WO2013127076A1

WO2013127076A1 - Enhanced discontinuous reception to reduce power consumption in a wireless device

Info

Publication number: WO2013127076A1
Application number: PCT/CN2012/071794
Authority: WO
Inventors: Jing HAN; Haiming Wang; Chunyan Gao; Wei Bai; Petteri Kalle Kela
Original assignee: Renesas Mobile Corporation
Priority date: 2012-02-29
Filing date: 2012-02-29
Publication date: 2013-09-06

Abstract

The invention allows enhanced discontinuous reception (DRX) to reduce power consumption in a wireless device. In response to a predetermined first event which triggers active time of DRX in a DRX enabled wireless device: it is determined to monitor, for a first period, at least one physical downlink control channel to detect a predetermined second event; in response to not detecting the predetermined second event during the first period, it is determined to halt the monitoring for a second period; and it is determined to repeat the steps of monitoring and halting the monitoring until the predetermined second event is detected during the monitoring step.

Description

ENHANCED DISCONTINUOUS RECEPTION TO REDUCE POWER CONSUMPTION IN A WIRELESS DEVICE

BACKGROUND OF THE INVENTION:

Field of the Invention:

The invention relates generally to wireless communications. In particular, the invention relates to enhanced discontinuous reception to reduce power consumption in a wireless device.

Description of the Related Art:

Long Term Evolution (LTE) was introduced in release 8 of 3^rd Generation Partnership Project (3GPP) which is a specification for 3^rd generation mobile com- munication systems. LTE is a technique for mobile data transmission that aims to increase data transmission rates and decrease delays, among other things. LTE uses orthogonal frequency division multiple access (OFDMA) as its multiple access method in the downlink. The uplink uses single-carrier frequency division multiple access (SD-FDMA) . 3GPP release 10 introduced a next version of LTE, named LTE Advanced (LTE-A) , ful^¬ filling 4^th generation system requirements. In the following, the terms Long Term Evolution and LTE are used to refer to both the originally introduced Long Term Evolution of 3GPP release 8 and LTE Advanced of 3GPP release 10 and beyond.

Herein, the term "downlink" (DL) is used to refer to the link from the base station to the mobile device or user equipment, and the term "uplink" (UL) is used to refer to the link from the mobile or wire^¬ less device or user equipment (UE) to the base station

In the context of LTE, discontinuous recep^¬ tion (DRX) refers to a scheme for discontinuously mon- itoring and receiving physical downlink control channel (s) to save UE's power both in RRC_CONNECTED state and RRC_IDLE state. As in known in the art, RRC_CONNECTED and RRC_IDLE are the two radio resource control (RRC) states specified by 3GPP for UE . UEs in RRC_IDLE state show sporadic activity that mainly in- volves cell selection and reselection, whereas UEs in RRC_CONNECTED state have allocated radio resources in shared data channels specified by dedicated signaling performed via control channels.

DRX can be configured for ^,RRC_CONNECTED' UE so that it does not always need to monitor the down^¬ link channels. As shown in Figure la, a DRX cycle 103 consists of an ^,on-duration' or ^''active time' 101 dur^¬ ing which the UE should monitor the Physical Downlink Control Channel (PDCCH) , and a ^Λ DRX period' or ^Λ DRX opportunity' 102 during which the UE can skip recep^¬ tion of downlink channels for battery saving purposes.

However, there are situations in which the duration of the active time can be unusually long. Specification 3GPP TS 36.321 defines active time as follows:

one of timers onDurationTimer , drx- InactivityTimer, drx-RetransmissionTimer or mac- ContentionResolutionTimer is running;

a Scheduling Request (SR) is sent on a Physical Uplink Control Channel (PUCCH) and is pending;

- an uplink grant for a pending Hybrid Automatic Repeat Request (HARQ) retransmission can occur and there is data in the corresponding HARQ buffer; or

- a PDCCH indicating a new transmission ad- dressed to the Cell Radio Network Temporary Identifier

(C-RNTI) of the UE has not been received after suc^¬ cessful reception of a Random Access Response for the preamble not selected by the UE .

Therefore, as shown in Figure 2, for example for a scheduling request, in prior art UE needs to al^¬ ways monitor all possible downlink control channels after a scheduling request is sent 104 on PUCCH until it receives a corresponding uplink grant 105. In other words, the on-duration 101 of Figure 1 lasts the whole scheduling delay 106.

Power saving is particularly important for Diverse Data Applications (DDA) and low cost Machine Type Communication (MTC) UEs. As is known, MTC (also called M2M or Machine-to-Machine) means machine-to- machine communication, i.e. automated data exchange between machines. DDA and MTC traffic is characterized by small packets and long transmission intervals. In other words, the UEs will be temporarily inactive.

The time duration 106 could be very long, es^¬ pecially for background traffic for DDA or low cost MTC UEs, because of low scheduling priority for these kinds of UEs and large number of UEs to be scheduled.

Therefore, an object of the present invention is to alleviate the problems described above and to introduce a solution that allows enhancing the DRX procedure to further decrease the power consumption of the UE thereby extending the UE battery life.

SUMMARY OF THE INVENTION :

A first aspect of the present invention is a method in which, in response to a predetermined first event triggering active time of discontinuous recep^¬ tion, DRX, in a DRX enabled wireless device: it is de^¬ termined to monitor, for a first period, at least one physical downlink control channel to detect a prede^¬ termined second event; in response to not detecting the predetermined second event during the first period, it is determined to halt the monitoring for a second period; and it is determined to repeat the steps of monitoring and halting the monitoring until the predetermined second event is detected during the monitor- ing step.

A second aspect of the present invention is an apparatus which comprises at least one processor, and at least one memory including computer program code. The at least one memory and the computer program code are configured to, with the at least one proces^¬ sor, cause the apparatus at least to perform:

in response to a predetermined first event triggering active time of discontinuous reception, DRX, in a DRX enabled wireless device:

monitoring, for a first period, at least one physical downlink control channel to detect a prede- termined second event;

in response to not detecting the predetermined second event during the first period, halting the monitoring for a second period; and

repeating said monitoring and halting the monitoring until the predetermined second event is de^¬ tected during the monitoring.

A third aspect of the present invention is a computer program which comprises code adapted to cause the following when executed on a data-processing sys- tern:

determining to monitor, for a first period, at least one physical downlink control channel to de^¬ tect a predetermined second event;

in response to not detecting the predetermined second event during the first period, determin^¬ ing to halt the monitoring for a second period; and

determining to repeat said steps of monitor^¬ ing and halting the monitoring until the predetermined second event is detected during the monitoring step.

A fourth aspect of the present invention is an apparatus which comprises at least one processor means, and at least one memory means including com^¬ puter program code means. The at least one memory means and the computer program code means are, with the at least one processor means, for causing the ap^¬ paratus at least to perform:

monitoring, for a first period, at least one physical downlink control channel to detect a prede^¬ termined second event;

in response to not detecting the predeter- mined second event during the first period, halting the monitoring for a second period; and

In an embodiment of the invention, it is de^¬ termined to wait for an offset period after the prede^¬ termined first event before performing the step of monitoring for the first time.

In an embodiment of the invention, the ratio of the first period and the second period is one of: a predetermined fixed ratio and a ratio configured and signaled by higher layer signaling.

In an embodiment of the invention, at least one of the length of the first period and the length of the second period is one of: a predetermined fixed length and a length configured and signaled by higher layer signaling.

In an embodiment of the invention, the length of the offset period is one of: a predetermined fixed length, a length configured and signaled by higher layer signaling, a length indicated implicitly, and a length indicated dynamically.

In an embodiment of the invention, the higher layer signaling comprises radio resource control, RRC, signaling. In an embodiment of the invention, the wire^¬ less device comprises a long term evolution, LTE, enabled wireless device.

In an embodiment of the invention, the wire- less device comprises at least one of a machine type communication, MTC, enabled wireless device and a di^¬ verse data application, DDA, enabled wireless device.

In an embodiment of the invention, predetermined first event comprises sending of a scheduling request and the predetermined second event comprises receipt of an uplink grant responsive to the schedul^¬ ing request.

In an embodiment of the invention, in re^¬ sponse to the predetermined first event a DRX short cycle timer is triggered, and the monitoring and halt^¬ ing of the monitoring are performed in accordance with short DRX cycles until the expiry of the DRX short cy^¬ cle timer.

In an embodiment of the invention, the com- puter program of the third aspect is stored on a com^¬ puter readable medium.

It is to be understood that the aspects and embodiments of the invention described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the invention. A method, an apparatus, or a computer program which is an aspect of the invention may comprise at least one of the embodiments of the invention described above.

The invention allows enhancing the DRX procedure to further decrease the power consumption of the UE thereby extending the UE battery life. The invention further allows distributing scheduling burden uniformly in time domain. The invention further allows fair scheduling opportunities for multiple UEs.

BRIEF DESCRIPTION OF THE DRAWINGS : The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illus^¬ trate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

Figure la illustrates a DRX Cycle according to prior art;

Figure lb illustrates a DRX Cycle according to prior art in which the on-duration lasts the whole scheduling delay;

Figure 2 is a flow diagram illustrating a method according to an embodiment of the present in^¬ vention ;

Figure 3 is a block diagram illustrating an apparatus according to an embodiment of the present invention ;

Figure 4 illustrates the comb-like monitoring pattern of the present invention; and

Figure 5 illustrates another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Reference will now be made in detail to the embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Figure 2 is a flow diagram illustrating a method according to an embodiment of the present in^¬ vention .

The method begins at step 200.

At step 202, a predetermined first event 401 (see Figure 4) triggers active time of discontinuous reception (DRX) in a DRX enabled wireless device. The wireless device may comprise a long term evolution (LTE) enabled wireless device. The wireless device may further comprise at least one of a machine type commu^¬ nication (MTC) enabled wireless device and a diverse data application (DDA) enabled wireless device. The predetermined first event 401 may comprise e.g. send^¬ ing of a scheduling request (SR) from the wireless de^¬ vice .

At an optional step 204, in response to the triggering, it is determined to wait for an offset pe^¬ riod 404 (see Figure 4) after the predetermined first event 401.

At step 206, further in response to the trig- gering, it is determined to monitor, for a first pe^¬ riod tl (405 in Figure 4), at least one physical down^¬ link control channel (PDCCH) to detect a predetermined second event 402 or 403 (see Figure 4) . The predeter^¬ mined second event may comprise e.g. receipt of an up- link grant 402 or 403 responsive to the sent schedul^¬ ing request 401.

At step 208, it is determined whether the predetermined second event 402 or 403 was detected during the first period tl at step 206.

If at step 208 it is determined that the pre^¬ determined second event was not detected during the first period tl, the method proceeds to step 210, at which it is determined to halt the monitoring for a second period t2 (406 in Figure 4) .

After the second period t2, the method re^¬ turns to step 206 and starts the monitoring again. If at step 208 it is determined that the predetermined second event was detected during the first period tl, the method proceeds to step 212 and ends.

In other words, it is determined to repeat the steps of monitoring 206 and halting 210 the moni^¬ toring until the predetermined second event is de^¬ tected during the monitoring step 206.

Figure 3 is a block diagram illustrating an apparatus 300 according to an embodiment of the pre^¬ sent invention. The apparatus 300 comprises at least one processor 302, and at least one memory 304 includ- ing computer program code 306. The at least one memory 304 and the computer program code 306 are configured to, with the at least one processor 302, cause the ap^¬ paratus 300 at least to perform:

The at least one memory 304 and the computer program code 306 may further be configured to, with the at least one processor 302, cause the apparatus 300 to further perform:

waiting for an offset period after the prede^¬ termined first event before performing the step of monitoring for the first time.

The apparatus 300 may comprise the DRX en- abled wireless device, such as a long term evolution (LTE) enabled wireless device, and/or a machine type communication (MTC) enabled wireless device and/or a diverse data application (DDA) enabled wireless device.

The length of the first period tl may be e.g. a predetermined fixed length. Alternatively, it may be a length configured and signaled by higher layer sig^¬ naling, such as radio resource control (RRC) signaling. It may be sent e.g. in DRX-config IE in MAC-MainConfig IE. Similarly, the length of the second period t2 may be e.g. a predetermined fixed length, or a length con^¬ figured and signaled by higher layer signaling, such as RRC signaling, and sent e.g. in DRX-config IE in MAC-MainConfig IE.

The length of the offset period may be e.g. a predetermined fixed length. Alternatively, it may be a length configured and signaled by higher layer signal^¬ ing, such as radio resource control (RRC) signaling. It may be sent e.g. in DRX-config IE in MAC-MainConfig IE. Alternatively, it may be a length indicated im^¬ plicitly by e.g. mapping it to UE ID. Alternatively, it may be a length indicated dynamically in a physical control channel or MAC CE . For example, this offset value may be added in DCI format 1/lA, or a new MAC CE may be designed which is related to the existing MAC sub-header for DRX command.

The ratio of the first period tl and the sec^¬ ond period t2 may be e.g. a predetermined fixed ratio. Alternatively, it may be a ratio configured and sig^¬ naled by higher layer signaling, such as radio resource control (RRC) signaling. It may be sent e.g. in DRX-config IE in MAC-MainConfig IE.

Figure 4 further illustrates the comb-like monitoring pattern of the present invention in time domain. As can be seen, after the first event 401 (such as sending of a scheduling request SR) , first there's the offset period 404. Then, monitoring-on du^¬ rations tl 405, 407, 409, 411, and monitoring-off du^¬ rations t2 406, 408, 410 follow in a comb-like pattern Two second events 402, 403 (such as receipt of an up^¬ link grant responsive to the sent scheduling request 401) are depicted in the example of Figure 4, the lat^¬ ter of which coincides with the monitoring-on duration 411 and will therefore be detected.

Figure 5 illustrates an embodiment in which, in response to the predetermined first event a DRX short cycle timer 503 is triggered, and the monitoring tl and halting t2 of the monitoring are performed in accordance with short DRX cycles until the expiry of the DRX short cycle timer. That is, short DRX cycles 502 may be used e.g. in situations in which a schedul^¬ ing request 501 is sent on the Physical Uplink Control Channel (PUCCH) and is pending. After SR 502 is sent and pending, UE does not monitor the Physical Downlink Control Channel (PDCCH) all the time. Rather, it moni^¬ tors the PDCCH according to the short DRX cycles 502 instead. As shown in Figure 5, drxShortCycleTimer 503 is triggered when SR 501 is sent. Then, DRX cycles 502 are used until drxShortCycleTimer 503 expires. This allows saving power since when drxShortCycleTimer 503 expires and the UE enters long DRX cycle 504, the UE could deactivate its modem.

Compared with prior art, the invention allows enhancing the DRX procedure to further decrease the power consumption of the UE thereby extending the UE battery life. The invention further allows distribut^¬ ing scheduling burden uniformly in time domain. No large scheduling burden is introduced even in the case of large number of DDA and/or MTC UEs.

The invention further allows fair scheduling opportunities for multiple UEs, particularly for a service with specific QoS requirement ( s ) and with a considerable number of UEs.

The invention further allows less maximum UL grant delay for the UE . Even if an enhanced NodeB (eNB) or a base station or other scheduling related network node misses its scheduling chance, the UE does not need to wait for a whole DRX cycle. Since the DRX cy- cle for DDA and MTC UEs may be rather long considering the traffic characteristic, this maximum UL grant de^¬ lay could be very large in prior art. The invention allows shortening this maximum UL grant delay for the UE.

Even though the sending of the scheduling request and receipt of the uplink grant responsive to the sent scheduling request are used above as examples of the first and second event, respectively, it is to be understood that the invention is not limited to these. Instead, for example events related to the fol^¬ lowing active time definitions in Specification 3GPP TS 36.321 could be used:

- an uplink grant for a pending Hybrid Auto- matic Repeat Request (HARQ) retransmission can occur and there is data in the corresponding HARQ buffer; or

- a PDCCH indicating a new transmission addressed to the Cell Radio Network Temporary Identifier (C-RNTI) of the UE has not been received after suc- cessful reception of a Random Access Response for the preamble not selected by the UE .

The exemplary embodiments can include, for example, any suitable laptop computers, Internet ap^¬ pliances, handheld devices, cellular telephones, smart phones, wireless devices, and the like, capable of performing the processes of the exemplary embodiments. The devices and subsystems of the exemplary embodi^¬ ments can communicate with each other using any suitable protocol and can be implemented using one or more programmed computer systems or devices.

Embodiments of the present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. In an example embodiment, the application logic, software or instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "computer-readable me^¬ dium" may be any media or means that can contain, store, communicate, propagate or transport the in- structions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. A computer-readable medium may comprise a computer-readable storage medium that may be any me^¬ dia or means that can contain or store the instruc^¬ tions for use by or in connection with an instruction execution system, apparatus, or device, such as a com- puter. The exemplary embodiments can store information relating to various processes described herein. This information can be stored in one or more memories, such as a hard disk, optical disk, magneto-optical disk, RAM, and the like. One or more databases can store the information used to implement the exemplary embodiments of the present inventions. The databases can be organized using data structures (e.g., records, tables, arrays, fields, graphs, trees, lists, and the like) included in one or more memories or storage de- vices listed herein. The processes described with re^¬ spect to the exemplary embodiments can include appro^¬ priate data structures for storing data collected and/or generated by the processes of the devices and subsystems of the exemplary embodiments in one or more databases.

All or a portion of the exemplary embodiments can be conveniently implemented using one or more gen^¬ eral purpose processors, microprocessors, digital sig^¬ nal processors, micro-controllers, and the like, pro- grammed according to the teachings of the exemplary embodiments of the present inventions, as will be ap^¬ preciated by those skilled in the computer and/or software art(s) . Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as will be ap^¬ preciated by those skilled in the software art. In ad^¬ dition, the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be appre^¬ ciated by those skilled in the electrical art(s) . Thus, the exemplary embodiments are not limited to any spe^¬ cific combination of hardware and/or software.

Stored on any one or on a combination of computer readable media, the exemplary embodiments of the present inventions can include software for control^¬ ling the components of the exemplary embodiments, for driving the components of the exemplary embodiments, for enabling the components of the exemplary embodi^¬ ments to interact with a human user, and the like. Such software can include, but is not limited to, de^¬ vice drivers, firmware, operating systems, development tools, applications software, and the like. Such com^¬ puter readable media further can include the computer program of an embodiment of the present inventions for performing all or a portion (if processing is distributed) of the processing performed in implementing the inventions. Computer code devices of the exemplary em^¬ bodiments of the present inventions can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs) , Java classes and applets, complete executable programs, Common Ob^¬ ject Request Broker Architecture (CORBA) objects, and the like. Moreover, parts of the processing of the exemplary embodiments of the present inventions can be distributed for better performance, reliability, cost, and the like.

As stated above, the components of the exem^¬ plary embodiments can include computer readable medium or memories for holding instructions programmed ac^¬ cording to the teachings of the present inventions and for holding data structures, tables, records, and/or other data described herein. Computer readable medium can include any suitable medium that participates in providing instructions to a processor for execution. Such a medium can take many forms, including but not limited to, non-volatile media, volatile media, trans- mission media, and the like. Non-volatile media can include, for example, optical or magnetic disks, mag^¬ neto-optical disks, and the like. Volatile media can include dynamic memories, and the like. Transmission media can include coaxial cables, copper wire, fiber optics, and the like. Transmission media also can take the form of acoustic, optical, electromagnetic waves, and the like, such as those generated during radio frequency (RF) communications, infrared (IR) data com- munications, and the like. Common forms of computer- readable media can include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other suitable magnetic medium, a CD-ROM, CD±R, CD±RW, DVD, DVD-RAM, DVD1RW, DVD±R, HD DVD, HD DVD-R, HD DVD-RW, HD DVD-RAM, Blu-ray Disc, any other suitable optical medium, punch cards, paper tape, optical mark sheets, any other suitable physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other suitable memory chip or cartridge, a carrier wave or any other suitable medium from which a computer can read.

If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other.

While the present inventions have been de^¬ scribed in connection with a number of exemplary embodiments, and implementations, the present inventions are not so limited, but rather cover various modifica^¬ tions, and equivalent arrangements, which fall within the purview of prospective claims.

Claims

WHAT IS CLAIMED IS :

1. A method, comprising:

in response to not detecting the predeter- mined second event during the first period, determin^¬ ing to halt the monitoring for a second period; and

2. The method according to claim 1, further comprising :

determining to wait for an offset period af^¬ ter the predetermined first event before performing the step of monitoring for the first time.

3. The method according to claim 1 or 2, wherein the ratio of the first period and the second period is one of: a predetermined fixed ratio and a ratio configured and signaled by higher layer signal^¬ ing .

4. The method according to any of claims 1-3, wherein at least one of the length of the first period and the length of the second period is one of: a pre^¬ determined fixed length and a length configured and signaled by higher layer signaling.

5. The method according to any of claims 1-4, wherein the length of the offset period is one of: a predetermined fixed length, a length configured and signaled by higher layer signaling, a length indicated implicitly, and a length indicated dynamically.

6. The method according to any of claims 1-5, wherein the higher layer signaling comprises radio resource control, RRC, signaling.

7. The method according to any of claims 1-6, wherein the wireless device comprises a long term evo^¬ lution, LTE, enabled wireless device.

8. The method according to any of claims 1-7, wherein the wireless device comprises at least one of a machine type communication, MTC, enabled wireless device and a diverse data application, DDA, enabled wireless device.

9. The method according to any of claims 1-8, wherein predetermined first event comprises sending of a scheduling request and the predetermined second event comprises receipt of an uplink grant responsive to the scheduling request.

10. The method according to any of claims 1-9, wherein in response to the predetermined first event a

DRX short cycle timer is triggered, and the steps of monitoring and halting the monitoring are performed in accordance with short DRX cycles until the expiry of the DRX short cycle timer.

11. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

the at least one memory and the computer pro- gram code configured to, with the at least one proces^¬ sor, cause the apparatus at least to perform:

in response to not detecting the predetermined second event during the first period, halting the monitoring for a second period; and repeating said monitoring and halting the monitoring until the predetermined second event is de^¬ tected during the monitoring.

12. The apparatus according to claim 11, wherein the at least one memory and the computer pro^¬ gram code are further configured to, with the at least one processor, cause the apparatus to further perform:

13. The apparatus according to claim 11 or 12, wherein the ratio of the first period and the second period is one of: a predetermined fixed ratio and a ratio configured and signaled by higher layer signal- ing.

14. The apparatus according to any of claims 11-13, wherein at least one of the length of the first period and the length of the second period is one of: a predetermined fixed length and a length configured and signaled by higher layer signaling.

15. The apparatus according to any of claims 11-14, wherein the length of the offset period is one of: a predetermined fixed length, a length configured and signaled by higher layer signaling, a length indi- cated implicitly, and a length indicated dynamically.

16. The apparatus according to any of claims 11-15, wherein the higher layer signaling comprises radio resource control, RRC, signaling.

17. The apparatus according to any of claims 11-16, wherein the wireless device comprises a long term evolution, LTE, enabled wireless device.

18. The apparatus according to any of claims 11-17, wherein the wireless device comprises at least one of a machine type communication, MTC, enabled wireless device and a diverse data application, DDA, enabled wireless device.

19. The apparatus according to any of claims 11-18, wherein predetermined first event comprises sending of a scheduling request and the predetermined second event comprises receipt of an uplink grant re- sponsive to the scheduling request.

20. The apparatus according to any of claims 11-19, wherein in response to the predetermined first event a DRX short cycle timer is triggered, and the monitoring and halting of the monitoring are performed in accordance with short DRX cycles until the expiry of the DRX short cycle timer.

21. A computer program, comprising code adapted to cause the following when executed on a da^¬ ta-processing system:

determining to monitor, for a first period, at least one physical downlink control channel to de- tect a predetermined second event;

determining to repeat said steps of monitor- ing and halting the monitoring until the predetermined second event is detected during the monitoring step.

22. The computer program according to claim 19, wherein the computer program is stored on a computer readable medium.