Provision of time information to a wireless device

There is provided provision of timing information of a first timing information source using timing information of a second timing information source to a wireless device. A network node determines that second timing information from the second timing information source is available and that timing information from the first timing information source is derivable from the second timing information. The network node instructs the wireless device to use the second timing information as a source for deriving first timing information of the first timing information source.

TECHNICAL FIELD

Embodiments presented herein relate to provision of time information to a wireless device, and particularly to a method, a network node, a computer program, and a computer program product for providing timing information to a wireless device, and a method, a wireless device, a computer program, and a computer program product for acquiring timing information.

BACKGROUND

In communications networks, there may be a challenge to obtain good to performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.

For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is the availability of accurate system time information.

For example, accurate system time information may be required in radio based communications networks in order to facilitate good sleep opportunities for both wireless devices and network nodes, saving significant power on both sides, without introducing any ambiguities in the communication links between the wireless devices and the network nodes. In general terms, time information is to the wireless device provided by the network node in the serving cell of the wireless device. By maintain per cell time information the need to synchronize cells is removed, simplifying deployment of radio based communications networks.

Time information is provided in system broadcasts and the frequency and granularity of the information is a trade-off between sleep efficiency of the wireless devices, the maximum sleep time of the wireless devices, and system overhead. For example in telecommunications networks based on the long term evolution (LTE) standards the system frame number is provided in the master information block (MIB) which is transmitted once every 10 ms. The time granularity is 10.24 seconds, or 1024 frames, limited by the number of bits used in the MIB to signal the frame number.

It has been considered to extend the time information in communications networks to enable longer sleep-times for the wireless device, for example by reserving additional bits for signaling or to introduce new messages for providing a secondary timing, differentiating between cycles of the existing timing.

However, in some communications networks, such as in some multi-layer multi technology environments, the ability of network energy saving by network node dormancy and overhead saving is reduced by the need to provide frequent time-information to enable efficient sleep of the wireless devices. The network node still frequently needs to provide time information in order for the wireless device to quickly (re-)acquire timing information.

Hence, there is still a need for an improved provision of time information to a wireless device.

SUMMARY

An object of embodiments herein is to provide improved provision of time information to a wireless device.

According to a first aspect there is presented a method for providing timing information of a first timing information source using timing information of a second timing information source to a wireless device. The method is performed by a network node. The method comprises determining that second timing information from the second timing information source is available and that timing information from the first timing information source is derivable from the second timing information. The method comprises instructing the wireless device to use the second timing information as a source for deriving first timing information of the first timing information source.

Advantageously this enables efficient provision of time information to the wireless device.

Advantageously this enables for long sleep-time in the wireless device and network nodes while reducing the overhead from providing timing information in the communications network.

According to a second aspect there is presented a network node for providing timing information of a first timing information source using timing information of a second timing information source to a wireless device. The network node comprises a processing unit. The processing unit is configured to determine that second timing information from the second timing information source is available and that timing information from the first timing information source is derivable from the second timing information. The processing unit is configured to instruct the wireless device to use the second timing information as a source for deriving first timing information of the first timing information source.

According to a third aspect there is presented a computer program for providing timing information of a first timing information source using timing information of a second timing information source to a wireless device, the computer program comprising computer program code which, when run on a processing unit, causes the processing unit to perform a method according to the first aspect.

According to a fourth aspect there is presented a method for acquiring timing information of a first timing information source using timing information of a second timing information source. The method is performed by a wireless device. The method comprises receiving instructions from a network node to use second timing information of the second timing information source as a source for deriving first timing information of the first timing information source. The method comprises receiving the second timing information from the second timing information source.

According to a fifth aspect there is presented a wireless device for acquiring timing information of a first timing information source using timing information of a second timing information source. The wireless device comprises a processing unit. The processing unit is configured to receive instructions from a network node to use second timing information of the second timing information source as a source for deriving first timing information of the first timing information source. The processing unit is configured to receive the second timing information from the second timing information source.

According to a sixth aspect there is presented a computer program for acquiring timing information of a first timing information source using timing information of a second timing information source, the computer program comprising computer program code which, when run on a processing unit, causes the processing unit to perform a method according to the fourth aspect.

According to a seventh aspect there is presented a computer program product comprising a computer program according to at least one of the third aspect ad the sixth aspect and a computer readable means on which the computer program is stored.

It is to be noted that any feature of the first, second, third, fourth, fifth, sixth and seventh aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, fifth, sixth, and/or seventh aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

DETAILED DESCRIPTION

FIG. 1ais a schematic diagram illustrating a communications network10awhere embodiments presented herein can be applied. The communications network10acomprises radio transceiver devices11a,11bin the form of network nodes (NNs). The network nodes may be provided as any combination of radio access network nodes such as base transceiver stations (BTSs), Node Bs, Evolved Node Bs, or access points, such as access points for Wi-Fi. The radio transceiver devices11a,11binFIG. 1aare configured to provide network coverage in cells16a,16bto a radio transceiver device12in the form of a wireless device (WD). The wireless device may be a portable wireless transceiver device, such as a mobile phone, a smartphone, a tablet computer, a laptop computer or the like, or other type of user equipment (UE) or Wi-Fi device. Within the cells16a,16bthe radio transceiver devices11a,11bthus act as radio base stations for the radio transceiver device12. The radio transceiver devices11a,11band the radio transceiver device12are configured to be operatively connected via wireless links15a,15b. The communications network10afurther comprises a core network13. The radio transceiver devices11a,11bare operatively connected to the core network13. The core network13is in turn operatively connected to an Internet Protocol (IP) based service network14. The radio transceiver device12is thereby enabled to access content and services as provided by the IP based service network14via the wireless links15a,15b.

FIG. 1bis a schematic diagram illustrating a communications network bob where embodiments presented herein can be applied. The communications network bob is similar to the communications network10aofFIG. 1aand comprises a radio transceiver device11in the form of a network node11aconfigured to provide network coverage to a radio transceiver device12in the form of a wireless device. The radio transceiver device11ais configured to provide network coverage in cells16a,16b, for example using different radio access technologies. Hence, the radio transceiver device11amay alternatingly in time or frequency or at the same time and/or frequency act as a base transceiver station (BTS), a Node B, an Evolved Node B, and an access point. The communications network10bfurther comprises a core network13as disclosed with reference toFIG. 1aand a service network14as disclosed with reference toFIG. 1a.

Each network node11a,11bcomprises a timing information source17a,17bto and is configured to provide timing information to the wireless device12. In the example ofFIG. 1athe network node11acomprises a first timing information source17aand the network node11bcomprises a second timing information source17b. In the example ofFIG. 1bthe network node11acomprises a first timing information source17aand a second timing information source17b. The timing information may represent system time information in the communications network10a,11b. At least some of the herein disclosed embodiments enable a network node11a(or timing information source) of a first cell16ato inform a wireless device12about timing information of a second cell16band/or a network node11a(or timing information source) of a first cell16ato provide the wireless device12with information about a second cell16bthat can provide timing information to the wireless device12of the first cell16a. At least some of the herein disclosed embodiments enable a wireless device12to utilize this information to derive timing for monitoring a downlink channel and to improve its sleep time.

The embodiments disclosed herein particularly relate to timing information related to a wireless device. In order to provide timing information of a first timing information source using timing information of a second timing information source to a wireless device there is provided a network node, a method performed by the network node, a computer program comprising code, for example in the form of a computer program product, that when run on a processing unit of the network node, causes the network node to perform the method. In order to acquire timing information of a first timing information source using timing information of a second timing information source there is further provided a wireless device, a method performed by the wireless device, a computer program comprising code, for example in the form of a computer program product, that when run on a processing unit of the wireless device, causes the wireless device to perform the method.

FIG. 2aschematically illustrates, in terms of a number of functional units, the components of a network node11aaccording to an embodiment. A processing unit21is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product41a(as inFIG. 4), e.g. in the form of a storage medium23. Thus the processing unit21is thereby arranged to execute methods as herein disclosed. The a storage medium23may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The network node11amay further comprise a communications interface22for communications with another network node11b, the core network13, and at least one wireless device12. As such the communications interface22may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of antennas for radio communications and a suitable number of ports for wired communications. The processing unit21controls the general operation of the network node11ae.g. by sending data and control signals to the communications interface22and the storage medium23, by receiving data and reports from the communications interface22, and by retrieving data and instructions from the storage medium23. Other components, as well as the related functionality, of the network node11aare omitted in order not to obscure the concepts presented herein.

FIG. 2bschematically illustrates, in terms of a number of functional modules, the components of a network node11aaccording to an embodiment. The network node11aofFIG. 2bcomprises a number of functional modules; a determine module21a, and an instruct module21b. The network node11aofFIG. 2bmay further comprises a number of optional functional modules, such as any of a provide module21c, a notify module21d, a send and/or receive module21e, and a check module21f. The functionality of each functional module21a-fwill be further disclosed below in the context of which the functional modules21a-fmay be used. In general terms, each functional module21a-fmay be implemented in hardware or in software. Preferably, one or more or all functional modules21a-fmay be implemented by the processing unit21, possibly in cooperation with functional units22and/or23. The processing unit21may thus be arranged to from the storage medium23fetch instructions as provided by a functional module21a-fand to execute these instructions, thereby performing any steps as will be disclosed hereinafter.

FIG. 3aschematically illustrates, in terms of a number of functional units, the components of a wireless device12according to an embodiment. A processing unit31is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product41b(as inFIG. 4), e.g. in the form of a storage medium43. Thus the processing unit31is thereby arranged to execute methods as herein disclosed. The storage medium33may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The wireless device12may further comprise a communications interface32for communications with at least one network node11a,11b. As such the communications interface32may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of antennas for radio communications. The processing unit31controls the general operation of the wireless device12e.g. by sending data and control signals to the communications interface32and the storage medium33, by receiving data and reports from the communications interface32, and by retrieving data and instructions from the storage medium33. Other components, as well as the related functionality, of the wireless device12are omitted in order not to obscure the concepts presented herein.

FIG. 3bschematically illustrates, in terms of a number of functional modules, the components of a wireless device12according to an embodiment. The wireless device12ofFIG. 3bcomprises a send and/or receive module31a. The wireless device12ofFIG. 3bmay further comprises a number of optional functional modules, such as any of a use module31b, a determine module31c, and a request module31d. The functionality of each functional module31a-dwill be further disclosed below in the context of which the functional modules31a-dmay be used. In general terms, each functional module31a-dmay be implemented in hardware or in software. Preferably, one or more or all functional modules31a-dmay be implemented by the processing unit31, possibly in cooperation with functional units32and/or33. The processing unit31may thus be arranged to from the storage medium33fetch instructions as provided by a functional module31a-dand to execute these instructions, thereby performing any steps as will be disclosed hereinafter.

FIG. 4shows one example of a computer program product41a,41bcomprising computer readable means43. On this computer readable means43, a computer program42acan be stored, which computer program42acan cause the processing unit21and thereto operatively coupled entities and devices, such as the communications interface22and the storage medium23, to execute methods according to embodiments described herein. The computer program42aand/or computer program product41amay thus provide means for performing any steps as herein disclosed. On this computer readable means43, a computer program42bcan be stored, which computer program42bcan cause the processing unit31and thereto operatively coupled entities and devices, such as the communications interface32and the storage medium33, to execute methods according to embodiments described herein. The computer program42band/or computer program product41bmay thus provide means for performing any steps as herein disclosed.

FIGS. 5 and 6are flow chart illustrating embodiments of methods for providing timing information of a first timing information source using timing information of a second timing information source to a wireless device as performed by the network node11a.FIGS. 7 and 8are flow chart illustrating embodiments of methods for acquiring timing information of a first timing information source using timing information of a second timing information source as performed by the wireless device12. The methods are advantageously provided as computer programs42a,42b.

Network Node

Reference is now made toFIG. 6illustrating a method for providing timing information of a first timing information source17ausing timing information of a second timing information source17bto a wireless device12as performed by a network node11aaccording to an embodiment. Parallel references are made to the signalling diagrams ofFIGS. 9 and 10.

The network node11ain a step S104determines that second timing information from the second timing information source17bis available. The network node11ain step S104further determines that timing information from the first timing information source17ais derivable from the second timing information. The network node11amay be configured to perform step S104by the processing unit21executing functionality of the determine module21a. The computer program42aand/or computer program product41amay thus provide means for this step.

The network node11ain a step S106instructs the wireless device12to use the second timing information as a source for deriving the timing information of the first timing information source17a. The network node11amay be configured to perform step S106by the processing unit21executing functionality of the instruct module21b. The computer program42aand/or computer program product41amay thus provide means for this step.

This enables a timing information source of one cell16ato provide time information to a wireless device12in a second cell16b, and by doing so enable the wireless device12to save power. This also enables overhead in the communications network10a,10bin an area where coverage already exist from a second timing information source to be reduced.

Reference is now made toFIG. 7illustrating methods for providing timing information of a first timing information source17ausing timing information of a second timing information source17bto a wireless device12as performed by a network node11aaccording to further embodiments. Parallel references are continued to the signalling diagrams ofFIGS. 9 and 10.

The timing information provided by the first timing information source17aand the second timing information source17bmay represent system time information in the communications network10a,10b. The second timing information may be provided on a separate (dedicated) carrier frequency. Further details of the timing information will be provided below.

There may be different ways for the network node11ato acquire the information that the second timing information is available. According to one general embodiment the information that the second timing information is available is acquired from the wireless device. According to one general embodiment the information that the second timing information is available is acquired from the second timing information source17b. According to one general embodiment the information that the second timing information is available is acquired from a network node11bof the second timing information source17b.

There are may be different types of timing information sources17a,17b. According to one general embodiment the first timing information source17ais a timing information source of a first cell16a. According to one general embodiment the second timing information source17bis a timing to information source of a second cell16b. The first cell16aand the second cell16bmay be served by the same network node11a. Hence the first timing information source17aand the second timing information source17bmay be provided in the same network node11a.

The first cell16amay be a serving cell of the wireless device12when the network node11ainstructs the wireless device12to use the second timing information as its source for timing information in step S106.

In some embodiments the first timing information source17aand the second timing information source17bare separable by having different geographical coverage area, be transmitted from separate points, such as from different network nodes11a,11b, be transmitted on different carrier frequencies and/or constitute different radio access technologies. The first timing information source17aand the second timing information source17bmay thus use the same or different radio access technologies (RATs) for transmitting timing information. The first timing information source17aand the second timing information source17bmay thus transmit in the same or different area. Hence the first timing information source17aand the second timing information source17bmay have the same or different network coverage. The first timing information source17aand the second timing information source17bmay thus use the same or different carrier frequency for transmitting timing information. Hence, according to one general embodiment at least one of RAT, network coverage, and carrier frequency of the first timing information source17aand the second timing information source17bis different. Hence, according to one general embodiment the first timing information source16ashare at least one of RAT, network coverage, and carrier frequency with the second timing information source17b.

The network node11amay also provide timing information to the wireless device12. Particularly, the network node11amay, in an optional step S108, provide timing information of the first timing information source17ato the wireless device12. The network node11amay be configured to perform step S108by the processing unit21executing functionality of the provide module21c. The computer program42aand/or computer program product41amay thus provide means for this step. The timing information of the first timing information source17aand the timing information of the second timing information source17bmay by the wireless device12be used separately, complementary, or joint. In some embodiments the network node11anotifies the wireless device12served by the network node11aof the first timing information source17ato acquire a better time resolution by combining timing information from first timing information source17aand the second timing information source17b. Thus, the network node11amay, in an optional step S110, instruct the wireless device12to combine the timing information of the second timing information source17band the timing information of the first timing information source17a. The network node11amay be configured to perform step S110by the processing unit21executing functionality of the instruct module21b. The computer program42aand/or computer program product41amay thus provide means for this step

In some embodiments a first timing information source17aprovides timing information with a first resolution and a second cell timing information source17bprovides timing information of a second resolution, where resolution here refers to the time duration of a time-cycle in a first cell16aand a second cell10, or the time between messages as issued by the first timing information source17aand the second timing information source17bindicating current system time. The timing information of the second timing information source17band the timing information of the first timing information source17amay thus have different resolution. This is illustrated inFIG. 11(see below). For example, the timing information of the second timing information source17bmay have higher resolution than the timing information of the first timing information source17a. This is illustrated inFIG. 11(see below). The resolution may thus be defined by a time duration of a time-cycle or a time duration between two messages indicating current system time.

In some embodiments the time granularity of the first timing information source17aand the second timing information source17bis the same, but the frequency of providing time information is different. In this case it may be sufficient to inform the wireless device12about a relation in time between the first timing information source17aand the second timing information source17b. Further, the timing information of the second timing information source17band the timing information of the first timing information source17amay thus have same time granularity. A frequency of providing the timing information of the second timing information source17band the timing information of the first timing information source17bmay thus be different.

The total time cycle length of the timing information of the first timing information source17amay be different from the total cycle length of the timing information of the second timing information source17b. This is illustrated inFIG. 11(see below). Thus, in some embodiments the total time cycle length of the first timing information source17ais different from the total cycle length of the second timing information source17b. If the difference in cycle length is kept a non-multiple of each other, the two timing information sources17a,17bwill drift in relation to each other in frame number in a predictable way, thereby enabling the timing information from the two timing information sources17a,17bto be combined, thus enabling an extended time granularity to be determined. As an example, consider timing information sources17a,17bof two long term evolution (LTE) cells where the timing information source17bof one cell makes a slight intentional time-error such that the time-cycle of one cell is 10.23 s while the other cell has a time-cycle of 10.24 s. This would effectively scale up the granularity of the timing information up to more than 100 s. A wireless device12may then be configured to monitor paging in any radio-frame fulfilling its paging occasion in both cells simultaneously, giving a significantly longer, but still deterministic paging cycle.

Properties of the first timing information source17aand the second timing information source17bmay be reported to the wireless device12. For example, the network node11amay, in an optional step S112, notify the wireless device12about a relation in time between the timing information of the second timing information source17band the timing information of the first timing information source17a. The network node11amay be configured to perform step S112by the processing unit21executing functionality of the notify module21d. The computer program42aand/or computer program product41amay thus provide means for this step. In some embodiments the network node11anotifies the wireless device12about a maximum drift in time between the first timing information source17aand the second timing information source17b. Thus, the network node11amay, in an optional step S114, notify the wireless device12about a drift in time between the timing information of the first timing information source17aand the timing information of the second timing information source17b. The network node11amay be configured to perform step S114by the processing unit21executing functionality of the notify module21d. The computer program42aand/or computer program product41amay thus provide means for this step.

There may be different reasons for the network node11ato determine that second timing information from the second timing information source17bis available, as in step S104. In some embodiments the wireless device12reports to the network node11ain its serving cell if it has sufficient coverage from a second timing information source17bto use it for time reference. Thus, the determining in step S104may be triggered by a request from the wireless device12. Hence, the network node11amay, in an optional step S102, receive a request from the wireless device12to provide timing information. The network node11amay be configured to perform step S102by the processing unit21executing functionality of the send and/or receive module21e. The computer program42aand/or computer program product41amay thus provide means for this step

The determining in step S104and the instructing in step S106may then be performed in response to the request being received by the network node11aas in step S102. The network node11amay be configured to handle the request received in step S102based on at least one property of the wireless device12sending the request. One such property is a subscription. Particularly, the network node11amay, in an optional step S118, check a subscription criterion of the wireless device12. The network node11amay be to configured to perform step S118by the processing unit21executing functionality of the check module21f. The computer program42aand/or computer program product41amay thus provide means for this step. The instructing in step S102may then be performed only if the subscription criterion is fulfilled. The subscription criterion may relate to a subscription to additional timing information (in addition to timing information as provided by the timing information source17aof the serving network node11aof the wireless device12). Hence the instructing in step S102may be performed only if the wireless device12has a subscription to such additional timing information.

In some embodiments additional information is provided at the time-occasions when timing information is provided, where this additional information provides information about the need for the wireless device12to in the following time period wake up and monitor for scheduling. As an example, a signal which provides timing information of a specific granularity may be accompanied by a signal indication if the network node11ahas any pending paging messages to be delivered, to all or a subset of served wireless devices12until the next occasion of a signal providing timing information of the same granularity. This can be provided in a multi-step signaling approach, where timing information is provided on multiple levels of granularity.

In some embodiments additional resources may be configured by a network node11ato provide timing information, for example in the case that the network node11aserves a wireless device12without coverage from any second timing information source17b. The network node11amay thus, in an optional step S120, provide further timing information to the wireless device12. The network node11amay be configured to perform step S120by the processing unit21executing functionality of the provide module21c. The computer program42aand/or computer program product41amay thus provide means for this step. This further timing information may be different from or identical to the timing information of the second timing information source17b. For example, the network node11amay, in an optional step S116, receive an indication from the wireless device12that the timing information of the second timing information source17bis not available. The network node11amay be configured to perform step S116by the processing unit21executing functionality of the send and/or receive module21e. The computer program42aand/or computer program product41amay thus provide means for this step. The further timing information may then be provided to the wireless device12in response thereto. For example, the wireless device12may be outside coverage16bof the second timing information source17band hence not be able to directly receive any timing information from the second timing information source17b. The wireless device12may then request further timing information from the network node11a. The further timing information may by the network node11abe provided to the wireless device12during a time interval in which the wireless device12is configured to wake up and monitor for scheduling.

In some embodiments it is the second timing information source17bthat provides the wireless device12with information about time information for the first timing information source17a. This information may for example be provided in system broadcast where the second timing information source17bmay point out one or multiple other cells, for which it can provide a time reference.

In some embodiments it is not a specific cell that is indicated but a carrier frequency, where any cell on the indicated carrier frequency can be used for time reference or use this cell as time reference. An example of such a communications network is where a new radio access technology that provides system information, and related timing information on a slow time-scale, e.g. by a broadcast message sent ones every 10.24 second is added to an existing communications network. If this new radio access technology is deployed in an area with at least partial existing network coverage, such as long term evolution (LTE) coverage, the wireless device12may be informed, from the network node11aof the serving cell16aor from the LTE cell (as exemplified by cell16b), that these two cells share a timing relation, or a maximal time drift. The wireless device12may then utilize this information to wake up and monitor the time-information on the LTE cell, provided every 10 ms, to correct its current clock-timing towards the serving cell16a. This enables the wireless device12longer sleep-time and more accurate wake-up, thus saving power in the wireless device12.

Wireless Device

Reference is now made toFIG. 8illustrating a method for acquiring timing information of a first timing information source17ausing timing information of a second timing information source17bas performed by a wireless device12according to an embodiment. Parallel references are continued to the signalling diagrams ofFIGS. 9 and 10.

The wireless device12in a step S208receives instructions from a network node11ato use second timing information of a second timing information source17bas a source for deriving first timing information of the first timing information source17b. The wireless device12may be configured to perform step S208by the processing unit31executing functionality of the send and/or receive module31a. The computer program42band/or computer program product41amay thus provide means for this step.

The wireless device12in a step S210receives the second timing information from the second timing information source17b. The wireless device12may be configured to perform step S210by the processing unit31executing functionality of the send and/or receive module31a. The computer program42band/or computer program product41amay thus provide means for this step.

Reference is now made toFIG. 9illustrating methods for acquiring timing information of a first timing information source17ausing timing information of a second timing information source17bas performed by a wireless device12according to further embodiments. Parallel references are continued to the signalling diagrams ofFIGS. 9 and 10.

The wireless device12may, in an optional step S212, use the second timing information as its source for timing information. The wireless device12may be configured to perform step S212by the processing unit31executing functionality of the use module31b. The computer program42band/or computer program product41amay thus provide means for this step. There are different ways for the wireless device12to use the second timing information as its source for timing information. For example, the wireless device may, in an optional step S214, determine, based on the second timing information, timing for when to transmit an uplink signal to the network node11aof the first timing information source17a. The wireless device12may be configured to perform step S214by the processing unit31executing functionality of the determine module31c. The computer program42band/or computer program product41amay thus provide means for this step. In some embodiments the wireless device12uses the provided timing information to e.g. calculate time occasions to monitor a downlink channel. Thus, the wireless device may, in an optional step S216, determine, based on the second timing information, timing for when to monitor a downlink channel. The wireless device12may be configured to perform step S216by the processing unit31executing functionality of the determine module31c. The computer program42band/or computer program product41amay thus provide means for this step.

As disclosed above, one reason for the network node11ato determine that second timing information from the second timing information source17bis available, as in step S104, is a request as received by the network node11a, as in step S102, from the wireless device12. Hence, the wireless device12may, in an optional step S202, request timing information from the network node11aof the first timing information source17a. The wireless device12may be configured to perform step S202by the processing unit31executing functionality of the request module31d. The computer program42band/or computer program product41amay thus provide means for this step.

Further, the wireless device12may, in an optional step S204, determine that the wireless device12has sufficient coverage16bfrom the second timing information source16b. The wireless device12may be configured to perform step S204by the processing unit31executing functionality of the determine module31c. The computer program42band/or computer program product41amay thus provide means for this step. The wireless device12may then, in an optional step S206, send a report thereof to the network node11aof the first timing information source17a. The wireless device12may be configured to perform step S206by the processing unit31executing functionality of the send and/or receive module31a. The computer program42band/or computer program product41amay thus provide means for this step. The network node11amay then determine whether or not to instruct the wireless device12to use the use the second timing information as its source for timing information.

As disclosed above, the network node11amay, in an optional step S116, receive an indication from the wireless device12that the timing information of the second timing information source17bis not available. In some embodiments there may thus be occasions where the wireless device12does not have sufficient coverage from the second timing information source17b. This can however be detected by the wireless device12, and may result in the wireless device12having to keep track of the timing information provided by the network node11of its serving cell. This would remove the power saving opportunity for this specific wireless device12but not break the system operation. Therefore, the wireless device12may, in an optional step S218, determine that the wireless device12does not have sufficient coverage16bfrom the second timing information source17b. The wireless device12may be configured to perform step S218by the processing unit31executing functionality of the determine module31c. The computer program42band/or computer program product41amay thus provide means for this step. The wireless device12may then, in an optional step S220, send a report thereof to the network node11aof the first timing information source17a. The wireless device12may be configured to perform step S220by the processing unit31executing functionality of the send and/or receive module31a. The computer program42band/or computer program product41amay thus provide means for this step. The network node11amay then determine whether or not to provide further timing information to the wireless device12, as in step S120.

Examples

As an example, consider a wireless device12camping on a carrier frequency in a serving cell16athat does not provide any timing information except for a periodic sync signal sent out with a periodicity Psyncof subframes. The timing information of the first timing information source17amay thus represent such as periodic sync signal. On a separate carrier frequency, another cell16bcovers the same area providing time resolution of up to 10.24 s in CellBSFN, where SFN is short for system frame number, and where CellB is the cell of the second timing information source17b. A wireless device12could then derive a set of subframes (SF) to monitor a control channel as all subframes fulfilling:
SF mod Psync=n; and
floor(CellBSFN/k)*qmod 1024=m,
where n, k, q and m are parameters (derived or configured) for the wireless device12. Hence the set of subframes SF may be written as SF={all x; x mod Psync=n} and the set of possible SFN may be written as SFN={all y; floor(CellBy/k)*q mod 1024=m}, where CellByis system frame number y. Hence, SF is a subframe number in cell16a(using the first timing information source17a), and SFN is a subframe number in cell16b(using the second timing information source17b). The subframe monitoring would hence be done in SF number n of the serving cell16aof the wireless device12, but only during time durations where the timing information of the second timing information source17bfulfills some condition.

FIG. 11schematically illustrates an example of two timing information sources17a,17boperating with different time information, where the first timing information source17has a larger maximum time and where the second timing information source17bprovides more frequent time information. As an example, a timing information system for providing system time to a wireless device12may be formed by multiple signals, e.g. one timing signal T1sent every N subframes (as represented by the first timing information source17ain part (a) ofFIG. 11) and a second timing signal T2sent every m*N subframes (as represented by the second timing information source17bin part (b) ofFIG. 11), and so on. A wireless device12(as represented by the wireless device in part (c) ofFIG. 11) waking up from a very long sleep time would first have to locate the second timing signal T2(at time t1inFIG. 11) to find timing information of needed granularity. After finding the T2timing information the wireless device12may go back to sleep (at time t2inFIG. 11) to wake up (at time t3inFIG. 11) and find T1to finally wake up at the paging occasion (at time t4inFIG. 11) relative T2and T1and then go to sleep again (at time t5inFIG. 11). The wireless device12may also back to sleep again (at time t5inFIG. 11) and skip the paging occasion if information that no paging is sending is received at the occasion of T2or T1(e.g., at time t4inFIG. 11).