Node b and method for prioritization of retransmission of protocol data units to assist radio-link-control retransmission

ES 2 325 366 T3

DESCRIPTION

Node B and method for prioritization of protocol data unit retransmission to aid RLC (radio link control) retransmission.

Field of the invention

The present invention relates to the field of wireless communications. More specifically, the present invention relates to a system and method for prioritizing the retransmission of protocol data units (PDUs) to aid radio link control layer (RLC) retransmission.

Background

In third-generation (3G) cellular systems for Frequency Division Duplex (FDD) and Time Division Duplex (TDD), there are retransmission mechanisms in the layer acknowledgment mode. radio link control (RLC) for highly reliable end-to-end data transmissions. The radio link control layer (RLC) is an equal entity both in the radio network controller (RNC: Radio Network Controller) and in the user equipment (UE: User Equipment).

Figure 1 illustrates a block diagram of a MAC-hs layer architecture (Media Access Control high speed = Support Access Control - high speed) of a UMTS Terrestrial Radio Access Network (UTRAN), and in Figure 2 shows a block diagram of the MAC-hs architecture (Media Access Control - high speed = Media Access Control - high speed) of the user equipment (UE). The architecture shown in Figures 1 and 2 is described in detail in co-pending US patent application, publication number US 2003/0086391, filed October 15, 2002, which is assigned to the present assignee. The UTRAN MAC-hs 30 shown in Figure 1 comprises a transport format resource indicator (TFRI) selector 31, a scheduling and prioritization entity 32, a plurality of automatic repeating processors 33a, 33b (H-ARQ = Hybrid Automatic Repeat), a flow controller 34 and a transmission sequence number and priority class setting entity (TSN) 35.

The UE MAC-hs 40 comprises a hybrid automatic repeat (H-ARQ) processor 41. As will be explained with reference to both Figures 1 and 2, the hybrid auto-repeat (H-ARQ) processors 33a, 33b in the UTRAN MAC-hs 30 and the hybrid auto-repeat (H-ARQ) processor 41 in the UE MAC -hs 40 work together to process blocks of data.

The 33a, 33b Hybrid Automatic Repeat (H-ARQ) processors in the UTRAN MAC-hs 30 handle all the tasks that are necessary for the Hybrid Automatic Repeat (H-ARQ) process to generate streams and retransmissions for any stream you have error. The hybrid automatic repeat (H-ARQ) processor 41 in the UE MAC-hs 40 is responsible for generating an acknowledgment (ACK) to indicate a successful transmission and for generating a negative acknowledgment (NACK) to indicate a transmission. faulty. Hybrid Automatic Repeat (H-ARQ) processors 33a, 33b, and 41 process sequential data streams for each user data stream.

As will be described in more detail hereinafter, the data blocks received in each user data stream are assigned to the Hybrid Automatic Repeat (H-ARQ) processors 33a, 33b. Each hybrid auto-repeat (H-ARQ) processor 33a, 33b initiates a transmission and, in the event of an error, the hybrid auto-repeat (H-ARQ) processor 41 requests a retransmission. In subsequent transmissions, the modulation and coding rate can be changed to ensure successful transmission. The data block to be retransmitted and any new transmissions to the user equipment (UE) are provided by the planning and prioritization entity 32 to the hybrid automatic repeat (H-ARQ) entities 33a, 33b.

The planning and prioritization entity 32 functions as a radio resource manager and determines the transmission latency to support the necessary quality of service. Based on the outputs of the Hybrid Automatic Repeat (H-ARQ) processors 33a, 33b and the priority of a new data block that is transmitted, the planning and prioritization entity 32 sends the data block to the indicator selector 31 transport format resources (TFRI).

Transport Format Resource Indicator (TFRI) selector 31, coupled to scheduling and prioritization entity 32, receives the data block to be transmitted and selects an appropriate dynamic transport format for the data block to be transmitted. With respect to hybrid automatic repeat (H-ArQ) transmissions and retransmissions, the Transport Format Resource Indicator (TFRI) selector 31 determines the modulation and encoding.

It is highly desirable that the retransmitted data blocks reach the receiving side radio link control entity (RLC) (ie user equipment (UE)) as soon as possible for various reasons. First, the missing data block will prevent subsequent data blocks from being sent to higher layers due to the requirement of sequential provisioning. Second, the user equipment (UE) buffer needs to be sized

ES 2 325 366 T3 large enough to accommodate retransmission latency while still maintaining efficient data rates. The higher the latency, the larger the user equipment (UE) buffer size has to be to take into account that the user equipment (UE) buffers both the blocks of data that are stopped and the receptions of continuous data until the correct sequence data block is sent to higher layers. The larger buffer size results in increased hardware costs for user equipment (UEs). This is very undesirable.

Referring to Figure 3, a simplified flow diagram of the data flow between a Node B (shown in the lower part of Figure 3) and a user equipment (UE) (shown in the upper part of Figure 3) is shown ). Protocol data units (PDUs) from higher level processing are scheduled and can be multiplexed into one data block. A data block can only contain higher layer Protocol Data Units (PDUs) of the same priority. A unique Transmission Sequence Number (TSN) is assigned to each data block by the scheduler. Upper layers may provide a plurality of different priority streams of Protocol Data Units (PDUs), each priority having a sequence of Transmission Sequence Numbers (TSNs). The scheduler then dispatches the data blocks to the plurality of processors P1_B-P5_B Hybrid Auto Repeat (H-ARQ). Each P1 processor_B-P5_B Hybrid Automatic Repeat (H-ARQ) is responsible for processing a single block of data at a time. For example, as shown in Figure 3, priority 1 protocol data units (PDUs) comprise a sequence illustrated as B1₁-B1_N. Likewise, priority 2 protocol data units (PDUs) are sequenced from B2i-B2_N and priority 3 protocol data units (PDUs) are sequenced from B3₁-B3_N. These protocol data units (PDUs) are scheduled (and can be multiplexed) and attached to a transmission sequence number (TSN) by the common scheduler. For the purposes of describing the invention, it is assumed that one protocol data unit (PDU) equals one data block. After a block of data is scheduled to be processed by a particular processor P1_B-P5_B, each data block is associated with a processor identifier that identifies processor P1_B-P5_B that processes the data block.

The data blocks are then fed into the scheduled processors P1_B-P5_B Hybrid Automatic Repeat (H-ARQ) devices from Node B that receive and process each block of data. Each P1B-P5B Hybrid Automatic Repeat (H-ARQ) processor on Node B corresponds to one P1 processor_EU-P5_EU Hybrid Auto Repeat (H-ARQ) within User Equipment (UE). Consequently, the first Hybrid Automatic Repeat (H-ARQ) processor P1B in Node B communicates with the first processor P1_EU of H-ARQ on the user equipment (UE). Likewise, the second processor P2_B H-ARQ on Node B communicates with the second processor P2_EU of H-ARQ in the user equipment (UE), and so on for the remaining processors P3B-P5B of H-ARQ in Node B and their counterpart processors P3UE-P5UE of H-ARQ, respectively, within the user equipment (EU). H-ARQ processes are timely multiplexed over the air interface and there is only one hybrid automatic repeat (H-ARQ) transmission on the air interface at a time.

For example, taking the first pair of P1 processors_B-P1_EU communicating H-ARQ, processor P1_B H-ARQ processes a block of data, for example B1₁, and sends it to multiplex it and transmit it over the interface with the air. When this data block B11 is received by the first H-ARQ processor P1UE, the processor P1UE determines whether or not it was received without error. If the data block B11 was received without error, the first H-ARQ processor P1UE transmits an acknowledgment (ACK) to indicate to the transmitting H-ARQ processor P1B that it has been received successfully. Conversely, if there is an error in the received data block B1, the receiving processor P1_EU H-ARQ transmits a negative acknowledgment (NACK) to transmitting processor P1_B by H-ARQ. This process continues until the transmitter processor P1_B receives an acknowledgment (ACK) for block B1₁ of data. Once an acknowledgment (ACK) is received, that processor P1_B it is "freed" to process another block of data. The scheduler will assign processor P1_B another data block if available, and you can choose to transmit or start a new transmission at any time.

Once H-ARQ's P1UE-P5UE receiver processors process each block of data, it is sent to the R buffers.₁, R₂, R₃ reorder based on its priority, a reorder buffer for each data priority level. For example blocks B1₁-B1_N priority 1 data will be received and reordered in priority 1 reorder buffer R1, blocks B21 -B2N of priority 2 data will be received and reordered in buffer R₂ priority 2 reordering and B3 blocks₁ -B3_Npriority 3 data will be received and reordered by buffer R₃ reordering priority 3.

Due to the pre-processing of data blocks by H-ARQ's P1UE-P5UE receiver processors and the ACK / NACK acknowledgment procedure, data blocks are frequently received in an order that is not sequential with respect to their numbers. Sequence Transmission (TSNs). Buffers R₁-R₃ Reordering machines receive the data blocks out of sequence and attempt to reorder the data blocks in a sequential manner before sending them to the radio link control layer (RLC). For example, priority 1 reorder buffer R1 receives and reorders the first four B1 blocks₁-B1₄ data priority 1. As the data blocks are received and reordered, they will be passed to the radio link control layer (RLC).

On the receiving side, the User Equipment Support-High-Speed ​​Access Control (UE MAC-hs) (which has been graphically illustrated as MAC-hs control) reads the processor identifier from H-ARQ, whether it is sent on a control channel such as HS-SCCH (High Speed ​​Shared Control Channel) as if the data block has been tagged, to determine which H-ARQ processor P1UE-P5UE

ES 2 325 366 T3 has been used. If the user equipment (UE) receives another data block to be processed by the same processor P1_EU-P5_EU of H-ARQ, the user equipment (UE) knows that that particular processor P1_EU-P5_EU H-ARQ has been released regardless of whether the previous data block processed by that processor P1_EU-P5_EU of H-ARQ has been received satisfactorily or not.

Figure 4 is an example of a prior art system that includes a radio network controller (RNC), a Node B, a user equipment (UE), and their associated buffers. This example assumes that User Equipment (UE) is the receiving entity and Node B is the transmitting entity. In this prior art system, a protocol data unit (PDU) with sequence number = 3 is not satisfactorily received by the user equipment (UE). Therefore, the radio link control (RLC) in the UE requests its radio link control (RLC) peer layer in the radio network controller (RNC) for a retransmission. Meanwhile, protocol data units (PDUs) with sequence numbers = 6-9 are buffered at Node B, and protocol data units (PDUs) with sequence numbers = 4 and 5 are stored. buffered in the UE. It should be noted that although Figure 4 shows only several protocol data units (PDUs) that are buffered, actually many more protocol data units (PDUs) (such as 100 or more) and PDUs from other entities. Radio link control (RLC) can be buffered.

As shown in Figure 5, if a retransmission of the protocol data unit (PDU) with sequence number = 3 is required, it must wait at the end of the queue in the Node B buffer, and it will be transmitted only after which are transmitted protocol data units (PDUs) with sequence numbers = 6-9. Protocol data units (PDUs) in the UE cannot be sent to the upper layers until all PDUs are received in sequence.

In this case, the protocol data unit (PDU) with sequence number = 3 for the issuance of subsequent protocol data units (PDUs) to higher layers (that is, sequence numbers = 4-9), assuming that all protocol data units (PDUs) are successfully transmitted. Again, it should be noted that this example only reflects 11 PDUs whereas in normal operation hundreds of PDUs can be scheduled ahead of retransmitted data PDUs, further exacerbating data buffering and transmission latency issues.

It would be desirable to have a system and method by which the retransmitted data can avoid delays due to transmission congestion, buffers. Document WO 02/05496 (EP 1225735) describes a communication system capable of eliminating the retransmission of useless data that is too late for the playback time on the receiving side.

US 5 684 791 describes methods for ATM cell relay (Asynchronous Transfer Mode) and buffer requirements depending on ATM classes of service.

In addition, the document entitled "Link Layer Buffer Size Distributions for HTTP (Hypertext Transfer Protocol) and FTP (File Transfer Protocol) Applications in an IS-2000 System", by Khan F., at the VTC- 2000 (Vehicular Technology Conference) of the IEEE, describes the transmission of new data and retransmitted data in the memory of a transmitter.

Compendium

The present invention is a method and a Node B according to claims 1 and 8, respectively, for transferring data in a wireless communication system. A plurality of data blocks are received and temporarily stored in a first memory. Then the plurality of data blocks are transmitted. Then, a determination is made as to whether each of the transmitted data blocks was successfully received or needs to be retransmitted because the data block was not successfully received. Each of the transmitted data blocks that needs to be retransmitted is marked and stored in a second memory that has a higher priority than the first memory. The marked data blocks stored in the second memory are transmitted before transmitting data blocks stored in the first memory.

Each marked data block may include a common channel priority indicator (CmCH-Pi). The CmCH-Pi of the marked data block is read and used to determine in which of a plurality of memories to place the marked data block based on the CmCH-Pi.

According to an example of the present invention, a wireless communication system for transferring data includes a user equipment (UE), the Node B in communication with the UE, and a radio network controller (RNC) in communication with the Node. B and the UE. The RNC transmits a plurality of data blocks to the UE via Node B. The UE sends a status report to the RNC. The report indicates whether each of the transmitted data blocks was successfully received by the UE or needs to be retransmitted because the data block was not successfully received by the UE. The RNC marks each of the data blocks that needs to be retransmitted and sends the marked data blocks to Node B. Node B receives, temporarily stores and prioritizes the transmission of the marked data blocks with respect to other data blocks previously received and stored in Node B. Node B transmits the marked data blocks to the UE before the other data blocks .

ES 2 325 366 T3

Brief description of the drawings

A more detailed understanding of the invention may be obtained from the following description given by way of example and to be understood in conjunction with the accompanying drawings, in which:

Figure 1 is a Support Access Control - high speed of a UMTS Terrestrial Radio Access Network (UTRAN MAC-hs).

Figure 2 is a prior art User Equipment High Speed ​​Media Access Control (UE MAC-hs).

Figure 3 is a block diagram of the data flow between a Node B and a user equipment (UE).

Figure 4 is a radio link control layer (RLC) diagram exhibiting a lost protocol data unit (PDU) transmission.

Figure 5 is a radio link control layer (RLC) retransmission diagram of the lost protocol data unit (PDU) transmission.

Figure 6 is a signal diagram of a method for prioritizing retransmissions in accordance with the present invention.

Figure 7 is a block diagram of the data flow between a Node B and a user equipment (UE), whereby retransmissions are assigned to a higher priority queue.

Figure 8 is a block diagram of the data flow of a downlink shared channel (DSCH) transmission that schedules protocol data units (PDUs) with common channel priority indications (CmCH-Pi).

Figures 9 and 10 are radio link control layer (RLC) retransmission diagrams of a lost protocol data unit (PDU) transmission in accordance with the present invention.

Detailed description of the preferred embodiments

Preferred embodiments will be described with reference to the drawing figures where like numbers represent like elements throughout.

In describing the present invention, reference may be made to the terminology "buffer" and "memory". These terms are intended to be equivalent and are used to indicate a plurality of data blocks or protocol data units (PDUs) in a successive queue.

To reduce the latency of a radio link control layer (RLC) retransmission, the present invention prioritizes a retransmission of a protocol data unit (PDU) over a subsequent PDU in the memory of an intermediate node such as a Node B. for instance.

In the downlink direction (data transmissions from the serving radio network controller (serving RNC: SRNC) to the user equipment (UE)), a source of retransmission latency is generated in applications that store in memory intermediate in the UTRAN outside the Serving Radio Network Controller (SRNC). For example, buffering for an application could occur at the command radio network controller (Controlling RNC: CRNC) or at Node B. In various applications, the radio network controller (RNC) radio link controller (RLC) sends the protocol data unit (PDU) to the Support Access Control-dedicated channels (MAC-d) in the RNC which creates a MAC-d PDU that is sent to the CRNC and then to Node B (note that in the case that a UE has not left the cell coverage of the SRNC, the CRNC will be the same RNC and, therefore, any messages sent they are internal. When the UE has left the cell coverage of the SRNC, the new CRNC is known as the Drift Radio Network Controller (Drift RNC: DRNC). For simplicity, in both cases the RNC will be referred to as a CRNC).

As the Media Access Control protocol data unit (PDU) - dedicated channels (MAC-d) contains exactly 1 RLC PDU (plus other potential Media Access Control information), a MAC-d PDU can be considered equivalent to an RLC PDU. Although the discussion of PDUs at the CRNC or Node B in the present application refers to MAC-d PDUs (not RLC PDUs), they can be considered equivalent for the purposes of the present invention and the term protocol data unit (PDU) will be used hereinafter to refer to both.

To account for the continuous data flow, PDUs from the RNC's RLC are usually queued in buffers of the CRNC or Node B for a while, before they are transmitted to the UE and, therefore, to the control of radio link (RLC) the same. As will be described in detail hereinafter, the inventive method

The current ES 2 325 366 T3 to retransmit data with a higher priority bypasses the memory storage / queuing of data in the UTRAN.

One embodiment of the present invention is radio link control (RLC) retransmissions from the radio network controller (RNC) to the user equipment (UE) of a system employing high speed downlink packet access (HSDPA: High Speed ​​Downlink Packet Access). A method 100 for reducing retransmission latency in accordance with the present invention is depicted in Figure 6. Figure 6 shows the communications between an RNC 102, a Node B 104 and a UE 106.

The RLC layer in the UE 106 generates a status report PDU (step 108) indicating the status of PDUs received (ie, successfully transmitted) or lost (ie, unsuccessfully transmitted). This status report PDU is transmitted (step 110) to RNC 102. Once the RLC layer in RNC 102 receives the status report PDU from its peer entity in UE 106, RNC 102 prepares the relay of the lost PDU (step 112).

The present invention implements a method to allow Node B to distinguish the retransmitted PDU from other PDUs. In a first embodiment, the RNC 102 marks the retransmitted PDU using a bit field in its Frame Protocol (FP) auxiliary resources. The retransmitted PDU includes a common channel priority indicator (CmCh-Pi) that is updated (or incremented) each time the PDU is sent (step 114) from RNC 102 to Node B 104. This allows Node B 104 to track the number of times the PDU is sent and thus identify the appropriate queue in which to place the PDU. Preferably, the common channel priority indicator (CmCH-Pi) is typically set and updated at the RNC 102. However, this function can also be performed at Node B 104. Node B 104 reads the CmCH-Pi and determines the appropriate priority queue for the PDU (step 116). The transmission scheduler at Node B 104 brings the higher priority queues into service before the lower priority queues. The Node B 104 places the PDU to be retransmitted in a buffer that has a higher priority than it originally had when the PDU was originally transmitted as a result of the CmCH-Pi arrangement by the RNC 102.

The PDU is then retransmitted (step 118) into a buffer (ie, memory) that has a higher priority than the priority of the original transmission. Other transmissions for this UE may be stored in memory in the lowest priority transmission queue of Node B 104 at the time of PDU retransmission. The provision of the increased CmCH-Pi for retransmitted PDUs results in the transmission scheduling before other PDUs previously received and stored at Node B 104.

Referring to Figure 7, retransmissions are assigned a higher priority queue so that they replace the transmission of other data blocks originating from the same "original" transmission buffer. Once the P1 receiver processors_EU-P5_EU H-ARQ processes each block of data, they are sent to the buffers R_B R₂, R₃ reorder based on its priority, a reorder buffer for each data priority level. For example, the buffer R₂ reordering reorders blocks B2₁, B2₂ and B2₄ of data. The reordering buffer R3 reorders the B3 blocks₃, B3₄ and B3₆of data. A block ("X") of data is missing between the B2 blocks₂ and B2₄ of data. An additional data block ("X") is missing between the B3 blocks₄ and B3₆ of data. Thus, the expected data blocks B2₃ and B3₅ they are not received, for example, because a negative acknowledgment message (NACK) is misinterpreted as being an acknowledgment message (ACK).

The missing data blocks are then retransmitted. Normally, block B23 of data would have been placed in the priority 2 transmit buffer. However, since block B23 of data was missing and had to be retransmitted, block B2₃ Data is placed in a higher priority transmission buffer (in this case, the priority 1 transmission buffer) and is therefore sent earlier than if it were placed in the priority 2 or 3 transmission buffers. Similarly, block B3₅ data would normally have been placed in the priority 3 transmit buffer. However, as block B3₅ data was missing and had to be retransmitted, block B3₅ data is placed in the priority 1 or priority 2 transmission buffer so that it is transmitted earlier than if it had been placed in the priority 3 transmission buffer.

After receipt of PDUs at Node B, the common channel priority indicator (CmCH-Pi) is used to determine queue B1_n-B3_n priority. The scheduler brings the highest priority queues into service first and assigns transmissions to transmitting processors P1_b-b5_b by H-ARQ. After successful transmission to the user equipment (UE), the receiving processors P1_EU-P5_EU H-ARQs send the relayed PDUs to the radio link control layer (RLC).

This procedure can also be applied for a Downlink Shared Channel (DSCH) system except that the intermediate node is the command radio network controller (CRNC) instead of Node B. Referring to Figure 8, PDUs 805 with CmCH-Pi indications are given priority by a prioritization entity 810 and are scheduled for transmission by Shared Channel-Support Access Control (MAC-sh) at the CRNC. The MAC-sh maintains multi-priority queues 815A, 815B, and a downlink shared channel (DSCH) transmission scheduler 820 determines which PDU 805 is to be transmitted based on the priority of that data. Therefore, by arranging increased CmCH-Pi for DSCH retransmissions,

ES 2 325 366 T3 these transmissions will be brought into service before other data for the user equipment (UE). This is similar to the case of HS-DSCH (High Speed ​​- Downlink Shared Channel = high speed downlink shared channel) where the MAC-hs entity of Node B schedules the transmissions.

Referring to Figure 9, a system in accordance with the present invention is shown that implements the prioritization method of Figure 6. After the RLC layer in the UE transmits a status report PDU to the RLC layer in the RNC indicating that the PDU with sequence number = 3 has not been received successfully, the radio network controller (RNC) sends a retransmission of the PDU with sequence number = 3. The PDU will be prioritized over other PDUs in the intermediate node buffer by placement within a higher priority buffer. It should be noted that although only 11 PDUs are displayed, there may actually be hundreds of PDUs in the queue.

The benefits of the present invention can be seen with reference to Figure 10 which depicts the result of the prioritization function in the receiving buffer. The retransmitted PDU with sequence number = 3 reaches the receiving buffer, and the PDUs in sequence with sequence numbers = 3 to 5 can be sent to the upper layer much faster than in the prior art scenario depicted in Figure 5.

Although the present invention has been described in terms of the preferred embodiment, other variations that are within the scope of the invention, as explained in general terms in the following claims, will be apparent to those skilled in the art.