GB2395398A

GB2395398A - A communication unit and method of communicating measurement reports therefor

Info

Publication number: GB2395398A
Application number: GB0225979A
Authority: GB
Inventors: Peter Jonathon Legg
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2002-11-07
Filing date: 2002-11-07
Publication date: 2004-05-19
Anticipated expiration: 2022-11-07
Also published as: GB0225979D0; EP1563703A1; GB2395398B; WO2004043101A1; AU2003283440A1; CN100553376C; CN1711795A

Abstract

A base station (101) comprises a measurement processor (117) determining physical layer measurement characteristics, such as a filtered transmit power, in response to an air interface physical layer parameter, such as the unfiltered transmit power, associated with a subscriber unit (103). It further comprises a communication element (119) for communicating measurement reports to a network element (109), such as an RNC. Further, the base station (101) comprises an update processor (121) for dynamically updating an interval between measurement reports in response to an operating characteristic of the cellular communication system. The interval may be updated by changing a measurement report frequency depending on the number of subscriber units supported, the duration they have been supported and the available resource. The interval may also be updated by a new measurement report only being generated when the physical layer measurement characteristic differs from the last reported physical layer measurement characteristic by more than a threshold.

Description

A COMMUNICATION UNIT AND METHOD OF COMMUNICATING

MEASUREMENT REPORTS THEREFOR

5 Field of the invention

The invention relates to a communication unit and method of communicating measurement reports therefor and in particular to a system of communicating measurements in a cellular communication l0 system. Background of the Invention

15 FIG. 1 illustrates the principle of a conventional cellular communication system 100 in accordance with prior art. A geographical region is divided

into a number of cells 101, 103, 105, 107 each of which is served by base station 109, 111, 113, 115. The base stations are interconnected by a fixed network which can communicate data between the base stations 101, 103, 20 105, 107. A mobile station is served via a radio communication link by the base station of the cell within which the mobile station is situated. In the example if FIG. 1, mobile station 117 is served by base station 109 over radio link 119, mobile station 121 is served by base station 111 over radio link 123 and so on.

As a mobile station moves, it may move from the coverage of one base station to the coverage of another, i.e. from one cell to another. For example mobile station 125 is initially served by base station 113 over radio link 127. As it moves towards base station 115 it enters a region of 30 overlapping coverage of the two base stations 111 and 113 and within this overlap region it changes to be supported by base station 115 over radio link 129. As the mobile station 125 moves further into cell 107, it i

continues to be supported by base station 115. This is known as a handover or handoff of a mobile station between cells.

A typical cellular communication system extends coverage over typically 5 an entire country and comprises hundred 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 uplink, and communication from a base station to a mobile station is known as 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 15 networks such as 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 20 routing data, admission control, resource allocation, subscriber billing, mobile station authentication etc. Currently the most ubiquitous cellular communication system is the 2nd generation communication system known as the Global System for Mobile 25 communication (GSM). GSM uses a technology known 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. A base station may be allocated a single carrier or a multiple of carriers. One carrier is used for a pilot signal which further 30 contains broadcast information. This carrier is used by mobile stations for measuring of the signal level of transmissions from different base stations, and the obtained information is used for determining a suitable serving

cell during initial access or handovers. Further description of the GSM

TDMA communication system can be found in 'The GSM System for Mobile Communications' by Michel Mouly and Marie Bernadette Pautet, Bay Foreign Language Books, 1992, ISBN 2950719007.

Presently, 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) wherein user separation is obtained by allocating lO different spreading and scrambling codes to different users on the same carrier frequency. The transmissions are spread by multiplication with the allocated codes thereby causing the signal to be spread over a wide bandwidth. At the receiver, the codes are used to de-spread the received signal thereby regenerating the original signal. Each base station has a 15 code dedicated for a pilot and broadcast signal, and as for GSM this is used for measurements of multiple cells in order to determine a serving cell. An example of a communication system using this principle is the Universal Mobile Telecommunication System (UMTS), which is currently being deployed. Further description of CDMA and specifically of the

20 Wideband CDMA (WCDMA) mode of UMTS can be found in 'WCDMA for UMTS', Harri Holma (editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876.

In a UMTS CDMA communication system, the fixed network comprises a 25 core network and a Radio Access Network (RAN). The core network is operable to route 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 support wireless user 30 equipment over a radio link being part of the air interface. The RAN of a UMTS cellular communication network comprises the base stations, known as Node Bs, as well as Radio Network Controllers (RNCs). 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 Node Bs. It further provides the interface between the RAN and the core network. An RNC and associated Node Bs is known as a 5 Radio Network System (RNS).

Common for all types of cellular communication systems is that it is imperative to manage the radio links between the base stations such that the resource used by a given communication link is as low as possible.

10 Thus, it is 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. Furthermore, it is important that resource allocation is optimised as far as possible in order to maximise the communication capacity of the communication system.

15 Specifically, for packet communication, it is important that packets are scheduled such that the capacity of the communication system may be optimised and the required quality of service parameters may be achieved.

In a UMTS communication system, significant amounts of the air 20 interface management is performed in the RNC. For example, traffic schedulers for packet communication are implemented in the RNCs. In order for these air interface management functions to be effectively performed in the RNC, it is important that the RNC receives information of various current air interface characteristics and parameters. For 25 example, in order to perform an efficient scheduling, the scheduler typically requires information related to the expected transmit power and thus interference caused for data packets for different users. Accordingly, the Node Bs need to communicate substantial amounts of information related to the air interface to the Node B. and in particular to 30 communicate substantial amounts of measurement information.

Accordingly, the UMTS specifications provide for measurement messages

to be reported between a Node B and an RNC at a given frequency.

However, for higher reporting frequencies the computational resource requirements in generating and processing the measurement reports 5 increases. In addition, the communication load on the communication link between the Node B and the RNC increases and the communication capacity of the link may therefore be exceeded. However, for lower reporting frequencies, the probability of the measurements being inaccurate for the current conditions increases. Especially for a slow 10 moving mobile, an initial measurement report may not be representative of the typical or average conditions, but may represent a specific fade condition that is not typical for the mobile station.

The measurement reporting in a cellular communication system is thus 15 subject to a number of disadvantages. Hence, a system allowing for improved measurement reporting would be an advantage.

Summary of the Invention

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

25 Specifically, the Inventor has realised that the current approach for measurement reporting in a cellular communication system is suboptimal and can be improved. In particular, the inventor has realised that improved measurement reporting can be achieved by dynamically changing the parameters or characteristics of the measurement reporting.

According to a first aspect of the invention, there is provided a method of communicating measurement reports in a cellular communication system

having a fixed network supporting remote communication units; the method comprising the steps of: in a first communication unit determining physical layer measurement characteristics in response to an air interface physical layer parameter associated with a remote communication unit; 5 communicating measurement reports comprising the physical layer measurement characteristics from the first communication unit to a network element; further comprising the step of: dynamically updating an interval between measurement reports in response to an operating characteristic of the cellular communication system.

The invention allows for the measurement reporting from the first communication unit to the network element to be optimised to suit the current operating characteristics of the cellular communication system.

The measurement reporting may specifically be dynamically updated to 15 allow for an efficient trade off between the adverse effects of a specific reporting frequency. For example, the interval may be updated to provide for a suitable trade off between the communication and computational resource required, and the measurement reporting accuracy. For example, if there is sufficient communication and computational resource available, 20 a short interval may be set to improve the accuracy of the measurement reporting. If the available communication or computational resource decreases, the interval may be extended in return for a degraded accuracy.

Hence, the invention allows for improved measurement reporting in a 25 cellular communication system, and may specifically provide for increased flexibility, accuracy and reduced communication or computational resource usage. The first communication unit may specifically be a base station, such as a Node B. The network element may for example be a radio equipment controller, such as an RNC. The remote communication 30 unit may specifically be a subscriber unit, such as a wireless user equipment, a mobile station, a communication terminal, a personal digital

assistant, a laptop computer, an embedded communication processor or any other communication element communicating over the air interface.

According to a feature of the invention, the operating characteristic 5 comprises a number of remote communication units that are supported by the first communication unit. Preferably, the interval between measurement reports is dynamically updated in response to how many remote communication units are supported by the first communication unit. The computational and communication resource of the first 10 communication unit typically increases for increasing numbers of remote communication units being supported. Updating the interval in response thereto allows for adjusting the measurement reporting to suit the current resource requirements and availability.

15 According to another feature of the invention, the operating characteristic comprises a number of remote communication units that are supported by the network element. Preferably, the interval between measurement reports is dynamically updated in response to how many remote communication units are supported by the network element. The 20 computational and communication resource of the network element typically increases for increasing numbers of remote communication units being supported by the network element. Updating the interval in response thereto allows for adjusting the measurement reporting to suit the current resource requirements and availability.

According to another feature of the invention, the operating characteristic comprises a duration that the remote communication unit has been supported by the first communication unit. Specifically, the interval may be increased for an increasing duration. The accuracy of physical layer 30 measurement characteristics tend to increase the longer a remote communication unit has been supported by a given first communication unit. Specifically the accuracy may increase as the time available for

averaging of measurements increases. Updating the interval in response thereto allows for adjusting the measurement reporting to suit the current measurement accuracies.

5 According to another feature of the invention, the operating characteristic comprises a difference between a physical layer measurement characteristic of a first measurement report and a physical layer measurement characteristic of a second measurement report. For example, the interval may be set to correspond to a time taken until the physical 10 layer measurement characteristic has changed by a given value.

Specifically, if the physical layer measurement characteristic for example relates to a transmit power, the interval may be updated by the second measurement report being transmitted when the transmit power has changed by more than a given amount. This allows for the measurement 15 reporting to be adapted to the dynamic variation of the physical layer measurement characteristics.

According to another feature of the invention, the operating characteristic comprises an available communication capacity of a connection between 20 the first communication unit and the network element. This allows for the available communication capacity to be efficiently used yet reduces the probability of it being exceeded.

According to another feature of the invention, the measurement reports 25 are communicated substantially periodically and the interval between measurement reports is updated by modifying the frequency of the measurement reports. This allows for a suitable, effective and easy way to implement the updating of the interval between measurement reports.

30 According to another feature of the invention, a measurement report is communicated when a first value of the physical layer measurement characteristic differs from a reported value of the physical layer

measurement characteristic in a previous measurement report by more than a threshold. Preferably, the threshold relates to an increased and/or decreased value of the physical layer measurement characteristic. This allows for measurement reports to be communicated only when significant 5 changes to the measured parameters have occurred. A new measurement report may specifically be communicated when the physical layer measurement characteristic reaches a value given as a threshold difference from a previously reported physical layer measurement characteristic. Preferably, the threshold is determined in response to a previous physical layer measurement characteristic, and specifically the previous physical layer measurement characteristic may be comprised in a previous measurement report. Specifically, the threshold value may be dependent 15 on a previous measurement value or reported physical layer measurement characteristic. In particular, the threshold may be a relative value of a previous reported physical layer measurement characteristic, such as for example 10% of the previously reported physical layer measurement characteristic. This may allow for the measurement reporting to be 20 adapted to the currently prevailing operating conditions and specifically to the currently prevailing measurement values.

According to another feature of the invention, the network element comprises a resource allocator. An efficient measurement reporting 25 adapted to the current conditions may thus be provided to a network element for use in resource allocation, thereby enabling an improved resource allocation and thus the possibility of an increased capacity and/or quality of service for the communication system.

30 According to another feature of the invention, the network element comprises a traffic scheduler. An efficient measurement reporting adapted

to the current conditions may thus be provided to a network element for use in traffic scheduling, thereby enabling an improved traffic scheduling.

According to another feature of the invention, the physical layer 5 measurement characteristic is a power measurement characteristic, and the air interface physical layer parameter is a transmit power associated with the remote communication unit. Preferably, the transmit power associated with the remote communication unit is a transmit power of the first communication unit when transmitting to the remote communication 10 unit. The measurement reporting of a transmit power associated with the remote communication unit may thus be adapted to the current operating conditions, thereby allowing an improved measurement reporting, and thus the possibility of improved accuracy. This may for example assist a resource allocation or traffic scheduling and thus allows for improved IS performance of the communication system.

According to a second aspect of the invention, there is provided a communication unit for a cellular communication system having a fixed network supporting remote communication units; the communication unit 20 comprising: a measurement processor for determining physical layer measurement characteristics in response to an air interface physical layer parameter associated with a remote communication unit; a communication element for communicating measurement reports comprising the physical layer measurement characteristics to a network element; and an update 25 processor for dynamically updating an interval between measurement reports in response to an operating characteristic of the cellular communication system.

According to another feature of the invention, the communication unit 30 further comprises: a measurement unit for performing power measurements; a filter for generating filtered power measurements from the power measurements at a first rate; and wherein the measurement

processor is operable to generate the physical layer measurement characteristics from the filtered power measurements substantially at the first rate; and the communication element is operable to update the interval between measurement reports by not communicating some power 5 measurement characteristics to the network element.

Brief Description of the Drawings

10 An embodiment of the invention will be described, by way of example only, with reference to the drawings, in which FIG.lis an illustration of a cellular communication system in accordance with the prior art;

FIG.2is an illustration of a UMTS communication system comprising a base station in accordance with an embodiment of the invention; FIG.3 illustrates an example of a measurement processor in accordance 20 with an embodiment of the invention; FIG.4is an illustration of an example of a physical layer characteristic variation as a function of time, and of the resulting filtered and measured values; FIG.5is an illustration of a method of communicating measurement reports in accordance with an embodiment of the invention; FIG.6 illustrates an example of a dynamically updated measurement 30 reporting of a physical layer characteristic in accordance with an embodiment of the invention; and

FIG. 7 illustrates an example of a dynamically updated measurement reporting of a physical layer characteristic in accordance with an embodiment of the invention.

Detailed Description of a Preferred Embodiment of the Invention

The following description focuses on an embodiment for a UMTS

communication system but it will be apparent that the invention is not lO limited to this application but may be applicable to many other cellular communication systems.

FIG. 2 is an illustration of a UMTS communication system 100 comprising a base station 101 in accordance with an embodiment of the invention. In 15 the shown example, the base station 101 is supporting 3 different remote communication units, which specifically are subscriber units 103, 105.

Communication between the subscriber units 103, 105 and the base station 101 are by means of communication links 107 over the air interface. The base station 101 is connected to a Radio Network Controller 20 (RNC) 109. In addition other base stations 111 are connected to the RNC 109. The RNC 109 performs a number of radio and air interface management functions for the base stations 101, 111 including resource allocation, 25 traffic scheduling, quality of service management and handover management. Many of these functions are based on air interface parameters that can only be determined at the base stations 109, 111 or subscriber units 103, 105. Accordingly, the base stations 101, 111 and/or subscriber units 103, 105 perform a number of measurements of 30 characteristics related to the physical layer of the air interface. These measurements may include determination of internal parameters such as the transmit power used to communicate with a specific subscriber unit or

base station. Alternatively or additionally, the measurements may include measurements of external parameters, and specifically of parameters associated with the radio environment such as an interference level.

5 The base station 101 is connected to the RNC 109 by a fixed line communication link, 113. The interface between an RNC and a base station is in UMTS known as the tub interface.

The RNC 109 is connected to a Mobile Switching Centre (MSC) 115. In a lO typical UMTS cellular communication system, a large number of RNCs are connected to an MSC. The MSC is a central switch centre that switches communication between different RNCs such that subscriber units connected to one RNC can communicate with subscriber units associated with another RNC. In addition, the MSC is responsible for interfacing 15 with other networks, performing authentication, some mobility management etc. In a typical UMTS communication system, the RNC 109 is typically also connected to one or more Serving GPRS Service Nodes (SGSN) which are 20 operable to route packet data towards the packet destination.

In the preferred embodiment, the RNC 109 specifically comprises a resource allocator that allocates available radio resource between different services and subscriber units. The resource allocation is partially based on 25 the physical layer measurement characteristics received from the base station. Alternatively or additionally, the RNC 109 comprises a traffic scheduler that schedules packet transmissions to the different subscriber units. In order to effectively schedule packet transmissions, the radio conditions for different subscriber units must be taken into account, and 30 thus the scheduling is performed in response to the physical layer measurement characteristics received from the base stations. Specifically, the transmit power of a base station may in many cases be a limiting

factor for resource allocation and scheduling. Accordingly, the physical layer measurement characteristics received from the base station comprise an indication of an expected transmit power for communicating with a specific subscriber unit. The resource allocation and scheduling is thus 5 performed such that the combined expected transmit powers for a base station is below the maximum available.

The base station 101 comprises a measurement processor 117. The measurement processor 117 determines physical layer measurement 10 characteristics associated with at least one air interface physical layer parameter. The physical layer parameter is associated with a remote communication unit. In the preferred embodiment, the physical layer parameter is a transmit power used or required by the base station 101 to communicate with a specific subscriber unit 103. The transmit power is l 5 controlled by a power control loop to meet a given quality of service level (and specifically the power control loop controls the transmit power to provide a given signal to interference ratio). The transmit power is measured from the parameter values and/or settings generated by the power control loop. In the preferred embodiment, the physical layer 20 measurement characteristic specifically corresponds to a filtered version of the physical layer parameter measurements.

The base station 101 further comprises a communication element 119 for communicating measurement reports comprising the physical layer 25 measurement characteristics to a network element of the fixed network, which in the example of FIG. 2 specifically is the RNC 109.

FIG. 3 illustrates an example of a measurement processor 117 in accordance with an embodiment of the invention. The measurement 30 processor 117 comprises a first filter 301 which receives measurements related to the physical layer. Specifically, the measurements may be a measurement of a transmit power as controlled by the power control loop.

The measurements may be received from any suitable source including internal measurements in the base station, or measurements received over the air interface from a subscriber unit. The measurements may relate to internal parameters or external parameters.

In the preferred embodiment, the base station 101 further comprises a measurement unit (not shown) which performs power measurements, and in particular by deriving a transmit power estimate from the status of the power control loop. The power measurements are provided to the first lO filter 301 at any suitable rate. The first filter 301 generates filtered power values, which for a typical UMTS base station are fed to a second filter 303. The second filter 303 provides further filtering of the power measurements in accordance with a set of parameters received from an input 305. Hence, the second filter 303 generates filtered power 15 measurements from the power measurements. The power measurements are provided periodically at a given frequency. In a conventional base station, the frequency may be set to a value between 10Hz and 1 Hz but is maintained constant once set.

20 The second filter 303 is connected to a measurement report generator 307.

The filtered power measurements are fed to the measurement report generator 307, which includes the power measurements in a measurement report. The measurement report is then fed to the communication element 119 for transmission to the RNC 109. The measurement report generator 25 307 may receive further measurement values through a second measurement input 311. The measurement reports are generated in response to a number of pre-selected parameters, which are received through a parameter input 309. In a conventional UMTS base station, the measurement reports are communicated at a constant frequency. The 30 constant measurement reporting frequency may be set to be between lHz and 10 Hz.

FIG. 4 is an illustration of an example of a physical layer characteristic variation as a function of time and of the resulting filtered and measured values. FIG. 4 shows a measurement reporting typical for a conventional UMTS base station. FIG. 4 illustrates a specific example of a variation of 5 transmit power as a function of time 401. Additionally, the filtered transmit power value 403 is shown as a function of time. The example shown corresponds to a measurement process performed at the start of atransmission and thus reflects the initial variations of the transmit power value and the filtered power values. The transmit power varies lO substantially and is initially relatively low corresponding to favourable propagation conditions. The transmit power consequently increases as the subscriber unit enters a fade and the transmit power continues to vary according to the changes in the propagation and interference conditions.

The filtered transmit power value 403 is initially substantially identical to 15 the transmit power, but moves towards an average value as the time over which the averaging may be performed increases.

FIG. 4 further illustrates the transmit power values reported at a reporting rate of 10Hz 405 and a reporting rate of lHz 407 20 respectively. In the example, power measurements begin when the path loss is small (anti-fade), so the first measurement report 405, 407 after lOOms is much lower than the typical or average transmit power value. As such, the measurement is not representative of the expected transmit power, and the use of this reported measurement value is 25 likely to result in suboptimal performance of for example a resource allocator or traffic scheduler in the RNC 109. For the maximum reporting rate of 10 Hz, the reported power measurement values 405 quickly tend towards the average or typical value, reflecting the convergence in the second filter 303. However, for the 1 Hz reporting 30 rate, a new measurement report is not received until 1 second after the first measurement report. During this interval, any functionality in the RNC 109 relies on the unrepresentative value of the first

measurement report. This will cause significant degradation in the performance of, for example, a traffic scheduler. After the second measurement report, the measurement value should be representative and equal performance can be expected for the two measurement rates 5 thereafter.

Hence, a low frequency measurement reporting provides reduced performance in the RNC 109. However, a higher reporting rate provides an excessive burden on the communication capacity of the lO communication link 113 between the base station 101 and the RNC 109 (the Iub interface). It further requires excessive computational resource in the base station 101 in order to generate the measurement reports and in the RNC 109 in order to process the measurement reports. In the preferred embodiment, the base station 101 further comprises an update processor 121. The update processor 121 is connected to the measurement processor 117 and is operable to dynamically update an interval between measurement reports in response to an operating 20 characteristic of the cellular communication system.

FIG. 5 is an illustration of a method of communicating measurement reports in accordance with an embodiment of the invention. The method is applicable to the base station 101 of FIG. 2 and will be 25 described with reference to this.

In step 501, physical layer measurement characteristics are determined in response to an air interface physical layer parameter associated with a remote communication unit. In the preferred embodiment, the 30 measurement processor generates the physical layer measurement characteristics from a filtering of transmit power measurements. In step 503, the update processor 121 determines a suitable interval between

measurement reports. In step 505, the measurement report is generated at the appropriate time as determined by the update processor.

Specifically, the update processor may update the interval by detecting the occurrence of a specific event or condition and trigger a measurement 5 report generation in response. In step 507, the measurement report comprising the physical layer measurement characteristics is transmitted to the RNC 109 by the communication element 119.

The interval between measurement reports may be updated in any lO suitable way. In the preferred embodiment, the interval is controlled by transmitting the measurements substantially periodically but at a dynamically updated frequency. For example, a first reporting frequency may be used in an initial time interval after which a second and slower frequency rate may be used. FIG. 6 illustrates an example of a 15 dynamically updated measurement reporting of a physical layer characteristic in accordance with an embodiment of the invention. FIG. 6 illustrates the same transmit power variation 401 and filtered transmit power variation 403 as FIG. 4.

20 In this example, measurement reports are initially generated at a higher rate. Thus, as shown in FIG. 6, measurement reports 601 are generated at a rate of 10Hz, i.e. with a measurement report interval of 100ms. After the initial 500 ms, it is assumed that the filter output has converged reasonably towards the typical value (as is the case in the example shown 25 in FIG. 6). Accordingly, the measurement reporting changes to a lower frequency. In the example of FIG. 6, this frequency corresponds to a measurement report interval of 600ms and the next measurement report 603 is generated 1 second after the first measurement. The measurement reports may after this be reported at a lower rate and specifically may be 30 reported at the lowest possible rate, which for a UMTS node B is lHz.

l Hence, this approach allows for the measurement reporting to be high during the initial period, when the measurements reported are likely to be inaccurate and changing substantially, and to be low following the initial period thus reducing the communication and computational resource 5 burden.

The interval between measurement reports may be updated in response to any suitable operating characteristic of the cellular communication system. In one embodiment, the operating characteristic comprises a number of remote communication units that are supported by the first communication unit. In the preferred embodiment, the interval is set in response to the number of subscriber units for which the base station is 15 the serving base station. The more subscriber units that are served by a given base station, the more measurement reports need to be generated by the base station and thus communicated to the RNC. As both the computational and communication resource is typically substantially constant, a lower number of supported subscriber units allows for more 20 communication and computational resource to be available for each, thereby allowing for an increased frequency of measurement reports for each subscriber unit. In the preferred embodiment, the interval between measurement reports is therefore increased for increasing numbers of subscriber units supported by that base station. Specifically, the number 25 of subscriber units supported by a base station may in the preferred embodiment be determined as the number of subscriber units that are allocated a dedicated control channel.

Alternatively or additionally, the operating characteristic may comprise a 30 number of remote communication units that are supported by the network element. As for the base station, the resource requirements of the network element typically increase for an increasing number of measurement

reports. Accordingly, the interval between measurement reports may preferably be increased for increasing an number of remote communication units supported. In the preferred embodiment, the network element, in the form of an RNC, may determine how many 5 subscriber units are supported by the base stations served by the RNC, and the available resource for measurement reporting for each base station may be determined. This value may be reported to the base stations, which may then individually adjust the measurement report intervals for each subscriber unit, such that the total allocated number of 10 measurement reports is not exceeded.

Alternatively or additionally, the operating characteristic may comprise a duration that the remote communication unit has been supported by the first communication unit. For example, as described previously a high 15 measurement report frequency may be set for an initial interval and a lower measurement report frequency may be set for subsequent intervals.

This effectively allocates the measurement report resource to subscriber units for which the measurement values may not have converged substantially, and thus may vary significantly in shorter time intervals. In 20 the preferred embodiment, the base station may specifically detect for how long a subscriber unit has been allocated a dedicated control channel and set the measurement reporting frequency in response to this.

Alternatively or additionally, the operating characteristic comprises a 25 difference between a physical layer measurement characteristic of a first measurement report, and a physical layer measurement characteristic of a second measurement report. Specifically, the measurement report interval or frequency may be set in response to the difference between the measurement values of subsequent measurement reports. For example, 30 the difference between two measurement values of subsequent measurement reports may be detected, and the interval to the next measurement report may be increased for lower differences. In another

embodiment, a measurement report frequency may dynamically and continuously be updated in response to the difference between measurement values of the measurement reports. In particular, this approach may be used to detect that the measurement report values are 5 converging towards a steady value, such that the measurement report frequency can be increased.

Alternatively or additionally, the operating characteristic may comprise an available communication capacity of a connection between the first 10 communication unit and the network element. In the preferred embodiment, the interval may further be set in response to the spare capacity of the communication link 113 between the base station 101 and the RNC 109. Hence, the measurement report frequency may be increased when communication capacity is available and reduced when the 15 maximum capacity is approached.

In one embodiment, the interval is updated by communicating a new measurement only when a specific condition occurs. Specifically, a new measurement report is communicated when a first value of the physical 20 layer measurement characteristic differs from a reported value of the physical layer measurement characteristic in a previous measurement report by more than a threshold. In the embodiment, the physical layer parameter, such as the transmit power, is continuously monitored, and when it deviates from the last reported measurement by a given amount, a 25 new measurement is generated and communicated. Specifically, the physical layer measurement characteristics may be used as representing the physical layer parameter, and thus a new measurement may be generated when a physical layer measurement characteristic differs from the previously reported physical layer measurement characteristic by 30 more than a given threshold.

In the embodiment, the update processor 121 for each measurement report determines an upper value and a lower value that the physical layer parameter or physical layer measurement characteristic must exceed before a new measurement report is sent. The upper value is determined 5 by adding the threshold to the measurement value of the previous measurement report, and the lower value is determined by subtracting the threshold from the measurement value of the measurement report. In the preferred embodiment, the same threshold is used for determining the upper and lower values, but in other embodiments, different thresholds lO may be used for the upper and lower values.

In the embodiment, the threshold by which the physical layer parameter should increase or decrease before a new measurement report is generated is determined in response to a previous physical layer measurement 15 characteristic. For example, a threshold may be given as a percentage of the previously reported measurement value, thereby providing for a new measurement report to be generated for the same relative difference regardless of the absolute values. In some embodiments, the threshold may be determined in response to an initial physical layer measurement 20 characteristic. For example, the threshold may be varied in response to a duration since the initial measurement report.

FIG. 7 illustrates an example of a dynamically updated measurement reporting of a physical layer characteristic in accordance with an 25 embodiment of the invention, wherein the measurement reports are generated in response to a specific condition occurring. FIG. 7 illustrates the same transmit power variation 401 and filtered transmit power variation 403 as FIG. 4 and 6.

30 In the example of FIG. 7, a first measurement report 701 is communicated after 100ms. The update processor 121 determines a first upper threshold value 703 by adding a predetermined absolute threshold value to the

measurement value of the first measurement report 701. It further subtracts the threshold value from the measurement value of the first measurement report 701. However, this results in a negative transmit power threshold, and therefore a first lower threshold value 705 is set at 5 half the measurement value of the first measurement report 701.. The first upper and lower threshold values 703, 705 are communicated to the measurement processor 117, which continually monitors the filtered transmit power values to detect if the threshold values are reached.

lO In the example of FIG. 7, the first upper threshold value 703 is reached by the filtered transmit power variation 403, and accordingly a second measurement report 707 is generated and communicated to the RNC 109.

In response, the update processor 121 generates a second upper threshold value 709 by adding the threshold to the measurement value of the second 15 measurement report 707, and a second lower threshold value 711 by subtracting the threshold from the measurement value of the second measurement report 707. These values 709, 711 are communicated to the measurement processor 117. When the measurement processor 117 detects that the upper threshold value is exceeded by the filtered transmit 20 power, a third measurement report 713 is generated and communicated to the RNC 109. Consequently, the update processor 709 determines third upper and lower threshold values 715, 717. In the specific example of FIG. 7, these threshold values are not exceeded, and thus no further measurement reports are generated.

In this embodiment, it is ensured that significant variations in the physical layer measurement characteristic is always known at the network element (e.g the RNC 109), while only the necessary measurement reports to provide this information are communicated. It 30 thus provides for high accuracy at a low communication and computational resource requirement.

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. However, preferably, the invention is implemented as computer software running on one or more data processors. The elements and components of an 5 embodiment of the invention may be located in the core network, the radio access network or any suitable physical or functional location. 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 10 distributed in the network.

Although the present invention has been described in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only IS by the accompanying claims.

Claims

1. A method of communicating measurement reports in a cellular 5 communication system having a fixed network supporting remote communication units; the method comprising the steps of in a first communication unit determining physical layer measurement characteristics in response to an air interface physical layer parameter associated with a remote communication unit; 10 communicating measurement reports comprising the physical layer measurement characteristics from the first communication unit to a network element; further comprising the step of: dynamically updating an interval between measurement reports in 15 response to an operating characteristic of the cellular communication system.

2. A method as claimed in claim 1 wherein the operating characteristic comprises a number of remote communication units that are supported by 20 the first communication unit.

3. A method as claimed in any previous claim wherein the operating characteristic comprises a number of remote communication units that are supported by the network element.

4. A method as claimed in any previous claim wherein the operating characteristic comprises a duration that the remote communication unit has been supported by the first communication unit.

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5. A method as claimed in any previous claim wherein the operating characteristic comprises a difference between a physical layer

measurement characteristic of a first measurement report and a physical layer measurement characteristic of a second measurement report.

6. A method as claimed in any previous claim wherein the operating S characteristic comprises an available communication capacity of a connection between the first communication unit and the network element.

7. A method as claimed in any previous claim wherein the 10 measurement reports are communicated substantially periodically and the interval between measurement reports is updated by modifying the frequency of the measurement reports.

8. A method as claimed in any previous claim wherein a measurement 15 report is communicated when a first value of the physical layer measurement characteristic differs from a reported value of the physical layer measurement characteristic in a previous measurement report by more than a threshold.

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9. A method as claimed in claim 8 wherein the threshold relates to an increased value of the physical layer measurement characteristic.

10. A method as claimed in claim 8 wherein the threshold relates to a decreased value of the physical layer measurement characteristic.

11. A method as claimed in any previous claim 8 to 10 wherein the threshold is determined in response to a previous physical layer measurement characteristic.

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12. A method as claimed in claim 11 wherein the previous physical layer measurement characteristic is comprised in a previous measurement report.

13. A method as claimed in any previous claim 11 to 12 wherein the previous physical layer measurement characteristic is an initial physical layer measurement characteristic.

14. A method as claimed in any previous claim wherein the first communication unit is a base station.

15. A method as claimed in any previous claim wherein the network 10 element comprises a resource allocator.

16. A method as claimed in any previous claim wherein the network element comprises a traffic scheduler.

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17. A method as claimed in any previous claim wherein the remote communication unit is supported by the first communication unit.

18. A method as claimed in claim 17 wherein the physical layer measurement characteristic is a power measurement characteristic and 20 the air interface physical layer parameter is a transmit power associated with the remote communication unit.

19. A method as claimed in any previous claim wherein the transmit power associated with the remote communication unit is a transmit power 25 of the first communication unit when transmitting to the remote communication unit.

20. A computer program enabling the carrying out of a method according to any of the previous claims.

21. A communication unit for a cellular communication system having a fixed network supporting remote communication units; the communication unit comprising: a measurement processor for determining physical layer 5 measurement characteristics in response to an air interface physical layer parameter associated with a remote communication unit; a communication element for communicating measurement reports comprising the physical layer measurement characteristics to a network element; and 10 an update processor for dynamically updating an interval between measurement reports in response to an operating characteristic of the cellular communication system.

22. A communication unit as claimed in claims 21 wherein the 15 operating characteristic comprises a number of remote communication units that are supported by the first communication unit.

23. A communication unit as claimed in any of the previous claims 21 to 22 wherein the operating characteristic comprises a number of remote 20 communication units that are supported by the network element.

24. A communication unit as claimed in any of the previous claims 21 to 23 wherein the operating characteristic comprises a duration that the remote communication unit has been supported by the first 25 communication unit.

25. A communication unit as claimed in any of the previous claims 21 to 24 wherein the operating characteristic comprises a difference between a physical layer measurement characteristic of a first measurement report 30 and a physical layer measurement characteristic of a second measurement report.

26. A communication unit as claimed in any of the previous claims 21 to 25 wherein the communication element is operable to communicate a measurement report when a first value of the physical layer measurement characteristic differs from a reported value of the physical layer 5 measurement characteristic in a previous measurement report by more than a threshold.

27. A communication unit as claimed in any of the previous claims 21 to 26 wherein the physical layer measurement characteristic is a power 10 measurement characteristic and the air interface physical layer parameter is a transmit power associated with the remote communication unit.

28. A communication unit as claimed in claim 27 wherein the transmit power associated with the remote communication unit is a transmit power 15 of the communication unit when transmitting to the remote communication unit.

29. A communication unit as claimed in of the previous claims 27 to 28 further comprising: 20 a measurement unit for performing power measurements; a filter for generating filtered power measurements from the power measurements at a first rate; and wherein the measurement processor is operable to generate the power measurement characteristics from the filtered power measurements 25 substantially at the first rate; and the communication element is operable to update the interval between measurement reports by not communicating some power measurement characteristics to the network element. 30

30. A communication unit as claimed in any of the previous claims 21 to 29 wherein the communication unit is a base station.