GB2555143A

GB2555143A - QoS management for multi-user EDCA transmission mode in wireless networks

Info

Publication number: GB2555143A
Application number: GB1617881.6A
Authority: GB
Inventors: Nezou Patrice; Baron Stéphane; Viger Pascal
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2016-10-21
Filing date: 2016-10-21
Publication date: 2018-04-25
Anticipated expiration: 2036-10-21
Also published as: GB2555143B; GB201617881D0

Abstract

A communications method in a communications network which comprises a plurality of nodes, at least one node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communications channel in order to transmit data from the traffic queue. The method comprises, at the node, transmitting data in at least one traffic queue in a resource unit (RU) within a transmission opportunity (TxOP) and upon transmitting the data setting each transmitting traffic queue into a multiple user (MU) contention mode, during which the respective queue contention parameters are set to MU values different from the legacy values. A method at an access point in a communications network is also presented.

Description

(54) Title of the Invention: QoS management for multi-user EDCA transmission mode in wireless networks Abstract Title: Dynamic modification of traffic queue contention parameters in a wireless communications network (57) A communications method in a communications network which comprises a plurality of nodes, at least one node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communications channel in order to transmit data from the traffic queue. The method comprises, at the node, transmitting data in at least one traffic queue in a resource unit (RU) within a transmission opportunity (TxOP) and upon transmitting the data setting each transmitting traffic queue into a multiple user (MU) contention mode, during which the respective queue contention parameters are set to MU values different from the legacy values. A method at an access point in a communications network is also presented.

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QoS MANAGEMENT FOR MULTI-USER EDCA TRANSMISSION MODE IN WIRELESS NETWORKS

FIELD OF THE INVENTION

The present invention relates generally to communication networks and more specifically to communication networks offering channel accesses to nodes through contention and providing secondary accesses to the nodes to sub-channels (or Resource Units) splitting a transmission opportunity TXOP granted to an access point, in order to transmit data.

The invention finds application in wireless communication networks, in particular in

802.11 ax networks offering, to the nodes, an access to an 802.11 ax composite channel and/or to OFDMA Resource Units forming for instance an 802.11 ax composite channel granted to the access point and allowing Uplink communication to be performed.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC standard defines the way Wireless local area networks (WLANs) must work at the physical and medium access control (MAC) level. Typically, the

802.11 MAC (Medium Access Control) operating mode implements the well-known Distributed Coordination Function (DCF) which relies on a contention-based mechanism based on the socalled “Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA) technique.

The 802.11 medium access protocol standard or operating mode is mainly directed to the management of communication nodes waiting for the wireless medium to become idle so as to try to access to the wireless medium.

The network operating mode defined by the IEEE 802.11ac standard provides very high throughput (VHT) by, among other means, moving from the 2.4GHz band which is deemed to be highly susceptible to interference to the 5GHz band, thereby allowing for wider frequency contiguous channels of 80MHz to be used, two of which may optionally be combined to get a 160MHz channel as operating band of the wireless network.

The 802.11ac standard also tweaks control frames such as the Request-To-Send (RTS) and Clear-To-Send (CTS) frames to allow for composite channels of varying and predefined bandwidths of 20, 40 or80MHz, the composite channels being made of one or more communication channels that are contiguous within the operating band. The 160MHz composite channel is possible by the combination of two 80MHz composite channels within the 160MHz operating band. The control frames specify the channel width (bandwidth) for the targeted composite channel.

A composite channel therefore consists of a primary channel on which a given node performs EDCA backoff procedure to access the medium, and of at least one secondary channel, offer example 20MHz each.

EDCA (Enhanced Distributed Channel Access) defines traffic categories and four corresponding access categories that make it possible to handle differently high-priority traffic compared to low-priority traffic.

Implementation of EDCA in the nodes can be made using a plurality of traffic queues (known as “Access Categories”) for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value. The queue backoff value is computed from respective queue contention parameters, e.g. EDCA parameters, and is used to contend for access to a communication channel in order to transmit data stored in the traffic queue.

Legacy EDCA parameters include CW_min, CW_max and AIFSN for each traffic queue, wherein CW_min and CW_max are the lower and higher boundaries of a selection range from which an EDCA contention window CW is selected for a given traffic queue. AIFSN stands for Arbitration Inter-Frame Space Number, and defines the number of time slots (usually 9 ps), additional to a DIFS interval (the total defining the AIFS period) the node must sense the medium as idle before decrementing the queue backoff value associated with the traffic queue considered.

The EDCA parameters may be defined in a beacon frame sent by a specific node in the network to broadcast network information.

The contention windows CW and the queue backoff values are EDCA variables.

Conventional EDCA backoff procedure consists for the node to select a queue backoff value for a traffic queue from the respective contention window CW, and then to decrement it upon sensing the medium as idle after the AIFS period. Once the backoff value reaches zero, the node is allowed to access the medium.

The EDCA queue backoff values or counters thus play two roles. First, they drive the nodes in efficiently accessing the medium, by reducing risks of collisions; second, they offer management of quality of service, QoS, by mirroring the aging of the data contained in the traffic queue (the more aged the data, the lower the backoff value) and thus providing different priorities to the traffic queues through different values of the EDCA parameters (especially the AIFSN parameter that delays the start of the decrementing of the EDCA queue backoff values).

Thanks to the EDCA backoff procedure, the node can thus access the communication network using contention type access mechanism based on the queue contention parameters, typically based on the computed queue backoff counter or value.

The primary channel is used by the communication nodes to sense whether or not the channel is idle, and the primary channel can be extended using the secondary channel or channels to form a composite channel. The primary channel can also be used alone.

Given a tree breakdown of the operating band into elementary 20MHz channels, some secondary channels are named tertiary or quaternary channels.

In 802.11ac, all the transmissions, and thus the possible composite channels, include the primary channel. This is because the nodes perform full Carrier Sense Multiple

Access/Collision Avoidance (CSMA/CA) and Network Allocation Vector (NAV) tracking on the primary channel only. The other channels are assigned as secondary channels, on which the nodes have only capability of CCA (clear channel assessment), i.e. detection of an idle or busy state/status of said secondary channel.

An issue with the use of composite channels as defined in the 802.11n or 802.11ac (or 802.11 ax) is that the nodes compliant with a use of composite channels (i.e. 802.11η and 802.11ac-compliant nodes or “HT nodes” standing for High Throughput nodes) have to co-exist with legacy nodes not able to use composite channels but relying only on conventional 20MHz channels (i.e. non-HT nodes compliant only with for instance 802.11a/b/g) exist within the same wireless network, and thus have to share the same 20MHz channels.

To cope with this issue, the 802.11η and 802.11ac and 802.11 ax standards provide the possibility to duplicate control frames (e.g. RTS/CTS or CTS-to-Self or ACK frames to acknowledge correct or erroneous reception of the sent data) over each 20MHz channel in an 802.11a legacy format (called as “non-HT”) to establish a protection of the requested TXOP over the whole composite channel.

This is for any legacy 802.11a node that uses any of the 20MHz channel involved in the composite channel to be aware of on-going communications on the 20MHz channel. As a result, the legacy node is prevented from initiating a new transmission until the end of the current composite channel TXOP granted to an 802.11 n/ac/ax node.

As originally proposed by 802.11η, a duplication of conventional 802.11a or “nonHT” transmission is provided to allow the two identical 20MHz non-HT control frames to be sent simultaneously on both the primary and secondary channels forming the used composite channel.

This approach has been widened for 802.11ac to allow duplication over the channels forming an 80MHz or 160MHz composite channel. In the remainder of the present document, the “duplicated non-HT frame” or “duplicated non-HT control frame” or “duplicated control frame” means that the node device duplicates the conventional or “non-HT” transmission of a given control frame over secondary 20MHz channels) of the (40MHz, 80MHz or 160MHz) operating band.

In practice, to request a composite channel (equal to or greater than 40MHz) for a new TXOP, an 802.11n/ac node performs an EDCA backoff procedure in the primary 20MHz channel as mentioned above. In parallel, it performs a channel sensing mechanism, such as a Clear-Channel-Assessment (CCA) signal detection, on the secondary channels to detect the secondary channel or channels that are idle (channel state/status is “idle”) during a PIFS interval before the start of the new TXOP (i.e. before any queue backoff counter expires).

More recently, Institute of Electrical and Electronics Engineers (IEEE) officially approved the 802.11 ax task group, as the successor of 802.11ac. The primary goal of the 802.11ax task group consists in seeking for an improvement in data speed to wireless communicating devices used in dense deployment scenarios.

Recent developments in the 802.11ax standard sought to optimize usage of the composite channel by multiple nodes in a wireless network having an access point (AP). Indeed, typical contents have important amount of data, for instance related to high-definition audio-visual real-time and interactive content. Furthermore, it is well-known that the performance of the CSMA/CA protocol used in the IEEE 802.11 standard deteriorates rapidly as the number of nodes and the amount of traffic increase, i.e. in dense WLAN scenarios.

In this context, multi-user (MU) transmission has been considered to allow multiple simultaneous transmissions to/from different users in both downlink (DL) and uplink (UL) directions from/to the AP and during a transmission opportunity granted to the AP. In the uplink, multi-user transmissions can be used to mitigate the collision probability by allowing multiple non-AP stations or nodes to simultaneously transmit.

To actually perform such multi-user transmission, it has been proposed to split a granted communication channel into sub-channels, also referred to as resource units (RUs), that are shared in the frequency domain by multiple users (non-AP stations/nodes), based for instance on Orthogonal Frequency Division Multiple Access (OFDMA) technique. Each RU may be defined by a number of tones, the 80MHz channel containing up to 996 usable tones.

OFDMA is a multi-user variation of OFDM which has emerged as a new key technology to improve efficiency in advanced infrastructure-based wireless networks. It combines OFDM on the physical layer with Frequency Division Multiple Access (FDMA) on the MAC layer, allowing different subcarriers to be assigned to different stations/nodes in order to increase concurrency. Adjacent sub-carriers often experience similar channel conditions and are thus grouped to sub-channels: an OFDMA sub-channel or RU is thus a set of sub-carriers.

As currently envisaged, the granularity of such OFDMA sub-channels is finer than the original 20MHz channel band. Typically, a 2MHz or 5MHz sub-channel may be contemplated as a minimal width, therefore defining for instance 9 sub-channels or resource units within a single 20MHz channel.

The multi-user feature of OFDMA allows the AP to assign or offer different RUs to different non-AP stations/nodes in order to increase competition. This may help to reduce contention and collisions inside 802.11 networks.

Contrary to downlink OFDMA wherein the AP can directly send multiple data to multiple stations (supported by specific indications inside the PLCP header), a trigger mechanism has been adopted for the AP to trigger multi-user uplink (MU UL) OFDMA communications from various nodes.

To support multi-user uplink, i.e. uplink transmission to the 802.11 ax access point (AP) during a pre-empted TXOP, the 802.11ax AP has to provide signalling information for the legacy nodes (non-802.11 ax nodes) to set their NAV and for the 802.11 ax nodes to determine the allocation of the resource units RUs provided by the AP.

The 802.11ax standard defines a trigger frame (TF) that is sent by the AP to the

802.11 ax nodes to trigger Multi-User uplink communications.

The document IEEE 802.11-15/0365 proposes that a ‘Trigger’ frame (TF) is sent by the AP to solicit the transmission of uplink (UL) Multi-User (OFDMA) PPDU from multiple nodes. The TF defines the resource units as provided by the AP to the nodes. In response, the nodes transmit UL MU (OFDMA) PPDU as immediate responses to the Trigger frame. All transmitters can send data at the same time, but using disjoint sets of RUs (i.e. of frequencies in the OFDMA scheme), resulting in transmissions with less interference.

The bandwidth or width of the targeted composite channel is signalled in the TF frame, meaning that the 20, 40, 80 or 160 MHz value is added. The TF frame is sent over the primary 20MHz channel and duplicated (replicated) on each other 20MHz channels forming the targeted composite channel, if appropriate. As described above for the duplication of control frames, it is expected that every nearby legacy node (non-HT or 802.11ac nodes) receiving the TF on its primary channel, then sets its NAV to the value specified in the TF. This prevents these legacy nodes from accessing the channels of the targeted composite channel during the TXOP.

A resource unit RU can be reserved for a specific node, in which case the AP indicates, in the TF, the node to which the RU is reserved. Such RU is called Scheduled RU. The indicated node does not need to perform contention on accessing a scheduled RU reserved to it.

The type of data the node is allowed to transmit in the Scheduled RU may be specified by the AP in the TF. For instance, the TF includes a 2-bit “Preferred AC” field in which the AP indicates one of the four EDCA traffic queues. On the other hand, the AP may let the Scheduled RU be opened to any type of data. To activate or not the “Preferred AC”, the TF includes another 1 -bit field, namely “AC Preference Level”.

In order to better improve the efficiency of the system with regards to un-managed traffic to the AP (for example, uplink management frames from associated nodes, unassociated nodes intending to reach an AP, or simply unmanaged data traffic), resource units may be proposed by the AP to the 802.11 ax nodes through contention-based access. In other words, the resource unit RU can be randomly accessed by more than one node (of the group of nodes registered with the AP). Such RU is called Random RU and is indicated as such in the TF. Random RUs may serve as a basis for contention between nodes willing to access the communication medium for sending data.

An exemplary random resource selection procedure is defined in document IEEE 802.11-15/1105. According to this procedure, each 802.11 ax node maintains a dedicated backoff engine, referred below to as OFDMA or RU (for resource unit) backoff engine, using RU contention parameters, including an RU backoff value, to contend for access to one of the random RUs. Once its OFDMA or RU backoff value reaches zero (it is for instance decremented at each new TF-R frame by the number of random RUs defined therein), a node becomes eligible for RU access and thus randomly selects one RU from among all the random

RUs defined in the received trigger frame. It then uses the selected RU to transmit data of at least one of the traffic queues.

As readily apparent from the above, the Multi User Uplink medium access scheme (or OFDMA or RU access scheme) allows the number of collisions generated by simultaneous medium access attempts to be reduced, while also reducing the overhead due to the medium access since the medium access cost is shared between several nodes. The OFDMA or RU access scheme thus appears to be quite more efficient (with regards of the medium usage) than the conventional EDCA contention-based medium access scheme (in the context of a high density 802.11 cell).

Although the OFDMA or RU access scheme seems more efficient, the EDCA access scheme must also survive and thus coexist with the OFDMA or RU access scheme.

This is mainly due to the existence of legacy 802.11 nodes which must still have the opportunity to access the medium, while they are not aware of the OFDMA or RU access scheme. And the global fairness about the medium access must be ensured.

This is also all the more necessary that the 802.11 ax nodes should also have the opportunity to gain access to the medium through conventional EDCA contention-based medium access, for instance to send data to another node (i.e. for traffic different from uplink traffic to the AP).

So the two medium access schemes, EDCA and OFDMA/RU access schemes, have to coexist.

This coexistence has downsides.

For instance, 802.11 ax nodes and legacy nodes have the same medium access probability using the EDCA access scheme. However, the 802.11 ax nodes have additional medium access opportunities using the MU Uplink or OFDMA or RU access scheme.

It results that access to the medium is not fully fair between the 802.11 ax nodes and the legacy nodes.

To restore some fairness between the nodes, solutions have been proposed to modify, upon successfully transmitting data over an accessed resource unit (i.e. through UL OFDMA transmission), a current value of at least one queue contention parameter into a penalized or degraded value, to reduce a probability for the node to access a communication channel through (EDCA) contention. For instance, the penalized or degraded value is more restrictive than the original (or legacy) value.

For instance, document IEEE 802.11-16/1180 entitled “Proposed text changes for MU EDCA parameters proposes that, upon successfully (MU UL OFDMA) transmitting data in a resource unit, RU, reserved by the AP, a node is set in a MU EDCA mode for a predetermined duration counted down by a timer (noted HEMUEDCATimer below, standing for High Efficiency Multi-User EDCA Timer), in which the EDCA parameters are set to values, referred to as MU EDCA parameters values or MU values, different from legacy values used in a legacy EDCA mode. The MU parameter values are set to more restrictive values than the legacy values: more restrictive values for EDCA parameters means that a probability for a node to access the communication channel through EDCA access scheme using the MU values is reduced relatively to an access using the legacy values.

In other words, as soon as the node transmits some data from one or more traffic queues using a scheduled RU assigned to the node by the AP, the node shall modify the EDCA parameters associated with the transmitting traffic queue(s) (here below “degraded”, “penalized” or “blocked” traffic queue(s)), with some special more restrictive (“MU” or “degraded”) values that may be provided by the AP in a dedicated Information Element of a beacon frame, which also includes the value to be used by the nodes for their HEMUEDCATimer.

One may thus note that the AP sends, to the nodes, the more restrictive values to drive the node in modifying current values of their EDCA parameters into the MU values upon the node successfully transmitting data over the accessed resource unit. This is also to reduce a probability for the node to access the communication channel through EDCA access scheme.

In addition, the AP may determine the more restrictive values based on a history of data received from the nodes (e.g. through RUs).

The disclosed approach suggests increasing only the value of AIFSN for each transmitting traffic queue, while keeping CW_min, and CW_max unchanged. As the corresponding AIFS period increases, the traffic queue in the MU EDCA mode is prevented (or at least substantially delayed) from having its queue backoff value or counter been decremented upon sensing the medium free, in particular in high density environment in which the medium does not remain free for a long time. New accesses to the medium using EDCA access scheme are statistically substantially reduced, or even no longer possible.

Upon switching into the MU EDCA mode, the node starts its HEMUEDCATimer countdown. The HEMUEDCATimer is reinitialized each time the node successfully (MU UL OFDMA) transmits data in a new reserved RU. The initializing value of HEMUEDCATimer is suggested to be high (e.g. tens of milliseconds) in order to encompass several new opportunities for MU UL transmissions.

The HEMUEDCATimer mechanism means the node remains in the MU EDCA state as long as the AP provides reserved RUs to the node.

When the HEMUEDCATimer lapses, the traffic queues in MU EDCA mode are switched back to the legacy EDCA mode with legacy EDCA parameters, thereby exiting the queues from the MU EDCA mode.

Thus, this mechanism of double operating modes, legacy EDCA mode and MU EDCA mode, promotes the usage of the MU UL mechanism by reducing the probability of a MU UL transmitting node to gain access to the medium using the EDCA mechanism.

One drawback of preventing (or substantially slowing it down) the decrementing of the queue backoff values in the MU EDCA mode while data of these queues are transmitted in the accessed RUs, is that the queue backoff values no longer mirror which traffic queue should have the highest priority of transmission in the meaning of conventional EDCA (e.g. with oldest data stored in it).

For instance, if several traffic queues of a node are in the MU EDCA mode, their queue backoff values are no longer decremented upon sensing the medium as free (with use of more restrictive MU EDCA parameters). Thus each time a new RU is assigned to the node remaining in the MU EDCA mode, the node may be led to always select the same traffic queue to transmit data (e.g. because it has the lowest backoff value), while oldest data are available in the other traffic queues set in the MU contention mode.

The QoS in the network is thus severely deteriorated.

SUMMARY OF INVENTION

The present invention seeks to overcome the foregoing limitations. In particular, it seeks to overcome the loss of QoS handling resulting from the introduction of the MU UL OFDMA transmissions.

From 802.11e introduction, the priority of the data is handled via the EDCA backoff mechanism, together with the four Access Categories traffic queues. The introduction of the MU UL OFDMA communication has broken the ability of the EDCA backoff counters to mirror the relative priorities of the four AC traffic queues, due to the non-evolution of the EDCA backoff counters upon transmission of data over MU UL OFDMA resource units.

The invention thus intends to restore some EDCA-like behaviour to the queue backoff counters, with the view of restoring a relevant mirroring of the relative priorities of the AC queues.

In this context, the present invention proposes a communication method in a communication network comprising a plurality of nodes, at least one node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communication channel in order to transmit data stored in the traffic queue;

the method comprising, at the node:

transmitting data stored in at least one traffic queue, in an accessed resource unit provided by another node within a transmission opportunity granted to the other node on the communication channel; and upon transmitting the data in the accessed resource unit:

setting each transmitting traffic queue in a MU contention mode, for a predetermined duration, in which the respective queue contention parameters are set to MU values different from the legacy values; and then modifying at least one queue backoff value associated with a traffic queue while the latter is in the MU contention mode.

Legacy contention mode may mean legacy EDCA mode, while MU contention mode may refer to MU EDCA mode.

As one would easily understand, a transmitting traffic queue is a traffic queue from which data are transmitted in the accessed resource unit.

At least one backoff counter is modified although no legacy contention access has been performed by the transmitting node. Variations of the backoff counters when data are transmitted over MU UL OFDMA RUs are thus restored, and some QoS management is recovered.

One may note that other traffic queues (i.e. not transmitting during the mentioned TXOP) may already be set in the MU contention mode, for instance due to previous access to MU UL OFDMA RUs and because their respective predetermined duration has not yet ended. In the context of the invention, these other traffic queues in the MU contention mode may also be subject to backoff value modification upon MU UL OFDMA transmission.

MU values different from the legacy values for a traffic queue means that the MU and legacy values for at least one same contention parameter differ one from the other, regardless of whether the MU and legacy values of the other contention parameters are equal or differ.

Correspondingly, the invention also regards a communication device node in a communication network comprising a plurality of nodes, the communication device comprising:

a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communication channel in order to transmit data stored in the traffic queue; and at least one microprocessor configured for carrying out the following steps: transmitting data stored in at least one traffic queue, in an accessed resource unit provided by another node within a transmission opportunity granted to the other node on the communication channel; and upon transmitting the data in the accessed resource unit:

The device node has the same advantages as the method defined above.

Optional features of the invention are defined in the appended claims. Some of these features are explained here below with reference to a method, while they can be transposed into system features dedicated to any device node according to the invention.

In embodiments, modifying at least one queue backoff value includes computing, for one transmitting traffic queue, a new queue backoff value from the respective queue contention parameters set with the MU values. This may include computing a new contention window CW if degraded parameters CW_min and CW_max have new values, and then selecting the new queue backoff value from the obtained new contention window CW.

This approach restores a fairer QoS management because the same behavior as conventional EDCA is applied here (new backoff value for a traffic queue each time it transmits).

In specific embodiments, a new queue backoff value is computed only for the transmitting traffic queue from which data are transmitted at the beginning of the accessed resource unit. Usually, the first transmitting queue is supposed to transmit the majority of the data in the accessed resource unit. The other transmitting queue or queues only send few data to fill the bandwidth available in the accessed resource unit (given the TXOP). In this respect, drawing a new backoff value for these “secondary” queues would be very damageable for their remaining data, which thus would have to wait for a longer time than with a direct OFDMA access. Consequently, the proposed implementation keeps fairness with regards to these secondary queues, by keeping their same future probability of transmission.

In variants, a new queue backoff value is computed for each transmitting traffic queue. A fair QoS management is thus achieved since exactly the same behavior as conventional EDCA is applied.

In other embodiments, modifying at least one queue backoff value includes decreasing each queue backoff value associated with a non-transmitting MU traffic queue by a decrement value, a non-transmitting MU traffic queue being a traffic queue in the MU contention mode and from which no data are transmitted in the accessed resource unit. The nontransmitting MU traffic queue may have entered the MU contention mode after transmission in a previous TXOP.

These embodiments emulate the conventional decrementing of the EDCA backoff counters for the traffic queues that do not access the medium. It results that even more fairness is restored with respect to the non-transmitting ACs, compared to conventional EDCA.

The more fairness is restored, the more efficient the overall network operates.

In specific embodiments, the queue backoff values of all the non-transmitting MU traffic queues are decreased by the same predetermined value. This configuration makes the handling of the EDCA backoff counters very simple to handle.

In other specific embodiments, the queue backoff value of each non-transmitting MU traffic queue is decreased by a respective decrement value function of the priority of the non-transmitting MU traffic queue. The priority here is seen as the category of the traffic queue. This configuration means that the backoff decrements are different from one traffic queue to the other.

This advantageously mirrors the priorities in the management of the backoff counters, as in the conventional EDCA mechanism. In particular, it is a simple and efficient way to compensate the lack of AIFSN to update the backoff counters after a MU UL OFDMA transmission.

According to a feature, the decrement values for all the non-transmitting MU traffic queues are computed from the same predetermined value. This is to try to reach an optimal value with regards to global cell efficiency. Indeed, the predetermined value could be computed in advance, by simulation or test, depending on the MU queue contention parameters. It could even be transmitted by the AP to the nodes, in order to reflect the will of the AP to efficiently share the medium between EDCA and MU UL medium access, especially when considering a ratio of legacy nodes from among all the nodes registered to the AP.

According to another feature, the decrement values for all the non-transmitting MU traffic queues are computed from non-zero Arbitration Inter-Frame Space Numbers, AIFSNs, defined as respective queue contention parameters of the traffic queues. This is a simple way to take into account the priorities of each traffic queue (as the AIFSN are set according to said priorities).

According to a specific embodiment, the decrement value for a non-transmitting US traffic queue 1' equals max[0, predetermined value - (AIFSN[i] - min(AIFSN)], wherein AIFSN[i] is the AIFSN of traffic queue 1', and min(AIFSN) is the minimum value from among the non-zero AIFSNs of all the traffic queues. Here all the traffic queues are taken into account in order to know the minimum AIFSN value for instance. This value is used as an offset to decrease the backoff value of each queue in the MU contention mode.

This approach makes it possible to keep relative priorities between the traffic queues, while avoiding decreasing the backoff counters by a too high decrement which would handicap the legacy nodes.

According to a feature, the predetermined value equals the (non zero) lowest value taken by the queue backoff values associated with the transmitting traffic queues, when the node transmits the data in the accessed resource unit. In particular this may be combined with the selection of the traffic queues with the (non zero) lowest backoff values to determine which data to be transmitted in the accessed resource unit.

It results that this configuration minimizes the risk of having a modified queue backoff value negative. The management of the queue backoff counters is thus made simple.

According to another feature, the predetermined value equals the queue backoff value, when the node transmits the data in the accessed resource unit, associated with a preferred traffic queue indicated by the other node.

Indeed, if a preferred traffic queue is indicated by the other node (usually the AP), the major part of the data transmitted by the nodes in the accessed resource units are of the preferred type, even if aggregation rules allow data from higher priority queues to be added if space remains. The above implementation ensures the behavior of the backoff counters reflects the overall behavior of the node. This is in line with fairness requirements.

According to a specific feature, the preferred traffic queue indication is included in a trigger frame received from the other node, the trigger frame reserving the transmission opportunity granted to the other node on the communication channel and defining resource units, RUs, forming the communication channel including the accessed resource unit.

As the preferred traffic queue indication is used by the AP if it decides to handle the QoS of the cell by itself. The above configuration thus ensures the nodes follow the AP preference, and not their own priority.

In embodiments, the transmitting traffic queue or queues are set in the MU contention mode only upon successfully transmitting the data in the accessed resource unit. This configuration guarantees fairness. Indeed, in the philosophy of contention mode switching, the MU EDCA mode should only be implemented to compensate the existence of other transmission opportunities (here through RUs), meaning data are successfully transmitted.

In some embodiments, the MU values of the queue contention parameters include a degraded Arbitration Inter-Frame Space Number, AIFSN, compared to the legacy values of the queue contention parameters used for the traffic queue not set in the legacy contention mode. This configuration is simple to implement in order to directly reduce (up to a desired level) the chances of a specific traffic queue to access the medium through EDCA.

In particular, each queue backoff value may be initially selected from a respective contention window, the queue backoff value being decreased by the node over time to access the communication channel upon reaching zero, and the MU values of the queue contention parameters may include the same lower boundary CW_min and/or higher boundary CW_max, both defining a selection range from which a size of the contention window is selected, as the legacy values.

This configuration simplifies the entering into and the exiting from the MU contention mode (e.g. MU EDCA mode) since the contention window can be kept unchanged. However, variants may contemplate having different boundaries between the legacy and MU values.

In some embodiments, all the traffic queues in the MU contention mode share the same predetermined duration, so that all the traffic queues in the MU contention mode exit the MU contention mode by restoring their respective queue contention parameters to legacy values, upon the predetermined duration lapsing without any data from the node being transmitted in any resource unit provided by the other node within subsequent transmission opportunities granted to the other node during the predetermined degrading duration.

In yet other embodiments, the method further comprises, at the node, upon accessing a resource unit provided by the other node within a new transmission opportunity granted to the other node:

selecting data from the traffic queues, including the traffic queue or queues in the MU contention mode, based on associated current queue backoff values, including the modified queue backoff value or values, transmitting the selected data in the accessed resource unit within the new transmission opportunity.

Next to the transmission, the teachings of the present invention may be applied again, meaning the transmitting traffic queues are switched into MU contention mode.

The above configuration illustrates the modified backoff values (according to the invention - i.e. subsequently to MU UL OFDMA transmission) are taken into account in the process of selecting new data to be transmitted. It clearly shows that a data QoS management is reintroduced through post-OFDMA-transmission-varying backoff counters.

In embodiments, the method further comprises, at the node, contending for access to the communication channel using the modified queue backoff value or values. This illustrates that the backoff values modified according to the teachings ofthe invention correspond to the known EDCA backoff counters.

In embodiments, the method further comprises, at the node, periodically receiving a beacon frame from an access point, each beacon frame broadcasting network information about the communication network to the plurality of nodes, wherein at least one received beacon frame includes legacy values and MUvalues for the queue contention parameters ofthe plurality of traffic queues.

According to a specific feature, the received beacon frame also includes the predetermined duration.

In some embodiments ofthe invention, the accessed resource unit over which the data are transmitted is a random resource unit, the access of which being made through contention using separate RU contention parameters (separate from the above-mentioned queue contention parameters).

In other embodiments, the accessed resource unit over which the data are transmitted is a scheduled resource unit, the scheduled resource being assigned by the other node to the node.

Of course, some nodes may access scheduled RUs while other nodes may simultaneously access random RUs, resulting in having simultaneously various nodes in the MU contention mode (for one or more AC queues).

In some embodiments, the other node is an access point of the communication network to which nodes register. This provision advantageously takes advantage ofthe central position ofthe access point.

From the Access Point perspective, the present invention proposes a communication method in a communication network comprising a plurality of nodes and an access point, each node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communication channel in order to transmit data stored in the traffic queue;

the method comprising, at the access point:

accessing the communication channel to send a trigger frame reserving a transmission opportunity on the communication channel and defining resource units, RUs, forming the communication channel for the nodes to transmit data to the access point sending, to the nodes, a set of legacy values of the queue contention parameters and a set of MU values of the queue contention parameters, different from the set of legacy values, to configure each node when a traffic queue of the node switches between a legacy contention mode in which the respective queue contention parameters are set to the legacy values and a MU contention mode in which the respective queue contention parameters are set to the MU values.

Correspondingly, an access point in a communication network also comprising a plurality of nodes, each node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communication channel in order to transmit data stored in the traffic queue;

the access point comprising at least one microprocessor configured for carrying out the following steps:

The access point may thus efficiently control fairness in the network. Indeed, through the MU values, the access point may drive the nodes to adjust their EDCA access scheme under MU contention mode, different from the conventional legacy mode.

Preferably, the legacy and MU values can be evaluated based on history of past transmissions from the nodes, in particular in RUs provided by the access point (random or scheduled RUs).

In some embodiments, the sets of legacy values and of MU values are transmitted within one or more beacon frames, periodically transmitted by the access point to broadcast network information about the communication network to the plurality of nodes.

In other embodiments, the access point also sends, to the nodes, a duration to drive the nodes entering the MU contention mode to remain in such mode at least the duration. It may also be included in the beacon frame.

In yet other embodiments, the sets of legacy values and of MU values differ by different Arbitration Inter-Frame Space Numbers, AIFSNs.

In particular, each queue backoff value of a node may be initially selected from a respective contention window, the queue backoff value being decreased by the node over time to access the communication channel upon reaching zero, and the sets of legacy values and of MU values may include the same lower boundary CW_min and/or higher boundary CW_max, both defining a selection range from which a size of the contention window is selected.

Another aspect of the invention relates to a non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device, causes the device to perform any method as defined above.

The non-transitory computer-readable medium may have features and advantages that are analogous to those set out above and below in relation to the methods and devices.

Another aspect of the invention relates to a method, substantially as herein described with reference to, and as shown in, Figure 5b, or Figure 11, or Figures 11 and 12, or Figures 11,12 and 14b of the accompanying drawings.

At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a circuit, module or system. Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent to those skilled in the art upon examination of the drawings and detailed description. Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings.

Figure 1 illustrates a typical wireless communication system in which embodiments of the invention may be implemented;

Figures 2a, 2b illustrate the IEEE 802.11e EDCA involving access categories;

Figure 2c illustrates an example of values for the degraded EDCA parameter set.

Figure 3a illustrates 802.11ac mechanism for the backoff counter countdown;

Figure 3b illustrates an example of mapping between eight priorities of traffic class and the four EDCA ACs.

Figure 4 illustrates an example of 802.11 ax uplink OFDMA transmission scheme, wherein the AP issues a Trigger Frame for reserving a transmission opportunity of OFDMA subchannels (resource units) on an 80 MHz channel as known in the art;

Figure 4a illustrates 802.11ac channel allocation that support channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

Figure 5a illustrates the evolution of the backoff counters and associated data selection as known in the prior art;

Figure 5b illustrates the evolution of the backoff counters and the associated data selection according to embodiments of the invention;

Figure 6 shows a schematic representation a communication device or station in accordance with embodiments of the present invention;

Figure 7 shows a schematic representation of a wireless communication device in accordance with embodiments of the present invention;

Figure 8 illustrates an exemplary transmission block of a communication node according to embodiments of the invention;

Figure 9 illustrates, using a flowchart, main steps performed by a MAC layer of a node, when receiving new data to transmit, in embodiments of the invention;

Figure 10 illustrates, using a flowchart, steps of accessing the medium based on the EDCA medium access scheme, in both situations with non-degraded EDCA parameters or with degraded EDCA parameters, according to embodiments of the invention;

Figure 11 illustrates, using a flowchart, steps of accessing resource units based on an RU or OFDMA access scheme upon receiving a trigger frame defining RUs according to embodiments of the invention;

Figure 12 illustrates, using a flowchart, the node management to switch back to the non-degraded mode, according to embodiments of the invention;

Figure 13 illustrates the structure of a trigger frame as defined in the 802.11 ax standard;

Figure 14a illustrates the structure of a standardized information element used to describe the parameters of the EDCA in a beacon frame; and

Figure 14b illustrates an exemplary structure of a dedicated information element to transmit the degraded EDCA parameter values according to embodiments of the invention, as well as the HEMUEDCATimer value.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limiting exemplary embodiments and by reference to the figures.

Figure 1 illustrates a communication system in which several communication nodes (or stations) 101-107 exchange data frames over a radio transmission channel 100 of a wireless local area network (WLAN), under the management of a central station, or access point (AP) 110 with which the nodes have registered. The radio transmission channel 100 is defined by an operating frequency band constituted by a single channel or a plurality of channels forming a composite channel.

Access to the shared radio medium to send data frames is based on the CSMA/CA technique, for sensing the carrier and avoiding collision by separating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtual mechanisms. Virtual carrier sensing is achieved by transmitting control frames to reserve the medium prior to transmission of data frames.

Next, a source or transmitting node, including the AP, first attempts, through the physical mechanism, to sense a medium that has been idle for at least one DIFS (standing for DCF InterFrame Spacing) time period, before transmitting data frames.

However, if it is sensed that the shared radio medium is busy during the DIFS period, the source node continues to wait until the radio medium becomes idle.

To access the medium, the node starts a countdown backoff counter designed to expire after a number of timeslots, chosen randomly in a so-called contention window [0, CW], CW (integer). This backoff mechanism or procedure, also referred to as channel access scheme, is the basis of the collision avoidance mechanism that defers the transmission time for a random interval, thus reducing the probability of collisions on the shared channel. After the backoff time period (i.e. the backoff counter reaches zero), the source node may send data or control frames if the medium is idle.

One problem of wireless data communications is that it is not possible for the source node to listen while sending, thus preventing the source node from detecting data corruption due to channel fading or interference or collision phenomena. A source node remains unaware of the corruption of the data frames sent and continues to transmit the frames unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positive acknowledgement (ACK) of the sent data frames by the receiving node if the frames are received with success, to notify the source node that no corruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame, immediately after a period of time called Short InterFrame Space (SIFS).

If the source node does not receive the ACK within a specified ACK timeout or detects the transmission of a different frame on the channel, it may infer data frame loss. In that case, it generally reschedules the frame transmission according to the above-mentioned backoff procedure.

To improve the Collision Avoidance efficiency of CSMA/CA, a four-way handshaking mechanism is optionally implemented. One implementation is known as the RTS/CTS exchange, defined in the 802.11 standard.

The RTS/CTS exchange consists in exchanging control frames to reserve the radio medium prior to transmitting data frames during a transmission opportunity called TXOP in the

802.11 standard, thus protecting data transmissions from any further collisions. The four-way CTS/RTS handshaking mechanism is well known, and thus not further described here. Reference is made to the standard for further details

The RTS/CTS four-way handshaking mechanism is very efficient in terms of system performance, in particular with regard to large frames since it reduces the length of the messages involved in the contention process.

In detail, assuming perfect channel sensing by each communication node, collision may only occur when two (or more) frames are transmitted within the same time slot after a DIFS (DCF inter-frame space) or when the backoff counters of the two (or more) source nodes have reached zero nearly at the same time. If both source nodes use the RTS/CTS mechanism, this collision can only occur for the RTS frames. Fortunately, such collision is early detected by the source nodes upon not receiving a CTS response.

Management of quality of service (QoS) has been introduced at node level in such wireless networks, through well-known EDCA mechanism defined in the IEEE 802.11e standard.

Indeed, in the original DCF standard, a communication node includes only one transmission queue/buffer. However, since a subsequent data frame cannot be transmitted until the transmission/retransmission of a preceding frame ends, the delay in transmitting/retransmitting the preceding frame prevented the communication from having QoS.

Figures 2a, and 2b illustrate the IEEE 802.11e EDCA mechanism involving access categories, in order to improve the quality of service (QoS).

The 802.11e standard relies on a coordination function, called hybrid coordination function (HCF), which has two modes of operation: enhanced distributed channel access (EDCA) and HCF controlled channel access (HCCA).

EDCA enhances or extends functionality of the original access DCF method: EDCA has been designed to support prioritized traffics similar to DiffServ (Differentiated

Services), which is a protocol for specifying and controlling network traffic by class so that certain types of traffic get precedence.

EDCA is the dominant channel access scheme or mechanism in WLANs because it features a distributed and easily deployed mechanism. The scheme contends for access to at least one communication channel of the communication network using contention parameters, in order for the node to transmit data stored locally over an accessed communication channel.

The above deficiency of failing to have satisfactory QoS due to delay in frame retransmission has been solved with a plurality of transmission queues/buffers.

QoS support in EDCA is achieved with the introduction of four Access Categories (ACs), and thereby of four corresponding transmission/traffic queues or buffers (210). Usually, the four ACs are the following in decreasing priority order: voice (or “AC_VO”), video (or “AC_VI”), best effort (or“AC_BE”) and background (or“AC_BG”).

Of course, another number of traffic queues may be contemplated.

Each AC has its own traffic queue/buffer to store corresponding data frames to be transmitted on the network. The data frames, namely the MSDUs, incoming from an upper layer of the protocol stack are mapped onto one of the four AC queues/buffers and thus input in the mapped AC buffer.

Each AC has also its own set of queue contention parameters, and is associated with a priority value, thus defining traffics of higher or lower priority of MSDUs. Thus, there is a plurality of traffic queues for serving data traffic at different priorities. The queue contention parameters usually include CW_min, CW_max, AIFSN and TXOPJJmit parameters for each traffic queue. CW_min and CW_max are the lower and higher boundaries of a selection range from which the EDCA contention window CW is selected for a given traffic queue. AIFSN stands for Arbitration Inter-Frame Space Number, and defines a number of time slots (usually 9 ps), additional to a DIFS interval (the total defining the AIFS period), the node must sense the medium as idle before decrementing the queue backoff value/counter associated with the traffic queue considered. TXOPJJmit defines the maximum size of a TXOP the node may request.

That means that each AC (and corresponding buffer) acts as an independent DCF contending entity including its respective queue backoff engine 211. Thus, each queue backoff engine 211 is associated with a respective traffic queue 210 for using queue contention parameters and setting a respective queue backoff value/counter (randomly selected from the CW), to be used to contend for access to at least one communication channel in order to transmit data stored in the respective traffic queue over an accessed communication channel.

The contention window CW and the queue backoff value/counter are known as EDCA variables.

It results that the ACs within the same communication node compete one with each other to access the wireless medium and to obtain a transmission opportunity, using the conventional EDCA access scheme as explained above for example.

Service differentiation between the ACs is achieved by setting different queue backoff parameters between the ACs, such as different CW_min, CW_max, AIFSN and/or different transmission opportunity duration limits (TXOPJJmit). This contributes to adjusting QoS.

The usage of the AIFSN parameter and queue backoff values to access the medium in the EDCA mechanism is described below with reference to Figure 3a.

Figure 2b illustrates default values for the CW_min, CW_max and AIFSN parameters.

In this table, typical respective values for aCWmin and aCWmax are defined in the above-mentioned standard as being respectively 15 and 1023. Other values may be set by a node in the network (typically an Access Point) and shared between the nodes. This information may be broadcast in a beacon frame.

To determine the delay, AlFS[i], between the detection of the medium being free and the beginning of the queue backoff value decrementing for traffic queue T, the node multiplies the value indicated in the AIFSN parameter for traffic queue T, i.e. AIFSN[i], by a time slot duration (typically 9 micro second), and adds this value to a DIFS duration.

As shown in Figure 3a, it results that each traffic queue waits an AIFS[i] period (that includes the DIFS period deferring access to the medium) before decrementing its associated queue backoff value/counter. The Figure shows two AIFS[i] corresponding to two different ACs. One can see that one prioritized traffic queue starts decrementing its backoff value earlier than the other less prioritized traffic queue. This situation is repeated after each new medium access by any node in the network.

This decrementing deferring mechanism, additional to the use of an on-average lower CW, makes that high priority traffic in EDCA has a higher chance to be transmitted than low priority traffic: a node with high priority traffic statistically waits a little less before it sends its packet, on average, than a node with low priority traffic.

The EDCA queue backoff values or counters thus play two roles. First, they drive the nodes in efficiently accessing the medium, by reducing risks of collisions. Second, they offer management of quality of service, QoS, by mirroring the aging of the data contained in the traffic queue (the more aged the data, the lower the backoff value) and thus providing different priorities to the traffic queues through different values of the EDCA parameters (especially the AIFSN parameter that delays the start ofthe decrementing ofthe EDCA queue backoff values).

Referring to Figure 2a, buffers AC3 and AC2 are usually reserved for real-time applications (e.g., voice AC_VO or video AC_VI transmission). They have, respectively, the highest priority and the last-but-one highest priority.

Buffers AC1 and AC0 are reserved for best effort (AC_BE) and background (AC_BG) traffic. They have, respectively, the last-but-one lowest priority and the lowest priority.

Each data unit, MSDU, arriving at the MAC layer from an upper layer (e.g. Link layer) with a priority is mapped into an AC according to mapping rules. Figure 3b shows an example of mapping between eight priorities of traffic class (User Priorities or UP, 0-7 according to IEEE 802.1d) and the four ACs. The data frame is then stored in the buffer corresponding to the mapped AC.

When the backoff procedure for a traffic queue (or an AC) ends, the MAC controller (reference 704 in Figure 7 below) of the transmitting node transmits a data frame from this traffic queue to the physical layer for transmission onto the wireless communication network.

Since the ACs operate concurrently in accessing the wireless medium, it may happen that two ACs of the same communication node have their backoff ending simultaneously. In such a situation, a virtual collision handler (212) of the MAC controller operates a selection of the AC having the highest priority (as shown in Figure 3b) between the conflicting ACs, and gives up transmission of data frames from the ACs having lower priorities.

Then, the virtual collision handler commands those ACs having lower priorities to start again a backoff operation using an increased CW value.

The QoS resulting from the use of the ACs may be signalled in the MAC data frames, for instance in a QoS control field included in the header of the IEEE 802.11e MAC frame.

To meet the ever-increasing demand for faster wireless networks to support bandwidth-intensive applications, 802.11ac is targeting larger bandwidth transmission through multi-channel operations. Figure 4a illustrates 802.11ac channel allocation that support composite channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz

IEEE 802.11ac introduces support of a restricted number of predefined subsets of 20MHz channels to form the sole predefined composite channel configurations that are available for reservation by any 802.11ac node on the wireless network to transmit data.

The predefined subsets are shown in the Figure and correspond to 20 MHz, 40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHz and 40 MHz supported by 802.11η. Indeed, the 20 MHz component channels 300-1 to 300-8 are concatenated to form wider communication composite channels.

In the 802.11ac standard, the channels of each predefined 40MHz, 80MHz or 160MHz subset are contiguous within the operating frequency band, i.e. no hole (missing channel) in the composite channel as ordered in the operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels that may or may not be frequency contiguous. The 80 MHz and 40 MHz channels are respectively composed of two frequency-adjacent or contiguous 40 MHz and 20 MHz channels, respectively. However the present invention may have embodiments with either composition of the channel bandwidth, i.e. including only contiguous channels or formed of non-contiguous channels within the operating band.

A node is granted a TXOP through the enhanced distributed channel access (EDCA) mechanism on the “primary channel” (400-3). Indeed, for each composite channel having a bandwidth, 802.11ac designates one channel as “primary” meaning that it is used for contending for access to the composite channel. The primary 20MHz channel is common to all nodes (STAs) belonging to the same basic set, i.e. managed by or registered with the same local Access Point (AP).

However, to make sure that no other legacy node (i.e. not belonging to the same set) uses the secondary channels, it is provided that the control frames (e.g. RTS frame/CTS frame) reserving the composite channel are duplicated over each 20MHz channel of such composite channel.

As addressed earlier, the IEEE 802.11ac standard enables up to four, or even eight, 20 MHz channels to be bound. Because of the limited number of channels (19 in the 5 GHz band in Europe), channel saturation becomes problematic. Indeed, in densely populated areas, the 5 GHz band will surely tend to saturate even with a 20 or 40 MHz bandwidth usage per Wireless-LAN cell.

Developments in the 802.11 ax standard seek to enhance efficiency and usage of the wireless channel for dense environments.

In this perspective, one may consider multi-user (MU) transmission features, allowing multiple simultaneous transmissions to/from different users in both downlink (DL) and uplink (UL) directions with a main node, usually an AP. In the uplink, multi-user transmissions can be used to mitigate the collision probability by allowing multiple nodes to simultaneously transmit to the AP.

To actually perform such multi-user transmission, it has been proposed to split a granted 20MHz channel (400-1 to 400-4) into sub-channels 410 (elementary sub-channels), also referred to as sub-carriers or resource units (RUs), that are shared in the frequency domain by multiple users, based for instance on Orthogonal Frequency Division Multiple Access (OFDMA) technique.

This is illustrated with reference to Figure 4.

The multi-user feature of OFDMA allows, a node, usually an access point, AP, to assign different RUs to different nodes in order to increase competition. This may help to reduce contention and collisions inside 802.11 networks.

Contrary to MU downlink OFDMA wherein the AP can directly send multiple data to multiple nodes (supported by specific indications inside the PLCP header), a trigger mechanism has been adopted for the AP to trigger MU uplink communications from various nodes.

To support a MU uplink transmission (during a TxOP pre-empted by the AP), the

802.11 ax AP has to provide signalling information for both legacy nodes (non-802.11ax nodes) to set their NAV and for 802.11 ax nodes to determine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11 ax nodes, meaning 802.11 nodes of previous technologies that do not support OFDMA communications.

As shown in the example of Figure 4, the AP sends a trigger frame (TF) 430 to the targeted 802.11 ax nodes. The bandwidth or width of the targeted composite channel is signalled in the TF frame, meaning that the 20, 40, 80 or 160 MHz value is signalled. The TF frame is sent over the primary 20MHz channel and duplicated (replicated) on each other 20MHz channels forming the targeted composite channel. As described above for the duplication of control frames, it is expected that every nearby legacy node (non-HT or 802.11ac nodes) receiving the TF frame (or a duplicate thereof) on its primary channel, then sets its NAV to the value specified in the TF frame. This prevents these legacy nodes from accessing the channels of the targeted composite channel during the TXOP.

Based on an AP’s decision, the trigger frame TF may define a plurality of resource units (RUs) 410, or “Random RUs”, which can be randomly accessed by the nodes of the network. In other words, Random RUs designated or allocated by the AP in the TF may serve as basis for contention between nodes willing to access the communication medium for sending data. A collision occurs when two or more nodes attempt to transmit at the same time over the same RU.

In that case, the trigger frame is referred to as a trigger frame for random access (TF-R). A TF-R may be emitted by the AP to allow multiple nodes to perform MU UL (Multi-User UpLink) random access to obtain an RU for their UL transmissions.

The trigger frame TF may also designate Scheduled resource units, in addition to or in replacement of the Random RUs. Scheduled RUs may be reserved by the AP for certain nodes in which case no contention for accessing such RUs is needed for these nodes. Such RUs and their corresponding scheduled nodes are indicated in the trigger frame. For instance, a node identifier, such as the Association ID (AID) assigned to each node upon registration, is added, in the TF frame, in association with each Scheduled RU in order to explicitly indicate the node that is allowed to use each Scheduled RU.

An AID equal to 0 may be used to identify random RUs.

The multi-user feature of OFDMA allows the AP to assign different RUs to different nodes in order to increase competition. This may help to reduce contention and collisions inside

802.11 networks.

In the example of Figure 4, each 20MHz channel (400-1,400-2, 400-3 or 400-4) is sub-divided in the frequency domain into four sub-channels or RUs 410, typically of size 5 Mhz.

Of course the number of RUs splitting a 20MHz channel may be different from four. For instance, between two to nine RUs may be provided (thus each having a size between 10 MHz and about 2 MHz).

Once the nodes have used the RUs to transmit data to the AP, the AP responds with an acknowledgment ACK (not show in the Figure) to acknowledge the data on each RU, making it possible for each node to know when its data transmission is successful (reception of the ACK) or not (no ACK after expiry of a time-out).

Document IEEE 802.11-15/1105 provides an exemplary random allocation procedure that may be used by the nodes to access the Random RUs indicated in the TF. This random allocation procedure, referred to as RU contention scheme, is managed by a dedicated RU access module separate from the above-mentioned channel access module and is configured to manage access to at least one resource unit provided by another node (usually the AP) within a transmission opportunity granted to the other node on the communication channel, in order to transmit data stored locally over an accessed resource unit. Preferably, the RU access module includes an RU backoff engine separate from the queue backoff engines, which uses RU contention parameters, including a computed RU backoff value, to contend for access to the random RUs.

In other words, the RU contention scheme is based on a new backoff counter, referred to as the OFDMA or RU backoff counter/value (or OBO), inside the 802.11 ax nodes for allowing a dedicated contention when accessing a random RU to send data.

Each node STA1 to STAn is a transmitting node with regards to receiving AP, and as a consequence, each node has an active RU backoff engine separate from the queue backoff engines, for computing an RU backoff value (OBO) to be used to contend for access to at least one random resource unit splitting a transmission opportunity granted on the communication channel, in order to transmit data stored in either traffic queue AC.

The random allocation procedure in this document comprises, for a node of a plurality of nodes having an active RU backoff value OBO, a first step of determining from the trigger frame the random sub-channels or RUs of the communication medium available for contention, a second step of verifying if the value of the active RU backoff value OBO local to the considered node is not greater than a number of detected-as-available random RUs, and then, in case of successful verification, a third step of randomly selecting a random RU among the detected-as-available random RUs for sending data. In case the second step is not verified, a fourth step (instead of the third) is performed in order to decrement the RU backoff value OBO by the number of detected-as-available RUs.

As shown in the Figure, some Resource Units may not be used (41 Ou) because no node with an RU backoff value OBO less than the number of available random RUs has randomly selected one of these random RUs, whereas some other have collided (as example 410c) because two of these nodes have randomly selected the same RU.

The MU Uplink (UL) medium access scheme, including both scheduled RUs and random RUs, proves to be very efficient compared to conventional EDCA access scheme. This is because the number of collisions generated by simultaneous medium access attempts and the overhead due to the medium access are both reduced.

However, the EDCA access scheme and MU UL OFDMA/RU access scheme have to coexist, in particular to allow legacy 802.11 nodes to access the medium and to allow even the 802.11 ax nodes to initiate communication with nodes other than the AP.

Although the EDCA access scheme taken alone provides a fair access to the medium throughout all the nodes, its association with the MU UL OFDMA/RU access scheme introduces a drift in fairness. This is because, compared to the legacy nodes, the 802.11 ax nodes have additional opportunities to send data through the resource units offered in the transmission opportunities granted to another node, in particular to the AP.

To restore some fairness between the nodes, solutions have been proposed,

For instance in co-pending UK application No 1612151.9 filed on 13 July 2016, a current value of at least one EDCA parameter is modified into different values (MU EDCA parameters), upon successfully transmitting data over an accessed resource unit (i.e. through UL OFDMA transmission). This is to reduce a probability for the node to access a communication channel through (conventional EDCA) contention.

In this framework, a mechanism has been proposed to reduce the node’s probability of EDCA-based transmission (i.e. using the EDCA medium access scheme) as soon as the node successfully uses the MU UL mechanism to transmit its data. This reduction is made by modifying the well-known EDCA parameters.

The proposed mechanism, as described in document IEEE 802.11-16/1180 entitled “Proposed text changes for MU EDCA parameters, sets each transmitting traffic queue in a MU EDCA mode in response to successfully transmitting the data in the accessed MU UL OFDMA resource unit. The setting is done for a predetermined duration, known as HEMUEDCATimer. The MU EDCA mode is a mode in which the respective EDCA parameters are set to MU values, different from legacy values used in a different legacy EDCA mode.

To switch from legacy EDCA contention access mode to the MU EDCA mode, the node may modify its EDCA parameters (AIFSN, CW_min, and/or CW_max) for all the traffic queues having successfully transmitted some data in the accessed resource unit. The switch back to the legacy EDCA mode may occur upon expiry of the HEMUEDCATimer, being noted that this timer is reset to its initial value each time the node transmits again new data (from either AC) during newly accessed resource units provided by the AP. The initializing value of HEMUEDCATimer is suggested to be high (e.g. tens of milliseconds) in order to encompass several new opportunities for MU UL transmissions.

The MU values for the EDCA parameters may be transmitted by the AP in a Dedicated Information Element, typically sent within a beacon frame broadcasting network information to the nodes.

The disclosed approach suggests increasing only the value of AIFSN for each transmitting traffic queue, while keeping CW_min, and CW_max unchanged. As the corresponding AIFS period increases, each traffic queue in the MU EDCA mode is prevented (or at least substantially delayed) from having its queue backoff value or counter been decremented upon sensing the medium free again. New accesses to the medium using EDCA access scheme are statistically substantially reduced, or even no longer possible, during the above-mentioned predetermined duration.

The MU-mode AIFSN value may be very restrictive. So, in high density environment where the medium is busy most of the time (and thus remain free for very short time), the node in MU EDCA mode must wait for the corresponding very restrictive AIFS period, and thus does not decrement the backoff value of the AC queue in MU EDCA mode very often. The result is that the node cannot EDCA-contend for access to the medium very often.

Note that a specific configuration in the publication tends to totally prevent (except if the network is not used at all) the transmitting traffic queues from EDCA-accessing the medium while in the MU EDCA mode. The AP specifies this particular operating mode by indicating a specific value of the AIFSN parameter (typically 0) in the set of MU EDCA parameters. Such specific value means for the node that it shall use a very high value for its AIFSN, which value is equal to the HEMUEDCATimer as transmitted by the AP (it is reminded its value should be high, about tens of milliseconds, to be compared to less than 0,1 millisecond for the worst AIFS[i] in the legacy EDCA mode).

Unfortunately, by greatly modifying the EDCA parameters and especially the AIFSN values, the known mechanism to control the drift in fairness prevents the queue backoff values of each traffic queue in the MU EDCA mode, to evolve (be decremented). The queue backoff values thus no longer mirror which traffic queue should have the highest priority of transmission in the meaning of EDCA (e.g. with oldest data stored in it).

The relative priorities of the traffic queues can no longer be used in the process of data transmission. This is contrary to the QoS principle as described in the 802.11e standard.

This is now illustrated with reference to Figure 5a which describes an example of application using MU EDCA parameters as described in the above-mentioned publication.

In this Figure, the four values 530 represent the queue backoff values BC[AC] associated with the four traffic queues 210. A graphical code is used to distinguish between the different states in which the queue backoff values may be. The graphical code is provided as a legend directly in the Figure.

In the first phase shown (each phase correspond to a period from when the network becomes available until the end of a granted TXOP), the node STA 502 accesses the medium through EDCA when BC[VI] reaches zero (counter in a dashed line box), while the best queue backoff value of the AP 501 only reaches 4. The black portions 540 before decrementing the queue backoff values correspond to the AIFS[AC] (the different sized thereof not being shown).

Then, video data from AC[2] (i.e. the traffic queue of AC_VI) are sent during the granted TXOP 550. A new queue backoff value is generated for AC_VI (white figure in black box).

In the second phase, the AP 501 accesses first the network after its AIFS 540 and the countdown of its backoff value 710, and then sends a trigger frame 1300. The TF 1300 provides at least one scheduled RU for node 502.

The TF 1300 does not indicate any preferred AC in corresponding fields (preferred AC level field 1330 shown in Figure 13 set to 0). So, node 502 needs to determine which AC queue has the highest priority to select corresponding data for MU UL OFDMA transmission.

To do so, node 502 selects the AC queue with the lowest current backoff counter value. In the present example, the first AC queue (corresponding to the VO queue) is selected since its associated queue backoff value equals 1 (compared to 4, 6 and 12 for the other AC queues).

Data from AC_VO can thus be transmitted (560) in the accessed resource unit

After successful MU UL OFDMA transmission 560 of the data, the corresponding traffic queue enters the MU EDCA mode, wherein the EDCA parameters of this transmitting traffic queue, here AC_VO, are modified with MU values. The traffic queues in MU EDCA mode are shown in the Figure using thick line boxes.

An example of MU values, not disclosed in the prior art, is provided in Figure 2c, which shows more restrictive values for the AIFSN parameter.

During this second phase, the queue backoff counter 580 associated with the transmitting traffic queue AC_VO is frozen, meaning it is not updated and keeps its previous value, here T.

The third phase thus starts with node 502 entering in deferred transmission state, by waiting for the end of the AIFS[i] timers (570) before decrementing the queue backoff values BC[i] 530.

For the traffic queues in MU EDCA mode with more restrictive EDCA parameters, such as higher AIFSN, the modified value of the AIFS 570 prevents from decrementing the corresponding queue backoff values BC[AC], So when the AP 501 sends a new trigger frame 1300-2 upon EDCA-based accessing the medium, node 502 to which a new scheduled RU is offered determines which traffic queue has the lowest current queue backoff value.

Again, this is BC[3] with the backoff value 1. It means that node 502 transmits (590) again data from AC_VO in the accessed RU.

After a while, if several, particularly if all traffic queues entered the MU EDCA mode, the associated queue backoff values are blocked. Priority is thus always given to the same traffic queue for MU UL OFDMA transmission. The backoff-based QoS requirement is no longer satisfied.

The lack of dynamicity of the backoff counters due to their freezing in case of MU UL OFDMA transmissions should be restored so that they still efficiently mirror the relative priorities of the AC queues. Advantageously, the restoring should maintain the reduction of EDCA-based transmission probability (through the MU EDCA mode), and also maintain the principle of evolution of the backoff counters.

It is within this framework that the present invention proposes to restore a dynamic EDCA-like behavior of the AC backoff counters by modifying at least one queue backoff value associated with a traffic queue while it is currently in the MU EDCA mode, in response to transmitting data in the accessed resource unit, preferably to successful transmission only.

Two main actions may be taken.

On one hand, modifying at least one queue backoff value may include computing, for one transmitting traffic queue, a new queue backoff value from the respective EDCA parameters set with the MU values. Thus, the EDCA approach to select a new backoff value each time the node sends data over the accessed medium is restored.

On the other hand, modifying at least one queue backoff value may include decreasing each queue backoff value associated with a non-transmitting MU traffic queue by a decrement value, a non-transmitting MU traffic queue being a traffic queue in the MU EDCA mode and from which no data are transmitted in the accessed resource unit.

Thus the EDCA behavior of backoff evolution is restored. Dynamic relative priorities between the traffic queues are thus reinstated.

The result of one implementation of the present invention is now illustrated with reference to Figure 5b which describes, with the same sequence as in Figure 5a, the restoring of QoS through relative EDCA-based priorities between the ACs.

The first phase remains unchanged.

During the second phase, node 502 receives the TF 1300 from the AP 501. The AC queue selection algorithm in the node determines that the traffic queue AC_VO has the highest priority due to a lowest queue backoff value (as in the example of Figure 5a). The MU UL OFDMA transmission happens with data from AC_VO.

After successful transmission 560 of the data in the accessed RU, AC_VO enters the MU EDCA mode (backoff value in a thick line box), and the present invention proposes to select a new backoff value 580 (white figures in a black box, here having the value ‘15’) for the transmitting traffic queue AC_VO, from the associated contention window.

Furthermore, all the queue backoff counters associated with traffic queues in MU EDCA mode are decremented by a decrement value. As no other traffic queue is in the MU EDCA mode in the second phase, no backoff value decrement is performed.

Next, in the third phase, the same approach is performed: node 502 receives the TF 1300-2 from the AP 501. The AC queue selection algorithm in the node determines that the traffic queue AC_VI has the highest priority due to a lowest queue backoff value (because BC[VO] is now with a value 15) The MU UL OFDMA transmission in an accessed RU thus happens with data from AC_VO.

One may note that, compared to Figure 5a, another traffic queue is solicited for the MU UL OFDMA transmission in the third phase. Thus, the relative priorities between the traffic queues are reinstated for the OFDMA transmitting traffic queues.

After successful transmission 590 of the data in the accessed RU, AC_VI also enters the MU EDCA mode (backoff value in a thick line box; while AC_VO is already in the MU EDCA mode), and a new backoff value 582 (white figures in a black box, here having the value ‘1T) is selected for the transmitting traffic queue AC_VI, from the associated contention window

Furthermore, all the queue backoff counters associated with traffic queues in MU EDCA mode, here AC_VO only, are decremented by a decrement value. In this example, the decrement value is a predetermined value equal to the lowest value taken by the queue backoff values associated with the transmitting traffic queues (here only AC_VI is transmitting, the associated value of which being 3), when the node transmits the data in the accessed resource unit.

The queue backoff counter of AC_VO thus goes from 15 to 12 (see reference 581).

The same applies during the fifth phase show, wherein the most prioritized traffic queue, AC_BG, is selected for MU UL OFDMA transmission; AC_BG thus enters the MU EDCA mode and a new value, namely ‘18’ is selected as new backoff value for that traffic queue. Also the other traffic queues in the MU EDCA mode (i.e. AC_VO and AC_VI) have their associated backoff values decreased by 10, representing the lowest backoff value at that time.

This updating also reflecting the aging of the data stored in the traffic queues.

So the full functional behavior of the EDCA backoffs, and thus QoS, are restored, in particular dynamic relative EDCA-based priorities between the traffic queues are reinstated.

Figure 6 schematically illustrates a communication device 600 of the radio network 100, configured to implement at least one embodiment of the present invention. The communication device 600 may preferably be a device such as a micro-computer, a workstation or a light portable device. The communication device 600 comprises a communication bus 613 to which there are preferably connected:

• a central processing unit 611, such as a microprocessor, denoted CPU;

• a read only memory 607, denoted ROM, for storing computer programs for implementing the invention;

• a random access memory 612, denoted RAM, for storing the executable code of methods according to embodiments of the invention as well as the registers adapted to record variables and parameters necessary for implementing methods according to embodiments of the invention; and • at least one communication interface 602 connected to the radio communication network 100 over which digital data packets or frames or control frames are transmitted, for example a wireless communication network according to the 802.11ax protocol. The frames are written from a FIFO sending memory in RAM 612 to the network interface for transmission or are read from the network interface for reception and writing into a FIFO receiving memory in RAM 612 under the control of a software application running in the CPU 611.

Optionally, the communication device 600 may also include the following components:

• a data storage means 604 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention;

• a disk drive 605 for a disk 606, the disk drive being adapted to read data from the disk 606 or to write data onto said disk;

• a screen 609 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 610 or any other pointing means.

The communication device 600 may be optionally connected to various peripherals, such as for example a digital camera 608, each being connected to an input/output card (not shown) so as to supply data to the communication device 600.

Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 600 or connected to it. The representation of the bus is not limiting and in particular the central processing unit is operable to communicate instructions to any element of the communication device 600 directly or by means of another element of the communication device 600.

The disk 606 may optionally be replaced by any information medium such as for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, a USB key or a memory card and, in general terms, by an information storage means that can be read by a microcomputer or by a microprocessor, integrated or not into the apparatus, possibly removable and adapted to store one or more programs whose execution enables a method according to the invention to be implemented.

The executable code may optionally be stored either in read only memory 607, on the hard disk 604 or on a removable digital medium such as for example a disk 606 as described previously. According to an optional variant, the executable code of the programs can be received by means of the communication network 603, via the interface 602, in order to be stored in one of the storage means of the communication device 600, such as the hard disk 604, before being executed.

The central processing unit 611 is preferably adapted to control and direct the execution of the instructions or portions of software code of the program or programs according to the invention, which instructions are stored in one of the aforementioned storage means. On powering up, the program or programs that are stored in a non-volatile memory, for example on the hard disk 604 or in the read only memory 607, are transferred into the random access memory 612, which then contains the executable code of the program or programs, as well as registers for storing the variables and parameters necessary for implementing the invention.

In a preferred embodiment, the apparatus is a programmable apparatus which uses software to implement the invention. However, alternatively, the present invention may be implemented in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC).

Figure 7 is a block diagram schematically illustrating the architecture of a communication device or node 600, in particular one of nodes 100-107, adapted to carry out, at least partially, the invention. As illustrated, node 600 comprises a physical (PHY) layer block 703, a MAC layer block 702, and an application layer block 701.

The PHY layer block 703 (here an 802.11 standardized PHY layer) has the task of formatting frames, modulating frames on or demodulating frames from any 20MHz channel or the composite channel, and thus sending or receiving frames over the radio medium used 100. The frames may be 802.11 frames, for instance medium access trigger frames TF 430 to define resource units in a granted transmission opportunity, MAC data and management frames based on a 20 MHz width to interact with legacy 802.11 stations, as well as of MAC data frames of OFDMA type having smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/from that radio medium.

The MAC layer block or controller 702 preferably comprises a MAC 802.11 layer

704 implementing conventional 802.11 ax MAC operations, and an additional block 705 for carrying out, at least partially, the invention. The MAC layer block 702 may optionally be implemented in software, which software is loaded into RAM 512 and executed by CPU 511.

Preferably, the additional block, referred to as EDCA parameters update module

705 implements the part of the invention that regards node 600, i.e. modification of one or more queue backoff values associated with a traffic queue while the latter is currently in the MU EDCA mode. This module thus performs the selection of a new backoff value for one or each transmitting traffic queue upon (preferably successful) transmission in an accessed Ressource Unit, and performs the decrementing of each backoff counter associated with an AC in the MU EDCA mode.

From the AP perspective, this EDCA parameters update module 705 may be provided to send, to the nodes, the set of legacy values of the EDCA parameters and the set of MU values of the EDCA parameters, different from the legacy values, possibly together with the duration HEMUEDCATimer to drive the nodes entering the MU EDCA mode to remain in such mode at least the duration. These values thus drive each node in configuring itself when one of its traffic queues switches between a legacy EDCA mode in which the respective EDCA parameters are set to the legacy values and a MU EDCA mode in which the respective EDCA parameters are set to the MU values.

MAC 802.11 layer 704 and EDCA parameters update module 705 interact one with the other in order to provide management of the channel access module handling the queue backoff engines and a RU access module handling the RU backoff engine as described below.

On top of the Figure, application layer block 701 runs an application that generates and receives data packets, for example data packets of a video stream. Application layer block 701 represents all the stack layers above MAC layer according to ISO standardization.

Embodiments of the present invention are now illustrated using various exemplary embodiments. Although the proposed examples use the trigger frame 430 (see Figure 4) sent by an AP for a multi-user uplink transmissions, equivalent mechanisms can be used in a centralized or in an ad-hoc environment (i.e. without an AP). It means that the operations described below with reference to the AP may be performed by any node in an ad-hoc environment.

These embodiments are mainly described in the context of IEEE 802.11 ax by considering OFDMA resource units. Application of the invention is however not limited to the IEEE 802.11 ax context.

Also the present invention does not necessarily rely on the usage of a MU access scheme as described in 802.11 ax. Any other RU access scheme defining alternate medium access schemes allowing simultaneous access by the nodes to the same medium can also be used.

The set of MU values may be more restrictive than the set of legacy values, resulting for a traffic queue being in the MU EDCA mode to access less often the medium using EDCA contention access scheme.

However, the set of MU values may be more permissive in some embodiments.

For the sake of clarity, the explanations below focus on a set of MU values that is more restrictive. In this context, the MU EDCA mode is referred to as the “degraded” mode, while the legacy EDCA mode is referred to as “non-degraded” mode.

Figure 8 illustrates an exemplary transmission block of a communication node 600 according to embodiments of the invention.

As mentioned above, the node includes a channel access module and possibly an RU access module, both implemented in the MAC layer block 702. The channel access module includes:

a plurality of traffic queues 210 for serving data traffic at different priorities; a plurality of queue backoff engines 211, each associated with a respective traffic queue for using EDCA parameters, in particular for computing a respective queue backoff value, to be used to contend for access to at least one communication channel in order to transmit data stored in the respective traffic queue. This is the EDCA access scheme.

The RU access module includes an RU backoff engine 800 separate from the queue backoff engines, for using RU contention parameters, in particular for computing an RU backoff value, to be used to contend for access to the OFDMA random resource units defined in a received TF (sent by the AP for instance), in order to transmit data stored in either traffic queue in an OFDMA RU. The RU backoff engine 800 is associated with a transmission module, referred to as OFDMA muxer 801. For example OFDMA muxer 801 is in charge, when the RU backoff value OBO described below reaches zero, of selecting data to be sent from the AC queues 210.

The conventional AC queue back-off registers 211 drive the medium access request along EDCA protocol (channel contention access scheme), while in parallel, the RU backoff engine 800 drives the medium access request onto OFDMA multi-user protocol (RU contention access scheme).

As these two contention access schemes coexist, the source node implements a medium access mechanism with collision avoidance based on a computation of backoff values:

- a queue backoff counter value corresponding to a number of time-slots the node waits (in addition to a DIFS period), after the communication medium has been detected to be idle, before accessing the medium. This is EDCA, regardless of whether it is in a degraded or non-degraded state;

- an RU backoff counter value (OBO) corresponding to a number of idle random RUs the node detects, after a TXOP has been granted to the AP or any other node over a composite channel formed of RUs, before accessing the medium. This is OFDMA. A variant to counting down the OBO based on the number of idle random RUs may be based on a timebased countdown.

Figure 9 illustrates, using a flowchart, main steps performed by MAC layer 702 of node 600, when receiving new data to transmit. It illustrates a conventional FIFO feeding in 802.11 context.

At the very beginning, none traffic queue 210 stores data to transmit. As a consequence, no queue backoff value 211 has been computed. It is said that the corresponding queue backoff engine or corresponding AC (Access Category) is inactive. As soon as data are stored in a traffic queue, a queue backoff value is computed (from corresponding queue backoff parameters), and the associated queue backoff engine or AC is said to be active.

When a node has data ready to be transmitted on the medium, the data are stored in one of the AC queue 210, and the associated backoff 211 should be updated.

At step 901, new data are received from an application running on the device (from application layer 701 for instance), from another network interface, or from any other data source. The new data are ready to be sent by the node.

At step 902, the node determines in which AC queues 210 the data should be stored. This operation is usually performed by checking the TID (Traffic Identifier) value attached to the data (according to the matching shown in Figure 3b).

Next, step 903 stores the data in the determined AC queue. It means the data are stored in the AC queue having the same data type as the data.

At step 904, conventional 802.11 AC backoff computation is performed by the queue backoff engine associated with the determined AC queue.

If the determined AC queue was empty just before the storage of step 903 (i.e. the AC is originally inactive), then there is a need to compute a new queue backoff value for the corresponding backoff counter.

The node thus computes the queue backoff value as being equal to a random value selected in range [0, CW], where CW is the current value of the CW for the Access Category considered (as defined in 802.11 standard and updated for instance according to some embodiments of the invention as described in step 1180 below). It is recalled here that the queue backoff value will be added to the AIFSN (which may be degraded in the MU EDCA mode) in order to implement the relative priorities of the different access categories. CW is a congestion window value that is selected from selection range [CW_min, CW_max], where both boundaries CW_min and CW_max (possibly degraded) depend on the Access Category considered.

As a result the AC is made active.

The above parameters CW, CW_min, CW_max, AIFSN, and Backoff value form the EDCA parameters and variables associated with each AC. They are used to set the relative priorities to access the medium for the different categories of data.

The EDCA parameters have usually a fixed value (e.g. CW_min, CW_max, and AIFSN), while the EDCA variables (CW and backoff value) evolve overtime and medium availability. As readily apparent from the above, the present invention provides evolution of the EDCA parameters through the switching between degraded and non-degraded parameter values.

Also step 904 may include computing the RU backoff value OBO if needed. An RU backoff value OBO needs to be computed if the RU backoff engine 800 was inactive (for instance because there were no data in the traffic queues until previous step 903) and if new data to be addressed to the AP have been received.

The RU backoff value OBO may be computed in a similar fashion as the EDCA backoff value, i.e. using dedicated RU contention parameters, such as a dedicated contention window [0, CWO] and a selection range [CWO_min, CWO_max],

Note that some embodiments may provide distinction between data that can be sent through resource units (i.e. compatible with MU UL OFDMA transmission) and those that cannot. Such decision can be made during step 902, and a corresponding marking item can be added to the stored data.

In such a case, the RU backoff value OBO is computed only if the newly stored data are marked as compatible with MU UL OFDMA transmission.

Next to step 904, the process of Figure 9 ends.

Once data are stored in the AC queues, the node may access the medium directly through EDCA access scheme (either with the legacy EDCA mode or with the degraded MU EDCA mode) as illustrated below with reference to Figure 10, or through resource units provided by the AP through one or more trigger frames, as illustrated below with reference to

Figure 11.

Figure 10 illustrates, using a flowchart, steps of accessing the medium based on the (legacy or degraded MU) EDCA medium access scheme. For instance, this illustrates node 702’s behavior in the first or fourth phase of Figure 5b.

Steps 1000 to 1020 describe a conventional waiting introduced in the EDCA mechanism to reduce the collision on a shared wireless medium. In step 1000, node 600 senses the medium waiting for it to become available (i.e. detected energy is below a given threshold on the primary channel).

When the medium becomes free during an AIFS[i] period (including a DIFS period and the AIFSN[i] period - see Figure 3a), step 1010 is executed in which node 600 decrements all the active (non-zero) AC[] queue backoff counters 211 by one. In other words, the node decrements the queue backoff values each elementary time unit the communication channel is detected as idle.

Next, at step 1020, node 600 determines if at least one of the AC backoff counters reaches zero.

If no AC queue backoff reaches zero, node 600 waits for another backoff timeslot (typically 9ps), and thus loops back to step 1000 in order to sense the medium again during the next backoff timeslot. This makes it possible to decrement the AC backoff counters at each new backoff timeslot when the medium is sensed as idle, as soon as their respective AIFS[i] have expired.

If at least one AC queue backoff reaches zero, step 1030 is executed in which node 600 (more precisely virtual collision handler 212) selects the active AC queue having a zero queue backoff counter and having the highest priority.

At step 1040, an appropriate amount of data is selected from this selected AC for transmission, to match the bandwidth of the TXOP.

Next, at step 1050, node 600 initiates an EDCA transmission, in case for instance an RTS/CTS exchange has been successfully performed to have a TXOP granted. Node 600 thus sends the selected data on the medium, during the granted TXOP.

Next, at step 1060, node 600 determines whether or not the EDCA transmission has ended, in which case step 1070 is executed.

At step 1070, node 600 updates the contention window CW of the selected traffic queue, based on the status of transmission (positive or negative ack, or no ack received). Typically, node 600 doubles the value of CW if the transmission failed, until CW reaches the maximum value CW_max (either degraded or not) which depends on the AC type of the data. On the other hand, if the EDCA transmission is successful, the contention window CW is set to the minimum value CW_min (either degraded or not) which is also dependent on the AC type of the data.

Next, if the selected traffic queue is not empty after the EDCA data transmission, a new associated queue backoff counter is randomly selected from [0,CW], similar to step 904.

This ends the process of Figure 10.

Figure 11 illustrates, using a flowchart, steps of accessing resource units based on an RU or OFDMA access scheme upon receiving a trigger frame defining RUs. For instance, this illustrates node 502’s behavior in phases 2 or 3 or 5 of Figure 5b.

At step 1110, the node determines whether a trigger frame is received from the access point in the communication network, the trigger frame reserving a transmission opportunity granted to the access point on the communication channel and defining resource units, RUs, forming the communication channel. If so, the node analyses the content of the received trigger frame.

At step 1120, the node determines whether or not it can transmit data over one of the RUs defined in the received trigger frame. The determination may involve one or both of two conditions, regarding in particular the type of RUs.

By analysing the content of the received TF, the node determines whether or not a defined RU is a scheduled resource unit assigned by the access point to the node. This may be done by looking for its own AID in the received TF, which AID is associated with a specific scheduled RU to be used for MU UL OFDMA transmission.

Also, by analysing the content of the received TF, the node determines whether or not one or more random RUs are defined in the TF, i.e. RUs the access of which is made through contention using dedicated RU contention parameters (including the above-mentioned OBO value 800). In that case, the node also determines whether or not its current OBO value 800 allows one random RU to be selected (for instance if OBO 800 is less than the number of random RUs in the TF).

If one scheduled RU is assigned to the node or the latter is allowed (after contention) to access one random RU, the node determines the size of the random/scheduled RU or RUs to be used and step 1130 is executed. Otherwise, the node decrements the RU backoff value OBO 800 based on the number of random resource units defined in the received trigger frame, and the process ends as the node cannot access any RU defined by the received TF.

At step 1130, the node selects at least one of the traffic queues 210 from which the data to be transmitted are selected, and adds data of the selected queue or queues to the transmission buffer until the quantity of data reaches the size of the selected resource unit to be used.

Various criteria to select a current traffic queue may be involved.

For instance, this may be done by:

selecting a traffic queue 210 having the lowest associated queue backoff value, as proposed in the example of Figure 5b. The selection of the traffic queue thus depends on the values of the EDCA backoffs 211, thereby guaranteeing that the node respects the EDCA principle and that correct QoS is implemented for its data);

selecting randomly one non-empty traffic queue from the traffic queues; selecting a traffic queue storing the biggest amount of data (i.e. the most loaded); selecting a non-empty traffic queue having the highest associated traffic priority (given the AC categories shown in Figure 3b);

selecting a non-empty traffic queue associated with a data type matching a data type associated with the resource unit over which the data to select are to be transmitted. Such specified data type may be a traffic queue indicated by the AP in the trigger frame, for instance using the Preferred AC field 1340 of Figure 13 when the AC Preference Level field is set to 1.

Next to step 1130, step 1140 provides that the node sets or updates a list of emitting/transmitting queues by inserting the current traffic queue from which the data selected in step 1130 come. The list keeps the order of insertion of the emitting/transmitting queues, so that for instance a primary emitting/transmitting queue (first queue selected on step 1030) and subsequent emitting/transmitting queues can be easily identified.

In addition, the node may store during step 1140 an item of information representing the amount of data thus selected from the current traffic queue, for transmission in the RU. For instance, then node updates the list of emitting queues by also inserting the quantity of data selected from the current traffic queue.

This list of emitting/transmitting queues can be implemented through a table containing for each traffic queue, the rank of the transmitting queue (which may be simplified to “primary” or “secondary” queue) and the quantity of data put in the transmission buffer.

At step 1150, the node determines whether or not the amount of data stored in the transmission buffer is enough to fill the selected resource unit.

If not, there is still room for additional data in the resource unit. Thus the process loops back to step 1130 during which another traffic queue may be selected, using the same selection criteria. In such a way, the transmission buffer is progressively filled up to reach the selected resource unit size.

One may thus note that a plurality of transmitting traffic queues of the same node may be involved during a MU UL OFDMA transmission, thereby resulting in having the plurality of queues entering the MU EDCA mode.

In a variant which avoids mixing data from two or more traffic queues (i.e. the data for the selected RU are selected from a single traffic queue), padding data may be added to entirely fill the selected RU. This is to ensure the whole RU duration has energy that can be detected by legacy nodes.

According to another variant implementing a specific data aggregation rule, if the first selected traffic queue has not data enough to fully fill in the accessed resource unit, data from higher priority traffic queues may be selected.

Once, the transmission buffer is full for the selected RU, step 1160 initiates the MU UL OFMDA transmission of the data stored in the transmission buffer, to the AP. The OFDMA transmission is based on the OFDMA sub-channel and modulation defined in the received trigger frame and especially in the RU definition.

Next, once the transmission has been performed, and preferably upon successful transmission (i.e. an acknowledgment is received from the AP), step 1170 determines the new value or values to be applied to one or more EDCA parameters of the traffic queue or queues, in order to modify it or them into penalized value or values.

The transmitting queues added in the list at step 1140 thus enter the MU EDCA mode, meaning that their EDCA or “queue contention” parameter set should be modified, in particular into degraded parameter values to be determined. One or more transmitting queues may already be in the MU EDCA mode. However, the degraded parameter values are also to be determined (they may be modified by a beacon frame recently received with new degraded values).

During step 1170, the degraded parameter values are determined.

In embodiments, the degraded values of the EDCA parameters include a degraded Arbitration Inter-Frame Space Number, AIFSN, compared to non-degraded values of the EDCA parameters used for the traffic queue not set in the MU EDCA mode. In other words, the AIFSNs of the transmitting queues are set to degraded values.

In some embodiments, AIFSN is the only one parameter modified when switching into the MU EDCA mode. It means the degraded values of the EDCA parameters include the same lower boundary CW_min and/or higher boundary CW_max as the non-degraded values used for legacy EDCA mode, both CW_min and CW_max defining a selection range from which a size of the contention window is selected,.

The degraded values used for this step are preferably selected in the last received Dedicated Information Element, usually forming part of a beacon frame transmitted by the AP. Thus, for a node periodically receiving a beacon frame from the access point, each beacon frame broadcasting network information about the communication network to the plurality of nodes, a received beacon frame thus includes, usually in addition to non-degraded (or legacy EDCA) values, the degraded values for the EDCA parameters of the plurality of traffic queues switching into the MU EDCA mode.

If such degraded values are not received from the AP, by-default values as described in the standard may be used.

Step 1170 may also include determining the predetermined degrading duration HEMUEDCATimer value defining the period during which the node must remain in the MU EDCA mode. This information may also be obtained from the AP, for instance from an specific Dedicated Information Element of a received beacon frame.

Next to step 1170, step 1180 actually replaces the current values of the EDCA parameters associated with the transmitting traffic queue(s) by the degraded values determined at step 1170.

In case parameters CW_min and/or CW_max have new values, the current CW of one or more traffic queues may be out-of-date. In that case, a new CW may be selected from newly defined range [CW_min, CW_max],

Also, a timer may be initialized with the HEMUEDCATimer, which timer progressively elapses as the time goes. Note that if the timer is already elapsing when step 1180 is performed (meaning the node was already in the MU EDCA mode), the timer is reinitialized again to HEMUEDCATimer in order to keep the node in MU EDCA mode for a next HEMUEDCATimer period.

Next step 1190 is executed.

This step makes it possible to restore the QoS feature supported by the backoff counters.

Step 1190 modifies at least one queue backoff value associated with a degraded traffic queue while the latter is in the degraded MU EDCA mode.

It includes both computing, for one or all transmitting traffic queues, a new queue backoff value from the respective degraded EDCA parameters, and decreasing each queue backoff value associated with a non-transmitting degraded traffic queue by a decrement value, as explained above with reference to Figure 5b. Any of these two operations is enough to guaranty an evolution of the backoff counters of the traffic queues in MU EDCA mode, thereby ensuring a dynamic evolution of the backoff counters to be obtained.

Various embodiments for decrementing the queue backoff values of the nontransmitting AC queues can be contemplated.

In first embodiment, a same predetermined value is used as a backoff decrement (BD) value to decrease the queue backoff values of all the non-transmitting degraded traffic queues in the MU EDCA mode.

This unique BD value can be the lowest queue backoff value associated with the transmitting queues as mentioned above. In a variant, the unique BD value may be the queue backoff value (upon the node transmitting during step 1160 the data in the accessed resource unit) associated with a preferred traffic queue indicated by the AP. The preferred traffic queue indication is included in the trigger frame received from the AP, through field 1340 mentioned above (thus if the Preference AC Level field 1330 is set to 1).

In second embodiments, the queue backoff value of each non-transmitting degraded traffic queue is decreased by a respective decrement value function of the priority of the non-transmitting degraded traffic queue. It means that the BD value is different for one traffic queue in MU EDCA mode to the other. This is to restore the different speeds of decrement of the backoff counters that are applied in the legacy EDCA medium access scheme.

To determine the different Backoff Decrement BD[AC] values for the traffic queues AC, the node can use on one hand a predetermined value (referred below as UBD) as defined above with reference to the first embodiments, and on the other hand an offset value which depends on each traffic queue.

In implementation where the degraded values mainly distinguish from the nondegraded values by the AIFSN, the BD[AC] values for all the non-transmitting degraded traffic queues may be computed from non-zero Arbitration Inter-Frame Space Numbers, AIFSNs, defined as respective EDCA parameters of the traffic queues.

Typically, BD[i]=max (0,UBD-(AIFSN[i]-min(AIFSN).

Taking the EDCA parameter example of Figure 2c, if we consider a predetermined value UBD of 5, the following backoff decrements are obtained: BD[0]= max (0, 10-(14-9)) = 5, while BD[3]= max(0, 10-(9-9))=10.

One thus notes that by using this formula, some backoff values associated with degraded traffic queues may not necessarily decrease.

Various embodiments for computing, for one or all transmitting traffic queues, new queue backoff values can also be contemplated.

In first embodiments, a new queue backoff value is computed only for the transmitting traffic queue from which data are transmitted at the beginning of the accessed resource unit. Based on the list generated at step 1140, it means only the primary transmitting queue has a new backoff value, by randomly selecting a value within the range [0, CW].

In second embodiments, a new queue backoff value is computed for each transmitting traffic queue, using for instance the same mechanism as described in the first embodiments.

By applying the two backoff counter modifications (decrementing the backoff of the queues in the MU EDCA mode and selecting a new backoff value for one or each transmitting queue), the node ensures an evolution of the backoff counters to be performed, that reflects the relative priorities between the queues with regards to EDCA policy.

Figure 12 illustrates, using a flowchart, the node management to switch back to the non-degraded legacy EDCA mode in the examples above. This management is based on the HEMUEDCATimer mentioned above. Indeed, the node may remain in the MU EDCA mode as long as this timer has not lapsed.

Thus at step 1210, it is checked whether or not the HEMUEDCATimer has lapsed/expired, i.e. has reached the value 0.

In the affirmative, the node switched back to the EDCA mode at step 1220.

In this embodiment, all the degraded traffic queues share the same predetermined degrading duration HEMUEDCATimer, so that all the degraded traffic queues exit the degraded MU EDCA mode by restoring their respective EDCA parameters to non-degraded values, upon the predetermined degrading duration lapsing. Note that due to the re-initialization of the timer at each new step 1180 in the node, the expiry of the timer only occurs when no data is transmitted, from the node, in any OFDMA resource unit provided by the AP within subsequent TXOPs granted to the AP during the predetermined degrading duration HEMUEDCATimer.

Next, the process ends at step 1230.

Figure 13 illustrates the structure of a trigger frame as defined in the 802.11ax draft standard.

The trigger frame 1300 is composed of a dedicated field 1310 called User Info Field. This field contains a “Trigger dependent Common info” field 1320 which contains the “AC Preference Level” field 1330 and “Preferred AC” field 1340.

The Preferred AC field 1340 is a 2-bit field indicating the AC queue (value from 0 to 3) from which data should be sent by the node on the RU allocated to that node in the trigger frame.

The AC preference Level field 1330 is a bit indicating if the value of the Preferred AC field 1340 is meaningful or not. If the field 1340 is set to 1, then the node should take into account the preferred AC field 1340 when selecting data at step 1130. If the field 1330 is set to 0, the node is allowed to send data from any AC queue, regardless of the preferred AC field 1340 value.

The other fields ofthe trigger frame are defined in the 802.11 ax standard.

The AP may also be in charge of broadcasting the EDCA parameters for both EDCA mode and MU EDCA mode. It preferably performs the broadcasting using a well-known beacon frame, dedicated to configure all the nodes in an 802.11 cell. Note the if the AP fails to broadcast the EDCA parameters, the nodes are configured to fail-back to by-default values as defined in the 802.11 ax standard.

Figure 14a illustrates the structure of a standardized information element 1410 used to describe the parameters ofthe EDCA in a beacon frame.

Fields 1411, 1412, 1413, 1414 describes the parameters associated with each traffic queue 210. For each traffic queue, a subfield 1415 includes the EDCA parameters: AIFSN as a delay before starting to decrease the associated backoff value, the ECWmin and ECWmax as the values of the minimum CW_min and maximum CW_max contention window and finally the TXOP limit as the maximum transmitting data time for an 802.11 device.

All the others fields ofthe information element are those described in the 802.11 standard.

Figure 14b illustrates an exemplary structure of a dedicated information element 1420 to transmit the degraded EDCA parameter values according to the invention, as well as the HEMUEDCATimer value. The dedicated information element 1420 may be included in a beacon frame sent by the AP.

The dedicated information element 1420 includes, for each AC queue, the degraded EDCA parameters (1421,1422,1423,1424) to be used by the nodes in the MU EDCA mode. It also includes a subfield 1425 specifying the value ofthe HEMUEDCATimer.

Each subfield 1421,1422,1423,1424 includes the degraded AIFSN value for the corresponding traffic queue, as well as the degraded ECWmin value and degraded ECWmax value (they can be the same as the legacy EDCA values).

As both non-degraded values and degraded values must be known by the nodes, the AP may send, to the nodes, a set of non-degraded values ofthe EDCA parameters (as in Figure 14a) and a set of degraded values of the EDCA parameters (as in Figure 14a), to configure each node when a traffic queue ofthe node switches between a non-degraded legacy EDCA mode in which the respective EDCA parameters are set to the non-degraded values and a degraded MU EDCA mode in which the respective EDCA parameters are set to the degraded values. This sending may be accompanied with the degrading duration HEMUEDCATimer to drive the nodes entering the MU EDCA mode to remain in such mode at least the degrading duration.

In this example, the sets of non-degraded values and of degraded values, as well as HEMUEDCATimer value are transmitted within a beacon frame, periodically transmitted by the access point to broadcast network information about the communication network to the plurality of nodes.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.

For instance, while the EDCA parameters and the degraded MU EDCA parameters are broadcasted in dedicated Information Elements of the same beacon frame in the above explanations, variations may contemplate alternating between a beacon frame sending the EDCA parameters and another beacon frame broadcasting the degraded MU EDCA parameters.

Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims

1. A communication method in a communication network comprising a plurality of nodes, at least one node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communication channel in order to transmit data stored in the traffic queue;

the method comprising, at the node:

2. The method of Claim 1, wherein modifying at least one queue backoff value includes computing, for one transmitting traffic queue, a new queue backoff value from the respective queue contention parameters set with the MU values.

3. The method of Claim 2, wherein a new queue backoff value is computed only for the transmitting traffic queue from which data are transmitted at the beginning of the accessed resource unit.

4. The method of Claim 2, wherein a new queue backoff value is computed for each transmitting traffic queue.

5. The method of Claim 1, wherein modifying at least one queue backoff value includes decreasing each queue backoff value associated with a non-transmitting MU traffic queue by a decrement value, a non-transmitting MU traffic queue being a traffic queue in the MU contention mode and from which no data are transmitted in the accessed resource unit.

6. The method of Claim 5, wherein the queue backoff values of all the nontransmitting MU traffic queues are decreased by the same predetermined value.

7. The method of Claim 5, wherein the queue backoff value of each nontransmitting MU traffic queue is decreased by a respective decrement value function of the priority of the non-transmitting MU traffic queue.

8. The method of Claim 7, wherein the decrement values for all the nontransmitting MU traffic queues are computed from the same predetermined value.

9. The method of Claim 7, wherein the decrement values for all the nontransmitting MU traffic queues are computed from non-zero Arbitration Inter-Frame Space Numbers, AIFSNs, defined as respective queue contention parameters of the traffic queues.

10. The method of Claim 8 or 9, wherein the decrement value for a nontransmitting MU traffic queue 1' equals max[0, predetermined value - (AIFSN[i] - min(AIFSN)], wherein AIFSN[i] is the AIFSN of traffic queue ‘i1, and min(AIFSN) is the minimum value from among the non-zero AIFSNs of all the traffic queues.

11. The method of Claim 6 or 8, wherein the predetermined value equals the lowest value taken by the queue backoff values associated with the transmitting traffic queues, when the node transmits the data in the accessed resource unit.

12. The method of Claim 6 or 8, wherein the predetermined value equals the queue backoff value, when the node transmits the data in the accessed resource unit, associated with a preferred traffic queue indicated by the other node.

13. The method of Claim 12, wherein the preferred traffic queue indication is included in a trigger frame received from the other node, the trigger frame reserving the transmission opportunity granted to the other node on the communication channel and defining resource units, RUs, forming the communication channel including the accessed resource unit.

14. The method of Claim 1, wherein the transmitting traffic queue or queues are set in the MU contention mode only upon successfully transmitting the data in the accessed resource unit.

15. The method of Claim 1, wherein the MU values of the queue contention parameters include a degraded Arbitration Inter-Frame Space Number, AIFSN, compared to the legacy values of the queue contention parameters used for the traffic queue not set in the legacy contention mode.

16. The method of Claim 1, wherein each queue backoff value is initially selected from a respective contention window, the queue backoff value being decreased by the node overtime to access the communication channel upon reaching zero, and the MU values of the queue contention parameters include the same lower boundary CWmin and/or higher boundary CWmax, both defining a selection range from which a size of the contention window is selected, as the legacy values.

17. The method of Claim 1, wherein all the traffic queues in the MU contention mode share the same predetermined duration, so that all the traffic queues in the MU contention mode exit the MU contention mode by restoring their respective queue contention parameters to legacy values, upon the predetermined duration lapsing without any data from the node being transmitted in any resource unit provided by the other node within subsequent transmission opportunities granted to the other node during the predetermined degrading duration.

18. The method of Claim 1, further comprising, at the node, upon accessing a resource unit provided by the other node within a new transmission opportunity granted to the other node:

19. The method of Claim 1, further comprising, at the node, contending for access to the communication channel using the modified queue backoff value or values.

20. The method of Claim 1, further comprising, at the node, periodically receiving a beacon frame from an access point, each beacon frame broadcasting network information about the communication network to the plurality of nodes, wherein at least one received beacon frame includes MU values and legacy values for the queue contention parameters of the plurality of traffic queues.

21. The method of Claim 20, wherein the received beacon frame also includes the predetermined duration.

22. A communication method in a communication network comprising a plurality of nodes and an access point, each node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communication channel in order to transmit data stored in the traffic queue;

the method comprising, at the access point:

23. The method of Claim 22, wherein the sets of legacy values and of MU values are transmitted within one or more beacon frames, periodically transmitted by the access point to broadcast network information about the communication network to the plurality of nodes.

24. The method of Claim 22, wherein the access point also sends, to the nodes, a duration to drive the nodes entering the MU contention mode to remain in such mode at least the duration.

25. The method of Claim 22, wherein the sets of legacy values and of MU values differ by different Arbitration Inter-Frame Space Numbers, AIFSNs.

26. The method of Claim 25, wherein each queue backoff value of a node is selected from a respective contention window, the queue backoff value being decreased by the node overtime to access the communication channel upon reaching zero, and the sets of legacy values and of MU values may include the same lower boundary CWmin and/or higher boundary CWmax, both defining a selection range from which a size of the contention window is selected.

27. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device, causes the device to perform the method of Claim 1 or 22.

28. A communication device node in a communication network comprising a plurality of nodes, the communication device comprising:

29. An access point in a communication network also comprising a plurality of nodes, each node comprising a plurality of traffic queues for serving data traffic at different priorities, each traffic queue being associated with a respective queue backoff value computed from respective queue contention parameters having legacy values in a legacy contention mode and used to contend for access to a communication channel in order to transmit data stored in the traffic queue;

the access point comprising at least one microprocessor configured for carrying out 5 the following steps:

accessing the communication channel to send a trigger frame reserving a transmission opportunity on the communication channel and defining resource units, RUs, forming the communication channel for the nodes to transmit data to the access point sending, to the nodes, a set of legacy values of the queue contention parameters 10 and a set of MU values of the queue contention parameters, different from the set of legacy values, to configure each node when a traffic queue of the node switches between a legacy contention mode in which the respective queue contention parameters are set to the legacy values and a MU contention mode in which the respective queue contention parameters are set to the MU values.

Intellectual

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