Method and apparatus for supporting mobile station disconnected from a base station in wireless communication system

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

0001The present application is related to and claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Jan. 28, 2011 and assigned Serial No. 10-2011-0008608, the contents of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

0002The present disclosure relates generally to a wireless communication system, and in particular, to a method and apparatus for supporting a Mobile Station (MS) located in a collapsed cell area in a wireless communication system.

BACKGROUND OF THE INVENTION

0003In preparation for an emergency state such as a disaster, a wireless communication system provides a service for notifying that a user is in an emergency state. For example, the wireless communication system provides an emergency call service for transmitting, when a user is in an emergency state, an emergency signal to request the assistance of relevant agencies or other users.

0004However, a Base Station (BS) may malfunction due to disasters such as earthquakes, fires, and terrors. In this case, a cell area of the BS may collapse, and Mobile Stations (MSs) in the collapsed cell area may be disconnected from the BS to fail to receive the emergency call service.

0005What is therefore required is a scheme for supporting an emergency call service for MSs that are disconnected from a BS due to the collapse of a cell area of the BS.

SUMMARY OF THE INVENTION

0006To address the above-discussed deficiencies of the prior art, it is a primary object to provide a method and apparatus for supporting a Mobile Station (MS) located in a collapsed cell area to be disconnected from a Base Station (BS) in a wireless communication system.

0007Another object of the present disclosure is to provide a method and apparatus for relaying, by a normal MS located in a normal cell area, a signal of a MS located in a collapsed cell area to be disconnected from a BS in a wireless communication system.

0008Another object of the present disclosure is to provide a method and apparatus for operating a normal MS, which is located in a normal cell area, as a master MS for an MS, which is located in a collapsed cell area to be disconnected from a BS, to connect the disconnected MS and the BS in a wireless communication system.

0009Another object of the present disclosure is to provide a method and apparatus for determining, by a BS, a master MS for supporting an MS located in a collapsed cell area to be disconnected from a BS in a wireless communication system.

0010Another object of the present disclosure is to provide a method and apparatus for selecting a master MS by an MS located in a collapsed cell area to be disconnected from a BS in a wireless communication system.

0011According to an aspect of the present disclosure, a method of an Mobile Station (MS) for supporting an MS disconnected from a Base Station (BS) in a wireless communication system includes: receiving a rescue signal from the disconnected MS; collecting information necessary to determine a support MS for the disconnected MS; and transmitting the collected information to a serving BS.

0012According to another aspect of the present disclosure, a method of a Base Station (BS) for supporting a Mobile Station (MS) disconnected from a BS in a wireless communication system includes: receiving information, which is necessary to determine a support MS for the disconnected MS, from at least one MS in a cell; determining a support MS for the disconnected MS on the basis of the received information; and transmitting a support command signal for the disconnected MS to the support MS.

0013According to another aspect of the present disclosure, a method of a Mobile Station (MS) disconnected from a Base Station (BS) in a wireless communication system includes: transmitting a rescue signal when a preamble signal is not received from a BS; receiving a preamble signal from at least one adjacent MS; determining a support MS on the basis of the received (RX) strength of the preamble signal received from the adjacent MS; and attempting a connection to the support MS.

0014According to another aspect of the present disclosure, an apparatus of a Mobile Station (MS) for supporting an MS disconnected from a Base Station (BS) in a wireless communication system includes: a receiving unit for receiving a rescue signal from the disconnected MS; a control unit for collecting information necessary to determine a support MS for the disconnected MS; and a transmitting unit for transmitting the collected information to a serving BS.

0015According to another aspect of the present disclosure, an apparatus of a Base Station (BS) for supporting a Mobile Station (MS) disconnected from a BS in a wireless communication system includes: a receiving unit for receiving information, which is necessary to determine a support MS for the disconnected MS, from at least one MS in a cell; a control unit for determining a support MS for the disconnected MS on the basis of the received information; and a transmitting unit for transmitting a support command signal for the disconnected MS to the support MS.

0016According to another aspect of the present disclosure, an apparatus of a Mobile Station (MS) disconnected from a Base Station (BS) in a wireless communication system includes: a transmitting unit for transmitting a rescue signal when a preamble signal is not received from a BS; a receiving unit for receiving a preamble signal from at least one adjacent MS; and a control unit for determining a support MS on the basis of the received (RX) strength of the preamble signal received from the adjacent MS, and attempting a connection to the support MS.

BRIEF DESCRIPTION OF THE DRAWINGS

0017The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

0018<figref idref="DRAWINGS">FIG. 1</figref> illustrates a system configuration for supporting an MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure;

0019<figref idref="DRAWINGS">FIG. 2</figref> illustrates a signal flow for supporting an MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure;

0020<figref idref="DRAWINGS">FIG. 3</figref> illustrates an operation process of an MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure;

0021<figref idref="DRAWINGS">FIG. 4</figref> illustrates an operation process of an MS located in a normal area in a wireless communication system according to an exemplary embodiment of the present disclosure;

0022<figref idref="DRAWINGS">FIG. 5</figref> illustrates an operation process of a BS for supporting an MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure;

0023<figref idref="DRAWINGS">FIG. 6</figref> illustrates a signal flow for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure;

0024<figref idref="DRAWINGS">FIG. 7</figref> illustrates an operation process of an MS located in a normal area in a wireless communication system according to another exemplary embodiment of the present disclosure;

0025<figref idref="DRAWINGS">FIG. 8</figref> illustrates an operation process of a BS for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure;

0026<figref idref="DRAWINGS">FIG. 9</figref> illustrates a signal flow for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure;

0027<figref idref="DRAWINGS">FIG. 10</figref> illustrates an operation process of an MS located in a normal area in a wireless communication system according to another exemplary embodiment of the present disclosure;

0028<figref idref="DRAWINGS">FIG. 11</figref> illustrates an operation process of a BS for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure;

0029<figref idref="DRAWINGS">FIG. 12</figref> illustrates a MS in a wireless communication system according to an exemplary embodiment of the present disclosure; and

0030<figref idref="DRAWINGS">FIG. 13</figref> illustrates a BS in a wireless communication system according to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

0031<figref idref="DRAWINGS">FIGS. 1 through 13</figref>, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communication system. Exemplary embodiments of the present disclosure will be described herein below with reference to the accompanying drawings. In the following description, detailed descriptions of well-known functions or configurations will be omitted since they would unnecessarily obscure the subject matters of the present disclosure. Also, the terms used herein are defined according to the functions of the present disclosure. Thus, the terms may vary depending on users' or operators' intentions or practices. Therefore, the terms used herein must be understood based on the descriptions made herein.

0032The present disclosure provides a method and apparatus for supporting a Mobile Station (MS) located in a collapsed cell area in a wireless communication system.

0033<figref idref="DRAWINGS">FIG. 1</figref> illustrates a system configuration for supporting an MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure.

0034Referring to <figref idref="DRAWINGS">FIG. 1</figref>, the present disclosure will be described on the assumption that a cell area of a Base Station (BS) <b>102</b> collapses because the BS <b>102</b> fails to operate normally due to a failure. Also, the present disclosure will be described on the assumption that when a cell area of the BS <b>102</b> collapses due to a failure, MSs <b>100</b>-<b>1</b> to <b>100</b>-<b>5</b>, which have received a service from the BS <b>102</b>, fail to receive signals from any other BSs and are disconnected from any BSs.

0035The MSs <b>100</b>-<b>1</b> to <b>100</b>-<b>5</b> disconnected from the BS (hereinafter referred to as “disconnected MS” or “disconnected MSs”) transmit rescue signals in order to escape the state of disconnection from the BS. Upon receiving the rescue signals, mobiles stations <b>110</b>-<b>1</b> and <b>110</b>-<b>2</b> located in a normal cell area function as a master MS for the disconnected MSs <b>100</b>-<b>1</b> to <b>100</b>-<b>5</b> to transmit signals of the disconnected MSs <b>100</b>-<b>1</b> to <b>100</b>-<b>5</b> to serving BSs <b>112</b>-<b>1</b> and <b>112</b>-<b>2</b> and to transmit signals of the serving BSs <b>112</b>-<b>1</b> and <b>112</b>-<b>2</b> to the disconnected MSs <b>100</b>-<b>1</b> to <b>100</b>-<b>5</b>. Herein, the master MS may be determined by each of the disconnected MSs or by the relevant BS. Hereinafter, a detailed description will be give of three exemplary embodiments of a scheme for determining the master MS and supporting the disconnected MSs.

0036<figref idref="DRAWINGS">FIG. 2</figref> illustrates a signal flow for supporting an MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure. In <figref idref="DRAWINGS">FIG. 2</figref>, a first MS <b>200</b> is a disconnected MS that is located in a collapsed cell area to be disconnected from a BS. A second MS <b>202</b> is a normal MS that is located in a cell area supporting a normal service. A BS <b>204</b> is a serving BS that provides a service to the second MS <b>202</b>.

0037Referring to <figref idref="DRAWINGS">FIG. 2</figref>, when a preamble signal is detected, the first MS <b>200</b> transmits a rescue signal in step <b>210</b>. Herein, the preamble signal may be a preamble signal of a BS or a preamble signal of a master MS. When the preamble signal is detected, the first MS <b>200</b> attempts a connection to an MS or a BS corresponding to the detected preamble signal, without performing the process of <figref idref="DRAWINGS">FIG. 2</figref>.

0038Upon receiving the rescue signal, the second MS <b>202</b> transmits a preamble allocation request to the BS <b>204</b> in step <b>212</b>. In step <b>214</b>, the BS <b>204</b> determines a preamble for the second MS <b>202</b> and transmits a preamble allocation approval signal including the determined preamble information (e.g., preamble index) to the second MS <b>202</b>.

0039In step <b>216</b>, the second MS <b>202</b> transmits the allocated preamble to the first MS <b>200</b> at predetermined periods. In this case, the second MS <b>202</b> may stop an operation of detecting a rescue signal transmitted by the disconnected MS.

0040Upon receiving the preamble from the second MS <b>202</b>, the first MS <b>200</b> determines whether to determine the second MS <b>202</b> as the first MS <b>200</b> own master MS on the basis of the received (RX) strength of the preamble signal. For example, when the RX strength of the preamble signal received from the second MS <b>202</b> is equal to or greater than a predetermined threshold value, the first MS <b>200</b> may determine the second MS <b>202</b> as the first MS <b>200</b> own master MS. Also, when receiving preambles from a plurality of MSs, the first MS <b>200</b> may determine the MS corresponding to the preamble of the greatest RX strength as the first MS <b>200</b> own MS. When determining the second MS <b>202</b> as the first MS <b>200</b> own master MS, the first MS <b>200</b> attempts a connection to the second MS <b>202</b> in step <b>218</b>.

0041Upon detecting the connection attempt of the first MS <b>200</b>, the second MS <b>202</b> transmits a master MS authority request to the BS <b>204</b> in step <b>220</b>. In step <b>222</b>, the BS <b>204</b> transmits a master MS authority approval signal to the second MS <b>202</b>.

0042Upon receiving the master MS authority from the BS <b>204</b>, the second MS <b>202</b> may establish a communication link with the first MS <b>200</b> to transmit a signal of the first MS <b>200</b> to the BS <b>204</b> and to transmit a signal of the BS <b>204</b> to the first MS <b>200</b>.

0043Hereinafter, an operation process of a disconnected MS, an operation process of a normal MS, and an operation process of a serving BS of the normal MS will be described with reference to <figref idref="DRAWINGS">FIGS. 3 to 5</figref> based on the signal flow of <figref idref="DRAWINGS">FIG. 2</figref>.

0044<figref idref="DRAWINGS">FIG. 3</figref> illustrates an operation process of a MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure.

0045Referring to <figref idref="DRAWINGS">FIG. 3</figref>, in step <b>301</b>, the disconnected MS determines whether a preamble of a BS or a preamble signal of a master MS is detected.

0046When a preamble of the BS or a preamble signal of the master MS is not detected, the disconnected MS proceeds to step <b>303</b>. In step <b>303</b>, the disconnected MS determines that is located in a collapsed cell area or is located outside a cell area to be in a disconnected state, and transmits a rescue signal. Herein, the rescue signal may be broadcasted.

0047In step <b>305</b>, the disconnected MS determines whether a preamble signal is detected. When the preamble signal is not detected, the disconnected MS returns to step <b>303</b> to transmit a rescue signal. That is, the disconnected MS continues to transmit the rescue signal until receiving a preamble of the BS or a preamble signal of the master MS

0048When the preamble is received, the disconnected MS proceeds to step <b>307</b>. In step <b>307</b>, the disconnected MS determines its own master MS based on the RX strength of the preamble signal. For example, when the RX strength of the preamble signal is equal to or greater than a predetermined threshold value, the disconnected MS may determine the MS corresponding to the preamble as the disconnected MS's own master MS. On the other hand, when the RX strength of the preamble signal is smaller than the predetermined threshold value, the disconnected MS may disregard the received preamble and return to step <b>303</b> to transmit a rescue signal. Also, when receiving preambles from a plurality of MSs, the disconnected MS may compare the RX strengths of the preamble signals and determine the MS corresponding to the preamble of the greatest RX strength as the disconnected MS's own master MS.

0049In step <b>309</b>, the disconnected MS attempts a connection to the master MS. In step <b>311</b>, the disconnected MS determines whether the connection to the master MS succeeds. When the connection to the master MS fails, the disconnected MS return to step <b>303</b> to transmit an SOS signal.

0050When the connection to the master succeeds, the disconnected MS proceeds to step <b>313</b>. In step <b>313</b>, the disconnected MS communicates through the master MS. Thereafter, the disconnected MS ends the algorithm according to the present disclosure.

0051<figref idref="DRAWINGS">FIG. 4</figref> illustrates an operation process of an MS located in a normal area in a wireless communication system according to an exemplary embodiment of the present disclosure.

0052Referring to <figref idref="DRAWINGS">FIG. 4</figref>, in step <b>401</b>, the MS located in the normal area (hereinafter referred to as “normal MS”) determines whether a rescue signal is detected. When the rescue signal is detected, the normal MS determines that there is a peripheral MS in a disconnected state. In step <b>403</b>, the normal MS transmits a preamble allocation request to the normal MS's own serving BS.

0053In step <b>405</b>, the normal MS receives a preamble allocation from the serving BS. In step <b>407</b>, the normal MS transmits a preamble periodically.

0054In step <b>409</b>, the normal MS determines whether there is an MS attempting a connection to the normal MS. When there is no MS attempting a connection to the normal MS, the normal MS returns to step <b>407</b> to transmit a preamble periodically. Although not illustrated in <figref idref="DRAWINGS">FIG. 4</figref>, when a connection-attempting MS is not present for a predetermined period of time, the normal MS may stop the preamble transmitting operation and end the algorithm according to the present disclosure.

0055When there is a connection-attempting MS, the normal MS proceeds to step <b>411</b>. In step <b>411</b>, the normal MS transmits a master MS authority request to the serving BS. In step <b>413</b>, the normal MS receives a master MS authority approval signal from the serving BS.

0056Thereafter, the normal MS functions as a master MS for the connection-attempting MS. In step <b>415</b>, the normal MS establishes a communication link with the connection-attempting MS to perform communication. That is, the normal MS may transmit a signal of a disconnected MS, which has connected to the normal MS, to the serving BS, and transmit a signal of the serving BS to the disconnected MS.

0057Thereafter, the normal MS ends the algorithm according to the present disclosure.

0058<figref idref="DRAWINGS">FIG. 5</figref> illustrates an operation process of a BS for supporting an MS disconnected from a BS in a wireless communication system according to an exemplary embodiment of the present disclosure.

0059Referring to <figref idref="DRAWINGS">FIG. 5</figref>, in step <b>501</b>, the BS determines whether a preamble allocation request signal is received from an MS within the BS's cell.

0060When the preamble allocation request signal is received, the BS proceeds to step <b>503</b>. In step <b>503</b>, the BS determines a preamble to be allocated to the MS and transmits the determined preamble information to the MS.

0061In step <b>505</b>, the BS determines whether a master MS authority request signal is received from the MS. When the master MS authority request signal is received, the BS proceeds to step <b>507</b>. In step <b>507</b>, the BS transmits a master MS authority approval signal to the MS.

0062Thereafter, the BS ends the algorithm according to the present disclosure.

0063As described with reference to <figref idref="DRAWINGS">FIGS. 2 to 5</figref>, the disconnected MS determines its own master MS in an exemplary embodiment of the present disclosure. Accordingly, it is possible for the disconnected MS to determine an MS having the best downlink channel environment as the disconnected MS's own master MS.

0064<figref idref="DRAWINGS">FIG. 6</figref> illustrates a signal flow for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure. In <figref idref="DRAWINGS">FIG. 6</figref>, a first MS <b>600</b> is a disconnected MS that is located in a collapsed cell area to be disconnected from a BS. A second MS <b>602</b> is a normal MS that is located in a cell area supporting a normal service. A BS <b>604</b> is a serving BS that provides a service to the second MS <b>602</b>.

0065Referring to <figref idref="DRAWINGS">FIG. 6</figref>, when a preamble signal is not detected, the first MS <b>600</b> transmits a rescue signal in step <b>610</b>. Herein, the preamble signal may be a preamble signal of a BS or a preamble signal of a master MS. When the preamble signal is detected, the first MS <b>600</b> attempts a connection to an MS or a BS corresponding to the detected preamble signal, without perforating the process of <figref idref="DRAWINGS">FIG. 6</figref>.

0066Upon receiving the rescue signal, the second MS <b>602</b> transmits information related to the rescue signal to the second MS <b>602</b> serving BS <b>604</b> in step <b>612</b>. Herein, the rescue signal-related information may include information about the residual power of the second MS <b>602</b>, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the second MS <b>602</b>.

0067Upon receiving the rescue signal-related information, the serving BS <b>604</b> determines a master MS for disconnected MSs based on the received information. When receiving rescue signal-related information from a plurality of MSs within the serving BS's <b>604</b> cell, the serving BS <b>604</b> uses the received information to select at least one MS suitable for supporting a disconnected MS, among the MSs transmitting the rescue signal-related information, and determines the selected MS as a master MS. Herein, the serving BS may restrict the number of master MSs to prevent an excessive number of master MSs from being set in the cell, thereby making it possible to prevent a degradation in the overall system performance. That is, the serving BS may determine the maximum number of master MSs. The maximum number of master MSs may be predetermined by a service provider and a designer, or may be changed dynamically according to the cell states.

0068When the second MS <b>602</b> is determined as a master MS, the serving BS <b>604</b> transmits a master MS function command signal to the second MS <b>602</b> in step <b>614</b>. Herein, the serving BS <b>604</b> may allocate a preamble to the second MS <b>604</b>. On the other hand, when the second MS <b>602</b> is not determined as a master MS, the serving BS <b>604</b> may not transmit any signal or may transmit a signal indicating that the second MS <b>602</b> is not determined as a master MS.

0069In step <b>616</b>, the second MS <b>602</b> transmits the allocated preamble to the first MS <b>600</b> at predetermined periods. In this case, the second MS <b>602</b> may stop an operation of detecting a rescue signal transmitted by the disconnected MS.

0070Upon receiving the preamble from the second MS <b>602</b>, the first MS <b>600</b> determines whether to determine the second MS <b>602</b> as the first MS's <b>600</b> own master MS based on the RX strength of the preamble signal. For example, when the RX strength of the preamble signal received from the second MS <b>602</b> is equal to or greater than a predetermined threshold value, the first MS <b>600</b> may determine the second MS <b>602</b> as the first MS's <b>600</b> own master MS. On the other hand, when the RX strength of the preamble signal is smaller than the predetermined threshold value, the first MS <b>600</b> may return to step <b>610</b> to transmit a rescue signal.

0071When the first MS <b>600</b> determines the second MS <b>602</b> as the first MS <b>600</b> own master MS, the first MS <b>600</b> attempts a connection to the second MS <b>602</b> in step <b>618</b>. Then, the second MS <b>602</b> may set a communication link with the first MS <b>600</b> to transmit a signal, of the first MS <b>600</b> to the serving BS <b>604</b> and to transmit a signal of the serving BS <b>604</b> to the first MS <b>600</b>.

0072Hereinafter, an operation process of a normal MS and an operation process of a serving BS of the normal MS will be described with reference to <figref idref="DRAWINGS">FIGS. 7 and 8</figref> based on the signal flow of <figref idref="DRAWINGS">FIG. 6</figref>. An operation of a disconnected MS in <figref idref="DRAWINGS">FIG. 6</figref> may be performed similarly to the process described in <figref idref="DRAWINGS">FIG. 3</figref>, and thus a description thereof will be omitted for conciseness.

0073<figref idref="DRAWINGS">FIG. 7</figref> illustrates an operation process of an MS located in a normal area in a wireless communication system according to another exemplary embodiment of the present disclosure.

0074Referring to <figref idref="DRAWINGS">FIG. 7</figref>, in step <b>701</b>, the normal MS determines whether a rescue signal is detected. When the rescue signal is detected, the normal MS determines that there is a peripheral MS in a disconnected state. In step <b>703</b>, the normal MS transmits rescue signal-related information to a serving BS. Herein, the rescue signal-related information may include information about the residual power of the normal MS, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the normal MS.

0075In step <b>705</b>, the normal MS determines whether a master MS function command signal is received from the serving BS. When the master MS function command signal is not received, the normal MS returns to step <b>701</b>.

0076On the other hand, when the master MS function command signal is received, the normal MS proceeds to step <b>707</b>. In step <b>707</b>, the normal MS enters a master MS mode and transmits a preamble periodically. Herein, the preamble may be allocated from a BS when the master MS function command signal is received. Also, the normal MS may stop an operation of detecting a rescue signal transmitted by a disconnected MS.

0077In step <b>709</b>, the normal MS determines whether there is an MS attempting a connection to the normal MS. When there is no MS attempting a connection to the normal MS, the normal MS returns to step <b>707</b> to transmit a preamble periodically. Herein, the normal MS performs steps <b>707</b> and <b>709</b> repetitively. However, when a connection-attempting MS is not present for a predetermined period of time, the normal MS may convert to a general MS mode and transmit a general MS mode conversion signal to the serving BS, without operating as a master MS.

0078On the other hand, when there is an MS attempting a connection to the normal MS, the normal MS proceeds to step <b>711</b>. In step <b>711</b>, the normal MS establishes a communication link with the MS to perform communication. That is, the normal MS may transmit a signal of a disconnected MS, which has connected to the normal MS, to the serving BS, and transmit a signal of the serving BS to the disconnected MS.

0079Thereafter, the normal MS ends the algorithm according to the present disclosure.

0080<figref idref="DRAWINGS">FIG. 8</figref> illustrates an operation process of a BS for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure.

0081Referring to <figref idref="DRAWINGS">FIG. 8</figref>, in step <b>801</b>, the BS determines whether a signal including rescue signal-related information is received. When the rescue signal-related information is received, the BS proceeds to step <b>803</b>. In step <b>803</b>, the BS determines a master MS within the BS's cell by using information included in the received signal. Herein, the rescue signal-related information may include information about the residual power of an MS having transmitted the signal, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the MS. When receiving rescue signal-related information from a plurality of MSs within the BS's cell, the BS uses the received information to select at least one MS suitable for supporting a disconnected MS, among the MSs transmitting the rescue signal-related information, and determines the selected MS as a master MS. For example, first to third MSs having transmitted a signal including rescue signal-related information are located within a threshold distance, the BS may determine the MS among the first to third MSs, from which a rescue signal is most frequently received, as a master MS, or may determine the MS of the greatest residual power as a master MS. The present disclosure is not limited thereto, and the BS may determine a master MS in various ways.

0082When determining a master MS, the BS may set the maximum number of master MSs. The maximum number of master MSs may be predetermined by a service provider and a designer, or may be changed dynamically according to the cell states. Thus, in step <b>803</b>, when the number of MSs operating as a master MS is equal to the maximum number of master MSs, the BS may not determine the MS, which has transmitted the rescue signal-related information, as a master MS even when the MS can function as a master MS.

0083When an MS having transmitted the rescue signal-related information is determined as a master MS, the BS commands the determined MS to function as a master MS, in step <b>805</b>. Although not illustrated in <figref idref="DRAWINGS">FIG. 8</figref>, when an MS having transmitted the rescue signal-related information is not determined as a master MS, the BS may not transmit any signal or may transmit, to the MS, a signal indicating that the MS is not determined as a master MS.

0084Thereafter, the BS ends the algorithm according to the present disclosure.

0085<figref idref="DRAWINGS">FIG. 9</figref> illustrates a signal flow for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure. In <figref idref="DRAWINGS">FIG. 9</figref>, a first MS <b>900</b> is a disconnected MS that is located in a collapsed cell area to be disconnected from a BS. A second MS <b>902</b> is a normal MS that is located in a cell area supporting a normal service. A BS <b>904</b> is a serving BS that provides a service to the second MS <b>902</b>.

0086Referring to <figref idref="DRAWINGS">FIG. 9</figref>, when a preamble signal is detected, the first MS <b>900</b> transmits a rescue signal in step <b>910</b>. Herein, the preamble signal may be a preamble signal of a BS or a preamble signal of a master MS. When the preamble signal is detected, the first MS <b>900</b> attempts a connection to an MS or a BS corresponding to the detected preamble signal, without performing the process of <figref idref="DRAWINGS">FIG. 9</figref>.

0087Upon receiving the rescue signal, the second MS <b>902</b> transmits information related to the rescue signal to the second MS's <b>902</b> serving BS <b>904</b> in step <b>912</b>. Herein, the rescue signal-related information may include information about the residual power of the second MS <b>902</b>, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the second MS <b>902</b>.

0088Upon receiving the rescue signal-related information, the serving BS <b>904</b> determines a candidate master MS for disconnected MSs based on the received information. When receiving rescue signal-related information from a plurality of MSs within the serving BS's <b>904</b> cell, the serving BS <b>904</b> uses the received information to select at least one MS suitable for supporting a disconnected MS, among the MSs transmitting the rescue signal-related information, and determines the selected MS as a candidate master MS. Herein, the serving BS may restrict the number of candidate master MSs, and the maximum number of candidate master MSs may be determined and changed according to the number of master MSs.

0089When the second MS <b>902</b> is determined as a candidate master MS, the serving BS <b>904</b> transmits a candidate master MS function command signal to the second MS <b>902</b> in step <b>914</b>. Herein, the serving BS <b>904</b> may allocate a preamble to the second MS <b>904</b>. On the other hand, when the second MS <b>902</b> is not determined as a candidate master MS, the serving BS <b>904</b> may not transmit any signal or may transmit a signal indicating that the second MS <b>902</b> is not determined as a candidate master MS.

0090In step <b>916</b>, the second MS <b>902</b> transmits the allocated preamble to the first MS <b>900</b> at predetermined periods. In this case, the second MS <b>902</b> may stop an operation of detecting a rescue signal transmitted by the disconnected MS.

0091Upon receiving the preamble from the second MS <b>902</b>, the first MS <b>900</b> determines whether to determine the second MS <b>902</b> as the first MS's <b>900</b> own candidate master MS based on the RX strength of the preamble signal. For example, when the RX strength of the preamble signal received from the second MS <b>902</b> is equal to or greater than a predetermined threshold value, the first MS <b>900</b> may determine the second MS <b>902</b> as the first MS's <b>900</b> own candidate master MS. On the other hand, when the RX strength of the preamble signal is smaller than the predetermined threshold value, the first MS <b>900</b> may return to step <b>910</b> to transmit a rescue signal.

0092When the first MS <b>900</b> determines the second MS <b>902</b> as the first MS's <b>900</b> own candidate master MS, the first MS <b>900</b> attempts a connection to the second MS <b>902</b> in step <b>918</b>. Upon detecting the connection attempt of the first MS <b>900</b>, the second MS <b>902</b> transmits a master MS authority request signal to the serving BS <b>904</b> in step <b>920</b>.

0093Upon receiving the master MS authority request signal, the serving BS <b>904</b> determines whether the number of MSs operating as a master MS in the serving BS's <b>904</b> cell is smaller than the maximum number of master MSs. When the number of MSs operating as a master MS in the serving BS's <b>904</b> cell is smaller than the maximum number of master MSs, the serving BS <b>904</b> determines the second MS <b>902</b> as a master MS. In step <b>922</b>, the serving BS <b>904</b> transmits a master MS authority approval signal to the second MS <b>902</b>. On the other hand, when the number of MSs operating as a master MS in the serving BS's <b>904</b> cell is equal to the maximum number of master MSs, the serving BS <b>904</b> may disapprove the master MS authority of the second MS <b>902</b>.

0094Upon receiving the master MS authority from the serving BS <b>904</b>, the second MS <b>902</b> may establish a communication link with the first MS <b>900</b> to transmit a signal of the first MS <b>900</b> to the serving BS <b>904</b> and to transmit a signal of the serving BS <b>904</b> to the first MS <b>900</b>.

0095Hereinafter, an operation process of a normal MS and an operation process of a serving BS of the normal MS will be described with reference to <figref idref="DRAWINGS">FIGS. 10 and 11</figref> based on the signal flow of <figref idref="DRAWINGS">FIG. 9</figref>. An operation of a disconnected MS in <figref idref="DRAWINGS">FIG. 9</figref> may be performed similarly to the process described in <figref idref="DRAWINGS">FIG. 3</figref>, and thus a description thereof will be omitted for conciseness.

0096<figref idref="DRAWINGS">FIG. 10</figref> illustrates an operation process of an MS located in a normal area in a wireless communication system according to another exemplary embodiment of the present disclosure.

0097Referring to <figref idref="DRAWINGS">FIG. 10</figref>, in step <b>1001</b>, the normal MS determines whether a rescue signal is detected. When the rescue signal is detected, the normal MS determines that there is a peripheral MS in a disconnected state. In step <b>1003</b>, the normal MS transmits rescue signal-related information to a serving BS. Herein, the rescue signal-related information may include information about the residual power of the normal MS, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the normal MS.

0098In step <b>1005</b>, the normal MS determines whether a candidate master MS function command signal is received from the serving BS. When the candidate master MS function command signal is not received, the normal MS returns to step <b>1001</b>.

0099On the other hand, when the candidate master MS function command signal is received, the normal MS proceeds to step <b>1007</b>. In step <b>1007</b>, the normal MS enters a candidate master MS mode and transmits a preamble periodically. Herein, the preamble may be allocated from a BS when the candidate master MS function command signal is received. Also, the normal MS may stop an operation of detecting a rescue signal transmitted by a disconnected MS.

0100In step <b>1009</b>, the normal MS determines whether there is an MS attempting a connection to the normal MS. When there is no MS attempting a connection to the normal MS, the normal MS returns to step <b>1007</b> to transmit a preamble periodically. Herein, the normal MS performs steps <b>1007</b> and <b>1009</b> repetitively. However, when a connection-attempting MS is not present for a predetermined period of time, the normal MS may convert to a general MS mode and transmit a general MS mode conversion signal to the serving BS, without operating as a master MS.

0101On the other hand, when there is an MS attempting a connection to the normal MS, the normal MS proceeds to step <b>1011</b>. In step <b>1011</b>, the normal MS transmits a master MS authority request signal to the serving BS. In step <b>1013</b>, the normal MS determines whether a master MS authority approval signal from the serving BS. When a master MS authority disapproval signal is received from the serving BS, or when no signal is received for a predetermined period of time, the normal MS ends the algorithm according to the present disclosure.

0102On the other hand, when the master MS authority approval signal is received from the serving BS, the normal MS proceeds to step <b>1015</b>. In step <b>1015</b>, the normal MS establishes a communication link with the relevant MS to perform communication. That is, the normal MS may transmit a signal of a disconnected MS, which has connected to the normal MS, to the serving BS, and transmit a signal of the serving BS to the disconnected MS.

0103Thereafter, the normal MS ends the algorithm according to the present disclosure.

0104<figref idref="DRAWINGS">FIG. 11</figref> illustrates an operation process of a BS for supporting an MS disconnected from a BS in a wireless communication system according to another exemplary embodiment of the present disclosure.

0105Referring to <figref idref="DRAWINGS">FIG. 11</figref>, in step <b>1101</b>, the BS determines whether a signal including rescue signal-related information is received. When the rescue signal-related information is received, the BS proceeds to step <b>1103</b>. In step <b>1103</b>, the BS determines a candidate master MS within the BS's cell by using information included in the received signal. Herein, the rescue signal-related information may include information about the residual power of an MS having transmitted the signal, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the MS. When receiving rescue signal-related information from a plurality of MSs within the BS's cell, the BS uses the received information to select at least one MS suitable for supporting a disconnected MS, among the MSs transmitting the rescue signal-related information, and determines the selected MS as a candidate master MS. For example, first to third MSs having transmitted a signal including rescue signal-related information are located within a threshold distance, the BS may determine the first MS, from which a rescue signal is received most frequently, and the third MS, from which a rescue signal is received second-most frequently, as candidate master MSs, or may determine the MS of the greatest residual power and the MS of the second-greatest residual power as candidate master MSs. The present disclosure is not limited thereto, and the BS may determine a candidate master MS in various ways.

0106When determining the candidate master MS, the BS may set the maximum number of candidate master MSs. The maximum number of candidate master MSs may be predetermined by a service provider and a designer, or may vary be changed dynamically according to the cell states. Thus, in step <b>1103</b>, when the number of MSs operating as a candidate master MS is equal to the maximum number of candidate master MSs, the BS may not determine an MS, which has transmitted the rescue signal-related information, as a candidate master MS even when the MS can function as a candidate master MS.

0107When an MS having transmitted the rescue signal-related information is determined as a candidate master MS, the BS proceeds to step <b>1105</b>. In step <b>1105</b>, the Bs commands the determined MS to function as a candidate master MS. Although not illustrated in <figref idref="DRAWINGS">FIG. 11</figref>, when an MS having transmitted the rescue signal-related information is not determined as a candidate master MS, the BS may not transmit any signal or may transmit, to the MS, a signal indicating that the MS is not determined as a candidate master MS.

0108In step <b>1107</b>, the BS determines whether a master MS authority request signal is received from a candidate master MS.

0109When a master MS authority request signal is received from the candidate master MS, the BS proceeds to step <b>1109</b>. In step <b>1109</b>, in consideration of the maximum number of master MSs, the BS determines whether to approve the master MS authority of the candidate master MS. That is, when the number of MSs operating as a master MS in the BS's cell area is smaller than the maximum number of master MSs, the BS may approve the master MS authority of the candidate master MS. On the other hand, when the number of MSs operating as a master MS in the BS's cell area is equal to the maximum number of master MSs, the BS may disapprove the master MS authority of the candidate master MS.

0110In step <b>1111</b>, the BS transmits a master MS authority approval/disapproval signal to the candidate master MS. When the candidate master MS is not determined as a master MS, the BS may not transmit any signal.

0111Thereafter, the BS ends the algorithm according to the present disclosure.

0112<figref idref="DRAWINGS">FIG. 12</figref> illustrates a MS in a wireless communication system according to an exemplary embodiment of the present disclosure.

0113Referring to <figref idref="DRAWINGS">FIG. 12</figref>, the MS may include a control unit <b>1200</b>, a communication module <b>1210</b>, a display unit <b>1220</b>, an input unit <b>1230</b>, and a storage unit <b>1240</b>. The control unit <b>1200</b> may include a disconnected state controlling unit <b>1202</b> and a disconnected MS support controlling unit <b>1204</b>.

0114The control unit <b>1200</b> controls and processes an overall operation of the MS. According to the present disclosure, the control unit <b>1200</b> controls the disconnected state controlling unit <b>1202</b> to detect a disconnected state, in which the MS is located in a collapsed cell area or is located outside a cell area to be unable to receive a communication service from a BS, and to transmit a rescue signal to receive a communication service through an MS located in a normal cell area. That is, when a preamble signal transmitted from a peripheral BS or MS is not detected, the disconnected state controlling unit <b>1202</b> may determine that the MS is in a disconnected state. In this case, the disconnected state controlling unit <b>1202</b> controls the communication module <b>1210</b> to transmit a predetermined rescue signal. When detecting a preamble signal, which is transmitted from a MS located in a normal cell area, through the communication module <b>1210</b>, the disconnected state controlling unit <b>1202</b> determines a master MS based on the RX strength of the preamble signal and connects to the master MS.

0115Also, the control unit <b>1200</b> controls the disconnected MS support controlling unit <b>1204</b> to support MSs that are in a disconnected state. When a rescue signal is received through the communication module <b>1210</b>, the disconnected MS support controlling unit <b>1204</b> transmits a master MS authority request signal or rescue signal-related information to a serving BS. Herein, the rescue signal-related information may include information about the residual power of the MS, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the MS. When a master MS authority approval signal or a candidate master MS authority approval signal is received from the serving BS, the disconnected MS support controlling unit <b>1204</b> detects a preamble allocated from the serving BS and transmits the allocated preamble periodically. When there is a disconnected MS attempting to a connection to the MS, the disconnected MS support controlling unit <b>1204</b> directly establishes a communication link with the disconnected MS according to the master MS authority approval of the serving BS or transmits a master MS authority request signal to the serving BS.

0116The communication module <b>1210</b> includes a transmitting unit (not illustrated) for transmitting signals and a receiving unit (not illustrated) for receiving signals. The communication module <b>1210</b> transmits signals under the control of the control unit <b>1200</b>. Under the control of the control unit <b>1200</b>, the communication module <b>1210</b> may transmit a rescue signal when the MS is in a disconnected state. Also, under the control of the control unit <b>1200</b>, the communication module <b>1210</b> periodically transmits a preamble allocated from a serving BS, transmits a master MS authority request signal to the serving BS, and receives a master MS authority approval signal from the serving BS.

0117The display unit <b>1220</b> displays numerals, characters, images, and status information generated during an operation of the MS. The input unit <b>1230</b> includes one or more function keys or touch sensors. The input unit <b>1230</b> provides the control unit <b>1200</b> with data corresponding to a user's touch or data corresponding to a key pressed by the user. The storage unit <b>1240</b> stores various programs and data for an overall operation of the MS.

0118<figref idref="DRAWINGS">FIG. 13</figref> illustrates a BS in a wireless communication system according to an exemplary embodiment of the present disclosure.

0119Referring to <figref idref="DRAWINGS">FIG. 13</figref>, the BS may include a control unit <b>1300</b>, a communication module <b>1310</b>, and a storage unit <b>1320</b>. The control unit <b>1300</b> may include a master MS determining unit <b>1302</b>.

0120The control unit <b>1300</b> controls and processes an overall operation of the BS. According to the present disclosure, the control unit <b>1300</b> includes the master MS determining unit <b>1302</b> to determine an MS, which is located in a cell of the BS, as a master MS to support a disconnected MS. That is, when rescue signal-related information is received from MSs located in the cell, the master MS determining unit <b>1302</b> may determine a candidate master MS or a master MS based on the rescue signal-related information. Herein, the master MS determining unit <b>1302</b> determines a master MS so that the number of master MSs in the cell does not exceed the maximum number of master MSs. Herein, the rescue signal-related information may include information about the residual power of a relevant MS, information about the reception/non-reception of a rescue signal, information about the number of received rescue signals, information about the strength of a received rescue signal, and information about the location of the MS. Also, the maximum number of master MSs may be predetermined by a service provider and a designer, or may be changed according to the cell states. Also, the master MS determining unit <b>1302</b> allocates a preamble to a master MS or a candidate master MS and transmits the allocated preamble. Also, when a master MS authority request signal is received from a candidate master MS, the master MS determining unit <b>1302</b> may compare the number of master MSs in the cell with the maximum number of master MSs and determine whether to approve the master MS authority of the candidate master MS.

0121The communication module <b>1310</b> includes a transmitting unit (not illustrated) for transmitting signals and a receiving unit (not illustrated) for receiving signals. The communication module <b>1310</b> communicates signals with MSs in the cell under the control of the control unit <b>1300</b>. Under the control of the control unit <b>1300</b>, the communication module <b>1210</b> receives a master MS authority request signal and a signal including rescue signal-related information from MSs in the cell and transmits a master MS authority approval signal to a relevant MS.

0122The storage unit <b>1320</b> stores various programs and data for an overall operation of the BS. According to the present disclosure, the storage unit <b>1320</b> stores the maximum number of master MSs and the number of MSs operating as a master MS in the cell.

0123As described above, according to the present disclosure, a normal MS located in a normal cell area in a wireless communication system detects a rescue signal of a disconnected MS located in a collapsed cell area to be disconnected from a BS, and operates as a master MS for the disconnected MS to connect the disconnected MS and the BS, thereby making it possible to support an emergency call service for the disconnected MS. Also, when the disconnected MS determines its own master MS, it is possible to select a master MS having an excellent downlink channel environment. When a BS determines a master MS for the disconnected MS, it is possible to perform efficient communication by controlling the number of master MSs in a cell area of the BS.

0124While the disclosure has been, shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims. Therefore, the scope of the disclosure is defined not by the detailed description of the disclosure but by the appended claims, and all differences within the scope will be construed as being included in the present disclosure.