Patent Publication Number: US-2022240195-A1

Title: Method for determining a plurality of possible emission power values, method for selecting from this plurality of possible emission power values for an uncoordinated access to the communication medium

Description:
FIELD OF THE INVENTION 
     The field of the invention is that of the management of the access to the communication medium as part of the deployment of the fifth generation of standards for mobile telephony or 5G. 
     More specifically, the invention relates to access to the communication medium by user equipment. 
     PRIOR ART AND ITS DRAWBACKS 
     The Internet of Things (or IoT) is the interconnection between the Internet and the objects called connected objects, such as, for example, sensors or probes. 
     One of the main 5G development scenarios is based on the IoT. In such a scenario, it is expected that a massive number of user equipment will be deployed. The explosion of the number of user equipment will result in an increase in data exchanges between this user equipment and telecommunication network access equipment such as base stations or access points. 
     The data exchanged by this user equipment with equipment located in a telecommunication network mainly consist of signalling messages whose volume generates a significant overload of the resources of the telecommunication network. 
     As the majority of the user equipment has only limited radio and energy resources, it is important to reduce the frequency of data exchanges as well as the volume of data exchanged with the access equipment. 
     In this context, one solution consists in the implementation of a scheme for accessing the resources of a telecommunication network called uncoordinated telecommunication network. An uncoordinated access scheme not only allows reducing the amount of resources used by the telecommunication network by reducing the number of signalling messages exchanged between the user equipment and the access equipment, but also not biasing the limited radio and energy resources of the user equipment beyond their capacities. 
     An example of an uncoordinated access scheme for the uplink direction, that is to say for communications from a user equipment to a base station, is described in the document J. Choi, “NOMA-based random access with multichannel ALOHA”,  IEEE Journal on Selected Areas in Commun., vol.  35, no. 12, pp.2736-2743, Dec. 2017. In this document, a NOMA (Non-Orthogonal Multiple Access) type scheme is implemented in conjunction with a multi-channel random access protocol such as the ALOHA protocol. 
       FIG. 1  represents a cell of a radio communication network of radius D=1 km comprising a base station BST and K=200 user equipment UE N , N∈[1, . . . , 200], identically distributed over the entire surface of the cell. Each active user equipment UE N  that is to say that it exchanges data with the base station BST, is associated with a probability p a  of access to the base station BST. Thus, at a given time, the cell has an effective average number of active user equipment  M =E{M}=Kp a . 
     The cell is subdivided into L=3 zones, called power zones Z 1 , Z 2  and Z 3 , each associated with a reference emission power. With reference to  FIG. 1 , the power zones Z 1 , Z 2  and Z 3  are represented by concentric circles centred on the base station BST. 
     The power zones Z 1 , Z 2  and Z 3  are delimited by thresholds {τ l } l=1   L , representing a distance from the base station BST. These thresholds τ l  are defined such that a user equipment UE N  has an equal probability of being located in one of the power zones while satisfying the condition: 
     
       
         
           
             
               P 
               ⁢ 
               
                 r 
                 ⁡ 
                 
                   ( 
                   
                     k 
                     ∈ 
                     
                       Z 
                       l 
                     
                   
                   ) 
                 
               
             
             = 
             
               
                 1 
                 L 
               
               . 
             
           
         
       
     
     Considering the assumption that the user equipment is uniformly distributed in the cell and neglecting the effects of masks, these thresholds τ l  are given by: 
     
       
         
           
             
               
                 τ 
                 l 
                 2 
               
               - 
               
                 τ 
                 
                   l 
                   - 
                   1 
                 
                 2 
               
             
             = 
             
               
                 
                   D 
                   2 
                 
                 L 
               
               . 
             
           
         
       
     
     Taking τ 0 =0, comes: 
     
       
         
           
             
               
                 τ 
                 l 
               
               = 
               
                 
                   D 
                   ⁢ 
                   
                     
                       l 
                       L 
                     
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   for 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   l 
                 
                 = 
                 1 
               
             
             , 
             … 
             ⁢ 
             
                 
             
             , 
             L 
           
         
       
     
     In this solution, each user equipment UE N  independently selects an emission power as well as a frequency sub-band of a radio signal that it will use to transmit data to the base station BST. The value of the emission power selected by a user equipment UE N  depends on the average power gain of the transmission channel established between the user equipment UE N  and the base station BST. The average power gain of the transmission channel is estimated, for example, using reference signals broadcast periodically by the base station BST to manage the access of the user equipment UE N  to the telecommunication network as well as their mobility to other base stations. 
     The user equipment UE N  has the possibility of transmitting data to the base station BST by transmitting radio signals in several different frequency bands. Such a set of frequency bands is called B. The index set of the active users which transmit in the frequency sub-band i is referred to as  . With this assumption, the radio signals received by the base station BST are written in the form: 
     
       
         
           
             
               
                 
                   
                     y 
                     i 
                   
                   = 
                   
                     
                       
                         ∑ 
                         
                           k 
                           ∈ 
                           
                             J 
                             i 
                           
                         
                       
                       ⁢ 
                       
                         
                           h 
                           
                             i 
                             , 
                             k 
                           
                         
                         ⁢ 
                         
                           
                             P 
                             
                               i 
                               , 
                               k 
                             
                           
                         
                         ⁢ 
                         
                           S 
                           
                             i 
                             , 
                             k 
                           
                         
                       
                     
                     + 
                     
                       n 
                       i 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where h i,k  represents the transmission channel of the user equipment kin the frequency sub-band i, P i,k  represents the transmission power allocated to the emission of a radio signal by the user equipment k in this frequency sub-band i and S i,k  represents the modulated symbols transmitted by the user equipment k in this frequency sub-band i. The amount n i  conventionally designates the additive noise of the transmission channel with n i ˜ (0,N 0 ). 
     The transmission channel h i,k  can then be factorized into the following form: 
     
       
         
           
             
               
                 
                   
                     
                       h 
                       
                         i 
                         , 
                         k 
                       
                     
                     = 
                     
                       
                         
                           α 
                           k 
                         
                         ⁢ 
                         
                           β 
                           
                             i 
                             , 
                             k 
                           
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         with 
                         ⁢ 
                         
                           : 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           α 
                           k 
                         
                       
                       ∈ 
                       
                         ℝ 
                         + 
                       
                     
                   
                   , 
                   
                     
                       β 
                       
                         i 
                         , 
                         k 
                       
                     
                     ∈ 
                     ℂ 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     The amount α k   2 = {|h i,k | 2 } is an attenuation corresponding to the large-scale fading coefficient of the user equipment k for all frequency sub-bands. The amount α k   2  takes into account the effect of remoteness of the user equipment k from the base station BST and a possible mask effect on the propagation of the radio signal due for example to the presence of an obstacle located between user equipment k and the base station BST. 
     The remoteness effect is characterised by a law in A 0 d k   −β  where 0&lt;d k ≤De is the distance between the user equipment k and the base station BST, β is the exponent of the path loss, and A 0  is a constant. 
     The amount β i,k  represents the small-scale fading coefficient of the user equipment k in the frequency sub-band i, it represents the multipath effect and the relationship: 
     
       
         
           
             
               𝔼 
               ⁢ 
               
                 { 
                 
                   | 
                   
                     β 
                     
                       i 
                       , 
                       k 
                     
                   
                   ⁢ 
                   
                     | 
                     2 
                   
                 
                 } 
               
             
             = 
             1 
           
         
       
     
     is satisfied. 
     In the remainder of the document, a simplifying assumption is made which consists in neglecting the rapid fading which amounts to saying that β i,k =1. In addition, concerning the definition of the power zones Z 1 , Z 2  and Z 3 , only the effect of the distance between a user equipment UE N  and the base station BST is taken into account. 
     In this solution, each user equipment UE N  chooses its power zone taking into account its remoteness from the base station BST. This effect is included in the estimated coefficient α k   2  from the reference signals transmitted by the base station BST 
     When B frequency sub-bands are available and in each of them a NOMA process is applied, the number of transmission sub-channels is equal to B×L. Subsequently, only a given frequency sub-band is considered and its index is omitted for the sake of simplification of the notations. 
     A user equipment k being located at an effective distance τ l-1 &lt;d k ≤τ l  from the base station BST selects a reference emission power v l  for emitting a radio signal to the base station BST. Such a reference emission power v l  is defined as follows: 
     
       
         
           
             
               
                 
                   
                     ν 
                     l 
                   
                   = 
                   
                     Γ 
                     ⁡ 
                     
                       ( 
                       
                         
                           V 
                           l 
                         
                         + 
                         1 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where Γ represents the minimum SINR (Signal plus Interferences to Noise Ratio) required to allow the decoding of the radio signal transmitted by the base station BST with a given transmission rate, that is to say a modulation and coding scheme of rate R in number of bits by use of b.p.c.u channel and where V l  for l∈[1, . . . , L], is given by: 
     
       
         
           
             
               
                 
                   
                     
                       V 
                       l 
                     
                     = 
                     
                       
                         ∑ 
                         
                           m 
                           = 
                           
                             l 
                             + 
                             1 
                           
                         
                         L 
                       
                       ⁢ 
                       
                         v 
                         m 
                       
                     
                   
                   , 
                   
                     l 
                     ∈ 
                     
                       [ 
                       
                         1 
                         , 
                         
                           L 
                           - 
                           1 
                         
                       
                       ] 
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     and for l=L, V L =0 
     It comes, by recurrence using (2) and (3), that 
     
       
         
           
             
               
                 
                   
                     
                       ν 
                       l 
                     
                     = 
                     
                       
                         Γ 
                         ⁡ 
                         
                           ( 
                           
                             Γ 
                             + 
                             1 
                           
                           ) 
                         
                       
                       
                         L 
                         - 
                         l 
                       
                     
                   
                   , 
                   
                     l 
                     ∈ 
                     
                       [ 
                       
                         1 
                         , 
                         L 
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     In other words, since ν 1 &gt;ν 2 &gt; . . . &gt;ν L  and τ L &gt;τ L-1 &gt; . . . &gt;τ 1 , the user equipment UE N  located away from the base station BST selects lower emission power levels than the user equipment UE N  located close to the base station BST to emit radio signals to the latter. 
     The user equipment k, after having selected a reference emission power, transmits this radio signal with the following transmitted symbol emission power: 
     
       
         
           
             
               
                 
                   
                     P 
                     k 
                   
                   = 
                   
                     
                       v 
                       l 
                     
                     
                       α 
                       k 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     The base station BST comprises a successive interference cancellation receiver which allows separating the different radio signals transmitted by the active user equipment UE N  in the cell. By assuming a noise power normalised to one (i.e. N 0 =1) and that all active user equipment UE N  choose different emission power levels to emit radio signals to the base station BST, the base station BST is capable of error-free decoding all received radio signals with the minimum SINR ratio Γ. 
     The value of the SINR of a user equipment which has chosen an emission power is given by: 
     
       
         
           
             
               
                 
                   
                     v 
                     l 
                   
                   
                     
                       
                         ∑ 
                         
                           m 
                           = 
                           
                             l 
                             + 
                             1 
                           
                         
                         L 
                       
                       ⁢ 
                       
                         v 
                         m 
                       
                     
                     + 
                     1 
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     which corresponds to the minimum SINR ratio Γ when the equations (2) and (3) are applied. 
     By considering a transmission rate R=log 2 (Γ+1), all radio signals transmitted by the active user equipment UE N  can then be iteratively decoded by the base station by implementing a successive interference cancellation method in descending order. 
     In this solution, in order for the BST base station to be able to decode all radio signals emitted by the M active user equipment UE N , it is necessary to have a number of emission power levels L greater than or equal to M. In addition, there should be at most one user equipment UE N  per power zone. Thus, in order to be able to meet the connectivity needs in a cell of a 5G-compliant telecommunication network, L must be in the range of a few dozen or even a few hundred levels. This assumption leads to the use of exponential transmission power levels depending on L as indicated by the equation (4) above. The use of such emission power levels exceeds the capacity of the used user equipment UE N  which are generally sensors with limited capacities due to the low costs of this equipment. 
     Even if the emission power levels were judiciously chosen in order to ensure a SINR diversity guaranteeing the decoding of all superimposed signals received by the base station BST, the deviation between two successive emission power levels remains large and increases with L. 
     Moreover, in the solution described above, it is assumed that the user equipment UE N  have knowledge of the value of |h i,k | 2  while, in practice, the user equipment UE N  have only knowledge of the value of the coefficient α k   2 . Thus, such a solution seems difficult to apply in the case of massive access of objects connected to the resources of a telecommunication network. 
     There is consequently a need for a solution allowing a massive access of user equipment to the resources of a telecommunication network not having these drawbacks. 
     DISCLOSURE OF THE INVENTION 
     The invention meets this need by proposing a method for selecting an emission power value of a radio signal implemented by at least one user equipment located in a first emission power zone defined around a base station to which said user equipment is attached, said method comprising:
         obtaining a plurality of possible emission power values for said first emission power zone, said possible emission power values for said first zone being determined depending on at least:   one reference emission power value for said first emission power zone,   one reference emission power value for at least one second emission power zone defined around said base station and adjacent to the first emission power zone,   one value of a discretisation step defining a level of disparity between the possible power values per power zone, and   selecting an emission power value from said plurality of possible emission power values for said first emission power zone.       

     By proposing the different user equipment to be able to select an emission power value from a set of possible emission power values depending on their location relative to the base station, the solution of the invention allows the base station to decode the radio signals emitted by a greater number of user equipment. 
     Such a solution allows, consequently, a massive user equipment access to the resources of a telecommunication network while limiting the risks of failure of a decoding of the radio signals received by the base station. 
     According to a first variant of the selection method, the selection of an emission power value from said plurality of possible emission power values for said first emission power zone is done according to a discrete probability distribution. 
     Thus, this limits the risk that different user equipment located in the same emission power zone selects the same emission power value. This solution allows ensuring that each user equipment accesses the resources of the telecommunication network. 
     According to a second variant of the selection method, obtaining the plurality of possible emission power values for said first emission power zone consists in receiving at least one message emitted by the base station comprising said plurality of possible emission power values for said first emission power zone 
     This solution is of interest when the user equipment is, for example, a sensor type connected object with limited calculation capacities. 
     According to a combination of the first and second variants of the selection method, at least one message emitted by the base station also comprises the discrete probability distribution according to which an emission power value is selected from said plurality of possible emission power values for said first emission power zone. 
     According to a third variant of the selection method, obtaining the plurality of possible emission power values for said first emission power zone consists in:
         receiving at least one message emitted by the base station comprising, among others, the reference emission power value for said first emission power zone, the reference emission power value for at least one second emission power zone defined around said base station and adjacent to the first emission power zone, a value of a discretisation step defining a level of disparity between the possible power values,   determining said possible emission power values for said first zone depending on the data included in said at least one received message.       

     In such an implementation, the user equipment itself performs all calculations instead of the base station. This allows resources at the base station to be freed. 
     According to a combination of the first and third variants of the selection method, said selection method further comprises determining the discrete probability distribution according to which an emission power value is selected from said plurality of possible emission power values for said first emission power zone depending on parameters relating to said discrete probability distribution included in the at least one received message. 
     According to a fourth variant of the selection method, the selection method comprises prior to obtaining:
         measuring reference radio signals transmitted by the base station   determining a coefficient α k   2  depending on the reference signals   determining, depending on the coefficient α k   2 , an effective distance separating the user equipment from the base station, said effective distance identifying the emission power zone in which the user equipment is located.       

     The invention also relates to a method for determining a plurality of possible emission power values of a radio signal, said radio signal being intended to be emitted by at least one user equipment located in a first emission power zone defined around a base station to which said user equipment is attached, said method being implemented by the base station and comprising:
         determining the plurality of possible emission power values for said first emission power zone, said possible emission power values for said first zone being determined depending on at least:   one reference emission power value for said first emission power zone,   one reference emission power value for at least one second emission power zone defined around said base station and adjacent to the first emission power zone,   one value of a discretisation step defining a level of disparity between the possible power values, and   transmitting said plurality of possible emission power values for said first emission power zone to said at least one user equipment.       

     According to a second variant of the determination method, it further comprises:
         determining a discrete probability distribution according to which said at least one user equipment selects an emission power value from said plurality of possible emission power values for said first emission power zone,   transmitting said discrete probability distribution to said at least one user equipment.       

     Another object of the invention is a user equipment located in a first emission power zone defined around a base station to which it is attached, said user equipment comprising at least one processor configured to:
         obtain a plurality of possible emission power values of a radio signal for said first emission power zone, said possible emission power values of a radio signal for said first zone being determined depending on at least:   one reference emission power value for said first emission power zone,   one reference emission power value for at least one second emission power zone defined around said base station and adjacent to the first emission power zone,   one value of a discretisation step defining a level of disparity between the possible power values, and   select an emission power value of a radio signal from said plurality of possible emission power values of a radio signal for said first emission power zone.       

     Such a user equipment can be a mobile phone or a connected object such as a temperature sensor, a motion sensor, a connected car, etc. 
     The invention also relates to a base station capable of determining a plurality of possible emission power values of a radio signal, said radio signal being intended to be emitted by at least one user equipment located in a first emission power zone defined around said base station to which said user equipment is attached, the base station comprising at least one processor configured to:
         determine the plurality of possible emission power values for said first emission power zone, said possible emission power values for said first zone being determined depending on at least:   one reference emission power value for said first emission power zone,   one reference emission power value for at least one second emission power zone defined around said base station and adjacent to the first emission power zone,   one value of a discretisation step defining a level of disparity between the possible power values, and   transmit said plurality of possible emission power values for said first emission power zone to said at least one user equipment.       

     Finally, the invention relates to computer program products comprising program code instructions for implementing the methods as previously described, when they are executed by a processor. 
     The invention also relates to a recording medium readable by a computer on which computer programs are recorded, comprising program code instructions for the execution the methods according to the invention as described above. 
     Such a recording medium can be any entity or device capable of storing the programs. For example, the medium may include a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or else a magnetic recording means, for example a USB key or a hard disk. 
     On the other hand, such a recording medium can be a transmissible medium such as an electrical or optical signal, which can be conveyed via an electrical or optical cable, by radio or by other means, such that the computer programs it contains can be executed remotely. The programs according to the invention can in particular be downloaded over a network, for example the Internet network. 
     Alternatively, the recording medium can be an integrated circuit in which the programs are incorporated, the circuit being adapted to execute or to be used in the execution of the aforementioned methods of the invention. 
    
    
     
       LIST OF FIGURES 
       Other aims, features and advantages of the invention will emerge more clearly on reading the following description, given by way of simple illustrative, and not limiting, example in relation to the figures, from which: 
         FIG. 1 : this figure represents a cell of a radio communication network in which a state-of-the-art solution is implemented, 
         FIG. 2 : this figure represents the steps of a method for selecting an emission power value of a radio signal according to a first embodiment of the invention, 
         FIG. 3 : this figure represents a probability mass function  (.), 
         FIG. 4 : this figure represents the steps of a method for selecting an emission power value of a radio signal according to a second embodiment of the invention, 
         FIG. 5 : this figure represents the average number of user equipment UE N  that successfully transmit their data packets, or normalised throughput in the figure, depending on the network load, or average traffic load in the figure, 
         FIG. 6 : this figure represents a user equipment according to one embodiment of the invention, 
         FIG. 7 : this figure represents a base station according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The invention is also implemented in a cell of a radio communication network of radius D comprising a base station BST and K user equipment UE N , N∈[1, . . . , K], identically distributed over the entire surface of the cell as described with reference to  FIG. 1 . Each active user equipment UE N , that is to say that it exchanges data with the base station BST, is associated with a probability of access to the base station BST p a . Thus, at a given time, the cell includes an effective average number of active user equipment  M =E{M}=Kp a . The cell is subdivided into L=3 zones, called power zones Z 1 , Z 2  and Z 3 , each associated with a reference emission power. 
     The power zones Z 1 , Z 2  and Z 3  are delimited by thresholds {τ l } l=1   L , representing a distance from the base station BST. These thresholds τ l  are defined such that a user equipment UE N  has an equal probability of being located in one of the power zones Z 1 , Z 2  and Z 3  while satisfying the condition: 
     
       
         
           
             
               
                 P 
                 ⁢ 
                 
                   r 
                   ⁡ 
                   
                     ( 
                     
                       k 
                       ∈ 
                       
                         Z 
                         1 
                       
                     
                     ) 
                   
                 
               
               = 
               
                 1 
                 L 
               
             
             , 
           
         
       
     
     under the assumption of a uniform distribution of the user equipment UE N  in the cell. 
     The general principle of the invention is based on the fact that each power zone Z 1 , Z 2  and Z 3  is associated with a set of n l  discrete emission power values, called possible power values, located around the value of a reference emission power ν l  of the considered power zone. Each user equipment UE N  located in a power zone Z 1 , Z 2  and Z 3  selects an emission power value X from the possible power values {ν l,n } n=1   n     l   . 
     The possible power values are distributed around the value of a reference emission power ν l  according to a discrete probability distribution f ν     l   ={Pr(X=ν l,1 ), . . . , Pr(X=ν l,n     l   )} where Pr(X=ν l,n ) gives the probability that a user equipment UE N  located in the power zone whose reference emission power is ν l  selects an emission power value equal to ν l,n . 
     The cell being divided into three power zones Z 1 , Z 2  and Z 3 , there are therefore L=3 distinct emission power levels. In the remainder of the document, there is M i =3 user equipment for a considered frequency sub-band i. 
     The three power zones Z 1 , Z 2  and Z 3  are associated with the possible emission power values {ν 1,n } n=1′   6 , {ν 2,n } n=1   6  and {ν 3,n } n=1   6 . The possible emission power values respectively follow discrete probability distributions f ν     1   , f ν     2    and f ν     3   . 
       FIG. 2  represents the steps of a method for selecting an emission power value of a radio signal according to a first embodiment of the invention. 
     In a step E1, the base station BST determines the different possible emission power values for the different emission power zones Z 1 , Z 2 , Z 3 . 
     To do this, the base station BST first determines a range I t  in which the possible emission power values are spread. 
     The values of the bounds of the range I t  are given by: 
     
       
         
           
             
               
                 
                   
                     I 
                     l 
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 [ 
                                 
                                   
                                     v 
                                     l 
                                   
                                   - 
                                   
                                     
                                       
                                         
                                           v 
                                           l 
                                         
                                         - 
                                         
                                           v 
                                           
                                             l 
                                             + 
                                             1 
                                           
                                         
                                       
                                       2 
                                     
                                     ⁢ 
                                     
                                       v 
                                       l 
                                     
                                   
                                   + 
                                   
                                     
                                       
                                         v 
                                         
                                           l 
                                           - 
                                           1 
                                         
                                       
                                       - 
                                       
                                         v 
                                         l 
                                       
                                     
                                     2 
                                   
                                 
                                 ] 
                               
                               , 
                               
                                 
                                   v 
                                   0 
                                 
                                 = 
                                 
                                   
                                     
                                       v 
                                       1 
                                     
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     for 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     l 
                                   
                                   = 
                                   
                                     
                                       1 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       … 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       L 
                                     
                                     - 
                                     1 
                                   
                                 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   [ 
                                   
                                     
                                       
                                         V 
                                         l 
                                       
                                       ⁢ 
                                       
                                         v 
                                         l 
                                       
                                     
                                     + 
                                     
                                       
                                         
                                           v 
                                           
                                             l 
                                             - 
                                             1 
                                           
                                         
                                         - 
                                         
                                           v 
                                           l 
                                         
                                       
                                       2 
                                     
                                   
                                   ] 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 for 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 l 
                               
                               = 
                               L 
                             
                           
                         
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     The number of possible emission power values for a given emission power zone Z is chosen such as to respect the proportionality between the two ranges 
     
       
         
           
             
               [ 
               
                 
                   
                     
                       v 
                       l 
                     
                     - 
                     
                       v 
                       
                         l 
                         + 
                         1 
                       
                     
                   
                   2 
                 
                 ⁢ 
                 
                   v 
                   l 
                 
               
               ] 
             
             ⁢ 
             
                 
             
             ⁢ 
             
               and 
               ⁢ 
               
                   
               
               [ 
               
                 
                   v 
                   l 
                 
                 ⁢ 
                 
                   
                     
                       v 
                       
                         l 
                         - 
                         1 
                       
                     
                     - 
                     
                       v 
                       l 
                     
                   
                   2 
                 
               
               ] 
             
           
         
       
     
     located on both sides of the probability distribution centred around the value of the reference power ν l  of the range bounds I l . 
     The maximum number of possible emission power values for each emission power zone Z is for example equal to the average number  M  of active user equipment UE N    
     Knowing the maximum number of possible emission power values for an emission power zone Z and knowing the bounds of the range I l , the base station BST then determines the different possible emission power values for an emission power zone Z. For this, a discretisation step 
     
       
         
           
             
               
                 Δ 
                 l 
               
               = 
               
                 
                   T 
                   l 
                 
                 
                   M 
                   _ 
                 
               
             
             , 
           
         
       
     
     where T l  represents the width of the range I l , is determined for an emission power zone Z. Such a discretisation step Δ l  allows offering a certain level of disparity between the possible power values thus increasing the probability that the base station BST separates all radio signals received in view of their decoding. 
     A minimum discretisation step threshold independent of the value  M , noted Δ, is defined. If the discretisation step Δ l  is less than or equal to the minimum discretisation step threshold Δ, then, it is the minimum discretisation step threshold value Δ which is used to determine the different possible emission power values for the emission power zone Z in order to guarantee a minimum level of disparity between the possible power values in each emission power zone Z. 
     In a step E 2 , the base station BST determines a discrete probability distribution according to which the user equipment UE N  located in a given emission power zone select an emission power value from the plurality of possible emission power values for the emission power zone in which they are located. 
     In the following example, the discrete probability distribution according to which the user equipment UE N  select an emission power value from the plurality of possible emission power values is a normal distribution of the discrete values. Of course, any discrete probability distribution can be used when implementing the selection method according to the first embodiment of the invention. 
     Thus, for a normal distribution, the probability mass function  (.) of a possible emission power value ν l,n  is given by: 
     
       
         
           
             
               
                 
                   
                     𝒫 
                     ⁡ 
                     
                       ( 
                       
                         X 
                         = 
                         
                           v 
                           
                             l 
                             , 
                             n 
                           
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       f 
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               v 
                               
                                 l 
                                 , 
                                 n 
                               
                             
                             ∖ 
                             
                               v 
                               l 
                             
                           
                           , 
                           
                             σ 
                             l 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         1 
                         A 
                       
                       ⁢ 
                       
                         1 
                         
                           
                             2 
                             ⁢ 
                             Π 
                             ⁢ 
                             
                               σ 
                               l 
                               2 
                             
                           
                         
                       
                       ⁢ 
                       
                         e 
                         
                           - 
                           
                             
                               
                                 ( 
                                 
                                   
                                     v 
                                     
                                       l 
                                       , 
                                       n 
                                     
                                   
                                   - 
                                   
                                     v 
                                     l 
                                   
                                 
                                 ) 
                               
                               2 
                             
                             
                               2 
                               ⁢ 
                               
                                 σ 
                                 l 
                                 2 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     where A is a valid normalisation constant which is 
     
       
         
           
             A 
             = 
             
               
                 ∑ 
                 
                   n 
                   = 
                   1 
                 
                 
                   n 
                   l 
                 
               
               ⁢ 
               
                 
                   1 
                   
                     
                       2 
                       ⁢ 
                       
                         ∏ 
                         
                           σ 
                           l 
                           2 
                         
                       
                     
                   
                 
                 ⁢ 
                 
                   
                     e 
                     
                       - 
                       
                         
                           
                             ( 
                             
                               
                                 v 
                                 
                                   l 
                                   , 
                                   n 
                                 
                               
                               - 
                               
                                 v 
                                 l 
                               
                             
                             ) 
                           
                           2 
                         
                         
                           2 
                           ⁢ 
                           
                             σ 
                             l 
                             2 
                           
                         
                       
                     
                   
                   . 
                 
               
             
           
         
       
     
     The deviation of the Gaussian σ l , is chosen, for example, such that 68% of the possible emission power values is comprised in the range [ν l −σ l   2 ν l +σ l   2 ]. 
     Such a probability mass function  (.) is represented in  FIG. 3 . 
     The calculations performed by the base station BST during steps E 1  and E 2  correspond to the following algorithm: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 
                   
                     
                       
                         
                           
                             If 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               Δ 
                               l 
                             
                           
                           ≥ 
                           Δ 
                         
                         , 
                         
                           
                             n 
                             l 
                             - 
                           
                           ← 
                           
                             ⌈ 
                             
                               
                                 
                                   
                                     v 
                                     
                                       l 
                                       - 
                                       1 
                                     
                                   
                                   - 
                                   
                                     v 
                                     l 
                                   
                                 
                                 
                                   
                                     v 
                                     
                                       l 
                                       - 
                                       1 
                                     
                                   
                                   - 
                                   
                                     v 
                                     
                                       l 
                                       + 
                                       1 
                                     
                                   
                                 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   
                                     M 
                                     _ 
                                   
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                             ⌉ 
                           
                         
                       
                     
                   
                 
               
               
                   
               
               
                 where n l   −  represents the number of possible emission power 
               
               
                 values greater than v l  and the notation ┌.┐ means rounded to 
               
               
                 the nearest next integer value 
               
               
                 Discretize [v l  − ( M  − 1 − n l   − ) Δ l v l  + Δ l n l   − ] using Δ l   
               
               
                 Output: {v l,n } n=1   n     l   ~f v     l    = {  (X = v l,n )} n=1   n     l     
               
               
                 Else 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           Discretize 
                           ⁢ 
                           
                               
                           
                           [ 
                           
                             
                               v 
                               l 
                             
                             - 
                             
                               
                                 
                                   
                                     v 
                                     l 
                                   
                                   - 
                                   
                                     v 
                                     
                                       l 
                                       + 
                                       1 
                                     
                                   
                                 
                                 2 
                               
                               ⁢ 
                               
                                 v 
                                 l 
                               
                             
                             + 
                             
                               
                                 
                                   v 
                                   
                                     l 
                                     - 
                                     1 
                                   
                                 
                                 - 
                                 
                                   v 
                                   l 
                                 
                               
                               2 
                             
                           
                           ] 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         using 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Δ 
                       
                     
                   
                 
               
               
                   
               
               
                 Output: {v l,n } n=1   n     l   ~f v     l    = {  (X = v l,n )} n=1   n     l     
               
               
                 End 
               
               
                   
               
            
           
         
       
     
     In a step E 3 , the base station BST broadcasts at least one message MGS 1  to the user equipment UE N . The message MSG 1  includes the different possible emission power values for each of the emission power zones Z 1 , Z 2  and Z 3  as well as the corresponding probability mass functions  (X=ν l,n ). 
     In a step E 4 , a user equipment UE N  receives the message MGS 1  broadcast by the base station BST. 
     In a step E 5 , a user equipment UE N  selects an emission power value from the possible emission power values for the emission power zone in which it is located. 
     In a step E 6 , a user equipment UE N  transmits a radio signal with the transmitted symbol emission power corresponding to the value of the possible emission power selected during step E 5 . 
     Prior to each emission of a radio signal, a user equipment UE N  updates the value of the coefficient α k   2  based on reference radio signals transmitted by the base station BST. The coefficient α k   2  represents, among other, a mask effect which may be due to the presence of an obstacle located between the user equipment UE N  and the base station BST, and the remoteness of the user equipment UE N  from the base station BST. Such a mask effect is generally characterised by a log-normal distribution: 
     
       
         
           
             
               f 
               ⁡ 
               
                 ( 
                 
                   
                     x 
                     ; 
                     μ 
                   
                   , 
                   σ 
                 
                 ) 
               
             
             = 
             
               
                 1 
                 
                   x 
                   ⁢ 
                   σ 
                   ⁢ 
                   
                     
                       2 
                       ⁢ 
                       π 
                     
                   
                 
               
               ⁢ 
               
                 exp 
                 [ 
                 
                   - 
                   
                     
                       
                         ( 
                         
                           
                             ln 
                             ⁡ 
                             
                               ( 
                               x 
                               ) 
                             
                           
                           - 
                           μ 
                         
                         ) 
                       
                       2 
                     
                     
                       2 
                       ⁢ 
                       
                         σ 
                         2 
                       
                     
                   
                 
                 ] 
               
             
           
         
       
     
     The user equipment UE N  deduces from the value of the updated coefficient α k   2  the effective distance d k  which separates it from the base station BST as well as the emission power zone in which it is located as follows: 
     
       
         
           
             
               d 
               k 
             
             = 
             
               
                 ( 
                 
                   
                     A 
                     0 
                   
                   
                     α 
                     k 
                     2 
                   
                 
                 ) 
               
               
                 1 
                 β 
               
             
           
         
       
     
     If the value of the selected possible emission power P k  is strictly greater than a maximum power value P max  of the user equipment UE N  then the user equipment UE N  transmits the radio signal with an emission power whose value is P max . The SINR associated with this radio signal is then calculated as follows 
     
       
         
           
             
               
                 γ 
                 _ 
               
               k 
             
             = 
             
               
                 
                   P 
                   
                     m 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ax 
                   
                 
                 ⁢ 
                 
                   α 
                   k 
                   2 
                 
               
               
                 
                   
                     ∑ 
                     
                       m 
                       = 
                       
                         l 
                         + 
                         1 
                       
                     
                     L 
                   
                   ⁢ 
                   
                     ν 
                     m 
                   
                 
                 + 
                 1 
               
             
           
         
       
     
     In one example implementation, on receipt of the message MSG 1 , the user equipment UE 1 , located in the emission power zone Z 1 , selects the emission power value ν 1,6 =ν 1 , while the user equipment UE 2  and UE 3  both located in the emission power zone Z 3 , respectively select the possible emission power values ν 3,1  and ν 3,6  which are distinct from each other. 
     The three user equipment UE 1 , UE 2  and UE3 each send a message MGS 2  to the base station. These three messages are emitted respectively to the emission powers ν 1 , ν 3,1  and ν 3,6 . 
     In a step E 7 , the base station BST receives the radio signals emitted by the three user equipment UE 1 , UE 2  and UE 3 . 
     The successive interference cancellation process implemented by the base station BST begins by decoding the radio signal emitted by the user equipment UE 1  because it is the one having the maximum received power. 
     The SINR associated with this radio signal is calculated as follows: 
     
       
         
           
             
               
                 
                   
                     γ 
                     1 
                   
                   = 
                   
                     
                       
                         
                           P 
                           1 
                         
                         ⁢ 
                         
                           α 
                           1 
                           2 
                         
                       
                       
                         
                           
                             P 
                             2 
                           
                           ⁢ 
                           
                             α 
                             2 
                             2 
                           
                         
                         + 
                         
                           
                             P 
                             3 
                           
                           ⁢ 
                           
                             α 
                             3 
                             2 
                           
                         
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           v 
                           
                             1 
                             , 
                             6 
                           
                         
                         
                           
                             v 
                             
                               3 
                               , 
                               6 
                             
                           
                           + 
                           
                             v 
                             
                               3 
                               , 
                               1 
                             
                           
                           + 
                           1 
                         
                       
                       = 
                       
                         
                           
                             v 
                             1 
                           
                           
                             
                               v 
                               3 
                             
                             + 
                             
                               4 
                               ⁢ 
                               
                                 Δ 
                                 3 
                               
                             
                             + 
                             
                               v 
                               3 
                             
                             - 
                             
                               Δ 
                               3 
                             
                             + 
                             1 
                           
                         
                         = 
                         
                           
                             Γ 
                             ⁡ 
                             
                               ( 
                               
                                 
                                   Γ 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       
                                         v 
                                         3 
                                       
                                       + 
                                       1 
                                     
                                     ) 
                                   
                                 
                                 + 
                                 
                                   v 
                                   3 
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                           
                             
                               2 
                               ⁢ 
                               
                                 v 
                                 3 
                               
                             
                             + 
                             
                               3 
                               ⁢ 
                               
                                 Δ 
                                 3 
                               
                             
                             + 
                             1 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     It appears that the SINR γ 1  of the radio signal emitted by the user equipment UE 1  is strictly greater than Γ if 
     
       
         
           
             
               Δ 
               3 
             
             ≤ 
             
               
                 
                   Γ 
                   2 
                 
                 3 
               
               . 
             
           
         
       
     
     For Γ=6 dB and Δ=1, it is verified that Δ 3 =1.997&gt;Δ. In this case the condition 
     
       
         
           
             
               Δ 
               3 
             
             ≤ 
             
               
                 Γ 
                 2 
               
               3 
             
           
         
       
     
     is satisfied and the radio signal transmitted by the user equipment UE 1  is successfully decoded by the base station BST. 
     Having parameters representing the transmission channel established between it and the user equipment UE 1 , the base station BST can then subtract the signal emitted by the user equipment UE 1  already decoded from the other received radio signals. 
     The base station BST then proceeds to the decoding of the second radio signal whose emission power at the highest value, that is to say the radio signal emitted by the user equipment UE 2 . 
     The SINR associated with this radio signal emitted by the user equipment UE 2  is calculated as follows 
     
       
         
           
             
               
                 
                   
                     γ 
                     2 
                   
                   = 
                   
                     
                       
                         
                           P 
                           2 
                         
                         ⁢ 
                         
                           α 
                           2 
                           2 
                         
                       
                       
                         
                           
                             P 
                             3 
                           
                           ⁢ 
                           
                             α 
                             3 
                             2 
                           
                         
                         + 
                         1 
                       
                     
                     = 
                     
                       
                         
                           v 
                           
                             3 
                             , 
                             6 
                           
                         
                         
                           
                             v 
                             
                               3 
                               , 
                               1 
                             
                           
                           + 
                           1 
                         
                       
                       = 
                       
                         
                           
                             
                               v 
                               3 
                             
                             + 
                             
                               4 
                               ⁢ 
                               
                                 Δ 
                                 3 
                               
                             
                           
                           
                             
                               v 
                               3 
                             
                             - 
                             
                               Δ 
                               3 
                             
                             + 
                             1 
                           
                         
                         = 
                         
                           
                             Γ 
                             + 
                             
                               4 
                               ⁢ 
                               
                                 Δ 
                                 3 
                               
                             
                           
                           
                             Γ 
                             - 
                             
                               Δ 
                               3 
                             
                             + 
                             1 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     The base station BST can decode this second radio signal if γ 2 ≥Γ. This condition is satisfied since γ 2 =4.01 and that Γ=3.98. 
     The radio signal emitted by the user equipment UE 3  for its part cannot be decoded by the base station BST after the subtraction of the radio signal emitted by the user equipment UE 2  because γ 3 =Γ−Δ 3  and is therefore strictly less than Γ. 
     If the maximum emission power of a user equipment k is less than the value of the selected possible emission power associated 
     
       
         
           
             
               P 
               k 
             
             = 
             
               
                 v 
                 
                   l 
                   , 
                   n 
                 
               
               
                 α 
                 k 
                 2 
               
             
           
         
       
     
     with the target SINR Γ then the user equipment k decreases the value of SINR until reaching the value of the maximum target SINR that it can reach by considering that all power levels ν m , m&gt;l are occupied, that is to say by considering that all user equipment associated with the emission power levels m&lt;l have been subtracted by the base station BST during decoding. Thus, the user equipment k adapts its transmission rate R k  proportionally to the value of the estimated reception SINR γ k  in the case where there are no possible emission power values and for a transmission at full power P max    
     
       
         
           
             
               
                 γ 
                 ¯ 
               
               k 
             
             = 
             
               
                 
                   P 
                   
                     m 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ax 
                   
                 
                 ⁢ 
                 
                   α 
                   k 
                   2 
                 
               
               
                 
                   
                     ∑ 
                     
                       m 
                       = 
                       
                         l 
                         + 
                         1 
                       
                     
                     L 
                   
                   ⁢ 
                   
                     ν 
                     m 
                   
                 
                 + 
                 1 
               
             
           
         
       
     
     with in the ideal case given by the information theory 
     
       
         
           
             
               R 
               k 
             
             = 
             
               
                 log 
                 2 
               
               ⁡ 
               
                 ( 
                 
                   1 
                   + 
                   
                     
                       γ 
                       ¯ 
                     
                     k 
                   
                 
                 ) 
               
             
           
         
       
     
     It should be noted that this user equipment generates less interference on the other user equipment than when it transmits with the possible emission power 
     
       
         
           
             
               P 
               k 
             
             = 
             
               
                 
                   v 
                   
                     l 
                     , 
                     n 
                   
                 
                 
                   α 
                   k 
                   2 
                 
               
               . 
             
           
         
       
     
     Indeed, the user equipment then transmits at an emission power lower than that initially determined based on the value of the target SINR Γ in the case where there are possible emission power values, without its emission interfering with the decoding of the radio signals transmitted by other user equipment. 
     When the base station BST is unable to decode the superimposed signals in a given frequency sub-band, it requests their retransmission by sending a negative acknowledgment message or NACK to the concerned connected objects UE N . When retransmitting these radio signals, the concerned user equipment UE N  selects possible power values different from those chosen for the first transmission in order to improve the chances of a successful decoding by the base station BST. 
       FIG. 4  represents the steps of a method for selecting an emission power value of a radio signal according to a second embodiment of the invention. 
     In a step F1, the base station BST broadcasts at least one message MSG 3  to the user equipment UE N . The message MSG 3  comprises, among others, the reference emission power values for the different emission power zones Z 1 , Z 2  and Z 3 , the average number of active user equipment located in the different emission power zones Z 1 , Z 2  and Z 3 . 
     In a step F 2 , the user equipment UE N  determines the different possible emission power values for the different emission power zones Z 1 , Z 2 , Z 3 . 
     To do this, the user equipment UE N  first determines a range I l  in which the possible emission power values of an emission power zone Z spread. 
     The values of the bounds of the range I l  are given by: 
     
       
         
           
             
               
                 
                   
                     I 
                     l 
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 [ 
                                 
                                   
                                     v 
                                     l 
                                   
                                   - 
                                   
                                     
                                       
                                         
                                           v 
                                           l 
                                         
                                         - 
                                         
                                           v 
                                           
                                             l 
                                             + 
                                             1 
                                           
                                         
                                       
                                       2 
                                     
                                     ⁢ 
                                     
                                       v 
                                       l 
                                     
                                   
                                   + 
                                   
                                     
                                       
                                         v 
                                         
                                           l 
                                           - 
                                           1 
                                         
                                       
                                       - 
                                       
                                         v 
                                         l 
                                       
                                     
                                     2 
                                   
                                 
                                 ] 
                               
                               , 
                               
                                 
                                   v 
                                   0 
                                 
                                 = 
                                 
                                   
                                     
                                       v 
                                       1 
                                     
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     for 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     l 
                                   
                                   = 
                                   
                                     
                                       1 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       … 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       L 
                                     
                                     - 
                                     1 
                                   
                                 
                               
                             
                           
                         
                         
                           
                             
                               
                                 
                                   [ 
                                   
                                     
                                       
                                         v 
                                         l 
                                       
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       
                                         v 
                                         l 
                                       
                                     
                                     + 
                                     
                                       
                                         
                                           v 
                                           
                                             l 
                                             - 
                                             1 
                                           
                                         
                                         - 
                                         
                                           v 
                                           l 
                                         
                                       
                                       2 
                                     
                                   
                                   ] 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 for 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 l 
                               
                               = 
                               L 
                             
                           
                         
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     The number of possible emission power values for a given emission power zone Z is chosen so as to respect the proportionality between the two ranges 
     
       
         
           
             
               [ 
               
                 
                   
                     
                       v 
                       l 
                     
                     - 
                     
                       v 
                       
                         l 
                         + 
                         1 
                       
                     
                   
                   2 
                 
                 ⁢ 
                 
                   v 
                   l 
                 
               
               ] 
             
             ⁢ 
             
                 
             
             ⁢ 
             
               and 
               ⁢ 
               
                   
               
               [ 
               
                 
                   v 
                   l 
                 
                 ⁢ 
                 
                   
                     
                       v 
                       
                         l 
                         - 
                         1 
                       
                     
                     - 
                     
                       v 
                       l 
                     
                   
                   2 
                 
               
               ] 
             
           
         
       
     
     located on both sides of the probability distribution centred around the value of the reference power ν l  of the range bounds I l . 
     The maximum number of possible emission power values for each emission power zone Z is for example equal to the average number  M  of active user equipment UE N . 
     Knowing the maximum number of possible emission power values for an emission power zone Z and knowing the bounds of the range I l , the user equipment UE N  then determines the different possible emission power values for the emission power zone Z. For this, a discretisation step 
     
       
         
           
             
               
                 Δ 
                 1 
               
               = 
               
                 
                   T 
                   l 
                 
                 
                   M 
                   _ 
                 
               
             
             , 
           
         
       
     
     where T l  represents the width of the range I l , e is determined for the emission power zone Z. Such a discretisation step Δ l  pe allows offering a certain level of disparity between the possible power values and allows increasing the probability for the base station BST to be able to separate all received radio signals. 
     A minimum discretisation step threshold, noted Δ, is defined. If the discretisation interval Δ 1  is less than or equal to the minimum discretisation step threshold, then, it is the minimum discretisation step threshold value Δ which is used to determine the different possible emission power values for the emission power zone Z. 
     In a step F 3 , the user equipment UE N  determines a discrete probability distribution according to which, depending on the emission power zone in which it is located, it selects an emission power value from the plurality of possible emission power values for the emission power zone in which it is located. 
     In the following example, the discrete probability distribution according to which the user equipment UE N  select an emission power value from the plurality of possible emission power values is a normal distribution of the discrete values. Of course, any discrete probability distribution can be used when implementing the selection method according to the first embodiment of the invention. 
     Thus, for a normal distribution, the probability mass function  (.) of a possible emission power value ν l,n  is given by: 
     
       
         
           
             
               
                 
                   
                     ⁢ 
                     
                       ( 
                       
                         X 
                         = 
                         
                           v 
                           
                             l 
                             , 
                             n 
                           
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       f 
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               v 
                               
                                 l 
                                 , 
                                 n 
                               
                             
                             ∖ 
                             
                               v 
                               l 
                             
                           
                           , 
                           
                             σ 
                             l 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         1 
                         A 
                       
                       ⁢ 
                       
                         1 
                         
                           
                             2 
                             ⁢ 
                             Π 
                             ⁢ 
                             
                               σ 
                               l 
                               2 
                             
                           
                         
                       
                       ⁢ 
                       
                         e 
                         
                           
                             
                               ( 
                               
                                 
                                   v 
                                   
                                     l 
                                     , 
                                     n 
                                   
                                 
                                 - 
                                 
                                   v 
                                   l 
                                 
                               
                               ) 
                             
                             2 
                           
                           
                             2 
                             ⁢ 
                             
                               σ 
                               l 
                               2 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     where A is a normalisation constant which is 
     
       
         
           
             A 
             = 
             
               
                 ∑ 
                 
                   n 
                   = 
                   1 
                 
                 
                   n 
                   l 
                 
               
               ⁢ 
               
                 
                   1 
                   
                     
                       2 
                       ⁢ 
                       Π 
                       ⁢ 
                       
                         σ 
                         l 
                         2 
                       
                     
                   
                 
                 ⁢ 
                 
                   
                     e 
                     
                       - 
                       
                         
                           
                             ( 
                             
                               
                                 v 
                                 
                                   l 
                                   , 
                                   n 
                                 
                               
                               - 
                               
                                 v 
                                 l 
                               
                             
                             ) 
                           
                           2 
                         
                         
                           2 
                           ⁢ 
                           
                             σ 
                             l 
                             2 
                           
                         
                       
                     
                   
                   . 
                 
               
             
           
         
       
     
     The deviation of the Gaussian σ l , chosen, for example, such that 68% of the possible emission power values are comprised within the range [ν l −σ l   2 ν l +σ l   2 ]. 
     Such a probability mass function  (.) is represented in  FIG. 3 . 
     The calculations performed by the user equipment UE N  during steps F 2  and F 3  correspond to the following algorithm: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 
                   
                     
                       
                         
                           
                             If 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               Δ 
                               l 
                             
                           
                           ≥ 
                           Δ 
                         
                         , 
                         
                           
                             n 
                             l 
                             - 
                           
                           ← 
                           
                             ⌈ 
                             
                               
                                 
                                   
                                     v 
                                     
                                       l 
                                       - 
                                       1 
                                     
                                   
                                   - 
                                   
                                     v 
                                     l 
                                   
                                 
                                 
                                   
                                     v 
                                     
                                       l 
                                       - 
                                       1 
                                     
                                   
                                   - 
                                   
                                     v 
                                     
                                       l 
                                       + 
                                       1 
                                     
                                   
                                 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   
                                     M 
                                     _ 
                                   
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                             ⌉ 
                           
                         
                       
                     
                   
                 
               
               
                   
               
               
                 where n l   −  represents the number of possible emission power 
               
               
                 values greater than v l , and the notation ┌.┐ means rounded to 
               
               
                 the nearest next integer 
               
               
                 Discretize [v l  − ( M  − 1 − n l   − ) Δ l v l  + Δ l n l   − ] using Δ l   
               
               
                 Output: {v l,n } n=1   n     l   ~f v     l    = {  (X = v l,n )} n=1   n     l     
               
               
                 Else 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           Discretize 
                           ⁢ 
                           
                               
                           
                           [ 
                           
                             
                               v 
                               l 
                             
                             - 
                             
                               
                                 
                                   
                                     v 
                                     l 
                                   
                                   - 
                                   
                                     v 
                                     
                                       l 
                                       + 
                                       1 
                                     
                                   
                                 
                                 2 
                               
                               ⁢ 
                               
                                 v 
                                 l 
                               
                             
                             + 
                             
                               
                                 
                                   v 
                                   
                                     l 
                                     - 
                                     1 
                                   
                                 
                                 - 
                                 
                                   v 
                                   l 
                                 
                               
                               2 
                             
                           
                           ] 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         using 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Δ 
                       
                     
                   
                 
               
               
                   
               
               
                 Output: {v l,n } n=1   n     l   ~f v     l    = {  (X = v l,n )} n=1   n     l     
               
               
                 End 
               
               
                   
               
            
           
         
       
     
     The user equipment UE N  then implements steps E 5  and E 6  described with reference to  FIG. 2  and the base station BST implements step E 7 , also described with reference to  FIG. 2 . 
       FIG. 5  represents the average number of user equipment UE N  which manage to successfully transmit their data packets, or normalised throughput in the Figure, depending on the network load, or average traffic load in the figure. 
     The network load is given by: 
     
       
         
           
             
               traffic 
               ⁢ 
               
                   
               
               ⁢ 
               load 
             
             = 
             
               
                 M 
                 _ 
               
               
                 L 
                 ⁢ 
                 B 
               
             
           
         
       
     
     A Monte-Carlo simulation is applied by considering the following simulation parameters:
         K=200 pieces of user equipment; D=1 Km ; L=12 emission power levels; B=6 frequency sub-bands,   Target transmission rate R=0.5 b.p.c.u corresponding to a target SINR Γ=3.8 dB,   Transmission channel parameters: Block-fading Rayleigh channel that changes with each new transmission, but remains constant during the retransmissions associated with a given transmission; A 0 =1; β=3.5,   No power limitation at user equipment,   The frequency sub-band is chosen independently and according to a uniform discrete probability distribution by user equipment,   The possible emission power values per emission power zone Z are constructed with Δ=10 −4      SISO scheme; ARQ protocol truncated with maximum number of retransmissions Tr=10;   The transmissions are made with a recurrence of T=Tr       

     The results of this simulation are represented in  FIG. 5  where the MPS (Multiple Power Shades) curve represents the average number of user equipment UE N  which manage to successfully transmit their data packets depending on the network load when the method according to the invention is implemented; and SPL (Single Power Level) represents the average number of user equipment UE N  which manage to successfully transmit their data packets depending on the load of the network when the method according to the prior art is implemented. 
       FIG. 6  represents a user equipment UE N  according to one embodiment of the invention. Such a user equipment UE N  is capable of implementing the different embodiments of the method described with reference to  FIGS. 2 and 4 . 
     A user equipment UE N  can include at least one hardware processor  601 , a storage unit  602 , an input device  603 , a display device  604 , an interface  605 , and at least one network interface  606  which are connected to each other through a bus  607 . Of course, the constituent elements of the user equipment UE N  can be connected by means of a connection other than a bus. 
     The processor  601  controls the operations of the user equipment UE N . The storage unit  602  stores at least one program for implementing the method according to one embodiment of the invention to be executed by the processor  601 , and various data, such as parameters used for calculations performed by the processor  601 , intermediate data of calculations performed by the processor  601 , etc. The processor  601  may be formed by any known and appropriate hardware or software, or by a combination of hardware and software. For example, the processor  601  can be formed by dedicated hardware such as a processing circuit, or by a programmable processing unit such as a Central Processing Unit which executes a program stored in a memory thereof. 
     The storage unit  602  may be formed by any appropriate means capable of storing the program(s) and data in a computer readable manner. Examples of storage unit  602  comprise computer-readable non-transitory storage media such as semiconductor memory devices, and magnetic, optical, or magneto-optical recording media loaded in a read and write unit. 
     The input device  603  may be formed by a keyboard, a pointing device such as a mouse to be used by a user to enter commands. The display device  604  can also be formed by a display module, such as for example a graphical user interface or GUI. 
     The interface  605  provides an interface between the user equipment UE N  and other equipment not represented in the figure. 
     At least one network interface  606  provides a connection between the user equipment UE N  and the base station BST via a radio connection. 
       FIG. 7  represents a base station BST according to one embodiment of the invention. Such a base station BST is capable of implementing the different embodiments of the method described with reference to  FIGS. 2 and 4 . 
     A base station BST can include at least one hardware processor  701 , a storage unit  702 , an input device  703 , a display device  704 , an interface  705 , and at least one network interface  706  which are connected to each other through a bus  707 . Of course, the constituent elements of the base station BST can be connected by means of a connection other than a bus. 
     The processor  701  controls the operations of the base station BST. The storage unit  702  stores at least one program for implementing the method according to one embodiment of the invention to be executed by the processor  701 , and various data, such as parameters used for calculations performed by the processor  701 , intermediate data of calculations performed by the processor  701 , etc. The processor  701  may be formed by any known and appropriate hardware or software, or by a combination of hardware and software. For example, the processor  701  can be formed by dedicated hardware such as a processing circuit, or by a programmable processing unit such as a Central Processing Unit which executes a program stored in a memory thereof. 
     The storage unit  702  may be formed by any appropriate means capable of storing the program(s) and data in a computer readable manner. Examples of storage unit  702  comprise computer-readable non-transitory storage media such as semiconductor memory devices, and magnetic, optical, or magneto-optical recording media loaded in a read and write unit. 
     The input device  703  may be formed by a keyboard, a pointing device such as a mouse to be used by a user to enter commands. The display device  704  can also be formed by a display module, such as for example a graphical user interface or GUI. 
     The interface  705  provides an interface between the base station BST and another equipment not represented in the figure. 
     At least one network interface  706  provides a connection between the base station BST and at least one user equipment UE N  via a radio connection.