WO2008123681A1

WO2008123681A1 - Method for constructing map in wireless communication system based on ofdma, and apparatus for transmitting frame using the same

Info

Publication number: WO2008123681A1
Application number: PCT/KR2008/001868
Authority: WO
Inventors: Kuk-Jin Song; Jae-Hyun Ahn
Original assignee: Posdata Co., Ltd.
Priority date: 2007-04-05
Filing date: 2008-04-03
Publication date: 2008-10-16
Also published as: KR100877746B1; KR20080090709A

Abstract

A method for constructing a MAP in Orthogonal Frequency Division Multiple Access (OFDMA)-based wireless communication system is provided. The method includes generating a first sub-MAP group by grouping at least one Connection IDentifier (CID) whose Modulation and Coding Scheme (MCS) level is greater than or equal to a reference MCS level, among received CIDs; generating a second sub-MAP group by grouping at least one CID whose CID reducing gain is greater than or equal to a threshold; generating a normal MAP for at least one CID not included in the first and second sub-MAP groups; and generating a sub-MAP for the first and second sub-MAP groups using a pointer Information Element (IE).

Description

Method for constructing MAP in wireless communication system based on OFDMA, and apparatus for transmitting frame using the same Technical Field

[1] The present invention relates generally to MAP construction in wireless communication system, and in particular, to a method for constructing a MAP in wireless communication system based on Orthogonal Frequency Division Multiple Access (OFDMA), and an apparatus for transmitting a frame using the same. Background Art

[2] One of the important merits of an IEEE (Institute of Electrical and Electronics

Engineers) 802.16d/e system consists in the OFDMA-based physical layer structure. In OFDMA, resources are allocated to users on a two-dimensional frequency-time domain. Such resource allocation can provide users with both frequency and time diversity gains, and each user can obtain a different Modulation and Coding Scheme (MCS).

[3] In order to deliver such information to users, the OFDMA system needs a location indicator. In the IEEE 802.16d/e system, such information is included in a MAP message and then broadcasted to users.

[4] FIG. 1 illustrates a frame structure in general OFDMA-based wireless communication system.

[5] As illustrated in FIG. 1, in the OFDMA standard, a data transmission unit in the conceptual frequency and time domains is represented by subchannels and symbols, respectively, and the minimum data unit which can be transmitted to one user (i.e., Mobile Station (MS)) is composed of one subchannel and one symbol.

[6] The y-axis represents indexes of subchannels which are allocation units of the frequency resources, and one frame includes (L+ 1) subchannels of s"¹ through (s+L)"¹ subchannels.

[7] The x-axis represents indexes of Orthogonal Frequency Division Multiplexing

(OFDM) symbols which are allocation units of the time resources, and one frame includes (M+ 1) Down-Link (DL) OFDM symbols of k"¹ through (k+M)"¹ symbols, and N Up-Link (UL) OFDM symbols of (k+M+l)^th through (k+M+N)"¹ symbols. In addition, the frame has a Transmit/receive Transition Gap (TTG), which is a guard region, intervening between the DL and the UL, and also has a Receive/transmit Transition Gap (RTG) intervening between the UL of the current frame and the DL of the next frame. [8] Such an OFDMA frame includes preamble, Frame Control Header (FCH), DL-MAP,

UL-MAP and DL bursts in the DL interval, and includes ranging subchannel and UL bursts in the UL interval.

[9] The preamble is used for providing time/frequency synchronization and cell information to users, FCH includes information used for decoding DL-MAP, and the DL-MAP includes information indicating to which user the DL bursts transmitted by a base station belong, and also indicating in which region the DL bursts are located in the frame. The UL-MAP includes information on UL bursts transmitted by users (MSs).

[10] The MAP messages may reduce the system throughput since they are overhead rather than data, and a size of the MAP messages increases with the number of the bursts.

[11] In order to solve the problems stated above, if Quadrature Amplitude Modulation

(QAM) 1/2 is used as an MCS of the MAP message based on the characteristic that a normal MAP message has a fixed MCS (in the worst case, Quadrature Phase Shift Keying (QPSK) 1/2, repetition 6), a size of the MAP message can be reduced to a half of the MAP message modulated by an MCS (QPSK 1/2, repetition 1). However, as to the MAP message modulated by simply applying only the high-efficiency MCS in this way, a receiver cannot correctly receive the corresponding MAP message when it has a poor channel environment.

[12] To compensate for the decrease in the system throughput due to the MAP message, the IEEE 802.16e standard has suggested a Sub-DL/UL-MAP message (hereinafter referred to as 'sub-MAP message'). This standard allows a transmitter to perform modulation with various MCS levels by means of the sub-MAP message. That is, a sub-MAP has various MCS levels with use of a pointer Information Element (IE). However, since this pointer IE is also overhead, when a gain obtained by means of the various MCS levels is significantly low, its MAP size may be much greater than the size of the normal MAP.

[13] In addition, although it has been stated that the foregoing sub-MAP could reduce the

MAP size by means of Reduced Connection IDentifier (RCID), nothing has been proposed regarding the time, the way and the criterion of its implementation. Disclosure of Invention Technical Problem

[14] An aspect of the present invention is to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method for constructing a sub-MAP in Orthogonal Frequency Division Multiple Access (OFDMA)-based wireless communication system, and an apparatus for transmitting a frame using the same. [15] Another aspect of the present invention is to provide a method for adaptively constructing a MAP in OFDMA-based wireless communication system, and an apparatus for transmitting a frame using the same.

[16] Further another aspect of the present invention is to provide a MAP construction method for defining a reference MCS level for use of a sub-MAP so as to adaptively use a normal MAP and a sub-MAP in OFDMA-based wireless communication system, and an apparatus for transmitting a frame using the same.

[17] Yet another aspect of the present invention is to provide a MAP construction method for providing an appropriate threshold for a CID reducing gain and a threshold for the total overhead rate so as to adaptively use a normal MAP and a sub-MAP in OFDMA- based wireless communication system, and an apparatus for transmitting a frame using the same. Technical Solution

[18] According to one aspect of the present invention, there is provided a method for constructing a MAP in Orthogonal Frequency Division Multiple Access (OFDMA)-based wireless communication system. The method includes generating a first sub-MAP group by grouping at least one Connection IDentifier (CID) whose Modulation and Coding Scheme (MCS) level is greater than or equal to a reference MCS level, among received CIDs; generating a second sub-MAP group by grouping at least one CID whose CID reducing gain is greater than or equal to a threshold; generating a normal MAP for at least one CID not included in the first and second sub-MAP groups; and generating a sub-MAP for the first and second sub-MAP groups using a pointer Information Element (IE).

[19] According to another aspect of the present invention, there is provided a method for constructing a MAP in Orthogonal Frequency Division Multiple Access (OFDMA)-based wireless communication system. The method includes generating a sub-MAP group for at least one received Connection IDentifier (CID) using at least one of Modulation and Coding Scheme (MCS) level information and CID reducing gain information; and generating a sub-MAP for the sub-MAP group using a pointer Information Element (IE), and generating a normal MAP for at least one CID not included in the sub-MAP group.

[20] According to further another aspect of the present invention, there is provided an apparatus for transmitting a frame in Orthogonal Frequency Division Multiple Access (OFDMA)-based wireless communication system. The apparatus includes a first sub- MAP group establisher for grouping, into a first sub-MAP group, at least one Connection Identifier (CID) whose Modulation and Coding Scheme (MCS) level of a received CID is greater than or equal to a reference MCS level; a reducing gain processor for calculating at least one CID reducing gain for each Reduced CID (RCID) type and selecting an RCID type having the highest CID reducing gain; a second sub- MAP group establisher for grouping CIDs corresponding to the selected RCID type into a second sub-MAP group; and a sub-MAP determiner for determining to generate a sub-MAP when there is at least one of the first sub-MAP group and the second sub- MAP group.

Advantageous Effects

[21] As is apparent from the foregoing description, the present invention generates a normal MAP and/or a sub-MAP and applies the generated MAP message to the frame transmission apparatus, making it possible to realize the sub-MAP specified by the IEEE 802.16e standard in detail and adaptively apply the sub-MAP and the existing normal MAP message, thereby contributing to a reduction in the MAP size of the transmission frame.

[22] The present invention suggests the detailed application time and method of the sub-

MAP message specified by the IEEE 802.16e standard, thereby contributing to activation of the standard.

[23] Further, the present invention generates a sub-MAP and/or a normal MAP through appropriate selection of a Modulation and Coding Scheme (MCS) level and/or a Reduced Connection IDentifier (RCID), thereby contributing to an efficient reduction in the total size of the MAP message.

[24] Moreover, the present invention suggests a detailed threshold necessary for selection of the MCS level and the RCID gain, ensuring efficient use of the MAP message.

[25] While the invention has been shown and described with reference to a certain preferred 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. Brief Description of the Drawings

[26] The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

[27] FIG. 1 is a diagram illustrating a frame structure in general OFDMA-based wireless communication system;

[28] FIG. 2 is a diagram illustrating a normal MAP message according to the present invention;

[29] FIG. 3 is a diagram illustrating a sub-MAP message according to the present invention;

[30] FIG. 4 is a diagram illustrating a structure of OFDMA-based frame transmission apparatus according to the present invention; [31] FIG. 5 is a diagram illustrating a structure of the sub-MAP processor shown in FIG.

4;

[32] FIG. 6 is a diagram illustrating a structure of the MAP generator shown in FIG. 4;

[33] FIG. 7 is a flowchart illustrating a procedure for generating a sub-MAP according to the present invention; and

[34] FIGs. 8 to 11 are diagrams illustrating sequential generation of a sub-MAP according to the present invention. Mode for the Invention

[35] Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness.

[36] FIG. 2 is a diagram illustrating a normal MAP message according to an embodiment of the present invention.

[37] As illustrated in FIG. 2, in a frame, a normal MAP message includes a DL-MAP and a UL-MAP, and the DL-MAP and the UL-MAP include user information of each of DL bursts transmitted by a base station, and a MAP Information Element (MAP IE) indicating location information (DL-MAP IE) of the corresponding burst and UL burst information (UL-MAP IE) transmitted by users (i.e., Mobile Stations (MSs)). Therefore, each user (MS) can selectively receive corresponding data using the user information and burst location information included in the MAP IE.

[38] The normal MAP message generated in this scheme is modulated in a physical layer and then transmitted to users on a broadcast basis, and numerals written in the normal MAP of FIG. 2 represent the number of repetitions.

[39] FIG. 3 is a diagram illustrating a sub-MAP message according to the present invention.

[40] As illustrated in FIG. 3, in a compressed MAP, a sub-MAP is generated using a pointer IE, and the sub-MAP allocates burst location information using a MAP IE. Therefore, a receiver finds a corresponding sub-MAP using the pointer IE, and receives its own data using the MAP IE of the corresponding sub-MAP.

[41] In this case, if the channel state is good (High Signal-to-interference and Noise Ratio

(SINR)), the sub-MAP can apply a Modulation and Coding Scheme (MCS) level higher than the MCS level (e.g., Quadrature Phase Shift Keying (QPSK) 1/2, repetition 6) which is applied in the worst channel environment. In order to obtain such a modulation gain, the sub-MAP uses a pointer IE, and the pointer IE provides different sub-MAPs so that the sub-MAPs may have different MCS levels.

[42] The sub-MAP pointer IE corresponds to the overhead which additionally occurs due to the application of the sub-MAP. Therefore, if a gain by the higher MCS is insufficient, the MAP size may be much greater than the size of the normal MAP.

[43] Also, the sub-MAP can reduce the MAP size by means of Reduced Connection

IDentifier (RCID). This embodiment classifies the RCID into three types: RCID-I l, RCID-7 and RCID-3, where each numeral means the number of different Least Signification Bit (LSB) bits in each Connection IDentifier (CID), and the number of reduced bits decreases with an increase in the numeral. Instead, the number of users included in the same type can increase. In this way, it is possible to reduce the total MAP size by generating the sub-MAP using the MCS level and the RCID, and a detailed description thereof will be given below with reference to FIGs. 4 to 7.

[44] FIG. 4 illustrates a structure of an OFDMA-based frame transmission apparatus according to the present invention.

[45] As illustrated in FIG. 4, a frame transmission apparatus includes a scheduler 100 for scheduling transmission packets, a sub-MAP processor 200 for determining whether to apply a sub-MAP, a MAP generator 300 for generating a normal MAP or a sub-MAP according to an indication from the scheduler 100 and the sub-MAP processor 200, and a transmission modem 400 for transmitting the generated MAP.

[46] When user packets are input from an upper layer to a Medium Access Control

(MAC) layer, the scheduler 100 schedules transmission packets for each user (MS) based on scheduling information. That is, the scheduler 100 determines a MAP IE of DL-MAP and UL-MAP constituting a frame, and also appropriately determines a burst profile of the MAP IE so that it can communicate with each MS. Herein, the scheduling information includes Carrier-to-interference and Noise Ratio (CINR) information based on Channel Quality Indicator (CQI), a CID list based on Queue Management System (QMS), Burst Profile Management (BPM), etc.

[47] The sub-MAP processor 200 determines whether there is any one of the scheduled packets, which needs sub-MAP application. Although the sub-MAP processor 200 is implemented separately from the scheduler 100 in this embodiment, it can also be implemented in the scheduler 100 in an alternative embodiment. A detailed description of the sub-MAP processor 200 will be made with reference to FIG. 5.

[48] The MAP generator 300 generates a MAP message by allocating the scheduled packets to a particular time-frequency resource region according to the indications from the scheduler 100 and the sub-MAP processor 200. Examples of the MAP message include a normal MAP message and a sub-MAP message, and a description of their structures has been made with reference to FIGs. 2 and 3. The transmission modem 400 broadcasts the MAP message generated by the MAP generator 300 to an MS (not shown) by applying a corresponding MCS level.

[49] FIG. 5 illustrates a structure of the sub-MAP processor shown in FIG. 4.

[50] As illustrated in FIG. 5, the sub-MAP processor 200 includes a first sub-MAP group establisher 210, a reducing gain processor 220, a second sub-MAP group establisher 230, and a sub-MAP determiner 240, and further includes an MCS level table 250.

[51] The first sub-MAP group establisher 210 receives a CINR for each CID, and based on the MCS level table 250, if an MCS level assigned to the CINR is greater than or equal to a reference MCS level, the first sub-MAP group establisher 210 groups CIDs having the CINR into a first sub-MAP, determining that the channel environment is good. The first sub-MAP group establisher 210, to be specific, includes a CINR receiver 212, an MCS level comparator 214, and a first sub-MAP grouping unit 216. The CINR receiver 212 receives a CINR for each CID through a CQI channel. The MCS level comparator 214 extracts an MCS level assigned to each CINR based on the MCS level table 250 that has determined an MCS level depending on its received CINR, and makes a comparison to determine whether the MCS level is greater than or equal to a reference MCS level. When the MCS level comparator 214 has made the comparison for all CINRs, the first sub-MAP grouping unit 216 groups, into a first sub-MAP group, CIDs having a CINR greater than or equal to the reference MCS level as a result of the comparison. An MCS level lower than the reference MCS level is applied to the first sub-MAP group, and preferably, an MCS level which is two levels lower than the reference MCS level can be applied, considering that the received CINR may suffer a significant change due to a delay of the CQI channel, caused by an abrupt change in the channel environment.

[52] For example, when the reference MCS level is set to 64-ary Quadrature Amplitude

Modulation (64QAM) 1/2, the first sub-MAP grouping unit 216 groups CIDs having an MCS level greater than or equal to 64QAM 1/2 into a first sub-MAP, and applies an MCS level lower than or equal to 16QAM 3/4, which is at least one level lower than 64QAM 1/2. It is preferable to apply 16QAM 1/2 which is two levels lower than 64QAM 1/2, considering that the received CINR may suffer a significant change due to a delay of the CQI channel, caused by an abrupt change in the channel environment. The reducing gain processor 220 searches for an RCID type having the highest overhead reduction rate, and selects the searched RCID type. The reducing gain processor 220 includes a reducing gain calculator 222 and an RCID type selector 224. The reducing gain calculator 222 calculates a CID reducing gain for each RCID type. The calculation of the CID reducing gain is defined as Equation 1, and a detailed description thereof will be given with reference to Equation 1. When the CID reducing gain is calculated for each RCID type in this way, the RCID type selector 224 selects a RCID type having the highest CID reducing gain. This embodiment suggests three RCID types: for example, RCID-3, RCID-7 and RCID-I l, where numeral after 'RCID' represents the number of different bits for each CID.

[53] The second sub-MAP group establisher 230 groups CIDs corresponding to a particular RCID type into a second sub-MAP group using the CID reducing gain. The second sub-MAP group establisher 230 includes a reducing gain comparator 232 and a second sub-MAP grouping unit 234. The reducing gain comparator 232 compares the CID reducing gain of the RCID type selected by the RCID type selector 224 with a threshold predetermined according to the channel environment, and when the CID reducing gain of the selected RCID type is greater than the threshold, the second sub- MAP grouping unit 234 sets CIDs corresponding to the RCID type as a second sub- MAP group.

[54] The sub-MAP determiner 240 determines whether to generate a sub-MAP based on the first sub-MAP group and the second sub-MAP group. The sub-MAP determiner 240 includes a group checker 242, an overhead calculator 244, and an overhead comparator 246. The group checker 242 checks whether there is at lease one of the first sub-MAP group and the second sub-MAP group. If there is no grouped CID, the group checker 242 does not apply the sub-MAP since use of the normal MAP is advantageous for the overhead reduction. The overhead calculator 244 calculates an overhead rate reduced during application of a sub-MAP, and calculates an overhead rate during non-application of a sub-MAP. The overhead comparator 246 compares the calculated overhead rate reduced during application of a sub-MAP with the calculated overhead rate during non- application of a sub-MAP, and instructs generation of a sub- MAP if the overhead rate reduced during application of a sub-MAP is greater than the overhead rate during non- application of a sub-MAP. The comparison result of the overhead comparator 246 is expressed as a specific rate as shown in Equation 2.

[55] FIG. 6 illustrates a structure of the MAP generator shown in FIG. 4.

[56] As illustrated in FIG. 6, the MAP generator 300 includes a normal MAP generator

310 for generating a normal MAP message, a sub-MAP generator 320 for generating a sub-MAP message, and a Hybrid Automatic Repeat reQuest (HARQ) processor 330.

[57] The normal MAP generator 310 generates information on a DL burst and information on a UL burst using a MAP IE, and generates a normal MAP by means of the burst information, and a detailed description thereof has been made with reference to FIG. 2.

[58] The sub-MAP generator 320 generates a sub-MAP by assigning different MCS levels to CIDs included in the first sub-MAP group and/or second sub-MAP group, and a detailed description thereof has been given with reference to FIG. 3.

[59] The HARQ processor 330 sets (assigns a binary 1) or resets (assigns a binary 0) an

HARQ ACKnowledge (ACK) offset for a CID group to which CID reducing gain is applied, i.e. for the second sub-MAP group. Since each MS cannot know the number of MSs to which a different MCS level is applied, the HARQ processor 330 cannot perform appropriate setting on the HARQ ACK offset in a UL-MAP during UL transmission. Therefore, with the use of the HARQ processor 330, the MAP generator 300 determines the presence/absence of a CID group to which CID reducing gain is applied, during sub-MAP generation, and provides information on an appropriate HARQ ACK offset to the MS. Operations of the sub-MAP processor and the normal MAP generator will be described with reference to FIGs. 7 to 11.

[60] FIG. 7 is a flowchart illustrating a procedure for generating a sub-MAP according to the present invention, and FIGs. 8 to 11 are diagrams illustrating sequential generation of a sub-MAP according to the present invention.

[61] For a better understanding of the present invention, it will be assumed herein that the

MCS level assigned during sub-MAP generation includes only QPSK 1/2 and 16QAM 1/2, and QPSK 1/2 is assigned to the normal MAP in default.

[62] First, a CINR receiver 212 receives a CINR for each CID through a CQI channel

(Step S701). Thereafter, an MCS level comparator 214 determines whether an MCS level corresponding to the received CINR is greater than or equal to a reference MCS level, referring to an MCS level table 250 (Step S703). Such determination is made for all received CINRs. For example, step S703 corresponds to FIG. 8. Referring to FIG. 8, MAP IEs of a normal MAP message are marked out as individual blocks in a region A. Each of the blocks is mapped to a MAP IE allocated to its associated CID. Among these blocks, the hatched blocks, like the region B, are MAP IEs defined by performing step S703. That is, the region B has MAP IEs of at least one CID whose MCS level is greater than or equal to the reference MCS level (e.g., 16QAM 1/2).

[63] If it is determined that there is at least one MAP IE, a first sub-MAP grouping unit

216 groups a MAP IE(s) of at least one CID satisfying step S703 into a first sub-MAP using a pointer IE (Step S705). Further, the first sub-MAP grouping unit 216 applies an MCS level lower than the reference MCS level to the first sub-MAP group. Preferably, the first sub-MAP grouping unit 216 applies an MCS level which is two levels lower than the reference MCS level. For example, when the reference MCS level is 64QAM 1/2, the first sub-MAP grouping unit 216 applies 16QAM 1/2, which is two levels lower than 64QAM 1/2, to the first sub-MAP group. An illustration of step S705 is given in FIG. 9. Referring to FIG. 9, MAP IEs of a normal MAP message are marked out as individual blocks in a region A, and a first sub-MAP message is shown in a region D. Here, a region C is mapped to a pointer IE, and regions B in the region D are mapped to the MAP IEs grouped through step S705.

[64] Next, a reducing gain calculator 222 calculates a CID reducing gain for each RCID type (Step S707). RCID types provided in this embodiment include RCID-I l, RCID-7 and RCID-3, where numeral after 'RCID' represents the number of different bits for each CID. For example, when 16 bits are allocated to a CID, RCID-11 has 5 equal bits, RCID-7 has 9 equal bits, and RCID-3 has 13 equal bits. Then, the number of CIDs corresponding to RCID-11 will be much greater than the number of CIDs corresponding to RCID-3. Therefore, the number of reduced bits for each RCID type and the number of CIDs corresponding to the RCID type will undergo an appropriate trade-off.

[65] The reducing gain calculator 222 calculates a CID reducing gain for each RCID type using Equation 1.

[66] [Equation 1]

¹⁶⁷¹ _GRA0/0) JLa_D - L_RaD)x N_RC - (P ₊ O) _{χ m} βRC

[68] where G_RC(%) denotes a CID reducing gain, L_Ci_D denotes a CID length (e.g., 16 bits),

L_RCΠD denotes an RCID length for each RCID type, N_RC denotes the number of MAP IEs to which RCID is applied, P denotes a length (e.g., 24 bits) of HARQ and sub- MAP pointer IE, O denotes a sub-MAP message overhead (e.g., 40 bits in DL, and 56 bits when UL is added), and B_RC denotes the total number of bits of MAP IEs to which RCID is applied.

[69] Thereafter, an RCID type selector 224 selects an RCID type having the highest CID reducing gain among the reducing gains for each RCID type, calculated in step S707, and removes the same bits of each CID according to the selected RCID type (Step S709).

[70] An illustration of step S709 is given in FIG. 10. Referring to FIG. 10, MAP IEs of a normal MAP message are marked out as individual blocks in a region A, and MAP IEs in a region E and a region F, expressed in a different way from FIG. 9, are additionally shown. The region E represents the same bits of a CID in the MAP IE, and the region F is a CID part from which the same bits are removed.

[71] Next, a reducing gain comparator 232 compares the CID reducing gain of the RCID type selected in step S709 with a threshold T_CID (Step S711). The threshold can have a value of approximately 30% through 50% of the gain before CID reduction. However, such a figure is determined according to the channel environment or the intention of the designer.

[72] If the CID reducing gain is greater than or equal to the threshold T_Ci_D as a result of the comparison in step S711, a second sub-MAP grouping unit 234 groups MAP IEs of CIDs corresponding to the selected RCID type into a second sub-MAP group using a pointer IE (Step S713). For example, in FIG. 10, the second sub-MAP shown in FIG. 11 is generated through the comparison of step S711. Referring to FIG. 11, MAP IEs of a normal MAP message are marked out as individual blocks in a region A. Here, regions C and C2 are mapped to a pointer IE, a region D is mapped to a first sub-MAP message, and a region G is mapped to a second sub-MAP message. That is, step S713 generates a second sub-MAP message for the region E of FIG. 10 using a pointer IE (region C2).

[73] A group checker 242 checks if there is at least one sub-MAP group made up to now

(Step S715). The group checker 242 can check the following cases: 1) presence of the first sub-MAP group and the second sub-MAP group, 2) presence of the first sub-MAP group but absence of the second sub-MAP group, 3) absence of the first sub-MAP group but presence of the second sub-MAP group, and 4) absence of the first sub-MAP group and the second sub-MAP group. In case 4), the group checker 242 generates a normal MAP without generation of the sub-MAP (Step S725).

[74] Thereafter, an overhead calculator 244 calculates an overhead rate reduced during application of the first and/or second sub-MAP groups (Step S717). That is, an overhead rate G_τ(%) reduced by the sub-MAP groups can be expressed as Equation 2.

[75] [Equation 2]

^[76] G_T (%) = ^{LN "} ^ x IOO

L_N

T - ^BN N^~ K OCΛ

[77] where L_N denotes a length of a normal MAP message modulated by a default MCS level (QPSK 1/2, repetition 1), L_s denotes a length of a sub-MAP message, L_CID denotes a CID length (e.g., 16 bits), L_RCi_D denotes an RCID length, B_N denotes the total number of bits of a normal MAP message,

denotes a sum of the total number of bits of MAP IEs belonging to a first sub-MAP group, R_N denotes a default MCS rate (1/2, QPSK 1/2, repetition 1), R_s denotes an MCS rate of a sub-MAP message for a first sub-MAP group, N_RC denotes the number of MAP IEs belonging to a second sub-MAP group, P_Gi denotes a length (e.g., 24 bits) of HARQ and sub-MAP pointer IE for the first sub-MAP group, P_G2 denotes a length (e.g., 24 bits) of HARQ and sub-MAP pointer IE for the second sub-MAP group, O_Gi denotes a MAP message overhead (e.g., 24 bits in DL, and 40 bits when UL is added) for the first sub-MAP group, O_G2 denotes a MAP message overhead (e.g., 40 bits in DL, and 56 bits when UL is added) for the second sub-MAP group, and G_τ denotes the total gain obtained through the entire sub-MAP generation process. [78] Next, an overhead comparator 246 compares an overhead rate G_τ reduced during ap- plication of the first and/or second sub-MAP groups with an overhead rate T₀ during non- application of a sub-MAP (Step S719).

[79] If G_τ < T₀ as a result of the comparison, a normal MAP generator 310 generates a normal MAP without sub-MAP generation (Step S725). However, if G_τ ) T₀, a sub- MAP generator 320 generates a sub-MAP using the first and/or second sub-MAP groups checked in step S715 (Step S721). At this point, CIDs not included in the first and/or second sub-MAP groups are generated as a normal MAP (Step S725).

[80] In step S721, a sub-MAP is generated as shown in FIG. 3. That is, the sub-MAP generator 320 generates a sub-MAP using a pointer IE, and allocates burst location information to a MAP IE of the sub-MAP.

[81] Meanwhile, an HARQ processor 330 sets (assigns a binary 1) or resets (assigns a binary 0) an HARQ ACK offset for a CID group to which at least one CID reducing gain is applied, i.e., for the second sub-MAP group (Step S723). More specifically, the HARQ processor 330 determines the presence/absence of HARQ in the second sub- MAP group of step S713, and if it is determined that there is HARQ in the second sub- MAP group, the HARQ processor 330 sets an HARQ ACK offset as an HARQ ACK offset indicator field T to provide an MS with information on an HARQ ACK offset location for at least one CID corresponding to the second sub-MAP group. However, if there is no HARQ, the HARQ processor 330 resets the HARQ ACK offset as an HARQ ACK offset indicator field '0' That is, when a sub-MAP message is applied to the transmission frame according to the proposed embodiment, since an MS corresponding to the CID of the second sub-MAP group cannot know the number of CIDs corresponding to the first sub-MAP group, the HARQ processor 330 cannot perform appropriate setting on the HARQ ACK offset in the UL-MAP. In order to compensate for this, the HARQ processor 330 determines the presence/absence of HARQ in the second sub-MAP group during sub-MAP generation, and provides information on an appropriate HARQ ACK offset to the MS with a CID belonging to the second sub- MAP group.

[82] While the invention has been shown and described with reference to certain exemplary embodiments 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. Therefore, the spirit and scope of the present invention must be defined not by described embodiments thereof but by the appended claims and equivalents of the appended claims.

Claims

[1] A method for constructing a MAP in Orthogonal Frequency Division Multiple

Access (OFDMA)-based wireless communication system, the method comprising: generating a first sub-MAP group by grouping at least one Connection IDentifier

(CID) whose Modulation and Coding Scheme (MCS) level is greater than or equal to a reference MCS level, among received CIDs; generating a second sub-MAP group by grouping at least one CID whose CID reducing gain is greater than or equal to a threshold; generating a normal MAP for at least one CID not included in the first and second sub-MAP groups; and generating a sub-MAP for the first and second sub-MAP groups using a pointer

Information Element (IE).

[2] The method of claim 1, wherein the step generating the first sub-MAP group comprises: acquiring a Carrier-to-interference and Noise Ratio (CINR) for each CID through a Channel Quality Indicator (CQI), and grouping at least one CID whose

MCS level corresponding to the CINR is greater than or equal to the reference

MCS level.

[3] The method of claim 1, wherein the step generating the second sub-MAP group comprises: selecting a Reduced CID (RCID) type having the highest CID reducing gain, and grouping at least one CID whose CID reducing gain of the selected RCID type is greater than or equal to the threshold.

[4] The method of claim 1, wherein the step generating the sub-MAP comprises: calculating an overhead rate reduced in the sub-MAP group and an overhead rate during application of the normal MAP, and generating the sub-MAP when the overhead rate reduced in the sub-MAP group is greater than the overhead rate during application of the normal MAP.

[5] The method of claim 1, further comprising: setting, after the generating the sub-MAP, a Hybrid Automatic Repeat reQuest

(HARQ) ACKnowledgement (ACK) offset when there is an HARQ in the second sub-MAP group, and resetting the HARQ ACK offset when there is no

HARQ in the second sub-MAP group.

[6] A method for constructing a MAP in Orthogonal Frequency Division Multiple

Access (OFDMA)-based wireless communication system, the method comprising: generating a sub-MAP group for at least one received Connection IDentifier (CID) using at least one of Modulation and Coding Scheme (MCS) level information and CID reducing gain information; and generating a sub-MAP for the sub-MAP group using a pointer Information Element (IE), and generating a normal MAP for at least one CID not included in the sub-MAP group.

[7] The method of claim 6, wherein the sub-MAP group comprises a first sub-MAP group; wherein the first sub-MAP group is defined by grouping at least one CID whose MCS level corresponding to a Carrier-to-interference and Noise Ratio (CINR) of the received CID is greater than or equal to a reference MCS level.

[8] The method of claim 7, wherein the MCS level corresponding to a CINR of the received CID is extracted from an MCS level table that has determined MCS levels corresponding to CINRs.

[9] The method of claim 6, wherein the sub-MAP group comprises a second sub-

MAP group; wherein the second sub-MAP group is defined by selecting a Reduced CID (RCID) type having a highest CID reducing gain, and grouping at least one CID whose CID reducing gain of the selected RCID type is greater than or equal to a threshold.

[10] The method of claim 9, wherein the RCID type comprises an RCID-3, an RCID-

7 and an RCID-11, where numeral after the RCID indicates the number of different bits for each CID.

[11] The method of claim 6, wherein the CID reducing gain is expressed as the following equation;

G_RC(%) J^Lc>r, -^L«ao^{) x} N_RC -⁽P + 0) _{χ m}

where G_RC(%) denotes a CID reducing gain, L_CID denotes a CID length, L_RCi_D denotes an RCID length for each RCID type, N_RC denotes the number of MAP IEs to which RCID is applied, P denotes a length of Hybrid Automatic Repeat reQuest (HARQ) and sub-MAP pointer IE, O denotes a sub-MAP message overhead, and B_RC denotes the total number of bits of MAP IEs to which RCID is applied.

[12] The method of claim 6, wherein the step generating the sub-MAP for the sub-

MAP group comprises: calculating an overhead rate reduced in the sub-MAP group and an overhead rate during application of the normal MAP, and generating the sub-MAP when the overhead rate reduced in the sub-MAP group is greater than the overhead rate during application of the normal MAP.

[13] The method of claim 6, wherein the step generating the sub-MAP for the sub-

MAP group comprises: calculating an overhead rate reduced in the sub-MAP group and an overhead rate during application of the normal MAP, and generating the normal MAP when the overhead rate reduced in the sub-MAP group is less than the overhead rate during application of the normal MAP.

[14] The method of claim 13, wherein the overhead rate reduced in the sub-MAP is expressed as the following equation;

G_T(%) = ^{LN ~ Z}'^V X 100

L - **-

^{N ~} R,

, _ B_N - {B_St - P_a} - {(L_aD - L_RCID)x N_κ. - P_al - O_a2] _| B_Sι + O_aι s —

R_N R_S where L_N denotes a length of a normal MAP message modulated by a default MCS level, L_s denotes a length of a sub-MAP message, L_Ci_D denotes a CID length, L_RCΠD denotes an RCID length, B_N denotes the total number of bits of a normal MAP message,

^Bs denotes a sum of the total number of bits of MAP IEs belonging to a first sub- MAP group, R_N denotes a default MCS rate, R_s denotes an MCS rate of a sub- MAP message for the first sub-MAP group, N_RC denotes the number of MAP IEs belonging to the second sub-MAP group, P_Gi denotes a length of Hybrid Automatic Repeat reQuest (HARQ) and sub-MAP pointer IE for the first sub- MAP group, P_G2 denotes a length of HARQ and sub-MAP pointer IE for the second sub-MAP group, O_Gi denotes a MAP message overhead for the first sub- MAP group, O_G2 denotes a MAP message overhead for the second sub-MAP group, and G_τ denotes the total gain obtained through the entire sub-MAP generation process.

[15] The method of claim 6, wherein the step generating the sub-MAP for the sub-

MAP group comprises; generating a sub-MAP by applying an MCS level lower than the reference MCS level to the first sub-MAP group.

[16] The method of claim 6, further comprising: setting, after the generating the sub-MAP for the sub-MAP group, an Hybrid Automatic Repeat reQuest (HARQ) ACKnowledgement (ACK) offset indicator field when there is HARQ in the second sub-MAP group, and resetting the HARQ ACK offset indicator field when there is no HARQ in the second sub- MAP group.

[17] An apparatus for transmitting a frame in Orthogonal Frequency Division

Multiple Access (OFDMA)-based wireless communication system, the apparatus comprising: a first sub-MAP group establisher for grouping, into a first sub-MAP group, at least one Connection Identifier (CID) whose Modulation and Coding Scheme

(MCS) level of a received CID is greater than or equal to a reference MCS level; a reducing gain processor for calculating at least one CID reducing gain for each

Reduced CID (RCID) type and selecting an RCID type having the highest CID reducing gain; a second sub-MAP group establisher for grouping CIDs corresponding to the selected RCID type into a second sub-MAP group; and a sub-MAP determiner for determining to generate a sub-MAP when there is at least one of the first sub-MAP group and the second sub-MAP group.

[18] The apparatus of claim 17, wherein the first sub-MAP group establisher receives a Carrier-to-interference and Noise Ratio (CINR), and groups CIDs corresponding to the CINR into a first sub-MAP group when an MCS level assigned to the CINR is greater than or equal to the reference MCS level.

[19] The apparatus of claim 17, further comprising: a MAP generator including a sub-MAP generator for generating a sub-MAP for at least one CID for which generation of the sub-MAP is determined, and a normal MAP generator for generating a normal MAP for at least one CID for which the generation of the sub-MAP is not determined.

[20] The apparatus of claim 19, wherein the sub-MAP generator generates a sub-

MAP by applying an MCS level lower than the reference MCS level to the first sub-MAP group.

[21] The apparatus of claim 17, further comprising: a Hybrid Automatic Repeat reQuest (HARQ) processor for setting or resetting an HARQ ACKnowledgement (ACK) offset.

[22] The apparatus of claim 17, wherein the first sub-MAP group establisher comprises: a CINR receiver for receiving a CINR for each CID through a Channel Quality Indicator (CQI) channel; an MCS level comparator for determining whether an MCS level assigned to the CINR is greater than or equal to the reference MCS level; and a first sub-MAP grouping unit for grouping, into a first sub-MAP group, at least one CID having a CINR, an MCS level associated to which is greater than or equal to the reference MCS level according to a result of the determination.

[23] The apparatus of claim 17, wherein the reducing gain processor comprises: a reducing gain calculator for calculating at least one CID reducing gain for each RCID type; and an RCID type selector for selecting an RCID type having the highest CID reducing gain.

[24] The apparatus of claim 23, wherein the RCID type comprises an RCID-3, an

RCID-7 and an RCID-11, where numeral after the RCID indicates the number of different bits for each CID.

[25] The apparatus of claim 17, wherein the second sub-MAP group establisher comprises: a reducing gain comparator for comparing at least one CID reducing gain of the selected RCID type with a threshold predetermined according to a channel environment; and a second sub-MAP grouping unit for grouping at least one CID corresponding to the RCID type into a second sub-MAP group when the CID reducing gain of the selected RCID type is greater than the threshold.

[26] The apparatus of claim 17, wherein the sub-MAP determiner comprises: a group checker for checking whether there is at least one of the first sub-MAP group and the second sub-MAP group; a overhead calculator for calculating an overhead rate reduced by the checked sub-MAP group, and calculating an overhead rate during non- application of a sub-MAP; and an overhead comparator for comparing the overhead rate reduced by the sub- MAP group with the overhead rate during non-application of a sub-MAP, and instructing generation of the sub-MAP when the overhead rate reduced by the sub- MAP group is greater than the overhead rate during non-application of a sub- MAP.