WO2009045080A2

WO2009045080A2 - Map message generating method and apparatus for enhancing map coverage in a wireless communication system

Info

Publication number: WO2009045080A2
Application number: PCT/KR2008/005837
Authority: WO
Inventors: Jae-Hyun Ahn; Dong-Hee Kwon; Jun-Seong Park; Kuk-Jin Song
Original assignee: Posdata Co., Ltd.
Priority date: 2007-10-04
Filing date: 2008-10-02
Publication date: 2009-04-09
Also published as: WO2009045080A3; KR100905281B1; KR20090034610A

Abstract

An apparatus is provided for generating a MAP message in a wireless communication system supporting Orthogonal Frequency Division Multiple Access (OFDMA). The MAP message generation apparatus includes a controller for determining MAP Information Elements (IEs) to be included in MAP of a transmission frame, and controlling the MAP IEs to include Connection Identifier (CID) information and Modulation and Coding Scheme (MCS) level information; a Sub-MAP processor for comparing a total size of MAP IEs corresponding to the lowest MCS level in channel quality among the MAP IEs, with a preset maximum Forward Error Correction (FEC) block size, and grouping the MAP IEs into Sub-MAP groups having the maximum FEC block size according to the comparison result; and a Sub-MAP generator for generating Sub- MAP messages with the MAP IEs of the Sub-MAP groups.

Description

Description MAP message generating method and apparatus for enhancing

MAP coverage in a wireless communication system Technical Field

[1] The present invention relates generally to a scheme for generating a MAP message in a wireless communication system, and in particular, to a method and apparatus for determining Medium Access Protocol Information Elements (MAP IEs) written in MAPs of a transmission frame and generating Sub-MAPs using the determined MAP IEs to enhance MAP coverage in a wireless communication system. Background Art

[2] A Mobile Worldwide Interoperability for Microwave Access (WiMAX) system consists of protocols of a message-based Medium Access Control (MAC) layer and an Orthogonal Frequency Division Multiple Access (OFDMA)-based physical (PHY) layer. On the OFDMA physical layer, one frequency band is split into a plurality of subcarriers and each subcarrier is orthogonal to other subcarriers. Due to the orthogonality, OFDMA can have a two-dimensional communication space: frequency and time spaces. In a cell, a Base Station (BS) allocates bursts to each Mobile Station (MS), and the bursts can each be indicated by MAP IEs. The MAP IEs are written in a MAP message, generating one frame. The frame will now be described in detail.

[3] FIG. 1 is a diagram illustrating a frame structure in a wireless communication system supporting OFDMA.

[4] Referring to FIG. 1, the frame is divided into a Down-Link (DL) subframe generated to transmit data from a BS to an MS, and an Up-Link (UL) subframe generated to transmit data from an MS to a BS.

[5] The DL subframe is composed of Preamble, Frame Control Header (FCH), DL MAP,

UL MAP, and DL bursts, and the UL subframe is composed of control symbols (Ranging, Acknowledgement (ACK), and Channel Quality Indicator (CQI)) and UL bursts. Between DL and UL exists a Transmit/receive Transition Gap (TTG), or a guard region.

[6] Preamble is used for providing time/frequency synchronization and cell information to an MS. FCH contains frame information and DL MAP decoding information. In DL MAP is written information on positions and usages of DL bursts that the BS transmits, by means of DL MAP IEs. In UL MAP is written information on positions and usages of UL bursts that the MSs transmit, by means of UL MAP IEs. In the generated frame, the DL MAP and UL MAP are transmitted in the form of a message. The MAP message will now be described in more detail. [7] FIG. 2 is a diagram illustrating a Normal MAP message generated in a BS supporting

OFDMA.

[8] Referring to FIG. 2, in a frame, a Normal MAP message includes DL MAP and UL

MAP, which include therein MAP IEs indicating user information of DL bursts that a BS transmits and position information of the corresponding bursts, and UL burst information that users (or MSs) transmit. Therefore, each user (or MS) can selectively receive the corresponding data using the user information and burst position information included in the MAP IEs. The generated Normal MAP message is modulated in a physical layer and then transmitted to users in a broadcasting manner. In FIG 2, numerals written in the Normal MAP indicate the number of repetitions. Since the MAP messages are control messages related to a particular goal (e.g., network entry) indicated by the MAP messages, the MAP messages should necessarily be decoded by MSs in order to achieve the goal.

[9] In an OFDMA-based BS, a packet is defined in a MAC layer. When a burst of a

MAP message is generated, at least one packet is included therein, and the one packet is made by packing at least one Forward Error Correction (FEC) block. In this case, an error occurrence probability in the packet is higher than an error occurrence probability in the FEC block. This is because if an error occurs in at least one FEC block, a packet including the FEC block necessarily has an error. In this principle, it can be appreciated that as a size of the MAP message increases, the error probability also increases.

[10] The MAP message is a kind of burst, and there is coverage for the MAP message.

The term 'coverage' as used herein refers to a communication range having an allowable error probability. Data coverage is related to Quality-of-Service (QoS). Even if an MS is out of the data coverage, its data communication is not totally disconnected. However, if the MAP message is not received at an MS, the MS can neither decode data burst nor transmit its data, causing a waste of system resources.

[11] In order to resolve such problems, the MAP message is encoded by the most invulnerable modulation scheme (Quadrature Phase Shift Keying (QPSK) 1/2 with repetition 6) to decrease error probability. Thus, the MAP message is generated quite large. The large size of the MAP message increases an error probability of the MAP message when an MS decodes the MAP message, causing a decrease in data transmission capacity in the DL and a reduction in MAP coverage.

[12] Meanwhile, a size of MAP in a frame that a BS transmits is proportional to the number of MSs covered by the BS. For example, as the number of MSs covered by the BS increases, the size of the MAP increases more and more. The increase in size of the MAP message, as described above, increases an error probability of the MAP message when the MS decodes the MAP message, causing a decrease in data transmission capacity in the DL and a reduction in MAP coverage.

[13] Therefore, there is a need to study a scheme capable of enhancing the communication coverage by efficiently reducing the size of the MAP message. Disclosure of Invention

Technical Problem

[14] Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a MAP message generation method and apparatus for enhancing coverage of a MAP message by reducing a burst size of the MAP message using Sub-MAPs to reduce an error probability of the MAP message, which may occur when an MS decodes the MAP message, in a wireless communication system. Technical Solution

[15] According to one aspect of the present invention, there is provided a method for generating a MAP message in a wireless communication system supporting Orthogonal Frequency Division Multiple Access (OFDMA), the method comprising: (a) determining a MAP Information Element (IE) based on Connection Identifier (CID) information and Modulation and Coding Scheme (MCS) level information for each Mobile Station (MS); (b) grouping the MAP IEs into Sub-MAP groups having a maximum Forward Error Correction (FEC) block size until the number of Sub-MAP groups reaches the maximum number of Sub-MAP messages that can be generated in one frame; and (c) generating Sub-MAP messages with the MAP IEs of the Sub-MAP groups.

[16] According to another aspect of the present invention, there is provided an apparatus for generating a MAP message in a wireless communication system supporting Orthogonal Frequency Division Multiple Access (OFDMA), the apparatus comprising: a controller for determining MAP Information Elements (IEs) to be included in MAP of a transmission frame, and controlling the MAP IEs to include Connection Identifier (CID) information and Modulation and Coding Scheme (MCS) level information; a Sub-MAP processor for comparing a total size of MAP IEs corresponding to the lowest MCS level in channel quality among the MAP IEs, with a preset maximum Forward Error Correction (FEC) block size, and grouping the MAP IEs into Sub-MAP groups having the maximum FEC block size according to the comparison result; and a Sub-MAP generator for generating Sub-MAP messages with the MAP IEs of the Sub- MAP groups.

Advantageous Effects

[17] According to the present invention, the wireless communication system generates

Sub-MAPs for MSs having a low MCS level, in an FEC block size where an FEC block error rate (BLER) is minimized in Convolutional Turbo Codes (CTC), thereby reducing error probability of a MAP message and thus enhancing coverage of the MAP message. As a result, it is possible to increase the DL data transmission capacity and system resource efficiency. Brief Description of the Drawings

[18] 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:

[19] FIG. 1 is a diagram illustrating a frame structure in a wireless communication system supporting OFDMA;

[20] FIG. 2 is a diagram illustrating a Normal MAP message generated in a BS supporting

OFDMA;

[21] FIG. 3 is a diagram illustrating a Sub-MAP message generated according to an embodiment of the present invention;

[22] FIG. 4 is a diagram illustrating a structure of a BS supporting OFDMA according to an embodiment of the present invention;

[23] FIG. 5 is a diagram illustrating a structure of a scheduler according to an embodiment of the present invention;

[24] FIGs. 6 and 7 are flowcharts illustrating an operation a Sub-MAP processor according to an embodiment of the present invention; and

[25] FIG. 8 is a diagram illustrating system-level simulation results on the Sub-MAP generated according to the present invention and the conventional Normal MAP. Mode for the Invention

[26] 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.

[27] FIG. 3 is a diagram illustrating a Sub-MAP message generated according to an embodiment of the present invention.

[28] Referring to FIG. 3, MAP of a frame is generated as a Compressed MAP or a Normal

MAP. MAP IEs of the Compressed MAP or the Normal MAP are allocated in Sub- MAP by means of Sub-MAP Pointer IEs, and the Sub-MAP includes Sub-MAP IEs having burst allocation information in the frame.

[29] The Sub-MAP, unlike the Normal MAP which is encoded with the most invulnerable modulation scheme (QPSK 1/2 with repetition 6), obtains a constant modulation gain by applying a higher Modulation and Coding Scheme (MCS) level (e.g., 16-ary Quadrature Amplitude Modulation (16QAM) 1/2) to the users having a good channel state (high Signal-to-Interference and Noise Ratio (SINR)). For the modulation gain, the Sub-MAP uses a Sub-MAP Pointer IE, and the Sub-MAP Pointer IE has different MCS levels for different Sub-MAPs. Here, the Sub-MAP Pointer IE corresponds to overhead that does not exist in the Normal MAP. Therefore, the total MAP size can be reduced by making a trade-off between an operation in which the Sub-MAP Pointer IE is used as overhead and an operation in which a modulation gain is obtained as Sub- MAP Pointer IEs have different MCS levels.

[30] In addition, the Sub-MAP can be generated in a reduced structure capable of reducing the total MAP size through a Reduced Connection Identifier (RCID). The term 'RCID' as used herein means a Reduced CID, and is used in the Compressed MAP format. For RCID, there are three types: RCID 11, RCID 7, and RCID 3, where each numeral means a different Least Significant Bit (LSB) in CID. Thus, as the numeral is larger, the number of saved bits decreases but the number of MSs included in the same type increases. Therefore, it is possible to reduce the total MAP size by using a trade-off between the number of saved bits and the number of MSs.

[31] In generating the Sub-MAP, the present invention first packs MAP IEs for an MS(s) having a low channel quality (e.g., QPSK 1/2 with repetition 6) in possible small pieces using Sub-MAP (SUB-DL-UL-MAP). By packing MAP IEs in the small pieces, it is possible to reduce an error probability of a Sub-MAP message when an MS decodes the Sub-MAP message, enabling enhancement of MAP coverage. As for a size of the packing pieces, for example, in Convolutional Turbo Codes (CTC), when a size of one FEC block is maximized (10 slots for QPSK 1/2), a corresponding FEC block error rate (BLER) is minimized (see IEEE P802.16 (Draft MAR 2007), 2007), the size of the packing pieces corresponds to the maximum FEC block size (i.e., 10 slots for QPSK 1/2).

[32] As the number of Sub-MAPs generated in the maximum FEC block size is larger, the obtained grouping gain is higher, but the maximum possible number of Sub-MAP messages generated per frame is limited (e.g., limited to 3 in IEEE 802.16d/e). Therefore, the present invention generates the maximum number of Sub-MAP messages in one frame using MAP IEs corresponding to the lowest MCS level, and the maximum number can be set to, for example, 3 as in IEEE 802.16d/e. In some cases, it is happened not to fully fill the maximum number of Sub-MAP messages even with the MAP IEs corresponding to the lowest MCS level in channel quality. To this end, the present invention generates a number M of Sub-MAPs (where M denotes the number of remaining Sub-MAPs, or a difference between the maximum number of Sub-MAPs and the number of already generated Sub-MAPs) in the maximum FEC block size using the remaining MAP IEs (MAP IEs corresponding to an MCS level having QPSK 1/2 with repetition 6 are excluded) except for the MAP IEs used for generating the Sub-MAP messages, and enhances the coverage by reducing the MAP size.

[33] A detailed description will now be made of an apparatus and method for generating

Sub-MAPs according to an embodiment of the present invention.

[34] FIG. 4 is a diagram illustrating a structure of a BS supporting OFDMA according to an embodiment of the present invention.

[35] As illustrated in FIG. 4, a BS includes an interface 100, a band signal processing module 200, a transmission module 300, a reception module 600, a scheduler 500, and an antenna 400. The BS can be divided into a reception path and a transmission path for supporting Time Division Duplex (TDD).

[36] In the reception path, the reception module 600 receives one or more radio signals that MSs transmit, via the antenna 400, and converts the received radio signals into baseband signals. For example, for data reception of the BS, the reception module 600 removes noises from the received signal, amplifies the noise-removed signal, down- converts the amplified signal into a baseband signal, and digitalizes the down- converted baseband signal. The band signal processing module 200 extracts information or data bits from the digitalized signal, and performs demodulation, decoding, error correction processes thereon. The received information is delivered to adjacent wire/wireless networks via the interface 100, or is transmitted back to other MSs being serviced by the BS through the transmission path.

[37] In the transmission path, the interface 100 receives voice, data and/or control information from a base station controller or radio network, and the band signal processing module 200 encodes the voice, data and/or control information, and outputs the results to the transmission module 300. The transmission module 300 modulates the encoded voice, data and/or control information with a carrier signal having a desired transmission frequency or frequencies, amplifies the modulated carrier signal to a level suitable for transmission, and transmits the amplified carrier signal over the air via the antenna 400.

[38] The scheduler 500 controls operations and elements of the reception path and the transmission path. In particular, according to the present invention, the scheduler 500 generates a maximum number of Sub-MAP messages using MAP IEs, for a frame to be transmitted to each MS, and generates each Sub-MAP message in the maximum FEC block size. The scheduler 500 will be described in more detail with reference to the accompanying drawings.

[39] FIG. 5 is a diagram illustrating a structure of a scheduler according to an embodiment of the present invention.

[40] As illustrated in FIG. 5, the scheduler 500 includes a controller 510, a Sub-MAP processor 520, and a Sub-MAP generator 530. [41] The controller 510, when user packets are input from an upper layer to a MAC layer in the transmission path, schedules packets to be transmitted to each of MSs based on scheduling information. That is, the controller 510 determines MAP IEs of DL MAP and UL MAP constituting a frame, and also determines a burst profile of the MAP IEs so as to be suitable for communication with each MS. The scheduling information includes CQI-based Carrier-to-interference and Noise Ratio (CINR) information, Queue Management System (QMS)-based CID list, Burst Profile Management (BPM), etc.

[42] The Sub-MAP processor 520 preferentially groups MAP IEs corresponding to the lowest MCS level (e.g., QPSK 1/2 with repetition 6) in channel quality into Sub-MAP groups having the maximum FEC block size. While making the Sub-MAP groups, the Sub-MAP processor 520 makes a maximum number (e.g., 3) of the Sub-MAP groups with MAP IEs whose channel quality corresponds to the lowest MCS level. In some cases, however, the Sub-MAP processor 520 cannot make the maximum number of Sub-MAP groups only with the MAP IEs corresponding to the lowest MCS level in channel quality. In this case, the Sub-MAP processor 520 additionally makes Sub- MAP groups, the number of which is equal to the number of remaining Sub-MAP groups (or a difference between the maximum number and the number of Sub-MAP groups made with MAP IEs whose channel quality corresponds to the lowest MCS level). Here, the Sub-MAP processor 520 groups the remaining MAP IEs except for the previously grouped MAP IEs into Sub-MAP groups having the maximum FEC block size, so as to reduce a size of the entire MAP message.

[43] The Sub-MAP generator 530 generates Sub-MAP messages using a Sub-MAP

Pointer IE, for the MAP IEs grouped by the Sub-MAP processor 520. The Sub-MAP Pointer IE contains position information of MAP IEs.

[44] A detailed description will now be made of the Sub-MAP processor 520 according to an embodiment of the present invention.

[45] Referring again to FIG. 5, the Sub-MAP processor 520 includes a list storing means

521, a counting means 522, a size comparison means 523, a Sub-MAP grouping means 524, and a reduction gain processing means 525.

[46] The list storing means 521 receives and stores a list of MAP IEs determined by the controller 510. The MAP IEs each include CID information and MCS level information for bursts. Each time one Sub-MAP group is made in the Sub-MAP grouping means 524, the list storing means 521 deletes at least one MAP IE used for making the Sub-MAP group, from the list. The list storing means 521 stores the number of remaining Sub-MAP groups and a list of MAP IEs used for making the remaining Sub-MAP groups, and when the Sub-MAP grouping means 524 makes Sub- MAP groups, the number of which is equal to the number of remaining Sub-MAP groups, the list storing means 521 deletes, from the list, the MAP IEs used for making the Sub-MAP groups.

[47] The counting means 522 counts the number of Sub-MAP groups made in the Sub-

MAP grouping means 524. If the counted number of Sub-MAP groups is the maximum number (e.g., 3) available in one frame, the counting means 522 notifies the Sub-MAP generator 530 that the number of the made Sub-MAP groups has reached the maximum number. The counting means 522 counts down the number by the number of remaining Sub-MAP groups (i.e., a difference between the maximum number and the number of already made Sub-MAP groups). In this case, when the number of made Sub-MAP groups has arrived the maximum number (i.e., the counted- down number of remaining Sub-MAP groups is 0), the counting means 522 notifies the Sub-MAP generator 530 that the number of made Sub-MAP groups has reached the maximum number.

[48] The size comparison means 523 receives from the list storing means 521 MAP IEs whose channel quality corresponds to the lowest MCS level, and compares the total size of the MAP IEs with a preset maximum FEC block size. The present invention defines the maximum FEC block size as an FEC block size whose FEC block error rate (BLER) is minimized in case of CTC. The size comparison means 523 delivers the comparison results to the Sub-MAP grouping means 524 so that the Sub-MAP grouping means 524 groups the MAP IEs received from the list storing means 521 into Sub-MAP groups having the maximum FEC block size according to the comparison results.

[49] For the MAP IEs received from the list storing means 521, the Sub-MAP grouping means 524 groups the received MAP IEs into Sub-MAP groups of the maximum FEC block size according to the comparison results of the size comparison means 523. The Sub-MAP grouping means 524 groups the MAP IEs as many as a preset maximum number (e.g., 3). More specifically, if the total size of the MAP IEs whose channel quality corresponds to the lowest MCS level is greater than the maximum FEC block size as a result of the comparison, the Sub-MAP grouping means 524 groups the MAP IEs whose channel quality corresponds to the lowest MCS level into Sub-MAP groups of the maximum FEC block size. However, if total size of the MAP IEs whose channel quality corresponds to the lowest MCS level is less than the maximum FEC block size as a result of the comparison, the Sub-MAP grouping means 524 makes Sub-MAP groups having the maximum FEC block size using MAP IEs whose channel quality corresponds to the lowest MCS level, and MAP IEs whose channel quality corresponds to another MCS level, received from the list storing means 521. The Sub-MAP grouping means 524 groups M MAP IEs (where M denotes the number of remaining Sub-MAP groups; and the MAP IEs whose channel quality corresponds to the lowest MCS level are excluded) whose channel quality corresponds to another MCS level, received from the list storing means 521. Specifically, the Sub-MAP grouping means 524 receives a MAP size reduction factor (e.g., particular MCS level or particular RCID) selected by the reduction gain processing means 525, and makes Sub-MAP groups having the maximum FEC block size according to the selected MAP size reduction factor using the MAP IEs whose channel quality corresponds to another MCS level.

[50] The reduction gain processing means 525 determines a MAP size reduction factor capable of maximally reducing the total MAP size. The MAP size reduction factor is one of various MCS levels (e.g., QPSK 1/2 with repetition 4, QPSK 1/2 with repetition 2, QPSK 1/2, ..., 64QAM 4/5), or one of various RCIDs. The reduction gain processing means 525 calculates a reduction gain that can be obtained by making grouping for each of the MAP size reduction factors, and then selects a MAP size reduction factor having the maximum reduction gain. The reduction gain processing means 525 delivers the selected MAP size reduction factor to the Sub-MAP grouping means 524.

[51] Meanwhile, when the reduction gain processing means 525 is actually realized in the

BS, there is a need for considerably calculation and time for obtaining a reduction gain that can be obtained by performing grouping for each of the MAP size reduction factors. Therefore, in order to reduce the realization complexity, the reduction gain processing means 525, when the number M of remaining Sub-MAP groups is 2 or 3, delivers one to the Sub-MAP grouping means 524 by selecting a MAP size reduction factor based on the MCS level, and delivers another one to the Sub-MAP grouping means 524 by selecting a MAP size reduction factor based on the RCID type. However, when the number M of remaining Sub-MAP groups is 1, the reduction gain processing means 525 is designed such that it compares a first Sub-MAP group made by grouping MAP IEs selected based on the MCS level, with second, third and fourth Sub-MAP groups made by grouping MAP IEs which are selected based on 3 different RCID types, respectively, and selects a MAP size reduction factor for the Sub-MAP group having the maximum reduction gain as a MAP size reduction factor.

[52] With reference to FIGs. 6 and 7, a description will now be made of an operation a

Sub-MAP processor according to an embodiment of the present invention.

[53] Referring to FIG. 6, the list storing means 521 receives a list of MAP IEs used for generating Sub-MAPs, from the controller 510, and stores the received list (Step S601). In this case, the list storing means 521 stores even CID information and MCS level information for the MAP IEs together.

[54] Next, the counting means 522 checks if the number of Sub-MAP groups made up to now corresponds to the maximum number (Step S602). Herein, the number of Sub- MAP groups indicates the number of Sub-MAP groups made by grouping MAP IEs whose channel quality corresponds to the lowest MCS level among the MAP IEs stored in the list storing means 521, in the maximum FEC block size in Step S605, and the maximum number means the maximum number of Sub-MAP messages that can be generated in one frame.

[55] If it is checked in Step S602 that the number of Sub-MAP groups has reached the maximum number, the Sub-MAP grouping means 524 resets the maximum number of Sub-MAP groups previously made using the MAP IEs whose channel quality corresponds to the lowest MCS level, and regroups the MAP IEs whose channel quality corresponds to the lowest MCS level, back into the maximum number of Sub- MAP groups (Step S609). By performing the regrouping, it is possible to make the Sub-MAP groups in the maximum FEC block size if possible.

[56] However, if it is checked in Step S602 that the number of Sub-MAP groups has not arrived the maximum number, the size comparison means 523 compares the total size of the MAP IEs whose channel quality corresponds to the lowest MCS level among the MAP IEs stored in the list storing means 521, with the maximum FEC block size (Step S603). Herein, the maximum FEC block size, as defined above, is an FEC block size whose FEC block error rate (BLER) is minimized in case of CTC.

[57] If the total size of the MAP IEs whose channel quality corresponds to the lowest

MCS level is greater than the maximum FEC block size as a result of the comparison in Step S603, the counting means 522 increases the number of Sub-MAP groups by 1, and the Sub-MAP grouping means 524 groups the MAP IEs whose channel quality corresponds to the lowest MCS level, into Sub-MAP groups of the maximum FEC block size (Steps S604-S605). Thereafter, the list storing means 521 deletes the MAP IEs grouped into the Sub-MAP groups from the list of the MAP IEs (Step S606), and then returns to Step S602.

[58] However, if the total size of the MAP IEs whose channel quality corresponds to the lowest MCS level is less than the maximum FEC block size as a result of the comparison in Step S603, the Sub-MAP grouping means 524 makes Sub-MAP groups of the maximum FEC block size using the MAP IEs whose channel quality corresponds to the lowest MCS level and the MAP IEs whose channel quality corresponds to another MCS level (e.g., another MCS level except for the MCS level having QPSK 1/2 with repetition 6) except for the MAP IEs whose channel quality corresponds to the lowest MCS level among the MAP IEs stored in the list storing means 521 (Step S607). Thereafter, the list storing means 521 deletes, from the list, the MAP IEs grouped into the Sub-MAP groups in Step S607 (Step S608).

[59] In this manner, the Sub-MAP processor 520 preferentially groups MAP IEs corresponding to the lowest MCS level (e.g., QPSK 1/2 with repetition 6) in channel quality, into the maximum number of Sub-MAP groups having the maximum FEC block size.

[60] In some cases, however, the Sub-MAP processor 520 cannot make the maximum number of Sub-MAP groups only with the MAP IEs whose channel quality corresponds to the lowest MCS level. That is, these cases correspond to the case where the number of Sub-MAP groups cannot reach the maximum number even though the grouping is performed in Step S607. In this case, the Sub-MAP processor 520 additionally makes Sub-MAP groups as many as the number M of remaining Sub-MAP groups (where M denotes a difference between the maximum number and the number of Sub-MAP groups made with the MAP IEs whose channel quality corresponds to the lowest MCS level). Here, the Sub-MAP processor 520 makes the Sub-MAP groups of the maximum FEC block size with the remaining MAP IEs except for the MAP IEs whose channel quality corresponds to the lowest MCS level, so as to reduce a size of the entire MAP message.

[61] Referring to FIG. 7, the list storing means 521 receives a list of remaining MAP IEs after the update in Step S608 (Step S621). In this case, the list storing means 521 receives not only the CID information and MCS level information for the MAP IEs, but also the number N of Sub-MAP groups made in Steps S601 to S608.

[62] If the number M of remaining Sub-MAPs is at least 1, the reduction gain processing means 525 selects a MAP size reduction factor for maximally reducing the total MAP size, decreases the number M of remaining Sub-MAP groups, and groups MAP IEs corresponding to the MAP size reduction factor into Sub-MAP groups having the maximum FEC block size (Steps S623-S625). Thereafter, the list storing means 521 deletes, from the list, the MAP IEs grouped in Step S625 (Step S626). For example, if the selected MAP size reduction factor is an MCS level with 64QAM 1/2, since the MAP IEs whose MCS level is higher than this MCS level are all grouped into Sub- MAP groups at the MCS level with 64QAM 1/2, the list storing means 521 deletes all of the MAP IEs whose MCS level is higher than 64QAM 1/2. By doing so, even though the Sub-MAP processor 520 cannot make the maximum number of Sub-MAP groups with the MAP IEs whose channel quality corresponds to the lowest MCS level, the Sub-MAP processor 520 can determine a MAP size reduction factor capable of maximally reducing the total MAP size for the remaining Sub-MAP groups, and group the MAP IEs whose channel equality corresponds to the determined MAP size reduction factor, into Sub-MAP groups of the maximum FEC block size.

[63] Through the entire process, the MAP IEs for Sub-MAP generation can be grouped into the maximum number of Sub-MAP groups of the maximum FEC block size, and thereafter, the Sub-MAP generator 530 generates Sub-MAP messages with the grouped MAP IEs using the Sub-MAP Pointer IE.

[64] FIG. 8 is a diagram illustrating system-level simulation results on the Sub-MAP generated according to the present invention and the conventional Normal MAP, and shown are error probabilities for the Sub-MAP and the Normal MAP with respect to a distance between a BS and an MS.

[65] Referring to FIG. 8, it can be appreciated that as the distance increases, error probabilities for both the Sub-MAP and the Normal MAP increase, but a difference in error probability between the Sub-MAP and the Normal MAP noticeably increases. In the example shown, the case of transmitting a frame using the proposed Sub-MAP shows an error probability reduction of approximately 33%, compared with the case of transmitting a frame using the Normal MAP.

[66] 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.

Claims

[1] A method for generating a MAP message in a wireless communication system supporting Orthogonal Frequency Division Multiple Access (OFDMA), the method comprising:

(a) determining a MAP Information Element (IE) based on Connection Identifier (CID) information and Modulation and Coding Scheme (MCS) level information for each Mobile Station (MS);

(b) grouping the MAP IEs into Sub-MAP groups having a maximum Forward Error Correction (FEC) block size until the number of Sub-MAP groups reaches the maximum number of Sub-MAP messages that can be generated in one frame; and

(c) generating Sub-MAP messages with the MAP IEs of the Sub-MAP groups.

[2] The method of claim 1, wherein the step (b) composes: preferentially grouping lowest MCS level MAP IEs among the MAP IEs into Sub-MAP groups having the maximum FEC block size.

[3] The method of claim 2, further comprising: when the number of Sub-MAP groups including the lowest MCS level MAP IEs reaches the maximum number of Sub-MAP messages, regrouping the MAP IEs into Sub-MAP groups having the maximum FEC block size for optimization.

[4] The method of claim 2, further comprising: when the number of Sub-MAP groups is less than the maximum number of Sub- MAP messages and a total size of the lowest MCS level MAP IEs is less than the maximum FEC block size, additionally grouping the remaining MAP IEs except for the lowest MCS level MAP IEs, into Sub-MAP groups having the maximum FEC block size.

[5] The method of claim 4, wherein the number of Sub-MAP groups including the remaining MAP IEs is equal to a difference between the maximum number of Sub-MAP messages and the number of Sub-MAP groups including the lowest MCS level MAP IEs.

[6] The method of claim 4, further comprising: selecting a MAP size reduction factor having a maximum reduction gain according to an MCS level or a Reduced CID (RCID) type, for the remaining MAP IEs, and grouping MAP IEs corresponding to the selected MAP size reduction factor into Sub-MAP groups having the maximum FEC block size.

[7] The method of claim 5, further comprising: when the difference is greater than 1, grouping MAP IEs selected based on the MCS level among the remaining MAP IEs into Sub-MAP groups having the maximum FEC block size, and grouping MAP IEs selected based on the RCID type among the remaining MAP IEs into Sub-MAP groups having the maximum FEC block size.

[8] The method of claim 5, further comprising: when the difference is 1, comparing a reduction gain of the MAP message obtained by grouping MAP IEs selected based on the MCS level among the remaining MAP IEs into Sub-MAP groups having the maximum FEC block size, with a reduction gain obtained by grouping MAP IEs selected based on the RCID type among the remaining MAP IEs into Sub-MAP groups having the maximum FEC block size, and grouping the MAP IEs corresponding to the maximum reduction gain into Sub-MAP groups having the maximum FEC block size.

[9] The method of claim 1, wherein the maximum FEC block size is an FEC block size whose FEC block error rate (BLER) is minimized in case of Convolutional Turbo Codes (CTC).

[10] The method of claim 4, wherein the lowest MCS level corresponds to Quadrature

Phase Shift Keying (QPSK) 1/2 with repetition 6.

[11] An apparatus for generating a MAP message in a wireless communication system supporting Orthogonal Frequency Division Multiple Access (OFDMA), the apparatus comprising: a controller for determining MAP Information Elements (IEs) to be included in

MAP of a transmission frame, and controlling the MAP IEs to include

Connection Identifier (CID) information and Modulation and Coding Scheme

(MCS) level information; a Sub-MAP processor for comparing a total size of MAP IEs corresponding to the lowest MCS level in channel quality among the MAP IEs, with a preset maximum Forward Error Correction (FEC) block size, and grouping the MAP

IEs into Sub-MAP groups having the maximum FEC block size according to the comparison result; and a Sub-MAP generator for generating Sub-MAP messages with the MAP IEs of the Sub-MAP groups.

[12] The apparatus of claim 11, wherein the Sub-MAP processor preferentially groups

MAP IEs corresponding to the lowest MCS level in channel quality, into the Sub-MAP groups.

[13] The apparatus of claim 11, wherein the Sub-MAP processor groups the MAP IEs into Sub-MAP groups having the maximum FEC block size until the number of Sub-MAP groups reaches the maximum number of Sub-MAP messages that can be generated in one frame.

[14] The apparatus of claim 11, wherein the lowest MCS level corresponds to Quadrature Phase Shift Keying (QPSK) 1/2 with repetition 6.

[15] The apparatus of claim 11, wherein the maximum FEC block size is an FEC block size whose FEC block error rate (BLER) is minimized in case of Con- volutional Turbo Codes (CTC).

[16] The apparatus of claim 11, wherein the Sub-MAP processor comprises size comparison means for comparing a total size of the MAP IEs corresponding to the lowest MCS level in channel quality, with the maximum FEC block size.

[17] The apparatus of claim 11, wherein the Sub-MAP processor comprises Sub-MAP grouping means for preferentially grouping MAP IEs corresponding to the lowest MCS level in channel quality, into the Sub-MAP groups.

[18] The apparatus of claim 17, wherein when the number of Sub-MAP groups is less than the maximum number of Sub-MAP messages and the total size of the lowest MCS level MAP IEs is less than the maximum FEC block size, the Sub-MAP grouping means additionally groups the remaining MAP IEs except for the lowest MCS level MAP IEs into Sub-MAP groups having the maximum FEC block size.

[19] The apparatus of claim 18, wherein the number of Sub-MAP groups including the remaining MAP IEs is equal to a difference between the maximum number of Sub-MAP messages and the number of Sub-MAP groups including the lowest MCS level MAP IEs.

[20] The apparatus of claim 11, wherein the Sub-MAP processor comprises reduction gain processing means for selecting a MAP size reduction factor having a maximum reduction gain according to an MCS level or a Reduced CID (RCID) type, for the remaining MAP IEs except for the lowest MCS level MAP IEs.

[21] An apparatus for generating a MAP message in a wireless communication system supporting Orthogonal Frequency Division Multiple Access (OFDMA), the apparatus comprising: a controller for determining MAP Information Elements (IEs) to be included in

MAP of a transmission frame, and controlling the MAP IEs to include

Connection Identifier (CID) information and Modulation and Coding Scheme

(MCS) level information; a Sub-MAP processor for preferentially grouping MAP IEs corresponding to the lowest MCS level in channel quality among the MAP IEs, into Sub-MAP groups having a maximum Forward Error Correction (FEC) block size; and a Sub-MAP generator for generating Sub-MAP messages with the MAP IEs of the Sub-MAP groups.