WO2024245520A1

WO2024245520A1 - Multi-layer modulation based full-duplex operation

Info

Publication number: WO2024245520A1
Application number: PCT/EP2023/064200
Authority: WO
Inventors: Leif Wilhelmsson; Abhishek AMBEDE
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-05-26
Filing date: 2023-05-26
Publication date: 2024-12-05
Anticipated expiration: 2025-11-26

Abstract

Multi-layer modulation based full-duplex operation A wireless communication device (10) sends a first wireless signal (51, 52). During ongoing transmission of the first wireless signal (51, 52), the wireless communication device receives a second wireless signal (53) from a further wireless communication device (20). The second wireless signal (53) is based on a multi-layer modulation scheme which simultaneously modulates information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

Description

Multi-layer modulation based full-duplex operation

Technical Field

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

Background

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”. In the WLAN technology, a wireless communication device is typically denoted a STA (station). Such a STA may be an AP (access point) or a non-AP STA.

In view of increasing interest in wireless communication offering low or bounded latency and/or high reliability, the IEEE 802.11 working group has created an Ultra High Reliability (UHR) study group in July 2022 whose objective is to develop a Project Authorization Request (PAR) and a Criteria for Standards Development (CSD) for a new 802.11 MAC/PHY amendment. The emphasis in the UHR study group is on improvements to the IEEE 802.11 standard to increase the reliability of wireless connectivity and to better support applications requiring lower or more deterministic latencies. Drivers for such requirements concerning latency or reliability include for example extended reality (XR) applications, wireless control of industrial processes, and online gaming services. In such applications a maximum allowed end-to-end latency is often 5 ms or lower, e.g., 1 ms.

While operating in license-exempt frequency spectrum, wideband wireless communication systems, such as WLAN systems, typically operate using a listen before talk (LBT) mechanism, also referred to as carrier sense multiple access with collision avoidance (CSMA/CA). In such an LBT mechanism, before initiating a transmission, a STA listens on the wireless medium to determine whether the medium is busy or available and performs the transmission only if the medium is available. Correspondingly, in a typical basic service set (BSS) comprising an AP device and multiple non-AP STAs, the wireless communications are based on contentionbased channel access operations: Multiple STAs contend for winning a transmission opportunity (TXOP), and the STA winning the contention can then get exclusive access to the channel for a certain period of time, i.e., for the duration of the TXOP.

WLAN systems may use unscheduled uplink (UL) transmissions, which means that non-AP devices independently contend for channel access and undertake their own transmissions whenever they have data to transmit. However, a recent amendment to the IEEE 802.11 standard, “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 Amendment 1 : Enhancements for High- Efficiency WLAN”, in the following denoted as “802.11 ax amendment”, introduced support of two further modes of operation: an orthogonal frequency-division multiple access (OFDMA) based mode of operation and a trigger-based UL mode of operation. In these modes of operation, an AP device can schedule UL transmissions from one or more specific non-AP devices in its BSS and also select timing and transmission parameters of the UL transmissions. Thus, these mechanisms can help an AP device to better orchestrate UL communications in its BSS and thereby improve the overall performance of the BSS. This works particularly well when the data traffic is deterministic, so that the AP knows which non-AP STAs may have data to transmit and when such transmissions are needed. However, when the data traffic is event based and non-deterministic, it can be very challenging for an AP device to provision for appropriate and timely UL transmissions or to orchestrate scheduled UL transmissions.

One way to improve the handling of non-deterministic data traffic is to use full-duplex (FD) operation, e.g., as for example described in WO 2023/046287 A1. In FD operation, a wireless communication device can simultaneously transmit a first wireless signal, in the following denoted as “TX signal” and receive a second wireless signal, in the following denoted as “RX signal”. For this reason, FD operation may also be referred to as simultaneous transmit and receive (STR) operation. In STR operation, the TX signal and the RX signal may either use the exact same frequency resources or may use adjacent, non-overlapping resources within the same channel. The former case is often referred to as in-band full duplex (IBFD) or single frequency full duplex (SFFD), and the latter case is often referred to as sub-band full duplex (SBFD). In the case of a WLAN system, the FD operation could for example enable scenarios where an AP contends for the medium to send downlink (DL) data, and a non-AP STA associated with the AP sends UL data during the ongoing transmission of the DL data, without requiring that the non-AP STA contends for access to the medium or that the transmission of the UL data is scheduled by the AP.

For a device that is capable of STR operation, it may however be challenging to ensure a high probability of successfully receiving an unscheduled RX signal while transmitting a TX signal. In typical scenarios, the TX signal is on the order of 80-140 dB stronger than the RX signal, which means that self-interference (SI) from the TX signal to the RX signal must be suppressed to a significant extent. How much suppression is needed depends on the TX power, the RX power, and the required signal-to-interference-ratio (SIR). As an example, if the TX power is 20 dBm, the RX power is -80 dBm, and the required SIR is 20 dB, then the suppression must be at least 120 dB since the SI must be below -100 dBm. In case of SBFD, significant part of this suppression can be readily achieved by simply adhering to the specified spectral masks that define unwanted emission requirements, e.g., in terms of an adjacent channel leakage ratio (ACLR). For this reason, SBFD is often considered to be easier to implement.

How difficult it is to enable STR operation depends on the amount of suppression of SI that is needed. Whereas 80 dB may be relatively easy to achieve, achieving a suppression of 140 dB may not be feasible at all. Since the amount of suppression that is feasible can be considered as a known parameter, it is possible to determine what combinations of TX power, RX power, and receiver sensitivity allow for using STR operation. It may be the case that less suppression can be achieved for higher TX power, e.g., due to certain non-linear effects being more pronounced and making cancellation of SI more challenging. However, also such non-linear effects can be assumed to be known parameters which can be taken into account rather easily when assessing feasibility of STR operation.

When now assuming that an AP is capable of STR under the condition that the required SI suppression is not too large, the AP may schedule or trigger UL transmissions and also decide the modulation and coding scheme (MCS) and TX power to be used for the UL transmissions. In this way, the AP can in principle ensure that STR becomes feasible for these UL transmissions and DL transmissions from the AP. Of course, there may be cases where STR is practically not feasible, e.g., if a STA sending a UL transmission is too far from the AP, so that the required TX power to enable STR operation exceeds a maximum possible TX power. Accordingly, STR operation may be feasible in many scenarios where the AP can schedule a DL transmission and an UL transmission so that the requirement for SI suppression is met. In other cases, the AP may decide to schedule only DL transmissions or only UL transmissions at a time.

In scenarios where the AP does not schedule the UL transmissions, the STA transmitting in the UL typically is not aware of the TX power used by the AP and thus cannot determine what is a suitable MCS to use in the UL in order to allow for STR at the AP. It may even be the case that the STA is not aware whether the AP is transmitting in the DL. But even when the AP is scheduling the UL transmissions to the AP, there may be issues when the duration of the DL transmissions and UL transmissions are not the same, e.g., if the AP would transmit two different packets to two different STAs in the DL during the reception of one UL packet.

Further, when the AP uses STR operation, the AP could be transmitting to one STA in the DL at the same time as the AP is receiving in the UL from another STA. This may result in a challenging interference situation at the STA receiving the DL signal from the AP, due to interference caused by the UL transmission from the other STA. Although the level of interference may be rather low, the interference can be problematic because the interfering signal is not known to the interfered STA, e.g., because the power of the interfering UL signal changes, the STA transmitting the interfering UL signal moves, the STA receiving the DL signal moves, or there are other movements or changes in the environment of the STAs. In such situations, suppression or cancellation of the interference at the interfered STA may be very demanding or even impossible so that efficient usage of STR by the interfered STA is not possible or at least very difficult to achieve.

Effective use of STR operation benefits from matching of the transmissions in both directions. That is to say, for a given transmission in one direction, the transmission in the other direction should be supporting a data rate which is as high as possible. Such matching may however require coordination between the two directions in terms of transmission power, MCS, and the required sensitivity in the device using STR operation. As mentioned above, such coordination is, however not always possible or can be done to only a limited extent, e.g., in the case of unscheduled or otherwise non-deterministic UL transmissions. For example, in the case of an AP using STR operation, the STA sending the UL signal to the AP could be using an MCS of an order which is too high in view of the received power of the UL signal and the TX power in the DL. As a result, the reception of the UL signal by the AP may fail. On the other hand, if the STA sending the UL signal uses an MCS of low order to safely enable STR operation, it could happen that the AP is not transmitting at all in the DL, so that usage of a much higher order MCS would be possible, meaning that channel is not utilized in an efficient manner. Accordingly, there is a need for techniques which allow for efficiently utilizing STR operation for wireless communication, in particular in situations where coordination of transmissions of different directions is not possible or possible to only a limited extent, e.g., in the case of transmissions which are, at least in part, unscheduled or otherwise non-deterministic.

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 sends a first wireless signal. During ongoing transmission of the first wireless signal, the wireless communication device receives a second wireless signal from a further wireless communication device. The second wireless signal is based on a multi-layer modulation scheme which simultaneously modulates information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

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 a first wireless signal. During ongoing reception of the first wireless signal, the wireless communication device sends a second wireless signal to a further wireless communication device. The second wireless signal is based on multi-layer modulation scheme which simultaneously modulates information to at least a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

According to a further embodiment, a wireless communication device for a wireless communication system is provided. The wireless communication device is configured to send a first wireless signal. Further, the wireless communication device is configured to, during ongoing transmission of the first wireless signal, receive a second wireless signal from a further wireless communication device. The second wireless signal is based on a multi-layer modulation scheme which simultaneously modulates information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

According to a further embodiment, a wireless communication device for a wireless communication system 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 send a first wireless signal. Further, the memory contains instructions executable by said at least one processor, whereby the wireless communication device is operative to, during ongoing transmission of the first wireless signal, receive a second wireless signal from a further wireless communication device. The second wireless signal is based on a multi-layer modulation scheme which simultaneously modulates information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

According to a further embodiment, a wireless communication device for a wireless communication system is provided. The wireless communication device is configured to receive a first wireless signal. Further, the wireless communication device is configured to, during ongoing reception of the first wireless signal, send a second wireless signal to a further wireless communication device. The second wireless signal is based on multi-layer modulation scheme which simultaneously modulates information to at least a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

According to a further embodiment, a wireless communication device for a wireless communication system 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 a first wireless signal. Further, the memory contains instructions executable by said at least one processor, whereby the wireless communication device is operative to, during ongoing reception of the first wireless signal, send a second wireless signal to a further wireless communication device. The second wireless signal is based on multi-layer modulation scheme which simultaneously modulates information to at least a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

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 for a wireless communication system. Execution of the program code causes the wireless communication device to send a first wireless signal. Further, execution of the program code causes the wireless communication device to, during ongoing transmission of the first wireless signal, receive a second wireless signal from a further wireless communication device. The second wireless signal is based on a multi-layer modulation scheme which simultaneously modulates information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness. 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 for a wireless communication system. Execution of the program code causes the wireless communication device to receive a first wireless signal. Further, execution of the program code causes the wireless communication device to, during ongoing reception of the first wireless signal, send a second wireless signal to a further wireless communication device. The second wireless signal is based on multi-layer modulation scheme which simultaneously modulates information to at least a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

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

Brief of the

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

Fig. 2 schematically illustrates an example of STR operation in accordance with an embodiment of the present disclosure.

Fig. 3 illustrates an example of a modulation symbol constellation in accordance with an embodiment of the present disclosure.

Figs. 4A and 4B schematically illustrate an example of multi-layer modulation in accordance with embodiments of the present disclosure.

Fig. 5 shows a flowchart for schematically illustrating a method according to an embodiment of the present disclosure.

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

Fig. 7 schematically illustrates structures of a wireless communication device according to an embodiment of the present disclosure. Detailed

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 control of wireless communication in a wireless communication system, also in view of the possibility of unscheduled wireless transmissions or otherwise non- deterministic wireless transmissions, e.g., carrying event-based or other kinds of non- deterministic traffic. In this context, a scheduled wireless transmission, i.e., a wireless transmission which is planned beforehand and for which the involved wireless communication devices, such as transmitter(s) and receiver(s), are specifically chosen may be considered as a wireless transmission which is completely deterministic. Such scheduling may involve requesting resources for the wireless transmission and performing the wireless transmission in response to such request being granted. Such scheduling may also involve specifically assigning timing and/ or transmit parameters for the wireless transmission(s) and performing the wireless transmission(s) based on the assigned parameters. Also, wireless transmissions which are performed on periodically assigned resources, e.g., based on semi-persistent scheduling or based on system configuration may be considered as deterministic. On the other hand, wireless transmissions which are not predictable or only predictable to some degree, such as random access transmissions or wireless transmissions triggered by an event at the transmitter, may be considered as non-deterministic. The wireless communication system may be a WLAN system based on 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 (3rd Generation Partnership Project) or to the Bluetooth technology.

In the illustrated concepts, multi-layer (ML) modulation may be utilized to enhance performance and/or reliability of wireless transmissions using STR operation, herein also denoted as FD operation. In STR operation, a wireless communication device, e.g., an AP, will receive an RX signal during ongoing transmission of a TX signal by the device. The ML modulation is based on modulating data on the RX signal using multiple modulation layers of different robustness level. The multiple modulation layers include a modulation layer with a high level of robustness and a modulation layer with low level of robustness, i.e., lower than the high level of robustness. Further modulation layers of intermediate level of robustness, i.e., lower than the high level, but higher than the low level, could be included as well. The modulation layers with higher level of robustness allow for increased chances to correctly receive the data, while the modulation layers with lower level of robustness may offer higher data rates. For example, for a wireless signal received in STR operation, the modulation layer with the highest level of robustness could allow for correct reception of the data at relatively poor receiver conditions, while the modulation layer(s) with lower level of robustness may provide enhanced data rate at more favorable receiver conditions. The difference between the highest robustness level and the lowest robustness level may be 20 dB or more (in terms of minimum required signal strength of the receivable signal). The number of modulation layers with intermediate levels of robustness may be two or three, but higher numbers of modulation layers could be used as well.

In a WLAN scenario with an AP which is capable of STR operation, herein also denoted as STR AP, the ML modulation can be applied to a UL transmission from a STA to the AP. In such case, the UL transmission would be carried by the RX signal transmitted from the STA to the STR AP. The TX signal transmitted by the STR AP could in turn carry one or more DL transmissions to the STA and/or one or more other STAs associated with the AP. The modulation layer with the highest level of robustness could then ensure that the AP can receive the UL signal while the AP is also transmitting a DL signal. For the modulation layers with lower level of robustness it may in turn not be necessary that they are correctly received while the AP is transmitting a DL signal, but such modulation layers may in turn allow for providing enhanced data rate while the AP is not transmitting in the DL.

In order to be able to account for a limitation of the dynamics of ML modulation to around 20 dB, some information may be provided from the device using STR to the sender of the RX signal, e.g., from an STR AP to a STA associated with the AP. Such information may in particular indicate receiver conditions, e.g., in terms of expected SINR (signal-to-interference plus noise ratio). Such receiver conditions can for example correspond to a scenario with most favorable receiver conditions, when no TX signal is being transmitted from the device. Based on such information, the sender of the RX signal can select coding schemes for the different modulation layers.

In a scenario involving an STR AP with multiple associated STAs, the ML modulation for the UL signals from these STAs can be configured individually per STA, e.g., with robustness levels differing between the STAs.

In some scenarios, an STR AP could also apply ML modulation to a DL transmission from the STR AP to an associated STA. This may for example allow for addressing issues with uncertain or variable receiver conditions at the STA, specifically with respect to interference caused by a concurrent UL transmission from another STA to the STR AP. If the STR AP schedules UL transmissions to the STR AP, the STR AP may have some knowledge about the interference situation at the STA which is the intended recipient of the DL transmission. In some cases, the STR AP may determine that the interference resulting from the concurrent UL transmission can be neglected and refrain from using ML modulation for the DL transmission. In other cases, the STR AP could determine that the interference caused by the UL transmission is not negligible and, in response, decide to apply ML modulation for the DL transmission, so that the chances of successful reception by the STA can be improved.

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 , STA21 , STA22, STA31 , and STA41. STA11 is served by AP1 , in a first BSS 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 communication 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.

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 (Orthogonal Frequency Division Multiplexing) using one or more carriers from a frequency spectrum which is shared on the basis of a contention-based mechanism, e.g., an unlicensed or license-exempt 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.

For at least some of the radio links between the APs 10 and stations 20, a STR operation may be utilized. In some examples, the device utilizing the STR operation may be an AP 10. Fig. 2 illustrates a corresponding example. However, it is noted that in some scenarios also a station could utilize STR operation. The STR operation is supported by applying ML modulation to one or more UL transmissions from the one or more of the stations 20 to the AP 10 and/or by applying ML modulation to one or more DL transmissions from the AP 10.

In the example of Fig. 2, an AP 10 communicates with a number of associated stations 20, denoted STA1 , STA2, and STA3. As further illustrated, the AP 10 may send a first DL transmission 51 to STA1 and a second DL transmission 52 to STA3. Further, the AP 10 may receive a UL transmission 53 from STA2. The AP 10 may for example be capable of suppressing SI by 80 dB, so that STR operation becomes possible under certain conditions. As illustrated, in the example of Fig. 2, STA1 is assumed to be closer to the AP 10 than STA2 and STA3, and STA2 is closer to the STR AP 10 than STA3. It is however noted that Fig. 2 is schematic in the sense that the illustrated differences in distance are not to scale.

In the example of Fig. 2, it is further assumed that the AP 10 uses transmit power control (TPC), and that for the DL transmission 51 to STA1 the AP 10 applies a TX power of 0 dBm, whereas for the DL transmission 52 to STA3 the AP 10 applies a TX power of 15 dBm. When now further assuming that the maximum TX power of STA2 is 20 dBm and that the pathloss between STA2 and the AP 10 is 80 dB, the maximum received signal power of the UL transmission 53 at the STR AP 10 would be -60 dBm. When now considering a situation where, at a given time, the AP 10 is sending the DL transmission 51 to STA1 and STA2 sends the UL transmission 53 while the DL transmission 51 is ongoing, but the DL transmission to STA3 is performed at some other time, the assumed suppression of SI by 80 dB would result in that, for the UL transmission 53 from STA2, the SIR at the AP 10 would be 20 dB. When assuming that that the channel bandwidth is 80 MHz, the value for the thermal noise floor is -87 dBm (based on a noise figure of roughly 7 dB), the level of interference would be considerably above the noise floor and the effective SINR of the UL transmission 53 as received by the AP 10 would be approximately the same as the SIR, i.e., about 20 dB. As compared to that, when considering a situation where the AP 10 sends DL transmission 52 to STA3 while STA2 sends the UL transmission 53 to the AP, the TX power of 15 dBm applied for the DL transmission 52 will result in a level of SI of -65 dBm, which means that the SIR of the UL transmission 53 as received by the AP 10 would be only about 5 dB. Comparing the two exemplary situations, it can be seen that STR could be relatively easily achieved while the AP 10 is transmitting to STA1 , whereas usage of STR would be challenging while the AP 10 is transmitting to STA3. If STA2 has no information about the DL transmissions 51 , 52 from the AP 10, it may for example transmit in an opportunistic way, using an MCS that would require about 20 dB SIR, with the risk that reception of the UL transmission 53 fails if the AP 10 simultaneously transmits to STA3. Alternatively, STA2 uses a more conservative approach and select an MCS which would allow for successful reception even at 5 dB SIR, however with comparatively lower data rate. In that case, there would be a risk that, in case of the AP 10 not transmitting to STA3, the achievable data rate is unnecessarily low, requiring a much longer transmit duration. In the illustrated concepts, such issues may be addressed by using ML modulation for the UL transmission 53, with a first modulation layer that allows for reception of the UL transmission 53 at 5 dB SIR and at least one further modulation layer of lower robustness and offering a higher data rate under more favorable receiver conditions.

It may also occur that the UL transmission 53 from STA2 causes interference at STA3, and that the level of this interference is not known or only very roughly known to the AP 10. For example, the AP 10 could be able to estimate the interference level at STA3 with an accuracy of 10 dB. As a result of such limited knowledge of the interference situation, it may be difficult for the AP 10 to determine the optimum MCS to be used in the DL transmission 52 to STA3. In the illustrated concepts, such issues may be addressed by using ML modulation for the DL transmission 52, e.g., with a first modulation layer that allows for reception of the DL transmission 52 under estimated worst-case interference conditions and at least one further modulation layer of lower robustness and offering a higher data rate under more favorable interference conditions.

In another exemplary situation, the AP 10 could be instead transmitting the DL transmission 51 to STA1 while STA2 performs the UL transmission 53 to the AP 10. In such case, the AP 10 could determine that that the interference caused by the UL transmission 53 from STA2 will not have any noticeable effect, i.e. , that the interference caused at STA1 is negligible. The AP 10 may in this case determine the optimum MCS to use under the assumption that there is no interference at STA1 and may decide not to use ML modulation for the DL transmission 51. The ML modulation may for example be implemented based on the principles as described “Opportunistic Multi-Layer Transmission over Unknown Channels”, by R. Gubbi Suresh et. al., IEEE Vehicular Technology Conference-Spring 2021 , in WO 2019/192684 A1 , or in WO 2020/165421 A1. In ML modulation as utilized in the illustrated concepts, it can be exploited that different bits of a modulation symbol may have different reliability, which means that they effectively carry different amounts of information. Fig. 3 illustrates these principles by referring to an example assuming 16-QAM (16 level Quadrature Amplitude Modulation) with Gray mapping.

In the example of Fig. 3, it can be seen that, even if a modulation symbol is in error, not all of the bits represented by the modulation symbol will be affected by the error. Examining the mapping a bit closer, it can be seen that the first bit determines whether the 16-QAM symbol is on the right or to the left of the imaginary part axis, whereas the second bit determines whether the 16-QAM symbol is above or below the real part axis. The third bit determines whether the 16-QAM symbol is in the inner two columns, i.e. , the two columns closest to the imaginary part axis, and the fourth bit determines whether the 16-QAM symbol is in the inner two rows, i.e., the two rows closest to the real part axis. Using information theoretical arguments, it can be shown that bits 1 and 2 carry more information than bits 3 and 4. The total information sent is the sum of the information sent by the four bits.

The fact that the different bits effectively carry different amounts of information can be exploited in the following manner: When for example using a rate 3/4 code, instead of mapping the code bits on a 16-QAM symbol, two codewords can be generated and the first codeword mapped to bits b1 and b2 and the second codeword be mapped to bits b3 and b4. What this means in practice is that in the proposed scheme two codewords will be sent in parallel, but the duration of a codeword will be twice as long so that the data rate in both cases will be identical. This is illustrated in Figs. 4A and 4B. Fig. 4A illustrates conventional modulation where the code bits of a first codeword (codeword 1) are mapped to bits b1-b4 of the 16-QAM symbol constellation, and subsequently the code bits of a second codeword (codeword 2) are mapped to bits b1-b4 of the 16-QAM symbol constellation. Fig. 4B illustrates an example of ML modulation, where the code bits of a first codeword (codeword 1) are mapped to bits b1-b2 of the 16-QAM symbol constellation, and simultaneously the code bits of a second codeword (codeword 2) are mapped to bits b3-b4 of the 16-QAM symbol constellation and the first and second codewords are sent in parallel. In this example, codeword 1 corresponds to a first modulation layer and codeword 2 corresponds to a second modulation layer. In WO 2019/192684 A1 and WO 2020/165421 A1 , it was shown that ML modulation based on multiple modulation layers of fixed robustness level can provide improved performance under varying channel conditions which are not known to the transmitter. However, due to the fixed robustness levels of the different modulation layers, there may be situations where the resulting performance is not satisfactory. When for example considering the above example of 16-QAM, the two modulation layers of the ML modulation may require that the SNR at the receiver is roughly 7 dB and 11 dB, respectively. On the other hand, if the code bits were mixed within a single codeword (such as in the example of Fig. 4A), the required SNR would be about 9 dB. In some situations, the receiver conditions may be hard to predict, and usage of the ML modulation may be preferred in view of the achievable result, e.g., in terms of data rate and reliability. In other situations, the channel conditions may be easier to predict. In the latter case, it may be preferable to use single layer modulation combined with link adaptation (LA), i.e. , adaptation of MCS based on the estimated receiver conditions. The above example of ML modulation based on 16-QAM corresponds to four modulation layers, of which two have a high level of robustness, i.e., high reliability, and the other two have lower level of robustness, i.e., lower reliability. The presence of two modulation layers with the same reliability can be attributed to the symmetry of the in-phase and quadrature-phase in the QAM symbol constellation, which can be observed in Fig. 3.

It is noted that ML modulation based on 16-QAM is one example and that ML modulation based on higher level QAM, such as 64-QAM or 256-QAM could be used as well. With such higher level QAM, the number of modulation layers would be higher and the difference in reliability of the different modulation layers can be larger. As an example, in the case of ML modulation based on 256-QAM, there would be eight modulation layers, with two of the modulation layers having the same reliability. For a typical Gray mapping, the robustness levels of the modulation layers are such that there are four different robustness levels, each with two modulation layers.

Simulation results with a LDPC (Low Density Parity Check) code of rate 1/2 using ML modulation show that the two most robust modulation layers (Layer 1 and Layer 2) require about 5 dB SNR, the two following modulation layers (Layer 3 and Layer 4) need about 6 dB more SNR, i.e., 11 dB, the next two modulation layers (Layer 5 and Layer 6) need yet another 6 dB, i.e., 17 dB SNR, and, finally, the two modulation layers (Layer 7 and Layer 8) with the lowest robustness level require roughly 21 dB SNR. When considering the UL transmission 53 in the example of Fig. 2, it can be assumed that with ML modulation based on 256-QAM, Layers 1 and 2 can be expected to always be correctly received by the AP 10 whereas for the remaining layers (i.e., Layer 3 - Layer 8), it can be expected that there will be reception errors if the UL transmission 53 to STA2 is performed simultaneously with the DL transmission 52 to STA3. On the other hand, when the UL transmission 53 is performed simultaneously with the DL transmission 51 to STA1 , it can be expected that Layer 1 - Layer 6 are correctly received by the AP 10 whereas for Layer 7 and Layer 8 correct reception is critical. In the case without any DL transmission, there would be no SI at the AP 10, so that it can be expected that all eight modulation layers are correctly received by the AP 10.

As can be seen, in a scenario where an AP may apply STR in wireless communication with one or more associated STAs, e.g., as in the example of Fig. 2, ML modulation may help to enable STR operation in an efficient way, without requiring detailed knowledge of the receiver conditions. Still, it should be noted that ML modulation does not provide better sensitivity than transmitting with the most robust MCS. This implies that if the receiver is on the edge of coverage where at best only the most robust modulation layer(s) can be expected to be correctly received, there is no need to use ML modulation. Rather, it can be assumed that using single layer modulation with the most robust MCS provides slightly better performance, so that using single layer modulation with the most robust MCS may be preferable. The modulation level, e.g., selection of QAM level, can be determined based on the estimated SNR in case of no simultaneous DL transmission. In principle, selection of a higher level modulation does not constitute a major problem. If the selected level is excessively high, it may however occur that some modulation layers are never correctly received. In such cases, the higher level modulation may add unnecessary complexity. Further, it could occur that the presence of the higher layers may have slight negative impact on sensitivity of the lower layers. Further, it should be noted that the experienced SINR for a UL transmission will typically depend on which STA is transmitting in the UL and what TX power is used by the AP for the simultaneous DL transmission and/or to which STA the simultaneous DL transmission is intended. It may therefore be possible to select transmission parameters, e.g., code rate, for the different modulation layers accordingly. For example, since the AP will know which different TX powers will be used for DL transmissions to the different STAs, the AP can attempt to achieve more decodable modulation layers by lowering the code rate of one or more modulation layers. For example when considering the above example of ML modulation based on 256-QAM, Layer 5 and Layer 6 need about 17 dB SNR to be correctly decoded with a rate 1/2 code. If the AP estimates that for many DL transmissions the resulting SNR would be only 15 dB, the AP could inform the STA accordingly, and the STA could for example reduce the code rate to 1/3 so that the also Layer 5 and Layer 6 can be expected to be correctly decoded. The above criteria may be considered individually per STA, so that it can be taken into account that the receiver conditions at the AP will be different from STA to STA, e.g., due to different propagation losses and/or different applied TX powers. Although the above examples focused on scenarios where an STR capable AP communicates with one or more associated STAs, it is noted that similar principles could also be applied for an STR capable STA. In some scenarios, also both the AP and the STA(s) communicating with the AP could be capable of STR and apply the illustrated principles. For example, both an AP and a STA associated with the AP could use STR operation and apply ML modulation to at least one of a UL transmission from the STA to the AP and a DL transmission from the AP to the STA or to some other STA.

In some scenarios, the ML modulation may be applied to one or more UL transmissions from a STA to an AP which is capable of STR operation. The STR operation could be based on SFFD or on SBFD. In this case, the ML modulation may address variations of the receiver conditions at the AP, without requiring detailed knowledge of the receiver conditions by the STA. Such variations may for example result from varying level of SI at the AP, e.g., depending on the DL transmissions performed by the AP. The usage of the ML modulation may be regarded as being opportunistic in the sense that the selection of the modulation configuration for a specific STA may be based on the highest expected SINR that can be obtained for a UL transmission from this STA. This highest SINR level may correspond to the case when the AP is not transmitting in the DL. Such selection may be performed individually per STA. The selection of code rates may differ between the modulation layers. Further, also the code rates for the different modulation layers may be selected individually per STA, e.g., taking into account how the SI, and as a result the effective SINR at the AP, depends on the DL transmissions to the different STAs.

In some scenarios, the ML modulation may be used in a selective manner to one or more UL transmissions from a STA to an AP which is capable of STR operation. The STR operation could be based on SFFD or on SBFD. For example, as mentioned above, in some situations the use of ML modulation can be expected to provide to gain in performance or even slightly reduced performance as compared to single layer modulation with the most robust MCS or as compared to modulation with an MCS which is adapted based on more detailed knowledge of receiver conditions. For example, it cases where the receiver conditions at the AP are known to the STA or at least can be predicted with high certainty, e.g., of 99%, the STA could decide to refrain from using ML modulation for the UL transmission and instead perform the UL transmission based on an MCS which is adapted based on the known or estimated receiver conditions. Similarly, the STA could decide to perform the UL transmission based on the most robust MCS if the STA determines that it is close to the edge of coverage of the AP, so that higher modulation layers would not be correctly received anyway. Accordingly, the usage of ML modulation may be combined with non-ML modulation by using the ML modulation in a selective manner, in response to the receiver conditions being unpredictable or unknown, and using non-ML modulation is used when the receiver conditions are considered to sufficiently known so that the MCS can be selected or adapted based on this knowledge.

In some scenarios, the ML modulation may be applied to UL transmissions from a STA to an AP, with the purpose of addressing inter-node interference, i.e., interference at a network node, such as an AP, which is caused by another network node, e.g., another AP or a base station of another wireless communication technology, e.g., a 3GPP system. Such inter-node interference may include inter-site interference, e.g., intra-operator or inter-operator interference, and/or co-located interference, e.g., inter-sector interference or inter-operator interference. Such inter-node interference is typically difficult to predict. Such inter-node interference may also be due to allowing STR and/or dynamic TDD (Time Division Duplex), which may result in situations where one node is transmitting while the another is receiving. The inter-node interference may of course also occur in addition to SI, making the receiver conditions even harder to predict. While the SI is caused by the same device that is the intended receiver, the inter-node interference is due to the transmission by another device, which may even operate on the basis of a completely different wireless technology. The possibility of such intern-node interference may thus significantly contribute to unpredictability of receiver conditions at the STR capable device.

In some scenarios, the ML modulation could also be applied to DL transmissions from an AP using STR operation. In this case, the ML modulation may help to address unknown interference conditions at the intended receiver of the DL transmission, in particular including interference from the UL transmission simultaneously received by the AP.

Fig. 5 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. 5 may be used for implementing the illustrated concepts in a wireless communication device operating in a wireless communication system, e.g., in an AP of the wireless communication system, e.g., one of the above-mentioned APs 10, or in a non- AP STA, such as 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.

If a processor-based implementation of the wireless communication device is used, at least some of the steps of the method of Fig. 5 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. 5.

At step 510, the wireless communication device sends a first wireless signal. The DL transmissions 51 and 52 in the scenario of Fig. 2 are examples of such first wireless signal. Accordingly, if the wireless communication device is an AP, the first wireless signal may correspond to a DL transmission from the AP, e.g., to a certain non-AP STA associated with the AP. It is however noted that in scenarios where the wireless communication device corresponds to a non-AP STA, the first wireless signal could be a UL transmission to an AP.

The wireless communication device may send the first wireless signal on first frequency resources, e.g., on a frequency channel or on a subband within a frequency channel.

At step 520, the wireless communication device receives a second wireless signal from a further wireless communication device. The UL transmission 53 in the scenario of Fig. 2 is an example of such second wireless signal. Accordingly, if the wireless communication device is an AP, the second wireless signal may correspond to a UL transmission from a non-AP STA. The further wireless communication device may be different from the intended recipient of the first wireless signal, like for example illustrated in the scenario of Fig. 2, where the DL transmission 51 is intended for STA1 , the DL transmission 52 is intended for STA3, and the UL transmission comes from STA2. It is however noted that in scenarios where the wireless communication device corresponds to a non-AP STA, the second wireless signal could be a DL transmission. Accordingly, in some scenarios the further wireless communication device could also be the destination of of the first wireless signal. In other scenarios, the further wireless communication device could be different from the destination of the first wireless signal.

The wireless communication device receives the second wireless signal during ongoing transmission of the first wireless signal. That is to say, the wireless communication at least temporarily uses STR operation for simultaneously sending the first wireless signal and receiving the second wireless signal. For this purpose, the wireless communication device may perform cancellation or suppression of SI caused by the first wireless signal.

The second wireless signal is based on an ML modulation scheme which simultaneously modulates information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness, examples of such ML modulation schemes are explained in connection with Figs. 3, 4A, and 4B. The ML modulation scheme may be based on a modulation symbol constellation assigning multiple bits to each symbol of the constellation in such a way that multiple bits have different reliability. For example, the assignment of the multiple bits to the symbols may be based on a Gray mapping. The ML modulation scheme may be based on QAM modulation. However, other types of modulation could be used as well.

In some scenarios, the ML modulation scheme is based on at least one further modulation layer having an intermediate level of robustness between the high level of robustness and the low level of robustness. Further, it is noted that the ML modulation scheme may also include modulation layers of the same level of robustness, e.g., like in the above-explained modulation symbol constellation based on 256-QAM modulation.

The wireless communication device may receive the second wireless signal on second frequency resources, e.g., on a frequency channel or on a subband within a frequency channel. The second frequency resources may be at least partially overlapping with the first frequency resources, such as in the case of implementing the STR operation based on SFFD. Alternatively, the second frequency resources could be non-overlapping with the first frequency resources, such as in the case of implementing the STR operation based on SBFD.

In some scenarios, the wireless communication device could also send information indicating one or more receiver conditions at the wireless communication device to the further wireless communication device. The one or more receiver conditions may enable the further wireless communication device to adapt the sending of the second wireless signal, e.g., by controlling the ML modulation scheme. In some cases, such information could be conveyed by the first wireless signal sent at step 510, e.g., in an initial part of the first wireless signal which is sent before reception of the second wireless signal starts. In other cases, the information indicating the one or more receiver conditions could also be sent separately from the first wireless signal, e.g., as part of control signaling. The one or more receiver conditions may correspond to a situation where the first wireless signal is absent.

In some scenarios, the ML modulation scheme may be applied in a selective manner. In a first mode of operation, the wireless communication device may receive the second wireless signal based on the ML modulation scheme, and in a second mode of operation, the wireless communication device may receive the second wireless signal based on a single-layer modulation scheme. In the second mode of operation, an MCS used in the single-layer modulation scheme could be selected based on LA, considering observed or estimated information of receiver conditions at the wireless communication device. Switching between the first mode of operation and the second mode of operation may depend on a level of predictability of channel conditions between the wireless communication device and the further wireless communication device and/or predictability of receiver conditions at the wireless communication device.

In some scenarios, also the first wireless signal is based on a ML modulation scheme. Such ML scheme applied for the first wireless signal could simultaneously modulate information to a third modulation layer having a high level of robustness and a fourth modulation layer having a low level of robustness. Also in this case, the ML modulation scheme may be based on QAM modulation. However, other types of modulation could be used as well. Further, also the ML modulation scheme applied for the first wireless signal may be based on at least one further modulation layer having an intermediate level of robustness between the high level of robustness and the low level of robustness and could include modulation layers of the same level of robustness, e.g., like in the above-explained modulation symbol constellation based on 256-QAM modulation. The ML modulation scheme applied for the first wireless signal and the ML modulation signal applied for the second wireless signal may be similar but may differ with respect to the configuration of the modulation layers, e.g., number of modulation layers and/or codes applied with respect to the different modulation layers.

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 operating in a wireless communication system, e.g., in a non- AP STA, such as one of the above-mentioned stations 20, or in an AP of the wireless communication system, e.g., 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.

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.

At step 610, the wireless communication device receives a first wireless signal. The DL transmissions 51 and 52 in the scenario of Fig. 2 are examples of such first wireless signal. Accordingly, if the wireless communication device is a non-AP STA, the first wireless signal may correspond to a DL transmission to the non-AP STA, e.g., from an AP to which the non- AP STA is associated. It is however noted that in scenarios where the wireless communication device corresponds to an AP, the first wireless signal could be a UL transmission to the AP, e.g., from a non-AP STA associated to the AP.

The wireless communication device may receive the first wireless signal on first frequency resources, e.g., on a frequency channel or on a subband within a frequency channel.

At step 620, the wireless communication device sends a second wireless signal to a further wireless communication device. The UL transmission 53 in the scenario of Fig. 2 is an example of such second wireless signal. Accordingly, if the wireless communication device is a non-AP STA, the second wireless signal may correspond to a UL transmission to an AP, e.g., an AP to which the non-AP STA is associated. It is however noted that in scenarios where the wireless communication device corresponds to an AP, the second wireless signal could be a DL transmission. In some scenarios the further wireless communication device could also be the source of the first wireless signal. In other scenarios, the further wireless communication device could be different from the source of the first wireless signal.

The wireless communication device sends the second wireless signal during ongoing reception of the first wireless signal. That is to say, the wireless communication at least temporarily uses STR operation for simultaneously receiving the first wireless signal and sending the second wireless signal. For this purpose, the wireless communication device may perform cancellation or suppression of SI caused by the second wireless signal.

The wireless communication device may send the second wireless signal on second frequency resources, e.g., on a frequency channel or on a subband within a frequency channel. The second frequency resources may be at least partially overlapping with the first frequency resources, such as in the case of implementing the STR operation based on SFFD. Alternatively, the second frequency resources could be non-overlapping with the first frequency resources, such as in the case of implementing the STR operation based on SBFD.

In some scenarios, the wireless communication device could also receive information indicating one or more receiver conditions at the further wireless communication device from the further wireless communication device. Based on the one or more receiver conditions, the wireless communication device may adapt the sending of the second wireless signal, e.g., by controlling the ML modulation scheme. In some cases, such information could be conveyed by the first wireless signal received at step 610, e.g., in an initial part of the first wireless signal which is received before reception of the second wireless signal starts. In other cases, the information indicating the one or more receiver conditions could also be received separately from the first wireless signal, e.g., as part of control signaling. The one or more receiver conditions may correspond to a situation where the first wireless signal is absent.

In some scenarios, the ML modulation scheme may be applied in a selective manner. In a first mode of operation, the wireless communication device may send the second wireless signal based on the ML modulation scheme, and in a second mode of operation, the wireless communication device may send the second wireless signal based on a single-layer modulation scheme. In the second mode of operation, an MCS used in the single-layer modulation scheme could be selected based on LA, considering observed or estimated information of receiver conditions at the further wireless communication device. Switching between the first mode of operation and the second mode of operation may depend on a level of predictability of channel conditions between the wireless communication device and the further wireless communication device and/or predictability of receiver conditions at further the wireless communication device.

Fig. 7 illustrates a processor-based implementation of a wireless communication device 700. The structures as illustrated in Fig. 7 may be used for implementing the above-described concepts. The wireless communication device 700 may for example correspond to one of above-mentioned APs 10 or to one of the above-mentioned stations 20.

As illustrated, the wireless communication device 700 includes a radio interface 710. The radio interface 710 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 wireless communication device 700 may be provided with a network interface 720 for connecting to a data network, e.g., using a wire-based connection.

Further, the wireless communication device 700 may include one or more processors 750 coupled to the interfaces 710, 720, and a memory 760 coupled to the processor(s) 750. By way of example, the interfaces 710, 720, the processor(s) 750, and the memory 760 could be coupled by one or more internal bus systems of the wireless communication device 700. The memory 760 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 760 may include software 770 and/or firmware 780. The memory 760 may include suitably configured program code to be executed by the processor(s) 750 so as to implement the above-described functionalities for controlling wireless transmissions, such as explained in connection with the method of Fig. 5 or the method of Fig. 6.

It is to be understood that the structures as illustrated in Fig. 7 are merely schematic and that the wireless communication device 700 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 760 may include further program code for implementing known functionalities of an AP or non-AP 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 communication device 700, e.g., in the form of a physical medium storing the program code and/or other data to be stored in the memory 760 or by making the program code available for download or by streaming.

As can be seen, the concepts as described above may be used for efficiently using STR operation in a wireless communication system. More specifically, the STR operation may also be used in a reliable and efficient manner in the case of limited knowledge of channel conditions or receiver conditions.

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. 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

1. A method of controlling wireless transmissions in a wireless communication system, the method comprising: a wireless communication device (10, 20; 700) sending a first wireless signal (51 , 52); and during ongoing transmission of the first wireless signal (51 , 52), the wireless communication device (10, 20; 700) receiving a second wireless signal (53) from a further wireless communication device (10, 20; 700), wherein the second wireless signal (53) is based on a multi-layer modulation scheme which simultaneously modulates information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

2. The method according to claim 1 , wherein the multi-layer modulation scheme is based on at least one further modulation layer having an intermediate level of robustness between the high level of robustness and the low level of robustness.

3. The method according to claim 1 or 2, comprising: the wireless communication device (10, 20; 700) sending, to the further wireless communication device (10, 20; 700), information indicating one or more receiver conditions at the wireless communication device (10, 20; 700).

4. The method according to claim 3, wherein the one or more receiver conditions correspond to a situation where the first wireless signal (53) is absent.

5. The method according to any one of the preceding claims, comprising: in a first mode of operation, receiving the second wireless signal (53) based on the multi-layer modulation scheme; and in a second mode of operation, receiving the second wireless signal (53) based on a singlelayer modulation scheme.

6. The method according to claim 5, wherein switching between the first mode of operation and the second mode of operation depends on a level of predictability of channel conditions between the wireless communication device (10, 20; 700) and the further wireless communication device (10, 20; 700).

7. The method according to any one of the preceding claims, wherein the multi-layer modulation scheme is based on Quadrature Amplitude Modulation.

8. The method according to any one of the preceding claims, wherein the first wireless signal (51 , 52) is sent on first frequency resources, and wherein the second wireless signal (53) is received on second frequency resources which are at least partially overlapping with the first frequency resources.

9. The method according to any one of claims 1 to 7, wherein the first wireless signal (51 , 52) is sent on first frequency resources, and wherein the second wireless signal (53) is received on second frequency resources which are non-overlapping with the first frequency resources.

10. The method according to any of the preceding claims, wherein the first wireless signal (51 , 52) is based on a multi-layer modulation scheme which simultaneously modulates information to a third modulation layer having a high level of robustness and a fourth modulation layer having a low level of robustness.

11. The method according to any one of the preceding claims, wherein the first wireless signal is sent to the further wireless communication device (10, 20; 700).

12. The method according to any one of claims 1o to 10, wherein the first wireless signal is sent to a destination different from the further wireless communication device (10, 20; 700).

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

14. The method according to claim 13, wherein the wireless communication device (10, 20; 700) is an access point device.

15. The method according to claim 13, wherein the wireless communication device (10, 20; 700) is a non-access point device.

16. A method of controlling wireless transmissions in a wireless communication system, the method comprising: a wireless communication device (10, 20; 700) receiving a first wireless signal (51 , 52); and during ongoing reception of the first wireless signal (51 , 52), the wireless communication device (10, 20; 700) sending a second wireless signal (53) to a further wireless communication device (10, 20; 700), wherein the second wireless signal (53) is based on multi-layer modulation scheme which simultaneously modulates information to at least a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

17. The method according to claim 16, wherein the multi-layer modulation scheme is based on at least one further modulation layer having an intermediate level of robustness between the high level of robustness and the low level of robustness.

18. The method according to claim 16 or 17, comprising: the wireless communication device (10, 20; 700) receiving, from the further wireless communication device (10, 20; 700), information indicating one or more receiver conditions at the further wireless communication device (10, 20; 700); and the wireless communication device (10, 20; 700) controlling the multi-layer modulation scheme based on the received information.

19. The method according to claim 18, wherein the one or more receiver conditions correspond to a situation where the first wireless signal (53) is absent.

20. The method according to any one of claims 18 to 19, comprising: in a first mode of operation, sending the second wireless signal (53) based on the multi-layer modulation scheme; and in a second mode of operation, sending the second wireless signal (53) based on a singlelayer modulation scheme.

21. The method according to claim 20, wherein switching between the first mode of operation and the second mode of operation depends on a level of predictability of channel conditions between the wireless communication device (10, 20; 700) and the further wireless communication device (10, 20; 700).

22. The method according to any one of claims 16 to 21 , wherein the multi-layer modulation scheme is based on Quadrature Amplitude Modulation.

23. The method according to any one of claims 16 to 22, wherein the first wireless signal (51 , 52) is received on first frequency resources, and wherein the second wireless signal (53) is sent on second frequency resources which are at least partially overlapping with the first frequency resources.

24. The method according to any one of claims 16 to 23, wherein the first wireless signal (51 , 52) is received on first frequency resources, and wherein the second wireless signal (53) is sent on second frequency resources which are nonoverlapping with the first frequency resources.

25. The method according to any of claims 16 to 24, wherein the first wireless signal (51 , 52) is based on a multi-layer modulation scheme which simultaneously modulates information to a third modulation layer having a high level of robustness and a fourth modulation layer having a low level of robustness.

26. The method according to any one of claims 16 to 25, wherein the first wireless signal is received from the further wireless communication device (10, 20; 700).

27. The method according to any one of claims 16 to 25, wherein the first wireless signal is received from a source different from the further wireless communication device (10, 20; 700).

28. The method according to any one of claims 16 to 27, wherein the wireless communication system is based on a Wireless Local Area Network technology according to the IEEE 802.11 standards family.

29. The method according to claim 28, wherein the wireless communication device (10, 20; 700) is a non-access point device.

30. The method according to claim 28, wherein the wireless communication device (10, 20; 700) is an access point device.

31. A wireless communication device (10, 20; 700) for a wireless communication system, the wireless communication device (10, 20; 700) being configured to: send a first wireless signal (51 , 52); and during ongoing transmission of the first wireless signal (51 , 52), receive a second wireless signal (53) from a further wireless communication device (10, 20; 700), wherein the second wireless signal (51 , 52) is based on multi-layer modulation simultaneously modulating information to a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

32. The wireless communication device (10, 20; 700) according to claim 31 , wherein the wireless communication device (10, 20; 700) is configured to perform a method according to any one of claims 2 to 15.

33. The wireless communication device (10, 20; 700) according to claim 31 or 32, comprising: at least one processor (750), and a memory (760) containing program code executable by the at least one processor (750), whereby execution of the program code by the at least one processor (750) causes the wireless communication device (10, 20; 700) to perform a method according to any one of claims 1 to 15.

34. A wireless communication device (10, 20; 700) for a wireless communication system, the wireless communication device (10, 20; 700) being configured to: receive a first wireless signal (51 , 52); and during ongoing reception of the first wireless signal (51 , 52), send a second wireless signal (53) to a further wireless communication device (10, 20; 700), wherein the second wireless signal (53) is based on a multi-layer modulation scheme simultaneously modulating information to at least a first modulation layer having a high level of robustness and a second modulation layer having a low level of robustness.

35. The wireless communication device (10, 20; 700) according to claim 34, wherein the wireless communication device (10, 20; 700) is configured to perform a method according to any one of claims 17 to 30.

36. The wireless communication device (10, 20; 700) according to claim 34 or 35, comprising: at least one processor (750), and a memory (760) containing program code executable by the at least one processor (750), whereby execution of the program code by the at least one processor (750) causes the wireless communication device (10, 20; 700) to perform a method according to any one of claims 16 to 30.

37. A computer program or computer program product comprising program code to be executed by at least one processor (750) of a wireless communication device (10, 20; 700), whereby execution of the program code causes the wireless communication device (10, 20; 700) to perform a method according to any one of claims 1 to 30.