Title of Invention

A METHOD AND NETWORK CONTROLLER FOR CONTROLLING A CELL RESELECTION MODE OF A MOBILE STATION WHILE THE MOBILE STATION RESIDES IN A CELL

Abstract A communication system (200) controls a cell reselection mode of a mobile station (202) while the mobile station resides in a cell (210) by determining a cell reselection mode of the mobile station, determining whether the mobile station is experiencing a change in radio frequency (RF) conditions, and when the mobile station is experiencing a change in RF conditions, instructing the mobile station to change a cell reselection mode used by the mobile station.
Full Text DESCRIPTION
A METHOD AND NETWORK CONTROLLER FOR CONTROLLING
A CELL RESELECTION MODE OF A MOBILE STATION WHILE
THE MOBILE STATION RESIDES IN A CELL
Reference(s) to Related Application(s)
The present application claims priority from provisional application serial no.
60/519,874, entitled "Method and Apparatus for Controlling a Cell Reselection Mode,"
filed November 13, 2003, which is commonly owned and incorporated herein by
reference in its entirety.
Field of the Invention
The present invention relates to a method and network controller for controlling a
cell reselection mode of a mobile station whie the mobile station resides in a cell, and
generally to cellular communication systems, and, in particular, to cell reselection in a
cellular communication system.
Background of the Invention
The General Packet Radio Service (GPRS) standard provides a compatibility
standard for cellular mobile telecorr munications systems. The GPRS standard ensures
that a mobile station (MS) operating in a GPRS system can obtain communication
services when operating in a system manufactured according to the standard. To ensure
compatibility, radio system paramete s and call processing procedures are specified by the
standard, including call processing steps that are executed by an MS and a network in
order to provide for cell reselection.
FTG. 1 is a block diagram of an exemplary GPRS communication system 100 of
the prior art. Communication system 100 includes multiple base transceiver stations
(BTSs) 110, 112 mat are each coupled to a Base Station Controller (BSC) 114. Each
BTS 110, 112 provides communica:ion services to a respective coverage area, or cell,
serviced by the BTS. BSC 114 is f .irther coupled to a Packet Control Unit (PCU) 116.


PCU 116 is coupled to a Serving GPRS Support Node (SGSN) 118 that is, in turn,
coupled to a Gateway GPRS Su sport Node (GGSN) 120, and via the GGSN, to an
external network 130. BTSs 110 and 112, BSC 114, PCU 116, SGSN 118, and GGSN
120 are collectively referred to as i. communication system network 122. Communication
system 100 further includes an VIS 102 that resides in a first cell and is provided
communication services by a BTS 110 serving that cell. MS 102 and serving BTS 110
communicate via an air interface 104 comprising a downlink 105 and a uplink 106.
Downlink 105 comprises multipl; logical channels, including a broadcast channel, at
least one traffic channel, and at l;ast one control channel. Uplink 106 also comprises
multiple logical channels, including an access channel, at least one traffic channel, and at
least one control channel.
When MS 102 activates in communication system 100, the MS is conveyed a
Neighbor List by the serving cell, ihat is, the cell associated serving BTS 110. Typically,
the Neighbor List includes a list :>f multiple broadcast channels, typically 32 broadcast
channels, associated with corresponding neighbor cells, such as a neighbor cell associated
with BTS 112. MS 102 then monitors the listed broadcast channels.
Tn a typical GPRS communication system such as communication system 100,
when MS 102 activates in, or roams into, the cell serviced by serving BTS 110, die MS is
further is informed, via a Packet System Information (PSI) message transmitted by the
BTS, of a cell reselection mode supported by the serving cell. In a GPRS communication
system, the cell reselection mode may be any one of three modes. In a first cell
reselection mode, NC0 (Network Control Order 0), cell reselection is autonomously
performed by an MS based on a strength of a received downlink signal associated with
the serving cell, that is, of a signa received by MS 102 from BTS 110 via downlink 105.
In a second cell reselection mode, NCI, cell reselection is autonomously performed by an
MS based on a received signal strength of a signal received via a broadcast channel of the
Neighbor List, such as a signal received by MS 102 from BTS 112 via a downlink 108
associated with BTS 112. Tn cell reselection mode NCI, the MS is further required to
send measurement reports to the network. In a third cell reselection mode, NC2, cell
reselection is controlled by a network, such as network 122. In the third cell reselection
mode, an MS sends Packet Measurement Reports (PMRs) to me network, which PMRs
include received signal strength measurements associated with the serving cell, such as
the cell associated with serving BTS 110, and with multiple, typically six, broadcast
channels of the Neighbor List. Based on the received PMRs, network 122 may then
instruct MS 102 to perform a cell res election.
In GPRS communication sys ems, the cell reselection mode supported by a cell is
uniformly applied throughout the eel . That is, all MSs serviced by the cell, that is, by the
BTS serving the cell, must use a same, fixed cell reselection mode. A result of the
uniform application of a cell reselection procedure is a sub-optimal execution of cell
reselections and unnecessarily conge sted air interfaces. For example, in cell reselection
modes NCO and NCI, an MS such as MS 102 is not aware of congestion level of a cell
selected by the MS as a target cell. As a result, in cell reselection modes NCO and NCI,
an MS may request a handoff to a congested target cell with a result that the MS and other
users actively engaged in a communication in the target cell experience degradation in a
quality of their communications. Th s result is particularly undesirable when the MS may
have been experiencing acceptable conditions in its current cell. By way of another
example, cell reselection modes NCI and NC2 require an MS, such as MS 102, to
periodically transmit measurement reports to a network, such as network 122. When the
channel conditions experienced by MS 102 are consistently of acceptable quality, the
periodic measurement reports transrritted by the MS are, in essence, redundant and are of
no use to the network. As a result, when the cell serviced by a BTS, such as BTS 110,
includes a large number of MSs, air interface 104, and in particular uplink 106, may
become congested with redundant measurement reports that are of little, if any, value to
the network. This is of particula- importance in light of the fact that over-the-air
bandwidth is often a constraining factor in system performance.
Therefore, a need exists for of cell reselection modes in a cell.
Summary of the Invention
Accordingly, the present invention provides a method for controlling a cell
reselection mode of a mobile station while the mobile station resides in a cell comprising:
determining a cell reselection moce of the mobile station, wherein the cell reselection
mode comprises one or more of (i) whether a cell reselection will be autonomous or
network-controlled and (ii) the reporting requirements of the mobile station; determining
a. signal quality metric associated with the mobile station; determining an uplink coding
scheme based on the signal quality metric; determining whether the mobile station is
experiencing a change in radio frequency (RF) conditions based on the determined uplink
coding scheme; and when the mobile station is experiencing a change in RF conditions,
instructing the mobile station to change the cell reselection mode used by the mobile
station.
The present invention also provides a network controller comprising: at least one
memory device that stores a default cell reselection mode associated with a cell serviced
by the network controller; and a processor coupled to the at least one memory device that
determines a cell reselection mode of a mobile station located in the cell, wherein the cell
reselection mode comprises one or more of (i) whether a cell reselection will be
autonomous or network-controlled and (ii) the reporting requirements of the mobile
station, determines a signal quality metric associated with the mobile station, determines
an uplink coding scheme based or the signal quality metric, determines whether the
mobile station is experiencing a change in radio frequency (RF) conditions based on the
determined uplink coding scheme, and when the mobile station is experiencing a change
in RF conditions, instructs the mobile station to change the cell reselection mode.
Preferably, determining whe her the mobile station is experiencing a change in
radio frequency (RF) conditions comprises evaluating a downlink signal and instructing
the mobile station to change a cell reselection mode used by the mobile station comprises:
when the evaluation of the downlink signal indicates a deterioration of radio frequency
(RF) conditions experienced by the mobile station and the mobile station is using an
autonomous cell reselection mode, instructing the mobile station to switch to a network-
controlled cell reselection mode; and when the evaluation of the downlink signal
indicates an improvement of radio frequency (RF) conditions experienced by the mobile
station and the mobile station is using a network-controlled cell reselection mode,
instructing the mobile station to switch to an autonomous cell reselection mode.
Determining whether the mobile station is experiencing a change in radio frequency (RF)
conditions may comprise evaluating a downlink signal and changing a cell reselection
mode of the mobile station may conprise, when the evaluation of the downlink signal
indicates an improvement of radio frequency (RF) conditions experienced by the mobile
station and the mobile station is using an autonomous cell reselecdon mode that requires
reporting, instructing the mobile station to switch to an autonomous cell reselection mode
that does not require reporting. Determining whether the mobile station is experiencing a
change in radio frequency (RF) conditions may comprise evaluating an uplink signal and
changing a cell reselection mode of the mobile station may comprise: when the evaluation
of die uplink signal indicates a deterioration of radio frequency (RF) conditions
experienced by the mobile station and the mobile station is using an autonomous cell
reselection mode, instructing the mobile station to switch to a network-controlled cell
reselection mode; and when the evaluation of the uplink signal indicates an improvement
of radio frequency (RF) conditions experienced by the mobile station and the mobile
station is using a network-controlled cell reselection mode, instructing the mobile station
to switch to an autonomous cell reelection mode. Determining whether the mobile
station is experiencing a change in adio frequency (RF) conditions may also comprise
evaluating an uplink signal and eta nging a cell reselection mode of the mobile station
may comprise, when the evaluation of die uplink signal indicates an improvement of
radio frequency (RF) conditions experienced by the mobile station and the mobile station
is using an autonomous cell reselection mode diat requires reporting, instructing the
mobile station to switch to an autonomous cell reselection mode that does not require
reporting. Determining whetiier the mobile station is experiencing a change in radio
frequency (RF) conditions may comprise evaluating a downlink signal and instructing the
mobile station to switch a cell reselection mode used by the mobile station may comprise,
when the evaluation of the downlink signal indicates an improvement of radio frequency
(RF) conditions experienced by the mobile station, instructing the mobile station to
lengthen a reporting period associated with a cell reselection mode used by the mobile
station.
Preferably, the processor determines whether the mobile station is experiencing a
change in radio frequency (RF) conditions by evaluating a downlink signal quality metric
associated with a downlink signal and the processor instructs the mobile station to change
a cell reselection mode used by tie mobile station by, when the evaluation of the
downlink signal quality metric indicates a deterioration of radio frequency (RF)
conditions experienced by the mobile station and the mobile station is using an
autonomous cell reselection mode, instructing the mobile station to switch to a network-
controlled cell reselection mode, and when the evaluation of the downlink signal quality
metric indicates an improvement of "adio frequency (RF) conditions experienced by the
mobile station and the mobile station is using a network-controlled cell reselection mode,
instructing the mobile station to svĀ» itch to an autonomous cell reselection mode. The
processor may determine whether the mobile station is experiencing a change in radio
frequency (RF) conditions by evaluating a downlink signal quality metric associated with
a downlink signal and the processor instructs the mobile station to change a cell
reselection mode used by the mobile station by, when the evaluation of the downlink
signal quality metric indicates an improvement of radio frequency (RF) conditions
experienced by the mobile station and the mobile station is using an autonomous cell
reselection mode that requires reporting, instructing the mobile station to switch to an
autonomous cell reselection mode that does not require reporting. The processor may
preferably determine whether the mobile station is experiencing a change in radio
frequency (RF) conditions by evaluating an uplink signal quality metric associated with
an uplink signal and the processor -nstructs the mobile station to change a cell reselection
mode used by the mobile station by, when the evaluation of the uplink signal quality
metric indicates a deterioration ol radio frequency (RF) conditions experienced by the
mobile station and the mobile stition is using an autonomous cell reselection mode,
instructing the mobile station to switch to a network-controlled cell reselection mode, and
when the evaluation of the uplink signal quality metric indicates an improvement of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using a network-controlled cell re-election mode, instructing the mobile station to switch
to an autonomous cell reselection mode. Preferbly, the processor determines whether the
mobile station is experiencing a change in radio frequency (RF) conditions by evaluating
an uplink signal quality metric associated with an uplink signal and the processor
instructs the mobile station to dunge a cell reselection mode used by the mobile station
by, when the evaluation of the uplink signal quality metric indicates an improvement of
radio frequency (RF) conditions experienced by the mobile station and the mobile station
is using an autonomous cell reselection mode that requires reporting, instructing the
mobile station to switch to an autonomous cell reselection mode that does not require
reporting. Preferably, the proces.sor determines whether the mobile station is experiencing
a change in radio frequency (RF) conditions by evaluating a downlink signal quality
metric associated with a downlink signal and the processor instructs the mobile station to
switch a cell reselection mode used by the mobile station by, when the evaluation of the
downlink signal indicates an irr provement of radio frequency (RF) conditions
experienced by the mobile station, instructing the mobile station to lengthen a reporting
period associated with a cell reselection mode used by the mobile station. The network
controller preferably comprises at least one of a Base Station Controller, a Packet Control
Unit, and a Packet Control Function.
Brief Description of the Accompanying Drawings
FIG. 1 is a block diagram of a wireless communication system of the prior art.
FIG. 2 is a block diagram of a wireless communication system in accordance with
an embodiment of the present invention.
FIG. 3 is a logic flow diagrim of a method by which the communication system of
FIG. 2 executes a dynamic, intra-cell adjustment of a cell reselection mode in accordance
with various embodiments of the present invention.
Detailed Description of the Invention
To address the need for a method and apparatus that optimizes an application of
cell reselection modes in a cell, ;t communication system is provided that controls a cell
reselection mode of a mobile station while the mobile station resides in a cell by
determining a cell reselection mode of the mobile station, determining whether the
mobile station is experiencing a change in radio frequency (RF) conditions, and when the
mobile station is experiencing a change in RF conditions, instructing the mobile station to
change a cell reselection mode used by the mobile station.
Generally, an embodiment of the present invention encompasses a method for
controlling a cell reselection mode of a mobile station while the mobile station resides in
a cell. The method includes determining a cell reselection mode of the mobile station,


determining whether the mobile station is experiencing a change in radio frequency (RF)
conditions, and when the mobile station is experiencing a change in RF conditions,
instructing the mobile station to change a cell reselection mode used by the mobile
station.
Another embodiment of the present invention encompasses a network controller
comprising at least one memory device that stores a default cell reselection mode
associated with a cell serviced by the network controller. The network controller further
comprises a processor coupled to tie at least one memory device that determines a cell
reselection mode of a mobile static n located in the cell, determines whether the mobile
station is experiencing a change in radio frequency (RF) conditions, and when the mobile
station is experiencing a change in RF conditions, instructs the mobile station to change a
cell reselection mode.
The present invention may be more fully described with reference to FTGs. 2-3.
FIG. 2 is a block diagram of a wirek ss communication system 200 in accordance with an
embodiment of the present invention. Communication system 200 includes multiple
transceivers 220, 222 (two shown), such as Base Transceiver Stations (BTSs), that are
each opcrably coupled to a netwerk controller 230. Network controller 230 may
comprise one or more of a Base Station Controller (BSC), a Packet Control Unit (PCU),
and a Packet Control Function (PCF) and the functions of network controller 230 may be
implemented in any one of such elements or may be distributed among such elements. In
other embodiments of the present irvention, each BTS 220, 222 may be coupled to a
separate network controller, or may share some elements of the network controller, such
as a PCU, and be separately coupled :o other elements of the network controller, such as
BSCs. Each BTS 220, 222 provides wireless communication services to mobile stations
(MSs) located in a respective coverage area, or cell, 210, 212 associated with the BTS.
Communication system 200 further includes at least one mobile station (MS) 202
thai, is provided communication services by a source BTS, that is, BTS 220, that services
a cell 210 in which the MS resides. MS 202 and BTS 220 communicate via an air
interface 214 comprising a downlink 216 and an uplink 218. Downlink 216 comprises
multiple logical channels, including tt least one broadcast channel, at least one traffic
channel, and at least one control channel. Uplink 218 also comprises multiple logical

channels, including an access channel, at least one traffic channel, and at least one control
channel.
Communication system 200 further includes a Support Node 240 coupled to
network controller 230. Support Node 240 typically includes one or more Serving GPRS
Support Nodes (SGSNs) that are c ach coupled to one or more Gateway GPRS Support
Nodes (GGSNs). However, the precise architecture of Support Node 240 is up to an
operator of communication systen 200 and is not critical to the present invention.
Together, the multiple BTSs 220, 2 22, network controller 230, and Support Node 240 are
collectively referred to herein as a communication system network 250.
Each of MS 202, network controller 230, and Support Node 240 includes a
respective processor 204, 232, 242, operably coupled to, or associated with, a respective
at least one memory device 206, 234, 244. Each of processors 204, 232, and 242
comprises one or more microprocessors, microcontrollers, digital signal processors
(DSPs), combinations thereof or such other devices known to those having ordinary skill
in the art. Each of the at least one memory devices 206, 234, and 244 comprises one or
more memory devices such as a r.indom access memory (RAM), a dynamic random
access memory (DRAM), and/or a read only memory' (ROM) or equivalents thereof, that
stores data and programs that may be executed by the corresponding processor.
Network controller 230 mainiains a record, in the at least one memory device 234,
of each MS active in communicatior system 200 and serviced by the network controller.
Preferably, network controller 230 maintains the records of active MS's by storing an MS
identifier uniquely associated with ei.ch such active MS. Network controller 230 further
maintains a record in memory device 234 and in association with each cell and associated
BTS, such as cell 210 and BTS 220, of a default cell reselection mode associated with the
cell and BTS. Support Node 240 ma: ntains, in the at least one memory device 244 of the
Support Node, a record of Neighbor List associated with each MS serviced by the
Support Node.
Communication system 200 comprises a wireless packet data communication
system. In order for MS 202 to establish a packet data connection with an external
network 260, each of MS 202, BTSs 120 and 222, network controller 230, and SGSN 240

operates in accordance with the General Packet Radio Service (GPRS) standard, and in
particular with 3GPP (Third Generation Partnership Project) TS (Technical Specification)
04.60 version 8.9.0, TS 05.02, version 8.10.0, and 3GPP TS 05.08 version 8.18.0, which
standards are hereby incorporatec. by reference herein and copies of which may be
obtained from the 3GPP via the Internet or from the 3GPP Organization Partners'
Publications Offices at Mobile Competence Centre 650, route des Lucioles, 06921
Sophia-Antipolis Cedex, France. The GPRS standards specify wireless
telecommunications system operating protocols, including radio system parameters and
call processing and handoff proce iures, for GPRS communication systems. By operating
in accordance with the GPRS stardard, a user of MS 202 can be assured that MS 202 will
be able to communicate with conmunication system network 250 and establish a packet
data communication link witr an external network, such as network 260, via
communication system network 250.
GPRS communication systems, such as communication system 200, use a
combination of frequency and lime division multiplexing to define a physical channel,
with the result that a physical channel is defined as a sequence of radio frequency
channels and timeslots. The physical channel comprises multiple logical channels,
wherein each logical channel comprises a portion of the physical channel, such as a
portion of a timeslot, a timeslo:, or multiple timeslots, that is allocated for conveyance of
control or traffic data. Typically, a radio frequency channel comprises eight time slots,
which eight time slots constitute a frame. A 52-mulitframe, comprising 52 frames, is
typically used to support packet data traffic and associated control channels and a 51-
multiframe, comprising 51 frames, is typically used to support broadcast and common
control channels.
When MS 202 activates in communication system 200, Support Node 240
assembles and conveys to the MS a Neighbor List comprising logical channels associated
with neighboring cells, such as cell 212 serviced BTS 222, that are potential handoff or
reselection candidates for V.S 202. Typically, the Neighbor List comprises a list of
broadcast channels (BCCH) associated with each cell of multiple neighbor cells, such as a
broadcast channel associatei with neighbor cell 212 and neighbor BTS 222. Upon
receiving the Neighbor List, MS 202 stores the Neighbor List in the at least one memory
device 206 of the MS. In order to determine whether to engage in a cell reselection, MS
202 monitors a downlink signal, typically a pilot signal, of each broadcast channel
identified in the Neighbor List an J determines a signal quality metric, such as a signal
strength, a signal-to-noise ratio (SNR), or a bit error rate (BER), with respect to each
monitored signal. MS 202 further determines a signal quality metric with respect to
signals received from serving BTS 220.
In addition, BTS 220 broadcasts system operating parameters in Packet System
Information (PSI) messages via a broadcast channel of downlink 216. PSI messages are
described in detail in 3GPP TS 05.02. Among the system operating parameters included
in die PSI messages is a cell reselection mode supported by cell 210 and associated BTS
220. The cell reselection mode ma/ be any one of multiple modes. For example, a first
cell reselection mode, NC0 (Netwo k Control Order 0), provides for an autonomous cell
reselection by an MS based on a signal quality metric determined by the MS with respect
to a downlink signal associated with serving cell 210, that is, with a signal transmitted by
BTS 220. By way of another example, a second cell reselection mode, NCI, provides for
an autonomous cell reselection by an MS based on signal quality metric determined by
the MS with respect to a broadcasi channel of the Neighbor List, such as a downlink
signal associated with cell 212 and transmitted by BTS 222. In cell reselection mode
NCI, the MS is further required to s;nd measurement reports to network 250. By way of
yet another example, a third cell reselection mode, NC2, provides for a network-
controlled cell reselection based on iignal quality metrics determined by an MS, such as
MS 202, with respect to a serving c:ll 210 and an associated BTS 220 and further with
respect to at least one broadcast channel of the Neighbor List, such as a downlink signal
associated with neighbor cell 212 and transmitted by neighbor BTS 222. The MS
conveys the signal quality metrics to network 250, and in particular to network controller
230. For example, MS 202 may convey the signal quality metrics to network 250 in a
format of a Packet Measurement Report (PMR). Based on the received signal quality
metrics, network 250 then instructs the MS to perform a cell reselection.
In the prior art, each cell in i. communication system, such as a cell serviced by
BTS 110, uniformly applies a cell reselection mode to all MSs serviced by the cell. A
result of the uniform application of a cell reselection mode may be an inappropriate
execution of cell reselection and a congested aii interface. In order to overcome these
problems, communication system 200 provides for dynamic, intra-cell adjustment of a
cell reselection mode on an MS-by-MS basis.
FIG. 3 is a logic flow diagram 300 of a method by which communication system
200 executes a dynamic, intra-cel. adjustment of a cell reselection mode in accordance
with various embodiments of the present invention. Logic flow diagram 300 begins (302)
when network 250, and in particular network controller 230, determines (304) a cell
selection mode used by an MS, such as MS 202, serviced by the controller. In one
embodiment of the invention, whan MS 202 activates in, or roams into, a cell serviced by
controller 230, such as cell 210 network controller 230 instructs the MS 202 to use a
default cell selection mode for tie cell. Network controller 230 further stores the MS's
cell reselection mode in associntion with the MS, such as in association with tan MS
identifier uniquely associated with the MS, in the at least one memory device 234 of the
network controller. Step 304 then comprises determining the default cell reselection
mode of the cell.
For example, when MS 202 activates in cell 210 or roams into cell 210, network
controller 230 may instruct the MS to use an autonomous cell reselection mode, such as
an NC0 mode or an NCI moce, or may instruct the MS to use a network-controlled cell
reselection mode, such as an NC2 mode. The default cell reselection mode associated
with any particular cell, and i. corresponding BTS serving the cell, is up to a designer of
system 200 and is not critical to the present invention. As noted above, such an
instruction is typically conveyed via a PSI message that is broadcast via a broadcast
channel of downlink 216.
In another embodirrent of the present invention, MS 202 may have already
adopted a cell reselection mode pursuant to an earlier instruction received from network
controller 230 via serving BTS 220. In such an embodiment, step 304 may comprise
network controller 230 determining a current cell reselection mode of the MS by
reference to the at least one memory device 234 of the network controller. Unless
otherwise specified herein, the functions performed herein by network controller 230 are
performed by processor 232 of the network controller, and the functions performed herein
by network 250 are performed by network controller 230. Also, unless otherwise

specified herein, the functions performed herein by MS 202 are performed by processor
204 of the MS.
In response to determining a cell reselection mode of the MS, that is, MS 202,
network 250, and in particular network controller 230, determines (306) whether the MS
is experiencing a change in radio frequency (RF) conditions. When network 250, and in
particular network controller 230, determines that the MS is experiencing a change in RF
conditions, the network, and in particular the network controller, instructs (308) the MS
to switch cell reselection modes. In response to instructing MS 202 to change cell
reselection modes, network 250 stores (310) the new cell reselection mode used by the
MS in association with the MS in the at least one memory device 234 of network
controller 230 and logic flow 300 then ends (314).
In one embodiment of the present invention, step 306 may comprise a
determination that an MS in an autonomous cell reselection mode, such as NC0 or NCI,
has experienced a deterioration of RF conditions. In response to determining that the MS
has experienced a deterioration of RF conditions, step 308 then comprises network
controller instructing the MS to clu nge to a network-controlled cell reselection mode,
such as NC2.
Tn one "deteriorating cond tions" embodiment of the present invention, a
determination that MS 202 has experienced a deterioration in RF conditions may be
based on an evaluation of downlink signals received by MS 202 from serving BTS 220.
For example, in one "downlink signal based" embodiment, while serviced by serving
BTS 220, MS 202 monitors downlink signals received by the MS from serving BTS 220
and from cells associated with the Neighbor List:, such as cell 212 and associated BTS
222, typically signals received via broadcast channels included in the Neighbor List. MS
202 determines a downlink signal quality metric with respect to each monitored downlink
signal. Preferably, the downlink signal quality metric comprises a received signal level
(Rxlev); however those who are of ordinary skill in the art realize that any signal quality
metric, such as a bit error rate (BER) or a signal-to-noise ratio (SNR), may be used herein
without departing from the spirit and scope of the present invention. MS 202 then
conveys the downlink signal quality metrics to network 250, and in particular to network
controller 230. For example, the downlink signal quality metrics may be conveyed by

MS 202 to network 250 in Packet Measurement Reports (PMRs). Based on the received
downlink signal quality metrics, ne work controller 230 determines whether MS 202 is
experiencing deteriorating RF conc.itions in serving cell 210. For example, network
controller 230 may compare one or more received downlink signal quality metrics
associated with a logical channel associated with MS 202 and serving BTS 220 to a
downlink signal quality metric threshold. When MS 202 is in an autonomous cell
reselection mode and one or more -eceived signal quality metrics compare unfavorably
with the threshold, for example, fal s below a received signal strength (Rxlev) threshold
oir an SNR threshold, then network controller 230 may determine mat MS 202 is
experiencing deteriorating RF condi' ions.
By way of another example, in another "downlink signal based" embodiment, MS
202 determines downlink signal qui.lity metrics such as such as C2I blur and block error
rate based on downlink signals received by the MS. MS 202 conveys these downlink
signal quality metrics to network 250, and in particular network controller 230, via
serving BTS 220 in a Packet Measurement Report (PMR). Based on the downlink signal
quality metrics received from MS 202, network controller 230 determines a channel
coding scheme that MS 202 shall use when transmitting on uplink 218. For example, TS
04.06, Sections 11.2.28 and 11.2.2), provides four coding schemes CS-1, CS-2, CS-3,
and CS-4 that the MS may be instructed to use. When MS 202 is in an autonomous cell
reselection mode and the determined coding scheme involves a downgrade of a current
coding scheme, for example a downgrade of a coding scheme from CS-4 to CS-2 or CS-
1, then network controller 230 ma) determine that me MS is experiencing deteriorating
RF conditions.
In another "deteriorating conditions" embodiment of the present invention, a
determination that MS 202 has experienced a deterioration in RF conditions may be
based on an evaluation of uplink signals received from MS 202. For example, network
2.50 may monitor access messages :onveyed by MS 202 to the network via serving BTS
220 and an access channel of uplink 218. Access messages are advantageous to measure
because MSs typically transmit access messages at full power. However, the monitored
message is up to a designer of communication svstem 200 and can be any uplink message
that permits a determination by a receiving network of a degradation in an RF condition
of an MS.
Based on the monitored sign lis, network 250, and in particular network controller
230, determines whether MS 202 is experiencing deteriorating RF conditions in serving
cell 210. For example, in one embodiment of the present invention, network 250, and in
particular network controller 230, may determine an uplink signal quality metric with
respect to each received uplink signal. Network controller 230 compares the determined
uplink signal quality metrics to an uplink signal quality metric threshold. When the one
or more uplink signal quality meirics compare unfavorably with the threshold, for
example, falls below a received sigr al strength (Rxlev) threshold or falls below an SNR
threshold, then network controller 230 determines that MS 202 is experiencing
deteriorating RF conditions.
When MS 202 is in an autonomous cell reselection mode and network controller
230 determines that the MS is experiencing deteriorating RF conditions, step 308 then
comprises network controller instructing MS 202 to change cell reselection modes to a
network-controlled mode, such as NC2. Network controller 230 may instruct MS 202 to
switch cell reselection modes by conveying to the MS a 'change cell reselection mode'
instruction, such as by embedding ihz instruction in a Packet Measurement Order (PMO)
message that has been modified to include a change cell reselection mode data field in
which the instruction is embedded. By instructing the MS to switch to a network-
controlled cell reselection mode, network 250 may prevent an MS likely to engage in a
cell reselection from reselecting a congested cell and may further prevent the MS from
engaging in multiple cell reselections in a short period of time, which multiple cell
reselections may reduce overall throughput for the MS.
In addition, to prevent MS 202 from bouncing back and forth among cell
reselection modes, step 306 may farther include an evaluation period. That is, the
determination that MS 202 is experiencing deteriorating RF conditions may be based on
signal quality metrics that consistently compare unfavorably with an associated signal
quality metric threshold over a predetermined period of time. Or a determination that MS
202 is experiencing deteriorating F F conditions may be based on a coding scheme
associated with MS 202 changing an J then remaining at the changed level, such as CS-1
or CS-2, for a predetermined period of time.
In another embodiment of ihe present invention, an "improving conditions"
embodiment, step 306 may comprise a determination that an MS in a network-controlled
cell reselection mode, such as NC2, has experienced an improvement of RF conditions.
In response to determining that the MS has experienced an improvement of RF
conditions, step 308 then comprises network controller 230 instructing the MS to change
to an autonomous cell reselection mode, such as NCO or NCI. In addition, when the
autonomous cell reselection mode n quires periodic reporting by the MS of RF conditions
experienced by the MS, such as cell reselection mode NCI, network controller 230 may
further instruct (312) the MS to convey the reports less often, that is, to increase or
lengthen the reporting period, and thereby lessen uplink 218 congestion, or the network
controller may further instruct the VIS to switch to a cell reselection mode, that is, NCO,
that does not require measurement reports.
Similar to the "deteriorating conditions'" embodiments of the present invention, in
one an "improving conditions" embodiment of the present invention a determination that
MS 202 has experienced an improvement in RF conditions may be based on an
evaluation of downlink signals received by MS 202 from serving BTS 220. That is, while
serviced by serving BTS 220, VS 202 monitors downlink signals received by the MS
from serving BTS 220 and from :ells associated with the Neighbor List, such as cell 212
and associated BTS 222. MS 202 determines a downlink signal quality metric with
respect to each monitored downlink signal and conveys the downlink signal quality
metrics to network 250, and in particular to network controller 230. Based on the
received downlink signal quality metrics, network controller 230 determines whether MS
202 is experiencing improved RF conditions in serving cell 210.
In one embodiment of the present invention, when MS 202 is in a network-
controlled cell reselection mode, such as NC2, and network controller 230 determines
that the MS is experiencing improved RF conditions, step 308 may then comprise
network controller instructing MS 202 to change cell reselection modes to an autonomous
mode, such as NCO or NCI. In another embodiment of the present invention, when MS
202 is in an autonomous cell reselection mode that required s reporting, such as NCI, and
network controller 230 determines that the MS is experiencing improved RF conditions,
step 308 may then comprise network controller instructing MS 202 to change cell
reselection modes to an autonomous mode that does not require reporting, such as NCO.
Network controller 230 may instruct MS 202 to switch cell reselection modes by
conveying to the MS the 'change cell reselection mode' instruction, such as by
embedding the instruction in a Packet Measurement Order (PMO) message that has been
modified to include a change cell re-election mode data field in which the instruction is
embedded.
In one embodiment of the present invention, network controller 230 may
determine whether MS 202 is experiencing improved RF conditions as follows. Network
controller 230 compares one or more received downlink signal quality metrics associated
with a logical channel associated with MS 202 and serving BTS 220 to a downlink signal
quality metric threshold. When the one or more received downlink signal quality metrics
compare favorably with the threshold, for example, exceeds a received signal strength
(Rxlev) threshold or an SNR threshold, then network controller 230 determines that MS
202 is experiencing improved RF conditions. In another embodiment of the present
invention, network controller 230 nay determine whether MS 202 is experiencing
improved RF conditions as follows. Based on downlink signal quality metrics received
from MS 202, such as C2I blur and t lock error rate, network controller 230 determines a
channel coding scheme, such as cod ng schemes CS-1, CS-2, CS-3, and CS-4, that MS
202 shall use when transmitting on uplink 218. When the determined coding scheme
involves an upgrade of a current coding scheme, for example an upgrade of a coding
scheme from CS-1 to CS-2 or CS-2 to CS-3, then network controller 230 determines that
the MS is experiencing improved RF conditions.
In another embodiment of the present invention, a determination that MS 202 has
experienced an improvement in RF conditions may be based on an evaluation of uplink
signals received from MS 202. Again, network controller 230 may monitor uplink
signals received from MS 22 via uplink 218 and serving BTS 220. Based on the
monitored signals, network 250, and in particular network controller 230, determines
whether MS 202 is experiencing improved RF conditions in serving cell 210. For
example, network 250, and in particular network controller 230, may determine an uplink
signal quality metric with respect to each received uplink signal and compare the
determined signal quality metrics to an uplink signal quality metric threshold. When the
one or more uplink signal quality metrics compares favorably with the threshold, for
example, exceeds a received signal strength (Rxlev) threshold or an SNR threshold, then
network controller 230 determines that MS 202 is experiencing improved RF conditions.
When MS 202 is in a network-controlled cell reselection mode, such as NC2, in
response to determining that MS 202 is experiencing improved RF conditions, network
controller 230 may then instruct MS 202 to change cell reselection modes to an
autonomous mode, such as NC0 or NCI. In another embodiment of the present
invention, when MS 202 is in t.n autonomous cell reselection mode that requires
reporting, such as NCI, in response to determining that MS 202 is experiencing improved
RF conditions, network controller 230 may then instruct MS 202 to change cell
reselection modes to an autonomous mode that does not require reporting, such as NC0.
By switching MS 202 to an autonomous cell reselection mode when RF conditions are
improved, network 250 is permitting the MS to operate in an autonomous cell reselection
mode in a situation where there ij a reduced likelihood of the MS engaging in multiple
cell reselections in a short period of time. Furthermore, by switching MS 202 to an
autonomous cell reselection mode that does not require reporting when RF conditions are
improved, network 250 reduces a lumber of redundant measurement reports conveyed by
the MS to the network that will each merely confirm the improved RF conditions and will
provide little information that is of use to the network.
Also, to prevent MS 202 from bouncing back and forth among cell reselection
modes, step 306 involving determining whether MS 202 is experiencing a change in RF
conditions may further include nn evaluation period. That is, one embodiment of the
present invention, the determination that MS 202 is experiencing deteriorating or
improved RF conditions may be oased on signal quality metrics that consistently compare
unfavorably or favorably, whichever is appropriate, with the appropriate signal quality
metric threshold over an evaluation period, that is, a predetermined period of time. Tn
another embodiment of the present invention, the determination that MS 202 is
experiencing deteriorating or irr proved RF conditions may be based on a coding scheme
change that persists over an evaluation period.
By changing a cell reselection mode used by MS 202 based on a change in RF
conditions experienced by the MS, communication system 200 is able to reduce a
likelihood that an MS will execute an undesirable cell reselection to a congested cell and
is further able to minimize air interface congestion that results from conveyance, by the
MS, of redundant measurement repor;s that are of little, if any, value to the network. For
example, when network 250 determines an improvement in RF conditions and the MS is
using a network-controlled cell reselection mode, the network may instruct the MS to
switch to an autonomous cell reselection mode, such as NCO and NCI, or to an
autonomous cell reselection mode, ;,uch as NCO, that does not require reporting by the
MS. By way of another example, when network 250 determines a deterioration in RF
conditions and the MS is using an autonomous cell reselection mode, the network may
instruct the MS to switch to network-controlled cell reselection mode, such as NC2.
While the present invention has been particularly shown and described with
reference to particular embodiment.1; thereof, it will be understood by those skilled in the
art that various changes may be rrade and equivalents substituted for elements thereof
without departing from the scope of the invention as set forth in the claims below.
Accordingly, the specification and figures are to be regarded in an illustrative rather then
a restrictive sense, and all such cnanges and substitutions are intended to be included
within the scope of the present invention.
Benefits, other advantages, and solutions to problems have been described above
with regard to specific embodiments. However, the benefits, advantages, solutions to
problems, and any element(s) that may cause any benefit, advantage, or solution to occur
or become more pronounced are not to be construed as a critical, required, or essential
feature or element of any or all the claims. As used herein, the terms "comprises,"
"comprising," or any variation thereof, are intended to cover a non-exclusive inclusion,
such that a process, method, arti;le, or apparatus that comprises a list of elements does
not include only those elements but may include other elements not expressly listed or
inherent to such process, method article, or apparatus.
WE CLAIM :
1. A method for controlling a cell reselection mode of a mobile station while the
mobile station resides in a cell comprising:
determining a cell reselection mode of the mobile station, wherein the cell
reselection mode comprises one cr more of (i) whether a cell reselection will be
autonomous or network-controlled and (ii) the reporting requirements of the mobile
station;
determining a signal quality metric associated with the mobile station;
determining an uplink coding scheme based on the signal quality metric;
determining whether the mobile station is experiencing a change in radio
frequency (RF) conditions based on the determined uplink coding scheme; and
when the mobile station is experiencing a change in RF conditions, instructing the
mobile station to change the cell re-election mode used by the mobile station.
2. The method as claimed in claim 1, wherein determining whether the mobile
station is experiencing a change in radio frequency (RF) conditions comprises evaluating
a downlink signal and wherein instructing the mobile station to change a cell reselection
mode used by the mobile station comprises:
when the evaluation of the downlink signal indicates a deterioration of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using an autonomous cell reselec ion mode, instructing the mobile station to switch to a
network-controlled cell reselectio i mode; and
when the evaluation of the downlink signal indicates an improvement of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using a network-controlled cell reselection mode, instructing the mobile station to switch
to an autonomous cell reselectior mode.
3. The method as claimed in claim 1, wherein determining whether the mobile
station is experiencing a change in radio frequency (RF) conditions comprises evaluating
a downlink signal and wherein changing a cell reselection mode of the mobile station
comprises, when the evaluation of the downlink signal indicates an improvement of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using an autonomous cell reselection mode that requires reporting, instructing the mobile
station to switch to an autonomous coll reselection mode that does not require reporting.
4. The method as claimed in claim 1, wherein determining whether the mobile
station is experiencing a change in radio frequency (RF) conditions comprises evaluating
an uplink signal and wherein changing a cell reselection mode of the mobile station
comprises:
when the evaluation of the uplink signal indicates a deterioration of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using an autonomous cell reselection mode, instructing the mobile station to switch to a
neiwork-controlled cell reselection mode; and
when the evaluation of the uplink signal indicates an improvement of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using a network-controlled cell reselection mode, instructing the mobile station to switch
to an autonomous cell reselection mode.
5. The method as claimed in claim I, wherein determining whether the mobile
station is experiencing a change in radio frequency (RF) conditions comprises evaluating
an uplink signal and wherein changing a cell reselection mode of the mobile station
comprises, when the evaluation of the uplink signal indicates an improvement of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using an autonomous cell reselection mode that requires reporting, instructing the mobile
station to switch to an autonomous cell reselection mode that does not require reporting.
6. The method as claimed in claim 1, wherein determining whether the mobile
station is experiencing a change in radio frequency (RF) conditions comprises evaluating
a downlink signal and whereir instructing the mobile station to switch a cell reselection
mode used by the mobile station comprises, when the evaluation of the downlink signal
indicates an improvement of radio frequency (RF) conditions experienced by the mobile
station, instructing the mobile station to lengthen a reporting period associated with a cell
reselection mode used by the mobile station.
7. A network controller compris ng:
at least one memory device that stores a default cell reselection mode associated
with a cell serviced by the network controller; and
a processor coupled to the at least one memory device that determines a cell
reselection mode of a mobile station located in the cell, wherein the cell reselection mode
comprises one or more of (i) whether a cell reselection will be autonomous or network-
controlled and (ii) the reporting requirements of the mobile station, determines a signal
quality metric associated with the mobile station, determines an uplink coding scheme
based on the signal quality metric, determines whether the mobile station is experiencing
a change in radio frequency (RF) :onditions based on the determined uplink coding
scheme, and when the mobile statior is experiencing a change in RF conditions, instructs
the mobile station to change the cell -eselection mode.
8. The network controller as claimed in claim 7, wherein the processor determines
whether the mobile station is experiencing a change in radio frequency (RF) conditions by
evaluating a downlink signal quality metric associated with a downlink signal and
wherein the processor instructs the mobile station to change a cell reselection mode used
by the mobile station by, when the evaluation of the downlink signal quality metric
indicates a deterioration of radio frequency (RF) conditions experienced by the mobile
station and the mobile station is using an autonomous cell reselection mode, instructing
the mobile station to switch to a network-controlled cell reselection mode, and when the
evaluation of the downlink signal quality metric indicates an improvement of radio
frequency (RF) conditions experienced by the mobile station and the mobile station is
using a network-controlled cell rese ection mode, instructing the mobile station to switch
to an autonomous cell reselection mode.
9. The network controller as claimed in claim 7, wherein the processor determines
whether the mobile station is experiencing a change in radio frequency (RF) conditions by
evaluating a downlink signal quality metric associated with a downlink signal and
wherein the processor instructs the mobile station to change a cell reselection mode used
by ;he mobile station by, when the evaluation of the downlink signal quality metric
indicates an improvement of radio frequency (RF) conditions experienced by the mobile
station and the mobile station is using an autonomous cell reselection mode that requires
reporting, instructing the mobile stati in to switch to an autonomous cell reselection mode
that does not require reporting.
1(1. The network controller as claimed in claim 7, wherein the processor determines
whether the mobile station is experiencing a change in radio frequency (RF) conditions by
evaluating an uplink signal quality metric associated with an uplink signal and wherein
the processor instructs the mobile station to change a cell reselection mode used by the
mobile station by, when the evaluation of the uplink signal quality metric indicates a
deterioration of radio frequency (RF) conditions experienced by the mobile station and
the mobile station is using an autonomous cell reselection mode, instructing the mobile
station to switch to a network-controlled cell reselection mode, and when the evaluation
of the uplink signal quality metric indicates an improvement of radio frequency (RF)
conditions experienced by the mobile station and the mobile station is using a network-
controlled cell reselection mode, instructing the mobile station to switch to an
autonomous cell reselection mode.
11. The network controller as c.aimed in claim 7, wherein the processor determines
whether the mobile station is experiencing a change in radio frequency (RF) conditions by
evaluating an uplink signal quality metric associated with an uplink signal and wherein
the processor instructs the mobile station to change a cell reselection mode used by the
mobile station by, when the evaluation of the uplink signal quality metric indicates an
improvement of radio frequency (RF) conditions experienced by the mobile station and
the mobile station is using an autoiomous cell reselection mode that requires reporting,
instructing the mobile station to switch to an autonomous cell reselection mode that does
not require reporting.
12. The network controller as claimed in claim 7, wherein the processor determines
whether the mobile station is exper encing a change in radio frequency (RF) conditions by
evaluating a downlink signal qu ility metric associated with a downlink signal and
wherein the processor instructs the mobile station to switch a cell reselection mode used
by the mobile station by, when the evaluation of the downlink signal indicates an
improvement of radio frequency (RF) conditions experienced by the mobile station,

instructing the mobile station to lengthen a reporting period associated with a cell
reselection mode used by the mobile station.
13. The network controller as claimed in claim 7, wherein the network controller
comprises at least one of a Base Station Controller, a Packet Control Unit, and a Packet
Control Function.


A communication system (200) controls a cell reselection mode of a mobile
station (202) while the mobile station resides in a cell (210) by determining a cell
reselection mode of the mobile station, determining whether the mobile station is
experiencing a change in radio frequency (RF) conditions, and when the mobile station is
experiencing a change in RF conditions, instructing the mobile station to change a cell
reselection mode used by the mobile station.

Documents:

00993-kolnp-2006 abstract.pdf

00993-kolnp-2006 claims.pdf

00993-kolnp-2006 correspondence others.pdf

00993-kolnp-2006 drawings.pdf

00993-kolnp-2006 form-1.pdf

00993-kolnp-2006 form-3.pdf

00993-kolnp-2006 form-5.pdf

00993-kolnp-2006 international publication.pdf

00993-kolnp-2006 pct form.pdf

00993-kolnp-2006 priority document.pdf

00993-kolnp-2006-assignment.pdf

00993-kolnp-2006-correspondence others-1.1.pdf

00993-kolnp-2006-form-3-1.1.pdf

00993-kolnp-2006-priority document-1.1.pdf

00993-kolnp-2006.description(complete).pdf

993-KOLNP-2006-(03-11-2011)-OTHER PATENT DOCUMENTS.pdf

993-KOLNP-2006-(20-04-2012)-CORRESPONDENCE.pdf

993-KOLNP-2006-(20-04-2012)-OTHERS.pdf

993-KOLNP-2006-(20-04-2012)-PA-CERTIFIED COPIES.pdf

993-KOLNP-2006-(26-03-2012)-ASSIGNMENT.pdf

993-KOLNP-2006-(26-03-2012)-CORRESPONDENCE.pdf

993-KOLNP-2006-(26-03-2012)-FORM-16.pdf

993-KOLNP-2006-(26-03-2012)-PA-CERTIFIED COPIES.pdf

993-KOLNP-2006-ABSTRACT-1.1.pdf

993-KOLNP-2006-ABSTRACT-1.2.pdf

993-KOLNP-2006-CANCELLED DOCOMENT.pdf

993-KOLNP-2006-CLAIMS.pdf

993-KOLNP-2006-DESCRIPTION COMPLETE.pdf

993-KOLNP-2006-DRAWINGS.pdf

993-KOLNP-2006-FORM 1.pdf

993-KOLNP-2006-FORM 3.pdf

993-KOLNP-2006-FORM-27.pdf

993-kolnp-2006-granted-abstract.pdf

993-kolnp-2006-granted-assignment.pdf

993-kolnp-2006-granted-claims.pdf

993-kolnp-2006-granted-correspondence.pdf

993-kolnp-2006-granted-description (complete).pdf

993-kolnp-2006-granted-drawings.pdf

993-kolnp-2006-granted-examination report.pdf

993-kolnp-2006-granted-form 1.pdf

993-kolnp-2006-granted-form 18.pdf

993-kolnp-2006-granted-form 3.pdf

993-kolnp-2006-granted-form 5.pdf

993-kolnp-2006-granted-gpa.pdf

993-kolnp-2006-granted-reply to examination report.pdf

993-kolnp-2006-granted-specification.pdf

993-KOLNP-2006-OTHERS.pdf

993-KOLNP-2006-PETITION UNDER RULE 137.pdf

993-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

abstract-00993-kolnp-2006.jpg


Patent Number 241045
Indian Patent Application Number 993/KOLNP/2006
PG Journal Number 25/2010
Publication Date 18-Jun-2010
Grant Date 17-Jun-2010
Date of Filing 19-Apr-2006
Name of Patentee MOTOROLA, INC.
Applicant Address 1303 EAST ALGONQUIN ROAD, SCHAUMBURG, ILLINOIS
Inventors:
# Inventor's Name Inventor's Address
1 VASUDEVAN DAMODARAN 1910 CAMBRIDGE COURT, APT. 3A PALATINE ILLINOIS 60074
2 RAVAL, TUSHAR 404 ROYAL ST. GEORGE, VERNON HILLS, ILLINOIS 60061
3 JAKHER, NARENDER K. 980 NORTH COUNTRYSIDE DRIVE, APT. 217, PALATINE, ILLINOIS 60067
PCT International Classification Number H04M
PCT International Application Number PCT/US2004/037912
PCT International Filing date 2004-11-12
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/519,874 2003-11-13 U.S.A.
2 10/796,326 2004-03-09 U.S.A.