GB2407233A

GB2407233A - Power control in a wireless communication system

Info

Publication number: GB2407233A
Application number: GB0324264A
Authority: GB
Inventors: Asoka Korale; Luis Lopes
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2003-10-16
Filing date: 2003-10-16
Publication date: 2005-04-20
Anticipated expiration: 2023-10-16
Also published as: GB2407233B; GB0324264D0

Abstract

In a wireless communication system employing discontinuous transmission, an outer power control loop quality target is determined for use during a period when data is not being received based on quality measurements made during a period when data is being received. When data is being received a signal to interference ratio (SIR) target is determined from block error rate (BLER) on a data channel (DPDCH). During a period of no data transmission the SIR is determined from a bit error rate (BER) of a control channel (DPCCH) which has been updated and stored in a previous data transmission period.

Description

POWER CONTROL METHOD AND APPARATUS

The present invention relates to a method and apparatus for power control in a wireless communication system. The invention is particularly, but not exclusively, applicable to setting power control loop quality targets in a wireless communication system.

It is known to implement power control in wireless communication systems to ensure that only a minimum amount of power is used to transmit a signal reliably between a transmitting and a receiving unit irrespective of the radio propagation conditions. As is known, the radio propagation conditions may vary in dependence on a number of factors including, but not limited to, distance between the transmitting and receiving units, obstructions such as a mountain or tall building between the transmitting and receiving units, how fast a transmitting and/or receiving unit is moving and whether the transmitting and/or receiving unit is in a building. By using power control, the power at which the signal is transmitted can be adjusted such that the transmitted signal can only just be reliably received, resulting in the least overall interference within the communication system. In COMA systems in particular the transmitted power from other users in the system is a cause of interference. As a result, reducing the transmitted power from each user helps to reduce the overall interference seen by all users in the system.

In one particular form of power control an inner power control loop and an outer control power loop are implemented. The inner loop power control directly controls the power at which a signal is transmitted. Typically this is achieved by comparing the measured quality of the received signal with a threshold quality.

The transmitted power is adjusted upwards if the measured quality is below the threshold quality and the transmitted power is adjusted downwards if the measured quality is above the threshold quality. Typically, the measured quality for the inner power control loop is a quality that relates directly to the radio i: ::e:: propagation conditions, such as the received signal to interference ratio (SIR) for example. The outer power control loop sets the quality threshold for the inner power control loop by comparing a second quality measurement with a second threshold. If the second quality measurement is above the second threshold, the outer power control loop can lower the quality threshold for the inner power control loop: if the second quality measurement is below the second threshold, the outer power control loop can increase the quality threshold for the inner control loop. Typically the measured quality for the outer power control loop is a measurement of the quality perceived by the user, for example Block Error Rate (BLER) or Bit Error Rate (BER).

Some communication systems are able to operate in different modes of operation. Power loop control algorithms that operate in different modes may have to use different quality measurements and targets during the different modes of operation, because some quality measures may not be available in all modes of operation. For example, no block error rate measurement is possible in measurement periods when no data transmission has taken place. In such communication systems, successful operation requires a close correspondence to exist between the different quality measures and quality targets used in the different modes. However, such a close correspondence is difficult to achieve in an operational system.

One example of a communication system type in which this problem arises is a Code Division Multiple Access (COMA) system in which data is transmitted on a data channel only intermittently, while a control channel is transmitted continuously. During periods where data is being transmitted on the data channel, the outer power control loop may use measurements of the block error rate (BLER) on the data channel to determine a signal to interference ratio (SIR) target for the inner power control loop. However, during periods where no data is being transmitted, the BLER measurement is not available, and therefore the SIR :e::e.::.

target for the inner power control loop must be set by the outer power control loop in some other way.

One previous approach is merely to freeze (not update or change) the existing SIR target for the inner power control loop during periods where no data is being transmitted. However this approach assumes that the radio propagation conditions do not change significantly during the period that no data is being transmitted, such that the SIR target required to ensure only just sufficient reception does not change during this time. This is clearly not necessarily the case in an operational system.

Another previous approach is to use a bit error rate (BER) measurement of the control channel and a fixed BER target in the outer power control loop to adjust the SIR target for the inner power control loop during the period that no data is being transmitted. However, this approach assumes that there is a close correspondence between the BLER target used during a data transmission period and the BER target used during periods when there is no data being transmitted. However, the most suitable BER target will vary with various factors, including but not limited to the speed of the transmitting/receiving units, time- varying radio conditions and the soft handoff state.

In order to ensure reliable operation of the communication system, systems using this approach typically select a BER target that will ensure that the SIR level is set at a level that will result in a good BLER in the next data transmission period.

However, the BER target will then be lower than is required for many situations, resulting in a higher transmit power being set than is required, leading in turn to an undesirable increase in interference in the communication system. In COMA systems in particular, increased interference results in lower system capacity.

Lower capacity in effect means that fewer users can be supported at any given time.

1.. a.

The invention seeks at least partially to reduce or eliminate some of the

problems of the prior art.

In accordance with a first aspect of the invention, there is provided a method for power control in a wireless communication system as claimed in claim 1.

In accordance with a second aspect of the invention, there is provided an apparatus for power control in a wireless communication system as claimed in claim 12.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a communication system in accordance with an exemplary embodiment; Figure 2 illustrates quality measurements made on communication channels used in the communication system shown in Figure 1 Figure 3 is a flow chart illustrating a method in accordance with an embodiment.

The present invention will be described with regard to a communication system operating in accordance with the Universal Mobile Telecommunication System (UMTS). However, it will be appreciated by a skilled person that the invention is not limited to the described embodiment or to UMTS, but instead is applicable to other communication systems.

Figure 1 shows a communication system in accordance with an exemplary embodiment.

In the described embodiments, the quality measures used and quality targets set are based on Block Error Rate (BLER), Bit Error Rate (BER) and the Signal to cecese's:' :: .::.e Interference Ratio (SIR). However, the skilled person will understand that the use of these particular parameters is not essential and other quality parameters may be used as selected by the skilled person.

A base station 10 (called a node B in UMTS terminology) provides communication services over a communication link 15 with subscriber units 20 (called user equipment UE in UMTS terminology) within a coverage area, or cell, associated with the base station 10. Only one subscriber unit 20 is shown, for clarity, but a skilled person will appreciate that in general a base station will be able to provide communication services to a large number of subscriber units 20 within its associated cell. The communication link 15 is bidirectional: the direction from the base station 10 to the subscriber unit 20 is called the downlink or forward link: the direction from the subscriber unit 20 to the base station 10 is called the uplink or reverse link. The base station is operably coupled to and is controlled by a base station controller 25 (called a Radio Network Controller RNC in UMTS terminology). In turn, the base station controller is operably coupled to the communication system core network 30.

It will be apparent to a skilled person that in the exemplary UMTS communication system operating a COMA air interface, the UE 20 may be in a soft handoff state and therefore may be in communication with two or more node Bs 10. However, this has not been illustrated, for clarity.

In operation of the communications system, the base station 10 transmits traffic and/or control and signaling data to the subscriber unit 20 on the downlink and/or receives traffic and/or control and signaling data from the subscriber unit 20 on the uplink using the traffic and control/signaling channels in accordance with the communication system operation, as selected by the skilled person. The base station 10 also receives traffic data for the subscriber unit 20 from the core network 30 and/or transmits traffic data received from the subscriber unit 20 to the core network 30 via the base station controller 25, again using the traffic and e e ee.

e ce e e a e e e e c e e e e e e e ace e eve e control and/or signaling channels in accordance with the communication system operation, as selected by the skilled person. Since the general operation of the communication system will be known to a skilled person, and is not relevant to the present invention, a more detailed explanation of the operation of the communication system will be omitted except where such explanation contributes to an understanding of the exemplary embodiment.

The provision for power control in the exemplary embodiment will now be described. As indicated above, the purpose of power control in a wireless communication system, such as the exemplary embodiment, is to ensure that the transmission power used is only just sufficient to result in reliable reception of the transmitted signal. Reliable reception means the ability of the receiver to correctly decode the transmitted information to within a given margin of error.

The present description is directed to power control of the uplink i.e. transmissions from the UE 20 to the node B 10. Power control of the downlink is carried out by the UE (both outer and inner loop power control), but similar procedures to those described below for an unlink can be devised by a skilled person.

The RNC 25 is provided with an outer power control loop controller 26 and an associated outer power control loop memory 28. The outer power control loop controller 26 may typically be a processor running a program implementing an outer power control loop algorithm. The processor may be a dedicated processor, or the program implementing an outer power control loop algorithm may be part of a bigger program running on a processor of the RNC 25. The outer power control loop memory 28 stores target information and other information needed by the outer power control loop controller 26. The information stored may record quantities like the SIR, SIR target, BLER and BER and associated targets. The outer power control loop memory 28 may be c . . . . . . ... . . implemented as a dedicated memory, or as a part of a larger memory, and may be implemented in RAM or any type of updateable memory.

The node B 10 is provided with an inner power control loop controller 12 and with quality measurement means to make quality measurements on unlink channels.

The inner power control loop controller 12 is operably coupled to the outer power control loop controller 26 and to the quality measurement means and implements an inner loop power control algorithm. The quality measurement means are also operably coupled to the outer power control loop controller 26 to provide quality measurements to the outer power control loop controller 26.

Again, the inner power control loop controller 12 may typically be a processor running a program implementing an inner power control loop algorithm. The processor may be a dedicated processor, or the program implementing an inner power control loop algorithm may be part of a bigger program running on a processor of the node B 10. The quality measurement means are usually implemented in hardware that can to be configured via a program or algorithm running in software. The quality measurement itself may be stored as a record in memory (any kind of memory) and could be manipulated by a program implemented in software.

In the exemplary embodiment the quality measurement means comprises a Block Error Rate (BLER) measurement means 14, a Bit Error Rate (BER) measurement means 16 and a Signal to Interference Ratio (SIR) measurement means 18. In the exemplary embodiment the BLER measurement means 14 determines the block error rate for received traffic data, the BER measurement means 16 determines the bit error rate for received control/signaling data and the SIR measurement means 18 determines the received signal to interference ratio for the total signal received from the UE 20. It should be noted that it is also possible in some embodiments to determine bit error rate for the received traffic data. In addition, in other embodiments, the measures of quality may be used.

. . . . c. . e e e . ese The power control therefore operates as follows: the inner power control loop controller 12 receives SIR measurements from the SIR measurement means 18 and compares the SIR measurements with a SIR target. The inner power control loop controller 12 then causes the power at which the UE 20 is transmitting to be adjusted, for example by sending Power up" or "power down" messages to the UE 20 depending upon whether the results of the comparison show that the received SIR is below or above the target SIR, respectively. In addition, the BLER measurement means 14 and the BER measurement means 16 provide respective quality measurements to the outer power control loop controller 26.

The outer power control loop controller 26 periodically compares the BLER and/or the BER quality measurements with a target quality value stored in the outer power control loop memory 28 and adjusts the SIR target used by the inner power control loop controller 12 up or down depending upon whether the results of the comparison show that the BLER and/or BER measurements are above or below the target quality value, respectively. The adjustment of the SIR target value may be achieved by the outer power control loop controller sending the new SIR target value to the inner power control loop controller 12 or may also be achieved by the outer power control loop controller 26 sending "SIR target up" or SIR target down" commands, as appropriate, to the inner power control loop controller 12.

As indicated above, in a system such as the UMTS system of the exemplary embodiment, the UE 20 may be in soft handoff and therefore in communication with more than one node B 10. In this situation the uplink signals from the UE 20 will be received by more than one node B 10, and the RNC 25 will implement a power control loop for each of the node Be independently. However, for simplicity in the illustrative embodiment the UE 10 is shown in communication with only a single node B 20. Each node B that the UE 20 is in soft handoff with will have the same SIR target provided by the outer loop power controller 26 of the controlling RNC 25.

- ë e e e - The inventive concepts of the present invention relate primarily to the setting of a quality measurement target, and will be described in more detail with reference to Figures 2 and 3.

Figure 2 illustrates quality measurements made on communication channels used in the exemplary communication system shown in Figure 1, which operates in accordance with UMTS.

As will be known to a skilled person, in the exemplary UMTS communication system, a UE 20 may be allocated a dedicated physical channel (DPCH), comprising a dedicated physical control channel (DPCCH) for control and signaling data and a dedicated physical data channel (DPDCH) for traffic data, for uplink communications. The DPCCH and DPDCH are COMA code channels, as will be known to a skilled person: however, the exact nature of the channels is unimportant to the inventive concepts described herein. As shown, while the dedicated physical channel is allocated to a UE 10, the DPCCH is transmitted continuously: however, traffic data is only transmitted on the DPDCH intermittently, as illustrated. This is termed discontinuous transmission (DTx).

Three windows 1, II, lil are illustrated in Figure 2 and will be used to explain the inventive concepts of the present application. In window I both the DPDCH and the DPCCH are being received throughout the entire window period. In window 11 the DPCCH is being received throughout the entire window period, but the DPDCH is being received during only part of the window period. In window lil the DPCCH is being received throughout the entire window period, but the DPDCH is not received at all.

Figure 3 is a flow chart illustrating a method in accordance with an embodiment.

. . . . - e a. C,

. . . ... . . The flow chart starts in step s1 in a first mode, for example one in which data is being received i.e. as window I shown in Figure 2. In window I both BLER measurements made on the received data channel DPDCH and BER measurements made on the received control channel DPCCH are available to the outer power control loop controller 26 from the BLER measurement means 14 and the BER measurement means 16 respectively.

In step s2 the outer power control loop controller 26 uses quality measurements to adjust the SIR target for the inner loop power controller. In one embodiment, only the BLER measurement from the BLER measurement means 14 is used. In this embodiment, the outer power control loop controller 26 compares the BLER measurement with the BLER target stored in the outer power control loop memory 28 and adjusts the SIR target for the inner loop power controller 12 accordingly. In other embodiments, both the BLER and the BER measurements, or only the BER measurements, or other quality measurements may be used by the outer power control loop controller 26 to implement the outer loop power control.

Step s3 indicates that, whether or not BER measurement is used in the outer power control loop algorithm implemented in step s2, the BER measurement means 16 provides at least one BER measurement to the outer power control loop during window 1.

In step s4 an updated BER target is calculated by the outer power control loop controller 26 from the measured data and the updated BER target is stored in the outer power control loop memory 28. The updated BER target can then be used subsequently as the new BER target value for all calculations. In particular, the updated BER target can be used for comparison with measured BER values in the outer power control loop determination process during DTx periods to adjust the inner loop SIR target values, as will be explained later with reference to step s6. In addition, in embodiments in which BER measurements are used in the a ë a- a a e a a e a outer power control loop determination process during data transmission periods (i.e. in step s2 above) the new BER target can be used.

The updated BER target can be determined in different ways, as will be apparent to a skilled person. In a simple embodiment, measured BER values may be stored directly, or after averaging of a number of measured values, in the outer power control loop memory 28. In other embodiments, the updated target BER value may be calculated based on both BER and BLER measurements and/or any other quality measurement reported to the outer power control loop controller 26, whether such measurements are single values or are values obtained after averaging a number of such values. One or more previous values of the BER target may also be used in calculating an updated BER target.

Equation 1 is an example of an equation that may be used by the outer power control loop controller 26 to determine an updated BER target: BERtarget = (I-Cold Larger + iBERmeasured +k BLERerror ABLER] where BERN is the new BER target BERo/d targets a previous BER target BERmeasured is the measured BER value BLERe,,o,is the difference between measured BLER and target BLER and the remaining values are parameters selected as appropriate by a skilled person. For example the parameter alpha may be a function of the proportion of data blocks actually received in the measurement period. Parameter k controls the degree to which the BLER is taken into consideration in determining a target BER.

. . <ë e < . * . < . . . . - In step s5 it is determined whether operation is continuing in the first mode, i.e. a data transfer mode of operation in which data is being received, as indicated above, or whether operation is now in a second mode of operation, which is at least substantially free of data transfer. If operation is continuing in the first mode (s5-y) the method returns to step s2 and steps s2-s4 are repeated. If operation is now in the second mode, operation now proceeds to step s6.

In window 11 of Figure 2, the operation as set out in steps s2-s4 above may be repeated. Specifically, in step s2 the outer power control loop controller 26 uses quality measurements to adjust the SIR target for the inner loop power controller.

In embodiments in which BER measurements are used, alone or in combination with other quality measures, by the outer power control loop controller 26 to implement the outer loop power control, the newly updated BER target is used as the BER target. Again, the BER measurement means 16 provides at least one BER measurement to the outer power control loop during window 11, step s3.

Then, in step s4 an updated BER target value is calculated by the outer power control loop controller 26 and the updated BER target value is stored in the outer power control loop memory 28 for use subsequently as the new BER target value for all calculations.

If it is determined in step s5 that operation is not continuing in the first mode, i.e. one in which data is being received, so that operation is now in a second mode substantially free of data transfer, i.e. a DTx mode (step s5-n), as illustrated by window lil in Figure 2, the outer power control loop controller 26 operation moves to step s6. In this second mode, quality measures for power control algorithms that are available during the first, data transmission, mode, such as BLER, are no longer available. Thus in step so, the outer power control loop controller 26 compares the BER measurement with the target BER value stored in the outer power control loop memory 28 in order to determine any necessary adjustment to the SIR target for the inner power loop controller 12.

e e-.

ce a e a The SIR target for the inner power control loop controller may be obtained in many ways. However, the use of the target BER value as described above means that the adjustment of the SIR target during periods of operation in the second mode, when there is no data transmission, is carried out in such a way that the adjustment is sensitive to the difference between the BER measured during the adjustment period and the target BER.

Equation 2 is one example of an equation that may be used to obtain updated SIR values in step s6.

SlRn+l = SlRn + a_cons t(BER,, meas BERtaget)l BERtaget where SlRn+, is the new SIR target SlRn is the old SIR target BERmjn_meas is the measured BER (or the minimum measured BER if more than one available, for example from different node Bs if the UE is in soft handoff) BERM, is the target BER. As indicated above, this BER target is updated in accordance with the inventive concepts described herein.

However, clearly it would also be possible in a simple embodiment merely to incrementally increase/decrease the SIR target depending on a simple comparison between the BER measurement and the BER target.

In step s7 it is determined whether the operation is continuing in the second mode of operation, in which no data is being transmitted (DTx mode) or whether operation is continuing in the first mode of operation, in which data is being transmitted. If operation is continuing in the second mode of operation (step s7-y) step s6 is repeated. If operation is continuing in the first mode of operation, the outer power control loop controller returns to step s2.

. . * c . . . . . . . . . . . . - . . Thus a dynamic BER target value for use during periods when data is not being transmitted is set based on measurements of at least BER during periods when data is being transmitted. This BER target may also be used to update the SIR target during periods that have a mix of data and DTx. In other words the BER target estimated via step s2, could be used to update the SIR target during window 11, Figure 2 for example. Since the BER target value is set depending on measurements, the BER target value may better reflect the true state of the radio conditions, and therefore may enable better performance of the communication system as a whole by eliminating the need for over-dimensioning of the target BER value. A sub-optimal BER target would have to be set in the case of an algorithm that did not attempt to measure the required or true BER target based on the conditions seen by the UK. The initial value of the BER target would have to be set based on simulations and experience and as a result would be subject to error. However, as subsequent values for the BER target are set based on measured values, any error in the initialization of the target BER figure may be eliminated relatively easily.

It should be noted that the BER measurements used to set the BER target value as outlined above may be measured across the node B active set, or across the cells, as desired by a skilled person. BER measurements are available from every node B that the UE has a soft hand off connection to. All of these measurements are available to the outer loop power controller 26 in the RNC 25.

These measurements may be combined (averaged, filtered, or subject to any kind of mathematical function) in any suitable way to arrive at the BER target described in step s4.

It should be noted that in the exemplary embodiment described above a service with a single transport channel is used as an example. However, the concepts described herein apply equally when there is more than one transport channel. It is worth noting that the BLER is generally measured with respect to a particular transport channel. A UE may have more than one transport channel active at any . . . . . . .. . . . . . . . . . . . given time. As a result the outer loop power controller 26 has access to a BLER measurement on each transport channel. However there is only a single control/signaling channel even in the case where multiple transport channels are in use. These measurements can be stored within the outer loop memory area 28. In particular, the outer power control loop controller 26 may operate different SIR adjustment loops in parallel on a per transport channel basis, and the concepts described herein may be applied to one or some or all of the SIR adjustment loops for a particular UE 20. The decisions of these multiple loops may be combined to give a final adjustment with respect to the SIR target or any of the other quantities used by the outer loop powercontroller.

It should be noted that the use of averaging windows as such, such as windows 1, 11 and 11 is not necessary. Moreover, if averaging windows are used, it is not necessary that the BER target is always updated at the end of each averaging window. For example, if the number of data blocks received in window 11 is considered to be too small, the BER target value determined during the previous window, window 1, need not be updated.

It should be noted that it is not necessary that the averaging periods (windows 1, 11 and 111) are the same length and the length of the averaging periods may be varied. In particular, the length of the averaging periods may be altered depending on one or more factors such as network conditions, carried traffic, radio conditions encountered etc. In addition, averaging or measurement windows, if used, may overlap i.e. may be moving average windows. As a result, although in the described embodiment above the BER target value is updated at the end of each averaging window, in practice the update could be done at any time. In particular, the update may be done in response to one or more conditions or triggers, for example: some threshold condition in the radio conditions; network load; carried traffic on the channel or on a selected transport channel; etc. e *he * * * * * C * * * C * * e * e e * e e e e Thus, implementation of the concepts described herein may lead to one or more of the following benefits: The BER target may vary so that it more accurately reflects radio conditions, that are also time-varying The requirement to over-dimension the BER target to ensure reliable operation when entering the data transmission mode again may be reduced or eliminated by setting the BER target based on measurements The SIR target may be adapted during periods when data is not transmitted via a mechanism that is sensitive to difference between measured and target BER Several SIR target adjustment loops may operate in parallel, training on respective transport channels.

Claims

. . . . . . . . . . . . . - . . - . CLAIMS

1. A method for power control in a wireless communication system, comprising the step of determining an outer power control loop quality target for use during a second operational mode period from at least one quality measurement made during a first operational mode period.

2. The method as claimed in claim 1 wherein the first operational mode is a data transfer mode of operation and the second operational mode is at least substantially free of data transfer.

3. The method as claimed in claim 1 or 2, wherein during the second operational mode period an inner power control loop quality target is determined from or adjusted in dependence on at least one quality measurement made during the second operational mode period and the determined outer power control loop quality target.

4. The method as claimed in claim 3 wherein a quality measurement made during the second operational mode period is a bit error rate measurement.

5. The method as claimed in one of claims 3 or 4 wherein during the first operational mode period an inner power control loop quality target is determined from or adjusted in dependence on at least one quality measurement made during the first operational mode period and a corresponding outer power control loop quality target.

6. The method as claimed in claim 5 wherein at least one quality measurement comparison made during the first operational period relates to a quantity that is not available during the second operational mode period c c e cee ce C e C C C C C * C C

7. The method as claimed in claim 5 or 6 wherein a quality measurement made during the first operational period is a block error rate measurement.

8. The method as claimed in any preceding claim wherein a required transmit power or adjustment to transmit power is determined in response to the result of a comparison of at least one quality measurement with the corresponding inner power control loop quality target.

9. The method as claimed in any preceding claim wherein the step of determining or adjusting a quality target occurs in response to one or more of the following: position in a measuring window; radio conditions threshold; network load; carried traffic; or selected transport channel.

10.The method as claimed in any preceding claim wherein the step of making quality measurements occurs in response to one or more of the following: position in a measuring window; radio conditions threshold; network load; carried traffic; or selected transport channel.

11. Computer readable medium storing processor implementable instructions for carrying out the method of any preceding claim

12.An apparatus for power control in a wireless communication system, comprising a controller for determining an outer power control loop quality target for use during a second operational mode period from at least one measurement made during a first operational mode period.

13.The apparatus as claimed in claim 12 further comprising storage means for storing the determined quality target.

. * . . . . . . * .

14.The apparatus as claimed in claim 12 or 13 wherein the first operational mode is a data transfer mode of operation and the second operational mode is at least substantially free of data transfer.

15.The apparatus as claimed in one of claims 11-14, wherein during the second operational mode period an inner power control loop quality target is determined by the controller from, or adjusted by the controller in dependence on, at least one quality measurement made during the second operational mode period and the determined outer power control loop quality target.

16.The apparatus as claimed in claim 15 wherein a quality measurement made during the second operational mode period is a bit error rate measurement.

17.The apparatus as claimed in one of claims 15 or 16 wherein during the first operational mode period an inner power control loop quality target is determined by the controller from, or adjusted by the controller in dependence on, at least one quality measurement made during the first operational mode period and a corresponding outer power control loop quality target.

18.The apparatus as claimed in claim 17 wherein at least one quality measurement comparison made during the first operational period relates to a quantity that is not available during the second operational mode period

19. The apparatus as claimed in claim 17 or 18 wherein a quality measurement made during the first operational period is a block error rate measurement.

e e e e c c e c e c e * e e e # e e c ce* ce. e

20. The apparatus as claimed in one of claims 12-19 wherein a required transmit power or adjustment to transmit power is determined in response to the result of a comparison of at least one quality measurement with the corresponding inner power control loop quality target.

21.The apparatus as claimed in one of claims 12-20 wherein the step of determining or adjusting a quality target occurs in response to one or more of the following: position in a measuring window; radio conditions threshold; network load; carried traffic; or selected transport channel.

22.The apparatus as claimed in one of claims 12-21 wherein the step of making quality measurements occurs in response to one or more of the following: position in a measuring window; radio conditions threshold; network load; carried traffic; or selected transport channel.

23. A base station controller comprising apparatus as claimed in one of claims 1 2-22.

24. A subscriber unit comprising apparatus as claimed in one of claims 1222.