WO2010059085A1

WO2010059085A1 - Power control in a cellular mbms system

Info

Publication number: WO2010059085A1
Application number: PCT/SE2008/051328
Authority: WO
Inventors: Rui Tian; Jie Mao; Lin Dong
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2008-11-19
Filing date: 2008-11-19
Publication date: 2010-05-27

Abstract

The present invention relates to Multimedia Broadcast Multicast Service, MBMS, transmissions to User Equipments in a cell of a cellular system. A Radio Base Station performs (705) directional MBMS point-to-multipoint transmissions to on or more User Equipments in the cell. A User Equipment receiving (805) the directional MBMS point-to-multipoint transmissions evaluates (810) the received signal quality and transmits (865) feedback signals to the Radio Base Station. The feedback signals are generated, based on the evaluation of the received signal quality, to indicate whether the Radio Base Station should increase or decrease the transmission power level of the directional MBMS point -to-multipoint transmissions in the direction of the User Equipment. Upon receipt (710) of feedback signals from at least one User Equipment in a certain direction, the Radio Base Station adjusts (765) the transmission power level of the directional MBMS point-to-multipoint transmissions in said direction in accordance with said received feedback signals.

Description

POWER CONTROL IN A CELLULAR MBMS SYSTEM

TECHNICAL FIELD The present invention discloses a radio base station and a user terminal for use in a cellular system which can provide MBMS services, Multimedia Broadcast Multicast Services.

BACKGROUND In cellular systems of the TD-SCDMA kind, Time Division Synchronous Code Division Multiple Access, there can be so called MBMS services, Multimedia Broadcast Multicast Services. MBMS services can also be provided in so called LTE systems, Long Term Evolution.

As the name implies, MBMS traffic is sent as broadcast traffic within a TD- SCDMA or LTE cell.

When an RBS initiates MBMS transmissions, the output power level which should be used for those transmissions is set for the RBS by the so called RNC, Radio Network Controller of the system, or by a corresponding function in the system. The output power level for the MBMS transmission in the cell then remains fixed for the duration of the MBMS session.

SUMMARY It is an object of the present invention to provide a solution by means of which an RBS which provides MBMS services in its cell can adjust the output power level of the MBMS transmissions according to the users' needs.

Such a solution is provided by the present invention in that it discloses a Radio Base Station, an RBS, for providing Multimedia Broadcast Multicast Service, MBMS, to User Equipments, UEs, in a cell of a cellular system. The RBS of the invention comprises:

• a transmitter which is adapted to perform directional MBMS point-to- multipoint transmissions to one or more UEs in the cell,

• a receiver which is adapted to receive feedback signals associated with the directional MBMS point-to-multipoint transmissions, wherein feedback signals received from at least one UE in a certain direction indicate whether the RBS should increase or decrease a transmission power level of the directional MBMS point-to-multipoint transmissions in that direction, • a beam forming control unit which is operably connected to the transmitter and the receiver and which is adapted to adjust the transmission power level of the directional MBMS point-to-multipoint transmissions in the direction mentioned above direction in accordance with the received feedback signals.

In one embodiment of the RBS of the invention, the receiver is adapted to receive the feedback signals as synchronization signals from the at least one UE.

In one embodiment, the RBS is an RBS for a TD-SCDMA system, Time Division Synchronous Code Division Multiple Access, and the receiver of the RBS is adapted to receive the feedback signals as the SYNC_UL signals of TD-SCDMA.

In one embodiment of the RBS, the receiver is adapted to receive the indication regarding an increase or decrease of power in the feedback signals by means of different codes used by the UE for the synchronization signals. In one embodiment, the RBS is an RBS for an LTE system, and the receiver of the RBS is adapted to receive the feedback signals as sounding pilot signals from the least one UE.

In one embodiment, the RBS is an RBS for an LTE system, and the receiver of the RBS is adapted to receive the feedback signals as MBMS quality feedback signals from the least one UE.

In one version of the embodiments enumerated above, the receiver of the RBS is adapted to receive the indication regarding an increase or decrease of power in the feedback signals by means of the repetition frequency with which the feedback signals are transmitted by the at least one UE.

In one version of the embodiments enumerated above, the receiver of the RBS is adapted to receive the indication regarding an increase or decrease of power as comprised in the received power level of the feedback signals from the UE at the RBS.

The invention also discloses a User Equipment, a UE, for receiving Multimedia Broadcast Multicast Service, MBMS, transmissions in a cell of a cellular system.

The UE of the invention comprises:

• a receiver which is adapted to receive directional MBMS point-to- multipoint transmissions from a Radio Base Station, RBS, serving the cell,

• a signal quality evaluating unit which is operably connected to the receiver and which is adapted to evaluate the received signal quality of the received directional MBMS point-to-multipoint transmissions, • a transmitter, which is operably connected to the signal quality evaluating unit, and which is adapted to transmit feedback signals to the RBS, the feedback signals being generated based on the evaluation of the received signal quality to indicate whether the RBS should increase or decrease the transmission power level of the directional MBMS point-to-multipoint transmissions in the direction of the UE.

In one embodiment of the UE of the invention, the transmitter is adapted to use synchronization signals as the feedback signals to the RBS.

In one embodiment, the UE of the invention is UE for a TD-SCDMA system, Time Division Synchronous Code Division Multiple Access, in which the transmitter is adapted to use the SYNC_UL signals of TD-SCDMA as said synchronization signals.

In one embodiment with synchronization signals, the UE of the invention uses different codes for the synchronization signals in order to accomplish the indication regarding an increase or decrease of the transmission power level from the RBS.

In one embodiment, the UE of the invention is UE for an LTE system, with the transmitter being adapted to use sounding pilot signals as the feedback signals to the RBS.

In one embodiment, the UE of the invention is a UE for an LTE system, in which the transmitter is adapted to use MBMS quality feedback signals as the feedback signals to the RBS.

In a version of any of the embodiments enumerated above, the transmitter of the UE is adapted to use the repetition frequency with which the feedback signals are transmitted by the UE in order to accomplish the indication regarding an increase or decrease of transmission power level from the RBS. In a version of any of the embodiments of an UE of the invention enumerated above, the indication regarding an increase or decrease of power is comprised in the output power level from the UE of said feedback signals.

The invention also discloses a method for use in an RBS and a method for use in a UE, as will be explained in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, with reference to the appended drawings, in which

Fig 1 shows a schematic view of a system in which the invention can be applied, and

Fig 2 shows an application of the invention, and

Fig 3 shows a time frame in a TD-SCDMA system, and

Fig 4 shows a principle used in one embodiment of the invention, and

Fig 5 shows a block diagram of a base station in one embodiment of the invention, and

Fig 6 shows a block diagram of a user terminal in one embodiment of the invention, and

Figs 7 and 8 show flow charts of embodiments of methods of the invention.

DETAILED DESCRIPTION

Fig 1 shows a schematic overview of a system 10 in which the invention can be applied. As non-limiting examples, the invention may be applied in, for example, systems of the TD-SCDMA kind, Time Division Synchronous Code Division Multiple Access, or of the LTE kind, Long Term Evolution. However, the invention will be described below using TD-SCDMA terminology, which is merely in order to facilitate the reader's understanding of the invention, and should not be used to limit the scope of protection sought or granted for the invention.

As shown in fig 1 , the system 10 comprises a number of cells, one of which is shown in fig 1 with the reference number 11. Each cell can accommodate a number of user terminals, "UEs" (User Equipment), two of which are shown in fig 1 , with the reference numbers 13 and 14.

For each cell in the system 10, there is also a so called Radio Base Station, an RBS. In a TD-SCDMA system, Time Division Synchronous Code Division Multiple Access, the RBS is also sometimes referred to as a NodeB. The RBS of the cell 11 is shown with the reference number 12 in fig 1. One of the functions of the RBS is to control the traffic to and from the UEs in the cell 11.

One type of TD-SCDMA (or LTE) system is a system which can provide so called MBMS services, Multimedia Broadcast Multicast Services, which are provided as broadcast or point-to multipoint transmissions by the RBS in the cell 11.

As stated above, a problem in MBMS systems is that there is no way for the RBS 11 to regulate its output power in the MBMS broadcast or point-to multipoint transmissions.

Fig 2 schematically shows how this problem is addressed by the present invention: according to the invention, the RBS 12 is provided with means for making transmissions to the UEs in a directional manner, i.e. so called "beam forming", towards one or more of the UEs. This is shown in fig 2 by means of two beams 15, 16, one towards each of the UEs 13, 14. These MBMS transmission can also be seen as point-to-multipoint transmissions from the RBS to the UEs. Although not known or previously used in MBMS, beam forming as such is well known to those skilled in the field, and will for that reason not be described in depth here, but examples of beam forming techniques which may be used by the RBS 12 are phase or frequency controlled antenna arrays, the term "array" here being used to include a plurality of antenna elements in the RBS. Other examples include digital beam forming at the baseband level or a beam-forming network at RF-level by means of passive devices such as 3 dB hybrid couplers, fixed phase shifters and delay lines, or a Butler matrix.

An additional advantage given by the use of beam forming towards individual UEs in the cell is that the "power spill" in the cell 11 and towards adjacent cells is reduced, as compared to conventional MBMS transmissions.

Each UE can also detect the power level with which it receives the MBMS transmissions, and can, according to another feature of the invention, signal to the RBS 12 a need for increased or decreased output power level in the transmissions from the RBS in the direction of the UE.

This signalling regarding the MBMS power level is, according to the invention, indicated by means of feedback signals from the UEs. The feedback signals can be of different kinds, as will be elaborated upon later in this text. For example, in one embodiment, the feedback signals can be so called synchronization signals, which can be of different kinds and used in different ways in order to signal the need for more or less output power from the RBS.

However, with continued reference to a TD-SCDMA system, fig 3 shows how synchronization signals are used in TD-SCDMA: transmissions are divided into so called radio frames, RF, which last 10 ms each. Each radio frame is divided into two half frames, HF, of 5 s duration each, with each HF comprising a number of subframes, SF, with each HF usually comprising 9 SFs, although only three SFs are shown in fig 3.

Some of the subframes in a half frame may be used for downlink, DL, while others may be used for uplink, UL. In the example shown in fig 3, SF 0 is used for DL, and SF 2 is used for UL. SF 1 then becomes a so called

"switching point" between DL and UL. As shown in fig 3, a switching point comprises three parts, DwPTS, UpPTS and GP, where the GP, the Guard

Period, is a period when no transmissions may be made by any part in the system, neither UL nor DL transmissions, while DwPTS and UpPTS are special slots reserved for other use.

During UpPTS, the UEs can make so called SYNC_UL transmissions, which, according to the invention, can be used for power control by means of the following principles:

One way of letting the UEs signal the need for power adjustment by means of transmitting the UL_SYNC signals is by defining alternate repetition frequencies for the UL_SYNC signals. For example, one repetition frequency for the UL_SYNC signals could be defined for use by UEs which need a power increase, and another repetition frequency for UL_SYNC signals by UEs which can stand a decrease in power.

This is shown in fig 4: one repetition frequency, f1 , is used by UEs which need more power, and another repetition frequency, f2, is used by UEs which can stand a reduced power level. When the RBS receives transmissions with the repetition frequency f1 from a certain UE, it steps up the power level in the transmission to that UE by a predefined amount, +Δ, while transmissions with another repetition frequency, f2, causes the RBS to reduce the output power to that UE by a predefined amount -Δ. The repetition frequency can also be referred to as the pulse repetition frequency, the PRF. In this embodiment, the RBS could count the number of SYNC_UL signals received from the UE during a certain period of time. For example, if the number of SYNC_UL received from one or several UE is above a certain threshold value, the NodeB increases the output transmission power to the UE(s), and if the number of SYNC_UL received from one or several UE is below a certain threshold (the same as for the increase, or another value), the NodeB decreases its output transmit power to the UE(s).

In this way, as shown in fig 4, the output power can be stepped up and down by the RBS until a satisfactory level is reached.

The invention's feature of using the repetition frequency of a message in order to indicate a need for more or less output power from the RBS is not limited to the synchronization signals, but can be applied to a wide variety of signals in the system, some of which will be enumerated later in this text.

Another, or complementary, way of letting the UEs signal their need for output power from the RBS is to let the UEs' information regarding the output power level needed from the RBS be comprised in different codes which are used by the UEs for their synchronization message SYNC_UL.

This can be done in the following way: in a TD-SCDMA system, there are 256 different SYNC_UL codes available for the entire system, which are divided into 32 code groups, with 8 SYNC_UL codes in each code group. Each cell in the system can use one of the code groups. In this aspect of the invention, one or more of the 8 codes which are available to a cell is/ are assigned for use by a UE if the UE needs more power, while one or more of the other codes are assigned to be used by a UE which can withstand a decrease in output power from the RBS.

An additional method of letting the RBS interpret signals from the UEs regarding the amount of power which should be used in transmissions towards the UEs is to use the received power level of the message at the RBS. In other words, if, for example, a SYNC_UL message from a UE is received at a low power level at the RBS, the RBS will interpret this as meaning that the RBS's transmissions towards that UE should have an increased output power level, and conversely, if the SYNC_UL signals from the UE are received with a very high power level, the RBS will interpret this as meaning that the RBS's transmissions towards that UE can be reduced in terms of output power.

The invention's feature of using the output power from the UE used for feedback signalling in order to indicate a need for more or less output power from the RBS is not limited to the synchronization signals, but can be applied to a wide variety of signals in the system, some of which will be enumerated later in this text.

So far, the signals which have been disclosed as being used for letting the UEs "signal" the need for more or less output power from the RBS have been the SYNC_UL signals. However, other signals can also be reused for this purpose, in more or less the same way, i.e. using different codes or transmission frequencies or different output power levels. Naturally, it is also possible to introduce dedicated signals for signalling a need for more or less output power from the RBS.

For example, one alternative feedback signals or group of feedback signals which could be used instead of, or as complements to, the SYNC_UL signals could be signals which are used to provide quality feedback from the UEs to the RBS regarding the MBMS services. Another alternative is to use so called sounding pilot signals from the least one UE. Both of these alternatives are primarily of interest in an LTE system.

Fig 5 shows a schematic block diagram of an RBS 50 in one exemplary embodiment of the invention. As indicated in fig 5, the RBS 50 comprises an antenna, shown as block 51 , and also comprises a receiver part 52 and a transmitter part 53. In addition, the RBS 50 also comprises a control means 54 such as a micro processor, as well as a memory 55. Furthermore, the RBS 50 also comprises an interface 56 towards other components in the system apart from the UEs.

The control unit 54 together with the memory 55 will suitably serve to "decode" the feedback signals from the UEs which have been received through the antenna 51 and the receiver 52, and will also serve as a beam forming control unit for the RBS 50, and will adjust the transmission power level of the directional MBMS transmissions in accordance with the received feedback signals.

The transmitter 53 is, together with the antenna 51 , adapted to perform directional transmission to one or more UEs in the cell, as controlled by the beam forming control unit 54, 55.

The invention also discloses a user terminal, a UE, which functions as the UEs described above. Fig 6 shows a schematic block diagram of such a user terminal, a UE, 60 in one exemplary embodiment of the invention. It will be realized that the UE 60 in its "block diagram form" is similar to the RBS 50 in many ways, since both of these units basically are radio transceivers.

As indicated in fig 6, the UE 60 comprises an antenna, shown as block 61 , and also comprises a receiver part 62 and a transmitter part 63. In addition, the UE 60 also comprises a control means 64 such as a micro processor, as well as a memory 65.

In the UE 60, the receiver 62 is adapted to receive directional MBMS point- to-multipoint transmissions from a Radio Base Station, RBS, which serves the cell. The control unit 64, together with the memory 65 serves as a signal quality evaluating unit, i.e. for evaluating the MBMS signals from the RBS to see if more or less output power is needed from the RBS, and the signal evaluating unit is, for this purpose operably connected to the receiver 62.

The transmitter 63 is operably connected to the signal quality evaluating unit 64, 65, and is adapted to transmit the feedback signals to the RBS, which, as has been explained above, are generated based on the evaluation of the received signal quality, in order to indicate whether the RBS should increase or decrease the transmission power level of the directional MBMS point-to- multipoint transmissions in the direction of the UE.

In alternative embodiments of the invention, the beam forming control unit of the RBS of the invention and the signal quality evaluation unit of the UE may be implemented utilizing other forms of digital data processing circuitry, such as e.g. ASICs, FPGAs or DSPs.

Fig 7 shows a flow chart of a method 700 in one exemplary embodiment of the invention. Options or alternatives are indicated with dashed lines.

The method 700 is intended for use in a Radio Base Station, an RBS, for Multimedia Broadcast Multicast Service, MBMS, transmissions to User Equipments, UEs, in a cell of a cellular system, and comprises:

• performing, step 705, directional MBMS point-to-multipoint transmissions to one or more UEs in the cell: • receiving, step 710, feedback signals associated with the directional

MBMS point-to-multipoint transmissions, wherein feedback signals received from at least one UE in a certain direction indicate whether the RBS should increase or decrease a transmission power level of the directional MBMS point-to-multipoint transmissions in said direction. The feedback signals which are used in the invention in order to indicate an increase or a decrease in the transmission power level can be various kinds of signals, as shown in fig 7, and as described below:

In one embodiment of the method 700, as shown in box 720, synchronization signals are used as the feedback signals from the at least one UE. In one version of this embodiment, as seen in box 735, the method is applied in a TD-SCDMA system, and the synchronization signals are the SYNC_UL signals of TD-SCDMA. In a TD-SCDMA application, as shown in box 740, the indication regarding an increase or decrease of transmission power level can be comprised in the signals by means of different codes used by the at least one UE for the synchronization signals, for example the SYNC_UL codes.

As shown in box 725, the method can also be applied in an LTE system, in which case the feedback signals can in one embodiment be sounding pilot signals from the least one UE. Alternatively, in an LTE system, as shown in box 730, MBMS quality feedback signals from the least one UE can also be used as the feedback signals.

As shown in box 750, in one embodiment of the method 700, the indication regarding an increase or decrease of transmission power is comprised in the feedback signals by means of the pulse repetition frequency, the PRF, with which the feedback signals are transmitted by the at least one UE.

Box 755 shows that in one embodiment of the method 700, the indication regarding an increase or decrease of power is comprised in the received power level of the signals at the RBS.

At step 765, the transmission power level of the directional MBMS point-to- multipoint transmissions is adjusted in said direction in accordance with said received feedback signals. Fig 8 shows a flow chart of a method 800 according to an exemplary embodiment of the invention which is intended for use in a UE. Options or alternatives are indicated with dashed lines.

As has emerged from the previous description, the method 800 is intended for use in a User Equipment, UE, for receiving Multimedia Broadcast Multicast Service, MBMS, transmissions in a cell of a cellular system. The method 800 comprises:

• receiving, step 805, directional MBMS point-to-multipoint transmissions from a Radio Base Station, RBS, serving the cell;

• evaluating, step 810, the received signal quality of the received directional MBMS point-to-multipoint transmissions.

• transmitting, step 865, feedback signals to the RBS, with the feedback signals being generated based on the evaluation of the received signal quality, in order to indicate whether the RBS should increase or decrease the transmission power level of the directional MBMS point- to-multipoint transmissions in the direction of the UE.

As indicated in the boxes between step 810 and step 865, the feedback signals which are transmitted to the RBS at step 865 can be of various kinds in various embodiments of the invention, as explained in the following:

As shown in box 820, in one embodiment, synchronization signals are used as the feedback signals to the RBS. In a version of this embodiment, as shown in box 825, the method is applied in a TD-SCDMA system, and the SYNC_UL signals of TD-SCDMA are used as the synchronization signals.

In an alternative or complementary version of the embodiment with the synchronization codes, as indicated in box , different codes for the synchronization signals are used in order to accomplish the indication regarding an increase or decrease of the transmission power level from the RBS.

As shown in box 840, the method 800 can also be applied in an LTE system, in which case sounding pilot signals can be used as feedback signals to the RBS.

Box 845 shows that in one embodiment, the method 800 is applied in an LTE system and MBMS quality feedback signals are used as the feedback signals to the RBS.

As indicated in box 850, in one embodiment of the invention, the pulse repetition frequency, the PRF, with which the signals are transmitted by the UE is used in order to accomplish the indication regarding an increase or decrease of transmission power level from the RBS.

In another embodiment, as shown in box 855, the indication regarding an increase or decrease of power is comprised in the output power level from the UE of the feedback signals.

The invention is not limited to the examples of embodiments described above and shown in the drawings, but may be freely varied within the scope of the appended claims.

Claims

1. A Radio Base Station, an RBS (50), for providing Multimedia Broadcast Multicast Service, MBMS, to User Equipments, UEs, in a cell of a cellular system, the Radio Base Station characterized by:

• a transmitter (53) adapted to perform directional MBMS point-to- multipoint transmissions to one or more UEs in the cell;

• a receiver (52) adapted to receive feedback signals associated with the directional MBMS point-to-multipoint transmissions, wherein feedback signals received from at least one UE in a certain direction indicate whether the RBS should increase or decrease a transmission power level of the directional MBMS point-to-multipoint transmissions in said direction;

• a beam forming control unit (54, 55) operably connected to the transmitter and the receiver and adapted to adjust the transmission power level of the directional MBMS point-to-multipoint transmissions in said direction in accordance with said received feedback signals.

2. The RBS (50) of claim 1 , in which the receiver (52) is adapted to receive said feedback signals as synchronization signals from the at least one UE.

3. The RBS (50) of claim 2, being an RBS for a TD-SCDMA system, Time Division Synchronous Code Division Multiple Access, in which RBS the receiver is adapted to receive said feedback signals as the SYNC_UL signals of TD-SCDMA.

4. The RBS (50) of claim 1 , being an RBS for an LTE system, Long Term Evolution, in which the receiver (52) is adapted to receive said feedback signals as sounding pilot signals from the least one UE.

5. The RBS (50) of claim 1 , being an RBS for an LTE system, in which the receiver (52) is adapted to receive said feedback signals as MBMS quality feedback signals from the least one UE.

6. The RBS (50) of any of claims 1 -5, in which the receiver (52) is adapted to receive the indication regarding an increase or decrease of power in the feedback signals by means of the repetition frequency with which the feedback signals are transmitted by the at least one UE.

7. The RBS (50) of claim 3, in which the receiver (52) is adapted to receive the indication regarding an increase or decrease of power in the feedback signals by means of different codes used by the UE for the synchronization signals.

8. The RBS (50) of any of claims 1-6, in which the receiver is adapted to receive said indication regarding an increase or decrease of power as comprised in the received power level of the feedback signals at the RBS.

9. A User Equipment, a UE (60), for receiving Multimedia Broadcast Multicast Service, MBMS, transmissions in a cell of a cellular system, the UE being characterized by:

• a receiver (62) adapted to receive directional MBMS point-to- multipoint transmissions from a Radio Base Station, RBS, serving the cell; • a signal quality evaluating unit (64, 65) operably connected to the receiver (62) and adapted to evaluate the received signal quality of the received directional MBMS point-to-multipoint transmissions;

• a transmitter (63), operably connected to the signal quality evaluating unit (64, 65), and adapted to transmit feedback signals to the RBS, said feedback signals generated based on the evaluation of the received signal quality to indicate whether the RBS should increase or decrease the transmission power level of the directional MBMS point- to-multipoint transmissions in the direction of the UE.

10. The UE (60) of claim 9, in which the transmitter (63) is adapted to use synchronization signals as the feedback signals to the RBS.

11. The UE (60) of claim 10, being a UE for a TD-SCDMA system, Time Division Synchronous Code Division Multiple Access, in which the transmitter (63) is adapted to use the SYNCJJL signals of TD-SCDMA as said synchronization signals.

12. The UE (60) of claim 9, being a UE for an LTE system, Long Term Evolution, in which the transmitter (63) is adapted to use sounding pilot signals as the feedback signals to the RBS.

13. The UE (60) of claim 9, being a UE for an LTE system, Long Term Evolution, in which the transmitter (63) is adapted to use MBMS quality feedback signals as the feedback signals to the RBS.

14. The UE (60) of any of claims 9-13, in which the transmitter (63) is adapted to use the repetition frequency with which the feedback signals are transmitted by the UE in order to accomplish said indication regarding an increase or decrease of transmission power level from the RBS.

15. The UE (60) of claim 10 or 11 , which uses different codes for the synchronization signals in order to accomplish said indication regarding an increase or decrease of the transmission power level from the RBS.

16. The UE (60) of any of claims 9-13, in which the indication regarding an increase or decrease of power is comprised in the output power level from the UE of said feedback signals.

17. A method (700) for use in a Radio Base Station, an RBS, for Multimedia Broadcast Multicast Service, MBMS, transmissions to User Equipments, UEs, in a cell of a cellular system, the method being characterized by:

• performing (705) directional MBMS point-to-multipoint transmissions to one or more UEs in the cell:

• receiving (710) feedback signals associated with the directional MBMS point-to-multipoint transmissions, wherein feedback signals received from at least one UE in a certain direction indicate whether the RBS should increase or decrease a transmission power level of the directional MBMS point-to-multipoint transmissions in said direction;

• adjusting (765) the transmission power level of the directional MBMS point-to-multipoint transmissions in said direction in accordance with said received feedback signals.

18. The method (700, 720) of claim 17, according to which synchronization signals are used as said feedback signals from the at least one UE.

19. The method (700, 735) of claim 18, applied in a TD-SCDMA system, and according to which the synchronization signals are the SYNC_UL signals of TD-SCDMA.

20. The method (700, 725) of claim 17, applied in an LTE system, and according to which said feedback signals are sounding pilot signals from the least one UE.

21. The method (700, 730) of claim 17, applied in an LTE system, and according to which MBMS quality feedback signals from the least one UE is used as said feedback signals.

22. The method (700, 740) of claim 18 or 19, according to which the indication regarding an increase or decrease of transmission power level is comprised in the feedback signals by means of different codes used by the at least one UE for the synchronization signals.

23. The method (700, 750) of any of claims 17-21 , according to which the indication regarding an increase or decrease of transmission power is comprised in the feedback signals by means of the repetition frequency with which the feedback signals are transmitted is performed by the at least one UE.

24. The method (700, 755) of any of claims 17-21 , according to which said indication regarding an increase or decrease of power is comprised in the received power level of the feedback signals at the RBS.

25. A method (800) for use in a User Equipment, UE, for receiving Multimedia Broadcast Multicast Service, MBMS, transmissions in a cell of a cellular system, the method characterized by:

• receiving (805) directional MBMS point-to-multipoint transmissions from a Radio Base Station, RBS, serving the cell;

• evaluating (810) the received signal quality of the received directional MBMS point-to-multipoint transmissions;

• transmitting (865) feedback signals to the RBS, said feedback signals generated, based on the evaluation of the received signal quality, to indicate whether the RBS should increase or decrease the transmission power level of the directional MBMS point-to-multipoint transmissions in the direction of the UE.

26. The method (800, 820) of claim 25, according to which synchronization signals are used as the feedback signals to the RBS.

27. The method (800, 825) of claim 26, applied in a TD-SCDMA system, and according to which the SYNC_UL signals of TD-SCDMA are used as the synchronization signals.

28. The method (800, 840) of claim 25, applied in an LTE system, and according to which sounding pilot signals are used as the feedback signals to the RBS.

29. The method (800, 845) of claim 25, applied in an LTE system, and according to which MBMS quality feedback signals are used for the feedback signals to the RBS.

30. The method (800, 850) of any of claims 25-29, according to which the repetition frequency with which the feedback signals are transmitted by the UE is used in order to accomplish said indication regarding an increase or decrease of transmission power level from the RBS.

31. The method (800, 830) of claim 26 or 27, according to which different codes for the synchronization signals are used in order to accomplish the indication regarding an increase or decrease of the transmission power level from the RBS.

32. The method (800, 855) of any of claims 25-31 , according to which the indication regarding an increase or decrease of power is comprised in the output power level from the UE of said feedback signals.