Retransmission method and user equipment

Abstract

The present invention provides a retransmission method executed by a base station or a user equipment, and a user equipment. The method provided in one aspect of the present invention comprises: for an RLC SDU, when an automatic retransmission condition is met, determining whether the RLC SDU has been identified for retransmission; when it is determined that the RLC SDU has not yet been identified for retransmission, determining that retransmission needs to be executed for the RLC SDU; and for the RLC SDU, triggering retransmission caused by the automatic retransmission condition being met.

Description

Re-transmission method and user equipment TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless communication, and more particularly, to a re-transmission method performed by a user equipment or a base station, and a corresponding base station and user equipment. BACKGROUND

[0002] The transmission of the RLC layer can be divided into three modes, AM, UM and TM. In the AM mode, the reliability of data transmission is guaranteed through the ARQ transmission mechanism.

[0003] However, in order to achieve such reliability, the sending UE first needs to receive the status report (SR) sent by the opposite UE. The opposite UE indicates the information of the correctly received data packet and the information of the data packet that has not been correctly received in the status report. Based on the received status report, the UE retransmits the data packet that has not been correctly received to the opposite UE. Then the UE continues to wait for the opposite UE to send the status report to determine whether it needs to retransmit again. The above operation will continue until the opposite UE confirms in the subsequent status report that the data packet is successfully received or until the number of transmissions of the data packet reaches the maximum number allowed. It can be seen that the retransmission mechanism based on the status report will cause a time delay problem in data transmission.

[0004] In order to solve this time delay problem, an automatic retransmission mechanism is discussed. The UE configured with the RLC AM transmission mode can trigger or start the automatic retransmission mechanism under certain conditions, and still start the retransmission of the data packet without receiving the status report from the opposite UE, thereby shortening the transmission time delay.

[0005] However, the triggering time of the automatic retransmission mechanism is uncertain. It can occur before or after the relevant status report is received, or even at the same time. For a data packet, the UE can start the retransmission preparation of the data packet when the automatic retransmission mechanism is triggered, and can also start the retransmission preparation of the data packet after receiving the status report indicating that the data packet has not been correctly received. Therefore, how to avoid repeated triggering of the retransmission of the same data in the same period of time is a problem to be solved. SUMMARY

[0006] The purpose of the present application is to avoid triggering the retransmission of the RLC SDU that has been triggered for retransmission again.

[0007] According to an aspect of the present application, there is provided a retransmission method performed by a base station or a user equipment, the retransmission method comprising: determining, for a certain RLC SDU, whether the RLC SDU has been determined to require retransmission in case that an automatic retransmission condition is met; determining that retransmission needs to be performed for the RLC SDU when it is determined that the RLC SDU has not been determined to require retransmission; and triggering retransmission for the RLC SDU due to the automatic retransmission condition being met.

[0008] According to an aspect of the present application, there is provided a retransmission method performed by a base station or a user equipment, the retransmission method comprising: determining, for a certain RLC SDU, whether the RLC SDU has been determined to require retransmission in case that an automatic retransmission condition is met; determining that retransmission needs to be performed for the RLC SDU when it is determined that the RLC SDU has not been determined to require retransmission; and triggering retransmission for the RLC SDU due to the automatic retransmission condition being met.

[0009] According to an aspect of the present application, there is provided a user equipment comprising: a processor; and a memory storing instructions; wherein the instructions, when executed by the processor, perform the method as described above.

[0010] According to the retransmission method of the present application, repeated triggering of retransmission for the same RLC SDU can be avoided. For example, retransmission for a certain RLC SDU can be avoided due to the automatic retransmission mechanism in case that retransmission for the RLC SDU has already been triggered based on a negative acknowledgement. For another example, retransmission for a certain RLC SDU can be avoided due to the reception of a negative acknowledgement in case that retransmission for the RLC SDU has already been triggered based on the automatic retransmission mechanism. BRIEF DESCRIPTION OF DRAWINGS

[0011] Fig. 1 is a schematic diagram for illustrating RLC AM mode.

[0012] Fig. 2 is a flow chart of a retransmission method according to an embodiment of the present application.

[0013] Fig. 3 is a flow chart of a retransmission method according to another embodiment of the present application.

[0014] Fig. 4 is a schematic block diagram of a user equipment UE according to the present application. DETAILED DESCRIPTION

[0015] The present application will be described in detail by making reference to the accompanying drawings and specific embodiments. It should be noted that the present application should not be limited to the specific embodiments described below. In addition, detailed descriptions of well-known technology related to the present application are omitted to prevent obscuring the understanding of the present application.

[0016] Before specific descriptions, several terms mentioned in the present application are explained as follows. Unless otherwise indicated, the terms involved in the present application have the following meanings.

[0017] UE User Equipment

[0018] NR New Radio

[0019] LTE Long Term Evolution

[0020] eLTE Enhaced Long Term Evolution

[0021] RRC Radio Resource Control (layer)

[0022] MAC Medium Access Control (layer)

[0023] PUSCH Physical Uplink Shared Channel

[0024] PDCCH Physical Downlink Control Channel

[0025] RNA RAN-based Notification Area

[0026] SDAP Service Data Adaptation Protocol

[0027] AM Acknowledged Mode

[0028] AMD AM Data

[0029] ARQ Automatic Repeat request

[0030] gNB the next Generation Node B, next generation base station

[0031] PDU Protocol Data Unit, protocol data unit

[0032] PDCP Packet Data Convergence Protocol, packet data convergence protocol (layer)

[0033] HARQ Hybrid Automatic Repeat reQuest, hybrid automatic repeat request

[0034] RLC Radio Link Control, radio link control

[0035] SDU Service Data Unit, service data unit

[0036] SN Sequence Number, sequence number

[0037] SO Segment Offset, segment offset

[0038] The following describes in detail a plurality of embodiments according to the present application, taking the NR mobile communication system and its subsequent evolution versions as an example application environment, and taking the base stations and UE devices supporting NR as an example. However, it needs to be pointed out that the present application is not limited to the following embodiments, but can be applied to more other wireless communication systems, such as eLTE, communication systems, or NB-Iot systems, or LTE-M systems. Moreover, it can be applied to other base stations and UE devices, such as base stations and UE devices supporting eLTE / NB-Iot / LTE-M.

[0039] The functions of the RLC layer are implemented by RLC entities, one RLC entity can receive one or more RLC SDUs from its upper layer, usually the PDCP layer, and then send the corresponding RLC PDUs to the peer RLC entity via lower layers, usually the MAC layer and the physical layer, etc.; one RLC entity can also receive one or more RLC PDUs from its peer RLC entity via lower layers, and then deliver the corresponding RLC SDUs to the upper layer.

[0040] RLC AM mode

[0041] As shown in Figure 1, in RLC AM mode, there is a transmitting side of an RLC entity and a receiving side of an RLC entity. Generally, the transmitting side can be located at gNB / UE side, while the receiving side is located at another UE side, or the transmitting side is located at UE side, while the receiving side is located at gNB / another UE.

[0042] RLC data PDUs submitted or received by an AM RLC entity are called AMD PDUs. An AMD PDU contains a complete RLC SDU or a segment of a RLC SDU. RLC control PDUs submitted or received by an AM RLC entity include STATUS PDUs

[0043] Transmitting side of an AM RLC entity

[0044] The transmitting side maintains a transmit window according to the state variable TX_Next_Ack:

[0045] If TX_Next_Ack <= SN < TX_Next_Ack + AM_Window_Size, then the SN falls within the transmit window, otherwise, the SN falls outside the transmit window.

[0046] For SNs falling outside the transmit window, the transmitting side will not submit them to lower layer transmission.

[0047] For each RLC SDU received from upper layer (PDCP), the RLC entity working in AM mode will associate a SN to the RLC SDU, which can be considered as the SN of the RLC SDU or the SN associated with it. The SN is the value of the current variable TX_Next, then an AMD PDU is generated, and the SN of the AMD PDU is set to the value of the current variable TX_Next, then the value of the variable TX_Next is increased by 1, i.e. a new variable TX_Next is obtained, whose value is the value of the current variable TX_Next plus 1.

[0048] When submitting an AMD PDU containing a segment of a RLC SDU to lower layer transmission, the transmitting side of an AM RLC entity will set the SN of the AMD PDU to the SN associated with the RLC SDU.

[0049] The transmitting side of an AM RLC entity can receive a STATUS PDU sent from the receiving side of the peer RLC entity, i.e. the receiving side of the AM RLC entity. The STATUS PDU is used by the receiving side of the peer RLC entity to confirm the successful reception of an RLC SDU, i.e. to provide a positive acknowledgement (ACK) of an RLC SDU. When an RLC SDU is confirmed to be successfully received by the receiving side of the peer RLC entity, or in other words, when the receiving side of the peer RLC entity provides a positive acknowledgement of an RLC SDU, the transmitting side of the RLC entity indicates to the upper layer that the RLC SDU is successfully transmitted, and then updates the value of the variable TX_Next_Ack to be the smallest SN among one or more SNs that fall within the interval TX_Next_Ack <= SN <= TX_Next and have not been confirmed to be successfully received.

[0050] The receiving side of an RLC entity

[0051] The receiving side of an AM RLC entity

[0052] The receiving side maintains a reception window according to the state variable RX_Next

[0053] If RX_Next <= SN < RX_Next + AM_Window_Size, then the SN falls within the reception window, otherwise it falls outside the reception window.

[0054] For an AMD PDU received, the receiving side of the AM RLC entity either discards the AMD PDU or stores it in the reception buffer.

[0055] For an SN that falls outside the reception window, the receiving side can discard the AMD PDU. In addition, for an AMD PDU containing a segment of an RLC SDU, the receiving side can discard the AMD PDU if it is confirmed that the segment has been received.

[0056] For an AMD PDU stored in the reception buffer, the receiving side can have the following processing

[0057] Update one or more state variables, reassemble the RLC SDU, deliver the reassembled RLC SDU to the upper layer, and if necessary, stop or start a corresponding timer.

[0058] Specifically, for an AMD PDU with SN=X, when it is stored in the receiving buffer,

[0059] If x >= RX_Next_Highest, then the value of RX_Next_Highest is updated, and the new value of RX_Next_Highest is the value of the current RX_Next_Highest plus one.

[0060] If all segments of the RLC SDU associated with SN=X have been received, then the segments are reassembled into the RLC SDU, and the reassembled RLC SDU is delivered to the upper layer.

[0061] If x=RX_Highest_Status, then the value of RX_Highest_Status is updated, and the new value of RX_Highest_Status is the SN associated with the RLC SDU that is first in order among the one or more SNs whose values are greater than the value of the current RX_Highest_Status, where first in order can mean that the SNs are ordered according to their values, with the SN having the smallest value being first, and the value of the updated RX_Highest_Status is the value of this SN having the smallest value.

[0062] If x=RX_Next, then the value of RX_Next is updated, and the new value of RX_Next is the SN associated with the RLC SDU that is first in order among the one or more SNs whose values are greater than the value of the current RX_Next, where first in order can mean that the SNs are ordered according to their values, with the SN having the smallest value being first, and the value of the updated RX_Next is the value of this SN having the smallest value.

[0063] ARQ transmission

[0064] The transmitting side of an RLC entity can obtain a notification of reception failure or a negative acknowledgement (NACK) of a RLC SDU and RLC SDU segments by receiving a STATUS PDU sent from the opposite side (the receiving side of the RLC entity). Since the STATUS PDU contains a status report, the STATUS PDU and the status report can be used interchangeably in this document. The status report or the STATUS PDU can contain at least one or more of the following:

[0065] For an RLC SDU, if no segment containing any byte belonging to the RLC SDU has been received, the value of NACK_SN in the STATUS PDU is set to the value of the SN of the RLC SDU;

[0066] For an RLC SDU that has been partially received, if there is still a continuous sequence of byte segments that has not been received, the STATUS PDU contains the parameters NACK_SN, SOstart, SOend, where:

[0067] The value of NACK_SN is set to the value of the SN of the RLC SDU;

[0068] The value of SOstart is set to indicate the position of the first byte of the portion of the RLC SDU that has been detected as lost at the receiving side of the AM RLC entity, in bytes within the original RLC SDU;

[0069] The value of SOend indicates the position of the last byte of the portion of the RLC SDU, that has been detected as lost at the receiving side of the AM RLC entity, in bytes within the original RLC SDU;

[0070] For a number of consecutive RLC SDUs that have not been received, the parameter NACK_SN and NACK range are included in the STATUS PDU. Wherein:

[0071] The value of NACK_SN is set to the value of the SN of the first RLC SDU of the number of consecutive RLC SDUs that have not been received;

[0072] The value of NACK range is set to the number of consecutively lost RLC SDUs starting from and including NACK_SN;

[0073] The value of ACK_SN is set to the SN of the next not received RLC SDU which is not indicated as missing.

[0074] When a negative acknowledgement is received for a certain RLC SDU, or a negative acknowledgement is received for a segment of a certain RLC SDU, then the RLC SDU or the segment of the RLC SDU is considered for retransmission if the value of the SN of the RLC SDU is greater than or equal to TX_Next_Ack and less than or equal to the maximum value of the SN of the AMD PDU submitted to the lower layer for transmission.

[0075] In case of retransmission of an RLC SDU or a segment of an RLC SDU, a new AMD PDU can be generated and then submitted to lower layer for transmission. The transmitting side of the RLC entity can trigger or initiate retransmission of an RLC SDU or a segment of an RLC SDU upon receiving a status report or a STATUS PDU. Such mechanism can be referred to as STATUS PDU based retransmission mechanism.

[0076] Autonomous Retransmission

[0077] In case of not receiving a STATUS PDU sent by the peer side, the transmitting side of the RLC entity can trigger or initiate retransmission of an RLC SDU autonomously (or spontaneously) in the following cases. Such mechanism can be referred to as autonomous retransmission mechanism:

[0078] - The RLC entity receives an indication from upper layer, e.g. from PDCP layer above RLC layer, indicating that for a certain RLC SDU, the remaining delay value (or time value) associated with the RLC SDU is lower than (or not higher than) a pre-configured threshold value, or for a certain RLC SDUs, the minimum value of the remaining delay values (or time values) associated with the RLC SDUs is lower than (or not higher than) a pre-configured threshold value; based on such indication, the RLC entity can initiate or trigger retransmission of the RLC SDU or the RLC SDUs;

[0079] - The RLC entity receives an indication from lower layer, e.g. from MAC layer below RLC layer, indicating that the number of HARQ retransmission for a certain RLC SDU or certain RLC SDUs reaches or exceeds a pre-configured value.

[0080] - A retransmission timer expires, which can be configured at the transmitting side of the RLC entity and can be associated with at least one RLC SDU. When the timer expires, the RLC entity can initiate or trigger retransmission of the RLC SDU or RLC SDUs associated with the timer. Such retransmission timer can be started upon receiving an indication from upper layer, e.g. the aforementioned indication from PDCP, or upon receiving an indication from lower layer, e.g. the aforementioned indication from MAC layer.

[0081] In other cases, the transmitting side of the RLC entity of the UE can also trigger or initiate autonomous retransmission, which are not listed here. It can be considered that retransmission triggered by receiving a STATUS PDU is non-autonomous retransmission, while retransmission triggered in other cases (not receiving a STATUS PDU) is autonomous retransmission.

[0082] Discarding of RLC SDUs in existing mechanisms

[0083] When the upper layer of the UE, the PDCP layer, instructs the RLC layer to discard a specific RLC SDU, the transmitting end of the RLC entity determines whether the RLC SDU or the segment of the RLC SDU has been delivered to the lower layer for transmission. If the RLC SDU or the segment of the RLC SDU has not been delivered to the lower layer for transmission, i.e., all segments of the RLC SDU have not been delivered to the lower layer, the transmitting end of the RLC entity can discard the RLC SDU. If the RLC SDU or the segment of the RLC SDU has been delivered to the lower layer for transmission, i.e., at least one of the segments has been delivered to the lower layer, the transmitting end of the RLC entity does not perform any operation, but lets the RLC SDU or the segment thereof be sent to the opposite end according to the foregoing procedure.

[0084] State variables

[0085] The value of the TX_Next_Ack variable is equal to the value of the SN of the next RLC SDU for which a positive acknowledgment is to be received in-sequence, and it also represents the acknowledgment start sequence number of the transmitting window.

[0086] The value of the TX_Next variable is equal to the SN of the next newly generated AMD PDU.

[0087] The value of the RX_Next variable is equal to the value of the SN following the last in-sequence completely received RLC SDU, and it also represents the start sequence number of the receiving window.

[0088] The value of the RX_Highest_Status variable is equal to the value of the largest or highest SN that is positively acknowledged by the receiving end when a STATUS PDU is constructed, i.e., the highest sequence number in the STATUS PDU.

[0089] The value of the RX_Next_Highest variable is equal to the value of the SN following the SN of the RLC SDU with the highest SN among received RLC SDUs in the status report of the highest sequence number.

[0090] The outline of the embodiment of the present application will be described below with reference to FIG. 2 and FIG. 3. In each operation described below with reference to the accompanying drawings, some operations are not necessarily essential and can be omitted.

[0091] FIG. 2 is a flowchart of a retransmission method according to an embodiment of the present application.

[0092] In S202, it is determined whether an automatic retransmission condition is satisfied for a certain RLC SDU. As for the specific automatic retransmission condition, various conditions well known in the art can be applied, and the present application is not limited in this regard.

[0093] In the case where the automatic retransmission condition is satisfied, in S204, it is determined whether the RLC SDU has been determined to require retransmission.

[0094] When it is determined that the RLC SDU has not been determined to require retransmission, in S206, it is determined that retransmission needs to be performed for the RLC SDU. Also, in S208, retransmission due to satisfaction of the automatic retransmission condition is triggered for the RLC SDU.

[0095] When it is determined that the RLC SDU has been determined to require retransmission, in S210, it is determined that retransmission does not need to be performed for the RLC SDU. Also, in S212, retransmission due to satisfaction of the automatic retransmission condition is not triggered for the RLC SDU.

[0096] Upon determining that retransmission does not need to be performed for the RLC SDU, a retransmission timer corresponding to the RLC SDU can be restarted.

[0097] FIG. 3 is a flowchart of a retransmission method according to another embodiment of the present application.

[0098] In S302, a status PDU is received.

[0099] Upon receiving the status PDU, in S304, it is determined whether a negative acknowledgement regarding the RLC SDU associated with the status PDU is included in the status PDU. If the determination result in S304 is YES, in S306, it is determined whether the RLC SDU has been determined to require retransmission.

[0100] In a case where it is determined that the RLC SDU has not been determined to require retransmission, it is determined, at S306, that retransmission needs to be performed for the RLC SDU. And, at S310, retransmission due to reception of a negative acknowledgement is triggered for the RLC SDU.

[0101] In a case where it is determined that the RLC SDU has been determined to require retransmission, it is determined, at S312, that retransmission does not need to be performed for the RLC SDU. And, at S314, retransmission is not triggered for the RLC SDU.

[0102] In one example, it can be that, in a case where the negative acknowledgement is a negative acknowledgement for a segment of the RLC SDU, if the RLC SDU has been determined to require retransmission, retransmission of the RLC SDU is cancelled, and retransmission is triggered for the segment of the RLC SDU.

[0103] In one example, upon reception of a status PDU including a positive acknowledgement, retransmission can be cancelled for one or more RLC SDUs or segments of RLC SDUs having sequence numbers smaller than an acknowledgement sequence number ACK CN included in the status PDU among RLC SDUs in a pending retransmission state.

[0104] In one example, it can be determined that the RLC SDU has been determined to require retransmission when at least one of the following is met: a negative acknowledgement for the RLC SDU or a segment of the RLC SDU has been received; the RLC SDU or the segment of the RLC SDU has been marked for retransmission; the RLC SDU or the segment of the RLC SDU is in a pending retransmission state; the RLC SDU or the segment of the RLC SDU is contained in at least one RLC PDU to be retransmitted.

[0105] Hereinafter, several embodiments of the present application will be described in detail.

[0106] It should be noted that the transmitting end of the RLC entity and the receiving end of the RLC entity in this document can be located at different UE sides, or can be located at the UE side and the base station side respectively, or at the UE side and the base station side. In this document, the UE side is taken as an example.

[0107] Embodiment One

[0108] For one RLC SDU, when the UE determines that the condition (or case) for automatic initiation or triggering of retransmission for one RLC SDU is met (also referred to as automatic retransmission condition), the UE determines whether this RLC SDU or any segment of this RLC SDU is pending for retransmission. For example, the automatic retransmission condition can be determined to be met when any of the following conditions occurs:

[0109] - the RLC entity receives an indication from an upper layer, e.g. from a PDCP layer above the RLC layer, indicating that for a certain RLC SDU, the remaining time delay value (or time value) associated with the RLC SDU is lower than (or not higher than) a pre-configured threshold value, or for certain RLC SDUs, the minimum value of the remaining time delay values (or time values) associated with the RLC SDUs is lower than (or not higher than) a pre-configured threshold value; based on such indication, the RLC entity can initiate or trigger retransmission for this or these RLC SDUs;

[0110] - the RLC entity receives an indication from a lower layer, e.g. from a MAC layer below the RLC layer, indicating that the number of HARQ retransmissions for a certain or certain RLC SDU(s) reaches or exceeds a pre-configured value.

[0111] - a retransmission timer expires, which can be configured at the transmitting side of the RLC entity, and can be associated with at least one RLC SDU, when the timer expires, the RLC entity can initiate or trigger retransmission for the RLC SDU(s) associated with the timer, such retransmission timer can be started upon receiving an indication from an upper layer, e.g. the aforementioned indication from the PDCP, or can be started upon receiving an indication from a lower layer, e.g. the aforementioned indication from the MAC layer.

[0112] The UE can determine whether this RLC SDU or any segment of this RLC SDU is pending for retransmission in the following ways.

[0113] It can be determined whether this RLC SDU or any segment of this RLC SDU has been considered for retransmission.

[0114] Alternatively, it can be determined whether this RLC SDU or at least one segment of this RLC SDU has received a negative acknowledgement.

[0115] Alternatively, it can be determined whether the RLC SDU or at least one segment of the RLC SDU is contained in at least one RLC PDU and the RLC PDU is pending for retransmission.

[0116] In one case, the UE can determine that the RLC SDU or all segments of the RLC SDU are not pending for retransmission, in case that:

[0117] For example, the UE determines that the RLC SDU or any segment of the RLC SDU has not been considered for retransmission; for example, the UE determines that no negative acknowledgement is received for the RLC SDU or for any segment of the RLC SDU; for example, the UE determines that the RLC SDU or all segments of the RLC SDU are not pending for retransmission (or none of the segments belonging to the RLC SDU is pending for retransmission); for example, the UE determines that none of the RLC PDUs pending for retransmission contains the RLC SDU or any segment of the RLC SDU.

[0118] In such a case, upon occurrence of any of the aforementioned conditions that can cause the UE to automatically initiate or trigger retransmission, the UE can consider that the RLC SDU is subject to retransmission, in particular the UE can consider that the RLC SDU is subject to negative acknowledgement, or is in a state of negative acknowledgement, or is marked for negative acknowledgement, and preferably triggers or initiates a retransmission procedure for the RLC SDU. Such a retransmission procedure can be considered as a retransmission due to the satisfaction of the automatic retransmission condition. The retransmission procedure can comprise one or more of the following operations, but is not limited to:

[0119] - setting a value of a counter associated with the RLC SDU, for example setting an initial value of zero;

[0120] - updating the value of the counter, for example incrementing the value of the counter by one, and in case that the value of the counter is equal to or not less than a preconfigured threshold, indicating to an upper layer of the RLC (for example, the RRC layer) that the maximum number of retransmission is reached;

[0121] - forming at least one RLC PDU containing the RLC SDU or a segment of the RLC SDU,

[0122] - store the generated RLC PDU in a RLC retransmission buffer;

[0123] - submit the generated RLC PDU to lower layer for transmission.

[0124] In addition, in one case, the UE determines that the RLC SDU or at least one segment of the RLC SDU is in a pending retransmission state, for example, the RLC SDU or at least one segment of the RLC SDU is considered to be in need of retransmission, or the RLC SDU is pending for retransmission, or at least one segment of the RLC SDU is determined to be pending for retransmission, or the RLC PDU containing the RLC SDU or at least one segment of the RLC SDU is determined to be in a pending retransmission state, then when any of the aforementioned cases occurs that can cause the UE to automatically start or trigger retransmission, the UE can consider that the RLC SDU does not need to be retransmitted, and preferably, the UE can restart the retransmission timer corresponding to or associated with the RLC SDU.

[0125] The aforementioned "in a pending retransmission state" can also mean that the RLC SDU or segment of the RLC SDU is marked for retransmission, or is considered to be in need of retransmission, or has received a negative acknowledgement for the RLC SDU or segment of the RLC SDU in a STATUS PDU, or the RLC PDU containing the RLC SDU or segment of the RLC SDU has been placed in a retransmission buffer, and preferably, the RLC SDU or segment of the RLC SDU in a pending retransmission state, the corresponding retransmission RLC PDU has not been submitted to the lower layer for transmission.

[0126] One variation of the aforementioned embodiment can be:

[0127] In case that the UE determines that the RLC SDU or all segments of the RLC SDU are not considered to be required for retransmission, or in case that the UE determines that the RLC SDU or all segments of the RLC SDU are not in pending retransmission state (or none of the segments belonging to the RLC SDU is in pending retransmission state), or in case that the RLC PDU in pending transmission does not contain the RLC SDU or any segment of the RLC SDU, the transmitting end of the RLC entity can consider that the RLC SDU is required for retransmission in case that any of the following occurs, which includes that the UE can consider that the RLC SDU receives a negative acknowledgement, or consider that the RLC SDU is in a negative acknowledgement state, or mark the RLC SDU as a negative acknowledgement, and preferably, trigger or initiate a retransmission procedure for the RLC SDU, which can be regarded as a retransmission due to the satisfaction of the automatic retransmission condition, and the operation of the retransmission procedure can be as described above:

[0128] - the RLC entity receives an indication from an upper layer, e.g. from a PDCP layer above the RLC layer, indicating that for a certain RLC SDU, the remaining delay value (or time value) associated with the RLC SDU is lower than (or not higher than) a preconfigured threshold value, or for certain RLC SDUs, the minimum value of the remaining delay values (or time values) associated with the RLC SDUs is lower than (or not higher than) a preconfigured threshold value; based on such indication, the RLC entity can initiate or trigger a retransmission for the RLC SDU or the RLC SDUs; or

[0129] - the RLC entity receives an indication from a lower layer, e.g. from a MAC layer below the RLC layer, indicating that the number of HARQ retransmissions for a certain RLC SDU or certain RLC SDUs reaches or exceeds a preconfigured value; or

[0130] - a retransmission timer expires, which can be configured at the transmitting end of the RLC entity and can be associated with at least one RLC SDU, when the timer expires, the RLC entity can initiate or trigger a retransmission for the RLC SDU or RLC SDUs associated with the timer, such retransmission timer can be initiated upon receiving an indication from an upper layer, e.g. the aforementioned indication from the PDCP, or can be initiated upon receiving an indication from a lower layer, e.g. the aforementioned indication from the MAC.

[0131] Embodiment two

[0132] The transmitting end of the RLC entity of the UE receives a STATUS PDU sent from the opposite end (the receiving end of the RLC entity), which contains at least one or more of the following information:

[0133] - NACK_SN

[0134] - NACK_SN, and associated SOstart, and SOend

[0135] - NACK_SN, and associated NACK range

[0136] Where the value of NACK_SN is the SN of a certain RLC SDU, and for such RLC SDU, it can be considered that the negative acknowledgement for the RLC SDU has been received.

[0137] If the NACK_SN is also associated with SOstart, and SOend, it can be considered that the negative acknowledgement has been received for the segments of the RLC SDU corresponding to the value of NACK_SN.

[0138] If the NACK_SN is also associated with NACK range, it can be considered that the negative acknowledgement has been received for the RLC SDU corresponding to the value of NACK_SN and the (NACK range - 1) continuous RLC SDUs following it, for example, if the value of NACK_SN is 101 and the value of NACK range is 5, then the negative acknowledgement is considered to have been received for the RLC SDUs with SNs of 101, 102, 103, 104, and 105.

[0139] For the RLC SDU or the segments of the RLC SDU for which the negative acknowledgement has been received from the STATUS PDU, the UE determines that the RLC SDU or all segments of the RLC SDU are not in the pending retransmission state, which can include the following cases.

[0140] For example, the UE determines that the RLC SDU or any segment of the RLC SDU has not been considered to need retransmission; for another example, the UE determines that no negative acknowledgement has been received for the RLC SDU or any segment of the RLC SDU; for another example, the UE determines that the RLC SDU or all segments of the RLC SDU are not in the pending retransmission state (or none of the segments belonging to the RLC SDU is in the pending retransmission state); for another example, the UE determines that none of the RLC PDUs in the pending retransmission state contains the RLC SDU or any segment of the RLC SDU.

[0141] In such a case, after receiving the aforementioned STATUS PDU, the UE can consider that the RLC SDU needs to be retransmitted, specifically, the UE can consider that the RLC SDU has received a negative acknowledgement, or consider that the RLC SDU is in a state of negative acknowledgement, or mark the RLC SDU as a negative acknowledgement, and preferably, trigger or start a retransmission procedure for the RLC SDU, such a retransmission procedure can be regarded as a retransmission due to the reception of the negative acknowledgement, and the operation of the retransmission procedure can be as described above.

[0142] Preferably, the SN of the RLC SDU is greater than or equal to TX_Next_Ack and less than or equal to the maximum SN value in the AMD PDU submitted to the lower layer for transmission.

[0143] In addition, in one case, the UE determines that the RLC SDU or at least one segment of the RLC SDU is in a pending retransmission state, for example, the RLC SDU or at least one segment of the RLC SDU has been considered to need retransmission, or the RLC SDU is in a pending retransmission state, or at least one segment of the RLC SDU is determined to be in a pending retransmission state, or the RLC PDU containing the RLC SDU or at least one segment of the RLC SDU is determined to be in a pending retransmission state, then after the UE receives the aforementioned STATUS PDU, the UE can consider that the RLC SDU does not need to be retransmitted, and preferably, the UE can restart the retransmission timer corresponding to or associated with the RLC SDU.

[0144] Embodiment one and embodiment two can be implemented alone or in combination to avoid repeated retransmission.

[0145] Embodiment three

[0146] On the basis of embodiment two, in the case that the STATUS PDU contains NACK_SN, and the associated SOstart, and SOend, the UE can consider that the segments of the RLC SDU corresponding to the value of NACK_SN have received negative acknowledgement. If the UE determines that this RLC SDU is considered to need retransmission, or is deemed to be in pending retransmission state, then after receiving the aforementioned STATUS PDU, the UE can consider that only the segments of this RLC SDU need retransmission. Specifically, the UE can cancel the retransmission of this RLC SDU, and can only retransmit the segments of this RLC SDU, which are determined based on the parameters SOstart, and SOend. Specifically, the UE can remove or discard the RLC PDUs containing this RLC SDU from the retransmission buffer, and / or generate a RLC PDU containing only the segments of the RLC SDU for retransmission.

[0147] Embodiment three can be used in combination with embodiment one or two, and can also be used in combination with embodiment one and two, to avoid repeated transmission.

[0148] Embodiment four

[0149] The STATUS PDU received in embodiment two can also contain ACK_SN.

[0150] Suppose the value of the received ACK_SN is X, for any RLC SDU with SN value less than X, if the UE determines that this RLC SDU belongs to the pending retransmission state, or determines that at least one segment of this RLC SDU is in the pending retransmission state, then the UE can cancel the retransmission of this RLC SDU or this RLC SDU segment, which can specifically be removing or discarding the RLC PDUs containing this RLC SDU or the segments of the RLC SDU from the retransmission buffer, or removing the retransmission flag of this RLC SDU, etc.

[0151] Embodiment four can be used in combination with embodiment one or two, and can also be used in combination with embodiment one and two, to avoid repeated transmission.

[0152] FIG. 4 is a brief block diagram of a user equipment UE to which the present application relates. As shown in FIG. 4, the user equipment UE 400 includes a processor 401 and a memory 402. The processor 401 can include, for example, a microprocessor, a microcontroller, an embedded processor, or the like. The memory 402 can include, for example, a volatile memory (e.g., a random access memory (RAM)), a hard disk drive (HDD), a non-volatile memory (e.g., a flash memory), or other storage media. The memory 402 stores program instructions thereon. The instructions, when executed by the processor 401, can perform the above-described method executed by the user equipment in detail.

[0153] A program running on the apparatus according to the present application can be a program for causing a computer to implement the functions of the embodiments of the present application by controlling a central processing unit (CPU). The program or information processed by the program can be temporarily stored in a volatile memory (e.g., a random access memory (RAM)), a hard disk drive (HDD), a non-volatile memory (e.g., a flash memory), or other storage media.

[0154] A program for implementing the functions of the embodiments of the present application can be recorded on a computer-readable recording medium. The corresponding functions can be implemented by causing a computer system to read the program recorded on the recording medium and execute the program. The so-called "computer system" herein can be a computer system embedded in the apparatus and can include an operating system or hardware (e.g., a peripheral device). The "computer-readable recording medium" can be a semiconductor recording medium, an optical recording medium, a magnetic recording medium, a short-time dynamic storage program recording medium, or any other computer-readable recording medium.

[0155] The various features or function modules of the apparatus used in the above-described embodiments can be implemented or executed by a circuit (e.g., a single-chip or multi-chip integrated circuit). The circuit designed to perform the functions described in the present specification can include a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or any combination thereof. The general-purpose processor can be a microprocessor, but implementation is not limited thereto. The general-purpose processor can also be any existing processor, controller, microcontroller, or state machine. The above-described circuit can be a digital circuit, and also can be an analog circuit. If new integrated circuit technologies appear due to the advancement of semiconductor technologies, one or more embodiments of the present application can also be implemented using such new integrated circuit technologies.

[0156] Furthermore, the present application is not limited to the above-described embodiments. Although various examples of the embodiments have been described, the present application is not limited thereto. Stationary or non-mobile electronic devices installed indoors or outdoors can be used as terminal devices or communication devices, such as AV devices, kitchen devices, cleaning devices, air conditioners, office devices, vending machines, and other home appliances.

[0157] As described above, the embodiments of the present application have been described in detail with reference to the accompanying drawings. However, the specific configuration is not limited to the above-described embodiments, and the present application includes any design modification without departing from the gist of the present application. In addition, various modifications can be made to the present application within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present application. Furthermore, components described in the above-described embodiments having the same effect can be substituted for each other.

Claims

1. A retransmission method performed by a base station or a user equipment, the retransmission method comprising: determining, for a certain RLC SDU, whether the RLC SDU has been determined to require retransmission in a case where an automatic retransmission condition is satisfied; determining that retransmission needs to be performed for the RLC SDU when it is determined that the RLC SDU has not been determined to require retransmission; and triggering retransmission for the RLC SDU due to the automatic retransmission condition being satisfied. 2.The retransmission method according to claim 1, further comprising: determining that retransmission does not need to be performed for the RLC SDU, and not triggering retransmission for the RLC SDU due to the automatic retransmission condition being satisfied, when it is determined that the RLC SDU has been determined to require retransmission. 3.The retransmission method according to claim 2, further comprising: restarting a retransmission timer corresponding to the RLC SDU when it is determined that retransmission does not need to be performed for the RLC SDU. 4.The retransmission method according to claim 2, the RLC SDU having not been determined to require retransmission comprising: all segments of the RLC SDU having not been determined to require retransmission. 5.A retransmission method performed by a base station or a user equipment, the retransmission method comprising: upon receiving a status PDU, determining, for a RLC SDU associated with the status PDU, whether the RLC SDU has been determined to require retransmission in a case where a negative acknowledgement about the RLC SDU is included in the status PDU; determining that retransmission needs to be performed for the RLC SDU when it is determined that the RLC SDU has not been determined to require retransmission; and triggering retransmission for the RLC SDU due to the negative acknowledgement being received. 6.The retransmission method according to claim 5, further comprising: not triggering retransmission for the RLC SDU when it is determined that the RLC SDU has been determined to require retransmission. 7.The retransmission method according to claim 5 or 6, further comprising: in a case where the negative acknowledgement is a negative acknowledgement for a segment of the RLC SDU, cancelling retransmission of the RLC SDU and triggering retransmission for the segment of the RLC SDU if the RLC SDU has been determined to require retransmission. 8.The retransmission method according to any one of claims 1 to 6, further comprising: upon receiving a status PDU including a positive acknowledgement, cancelling retransmission of one or more RLC SDUs or segments of RLC SDUs having a sequence number smaller than a positive acknowledgement sequence number ACK CN included in the status PDU among RLC SDUs in a pending retransmission state. 9.The retransmission method according to any one of claims 1 to 6, further comprising: determining that the RLC SDU has been determined to require retransmission in a case where at least one of the following is satisfied: ​ ​ ​ a negative acknowledgement has been received for the RLC SDU or a segment of the RLC SDU; the RLC SDU or the segment of the RLC SDU has been marked for retransmission; the RLC SDU or the segment of the RLC SDU is in a pending retransmission state; the RLC SDU or the segment of the RLC SDU is contained in at least one RLC PDU pending retransmission.

10. A user equipment comprising: a processor; and a memory having instructions stored therein; wherein the instructions, when executed by the processor, perform the method of any one of claims 1 to 9.

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