Apparatus and method for supporting synchronous hybrid automatic repeat request in broadband wireless communication system

An apparatus and a method for supporting an HARQ scheme in a wireless communication system are provided. In a method for operating a base station, whether a resource used for a system of a different standard and a resource used for one of an HARQ reply and an HARQ retransmission packet by a synchronous HARQ scheme collide with each other is estimated. A collision packet ID is allocated to an HARQ subburst corresponding to one of an HARQ reply and an HARQ retransmission packet estimated to collide, and an offset of the one of the HARQ reply and the HARQ retransmission packet is changed. A MAP message including at least one of the collision packet ID, and changed offset information is generated. The MAP message is transmitted.

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 Apr. 18, 2008 and assigned Serial No. 10-2008-0036029 and a Korean patent application filed in the Korean Intellectual Property Office on Apr. 18, 2008 and assigned Serial No. 10-2008-0036024, the entire disclosures of both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and a method for supporting a synchronous Hybrid Automatic Repeat reQuest (HARQ) technique in a broadband wireless communication system.

2. Description of the Related Art

Currently, there is active research regarding the providing of services having various Qualities of Service (QoS). More specifically, there is research for providing users with services having a transmission speed of about 100 Mbps in a 4thGeneration (4G) communication system. Particularly, active research is being conducted regarding the supporting of a high speed service in the form of guaranteeing mobility and QoS to a Broadband Wireless Access (BWA) communication system such as a wireless local area network system and a wireless metropolitan area network system. An example of a representative BWA communication system includes an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system. The IEEE 802.16 system is a communication system which applies an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme in order to support a broadband transmission network in a physical channel.

A broadband wireless communication system such as the IEEE 802.16 system uses a Hybrid Automatic Repeat reQuest (HARQ) technique properly combining a Forward Error Correction (FEC) technique and an Automatic Repeat reQuest (ARQ) technique in order to increase reliability of data transmission. The HARQ scheme attempts error correction of initially received data, and then determines whether to retransmit data using a simple error detection code such as a Cyclic Redundancy Check (CRC). Here, the HARQ scheme is classified into a synchronous HARQ scheme and an asynchronous HARQ scheme depending on the method of determining a resource used for initial transmission, a reply to whether an error occurs, and retransmission.

The asynchronous HARQ scheme does not fix resources used for initial transmission, a reply to whether an error occurs, and retransmission. That is, in the case where the asynchronous HARQ scheme is used, a base station should separately allocate a resource for initial transmission, a resource for a reply to whether an error occurs, and a resource for retransmission. In contrast, in the synchronous HARQ scheme, resources used for initial transmission, a reply to whether an error occurs, and retransmission are fixed by resources used for the initial transmission. That is, in the case where the synchronous HARQ scheme is used, a base station allocates only a resource for initial transmission, and does not additionally allocate resources for a reply to whether an error occurs, and retransmission. Therefore, in the case where the asynchronous HARQ scheme is used, a base station should inform a terminal of resource allocation information during retransmission. In contrast, in the case where the synchronous HARQ scheme is used, a base station does not need to inform a terminal of resource allocation information for retransmission and a reply to whether an error occurs.

In a system using a synchronous HARQ scheme, there may be a case of having to allocate a resource for a system of a different standard. For example, there may be a case where an advanced system accommodates a previous system in order to guarantee a backward compatibility. At this point, when a resource allocated to a system of a different standard is not fixed, an obstacle is generated in applying a synchronous HARQ scheme. In other words, when a base station selectively allocates some resources inside a frame to a system of a different standard depending on existence of a terminal of the system of the different standard, an obstacle is generated in applying the synchronous HARQ scheme. For example, in the case where, after initial transmission is performed, a resource for a system of a different standard is allocated to the same position of the next frame as the position of a resource of the initial transmission, a resource for retransmission and the resource for the system of the different standard collide with each other.

As described above, in the case where a system using a synchronous HARQ scheme supports a system of a different standard, a resource for retransmission or a reply to whether an error occurs may not be used. Therefore, there is a need to address an obstacle caused by resource collision in using the synchronous HARQ scheme.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and a method for supporting a system of a different standard and simultaneously using a synchronous HARQ scheme in a broadband wireless communication system.

Another aspect of the present invention is to provide an apparatus and a method for avoiding collision between a resource for retransmission by a synchronous HARQ scheme and a resource for a system of a different standard in a broadband wireless communication system.

Still another aspect of the present invention is to provide a scheduling apparatus and a method thereof for reducing collision of a resource for synchronous HARQ when a wireless communication system provides a communication service of a different standard.

Yet another aspect of the present invention is to provide an apparatus and a method for temporarily applying an asynchronous HARQ scheme to an HARQ channel which is expected to collide in a broadband wireless communication system.

Further another aspect of the present invention is to provide an apparatus and a method for changing a reply or retransmission offset with respect to an HARQ channel which is expected to collide in a broadband wireless communication system.

Still further another aspect of the present invention is to provide an apparatus and a method for allocating a collision packet IDentifier (ID) to an HARQ channel which is expected to collide in a broadband wireless communication system.

Yet further another aspect of the present invention is to provide an apparatus and a method for discriminating an ARQ reply by a synchronous HARQ scheme and an ARQ reply by an asynchronous HARQ scheme in a broadband wireless communication system.

According to an aspect of the present invention, a method for operating a base station in a broadband wireless communication system is provided. The method includes determining whether a resource used for a system of a different standard and a resource used for one of a Hybrid Automatic Repeat reQuest (HARQ) reply and an HARQ retransmission packet by a synchronous HARQ scheme collide with each other, allocating a collision packet IDentifier (ID) to an HARQ subburst corresponding to the one of the HARQ reply and the HARQ retransmission packet estimated to collide and changing an offset of the one of the HARQ reply and the HARQ retransmission packet, generating a MAP message including at least one of resource allocation information, the collision packet ID, and changed offset information and transmitting the MAP message.

According to another aspect of the present invention, a method for operating a terminal in a broadband wireless communication system is provided. The method includes receiving a MAP message comprising at least one of a changed offset of an HARQ reply or an HARQ retransmission and collision packet Identifier (ID) for an HARQ subburst, updating an offset of the HARQ reply or the HARQ retransmission for the HARQ subburst according to the changed offset, and receiving an HARQ reply or an HARQ retransmission packet via a resource indicated by the updated offset of the HARQ reply or the HARQ retransmission.

According to still another aspect of the present invention, a method for operating a base station in a broadband wireless communication system is provided. The method includes estimating whether a resource used for a system of a different standard and one of an HARQ reply and an HARQ retransmission packet by a synchronous HARQ scheme collide with each other and, when the collision is estimated, delaying resource allocation for the system of the different standard until an HARQ process corresponding to the one of the HARQ reply and the HARQ retransmission packet is ended.

According to yet another aspect of the present invention, a base station of a broadband wireless communication system is provided. The base station includes a scheduler for determining whether a resource used for a system of a different standard and a resource of one of an HARQ reply and an HARQ retransmission packet by a synchronous HARQ scheme collide with each other, for allocating a collision packet ID to an HARQ subburst corresponding to the one of the HARQ reply and the HARQ retransmission packet estimated to collide and for changing an offset of the one of the HARQ reply and the HARQ retransmission packet, and a generator for generating a MAP message including at least one of the collision packet ID, and changed offset information, and a transmitter for transmitting the MAP message.

According to further another aspect of the present invention, a terminal of a broadband wireless communication system is provided. The terminal includes a receiver for receiving a MAP message comprising at least one of a changed offset of an HARQ reply or an HARQ retransmission and collision packet ID for an HARQ subburst, and a controller for updating an offset of the HARQ reply or the HARQ retransmission for the HARQ subburst according to the changed offset, and for controlling to receive an HARQ reply or an HARQ retransmission packet via a resource indicated by the updated offset of the HARQ reply or the HARQ retransmission.

According to still yet another aspect of the present invention, a base station of a broadband wireless communication system is provided. The base station includes a scheduler for estimating whether a resource used for a system of a different standard, and one of an HARQ reply and an HARQ retransmission packet by a synchronous HARQ scheme collide with each other, and, when the collision is estimated, delaying resource allocation for the system of the different standard until an HARQ process corresponding to the one of the HARQ reply and the HARQ retransmission packet is ended.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention provide a technique for avoiding collision between a resource for retransmission by a synchronous HARQ scheme and a resource for a system of a different standard. Here, the system of the different standard denotes a system having a standard different from that of a system of the present invention. For example, in the case where a system according to the present invention is a system advanced from a legacy system, the legacy system may be the system of the different standard. That is, the system of the present invention and the system of the different standard may have relation of an advanced system and a legacy system. For example, the advanced system may be an IEEE 802.16m system, and the legacy system may be an IEEE 802.16e. Hereinafter, a wireless communication system using an OFDM/OFDMA scheme is illustrated by way of example. Note that exemplary embodiments of the present invention are applicable to a wireless communication system using a different scheme.

A frame structure of a system considered in an exemplary embodiment of the present invention is illustrated inFIG. 1.

Referring toFIG. 1, there exists a frame110including sections for uplink communication and downlink communication. A superframe120includes a plurality of frames110. The frame110includes a plurality of subframes130. The sections for uplink communication and downlink communication are divided by the subframe130. That is, in one frame110including K subframes130, n subframes are used for downlink communication while (K-n) subframes are used for uplink communication. Also, the subframe130includes a plurality of OFDMA symbols140. A MAP message informing of resource allocation information is transferred on a subframe basis. Also, a superframe header101is transmitted every superframe. Here, the superframe header101includes a preamble and a Broadcast CHannel (BCH).

In the case where the frame of the structure illustrated inFIG. 1is used, resources used for initial transmission, a reply to whether an error occurs, and retransmission by a synchronous HARQ scheme are illustrated inFIGS. 2A to 2C.FIG. 2Aillustrates a case where a ratio of a downlink section201to an uplink section202is 4:4.FIG. 2Billustrates a case where a ratio of a downlink section201to an uplink section202is 5:3.FIG. 2Cillustrates a case where a ratio of a downlink section201to an uplink section202is 6:2. InFIGS. 2A to 2C, subframes marked by the same number of dots denote subframes cooperating dependently as initial transmission is performed.

For example, inFIG. 2A, a reply, for example, ACK (ACKnowledge)/NACK(Non-ACK) to whether an error occurs with respect to a packet initially transmitted via a subframe1-D1is transmitted via a subframe1-U1. A retransmission packet with respect to an initially transmitted packet is transmitted via a subframe2-D1, and ACK/NACK is transmitted via a subframe2-U1. In cases ofFIGS. 2B and 2C, since a ratio of subframes used for downlink communication and subframes used for uplink communication is not symmetrical, a plurality of downlink subframes correspond to one uplink subframe, and a correspondence rule is determined according to a system design scheme.

In case of supporting a system of a different standard, a frame is used as illustrated inFIGS. 3A to 3C,4A to4D, or5A to5E.FIGS. 3A to 3Cillustrate cases where a ratio of a downlink section:an uplink section is 4:4.FIGS. 4A to 4Dillustrate cases where a ratio of a downlink section:an uplink section is 5:3.FIGS. 5A to 5Eillustrate cases where a ratio of a downlink section:an uplink section is 6:2.

InFIG. 3A, one subframe of a downlink section301is allocated for a system of a different standard, and a resource having a size corresponding to the one subframe in an uplink section302is allocated for the system of the different standard. That is, a resource for the system of the different standard is allocated in the downlink section301by a time division scheme, and the resource for the system of the different standard is allocated in the uplink section302by a frequency division scheme. As resources allocated to the system of the different standard increase, resources are divided as illustrated inFIGS. 3B and 3C. When all resources are allocated to the system of the different standards, a system according to an exemplary embodiment of the present invention operates in substantially the same way as the system of the different standard. Herein, dividing resources for each system by the frequency division scheme in the uplink section302is an exemplary embodiment. According to another exemplary embodiment, the division of resource for each system may be divided by a time division scheme in the uplink section402.

However, inFIG. 3C, three subframes allocated for the system of the different standard in the downlink section are not continuous in a time axis. This is a result of allocation with consideration of a processing delay of a terminal or a base station. That is, when an HARQ packet is received via a subframe located right before the uplink section, it is difficult to secure a processing time for error test and ACK/NACK signal generation. Therefore, downlink resources and uplink resources for the system may not be continuous in the time axis in order to secure the processing time.

InFIG. 4A, one subframe of a downlink section401is allocated for a system of a different standard, and a resource having a size corresponding to the one subframe in an uplink section402is allocated for the system of the different standard. That is, a resource for the system of the different standard is allocated in the downlink section401by a time division scheme, and the resource for the system of the different standard is allocated in the uplink section402by a frequency division scheme. As resources allocated to the system of the different standard increase, resources are divided as illustrated inFIGS. 4B,4C, and4D. When all resources are allocated to the system of the different standards, a system according to an exemplary embodiment of the present invention operates in substantially the same way as the system of the different standard. Herein, dividing resources for each system by the frequency division scheme in the uplink section402is an exemplary embodiment. According to another exemplary embodiment, the division of resource for each system may be divided by the time division scheme in the uplink section402.

However, inFIG. 4D, four subframes allocated for the system of the different standard in the downlink section are not continuous in a time axis. This is a result of allocation with consideration of a processing delay of a terminal or a base station. That is, when an HARQ packet is received via a subframe located right before the uplink section, it is difficult to secure a processing time for error test and ACK/NACK signal generation. Therefore, downlink resources and uplink resources for the system may not be continuous in the time axis in order to secure the processing time.

InFIG. 5A, one subframe of a downlink section501is allocated for a system of a different standard, and a resource having a size corresponding to the one subframe in an uplink section502is allocated for the system of the different standard. That is, a resource for the system of the different standard is allocated in the downlink section501by a time division scheme, and the resource for the system of the different standard is allocated in the uplink section502by a frequency division scheme. As resources allocated to the system of the different standard increase, resources are divided as illustrated inFIGS. 5B,5C,5D, and5E. When all resources are allocated to the system of the different standards, a system according to an exemplary embodiment of the present invention operates in substantially the same way as the system of the different standard. Herein, dividing resources for each system by the frequency division scheme in the uplink section402is an exemplary embodiment. According to another exemplary embodiment, the division of resource for each system may be divided by the time division scheme in the uplink section402.

However, inFIG. 5Dor5E, subframes allocated for the system of the different standard in the downlink section are not continuous in a time axis. This is a result of allocation with consideration of a processing delay of a terminal or a base station. That is, when a packet is received via a subframe located right before the uplink section, it is difficult to secure a processing time for error test and ACK/NACK signal generation. Therefore, downlink resources and uplink resources for the system may not be continuous in the time axis in order to secure the processing time.

A system according to an exemplary embodiment of the present invention uses the frame having the structure ofFIG. 1in a fashion illustrated inFIGS. 2A to 5Ein order to support a system of a different standard. Particularly, referring toFIGS. 2A to 2C, time points for ACK/NACK transmission and retransmission packet transmission are determined depending on an initial transmission point of a packet according to a synchronous HARQ scheme. At this point, in the case where resources are used for a system of a different standard as illustrated inFIGS. 3A to 5E, a subframe through which ACK/NACK and a retransmission packet should be transmitted according to a synchronous HARQ scheme, and a resource used for a system of a different standard may collide. Therefore, a system has a function of avoiding the collision. To avoid the collision, the system delays transmission of data estimated to collide through resource scheduling, or temporarily applies an asynchronous HARQ scheme to HARQ ACK/NACK or an HARQ retransmission packet estimated to collide.

First, an exemplary process of delaying transmission of data estimated to collide through resource scheduling is described with reference toFIGS. 6A and 6B.FIG. 6Aillustrates a case of uplink HARQ packet transmission, andFIG. 6Billustrates a case of downlink HARQ packet transmission.

Referring toFIG. 6A, in a subframe (j)-D1, a base station transmits a MAP message including resource allocation information for HARQ packet transmission through a subframe (j)-U1. At this point, it is assumed that during the j-th frame610, a terminal of a system of a different standard requests a service. The base station determines to support the system of the different standard in a (j+1)-th frame620, and thus determines to allocate a subframe (j+1)-D1of the (j+1)-th frame620for the system of the different standard. After that, the base station receives an HARQ packet from the terminal via the subframe (j)-U1. Accordingly, the base station determines to transmit a reply to the HARQ packet, that is, ACK/NACK via the subframe (j+1)-D1of the (j+1)-th frame620according to the synchronous HARQ scheme. However, the base station recognizes that the subframe (j+1)-D1is a predefined resource for use for the system of the different standard, and may not be used for transmission of ACK/NACK. In other words, the base station recognizes resource collision. Therefore, to avoid the collision, the base station delays resource allocation for the system of the different standard. That is, the base station does not perform support for the system of the different standard via the subframe (j+1)-D1, but gives priority to the transmission of ACK/NACK. At this point, when the reception of the HARQ packet is successful, ACK is transmitted via the subframe (j+1)-D1, and the base station performs support for the system of the different standard from a (j+2)-th frame. In contrast, when the reception of the HARQ packet is not successful, NACK is transmitted via the subframe (j+1)-D1, and the base station delays resource allocation for the system of the different standard until the reception of the HARQ packet is successful. In other words, the base station delays resource allocation for the system of the different standard until an HARQ process corresponding to the HARQ packet is ended. InFIG. 6A, in the uplink section, resources used for the system of the different standard in the uplink section are divided in a frequency axis. However, division in the frequency axis is exemplary, and the resources used for the system of the different standard in the uplink section may be divided in a time axis.

Referring toFIG. 6B, in a subframe (j)-D1, a base station transmits a MAP message including resource allocation information for HARQ packet transmission through a subframe (j)-D1, and an HARQ packet. At this point, it is assumed that during the j-th frame630, a terminal of a system of a different standard requests a service. The base station determines to support the system of the different standard in a (j+1)-th frame640, and determines to use a subframe (j+1)-D1of the (j+1)-th frame640for the system of the different standard. After that, the base station receives ACK/NACK from the terminal through a subframe (j)-U1. At this point, it is assumed that NACK is received. The base station determines that an HARQ retransmission packet should be transmitted via the subframe (j+1)-D1of the (j+1)-th frame640according to the synchronous HARQ scheme. However, the base station recognizes that the subframe (j+1)-D1is a predetermined resource for use for the system of the different standard, and may not be used for transmission of ACK/NACK. That is, the base station recognizes resource collision. Therefore, to avoid the collision, the base station delays resource allocation for the system of the different standard. That is, the base station does not support the system of the different standard in the subframe (j+1)-D1, but gives priority to the transmission of the HARQ retransmission packet. The base station receives ACK/NACK through a subframe (j+1)-U1. At this point, when reception of the HARQ retransmission packet is successful, that is, when ACK is received, transmission of the HARQ packet is completed, and the base station supports the system of the different standard in a (j+2)-th frame. In contrast, when the reception of the HARQ retransmission packet is not successful, that is, when NACK is received, the HARQ retransmission packet is transmitted in the (j+2)-th frame, and the base station delays resource allocation for the system of the different standard until the reception of the HARQ packet is successful. In other words, the base station delays resource allocation for the system of the different standard until an HARQ process corresponding to the HARQ reply is ended. InFIG. 6B, in the uplink section, resources used for the system of the different standard in the uplink section are divided in a frequency axis. However, division in the frequency axis is exemplary, and the resources used for the system of the different standard in the uplink section may be divided in a time axis.

Next, an exemplary process of temporarily applying an asynchronous HARQ scheme is described with reference toFIG. 7.FIG. 7Aillustrates a case of uplink HARQ packet transmission, andFIG. 7Billustrates a case of downlink HARQ packet transmission.

Referring toFIG. 7A, in a subframe (j)-D1, a base station transmits a MAP message including resource allocation information for HARQ packet transmission through a subframe (j)-U1. At this point, when allocating a resource to a (j)-th frame710, the base station recognizes that a subframe (j+1)-D1is to be used for a system of a different standard and so estimates that ACK/NACK in response to an HARQ packet may not be transmitted via the subframe (j+1)-D1, that is, a collision will occur. Therefore, the base station determines to temporarily apply an asynchronous HARQ scheme to the HARQ packet to be transmitted via the subframe (j)-U1. Accordingly, the base station allocates a collision packet ID to an HARQ channel of the HARQ packet, and changes a reply offset of the HARQ packet. That is, in the case where the synchronous HARQ scheme is applied, the reply offset is effectively set to 0, and, in the case where the asynchronous HARQ scheme is applied, the reply offset is changed to a value equal to or greater than 1. Here, a unit of the offset is a subframe.

In other words, the base station allocates the collision packet ID to the HARQ channel of the HARQ packet, and transmits a MAP message including resource allocation information for HARQ packet transmission via the subframe (j)-D1and the collision packet ID. Simultaneously, in (j)-th frame720, the base station broadcasts information informing of the supporting of the system of the different standard. Here, the information informing the system that the different standard is supported includes information informing that a service for the system of the different standard starts and information regarding an amount of resources for the system of the different standard. For example, the base station may use a ‘legacy mode transition indicator’ defined in the IEEE 802.16m standard as the information informing of the service start of the system of the different standard. Here, the legacy mode transition indicator may be a variable set to true depending on determination of a resource to be used for the system of the different standard. Therefore, during allocation of resources, the base station recognizes that some resources of the (j+1)-th frame720are used for the system of the different standard through the legacy mode transition indicator. When the base station transmits a MAP message, a terminal determines that a resource for HARQ packet transmission has been allocated via the subframe (j)-D1using the MAP message. After that, in the subframe (j)-U1, the terminal transmits an HARQ packet to the base station via the allocated resource.

In the subframe (j+1)-D1, the base station performs communication with a terminal of a system that uses a different standard. Subsequently, the base station transmits ACK/NACK to the terminal. Here, ACK/NACK is a reply to the HARQ packet transmitted via the subframe (j)-U1, and should be transmitted via the subframe (j+1)-D1according to a rule of a synchronous HARQ scheme. However, since the subframe (j+1)-D1is used for the system of the different standard, the base station transmits ACK/NACK through a subframe (j+1)-D2. At this point, ACK/NACK to an HARQ packet transmitted through a subframe (j)-U2will be transmitted via the subframe (j+1)-D2. That is, in the subframe (j+1)-D2, both ACK/NACK to the HARQ packet transmitted via the subframe (j)-U1and ACK/NACK to the HARQ packet transmitted via the subframe (j)-U2are transmitted.

Therefore, in the subframe (j+1)-D2, the base station transmits ACK/NACK to the HARQ packet received via the subframe (j)-U2according to the synchronous HARQ scheme, and transmits ACK/NACK to the HARQ packet received via the subframe (j)-U1and resource allocation information including the collision packet ID of the HARQ packet according to the temporary asynchronous HARQ scheme. Here, the resource allocation information denotes a resource for ACK/NACK to the HARQ packet received via the subframe (j)-U1. Therefore, the terminal confirms a collision packet ID using the MAP message received via the subframe (j)-D1, confirms a resource for ACK/NACK to an HARQ packet transmitted via the subframe (j)-U1using the collision packet ID, and then receives ACK/NACK. When NACK is received, the terminal transmits an HARQ retransmission packet via the subframe (j+1)-U1. At this point, the form of the HARQ retransmission packet changes depending on a retransmission scheme. The retransmission scheme may be an HARQ Chase Combining (CC) scheme or an HARQ Incremental Redundancy (IR) scheme.

InFIG. 7A, resources used for the system of the different standard in the uplink section are divided along a frequency axis. However, division in the frequency axis is exemplary, and the resources used for the system of the different standard in the uplink section may be divided along a time axis. In this case, like ACK/NACK, an HARQ retransmission packet collides. Therefore, the base station allocates a resource for transmission of an HARQ retransmission packet to a subframe (j+1)-U2, and incorporates a collision packet ID into resource allocation information.

Referring toFIG. 7B, in the subframe (j)-D1, the base station transmits a MAP message including resource allocation information for an HARQ packet and the HARQ packet via the subframe (j)-D1. At this point, when allocating resources of a (j)-th frame730, the base station recognizes that the subframe D1of the j+1)-th frame740is used for the system of the different standard, and thus estimates that the HARQ packet may not be retransmitted via the subframe (j+1)-D1when reception of the HARQ packet is not successful. Therefore, the base station determines to temporarily apply an asynchronous HARQ scheme to the HARQ packet to be transmitted via the subframe (j)-D1. Accordingly, the base station allocates a collision packet ID to an HARQ channel of the HARQ packet, and changes a retransmission offset. That is, in the case where the synchronous HARQ scheme is applied, the retransmission offset is effectively set to 0. However, in the case where the asynchronous HARQ scheme is applied, the retransmission offset is changed to a value equal to or greater than 1. Here, a unit of the offset is a subframe.

In other words, the base station allocates the collision packet ID to the HARQ channel of the HARQ packet, and then transmits a MAP message including resource allocation information for HARQ packet transmission via the subframe (j)-D1and the collision packet ID and the HARQ packet. Simultaneously, the base station broadcasts a mode transition indicator, and ratio information of a resource in a frame used for a system of a different standard through a (j)-th frame730. Accordingly, a terminal confirms that a resource of the subframe (j)-D1is allocated to receive the HARQ packet using the MAP message, and then receives the HARQ packet from the base station via the allocated resource. After that, in the subframe (j)-U1, the terminal transmits ACK/NACK with respect to the HARQ packet. At this point, it is assumed that NACK has been transmitted.

In the subframe D1of the j+1)-th frame740, the base station performs communication with a terminal of a system of a different standard. In a subframe (j+1)-D2, the base station transmits an HARQ retransmission packet to the terminal. Here, the HARQ retransmission packet is transmitted in response to NACK transmitted in the subframe (j)-U1, and should be transmitted via the subframe (j+1)-D1according to a rule of the synchronous HARQ scheme. However, since the subframe (j+1)-D1is used for the system of the different standard, the base station transmits the HARQ retransmission packet through a subframe (j+1)-D2. At this point, an HARQ retransmission packet in response to NACK transmitted through a (j)-U2will be also transmitted via the subframe (j+1)-D2. That is, in the subframe (j+1)-D2, both the HARQ retransmission packet due to NACK transmitted via the subframe (j)-U1and the HARQ retransmission packet due to NACK transmitted via the subframe (j)-U2are transmitted.

Therefore, in the subframe (j+1)-D2, the base station transmits the HARQ retransmission packet by NACK received via the subframe (j)-U2according to the synchronous HARQ scheme, and transmits the HARQ retransmission packet by NACK received via the subframe (j)-U1and resource allocation information including a collision packet ID of NACK received via the subframe (j)-U1according to the temporary asynchronous HARQ scheme. Accordingly, the terminal confirms the collision packet ID using the MAP message received via the subframe (j)-D1, confirms a resource for the HARQ retransmission packet by NACK transmitted via the subframe (j)-U1from a MAP message of the subframe (j+1)-D2using the collision packet ID, and then receives the HARQ retransmission packet. The terminal transmits ACK/NACK with respect to the retransmitted HARQ packet through a subframe (j+1)-U1.

InFIG. 7B, in the uplink section, resources used for the system of the different standard in the uplink section are divided in a frequency axis. However, division in the frequency axis is exemplary, and the resources used for the system of the different standard in the uplink section may be divided in a time axis. In this case, like an HARQ retransmission packet, ACK/NACK with respect to an HARQ retransmission packet collides. Therefore, the base station allocates a resource for transmission of ACK/NACK with respect to an HARQ retransmission packet to a subframe (j+1)-U2, and incorporates a collision packet ID into resource allocation information.

According to an exemplary embodiment of the present invention described with reference toFIG. 7, the temporary asynchronous HARQ scheme is applied. The asynchronous HARQ scheme is applied to only an HARQ process estimated to collide. After an HARQ process according to the temporary asynchronous HARQ scheme is ended, a new HARQ process conforms to the synchronous HARQ scheme again. At this point, an exemplary embodiment of the present invention includes a signaling procedure for the temporary asynchronous HARQ scheme. The signaling procedure is described below.

FIG. 8illustrates signaling for avoiding resource collision in a broadband wireless communication system according to an exemplary embodiment of the present invention.FIG. 8illustrates an example of uplink communication.

Referring toFIG. 8, a base station800allocates a resource according to the synchronous HARQ scheme in step801. That is, the base station800allocates a resource with an HARQ reply offset of an HARQ subburst set to 0. Accordingly, the base station800transmits uplink MAP IE for the synchronous HARQ scheme in step803. For example, uplink MAP IE for the synchronous HARQ scheme is illustrated in Table 1 below.

A terminal810which has received uplink MAP IE illustrated in Table 1 confirms a resource allocated for HARQ packet transmission through uplink MAP IE in step805. Herein, the MAP IE illustrated in Table 1 is unicasted to a corresponding terminal for HARQ initial packet transmission when allocating resources according to the synchronous HARQ scheme. Explaining essential parameters of the MAP IE in Table 1, ‘Extended-2 UIUC’ represents a purpose of a MAP IE. For instance, ‘Extended-2 UIUC’ indicates one of a resource allocation for Multiple Input Multiple Output (MIMO), power control, and so on. Therefore, by using ‘Extended-2 UIUC’, the base station800may indicate an uplink MAP IE for asynchronous HARQ scheme, that is, a legacy transition IE described below. ‘Reduced Connection Identifier (RCID) type’ represents whether using RCID which has a purpose to reduce a size of the MAP IE when Multicast CID (MCID) or Basic CID (BCID) is used. However, in exemplary embodiment of the present invention, since the MCID or BCID is not used, the RCID is not used. ‘Mode’ represents an HARQ retransmission scheme, that is, one of CC and IR. The terminal810which has received uplink MAP IE transmits an HARQ packet through the confirmed resource in step807.

The base station800estimates collision between a resource through which ACK/NACK to the HARQ packet should be transmitted, and a resource used in step809. Accordingly, the base station800changes parameters for the HARQ subburst of the terminal800according to the synchronous HARQ scheme at present time in step811. That is, the base station800changes the HARQ reply offset of the HARQ subburst to a non-0 value in order to avoid the collision The base station800transmits uplink MAP IE for the temporal asynchronous HARQ scheme in step813. The uplink MAP IE for the temporal asynchronous HARQ scheme may be transmitted in a collision-expected frame or a previous frame of the collision-expected frame. In case of transmitting in the previous frame, the uplink MAP IE is transmitted via a subframe in which HARQ reply is transmitted. In case of transmitting in the collision-expected frame, the uplink MAP IE is transmitted via a subframe in which HARQ reply according to the changed offset is transmitted. For example, uplink MAP IE for the temporal asynchronous HARQ scheme is illustrated in Table 2 below.

The terminal810which has received uplink MAP IE illustrated in Table 2 confirms that the asynchronous HARQ scheme is applied through uplink MAP IE. A MAP IE in Table 2 is used in order to avoid the collision by using temporal asynchronous HARQ scheme when supporting the system of the different standard. ‘CPID’ is used to distinguish collision-expected HARQ packets. Additionally, since a collision between an ACK channel and resource may be expected to occur, a change of the ACK channel is informed using ‘ACH CH Subframe Offset’. When 2 bits are allocated to the ‘ACH CH Subframe Offset’, the ACK channel could be relocated in the range of 4 subframes. ‘OFDMA symbol offset’ and ‘subchannel offset’ represent a change of resource for transmitting HARQ retransmission packet. However, depending on a resource allocation scheme, the ‘OFDMA symbol offset’ would be omitted. In addition, when resources for each system are divided by the frequency division scheme in the uplink section, ‘Subframe Offset’ would substitute the ‘OFDMA symbol offset’

The terminal810updates parameters for the HARQ subburst so that resource collision does not occur in step815. The terminal810transmits an HARQ packet through the allocated resource according to changed parameters in step817. After the parameters are changed, the terminal810applies the synchronous HARQ scheme based on the changed parameters.

The following exemplary embodiments of the present invention are described in more detail to illustrate operation procedures of a base station and a terminal which use an HARQ scheme according to the above-described scheme with reference to the accompanying drawings.

FIG. 9illustrates an operation procedure of a base station in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring toFIG. 9, in step901, the base station determines whether to perform support for a system of a different standard. For example, the base station determines whether a terminal of a different standard to which a service may be provided by the base station requests a service.

When supporting the system of the different standard, in step903, the base station determines an amount of a resource to be allocated for supporting the system of the different standard. At this point, the amount of the resource for the system of the different standard is determined on a subframe basis. However, in case of an uplink section, the base station may use a bandwidth corresponding to a subframe size as a basis.

After determining the amount of the resource to be used for supporting the system of the different standard, in step905, the base station determines whether resource collision by the synchronous HARQ scheme occurs. In other words, the base station determines whether an HARQ reply or an HARQ retransmission packet should be transmitted through a resource intended for the system of the different standard.

When the resource collision occurs, in step907, the base station performs resource scheduling with consideration of a subframe where the resource collision occurs. That is, the base station performs the resource scheduling such that data transmission of the system of the different standard through the resource intended for the system of the different standard is delayed, and priority is given to transmission of an HARQ reply or an HARQ retransmission packet according to the synchronous HARQ scheme. In other words, the base station temporarily suspends resource allocation to the rest except the HARQ reply or the HARQ retransmission packet among data to be transmitted via the subframe where the resource collision occurs.

After performing the resource scheduling, in step909, the base station transmits the HARQ reply or the HARQ retransmission packet according to a scheduling result. That is, the base station delays service providing for the system of the different standard via the subframe scheduled to be used for the system of the different standard, and transmits the HARQ retransmission packet or the HARQ reply according to the synchronous HARQ scheme.

The base station returns to step905and determines again whether resource collision by the synchronous HARQ scheme occurs. That is, when packet transmission is completed by the HARQ retransmission packet transmitted in step909, the resource collision does not occur. When the packet transmission is not completed, the resource collision occurs again. When the resource collision occurs, the base station performs step907.

In contrast, when the resource collision does not occur, in step911, the base station broadcasts information informing that the base station supports the system of the different standard. Here, the information informing that the base station supports the system of the different standard includes information informing that a service for the system of the different standard starts and information informing that an amount of a resource intended for the system of the different standard. For example, the base station may use a legacy mode transition indicator defined in an IEEE 802.16m standard as the information informing that the service for the system of the different standard starts.

After informing of the supporting of the system of the different standard, in step913the base station provides a service for the system of the different standard through some of the subframes inside a frame.

As described with reference toFIG. 9, to avoid collision between a resource for the system of the different standard and a resource for the synchronous HARQ scheme, the base station delays providing service for the system of the different standard until transmission of an HARQ retransmission packet is completed. At this point, to reduce a frequency of retransmitting a packet using a resource to be allocated for the system of the different standard, the base station performs scheduling as illustrated inFIG. 10.

FIG. 10illustrates a scheduling procedure of a base station in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring toFIG. 10, in step1001, the base station determines whether resource collision occurs in a k-th subframe. In other words, the base station determines whether packet retransmission according to the synchronous HARQ scheme should be performed through the k-th subframe and simultaneously the k-th subframe is allocated as a resource for a system of a different standard. That is, the base station determines whether collision with a resource allocated for the synchronous HARQ scheme occurs due to allocation of a resource for the system of the different standard in the k-th subframe. For example, the base station determines whether the resource of the k-th subframe is allocated for the system of the different standard by checking a resource collision indicator of the k-th subframe. Here, k is an index of a subframe and is initialized to 1 when the present procedure starts.

When the k-th subframe is allocated for the system of the different standard, in step1003, the base station performs scheduling such that only a retransmission packet according to the synchronous HARQ scheme is transmitted through the k-th subframe. That is, the base station performs scheduling such that data transmission of the system of the different standard through the resource allocated for the system of the different standard is delayed, and only the retransmission packet is transmitted. In other words, the base station temporarily suspends resource allocation for the rest except the retransmission packet among data to be transmitted through the k-th subframe.

In step1005, the base station determines whether resource allocation of all subframes has been completed. When the resource allocation of all subframes has not been completed, in step1007, the base station increases k by 1 and then returns to step1001.

In contrast, when it is determined that the k-th subframe is not allocated as a resource for the system of the different standard in step1001, the base station performs scheduling such that an HARQ retransmission packet and new packet are transmitted through the k-th subframe in step1009. In step1005, the base station determines whether resource allocation of all of the subframes has been completed. At this point, when the resource allocation of all of the subframes has been completed, the base station ends the present procedure.

FIG. 11illustrates an operation procedure of a base station in a previous frame of a collision-expected frame in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring toFIG. 11, in step1101, the base station determines whether a k-th subframe of the next frame is used for a system of a different standard. That is, the base station estimates whether a resource for the system of the different standard collides with a resource for ACK/NACK or an HARQ retransmission packet according to the synchronous HARQ scheme. At this point, the base station determines whether some of subframes of the next frame are used for the system of the different standard with reference to a mode transition indicator, and determines the position of a subframe used for the system of the different standard with reference to resource ratio information. Here, k is initialized to 1 when the present procedure starts.

When the k-th subframe of the next frame is not used for the system of the different standard, in step1103, the base station allocates a resource to HARQ packets of the k-th subframe without collision packet ID allocation and offset change. At this point, the HARQ packets of the k-th subframe include both HARQ packets transmitted through a k-th downlink subframe and HARQ packets transmitted through an uplink subframe corresponding to the k-th downlink subframe.

After allocating a resource to the HARQ packets, in step1105, the base station allocates a resource to packets except the HARQ packet of the k-th subframe.

In step1107, the base station generates a MAP message of the k-th subframe. That is, the base station generates the MAP message representing resource allocation results performed in steps1103and1105. Then, the base station performs step1115.

In step1101, when it is determined that the k-th subframe of the next frame is used for the system of the different standard, in step1109, the base station allocates a collision packet IDs to HARQ subbursts of HARQ packets of the k-th subframe, changes a retransmission offset, and allocates a resource. That is, the base station allocates the collision packet ID in order to temporarily apply the asynchronous HARQ scheme to the ACK/NACKs or the HARQ packets of the k-th subframe. That is, the base station allocates the collision packet ID to the HARQ subburst corresponding to ACK/NACK or an HARQ retransmission packet estimated to collide, and changes an offset.

In step1111, the base station allocates a resource to packets except the HARQ packets of the k-th subframe.

In step1113, the base station generates a MAP message of the k-th subframe including at least one of the collision packet ID and changed offset information. For example, the base station generates the MAP message including a MAP IE as illustrated Table 2. That is, the base station generates the MAP message representing resource allocation results performed in steps1109and1111.

After generating the MAP message, in step1115, the base station determines whether resource allocation for all subframes has been completed. When the resource allocation for all the subframes has not been completed, in step1117, the base station increases k by 1, and returns to step1101.

In contrast, when the resource allocation of all the subframes has been completed, in step1119, the base station transmits a MAP message every subframe, and performs communication according to a resource allocation result. That is, during a downlink section, the base station transmits HARQ packets, HARQ replies, HARQ retransmission packets, and non-HARQ packets, and during an uplink section, receives HARQ packets, HARQ replies, HARQ retransmission packets, and non-HARQ packets.

In operation of the base station as described with reference toFIG. 11, a MAP IE for a temporal asynchronous HARQ scheme is transmitted in a previous frame of a collision-expected frame. According to another exemplary embodiment of the present invention, the MAP IE for the temporal asynchronous HARQ scheme may be transmitted in the collision-expected frame. In this case, the base station transmits the MAP IE for the temporal asynchronous HARQ scheme via a subframe determined by the changed offset among subframes in the collision-expected frame.

FIG. 12illustrates an operation procedure of a base station in a collision-expected frame in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring toFIG. 12, in step1201, the base station determines whether a k-th subframe is a subframe used for a system of a different standard. Here, k is initialized to 1 when the present procedure starts.

When it is determined that the k-th subframe is the subframe used for the system of the different standard, in step1203, the base station allocates a resource of the k-th subframe according to the different standard. Then, the base station performs step1217.

In contrast, when it is determined that the k-th subframe is not the subframe used for the system of the different standard, in step1205, the base station allocates a resource to an HARQ reply and an HARQ retransmission packet having a non-zero offset. That is, the base station allocates the resource to the HARQ reply and the HARQ retransmission packet to which the synchronous HARQ scheme is applied.

In step1207, the base station allocates a resource to a packet except the HARQ reply and the HARQ retransmission packet. For example, the base station allocates a resource to an HARQ packet and a non-HARQ packet.

In step1209, the base station determines whether there exists an HARQ reply or an HARQ retransmission packet having a non-zero offset which indicates the k-th subframe. That is, the base station determines whether there exists the HARQ reply or the HARQ retransmission packet to which the asynchronous HARQ scheme is applied and which is to be transmitted through the k-th subframe. When there does not exist the HARQ reply or the HARQ retransmission packet having a non-zero offset which indicates the k-th subframe, the base station proceeds to step1213.

In contrast, when there exists the HARQ reply or the HARQ retransmission packet having a non-zero offset which indicates the k-th subframe, in step1211, the base station allocates a resource to the HARQ reply or the HARQ retransmission packet having a non-zero offset.

In step1213, the base station generates a MAP message for the k-th subframe. That is, the base station generates the MAP message representing resource allocation results performed in steps1205and1211.

After generating the MAP message, in step1215, the base station determines whether resource allocation of all subframes has been completed. When the resource allocation of all the subframes has not been completed, in step1217, the base station increases k by 1 and returns to step1201.

In contrast, when the resource allocation of all the subframes has been completed, in step1219, the base station transmits a MAP message every subframe, and performs communication according to the resource allocation result. That is, during a downlink section, the base station transmits HARQ packets, HARQ replies, HARQ retransmission packets, and non-HARQ packets, and during an uplink section, receives HARQ packets, HARQ replies, HARQ retransmission packets, and non-HARQ packets. At this point, in a subframe where ACK/NACK or an HARQ retransmission packet corresponding to the collision packet ID is transmitted, the base station transmits a MAP message including the collision packet ID.

FIG. 13illustrates an operation procedure of a terminal in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring toFIG. 13, in step1301, the terminal determines whether a MAP message for a temporal asynchronous HARQ scheme is received. The terminal has at least one HARQ subburst according to a synchronous HARQ scheme, and determines whether the MAP message to change ACK/NACK offset or retransmission offset of the HARQ subburst. For instance, the MAP message for the temporal asynchronous HARQ scheme includes a MAP IE as illustrated in Table 2.

When the MAP message for the temporal asynchronous HARQ scheme is received, in step1303, the terminal confirms information on changed offset included in the MAP message. Then, the terminal updates parameters for the HARQ subburst according to the information.

After updating the parameters, in step1305, the terminal receives an HARQ reply or an HARQ retransmission packet via a resource indicated by updated parameters. Herein, the synchronous HARQ scheme is applied to the HARQ subburst based on updated parameters. Therefore, after updating the parameters, the terminal applies the synchronous HARQ scheme to the HARQ subburst based on updated parameters.

Now, exemplary embodiments of the present invention are described in more detail to illustrate constructions of a base station and a terminal which use the HARQ scheme according to the above-described scheme with reference to the accompanying drawings.

FIG. 14illustrates a block diagram of a base station in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring toFIG. 14, the base station includes a scheduler1402, a message generator1404, a data buffer1406, an encoder1408, a symbol modulator1410, a subcarrier mapping unit1412, an OFDM modulator1414, a Radio Frequency (RF) transmitter1416, an RF receiver1418, an OFDM demodulator1420, a subcarrier demapping unit1422, a symbol demodulator1424, a decoder1426, an error checking unit1428, an HARQ buffer1430, and a message reader1432.

The scheduler1402allocates resources inside a frame to terminals. Also, in the case where a terminal of a system of a different standard requests a service, the scheduler1402determines a point of time to support the system of the different standard and allocates a resource to be used for the system of the different standard in a frame in which the service for the system of the different standard is performed. Accordingly, the scheduler1402sets a mode transition indicator. In allocating resources, the scheduler1402allocates a resource for the system of the different standard by a time division scheme in a downlink section, and allocates a resource for the system of the different standard by a frequency division scheme in an uplink section. In addition, the scheduler1402allocates a resource for transmitting an HARQ initial transmission packet according to a synchronous HARQ scheme. Particularly, the scheduler1402estimates collision between a resource for ACK/NACK or an HARQ retransmission packet and the resource for the system of the different standard, and performs scheduling for avoiding the collision.

According to an exemplary embodiment of the present invention, the scheduler1402performs resource scheduling such that data transmission of the system of the different standard through the resource for the system of the different standard is delayed, and priority is given to transmission of an HARQ reply or an HARQ retransmission packet according to the synchronous HARQ scheme. In other words, the scheduler1402temporarily suspends resource allocation to the rest except the HARQ reply or the HARQ retransmission packet among data to be transmitted via the subframe where the collision occurs. At this point, the delay of a service for the system of the different standard continues until reception of the HARQ packet is successful.

According to an exemplary embodiment of the present invention, the scheduler1402temporarily applies the asynchronous HARQ scheme to ACK/NACK or an HARQ retransmission packet estimated to collide. That is, the scheduler1402estimates whether a resource used for a system of a different standard, and an HARQ reply or an HARQ retransmission packet according to the synchronous HARQ scheme collide with each other, and allocates a collision packet ID to an HARQ subburst corresponding to the HARQ reply or the HARQ retransmission packet estimated to collide. Also, the scheduler1402changes an offset of ACK/NACK or an HARQ retransmission packet for the HARQ subburst. In other words, the scheduler1402applies the temporal asynchronous HARQ scheme to the HARQ subburst by performing a collision packet ID allocation and offset change which are not performed in the synchronous HARQ scheme. At this point, the scheduler1402estimates collision by checking whether some subframes of the next frame are used for the system of the different standard with reference to a mode transition indicator, and checking whether the subframe used for the system of the different standard has the same position as that of a subframe through which the HARQ reply or the HARQ retransmission packet is transmitted with reference to ratio information of the resource. In addition, during allocation of a resource of a subframe in the frame in which the service for the system of the different standard is performed, the scheduler1402allocates a resource to the one of an HARQ reply and an HARQ retransmission packet when there exists one of the HARQ reply and the HARQ retransmission packet having a non-zero offset indicating the subframe,

The data buffer1406temporarily stores data to be transmitted to a terminal and data received from the terminal, and outputs stored data to the encoder1408depending on a resource allocation result of the scheduler1402. The encoder1408channel-codes an information bit row provided from the message generator1404and the data buffer1406. The symbol modulator1410modulates the channel-coded bit row and converts the same into complex symbols. The subcarrier mapping unit1412maps the complex symbols to a frequency domain depending on a resource allocation result of the scheduler1402. The OFDM modulator1414converts the complex symbols mapped to the frequency domain into signals in a time domain by performing Inverse Fast Fourier Transform (IFFT), and forms OFDM symbols by inserting a Cyclic Prefix (CP). The RF transmitter1416up-converts a baseband signal into an RF signal, and transmits the RF signal via an antenna.

The RF receiver1418down-converts an RF signal received via the antenna into a baseband signal. The OFDM demodulator1420divides signals provided from the RF receiver1418on an OFDM symbol basis, removes a CP, and recovers complex symbols mapped to the frequency domain by performing FFT. The subcarrier demapping unit1422extracts signals mapped to a resource allocated to the terminal itself from the complex symbols mapped to the frequency domain. The symbol demodulator1424converts the complex symbols into a bit row by demodulating the complex symbols. The decoder1426channel-decodes the bit row. The error checking unit1428determines whether an error of a received packet occurs.

The HARQ buffer1430temporarily stores a received uplink HARQ packet in order to combine with an HARQ retransmission packet, and temporarily stores an HARQ packet generated for transmission of a downlink HARQ retransmission packet. That is, the HARQ buffer1430stores a downlink HARQ packet generated by the encoder1408, and provides the downlink HARQ retransmission packet to the symbol modulator1410during retransmission. Also, the HARQ buffer1430stores an uplink HARQ packet provided from the symbol demodulator1424, and deletes the stored uplink HARQ packet depending on reception success notice of the error checking unit1428. The message reader1432reads a control message received from the terminal. For example, the message reader1432confirms ACK/NACK to a downlink HARQ packet, received from the terminal, and informs the scheduler1402of whether transmission of the downlink HARQ packet is successful.

FIG. 15illustrates a block diagram of a terminal in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring toFIG. 15, the terminal includes an RF receiver1502, an OFDM demodulator1504, a subcarrier demapping unit1506, a symbol demodulator1508, a decoder1510, an error checking unit1512, a message reader1514, a data buffer1516, a message generator1518, an encoder1520, a symbol modulator1522, a subcarrier mapping unit1524, an OFDM modulator1526, an RF transmitter1528, an HARQ buffer1530, and a communication controller1532.

The RF receiver1502down-converts an RF signal received via an antenna into a baseband signal. The OFDM demodulator1504divides signals provided from the RF receiver1502on an OFDM symbol basis, removes a CP, and recovers complex symbols mapped to the frequency domain by performing FFT. The subcarrier demapping unit1506extracts signals mapped to a resource allocated to the terminal itself from the complex symbols mapped to the frequency domain. The symbol demodulator1508converts the complex symbols into a bit row by demodulating the complex symbols. The decoder1510channel-decodes the bit row. The error checking unit1512determines whether an error of a received packet occurs.

The message reader1514reads a control message received from a base station. For example, the message reader1514confirms ACK/NACK to an uplink HARQ packet, received from the base station, and informs the communication controller1532of whether transmission is successful. Also, the message reader1514confirms resource allocation information by reading a MAP message received from the base station every subframe, and provides the resource allocation information to the communication controller1532. For instance, the message reader1514confirms the resource allocation according to the synchronous HARQ scheme through a MAP ID as illustrated in Table 1. Particularly, according to an exemplary embodiment of the present invention, when a MAP message to change an ACK/NACK offset or a retransmission offset of an HARQ subburst is received, the message reader1514confirms information on changed offset included in the MAP message. The MAP message may be transmitted in a frame in which is the service of the system of the different standard is provided or a previous frame of a frame in which the service of the system of the different standard is provided. For instance, the MAP message includes a MAP IE as illustrated in Table 2.

The data buffer1516temporarily stores data to be transmitted to the base station and data received from the base station, and outputs the stored data to the encoder1520according to a control of the communication controller1532. The message generator1518generates a control message to be transmitted to the base station. For example, the message generator generates ACK/NACK to a downlink HARQ packet.

The encoder1520channel-codes an information bit row provided from the message generator1504and the data buffer1506. The symbol modulator1522converts a channel-coded bit row into complex symbols by modulating the channel-coded bit row. The subcarrier mapping unit1524maps the complex symbols into the frequency domain. The OFDM modulator1526converts the complex symbols mapped into the frequency domain into signals in the time domain by performing IFFT, and forms OFDM symbols by inserting a CP. The RF transmitter1528up-converts a baseband signal into an RF signal, and transmits the RF signal via the antenna.

The HARQ buffer1530temporarily stores a received downlink HARQ packet in order to combine with an HARQ retransmission packet, and temporarily stores an uplink HARQ packet generated for transmission of an HARQ retransmission packet. That is, the HARQ buffer1530stores an uplink HARQ packet generated by the encoder1520, and provides an HARQ retransmission packet to the symbol modulator1522during retransmission. Also, the HARQ buffer1530stores a downlink HARQ packet provided from the symbol demodulator1508, and deletes the received downlink HARQ packet depending on reception success notice of the error checking unit1512.

The communication controller1532controls an operation for communication of the terminal. That is, the communication controller1532controls an output of the data buffer1516according to resource allocation information confirmed by the message reader1514. Also, the communication controller1532controls the message generator1518to generate ACK/NACK depending on an error check result of the error checking unit1512. Particularly, according to an exemplary embodiment of the present invention, when a MAP message to change an ACK/NACK offset or a retransmission offset for an HARQ subburst is received, the communication controller1532updates the ACK/NACK offset or the retransmission offset for the HARQ subburst according to information on changed offset, and controls to receive an ACK/NACK or an HARQ retransmission packet via a resource indicated by the changed offset. At this time, the communication controller1532applies the synchronous HARQ scheme to the HARQ subburst based on the changed offset. In addition, the communication controller1532determines a subframe used for a system of a different standard through a mode transition indicator and ratio information of a resource received from a previous frame of a frame used for the system of the different standard. Accordingly, the communication controller1532controls the terminal not to perform communication through the determined subframe.

Exemplary embodiments of the present invention may support the HARQ scheme without resource collision by temporarily applying the asynchronous HARQ scheme in order to avoid the resource collision which occurs in the case where the synchronous HARQ scheme is used in a broadband wireless communication system. Therefore, since a resource inside a subframe where collision is expected to occur may be used, a resource use efficiency increases.