COMMUNICATION SYSTEM, DATA TRANSMISSION METHOD THEREOF, AND USER EQUIPMENT THEREOF

Abstract

To provide a communication system, a data transmission method thereof, and a user device thereof to reduce the number of retransmissions between the user device and a base station.SOLUTION: In a communication system 1000, a first transmitting Radio Link Control (Tx RLC) entity 130 of a first base station 100 transmits a first Protocol Data Unit (PDU) to a first receiving Radio Link Control (Rx RLC) entity 331 of a user device via a first leg. A second Tx RLC entity 230 of a second base station transmits a second PDU to a second Rx RLC entity 332 of the user device via a second leg. If the first Rx RLC entity 331 successfully receives the first PDU or the second Rx RLC entity 332 successfully receives the second PDU, the first Rx RLC entity 331 and the second RLC entity 332 return Acknowledgement (ACK) messages.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to electronic systems, methods of operation thereof, and electronic devices thereof, and more particularly to communication systems, methods of data transmission thereof, and user devices thereof. [Background technology]

[0002] 2. Description of the Related Art With the advancement of wireless communication technology, various wireless communication devices have been developed, such as smart mobile phones, tablet computers, notebook computers, in-vehicle devices, etc. These wireless communication devices have brought considerable convenience to people's lives.

[0003] A wireless communication device can download data via a base station. For example, multi-point transmission is disclosed in Patent Document 1. However, in practical applications, the quality of the signal may be affected by weather factors, surrounding wireless signal interference, or the movement of the wireless communication device. If the wireless communication device cannot successfully obtain the data, the wireless communication device requests the base station for retransmission. In wireless communication technology, excessive retransmissions have a significant impact on transmission efficiency. Researchers are working on reducing the number of retransmissions between wireless communication devices and base stations to improve transmission efficiency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2016 / 0037511 Summary of the Invention

[0005] The present disclosure relates to a communication system, a data transmission method thereof, and a user equipment thereof. Intercommunication is used to reduce the number of retransmissions between a user equipment and a base station.

[0006] According to one embodiment, a data transmission method for a communication system is provided. The data transmission method includes the following steps: A first transmit radio link control (Tx RLC) entity of a first base station transmits a first protocol data unit (PDU) to a first receive RLC (Rx RLC) entity of a user equipment over a first interval; A second Tx RLC entity of a second base station transmits a second PDU to a second Rx RLC entity of the user equipment over a second interval; If the first Rx RLC entity successfully receives the first PDU or the second Rx RLC entity successfully receives the second PDU, the first Rx RLC entity and the second Rx RLC entity respectively return an acknowledgement (ACK) message to the first Tx RLC entity and the second Tx RLC entity.

[0007] According to another embodiment, a user equipment is provided. The user equipment includes a first receive radio link control (Rx RLC) entity and a second Rx RLC entity. The first Rx RLC entity is configured to receive a first protocol data unit (PDU) transmitted from a first transmit radio link control (Tx RLC) entity of a first base station over a first interval. The second Rx RLC entity is configured to receive a second PDU transmitted from a second Tx RLC entity of a second base station over a second interval. When the first Rx RLC entity successfully receives the first PDU or the second Rx RLC entity successfully receives the second PDU, the first Rx RLC entity and the second Rx RLC entity respectively return an acknowledgement (ACK) message to the first Tx RLC entity and the second Tx RLC entity.

[0008] According to an alternative embodiment, a communication system is provided. The communication system includes a first base station, a second base station, and a user equipment. The first base station includes a first transmit radio link control (Tx RLC) entity. The first Tx RLC entity is configured to transmit a first protocol data unit (PDU). The second base station includes a second Tx RLC entity. The second Tx RLC entity is configured to transmit a second PDU. The user equipment includes a first receive radio link control (Rx RLC) entity and a second Rx RLC entity. The first Rx RLC entity is configured to receive the first PDU over a first interval. The second Rx RLC entity is configured to receive the second PDU over a second interval. If the first Rx RLC entity successfully receives the first PDU or the second Rx RLC entity successfully receives the second PDU, the first Rx RLC entity and the second Rx RLC entity return an acknowledgement (ACK) message to the first Tx RLC entity and the second Tx RLC entity, respectively. [Brief description of the drawings]

[0009] [Figure 1] 1 shows a schematic diagram of a communication system according to one embodiment; [Diagram 2] 2 shows a schematic diagram of a communication system according to another embodiment; [Diagram 3] 2 shows a schematic diagram of a communication system according to another embodiment; [Figure 4] 2 shows a schematic diagram of a communication system according to another embodiment; [Diagram 5] 2 illustrates a control method for a first receiving radio link control (Rx RLC) entity; [Figure 6] 4 shows a method for controlling the second Rx RLC entity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. However, it will be apparent that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are diagrammatically shown to simplify the drawings.

[0011] Please refer to FIG. 1, which shows a schematic diagram of a communication system 1000 according to one embodiment. The communication system 1000 includes a first base station 100, a second base station 200, and a user equipment 300. The first base station 100 and the second base station 200 are, for example, macrocells, small cells, femtocells, picocells, or microcells. The user equipment 300 is, for example, a smart mobile phone, a tablet, a laptop, or a vehicle-mounted device. The communication system 1000 uses Packet Data Convergence Protocol (PDCP) Duplication to enable the first base station 100 and the second base station 200 to coordinate the transmission of the same data.

[0012] The first base station 100 includes a transmit packet data convergence protocol (Tx PDCP) entity 190, a first transmit radio link control (Tx RLC) entity 130, and a lower layer 150. The lower layer 150 is, for example, a media access control (MAC) layer or a physical layer. The second base station 200 includes a second Tx RLC entity 230 and a lower layer 250. The lower layer 250 is, for example, a MAC layer or a physical layer. The user equipment 300 includes a lower layer 351, a first receive radio link control (Rx RLC) entity 331, a lower layer 352, a second Rx RLC entity 332, and a receive packet data convergence protocol (Rx PDCP) entity 390. The lower layer 351 and the lower layer 352 are, for example, a MAC layer or a physical layer.

[0013] The following figure is used to illustrate the data transmission method using PDCP duplication in this embodiment. As shown in Figure 1, in step S11, the Tx PDCP entity 190 of the first base station 100 transmits a first protocol data unit (PDU) PDU1 to the first Tx RLC entity 130.

[0014] In step S12, the Tx PDCP entity 190 replicates the first PDU PDU1 into a second PDU PDU2 and transmits the second PDU PDU2 to the second Tx RLC entity 230.

[0015] Then, in step S13, the first Tx RLC entity 130 transmits the first PDU PDU1 to the first Rx RLC entity 331 of the user equipment 300 via the first leg. In the embodiment of Fig. 1, the first Rx RLC entity 331 successfully receives the first PDU PDU1. Thus, in step S14, the first Rx RLC entity 331 returns an acknowledgement (ACK) message ACK1 to the first Tx RLC entity 130.

[0016] In step S15, the second Tx RLC entity 230 transmits the second PDU PDU2 via the second leg towards the second Rx RLC entity 332 of the user equipment 300. In the embodiment of Fig. 1, the second Rx RLC entity 332 also successfully receives the second PDU PDU2. Thus, in step S16, the second Rx RLC entity 332 returns an ACK message ACK2 to the second Tx RLC entity 230.

[0017] In one embodiment, the first Tx RLC entity 130 and the second Tx RLC entity 230 transmit the first PDU PDU1 and the second PDU PDU2 simultaneously.

[0018] Because the first Rx RLC entity 331 has successfully received the first PDU PDU1 and the second Rx RLC entity 332 has successfully received the second PDU PDU2, in steps S17 and S18, the Rx PDCP entity 390 is able to receive the first PDU PDU1 from the first Rx RLC entity 331 and the second PDU PDU2 from the second Rx RLC entity 332.

[0019] In the case of Fig. 1, the conditions of the first and second legs are quite good and the first Rx RLC entity 331 and the second Rx RLC entity 332 are able to successfully receive the first PDU PDU1 and the second PDU PDU2. The first Tx RLC entity 130 and the second Tx RLC entity 230 confirm by the ACK messages ACK1 and ACK2 that no retransmission is necessary.

[0020] Please refer to Fig. 2 which shows a schematic diagram of a communication system 1000 according to another embodiment. In step S15' in Fig. 2, the second Tx RLC entity 230 transmits a second PDU PDU2 via a second leg towards the second Rx RLC entity 332 of the user equipment 300. In the embodiment of Fig. 2, the second Rx RLC entity 332 has not successfully received the second PDU PDU2 within a predefined time period.

[0021] Next, in step S151, the second Rx RLC entity 332 sends a request message RM2 to the first Rx RLC entity 331 to check whether the first Rx RLC entity 331 has successfully received the first PDU PDU1.

[0022] Then, in step S152, the first Rx RLC entity 331 returns a response message RP1 to the second Rx RLC entity 332. In the embodiment of Fig. 2, the second Rx RLC entity 332 knows through the response message RP1 that the first Rx RLC entity 331 has successfully received the first PDU PDU1.

[0023] Thus, in step S16′, the second Rx RLC entity 332 returns an ACK message ACK2 to the second Tx RLC entity 230.

[0024] Since only the first Rx RLC entity 331 has successfully received the first PDU PDU1, the Rx PDCP entity 390 only receives the first PDU PDU1 from the first Rx RLC entity 331 in step S17.

[0025] 2, the condition of the second leg is poor, so the second PDU PDU2 is not received by the second Rx RLC entity 332. Since the first Rx RLC entity 331 successfully receives the first PDU PDU1, the second Rx RLC entity 332 sends an ACK message ACK2 to the second Tx RLC entity 230 to inform the second base station 200 that no retransmission is necessary.

[0026] In this way, the first base station 100 and the second base station 200 can immediately transmit the next message without time-consuming retransmission, which greatly improves the transmission efficiency.

[0027] Please refer to Fig. 3, which shows a schematic diagram of a communication system 1000 according to another embodiment. In step S13' in Fig. 3, the first Tx RLC entity 130 transmits a first PDU PDU1 towards the first Rx RLC entity 331 of the user equipment 300 during a first interval. In the embodiment of Fig. 3, the first Rx RLC entity 331 has not successfully received the first PDU PDU1 within a predefined time period.

[0028] Next, in step S141, the first Rx RLC entity 331 sends a request message RM1 to the second Rx RLC entity 332 to check whether the second Rx RLC entity 332 has successfully received the second PDU PDU2.

[0029] Then, in step S142, the second Rx RLC entity 332 returns a response message RP2 to the first Rx RLC entity 331. In the embodiment of Fig. 3, the first Rx RLC entity 331 knows through the response message RP2 that the second Rx RLC entity 332 has successfully received the second PDU PDU2.

[0030] Thus, in step S 14 ′, the first Rx RLC entity 331 returns an ACK message ACK 1 to the first Tx RLC entity 130 .

[0031] Since only the second Rx RLC entity 332 has successfully received the second PDU PDU2, in step S18 the Rx PDCP entity 390 only receives the second PDU PDU2 from the second Rx RLC entity 332.

[0032] In the case of Fig. 3, since the conditions of the first leg are bad, the first Rx RLC entity 331 does not successfully receive the first PDU PDU1, and since the second Rx RLC entity 332 successfully receives the second PDU PDU2, the first Rx RLC entity 331 sends an ACK message ACK1 to the first Tx RLC entity 130 to inform the first base station that no retransmission is necessary.

[0033] In this way, the first base station 100 and the second base station 200 can immediately transmit the next information without time-consuming retransmission, which greatly improves the transmission efficiency.

[0034] Please refer to Fig. 4 which shows a schematic diagram of a communication system 1000 according to another embodiment. In step S13" in Fig. 4, the first Tx RLC entity 130 transmits a first PDU PDU1 towards the first Rx RLC entity 331 of the user equipment 300 over a first leg. In the embodiment of Fig. 4, the first Rx RLC entity 331 has not successfully received the first PDU PDU1 within a predefined time period.

[0035] Next, in step S141, the first Rx RLC entity 331 sends a request message RM1 to the second Rx RLC entity 332 to check whether the second Rx RLC entity 332 has successfully received the second PDU PDU2.

[0036] Then, in step S142, the second Rx RLC entity 332 returns a response message RP2 to the first Rx RLC entity 331. In the embodiment of Fig. 4, the first Rx RLC entity 331 learns through the response message RP2 that the second Rx RLC entity 332 has not successfully received the second PDU PDU2.

[0037] Thus, in step S14'', the first Rx RLC entity 331 returns a negative acknowledgement (NACK) message NACK1 to the first Tx RLC entity 130.

[0038] In step S15″ of FIG. 4, the second Tx RLC entity 230 transmits a second PDU PDU2 via a second leg towards the second Rx RLC entity 332 of the user equipment 300. In the embodiment of FIG. 4, the second Rx RLC entity 332 has not successfully received the second PDU PDU2 within a predefined time period.

[0039] Next, in step S151, the second Rx RLC entity 332 sends a request message RM2 to the first Rx RLC entity 331 to check whether the first Rx RLC entity 331 has successfully received the first PDU PDU1.

[0040] Then, in step S152, the first Rx RLC entity 331 returns a response message RP1 to the second Rx RLC entity 332. In the embodiment of Fig. 4, the second Rx RLC entity 332 knows through the response message RP1 that the first Rx RLC entity 331 has not successfully received the first PDU PDU1.

[0041] Thus, in step S16″, the second Rx RLC entity 332 returns a NACK message NACK2 to the second Tx RLC entity 230.

[0042] Since neither the first Rx RLC entity 331 nor the second Rx RLC entity 332 successfully received the first PDU PDU1 and the second PDU PDU2, the Rx PDCP entity 390 cannot receive the first PDU PDU1 or the second PDU PDU2 at all.

[0043] 4, the conditions of the first and second sections are both poor, so the first Rx RLC entity 331 and the second Rx RLC entity 332 do not successfully receive the first PDU PDU1 and the second PDU PDU2, and therefore the first Rx RLC entity 331 and the second Rx RLC entity 332 send NACK messages NACK1, NACK2 to the first Tx RLC entity 130 and the second Tx RLC entity 230 to inform the first base station 100 and the second base station 200 that retransmission is required.

[0044] In this way, the first base station 100 and the second base station 200 retransmit only when there is a real need, greatly improving transmission efficiency.

[0045] According to the various embodiments described above, if the first Rx RLC entity 331 successfully receives the first PDU PDU1 or the second Rx RLC entity 332 successfully receives the second PDU PDU2, the first Rx RLC entity 331 and the second Rx RLC entity 332 send back ACK messages ACK1, ACK2 to the first Tx RLC entity 130 and the second Tx RLC entity 230, respectively.

[0046] Only if the first Rx RLC entity 331 does not successfully receive the first PDU PDU1 and the second Rx RLC entity 332 does not successfully receive the second PDU PDU2, the first Rx RLC entity 331 and the second Rx RLC entity 332 send back NACK messages NACK1, NACK2 to the first Tx RLC entity 130 and the second Tx RLC entity 230, respectively.

[0047] In the present invention, a request message RM2 is sent if the second Rx RLC entity 332 does not successfully receive the second PDU PDU2, and a request message RM1 is sent if the first Rx RLC entity 331 does not successfully receive the first PDU PDU1.

[0048] To summarize, see Table 1 below. In the following four cases, only the fourth case needs to request retransmission from the first base station 100 and the second base station 200, which greatly improves transmission efficiency. TIFF0007659428000001.tif72139

[0049] A control method of the first Rx RLC entity 331 in the above process is shown in Fig. 5. In step S510, it is determined whether the first Rx RLC entity 331 successfully receives the first PDU PDU1. If the first Rx RLC entity 331 successfully receives the first PDU PDU1, the process proceeds to step S520, and if the first Rx RLC entity 331 does not successfully receive the first PDU PDU1, the process proceeds to step S540.

[0050] In step S520, the first Rx RLC entity 331 returns an ACK message ACK1 to the first Tx RLC entity .

[0051] In step S 530 , the first Rx RLC entity 331 transmits the first PDU PDU 1 to the Rx PDCP entity 390 .

[0052] In step S 540 , the first Rx RLC entity 331 sends a request message RM 1 to the second Rx RLC entity 332 .

[0053] In step S550, the first Rx RLC entity 331 receives a response message RP2 from the second Rx RLC entity 332.

[0054] In step S560, it is determined whether the response message RP2 indicates successful or unsuccessful reception of the second PDU PDU2 by the second Rx RLC entity 332. If the response message RP2 indicates successful reception of the second PDU PDU2 by the second Rx RLC entity 332, processing proceeds to step S520, and if the response message RP2 indicates unsuccessful reception of the second PDU PDU2 by the second Rx RLC entity 332, processing proceeds to step S570.

[0055] In step S570, the first Rx RLC entity 331 returns a NACK message NACK1 to the first Tx RLC entity .

[0056] According to the above control procedure, once the first Rx RLC entity 331 successfully receives the first PDU PDU1 or the second Rx RLC entity 332 successfully receives the second PDU PDU2, control passes to step S520, causing the first Rx RLC entity 331 to return an ACK message ACK1.

[0057] If neither the first Rx RLC entity 331 nor the second Rx RLC entity 332 successfully receives the first PDU PDU1 and the second PDU PDU2, control proceeds to step S570 where the first Rx RLC entity 331 returns a NACK message NACK1. Only in this case is a request for retransmission to the first base station 100 and the second base station 200 necessary, which greatly improves transmission efficiency.

[0058] The control method of the second Rx RLC entity 332 in the above process is as shown in Fig. 6. In step S610, it is determined whether the second Rx RLC entity 332 successfully receives the second PDU PDU2. If the second Rx RLC entity 332 successfully receives the second PDU PDU2, the process proceeds to step S620, and if the second Rx RLC entity 332 does not successfully receive the second PDU PDU2, the process proceeds to step S640.

[0059] In step S620, the second Rx RLC entity 332 returns an ACK message ACK2 to the second Tx RLC entity 230.

[0060] In step S630, the second Rx RLC entity 332 transmits the second PDU PDU2 to the Rx PDCP entity 390.

[0061] In step S640, the second Rx RLC entity 332 sends a request message RM2 to the first Rx RLC entity 331.

[0062] In step S650, the second Rx RLC entity 332 receives the response message RP1 from the first Rx RLC entity 331.

[0063] In step S660 it is determined whether the response message RP1 indicates successful or unsuccessful reception of the first PDU PDU1 by the first Rx RLC entity 331. If the response message RP1 indicates successful reception of the first PDU PDU1 by the first Rx RLC entity 331, processing proceeds to step S620, and if the response message RP1 indicates unsuccessful reception of the first PDU PDU1 by the first Rx RLC entity 331, processing proceeds to step S670.

[0064] In step S670, the second Rx RLC entity 332 returns a NACK message NACK2 to the second Tx RLC entity 230.

[0065] According to the above control procedure, once the first Rx RLC entity 331 successfully receives the first PDU PDU1 or the second Rx RLC entity 332 successfully receives the second PDU PDU2, control proceeds to step S620 to cause the second Rx RLC entity 332 to return an ACK message ACK2.

[0066] If neither the first Rx RLC entity 331 nor the second Rx RLC entity 332 successfully receives the first PDU PDU1 and the second PDU PDU2, control proceeds to step S670 where the second Rx RLC entity 332 returns a NACK message NACK2. Only in this case is a request for retransmission to the first base station 100 and the second base station 200 required, which greatly improves the transmission efficiency.

[0067] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. transmitting a first protocol data unit (PDU) by a first transmit radio link control (Tx RLC) entity of the first base station to a first receive RLC (Rx RLC) entity of the user equipment over a first leg; transmitting a second PDU by a second Tx RLC entity of a second base station to a second Rx RLC entity of the user equipment over a second leg; if the first Rx RLC entity successfully receives the first PDU or the second Rx RLC entity successfully receives the second PDU, returning one acknowledgement (ACK) message from the first Rx RLC entity to the first Tx RLC entity and returning another acknowledgement (ACK) message from the second Rx RLC entity to the second Tx RLC entity; Including, the content of the first PDU is the same as the content of the second PDU; 1. A method for transmitting data in a communication system, wherein a request message is used for the first Rx RLC entity and the second Rx RLC entity to confirm whether the first Rx RLC entity has successfully received the first PDU or the second Rx RLC entity has successfully received the second PDU.

2. 2. The method of claim 1, further comprising: if the first Rx RLC entity does not successfully receive the first PDU and the second Rx RLC entity does not successfully receive the second PDU, returning a negative acknowledgement (NACK) message from the first Rx RLC entity and the second Rx RLC entity to the first Tx RLC entity and the second Tx RLC entity, respectively.

3. transmitting the first protocol data unit (PDU) to the first Tx RLC entity by a Transmit Packet Data Convergence Protocol (Tx PDCP) entity of the first base station; replicating the first PDU into the second PDU by the Tx PDCP entity and transmitting the second PDU by the Tx PDCP entity to the second Tx RLC entity; The data transmission method of claim 2 further comprising:

4. 4. The method of claim 3, wherein the first Tx RLC entity and the second Tx RLC entity transmit the first PDU and the second PDU simultaneously.

5. The data transmission method of claim 4 , wherein the request message is sent by the second Rx RLC entity if the second Rx RLC entity does not successfully receive the second PDU.

6. 2. The method of claim 1, further comprising receiving at least one of the first PDU and the second PDU by an Rx PDCP entity of the user equipment.

7. a first receiving radio link control (Rx RLC) entity configured to receive a first protocol data unit (PDU) transmitted from a first transmitting radio link control (Tx RLC) entity of the first base station over a first leg; and a second Rx RLC entity configured to receive a second PDU transmitted from a second Tx RLC entity of a second base station over a second leg, wherein a content of the first PDU is the same as a content of the second PDU; if the first Rx RLC entity successfully receives the first PDU or the second Rx RLC entity successfully receives the second PDU, the first Rx RLC entity returns an acknowledgement (ACK) message to the first Tx RLC entity, and the second Rx RLC entity returns another acknowledgement (ACK) message to the second Tx RLC entity; wherein a request message is used for the first Rx RLC entity and the second Rx RLC entity to confirm whether the first Rx RLC entity has successfully received the first PDU or the second Rx RLC entity has successfully received the second PDU.

8. 8. The user equipment of claim 7, wherein if the first Rx RLC entity does not receive the first PDU and the second Rx RLC entity does not receive the second PDU, the first Rx RLC entity and the second Rx RLC entity return a negative acknowledgement (NACK) message to the first Tx RLC entity and the second Tx RLC entity, respectively.

9. The user equipment of claim 8 , wherein the first Tx RLC entity and the second Tx RLC entity transmit the first PDU and the second PDU simultaneously.

10. The user equipment of claim 9, wherein the request message is sent by the second Rx RLC entity if the second Rx RLC entity does not successfully receive the second PDU.

11. The user equipment of claim 7, further comprising: an Rx PDCP entity configured to receive at least one of the first PDU and the second PDU.

12. a first base station including a first transmit radio link control (Tx RLC) entity configured to transmit a first protocol data unit (PDU); a second base station including a second Tx RLC entity configured to transmit a second PDU; a first receiving radio link control (Rx RLC) entity configured to receive the first PDU over a first leg; and a second Rx RLC entity configured to receive the second PDU over a second leg, the content of the first PDU being the same as the content of the second PDU; and a user device including: if the first Rx RLC entity successfully receives the first PDU or the second Rx RLC entity successfully receives the second PDU, the first Rx RLC entity returns an acknowledgement (ACK) message to the first Tx RLC entity, and the second Rx RLC entity returns another acknowledgement (ACK) message to the second Tx RLC entity; 11. A communication system, comprising: a first Rx RLC entity and a second Rx RLC entity, and a request message is used to confirm whether the first Rx RLC entity has successfully received the first PDU or the second Rx RLC entity has successfully received the second PDU.

13. 13. The communication system of claim 12, wherein if the first Rx RLC entity does not receive the first PDU and the second Rx RLC entity does not receive the second PDU, the first Rx RLC entity and the second Rx RLC entity return a negative acknowledgement (NACK) message to the first Tx RLC entity and the second Tx RLC entity, respectively.

14. 14. The communication system of claim 13, wherein the first base station further includes a Transmit Packet Data Convergence Protocol (Tx PDCP) entity, the Tx PDCP entity configured to transmit the first PDU to the first Tx RLC entity, replicate the first PDU into the second PDU, and transmit the second PDU to the second Tx RLC entity.

15. The communication system of claim 13 , wherein the first Tx RLC entity and the second Tx RLC entity transmit the first PDU and the second PDU simultaneously.

16. The communication system of claim 15, wherein the request message is sent by the second Rx RLC entity if the second Rx RLC entity does not successfully receive the second PDU.

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