Abstract:
The subject of the invention is a process for associating an apparatus to a first communication network, the transmissions in the first network being performed on a first channel. The process comprises:
       detection by said apparatus of the first transmission channel;   determination of collision on said channel between signals originating from the first network and from a second network;   in case of collision, transmission of a change of channel request to the first network.
 
The invention applies in particular within the framework of local networks such as HIPERLAN 2.

Description:
This application claims the benefit under 35 U.S.C. § 365 of International Application PCT/FR00/02694, filed Sep. 28, 2000, which claims the benefit of French Application No. 9912051, filed Sep. 28, 1999. 
   The invention relates to a process for associating an apparatus to a communication network, in particular a local network, capable of sharing the same transmission frequency resource as another neighboring network. The invention applies in particular within the framework of broadband radio access networks (BRAN), when an apparatus is to be associated with an existing network. 
   BACKGROUND OF THE INVENTION 
   Local networks using sharing of the radio resource in FDMA mode are required to use one channel from among a finite set of channels, which is given and granted by the standardizing bodies. 
   In order to avoid mutual disturbance, it is often advisable to implement techniques for probing the various channels. It is entirely possible to limit oneself to listening to a subset of channels or to explore all the channels. At the end of this listening phase, the equipment wishing to create a network will choose a channel which it deems to be free of any radio activity. We will then speak of a dynamic frequency selection (DFS) mechanism. 
   In an environment made up of multiple local networks, it is possible that two networks, though geographically close, may have chosen the same frequency, without however interfering with one another. This is all the more probable the lower the number of channels dedicated to this service. 
   However, it may happen that an apparatus which has to associate itself with a network may also be able to communicate with a base station of another network. The problem then arises of the collision of the frames originating from the two networks at the level of this apparatus. 
   The aim of the invention is to remedy this problem. 
   SUMMARY OF THE INVENTION 
   The subject of the invention is a process for associating an apparatus to a first communication network, the transmissions in the first network being performed on a first channel, characterized in that said process comprises the steps of: 
   (a) detection by said apparatus of the first transmission channel; 
   (b) determination of collision on said channel between signals originating from the first network and from a second network; 
   (c) in case of collision, transmission of a change of channel request to the first network. 
   According to a particular embodiment, the process furthermore comprises the step of associating the apparatus with a base station of the first network, following non-detection of collision. 
   According to a particular embodiment, the process furthermore comprises a repeating of the steps of the claim (a) to (c) until the first network locks onto a channel for which no collision is detected. 
   According to a particular embodiment, the change of channel request comprises at least one of the following parameters: an identifier of the first network, an identifier of the apparatus, the number of times that the request has been sent, a suggestion of transmission channel for the first network. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Other characteristics and advantages of the invention will become apparent through the description of a particular exemplary embodiment, described with the aid of the appended drawings and among which: 
       FIG. 1  diagrammatically represents two local networks implementing the process according to the present exemplary embodiment: 
       FIG. 2  is a flowchart of the process according to the present exemplary embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present example lies within the framework of local networks of the HIPERLAN 2 TYPE (&lt;&lt;High Performance Radio Local Network Type 2&gt;&gt;). This type of network is currently undergoing specification at the European Telecommunication Standards Institute (ETSI). Fuller details regarding this network can be found in particular in the following documents, published by the ETSI: 
   (a) ETR0230002 V 0.1.2 (April 1999) Broadband Radio Access Networks (BRAN); High Performance Radio Local Area Networks (HIPERLAN) Type 2; System overview 
   (b) DTS/BRAN030003-1 V 0.h (August 1999) Broadband Radio Access Networks (BRAN); HIPERLAN Type 2 Functional Specification Data Link Control (DLC) layer Part 1—Basic Data Transport Function 
   (c) DTS/BRAN-00240004-2 V 0.a (August 1999) Broadband Radio Access Networks (BRAN) Packet based Convergence Layer for HIPERLAN and HIPERACCESS; Part 2: Ethernet Service Specific Convergence Sublayer 
   (d) DTS/BRAN-0020004-2 V 0.a (July 1999) Broadband Radio Access Networks (BRAN); HIPERLAN Type 2 Functional Specification; Radio Link Control (RLC) sublayer 
   (e) DTS/BRAN030003-1 V 0.j (September 1999) Broadband Radio Access Networks (BRAN); HIPERLAN Type 2 Functional Specification Part 1—Physical (PHY) layer 
   Other ETSI documents relating to HIPERLAN 2 are referenced in document (a). 
     FIG. 1  is a diagram of two dwellings each possessing a local network, N 1  and N 2  respectively. Of course, the invention is not limited to this particular case, and two networks may perfectly well be situated in one and the same building. Each network comprises a central device or base station AP 1 , AP 2 . These base stations are the respective central facilities of each of the networks N 1  and N 2 . In function terms, they comprise the functionality of &lt;&lt;central controllers&gt;&gt; of the HIPERLAN 2 environment. 
   Each network furthermore comprises mobile terminals MTx, communicating with the access point associated with the network. In this regard, the network N 1  comprises the terminals MT 1  and MT 2 , while the network N 2  comprises the terminals MT 3  and MT 4 . 
   When a new mobile terminal MT 5  is to be integrated into an existing network, this terminal traverses the frequency channels on which the networks may transmit until a signal of sufficient power and intelligibility is detected. The intelligibility is related to the error rate detected by the terminal in the data received. 
   In what follows it will be assumed that initially the two terminal N 1  and N 2  use the same transmission channel. Moreover, for the sake of the example, it is assumed that the terminal MT 5  can communicate both with the base station of the network N 1  and with the base station of the network N 2 . 
   In the case where the traffic on each of the two networks N 1  or N 2  does not occupy the whole of the time frame, the new terminal has the possibility of intelligibly receiving the information from at least one of the networks. According to the present example, this is the network N 1 . Generally, the first few items of information thus collected relate to the identity of the network N 1  and to the access entitlements. This information allows the terminal to determine whether it has the access entitlements with regard to this network N 1 . 
   According to the present example, the terminal MT 5  has prior knowledge of the identifier of the network with which it is assumed to associate itself. It thus recognizes the frame corresponding to this network. This identifier may be the &lt;&lt;Network_Operator_ID&gt;&gt; identifier. 
   In the case where the terminal is entitled to access this network N 1 , it initiates a procedure called association, and via which the terminal registers itself in the network N 1  and obtains an identity in return. The protocols generally implemented in respect of this operation require dialogs between on the one hand the terminal and on the other hand the network already formed. For example, it is often necessary to carry out the authentication of the terminal before granting it an identity in the network. 
   In the present case, the communications between the terminal and the network N 1  are subjected to the disturbances emanating from the network N 2 . Thus, there is nothing to guarantee that the association procedure will be performed correctly, since it is strongly dependent on the activity on the concurrent network N 2 . The response of the network N 1  to the association request of the terminal can collide at the level of the terminal with a portion of traffic of the network N 2 . This is detected by the terminal MT 5  by the fact that certain frames or parts of frames are not decodable. The terminal MT 5  will declare that it is in a situation of interference when it is not able correctly to receive these association messages originating from the network N 1 . Thus, the interfering signal, for example a frame of another network, need not be intelligible in respect of the apparatus seeking to detect the interference. The terminal simply has to know the address of the access point of the network with which it wishes to associate itself. 
   Thus, instead of initiating a conventional association procedure, the terminal sends the network N 1  a so-called emergency request, consisting in asking the network N 1  to initiate a dynamic frequency selection, to the exclusion of the current frequency. This request also contains the identity of the network N 1 , so as to prevent the two networks N 1  and N 2  from changing frequency simultaneously: the networks detect the identity and react only if it is addressed to them. 
   The emergency request is transmitted in the RCH field of the HIPERLAN 2 frame of the network N 1 . 
   According to the present example, the emergency request comprises the following parameters: 
   
     
       
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Parameter 
               Description 
             
             
                 
             
           
           
             
               AP_ID or CC_ID 
               Identifies the base station (AP: access point, 
             
             
                 
               CC: Central controller) 
             
             
                 
               Content of the BCCH field of the frame re- 
             
             
                 
               ceived from the network N1 
             
             
               NET_ID 
               Content of the BCCH field of the frame re- 
             
             
                 
               ceived from the network N1 
             
             
               ‘Number_of_Request’ 
               Indicates the number of times that the message 
             
             
                 
               has been sent 
             
             
               ‘Frequency_index’ 
               Index of the frequency/of the suggested channel 
             
             
                 
             
           
        
       
     
   
   The third parameter can influence the decision of the base station AP 1  to accept or reject the request of the terminal, in the event of poor operation of the mobile terminal. This field is optional. 
   The BCCH field is a field of the frame defined by the documents relating to HIPERLAN  2 . 
   According to a variant embodiment, the emergency request furthermore comprises a channel suggestion on the part of the terminal. This suggestion can be determined as follows: the terminal monitors the activity on various channels, for example for a predetermined time, and thus determines which channels are liable to be unoccupied. 
   This technique guarantees that the terminal is correctly understood by the network N 1 , since the terminal has transmitted its request in the scheduled area of the frame of the network N 1 . The network A has recognized its identity in this request and initiates a DFS. At the end of the DFS, the network N 1  will have changed frequency and so the terminal will initiate a normal association procedure with regard to this new frequency, on condition of course that there has been no collision with a third network. 
   The emergency request of the terminal will be received by members of the network N 2  either intelligibly, or in collision with a portion of the traffic of this network. 
   In the case of a collision, the latter is resolved by the repetition mechanism or by the error correcting coding used by the network N 2 . This request being short, it only very locally disturbs the activity of the network N 2 . 
   In the case of intelligible decoding of the request, the members of the network N 2  understand that the DFS request relates to the network N 1 , and thus no DFS is implemented.