WO2006064391A1

WO2006064391A1 - Method and apparatus for use in handover measurement process

Info

Publication number: WO2006064391A1
Application number: PCT/IB2005/054041
Authority: WO
Inventors: Ni Ma; Xuejun Zhang
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-12-13
Filing date: 2005-12-05
Publication date: 2006-06-22

Abstract

Measurement method to be executed in a UE, comprising the steps of: performing a measurement process based on the initialized measurement instruction from a network system; reporting to the network system the measurement results obtained in the measurement process; receiving the measurement parameters generated by the network system based on the measurement results; performing the corresponding measurement process based on the measurement parameters.

Description

METHOD AND APPARATUS FOR USE IN HANDOVER MEASUREMENT

PROCESS

FIELD OF THE INVENTION The present invention relates generally to a communication method and apparatus, and more particularly, to a method and apparatus for use in handover measurement process.

BACKGROUND OF THE INVENTION Handover refers to a procedure by which a UE (user equipment) in initial call setup status or busy status switches to a new traffic channel.

With rapid development of mobile communication technologies, multiple communication systems adopting different communication standards, such as WCDMA, CDMA2000 and TD-SCDMA, and communication systems adopting the same communication standard but occupying different radio carrier frequency bands, such as

GSM900 and GSMl 800 dual-frequency communication system, will coexist in the framework of global cellular mobile communication system. Handover, therefore, will play an important role in the framework of future mobile communication systems.

In cellular mobile communication systems, possible handover types are as follows: (1) Intra- system intra-frequency handover, for example, the soft handover within the same communication system and within the same radio carrier frequency band from one cell to another cell in WCDMA or CDMA2000 communication system.

(2) Intra- system inter- frequency handover, for example, the handover between different radio carrier frequency bands in UTRA TDD or TD-SCDMA communication system, wherein UTRA TDD (UMTS Terrestrial Radio Access - TDD) is a HCR - TDD

(High Chip Rate - Time Division Duplex) wireless communication system and TD-SCDMA is a LCR - TDD (Low Chip Rate - Time Division Duplex) wireless communication system in 3GPP. The handover between GSM900 and GSM 1800 in the GSM communication system also belongs to this intra- system inter- frequency handover. (3) Inter-system handover, for example, handover among GSM, WCDMA and UTRA

TDD/TD-SCDMA communication systems.

No matter in intra-system intra-frequency handover, intra-system inter-frequency handover or inter-system handover, both the robustness and the successful handover rate will have a direct impact upon the system performance and QoS of the mobile communication network. Thus it is particularly important in current wireless communication fields to launch in-depth investigations and researches on the handover issue.

In mobile communication, it's decided by the network side whether a communicating UE should perform handover procedure or not. In another word, whether to launch handover procedure or not is decided by the network side based on the measurement report sent from the UE and the measurement results of the network side itself. For example, in CDMA system, when a UE detects that the pilot signal strength over the radio link transferring traffic data is below a certain threshold, it may send a pilot signal strength measurement message to the serving cell, so as to facilitate the network side to make decision about the handover procedure. Take another example, when a UE is communicating in the overlaying coverage of two cells, if the traffic in the cell to which its traffic channel belongs is very heavy, the network side can notify the UE of testing the signal strength and channel quality of the adjacent cells according to the radio resource utilization of the cell, and decide whether or not to switch to another cell according to the reported measurement results from the UE. Handover in this scenario is also called handover based on traffic balance. Fig.l illustrates the handover measurement process being performed by a moving UE.

First, the network side in the cell where the UE is camping sends an initialized handover measurement instruction to the UE, to notify the UE of the relevant information about its adjacent cells and indicate the UE to measure the signal strength of BCCH of the adjacent cells, and the signal strength and transmission quality of the occupied traffic channel as well. After receiving the measurement results reported from the UE, the network side determines whether the UE needs to continue the handover measurement process based on the measurement report, and accordingly indicates the UE to continue or stop handover measurement process. Finally, based on these handover measurement results sent from the UE, the network side lists and sorts (or namely locates) the channel qualities of the adjacent cells, so as to determine whether to switch, when to switch and to which adjacent cell to switch.

When the UE performs a handover measurement process, the handover measurement parameters used are generally predefined by the system according to the communication standard adopted.

For example, in TD-SCDMA system, the UE performs handover measurement process in every fixed duration, which is preset by the network side according to the communication protocol. The fixed duration is from the starting timeslot for performing a handover measurement to the starting timeslot for performing the next handover measurement, and the time between is also called handover measurement interval. The handover measurement interval can be the time duration of 1 timeslot, or 1 subframe (1 subframe comprises 7 timeslots), or 1 radio frame (1 radio frame comprises 2 subframes), or multiple radio frames. According to the predefined handover measurement interval, within the duration for performing a handover measurement, the UE can make use of some spare radio resource (e.g., idle timeslot) or pause reception/transmission for a moment (named as compressed mode), to perform handover measurement over the relevant channels in the serving cell and its adjacent cells. The radio resource for handover measurement is also called handover measurement window.

Fig.2 gives an example illustrating a UE performing inter-system handover from TD-SCDMA system to WCDMA system. As shown in Fig.2, during the handover measurement process, the UE performs a handover measurement in the duration of 1 subframe, that is, the handover measurement interval is equal to 1 subframe. In this handover measurement interval, except an uplink timeslot TX and a downlink timeslot RX for voice communication, A idle timeslots between TX and RX, combining with B idle timeslots between RX and GP (guard period) C and the GP C itself constitute the measurement window, that is, the measurement window = A+B+C. Wherein, guard period C = DwPTS + GP + UpPTS. In order to synchronize with the target system WCDMA, the length of the reserved handover measurement window should at least guarantee that the

UE can capture the pilot signals of the target system (e.g. SCH in WCDMA system or FCCH in GSM system), so as to facilitate UE to obtain the timing of the timeslot and the radio frame in WCDMA system.

When the UE performs handover measurement process using the handover measurement parameters shown in Fig.2, if the radio channel of the UE is in good condition, e.g. the UE is moving slowly or the UE is not far away from the central position of the cell, or the UE can easily capture SCH signals of WCDMA, it will facilitate the full utilization of the radio resource to reallocate some radio resource occupied by the handover measurement to be used in carrying traffic data. But in current handover measurement process, even if the radio link status permits, the radio resource occupied by handover measurement can't be reallocated to carry traffic data, thus the number of timeslots for transferring traffic data is obviously restricted in this scenario. Conversely, if the radio channel of the UE is not in good condition, e.g. the UE is moving fast or the channel condition deteriorates seriously or the UE can't capture SCH signals of WCDMA easily, it may be not sufficient for the network side to make the right handover decision with the preset handover measurement parameters (or namely the handover measurement interval and window). It is, therefore, necessary to provide a new method to replace the conventional handover measurement method adopting fixed handover measurement parameters.

OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for use in handover measurement process, which can make best use of the limited radio resource and improve handover measurement precision.

A measurement method to be executed in a UE according to the present invention, comprising the steps of: performing a measurement process based on the initialized measurement instruction from a network system; reporting to the network system the measurement results obtained in the measurement process; receiving the measurement parameters generated by the network system based on the measurement results; performing the corresponding measurement process based on the measurement parameters.

A measurement method to be executed in a network system according to the present invention, comprising the steps of: receiving the measurement results obtained in a measurement process from the UE; generating the corresponding measurement parameters based on the measurement results; sending the measurement parameters to the UE so that the UE can perform corresponding measurement process based on the measurement parameters.

A UE according to the present invention, comprising: a measuring unit, for performing a measurement process based on the initialized measurement instruction from a network system; a transmitting unit, for reporting to the network system the measurement results obtained in the measurement process; a receiving unit, for receiving the measurement parameters generated by the network system based on the measurement results; wherein the measuring unit performs the corresponding measurement process based on the measurement parameters.

A network system according to the present invention, comprising: a receiving unit, for receiving the measurement results obtained in a measurement process from the UE; a generating unit, for generating the corresponding measurement parameters based on the measurement results; a transmitting unit, for sending the measurement parameters to the UE so that the UE can perform corresponding measurement process based on the measurement parameters. Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:

Fig.l illustrates a schematic diagram of a UE performing handover measurement process;

Fig.2 illustrates the handover measurement parameters adopted by the conventional UE in performing handover measurement;

Fig.3 illustrates the flowchart of the method to be executed in the handover measurement process in accordance with an embodiment of the present invention;

Fig.4 illustrates the handover measurement parameters adopted by the UE in performing handover measurement in accordance with an embodiment of the present invention;

Fig.5 illustrates the handover measurement parameters adopted by the UE in performing handover measurement in accordance with another embodiment of the present invention;

Fig.6 illustrates the configurations of the UE and the network system when the method for use in handover measurement process described in the present invention is implemented in hardware.

Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions.

DETAILED DESCRIPTION OF THE INVENTION

According to the method for use in handover measurement process of the present invention, after receiving the handover measurement results reported from the UE, the network side generates the corresponding handover measurement parameters like handover measurement interval and window based on the radio link status and/or traffic load situation, and sends the new handover measurement parameters to the UE. After receiving the new handover measurement parameters, the UE can continue to perform handover measurement process according to the new handover measurement parameters.

A UE in TD-SCDMA communication system will be taken as an example below to describe the steps to be completed by the network side and the UE respectively in performing handover measurement process, in conjunction with Fig.3.

As shown in Fig.3, in a communication procedure, the network side first determines whether to initiate handover measurement process based on the measurement report sent from the UE and the measurement results of the network itself (step SlO), wherein the measurement report may be, for example, the pilot signal strength of the traffic channel detected by the UE and the measurement results may be, for example, the current traffic load of the UE detected by the network side. If the network side determines to initiate handover measurement process, it sends an initialized handover measurement instruction to the UE (step S20), to notify the UE of the handover measurement indication information such as which adjacent cells to be detected and which parameters of the adjacent cells to be measured, and also the preset handover measurement parameters such as handover measurement interval and window. After receiving the initialized handover measurement instruction (step S30), the UE performs handover measurement process in the preset handover measurement window according to the preset handover measurement interval (step S40), and reports the measurement results to the network side (step S50).

On receipt of the handover measurement results from the UE (step S60), the network side determines whether to continue handover measurement process or not, according to the current radio link status of the UE reflected by the handover measurement results and the current traffic load condition of the UE learned by the network side (step S70), and generates the corresponding indication information on the relevant handover measurement.

Based on the handover measurement indication information (step S80), if the network side determines to stop the handover measurement process, it sends to the UE the handover measurement instruction containing the indication information on stopping the handover measurement process (step S90), and then the network side terminates the handover measurement process (step SlOO).

If the network side decides to continue the handover measurement process, it further computes the new handover measurement parameters suitable for the current UE according to the radio link status and traffic load condition (step SIlO). Description will be given below to the procedure of computing the new handover measurement parameters, in conjunction with specific examples.

After computing and generating the new handover measurement parameters, the network side sends the handover measurement indication to the UE via downlink, such as downlink control channel or downlink traffic channel (step S 120), the handover measurement indication comprises the indication information on continuing handover measurement process and the new handover measurement parameters.

Then, the network side returns to step S60, waiting for the handover measurement report from the UE.

On receipt of the handover measurement indication from the network side (step S 130), the UE first determines whether the network side indicates it to stop or continue handover measurement process, based on the indication information relating to handover measurement process included in the handover measurement indication (step S 140).

If the received indication indicates to continue handover measurement process, the UE continues to perform handover measurement process in the new handover measurement window, according to the new handover measurement interval, based on the new handover measurement parameters included in the handover measurement indication (step S 150), and then executes subsequent steps. If the received indication indicates to stop handover measurement process, the UE terminates handover measurement process (step S160). As to the procedures by which the network side lists and sorts the channel qualities of the adjacent cells based on the handover measurement results and determines whether to switch, when to switch and to which adjacent cell to switch, and also the procedures by which the UE performs handover operations based on the network side's decision, they are similar to those in conventional handover mode and are not the main object of the present invention, and thus no detailed description is given to them herein.

Detailed description is given below to the procedures by which the network side computes the above new handover measurement parameters, exemplified by the new handover measurement interval based on the radio link status (alternatively, only handover measurement window is generated or both handover measurement interval and window are generated).

First, different handover measurement intervals are set in the network side corresponding to different radio link status, such as different SIR (Signal to Interference Ratio) or different BER (Bit-Error-Rate), as shown in Table.1.

It's assumed that SIR (to be represented as S) stands for radio link quality T, T₁^dB, T₂=IOdB and Io=l radio frame (=2 subframes). The new handover measurement interval can be computed and generated based the following criteria:

Table. 1 : determine the handover measurement interval based on the measured radio link quality

(1) If 4dB^S^10dB, the handover measurement interval needs no change according to Table.1, and I=I radio frame = 2 subframes, that is, the handover measurement process is executed a time during each two subframes.

(2) If S>10dB, the handover measurement interval can be correspondingly enlarged according to Table.1, to decrease the number of handover measurement. Ii=2I₀ = 4 subframes, that is, the handover measurement process is executed a time during each four subframes. In this case, the original radio resource used by handover measurement can be reallocated to carry traffic data.

(4) If S<4dB, the handover measurement interval can be correspondingly shortened according to Table.1, to increase the number of handover measurement. I₂= J^ Io = 1 subframe, that is, the handover measurement process is executed a time during each subframe. Shortening of handover measurement interval will affect the transfer rate of the traffic data to some extent, but the corresponding handover precision will be enhanced greatly.

Alternatively the above handover measurement interval can be further subdivided based on finer threshold, for example, it can be subdivided to the minimum unit - timeslot of the handover measure interval, which depends on the requirements of the radio system and whether the UE supports finer handover measurement interval.

Moreover, other algorithms can also be adopted to determine the change of the handover measurement interval. For example, if S>10dB, Ii=3Io; if S<4dB, I₂= j4 Io.

The above description is given to the specific procedure by which the network side generates new handover measurement interval based on the radio link status, in conjunction with Table.1. In practical applications, the network side can also adjust the handover measurement window according to the radio link status. Specifically, when the radio link quality is good (for example, the measured SIR is above a predefined value), the timeslots previously belonging to handover measurement window can be reallocated to carry traffic data; when the radio link quality deteriorates (for example, the measured SIR is below a predefined value), the timeslots previously used for carrying traffic data can also be reallocated for use in handover measurement to enhance the handover measurement precision.

Fig.4 and Fig.5 illustrate how to adjust the handover measurement interval and how to adjust the handover measurement window respectively in accordance with embodiments of the present invention.

Compared with prior art as shown in Fig.2 where the UE performs handover measurement according to preset handover measurement interval, when the radio channel is in good condition, for example, SIR is above a predefined threshold, the handover measurement interval will be prolonged to the time duration of 2 subframes according to the present invention, as shown in Fig.4. At this time, the saved timeslots can be reallocated to transfer traffic data, referring to the timeslots reallocated to receive/transmit data as shown in subframe i (alternatively, the timeslots for handover measurement in subframe i-1 can also be reallocated to receive/transmit data). When the radio channel deteriorates, for example, SIR is below a predefined threshold, the number of timeslots for handover measurement will be unable to meet the requirement of the measurement precision if the handover measurement is still performed a time every subframe, as shown in Fig.2. According to the present invention, the handover measurement window can be adjusted, i.e. the timeslots in the subframe previously for carrying traffic data can also be used for handover measurement, referring to timeslot RX in subframe i-1 in Fig.5. In this case, handover measurement occupies some radio resource previously used for transferring traffic data, and the data transfer tend to be affected to some extent, but the whole handover precision will be enhanced greatly.

As to the method for use in handover measurement process, it can be implemented in software or in hardware, or in combination of both.

Fig.6 illustrates the configurations of the UE and network system when the proposed method for use in handover measurement process is implemented in hardware, wherein the components same as those in conventional UE and network system are not given here.

As shown in Fig.6, first, handover measurement unit 10 in the UE performs a handover measurement process based on the initialized handover measurement instruction from network system 100, and reports to the network system 100 via transmitting unit 20 the handover measurement results obtained in the handover measurement process. The handover measurement results usually comprise information on the radio link status of the

UE, such as SIR and/or BER.

Receiving unit 110 in network system 100 provides the received handover measurement results from the UE to generating unit 120. Generating unit 120 generates the corresponding handover measurement parameters based on the handover measurement results, and sends the handover measurement parameters to the UE via transmitting unit 130. The handover measurement parameters may comprise handover measurement interval and/or handover measurement window for use in handover measurement process. Receiving unit 30 in the UE provides the received handover measurement parameters from network system 100 to handover measurement unit 10, so that handover measurement unit 10 can perform the corresponding handover measurement process based on the handover measurement parameters.

Beneficial Results of the Invention

As described above, according to the method for use in handover measurement process of the present invention, the network side can adjust handover measurement parameters such as handover measurement interval and window based on the current radio link status reflected by the handover measurement results from the UE and/or the current traffic load condition of the UE, and send the new handover measurement parameters to the UE so that the UE can continue to perform handover measurement process according to the new handover measurement parameters. Therefore, the present invention can take full advantage of the limited radio resource and improve the handover measurement precision effectively. The proposed method for use in handover measurement process is particularly suitable for inter-system handover measurement process from high-speed data rate system to low speed data rate system, due to good balance of between resource occupation and traffic load status.

The proposed method for adaptively changing handover measurement interval and window in handover measurement process is not only suitable for handover measurement process, but also equally applied in the occasions where measurement is needed, such as cell selection/reselection, DCA, timing in advance.

It's to be understood by those skilled in the art that the method and apparatus for use in handover measurement process as disclosed in this invention can be made of various modifications without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS:

1. A measurement method to be executed in a UE, comprising the steps of:

(a) performing a measurement process based on a initialized measurement instruction from a network system; (b) reporting to the network system measurement results obtained in the measurement process;

(c) receiving measurement parameters generated by the network system based on the measurement results;

(d) performing a corresponding measurement process based on the measurement parameters.

2. The measurement method according to claim 1, wherein said measurement parameters are generated by said network system based on traffic load of said UE.

3. The measurement method according to claim 1 or 2, wherein said measurement parameters comprise at least one of two parameters of handover measurement interval and window for use in a handover measurement process.

4. The measurement method according to claim 3, wherein step (d) comprises: performing the handover measurement process based on said handover measurement interval.

5. The measurement method according to claim 3, wherein step (d) comprises: performing the handover measurement process based on said handover measurement window.

6. The measurement method according to claim 1, wherein said measurement results are information indicating radio link status of the UE.

7. The measurement method according to claim 6, wherein said information indicating radio link status includes at least one of SIR and BER.

8. A measurement method to be executed in a network system, comprising the steps of: (a) receiving measurement results obtained in a measurement process from a UE;

(b) generating corresponding measurement parameters based on the measurement results;

(c) sending the measurement parameters to the UE so that the UE can perform a corresponding measurement process based on the measurement parameters.

9. The measurement method according to claim 8, wherein step (b) further comprises: generating said measurement parameters based on traffic load of said UE.

10. The measurement method according to claim 8 or 9, wherein said measurement parameters comprise at least one of two parameters of handover measurement interval and window for use in a handover measurement process.

11. The measurement method according to claim 8, wherein said measurement results are information indicating radio link status of the UE.

12. The measurement method according to claim 11, wherein said information indicating radio link status includes at least one of SIR and BER.

13. AUE, comprising: a measuring unit, for performing a measurement process based on a initialized measurement instruction from a network system; a transmitting unit, for reporting to the network system measurement results obtained in the measurement process; a receiving unit, for receiving the initialized measurement instruction from the network system and measurement parameters generated by the network system based on the measurement results; wherein the measuring unit performs a corresponding measurement process based on the measurement parameters.

14. The UE according to claim 13, wherein said measurement parameters comprise at least one of two parameters of handover measurement interval and window for use in a handover measurement process.

15. The UE according to claim 14, wherein said measuring unit performs the handover measurement process based on said handover measurement interval and/or said handover measurement window.

16. The UE according to claim 15, wherein said measurement results are information indicating radio link status of the UE.

17. A network system, comprising: a receiving unit, for receiving measurement results obtained in a measurement process from a UE; a generating unit, for generating corresponding measurement parameters based on the measurement results; a transmitting unit, for sending the measurement parameters to the UE so that the UE can perform a corresponding measurement process based on the measurement parameters.

18. The network system according to claim 17, wherein said measurement parameters comprise at least one of two parameters of handover measurement interval and window for use in a handover measurement process.

19. The network system according to claim 18, wherein said measurement results are information indicating radio link status of the UE.

20. The network system according to claim 19, wherein said information indicating radio link status includes at least one of SIR and BER.