GB2433383A

GB2433383A - Uplink power control for HSDPA in a cellular communication system

Info

Publication number: GB2433383A
Application number: GB0525811A
Authority: GB
Inventors: Fernando De La Cruz Moreno
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2005-12-19
Filing date: 2005-12-19
Publication date: 2007-06-20
Anticipated expiration: 2025-12-19
Also published as: GB2433383B; GB0525811D0

Abstract

In a High Speed Downlink Packet Access (HSDPA) service, control messages from the UE to the Node-B(103) are carried on the HS-DPCCH, which uses a transmit power which is offset relative to that of the DPDCH by a constant amount. When the DPDCH is operating in soft handoff, this may result in an inadequate transmit power for the HS-DPCCH. According to the invention, a RNC interface (209) transmits an indication of a quality characteristic, in particular an error rate, of the HS-DPCCH received from the UE at the Node-B to the RNC (109) The RNC uses this indication to determine a transmit power offset for the uplink HS-DPCCH, which it transmits to the UE.

Description

TRANSMIT POWER CONTROL IN A CELLULAR COMMUNICATION SYSTEM

Field of the invention

The invention relates to transmit power control in a cellular communication system and in particular, but not exclusively to power control in a Universal Mobile Telecommunication System (UMTS).

Background of the Invention

In a cellular communication system, a geographical region is divided into a number of cells served by base stations. The base stations are interconnected by a fixed network which a.....

can communicate data between the base stations. A mobile station is served via a radio communication link from the : 20 base station of the cell within which the mobile station is situated.

A typical cellular communication system extends coverage over an entire country and comprises hundreds or even thousands of cells supporting thousands or even millions of mobile stations. Communication from a mobile station to a base station is known as the uplink, and communication from a base station to a mobile station is known as the downlink.

The fixed network interconnecting the base stations is operable to route data between any two base stations, thereby enabling a mobile station in a cell to communicate with a mobile station in any other cell. In addition, the fixed network comprises gateway functions for interconnecting to external networks such as the Internet or the Public Switched Telephone Network (PSTN), thereby allowing mobile stations to communicate with landline telephones and other communication terminals connected by a landline. Furthermore, the fixed network comprises much of the functionality required for managing a conventional cellular communication network including functionality for routing data, admission control, resource allocation, subscriber billing, mobile station authentication etc. The most ubiquitous cellular communication system is the 2nd : .. generation communication system known as the Global System S...

", 15 for Mobile communication (GSM). GSM uses a technology known S...

as Time Division Multiple Access (TDMA) wherein user separation is achieved by dividing frequency carriers into 8 discrete time slots, which individually can be allocated to : a user. Further description of the GSM TDMA communication system can be found in The GSM System for Mobile * S Communications' by Michel Mouly and Marie Bernadette Pautet, Bay Foreign Language Books, 1992, ISBN 2950719007.

Currently, 3rd generation systems are being rolled out to further enhance the communication services provided to mobile users. The most widely adopted 3rd generation communication systems are based on Code Division Multiple Access (CDMA) technology. Both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) techniques employ this CDMA technology. In CDMA systems, user separation is obtained by allocating different spreading and scrambling codes to different users on the same carrier frequency and in the same time intervals. In TDD, additional user separation is achieved by assigning different time slots to different users in a similar way to TDMA. However, in contrast to TDMA, TDD provides for the same carrier frequency to be used for both uplink and downlink transmissions. An example of a communication system using this principle is the Universal Mobile Telecommunication System (UMTS). Further description of CDMA and specifically of the Wideband CDMA (WCDMA) mode of UMTS can be found in WCIDMA for UMTS', Harri Holma (editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876.

In a 3rd generation cellular communication system, the : .. communication network comprises a core network and a Radio S...

". 15 Access Network (RAN). The core network is operable to route S...

data from one part of the RAN to another, as well as * * interfacing with other communication systems. In addition, it performs many of the operation and management functions : of a cellular communication system. The RAN is operable to * 20 support wireless user equipment over a radio link of the air 0*..S.

* interface. The RAN comprises the base stations, which in UMTS are known as Node Bs, as well as Radio Network Controllers (RNCs) which control the base stations and the communication over the air interface.

The RNC performs many of the control functions related to the air interface including radio resource management and routing of data to and from appropriate base stations. It further provides the interface between the RAN and the core network. An RNC and associated base stations are collectively known as a Radio Network Subsystem (RNS).

3rd generation cellular communication systems have been specified to provide a large number of different services including efficient packet data services. For example, downlink packet data services are supported within the 3 Generation Partnership Project (3GPP) release 5 Technical Specifications in the form of the High Speed Downlink Packet Access (HSDPA) service.

In accordance with the 3GPP specifications, the HSDPA service may be used in both Frequency Division Duplex (FDD) mode and Time Division Duplex (TDD) mode.

In HSDPA, transmission code resources are shared amongst users according to their traffic needs. The base station S..

** 15 (also known as the Node-B for UMTS) is responsible for **5S allocating and distributing the HSDPA resources amongst the individual calls. In a UMTS system that supports HSDPA, some of the code allocation is performed by the RNC whereas other : code allocation, or more specifically, scheduling is performed by the base station. Specifically, the RNC *SSSS* * allocates a set of resources to each base station, which the base station can use exclusively for high speed packet services. The RNC furthermore controls the flow of data to and from the base stations. However, the base station is responsible for scheduling High Speed-Downhink Shared CHannel (HS-DSCH) transmissions to the mobile stations that are attached to it, for operating a retransmission scheme on the HS-DSCH channels, for controlling the coding and modulation for HS-DSCH transmissions to the mobile stations and for transmitting data packets to the mobile stations.

HSDPA seeks to provide packet access techniques with a relatively low resource usage and with low latency.

Specifically, HSDPA uses a number of techniques in order to reduce the resource required to communicate data and to increase the capacity of the communication system. These techniques include Adaptive Coding and Modulation (AMC), retransmission with soft combining and fast scheduling performed at the base station.

Although 3rd Generation cellular communication systems support soft handovers wherein transmissions between a mobile station and a plurality of base stations are combined ::::. for improved performance, HSDPA communications are designed to involve only a single cell. Accordingly, HSDPA relies on only a single radio link and soft handover of HSDPA signals * is not supported. Thus, in an HSDPA enabled cellular communication system some communication channels may support : soft handover whereas other communication channels (such as HSDPA channels) do not.

It is important to manage radio links between base stations and communication units such that the resource used by a given communication link is as low as possible. It is therefore important to minimise the interference caused by the communication to or from a mobile station, and consequently it is important to use the lowest possible transmit power. As the required transmit power depends on the instantaneous propagation conditions, it is necessary to dynamically control transmit powers to closely match the conditions. For this purpose, the base stations and mobile stations operate power control loops, where the receiving end reports information on the receive quality back to the transmitting end, which in response adjusts the transmit power.

Specifically, in WCDMA, the uplink power control operates by the base station calculating the signal to interference ratio (SIR), comparing this to a desired uplink SIR threshold and transmitting a power down control signal to the mobile station if the SIR is above the threshold. If the SIR is not above the threshold, the base station transmits a power up control signal.

If a mobile station is in an active soft handover, it may ::::. receive transmit power commands from the active base WI 15 stations. The mobile station will increase the transmit I...

: power only if all of the active base stations transmit a power up command. Thus, if one or more of the base stations transmit a power down command, this is an indication that at least one of the base stations of the active set receives * I S the uplink transmission at a sufficiently high quality. In soft handover the transmit power of the mobile station is accordingly selected to ensure that at least one soft handover link is of sufficient quality.

In order to avoid a high complexity, an individual power control loop is not implemented for each physical channel in a cellular communication system. Specifically, for a UMTS cellular communication system, the transmit power commands are determined by the base stations measuring the SIR of the uplink control channel known as the Dedicated Physical Data CHannel (DPDCH). The DPDCH may be operated in soft handover and thus the transmit power of the DPDCH will be controlled to ensure reliable communication to at least one of the base stations of the active set but not necessarily to all of the base stations.

When a mobile station is involved in an HSDPA service, a number of control messages are transmitted from the mobile station to the single base station supporting the HSDPA service. For example, the mobile station may transmit retransmission acknowledge messages (Hybrid ARQ ACK/NACK messages) and indications of the quality of the communication channel (CQI -Channel Quality Indicators).

These messages are transmitted on a continuous HSDPA uplink control channel known as the HS-DPCCH (High Speed - ::::. Dedicated Physical Control CHannel). The 3GPP Technical *::::* 15 Specifications do not allow for a separate power control loop being implemented for this channel. Rather the * Technical Specifications prescribe that the HS- DPCCH may use a transmit power which is given as a constant power offset : relative to the DPDCH.

However, when the DPDCH is in a soft handover state, this approach frequently results in the HS-DPCCH not being receivable at the base station supporting the HSDPA service.

This is due to the propagation conditions from the mobile station to the soft handover base stations typically varying such that the radio links to other base stations of the soft handover are dominant. In such cases, the power control loop for the DPDCH is effectively controlled by the channel characteristics of the dominant link(s). Thus, the transmit power of the mobile station will not ensure that the DPDCH can be received by the HS-DSCH serving base station (only that it can be received by one of the base stations in the soft handover).

Furthermore, unless the power offset between the HS-DPCCH and the DPDCH is sufficiently large, the HS-DPCHH cannot be received by the serving base station either. However, in this case the HS-DPCCH cannot be received by the RAN at all as the HS-DPCCH cannot be in a soft handover state. Setting the power offset sufficiently high to ensure that the HS-DPCCH can be received in all situations results in the transmit power being excessive for most of the time thereby causing increased interference and reduced capacity.

The Technical Specifications allow the RNC to signal to the .... 15 mobile station to use a different power offset. Furthermore, the transmissions on the HS-DPCCH may be repeated and the 0**.S* * RNC may also signal different repetition rates to the mobile station. This may allow the operator of the cellular : communication system to select the trade off between excessive resource usage and communication reliability.

Providing that the power offsets and repetition factors are set to be sufficiently large for the different conditions that may be experienced, the probability of the HS-DPCCH being received correctly at the serving base station may be improved. However, as the propagation conditions vary significantly, the required power offsets will typically be very high as they must allow for the worst case conditions for each scenario. Thus, although the approach may allow for a further refinement of the power offset it will typically lead to excessive transmit powers and/or lost HS-DPCCH transmissions. For example, if a power offset is selected to provide for acceptable performance for the HS-DPCCH in situations where the DPDCH is in a soft handover with another link being dominant, this will result in an unnecessarily high transmit power if the link to the serving base station is dominant.

Erroneous reception of HS-DPCCH may degrade the performance and efficient HSDPA services significantly. For example, retransmission acknowledgements/ non-acknowledgements (ACK/NACK) are transmitted on the HS-DPCCH and data errors may therefore affect the retransmission scheme resulting in reduced efficiency and increased resource consumption.

Furthermore, Channel Quality Indications (CQI) used by HSDPA schedulers at the base station are also transmitted on the HS-DPCCH and errors in the CQIs may result in an inefficient scheduling. This may reduce capacity and degrade the quality of service.

Hence, an improved system for power control in a cellular : communication system would be advantageous and in particular : 20 a system allowing increased flexibility, improved resource usage, reduced data loss, reduced interference, increased battery life, increased communication reliability and/or increased performance of the communication system would be advantageous.

Summary of the Invention

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to an aspect of the invention, there is provided a cellular communication system comprising: a radio network controller comprising power offset means for determining a transmit power offset for transmissions from a user equipment to a base station in a first air interface channel relative to transmissions from the user equipment to the base station in a second air interface channel, and first transmitting means for transmitting an indication of the transmit power offset to the user equipment; and the base station comprising means for receiving transmissions from the user equipment in the first air interface channel, and quality means for determining a communication quality characteristic for the first air interface channel in :,:::. response to measurements of the transmissions from the user * S..

15 equipment in the first air interface channel, and second transmitting means for transmitting an indication of the I **S*5 * communication quality characteristic to the radio network controller; and wherein the power offset means is arranged : to determine the transmit power offset in response to the indication of the communication quality characteristic received from the base station.

The invention may allow improved performance and may specifically in some embodiments allow an improved control of the transmissions from user equipment in a first air interface channel linked to a second air interface channel by a transmit power offset. In particular, a flexible and efficient control of the transmit power for the first air interface channel may be achieved in many embodiments.

Furthermore, a low complexity implementation may be achieved in many embodiments.

The invention may allow improved performance while complying with the standards of many cellular communication systems.

For example, no standardisation of additional signalling between the user equipment and the base stations or between base stations and RNCs will be necessary for a UMTS cellular communication system.

The invention may increase the reliability of communication in the first air interface channel and may in particular reduce the error rate of the signals of the first air interface channel. Alternatively or additionally, the invention may reduce resource consumption such as e.g. the transmit power of the user equipment and may e.g. reduce the interference caused by the user equipment resulting in an S...

improved quality of service and/or increased capacity of the cellular communication system as a whole.

The indication of the communication quality characteristic can for example be a suggested power offset or power offset change between the first and second air interface channels.

According to an optional feature of the invention, the communication quality characteristic is an error rate.

This may provide for a practical implementation and/or high performance. In particular, the error rate may be a particularly accurate indication of the reception quality of the signals in the first air interface channel. The error rate may for example be a BLock Error Rate (BLER) or a Bit Error Rate. The indication of the communication quality characteristic may for example be the error rate or a value derived from the error rate such as an absolute or relative suggested transmit power offset between the first and second air interface channels.

According to an optional feature of the invention, the indication of the communication quality characteristic is a Block Error Rate for the transmissions from the user equipment and the quality means are arranged to associate an error rate of the transmissions to a Block Error Rate in accordance with a predetermined relationship.

This may provide for a practical implementation and/or high performance. In particular, it may allow a low complexity determination of an accurate parameter for adjusting the transmit power offset while reducing the required amount of S..

... 15 signalling between the base station and the radio network controller.

S..... * .

According to an optional feature of the invention, the quality means is arranged to determine the communication quality characteristic by low pass filtering quality measurements for a plurality of transmissions received from the user equipment.

This may provide a practical implementation and/or high performance.

According to an optional feature of the invention, the quality means is arranged to reset the low pass filter in response to a detection of a change in handover state of the user equipment.

This may provide for a practical implementation and/or high performance. In particular, it may allow a fast response if the optimal offset between the first and second air interface channel changes abruptly due to a handover configuration change. The change in handover state may for example be a change in the number of legs supporting the second air interface channel.

According to an optional feature of the invention, the communication quality characteristic is for retransmission feedback messages for the first air interface channel.

This may provide for a practical implementation and/or high performance. Specifically, it may allow an accurate S...

e***s 15 adaptation of the transmit power offset which is suitable for existing communications such as UMTS.

* 0*S*I * S According to an optional feature of the invention, the communication quality characteristic comprises separate quality indications for positive and negative retransmission feedback messages.

This may provide improved performance and may provide additional flexibility in ensuring that acceptable performance is achieved for retransmission feedback messages which typically have very different desired error rates.

According to an optional feature of the invention, the indication of the communication quality characteristic comprises a quality indication for a plurality of message types and the power offset means is arranged to adjust the transmit power offset to increase the transmit power for the first air interface channel relative to the transmit power for the second air interface channel if the quality indication for at least one of the plurality of message types is indicative of a quality below a threshold.

This may provide improved performance and may provide additional flexibility in ensuring that acceptable performance is achieved for different message types which may have different characteristics and/or requirements.

According to an optional feature of the invention, the first air interface channel is a non-soft handover channel and the second air interface channel is a soft handover channel. * S. * . . S... e.

.., 15 The invention may allow improved performance in a cellular communication system using a transmit power offset between *5*SS * transmissions of a soft handover communication channel and transmissions of a non-soft handover communication channel. * S* * *. S. S

S:.e. 20 The invention may e.g. increase the reliability of the non-soft handover communication channel and may in particular reduce the error rate of the signals of the non-soft handover communication channel.

According to an optional feature of the invention, the cellular communication system comprises means for comparing the communication quality characteristic to a first threshold and the transmit power offset is modified by a first predetermined step if the communication quality characteristic is above the threshold.

This may provide for a practical implementation and/or high performance. Specifically, it may allow for an accurate and flexible adaptation of the transmit power offset while maintaining a low complexity implementation.

According to an optional feature of the invention, the means for comparing is arranged to compare the communication channel characteristic to a second threshold and the transmit power offset is modified by a second predetermined step if the communication characteristic is below the threshold, the first and second predetermined steps having opposite signs.

: This may provide for a practical implementation and/or high I...

15 performance. Specifically, it may allow for an accurate and flexible adaptation of the transmit power offset while a maintaining a low complexity implementation. The feature may allow for a desirable hysteresis to be applied to reduce the number of modifications to the transmit power offset.

I

The first and second predetermined steps may have the same magnitude.

According to an optional feature of the invention, the cellular communication system is a 3 Generation cellular communication system.

The invention may provide improved performance in a 3 Generation cellular communication system, such as a UMTS cellular communication system. In particular, the invention may improve performance of many 3rd Generation cellular communication systems while complying with the Technical Specifications defined by the 3rd Generation Partnership project.

According to an optional feature of the invention, the first air interface channel is a High Speed Downhink Packet Access (HSDPA) communication channel.

In particular, the non-soft handover communication channel may be a High Speed-Dedicated Physical Control CHannel (HS-DPCCH) channel, the soft handover communication channel may be a Dedicated Physical Dedicated CHannel (DPDCH) channel and the first base station may be operable to transmit an HSDPA signal to the user equipment on a High Speed-Downlink Shared CHannel (HS-DSCH). SI *

S .5.

* The invention may provide improved performance and may in

S

particular provide improved transmission control in a 3rd Generation cellular communication system supporting HSDPA . : services. The transmission control may be modified to improve performance while complying with the specifications for the cellular communication system and in particular for HSDPA services.

Specifically, in some embodiments, the invention may substantially improve reliability of signals transmitted on the HS-DPCCH while the DPDCH is operating in a soft handover state. Additionally or alternatively, the transmit power of the HS-DPCCH may e.g. be substantially reduced to match the current requirements rather than using a simple transmit power offset based on a worst case assumption.

According to an optional feature of the invention, the first transmitting means is arranged to transmit the indication of the transmit power offset in an RRC PHYSICAL LAYER RECONFIGURATION message.

This may provide high performance, practical implementation and/or improved backwards compatibility.

According to an optional feature of the invention, the second transmitting means is arranged to transmit the indication of the communication quality characteristic offset in an NBAB RL PARAMETER UPDATE INDICATION.

This may provide high performance, practical implementation I...

15 and/or improved backwards compatibility.

t a.s.

According to another aspect of the invention, there is provided a method of power control in a cellular communication system, the method comprising at a radio .: 20 network controller performing the steps of: determining a transmit power offset for transmissions from a user equipment to a base station in a first air interface channel relative to transmissions from the user equipment to the base station in a second air interface channel, and transmitting an indication of the transmit power offset to the user equipment; and at the base station performing the steps of: receiving transmissions from the user equipment in the first air interface channel, and determining a communication quality characteristic for the first air interface channel in response to measurements of the transmissions from the user equipment in the first air interface channel, and transmitting an indication of the communication quality characteristic to the radio network controller; and wherein the transmit power offset is determined in response to the indication of the communication quality characteristic received from the base station.

These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief Description of the Drawings

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which : * FIG. 1 is an illustration of a cellular communication system S..

incorporating some embodiments of the invention; * S S...

FIG. 2 illustrates an example of a base station in accordance with some embodiments of the invention; FIG. 3 illustrates an example of a radio network controller I.....

* . in accordance with some embodiments of the invention; FIG. 4 illustrates an example of a method of operation for a base station in accordance with some embodiments of the invention; and FIG. 5 illustrates an example of a signaling flow in accordance with some embodiments of the invention.

Detailed Description of Some Embodiments of the Invention The following description focuses on some embodiments of the invention applicable to a 3rd Generation cellular communication system and in particular to 3' Generation cellular communication system supporting HSDPA services. However, it will be appreciated that the invention is not limited to

this application but may be applied to many other communication systems and services.

FIG. 1 is an illustration of a UMTS cellular communication system 100 incorporating some embodiments of the invention.

In the example of FIG. 1, a user equipment 101 is supported by three base stations (node Bs) 103, 105, 107. The three : *** base stations 103-107 are coupled to a Radio Network S...

s... Controller (RNC) 109 which is coupled to a core network 111 SI..

as is typical for UMTS cellular communication systems. In :": 20 the example of FIG. 1, the user equipment 101 is in an overlap area between three different cells supported by the three different base stations 103-107. It will be appreciated that although each cell of the current example * is supported by a separate base station, individual base stations may in other examples support more than one cell.

The user equipment 101 may typically be a communication unit, a 3rd Generation User Equipment (UE), a subscriber unit, a mobile station, a communication terminal, a personal digital assistant, a laptop computer, an embedded communication processor or any physical, functional or logical communication element which is capable of communicating over the air interface of the cellular communication system.

In the current example, the user equipment 101 is communicating with a serving base station 103 through a first radio link 113 but is also communicating with two other base stations 105, 107 over other radio links 115, 117. Specifically, the user equipment 101 is currently in a soft handover configuration with an active set comprising the three base stations 103-107.

For clarity and brevity, FIG. 1 illustrates only aspects of the communication system required to describe exemplary embodiments of the invention. Similarly, only the functionality and features required to describe the embodiments will be described and it will be apparent to the : .. person skilled in the art that the illustrated elements will S...

be capable of performing other functions and provide other *SS* features required or desired for the operation of a 3rd :": 20 Generation cellular communication system as appropriate.

In the example of FIG. 1, the user equipment 101 is S currently involved in an HSDPA call supported by a first of S.....

* the base stations 103. Thus, the user equipment 101 is communicating with the first base station 103 using HSDPA communication channels. In particular, the first serving base station 103 is transmitting data to the user equipment 101 on an HS-DSCH (High Speed -Downlink Shared CHannel).

Similarly, an uplink HS-DPCCH (High Speed Dedicated Physical Control CHannel) has been setup to communicate control data from the user equipment 101 to the base station 103 as is known from conventional HSDPA systems. The HSDPA channels cannot be involved in soft handovers but are dedicated communication links between the user equipment 101 and the serving base station 103. Thus, HSDPA channels are non-soft handover communication channels. This facilitates operation for HSDPA services, and for example allows that a fast and individual resource allocation for HSDPA services can be performed by the individual base station 103 in response to fluctuations of the radio link 113 between the base station 103 and the user equipment 101.

The HS-DPCCH is used to transmit various control messages including Hybrid ARQ ACK/NACK and CQI (Channel Quality Indicator) data. The Hybrid ARQ ACK/NACK data comprises acknowledge data used by the Hybrid ARQ retransmission scheme of the HSDPA service whereas the CQI commands are indicative of a quality of the radio link 113 between the : .. serving base station 103 and the user equipment 101. The S..

user equipment 101 measures the current receive quality of a S...

pilot signal of the base station 103 and reports the result *SS*S* * . 20 by transmitting the CQI commands. Thus, the CQI commands are indicative of the current radio propagation conditions from the base station 103 to the user equipment 101 and are used by the scheduling function of the base station 103 to *5**SS * schedule HSDPA data on the shared HS-DSCH to user equipment experiencing advantageous conditions. Such link adaptation scheduling may result in a substantially improved efficiency of the resource usage and may increase the capacity of the cellular communication system as a whole.

Furthermore, in the example of FIG. 1, a number of non-HSDPA communication channels are set up for the user equipment 101. Specifically, the user equipment 101 is supporting a DPDCH (Dedicated Physical Data CHannel) for user data communication and a DPCCH (Dedicated Physical Control CHannel) which is used to transmit various control data and commands from the user equipment 101 to the fixed network.

In the specific example, downlink data channels and uplink control channels are thus setup. Furthermore, these channels are soft handover communication channel wherein the communication may be supported simultaneously by a plurality of base stations.

In the example, the non-HSDPA communication channels are in a soft handover state where the communication between the base stations 103-107 and the user equipment 101 utilise a plurality of propagation channels with the received signals of the plurality of propagation paths being combined by the receiving end (for example by selection combining). Thus, in : .. the example of FIG. 1, the user equipment 101 is in a configuration wherein it is simultaneously supporting HSDPA S...

channels which are not (and cannot be) in a soft handover :: 20 state and nOn-HSDPA channels which are in a soft handover state. I..

It is important to manage radio links between base stations * S....

and user equipments such that the resource used by a given communication link is as low as possible. Thus, it is important to minimise the interference caused by the transmission of signals from the communication unit to the base stations and therefore the lowest possible transmit power should be used by the user equipment 101 when transmitting to the base stations 103-107. Accordingly, the base stations 103-107 and user equipment 101 operate power control loops to dynamically control transmit powers to closely match the varying conditions.

Specifically, cellular communication systems such as UMTS operate both an inner power control loop and an outer power control loop. Conventionally, the inner power control loop measures the received signal to interference ratio (SIR) of pilot symbols of the DPCCH, and compares it to a locally stored target SIR. If the measured SIR is less than the target SIR, the base station transmits a power up command and otherwise it transmits a power down command. If the user equipment 101 is in a soft handover, each of the base stations 103-107 in the soft handover transmits a transmit power command to the user equipment 101. Thus, in the example of FIG. 1, the user equipment 101 receives a transmit power command from each of the three base stations 103-107. In the example, the user equipment 101 increases the transmit power only if all of the received transmit power commands are power up commands (in other examples, the :: 20 subscriber equipment may for example weight the received power control commands with the received quality from each * site and decide accordingly). However in the specific example, as long as one of the links 113-117 provides sufficient performance, the transmit power is not increased.

Accordingly, the transmit power is controlled such that the dominant link is of sufficient quality whereas other links of the soft handover may provide a poor quality signal.

However, in UMTS communication systems, power control is not operated individually for each communication channel, and in particular the same power control commands are used to control the transmit power of both the DPDCH channel and the HS-DPCCH channel. Specifically, the transmit power for the HS-DPCCH is set to a fixed offset relative to the transmit power for the DPDCH. For example, the HS-DPCCH transmit power may be set to be 10 dB higher than the transmit power of the DPDCH channel. However, in contrast to the DPDCH, the HS-DPCCH cannot be in a soft handover state. Thus, the transmit power control which is based on maintaining acceptable performance for a soft handover communication may be used for a non soft handover communication which may result in unacceptable performance. Specifically, if the link to the serving base station is not the dominant link of the DPDCH this may result in the HS-DPCCH not being received (or being received with too many errors) by the base station 103. For example, if the current path loss to the base station 103 is 20dB lower than the path loss to the base station 105, the 10 dB transmit power offset may be :.. insufficient to maintain acceptable performance to the base station 103.

Accordingly, although the 3GPP R5 standards allow for a power offset to be specified between the transmit power of $1. the DPDCH and the HS-DPCCH such that the HS-DPCCH is transmitted at a relatively higher power, this results in an inaccurate setting of the transmit power as it will typically either be too high (if the HS-DPCCH experiences better conditions than assumed when setting the power offset) or too low (if the HS-DPDCH experiences worse conditions than assumed when setting the power offset).

FIG. 2 illustrates an example of an inner power control of a base station. The base station may be the base station 103 of FIG. 1 and will be described with reference to this.

The base station 103 comprises a transmitter 201 which is connected to an antenna 203 and which is operable to transmit signals to the user equipment 101. The antenna 203 is also coupled to a receiver 205 (for example through a duplexer or a switch (not shown)). The receiver 203 is operable to receive signals transmitted over the air interface from the user equipment 101.

The receiver is coupled to a SIR processor 207 which is operable to determine a SIR indication based on a signal received from user equipment 101 and in particular based on a DPDCH signal transmitted from the user equipment 101. The person skilled in the art will be aware of many different techniques and algorithms for determining a SIR indication and any suitable algorithm or technique may be used without *. detracting from the invention. a... S...

The receiver 205 is furthermore coupled to an RNC interface * * 20 209 which is operable to communicate with the RNC 109 over a UMTS lub interface. In particular, the RNC interface 209 transmits received data to the RNC 109 and may receive a target parameter for the inner power control from the RNC 109. In the specific example, the RNC interface receives a SIR (Signal to Interference Ratio) reference from the RNC 109.

The SIR processor 207 and the RNC interface 209 are coupled to a comparator 211 which compares the estimated SIR value received from the SIR processor 207 and the SIR reference from the RNC interface and generates an error signal. In a simple embodiment, the error signal may be a filtered difference between the SIR estimate and the SIR reference.

The comparator 211 is coupled to a transmit command processor 213 which determines an appropriate power control command. In particular, in some embodiments, the transmit command processor 213 may simply select a power up command if the error signal indicates that the SIR estimate is below the SIR reference and a power down command otherwise. The transmit command processor 213 is coupled to the transmitter 201 which transmits the selected transmit power command to the user equipment 101.

Each of the base stations 105, 107 of the example of FIG. 1 comprises an inner power control loop as the one described with reference to FIG. 2. Thus, when in soft handover, the ::". user equipment 101 receives transmit power commands from all three base stations 103-107. *.S.

In accordance with the UMTS Technical Specifications, the user equipment 101 proceeds to adjust the transmit powers of * the soft handover channels (including the DPDCH) in response * to the received transmit power commands. In particular, it proceeds to determine if any of the received transmit power commands are power down commands and if so it proceeds to decrease the transmit power. If all transmit power commands are power up commands, the user equipment 101 increases the transmit power.

Furthermore, the user equipment 101 proceeds to control the transmit power of non-soft handover channels, and in particular the HS-DPCCH channel, to match the fluctuations for the soft handover channels. Specifically, the user equipment 101 transmits the HS-DPCCH at a transmit power which is a fixed offset of the transmit power of the DPDCH (the offset may be zero).

Although this approach provides very accurate power control for the DPDCH channel, the power control of the HS-DPCCH tends to be relatively inflexible and suboptimal. However, in accordance with some embodiments, the power control of the HS-DPCCH is improved by the base station monitoring quality characteristics directly on the HS-DPCCH and forwarding this information to the RNC 109 which accordingly adjusts the offset of the transmit power offset between the DPDCH and the HS-DPCCH.

Specifically, the base station 103 comprises a quality processor 215 which determines a communication quality characteristic for the HS-DPCCH channel i.e. for the air interface channel that is power controlled by a simple transmit power offset to another air interface channel (in the specific example the DPDCH). * *. S. *

The quality processor 215 determines the communication quality characteristic from measurements of the transmissions which are received from the user equipment 101 in the HS-DPCCH. Specifically, the quality processor 215 determines an error rate for one or more of the messages which are transmitted on the HS-DPCCH.

The quality processor 215 is coupled to the RNC interface 209 which is arranged to transmit an indication of the communication quality characteristic to the RNC 109.

Specifically, for a UMTS cellular communication system, the RNC interface 209 is arranged to transmit an NBAB RL PARAMETER UPDATE INDICATION to the RNC 109 comprising the indication of the communication quality characteristic. The indication may for example be the communication quality characteristic itself, an coded representation of this or the result of an evaluation of the communication quality characteristic performed at the base station.

Thus, the indication of the communication quality characteristic is an indication of the performance of the HS-DPCCH and of the power control operation for this channel determined on the basis of signals received in this channel itself.

The indication can specifically be an error rate of some or all communication on the HS-DPCCH or can e.g. be a suggested a.". offset for the HS-DPCCH relative to the DPDCH.

*I....

* 20 The RNC 109 receives the indication of the communication quality characteristic from the base station 103 and is arranged to adjust the transmit power offset to be applied by the user equipment 101 between the DPCCH and the HS-DPCCH depending on this indication. The determined transmit power offset is then transmitted to the user equipment (via the base station 103).

FIG. 3 illustrates a simplified block diagram of the RNC 109 of FIG. 1.

As will be well known to the person skilled in the art, the RNC 109 can comprise functionality (not shown) for setting the SIR target for the inner power control loop of the base station 103 in response to characteristics of the DPDCH communication. This outer power control loop can improve the performance of the power control but does not address the problems associated with a fixed transmit power offset between the different air interface channels.

However, the RNC 109 further comprises functionality for adjusting the transmit power offset between the DPDCH and the HS-DPCCH channels depending on the indication of the communication quality characteristic received from the base station 103.

Specifically, the RNC 109 comprises a base station interface 301 which is coupled to the three base stations 103, 105 and 107. The base stations 103-107 receive signals from the user :.:::. equipment 101 transmitted both in the DPDCH and the HS-DPCCH channels. The demodulated and decoded signals are forwarded to the base station interface 301 of the RNC 109. II* * 20

The base station interface 301 is coupled to a quality indication processor 303 which is arranged to receive the indication of the communication quality characteristic from the first base station 103. In the specific example, the indication of the communication quality characteristic can be a BLock Error Rate for transmissions on the HS-DPCCH. In other embodiments, the indication of the communication quality characteristic can be a suggested power offset or power offset change for the HS-DPCCH as determined by the base station 103.

The quality indication processor 303 is coupled to a BLER comparator 305 which is furthermore coupled to a BLER target processor 307. The BLER target processor 307 determines a desired BLER value for the HS-DPCCH communication channel between the user equipment 101 and the base station 103. The BLER target processor 307 may in particular determine the desired BLER simply by providing a BLER target which has been received from an external source, such as an Operations and Management Centre (OMC). Thus, the BLER comparator 305 compares the BLER measure from the first base station 103 to the BLER reference from the BLER target processor 307 and generates an error signal. Specifically, the BLER comparator 305 may simply determine the error signal as the filtered difference between the BLER measure and the BLER reference.

As another example, the BLER comparator 305 may simple indicate the difference as a binary value indicating if the BLER is higher or lower than the BLER reference. S... * S S...

The BLER comparator 305 is coupled to a transmission * IS* S * * 20 parameter processor 309 which determines a transmit power offset for transmissions of signals from the user equipment in the HS-DPCCH and the DPDCH in response to the indication of the communication quality characteristic and in I,....

* particular in response to the error signal generated by the BLER comparator 305.

As a specific example, the transmission parameter processor 309 may simply determine if the BLER measure of the quality indication processor 303 is above or below the BLER reference. If the BLER measure is below the reference, a first transmit power offset is determined and if the BLER estimate is above the reference, a second transmit power offset is determined, where the second transmit power offset is higher than the first. For example, if the BLER measure for the HS-DPCCH is low (below the reference) a transmit power offset of, say, 6 dB may be used and if the BLER measure is high (above the reference) a much higher transmit power offset of, say, 10 dB may be used.

As another example, a given increment may be added to the current value of offset being used, e.g. +1dB, in the case that BLER is too high (or if BLER is too low a given decrement, e.g. -1dB may be added). This may be implemented using a single threshold value and the updates may for example be made periodically or could e.g. be event driven.

In some examples, there may be two thresholds in which case an increment could be made when the BLER is above the first threshold and a decrement made when the BLER is below the second threshold. a... a a...

* In some embodiments, the base station 103 may comprise *0.aSS * 20 functionality for evaluating the error rate of the HS-DPCCH and for determining a transmit power offset in response : thereto. For example, the base station 103 may comprise the functionality described with reference to the RNC 109 and may determine the specific suggested power offset by a similar process. This suggested power offset may then be transmitted to the RNC 109 and may be fed directly to the transmission parameter processor 309.

Thus, the trade-off between the reliability of the HS-DPCCH communication and the resource usage may be dynamically and effectively varied leading to reduced resource usage and/or improved reliability of the HS-DPCCH communication.

Furthermore, the transmit power for the HS-DPCCH transmissions are directly controlled by the performance of the HS-DPCCH rather than by the performance of another channel.

It will be appreciated that more complex algorithms may be used by the transmission parameter processor 309 to determine the transmit power offset. For example, the RNC 109 may use two or more thresholds and may determine e.g. a specific transmit offset for each threshold. As another example, the transmission parameter processor 309 may determine a transmit power offset as a mathematical function of the difference between the BLER measure and the BLER reference.

The transmission parameter processor 309 is coupled to a message processor 311 which is coupled to the base station *5S* S..',. interface 301. The message processor 311 receives the transmit power offset from the transmission parameter processor 309 and generates a reconfiguration message comprising an indication of the modified transmit power offset. Specifically for a UMTS communication system, the message processor 311 can generate an RRC PHYSICAL LAYER RECONFIGURATION message comprising the transmit power offset to be used for the HS-DPCCH channel.

The message processor 311 feeds the reconfiguration message to the base station interface 301 which transmits it to the base station 103. The base station 103 then transmits the reconfiguration message to the user equipment 101 over the air interface. When the reconfiguration message is received, the user equipment 101 proceeds to transmit on the HS-DPCCH using the prescribed transmit power offset. Thus, the user equipment 101 proceeds to determine the transmit power for the non-soft handover communication channel, the HS-DPCCH, in response to the power control operation of the soft handover communication channel, the DPDCH, while applying the modified transmit power offset to provide a desired margin.

Thus, the described embodiments may allow an efficient communication system which is compatible with the Technical Specifications for UMTS while allowing reduced resource usage and improved reliability of HSDPA communications.

It will be appreciated that different communication quality characteristics can be used in different embodiments. For example, the communication quality characteristic can comprise a plurality of error rates determined for individual message types communicated on the HS-DPCCH.

Specifically, a block error rate is determined for ACK messages, NACK messages and CQI messages. * *.

As a specific example of the operation of the base station 103, the quality processor 213 can include a low pass filtering by averaging error rates detected within an observation or averaging window. Within each averaging interval or observation window, all detected errors in decoding the CQI and ACK/NACK fields can be determined in the following way:

CQI field

The base station 103 knows when the user equipment 101 sends CQI information, which is encoded with a (20,5) linear code.

Accordingly, the quality processor 215 can detect and correct up to 3 errors in the code word. Thus, whenever a CQI message is expected the quality processor 213 determines: * A Decision: Estimated CQI sent by the user equipment 101: CQI(t1) * An Error count: Number of errors detected and corrected in the code word: Num Error CQI(t1)

ACK / NACK field

The base station 103 knows when the user equipment 101 sends ACK / NACK information, which is encoded as 10 times repetition of 1 bit (1 for ACK, 0 for NACK). Accordingly, the quality processor 215 can detect up to 4 errors in the code word. Thus, whenever an ACK/NACK message is expected the quality processor 213 determines: Iii.. *

* A Decision: Estimated ACK / NACK sent by the user equipment 101: ACKNACK(tI) ItS

V SS *1 S

* An Error count: Number of errors detected and corrected in the code word: o If estimated ACK: Num Error ACK(t1) o If estimated NACK: Num Error NACK(t1) At the end of the averaging interval, the quality processor 215 can calculate the estimated error probability for each

field as follows:

CQI field

-NumErrorCQl(t,) -2O*N, where: Ncç,j: Number of CQI transmissions expected during the observation window ACK reception Num -Error -AcK(t,) fl('K -where: NACK: Number of estimated ACK receptions during the observation window NACK reception Num -Error -NA (7K (t1) NA(K,. T IJiVfl(j< where: NNACK: Number of estimated NACK receptions during the . observation window I... S... * . * .*.

It will be appreciated that the above example used a simple * a S...

averaging window but that other low pass filtering functions can be applied including the use of a sliding window or an hR or FIR filter. * . S 4* S a

1.55*5 * The estimated error probabilities are in the specific example mapped into an estimated BLock Error Rate (BLER).

This can be performed by the quality processor 215 using a predetermined relationship between bit error rates and BLER5 for the given message type (e.g. determined by simulations).

For example, a look up table can be used.

In the embodiment of FIG. 3, the base station 103 communicates a communication quality characteristic in the form of a BLER indication for different message types to the RNC 109. This BLER is then compared to a threshold in the RNC 109. However, it will be appreciated that in other embodiments, the measured values can be evaluated in the base station 103 and the indication of the communication quality characteristic communicated to the RNC 109 can for example be a request for a specific change of the transmit power offset.

For example, in such an embodiment the quality processor 215 can comprise means for comparing the measured BLERs of the different message types to target values and for transmitting the result or a specific transmit power offset change request to the RNC 109.

For example, the following target values can be used: * ** * S S 58* ___________________ Measurement Target *SS*

BLER

CQI lOe-2 ACK lOe-2 NACK lOe-4 * 20 *55*55 * S In this example, the transmit power offset is increased towards increasing transmit power of the HS-DPCCH when BLER is above target value and towards decreasing power when the BLER is below target. The transmit power offset modification for the CQI, ACK and NACK messages can be determined by (e.g. in the base station 103 or the RNC 109) CQI: If BLERCQI > BLERTARGETCQI (1--) Then POCQI = CQI + 4STEPUP Else If BLERCQI < BLERTARGETCQI (l-E) Then POCQI = PO01 --1STEP DOWN Else Do not change P0c01 End If ACK: If BLERACK > BLER TARGETACK * (l+<) Then POACK = POACK + LISTEPUP Else If BLERACK < BLER TARGETACK (l-) Then POACK = PO/ICK --1STEP DOWN Else Do not change POACK End If *. 25 NACK: *ISS If BLERNACK > BLER TARGETWACK * Then S..

PONACK = NACK + LISTED VP * S 1.55 * Else If BLERNACK < BLER TARGETNACK (1 -ENACK) Then PONACK = PONACK -ASTEP DOWN : Else * Do not change NACK Ste*SS * * End If In the above examples, hysteresis isintroduced by the parameter which may be different for different message types. Specifically, for the above equations, the following parameters are used:

PARAMETER DESCRIPTION UNIT RANGE INITIAL

VALUE

MEASINTERV Measurement interval s [1. .60] 5 AL for evaluating new HS-DPCCH power offsets CQI Hysteresis value for Inte [1. .101 2 CQI BLER comparison ger CACK Hysteresis value for Inte [1. .101 2 ACK BLER comparison ger INACK Hysteresis value Inte [1. .10] 2 NACK BLER comparison ger A_STEP UP Power offset Inte [1. .8] 1 increase ger A STEP DOWN Power offset Inte [1. .8] 1 decrease ger BLER TARGET BLER target for CQI Floa [lOe-10. lOe-2

: .. CQI field t

5.lOe-1] * BLER TARGET BLER target for Floa [lOe-10. lOe-2

ACK ACK/NACK field when t

receiving ACK 5.lOe-1] : BLER TARGET BLER target for Floa [lOe-10. lOe-4

NACK ACK/NACK field when t

receiving NACK 5*lOe-1] An example of a specific operation that can be performed by the quality processor 215 is illustrated in FIG. 4. In this example, the base station 103 comprises the functionality for directly determining a suggested power offset for the HS-DPCCH channel which is then sent to the RNC 109.

When new transmit power offsets have been determined, the base station 103 can transmit the request to the RNC 109 in the NBAP RL PARAMETER UPDATE INDICATION message which specifically can comprise the values: POCQI, POACK and PONACK.

Upon reception at the RNC 109, the RNC 109 shall reconfigure the existing power offsets using the 3GPP radio link reconfiguration and physical channel reconfiguration procedures as indicated in FIG. 5.

It will be appreciated that significant advantages can be obtained by considering the different message types individually and in particular by considering the operation of ACK and NACK messages individually. In particular, the impact of a wrongly detected ACK message (resulting in loss of data packet) is substantially more significant than a S...

wrongly detected NACK message (resulting in retransmission * SSS by higher layers) and therefore the error rate is typically selected very differently. By adjusting the transmit power offset if unacceptable performance is determined for either of these messages, it can be ensured that both message types are received with sufficient reliability.

*.SSSS * S In some embodiments, the low pass filtering of measurements is reset whenever a change in the handover state of the user equipment occurs. This may allow a fast adaptation of the suitable transmit power offset between the HS-DPCCH and the DPDCH in critical situations. Specifically, when the DPCCH switches from one soft handover configuration (say supported by two legs/base stations) to another (say supported by three leg/base stations), the optimal transmit power of the user equipment 101 for the DPCCH changes while the HS-DPCCH (which is a non-soft handover channel) remains unchanged.

Accordingly, by resetting the filtering, the impact of the previous configuration on the current transmit power setting is reduced. The resetting can for example be achieved by initiating a new averaging window.

It will be appreciated that the above description for clarity has described embodiments of the invention with reference to different functional units and processors.

However, it will be apparent that any suitable distribution of functionality between different functional units or processors may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Hence, references to specific functional units are only to be seen 4*S* as references to suitable means for providing the described I...

functionality rather than indicative of a strict logical or physical structure or organization.

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of *.Ss..

* these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a : single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also the inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate. Furthermore, the order of features in the claims does not imply any specific order in which the features must be worked and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order.

Claims

CLAIMS

1. A cellular communication system comprising a radio network controller comprising power offset means for determining a transmit power offset for transmissions from a user equipment to a base station in a first air interface channel relative to transmissions from the user equipment to the base station in a second air interface channel, and first transmitting means for transmitting an indication of the transmit power offset to the user equipment; and the base station comprising means for receiving transmissions from the user equipment in the first air interface channel, and quality means for determining a communication * quality characteristic for the first air interface channel in response to measurements of the transmissions from the user equipment in the first air interface channel, and second transmitting means for transmitting an indication of the communication quality *1S**.

* characteristic to the radio network controller; and wherein the power offset means is arranged to determine the transmit power offset in response to the indication of the communication quality characteristic received from the base station.

2. The cellular communication system of claim 1 wherein the communication quality characteristic is an error rate.

3. The cellular communication system of claim 1 or 2 wherein the indication of the communication quality characteristic is a Block Error Rate for the transmissions from the user equipment and the quality means are arranged to associate an error rate of the transmissions to a Block Error Rate in accordance with a predetermined relationship.

4. The cellular communication system of any previous claim wherein the quality means is arranged to determine the communication quality characteristic by low pass filtering quality measurements for a plurality of transmissions received from the user equipment.

5. The cellular communication system of claim 4 wherein the quality means is arranged to reset the low pass filter : * in response to a detection of a change in handover state of the user equipment.

6. The cellular communication system of any previous claim wherein the communication quality characteristic is for retransmission feedback messages for the first air interface channel.

* **S.* 7. The cellular communication system of claim 6 wherein the communication quality characteristic comprises separate quality indications for positive and negative retransmission feedback messages.

8. The cellular communication system of any previous claim wherein the indication of the communication quality characteristic comprises a quality indication for a plurality of message types and the power offset means is arranged to adjust the transmit power offset to increase the transmit power for the first air interface channel relative to the transmit power for the second air interface channel if the quality indication for at least one of the plurality of message types is indicative of a quality below a threshold.

9. The cellular communication system of any previous claim wherein the first air interface channel is a non-soft handover channel and the second air interface channel is a soft handover channel.

10. The cellular communication system claimed in any previous claim comprising means for comparing the ::. communication quality characteristic to a first threshold and wherein the transmit power offset is modified by a first predetermined step if the communication quality characteristic is above the threshold.

11. The cellular communication system claimed in claim 10 wherein the means for comparing is arranged to compare the * 1 communication channel characteristic to a second threshold and wherein the transmit power offset is modified by a second predetermined step if the communication characteristic is below the threshold, the first and second predetermined steps having opposite signs.

12. The cellular communication system claimed in any previous claim wherein the cellular communication system is a 3rd Generation cellular communication system.

13. The cellular communication system claimed in claim 12 wherein the first air interface channel is a High Speed Downhjnk Packet Access (HSDPA) communication channel.

14. The cellular communication system claimed in claim 13 wherein the first air interface channel is a High Speed-Dedicated Physical Control CHannel (HS-DPCCH) channel.

15. The cellular communication system claimed in any of the claims 12 to 14 wherein the second air interface channel is a Dedicated Physical Data CHannel (DPDCH) channel.

16. The cellular communication system claimed in any of the claims 12 to 15 wherein the first transmitting means is arranged to transmit the indication of the transmit power *, 20 offset in an RRC PHYSICAL LAYER RECONFIGURATION message.

* .. * 17. The cellular communication system claimed in any of the claims 12 to 16 wherein the second transmitting means is arranged to transmit the indication of the communication * 25 quality characteristic in an NBAB RL PARAMETER UPDATE I **eI* * INDICATION.

18. A method of power control in a cellular communication system, the method comprising at a radio network controller performing the steps of: determining a transmit power offset for transmissions from a user equipment to a base station in a first air interface channel relative to transmissions from the user equipment to the base station in a second air interface channel, and transmitting an indication of the transmit power offset to the user equipment; and at the base station performing the steps of: receiving transmissions from the user equipment in the first air interface channel, and determining a communication quality characteristic for the first air interface channel in response to measurements of the transmissions from the user equipment in the first air interface channel, and transmitting an indication of the communication quality characteristic to the radio network controller; and wherein the transmit power offset is determined in response to the indication of the communication quality characteristic received from the base station. *SS * * S

S

Amendments to the claims have been filed as follows 1. A cellular communication system comprising a radio network controller comprising power offset means for determining a transmit power offset for transmissions from a user equipment to a base station in a first air interface channel relative to transmissions from the user equipment to the base station in a second air interface channel, and first transmitting means for transmitting an indication of the transmit power offset to the user equipment; and the base station comprising means for receiving transmissions from the user equipment in the first air interface channel, and quality means for determining a communication quality characteristic for the first air interface channel in response to measurements of the transmissions from the user equipment in the first air interface channel, wherein the communication quality characteristic comprises a quality indication for at least one of a plurality of message types; and second transmitting means for transmitting an indication of the communication quality characteristic to the radio network controller; and wherein the power offset means is arranged to determine the transmit power offset to adjust the transmit power for the first air interface channel relative to the transmit power for the second air interface channel in response to the indication of the communication quality characteristic received from the base station for at least one of the plurality of message types in relation to a threshold.

2. The cellular communication system of claim 1 wherein the communication quality characteristic is an error rate.

3. The cellular communication system of claim 1 or 2 wherein the indication of the communication quality characteristic is a Block Error Rate for the transmissions from the user equipment and the quality means are arranged to associate an error rate of the transmissions to a Block Error Rate in accordance with a predetermined relationship.

4. The cellular communication system of any previous claim wherein the quality means is arranged to determine the communication quality characteristic by low pass filtering quality measurements for a plurality of transmissions received from the user equipment.

5. The cellular communication system of claim 4 wherein the quality means is arranged to reset the low pass filter in response to a detection of a change in handover state of the user equipment.

6. The cellular communication system of any previous claim wherein the communication quality characteristic is for retransmission feedback messages for the first air interface channel.

7. The cellular communication system of claim 6 wherein the communication quality characteristic comprises separate quality indications for positive and negative retransmission feedback messages.

8. The cellular communication system of any previous claim wherein the first air interface channel is a non-soft handover channel and the second air interface channel is a soft handover channel.

9. The cellular communication system claimed in any previous claim comprising means for comparing the communication quality characteristic to a first threshold and wherein the transmit power offset is modified by a first predetermined step if the communication quality characteristic is above the threshold.

10. The cellular communication system claimed in claim 9 wherein the means for comparing is arranged to compare the communication channel characteristic to a second threshold and wherein the transmit power offset is modified by a second predetermined step if the communication characteristic is below the threshold, the first and second predetermined steps having opposite signs.

11. The cellular communication system of claim 10 wherein the first and second predetermined steps have the same magnitude.

12. The cellular communication system claimed in any previous claim wherein the cellular communication system is a 3rd Generation cellular communication system.

13. The cellular communication system claimed in claim 12 wherein the first air interface channel is a High Speed Downlink Packet Access (HSDPA) communication channel.

14. The cellular communication system claimed in claim 13 wherein the first air interface channel is a High Speed-Dedicated Physical Control CHannel (HS-DPCCH) channel.

15. The cellular communication system claimed in any of the claims 12 to 14 wherein the second air interface channel is a Dedicated Physical Data CHannel (DPDCH) channel.

16. The cellular communication system claimed in any of the claims 12 to 15 wherein the first transmitting means is arranged to transmit the indication of the transmit power offset in an RRC PHYSICAL LAYER RECONFIGURATION message.

17. The cellular communication system claimed in any of the claims 12 to 16 wherein the second transmitting means is arranged to transmit the indication of the communication quality characteristic in an NEAB RL PARAMETER UPDATE INDICATION.

18. A method of power control in a cellular communication system, the method comprising at a radio network controller performing the steps of: determining a transmit power offset for transmissions from a user equipment to a base station in a first air interface channel relative to transmissions from the user equipment to the base station in a second air interface channel, and transmitting an indication of the transmit power offset to the user equipment; and at the base station performing the steps of: receiving transmissions from the user equipment in the first air interface channel, and determining a communication quality characteristic for the first air interface channel in response to measurements of the transmissions from the user equipment in the first air interface channel, wherein the communication quality characteristic comprises a quality indication for at least one of a plurality of message types; and transmitting an indication of the communication quality characteristic to the radio network controller; and wherein the transmit power offset to adjust the transmit power for the first air interface channel relative to the transmit power for the second air interface channel in response to the indication of the communication quality characteristic received from the base station for at least one of the plurality of message types in relation to a threshold.