Title of Invention	METHOD FOR HANDLING LATE ARRIVAL OF PACKET DATA UNIT AFTER RESET/RE-ESTABLISHMENT OF RADIO LINK CONTROL ENTITY IN A WIRELESS COMMUNICATION SYSTEM
Abstract	ABSTRACT Methods for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system are disclosed. In one embodiment, both the peer RLC entities shall start a timer, called WAIT_TIMER, after re¬initialization. The transmitting RLC entity shall not transmit any PDUs before the expiry of the TX_WAIT_TIMER. Further, the peer receiving RLC entity shall discard all PDUs received before the expiry of the RX_WAIT_TIMER. In other embodiment, after a re-initialization of the RLC entity is triggered, the HARQ entity on the transmitting RLC side shall discard all the buffers which contain a RLC PDU from the re-initialized RLC entity. Further, on the receiving side, there is no additional action required to be taken by either of the RLC entity or the HARQ entity. In another embodiment, the transmitting RLC entity shall inform the value of its protocol variable TX_SN_TO_BE_TRANSMITTED to the peer receiving RLC entity. Further, the receiving entity shall discard any PDUs which are received after re-initialization with sequence number less than this value. In yet another embodiment, the transmitting as well as the receiving RLC entities shall have a bit, called R bit, stored in their context for referring to the re¬initialization count. This bit shall be toggled after each re-initialization. The sequence number of transmitted PDUs shall always have their first bit set equal to R bit. Any PDU received with its first bit different from the R bit shall be discarded.

Title of Invention

METHOD FOR HANDLING LATE ARRIVAL OF PACKET DATA UNIT AFTER RESET/RE-ESTABLISHMENT OF RADIO LINK CONTROL ENTITY IN A WIRELESS COMMUNICATION SYSTEM

Abstract

ABSTRACT Methods for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system are disclosed. In one embodiment, both the peer RLC entities shall start a timer, called WAIT_TIMER, after re¬initialization. The transmitting RLC entity shall not transmit any PDUs before the expiry of the TX_WAIT_TIMER. Further, the peer receiving RLC entity shall discard all PDUs received before the expiry of the RX_WAIT_TIMER. In other embodiment, after a re-initialization of the RLC entity is triggered, the HARQ entity on the transmitting RLC side shall discard all the buffers which contain a RLC PDU from the re-initialized RLC entity. Further, on the receiving side, there is no additional action required to be taken by either of the RLC entity or the HARQ entity. In another embodiment, the transmitting RLC entity shall inform the value of its protocol variable TX_SN_TO_BE_TRANSMITTED to the peer receiving RLC entity. Further, the receiving entity shall discard any PDUs which are received after re-initialization with sequence number less than this value. In yet another embodiment, the transmitting as well as the receiving RLC entities shall have a bit, called R bit, stored in their context for referring to the re¬initialization count. This bit shall be toggled after each re-initialization. The sequence number of transmitted PDUs shall always have their first bit set equal to R bit. Any PDU received with its first bit different from the R bit shall be discarded.

Full Text	FIELD OF THE INVENTION The present invention, in general, relates to the field of wireless communication. In particular, the present invention proposes various methods for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization. More particularly, the present invention relates to various methods for handling late arrival of a PDU after reset/re-establishment of a Radio Link Control (RLC) entity of a wireless communication system, which is applicable to any ARQ mechanism with an underlying HARQ layer. DESCRIPTION OF PRIOR ART UMTS is a third generation mobile communication system developed in Europe. The UMTS employs a WCDMA as radio access technique. The WCDMA is DS-CDMA technique of a FDD scheme, which transmits data using bandwidth of 5 MHz in frequency band of 2 GHz. A HARQ is a physical layer retransmission function in the WiMax IEEE 802.16 protocol with variants in several cellular protocols, such as in UMTS. HARQ is a link adaptation technique where link layer acknowledgements are used for re¬transmission decisions at the physical layer. IEEE 802.16 defines two levels of retry attempts wherein, the first level as in HARQ on the physical layer and the second level is on a higher layer protocol such as standard ARQ on the data plane, or MAC timers on the control plane. Figure 1 illustrates the radio interface protocol architecture layer proposed for a 3G wireless network and is reproduced from the 3GPP TS 25.301. Layer-1 or the physical layer of the UMTS radio interface is responsible for coding and modulation of data transmitted over the air. Layer-2 or the data link layer is subdivided into a RLC sublayer and a MAC sublayer. The service provided by layer-2 is referred to as the radio bearer. The control plane radio bearers, which are provided by RLC to RRC, are denoted as signaling radio bearers. The separation in MAC and RLC sublayers is motivated by the need to support a wide range of upper layer services, and also the requirement to provide high efficiency and low latency data services over a wide performance range, i.e. from 1.2 Kbps to greater than 2 Mbps. Other motivators are the need for supporting high QoS delivery of circuit and packet data services, such as limitations on acceptable delays and/or data BER, and the growing demand for advanced multimedia services. Each multimedia service has different QoS requirements. The data link layer also comprises a C-plane signaling and a U-plane information for separating the information from control signals. The RLC layer receives data packets from the higher layers, such as IP, through SAP, and delivers RLC frames to the MAC sublayer. The RLC frames are queued into logical channels. At the MAC sublayer, the RLC frames are multiplexed onto transport channels. The transport channels are the interface of the physical layer to the data link layer. In fact, data link layer functions are divided in two parts, PLICF handled in the RLC, and PLDCF included in the MAC. It is assumed that there is one instance of RLC for each data application/session. Multiple types (common and shared) of transport channels are provided based on the method of data transmission. Multiple types (traffic and control) of logical channels are provided according to the type of transmitted information. RRC is the only radio protocol in L3 and is only defined in the control plane. It controls the logical, transport and physical channels in relation to the setup, modification and release of the RBs. More precisely, the RLC functionality is independent of its location (in UE or UTRAN) and only depends on whether it receives the RLC PDUs from the lower layer or RLC SDUs from the upper layer. A transmitting RLC entity receives the RLC SDUs from the upper layer. A receiving RLC entity receives the RLC PDUs from the lower layer. A transmitting RLC entity receives RLC SDUs from the upper layers and segments and/or concatenates the SDUs and makes fresh data units, called RLC PDUs. The RLC PDUs are submitted to MAC which in turn submits them to PHY. PHY transfers these PDUs to the peer PHY. Further, at the peer end, the RLC PDUs are finally submitted to a receiving RLC entity via MAC. The RLC SDUs are re-assembled from the received RLC PDUs and ultimately submitted to the upper layers. The flow control between the peer RLC entities is achieved by using a well- known scheme in the field of communication protocols called sliding window mechanism. The transmitting RLC entity maintains, among others, protocol variables TX SN TO BE ACKNOWLEDGED and TX_SN_TO_BE_TRANSMITTED. TX_SN_TO_BE_TRANSMITTED indicates the sequence number of the next PDU to be transmitted. This is maintained as one higher than the sequence number of the PDU that was transmitted to the peer RLC entity with the highest sequence number. TX_SN_TO_BE_ACKNOWLEDGED indicates the next in-sequence PDU which is pending for acknowledgement from the peer receiving entity. It is maintained as one higher than the sequence number up to which all PDUs have been acknowledged by the peer RLC entity. . The receiving RLC entity maintains, among others, protocol variables RX_SN_TO_BE_RECEIVED and RX_SN_HIGHEST. RX_SN_HIGHEST indicates the sequence number one higher than that of the PDU that was received from the peer transmitting entity bearing the highest sequence number. RX_SN_TO_BE_RECEIVED indicates the next in-sequence PDU which might be expected to be received from the peer transmitting entity. It is maintained as one higher than the sequence number up to which all PDUs have been sequentially received. The protocol variables described above are numbered by modulo integer sequence numbers cycling through the field: 0 to SEQUENCE_NUMBER_RANGE - 1. The variable SEQUENCE_NUI\/1BER_RANGE is a protocol constant. The flow control mechanism of the sliding window protocol is controlled by the configuration of a variable WINDOW_SIZE by the upper layer (RRC). The variable for the transmitting RLC entity is called TX_WINDOW_SIZE. The variable for the receiving RLC entity is called RX_WINDOW_SIZE. The value of TX_WINDOW_SIZE for a transmitting entity is usually smaller than or equal to the value of RX_WINDOW_SIZE for the peer receiving entity. The transmit window spans from TX_SN_TO_BE_TRANSMITTED to TX_SN_TO_BE_TRANSMITTED + TX_WINDOW_SIZE - 1. The PDUs falling outside the transmit window are not transmitted. The receive window spans from RX_SN_TO_BE_RECEIVED (RX_SN_TO_BE_RECEIVED + RX_WINDOW_SIZE - 1). The PDUs falling outside the receive window are discarded. The receiving RLC entity apprises its peer transmitting entity of the PDU status according to the reporting configuration received from the upper layer e.g. periodically. The transmitting entity may also poll the peer receiving entity for the status of the PDUs that were transmitted to it. The RLC entities require a re-initialization when, for example, a protocol error is detected. A protocol error is a scenario which is un-imaginable if both the peer entities are assumed to work strictly according to the specifications. A protocol error may occur due to, among others, some problem with the underlying physical link resulting into a corruption or sustained loss of data. Figure 2 illustrates abstraction of the RLC protocol. As shown in the figure 2, the receiving RLC entity receives the information sent by the transmitting RLC entity through defined medium. There are two methods of re-initializing of an RLC entity: via peer to peer communication called RESET (involving the exchange of a control PDU, called RESET PDU, and an acknowledgement thereof) or controlled by the upper layer called RE-ESTABLISHMENT. All the PDUs (Packet Data Units) stored in the transmission buffer of the transmitting RLC entity are flushed out on re-initialization. All the PDUs stored in the reception buffer of the receiving RLC entity are flushed out on re¬initialization. All the protocol variables are also set to their initial values by both the transmitting as well as the receiving RLC entities on re-initialization. Figure 3 depicts protocol layering and position of HARQ functionality. With the introduction of HARQ at MAC layer between the RLC and PHY layers as shown in the figure 3, it is possible that RLC PDUs may be received out of order. Therefore, it is also possible that a PDU transmitted before the re-initialization of the peer RLC entities is received after the re-initialization has been performed. The receiving entity, following the normal course of action, shall report the status for the received PDU(s) to the peer transmitting entity. But, the transmitting entity does not have any record of the PDUs transmitted before re-initialization since all the protocol variables are reset to their initial values. Therefore, the unexpected status report amounts to a protocol error at the transmitting entity. This shall result into another re-initialization being triggered by the transmitting entity. It is clear that, in fact, no protocol error had occurred when the re-initialization was triggered by the transmitting entity. The problem was caused entirely due to the late arrival of the RLC PDUs transmitted before the re-initialization. Therefore, a method is needed to handle the late arrival of the RLC PDUs to overcome the crises raised by it. In the state of the art literature, the patent application titled "Data packet transmission" (patent no. US 2007/0133605) describes using the attribute priority to achieve a stronger FEC for RLC Control PDUs transmitted via the HS-DSCH also entails prioritized handling so that an RLC Control PDU is likely to overhaul an RLC Data PDU. As a consequence the RLC protocol operation can severely be disturbed, since it relies on in-sequence delivery of control and data PDUs. According to an exemplary embodiment of the present invention, two types of containers are provided in which data packets may be transmitted, wherein the first type of container is provided with a stronger error coding than the second type of container and wherein data packets which comprise control instructions are only transmitted in the first container type with the stronger error correction. Due to this, an improved forward error correction for control PDUs of the AM RLC protocol of UMTS may be provided. The patent application proposes a method and system for transmitting data packets (first data packets and second data packets) from a transmitting station to a receiving station over a high speed downlink shared channel in UMTS. The first data packets are RLC control PDUs while the second data packets RLC data PDUs. According to an embodiment, after the RLC RESET procedure is finished, the transmitting and receiving windows are not initialized to the sequence number 0. Instead, the lower edge of these windows is set equal to the lower edge of the transmitting window immediately before the RLC RESET procedure is Initiated. However, the application does not mention starting timers (at both the transmitting and the receiving sides) after re-initialization and not transferring or receiving PDUs until the timers expire. Further, the application also does not propose discarding all buffers containing an RLC PDU from the re-initialized RLC entity by an HARQ entity on the transmitting side. Additionally, the application also does not disclose anything starting sequence numbers of PDUs sent after re-initialization with an R bit and discarding PDUs received which start with a bit different from the R bit. In another US patent application titled "Method of retransmission protocol reset synchronisation" (patent no. US 2004/0208160), it discloses a method of retransmission protocol reset synchronization in a radio network of a communication system, said radio network including at least one radio network controller RNC for controlling a plurality of base stations in communication with mobile terminals, wherein the RNC communicates with a communication terminal using a radio link control RLC procedure and the plurality of base stations communicate with the mobile terminals using a medium access control MAC procedure, comprising the steps of initiating a RLC reset procedure upon occurrence of an unrecoverable protocol error and initiating a MAC reset procedure in response to a RLC reset procedure. The patent application proposes a method for retransmission protocol reset synchronization in a radio network. The method proposes initiating RLC reset procedure upon occurrence of unrecoverable protocol error or upon reaching a predetermined number of retransmissions or upon transmitting a discard notification for a predetermined number of times. The application mentions flushing MAC-hs PDUs containing old RLC PDUs and remaining in UE reordering buffer and soft buffer as well as resetting related HARQ processes. However, the application does not explicitly mention an HARQ entity on the transmitting side discarding all buffers containing an RLC PDU from the re¬initialized RLC entity. Further, the application does not mention starting timers (at both the transmitting and the receiving sides) after re-initialization and not transferring or receiving PDUs until the timers expire. The application also does not disclose the transmitting RLC entity informing value of its protocol variable (TX_SN_TO_BE_TRANSMITTED) to the receiving RLC entity; and receiving RLC entity discarding PDUs having sequence number less than this value after re-initialization. Additionally, the application also, does not disclose starting sequence numbers of PDUs sent after re-initialization with an R bit and discarding PDUs received which start with a bit different from the R bit. Based on these premises, the present invention is detailed herein. The present invention proposes different methods for avoiding additional re-initiatization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization. More precisely, the present invention relates to various methods for handling of the lateral arrival of a PDU after reset/re-establishment of RLC in wireless communication system. SUMMARY OF THE INVENTION It is therefore the primary objective of the invention to propose a method(s) to avoid additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization. It is another objective of the invention to provide more than one method to handle the late arrival of a PDU after reset/re-establishment of RLC in wireless communication system. It is yet another object of the invention to have a mechanism that relates to the long-term evolution of 3GPP UMTS protocols. Accordingly, the present invention proposes a method for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system, the method comprising, • Sending a signaling message to the peer receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity; • Re-initializing of the receiver RLC entity on reception of the signaling message, and starting the RX_WAIT_TIMER; • Sending a response message to the peer transmitting RLC entity; • Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by starting the TX_WAIT_TIMER; and • Halting the reception of PDUs by the receiving RLC entity until the expiry of the RX_WAIT_TIMER, and transmitting of the PDUs by the transmitter RLC entity only on the expiry of TX_WAIT_TIMER respectively. Also, the present invention proposes another method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, wherein after the re-initialization of RLC entity is triggered, the HARQ entity on the transmitting RLC side discards all the buffers which contain a RLC PDU from the re-initialized RLC entity, and the corresponding buffers in the HARQ entity on the receiving side is discarded (automatically ovenwritten) after fresh PDUs are scheduled for transmission on the transmitting side. Invention provides yet another method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re¬initialization, the method comprising, • Sending a signaling message to the receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity, which also contains the value of TX SN TO BE TRANSMITTED. • Re-initializing of the receiver RLC entity on reception of the signaling message, and setting the variables RX_SN_HIGHEST and RX_SN_TO_BE_RECEIVED to TX_SN_TO_BE_TRANSMITTED. • Sending a response message to the peer transmitting RLC entity. • Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by setting TX_SN_TO_BE_ACKNOIWLEDGED to TX_SN_TO_BE_TRANSMITTED. The present invention also proposes another method for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system, wherein both the transmitting as well as the receiving RLC entities maintain a protocol variable 'R' preset to a value '0' or '1', the method comprising, • Sending a signaling message to the receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity; • Re-initializing of the receiver RLC entity on reception of the signaling message, and toggling the value of 'R'; • Sending a response message to the peer transmitting RLC entity; and • Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, and toggling the value of 'R' before resuming the transmission of PDUs. These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF ACCOMPANYING FIGURES Figure 1 illustrates the radio interface protocol architecture Figure 2 illustrates abstraction of the RLC protocol Figure 3 illustrates the protocol layering and position of HARQ functionality Figure 4 illustrates a methodology to handle lateral arrival of a PDU after reset/re-establishment of RLC based on a WAIT_TIMER mechanism in accordance with one aspect. Figure 5 illustrates a methodology to handle lateral arrival of a PDU after reset/re-establishment of RLC based on exchange of TX_SN in accordance with one aspect. DETAILED DESCRIPTION OF INVENTION The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. \t should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. The present invention describes various methods for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization. More precisely, the present invention relates to different methods for handling of the lateral arrival of a PDU after reset/re-establishment of RLC in wireless communication system. The detailed descriptions of the various embodiments of the present invention are given in the following paragraphs. Figure 4 illustrates a methodology to handle the lateral arrival of a PDU after reset/re-establishment of RLC, based on a WAIT_TIMER mechanism in accordance with one embodiment of the present invention. Accordingly, on detection of a trigger for re-initialization in transmitter, a signaling message in RESET PDU is sent to the peer receiving RLC entity. Further, on reception of a signaling message for re-initialization, the receiver RLC entity is re-initialized and the RX_WAIT_TIMER is started. A response message is then sent in RESET ACK PDU to the peer transmitting RLC entity. Additionally, in case of a re¬initialization controlled by the upper layer in both transmitting and receiving RLC entity, the signaling can be performed by the corresponding upper layers. On reception of the acknowledgement of the signaling message, the RLC transmitter entity is re-initialized and the TX_WAIT_TIMER is started. Further, the reception of PDUs will be halted by the receiver and the reception of PDUs is resumed only on the RX_WAIT_TIMER expiry. Similarly, transmission of PDUs is resumed on the TX_WA!T_TIMER expiry. Further, the values of TX_WAIT_TIMER and RX_WAIT_TIMER can be chosen in such a way that the receiving RLC entity cannot resume reception of PDUs before all the old PDUs are flushed out from the HARQ (Hybrid Automatic Repeat Request) buffers, and the transmitting RLC entity cannot resume transmission of PDUs more than propagation delay, usually half the RTT, earlier than the receiving RLC entity has resumed reception. Additionally, it should be noted that the value of the TX_WAIT_TIMER can be different from that of RX_WAIT_TIMER since the transmitting RLC entity stops the transmission of PDUs even before starting the TX_WAIT_TIMER as shown in figure 4. Ideally, TX_WAIT_TIMER should be equal to RX_WAIT_TIMER -RTT. More precisely, in one exemplary embodiment of the present invention, both the peer RLC entities start a timer, called WAIT_TIMER, after re-initialization. The transmitting RLC entity shall not transmit any PDUs before the expiry of the TX_WAIT_TIMER. Further, the peer receiving RLC entity discard all PDUs received before the expiry of the RX_WAIT_TIMER. In another exemplary embodiment of the present invention, after re-initialization of the RLC entity is triggered, the HARQ entity on the transmitting RLC side discards all the buffers which contain a RLC PDU from the re-initialized RLC entity. The corresponding buffers in the HARQ entity on the receiving side can be discarded (automatically overwritten) after fresh PDUs are scheduled for transmission on the transmitting side. Further, on the receiving side, there is no additional action required to be taken by either the RLC entity or the HARQ entity. Since all the PDUs transmitted before the re-initialization are already discarded, the data transfer can be resume immediately after the re-initialization is completed at both the transmitting and receiving RLC entities. In another exemplary embodiment of the present invention, the re-initialization does not involve re-setting the protocol variables to their initial values. Both the transmitting and the receiving RLC entities only flush out their transmission and reception buffers respectively. Additionally, the transmitting RLC entity can inform the value of its protocol variable TX_SN_TO_BE_TRANSMITTED to the receiving entity. It is to be appreciated that, by including the value of TX_SN_TO_BE_TRANSMITTED in the peer-to-peer signalling message in RESET PDU, the late arrival of PDU can be handled. In case of a re-initialization controlled by the upper layer, this value shall be included in the signalling message of the upper layer. Further, after re-initialization, the receiving RLC entity can discard any PDUs which are received with sequence number less than this value. Additionally, this is achieved by setting both the variables RX SN TO BE RECEIVED and RX SN HIGHEST to the value of TX_SN_TO_BE_TRANSMITTED received from'the peer transmitting entity. This makes the receive window span from TX_SN_TO_BE_TRANSMITTED to TX_SN_TO_BE_TRANSMITTED + RX_WINDOW_SIZE - 1. Consequently, any PDUs bearirig sequence numbers less than the value of TX_SN_TO_BE_TRANSMITTED, as received from the peer transmitting RLC entity, can be discarded for they fall outside the receive window. On the transmitting side, on reception of the signalling message acknowledging the re-initialization, the variable TX_SN_TO_BE_ACKtsiOWLEDGED is set to TX_SN_TO_BE_TRANSMITTED. This makes the transmit window span from TX_SN_TO_BE_TRANSMITTED to TX_SN_TO_BE_TRANSMITTED + TX_WINDOW_SIZE - 1. Since, the protocol variabfes are not reset, the transmission continues normally from TX_SN_TO_BE_TRANSMITTED onwards after re-initialization. Since, the PDUs transmitted before the re-initialization bear sequence numbers less than the value of ■TX_SN_TO_BE_TRANSMITTED signalled to the receiving entity, they are correctly discarded. Additionally, it should be noted that protocol variables RX_SN_TO_BE_RECEIVED and RX_SN__HIGHEST for the receiving RLC entity, which are being set to TX_SN_TO_BE_TRANSMITTED on re¬initialization, can keep moving on in their normal course of action on the resumption of the data transfer. Therefore, there is no danger of discard of all the future PDUs bearing sequence numbers less than the TX_SN_TO_BE_TRANSMITTED received from the peer RLC entity. Figure 5 illustrates a methodology to handle lateral arrival of a PDU after reset/re-establishment of RLC based on exchange TX_SN in accordance with one aspect. On detection of a trigger for re-initialization, the transmitting RLC entity can send a signalling message to the receiving RLC entity also containing the value of TX_SN_TO_BE_TRANSMITTED. Additionally, in case of a re¬initialization controlled by the upper layer, the signalling shall be performed by the corresponding upper layer and the value of TX_SN_TO_BE_TRANSMITTED can be included therein. Further, at the receiving RLC entity, on reception of a signalling message for re-initialization, the receiving RLC entity is re-initialized and both the variables RX_SN_TO_BE_RECEIVED and RX_SN_HIGHEST is set to the value received in the signalling message i.e, RLC or the upper layer, as the case may be and a response message is sent to the transmitting RLC entity. Additionally, in case of a re-initialization controlled by the upper layer, the signalling is performed by the corresponding upper layer at the receiving RLC entity. At the transmitting RLC entity, on reception of the acknowledgement of the signalling message, the transmitting RLC entity is re-initialized and TX_SN_TO_BE_ACKNOIWLEDGED is set to TX_SN_TO_BE_TRANSMITTED. Further, the transmission of PDUs is resumed by the transmitting RLC entity. In yet another exemplary embodiment of the present invention, both the transmitting as well as the receiving RLC entity maintains a protocol variable, R which can be initialized to a predefined value either 0 or 1. The transmitting RLC entity can set the first bit in the sequence numbers of the outgoing PDUs to R. The receiving RLC entity, on the other hand, will discard any PDUs with sequence numbers not starting with R i.e. which do not have their first bit set to The functional steps for the said embodiment are as follows: On detection of a trigger for re-initialization, a signaling message can be sent to the receiving RLC entity. Additionally, in case of a re-initialization controlled by the upper layer, the signaling can be performed by the corresponding upper layer. Further, on reception of a signaling message for re-initialization, the receiving RLC entity is re-initialized, the R bit is toggled, and a response message is sent to the transmitting RLC entity. Additionally, in case of a re-initialization controlled by the upper layer, the,signaling will be performed by the corresponding upper layer. On reception of the acknowledgement of the signaling message, the RLC transmitting entity is re-initialized and the R bit shall be toggled and the transmission of PDUs can be resumed. The present invention enables the RLC to avoid additional re-initialization(s) caused by the late arrival of an RLC PDU transmitted before the (original) re¬initialization. Therefore; the present invention can solve the problems raised by late arrival of the RLC PDU in the wireless communication system. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart there from. Glossary of Terms and their definitions: ARQ: Automatic Repeat Request HARQ: Hybrid Automatic Repeat Request MAC: Medium Access Control (Protocol) OSI: Open System Interconnection (Protocol Reference Model) PDU: Packet Data Unit RB: Radio Bearer RLC: Radio Link Control (Protocol) RRC: Radio Resource Control (Protocol) SDU: Service Data Unit TTI: Transmission Time Interval UE: User Equipment E-UTRAN: Enhanced Universal Terrestrial Radio Access Network UMTS; Universal Mobile Telecommunications Service We Claim: 1. A method for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system, the method comprising, • Sending a signaling message to the peer receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity; • Re-initializing of the receiver RLC entity on reception of the signaling message, and starting the RX_WAIT_TIMER; • Sending a response message to the peer transmitting RLC entity; • Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by starting the TX_WAIT_TIMER; and • Halting the reception of PDUs by the receiving RLC entity until the expiry of the RX_WAIT_TIMER, and transmitting of the PDUs by the transmitter RLC entity only on the expiry of TX_WAIT_TIMER respectively. 2. The method as claimed in claim 1, wherein the values of RX_WAIT_TIIVIER and TX_WAIT_TIMER are so chosen that that the receiving RLC entity can not resume reception of PDUs before all the old PDUs are flushed out from the HARQ buffers, and the transmitting RLC entity can't resume transmission of PDUs not earlier than the receiving RLC entity had resumed reception. , 3. The method as claimed in claim 1, wherein the value of TX_WAIT_TIMER is different from RX_WAIT__TIMER since the transmitting RLC entity stops the transmission of PDUs even before starting the TX_WAIT_TIMER. 4. A method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, wherein after the re-initialization of RLC entity is triggered, the HARQ entity on the transmitting RLC side discards all the buffers which contain a RLC PDU from the re-initialized RLC entity, and the corresponding buffers in the HARQ entity on the receiving side is discarded (automatically overwritten) after fresh PDUs are scheduled for transmission on the transmitting side. 5. The method as claimed in claim 4, wherein no additional action is required to be taken by either the RLC entity or the HARQ entity on the receiving side. 6. A method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, the method comprising, • Sending a signaling message to the receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity, which also contains the value of TX_SN_TO_BE_TRANSMITTED; • Re-initializing of the receiver RLC entity on reception of the signaling message, and setting the variables RX_SN_HIGHEST and RX_SN_TO_BE_RECEIVED to TX_SN_TO_BE_TRANSMITTED.; • Sending a response message to the peer transmitting RLC entity; • Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by setting TX_SN_TO_BE_ACKNOIWLEDGED to TX_SN_TO_BE_TRANSMITTED. 7. The method as claimed in claim 6, wherein the protocol variables are not reset post re-initialization. 8. The method as claimed in claim 6, wherein the receiving RLC entity discards any PDUs that it receives with a sequence number lesser than the value of TX_SN_TO_BE_TRANSMITTED, post re-initialization. 9. A method for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system, wherein both the transmitting as well as the receiving RLC entities maintain a protocol variable 'R' preset to a value '0' or '1', the method comprising, • Sending a signaling message to the receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity; • Re-initializing of the receiver RLC entity on reception of the signaling message, and toggling the value of 'R'; • Sending a response message to the peer transmitting RLC entity; • Re-initializing the transmitter RLC entity on reception of tlie acknowledgement of the signaling message, and toggling the value of 'R' before resuming the transmission of PDUs. 10. The method as claimed in claim 9, wherein receiving RLC entity discards any PDUs having sequence numbers not starting with R. 11.The methods as claimed in claims 1, 6 & 9, wherein if the re-initialization is controlled by the upper layers in the transmitting and receiving RLC entities, the corresponding signaling is also performed by the respective upper layers. 12. A method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, substantially as herein described with respect to the accompanying drawings.

Full Text

FIELD OF THE INVENTION
The present invention, in general, relates to the field of wireless communication. In particular, the present invention proposes various methods for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization. More particularly, the present invention relates to various methods for handling late arrival of a PDU after reset/re-establishment of a Radio Link Control (RLC) entity of a wireless communication system, which is applicable to any ARQ mechanism with an underlying HARQ layer.
DESCRIPTION OF PRIOR ART
UMTS is a third generation mobile communication system developed in Europe. The UMTS employs a WCDMA as radio access technique. The WCDMA is DS-CDMA technique of a FDD scheme, which transmits data using bandwidth of 5 MHz in frequency band of 2 GHz.
A HARQ is a physical layer retransmission function in the WiMax IEEE 802.16 protocol with variants in several cellular protocols, such as in UMTS. HARQ is a link adaptation technique where link layer acknowledgements are used for re¬transmission decisions at the physical layer. IEEE 802.16 defines two levels of retry attempts wherein, the first level as in HARQ on the physical layer and the second level is on a higher layer protocol such as standard ARQ on the data plane, or MAC timers on the control plane.

Figure 1 illustrates the radio interface protocol architecture layer proposed for a 3G wireless network and is reproduced from the 3GPP TS 25.301. Layer-1 or the physical layer of the UMTS radio interface is responsible for coding and modulation of data transmitted over the air. Layer-2 or the data link layer is subdivided into a RLC sublayer and a MAC sublayer. The service provided by layer-2 is referred to as the radio bearer. The control plane radio bearers, which are provided by RLC to RRC, are denoted as signaling radio bearers. The separation in MAC and RLC sublayers is motivated by the need to support a wide range of upper layer services, and also the requirement to provide high efficiency and low latency data services over a wide performance range, i.e. from 1.2 Kbps to greater than 2 Mbps. Other motivators are the need for supporting high QoS delivery of circuit and packet data services, such as limitations on acceptable delays and/or data BER, and the growing demand for advanced multimedia services. Each multimedia service has different QoS requirements. The data link layer also comprises a C-plane signaling and a U-plane information for separating the information from control signals.
The RLC layer receives data packets from the higher layers, such as IP, through SAP, and delivers RLC frames to the MAC sublayer. The RLC frames are queued into logical channels. At the MAC sublayer, the RLC frames are multiplexed onto transport channels. The transport channels are the interface of the physical layer to the data link layer. In fact, data link layer functions are divided in two parts, PLICF handled in the RLC, and PLDCF included in the MAC. It is assumed that there is one instance of RLC for each data

application/session. Multiple types (common and shared) of transport channels are provided based on the method of data transmission. Multiple types (traffic and control) of logical channels are provided according to the type of transmitted information. RRC is the only radio protocol in L3 and is only defined in the control plane. It controls the logical, transport and physical channels in relation to the setup, modification and release of the RBs.
More precisely, the RLC functionality is independent of its location (in UE or UTRAN) and only depends on whether it receives the RLC PDUs from the lower layer or RLC SDUs from the upper layer. A transmitting RLC entity receives the RLC SDUs from the upper layer. A receiving RLC entity receives the RLC PDUs from the lower layer.
A transmitting RLC entity receives RLC SDUs from the upper layers and segments and/or concatenates the SDUs and makes fresh data units, called RLC PDUs. The RLC PDUs are submitted to MAC which in turn submits them to PHY. PHY transfers these PDUs to the peer PHY. Further, at the peer end, the RLC PDUs are finally submitted to a receiving RLC entity via MAC. The RLC SDUs are re-assembled from the received RLC PDUs and ultimately submitted to the upper layers.
The flow control between the peer RLC entities is achieved by using a well-
known scheme in the field of communication protocols called sliding window
mechanism. The transmitting RLC entity maintains, among others, protocol
variables TX SN TO BE ACKNOWLEDGED and

TX_SN_TO_BE_TRANSMITTED. TX_SN_TO_BE_TRANSMITTED indicates the sequence number of the next PDU to be transmitted. This is maintained as one higher than the sequence number of the PDU that was transmitted to the peer RLC entity with the highest sequence number. TX_SN_TO_BE_ACKNOWLEDGED indicates the next in-sequence PDU which is pending for acknowledgement from the peer receiving entity. It is maintained as one higher than the sequence number up to which all PDUs have been acknowledged by the peer RLC entity. .
The receiving RLC entity maintains, among others, protocol variables RX_SN_TO_BE_RECEIVED and RX_SN_HIGHEST. RX_SN_HIGHEST indicates the sequence number one higher than that of the PDU that was received from the peer transmitting entity bearing the highest sequence number. RX_SN_TO_BE_RECEIVED indicates the next in-sequence PDU which might be expected to be received from the peer transmitting entity. It is maintained as one higher than the sequence number up to which all PDUs have been sequentially received.
The protocol variables described above are numbered by modulo integer
sequence numbers cycling through the field: 0 to
SEQUENCE_NUMBER_RANGE - 1. The variable
SEQUENCE_NUI\/1BER_RANGE is a protocol constant. The flow control mechanism of the sliding window protocol is controlled by the configuration of a variable WINDOW_SIZE by the upper layer (RRC). The variable for the transmitting RLC entity is called TX_WINDOW_SIZE. The variable for the

receiving RLC entity is called RX_WINDOW_SIZE.
The value of TX_WINDOW_SIZE for a transmitting entity is usually smaller than or equal to the value of RX_WINDOW_SIZE for the peer receiving entity. The transmit window spans from TX_SN_TO_BE_TRANSMITTED to TX_SN_TO_BE_TRANSMITTED + TX_WINDOW_SIZE - 1. The PDUs falling outside the transmit window are not transmitted.
The receive window spans from RX_SN_TO_BE_RECEIVED (RX_SN_TO_BE_RECEIVED + RX_WINDOW_SIZE - 1). The PDUs falling outside the receive window are discarded. The receiving RLC entity apprises its peer transmitting entity of the PDU status according to the reporting configuration received from the upper layer e.g. periodically. The transmitting entity may also poll the peer receiving entity for the status of the PDUs that were transmitted to it.
The RLC entities require a re-initialization when, for example, a protocol error is detected. A protocol error is a scenario which is un-imaginable if both the peer entities are assumed to work strictly according to the specifications. A protocol error may occur due to, among others, some problem with the underlying physical link resulting into a corruption or sustained loss of data.
Figure 2 illustrates abstraction of the RLC protocol. As shown in the figure 2, the receiving RLC entity receives the information sent by the transmitting RLC entity through defined medium. There are two methods of re-initializing of an RLC

entity: via peer to peer communication called RESET (involving the exchange of a control PDU, called RESET PDU, and an acknowledgement thereof) or controlled by the upper layer called RE-ESTABLISHMENT.
All the PDUs (Packet Data Units) stored in the transmission buffer of the transmitting RLC entity are flushed out on re-initialization. All the PDUs stored in the reception buffer of the receiving RLC entity are flushed out on re¬initialization. All the protocol variables are also set to their initial values by both the transmitting as well as the receiving RLC entities on re-initialization.
Figure 3 depicts protocol layering and position of HARQ functionality. With the introduction of HARQ at MAC layer between the RLC and PHY layers as shown in the figure 3, it is possible that RLC PDUs may be received out of order. Therefore, it is also possible that a PDU transmitted before the re-initialization of the peer RLC entities is received after the re-initialization has been performed.
The receiving entity, following the normal course of action, shall report the status for the received PDU(s) to the peer transmitting entity. But, the transmitting entity does not have any record of the PDUs transmitted before re-initialization since all the protocol variables are reset to their initial values. Therefore, the unexpected status report amounts to a protocol error at the transmitting entity. This shall result into another re-initialization being triggered by the transmitting entity.
It is clear that, in fact, no protocol error had occurred when the re-initialization

was triggered by the transmitting entity. The problem was caused entirely due to the late arrival of the RLC PDUs transmitted before the re-initialization. Therefore, a method is needed to handle the late arrival of the RLC PDUs to overcome the crises raised by it.
In the state of the art literature, the patent application titled "Data packet transmission" (patent no. US 2007/0133605) describes using the attribute priority to achieve a stronger FEC for RLC Control PDUs transmitted via the HS-DSCH also entails prioritized handling so that an RLC Control PDU is likely to overhaul an RLC Data PDU. As a consequence the RLC protocol operation can severely be disturbed, since it relies on in-sequence delivery of control and data PDUs. According to an exemplary embodiment of the present invention, two types of containers are provided in which data packets may be transmitted, wherein the first type of container is provided with a stronger error coding than the second type of container and wherein data packets which comprise control instructions are only transmitted in the first container type with the stronger error correction. Due to this, an improved forward error correction for control PDUs of the AM RLC protocol of UMTS may be provided.
The patent application proposes a method and system for transmitting data packets (first data packets and second data packets) from a transmitting station to a receiving station over a high speed downlink shared channel in UMTS. The first data packets are RLC control PDUs while the second data packets RLC data PDUs. According to an embodiment, after the RLC RESET procedure is finished, the transmitting and receiving windows are not initialized to the

sequence number 0. Instead, the lower edge of these windows is set equal to the lower edge of the transmitting window immediately before the RLC RESET procedure is Initiated.
However, the application does not mention starting timers (at both the transmitting and the receiving sides) after re-initialization and not transferring or receiving PDUs until the timers expire. Further, the application also does not propose discarding all buffers containing an RLC PDU from the re-initialized RLC entity by an HARQ entity on the transmitting side. Additionally, the application also does not disclose anything starting sequence numbers of PDUs sent after re-initialization with an R bit and discarding PDUs received which start with a bit different from the R bit.
In another US patent application titled "Method of retransmission protocol reset synchronisation" (patent no. US 2004/0208160), it discloses a method of retransmission protocol reset synchronization in a radio network of a communication system, said radio network including at least one radio network controller RNC for controlling a plurality of base stations in communication with mobile terminals, wherein the RNC communicates with a communication terminal using a radio link control RLC procedure and the plurality of base stations communicate with the mobile terminals using a medium access control MAC procedure, comprising the steps of initiating a RLC reset procedure upon occurrence of an unrecoverable protocol error and initiating a MAC reset procedure in response to a RLC reset procedure.

The patent application proposes a method for retransmission protocol reset synchronization in a radio network. The method proposes initiating RLC reset procedure upon occurrence of unrecoverable protocol error or upon reaching a predetermined number of retransmissions or upon transmitting a discard notification for a predetermined number of times. The application mentions flushing MAC-hs PDUs containing old RLC PDUs and remaining in UE reordering buffer and soft buffer as well as resetting related HARQ processes.
However, the application does not explicitly mention an HARQ entity on the transmitting side discarding all buffers containing an RLC PDU from the re¬initialized RLC entity. Further, the application does not mention starting timers (at both the transmitting and the receiving sides) after re-initialization and not transferring or receiving PDUs until the timers expire. The application also does not disclose the transmitting RLC entity informing value of its protocol variable (TX_SN_TO_BE_TRANSMITTED) to the receiving RLC entity; and receiving RLC entity discarding PDUs having sequence number less than this value after re-initialization. Additionally, the application also, does not disclose starting sequence numbers of PDUs sent after re-initialization with an R bit and discarding PDUs received which start with a bit different from the R bit.
Based on these premises, the present invention is detailed herein. The present invention proposes different methods for avoiding additional re-initiatization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization. More precisely, the present invention relates to various methods for handling of

the lateral arrival of a PDU after reset/re-establishment of RLC in wireless communication system.
SUMMARY OF THE INVENTION
It is therefore the primary objective of the invention to propose a method(s) to avoid additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization.
It is another objective of the invention to provide more than one method to handle the late arrival of a PDU after reset/re-establishment of RLC in wireless communication system.
It is yet another object of the invention to have a mechanism that relates to the long-term evolution of 3GPP UMTS protocols.
Accordingly, the present invention proposes a method for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system, the method comprising,
• Sending a signaling message to the peer receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity;
• Re-initializing of the receiver RLC entity on reception of the signaling message, and starting the RX_WAIT_TIMER;
• Sending a response message to the peer transmitting RLC entity;

• Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by starting the TX_WAIT_TIMER; and
• Halting the reception of PDUs by the receiving RLC entity until the expiry of the RX_WAIT_TIMER, and transmitting of the PDUs by the transmitter RLC entity only on the expiry of TX_WAIT_TIMER respectively.
Also, the present invention proposes another method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, wherein after the re-initialization of RLC entity is triggered, the HARQ entity on the transmitting RLC side discards all the buffers which contain a RLC PDU from the re-initialized RLC entity, and the corresponding buffers in the HARQ entity on the receiving side is discarded (automatically ovenwritten) after fresh PDUs are scheduled for transmission on the transmitting side.
Invention provides yet another method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re¬initialization, the method comprising,
• Sending a signaling message to the receiving RLC entity on detection of
re-initialization trigger in transmitter RLC entity, which also contains the
value of TX SN TO BE TRANSMITTED.

• Re-initializing of the receiver RLC entity on reception of the signaling message, and setting the variables RX_SN_HIGHEST and RX_SN_TO_BE_RECEIVED to TX_SN_TO_BE_TRANSMITTED.
• Sending a response message to the peer transmitting RLC entity.
• Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by setting TX_SN_TO_BE_ACKNOIWLEDGED to TX_SN_TO_BE_TRANSMITTED.
The present invention also proposes another method for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system, wherein both the transmitting as well as the receiving RLC entities maintain a protocol variable 'R' preset to a value '0' or '1', the method comprising,
• Sending a signaling message to the receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity;
• Re-initializing of the receiver RLC entity on reception of the signaling message, and toggling the value of 'R';
• Sending a response message to the peer transmitting RLC entity; and
• Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, and toggling the value of 'R' before resuming the transmission of PDUs.

These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1 illustrates the radio interface protocol architecture
Figure 2 illustrates abstraction of the RLC protocol
Figure 3 illustrates the protocol layering and position of HARQ functionality
Figure 4 illustrates a methodology to handle lateral arrival of a PDU after reset/re-establishment of RLC based on a WAIT_TIMER mechanism in accordance with one aspect.
Figure 5 illustrates a methodology to handle lateral arrival of a PDU after reset/re-establishment of RLC based on exchange of TX_SN in accordance with one aspect.
DETAILED DESCRIPTION OF INVENTION
The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. \t should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the

claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail.
The present invention describes various methods for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization. More precisely, the present invention relates to different methods for handling of the lateral arrival of a PDU after reset/re-establishment of RLC in wireless communication system. The detailed descriptions of the various embodiments of the present invention are given in the following paragraphs.
Figure 4 illustrates a methodology to handle the lateral arrival of a PDU after reset/re-establishment of RLC, based on a WAIT_TIMER mechanism in accordance with one embodiment of the present invention. Accordingly, on detection of a trigger for re-initialization in transmitter, a signaling message in RESET PDU is sent to the peer receiving RLC entity. Further, on reception of a signaling message for re-initialization, the receiver RLC entity is re-initialized and the RX_WAIT_TIMER is started. A response message is then sent in RESET ACK PDU to the peer transmitting RLC entity. Additionally, in case of a re¬initialization controlled by the upper layer in both transmitting and receiving RLC entity, the signaling can be performed by the corresponding upper layers. On reception of the acknowledgement of the signaling message, the RLC transmitter entity is re-initialized and the TX_WAIT_TIMER is started. Further, the reception

of PDUs will be halted by the receiver and the reception of PDUs is resumed only on the RX_WAIT_TIMER expiry. Similarly, transmission of PDUs is resumed on the TX_WA!T_TIMER expiry.
Further, the values of TX_WAIT_TIMER and RX_WAIT_TIMER can be chosen in such a way that the receiving RLC entity cannot resume reception of PDUs before all the old PDUs are flushed out from the HARQ (Hybrid Automatic Repeat Request) buffers, and the transmitting RLC entity cannot resume transmission of PDUs more than propagation delay, usually half the RTT, earlier than the receiving RLC entity has resumed reception.
Additionally, it should be noted that the value of the TX_WAIT_TIMER can be different from that of RX_WAIT_TIMER since the transmitting RLC entity stops the transmission of PDUs even before starting the TX_WAIT_TIMER as shown in figure 4. Ideally, TX_WAIT_TIMER should be equal to RX_WAIT_TIMER -RTT.
More precisely, in one exemplary embodiment of the present invention, both the peer RLC entities start a timer, called WAIT_TIMER, after re-initialization. The transmitting RLC entity shall not transmit any PDUs before the expiry of the TX_WAIT_TIMER. Further, the peer receiving RLC entity discard all PDUs received before the expiry of the RX_WAIT_TIMER.
In another exemplary embodiment of the present invention, after re-initialization of the RLC entity is triggered, the HARQ entity on the transmitting RLC side discards all the buffers which contain a RLC PDU from the re-initialized RLC

entity. The corresponding buffers in the HARQ entity on the receiving side can be discarded (automatically overwritten) after fresh PDUs are scheduled for transmission on the transmitting side.
Further, on the receiving side, there is no additional action required to be taken by either the RLC entity or the HARQ entity. Since all the PDUs transmitted before the re-initialization are already discarded, the data transfer can be resume immediately after the re-initialization is completed at both the transmitting and receiving RLC entities.
In another exemplary embodiment of the present invention, the re-initialization does not involve re-setting the protocol variables to their initial values. Both the transmitting and the receiving RLC entities only flush out their transmission and reception buffers respectively. Additionally, the transmitting RLC entity can inform the value of its protocol variable TX_SN_TO_BE_TRANSMITTED to the receiving entity. It is to be appreciated that, by including the value of TX_SN_TO_BE_TRANSMITTED in the peer-to-peer signalling message in RESET PDU, the late arrival of PDU can be handled. In case of a re-initialization controlled by the upper layer, this value shall be included in the signalling message of the upper layer. Further, after re-initialization, the receiving RLC entity can discard any PDUs which are received with sequence number less than this value.
Additionally, this is achieved by setting both the variables RX SN TO BE RECEIVED and RX SN HIGHEST to the value of

TX_SN_TO_BE_TRANSMITTED received from'the peer transmitting entity. This makes the receive window span from TX_SN_TO_BE_TRANSMITTED to TX_SN_TO_BE_TRANSMITTED + RX_WINDOW_SIZE - 1. Consequently, any PDUs bearirig sequence numbers less than the value of TX_SN_TO_BE_TRANSMITTED, as received from the peer transmitting RLC entity, can be discarded for they fall outside the receive window.
On the transmitting side, on reception of the signalling message acknowledging the re-initialization, the variable TX_SN_TO_BE_ACKtsiOWLEDGED is set to TX_SN_TO_BE_TRANSMITTED. This makes the transmit window span from TX_SN_TO_BE_TRANSMITTED to TX_SN_TO_BE_TRANSMITTED + TX_WINDOW_SIZE - 1. Since, the protocol variabfes are not reset, the transmission continues normally from TX_SN_TO_BE_TRANSMITTED onwards after re-initialization. Since, the PDUs transmitted before the re-initialization bear sequence numbers less than the value of ■TX_SN_TO_BE_TRANSMITTED signalled to the receiving entity, they are correctly discarded.
Additionally, it should be noted that protocol variables RX_SN_TO_BE_RECEIVED and RX_SN__HIGHEST for the receiving RLC entity, which are being set to TX_SN_TO_BE_TRANSMITTED on re¬initialization, can keep moving on in their normal course of action on the resumption of the data transfer. Therefore, there is no danger of discard of all the future PDUs bearing sequence numbers less than the TX_SN_TO_BE_TRANSMITTED received from the peer RLC entity.
Figure 5 illustrates a methodology to handle lateral arrival of a PDU after

reset/re-establishment of RLC based on exchange TX_SN in accordance with one aspect. On detection of a trigger for re-initialization, the transmitting RLC entity can send a signalling message to the receiving RLC entity also containing the value of TX_SN_TO_BE_TRANSMITTED. Additionally, in case of a re¬initialization controlled by the upper layer, the signalling shall be performed by the corresponding upper layer and the value of TX_SN_TO_BE_TRANSMITTED can be included therein. Further, at the receiving RLC entity, on reception of a signalling message for re-initialization, the receiving RLC entity is re-initialized and both the variables RX_SN_TO_BE_RECEIVED and RX_SN_HIGHEST is set to the value received in the signalling message i.e, RLC or the upper layer, as the case may be and a response message is sent to the transmitting RLC entity. Additionally, in case of a re-initialization controlled by the upper layer, the signalling is performed by the corresponding upper layer at the receiving RLC entity. At the transmitting RLC entity, on reception of the acknowledgement of the signalling message, the transmitting RLC entity is re-initialized and TX_SN_TO_BE_ACKNOIWLEDGED is set to TX_SN_TO_BE_TRANSMITTED. Further, the transmission of PDUs is resumed by the transmitting RLC entity.
In yet another exemplary embodiment of the present invention, both the transmitting as well as the receiving RLC entity maintains a protocol variable, R which can be initialized to a predefined value either 0 or 1. The transmitting RLC entity can set the first bit in the sequence numbers of the outgoing PDUs to R. The receiving RLC entity, on the other hand, will discard any PDUs with sequence numbers not starting with R i.e. which do not have their first bit set to

The functional steps for the said embodiment are as follows: On detection of a trigger for re-initialization, a signaling message can be sent to the receiving RLC entity. Additionally, in case of a re-initialization controlled by the upper layer, the signaling can be performed by the corresponding upper layer. Further, on reception of a signaling message for re-initialization, the receiving RLC entity is re-initialized, the R bit is toggled, and a response message is sent to the transmitting RLC entity. Additionally, in case of a re-initialization controlled by the upper layer, the,signaling will be performed by the corresponding upper layer. On reception of the acknowledgement of the signaling message, the RLC transmitting entity is re-initialized and the R bit shall be toggled and the transmission of PDUs can be resumed.
The present invention enables the RLC to avoid additional re-initialization(s) caused by the late arrival of an RLC PDU transmitted before the (original) re¬initialization. Therefore; the present invention can solve the problems raised by late arrival of the RLC PDU in the wireless communication system.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart there from.

Glossary of Terms and their definitions:
ARQ: Automatic Repeat Request
HARQ: Hybrid Automatic Repeat Request
MAC: Medium Access Control (Protocol)
OSI: Open System Interconnection (Protocol Reference Model)
PDU: Packet Data Unit
RB: Radio Bearer
RLC: Radio Link Control (Protocol)
RRC: Radio Resource Control (Protocol)
SDU: Service Data Unit
TTI: Transmission Time Interval
UE: User Equipment
E-UTRAN: Enhanced Universal Terrestrial Radio Access Network
UMTS; Universal Mobile Telecommunications Service

We Claim:
1. A method for handling late arrival of PDU after reset/re-establishment of
RLC entity in a wireless communication system, the method comprising,
• Sending a signaling message to the peer receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity;
• Re-initializing of the receiver RLC entity on reception of the signaling message, and starting the RX_WAIT_TIMER;
• Sending a response message to the peer transmitting RLC entity;
• Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by starting the TX_WAIT_TIMER; and
• Halting the reception of PDUs by the receiving RLC entity until the expiry of the RX_WAIT_TIMER, and transmitting of the PDUs by the transmitter RLC entity only on the expiry of TX_WAIT_TIMER respectively.
2. The method as claimed in claim 1, wherein the values of
RX_WAIT_TIIVIER and TX_WAIT_TIMER are so chosen that that the
receiving RLC entity can not resume reception of PDUs before all the old
PDUs are flushed out from the HARQ buffers, and the transmitting RLC
entity can't resume transmission of PDUs not earlier than the receiving
RLC entity had resumed reception. ,

3. The method as claimed in claim 1, wherein the value of TX_WAIT_TIMER is different from RX_WAIT__TIMER since the transmitting RLC entity stops the transmission of PDUs even before starting the TX_WAIT_TIMER.
4. A method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, wherein after the re-initialization of RLC entity is triggered, the HARQ entity on the transmitting RLC side discards all the buffers which contain a RLC PDU from the re-initialized RLC entity, and the corresponding buffers in the HARQ entity on the receiving side is discarded (automatically overwritten) after fresh PDUs are scheduled for transmission on the transmitting side.
5. The method as claimed in claim 4, wherein no additional action is required to be taken by either the RLC entity or the HARQ entity on the receiving side.
6. A method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, the method comprising,

• Sending a signaling message to the receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity, which also contains the value of TX_SN_TO_BE_TRANSMITTED;
• Re-initializing of the receiver RLC entity on reception of the signaling message, and setting the variables RX_SN_HIGHEST

and RX_SN_TO_BE_RECEIVED to
TX_SN_TO_BE_TRANSMITTED.;
• Sending a response message to the peer transmitting RLC entity;
• Re-initializing the transmitter RLC entity on reception of the acknowledgement of the signaling message, followed by setting TX_SN_TO_BE_ACKNOIWLEDGED to TX_SN_TO_BE_TRANSMITTED.

7. The method as claimed in claim 6, wherein the protocol variables are not reset post re-initialization.
8. The method as claimed in claim 6, wherein the receiving RLC entity discards any PDUs that it receives with a sequence number lesser than the value of TX_SN_TO_BE_TRANSMITTED, post re-initialization.
9. A method for handling late arrival of PDU after reset/re-establishment of RLC entity in a wireless communication system, wherein both the transmitting as well as the receiving RLC entities maintain a protocol variable 'R' preset to a value '0' or '1', the method comprising,

• Sending a signaling message to the receiving RLC entity on detection of re-initialization trigger in transmitter RLC entity;
• Re-initializing of the receiver RLC entity on reception of the signaling message, and toggling the value of 'R';
• Sending a response message to the peer transmitting RLC entity;

• Re-initializing the transmitter RLC entity on reception of tlie acknowledgement of the signaling message, and toggling the value of 'R' before resuming the transmission of PDUs.
10. The method as claimed in claim 9, wherein receiving RLC entity discards any PDUs having sequence numbers not starting with R.
11.The methods as claimed in claims 1, 6 & 9, wherein if the re-initialization is controlled by the upper layers in the transmitting and receiving RLC entities, the corresponding signaling is also performed by the respective upper layers.
12. A method for avoiding additional re-initialization(s) at RLC due to the late arrival of an RLC PDU transmitted before the re-initialization, substantially as herein described with respect to the accompanying drawings.

Documents:

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Patent Number

279383

Indian Patent Application Number

1853/CHE/2007

PG Journal Number

03/2017

Publication Date

20-Jan-2017

Grant Date

19-Jan-2017

Date of Filing

20-Aug-2007

Name of Patentee

SAMSUNG R&D INSTITUTE INDIA-BANGALORE PRIVATE LIMITED

Applicant Address

#2870 ORION BUILDING BAGMANE CONSTELLATION BUSINESS PARK OUTER RING ROAD DODDANEKUNDI CIRCLE MARATHAHALLI POST BANGALORE 560037

Inventors:

#	Inventor's Name	Inventor's Address
1	KUNDAN KUMAR LUCKY	2ND FLOOR, 12/13, MOUNAGURU MATT ROAD, THIMMAIAH GARDEN, COX TOWN, BANGALORE, INDIA-560 005.
2	SOENG HUN KIM	YOUNGTONG-GU, YOUNGTONG-DONG 1153, SUWON-SI, KYUNGGI-DO, KOREA
3	GERT-JAN VAN LIESHOUT	SOERENSEWEG 40, 7314CG APELDOORN, THE NETHERLANDS.

PCT International Classification Number

H04L 7/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA