WO2010121635A1

WO2010121635A1 - Power control in femto cells

Info

Publication number: WO2010121635A1
Application number: PCT/EP2009/003019
Authority: WO
Inventors: Xiao Yi Wang
Original assignee: Nokia Siemens Networks Oy
Priority date: 2009-04-24
Filing date: 2009-04-24
Publication date: 2010-10-28

Abstract

Embodiments of the present invention relate to method and apparatuses for providing power control in a mobile network such as a femto cell. In accordance with one or more of the embodiments, a base station calculates a power control value for at least one terminal such as a mobile station based on parameters received from another base station, and transmits the generated power control value to the at least one terminal.

Description

Power Control in Femto Cells

FIELD OF THE INVENTION

The present invention relates to methods and apparatuses for providing power control in wireless access, e.g. to a communication or data network such as e.g. a local area or core network.

BACKGROUND OF THE INVENTION

Femto base stations such as home base stations, base transceiver stations, home NodeBs, femto enhanced node Bs, eNodeBs, or any other type of home access device, in the following generally referred to as "femto base stations", usually provide limited coverage area but allow, e.g. when deployed in homes and offices of a building, subscribers to use their existing handsets with significantly improved coverage and quality and e.g. increased broadband wireless performance.

A femto base station or base transceiver station, BTS₁ is able to provide in-home mobility with high user data rates, without loading the macro BTS. Femto home base stations may access the network such as a provider network of core network e.g. through a publicly-switched telephone network, which is typically available through a residential digital subscriber line, DSL. A handset such as a mobile station of a user e.g. only communicates to the femto station in the home or office, completely offloading that user from the macrocell.

Femto base stations may be used to provide an advanced air interface in order to meet the requirements of next generation mobile networks, offering fully mobile multimedia experience even in cases of otherwise limited available reception, especially in remote areas and in residences. Existing mobile communication systems (e.g. Global System for Mobile communications (GSM), Wideband Code Division Multiple Access (WCDMA/HSDPA), developed and defined under the assumption of coordinated network deployment may be used, although not optimally suited, for such home-based application. Base stations such as femto base stations are typically associated with uncoordinated and large scale deployment.

In femto base station scenarios, an end user may install a femto base station similar to a wireless local area network (WLAN) like product at his office or home for providing coverage/service to the terminals registered by the owner of the femto base station. The femto base station may use the same spectrum owned by an operator and as such at least partly the spectrum the operator is also using to provide macro cell coverage of a macro base station to the area partially covered by the femto base station, too.

A Femto base station or BTS may be considered as a kind of network organization mode. Operators allow and encourage users to use a femto base station to enhance signalling strength in their own home. However, unlike a traditional cellular BTS, femto base stations are hardly for network planning. The users normally want to put the femto BTS in a place at home just like a wireless local area network access point, WLAN AP.

A difference between a femto base station and a WLAN access point, AP, is that the Femto base station is still a part of the network such as a communication or mobile network, e.g. a worldwide interoperability for microwave access, WiMAX, network. In many cases, femto base station and macro base station may work in the same carrier.

Further, in some cases, multiple femto base stations may be deployed in close proximity, e.g. in several offices or rooms of the same building. Such plural base stations may e.g. be controlled in independent form or as a self-organized network. Yet, severe interference may occur, e.g. if the base stations use the same physical layer (PHY) resource. SUMMARY

Embodiments of the invention provide reduce interference and thus good signal quality. A power control, PC, for at least one of femto cells, femto base stations, and terminals such as mobile stations configured to communicate with the at least femto cell, is proposed in accordance with one or more of the embodiments.

According to an aspect of embodiments of the invention, an apparatus is configured to receive at least one parameter for power control of a transmit power of a device such as a terminal or mobiie station, to generate a power control value based on the received at least one parameter, and to transmit the generated power control value to the device. The device may e.g. be a terminal or mobile station configured to communicate with or attach to the apparatus such as a femto base station.

The at least one parameter may at least be one of a load factor, a load information or long-term load information of a macro cell, a calibration factor, and a margin, etc. The control of a cell of a first type of a cellular network such as a femto cell may therefore take account of the conditions in a cell of another type such as a macro cell.

The power control value may for example indicate a transmission power of a ter- minal, e.g. a mobile station, such as maximum allowed or desired transmission power of the terminal or mobile station. A terminal receiving this power control value is configured to control its maximum transmission power when sending uplink information, user traffic, or signaling so as to be limited to, or below, the maximum allowed transmission power. The power control value may e.g. indicate a calcu- lated and/or calibrated maximum allowed transmission power, or a maximum allowed power spectrum density or transmission power spectrum density, allowing effective power control . Power spectrum density is the transmission power per certain bandwidth. In this example, the power spectrum density may indicate the maximum allowed transmission power per certain bandwidth, such as transmission power per each 10OkHz, or 20OkHz or 50OkHz or the like.

The power control value may be calculated based on at least one of a distance between said apparatus and an apparatus generating the parameter, and an actual coverage of said apparatus. Such parameters may basically influence the expected interference.

The apparatus may be configured to calculate the power control value, PSD_Fin_ai, based on the following equation: PSD_Final = PSD_mlculated + PL_serving x ε - f + ηPSD. where, PSD_calctUaled is a calculated maximum transmission power of a mobile station or terminal, or a power spectrum density, PSD, of a mobile station or terminal, as calculated by the apparatus; PL_servjng is a pathloss, estimated by the apparatus, between the apparatus and a macro base station; PSD_1x is a downlink, DL, transmitting power or power spectrum density PSD, of the apparatus, and ε ,f,η are parameters received from a serving macro base station, ε is the load factor of the serving macro base station 1 , / is the calibration factor to downlink transmit PSD, η is the margin level given from the macro base station, allowing good signal quality with sufficient interference avoidance.

In accordance with one or more of the embodiments, the generated power control value may be transmitted to, and received by, the device via a broadcast channel, enabling the terminals to efficiently receive the power control even when e.g. newly attaching to the base station.

Advantageously, the apparatus or method may be configured to repeatedly or periodically generate or receive the at least one parameter. Thus, the power control value may be repeatedly or periodically calculated and updated.

In accordance with one or more of the embodiments, the apparatus may be a base station, a femto base station, or a part, module or chipset of or for such a femto base station. According to another aspect, an apparatus may be configured to generate at least one parameter for power control of a transmit power of a device, and to transmit the generated parameter to a base station or apparatus such as a fem- to base station.

The apparatus may for example be implemented as a macro base station, or a part, module or chipset of or for a macro base station.

Further, an apparatus may be configured to receive a power control value from another apparatus such as a femto base station, and to limit a maximum uplink transmit power based on the received power control value. The apparatus may for example be a mobile station, or a part, module or chipset of or for a mobile station.

According to a further aspect, a method is provided which comprises: receiving at least one parameter for power control of a transmit power of a transmitting device; generating a power control value based on the received at least one parameter; and transmitting the generated power control value to the transmitting device.

Such a method may comprise at least one of: the at least one parameter is at least one of a load factor, calibration factor, margin, the power control value is a calculated and optionally calibrated power spectrum density, transmitting the generated power control value to the at least one device via a broadcast channel, generating the at least one parameter at a macro base station, and transmitting the generated parameter to a femto base station, limiting a maximum uplink transmit power of the at least one device configured to attach to, or communicate with, the femto base station, based on the received power control value. Further, a computer program or computer program product is provided which comprises code means for carrying out a method as defined above or below, e.g. when running on a computer or processor.

Embodiments of the present invention relate to method and apparatuses for providing power control in a mobile network such as a femto cell. A base station such as a femto base station calculates a power control value for at least one terminal or mobile station based on parameters received from another base station, and transmits, e.g. broadcasts, the generated power control value to the at least one terminal or mobile station. The terminal or station may limit its maximum transmission power based on the received power control value.

In accordance with one or more of the proposed embodiments, a hierarchical power control, PC, is provided. Parameters for a power calculation in a femto base station may be sent by at least one macro base station to at least one femto base station. Based on these macro base station parameters, the at least one femto base station may calculate a maximum transmitting power value, for example a maximum transmitting power spectrum density, PSD, for all mobile stations, MS, connecting to it. The calculated maximum transmitting power value is sent to the mobile stations, and used by the mobile stations, to limit their maximum transmission power to the received value. The parameters for power calculation in the femto base station may be repeatedly or periodically updated and sent by the at least one macro base station to the at least one femto base station.

In accordance with one or more of the proposed embodiments, formulas for power calculation in a femto base station are provided, together with parameters provided by a macro base station.

Further, in accordance with one or more of the embodiments, one or more signali- zation messages between a macro base station and a femto base station are proposed. In accordance with at least one or optionally all of the embodiments, an improved performance of a femto base station is provided.

In accordance with one or more of the embodiments, a hierarchical power control instead of single layer power control is implemented. A specific signalization between macro and femto base stations may be implemented for power control in the femto cell in accordance with one or more of the embodiments.

In accordance with one or more embodiments, a node such as a femto base sta- tion is configured to estimate the distance between the node itself and a macro base station, e.g. for proper transmission, and to use this value to limit (e.g. decide on the maximum value of) the transmission power of other nodes (such as all mobile stations, MS, e.g. user terminals or user equipment, that are attached to this femto base station). In this implementation, there are basically three parties in- volved, macro base station, femto base station and mobile station.

In accordance with one or more of the embodiments, interference in the femto cells is considered, and fractional compensation on the pathloss between femto base station and macro base station is provided, e.g. when performing a calibra- tion of the femto and/or macro base station, where the fractional factor is optionally considering the load factor of the macro base station.

Embodiments provide architectural aspects for implementing the invention.

Embodiments of the invention are applicable to any kind of networks such as - but not limited to - universal mobile communication system (UMTS) or long term evolution (LTE) networks, etc.

Other advantageous modifications are defined in the dependent claims or will be- come apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail based on embodiments with reference to the accompanying drawings in which:

Fig. 1 shows a schematic network architecture with a macro cell and several femto cells; Fig. 2 shows a schematic block diagram of an embodiment having overlapping coverage between femto and macro cells;

Fig. 3 shows a schematic diagram of interference from femto cells to a macro cell; Fig. 4 shows an embodiment of a broadcast message; Fig. 5 shows embodiments of a femto base station and a macro base station; Fig. 6 shows an embodiment of a mobile station; and

Fig. 7 shows exemplary implementations of methods implemented in embodiments of base station, femto base station and mobile station, and of a signaling between these apparatuses.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be described based on exemplary and non-limiting network architectures.

Fig. 1 illustrates an embodiment in accordance with an implementation of the invention, showing a schematic network architecture comprising one or more macro base stations 1 and one or more femto base stations 8 according to embodiments.

In accordance with one or more of the embodiments, one or more of the femto base stations 8 provide power control for some or all mobile stations, MS, 10 connecting to this femto base station 8. The femto base station 8 may e.g. determine the maximum transmitting power such as maximum transmitting power spectrum density (PSD)₁ optionally use a generic algorithm as a normal mobile station, MS.

In one or more of the embodiments, a femto base station 8 may calculate an uplink power such as an uplink power spectrum density, UL PSD, e.g. in a similar manner as a mobile station connecting to a macro base station. The calculation may e.g. be performed according to an open loop power control (OLPC), based e.g. on a target signal to interference plus noise ratio, SINR₁ or interference constraint power control, ICPC, or another scheme. With an optional certain degree of calibration, the femto base station or cell may broadcast that calculated uplink power value such as uplink PSD, as a maximum transmitting value or PSD to any MS attached or attaching to this femto base station.

The power calculated by the femto base station may be calibrated considering one, more or all of the following factors: - long term load information of macro cell (small load means smaller average interference);

- configured coverage of current femto base station, e.g. relative to the downlink, DL, preamble transmitting power;

- a pre-determined power margin which may e.g. be decided by macro base sta- tion. This margin is to make sure that the arrival interference power from femto mobile station, i.e. a mobile station served by the femto base station is not larger than signal power from a macro MS, that is a mobile station served by the macro base station.

As shown in Fig. 1 , the network architecture comprises at least one macro cell 3 and at least one femto cell 9. The base station 1 is a macro base station in form of cellular base station such as a base transceiver station, a node B, etc, and comprises a transceiver tower 2 which defines the macro cell 3 providing direct radio links to a mobile station 4 such as a cell phone, terminal, user equipment, comput- er or the like. The base station 1 is connected to a communication network 5 such as a core network. The network 5 may be connected with a router device 6, for example an internet service provider router which may comprise digital lines such as asynchronous digital subscriber line, ADSL, devices like cards or the like.

The device 6 is connected via one or more lines 7 such as digital lines, subscriber lines or residential digital subscriber lines, to one, more or all of the femto base stations 8. The femto base stations 8 define local femto cells 9 to which one or more terminals 10 such as mobile stations may be connected or attached. The terminal or terminals 10 may be a customary mobile terminal, or may also be a mobile or stationary device only usable in the respective femto cell. In Fig. 1 , several femto base stations 8 may be provided in a building 11 , for example a concrete high-rise apartment building.

The left-hand scenario in Fig. 1 represents a traditional direct connection from the mobile station 4 such as a cell phone 4 or handset, to the cellular tower 2 of the macro base station 1. This direct connection usually has relatively low loss and good signal quality in an area close to the cellular macro base station 1.

In the embodiment of Fig. 1 , the building 11 at the right-hand part of Fig. 1 comprises several femto base stations 8 installed e.g. in apartments of the building 11. The network feed to the femto base stations 8 is provided through the digital lines, e.g. residential DSL lines or ADSL, 7. In this scenario, the direct radio signal con- nection / strength between the macro cell 3 and the terminals 10 in the building 11 is weak. The femto stations 8, 9 act as personal, dedicated base stations and do not talk to the macrocell(s) 3 for transmitting user traffic.

Fig. 2 illustrates an embodiment wherein the multiple femto base stations 8 are deployed in very close proximity, e.g. in form of a self-organized network. The macro base station 1 is connected, e.g. via an asynchronous transfer mode, ATM, line 12 to an access service network, for example an access service network gateway, ASN-GW, 13 of WiMAX. The femto base stations 8 may be connected via the digital subscriber lines 7 and possibly via the internet 14 to the access service network of the macro base station 1 such as the access service network gateway 13.

In the embodiment of Fig. 2, the femto cells 9 are largely overlapping so that there is some possibility of severe interference e.g. if the femto cells 9 use the same physical, PHY, resource. The macro base station 1 may give orthogonal resource to some of the femto base stations 8 or femto cells simultaneously since femto base stations normally do not use all the bandwidth. However, such a method is relying on, and requiring, orthogonal resource allocation. In some cases, as shown in Fig. 3, one or more of the femto base stations 8 may be located close to the macro base station 1 as well. In such a situation, interference from one or more of the femto mobile stations 10 to the macro base station 1 in the uplink direction, UL, may be severe. Interference links 15 from the femto cells 9 and terminals 10 are shown by lines 15. A signaling link between the macro base station 1 and the terminal 4 is labeled with numeral 16. Fractional frequency reuse, FFR, may be provided. Yet, when giving dedicated PHY resource to some femto base stations, the available bandwidth of the macro base station 1 will be reduced. In particular in case of a high number of femto cells 9, the performance of macro base station 1 may be degraded significantly. Such a disadvantageous effect may be avoided in accordance with embodiments according to the invention as described below.

In accordance with one or more embodiments, one, more or all femto base stations 8 are configured to provide power control to decide and determine a maximum transmitting power such as power spectrum density (PSD) for some or all mobile stations 10 connecting to the respective femto base station(s) 8. The base station 8 may use a generic algorithm as employed in a MS, e.g. station 4 con- nected to a macro base station.

In accordance with one or more of the embodiments, the femto base station 8 calculates a power value for the uplink, UL, transmission direction of the mobile stations connected to the base station 8. This power value may for example be a maximum transmit power value for some or all mobile stations 10 connected to the respective femto base station(s) 8, such as maximum transmitting power spectrum density, PSD, for some or all mobile stations 10 connected to the respective femto base station(s) 8. The femto base station 8 may calculate the maximum transmitting power value of the mobile stations connected thereto according to an open loop power control, OLPC, scheme, e.g. based on a target signal-to interference- plus-noise ratio, SINR, or interference constraint power control, ICPC, or other scheme. The femto base station 8 may optionally calibrate the calculated transmit power value. The femto base station 8 signals, e.g. broadcasts, the calculated or calibrated maximum transmit power value, e.g. PSD, as a maximum transmitting power value to any MS 10 attached or attaching to this femto base station 8.

In accordance with one or more of the embodiments, the calculated power calculated by the femto base station may be calibrated using the following equation:

Power _Fmal = Powe_rcalculaled + PL_servmg * ε - f + ηPower^

where, Power_calculaled is the power calculated by the femto base station for the terminal such as mobile station,

PL_servmg '^{s tne} pathloss, estimated by the femto base station 8 between the macro base station 1 and the femto base station(s) 8, Power_tt is the femto base station downlink, DL, transmitting power.

^*AII values are in dB.

As an example, the femto base station 8 may calculate and calibrate the maximum uplink transmit power PSDF_1113I of the stations 10 connected to the femto base sta- tion 8 using the following equation:

PSD_Fmal = PSD _∞tø(W + PL_servmg x ε - f + ηPSD.

where, PSD_calculated is the PSD calculated by the femto base station 8, e.g. using OLPC for MS as defined in 16m. PL_servmg is the pathloss, estimated by the femto base station 8, between macro and femto base stations.

PSD_1x is the femto base station downlink, DL, transmitting power spectrum density PSD.

*AII values are in dB. ε,f,η are all parameters indicated by serving macro base station 1 to the femto base station 8 e.g. through ADSL or other backbone networks, ε is the load factor of serving macro base station 1 , / is the calibration factor to femto DL Tx PSD, η is the margin level given from macro base station 1. The serving base station 1 of the macro cell 3 optionally sends a message including one more or all of those parameters ε,f,ηto all femto base stations 8 once or repeatedly, e.g. periodically. The details of sending repetition or periodicity may be implementation related. A typical periodicity may be 500ms or 1s, or any value between 100ms and 2s.

In above equation, the following factors are considered:

1. Long term load information of macro cell. Small load means smaller aver- age interference.

2. Configured coverage of current femto base station, (e.g. relative to DL preamble transmitting power). The femto DL transmission power will optionally be adjusted adapting it to the interference status between femto base station and macro base station. The downlink, DL, interference status may be reused for uplink UL, e.g. UL interference status.

3. A pre-determined power margin. The power margin may be decided by the macro base station. This margin is to make sure that the arrival interference power from femto terminal such as mobile station MS 10 is less than signal power from macro mobile station MS 4.

If femto base station 8 cannot detect any preamble from macro base station 1 , it may decide not to calculate the uplink transmit, UL TX, power of the mobile stations) 10 attaching or attached to the femto base station 8. In such a case, the femto base station 8 may freely decide UL TX of MS attaching to it.

The macro base station 1 may optionally, e.g. repeatedly or periodically, inform the femto base stations about the needed parameters including the load factor, calibration factor on femto DL TX Power, and margin level, etc.

Following are examples of messages carrying those information: Example of a signaling message between serving (macro) base station 1 and the femto base station 8,

Syntax Size (bit) Notes

Femto power control, PC message {

TLV Variable

}

TLV stands for type-length-value or TLV element of a protocol. The type and length fields may be fixed in size (typically 1-4 bytes), and the value field is of variable size. These fields may be used as follows: Type is represented by a numeric code indicating the kind of field, length indicates the size of the value field, and value may have variable size and contains the data for this message.

TLV for Load factor

Type Length Value Note

The load factor of serving BS. 0: Load factor=0

Xxx(TBD) 0-255 255:Load factor=1 Granularity is 1/255

The load factor of serving base station, e.g. macro base station 1 may be appropriately defined. A value 0 indicates a load factor=0; a value 255 a load factor=1 , with intermediate load factors being indicated with a granularity of e.g. 1/255 TLV for calibration factor Type Length Value Note

The calibration portion on Femto DL Transmission power

Xxx(TB D) 0-255 0: Calibration factor=0 255:Calibration factor =1 Granularity is 1/255

TLV for margin level Type Length Value Note Margin level

Range at [-5,5] in unit of dB.

Xxx(TBD) 0-255 0: -5dB 255: 5dB, Granularity is 1/255.

The maximum power value such as power spectrum density (PSD) decided by the femto base station 8 will be broadcasted by the femto base station 8, e.g. in femto broadcast channel BCH. All mobile stations 10 accessing to this femto base station 8 are optionally configured to limit their transmit power, e.g. TX PSD, to the broadcasted maximum power value . (Slow frequency hopping, SFH, is applied in the broadcasted channel, and S-SFH is divided into multiple sub-packet). A typical broadcasting periodicity is 100ms but may also range between e.g. 10ms to 2s. An example of such a packet used for transmit power control is shown in Fig. 4. The broadcast channel from the femto base station 8 to the mobile stations 10 transmits a sub-packet 3 of the broadcast channel which sub-packet includes a field P_{τχ MAX} as shown in the last line of Fig. 4. The field P_{τx MAX} may have a size of e.g. 8 bits and indicate the maximum transmission power for the mobile stations 10, optionally indicated per subcarrier and having a value which may e.g. range between -1OdBm and -23dBm.

A variety of power control schemes may be used for the mobile stations 10. As an example, a PC, power control, scheme used or selected in standard IEEE 802.16m as PC scheme for data, may be used to obtain the calculated power Power_calculaled such as PSD_calculaled in the above described embodiments.

In an embodiment, a full compensation power control may be provided as follows:

Full compensation Power control :

PSD_a*+* = SINRr + IoT + Noise + PL_servmg where PSDcaicuiated is the calculated transmit power calculated by the femto base station 8, see the above equations, IoT is the interference over noise, PL is the pathloss between BS and MS. SINRt is the target SINR broadcasted by BS.

In another embodiment, a fractional power control may be provided:

Fractional power control

PSD = SINR₇. + IoT + Noise + a x PL_servmg where IoT is the interference over noise, PL is the pathloss between BS and MS. SINRt is the target SINR broadcasted by BS. In a further embodiment, an interference constraint power control may be provided:

Interference Constraint Power Control : PSD = NRT +Noise - g all ι=0 where g, is the pathgain from MS to BS i. NRT is the Noise Raise Target value broadcasted from BS

Fig. 5 shows a schematic block diagram of a macro base station 1 and a femto base station 8 according to various embodiments. The base station 1 comprises a processor or processing unit 21 for performing base station-related signal and control processing as described above and below, and a transceiver 22 for transmit- ting and receiving signals to and from mobile stations 4 connected to the base station 1 , as well as between the base station 1 and the femto base station 8. The base station 8 likewise comprises a processor or processing unit 81 for performing base station-related signal and control processing as described above and below, a memory for parameter storage 83, and a transceiver 82 for transmitting and re- ceiving signals to and from mobile stations 10 connected to the base station 8, as well as between the macro base station 1 and the femto base station 8.

The processors 21 , 81 may be implemented as a software controlled central processing unit (CPU) or any other processor device. Some or all of the above and below described functions may be implemented as subroutines which control the processor 21 or 81 , or as a separate software-controlled CPU or any other processor device.

Fig. 6 shows a schematic block diagram of an alternative software-based imple- mentation according to an embodiment of a mobile station 10. The proposed or required functionalities can be implemented in any device or network entity with a processing unit 101 , which may be any processor or computer device with a con- trol unit which performs control based on software routines of a control program stored in a memory. The control program may also be stored separately on a computer-readable medium. Program code instructions are fetched from the memory and are loaded to the control unit of the processing unit 101 in order to perform the processing steps of the above device-specific functionalities which may be implemented as the above mentioned software routines. The processing steps may be performed on the basis of input data Dl received via a transceiver 100. A power controller 102 controlled by the processor is configured to generate power control signals for controlling the transmission power of the uplink signals transmitted by the transceiver 100 so as to be limited to the calculated and optionally calibrated maximum transmission power. The power controller 102 controls the transceiver 100 by applying control signals DO.

Consequently, the above embodiments or functions of the base stations 1 , 8, and mobile stations 10 may be implemented as a computer program product comprising code means for generating each individual step of the procedures for the respective entity when run on a computer device or data processor of the respective entity at the base station 1 , 8 or mobile station 10 or any corresponding network entity.

Fig. 7 illustrates an embodiment of a method in accordance with an implementation of the invention. A macro base station such as base station 1 performs a function 1 of parameter generation for generating one or more of the above described parameters for power control such as load factor ε , calibration factor / , margin η . In a process or function 2, these parameters are sent from the serving macro base station 1 to the femto base station 8. Optionally a confirmation may be returned from the base station 8 to the base station 1. The femto base station 8 performs a process or function 4 of calculating, and optionally calibrating, a maximum uplink transmit power of or for all the terminals or mobile stations 10 attached to this femto base station 8, e.g. in the manner as described above. The calculated and optionally calibrated maximum transmit power of the terminals or mobile stations 10 attached to this femto base station 8, or a value indicating, or allowing to determine, this maximum transmit power, is broadcast or otherwise sent to the at least one or all mobile stations 10 communicating with or attached to the femto base station 8 in a message 5, power info.

The terminals or mobile stations 10 set their maximum uplink transmit power in accordance with the information received in message 5, see process or function 6. The mobile stations 10 and the femto base station 8 may now communicate respecting the limited uplink transmission power of the terminals or stations 10, cf. process 7.

It is apparent that the invention can easily be extended to any other service and network environment and is not restricted to the LTE technology area and in particular not to base stations. The described embodiments can be implemented in connection with any base station with limited coverage (usually employed for indoor coverage and improved user experience in the home area) deployed in a wireless network. Any one of the above described functions or features of embodiments may be used in isolation without any one of the other disclosed features, or may also freely and arbitrarily be combined with one or more or all of the other disclosed features as described above.

Claims

1. An apparatus, configured to receive at least one parameter for power control of a transmit power of at least one device configured to communicate with or attach to the apparatus, to generate a power control value based on the received at least one parameter, and to transmit the generated power control value to the at least one device.

2. Apparatus according to claim 1 , wherein the at least one parameter is at least one of a load factor, a load information or long-term load information of a macro cell, a calibration factor, and a margin .

3. Apparatus according to claim 1 , wherein the power control value is or indicates a calculated and/or calibrated transmission power or transmission power spectrum density of the at least one device .

4. Apparatus according to claim 1 , wherein the apparatus is configured to calculate the power control value based on at least one of a distance between said appara- tus and an apparatus generating the parameter, and an actual coverage of said apparatus.

5. Apparatus according to claim 1 , wherein the apparatus is configured to calculate the power control value PSDpmai based on the following equation: PSD_Fmal = PSD_∞ladated + PL_servmg x ε - f + ηPSD. where, PSD_calctllaled is a calculated transmission power of the at least one devicen or a calculated transmission power spectrum density, PSD, of the at least one device, calculated by the apparatus,

PL_servmg is a pathloss, estimated by the apparatus, between the appa- ratus and a macro base station,

PSD_1x is a downlink, DL, transmitting power or power spectrum density

PSD, of the apparatus, and £^•,/,;/ are parameters received from a serving macro base station, ε is the load factor of the serving macro base station 1 , / is the calibration factor to downlink transmit PSD, η is the margin level given from the macro base station.

6. An apparatus according to claim 1 , configured to transmit the generated power control value to the at least one device via a broadcast channel.

7. An apparatus according to claim 1 , configured to repeatedly or periodically receive the at least one parameter for repeatedly or periodically calculating the power control value.

8. Apparatus according to claim 1 , wherein the apparatus is a femto base station, or a part, module or chipset of or for a femto base station.

9. An apparatus, configured to generate at least one parameter for power control of a transmit power of a device configured to communicate with a femto base station, and to transmit the generated parameter to the femto base station.

10. Apparatus according to claim 9, wherein the apparatus is a macro base station, or a part, module or chipset of or for a macro base station.

11. An apparatus, configured to receive a power control value from a femto base station, and to limit a maximum uplink transmit power of the apparatus based on the received power control value.

12. Apparatus according to claim 11 , wherein the apparatus is a terminal, a mobile station, or a part, module or chipset of or for a terminal or mobile station.

13. Method, comprising: receiving at least one parameter for power control of a transmit power of at least one device, generating a power control value based on the received at least one parameter, and transmitting the generated power control value to the at least one device.

14. Method according to claim 13, comprising at least one of: the at least one parameter is at least one of a load factor, calibration factor, margin, the power control value is or indicates a calculated and optionally calibrated maximum transmission power or power spectrum density, transmitting the generated power control value to the at least one device via a broadcast channel, generating the at least one parameter at a macro base station, and transmitting the generated at least one parameter to a femto base station, limiting a maximum uplink transmit power of the at least one device configured to attach to, or communicate with, the femto base station based on the received power control value.

15. A computer program product, comprising code means for carrying out a method according to claim 13 or 14.