Patent Abstract:
A method and apparatus for transmitting and receiving a signal in a wireless communication system are provided in which, when a relay request message is received from a transmitter, a first receiver transmits a relay response message including a relay possible information to the transmitter, the relay possible information including information indicating whether the first receiver can perform a relay function, and relays a signal between the transmitter and a second receiver, when a relay confirm message is received from the transmitter after transmitting the relay response message. Herein, the first receiver is different from the second receiver.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
     The present application claims the benefit under 35 U.S.C. §119(a) of a Korean Patent Application filed in the Korean Intellectual Property Office on Jun. 29, 2007 and assigned Serial No. 2007-65533, the entire disclosure of which is hereby incorporated by reference. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention generally relates to a method and apparatus for transmitting and receiving a signal in a wireless communication system. 
     BACKGROUND OF THE INVENTION 
     Typically, a wireless communication system makes communications between a fixed base station (BS) and a mobile station (MS) using a single direct link, thus having low flexibility in configuring a wireless network. That is, it is difficult to configure a wireless network to provide services in a wireless environment experiencing fluctuating changes in traffic distribution or the number of required calls. 
     In this context, studies have been conducted on relaying data over multiple hops using relay stations (RSs) in a wireless communication system. The relay service enables the wireless communication system to reconfigure a network quickly according to a communication environment change and to efficiently operate the entire wireless network. Also, the wireless communication system can provide a high-speed radio channel to an MS by establishing an RS between a BS and the MS. Therefore, the use of RSs provides a high-speed data channel to MSs in poor channel conditions at a cell boundary and expands cell coverage. 
     The configuration of a conventional wireless communication system for providing a relay service will be described below with reference to  FIG. 1 . 
     Referring to  FIG. 1 , in the relay wireless communication system, MSs  140 ,  150 ,  160  and  170  (MS 1 , MS 2 , MS 3  and MS 4 , respectively) receive services from a BS  100  and RSs  110 ,  120 , and  130  (RS 1 , RS 2  and RS 3 , respectively). 
     MS 1  and MS 2  within a service area  101  of the BS  100  communicate with the BS  100  using direct BS-MS links L 1 . MS 2 , which is in poor channel conditions, receives a high-speed data channel using RS-MS link of RS 3 , L 2 . 
     MS 3  and MS 4  outside the service area  101  of the BS  100  communicate with the BS  100  using RS-MS links of RS 1 , L 3 . That is, the BS  100  can expand its service area by providing communication links to MS 3  and MS 4  outside the service area  101  using RS 1 . For MS 4  that is at a cell boundary of the service area of RS 1  and thus in poor channel conditions, transmission capacity can be increased using an RS-MS link of RS 2 , L 4 . 
     As described above, the wireless communication system can expand cell coverage and increase transmission capacity by providing control channels and high-speed data channels to MSs that are located at a cell boundary and in a shadowing area and thus are in poor channel conditions, by use of RSs. The relay service can be supported using neighbor MSs or separately procured RSs for a relay function. 
     However, when an MS supports the relay function, the MS consumes its limited power to relay a signal for another MS. The resulting power shortage may impede signal processing in the MS. 
     Conventionally, there was no sufficient motivation to use an MS capable of operating as an RS in relaying a signal for another MS at the expense of its power consumption in a cellular relay service system designed for expanding cell coverage or increasing transmission capacity, and no related procedures were specified. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, it is a primary aspect of exemplary embodiments of the present invention to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide a method and system for transmitting and receiving a signal more efficiently by use of an MS equipped with a relay function in a wireless communication system. 
     In accordance with an aspect of exemplary embodiments of the present invention, a method for transmitting and receiving a signal in a first receiver in a wireless communication system is provided. The method includes transmitting, when a relay request message is received from a transmitter, a relay response message including a relay possible information is transmitted to the transmitter, the relay possible information including information indicating whether the first receiver can perform a relay function, and relaying a signal between the transmitter and a second receiver, when a relay confirm message is received from the transmitter after transmitting the relay response message. Herein, the first receiver is different from the second receiver. 
     In accordance with another aspect of exemplary embodiments of the present invention, a method for transmitting and receiving a signal in a transmitter in a wireless communication system is provided. The method includes transmitting a relay request message to first receivers capable of performing a relay function among a plurality of receivers, receiving from each of the first receivers a relay response message including relay possible information that includes information indicating whether each of the first receivers can perform a relay function, selecting a second receiver from among the first receivers to perform the relay function using the received relay possible information, transmitting a relay confirm message to the second receiver, and transmitting and receiving signals to and from a third receiver among the plurality of receivers using the second receiver. Herein, the first receiver, the second receiver, and the third receiver are different receivers. 
     In accordance with a further aspect of exemplary embodiments of the present invention, an apparatus for transmitting and receiving a signal in a wireless communication system is provided. The apparatus includes a first receiver for transmitting, when a relay request message is received from a transmitter, a relay response message including a relay possible information to the transmitter, the relay possible information including information indicating whether the first receiver can perform a relay function, and relaying a signal between the transmitter and a second receiver, when a relay confirm message is received from the transmitter after transmitting the relay response message. Herein, the first receiver is different from the second receiver. 
     In accordance with still another aspect of exemplary embodiments of the present invention, an apparatus for transmitting and receiving a signal in a wireless communication system is provided. The apparatus includes a transmitter for transmitting a relay request message to first receivers capable of performing a relay function among a plurality of receivers, receiving from each of the first receivers a relay response message including a relay possible information that includes information indicating whether each of the first receivers can perform a relay function, selecting a second receiver from among the first receivers to perform the relay function using the received relay possible information, transmitting a relay confirm message to the second receiver, and transmitting and receiving signals to and from a third receiver among the plurality of receivers using the second receiver. Herein, the first receiver, the second receiver, and the third receiver are different receivers. 
     Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  illustrates the configuration of a conventional wireless communication system for providing a relay service; 
         FIG. 2  illustrates the configuration of a wireless communication system for providing a relay service according to an exemplary embodiment of the present invention; 
         FIG. 3  is a diagram illustrating a signal flow for an operation between a serving BS and MSs according to an exemplary embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating an operation of the serving BS according to an exemplary embodiment of the present invention; and 
         FIG. 5  is a flowchart illustrating an operation of a candidate relay MS according to an exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features and structures. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 2 through 5 , 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 wireless communication system. 
     Exemplary embodiments of the present invention provide a method for supporting a relay service using an MS in a multi-hop relay wireless communication system. The MS can be any mobile device that can provide a communication service, such as a portable phone, a laptop, a personal digital assistant (PDA), and so forth. 
       FIG. 2  illustrates the configuration of a wireless communication system for providing a relay service according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the wireless communication system for providing a relay service includes MSs  210 ,  220 ,  230  and  240  (MS 1 , MS 2 , MS 3  and MS 4 , respectively) and a serving BS  200  for providing a voice service or a packet data service to the MSs. Among the MSs, MS 4  is located outside the cell area of the serving BS  200  and thus cannot receive a service from the service BS  200  using a direct link. MS 4  should receive the service from the serving BS  200  by relaying from one of MS 1 , MS 2  and MS 3  having a relay function (hereinafter, referred to as relay MSs). For better understanding of the present invention, it is assumed that the serving BS  200  provides a communication service to a plurality of MSs in a centralized cellular communication system. Notably, the serving BS  200  can be any upper node of MSs. 
     While  FIG. 2  shows only a case of relaying for expanding cell coverage, the same thing applies to relaying for increasing transmission capacity for a target MS within the same cell. 
       FIG. 3  is a diagram illustrating a signal flow for an operation between a serving BS and MSs according to an exemplary embodiment of the present invention. In the illustrated case of  FIG. 3 , the operation is carried out among a serving BS  301 , candidate relay MSs  303 ,  305  and  307  (candidate relay MS 1 , candidate relay MS 2 , and candidate relay MS 3 , respectively), and a target MS  309  (target MS 4 ). 
     The serving BS  301  manages a candidate relay MS list of MSs capable of providing a relay function from among MSs within its cell area. As stated before with reference to  FIG. 2 , a service provider that operates the serving BS  301  acquires knowledge of whether each MS supports the relay function from the user of the MS. 
     Referring to  FIG. 3 , the serving BS  301  transmits a Relay REQuest (RREQ) message to a predetermined number of MSs  303 ,  305  and  307  among candidate relay MSs that it manages in steps  311 ,  312  and  315 , respectively. Candidate relay MS 1 , candidate relay MS 2 , and candidate relay MS 3  may exist on a communication path between the serving BS  301  and the target MS  309 . Hence, MSs transmits their global positioning system (GPS)-based location information to the serving BS  301 , periodically or non-periodically. 
     The RREQ message requests relay possible information, a remaining battery power, and a signal strength. The request of the relay possible information is for querying about support of the relay service of an MS according to a user selection in a real communication system even though the user of the MS has approved use of the MS as a relay. Therefore, even if a user agreed on use of his MS as a relay but does not want to use as a relay at a given time due to shortage of remaining power, a bad wireless communication environment, or other factors, the MS transmits a Relay REPly (RREP) message with relay possible information set to impossible to the serving BS  301 . If the MS user cannot receive the RREQ message, the MS can automatically reply to the serving BS  301 , taking into account its remaining power or its signal strength. The request of the remaining power by the RREQ message queries about the current remaining power of the relay MS. The remaining power can be expressed as an absolute power of the power that the MS preserves or a relative power value in percentage. The signal strength is the downlink signal strength of a reference signal such as a preamble or a pilot signal that the relay MS receives from the serving BS. The signal strength can be a signal-to-interference and noise ratio (SINR), a received signal strength indicator (RSSI), or a carrier-to-interference ratio (C/I). 
     Upon receipt of the RREQ message, candidate relay MS 1 , candidate relay MS 2 , and candidate relay MS 3  transmit RREP messages each including relay possible information, remaining power information, and signal strength information to the serving BS  301  in steps  317 ,  319  and  321 , respectively. For example, candidate relay MS 1  transmits an RREP message with relay possible information set to possible, remaining power information set to 80%, and signal strength information set to 10 dB to the serving BS  301  in step  317 . Candidate relay MS 2  transmits an RREP message with relay possible information set to possible, remaining power information set to 30%, and signal strength information set to 12 dB to the serving BS  301  in step  319 . Candidate relay MS 3  transmits an RREP message with relay possible information set to impossible, remaining power information set to 50%, and signal strength information set to 9 dB to the serving BS  301  in step  321 . The serving BS  301  selects a final relay MS based on a predetermined criterion. For instance, the serving BS  301  first excludes an MS that cannot support the relay function by setting relay possible information to impossible and then selects a candidate relay MS with the largest remaining power or the strongest signal strength depending on whether the determination criterion is remaining power or signal strength. Alternatively, the serving BS  301  can select a final relay MS in a comprehensive manner by weighting remaining powers and signal strengths. In the illustrated case of  FIG. 3 , the serving BS  301  first excludes candidate relay MS 3  that answers negative as to relay possibility from the selection and finally selects candidate relay MS 1  between candidate relay MS 1  and candidate relay MS 2  based on their remaining power in step  323 . 
     Meanwhile, if a relay candidate MS is in charge mode in which there is no limit to its remaining power, it notifies the serving BS  301  of the charge mode by the RREP message. In the charge mode, the relay candidate MS is being charged. Upon receipt of information indicating the charge mode from the candidate relay MS, the serving BS  301  can give a higher priority to the charge mode than remaining power and signal strength in selection of a final candidate relay MS. Therefore, if a candidate relay MS is in the charge mode and can perform the relay function, the serving BS  301  selects the candidate relay MS as a final one. 
     Then the serving BS  301  transmits a Relay CONfirm (RCON) message to the selected MS  303 , thereby notifying it that it will relay a signal in step  325 . In step  327 , the serving BS  301  can provide a communication service to the target MS  309  by relaying of the MS  303 . 
     With reference to  FIG. 4 , an operation of the serving BS according to an exemplary embodiment of the present invention will be described.  FIG. 4  is a flowchart illustrating an operation of the serving BS for providing a communication service to a target MS using a relay MS according to an exemplary embodiment of the present invention. 
     When the serving BS determines that a communication service needs to be provided using a relay MS, it transmits an RREQ message to candidate relay MSs in step  400 . As described with reference to  FIG. 3 , the candidate relay MSs can be MSs that are located on a communication path between the serving BS  301  and a target MS among MSs that have agreed to the relay function with the service provider. For the relay function, the MSs report their GPS-based location information to the serving BS, periodically or non-periodically. Or the serving BS can select candidate relay MSs by roughly estimating the location of each MS based on the direction of angle (DoA) of an uplink signal received from the MS. 
     The RREQ message requests relay possible information, remaining powers, and signal strengths of the candidate relay MSs, as described before. 
     In step  410 , the serving BS receives RREP messages from the candidate relay MSs. Information included in the RREP messages has been described before, and thus its description is avoided herein. 
     The serving BS selects a final relay MS according to a predetermined criterion using the information received in the RREP messages in step  420 . The determination criterion has been described before with reference to  FIG. 3 , and thus its description will not be provided herein redundantly. 
     In step  430 , the serving BS transmits an RCON message to the selected relay MS. Then the serving BS provides a communication service to the target MS using the relay MS in step  440 . 
       FIG. 5  is a flowchart illustrating an operation of a candidate relay MS according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , the candidate relay MS receives an RREQ message from the serving BS in step  500 . In step  510 , the candidate relay MS determines whether to support the relay function and measures its remaining power and downlink signal strength. The decision whether to support the relay function can be made directly by the user of the candidate relay MS or according to a pre-stored decision criterion by the candidate relay MS. For example, in the absence of a direct input from the user, the candidate relay MS can determine whether to support the relay function based on its remaining power or downlink signal strength according to the decision criterion. The candidate relay MS may not receive an external input from the user for a period of time because the user is physically remote from the candidate relay MS or he cannot enter some input to the candidate relay MS for some reason. 
     The candidate relay MS can measure its remaining power in the percentage of a current remaining battery power to a full battery power or in an absolute value. For instance, the remaining power can be 30% or 10 mW. 
     The candidate relay MS measures the downlink signal strength by measuring the SINR, RSSI or C/I of a reference signal such as a preamble or a pilot signal received from the serving BS. 
     In step  520 , the candidate relay MS transmits the determined relay possible information, remaining power information, and signal strength information to the serving BS by an RREP message. Then the candidate relay MS monitors reception of an RCON message in step  530 . Upon receipt of the RCON message, the candidate relay MS relays communication data information to a target MS from the serving BS in step  540 . If the candidate relay MS has not received the RCON message in step  530 , the candidate relay MS does not perform the relay function. 
     As is apparent from the above description, the present invention advantageously selects a relay MS based on the channel conditions, remaining powers, and user intentions of candidate relay MSs in a communication system that should provide a relay service using a relay MS. Therefore, the relay service can be provided on a reasonable basis. 
     Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

Technology Classification (CPC): 8