A method of performing a polling procedure in a wireless communication system

<u style="single">TECHNICAL FIELD</u>

0001The present invention relates to a wireless communication system, and more particularly, to a method of generating a data block for performing a polling procedure in a wireless communication system, a method of transmitting data and a method of performing a polling procedure.

<u style="single">BACKGROUND ART</u>

0002Various types of data retransmission methods can be used to ensure certainty of data transmission to a receiving side in a wireless communication system. Particularly, the need to use a retransmission method increases when the receiving side should necessarily receive non-real time packet data such as signaling data or TCP/IP data.

0003An example of the data transmission method used in the wireless communication system will be described as follows. The receiving side transmits a status report to a transmitting side to report that at least one or more data blocks transmitted from the transmitting side have been successfully received. The transmitting side retransmits data blocks that the receiving side has failed to receive, to the receiving side using the status report. For application of the retransmission method, data which have been transmitted once should be stored in a buffer for a certain time period without discard. Accordingly, a transmission buffer and a retransmission buffer are required, wherein data which have never been transmitted to the receiving side are stored in the transmission buffer and data which have been transmitted to the receiving side but need to be on standby for retransmission are stored in the retransmission buffer.

0004The transmitting side can request the receiving side to transmit the status report. This procedure is referred to as a polling procedure. If the status report transmitted from the receiving side is lost during transmission or the receiving side does not transmit the status report to the transmitting side timely, the transmitting side can perform the polling procedure. Alternatively, the transmitting side can perform the polling procedure periodically.

<u style="single">DISCLOSURE OF THE INVENTION</u>

0005A transmitting side has to use additional radio resources to perform a polling procedure. Accordingly, for efficient use of radio resources, the polling procedure should be prevented from being used unnecessarily. To this end, reasonable standards as to when the transmitting side should perform the polling procedure are required.

0006Accordingly, the present invention is directed to a method of generating a data block for performing a polling procedure in a wireless communication system, a method of transmitting data and a method of performing a polling procedure, which substantially obviate one or more problems due to limitations and disadvantages of the related art.

0007An object of the present invention is to provide a method of generating a data block for performing a polling procedure in a wireless communication system, a method of transmitting data and a method of performing a polling procedure, in which the polling procedure is performed while radio resources are being used efficiently.

0008Another object of the present invention is to provide a method of generating a data block for performing a polling procedure in a wireless communication system, a method of transmitting data and a method of performing a polling procedure, in which a transmitting side performs the polling procedure timely to prevent communication from being stopped unexpectedly.

0009In a wireless communication system, a data retransmission function is performed by a specific protocol layer. To perform the data retransmission function, the protocol layer is equipped with a transmission buffer and a retransmission buffer. The protocol layer can determine whether to perform a polling procedure considering statuses of the transmission buffer and the retransmission buffer, i.e., the amount of data stored in the transmission buffer and the retransmission buffer.

0010In one aspect of the present invention, the protocol layer performs the polling procedure for requesting a receiving side to transmit a status report if there are no data to be transmitted to the receiving side in both the transmission buffer and the retransmission buffer. When determining whether there are no data to be transmitted to the receiving side in the retransmission buffer, it is preferable that a data block for which retransmission request information is not received from the receiving side is excluded.

0011In another aspect of the present invention, the protocol layer performs the polling procedure considering the amount of data transmitted to the receiving side. Namely, the protocol layer performs the polling procedure if the amount of data transmitted to the receiving side reaches a certain level or greater. This procedure can be performed repeatedly.

0012According to the present invention, radio resources can efficiently be used during the polling procedure, and the transmitting side can perform the polling procedure timely, whereby communication can be prevented from being stopped unexpectedly.

<u style="single">BRIEF DESCRIPTION OF THE DRAWINGS</u>

0013The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a diagram illustrating a network structure of an E-UMTS (Evolved Universal Mobile Telecommunications System);</li><li><figref idref="f0002">FIG. 2</figref> is a schematic view illustrating an E-UTRAN (Evolved Universal Terrestrial Radio Access Network);</li><li><figref idref="f0003">FIG. 3A</figref> and <figref idref="f0004">FIG. 3B</figref> are diagrams illustrating a structure of a radio interface protocol between a user equipment (UE) and E-UTRAN, in which <figref idref="f0003">FIG. 3A</figref> is a schematic view of a control plane protocol and <figref idref="f0004">FIG. 3B</figref> is a schematic view of a user plane protocol;</li><li><figref idref="f0005">FIG. 4</figref> is a diagram illustrating an example of a functional block of RLC AM entity;</li><li><figref idref="f0006">FIG. 5</figref> is a diagram illustrating a basic structure of AMD PDU;</li><li><figref idref="f0007">FIG. 6</figref> is a flow chart illustrating a procedure according to one embodiment of the present invention;</li><li><figref idref="f0008">FIG. 7</figref> is a diagram illustrating the embodiment of <figref idref="f0007">FIG. 6</figref> in view of another aspect; and</li><li><figref idref="f0009">FIG. 8</figref> is a diagram illustrating another embodiment of the present invention.</li></ul>

<u style="single">BEST MODE FOR CARRYING OUT THE INVENTION</u>

0014Hereinafter, structures, operations, and other features of the present invention will be understood readily by the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Embodiments described later are examples in which technical features of the present invention are applied to an E-UMTS (Evolved Universal Mobile Telecommunications System). However, it should be noted that an embodiment of the present invention can be applied to a wireless communication system other that the E-UMTS.

0015<figref idref="f0001">FIG. 1</figref> is a diagram illustrating a network structure of an E-UMTS. An E-UMTS is a system evolving from the conventional WCDMA UMTS and its basic standardization is currently handled by the 3GPP (3^rd Generation Partnership Project). The E-UMTS can also be called an LTE (Long Term Evolution) system.

0016Referring to <figref idref="f0001">FIG. 1</figref>, an E-UTRAN includes base stations (hereinafter, referred to as 'eNode B' or 'eNB'), wherein respective eNBs are connected with each other through X2 interface. Also, each of eNBs is connected with a user equipment (UE) through a radio interface and connected with EPC (Evolved Packet Core) through S 1 interface. The EPC includes a mobility management entity/system architecture evolution (MME/SAE) gateway.

0017Layers of a radio interface protocol between a user equipment and a network can be classified into a first layer L1, a second layer L2 and a third layer L3 based on three lower layers of OSI (open system interconnection) standard model widely known in communication systems. A physical layer belonging to the first layer L1 provides an information transfer service using a physical channel. A radio resource control (hereinafter, abbreviated as 'RRC') located at the third layer plays a role in controlling radio resources between the user equipment and the network. For this, the RRC layer enables RRC messages to be exchanged between the UE and the network. The RRC layer can be distributively located at network nodes including Node B, an AG and the like or can be independently located at either the Node B or the AG.

0018<figref idref="f0002">FIG. 2</figref> is a schematic view illustrating an E-UTRAN (Evolved Universal Terrestrial Radio Access Network). In <figref idref="f0002">FIG. 2</figref>, a hatching part represents functional entities of a user plane, and a non-hatching part represents functional entities of a control plane.

0019<figref idref="f0003">FIG. 3A</figref> and <figref idref="f0004">FIG. 3B</figref> illustrate a structure of a radio interface protocol between the user equipment (UE) and the E-UTRAN, in which <figref idref="f0003">FIG. 3A</figref> is a schematic view of a control plane protocol and <figref idref="f0004">FIG. 3B</figref> is a schematic view of a user plane protocol. Referring to <figref idref="f0003">FIG. 3A</figref> and <figref idref="f0004">FIG. 3B</figref>, a radio interface protocol horizontally includes a physical layer, a data link layer, and a network layer, and vertically includes a user plane for data information transfer and a control plane for signaling transfer. The protocol layers in <figref idref="f0003">FIG. 3A</figref> and <figref idref="f0004">FIG. 3B</figref> can be classified into L1 (first layer), L2 (second layer), and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.

0020The physical layer as the first layer provides an information transfer service to an upper layer using physical channels. The physical layer (PHY) is connected to a medium access control (hereinafter, abbreviated as 'MAC') layer above the physical layer via transport channels. Data are transferred between the medium access control layer and the physical layer via the transport channels. Moreover, data are transferred between different physical layers, and more particularly, between one physical layer of a transmitting side and the other physical layer of a receiving side via the physical channels. The physical channel of the E-UMTS is modulated in accordance with an orthogonal frequency division multiplexing (OFDM) scheme, and time and frequency are used as radio resources.

0021The medium access control (hereinafter, abbreviated as 'MAC') layer of the second layer provides a service to a radio link control (hereinafter, abbreviated as 'RLC') layer above the MAC layer via logical channels. The RLC layer of the second layer supports reliable data transfer. In order to effectively transmit data using IP packets (e.g., IPv4 or IPv6) within a radio-communication period having a narrow bandwidth, a PDCP layer of the second layer (L2) performs header compression to reduce the size of unnecessary control information.

0022A radio resource control (hereinafter, abbreviated as `RRC') layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers (hereinafter, abbreviated as 'RBs') to be in charge of controlling the logical, transport and physical channels. In this case, the RB means a service provided by the second layer for the data transfer between the user equipment and the UTRAN.

0023Examples of downlink transport channels carrying data from the network to the user equipments include a broadcast channel (BCH) carrying system information, a paging channel (PCH) carrying paging message, and a downlink shared channel (SCH) carrying user traffic or control messages. The traffic or control messages of a downlink multicast or broadcast service can be transmitted via the downlink SCH or an additional downlink multicast channel (MCH). Meanwhile, examples of uplink transport channels carrying data from the user equipments to the network include a random access channel (RACH) carrying an initial control message and an uplink shared channel (UL-SCH) carrying user traffic or control message.

0024Examples of logical channels located above the transport channels and mapped with the transport channels include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic channel (MTCH).

0025As described above, the RLC layer of the second layer supports reliable data transfer. Also, the RLC layer serves to perform segmentation and/or concatenation for data received from its upper layer to control a size of the data so that the lower layer can transmit the data to a radio interval. Also, in order to ensure various quality of services (QoS) required by each radio bearer, the RLC layer of the second layer provides three types of operation modes, transparent mode (TM), un-acknowledged mode (UM), and an acknowledged mode (AM). Particularly, the AM RLC layer performs a retransmission function through an automatic repeat and request (ARQ) function for reliable data transmission. Hereinafter, the UM mode and the AM mode of the RLC layer will be described in more detail.

0026The UM RLC layer transmits PDUs by adding a PDU header to each PDU, so that the receiving side can identify what PDU has been lost during transmission, wherein the PDU header includes a sequence number (hereinafter, abbreviated as "SN"). In accordance with this function, the UM RLC layer mainly serves to transmit broadcast/multicast data or real-time data such as voice (for example, VoIP) or streaming of a packet service domain (hereinafter, abbreviated as "PS domain") in a user plane. Also, the UM RLC layer serves to transmit RRC message, which does not need acknowledgement, among RRC messages transmitted to a specific user equipment or a specific user equipment group within a cell, in a control plane.

0027Like the UM RLC layer, the AM RLC layer constitutes RLC PDUs by adding a PDU header including SN thereto. However, the AM RLC layer is different from the UM RLC layer in that the receiving side performs acknowledgement in response to the PDUs transmitted from the transmitting side. The reason why the receiving side performs acknowledgement in the AM RLC layer is to request the transmitting side to re-transmit PDU which the receiving side has not received. This retransmission function is a main feature of the AM RLC layer. Accordingly, the AM RLC layer is to ensure error-free data transmission through re-transmission. For this reason, the AM RLC layer serves to transmit unreal time packet data such as TCP/IP of the PS domain in the user plane. Also, the AM RLC layer serves to transmit RRC message, which necessarily requires acknowledgement, among the RRC messages transmitted to a specific user equipment within a cell, in the control plane.

0028In view of a directional aspect, the UM RLC layer is used for uni-directional communication whereas the AM RLC layer is used for bi-directional communication due to a feedback from the receiving side. The UM RLC layer is also different from the AM RLC layer in view of a structural aspect. Namely, although the UM RLC layer allows one RLC entity to perform a transmission function or a receiving function, the AM RLC layer allows both an entity performing a transmission function and an entity performing a receiving function to exist in one RLC entity.

0029The reason why that the AM RLC layer is complicated is caused by a retransmission function. For retransmission management, the AM RLC entity includes a retransmission buffer in addition to a transmission buffer and uses a transmission and reception window for flow control. The AM RLC entity of the transmitting side performs a polling procedure to request a peer RLC entity of the receiving side to transmit a status report, and the receiving side transmits the status report to the transmitting side to report reception acknowledgement information. Also, the AM RLC entity performs a function constituting a status PDU to transfer the status report.

0030The AM RLC entity supports the aforementioned functions using a plurality of protocol parameters, status parameters, timers, etc. In the AM RLC layer, PDUs used to control transmission of data such as status report or status PDU will be referred to as control PDUs, and PDUs used to transfer user data will be referred to as data PDUs.

0031As described above, the AM RLC entity of the transmitting side includes two buffers, i.e., a transmission buffer and a retransmission buffer. Data which have not yet been included in RLC PDU, among data transferred from an upper entity, are stored in the transmission buffer. RLC PDU transferred to a lower entity is stored in the retransmission buffer until the receiving side acknowledges that the RLC PDU has been successfully received therein.

0032<figref idref="f0005">FIG. 4</figref> is a diagram illustrating an example of a functional block of the RLC AM entity.

0033Referring to <figref idref="f0005">FIG. 4</figref>, an RLC SDU (Service Data Unit) transferred from the upper layer (RRC layer or PDCP sub-layer) is stored in a transmission buffer 41. A segmentation/concatenation module 42 performs segmentation and/or concatenation for at least one RLC SDU transferred from the transmission buffer 41. Segmentation and/or concatenation is performed at a specific transmission opportunity in accordance with a transport block size reported from the lower layer. As a result, the RLC PDU generated by the RLC AM entity can have a size desired by the lower layer. An RLC header adding module 43 adds an RLC header to a data block transferred from the segmentation/concatenation module 42. An RLC AMD PDU is generated as the RLC PDU header is added to the data block.

0034<figref idref="f0006">FIG. 5</figref> is a diagram illustrating a basic structure of the AMD PDU. The AMD PDU includes a PDU header part and a data field part. The header can include a fixed part and an extended part, wherein the fixed part exists in every AMD PDU and the extended part is included in the AMD PDU only if necessary. The extended part is included in the AMD PDU if one or more data field elements exist in the AMD PDU.

0035The fixed part includes a D/C field, a re-segmentation flag (RF) field, a polling (P) field, a framing info (FI) field, an extension bit (E) field and a sequence number (SN) field. The D/C field includes information identifying whether a corresponding AMD PDU is a data PDU or a control PDU. The RF field includes information indicating whether a corresponding RLC PDU is a single perfect AMD PDU or a part of another AMD PDU. The polling field includes information indicating whether the AM RLC entity of the transmitting side will request the peer AM RLC entity of the receiving side to transmit status report. The FI field includes information indicating that the RLC SDU included in the AMD PDU has been segmented from a start part and/or an end part of the data field. The E field includes information indicating whether the data field starts behind the fixed part or whether additional E field and LI field follow behind the fixed part. The SN field includes a sequence number of the AMD PDU.

0036Referring to <figref idref="f0005">FIG. 4</figref> again, the AMD PDU generated as the header is added by the RLC header adding module 43 is transferred to the lower layer, for example, a MAC layer. Before the AMD PDU is transferred to the lower layer, additional procedure such as ciphering can be performed for the AMD PDU if necessary. The AMD PDU transferred to the lower layer is stored in the retransmission buffer 44 to perform a retransmission function.

0037If the RLC AM entity performs a receiving function, a routing module 46 performs routing for the received RLC PDU in accordance with a type of the RLC PDU, so as to transfer a control PDU to an RLC control module 45 and an AMD PDU to a receiving buffer/HARQ reordering module 47. The receiving buffer/HARQ reordering module 47 stores AMD PDUs transferred from the routing module 46, and aligns them in the order of SN if they are not received in the order of SN. An RLC header removing module 48 removes the RLC header from the AMD PDU and transfers the resultant data to an SDU reassembly module 49. The SDU reassembly module 49 reassembles at least one or more RLC SDUs using the data transferred from the RLC header removing module and then transfers the resultant data to the upper layer.

0038The RLC AM entity of the receiving side transfers the status report to the transmitting side through the status PDU to report whether the at least one or more RLC PDUs transmitted from the transmitting side have been successfully received.

0039<figref idref="f0007">FIG. 6</figref> is a flow chart illustrating a procedure according to one embodiment of the present invention. The embodiment of <figref idref="f0007">FIG. 6</figref> relates to an example of determining whether the RLC AM entity performs a polling procedure in accordance with the statuses of the transmission buffer and the retransmission buffer. Namely, if there are no data to be transmitted to the receiving side in both the transmission buffer and the retransmission buffer, the RLC AM entity performs the polling procedure to request the receiving side to transmit the status report. When determining whether there are data to be transmitted to the receiving side in the retransmission buffer, a data block for which retransmission request information is not received from the receiving side is excluded.

0040Referring to <figref idref="f0005">FIG. 4</figref> and <figref idref="f0007">FIG. 6</figref>, the AM RLC entity checks the status of the transmission buffer 41 [S61] and identifies whether data to be transmitted to the receiving side are stored in the transmission buffer 41 [S62]. If the data to be transmitted to the receiving side are stored in the transmission buffer 41, the AM RLC entity does not perform the polling procedure. Namely, the AM RLC entity sets the P field to "0," wherein the P field exists in a header of the AMD PDU to be transmitted to the receiving side [S66]. If the P field receives the AMD PDU set to "0," the receiving side regards that the transmitting side does not request transmission of the status report.

0041If the data to be transmitted to the receiving side are not stored in the transmission buffer 41, i.e., if the transmission buffer 41 is empty, the AM RLC entity checks the status of the retransmission buffer 44 [S63] to identify whether data to be transmitted to the receiving side are stored in the retransmission buffer [S64]. When determining whether the data to be transmitted to the receiving side are stored in the retransmission buffer 44, a data block for which retransmission request information is not received from the receiving side is excluded. In other words, even though at least one RLC PDU is stored in the retransmission buffer 44, if the status report or acknowledgement for the at least one RLC PDU is not received from the receiving side, it is regarded that the retransmission buffer 44 is empty.

0042In step S64, if the data to be transmitted to the receiving side are stored in the retransmission buffer 44, the AM RLC entity does not perform the polling procedure. Namely, the AM RLC entity sets the P field to "0," wherein the P field exists in the header of the AMD PDU to be transmitted to the receiving side [S66].

0043If the data to be transmitted to the receiving side are not stored in the retransmission buffer 44, the AM RLC entity performs the polling procedure. Namely, the AM RLC entity sets the P field to "1," wherein the P field exists in the header of the AMD PDU to be transmitted to the receiving side [S65]. If the P field receives the AMD PDU set to "1", the receiving side regards that the transmitting side requests transmission of the status report, and transmits to the transmitting side the status report for at least one RLC PDU received from the transmitting side.

0044In the embodiment of <figref idref="f0007">FIG. 6</figref>, although the status of the retransmission buffer has been checked after the status of the transmission buffer is checked, this checking order may be changed. Namely, the status of the transmission buffer may be checked after the status of the retransmission buffer is checked. Also, the status of the transmission buffer and the status of the retransmission buffer may simultaneously be checked.

0045<figref idref="f0008">FIG. 7</figref> is a diagram illustrating the embodiment of <figref idref="f0007">FIG. 6</figref> in view of another aspect. In <figref idref="f0008">FIG. 7</figref>, a horizontal axis is a time axis, and a vertical axis represents the amount of data stored in the transmission buffer and the retransmission buffer. Although the transmission buffer is empty at a timing point "A," since data to be transmitted to the receiving side are stored in the retransmission buffer, the polling procedure is not triggered. The data to be transmitted to the receiving side will not remain in the transmission buffer and the retransmission buffer at a timing point "B." At this time, the AM RLC layer performs the polling procedure.

0046There are no data to be transmitted to the receiving side in the transmission buffer at a timing point "C" but at least one RLC PDU is stored in the retransmission buffer. However, if acknowledgements for the at least one RLC PDU stored in the retransmission buffer is not received from the receiving side, it is regarded that there are no data to be transmitted to the receiving side in the retransmission buffer. Accordingly, the RLC AM entity performs the polling procedure even at the timing point "C." Although the retransmission buffer is empty at a timing point "D," since data to be transmitted to the receiving side are stored in the transmission buffer, the RLC AM entity does not perform the polling procedure.

0047According to other embodiments of the present invention, it is considered that the RLC AM entity performs the polling procedure considering the sequence number of the RLC PDU in addition to the status of the transmission buffer and the status of the retransmission buffer. Namely, in a state that data to be transmitted to the receiving side do not remain in the transmission buffer and the retransmission buffer, the polling procedure can be performed for each of the following cases: <ol id="ol0001" compact="compact"><li>1. When an AMD PDU stored in the retransmission buffer is transmitted, in case where the AMD PDU has the highest sequence number among AMD PDUs to be retransmitted;</li><li>2. When an AMD PDU stored in the retransmission buffer is transmitted, in case where the AMD PDU has the highest sequence number among AMD PDUs for which status report indicating that the receiving side has not received successfully the AMD PDUs is received;</li><li>3. When an AMD PDU stored in the retransmission buffer is transmitted, in case where the AMD PDU is generated most recently among AMD PDUs to be retransmitted;</li><li>4. When an AMD PDU stored in the retransmission buffer is transmitted, in case where the AMD PDU is generated most recently among AMD PDUs for which NACKs have been received from the receiving side;</li><li>5. When an AMD PDU is transmitted from the transmission buffer, in case where the AMD PDU is generated most recently;</li><li>6. When an AMD PDU is transmitted from the transmission buffer, in case where data to be transmitted to the receiving side do not remain in the transmission buffer and the retransmission buffer any more;</li><li>7. When an AMD PDU is transmitted from the transmission buffer, in case where neither data to be transmitted to the receiving side nor AMD PDU to be retransmitted remain in the transmission buffer;</li><li>8. When an AMD PDU is transmitted from the transmission buffer, in case where neither data to be transmitted to the receiving side nor AMD PDU waiting for retransmission remain in the transmission buffer;</li><li>9. When an AMD PDU is transmitted from the transmission buffer, in case where data to be transmitted to the receiving side do not remain in the transmission buffer any more and at the same time an AMD PDU for which NACK has been received from the receiving side does not remain in the retransmission buffer;</li><li>10. When an AMD PDU is transmitted from the retransmission buffer, in case where the AMD PDU has the highest sequence number among the AMD PDUs to be retransmitted, and data to be transmitted to the receiving side do not remain in the transmission buffer;</li><li>11. When an AMD PDU is transmitted from the retransmission buffer, in case where the AMD PDU has the highest sequence number among the AMD PDUs for which NACKs have been received from the receiving side, and data to be transmitted to the receiving side do not remain in the transmission buffer; and</li><li>12. When an AMD PDU is transmitted from the retransmission buffer, in case where the AMD PDU is generated most recently among the AMD PDUs to be retransmitted, and data to be transmitted to the receiving side do not remain in the transmission buffer.</li></ol>

0048<figref idref="f0009">FIG. 8</figref> is a diagram illustrating another embodiment of the present invention. In the embodiment of <figref idref="f0009">FIG. 8</figref>, an AM RLC entity performs a polling procedure at the time when sum of data included in AMD PDUs transmitted to the receiving side reaches a threshold value, which is previously set.

0049Referring to <figref idref="f0009">FIG. 8</figref>, supposing that PDU 1 to PDU 5 are transmitted to the receiving side in due order, sum of the data transmitted to the receiving side reaches a threshold value or greater at the time when PDU 5 is transmitted. At this time, the AM RLC entity performs the polling procedure. Namely, the AM RLC entity requests the receiving side to transmit the status report by setting a P field included in a header of PDU 5 to "1".

0050If the polling procedure is performed once, sum of data calculated to trigger the polling procedure is calculated again from the beginning. Namely, in <figref idref="f0009">FIG. 8</figref>, since sum of data exceeds the threshold value at the time when PDU 6 to PDU 13 are transmitted after the polling procedure is performed through PDU 5, the P field included in a header of PDU 13 is set to "1" again.

0051The embodiment of <figref idref="f0009">FIG. 8</figref> can be achieved using a parameter named BYTE_SENT. Namely, BYTE_SENT is initiated to 0, and the RLC AM entity adds a size value of data included in an AMD PDU to BYTE_SENT whenever the AMD PDU is transmitted. The RLC AM entity performs the polling procedure by setting the P field included in the header of the AMD PDU transmitted at the time when BYTE_SENT exceeds the threshold value to "1". If the polling procedure is performed, the RLC AM entity resets BYTE_SENT to "0" and repeats the same procedure.

0052If the size of the data included in the AMD PDU transmitted to the receiving side is added to BYTE_SENT, various methods can be considered with respect to what value is taken as the size of the data. As described above, an AMD PDU includes a header part and a data field part, wherein the header part includes a fixed part and an extended part. Accordingly, a total size of the AMD PDU, a size of the data field part, or the size of the other part excluding the fixed part in the header could be the part added to the value BYTE_SENT.

0053For example, if the size of the data included in the data field part of the AMD PDU is only considered when sum of the size of the data is calculated, the data field is aligned per 1 byte. Accordingly, a counter can be increased per 1 byte of the data field included in each AMD PDU, and the polling procedure can be performed at the time when the counter value calculated for the AMD PDUs transmitted to the receiving side exceeds a predetermined threshold.

0054The aforementioned embodiments are achieved by combination of structural elements and features of the present invention in a predetermined type. Each of the structural elements or features should be considered selectively unless specified separately. Each of the structural elements or features may be carried out without being combined with other structural elements or features. Also, some structural elements and/or features may be combined with one another to constitute the embodiments of the present invention. The order of operations described in the embodiments of the present invention may be changed. Some structural elements or features of one embodiment may be included in another embodiment, or may be replaced with corresponding structural elements or features of another embodiment. Moreover, it will be apparent that some claims referring to specific claims may be combined with another claims referring to the other claims other than the specific claims to constitute the embodiment or add new claims by means of amendment after the application is filed.

0055The embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or their combination. If the embodiment according to the present invention is implemented by hardware, the embodiment of the present invention may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc.

0056If the embodiment according to the present invention is implemented by firmware or software, the method of transmitting and receiving data in the wireless communication system according to the embodiment of the present invention may be implemented by a type of a module, a procedure, or a function, which performs functions or operations described as above. A software code may be stored in a memory unit and then may be driven by a processor. The memory unit may be located inside or outside the processor to transmit and receive data to and from the processor through various means which are well known.

0057It will be apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential characteristics of the invention. Thus, the above embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention should be determined by reasonable interpretation of the appended claims and all change which comes within the equivalent scope of the invention are included in the scope of the invention.

<u style="single">INDUSTRIAL APPLICABILITY</u>

0058The present invention can be used in a wireless communication system such as a mobile communication system or a wireless Internet system.