GB2542819A - Methods and systems for reserving a transmission opportunity for a collaborative group, and managing the reserved transmission opportunity - Google Patents

Abstract

A transmission opportunity (TxOP) is granted for at least one first sub-channel of a composite channel to a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network. A method comprises, at a collaborative node, upon detecting, during the granted transmission opportunity, an end of occupancy of at least one second sub-channel different from said first sub-channel, managing the granted transmission opportunity to widen it to include said second sub-channel so that said managed transmission opportunity is for a widened set of sub channels made up of at least said first sub-channel and said second sub-channel. There is also provided a method for reserving such a transmission opportunity (TXOP) for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network. An embodiment describes use within a Wireless Local Area Network (WLAN) utilizing Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). It is particular relevant to very high throughput (VHT) WLANs where channels may be combined to create a wider channel of wider bandwidth.

Description

METHODS AND SYSTEMS FOR RESERVING A TRANSMISSION OPPORTUNITY FOR A COLLABORATIVE GROUP, AND MANAGING THE RESERVED TRANSMISSION OPPORTUNITY

FIELD OF THE INVENTION

The present invention relates generally to communication networks and more specifically to methods and devices for data communication over a communication network using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), the network being accessible by a plurality of stations.

BACKGROUND OF THE INVENTION

Wireless local area networks (WLANs), such as a wireless medium in a communication network using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), are founded on the principles of collision avoidance. Such networks may also conform to a communication standard such as a communication protocol of 802.11 type e.g. Medium Access Control (MAC).

The IEEE 802.11 MAC standard defines the way 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 so-called “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 (or stations) 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 to the 5GHz band. This is because the 2.4GHz band is deemed to be highly susceptible to interference. This allows 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 provides for 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 or 80MHz, the composite channels being made of one or more sub-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 (RTS and CTS) 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. Both primary and secondary channels may be of 20MHz. 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. Given a tree breakdown of the operating band into elementary 20MHz channels, some secondary sub-channels are named tertiary or quaternary channels.

According to the 802.11ac standard, 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 Clear Channel Assessment (CCA), i.e. detection of an availability state/status (idle or busy) of said secondary channel. A node (also referred to as a station) is allowed to use as much channel capacity (or bandwidth, i.e. of (sub-)channels in the composite channel) as is available. The constraint is that the combined channels need to be contiguous within the operating band for a node having a single antenna (or single spatial stream).

However, noise or interference even on a small portion (e.g. on one of the 20MHz channels) of the composite channel may substantially reduce the available bandwidth of the composite channel to only 40 or 20 MHz, since the resulting reserved bandwidth must meet the 20MHz, 40MHz, 80MHz or 160MHz channel configurations allowed by the standard.

The 802.11ac standard only allows a restricted number of composite channel configurations, i.e. of predefined subsets of 20MHz channel that can be reserved by the 802.11ac nodes to wireless communicate and thus transmit data. These configurations correspond to contiguous composite channels of 20, 40, 80MHz bandwidth in the case of single antenna node devices.

Consequently, the non-contiguous sub-channel or sub-channels within the operating band are not reachable for wireless communication, although they are idle and thus free.

Thus, a major deficiency of the 802.11ac standard spectral usage lies in that banded channel utilization is limited to contiguous channels for a single-antenna device at the date of medium access reservation (RTS/CTS handshake). However, the more channels used, the greater probability of co-channel operation and lower probability to have the required contiguous channels to transmit in 80MHz, especially when there is a large number of competing stations (saturated traffic scenarios, also called dense network scenarios).

As a result, this leads to an even less optimized usage of the wireless channel capacity, since the temporary occupancy of a sub-channel may waste a huge part of spectrum resources.

There is therefore a need to optimize the usage of channels (sub-channels) over time. In particular, there is a need to optimize the usage of channels (subchannels) over time in a context of single antenna devices.

SUMMARY OF THE INVENTION

The present invention has been devised to address one or more of the foregoing concerns.

In this context, according to a first aspect of the invention, there is provided a method for managing a transmission opportunity (TXOP), the transmission opportunity being granted for at least one first sub-channel of a composite channel to a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network. The method comprises, at a collaborative node of the collaborative group, upon detecting, during the granted transmission opportunity, an end of occupancy of at least one second sub-channel of the composite channel, the at least one second sub-channel being different from the first sub-channel, managing the granted transmission opportunity for the collaborative group to widen it to include the at least one second sub-channel so that the managed transmission opportunity is for a widened set of sub-channels made of at least the at least one first sub-channel and the at least one second sub-channel.

Thanks to the invention, the usage of free or partially free channels composed of at least one sub-channel in a context of single antenna devices is improved. The whole transmission bandwidth (within the current TXOP) is thus improved.

This is achieved first by requesting a reservation of a transmission opportunity for more than one collaborative device within the collaborative group on at least one sub-channel of the composite channel which is seen as idle. As a result, it avoids collaborative devices repeating the RTS/CTS sequence as they can transmit data within the reserved transmission opportunity.

This is also achieved by managing the reserved transmission opportunity for reserving at least one second sub-channel that was detected as being busy during the reservation, but that have become free (idle) after the grant of the transmission opportunity for the first sub-channel(s). Thus, as soon as such second sub-channel is detected as being available (idle) anew, the transmission opportunity may be widened to include the newly available second sub-channel. In other words, the bandwidth is increased by the second sub-channel during the on-going transmission opportunity.

Therefore, even if a sub-channel is seen as busy during the medium access reservation, the present invention allows communications over this channel when it becomes free (idle) before the end of the transmission opportunity.

Optional features of the invention are further defined in the dependent appended claims.

According to embodiments, managing the granted transmission opportunity comprises sending at least one control frame on the at least one second sub-channel, in order to add the second sub-channel to the first sub-channels reserved for the transmission opportunity.

Advantageously, there is no need to repeat the RTS/CTS sequence to reserve the second sub-channel and the additional control frame is sent without waiting for another request control frame.

According to embodiments, the control frame is a CTS or a CTS-to-self message.

These control frames allow respectively the other nodes of the community to be informed of the change of bandwidth for the reservation, for the next TDMA slot.

According to embodiments, the widened set of sub-channels is made only of contiguous sub-channels.

Banded channel utilization is thus possible on the widened set of subchannels for a single-antenna device.

According to embodiments, the method further comprises sending a notification message to indicate to the nodes of the collaborative group that the granted transmission opportunity has been managed, the managed transmission opportunity being for the widened set of sub-channels.

According to embodiments, the notification message indicates the bandwidth of the widened set of sub-channels.

Therefore, all the collaborative nodes know the new parameters of the granted transmission opportunity for the next slot, in particular the new frequency bandwidth.

According to embodiments, the notification message is a Notify Channel Width Action frame or an Operating Mode Notification frame.

According to embodiments, the collaborative group shares the medium using TDMA.

According to embodiments, the granted transmission opportunity is managed by the node of the collaborative group having the TDMA slot the closest to the detected end of occupancy.

This allows the medium to be blocked (reserved) as soon as possible, thereby minimizing the bandwidth waste.

According to embodiments, the detecting step is triggered upon determination that a number of detected request control frames sent by a sending node belonging to the collaborative group to reserve the transmission opportunity is different from a number of detected response control frames, or upon determination that a number of detected request control frames is different from a piece of information included in a header of detected request control frames sent by a sending node belonging to the collaborative group to reserve the transmission opportunity.

More specifically, nodes of the collaborative group have performed a reservation process to be granted the transmission opportunity, and the at least one second sub-channel was seen as busy by at least one of the nodes during the reservation process.

Therefore, even if one of the nodes performing the RTS/CTS handshake sees the second sub-channel as busy, this second sub-channel may be reserved by other nodes seeing this second sub-channel as idle. The bandwidth occupation is thus improved for the whole collaborative group.

According to a second aspect of the invention, there is provided a method for reserving a transmission opportunity (TXOP) for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network. The method comprises, at a sending node or at an addressee node belonging to the collaborative group: reserving, with the addressee node or the sending node, a transmission opportunity to be granted for the collaborative group for at least one first sub-channel of a composite channel seen as idle by both sending and addressee nodes while at least one second sub-channel of the composite channel is seen as busy by the sending node or the addressee node ; and upon detecting, during the granted transmission opportunity and subsequently to an end of occupancy of the at least one second sub-channel, a reception of at least one control frame from a node of the collaborative group on the at least one second sub-channel, managing the granted transmission opportunity to widen it to include the at least one second sub-channel so that the managed transmission opportunity is for a widened set of sub-channels made of at least the at least one first subchannel and the at least one second sub-channel.

According to a third aspect of the invention, there is provided a system for managing a transmission opportunity (TXOP) that has been granted for at least one first sub-channel of a composite channel to a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network, a collaborative node of the collaborative group being configured to: - perform detection, during the granted transmission opportunity, an end of occupancy of at least one second sub-channel of the composite channel, the at least one second sub-channel being different from the at least one first subchannel; - upon the detection, manage the granted transmission opportunity for the collaborative group to widen it to include the at least one second sub-channel, so that the managed transmission opportunity is for a widened set of sub-channels made of at least the at least one first sub-channel and the at least one second subchannel.

According to a fourth aspect of the invention, there is provided a system for reserving a transmission opportunity (TXOP) for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network, the collaborative group comprising a sending node, an addressee node and other nodes, the sending node and the addressee node being configured to: reserve, together, a transmission opportunity to be granted for the collaborative group for at least one first sub-channel of a composite channel seen as idle by both sending and addressee nodes while at least one second sub-channel of the composite channel is seen as busy by the sending node or the addressee node ; and manage, upon detecting, during the granted transmission opportunity and subsequently to an end of occupancy of the at least one second sub-channel, a reception of at least one control frame from a node of the collaborative group on the at least one second sub-channel, the granted transmission opportunity, to widen it to include the at least one second sub-channel, so that the managed transmission opportunity becomes for a widened set of sub-channels made of at least the at least one first sub-channel and the at least one second sub-channel.

The second, third and fourth aspects of the present invention provide advantages similar to the first aspect above-mentioned.

The invention also concerns a method for reserving a transmission opportunity for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network substantially as described herein with reference to Figures 9, 10 and 11 of the accompanying drawings, and a system for reserving a transmission opportunity for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network substantially as described herein with reference to Figures 9, 10 and 11 of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which:

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

Figure 2 is a timeline schematically illustrating a conventional communication mechanism according to the IEEE 802.11 standard; - Figure 3a illustrates the 802.11ac channel allocation that supports channel bandwidths of 20MHz, 40MHz, 80MHz or 160MHz as known in the state of the art; - Figure 3b illustrates an example of 802.11ac multichannel transmission opportunity on an 80MHz channel as known in the state of the art;

Figure 4 illustrates the fallback mechanism in an 80MHz operating band as known in the state of the art;

Figure 5 illustrates three examples of dynamic fallback to narrower channel widths in the presence of co-channel interference or noise that only affects a portion of the larger channel;

Figure 6 illustrates a collaborative group configuration, a corresponding channel allocation and timeline;

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

Figure 8 shows a schematic representation of a wireless communication device in accordance with embodiments of the present invention;

Figures 9 and 10 show exemplary communication timelines illustrating embodiments of the present invention;

Figure 11 shows, using a flowchart, steps of an algorithm for optimizing channel usage in multi-channel wireless network in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described by means of specific non-limiting exemplary embodiments and by reference to Figures.

Figure 1 illustrates a communication system in which several communication nodes exchange data frames over a radio transmission channel 100 of a wireless local area network (WLAN).The radio transmission channel 100 is defined by an operating band, for instance with a bandwidth available for the communication nodes.

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 node 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 do so, it starts a countdown backoff counter designed to expire after a number of timeslots, chosen randomly between [0, CW], CW (integer) being referred to as the Contention Window. This backoff mechanism or procedure 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, 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. However, this can be seen as a bandwidth waste if only the ACK has been corrupted but the data frames were correctly received by the receiving node.

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 handshake comprises exchanging control frames to reserve the radio medium prior to transmitting data frames during a transmission opportunity called TXOP in the 802.11 standard as described below, thus protecting data transmissions from any further collisions.

Figure 2 illustrates the behaviour of three groups of nodes during a conventional communication over the 802.11 medium: transmitting or sending or source node 20, receiving or addressee or destination node 21 and other nodes 22 not involved in the current communication.

Upon starting the backoff process 270 prior to transmitting data, a station e.g. source node 20, initializes its backoff time counter to a random value as explained above. The backoff time counter is decremented once every time slot interval 260 for as long as the radio medium is sensed idle (countdown starts from time TO (23) as shown in Figure 2).

The time unit in the 802.11 standard is the slot time called ‘aSlotTime’ parameter. This parameter is specified by the PHY (physical) layer (for example, aSlotTime is equal to 9ps for the 802.11n standard). All dedicated space durations (e.g. backoff) are multiples of this time unit.

The backoff time counter is ‘frozen’ or suspended when a transmission is detected on the radio medium channel (countdown is stopped at time T1 (24) for other nodes 22 having their backoff time counter decremented).

The countdown of the backoff time counter is resumed or reactivated when the radio medium is sensed idle anew, after a DIFS time period. This is the case for the other nodes at time T2 (25) as soon as the transmission opportunity TXOP granted to source node 20 ends and the DIFS period 28 elapses. DIFS 28 (DCF inter-frame space) thus defines the minimum waiting time for a source node before trying to transmit some data. In practice, DIFS = SIFS + 2 * aSlotTime.

When the backoff time counter reaches zero (26) at time T1, the timer expires, the corresponding node 20 will request access onto the medium in order to be granted a TXOP, and the backoff time counter is reinitialized 29 using a new random backoff value.

In the example of Figure implementing the RTS/CTS scheme, at time T1, the source node 20 that wants to transmit data frames 230 sends a special short frame or message acting as a medium access request to reserve the radio medium, instead of the data frames themselves, just after the channel has been sensed idle for a DIFS or after the backoff period as explained above.

The medium access request is known as a Request-To-Send (RTS) message or frame. The RTS frame generally includes the addresses of the source and receiving nodes ("destination 21") and the duration for which the radio medium is to be reserved for transmitting the control frames (RTS/CTS) and the data frames 230.

Upon receiving the RTS frame and if the radio medium is sensed as being idle, the receiving node 21 responds, after a SIFS time period 27 (for example, SIFS is equal to 16 με for the 802.11η standard), with a medium access response, known as a Clear-To-Send (CTS) frame. The CTS frame also includes the addresses of the source and receiving nodes, and indicates the remaining time required for transmitting the data frames, computed from the time point at which the CTS frame starts to be sent.

The CTS frame is considered by the source node 20 as an acknowledgment of its request to reserve the shared radio medium for a given time duration.

Thus, the source node 20 expects to receive a CTS frame 220 from the receiving node 21 before sending data 230 using unique and unicast (one source address and one addressee or destination address) frames.

The source node 20 is thus allowed to send the data frames 230 upon correctly receiving the CTS frame 220 and after a new SIFS time period 27.

An ACK frame 240 is sent by the receiving node 21 after having correctly received the data frames sent, after a new SIFS time period 27.

If the source node 20 does not receive the ACK 240 within a specified ACK Timeout (generally within the TXOP), or if it detects the transmission of a different frame on the radio medium, it reschedules the frame transmission according to the backoff procedure.

Since the RTS/CTS four-way handshaking mechanism 210/220 is optional in the 802.11 standard, it is possible for the source node 20 to send data frames 230 immediately upon its backoff time counter reaching zero (i.e. at time T1).

The requested time duration for transmission defined in the RTS and CTS frames defines the length of the granted transmission opportunity TXOP, and can be read by any listening node ("other nodes 22" in Figure 2) in the radio network.

To do so, each node has in memory a data structure known as the network allocation vector or NAV to store the time duration for which it is known that the medium will remain busy. When listening to a control frame (RTS 210 or CTS 220) not addressed to itself, a listening node 22 updates its NAVs (NAV 255 associated with RTS frames and NAV 250 associated with CTS) with the requested transmission time duration specified in the control frame. The listening nodes 22 thus keep in memory the time duration for which the radio medium will remain busy.

Access to the radio medium for the other nodes 22 is consequently deferred 30 by suspending 31 their associated timer and then by later resuming 32 the timer when the NAV has expired.

This prevents the listening nodes 22 from transmitting any data or control frames during that period.

It is possible that the receiving node 21 does not receive the RTS frame 210 correctly due to a message/frame collision or to fading. Even if it does receive it, the receiving node 21 may not always respond with a CTS frame 220 because, for example, its NAV is set (i.e. another node has already reserved the medium). In any case, the source node 20 enters into a new backoff procedure.

The RTS/CTS four-way handshaking mechanism is very efficient in terms of system performance, in particular concerning 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 28 (DCF inter-frame space) or when their own back-off counter has reached zero (nearly at the same time T1). 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 since it is quickly determined that no CTS response has been received.

As described above, the original IEEE 802.11 MAC always sends an acknowledgement (ACK) frame 240 after each data frame 230 received.

However, such collisions limit the optimal functioning of the radio network. As described above, simultaneous transmit attempts from a number of wireless nodes lead to collisions. The backoff procedure for the family of IEEE 802.11 standards was first introduced for the DCF mode as the basic solution for collision avoidance, and further employed by the IEEE 802.11e to solve the problem of internal collisions between enhanced distributed channel access functions (EDCAFs). In the emerging IEEE 802.11n/ac standards, the backoff procedure is still used as the fundamental approach for supporting distributed access among mobile nodes.

The rapid growth of smart mobile devices is driving mobile data usage and 802.11 WLAN proliferation, creating an ever-increasing demand for faster wireless networks to support bandwidth-intensive applications, such as web browsing and video streaming. The new IEEE 802.11ac standard is designed to meet this demand, by providing major performance improvements compared to previous 802.11 generations.

The IEEE 802.11ac standard is an emerging very high throughput (VHT) wireless local access network (WLAN) standard that can achieve physical layer (PHY) data rates of up to 7 Gbps for the 5 GHz band.

The scope of 802.11ac includes single link throughput supporting at least 500 Mbps, multiple-station throughput of at least 1 Gbps, and backward compatibility and coexistence with legacy 802.11 devices in the 5 GHz band.

Consequently, this standard is targeted at higher data rate services such as high-definition television, wireless display (high-definition multimedia interface - HDMI - replacement), wireless docking (wireless connection with peripherals), and rapid sync-and-go (quick upload/download).

In general, 802.11ac could be schematized as an extension of IEEE 802.11η in which the two basic notions of multiple-input, multiple-output (ΜΙΜΟ) and wider channel bandwidth are enhanced for greater efficiency.

Using optional ΜΙΜΟ feature, an access point AP (having multiple antennae) may communicate with several nodes simultaneously using Spatial Division Multiple Access (SDMA). SDMA multiple access scheme enables multiple streams transmitted to different receivers at the same time to share the same frequency channel. This invention is not devised for such sender device having several antennae but could be applied to it with some extra advantages.

Contrary to the 802.11η standard where each node should support up to 2 spatial streams (SSs) and 40MHz transmissions, only one spatial stream is required in 802.11ac but support for 80MHz channel bandwidth is added. One reason for such a change is that increasing the number of antennae often results in higher cost. Supporting multiple Spatial Streams (SS) implies having at least the same number of antennae (and as much reception chains behind these antennae), thus important costs.

Consequently a lot of devices available on the market could only support one SS. In the 802.11ac standard, support for only one SS is required so that devices, and especially smartphones, could be labelled as ‘802.11ac compliant’. The 80MHz mode is made mandatory as a lower cost alternative to the two SS and 40MHz configuration. Hence, the modes that utilize more than one spatial stream are now optional in the 802.11ac standard.

As a result, 802.11ac is targeting larger bandwidth transmission through multi-channel operations. The wider channel aspect will be further described with reference to Figure 3. A MAC mechanism for dynamically protecting and allocating multiple channels will be presented with reference to Figure 4.

In order to support wider channel bandwidths (Figure 3a), the IEEE 802.11ac standard introduces support for 20MHz, 40MHz, 80MHz, and 160MHz channel bandwidths, including the so-called “primary” sub-channel (here 300-3), compared to only 20MHz and 40MHz supported by the 802.11η standard. The 20MHz component channels 300-1 to 300-8 may be concatenated to form a larger communication channel.

The 160MHz channel bandwidth is composed of two 80MHz channels that may or may not be contiguous. The 80MHz and 40MHz channels are respectively composed of two adjacent (contiguous) 40MHz and 20MHz channels, respectively. The support for 40MHz and 80MHz channel bandwidths is mandatory while the support for 160MHz and 80 + 80MHz is made optional in the standard (80+80MHz means that the operating band is made of two non-frequency-contiguous wide channels having each a bandwidth of 80MHz). A multi-channel node (supporting 80MHz transmissions in the illustrated example of Figure 3b) is granted a TXOP through the enhanced distributed channel access (EDCA) mechanism on the “primary channel” (300-3). For each channel bandwidth, the 802.11ac standard designates one channel as “primary sub-channel” meaning that it is used for control of transmission on that bandwidth.

It will, however, transmit a 80MHz PPDU (PPDU means PLCP Protocol Data Unit, with PLCP for Physical Layer Convergence Procedure; basically a PPDU refers to an 802.11 physical frame) only if all other secondary channels have been idle for at least a point coordination function (PCF) inter-frame spacing (PIFS). If at least one of the secondary sub-channels has not been sensed as idle for a PIFS, then the node must either restart its backoff count, or use the obtained TXOP for 40MHz or 20MHz PPDUs.

The vertical aggregation scheme reflects the extension of the payload 230 to all channels. If there is only one collision in one of the sub-channels at a given time, the risk of having a corrupted segment of these sequences is very high despite the error-correcting decoding process. All MPDU (MAC Protocol Data Unit) frames could thus automatically be considered as incorrect. Thus in high load BSSs, a DATA packet split over multiple channels may encounter more collisions, thus wasting the channel resource.

In the description below, the words “channel·’, “20MHz channel·’ or “subchannel·’ mainly refer to the same technical feature, i.e. any channel that complies with 802.11η or older standards. “Composite channel·’ thus refers to the additional feature according to which a composite channel is made of one or more sub-channels that are contiguous within the operating band of the wireless network. In 802.11ac, the composite channels are 20MHz wide (if made of only one sub-channel) or 40MHz wide or80MHzwide or, optionally, 160MHzwide.

Relying to its multi-channel capacity, the 802.11ac standard supports enhanced protection in which the RTS/CTS handshake mechanism is modified to support static or dynamic bandwidth reservation and carry the channel bandwidth information. This is now explained with reference to Figure 4.

Bandwidth signalling is added to the RTS and CTS frames (only 20, 40, 80MHz values). For instance, a two-bit field is provided in the frame header to specify one of the 20, 40, 80 or 160MHz bandwidth values.

As mentioned above, the frame MAC header of control frames (e.g. RTS or CTS) includes the addresses of the source node (TA for transmitter address) and of the receiving node (RA for receiver address).

According to the 802.11ac standard, the TA indicates the presence of additional signalling relating to the bandwidth to be used in subsequent transmissions, by using an IEEE medium access control (MAC) individual address of the source node with an Individual/Group bit set to 1 in the frame header also.

The additional information, e.g. support for dynamic or static bandwidth operation and the channel width occupied by the frame, are signalled in the SERVICE field of RTS frames (same case for CTS frame). As mentioned, the conventional 802.11a frame format comprises a PHY preamble (including the legacy short training field (L-STF), legacy long training field (L-LTF) and legacy signal field (L-SIG)) followed by a data payload (including the said SERVICE field, user data (PSDU), pad bits and tail bits).

The additional signalling in the frame header includes a two-bit field set to indicate the bandwidth of the target composite channel for the intended transmission.

The source node thus generates the RTS frame with the two-bit field set to the appropriate value. The RTS frame is sent over the primary 20MHz sub-channel and replicated (duplicated) on each other (i.e. secondary) 20MHz sub-channel forming the target composite channel.

The receiving node replies with a CTS frame on each (sub-)channel sensed as free using for instance CCA. Both nodes follow the non-HT duplicated RTS/CTS frame handshake procedure.

As an example shown in the Figure, prior to transmission of an 80MHz data frame, the source node STA1 may transmit an RTS frame 410 configured to use the 20MHz channel bandwidth to each of the 20MHz sub-channels forming the 80MHz operating band. That is, in association with the 80MHz channel bandwidth, a total of four RTS frames are transmitted in the form of a duplicated PPDU over the four 20MHz sub-channels.

The receiving node STA2 may answer each 20MHz channel in which RTS frames transmitted from the source node STA1 have been successfully received using a CTS frame configured to use the 20MHz channel bandwidth. If the receiving node STA2 has successfully received RTS frames from the entire 80MHz bandwidth, a total of four CTS frames should be transmitted to cover the 80MHz channel bandwidth.

If the source node STA1 receives all the CTS frames relating to the 80MHz channel (i.e. if the source node STA1 receives a total of four CTS frames), a DATA 430-1 frame is transmitted using the 80MHz channel bandwidth.

It is expected that every nearby device (legacy or 802.11ac compliant) can receive an RTS frame on its primary channel. Each of these devices then sets its NAV. Before a client replies with a CTS frame, it checks if any of the channels in the 80MHz band is busy. The receiving node STA2 only replies with a CTS frame on those channels that are idle, and reports the total bandwidth of the replicated CTS frame. As with the RTS frame, the CTS frame is sent in an 802.11a (non-HT) PPDU format on the primary sub-channel and is replicated over the different 20MHz secondary subchannels that have been sensed as idle by the receiving node.

Still referring to Figure 4, a nearby node of receiving node STA2 is already transmitting before source node STA1 starts sending the RTS frames (only interfering with receiving node STA2). Therefore receiving node STA2 has to inform source node STA1 by replying CTS frames only on some of the idle channels, here two CTS frames are transmitted, and the source node STA1 uses the obtained transmission opportunity TXOP over a band of 40MHz.

The Figure 5 illustrates a scenario of dynamic fallback to narrower channel widths in the presence of co-channel interference or noise that only affects a portion of the larger channel. A channel interference is typically performed by a legacy 802.11a or 802.11η compliant node (transmitting on a 20MHz channel), so that the 802.11ac compliant node may transmit over a fraction of the original requested bandwidth: depending of which 20MHz channel (300) is busy, the channel width of resulting composite channel is reduced from 80MHz to 40MHz (cases 510 and 511), or 20MHz (case 520).

According to the 802.11ac standard, spectral usage is limited to contiguous sub-channels that are detected as idle during the medium access reservation (RTS/CTS handshake). However, the 802.11ac standard has not envisaged using the other sub-channels, i.e. the sub-channels detected as busy during the reservation, whereas they can become free later on.

This bandwidth allocation deficiency is illustrated in Figure 6, where four nodes: STA1, STA2, STA3 and STA4 (respectively 611, 612, 613 and 614) belonging to the same wireless cell 610 exchange data, but the community is disturbed by a legacy node 601 (i.e. not belonging to the collaborative group).

Thereby as illustrated in the low part of Figure 6, a sending node 611 sends a non-HT duplicated RTS frame 620 on the sub-channels it senses as free. An addressee node 612 responds with a non-HT duplicated CTS frame 621 on each available sub-channel (i.e. seen as idle/free) on which an RTS frame 620 has been sent.

Next, the sending node sends its data 622 on the TXOP reserved by the RTS/CTS handshake.

As the legacy node 601 uses the third sub-channel 300-2 (630) for its communication 625, no RTS frame has been sent on this third sub-channel and the data transmission 622 can only be performed on the 40MHz primary channel composed of contiguous sub-channels 300-3 and 300-4.

However, during data transmission 622, the legacy communication 625 may end and thus the third sub-channel 300-2 becomes free (idle). Thus, the contiguous channel used for the data transmission 622 could be enlarged or widened with the sub-channels 300-1 and 300-2 that are now available.

The present invention provides communication methods and devices for data communication over an ad-hoc wireless network, the physical medium of which being shared between a plurality of communication stations (equally well called nodes or devices). An exemplary ad-hoc wireless network is an IEEE 802.11ac network (and upper versions). But the invention applies to any wireless network where a source node (sending node) 101-107 sends data of a data stream to a receiving node (or addressee node) 101-107 using multiple sub-channels. The invention is especially suitable for wireless stations having only one Spatial Stream, labeled as ‘802.11ac compliant’. The behavior of communication nodes during a conventional communication over an 802.11 medium has been described with reference to Figures 1 to 4.

One aspect of the present invention provides for forming a group of peer nodes exchanging highly interactive data such as live video streams. Those peer nodes are also called collaborative nodes, in the sense they collaborate in order to provide an efficient channel allocation according to the method of the invention for their group communication. It is assumed that there will also be nodes outside of the collaborative group, which may be referred to as legacy (802.11) nodes. A legacy environment typically describes a situation where nodes are independent and do not interact or cooperate with each other, as opposed to the collaborative group of nodes. A peer node may request access to the shared 802.11 type medium according to the 802.11 legacy protocol, and upon grant of access, several peer nodes may communicate with one or more peer nodes according to a collaborative protocol during the reserved talk time. Thus, if the back-off count reaches zero on the primary sub-channel for one peer node among the group, said node reserves a medium access (through the conventional multiple RTS/CTS scheme of the 802.11ac standard) on a maximum number of available contiguous sub-channels in a target composite channel for the group, and lets the group communicate over the reserved aggregated subchannels during this granted 802.11 timeslot. It will become apparent that the aggregated channel obtained according to embodiments of the present invention is formed of more free sub-channels 300 than in the 802.11ac prior art.

Figure 7 schematically illustrates a communication device 700 of the radio network 100, configured to implement at least one embodiment of the present invention. The communication device 700 may be a device such as a micro-computer, a workstation or a light portable device. The communication device 700 comprises a communication bus 713 to which there are preferably connected: - a central processing unit 711, such as a microprocessor, denoted CPU; - a read only memory 707, denoted ROM, for storing computer programs for implementing the invention; - a random access memory 712, 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 702 connected to the radio communication network 100 over which digital data packets or frames are transmitted, for example a wireless communication network according to the 802.11η protocol. The data frames and aggregated frames are written from a FIFO sending memory in RAM 712 to the network interface for transmission or are read from the network interface for reception and writing into a FIFO receiving memory in RAM 712 under the control of a software application running in the CPU 711.

Optionally, the communication device 700 may also include the following components: - a data storage means 704 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention; a disk drive 705 for a disk 706, the disk drive being adapted to read data from the disk 706 or to write data onto said disk; a screen 709 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 710 or any other pointing means.

The communication device 700 can be connected to various peripherals, such as for example a digital camera 708, each being connected to an input/output card (not shown) so as to supply data to the communication device 700.

The communication bus provides communication and interoperability between the various elements included in the communication device 700 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 700 directly or by means of another element of the communication device 700.

The disk 706 can 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 be stored either in read only memory 707, on the hard disk 704 or on a removable digital medium such as for example a disk 706 as described previously. According to a variant, the executable code of the programs can be received by means of the communication network 703, via the interface 702, in order to be stored in one of the storage means of the communication device 700, such as the hard disk 704, before being executed.

The central processing unit 711 is 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 nonvolatile memory, for example on the hard disk 704 or in the read only memory 707, are transferred into the random access memory 712, 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 this embodiment, the apparatus is a programmable apparatus which uses software to implement embodiments of the invention. However, alternatively, embodiments of the present invention may be implemented in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC).

Figure 8 is a block diagram schematically illustrating the architecture of a node 700 adapted to carry out, at least partially, the invention. As illustrated, node 700 comprises a physical (PHY) layer block 803, a MAC layer block 802, and an application layer block 801.

The PHY layer block 803 (here a 802.11 standardized PHY layer) has the task of formatting and sending or receiving frames over the radio medium used 100, such as a medium access request of the RTS type to reserve a transmission slot, a medium access response of the CTS type to acknowledge reservation of a transmission slot, as well as of MAC data frames and aggregated frames to/from that radio medium.

The MAC layer block or controller 802 comprises a standard MAC 802.11 layer 804 and two additional blocks 805 to 806 that may carry out, at least partially, embodiments of the invention. The MAC layer block 802 may be implemented in software, which software is loaded into RAM 712 and executed by CPU 711.

The Group management module 805 implements the management of devices and associated streams relating to the collaborative community: typically, an identifier is maintained for a configuration set of registered devices and streams.

The Channel allocation module 806 mainly implements steps of an algorithm according to embodiments of the invention, relating to reaching all free channels during the enhanced dynamic channel allocation procedure and to enlarge the composite channel if one sub-channel becomes free during the current TXOP. In combination with Group management module 805, it supports a dynamic determination of a data stream allocation upon each a granted composite channel for the community of nodes of the invention.

Finally, the application layer block 801 implements an application that generates and receives data packets, for example data packets of a video stream. This application layer block 801 represents all the stack layers above MAC layer according to ISO standardization.

Figures 9 and 10 represent exemplary communication timelines illustrating the principle of multiple node simultaneous transmission and dynamic channel reservation during TXOP according to availability of the sub-channels.

In these embodiments, there are four nodes STA1, STA2, STA3 and STA4 forming a collaborative group sharing the medium using TDMA. The invention is not limited thereto. STA1 is assumed to be a sending node, STA2 is assumed to be an addressee node and STA3 and STA4 are called “other nodes”. All the nodes belonging to the collaborative group are able to listen to (i.e. to detect or sense) control frames that are exchanged between nodes of the collaborative group.

According to the invention, a transmission opportunity (TXOP) is reserved by first devices (sending node STA1 and addressee node STA2) belonging to the collaborative group, on at least one first sub-channel (here sub-channels 300-3 and 300-4) of a target composite channel here made of four sub-channels 300-1 to 300-4, for all the nodes belonging to the collaborative group. The first sub-channels are seen as idle by the first devices when reserving the TXOP while at least one of the first devices sees one or more of the other sub-channels as busy (here sub-channel 300-2), meaning that no RTS frame or CTS frame is sent for the one or more other subchannels. A first transmission of data may thus happen on the reserved first subchannels.

According to a principle of the present invention, one of the other subchannels seen as busy at the time of the reservation (i.e. at the RTS/CTS handshake) will become free (idle) during the first transmission on the first sub-channels. A node of the collaborative group, called second device, will detect (monitor) this newly free subchannel (called second sub-channel) and manage the reserved TXOP (previously reserved by the first devices), i.e. will reserve this second sub-channel for the whole collaborative group. Thus, upon detecting availability (i.e. end of occupancy) of at least one second sub-channel of the composite channel that is different from the reserved first sub-channel(s), during the TXOP (i.e. during a first transmission of data on said at least one first sub-channel from at least one of said devices of the collaborative group within the reserved transmission opportunity (TXOP)), the collaborative node manages the granted transmission opportunity (TXOP) for the collaborative group to widen it to include the at least one second sub-channel.

In practice, the second device will change the parameters of the TXOP in order to allow the nodes of the collaborative group to transmit data on a larger set of sub-channels than the set of first sub-channels initially reserved. Thus, the managed TXOP will be reserved for a set made of at least the first sub-channel(s) and the detected second sub-channel(s).

Further transmissions of next TDMA slots will occur in the resulting wider (managed) set of sub-channels comprising the first sub-channels initially reserved and the second sub-channel(s) newly reserved.

In the example of Figure 9, the nodes forming the collaborative group sharing the medium using TDMA are all disturbed by a legacy node performing a legacy communication 940 on the sub-channel 300-2.

The sending node STA1 and the addressee node STA2 use the standard RTS/CTS handshake over the multiple sub-channel according 802.11ac in order to reserve a TXOP for the collaborative group on the 80MHz target composite channel.

In practice, the sending node STA1 sends RTS frames on first subchannels, here the primary 40MHz composed of sub-channels 300-3 and 300-4, but not on the other sub-channels since the legacy communication 940 is detected on the sub-channel 300-2.

Each RTS frame includes bandwidth information indicating the size of the target composite channel for which the TXOP should be reserved (field called ‘BW of VHT-SIG-A portion of 802.11ac PLCP preamble according to 802.11ac protocol or in the TA field in the non-HT duplicated frame). Thus, the set of first sub-channels on which RTS frames are sent is a sub part of the target composite channel the bandwidth of which is indicated in the BW field of each RTS frame.

The addressee node STA2 then replies to RTS frames with CTS frames 920 on each first sub-channel sensed as free, here 300-3 and 300-4.

After the reception of the CTS frames, the TXOP is reserved for the first sub-channels and a communication can start using TDMA on the primary 40MHz. In the given example, a first node sends first data 950-1 in a first TDMA time slot, and then a second node sends second data 950-2 in a second TDMA time slot. For instance, first and second data transmissions 950-1 and 950-2 are between the sending node STA1 (611) and the addressee node STA2 (612). However, since the TXOP has been granted to the collaborative group, any collaborative node can perform the first and second data transmissions 950-1 and 950-2. Collaborative medium access rules known by all the collaborative nodes make it possible for each of them to determine whether or not it is time to transmit data.

Another node STA3 which is not involved in any on-going transmission can monitor the medium to try to enlarge the set of sub-channels reserved for the TXOP with at least one second sub-channel (newly free), as explained before. This enlargement results in increasing or widening the bandwidth available to the collaborative nodes during the TXOP.

In practice, the other node (here STA3) senses the medium to check if the legacy communication is over. At the end of the legacy communication 940, the node STA3 senses the medium remaining idle during a period equal to at least a SIFS period, for instance a PIFS period, and then sends a CTS frame 930 on each free subchannel (here sub-channels 300-2 and 300-1) of the target composite channel in order to reserve the medium on these sub-channels. Therefore, the TXOP is managed to be extended to all four contiguous sub-channels (i.e. including first and second subchannels originally non-available) of the target composite channel.

In embodiments, at the end of the data transmission 950-2 (on-going transmission when sending CTS frames 930), the node STA3 (613) sends a NCW frame 950-3 (for Notify Channel Width action frame) to inform the other nodes of the community of the change of bandwidth for the reservation, for the next TDMA slot. The NCW frame may be used by a non-access-point node to notify another node that it wishes to receive frames in the indicated sub-channel width. In variants (not shown), another kind of frame may be used in place of the NCW frame, for instance the Operating Mode Notification frame which describes the current channel width and number of active spatial streams.

In embodiments, several collaborative nodes are available to monitor the medium and detect that sub-channels of the target composite channel become free while data transmission on the first sub-channels 300-3 and 300-4 is running. Thus, the CTS and NCW messages may be sent by the node which will be the first to transmit, i.e. to which the next (closest) TDMA slot has been assigned based on collaborative medium access rules. This allows the medium on the sub-channels 300-2 and 300-1 to be blocked (reserved) as soon as possible, i.e. the time 960 is the minimum to avoid bandwidth waste.

In alternative embodiments, the collaborative nodes are able to send/receive data and, at the same time, monitor the medium and receive the CTS frames 930. Therefore, no NCW frame or equivalent has to be sent since in practice, the number of CTS frames 930 or the bandwidth information (field called ‘BW of VHT-SIG-A portion of 802.11ac PLCP preamble according to 802.11ac protocol or in the TA field in the non-HT duplicated frame) indicates the reserved sub-channels for the next TDMA slot.

Advantageously, more data transmissions can occur in the managed TXOP due to the additional sub-channel(s) reserved (second sub-channel). Thus, on the next TDMA slot, a node of the collaborative group (in this example, STA3) may transmit data 950-4 on an aggregated channel of 80MHz, instead of only 40MHz before implementing the sub-channel recycling of the invention

Figure 10 illustrates an alternative embodiment of Figure 9, where a hidden node problem occurs. It is recalled that the hidden node problem occurs when a node is visible from a sub-part of a group of nodes, but not from the other nodes of the group that communicate with a node able to see the hidden node. Therefore, the RTS/CTS handshake may provide partial information of the channel occupancy through the different spatial positions of the nodes.

Thus, in the given example, only some of the devices (e.g. the addressee node STA2 and the other node STA4) can see the hidden node (legacy node) while the other nodes (sending node STA1 and node STA3) do not see the hidden node.

The sending node STA1 thus sees all the sub-channels as free so it sends four replicated RTS frames 1010. In response, only two CTS frames 1020 are sent by the addressee node STA2 due to the hidden legacy node.

Consequently, there is a difference in the number of RTS frames and CTS frames that triggers the mechanism of monitoring the medium described with reference to Figure 9. It should be noted that the management of the TXOP may be triggered by a difference existing between the number of RTS frames and the number of CTS frames or between the bandwidth of the set of first sub-channels on which RTS frames are sent and the desired bandwidth indicated in the BW field of the RTS frames.

In the example of Figure 10, a first transmission of data 1050-1 occurs during a first time slot, a second transmission of data 1050-2 occurs during a second time slot and a third transmission of data 1050-3 occurs during a third slot, on the set of first sub-channels. In this example, it is assumed that STA3 is involved in the data transmission 1050-2 as the receiver of the data and thus cannot monitor the medium during this time slot. On the contrary, the node STA4 (614), that also sees the hidden node and thus the legacy transmission can monitor the medium and send the CTS frames 1030 to reserve the medium on the sub-channels 300-1 and 300-2 during a time 1060.

At the end of the third data transmission 1050-3, the node STA4 (614) sends a NCW frame 1050-4 (for Notify Channel Width action frame) to inform the other nodes of the community of the change of bandwidth for the reservation, for the next TDMA slot.

In alternative embodiments (not shown), all the nodes that can see the hidden node are able to send or receive data and, at the same time, to monitor the medium. Consequently, the blocking period will be the same as in the previous figure since STA3 will be able to send the CTS frames even if it is involved in data transmission 1050-2.

Thanks to the invention, the usage of free or partially free channels composed of at least one sub-channel is improved.

Figure 11 shows steps of an algorithm for optimizing channel usage in a multi-channel wireless network in accordance with embodiments of the present invention.

At step 1100, a TDMA TXOP on at least one first sub-channel of a composite channel is reserved by first devices of the collaborative group, typically sending node STA1 and addressee node STA2. To that end, the RTS/CTS handshake procedure of the 802.11ac standard may be used.

In practice, replicated control frames (RTS frames) indicating requests to transmit are transmitted on first sub-channels, by the sending node STA1 to the addressee node STA2. All the other nodes (STA3 and STA4) are able to detect (listen to) the control frames exchanged in the medium. According to the 802.11ac standard, the RTS frame includes bandwidth information to indicate the desired bandwidth of the data frame (field called ‘BW of VHT-SIG-A portion of 802.11ac PLCP preamble according to 802.11ac protocol or in the TA field in the non-HT duplicated frame), thereby defining a target composite channel.

Based on techniques such as described in the 802.11ac standard i.e., energy detection, preamble detection and/or plural channel decoders, the sending node STA1 can determine which of the communication channels are idle for sending the RTS frames, and applies a fallback mechanism if one of the component subchannel is detected as busy (the bandwidth indication keeping the value of whole targeted bandwidth).

In practice, any node of the collaborative group may determine that the TXOP will be shared according to the invention by the analysis of the source address and/or the receiver address of the RTS frames. To do so, receiving nodes STA2, STA3, STA4 belonging to the collaborative group have to check the MAC source address and/or MAC receiver address of RTS frame in order to verify that the source address and/or receiver address belongs to the group, thus knowing whether the current medium access is a collaborative access.

Also, any receiving node STA2, STA3, STA4 may determine the availability (busy or free/idle) of the sub-channels. The channel availability may be based on which sub-channels the CTS frames from the addressee STA2 are sent, on the number of replicated RTS frames detected, and/or on the original bandwidth indication located in the RTS header.

Therefore, all nodes of the group know the availability of the first subchannels for communication by the collaborative nodes during the granted TXOP. Collaborative medium access rules defining how the collaborative nodes share the reserved sub-channels using TDMA may be known by all the collaborative nodes.

At step 1101, a first transmission is performed on the reserved first subchannels during TDMA slot(s).

At step 1102, a second device checks if a sub-channel (second subchannel within the target composite channel) that was detected as busy at step 1100 is now free. For instance, as described with reference to Figures 9 and 10, a legacy communication ends and thus the medium becomes free on this second sub-channel.

In practice, the second device is not involved in the first transmission of step 1101. In other embodiments, the second device is involved in the transmission of step 1101 but it is able to listen to the medium at the same time.

At step 1103, the second device reserves the second sub-channel detected at step 1102 by sending CTS frames to sending node STA1 on the sub-channel 300-2 released by the legacy node and also on the sub-channel contiguous to this released sub-channel 300-1 which becomes available for the transmission due to the need for contiguity introduced by the 802.11ac standard in the reservation of a composite channel. The available bandwidth for the current TXOP is thus increased.

In this step, a notification of channel switch (NWC 950-3 and 1050-4 respectively in Figures 9 and 10) is sent over the sub-channels 300-4 and 300-3 to inform the whole community that the next TDMA slot will occur on a wider set of reserved sub-channels. Typically, this notification is sent by the second node just before a TDMA slot that is assigned to it according to the collaborative medium access rules.

At step 1104, a second transmission occurs on the wider set of reserved sub-channels (first sub-channel(s) and second sub-channel(s) newly reserved) during the next TDMA slots of the granted TXOP.

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 which lie within the scope of the present invention will be apparent to a person skilled in the art. 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 as determined by the appended claims. In particular different features from different embodiments may be interchanged, where appropriate.

Claims (16)

1. A method for managing a transmission opportunity (TXOP), the transmission opportunity being granted for at least one first sub-channel of a composite channel to a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network, the method comprising, at a collaborative node of the collaborative group: upon detecting, during the granted transmission opportunity, an end of occupancy of at least one second sub-channel of the composite channel, said at least one second sub-channel being different from said first sub-channel, managing the granted transmission opportunity for the collaborative group to widen it to include said at least one second sub-channel so that said managed transmission opportunity is for a widened set of sub-channels made of at least said at least one first sub-channel and said at least one second sub-channel.

2. The method according to claim 1, wherein managing the granted transmission opportunity comprises sending at least one control frame on said at least one second sub-channel, in order to add the second sub-channel to the first subchannels reserved for the transmission opportunity.

3. The method according to claim 2, wherein said control frame is a CTS or a CTS-to-self message.

4. The method according to any one of claims 1 to 3, wherein said widened set of sub-channels is made only of contiguous sub-channels.

5. The method according to any one of claims 1 to 4, further comprising sending a notification message to indicate to the nodes of the collaborative group that the granted transmission opportunity has been managed, said managed transmission opportunity being for said widened set of sub-channels.

6. The method according to claim 5, wherein the notification message indicates the bandwidth of the widened set of sub-channels.

7. The method according to claim 5 or 6, wherein said notification message is a Notify Channel Width Action frame or an Operating Mode Notification frame.

8. The method according to any one of claims 1 to 7, wherein the collaborative group shares the medium using TDMA.

9. The method according to claim 8, wherein said granted transmission opportunity is managed by the node of the collaborative group having the TDMA slot the closest to the detected end of occupancy.

10. The method according to any one of claims 1 to 9, wherein the detecting step is triggered upon determination that a number of detected request control frames sent by a sending node belonging to the collaborative group to reserve the transmission opportunity is different from a number of detected response control frames, or upon determination that a number of detected request control frames is different from a piece of information included in a header of detected request control frames sent by a sending node belonging to the collaborative group to reserve the transmission opportunity.

11. The method according to any one of claims 1 to 10, wherein nodes of the collaborative group have performed a reservation process to be granted the transmission opportunity, and wherein said at least one second sub-channel was seen as busy by at least one of said nodes during the reservation process.

12. A method for reserving a transmission opportunity (TXOP) for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network, the method comprising, at a sending node or at an addressee node belonging to the collaborative group: reserving, with said addressee node or said sending node, a transmission opportunity to be granted for the collaborative group for at least one first subchannel of a composite channel seen as idle by both sending and addressee nodes while at least one second sub-channel of the composite channel is seen as busy by the sending node or the addressee node ; and upon detecting, during the granted transmission opportunity and subsequently to an end of occupancy of the at least one second sub-channel, a reception of at least one control frame from a node of the collaborative group on the at least one second sub-channel, managing the granted transmission opportunity to widen it to include said at least one second sub-channel so that the managed transmission opportunity is for a widened set of sub-channels made of at least said at least one first sub-channel and said at least one second sub-channel.

13. A system for managing a transmission opportunity (TXOP) that has been granted for at least one first sub-channel of a composite channel to a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network, a collaborative node of the collaborative group being configured to: perform detection, during the granted transmission opportunity, an end of occupancy of at least one second sub-channel of the composite channel, said at least one second sub-channel being different from said at least one first subchannel; upon said detection, manage the granted transmission opportunity for the collaborative group to widen it to include said at least one second sub-channel, so that said managed transmission opportunity is for a widened set of sub-channels made of at least said at least one first sub-channel and said at least one second sub-channel.

14. A system for reserving a transmission opportunity (TXOP) for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network, said collaborative group comprising a sending node, an addressee node and other nodes, said sending node and said addressee node being configured to: - reserve, together, a transmission opportunity to be granted for the collaborative group for at least one first sub-channel of a composite channel seen as idle by both sending and addressee nodes while at least one second sub-channel of the composite channel is seen as busy by the sending node or the addressee node ; and manage, upon detecting, during the granted transmission opportunity and subsequently to an end of occupancy of the at least one second sub-channel, a reception of at least one control frame from a node of the collaborative group on the at least one second sub-channel, the granted transmission opportunity, to widen it to include said at least one second sub-channel, so that the managed transmission opportunity becomes for a widened set of sub-channels made of at least said at least one first sub-channel and said at least one second sub-channel.

15. A method for reserving a transmission opportunity for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network substantially as described herein with reference to Figures 9, 10 and 11 of the accompanying drawings.

16. A system for reserving a transmission opportunity for a plurality of collaborative nodes belonging to a collaborative group in a wireless communication network substantially as described herein with reference to Figures 9, 10 and 11 of the accompanying drawings.