WO2008066431A1

WO2008066431A1 - Power offset variation in relation to different transmission channels

Info

Publication number: WO2008066431A1
Application number: PCT/SE2006/050523
Authority: WO
Inventors: Mårten ERICSON; Kjell Larsson; Hans Hannu; Peter ÖKVIST
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2006-11-29
Filing date: 2006-11-29
Publication date: 2008-06-05

Abstract

The invention is directed towards a method and channel offset determining device for adjusting the power offset of at least one transmission channel in relation to another transmission channel in uplink communications between a mobile station and a cell in a wireless network. According to the invention measurement data (RC) of radio conditions of the uplinks for the mobile station is obtained (34). Based on this data a determination (36) is made if the offset should be adjusted or not. If an adjustment should be made (36), the change in offset (38) is determined based on said obtained data and the offset is then adjusted according to the determined change (40).

Description

POWER OFFSET VARIATION IN RELATION TO DIFFERENT TRANSMISSION

CHANNELS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of mobile station power control and resource management in wireless networks. The invention more particularly relates to a method of adjusting the power offset of at least one transmission channel in relation to another transmission channel in uplink communications between at least one first group of mobile stations including at least one mobile station and a cell in a wireless network as well as a channel offset determining device for a cell in a wireless network.

DESCRIPTION OF RELATED ART

In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones ("cellular" telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, handheld, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.

The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the mobile user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto.

One example of a radio access network is the Universal Mobile Telecommunications

(UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM). UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies.

In a WCDMA system there are basically two types of power control algorithms; inner and outer-loop power. The inner-loop power control, which is fast, adjusts the transmit power of a sending entity towards a specific signal-to-carrier ratio (SIR) target at a receiving entity, whereas the outer-loop power control (OLPC) , which is slow, adjusts the SIR target of the inner loop power control in order to maintain a specified quality-based target. In the uplink, i.e. from mobile station to base station, OLPC is used both for DCH (Dedicated Channel) and E-DCH (Enhanced Data Channel) channels, but in a slightly different manner. Due to the use of HARQ (Hybrid Automatic Repeat Request) protocol in EUL (Enhanced Uplink), the currently used OLPC quality target is the number of transmission attempts. As an alternative to OLPC it is also possible to perform some other kind of suitable filtering.

It is expected that EUL will eventually replace ordinary so-called R99 uplink solutions, at least in hot spots. Such examples might be that VoIP (Voice over IP) replaces CS (Circuit- Switched) speech and that services requiring higher bit rates are/will be deployed on E- DCH instead of R99 DCHs. However, to make this scenario happen, the capacity and coverage for e.g. a VoIP solution must be equally efficient as CS speech, and higher bit rate services deployed on EUL must outperform their R99 counterparts.

The transmission of data over the air is performed by using several different physical channels, for example DPCCH (Dedicated Physical Control Channel), DPDCH (Dedicated Physical Data Channel) E-DPCCH (E-DCH Dedicated Physical Control Channel) and E- DPDCH (E-DCH Dedicated Physical Data Channel), where E-DCH means Enhanced Dedicated Transport Channel.

The power consumptions of these are related to each other by power offsets, i.e. β- values. These β-values are set so that the quality for all channels is fulfilled when the targeted number of transmissions attempts is used. Default E-DPDCH power offset is typically designed to give best throughput with lowest signal-to-interference ratio (SIR) for a given delay. It is typically fixed for each radio bearer and not designed for 'lowest delay' or 'best coverage', or sometimes not even 'best capacity'.

Current solution with same power offsets either gives:

• bad coverage and good capacity, or;

• good coverage and bad capacity

There is therefore a need for an improvement in the field of offsets provided between different transmission channels, which allows a network to adapt to various network and mobile station conditions.

SUMMARY OF THE INVENTION

The present invention is therefore directed towards providing an improved and flexible determination of the offsets provided between different transmission channels, which allows a network to adapt the power offsets to various network and mobile station conditions.

This is generally solved through obtaining measurement data of radio conditions of the uplinks for mobile stations. Based on this data a determination is made if the power offsets should be adjusted. If they should, the change in offset is determined based on the obtained data and thereafter implemented.

One object of the present invention is thus to provide a method of adjusting the power offset of at least one transmission channel in relation to another transmission channel in uplink communications between at least one first group of mobile stations including at least one mobile station and a cell in a wireless network, which method allows the network to adapt the power offsets to various network and mobile station conditions.

This object is according to a first aspect of the present invention achieved through a method of adjusting the power offset of at least one transmission channel in relation to another transmission channel in uplink communications between at least one first group of mobile stations including at least one mobile station and a cell in a wireless network. The method includes the steps: obtaining measurement data of the radio conditions of the uplinks between the mobile stations of the group and the cell and determining, based on the obtained data, whether the offset should be adjusted or not. In case the determination indicates that an adjustment should be made, the change in offset is then determined based on the obtained data followed by adjustment of the offset according to the determined change.

Another object of the present invention is to provide a channel offset determining device for a cell in a wireless network, which allows the network to adapt the power offsets to various network and mobile station conditions.

This object is according to a second aspect of the present invention achieved through a channel offset determining device for a cell in a wireless network, where at least one first group of mobile stations, including at least one mobile station, is communicating with the cell. The device comprises a radio condition measurement obtaining unit configured to obtain measurement data of the radio conditions of the uplinks between the mobile stations of the group and the cell and an offset determining unit. The offset determining unit is here configured to determine, based on the obtained data, whether the offset should be adjusted or not. In case the determination indicates that an adjustment should be made it furthermore determines, based on the obtained data, the change in offset and supplies a control signal indicative of the determined offset.

The present invention has many advantages. One benefit is that it adaptively increases uplink coverage when necessary, and at the same time maintains the maximum capacity. It also provides a good throughput. It may adapt channel power offset based in the load on a cell or the location of a mobile station within the cell. Other factors that may be considered are the size of the cell and the quality of the link between cell and mobile station. It may furthermore also consider such things as E-TFC and delay. In this way an adaptation of the network is made to the changing conditions for the mobile station and/or the network.

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail in relation to the enclosed drawings, in which:

fig. 1 schematically shows an access network connected to a core network as well as a mobile station connected to a cell handled by a cell handling device of the access network, fig. 2 shows a block schematic of a channel offset determining device according to the present invention being connected to power control functionality for a cell, fig. 3 shows a block schematic of a channel offset determining device according to the present invention, fig. 4 shows a flow chart of a number of general method steps taken according to a variation of the present invention in order to adjust the channel offsets, fig. 5 shows a cell, where different offsets have been provided for different distances from the base station, and fig. 6 shows a flow chart of a number of method steps taken according to a variation of the present invention in order to adjust the offsets.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

The present invention is directed towards providing differentiated sets of power offsets for channels between mobile stations and a base station in a cell of a wireless network, like a wide area network in the form of a WCDMA network. As mentioned above, the power offset between different transmission channels according to the state of the art is typically fixed for each radio bearer for a given amount of data that is to be transmitted within a certain time interval with the transmit power that is available (E-TFC). This means that the power offset does not consider the various network conditions of a cell or the size of the cell. This also means that it may in some instances be hard to provide good capacity, throughput and coverage. The present invention solves this problem through varying the offsets.

However, to fulfill good capacity, throughput and coverage is not that easy. To have good capacity, the power offsets must not be set too high, i.e. not creating unnecessary high interference. On the other hand, to have good coverage, the power offsets should be set as high as possible. The optimal power offset values for capacity and coverage are not the same.

The present invention seeks to solve this through considering various radio conditions and adaptively setting a set of offsets based on these radio conditions.

The present invention will now be described in more detail in the non-limiting example context of a Universal Mobile Telecommunications (UMTS) network shown in fig. 1. A core network CN has a first connection-oriented service node 20, which may be a Mobile Switching Centre (MSC) that provides circuit-switched services. The core network CN also includes a second General Packet Radio Service (GPRS) node 21 tailored to provide packet-switched type services, which is sometimes referred to as the serving GPRS service node (SGSN). The service node 20 may be connected to circuit switched networks such as PSTN (Public Switched Telephone Network) or GSM (Global System for Mobile communication). The node 21 may be connected to connectionless-oriented networks such as the Internet.

Each of the core network service nodes 20 and 21 connects to an access network AN, which is here a UMTS Terrestrial Radio Access Network (UTRAN). UTRAN AN includes one or more radio network controllers (RNC), where only one RNC 18 is shown in fig. 1. The RNC 18 is connected to a plurality of cells. The RNC 18 is connected to a first cell handling device 10, a second cell handling device 12 and a third cell handling device 14. Each of these cell handling devices 10, 12 and 14 control communication within a cell. Here it should be realised that one cell handling device may handle more than one cell. In the figure only one cell 11 associated with the first cell handling device 10 is shown. The cells are provided in a geographical area covered by the access network AN. The cell handling devices are within these types of networks base stations. In fig. 1 one user equipment unit in the form of a mobile station 16 is shown in the cell 11 handled by the base station 10 in the access network AN and shown as communicating with this base station 10. It should be realised that normally there may be provided several mobile stations communicating with a base station.

Fig. 2 shows a block schematic of a channel offset determining device 23 according to the present invention being connected to the power control functionality 22 (indicated with a dashed box) for the cell shown in fig. 1. In the drawing only the parts of the power control functionality 22 that are relevant to the present invention are shown. It should be realised that it may include several more entities than the ones shown and to be described here. One or more antennas are provided for communicating with the mobile station 16.

However, in the figure there is only shown one such antenna. This antenna is connected to an output of an inner-loop power control unit 28, which has an input that in turn is connected to an output of a SIR-filtering device 26 via a first adding element. The SIR- filtering device is here provided in the form of an outer-loop power control unit 26. The antenna is also connected to this first adding element. The input of the outer loop power control unit 26 is in turn also connected to the antenna. The channel offset determining device 23 according to the present invention supplies a control signal C to the power control functionality 22. The channel offset determining device 23 furthermore has an input on which it receives input data in the form of measurement data RC relating to the radio conditions of the uplinks between the mobile station 16 and the cell. This data is used for adjusting power offsets between various transmission channels in line with the principles of the present invention. This data RC is normally obtained from the base station, which in turn may receive most of this data from the different mobile stations 16 connected to it. However some may also be received from the radio network controller of fig. 1 or the base station may gather some of it itself. The outer-loop power and inner-loop control units 26 and 28 of the power control functionality 22 may be provided in the radio network controller. However, they may also be provided in the base station 10.

In operation the inner-loop power control unit 28 adjusts the transmit power of the sender towards a specific link quality target at the receiver. The link quality is here provided in the form of a signal-to-carrier ratio (SIR). The outer-loop power control unit (OLPC) 26 adjusts the SIR target of the inner loop power control unit 28 in order to maintain a specified quality-based target. One way to do this is to have the outer-loop power control for uplink channels adjust the uplink SIR-target so that a given quality target is fulfilled. The quality target is the fraction of blocks that is expected to need more than targeted transmission attempts to be successfully decoded. If a block is correctly decoded by the base station and the used number of transmission attempts is higher than the target, an OLPC up-step is initiated If there is a residual error that is higher than an acceptable level after the targeted number of transmission attempts have been run through, the SIR target is changed. If the transmission is not successfully decoded after for instance a TA target of three transmissions, the SIR target is increased by e.g. 0.5 dB. For every successfully decoded transmission, the corresponding SIR target is decreased by a factor inversely proportional to the error probability, e.g. about 0.01 dB if the error rate is 2%. As an alternative to OLPC it is also possible to perform some kind of suitable SIR-filtering.

The power control functionality 22 furthermore provides a set of power offsets β, that it applies on the different radio channels. The offsets of this set are related to the power used on the DPCCH (Dedicated Physical Control Channel), which may be seen as a basic control channel. The E-DPCCH and the E-DPDCH each have its own power offset. The power offset for the E-DPCCH is typically the same regardless of what kind of service that is transmitted. The power offset for the E-DPDCH is however different for different services. One important factor that decides the power offset is the bit-rate, or more specifically the E-TFC used. The power offset is also changed if the E-TFC is changed. In the present invention the power offset may be modified even if the E-TFC remains constant.

According to the present invention the set of β-offset values are varied by the device 23.

Fig. 3 shows a block schematic of a general structure of the channel offset determining device 23 according to the present invention. It includes a radio condition measurement obtaining unit 30 receiving measurement data RC of the radio conditions of the uplinks between the mobile stations and the cell. The measurement data can be obtained from both the mobile stations and the base station. There is also a channel offset determining unit 32, which receives the different types of data RC and determines a control signal C that indicates a change in the set of channel offsets that is to be supplied to the power control functionality for the cell.

Now will follow a first general description of the operation of the channel offset determining device according to a first variation of the present invention, with reference being made to fig. 3 and 4, where the latter shows a flow chart of a number of general method steps taken according to the present invention in order to adjust the set of channel offsets β.

The radio condition measurement obtaining unit 30 of the channel offset determining device 23 first obtains radio condition measurement data RC, step 34. This data normally includes cell load measurements, which are typically uplink interference measurements for the mobile station 16. It is here possible to use also other radio condition measurements like transmission power measurements, i.e. measurements relating to transmission power used by a mobile station. This may be in the form of code power measurement data that is obtained either from the mobile station or the base station. As an alternative to code power it is also possible to obtain other types of transmission power data, for instance measurements of the power headroom, i.e. the remaining power left to use in the mobile station. Other types of data that can be measured are the application delay, used E-TFC and timing advance data. E-TFC (E-DCH Transport Format

Combination) in essence provides a measure of a selection by a mobile station of the amount of data that is to be transmitted within a certain time interval with the transmit power that is available. It is also closely linked to the β-value of the channel. The timing advance data is data that relates to the time with which a mobile station has to alter its transmission structure in order to fit into the reception structure provided by a base station. This timing advance data is indicative of the distance between the mobile station 16 and the base station 10. All the gathered data is then forwarded to the channel offset determining unit 32, which goes on and decides if the set of channel offsets β is to be adjusted or not, step 36, and if this is not the case the power control functionality for the cell is informed that no change is to be made. Thereafter the channel offset determining unit 32 returns and obtains new radio condition measurement data, step 34. If however the unit 32 determines that a change should be made, step 36, it then determines the change, step 38. The determination of a change here involves the direction of change as well as the amount of change. The amount of change may vary or it may be provided as incremental or decremental steps. Here also the cell radius may be used in determining the amount of change, where a larger cell radius may provide a bigger change in offset and a smaller cell radius may provide a smaller change in offset. If the load on a cell having a small cell radius is high, it is also possible to also provide a bigger change in offset. The new set of β-offset values or possibly a deviation from the original set of β- offset values is then supplied as a signal C to the power control functionality. Thereafter the power control functionality may adapt the set of β-offset values with the change provided by the control signal C, and thus change the set of power offsets PO according to the determination, step 40.

The determination of change may, apart from the above mentioned factors also be based on the transmission power per bit. The transmission power per bit may be obtained through the E-TFC and used transmission power. It is also possible to obtain it from knowledge about the service requirements of the service provided to the mobile station together with the used transmission power.

Generally speaking the offsets are increased if the load on the cell is low, while the communication between mobile station and base station has quality problems, while a decrease may be contemplated if the load on the cell is high.

When the uplink interference is high, the cell/system is interference-limited, i.e. cells are small, and the power offsets should be optimized for capacity. When the uplink interference is low, the power offsets can be increased if necessary, e.g. if some mobile stations use very high code power i.e. UE transmission power.

The adaptive power offset solution is thought be a slow process, with processing time of several seconds or more.

The procedure described above is applied before communication is started with a mobile station. However it may also be performed during communication, in which case the offsets are changed according to the way described in 3GPP TS 25.433 V6.10.0 "UTRAN lub interface Node B Application Part (NBAP) signalling", which is herein incorporated by reference. The power offset of E-DPDCH cannot be set too high, since then the DPCCH will be "suppressed" by the high power for the data channel. The DPCCH carries the pilot bits for channel estimation. When DPCCH is suppressed the quality of the bits gets worse due to worse channel estimations.

In this way it is possible to adjust the power offsets for channels of the cell. Such offset changes may be determined as a total value for all mobile devices of the cell. However, it is also possible to determine on a mobile station to mobile station basis, i.e. independently for each mobile station communicating with the cell. Preferably, only the mobile stations using high code power, which indicates a coverage problem, should get their power offsets changed since this minimizes the interference.

According to a second variation of the present invention it is as an alternative possible to use another approach for determining different offsets. This will now be described with reference being made to fig. 5, which schematically shows the cell 11 with the base station 10. The cell 11 has here been divided into different regions R1 , R2 and R3. Here an innermost region R1 , that is shown as encircling or covering the base station 10 is associated with a first set of channel offsets, an intermediate region R2 encircling or covering the inner region R1 is associated with a second set of channel offsets while an outer region R3 encircling or covering the intermediate region R2 is associated with a third set of channel offsets. Here the regions are associated with the distances from the base station 10 up to the edge of the cell 11. The innermost region R1 covers distances closest to the base station up to a first distance threshold, the second region R2 covers intermediate distances that are between the first distance threshold and a second higher distance threshold, and the third region covers distances from the second distance threshold to a third even higher distance threshold. In the present case the third distance threshold also makes up the edge of the cell. It should here be realised that more or fewer regions and thresholds may be provided.

The regions are associated with different sets of power offsets, where the set of power offsets of the inner region R1 is lower than the set of power offsets of the intermediate region R2, which in turn is lower than the set of power offsets of the outer region R3. Mobile stations will here be assigned offset sets to be applied on the transmission channels according to the region they are perceived as being located in by the system. The location of the mobile stations may here be determined based on code power or other related power measurement values like power headroom or be based on a timing advance value obtained from the mobile station. The distance can also be obtained in other ways, for instance through obtaining position data associated with positioning units in the mobile stations, like GPS units, or through triangulation via a number of base stations. Thus the set of offsets are here changed when the mobile station moves towards or away from the base station 10.

Now another version of the method will be described in more detail with reference being made to made to fig. 1 , 2, 3 and 6, which latter figure shows a flow chart of a number of method steps taken according to a third variation of the present invention in order to adjust the set of power offsets β.

Also this method may be applied singly or jointly for all of mobile stations communicating with the cell. In the description below focus will however be on a single mobile station.

The radio condition measurement obtaining unit 30 of the channel offset determining device 23 first obtains radio condition measurements RC in the form of load measurements, step 42, which are normally measurements on the uplink interference. These are then compared by the channel offset determining unit 32, with a first load threshold T1. If the interference is below this threshold T1 , step 44, which indicates that the interference is low, the channel offset determining unit 32 then obtains further radio condition measurements from the radio condition measurement obtaining unit 30, step 46. These measurements include measurements relating to code power CP, the signal to carrier interference (SIR) target and the path gain. The transmission attempt determining unit 32 then compares these measurements with certain criteria indicative of acceptable radio conditions. These criteria are not fulfilled if the code power is above a first code power threshold, which threshold indicates a high code power, if the power does not meet the signal to carrier interference (SIR) target or if the path gain is bad. A high code power here indicates that the mobile station may be located close to the edge of the cell. An alternative to investigating code power is the power headroom. It is furthermore also possible to investigate timing advance. When the criteria are not fulfilled, step 48, for the cases of a high code power, inability to meet SIR or a bad path gain, an increase in the set of power offsets PO is made, step 50. If the criteria are fulfilled, step 48, there is no change in the set of power offsets, step 58. If the load was not below the first load threshold, step 44, it is compared with a second load threshold T2, which indicates a high load. If the load on the cell is not above this second threshold, step 52, then the set of power offsets is kept unchanged, step 58. If however, the load is above the threshold T2, step 52, there is an investigation being made if there was a previous increase in the set of channel offsets for the mobile station. In case there has been no such change, step 54, then the set of power offsets PO is kept unchanged, step 58. If however there was such a previous increase, step 54, then a decrease in the set of power offsets is performed, step 56. As an alternative it may be possible to also decrease the power offset also when there has not been a previous increase.

The above mentioned method steps may then be continuously repeated.

The present invention has many advantages. The main benefit of the proposed invention is that it adaptively increases uplink coverage when necessary, and at the same time maintains the maximum capacity. It also provides a good throughput. It adapts the channel offsets based on the load on a cell or the location of the mobile station within the cell. Other factors that may be considered are the size of the cell and the quality of the link between cell and mobile station. It may furthermore also consider such things as E-TFC and delay. In this way an adaptation of the system is made to the changing conditions for the mobile station and/or the network. It therefore increases user throughput by adopting a low power offset for a user close to a base station, it increases system capacity and stability when users are far away from the base station.

The channel offset determining device according to the present invention can be implemented through one or more processors together with computer program code for performing the functions of the invention. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the method according to the present invention when being loaded into a computer. The channel offset determining device may furthermore be provided as a separate device or as a part of another entity in the network, such as a part of a communication control device, like a base station or a radio network controller. The control signal mentioned above may furthermore be supplied to any power control unit where the transmission power of mobile stations is controlled. While the invention has been described in connection with what is presently considered to be most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements. Therefore the present invention is only to be limited by the following claims.

Claims

1. Method of adjusting the power offset of at least one transmission channel in relation to another transmission channel in uplink communications between at least one first group of mobile stations including at least one mobile station

(16) and a cell (11 ) in a wireless network, comprising the steps of: obtaining measurement data (RC) of the radio conditions of the uplinks between the mobile stations of the group and said cell, (34; 42, 46), determining based on said obtained data whether the offset should be adjusted or not, (36; 48) and in case the determination indicates (36) that an adjustment should be made determining, based on said obtained data, the change in offset (38), and adjusting the offset according to the determined change (40; 50, 56).

2. Method according to claim 1 , wherein said measurement data of the radio conditions comprise data indicative of the load on said cell (42).

3. Method according to claim 2, wherein the step of determining the change in offset also considers the cell radius.

4. Method according to claim 3, wherein a small cell radius provides a lower channel offset and a large cell radius provides a higher channel offset.

5. Method according to any of claims 2 -4, wherein said radio conditions are compared with criteria indicative of acceptable radio conditions and an increase (48) is determined if these criteria are not met while the load is below (44) a low load threshold (T1 ).

6. Method according to claim 5, wherein the offset is decreased if the load is above (52) a high load threshold (T2) and has previously been increased (54).

7. Method according to any previous claim, wherein said measurement data of the radio conditions comprise data indicative of transmission power of the mobile stations in said group.

8. Method according to claim 6, wherein the step of determining the change in offset considers the transmission power per bit of the channel.

9. Method according to any previous claim, wherein the measurement data comprises a transmission block size related value (E-TFC).

10. Method according to any previous claim, wherein the measurement data comprises data indicative of the distance between each mobile station in the group and a base station handling communication for the cell.

11. Method according to claim 10, wherein there are different offsets provided for different distances to said base station.

12. Method according to any previous claim, wherein the group only includes one mobile station.

13. Method according to any of claims 1 - 11 , wherein the group includes several mobile stations and the change in offset is determined jointly for all mobile stations of the group.

14. Channel offset determining device (23) for a cell (11 ) in a wireless network, where at least one first group of mobile stations including at least one mobile station (16) is communicating with the cell, said device (23) comprising: a radio condition measurement obtaining unit (30) configured to obtain measurement data (RC) of the radio conditions of the uplinks between the mobile stations of the group and said cell, and an offset determining unit (32) configured to determine based on said obtained data whether the offset should be adjusted or not, and in case the determination indicates that an adjustment should be made determining, based on said obtained data, the change in offset, and supply a control signal (C) indicative of the determined offset.

15. Channel offset determining device (23) according to claim 14, wherein it is a part of a communication control device.

16. Channel offset determining device (23) according to claim 15, wherein the communication control device is a cell handling device (10).

17. Channel offset determining device (23) according to claim 15, wherein the communication control device is a radio network controller (18).