WO2019108097A1

WO2019108097A1 - Station, access point and method in a wireless communications network

Info

Publication number: WO2019108097A1
Application number: PCT/SE2017/051181
Authority: WO
Inventors: Dennis SUNDMAN; Luis Felipe DEL CARPIO VEGA; Miguel Lopez; Yu Wang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-11-28
Filing date: 2017-11-28
Publication date: 2019-06-06

Abstract

A method performed by a Station (STA) for reducing packet collision probability when transmitting data packets to an Access Point (AP) in a wireless communications network is provided. The AP and the STA operate in the wireless communications network. The STA obtains (302) for each group of Resource Units (RUs) out of a collection of groups of RUs, a respective probability value which represents a decided probability for the STA to select that group of RUs. At least two of the respective probability values are different. The STA performs (303) a random selection of the first group of RUs from the collection of groups of RUs. The random selection is such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs. The STA then transmits (304) the data packets to the AP using the selected first group of RUs.

Description

STATION, ACCESS POINT AND METHOD IN A WIRELESS COMMUNICATIONS

NETWORK

TECHNICAL FIELD

Embodiments herein relate to a station, an access point and methods therein. In particular, they relate to reducing packet collision probability when transmitting data packets to an Access Point (AP) in a wireless communications network.

BACKGROUND

In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, Stations (STAs) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio network node such as a radio access node e.g. an AP such as e.g. a Wi-Fi access point, a Wireless Local Area Network (WLAN) AP or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or“eNodeB”. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.

A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks. Specifications for the Evolved Packet System (EPS), also called a Fourth

Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network also referred to as New Radio (NR) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E- UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially“flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E- UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface.

Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a Multiple-Input Multiple-Output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO.

The Institute of Electrical and Electronics Engineers (IEEE) 802.11ax standard, also referred to as High-Efficiency Wireless (HEW), has the challenging goal of improving the average throughput per wireless communication device. This standard focuses on implementing mechanisms to serve more wireless communication devices a consistent and reliable stream of data, average throughput, in the presence of many other wireless communication devices.

The IEEE 802.11 ax standard uses Orthogonal Frequency-Division Multiple Access (OFDMA) to multiplex more wireless communication devices in the same channel bandwidth, which is a technological improvement from the 4G cellular technology.

Building on the existing orthogonal frequency-division multiplexing (OFDM) digital modulation scheme that the WiFi standard already uses, the IEEE 802.11 ax standard further assigns specific sets of subcarriers to individual users. That is, it divides the existing IEEE 802.11 channels, 20, 40, 80 and 160 MHz wide, into smaller sub-channels with a predefined number of subcarriers. The 802.11 ax standard names the smallest sub- channel a Resource Unit (RU), with a minimum size of 26 subcarriers, as in the LTE terminology.

Based on multi-user traffic needs, an AP decides how to allocate the channel, always assigning all available RUs on the downlink. It may allocate the whole channel to only one wireless communication device at a time - just as IEEE 802.11ac currently does, or it may partition it to serve multiple wireless communication devices simultaneously.

With the introduction of OFDMA in the IEEE 802.11 ax, a new management frame named Trigger Frame (TF) was introduced. Trigger frames are used to schedule UL access, but since there are circumstances where UL random access is desirable, e.g. the AP does not always know whether wireless communication device such as a STA has data for UL transmission, a special type of TF called TF for Random Access (TF-R) was introduced. Moreover, the standard allows a Trigger Frame to schedule RUs for deterministic access and RUs for random access meaning that the TF and TF-R are potentially combined on the same frame.

The following snapshot from the IEEE 802.11 ax standard specification describes the operation of the TF-R.

27.5.2.2.1 General

An AP shall not send to a STA a Medium Access Control (MAC) Protocol Data Unit (MPDU) that contains an Uplink Multi-User (UL MU) Response Scheduling A-Control subfield, unless the STA has set the UL MU Response Scheduling Support subfield to 1 in the High Efficiency (HE) Capabilities element it transmits.

An AP may transmit a Physical Layer (PHY) Protocol Data Unit (PPDU) that elicits an HE trigger- based PPDU from one or more STAs by including in the PPDU:

— One or more Trigger frames that includes one or more User Info fields addressed to one or more of the recipient STAs. For recipient STAs that are associated with the AP, the User Info field is addressed to a recipient STA if the value of the AID 12 subfield of the User Info field is equal to the AID of the STA or to 0 (indicating a random access allocation).. A value of 0 also indicates that non-associated STAs can transmit on the allocated resource using the random access procedure as described in 27.5.2.6 (UL OFDMA-based random access).

OFMDA Backoff process

A TF-R allows the STAs to contend for the medium, but unlike Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), there is contention for RU’s in the frequency domain. To this end, a new backoff counter, called OFDMA Backoff (OBO) counter has been defined.

The following snapshot from the IEEE 802.11 ax standard specification illustrates how channel contention works for TF-R based random access.

The non-AP STA with dotl lOFDMARandomAccessOptionlmlemented set to true shall maintain an internal OFDMA backoff (OBO) counter. The HE STA shall follow the random access procedure defined in 27.5.2.6.2 (Random access procedure) to contend for an RU assigned for random access.

27.5.2.6.2 Random access procedure

In this subclause, the random access procedure is described with respect to UL OFDMA contention parameters. The procedure is also illustrated in Figure 27-1 (Illustration of the UL OFDMA-based random access procedure). The OFDMA contention window (OCW) is an integer with an initial value of OCWmin.

Figure 1 , depicts the Figure 27-1 in the IEEE 802.11 ax standard specification, illustrating Illustration of the UL OFDMA-based random access procedure, wherein SIFS is the abbreviation for Short Interframe Space and ACK / MB-A is the abbreviation for Acknowledgement / Multiple Block Acknowledgement.

Multiple sub-channels CSMA

A problem appears when a number of channels are available at the same time, either because there are no channel specific backoff timers such as OBO timers, or that many of the timers have expired at the same time slot.

SUMMARY

It is an object of embodiments herein to improve the performance of a wireless communications network.

According to a first aspect of embodiments herein, the object is achieved by a method performed by a Station, STA, for reducing packet collision probability when transmitting data packets to an Access Point, AP, in a wireless communications network. The AP and the STA operate in the wireless communications network.

The STA obtains for each group of Resource Units, RUs, out of a collection of groups of RUs, a respective probability value which represents a decided probability for the STA 121 to select that group of RUs. At least two of the respective probability values are different. The STA performs a random selection of the first group of RUs from the collection of groups of RUs. The random selection is such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs. It should be noted that the term “first” in“first group of RUs” is simply used as a name of the group of RUs that has been selected: This is to differentiate the selected group of RUs from the other groups of RUs.

The STA then transmits the data packets to the AP using the selected first group of

RUs.

According to a second aspect of embodiments herein, the object is achieved by a method performed by an Access Point, AP, for reducing packet collision probability when a Station, STA, transmits data packets to the AP in a wireless communications network. The AP and the STA operate in the wireless communications network.

The AP decides for each group of Resource Units, RUs out of a collection of groups of RUs, a respective probability value which represents a decided probability for one or more STAs to select that group of RUs. At least two of the respective probability values are different. The AP transmits the decided probability values to the STA 121 and then receives the data packets, transmitted by the STA in a first group of RUs. The first group of RUs was selected by the STA from the collection of groups of RUs, according to the decided probability values.

According to a third aspect of embodiments herein, the object is achieved by a Station, STA, for reducing packet collision probability when transmitting data packets to an Access Point, AP, in a wireless communications network. The AP and the STA are operable in the wireless communications network. The STA is configured to:

obtain for each group of Resource Units, RUs, out of a collection of groups of RUs, a respective probability value which represents a decided probability for the STA to select that group of RUs, wherein at least two of the respective probability values are adapted to be different,

perform a random selection of the first group of RUs from the collection of groups of RUs, the random selection being such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs, and

transmit the data packets to the AP using the selected first group of RUs. According to a fourth aspect of embodiments herein, the object is achieved by an Access Point, AP, for reducing packet collision probability when a Station, STA, transmits data packets to the AP in a wireless communications network. The AP and STA are operable in the wireless communications network. The AP is configured to:

decide for each group of Resource Units, RUs out of a collection of groups of RUs, a respective probability value which represents a decided probability for one or more STAs to select that group of RUs, wherein at least two of the respective probability values are different,

transmit the decided probability values to the STA, and

receive the data packets, transmitted by the STA a first group of RUs, which first group of RUs is adapted to be selected by the STA from the collection of groups of RUs, according to the decided probability values.

Since The STA performs a random selection of the first group of RUs from the collection of groups of RUs wherein the random selection is such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs, the packet collision probability is reduced when the STA transmits the data packets to the AP by the selected first group of RUs. This in turn results in an improved performance of the wireless communications network.

An advantage of embodiments herein is that when multiple STAs have access to multiple channels such as groups of RU’s, embodiments herein provide reduced packet collision probability and improved successful transmission rate.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments herein are described in more detail with reference to attached drawings in which:

Figure 1 is a schematic block diagram illustrating prior art.

Figure 2 is a schematic block diagram illustrating embodiments of a wireless

communications network.

Figure 3 is a flowchart depicting embodiments of a method in a STA. Figure 4 is a flowchart depicting embodiments of a method in an AP.

Figure 5 is a schematic diagram illustrating embodiments herein.

Figure 6 is a schematic diagram illustrating embodiments herein.

Figure 7 is a schematic diagram illustrating embodiments herein.

Figure 8 is a schematic diagram illustrating embodiments herein.

Figure 9 is a schematic block diagram illustrating embodiments of a STA.

Figure 10 is a schematic block diagram illustrating embodiments of an AP.

DETAILED DESCRIPTION

As part of developing embodiments herein a problem will first be identified and discussed.

A problem appears when a number of channels are available at the same time, either because there are no channel specific backoff timers such as OBO timers, or that many of the STAs has timers that have expired.

According to the current specification, when a number of RUs are allocated for random access by a TF-R, the OBO timer will expire fast. For example, with 9 Random Access (RA) RUs and Contention Window (CW)min=7, the OBO counters of all RA STAs will be reduced to zero with one single TF-R. In this case, it’s up to the randomness in RU selection to manage the packet collision probability, i.e. the probability of two STAs selecting the same RU from RA transmissions. The current standard implies that the RU selection should be performed uniformly at random.

Embodiments herein relate to methods to reduce transmission collision in radio networks such as wireless communications networks.

A wireless communications network 100, in which embodiments herein may be implemented, is schematically illustrated in Figure 2.

The wireless communication network 100 comprises one or more RANs, e.g. a RAN 102, and one or more CNs, e.g. a CN 104. The wireless communications network 100 may be a cellular communications network, and may use a number of different technologies, such as Wireless Local Area Network (WLAN) Wi-Fi, LTE, LTE-Advanced, 5G, WCDMA, Global System for Mobile communications/enhanced Data rate for GSM Evolution (GSM/EDGE), NB-loT just to mention a few possible implementations.

Embodiments herein relate to recent technology trends that are of particular interest in a 5G context however, embodiments are also applicable in further development of the existing wireless communication systems such as e.g. GSM, WCDMA and LTE.

One or more radio network nodes such as an AP 110, operate in the wireless communications network 100. The AP 110 provides radio access to the wireless communications network 100 over an area 11 to wireless devices such as Stations (STAs). According to embodiments herein the AP 110 may assign available radio resources such as RUs to serve multiple wireless communication devices such as STAs simultaneously. A group of RUs is simply a set comprising of at least one RU. The AP 110 may be a transmission and reception point e.g. a radio access network node such as a Wireless Local Area Network (WLAN) access point or an Access Point Station (AP STA), an access controller, a base station, e.g. a radio base station such as a NodeB, an evolved Node B (eNB, eNode B), a base transceiver station, a radio remote unit, an Access Point Base Station, a base station router, a transmission arrangement of a radio base station, a stand-alone access point or any other network unit capable of

communicating with a wireless device such as a STA within the service area served by the AP 110 depending e.g. on the radio access technology and terminology used.

Other examples of the AP 110 are Multi-Standard Radio (MSR) nodes such as MSR BS, network controllers, Radio Network Controllers (RNCs), Base Station Controllers (BSCs), relays, donor nodes controlling relay, Base Transceiver Stations (BTSs), Access Points (APs), transmission points, transmission nodes, Remote Radio Units (RRUs), Remote Radio Heads (RRHs), nodes in Distributed Antenna System (DAS) etc.

Wireless devices such as STAs operate in the wireless communication network 100, e.g. one or more STAs comprising a STA 121 and further one or more second STAs 122. Each STA 121 , 122 may be any of a mobile station, a non-Access Point (non-AP) STA, a wireless device, a user equipment, a wireless terminal, and communicate via one or more RANs such as the RAN 102, to one or more CNs such as the CN 104.

The term“STA” when used herein means any wireless device, terminal,

communications device, wireless communication terminal, user equipment, Machine-Type Communication (MTC) device, Device-to-Device (D2D) terminal, or node e.g. smart phone, laptop, mobile phone, sensor, relay, mobile tablets, an Internet-of-Things (loT) device, e.g. a Cellular loT (CloT) device or even a small base station communicating within a service area. Please note the term user equipment and wireless device used in this document also covers other wireless devices such as Machine-to-Machine (M2M) devices, and loT devices even though they do not have any user.

The AP 110 may be referred to as a serving radio network node and communicate with one or more wireless devices 121 , 122 with Downlink (DL) transmissions to the one or more STAs 121 , 122 and Uplink (UL) transmissions from the one or more STAs 121 , 122. The AP 110 may communicate with the STA 121 when connected to it, over a channel between the AP 110 and the STA 121 at the same time as it communicates with the one or more second STAs 122 when being connected to them, by using the same channel between the radio network node 110 and respective one or more wireless devices 122.

Some actions in methods herein are performed by the AP 110. As an alternative, any Distributed network Node (DN) 130 and functionality, e.g. comprised in a cloud 140 may be used for performing these actions.

Embodiments herein provide methods to enable control over a selection of a group of RUs for transmission such as e.g. a RA RU selection.

As mentioned above, the IEEE 802.11 ax standard assigns specific sets of subcarriers to individual users by dividing the existing channels into smaller sub-channels with a predefined number of subcarriers, wherein the smallest sub-channel is an RU. A group of RUs may comprise multiple RUs or only a single RU.

As mentioned above, the term“first” in“first group of RUs” is simply used as a name of the group of RUs that has been selected: This is to differentiate the selected group of RUs from the other groups of RUs.

The AP 110 provides a number of available RUs for multi-user traffic that may be used by the STAs 121 , 122 for transmitting data packets to the AP 110. The term

“collection of groups of RUs” when used herein means a collection of groups of RUs from which the selection of the first group which will be used for transmission is made. The collection of groups of RUs may comprise all the available RUs provided by the AP A probability value associated with a group of RUs in the collection is herein a value that corresponds to a decided probability of selecting the associated group of RUs as the first group of RUs. As a basis for selecting a group of RUs which reduces the packet collision probability and improves the successful transmission rate, probability values are obtained according to embodiments herein. These probability values comprise a respective probability value for each group of RUs out of the collection of groups of RUs. These probability values may also be referred to collectively as the selection probability distribution. The selection probability distribution may differ between STAs, even when the same collection of groups of RUs is considered.

Example embodiments of a method performed by the STA 121 for reducing a packet collision probability when transmitting data packets to an AP 110 in the wireless communications network 100 will now be described with reference to a flowchart depicted in Figure 3. The wording“packet collision probability” when used herein means the probability of two STAs at the same time selecting the same RU or group of RUs for transmissions, e.g. RA transmissions. I.e. the probability that the STA 121 served by the AP 110 selects the same RU or group of RUs for transmissions at the same as another STA served by the AP 110. As mentioned above, the AP 110 and the STA 121 operate in the wireless communications network 100.

The method will first be described in a view seen from the STA 121 together with Figure 3, and then be described in a view seen from the AP 110 together with Figure 4, followed by more detailed explanations and examples.

The method comprises the following actions, which actions may be taken in any suitable order. Actions that are optional are presented in dashed boxes in Figure 3.

Action 301

In this optional action, the STA 121 obtains information about data traffic between one or more STAs 121 , 122 and the AP 110. This may e.g. comprise any one out of: Overheard transmission of second STAs 122, and transmission collision history with second STAs 122. This will be used in some embodiments wherein the STA 121 obtains the probability values by deciding them in the STA 121 , which e.g. may be based on the information about data traffic.

Action 302 To be able to select a group of RUs that reduces the packet collision probability when transmitting data packets to the AP 110, the STA 121 obtains probability values.

The STA 121 thus obtains a respective probability value for each group of RUs out of the collection of groups of RUs. The respective probability value represents a decided probability for the STA 121 to select that group of RUs. At least two of the respective probability values are different. This may e.g. be performed by specifying non-uniform distributed selection probability among the groups of RUs out of the collection of groups of RUs such as among the RUs e.g. RA RUs. Having two of the probability values different allows for reducing collision probability since the probability of two STAs selecting any same groups of RU can be reduced by controlling the RU group selection probability, but also maintains fairness by keeping the same probability for each STA selecting one of the RU groups from the RU group collection.

The obtained respective probability value may be determined based on information about data traffic between the AP 110 and one or more STAs 121 , 122. For example, if there are only a few STAs in the data traffic, the probability values are determined such that the probability that the STAs select different groups of RUs is increased, this is since comparing to the equal probability of selecting any group of RUs in the collection of RU groups the STAs can be controlled to have higher probability to select different groups of RUs. This means that when only a few STAs are in the traffic, the probability for the STA 121 to select the same group of RUs as another STA is affected by being smaller.

The information about data traffic between one or more STAs 121 , 122 and the AP 110 may comprise any one or more out of:

- The number of the one or more STAs 121 , 122 associated with the AP 110, which affects the probability for the STA 121 to select a group of RUs such that the number of STAs being dense increases the probability of collision if the same group of RUs is selected.

- Uplink traffic pattern of the one or more STAs 121 , 122, which affects the probability for the STA 121 to select a group of RUs, such that the uplink pattern being dense increases the probability of collision if the same group of RUs is selected.

- Buffer status of the one or more STAs 121 , 122, which affects the probability for the STA 121 to select a group of RUs such that if the buffer is full, that means that the uplink traffic pattern may be dense which increases the probability of collision if the same group of RUs is selected.

- Historical transmission statistics of the one or more STAs 121 , 122, and - Predicted uplink traffic of the one or more STAs 121 , 122, which affects the probability for the STA 121 to select a group of RUs such that if the predicted uplink traffic is dense it will increase the probability of collision if the same group of RUs is selected.

The obtaining of the respective probability values may comprise obtaining any one out of: A Probability Mass Function (PMF), a Probability Density Function (PDF), an indication of a PMF, and an indication of a PDF.

In probability and statistics, a PMF is a function that gives the probability that a discrete random variable is exactly equal to some value. The PMF is often a primary means of defining a discrete probability distribution, and such functions exist for either scalar or multivariate random variables whose domain is discrete.

A PMF differs from a PDF in that the latter is associated with continuous rather than discrete random variables; the values of the PDF are not probabilities as such, a PDF must be integrated over an interval to yield a probability.

To determine the above-mentioned probability values from a PMF or a PDF is convenient, since there exists a profusion of such functions to choose from in probability theory and statistics. Moreover, these functions are often defined in terms of one or parameters, so that whole families of functions can be generated by simply selecting the parameters in different ways.

When a PMF is applied, the PMF determines the assigned probability value of each element in the discrete sample space of a discrete random variable. Each element in the discrete sample space of the random variable represents one RU group in the collection of the RU groups. The probability value assigned to each element in the sample space according to the PMF equals to the probability of the corresponding RU group to be selected from the collection of the RU groups.

When a PDF is applied, the integral of the PDF over a range determines the probability that a realization of a continuous random variable falls in the range. The whole span of the continuous sample space of the random variable is segmented into many ranges the number of which equals to the total number of RU groups in the collection of the RU groups. The integral of the PDF over each of the range equals to the probability of the corresponding RU group to be selected from the collection of the RU groups.

Alternatively, a PDF may also be discretized/lumped into a discrete function, which can be used in a similar way as a PMF.

It is understood that when a PMF or a PDF is mentioned that a cumulative distribution function (CDF) may alternatively be used instead. The respective probability value for each group of RUs out of the collection of groups of RUs, may be obtained by any one out of: Receiving them from the AP 110 also referred to as the decision being made in a central node, receiving them from a network node operating in the wireless communications network 100 also referred to as the decision being made in a central node, and deciding them in the STA 121 , also referred to as the decision being made in the distributed manner.

In some embodiments, the respective probability values may be obtained e.g. decided, based on coordination with one or more other STAs 122. Information for the coordination may e.g. be exchanged between the STAs, received from the AP, or the STA 120 may monitor the activity of other STAs.

Action 303

When the STA 121 has obtained all the respective probability values, e.g. in the form of a PM F or a PDF, and also referred to as the decided selection probability distribution, the STA 121 will follow the obtained selection probability distribution when selecting a group of RUs out of the collection of RUs for its transmissions.

The STA 121 then performs a random selection of the first group of RUs from the collection of groups of RUs. The random selection is being such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs

The selection will be explained more in detail below.

The selected group of RUs will then be then used for a transmission in the next action 304.

Action 304

The STA 121 then transmits the data packets to the AP 110 using the selected first group of RUs. These data packets may in some embodiments be RA data packets.

By performing this way of selecting the first group of RUs when multiple STAs including the first STA 121 have access to multiple RU’s, the packet collision probability is reduced and the successful transmission rate is improved for transmission using the selected first group of RUs.

Example embodiments of a method performed by the AP 110 for reducing packet collision probability when the STA 121 transmits data packets to the AP 110 in the wireless communications network 100 will now be described with reference to a flowchart depicted in Figure 4. In these embodiments, the AP 110 decides for each group of RUs out of a collection of groups of RUs, a respective probability value which is then transmitted to be obtained by the AP 121. As mentioned above, the AP 110 and STA 121 operate in the wireless communications network 100.

The method will now be described in a view seen from the AP 110 together with Figure 4, followed by more detailed explanations and examples. Examples and definitions explained in the method described above together with Figure 3 are also applicable in the following text and will not be described again here.

The method comprises the following actions, which actions may be taken in any suitable order. Actions that are optional are presented in dashed boxes in Figure 4.

Action 401

In this optional action, the AP 121 obtains the information about data traffic between one or more STAs 121 , 122 and the AP 110 according to any one out of: receiving the information from the one or more second STAs 121 , 122, and learning the information by performing machine learning algorithms.

This will be used in some embodiments wherein the AP 121 decides the probability values based on the information about data traffic.

Action 402

The AP 110 decides for each group of RUs out of a collection of groups of RUs, a respective probability value. Each respective probability value represents a decided probability for one or more STAs 121 , 122 to select that group of RUs At least two of the respective probability values are different.

The deciding of the respective probability values may comprise deciding any one out of: a PMF, a PDF, an indication of a PMF, and an indication of a PDF. This will be explained more in detail below.

The probability values may be decided individually for the STA 121 to be assisted. This means that in some embodiments, the decision of the respective probability values are performed for each STA individually including the STA 121. According to an example, a decision of the RU selection PMF is performed for each STA.

The respective probability value may be decided based on information about data traffic between the AP 110 and one or more STAs 121 , 122, such as e.g. the formation about data traffic obtained in Action 401. The information about data traffic between one or more STAs 121 , 122 and the AP 110 comprises e.g. any one or more out of:

- The number of the one or more STAs 121 , 122 associated with the AP 110,

- uplink traffic pattern of the one or more STAs 121 , 122,

- buffer status of the one or more STAs 121 , 122,

- historical transmission statistics of the one or more STAs 121 , 122, and

- predicted uplink traffic of the one or more STAs 121 , 122.

Action 403

The AP 110 then transmits the decided probability values to the STA 121.

Action 404

The AP 110 receives the data, transmitted by the STA 120 in the first group of RUs. The first group of RUs was selected by the STA 121 from the collection of groups of RUs, according to the decided probability values.

Embodiments herein will now be further described and exemplified. The text below is applicable to and may be combined with any suitable embodiment described above.

Embodiments herein enable mechanisms for reducing packet collision probability and to improve the successful transmission rate when multiple STAs have access to multiple channels such as e.g. RU’s or groups of RUs.

By numerical evaluation such as obtaining a respective probability value for each group of RUs out of the collection of groups of RUs. The respective probability value represents a decided probability for the STA 121 to select that group of RUs. At least two of the respective probability values are different, it can be seen that for a specific example, an unequal RU access probability leads to a collision rate of 16% and improved successful-transmission rate by 18% in a case with a total of two groups of RUs in the collection of groups of RUs which in the example is 2 RUs in the collection of RUs and 4 STAs whereof one of them e.g. is the STA 121. By numerical evaluation is e.g. meant a Monte-Carlo system simulation of the specific example. An unequal RU access probability means that at least two of the respective probability values are different. Unequal RU access probability is used to balance the RU utilization by the STAs such that less collisions are occurring, and total system capacity increases. The collision rate is defined as C_n, where C_n =

(1, if there is any collision in timeslot n

and N is the total number of timeslots of a Monte- 1 0, if there is no collision in timeslot n

Carlo simulation.

The successful-transmission is defined rate as where S_n is the number of

successful transmissions, i.e., transmission on a RU or group of RUs without any collision, in timeslot n, of the Monte-Carlo simulation and T_n is the total number of transmissions in timeslot n of the Monte-Carlo simulation N is the total number of timeslots of the Monte- Carlo simulation. Note that the successful-transmission rate is a global performance measurement. This means it is advised to be extra careful when applying it to ensure that fairness is achieved in the system. However, fairness will not be further discussed here.

An object of embodiments herein is to reduce the collision rate and increase the successful-transmission rate.

Example with X STAs and Y groups of RUs

To explain embodiments herein in a general way, assume a scenario with X STAs and Y groups of RUs. For the m-th STA of the X STAs, the probability of selecting the n-th group of RUs from the Y groups of RUs is P(m, n). For any STA, the sum of the probability assigned to each groups of RUs is one, i.e.

= 1. For any STA, at least two groups of RUs have different assigned probability, i.e. there are distinct n1 and n2 such that P(m, nl) ¹ P(m, n2).

For any group of RUs, the probability of any two STAs assigned to the same group of RUs may or may not be the same.

Example with 4 STAs and 2 RUs

To compare embodiments herein with prior art, the case where there are 4 STAs, A, B, C and D, that want to communicate using a collection comprising two groups of RUs, RU 1 and RU2 have been numerically evaluated. This means that a respective probability value for each group of RUs, RU1 and RU2, out of the collection of groups of RUs has been obtained. In this example let P(A, 1) be the probability that STA A selects RU 1 ,and P(A, 2) be the probability that STA A selects RU 2. Allow for the non-uniform channel allocation distribution i.e. P(A, 1) ¹ P(A, 2), to take the form of P(A, 1) = P(B, 1) = P(C, 2) = P(D, 2 ) = a

P(A, 2) = P(B, 2) = P(C, 1) = P(D, 1) = 1 - a

The wording“non-uniform channel allocation distribution” when used herein means that a is 0 £ a £ 1, and that a ¹ 0.5. From the above equations, it can be seen that the traditional, prior art, corresponds to a = 0.5.

It shall now be shown that other choices of a than a = 0.5 according to

embodiments herein may be a better alternative. The other choices of a corresponds to that the obtained respective probability value for each group of RUs out of the collection of groups of RUs are different. Thus, at least two of the respective probability values are different, means that a ¹ 0.5.

Figure 5, depicts a diagram showing the collision rate as a function of a and P

The x axis represents P which is defined as the a priori probability that a STA will transmit in a current iteration of the Monte-Carlo simulation. In this example, all the STAs A, B, C, and D have the same P. The y axis represents a which is a function parameter describing a PMF according to the equation system above. The z axis represents the collision rate as defined above.

The stars mark the choice of a that minimizes the collision rate for a given P. An example where a =0,5 is marked, to show that the prior art choice of a (= 0.5) is not the choice that minimizes the collision rate. From the diagram it can be seen that, at P = 0.4, by choosing a = 0 instead of the prior art a = 0.5, the collision rate is reduce with (0.3517- 0.2949)/0.3517 = 16%. This means that the total system capacity can be improved with the methods from herein. Note that in this particular example with 4 STAs and 2 RUs, and equal load requirements from the STAs, the choice of a = 0 (or equivalently a = 1) is optimal. However, in general, there is no clear choice that is always the best. Instead one must gather data shall preferably be gathered and a similar analysis performed to decide the PMF for groups of RUs in the specific situation.

Figure 6 depicts a diagram showing the successful-transmission rate as a function of P and a. The x axis represents P which is defined as the a priori probability that a STA will transmit in a current iteration of the Monte-Carlo simulation. In this example, all the STAs A, B, C, and D have the same P. The y axis represents a which is defined as a function parameter describing a PMF according to the equation system above. The z axis represents the successful-transmission rate as defined above.

The stars mark the choice of alpha that maximizes the successful-transmission rate for a given P. An example where a =0,5 is marked, to show that the prior art choice of alpha (= 0.5) is not the choice that that maximizes the successful-transmission rate. The jitter is due to insufficient monte-carlo simulations for collecting statistics. Note that, at P = 0.4, by choosing a = 0 instead of the prior art a = 0.5, we increase the successful- transmission rate with (0.6029-0.5088)/0.5088 = 18%. Also note that it is not always obvious which a is the best choice. Fairness may be ensured by randomly flip the allocations between a and 1 - a such that in average, the channel allocation distribution is uniform. It can be noted from the figure that the successful-transmission rate can be increased, which in turn will improve total system capacity.

In a radio system where UL Random Access (RA) transmissions are solicited by a Trigger Frame - Random access (TF-R) frame, a collection of frequency RUs or groups of RUs may be indicated in the TF-R as available for RA. A device, e.g. a STA in a WLAN system, should select one RU or a group of RUs from all the available RUs or groups of RUs for the RA transmission.

Embodiments herein provide methods that e.g. enable the control of the selection probability of a group of RUs by using the PMF, where different STAs 121 ,122 have different PMFs. A WLAN system is used to exemplify the methods but embodiments herein may be applied to any system involving the selection of a subset of available radio resources e.g. for random access.

An example method according to embodiments herein involves the following steps:

- The AP 110 or the STA 120 decides the probability of RUs to be selected for random access in the STA 120, this is related to action 302 and 402 above.

- If decided in the AP 110, the AP 110 communicates the decision to the STA 120 this is related to action 302 and 403 above.

- After receiving the decision from the AP110 or after deciding it in the STA 120, the STA 120 applies the probability in a transmission such as e.g. in a RA procedure to select a group of RUs or an RU for a transmission such as e.g. a RA transmission this is related to action 303. Decision of probability for the STA 121 to select the first group of RUs.

The respective probability value for each group of RUs out of the collection of groups of RUs, represents a decided probability for the STA 121 to select that group of RUs. At least two of the respective probability values are different. This is related to Action 302 and 402 described above.

The decided probability for the STA to select that group of RUs is in one example referred to as the selection probability of RUs for transmission. The selection probability of a group of RUs for transmission may e.g. be represented as a PMF or a PDF. Figure 7 depicts probability for the STA 121 to select different groups of RUs. As shown in Figure 7, the groups of RUs 2, 3 and 4 are available for transmissions such as RA and the selection probability of each RU is P2, P3 and P4 are shown in the diagram of Figure 7. In other words the collection of groups of RUs comprises three groups, group P2, group P3 and group P4 and the respective probability value for each group of RUs, out of the collection of groups of RUs are shown in Figure 7.

How the probability values are decided for each STA such as the STA 121 is important to be able to select the first group of RUs for transmission that achieves the reduced packet collision probability and the improved successful transmission rate.

Therefore information about data traffic between one or more STAs and the AP 110 may preferably be taken into account for the decision

The data traffic metrics may be used by the AP 110 or the STA 121 to set up a Monte-Carlo simulation similar to the one presented in the previous example. In the simulation, a number of PMFs are evaluated and the PMF providing the best performance is chosen as the PMF to be used.

In another embodiment, the data traffic metrics may be used as input features to a machine learning algorithm. The output of the algorithm is the PMF for each STA 121 , 122 to select the respective group of RUs for transmission. The algorithm uses training data to train a model which generate the output PMF for any given values of the input features. The training data may be obtained from the Monte-Carlo simulation or real network measurements. Examples of the machine learning algorithm are supervised learning algorithms including linear regression, random forest, neural networks, deep learning, etc. Another example of the machine learning algorithm is reinforcement learning.

The decision may be made in either a centralized or distributed manner.

Centralized manner. When the decision is made in a centralized manner, a central node, such as e.g. the AP 110 in the example below will perform the decision. The AP 110 maintains information necessary for the proper decision of probability value for each STA. Such information includes information about data traffic between one or more STAs and an AP e.g.

comprising the number of associated STAs, the UL traffic pattern of the STAs, the buffer status of the STAs, the historic transmission statistics of the STAs, etc. The knowledge may be acquired by signaling from STAs e.g. including the STA 121 or other methods like various machine learning algorithms. This relates to Action 301 and 401 described above. Based on the knowledge comprising the information about data traffic, the AP 110 may decide the probability for the STA 121 to select the different groups of RUs so that the collision probability is reduced comparing to a uniformly random selection. In other words, coordinate the selection of one group of RUs from the collection of groups of RUs for different STAs whereof the STA 121 may be one of them, so that the collision probability is reduced comparing to a uniformly random selection. It has been described in an example above, that when there are two groups of RUs and four STAs, letting the STAs perform random access on only one group of RUs is beneficial compared to letting them perform random access on all groups of RUs of the collection of groups of RUs, which also means that when there are two groups of RUs and four STAs 121 , 122, letting the STAs 121 , 122, perform data transmission such as random access on only one group of RUs is beneficial compared to letting them perform random access on all groups of RUs out of the collection of groups of RUs. Similarly, in larger scenarios, if there are several STAs and groups of RUs in the collection, letting the STAs 121 , 122 perform data transmissions such as e.g. random access such that there is a higher probability to choose some groups of RUs, and making sure that STAs have higher probabilities on different groups of RUs, reduces the collision probability. One example of such a selection is the example provided in the description related to Figures 6 and 7 above. The coordination with other STAs may be used to make sure that the different STAs have non- uniform PM Fs with different shape.

Distributed manner

When the decision is made in a distributed manner, each STA such as the STA 121 may make the decision. The STA 121 may learn the information about data traffic between one or more STAs and an AP e.g. comprising the number of associated STAs, the UL traffic pattern of the STAs, the buffer status of the STAs, the historic transmission statistics of the STAs, etc. such as the traffic pattern and RA RU selection strategies of other STAs based on overheard transmissions or collision history. Overheard

transmission when used herein means transmissions from an AP to a STA, or from a STA to the AP.

Based on the knowledge comprising the information about data traffic, the STA 121 may obtain the probability values for the STA 121 to select the different groups of RUs by deciding it so that the collision probability is reduced comparing to a uniformly random selection. In other words, coordinate the selection of one group of RUs for the STAs so that the collision probability is reduced compared to a uniformly random selection.

One approach to obtain suitable probability values is to select a well-known non- uniform PMF. By using a PMF, a large set of probability values can be derived by one or more parameters defining the PMF. This has the advantage of simplifying the coordination of the probability values among the STAs since they can derive the probability values based on the one or more parameters defining the PMF. One example of a suitable PMF may be the binomial distribution B(p_b, n_b ) for all STAs. The binomial distribution has two parameters p_b e [0,1] and n_b > 0. In B(p_b, n_b ), p_b represents the success probability of each trial, and n_b the total number of trials. The binomial distribution has support over the set k_b = 0, ... , n_b. The PMF of B(p_b, n_b) is given as follows:

for 0 £ k_b £ n_b. For the purpose of illustration, let n_b correspond the total number of groups of RUs in a collection for a STA, let p_b represent a parameter specific to the STA. By letting each STA have different p_b, and possibly also different n_b, such that the probability that multiple STAs choose the same group of RUs is reduced, improved system performance will be obtained. Coordination is an important means to ensure that the distribution parameters with other STAs are not the same. We show how the binomial distribution can be used to obtained probability values by the following example. Assume there are a total of 4 groups of RUs, labeled 0, 1 , 2, 3, and a total of 2 STAs, STA A and STA B. Furthermore, assume that both STA A and STA B have the same 4 groups of RUs in the collection. It is then possible to choose that n_b = 3, and as an example let STA A have S(0.1,3), and STA B have B{ 0.9,3). This will generate probabilities for STA A to select RU groups 0, ... ,3 according to [0.729,0.243, 0.027, 0.001], respectively. Similarly, the probabilities for STA B to select RU groups 0, ...3 will get the following probabilities, [0.001 , 0.027, 0.243, 0.729], respectively. Other methods for choosing the probability values are possible, for example by using other distributions with one or more parameters. Transmission of the decided probability for the STA 121 to select the different groups of RUs

This is related to Action 403 described above. When the decision is made in a Centralized manner, such as by the AP 110, the AP 110 transmits the decided probability values to the STA 121. E.g. the decided PMF is transmitted from the AP 110 to the STA 121 by signaling. Such signaling shall preferably be sufficiently flexible so that the AP 110 can update decided probability values such as the PMF to the STA 121 when the traffic condition is changed. Meanwhile, the overhead introduced by the signaling should preferably be as small as possible. The probability values to the STA 121 may be decided and sent when new STAs join the same BSS, or present STAs leave it.

In one embodiment, a dedicated management or control frame such as e.g.

RA_PMF is used to transmit the probability values such as the PMF. The RA_PMF frame is destined to one or a group of STAs for the PMF configuration.

The content of the RA_PMF frame may be either explicit PMF, i.e. the selection probability of each RU for RA, or be indicated such as an implicit PMF, e.g. comprising an index pointing to a pre-defined PMF shape, e.g., beta-binomial distribution. The PMF may also be a PDF which may be approximated by a PMF.

It should be noticed that the available groups of RUs for transmission such as RA may be indicated in the TF-R frame. It is referred to such a set of groups of RUs as the collection of groups of RUs. It implies that each TF-R frame may indicate a different collection of groups of RUs for RA. It’s also assumed that the RA_PMF transmission is less frequent than the TF-R transmission. Therefore, the PMF configuration in the RA_PMF frame shall preferably accommodate the different collections of available groups of RUs or RUs for transmission such as RA. One alternative is that the PMF transmitted such as signaled to the STA 121 indicates the decided probability values for all the groups of RUs. When a subset in the collection of groups of RUs is available for RA, the STA 121 may perform a normalization before the selection of the first group of RUs so that the sum of groups of RUs selection probability over the available groups of RUs is still one. If such a subset is available, it will after normalization, form a new collection of groups of RUs for the STA.

When the decision is made in the distributed manner, the PMF is decided by each STA such as the STA 121. To enable the STA 121 to apply an arbitrary PMF according to embodiments herein, the AP 110 may switch to group of RUs selection for transmissions such as RA to an autonomous mode in the STAs such as the STA 121. In this case, the AP 110 may signal the mode switching to the STAs such as the STA 121. Performing random selection of a first group of RUs from the collection

This is related to Action 303 described above.

For example, when a transmission such as a RA transmission is triggered, e.g. after the completion of an OBO procedure, the STA 121 performs random selection of a first group of RUs from the collection of groups of RUs, such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs.

Once the probability values of the groups of RUs have been obtained, e.g. via the use of a PMF or PDF, the STA 121 applies them to select a group of RUs from the collection for e.g. random access. After receiving a TF-R and an OBO procedure is completed, the STA 121 performs a random selection of the first group of RUs from the collection of groups of RUs. The selected group of RUs, herein denoted as the first group of RUs, is used for e.g. a data transmission.

The selection of the first group of RUs, may be done with the aid of a random number generator. In principle the random number generator may generate random numbers according to any PMF or PDF - here PMF and PDF is related to the random number generator and should not be confused with any PMF or PDF used to determine the probability values associated with the groups of RUs. An exemplary procedure may be as follows. Assuming a random number generator which generates random numbers in accordance with a PDF with support K, the support K is divided into a number of regions, e.g. non-intersecting intervals, where each region corresponds to a respective one of the groups of RUs in the collection. The regions are constructed such that integration of the PDF over a region yields a value corresponding to the probability value of the group of RUs associated with the region. The selection procedure may then comprise to generate a random number and identify the region where the random number lies; the group of RUs corresponding to the identified region is then selected as the first group of RUs. A practical example is illustrated in the diagram shown in Figure 8. Here, a random number generator with a uniform PDF distribution with support K = [0,1] is utilized. The x axis represents random numbers from 0 to 1 , and there are now 5 groups of RUs to select from, with p1 , p2, p3, p4, p5 being the respective probability values of the groups of RUs. The regions are here 5 non-intersecting intervals with widths

corresponding to the probability values p1-p5. In the example of Figure 8, the STA 121 has generated the random number rn, which lies in the fourth interval, and therefore selects the corresponding fourth group of RUs. To perform the method actions for reducing packet collision probability when transmitting data packets to the AP 110 in a wireless communications network 100, the STA 121 may comprise the following arrangement depicted in Figure 9. As mentioned above, the AP 110 and the STA 121 are operable in the wireless communications network 100.

The STA 121 comprises an input and output interface 900 configured to communicate with one or more wireless devices such as the STAs 121 , 122. The input and output interface 900 may comprise a receiver (not shown) and a transmitter (not shown).

The radio network node 110 is configured to, e.g. by means of an obtaining circuit 910 in the STA 121 configured to, obtain for each group of RUs out of a collection of groups of RUs, a respective probability value which represents a decided probability for the STA 121 to select that group of RUs. The at least two of the respective probability values are adapted to be different.

In some embodiments, the STA 121 is further configured to obtain the respective probability values as being any one out of: a PMF, a PDF, an indication of a PMF, and an indication of a PDF.

The STA 121 may be configured to e.g. by means of the obtaining unit 910 in the STA 121 being further configured to, obtain the respective probability values based on coordination with one or more other STAs 122.

The respective probability value for each group of RUs out of the collection of groups of RUs, may be adapted to be obtained by any one out of: receiving them from the AP 110, receiving them from a network node operating in the wireless communications network 100, deciding them in the STA 121.

As mentioned above, the respective probability value for each group of RUs out of the collection of groups of RUs, may be adapted to be obtained by deciding them in the STA 121. In these embodiments, STA 121 may further be configured to, e.g. by means of the obtaining unit 910 in the STA 121 being further configured to obtain the information about data traffic between one or more STAs 121 , 122 and the AP 110 based on any one out of: - overheard transmission of second STAs 122, and - transmission collision history with second STAs 122.

The obtained probability values may be adapted to be determined based on information about data traffic between the AP 110 and one or more STAs 121 , 122. In some embodiments, the information about the data traffic between one or more STAs 121 , 122 and the AP 110 may be adapted to comprise any one or more out of:

- the number of the one or more STAs 121 , 122 associated with the AP 110,

- uplink traffic pattern of the one or more STAs 121 , 122,

- buffer status of the one or more STAs 121 , 122,

- historical transmission statistics of the one or more STAs 121 , 122,

- predicted uplink traffic of the one or more STAs 121 , 122.

The radio network node 110 further is configured to, e.g. by means of an

performing unit 920 in the STA 121 configured to, perform a random selection of the first group of RUs from the collection of groups of RUs. The random selection is such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs.

The radio network node 110 further is configured to, e.g. by means of an

transmitting unit 930 in the STA 121 configured to, transmit the data packets to the AP 110 using the selected first group of RUs.

The embodiments herein for reducing packet collision probability when transmitting data packets to the AP 110 in a wireless communications network 100, the STA 121 may be implemented through one or more processors, such as a processor 940 of a processing circuitry in the STA 121 depicted in Figure 9, together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the STA 121. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the STA 121.

The STA 121 may further comprise a memory 950 comprising one or more memory units. The memory 950 comprises instructions executable by the processor 940.

The memory 950 is arranged to be used to store probability values, PMFs, PDFs, information about data traffic between one or more STAs 121 , 122 and the AP 110, user data, applications etc. to perform the methods herein when being executed in the STA 121. In some embodiments, a computer program 960 comprises instructions, which when executed by the at least one processor 940, causes the at least one processor 940 to perform the method according to any of the Actions 301-304.

In some embodiments, a carrier 970 comprises the computer program 960, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer- readable storage medium.

Those skilled in the art will also appreciate that the units in the radio STA 121 , described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in the memory 950, that when executed by the one or more processors such as the processor 940 as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

To perform the method actions for reducing packet collision probability when the STA 121 transmits data packets to the AP 110 in a wireless communications network 100, the AP 110 may comprise the following arrangement depicted in Figure 10.

The AP110 comprises an input and output interface 1000 configured to communicate with one or more wireless devices such as the STAs 121 , 122. The input and output interface 10000 may comprise a receiver (not shown) and a transmitter (not shown). As mentioned above, the AP 110 and the STA 121 are operable in the wireless communications network 100.

The AP 110 is configured to, e.g. by means of a deciding unit 1010 in the AP 110 configured to, decide for each group of RUs out of a collection of groups of RUs, a respective probability value which represents a decided probability for one or more STAs 121 , 122 to select that group of RUs, wherein at least two of the respective probability values are different.

In some embodiments, the AP 110 is further configured to, e.g. by means of the deciding unit 1010 further configured to, decide the respective probability values as being any one out of: a PMF, a PDF, an indication of a PMF, and an indication of a PDF. The probability values may be adapted to be decided individually for the STA 121 to be assisted.

The respective probability value may be adapted to be decided based on information about data traffic between the AP 110 and one or more STAs 121 , 122.

The information about data traffic between the one or more STAs 121 , 122 and the AP 110 may be adapted to comprise any one or more out of:

- the number of the one or more STAs 121 , 122 associated with the AP 110,

- uplink traffic pattern of the one or more STAs 121 , 122,

- buffer status of the one or more STAs 121 , 122,

- historical transmission statistics of the one or more STAs 121 , 122,

- predicted uplink traffic of the one or more STAs 121 , 122.

The AP 110 is further configured to, e.g. by means of a transmitting unit 1020 in the AP 110 configured to, transmit the decided probability values to the STA 121.

The AP 110 is further configured to, e.g. by means of a receiving unit 1030 in the AP 110 configured to, receive the data packets, transmitted by the STA 120 in a first group of RUs. The first group of RUs is adapted to be selected by the STA 121 from the collection of groups of RUs, according to the decided probability values.

The AP 110 may further configured to, e.g. by means of a obtaining unit 1040 in the AP 110 configured to, obtain the information about data traffic between one or more STAs 121 , 122 and the AP 110 according to any one out of:

- receiving the information from the one or more second STAs 121 , 122,

- learning the information by performing machine learning algorithms.

The embodiments herein for reducing packet collision probability when a STA 121 transmits data packets to the AP 110 in a wireless communications network 100,, may be implemented through one or more processors, such as a processor 1050 of a processing circuitry in the AP 110 depicted in Figure 10, together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the

embodiments herein when being loaded into the AP 110. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the AP 110.

The AP 110 may further comprise a memory 1060 comprising one or more memory units. The memory 1060 comprises instructions executable by the processor 1050.

The memory 1060 is arranged to be used to store probability values, PMFs, PDFs, information about data traffic between one or more STAs 121 , 122 and the AP 110, user data, applications etc. to perform the methods herein when being executed in the AP 110. In some embodiments, a computer program 1070 comprises instructions, which when executed by the at least one processor 1050, causes the at least one processor 1050 to perform the method according to any of the Actions 401-404.

In some embodiments, a carrier 1080 comprises the computer program 1070, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

Those skilled in the art will also appreciate that the units in the AP 110, described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in the memory 1060, that when executed by the one or more processors such as the processor 1050 as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

Claims

1. A method performed by a Station, STA, (121) for reducing packet collision

probability when transmitting data packets to an Access Point, AP, (110) in a wireless communications network (100), which AP (110) and STA (121) operate in the wireless communications network (100), the method comprising:

obtaining (302) for each group of Resource Units, RUs, out of a collection of groups of RUs, a respective probability value which represents a decided probability for the STA (121) to select that group of RUs, wherein at least two of the respective probability values are different,

performing (303) a random selection of the first group of RUs from the collection of groups of RUs, the random selection being such that a probability that any group of RUs in the collection of groups of RUs is selected as the first group of RUs corresponds to the respective probability value of that group of RUs, and transmitting (304) the data packets to the AP (110) the selected first group of

RUs.

2. The method according to claims 1 , wherein obtaining (302) the respective

probability values comprises obtaining any one out of: a Probability Mass Function, PMF, a Probability Density Function, PDF, an indication of a PMF, and an indication of a PDF.

3. The method according to any of the claims 1-2, wherein obtaining (302) the

respective probability values is performed based on coordination with one or more other STAs (122).

4. The method according to any of the claims 1-3, wherein the obtained probability values are determined based on information about data traffic between the AP (110) and one or more STAs (121 , 122).

5. The method according to claim 4, wherein the information about data traffic

between one or more STAs (121 , 122) and the AP (110) comprises any one or more out of:

- the number of the one or more STAs (121 , 122) associated with the AP

(1 10), - uplink traffic pattern of the one or more STAs (121 , 122),

- buffer status of the one or more STAs (121 , 122),

- historical transmission statistics of the one or more STAs (121 , 122),

- predicted uplink traffic of the one or more STAs (121 , 122).

6. The method according to any of the claims 1-5, wherein the respective probability value for each group of RUs out of the collection of groups of RUs, are obtained by any one out of:

receiving them from the AP (110),

receiving them from a network node operating in the wireless communications network (100)

deciding them in the STA (121).

7. The method according to claim 6 depending on claim 4 or 5, wherein the respective probability value for each group of RUs out of the collection of groups of RUs, are obtained by deciding them in the STA (121), further comprising

obtaining (301) the information about data traffic between one or more STAs (121 , 122) and the AP (110) based on any one out of:

- overheard transmission of second STAs (122),

- transmission collision history with second STAs (122).

8. A computer program (960) comprising instructions, which when executed by a processor (940), causes the processor (940) to perform actions according to any of the claims 1-7.

9. A carrier (970) comprising the computer program (960) of claim 8, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

10. A method performed by an Access Point, AP, (110) for reducing packet collision probability when a Station, STA, (121) transmits data packets to the AP (110) in a wireless communications network (100), which AP (110) and STA (121) operate in the wireless communications network (100), the method comprising: deciding (402) for each group of Resource Units, RUs out of a collection of groups of RUs, a respective probability value which represents a decided probability for one or more STAs (121 , 122) to select that group of RUs, wherein at least two of the respective probability values are different,

transmitting (403) the decided probability values to the STA (121), and receiving (404) the data packets, transmitted by the STA (120) in a first group of RUs, which first group of RUs was selected by the STA (121) from the collection of groups of RUs, according to the decided probability values.

11. The method according to claim 10, wherein deciding (402) the respective

probability values comprises deciding any one out of: a Probability Mass Function, PMF, a Probability Density Function, PDF, an indication of a PMF, and an indication of a PDF.

12. The method according to any of the claims 10-11 , wherein the probability values are decided individually for the STA (121) to be assisted.

13. The method according to any of the claims 10-12, wherein the respective

probability value is decided based on information about data traffic between the AP (110) and one or more STAs (121 , 122).

14. The method according to claim 13, wherein the information about data traffic

- the number of the one or more STAs (121 , 122) associated with the AP

(1 10),

- uplink traffic pattern of the one or more STAs (121 , 122),

- buffer status of the one or more STAs (121 , 122),

- historical transmission statistics of the one or more STAs (121 , 122),

- predicted uplink traffic of the one or more STAs (121 , 122).

15. The method according to any of the claims 13 -14, further comprising:

obtaining (401) the information about data traffic between one or more STAs (121 , 122) and the AP (110) according to any one out of:

- receiving the information from the one or more second STAs (121 , 122), - learning the information by performing machine learning algorithms.

16. A computer program (1070) comprising instructions, which when executed by a processor (1050), causes the processor (1050) to perform actions according to any of the claims 10-15.

17. A carrier (1070) comprising the computer program (1060) of claim 16, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

18. A Station, STA, (121) for reducing packet collision probability when transmitting data packets to an Access Point, AP, (110) in a wireless communications network (100), which AP (110) and STA (121) are operable in the wireless communications network (100), the STA (121) being configured to:

obtain for each group of Resource Units, RUs, out of a collection of groups of RUs, a respective probability value which represents a decided probability for the STA (121) to select that group of RUs, wherein at least two of the respective probability values are adapted to be different,

transmit the data packets to the AP (110) using the selected first group of RUs.

19. The STA (121) according to claims 18, wherein the STA (121) is further configured to obtain the respective probability values as being any one out of: a Probability Mass Function, PMF, a Probability Density Function, PDF, an indication of a PMF, and an indication of a PDF.

20. The STA (121) according to any of the claims 18-19, wherein the STA (121) is configured to obtain the respective probability values based on coordination with one or more other STAs (122).

21. The STA (121) according to any of the claims 18-20, wherein the obtained probability values are adapted to be determined based on information about data traffic between the AP (110) and one or more STAs (121 , 122).

22. The STA (121) according to claim 21 , wherein the information about data traffic between one or more STAs (121 , 122) and the AP (110) is adapted to comprise any one or more out of:

- the number of the one or more STAs (121 , 122) associated with the AP

(1 10),

- uplink traffic pattern of the one or more STAs (121 , 122),

- buffer status of the one or more STAs (121 , 122),

- historical transmission statistics of the one or more STAs (121 , 122),

- predicted uplink traffic of the one or more STAs (121 , 122).

23. The STA (121) according to any of the claims 18-22, wherein the respective

probability value for each group of RUs out of the collection of groups of RUs, are adapted to be obtained by any one out of:

receiving them from the AP (110),

deciding them in the STA (121).

24. The STA (121) according to claim 23 depending on claim 21 or 22, wherein the respective probability value for each group of RUs out of the collection of groups of RUs, are adapted to be obtained by deciding them in the STA (121), wherein the STA (121) is further configured to:

obtain the information about data traffic between one or more STAs (121 , 122) and the AP (110) based on any one out of:

- overheard transmission of second STAs (122),

- transmission collision history with second STAs (122).

25. An Access Point, AP, (110) for reducing packet collision probability when a Station, STA, (121) transmits data packets to the AP (110) in a wireless communications network (100), which AP (110) and STA (121) are operable in the wireless communications network (100), the AP (110) being configured to: decide for each group of Resource Units, RUs out of a collection of groups of RUs, a respective probability value which represents a decided probability for one or more STAs (121 , 122) to select that group of RUs, wherein at least two of the respective probability values are different,

transmit the decided probability values to the STA (121), and

receive the data packets, transmitted by the STA (120) in a first group of RUs, which first group of RUs is adapted to be selected by the STA (121) from the collection of groups of RUs, according to the decided probability values.

26. The AP (110) according to claim 25, wherein the AP (110) is further configured to decide the respective probability values as being any one out of: a Probability Mass Function, PMF, a Probability Density Function, PDF, an indication of a PMF, and an indication of a PDF.

27. The AP (110) according to any of the claims 25-26, wherein the probability values are adapted to be decided individually for the STA (121) to be assisted.

28. The AP (110) according to any of the claims 25-27, wherein the respective

probability value is adapted to be decided based on information about data traffic between the AP (110) and one or more STAs (121 , 122).

29. The AP (110) according to claim 28, wherein the information about data traffic

between one or more STAs (121 , 122) and the AP (110) adapted to comprise any one or more out of:

- the number of the one or more STAs (121 , 122) associated with the AP

(1 10),

- uplink traffic pattern of the one or more STAs (121 , 122),

- buffer status of the one or more STAs (121 , 122),

- historical transmission statistics of the one or more STAs (121 , 122),

- predicted uplink traffic of the one or more STAs (121 , 122).

30. The AP (110) according to any of the claims 27 -28, wherein the AP (110) is further configured to:

obtain the information about data traffic between one or more STAs (121 , 122) and the AP (110) according to any one out of: - receiving the information from the one or more second STAs (121 , 122),

- learning the information by performing machine learning algorithms.