1 below.

[0030] In some examples, when the ACK Policy subfield is set to indicate an immediate acknowledgement, which in Table 1 above corresponds to "Normal Ack or Implicit Block Ack Request" and a bit sequence "00", another subfield (a second subfield or a MU ACK Policy subfield) indicates if the follow-up acknowledgement shall be a single user (SU) acknowledgement or an MU acknowledgement. Therefore, the MU acknowledgement that follows immediately after the DL MU PPDU transmission happens from those STAs for which the ACK Policy subfield is set to an immediate acknowledgement and the MU ACK Policy subfield is set to an MU acknowledgement. For example, both STA1 and STA2 in Figure 5B received MPDUs in which the ACK Policy subfield is set to an immediate acknowledgment (e.g., "00") and the MU ACK Policy subfield is set to "MU acknowledgement". Accordingly, both STA1 and STA2 may participate in an UL MU acknowledgement immediately following the DL MU transmission. Both the DL and UL MU transmissions may be an OFDMA transmission and / or may incorporate MU-MIMO techniques.

[0031] Conversely, those STAs that the ACK Policy subfield is set to immediate acknowledgement and the MU ACK Policy subfield is not set to "MU acknowledgement" and instead is set to "SU acknowledgement", or cannot interpret the MU ACK Policy subfield, will send acknowledgement frames in single user transmission manner as shown in the examples in Figure 1A and Figure 1B. For example, a STA may transmit an acknowledgment or a block acknowledgement in an SU manner immediately after the DL MU transmission or may wait for a BAR frame from the AP before transmitting an acknowledgment or a block acknowledgement in an SU manner.

[0032] In one example, the QoS AP PS Buffer State subfield in the QoS Control field is used as the MU ACK Policy subfield. In particular, in one example, the 8th bit (B8) of the QoS AP PS Buffer State subfield is used as the MU ACK Policy subfield. In one example, if the MU ACK Policy subfield is set to a MU acknowledgement state, there is a second part in the DL MU PPDU that indicates (1) UL MU transmission method / scheme (e.g., MU-MIMO and / or OFDMA) and / or (2) resource allocation information for the MU acknowledgement frame transmission. In another example, if the MU ACK Policy subfield is set to a MU acknowledgement state, resource allocation information regarding the UL MU transmission follows a pre-determined rule set and no explicit indication of the resource allocation information regarding UL MU transmission is included in the DL MU PPDU.

[0033] At sub-operation 501B, the AP may generate MPDUs for legacy STAs (e.g., VHT STAs, HT STAs, or any STA implementing a protocol that does not support UL MU transmissions). Similar to operation 501A for non-legacy STAs, operation 501B may include setting an ACK Policy subfield in a QoS Control Field of a MAC header. In one example, the ACK Policy subfield for legacy STAs may be set to a state that indicates non-immediate acknowledgement, which in Table 1 above corresponds to "Block Ack". In particular, as shown in Figure 5B, when "Block Ack" is selected, the AP may subsequently transmit a BAR frame to trigger STA3 to transmit an acknowledgment or a block acknowledgement in an SU manner. In another example, the ACK Policy subfield for a legacy STA may be set to an immediate acknowledgement. In this example, the ACK Policy subfield for all other scheduled STAs, including STAs that support UL MU transmissions, is to be a non-immediate acknowledgement. For example, STAs that are set to transmit a non-immediate MU acknowledgement will wait for a MU-BAR (i.e., a trigger frame) before transmitting.

[0034] Following generation of the DL MU frame / PPDU at operation 501, the method 500 may move to operation 503. At operation 503 the AP transmits the DL MU frame / PPDU to the addressed / targeted STAs. For example, as shown in Figure 5B, the DL MU PPDU may be transmitted to the non-legacy STA1 and STA2 and the legacy STA3. As noted above, the DL MU PPDU may utilize OFDMA and / or MIMO MU transmission techniques.

[0035] At operation 505 each STA addressed by the DL MU PPDU may receive and attempt to decode the DL MU PPDU. In particular, each targeted STA receives the DL MU PPDU and determines resource units or particular portions of the frame assigned to the STA by examining the preamble portion of the DL MU PPDU / frame. Further, the target STAs may examine decoded MPDUs to determine acknowledgement scheme information / properties / characteristics including (1) whether acknowledgement of the DL MU frame is immediate or non-immediate, (2) whether the acknowledgement is multi-user or single user, and / or (3) scheduling information (e.g., a resource unit within a UL transmission) when a multi-user acknowledgement is selected.

[0036] At operation 507, the STAs that successfully received and decoded the appropriate portions of the DL MU PPDU may acknowledge receipt through the generation and the transmission of acknowledgement frames by each respective STA according to the acknowledgement information extracted from the DL frame. Acknowledgment may be performed after a predetermined period has elapsed since receipt of the DL frame (e.g., a short interframe space (SIFS) period or another interframe space (IFS) period). As described above, non-legacy STAs may examine the ACK policy subfield and the MU ACK policy subfield in the corresponding MPDU to determine the acknowledgement scheme the STA should use. For example, as shown in Figure 5B and described above, ACK policy and the MU ACK policy subfields for STA1 and STA2 indicate that these devices are to participate in an immediate MU acknowledgement while STA3 is to perform a non-immediate (i.e., triggered by a BAR frame) SU acknowledgement. On this basis, STA1 and STA2 may participate in the transmission of a MU acknowledgement while STA3 may await a BAR frame before transmitting a SU acknowledgement. The UL MU transmission may be an OFDMA transmission and / or may incorporate MU-MIMO techniques.

[0037] As described above, the method 500 allows non-legacy devices to acknowledge receipt of a DL PPDU in an efficient manner through the use of UL MU techniques while remaining backwards compatible with legacy devices.

[0038] Turning now to Figure 6A, a method 600 will be described for coordinating UL MU acknowledgement / response transmissions to a DL MU transmission according to another example. As will explained in further detail below, the proposed method 600 facilitates UL MU acknowledgement / response transmissions for more advanced STAs (e.g., HE STAs), which support UL MU capabilities (e.g., UL OFDMA or UL MU-MIMO).

[0039] Similar to the method 500, the method 600 may be performed by one or more devices in the network 200. For example, one or more operations or sub-operations of the method 600 may be performed by the device 211, which is operating as an AP in the network 200, and / or the devices 212-215, which are operating as STAs in the network 200.

[0040] Each operation of the method 600 will be described by way of example below in relation to the transmission diagram shown in Figure 6B. Although one or more operations or sub-operations are described or shown in a particular sequential order, in other examples the operations / sub-operations may be rearranged in a different order, which may include performance of multiple operations in at least partially overlapping time periods.

[0041] The method 600 may commence at operation 601 with the generation of a DL MU frame by an AP. The DL MU frame may be addressed to a set of STAs operating in a network. For example, as shown in Figure 6B, the DL MU frame may be addressed to STA1 and STA2. In this example, the AP schedules STA1 and STA2 for a DL OFDMA transmission, wherein STA1 is allocated a lower half of the transmission bandwidth and STA2 is allocated an upper half of the transmission bandwidth. In this example, STA1 and STA2 are HE STAs or other devices that support UL MU transmissions. Although shown as an OFDMA frame / PPDU, the generated DL MU frame may be a MU-MIMO frame / PPDU. The generation of the frame at operation 601 may include the sub-operations described below.

[0042] At sub-operation 601A, the AP may generate a data MPDU for each STA participating in the DL MU transmission. For example, as shown in Figure 6B, the DL MU PPDU / frame may include a data MPDU for STA1 and a data MPDU for STA2. The data MPDU may include any type of data (e.g., voice, video, best effort, background, or control data) that is specifically intended for the particular STA and may be placed in resource units within the DL MU frame assigned / allocated to each respective STA. The resource units may be particular spatial streams or sub-channels of a wireless channel upon which the DL MU frame will be transmitted. In one example, the generation of the data MPDU at sub-operation 601A may include setting acknowledgment information in a header of the MPDU (e.g., the MAC header of the data MPDU). The acknowledgment information may describe / indicate properties of an acknowledgement technique / scheme used by the corresponding STA to acknowledge receipt of the MPDU. For example, the acknowledgment information may include an ACK Policy subfield and / or a MU ACK Policy subfield. As noted above in relation to the method 500, the ACK Policy subfield may indicate whether the acknowledgement is immediate or non-immediate (e.g., corresponding to values represented in Table 1) and the MU ACK Policy subfield may indicate whether the acknowledgment is MU or SU. In some embodiments, the MU ACK Policy subfield is optional in the data MPDU.

[0043] At sub-operation 601B, the AP may generate an ACK Info MPDU for each STA participating in the DL MU transmission that includes additional acknowledgement information. For example, the DL MU PPDU / frame may include an ACK Info MPDU for STA1 and an ACK Info MPDU for STA2 as both of these stations are participating in the UL MU acknowledgment transmission. The ACK Info MPDU further describes / indicates acknowledgement technique / scheme and other information / properties / characteristics (in addition to the acknowledgment information in the data MPDU) needed for each respective STA to acknowledge successful receipt of the DL MU transmission. For example, each ACK Info MPDU may indicate whether the acknowledgement is (1) immediate or non-immediate, (2) multi-user or single user, and / or (3) scheduling information (e.g., a resource unit within a UL transmission) when a multi-user acknowledgement is selected as shown in Figure 6B. For instance, in some examples the ACK Info MPDU may only be present when the MU ACK Info subfield of the corresponding data MPDU is set to indicate a MU UL acknowledgment. In another example, the data MPDU does not include acknowledgment information and all acknowledgment information is included in the ACK Info MPDU. In still another example, the data MPDU includes an ACK Policy subfield and this subfield is interpreted by STAs to indicate immediate / non-immediate and MU / SU acknowledgment. In this example, the ACK Info MPDU includes scheduling / trigger information when an MU acknowledgment is scheduled. As legacy STAs cannot participate in UL MU transmissions, legacy STAs will be assigned SU acknowledgements, while non-legacy STAs (i.e., STAs that support UL MU transmissions) can be assigned MU acknowledgements.

[0044] In one example, the scheduling information for the UL MU acknowledgement frame transmission includes common information and a per-STA information. The common information is information that is the same for every STA in the UL MU acknowledgement frame transmission and the per-STA information is specific resource allocation for each STA. Thus, different STAs scheduled in the same DL MU PPDU have different per-STA information while each STA has the same common information.

[0045] In some examples, the data MPDU and ACK Info MPDU for each STA may be aggregated into an A-MPDU at operation 601C. Accordingly, the DL MU transmission includes a single A-MPDU for each STA that includes both data and acknowledgement scheduling information. In some examples, the ACK Info MPDU is the first MPDU in each A-MPDU while in other embodiments ACK Info MPDU is in another position in each A-MPDU, such as the last MPDU in each A-MPDU.

[0046] Although described and shown as including a single data MPDU, in other examples, each A-MPDU may include one or more data MPDUs. Further, in some examples, each STA may receive multiple A-MPDUs in a single DL MU frame / PPDU.

[0047] Following generation of the DL MU frame / PPDU at operation 601, the method 600 may move to operation 603. At operation 603, the AP transmits the DL MU frame / PPDU to the addressed / target STAs. For example, as shown in Figure 6B , the DL MU PPDU may be sent to the non-legacy STA1 and STA2. As noted above, the DL MU PPDU may utilize OFDMA and / or MIMO MU transmission techniques.

[0048] At operation 605, each STA addressed by the DL MU PPDU may receive and attempt to decode the DL MU PPDU. In particular, each targeted STA receives the DL MU PPDU and checks the preamble portion of the frame. In some examples, the preamble portion of the frame indicates the allocated resource for each target receiver in the MU transmission. Each STA1 and STA2, including (1) whether acknowledgement of the DL MU frame is immediate or non-immediate, (2) whether the acknowledgement is multi-user or single user, and / or (3) scheduling information (e.g., a resource unit within a UL transmission) when a multi-user acknowledgement is selected. In contrast, the unicast transmission directed to STA1 is data specifically intended for this device. In some embodiments, the broadcast / multicast frame may include scheduling / trigger information for coordinating the UL MU acknowledgment transmission while one or more data MPDUs addressed to each STA may include indications of whether the acknowledgment transmission is immediate / non-immediate and / or MU / SU.

[0049] At operation 807, the STAs that successfully received and decoded the appropriate portions of the DL MU PPDU may acknowledge receipt through the generation and the transmission of acknowledgement frames by each respective STA according to the acknowledgement information extracted from the DL frame. Acknowledgment may be performed after a predetermined period has elapsed since receipt of the DL frame (e.g., a short interframe space (SIFS) period or another interframe space (IFS) period). In one example shown in Figure 8B , STA1 and STA2 may participate in an UL MU acknowledgement based on scheduling information included in a multicast / broadcast MPDU. As shown, STA1 is allocated the lower half of an UL OFDMA frame while STA2 is allocated the upper half of the UL OFDMA frame to carry an acknowledgement (e.g., a BA / ACK).

[0050] As described in methods 500, 600, 700, and 800, each target STA of a DL MU transmission may transmit an acknowledgement according to one or more schemes / techniques. In some examples, the acknowledgement schemes / techniques may involve a delayed acknowledgement. In these situations, the AP may transmit a trigger frame to trigger the STAs participating in the delayed acknowledgement to transmit a respective portion of the acknowledgement frame. For example, Figure 9 show one example of this procedure.

[0051] As shown in Figure 9, an access point transmits a DL MU frame to a set of target STAs (e.g., STA1, STA2, STA3, and STA4). The DL MU frame may indicate that a non-immediate acknowledgement is to be transmitted by one or more of the target STAs. As shown in Figure 9, the ACK policy subfield for each target STA is set to "11", which indicates that each STA is to participate in a non-immediate (i.e., block) acknowledgement.

[0052] The participating STAs may wait for a BAR or a MU BAR frame (hereinafter to be described in relation to MU BAR for simplicity). The MU BAR frame may be a trigger frame that includes trigger information and per-STA BAR control and bitmap information. Upon receipt of the MU BAR, each STA retrieves corresponding scheduling information from the MU BAR frame. The BAR frame may be implemented using various schemes and techniques. For example, a single MU BAR frame may be constructed and transmitted by the AP, wherein the MU BAR frame comprises BAR information for each scheduled STA and UL BA transmission scheduling information for each scheduled STA. In another example embodiment, an AP sends an A-MPDU to each scheduled STA in the DL MU transmission and the A-MPDU comprises BAR information and UL BA transmission scheduling information. In another embodiment, an AP sends the following frames in a DL MU transmission: 1) one BAR frame to each STA and 2) one broadcast / multicast frame for UL MU BA transmission. Based on the scheduling information, each STA participates in the MU acknowledgement a predetermined period following receipt of the MU BAR (e.g., a SIFS period).

[0053] In some examples, either a SU or MU immediate acknowledgement may be scheduled by the DL MU frame and may be transmitted prior to the MU BAR and consequential MU delayed acknowledgement. In some examples, multiple delayed SU or MU acknowledgements may be triggered for one DL MU frame and different sets of STAs. For example, a DL MU frame may be addressed to a first set of STAs and a second set of STAs. The AP may transmit a first BAR to trigger an acknowledgment transmission from the first set of STAs and a second BAR to trigger an acknowledgement transmission from the second set of STAs.

[0054] Although the methods and techniques above are described and shown separately, in one or more embodiments, these methods and techniques may be combined. In some examples, acknowledgment information for a first STA may be located in the header of a data MPDU while acknowledgment information for a second STA may be located in a separate MPDU. In this example, the acknowledgment information may facilitate / trigger both the first and second STA to participate in the same UL MU transmission or in separate UL SU / MU transmissions.

[0055] Although the methods and techniques above have been described in relation to pure acknowledgment transmissions, in some examples the UL MU acknowledgment transmission may allow data transmission from some STAs. For example, a first set of STAs may transmit a set of acknowledgements while a second set of STAs may transmit data (e.g.,

[0056] According to the invention, if a control response frame is to be transmitted in an UL MU PPDU, the number of spatial streams (or space-time streams) per STA shall be limited to one. Therefore, every STA participating a UL MU transmission in response to a DL MU transmission will send an ACK / BA frame having the same number of HE-LTF symbols regardless of other participating STAs' channel conditions. Since each STA transmits the same number of HE-LTF symbols (e.g., one), the HE-LTF section of the ACK / BA frame can start and end at the same time for all transmission without knowing the transmission conditions for other STAs.

[0057] In some examples, a UL MU transmission may include both acknowledgment frames from a first set of STAs and data frames from a second set of STAs. In this case, the first set of STAs would transmit using a single spatial stream.

[0058] This above concept may be achieved in multiple ways. Some of the possible implementations are described herein; however, embodiments mentioned herein do not limit the applicability of the above concept.

[0059] In one example, if a control response frame is to be transmitted in a UL MU manner, all participating STAs transmit the control response frame at a predetermined time after receiving an eliciting frame (e.g., a SIFS period or another IFS period). Further, the transmission sets the number of HE-LTF symbols to a value corresponding to a single space-time stream. The HE-LTF symbols provide a means for the receiver to estimate the MIMO channel between the set of constellation mapper outputs and the receive chain. Figure 12 shows an example of this embodiment. In this example, an AP transmits data frames to STA1 and STA2 in a DL OFDMA manner, wherein STA1's data is assigned to the upper half of the channel bandwidth and STA2's data is assigned to the lower half of the channel bandwidth. Due to different channel conditions, the AP uses a single stream transmission to STA1 and two stream transmissions (spatial multiplexing) to STA2. To align the transmission time, the AP uses HE-LTF symbols corresponding to a two stream transmission (i.e., the number of HE-LTF symbols is two) for both STA1 and STA2.

[0060] After successfully decoding the DL OFDMA frame, STA1 and STA2 send back acknowledgement (ACK or BA) frames in an OFDMA manner a predetermined time (e.g., SIFS) after receiving the DL OFDMA frame. When STA1 and STA2 construct the acknowledgement frame in an OFDMA manner, the number of HE-LTF symbols is set to a value corresponding to a single space-time stream (i.e., the number of HE-LTF symbols is equal to one). Although a single space-time stream is used herein, in other examples, other numbers of space-time streams may be used (e.g., two space-time streams may be used, which would correspond to two HE-LTF symbols in the UL MU frame)

[0061] In some examples, Space-Time-Block-Coding (STBC) shall be disabled for the acknowledgement frame transmission. For example, STBC may be disabled when the number of space-time streams is equal to one.

[0062] In one example in which the number of HE-LTF symbols in a UL MU transmission is set to a value, a first value is indicated by the transmitter of the eliciting frame as the length of the control response frame and the MCS of the control response frame is set such that the length of the control response frame is not greater than the first value.

[0063] For example, the first value may be included in the eliciting frame. In another example the first value is indicated before sending the eliciting frame (e.g., the first value is included in a first management frame (e.g., a beacon frame, a Probe Response frame, or an Association response frame) sent by the transmitter of the eliciting frame).

[0064] In one example, if a control response frame is to be transmitted in a UL MU manner, an MCS shall be selected from a first set, wherein the MCS defines modulation / coding schemes and the number of space-time streams, wherein the number of space-time streams of the first set is limited to one. In one example, all <VHT-MCS, NSS> tuples defined in the IEEE 802.11ac standard are further eliminated from the first set. In one embodiment, all MCSs that have a data rate greater than the data rate of the eliciting PPDU are further eliminated from the first set. In one embodiment, a transmitter of an eliciting frame for the control response frame further informs information related to the length of the control response frame. All MCSs that result in the encoded control response frame having a length that exceeds the informed length are further eliminated from the first set. In one embodiment, all MCSs that do not meet certain criteria are further eliminated from the first set and if the first set is empty, the MCS shall be selected from a second set.

[0065] In another example, if a control response frame is to be transmitted in a UL MU manner, all participating STAs transmit the control response frame in a predetermined time (e.g., SIFS) after receiving an eliciting frame. In this embodiment, the eliciting frame may indicate that the number of HE-LTF symbols for the control response frame is a second value. In some embodiments, the second value is indicated by the transmitter of the eliciting frame and the HE-LTF symbols provide a means for the receiver to estimate the MIMO channel between the set of constellation mapper outputs and the receive chain. In one embodiment, a first value is indicated by the transmitter of the eliciting frame as the length of the control response frame. The MCS of the control response frame is set such that the length of the control response frame is not greater than the first value. In one embodiment, the first value and / or the second value are included in the eliciting frame. In another embodiment, the first value and / or the second value are indicated before sending the eliciting frame. For example, the first value is included in a first management frame (e.g., a Beacon Frame, a Probe Response frame, or Association Response frame) sent by the transmitter of the eliciting frame.

[0066] In another example, if a control response frame is to be transmitted in a UL MU manner, an MCS shall be selected from a first set, wherein the MCS defines modulation / coding schemes and the number of space-time streams. In this embodiment, the number of space-time streams of the first set is limited to a second value. In one embodiment, information on the second value is included in the eliciting frame. In another embodiment, the second value is indicated before sending the eliciting frame. For example, the second value is included in a first management frame (e.g., a Beacon Frame, a Probe Response frame, or an Association Response frame) sent by the transmitter of the eliciting frame. In one embodiment, all <VHT-MCS, NSS> tuples defined in the IEEE 802.11ac standard are further eliminated from the first set. In one embodiment, all MCSs that have a data rate greater than the data rate of the eliciting PPDU are further eliminated from the first set. In one embodiment, a transmitter of an eliciting frame for the control response frame further informs information related to the length of the control response frame, and all MCSs that the length of the encoded control response frame exceeds the informed length of the control response frame are further eliminated from the first set. In one embodiment, upon determining that the highest number of spatial streams (or space-time streams) value of the MCS in the first set is less than or equal to a third number of spatial streams (or space-time streams) value of the received frame, eliminating all MCSs from the first set that have the number of spatial streams (or space-time streams) value that is not equal to the third number of streams. In one embodiment, all MCSs that do not meet certain criteria are further eliminated from the first set and if the first set is empty, the MCS shall be selected from a second set.

[0067] Nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

[0068] In the detailed description, it can be seen that the description provides illustrative examples and the various features are grouped together in various implementations for the purpose of streamlining the disclosure. The method of disclosure is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed configuration or operation.

Claims

1. A method for transmitting a response frame in a wireless network (200), the method comprising: receiving, by a wireless device, a downlink, DL, multi-user, MU, frame from an access point, wherein the DL MU frame is addressed to a plurality of stations (212-215) in the wireless network (200), including the wireless device, wherein a respective number of spatial streams is assigned to each station (212-215) of the plurality of stations (212-215), and wherein the wireless device receives no trigger frame from the access point, such that the wireless device has no information regarding the number of spatial streams assigned to other stations of the plurality of stations (212-215), wherein a trigger frame is a separate frame to be sent to the plurality of stations (212-215) in a broadcast or multicast manner to cause the plurality of stations (212-215) to participate in an UL MU acknowledgement; generating, by the wireless device, an uplink, UL, MU response frame responsive to the DL MU frame, wherein the UL MU response frame is an acknowledgement frame and includes only a single high efficiency long training field, HE-LTF, that consists of a single orthogonal frequency-division multiplexing, OFDM, symbol, regardless of the respective number of spatial streams assigned to each station (212-215) of the plurality of stations (212-215), in order to align HE-LTF transmission with the other stations of the plurality of stations (212-215); and transmitting, by the wireless device to the access point, the UL MU response frame, using a single spatial stream.

2. The method of claim 1, further comprising the step of identifying, by the wireless device, scheduling information in the DL MU frame, the scheduling information soliciting the UL MU response frame from the wireless device, wherein the wireless device generates the UL MU response frame based on the scheduling information, in response to the scheduling information being located in a Media Access Control, MAC, header in the DL MU frame.

3. The method of claim 2, wherein the UL MU response frame is transmitted using a single spatial stream in response to the scheduling information being located in the MAC header in the DL MU frame.

4. The method of claim 3, wherein the UL MU response frame is part of a MU frame, and wherein the scheduling information includes assignment of resource units in the DL MU frame to the plurality of stations (212-215).

5. The method of claim 3, wherein the scheduling information provides an implicit indication for the wireless device to generate the UL MU response frame with the single HE-LTF consisting of the single OFDM symbol and to transmit the UL MU response frame using a single spatial stream.

6. The method of claim 1, wherein generating the UL MU response frame includes providing an acknowledgement, ACK, or a block acknowledgement, BA, in the UL MU response frame.

7. The method of claim 6, wherein the ACK or BA in the UL MU response frame indicates successful receipt of a media access control, MAC, Protocol Data Unit, MPDU, within the DL MU frame and the MAC header is within the MPDU.

8. The method of claim 1, wherein the UL MU response frame is transmitted with space-time block coding disabled in response to the scheduling information being located in the MAC header in the DL MU frame.

9. A wireless device (300) for transmitting a response frame in a wireless network (200), the wireless device comprising: one or more memories (340); and one or more processors (310) coupled to the one or more memories (340), the one or more processors (310) being configured to: process a downlink, DL, multi-user, MU, frame received from an access point, wherein the DL MU frame is addressed to a plurality of stations (212-215) in the wireless network (200), including the wireless device, wherein a respective number of spatial streams is assigned to each station (212-215) of the plurality of stations (212-215), and wherein the wireless device receives no trigger frame from the access point, such that the wireless device has no information regarding the number of spatial streams assigned to other stations of the plurality of stations (212-215), wherein a trigger frame is a separate frame to be sent to the plurality of stations (212-215) in a broadcast or multicast manner to cause the plurality of stations (212-215) to participate in an UL MU acknowledgement; generate an uplink, UL, MU response frame to the DL MU frame, wherein the UL MU response frame is an acknowledgement frame and includes only a single High Efficiency Long Training Field, HE-LTF, consisting of a single orthogonal frequency-division multiplexing, OFDM, symbol, regardless of the respective number of spatial streams assigned to each station (212-215) of the plurality of stations (212-215), in order to align HE-LTF transmission with the other stations of the plurality of stations (212-215); and transmit, to the access point, the UL MU response frame using a single spatial stream.

10. The wireless device of claim 9, wherein the one or more processors are further configured to identify scheduling information in the DL MU frame, the scheduling information soliciting the UL MU response frame from the wireless device, and to generate the UL MU response frame based on the scheduling information, in response to the scheduling information being located in a Media Access Control, MAC, header in the DL MU frame.

11. The wireless device of claim 10, wherein the one or more processors are further configured to transmit the UL MU response frame using a single spatial stream in response to the scheduling information being located in the MAC header in the DL MU frame.

12. The wireless device of claim 10, wherein the scheduling information includes assignment of resource units in the DL MU frame to the plurality of stations (212-215).

13. The wireless device of claim 10, wherein the scheduling information provides an implicit indication for the wireless device to generate the UL MU response frame with the single HE-LTF consisting of the single OFDM symbol and to transmit the UL MU response frame using a single spatial stream.

14. The wireless device of claim 9, wherein generating the UL MU response frame includes providing an acknowledgement, ACK, or a block acknowledgement, BA, in the UL MU response frame.

15. The wireless device of claim 14, wherein the ACK or BA in the UL MU response frame indicates successful receipt of a media access control, MAC, Protocol Data Unit, MPDU within the DL MU frame and the MAC header is within the MPDU.

16. The wireless device of claim 10, wherein the UL MU response frame is transmitted with space-time block coding disabled in response to the scheduling information being located in the MAC header in the DL MU frame.