WO2012052683A1

WO2012052683A1 - Method, devices, and computer program for dynamically selecting frequency bands for uplink communication for ofdma or sc-fdma terminals, the power of which is controlled

Info

Publication number: WO2012052683A1
Application number: PCT/FR2011/052442
Authority: WO
Inventors: Salah Eddine El Ayoubi; Maria Dolores Garcia Alvarez
Original assignee: France Telecom
Priority date: 2010-10-22
Filing date: 2011-10-19
Publication date: 2012-04-26
Also published as: EP2649743A1; FR2966684A1

Abstract

The invention relates to the selection of a frequency sub-band in a base station for a cellular network, the sub-band belonging to a frequency band that can be used by a mobile terminal for establishing uplink communication with the base station. After having estimated (220) a minimum transmission power of the terminal, the estimated transmission power is compared to at least one power interval defined by at least one previously calculated power threshold. A frequency sub-band is selected (225) in response to said comparison, the selected sub-band being associated, according to a predetermined rule, with said at least one power interval. An identifier of the selected sub-band is then transmitted (230) to the terminal, which uses said sub-band to establish uplink communication with the base station.

Description

Method, devices and computer program

of dynamic selection of frequency bands for the upstream communication of OFDMA or SC-FDMA terminals controlled by power

The present invention relates to the communication between a mobile terminal and a base station in a cellular communication architecture and more particularly a method, devices and a computer program for dynamic selection of frequency bands for the upstream communication of terminals of type OFDMA or SC-FDMA power controlled. The technical field considered here is that of the reduction of uplink interferences of 3G LTE type mobile networks (3rd Generation Long Term Evolution acronym in English terminology) or, more generally, mobile networks operating by frequency allocation. such as networks OFDMA type (acronym Orthogonal Frequency Multiple Access Division in English terminology) or SC-FDMA (acronym for Single-Carrier Frequency-Multiple Access Division in English terminology).

According to a current architecture, a mobile terminal communicates with a base station offering a communication perimeter, called a cell, in a bidirectional mode comprising a downward direction (from the base station to the mobile terminal) and a rising direction (of the mobile terminal to the base station). Several base stations, located next to each other, form a cellular network covering a given geographical extent. There are, within a cell, mechanisms for reducing interference between uplink communications from multiple mobile terminals. However, depending on the transmission power of the mobile terminals, there may be interference, at the base stations of two neighboring cells, between upstream communications originating from a first mobile terminal of the first cell and a second terminal. second cell, if the frequencies used for these communications are identical or close.

Interference reduction is an important upstream area for OFDMA-based networks, such as 3G LTE, and WiMAX. Different interference reduction methods have been developed based on fractional frequency utilization.

Thus, for example, some solutions propose to divide the frequency band used into several frequency sub-bands, each corresponding to an attenuation group, and to use a power control threshold for each group. However, this approach uses signal attenuation as a determinant of power, which is not always optimal.

Alternatively, there are interference reduction schemes based on load or interference information from neighboring base stations. However, such solutions require knowledge, by each mobile, of information relating to neighboring base stations. Alternatively, the choice of the frequency sub-band used by a terminal to communicate with a base station is based on the attenuation of a signal received from neighboring base stations.

On the other hand, it has been observed that while the reduction of the transmission power of mobile terminals may make it possible to reduce interference between the transmitted signals, this is not necessarily the case. In addition, the use of information relating to neighboring cells, including interference or load information, requires the transmission of information between base stations, which can be complex.

The invention aims, for a mobile terminal, the selection of a sub-frequency band according to the transmission power of the latter in order to choose, in coordination with its server base station, the most suitable sub-band for limit interference without necessarily changing the transmission power.

The subject of the invention is therefore a method of selecting a frequency subband in a frequency-allocating cellular network base station, said frequency sub-band belonging to a plurality of frequency sub-bands. a frequency band that can be used by a mobile terminal to establish an uplink communication with said base station, this method comprising a step of estimating a level of performance achieved by said at least one mobile terminal according to a criterion predetermined, and further comprising the steps of:

estimating a minimum transmission power of said at least one mobile terminal required to reach said performance level;

comparing said estimated transmission power with at least one power interval defined by at least one previously calculated power threshold;

in response to said comparison, selecting a frequency sub-band of said plurality of frequency sub-bands, said selected frequency sub-band being associated, according to a predetermined rule, with said at least one power interval; and,

transmitting an identifier of said selected frequency sub-band to said at least one mobile terminal, said at least one mobile terminal to use said selected frequency sub-band to establish an uplink communication with said base station.

The method according to the invention thus makes it possible, when implemented in base stations of at least two neighboring cells, to reduce interference, at the base station level, between upstream communications originating from mobile terminals. a cell and mobile terminals of neighboring cells.

According to particular features, said performance level according to a predetermined criterion is associated with a predetermined modulation and coding scheme.

Thanks to these arrangements, it is advantageous to reduce interference, while taking into account the technical constraints (modulation and coding) imposed by the (or the) radio access technology (s) ("Radio Access Technology" or RAT in English) implemented in the cells concerned.

According to even more particular characteristics, said performance level according to a predetermined criterion is associated with a modulation and coding scheme corresponding to a maximum transmission power of said at least one mobile terminal.

With these provisions, as explained in detail below, we can implement the invention in the context of power control according to current standards.

According to even more particular characteristics, said performance level according to a predetermined criterion is the maximum bit rate accessible to said at least one mobile terminal.

Thanks to these provisions, the implementation of the invention is advantageously simple since it is conventional, especially in the current user terminals, to estimate the maximum throughput accessible to the terminal given the interference present at the place where it turns out that.

According to other particular features, the method also advantageously comprises a step of transmitting to said at least one mobile information terminal enabling it to calculate a transmission power in order to optimize it and, consequently, to reduce interference and limit the power consumption of the terminal.

According to a particular embodiment, said steps of evaluating a transmission power, comparing said estimated transmission power with at least one power interval, selecting a sub-band of frequencies and transmitting an identifier of said selected frequency sub-band is executed periodically or upon detection of a particular event. Thus, step by step, the method converges to a state optimizing, at least partially, the reduction of interference and the transmission power of the mobile terminals.

Still according to a particular embodiment, the method further comprises a step of calculating said at least one power threshold, said at least one power threshold being calculated as a function of the size of said frequency band, of the size of sub. frequency bands of said plurality of frequency subbands and an estimated transmission power of a plurality of mobile terminals in communication with said base station.

Thus, the selection of the sub-band to be used by a mobile terminal is performed according to the use of the frequency band by mobile terminals communicating with the same base station and their transmission power.

The method further comprises, preferably, a step of cutting said frequency band into said plurality of frequency subbands.

According to a particular embodiment, said frequency band is divided into four frequency sub-bands, a first frequency sub-band being associated with estimated transmission powers greater than a first power threshold, at least one second under -band of frequencies being associated with estimated transmission powers lower than a second power threshold and a third sub-band of frequencies being associated with estimated transmit powers between said first and second power thresholds.

The invention also relates to a computer program comprising instructions adapted to the implementation of each of the steps of the method described above when said program is executed on a computer and a base station comprising means adapted to the implementation of each of the steps of the method described above.

The subject of the invention is also a cellular network comprising at least two base stations, each of the said at least two base stations comprising means for implementing the method described above, the rules for associating a sub-band of frequencies at a power threshold being such that if a sub-frequency band is selected in one of said at least two base stations for a mobile terminal having an estimated transmit power greater than a high power threshold of said one of said at least two base stations, the same frequency sub-band is selected in the other of said at least two base stations for a mobile terminal having an estimated transmit power lower than a low power threshold of said other one of said at least two base stations.

Advantageously, the cellular network comprises a plurality of base stations, each of said base stations defining a cell, according to which the association between at least one frequency subband and an estimated transmission power range is an association. different injective for any pair of adjacent cells in the cellular network.

The benefits provided by the computer program, the base station and the cellular network are similar to those mentioned above.

Other advantages, aims and features of the present invention will emerge from the detailed description which follows, given by way of non-limiting example, with reference to the accompanying drawings in which:

FIG. 1, comprising FIGS. 1a and 1b, diagrammatically represents examples of splitting of a mobile terminal transmission frequency band;

FIG. 2 diagrammatically illustrates an example of an algorithm implemented in a base station for selecting a sub-band of frequencies according to the estimated transmission power of a mobile terminal;

FIG. 3, comprising FIGS. 3a and 3b, represents an example of results expected by an implementation of the invention; and,

FIG. 4 is an example of a hardware architecture adapted to implement certain steps of the invention, in particular the algorithm described with reference to FIG. 2.

In general, the object of the invention is to determine a sub-band of frequencies to be used by a mobile terminal to establish upstream communication to a base station in a cellular network operating by frequency allocation, that is to say say, for example, a network of OFDMA or SC-FDMA type, the sub-band being selected according to the estimated transmission power of this mobile terminal. In thus choosing the frequency sub-bands used by mobile terminals in uplink communications, it is possible to reduce interference and, as a consequence, to limit the transmission power of these mobile terminals (no power restrictions is imposed on the terminals). The estimated transmit powers of the mobile terminals are here calculated by the base stations in a conventional manner.

An embodiment of the invention is now considered in which the mobile terminals are power controlled. This check may, for example, comply with 3GPP standard TS 36.213 (3 ^rd Generation Partnership Project in English terminology). According to this standard, the base station communicates to each associated terminal, at predetermined times, information concerning the quality of the link between it and the terminal (typically a transmission error rate). On this basis, the terminal determines the minimum transmission power necessary to achieve, with a target link quality (expressed by an error rate below a predefined maximum threshold), the modulation scheme and coding that the terminal could reach with its maximum transmit power (assuming the interference level is medium); this minimum power generally coincides with the minimum power necessary to allow the terminal to transmit with the maximum possible flow rate given the interference present at the location where it is located. The terminal then transmits to the base station at a power equal to this minimum transmission power. This minimum power calculation is standard and can be done also by the base station. In the remainder of the description, such a power calculated by the base station is called the "estimated power" of the mobile terminal.

For these purposes, the frequency band used by the mobile terminals of a cellular network is divided into frequency sub-bands. The subbands are preferably the same for all the cells of the cellular network.

FIG. 1, comprising FIGS. 1a and 1b, illustrates examples of splitting a frequency band between the frequencies F _min and F _max . The size of the frequency band is here N basic elements, called chunks or resource blocks in English terminology.

According to the example illustrated in FIG. 1a, the frequency band is divided into a number P of subbands. Thus, a first sub-band is defined by the frequency range [F _min ; F,], a second sub-band is defined by the frequency range [F,; F ₂ ] and so on up to the frequency range [F _P .,; F _max ].

However, the sizes of the frequency sub-bands are not necessarily identical. Thus, as illustrated in FIG. 1b, a frequency band can be divided into four frequency sub-bands where the first sub-band, defined by the frequency range [F ₃ ; F _max ] has a size equal to Λ /, and where the second, third and fourth frequency sub-bands defined by the frequency ranges [F ₂ ; F ₃ ], [F,; F ₂ ] and [F _min ; F,], respectively, have a size equal to N ₂ , where Λ /, is different from N ₂ . As indicated above, the selection of a sub-band of frequencies to be used by a mobile terminal is determined according to the estimated transmission power of this mobile terminal. For these purposes, the estimated transmit power of a mobile terminal is compared with power intervals, defined by previously calculated power thresholds, and associated with the frequency subbands that can be used. The power intervals are here defined by calculated power thresholds as well as minimum and maximum values of transmission power, typically zero and the maximum transmission power of the mobile terminal, respectively.

These power intervals are advantageously calculated and associated with the frequency subbands dynamically, for each cell of the cellular network (independently). For each cell, the calculation of the power thresholds and the association of the power intervals corresponding to the frequency sub-bands can be carried out periodically, for example every second or during the detection of a particular event such as the variation of the average traffic associated with the terminals of the cell. Alternatively, the power thresholds are static and determined empirically.

According to a particular embodiment, these thresholds or power intervals are computed statistically in order to ensure an almost uniform distribution of the frequency sub-bands to the mobile terminals communicating with the base station in question, that is to say to the mobile terminals belonging to the corresponding cell.

The association of power intervals with the frequency sub-bands is carried out in such a way that the interferences that can occur between upstream communications of mobile terminals of nearby cells essentially occur between mobile terminals, belonging to a first cell, requiring a strong transmission power and mobile terminals, belonging to a second cell, requiring a low transmission power. In other words, the same sub-band is selected, in a first cell, for terminals requiring a high transmission power and, in a second cell, for mobile terminals requiring a low transmission power.

Such a selection is made according to predetermined rules of association of transmission power intervals and frequency sub-bands.

Thus, after having cut out a frequency band used in frequency sub-bands, n power thresholds (6> ,, θ ₂ , ..., θ _η where θ ₁ <θ ₂ ... <θ _η ) are determined . Some power threshold intervals ([Θ,; 6>, ₊ ,]) are then injectively assigned to frequency subbands. Thus, by comparing the estimated transmission power of a mobile terminal with the determined power intervals, it is possible to identify the power range to which the estimated transmission power belongs and, therefore, to identify the associated frequency band which is then used by the mobile terminal in question.

The injective association between a transmission power interval and a frequency sub-band is different for at least one pair of neighboring cells so that a same selected sub-band in a cell for mobile terminals requiring high transmission power is selected in a neighboring cell for mobile terminals requiring low transmission power.

By way of illustration, the fourth frequency sub-band illustrated in FIG. 1b can be associated with the terminals of a first cell having a transmission power greater than a threshold θ ₂ defined in this first cell; ie having a transmission power belonging to the interval [θ ₂ ; + "{, while it can be associated with the terminals of a second cell having a transmission power lower than another defined threshold ΘΊ in this second cell, i.e. having a transmission power belonging to the interval [0; 0 '[.

In general, a rule of association of a sub-frequency band with a power interval is such that, for two neighboring cells, if a sub-frequency band is selected in a base station of one of these cells, for a mobile terminal having an estimated transmission power higher than a high power threshold of this base station, the same frequency sub-band is selected in the base station of the other cell for a mobile terminal having an estimated transmit power lower than a low power threshold of the base station of that other cell. A high power threshold corresponds, for example, to a power greater than the average transmission power of mobile terminals while a low power threshold corresponds, for example, to a power less than the average terminal transmission power. mobile.

FIG. 2 schematically illustrates an exemplary algorithm implemented in a base station for selecting a frequency sub-band according to the estimated transmission power of a mobile terminal.

As illustrated, a first step (step 200) is to cut the frequency band used in frequency subbands, that is to say to define the terminals F, of each sub-band. As indicated above, the terminals F, are preferably the same for each cell of the cellular network. Therefore, these terminals can be calculated by each base station, similarly, or be predetermined and received from another system.

A next step (step 205) is to calculate power thresholds 0 _kJ where / ^' represents a threshold index and k a cell index. As previously described, the power thresholds are, according to a particular embodiment, defined statistically. The power thresholds are determined dynamically to obtain a fair traffic distribution between the frequency sub-bands. The proportion of mobile terminals allocated to a sub-band is here equal to the ratio between the size of this sub-band and the size of the frequency band.

By way of illustration, the size frequency band Λ / is divided into four sub-bands, three sub-bands having the same size N ₂ and a sub-band having a size equal to N _u as illustrated in FIG. b. In this example, the cellular network is a network to omnidirectional hexagonal cells. Two power thresholds 6>, and θ ₂ (6>, <θ ₂ ) are determined to identify the mobile terminals having a high transmission power

(transmission power greater than θ ₂ , that is to say belonging to the interval [θ ₂ ; + ∞ [) and mobile terminals having a low transmission power (transmission power less than 6> ,, that is, belonging to the interval [0; 6>, [).

Thresholds θ ₁ and θ ₂ are recalculated periodically. Between two updates of these thresholds, the distribution of the estimated transmission power of the mobile terminals, called P _e , is calculated. The thresholds are then updated in such a way that:

2N N

P _{r (} P _{e <} 0 _{i) =} _L and Pr (P _e > 0 ₂ ) = ^ where Pr () expresses a probability.

These relationships can be expressed in the following form:

where f () is the distribution function of P _e .

It is observed here that the power thresholds being calculated here according to characteristics of each cell, the thresholds Θ of a base station / (are, a priori, different from the thresholds θ, of a base station k '.

The power intervals defined by these thresholds (considered in an ordered manner) are then associated with frequency sub-bands according to predetermined rules specific to each cell so that a same sub-frequency band is associated with mobile terminals having a specific frequency. high transmit power in a cell and to mobile terminals having low transmit power in neighboring cells.

Thus, for example, the four frequency sub-bands illustrated in FIG. 1b can be associated with terminals according to the following rules,

in cell k:

the first frequency sub-band ([F ₃ ; F _ma J) is associated with mobile terminals having an average estimated transmission power, that is to say with terminals having an estimated transmission power P _e included between the thresholds é¾, i and é¾ _j2 <P _e <θ ^ Σι;

the second frequency sub-band ([F ₂ ; F ₃ ]) is associated with mobile terminals having a high estimated transmission power, that is to say terminals having an estimated transmission power greater than the threshold Θ _Κ2 {Θ ₂ <P _e <+ ∞); and,

the third and fourth frequency sub-bands ([F 1; F ₂ ] and [F _min ; F 1]) are associated with the mobile terminals having an estimated low transmission power, that is to say at the terminals having an estimated transmission power less than the threshold Θ ₁ (0 <P _e <(¾,) The third and fourth frequency sub-bands are associated in a balanced manner with the mobile terminals having a low transmission power;

in the cell k + 1, next to the cell k:

the first frequency sub-band ([F ₃ ; F _max ]) is associated with mobile terminals having an average estimated transmission power, that is to say terminals having an estimated transmission power between thresholds and ôk + 1,2 (0k + i, i <P _e <k + 1,2);

the second frequency sub-band ([F ₂ ; F ₃ ]) is associated with the mobile terminals having an estimated low transmission power, that is to say the terminals having an estimated transmission power lower than the threshold 0 _{k + 1} (0 <

the third frequency sub-band ([F,; F ₂ ]) is associated with mobile terminals having a high estimated transmission power, that is to say terminals having an estimated transmission power greater than the threshold 0 _{k + 2}

the fourth frequency sub-band ([F _min ; F,]) is associated with the mobile terminals having an estimated low transmission power, that is to say the terminals having an estimated transmission power lower than the threshold 0 _{k + 1} (0 <P _e <(¾ _{+ /} , _/ ) The second and fourth frequency sub-bands are associated in a balanced manner with the mobile terminals having a low transmission power;

in the cell k + 2, neighbor of the cell k:

the first frequency sub-band ([F ₃ ; F _ma J) is associated with the mobile terminals having an average estimated transmission power, that is to say the terminals having an estimated transmission power comprised between thresholds

Sk + 2.1 tt _{+ 2j2} (έ¾ ₊ 2, ί <P _e <& k + 2.2)

the second and third frequency sub-bands ([F ₂ ; F ₃ ] and [F 1; F ₂ ]) are associated with the mobile terminals having an estimated low transmission power, that is to say at the terminals having an estimated transmit power less than the threshold e _{k + 2} , i (0 <P _e <e _{k + 2} , i). The second and third frequency sub-bands are associated in a balanced manner with the mobile terminals having a low transmission power; and,

the fourth frequency sub-band ([F _min ; F,]) is associated with mobile terminals having a high estimated transmission power, that is to say terminals having an estimated transmission power greater than the threshold e _{k + 2} , 2

(& k ₊ 2,2 <Pe <+ ∞) ^■ According to this example, the first frequency subband ([F ₃ ; F _ma J) is similarly used in neighboring cells (frequency sub-band used by the mobile terminals having an average transmit power). Therefore, the size of this frequency subband is preferably greater than that of the other subbands. The latter are used differently in each neighboring cell so that, preferably, a sub-band is associated with mobile terminals having a high transmission power only in a single cell among a set of neighboring cells.

Returning to FIG. 2, a test is then performed to determine whether the power thresholds must be recalculated or not (step 210). This test consists of identifying the end of a predetermined period of time or detecting a particular event. If so, the step of calculating the power thresholds (step 205) is executed.

If it is not necessary to recalculate the power thresholds, another test is performed to determine whether a sub-frequency band should be selected for a mobile terminal (step 215). The response to this test is positive when a mobile terminal tries to establish an upward communication with the base station and negative otherwise. If a frequency sub-band should not be selected for a mobile terminal, the algorithm returns to step 210 to determine whether or not it is necessary to recalculate power thresholds.

In the opposite case, if a sub-band of frequencies must be selected for a mobile terminal y, the transmission power of this mobile terminal is estimated (step 220). The estimated transmission power of the mobile terminal j is here denoted P _ej . As previously stated, the estimated transmission power is the smallest transmission power needed to reach the modulation and coding scheme that the terminal would have reached with its maximum power (assuming the interference level is average, that is, that is, according to the previous example, assuming that the frequency subband used is the first subband).

In a next step, a sub-frequency band is selected for use by the mobile terminal in question (step 225). For these purposes, the previously estimated transmission power (P _ej ) is compared with the power intervals defined by the previously calculated thresholds 6. A frequency subband (SBj) is then identified according to the result of the comparison and the Association rules between power intervals and frequency subbands.

A reference of the selected sub-band (SBj) as well as, preferably, information (Infoj) on the quality of the link (to enable the mobile terminal, as previously described, to calculate the required transmission power) are then transmitted. to the relevant mobile terminal (step 230) and the algorithm loops back to step 210 to recalculate, if necessary, the power thresholds and continue the selection of transmit frequency subbands for the mobile terminals of the cell. The received reference to a frequency subband is used by the mobile terminal in question to establish uplink communication with the base station implementing the algorithm. Furthermore, advantageously, the resulting transmission power of the mobile terminal reduces the interference in the cellular network as well as the power consumption of the terminal, compared with the prior art.

It is observed here that if the power thresholds (6y are static and predetermined, it is not necessary to reevaluate them, therefore step 210 is not useful and step 205 essentially aims at the association of power thresholds at the frequency subbands.

The selection of frequency subbands for the establishment of uplink communication between mobile terminals and base stations according to the estimated transmission power of the mobile terminals according to the invention makes it possible to reduce the interference between communications and therefore, to reduce the transmission power required for each mobile terminal between each frequency subband selection cycle. Thus, dynamically, the network converges to a state optimized in terms of interference and transmission power of the mobile terminals.

FIG. 3, comprising FIGS. 3a and 3b, represents an example of results expected by an implementation of the invention. These results, given here by way of illustration, were obtained by simulation. However, it should be noted that the actual performance of a system embodying the invention is related to actual conditions and, therefore, may vary from the theoretical results.

FIG. 3a represents the average rate of a cell as a function of the arrival rate of mobile terminals in the cell when the invention is implemented (continuous line comprising circles), when a frequency reuse equal to one is implementation (single continuous line), when a frequency reuse equal to three is implemented (continuous line comprising crosses) and when fractional frequency reuse is implemented (continuous line comprising triangles). A frequency reuse equal to one here is a system in which all frequencies are used in an equivalent manner in the cell. A frequency reuse of three allocates one-third of the frequency band to one cell and prohibits it from using the remainder of the available frequencies, so that two neighboring cells use different frequencies. Finally, a fractional frequency reuse classifies the mobile terminals according to their position in the cell and limits the transmission powers according to the allocated band. These mechanisms are notably described in the proposal of the company Nokia entitled "Uplink inter-eye interference mitigation and text proposed", 3GPP TSG-RAN WG1 # 44, R1 -060298, Denver, USA, February 2006.

FIG. 3b represents the transmitted power as a function of the distance of the mobile terminals to the base station when the invention is implemented (continuous line comprising circles), when a frequency reuse equal to one is implemented ( single continuous line), when a frequency reuse equal to three is implemented (continuous line including crosses) and when fractional frequency reuse is implemented (solid line including triangles).

According to FIG. 3, the invention makes it possible to reduce the power consumed by the mobile terminals and to increase the data rate exchanged.

FIG. 4 illustrates an exemplary hardware architecture of a device 400 adapted to implement certain steps of the invention, in particular the steps described with reference to FIG. 2. The device 400 is, for example, a computer or a computer belonging to a base station. It comprises here a communication bus 405 to which are connected:

one or more central processing units or microprocessors 410 (CPU);

a read only memory 415 (ROM, acronym for Read Only Memory in English terminology) which may include programs (prog, progl and prog2) necessary for the implementation of the invention;

a random access memory or cache memory 420 (RAM, acronym for Random Access Memory in English terminology) comprising registers adapted to record variables and parameters created and modified during the execution of the aforementioned programs; and

a communication interface 450 adapted to transmit and receive data.

The device 400 also preferably has a hard disk 435 that can include the aforementioned programs as well as information processed or to be processed according to the invention and a memory card reader 440 adapted to receive a memory card 445 and to read or write processed or processed data according to the invention.

The communication bus allows communication and interoperability between the various elements included in the device 400 or connected to it. The representation of the bus is not limiting and, in particular, the central unit is able to communicate instructions to any element of the device 400 directly or through another element of the device 400.

The executable code of each program enabling the programmable device to implement the processes according to the invention can be stored, for example, in the hard disk 435 or in the read-only memory 415.

According to one variant, the memory card 445 may contain information, in particular information to be processed according to the invention, as well as the executable code of the aforementioned programs which, once read by the device 400, is stored in the hard disk 435.

According to another variant, the executable code of the programs and the information to be processed according to the invention may be received, at least partially, via the interface 450, to be stored in a manner identical to that described above.

More generally, the program (s) and the information to be processed according to the invention may be loaded into one of the storage means of the device 400 before being executed. The central unit 410 will control and direct the execution of the instructions or portions of software code of the program or programs according to the invention, instructions which are stored in the hard disk 435 or in the read-only memory 415 or else in the other elements of aforementioned storage. When powering on, the program or programs that are stored in a non-volatile memory, for example the hard disk 435 or the read only memory 415, are transferred into the random access memory 420 which then contains the executable code of the program or programs according to the invention, as well as registers for storing the variables and parameters necessary for the implementation of the invention.

Naturally, to meet specific needs, a person skilled in the field of the invention may apply modifications in the foregoing description.

Claims

1. A method of selecting a frequency sub-band in a frequency-allocating cellular network base station, said frequency sub-band belonging to a plurality of frequency sub-bands of a frequency band capable of be used by a mobile terminal to establish an uplink communication with said base station, said method comprising a step of estimating a performance level achieved by said at least one mobile terminal according to a predetermined criterion, and being characterized in that it further comprises the following steps:

estimating (220) a minimum transmit power of said at least one mobile terminal required to reach said performance level;

in response to said comparison, selecting (225) a sub-frequency band of said plurality of frequency sub-bands, said selected frequency sub-band being associated, according to a predetermined rule, to said at least one interval of power ; and,

transmitting (230) an identifier of said selected frequency sub-band to said at least one mobile terminal, said at least one mobile terminal to use said selected frequency sub-band to establish an uplink communication with said base station.

2. Method according to claim 1, characterized in that said performance level according to a predetermined criterion is associated with a predetermined modulation and coding scheme.

3. Method according to claim 2, characterized in that said performance level according to a predetermined criterion is associated with a modulation and coding scheme corresponding to a maximum transmission power of said at least one mobile terminal.

4. Method according to claim 3, characterized in that said performance level according to a predetermined criterion is the maximum rate accessible to said at least one mobile terminal.

5. Method according to any one of claims 1 to 4, further comprising a step of transmitting (230) to said at least one mobile information terminal enabling it to calculate a transmission power.

The method of any one of claims 1 to 5, wherein said steps of estimating transmission power, comparing said estimated transmit power to at least one power interval, selecting a a sub-band of frequency and transmission of an identifier of said selected frequency sub-band are performed periodically or upon detection of a particular event.

7. Method according to any one of claims 1 to 6, further comprising a calculation step (205) of said at least one power threshold, said at least one power threshold being calculated according to the size of said band of power. frequencies, the size of frequency subbands of said plurality of frequency subbands and an estimated transmission power of a plurality of mobile terminals in communication with said base station.

The method of any preceding claim further comprising a step of splitting (200) said frequency band into said plurality of frequency subbands.

9. The method as claimed in claim 1, said frequency band being divided into four frequency sub-bands, a first frequency sub-band being associated with estimated transmission powers greater than a first power threshold. at least one second frequency sub-band being associated with estimated transmission powers lower than a second power threshold and a third frequency sub-band being associated with estimated transmission powers between said first and second thresholds of power.

Computer program comprising instructions adapted to the implementation of each of the steps of the method according to any one of the preceding claims when said program is executed on a computer.

1 1. Base station comprising means adapted to the implementation of each of the steps of the method according to any one of claims 1 to 9.

A cellular network comprising at least two base stations, each of said at least two base stations comprising means for implementing the method according to any one of claims 1 to 9, the association rules of a sub-base station, and frequency band at a power threshold being such that if a sub-frequency band is selected in one of said at least two base stations for a mobile terminal having an estimated transmit power greater than a high power threshold of said one of said at least two base stations, the same frequency sub-band is selected in the other of said at least two base stations for a mobile terminal having an estimated transmit power lower than a low power threshold of said other of said at least two base stations.

The cellular network of claim 12 comprising a plurality of base stations, each of said base stations defining a cell, wherein the association between at least one frequency subband and an estimated transmit power range is a different injective association for any pair of adjacent cells in the cellular network.