Description

APPARATUS AND METHOD FOR TRANSMITTING/ RECEIVING ARQ PACKET IN MOBILE COMMUNICATION

SYSTEM

Technical Field

[1] The present invention relates to a method and an apparatus for reducing overhead of a wireless channel in a mobile communication system which employs ciphering/deciphering and Automatic Retransmission reQuest (ARQ).

Background Art

[2] A Universal Mobile Telecommunication Service (UMTS) system is a 3 (3G) asynchronous mobile communication system that uses a wideband Code Division Multiple Access (CDMA) scheme based on a General Packet Radio Services (GPRS) system and a Global System for Mobile Communications (GSM) system, which are European mobile communication systems.

[3] In the 3 ^rd Generation Partnership Project (3GPP) for standardization of the UMTS, discussion about Long Term Evolution (LTE) is now in progress. The LTE is technology for implementing a high speed packet based telecommunication of about 100 Mbps, targeting its commercialization by the year 2010. To this end, various schemes are being discussed, which include, for example, a scheme of reducing the number of nodes located in a communication line by simplifying the structure of a network, and a scheme of causing wireless protocols to approach a wireless channel as much as possible. In the long run, the structure of the LET is expected to change from the existing 4 node structure to a 2 node or 3 node structure. For example, it may be simplified into a 2 node structure that includes node Bs and anchor nodes.

[4] A node B is connected with a User Equipment (UE) through a wireless channel. In the LTE, all user traffic, including a real-time service such as Voice over Internet Protocol (VoIP), will be serviced through a shared channel. This implies that the LTE requires an apparatus for collecting status information of UEs and performing scheduling based on the collected status information. The node B performs such scheduling operation. As in the High Speed Downlink Packet Access (HSDPA) or Enhanced Uplink Dedicated Channel (EDCH), Hybrid ARQ (HARQ) is also performed between the node B and the UE in the LTE . Because it is impossible to satisfy various Quality of Service (QoS) requirements by using only the HARQ, a separate Automatic Retransmission Request (ARQ) may be performed in a higher layer. In this case, the separate ARQ is also performed between the UE and the node B.

[5] FIG. 2 briefly illustrates a typical HARQ process.

[6] Referring to FlG. 2, a transmitter transmits a HARQ packet to a receiver in step

202. Then, in step 204, the receiver checks if the HARQ packet has an error by using, for example, Cyclic Redundancy Codes (CRC) included in the HARQ packet. When the CRC checking of the HARQ packet results in failure, the receiver determines that the HARQ packet has an error, and then feeds back a HARQ NACK (Negative ACK) signal to the transmitter in step 206. Then, in step 208, the transmitter retransmits the HARQ packet in response to the NACK signal. In step 210, the receiver performs CRC checking of the retransmitted packet. When the CRC checking of the retransmitted packet results in success, the receiver feeds back a HARQ ACK signal to the transmitter in step 212. Then, in step 214, the transmitter transmits a new HARQ packet to the receiver.

[7] In order to prevent divulgence of user data, the user data must be ciphered before being transmitted. A ciphering entity for performing the ciphering is located in an anchor node.

[8] Therefore, in the LTE system, a protocol stack has a format as shown in FlG. 3.

[9] Ciphering entities 305 and 345 are located in both the UE and the anchor node, and

ARQ/framing entities 310 and 327 are located in both the UE and the node B.

[10] The anchor node and node B may be interconnected through predetermined bearers

330 and 335, and ciphered packets are transmitted through the transport bearers 330 and 335.

[11] The ARQ/framing entities 310 and 327 perform transmission/reception of ARQ packets between the UE and the node B. The ARQ/framing entity of the transmitter receives a higher layer packet from the ciphering entity, frames the packet into a packet having a size proper for transmission of the packet through a wireless channel, constructs an ARQ packet 350 by inserting a sequence number (ASN) 365 and other header information 370 into the packet, and transmits the ARQ packet to the ARQ/ framing entity of the receiver. The ARQ/framing entity of the receiver reconstructs the received ARQ packet into the original higher layer packet and transmits a retransmission request when there is a packet which the entity of the receiver has failed to receive.

[12] The ciphering entities 305 and 345 are devices for ciphering and deciphering higher layer packets. That is, each of the ciphering entities 305 and 345 ciphers a user packet into data which a third party cannot interpret and deciphers the ciphered data into the original plan text by using predetermined algorithms and parameters.

[13] When the ciphering entity and the ARQ/framing entity are located in different nodes, it is impossible to use the same sequence number for ciphering and the same sequence number for ARQ, which increases the overhead to the packet.

[14] FlG. 4 illustrates a process of transmission of a packet (for example, an IP packet)

generated in a higher layer to a receiver through an LTE system, in order to show the problems of the prior art.

[15] When a packet 410 is input to a ciphering entity 403, the ciphering entity 403 generates a ciphered packet 425 by performing a special operation on the packet 410 by using a ciphering key 405 and a counter value 415.

[16] The counter value 415 is a value increasing one by one for each ciphered packet and is used in order to prevent the replay attack, etc. In order to decipher the ciphered packet 425, the receiver must know the counter value 415. Therefore, the counter value 415 is transmitted together with the ciphered packet 425 to the receiver. At this time, either all or a part of the counter value 415 may be transmitted. For example, if the counter value is an integer of four bytes, the transmitter may transmit only the last one byte among the four bytes and the receiver may restore the original four byte counter value by using the received one byte. For convenience of description, the counter value of a part thereof transmitted together with a packet is referred to as a "Ciphering Sequence Number (CSN) 420".

[17] The packet to which the CSN 420 is attached is transferred to the ARQ/framing entity 430. The ARQ/framing entity 430 reconstructs the packet into a size proper for transmission through a wireless channel, manages an ARQ Sequence Number (ARQ SN or ASN) for Automatic Retransmission reQuest (ARQ) of a packet and attaches the ASN to each packet.

[18] The packet having been subjected to the ARQ/framing step has an ASN 437 and a

CSN 438 attached thereto. The packet is transmitted to the receiver after being subjected to the HARQ steps. The ARQ/framing entity 460 of the receiver reconstructs the original packet by referring to the ASN 445 and transfers the reconstructed packet to the deciphering entity 475. At this time, the CSN 465 of the packet or the counter value and the ciphering key 480 restored through the CSN are input to the deciphering entity 475 and are used to decipher the ciphered packet 470 into the original packet 485.

Disclosure of Invention Technical Problem

[19] As described above, two sequence numbers including the ASN 437 or 445 and the

CSN 438 or 450 are used for the packet transmitted through the wireless channel. This results in ineffective use of wireless resources. Technical Solution

[20] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a method and an apparatus, in which only one of a ciphering sequence number and an

Automatic Retransmission reQuest (ARQ) sequence number is transmitted while a predetermined relation is maintained between them in a mobile communication system employing ciphering/deciphering and the ARQ, so that it is possible to reduce overhead in a wireless channel by transmitting and to achieve efficient use of radio resources.

[21] In order to accomplish this object, there is provided a method for transmitting a packet to a User Equipment (UE) through a wireless channel by a node B in a mobile communication system supporting an Automatic Retransmission reQuest (ARQ), the method comprising the steps of: receiving a ciphered packet in which a ciphering sequence number is inserted from an anchor node; setting a retransmission sequence number and calculating a difference between the ciphering sequence number and the retransmission sequence number; and transmitting the retransmission sequence number and the difference together with the ciphered packet to the UE.

[22] In accordance with another aspect of the present invention, there is provided a method for receiving a packet through a wireless channel in a mobile communication system supporting an Automatic Retransmission reQuest (ARQ), the method comprising the steps of: receiving a ciphered ARQ packet from a node B; determining if a difference between a retransmission sequence number and a ciphering sequence number is signaled in the received packet; calculating the ciphering sequence number from the retransmission sequence number according to if the difference has been signaled; and deciphering the ciphered ARQ packet by using the calculated ciphering sequence number.

[23] In accordance with another aspect of the present invention, there is provided an apparatus for transmitting a packet to a User Equipment (UE) through a wireless channel by a node B in a mobile communication system supporting an Automatic Retransmission reQuest (ARQ), the apparatus comprising: a ciphering entity for receiving a ciphered packet from an anchor node; a CSN attach unit for inserting a ciphering sequence number in the received packet; an ASN calculation unit for receiving the ciphering sequence number from the CSN attach unit and calculating a retransmission sequence number by using the ciphering sequence number; an ARQ header inserter for removing the ciphering sequence number from the packet and inserting an ARQ header including the retransmission sequence number into the packet; and a transmission unit for transmitting the packet including the ARQ header through a wireless channel.

[24] In accordance with another aspect of the present invention, there is provided an apparatus for receiving a packet through a wireless channel in a mobile communication system supporting an Automatic Retransmission reQuest (ARQ), the apparatus comprising: a reception unit for receiving a ciphered ARQ packet from a node B; an ARQ header remover for removing an ARQ header from the received packet; a CSN

calculation unit for calculating the ciphering sequence number from the retransmission sequence number of the packet from which the ARQ header has been removed; and a deciphering entity for obtaining a counter value from the calculated ciphering sequence number and deciphering the ciphered ARQ packet by using the counter value. Advantageous Effects

[25] In a mobile communication system employing ciphering/deciphering and ARQ according to the present invention, only one of a ciphering sequence number and an Automatic Retransmission reQuest (ARQ) sequence number is transmitted while a predetermined relation is maintained between them. Therefore, the present invention can reduce overhead in a wireless channel by transmitting and can achieve efficient use of radio resources. Brief Description of the Drawings

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

[27] FlG. 1 illustrates a structure of a Long Term Evolution (LTE) mobile communication system according to the present invention;

[28] FIG. 2 briefly illustrates a typical HARQ process;

[29] FIG. 3 illustrates a structure of an LTE system;

[30] FIG. 4 illustrates a process of transmission of a packet generated in a higher layer to a receiver through an LTE system, in order to show the problems of the prior art;

[31] FIG. 5 is a structure of a system according to the present invention;

[32] FIG. 6 illustrates a downlink operation according to a preferred embodiment of the present invention;

[33] FIG. 7 illustrates the entire process according to a preferred embodiment of the present invention in detail;

[34] FIG. 8 is a flow diagram illustrating an operation of an ARQ/framing entity of the transmitter according to a first embodiment of the present invention;

[35] FIG. 9 is a flow diagram illustrating an operation of an ARQ/framing entity of the transmitter according to a second embodiment of the present invention;

[36] FIG. 10 is a flow diagram illustrating an operation of an ARQ/framing entity of the transmitter according to a third embodiment of the present invention;

[37] FIG. 11 is a flow diagram illustrating the operation of the ARQ/framing entity of the receiver according to an embodiment of the present invention;

[38] FIG. 12 illustrates a packet loss indication;

[39] FIG. 13 is a flow diagram illustrating the operation of the ARQ/framing entity of the receiver having received the packet loss indication;

[40] FlG. 14 illustrates a structure of a transmitter according to an embodiment of the present invention;

[41] FlG. 15 illustrates a structure of a receiver according to an embodiment of the present invention;

[42] FlG. 16 illustrates formats of the RLC PDU and the PDCP PDU; and

[43] FlG. 17 illustrates a general operation of the entire system according to the fourth embodiment of the present invention. Best Mode for Carrying Out the Invention

[44] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same elements will be designated by the same reference numerals although they are shown in different drawings. Further, various specific definitions found in the following description are provided only to help general understanding of the present invention, and it is apparent to those skilled in the art that the present invention can be implemented without such definitions. Further, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

[45] According to the present invention as described above, it is necessary to maintain a predetermined relation between the ASN and the CSN. To this end, the following two conditions should be guaranteed.

[46] First, ciphering/deciphering shall be performed packet by packet of a higher layer

(for example, IP packet by IP packet). Therefore, the CSN increases one by one for each higher layer packet.

[47] Second, the ARQ/framing entity is provided an ASN for each higher layer packet.

That is, the ASN increases one by one for each higher layer packet. Therefore, one CSN and one ASN are provided to the same packet.

[48] If the above conditions are met, and the transmitter and the receiver recognize the difference between the CSN and the ASN in advance, the receiver can calculate the CSN from the received ASN. It is acceptable to transmit only the ASN through the wireless channel.

[49] Specifically, as shown in FlG. 5, only the ASN 538 or 550 and the ciphered packet

539 or 555 are transmitted through the wireless channel, and the receiver calculates the CSN 583 based on the received ASN 565 and transfers the calculated CSN 583 to the deciphering entity 575.

[50] The deciphering entity 575 deciphers the ciphered packet 570 into the original packet 585 by using the CSN 583 and the ciphering key 580 and then transfers the deciphered packet to the higher layer.

[51] FlG. 6 illustrates a downlink operation according to a preferred embodiment of the present invention.

[52] The ciphering entities 605 and 645 are located within the UE and the anchor node, respectively. The ARQ/framing entities 610 and 627 are located within the UE and the node B.

[53] After the ciphering entity 645 ciphers the packet, the anchor node attaches the CSN

640 to the packet, and then transmits the packet to the node B. The anchor node and the node B are interconnected through predetermined transport bearers 630 and 635. For example, either a tunneling protocol using Internet Protocol/User Datagram Protocol (IPAJDP), or a GPRS Tunneling Protocol (GTP) may be used as the transport bearers. When the tunneling protocol has a sequence number, it is possible to reduce the transmission overhead between the anchor node and the node B by inserting the CSN to the sequence number field.

[54] When the anchor node transmits a ciphered packet to the node B, the ARQ/framing entity 627 of the node B calculates the difference (delta) 625 between the CSN and the ASN. As described above, the CSN and the ASN are provided one for one packet. Therefore, the difference (delta) between the CSN and the ASN is always constant as long as a packet is not lost between the anchor node and the node B.

[55] delta = ASN - CSN (1)

[56] The ARQ/framing entity 627 transfers the delta 625 to the ARQ/framing entity 610 of the UE.

[57] Further, the ARQ/framing entity 627 removes the CSN from the packet which it received from the anchor node, attaches the ASN to the packet, and then transmits the ASN-attached packet to the ARQ/framing entity 610 of the UE.

[58] After receiving the delta 625, the ARQ/framing entity 610 of the UE memorizes the received delta, calculates the CSN 620 from the ASN of a packet received thereafter by using the memorized delta value, and then transfers the calculated CSN 615 to the ciphering entity 605.

[59] CSN = ASN - delta (2)

[60] The ciphering entity 605 of the UE deciphers the packet by using the CSN 615 and the ciphering key which it has possessed in advance.

[61] FlG. 7 illustrates the entire process according to a preferred embodiment of the present invention in detail.

[62] First, in step 720, bearers are set between the UE 705, the node B (ENB) 710, and the anchor node 715. This setup includes setup of a ciphering entity, an ARQ/framing entity, and a HARQ entity for the UE 705, setup of an ARQ/framing entity and a HARQ entity for the ENB 710, setup of a ciphering entity for the anchor node 715, and setup of a transport bearer between the ENB 710 and the anchor node 715, in order to

provide a specific packet flow.

[63] In the following description, steps 725 to 760 correspond to the downlink operation, and steps 770 to 795 correspond to the uplink operation. The downlink operation and the uplink operation are independent of each other without a temporal sequence between them. Therefore, the downlink operation and the uplink operation may be simultaneously performed, or the uplink operation may be performed before the downlink operation.

[64] First, the downlink operation will be described below.

[65] In step 725, when the first packet from an outer network arrives at the anchor node

715, the anchor node 715 performs ciphering while applying a proper counter value to the packet. Further, the anchor node 715 attaches the CSN to the ciphered packet, and then transmits the packet to the ENB 710.

[66] Next, the ENB 710 inputs the received packet to the ARQ/framing entity. The

ARQ/framing entity of the transmitter provides an ASN to the packet. Then, in step 830, the ARQ/framing entity of the transmitter calculates the difference (delta) between the ASN and the CSN. This difference is continuously used in determining the ASN of a following ARQ packet. That is, when determining the ASN of a following ARQ packet, the ARQ/framing entity uses a value obtained by adding the delta to the CSN of the packet, as the ASN of the corresponding packet.

[67] In step 735, the ARQ/framing entity of the transmitter reports the calculated delta to the ARQ/framing entity of the receiver. Then, in steps 740 and 755, the ARQ/framing entity of the transmitter transmits the ARQ packets having the ASN attached thereto to the UE 705 by using a predetermined method.

[68] In step 750 and 760, the ARQ/framing entity of the receiver obtains the CSN of the received ARQ packet by subtracting the delta from the received ARQ packet, and transfers the packet and the calculated CSN to the ciphering entity. The ciphering entity deciphers the packet by using the CSN and a predetermined ciphering key.

[69] The ARQ/framing entity of the receiver repeats the above process whenever it receives the ARQ packet.

[70] Next, the uplink operation will be described.

[71] In step 765, when a first packet occurs in a higher layer of the UE 705, the ciphering entity of the UE 705 performs ciphering while applying a proper counter value to the packet. Further, the ciphering entity of the UE 705 transfers the ciphered packet and CSN to the ARQ/framing entity.

[72] The ARQ/framing entity provides an ASN to the packet. Then, in step 770, the

ARQ/framing entity calculates the difference (delta) between the ASN and the CSN. The difference is continuously used in determining the ASN of the following ARQ packet. That is, the ARQ/framing entity determines the ASN of the packet by adding

the delta to the CSN of the packet received from the ciphering entity.

[73] In step 775, the ARQ/framing entity reports the calculated delta to the ARQ/ framing entity of the receiver. When the above process has been completed, the ARQ/ framing entity of the transmitter transmits the ASN-attached ARQ packets to the ENB 705 according to a predetermined method in steps 780 and 792.

[74] The ARQ/framing entity of the receiver obtains the CSN of the received ARQ packet by subtracting the delta from the ASN of the received ARQ packet in steps 790 and 795, and transfers the packet and the obtained CSN to the ciphering entity of the anchor node 715 in steps 785 and 793. The ciphering entity of the anchor node 715 deciphers the packet by using the CSN and a predetermined ciphering key.

[75] The ARQ/framing entity of the receiver repeats the above process whenever it receives an ARQ packet.

[76] FIGs. 8, 9, and 10 illustrate an operation of the ARQ/framing entity of the transmitter.

[77] According to an embodiment of the present invention, based on the fact that the relation between the CSN and the ASN is always constant, the ARQ/framing entity of the transmitter calculates the ASN based on the CSN of the packet received from the ciphering entity, and the ARQ/framing entity of the receiver calculates back the CSN based on the received ASN.

[78] The simplest relation between the ASN and the CSN may be, for example, the case in which the ASN and the CSN are always the same. An operation of the ARQ/framing entity of the transmitter in that situation is shown in FIG. 8.

[79] In order to allow the possibility that the ASN and the CSN are not the same, the

ARQ/framing entity of the transmitter must report the relation between the ASN and the CSN to the ARQ/framing entity of the receiver in advance. The operation of the ARQ/framing entity of the transmitter in this case is shown in FIG. 9.

[80] Further, if the possibility that the ASN and the CSN are not the same is allowed, and if the difference (delta) is signaled only when the ASN and the CSN are not the same, the operation is usually possible without signaling the delta. The operation of the ARQ/framing entity of the transmitter in this situation is shown in FIG. 10.

[81] Further, the operation of the ARQ/framing entity of the transmitter in all of the three cases is shown in FIG. 11.

[82] First, the operation of the ARQ/framing entity of the transmitter according to the first embodiment of the present invention, in which the ASN and the CSN are set to be always the same in the system, will be described hereinafter with reference to FIG. 8.

[83] Usually, the ASN and the CSN are set to have an initial value of 0 and to increase one for each packet. Therefore, the ASN and the CSN have always the same value as long as the packet is not lost between the ciphering entity and the ARQ/framing entity

of the transmitter.

[84] When the ARQ/framing entity has received a packet from the ciphering entity in step 805, the ARQ/framing entity sets the ASN and the CSN of the packet to have the same value and constructs the ARQ packet in step 810.

[85] Then, in step 815, the ARQ/framing entity checks the CSN of the received packet in order to determine if there has been loss of a packet between the ciphering entity and the ARQ/framing entity. For example, it may be determined that there has been loss of a packet, when the following situation occurs.

[86] On the assumption that the CSN of a packet received for the x time is put as

CSN(x), and the CSN of a packet received for the (x+1)* time is put as CSN(x+l), if CSN(x+l) - CSN(x+l) > 1, it implies that it is probable that one or more packets have been lost. However, it is also possible that the packet presumed lost may be received later. Therefore, the ARQ/framing entity of the transmitter regards packets as lost only when the packets have not arrived during a predetermined time interval.

[87] As a result of the determination in step 815, the ARQ/framing entity of the transmitter proceeds to step 820 when it is concluded that the packet has been lost, and proceeds to step 825 when it is concluded that the packet has not been lost. In step 825, the ARQ/framing entity of the transmitter transmits the ARQ packet constructed in step 810.

[88] In step 820, the ARQ/framing entity reports to the ARQ/framing entity of the receiver that the lost packets will not arrive. For example, if a packet having a CSN of y is lost at a predetermined time point while it is transmitted from the ciphering entity to the ARQ/framing entity of the transmitter, it implies that the packet having a CSN of y is not received by the ARQ/framing entity of the transmitter, even though a packet having a CSN of (y-1) and a packet having a CSN of (y+1) have been received. At this time, the ARQ/framing entity of the transmitter sets the ASN of the packet having a CSN of (y-1) as (y-1) and sets the ASN of the packet having a CSN of (y+1) as (y+1) before transmitting them. Therefore, the ARQ/framing entity of the receiver will transmit a retransmission request for the packet in expectation of receiving the packet having a ASN of y. However, the ARQ/framing entity of the transmitter could not receive the packet having a ASN of y from the first, and thus cannot respond to the retransmission request. In order to overcome such a problem, if packet loss is detected, the ARQ/framing entity of the transmitter reports to the ARQ/framing entity of the receiver that the packet having an ASN which might have been allocated to a lost packet will not arrive. Hereinafter, for convenience of description, this information will be referred to as "Packet loss indication", which will be described later in more detail with reference to FIG. 12.

[89] In step 825, the ARQ/framing entity of the transmitter transmits the ARQ packet

constructed in step 810, and then returns to step 805, in which the ARQ/framing entity of the transmitter waits for reception of the next packet.

[90] Next, the second embodiment of the present invention, in which the CSN and the

ASN have different values, will be described hereinafter with reference to FlG. 9.

[91] Because the ciphering entity and the ARQ/framing entity are different devices, it is preferred that they use independent schemes of setting the sequence number. To this end, as described above, the ARQ/framing entity of the transmitter may report the relation between the ASN and the CSN to the ARQ/framing entity of the receiver by using the delta value.

[92] When the first packet arrives after a bearer is set in the ARQ/framing entity of the transmitter in step 905, application of the second embodiment of the present invention is initiated. In step 910, the ARQ/framing entity of the transmitter sets an ASN to be applied to the packet. Although the ASN usually starts from 0, it may start from any value from which the ARQ/framing entity of the transmitter wants.

[93] In step 915, the ARQ/framing entity of the transmitter sets a value obtained by subtracting the CSN of the received packet from the setup ASN as delta.

[94] In step 920, the ARQ/framing entity of the transmitter reports the delta to the ARQ/ framing entity of the receiver. In order to secure reliability in transmission of the delta, the delta may be retransmitted several times.

[95] When it is convinced that the delta has been successfully transmitted to the receiver, the ARQ/framing entity of the transmitter starts transmission of the ARQ packet in step 925. Of course, the transmission of the delta and the transmission of the ARQ packet may be simultaneously performed, or the delta may be piggybacked on the transmitted ARQ packet.

[96] The ARQ/framing entity of the transmitter calculates the ASN of the next packet by using the CSN and delta of the packet in step 935, and then transmits the packet given the calculated ASN in step 940. The ARQ/framing entity of the transmitter repeats execution of steps 930 to 940 for the packets arriving thereafter.

[97] When the CSN is newly set up due to a certain reason during the communication, the ARQ/framing entity of the transmitter restarts the process from step 905.

[98] Meanwhile, in step 905, the ARQ/framing entity of the transmitter should be capable of recognizing that the received packet is the first packet. However, if revision-in-sequence occurs between the ciphering entity and the ARQ/framing entity, the operation of the ARQ/framing entity of the transmitter may become obscure. Therefore, the ciphering entity may insert a clear indicator in the first packet transmitted to the ARQ/framing entity, so that the ARQ/framing entity of the transmitter can set the delta value after receiving the packet in which the indicator is inserted, for convenience of description, the indicator indicating the first packet is

referred to as "first CSN indication".

[99] The ciphering entity inserts the first CSN indication into the first packet transmitted after the CSN is initialized. The first CSN indication may be transmitted as either the header information of the transport bearer or separate control information.

[100] Next, the third embodiment of the present invention, in which the delta is not signaled when it is 0 and is signaled only when it is not 0, will be described hereinafter with reference to FlG. 10.

[101] In step 1005, the ARQ/framing entity of the transmitter receives a packet including the first CSN indication from the ciphering entity and determines an ASN to be applied to the packet. The ARQ/framing entity of the transmitter manages the ASN to be applied to packets such that the ASN may be, for example, initialized to 0, and then increased by 1 whenever the packet is transmitted. The ARQ/framing entity compares the ASN with the CSN of the packet including the first CSN indication, and proceeds to step 1025 for transmitting the ARQ packet when the two values are the same, and proceeds to step 1015 when the two values are not the same.

[102] The ARQ/framing entity of the transmitter obtains the delta by subtracting the CSN from the ASN in step 1015, transmits the calculated delta to the ARQ/framing entity of the receiver in step 1020, and transmits the ARQ packet in step 1025. The ASN to be applied to the ARQ packet corresponds to a sum of the CSN and the delta. In step 1010, if the ASN is equal to the CSN, the delta is considered as 0.

[103] FlG. 11 is a flow diagram illustrating the operation of the ARQ/framing entity of the receiver according to an embodiment of the present invention.

[104] The ARQ/framing entity of the receiver receives an ARQ packet in step 1105, and determines in step 1110 if "delta" has been signaled. The ARQ/framing entity of the receiver proceeds to step 1115 when the delta has been signaled and proceeds to step 1120 when the delta has not been signaled.

[105] The ARQ/framing entity of the receiver obtains the CSN by subtracting the most recently signaled delta from the ASN of the received ARQ packet in step 1115, and then transfers the obtained CSN and the packet to the ciphering entity in step 1125.

[106] In step 1120, the ARQ/framing entity of the receiver sets the ASN of the received

ARQ packet by the CSN (because the ASN is equal to the CSN) and then transfers the packet to the ciphering entity.

[107] According to an embodiment of the present invention as described above, it is necessary to maintain a constant relation between the ASN and the CSN as long as there is not a new process of calculating the delta. This implies that an ARQ packet having a specific ASN may not be generated. In order to deal with such a case, the present invention proposes use of a new control signal named "Packet loss indication".

[108] FlG. 12 illustrates a "Packet loss indication".

[109] The ARQ/framing entity of the transmitter 1205 transmits packets including an

ARQ packet having an ASN of (x- 10) 1215 to an ARQ packet having an ASN of (x+9) 1220. Therefore, the packets which the ARQ/framing entity of the transmitter 1205 has received from the ciphering entity have CSNs of (x-10-delta) to (x+9-delta).

[110] The ARQ/framing entity of the transmitter 1205 has failed to receive a packet 1225 having a CSN of (x+6-delta) from among the packets mentioned above. Further, a packet 1215 having an ASN of (x-10) and a packet 1230 having an ASN of (x-1) are lost while they are transmitted to the receiver 1210.

[Ill] Therefore, the ARQ/framing entity of the receiver cannot receive those packets

1215, 1225, and 1230 and will request that the transmitter 1205 retransmit those packets. However, since the transmitter 1205 cannot retransmit the packet 1225 having an ASN of (x+6) which the transmitter originally failed to receive, the ARQ/framing entity of the receiver 1210 will thus continuously request retransmission of the packet. In order to prevent waste of resources due to the retransmission request, the transmitter 1205 reports the ASN which might have been allocated to a lost packet to the ARQ/ framing entity of the receiver 1210.

[112] Specifically, in FIG. 12, the ARQ/framing entity of the transmitter 1205 transmits a packet loss indication for the ASN of (x+6) to the receiver 1210.

[113] The packet loss indication 1255 may be included in the transmitted ARQ packet

1240. For example, an indication that certain control information is included is inserted in an ARQ header 1245, and a packet loss indication 1255 is inserted in a rear portion of the ARQ packet.

[114] The packet loss indication 1255 may include a control info type field 1260 and an

ASN field 1265 of the lost packet according to a typical Type Value (TV) coding.

[115] FIG. 13 is a flow diagram illustrating the operation of the ARQ/framing entity of the receiver having received the packet loss indication 1255.

[116] When the ARQ/framing entity of the receiver receives a packet loss indication from the transmitter in step 1305, it considers the ARQ packet corresponding to the ASN of the received packet loss indication as correctly received even when the packet has not been received yet. For example, referring to FIG. 12, the ARQ/framing entity of the receiver considers the packet 1225 having an ASN of (x+6) as correctly received although it has not actually received the packet 1225, and the ARQ/framing entity of the receiver does not request retransmission of the packet. If an in-sequence delivery is constructed in the ARQ/framing entity, the packets having sequence numbers lower than that of the packet 1225 having an ASN of (x+6) include packets that are not received yet. Therefore, the packets are not transferred to the higher layer before the packets that are not received yet are received. In contrast, if an out-of-sequence delivery is constructed in the ARQ/framing entity, packets including a packet having

an ASN of x to a packet having an ASN OF (x+9) will be transferred to the higher layer. [117] FIG. 14 illustrates a structure of a transmitter according to an embodiment of the present invention. [118] The ciphering entity 1405 is connected to a higher layer and ciphers a packet generated in the higher layer. At this time, the ciphering entity 1405 prevents replay attack by using the counter value. [119] The CSN attach unit 1410 is a device for attaching a CSN to a ciphered packet in order to inform the ciphering entity of a counter value. As described above, the CSN may either have the same value or be a part of the counter value. [120] The packet output from the CSN attach unit 1410 is input to the ARQ header attach

1415, and the CSN of the packet is input to the ASN calculation unit 1420. The ASN calculation unit 1420 calculates the ASN by using the CSN. [121] The ARQ header attach unit 1415 removes the CSN from the packet received from the CSN attach unit 1410, and inserts an ARQ header including the ASN calculated by the ASN calculation unit 1420 into the packet. [122] The transmission (Tx) buffer 1425 stores the ARQ packet before the packet is transmitted through a wireless channel. [123] Usually, one ARQ packet includes one IP packet, and it is often impossible to transmit an IP packet having a size up to 1500 bytes at one time. Therefore, it is necessary to segment the ARQ packet into segmented packets having a size proper for transmission through a wireless channel. At this time, the segmentation index attach unit 1430 attaches indexes to the segmented packets so that the receiver can restore the original ARQ packet. [124] The retransmission buffer 1435 is a device for storing packets for which ACK signals are not received yet, in order to retransmit the packets. [125] The HARQ/transmission unit 1440 is a device for actually transmitting the ARQ packet through a wireless channel according to a HARQ scheme. [126] FIG. 15 illustrates a structure of a receiver according to an embodiment of the present invention. [127] The HARQ/reception unit 1540 is a device for receiving an ARQ packet through a wireless channel. [128] The reception (Rx) buffer 1530 is a device for storing the ARQ packet transferred from the HARQ/reception unit 1540. [129] The reassembly unit 1525 is a device for reassembling the segmented ARQ packets into the original ARQ packets. [130] The ARQ header detach unit 1515 removes the header from the ARQ packet and transfers the header-removed packet to the CSN calculation unit 1520.

[131] The CSN calculation unit 1520 is a device for calculating the CSN from the ASN of the ARQ packet and transferring the calculated CSN to the ciphering entity 1505.

[132] The ciphering entity 1505 calculates back the counter from the CSN calculated by the ciphering entity 1505, and deciphers the ARQ header-removed packet by using the calculated counter.

[133] Meanwhile, the current standard for the LTE defines that the ARQ operation be performed by a protocol layer device named RLC, that the ciphering/deciphering be performed by a protocol layer device named Packet Data Convergence Protocol (PDCP), and that packets processed by the protocol entities are named RLC PDU and PDCP PDU, respectively.

[134] FTG. 16 illustrates formats of the RLC PDU and the PDCP PDU.

[135] Referring to FIG. 16, the PDCP device ciphers a higher layer packet such as the IP packet according to a predetermined scheme, constructs a PDCP PDU 1605 by inserting a header such as the PDCP SN 1610 into the ciphered higher layer packet 1615, and transfers the constructed PDCP PDU 1605 to an RLC unit. At this time, a CSN used in the ciphering is inserted in the SN field of the PDCP.

[136] The RLC unit reconstructs the PDCP PDU to have a proper size and transmits the reconstructed PDCP PDU through a wireless channel. Therefore, either a part of the PDCP PDU or the entire PDCP PDU may be inserted in one RLC PDU. For the ARQ operation, one RLC SN is given to one RLC PDU.

[137] According to the present invention as described above, only the ASN, without the

CSN, is transmitted through a wireless channel by setting the ASN either equally to the CSN or to have a predetermined difference from the CSN. That is, it is possible to set the RLC SN and the PDCP SN either equally or to have a predetermined difference between them. However, when one PDCP PDU 1635 is divided and inserted in multiple RLC PDUs 1640 and 1645, RLC PDUs containing the same PDCP PDU are identified by separate sub-sequence numbers 1655 and 1665 because they must have the same RLC SN 1650 or 1660. As a result, the RLC SN is repeatedly transmitted without transmission of the PDCP SN, thereby largely reducing the gain obtainable through the sharing of the PDCP SN and the RLC SN or degrading the efficiency against expectation.

[138] The method of sharing the PDCP SN and the RLC SN can achieve an expected gain when the one-to-one relation is maintained between the PDCP PDU and the RLC PDU, and it is preferred that this method is not used when one PDCP PDU is segmented and the segmented PDUs are inserted in multiple RLC PDUs.

[139] However, the size of the RLC PDU is changeable according to the channel status.

The possibility of segmentation increases as the size of the PDCP PDU increases, while it decreases as the size of the PDCP PDU decreases. Further, the sizes of the

generated packets according to the types of the services are usually predictable.

[140] For example, in the case of the VoIP service, small packets of about 30 bytes are mainly generated, and it is thus highly probable that one PDCP PDU is inserted in one transmitted RLC PDU. In contrast, in the case of the File Transfer Protocol (FTP) service, large packets of several hundred bytes are mainly generated, and it is thus highly probable that multiple segmented PDCP PDUs are inserted in multiple transmitted RLC PDUs when the channel condition is poor.

[141] Therefore, the fourth embodiment of the present invention proposes a method of determining whether to share the PDCP SN and the RLC SN by a network according to the type of the service set by a UE.

[142] FIG. 17 illustrates a general operation of the entire system according to the fourth embodiment of the present invention.

[143] Referring to FIG. 17, when a user commands to start a predetermined service, the

UE 1705 transmits a service setup request message to the anchor node 1715. The service setup request message contains information such as service types or requested QoS.

[144] In step 1725, the anchor node 1715 determines the type of a radio bearer to be set, in consideration of the service type requested by the UE 1705, requested QoS, etc. The radio bearer is a general name for the PDCP, RLC, MAC, etc., which are constructed in order to support a specific service. According to the present invention, the radio bearer can be divided into two types as follows:

[145] Radio bearer type 1 : bearer by which the PDCP SN and the RLC SN are independently set and analyzed; and

[146] Radio bearer type 2: bearer by which the PDCP SN and the RLC SN are the same or set to maintain a predetermined relation between them.

[147] The anchor node 1715 sets the radio bearer of type 1 for a service which is expected to generate either large packets or packets having sizes which are difficult to estimate, and sets the radio bearer of type 2 for a service which is expected to generate small packets, for example, the VoIP service.

[148] Then, in step 1730, the anchor node 1715 sets the PDCP according to the determined bearer type, and transmits a radio bearer setup request message to the ENB 1710.

[149] In step 1735, the ENB 1710 sets a radio bearer based on the received radio bearer setup request message, and transmits the radio bearer setup request message to the UE 1705, so that the UE 1705 can set the radio bearer.

[150] If the radio bearer of type 1 has been set during the radio bearer setup process, the

RLC SN and the PDCP SN of the RLC PDU and the PDCP PDU exchanged between the UE 1705, the ENB 1710, and the anchor node 1715 are not related from each other,

and the RLC unit and the PDCP unit perform predetermined operations by using sequence numbers inserted in the RLC PDU and the PDCP PDU in step 1740.

[151] In contrast, if the radio bearer of type 2 has been set during the radio bearer setup process, the RLC SN and the PDCP SN of the RLC PDU and the PDCP PDU exchanged between the UE 1705, the ENB 1710, and the anchor node 1715 are either the same or have a predetermined difference between them. Then, in step 1745, the RLC transmission unit receives the PDCP PDU, obtains the RLC SN by adding or subtracting a predetermined value to or from the PDCP SN with reference to the PDCP SN, and sets the sequence number of the RLC PDU for containing the PDCP PDU as the RLC SN. Further, the RLC transmission unit transmits the PDCP PDU after removing the sequence number from the PDCP PDU. Further, when the RLC reception unit receives the RLC PDU, the RLC reception unit obtains the PDCP SN by subtracting or adding a predetermined value from or to the RLC SN, restores the original PDCP PDU by inserting the obtained PDCP SN into the PDCP PDU inserted in the received RLC PDU, and then transfers the restored PDCP PDU to the PDCP layer.

[152] While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.