WO2011069561A1

WO2011069561A1 - Synchronised data transmissions

Info

Publication number: WO2011069561A1
Application number: PCT/EP2009/066992
Authority: WO
Inventors: Kalle Petteri Kela
Original assignee: Nokia Corporation; Eerolainen, Lauri Johannes
Priority date: 2009-12-11
Filing date: 2009-12-11
Publication date: 2011-06-16

Abstract

During data transmission in a time synchronized system it can be determined that the time synchronisation may be invalid, In response thereto transmission of data is paused and data scheduled for transmission is buffered into at least one memory of the device. In response to subsequent determination that time synchronisation of is valid the transmission of data is continued. At least one request for retransmission of at least some of the buffered data can then be received. The request is responds by transmitting data from the at least one memory.

Description

Synchronised data transmissions

The invention relates to transmission of data, and more particularly to transmission of data in a time synchronised system.

Data can be received and/or transmitted via a communication system or communicated directly between users by means of appropriate communication devices. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling the communications. A communication device can thus be seen as a facility that enables communication sessions between two or more parties. For example, communications of data on wireless interfaces between mobile communication devices and base stations and/or other stations can be provided. A communication device of a user is often referred to as user equipment (UE). The communications may comprise, for example, communication of data such as audio data, electronic mail (email), text messages, multimedia, other data and so on. Users may be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet.

A communication system facilitating data communications can be provided for example by means of a communication network and one or more compatible communication devices. The communication network may be a large network proving nationwide cover, continent wide cover or even global cover, or be provided by a local network. In a wireless communication system at least a part of communications between at least two stations occurs over a wireless link. Examples of wireless systems include public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). A user can access the communication system via an access system thereof. The access system can be provided, for example, by a base station or a group of base stations and associated controllers.

A communication system and associated devices typically operate in accordance with a given standard and/or specifications which set out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. For example, the multiplexing techniques and/or the type or types of the access technology compatible communication devices shall use can be defined.

A more detailed example of standards and protocols relates to the way how the communications are timed and how to synchronise the timing between various devices in a communication system. The commonly accepted 'rules' for providing synchronisation enable a communication device to be synchronized in time with the other party of the communication, typically a base station of a communication network or another user device, and maintaining of the synchronisation without a need for the user of the device to take any action, The synchronisation procedures typically set various requirements and tasks for the communicating devices to achieve this. For example, the third generation partnership project (3GPP) access network specifications require that user equipment flushes all hybrid automatic retransmission request (HARQ) buffers thereof and clears all configured downlink assignments and uplink grants after expiry of a time alignment timer. Once the uplink timing synchronisation is again valid, the base station no longer can request retransmissions for any non-transmitted data since these were flushed due to expiry of the timer. However, there are instances where the synchronisation is not lost for real, for example when the network is late in providing latest timing information, and thus the buffers can become flushed even in cases where the timer triggered even though the synchronisation may still be valid. In other word, it is possible that data transmissions may fail unnecessarily in response to detection of a possibility of lost timing synchronisation. Embodiments of the invention aim to address one or several of the above issues.

In accordance with an embodiment there is provided a method comprising transmitting data from a device in a time synchronized system, determining possibility of invalid time synchronisation, pausing transmission of data from the device, buffering data scheduled for transmission into at least one memory of the device, the at least one memory being configured for storing data for the purposes of responding retransmission requests, and in response to subsequent determination that time synchronisation of the device is valid, continuing transmission of data, receiving at least one request for retransmission of at least some of the buffered data, and responding the request by transmitting data from the at least one memory. In accordance with another embodiment there is provided a method, comprising receiving data from a transmitting device in a time synchronized system, determining an irregularity in time synchronisation with the transmitting device, sending timing information to the transmitting device, successfully receiving data from the transmitting device, determining that at least some data scheduled for transmission during the irregularity has not been received, sending at least one request for retransmission of said non- received data, and receiving in response data from at least one memory for storing data for the purposes of responding retransmission requests and configured to store data scheduled for transmission during possible timing synchronisation irregularities.

In accordance with another embodiment there is provided an apparatus comprising means for controlling transmission of data in a time synchronized system, the means for controlling being configured to determine a possibility of invalid time synchronisation and in response thereto to cause pausing the transmission of data and to subsequently determine that the time synchronisation is valid and in response to determination of valid time synchronisation to cause continuation of the transmission of data, means for buffering data scheduled for transmission, the means for buffering being configured to store data for the purposes of responding retransmission requests, wherein the means for controlling are further configured to cause buffering of unsent scheduled data in the means for buffering, and means for handling retransmission requests, the means for handling retransmission request being configured to receive at least one request for retransmission of at least some of the buffered unsent scheduled data and to respond the request by causing sending of data from the means for buffering.

In accordance with another embodiment there is provided an apparatus comprising controller means for determining irregularity in time synchronization with a transmitting device, for causing sending of timing information to the transmitting device, for determining that reception of data from the transmitting device is continued, for determining that at least some data scheduled for transmission by the transmitting device has not been received, for causing sending of at least one request for retransmission of said non-received data, and for processing data received in response to said at least one request for retransmission from at least one memory configured to store data scheduled for transmission during possible timing synchronisation irregularities.

In accordance with another embodiment there is provided an apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to control transmission of data in a time synchronized system, to determine a possibility of invalid time synchronisation, and in response to determination that the synchronisation is possibly invalid, to cause pausing of said transmission of data and buffering of data scheduled for transmission into at least one memory configured for storing data for the purposes of responding retransmission requests, and in response to a subsequent determination that time synchronisation is valid, to cause continuation of the transmission of data, and to handle at least one received request for retransmission of at least some of the buffered scheduled data by causing sending of said requested buffered scheduled data. In accordance with another embodiment there is provided an apparatus, comprising at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to control receiving of data from a transmitting device in a time synchronized system, to detect an irregularity in the time synchronisation and subsequently to send timing information to the transmitting device, to determine that at least some data scheduled for transmission by the transmitting device during the irregularity has not been received, to cause sending of at least one request for retransmission of said non-received data, and to receive, in response to said at feast one request, data from at least one memory configured to store data scheduled for transmission during possible timing synchronisation irregularities.

In accordance with a more detailed embodiment the possibility of invalid time synchronisation or irregularity is determined based on expiry of a synchronisation timer. The synchronisation timer can comprise a time alignment timer.

Instructions to save the data scheduled for transmission in case of invalid time synchronisation may be communicated from a receiving device to a transmitting device. The instructions may be communicated in a radio resource control message. According to a possibility the buffering of data scheduled for transmission is a mandatory response to the determining of possibly invalid time synchronisation.

Validity of the time synchronisation may be determined based on timing information provided by the receiving device. The timing information may comprise a timing advance command.

The retransmission requests may comprise hybrid automatic retransmission requests (HARQs). The buffering may comprise storing medium access control protocol data units for already configured uplink grants to a HARQ buffer after expiry of a time alignment timer.

The transmitting device may be disabled by causing an irregularity in timing by belated communication of timing information.

A computer program comprising program code means adapted to perform one or more of the herein disclosed methods is also provided. The computer executable program code components can be stored on a computer-readable storage medium.

Various other aspects and further embodiments are also described in the following detaiied description and in the attached claims. The embodiments of the invention will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which:

Figure 1 shows an example of a communication system wherein below described examples of the invention may be implemented;

Figure 2 shows an example of a communication device;

Figures 3 and 4 are flowcharts illustrating exemplary embodiments; and Figures 5A and 5B show a further example. In the following certain exemplifying embodiments are explained with reference to wireless or mobile communication systems where fixedly positioned base stations serve mobile communication devices, Before explaining in detail the certain exemplifying embodiments, certain general principles of wireless or mobile communication systems are briefly explained with reference to Figures 1 and 2 to assist in understanding the context of the herein described examples.

A mobile communication device can be used for accessing various services and/or applications provided via a communication system. In wireless or mobile communication systems wireless interfaces can be provided between mobile communication devices 1 and other stations. More particularly, in the Figure 1 example mobile communication devices 1 are provided wireless access via a base station 12 or similar wireless transmitter and/or receiver node of an access system 10. Each mobile communication device 1 and base station 12 may have one or more channels or subchannels open at the same time and may receive signals from more than one source, it is noted that although only one access system 10 is shown in Figure 1 , a number of access systems, such as radio access networks, can be provided, and that a mobile communication device may move from an access system to another.

An access system and a base station thereof are typically controlled by at least one appropriate controller so as to enable operation thereof and management of mobile communication devices in communication with the base station. The control apparatus can be interconnected with other control entities. In Figure 1 a controller is shown to be provided by block 13. A control apparatus for a base station is typically provided with memory capability 15 and at least one data processor 14. It shall be understood that the control apparatus and functions may be distributed between a plurality of controller units. The control apparatus 13 can be arranged to provide control on communications by roaming mobile communication devices that have entered the area of the access system. The control apparatus 13 can be configured to execute an appropriate software code to provide the control functions as explained below where more detailed examples for different control functions to provide and maintain synchronisation are given.

A non-limiting example of access systems is the radio access network (RAN) of the third generation (3G) mobile communication system, sometimes termed as the Universal Mobile Telecommunications System (UMTS). An example of the more recent developments is the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE employs a mobile access architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). LTE technology is currently ongoing standardization by the 3^rd Generation Partnership Project (3GPP). A further development of the LTE is referred to as LTE-Advanced, or LTE-A. Other examples of radio access systems include those provided by base stations of access systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access). An example of a base station of an access system is the NodeB or enhanced NodeB (eNB) as defined by the 3GPP specifications.

In the Figure 1 example the access system 10 is connected to a wider communications network 16, sometimes referred to as the core network. A communication system may be provided by one or more of such networks and the elements thereof. One or more gateways may be provided for interconnecting the different networks. Figure 2 shows a schematic, partially sectioned view of a communication device 1 that can be used for communication with a communication system and/or other mobile communication devices. An appropriate mobile communication device may be provided by any device capable of sending and receiving wireless signals. 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. A mobile communication device may be used for voice and video calls, for accessing service applications and so on. The mobile device 1 may receive signals over an air interface 11 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting signals. In Figure 2 a transceiver component is designated schematically by block 7. The transceiver apparatus 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 mobile device. Appropriate modem apparatus 9 is also provided to enable modulation and demodulation of wireless signals. A communication device is also typically provided with at least one data processing entity 3, at least one memory 4 and other possible components for use in software aided execution of tasks it is designed to perform. Such tasks include control of access to and communications with other parties, such as access systems and/or other communication devices and timing of the communications, The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 6. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 2, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 5, a speaker and a microphone are also typically provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories and peripherals, for example hands-free equipment, thereto.

The communication devices may need to be able to synchronize to frame timing of the access network. In practice this means that each mobile device 1 should know the exact time when it can receive data from the base station (BS) 12 and the exact time when it can transmit data to the base station. A functionality of the control apparatus 13 at the communication system side is to maintain common system features such as the timing or clock of the system. The control apparatus can transmit information of the timing and/or specific synchronisation or reference signals to the mobile communication devices. The communication devices 1 can synchronize themselves with the system based on these signals. If a mobile device is moving, the signal propagation delay between the device and the base station may change, and therefore the timing of reception and transmission of signals may need to be adjusted from time to time.

For example, in a EUTRAN compatible access system a mobile device can have the responsibility of autonomously maintaining downlink (DL) and uplink (UL) timing towards the network. On the other hand, the 3GPP standard sets certain restrictions on autonomous uplink timing adjustments and rate thereof. If the mobile device moves rapidly the procedure of autonomously maintaining the timing may not be adequate in all situations. In such instances the EUTRAN system can update the uplink reference timing of the mobile device by signalling a new reference time to the mobile device. The new uplink timing can be signalled, for example, in a message such as Timing Advance Command (TAC).

Network can also configure a mobile device to run a timer for the purposes of time alignment, in the context of the 3GPP that has been used as an example herein this is provided by a Time Alignment Timer (TAT). Such a timer is denoted by timer 8 of a synchronisation block in Figure 2. A time alignment timer and the relevant control software/hardware can be configured such that it triggers in situations where uplink synchronization is deemed to be lost. The time alignment timer can be re-started in response receiving new uplink timing from the base station. For example, timer 8 can be re-started in response to a new Timing Advance Command (TAC). If the new timing information is not signalled before timer 8 expires, the mobile communication device 1 can be configured to assume that the uplink timing is invalid, and can take appropriate action, for example cancel all uplink data transmissions.

For example, EUTRAN employs hybrid automatic retransmission request (HARQ) for uplink data transfer. More particularly, the hybrid automatic retransmission request (HARQ) is provided for Layer 1 (L1) of the layered model by means of synchronous 8-process Stop-And-Wait HARQ. The purpose of the retransmission functionality is to ensure reliable data delivery between the layer 1 entities in the mobile device and the base station.

In accordance with a possible operational scenario the mobile device can maintain at least one hybrid automatic retransmission request (HARQ) buffer for transmitted data. This buffer is denoted by 20 in Figure 2. An appropriate network entity, for example a base station, can request for re-transmissions of all or part of the data it received incorrectly or did not receive at ail. As the data subject to a re-transmission request is saved in the at least one buffer, it is readily available and can be sent in response to the request to the base station from the mobile communication device 1.

A requirement by the 3GPP specifications for EUTRAN is that the mobile device shall flush the HARQ buffer 20 if the time alignment timer 8 expires. Therefore, when the control apparatus of the mobile device 1 determines that the synchronisation of uplink timing has been lost it should discard all ongoing uplink transmissions. On the layer 1 entity level data transmission is currently considered as being failed for all data that is stored in the HARQ buffer. Such immediate HARQ flush procedure, however, may not be adequate in all situations. For example, an immediate flush may not be adequate in a situation where the timing synchronisation may not have been lost after all, despite it can look like that, and thus the mobile device may be reacting too hard on what might only be a possible, but non-confirmed loss of synchronisation. For example, the network may just be late in updating the timing advance command, or the command has been lost, before the expiry of the synchronisation timer 8 in the mobile device 1 , and thus the timing may be still valid. Despite this the control procedure can act on the trigger by the timer as if the synchronisation had been lost.

On the other hand, the current 3GPP specifications also define that a mobile device can apply a late timing advance command after the expiry of the timing advance timer. Therefore the 3GPP specifications do not, strictly speaking, prevent arrangements where uplink timing can be recovered after the expiry of the time alignment timer. The following examples illustrate in more detail how it is possible to continue the uplink HARQ data retransmission process after the timing has been recovered, or it has been detected that the timing was not lost in the first place, and thus avoid flushing of the HARQ buffers at the expiry of the time alignment timer or because of some other reasons which make it look like that there are irregularities in the time synchronisation.

In accordance with the exemplifying embodiment shown in the flowchart of Figure 3, a device transmits data in a time synchronized system at 100. It can be determined at 102 that there is a possibility of invalid time synchronisation. For example, the determination may be made in response to expiry of a synchronisation timer. If no loss of synchronisation is detected, the data transmission continues at 100. If it is determined at 102 that synchronisation is lost, the transmitting device can pause transmission of data at 104. Whilst the transmission is paused, the transmitting device can buffer data that is scheduled for transmission into at least one memory of the device at 106. The memory can be one that is typicaily used for storing data for the purposes of responding retransmission requests. It can then subsequently be determined at 108 that time synchronisation of the device is again valid, where after transmission of data in the time synchronized system can be continued at 110. The determination at step 108 can be, for example, made based on reception of valid timing information or in response to detection that he timing was not lost in the first place. The device can then receive at 112 at least one request for retransmission of at least some of the data buffered at 106. In response to the request data is transmitted from the at least one memory to the requesting party at 114.

The buffering at 106 may be triggered based on instructions to save the data scheduled for transmission instead of flushing it. The instructions can be sent by the receiving device, or another entity providing at least partial control on the communications links between the two devices. According to another example of possible launch mechanisms buffering of data scheduled for transmission in response to detection of an irregularity in synchronisation may be defined as a mandatory operation. In this exemplifying scenario the transmitting device shall, for example, always buffer the scheduled data in response to determining at 102 that the time synchronisation is invalid based on expiry of a time alignment timer.

Figure 4 is a flowchart illustrating an example for operation at the receiving side of a transmitter-receiver pair. At 120 data is received from a transmitting device in a time synchronized system. Irregularities in time synchronisation between the devices can be monitored at 121. If no irregularity such as real or potential loss of synchronisation is detected, the operation and data reception continues at 120. However, if it is determined at 121 that the relevant time synchronisation is not valid and/or that no data is received and thus the reception of data is discontinued. According to a possibility it can be determined that sending of a timing update to the transmitting device is needed. For example, although a loss of synchronisation is not detected, it can be determined that the previous timing synchronisation message is lost, delayed or that an update of the timing information is needed for some other reason.

The reception of data may stop as nothing is sent by the transmitting device if it has paused data transmission in response to assumed or real loss of synchronisation. The receiving station can determine that the transmission is paused based on various indicators. For example, a receiving station such as a base station may be aware of the transmitting devices uplink buffer status based on received buffer status reports. If a synchronisation timer, for example a time alignment timer, of the base station expires and it is aware that there is data in the buffers of the downlink device, the base station can be allowed to sent or resend timing information on the downlink. The base station may also detect that timing information was sent but the transmitting device still does not send any data, in which case the base station may send/resend the timing information,.

Regardless of the trigger, timing information can be sent or resent at 122 to the transmitting device. The receiving device can determine that at least some data that was scheduled for transmission has not been received during the irregularity at 124. Either before, at the same time or after this determining the receiving device can also determine that the time synchronisation is again valid. For example, the receiving station can assume that the synchronisation is in order once it starts again receiving data from the transmitting device at 123.

If the receiving device determines at 124 that not all scheduled data was received, it can send at least one request for retransmission of said non- received data from at least one memory of the device at 128. One or more responses to the request can then be received 130, the response(s) containing at least one data unit from a memory of the transmitting device for storing data for retransmission purposes. For example, after detection of loss of uplink synchronization for a certain transmitting device and sending/resending new timing information, a base station can detect at 124 that not all uplink data corresponding to scheduled uplink allocations is received and request for retransmission of missing data. According to a possibility the base station can ignore all uplink transmissions after expiry of a synchronisation timer and request retransmissions for all uplink data allocations after the expiry.

In accordance with an embodiment, if the base station successfully receives retransmissions, the synchronization can be considered as being recovered.

Once all data is received, the recover is complete at 132, and data reception can continue in the usual manner in the time synchronised system.

If all data is considered as being received already at 124, reception of data can also continued in the normal manner at 126 in the time synchronized system.

In accordance with a more detailed example, if a time alignment timer 8 of a communication device 1 of Figure 2 expires, the communication device can store medium access control protocol data units (MAC PDUs) for the already configured uplink grants to an uplink HARQ buffer 20 thereof without transmission and freeze the uplink HARQ buffer until it is determined that the uplink timing is again valid. The storage can be provided by means of the same buffer memory as used for arrangements where the buffer is flushed by configuring the buffer control software such that the buffer 20 does not become automatically flushed in response to expiry of the synchronisation timer 8. The buffering may be made to be a mandatory response to the expiry of the timer. Alternatively, the base station may be configured to instruct the mobile device to save the HARQ buffers instead of flushing it when the time alignment timer expires. Such an instruction may be sent beforehand, for example when a communication device enters the area of a base station. The configuration of the downlink device how to act when the time alignment timer expires can be provided, for example, by means of radio resource control (RRC) parameters. For example, time alignment timer expiry recovery actions can be simply enabled/disabled with a single configuration bit.

In accordance with an embodiment, a base station can send acknowledgement without uplink grant for all HARQ processes during periods without valid uplink timing. If the transmitting device receives acknowledgements without uplink grant for only certain HARQ process, this servers as a trigger for buffering in the HARQ buffer for the purposes of subsequent retransmission requests. Buffering of the data instead of discarding it allows for utilisation of belatedly received timing information, for example a late timing advance command. When the uplink timing is again valid, the base station can recover the 'paused' uplink transmissions by sending a retransmission requests for those transmissions the communication device cancelled and which the base station did hence not ever even receive. By means of this uplink transmissions can be continued seamlessly, even if the data is received a bit later, despite the synchronisation timer having been expired.

Thus, for example in EUTRAN it is not necessary for a communication device to immediately flush a HARQ buffer if a time alignment timer expires. Instead, a procedure as illustrated in Figures 5A and 5B can be followed to enable recovery of a communication device and a base station from a late timing advance command update. More particularly, in Figure 5A the consecutive uplink (UL) sub-frames illustrate HARQ transmissions as they are scheduled to be transmitted in the respective frames such that the MAC PDU for subframe n is shown to be transmitted in uplink HARQ ID 6. The earlier subframes are denoted as n-1 , n- 2, n-3 and so forth, as shown in the table of Figure 5B, and the subsequent subframes are denoted as n+1 , n+2, and so on. The downlink (DL) subframes illustrate correspondingly the scheduling of the HARQ requests in the downlink. At the beginning of the exemplifying situation, at 40, the uplink timing is considered as valid. However, at 41 the time alignment timer of the mobile communication device expires, and therefore there is no uplink timing starting from frame UL HARQ ID 6. Therefore, as shown by the table of Figure 5B MAC PDUs for subframes for n, n+1 , n+2 are not transmitted as the mobile communication device cancels scheduled transmissions on the uplink because of the timer expiry at 41. After MAC PDU for n+2 (ID=0) at time 44 there are no scheduled transmissions on the uplink.

When the timer expires at 41 , the mobile communication device can freeze HARQ buffering. That is, if a time alignment timer expires at 41 the communication device can cancel, for configured uplink grants, transmissions while storing corresponding unsent UL MAC PDUs to a HARQ buffer thereof. The communication device can also take some other actions, such as cancel all uplink assignments until uplink timing is valid, and clear any configured downlink assignments.

The communication device can then receive at time 42 a downlink MAC PDU 2 from the base station carrying a new timing advance command (TAC) in downlink subframe n. Sending of a TAC can be triggered, for example, based on timing measurements in the network side, when a time alignment timer (TAT) timer expires in the network side, or if no data was received even though a TAC was updated. The received timing information is to be applied starting from the uplink subframe n+6. Therefore the communication device will now have a valid uplink timing for this subframe, and for the subsequent subframes n+7, n+8 and so forth. In response to the timing information received at 42 the time alignment timer can be restarted at 43.

When the uplink timing is again valid for transmissions on the uplink the transmissions can be continued at 45. The base station can determine the timing to be valid since it is again receiving retransmissions and/or new data successfully from the downlink device. Once uplink timing is valid, the base station can request for new transmissions and recover from the timer expiry by sending requests for retransmissions corresponding to those scheduled transmissions it did not receive as they were cancelled due to the timer expiry, that is for subframes n to n+2.

For the scheduled but non-transmitted and frozen subframes n+2, n and n+ of the table of Figure 5B the following procedure can be followed. An adaptive retransmission request can be sent at 46 in downlink subframe n+6 on physical downlink control channel (PDCCH) to request for retransmission of UL HARQ ID = 0 for MAC PDU for n+2. Non-adaptive retransmission can be triggered with sending of a non-acknowledgement (NACK) message on physical hybrid ARQ indication channel (PHICH). In accordance with an embodiment the base station can transmit, during period without valid uplink timing, ACK on the PHICH (with no uplink grant on the PDCCH) for all uplink HARQ processes to avoid unnecessary retransmissions. The MAC PDU for n+2 can then be received at 47 on physical uplink shared channel (PUSCH) in uplink subframe n+10. Another retransmission request is sent at 48 in downlink subframe n+12 for retransmission of UL HARQ ID = 6 to fetch the MAC PDU for n. The MAC PDU for n can then be received at 50 in uplink subframe n+16. Similarly, a retransmission request can be sent at 49 in downlink subframe n+13 for retransmission of UL HARQ ID = 7 for MAC PDU for n+1. The MAC PDU for n+1 can then be received at 51 in uplink subframe n+17. If the retransmissions were successful, a recovery for the time alignment timer expiry is completed for the scheduled transmissions. As there were no scheduled transmissions in frames n+3, n+4 and n+5, no recovery of these is needed. In certain scenarios it is possible that a base station may send uplink allocations for uplink subframes without valid uplink timing. Foe example, if the base station does not notice a time alignment timer expiry for a certain communication device and new data allocations has been sent for subframes n+3, n+4 and n+5, retransmissions may then be requested also for those subframes. However, in applications where a Stop-and-Wait type HARQ is used there should not be, in typical situations, new allocations before data is received from the HARQ buffer of the transmitting device after the timing is valid again.

In accordance with an embodiment a communication device may receive new uplink allocations in during the period of timing irregularity. The communication device may buffer also data that scheduled data, for example the corresponding protocol data unit or units to a corresponding HARQ buffer.

The above described exemplifying embodiments can provide advantage in that the packet latency can be made lower than in solutions where the retransmission buffer is discarded if it is determined that the synchronisation is lost. In some occasions advantage may be obtained since re-transmissions above MAC layer may not be needed because uplink data has not been immediately discarded. Certain embodiments also enable disablement of certain transmitting devices for short periods by delaying sending of timing information, for example delaying sending of timing advance command, transmission.

The computations and other functions of the apparatus may be provided by means of an appropriate circuit or circuits and/or one or more data processors. The described functions may be provided by separate processors or by an integrated processor. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant control apparatus. An appropriately adapted computer program code product or products may be used for implementing the embodiments, when loaded on an appropriate data processing apparatus, for example in a data processing apparatus of the mobile communication device 1 of Figure 2 and/or in the control apparatus of the base station of Figure 1. The program code product for providing the operation may be stored on, provided and embodied by means of an appropriate carrier medium. An appropriate computer program can be embodied on a computer readable record medium. A possibility is to download the program code product via a data network. All or part of the calculations can also be implemented in an application-specific integrated circuit ASiC. An application-specific integrated circuit (ASIC) is typically customized for a particular use. ASICs can include processor and memory blocks including read-only memories (ROM), random access memories (RAM), electrically erasable programmable read-only memories (EEPROM), Flash and other building blocks.

The herein described embodiments and principles can be used for example in wireless systems where E-UTRAN compatible communication devices are used. However, it is noted that the embodiments of the invention are applicable also elsewhere than in E-UTRAN transmitter and receivers, and therefore it is noted that whilst certain embodiments have been described in relation to communications system such as those based on the LTE and 3GPP based systems, similar principles can be applied to other communication systems and techniques. It is particularly noted that the above discusses only examples, and the issues are not limited to any particular communication environment, standard, specification and so forth, but may occur in any appropriate communication system where loss of synchronisation may cause loss of data. For example, instead of communications between a base station and a communication device the communications may be provided directly between two or more communication devices. For example, this may be the case in application where no fixed equipment is provided but a communication system is provided by means of a plurality of user equipment, for example in ad hoc networks. Therefore, although certain embodiments were described above by way of example with reference to certain exemplifying architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

It is also noted herein that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the spirit and scope of the present invention.

Claims

1. A method, comprising:

transmitting data from a device in a time synchronized system;

determining possibility of invalid time synchronisation;

pausing transmission of data from the device;

buffering data scheduled for transmission into at least one memory of the device, the at least one memory being configured for storing data for the purposes of responding retransmission requests;

in response to subsequent determination that time synchronisation of the device is valid, continuing transmission of data;

receiving at least one request for retransmission of at least some of the buffered data; and

responding the request by transmitting data from the at least one memory.

2. A method in accordance with claim 1 , wherein the determining of possibility of invalid time synchronisation comprises detecting expiry of a synchronisation timer.

3. A method in accordance with claim 2, wherein the synchronisation timer comprises a time alignment timer.

4. A method in accordance with any preceding claim, comprising receiving instructions to save the data scheduled for transmission in case of detecting a possibility of invalid time synchronisation.

5. A method in accordance with claim 4, comprising:

receiving the instructions in a radio resource control message, and configuring the device to operate accordingly when a possibility of invalid time synchronisation is detected.

6. A method in accordance with any of claims 1 to 3, wherein said buffering of data scheduled for transmission is a mandatory response to the determining of a possibility of invalid time synchronisation.

7. A method in accordance with any preceding claim, comprising receiving timing information from the receiving device, and subsequent to reception of the timing information determining that the time synchronisation is valid.

8. A method in accordance with claim 7, wherein the receiving of the timing information comprises receiving a timing advance command.

9. A method in accordance with any preceding claim, comprising:

receiving a new allocation after the determining of possibility of invalid timing synchronisation, and

buffering the corresponding data unit,

10. A method in accordance with any preceding claim, wherein the retransmission requests comprise hybrid automatic retransmission requests (HARQs).

11. A method in accordance with any preceding claim, wherein the buffering comprises storing medium access control protocol data units for already configured uplink grants to a HARQ buffer after expiry of a time alignment timer.

12. A method, comprising:

receiving data from a transmitting device in a time synchronized system;

determining an irregularity in time synchronisation with the transmitting device;

sending timing information to the transmitting device;

successfully receiving data from the transmitting device;

determining that at least some data scheduled for transmission during the irregularity has not been received; sending at feast one request for retransmission of said non-received data; and

receiving in response data from at least one memory for storing data for the purposes of responding retransmission requests and configured to store data scheduled for transmission during possible timing synchronisation irregularities.

13. A method in accordance with claim 12, comprising sending instructions to the transmitting device to save any data scheduled for transmission in response to a detected time synchronisation irregularity.

14. A method in accordance with claim 12 or 13, comprising sending the timing information in a timing advance command.

15. A method in accordance with any of claims 12 to 14, wherein the determining of an irregularity in time synchronisation comprises detecting expiry of a synchronisation timer.

16. A method in accordance with any of claims 12 to 15, wherein the sending of at one least request for retransmission of non-received data comprises sending of a request for all data scheduled for transmission during the irregularity.

17. A method in accordance with any of claims 12 to 16, comprising temporarily disabling the transmitting device by causing the irregularity by belated sending of timing information to the transmitting device.

18. A method in accordance with any of claims 12 to 17, wherein the retransmission requests comprise hybrid automatic retransmission requests (HARQs).

19. An apparatus comprising:

means for controlling transmission of data in a time synchronized system, the means for controlling being configured to determine a possibility of invalid time synchronisation and in response thereto to cause pausing the transmission of data and to subsequently determine that the time synchronisation is valid and in response to determination of valid time synchronisation to cause continuation of the transmission of data;

means for buffering data scheduled for transmission, the means for buffering being configured to store data for the purposes of responding retransmission requests, wherein the means for controlling are further configured to cause buffering of unsent scheduled data in the means for buffering; and

means for handling retransmission requests, the means for handling retransmission request being configured to receive at least one request for retransmission of at least some of the buffered unsent scheduled data and to respond the request by causing sending of data from the means for buffering.

20. An apparatus in accordance with claim 19, wherein the means for controlling are configured to the detect expiry of a synchronisation timer, and in response thereto to pause the transmission of data and cause buffering of the scheduled unsent data.

21. An apparatus in accordance with claim 19 or 20, wherein the means for controlling are configured to receive timing information from the receiving device, and subsequent to reception of the timing information to determine that the time synchronisation is valid and to cause continuing of the transmission of data.

22. An apparatus in accordance with any of claims 19 to 21 , wherein the means for controlling are configured to cause buffering of medium access control protocol data units for already configured uplink grants to a HARQ buffer after expiry of a time alignment timer.

23. An apparatus, comprising controller means for determining irregularity in time synchronization with a transmitting device, for causing sending of timing information to the transmitting device, for determining that reception of data from the transmitting device is continued, for determining that at least some data scheduled for transmission by the transmitting device has not been received, for causing sending of at least one request for retransmission of said non-received data, and for processing data received in response to said at least one request for retransmission from at least one memory configured to store data scheduled for transmission during possible timing synchronisation irregularities.

24. An apparatus in accordance with claim 23, wherein the controller means are configured to send instructions to the transmitting device to save data scheduled for transmission in response to a detected time synchronisation irregularity.

25. An apparatus in accordance with claim 23 or 24, wherein the controller means are configured to cause sending of a request for all data scheduled for transmission during the irregularity.

26. An apparatus in accordance with any of claims 23 to 25, wherein the controller means are configured to temporarily disable the transmitting device by causing the irregularity by belated sending of timing information to the transmitting device.

27. An apparatus comprising:

at least one processor, and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured, with the at least one processor,

to control transmission of data in a time synchronized system, to determine a possibility of invalid time synchronisation, and in response to determination that the synchronisation is possibly invalid, to cause pausing of said transmission of data and buffering of data scheduled for transmission into at least one memory configured for storing data for the purposes of responding retransmission requests,

in response to a subsequent determination that time synchronisation is valid, to cause continuation of the transmission of data, and

to handle at least one received request for retransmission of at least some of the buffered scheduled data by causing sending of said requested buffered scheduled data.

28. An apparatus in accordance with claim 27, wherein the apparatus comprises a synchronisation timer, and the at least one memory and the computer program code are configured, with the at least one processor, to determine the possibility of invalid time synchronisation based on expiry of a synchronisation timer,

29. An apparatus in accordance with claim 28, wherein the synchronisation timer comprises a time alignment timer.

30. An apparatus in accordance with any of claims 27 to 29, wherein the computer program code is configured, with the at least one processor, to determine that the time synchronisation is valid based on processing of timing information received from the receiving device.

31. An apparatus, comprising

at least one processor, and

at least one memory including computer program code,

to control receiving of data from a transmitting device in a time synchronized system;

to detect an irregularity in the time synchronisation and subsequently to send timing information to the transmitting device;

to determine that at least some data scheduled for transmission by the transmitting device during the irregularity has not been received, to cause sending of at least one request for retransmission of said non-received data; and

to receive, in response to said at least one request, data from at least one memory configured to store data scheduled for transmission during possible timing synchronisation irregularities.

32. An apparatus in accordance with claim 31 , comprising a synchronisation timer, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause sending of said timing information in response to expiry of the timer.

33. An apparatus according to any of claims 19 to 32, wherein the apparatus is configured to operate in an Evolved Universal Terrestrial Radio Access Network (E-UTRAN).

34. A communication device comprising apparatus in accordance with any of claims 19 to 22 or 27 to 30.

35. A communication system comprising an apparatus in accordance with any of claims 19 to 33.

36. A computer program comprising program code means adapted to perform the steps of any of claims 1 to 18 when the program is run on a data processing apparatus.