WO2008041189A2

WO2008041189A2 - Method for transmission error control of sdu segments

Info

Publication number: WO2008041189A2
Application number: PCT/IB2007/054021
Authority: WO
Inventors: Haitao Tang; Kimmo Kettunen; Tatikonda Sivakumar
Original assignee: Nokia Corporation; Nokia Inc.
Priority date: 2006-10-04
Filing date: 2007-10-03
Publication date: 2008-04-10
Also published as: WO2008041189A3

Abstract

The present invention provides a method, apparatuses and system for carrying out transmission error control while reducing the amount of resources required to effectuation the transmission error control. Accordingly, in an exemplary embodiment of the invention a refinement sequence number is generated and added, for example by a protocol layer, to a segment of a data unit, such as a service data unit (SDU) or protocol data unit (PDU). The refinement sequence number may then be used by protocol layers such as the radio link control (RLC) layer or media access control (MAC) layer for transmission error control at the segment level and data unit level between peer entities.

Description

METHOD, APPARATUS AND SYSTEM FOR TRANSMISSION ERROR CONTROL

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/849,505 filed October 4, 2006.

FIELD OF THE INVENTION

The present invention pertains to the field of telecommunications. More particularly, the present invention relates to the provision of information between peer entities in a communications network to reduce the amount of transmission resources required for the retransmission of information.

BACKGROUND OF THE INVENTION

A universal mobile telecommunications system (UMTS) is a third-generation mobile communications system that evolved from a global system for mobile communications system (GSM). The UMTS is intended to provide enhanced mobile communications services based on the GSM core network and wideband code- division multiple-access (WCDMA) technology. The UMTS terrestrial radio access network (UTRAN) is a radio access network for supporting WCDMA access technology in the UMTS. Long term evolution (LTE) of 3GPP may involve "evolved UMTS Terrestrial Radio Access Network," or E-UTRAN.

In general, the interface between a user equipment (UE) and the UTRAN or E-UTRAN has been realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1 ), a data link layer (L2) and a network layer (L3). For example, the physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer of the second layer (L2). Data travels between the MAC layer at L2 and the physical layer at L1 , via a transport channel. The transport channel is divided into a dedicated transport channel and a common transport channel depending on whether a channel is shared. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (receiver). Typically, the second layer (L2) may include the MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer. The MAC layer maps various logical channels to various transport channels. The MAC layer also multiplexes logical channels by mapping several logical channels to one transport channel. The MAC layer is connected to an upper RLC layer via the logical channel. The logical channel can be divided into a control channel for transmitting control plane information, such as control signaling, and a traffic channel for transmitting user plane information, such as data information. The MAC layer within L2 is divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs sublayer and a MAC-e sublayer according to the type of transport channel being managed. The MAC-b sublayer manages a broadcast channel (BCH), which is a transport channel handling the broadcast of system information. The MAC-c/sh sublayer manages common transport channels such as an FACH (Forward Access Channel) or a DSCH (Downlink Shared Channel) that is shared by other terminals. The MAC-d sublayer handles the managing of a DCH (Dedicated Channel), namely, a dedicated transport channel for a specific user equipment (UE) terminal. In order to support uplink and downlink high speed data transmissions, the MAC-hs sublayer manages an HS-DSCH (High Speed Downlink Shared Channel), namely, a transport channel for high speed downlink data transmission, and the MAC-e sublayer manages an E-DCH (Enhanced Dedicated Channel), namely, a transport channel for high speed uplink data transmissions. The RLC layer within L2 provides the establishment and release of a radio link. The RLC may also perform segmentation and concatenation relating to RLC service data units (SDU). A SDU describes the information transferred between peer layer entities. The size of an RLC SDU may be adjusted to fit a processing capacity in the RLC layer. Header information may be added to the SDU to form a protocol data unit (PDU). The RLC SDU is transferred to the MAC layer. The entity transmitting the SDU or PDU is referred to as the transmitting entity, and the entity receiving the SDU or PDU is referred to as the receiving entity.

Three modes exist for the function of the RLC layer. The three modes are the transparent mode, the unacknowledged mode, and the acknowledged mode. In the transparent mode, no header information is added to the RLC SDU, and generally segmentation and reassembly are not performed. In the unacknowledged mode, retransmission does not occur when transmission of a RLC data unit, such as a SDU or PDU fails. Therefore, a receiving side does not demand the retransmission when data is lost or when problems occur during transmission. Instead, the receiving side discards the related data.

Retransmission of a data unit occurs when the transmission of a data unit, such as SDU or PDU fails. In order to determine when retransmission should occur, the RLC layer of a transmitting side receives information from the receiving side that indicates the success or failure of the transmission. In response to an indication of a failure, the transmitting side RLC layer then retransmits the data units that were not received. This may be accomplished through the generation of a sequence number by the PDCP, which is assigned to a data unit, such as either a SDU or a PDU based on the order the data unit was submitted or received. For example, the first data unit submitted is assigned "0", and sequence number is incremented by "1 " for each subsequent data unit received. The transmitting side PDCP generates a sequence number (SN) that corresponds to a particular data unit. The sequence number is not added to the header of the data unit, but instead is provided in a primitive from the transmitting entity's PDCP layer to the transmitting entity's RLC/MAC layers. The transmitting and receiving entities can use the sequence number for transmission error control of the given data unit. The receiving entity forwards the sequence number to the PDCP layer from the RLC/MAC layers by means of a primitive. This also allows the PDCP layer of the receiving entity to perform re-ordering of the received data unit, and any required decryption. However, if a transmission error is detected due to the absence of a sequence number corresponding to a data unit, the receiving entity has to request retransmission of the entire data unit from the transmitting entity. As stated previously, in some situations a data unit may be divided into pre-defined sizes by segmentation/concatenation. Therefore, transmission resources may be wasted by retransmission of the entire data unit when the error only involved one segment.

What is needed is a mechanism that provides for indication of the particular segments that are lost or contain errors, and therefore avoid the need to retransmit the complete data unit, and only requiring retransmission of the lost or incorrect segments of a data unit. The present invention seeks to accomplish this by associating a short refinement sequence number with each segment of a data unit.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

According to a first aspect of the present invention, a method is provided that includes associating a segment indicator with a segment of a data unit including a plurality of segments, and transmitting at least the segment indicator to a receiving entity.

According to the first aspect of the present invention, associating the segment includes generating the segment indicator, and adding the segment indicator to the segment.

According to the first aspect of the present invention, the method may also include receiving a request for transmission of an expected segment from the receiving entity, and the request for transmission is based on a comparison of the segment indicator with an expected segment indicator associated with the expected segment.

According to the first aspect of the present invention, the method may also include transmitting the expected segment to the receiving entity.

According to the first aspect of the present invention, the method may also include incrementing the segment indicator by one, and associating the incremented segment indicator with a next segment of the data unit.

According to the first aspect of the present invention, the method may also include associating a sequence number with the data unit, and transmitting the sequence number to the receiving entity. According to the first aspect of the present invention, the method may also include receiving a request for transmission of an expected segment from the receiving entity, and the request for transmission is based on a comparison of the segment indicator and the sequence number with an expected segment indicator and expected sequence number associated with the expected segment.

According to the first aspect of the present invention, the receiving entity is a network element.

According to the first aspect of the present invention, the receiving entity is a user equipment terminal. According to the first aspect of the present invention, the data unit is a service data unit.

According to the first aspect of the present invention, a number of bits including the segment indicator is based upon a maximum number of segments required for the data unit. According to the first aspect of the present invention, transmitting the segment indicator includes transmitting the segment indicator inside a frame.

According to a second aspect of the present invention, a method is provided that includes receiving a segment indicator associated with a segment of a data unit including a plurality of segments, and comparing the segment indicator with an expected segment indicator.

According to the second aspect of the present invention, when the segment indicator does not correspond to the expected segment indicator, the method further includes requesting transmission of the segment associated with the expected segment indicator from a transmitting entity. According to the second aspect of the present invention, the segment indicator is received from a transmitting entity.

According to a third aspect of the present invention, an apparatus is provided that includes a processor for associating a segment indicator with a segment of a data unit including a plurality of segments, and a transmitter for transmitting at least the segment indicator to a receiving entity. According to the third aspect of the present invention, the processor includes a generator for generating the segment indicator, and an adder for adding the segment indicator to the segment.

According to the third aspect of the present invention, the apparatus may also include a receiver for receiving a request for transmission of an expected segment from the receiving entity, wherein the request for transmission is based on a comparison of the segment indicator with an expected segment indicator associated with the expected segment.

According to the third aspect of the present invention, the transmitter is configured for transmitting the expected segment to the receiving entity.

According to the third aspect of the present invention, the processor is configured for incrementing the segment indicator by one, and associating the incremented segment indicator with a next segment of the data unit.

According to the third aspect of the present invention, the processor is configured for associating a sequence number with the data unit, and the transmitter is configured for transmitting the sequence number to the receiving entity.

According to the third aspect of the present invention, the apparatus may also include a receiver for receiving a request for transmission of an expected segment from the receiving entity, wherein the request for transmission is based on a comparison of the segment indicator and the sequence number with an expected segment indicator and expected sequence number associated with the expected segment.

According to the third aspect of the present invention, the apparatus may be or be included in a network element. According to the third aspect of the present invention, the apparatus may be or be included in a user equipment terminal.

According to a fourth aspect of the present invention, an apparatus is provided that includes means for associating a segment indicator with a segment of a data unit including a plurality of segments, and means for transmitting at least the segment indicator to a receiving entity.

According to a fifth aspect of the present invention, an apparatus is provided that includes a receiver for receiving a segment indicator associated with a segment of a data unit including a plurality of segments, and an error module for comparing the segment indicator with an expected segment indicator.

According to the fifth aspect of the present invention, when the error module determines that the segment indicator does not correspond to the expected segment indicator, the error module is configured for requesting transmission of the segment associated with the expected segment indicator from a transmitting entity.

According to the fifth aspect of the present invention, the segment indicator is received from a transmitting entity.

According to a sixth aspect of the present invention, an apparatus is provided that includes means for receiving a segment indicator associated with a segment of a data unit including a plurality of segments, and means for comparing the segment indicator with an expected segment indicator.

According to a seventh aspect of the present invention, a computer readable storage structure is provided embodying computer program code thereon for execution by a computer processor, wherein the computer program code includes instructions for performing the method including the steps of associating a segment indicator with a segment of a data unit including a plurality of segments, and transmitting at least the segment indicator to a receiving entity.

According to an eighth aspect of the present invention, a computer readable storage structure is provided embodying computer program code thereon for execution by a computer processor, wherein the computer program code includes instructions for performing the method including the steps of receiving a segment indicator associated with a segment of a data unit including a plurality of segments, and comparing the segment indicator with an expected segment indicator. According to a ninth aspect of the present invention, a system is provided that includes a transmitting entity configured to generate a segment indicator, and to add the segment indicator to a segment of a data unit including a plurality of segments, and a receiving entity, responsive to the segment indicator, configured to compare the segment indicator with an expected segment indicator. BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with accompanying drawings, in which:

Figure 1 is a flow diagram of a method according to an aspect of the present invention.

Figure 2 is a block diagram of a communication device, such as a user equipment terminal or Node B, according to an aspect of the present invention. Figure 3 is a block diagram showing communication between communication devices embodying protocol layers according an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a flow chart according to an exemplary embodiment of the invention in which transmission error control of data units is performed at the radio link control (RLC) and/or media access control (MAC) layers through the generation and addition of a sequence indicator, such as a short refinement sequence number, to segments of a data unit. Prior to the transmission of RLC/MAC data units such as service data units (SDU) a short refinement sequence number is generated in step S10 for each segment of the SDU, and then added or associated with each of the segments of the SDU in step S1 1. Each data unit, i.e. SDU may also be associated with a sequence number indicating the order in which the SDU was transmitted from a transmitting entity to a receiving entity. Therefore, in accord with this exemplary embodiment of the present invention, each segment for an SDU has a refinement sequence number added to or associated with the segment, as well as a sequence number indicating the SDU to which the segment is part of. Errors may occur during transfer of data units between peer entities, i.e. receiving and transmitting entities, resulting in lost or incomplete data units. The refinement sequence number that has been added or associated with each segment of the data unit can be used by the receiving entity to indicate to the transmitting entity which segment was not received or incompletely received in step S12. The transmitting entity can then respond by retransmitting the particular segment indicated by the refinement sequence number in step S13. In this manner, errors that have occurred during transmission of data units can be corrected without the need to retransmit the entire data unit.

Figure 2 shows some components of a communication terminal 1 1 , which could be either a user equipment (UE) terminal, or a Node B or an evolved Node B (e-Node B). The communication terminal includes a processor 22 for controlling operation of the device, including all input and output. The processor, whose speed/timing is regulated by a clock 22a, may include a BIOS (basic input/output system) or may include device handlers for controlling user audio and video input and output as well as user input from a keyboard. The BIOS/device handlers may also allow for input from and output to a network interface card. The BIOS and/or device handlers also provide for control of input and output to a transceiver (TRX) 26 via a TRX interface 25 including possibly one or more digital signal processors (DSPs), application specific integrated circuits (ASICs), and/or field programmable gate arrays (FPGAs). The TRX enables communication over the air with another similarly equipped communication terminal.

Still referring to Figure 2, the communication terminal 1 1 may also include volatile memory, i.e. so-called executable memory 23, and also non-volatile memory 24, i.e. storage memory. The processor 22 may copy applications (e.g. a calendar application or a game) stored in the non-volatile memory into the executable memory for execution. The processor functions according to an operating system, and to do so, the processor may load at least a portion of the operating system from the storage memory to the executable memory in order to activate a corresponding portion of the operating system. Other parts of the operating system, and in particular often at least a portion of the BIOS, may exist in the communication terminal as firmware, and are then not copied into executable memory in order to be executed. The booting up instructions are such a portion of the operating system.

Still referring to Figure 2, the communication terminal 1 1 , such as a user equipment (UE) terminal or a Node B or evolved Node B (eNode B), may also include a generator 21 that may be configured to generate a sequence indicator, such as a refinement sequence number, and may also include an adder 28 configured to add or associate the refinement sequence number with a segment of a data unit, such as a RLC/MAC SDU. The adder 28 may be configured to add the refinement sequence number as a number of bits carried inside the frame between a transmitting entity and receiving entity. The number of bits required for the refinement sequence number may be dependent upon the maximum number of possible segments of the data unit, such as the RLC/MAC SDU. Therefore, when in combination with the PDCP sequence number (SN), the refinement sequence number provides a unique identification for a particular segment. When the RLC/MAC SDU is transmitted to the receiving entity, the receiving entity can identify specifically which segment of the RLC/MAC SDU needs to be transmitted as a result loss of or error with the segment. In this manner, retransmission of incomplete SDUs can be accomplished without retransmission of the entire SDU, since only the segment corresponding to the refinement sequence number needs to be retransmitted so that complete transmission can occur. It is understood that the generator 21 and adder 28 may be embodied as modules separate from the processor 22, or as modules embodied in the processor 22. The communication terminal 11 , which may be either the UE terminal or the

Node B may also include an error module 29 for providing an indication that a particular segment associated with a refinement sequence number experienced an error during the transmission of the segment, and should be retransmitted. This indication may be provided to the transmitting entity so that the transmitting entity is informed which segments of a corresponding RLC/MAC SDU should be retransmitted.

Referring now to Figure 3, an aspect of the present invention is shown from the perspective of layers of a protocol according to which communication is performed. The layers of protocol form a protocol stack, and include CN protocol layers L3, located in, for example a user equipment (UE) terminal 31 and a core network 34, and radio protocol layers L2 located in the UE terminal 31 and in the Node B or e-Node B 32. Communication is peer-to-peer. Thus, a CN protocol layer in the UE communicates with a corresponding layer in the CN, and vice versa, and the communication is provided via lower/intervening layers. The lower/intervening layers thus provide as a service to the layer immediately above them in the protocol stack the packaging or unpackaging of a unit of communication (a control signal or data information). In accordance with an aspect of the invention, the radio link control (RLC) and/or medium access control (MAC) layers (not shown) may be configured to generate and add a short refinement sequence number to each segment of a data unit, such as a RLC/MAC SDU that the RLC and/or MAC layers transmit or prepare to transmit. In this manner, the RLC/MAC may use the refinement sequence number for transmission error control at the segment level, in addition to transmission error control at the RLC/MAC SDU level.

The functionality described above (for both the radio access network and the UE) can be implemented as software modules stored in a non-volatile memory, and executed as needed by a processor, after copying all or part of the software into executable RAM (random access memory). Alternatively, the logic provided by such software can also be provided by an ASIC (application specific integrated circuit). In case of a software implementation, the invention can be provided as a computer program product including a computer readable storage structure embodying computer program code~i.e. the software-thereon for execution by a computer processor.

It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope of the present invention, and the appended claims are intended to cover such modifications and arrangements.

Claims

What is claimed is:

1. A method, comprising: associating a segment indicator with a segment of a data unit comprising a plurality of segments, and transmitting at least the segment indicator to a receiving entity.

2. The method according to claim 1 , wherein associating the segment comprises generating the segment indicator, and adding the segment indicator to the segment.

3. The method according to claim 1 , further comprising receiving a request for transmission of an expected segment from the receiving entity, wherein the request for transmission is based on a comparison of the segment indicator with an expected segment indicator associated with the expected segment.

4. The method according to claim 3, further comprising transmitting the expected segment to the receiving entity.

5. The method according to claim 1 , further comprising incrementing the segment indicator by one, and associating the incremented segment indicator with a next segment of the data unit.

6. The method according to claim 1 , further comprising associating a sequence number with the data unit, and transmitting the sequence number to the receiving entity.

7. The method according to claim 6, further comprising receiving a request for transmission of an expected segment from the receiving entity, wherein the request for transmission is based on a comparison of the segment indicator and the sequence number with an expected segment indicator and expected sequence number associated with the expected segment.

8. The method according to claim 1 , wherein the receiving entity is a network element.

9. The method according to claim 1 , wherein the receiving entity is a user equipment terminal.

10. The method according to claim 1 , wherein the data unit is a service data unit.

1 1. The method according to claim 1 , wherein a number of bits comprising the segment indicator is based upon a maximum number of segments required for the data unit.

12. The method according to claim 1 , wherein transmitting the segment indicator comprises transmitting the segment indicator inside a frame.

13. A method, comprising: receiving a segment indicator associated with a segment of a data unit comprising a plurality of segments, and comparing the segment indicator with an expected segment indicator.

14. The method according to claim 13, wherein when the segment indicator does not correspond to the expected segment indicator, the method further comprises requesting transmission of the segment associated with the expected segment indicator from a transmitting entity.

15. The method according to claim 13, wherein the segment indicator is received from a transmitting entity.

16. An apparatus, comprising: a processor for associating a segment indicator with a segment of a data unit comprising a plurality of segments, and a transmitter for transmitting at least the segment indicator to a receiving entity.

17. The apparatus according to claim 16, wherein the processor comprises a generator for generating the segment indicator, and an adder for adding the segment indicator to the segment.

18. The apparatus according to claim 16, further comprising a receiver for receiving a request for transmission of an expected segment from the receiving entity, wherein the request for transmission is based on a comparison of the segment indicator with an expected segment indicator associated with the expected segment.

19. The apparatus according to claim 18, wherein the transmitter is configured for transmitting the expected segment to the receiving entity.

20. The apparatus according to claim 16, wherein the processor is configured for incrementing the segment indicator by one, and associating the incremented segment indicator with a next segment of the data unit.

21 . The apparatus according to claim 16, wherein the processor is configured for associating a sequence number with the data unit, and the transmitter is configured for transmitting the sequence number to the receiving entity.

22. The apparatus according to claim 21 , further comprising a receiver for receiving a request for transmission of an expected segment from the receiving entity, wherein the request for transmission is based on a comparison of the segment indicator and the sequence number with an expected segment indicator and expected sequence number associated with the expected segment.

23. The apparatus according to claim 16, wherein the apparatus comprises a network element.

24. The apparatus according to claim 16, wherein the apparatus comprises a user equipment terminal.

25. An apparatus, comprising: means for associating a segment indicator with a segment of a data unit comprising a plurality of segments, and means for transmitting at least the segment indicator to a receiving entity.

26. An apparatus, comprising: a receiver for receiving a segment indicator associated with a segment of a data unit comprising a plurality of segments, and an error module for comparing the segment indicator with an expected segment indicator.

27. The apparatus according to claim 26, wherein when the error module determines that the segment indicator does not correspond to the expected segment indicator, the error module is configured for requesting transmission of the segment associated with the expected segment indicator from a transmitting entity.

28. The apparatus according to claim 26, wherein the segment indicator is received from a transmitting entity.

29. An apparatus, comprising: means for receiving a segment indicator associated with a segment of a data unit comprising a plurality of segments, and means for comparing the segment indicator with an expected segment indicator.

30. A computer readable storage structure embodying computer program code thereon for execution by a computer processor, wherein the computer program code comprises instructions for performing the method according to claim 1.

31. A computer readable storage structure embodying computer program code thereon for execution by a computer processor, wherein the computer program code comprises instructions for performing the method according to claim 13.

32. A system, comprising: a transmitting entity configured to generate a segment indicator, and to add the segment indicator to a segment of a data unit comprising a plurality of segments, and a receiving entity, responsive to the segment indicator, configured to compare the segment indicator with an expected segment indicator.