Patent Application
20080285566
This application is related to wireless communications.
Hybrid automatic repeat request (HARQ)-assisted radio link control (RLC) delivery notification or confirmation services, (i.e., HARQ-assisted automatic repeat request (ARQ)), have been proposed. In HARQ-assisted RLC delivery notification or confirmation services, the medium access control (MAC) layer provides delivery notification or confirmation of an RLC protocol data unit (PDU) to the RLC ARQ entity. If the HARQ transmitter detects a failed delivery of a transport block (TB), (e.g., due to reaching a maximum retransmission limit), a relevant ARQ entity is notified of the failed delivery of an underlying RLC PDU and retransmissions and/or re-segmentation of the RLC PDU may be triggered. This service is referred to as MAC delivery notification services.
An acknowledged mode (AM) RLC entity provides RLC delivery notification or confirmation services to upper layers, such as packet data convergence protocol (PDCP) entity. The RLC delivery notification or confirmation services are based on RLC ARQ acknowledgements, (i.e., status reports). The RLC-AM-DATA-Conf primitive is used by the AM RLC entity to confirm to the upper layers the reception of an RLC service data unit (SDU) by the peer RLC AM entity or to inform the upper layers of a discarded SDU. These services are referred to as ARQ-based RLC delivery notification services.
In universal terrestrial radio access network (UTRAN), RLC transparent mode (TM), unacknowledged mode (UM), or AM can utilize a timer-based discard mechanism, (e.g., for clearing the RLC buffers after a certain time from the reception of the RLC SDU from the upper layers). Upon discarding the RLC SDU, RLC-UM-DATA-Conf is used by the UM RLC entity to inform the upper layers of the discarded RLC SDU. However, such discarding is not based on transmission status acknowledgements, but purely timer-based. In other words, RLC-UM-DATA-Conf does not convey any information on whether an RLC SDU was successfully delivered or not. Such services are referred to as RLC discard notification services.
A method and apparatus for providing and utilizing RLC and MAC packet delivery notification are disclosed. A MAC entity tracks a delivery status of a MAC PDU and sends MAC service data unit (SDU) delivery notification to an RLC entity and/or an upper layer upon occurrence of a triggering event. The triggering event may be expiration of a timer, a packet discard decision, MAC reset, MAC re-establishment, or a request from the upper layer. The RLC entity may also track a delivery status of an RLC SDU and send RLC delivery notification to the upper layer. An upper layer including a header compression entity may adjust a header compression parameter based on the RLC delivery notification or the MAC delivery notification. The RLC delivery notification may be used for lossless handover. Retransmission may be performed at the upper layer based on the RLC delivery notification or the MAC delivery notification.
A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:
When referred to hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “Node B” includes but is not limited to a base station, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment.
Hereinafter, the terminology “state” and “status” and “notification” and “confirmation” will be used interchangeably, respectively.
Embodiments disclosed herein are applicable to any wireless communication systems, such as third generation partnership project (3GPP) universal mobile telecommunication system (UMTS), long term evolution (LTE), high speed packet access enhancements (HSPA+), etc., and their constituent apparatus, such as WTRUs and Node Bs, etc.
The HARQ entity 115, 125 implement a HARQ transmission and retransmission mechanism based on HARQ feedback for delivery of a HARQ PDU. The MAC layer 114, 124 (or the HARQ entity 115, 125 in the MAC layer 114, 124) is configured to provide a MAC delivery notification services to indicate the delivery status of a MAC SDU or a MAC PDU to the RLC layer 116, 126 or the higher layers 118, 128.
The MAC layer 114, 124 tracks a delivery status of a MAC PDU. Each HARQ PDU may be in one of three (3) HARQ PDU delivery statuses: pending, success, or failure as shown in
The status of a HARQ PDU begins from the pending state, while the HARQ PDU is in the process of being transmitted or retransmitted by the HARQ entity 115, 125, and final status (success or failure) is yet to be determined.
Upon occurrence of an event A, the HARQ PDU delivery status changes from pending to success. The event A includes, but is not limited to, the following events:
Upon occurrence of an event B, the HARQ PDU delivery status changes from pending to failure. Event B includes, but is not limited to, the following events:
Upon occurrence of an event C, the HARQ PDU delivery status remains as pending. Event C may be reception of HARQ NACK, and not reaching the maximum number of HARQ retransmission attempts.
Multiple HARQ SDUs may be included in one HARQ PDU, (i.e., multiple HARQ SDUs may be multiplexed or concatenated into one HARQ PDU). The MAC SDU, (i.e., RLC PDU), inherits the status, (i.e., success, failure, or pending), of the underlying HARQ PDU. For example, if HARQ PDU status becomes successful, then all of the MAC SDUs, (i.e., RLC PDUs), contained in the HARQ PDU will have a successful delivery status.
The MAC layer 114, 124 sends MAC delivery notification to the RLC layer 116, 126 or upper layers 118. 128, (such as PDCP layer, radio resource control (RRC) layer, non-access stratum (NAS) layer, etc.). The MAC delivery notification may be triggered by certain events including, but not limited to, the following events:
The RLC layer 116, 126 or upper layer 118, 128 may or may not wish to be notified of the MAC SDU delivery status. It may be indicated to the MAC layer 114, 124 through a primitive that the RLC layer uses to request transmission of a MAC SDU. Alternatively, a configuration parameter may be used to activate or de-activate notification for a certain logical channel.
Besides the MAC delivery notification, the RLC layer 116, 126 may also provide RLC delivery notification services to upper layer 118, 128, (such as PDCP layer, RRC layer, NAS layer, etc.). The RLC entity 116, 126 may be a TM RLC entity, a UM RLC entity, or an AM RLC entity. The RLC entity 116, 126 may make the RLC delivery notification based on the MAC delivery notification from the MAC layer 114, 124, (i.e., HARQ-assisted RLC delivery notification), and/or based on ARQ mechanism at the RLC layer 116, 126, (i.e., ARQ-based RLC delivery notification).
An RLC SDU may be in one of three (3) delivery states with respect to its delivery status: pending, success, or failure, as shown in
The state of an RLC SDU begins in the pending state. Upon occurrence of an event A, the RLC SDU delivery status changes from pending to success. Event A includes, but is not limited to, the following events:
Upon occurrence of an event B, the RLC SDU delivery status changes from pending to failure. Event B includes, but is not limited to, the following events:
Upon occurrence of an event C, the RLC SDU delivery status remains as pending. Event C includes, but is not limited to, the following events:
Alternatively, the RLC entity 116, 126 may make the RLC delivery notification based on RLC level ARQ feedback from the peer RLC entity. The RLC ARQ mechanism provides retransmission service on an RLC PDU level. RLC ARQ status reports are sent by the receiver to the transmitter to indicate the delivery status of RLC PDUs, (i.e., ARQ ACK/NACK). The RLC entity 116, 126 may send RLC delivery notification to higher layers 118, 128, (such as RRC layer, PDCP layer, NAS layer, or the like), based on the ARQ mechanism only, based on MAC/HARQ delivery notification only, or based on both.
Referring again to
Upon occurrence of an event A, an RLC SDU delivery status changes from pending to success. Event A includes, but is not limited to, the following events:
Upon occurrence of an event B, the RLC SDU delivery status changes from pending to failure. Event B includes, but is not limited to, the following events:
Upon occurrence of an event C, the RLC SDU delivery status remains as pending. Event C includes, but is not limited to, the following events:
The RLC delivery notification to the upper layers 118, 128, (e.g., PDCP, RRC, NAS, etc.), for an RLC SDU, (e.g., PDCP PDU, RRC PDU, or the like), may be triggered upon certain events. The triggering events include, but are not limited to, the following events:
The upper layer 118, 128, (e.g., PDCP, RRC or NAS), may or may not wish to be notified of the packet delivery status. A primitive that the upper layer uses to request transmission of an RLC SDU may or may not request a notification or confirmation from the RLC entity 116, 126. Alternatively, a configuration parameter may be used to activate or de-activate notification for a certain radio bearer.
Furthermore, the primitive that the upper layer 118, 128 uses to request transmission of an RLC SDU, (e.g., RLC-AM-DATA-Req), may indicate whether delivery notification should be based on the ARQ-based mechanism only, the MAC/HARQ delivery notification mechanism only, or both. The primitive used to confirm to the upper layer 118,128, (e.g., RLC-AM-DATA-Conf), may contain multiple status fields to indicate the delivery status based on MAC/HARQ delivery notification and the delivery status that is ARQ-based. Alternatively, if desired, a single status field based on either one only, or combining the results from both mechanisms may be utilized.
In accordance with another embodiment, adaptive header compression, (e.g., robust header compression (ROHC)), may take into account the RLC delivery notification provided by the RLC entity 116, 126, (e.g., HARQ-assisted RLC delivery notification or ARQ-based RLC delivery notification services), or the MAC delivery notification directly provided by the MAC entity 114, 124.
An ROHC compressor may adapt its compression behavior based on the RLC delivery notification services or the MAC delivery notification. For example, when the ROHC compressor (located in a WTRU or a Node B) is notified of one or more RLC SDU error(s), (e.g., potentially after a given threshold), the ROHC compressor may adapt its behavior and produce more robust header, (e.g., via moving into a lower compression state such as Initialization and Refresh (IR) or First Order (FO) states). On the other hand, when the ROHC compressor is notified of one or more RLC SDU delivery success, (e.g., potentially after a given threshold), the ROHC compressor may adapt its behavior and produce more efficient header, (e.g., via moving into a higher compression state such as Second Order (SO) or FO states).
The ROHC compressor may request an RLC or MAC delivery notification for packets that are deemed important, (such as context initialization or update packets), in order to conduct fast retransmission of such packets in case of delivery failure. A decompressor at the receiver side may also be able to make use of MAC or RLC delivery notification information.
Lossless handover has been considered for services that require reliability, (e.g., transmission control protocol (TCP)), and typically make use of RLC AM. In accordance with another embodiment, data forwarding from a source Node B to a target Node B for lossless handover for RLC UM or TM services may be facilitated using HARQ-assisted RLC delivery notification services. For example, during handover, the source Node B may utilize the HARQ-assisted RLC SDU delivery status information to forward all packets that are still stored in the source Node B, (e.g., in the PDCP layer), and that do not have successful delivery status according to the HARQ-assisted RLC delivery notification service. This is useful for performing data forwarding for applications such as voice over IP (VoIP) or video for example.
During handover, a WTRU may start sending data on a given HARQ process, but due to the need to handover immediately to the target cell, the WTRU may not be able to continue sending or resending the HARQ PDU in the target cell. In accordance with the conventional standards, HARQ and RLC resets are required when a WTRU moves to the target Node B. For RLC AM services, the ARQ mechanism may cover the potential data loss in this case since ARQ may provide reliable retransmission. However, RLC UM or TM services may experience some loss due to the RLC and HARQ reset. In order to prevent such loss during the handover for RLC UM or TM (or even AM) services, (e.g., VoIP or video over IP), the HARQ-level transmission in the target Node B may be reinitialized.
Packets that were not delivered in the source cell are not discarded at MAC or HARQ reset or re-establishment due to handover, but maintained, and their HARQ transmissions are restarted in the target cell. For example, upon detecting a handover event, the WTRU may re-start the HARQ transmission in the target cell for the same packet that the WTRU was transmitting or re-transmitting in the source cell, and also potentially reset the number of HARQ retransmissions that have occurred in the source cell. In prior art, UM or TM services cannot be retransmitted upon a MAC/RLC reset due to handover, and the MAC SDUs or RLC SDUs would be lost. In order to prevent such loss during handover, the MAC SDUs may be retransmitted via restarting HARQ retransmissions in the target cell.
Alternatively, PDCP-level retransmission may be performed. The PDCP layer may utilize the RLC delivery notification services, (i.e., HARQ-assisted and/or ARQ-based), and/or its knowledge of handover event in order to conduct PDCP-level retransmission for those packets that are in the PDCP buffer and whose delivery status became failure during the handover procedure.
Any higher level application may make use of the packet delivery notification/confirmation mechanisms disclosed herein, (i.e., the HARQ-assisted RLC delivery notification services, ARQ-based RLC delivery notification services, and/or MAC delivery notification services). For example, transport layer protocols such as user datagram protocol (UDP), real time transmit protocol (RTP), real time transmission control protocol (RTCP), TCP, IP, or the like may utilize the HARQ-assisted or ARQ-based RLC SDU delivery notification services to trigger a specific action, (e.g., retransmission), or to adapt their behavior, (e.g., flow control).
Voice, (e.g., VoIP), or video application may make use of the delivery notification services in a multitude of ways. For example, VoIP applications or any other applications dependent on protocols like RTP and RTCP and using RLC UM or TM may make use of the RLC packet delivery notifications to control delay or jitter effects.
The RLC delivery notification services, (i.e., HARQ-assisted or ARQ-based), may also be used to optimize RLC functions, such as its window-based flow control mechanism. The transmit window may be adjusted based on HARQ-assisted RLC packet delivery information. For example, the window size may be adjusted upon receipt of HARQ-assisted error notification for faster recovery from the situation where the link condition is very bad. The same may be applied for optimizing other L2/L3 or even L1 functions.
Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).
Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine.
A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB) module.
This application claims the benefit of U.S. provisional application No. 60/914,402 filed Apr. 27, 2007, which is incorporated by reference as if fully set forth.
| Number | Date | Country | |
|---|---|---|---|
| 60914402 | Apr 2007 | US |
