the following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents . it includes various specific details to assist in that understanding but these are to be regarded as merely exemplary . accordingly , those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention . in addition , descriptions of well - known functions and constructions may be omitted for clarity and conciseness . the terms and words used in the following description and claims are not limited to the bibliographical meanings , but , are merely used by the inventor to enable a clear and consistent understanding of the invention . accordingly , it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents . it is to be understood that the singular forms “ a ,” “ an ,” and “ the ” include plural referents unless the context clearly dictates otherwise . thus , for example , reference to “ a component surface ” includes reference to one or more of such surfaces . exemplary embodiments of the present invention focus on a scenario that a demodulation reference signal ( dmrs ) is used for enhanced control channel ( e - cch ) transmission . e - cch is transmitted on n number of e - cchs . namely , an enhanced control channel element ( e - cce ) is a transmission unit of e - cch . here , n may have one value of 1 , 2 , 4 and 8 according to exemplary embodiments of the present invention . a 4 e - cce per resource block ( rb ) structure was illustrated in fig2 , where an rb consists of 4 logical e - cces . the e - cce is the basic unit for e - cch transmission . an e - cch can use 1 / 2 / 4 / 8 e - cces for transmission . when aggregating e - cces in localized mode , the system aggregates those consecutive e - cces in the configured rb resources , so that the resulting e - cch also consists of consecutive resources . when there are four e - cces in an rb , the e - cch with 1 , 2 , 4 , 8 aggregation levels will occupy 1 / 4 , 1 / 2 , 1 , 2 rbs respectively . fig3 is an illustration of the possible multiplexing of multiple e - cchs in an rb according to an exemplary embodiment of the present invention . referring to fig3 , it is noted that an e - cch with aggregation level one can start from any e - cce index i , an e - cch with aggregation level two can only start from any e - cce index i with imod2 = 0 , an e - cch with aggregation level four can only start from any e - cce index i with imod4 = 0 , and an e - cch with aggregation level eight can only start from any e - cce index i with imod8 = 0 . for simplicity , it is assumed that the e - cch transmission is restricted with rank 1 , and one dmrs port is necessary for each of the e - cchs . in alternative exemplary implementations , it is also possible to higher rank transmission , e . g ., rank 2 , wherein two dmrs ports are necessary for each of the e - cchs . when an rb is multiplexed with four e - cchs with aggregation level one , four dmrs ports are needed for each of the e - cch . when an rb is multiplexed with three e - cchs with aggregation levels one and two , three dmrs ports are needed for each of the e - cch . when an rb is multiplexed with two e - cchs with aggregation level two , two dmrs ports are needed for each of the e - cch . when an rb is multiplexed with one e - cch with aggregation level four or eight , one dmrs port is needed for the e - cch . it is further assumed that a user equipment ( ue ) will receive indication as to which dmrs port is allocated for a certain e - cch or search space . this indication could be explicitly configured by higher layer configuration , or implicitly indicated with other conditions , e . g , the dmrs port is related to the e - cce index , or the starting e - cce index of an e - cch . because the detailed indication method is beyond the scope of the present invention , it will not be treated further . fig4 is an illustration of dmrs configuration and e - cce mapping of method 0 according to an exemplary embodiment of the present invention . referring to fig4 , in method 0 , the system always configures 4 dmrs ports for any aggregation level of e - cch . although for aggregations four and eight , only one dmrs port is necessary , and the resource elements ( res ) for dmrs ports 9 ˜ 10 are still configured . when allocating e - cch payload to the res , those dmrs res for ports 9 ˜ 10 are left unused , or these res are used for other purposes . at the ue side , the ue will always assume all the rbs carrying e - cchs are configured with 4 dmrs ports , regardless of their actual aggregation levels . no e - cch symbols are mapped onto those dmrs res , regardless if they are used for dmrs , blank , or used for other purposes . a benefit of method 0 is that it is simple for ue operation . however , it may have unused / wasted res when two or less dmrs is needed . in an exemplary embodiment , the system will configure 4 dmrs port resources for those rbs with at least one e - cch of aggregation level one or two , and configure 2 dmrs port resources for those rbs with aggregation level four or eight . note that for the case when two e - cchs with aggregation level two are multiplexed in one rb , only two dmrs ports are needed . however , when a ue detects an e - cch with aggregation level two , it will have no knowledge if the remaining two e - cces in the same rb will be allocated as one e - cch of aggregation level two , or two e - cchs of aggregation level one . thus , for the case of e - cch of aggregation level two , 4 dmrs port res are assumed . at the ue side , the ue will first generate search spaces for each aggregation level . a search space is defined as a set of resources where an e - cch for the particular ue can be transmitted . the amount of search space is limited for simplicity . the ue will try to decode each search space of every aggregation level . if the cyclic redundancy check ( crc ) of the decoded sequence passed , the ue will assume the decoding of the e - cch is successful . based on the above - discussed description , an exemplary embodiment of the present invention will be now described . first , the following description assumes that in any rb , four kinds of signals , e - cch ( or the physical downlink scheduling channel ( pdsch ), the same will apply hereinafter ) of one ue , dmrs of one ue , e - cch of another ue , and dmrs of another ue , are transmitted . fig5 is an illustration of dmrs configuration and e - cce mapping of method 1 according to an exemplary embodiment of the present invention . referring to fig5 , resource or resources for one or more ues may be allocated to one resource block , and resource allocating information is transmitted to the ue from the enb through the e - cch . in this case , if the e - cch with at least one of aggregation levels 1 and 2 is transmitted , the first ue , as illustrated in fig3 , recognizes that resource allocating information about another ue is contained in a corresponding resource block that transmits the e - cch . thus , if the dmrs for the first ue is transmitted through the dmrs ports 7 ˜ 8 as illustrated in fig5 , the first ue assumes that the dmrs of the other ue is transmitted through the dmrs ports 9 ˜ 10 illustrated in fig5 . this is because , as described above , if the aggregation level of the e - cch is at least one of the aggregation levels 1 and 2 , a resource of any ue other than the first ue may be allocated , and accordingly , the dmrs for the first ue and the other ue should be transmitted in a corresponding resource block . as a consequence , the first ue assumes that if the aggregation level is at least one of aggregation levels 1 and 2 , e - cch is not transmitted at the region corresponding to dmrs ports 9 ˜ 10 . namely , the first ue assumes that the e - cch is transmitted on the rest of resources except resources corresponding to the dmrs ports 7 ˜ 10 . meanwhile , in the case of transmitting the e - cch with the aggregation level 4 or 8 , the first ue recognizes that , as illustrated in fig3 , the resource allocation information and data of the first ue itself , not of the other ue , are transmitted on the corresponding resource block . thus , if the dmrs of the first ue is transmitted on the dmrs ports 7 ˜ 8 as illustrated in fig5 , the first ue assumes that the e - cch of the first ue , not the dmrs of the other ue , is transmitted on the region corresponding to the dmrs ports 9 ˜ 10 . this is because , as described above , in case where the aggregation level of e - cch is either 4 or 8 , only a resource of the first ue can be allocated in the corresponding resource block . consequentially , the first ue assumes that if the aggregation level is either 4 or 8 , the e - cch is transmitted on the region corresponding to the dmrs ports 9 ˜ 10 . namely , the first ue assumes that the e - cch is transmitted on the rest of resources except the region corresponding to the dmrs ports 7 ˜ 8 . as discussed above , according to an exemplary embodiment of the present invention , the ue determines the size of resources depending on the aggregation level of the e - cch , and performs the decoding process using the determined size of resources . fig8 a and 8b are illustrations of an enb &# 39 ; s and a ue &# 39 ; s corresponding procedures of method 2 according to exemplary embodiments of the present invention . referring to fig8 a , an enb first configures the ue for its e - cch configuration ( configuration related to e - cch region ) in step s 810 . in an exemplary implementation , the configuration can be part of higher layer radio resource control ( rrc ) signaling . in step s 820 , the enb schedules the ue for each subframe . in an exemplary implementation , if a ue is scheduled , the enb continues to schedule its e - cch resources if configured . the e - cch scheduling includes e - cch aggregation level , and e - cces to carry the e - cch . in step s 830 , if a ue &# 39 ; s e - cch has been configured as localized mode based on dmrs , the enb will configure the dmrs port according to the aggregation level of the e - cch . if the e - cch is of aggregation level one or two , the enb will configure four dmrs port resources ( i . e ., port 7 ˜ 10 ) in the rb which carries the e - cch . if the e - cch is of aggregation level four or eight , the enb will configure two dmrs port resources ( i . e ., port 7 ˜ 8 ) in the rb ( s ) which carries the e - cch . in step s 840 , the enb continues to map e - cch payload symbols to allocated e - cces . rate matching is performed around the configured dmrs res , i . e ., the enb will allocate e - cch symbol to next available re by skipping the dmrs res . in step s 850 , the enb transmits the scheduled e - cch in the subframe . a corresponding exemplary procedure at the ue is illustrated in fig8 b . in step s 860 , the ue first receives the configuration of its e - cch from the enb . in step s 870 , when the ue is configured with localized mode e - cch based on dmrs , for each subframe received , the ue first generates the search spaces for each aggregation level . in step s 880 , the ue starts blind decoding for each search space . when the search space is of aggregation level one or two , the ue will assume 4 dmrs port resources are configured and no e - cch is mapped onto those dmrs res . when the search space is of aggregation level four or eight , the ue will assume 2 dmrs port resources are configured and no e - cch is mapped onto those dmrs res . the ue decides if an e - cch is successfully received or not after blindly decoding all the search spaces . if an e - cch is received , the ue will perform corresponding procedures . fig6 is an illustration of dmrs configuration and e - cce mapping of method 2 according to an exemplary embodiment of the present invention . in another exemplary embodiment , the system will configure only the necessary number of dmrs resources for e - cch . for the example in fig3 , 4 dmrs port resources are configured for case ( a ) and ( b ), and 2 dmrs port resources are configured for case ( c ) and ( d ). in cases when 4 dmrs port resources are configured , for the e - cchs port 7 or 8 are assigned for demodulation , the enb will assume rate matching only for two dmrs ports ( ports 7 ˜ 8 ), and perform symbol puncturing for dmrs res for another two ports ( ports 9 ˜ 10 ), as shown in fig6 for the e - cchs port 9 or 10 are assigned for demodulation , rate matching is performed for dmrs res for ports 9 ˜ 10 . in cases when 2 dmrs port resources are configured , the enb behaves the same as what is described in method 1 , and performs rate matching for the dmrs res . here , puncturing the e - cch symbol means an e - cch symbol is assign to the dmrs port 9 ˜ 10 res , but replaced by the dmrs symbol for actual transmission . at the ue side , the ue will assume only 2 dmrs port resources are configured for e - cch search spaces assigned with ports 7 ˜ 8 regardless of their aggregation level and assume 4 dmrs port resources are configured for e - cch search spaces assigned with ports 9 ˜ 10 . when an e - cch symbol is actually punctured by a dmrs re , the ue is unaware of the puncturing and will take the dmrs re as a received e - cch symbol for decoding . fig9 a and 9b are illustrations of an enb &# 39 ; s and a ue &# 39 ; s corresponding procedures according to method 2 according to an exemplary embodiment of the present invention . referring to fig9 a , an enb first configures the ue for its e - cch configuration in step 910 . in an exemplary implementation , the configuration can be part of higher layer rrc signaling . in step 920 , the enb schedules the ue for each subframe . if a ue is scheduled , the enb continues to schedule its e - cch resources if configured . the e - cch scheduling includes e - cch aggregation level , and e - cces to carry the e - cch . in step 930 , if the ue &# 39 ; s e - cch has been configured as a localized mode based on dmrs , the enb will configure a dmrs port of each e - cch rb according to the number of e - cchs multiplexed in the rb . if more than two e - cchs are multiplexed , the enb will configure four dmrs port resources ( i . e ., ports 7 ˜ 10 ) in the rb which carries the e - cch . otherwise , the enb will configure two dmrs port resources ( i . e ., ports 7 ˜ 8 ) in the rb ( s ) which carries the e - cch . in step 940 , the enb continues to map e - cch payload symbols to allocated e - cces . for an e - cch assigned with port 7 or 8 , rate matching is performed around the configured dmrs res for ports 7 ˜ 8 . if ports 9 ˜ 10 are also configured , the enb will puncture corresponding e - cch symbols which are mapped to the dmrs ports 9 ˜ 10 res . for an e - cch assigned with port 9 or 10 , rate matching is performed around the configured dmrs res for ports 7 ˜ 10 . in step 950 , the enb transmits the scheduled e - cch in the subframe . a corresponding exemplary procedure at the ue is illustrated in fig9 b . in step 960 , the ue first receives the configuration of its e - cch from the enb . in step 970 , when the ue is configured with localized mode e - cch based on dmrs , for each subframe received , the ue first generates the search spaces for each aggregation level . in step 980 , the ue starts blind decoding for each search space . if the search space is assigned with port 7 or 8 for demodulation , the ue will assume 2 dmrs port resources are configured and no e - cch is mapped onto dmrs ports 7 - 8 res . the ue will also assume e - cch symbols are transmitted on dmrs ports 9 ˜ 10 res . if the search space is assigned with port 9 or 10 for demodulation , the ue will assume 4 dmrs port resources are configured and no e - cch is mapped onto dmrs ports 7 - 10 res . the ue will also assume no e - cch symbols are transmitted on dmrs port 9 ˜ 10 res . the ue decides if an e - cch is successfully received or not after blindly decoding all the search spaces . if an e - cch is received , the ue will perform corresponding procedures . exemplary method 3 : dmrs port spreading factor depending on aggregation levels fig7 is an illustration of dmrs configuration and e - cce mapping of method 3 according to an exemplary embodiment of the present invention . referring to fig7 , the system will configure 2 dmrs port ( ports 7 ˜ 8 ) resources for those rbs with e - cch of aggregation level four or eight , and configure additional dmrs port ( ports 11 ˜ 12 ) resources for those rbs with at least one e - cch of aggregation level one or two . note that dmrs ports 11 - 12 use the same dmrs res as ports 7 ˜ 8 . when four ports 7 , 8 , 11 and 12 are configured , the spreading factor of four should be assumed for dmrs based channel estimation . for the enb , it will always configure dmrs port resources for ports 7 ˜ 8 . when more than two dmrs ports are necessary , the enb will transmit additional dmrs using ports 11 and 12 . rate matching is performed around the configured dmrs res for e - cch payload mapping . at the ue side , the ue will first generate search spaces for each aggregation level . when the aggregation level of a search space is one or two , the ue will assume dmrs with a spreading factor of four for channel estimation of the rb where the search space is located . when the aggregation level of a search space is four or eight , the ue will assume dmrs with a spreading factor of two for channel estimation of the rb where the search space is located . fig1 a and 10b are illustrations of an enb &# 39 ; s and a ue &# 39 ; s corresponding procedures of method 3 according to an exemplary embodiment of the present invention . referring to fig1 a , an enb first configures the ue for its e - cch configuration in step 1010 . in an exemplary implementation , the configuration can be part of higher layer rrc signaling . in step 1020 , the enb schedules the ue for each subframe . if a ue is scheduled , the enb continues to schedule its e - cch resources if configured . the e - cch scheduling includes e - cch aggregation level , and e - cces to carry the e - cch . in step 1030 , if a ue &# 39 ; s e - cch has been configured as a localized mode based on dmrs , the enb will configure a dmrs port according to the aggregation level of the e - cch . if more than two e - cchs are multiplexed , the enb will configure four dmrs port resources ( i . e ., port 7 , 8 , 11 , 12 ) in the rb which carries the e - cch when necessary . otherwise , the enb will configure two dmrs port resources ( i . e ., port 7 ˜ 8 ) in the rb ( s ) which carries the e - cch . in step 1040 , the enb continues to map e - cch payload symbols to allocated e - cces . rate matching is performed around the configured dmrs res , i . e ., the enb will allocate e - cch symbol to next available re by skipping the dmrs res . in step 1050 , the enb transmits the scheduled e - cch in the subframe . a corresponding exemplary procedure at the ue is illustrated in fig1 b . in step 1060 , the ue first receives the configuration of its e - cch from enb . in step 1070 , when the ue is configured with localized mode e - cch based on dmrs , for each subframe received , the ue first generates the search spaces for each aggregation level . in step 1080 , the ue starts blind decoding for each search space . when the search space is of aggregation level one or two , the ue will assume dmrs port 7 , 8 , 11 , 12 resources are configured with spreading factor four . when the search space is of aggregation level four or eight , the ue will assume dmrs port 7 , 8 resources are configured with spreading factor two . the ue will use a corresponding spreading factor for dmrs channel estimation . the ue assumes rate matching for e - cch for the dmrs res , and no e - cch is mapped onto those dmrs res . the ue decides if an e - cch is successfully received or not after blindly decoding all the search spaces . if an e - cch is received , the ue will perform corresponding procedures . fig1 is a block diagram illustrating an inner structure of a ue in accordance with an exemplary embodiment of the present invention . referring to fig1 , the ue may include a communication unit 1110 ( e . g ., a transceiver ), a storage unit 1120 , and a control unit 1130 . the communication unit 1110 may transmit or receive a signal to or from the enb . the signal transmitted or received to or from the enb may include a data channel , a control channel , and the like . the storage unit 1120 may store programs required for operation of the ue . particularly , the storage unit 1120 may store programs that perform a series of processes for determining the size of resources allocated to the control channel depending on an aggregation level of the control channel . the control unit 1130 controls signal flows between internal blocks of the ue to perform operations of the ue . more particularly , the control unit 1130 controls to receive configuration information related to the control channel from the enb , and to identify an aggregation level of the control channel . the control unit 1130 controls to determine the size of a resource that is allocated to the control channel depending on the identified aggregation level and to decode subframes received from the base station depending on results of the determination . more particularly , if the identified aggregation level is at least one of 1 and 2 , the control unit 1130 determines that resources of the control channel are the rest of resources except resources for dmrs related to all ues capable of being scheduled among resource blocks . additionally , if the aggregation level is either 4 or 8 , the control unit 1130 determines that resources of the control channel are the rest of resources except resources for dmrs related to the ue . here , the control channel may be enhanced — physical downlink control channel ( e - pdcch ). fig1 is a block diagram illustrating an inner structure of an enb in accordance with an embodiment of the present invention . referring to fig1 , the enb may include a communication unit 1210 ( e . g ., a transceiver ), a storage unit 1220 , and a control unit 1230 . the communication unit 1210 may transmit or receive a signal to or from the ue . the signal transmitted or received to or from the ue may include a data channel or a control channel . the storage unit 1220 may store programs required for operation of the enb . more particularly , the storage unit 1220 may store programs that perform a series of processes for determining resources for dmrs depending on an aggregation level of control channels that will be transmitted to the ue . the control unit 1230 controls signal flows between internal blocks of the enb to perform operations of the enb . more particularly , the control unit 1230 controls to transmit configuration information of the control channel for the ue to the ue , and to generate a control channel that includes control information related to the ue scheduled in any subframe . and the control unit 1230 controls to identify the aggregation level of the generated control channel , to determine resources for a dmrs depending on the identified aggregation level , and to transmit the control channel through the determined resources to the ue . more particularly , if the identified aggregation level is at least one of 1 and 2 , the control unit 1230 determines that resources of the control channel are the rest of resources except resources for dmrs related to all ues capable of being scheduled among resource blocks . if the aggregation level is either 4 or 8 , the control unit 1230 determines that resources of the control channel are the rest of resources except resources for dmrs related to the ue . according to the above - discussed exemplary embodiments of the present invention , the enb can implicitly indicate the dmrs configuration to the ue , and the ue can determine a size and a region of the control channel allocated to itself without separate signaling . accordingly , it is possible for the wireless communication system to use limited resources efficiently and reduce the load . while this invention has been particularly shown and described with reference to an exemplary embodiment thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents .