Devices and methods for efficient MIMO transmissions in a wireless network

Abstract

A Wi-Fi transmitter station for communication with at least one Wi-Fi receiver station (120; 110) comprising a communication interface (113; 123), further comprising one or more power amplifiers (113a; 123a) and a plurality of antennas (113b; 123b) configured for a multiple- input multiple-output, MIMO, transmission to the at least one Wi-Fi receiver station with a power back-off of a maximum transmission power of the Wi-Fi transmitter station, wherein the communication interface is further configured to transmit to and / or receive from the at least one Wi-Fi receiver station an indication of, i.e. information about a power back-off correction value for adjusting the maximum transmission power. Moreover, the Wi-Fi transmitter station comprises processing circuitry configured to determine, i.e. set a transmission power for the MIMO transmission to the at least one Wi-Fi receiver station based on the maximum transmission power and a power back-off value reduced by the power back-off correction value.

Description

[0001] DEVICES AND METHODS FOR EFFICIENT MIMO TRANSMISSIONS IN A WIRELESS NETWORK

[0002] TECHNICAL FIELD

[0003] The present invention relates to wireless communications. More specifically, the present invention relates to devices and methods for efficient MIMO transmissions in a wireless network, in particular a Wi-Fi network.

[0004] BACKGROUND

[0005] IEEE 802.11 -based WLANs (also referred to as Wi-Fi networks) have become popular at an unprecedented rate. MIMO (Multiple Input Multiple Output) techniques are widely used in wireless local area networks, WLANs, in particular Wi-Fi networks to achieve better spectral efficiency and to increase the throughput. This includes single-user, SU, and multi-user, MU, MIMO in both trigger based, TB, and non-TB physical protocol data units, PPDUs. In order to exploit the maximum gain of MIMO transmissions, non-linear detection is often applied at the receiver side. However, non-linear detection is usually very sensitive to the RF impairments. Therefore, a maximum acceptable transmit error vector magnitude, EVM, level has been defined in the IEEE 802.11 framework of standards, however, for a single stream transmission over an additive white Gaussian noise, AWGN, channel. MIMO transmissions may require a higher transmit EVM threshold to achieve the desired performance. Moreover, even relatively small change in impairments may have a significant impact on the performance. In many scenarios, when MIMO techniques are applied, the noise level at the receiver is relatively low and Tx EVM defines the performance.

[0006] SUMMARY

[0007] It is an objective to provide improved devices and methods for efficient MIMO transmissions in a wireless network, in particular an IEEE 802.11 based Wi-Fi network.

[0008] The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. According to a first aspect a Wi-Fi transmitter station for communication with at least one Wi-Fi receiver station is provided. In an implementation form the Wi-Fi transmitter station is an access point, AP, or a non-AP station. The Wi-Fi transmitter station according to the first aspect comprises a communication interface comprising one or more power amplifiers and a plurality of antennas configured for a multiple-input multiple-output, MIMO, transmission to the at least one Wi-Fi receiver station with a power back-off of a maximum transmission power of the Wi-Fi transmitter station. The communication interface is further configured to receive from the at least one Wi-Fi receiver station an indication of, i.e. information about a power back-off correction value for adjusting the maximum transmission power. Moreover, the Wi-Fi transmitter station according to the first aspect comprises a processing circuitry configured to determine, i.e. set a transmission power for the MIMO transmission to the at least one Wi-Fi receiver station based on the maximum transmission power and a power backoff value reduced by the power back-off correction value. The indication of the power backoff correction value allows for more efficient and, thus, improved MIMO transmissions in a wireless network, in particular an IEEE 802.11 based Wi-Fi network.

[0009] In a further possible implementation form, the communication interface is configured to transmit to and / or receive from the at least one Wi-Fi receiver station a frame, wherein the frame comprises the indication of the power back-off correction value.

[0010] In a further possible implementation form, the frame comprises a power back-off correction field and the power back-off correction field comprises the indication of the power back-off correction value.

[0011] In a further possible implementation form, the power back-off correction field comprises a plurality of bits, in particular 3 bits defining a plurality of bit sequences, wherein each of the plurality of bit sequences encodes a different power back-off correction value.

[0012] In a further possible implementation form, wherein the plurality of bit sequences comprise a bit sequence encoding a zero power back-off correction value.

[0013] In a further possible implementation form, the frame further comprises a MIMO configuration field indicative of a MIMO configuration the power back-off correction value is applied to, wherein the MIMO configuration defines a modulation and coding scheme, MCS, a number of MIMO spatial streams and / or single-user or multi-user transmission scheme used for the MIMO transmission to the Wi-Fi receiver station. In a further possible implementation form, the MIMO configuration field comprises a plurality of bits, in particular 8 bits, defining a plurality of bit sequences, wherein each of the plurality of bit sequences encodes a different MIMO configuration.

[0014] In a further possible implementation form, the frame further comprises a back-off correction support field indicative of whether the Wi-Fi transmitter station is capable of applying the power back-off correction value for the MIMO transmission.

[0015] In a further possible implementation form, the frame further comprises a back-off field indicative of the power back-off value used for the MIMO transmission and / or an Error Vector Magnitude, EVM, field indicative of an EVM value for the MIMO transmission.

[0016] In a further possible implementation form, the frame is a beacon frame or trigger frame.

[0017] In a further possible implementation form, the communication interface is configured to periodically transmit the frame to the at least one Wi-Fi receiver station with respect to the MIMO transmission and / or periodically receive the frame from the at least one Wi-Fi receiver station with respect to the MIMO transmission.

[0018] In a further possible implementation form, the communication interface is configured to transmit a further frame to the at least one Wi-Fi receiver station with respect to the MIMO transmission and / or receive a further frame from the at least one Wi-Fi receiver station with respect to the MIMO transmission, wherein the further frame comprises a back-off correction support field indicative of whether the Wi-Fi transmitter station is capable of applying the power back-off correction value for the MIMO transmission.

[0019] In a further possible implementation form, the further frame comprises a back-off field indicative of the power back-off value used for the MIMO transmission and / or an Error Vector Magnitude, EVM, field indicative of an EVM value for the MIMO transmission.

[0020] In a further possible implementation form, the communication interface is configured to transmit the further frame to the at least one Wi-Fi receiver station with respect to the MIMO transmission, in response to receiving a poll frame from the at least one Wi-Fi receiver station with respect to the MIMO transmission. In a further possible implementation form, the poll frame comprises an identifier of the Wi-Fi transmitter station with respect to the MIMO transmission and / or one or more identifiers indicative of one or more modulation and coding schemes, MCS.

[0021] In a further possible implementation form, the communication interface is configured to perform the MIMO transmission with a currently selected MIMO configuration of a plurality of selectable MIMO configurations and the power back-off correction value applies to all of the plurality of selectable MIMO configurations.

[0022] In a further possible implementation form, the communication interface is configured to perform the MIMO transmission with a currently selected MIMO configuration of a plurality of selectable MIMO configurations and the power back-off correction value applies to one MIMO configuration of the plurality of selectable MIMO configurations. As will be appreciated, for a different transmission a different MIMO configuration with a different power back-off correction value may be selected by the Wi-Fi transmitter station.

[0023] In a further possible implementation form, the communication interface is configured to perform the MIMO transmission with a currently selected MIMO configuration of a plurality of selectable MIMO configurations, wherein the indication is indicative of a plurality of power back-off correction values and wherein each power back-off correction value applies to one or more of the plurality of selectable MIMO configurations.

[0024] In a further possible implementation form, the plurality of selectable MIMO configurations define a modulation and coding scheme, MCS, a number of MIMO spatial streams and / or single-user or multi-user transmission scheme.

[0025] In a further possible implementation form, the Wi-Fi transmitter station is further configured to determine a headroom value in the standardized way as a difference between the transmission power and the maximum transmission power adjusted by the power back-off correction value.

[0026] In a further possible implementation form, the Wi-Fi transmitter station is further configured to transmit the headroom value to the Wi-Fi receiver station.

[0027] According to a second aspect a method for operating a Wi-Fi transmitter station is provided for communication with at least one Wi-Fi receiver station, wherein the Wi-Fi transmitter station comprises a communication interface with one or more power amplifiers and a plurality of antennas configured for a multiple-input multiple-output, MIMO, transmission to the at least one Wi-Fi receiver station with a power back-off of a maximum transmission power of the Wi-Fi transmitter station. The method comprises the steps of transmitting to and / or receiving from the at least one Wi-Fi receiver station an indication of, i.e. information about a power back-off correction value for adjusting the maximum transmission power; and determining, i.e. setting a transmission power for the MIMO transmission to the at least one Wi-Fi receiver station based on the maximum transmission power reduced by the power backoff correction value. The indication of the power back-off correction value allows for more efficient and, thus, improved MIMO transmissions in a wireless network, in particular an IEEE 802.11 based Wi-Fi network.

[0028] The method according to the second aspect of the present disclosure can be performed by the Wi-Fi transmitter station according to the first aspect of the present disclosure. Thus, further features of the method according to the second aspect of the present disclosure result directly from the functionality of the Wi-Fi transmitter station according to the first aspect of the present disclosure as well as its different implementation forms described above and below.

[0029] According to a third aspect a computer program product is provided, comprising program code which causes a computer or a processor to perform the method according to the second aspect, when the program code is executed by the computer or the processor.

[0030] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

[0033] Fig. 1 is a schematic diagram showing a Wi-Fi transmitter station according to an embodiment exchanging one or more frames with a Wi-Fi receiver station; Fig. 2 shows a back-off correction field of a frame exchanged between a Wi-Fi transmitter station according to an embodiment and a Wi-Fi receiver station;

[0034] Fig. 3 shows a back-off correction table with a plurality of back-off correction values exchanged between a Wi-Fi transmitter station according to an embodiment and a Wi-Fi receiver station;

[0035] Fig. 4a shows a MIMO configuration field of a frame exchanged between a Wi-Fi transmitter station according to an embodiment and a Wi-Fi receiver station;

[0036] Fig. 4b shows a MIMO configuration table with a plurality of MIMO configurations and a back-off correction value for each MIMO configuration exchanged between a Wi-Fi transmitter station according to an embodiment and a Wi-Fi receiver station;

[0037] Fig. 5 shows a back-off correction support capability field of a frame exchanged between a Wi-Fi transmitter station according to an embodiment and a Wi-Fi receiver station;

[0038] Fig. 6 shows a back-off and Tx EVM indication capability field of a frame exchanged between a Wi-Fi transmitter station according to an embodiment and a Wi-Fi receiver station;

[0039] Fig. 7 shows a back-off and Tx EVM indication field of a frame exchanged between a WiFi transmitter station according to an embodiment and a Wi-Fi receiver station; and

[0040] Fig. 8 shows a flow diagram illustrating steps of a method of operating a Wi-Fi transmitter station according to an embodiment for communication with at least one Wi-Fi receiver station.

[0041] In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0042] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0044] For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically noted otherwise.

[0045] Figure 1 shows an exemplary wireless communication network 100, in particular a Wi-Fi network 100 including an access point, AP, 120 and a non-AP station 110 in the form of a smartphone 110 as an example for a plurality of non-AP stations which may be associated and communicate with the AP 120. In an embodiment, the wireless communication network 100 is a WLAN in accordance with the IEEE 802.11 framework of standards (also referred to as a Wi-Fi network 100).

[0046] As illustrated in figure 1, the non-AP station 110 comprises processing circuitry 111 and a communication interface 113, in particular a wireless communication interface 113 in accordance with the IEEE 802.11 framework of standards. The communication interface 113 comprises one or more power amplifiers 113a and a plurality of antennas 113b configured for a multiple-input multiple-output, MIMO, transmission to the AP 120 with a power back-off of a maximum transmission power of the non-AP station 110. The processing circuitry 111 of the non-AP station 110 may be implemented in hardware and / or software and may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. The non-AP station 110 may further comprise a memory 115 configured to store executable program code which, when executed by the processing circuitry 111, causes the non-AP station 110 to perform the functions and methods described herein.

[0047] Likewise, the AP 120 illustrated in figure 1 comprises processing circuitry 121 and a communication interface 123, in particular a wireless communication interface 123 in accordance with the IEEE 802.11 framework of standards. The communication interface 123 comprises one or more power amplifiers 123a and a plurality of antennas 123b configured for a MIMO transmission to the non-AP station 110 with a power back-off of a maximum transmission power of the AP 120. The processing circuitry 121 of the AP 120 may be implemented in hardware and / or software and may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. As illustrated in figure 1, the AP 120 may further comprise a memory 125 configured to store executable program code which, when executed by the processing circuitry 121, causes the AP 120 to perform the functions and methods described herein.

[0048] As described above, both the non-AP station 110 and the AP 120 are a Wi-Fi transmitter station configured to perform MIMO transmission to the other station (herein referred to as Wi-Fi receiver station), i.e. the AP 120 or the non-AP station 120. In the following detailed embodiments will be described, where the Wi-Fi transmitter station is the non-AP station 110 and the Wi-Fi receiver station is the AP 120. As will be appreciated, however, these embodiments apply as well to a scenario, where the Wi-Fi transmitter station is the AP 120 and the Wi-Fi receiver station is the non-AP station 110.

[0049] As already described above, the communication interface 113 of the non-AP station 110, i.e. the Wi-Fi transmitter station is configured for a MIMO transmission to the AP 120 with a power back-off of a maximum transmission power of the non-AP station 110. As will be appreciated, the power back-off may be defined as the difference between the mean power of the transmitted signal and the maximum available power level. As used herein, the maximum power level may be the maximum allowed power per of a respective modulation and coding scheme (MCS). A larger power back-off value results in a lower actual transmission power and, thus, decreases, for instance, the signal to noise ratio (SNR) at the Wi-Fi receiver station. In an embodiment, the maximum transmission power of the non-AP station 110 may be determined by hardware capabilities of the non-AP station 110 and / or may be set to comply with one or more constraints, which may be related to or based on an error vector magnitude (EVM) threshold defined by the IEEE 802.11 framework of standards.

[0050] As will be described in more detail below, the communication interface 113 of the non-AP station 110, i.e. the Wi-Fi transmitter station is further configured to transmit to and / or receive from the AP 120, i.e. the Wi-Fi receiver station an indication of a power back-off correction value and the processing circuitry 111 of the non-AP station 110 is configured to determine an actual transmission power for the MIMO transmission to the AP 120, i.e. the Wi-Fi receiver station to meet the required target power at the AP 120, i.e. the Wi-Fi receiver station. To this end, the processing circuitry 111 of the non-AP station 110 is configured to determine the actual maximum transmission power based on the nominal maximum power minus the back-off correction value. In an embodiment, the power back-off correction value may be a value that results in an adjusted power back-off value (i.e. original power back-off value plus the power back-off correction value) that is larger than the original power back-off value, so that, in turn, the actual transmission power determined on the basis of the adjusted power back-off value is smaller than the transmission power determined on the basis of the original power back-off value.

[0051] Using a suitable power back-off correction value may provide significant improvements for the performance of MIMO transmissions, because, for instance, the Wi-Fi receiver station may use a non-linear decoder. As will be appreciated, the exact value of the power back-off correction value may depend on the specific MIMO scheme, properties of the one or more power amplifiers 113a as well as the type of the detection applied by the Wi-Fi receiver station. In an embodiment, the power back-off correction value may be indicated in advance and applied for SU MIMO transmissions (both for UL and DL) and also be adjusted per transmission in case of a MIMO transmission of trigger based PPDUs.

[0052] In an embodiment, the power back-off correction value may be included in one or more frames 130 exchanged between the non-AP station 110 and the AP, as illustrated in figure 1. In an embodiment, the frame(s) 130 may include a power back-off correction field, wherein the power back-off correction field contains the power back-off correction value 131, as illustrated in figure 2. In an embodiment, the power back-off correction field may have a size of, for instance, 3 bits allowing to efficiently encode a plurality of power back-off correction values 131 with an accuracy of 0.5dB and a maximum power back-off correction value of 2dB. In an embodiment, one of the plurality of bit sequences encoded by the multibit power back-off correction field may indicate a zero power back-off correction value (i.e. no adjustment of the power back-off is required).

[0053] As illustrated in figure 2, the BO correction field of the frame(s) 130 may indicate a single power back-off correction value 131 to be applied for all MIMO transmissions. In a further embodiment, the BO correction field of the frame(s) 130 may indicate a power back-off correction value 131 per MIMO transmission indication, for example in the trigger frame (TF).

[0054] In a further embodiment, the indication of the power back-off correction value may comprise the power back-off correction table illustrated in figure 3 for indicating a plurality of power back-off correction values 131a-n. In an embodiment, the power back-off correction table may include a respective power back-off correction value 13 la-n for each of a plurality of selectable MIMO configurations of the non-AP station 110. In an embodiment, each of the plurality of MIMO configurations may define a modulation and coding scheme, MCS, a number of MIMO spatial streams and / or single-user or multi-user transmission scheme.

[0055] In an embodiment, the power back-off correction table shown in figure 3 may be included in a beacon frame 130 transmitted by the AP 120 to the non-AP station 110. In a further embodiment, the power back-off correction table shown in figure 3 may be included in a trigger frame 130 transmitted by the AP 120 to the non-AP station 110.

[0056] In order to allow an indication of power back-off correction values for a subset of MIMO configurations of the non-AP station 110, the AP 120 may further transmit an indication of a specific MIMO configuration to the non-AP station 110 in the MIMO configuration field 132 illustrated in figure 4a. The MIMO configuration field 132 may be part of one or more of the frames 130 any may have a size of, for instance, 1 byte. In a further embodiment, a plurality of selectable MIMO configurations may be indicated with a plurality of the MIMO configuration fields 132a-n together with the respective power back-off correction value 13 la-n in the MIMO configuration table shown in figure 4b. In an embodiment, the MIMO configuration table may be part of one or more of the frames 130. In order to ensure that the power back-off correction value can be applied and in order to avoid wasting transmit power the non-AP station 110 and / or the AP 120 according to an embodiment are further configured to indicate that power back-off correction is supported. Thus, in an embodiment, the non-AP station 110 and / or the AP 120 may include a power back-off correction support field 135 in one or more of the frames 130, as illustrated in figure 5. In an embodiment, the power back-off correction support field 135 may have a size of 1 bit, i.e. a flag bit.

[0057] In a further embodiment, the non-AP station 110 may be configured to indicate whether it supports the indication of specific power back-off values or specific Tx EVMs per configured parameters (in a similar way as the standardized UL power headroom). This may be achieved according to an embodiment by the back-off and Tx EVM indication capability field 136 shown in figure 6. In the embodiment shown in figure 6, the back-off and Tx EVM indication capability field 136 may have a size of, for instance, 2 bits, i.e. 2 flag bits. In an embodiment, the back-off and Tx EVM indication capability field 136 may be included in one or more of the frames 130.

[0058] In an embodiment, the AP 120 may be configured to periodically update the power back-off correction value and / or its support for power back-off correction. To this end, the AP 120 may be configured to include the power back-off correction value 131 of figure 2 or the power back-off correction table of figure 3 with the plurality of power back-off correction values in a beacon frame 130. The corresponding field of the beacon frame 130 may further comprise the indication whether power back-off correction is currently supported (for instance the indication in the power back-off correction support field 135 of figure 5). This may be beneficial, because, for instance, the AP 120 may stop using a non-linear decoder due to low power or any other reason and thus stop supporting power back-off correction. Likewise, as already described above, the non-AP station 110 may indicate whether power back-off correction is currently supported or not, for instance, by means of the power back-off correction support field 135 of figure 5.

[0059] In an embodiment, as illustrated in figure 7, the non-AP station 110 (that supports indication of back-off and / or Tx EVM values) may indicate the power back-off 137 and / or Tx EVM 138 similar to the conventional UL Power Headroom as a respective control field per MCS in an UL frame 130. In an embodiment, where the power back-off values are within a range of 4 to 12dB and an accuracy of 0.5dB is required for accurate indication, up to 5 bits may be necessary to cover the entire range. Moreover, a range of 32dB of EVM values may be assumed requiring 5 bits as well, as illustrated in figure 7. In an embodiment, both the power back-off 137 and the EVM 138 may be indicated for a current Tx configuration as set by TF or for a maximum power per MCS.

[0060] In an embodiment, the AP 120 may be configured to request the indication of the power backoff values 137 and the Tx EVM values 138 from the non-AP station 110 or a group of non-AP stations, including the non-AP station 110. In an embodiment, this request may be part of a trigger frame 130 or issued by the AP as a stand-alone dedicated poll frame 130. In an embodiment, the poll frame 130 may include one or more identifiers of the non-AP station(s) 110 (e.g. a STA ID List) and / or an indication of one or more MCSs (e.g. a MCSs List).

[0061] As already described above, the non-AP station 110 is configured to apply the power back-off correction value 131, 13 la-n as indicated by the AP 120 for its MIMO transmissions, in particular trigger based and single user MIMO transmissions. In case no power back-off correction is indicated by the AP 120, the non-AP station 110 may be configured to apply a default power back-off correction (which may be defined by the IEEE 802.11 framework of standards). In a further embodiment, if the non-AP station 110 is reporting headroom values to the AP 120, it applies the power back-off correction value(s) 131, 13 la-n indicated by the AP 120. As will be appreciated, a headroom value indicates the difference between the current transmission power (as set, for instance, to achieve a requested target RSSI) and the maximum available power (for a selected MCS).

[0062] Figure 8 shows a flow diagram illustrating steps of a method 800 for operating a Wi-Fi transmitter station, such as the non-AP station 110 or the AP 120, for communication with at least one Wi-Fi receiver station, such as the AP 120 or the non-AP station 110. As already described above, the Wi-Fi transmitter station 110 or 120 comprises a communication interface 113 or 123 with one or more power amplifiers 113a or 123a and a plurality of antennas 113b or 123b configured for a MIMO transmission to the at least one Wi-Fi receiver station 120 or 110 with a power back-off of a maximum transmission power of the Wi-Fi transmitter station 110 or 120. The method 800 comprises a step 801 of transmitting to and / or receiving from the at least one Wi-Fi receiver station 120 or 110 an indication 131 or 13 la-n of a power back-off correction value. Moreover, the method 800 comprises a step 803 of determining, i.e. setting an actual transmission power for the MIMO transmission to the at least one Wi-Fi receiver station 120 or 110 based on the maximum transmission power reduced by the power back-off correction value.

[0063] As the method 800 can be implemented by the Wi-Fi transmitter station, e.g. the non-AP station 110 or the AP 120, further features of the method 800 result directly from the functionality of the Wi-Fi transmitter station 110 or 120 as well as its different embodiments described above and below.

[0064] The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

[0065] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

[0066] The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

[0067] In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

CLAIMS1. A Wi-Fi transmitter station (110; 120) for communication with at least one Wi-Fi receiver station (120; 110), wherein the Wi-Fi transmitter station (110; 120) comprises: a communication interface (113; 123) comprising one or more power amplifiers (113a; 123a) and a plurality of antennas (113b; 123b) configured for a multiple-input multiple-output, MIMO, transmission to the at least one Wi-Fi receiver station (120; 110) with a power backoff of a maximum transmission power of the Wi-Fi transmitter station (110; 120), wherein the communication interface (113; 123) is further configured to transmit to and / or receive from the at least one Wi-Fi receiver station (120; 110) an indication (131; 13 la-n) of a power backoff correction value; and a processing circuitry (111; 121) configured to determine a transmission power for the MIMO transmission to the at least one Wi-Fi receiver station (120; 110) based on the maximum transmission power and a power back-off value reduced by the power back-off correction value.

2. The Wi-Fi transmitter station (110; 120) of claim 1, wherein the communication interface (113; 123) is configured to transmit to and / or receive from the at least one Wi-Fi receiver station (120; 110) a frame (130), wherein the frame (130) comprises the indication (131; 13 la-n) of the power back-off correction value.

3. The Wi-Fi transmitter station (110; 120) of claim 2, wherein the frame (130) comprises a power back-off correction field (131) and wherein the power back-off correction field (131) comprises the indication (131) of the power back-off correction value.

4. The Wi-Fi transmitter station (110; 120) of claim 3, wherein the power back-off correction field (131) comprises a plurality of bits defining a plurality of bit sequences, wherein each of the plurality of bit sequences encodes a different power back-off correction value.

5. The Wi-Fi transmitter station (110; 120) of claim 4, wherein the plurality of bit sequences comprise a bit sequence encoding a zero power back-off correction value.

6. The Wi-Fi transmitter station (110; 120) of any one of claims 2 to 5, wherein the frame (130) further comprises a MIMO configuration field (133) indicative of a MIMO configuration the power back-off correction value is applied to and wherein the MIMO configuration defines a modulation and coding scheme, MCS, a number of MIMO spatial streams, and / or single-user or multi-user transmission scheme.

7. The Wi-Fi transmitter station (110; 120) of claim 6, wherein the MIMO configuration field (133) comprises a plurality of bits defining a plurality of bit sequences, wherein each of the plurality of bit sequences encodes a different MIMO configuration.

8. The Wi-Fi transmitter station (110; 120) of any one of claims 2 to 7, wherein the frame (130) further comprises a back-off correction support field (135) indicative of whether the Wi-Fi transmitter station (110; 120) is capable of applying the power back-off correction value for the MIMO transmission.

9. The Wi-Fi transmitter station (110; 120) of any one of claims 2 to 8, wherein the frame (130) further comprises a back-off field (136) indicative of the power back-off value used for the MIMO transmission and / or an Error Vector Magnitude, EVM, field (136) indicative of an EVM value for the MIMO transmission.

10. The Wi-Fi transmitter station (110; 120) of any one of claims 2 to 9, wherein the frame (130) is a beacon frame (130) or trigger frame (130).

11. The Wi-Fi transmitter station (110; 120) of any one of claims 2 to 10, wherein the communication interface (113; 123) is configured to periodically transmit to and / or periodically receive from the at least one Wi-Fi receiver station (120; 110) the frame (130).

12. The Wi-Fi transmitter station (110; 120) of any one of claims 2 to 7, wherein the communication interface (113; 123) is configured to transmit to and / or receive from the at least one Wi-Fi receiver station (120; 110) a further frame and wherein the further frame comprises a back-off correction support field (135) indicative of whether the Wi-Fitransmitter station (110; 120) is capable of applying the power back-off correction value for the MEMO transmission.

13. The Wi-Fi transmitter station (110; 120) of claim 12, wherein the further frame comprises a back-off field (136) indicative of the power back-off value used for the MEMO transmission and / or an Error Vector Magnitude, EVM, field (136) indicative of an EVM value for the MEMO transmission.

14. The Wi-Fi transmitter station (110; 120) of any one of claims 12 or 13, wherein the communication interface (113; 123) is configured to transmit the further frame to the at least one Wi-Fi receiver station (120; 110), in response to receiving a poll frame from the at least one Wi-Fi receiver station (120; 110).

15. The Wi-Fi transmitter station (110; 120) of claim 14, wherein the poll frame comprises an identifier of the Wi-Fi transmitter station (110; 120) and / or one or more identifiers indicative of one or more modulation and coding schemes, MCS.

16. The Wi-Fi transmitter station (110; 120) of any one of the preceding claims, wherein the communication interface (113; 123) is configured to perform the MIMO transmission with a currently selected MIMO configuration of a plurality of selectable MIMO configurations and wherein the power back-off correction value applies to the plurality of selectable MIMO configurations.

17. The Wi-Fi transmitter station (110; 120) of any one of claims 1 to 15, wherein the communication interface (113; 123) is configured to perform the MIMO transmission with a currently selected MIMO configuration of a plurality of selectable MIMO configurations and wherein the power back-off correction value applies to one MIMO configuration of the plurality of selectable MIMO configurations.

18. The Wi-Fi transmitter station (110; 120) of any one of claims 1 to 15, wherein the communication interface (113; 123) is configured to perform the MIMO transmission with a currently selected MIMO configuration of a plurality of selectable MIMO configurations, wherein the indication (13 la-n) is indicative of a plurality of power back-off correction valuesand wherein each power back-off correction value applies to one or more MIMO configurations of the plurality of selectable MIMO configurations.

19. The Wi-Fi transmitter station (110; 120) of any one of claims 16 to 18, wherein the plurality of selectable MIMO configurations define a modulation and coding scheme, MCS, a number of MIMO spatial streams and / or single-user or multi-user transmission scheme.

20. The Wi-Fi transmitter station (110; 120) of any one of the preceding claims, wherein the Wi-Fi transmitter station (110; 120) is further configured to determine a headroom value as a difference between the transmission power and the maximum transmission power adjusted by the power back-off correction value.

21. The Wi-Fi transmitter station (110; 120) of claim 20, wherein the Wi-Fi transmitter station (110; 120) is further configured to transmit the headroom value to the Wi-Fi receiver station (120; 110).

22. The Wi-Fi transmitter station (110; 120) of any one of the preceding claims, wherein the Wi-Fi transmitter station (110; 120) is an access point, AP, (120) or a non-AP station (HO).

23. A method (800) for operating a Wi-Fi transmitter station (110; 120) for communication with at least one Wi-Fi receiver station (120; 110), the Wi-Fi transmitter station (110; 120) comprising a communication interface (113; 123) with one or more power amplifiers (113a; 123a) and a plurality of antennas (113b; 123b) configured for a multipleinput multiple-output, MIMO, transmission to the at least one Wi-Fi receiver station (120;110) with a power back-off of a maximum transmission power of the Wi-Fi transmitter station (110; 120), wherein the method (800) comprises: transmitting (801) to and / or receiving from the at least one Wi-Fi receiver station (120; 110) an indication (131; 13 la-n) of a power back-off correction value; and determining (803) a transmission power for the MIMO transmission to the at least one Wi-Fi receiver station (120; 110) based on the maximum transmission power reduced by the power back-off correction value.

24. A computer program product comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method (800) of claim 23 when the program code is executed by the computer or the processor.

Images