GB2516280A - Method and device for data communication over a shared communication network - Google Patents

Abstract

The present invention relates generally to communication networks and more specifically to methods and devices for data communication over a communication network having a medium shared between a plurality of communication nodes. The method comprises: obtaining an estimated frequency at which a second communication node is expected to request an access to the medium to send data to an addressee node; requesting, based on the estimated frequency and prior to the second communication node, an access to the medium to be granted a transmission opportunity 60; and allocating a first transmission period 63 of the granted transmission opportunity, to the second communication node for the latter to send the data to the addressee node. In that way, the first node anticipates requests for medium access from the second node, thus reducing risks of collision.

Description

METHOD AND DEVICE FOR DATA COMMUNICATION OVER A SHARED

COMMUNICATION NETWORK

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 having a medium shared between a plurality of communication nodes.

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 (CSMAJCA), 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) relies on a contention-based mechanism based on the so-called "Carrier Sense Multiple Access with Collision Avoidance" (CSMAICA) technique.

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

Figure 1 illustrates a communication system in which several communication nodes exchange data packets over a radio transmission channel 100 of a wireless local area network (WLAN).

Access to the shared radio medium to send data packets 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. The virtual carrier sensing is achieved by transmitting control packets to reserve the medium prior to transmission of data packets.

Then after, through the physical mechanism, a transmitting node first attempts to sense a medium that has been idle for at least one DIFS (standing for Distributed lnterFrame Spacing) time period, before transmitting data packets.

However, if it is sensed that the shared radio medium is busy during the DIFS period, the transmitting node still waits 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 transmitting node may send the data packets.

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

Collision Avoidance mechanism of CSMAICA thus provides positive acknowledgement (ACK) of the sent data packets by the receiving node in case of successful packet reception, to notify the transmitting node that no corruption of the sent data packets occurred.

The ACK is transmitted at the end of reception of the data packet, immediately after a period of time called Short InterErame Space (SIES).

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

To improve the Collision Avoidance efficiency of CSMNCA, 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 packets to reserve the radio medium prior to transmitting data packets during a transmission opportunity called TXOF in the 802.11 standard as described below, thus protecting data transmissions from any further collisions.

The backoff procedure is one of the first processes to be implemented in the communication nodes.

Figure 2 illustrates the behaviour of three groups of nodes during the back-off procedure: transmitting or source node 20, receiving or addressee or destination node 21 and other nodes 22.

Upon starting the backoff process 270 prior to transmitting data! a station e.g. transmitting 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 so long as the radio medium is sensed idle (count down is starting from TO, 23 as shown in the Figure).

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 802.11 n standard). All dedicated space durations (e.g. backoff) are multiple of this time unit.

The communication nodes forming the same 802.11 cell of the radio network have quasi-synchronous clock to ensure a consistent number of time slots 260 to be expired simultaneously by all communication nodes, e.g. during a back-off countdown procedure.

The backoff time counter is frozen' or suspended when a transmission is detected on the radio medium channel (countdown is stopped at Ti, 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 T2, 25 as soon as the transmission opportunity TXOP granted to transmitting node 20 ends and the DIES period 28 lapses.

When the backoff time counter reaches zero 26 at Ti, the timer expires, the corresponding node 20 is granted a TXOP, and the backoff time counter is reinitialized 29 using a new random backoff value.

In the example of the Figure implementing the RTSICTS scheme, at Ti, the transmitting node 20 that wants to transmit data packets 230 sends a special short frame or message acting as a medium access request to reserve the radio medium, instead of the data packets themselves, just after the channel has been sensed idle for a DIES 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 address of the receiving node ("destination 21") and the duration for which the radio medium is to be reserved for transmitting the control packets (RTS/CTS) and the data packets 330.

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

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

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

The transmitting node 20 is thus allowed to send the data packets 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 packets sent, after a new SIFS time period 27.

If the transmitting node 20 does not receive the ACK 240 within a specified ACK Timeout, or if it detects the transmission ot a different packet on the radio medium, it reschedules the packet 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 transmitting node 20 to send data packets 330 immediately upon having its backoff time counter reaching zero (i.e. at Ti).

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 be busy. When listening to a control packet (RTS 210 or CTS 220) not addressed to itself, a listening node 22 updates its NAys (NAV 255 associated with RTS and NAV 250 associated with CTS) with the requested transmission time duration specified in the control packet. The listening node 22 thus keeps 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 packets during that period.

It is possible that the destination 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 destination node 21 may not always respond with a CTS 220 because, for example, its NAV is set (i.e. another node has already reserved the medium). In any case, the transmitting 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 with regard to large packets 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) packets are transmitted within the same time slot after a DIFS or when their own back-off counter has reached zero nearly at the same time Ti). If both transmitting nodes use the RTS/CTS mechanism, this collision can only occur for the RTS frames. Fortunately, such collision is early detected by the transmitting nodes since it is quickly determined that no CTS response is received.

However, such collisions are limiting the optimal functioning of the radio network. This is an aim of the present invention to reduce such collisions to improve radio medium access.

In an illustrative example, a collision occurring when a communication node has high priority data to send is liable to detrimentally postpone the sending of such high priority data.

In another illustrative example, the inventors have contemplated the case where collaborative communication nodes share the radio medium using a collaborative radio medium access scheme. An example of such collaborative mechanism is disclosed in publication GB2490963 and provides efficient radio medium access with full collision avoidance within the community or group of collaborative nodes.

However, in this situation, any legacy node outside the community may collide with collaborative nodes upon requesting radio medium access.

In any case, the communication nodes, including the collaborative nodes, may have interest to further reduce collision, thus improving collision avoidance.

US 7 808 941 publication provides dynamic and adaptive control of radio medium access via a polling-based centralized medium access mode and a distributed contention-based medium access mode. Although collisions are reduced, this is due to the central role of a coordinator (access point). Collision avoidance would not be improved in a fully distributed medium access mode.

A collision domain also exists in wired networks having a shared medium, thus resulting in similar difficulties.

The present invention has been devised to address at least one of the foregoing concerns.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a method for data communication in a communication network having a medium shared between a plurality of communication nodes, the method comprising, at a first communication node: obtaining an estimated frequency at which a second communication node is expected (or intended) to lequest, or contend, an access to the medium to send data to an addressee node. This is an estimate of a medium access frequency of the second communication node to send data to the addressee node; requesting, based on the estimated frequency and prior to the second communication node, an access to the medium to be granted a transmission opportunity; allocating a first transmission period of the granted transmission opportunity, to the second communication node for the latter to send the data to the addressee node.

This data communication scheme further reduces risks of collision due to a medium access request by a node desiring to send data (the second node).

This is achieved by another node (the first node) anticipating any second node's medium access requests, which first node being granted a transmission opportunity to allocate granted transmission timeslots to the second node for the latter to send its data. Anticipation is achieved by requesting a medium access at a frequency adapted compared to the access request frequency by the second node.

The first communication node thus requests access to the medium prior to a time at which the second communication node is intended to request such access.

Such anticipation prevents the second node to request medium accesses (more generally reduces medium accesses triggered by the second node itself), thus resulting in the absence of collision (more generally in less risks of collision) due to the second node. This is particularly interesting for a group of collaborative nodes that implements a collision free medium access scheme within the community. and that would like to prevent one or more legacy nodes to induce collisions by using the scheme of the invention.

One skilled in the art knows that frequency and time are closely related. In particular, the frequency is the reciprocal of the time period. In this context, the invention also applies when an estimated time at which the second node is expected to request the access is obtained. This is because from the estimated time (compared to the present time) it may be inferred an estimated time period and thus an estimated frequency.

Particular issues to provide an optimal scheme of the invention are detailed below, e.g. to be able to estimate the frequency at which the second node is intended to send a RTS frame in a radio or wireless network, to allocate an optimal first transmission period to avoid the second node to request an additional medium access, etc. Correspondingly, according to a second aspect of the invention, there is provided a communication device in a communication network having a medium shared between a plurality of communication nodes, comprising: a request frequency estimator configured to obtain an estimated frequency at which a second communication node is expected to request, or contend, an access to the medium to send data to an addressee node; a medium access requesting module configured to request, based on the estimated frequency and prior to the second communication node, an access to the medium for the communication device to be granted a transmission opportunity; a communication timeslot allocator configured to allocate a first transmission period of the granted transmission opportunity to the second communication node for the latter to send the data to the addressee node.

According to a third aspect of the invention, there is provided a communication network system having a medium and a plurality of communication nodes sharing the medium, at least one of which being as defined above, wherein the second and addressee nodes are nodes of the plurality of communication nodes.

The communication device and system have the same advantages as the above-defined method.

Further features of embodiments of the invention are defined in the dependent appended claims and are explained below in terms of method features.

According to one embodiment, the first communication node allocating the first transmission period of its granted transmission opportunity to the second communication node is the addressee node to which the second communication node sends the data. This provision is because the addressee node is often aware of a data stream that the second node wants to send to it, for example because a communication session has been setup. In that situation where the first node knows characteristics of the data stream, the above provision ensures the first node to take control on the second node by efficiently anticipating medium accesses from the latter.

In a variant regarding the above-defined collaborative community, the first communication node is one collaborative node different from the addressee node, among collaborative nodes, including the addressee node, that share a collaborative medium access scheme to access the medium, and the second communication node is a legacy node external to the group of collaborative nodes. As already mentioned above, this configuration helps the collaborative nodes to prevent or substantially reduce any risk of collision due to a legacy node requesting access to the medium.

One skilled in the art would directly understand that the invention also apply to the case where the first communication node is a collaborative node and is the addressee node. This is detailed in the following description.

In particular, obtaining an estimated frequency comprises receiving, from the addressee node, traffic specifications relating to a data stream from the second and legacy communication node to the addressee node; and using the received traffic specifications to obtain an estimated frequency at which the second and legacy communication node requests an access to the medium to send data of the data stream to the addressee node. This provision makes it possible for the first node different from the addressee node to be aware of a data stream between two nodes that is about to require medium accesses and network bandwidth. Therefore, the first node is able to efficiently anticipate legacy node's medium access requests and to allocate the required communication timeslots (first communication period) to the legacy node to avoid legacy node's explicit requests (e.g. RTS) to the medium.

In embodiments, obtaining an estimated frequency comprises determining a minimum Service Interval defining the minimum allowed time between two transmissions for the data to be sent to the addressee node. This may derives from traffic specifications relating to the data stream. The minimum Service Interval thus defines a minimum period at which the second and legacy node will try to access the medium. The first node will then try to access the medium with a lower period, i.e. a higher frequency.

In other embodiments, upon detecting a medium access request from the second communication node and a subsequent sending of data from the second communication node during a period having a transmission time length, increasing the first transmission period allocated to the second communication node in a next transmission opportunity granted to the first communication node based on the transmission time length (for example by the transmission time length). This provision ensures the scheme according to the invention to dynamically adapt the allocated transmission period to the second node's needs with a view of preventing the second node to directly request access to the medium.

In other embodiments, upon detecting a medium access request from the second communication node, reducing a size of a contention window based on which the first communication node accesses the medium. Again, this provision aims at dynamically adapting the allocated transmission period (here in frequency) to the second node's needs. This is because, in the situation detected, the allocated transmission period appears to occur too rarely given the contention window size. The contention window size is thus reduced to provide more frequent transmission periods.

In particular, reducing the contention window size is performed upon detecting a medium access request from the second communication node while the second communication node does not use the entire allocated first transmission period to send data. This is to provide more frequent transmission times to the second node since its direct accesses to the medium seem not to be due to a lack of transmission duration but to a too rare access.

According to a particular feature, the contention window size is reduced iteratively each time a medium access request from the second communication node is detected, until no new medium access request from the second communication node is further detected. This is an iterative process to smoothly find the appropriate trade-off between the second node's bandwidth and access needs and the interest for the other nodes to avoid medium access request from the second node.

In some embodiments, upon detecting low use by the second communication node of the allocated first transmission period to send data, increasing a size of a contention window based on which the first communication node accesses the medium. This provision reduces risks of collisions in the network while the first node keeps the lead on when the second node actually is provided transmission time duration to send data. Such CW size increasing should be performed in case the first node no longer detects a medium access request from the second node. As a result, the first node requests medium access at a lower frequency.

In embodiments, requesting a medium access comprises using a medium access scheme based on a contention window defining a frequency of medium access request greater than the estimated frequency. This is because the first communication node will thus be granted regularly an access to the network at worst at the end of the contention window and before the second node. The first communication node will therefore provide (allocate) communication time duration to the second node before the latter tries to access the medium.

In other embodiments, requesting a medium access comprises sending, by the first communication node over the communication network, a request-to-send frame that includes, as receiver address, an address of the second communication node. Using the address of the second node as receiver address of RTS sent by the first node, while the first node has generally no data to send to the second node (in fact this is the second node that has data to send to the addressee node which may be different from the first node) is an original way to control medium access from the second node. The above provision is to make it possible to exchange control data between the first and second nodes with a view of providing the allocated transmission period to the second node.

In particular, the first communication node uses address spoofing to send the request-to-send frame with an address of the addressee node as source address.

Again, using the address of the addressee node (which will receive the data from the second node) to send the RTS, while the first node may be different from the addressee node), is an original way to force the second node to accept exchange of data (intended to the addressee node) with the first node. Address spoofing is a very efficient way to obtain such result.

In embodiments, allocating, to the second communication node, a first transmission period of the transmission opportunity granted to the first communication node comprises sending a frame transferring rights on the first transmission period so that the second communication node takes control for data transmission over the communication network during the first transmission period.

In case of a radio or wireless network compliant to the IEEE 802.lln standard, this may be performed by sending a frame including an enabled Reverse Direction Grant flag according to the IEEE 802.11 n standard. The RDG flag is indeed a flag transferring rights to send data since it allows the node receiving the RDG flag to send data during the TXOP granted to the node sending the RDG flag.

These provisions thus efficiently contiol the allocation of tiansmission period to the second communication node. In particular, this is combined with the above use of the address of the addressee node in the RTS, because in that situation the second node believes that it is exchanging with the addiessee node, thus not refusing to send the data.

Accoiding to a particular feature, the second communication node sends data during the allocated first transmission period using the Reverse Direction protocol according to the IEEE 802.lln standard. This is an efficient way to take advantage of the RDG flag in order to use the allocated first period.

According to another particular feature, the transferring rights frame further includes a data field defining the time length (or duration) of the allocated first transmission period. This is for the second communication node, using generally the Reverse Direction protocol, to know how many data it can send.

According to yet another particular feature, the first transmission period allocated to the second communication node staits after a SIFS inteival following the transfeiring rights frame. This is to be compliant with the IEEE 802.11 standard.

In embodiments, a second transmission period of the granted tiansmission opportunity is used by the first node to send data to at least one other communication node of the communication network. In particular this may be to a collaborative node as intioduced above.

This provision shows an optimal situation of the invention where the first and second nodes have both communication time durations to send data to different destination or addressee nodes within the same TXOP.

In other embodiments, a second transmission peiiod of the tiansmission opportunity is shared between active nodes of a set of collaborative nodes that share a collaborative medium access scheme to access the communication network, for the active nodes to send data to other nodes of the communication network. This may be possible for example by providing a time division multiplexing access among the collaborative nodes within the second transmission period. This provision improves the use of the reserved transmission period and thus reduces any waste of reserved time.

In paiticulai embodiments relating to the communication network system, the addressee node is one collaborative node among collaborative nodes thaI share a collaborative medium access scheme to access the medium; the second communication node is a legacy node external to the group of collaborative nodes; and the addressee node is configured to send, to at least one other collaborative node, data stream specifications relating to the data to be sent by the legacy node to the addressee node.

In that situation, the addressee node and the at least one other collaborative node are able to implement simultaneously the data communication scheme of the invention, meaning that each time one of these nodes accesses the medium, it allocates a first transmission period of the granted transmission opportunity to the legacy node for the latter to send the data to the addressee node. This increases the transmission time duration provided to the legacy node to send its data.

In particular, the addressee node is configured to send the data stream specifications to a new other collaborative node to ask the latter to allocate an additional first transmission period to the legacy node, each time the addressee node determines a new medium access request from the legacy node. This is because such request means that the first transmission periods currently allocated to the legacy node by the collaborative nodes enrolled to implement the scheme of the invention are not sufficient for the legacy node to send all the data. Of course such approach of progressively enrolling new collaborative nodes may be combined with mechanisms enabling the allocated first transmission periods to be made longer (up to a maximum length for first transmission periods).

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 communication device of a communication network having a medium shared between a plurality of communication nodes, causes the communication device to perform the steps of: obtaining an estimated frequency at which a second communication node is expected (or intended) to request, or contend, an access to the medium to send data to an addressee node; requesting, prior to the second communication node, an access to the medium, to be granted a transmission opportunity; allocating a first transmission period of the granted transmission opportunity to the second communication node for the latter to send the data to the addressee node.

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 method, device and system, in particular that of improving collision avoidance.

Another aspect of the invention relates to a method for data communication in a communication network having a medium shared between a plurality of communication nodes substantially as herein described with reference to, and as shown in, Figures 6, 7 and 8; Figures 9, 10, 11 and 12 of the accompanying drawings.

Yet another aspect of the invention relates to a communication device in a communication network having a medium shared between a plurality of communication nodes substantially as herein described with reference to, and as shown in, Figure 5 of the accompanying drawings.

At least parts of the method 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, micro-code, etc.) or an embodiment combining software and hardware aspects which 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, for example a tangible carrier medium or a transient carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, 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 RE signal.

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 the conventional RTS/CTS exchange mechanism according to 802.11 and the backoff procedure; Figure 3 is a timeline schematically illustrating a backoff-based collaborative medium access scheme shared by a group of collaborative nodes; Figure 4 is a block diagram illustrating components of a communication device in which embodiments of the invention may be implemented; Figure 5 illustrates function blocks of the same communication device; Figure 6 is a timeline schematically illustrating first embodiments of the invention; Figure 7 is a flowchart illustrating steps of a processing at an addressee node in the scheme of Figure 6 when detecting a data stream from a source node; Figure 8 is a flowchart illustrating steps of a processing at an addressee node in the scheme of Figure 6 upon expiry of its backoff counter; Figure 9 is a timeline schematically illustrating second embodiments of the invention relying on collaborative nodes; Figure 10 is a flowchart illustrating steps of a processing at a collaborative and addressee node in the scheme of Figure 9 when detecting a data stream from a souice node; Figure 11 is a flowchart illustrating steps of a processing at a collaborative node different from the addressee node in the scheme of Figure 9 when receiving data

stream specification from the addressee node; and

Figure 12 is a flowchart illustrating steps of a processing at any collaborative node in the scheme of Figure 9 upon expiry of its backoff counter;

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention provides communication methods, devices and systems for data communication over a communication network, the physical medium of which being shared between a plurality of communication nodes or devices.

The invention is particularly suitable for radio or wireless networks which may face collisions more often than wired networks. However, the invention can also apply with wired networks facing such collisions. The description below concentrates on radio networks.

As introduced above, a goal of the data communication scheme according to the invention in radio networks is to reduce collision between communication nodes when a DIFS lapses or when several nodes have their backoff counter expiring within the same time slot. Indeed, a collision may appear for a single node involved in several data communications, when source nodes of these communications collide upon trying each simultaneously to be granted transmission timeslots in direction to the receiver node.

This is because the nodes have no mean to know the communication timeslot which is going to be requested by and granted to other nodes.

A communication device according to the invention achieves this goal by anticipating the access to the radio medium by another node to offer transmission time duration to the other node. To do so, it obtains an estimated frequency at which the other node is expected/intended to request medium access, and then it requests the radio medium access prior to the other node and allocates or "subleases" part of the transmission opportunity that is granted to it, to the other node for the latter to send data and empty its sending memory (FIFO). As a consequence of emptying its sending memory, the other node will not request access to the radio medium for a while.

The communication device thus controls the access of the other node to the radio medium.

This may be implemented as soon as one communication device wishes to control the access to the network. Indeed, by anticipating accesses by the other nodes, it avoids radio medium access requests from the other nodes and thus avoids collision.

A better functioning of the radio network is therefore obtained.

While the invention may apply to any node of a radio network, the following description sometimes focuses on a radio network having collaborative nodes that shaie a collaborative radio medium access scheme to access the radio medium, thus providing free collision within the collaborative group. In that situation, a legacy" node external to the group of collaborative nodes may wish to send data to one of the collaborative nodes. With known techniques to access the medium, the legacy node is liable to collide with a collaborative node while accessing the radio medium. The invention intends to overcome such drawback.

The man skilled in the art would be able to adapt these collaborative-related parts of the description below to the case where no collaborative community or group is implemented. Similarly, the RTS/CTS mechanism involved in the examples below remains optional as in the IEEE 802.11 standard.

In the example of a 802.11-based wireless communication network implementing CSMAICA mechanism with RTSICTS exchange as shown in Figures 1 and 2, several communication nodes 101, 102, 103, 104, 105, 106, 107 exchange data packets through a transmission channel 100 that may drop or corrupt the data packets.

The communication nodes can be divided into two groups: a first group of Nb! nodes 101 to 103 (where i is an integer between 1 and 3) implementing the conventional 802.11 standard but not the invention (they are named legacy nodes since each of them is independent and does not interact or cooperate with each other), and a second group of Nc] nodes 104 to 107 (wherej is an integer between 1 and 4) implementing the 802.11 standard and the mechanisms of the invention to control radio medium access by the legacy nodes Nbi.

For the sake of illustration, all data exchanges between nodes of the communication system, that is to say nodes Nc, and nodes Nb,, are managed through the standardized 802.lln MAC/PH'! layers.

The problem addressed by the present invention arises when a legacy node (Nbi node, e.g. either 101 to 103) communicates (i.e. sends data) in direction to a No] node that wishes to reduce risks of message collision (for example because it belongs to a synchronized group of collaborative nodes and wants to avoid degrading the collision free mechanism for radio medium access within the collaborative group).

In a particular and optional embodiment, the communication nodes Nc] 104 to 107 form a collaborative group of nodes that share a collaborative radio medium access scheme to access the radio medium.

Collaborative radio medium access consists in a distributed mechanism providing a distinct backoff count for each collaborative node of the group, in order that no backoff time count duplication occurs. It results that collision avoidance in medium access is provided within the collaborative group.

An additional feature of the collaborative group is the sharing of granted transmission slot: once the backoff count reduces to zero for one collaborative node, that collaborative node reserves medium access (through classical RTS/CTS scheme) for the whole group and may let the group share this granted 802.11 timeslot between all or part of the collaborative nodes (those which have data to be sent). As a result, this collaborative sub-network allows low jitter and regular access onto the radio medium for the collaborative nodes, which is extremely useful for conveying data of real-time acquisition applications.

Figure 3 schematically illustrates the mechanisms within the collaborative group to provide a free collision collaborative radio medium access scheme. An example of such scheme is described in publication GB2490963.

To ensure free collision within the collaborative group, the collaborative nodes use different backoff values, the expiries of which thus occurring at different times. More precisely, collaborative radio medium access is performed by watching the "random values" used to initialize the backoff time counters among the collaborative group, in order that no backoff time count duplication occurs.

As an example, the collaborative node may implement the same pseudo-random generator algorithm using the node IDs to generate the backoff value. In this situation, each collaborative node is able to know the current backoff value of each collaborative node. It will use the pseudo-random generator algorithm once or several times until generating an own backoff value that is different from the current backoff values (being decremented according to the conventional backoff procedure).

As a variant, each collaborative node may transmit periodically its backoff value to the other collaborative nodes.

Each collaborative node thus has a virtual local image storing the current backoff time counter values of the other collaborative nodes.

In Figure 3, the backoff slots 260 have been numbered. The idea of the collaborative scheme is to position the expiry of the backoff counters of the collaborative nodes in different backoff slots: as example, by considering an absolute scale of backoff slots, the current backoff slot being number n 300, the collaborative scheme 330 would select n+3' 310 and n÷1 0' 320 for two distinct collaborative nodes.

Each collaborative node can follow the decrementing of the backoff time values of the other collaborative nodes and can predict any attempt to access the wireless medium by such other nodes. Since it has a different backoff time value, the collaborative node will access the network in a distinct backoff slot to the other nodes, avoiding any access collision among the group of collaborative nodes.

In the example of Figure 3, the collaborative node having its backoff counter expiring at backoff slot n+3' sends data during the transmission slot 230. Of course the RTS/CTS mechanism may be implemented prior to the transmission slot 230.

In a variant, the transmission slot 230 may be shared with all or part of the collaborative nodes. For example it may be decided to split 230 into a plurality of elementary transmission time slots, each being allocated to one collaborative node, using TDMA. The order for allocation can be the order of node IDs known by each collaborative node.

Figure 4 schematically illustrates a communication device 400 of the radio network 100, configured to implement at least one embodiment of the present invention when it is one of the nodes Ncj. The communication device 400 may be a device such as a micro-computer, a workstation or a light portable device. The communication device 400 comprises a communication bus 413 to which there are preferably connected: -a central processing unit 411, such as a microprocessor, denoted CPU; -a read only memory 407, denoted ROM, for storing computer programs for implementing the invention; -a random access memory 412, 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 402 connected to the radio communication network 100 over which digital data packets are transmitted, for example a wireless communication network according to the 802.lln protocol. The data packets are written from a FIFO sending memory in RAM 412 to the network interface for transmission or are read from the network interface for reception and write into a FIFO receiving memory in RAM 412 under the control of a software application running in the CPU 411.

Optionally, the communication device 400 may also include the following components: -a data storage means 404 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention; -a disk drive 405 for a disk 406, the disk drive being adapted to read data from the disk 406 or to write data onto said disk; -a screen 409 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 410 or any other pointing means.

The communication device 400 can be connected to various peripherals, such as for example a digital camera 408, each being connected to an input/output card (not shown) so as to supply data to the communication device 400.

The communication bus provides communication and interoperability between the various elements included in the communication device 400 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 400 directly or by means of another element of the communication device 400.

The disk 406 can be replaced by any information medium such as for example a compact disk (CD-ROM), rewritable or not, a ZIP disk 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 407, on the hard disk 404 or on a removable digital medium such as for example a disk 406 as described previously. According to a variant, the executable code of the programs can be received by means of the communication network 403, via the interface 402, in order to be stored in one of the storage means of the communication device 400, such as the hard disk 404, before being executed.

The central processing unit 411 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 non-volatile memory, for example on the hard disk 404 or in the read only memory 407, are transferred into the random access memory 412, 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 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 5 is a block diagram schematically illustrating the architecture of a node 400 adapted to carry out, at least partially, the invention, for example a node Nc1 of Figure 1. As illustrated, node 400 comprises a physical (PHY) layer block 503, a MAC layer block 502, and an application layer block 501.

The PHY layer block 503 (here a 802.11 standardized PHY layer) has the task of formatting and sending or receiving data packets 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 data packets to/from that radio medium.

The MAC layer block 502 comprises a standard MAC 802.11 layer 504 and four additional blocks 505 to 508 for carrying out, at least partially, the invention. The MAC layer block 502 may be implemented in software, which software is loaded into RAM 312 and executed by CPU 311.

According to a particular embodiment, the node data transmission block 505 performs the task of exchanging data packets with the PHY layer 503 and the application layer 501.

The RTSICTS module 506 has the task of managing Request-To-Send (RTS) and Clear-To-Send (CTS) frames as described below according to the invention.

The Legacy source node management module 507 is contigured to implement part of the invention, in particular in handling specifications of data stream from a legacy source node Nbi to obtain an estimated frequency at which the legacy souice node is expected/intended to request (or contend) an access to the radio medium to send data to an addressee node, either the communication device 400 or another collaborative node with which the communication device 400 shares a collaborative radio medium access scheme as introduced above.

The backoff management block 508 has the task of managing the backoff value used by the node in a collision avoidance scheme. In embodiments, it manages the collaborative backoff procedure as introduced above.

The Legacy source node management module 507 works together with the backoff management block 508 to request, prior to the legacy source node, an access to the radio medium for the communication device 400 to be granted a transmission opportunity TXOP. As described below, this may be done by selecting a contention window (defining the maximum backoff value) function of the estimated frequency to ensure the access request to occur before an access request by the legacy source node.

Upon having the TXOP granted, the communication device 400 can allocate a first transmission period of the granted transmission opportunity, to the legacy source node for the latter to send the data to the addressee node.

Finally, the application layer block 501 implements an application that generates and receives data packets, for example data packets of a video stream.

Figures 6 to 8 illustrate a first implementation of the invention, considering two communication nodes: legacy source node Nbi and addressee or destination node Ncj implementing the mechanism of the invention.

Figure 6 is a tirrieline showing the transmission of messages and data on the network by the two nodes Nb! and Ncj when the latter implements the invention.

Figures 7 and 8 are flowcharts illustrating steps performed at destination node Ncj.

Figure 7 illustrates the processing performed by addressee node Nc] upon detecting a data stream from the legacy source node Nb!.

Step 700 consists in detecting such new data stream from the legacy source node Nbi that is addressed to node Nc].

Known techniques make it possible to perform direct discovery between devices to provide proximity-based services such as peer to peer (P2P) communication between communication devices.

As an example, Wi-Fi Alliance (WFA) is evaluating enhancements needed to enable proximity based services and service discovery. Recently, a Wi-Fi display (WFD) standard has been newly defined based on a requirement to transmit audio/video (AV) data while satisfying high quality and low latency. The WFD standard considers AV data transmission and control via a user input in a source device.

Typical connection cycle for such P2P communication is the following: (1) perform a device and service discovery process of proximal devices.

This is similar to scanning for device and service notification messages from proximal devices; (2) perform an authentication; (3) perform association and application level session setup.

The addressee node, here Nc], may be aware of the specifications of upcoming data streaming either or both at pre-association P2P step (previous step (1)) or session setup step (3).

As an example, according to WFD standard, first, the device and service discovery at OSI Layer 2 (L2) is performed between a source node Nbi and an addressee node Nc] supporting WED. Then, an [2 secure setup is performed, followed by a OSI-Layer 3 WED discovery, in which detailed device information and service information is exchanged. An L3 Audio-Video (AV) session is then established: for example an RTSP (real-time streaming protocol) is used for an AV control session, an RTP is used for an AV data session, and a high-bandwidth digital content protection (HDCP) 2.0 is used for content protection.

AV data is converted into a data unit meeting the requirements of MPEG2 IS or H.264, and is transmitted from the source node Nbi to the addressee node Nc] via the RTP session. As the node Nci is the recipient of the L3 AV session, it is fully

aware of the AV stream specifications.

This is step 700 of Figure 7.

Alternative protocols allowing stream specification discovery include: -Wi-Ei protected setup (WPS) protocol offering discovery of services, audio/video profile prior to 051-Layer 2 connection; -OSI-Layer 3 discovery protocols, such as UFnF, Bonjour; -Session Description Eile (SDE) of a session description protocol (SDP, REC2327), which can have been downloaded by addressee node Nc] though HTTP or RTSP protocols at the session start or prior announced via a session announcement protocol (SAP).

Once the new data stream from the legacy source node Nbi has been identified, the main information (specifications) about the data can be analyzed in terms of: -Mean Data Rate, which specifies, in bits per second, what the expected throughput is for the data stream; -Nominal MSDU Size, which specifies the expected packet size; -Delay bound, which specifies the maximum allowed delay for successful packet delivery; and -Minimum Service Interval (minSl), which specifies, in milli-seconds (msec), the minimum allowed time between two TXOPs. If required, the minimum service interval can be determined by the addressee node Nc] as the nominal MSDU size/mean data rate. This is a minimum period at which the source node Nbi is expected/intended to request access to the radio medium. It corresponds to a maximum frequency, which is an estimated frequency, for such requests.

Based on these parameters, the addressee node Nc] creates a TSPEC message defining that data stream to be received, i.e. a "virtual" stream (virtual means the stream is not being sourced locally, but at the remote legacy source node). Such TSPEC message may be used to exchange stream information with other collaborative nodes in the community-based embodiments described below with reference to Figures 9 to 12.

These parameters make it possible for the addressee node Nc] to efficiently request access to the network and allocate appropriate transmission time duration (see references 63 and 230A in Figure 6) to the legacy source node Nb!. To do so, the addressee node Ncj has to compute the length (or duration) 63 of the transmission timeslot 230A to allocate, referred to TXOP(230A). It also has to use a backoff counter that expires before a time estimated at which the legacy source node Nbi is intended to access the network. An idea of the invention is for the addressee node Ncj to request access to the radio medium at a higher frequency than NBj's frequency which is higher or equal to lIminSI. As the backoff value is selected from [0, CW], this is the contention window CW that defines a frequency for access requests by the addressee node Nc].

As a result, the embodiment of the invention provides computation of CW size based

on stream specifications.

This is step 701.

First the length 63 of the transmission timeslot 230A to allocate must be computed.

As an embodiment, the Simple Scheduler as defined in IEEE 802.lle standard for HCCA can be used in order to compute 63TX0P(230A) in such a way the AV data stream from the legacy source node Nb/is conveyed at each considered service interval rn/aS!. In variants, other schedulers may be considered.

To obtain the length 63TX0P(230A) of transmission timeslot to allocate, the addressee node Nc] first calculates the number of MSDUs that arrive at the mean data rate during the minSi: N = SI * Mean_Data_Rate / Nominal MSDU size Then, the addressee node Nc] calculates the duration or length 63 of TXOP(230A) as the time needed to transmit N frames at physical rate R of the radio network: 63 = TXOF(230A) = N * Nominal MSDU Size / R. Then, the contention window based on which the backoff procedure is performed can be computed.

As an exemplary approach, the addressee node Ncj determines the minimum number of largest transmissions that can occur before the minS! deadline: CW = rninSl I TXOP Limit where TXOPLimit is the maximum data transmission duration allowable according to the IEEE 802.11 standard.

TXOP_Limit ensures CW size to be less than mins!. In other words, the addressee node Nc] is liable to request access to the radio medium at a higher frequency than the legacy source node NbL In case the above calculations cannot be performed (e.g. because specification data is missing), the addressee node Nc] can use the maximum size of contention window CW as defined in IEEE 802.11 that is associated with the stream category corresponding to the data stream from the legacy source node Nbi (e.g. audio-video data).

This is the end of step 701.

The obtained values are theoretical given the data stream specifications.

However, the radio network can face perturbations or fading or interference or collision phenomenon in such a way the above values are not fully adapted to avoid radio medium access from the legacy source node Nbi.

This is why the process of Figure 7 also includes monitoring steps to dynamically adapt the duration or length 63 of TXOP(230A) and the CW size (steps 730, 731).

In details, later on, during stream communication, the addressee node Ncj monitors (step 730) activity over the radio medium from the legacy source node Nbi, in particular transmission activity relating to the considered AV stream. This is to detect whether the legacy source node Nbi still perform medium access.

Two mechanisms can be implemented to face remaining medium accesses by the legacy source node NW, to update the stream specifications and/or the duration 63 of TXOP(230A) and/or the contention window size (step 731). This is to provide more bandwidth to the legacy source node Nbi.

First, upon detecting a radio medium access request from the legacy source node Nbi and a subsequent sending of data from the second communication node during a period having a transmission time length, the addressee node Nc] increases the duration or length 63 of TXOP(230A) allocated to the legacy source node Nbi in a next transmission opportunity granted to the the addressee node Nc] based on the transmission time length! for example by the whole transmission time length or by a part of it (e.g. 20% or 50%).

In that way, the legacy source node Nbi is allocated a longer transmission duration 63 and thus more bandwidth.

Then, for example it a maximum duration is already allocated to the legacy source node Nbi in each transmission opportunity TXOP, upon detecting a radio medium access request from the legacy source node Nb!, the addressee node Ncj reduces the size of its contention window. Again, this is to provide more often transmission timeslot 230A with duration 63 to the legacy source node Nbi and thus bandwidth more regularly. This process makes it possible to adjust an estimation of the frequency at which the legacy source node requests an access to the radio medium, and then to update the frequency at which the addressee node requests such access to anticipate legacy source node's requests.

Although the first mechanism may be implemented as long as the duration or length 63 of TXOP(230A) has not reached the maximum duration and then the second mechanism is implemented to provide more frequent TXOP(230A) , the two mechanisms can be implemented independently and/or in a reverse order.

In an embodiment, the reduction of CW size is implemented upon detecting a radio medium access request from the legacy source node Nbi while the latter does not use the entire allocated TXOP(230A) to send data.

Note that feature, the contention window size may be reduced iteratively each time a radio medium access request from the legacy source node Nb! is detected (possibly while the latter does not use the entire allocated first transmission period to send data), until no new radio medium access request from the legacy source node Nbi is further detected. This is to iteratively suppress all radio medium accesses by the legacy source node.

Reversely, a mechanism can also be implemented to update contention window size in case no more medium access by the legacy source node Nbi is detected (step 731).

In particular, upon detecting low use by the legacy source node Nb! of the allocated TXOP(230A) to send data, the addressee node Nc] may increase the size of its contention window. This is to decrease risks of collisions.

"low use" may be defined as a ratio of the allocated TXOP(230A), for example lower than 75%. That means that if more than 75% of the allocated TXOP(230A) is used while no new medium access is requested by the legacy source node Nbi, the allocation scheme is in a steady state.

It results that the CW size is directly linked to the medium access periodicity for Nci node, which is most probably lesser than the legacy source's one.

Since any backoff value randomly generated for the addressee node Nc] is obtained from a range defined by zero and the current contention window (OW) (value = [0; CW]) according to the 802.11 standard, the CW is directly linked with the medium access periodicity for the addressee node Nc], which is most probably lesser than the legacy source node's one given the mechanisms above.

Note that the duration or length 63 of TXOP(230A) does not necessarily need to be decreased in such situation (of course even if it may be), because the addressee node Ncj is able to detect ends of TXOP(230A) (thanks to the following SIES interval 27) and can use the remaining transmission time in the granted transmission opportunity TXOP 60.

Figure 8 illustrates the processing performed by the addressee node Ncj upon detecting expiry of its backoff counter, which has been randomly selected from [0, OW] where OW is as defined in above steps 701 and/or 731. The goal for the addressee node Ncj is to poll the legacy source node Nb/ in advance to the legacy source node's data transmission (to avoid contention by the legacy node which could generate collisions), in such a way a transmission opportunity TXOP 60 granted to the addressee node Ncj includes a first transmission period or part 230A dedicated for data transmission from the legacy source node Nbi.

In the context of the invention, the addressee node Ncj requests, prior to the legacy node, an access to the radio medium to be granted a transmission opportunity; and allocates a first transmission period TXOP(230A) of the granted transmission opportunity TXOP, to the legacy source node Nbj for the latter to send the data to the addressee node.

At step 800, the addressee node Nc] sends a request-to-send (RTS) frame (210 in Figure 6) that includes, as receiver address, an address of the legacy source node Nbi, e.g. a MAC address, even if the addressee node Ncj also wants to send data to another node. The RTS frame 210 also includes a duration field greater than the duration or length 63 of TXOP(230A) (calculated at step 701 and/or 731) plus a duration for the addressee node Ncj to send data during time slot 230B of Figure 6.

The addressee node Nc] is able to determine the duration for transmission slot 230B based on the filling level of an internal MAC TX FIFO (transmission FIFO memory at the MAC level).

In detail with reterence to Figure 6, the duration specified in RTS frame 210 is defined to prevent transmission by other nodes during the time slot 60 period, i.e. during the requested transmission opportunity TXOP. RTS frame's duration field contains a value in microseconds of time needed to transmit CTS 220, polling frame 630, plus legacy source node's data 230A, plus addressee node Ncfs data 23DB to other destination nodes, plus the time for the SIFS intervals between each of these transmissions.

Therefore, the network allocation vector (NAV) of the other nodes will be set accordingly to cover the whole duration of the transmission opportunity TXOP 50 when receiving the RTS frame.

At step 801, the addressee node Nc] waits for a medium access acknowledgment, i.e. a CTS message 220 from the legacy source node Nb].

Of course, where the optional RTS/CTS mechanism is not implemented, the process starts at step 802.

At step 802, the addressee node Nc] sends a frame 630 transferring rights on the TXOP(230A) so that the legacy source node Nbj takes control for data transmission over the radio network during the TXOP(230A).

Frame 630 or "polling frame" starts a first period 62 of the TXOP 60 which is specific to the invention since it includes the mechanisms making it possible for the addressee node Nc] to control the legacy source node Nb] and to allocate it a transmission timeslot 230A of duration 63.

To comply with 802.11 standard, polling frame 630 may be a Null Data frame or a QoS-Null Data frame according to the standard. (QoS)Null Data frame is a frame meant to contain no data but flag information (header with empty payload).

Such (OoS)Null Data frame is used in particular when the addressee node Nc] has no data to send to the legacy source node Nb] (which is often the case).

Of course, in case the addressee node Nc] has data to send to the legacy source node Nb], the former can send a conventional Data frame as polling frame 630.

What is important in the present embodiments is that the polling frame 630 makes it possible to transfer rights on transmission time slot 230A to another node, here the legacy source node Nb].

To do so, embodiments illustrated in Figure 6 provides that the polling frame 630 includes control information 650.

For example, the control information 650 indicates the end of communication by the addressee node Nc] and the subleasing or allocation of a time slot (typically duration 63 which is less than the access time granted to Nd through TXOP) for the source legacy node Nbi. The control information 650 thus transfers the lead on communication to the source legacy node Nbi.

In one embodiment, the polling frame 630 including the control information 650 takes the form of a short frame according to the "reverse direction" (RD) feature of IEEE 802.lln standard.

As known, the 802.lln RD protocol aims at providing more efficiently transfer data between two 802.11 nodes during a TXOP by eliminating the need for either device to initiate a new data transfer. RD data flow is very useful for traffic streams that have a bi-directional nature, for example like VoIP or TOP traffic (the latter because of backward TCP acknowledgment flow).

With RD protocol, once the transmitting node has obtained a TXOP, it may essentially grant permission to the other node to send information back during the TXOP. This requires that two roles be defined: RD initiator and RD responder.

The RD initiator sends its permission to the RD responder using a Reverse Direction Grant (RDG) in the RDG!More PPDU field of the HT Control field in the MAO frame. This bit is used by the RD initiator for granting permission (RDG) to the RD responder, and it is used by the RD responder to signal whether or not it is sending more frames immediately following the one just received (More PPDU).

Back to the example of Figure 6, the control information 650 may thus comprise an enabled Reverse Direction Grant flag according to the IEEE 802.lln standard, i.e. a RDG flag set to 1.

In addition, it comprises a data field defining the time length 63 of the allocated TXOP(230A). This is to notify the legacy source node Nbj of for how long it can send data.

Upon transmitting the polling frame 630, the addressee node Nd goes to step 803 waiting for data from the legacy source node Nb] and thus receiving the data.

Meanwhile, the legacy source node Nb] receives the polling frame 630 with the RDG flag set to 1. In response, it takes the lead on data transmission and sends, to the addressee node Nd, as much data stored in its MAC TX FIFO as possible given the allocated TXOP(230A), i.e. given the duration 63 specified in the polling frame 630.

The legacy source node Nb] sends the data during the allocated TXOP(230A) using the Reverse Direction protocol according to the IEEE 802.lln standard.

Next to step 803, the addressee node Nci detects end of data transmission from the legacy source node Nb], e.g. by detecting a SIFS interval 27.

At step 804, if the addressee node Nci has data to send to other nodes, it uses the remaining time of granted TXOP 60 to send such data. This defines a second transmission period 230B.

Next, at step 805, the addressee node Nd computes a new backoff value randomly based on the OW obtained at step 701 and/or 731 (if updated).

Figure 6 clearly shows that the TXOP is mainly split into two periods: a first period 62 dedicated to allocating transmission time slot to the legacy source node Nb] that the addressee node Nd wants to control; and a second period 61 which corresponds to the conventional transmission time slot granted to the addressee node Nc! for its own data transmissions. Due to the polling frame 630, the allocated transmission time slot 230A is less than the whole reserved time by the addressee node in the TXOP.

This scheme supports a standard MAO frame addressing to the legacy souice node (i.e. the legacy source node Nbj is able to interpret the communication slot 62) and a standard MAC frame addressing distinct destination nodes (such that the legacy source node Nb] interprets the second period 61 as a non-activity period).

Figures 9 to 12 illustrate a second implementation of the invention, considering a group of collaborative nodes Nc] as introduced above and at least one legacy source node Nbi that wants to send data to a addressee node which is one of the collaborative nodes.

All or part of the collaborative nodes Nc] implement the mechanism of the invention, including at least the collaborative and addressee node.

In case only the collaborative and addressee node implements the mechanism of the invention, the process as described above with reference to Figures 6 to 8 applies which is similar to the process below for that specific situation.

Therefore, the description below focuses on the case where several collaborative nodes implements the invention thus collaboratively controlling medium access by the legacy source node Nbi and allocating transmission time to the latter.

Figure 9 is a tinieline showing the transmission of messages and data on the network involving a group of collaborative nodes Nc] and a legacy source node Nbi.

Figures 10 to 12 are flowcharts illustrating steps performed at the collaborative nodes Nc].

Figure 10 illustrates the processing performed by the collaborative and addressee node Nc] upon detecting a data stream from the legacy source node Nb!.

The process is the same as in Figure 7 with steps 700, 701, 730 and 731, except that, following step 701, the addressee node Ncj notifies, at step 1020, the other collaborative nodes implementing the invention of the characteristics of the admitted stream flow from the legacy source node NbL For example it is done by sending the TSPEC message as created above to the other collaborative nodes. As example, the TSPEC message is performed by using ADDTS framing specified in 802.lle Quality of Service standard.

When sending such TSPEC message, the addressee node also defines the data stream as a virtual source" to indicate that it has to behave in such a way to allocate transmission time to the legacy source node.

Note that, thanks to this sending, the collaborative nodes receiving it know the MAC address of the addressee node Ncj and the MAC address of the legacy source node NbL In a variant, the addressee node Nc] can directly send the calculated duration or length 63 of TXOP(230A) and the CW size and the MAC address of the legacy source node Nb!, to the other collaborative nodes.

Also note that the sending of the TSPEC message can be progressive to progressively enroll new other collaborative nodes in the allocation process, as the allocated transmission time slot appears insufficient for the legacy source node Nb] to send all the data in due time.

For example, if the monitoring phase (730) shows that sufficient time is offered to poll (i.e. is allocated to) the legacy source node, only the addressee node Nd is considered for allocating transmission time slot 230A163. That means the allocation scheme only occur upon expiry of the backoff counter in the addressee node NcL As defined above, the length of the allocated transmission time slot 230A/63 may be increased depending on the legacy source node's activity on the network, up to a maximum value.

Once the maximum value is reached and if the allocated transmission time slot 230A/63 seems not sufficient, the addressee node may want to enroll one or more other collaborative nodes to allocate additional transmission time through TXOP granted for these other collaborative nodes. The addressee node thus sends the TSPEC message to a new collaborative node which will sublease a transmission time slot 230A of its own granted TXOP.

Progressively, the addressee node may enroll new collaborative nodes.

Once all the possible collaborative nodes have been enrolled, the adjustment (reduction) of the CW size may be performed as defined above (if legacy node Nb] is still active on the network with new tries to access the medium). Since the CW may be shared by all the collaborative nodes, such reduction will result in a more frequent medium access by all the collaborative nodes, thus liable to increase risks of collision with legacy nodes.

Similar to Figure 7, the process of Figure 10 makes it possible for the addressee node Nc] to dynamically adapt the duration or length 63 of TXOP(230A) and the CW size (steps 730, 731), depending on the activity of the legacy source node Nbi on the network.

Figure 11 illustrates the processing performed by any collaborative node different from the addressee node Ncj that implements the mechanism of the invention.

It is recalled here that during the process of Figure 10, the addressee node Nc] sends a TSPEC message to such collaborative node.

At step 1100, the collaborative node receives the TSPEC message or the like. A step 701 may be provided at this stage of the process to compute the duration or length 63 of TXOP(230A) and the OW size.

In other words, the collaborative node receives, from the addressee node, traffic specifications relating to a data stream from the legacy source node to the addressee node; and uses the received traffic specifications to obtain an estimated frequency at which the legacy source node is expected/intended to request an access to the radio medium to send data of the data stream to the addressee node.

This is for the collaborative know to be aware of the requirement of the transmission time slot 62 to be subleased to the legacy source node Nb].

Then, the collaborative node is managed in term of backoff synchronization management inside the collaborative group according to the requirements of the data stream specification (length 63 of TXOF(230A) and CW size). The collaborative medium access scheme may still be implemented considering the CW size to define different backoff values for the collaborative nodes.

This is why the collaborative node is attached a virtual' stream (step 1101), as if it would be the emitter of the data stream from the legacy source node Nb]: the collaborative node acts as a deputy of the legacy source node for medium access.

Then above-defined steps 730 and 731 are performed, meaning that same process behavior is performed among all the collaborative nodes but in a fully distributed way.

Figure 12 illustrates the processing performed by any collaborative node Nc] (including the addressee node) upon detecting (step 1210) expiry of its backoff counter, which has been randomly selected from [0, OW] where CW is as defined in above steps 701 and/or 731. Again, the goal here is for the enrolled collaborative nodes Nc] to poll the legacy source node Nbi in advance to the legacy source node's data transmission (to avoid contention by the legacy node which could generate collisions), and then to allocate part of their granted transmission opportunity TXOP 60 to the legacy source node Nbi for itto send data.

Upon detecting expiry of its backoff counter, the collaborative node first checks whether it belongs to an active collaborative group (step 1220). If not, the collaborative node uses the conventional 802.11 protocol to request access to the medium (step 1230), which will result in a unicast communication targeted to a legacy communication node.

If it belongs to an active collaborative group, the collaborative node uses either the collaborative communication scheme as introduced above (without the invention) or the communication scheme according to the invention as illustrated in Figure 9.

To distinguish between the two cases, step 1240 consists in determining whether the collaborative node is attached a virtual' stream (outcome of step 1101), meaning that it has to handle with a data stream from the legacy source node Nb].

In case no virtual' stream exists, the collaborative node selects the collaborative medium access scheme (without the invention) to be granted new TXOP (step 1260), meaning that its own MAC address is selected as source address for a RTS message 210 and the MAC address of a destination collaborative node is selected as destination address in the same RTS message 210. Note that a CW different from the dynamically adjusted CW used for the purpose of the invention may be used.

In case such a virtual' stream exists, the communication scheme of Figure 9 is applied.

However, since the addressee node and another collaborative node operate slightly in a different way, a second test 1241 makes it possible to determine whether the collaborative node is the addressee node of the data stream defined in the virtual' stream.

In case, the collaborative node is the addressee node (test 1241 positive), the collaborative and addressee node selects its own MAC address to be used as source address of the RTS frame 210 to be sent (similar to Figure 8), and selects the MAC address of legacy source node Nb] (known from the received TSPEC message) as the destination MAC address of the RTS frame. This is step 1251.

In case the collaborative node is not the addressee node (test 1241 negative), the collaborative node selects the MAC address of the addressee node corresponding to the virtual' stream (known by receiving the TSPEC message) to be used as source address of the RTS frame 210 to be sent, and selects the MAC address of legacy source node Nbj (known from the received TSPEC message) as the destination MAC address of the RTS frame 210. That means that the collaborative node has to masquerade virtual source's MAC address in the RTS frame 210 when issuing the latter. This is done at step 1250.

This may be done by using address spoofing to send the request-to-send frame with an address of the addressee node as source address.

As known, although a MAC address is intended to be a permanent and globally unique identification, it is possible to change it on most modern hardware. As example, changing MAC addresses is necessary in network virtualization. It can also be used in the process of exploiting security vulnerabilities. This is called MAC spoofing.

After steps 1250, 1251 or 1260, the collaborative node prepares the RTS frame 210 using the selected source and destination MAC addresses. Then the medium access is performed at step 800 by sending the prepared RTS frame 210.

Note that upon receiving this RTS frame 210, any other collaborative node is able to detect the source MAC address used in RTS frame. This makes it possible for the addressee node (when detecting its own MAC address) to be aware that a transmission time slot is being allocated to the legacy source node by other collaborative nodes.

As it transpires from a comparison between Figures 6 and 9, the same first period 62 is provided in the communication scheme according to the two embodiments.

In particular, the polling frame 630 makes it possible to allocate a transmission time slot 230A to the legacy source node Nb].

In the embodiment of Figure 9 which relies on collaborative nodes, the second transmission period 230B/61 of the transmission opportunity TXOP 60 is shaied between the collaborative nodes (possibly between only active nodes of the community, i.e. those having data to send), for them to send data to other collaborative nodes of the radio network. This is illustrated through the several elementary transmission time slots 940 separated by xIFS intervals. The elementary transmission time slots 940 can be assigned to the (active) collaborative nodes according to an increasing order of their MAC address.

That means that the collaborative node that is granted access to the communication medium, allocates a part of its access time (61) to other collaborative nodes. In the example of Figure 9, the access time slot 61 is shared into four timeslots Si, 52, 53 and S4 (940) allowing data exchange between four collaborative nodes Nc Nc2, Nc3 and Nc4. The timeslots 940 may have different durations and/or different distributions The xIFS 950 is a guard time interval between timeslots 940. The maximum limit for the guard time intervals is shorter than a SIFS so as not to let any IEEE 802.11 legacy node detects a change of medium talker during the TXOP 61 duration. Thus time slot period 61 is interpreted as a single data period, like data frame 230, by any legacy node.

In the embodiments of Figures 9 to 12 (involving collaborative nodes), since several collaborative nodes contribute to allocate transmission time to the legacy source node Nb], the idea is to determine a schedule of contentions for the collaborative nodes for a transmission opportunity to be granted, in advance to the legacy source node's contention.

The above embodiments show that the invention provides transparent insertion of a legacy source node inside the collaborative (backoff-synchronized sub-network) nodes. This makes it possible to benefit from this collaborative collision avoidance scheme for any detected legacy source node. This is particularly advantageous to avoid decreasing collision avoidance efficiency of a collaborative community sharing a collaborative radio medium access scheme.

Furthermore, the above implementations keep compliance with IEEE 802.11 CSMA'CA standard. Therefore, the invention is easy to implement within standard environment.

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 (27)

1. CLAIMS1. A method for data communication in a communication network having a medium shared between a plurality of communication nodes, the method comprising, at a first communication node: obtaining an estimated frequency at which a second communication node is expected to request an access to the medium to send data to an addressee node; requesting, based on the estimated frequency and prior to the second communication node, an access to the medium to be granted a transmission opportunity; allocating a first transmission period of the granted transmission opportunity, to the second communication node for the latter to send the data to the addressee node.
2. 2. The method of Claim 1, wherein the first communication node allocating the first transmission period of its granted transmission opportunity to the second communication node is the addressee node to which the second communication node sends the data.
3. 3. The method of Claim 1, wherein the first communication node is one collaborative node different from the addressee node, among collaborative nodes, including the addressee node, that share a collaborative medium access scheme to access the medium, and the second communication node is a legacy node external to the group of collaborative nodes.
4. 4. The method of Claim 3, wherein obtaining an estimated frequency comprises receiving, from the addressee node, traffic specifications relating to a data stream from the second and legacy communication node to the addressee node; and using the received traffic specifications to obtain an estimated frequency at which the second and legacy communication node requests an access to the medium to send data of the data stream to the addressee node.
5. 5. The method of Claim 1, wherein obtaining an estimated frequency comprises determining a minimum Service Interval defining the minimum allowed time between two transmissions for the data to be sent to the addressee node.
6. 6. The method of Claim 1, wherein upon detecting a medium access request from the second communication node and a subsequent sending of data from the second communication node during a period having a transmission time length, increasing the first transmission period allocated to the second communication node in a next transmission opportunity granted to the first communication node based on the transmission time length.
7. 7. The method of Claim 1, wherein upon detecting a medium access request from the second communication node, reducing a size of a contention window based on which the first communication node accesses the medium.
8. 8. The method of Claim 7, wherein reducing the contention window size is performed upon detecting a medium access request from the second communication node while the second communication node does not use the entire allocated first transmission period to send data.
9. 9. The method of Claim 7, wherein the contention window size is reduced iteratively each time a medium access request from the second communication node is detected, until no new medium access request from the second communication node is further detected.
10. 10. The method of Claim 1, wherein upon detecting low use by the second communication node of the allocated first transmission period to send data, increasing a size of a contention window based on which the first communication node accesses the medium.
11. 11. The method of Claim 1, wherein requesting a medium access comprises using a medium access scheme based on a contention window defining a frequency of medium access request greater than the estimated frequency.
12. 12. The method of Claim 1 or 11, wherein requesting a medium access comprises sending, by the first communication node over the communication network, a request-to-send frame that includes, as receiver address, an address of the second communication node.
13. 13. The method of Claim 12, wherein the first communication node uses address spoofing to send the request-to-send frame with an address of the addressee node as source address.
14. 14. The method of Claim 1, wherein allocating, to the second communication node, a first transmission period of the transmission opportunity granted to the first communication node comprises sending a frame transferring rights on the first transmission period so that the second communication node takes control for data transmission over the communication network during the first transmission period.
15. 15. The method of Claim 14, wherein sending a frame transferring rights comprises sending a frame including an enabled Reverse Direction Grant flag according to the IEEE 802.lln standard.
16. 16. The method of Claim 14, wherein the second communication node sends data during the allocated first transmission period using the Reverse Direction protocol according to the IEEE 802.lln standard.
17. 17. The method of Claim 14, wherein the transferring rights frame further includes a data field defining the time length of the allocated first transmission period.
18. 18. The method of Claim 14, wherein the first transmission period allocated to the second communication node starts after a SIFS interval following the transferring rights frame.
19. 19. The method of Claim 1, wherein a second transmission period of the granted transmission opportunity is used by the first node to send data to at least one other communication node of the communication network.
20. 20. The method of Claim 1, wherein a second transmission period of the transmission opportunity is shared between active nodes of a set of collaborative nodes that share a collaborative medium access scheme to access the communication network, for the active nodes to send data to other nodes of the communication network.
21. 21. A communication device in a communication network having a medium shared between a plurality of communication nodes, comprising: a request frequency estimator configured to obtain an estimated frequency at which a second communication node is expected to request an access to the medium to send data to an addressee node; a medium access requesting module configured to request, based on the estimated frequency and prior to the second communication node, an access to the medium for the communication device to be granted a transmission opportunity; a communication timeslot allocator configured to allocate a first transmission period of the granted transmission opportunity to the second communication node for the latter to send the data to the addressee node.
22. 22. A communication network system having a medium and a plurality of communication nodes sharing the medium, at least one of which, including the addressee node, being the communication device according to Claim 21, wherein the second and addressee nodes are nodes of the plurality of communication nodes.
23. 23. The communication network system of Claim 22, wherein the addressee node is one collaborative node among collaborative nodes that share a collaborative medium access scheme to access the medium; the second communication node is a legacy node external to the group of collaborative nodes: and the addressee node is configured to send, to at least one other collaborative node, data stream specifications relating to the data to be sent by the legacy node to the addressee node.
24. 24. The communication network system of Claim 22, wherein the addressee node is configured to send the data stream specifications to a new other collaborative node to ask the latter to allocate an additional first transmission period to the legacy node, each time the addressee node determines a new medium access request from the legacy node.
25. 25. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a communication device of a communication network having a medium shared between a plurality of communication nodes, causes the communication device to perform the steps of: obtaining an estimated frequency at which a second communication node is expected to request an access to the medium to send data to an addressee node; requesting, prior to the second communication node, an access to the medium, to be granted a transmission opportunity; allocating a first transmission period of the granted transmission opportunity to the second communication node for the latter to send the data to the addressee node.
26. 26. A method for data communication in a communication network having a medium shared between a plurality of communication nodes substantially as herein described with reference to, and as shown in, Figures 6, 7 and 8; Figures 9, 10, 11 and 12 of the accompanying drawings.
27. 27. A communication device in a communication network having a medium shaied between a plurality of communication nodes substantially as herein described with reference to, and as shown in, Figure 5 of the accompanying drawings.