WO2013001359A2

WO2013001359A2 - Method for mitigating interference in a heterogeneous network

Info

Publication number: WO2013001359A2
Application number: PCT/IB2012/001473
Authority: WO
Inventors: Lili Xie; Wenjun Wu; Zhenning Shi
Original assignee: France Telecom SA
Current assignee: Orange SA
Priority date: 2011-06-30
Filing date: 2012-06-27
Publication date: 2013-01-03
Anticipated expiration: 2013-12-30
Also published as: WO2013001359A3; WO2013000170A1

Abstract

The invention relates to a method for mitigating interference generated by a first access node covering a femto-cell on a first transmission channel established between a first mobile device and a second access node covering a macro-cell, the macro-cell overlapping the femto-cell, the method being run by the first access node and comprising the steps of: receiving a first parameter representing a pathloss of the first transmission channel, receiving a second parameter representing a pathloss of a second transmission channel established between a second mobile device and the first access node, choosing a frequency band among a frequency spectrum to be used for data transmission through the second transmission channel, based on the first and the second pathloss parameters, determining a transmission power for the frequency band to be used for data transmission through the second transmission channel.

Description

METHOD FOR MITIGATING INTERFERENCE IN A

HETEROGENEOUS NETWORK

The present invention generally relates to mitigating interference in a heterogeneous network.

A heterogeneous network consists of macro-cells and femto-cells overlapping each other. Such a network makes it possible to enhance the performance of indoors mobile devices by deploying femto-cells indoor.

A macro-cell is covered by a macro access node such as an enodeB or macro enodeB MenodeB. A femto-cell is covered by an access node with a small scale access or HenodeB. Users can be handover to or from HenodeB when they enter or exit the femto cell..

In closed subscriber group (CSG) mode, in order to communicate with a HenodeB in order to transmit data, a mobile device must subscribe to the HenodeB. The unsubscribed mobile devices are not allowed to communication with a HenodeB.

As a consequence of such a network topology, the interference environment of a heterogeneous network is more complicated than in a conventional network. Therefore, when an unsubscribed mobile device enters a femto-cell coverage area, the interference generated on the unsubscribed mobile device by the HenodeB is rather strong when both the MenodeB and the HenodeB reuse the same portion of a frequency spectrum.

There are two kinds of interference in a heterogeneous network: interference between devices in a same tier, e.g. interference between a HenodeB and a subscribed mobile device, or intra-tier interference, and interference between devices in different tiers, e.g. interference between a HenodeB and an unsubscribed mobile device, or cross-tier interference. The cross-tier interference can be relatively strong in a heterogeneous network, which results in large outage probability in macro-cells.

In order to mitigate cross-tier interference in a heterogeneous network, it is known to modify the transmission power of the HenodeB.

There are different methods for modifying the transmission power of a HenodeB, all of them implying allocating the transmission power across the entire bandwidth. For example, a first method consists in determining the transmission power based on the strongest received power from a MenodeB by the HenodeB. A second method consists in defining the transmission power of the HenodeB based on the pathloss of transmission channels established between the HenodeB and subscribed mobile devices.

One of the main drawbacks of these methods is that since the transmission power of the HenodeB is allocated in the whole operation bandwidth, the reduction of the transmission power according to any of the existing methods leads to a performance loss in the femto-cell, and the performance gain in the macro-cell is not significant enough to justify the performance loss in the femto-cell.

Hence there is a need to develop a method for mitigating interference in a heterogeneous network that can improve a favorable performance trade-off between the femto-cell and the macro-cell.

To this end, the present invention relates to a method for mitigating interference generated by a first access node covering a femto-cell on a first transmission channel established between a first mobile device and a second access node covering a macro-cell, the macro-cell overlapping the femto-cell, the method being run by the first access node and comprising the steps of: - receiving a first parameter representing a pathloss of the first transmission channel established between the first mobile device and the first access node,

- receiving a second parameter representing a pathloss of a second transmission channel established between a second mobile device and the first access node,

- choosing a frequency band among a frequency spectrum to be used for data transmission through the second transmission channel, based on the first and the second pathloss parameters,

- determining a transmission power for the frequency band to be used for data transmission through the second transmission channel.

The solution of the invention allows mitigating interference in a heterogeneous network.

In such a heterogeneous network, interference are generated by a first type of access node, such as Home enodeB HenodeB, on a transmission channel established between a mobile device and a second type of access node, such as Macro enodeB or MenodeB, resulting in the mobile device being allocated timeslots for transmitting data by the MenodeB with a low probability.

By reducing the transmission power allocated to the frequency band chosen for data transmission between the HenodeB and another mobile device attached to it using pathloss parameters relating to both a first transmission channel established between the mobile device and the MenodeB and a second transmission channel established between the other mobile device and the HenodeB, the solution of the invention makes it possible to enhance the transmission performance in the macro-cell while restraining the performance loss in the femto-cell.

In other words, the solution of the invention takes into account the interference generated by the HenodeB on the transmission channel established between the mobile device and the MenodeB to reduce the transmission power allocated to a frequency band used for data transmission within the femto-cell.

In doing so, timeslots for transmitting data are allocated to the mobile device by the MenodeB with a higher probability. This is possible with the assumption that the MenodeB uses a scheduling technique that takes into account the state of the transmission channel established between the mobile device and the MenodeB.

According to a characteristic of the method for mitigating interference of the invention, the first access node determines the transmission power for the frequency band to be used for data transmission through the second transmission channel using a power control function consisting of at least two parts: a first part related to a power control strength of a radio signal transmitted through the second transmission channel and a second part related to the interference generated by the first access node on the first transmission channel established.

Power control function refers to a scheme that can adjust the transmit power level of a radio signal in static, semi-static or dynamic ways. It can be as simple as setting transmit power to a fixed value, or a complex closed-loop power control employed by CDMA systems for example.

Such a power control function is designed to compensate both for the pathloss of the second transmission channel and to be proportional to the pathloss of the first transmission channel.

The invention also relates to a method for allocating frequency resource to a first mobile device, frequency resource being allocating by a first access node covering a macro-cell, a first transmission channel being established between the first access node and the first mobile device, the method comprising the steps of: - receiving a first parameter representing a pathloss of the first transmission channel,

- determining a frequency band, chosen by a second access node, covering a femto-cell overlapped by the macro-cell, among a frequency spectrum, to be used for data transmission through a second transmission channel established between a second mobile device and the second access node,

- allocating frequency resource to the first mobile device in the determined frequency band.

The first access node is, for example, a MenodeB. In this embodiment the MenodeB uses a scheduling algorithm that is aware of the channel state of all the transmission channels established between the MenodeB and the different mobiles devices of the macro-cell.

Since the MenodeB is aware of the channel state, it can determine the frequency band chosen by the second access node, for example a HenodeB, to be used for data transmission through a second transmission channel established between another mobile device and the HenodeB.

By modifying the transmission power allocated by HenodeB to the chosen frequency band the interference generated by the HenodeB on the first transmission channel are mitigated. As a result, the probability for the first mobile device to be scheduled in this frequency band by the MenodeB is increased.

Furthermore, such a method does not require exchanging information between MenodeB and HenodeB about the scheduling. This allows reducing the signaling between these two access nodes and facilitates implementation.

Another objective of the invention is a method of communication between a mobile device and a first access node covering a macro-cell, through a transmission channel established between the mobile device and the first access node, the method being run by the mobile device and comprising the steps of:

- measuring at least one parameter representing a pathloss of the transmission channel,

- determining, among the measured parameters representing a pathloss of the transmission channel, the parameter representing the smaller pathloss,

- determining if the smaller pathloss is due to a second access node covering a femto-cell, the macro-cell overlapping the femto-cell,

- should this happen, transmitting the determined parameter representing a pathloss of the transmission channel and an identification of the second access node.

The smaller the pathloss the higher the interference

The invention relates also to an access node covering a femto-cell and generating interference on a first transmission channel established between a first mobile device and another access node covering a macro-cell, the macro-cell overlapping the femto-cell, the access node comprising:

- means for receiving a first parameter representing a pathloss of the first transmission channel due to the access node,

- means for receiving a second parameter representing a pathloss of a second transmission channel established between a second mobile device and the access node,

- means for choosing a frequency band among a frequency spectrum to be used for data transmission through the second transmission channel, based on the first and the second pathloss parameters, - means for determining a transmission power for the frequency band to be used for data transmission through the second transmission channel.

The invention relates as well to an access node covering a macro- cell and allocating frequency resource to a first mobile device, a first transmission channel being established between the access node and the first mobile device, the access node comprising:

- means for receiving a first parameter representing a pathloss of the first transmission channel,

- means for determining a frequency band, chosen by another access node, covering a femto-cell overlapped by the macro-cell, among a frequency spectrum, to be used for data transmission through a second transmission channel established between a second mobile device and the other access node,

- means for allocating frequency resource to the first mobile device in the determined frequency band.

Another objective of the invention is a mobile device communicating with a first access node covering a macro-cell through a transmission channel established between the mobile device and the first access node, the mobile device comprising:

- means for measuring at least one parameter representing a pathloss of the transmission channel due to another access node,

- means for determining, among the measured parameters representing a pathloss of the transmission channel, the parameter representing the smaller pathloss,

- means for determining if the smaller pathloss is due to a second access node providing coverage to a femto-cell, - means for transmitting the determined parameter representing a pathloss of the transmission channel and an identification of the second access node.

The invention concerns a system for mitigating interference generated by a first access node covering a femto-cell on a first transmission channel established between a first mobile device and a second access node covering a macro-cell, the macro-cell overlapping the femto-cell, the first access node comprising means for:

- receiving a first parameter representing a pathloss of the first transmission channel due to the first access node,

- determining a transmission power for the frequency band to be used for data transmission through the second transmission channel, the second access node comprising means for:

- receiving the first parameter representing a pathloss of the first transmission channel,

- determining the frequency band chosen by the first access node to be used for data transmission through the second transmission channel,

- allocating frequency resource to the first mobile device in the determined frequency band,

the first mobile device comprising means comprising:

- measuring at least one parameter representing a pathloss of the first transmission channel due to another access node, - determining, among the measured parameters representing a pathloss of the first transmission channel, the parameter representing the smaller pathloss,

- determining if the smaller pathloss is due to the second access node,

- transmitting the determined parameter representing a pathloss of the first transmission channel and an identification of the second access node.

Finally, the invention concerns also three computer programs, in particular computer programs on or in an information medium or memory, suitable for implementing the three methods of the invention. These programs can use any programming language, and be in the form of source code, object code, or of code intermediate between source code and object code such as in a partially compiled form, or in any other desirable form for implementing the configuration method according to the invention.

The information medium may be any entity or device capable of storing the programs. For example, the medium can comprise 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 diskette (floppy disk) or a hard disk.

Moreover, the information medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The programs according to the invention may in particular be downloaded from a network of Internet type.

The present system and method are explained in further detail, and by way of example, with reference to the accompanying drawings wherein: FIG. 1 represents a network topology consisting of a macro-cell overlapping two femto-cells, in which the invention is run;

FIG. 2 represents the steps of the communication method of the invention;

FIG. 3 represents a small access node HenodeB capable of running the method of the invention;

FIG. 4 represents an access node MenodeB capable of running the method of the invention;

FIG. 5 represents a user equipment MUE capable of running the method of the invention.

Figure 1 represents a heterogeneous network in which the invention is run. Such a heterogeneous network comprises for example a macro- cell MC. Such a macro-cell MC is covered by an access node MenodeB, such as an enodeB. The macro-cell MC is overlapping a plurality of femto-cells FC1 , FC2. The first femto-cell FC1 is covered by a first small access node HenodeBI , such as a small access enodeB. The second femto-cell is covered by a second small access node HenodeB2.

A first user equipment MUE is attached to the access node MenodeB. Such a user equipment MUE is for example a mobile phone, or a tablet or a laptop. The first user equipment MUE is located in the coverage area of the first small access node HenodeB, i.e. the first user equipment MUE is located in the first femto-cell FC1. The user equipment MUE can not access the femto cell.

A second user equipment HUE1 is attached to the fist small access node HenodeBI . A user equipment HUE1 must subscribe to the small access node HenodeB for data transmission to take place between the first user equipment HUE1 and the small access node HenodeB. The unsubscribed user equipment are not allowed to communicate with a small access node HenodeBI , which is the case of the user equipment MUE.

Since the user equipment MUE is located in the coverage area of the first femto-cell FC1 , the first small access node HenodeBI generates interference on a transmission channel established between the first user equipment MUE and the access node MenodeB.

In order to mitigate the interference, the user equipment MUE collects data with the access nodes in its vicinity. The steps of this communication method are represented in figure 2.

In a step E1 , the user equipment UE measure a reference signal receive power RSRP from all the access nodes in the coverage zone of which the user equipment MUE is located, i.e. the macro-cell MC and the first femto-cell FC1 , in the frequency of the radio signal used by the user equipment MUE for communicating with the access node MenodeB. The reference signal receive power RSRP is measured using known techniques such as averaging the received power of the received radio signal on their occupied resource elements (RE) over a certain time window.

In a step E2, the user equipment MUE determines the type of access node generating the more interference on its transmission channel. If the access node generating the more interference is a small access node such as the small access node HenodeBI , then the user equipment MUE runs step E3. If the access node generating the more interference is the access node in the serving macro cell, then the user equipment MUE waits to be scheduled by access node MenodeB to exchange data through the transmission channel.

In step E3, the user equipment MUE measures a path loss PL_HeNBl→MUE of the transmission channel established between user equipment MUE and access node HenodeB, the pathloss PL_HeNBl→MUE being due to the small access node HenodeBI The pathloss PL_HeNB{→MUE is given by

PL_HeNBl__>MUE = ReferenceSignalPower - RSRP , where ReferenceSignalPower is provided to the user equipment MUE by higher layers, such as RRC (radio resource control) layer, and RSRP is the received power of Reference Signal from the small access node HenodeBI .

In step E4, the user equipment MUE determines a parameter, called pathloss level n , characterizing the pathloss PL_HeNBl→MUE . The pathloss level is given by:

PT — PT ^m

n = ^HeNBl→MUE HeNB\→MUE _{> where} „_e {Q. l, ...,#} , and A_pL IS the

PL

mm

In a step E5, the user equipment MUE determines if it can report the pathloss level « to the access node MenodeB. If it can, then the pathloss level n is transmitted to access node MenodeB with information regarding small access node HenodeBI identity, such as the cell Id of the small access node HenodeBI . If it can not, the pathloss level n is then transmitted to small access node HenodeBI .

Still in reference to figure 2, the small access node HenodeBI receives, in a step G1 , the pathloss level n determined by the user equipment MUE during step E4. Upon reception of this pathloss level « , the small access node HenodeBI knows it is generating interference on a transmission channel established between a user equipment MUE and an access node MenodeB. During step G1 , the small access node HenodeBI receives information regarding the user equipment identity as well, such as the MAC address of the user equipment MUE.

In a step G2, the small access node HenodeBI sends a request to report pathloss information to all the user equipments attached to it, such as the first user equipment HUE1. In step G3, the small access node HenodeBI receives a pathloss ^PLHeNB->HUE\ of the transmission channel established between the first user equipment HUE and the small access node HenodeBI .

In a step G4, the small access node HenodeBI chooses a frequency band among a frequency spectrum to be used for data transmission through established between the first user equipment HUE and the small access node HenodeBI using the information concerning the pathloss level « and the pathloss PL_HeNB__>Hum .

The small access node HenodeBI can determine the transmit power of radio signal, emitted by small access node HenodeBI toward the first user equipment HUE1 , in this frequency band according to a chosen power control function. In addition, the transmit power of radio signal emitted in other frequency bands among the frequency spectrum remains the same

Both the new transmit power of the emitted radio signal and the index of the chosen frequency band are transmitted to the first user equipment HUE1 in a strep G5. The frequency spectrum contains M frequency bands RBG, the index of which is {o,i, ..., -i} , and the frequency band RBG₀ is chosen to configure the transmit power of the radio signal emitted by the small access node HenodeBI as p_tx . The transmit power p_b of the radio signal emitted and the index of the frequency band RBG₀ which is set to Ό ' are transmitted to the first user equipment HUE1.

The transmit power of the small access access node HenodeBI is defined as:

^L P HeNBl_tx = mm(P p_0wer __Control ' P max ) , where ^¾Λ¾Ι_Λ is the transmit power of the small access node

HenodeBI , P_power __controi is the configured transmit power of the radio signal emitted by the small access node HenodeBI toward the first user equipment HUE1 based on the proposed power control scheme, and _max is the maximum value of transmit power of the access node.

When configuring the transmit power of the radio signal in the chosen frequency band instead of the whole frequency spectrum, it should be adjusted as:

¹ P HeNBl tx = ¹ P _0

HeNBl tx

1

where, P_{HENBL B} is the transmit power the small access node HenodeBI in the chosen frequency band, ^ is the number of frequency bands in the whole frequency spectrum, K₀ \S the number of the chosen frequency bands.

P power control is defined as.

_ f eNBl→HUEl . rHeNB\->MUE

power _control O J l , where f_Q ^HeNBl→HUEl _s t_ne transmit power to ensure sufficient signal power of the radio signal emitted by the small access node HenodeBI be rHeNB\→MUE

received by the first user equipment HUE1 , is the power offset considering the interference power generated by the small access node HenodeBI on the transmission channel established between the access node MenodeB and the user equipment UE.

r HeNB 1—)HUE 1 . . ,

The baseline power setting j₀ is given by:

f ro HeNB 1 - >HUE 1 = i 1n 0 · 1 log₁₀ + n₀ + i o · PL_HENBL→HUEL , where,

M is the frequency spectrum of the first user equipment HUE1 resource assignment expressed in number of frequency band that the first user equipment HUE1 uses, P₀ is a parameter provided by higher layers, such as RRC (radio resource control) layer, a is a parameter for compensating the pathloss PL_HeNB__>Hum , ae {0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} , and ^PLHeNB->HUEi is the estimated downlink pathloss.

The power offset ^HeNBl→MUE is designed as follows: →MUE

HeNBl→MUE

→MUE

where^ is the power step, with a negative value 5 {-\, -2,...} , n is the pathloss level, A_pz is the pathloss step, PL_HMI→MUE is the estimated downlink pathloss, Pi °_NB→MUE is the lower bound of the pathloss PL_HENB^_MUE , if the measured pathloss PL_HeNBl→MUE is lower than PL^_NB→MUE , then the value of power offset is SN , PL^m _NB→MUE is the upper bound of the pathloss PL_HeNB→MM , if the measured pathloss PL_HeNm→MUE \s higher than PL^_NB→MUE , the cross- tier interference is considered low enough to be ignored, thus the value of power offset is 0.

In a step G6, the small access node HenodeBI transmits data to the first user equipment HUE1 by emitting a radio signal with transmit power P in the chosen frequency band RBG₀ .

In reference to figure 2, the access node MenodeB allocates resource to the user equipment MUE based on information relative to the transmission channel state of the user equipment MUE.

In a step H1 , the access node MenodeB receives the pathloss level n , determined by the user equipment during step E4, along with information regarding small access access node HenodeBI identity, such as its cell ID.

In a step H2, the access node MenodeB can transmit the pathloss level n to the small access node HenodeBI . This information can be sent over the air through S1 or X2 interfaces disposed at access node MenodeB and small access node HenodeB. Since access node MenodeB uses a scheduling scheme that is aware of the transmission channel state, i.e. if the transmission channel suffers interference generated by another access node, the access node MenodeB is capable of determining the frequency band RBG₀, chosen by the access node generating the interference, i.e. the small access node HenodeB, to be used for data transmission with the first user equipment HUE, in a step H3.

In a step H4, the access node MenodeB allocates frequency resource to the user equipment MUE in the determined frequency band RBG₀. In doing so the interference generated by the small access node HenodeBI on the transmission channel established between the user equipment MUE and the access node MenodeB is mitigated and the user equipment MUE can be scheduled by the access node MenodeB with a higher probability.

Figure 3 represents a small access node HenodeB capable of running the method of the invention.

The small access node HenodeBI comprises receiving means 10 capable of receiving the pathloss level n determined by the user equipment MUE and information regarding the user equipment identity as well, such as the user ID of the user equipment MUE.

The small access node HenodeBI comprises means 1 1 of sending a request to report pathloss information to all the user equipments attached to it, such as the first user equipment HUE1. The sending means 11 being connected to the receiving means 10.

The small access node HenodeBI comprises receiving means 12 of a pathloss PL_HeNB__>HUEl of the transmission channel established between the first user equipment HUE and the small access node HenodeBI .

The small access node HenodeBI comprises means for choosing a frequency band 13 among a frequency spectrum to be used for data transmission through established channel between the first user equipment HUE and the small access node HenodeBI . The band-choosing means is connected to the receiving means 10 and 12.

The small access node HenodeBI comprises means for determining

14 the transmit power of radio signal, emitted by small access node HenodeBI toward the first user equipment HUE1 , in this frequency band according to a chosen power control function.

The small access node HenodeBI comprises means for transmitting

15 data to the first user equipment HUE1 by emitting radio signals with transmit power P_tx in the chosen frequency band.

Figure 4 represents an access node MenodeB capable of running the method of the invention.

The access node MenodeB comprises receiving means 20 for receiving the pathloss level « , determined by the user equipment, along with information regarding small access node HenodeBI identity, such as cell ID.

The access node MenodeB comprises means for transmitting 21 the pathloss level « to the small access node HenodeBI . This information can be sent over the air through S1 or X2 interfaces disposed at access node MenodeB and small access node HenodeB.

The access node MenodeB comprises means 22 of determining the frequency band RBG₀, chosen by the access node generating the interference, i.e. the small access S node HenodeB, to be used for data transmission with the first user equipment HUE, in a step H3.

The access node MenodeB comprises means for allocating 23 frequency resource to the user equipment MUE in the determined frequency band RBG₀. In doing so the interference generated by the small access node HenodeBI on the transmission channel established between the user equipment MUE and the access node MenodeB in mitigated and the user equipment MUE can be scheduled by the access node MenodeB with a higher probability.

Figure 5 represents a user equipment MUE capable of running the method of the invention.

The user equipment UE comprises means for measuring 30 a reference signal receive power RSRP from all the access nodes in the coverage zone of which the user equipment MUE is located, i.e. the macro-cell MC and the first femto-cell FC1 , in the frequency of the radio signal used by the user equipment MUE for communicating with the access node MenodeB.

The user equipment MUE comprises means for determining 31 the type of access node generating the more interference on its transmission channel. The means for determining 31 are connected to the means for measuring 30.

The user equipment MUE comprises means for measuring 32 a pathloss PL_HeNBl→_MUE of the transmission channel established between user equipment MUE and access node MenodeB, the pathloss PL_HeNm→MUE being due to the small access node HenodeBI .

The user equipment MUE comprises means 33 for determining a parameter, called pathloss level n , representing the pathloss PL_HeNm→MUE .

The user equipment MUE comprises means for determining 34 if it can report the pathloss level n to the access node MenodeB.

Claims

1. A method for mitigating interference generated by a first access node covering a femto-cell on a first transmission channel established between a first mobile device and a second access node covering a macro-cell, the macro-cell overlapping the femto-cell, the method being run by the first access node and comprising the steps of:

- receiving a first parameter representing a pathloss of the first transmission channel,

2. The method of claim 1 , wherein the first access node determines the transmission power for the frequency band to be used for data transmission through the second transmission channel using a power control function consisting in at least two parts: a first part related to a power control strength of a radio signal transmitted through the second transmission channel and a second part related to the interference generated by the first access node on the first transmission channel established.

3. Method for allocating frequency resource to a first mobile device, frequency resource being allocated by a first access node covering a macro-cell, a first transmission channel being established between the first access node and the first mobile device, the method comprising the steps of:

4. Method of communication between a mobile device and a first access node covering a macro-cell, through a transmission channel established between the mobile device and the first access node, the method being run by the mobile device and comprising the steps of:

- determining if the smaller pathloss is due to a second access node covering a femto-cell overlapped by the macro-cell,

5. Access node covering a femto-cell and generating interference on a first transmission channel established between a first mobile device and another access node covering a macro-cell, the macro-cell overlapping the femto-cell, the access node comprising: - means for receiving a first parameter representing a pathloss of the first transmission channel,

- means for choosing a frequency band among a frequency spectrum to be used for data transmission through the second transmission channel, based on the first and the second pathloss parameters,

- means for determining a transmission power for the frequency band to be used for data transmission through the second transmission channel.

6. Access node covering a macro-cell and allocating frequency resource to a first mobile device, a first transmission channel being established between the access node and the first mobile device, the access node comprising:

7. Mobile device communicating with a first access node covering a macro-cell through a transmission channel established between the mobile device and the first access node, the mobile device comprising: - means for measuring at least one parameter representing a pathloss of the transmission channel,

- means for determining if the smaller pathloss is due to a second access node covering a femto-cell, the macro-cell overlapping the femto- cell,

- means for transmitting the determined parameter representing a pathloss of the transmission channel and an identification of the second access node.

8. System for mitigating interference generated by a first access node covering a femto-cell on a first transmission channel established between a first mobile device and a second access node covering a macro-cell, the macro-cell overlapping the femto-cell, the first access node comprising means for:

- determining a transmission power for the frequency band to be used for data transmission through the second transmission channel, the second access node comprising node comprising means for:

- receiving the first parameter representing a pathloss of the first transmission channel, - determining the frequency band chosen by the first access node to be used for data transmission through the second transmission channel,

the first mobile device comprising means comprising:

- measuring at least one parameter representing a pathloss of the first transmission channel,

- determining, among the measured parameters representing a pathloss of the first transmission channel, the parameter representing the smaller pathloss,

- determining if the higher pathloss is due to the second access node,

9. Computer program characterized in that it comprises program code instructions for the implementation of the steps of the method for mitigating interference as claimed in claim 1 when the program is executed by a processor.

10. Computer program characterized in that it comprises program code instructions for the implementation of the steps of the method for allocating frequency resource as claimed in claim 3 when the program is executed by a processor.

11. Computer program characterized in that it comprises program code instructions for the implementation of the steps of the communication method as claimed in claim 4 when the program is executed by a processor.