FR2790901A1 - Digital communication between mobile stations includes facility for any mobile station to become base station if no base station is detected - Google Patents

Abstract

Requests for modulation level are transmitted and if no response is detected, the transmitting station becomes a base station. The procedure for establishing communication between two mobile stations is started when one of the mobile stations produces a synchronisation signal. This station then operates in base station mode, and the other station then synchronises itself on this signal and operates in mobile station mode. To establish communication between two stations operating in mobile station mode, one of the stations transmits a message requesting a modulation level to a station in base station mode with which the mobile station is in communication. In the absence of a response to this modulation level request, the mobile station which transmitted the request changes to operate in base station mode.

Description

The present invention relates to a method and a device for

  message communication over a network and systems implementing them. It applies, in particular, to wireless LANs with centralized architecture, for which each communication is organized between a so-called base communication station, also called "fixed part" and a station of

  mobile communication, also called "portable part".

  An example of such a communication network is given by the telephones using the European standard DECT (initials of the words "Digital Enhanced Cordless Telecommunications", which means

  "enhanced digital wireless telecommunications").

  In such a local area network, a base station provides a synchronization signal to all the mobile stations present in a cell of the network. All stations (the base station and one or more stations

  mobiles) which thus synchronize with each other, constitute a cell.

  The DECT radio communication standard published in 1992 (EN 300 175) by ETSI specifies the use of a Gaussian Minimum Shift Keying (GMSK) modulation method, which means in French minimal phase gradient modulation. Through the use of this modulation, so-called level 2 modulation, a DECT communication link can provide a bitrate

useful maximum of 552 kbps.

  The DECT standard now allows the use of two new modulations: PI / 4-DQPSK (abbreviation for "Differential Quaternary Phase Shift Keying", which means in English "differential quaternary phase modulation") and PI / 8-D8PSK ( abbreviation for "Differential Quaternary Phase Shift Keying", which means in English "eight-state differential phase modulation"). The first modulation, called level 4 modulation achieves a maximum payload of 1 Mbits / s and the second, called modulation level 8, achieves a useful bit rate

maximum of 2 Mbps.

  A DECT equipment or "station" must always be able to implement the level 2 modulation, but the implementation of the level 4 and / or 8 modulations is optional. This can cause that in the same cell (a base station with which one or more mobile stations are synchronized), DECT equipment coexist with different communication capabilities. In particular, when the base station of a cell does. allows the use of level 2 modulation, all communications inside the cell are limited to the rate of

552 kbps.

  The document "A guide to DECT services, features and standards", ETSI EPDECT, June 1998 describes the possible modulations for a

  DECT equipment (PI / 2-DPSK, PI / 4-DQPSK, Pl / 8-D8PSK).

  EP 845916 (Ericsson) describes a system that uses different modulation methods to take into account the level of interference, the distance, the bandwidth requirements. In this system, all communication devices support all the different types of modulation. He is not interested in the case of a heterogeneous cell, that is to say which includes stations that are not all capable of implementing

the same types of modulations.

  Patent EP 853400 (Deutsche Thomson Brandt) describes a radio transmission method in which, depending on the state of the transmission channel and as a function of the bit rate of the data to be transmitted, either QPSK modulation or DQPSK modulation is used. 16-QAM modulation. In this system, all communication devices support all the different types of modulation. He is not interested in the case of a heterogeneous cell, that is to say which includes stations that are not all capable of

  the same types of modulations.

  The present invention is particularly interested in networks whose stations are not likely to implement all the same modulations. It aims to use the best (highest) modulation level available between two mobile stations when the base station has

  communication capabilities limited by its maximum modulation level.

  Thus, the user of a DECT network does not have to change the base station when implementing DECT stations that support levels.

higher modulation.

  The present invention allows, for example, the creation of a new cell comprising only stations supporting modulation of

level strictly greater than 2.

  For this purpose, the present invention aims, in a first aspect, a method of communication between communication stations adapted to communicate with each other when at least one of said communication stations provides a synchronization signal, said station then operating in "base station" mode and the stations not providing a synchronization signal but synchronizing on a synchronization signal transmitted by a station operating in base station mode then operating in "mobile station" mode, characterized in that, for the setting up of a communication between two stations operating in mobile station mode, it comprises: - carried out by one of said stations operating in mobile station mode, the transmission to a base station with which said mobile station is synchronized, a message representative of a modulation level request and - in the absence of implementation of said modulation level p ar said base station, a switching operation of one of said stations

  operating in mobile station mode, in base station mode.

  Thanks to these arrangements, for a communication between two stations, a station can indicate which level of modulation, that is to say also what bandwidth is necessary, in order to obtain the transmission capacities of the stations present in the network. be used effectively. The invention also makes it possible to use stations capable of operating with a high level of modulation with base stations which

  are not able to work with high levels of modulation.

  According to a particular characteristic, parallel to said switching operation performed by one of said stations operating in mobile station mode, the other of said stations operating in mobile station mode performs a synchronization operation with the station which performs

the switching operation.

  Thanks to these arrangements, two communication stations can establish a direct link of communication, implementing said level

  modulation, and thus increase the available radio rate.

  According to one particular characteristic, the method comprises, in advance of said switching operation, in the absence of implementation of said modulation level by said base station, an evaluation operation of necessity of a switching operation during which determines whether the switching of one of the stations operating in

  mobile station is required for said communication between said stations.

  Thanks to these provisions, the procedure of placing in direct communication is carried out only if it brings a real advantage compared to a

  normal communication procedure (through a base station).

  As a variant, during the necessity evaluation operation, it is determined whether the amount of information to be transmitted between the stations operating in mobile station mode is greater than a value.

predetermined, or not.

  Thanks to these arrangements, two communication stations establish a link of direct communication, with said level of modulation, only when the amount of information to be exchanged is sufficient compared to the

  time required to establish direct communication.

  As a variant, during the necessity evaluation operation, it is determined whether the duration of the communication between the stations operating in

  mobile station mode is greater than a predetermined value, or not.

  These provisions make it possible to guarantee a minimum data transfer time, with respect to the capacities of the communication network. Thus one always chooses the path giving the minimum transfer time for the communication. As a variant, during the necessity evaluation operation, it is determined whether at least one of these stations operating in station mode

  mobile is in communication, or not.

  Thanks to these provisions, a communication in progress can not

  not be interrupted by the procedure of putting in direct communication.

  As a variant, during the necessity evaluation operation, it is determined whether at least one of these stations operating in station mode

  mobile is intended to be in communication with another station, or not.

  Thanks to these provisions, the procedure of putting in direct communication can not prevent a station which wishes to communicate with it.

another station.

  As a variant, during the necessity evaluation operation, it is determined whether each of said stations operating in mobile station mode is

  capable of implementing said required level of modulation.

  As a variant, during the necessity evaluation operation, one of the stations operating in mobile station mode performs a transmission operation of a message representative of a modulation level that said station is capable of setting. work for communication between

said stations.

  Thanks to one or other of the two provisions that have just been briefly exposed, it is possible to compare the performance that can be obtained by the normal path of communication with those obtained by the direct communication path. Thus, the mobile station having initiated the procedure can choose the most efficient path for the desired communication. As a variant, during the necessity evaluation operation, it is determined whether at least one of these stations operating in station mode

  mobile is able to switch to base station mode.

  As a variant, during the necessity evaluation operation, one of the stations operating in mobile station mode performs a transmission operation of a message representative of its capacity or its capacity.

  unable to switch to base station operating mode.

  Thanks to the provisions of these last two variants, the station initiating the request for a distributed call, for the implementation of said modulation level, determines its capacity to act as a base station and then indicates to the other said stations. involved in the communication the behavior it must follow namely either switch to base station mode or synchronize on the initiating station. This ensures the

  correct implementation of the distributed communication.

  The variants briefly described above are

mutually exclusive.

  The present invention also relates to a communication device between communication stations adapted to communicate with each other when at least one of said communication stations provides a synchronization signal, said station then operating in "base station" mode and the stations not providing a synchronization signal but synchronizing on a synchronization signal transmitted by a station operating in base station mode then operating in "mobile station" mode, characterized in that a station operating in mobile station mode comprises means adapted processing, for setting up a communication with another station operating in mobile station mode: - to send, to a base station with which said mobile station is synchronized, a message representative of a request modulation level and - in the absence of implementation of the said modulation level by

  said base station to switch to base station mode.

  The invention also relates to a network, a computer, a camera, a fax machine, a camera, a television set, a printer, a scanner and an audio / video player, characterized in that they comprise a

  device as succinctly set forth above.

  The invention also relates to: a means for storing information readable by a computer or a microprocessor retaining instructions of a computer program characterized in that it allows the implementation of the method of the invention as briefly described above, and - a removable information storage means, partially or completely, and readable by a computer or a microprocessor retaining instructions of a computer program characterized in that it allows the setting

  implementation of the method of the invention as briefly described above.

  The preferred or particular features and advantages of this device, this computer, this camera, this fax machine, this camera, this television, this printer, this scanner, this audio-video player and these means information storage being identical to those of the method as

  succinctly stated above, these benefits are not recalled here.

  Other benefits, goals and features of this

  invention will become apparent from the following description, made with reference to the drawings

  in which: - Figure 1 shows, schematically, the architecture of an electronic circuit incorporated in a station capable of operating in a mobile station, according to the present invention, and adapted to communicate with a communication station of which the electronic circuit is illustrated in FIG. 2; FIG. 2 schematically represents the architecture of an electronic circuit incorporated in a communication device according to the present invention, adapted to operate in base station mode; FIG. 3 schematically represents a network comprising a communication station operating in base station mode and two communication stations operating in mobile station mode, in accordance with the prior art; FIG. 4 is a schematic representation of FIG. , a network comprising a communication station operating in base station mode and two other stations of co. one, operating in mobile station mode and the other operating in base station mode, in accordance with the present invention; - Figures 5 and 6 show an algorithm executed by a source mobile station according to the present invention, of which an electronic circuit is illustrated in FIG. 1, to communicate with another mobile station called the destination, FIGS. 7 and 8 represent two algorithms executed by a station operating in base station mode in relation to a mobile station implementing FIG. algorithm illustrated in FIGS. 5 and 6, FIG. 9 represents an algorithm executed by a receiving mobile station according to the present invention, an electronic circuit of which is illustrated in FIG. 2, in relation with a source mobile station implementing the algorithm illustrated in Figures 5 and 6, - Figures 10, 11 and 12 show three successions of radio messages for the transmission of a m between a source mobile station and a destination mobile station that are capable of implementing a modulation level that the base station is not likely to

enforce.

  Knowing that "hybrid" communication stations can operate either in base station mode or in station mode

  in the remainder of the description, the term "base station" will encompass

  on the one hand the communication stations which can only operate according to the operating mode of base station, and, on the other hand, the hybrid communication stations operating temporarily in station mode of

  based. Similarly, in the rest of the description, the term "mobile station"

  include both communication stations that can only operate in the mobile station operating mode, and hybrid communication stations operating temporarily in the mobile mode.

mobile station.

  Figure 1 shows the electronic circuit of a wireless communication device, using the European standard DECT (specified by

  ETSI, ETS 300 175, 1991), operating in mobile station mode.

  This device can be either a DECT mobile station or a hybrid DECT station. This communication device can be integrated into a computer type equipment, printer, fax, ... or connected to one of the equipment mentioned above. The electronic circuit 100 comprises, interconnected by an address and data bus 102: a radio unit 101, provided with an antenna 103, an input / output controller 107, a central processing unit 106, a screen 110, a keyboard 111, a ROM 105, and

a RAM 104.

  Moreover, a power supply 109 is provided for supplying all the components of the electronic circuit 100 (the links

  electrical power supply 109 are not shown).

  The input / output controller 107 is connected to a source of information (for example an image, sound, text or graphics sensor, a telephone, a fax machine, a camera, a video camera, a camcorder ...) and / or to a recipient of information (eg a television, a monitor, a music channel, a telephone, a

  fax, VCR ....).

  All the components illustrated in FIG. 1 are well known to those skilled in the art of processor communication circuits and more generally information processing circuits. They are not detailed here. The electronic circuit 100 and, in particular, the central unit 106, are adapted to exploit all the capabilities of the known DECT standard as soon as possible.

before the present invention.

  The central unit 106 is further adapted to implement the method of the invention and, in particular, the flow charts illustrated in Figures 5, 6 and 9. The random access memory 104 keeps, in registers which, for convenience, each have the same name as the data it contains: "CRI" which represents the value of a retransmission counter of a "requestemodulation" message; "L" which represents a desired modulation level; - "CC" representing a direct communication request message content; and - "CR2" which represents the value of a retransmission counter

  a message "broadcastdistributed_query".

  The read-only memory 105 keeps, in registers which, for convenience bear, each, the same name as the data it contains: - "CRImax" which represents the maximum number of retransmissions of a "requestemodulation" message; for example, CRI_max = 3; - "TI", maximum duration allowed between the sending of a message "request_modulation_levels" and the reception of a message "confirmation_modulation_levels"; for example T1 = 500 ms; - "CR2_max" which represents the maximum number of retransmissions of a message "distributed_communication_query"; for example CR2_max = 3; "T2", the maximum time allowed between the sending of a "distributed_communication_disclosure" message and the receipt of a "distributed_communication_confirmation" message; for example T2 = 500 ms; - "TableLevelModulation">, table containing the list of all the modulation levels supported; - "TYPE": constant defining the type of the station (base station, mobile station, hybrid station); and - "RFPI": constant indicating the identity of the base station

  which is broadcast on radio waves.

  The read-only memory 105 constitutes a means of storing information readable by a computer or a microprocessor, retaining instructions of a computer program characterized in that it allows the implementation of the method of the invention. According to one variant, the read-only memory 105 is removable, partially or totally, and comprises, for example, a magnetic tape, a flash memory, a floppy disk or a compact memory disk.

frozen ("CD-ROM" in English).

  Figure 2 shows the electronic circuitry of a wireless communication device, using the European standard DECT (specified by ETSI, ETS 300 175, 1991), which can be connected to a PSTN type network

  (Switched Telecom Network), Ethernet, ...

  This device can be either a DECT base station or a hybrid DECT station. In particular, a DECT base station is responsible for providing system synchronization. A hybrid station is a communication station that can alternatively operate as a base station or as a mobile station. This communication device can be integrated into a computer type equipment, printer, fax, ... or connected to one of the equipment mentioned above. The electronic circuit 200 comprises interconnected by an address and data bus 202: a radio unit 201, equipped with an antenna 203, an input / output controller 207, a network controller 208, a unit central processing unit 206, a ROM 205, and

a RAM 204.

  Moreover, a power supply 209 is provided for supplying all the components of the electronic circuit 200 (the links

  electrical power supply 209 are not shown).

  The network controller 208 manages the interface with an external network

  210, for example of the type Switched Telephone Network.

  The input / output controller 207 is connected to a source of information (for example an image, sound, text or graphics sensor, a telephone, a fax machine, a camera, a video camera, a camcorder ...) and / or to a recipient of information (eg a television, a monitor, a music channel, a telephone, a

  fax, VCR ....).

  All the components illustrated in FIG. 2 are well known to those skilled in the art of processor communication circuits and more generally information processing circuits. They are not detailed here. The electronic circuit 200 and, in particular, the central unit 206, are adapted to exploit all the capabilities of the known DECT standard as soon as possible.

before the present invention.

  The central unit 206 is, furthermore, adapted to implement the method of the invention and, in particular, the flowcharts illustrated in FIGS.

7 and 8.

  The RAM 204 keeps, in registers which, for convenience, each have the same name as the data it contains: - "M" which represents a level of modulation; - "localization table": a variable containing information on the location and operational mode of mobile stations that are registered on the base station (recorded during a manual or automatic subscription phase as defined by the DECT standard); and - "CR3" which represents the value of a retransmission counter of a message "distributed.communication"; The ROM 205 keeps, in registers which, for convenience, bear, each, the same name as the data it contains: - "Table Level Modulation" table containing the list of all the modulation levels supported by the station base 300; "CR3_max" which represents the maximum number of retransmissions of a message "distributed.communication"; for example CR3_max = 3; - "T3", the maximum time allowed between the sending of a "distributedcommunicationcounter" message and the receipt of a "distributedCommunication_response" message; for example T3 = 500 ms; - "<T4", the period during which a mobile station must not plan to communicate before switching to the base station mode; for example T4 = 20 s; - "RFPR" which represents the identity to be broadcast on the radio when the device transmits as a base station, and - "TYPE": constant defining the type of the station (station

  basic, mobile station, hybrid station).

  The read-only memory 205 constitutes a means for storing information readable by a computer or a microprocessor, retaining instructions of a computer program characterized in that it allows the implementation of the method of the invention. According to one variant, the read-only memory 205 is removable, partially or totally, and comprises, for example, a magnetic tape, a flash memory, a floppy disk or a compact memory disk.

frozen ("CD-ROM" in English).

  FIGS. 3 and 4 show a local wireless communication network 310 comprising: a DECT base station 300, connected to a PSTN network 311, capable of supporting only the modulation level 2; a hybrid station 301 initially operating in a mode DECT mobile station, and capable of supporting the modulation levels 2, 4 and 8, - a hybrid station 302 initially operating in mobile station mode DECT, and capable of supporting the modulation levels 2, 4 and 8, at the initialization of this system, mobile stations 301 and 302

  are thus synchronized with the base station 300.

  In FIG. 3, it is observed that all communication between the mobile stations 301 and 302 is carried out via the base station 300, even though the highest levels of modulation that can be implemented by the mobile stations 301 and 302 are strictly higher than the highest level of modulation likely to be implemented by the base station 300. The bit rate of such communications is then limited to

552 kbps.

  On the contrary, according to the present invention, FIG. 4 shows that communication between the mobile stations 301 and 302 can be carried out directly between them when the highest levels of modulation can be implemented by the stations. 301 and 302 are strictly higher than the highest level of modulation that can be implemented by the base station 300.

  The maximum communication between stations 301 and 302 is 2 Mbps.

  Suppose that the station 301 is at the origin of the communication to be established with the station 302. The station 301 is then called "source station" and it implements the algorithms illustrated in FIGS. 5 and 6. The station 302 is then called "destination station" and it implements the algorithm illustrated in FIG. 9, while the base station 300 implements the algorithms

illustrated in Figures 7 and 8.

  During an operation 401, the central unit 106 initializes the value of the counter CR1 to the value "0". Then, during an operation 402, the central unit 106 controls: - the transmission to the base station 300, of a message "modulation_query_query <L>" in which the level "L" represents the level desired modulation; and - the initialization of a clock pulse down timer (in English)

  "timer") whose return time to "0" is equal to T1.

  For example, the L level is selected as the highest value in "Modulation_Tab_Table".

  Then, during a test 403, the CPU 106 determines whether a message "ConfirmationLevelModulation <M>" was received from the base station 300, or not. When the result of the test 403 is negative, during a test 404, the central unit 106 determines whether the value of the clock pulse timer T1 is equal to "0" or not. When the result of the test 404 is negative, the test 403 is reiterated. When the result of the test 404 is positive, during a test 405, the central unit 106 determines whether the value of CRI stored in RAM 104 is strictly less than the value of

  CR1_max kept in read-only memory 105, or not.

  When the result of the test 405 is negative, a failure procedure 406 is performed, during which the modulation level negotiation has failed, it is determined that the base station does not support the

  message "request_level_modulation".

  When the result of the test 405 is positive, during an operation 407, the value of the counter CRI is incremented by one unit. Then, the operation

402 is reiterated.

  When the result of the test 403 is positive, during a test 408, the central unit 106 determines whether the value of M is strictly less than the value of L, or not. When the result of the test 408 is negative, during an operation 409, the level of modulation selected for the operation of the station 301 during its communication with the mobile station 302 is equal to M. When the result of the test 408 is positive, during a test 410, the central unit 106 determines whether the requested communication is internal communication or not. For this there is a field of the message "catl set up" specified by the DECT ETS 300 175 standard, which indicates whether it is an internal call or a call to the network connected to the base station . When the result of the test 410 is negative, the operation 409 is performed. When the result of the test 410 is positive, during an operation 411, the central unit 106 performs an evaluation of the service offered with the level of modulation M. For example, if the communication to be implemented requires a duration of establishment very short, and shorter than the duration of the procedure illustrated in operations 413 and following, the service offered with the level of modulation M has a high level. Similarly, if the amount of data to be transferred is very small so that the transmission will be faster if one remains at the level of modulation M than if one carries out the procedure illustrated in operations 413 and following, the service offered by the level M is considered

as high.

  On the other hand, if the required bandwidth is greater than that allowed by the modulation level M, or if the duration of the

  communication is great, the service it offers is considered weak.

  Following the operation 411, during a test 412, the central unit 106 determines whether the service offered with the modulation level M is

  high or not, for communication with the mobile station 302.

  The test 412 constitutes a necessity evaluation of a switching operation during which the station 301 determines whether the switching of one of the stations operating in the mobile station mode (either the station 301 or the station 302) is necessary to said communication between said

stations.

  According to different non-exclusive variants: - during the necessity evaluation operation, it is determined whether the amount of information to be transmitted between the stations operating in the mobile station mode is greater than a predetermined value (result of the test 412 negative), or not; during the necessity evaluation operation, it is determined whether the duration of the communication between the stations operating in the mobile station mode is greater than a predetermined value (result of the negative test 412), or not; during the necessity evaluation operation, it is determined whether at least one of said stations operating in mobile station mode is in communication (result of the positive test 412), or not; during the necessity evaluation operation, it is determined whether at least one of said stations operating in mobile station mode is intended to be in communication with another station (result of the positive test 412), or not; during the necessity evaluation operation, it is determined whether each of said stations operating in mobile station mode is capable of implementing the level of modulation required by the station 301 during the operation 402 (test result 412 negative), or not - during the necessity evaluation operation, one of the stations operating in mobile station mode performs a transmission operation of a message representative of a modulation level that said station is capable of implementing for communication between said stations (this variant is explained below with regard to operation 802); during the necessity evaluation operation, it is determined whether at least one of said stations operating in mobile station mode is capable of switching in base station mode (result of the negative test 412), or not; during the necessity evaluation operation, one of the stations operating in mobile station mode performs a transmission operation of a message representing its capacity or its inability to switch to

  base station operating mode.

  When the result of the test 412 is positive, the operation 409 is performed. When the result of the test 412 is negative, during a test 413 (FIG. 6), the central unit 106 determines whether switching to the base station operating mode is possible for the station 301, or not. This test consists of reading the value of the TYPE field stored in read-only memory 105. If the TYPE field means that the station can only operate in mobile station mode, the result of test 413 is negative. If the TYPE field indicates that it is a hybrid station, that is to say capable of operating on the one hand at the base station and secondly as a mobile station, the central unit 106, determines the result of the test 413 to be positive if the station 301 has no communication in progress, and if no communication is to take place during a duration T4. If a communication is in progress or is planned

  during the next duration T4, the result of the test 413 is negative.

  When the result of the test 413 is positive, during an operation 414, the content of a field CC is set to a value representative of an attachment request ("Attach"). When the result of the test 413 is negative, during an operation 415, the content of a field CC is set to a value

  representative of a mode change request ("changemode").

  Following one or the other of the operations 414 or 415, the central unit 106 initializes the value of the counter CR2, to the value "0", during a

operation 416.

  Then, during an operation 417, the central unit 106 controls: the transmission to the base station 300 of a message "distributed_communication_search <CC, 302>" in which the level "CC" represents the message content and the last term (here "302") represents the destination station of the message; and - the initialization of a clock pulse down timer (in English)

  "timer") whose return time to "0" is equal to T2.

  Then, during a test 418, the central unit 106 determines whether a message "distributed_distribution_response <response, RFP lrep>" has been received from the base station 302, or not. When the result of the test 418 is negative, during a test 419, the central unit 106 determines whether the value of the clock pulse down timer is equal to "0" or not. When the result of the test 419 is negative, the test 418 is reiterated. When the result of the test 419 is positive, during a test 420, the central unit 106 determines whether the value of CR2 stored in RAM 104 is strictly less than the value of

  CR2 max stored in read-only memory 105, or not.

  When the result of the test 420 is negative, a failure procedure 421 is performed, during which it is determined that the direct communication between the two mobile stations 301 and 302 can not be done, then it is necessary to go to the step 409 to restore an internal connection through the station

base 300.

  When the result of the test 420 is positive, during an operation 422, the value of the counter CR2 is incremented by one unit. Then, operation 417 is reiterated. When the result of the test 418 is positive, during a test 423, the central unit 106 determines whether the content of the message "response_communication_distributed <response, RFPI rep>" is representative of an acceptance, or not. When the result of the test 423 is negative, the operation 421 is performed. When the result of the test 423 is positive, during a test 424, the central unit 106 of the base station 301 determines whether the field "RFPI rep" of the message "distributed communication response <response, RFPlrep>" received is equal at

  "RFPI" (value read in ROM 105), or not.

  When the result of the test 424 is positive, the station 301 switches

  in base station operating mode, during an operation 425.

  When the result of the test 424 is negative, the mobile station 301 desynchronizes with the base station 300 and synchronizes with the station 302 become, during the implementation of the flowchart illustrated in FIGS.

and 6, a base station.

  In FIG. 7, it is observed that, first of all, during a test 501, the central unit 206 of the base station 300 determines whether or not a message "request_new modulation_multi <L>" has been received. When the result of the test 501 is negative, it is reiterated. When the result of the test 501 is positive, during a test 502, the central unit 206 determines whether the modulation level L is supported by the base station 300, or not. When the result of the test 502 is positive, during an operation 503, the value of M is fixed at the value of L. When the result of the test 502 is negative, during an operation 504, the value of M is set to the highest level of modulation supported by the base station 300, this level is selected as the highest value contained in "modelevel_count", while being lower than the level L proposed by the mobile station 301 (it is assumed that if station 301 did not propose a level higher than L, it is not able to support it). Following one or the other of the operations 503 or 504, the central unit 206 performs an operation 505 during which it causes the transmission, to the station 301 of a message "confirmationLevelModulation <M > ". FIG. 8 shows that, firstly, during a test 601, the central unit 206 of the base station 300 determines whether a message "distributed communication request" <CC, 302> "has been received, or when the test result 601 is negative, it is reiterated When the result of the test 601 is positive, during an operation 602, the value of the counter CR3 is initialized to "0". In an operation 603, the central unit 206 controls: - the transmission to the mobile station 302 of a message "distributed communication board <CC, 301>" in which CC is equal to the value of CC received in the message "distributed_distribution_query"; and the initialization of a clock pulse down timer whose

  return time at "0" is equal to T3.

  Then, during a test 604, the central unit 206 determines whether a message "Distributed_Communication_response <Answer, 301>" has been received from the station 302, or not. When the result of the test 604 is negative, during a test 605, the central unit 206 determines whether the value of the clock pulse down timer is equal to "0" or not. When the result of the test 605 is negative, the test 604 is reiterated. When the result of the test 605 is positive, during a test 606, the central unit 206 determines whether the value of CR3 stored in RAM 204 is strictly less than the value of

  CR3_max stored in ROM 205, or not.

  When the result of the test 606 is negative, a failure procedure 607 is performed, during which the direct communication attempt is canceled. Operation 610 may be following this failure operation so

  to inform the source station of this failure.

  When the result of the test 606 is positive, during an operation 608, the value of the counter CR3 is incremented by one unit. Then, the operation

603 is reiterated.

  When the result of the test 604 is positive, during a test 609, the central unit 206 determines whether the value of the "Response" field is representative.

acceptance, or not.

  When the result of the test 609 is negative, during an operation 610, the central unit 206 causes the sending, to the mobile station 301, of a message "Distributed communication_response <rejected, 301>", in which the field "rejected" is representative of a refusal on the part of the mobile station 302 to create a new cell with the mobile station 301 and the last term

  (here "301") is the identity of the destination station of the message.

  When the result of the test 609 is positive, during a test 611, the central unit 206 determines whether the content of the message "CC" is representative of an attachment, or not. When the result of the test 611 is positive, during an operation 612, the value of "RFPL_rep" is equal to "301" and when the result of the test 611 is negative, during an operation 613, the value of

"RFPl_rep" is equal to "302".

  Following one or the other of the operations 612 or 613, during an operation 614, the central unit 206 causes the transmission, to the mobile station 301, of a message

  "Distributed_distributed_response <accepted, RFPI rep>.

  Then, during an operation 615, the central unit 206 updates

  the station location table stored in RAM 204.

  FIG. 9 shows that, first of all, the central unit 106 of the mobile station 302 performs a test 701, during which it determines whether a

  message "distributedcommunication-board <CC, 301>" was received, or not.

  When the result of the test 701 is negative, it is reiterated. When the result of the test 701 is positive, during a test 702, the central unit 106 determines whether the field CC is representative of an attachment, or not. When the result of the test 702 is positive, during a test 703, the central unit 106 determines whether the

  communication with the mobile station 301 is accepted, or not.

  When the result of the test 703 is negative, during an operation 704, the central unit 106 causes the transmission, to the base station 300, of a message "Distributed_Communication_response <rejected, 301>", in which the last term (here 301) represents the final recipient of this message. When the result of the test 703 is positive, during an operation 705, the central unit 106 causes the transmission, to the base station 300, of a message "Distributed_distribution_response <accepted, 301>". Then, during an operation 706, the central unit 106 performs a desynchronization operation with the base station 300 and synchronization with the station 301, which, during the execution of the algorithm represented in FIG. figure 9, starts working

in base station mode.

  When the result of the test 702 is negative, during a test 707, the central unit 106 determines whether the content of the field "CC" is representative of a request for a change of operating mode, or not. When the result of the test 707 is negative, the operation 704 is performed. When the result of the test 707 is positive, during a test 708, the central unit 106 determines whether the switching in base station operating mode is accepted, or not by determining whether: - the value of the variable "TYP'E", stored in the ROM is representative of a hybrid station and

  - whether a call is in progress or not.

  When the result of the test 708 is negative, the operation 704 is performed. When the result of the test 708 is positive, during an operation 709, the central unit 106 causes the transmission to the base station

  300, of a message "Distributed_Communication_response <accepted, 301>".

  Then, during an operation 710, the central unit 106 switches its operating mode to the operating mode of

base station.

  Figure 10 shows the successive messages transmitted by stations 301 (left), 300 (center) and 302 (right).

  during the implementation of the algorithms illustrated in FIGS. 5 to 9.

  In a first variant, illustrated in FIG. 11, it can be seen that, before the mobile station 301 performs the operation 411: the mobile station 301 sends to the mobile station 302 a message "question_modulation_level" 801 which represents a request of the highest modulation level that is supported by the mobile station 302 and the mobile station 302 sends, to the mobile station 301, a message "modulation_level_response <X>" 802 in which the last term ( symbolized here by "X" represents the highest level of modulation

  supported by the mobile station 302).

  Upon receipt of this message, the central unit 106 of the station 302 performs an evaluation of the service offered by the modulation level M,

operation 411.

  It is observed that the messages specific to the present invention can be transmitted by implementing the user data field provided by the DECT standard (fields known under the name of "field B" (in English "B field")). Thus, a base station meeting this standard is capable of participating in the implementation of the present invention, even if it

  is of construction prior to the present invention.

  In a second variant illustrated in FIG. 12, and which corresponds to the case where the base station 300 is adapted to the implementation of this variant and, more generally, of the present invention: the message 801 is broken down into two messages 801A transmitted by station 301 to station 300 and then 801B transmitted by station 300 to station 302; and the message 802 is decomposed into two messages 802A transmitted by the station 302 to the station 300 and 802B transmitted by the station

300 at the station 301.

  In this second variant, the messages "question_level_modulation" and "response_level_modulation" do not transit

  more in the user field but in signaling messages, that is,

  say that the base station is able to parse these messages.

Claims (24)

  A method of communication between communication stations (300 to 302) adapted to communicate with one another when at least one of said communication stations provides a synchronization signal, said station then operating in "base station" mode and stations not providing a synchronization signal but synchronizing with a synchronization signal transmitted by a station operating in base station mode then operating in "mobile station" mode, characterized in that, for setting up a communication between two stations (301, 302) operating in mobile station mode, it comprises: - performed by one of said stations (301) operating in mobile station mode, the transmission to a base station (300) with which said mobile station is synchronized, a message representative of a modulation level request (402) and - in the absence of implementation of said modulation level by said base station (301), a switching operation of one of said   stations operating in mobile station mode, in base station mode.   2. The communication method as claimed in claim 1, characterized in that, parallel to said switching operation performed by one (301) of said stations operating in mobile station mode, the other (302) of said stations operating in mobile station mode. performs an operation   synchronization with the station that performs the switching operation.   3. Communication method according to any one of   1 or 2, characterized in that it comprises, preliminary to   said switching operation, in the absence of implementation of said modulation level by said base station, a necessity evaluation operation (412) of a switching operation in which it is determined whether the switching of one of the stations operating in station mode   mobile is necessary for said communication between said stations.   4. Communication method according to claim 3, characterized in that, during the necessity evaluation operation, it is determined whether the amount of information to be transmitted between the stations operating in   mobile station is greater than a predetermined value, or not.   5. Communication method according to any one of   claims 3 or 4, characterized in that during the operation   necessity evaluation, it is determined whether the duration of the communication between the stations operating in mobile station mode is greater than a value predetermined, or not.   6. Communication method according to any one of   Claims 3 to 5, characterized in that during the evaluation operation   of necessity, it is determined whether at least one of the said stations operating in   mobile station mode is in communication, or not.   7. Communication method according to any one of   Claims 3 to 6, characterized in that during the evaluation operation   of necessity, it is determined if at least one of said stations operating in mobile station mode is intended to be in communication with another station, or not.   8. Communication method according to any one of   Claims 3 to 7, characterized in that during the evaluation operation   of necessity, it is determined whether each of said stations operating in mobile station mode is capable of implementing said level of modulation required.   9. The communication method as claimed in claim 8, characterized in that, during the necessity evaluation operation, one of said stations operating in mobile station mode performs a transmission operation of a message representative of a modulation level that said station is able to implement for communication between said stations. 10. Communication method according to any one of   Claims 3 to 9, characterized in that during the evaluation operation   of necessity, it is determined whether at least one of the said stations operating in   Mobile station mode is able to switch to base station mode.   11. The communication method as claimed in claim 10, characterized in that, during the necessity evaluation operation, one of said stations operating in mobile station mode performs a transmission operation of a message representative of its ability or his inability to   switch to base station operating mode.   12. A communication device between communication stations (300 to 302) adapted to communicate with one another when at least one of said communication stations provides a synchronization signal, said station then operating in "base station" mode and the stations not providing a synchronization signal but synchronizing themselves to a synchronization signal transmitted by a station operating in base station mode then operating in "mobile station" mode, characterized in that a station operating in mobile station mode (301 ) comprises processing means (104 to 106) adapted for setting up a communication with another station (302) operating in mobile station mode: - to be sent to a base station (300) with which said mobile station is synchronized, a message representative of a modulation level request and - in the absence of implementation of said modulation level by   said base station to switch to base station mode.   13. Communication device according to claim 12, characterized in that the processing means is adapted, when the other station operating in mobile station mode switches to base station mode, to   synchronize with said station that performs the switching operation.   14. Communication device according to claim 12, characterized in that the processing means is adapted, in the absence of implementation of said modulation level by said base station, to evaluate the   need for a switching operation.   15. Network, characterized in that it comprises at least two   devices according to any one of claims 12 to 14.   16. Telephone, characterized in that it comprises a device according to   any of claims 12 to 14.   17. A camera, characterized in that it comprises a   Device according to one of Claims 12 to 14.   18. Printer, characterized in that it comprises a device   according to any one of claims 12 to 14.   19. Scanner, characterized in that it comprises a device according to   any of claims 12 to 14.   20. Camera, characterized in that it comprises a device according to   Any of claims 12 to 14.   21. Computer, characterized in that it comprises a device according to   any of claims 12 to 14.   22. Facsimile machine, characterized in that it comprises a device   according to any one of claims 12 to 14.   23. Television, characterized in that it comprises a device according to   any of claims 12 to 14.   24. Audio / video player, characterized in that it comprises a   Device according to one of Claims 12 to 14.