WO2015167370A1

WO2015167370A1 - Control apparatus and method of controlling the same

Info

Publication number: WO2015167370A1
Application number: PCT/SE2014/050514
Authority: WO
Inventors: Abin JOSE; Reman KRISHNAN; Kannan SURESH KUMAR
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-04-28
Filing date: 2014-04-28
Publication date: 2015-11-05

Abstract

A control apparatus in a CDMA-based communications system and a method of controlling the same. The control apparatus determines whether a strength of an active set of a user equipment in a particular cell satisfies a predetermined condition, and determines a soft handover load for the particular cell. The control apparatus generates a measurement control message in accordance with the strength of the active set being determined to satisfy the predetermined condition and the soft handover load for the particular cell. The control apparatus transmits the measurement control message to the user equipment.

Description

DESCRIPTION

CONTROL APPARATUS AND METHOD OF CONTROLLING THE SAME

TECHNICAL FIELD

[0001] The present invention generally relates to a control apparatus operable to transmit measurement control messages to a user equipment, and a method of controlling the same.

BACKGROUND

[0002] A soft handover (SHO) is a function used in

CDMA based communication systems. In an SHO, a user equipment (UE) is simultaneously connected to at least two radio links (RL) established with cells of radio base stations (RBS) . A softer handover is a special case of an SHO in which the cells that provide the RLs are controlled by the same radio base station.

[0003] In SHOs, the handover procedure includes a measurement phase, a decision phase, and an execution phase. The UE performs a signal measurement of a common pilot channel (CPICH) of a candidate cell, by measuring a characteristic, such as signal power, of the received signal. The UE confirms that the signal measurement satisfies criteria received from the RBS, and reports that the criteria is fulfilled to the RBS in accordance with a radio resource control (RRC) protocol. A network control apparatus (for example, a radio network controller (RNC) ) may then add an RL between the UE and the candidate cell in accordance with the measurement report, for example. For more detail, see "Radio Resource Control (RRC) ; Protocol specification", 3GPP TS 25.331, version 11.8.0, and "Requirements for support of radio resource management

(FDD)", 3GPP TS 25.133, version 12.2.0.

[0004] The UE is able to simultaneously receive and combine signals from the multiple RLs in an SHO situation with a rake receiver. Received signal levels coming from different RLs having the same data are added, resulting in a stronger signal. This is known as micro-diversity combining. In the uplink (UL) direction, the UE appends measured quality information to transmissions sent over the different RLs in the SHO. A network control apparatus such as a radio network controller (RNC) may select the best UL signal based on the quality information. This is known as macro- diversity combining.

[0005] In SHOs, macro-diversity and multipath diversity gain can be obtained, and RBS output power can be lowered while maintaining sufficient connection quality. However, compared to a single-link

connections, SHOs result in a larger decrease in

availability of system resources because multiple RLs are used. A UE involved in an SHO uses several radio links, more downlink (DL) channelization codes, and more DL power, for example, Because networks are increasingly under pressure in terms of capacity, there is a need for solutions that mitigate adverse effects of SHOs on resource availability while maintaining the benefits of SHOs.

SUMMARY

[0006] The present invention was conceived in view of the above circumstances, and it is an object thereof to provide a technique of mitigating the reduction of system resource availability due to soft handovers while maintaining benefits of soft handovers.

[0007] According to the first aspect of the present invention, there is provided a control

apparatus operable to transmit a first measurement control message, which is a message for controlling a first signal measurement, to a user equipment operable to communicate simultaneously over a plurality of radio links towards cells in a soft handover in a CDMA-based communications system. The user equipment is

configured to perform the first signal measurement, by measuring a characteristic of a received signal, for a particular cell, and control whether to transmit a first measurement report message, which includes information corresponding to the first signal

measurement, to the control apparatus in accordance with the first measurement control message and the first signal measurement. The control apparatus has a first determination unit configured to determine whether a strength of an active set of the user equipment satisfies a predetermined condition. The active set is a set of cells in the CDMA-based

communications system for which the user equipment simultaneously connects. The control apparatus also has a second determination unit configured to determine a soft handover load for the particular cell in the CDMA-based communications system. The soft handover load indicates a degree to which radio links of the particular cell are used for soft handovers. The control apparatus also has a generation unit configured to generate the first measurement control message in accordance with the strength of the active set being determined by the first determination unit to satisfy the predetermined condition and the soft handover load for the particular cell determined by the second determination unit. The control apparatus also has a communication unit configured to transmit the first measurement control message, generated by the

generation unit, to the user equipment.

[0008] According to the second aspect of the present invention, there is provided a method of controlling a control apparatus operable to transmit a first measurement control message, which is a message for controlling a first signal measurement, to a user equipment operable to communicate simultaneously over a plurality of radio links towards cells in a soft

handover in a CDMA-based communications system. The user equipment is configured to perform the first signal measurement, by measuring a characteristic of a received signal, for a particular cell, and control whether to transmit a first measurement report message, which includes information corresponding to the first signal measurement, to the control apparatus in

accordance with the first measurement control message and the first signal measurement. The method has a first determination step of determining whether a strength of an active set of the user equipment

satisfies a predetermined condition, the active set being a set of cells in the CDMA-based communications system for which the user equipment simultaneously connects. The method also has a second determination step of determining a soft handover load for the

particular cell in the CDMA-based communications system, the soft handover load indicating a degree to which radio links of the particular cell are used for soft handovers. The method also has a generation step of generating the first measurement control message in accordance with the strength of the active set being determined in the first determination step to satisfy the predetermined condition and the soft handover load for the particular cell determined in the second β determination step. The method also has a

communication step of transmitting the first

measurement control message, generated in the

generation step, to the user equipment.

[0009] By virtue of the above features, it is possible to mitigate the reduction of system resource availability due to soft handovers while maintaining benefits of soft handovers.

[0010] Further features and advantages of the present invention will be apparent from the following description with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF DRAWINGS

[0011] Fig. 1 is an overall view illustrating a user equipment (UE) in a soft handover (SHO) situation in a CDMA-based communications system according to some embodiments .

[0012] Fig. 2 is a graph for explaining a

condition indicated by a measurement control message transmitted from a control apparatus of the system to the UE according to some embodiments.

[0013] Fig. 3 is a graph for explaining conditions indicated by another measurement control message

transmitted from the control apparatus to the UE

according to some embodiments. [0014] Fig. 4 is a functional block diagram of the control apparatus according to some embodiments.

[0015] Fig. 5 is a flowchart for illustrating processing performed by the control apparatus for mitigation of resource availability loss due to SHOs according to some embodiments.

[0016] Fig. 6 is a flowchart for illustrating processing performed by the control apparatus for mitigation of resource availability loss due to SHOs according to some embodiments.

DETAILED DESCRIPTION

[0017] Fig. 1 is an overall view illustrating a user equipment (UE) 101 in an soft handover (SHO) situation in a CDMA-based communications system

according to some embodiments. The UE 101 is

communicating with a radio network controller (RNC) 102. This communication is realized by the UE 101

communicating simultaneously over radio links towards cells corresponding to radio base stations (RBS) 103 and 104, and the RBSs 103 and 104 communicating with the RNC 102. Explanation here will be given having the RNC 102 function as a control apparatus, but in other embodiments the control apparatus may be an RBS or a combination of RBSs and RNCs, for example. An RBS 105 is also connected communicably to the RNC 102, but there is no RL currently established between the RBS 105 and the UE 101. It should be understood that in an actual implementation, there may be more UEs, RBSs and RNCs comprised in the system.

[0018] The RNC 102 is operable to generate, and transmit to the UE 101 via the RBSs 103 and 104, measurement control messages in accordance with

embodiments. These measurement control messages are for controlling one or more signal measurements for a particular cell by the UE 101, and they contain

information based upon which the UE 101 will perform the signal measurements. For example, this information may include a list of information about cells in the system for which to perform measurements, information indicating a kind of signal measurement to perform, and condition information such as criteria for event-based or periodic measurement reporting. Note that in some embodiments, such a measurement control message may include other information, or may be broken up into a number of separate messages from the RNC 102 to the UE 101.

[0019] The list of information about cells may include information about cells to which the UE 101 is connected with RLs in an SHO situation, such as the cells of RBS 103 and RBS 104. The set of cells to which the UE 101 simultaneously connects in an SHO situation is referred to as an "active set" of the UE 101. The RNC 102 may instruct the UE 101 and relevant RBSs to update (add, remove, modify RLs) the active set of the UE 101 based on a measurement report message, which includes information corresponding to a signal measurement, from the UE 101, conditions of the system, or the like.

[0020] In addition, the list of information about cells may include information about cells with which the UE 101 does not have an RL established, such as the cell of RBS 105 in the example. Such cells are

referred to as "monitored cells", and the set of

monitored cells is referred to as a "monitored set".

Monitored cells are candidates for the active set. The list of information about the cells may also include frequency related information, and non-frequency

related information such as a later explained cell index offset, for example.

[0021] The condition information may include trigger conditions for various events based upon which the UE 101 will transmit a measurement report message to the RNC 102. These events may include a pilot channel of an active set candidate cell entering a reporting range, a pilot channel of a cell in the active set leaving a reporting range, or a pilot

channel of a cell becoming stronger or weaker than an absolute threshold, for example. The condition

information may indicate periodic measurement reporting.

[0022] Information indicating a kind of signal measurement that the UE 101 should perform may include, for example, information indicating signal measurement for a pilot channel such as information indicating measurement for Common Pilot CHannel (CPICH) Energy per chip over Noise (Ec/No) , CPICH Received Signal Code Power (RSCP) , pathloss, or Universal Mobile

Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) carrier received signal strength

indicator (RSSI), for example.

[0023] In accordance with the measurement control message, the UE 101 will perform one or more signal measurements for cells. When the condition is

determined to be satisfied in accordance with a signal measurement and information of the measurement control message, the UE 101 will generate, and transmit to the RNC 102 via the RBSs 103 and 104, a measurement report message .

[0024] The cell index offset information may be used in the condition used to trigger the UE 101 to transmit the measurement report message. The value of the cell index offset may cause the event to be more or less likely to be triggered, and thus cause the UE 101 to be more or less likely to transmit a corresponding measurement report message. This is explained in more detail, with reference to Fig. 2.

[0025] Fig. 2 is a graph for explaining a

condition indicated by a measurement control message transmitted from the control apparatus (for example, the RNC 102) to the UE 101 according to some

embodiments .

[ 0026] The condition represented by Fig. 2

corresponds to an event la which is for a pilot channel of an active set candidate cell entering a reporting range. In this example, the condition corresponds to Equation 1 below. Note that in other embodiments the condition may differ. The equations explained here are simplified for ease of explanation, and in other

embodiments, logarithm functions may be applied to the signal measurements, or elements may be multiplied by constants, for example.

NA

[ 0027 ] Mnew + ClOnew > W(∑ Mi) + (1 - W)MBest - (R - H/2)

i=l

Equation 1

[ 0028 ] In Equation 1, Mnew corresponds to a value for a signal measurement performed by the UE 101 for the RBS 105, which corresponds to a monitored cell of the UE 101. Mi to M_NA correspond to the signal

measurements for cells in the active set. NA is the number of cells not forbidden to affect the reporting range of the active set. MBest corresponds to the signal measurement of the cell in the active set with the strongest signal measurement. Note that all of the signal measurements in this example are for CPICH Ec/No, but, as explained previously, in other embodiments other types of signal measurement are used.

[0029] R corresponds to a reporting range within which the candidate cell must enter for the UE 101 to be triggered to transmit a measurement report. H is a hysteresis value. In this example, it is assumed that W, which is a weighting factor, is set to 0. Therefore, in the explanation, the Equation 1 simplifies to

Equation 2.

[ 0030 ] Mnew + CIOnew > MBest - (R - H/2) Equation 2

[ 0031 ] ClOnew corresponds to the cell index offset for the monitored cell (active set candidate cell) as describe above. As can be seen from Equations 1 and 2, the user equipment will be less likely to transmit the measurement report message triggered by this condition if the value of this offset is set to be lower.

Therefore, it is possible for the RNC 102 to make less likely (discourage) the UE 101 being triggered by the condition to send a measurement report message by setting the cell index offset appropriately. This has the effect of making less likely an addition of a new RL from the UE 101 to the candidate cell, in the case of event la.

[ 0032 ] In Fig. 2, the vertical axis corresponds to signal measurement value, and the horizontal axis corresponds to time. Two solid lines indicate the signal measurement values for RBS 103, which

corresponds to the cell in the active set with the best signal measurement (MBest in Equations 1 and 2), and for RBS 105 (Mnew in Equations 1 and 2) , which

corresponds to the cell index offset (ClOnew in

Equations 1 and 2) in the corresponding measurement control message from the RNC 102 to the UE 101.

[0033] The dotted line corresponds to the

difference between the signal measurement of the best signal measurement and the range R minus half of the hysteresis H, i.e. the right side of Equation 2, MBest - (R - H/2) . The dot-dash line represents the left side of Equation 2, Mnew + ClOnew (in this case ClOnew is a negative value) . Time 201 is the point in time at which the condition is satisfied, and the UE 101 is triggered to send the corresponding measurement report message .

[ 0034 ] Note that the measurement control message may indicate a condition for an event lb. Event lb is an event that is triggered when a pilot channel of a cell in the active set leaves the reporting range. In the case of event lb, a cell index offset may be set so as to make the event more likely to be triggered, for example. For example, a simplified version of the condition for event lb may be as follows.

[ 0035 ] Mold + CIOold < MBest - (R + H/2) Equation 3

Here, Mold corresponds to a signal measurement of the active set cell leaving the reporting range, and ClOold corresponds to the cell index offset for that cell. Here, setting ClOold to be lower makes the condition more likely to be satisfied. This may have the effect of making more likely a removal of an existing RL to a cell in the active set, i.e. of encouraging SHO RL deletion .

[0036] Note also that a time-to-trigger parameter may be used in determination of the measurement control message conditions described above in some embodiments. In such a case, the measurement report message is only transmitted to the control apparatus when the condition is satisfied over a duration indicated by the time-to- trigger parameter.

[0037] The RNC 102 is able to discourage SHO load for a particular cell by transmitting a measurement control message as described above for event la or event lb. This is because processing for SHO RL addition is performed in response to a measurement report message corresponding to event la, and

processing for SHO RL deletion is performed in response to a measurement report message corresponding to event lb. By making the measurement report message for event la less likely, or event lb more likely, the number of SHO RLs can be reduced and thus resource availability loss can be mitigated. As will be explained later, with reference to Fig.s 5 and 6, this technique of mitigating resource availability loss can be used while maintaining the benefits of SHOs according to embodiments .

[0038] Fig. 3 is a graph for explaining conditions indicated by another measurement control message transmitted from the control apparatus (RNC 102) to the UE 101 according to some embodiments.

[0039] The conditions represented by Fig. 3 correspond to an event le and an event If which

correspond to a signal of a pilot channel exceeding or ceasing to exceed an absolute threshold respectively. In some embodiments, the RNC 102 transmits such a measurement control message to the UE 101 to instruct the UE 101 to transmit a measurement report message when a signal measurement for an RBS in the active set of the UE 101 crosses a threshold indicating that the signal is strong enough to support a minimum

communication guality. The RNC 102 can then use the information of the measurement report message to determine whether a strength of the active set of the UE 101 satisfies a predetermined condition, in SHO resource availability loss mitigation processing explained in detail with reference to Fig. 5.

Specifically, when such a measurement report message is sent when event le is triggered, the RNC 102 can determine that a signal measurement of at least one cell in the active set exceeds a predetermined

threshold. Conversely, the RNC 102 can determine that no signal measurement of any cell in the active set exceeds the threshold, based on measurement report messages triggered by event If.

[0040] In Fig. 3, similarly to Fig. 2, the

vertical axis represents signal measurement and the horizontal axis represents time. The solid lines correspond to the CPICH Ec/No signal measurement values for RBS 103 and RBS 104. Other kinds of signal

measurement values, as explained above, are used in other embodiments.

[0041] Time 301 is a point in time at which the

CPICH Ec/No signal measurement for RBS 103 exceeds a threshold indicated by a horizontal dashed line. Note that this threshold may be specified by the measurement control message. In the case of event le, the UE 101 is triggered to send a corresponding measurement report message at time 301.

[0042] Similarly, time 302 is a point in time at which the CPICH Ec/No signal measurement for RBS 103 ceases to exceed the threshold. In the case of event If, the UE 101 is triggered to send a corresponding measurement report message at time 302. The RNC 102, having received such a measurement report message can then use the information of the message to make a determination regarding the strength of the active set of the UE 101 from which the message is sent, as is explained later in detail with reference to Fig. 5.

[0043] Fig. 4 is a functional block diagram of the control apparatus according to some embodiments. Note again that for simplicity, explanation here will be given having the RNC 102 function as the control

apparatus, but the control apparatus may encompass RNCs or RBSs or a combination of RNCS and RBSs, as described above .

[0044] The RNC 102 comprises a central processing unit (CPU) 401, a random access memory (RAM) 402, a read-only memory (ROM) 403, a communication unit 404, a first determination unit 405, a second determination unit 406, a third determination unit 407, and a

generation unit 408. Note that there may be multiple instances of a component. The components may be

connected by a bus, and capable of communication with each other thereupon.

[0045] The communication unit 404 may include wired links, such as an Ethernet cable for example. It may include wireless links, via sending/receiving antennas for example. It is capable of communication with external devices such as the UE 101 over one or more networks.

[0046] In some embodiments, the functionality of the units 405 through 408 is implemented by the CPU 401 executing a software program stored in the ROM 403 using the RAM 402 as a work area. In other embodiments, the units 404 through 408 are implemented using

dedicated hardware. In still other embodiments, the units 404 through 408 are implemented using a

combination of software and hardware. The detailed operation of the units 404 through 408 will be

described with reference to Fig. 5 and Fig. 6.

[0047] Fig. 5 is a flowchart for illustrating processing performed by the control apparatus for mitigation of resource availability loss due to SHOs according to some embodiments. Explanation will be given having the RNC 102 function as the control

apparatus, but as explained above, in other embodiments the control apparatus may be an RBS, or a combination of RBSs and RNCs, for example.

[0048] The processing of this flowchart may be performed by the RNC 102 periodically, or may be

triggered by the receipt of a measurement report

message, such as one triggered by event le or event If, for example, as described with reference to Fig. 3. In a case where this processing is triggered by event le or event If, there is the advantage that this

processing is only performed when necessary. Note that in some embodiments, the processing according to Fig. 5 is performed for each UE 101 in the cells controlled by the RNC 102. Furthermore, the processing may be

performed for each monitored cell (active set

candidate) in a case of discouraging SHO RL addition

(with event la) , or for each active set cell in a case of encouraging SHO RL deletion (with event lb), or both. In this example, explanation will be given using event la.

[0049] In step S501, the first determination unit

405 determines whether a strength of the active set of the UE 101 satisfies a predetermined condition. This predetermined condition may indicate that the active set is strong enough to sustain a minimum communication quality. When the active set of the UE 101 is

sufficiently strong, it may be advantageous to mitigate resource availability loss by discouraging the

establishment of SHO RLs to the UE 101, as described with reference to Fig. 2.

[0050] In some embodiments, the predetermined condition is satisfied when at least one cell in the active set exceeds a predetermined threshold. This threshold could be for a pilot channel signal

measurement, such as CPICH Ec/No, or the like, as described above.

[0051] In some embodiments, prior to step S501, the communication unit 404 of the RNC 102 transmits a measurement control message to the UE 101 including information instructing UE 101 to perform event-based measurement reporting for event le and event If, as described with reference to Fig. 3. Here, in some embodiments, the threshold for events le and If corresponds to the predetermined threshold

corresponding to the determination of step S501. At time 301, according to Fig. 3, UE 101 is triggered by event le to transmit a measurement report message because the CPICH Ec/No signal measurement of the RBS 103 exceeds the threshold, and the communication unit 404 of the RNC 102 receives the measurement report message from the UE 101. Based upon such a message, the first determination unit 405, in step S501, is able to determine whether the strength of the active set of the UE 101 satisfies the predetermined condition.

[0052] Note that the first determination unit 405 may determine whether the condition is satisfied based on a measurement report message from the UE 101 received when the signal measurements of all of the cells in the active set cease to exceed the threshold

(event If) . In such a case, the active set would be determined not to be strong in some embodiments. Also the first determination unit 405 may make the

determination based on other information indicating the strength of the active set. Note that the

determination of the active set strength is not limited to the condition that the CPICH Ec/No signal

measurement of at least one cell exceeds a

predetermined threshold. The active set may be

determined to be strong based on more than one cell in the active set, for example.

[0053] When the first determination unit 405 determines that the strength of the active set of the UE 101 satisfies the predetermined condition, the processing proceeds to step S502. Otherwise, the processing proceeds to step S505.

[0054] In step S502, the second determination unit

406 determines whether a soft handover load for a particular cell, such as the RBS 105, exceeds a predetermined value. Here, the SHO load indicates a degree to which radio links of a particular cell are used for soft handovers. The higher the degree to which radio links are used for soft handovers, the higher the degree of resource wastage there can be said to be. This is because in an SHO, the same data is transmitted over multiple RLs, and so each additional RL can be considered as resource wastage. Thus, when SHO load is determined to exceed a predetermined value indicating a high level of resource wastage, it may be advantageous for the RNC 102 to discourage SHO RL establishment as explained with reference to Fig. 2. Since the active set is determined to be sufficiently strong in step S501, this may lead to a significant increase in system resource availability without having an adverse effect on the quality of the communication by the UE 101.

[0055] The RNC 102 may maintain information in a storage unit such as the RAM 402 based upon which this SHO load can be determined. The RNC 102 may update this information when RLs to cells that it controls are established or removed, for example. Also, the RNC 102 may obtain such information by communicating with another control apparatus in the system. Note that in some embodiments, the determination of step S502 is performed before that of step S501.

[0056] When the second determination unit 406 determines that the SHO load for the particular cell of the UE 101 exceeds the predetermined value, the

processing proceeds to step S503. Otherwise, the processing proceeds to step S505.

[0057] In step S503, the generation unit 408 generates a measurement control message in accordance with the strength of the active set being determined by the first determination unit 405 to satisfy the

predetermined condition (step S501) and the SHO load for the particular cell being determined by the second determination unit 406 to exceed the predetermined value (step S502). The generation unit 408 may

generate the measurement control message such that the user equipment will be less likely to transmit a corresponding measurement report if the second

determination unit 406 determines the soft handover load to exceed the predetermined value than if the second determination unit 406 determines the soft handover load to not exceed the predetermined value. The generation unit 408 generates the measurement control message so that the user equipment will be less likely to transmit the measurement report message by setting a value of an offset for the particular cell to be lower, the offset used in a condition, comprised in the measurement control message, used to trigger the user equipment to transmit the measurement report message. In this example, the offset corresponds to the cell index offset, and the event corresponds to event la, as explained with reference to Fig. 2.

[0058] Note that event lb may also be used for the measurement control message, but that it may be more advantageous to use a measurement control message corresponding to event la because there is an overhead in establishing an RL in the first place. In this example event la is used and the value of the cell index offset for the particular cell is set to be cell index offset CIOl, which is lower than a default cell index offset value. This makes the event less likely to be triggered than in the default case.

[0059] After the message control message is generated in step S503, the processing proceeds to step S504, and the communication unit 404 transmits the measurement control message to the UE 101.

[0060] In step S505, processing is performed for normal working with respect to the particular cell. If the measurement control message according to

embodiments has yet to be sent to the UE 101 for the particular cell, it may be that no particular processing need be taken. However, if the UE 101 was previously sent the measurement control message in accordance with embodiments, another measurement control message may need to be generated and

transmitted to the UE 101 here to reset the cell index offset to the default value, due to a change in active set strength or SHO load, for example.

[0061] Fig. 6 is a flowchart for illustrating processing performed by the control apparatus for mitigation of resource availability loss due to SHOs according to some embodiments. In this flow, in addition to the active set strength and the SHO load, the resource utilization of the cell in question is considered in the generation of the message control message. Steps S601, S602, S606 and S607 are the same as step S501, S502, S504, and S505 respectively, so explanation thereof is omitted.

[0062] When the second determination unit 406 determines that the SHO load for the particular cell crosses a predetermined value in step S602, the processing proceeds to step S603. In step S603, the third determination unit 407 determines a resource utilization which indicates a degree to which radio resources are being used in the particular cell.

[0063] It may be advantageous for the generation unit 408 to generate the measurement control message in accordance with the resource utilization in addition to the active set strength and the SHO load. In some embodiments, establishment of SHO RLs with the UE 101 is discouraged more strongly when the resource

utilization of the predetermined cell is determined to be high. This is because in a situation in which the resource utilization of the predetermined cell is high, the benefit to mitigating resource availability loss due to SHOs may be higher.

[0064] The RNC 102 may maintain information in a storage unit such as the RAM 402 based upon which this resource utilization can be determined. The RNC 102 may update this information when RLs to cells that it controls are established or removed, for example. Also, the RNC 102 may obtain such information by

communicating with another control apparatus in the system. Note also, that step S603 may be performed before step S601 or step S602.

[0065] When, in step S603, the third determination unit 407 determines that the resource utilization of the particular cell does not exceed a predetermined value, the processing proceeds to step S604, and the generation unit 408 generates the message control message such that it includes the cell index offset CIOl, which is the same as that used in the explanation with reference to Fig. 5. Specifically, the generation unit 408 generates the measurement control message so that the UE 101 will be less likely to transmit the measurement report message than in the default case. In this example the measurement control message

corresponds to event la, and the value of the cell index offset for the particular cell is set to be cell index offset CI01, which is lower than the default cell index offset value. This makes a corresponding

measurement report less likely.

[0066] On the other hand, when the third

determination unit 407 determines that the resource utilization of the particular cell does exceed a

predetermined value, the processing proceeds to step S605. In step S605, the generation unit 408 generates the measurement control message so that the UE 101 will be even less likely to transmit the measurement report message than in the case of step S604. In this example, the value of the cell index offset for the particular cell is set to be cell index offset CI02, which is even lower than the cell index offset CIOl set in step S604.

[0067] After the message control message is

generated in step S604 or step S605, the processing proceeds to step S606, and the message is transmitted to the UE 101.

[0068] By virtue of embodiments according to Fig.

5, resource availability loss due to SHOs is mitigated by discouraging SHO RL establishment when the active set is strong and the SHO load is high. By virtue of embodiments according to Fig. 6, resource availability loss due to SHOs is further mitigated by further discouraging SHO RL establishment when resource utilization is high.

[0069] Accordingly, the embodiments enhance performance by mitigating resource availability loss due to SHOs while maintaining the benefits of SHOs. This results in improved accessibility in cells having high SHO load.

[0070] The present invention is not limited to the above-described embodiments, and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention, the following claims are made.

Claims

1. A control apparatus (102) operable to transmit a first measurement control message, which is a message for controlling a first signal measurement, to a user equipment (101) operable to communicate simultaneously over a plurality of radio links towards cells in a soft handover in a CDMA-based communications system, the user equipment being configured to perform the first signal measurement, by measuring a characteristic of a received signal, for a particular cell, and control whether to transmit a first measurement report message, which includes information corresponding to the first signal measurement, to the control apparatus in

accordance with the first measurement control message and the first signal measurement, the control apparatus comprising :

a first determination unit (405) configured to determine whether a strength of an active set of the user equipment satisfies a predetermined condition, the active set being a set of cells in the CDMA-based communications system for which the user equipment simultaneously connects;

a second determination unit (406) configured to determine a soft handover load for the particular cell in the CDMA-based communications system, the soft handover load indicating a degree to which radio links of the particular cell are used for soft handovers; a generation unit (408) configured to generate the first measurement control message in accordance with the strength of the active set being determined by the first determination unit to satisfy the

predetermined condition and the soft handover load for the particular cell determined by the second

determination unit; and

a communication unit (404) configured to transmit the first measurement control message, generated by the generation unit, to the user equipment.

2. The control apparatus according to claim 1, wherein

the strength of the active set satisfies the predetermined condition when a second signal

measurement for at least one cell in the active set exceeds a predetermined threshold.

3. The control apparatus according to claim 1 or 2, wherein

when the first determination unit determines that the strength of the active set satisfies the

predetermined condition,

the generation unit generates the first measurement control message so that the user equipment will be less likely to transmit the first measurement report message if the second determination unit determines the soft handover load to exceed a

predetermined value than if the second determination unit determines the soft handover load to not exceed the predetermined value.

4. The control apparatus according to claim 3, wherein

the generation unit generates the first

measurement control message so that the user equipment will be less likely to transmit the first measurement report message by setting a value of an offset for the particular cell to be lower, the offset being used in a triggering condition, indicated by the first

measurement control message, used to trigger the user equipment to transmit the first measurement report message .

5. The control apparatus according to claim 3 or 4, further comprising

a third determination unit (407) configured to determine a resource utilization level, which indicates a degree to which radio resources are being used, for the particular cell, wherein

the generation unit generates the first

measurement control message in accordance with the resource utilization level for the particular cell.

6. The control apparatus according to claim 5, wherein

predetermined condition and the second determination unit determines the soft handover load to exceed a predetermined value,

the generation unit generates the first measurement control message so that the user equipment will be less likely to transmit the first measurement report message if the third determination unit

determines the resource utilization level for the particular cell to exceed a predetermined level than if the third determination unit determines the resource utilization level for the particular cell to not exceed the predetermined level.

7 The control apparatus according any one of claims

1 to 6 , wherein

the particular cell is a monitored cell which is a candidate for the active set.

8. The control apparatus according to any one of claims 3 to 6 , wherein

the first measurement report message is a message based upon which the particular cell is caused to be added to the active set of the user equipment.

9. The control apparatus according to any one of claims 1 to 8, wherein

the signal measurement is for CPICH Ec/No, CPICH RSCP, or UTRA Carrier RSSI.

10. The control apparatus according to claim 2, wherein

a second measurement report message corresponding to the second signal measurement is transmitted by the user equipment to the control apparatus triggered by information of a second measurement control message transmitted from the control apparatus including an event corresponding to a value of the second signal measurement crossing the predetermined threshold.

11. The control apparatus according to claim 4 or 5, wherein

the triggering condition corresponds to an event for a pilot channel of an active set candidate cell entering a reporting range.

12. A method of controlling a control apparatus (102) operable to transmit a first measurement control message, which is a message for controlling a first signal measurement, to a user equipment (101) operable to communicate simultaneously over a plurality of radio links towards cells in a soft handover in a CDMA-based communications system, the user equipment being configured to perform the first signal measurement, by measuring a characteristic of a received signal, for a particular cell, and control whether to transmit a first measurement report message, which includes information corresponding to the first signal

measurement, to the control apparatus in accordance with the first measurement control message and the first signal measurement, the method comprising:

a first determination step (S501) of determining whether a strength of an active set of the user equipment satisfies a predetermined condition, the active set being a set of cells in the CDMA-based communications system for which the user equipment simultaneously connects;

a second determination step (S502) of determining a soft handover load for the particular cell in the CDMA-based communications system, the soft handover load indicating a degree to which radio links of the particular cell are used for soft handovers;

a generation step (S503) of generating the first measurement control message in accordance with the strength of the active set being determined in the first determination step to satisfy the predetermined condition and the soft handover load for the particular cell determined in the second determination step; and a communication step (S504) of transmitting the first measurement control message, generated in the generation step, to the user equipment.

13. The method according to claim 12, wherein

14. The method according to claim 12 or 13, wherein when, in the first determination step, it is determined that the strength of the active set

satisfies the predetermined condition,

the first measurement control message is generated, in the generation step, so that the user equipment will be less likely to transmit the first measurement report message if, in the second

determination step, it is determined that the soft handover load exceeds a predetermined value than if, in the second determination step, it is determined that the soft handover load does not exceed the

predetermined value.

15. The method according to claim 14, wherein

the first measurement control message is

generated, in the generation step, so that the user equipment will be less likely to transmit the first measurement report message by setting a value of an offset for the particular cell to be lower, the offset being used in a triggering condition, indicated by the first measurement control message, used to trigger the user equipment to transmit the first measurement report message .

16. The method according to claim 14 or 15, further comprising

a third determination step (S603) of determining a resource utilization level, which indicates a degree to which radio resources are being used, for the particular cell, wherein

the first measurement control message is

generated, in the generation step, in accordance with the resource utilization level for the particular cell.

17. The method according to claim 16, wherein

when, in the first determination step, it is determined that the strength of the active set

satisfies the predetermined condition and, in the second determination step, it is determined the soft handover load to exceed a predetermined value,

the first measurement control message is generated, in the generation step, so that the user equipment will be less likely to transmit the first measurement report message if, in the third

determination step, it is determined that the resource utilization level for the particular cell exceeds a predetermined level than if, in the third determination step, it is determined that the resource utilization level for the particular cell does not exceed the predetermined level.

18. The method according any one of claims 12 to 17, wherein

19. The method according to any one of claims 14 to 17, wherein

20. The method according to any one of claims 12 to 19, wherein

the signal measurement is for CPICH Ec/No, CPICH RSCP, or UTRA Carrier RSSI.

21. The method according to claim 13, wherein

22. The method according to claim 15 or 16, wherein the triggering condition corresponds to an event for a pilot channel of an active set candidate cell entering a reporting range.