the present invention relates to supporting hybrid automatic retransmission request ( harq ) in an orthogonal frequency division multiplexing access ( ofdma ) radio access system . specifically , the present invention relates to transmitting packet data in a wireless communication system configured to support multiple input and multiple output . reference will now be made in detail to the preferred embodiments of the present invention , examples of which are illustrated in the accompanying drawings . wherever possible , the same reference numbers will be used throughout the drawings to refer to the same or like parts . the present invention discloses a method for sending an ack or nack signal per layer when a multi - antenna system is applied to an uplink or downlink data burst . in other words , ack / nack signal transport channels amounting to the number of layers allocated to the data burst are allocated to the uplink or downlink data burst having the multi - antenna system applied thereto . when a mobile subscriber station supporting a multi - antenna in a downlink burst sends data loaded in the same frame or in case that several mobile stations send data loaded in the same frame , signals of all layers are loaded in the same frame . yet , a receiving side detects the signals and identifies the signal per the layer . and , it is able to know a presence or non - presence of error of the per layer signal by performing a cyclic redundancy check ( crc ) for the signal of the identified layer . the present invention intends to enable a transmitting side to know the presence or non - presence of error of the signal per layer by transmitting an ack or nack signal . to support this , allocation of an ack or nack channel per layer is needed so that the presence or non - presence of error can be carried . via the channels , a side having transmitted a burst can receive the ack or nack signal per layer and then decide a next transmission form . for example , by re - transmitting the signal of the layer corresponding to the received nack or by stopping transmission of the signal of the layer corresponding to the received ack until other layers receive the ack signals according to an implementation method of the system , interference with other signals is reduced . by loading other data , the system is able to increase a transmission capacity . thus , to use a different transmission method per layer , control information should be given to each layer . for example , in the related art , the combined control information is given since all layers receive the ack or nack together . yet , according to the present invention , various kinds of control information is preferably given such as information indicating whether each layer receives the ack or nack , whether to give a new burst , whether to retransmit a previous burst ( al_sn ), which redundancy bit of four types ( spid ) will be given and information regarding an h - arq channel id ( scid ). fig1 is a diagram of a data frame in an ofdma radio access system in accordance with a preferred embodiment of the present invention . preferably , an ack / nack transport channel allocating method conducted by a base station transmitting data by two layers to a plurality of mobile subscriber stations applying a multi - antenna system is shown . referring to fig1 , a base station allocates a downlink ack region ( dl - ack signal region ) to a downlink ( dl ) subframe and an uplink ack signal region ( ul - ack signal region ) to an uplink ( ul ) subframe . the downlink ack signal region is a region allocated for an ack or nack signal transmitted by the base station in response to data transmitted from a plurality of mobile subscriber stations . the uplink ack signal region is a region allocated for ack or nack signals transmitted by one or more of mobile subscriber stations in response to data transmitted from the base station . in case that the base station transmits data bursts comprising two layers , the mobile subscriber stations receiving the data bursts by the two layers check for a transmission error of the data transmitted per each layer of the base station ( e . g ., crc check ). if there is no transmission error per layer according to a checked result , a corresponding mobile subscriber station transmits an ack signal . if there exists the transmission error , a corresponding mobile subscriber station transmits a nack signal . one ack / nack transport channel is allocated for the mobile subscriber stations receiving the data burst transmitted with one layer by the base station . consequently , ack / nack transport channels # 1 - 1 , # 1 - 2 , # 2 - 1 , # 2 - 2 , # 3 , # 4 . . . amounting to the same number of layers used for the base station to transmit the respective data bursts are allocated to the uplink ack signal region of the uplink subframe for the mobile subscriber stations , respectively . within the downlink ack signal region , the base station allocates the ack / nack transport channels # 2 - 1 and # 2 - 2 per layer for the mobile subscriber station transmitting data by two layers and one ack / nack transport channel # 1 , # 3 , # 4 or the like for each of the mobile subscriber stations that use one layer each . the base station checks for a transmission error for the data transmitted from the corresponding mobile subscriber station ( e . g ., crc check ). if there is no transmission error per layer according to a checked result , the base station transmits an ack signal . if a transmission error exists , the base station transmits a nack signal . the ack / nack transport channel can be sequentially allocated along a time axis within the uplink ack signal region and the downlink ack signal region , along a frequency axis , or along frequency and time axes alternately . alternatively , a half subchannel may be used per one ack or nack signal to be allocated along frequency and time axes alternately in order , as shown in fig1 . preferably , the half subchannel includes twenty - four subcarriers . fig1 is an exemplary diagram of a method for allocating the ack / nack transport channels within uplink and downlink ack signal regions in accordance with another embodiment of the present invention . preferably , an uplink or downlink ack region for a mobile subscriber station having a multi - antenna system is separately allocated within an uplink ack signal region and a downlink ack signal region . referring to fig1 , for a mobile subscriber station transmitting a data burst by two layers ( 2 - layer ) within a downlink ack region , one ack / nack transport channel # 2 - 1 for a first layer is allocated together with an ack / nack transport channel for a mobile subscriber station transmitting a data burst by one layer . the other ack / nack transport channel # 2 - 2 for a second layer is allocated by establishing a separate ack region within the downlink ack region . preferably , the same method is applied to an uplink ack region ( ul - ack region ). in fig1 , a base station transmits an harq dl burst # 2 by four layers ( 4 - layer ). the separate ack region allocated for the second or higher - order layer is preferably allocated next to the region to which the ack / nack transport channel for the first layer is allocated . fig1 is an exemplary diagram of a method for allocating the ack / nack transport channels within uplink and downlink ack signal regions in accordance with another embodiment of the present invention . in fig1 , an uplink or downlink ack region for a mobile subscriber station having a multi - antenna system is separately allocated within an uplink ack signal region and a downlink ack signal region . the method shown in fig1 differs from the method embodied in fig1 in that a plurality of ack / nack transport channels # 2 - 2 , # 2 - 3 and # 2 - 4 for the same data burst having a plurality of layers applied thereto are allocated as one ack / nack transport channel using a codeword . namely , in the example shown in fig1 , the codeword is used to reduce a range of the uplink ack region because the range of the uplink ack region can be unnecessarily extended if the number of layers is raised . table 2 and table 3 show examples of codewords to support fig1 . in transmission of an uplink ack / nack signal , as mentioned in the foregoing description , a half subchannel includes twenty - four subcarriers per one ack or nack signal . if the codeword in table 2 or table 3 is used , it is able to transmit one to three ack or nack signals using the twenty - four subcarriers . the examples in table 2 and table 3 define the codeword for four layers , which are applicable to two or three layers as well . preferably , for the data burst having three layers applied thereto , the codeword associated with the layer - 4 in table 1 and table 3 is ignored . for the data burst having two layers applied thereto , the codewords associated with the layer - 4 and the layer - 3 in table 1 and table 3 are ignored . meanwhile , in case of downlink , like the related art method , the necessity for using the codeword is lowered if an ack / nack signal is transmitted using one bit . fig1 is an exemplary diagram of a method for allocating the ack / nack transport channels within uplink and downlink ack signal regions in accordance with another embodiment of the present invention . referring to fig1 , an ack region for a mobile subscriber station using a data burst and having a multi - antenna system applied thereto is separately allocated in the same manner as fig1 or fig1 . ack / nack transport channels are allocated to the rest uplink or downlink ack region . hence , an ack signal is sent only if a crc is not erroneous for all layers . otherwise , a nack signal is sent . table 4 and table 5 show formats of mimo compact dl - map ie and mimo compact ul - map ie according to one embodiment of the present invention , respectively . since it is unable to provide control information per layer , the related art information element ( ie ) is not capable of supporting the present invention . hence , the information message ( mimo compact dl / ul map ie ) to support the harq multi - antenna should be provided with various kinds of control information to enable each layer to have a different operation . in this case , the various kinds of control information include information indicating whether a new burst will be given or a previous burst will be retransmitted according to ack or nack provided to each layer ( al_sn ), information indicating which redundancy bit of the four types will be given ( spid ), and information of h - arq channel id ( scid ). the various kinds of control information can have fields directly arranged in the information message ( mimo compact dl / ul map ie ) supporting the harq multi - antenna if necessary . alternatively , the various kinds of control information can be used in a manner of inserting the related art information element ‘ control_ie ’ in the information message ( mimo compact dl / ul map ie ) supporting the harq multi - antenna . accordingly , in the present invention , in case that the multi - antenna system transmits signals by a plurality of antennas via the same uplink or downlink data burst , the ack or nack signal is transmitted per layer . hence , the present invention can reduce the overhead generated from the retransmission regardless of the transmission error . although the present invention is described in the context of mobile communication , the present invention may also be used in any wireless communication systems using mobile devices , such as pdas and laptop computers equipped with wireless communication capabilities . the preferred embodiments may be implemented as a method , apparatus or article of manufacture using standard programming and / or engineering techniques to produce software , firmware , hardware , or any combination thereof . the term “ article of manufacture ” as used herein refers to code or logic implemented in hardware logic ( e . g ., an integrated circuit chip , field programmable gate array ( fpga ), application specific integrated circuit ( asic ), etc .) or a computer readable medium ( e . g ., magnetic storage medium ( e . g ., hard disk drives , floppy disks , tape , etc . ), optical storage ( cd - roms , optical disks , etc . ), volatile and non - volatile memory devices ( e . g ., eeproms , roms , proms , rams , drams , srams , firmware , programmable logic , etc .). code in the computer readable medium is accessed and executed by a processor . the code in which preferred embodiments are implemented may further be accessible through a transmission media or from a file server over a network . in such cases , the article of manufacture in which the code is implemented may comprise a transmission media , such as a network transmission line , wireless transmission media , signals propagating through space , radio waves , infrared signals , etc . of course , those skilled in the art will recognize that many modifications may be made to this configuration without departing from the scope of the present invention , and that the article of manufacture may comprise any information bearing medium known in the art . preferably , the present invention may be embodied in a mobile communication device comprising the processor described above along with a plurality of antennas and channel encoders , as depicted in fig1 , and the components described in fig6 . it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions . thus , it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents .