Transmission device, receiving device and corresponding methods

Abstract

Transmission device comprising circuitry configured to set up a bidirectional link with a receiving device for transmission and reception of data units, transmit data units stored in a transmission queue for transmission using the bidirectional link to the receiving device; and delete a transmitted data unit from the transmission queue immediately after its transmission or if no response is received from the receiving device instructing the transmission device to retransmit said data unit.

Description

TRANSMISSION DEVICE, RECEIVING DEVICE AND CORRESPONDING METHODSBACKGROUNDFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to a transmission device, a receiving device and corresponding methods, in particular for the exchange of data units using a bidirectional link.DESCRIPTION OF RELATED ART

[0002] A bidirectional link is defined as a link between two communication devices (e.g. two stations (STAs) or an access point (AP) and a STA), generally herein referred to as transmission device and receiving device, that can be used in both directions by theapplication layer, i.e., user data units are bidirectionally conveyed / exchanged. An automatic repeat request (ARQ) mechanism used in current WLAN implementations provides that an erroneously received or erroneously decoded data unit shall be retransmitted, which may lead to a misalignment of downlink and uplink data units. For example, an uplink data unit that relates to a previously received downlink data unit may be retransmitted at a later point in time. This may lead to successful delivery of the uplink data unit but may create a misalignment between downlink and uplink data units or data streams.

[0003] The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.SUMMARY

[0004] It is an object to provide a transmission device, a receiving device and corresponding methods that contribute to or achieve avoiding or reducing misalignments between downlink and uplink data units or data streams within a bidirectional link. It is a further object to provide a corresponding method as well as a corresponding computer program and a non-transitory computer-readable recording medium that stores therein a computer program product for implementing said method.

[0005] According to an aspect there is provided a transmission device comprising circuitry configured to set up a bidirectional link with a receiving device for transmission and reception of data units; transmit data units stored in a transmission queue for transmission using the bidirectional link to the receiving device; and delete a transmitted data unit from the transmission queue immediately after its transmission or if no response is received from the receiving device instructing the transmission device to retransmit said data unit.

[0006] According to a further aspect there is provided a receiving device comprising circuitry configured to: set up a bidirectional link with a transmission device for transmission and reception of data units; receive data units from the transmission device using the bidirectional link; and provide the received data units to higher layer processing regardless of their reception state, according to which a data unit is received and decoded correctly or erroneously, wherein a reception state indicator indicating the reception state is provided to higher layer processing along with each data unit.

[0007] According to still further aspects corresponding methods, a computer program comprising program means for causing a computer to carry out the steps of the method disclosed herein, when said computer program is carried out on a computer, as well as a non- transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed are provided.

[0008] Embodiments are defined in the dependent claims. It shall be understood that the disclosed methods, the disclosed computer program and the disclosed computer-readable recording medium have similar and / or identical further embodiments as the claimed devices and as defined in the dependent claims and / or disclosed herein.

[0009] One of the aspects of the disclosure is to provide an enhanced ARQ operation which minimizes the delay and misalignment between data units (also called bidirectional traffic) conveyed in each direction of the bidirectional link comprising a forward link (from the transmission device to the receiving device) and a reverse link (from the receiving device to the transmission device). The transmission device generally discards all data units after transmission. A data unit is only retransmitted if explicitly instructed by the receiving device, i.e. , not all erroneously received or decoded data units will be retransmitted. The receiving device forwards all data units to higher layer regardless of the reception state (i.e., even if the reception state is “erroneous”) which is or should be indicated separately to the higher layer.

[0010] The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWING

[0011] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a schematic diagram illustrating a system setup and different options to achieve a bidirectional link.Fig. 2 shows a diagram of a conventional communication scheme that illustrates a misalignment between data units.Fig. 3 shows a diagram of the conventional communication scheme shown in Fig. 2 including an additional retransmission.Fig. 4 shows a diagram of an embodiment of a communication scheme according to the present disclosure.Fig. 5 shows a schematic diagram of the general architecture of a communication device according to the present disclosure.Fig. 6 shows a diagram comparing the conventional communication scheme with another embodiment of a communication scheme according to the present disclosure.Fig. 7 shows a diagram how a transmitter may detect a non-existing bidirectional link.Fig. 8 shows a diagram of a state machine illustrating the processing of the receiving device.Fig. 9 shows a diagram of another embodiment of a communication scheme according to the present disclosure.Fig. 10 shows a diagram of another embodiment of a communication scheme according to the present disclosure.Fig. 11 shows a flowchart of an embodiment of a transmission method according to the present disclosure.Fig. 12 shows a flowchart of an embodiment of a receiving method according to the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows a schematic diagram illustrating the system setup and different options to achieve a bidirectional link. Such a bidirectional link exists e.g. in interactive scenarios such as virtual reality applications in which downlink is video rendered according to motion information in uplink. Between the two communication devices shown in Fig. 1 that are generally both able to transmit and receive, but are herein also called transmission device STA 1 and receiving device STA 2, a bidirectional link exists that can be used in both directions by the application layer to exchange user data units bidirectionally. Such a link may be setup by different technological means, for example (as shown in Fig. 1):Time-division duplexing (TDD), in which communication from a first communication device to a second communication device (downlink) is alternating with communi-cation from the second communication device to the first communication device (uplink). In TDD a bidirectional communication is resembled by time interlaced unidirectional communications.Frequency-division duplexing (FDD), in which a downlink link and uplink link reside on different frequency bands. In FDD a simultaneous bidirectional communication may be achieved, i.e., downlink and uplink may exist at same time.In-band full duplex (IBFD), which is like FDD but with at least partially overlapping frequency bands.

[0013] In Fig. 1 , the data units (Dlls) that are transmitted by the first communication device STA 1 are indicated without prime, whereas the Dlls that are transmitted by the second communication device STA 2 are denoted with prime (’). The Block Acknowledgement (BAck) has a prime when it is a response to Dlls with a prime; hence, BAck’ is transmitted by STA 1 in response to Dll’ transmitted by STA 2.

[0014] In the following, the period in which a bidirectional data transfer happens is referred to as a bidirectional transmit opportunity (TXOP). The figures shown in the following consider the latter two options, FDD and IBFD, i.e., cases in which a bidirectional link exists simultaneously. However, the same problems and solution exist for the TDD case, i.e., the present disclosure is not limited to the use of FDD and IBFD.

[0015] In a link in which the application layer can exchange data units bidirectionally, often the traffic streams for downlink and uplink originating from the application layer relate to each other in the sense that an uplink data unit can be considered as a response to previous downlink data unit and vice versa. For example, the well-known TCP / IP protocol creates occasionally an uplink data unit that acknowledges previous downlink data units.

[0016] In this regard, the ARQ mechanism of the current WLAN implementation should be revised, because retransmissions of data units may lead to a misalignment of downlink and uplink data units. For example, an uplink data unit that relates to a previously received downlink data unit is retransmitted at a later point in time. This retransmission may lead to successful delivery of the uplink data unit; however, it creates a misalignmentbetween downlink and uplink data units or data streams. In general, different kinds of misalignment may happen: For example, the order in which data units are transmitted may be different than first-in first-out (FIFO) and / or a certain time dependency between downlink and uplink data units may exist such that a buffering of received data units may cause an unacceptable delay within the application layer. Further, since the ARQ mechanism tries to preserve the order of data units, not only the retransmitted data unit but also subsequent data units are generally affected.

[0017] Fig. 2 shows a diagram of operation of a conventional communication scheme that illustrates a misalignment between data units. The first row shows the content of the receive buffer of a receiving device (STA 2), the second row shows a higher layer output of the receiving device, and the third row shows the content of the receive buffer of a transmission device (STA 1). As shown in Fig. 2, the data unit (DU) #3 is erroneously received by STA 2, which causes the successfully received DUs #4 and #5 to be stored by STA 2 for later forwarding to higher layer. However, the data units that arrive at STA 1 (DU’) continue to be correctly received which causes the (exemplary) relation / alignment between the data units DU and DU’ to be broken. The receiving device STA 2 may check if a data unit is erroneous by e.g. checking a CRC (cyclic redundancy check) code included in a received data unit (e.g. in a PPDU (physical protocol data unit) or an MPDU (MAC protocol data unit)) or any other data included in a data unit for this purpose.

[0018] Fig. 3 shows a diagram of the conventional communication scheme shown in Fig. 2 including an additional retransmission. When the erroneously received data unit (DU #3) was successfully retransmitted (e.g. in response to a corresponding information from the transmission device STA 1 , e.g. in response to a corresponding Ack), this data unit (DU #3) and all subsequent and successfully received data units (DUs #4 and #5) are forwarded to higher layer. This may create a bandwidth issue too, because many data units may be released at the same time to higher layer.

[0019] Fig. 4 shows a diagram of an embodiment of a communication scheme according to the present disclosure. According to the present disclosure a receiver unit of any communication device participating in a bidirectional TXOP shall generally forward (rather than discard) a received data unit to higher layer although it may be erroneous. For improvederror resilience, the communication device may indicate as part of a separate signaling or via station management entity (SME) that the currently forwarded data unit is erroneous or which of the forwarded data units are erroneous.

[0020] As shown in Fig. 4, the erroneously received DU #3 is forwarded to higher layer. In addition, an indicator (herein also called “reception state indicator”) is provided to the higher layer, as shown in the last row of Fig. 4, indicating if a forwarded DU is correct (indicator “correct” in this example) or erroneous (indicator “wrong” in this example). As shown in Fig. 4, the exemplary relation is only broken for the erroneous data unit (DU #3) but not for the other data units, in contrast to the conventional communication scheme shown in Figs. 2 and 3. The operation of the higher layers shall, however, be resilient to such errors. For example, the higher layer may consider the lost packet as less important (e.g. in video transfer - important l-frame vs. less important P-frame), or the higher layer protocol may include an erasure correction code which can reconstruct the erroneous data unit. In general, the proposed communication scheme is particularly suitable for realtime, fast-response applications that need a stringent latency bound, but tolerate some errors such as VR / AR, video telephony, and machine control.

[0021] A bidirectional connection often features response frames, such as acknowledgements (e.g. Back frames shown in Fig. 1), to be transmitted. Such response frames are created by the MAC and need often to be transmitted on each link for regulatory reasons (detection of overlapping transmissions) and channel access retention. The content of acknowledging response frames transmitted as a response to one or more received data frames conventionally reflects the actual reception state, because it is needed for the transmission device receiving such Ack frames to adapt communication parameters (also called transmission parameters) such as modulation coding scheme (MCS) or spatial streams.

[0022] According to the present disclosure, the transmission device participating in bidirectional TXOP generally performs no action based on a response frame if it is an acknowledging response frame (e.g. Ack or BAck). Thus, the transmission device may, in one embodiment, discard any data unit that has been transmitted already as there is no future retransmission and shall generally not transmit a data unit more than once. Hence, according to one embodiment, no retransmission is made at all, whereas according to anotherembodiment a retransmission of one or more data units is only made if, in a response (e.g. Ack or Back), the receiving device explicitly requests a retransmission and / or explicitly indicates which one or more data units shall be retransmitted. Thus, according to the present disclosure, the transmission device deletes a transmitted data unit from its transmission queue (e.g. deletes it from its transmission buffer) immediately after its transmission or if no response is received from the receiving device instructing the transmission device to retransmit said data unit.

[0023] In the following, more details and embodiments of the present disclosure will be described, in particular explaining how a receiving device and a transmission device may operate. The transmission device is generally connected to a data unit source (e.g. a server, a user device, a central controller, a machine controller, content delivery system, game server, etc.), whereas the receiving device is connected to a data unit sink (e.g. another user device, a human interface device, VR glasses, a controlled device, manufacturing equipment, end-user device, etc.) . Generally, both the transmission device and the receiving device have transmitter and receiver functionality, e.g., the receiving device can transmit response frames, such as Ack or BAck, to the transmission device.

[0024] Fig. 5 shows a schematic diagram of the general architecture of a communication device 10 according to the present disclosure. This architecture holds both for a transmission device and a receiving device. The communication device 10 comprises a PHY layer 11 , a MAC layer 12, and (optionally) a logical link control (LLC) layer 13. Within these layers, data as well as control information can be exchanged. PHY layer 11 and MAC layer 12 are controlled by a STA management entity (SME) 14 which may also control higher layers such as an application layer 15. Each of the layers I entities may be implemented by respective units or circuitry, e.g. a processor, processing circuitry, a computer, dedicated hardware, etc., that carries out the functions of the device. Alternatively, a common unit or circuitry, e.g. a common processor or computer, may implement one or more of the layers I entities, or separate units or elements may be used that together represent the circuitry.

[0025] Before the mechanisms described herein can be used a setup procedure may be performed, in which both STAs are configured to use these mechanisms. The mecha-nisms for fast forwarding ARQ, which is part of this disclosure, may only apply to user data units and regular rules apply for all other frames such as control or management frames. Furthermore, the proposed mechanism may only apply to user data units originating at a specific source and / or sink, which may be defined by a specific traffic identifier (TID).

[0026] At the transmitter side, the MAC transmits each data unit only once and performs no retransmission action upon reception of an acknowledgement frame if it indicates an erroneous data unit. The transmitting STA may however use this information for link adaption, i.e. , to determine the link quality and if MCS needs to be changed, e.g. in order to lower the error rate.

[0027] For link adaption there are different options. According to one option a suggestion may be received from the receiving device that the transmitter shall change MCS to MCS A or use a particular TXVECTOR. According to another option the transmitter may count the number of correctly received data units and the number of erroneously received data units within a certain time span. It builds a ratio, and if there are too many erroneous data units, MCS is changed, and if there are a lot of correctly received data units, the MCS is fine and can be kept or changed to a higher MCS. Therefore, both successfully received data units and erroneously received data units (and also those erroneously received data units that require retransmission) are used.

[0028] Once a data unit was transmitted, the transmitting STA may discard it from its queue (unless a “three-state Ack” has been setup, as described below). Furthermore, the transmitting STA transmits the data units in first-in first-out (FIFO) manner.

[0029] Fig. 6 shows a diagram comparing the conventional communication scheme with another embodiment of a communication scheme according to the present disclosure for a frame exchange from STA 1 (transmitter) to STA 2 (receiver). At the same time, a reverse link exists, as shown in Fig. 1, which is not shown in Fig. 6. The link shown in Fig. 6 corresponds to Link 1 (Downlink) of the FDD scenario shown in Fig. 1. In the top row theconventional scheme (“current operation”) is shown; in the bottom row the proposed scheme (“new operation”) is shown.

[0030] At the beginning four data units (Dlls) are stored in a FIFO manner in a transmitter queue 20 (also called transmission queue or Tx queue). Once STA 1 gets channel access and has a bidirectional link established, it starts to transmit in FIFO order the Dlls. According to the conventional scheme, transmitted Dlls remain in the transmitter queue (as reflected in the transmitter queue 21) until STA 2 transmits a Block Acknowledgement (BAck) as response to the transmitted Dlls either confirming correct reception or indicating that one or more of the transmitted Dlls are erroneous. This response may be in the form of a one- bit indicator where a first value (e.g. 1) indicates correct reception and a second value (e.g. 0) indicates erroneous transmission. In Fig. 6 such an indicator (also called error indicator) is shown below the BAck in the form of “(x, y)”, wherein x represents the indicator for the first DU transmitted in the previous interval (or PPDU) and y represents the indicator for the second DU transmitted in the previous interval (or PPDU). This indication may be transmitted as part of the BAck or separately from the BAck as separate response.

[0031] If they have been correctly received, they are deleted from the transmitter queue. In the example shown in Fig. 6, DU #1 has been correctly received and is deleted from the transmitter queue after receipt of BAck 31 (as reflected in the transmitter queue 22), whereas DU #2 is erroneous and is hence not deleted from the transmitter queue after receipt of BAck 31 (as reflected in the transmitter queue 22 as well). The reception status is indicated from STA 2 to STA 1 by a corresponding response “(1 , 0)” (shown below BAck 31), wherein the 1 indicates correct reception of DU #1 and the 0 indicates erroneous reception of DU #2. Afterwards DU #2 is retransmitted, before the subsequent DU #3 is transmitted. They have both been received correctly by STA 2, which is confirmed by the next BAck 32, so that they are both deleted from the transmitter queue (as reflected in the transmitter queue 23).

[0032] According to the proposed scheme, the initial transmitter queue 24 is identical to the transmitter queue 21. Once a DU is transmitted, it is immediately deleted from the transmitter queue (as reflected in the transmitter queue 25). After DU#1 and #2 are transmitted,STA 2 transmits a Block Acknowledgement (BAck) 34 as a response to the Dlls. Although the BAck 34 indicates that DU#2 is erroneous, STA 1 continues to transmit the next DU in queue, namely DU #3 followed by DU #4, which are both removed from the transmitter queue after transmission (as reflected in the transmitter queue 26) regardless of the content of the BAck.

[0033] If the transmitter detects that a bidirectional link does not exist anymore, it may either discard or deprioritize the data units that belong to the bidirectional traffic stream. Both options may be selected during the setup, or it may be even implementation dependent. The deprioritization of data units means that the data units that belong to the bidirectional traffic stream are not transmitted; instead, data units belonging to other traffic streams are transmitted. The different traffic streams may be differentiated via TIDs (traffic identifiers) or SCS IDs (stream classification service, also called stream identifiers).

[0034] A non-existing bidirectional link means that at least one direction of the bidirectional link is not available or not operating as expected. The transmitter may detect a non-existing bidirectional link by one or more of the following options, which are all illustrated in Fig. 7 (the four cases do typically not appear at same time): a missing response frame such as a (Block) Acknowledgement to its first (initial) transmitted data units after channel access or two missing response frames to its non-first (non-initial) transmitted data units after channel access (case A in Fig. 7); a missing or erroneous PPDU in reverse link (case B in Fig. 7); if the BAck response to the received data units indicates that all or a certain percentage of received data units within the last received PPDU have been erroneous (unless a “three-state Ack” is used) (case C in Fig. 7); if in the initialization phase of a bidirectional link, the reverse link is not setup (i.e. a missing PPDU in reserve link) after a certain time interval (case D in Fig. 7).

[0035] If the MAC layer at the transmitter decides to use aggregation, it shall only aggregate data units that belong to the bidirectional traffic, i.e., that have the same TID within a A-MPDU (Aggregated MAC Protocol Data Unit). Furthermore, the MAC header of the MPDUs that are contained in the A-MPDU shall have the same settings and content in the MACheader, except for sequence numbers. This implies particularly that MAC header has the same length and the same optional subfields if present. If the transmitter decides to transmit the same data units multiple times to achieve e.g. more reliability, the repetition factor should be exchanged between transmitter and receiver during setup and the same repetition factor should be applied to each data unit (e.g. every data unit appears twice).

[0036] The reason for those restrictions will become apparent in the following description of the receiver operation. Within the receiver, special care should be taken that only data units (if erroneous or non-erroneous) are forwarded to higher layer that are directed to the receiving STA. Further, the fast forwarding operation should only be used for data units belonging to a bidirectional link and existing setup. For this purpose, a state machine may be used as illustrated in Fig. 8 showing an embodiment of a receiving method 100 carried out by a receiving apparatus.

[0037] If a PPDll is detected, it is first checked (step 101) if the PPDll preamble is valid (non- erroneous) and, if valid, if the PPDll is directed to the receiving STA (step 102). The latter check can only be done in PPDU types which have an indication of the receiving STA within the preamble. In case the PPDU preamble is erroneous or the PPDU is directed to a different STA, the PHY layer gives an indication to the MAC layer and / or SME that reception process ended via the PHY-RXEND. indication primitive (step 103), optionally with a detailed reason code attached.

[0038] When PPDU reception continues, the MAC layer checks if the first MPDU is erroneous (step 104). If not, it checks within the MAC header if the MPDU is directed to the receiving STA by evaluating MAC address and if the TID is present and if it belongs to bidirectional traffic (step 105). If yes, the receiving STA assumes the MAC header at least in terms of destination and TID to be valid for all other MPDUs within the PPDU if present (step 106). Next, the MAC layer processes the first MPDU and forwards the included data unit to higher layer via the MA-UNITDATA. indication including the result of CRC check which is valid (step 107). In case the first MPDU is erroneous, another first MPDU (if present) is determined (step 108). If no other MPDU can be determined or is not present, it is assumed that the PPDU ended which is indicated via PHY-RXEND. indication (step 109).

[0039] If after a first MPDll has been successfully detected and forwarded to higher layer, a second MPDll is determined if present (step 110) which is then processed according to the assumption that the MAC header of first MPDll applies at least in terms of destination and TID (step 111). The CRC result will be reflected in MA-UNITDATA. indication as well as the extracted data unit in case of valid CRC. In case of non-valid CRC, the inclusion of the (erroneous) data unit is optional, and the extraction of an erroneous data unit is done according to further settings within the MAC header of first MPDU such as length of the header or related information (e.g. present subfields). Further MPDUs are processed as second MPDUs.

[0040] The number of MPDUs that are considered to be the first MPDU in this process can be limited during the setup of a bidirectional link. This is because during this time, no output occurs at the MAC layer which would cause a relation of uplink and downlink data units to break. The MA-UNIDATA. indication can not only carry a data unit and the reception state, but also a sequence number from the MAC header which indicates the order of the received data unit. The sequence number signaling may replace the reception state signaling within MA-UNITDATA. indication.

[0041] The receiver MAC layer shall report the reception states in response frames if a received data unit solicited for an acknowledgement. The reception states shall reflect the true reception state and a BAck shall contain the reception states of the most recently received data units, i.e. the data units that caused at least a reception state to be signaled to higher layer via the MA-UNITDATA. indication as shown in Fig. 8 “add to BAck scoreboard” (steps 112, 113, 116).

[0042] In case the receiver detects a MPDU which is directed to itself but belongs to a non- bidirectional TID (step 114), the receiver performs regular processing, i.e., each MPDU is processed independently until the PPDU ended (step 115).

[0043] Fig. 9 shows a diagram of another embodiment of a communication scheme according to the present disclosure. The implementation of fast forwarding ARQ requires the higher layers (above MAC) to be error resilient. Depending on implementation of the higher layer,the error resilience has its limitations, in the sense that a certain error rate can be tolerated but a higher error rate causes the application to fail. For such cases, in an embodiment a “three-state Ack” mechanism may be used, in which the receiver determines the instantaneous error rate. If it drops below a certain threshold, which was set during setup phase, the receiver may request data units to be retransmitted. Thus, the acknowledgement has not only a signaling of “no error” (bit value 1 in the error indicator shown in Fig. 9) and “error but don’t retransmit” (bit value 0 in the error indicator shown in Fig. 9) but also “error and retransmit” (bit value 2 in the error indicator shown in Fig. 9). Hence, the error indicator may have three states.

[0044] The diagram shown in Fig. 9 illustrates the envisioned operation under the assumption that the receiver requires at least one successfully received data unit (DU) per frame exchange or transmitted PPDU by STA 1. STA 1 transmits DU #1 and DU #2 of the initial TX queue 41 to STA 2, which, however, receives both data units erroneously. Therefore, because both data units failed, STA 2 indicates within the subsequent BAck 51 that both DUs have been erroneous but only DU #2 should be retransmitted from the left. For this reason, only DU #1 is removed from the TX queue (as reflected by the TX queue 42). Subsequently, DU #2 and #3 are (re)transmitted which are assumed to be correctly received at STA 2 causing both DUs to be deleted from Tx queue (as reflected by the TX queue 42) in response to a corresponding BAck 52. Next, STA 1 transmits DU#4 and #5 to STA 2 of which only DU #5 fails. Since DU #4 was correctly received, there is no need to have a retransmission of DU #5; hence, the content of BAck 53 is accordingly set by STA 2 so that DU #4 and #5 are deleted from Tx queue (as reflected by the TX queue 44).

[0045] If transmitter and receiver agree on such a “three-state Ack” mechanism in the setup phase, the transmitter shall not discard a data unit before it received an Ack response which indicates either “no error” or “error but don’t retransmit” indication for that data unit. If the transmitter receives an “error and retransmit” indication for a certain data unit, the transmitter shall transmit this data unit as fast as possible, i.e. first before other data units to be transmitted and / or even before other control data units such as BAck or trigger frame to be transmitted.

[0046] Fig. 10 shows a diagram of another embodiment of a communication scheme according to the present disclosure that illustrates the misalignment between the data units of STA 1 and STA under operation of the “three-state Ack” scheme illustrated in Fig. 9. As can be seen, the retransmission essentially causes a time shift in the exemplary relation. There is only a misalignment of one data unit instead of two data units that would be caused by a retransmission of DU#1 and DU#2. Depending on the application, this may be less critical for a higher layer than having two subsequent data units that fail.

[0047] For operating using the mechanism(s) disclosed herein a new type of STAs may be deployed. However, WLAN features a lot of legacy devices in which case the following two settings can be made to achieve some of the features for fast forwarding ARQ (i.e. the mechanism disclosed herein). According to a first setting, the transmitter can set the lifetime of all data units belonging to a bidirectional link to zero, set the BAck window size to one and disallow fragmentation of data units. Such a BAck window (also called response window) defines the number of data units of which the reception state is reported that are included in the response (frame). For example, if the BAck window is set to N, it means that the response frame after the transmission of one or more data units, includes the reception state of the last (at least) N data units.

[0048] Alternatively, according to a second setting, the transmitter can set the lifetime of all data units belonging to a bidirectional link to zero and transmit the data units interlaced with Block Ack Requests (BAR) frames in the sense of DU, BAR, DU, BAR, DU, BAR, ... with DU, BAR as the basic element. The basic element shall be transmitted together, i.e., in the same PPDU.

[0049] The above settings provide that the transmitter discards all data units once transmitted. The receiver will forward all correct (non-erroneous) data units to higher layer. However, erroneous data units are discarded or skipped in the forwarding process to higher layer and also no indication happens to higher layer that the data unit is erroneous. Further, the receivers’ response in form of an acknowledgement may contain the reception status of only the last received data unit for which reason the link adaption at the transmitter has insufficient data to judge channel quality sufficiently. The “three-state Ack” is generally not supported, too.

[0050] Different pieces of information may be transmitted by a transmission device and / or a receiving device, for instance during the setup of the bidirectional link or included into I added to one or more data units. These pieces of information may include one or more of: a bidirectional identifier indicating which of the one or more data units belong to bidirectional traffic; a traffic identifier and / or a stream identifier indicating the traffic or transmission stream of a bidirectional traffic; a traffic identifier and / or a stream identifier indicating the type of traffic or transmission stream; a receiver identifier indicating the receiving device to which one or more bidirectional data units are addressed; an acknowledgement policy identifier indicating which acknowledgement policy to apply by the receiving device for acknowledging reception of data units; an error rate threshold above which the receiving device shall transmit a response to the transmission device instructing the transmission device to retransmit a data unit; and a link quality threshold below which the receiving device shall transmit a response including a suggestion for new transmission parameters.

[0051] Hence, according to the present disclosure a transmission method may be carried out by a first communication device acting as transmitting device and a receiving method may be carried out by a second communication device acting as receiving device that communicates with the first communication device via a bidirectional link.

[0052] A flowchart of an embodiment of a transmission method 200 according to the present disclosure is shown in Fig. 11. The transmission method 200 comprises a step 201 of setting up a bidirectional link with a receiving device for transmission and reception of data units, a step 202 of transmitting data units stored in a transmission queue for transmission using the bidirectional link to the receiving device, and a third step 203 of deleting a transmitted data unit from the transmission queue immediately after its transmission or if no response is received from the receiving device instructing the transmission device to retransmit said data unit.

[0053] A flowchart of an embodiment of a receiving method 300 according to the present disclosure is shown in Fig. 12. The receiving method 300 comprises a step 301 of setting up a bidirectional link with a transmission device for transmission and reception of data units, a step 302 of receiving data units from the transmission device using the bidirectional link, and a step 303 of providing the received data units to higher layer processing regardless of their reception state, according to which a data unit is received and decoded correctly or erroneously, wherein a reception state indicator indicating the reception state is provided to higher layer processing along with each data unit.

[0054] In summary, the present disclosure addresses MAC layer operation for bidirectional links in which data units are quasi-instantaneously exchanged between two communication devices. Thereby, any operational delay by the MAC layer, which may be due to ARQ operation, should be avoided. The present disclosure proposes an enhanced ARQ operation, which minimizes the delay and misalignment between data units conveyed in each direction. In an embodiment, the transmitter discards all data units after transmission, whereas the receiver forwards all data units to higher layer regardless of the reception state, which is however indicated separately to higher layer. Further embodiments address error handling and a three state Acknowledgement.

[0055] Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. As will be understood by those skilled in the art, the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting of the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

[0056] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0057] In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a non-transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. Further, such a software may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0058] The elements of the disclosed devices, apparatus and systems may be implemented by corresponding hardware and / or software elements, for instance appropriate circuits or circuitry. A circuit is a structural assemblage of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, standard integrated circuits, application specific standard products, and field programmable gate arrays. Further, a circuit includes central processing units, graphics processing units, and microprocessors which are programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the abovedescribed hardware executing software. A circuit or circuitry may be implemented by a single device or unit or multiple devices or units, or chipset(s), or processor(s).

[0059] It follows a list of further embodiments of the disclosed subject matter:1. Transmission device (STA 1) comprising circuitry configured to: set up a bidirectional link with a receiving device (STA 2) for transmission and reception of data units; transmit data units stored in a transmission queue for transmission using the bidirectional link to the receiving device; and delete a transmitted data unit from the transmission queue immediately after its transmission or if no response is received from the receiving device instructing the transmission device to retransmit said data unit.2. Transmission device according to embodiment 1, wherein the circuitry is configured to delete a transmitted data unit from the transmission queue immediately after its transmission regardless of reception of a response from thereceiving device, in particular within a response period, said response indicating if said data unit has been erroneously received or decoded or not by the receiving device.3. Transmission device according to embodiment 1 or 2, wherein the circuitry is configured to retransmit a data unit if a response is received from the receiving device, in particular within a response period, said response instructing the transmission device to retransmit said data unit; and delete said data unit from the transmission queue immediately after its retransmission.4. Transmission device according to embodiment 3, wherein the circuitry is configured to transmit data units stored in the transmission queue in first in first out order and retransmit any data unit before the subsequent data units stored in the transmission queue are transmitted.5. Transmission device according to any one of the preceding embodiments, wherein the circuitry is configured to adapt one or more transmission parameters of the link to the receiving device based on a response from the receiving device suggesting transmission parameters to be used and / or based on a received response from the receiving device instructing the transmission device to retransmit a data unit and / or indicating that a data unit has been erroneously received or decoded and / or indicating that a data unit has been correctly received or decoded by the receiving device.6. Transmission device according to any one of the preceding embodiments, wherein the circuitry is configured to aggregate one or more data units belonging to the bidirectional traffic, in particular having a traffic identifier or stream identifier which identifies a bidirectional traffic, into an aggregated data unit and to transmit the aggregated data unit.7. T ransmission device according any one of the preceding embodiments, wherein the circuity is configured to aggregate one or more data units belonging to the bidirectional traffic with data units that are not belonging to the bidirectional traffic, eachdata unit carrying a traffic identifier or stream identifier to identify the traffic type, into an aggregated data unit and to transmit the aggregated data unit.)8. Transmission device according to any one of the preceding embodiments, wherein the circuitry is configured to detect if the bidirectional link is available and operating; and, if it is detected that the bidirectional link is not available and / or not operating, discard or reduce transmission priority of remaining data units stored in the transmission queue and belonging to the bidirectional traffic.9. Transmission device according to embodiment 8, wherein the circuitry is configured to detect that the bidirectional link is not available and / or not operating by detecting one or more of: a missing response to the transmission of one or more data units from the receiving device within a response period; missing data units from the receiving device via a reverse link of the bidirectional link; reception of one or more erroneous data units from the receiving device via a reverse link of the bidirectional link; reception of at least a predefined number of erroneous data units from the receiving device via a reverse link of the bidirectional link; reception of a response from the receiving device indicating that multiple or all data units transmitted by the transmission device are erroneous; and missing reverse link setup.10. Transmission device according to any one of the preceding embodiments, wherein the circuitry is configured to transmit to the receiving device as part of the setup of the bidirectional link or to include into or add to one or more data units one or more of a bidirectional identifier indicating which of the one or more data units belong to bidirectional traffic; a traffic identifier and / or a stream identifier indicating the traffic or transmission stream of a bidirectional traffic;a traffic identifier and / or a stream identifier indicating the type of traffic or transmission stream; a receiver identifier indicating the receiving device to which one or more bidirectional data units are addressed; an acknowledgement policy identifier indicating which acknowledgement policy to apply by the receiving device for acknowledging reception of data units; an error rate threshold above which the receiving device shall transmit a response to the transmission device instructing the transmission device to retransmit a data unit; and a link quality threshold below which the receiving device shall transmit a response including a suggestion for new transmission parameters.11. T ransmission device according to any one of the preceding embodiments, wherein the circuitry is configured to agree with the receiving device to an acknowledgement policy indicating if a two-state or a three-state acknowledgment policy shall be applied by the receiving device, wherein according to the two-state acknowledgment policy a response shall be transmitted by the receiving device indicating, as first state, if a data unit has been correctly received and decoded or indicating, as second state, if a data unit has been erroneously received and / or decoded, and wherein according to the three-state acknowledgment policy a response shall be transmitted by the receiving device indicating, as a third state in addition to the first and second states, if a data unit shall be retransmitted.12. Transmission device according to any one of the preceding embodiments, wherein the circuitry is configured to perform one or more of setting the lifetime of data unit of the bidirectional traffic to zero; setting a response window size which defines the number of data units of which the reception state is reported in a response by the receiving device to one; disallowing fragmentation of data units; and alternatingly transmitting data units and acknowledgement requests requesting the receiving device to transmit a response.13. Receiving device (STA 2) comprising circuitry configured to: set up a bidirectional link with a transmission device (STA 1) for transmission and reception of data units; receive data units from the transmission device using the bidirectional link; and provide the received data units to higher layer processing regardless of their reception state, according to which a data unit is received and decoded correctly or erroneously, wherein a reception state indicator indicating the reception state is provided to higher layer processing along with each data unit.14. Receiving device according to embodiment 13, wherein an erroneous data unit is provided to higher layer processing by providing an empty or null data unit.15. Receiving device according to embodiment 13 or 14, wherein the circuitry is configured, as part of the higher layer processing, to ignore or correct a data unit for which the reception state indicator indicates that it is erroneously received and / or decoded.16. Receiving device according to any one of embodiments 13 to 15, wherein the circuitry is configured to receive from the transmission device as part of the setup of the bidirectional link or to derive from one or more data units one or more of a bidirectional identifier indicating if and which of the one or more data units belong to bidirectional traffic; a traffic identifier and / or a stream identifier indicating the traffic or transmission stream of bidirectional traffic; a receiver identifier indicating the receiving device to which one or more bidirectional data units are addressed; an acknowledgement policy identifier indicating which acknowledgement policy to apply by the receiving device for acknowledging reception of data units; an error rate threshold above which the receiving device shall transmit a response to the transmission device instructing the transmission device to retransmit a data unit; anda link quality threshold below which the receiving device shall transmit a response including a suggestion for new transmission parameters.17. Receiving device according to any one of embodiments 13 to 16, wherein the circuitry is configured to derive from a first data unit that is received and decoded correctly a traffic identifier and / or a stream identifier indicating the traffic or transmission stream and a receiver identifier indicating the receiving device to which the one or more data units are addressed; and assume, for one or more subsequently received data units, in particular all subsequent data units included in a physical layer protocol data unit (PPDll), that they belong to the same traffic or transmission stream and are addressed to the same receiving device.18. Receiving device according to any one of embodiments 13 to 17, wherein the circuitry is configured to transmit, if a data unit transmitted from the transmission device is received, a response to the transmission device suggesting transmission parameters to be used by the transmission device and / or a response to the transmission device instructing the transmission device to retransmit said data unit and / or indicating that said data unit has been erroneously received or decoded by the receiving device and / or indicating that said data unit was correctly received.19. Receiving device according to embodiment 18, wherein the circuitry is configured to transmit a response to the transmission device instructing the transmission device to retransmit a data unit only if an error rate threshold of said data units has been exceeded.20. Transmission method comprising setting up a bidirectional link with a receiving device (STA 2) for transmission and reception of data units; transmitting data units stored in a transmission queue for transmission using the bidirectional link to the receiving device; anddeleting a transmitted data unit from the transmission queue immediately after its transmission or if no response is received from the receiving device instructing the transmission device (STA 1) to retransmit said data unit.21. Receiving method comprising setting up a bidirectional link with a transmission device (STA 1) for transmission and reception of data units; receiving data units from the transmission device using the bidirectional link; and providing the received data units to higher layer processing regardless of their reception state, according to which a data unit is received and decoded correctly or erroneously, wherein a reception state indicator indicating the reception state is provided to higher layer processing along with each data unit.22. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment 20 or 21 to be performed.23. A computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment 20 or 21 when said computer program is carried out on a computer.

Claims

CLAIMS1 . T ransmission device comprising circuitry configured to: set up a bidirectional link with a receiving device for transmission and reception of data units; transmit data units stored in a transmission queue for transmission using the bidirectional link to the receiving device; and delete a transmitted data unit from the transmission queue immediately after its transmission or if no response is received from the receiving device instructing the transmission device to retransmit said data unit.

2. Transmission device according to claim 1 , wherein the circuitry is configured to delete a transmitted data unit from the transmission queue immediately after its transmission regardless of reception of a response from the receiving device, in particular within a response period, said response indicating if said data unit has been erroneously received or decoded or not by the receiving device.

3. Transmission device according to claim 1 , wherein the circuitry is configured to retransmit a data unit if a response is received from the receiving device, in particular within a response period, said response instructing the transmission device to retransmit said data unit; and delete said data unit from the transmission queue immediately after its retransmission.

4. Transmission device according to claim 3, wherein the circuitry is configured to transmit data units stored in the transmission queue in first in first out order and retransmit any data unit before the subsequent data units stored in the transmission queue are transmitted.

5. Transmission device according to claim 1 , wherein the circuitry is configured to adapt one or more transmission parameters of the link to the receiving device based on a response from the receiving device suggestingtransmission parameters to be used and / or based on a received response from the receiving device instructing the transmission device to retransmit a data unit and / or indicating that a data unit has been erroneously received or decoded and / or indicating that a data unit has been correctly received or decoded by the receiving device.

6. Transmission device according to claim 1, wherein the circuitry is configured to aggregate one or more data units belonging to the bidirectional traffic, in particular having a traffic identifier or stream identifier which identifies a bidirectional traffic, into an aggregated data unit and to transmit the aggregated data unit.

7. Transmission device according to claim 1, wherein the circuitry is configured to detect if the bidirectional link is available and operating; and, if it is detected that the bidirectional link is not available and / or not operating, discard or reduce transmission priority of remaining data units stored in the transmission queue and belonging to the bidirectional traffic.

8. Transmission device according to claim 7, wherein the circuitry is configured to detect that the bidirectional link is not available and / or not operating by detecting one or more of: a missing response to the transmission of one or more data units from the receiving device within a response period; missing data units from the receiving device via a reverse link of the bidirectional link; reception of one or more erroneous data units from the receiving device via a reverse link of the bidirectional link; reception of at least a predefined number of erroneous data units from the receiving device via a reverse link of the bidirectional link; reception of a response from the receiving device indicating that multiple or all data units transmitted by the transmission device are erroneous; and missing reverse link setup.

9. Transmission device according to claim 1 , wherein the circuitry is configured to transmit to the receiving device as part of the setup of the bidirectional link or to include into or add to one or more data units one or more of a bidirectional identifier indicating which of the one or more data units belong to bidirectional traffic; a traffic identifier and / or a stream identifier indicating the traffic or transmission stream of a bidirectional traffic; a traffic identifier and / or a stream identifier indicating the type of traffic or transmission stream; a receiver identifier indicating the receiving device to which one or more bidirectional data units are addressed; an acknowledgement policy identifier indicating which acknowledgement policy to apply by the receiving device for acknowledging reception of data units; an error rate threshold above which the receiving device shall transmit a response to the transmission device instructing the transmission device to retransmit a data unit; and a link quality threshold below which the receiving device shall transmit a response including a suggestion for new transmission parameters.

10. Transmission device according to claim 1 , wherein the circuitry is configured to agree with the receiving device to an acknowledgement policy indicating if a two-state or a three-state acknowledgment policy shall be applied by the receiving device, wherein according to the two-state acknowledgment policy a response shall be transmitted by the receiving device indicating, as first state, if a data unit has been correctly received and decoded or indicating, as second state, if a data unit has been erroneously received and / or decoded, and wherein according to the three-state acknowledgment policy a response shall be transmitted by the receiving device indicating, as a third state in addition to the first and second states, if a data unit shall be retransmitted.

11. T ransmission device according to claim 1 , wherein the circuitry is configured to perform one or more ofsetting the lifetime of data unit of the bidirectional traffic to zero; setting a response window size which defines the number of data units of which the reception state is reported in a response by the receiving device to one; disallowing fragmentation of data units; and alternatingly transmitting data units and acknowledgement requests requesting the receiving device to transmit a response.

12. Receiving device comprising circuitry configured to: set up a bidirectional link with a transmission device for transmission and reception of data units; receive data units from the transmission device using the bidirectional link; and provide the received data units to higher layer processing regardless of their reception state, according to which a data unit is received and decoded correctly or erroneously, wherein a reception state indicator indicating the reception state is provided to higher layer processing along with each data unit.

13. Receiving device according to claim 12, wherein the circuitry is configured, as part of the higher layer processing, to ignore or correct a data unit for which the reception state indicator indicates that it is erroneously received and / or decoded.

14. Receiving device according to claim 12, wherein the circuitry is configured to receive from the transmission device as part of the setup of the bidirectional link or to derive from one or more data units one or more of a bidirectional identifier indicating if and which of the one or more data units belong to bidirectional traffic; a traffic identifier and / or a stream identifier indicating the traffic or transmission stream of bidirectional traffic; a receiver identifier indicating the receiving device to which one or more bidirectional data units are addressed; an acknowledgement policy identifier indicating which acknowledgement policy to apply by the receiving device for acknowledging reception of data units;an error rate threshold above which the receiving device shall transmit a response to the transmission device instructing the transmission device to retransmit a data unit; and a link quality threshold below which the receiving device shall transmit a response including a suggestion for new transmission parameters.

15. Receiving device according to claim 12, wherein the circuitry is configured to derive from a first data unit that is received and decoded correctly a traffic identifier and / or a stream identifier indicating the traffic or transmission stream and a receiver identifier indicating the receiving device to which the one or more data units are addressed; and assume, for one or more subsequently received data units, in particular all subsequent data units included in a physical layer protocol data unit (PPDll), that they belong to the same traffic or transmission stream and are addressed to the same receiving device.

16. Receiving device according to claim 12, wherein the circuitry is configured to transmit, if a data unit transmitted from the transmission device is received, a response to the transmission device suggesting transmission parameters to be used by the transmission device and / or a response to the transmission device instructing the transmission device to retransmit said data unit and / or indicating that said data unit has been erroneously received or decoded by the receiving device and / or indicating that said data unit was correctly received.

17. Receiving device according to claim 16, wherein the circuitry is configured to transmit a response to the transmission device instructing the transmission device to retransmit a data unit only if an error rate threshold of said data units has been exceeded.

18. Transmission method comprising setting up a bidirectional link with a receiving device for transmission and reception of data units;transmitting data units stored in a transmission queue for transmission using the bidirectional link to the receiving device; and deleting a transmitted data unit from the transmission queue immediately after its transmission or if no response is received from the receiving device instructing the transmission device to retransmit said data unit.

19. Receiving method comprising setting up a bidirectional link with a transmission device for transmission and reception of data units; receiving data units from the transmission device using the bidirectional link; and providing the received data units to higher layer processing regardless of their reception state, according to which a data unit is received and decoded correctly or erroneously, wherein a reception state indicator indicating the reception state is provided to higher layer processing along with each data unit.

20. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to claim 18 or 19 to be performed.

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