Method, computer program and radio network node for null-steering beamforming

Abstract

The present invention relates to assigning a beam pattern with null-steering beamforming from a first radio network node. A method comprises determining a direction to a neighboring second radio network node, determining an indication of a traffic load on the second radio network node, and determining a direction of null steering of the null-steering beamforming based on the direction and the traffic load. A computer program and a radio network node are also disclosed.

Description

Technical Field

[0001] The present invention generally relates to a method for a radio network node, a computer program for implementing the method, and a radio network node. In particular, the present invention relates to a method and a first radio network node arranged to assign a beam pattern with null-steering beamforming to a neighboring second radio network node. Background Art

[0002] There is increasing interest in using unlicensed bands, such as the 2.45 GHz ISM (Industrial Scientific and Medical) band and the 5 GHz band. In order to ensure coexistence between different devices using a certain standard and between devices using different standards, some coexistence mechanism needs to be adopted. One commonly used coexistence mechanism is Listen Before Talk (LBT), also known as Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA). In CSMA / CA, a device that intends to use the wireless medium for transmission listens to the channel and determines whether the channel is busy (in use or occupied) or idle (not occupied). If the channel is determined to be busy, the transmission is postponed, and if the channel is determined to be idle, the transmission is initiated. As the name suggests, the idea of ​​CSMA / CA is to avoid collisions by only initiating transmissions when the channel is not busy.

[0003] Historically, the 5 GHz band has been used almost exclusively by IEEE 802.11 standards (e.g., IEEE 802.11a, IEEE 802.11n, and IEEE 802.11ac). Prior to the introduction of IEEE 802.11ac, all transmissions were between one transmitter and one receiver. In addition, a distributed coordination function (DCF) was often used to allocate channel access. Having individual devices contend for a channel when they have something to send simplifies system design. However, with increased spectrum usage, it has become clear that a more strictly scheduled approach can provide higher spectral efficiency. Specifically, it is desirable to support transmissions from one transmitter to many receivers, as well as transmissions from many transmitters to one receiver.

[0004] In radio, multiple-input and multiple-output (MIMO) is a method for multiplying the capacity of a radio link using multiple transmit and receive antennas. MIMO has become a common element in several wireless communication standards.

[0005] In IEEE 802.11ac, transmission from one transmitter to up to 4 receivers is supported with the help of multi-user MIMO (MU-MIMO) in the downlink (DL) (i.e., from the access point (AP) to the station (STA)). With the introduction of IEEE 802.11ax, transmission from many transmitters to one receiver is also enabled with the help of uplink (UL) MU-MIMO. In addition, in IEEE 802.11ax, orthogonal frequency division multiple access (OFDMA) is used for both DL and UL, allowing multi-user transmission in both UL and DL. OFDMA can also be combined with MU-MIMO so that some subchannels can be used for MU-MIMO, while other channels are used for single-user transmission.

[0006] Multi-user UL transmissions necessarily require scheduling by the AP, since the different transmissions should be received fairly aligned in time, frequency, and power. MU-DL transmissions are scheduled by the AP by default. The move toward more MU transmissions implies that the AP will increasingly control channel access and what transmissions are to be made. It is fair to say that the IEEE 802.11 standard is moving toward being more like the cellular standards developed in the 3rd Generation Partnership Project (3GPP), where the base station controls all transmissions.

[0007] Although a more tightly scheduled approach following the same spirit as the cellular standards could potentially result in higher spectral efficiency, the fundamental difference is that the cellular standards were developed for operation in licensed spectrum. Even systems operating in licensed spectrum suffer from interference from other cells (both co-channel and adjacent channel), but the interference level is known and under control to some extent.

[0008] Furthermore, multi-antenna capabilities play an important role in achieving high capacity and reliable transmission in wireless communication networks. High capacity is achieved by employing techniques such as spatial multiplexing, while transmission with spatial diversity improves reliability. In general, interference is one of the main impediments limiting capacity and reliability. Beamforming is a popular technique that can be employed to limit the impact of interference in multi-antenna systems. Beamforming uses spatial signal processing in order to adjust the weights in the antenna array to direct energy in a certain direction. Similarly, the beamforming weights can be adjusted to place nulls in different directions. However, placing nulls will typically be based on fairly specific knowledge, for example, based on the UL / DL structure.

[0009] US 2018 / 0026362 A1 discloses a method for providing reduced antenna gain in at least one direction. The direction can be determined when doing cell planning.

[0010] The problem with existing solutions for reducing the impact of interference is that they apply techniques only to the cell or basic service set (BSS) to which they belong at the beginning of transmission or during transmission. However, overlapping cells or BSSs may not perform well in the same way. In addition, those techniques rely on limited information. Then, they may not work properly. Therefore, for such overlaps, it may be expected that the link performance and possibly the system performance may be improved.

[0011] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0012] The present invention is based on the inventors' understanding that null steering of an AP's antenna towards sufficiently loaded neighboring nodes may provide that interference may be avoided or at least reduced for simultaneous transmissions by those nodes.

[0013] According to a first aspect, a method of assigning a beam pattern with null-steering beamforming from a first radio network node is provided. The method comprises determining a direction to a neighboring second radio network node, determining an indication of a traffic load on the second radio network node, and determining a direction of null steering of the null-steering beamforming based on the direction and the traffic load.

[0014] The determination of the direction may be made based on reception of a beacon from the second radio network node.Alternatively, the determination of the direction may be made based on a signalling interface between the first radio network node and the second radio network node.

[0015] The determination of the indication regarding traffic load may be made based on information in a beacon from the second radio network node.The information in the beacon may comprise any of: a number of stations associated to the second radio network node, and channel utilization.

[0016] Said determination of said indication of traffic load may be made according to a signalling interface between said first radio network node and said second radio network node.

[0017] The determination of the direction of the null may include prioritizing one of the directions towards a plurality of neighboring network nodes, wherein the prioritization includes prioritizing the direction based on an estimated distance from the neighboring radio network node based on the reception of the beacon from the neighboring radio network node, wherein a smaller estimated distance takes precedence over a larger estimated distance.

[0018] Each of the first radio network node and the second neighboring radio network node may form a basic service set BSS, and the first network node and the second network node may form an overlapping BSS (OBSS) in a communication system for a wireless local area network service.

[0019] For omni-directional transmission using cyclic delay diversity, the method may include assigning the null-steering in the determined directions of the null-steering and randomizing subcarriers in directions other than at least one direction of the null-steering.

[0020] According to a second aspect, a method of signal transmission from a radio network node is provided. The method comprises composing a frame to be sent, assigning a beam pattern with null-steering beamforming according to the first aspect, and transmitting the frame over the assigned beam pattern.

[0021] According to a third aspect, there is provided a computer program comprising instructions which, when executed on a processor of a radio network node, cause the radio network node to perform a method according to any one of the first and second aspects.

[0022] According to a fourth aspect, there is provided a first radio network node, the first radio network node being arranged to assign a beam pattern with null-steering beamforming towards an adjacent second radio network node. The first radio network node comprises a controller and a transceiver. The controller is arranged to compose a frame to be sent, determine a direction to the second radio network node, determine an indication of a traffic load on the second radio network node, and determine a direction of null steering of the null-steering beamforming based on the direction and the traffic load. The transceiver is arranged to transmit the frame by a signal, wherein the signal has null-steering beamforming in the direction.

[0023] The first radio network node may be arranged to determine the direction from reception of a beacon from the second radio network node via the transceiver.Alternatively, the first radio network node may be arranged to determine the direction from a signalling interface between the first radio network node and the second radio network node.

[0024] The first radio network node may be arranged to determine the indication of traffic load from information in a beacon received by the transceiver from the second radio network node. The information in the beacon may comprise any of: the number of stations associated to the second radio network node, and channel utilisation.

[0025] The first radio network node may be arranged to determine the indication of traffic load from a signalling interface between the first radio network node and the second radio network node.

[0026] The determination of the direction of the null may include prioritizing one of the directions towards a plurality of neighboring network nodes, wherein the prioritization may include prioritizing the direction based on an estimated distance from the neighboring radio network node based on the reception of the beacon from the neighboring radio network node by the transceiver, wherein an estimated smaller distance may be prioritized over an estimated larger distance.

[0027] Each of the first radio network node and the second neighboring radio network node may form a basic service set BSS, and the first network node and the second network node may form an overlapping BSS (OBSS) in a communication system for a wireless local area network service.

[0028] For omni-directional transmission using cyclic delay diversity, the first radio network node may be arranged to assign the null-steering in the determined directions of the null-steering and to randomize subcarriers in other directions except for at least one direction of the null-steering. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and additional objects, features and advantages of the present invention will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention with reference to the accompanying drawings.

[0030] Figure 1 is a flow chart illustrating a method according to an embodiment.

[0031] Figure 2 is a block diagram schematically illustrating a network node according to an embodiment.

[0032] Figure 3 A computer readable medium and a processing device are schematically shown.

[0033] Figure 4 Null adjustment in relation to neighbouring network nodes is schematically illustrated.

[0034] Figure 5 Examples are schematically shown where null adjustment provides benefits.

[0035] Figure 6 An example of null adjustment taking into account traffic load is schematically shown.

[0036] Figure 7 An example of null steering adjustment in the case of cyclic shift diversity providing omni-directional transmission is shown. DETAILED DESCRIPTION

[0037] In IEEE 802.11ax, it is preferred that the AP schedule both UL and DL. The AP will have to schedule DL, but in order to allow MU transmissions in UL, UL must also be scheduled by the AP.

[0038] In IEEE 802.11ax, UL scheduling is achieved through so-called trigger frames (TFs). TFs are sent from the AP to the STAs scheduled for UL transmission, indicating basic parameters for UL transmission. Such basic parameters may be, for example, what UL resources to use and what transmission power to use.

[0039] Before scheduling a DL transmission, the AP may send a request to send (RTS) packet to the STAs that it targets to send DL data. The STAs that are addressed by and can decode this RTS packet will respond with a clear to send (CTS) packet. The reason for this RTS-CTS exchange is that DL transmissions from the AP may not be heard by STAs that are not associated with the AP, and these STAs may then potentially initiate transmissions that will interfere with the DL transmissions. CTS packets sent from differently addressed STAs are exactly the same, and therefore the AP cannot, in general, accurately identify which of the addressed STAs responded with a CTS, only whether at least one response has been received. This process extends the single-user RTS-CTS mechanism that existed in previous versions of the IEEE 802.11 standard and is called multi-user RTS-CTS (MU-RTS-CTS).

[0040] There are several disadvantages to performing transmission as described above. The first disadvantage is that the AP may cause interference to neighboring BSSs in the direction of DL transmission, and STAs may also generate interference in UL transmission. If STAs belonging to neighboring BSSs are in the direction of transmission, they may suffer interference. Therefore, transmissions in those surrounding BSSs may fail. The second disadvantage is that STAs in neighboring BSSs may experience interference levels that cause the channel to be determined to be busy. Due to failures caused by interference, retransmissions may have to be performed until the current data frame is delivered. This causes the node to have the same old data for a long time. Therefore, STAs always contend for the channel. In order to address the above-mentioned disadvantages, the present disclosure proposes that the AP perform zero-steering adjustment (NA) in the direction in which it may cause interference.

[0041] Figure 1 is a flow chart illustrating a method according to an embodiment.Boxes with dashed lines indicate optional features that are used in various combinations in some of the example embodiments below.

[0042] According to one embodiment, a method of assigning a beam pattern with null-steering beamforming from a first radio network node relative to a neighboring second radio network node is provided. The background is that the neighboring radio network nodes are not aware of each other through any cell planning, the first radio network node has a certain antenna array arrangement for both reception and transmission, and the neighboring radio network node operates in an unlicensed band. In other words, the first network node needs to collect information and act accordingly. This is performed by the first radio network node when it determines 102 the direction to the second radio network node. The first radio network node can make this determination by listening to transmissions from the second radio network node (e.g., beacons transmitted by the second radio network node). The direction can be determined by observing the phase relationship of the reception in the array antenna. Here, for ease of understanding, an explanation is given for the relationship with the second radio network node, but the same principles apply to the relationship with multiple neighboring radio network nodes. In other words, the first radio network node can receive signals from multiple radio network nodes, but it may not be necessary to take any action on all of these multiple radio network nodes. For example, the neighboring radio network nodes may be too far away (i.e., the signals to / from them are weak) to have any practical impact. However, it is also considered that the radio network node is closer, and in the absence of ongoing active transmissions, there may not be any practical reason to take any special action. Therefore, the inventors suggest in the present disclosure that the network load of the neighboring radio network nodes should be considered. Therefore, the first radio network node determines 104 the traffic load of the second radio network node. For example, the beacon provided by the radio network node may provide information about the number of associated STAs and channel utilization (e.g., it is expressed as the percentage of time the channel is used). One or more of such provided information may be regarded as a measure of the traffic load for the neighboring radio network node. The first radio network node may determine whether to take any action based on the determined traffic load, that is, to ignore the neighboring radio network nodes with a traffic load below a threshold. For neighboring radio network nodes with a traffic load exceeding a threshold, for example, the action taken may be adjusted based on the determined traffic load. Therefore, the direction toward the neighboring radio network node (the second radio network node in this example) for reducing the transmit power of the beamforming is determined 106. For such a neighboring radio network node (the second radio network node in this example), the characteristic of the reduced signal power is assigned in the direction of the neighboring radio network node. The characteristics of the reduction in terms of attenuation and angular width in the determined directions may be based on the determined traffic load.

[0043] According to one embodiment, the transmission by the first radio network node is performed omni-directionally, which can be performed by applying cyclic shift diversity, which provides that each subcarrier becomes beamformed in a random direction. However, considering that the determination 102 of the direction, the determination 104 of the traffic load of the neighboring radio network nodes, and the determination 106 of the direction of the reduced transmission are performed as above. It is desirable to provide omni-directional transmission and reduced transmission in the determined direction. This is achieved by assigning 107 the reduced transmission (e.g. null steering) in the determined direction and randomizing 109 all other directions.

[0044] Figure 1 The flow chart also shows a method for transmission of a frame. A first radio network node composes 101 a frame to be sent. Determination of direction 102, determination of traffic load of neighboring radio network nodes 104, and determination of direction of reduced transmission 106 are performed as presented above to assign a desired beam pattern. The frame is then transmitted 111 with the assigned beam pattern. The assignment of the beam pattern may be provided, for example, with reference to assigning 107 a reduced transmission (e.g. null steering) in the determined direction as presented, and randomizing 109 the subcarriers in all other directions as presented above, for providing an almost omnidirectional transmission of the frame.

[0045] Figure 2 is a block diagram schematically illustrating a radio network node according to an embodiment. The radio network node comprises an antenna arrangement 202, a receiver 204 connected to the antenna arrangement 202, a transmitter 206 connected to the antenna arrangement 202, a processing element 208 which may comprise one or more circuits, one or more input interfaces 210 and one or more output interfaces 212. The interfaces 210, 212 may be operator interfaces and / or signal interfaces, e.g. electrical or optical. The radio network node 200 may be arranged to operate in a communication network based on a basic service set or a cell. In particular, by being arranged to perform a reference Figure 1 The processing element 208 of the illustrated embodiment, the radio network node is able to reduce interference with neighboring BSS or cells. The processing element 208 can also perform many tasks, from signal processing to enabling reception and transmission, as it is connected to the receiver 204 and the transmitter 206, thereby executing applications, controlling interfaces 210, 212, etc.

[0046] The method according to the invention is suitable for implementation by means of a processing means such as a computer and / or a processor, in particular for the case where the processing element 208 shown above comprises a processor handling the determination of the direction and controlling the nulling as discussed above. Thus, there is provided a method comprising being arranged to cause the processing means, the processor or the computer to execute the method according to the reference Figures 1 to 6A computer program of instructions for performing any of the steps of any of the methods of any of the described embodiments. The computer program preferably includes program code, which is stored on a computer readable medium 300 (such as Figure 3 As shown in ), the program code can be loaded and executed by the processing unit, processor or computer 302, so that it can perform the method according to the embodiment of the present invention (preferably with reference to Figure 1 The computer 302 and the computer program product 300 may be arranged to execute program code sequentially, wherein the actions of any of the methods are performed step by step. The processing unit, processor or computer 302 is preferably what is commonly referred to as an embedded system. Thus, Figure 3 The computer readable medium 300 and the computer 302 depicted in FIG. 1 should be interpreted as being used for illustrative purposes only to provide an understanding of the principle and not as any direct illustration of the elements.

[0047] In view of the methods, devices and computer programs presented above, several examples will be given below for further understanding of the features and benefits of the proposed methods. In order to make the language more fluent when describing the examples, the reduced transmission in (one or more) determined directions will be referred to as "nulling", "nulling", etc., but should be considered as reduction, which in its final form also includes not providing power in that direction, but may also include any significant reduction.

[0048] Figure 4 Schematically illustrates nulling adjustment (NA) associated with neighboring network nodes. To provide a tangible example, a WiFi scenario with three access points (APs) that may perform NA is shown. Generally speaking, an IEEE 802.11 AP periodically transmits a beacon B frame in a BSS. The beacon B frame contains network information such as a service set identification number (SSID). The main purpose of sending these frames is to synchronize the associated STA with it. In the case of an OBSS, it is possible that a B frame sent from one AP can be heard by an AP or a non-AP STA of the OBSS (if they are within each other's transmission range). Then, an AP with multi-antenna capabilities can directly obtain information from its neighboring APs and adjust its antenna nulling toward the direction in which the STA associated to other APs may be interfered. As a result, interference at neighboring APs will be mitigated and space is provided for performing simultaneous transmissions. Of course, for transmissions to its own STAs, directional beamforming is used, and nulling is adjusted to STAs in the OBSS.

[0049] Before data transmission begins, the AP first determines the directions in which to place its nulls to reduce interference in those directions where it believes interference will cause the most harm. An example of the process used to adjust the nulls is described below:

[0050] 1. All APs broadcast Beacon B messages periodically; typically every 100ms. Beacon B contains the number of STAs associated with the source AP as well as information on load and channel utilization.

[0051] 2. After receiving beacon B, the AP learns about other APs in the OBSS. It is also assumed here that when the AP receives beacon B, it can obtain information about the direction of the corresponding AP that sent beacon B.

[0052] 3. Based on the OBSS's information about load and channel utilization, the AP decides how to perform nulling adjustments relative to neighboring APs. Specifically, the AP may decide to place nullings only in directions where the OBSS activity is high enough, and do nothing if the activity in the OBSS is below a certain level.

[0053] NA can be performed in one of many existing methods, for example using a zero-forcing algorithm. The proposed solution does not involve how the nulling is performed, but only how to determine in what direction to place the null. Therefore, the present invention is applicable regardless of how NA is performed.

[0054] One benefit that NA can bring is interference mitigation to neighboring APs. APs can perform NA for both UL transmissions and DL transmissions. In the case of DL transmissions, the purpose of adopting NA is to minimize interference toward neighboring APs. Figure 5 In the example, AP1 performs NA for AP2 and AP3. Here, STA-1 represents a STA associated with AP1, STA-2 represents a STA associated with AP2, and so on. In the direction of AP2, interference caused by STA-1 500 close to STA-2 and STA-1 501 close to STA-3 is minimized because transmission is not possible at the STA-1 500, 501.

[0055] Similarly, for UL transmissions, utilizing the NA helps reduce the experienced interference at the performing AP from the determined direction. In any case, the NA direction needs to be determined prior to transmission.

[0056] One other benefit that can be provided is reduced contention for channel access within the BSS. Since STAs in the NA direction cannot transmit and receive from the AP, they do not affect transmissions to or from the AP. In this case, contention for the channel will mainly exist between nodes that are not in the NA direction. Therefore, the probability of collision of competing STAs can be reduced, which may improve throughput. Figure 5 In the example, only STA-1 502 contends for access to the channel to / from AP1.

[0057] One benefit may be to provide other APs with an opportunity to improve performance by efficiently utilizing the NA direction. An AP that is assisted by a NA-performing AP may even further improve its performance, such as throughput, by placing directional beamforming in the same direction. Figure 5 As shown in , AP2 gains more by placing its main lobe in the NA direction from AP1. Similarly, AP3 can do the same. This can be, for example, the result of AP1 limiting its beacon transmission in the direction towards AP2 and / or AP3.

[0058] In some embodiments discussed above, the AP performs NA towards other APs in the OBSS without considering the traffic conditions of the STAs in that direction. In addition, if there are more neighboring APs than APs to help by providing power limitation in their direction, the AP may select the neighboring APs to help randomly or in the order in which they are detected. In practice, the number of APs (for which NA is performed) may be determined by the number of null steering supported by the antenna, for example, the number of antenna elements and corresponding processing components used to form the radiation pattern. If the AP randomly selects a set of neighboring APs from the available APs in the OBSS, the performed NA is not fully utilized if the selected neighboring APs do not have many STAs and the traffic load in that direction is low (where the performance limitation caused by NA may be more than the benefit obtained at the neighboring BSS).

[0059] Therefore, in order to further improve the gain obtained from NA, the present disclosure proposes an embodiment for selecting a direction based on traffic load. Since there may be many OBSSs, the information obtained from the corresponding beacon can be used to determine whether it is necessary to place a null in a certain direction based on the load in the corresponding OBSS. Since the broadcast message B may contain information about the number of STAs associated with the neighboring AP, the AP can select a direction toward a neighboring AP with a larger traffic load. Then, the performance of the cooperative BSS in that direction can be maximized. Similarly, in UL transmission, an AP performing NA can take advantage of interference mitigation when it receives frames from STAs.

[0060] NA can adapt to the expected traffic load and provide improved network performance. Figure 6As depicted in , for AP1, it is better to perform NA in the direction toward AP2 because it is associated with four STA-2 600 in the direction 602 shown. In general, a higher STA density generates more interference in DL transmission. In DL transmission, implementing NA reduces interference to the target AP in the OBSS. Similarly, in UL transmission, areas with more STAs gain more benefits. Therefore, it makes sense to implement NA in areas with heavy traffic load. In the same figure, AP3 has fewer STA-3 604, and performing NA in this direction does not bring much benefit to performing NA in both the direction 602 toward AP2 and the direction 606 toward AP3. Therefore, NA is not performed in the direction 606 toward AP3, as shown by the intersection 610 of the lobe 608 and the direction line 606.

[0061] In any transmission of IEEE 802.11, some kind of transmission is uniformly transmitted. Examples of such transmissions are preambles of each packet, beacon, and control frames, such as acknowledgements (ACK) and clear channel assessments (CCA). In the case of a transmitter with multiple antennas, uniform transmission can be obtained through transmit diversity. With transmit diversity, unintended beamforming can be avoided through cyclic shift diversity (CSD). The effect of CSD is that each subcarrier is beamformed in a random direction.

[0062] In some embodiments, directional information of nearby BSSs is used to modify the uniform transmission. Nulls are placed in the direction towards the nearby BSS, while the subcarriers in the remaining available directions are randomized. Traditionally, this is done for all transmissions using transmit diversity, except for frames used by the AP to detect other APs, such as some beacons. Note that standard beacons should be transmitted with nulls so that the STA is associated with the correct AP. The frame used to detect the direction of other APs can be part of the beacon, i.e., the part that the STA does not use. Figure 7 An example is shown of how a conventional transmission using CSD can be modified to provide a null steering towards a neighboring AP. On the left, a conventional beam pattern is shown, and on the right, an adapted beam pattern is shown. In other words, in an adapted beamforming pattern, if the antenna system is properly calibrated, for example, CCA can be performed so that the null steering is placed in the direction 700, 702 of the neighboring AP.

Claims

1. A method of assigning a beam pattern with null-steering beamforming from a first radio network node, the method comprising: determining (102) a direction to a neighboring second radio network node; determining (104) an indication of a traffic load of the second radio network node; Determining (106) a direction of null steering of the null steering beamforming according to the direction and the traffic load; Wherein, for omnidirectional transmission using cyclic delay diversity, the method comprises: assigning (107) the null in the determined direction of the null; and Subcarriers in directions other than at least one direction of the null steering are randomized (109).

2. The method of claim 1, wherein: The determination of the direction is performed based on reception of a beacon from the second radio network node (106).

3. The method of claim 1, wherein: The determination of the direction is performed according to a signaling interface between the first radio network node and the second radio network node (106).

4. The method of claim 1, wherein: The determination of the indication of traffic load is made based on information in a beacon from the second radio network node (104).

5. The method of claim 4, wherein: The information in the beacon includes any one of the following: the number of stations associated to the second radio network node; and Channel utilization.

6. The method of claim 1, wherein: The determination of the indication regarding traffic load is performed according to a signaling interface between the first radio network node and the second radio network node (104).

7. The method of claim 2, wherein: The determination (106) of the direction of the null comprises prioritizing one of the directions towards a plurality of neighboring network nodes, wherein the prioritization comprises prioritizing the directions based on an estimated distance from the neighboring radio network node based on the reception of the beacon from the neighboring radio network node, wherein a smaller estimated distance is prioritized over a larger estimated distance.

8. The method according to any one of claims 1 to 7, wherein: Each of the first radio network node and the second radio network node forms a basic service set BSS, and the first radio network node and the second radio network node form an overlapping BSS (OBSS) in a communication system for a wireless local area network service.

9. A method of transmitting a signal from a radio network node, the method comprising: Composing (101) a frame to be sent; Assigning a beam pattern with null-steering beamforming according to any one of claims 1 to 8; and The frame is transmitted (111) via the assigned beam pattern.

10. A computer program product comprising instructions which, when executed on a processor of a radio network node, cause the radio network node to perform the method according to any of claims 1 to 9.

11. A first radio network node (AP1, 200), the first radio network node (AP1, 200) being arranged to assign a beam pattern with null-steering beamforming towards a neighboring second radio network node (AP2), wherein: The first radio network node (AP1, 200) comprises a controller (208) and a transceiver (204, 206), and wherein the controller (208) is arranged to: Composing the frame to be sent; determining a direction to the second radio network node; determining an indication of a traffic load of the second radio network node; as well as determining a direction of null steering of the null steering beamforming according to the direction and the traffic load (602), and the transceiver (206) is arranged to transmit the frame via a signal, wherein the signal has a null-steering beamforming in the direction (602); Therein, for omni-directional transmission using cyclic delay diversity, the first radio network node (AP1, 200) is arranged to: assigning the null in the determined direction of the null (602); as well as Subcarriers in directions other than at least one direction of the null steering are randomized.

12. The first radio network node (AP1, 200) of claim 11, arranged to determine the direction from reception of a beacon from the second radio network node (AP2) by the transceiver (204).

13. The first radio network node (AP1, 200) of claim 11, being arranged to determine the direction based on a signaling interface (210, 212) between the first radio network node (AP1, 200) and the second radio network node (AP2).

14. The first radio network node (AP1, 200) of claim 11, being arranged to determine the indication of traffic load from information in a beacon received via the transceiver (204) from the second radio network node (AP2).

15. The first radio network node (AP1, 200) according to claim 14, wherein The information in the beacon includes any one of the following: the number of stations (600) associated to the second radio network node (AP2); and Channel utilization.

16. The first radio network node (AP1, 200) according to claim 11, being arranged to determine the indication about the traffic load based on a signaling interface (210, 212) between the first radio network node (AP1, 200) and the second radio network node (AP2).

17. The first radio network node (AP1, 200) according to claim 12, wherein: The determination of the direction of the null sink includes prioritizing one of the directions toward a plurality of neighboring network nodes (AP2, AP3), wherein the prioritization includes prioritizing the direction based on an estimated distance from the neighboring radio network node (AP2, AP3) based on the reception of the beacon from the neighboring radio network node (AP2, AP3) by the transceiver (204), wherein a smaller estimated distance takes precedence over a larger estimated distance.

18. The first radio network node (AP1, 200) according to any one of claims 11 to 17, wherein: Each of the first radio network node (AP1, 200) and the second radio network node (AP2) forms a basic service set BSS, and the first radio network node (AP1, 200) and the second radio network node (AP2) form an overlapping BSS (OBSS) in a communication system for a wireless local area network service.

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