WO2010076481A1 - Method for transmitting data by a wireless network unit and unit - Google Patents

Method for transmitting data by a wireless network unit and unit Download PDF

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Publication number
WO2010076481A1
WO2010076481A1 PCT/FR2009/052535 FR2009052535W WO2010076481A1 WO 2010076481 A1 WO2010076481 A1 WO 2010076481A1 FR 2009052535 W FR2009052535 W FR 2009052535W WO 2010076481 A1 WO2010076481 A1 WO 2010076481A1
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Prior art keywords
preamble
entity
method
access point
transmitting data
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PCT/FR2009/052535
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French (fr)
Inventor
Laurent Cariou
Philippe Christin
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France Telecom
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Priority to FR0858610 priority Critical
Priority to FR0858610 priority
Application filed by France Telecom filed Critical France Telecom
Publication of WO2010076481A1 publication Critical patent/WO2010076481A1/en

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00Arrangements for synchronising receiver with transmitter
    • H04L7/04Speed or phase control by synchronisation signals
    • H04L7/041Speed or phase control by synchronisation signals using special codes as synchronising signal
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W74/00Wireless channel access, e.g. scheduled or random access
    • H04W74/08Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
    • H04W74/0833Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure
    • H04W74/0841Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure with collision treatment
    • H04W74/085Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure with collision treatment collision avoidance

Abstract

The invention relates to the transmission of blocks of data, transmitted via a common radio channel between units of a wireless network. The blocks of data (TR PHY) transmitted by a unit are preceded by a header (HEA) and a preamble (PRE) designed to be used by a physical layer. The preamble (PRE) contains information for synchronising a receiver unit for the block and estimating the broadcast channel as well as identification information (ID) of the block transmitting device.

Description


  Method of transmitting data by an entity of a wireless network and entity

  
Field of the invention

  
The present invention relates to the field of telecommunications. The invention relates more particularly to access techniques to a wireless network. Stations associated with a wireless network access point exchange information with this access point via a common radio channel. A station must be understood as being able to be fixed, portable or mobile equipment. The most common examples are a computer, a phone and a portable assistant (PDA). In this document, an entity is either a station or an access point.

  
The invention applies more particularly, but not only, to networks of the WIFI type, that is to say in accordance with one of the standards of the group 802.1 Ix, or of the WPAN type (Wireless Personal Area Networks: Bluetooth, Infrared, Zigbee ...). According to these standards, access to the radio channel is managed by the MAC layer. Access management must resolve collision cases. Prior art

  
Within the same basic service set (BSS) infrastructure of stations of a wireless radio system illustrated in Figure 1, in accordance with the basic specifications of the IEEE 802.11 standard defined in document P802.11-REVma-D9.0 the AP access point and associated STA1 STA2 stations exchange information on the same frequency band. To multiplex the exchanges between these entities in time, there are known methods.

   The CSMA / CA contention channel access techniques illustrated in Figure 2 require that each STAI station, ST A2 station, and AP access point entity listen for the channel for a random backoff time that follows a fixed DIFS time before to transmit a data frame TRA: if the channel is free after a certain duration DIFS + backoff associated with it, it can access the channel and thus start transmitting information,

  
- if the channel is not free Busy_Med, it waits for it to be free to resume the countdown of the backoff after a DIFS duration and apply to access the channel.

  
It can happen that several entities access the channel at the same time and simultaneously transmit on the channel. The information emitted is lost, we talk about collisions. These collisions occur: with reference to FIG. 3, when the backoff counters associated with two entities ENT2 and ENT3 are identical; these two entities will access the channel at the same time. There is collision Coll. between the transmitted TRA frames or, with reference to FIG. 1, when two stations STA1 and ST A2 are on both sides of the access point AP and sufficiently distant from each other not to detect the transmission from the other station; we are talking about hidden stations. In this case the STAL station, respectively the STA2 station, considers the channel as free and accesses the channel while the hidden station STA2, respectively STAl, can occupy the channel.

  
These contention techniques have several disadvantages. They impose the presence of unused periods during which a station that wants to transmit listens first to the radio channel to determine if it is free. Collision detection occurs only after the fact, there is no collision prevention. They require to multiplex in time the transmission and listening phases of the channel to detect collisions, they therefore impact the total transmission rate. Presentation of the invention

  
The invention proposes a method of transmitting data frames, transmitted by a common radio channel between entities of a wireless network which makes it possible to improve the treatment of collisions.

  
Thus, the subject of the invention is a method for transmitting data frames, transmitted by a common radio channel between entities of a wireless network, characterized in that: a data frame sent by an entity is preceded by a header and a preamble for use by a physical layer, the preamble contains information for synchronizing a receiving entity of the frame and for estimating the propagation channel; the preamble further comprises identification information; of the transmitting entity of the frame.

  
The invention further relates to an entity for implementing a method according to the invention.

  
Thus, an entity capable of communicating with a wireless network, via a radio channel, is adapted according to the invention to implement a method of transmitting data frames. The entity includes receiving means and data frame sending means preceded by a header and a preamble for use by a physical layer, the preamble comprising information for synchronizing a receiver of the frame and to estimate the propagation channel. The entity is adapted in that: the transmission means is adapted to transmit a preamble further comprising identification information of the entity. The method and the access entity according to the invention solve the problem.

   Indeed, any entity that listens to the channel can determine if several entities are transmitting by extracting an identification of a transmitting entity from the received data. The detection of two different identities for data received over the same time period less than the duration of two data frames makes it possible to determine that there is a collision between frames transmitted by the radio channel. The preamble is part of a frame exploited by a PHY physical layer, which makes it possible to determine the identity of the transmitting entity much faster than by exploiting identity information contained in a frame operated by a so-called access layer. MAC. With reference to the 802.11 standard, the preamble is a PLCP preamble adapted to include an identification of the transmitting entity.

   The exploitation of this identification information is therefore done at the level of the PLCP sub-layer of the PHY physical layer and no longer at the level of the MAC layer. Knowledge of the identity of the entity that occupies the channel is therefore much faster. According to a particular implementation, a listening entity can transmit simultaneously. In this case, if this entity receives a frame with an identification different from its own, it can conclude very quickly to a collision with its transmitted data.

  
The current systems respect a layered division including in particular a PHY physical layer and a MAC medium access layer. These two layers are partitioned.

  
The MAC layer defines techniques to organize the transmission of data from different users, to manage access to the channel, to manage collisions, to manage acknowledgments and retransmissions, to identify stations (address field of the MAC head of the MAC frame). The PHY physical layer defines techniques for providing data transmission at a fixed rate: the PLCP sublayer of the PHY physical layer defines synchronization and channel estimation. In this organization, the PLCP sublayer of the PHY layer has only the functions of synchronization, channel estimation, parameterization of the techniques of the PHY layer used. This partitioning impacts the rate of transmitted data.

   For example, the acknowledgment of a data frame takes place only after the complete reception of the acknowledgment frame managed by the MAC layer and in particular the decoding of the source and destination MAC addresses. Acknowledgment therefore occurs at the earliest 10 [mu] s (duration of the MAC frame) after the start of the frame. According to a particular embodiment, a method of transmitting data frames according to the invention is such that, upon reception of the data frame transmitted by the station, the access point transmits a preamble which comprises a copy of the data frame. identification information (ID) of the transmitting station of the frame.

  
The transmission of the preamble occurs as soon as the access point receives the first symbols of the header, for example PLCP Header with reference to the standard IEEE802.i l. As soon as the access point recognizes the PLCP header, it issues the preamble. Thus, any station that is in the coverage of the access point is informed of the occupation of the channel, even if it is a station hidden from the first station. The risk of collision between the first station and a second hidden station is therefore substantially reduced because the access point somehow extends the propagation area of the emission of the first station by issuing a preamble upon receipt of the first station. 'on your mind.

   In addition, any station can determine the identification of the transmitting station by exploiting the identification information field contained in the preamble re-issued by the access point.

  
When re-broadcasting this data frame by the access point (receiving entity), the insertion of the identification information of the station (transmitting station) is particularly advantageous for this station (transmitting station) since it allows this station to quickly recognize that it is at the origin of this frame and that it is not another station that occupies the channel.

  
According to this mode, the avoidance mechanism of the invention is integrated in any data frame and avoids the use of control frames dedicated to avoidance signaling which causes an overhead because these frames do not carry any data frame. data.

  
According to a particular embodiment, a method for transmitting data frames according to the invention is such that the synchronization information encodes the identification of the transmitting station.

  
In reference to the 802.11 standard, the synchronization information is contained in an STF sequence which contains a basic pattern repeated several times. This sequence is used in this mode not only to synchronize the receiver but also to encode the identification of the transmitting station.

  
According to a particular embodiment, a method of transmitting data frames according to the invention is such that the identification of the transmitting stations is coded by a code selected from a set of codes, the selection of the codes is such that those These show a high autocorrelation value compared to the cross-correlation values between the selected codes.

  
The high autocorrelation values compared to the cross correlation values allow a receiver to implement a synchronization function based on correlation calculations. The high autocorrelation values also make it possible, without disturbing the synchronization search, to determine the identification of a transmitting station with a minimum of false identifications by performing a correlation calculation between the received code and successively the different selected codes. The identification is therefore safe.

  
According to a particular embodiment, a method of transmitting data frames according to the invention is such that the codes consist of a succession of patterns each taken from N basic patterns.

  
The code is therefore the combination of the different successive patterns. The choice of a small number N, typically less than ten, makes it possible to have a relatively simple identification recognition module because, by reason of the code pattern, a maximum of N correlation calculations between the pattern and the basic patterns. The small number of basic patterns therefore limits the number of correlation calculations for each code pattern.

  
According to a particular embodiment, a method of transmitting data frames according to the invention is such that the access point transmits a preamble containing the identification of the access point, as soon as the access point detects two correlation peaks over the duration of a pattern of a code when receiving a preamble. The detection of two correlation peaks is an indicator of a collision between two emissions from two different stations. Indeed, the two peaks reflect the fact that there are two different basic patterns that resemble the pattern received and therefore that there are two different identification values for the received data. This received data therefore comes from two different transmitting stations.

   By issuing a preamble comprising identification information of the access point as soon as it detects this anomaly, the access point allows the transmitting stations that receive this preamble to detect in turn that there is a collision. The detection of two correlation peaks for M motifs makes it possible to reinforce confidence in collision detection. In addition, if M equals N then the access point can determine the identity of the transmitting stations participating in the collision. According to a particular embodiment, a method of transmitting data frames according to the invention is such that the preamble emitted by the access point further comprises a collision information.

  
With reference to the 802.11 standard, the collision information is according to the invention coded by the LTF sequence which contains two fields T1 and T2. The detection of this information by a station makes it possible to increase the confidence attributed to the detection of two correlation peaks.

  
According to a particular embodiment, a method for transmitting data frames according to the invention is such that the preamble transmitted by the access point further comprises a channel occupancy information. With reference to the 802.11 standard, the occupancy information is according to the invention coded by the LTF sequence which contains two fields T1 and T2. The detection of this information by a station makes it possible directly to know the state of the channel and to update a procedure for access to the channel.

  
According to a particular embodiment, a data frame transmission method according to the invention is such that a data frame sent by an entity, received in an integrity manner by an access point to the wireless network, is acknowledged by this access point by transmitting a preamble which includes information for synchronizing a preamble receiver, information for estimating the propagation channel and an acknowledgment information.

  
According to this mode, the transmitting entity of the frame therefore has confirmation that its frame has been correctly received by the access point and that it has not, in particular, been the subject of a collision. Acknowledgment is typically generated at a PHY physical layer and no longer at a MAC access layer. This acknowledgment is particularly advantageous in that it intervenes quickly, because it is generated by the PLCP sub-layer of the PHY physical layer as soon as the FEC decoding of the received data. According to a particular embodiment, a method of transmitting data frames according to the invention is such that the preamble further comprises identification information of the transmitting entity of the frame.

  
In reference to the 802.11 standard, the identification information is encoded by the short STF sequence which contains according to the standard a basic pattern repeated several times. This sequence is used in this mode not only to synchronize the receiver but also to encode the identification of the transmitting entity of the data frame. The addition of the identity of the issuing entity in the acknowledgment issued by the access point makes it possible to increase the robustness of the acknowledgment process.

  
According to a particular embodiment, an entity according to the invention further comprises a dedicated transmission channel and a dedicated reception channel coupled to a dedicated antenna to form dedicated channels independent of the transmitting means and the receiving means coupled to another antenna.

  
The presence of a dedicated reception channel coupled to a dedicated antenna allows an entity to listen to the channel simultaneously to a transmission by the data frame transmission means. Thus, the entity can detect very quickly if its transmitted data is the subject of a collision by detecting by means of the dedicated reception chain, the identification information contained in the received data. If these credentials identify an entity other than that entity, then the data from that entity is subject to a collision. The various previous embodiments may be combined or not with one or more of these modes to define another embodiment.

   The invention further relates to a telecommunication system adapted for implementing a method according to the invention.

  
Thus, a telecommunication system according to the invention comprises an entity according to the invention. According to a preferred implementation, the steps of the method for transmitting data frames are determined by the instructions of a data frame transmission program incorporated in an electronic circuit such as a chip itself that can be arranged in an electronic device. such as an access point of a wireless network or a station able to communicate with a wireless network via an access point. The method of transmitting data frames according to the invention can equally well be implemented when this program is loaded into a computing device such as a processor or equivalent whose operation is then controlled by the execution of the program.

  
Accordingly, the invention also applies to a computer program, including a computer program on or in an information carrier, adapted to implement the invention. This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code such as in a partially compiled form, or in any other form desirable to implement a method according to the invention.

  
The information carrier may be any entity or device capable of storing the program. For example, the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a floppy disk or a disk. hard.

  
Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

  
On the other hand, the program may be translated into a transmissible form such as an electrical or optical signal, which may be routed via an electrical or optical cable, by radio or by other means. The program according to the invention can be downloaded in particular on an Internet type network.

  
List of Figures

  
Other features and advantages of the invention will become apparent from the following description given with reference to the accompanying figures given by way of non-limiting examples.

  
FIG. 1 is a diagram illustrating a basic service set (BSS) infrastructure of STA, STA2 stations of a wireless radio system comprising a PA access point, the STA2 station being hidden from the STAL station, described with reference to FIG. prior art. Figure 2 is a diagram illustrating a basic CSMA / CA contention prevention method, described with reference to the prior art.

  
Fig. 3 is a diagram illustrating a collision, with a basic contention collision prevention method described with reference to the prior art. FIG. 4 is a diagram of a frame transmitted at the level of a physical layer PHY according to the invention.

  
Fig. 5 illustrates an STF sequence which contains a repeated repeated basic pattern used to encode the identification of the transmitting station.

  
Fig. 6 illustrates a STF sequence which contains a repeated repeated basic pattern used to encode the identification of the transmitting station [ft] this STAl.

  
FIG. 7 illustrates the detection of two correlation peaks for different sub-sequences, which is an indicator of a collision between two transmissions originating from the two different stations STAl and ST A2.

  
FIG. 8 illustrates the coverage extension function provided by a method according to the invention, due to the transmission of a HEA header by the access point AP as soon as it receives the header of the station transmits this STAL.

  
FIG. 9 illustrates the coverage extension function provided by a method according to the invention, due to the transmission of a HEA header adapted by the AP access point as soon as it receives the signal. head of the station emits this STAL. FIG. 10 illustrates a mode according to which the header transmitted by the access point AP is different from the header received from the transmitting station [pi] this STAl.

  
Fig. 11 illustrates a mode in which a data frame received in integrity by a receiving entity is acknowledged by sending a PLCP preamble Ack, generated at the physical layer. Fig. 12 illustrates a mode in which an aggregated data frame received in integrity by a receiving entity is acknowledged by issuing a PLCP Ack preamble after each data field generated at the physical layer.

  
Figure 13 is a diagram of an entity adapted for implementing a method according to the invention. Description of an embodiment of the invention

  
Referring to Figure 1, a STAL station accesses a wireless network using the AP access point

  
The STAL station has previously associated with the access point AP and possibly authenticated with this access point according to known procedures. The STAL station transmits data that the access point transfers to a destination not shown With reference to FIG. 4, the data DATA is encapsulated in a frame

  
TR PHY which typically starts with a HEA header preceded by a preamble PRE, typically according to the specifications of the PLC layer convergence layer of the 802.1 Ix MAC specification described in document P802.11- REVma-D9.0. The preamble contains STF, LTF sequences for synchronizing a receive entity of the frame and for estimating the propagation channel. According to the invention, the preamble further comprises identification information ID of the transmitting entity STAl of the TR PHY frame.

  
According to a particular embodiment, the synchronization information encodes the identification of the transmitting station. For example, in the case of the 802.11 standard, the synchronization information is contained in an STF sequence which contains a basic pattern repeated several times, illustrated by Figure 5. This sequence is used in this mode not only to synchronize the receiver but in addition to encode the identification ID of the transmitting station. In particular, the identification of a transmitting station STAl is coded by a code selected from a set of codes. The selection of the codes is such that they have a high autocorrelation value compared to the intercorrelation values between the selected codes.

   For example, the Zadoff-Chu CAZAC (constant amplitude zero autocorrelation) sequences described in D.C.Chu, "Polyphase codes with good periodic correlation properties," IEEE trans. Inform. Theory, vol. 18, pp. 531-532, July 1972, can be chosen to constitute a code set because they have excellent autocorrelation and intercorrelation properties. Their construction follows the following equation:
 <EMI ID = 10.1>
k = 0, 1, 2, - -, Nu - 1; U [iota] = 0 [Lambda], 2, - -, Nu - l

  
With Cm (k), the k <ieme> element of the u, <leme> sequence CAZAC of length Nu. There are Nu different CAZAC sequences of Naked length, respecting the excellent properties of autocorrelation and intercorrelation. For example, for a transmission according to one of the 802.11a / b / g / n standards of 20 MHz, each of the ten basic sequences of 800 ns constituting an STF sequence has a length of sixteen samples. For Nu = 16, there are N = 16 different CAZAC sequences respecting the autocorrelation and intercorrelation properties that determine sixteen basic motifs.

  
For example, among the sixteen sequences, only three basic sequences are retained and noted symbolically Sl, S2 and S3. Thus, the coding of the identification of the STAL station corresponds to a code which can for example be written in the form:

  
Sl S3 S1 S2 S1 Sl S3 Sl Sl S2

  
The STF sequence, contained in a frame transmitted by the STAL station, illustrated in FIG. 6, is such that: t, = S1, t2 = S3, t3 = S1, t4 = S2, t5 = S1, X6 = S1, t7 = S3, t8 = S1, t9 = S1, t1 = S2

  
The coding of the identification of the station STA2 corresponds to a code which can for example be written in the form

  
The sequence STF, contained in a frame transmitted by the station STA2, illustrated in FIG. 5, is such that: t1 = S1, t2 = S1, t3 = S2, t4 = S1, t5 = Sl, t6 = S3, t7 = Sl, t8 = S1, t9 = S2, tiO = S3

  
And so on for other entities [em] these.

  
The classical PN sequences and Walsh-Hadamard sequences, described in JG Proakis' book Digital Communications, McGraw HiIl International Editions, 3rd ed., 1995, are other examples of sequences with good autocorrelation properties. and intercorrelation.

  
The entity that receives the TR PHY frame transmitted by the STAL station performs a correlation between the received code and the various basic patterns retained, S1, S2 and S3 according to the example. Thus, with reference to FIG. 6, assuming that the receiving entity is the access point

  
AP then calculates the correlation between each sub-sequence t, the received STF sequence and the various basic patterns retained. The maximum correlation peak between the different values calculated for a given sub-sequence makes it possible to determine the basic pattern that corresponds to the received sub-sequence. The final code is thus determined by the detection of the maximum peaks for each of the sub-sequences. For the example, the method thus finds the code Sl S3 Sl S2 Sl Sl S3 Sl Sl S2 which gives the identification of STAl.

  
The high autocorrelation values compared to the cross-correlation values make it possible to determine the identification of an emitter station with a minimum of false identifications by selecting, for each subsequence received, the basic pattern that corresponds to the peak maximum correlation.

  
Referring to Figure 1, STA2 Station is hidden from the STAL station, it does not receive the frame transmitted by STAL and can therefore detect that the channel is occupied by the transmission of the STAL station.

  
The STA2 station may simultaneously transmit to the STAL station In this case, the access point detects two correlation peaks over the duration of a pattern of a code when receiving a preamble (which actually combines two preambles) as shown in Figure 7 The detection of two correlation peaks is an indicator of a collision between two emissions from the two different stations STAl and STA2 Indeed, the two peaks reflect the fact that there has two different basic patterns that resemble the pattern received and therefore there are two different identification values for the received data. This received data therefore comes from two different broadcast stations. According to the illustration,

   the access point detects two correlation peaks when the basic patterns are different and a peak correlation when the basic patterns are identical. According to the illustrated example, the method thus finds the code Sl S3 Sl S2 Sl Sl S3 Sl Sl S 2 which gives the identification of STAl and the code Sl Sl S2 Sl Sl S3 S1 Sl S2 S3 which gives the identification of STA2.

  
According to a particular embodiment of the invention, the access point transmits a preamble containing the identification of the access point, as soon as it detects two correlation peaks over the duration of a pattern of a code when the receipt of a preamble (which actually combines two preambles).

  
By issuing a preamble comprising an identification information of the access point as soon as it detects this anomaly, the access point thus allows the transmitting stations STAl and ST A2 which receive this preamble to detect in their turn that there has a collision.

  
According to a particular embodiment of the invention, the access point AP transmits a header HEA as soon as it receives the header of the STAL station, to prevent a collision. The transmission of this header HEA is shifted in time of the reception and decoding moment of the header received from the STAL station; that is, as soon as the receiver recognizes the STAL header. Typically and as illustrated in FIG. 8, the header may be preceded by a PRE preamble.

  
The header emitted by the access point AP may be a copy of the header received from the STAL station, the access point AP then acts as a relay with transmission of the head received. This embodiment makes it possible to have a simple implementation. However, it has the disadvantage of bringing to the knowledge of the hidden station STA2 a channel occupancy time which does not take into account the delay [Delta] between the reception / decoding of the header from STAL and the transmission of the header by AP access point, this corresponds to the illustration of Figure 8.

  
According to a particular embodiment of the invention illustrated in FIG. 9, the header transmitted by the access point AP is different from the header received from the transmitting station STAl. A modification consists of modifying the GIS field so that the duration information it contains takes into account the delay [Delta]. The hidden station STA2 thus determines the real end time of the frame transmitted by the STAL station from the received SIG field. This mode therefore makes it possible to increase the utilization rate of the channel by reducing the BUSY time during which it is considered occupied by the STA2 station. Typically, the GIS field may comprise a rate information (RATE) and a length information (LENGTH) characterizing the MPDU data field transmitted by the STAL station.

   Using both flow and length values allows you to determine the duration of the data field: time = bit rate (Mbps) x length (bits).

  
According to a particular embodiment of the invention illustrated by FIG. 10, the preamble emitted by the access point AP is adapted. The access point adapts the LTF sequence to encode control signal information. According to the IEEE802.11 standard, the sequence

  
LTF includes two fields that contain the same information. According to the invention, the LTF sequence comprises two fields of values that may be different and whose combination encodes a state of control signals: T1, T1: codes the busy state of the channel.

  
T1, T2: codes the detection of a collision on the channel, Ti is different from T2. T2, T2: indicates that the preamble is an acknowledgment preamble.

  
T2, T1: indicates that the corresponding frame comprises data, T "is different from T2.

  
According to the known techniques and more particularly described in the 802.11 standard, the acknowledgment of a data frame is generated at the level of the MAC layer. According to the invention, with reference to FIG. 11, a data frame received in an integrity manner by a receiving entity, typically an access point, is acknowledged by means of the transmission of a PLCP preamble generated at the physical layer and more particularly the PLCP sublayer. Acknowledgment is generated at a PHY physical layer and no longer at a MAC access layer as in the prior art. The PLCP Ack preamble includes information for synchronizing a preamble receiver, information for estimating the propagation channel, and acknowledgment information. Acknowledgment is encoded by the fields of the LTF sequence as previously seen.

   The acknowledgment is typically sent after an inter-frame time interval Ack_IFS. According to a particular mode, the preamble sent by the receiving entity comprises identification information of the entity transmitting the frame. According to this mode, the transmitting entity of the frame therefore has confirmation that its frame has been correctly received by the access point and that it has not, in particular, been the subject of a collision. With reference to the 802.11 standard, the identification information is encoded by the short STF sequence (formed of ti, t2, ... t [iota] o) which contains a basic pattern repeated several times. This sequence is used in this mode not only to synchronize the receiver but also to encode the identification of the transmitting entity of the data frame.

   This acknowledgment is particularly advantageous in that it intervenes quickly, because it is generated by the PLCP sub-layer of the PHY physical layer as soon as the FEC decoding of the received data. According to a particular embodiment illustrated in FIG. 12, an aggregated data frame received in an integrity manner by a receiving entity is acknowledged by sending a PLCP Ack preamble after each field of data of the frame, generated at the level of the physical layer.

  
Figure 13 is a diagram of an entity adapted for implementing a method according to the invention. The entity is able to communicate with a wireless network, via a radio channel, typically in accordance with a standard 1EEE802.11 x. The entity is adapted to implement a method according to the invention. The adapted entity ENT comprises, according to known techniques, a transmission channel EM and a reception channel RE respectively coupled to a transmitting antenna TX and a reception antenna RX as well as to a computer PRO. These strings are typically compliant with the 802.11 standard PHY Physical Layer description. These chains are found, for example, in a component of the AR5002X series or the AR5OO8X series of the Atheros company.

   The entity ENT is able to receive and transmit a data frame preceded by a header and a preamble, the preamble containing information for synchronizing a receiver of the frame and for estimating the propagation channel.

  
The entity ENT is adapted in that the computer PRO is adapted to issue a preamble PRE further comprising identification information of the entity. This adaptation consists of an LPre software module which makes it possible to code the identity ID of the entity typically by means of the STF sequence as described previously and illustrated in FIG.

  
The entity is further adapted in that it comprises a dedicated transmission channel coupled to a TXA dedicated transmission antenna to form a dedicated transmission channel independent of the EM transmission channel coupled to the antenna TX broadcast. This transmission channel is particularly interesting in the case of an access point. It allows the access point to issue a preamble which comprises, according to a particular mode, a copy of the identification information of the sending station of the frame upon reception by the reception channel RE of the transmitted data frame. by the station. The transmission of the preamble occurs as soon as the access point receives the first symbols of the header, for example PLCP Header with reference to the standard IEEE802.i l.

   Thus, any station that is in the coverage of the access point is informed of the occupation of the channel, even if it is a hidden station of the transmitting station. The risk of collision between the transmitting station and a hidden station is therefore substantially reduced because the access point somehow extends the transmission propagation zone of the transmitting station by issuing a preamble upon receipt of the transmission station. on your mind. In addition, any station can determine the identification of the transmitting station by exploiting the identification information field contained in the preamble re-issued by the access point.

   According to a particular mode, the dedicated transmission channel allows the access point to acknowledge a data frame received in an integrity manner, by means of the transmission of a preamble which includes information for synchronizing a receiver of the preamble, information for estimating the propagation channel and identification information of the transmitting entity of the frame. According to this mode, the transmitting entity of the frame therefore has confirmation that its frame has been correctly received by the access point and that it has not, in particular, been the subject of a collision. Acknowledgment is typically generated at a PHY physical layer and no longer at a MAC access layer.

   With reference to the 802.1 1 standard, the identification information is encoded by the short STF sequence (formed of t ", t2j ... t [iota] o) which contains a basic pattern repeated several times. This sequence is used in this mode not only to synchronize the receiver but also to encode the identification of the transmitting entity of the data frame. This acknowledgment is particularly advantageous in that it intervenes quickly, because it is generated by the PLCP sub-layer of the PHY physical layer as soon as the FEC decoding of the received data.

  
In a particular embodiment, the entity furthermore comprises, as illustrated in FIG. 13, a dedicated reception channel coupled to a dedicated reception antenna RXA to form a dedicated reception channel independent of the reception channel RE coupled to the reception antenna RX. . The presence of a dedicated reception channel coupled to a dedicated antenna allows an entity to listen to the channel simultaneously to a transmission by the transmission channel of a data frame. Thus, the entity can detect very quickly if its transmitted data is the subject of a collision by detecting by means of the dedicated reception chain, the identification information contained in the received data.

   If these credentials identify an entity other than that entity, then the data from that entity is subject to a collision. The detection of the identification information is typically done by a correlation calculation using the calculator PRO according to a previously described method.

  
According to a particular mode, the access point transmits a preamble containing the identification of the access point by means of its dedicated transmission chain, as soon as the access point detects a collision.

Claims

A method for transmitting data frames, transmitted by a common radio channel between entities (AP, STAl, STA2) of a wireless network, characterized in that: - a data frame (TR PHY) transmitted by a entity is preceded by a header (HEA) and a preamble for use by a physical layer, the preamble (PRE) contains information for synchronizing a receiving entity of the frame and for estimating the propagation channel, the preamble (PRE) further comprises identification information (ID) of the transmitting entity (STA1, STA2, AP, ENT) of the frame.
A method of transmitting data frames according to claim 1, wherein upon receipt of the data frame transmitted by the station, the access point (AP) transmits a preamble (PRE) which comprises a copy of the identification information (ID) of the transmitting station of the frame.
The method of transmitting data frames according to claim 1, wherein the synchronization information (STF) encodes the identification (ID) of the transmitting station.
The method of transmitting data frames according to claim 3, wherein the identification (ID) of the transmitting stations is coded by a code (S1 S2 ... S3) selected from a set of codes, the selection of the codes. is such that they have a high autocorrelation value compared to the cross-correlation values between the selected codes.
5. A method of transmitting data frames according to claim 4, wherein the codes consist of a succession of patterns each taken from N basic patterns (Sl, S2, S3).
A method of transmitting data frames according to claim 5, wherein the access point (AP) transmits a preamble containing the identification (ID) of the access point, as soon as the access point detects two correlation peaks over the duration of a pattern of a code when receiving a preamble.
The method of transmitting data frames according to one of claims 2 and 6, wherein the preamble (PRE) transmitted by the access point further comprises collision information.
The method of transmitting data frames according to one of claims 2 and 6, wherein the preamble (PRE) transmitted by the access point (AP) further comprises a channel occupancy information.
The method of transmitting data frames according to one of claims 1 to 5, wherein a data frame transmitted by an entity, received in an integrity manner by an access point (AP) to the wireless network, is acknowledged by this access point by transmitting a preamble (PLCP Ack) which includes information for synchronizing a preamble receiver, information for estimating the propagation channel and an acknowledgment information.
The method of transmitting data frames according to claim 9 wherein the preamble further comprises identification information (ID) of the transmitting entity of the frame.
11. Entity (ENT) capable of communicating with a wireless network, via a radio channel, adapted to implement a method for transmitting data frames, comprising a reception means and a data frame transmission means preceded by a header (HEA) and a preamble (PRE) for use by a physical layer, the preamble comprising information for synchronizing a receiver of the frame and for estimating the propagation channel characterized in that the transmission means is adapted to transmit a preamble (PRE) further comprising identification information (ID) of the entity.
The entity of claim 11, further comprising: a dedicated transmit chain (EMA) and a dedicated receive chain (REA) coupled to a dedicated antenna (TXA, RXA) to form dedicated channels independent of the means of transmission and receiving means coupled to another antenna (TX, RX).
Telecommunication system comprising an entity according to one of claims 11 and 12.
14. Computer program on an information carrier, said program comprising program instructions suitable for implementing a method of transmitting data frames according to any one of claims 1 to 10, when said program is loaded and executed in an entity (ENT), able to communicate with a wireless network via a radio channel and for implementing a method of transmitting data frames.
An information carrier having program instructions adapted to implement a method of transmitting data frames, according to any one of claims 1 to 10, when said program is loaded and executed in an entity (ENT), capable of communicating with a wireless network via a radio channel and intended to implement a method of transmitting data frames.
PCT/FR2009/052535 2008-12-15 2009-12-15 Method for transmitting data by a wireless network unit and unit WO2010076481A1 (en)

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