WO2009028910A1

WO2009028910A1 - Method and system for handshaking in wireless communication system

Info

Publication number: WO2009028910A1
Application number: PCT/KR2008/005098
Authority: WO
Inventors: Kuk-Jin Song
Original assignee: Posdata Co., Ltd.
Priority date: 2007-08-29
Filing date: 2008-08-29
Publication date: 2009-03-05

Abstract

A method and system is provided for performing handshaking in a wireless communication system. The method and system includes sending a Base Station (BS)-initiated Request and data grant information for a response to the BS-initiated Request; and receiving a response to the BS-initiated Request, which is allocated in an Up-Link (UL) burst region indicated by the data grant information, thereby efficiently performing handshaking.

Description

Description Method and system for handshaking in wireless communication system Technical Field

[1] The present invention relates generally to a method and system for performing handshaking between a Base Station (BS) and a Mobile Station (MS) in a wireless communication system, and in particular, to a handshaking method and system in which an MS can efficiently respond to a BS-initiated Request in a wireless communication system. Background Art

[2] In IEEE 802.16d/e, in order for an MS to transmit something to a BS over an Up-

Link (UL) channel, the MS should previously perform a ranging process and a Bandwidth Request (BWR)/GRANT process with the BS before it transmits bursts. Likewise, when an MS receives a request message from a BS, the MS cannot send a response message to the request message until it completes a BWR/GRANT process with the BS. However, if the BS wants the MS to respond to its BS-initiated Request in the next frame or within several frames, the BWR/GRANT process may be inefficient. A detailed description thereof will be given below.

[3] FIGs. 1 and 2 are diagrams illustrating a general Request/Response process between a BS and an MS. Specifically, FIG. 1 illustrates a process in which a BS sends a response to an MS-initiated Request, and FIG. 2 illustrates a process in which an MS sends a response to a BS-initiated Request.

[4] As illustrated in FIG. 1, in the general Request/Response process, a BS can immediately respond to an MS-initiated Request in the next frame.

[5] On the other hand, an MS, as illustrated in FIG. 2, cannot respond to a BS-initiated

Request until it receives a Data Grant from the BS. That is, if the BS sends a BS- initiated Request to the MS (n"¹ frame), the MS performs ranging on the BS ((n+l)"¹ frame), and according thereto, the BS sends a Code Division Multiple Access (CDMA) code to the MS through a CDMA allocation Information Element (IE) ((n+2)^th frame). Then the MS sends a BWR to the BS ((n+3)^th frame), and upon receipt of the BWR, the BS sends a Data Grant to the MS ((n+4)^th frame). Finally, the MS sends a response to the BS-initiated Request ((n+S)"¹ frame).

[6] However, in this conventional technology, the BS cannot receive an MS's response to its BS-initiated Request until at least the 5^th frame, causing an increase in the time required for the BS-initiated Request/Response process.

[7] Since the BWR by the MS is made on a contention basis, it is not guaranteed that the MS can surely obtain a Data Grant in the next frame. In addition, if the above-stated BWR/GRANT process is failed between the MS and the BS, the MS may never send its response to the BS-initiated Request.

[8] Further, since the BS defines no specific priority for the BWR, it cannot know an aim

(or use) of the BWR received from the MS. Accordingly, if a response to the BS- initiated Request is very urgent, the MS may fall in a serious situation. Therefore, there is a demand for a proper handshaking method capable of resolving the above-stated problems for the BS-initiated Request. Disclosure of Invention Technical Problem

[9] 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 handshaking method and system in which an MS can efficiently respond to a BS-initiated Request in a wireless communication system.

[10] It is another object of the present invention to provide a handshaking method and system in which an MS can respond to a BS-initiated Request without performing a BWR/GRANT process in an IEEE 802.16d/e-based wireless communication system.

[11] It is further another object of the present invention to provide a handshaking method and system in which an MS can efficiently respond to a BS-initiated Request by performing a reliable BWR/GRANT process in an IEEE 802.16d/e -based wireless communication system.

Technical Solution

[12] According to one aspect of the present invention, a method is provided for performing handshaking in a wireless communication system. The method includes sending a Base Station (B S) -initiated Request and data grant information for a response to the BS-initiated Request; and receiving a response to the BS-initiated Request, which is allocated in an Up-Link (UL) burst region indicated by the data grant information.

[13] According to another aspect of the present invention, a Base Station (BS) is provided for performing handshaking in a wireless communication system. The BS includes a scheduler for generating a frame including a BS-initiated Request and data grant information for a response to the BS-initiated Request; a transmitter for transmitting the generated frame to a Mobile Station (MS); and a receiver for receiving from the MS a response to the BS-initiated Request, which is allocated in an Up-Link (UL) burst region indicated by the data grant information.

Advantageous Effects

[14] In a wireless communication system, according to the present invention, a BS sends a BS-initiated Request and a Data Grant together so that an MS can send a response in the next frame, making it possible to the MS to rapidly respond to the BS-initiated Request.

[15] In an IEEE 802.16d/e-based wireless communication system, according to the present invention, a BS includes UL burst allocation information in a Request IE during their transmission, so that an MS can rapidly respond to a BS-initiated Request without undergoing a BWR/GRANT process.

[16] In an IEEE 802.16d/e-based wireless communication system, according to the present invention, a BS adaptively generates a frame for a BS-initiated Request according to a channel environment, thereby enabling efficient handshaking between a BS and an MS.

[17] In an IEEE 802.16d/e-based wireless communication system, according to the present invention, a BS includes a CDMA code in a BS-initiated Request during their transmission, so that an MS can rapidly and reliably respond to the BS-initiated

Request.

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 process in which a BS sends a response to an MS- initiated Request;

[20] FIG. 2 is a diagram illustrating a process in which an MS sends a response to a BS- initiated Request;

[21] FIG. 3 is a diagram illustrating a frame structure used in an IEEE 802.16d/e-based wireless communication system;

[22] FIG. 4 is a diagram illustrating a structure of an IEEE 802.16d/e -based BS according to an embodiment of the present invention;

[23] FIG. 5 is a diagram illustrating a structure of a scheduler according to first and second embodiments of the present invention;

[24] FIG. 6 is a diagram illustrating a frame structure according to the first embodiment of the present invention;

[25] FIG. 7 is a flowchart illustrating a frame generation method according to the first embodiment of the present invention;

[26] FIG. 8 is a flowchart illustrating a format of a request message according to the first embodiment of the present invention;

[27] FIG. 9 is a diagram illustrating a frame structure according to the second embodiment of the present invention; [28] FIG. 10 is a diagram illustrating a Request IE format according to the second embodiment of the present invention;

[29] FIG. 11 is a diagram illustrating a handshaking method for a BS-initiated Request according to a third embodiment of the present invention;

[30] FIG. 12 is a diagram illustrating a structure of a scheduler associated with the foregoing handshaking scheme according to the third embodiment of the present invention;

[31] FIG. 13 is a diagram illustrating a frame structure according to the third embodiment of the present invention; and

[32] FIG. 14 is a diagram illustrating a format of a BS-initiated Request message according to the third embodiment of the present invention. Mode for the Invention

[33] 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.

[34] FIG. 3 illustrates a frame structure used in an IEEE 802.16d/e-based wireless communication system.

[35] Referring to FIG. 3, a frame is formed in a time-frequency domain, and while a resource allocation unit of the time domain is an Orthogonal Frequency Division Multiplexing (OFDM) symbol, a resource allocation unit of the frequency domain is a subchannel. The minimum information transmission unit is formed of one Orthogonal Frequency Division Multiple Access (OFDMA) symbol and one subchannel.

[36] Meanwhile, in Time Division Duplex (TDD), the frame is divided into a Down-Link

(DL) subframe formed to transmit data from a BS to an MS, and a UL subframe formed to transmit data from an MS to a BS. Between the DL subframe and the UL subframe exists a Transmit/receive Transition Gap (TTG) which is a guard region. 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 Information Channel (CQICH)) and UL bursts.

[37] Preamble is used for providing time/frequency synchronization to an MS. FCH includes frame configuration information used for decoding DL MAP and UL MAP. DL MAP includes DL MAP IE in which information on positions and uses of the DL bursts that the BS transmits is written. UL MAP includes UL MAP IE in which information on positions and uses of the UL bursts that MSs transmit is written. [38] The BS broadcasts such generated frame to MSs, and each MS receives the frame, decodes each MAP, and then checks if there is any data burst allocated to the MS itself, and if any, the MS decodes the corresponding data bursts depending on MAP.

[39] FIG. 4 is a diagram illustrating a structure of an IEEE 802.16d/e-based BS according to an embodiment of the present invention.

[40] As illustrated in FIG. 4, a BS includes an interface 110, a baseband signal processor

120, a transmitter 130, a receiver 160, a scheduler 150, and an antenna 140. The BS supports TDD, and in this case, its signal processing path can be separated into a reception path and a transmission path.

[41] In the reception path, the receiver 160 receives one or more radio signals that MSs transmit, via the antenna 140, and converts them into baseband signals. For example, for data reception of the BS, the receiver 160 removes noises from the input signal, amplifies the noise-removed signal, down-converts the amplified signal into a baseband signal, and digitalizes the down-converted baseband signal. The baseband signal processor 120 extracts information or data bits from the digitalized signal, and performs demodulation, decoding and error correction processes thereon.

[42] In the transmission path, the interface 110 receives voice, data or control information from a Base Station Controller (BSC)/ Access Control Router (ACR) or a radio network, and the baseband signal processor 120 encodes the voice, data or control information, and transfers its output to the transmitter 130. The transmitter 130 modulates the encoded voice, data or control information into a signal having a desired transmission frequency, amplifies the modulated signal to a level suitable for its transmission, and transmits it over the air via the antenna 140.

[43] The scheduler 150 allocates DL MAP, UL MAP, DL bursts and UL bursts in the frame which is formed of symbols and subchannels for data exchange with MSs, thereby achieving scheduling. Particularly, according to the present invention, the scheduler 150 generates a frame so that an MS can send a response to a BS-initiated Request as fast as possible, thereby ensuring the optimal handshaking. To this end, the present invention proposes i) a Data Grant with Request Message scheme for sending a Data Grant along with a request message, ii) a Request IE with Burst Allocation scheme for sending a Request IE along with burst allocation, and iii) a CDMA Code with Request Message scheme for sending a CDMA code along with a request message.

[44] With reference to FIGs. 5 to 8, a description will now be made of a handshaking scheme according to a first embodiment of the present invention. For reference, the first embodiment of the present invention is related to the Data Grant with Request Message scheme.

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

[46] As illustrated in FIG. 5, the scheduler 150 includes a controller 151, a MAP generator 152, and a burst generator 153.

[47] The controller 151 generates MAP IEs to be separately written in UL MAP and DL

MAP, and determines separate regions where UL bursts and DL bursts are allocated. Specifically, the controller 151 generates a MAP IE (e.g., DL MAP IE) that includes burst use information, MS information (Connection Identifier (CID) information) and burst position information for a BS-initiated Request message. In addition, the controller 151 generates a MAP IE (e.g., UL Data Grant IE) that includes MS information and burst position information for a response message so that a corresponding MS can carry the response message to the BS-initiated Request message on a UL subframe. A detailed operation of the controller 151 will be described in the following embodiments.

[48] The MAP generator 152 generates DL MAP and UL MAP by allocating the MAP

IEs generated by the controller 151 in their corresponding regions of wireless resources formed in the time-frequency domain.

[49] The burst generator 153 allocates corresponding DL bursts in the DL burst allocation region determined by the controller 151.

[50] FIG. 6 is a diagram illustrating a frame structure according to the first embodiment of the present invention, and this represents the Data Grant with Request Message scheme. For reference, since the frame structure of FIG. 6 is similar to the above- described frame structure of FIG. 3, a description of its details will be omitted and only the difference therebetween will be described in brief.

[51] Referring to FIG. 6, in the frame, a BS-initiated Request message is allocated in a predetermined DL burst region, and a DL MAP IE including burst use information, MS information (CID information) and burst position information for the BS-initiated Request message is written in DL MAP. A UL MAP IE (UL Data Grant IE) including MS information and burst position information for a response message is written in UL MAP so that the MS can carry the response message to the BS-initiated Request message on a UL subframe.

[52] FIG. 7 is a flowchart illustrating a frame generation method according to the first embodiment of the present invention.

[53] Referring to FIG. 7, the scheduler 150 generates a DL MAP IE including burst use information, MS information and burst position information for a BS-initiated Request message, and generates a UL MAP IE including MS information and UL burst position information for a response message to receive the response message to the BS-initiated Request message (Step S710). The scheduler 150 includes the DL MAP IE and the UL MAP IE in DL MAP and UL MAP respectively (Step S720), and then generates a frame by allocating the BS-initiated Request message, as a DL burst, in a corresponding region (Step S730).

[54] Specifically, in step S710, the controller 151 generates a MAP IE (e.g., DL MAP IE) including burst use information, MS information (CID information) and burst position information for a request message. That is, the controller 151 writes, in the DL MAP IE, i) a CID indicating to which MS the request message is assigned, ii) a use indicating a purpose of the request message, and iii) a position indicating in which position the corresponding burst is allocated in the DL subframe. In addition, the controller 151 generates a MAP IE (e.g., UL Data Grant IE) including Data Grant information i.e. MS information and burst position information for a response message, so that the response message to the request message can be carried on the UL subframe.

[55] In step S720, the MAP generator 152 generates UL MAP and DL MAP using the generated MAP IEs. That is, the MAP generator 152 generates DL MAP and UL MAP by allocating the MAP IEs generated by the controller 151 in their corresponding regions of wireless resources formed in the time-frequency domain.

[56] In step S730, the burst generator 153 allocates the request message, as a DL burst, in a corresponding DL burst region.

[57] For reference, if the frame is generated as in the foregoing embodiment, even though an MS receives the frame and decodes DL MAP, UL MAP and DL bursts thereof, it cannot know a use of the UL burst region allocated for a response message to the request message. Therefore, in some cases, the MS may allocate UL bursts having another use in the region on which it should carry the response message in the next frame.

[58] In order to prevent this, the controller 151 can add an 'Allocated Response Region Indication' field in a request message, so the MS can carry a response message to the request message on a corresponding UL burst region in the next frame.

[59] FIG. 8 illustrates a format of a request message according to the first embodiment of the present invention.

[60] Referring to FIG. 8, the request message format is defined by adding the 'Allocated

Response Region Indication' field to the normal request message format. The request message in this format is carried on a payload of a Medium Access Control (MAC) Protocol Data Unit (PDU) by the scheduler 150, and this MAC PDU is mapped to DL bursts of a physical layer and then transmitted to an MS. Then the MS decodes the 'Allocated Response Region Indication' field, and if the field is set to, for example, T, the MS can send a response message to the request message to the BS on an assigned UL burst region (i.e., UL burst region designated in the Data Grant information) in the next frame. However, if the field is set to '0', the MS can send the response message to the BS through the Data Grant with Request Message process.

[61] When the BS broadcasts the generated frame, a corresponding MS sends a response message to the request message to the BS on a UL subframe in the next frame. In this manner, the MS can send a response message to the BS-initiated Request message in the next frame.

[62] With reference to FIGs. 5, 9 and 10, a description will now be made of a handshaking scheme according to a second embodiment of the present invention. For reference, the second embodiment of the present invention is related to the Request IE with Burst Allocation scheme.

[63] FIG. 9 is a diagram illustrating a frame structure according to the second embodiment of the present invention, and this represents the Request IE with Burst Allocation scheme.

[64] Referring to FIGs. 5 and 9, the scheduler 150 generates a frame by including a BS- initiated Request in UL MAP, not as DL control data but as a UL MAP IE (i.e., 'Request IE' in this embodiment). The Request IE includes a UL burst profile, and this UL burst profile defines characteristics (e.g., physical transmission properties such as encoding and modulation information) of a physical layer used for UL bursts, with which the MS will make a response.

[65] For this, the controller 151, as shown in FIG. 10, generates the Request IE in the form of 'UL MAP Extended UIUC IE'. Further, the MAP generator 152 generates UL MAP using the Request IE. That is, the MAP generator 152 generates UL MAP by allocating the Request IE generated by the controller 151 in a corresponding region of wireless resources formed in the time-frequency domain.

[66] FIG. 10 is a diagram illustrating a Request IE format according to the second embodiment of the present invention.

[67] Referring to FIG. 10, the Request IE includes an 'Extended UIUC (Uplink Interval

Usage Code)' field, a 'Length' field, a 'Request Type' field, a 'Response Included' field, and a 'TLV Encoded Information' field, and based on this, the BS describes a UL burst profile for the response message. The 'Extended UIUC field, which is composed of 4 bits, can map 16 kinds of request information. The 'Length' field, which is composed of variable bits as length information, can variably allocate its length. The 'Request Type' field, which is composed of 2 bits, can identify 4 request types. The 'Response Included' field, which is composed of 1 bit, indicates, as Data Grant information, whether there is a need for a response to the request. The 'TLV Encoded Information' field, having a variable size, includes various attribute information for the Request IE in the TLV (Type/Length/Value) form.

[68] According to this embodiment, if especially the 'Response Included' field is set to, for example, T, it indicates a need for an MS's response to the request. In this case, the Request IE further includes a 'duration' field, a 'UIUC field, and a 'Repetition Coding Indication' field, and the BS describes a UL burst profile for the response message in these fields. For example, the 'duration' field, which is composed of 6 bits, indicates an interval where an OFDM slot is allocated. The 'UIUC field, which is composed of 4 bits, indicates modulation information (e.g., Forward Error Correction (FEC) coding type and modulation type) for allocated bursts. The 'Repetition Coding Indication' field, which is composed of 2 bits, indicates repetition coding information for allocated bursts.

[69] If the BS generates the 'Request IE' as a UL MAP IE in this way and broadcasts the frame, the corresponding MS sends a response message to the request message to the BS on a UL subframe in the next frame. In this manner, the MS can send a response message to the BS-initiated Request message in the next frame.

[70] For reference, since the Data Grant with Request Message scheme according to the first embodiment of the present invention maps a request message to DL bursts, the MS should undergo again a process of decoding DL bursts after a MAP decoding process.

[71] On the other hand, in the Request IE with Burst Allocation scheme according to the second embodiment of the present invention, the MS only needs to decode UL MAP, and instead, the MAP size may increase. That is, in the first embodiment of the present invention, the BS can transmit the request message (in the DL burst form) by applying a Modulation and Coding Scheme (MCS) level of 64-ary Quadrature Amplitude Modulation (64 QAM) 5/6 according to the channel condition. However, in the second embodiment of the present invention, since the BS modulates UL MAP including the Request IE with an MCS level of Quadrature Phase Shift Keying (QPSK) 1/2 repetition 6, a size of MAP including the Request IE becomes larger.

[72] Therefore, it is preferable to selectively apply the foregoing schemes according to a channel environment (e.g., Quality of Service) for the MS. For example, the BS can generate a frame by applying the Data Grant with Request Message scheme, for an MS having a good channel environment, and can generate a frame by applying the Request IE with Burst Allocation scheme, for an MS having a poor channel environment.

[73] With reference to FIGs. 11 to 14, a description will now be made of a handshaking scheme according to a third embodiment of the present invention. For reference, the third embodiment of the present invention is related to the CDMA Code with Request Message scheme.

[74] FIG. 11 is a diagram illustrating a handshaking method for a BS-initiated Request according to the third embodiment of the present invention.

[75] Referring to FIG. 11, a BS sends a particular allocated CDMA code to an MS along with a BS-initiated Request message in an n"¹ frame. Subsequently, the MS decodes the request message and the CDMA code, and then sends a BWR to the BS for a response to the request message in an (n+l)"¹ frame. At this point, the MS sends the received CDMA code to the BS together. Then, the BS sends a Data Grant for a corresponding BWR to the MS in an (n+2)¹¹¹ frame, determining that the BWR transmitted along with the CDMA code is a BWR for a response to the BS-initiated Request message. Then, the MS sends a response to the request message to the BS on a UL burst region allocated through the Data Grant in an (n+S)"¹ frame.

[76] As described above, the BS can be convinced that it will receive a response from the

MS within a predetermined frame by sending a particular CDMA code along with the request message, making it possible to perform a reliable BS-initiated Request/ Response process. Herein, the CDMA code can be made in the form of one Pseudo Noise (PN) code by dividing a sequence generated through a Pseudo Random Binary Sequence (PRBS) by 144 bits. In this case, the number of available CDMA codes is 256, and among them, 48 CDMA codes are used in the present invention. Therefore, the CDMA code is formed of 8 bits.

[77] FIG. 12 is a diagram illustrating a structure of a scheduler associated with the foregoing handshaking scheme according to the third embodiment of the present invention.

[78] As illustrated in FIG. 12, the scheduler 150 includes a controller 151, a MAP generator 152, a burst generator 153, and a CDMA code checker 154. For reference, the controller 151, the MAP generator 152 and the burst generator 153 are associated with the transmission path, and the controller 151 and the CDMA code checker 154 are associated with the reception path.

[79] In the transmission path, the controller 151 generates a MAP IE (e.g., DL MAP IE) that includes burst use information, MS information (CID information) and burst position information for a BS-initiated Request message. The MAP generator 152 generates DL MAP and UL MAP by allocating the MAP IE generated by the controller 151 in a predetermined region of wireless resources formed in the time-frequency domain. The burst generator 153 allocates the corresponding DL bursts in the DL burst region determined by the controller 151.

[80] For reference, since MAP generally undergoes broadcasting, if Carrier- to-interference and Noise Ratio (CINR) information of MSs and MCS level information based on the CINR information are greater than or equal to a predetermined level during generation of DL MAP, the MAP generator 152 generates the DL MAP in a sub-MAP structure, and if the CINR information and MCS level information are less than the predetermined level, the MAP generator 152 generates the DL MAP in a normal MAP structure.

[81] Specifically, the scheduler 150 receives CINR of MSs, and determines if an MCS level corresponding to the CINR is greater than or equal to a reference MCS level. If the MCS level is greater than or equal to the reference MCS level, the scheduler 150, considering that their channel environment is good, groups the MSs having the CINR into a first sub-MAP group. In addition, the scheduler 150 searches for a Reduced Connection Identifier (RCID) type - RCID 11, RCID 7 and RCID 3 - having the highest CID reduction gain for the MSs, selects the RCID type, and groups the MSs corresponding to the a particular RCID type having the highest reduction gain into a second sub-MAP group. The scheduler 150 checks the presence/absence of at least one grouped MS in the first sub-MAP group and the second sub-MAP group, and in the presence of at least one grouped MS, the scheduler 150 determines whether to apply the sub-MAP. However, if there is no grouped MS, the scheduler 150 does not apply the sub-MAP since using the normal MAP is advantageous in reducing overhead. Subsequently, the scheduler 150 calculates an overhead rate reduced by the groups in the case where the sub-MAP is applied, and an overhead rate reduced by the groups in the case where the sub-MAP is not applied. Thereafter, if the overhead rate reduced by the groups in the case where the sub-MAP is applied, is greater than the overhead rate reduced by the groups in the case where the sub-MAP is not applied, the scheduler 150 generates the sub-MAP.

[82] In the reception path, the CDMA code checker 154 checks if the CDMA code included in a BWR received from an MS is identical to the CDMA code it sent along with the BS-initiated Request. If it is checked that there is a BWR including the CDMA code that the BS sent along with the request message, the controller 151 generates UL MAP including a Data Grant IE for the corresponding BWR.

[83] FIG. 13 is a diagram illustrating a frame structure according to the third embodiment of the present invention, and this represents the CDMA Code with Request Message scheme. For reference, since the frame structure of FIG. 13 is similar to the above- stated frame structure of FIG. 3, a description of its details will be omitted and only the difference therebetween will be described in brief.

[84] Referring to FIG. 13, in the frame, a BS-initiated Request message is allocated in a predetermined DL burst region, and a DL MAP IE including burst use information, MS information (CID information) and burst position information for the BS-initiated Request message is written in DL MAP. In the request message, a particular CDMA code is included so that the MS can request a bandwidth for a response to the request message.

[85] FIG. 14 is a diagram illustrating a request message format according to the third embodiment of the present invention.

[86] Referring to FIG. 14, the request message format is defined by adding a 'Ranging

Code Included' field and a 'Ranging Code' field to the general request message format. The request message in this format is carried on a payload of a MAC PDU by the scheduler 150, and this MAC PDU is mapped to DL bursts of a physical layer and then transmitted to an MS. In this case, if the 'Ranging Code Included' field is set to, for example, T, the MS can perform a BWR process for a response to the corresponding request message, and the 'Ranging Code' field includes a ranging code (i.e., CDMA code) for the BWR.

[87] The MS receives such generated frame, and then decodes DL MAP and the corresponding DL burst. Based on this, the MS receives the BS-initiated Request message and acquires a CDMA code. Thereafter, the MS sends the acquired CDMA code to the BS on a control symbol for a ranging channel of the UL subframe shown in FIG. 13. In reply thereto, the BS receives the BWR sent along with the CDMA code, and sends Data Grant information for the corresponding BWR to the MS, determining that the received BWR is a BWR for a response to its request message. Then the MS sends a response to the request message to the BS on a UL burst region designated in the Data Grant information. A reliable BS-initiated Request/Response process is performed by the foregoing process.

[88] 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 handshaking in a wireless communication system, the method comprising:

(a) sending a Base Station (B S) -initiated Request and data grant information for a response to the BS-initiated Request; and

(b) receiving a response to the BS-initiated Request, which is allocated in an Up- Link (UL) burst region indicated by the data grant information.

[2] The method of claim 1, wherein position information for the BS-initiated

Request is generated as a Down-Link (DL) MAP Information Element (IE) of a first frame, and the data grant information is generated as a UL MAP IE of the first frame.

[3] The method of claim 2, wherein the BS-initiated Request is allocated in a DL burst region of the first frame, which is indicated by the DL MAP IE of the first frame.

[4] The method of claim 2, wherein the BS-initiated Request includes an indicator field indicating inclusion of the data grant information.

[5] The method of claim 1, wherein the BS-initiated Request and the data grant information are generated as a UL MAP IE included in a UL MAP of a first frame.

[6] The method of claim 1, wherein a frame including a response to the BS-initiated

Request is a next frame of a frame including the BS-initiated Request.

[7] The method of claim 1, wherein the step (a) comprises:

(al) sending to a Mobile Station (MS) a first frame including a BS-initiated

Request and a Code Division Multiple Access (CDMA) code;

(a2) receiving from the MS a second frame in which a Bandwidth Request

(BWR) is included; and

(a3) checking if the CDMA code exists in the BWR, and if the CDMA code exists, sending to the MS a third frame including data grant information for a response to the BS-initiated Request in response to the BWR.

[8] The method of claim 7, wherein the BS-initiated Request includes a 'ranging code included' field indicating inclusion of the CDMA code, and a 'ranging code' field in which the CDMA code is allocated.

[9] The method of claim 8, wherein in the step (a2), the MS checks the 'ranging code included' field of the BS-initiated Request, and if the 'ranging code included' field is set to a predetermined value, the MS includes in the BWR the CDMA code in the 'ranging code' field of the BS-initiated Request, and sends the BWR to the BS.

[10] The method of claim 7, wherein the CDMA code is made in a form of one Pseudo Noise (PN) code by dividing a sequence generated through a Pseudo Random Binary Sequence (PRBS) by 144 bits.

[11] The method of claim 7, wherein a DL MAP of the first frame is formed in a sub-

MAP structure if Carrier-to-interference and Noise Ratio (CINR) information of the MS and Modulation and Coding Scheme (MCS) level information based on the CINR information are greater than or equal to a predetermined level, and the DL MAP of the first frame is formed in a normal MAP structure if the CINR information and the MCS level information are less than the predetermined level.

[12] The method of claim 7, wherein the first frame is the next frame of the second frame and the second frame is the next frame of the third frame.

[13] A Base Station (BS) for performing handshaking in a wireless communication system, the BS comprising: a scheduler for generating a frame including a BS-initiated Request and data grant information for a response to the BS-initiated Request; a transmitter for transmitting the generated frame to a Mobile Station (MS); and a receiver for receiving from the MS a response to the BS-initiated Request, which is allocated in an Up-Link (UL) burst region indicated by the data grant information.

[14] The BS of claim 13, wherein the scheduler comprises: a controller for generating a Down-Link (DL) MAP Information Element (IE) indicating a position of the BS-initiated Request, and generating the data grant information as a UL MAP IE; a MAP generator for generating a DL MAP and a UL MAP using the DL MAP IE and the UL MAP IE, respectively; and a burst generator for allocating the BS-initiated Request in a DL burst region indicated by the DL MAP IE.

[15] The BS of claim 14, wherein the BS-initiated Request includes an indicator field indicating inclusion of the data grant information.

[16] The BS of claim 13, wherein the scheduler comprises: a controller for generating the BS-initiated Request and the data grant information as a UL MAP IE; and a MAP generator for generating a UL MAP using the UL MAP IE.

[17] The BS of claim 13, wherein the scheduler comprises: a controller for generating a DL MAP IE of a first frame, which indicates a position of the BS-initiated Request including a Code Division Multiple Access (CDMA) code, and generating the data grant information as a UL MAP IE of a third frame in response to a Bandwidth Request (BWR) of a second frame, in which the CDMA code is included; a MAP generator for generating a DL MAP of the first frame by using the DL MAP IE of the first frame, and generating a UL MAP of the third frame using the UL MAP IE of the third frame; and a burst generator for allocating the BS-initiated Request in a DL burst region indicated by the DL MAP IE of the first frame.

[18] The BS of claim 17, wherein the DL MAP of the first frame is formed in a sub-

[19] The BS of claim 17, wherein the first frame is the next frame of the second frame and the second frame is the next frame of the third frame.