System for efficient recovery of node-b buffered data following mac layer reset

The present invention relates to the field of wireless communication, more specifically, to streamline data transmission between a pair of Layer 2 Automatic Repeat Request (ARQ) peer entities after a MAC layer reset of the intermediate node from which data transmission is distributed. Regarding recovery. An example of a handover scenario is a system that employs hybrid ARQ (H-ARQ) and adaptive modulation and coding (AM & C) techniques.

The 3rd Generation (3G) Universal Terrestrial Radio Access Network (UTRAN) has several Radio Network Controllers (RNCs), each associated with one or more Nodes B, each with one or more Nodes B. Associated with the cell.

3G FDD and TDD systems typically use RNCs to distribute (ie, buffer and schedule) data transmissions to the UE. However, for high-speed channels in 3G cellular systems, the data is distributed by node B. One of these high-speed channels is, for example, the high-speed downlink shared channel (HS-DSCH). Since the data is distributed by node B, it needs to be buffered to node B for transmission. If the distribution entity (node B) to which the user device (UE) is connected is changed, the data buffered in the distribution entity may be lost. The packet data unit (PDU) transmitted on the RNC is not up to date because the data is distributed by the midpoint (node B). For the UE, it is necessary to detect the data loss and request the RNC to retransmit the lost PDU together with the status PDU and so on. Situation Delayed generation of PDUs can result in longer latency for data retransmissions and can fail to meet QoS requirements.

The problem is that there are several node Bs associated with each RNC, and moving UEs are much more likely to require node B changes than RNC changes as a result of UE cell handover. , HS-DSCH is even worse.

HS-DSCH uses AMC to enable high-speed data transmission and H-ARQ to increase the likelihood of successful data delivery. Modifying the service HS-DSCH cell is when the UE must modify the cell associated with the UTRAN access point that is performing the transmission and reception of the service HS-DSCH radio link. The service HS-DSCH cell change is invoked when improved physical channel status and / or improved physical capacity is achieved within the alternate cell.

There are two types of service HS-DSCH cell changes. A service HS-DSCH cell change in node B is when the UE changes between two cells associated with the same node B. A service HS-DSCH cell change between node B is when the UE changes between two cells associated with different node B. In the cell change between nodes B, the node B before the service HS-DSCH cell change is called the source node B, and the node B after the service HS-DSCH cell change is called the target node B.

Both RNC and UE have peer radio link control (RLC) entities. The sending RLC entity originates the sequence number (SN) in the PDU header, which the receiving RLC entity uses to ensure that the PDU is not missing during transmission. If there are missing PDUs in transit, realized by out-of-order delivery of PDUs, the receiving RLC entity sends a status report PDU to notify the sending RLC entity that some PDUs are missing. Status reporting PDUs describe the success and / or failure of data transmission. It identifies the SN of the missing or received PDU. If the PDU is missing, the sending RLC entity will resend a copy of the missing PDU to the receiving RLC.

The sending RLC entity can also poll the status reporting PDU from the receiving RLC entity. This polling function provides a function for requesting the status of PDU transmission from the sending RLC entity. The H-ARQ operation eliminates any failed transmission and increases the probability of successful delivery of data, but ultimately it is the RLC protocol layer that guarantees successful delivery.

Due to the dynamic change in propagation state, HS-DSCH cell changes must be performed quickly to maintain quality of service. During the modification of the service HS-DSCH cell, the UE can suspend transmission and reception within the source cell until all PDUs currently stored on source node B have been successfully transmitted. Because the source node B performs data scheduling and buffering, and because the data rate is very fast (for example, 10 Mb / sec or higher), the UE makes a service HS-DSCH cell change (especially the handover between node B). Running (for) can result in the loss of a significant amount of data buffered within source node B. One of the reasons for this data loss is that there is no mechanism in the UTRAN architecture to transfer the data buffered at source node B to target node B. Since RNC has no way of knowing what data is buffered in source node B, when changing the service HS-DSCH cell, RNC has no information about how much data was lost.

Currently, there are two ways a prioritized system can handle the recovery of buffered data on Source Node B. Following the HS-DSCH cell change, 1) the RNC can explicitly poll the status PDU from the UE, or 2) the RNC initiates transmission within the target cell and in any order realized by the UE. Will generate a status PDU by delivery of.

In the first case where the RNC explicitly polls the status PDU, the RNC must first wait until a physical channel is established in the new cell. The status PDU request is then sent and received and processed by the UE. The UE generates a status PDU and sends it back to the RNC, which processes this status PDU to determine which PDU needs to be resent.

In the second case, where the RNC only starts transmitting the PDU from where it stopped in the source cell, the UE recognizes the out-of-order data delivery and generates a status PDU to send back to the RNC. The RNC processes the status PDU and learns which PDU needs to be resent.

In either of these two cases, if the data buffered in source node B needs to be recovered, the status PDU will be processed, but the correct reception of the data retransmitted by the UE will be significantly delayed. become. This is due to the delay in generating status PDUs by the UE and receiving status PDUs in the RNC. When transmission is performed in RLC acknowledgment mode, data is not passed to higher layers until sequential data delivery can be performed. Therefore, the UE needs to buffer the data in no particular order until the missing PDU can be retransmitted. As a result, not only is there a transmission delay, but the UE must have a memory that can buffer the data in order to continue receiving the data until the missing data can be successfully retransmitted. Otherwise, the effective data transmission rate will be reduced, which will affect the quality of service. Memory is very expensive and is an undesired design constraint.

Another problem facing handovers is the data buffered within the UE. The MAC layer typically has several H-ARQ processors that perform H-ARQ processing. As shown in FIG. 1, the H-ARQ process includes a plurality of parallel H-ARQ processors on the transmitting side (P1B to P5B) and a plurality of parallel H-ARQ processors corresponding to the receiving side (P1UE to P5UE). It is a scheme to prepare. Each processor pair (eg P1B and P1UE) attempts to transmit blocks of data iteratively and sequentially until successful transmission, ensuring that the data in each block is received error-free. For each data block, the time required to achieve successful H-ARQ transmission is different. Since several data blocks are processed in parallel, the transmission order may not be maintained. Therefore, once a data block has been successfully received by the receiving H-ARQ processor, it is transferred to a reordering buffer to provide ordered delivery to the RLC layer. The reordering buffer will reorder the data blocks based on their transmission sequence number and then transfer them to the RLC layer.

During handover between and within node B, RRC messages often carry the MAC layer reset indicator to the UE. When the UE receives the MAC layer reset indicator, it flushes the buffer for all configured H-ARQ processes (ie, disassembling all MAC-hs layer PDUs in the reordering buffer into MAC-d layer PDUs). ) And flushing the reordering buffer by delivering all MAC-d layer PDUs to the MAC-d layer and then to the associated RLC entity), but not limited to. , Performs a series of functions. During a handover between node B (and any in-node B handover), all H-ARQ processes and all reordering buffers are in the UE for data reception from the new MAC-hs entity on target node B. The MAC-hs layer needs to be reset.

After changing the service HS-DSCH cell, the correct status of successful or unsuccessful PDU reception cannot be obtained until the MAC layer reset procedure is completed and the data block is processed by RLC.

<p> In order to properly maintain the user's quality of service requirements, it is desirable to have a system and method that can explain the data buffered within the UE.</p>

<p> The present invention is a method and system for UEs and RNCs to perform a series of operations in order to reduce transmission latency and potentially prevent PDU loss during MAC layer reset. UE generation of status PDUs is combined with a MAC layer reset. The RNC produces a signal message with a MAC reset indication. Following a MAC layer reset upon receipt of a MAC layer reset request, all PDUs stored in the UE's MAC layer reordering buffer are flushed to the RLC entity and then processed by the RLC entity prior to generating the PDU status report. To. The PDU status report provides the RNC with the status of all successfully received PDUs. This provides rapid generation of PDU status reports. When the RNC receives the PDU status report, it recognizes the missing PDU and resends it to the UE.</p><p> Preferred embodiments of the present invention will be described with reference to charts in which the same numbers represent the same elements throughout.</p>

<figref num="1">It is a block diagram which shows the H-ARQ process of the prior art.</figref><figref num="2">It is a flow chart which shows the efficient procedure according to this invention for efficiently recovering the buffering data of a UE following a change of an HS-DSCH cell.</figref><figref num="3">It is a flow chart which shows the first alternative method used when RNC waits for a status PDU prior to the start of transmission of new data in a target cell.</figref><figref num="4">It is a flow chart which shows the 2nd alternative method used when RNC waits for a trigger prior to the start of transmission of new data in a target cell.</figref>

With reference to the flow diagram of FIG. 2, a first embodiment of the present invention is shown, comprising method 10 for determining the PDU transmission status to the UE with the least delay following the MAC layer reset state. This procedure begins when the RNC recognizes the need to reset the UE MAC layer (step 12).

One of the possible causes of UE MAC layer reset is changing the service HS-DSCH cell. RNC is a service in node B in the case of service HS-DSCH cell change between node B, and source node B is the same as target node B, but the transmission queue cannot reroute from source cell to target cell. In case of HS-DSCH cell change, notify node B of the HS-DSCH cell change (step 14). In both cases, a MAC reset is required. The UE is notified by the RNC of the MAC layer reset requirement via a radio resource control (RRC) message, as shown in the figure, along with the HS-DSCH cell change indication (step 16). Note that it is possible to call step 16 prior to step 14 without any adverse consequences.

Those skilled in the art will understand that there are many causes for MAC layer reset other than HS-DSCH cell change, in which Method 10 for RNC to determine PDU transmission status is applied following MAC reset. Let's do it. For example, a MAC layer reset can be justified whenever the H-ARQ process on node B needs to be reinitialized.

The RRC message has an identifier for the MAC layer to perform the reset. This identifier can be part of the service HS-DSCH cell change procedure, or as a result a MAC layer reset on node B and UE, either by a cell change between node B or a cell change within node B. It can be part of any other procedure that occurs. Those skilled in the art will appreciate that there are many aspects of the MAC layer, including the MAC-hs layer and the MAC-d layer. In order to make the description of the present invention easy to understand, the MAC layer is generally referred to below.

HS-DSCH is a data transfer channel. There can be multiple RLC instances on each data transfer channel. An RLC instance is essentially a logical channel that can be mapped to the same transport channel, for example several RLC entities can be mapped to a single transport channel HS-DSCH. When using ARQ to ensure proper transmission between peer RLC instances, the RLC instance is called acknowledgment mode (AM). A pair of AM RLC entities use a status PDU for the recipient to indicate to the sender the successful transmission status of the PDU. Following the occurrence of HS-DSCH cell changes and MAC layer resets, each AM RLC instance associated with a particular HS-DSCH generates a status PDU.

An RRC message is received with the MAC layer reset indicator and processed by the RRC in the UE (step 18). The UE RRC checks if the MAC layer reset indicator is set, and if so, the RRC notifies the MAC layer of the MAC layer reset request (step 20). Upon receiving the MAC layer reset request, the MAC layer resets and, in addition to other tasks, flushes all PDUs stored in the reordering buffer to the RLC entity mapped to HS-DSCH (step 22). All flushed PDUs are then processed by the RLC instance mapped to HS-DSCH (step 24), followed by a PDU status report (step 26).

In order to provide the RNC with accurate and complete transmission status, RLC's PDU processing in the reordering buffer must be stopped before generating the PDU status report. If a PDU status report is generated early (ie, before all PDUs buffered in the MAC reordering queue are processed by the RLC instance), some PDUs will not be considered unreceived. It can be shown properly, and as a result, RNC can generate unnecessary PDU retransmissions.

There are several ways to ensure that all PDUs have been processed by RLC, and as a result the AM RLC entity can get the correct status of all successfully received PDUs. First, the MAC layer forwards PDUs in order from each reordering queue and then generates a "end of PDU" indication for each reordering queue.

In the second alternative, the last PDU from each reordering queue has a special indicator. These are reports of the status of RLC PDUs received on the UE.

In the third alternative, the RLC confirms with the MAC layer when the PDU was processed, and when all PDU processing is complete, the MAC layer generates a PDU status request for the RLC. It should be understood that there are numerous ways to coordinate the processing between the MAC layer and RLC to ensure that all PDUs are processed by RLC before generating the PDU status message.

After receiving and processing the PDU, AM RLC generates a PDU status report indicating the success or failure of all PDU receptions (step 26). A PDU status report is generated for each AM RLC instance mapped to HS-DSCH. A PDU status report can be generated even if no PDUs have been forwarded from the MAC layer for that AM RLC instance. The UE then autonomously sends a PDU status report to RNC for each AM RLC instance associated with HS-DSCH.

The RNC assumes that the AM RLC and MAC entity have not been notified of the PDU transmission stop due to the MAC layer reset, and the RNC continues to transmit the PDU regardless of the MAC layer reset. Upon receiving a PDU status report for each AM RLC instance associated with the HS-DSCH, the RLC instance in the RNC processes the status report (step 28) to determine the lost PDU and ensure successful delivery. Generate a PDU retransmission if necessary to do so (step 30). In order to meet the service quality requirements, this retransmission can take precedence over the current transmission process.

It should be understood that the need for a MAC layer reset is generally associated with the need for PDU status report generation. An indication of either requirement, or some common indication, can be sent to the UE to both reset the MAC layer and generate a PDU status report. The UE will then perform each function in the order described.

In this first embodiment of the invention, as shown in FIG. 2, the RNC can maintain transmission to the UE while the data path is switched from one radio link to another. However, according to the two alternative embodiments of the invention shown in FIGS. 3 and 4, the data at the time of HS-DSCH cell change or other event required for MAC layer reset until a subsequent event occurs. Transmission is aborted. Note that the steps shown in FIGS. 3 and 4 having the same element numbers as the steps shown in FIG. 2 are identical. Therefore, the description of these steps will not be repeated when referring to FIGS. 3 and 4.

A second embodiment of the present invention comprises a method 40 for determining to transmit the PDU status to the UE with minimal delay following the MAC layer reset state, as shown in FIG. After the RNC recognizes the need for a MAC layer reset (step 12) and notifies nodes B and UE (steps 14 and 16), the RNC discontinues all downlink HS-DSCH transmissions (step 17). Note that step 17 can be performed prior to step 14 or 16 without any adverse consequences. The RNC then receives a PDU status report (step 32). The PDU status report indicates the loss of PDUs as a result of a MAC reset and the potential loss of additional PDUs on source node B in the event of an HS-DSCH cell change. The PDU status report is then processed (step 34) and the missing PDU is resent to the UE (step 36). The RNC initiates transmission within a new cell by first scheduling the transmission of the lost PDU that needs to be retransmitted. The RNC then resumes transmission of the PDU from the point where transmission was previously stopped in step 17 (step 38). Note that steps 36 and 38 may be performed at the same time.

With reference to FIG. 4, a method 50 of a third embodiment according to the present invention is shown. This method 50 is similar to the method 40 shown in FIG. However, instead of resuming downlink HS-DSCH transmission to the UE in response to receiving a PDU status report in step 32 as shown in FIG. 3, method 50 of this embodiment of the invention "triggers". Resume transmission at the time of reception or a predetermined event (step 19). In the first example, the trigger can include the establishment of a transport channel within the UTRAN achieved by the RNC with the new "target" node B originating a procedure, as will be appreciated by those skilled in the art. .. Receiving the confirmation generated by node B on the RNC is used as a trigger.

In the second example, the trigger can include receiving or detecting an "in-sync" indication. Establishing a dedicated resource within target node B allows node B to determine a "synchronous" indication if it is determined that the assigned physical channel is available for transmission within node B. The indication for this event can be relayed to the RNC and then used as a trigger.

In the third example, the trigger can include the completion of the RRC procedure (ie, confirmation of receipt of the RNC's UE RRC message). The RRC message sent in step 16 results in an RRC confirmation message generated by the UE and sent to the RNC. If this message is received by RNC, it can be used as a trigger.

It should be noted that there are many different signals transmitted between the UE and the RNC, and the user can choose one of these as desirable to act as a trigger according to the present invention. Therefore, the above three examples are enlightening rather than restrictive. Regardless of the trigger format, the RNC resumes HS-DSCH transmission after the trigger is received (step 21).