Abstract:
An apparatus and method for avoiding interference between a base station and a relay station when using full duplex relay in a multi-hop relay wireless communication system are provided. An operation of a mobile station includes measuring an strength of a receive signal from a base station and an strength of a receive signal from an relay station, calculating a receive signal strength ratio of base station to relay station by dividing the strength of the receive signal from the base station by the strength of the receive signal from the relay station, determining if interference occurs using the receive signal strength ratio, and transmitting a control message representing if interference occurs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    The present application claims priority under 35 U.S.C. § 119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Feb. 22, 2008 and assigned Serial No. 10-2008-0016219, the contents of which are herein incorporated by reference. 
       TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to a multi-hop relay wireless communication system. More particularly, the present invention relates to an apparatus and method for, when a Mobile Station (MS) is located in a cell boundary between a Base Station (BS) and a Relay Station (RS), avoiding interference between the BS and the RS when using Full Duplex Relay (FDR) in a multi-hop relay wireless communication system. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the 4 th  Generation (4G) communication system, that is the next generation communication system, intensive research is being conducted to provide users with services having various Qualities of Service (QoSs) using a data rate of about 100 Mbps. In particular, in the 4 G communication system, study is now made to support high-speed services in the way of guaranteeing mobility and QoS for a Broadband Wireless Access (BWA) communication system such as a wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system. Also, the typical 4 G communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system. 
         [0004]    The IEEE 802.16 communication system is a communication system applying Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) to support a broadband transmission network for a physical channel of the wireless communication system. Active research has been conducted to guarantee the mobility of an MS and the flexibility of wireless networking in the IEEE 802.16 communication system and provide service more efficiently under a wireless environment experiencing great changes in traffic distribution or required calls. As one method among them, a communication system applying a multi-hop relay data forward scheme using an RS is taken into consideration. 
         [0005]    A use of the RS in the broadband wireless communication system results in effects of an increase of coverage of a BS, throughput improvement, etc. That is, the broadband wireless communication system can improve a throughput by locating an RS in a specific area having poor channel environment. Also, the broadband wireless communication system can provide a service to enable communication between an MS out of the coverage of a BS and the BS by locating an RS near a cell boundary. 
         [0006]    As shown in  FIG. 1A , in a general relay system, a channel resource for signal transmission from a BS to an RS is separated from a channel resource for signal transmission from the RS to an MS. For example, if a channel resource is separated in time, transmission from an RS to an MS is performed after transmission from a BS to the RS is performed.  FIG. 1A  shows a Half Duplex Relay (HDR) wherein resources are separated in time axis. In  FIG. 1A , one square means one channel, a solid line square represents a transmission duration, and a dotted line square represents a reception duration. In view of an RS, HDR divides a channel resource for use and thus the frequency efficiency of the whole system is low. Unlike HDR, Full Duplex Relay (FDR) uses the same channel resource for each transmission between a BS and an RS and between the RS and an MS and, thus, the frequency efficiency is higher than HDR. 
         [0007]    Referring to  FIG. 1B , FDR has a great possibility to cause interference in communication of an MS compared to an HDR system. In the HDR of  FIG. 1A , frequency efficiency is low but, because only an RS or a BS transmits a signal for the same channel resource during a relay process, an MS does not have to consider interference from the RS. However, if adopting FDR to overcome a decrease of frequency efficiency, a transmit signal between a BS and an RS occupies the same channel resource as in  FIG. 1B . The influence of interference occurring due to the BS and the RS using the same channel resource is different depending on relative positions of a BS  201 , an RS  203 , and MSs  205  to  207  as shown in  FIG. 2 . In  FIG. 2 , the MSs  205  and  207  are in connection to the RS  203 . With respect to the MS B  207 , located out of cell coverage of the BS  201 , interference from the BS  201  does not matter. However, in the case of the MS A  205 , if a received signal ratio of the MS A  205  from the BS  201  and the RS  203  increases more than any level depending on a relative position, etc., interference occurs and, thus, a quality of relay communication is deteriorated. 
         [0008]    As described above, there is a problem that, when applying HDR, a transmit signal of a BS and a transmit signal of an RS occupy the same channel resource, thus causing interference. 
       SUMMARY OF THE INVENTION 
       [0009]    To address the above-discussed deficiencies of the prior art, it is a primary aspect of the present invention to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, one aspect of the present invention is to provide an apparatus and method for minimizing cell interference between a base station and a relay station for a mobile station when using frill duplex relay in a multi-hop relay wireless communication system. 
         [0010]    Another aspect of the present invention is to provide an apparatus and method for determining if interference occurs when using FDR in a multi-hop relay wireless communication system. 
         [0011]    The above aspects are achieved by providing an apparatus and method for avoiding interference between a BS and an RS when using FDR in a multi-hop relay wireless communication system. 
         [0012]    According to one aspect of the present invention, an operation method of a MS in a multi-hop relay wireless communication system is provided. The method includes measuring an strength of a received signal from a BS and an strength of a received signal from an RS, calculating a received signal strength ratio of BS to RS by dividing the strength of the received signal from the BS by the strength of the received signal from the RS, determining if interference occurs using the received signal strength ratio, and transmitting a control message representing if interference occurs. 
         [0013]    According to another aspect of the present invention, an operation method of a RS in a multi-hop relay wireless communication system is provided. The method includes determining if interference occurs using a control message comprising interference information received from a MS, reallocating resources to the MS if interference occurs, and performing communication with the MS through the reallocated resources. 
         [0014]    According to a further aspect of the present invention, a MS apparatus in a multi-hop relay wireless communication system is provided. The apparatus includes a measurer, a determiner, and a transmitter. The measurer measures an strength of a received signal from a BS and an strength of a received signal from an RS. The determiner calculates a received signal strength ratio of BS to RS by dividing the strength of the received signal from the BS by the strength of the received signal from the RS, and determines if interference occurs using the received signal strength ratio. The transmitter transmits a control message representing if interference occurs. 
         [0015]    According to a further another aspect of the present invention, an RS apparatus in a multi-hop relay wireless communication system includes an allocator and a transmitter. The allocator determines if interference occurs using a control message including interference information received from a MS, and reallocates resources to the MS if interference occurs. The transmitter transmits a signal to the MS through the reallocated resources. 
         [0016]    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; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. 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 
         [0017]    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: 
           [0018]      FIGS. 1A and 1B  are diagrams illustrating transmit/receive processes of half duplex relay and full duplex relay according to the conventional art; 
           [0019]      FIG. 2  is a diagram illustrating a mobile communication system in which a mobile station A is located in an area where interference occurs and an mobile station B is located in an area where no interference occurs; 
           [0020]      FIG. 3  is a diagram illustrating a transmit/receive process of a full duplex relay scheme for minimizing interference in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention; 
           [0021]      FIG. 4  is a block diagram illustrating a construction of an mobile station in an full duplex relay scheme for minimizing interference in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention; 
           [0022]      FIG. 5  is a block diagram illustrating a construction of a relay station in a full duplex relay scheme for minimizing interference in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention; 
           [0023]      FIG. 6  is a flow diagram illustrating a process of an mobile station in a full duplex relay scheme for minimizing interference in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention; and 
           [0024]      FIG. 7  is a flow diagram illustrating a process of an relay station in a full duplex relay scheme for minimizing interference in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]      FIGS. 3 through 7 , 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. 
         [0026]    A method and apparatus for minimizing interference when using full duplex relay in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention are described below. In an exemplary embodiment of the present invention, an OFDM/OFDMA wireless communication system is, for example, described below, but the present invention is also applicable to other wireless communication systems. 
         [0027]      FIG. 3  is a diagram illustrating a transmit/receive process of an FDR scheme for minimizing interference in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention. In  FIG. 3 , a solid line square represents a transmission duration and a dotted line square represents a reception duration. 
         [0028]    Referring to  FIG. 3 , in a first duration  301 , a BS transmits a signal s 1  to an RS and a MS over a 1 st  channel. The RS and the MS receive the signal s 1  from the BS over the 1 st  channel. 
         [0029]    In a second duration  303 , the BS transmits a signal s 2  to the RS and the MS over the 1 st  channel. The RS receives the signal S 2  from the BS over the 1 st  channel, changes the signal s 1  received from the BS in the first duration  301  into a signal s 1 ′, and transmits the signal s 1 ′ to the MS over the 1 st  channel. The change means that, by demodulating and again modulating a signal by the RS, data included is the same but a modulation scheme is changed. The MS receives the signal s 2  from the BS over the 1 st  channel and receives the signal s 1 ′ from the RS over the 1 st  channel. In view of the MS, the signal s 1 ′ and the signal s 1 ′ share the same channel, thus causing interference. Accordingly, the MS transmits interference information to the RS. The interference information means a control message including information on interference. 
         [0030]    In a third duration  305 , the BS transmits a signal s 3  to the RS and the MS over the 1 st  channel. The RS receives the signal s 3  from the BS over the 1 st  channel and, upon recognizing interference through the interference information, identifies map information of the BS. The RS transmits the signal s 2 ′ to the MS having sent the interference information through a vacant resource block not currently allocated by the BS. In  FIG. 3 , the vacant resource block is a 2 nd  channel. The MS simultaneously receives the signal S 3  and the signal S 2 ′ without interference by receiving the signal S 3  from the BS over the 1 st  channel and receiving the signal S 2 ′ from the RS over the 2 nd  channel. 
         [0031]      FIG. 4  is a block diagram illustrating a construction of an MS in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention. 
         [0032]    As shown in  FIG. 4 , the MS includes a Radio Frequency (RF) receiver  401 , an OFDM demodulator  403 , a subcarrier demapper  405 , a demodulator and decoder  407 , a message processor  409 , a signal measurer  411 , an interference determiner  413 , a controller  415 , a message generator  417 , an encoder and modulator  419 , a subcarrier mapper  421 , an OFDM modulator  423 , and an RF transmitter  425 . 
         [0033]    The RF receiver  401  down converts an RF band signal received through an antenna into a baseband signal. The OFDM demodulator  403  distinguishes the signal provided from the RF receiver  401  in an OFDM symbol unit, removes a Cyclic Prefix (CP), and then restores signals by subcarrier through a Fast Fourier Transform (FFT) operation. The subcarrier demapper  405  extracts signals to be demodulated and decoded among the signals by subcarrier provided from the OFDM demodulator  403 . The demodulator and decoder  407  converts the signals into a bit stream by demodulating and decoding the signals provided from the subcarrier demapper  405 . The message processor  409  analyzes messages within the bit stream provided from the demodulator and decoder  407 , identifies information included in the message, and provides the identified information to the controller  415 . 
         [0034]    The signal measurer  411  measures a strength of a received signal from a BS and a strength of a received signal from an RS using the signal provided from the subcarrier demapper  405 , and provides the measured strength values of the received signals to the interference determiner  413 . 
         [0035]    The interference determiner  413  calculates a received signal strength ratio of BS to RS using the strength of the received signal from the BS and the strength of the received signal from the RS provided from the signal measurer  411 . If the received signal strength ratio is equal to or more than a predetermined threshold value, the interference determiner  413  determines that interference occurs, and informs the controller  415  of interference or non-interference. 
         [0036]    The controller  415  performs a overall control for communication of an MS. For example, the controller  415  provides information representing interference or non-interference, which is identified through the received signal strength ratio, to the message generator  417 . That is, the controller  415  identifies interference or non-interference using the information provided from the interference determiner  413 , manages an available radio resource status, and controls the subcarrier demapper  405 , the demodulator and decoder  407 , the message processor  409 , the message generator  417 , the encoder and modulator  419 , and the subcarrier mapper  421 . 
         [0037]    The message generator  417  generates messages under the control of the controller  415 . Particularly, the message generator  417  generates a flag message including information for determining interference or non-interference, and outputs the flag message to the encoder and modulator  419 . The flag message is one example of a control message including information for informing interference or non-interference and is a message of one bit having ‘0’ or ‘1’. However, the flag message can be substituted with a control message of a different type according to another exemplary embodiment of the present invention. 
         [0038]    The encoder and modulator  419  converts the bit stream into complex symbols by encoding and modulating the bit stream provided from the controller  415 . The subcarrier mapper  421  maps the complex symbols, which are provided from the encoder and modulator  419 , to a subcarrier. The OFDM modulator  423  converts signals by subcarrier provided from the subcarrier mapper  421  into time-domain signals through an Inverse Fast Fourier Transform (IFFT) operation, inserts a CP, and thus constructs an OFDM symbol. The RF transmitter  425  up converts a baseband signal provided from the OFDM modulator  423  into an RF band signal and transmits the RF band signal through the antenna. 
         [0039]      FIG. 5  is a block diagram illustrating a construction of an RS in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention. 
         [0040]    As shown in  FIG. 5 , the RS includes an RF receiver  501 , an OFDM demodulator  503 , a subcarrier demapper  505 , a demodulator and decoder  507 , a message processor  509 , a resource allocator  511 , a message generator  513 , an encoder and modulator  515 , a subcarrier mapper  517 , an OFDM modulator  519 , and an RF transmitter  521 . 
         [0041]    The RF receiver  501  down converts an RF band signal received through an antenna into a baseband signal. The OFDM demodulator  503  distinguishes the signal provided from the RF receiver  501  in an OFDM symbol unit, removes a CP, and then restores signals by subcarrier through an FFT operation. The subcarrier demapper  505  extracts signals to be demodulated and decoded among the signals by subcarrier provided from the OFDM demodulator  503 . The demodulator and decoder  507  converts the signals into a bit stream by demodulating and decoding the signals provided from the subcarrier demapper  505 . 
         [0042]    The message processor  509  analyzes messages within the bit stream provided from the demodulator and decoder  507 , identifies information included in the message, and provides the identified information to the resource allocator  511 . Particularly, the message processor  509  identifies the contents of a flag message received from an MS and provides the identified contents to the resource allocator  511 . The flag message is one example of a control message including information for informing interference or non-interference and is a message of one bit having ‘0’ or ‘1’. However, the flag message can be substituted with a control message of a different type according to another exemplary embodiment of the present invention. 
         [0043]    The resource allocator  511  determines the occurrence or non-occurrence of interference using the information provided from the message processor  509 . The resource allocator  511  allocates resources for communication with an MS. If interference occurs, the resource allocator  511  reallocates resources to a vacant resource block not allocated by a BS using map information of the BS and, if interference does not occur, keeps allocating given resources. The resource allocator  511  provides a bit stream including the message to the message generator  513 . For example, if identifying that interference occurs in a 1 st  channel, the resource allocator  511  allocates a 2 nd  channel that is not allocated by a BS to avoid interference. If identifying that interference does not occur in the 1 st  channel, the resource allocator  511  allocates the 1 st  channel and performs communication. 
         [0044]    The message generator  513  generates a message including information provided from the resource allocator  511  and provides a bit stream of the generated message to the encoder and modulator  515 . The encoder and modulator  515  converts the bit stream into complex symbols by encoding and modulating the bit stream provided from the message generator  513 . The subcarrier mapper  517  maps the complex symbols, which are provided from the encoder and modulator  515 , to a subcarrier. The OFDM modulator  519  converts signals by subcarrier provided from the subcarrier mapper  517  into time-domain signals through an IFFT operation, inserts a CP, and constructs an OFDM symbol. The RF transmitter  521  up converts a baseband signal provided from the OFDM modulator  519  into an RF band signal and transmits the RF band signal through the antenna. 
         [0045]      FIG. 6  is a flow diagram illustrating an operation process of an MS in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention. 
         [0046]    As shown in  FIG. 6 , in step  601 , the MS identifies if a transmit signal of a BS and a transmit signal of an RS are received. 
         [0047]    If the transmit signal of the BS and the transmit signal of the RS are all received, in step  603 , the MS measures a strength of the received signal from the BS and a strength of the received signal from the RS. 
         [0048]    In step  605 , the MS measures a received signal strength ratio of BS to RS using the measured intensities of the received signals and identifies if the received signal strength ratio is equal to or more than a predetermined threshold value. The received signal strength ratio of BS to RS means that the strength of the received signal from the BS is divided by the strength of the received signal from the RS. 
         [0049]    If the received signal strength ratio is equal to or more than the threshold value, in step  607 , the MS recognizes that interference occurs and sets a value of a flag message to ‘1’. If the received signal strength ratio is less than the threshold value, in step  609 , the MS recognizes that interference does not occur and sets the value of the flag message to ‘0’. 
         [0050]    In step  611 , the MS transmits the generated flag message of step  607  or  609  set to ‘0’ or ‘1’ to the RS. Additionally, the flag message can be substituted with a control message of a different type according to another exemplary embodiment of the present invention. 
         [0051]    In step  613 , the MS performs communication through a channel resource allocated by an RS. The process of  FIG. 6  is repeatedly performed every transmit/receive duration. 
         [0052]      FIG. 7  is a flow diagram illustrating an operation process of an RS in a multi-hop relay wireless communication system according to an exemplary embodiment of the present invention. 
         [0053]    As shown in  FIG. 7 , in step  701 , the RS identifies if it receives a flag message representing if interference occurs. When interference occurs, the flag message is set to ‘1’ and, when interference does not occur, is set to ‘0’. 
         [0054]    If the flag message is received, the RS goes to step  703  and identifies if a value of the flag message is equal to ‘1’. If the flag message is not received, the RS returns to step  701 . If the value of the flag message is equal to ‘0’, the RS recognizes that interference does not occur and, in step  709 , performs communication. 
         [0055]    If the value of the flag message is equal to ‘1’, the RS recognizes that interference occurs and, in step  705 , identifies map information of a BS in order to reallocate channel resources to an MS transmitting the flag message. 
         [0056]    In step  707 , the RS allocates the MS channel resources not used by the BS among the map information to minimize interference having influence on the MS. For example, if it is identified that interference occurs in a 1 st  channel, the RS allocates resources to a 2 nd  channel that is not used by the BS to avoid the interference. 
         [0057]    In step  709 , the RS performs communication with the MS using the channel resources allocated to the MS. The process of  FIG. 7  is repeatedly performed every transmit/receive duration. 
         [0058]    As described above, when using FDR in a multi-hop relay wireless communication system, an exemplary embodiment of the present invention can minimize interference by allowing an MS to determine interference conditions, inform an RS of the interference conditions, and preferentially allocate resources of an RS to a vacant resource of the BS. 
         [0059]    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.