WO2006132469A2

WO2006132469A2 - A method of performing actions related to handover by a mobile station that is in power saving mode in a wireless mobile communication system

Info

Publication number: WO2006132469A2
Application number: PCT/KR2006/000858
Authority: WO
Inventors: Ki Seon Ryu; Beom Joon Kim
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2005-06-09
Filing date: 2006-03-10
Publication date: 2006-12-14
Anticipated expiration: 2007-12-09
Also published as: IL187801A0; CA2610154A1; EP1889502A4; CN102595579B; US8224403B2; EP2291030B1; US20120014302A1; US7672660B2; JP2012075142A; JP2008546346A; US8351998B2; US8478362B2; ATE548872T1; MX2007015349A; IL187801A; ATE522115T1; WO2006132469A3; AU2006255897B2; AU2006255897A1; KR100913087B1

Abstract

A method of performing actions related to handover by a mobile station (MS) in a wireless mobile communication system is disclosed. More specifically, the MS receives information from a base station (BS), wherein the information includes at least one action for performing handover and at least one condition corresponding to the at least one action. Furthermore, the MS transmits a request message to perform the at least one action based on the received information from the BS and receives a response message in response to the request message. Lastly, the MS performs the at least one action according to the received response message.

Description

A METHOD OF PERFORMING ACTIONS RELATED TO HANDOVER BY A

MOBILE STATION THAT IS IN POWER SAVING MODE IN A WIRELESS

MOBILE COMMUNICATION SYSTEM

Technical Field

The present invention relates to a performing action related to handover, and more

particularly, to a method of performing actions related to handover by a mobile station (MS)

that is in power saving mode in a wireless mobile communication system.

Background Art

In a broadband wireless access system, a power saving mode or a sleep mode can be

used to minimize power consumption of a mobile station (MS). The power saving mode

comprises a sleep interval and a listening interval, which are repeated during the operation

by the MS. A length (or duration) of the sleep interval is determined by a value of a sleep

window. Similarly, a length (or duration) of the listening interval is determined by a value

of a listening window. These values are respectively determined based on a characteristic of

a determined traffic of a corresponding MS. Furthermore, the MS can be represented by

three (3) types of power saving class according to the characteristics of traffic associated

with the power saving class.

More specifically, the three power saving class types are classified as a power

saving mode class type 1 (hereinafter "Class 1"), a power saving mode class type 2

(hereinafter "Class 2"), and a power saving mode class type 3 (hereinafter "Class 3"). Class 1 can be defined by an initial sleep window, a final window base, a final

window exponent, a listening window, and a start frame number of sleep window.

Furthermore, Class 1 focuses on features such as Best Effort (BE) which characterizes the

existing internet traffic or non-real-time variable rate (nrt-VR).

Class 2 can be defined by an initial sleep window, a listening window, and a start

frame number of sleep window. Furthermore, Class 2 focuses on features such as Voice

over Internet Protocol (VoIP ) and the nrt-VR.

Class 3 can be defined by a final window base, a final window exponent, and a start

frame number of sleep window. Furthermore, Class 3 is for periodically transmitting a

management message, such as a Downlink Channel Descriptor/Uplink Channel Descriptor

(DCD/UCD) and a neighbor advertisement (MOB_NBR_ADV), to the MS that is in power

saving mode or alternatively, for data transmitted via multicast transmission.

The above power saving class types describe different types of power saving modes.

The operations of these different class types are the basis for handover for the MS to a base

station (BS). While in power saving mode, the MS receives signal quality information of

neighbor base stations. The signal qualities of neighbor bases stations can be measured by

performing scan operation. Before handover operation is performed, a serving BS transmits

handover trigger information, which is used in performing handover, to the MS. Here, the

serving BS refers to the BS which granted the MS to enter the power saving mode. Using

the received handover trigger information, the MS performs handover when the condition

specified in the handover trigger information is satisfied. Even if the MS that is in power saving mode does not transmit and receive a scan

request message and a scan response message, respectively, the MS performs scan operation

on neighboring base stations and measures signal qualities of neighbor base stations. If the

results of the scan operation (e.g., signal qualities of the neighbor base stations, the received

signal strength, and/or transmission delay) are transmitted via scan report message to the

serving BS every time the scan operation is performed, the power consumption for uplink

transmission by the MS increases. At the same time, if the serving BS fails to receive the

scan results from the MS operating in power saving mode, then the handover operation of

the MS cannot be controlled properly.

Disclosure of the Invention

Accordingly, the present invention is directed to a method of performing actions

related to handover by a mobile station (MS) that is in power saving mode in a wireless

mobile communication system that substantially obviates one or more problems due to

limitations and disadvantages of the related art.

An object of the present invention is to provide a method of performing actions

mobile communication system.

Another object of the present invention is to provide a method of providing actions

related to handover by a base station (BS) for a mobile station (MS) that is in power saving

mode in a wireless mobile communication system. Additional advantages, objects, and features of the invention will be set forth in part

in the description which follows and in part will become apparent to those having ordinary

skill in the art upon examination of the following or may be learned from practice of the

invention. The objectives and other advantages of the invention may be realized and

attained by the structure particularly pointed out in the written description and claims hereof

as well as the appended drawings.

To achieve these objects and other advantages and in accordance with the purpose of

the invention, as embodied and broadly described herein, a method of performing actions

related to handover by a mobile station (MS) includes the MS which receives information

from a base station (BS), wherein the information includes at least one action for

performing handover and at least one condition corresponding to the at least one action.

Furthermore, the MS transmits a request message to perform the at least one action based on

the received information from the BS and receives a response message in response to the

request message. Lastly, the MS performs the at least one action according to the received

response message.

In another aspect of the present invention, a method of providing actions related to

handover by a base station (BS) for a mobile station (MS) that is in power saving mode

includes the MS which transmits information to the MS, wherein the information includes at

least one action for performing handover and at least one condition corresponding to the at

least one action. Thereafter, the MS receives a request message from the MS asking to perform at least one action based on the received information and transmits response

message in response to the request message.

It is to be understood that both the foregoing general description and the following

detailed description of the present invention are exemplary and explanatory and are

intended to provide further explanation of the invention as claimed.

Brief Description of the Drawings

The accompanying drawings, which are included to provide a further understanding

of the invention and are incorporated in and constitute a part of this application, illustrate

embodiment(s) of the invention and together with? the description serve to explain the

principle of the invention. In the drawings;

FIG. 1 is an exemplary diagram illustrating processes of a Power Saving Class 1;

FIG. 2 is an exemplary diagram illustrating processes of a Power Saving Class 2;

FIG. 3 is an exemplary diagram illustrating processes of a Power Saving Class 3;

FIG. 4 is another exemplary diagram illustrating processes of a Power Saving Class

3;

FIG. 5 shows an example of power saving modes of the MS illustrating various

service types;

FIG. 6 is an exemplary diagram illustrating handover processes by the MS;

FIG. 7 illustrates an example of an operation of a power saving mode when the

action for transmitting MOB_S CAN-REPORT is enabled; FIG. 8 illustrates an example of an operation of a power saving mode when the

action for transmitting handover request message (MOB_MSHO-REQ) is enabled;

FIG. 9 illustrates an example of an operation of a power saving mode when the

action for performing scan operation is enabled; and

FIG. 10 illustrates an example of an operation of a power saving mode when the

action for performing association is enabled.

Best Mode for Carrying Out the Invention

Reference will now be made in detail to the preferred embodiments of the present

invention, examples of which are illustrated in the accompanying drawings. Wherever

possible, the same reference numbers will be used throughout the drawings to refer to the

same or like parts.

As discussed above, there are three (3) types of power saving modes. For proper

execution of each power saving mode, the BS and the MS exchanges necessary information

such as parameters and a ranging response (RNG-RSP) message. The parameters are

included in the exchanged messages between the BS and the MS. These messages can be

defined by a sleep request (MOB SLP-REQ) message, a sleep response (MOB SLP-RSP)

message, and a traffic indication (MOB_TRF-IND) message, for example.

Table 1 illustrates an example of the sleep request (MOB_SLP-REQ) message. The

sleep request (MOB_SLP-REQ) message includes a request for entry into sleep mode and is

one of the messages transmitted by the MS to the serving BS. In the sleep request message, information pertaining to sleep interval(s) and listening interval(s) can be included.

Hereinafter, a term 'sleep interval' can be used interchangeably with terms 'sleep window'

or 'duration of sleep window/

[Table 1]

Table 2 illustrates an example of the sleep response (MOB_S LP-RSP) message. The

sleep response (MOB_SLP-RSP) message includes sleep mode related information and is

one of the messages transmitted from the BS to the MS. The sleep response message

includes grant of sleep mode along with sleep interval(s), listening interval(s), and sleep

identification, for example.

[Table 2]

Table 3 is an example of the traffic indication (MOB_TRF-IND) message

broadcasted periodically. The MS that is in sleep mode receives the broadcasted traffic

indication (MOB_TRF-IND) message during the listening interval and determines whether

to maintain the sleep mode, exit the sleep mode to receive downlink data, or perform

ranging operation during the sleep mode. [Table 3]

Table 4 illustrates an example of power saving class parameters included in the

ranging response (KNG-RSP) message. The power saving class parameters can have variable lengths. That is, the power saving class parameters can be defined as a specific type

parameter (e.g., type 21) and can be classified as a compound parameter which can

selectively include parameters having varying lengths.

[Table 4]

The operation of the MS prior to handover is as follows. First, the MS can perform

scan operation. The scan operation allows the MS to acquire signals of the neighbor base

stations and measure the signal qualities of the acquired signals to determine the BS having

optimum signal quality among the measured signals. To this end, the MS can use a scan

request (MOB_SCN-REQ) message to request a serving BS for permission to perform scan

operation. In response to the request, the serving BS can send a scan response (MOB_SCN-

RSP) message to allow the MS commence scan operation of neighbor base stations to

measure signal qualities. In the scan response message, parameters needed for performing

scan operation, such as for scan period, can be included.

Table 5 illustrates an example of a scan report (MOB_SCAN-REPORT) message.

[Table 5]

In operation, the MS can use the scan report message, such as the one of Table 5, to

transmit information (e.g., signal quality, strength of received signal, transmission delay)

acquired from the scan operation of the neighbor base stations to the serving BS. The

serving BS determines whether to allow MS to perform handover based on information of

neighbor BS scanned results.

A time it takes to perform handover can be shortened by performing association.

Association relates to a process or a procedure before performing actual handover. In detail,

the MS can first measure signal quality of neighbor base stations via scan operation and

execute initial ranging operation. Here, the ranging parameters used during the initial

ranging operation can be re-used during actual handover. More specifically, the MS can

send the scan request (MOB_SCN-REQ) message to the serving BS to request for

connection with the neighbor BS. The serving BS in response can provide parameters (e.g.,

connection execution time, resource information used at connection) necessary for

connecting with the neighbor BS via the scan response (MOB S CN-RSP) message.

As discussed above, the MS can measure signal qualities of the neighbor base

stations by using the scan operation and reports the results of the scan operation, including

the measured signal qualities, to the serving BS. Thereafter, the MS compares, using an

absolute or relative standard, levels of signal qualities that can be provided by the neighbor

base stations to level of the actual signal qualities received from the neighbor base stations.

After completing the comparison, the MS and/or the serving BS can determine whether to

perform handover. Conditions or values necessary for the MS to perform various operations can be

transmitted with specified parameters, as illustrated in Table 6. Here, the parameters can

include information related to operations such as scanning the neighbor base stations,

reporting the results of the scan operation, connecting with the neighbor BS, and performing

handover with the BS. These specified parameters can then be included in a Downlink

Channel Descriptor (DCD) of the serving BS or a neighbor BS advertisement (MOB-NBR-

ADV) message, and thereafter, transmitted to the MS from the serving BS.

Table 6 illustrates an example of values of a parameter used to trigger different

events.

[Table 6]

Table 7 illustrates an example of conditions of a parameter used to trigger different

events.

[Table 7]

Figure 1 is an exemplary diagram illustrating processes of a Power Saving Class 1.

In the Power Saving Class 1 of Figure 1, the MS sends a message to the BS to request for

entry into power saving mode, and the power saving mode is maintained until there is

downlink traffic to deliver to the corresponding MS, at which point, the power saving mode

is terminated. A more detailed description of the operation is provided below.

In detail, the MS sets the values of initial sleep window, final sleep window, and

listening window. These values are then included in the sleep request (MOB-SLP-REQ)

message transmitted to the BS to request for entry into power saving mode. When or if the

BS grants entry into the power saving mode, the BS includes, inter alia, an initial sleep

window, a final sleep window, a listening window, and a start frame of the initial sleep

window in the response message (i.e., MOB-SLP-RSP) to the corresponding MS.

When the MS enters the power saving mode, the MS remains in the power saving

mode for duration equaling duration of the initial sleep window. After the expiration of the

power saving mode, the MS receives traffic indication (MOB-TRF-IND) message(s) from

the BS during the listening interval. If there is no downlink traffic or data directed to the corresponding MS, referred to as negative indication, for example, then the MS re-enters

power saving mode. However, this time, the duration of the power saving mode is twice

longer than the previous duration.

If there continues to be no downlink traffic for the corresponding MS during the

listening interval(s), then the duration of the subsequent power saving mode increases by a

specified rate (i.e., two folds) each time the MS re-enters the power saving mode after

failing to receive downlink traffic after the listening interval. The following equation is an

example illustrating increase in duration of the power saving mode. Here, a size or duration

of a final sleep window can be determined using a final sleep window base and a final

window exponent included in the sleep response message.

[Equation 1]

Final Sleep Window = Final Sleep Window Base * 2 Final Window Exponent

On the contrary, if there is downlink traffic addressed to the MS during the listening

interval, indicated as positive indication, then the MS terminates the power saving mode.

Figure 2 is an exemplary diagram illustrating processes of a Power Saving Class 2.

In Figure 2, the diagram shows the MS using any one of an Unsolicited Grant Service

(UGS), which provides a fixed data rate, and a Real Time Variable Service (RT-VR), and

the operation processes of the MS in a Power Saving Class 2.

More specifically, the MS transmits a sleep request message, similar to the message

of Table 1, to the BS to request for entry to Power Saving Class 2. Upon receipt of the

request message, the BS grants entry to Power Saving Class 2 by sending a response message to the MS. The response message can include a sleep interval, a listening interval,

and a start frame of the power saving mode to be configured by the MS. Once the MS enters

the start frame, the MS stays in the power saving mode for the duration of the sleep interval.

After the sleep interval expires, the MS synchronizes with the BS to maintain

uplink/downlink communication. The MS can then receive downlink data from the BS and

at the same time, transmit uplink data to the BS during the listening interval. Once the

listening interval ends, the MS maintains the power saving mode for a period equaling that

of the sleep interval in order to minimize power consumption. Thereafter, the listening and

sleep intervals are repeated by the MS in Power Saving Class 2.

If the MS wishes to terminate Power Saving Class 2, the MS can send a sleep

request message, including a request to terminate Power Saving Class 2, to the BS during

the listening interval. Alternatively, the MS can transmit a user data to the BS during the

sleep interval. After Power Saving Class 2 is terminated, the MS is in normal operating

mode.

Figure 3 is an exemplary diagram illustrating processes of a Power Saving Class 3.

More specifically, Figure 3 shows the processes of Power Saving Class 3 by illustrating the

MS maintaining uplink/downlink communication with the BS and performing ranging

operations with the BS to reduce power consumption. In Figure 3, the MS enters normal

operation mode by powering on and executing network entry procedure. During normal

mode, the MS performs ranging operations periodically to maintain uplink/downlink

communication with the BS. In the process of periodic ranging operations, the MS acquires appropriate uplink transmission parameters. Furthermore, when it is time for the MS to

perform periodic ranging operations, the MS transmits a ranging request (RNG-REQ)

message to the BS.

After receiving the ranging request message (RNG-REQ) from the MS, the BS

responds by transmitting a ranging response (RNG-RSP) message, which includes adjusted

values of the uplink transmission parameters, to the corresponding MS. Here, the ranging

response message can include sleep window and start frame, for example, so that Power

Saving Class 3 can be activated.

After the MS receives the ranging response (RNG-RSP) message, which includes

information necessary to activate powering saving mode, the MS encounters the start frame

to indicate start of the power saving mode. Thereafter, the MS stays in the power saving

mode for the duration of the sleep window. When the sleep window period expires, the MS

is in a mode which allows the MS to communicate with the BS. The MS then performs

periodic ranging operation. During the ranging operation, the MS receives from the BS the

ranging response (RNG-RSP) message including the parameters related to uplink

transmission and power saving mode. When it is time to enter power saving mode, the MS

enters (or activates) the power saving mode and remains in the power saving mode for the

duration of the sleep window.

Figure 4 is another exemplary diagram illustrating processes of a Power Saving

Class 3. Figure 4 depicts the processes of Power Saving Class 3 employed by the MS,

which receives data from the BS via multicast connection, to conserve power. The BS transmits a sleep response (MOB_SLP-RSP)message to the MS to have the

MS activate Power Saving Class 3. When the MS receives the sleep response (MOB-SLP-

RSP) message, starting with the start frame, the MS enters or activates the sleep window

and remains in the power saving mode for the duration of the sleep window. At the

termination of the sleep window, the MS resumes a mode in which the MS is available to

communicate with the BS, and the MS receives data from the BS via multicast connection.

After the BS finishes transmitting data during multicast connection, the BS activates

Power Saving Class 3 by transmitting a sleep response (MOB_SLP-RSP) message to the

MS so that the power consumption can be reduced until the next data transmission via

multicast connection. As for the MS, the MS responds to the sleep response (MOB_SLP-

RSP) message by entering the power saving mode for the duration of the sleep window. In

order to reduce power consumption of the MS in the broadband wireless access system,

each connection may be associated with an individual context or power saving class

according to service type of the connection.

Figure 5 shows an example of power saving modes of the MS illustrating various

service types. As illustrated in Figure 5, the MS that has at least one power saving class

activated remains in the power saving mode during sleep windows where the sleep windows

overlap between each power saving class. As described above, the MS does not perform

uplink transmission with the BS during power saving mode.

As described above, the MS and the serving BS activates the power saving mode

based on each connection represented by a service type. As such, the MS can minimize power consumption. Alternatively, the MS, even during power saving mode, can perform

pre-handover operations before handover, such as scan operation which detects signal

quality levels received from neighbor base stations, and association procedures which

executes ranging operations with the BS prior to performing actual handover, during the

sleep window.

The serving BS transmits handover trigger information, which includes operations

such as scan, association, and handover, to the MS. As for the MS, the MS performs

necessary and appropriate operations when the situation satisfies the condition based on the

received handover trigger information.

Figure 6 is an exemplary diagram illustrating handover processes by the MS. In

Figure 6, the serving BS transmits handover trigger information by using the DCD, which is

a message used to transmit channel information parameters, or a neighbor advertisement

(MOB_NBR-ADV) message. As described above, the handover trigger information

includes information necessary for the MS to carry out handover operation.

After the MS receives the handover trigger information from the serving BS, the MS

can send a scan request (MOB_SCN-REQ) message to request assignment of scan period

(or duration) from the serving BS when the condition is met to perform scan on neighbor

base stations.

After receiving the scan request message, the serving BS allocates the scan period

(or duration) included in the scan response (MOB_SCN-RSP) message. During the scan period, the MS synchronizes downlink signal with the neighbor BS and measures signal

quality, signal strength, and transmission synchronization, among others.

After the MS completes scan, if the MS has to send the scan result of neighbor base

stations to the serving BS, the MS uses the scan report (MOB_SCAN-REPORT) message.

More specifically, the scan report includes information such as a Carrier-to-interference and

Noise Ratio (CINR), a Received Signal Strength Indicator (RSSI), and a Round Trip Delay.

If the MS has to perform association with the neighbor BS, the MS can transmit a

scan request (MOB-SCN-REQ) message to request association with the neighbor BS to the

serving BS. In response, the serving BS transmits via a scan response (MOB-SCN-RSP)

message parameters necessary for performing association with the neighbor BS. After

receiving the necessary parameters, the MS performs association with the neighbor BS.

After the MS performs scan or association operations, if the MS has to perform

handover operation with a particular BS after referring to a handover trigger information,

the MS can use a handover request (MOB_MSHO-REQ) message to request for handover

to the serving BS. Upon receipt, the serving BS transmits a handover response

(MOB_MSHO-RSP) message to the MS. Thereafter, the MS transmits a handover

indication (MOB HO-IND) message to the serving BS to request to cease or sever

connection with the serving BS. Then, the MS performs operations for re-entry to target BS

and the network.

Table 8 is an example of a sleep request (MOB_SLP-REQ) message.

[Table 8]

\L

If the MS wishes to convert to or enter power saving mode, the MS can make a

request for entry to power saving mode by transmitting the sleep request (MOB-SLP-REQ)

message. Here, the sleep request (MOB_SLP-REQ) message can include information

related to whether the MS that is in the power saving mode should perform each handover-

related operations for handover trigger information.

The information related to whether the MS that is in the power saving mode should

perform each handover-related operations for handover trigger information can be

transmitted via a specified field of the sleep request (MOB_SLP-REQ) message. Table 9 is

an example of the specified field, labeled as Εnabled-Trigger' field, of the sleep request

(MOB_SLP-REQ) message. In detail, Table 9 describes an example of a parameter for

enabling the event trigger operation. [Table 9]

The parameter of Table 9 is a Type Length Value (TLV) parameter, which can be

transmitted to the BS via a sleep request (MOB_SLP-REQ) message or a ranging request

(RNG-REQ) message. More specifically, the parameters of Table 9 can be used to negotiate whether each event is enabled or disabled when the MS enters the power saving mode.

Furthermore, the parameters of Table 9 can be included in sleep request (MOB_SLP-REQ),

sleep response (MOB-SLP-RSP), ranging request (RNG-REQ), and ranging response

(RNG-RSP) messages.

The Enabled-Trigger parameter can be in a bitmap format. The Enabled-Trigger

parameter in the bitmap format can be used to notify the serving BS that the corresponding

event is to be triggered by the MS. In operation, the MS can configure each bit as '1' (e.g.,

bit = 1), and transmit the configure bit(s) to the serving BS via the sleep request

(MOB_SLP-REQ) message. Based on the handover trigger information, if the event trigger

condition is satisfied with respect to the event configured to '1' during the power saving

mode of the MS, then the serving BS can be notified that the MS is to trigger the

corresponding event.

If the serving BS receives the sleep request (MOB_SLP-REQ) message including

the enabled-trigger parameter, the serving BS can configure the Enabled-Trigger parameter,

as illustrated in Table 9, and can transmit the configured information to the MS via the sleep

response (MOB_SLP-RSP) message. Alternatively, the sleep response (MOB_SLP-RSP)

message can include the Enabled-Trigger parameter configured according to Table 10.

Table 10 is an example of a sleep response (MOB_SLP-RSP) message.

[Table 10]

The Enabled-Trigger parameter included in the sleep response (MOB SLP-RSP)

message is in a bitmap format, as in the case with the sleep request (MOB_SLP-REQ)

message. Similarly, if each bitmap is set to '1,' and if the trigger condition is satisfied based

on the handover trigger information similar to that of Table 7 during power saving mode of

the MS, the serving BS notifies the MS to instruct the MS to trigger the corresponding event.

Figure 7 illustrates an example of an operation of a power saving mode when the

action for transmitting MOB_S CAN-REP ORT is enabled. More specifically, Figure 7

describes operations related to handover of the MS based on handover trigger information

during the operation of MS power saving mode initiated according to the Enabled-Trigger

parameter. In Figure 7, the MS receives the handover trigger information via the DCD message

or the MOB_NBR-ADV message. When making a request for entry to power saving mode,

the MS sets or configures a first bit (i.e., bit #0) of the Enabled-Trigger parameter to '1,' as

illustrated in Tables 8 and 9. Here, setting the first bit of the Enabled-Trigger parameter

means that the action for transmitting MOB_SCAN-REPORT is enabled. Thereafter, the

configured information is transmitted to the serving BS via the sleep request (MOB_SLP-

REQ) message.

The serving BS then sets (or configures) the first bit (i.e., bit#O) of the Enabled-

Trigger parameter to '1,' as illustrated in Tables 9 and 10, and transmits the configured

information to the MS via the sleep response (MOB_SLP-RSP) message. After receiving

the sleep response (MOB_SLP-RSP) message from the serving BS, the MS enters the

power saving mode.

The MS which is in power saving mode can perform scan operations on neighbor

base stations during the sleep interval or for the duration of the sleep window. When the MS

satisfies a condition after entering the power saving mode, then the MS is required to report

the scan result. Thereafter, the MS transmits the scan report (MOB_SCAN-REPORT)

message to the serving BS to provide the serving BS with the scan result relating to the

neighbor base stations. After reporting the scan results to the serving BS, the MS can then

maintain the power saving mode.

Figure 8 illustrates an example of an operation of a power saving mode when the

action for transmitting handover request message (MOB_MSHO-REQ) is enabled. As illustrate in Figure 8, the MS receives the handover trigger information via the DCD

message or the MOB_NBR-ADV message. When the MS makes a request for entry to

power saving mode, the MS sets or configures a second bit (i.e., bit #1) of the Enabled-

Trigger parameter to ' 1 , ' as illustrated in Tables 9 and 10. Here, setting the second bit of the

Enabled-Trigger parameter means that the action for transmitting MOB_MSHO-REQ is

enabled. Thereafter, the configured information is transmitted to the serving BS via the

sleep request (MOB SLP -REQ) message.

The serving BS then sets (or configures) the second bit (i.e., bit#l) of the Enabled-

information to the MS via the sleep response (MOB SLP -RSP) message. After receiving

the sleep response message from the serving BS, the MS enters the power saving mode.

The MS which is in power saving mode can perform neighbor BS scan operations

during the sleep interval or for the duration of the sleep window. When the MS satisfies a

condition after entering the power saving mode, the MS is required to report the scan result

to the serving BS. Thereafter, the MS terminates the power saving mode and transmits the

handover request (MOB_MSHO-REQ) message to the serving BS, thereby making a

request for handover with a different BS (e.g., BS2). In response to the handover request

(MOB_MSHO-REQ) message, the serving BS transmits a handover response

(MOB_MSHO-RSP) message to the MS. Thereafter, the MS requests for disconnect with the serving BS by transmitting a

handover indication (MOB_HO-IND) message to the serving BS. After the disconnect, the

MS performs necessary operations for entry to the target BS (i.e., BS2) and to the network.

Figure 9 illustrates an example of an operation of a power saving mode when the

action for requesting a scanning interval is enabled. In Figure 9, the MS receives the

handover trigger information via the DCD message or the MOB_NBR-ADV message.

When the MS makes a request to enter power saving mode, the MS sets or configures a

third bit (i.e., bit #2) of the Enabled-Trigger parameter to '1,' as illustrated in Tables 8 and 9.

Here, setting the third bit of the Enabled-Trigger parameter means that the action for

requesting MOB_SCN-REQ is enabled. Thereafter, the configured information is

transmitted to the serving BS via the sleep request (MOB_SLP-REQ) message.

The serving BS then sets (or configures) the third bit (i.e., bit#2) of the Enabled-

the sleep response message from the serving BS, the MS enters power saving mode.

When the MS satisfies a condition after entering the power saving mode, the MS is

required to perform neighbor BS scan operation after. Thereafter, the MS transmits a scan

request (MOB_SCN-REQ) message to the serving BS to request for allocation of scan

period. In response to the scan request (MOB S CN-REQ) message, the serving BS

transmits a scan response (MOBJSCN-RSP) message including allocation of the scan

period. During the scan period, the MS synchronizes downlink signal with the neighbor

base stations and measures, inter alia, signal quality from neighbor base stations, signal

strengths, and transmission delay. After performing the scan operation, the MS maintains

the power saving mode.

Figure 10 illustrates an example of an operation of a power saving mode when the

event for performing association is enabled. In Figure 10, the MS receives the handover

trigger information via the DCD message or the MOB NBR-AD V message. When the MS

makes a request for entry to power saving mode, the MS sets or configures a fourth bit (i.e.,

bit #3) of the Enabled-Trigger parameter to '1,' as illustrated in Tables 8 and 9. Here,

setting the fourth bit of the Enabled-Trigger parameter means that the action for performing

association is enabled. Thereafter, the configured information is transmitted to the serving

BS via the sleep request (MOB_SLP-REQ) message.

The serving BS then sets (or configures) the fourth bit (i.e., bit#3) of the Enabled-

the sleep response message from the serving BS, the MS enters power saving mode. Here,

the MS that is in the power saving mode can perform neighbor BS scan operation during

sleep mode.

required to perform association with a neighbor BS (i.e., BS2). Thereafter, the MS transmits

the scan request (MOB_SCN-REQ) message to the serving BS to request to perform association with the neighbor BS (i.e., BS2). In response to the scan request (MOB_SCN-

REQ) message, the serving BS transmits necessary parameters for performing association

with the neighbor BS (i.e., BS2) via the scan response (MOB-SCN-RSP) message.

Thereafter, the MS synchronizes in uplink/downlink directions with the neighbor BS (i.e.,

BS2) in order to perform association.

Further, the MS transmits a ranging request (RNG-REQ) message to the neighbor

BS (i.e., BS2). In response, the neighbor BS (i.e., BS2) transmits ranging control parameters

along with association parameters to the MS via a ranging response (RNG-RSP) message.

As a feature, the MS keeps the association parameters received from the neighbor BS (i.e.,

BS2) and in turn, can re-use the association parameters when performing handover with the

corresponding BS. After receiving the ranging response (RNG-RSP) message, the MS

maintains power saving mode.

As discussed above, the handover operation and related events performed by the MS

that is in power saving mode can be enabled or disabled by using the parameters disclosed

in the present invention. More specifically, whether to enable/disable can be represented in

a bitmap form at the time when the MS enters power saving mode. Here, a plurality of

events can be enabled or disabled as a group. In the embodiments of the present invention

represent examples where the plurality of events is enabled.

It will be apparent to those skilled in the art that various modifications and variations

can be made in the present invention without departing from the spirit or scope of the

inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and

their equivalents.

Claims

1. A method of performing an action related to handover by a mobile station

(MS) that is in power saving mode in a wireless mobile communication system, the method

comprising:

receiving information from a base station (BS), wherein the information

includes at least one action for performing handover and at least one condition

corresponding to the at least one action;

transmitting a request message to perform the at least one action based on the

received information from the BS;

receiving a response message in response to the request message; and

performing the at least one action according to the received response

message.

2. The method of claim 1, wherein the information defines a trigger type which

includes at least one of Carrier-to-interference and Noise Ratio (CINR), a Received Signal

Strength Indicator (RSSI), and a Round Trip Delay.

3. The method of claim 1, wherein the information defines a trigger function

which is a computation method for triggering action.

4. The method of claim 1, wherein the at least one action includes a scanning

request, a scanning report, and a handover request.

5. The method of claim 1, wherein the information defines a trigger value

which represents a value used for comparing to a measured value of at least one trigger type.

6. The method of claim 1, wherein the information defines a trigger average

duration which represents a time duration in which at least one trigger type is measured and

averaged for determining a condition for triggering at least one action.

7. The method of claim 6, wherein the trigger type which includes at least one

of Carrier-to-interference and Noise Ratio (CINR), a Received Signal Strength Indicator

(RSSI), and a Round Trip Delay.

8. The method of claim 1, wherein the request message is used for entering the

power saving mode.

9. The method of claim 8, wherein the request message includes a bitmap for

indicating the at least one action to be performed during the power saving mode.

10. The method of claim 9, wherein the bitmap represented by a plurality of bits,

the bit having a value of ^Λ 0' represents the action that is disabled.

11. The method of claim 10, wherein if each bit of the bitmap has a value of

^λ 0, ' which indicates that all the actions are disabled.

12. The method of claim 9, wherein the bitmap represented by a plurality of bits,

the bit having a value of ^λ 1 ' represents the action that is enabled.

13. The method of claim 1, wherein the response message includes a bitmap for

14. The method of claim 13, wherein the bitmap represented by a plurality of

bits, the bit having a value of ^Λ 0 ' represents the action that is disabled.

15. The method of claim 13, wherein the bitmap represented by a plurality of

bits, the bit having a value of ^Λ 1 ' represents the action that is enabled.

16. The method of claim 13, wherein the bitmap included in the response

message is same as the bitmap included in the request message.

17. The method of claim 13, wherein the bitmap included in the response

message is different from the bitmap included in the request message.

18. The method of claim 1, wherein the information is included in a Downlink

Channel Descriptor (DCD) message or a Neighbor Advertisement (MOB_NBR-ADV)

message.

19. The method of claim 1, wherein the request message is a sleep request

(MOB_SLP-REQ) message or a ranging request (RNG-REQ) message.

20. The method of claim 1, wherein the response message is a sleep response

(MOB_SLP-REQ) message or a ranging request (RNG-RSP) message.

21. The method of claim 1 , wherein the power saving mode is a sleep mode.

22. A method of providing actions related to handover by a base station (BS) for

a mobile station (MS) that is in power saving mode in a wireless mobile communication

system, the method comprising:

transmitting information to the MS, wherein the information includes at least

one action for performing handover and at least one condition corresponding to the at least

one action; receiving a request message from the MS asking to perform at least one

action based on the received information; and

transmitting a response message in response to the request message.