GB2494944A - Handling status Protocol Data Units via a timer - Google Patents

Abstract

In a Long Term Evolution (LTE) or UMTS communications system in which a User Equipment (UE, 110 fig. 1) receives two or more High Speed Downlink Packet Access (HSDPA) data streams containing out of order Protocol Data Units (PDUs), a Radio Link Control (RLC) reset procedure is only initiated if an invalid PDU is received when a timer is not running, with the PDU merely being discarded if the timer is running. The t-Reordering timer starts when a valid status PDU is received, and out of sequence PDUs (as indicated by a sequence number) are discarded until it expires.

Description

METHOD, APPARATUS AND COMPUTER PROGRAM

FOR HANDLING STATUS PROTOCOL DATA IJNTTS

Technical Field

The present invention relates to a method, apparatus and a computer program for handling status protocol data units.

Background

The following abbreviations are uscd in the present specification: 3G Third Generation 3GPP Third Gcncration Partnership Projcct AM acknowledged mode AMD acknowledged mode data cNB evolved Node B HS-DSCH High-Speed Downlink Sharcd Channel HSDPA High-Speed Downlink Packet Access HSPA High-Speed Packet Access LTE Long Term Evolution PDU protocol data unit RLC radio link control RNC radio network controller RRC radio resource control SDU servicc data unit TCP Transmission Control Protocol UE user equipment UMTS Universal Mobile Telecommunications System WCDMA Wideband Code Division Multiple Access WiMAX Worldwide Interoperability for Microwave Access In order to provide for a higher rate or throughput of data and control signals, it is known to use plural paths in order to carry the signals from one entity to another.

For example, in a cellular wireless system, two or more network cells can be used to transmit data over a corresponding number of two or more data streams to a wireless device, including in particular a user equipment or TIE.

As a particular example in the 3G (Third Generation) system, High-Speed Downlink Packet Access (HSDPA) is an enhanced 3G mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family. HSDPA can make use of so-called multiflow, in which two (or more) different paths can be taken by the data in order to reach the liE. (It will be understood that in principle any (reasonable) number of paths and cells may be used, but for simplicity, in this specification, reference will typically be made to the ease where there are two paths, via two network cells.) In essence, two data streams are delivered from two adjacent cells (which may in general be served by a single base station or by two separate base stations) to a single liE, instead of there being one data stream from one base station.

As well as improving data rates (typically up to double the data rate), HSDPA also decreases latency and thus the round trip time for applications. Moreover, when a UE falls into the softer or soft handover coverage region of two cells on the same carrier frequency, and the link from the serving cell is capacity or coverage limited and the non-serving cell in its active set has available resources, it would be beneficial to schedule packets to the TIE also from the non-serving cell and thereby improve this particular user's experience.

However, as noted in for example the submission R2-120725 by QUALCOMM Inc to the 3GPP TSG RAN WG2 Meeting #77 on 6th-lOth February 2012, in such a multiflow arrangement, RLC acknowledged mode (AM) status PDUs, which can be transmitted over different cells, can be received at the liE out of order.

For example, one serving HS-DSCH (a transport layer channel for HSDPA) may fail to transmit an earlier status PDU at the first transmission attempt whereas the assisting serving HS-DSCH cell manages to transmit a later status PDU to the TIE at the first attempt, resulting in the "later" status PDIJ being received before the "earlier" status PDU. This may cause the RL.C RESET procedure to be initiated, which flushes transmitter and receiver RLC buffers if the later received status PDU includes an erroneous Sequence Number (e.g. the SN is out of the reception window). This can lead to a large throughput loss, as well as TCP timeouts and retransmissions, and can also lead to call drops if there are undelivered signalling PDTJs.

In the case of status PDUs, a solution to this suggested by QUALCOMM in their submission R2-120725 is to ensure that the Radio Network Controller (RNC), which controls thc two NodeBs, uses only one of the NodeBs to send status PDUs over its HS-DSCH to the liE. However, this can still give rise to out-of-order delivcry of status PDUs during changeover of the serving cell, which is being used to transmit the status PDUs. Again for the ease of status PDUs, in the submission R2-12160 by Rencsas Mobile Europe Ltd to the 3GPP TSG-RAN W02 Meeting #77bis planned for 26th -30th March, 2012, it is proposed to introduce a sequence number for each status PDIJ transmitted by the RNC to the UE, and for the transmitter PLC entity of the UE which receives the status PDUs to discard and this ignore status PDUs that have earlier sequence numbers than the one that has already been received.

However, implementation of this may be relatively complex.

In the rather different case of data PDUs being sent over two different cells, Ericsson in their submission R2-120410 to the 3GPP TSG-RAN WG2 #77 meeting of 6th -10th February 2012 proposed the use of a timer (t-Reordering) at the receiver RLC entity of the liE. The t-Reordering timer starts when the receiver RLC receives out-of-sequence RLC data PDTJ(s). The receiver RLC of the IJE does not send back status PDUs for received RLC data PDUs while the t-Reordcring timer is running. In other words, negative acknowledgement by the liE is delayed until expiry of the t-Reorderthg timer.

Summary

According to a first aspect of the present invention, there is provided a method of handling receipt of status protocol data units by a user equipment, the method comprising: starting a timer at the user equipment upon receipt of a valid status protocol data unit from a network entity; and, if an invalid status protocol data unit is received at the user equipment whilst the timer is running, then discarding that invalid status protocol data unit, else if an invalid status protocol data unit is received at the user equipment whilst the timer is not running, then initiating a reset procedure.

In examples of embodiments of the present invention, this allows the data transmitting device to safely discard or ignore status PDUs that are received out of sequence or that are otherwise invalid (during the time period determined by the timer). However, the data transmitting device can still detect erroneous status PDU5 that are received even in the case of multiflow transmissions of status PDUs to the data transmitting device in the form of a UE, with the two transmitting and receiving entities of the UE and on the network side being reset or otherwise undertaking a reset procedure if necessary.

In an embodiment, the timer is configured in accordance with signalling sent by the network entity to the user equipment.

In an embodiment, the timer is also configured for use with handling transmission of status protocol data units by the user equipment in connection with data protocol data units that may be received at the user equipment out of sequence.

This may be the same t-Reordering timer mentioned above for the case of data PDUs.

In an embodiment, the user equipment receives status protocol data units delivered over plural wireless network cells. This may be in the context of I-ISDPA multifiow.

In an embodiment, the reset procedure is initiated by the user equipment and causes a reset of the network entity.

S In an embodiment, the reset procedure is a radio link control RESET procedure.

In an embodiment, the user equipment is operating in a Long Term Evolution or Universal Mobile Telecommunicatioim System, using for example WCDMA (Wideband Code Division Multiple Access), According to a second aspect of the present invention, there is provided apparatus comprising a processing system for a wireless device, the processing system being constructed and arranged to: start a timer upon receipt of a valid status protocol data unit from a network entity; and, if an invalid status protocol data unit is received whilst the timer is running, then discard that invalid status protocol data unit, else if an invalid status protocol data unit is received whilst the timer is not mnning, then initiate a reset procedure.

According to a third aspect of the present invention, there is provided a computer program comprising instructions such that when the computer program is executed on a computing device of a user equipment, the computing device is arranged to: start a timer at the user equipment upon receipt of a valid status protocol data unit from a network entity; and, if an invalid status protocol data unit is received at the user equipment whilst the timer is running, then discard that invalid status protocol data unit, else if an invalid status protocol data unit is reccivcd at the user equipment whilst the timer is not running, then initiate a reset procedure.

Further features and advantages of the invention will become apparent from the following description of some embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 shows a schematic diagram of a telecommunications network comprising examples of apparatus according to an embodiment of the present invention; and Figure 2 shows a schematic flow chart of an example of a method according to an embodiment of the present invention.

Detailed Description

"Wireless devices" include in general any device capable of connecting wirelesslyto a network, and includes in particular mobile devices including mobile or cell phones (including so-called "smart phones"), personal digital assistants, pagers, tablet and laptop computers, content-consumption or generation devices (for music and/or video for example), data cards, USB donglcs, etc., as well as fixed or more static devices, such as personal computers, game consoles and other generally static entertainment deviccs, various other domestic and non-domestic machines and devices, etc. The term "user equipment" or liE is often used to refer to wireless devices in general, and particularly mobile wireless devices.

The terms "transmitter" and "rcccivcr" are also used herein and are to be construed broadly to include the whole of a device that is transmitting/receiving wireless signak as well as only particular components of a device that are concerned with transmitting/receiving wireless signals or causing or leading to the transmission/reception of wireless signals.

Reference will sometimes be made in this specification to "network", "network control apparatus" and "base station". In this respect, it will be understood that the "network control apparatus" is the overall apparatus that provides for general management and control of the network and connected devices. Such apparatus may in practice be constituted by several discrete pieces of equipment. As a particular example in the context of UMTS (Universal Mobile Telecommunications System), the network control apparatus may be constituted by for example a so-called Radio Network Controller operating in conjunction with one or more Node Bs (which, in many respects, can be regarded as "base stations"). As another example, LTE (Long Term Evolution) makes use of a so-called evolved Node B (cNB) where the RF transceiver and resource management/control functions are combined into a single entity. Thc term "base station" is uscd in this specification to include a "traditional" base station, a Node B, an evolved Node B (eNB), or any other access point to a network, unless the context requires otherwise. Moreover for convenience and by convention, the tenm "network control apparatus" and "base station" will often be used interchangeably.

Figure 1 shows a schematic diagram of a telecommunications network comprising examples of apparatus according to some embodiments of the present invention. The network comprises a network entity 100 and a user equipment or UE connected by a wireless network 120. In practice, there will typically be many liEs 110 serviced by the wireless network 120.

The network entity (or network "node") 100 has a memory 102, a processor 104, an RLC (radio link control) entity 106, an RRC (radio resource control) entity 1 08 and one or more antennas (not shown). The RLC entity 106 comprises a transmitter part 106A and a receiver part 106B. In a particular embodiment, the network entity 100 comprises a radio network controller (RINC).

In the example of Figure 1, the network entity 100 comprises a single processor 104 which is depicted as separate to RLC entity 106 and RRC entity 108.

The processor 104 may comprise a processing system of one or more processors. In other embodiments, the network entity 100 comprises one or more further processors (not shown), for example a processor in the RL.C entity 106 and/or a processor in the RRC entity 108. Various data processing actions of embodiments described below are described as being carried out by the processor 104, but it will be understood that such actions could be carried out by one or more other processors, for example in RLC entity 106 and RRC entity 108 or any combination thereof. Indeed, in principle, there may be a single processor or processing system providing the functionality of the entire network entity 100.

The liE 110 has a memory 112, a processor 114, an RLC (radio link control) entity 116, an RRC (radio resource control) entity 118 and more or more antennas (not shown). The RLC entity 116 comprises a transmitter part I 16A and a receiver part 116B.

In the example of Figure 1, the liE 110 comprises a single processor 114 which is depicted as separate to RLC entity 116 and RRC entity 118. The processor 114 may comprise a processing system of one or more processors. In other embodiments, the UE 110 comprises one or more further processors (not shown), for example a processor in the RLC entity 116 and/or a processor in the RRC entity 118.

Various data processing actions of embodiments described below arc described as being carried out by the processor 114, but it will be understood that such actions could be caned out by one or more other processors, for example in RLC entity 116 and RRC entity 118 or any combination thereof Indeed, in principle, there may be a single processor or processing system providing the functionality of the entire UE 110.

The netDrk entity 100 and the liE 110 communicate data and control signals to and from each other using the wireless network 120. In a particular example, the wireless network 120 comprises plural network nodes, such as NodeBs 150, which each provide a network cell of coverage for liEs 110. The network entity 100 also communicates data and control signals to and from a core network 140.

As is known per so, in many communications systems, including LTE as a particular example, data and control signals are sent between transmitter and receiver entities (such as the RILC transmitter and receiver entities 106A,106B,1 16A,1 16B of the network entity 100 and the liE 1 0, via the NodeBs 150) in the form of individual packets of data known as protocol data units or PDUs. In general, in LTE for example, there arc RLC data PDUs, which may for example carry user data, and RLC control PDUs, which arc used in so-called acknowledged mode (AM) to carry control signals or data. The RLC control PDIJs include status PDUs (including piggybacked status PDIJs), which are used intcr alia by the receiver entity to inform the transmitter entity about missing and received RLC AMD PDUs (i.e. Acknowledged Mode Data PDUs, a type of data PDIJ used in acknowledged mode). The status PDIJs have a sequence number which corresponds to the received or missing RLC AMD PDU5 concerned.

In one example of an embodiment of the present invention, a timer is operated at a device, such as the UE, that is transmitting data to another device, such as a NodeB or other base station or network entity in general. If an invalid status PDU is received at the data transmitting device whilst the timer is running, then that invalid status PDU is discarded. If on the other hand an invalid status PDU is received whilst the timer is not ruiming, then a reset procedure may be initiated by the data transmitting device. This allows the data transmitting device to safely discard or ignore status PDUs that are received out of sequence (during the time period determined by the timer). However, the data transmitting device can still detect erroneous status PDUs that arc received even in the case of multiflow transmissions of status PDUs to the data transmitting device in the form of a liE, with the two transmitting and receiving entities of the liE and on the network side being reset or otherwise undertaking a reset procedure if necessary.

In a particular example, operation may be as follows. As an initial step, the network entity 100, such as an RNC 100, configures a timer for handling the status PDUs at the liE 110 via RRC signalling sent over the wireless network 120. The timer may be constituted in the transmitter RLC entity I 16A of the UE 110, or by the processor 114 at the liE 110 or otherwise provided separately. The RRC signalling that is used may be for example via a RRCConnectionSetup message; RRC reconfiguration messages (e.g. RadioBearerSetup, RadioBearerReconfiguration, RadioBearerRelease, TransportChannelkeconfigurat ion or PhysicaIChanne1Rcconfiguration) or an ActivcSetUpdate message. On receipt of the timer configuration via the RRC signalling, thc UE 110 configures thc timer at the transmitter RLC entity 116A. It may be noted that the configuration parameter(s) for this timer for handling the status PDUs at the liE 110 may be introduced so as to be dedicated for the status PDU handling described herein, or it may be possible to re-use the same timer (the t-Reordering timer mentioned above) configured for the data PDIJ5 according to the proposal by Ericsson in their submission R2-12041 discussed above if that is implemented at the liE 110. As one example only, a suitable duration for the timer is approximately 600 ms.

In use, and referring to Figure 2, the transmitter RLC entity 1 16A at the liE 110 starts or re-starts 200 the timer for handling the status PDUs (hereafter "the t-Reordering timer") whenever it receives a valid status PDU, i.e. a status PDU that does not have an erroneous Sequence Number. Upon receipt of an invalid status PDU (i.e. a status PDU including an erroneous Sequence Number, for example one that is before the sequence number included in a status PDIJ that has already been received): (i) if the t-Reordcring timer is running, the transmitter RLC entity II 6A discards the invalid status PDU (and in particular does not initiate an RLC RESET procedure) 210; (ii) else if the t-Reordering timer is not running, the transmitter RLC entity I 16A initiates an RLC RESET procedure in order to reset both the RLC entities (i.e. the liE 110 and the network entity 100, at least as far as this LiE 110 is concerned) 220.

In this way, the transmitter RLC entity 11 6A of the IJE 110 can safely discard out-of-sequence RLC status PDUs that are received during the time period determined by the timer. As noted above, out-of-sequence RLC status PDIJs can be received in particular in the case of HSDPA multiflow transmissions of the status PDUs to the TiE from two (or more) cells serviced by their own NodeBs 150. On the other hand, through the use of the timer, the transmitter RLC entity 1 16A can still detect erroneous status PDUs even in the case that I-ISDPA multiflow is configured whereby the status PDUs arc being delivered using plural cells serviced by the plural NodeBs 150. In particular, if after expiry of the timer, erroneous status PDUs are detected, appropriate action can be taken. This may be for example causing the transmitter RLC entity 116A of the tiE 110 and the corresponding transmitter RLC entity 106A of the network entity 100 to be reset. Thus, if for example some problem arises during communication, e.g. a network link error, over-the-air data corruption, etc., the TiE 110 can effectively detect the completely corrupted data and trigger the RLC RESET procedure so that it can recover the link problem. In addition, the connection is protected from malicious attack as the RLC entities will be reset in such cases.

An RLC RESET procedure to reset two RLC peer entities is set out in for example subclause F 1.4.2 of 3GPP TS25.322, the entire content of which is hereby incorporated by reference. In general terms (and subject to certain conditions, such as maximum number of attempts, as set out in 3GPP TS25.322), in this ease the transmitter RLC entity 116A of the tiE 110 will typically send a RESET PDtJ to the network entity 100, which will send an acknowledgement back, and both the transmitter RLC entity II6A of the TiE 110 and the transmitter RLC entity 106A of the network entity 100 will reset various reconfigurable parameters, timers, etc. to allow transmissions between the two entities to recommence correctly.

It will be understood that the processor or processing system or circuitry referred to herein may in practice be provided by a single chip or integrated circuit or plural chips or integrated circuits, optionally provided as a chipset, an application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), digital signal processor (DSP), etc. The chip or chips may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry, which are configurable so as to operate in accordance with the exemplary embodiments. In this regard, the exemplary embodiments may be implemented at least in part by computer software stored in memory and executable by the processor, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware).

Although at least some aspects of the embodiments described herein with refcrcncc to the drawings comprise computer processes performed in processing systems or processors, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice.

The program may be in the form of non-transitory source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other non-transitory form suitable for use in the implementation of processes according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a solid-state drive (SSD) or other semiconductor-based RAM; a ROM, for example a CD ROM or a scmiconductor ROM; a magnetic recording mcdium, for example a floppy disk or hard disk; optical memory devices in general; etc. Thc above embodiments arc to be understood as illustrative examples of thc invention. Further embodiments of the invention are envisaged. For example, whilst the specific example discussed abovc is primarily in the context of the case of HSDPA multiflow transmissions, embodiments of the present invention can in principle be applied to any communication system that has Layer 2 acknowledgement and which also has out-of-order data delivery, including for example systems that use bi-casting or multi-casting, such as in WiMAX. There may also be provided apparatus comprising: means for starting a timer upon receipt of a valid status protocol data unit from a network entity; and means for, if an invalid status protocol data unit is received whilst the timer is running, discarding that invalid status protocol data unit, else if an invalid status protocol data unit is received whilst the timer is not running, initiating a reset procedure. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments.

Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims (1)

1. <claim-text>CLAIMS1. A method of handling receipt of status protocol data units by a user equipment, the method comprising: S starting a timer at the user equipment upon receipt of a valid status protocol data unit from a network entity; and, if an invalid status protocol data unit is received at the user equipment whilst the timer is running, then discarding that invalid status protocol data unit, else if an invalid status protocol data unit is received at the uscr cquipment whilst the timer is not running, then initiating a reset proccdure.</claim-text> <claim-text>2. A method according to claim 1, wherein the timer is configured in accordance with signalling sent by the network entity to the user equipment.</claim-text> <claim-text>3. A method according to claim I or claim 2, wherein the timer is also configured for use with handling transmission of status protocol data units by the user equipment in connection with data protocol data units that may be received at the user equipment out of sequence.</claim-text> <claim-text>4. A method according to any of claims I to 3, wherein the user equipment receives status protocol data units delivered over plural wireless network cells.</claim-text> <claim-text>5. A method according to any of claims 1 to 4, wherein Ihe reset procedure is initiated by the user equipment and causes a reset of the network entity.</claim-text> <claim-text>6. A method according to any of claims I to 5, wherein the reset procedure is a radio link control RESET procedure.</claim-text> <claim-text>7. A method according to any of claims 1 to 6, wherein the user equipment is operating in a Long Term Evolution or Universal Mobile Telecommunications System.</claim-text> <claim-text>8. Apparatus comprising a processing system for a wireless device, the processing system being constructed and arranged to: start a timer upon receipt of a valid status protocol data unit from a network S entity; and, if an invalid status protocol data unit is received whilst the timer is running, then discard that invalid status protocol data unit, else if an invalid status protocol data unit is received whilst the timer is not running, then initiate a reset procedure.</claim-text> <claim-text>9. Apparatus according to claim 8, arranged such that the timer is configurable in accordance with signalling sent by the network entity.</claim-text> <claim-text>10. Apparatus according to claim 8 or claim 9, wherein the timer is also configured for use with handling transmission of status protocol data units in connection with data protocol data units that may be received out of sequence.</claim-text> <claim-text>11. Apparatus according to any of claims 8 to 10, arranged to receive and process status protocol data units delivered over plural wireless network cells.</claim-text> <claim-text>12. Apparatus according to any of claims 8 to 11, arranged such that the reset procedure causes a reset of the network entity.</claim-text> <claim-text>13. Apparatus according to any of claims 8 to 12, arranged such that the reset procedure is a radio link control RESET procedure.</claim-text> <claim-text>14. Apparatus according to any of claims 8 to 13, configured to operate in a Long Term Evolution or Universal Mobile Telecommunications System.</claim-text> <claim-text>15. A wireless device comprising apparatus according to any of claims 8 to 14.</claim-text> <claim-text>16. A computer program comprising instructions such that when the computer program is executed on a computing device of a user equipment, the computing device is arranged to: start a timer at the user equipment upon receipt of a valid status protocol data unit from a network entity; and, if an invalid status protocol data unit is received at the user equipment whilst the timer is running, then discard that invalid status protocol data unit, else if an invalid status protocol data unit is received at the user equipment whilst the timer is not running, then initiate a reset procedure.</claim-text> <claim-text>17. A computer program according to claim 16, comprising instructions such that thc timcr is configurable in accordancc with signalling scnt by the network entity.</claim-text> <claim-text>18. A computer program according to claim 16 or claim 17, comprising instructions such that the timer is also configured for use with handling transmission of status protocol data units in connection with data protocol data units that may be received out of sequence.</claim-text> <claim-text>19. A computer program according to any of claims 16 to 18, comprising instructions such that the reset procedure causes a reset of the network entity.</claim-text> <claim-text>20. A computer program according to any of claims 16 to 19, comprising instructions such that the reset procedure is a radio link control RESET procedure.</claim-text> <claim-text>21. A method of handling receipt of status protocol data units, substantially in accordance with any of the examples as described herein with reference to and illustrated by the accompanying drawings.</claim-text> <claim-text>22. Apparatus for handling receipt of status protocol data units, substantially in accordance with any of the examples as described herein with reference to and illustrated by the accompanying drawings.</claim-text>