U.S. patent application number 12/265702 was filed with the patent office on 2009-03-12 for method and apparatus for cell handoff.
This patent application is currently assigned to Huawei Technologies Co., Ltd.. Invention is credited to Yue Tu.
Application Number | 20090069012 12/265702 |
Document ID | / |
Family ID | 37510666 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090069012 |
Kind Code |
A1 |
Tu; Yue |
March 12, 2009 |
METHOD AND APPARATUS FOR CELL HANDOFF
Abstract
A method for handoff between cells in a communication system
includes the network sends a cell individual offset preset for a
cell in the active set relative to each of its neighboring cells
respectively to a terminal; after measuring the cell in the active
set and its neighboring cells, the terminal evaluates the
measurement in accordance with the measurement result and the cell
individual offset for the cell in the active set relative to its
each neighboring cell; the terminal then submits a measurement
report to the network in accordance with the measurement evaluation
result; the network instructs the terminal to perform a handoff
between cells in accordance with the measurement report. The
invention also discloses a network controller and a terminal
corresponding to the method. With the invention, the cell
individual offset for a cell is set relative to its each
neighboring cell so that the handoff between cells can be more
accurate. As a result, user of the terminal can obtain better
experience.
Inventors: |
Tu; Yue; (Shenzhen,
CN) |
Correspondence
Address: |
DARBY & DARBY P.C.
P.O. BOX 770, Church Street Station
New York
NY
10008-0770
US
|
Assignee: |
Huawei Technologies Co.,
Ltd.
Shenzhen
CN
|
Family ID: |
37510666 |
Appl. No.: |
12/265702 |
Filed: |
November 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CN2007/001742 |
May 31, 2007 |
|
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12265702 |
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Current U.S.
Class: |
455/436 |
Current CPC
Class: |
H04W 48/08 20130101;
H04W 36/0094 20130101; H04W 28/18 20130101; H04W 36/30 20130101;
H04W 24/00 20130101 |
Class at
Publication: |
455/436 |
International
Class: |
H04W 36/00 20090101
H04W036/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 5, 2006 |
CN |
200610100263.5 |
Claims
1. A method for handoff between cells, comprising: obtaining from a
network a cell individual offset for an adjacent cell of an active
set cell configured by the network, wherein each adjacent has such
an cell individual offset relative to the cell; measuring the
active set cell and the adjacent cell; evaluating the cell
measurement according to a result of the cell measurement and the
cell individual offset; submitting a measurement report to the
network according to a result of the measurement evaluation; and
receiving an instruction to perform handoff from the network,
wherein the instruction is made by the network according to the
measurement report.
2. The method of claim 1, wherein evaluating of the measurement
according to the measurement result and the cell individual offset
comprises: if, during a time period .DELTA.T of measurement report
triggering, the pilot signal quality of a target cell in a
monitored set meets a condition for adding a cell and the active
set is not full, adding the target cell to a cell list of the
active set of the terminal and marking the target cell as a cell to
be added to the active set; or if, during a time period .DELTA.T of
measurement report triggering, the pilot signal quality of a target
cell in the active set fulfills a condition for removing a cell,
removing the target cell from the active set of the terminal; or
if, during a time period .DELTA.T of measurement report triggering,
the pilot signal quality of a target cell in a monitored set
fulfills a condition for replacing a cell and the active set is
full, replacing the worst cell in the cell list of the active set
of the terminal with the target cell in the monitored set.
3. The method of claim 1, further comprising: receiving an adjusted
cell individual offset from the network, wherein the adjusted cell
individual offset is adjusted by the network according to a change
about the active set.
4. The method of claim 3, further comprising: measuring cell signal
quality of the active set in response to the change about the
active set; and sending the measured cell signal quality to the
network for adjusting the cell individual offset.
5. A method used for handoff between cells, comprising: sending to
a terminal, a cell individual offset for an adjacent cell of a cell
in an active set relative to the active set cell, wherein each
adjacent cell has such an cell individual offset independently
relative to the active set cell; receiving a cell measurement
report from the terminal device; and instructing the terminal
device to perform a handoff between cells according to the received
cell measurement report.
6. The method of claim 5, wherein instructing the terminal to
perform a handoff between cells comprises: performing a handoff
evaluation based on the received measurement report; and sending a
handoff instruction message to the terminal to perform the handoff
if a handoff condition is fulfilled according to the handoff
evaluation.
7. The method of claim 5, further comprising: in responsive to
acquiring a change about the active set, adjusting the cell
individual offset for the adjacent cell of corresponding active set
cell according to the change about the active set; and sending the
adjusted cell individual offset to the terminal.
8. The method of claim 7, wherein the change about the active set
includes a removal of a cell from the active set or a change of
strength of cell signal in the active set.
9. The method of claim 8, wherein if a cell in a monitored set is
an adjacent cell of plural cells in the active set, in response to
the change about the active set cell, obtaining, by the network,
cell signal quality of the active set from and measured by the
terminal; selecting a cell in the active set with the best signal
quality among those adjacent cells of the monitored set cell; and
taking, by the network, the cell individual offset of the selected
active set cell relative to the monitored set cell as a new cell
individual offset for the monitored set cell, and sending the new
cell individual offset for the monitored set cell to the
terminal.
10. The method of claim 8, wherein if a cell in a monitored set is
the adjacent cell of only one cell in the active set, in response
to the change of the cell signal strength in the active set,
keeping currently configured cell individual offset for the
monitored set cell unchanged; or, in response to the removal of a
cell from the active set, the network does not set the cell
individual offset for the monitored set cell if the removed active
set cell is the only one adjacent cell of the monitored set cell,
or, if the removed cell is any other cell in the active set,
keeping currently configured cell individual offset for the
monitored set cell unchanged.
11. A network controller in a network, comprising: a configuration
module, adapted to configure a cell individual offset for an
adjacent cell of a cell, wherein each adjacent cell has such an
independent cell individual offset relative to the cell; a sending
module, adapted to send the cell individual offset for an adjacent
cell of an active set cell configured by the configuration module
to a terminal, whereby the terminal evaluates a cell measurement
according to the cell individual offset and submits a measurement
report to the network controller; an instruction module, adapted to
instruct the terminal to perform a cell handoff in accordance with
the measurement report from the terminal.
12. The network controller of claim 11, further comprising: an
acquiring module, configured to acquire a change about the active
set; an adjustment module, adapted to adjust the cell individual
offset for an adjacent cell of the active set cell relative to the
corresponding active set cell according to the change about the
active set and send the adjusted cell individual offset to the
sending module, the sending module is adapted to send the adjusted
cell individual offset to the terminal.
13. The network controller of claim 12, wherein the adjustment
module comprises: a cell determination sub-module, adapted to
determine, in response to the change about the active set, a cell
in the active set with the best signal quality from those adjacent
cells of a cell in the monitored set, in accordance with the signal
quality reported by the terminal; and an adjustment sub-module,
adapted to take the cell individual offset of the determined cell
with the best signal quality relative to the monitored set cell as
a new cell individual offset for the monitored set cell and send
the new cell individual offset to the individual offset sending
module.
14. The network controller of claim 12, wherein the change about
the active set cell include a removal of a cell from the active or
a change of cell signal quality in the active set.
15. The network controller of claim 13, wherein the change about
the active set cell include a removal of a cell from the active or
a change of cell signal quality in the active set.
16. A terminal device comprising: an obtaining module, adapted to
obtain from a network a cell individual offset for an adjacent cell
of a cell in an active set preconfigured by the network, wherein
each adjacent cell of the active set cell has such an independent
cell individual offset relative to the active cell configured by
the network; a measurement module, adapted to measure the active
set cell and the adjacent cell; a measurement evaluation module,
adapted to evaluate the cell measurement according to the result of
the cell measurement and the cell individual offset; a measurement
report module, adapted to send a measurement report to the network
according to the result of the measurement evaluation; and a
handoff execution module, adapted to perform a handoff between
cells according a handoff instruction sent by the network.
17. The terminal device of claim 16, further comprising: means for,
in response to a change about the active set, measuring signal
quality of the cell in the active set and sending the measured
signal quality to the network.
18. The terminal device of claim 16, wherein the change about the
active set includes a removal of a cell from the active set or a
change of signal quality of a cell in the active set.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International Patent
Application No. PCT/CN2007/001742, filed May 31, 2007, which claims
the benefit and priority of Chinese Patent Application No.
200610100263.5, filed with the Chinese Patent Office on Jul. 5,
2006 and entitled "Method For Realizing Handoff Between Cells Based
on Cell Individual Offset", both of which are incorporated herein
by reference in their entireties.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of mobile
telecommunications, and in particular, to a method and apparatus
for handoff between cells in a mobile telecommunication system.
DESCRIPTION OF RELATED ART
[0003] In a cellular mobile communication system, when a terminal,
e.g., a User Equipment (UE) moves from one cell to another, the
terminal needs to be handed off from the cell it originally resided
in to the cell it newly enters. Through the handoff, the location
of the terminal and the resource the terminal uses are updated.
[0004] Handoff is the most important part in mobility management.
It refers to a process in which a link between an original sector
and the terminal is replaced by a link between a new sector and the
terminal when the terminal approaches the edge of an original
serving cell and is to enter another serving cell.
[0005] In a Wideband Code Division Multiple Access (WCDMA) network,
for example, the handoff during a call may be categorized into hard
handoff, soft handoff (handoff between cells in different Node Bs)
and softer handoff (handoff between sectors in the same Node B),
depending on the connection between the terminal and the network,
release of the connection and frequency utilization.
[0006] Soft Handoff (SHO) means that the terminal does not
disconnect from an original Node B when the terminal needs to
communicate with a new Node B. In other words, during a handoff
between the coverage edges of two or more Node Bs, the terminal
first establishes a connection with a new cell by using a same
frequency before disconnecting with the original cell, and receives
signals from several Node Bs at the same time until certain
conditions are met. During the handoff, the terminal communicates
with all candidate Node Bs at the same time over a traffic channel
(TCH).
[0007] The advantage of soft handoff is that it keeps
communications uninterrupted when the terminal is crossing a cell
edge, which greatly reduces call drops caused by handoff. In
addition, soft handoff enables a selective combination of uplink
signals and a maximal combination of downlink signals, which
further improves the performance of radio links.
[0008] Soft handoff in the WCDMA network involves a pilot channel
and a cell set. The WCDMA system uses a pilot channel to access and
handoff to a channel. The terminal identifies the strongest signal
by processing the pilot channel.
[0009] The WCDMA system uses the m sequence (short PN code) to
modulate the pilot channel. The time offsets of the PN code in
different pilots are different, and the offset between two
neighboring pilots is 64 chips. The terminal differentiates cells
by identifying the offset.
[0010] There are three types of cell sets in the WCDMA system:
active set, monitor set and detect set.
[0011] 1. Active set: a collection of cells corresponding to the
traffic channels to which the terminal is currently connected.
[0012] 2. Monitored set: the cells in a monitor set do not belong
to the active set but are configured as neighboring cells to the
cells in the active set and are sent to the terminal by included in
a measurement control message.
[0013] 3. Detected set: the cells in a detected set neither belong
to the active set nor being configured as adjacent cells of the
cells in the active set. These cells are not included in a
measurement control message.
[0014] During a handoff, the terminal often evaluates handoff
events in terms of quality.
[0015] During the evaluation, a cell individual offset (CIO) is
added as an offset value to a cell measurement quality so that the
evaluation of handoff event can be more accurate. For each cell in
a monitored set, there can be set a cell individual offset. This
offset can be either positive or negative. It is add as an offset
value to the cell measurement quality when the terminal performs a
handoff event evaluation.
[0016] As shown in FIG. 1, the dotted curve N1 denotes a threshold
for triggering event 1A, the curve N2 indicates the actual signal
quality of the primary common pilot channel (PCPICH) of a cell and
the curve N3 denotes the threshold after a cell individual offset
is added to the actual signal quality of the PCPICH of the
cell.
[0017] It can be seen from FIG. 1 that, if no cell individual
offset is configured, event 1A is triggered at point B instead of
at point A. In general, a telecom operator detects a sharp rise of
signal quality of a cell in advance by, e.g., a drive test and
configures a positive cell individual offset so that event 1A can
be triggered in advance and that a cell is added to an active set
in time.
[0018] In some special scenarios in an actual network, for example,
at a street corner or an overhead viaduct, the signal strength of a
cell may change suddenly. Therefore, to timely trigger a handoff or
avoid unnecessary handoff, it is very important to correctly
configure the cell individual offset.
[0019] In the prior art, the cell individual offset is configured
in allusion to a cell per se. Each cell has one unique cell
individual offset. Once the cell individual offset for a cell is
configured, it will not change. This unique offset, however, can
result in such a problem that the unique cell individual offset for
a cell does not apply to all adjacent cells of this cell. For
example, assume that cells 1, 2 and 3 are intra-frequency
neighboring cells each other, the cell individual offset for cell 1
is set to 3 dB which may intend to optimize the handoff from cell 2
to cell 1 in, e.g., a corner scenario, so that the handoff can be
triggered timely. Regarding the handoff from cell 3 to cell 2,
however, there is no such a scenario of corner and thus, it is not
required to use a cell individual offset for triggering the handoff
timely.
[0020] In addition, when a cell is added to or removed from an
active set, the information of intra-frequency neighboring cells or
inter-system neighboring cells needs to be modified accordingly. In
this case, the network needs to re-send an updated measurement
control message including the added and/or removed neighboring
cells, to a terminal. Because the cell individual offset is
configured in allusion to a cell itself and is unique, the
information of those unchanged cells and the cell individual offset
for them do not change even when adjacent cells are added or
removed. The unchanged unique cell individual offset for these
unchanged cells, however, may be unsuitable for the added adjacent
cells.
[0021] During the implementation of the present invention, the
inventor realized at least the following problems in the prior art:
the unique cell individual offset configured for a cell per ser may
do not apply to all adjacent cells of the cell. Furthermore, the
unchanged cell individual offset cannot reflect the actual change
of a cell. Therefore, a handoff event evaluation is not accurate
enough in the prior art.
SUMMARY
[0022] Embodiments of the present invention provide methods and
apparatus for handoff between cells so that the evaluation on
handoff events during handoff can be more accurate.
[0023] A method for handoff between cells provided in an embodiment
of the present invention includes:
[0024] sending, by a network, to a terminal a cell individual
offset of a cell in an active set relative to each adjacent cell
preconfigured by the network;
[0025] by the terminal, measuring the active set cell and its
adjacent cell and evaluating of the measurement in accordance with
a measurement result and the cell individual offset of the active
set cell with respective to each adjacent cell;
[0026] submitting, by the terminal, a measurement report to the
network according to the result of the measurement evaluation;
and
[0027] instructing, by the network, the terminal to perform a
handover between cells in accordance to the measurement report.
[0028] A network controller provided in an embodiment of the
present invention includes:
[0029] an individual offset configuration module, adapted to
configure a cell individual offset for each adjacent cell of an
active set cell relative to the active set cell;
[0030] an individual offset sending module, adapted to send the
cell individual offset of a cell in active set relative to each
adjacent cell configured by the configuration module to a terminal,
wherein the terminal performs an evaluation of a cell measurement
according to the cell individual offset and sends a measurement
report; and
[0031] a handoff instruction module, adapted to instruct the
terminal to perform a handoff between cells in accordance with the
measurement report from the terminal.
[0032] A terminal provided in an embodiment of the invention
includes:
[0033] an individual offset obtaining module, adapted to obtain
from a network a cell individual offset of an active set cell
relative to each of its adjacent cells;
[0034] a measurement module, adapted to measure the active set and
the adjacent cells;
[0035] a measurement reporting module, adapted to submit a
measurement report to the network in accordance with the result of
the measurement evaluation, so that the network send a handoff
instruction message to the terminal in accordance with the
measurement report; and
[0036] a handoff execution module, adapted to perform a handoff
between cells in accordance with the handoff instruction message
from the network.
[0037] In embodiments of the present invention, the cell individual
offset is configured based on adjacent relationship between two
cells, contrast to that one unique cell individual offset is set
with respective to a cell per se in the prior art. The cell
individual offset is set for each adjacent of a cell relative to
the cell, instead of the configured unique offset for the cell
itself in the prior. A terminal measures the cell and its adjacent
cells, evaluates the measurement in accordance with corresponding
cell individual offset, and submits a measurement report to the
network in accordance with the measurement evaluation result. The
network instructs the terminal to perform a handoff between cells
according to the measurement report. Therefore, the handoff between
cells can be more accurate and the handoff can be triggered in time
and thus avoids unnecessary handoff. As a result, users can obtain
a better experience.
BRIEF DESCRIPTION OF THE DRAWING
[0038] FIG. 1 shows an application of the cell individual offset in
a soft handoff according to prior art;
[0039] FIG. 2 shows a simplified flowchart of a method for handoff
between cells according to an embodiment of the present
invention;
[0040] FIG. 3 shows a simplified processing flowchart after a
change about a cell in the active set occurs;
[0041] FIG. 4 shows a simplified block diagram of a terminal
according to an embodiment of the present invention; and
[0042] FIG. 5 shows a simplified principle block diagram of a
network controller according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0043] The present invention is described in detail in conjunction
with the accompanying drawings and embodiments.
[0044] Embodiments of the present invention are described using a
WCDMA system that supports the third generation (3G) radio mobile
communication technology as an example in which the present can be
employed. It should be noted, however, that the present invention
also applies to other mobile communication systems, such as
CDMA2000 system or time division-synchronous code division multiple
access (TD-SCDMA) system of the 3G radio mobile communication
technology. Further, it also applies to the second generation (2G)
Narrowband Code Division Multiple Access (N-CDMA) communication
system.
[0045] According to an embodiment of the present invention, the
cell individual offset is configured by way of in allusion to
adjacent cells in the WCDMA network. The network sends to a
terminal a cell individual offset for an adjacent cell of an active
set cell relative to the active set cell preconfigured by the
network. Thus, the terminal can evaluate a cell measurement in
conjunction with the offset after the cell measurement. By this
way, the evaluation of handoff events can be more accurate and thus
a handoff between cells can be more accurate. As a result, users
can obtain a better experience.
[0046] FIG. 2 shows a simplified flowchart of the method for
handoff between cells according to an embodiment of the present
invention.
[0047] In block 21, the network sends a cell individual offset of a
cell in an active set relative to its adjacent cell preconfigured
by the network to the terminal.
[0048] For example, when the terminal accesses a cell initially,
the network sends the cell individual offset of the initial cell
relative to each adjacent cell to the terminal.
[0049] For each adjacent cell of each cell in the active set, the
network may pre-configure a cell individual offset relative to the
each active set cell. The network may set a cell individual offset
for each intra-frequency or inter-system cell. The cell individual
offset may be either positive or negative.
[0050] It should be noted that different adjacent cells of a cell
each has such an independent cell individual offset relative to the
cell. If the initial cell that the terminal enters is different,
the cell individual offset of the initial cell relative to its each
adjacent cell may also be different. For example, if cell 1 is a
cell in the active set and cell 2 is a cell in a monitored set, the
cell individual offset of cell 1 relative to cell 2 (cell
1->cell 2) may be set to X (dB); while if cell 3 is an active
set cell and cell 2 is a monitored set cell, the cell individual
offset of cell 3 relative to cell 2 (cell 3->cell 2) may be set
to Y (dB). If both cell 2 and cell 3 are adjacent cells of cell 1
in the active set, the cell individual offset of cell 1 relative to
cell 2 and the cell individual offset of cell 1 relative to cell 3
may be different from each other.
[0051] At the initial stage when a network is built, the cell
individual offset may not be set (the terminal considers the cell
individual offset to be 0 dB by default). During network
optimization processes, such as drive test and radio frequency (RF)
optimization, however, it may find such scenarios in which cell
individual offset is required. In this case, the cell individual
offset may be configured in accordance with the signals in actual
scenarios. Subsequently, a second round of drive test and RF
optimization is performed to check whether the cell individual
offset is set properly.
[0052] When the terminal enters a cell initially, that is, the
initial cell is the best cell, the network sends the CIO of this
initial cell relative to its individual adjacent cell to the
terminal by a measurement control mode, e.g., by an information
element (IE) CELL INFO contained in a measurement control message
sent from the network.
[0053] When the terminal enters a cell initially, this initial cell
is the best cell. If the initial cell that the terminal enters is
different, the cell individual offset of the initial cell relative
to its each adjacent cell may also be different.
[0054] In block 22, the terminal measures on the active set cell
and its adjacent cell(s), evaluates the measurement in accordance
with the measurement result and the cell individual cell for the
adjacent cell relative to the active set cell, and submits a
measurement report in accordance with the evaluation result to the
network.
[0055] In this block, the cell measurement is similar to prior art.
The cells measured may include the cells in the active set and the
cells in the monitored set. When the terminal accesses a cell
initially, the cells measured may involve this initial cell and its
adjacent cells. After the terminal enters the initial cell for a
time period, there may be plural cells in the active set. In this
case, the terminal also measures the plural cells in the active set
and their adjacent cells.
[0056] Examples may be as follows.
[0057] If, during a time period .DELTA.T of triggering a
measurement report, the terminal measures that the pilot signal
quality of a target cell in the monitored set or in a detected set
fulfills the following formula (1) and the active set is not full,
the target cell is added to a cell list of the active set of the
terminal and marked as a cell to be added to the active set and a
measurement report is submitted to the network. This event can be
called as event 1A or radio link addition event. If the formula (1)
is not fulfilled or the active set is full, the target cell still
belongs to the monitored set.
10 Log m New + C I O New .gtoreq. W 10 Log ( i = 1 N A M i ) + ( 1
- W ) 10 Log M Best - ( R 1 a - H 1 a / 2 ) , ( 1 )
##EQU00001##
[0058] where,
[0059] M.sub.New is the measurement result of the pilot signal
quality of the target cell.
[0060] CIO.sub.New is the cell individual offset of the active set
cell where the terminal currently locates relative to the target
cell, configured by network.
[0061] M.sub.i is the pilot signal quality of the active set
cell.
[0062] N.sub.A denotes the number of cells in the active set.
[0063] M.sub.Best refers to the measurement result of the pilot
signal quality of the best cell in the active set.
[0064] W is a weight parameter sent from the network to the
terminal.
[0065] R.sub.1a is the report threshold of event 1A.
[0066] H.sub.1a is the hysteresis parameter for event 1A.
[0067] Similarly, if, within the time period .DELTA.T of triggering
a measurement report, the pilot signal quality of a target cell in
the active set meets the following formula (2), this target cell is
removed from the active set of the terminal and a corresponding
measurement report is submitted to the network. This event is
called as event 1B or radio link removal event. If the formula (2)
is not fulfilled, this destination cell still belongs to the active
set.
10 Log m Old + C I O Old .gtoreq. W 10 Log ( i = 1 N A M i ) + ( 1
- W ) 10 Log M Best - ( R 1 b - H 1 b / 2 ) , ( 2 )
##EQU00002##
[0068] where,
[0069] M.sub.old is the measurement result of the pilot signal
quality of the destination cell.
[0070] CIO.sub.New is the cell individual offset of the best cell
in the active relative to the target cell configured by the
network.
[0071] M.sub.i is the pilot signal quality of in the active set
cell.
[0072] N.sub.A denotes the number of cells in the active set.
[0073] M.sub.Best refers to the pilot signal quality of the best
cell in the active set.
[0074] W is a weight parameter sent by the network to the
terminal.
[0075] R.sub.1b is the report threshold of event 1B.
[0076] H.sub.1b is the hysteresis parameter of event 1B.
[0077] If, within a time period .DELTA.T of triggering a
measurement report, the pilot signal quality of a target cell in a
monitored set meets the following formula (3) and the active set is
full, replace the worst cell in the cell list of the active set of
the terminal with this target cell and sends a measurement report
to the network, This is called event 1C or radio link replacement
event. If, however, the formula (3) is not fulfilled, this target
cell still belongs to the monitored set.
10Log M.sub.New+CIO.sub.New.gtoreq.10Log
M.sub.InAS+CIO.sub.InAS+H.sub.1c/2, (3)
[0078] Where,
[0079] M.sub.New is the measurement result of the pilot signal
quality of the target cell.
[0080] CIO.sub.New is the cell individual offset of the best cell
in the active set relative to the target cell configured by the
network.
[0081] M.sub.InAS is the measurement result of pilot signal quality
of the worst cell in the active set.
[0082] CIO.sub.InAS is the cell individual offset, configured by
the network, of the best cell relative to the worst cell in the
active set.
[0083] H.sub.1c is the hysteresis parameter for event 1C.
[0084] Some parameters in formulas (1), (2) and (3) above are sent
to the terminal by way of a measurement control mode. The terminal
then performs cell measurement and reports corresponding events,
including but not limited to the preceding three types of events,
to the network in accordance with a evaluation for the cell
measurement.
[0085] It can be seen from the preceding three formulas that the
cell individual cell directly affects the result of the evaluation
of events.
[0086] It can be understood that the evaluation conditions used for
the terminal to evaluate the measurement in accordance with the
cell individual offset for adjacent cell may be other conditions.
For example:
[0087] If, during the time period .DELTA.T, the following formula
(4) is fulfilled and the active set is not full, the terminal
submits a corresponding measurement report to the network and adds
the target cell in the monitored set to the cell list for the
active set of the terminal. This event is called event 1A or radio
link addition event.
Pilot_Ec/No+CIOnew>Best_Pilot_Ec/Io-Reporting_range+Hysteresis_event1-
A (4)
[0088] If, within the time period .DELTA.T, the following formula
(5) is met, the terminal will submit a corresponding measurement
report to the network and removes a cell in the active set from the
list of the active set of the terminal. This event is called event
1B or radio link removal event.
Pilot_Ec/No+CIOold<Best_Pilot_Ec/Io-Reporting_range+Hysteresis_event1-
B (5)
[0089] If, within a time period .DELTA.T, the formula (6) below is
fulfilled and the active set is full, the terminal submits a
corresponding measurement report to the network and uses the best
cell in the monitored set to replace the worst cell in the list of
cells of the active set of the terminal. This report event is also
called event 1C or radio link replacement event.
Best_Candidate_Pilot_Ec/No+CIOnew>Worst_Old_Pilot_Ec/Io+CIOworst+Hyst-
eresis_event1C (6)
[0090] The parameters in the formula (4)-(6) above are defined as
follows.
[0091] Reporting_range denotes the threshold of soft handoff.
[0092] Hysteresis_event1A is the addition hysteresis.
[0093] Hysteresis_event1B denotes the removal hysteresis.
[0094] Hysteresis_event1C is hysteresis of replacement.
[0095] .DELTA.T indicates the time for triggering a measure
report.
[0096] Best_Pilot_Ec/Io denotes the best/highest value of pilots
Ec/Io of all cells in the active set.
[0097] Worst_Old_Pilot_Ec/Io is the worst value of pilots Ec/Io of
all cells in the active set.
[0098] Best_candidate_Pilot_Ec/Io is the best value of the pilots
Ec/Io of all cells in the monitor set.
[0099] Pilot_Ec/Io: measured Ec/Io after filtering;
[0100] CIO.sub.new indicates the cell individual offset for the
cell to be added to the active set relative to the best cell in the
active set.
[0101] CIO.sub.old denotes the cell individual offset for the cell
to be removed from the active set relative to the best cell in the
active set.
[0102] CIO.sub.old is the cell individual offset of the worst cell
in the active set relative to the best cell in the active set.
[0103] Where, some of the parameters above are sent to the terminal
by way of measurement control mode. The terminal then performs cell
measurement and reports corresponding event to the network in
accordance with an evaluation of the measurement. It may be seen
that the cell individual offset directly affects the result of
evaluation on events.
[0104] In block 23, the network instructs the terminal to perform a
handoff between cells according to the measurement report submitted
by the terminal.
[0105] The network performs a handoff evaluation according to the
measurement report. If a handoff condition is fulfilled, the
network sends a handoff instruction message to the terminal. If a
handoff condition cannot be fulfilled, the network does not process
the measurement report.
[0106] The process of handoff between cells may be as follows.
[0107] The terminal sends a corresponding event measurement report
to the network according to the event evaluation process described
in block 22. For example, upon receiving an event 1A report from
the terminal, the network performs a handoff evaluation and, if a
handoff condition can be met, sends to the terminal a handoff
instruction message including the information of a target cell for
handoff. In response to receiving the handoff instruction message,
the terminal adds the target cell to the active set, marks the
target cell in the cell list of the active set as a cell that has
been added to the active set, and returns a handoff completion
message to the network. For another example, in response to
receiving a event 1B report from the terminal, the network performs
a handoff evaluation and sends to the terminal a handoff indication
message containing the information of the target cell for handoff
if a corresponding handoff condition can be met; upon receiving the
handoff indication message, the terminal removes the target cell
from the active set and responds a handoff completion message to
the network.
[0108] The processing for other event reports is similar and
therefore is not described in more detail here.
[0109] The adjacent cells of cells in the active set include the
adjacent cell(s) of the best cell in the active and may also
include the neighboring cells of other non-best active set cells.
Therefore, in an embodiment of the present invention, if the best
cell or any non-best cell in the active set changes, the network
may adjust the cell individual offset for individual adjacent cell
according to the change of the active set cell and sends the
adjusted cell individual offset to the terminal.
[0110] FIG. 3 shows the process if a cell in the active set changes
according to an embodiment of the present invention.
[0111] In block 31, the network acquires a change occurs on a cell
in the active set.
[0112] The change about the cell in the active set may be a removal
of a cell from the active set and/or a change of signal strength of
the cell(s) in the active set.
[0113] The acquirement of the change about active set cell is the
same as the prior art. Thus it is not described in detail in the
embodiment of the present invention.
[0114] In block 32, the network adjusts the cell individual offset
of the active set cell relative to adjacent cells.
[0115] In block 33, the network sends the adjusted cell individual
offset to the terminal.
[0116] In block 34, the terminal measures the adjacent cell and its
adjacent cells, evaluates the measurement according to the
measurement result and corresponding cell individual offset, and
submits a measurement report according to the evaluation
result.
[0117] In block 35, the network instructs the terminal to perform a
handoff between cells according to the measurement report from the
terminal.
[0118] By way of examples, the follows describes the process of
adjustment on the cell individual offset in response to the change
of the cell(s) in the active set.
[0119] Scenario 1: Assuming cell A in a monitored set is a common
neighboring cell of plural cells, e.g., cell 1, cell 2, in an
active set.
[0120] When the signal strength of a cell in the active set
changes, the adjustment of the cell individual offset for the
monitored cell may be as follows.
[0121] If the network knows the signal quality of all active set
cells, the network selects a cell having the best signal quality
among the adjacent cells of cell A in the active set and sets the
cell individual offset of the selected cell relative to cell A as a
new cell individual offset for cell A. If the best cells are the
same active set cell before and after the change of the signal
strength, the network keeps the cell individual offset currently
configured unchanged.
[0122] If the network does not know the signal quality of the cells
in the active set, the network keeps the cell individual offset
currently configured unchanged.
[0123] If a cell in the active set is removed, the adjustment on
the cell individual offset for the monitored cell may be as
follows:
[0124] If the network knows the signal quality of cells in the
active set, the network selects, in the active set, a cell with the
best signal quality among those adjacent cells of cell A and sets
the cell individual offset of the selected cell relative to cell A
as the new CIO for cell A. If the best cell before and after the
removal of cell are the same, the network keeps the cell individual
offset currently configured unchanged.
[0125] If the network does not know the signal quality of cells in
the active set and the active set cell corresponding to the current
cell individual offset is not removed (e.g., cell 1 in the active
cell is not removed), the network keeps the cell individual offset
currently configured unchanged. If the cell in the active set
corresponding to the current cell individual offset is removed
(e.g., cell 1 is removed), the network randomly selects an active
set cell, e.g., cell 2, from those cells which are the adjacent
cells of cell A and sets the cell individual offset of this
randomly selected cell relative to cell A as the new cell
individual offset for cell A.
[0126] It can be seen from the above that, regarding the network
knows the signal quality of cells in the active set, if the signal
strength of a cell in the active set changes or a cell is removed
from the active set, the terminal measures the signal quality of
the cells in the active set and reports the measurement result to
the network. The network then selects in the active set a cell
having the best signal quality among those adjacent cells of cell A
and then sets the cell individual offset for cell A. More detail
examples can be as follows.
[0127] For example, suppose there are three cells in the active
set: cell 1, cell 2 and cell 3, and there is only one cell in the
monitored set, cell A. Assuming that cell 1 is the best cell and
cell A is a common adjacent cell of both cell 1 and cell 2 but not
a adjacent cell of cell 3. In this case, For cell A, there are two
cell individual offset values configured in the network, one is the
cell individual offset of cell A relative to cell 1 (cell
1->cell A) and the other is the cell individual offset cell A
relative to cell 2 (cell 2->cell A). The network, however, does
not send both these two offset values to the terminal simultaneity.
Because, as specified in the protocol, in such case, for one
monitored cell (here for cell A), the network can send only one
cell individual offset to the terminal for evaluating the signal
quality of this monitored cell. In this example, the network sends
the cell individual offset of cell 1 relative cell A (cell
1->cell A) to the terminal for evaluating the signal quality of
cell A.
[0128] For another example, if the signal strength of a cell in the
active set changes, the network selects a cell in the active set
with the best signal quality from adjacent cells of cell A and
takes the cell individual offset of the selected cell relative to
cell A as the new offset for cell A. For example, if cell 2 has
better signal quality than cell 1 has and cell 2 becomes the best
cell in the active set, the cell individual offset of cell 2
relative to cell A is selected as the new CIO for cell A and sent
to the terminal for evaluating the signal quality of cell A.
[0129] For further another example, assuming cell 3 in the active
set becomes the best cell. In this situation, for cell A relative
to cell 3, there is no such a cell individual offset because cell A
is not an adjacent cell of cell 3. For cell A, however, it is still
required to set a corresponding cell individual offset because cell
A is still the adjacent cell of cell 1, cell 2 and still belongs to
the monitored set. In this case, selects the one with better signal
quality among cell 1 and cell 2 and sets the cell individual offset
of the selected cell relative to cell A as the new cell individual
offset for cell A and sent this new offset to the terminal. If the
signal quality of cell 1 is still better than that of cell 2, keeps
the cell individual offset currently configured unchanged.
[0130] For further another embodiment, if a cell in the active set
is removed, the network selects, from other cells left in the
active set, a cell with the best signal quality among those
adjacent cells of cell A and sets the cell individual offset of the
selected cell relative to cell A as the new cell individual offset
for cell A. For example, if the original best cell, cell 1, is
removed and cell 2 becomes the best cell, the network updates the
new cell individual offset for cell A using the offset of cell 2
relative to cell A (cell 2->cell A) and sends the updated offset
to the terminal. While if cell 1 is removed and cell 3 becomes the
best cell, regarding cell 3 relative to cell A, there is no such a
cell individual offset because cell A is not an adjacent cell of
cell 3. For cell A, however, it is still required to have a cell
individual offset because cell A is still the adjacent cell of cell
2 and thus still belongs to the monitored set. In this situation,
sets the cell individual offset cell 2 relative to cell A as the
new offset for cell A and sends the new cell individual offset for
cell A to the terminal. If the cell with the best signal cell in
the active set among those adjacent cells of cell A do not change
before and after the removal of a cell, for example, if cell 3 is
removed and the signal quality of cell 1 is still better than the
signal quality of cell 2 has, then keep the cell individual offset
currently configured unchanged. If the signal quality of cell 2
becomes better than that of cell 1, take the offset of cell 2
relative to cell A as the new cell individual offset for cell A and
send the new cell individual offset to the terminal.
[0131] For another example, if cell 1 is the best cell and cell A
is the adjacent cell of cell 2 and cell 3, when the signal strength
of a active set cell changes or is removed, the network always
selects a better one from cell 2 and cell 3 and takes the cell
individual offset of the selected better cell relative to cell A as
the new cell individual offset for cell A and sends it to the
terminal for evaluating the quality of cell A.
[0132] 2. Another scenario: If cell A in the monitored set is the
adjacent cell of only one cell, e.g., cell 1, in the active set,
the cell individual offset for cell A configured currently is that
of cell A relative to cell 1. Because cell 1 is the only adjacent
cell of cell A before and after the signal strength of a cell in
the active set changes. Therefore, keeps the currently configured
cell individual offset unchanged.
[0133] If a cell not cell 1 in the active set is removed, keeps the
cell individual offset currently configured unchanged. If cell 1 is
removed, then cell A does not belong to the monitored set. In this
case, for cell A, it does not need to configure a cell individual
offset for it.
[0134] In accordance with embodiments of the present invention, the
cell individual offset is configured based on adjacent relation
between two cells. For each adjacent cell of a cell, an independent
cell individual offset is pre-configured relative to the cell by a
network. The network sends the cell individual offset preconfigured
for an adjacent cell of an active set cell to a terminal. The
terminal evaluates on a cell measurement according to the cell
measurement result and the cell individual offset and submits a
measurement report to the network. The network performs a handoff
evaluation according to the measurement report and instructs the
terminal to perform a handoff between cells based on the evaluation
result. Therefore, the negative impact on the handoff between cells
caused by configuring a unique cell individual offset for each cell
itself as the prior art can be avoided.
[0135] According to embodiments of the present invention, the cell
individual offset is configured in allusion to adjacent cell. In an
embodiment, if the signal strength of a cell in an active set
change, the network adjusts the cell individual offset for adjacent
cell of corresponding cell relative to the cell in real time based
on the change of the signal quality accordingly. In another
embodiment, if a cell is removed from the active set, the network
adjusts the cell individual offset for the adjacent cell of a
corresponding cell accordingly. By this way, the accuracy of cell
measurement evaluation performed by the terminal can be further
ensured. The handoff can be triggered in time and can avoid any
unnecessary handoff, thus improving the handoff efficiency.
[0136] The method provided in the embodiments may applies to all
handoff that may use a cell individual offset technology, including
but not limited to intra-frequency and inter-system handoff, which
may be soft handoff, softer handoff, or hard handoff.
[0137] According to other embodiments of the present invention, a
terminal and a network controller are provided.
[0138] FIG. 4 is a simple block diagram of a terminal provided in
an embodiment of the present invention.
[0139] Please refer to FIG. 4, the terminal includes an individual
offset acquiring module 41, a measurement module 42, a measurement
evaluating module 43, a measurement reporting module 44 and a
handoff execution module 45. As an example, the terminal may
further include a reporting module 46. The individual offset
acquiring module 41 is adapted to obtain the cell individual offset
of an active set cell relative to each of its neighboring cells
from the network. The measurement module 42 is adapted to measure
the active set cell and its neighboring cells. The measurement
evaluating module 43 is adapted to perform an evaluation of the
measurement according to the measurement result provided by the
measuring module 42 and the cell individual offset. The measurement
reporting module 44 is adapted to submit a measurement report to
the network in accordance with the result of measurement evaluation
performed by the measurement evaluating module 43, so that the
network can send a handoff instruction message to the terminal
according to the measurement report. The handoff execution module
45 is adapted to perform a handoff between cells according to the
handoff instruction message from the network.
[0140] For the measurement evaluation performed by the measurement
evaluating module 43 in accordance with the measurement result
provided by the measuring module 42 and the cell individual offset,
it can refer to the corresponding description provided in the above
method embodiments of the present invention.
[0141] The terminal provided, according to another embodiment of
the present invention, further includes a reporting module 46,
which is adapted to measure the signal quality of the cell(s) in
the active set and to report the measurement to the network in
response a change about the cell in the active set. By this way,
the network can know the change of the cell in the active set based
on the signal quality of cell and, thus, adjusts the cell
individual offset of an active set cell relative to each
corresponding neighboring cell according to the signal quality
change and sends the adjusted offset to the terminal.
[0142] FIG. 5 shows a simple block diagram of a network controller
provided in an embodiment of the present invention. Refer to FIG.
5, the network controller includes an individual offset
configuration module 51, an individual offset sending module 52 and
a handoff instruction module 55. The individual offset
configuration module 51 is adapted to configure a cell individual
offset of an active set cell relative to its each adjacent cell.
For each different adjacent cell of a cell, there is such an
independent cell individual offset relative to the cell
preconfigured by the configuration module. The individual offset
sending module 52 sends the cell individual offset of an active set
cell relative to each of its adjacent cells to a terminal. The
terminal then evaluates a cell measurement and submits a
measurement report to the network. For example, when the terminal
enters a cell initially, the individual offset sending module 52
sends the cell individual offset of this initial cell relative to
each of its adjacent cells to the terminal. After the terminal
enters the initial cell, if the original cell(s) in the active set
changes, the network controller adjusts the cell individual offset
for each adjacent cell correspondingly based on the change. In this
case, the individual offset sending module 52 sends the adjusted
cell individual offset of active set cell relative to its each
adjacent cell to the terminal so as to ensure the correction and
veracity of the cell individual offset. The handoff instruction
module 55 instructs the terminal to perform a handoff between cells
according to the measurement report from the terminal.
[0143] According to an embodiment of the present invention, in
order to enable the terminal to obtain a proper cell individual
offset upon the change on the cell in the active set, the network
controller may further includes an active set cell change acquiring
module 53 and an individual offset adjustment module 54. The active
set cell change acquiring module 53 is adapted to acquire the
change about the active set. The individual offset adjustment
module 54, in response to the change of the active set cell, adjust
the cell individual offset for the adjacent cell of corresponding
active set cell and send the adjusted cell individual offset to the
individual offset sending module 52. The individual offset sending
module 52 sends the adjusted cell individual offset to the
terminal.
[0144] The change about the active set cell may be caused by a
removal of a cell from the active set, or a change of the signal
strength of an active set cell. For this change about the active
set, the network or the terminal may re-determine the cells in the
active set caused by the change. As shown in FIG. 5, in an
embodiment of the present invention, the individual offset
adjustment module 54 includes a cell determining sub-module 541 and
an adjustment sub-module 542. The cell determining sub-module 541,
in responsive to the change about the active set, determine a cell
in the active set with the best signal quality among those adjacent
cells of a cell in a monitored set according to the signal quality
reported by the terminal. The adjusting sub-module 542 sets the
cell individual offset of the determined cell with the best signal
quality relative to the monitored set cell as the offset for the
monitored set cell and sends the cell individual offset to the
individual offset sending module 52. For the adjustment of the cell
individual offset performed by the adjustment sub-module 542, it
can be referred to the corresponding description of the method
according to the preceding embodiments of the present
invention.
[0145] It can be seen that the terminal and the network controller
provided in embodiments of the present invention can eliminate the
negative and adverse effect on the handoff between cells caused by,
for each cell, configuring only one unique cell individual offset
in allusion to the cell itself in the prior art and thus, handoff
between cells can be more accurate. Therefore, in turn, users can
obtain a better experience.
[0146] Although the invention has been described by exemplary
embodiments, it should be noted that the invention is not limited
to such embodiments. Those skilled in the art will readily observe
that various modifications and alterations of the embodiment may be
made without departing from the spirit and scope of the invention
while retaining the teachings of the invention. The invention is
intended to cover those modifications and alterations provided that
they fall within the scope of protection defined by the following
claims or their equivalents.
* * * * *