WO2013167288A1

WO2013167288A1 - Repeat transmissions

Info

Publication number: WO2013167288A1
Application number: PCT/EP2013/052630
Authority: WO
Inventors: Kiran Kumar Mysore NATARAJ; Raghuram Reddy K
Original assignee: Nokia Siemens Networks Oy
Priority date: 2012-05-11
Filing date: 2013-02-11
Publication date: 2013-11-14

Abstract

A technique comprising: in a system in which an access node makes one or more repeat transmissions of a data unit for a communication device without waiting for feedback about an attempt by the communication device to decode a transmission of said data unit: adjusting the number of said repeat transmissions of a data unit according to an indicator of the condition of a wireless interface between the access node and the communication device for transmissions of earlier data units to said communication device.

Description

REPEAT TRANSMISSIONS

One technique aimed at achieving reliable communication of data over a wireless interface between an access node of a radio access network and a communication device, whilst making efficient use of radio resources, involves:

retransmitting a data unit in a response to an indication that the communication device has failed to correctly decode an earlier transmission of said data unit.

The inventors for the present application have identified the challenge of providing an alternative technique for achieving reliable communication of data to a communication device over a wireless interface whilst making efficient use of radio resources.

There is hereby provided a method, comprising: in a system in which an access node makes one or more repeat transmissions of a data unit for a communication device without waiting for feedback about an attempt by the communication device to decode a transmission of said data unit: adjusting the number of said repeat transmissions of a data unit according to an indicator of the condition of a wireless interface between the access node and the communication device for

transmissions of earlier data units to said communication device.

There is also provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: in a system in which an access node makes one or more repeat transmissions of a data unit for a communication device without waiting for feedback about an attempt by the communication device to decode a transmission of said data unit: adjust the number of said repeat transmissions of a data unit according to an indicator of the condition of a wireless interface between the access node and the communication device for transmissions of earlier data units to said communication device.

There is also provided a computer program product comprising program code means which when loaded into a computer controls the computer to: in a system in which an access node makes one or more repeat transmissions of a data unit for a

communication device without waiting for feedback about an attempt by the communication device to decode a transmission of said data unit: adjust the number of said repeat

transmissions of a data unit according to an indicator of the condition of a wireless interface between the access node and the communication device for transmissions of earlier data units to said communication device.

In one embodiment, said indicator is based on one or more reports by said communication device of one or more attempts by said communication device to decode one or more

transmissions of earlier data units.

In one embodiment, said indicator comprises the current value of one or more parameters of a buffer queue of failed data units awaiting retransmission from said access node to said communication device, wherein a failed data unit comprises a data unit for which said communication device has reported a decoding failure.

In one embodiment, said indicator comprises the current value of one or more parameters selected from: the number of failed data units currently in said buffer queue; the number of times the number of failed data units in said buffer queue exceeded a predetermined number within a predetermined time interval; the length of time that the number of data units in said buffer queue exceeded said predetermined number within said predetermined time interval; and the length of time elapsed since the most recent adjustment of the number of repeat transmissions of a data unit.

In one embodiment, said failed data unit comprises a data unit for which said communication has reported a decoding failure in a radio link control status report.

In one embodiment, said access node receives groups of data units for transmission and/or retransmission from said access node to said communication device in respective data frames from a radio link control entity; and said indicator is derived by said access node from an indication for each data frame as to what proportion of data units in said data frame are data units for retransmission. In one embodiment, said access node receives data units for transmission and/or retransmission from said access node to said communication device from a radio link control entity; and wherein said indicator comprises an indication of the classification by said radio link control entity of said communication device into one of a plurality of classes on the basis of radio link control status reports received at said radio link control entity from said communication device .

In one embodiment, said data units are packet data units at a medium access control layer.

Embodiments of the present invention are described in detail hereunder, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 illustrates an example of a cellular network in which an embodiment of the present invention is implemented; Figure 2 illustrates an example of apparatus for use at user equipment in Figure 1;

Figure 3 illustrates an example of apparatus for use at

NodeBs in Figure 1;

Figure 4 illustrates an example of apparatus for use at RNC in Figure 1;

Figures 5 (a) and 5 (b) together illustrate an example of a data frame for sending data units from RNC to NodeB in Figure 1;

Figure 6 illustrates a technique according to an embodiment of the present invention; and

Figure 7 illustrates a sequence of operations at NodeB of Figure 1 in accordance with an embodiment of the present invention.

Embodiments of the invention are described in detail below, by way of example only, in the context of a UMTS cellular network .

The cellular network illustrated in Figure 1 comprises an array of NodeBs (NBs) 2 having overlapping coverage areas

(cells) 4a, 4b, 4c. Only three NBs 2 and nine cells 4 are shown in Figure 1, but a mobile telecommunication network will typically comprise tens of thousands of cells and a correspondingly large number of NBs.

Each NB 2 is connected to a radio network controller (RNC) 10. Typically, the radio access network comprises a plurality of RNCs each associated with a respective group of NBs 2.

Each RNC is connected to a packet-switched core network (not shown) via a SGSN (Serving GPRS Support Node) , also not shown .

Figure 2 shows a schematic view of an example of user

equipment 8 that may be used for communicating with the NBs 2 of Figure 1 via a wireless interface. The user equipment (UE) 8 may be used for various tasks such as making and receiving phone calls, for receiving and sending data from and to a data network and for experiencing, for example, multimedia or other content.

The UE 8 may be any device capable of at least sending or receiving radio signals to or from the NBs 2 of Figure 1. Non-limiting examples include a mobile station (MS) , a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. The UE 8 may

communicate via an appropriate radio interface arrangement 205 of the UE 8. The interface arrangement may be provided for example by means of a radio part and associated antenna arrangement . The antenna arrangement may be arranged

internally or externally to the UE 8.

The UE 8 may be provided with at least one data processing entity 203 and at least one memory or data storage entity 217 for use in tasks it is designed to perform. The data

processor 213 and memory 217 may be provided on an

appropriate circuit board and/or in chipsets.

The user may control the operation of the UE 8 by means of a suitable user interface such as key pad 201, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 215, a speaker and a microphone may also be provided. Furthermore, the UE 8 may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

Figure 3 shows an example of apparatus for use at the NBs 2 of Figure 1 and for serving the cell 4 in which UE 8 is located. The apparatus comprises a radio frequency antenna array 301 configured to receive and transmit radio frequency signals; radio frequency interface circuitry 303 configured to interface the radio frequency signals received and

transmitted by the antenna 301 and the data processor 306. The radio frequency interface circuitry 303 may also be known as a transceiver. The apparatus also comprises an interface 309 via which, for example, it can communicate with e.g. RNC 10. The data processor 306 is configured to process signals from the radio frequency interface circuitry 303, control the radio frequency interface circuitry 303 to generate suitable RF signals to communicate information to the UE 8 via the wireless communications link, and also to exchange

information with other network nodes via the interface 309. The memory 307 is used for storing data, parameters and instructions for use by the data processor 306.

Figure 4 shows an example of apparatus for use at the RNC 10. The apparatus 400 includes a memory 402 for receiving and storing data of the kind mentioned below in the description of an embodiment of the present invention, and a data

processor 404 for processing data stored in memory 402 and making computations and determinations of the kind mentioned below in the description of an embodiment of the present invention. The apparatus also comprises an interface 406 via which it can send and receive information to and from other network nodes, such as NBs 2.

It would be appreciated that the apparatus shown in each of figures 2, 3 and 4 described above may comprise further elements which are not directly involved with the embodiments of the invention described hereafter.

Figure 6 illustrates the different protocols that operate at each of UE 8, NB 2 and RNC 10. Each protocol handles a respective function. The protocols are arranged into stacks that have several different layers arranged according to ITU- T recommendation X.200, known as the OSI model.

The physical layer (PHY or Layer 1(L1) is specified in the 3GPP TS25.200 series of technical specifications. The

physical layer interfaces the Medium Access Control (MAC) sub-layer of Layer 2(L2) and the Radio Resource Control (RRC) Layer of Layer 3 (not shown) .

The RRC controls the configuration of the lower layer

resources in the protocol stack, such as physical layer, MAC, and RLC . The RRC protocol of the UMTS air-interface is specified in 3GPP TS25.331 technical specification.

The Radio Link Control (RLC) is a link-layer protocol

responsible for error recovery and flow control in WCDMA networks. The RLC is specified in 3GPP technical

specification TS25.322. The RLC is a sublayer within Layer 2 (L2) . It provides radio link services for use between the mobile station and the network. In the network, the protocol end-point is typically located in the RNC . At higher layers, e.g., Packet Data Convergence Protocol (PDCP) , Radio Resource Control (RRC), Broadcast/Multicast Control (BMC), or circuit switched voice, data is provided Service Data Units (SDUs) . The SDUs are mapped at the RLC sublayer of RNC 10 into

Protocol Data Units (PDUs) , which are then sent to NB 2 on logical channels provided by the Medium Access Control (MAC) layer.

The MAC layer of the UMTS air-interface is specified in 3GPP TS25.321 technical specification. MAC functions include dynamic scheduling of UE 8, selection of the format of each transport channel, multiplexing and demultiplexing of higher layer protocol data units (PDUs) into transport block sets, transport channel type switching and several other functions. The MAC sublayer consists of entities. The MAC entities in UE 8 are not the same as the MAC entities in the radio access network. In the radio access network, MAC entities are typically located in the RNC 10 and in addition also in the NB 2. In particular, the MAC entities (MAC-hs and MAC-ehs) associated with the high speed downlink shared channel (HS- DSCH) on the air-interface between NB 2 and UE 8 are located in the NB 2.

MAC-ehs/MAC-hs protocol entities include a hybrid automatic repeat request (HARQ) entity. HARQ is an acknowledged

retransmission scheme that is used on the HS-DSCH. When UE 8 is in a connection mode that supports uplink transmissions, the HARQ entity in UE 8 checks the correctness of received PDUs and sends either a positive or a negative

acknowledgement back to the peer HARQ entity in the radio access network. The acknowledgement is typically sent on the high-speed dedicated physical control channel (HS-DPCCH) . The HARQ entity in the radio access network continues to store copies of transmitted PDUs in a HARQ buffer until a positive acknowledgement is received from UE 8. If a negative

acknowledgement is received for a transmitted PDU, NB 2 retransmits the PDU. If UE 8 continues to fail to

successfully decode one or more HARQ retransmissions of a PDU, the MAC layer in UE 8 indicates a transmission error to the RLC layer in UE 8, which triggers the transmission of a RLC status report from UE 8 to the peer RLC entity in the radio access network, as discussed below.

In some RRC states, additional PDUs are defined to permit bidirectional signalling between peer RLC entities.

Primarily, the added signalling is used by the receiving RLC entity to request the retransmission of missing or lost data. By monitoring the sequence numbers of the received PDUs, the receiving RLC entity can identify missing PDUs, which are typically missing because the quality of the radio channel at the times of transmission was so poor that it degraded the transmitted signal to such an extent that the receiving entity could not successfully decode the signal and retrieve the PDU (even after one or more HARQ retransmissions) . The receiving RLC entity in UE 8 sends status reports back to the RLC entity in RNC 10, requesting retransmission of missing PDUs.

Figures 6 and 7 illustrate a technique according to an embodiment of the present invention. NB 2 receives from RNC 10 MAC-d PDUs (STEP 702) for

transmission to UE 8. NB 2 receives the MAC-d PDUs for UE 8 together with information about whether each PDU is a new PDU for an initial transmission to UE 8 or a missing PDU (i.e. a PDU that was indicated to be missing in a RLC status report received at the RLC entity of RNC 10 from the RLC entity of UE 8) for retransmission to UE 8.

Figures 5 (a) and 5 (b) together illustrate an example of a data frame structure for sending MAC-d PDUs from RNC 10 to NB 2. The data frame structure is based on that illustrated at Figure 21B of 3GPP TS 25.435 V10.4.0. Figure 5(a)

illustrates the header of the data frame structure; and

Figure 5 (b) illustrates the payload of the data frame

structure. One option is to configure a rule that all n MAC-d PDUs included in a single data frame must either be all new PDUs or all retransmission PDUs, and to use one of the spare bits 605 in the 5th octet following the "New IE Flags" of the payload to indicate whether all MAC-d PDUs are retransmission PDUs (set spare bit to "1") or whether all MAC-d PDUs are new PDUs (set spare bit to "0") . Another option is to allow the RLC entity of RNC 10 to include a mixture of retransmission PDUs and new PDUs in a single data frame, and to either: (a) use the spare bit 604 immediately after the 11-bit

information element (IE) "MAC-d/c PDU length in block n" for each nth MAC-d PDU to indicate whether the respective nth MAC-d PDU is a retransmission PDU or a new PDU; or (b) use the spare bits in the 4th octet of the header to indicate which of the n PDUs included in the data frame are

retransmission PDUs and which are new PDUs. For (b) , there is specified a rule that all retransmitted PDUs included in the data frame must always be at the beginning; with such a rule, the inclusion of up to 7 retransmission PDUs in a single data frame can be indicated using only 3 bits.

Based on the above-mentioned indication, NB 2 adds each MAC-d PDU received from RNC 10 to the end of one of two buffer queues for UE 8 : a buffer queue for retransmission PDUs 710 and a buffer queue for new PDUs 708 (STEP 706) . NB 2 transmits MAC-d PDUs to UE 8 via the HS-DSCH (high speed data shared channel) according to their order in the buffer queues 708, 710. In certain RRC states (e.g. Enhanced

CELL_FACH) , NB 2 repeats the transmission of each MAC-d PDU a plurality of times, without waiting for feedback information from UE 8 about the result of the attempt by UE 8 to decode a transmission of the respective MAC-d PDU (STEP 712), i.e. without waiting for e.g. HARQ (Hybrid Automatic Repeat

Request) feedback for the respective PDU from UE 8.

Accordingly, NB 2 repeats the transmission of even those MAC- d PDUs whose first transmission happen to be successfully decoded by UE 8. Such repeat transmissions are referred to below as blind repeat transmissions.

The size of the buffer queue 710 for retransmission PDUs for UE 8 is taken as an indicator of the quality of radio

conditions of the wireless interface between NB 2 and UE 8. NB 2 monitors the size of the queue 710 for retransmission PDUs, and adjusts the number of blind repeat transmissions it makes for MAC-d PDUs for UE 8 according to the current size of the buffer queue 710 for retransmission PDUs for UE 8 For example, if the size of the buffer queue 710 for

retransmission PDUs for UE 8 falls below a predetermined lower threshold value, this is taken as an indicator of an improvement in the quality of the wireless interface between NB 2 and UE 8, and NB 2 reduces the number of blind repeat transmissions it makes for MAC-d PDUs for UE 8. On the other hand, if the size of the buffer queue 710 for retransmission PDUs increases above a predetermined higher threshold value, this is taken as an indicator of a deterioration in the quality of the wireless interface between NB 2 and UE 8, and NB 2 increases the number of blind repeat transmissions it makes for MAC-d PDUs for UE 8.

According to one variation of the above-described technique, NB 2 alternatively or additionally monitors one or more further parameters of the buffer queue 710 for retransmission PDUs for UE 8, and adjusts the number of blind repeat

transmissions for MAC-d PDUs for UE 8 according to the current value of these one or more further parameters. Examples of further parameters include: the number of times that the size of the buffer queue 710 for retransmission PDUs exceeds a predetermined threshold value within a

predetermined time interval; the length of time for which the size of the buffer queue 710 for retransmission PDUs exceeds a predetermined threshold value; and the length of time elapsed since NB 2 most recently adjusted the adjusts the number of blind repeat transmissions for each MAC-d PDU for UE 8 (which can be useful for avoiding hysteresis) .

According to another embodiment of the present invention, NB 2 does not have separate buffer queues for new PDUs and retransmission PDUs for UE 8, but instead maintains only a common buffer queue for both these types of PDUs for UE 8. NB 2 monitors information in the HS-DSCH data frame about which MAC-d PDUs received from RNC 10 for UE 8 are

retransmission PDUs and which are new PDUs, and adjusts the number of blind repeat transmissions of MAC-d PDUs for UE 8 according to the result of this monitoring.

According to another embodiment, RNC 10 monitors the number of retransmission PDUs for UE 8, and classifies UE 8 as either having a good quality wireless interface or a bad quality wireless interface, and provides the result of this classification to NB 2. NB 2 adjusts the number of blind repeat transmissions for MAC-d PDUs for UE 8 when there is a change in the classification of UE 8. NB 2 increases the number of blind repeat transmissions for PDUs for UE 8 when the classification for UE 8 changes from "good" to "bad"; and reduces the number of blind repeat transmissions for PDUs for UE 8 when the classification for UE 8 changes from "bad" to "good".

The above-described techniques can be particularly useful in systems where UE 8 may often switch between: (i) a connection mode (such as the CELL_DCH RRC connected mode defined in 3GPP TS 25.331) in which UE 8 can both receive downlink

transmissions (e.g. via high speed downlink packet access (HSPDA) channels) and make uplink transmissions (including HARQ feedback about received downlink transmissions) ; and (ii) a connection mode (such as the CELL FACH DL RRC connected mode defined in 3GPP TS25.331) in which UE 8 can receive downlink transmissions (e.g. via high speed downlink packet access (HSPDA) channels) but not make uplink

transmissions (including HARQ feedback) .

The above-described techniques can assist in avoiding wastage of HSPDA radio resources by tailoring the number of blind repeat transmissions of PDUs for UE 8 according to an

indicator of the quality of the wireless interface between NB 2 and UE 8.

The above-described operations may require data processing in the various entities. The data processing may be provided by means of one or more data processors. Similarly various entities described in the above embodiments may be

implemented within a single or a plurality of data processing entities and/or data processors. Appropriately adapted computer program code product may be used for implementing the embodiments, when loaded to a computer. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. A possibility is to download the program code product via a data network. Implementation may be provided with appropriate software in a server.

For example the embodiments of the invention may be

implemented as a chipset, in other words a series of

integrated circuits communicating among each other. The chipset may comprise microprocessors arranged to run code, application specific integrated circuits (ASICs) , or

programmable digital signal processors for performing the operations described above.

Embodiments of the invention may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a

semiconductor substrate.

Programs, such as those provided by Synopsys, Inc. of

Mountain View, California and Cadence Design, of San Jose, California automatically route conductors and locate

components on a semiconductor chip using well established rules of design as well as libraries of pre stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for

fabrication .

In addition to the modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described embodiment may be made within the scope of the invention.

Claims

1. A method, comprising: in a system in which an access node makes one or more repeat transmissions of a data unit for a communication device without waiting for feedback about an attempt by the communication device to decode a

transmission of said data unit: adjusting the number of said repeat transmissions of a data unit according to an indicator of the condition of a wireless interface between the access node and the communication device for transmissions of earlier data units to said communication device.

2. A method according to claim 1, wherein said indicator is based on one or more reports by said communication device of one or more attempts by said communication device to decode one or more transmissions of earlier data units.

3. A method according to claim 1, wherein said indicator comprises the current value of one or more parameters of a buffer queue of failed data units awaiting retransmission from said access node to said communication device, wherein a failed data unit comprises a data unit for which said

communication device has reported a decoding failure.

4. A method according to claim 3, wherein said indicator comprises the current value of one or more parameters

selected from: the number of failed data units currently in said buffer queue; the number of times the number of failed data units in said buffer queue exceeded a predetermined number within a predetermined time interval; the length of time that the number of data units in said buffer queue exceeded said predetermined number within said predetermined time interval; and the length of time elapsed since the most recent adjustment of the number of repeat transmissions of a data unit.

5. A method according to claim 3 or claim 4, wherein said failed data unit comprises a data unit for which said

communication has reported a decoding failure in a radio link control status report.

6. A method according to claim 1, wherein said access node receives groups of data units for transmission and/or

retransmission from said access node to said communication device in respective data frames from a radio link control entity; and said indicator is derived by said access node from an indication for each data frame as to what proportion of data units in said data frame are data units for

retransmission .

7. A method according to claim 1, wherein said access node receives data units for transmission and/or retransmission from said access node to said communication device from a radio link control entity; and wherein said indicator

comprises an indication of the classification by said radio link control entity of said communication device into one of a plurality of classes on the basis of radio link control status reports received at said radio link control entity from said communication device.

8. A method according to any preceding claim, wherein said data units are packet data units at a medium access control layer .

9. An apparatus comprising: a processor and memory

including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: in a system in which an access node makes one or more repeat transmissions of a data unit for a communication device without waiting for feedback about an attempt by the communication device to decode a transmission of said data unit: adjust the number of said repeat

10. An apparatus according to claim 9, wherein said

indicator is based on one or more reports by said

communication device of one or more attempts by said

communication device to decode one or more transmissions of earlier data units.

11. An apparatus according to claim 9, wherein said

indicator comprises the current value of one or more

parameters of a buffer queue of failed data units awaiting retransmission from said access node to said communication device, wherein a failed data unit comprises a data unit for which said communication device has reported a decoding failure.

12. An apparatus according to claim 11, wherein said indicator comprises the current value of one or more

parameters selected from: the number of failed data units currently in said buffer queue; the number of times the number of failed data units in said buffer queue exceeded a predetermined number within a predetermined time interval; the length of time that the number of data units in said buffer queue exceeded said predetermined number within said predetermined time interval; and the length of time elapsed since the most recent adjustment of the number of repeat transmissions of a data unit.

13. An apparatus according to claim 9, wherein said access node receives groups of data units for transmission and/or retransmission from said access node to said communication device in respective data frames from a radio link control entity; and said indicator is derived by said access node from an indication for each data frame as to what proportion of data units in said data frame are data units for

retransmission .

14. An apparatus according to claim 9, wherein said access node receives data units for transmission and/or

retransmission from said access node to said communication device from a radio link control entity; and wherein said indicator comprises an indication of the classification by said radio link control entity of said communication device into one of a plurality of classes on the basis of radio link control status reports received at said radio link control entity from said communication device.

15. A computer program product comprising program code means which when loaded into a computer controls the computer to: in a system in which an access node makes one or more repeat transmissions of a data unit for a communication device without waiting for feedback about an attempt by the

communication device to decode a transmission of said data unit: adjust the number of said repeat transmissions of a data unit according to an indicator of the condition of a wireless interface between the access node and the

communication device for transmissions of earlier data units to said communication device.