Time-gap based preemption enablement

Abstract

A wireless communication device (10; 20; 800; 900) generates a first data transmission and a second data transmission on a wireless channel based on Orthogonal Frequency Division Multiplexing, OFDM. The first data transmission and the second data transmission are separated by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allowing to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

Description

[0001] Time-gap based preemption enablement

[0002] Technical Field

[0003] The present invention relates to methods for controlling wireless transmissions and to corresponding devices, systems, and computer programs.

[0004] Background

[0005] Wireless communication technologies may use licensed frequency bands and / or licenseexempt frequency bands. A typical example of a wireless communication technology operating in license-exempt frequency bands is the WLAN (Wireless Local Area Network) technology, according to "IEEE Standard for Information Technology-Telecommunications and Information Exchange between Systems - Local and Metropolitan Area Networks-Specific Requirements - Part 11 : Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications," in IEEE Std 802.11-2020 (Revision of IEEE Std 802.11-2016), pp.1- 4379, 26 Feb. 2021 , in the following denoted as “IEEE 802.11 standard”. The WLAN technology based on the IEEE 802.11 Standard is also referred to as “Wi-Fi”.

[0006] Among the goals of next generation Wi-Fi standards is to improve the performance for low latency services such as automation, cloud gaming and XR (“extended reality”). For example, IEEE project authorization request document P802.11 bn, relating to study of UHR (Ultra High Reliability) enhancements of the IEEE 802.11 standard (available online under ” https: / / mentor.ieee.org / 802.11 / dcn / 23 / 11-23-0480”), refers to “at least one mode of operation capable of reducing latency by 25% for the 95th percentile of the latency distribution compared to the Extremely High Throughput MAC / PHY operation”.

[0007] A known feature which aims at handling low-latency traffic is referred to as R-TWT (Restricted Target Wakeup Time) and which allows an AP (access point) to set up a periodic schedule where certain low latency traffic can be prioritized to have better protection by involving nearby APs to also respect this agreement. However, as R-TWT sets up a periodic schedule for delivery, it is not well-suited for low-latency traffic that is more irregular such as event-based traffic or periodic traffic with jitter.

[0008] For handling event-based traffic, the introduction of preemption was also suggested. By using preemption, one may interrupt an ongoing transmission in order to prioritize another typically more critical transmission. For example, a longer physical layer protocol data unit (PPDU) can be divided into several small PPDUs in order to leave short time gaps that may be occupied by transmissions carrying low latency data, as for example described in ’’Preemption for Low Latency Application (follow up)” by J. Fang et al., IEEE document 802.11 -23 / 1229r1 , August 2023 (available online under “https: / / mentor.ieee.org / 802.11 / dcn / 23 / 11-23-1229-01-0uhr- preemption-for-low-latency-application-follow-up.pptx”) or in US 2023 / 0208774 A1. With preemption, there is no need to wait for the delivery of the entire PPDU before competing for channel access.

[0009] However, when dividing a large PPDU into two or more smaller PPDUs to allow for preemption, there is typically a need that the receiver of the small PPDU can smoothly continue the reception of the small PPDUs if no preemption happens. Since there will be a gap in the received signal, the receiver must ensure that the correct timing for the processing is maintained and that parameters that are tracked during the reception of a PPDU, like frequency and phase, are correctly estimated once the next PPDU starts. Moreover, in many situations the transmission that potentially is to be preempted may be over a large bandwidth while the low latency data requires only a much smaller bandwidth, implying that supporting preemption may be inefficient and wasteful in terms of bandwidth. Further, it can be expected that legacy devices, that do not support preemption, will need to be supported for a long time.

[0010] Accordingly, there is a need for techniques which allow for efficiently allowing preemption of ongoing data transmissions while also maintaining compatibility with legacy devices.

[0011] According to an embodiment, a method of controlling wireless transmissions in a wireless communication system is provided. According to the method, a wireless communication device generates, based on OFDM (Orthogonal Frequency Division Multiplexing), a first data transmission and a second data transmission on a wireless channel. The first data transmission and the second data transmission are separated by a time gap. The time gap corresponds to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0012] According to a further embodiment, a method of controlling wireless transmissions in a wireless communication system is provided. According to the method, a wireless communication device receives, based on OFDM, a first data transmission on a wireless channel. The first data transmission is separated from a second data transmission on the wireless channel by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0013] According to a further embodiment, a wireless communication device is provided. The wireless communication device is configured to generate, based on OFDM, a first data transmission and a second data transmission on a wireless channel. The first data transmission and the second data transmission are separated by a time gap. The time gap corresponds to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0014] According to a further embodiment, a wireless communication device is provided. The wireless communication device comprises at least one processor and a memory. The memory contains instructions executable by said at least one processor, whereby the wireless communication device is operative to generate, based on OFDM, a first data transmission and a second data transmission on a wireless channel. The first data transmission and the second data transmission are separated by a time gap. The time gap corresponds to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0015] According to a further embodiment, a wireless communication device is provided. The wireless communication device is configured to receive, based on OFDM, a first data transmission on a wireless channel. The first data transmission is separated from a second data transmission on the wireless channel by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0016] According to a further embodiment, a wireless communication device is provided. The wireless communication device comprises at least one processor and a memory. The memory contains instructions executable by said at least one processor, whereby the wireless communication device is operative to receive, based on OFDM, a first data transmission on a wireless channel. The first data transmission is separated from a second data transmission on the wireless channel by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap. According to a further embodiment, a computer program or computer program product is provided, e.g., in the form of a non-transitory storage medium, which comprises program code to be executed by at least one processor of a wireless communication device. Execution of the program code causes the wireless communication device to generate, based on OFDM, a first data transmission and a second data transmission on a wireless channel. The first data transmission and the second data transmission are separated by a time gap. The time gap corresponds to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0017] According to a further embodiment, a computer program or computer program product is provided, e.g., in the form of a non-transitory storage medium, which comprises program code to be executed by at least one processor of a wireless communication device. Execution of the program code causes the wireless communication device to receive, based on OFDM, a first data transmission on a wireless channel. The first data transmission is separated from a second data transmission on the wireless channel by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0018] Details of such embodiments and further embodiments will be apparent from the following detailed description.

[0019] Brief Description of the Drawings

[0020] Fig. 1 schematically illustrates a wireless communication system according to an embodiment.

[0021] Fig. 2A schematically illustrates an example of preemption of a downlink data transmission by another downlink transmission in accordance with the illustrated concepts.

[0022] Fig. 2B schematically illustrates an example of preemption of a downlink data transmission by an uplink data transmission in accordance with the illustrated concepts.

[0023] Fig. 2C schematically illustrates another example of preemption of a downlink data transmission by an uplink data transmission in accordance with the illustrated concepts.

[0024] Fig. 3A schematically illustrates an OFDM signal with a sequence of OFDM symbols separated by guard intervals. Fig. 3B schematically illustrates insertion of a time gap into the sequence of OFDM symbols.

[0025] Fig. 3C schematically illustrates a dimensioning of a time gap in accordance with embodiments of the present disclosure.

[0026] Fig. 4 schematically illustrates an example of preemption on a bandwidth portion in accordance with an embodiment of the present disclosure.

[0027] Fig. 5 schematically illustrates a further example of preemption on a bandwidth portion in accordance with an embodiment of the present disclosure.

[0028] Fig. 6 shows a flowchart for schematically illustrating a method according to an embodiment of the present disclosure.

[0029] Fig. 7 shows a flowchart for schematically illustrating a further method according to an embodiment of the present disclosure.

[0030] Fig. 8 schematically illustrates structures of an AP according to an embodiment of the present disclosure.

[0031] Fig. 9 schematically illustrates structures of a wireless device according to an embodiment of the present disclosure.

[0032] Detailed

[0033] In the following, concepts in accordance with exemplary embodiments of the invention will be explained in more detail and with reference to the accompanying drawings. The illustrated embodiments relate to controlling of wireless transmissions in a wireless communication system. The wireless communication system may be a WLAN system based on a IEEE 802.11 technology. However, it is noted that the illustrated concepts could also be applied to other wireless communication technologies, e.g., to contention-based modes of the LTE (Long Term Evolution) or NR (New Radio) technology specified by 3GPP (3rdGeneration Partnership Project).

[0034] In the illustrated concepts, preemption is enabled by inserting a time gap between OFDM based data transmissions on a wireless channel. The data transmissions may result from splitting a PPDU into smaller parts. Such smaller parts may herein also be referred to as packets or small PPDUs. The time gap may also be regarded as a specific type of Interframe Space (IFS). The duration of the time gap is selected to correspond to an integer multiple of the duration of an OFDM symbol plus guard interval (Gl) and to be sufficient to allow starting a transmission in the time gap to preempt the upcoming data transmission. By selecting the duration of the time gap in this way, it can be achieved that a receiver of the data transmissions maintains OFDM symbol timing without requiring resynchronization between the data transmissions. Further, maintaining a phase reference across OFDM subcarriers and / or fast channel tracking may be facilitated. Furthermore, the selection of the duration of the time gap may help to ensure that only a fraction of the available bandwidth of the wireless channel needs to be allocated to enable preemption. In this way high efficiency can be achieved. Further, adverse effects on legacy devices, which do not support preeemption, can be avoided so that coexistence of legacy devices with wireless communication devices supporting preemption in accordance with the illustrated concepts is possible.

[0035] Fig. 1 illustrates an exemplary wireless communication system according to an embodiment. In the illustrated example, the wireless communication system includes multiple APs 10, in the illustrated example referred to as AP1 , AP2, AP3, AP4, and multiple stations 20, in the illustrated example referred to as STA11 , STA12, STA13, STA21 , STA22, STA31 , and STA41 . STA11 , STA12, and STA13 are served by AP1 , in a first BSS (Basic Service Set) denoted as BSS1. STA21 and STA22 are served by AP2, in a second BSS denoted as BSS2. STA31 is served by AP3, in a third BSS denoted as BSS3. STA41 is served by AP4, in a fourth BSS denoted as BSS4. The stations 20 may be non-AP STAs and correspond to various kinds of wireless devices, for example user terminals, such as mobile or stationary computing devices like smartphones, laptop computers, desktop computers, tablet computers, gaming devices, or the like. Further, the stations 20 could for example correspond to other kinds of equipment like smart home devices, printers, multimedia devices, data storage devices, or the like.

[0036] In the example of Fig. 1 , each of the stations 20 may connect through a radio link to one of the APs 10. For example, depending on location or channel conditions experienced by a given station 20, the station 20 may select an appropriate AP 10 and BSS for establishing the radio link. The radio link may be based on one or more OFDM carriers from a frequency spectrum which is shared on the basis of a contention-based mechanism, e.g., an unlicensed or licenseexempt band like the 2.4 GHz ISM (Industrial, Scientific and Medical) band, the 5 GHz band, the 6 GHz band, or the 60 GHz band. Each AP 10 may provide data connectivity of the stations 20 connected to the AP 10. As further illustrated, the APs 10 may be connected to a data network (DN) 110. In this way, the APs 10 may also provide data connectivity between stations 20 connected to different APs 10. Further, the APs 10 may also provide data connectivity of the stations 20 to other entities, e.g., to one or more servers, service providers, data sources, data sinks, user terminals, or the like. Accordingly, the radio link established between a given station 20 and its serving AP 10 may be used for providing various kinds of services to the station 20, e.g., a voice service, a multimedia service, or other data service. Such services may be based on applications which are executed on the station 20 and / or on a device linked to the station 20. By way of example, Fig. 1 illustrates an application service platform 150 provided in the DN 110. The application(s) executed on the station 20 and / or on one or more other devices linked to the station 20 may use the radio link for data communication with one or more other stations 20 and / or the application service platform 150, thereby enabling utilization of the corresponding service(s) at the station 20. Further, it is noted that in some scenarios also direct radio links between stations 20 or radio links between the APs 10 could be utilized. The latter radio links could for example be used for forwarding data from one BSS to another BSS and / or for coordination of operation of the APs 10.

[0037] In accordance with the illustrated concepts preemption of data transmissions between at least some of the APs 10 and their associated stations 20 is enabled by providing time gaps in the OFDM signal of these data transmissions. The time gaps have a duration which is sufficient to allow starting a transmission which preempts the upcoming data transmission, so that a data transmission of low-latency data can be initiated. The time gaps may split larger PPDUs into smaller parts, so that there is no need to wait for the end of the PPDU before initiating a transmission of low-latency data. The duration of the time gaps is selected in accordance with the above-mentioned principles, i.e., to correspond to an integer multiple of the OFDM symbol duration plus Gl.

[0038] In examples as further detailed below, it is assumed that the data transmissions are between an AP 10 and one or more stations 20 associated to the AP 10. Further, it is assumed that the AP is in control of the wireless channel after having won contention for the wireless channel and then reserved the channel by means of a transmission opportunity (TXOP). The AP 10 is assumed to send downlink (DL) data to one or more of the associated stations 20 and / or receive uplink (UL) data from one or more of the associated stations 20. The DL data and / or the UL data may correspond to low-latency (LL) data or to non-LL data. Figs. 2A, 2B, and 2C illustrate examples where a transmission of DL data is preempted by starting a transmission in the time gap. In these examples, it is assumed that the transmission of DL data is from the AP to a first station (STA1). The time gaps split the DL transmission into multiple shorter parts and allow for initiating another transmission of data already before the transmission of DL data has ended. In the example of Fig. 2A, it is assumed that at some point LL data for a second station (STA2) arrives at the AP. In the next time gap (TG), the AP thus starts transmitting the LL data to STA2. After that, the transmission of DL data to STA1 may continue. In the example of Fig. 2B, it is assumed that at some point LL data for the AP arrives at a second station (STA2). In the next time gap (TG), STA2 thus starts transmitting the LL data to the AP. After that, the transmission of DL data to STA1 may continue. In the example of Fig. 2C, it is assumed that at some point LL data for the AP arrives at a second station (STA2). In the next time gap (TG), STA2 then sends a scheduling request (SR) to the AP. In response to the scheduling request, the AP sends a trigger frame (TF) to STA2. In response to the TF, STA2 transmits the LL data to the AP. After that, the transmission of DL data to STA1 may continue. Further details of such preemption processes may be similar as explained in ’’Preemption for Low Latency Application (follow up)” by J. Fang et al., IEEE document 802.11-23 / 1229r1 , August 2023 (available online under

[0039] “https: / / mentor.ieee.Org / 802.11 / dcn / 23 / 11 -23-1229-01 -Ouhr-preemption-for-low-latency- application-follow-up.pptx”) or in US 2023 / 0208774 A1. As can be seen from these examples, the current transmission of DL data may be preempted or will continue, depending on whether there was LL traffic or there was no LL traffic, respectively, and the preemption is possible by starting a transmission in the time gap. It is also noted that it can be expected that in the majority of cases, there will be no preemption. This can be attributed to the fact that for many (especially event-driven) LL applications, the LL data arrives relatively seldom but in an unpredictable manner.

[0040] When there is preemption, a typical duration of the LL data transmission would be in the order of 100us - 1 ms, meaning that once the transmission of the DL data is resumed the wireless channel between the transmitter and the receiver may have changed considerably and, also due to relative drift between the transmitter and the receiver, the time, frequency, and phase synchronization between the transmitter and the receiver are lost. This implies that a transmission of a part of the DL data that comes after a preemption may need to allow the receiver to resynchronize and perform channel estimation in a similar way as at the beginning of the transmission. Therefore, after a preemption the next part of the transmission of DL data may contain fields for parameter estimation. A natural choice may be to reuse the same fields that are used for the first transmission, i.e., a legacy preamble and a second preamble as specified in the IEEE 802.11 standard and the contents of which depend on the Wi-Fi generation. The following explanations focus on situations when there is no preemption and are thus applicable irrespectively of details related to resynchronization in case of preemption.

[0041] When there is no preemption, the parts of the transmission of DL data are separated only by the time gap, which has a much shorter duration than a LL data transmission. As regards the duration of the time gap, the following needs to be considered:

[0042] Criterion 1 : The duration of time gap should be sufficiently short to ensure that a device that is not intended to cause a preemption finds the channel busy. When a device is operating under the DCF (Distributed Coordination Function) channel access scheme of the IEEE 802.11 standard to transmit data, the shortest time the device has to find the channel to be idle is the DCF inter-frame space (DIFS), which equals 16 + 2x9 = 34 ps. Accordingly, any choice of the time gap which is less than 34 ps satisfies this requirement.

[0043] Criterion 2: The duration of the time gap should be sufficiently long so that a device that intends to cause a preemption is able to detect that the channel is idle, switch from receive to transmit, and start transmitting. This time may depend on implementation specific and may depend on device capability. However, since the slot time in Wi-Fi systems is 9 ps, this may serve as a reasonable limit for what can be achieved.

[0044] At a first glance, a promising choice for the time gap would seem to be 16 + 9 = 25 ps. However, such choice may in fact come with a drawback. To see this, one may first consider what an OFDM signal typically looks like: It consists of a number of OFDM symbols. The duration of an OFDM symbol is determined by sampling rate and the FFT (Fast Fourier Transform) size used for generating the OFDM symbol. Taking IEEE 802.11 ax as an example, for a 20 MHz channel bandwidth the sampling rate is 20 MHz and the FFT size is 256, resulting in a symbol duration of 256 / 20 MHz = 12.8 ps. Further, a Gl is added before each OFDM symbol. The duration of the Gl is selected based on the expected excess delay of the channel, and for IEEE 802.11 ax the Gl may be 0.8 ps, 1.6 ps, or 3.2 ps. For most cases, the shortest Gl = 0.8 ps is sufficient and when this Gl is used, the duration of OFDM symbol plus Gl equals 13.6 ps. Fig. 3A schematically illustrates such characteristics of an OFDM signal.

[0045] The receiver processing of a sequence of OFDM symbols typically contains many steps, but what can be noted is that the FFT is typically running on a fixed frequency, corresponding to applying the FFT every 13.6 ps. Here, it is also noted that the exact position of the FFT window is typically not critical for the performance (the Gl is typically selected with some margin, so moving the FFT window a few samples in either direction typically does not impact the performance). But once a position of the FFT window has been selected relative to the OFDM symbol timing, it should not be changed as this would cause the effective channel as seen after the FFT to change even if the physical channel remains the same. Such a change would for instance mean that the phase estimate must be updated even if the channel is static.

[0046] Fig. 3B schematically illustrates how the effect of a time gap of 25 ps in the OFDM signal affects the OFDM symbol timing after the time gap, namely in such a way that there is a shift of the OFDM symbol timing. Such shift would also require an update of the FFT window timing.

[0047] As discussed above, updating the timing of the FFT window relative to the OFDM symbol timing is typically desirable to avoid. To achieve this, the illustrated concepts involve a specific selection of the duration of the time gap, namely as a suitable multiple of the OFDM symbol duration plus Gl duration. Fig. 3C illustrates a corresponding example. In the example of Fig. 3C, the time gap is selected to be twice the duration of OFDM symbol plus Gl, i.e., 27.2 ps. Taking into account the above-mentioned considerations related to enablement of preemption, in particular above-described criterion 1 and criterion 2, a duration of the time gap corresponding to a single OFDM symbol plus Gl would be possible as well, whereas a time gap corresponding to three times the duration of OFDM symbol plus i Gl would result in an excessively long time gap (> 34 ps).

[0048] Accordingly, aligning the duration of the time gap with the OFDM symbol duration plus Gl as discussed above constitutes an attractive solution. In addition or as an alternative, it would also be possible to alternatively or additionally compensate for a (possibly residual) misalignment. Such compensation may be based on knowledge of the misalignment. When for example considering the above examples and assuming that the OFDM signal carries data of to a single user, if the misalignment is 2.2 ps (like in the scenario of Fig. 3B), the receiver may simply advance the FFT window by+++ the corresponding amount. If for example the sampling rate is 20 MHz, advancing the FFT window by 2.2 ps would correspond to advancing the FFT window by 20 x 2.2 = 44 samples. In such compensation, the advancement of the FFT window would be based on knowledge of characteristics of the transmitted OFDM signal, rather than on estimation at the receiver side. For example, if one would start each of the parts of the transmission with fields for estimation of, e.g., time, frequency, phase, and / or other channel properties, there would be a relatively high probability that, e.g., the estimated sample timing deviates by one or more samples from to the sample timing found for the previous parts of the transmission. In the discussion above, it was shown that it is not straightforward to for example use phase estimates from the previous part of the transmission in reception of the currently received part. However, based on the illustrated alignment of the time gap duration and / or compensation, it can be exploited that due to the short duration of the time gap, performing the estimation may not be needed and that the previous estimate can be reused even if it is slightly outdated. A generalization of such solutions to MU-OFDMA (Multi-User Orthogonal Frequency Division Multiplexing Access) transmissions will be discussed further below.

[0049] Having described various technical aspects related to preemption based on splitting a large data transmission, e.g., a PPDU, into smaller parts separated by time gaps, the example scenarios in accordance with the illustrated concepts include:

[0050] Example Scenario 1 : Alignment of duration of the time gap with OFDM symbol duration

[0051] In this example scenario, the duration of the time gap is selected as an integer multiple of the OFDM symbol duration plus Gl. If multiple Gl values are supported forthe same OFDM symbol duration, one option in this example scenario is that the time gap is selected to be aligned with respect to only one of the supported Gl values. Another option would be that the time gap is changed depending on which of the supported Gl values is actually used.

[0052] Example Scenario 2: Partial bandwidth DL preemption for multi-user DL transmission

[0053] In the above examples, preemption was discussed in situation where the preempted transmission was intended to a single recipient. The illustrated concepts are however also applicable for enabling preemption of multi-user transmissions. In the present example scenario, preemption of a multi-user transmission, e.g., using OFDMA, is considered, e.g., as illustrated in Fig. 4.

[0054] By way of example, Fig. 4 illustrates a transmission of DL data from the AP to / from four stations (STA1 , STA2, STA3, and STA4). The transmission may for example correspond to the situation where the total bandwidth of the wireless channel is 80 MHz and each one of the 4 stations are allocated a 20 MHz subchannel.

[0055] Since in many situations the LL data may correspond to only a small amount of data, the LL data does not need the full 80 MHz bandwidth. Therefore, according to the present example scenario, the preemption is limited to one of the users, in the illustrated example STA4. As explained above, the time gap for enabling the preemption may be aligned with the OFDM symbol duration in the above-described manner. This is beneficial because the transmission to all four stations is generated by a single IFFT. As a result, the OFDM symbols forthe different stations are aligned. The alignment of the time gap with the OFDM symbol duration plus Gl allows for efficiently maintaining this alignment.

[0056] It is also noted that the principles underlying this example scenario also allow for supporting preemption while communicating with legacy devices. Specifically, in order to introduce preemption, the station that may be preempted may need to be aware that there will be time gaps in the transmission. Such awareness may however not be assumed for legacy devices. In the example scenario of Fig. 4, it can however be seen that enabling the preemption for STA4 does not impact STA1 , STA2, and STA3. In other words, STA1 , STA2, and STA3 could be legacy devices.

[0057] Example Scenario 3: Partial bandwidth UL preemption for multi-user DL transmission

[0058] In the previous example scenario, the preemption was assumed to be initiated by the AP. As also explained in the context of Fig. 2A, preemption by a DL transmission substantially means that the AP replaces the transmission to one station (in the scenario of Fig. 2A STA1 , in the scenario of Fig. 4 STA4) with a transmission to another station. If, however, the LL transmission is from a STA to the AP, the station may need to interrupt the ongoing DL transmission. When the DL transmission is to multiple users and it is desirable to only introduce time gaps for only a fraction of the DL bandwidth, this may require that the AP is able to transmit and receive at the same time, although not on the same frequency. Such capability is often referred to as sub-band full duplex (SBFD). Although implementing SBFD may constitute a challenge, it can be expected that aligning the OFDM symbols for the UL transmission with the OFDM symbols for the DL transmission facilitates implementation of SBFD. Aligning the UL transmission with the DL transmission may be regarded as being a task for the station which sends the LL transmission. Approaches for achieving such alignment are for example described in WO 2023 / 046287 A1 and may be reused in the concepts of the present disclosure for aligning the UL transmission causing preemption of a DL transmission. Also, in the case of preemption by a UL transmission, the time gaps for enabling the preemption would be aligned with the OFDM symbol duration plus Gl, i.e., with the OFDM signal which is being sent in the DL. It is further noted that the time gaps which enable preemption by a UL transmission may at the same time also enable preemption by a DL transmission (e.g., like in the example of Fig. 4). Further, it is noted that also in scenarios where the time gaps are provided in only a part of the bandwidth to enable preemption by a UL transmission, coexistence with legacy devices may be provided in a similar manner as in the example of Fig. 4.

[0059] Example Scenario 4: Partial bandwidth UL preemption for multi-user UL transmission Analogous to example scenarios 2 and 3, preemption may also be enabled in a fraction of the bandwidth when the ongoing transmission (which can be preempted) is multi-user UL transmission, e.g., based on UL OFDMA.

[0060] For example, when again referring to Fig. 4, it can be assumed that STA1 , STA2, and STA3 send UL data in a contiguous and non-preemptible fashion to the AP, using their respectively allocated frequency resources, while STA4 sends data in a non-contiguous and preemptible fashion, i.e., split by the time gaps, to the AP. The time gaps between different parts of the UL transmission from STA4 may again correspond to integer multiples of OFDM symbol duration plus Gl. In this way, it can be ensured that there is no inter-OFDM symbol interference across the different bandwidth portions during reception at the AP. In such a situation, another station, e.g., STA5, could preempt the UL transmission of STA4 by transmitting during one of the time gaps. In such case, STA5 may use the required time on the corresponding subchannel to send its LL data to the AP. Alternatively, STA5 could only send a scheduling request to the AP, and upon reception of the scheduling request the AP may prioritize the scheduling of STA5 in the next triggered UL transmission opportunity. In the latter variant, STA4 could be able to resume its original transmission to the AP before STA5 begins transmitting the LL data.

[0061] It is also noted that the following situations could occur in example scenario 4:

[0062] • STA5 is in range of STA4. In this case, STA5 may be able to track the transmission of STA4 and identify the time gap and preemption opportunity in real time. Moreover, STA4 may be able to detect the transmission by STA5 and pause / discontinue its transmission in a timely manner.

[0063] • STA5 is not in range of STA4. In this case, STA5 may need to rely on an initial control frame, e.g., a trigger frame transmitted by the AP, to be able to estimate when to preempt STA4’s transmission at an appropriate time instance, i.e., an appropriate time that corresponds to one of the time gaps which would need to be estimated based on computations rather than based on real-time tracking of STA4’s transmissions. Additionally, STA4 might not be able to detect the transmission by STA5 and thus continue its original transmission. If this happens, STA5’s transmission would need to be received at the AP with a suitable signal to interference plus noise ratio (SINR) so that it can be successfully received.

[0064] Also in example scenario 4, preemption can be supported without affecting coexistence with legacy devices.

[0065] Example Scenario 5: Partial bandwidth DL preemption for multi-user UL transmission

[0066] In this example scenario, the AP may preempt an ongoing multi-user UL transmission over a fraction of the bandwidth, e.g., with the aim of sending urgent DL data to one of the associated stations.

[0067] Again referring to Fig. 4, the AP may transmit DL to a different STA5 during one of the time gaps between STA4’s UL transmissions. Similar to example scenario 4, this operation could make use of a SBFD capability of the AP, so that ongoing non-preempted UL transmissions may be successfully received while there is a DL transmission by the AP on a part of the bandwidth. If successful reception of the non-preempted UL transmissions is not a requirement, then the AP may simply transmit in DL and it may be tolerated that during that DL transmission period, at least a part of the ongoing UL transmissions may be incorrectly received.

[0068] Also, it is proposed for the time gaps to be integer multiples of OFDM symbol duration (including Gl), to ensure there is no inter-OFDM symbol interference across frequency portions during reception at the AP.

[0069] Also in example scenario 5, the time gaps between different parts of the UL transmission from STA4 may correspond to integer multiples of OFDM symbol duration plus Gl. In this way, it can be ensured that there is no inter-OFDM symbol interference across the different bandwidth portions during reception at the AP. Further, also in this example preemption can be supported without affecting coexistence with legacy devices.

[0070] Example Scenario 6: Partial bandwidth DL or UL preemption during single-user DL or UL transmissions

[0071] While in the above examples enablement of preemption on only a fraction of the channel bandwidth was explained in relation to multi-user transmissions where different users (e.g., stations) are allocated different portions of the bandwidth, enablement of preemption on only a fraction of the channel bandwidth may also be useful for single user (SU) transmissions. Fig.

[0072] 5 illustrates a corresponding example. In this example, time gaps are provided in only a fraction of the channel bandwidth to enable preemption of SU DL or UL transmissions.

[0073] In the present example scenario, the ongoing SU transmission in DL or UL may be preempted for facilitating an urgent DL transmission or UL transmissions in only a part of the channel bandwidth, while the ongoing SU transmission continues in a contiguous fashion over the remaining portions of the channel bandwidth. As an example, such a situation may occur when the SU DL or UL transmissions between two devices involve transmissions of independent packets, e.g., a mix of contiguous and non-preemptible packets on a first bandwidth portion, and non-contiguous and preemptible packets on another bandwidth portion. Such different bandwidth portions may for example correspond to non-overlapping subchannels of the wireless channel. In the specific example of Fig. 5, four parallel packets are being transmitted or received over different subchannels of the wireless channel. The fourth packet is split into sub-packets which are separated by time gaps. The preemption may occur during one of these time gaps.

[0074] Also in example scenario 5, the time gaps between different parts of the UL transmission from STA4 may correspond to integer multiples of OFDM symbol duration plus Gl, to facilitate reception of the non-preempted and contiguous transmissions.

[0075] Fig. 6 shows a flowchart for illustrating a method of controlling wireless transmissions in a wireless communication system, which may be utilized for implementing the illustrated concepts. The method of Fig. 6 may be used for implementing the illustrated concepts in a wireless communication device, e.g., one of the above-mentioned APs 10 or one of the above- mentioned stations 20. The wireless communication system may be based on a wireless local area network, WLAN, technology, e.g., according to the IEEE 802.11 standards family.

[0076] If a processor-based implementation of the wireless communication device is used, at least some of the steps of the method of Fig. 6 may be performed and / or controlled by one or more processors of the wireless communication device. Such wireless communication device may also include a memory storing program code for implementing at least some of the below described functionalities or steps of the method of Fig. 6.

[0077] At step 610, the wireless communication device generates data transmissions based on OFDM, in particular at least a first data transmission and a second data transmission. The wireless communication device may generate the data transmissions by splitting a PPDU into smaller parts. Accordingly, the data transmissions may correspond to parts or segments of a PPDU.

[0078] At step 620, the wireless communication device generates one or more time gaps separating the data transmissions. As a result, the first data transmission and the second data transmission are separated by a time gap. The time gap corresponds to an integer multiple of OFDM symbol duration plus Gl and allows to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0079] The first data transmission may have a first format, while the second data transmission has a second format which is different from the first format. For example, the second format may define less fields for parameter estimation than the first format. In this way, it can be taken into account that a receiver may reuse parameter estimation results from the first transmission for reception of the second transmission. An OFDM signal of the first data transmission and the second data transmission may be based on an IFFT, and the wireless communication device may generate the time gap(s) by setting inputs of the IFFT to zero.

[0080] In some scenarios, generating the data transmissions may involve that, by applying the OFDM in a first bandwidth portion of the wireless channel, the wireless communication device transmits the first data transmission and the second transmission to a first recipient, and by applying the OFDM in a second bandwidth portion of the wireless channel, the wireless communication device transmits one or more further data transmissions to a second recipient. In such scenarios, the wireless communication device may transmit the one or more further data transmissions without the time gap. Fig. 4 illustrates an example of such scenarios.

[0081] The time gap may enable the wireless communication device to preempt the second data transmission and initiate a third data transmission from the wireless communication device. The first data transmission and the second data transmission may be intended to a first recipient, while the third data transmission is intended to a second recipient. Figs. 2A and 4 show corresponding examples.

[0082] In addition or as an alternative, the time gap may enable another wireless communication device to preempt the second data transmission and initiate a fourth data transmission from the other wireless communication device. The fourth data transmission may then be intended to be received by the wireless communication device. In some scenarios, initiating the fourth data transmission may involve that the other wireless communication device starts the fourth data transmission in the time gap, e.g., like in the example of Fig. 2B. Alternatively, initiating the fourth data transmission may involve that the other wireless communication device transmits a request for scheduling of the fourth data transmission in the time gap. Fig. 2C shows a corresponding example.

[0083] At step 630, the wireless communication device may preempt the second data transmission by starting a transmission in the time gap. The transmission in the time gap may be used for transmission of LL data.

[0084] Fig. 7 shows a flowchart for illustrating a method of controlling wireless transmissions in a wireless communication system, which may be utilized for implementing the illustrated concepts. The method of Fig. 7 may be used for implementing the illustrated concepts in a wireless communication device, e.g., one of the above-mentioned stations or one of the above- mentioned APs 10. The wireless communication system may be based on a wireless local area network, WLAN, technology, e.g., according to the IEEE 802.11 standards family.

[0085] If a processor-based implementation of the wireless communication device is used, at least some of the steps of the method of Fig. 7 may be performed and / or controlled by one or more processors of the wireless communication device. Such wireless communication device may also include a memory storing program code for implementing at least some of the below described functionalities or steps of the method of Fig. 7.

[0086] At step 710, the wireless communication device receives a first data transmission on a wireless channel based on OFDM. The first data transmission is separated from a second data transmission on the wireless channel by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allowing to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

[0087] At step 720, the wireless communication device may preempt the second data transmission by starting a transmission in the time gap. The transmission in the time gap may be used for transmission of LL data.

[0088] The first data transmission may have a first format, while the second data transmission has a second format which is different from the first format. For example, the second format may define less fields for parameter estimation than the first format. In this way, it can be taken into account that a receiver may reused parameter estimation results from the first transmission for reception of the second transmission. If the second data transmission is not preempted, the wireless communication device may also receive the second data transmission.

[0089] For receiving the first data transmission and the second data transmission, the wireless communication device may process the first data transmission and the second data transmission based on a same FFT window timing relative to the OFDM symbols.

[0090] The time gap may enable the wireless communication device to preempt the second data transmission and initiate a third data transmission from the wireless communication device. The third data transmission may be intended to be received by another wireless communication device which corresponds to the transmitter of the first data transmission and the second data transmission, e.g., like in the examples of Figs. 2B and 2C. In some scenarios, initiating the third data transmission may involve that the wireless communication device starts the third data transmission in the time gap, e.g., like in the example of Fig. 2B. Alternatively, initiating the third data transmission may involve that the wireless communication device transmits a request for scheduling of the third data transmission in the time gap, e.g., like in the example of Fig. 2C.

[0091] Fig. 8 illustrates a processor-based implementation of an AP 800. The structures as illustrated in Fig. 8 may be used for implementing the above-described concepts. The AP 800 may for example correspond to one of above-mentioned APs 10.

[0092] As illustrated, the AP 800 includes a radio interface 810. The radio interface 810 may for example be based on a WLAN technology, e.g., according to an IEEE 802.11 family standard. However, other wireless technologies could be supported as well, e.g., the LTE technology or the NR technology. Further, the AP 800 is provided with a network interface 820 for connecting to a data network, e.g., using a wire-based connection.

[0093] Further, the AP 800 may include one or more processors 850 coupled to the interfaces 810, 820, and a memory 860 coupled to the processor(s) 850. By way of example, the interfaces 810, 820, the processor(s) 850, and the memory 860 could be coupled by one or more internal bus systems of the AP 800. The memory 860 may include a Read-Only-Memory (ROM), e.g., a flash ROM, a Random Access Memory (RAM), e.g., a Dynamic RAM (DRAM) or Static RAM (SRAM), a mass storage, e.g., a hard disk or solid state disk, or the like. As illustrated, the memory 860 may include software 870 and / or firmware 880. The memory 860 may include suitably configured program code to be executed by the processor(s) 850 so as to implement the above-described functionalities for controlling wireless transmissions, such as explained in connection with the method of Fig. 6 or in connection with the method of Fig. 7.

[0094] It is to be understood that the structures as illustrated in Fig. 8 are merely schematic and that the AP 800 may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces or further processors. Also, it is to be understood that the memory 860 may include further program code for implementing known functionalities of an AP in an IEEE 802.11 standard compliant technology. According to some embodiments, also a computer program may be provided for implementing functionalities of the AP 800, e.g., in the form of a physical medium storing the program code and / or other data to be stored in the memory 860 or by making the program code available for download or by streaming.

[0095] Fig. 9 illustrates a processor-based implementation of wireless device 900. The structures as illustrated in Fig. 9 may be used for implementing the above-described concepts. The wireless device 900 may for example correspond to one of above-mentioned stations 20. As illustrated, the wireless device 900 includes a radio interface 910. The radio interface 910 may for example be based on a WLAN technology, e.g., according to an IEEE 802.11 family standard. However, other wireless technologies could be supported as well, e.g., the LTE technology or the NR technology.

[0096] Further, the wireless device 900 may include one or more processors 950 coupled to the radio interface 910 and a memory 960 coupled to the processor(s) 950. By way of example, the radio interface 910, the processor(s) 950, and the memory 960 could be coupled by one or more internal bus systems of the wireless device 900. The memory 960 may include a ROM, e.g., a flash ROM, a RAM, e.g., a DRAM or SRAM, a mass storage, e.g., a hard disk or solid state disk, or the like. As illustrated, the memory 960 may include software 970 and / or firmware 980. The memory 960 may include suitably configured program code to be executed by the processor(s) 950 so as to implement the above-described functionalities for controlling wireless transmissions, such as explained in connection with the method of Fig. 7.

[0097] It is to be understood that the structures as illustrated in Fig. 9 are merely schematic and that the wireless device 900 may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces or further processors. Also, it is to be understood that the memory 960 may include further program code for implementing known functionalities of STA in an IEEE 802.11 standard compliant technology. According to some embodiments, also a computer program may be provided for implementing functionalities of the wireless device 900, e.g., in the form of a physical medium storing the program code and / or other data to be stored in the memory 960 or by making the program code available for download or by streaming.

[0098] As can be seen, the concepts as described above may be used for enabling preemption in an efficient manner, without adding excessive complexity to existing technologies. It may even be possible to simplify receiver processing and / or formats of data transmissions, e.g., by omitting fields for parameter estimation and related processing. Further, the concepts may be applied to enable preemption in only a fraction of the available bandwidth. This may further enhance efficiency, because other parts of the bandwidth are not affected. Further, this may allow for enabling preemption for only a part of the users of MU OFDM transmissions or for supporting coexistence with legacy devices that do not support preemption.

[0099] It is to be understood that the examples and embodiments as explained above are merely illustrative and susceptible to various modifications. For example, the illustrated concepts may be applied in connection with various kinds of wireless technologies, without limitation to WLAN technologies. Further, the illustrated concepts may be applied with respect to various categories of data traffic. Moreover, it is to be understood that the above concepts may be implemented by using correspondingly designed software to be executed by one or more processors of an existing device or apparatus, or by using dedicated device hardware. Further, it should be noted that the illustrated apparatuses or devices may each be implemented as a single device or as a system of multiple interacting devices or modules.

Claims

Claims1. A method of controlling wireless transmissions in a wireless communication system, the method comprising: based on Orthogonal Frequency Division Multiplexing, OFDM, a wireless communication device (10; 20; 800; 900) generating a first data transmission and a second data transmission on a wireless channel, wherein the first data transmission and the second data transmission being separated by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allowing to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

2. The method according to claim 1 , wherein the first data transmission has a first format and the second data transmission has a second format which is different from the first format.

3. The method according to claim 2, wherein the second format defines less fields for parameter estimation than the first format.

4. The method according to any of claims 1 to 3, comprising: the wireless communication device (10; 20; 800; 900) generating the first data transmission and the second data transmission by splitting a Protocol Packet Data Unit (PPDU).

5. The method according to any of claims 1 to 4, comprising: the wireless communication device (10; 20; 800; 900) generating an OFDM signal of the first data transmission and the second data transmission based on an Inverse Fast Fourier Transform, IFFT; and the wireless communication device (10; 20; 800; 900) generating the time gap by setting inputs of the IFFT to zero.

6. The method according to any of claims 1 to 5, comprising: by applying the OFDM in a first bandwidth portion of the wireless channel, the wireless communication device (10; 20; 800; 900) transmitting the first data transmission and the second transmission to a first recipient; and by applying the OFDM in a second bandwidth portion of the wireless channel, the wireless communication device (10; 20; 800; 900) transmitting one or more further data transmissions to a second recipient.

7. The method according to claim 6, wherein the wireless communication device (10; 20; 800; 900) transmits the one or more further data transmissions without the time gap.

8. The method according to any of claims 1 to 7, wherein the time gap enables the wireless communication device (10; 20; 800; 900) to preempt the second data transmission and initiate a third data transmission from the wireless communication device (10; 20; 800; 900).

9. The method according to claim 8, wherein the first data transmission and the second data transmission are intended to a first recipient, wherein the third data transmission is intended to a second recipient.

10. The method according to any of claims 1 to 8, wherein the time gap enables another wireless communication device (10; 20; 800; 900) to preempt the second data transmission and initiate a fourth data transmission from the other wireless communication device (10; 20; 800; 900).11 . The method according to claim 10, wherein the fourth data transmission is intended to be received by the wireless communication device (10; 20; 800; 900).

12. The method according to claim 11 , wherein initiating the fourth data transmission comprises that the other wireless communication device (10; 20; 800; 900) starts the fourth data transmission in the time gap.

13. The method according to claim 11 , wherein initiating the fourth data transmission comprises that the other wireless communication device (10; 20; 800; 900) transmits a request for scheduling of the fourth data transmission in the time gap.

14. The method according to any of claims 1 to 13, wherein the wireless communication device (10; 20; 800; 900) is an access point, AP, of the wireless communication system.

15. The method according to any of claims 1 to 13, wherein the wireless communication device (10; 20; 800; 900) is a non-AP station of the wireless communication system.

16. The method according to any one of claims 1 to 14, wherein the wireless communication system is based on a Wireless Local Area Network technology according to the IEEE 802.11 standards family.

17. A method of controlling wireless transmissions in a wireless communication system, the method comprising: based on Orthogonal Frequency Division Multiplexing, OFDM, a wireless communication device (10; 20; 800; 900) receiving a first data transmission on a wireless channel, wherein the first data transmission is separated from a second data transmission on the wireless channel by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allowing to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

18. The method according to claim 17, wherein the first data transmission has a first format and the second data transmission has a second format which is different from the first format.

19. The method according to claim 18, wherein the second format defines less fields for parameter estimation than the first format.

20. The method according to any of claims 17 to 19, comprising: the wireless communication device (10; 20; 800; 900) processing the first data transmission and the second data transmission based on a same Fast Fourier Transform, FFT, window timing relative to the OFDM symbols.21 . The method according to any of claims 17 to 20, wherein the time gap enables the wireless communication device (10; 20; 800; 900) to preempt the second data transmission and initiate a third data transmission from the wireless communication device.

22. The method according to claim 21 ,wherein the third data transmission is intended to be received by another wireless communication device (10; 20; 800; 900) which corresponds to the transmitter of the first data transmission and the second data transmission.

23. The method according to claim 22, wherein initiating the third data transmission comprises that the wireless communication device (10; 20; 800; 900) starts the third data transmission in the time gap.

24. The method according to claim 23, wherein initiating the third data transmission comprises that the wireless communication device (10; 20; 800; 900) transmits a request for scheduling of the third data transmission in the time gap-25. The method according to any of claims 17 to 24, wherein the wireless communication device (10; 20; 800; 900) is an access point, AP, of the wireless communication system.

26. The method according to any of claims 17 to 24, wherein the wireless communication device (10; 20; 800; 900) is a non-AP station of the wireless communication system.

27. The method according to any one of claims 17 to 26, wherein the wireless communication system is based on a Wireless Local Area Network technology according to the IEEE 802.11 standards family.

28. A wireless communication device (10; 20; 800; 900) for operation in a wireless communication system, the wireless communication device (10; 20; 800; 900) being configured to: based on Orthogonal Frequency Division Multiplexing, OFDM, generate a first data transmission and a second data transmission on a wireless channel, wherein the first data transmission and the second data transmission being separated by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allowing to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

29. The wireless communication device (10; 20; 800; 900) according to claim 28,wherein the wireless communication device (10; 20; 800; 900) is configured to perform a method according to any one of claims 2 to 16.

30. The wireless communication device (10; 20; 800; 900) according to claim 28 or 29, comprising: at least one processor (850; 950), and a memory (60; 960) containing program code executable by the at least one processor (850; 950), whereby execution of the program code by the at least one processor (850; 950) causes the wireless communication device (10; 20; 800; 900) to perform a method according to any one of claims 1 to 12.

31. A wireless communication device for operation in a wireless communication system, the wireless communication device being configured to: based on Orthogonal Frequency Division Multiplexing, OFDM, receive a first data transmission on a wireless channel, wherein the first data transmission is separated from a second data transmission on the wireless channel by a time gap corresponding to an integer multiple of OFDM symbol duration plus guard interval and allowing to preempt the second data transmission by starting a further transmission on the wireless channel during the time gap.

32. The wireless communication device (10; 20; 800; 900) according to claim 31 , wherein the wireless communication device (10; 20; 800; 900) is configured to perform a method according to any one of claims 18 to 27.

33. The wireless communication device (10; 20; 800; 900) according to claim 31 or 32, comprising: at least one processor (850; 950), and a memory (860; 960) containing program code executable by the at least one processor (850; 950), whereby execution of the program code by the at least one processor (850; 950) causes the wireless communication device (10; 20; 800; 900) to perform a method according to any one of claims 18 to 27.

34. A computer program or computer program product comprising program code to be executed by at least one processor (850; 950) of a wireless communication device (10; 20;800; 900), whereby execution of the program code causes the wireless communication device (10; 20; 800; 900) to perform a method according to any one of claims 1 to 16.

35. A computer program or computer program product comprising program code to be executed by at least one processor (850; 950) of a wireless communication device (10; 20;800; 900), whereby execution of the program code causes the wireless communication device (10; 20; 800; 900) to perform a method according to any one of claims 18 to 27.

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