WO2006037377A1

WO2006037377A1 - User terminal power resource management

Info

Publication number: WO2006037377A1
Application number: PCT/EP2004/052472
Authority: WO
Inventors: Mats SÅGFORS; Johan Torsner
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2004-10-07
Filing date: 2004-10-07
Publication date: 2006-04-13

Abstract

A method of controlling the operating state of a wireless user device, such as a cellular telephone, attached to a radio access network of a cellular communications system. The method comprises signalling an indication of electrical power availability at the device, from the device to the radio access network, and, at the radio access network, controlling the operating state of the wireless device in dependence upon the signalled indication of power availability.

Description

User Terminal Power Resource Management

Field of the Invention

The present invention relates to a power resource management method and apparatus for wireless communication terminals and in particular for wireless communication terminals arranged to communicate via a radio access network of a cellular communications system.

Background to the Invention

Mobile telephony devices or cell phones have developed rapidly over the past decade or so. Early devices tended to have a relatively poor battery life due to both the low power capacity of the batteries and the high consumption demands of the devices and the wireless communication protocols. Despite significant improvements in battery technologies, the battle to maintain high battery life is likely to continue due to the ever increasing sophistication of mobile devices and the greater use to which these devices are put.

A significant drain on battery power continues to result from the need to transmit radio signals to the Radio Access Network (RAN) of the cellular network and to process incoming radio signals. The transmission and reception activity level of the mobile device has a significant impact on the battery power consumption. RANs therefore typically deploy multiple operating states including some kind of dormant state, during which phone battery consumption is low.

Multiple operating states are also defined in order to optimise the use of radio resources amongst users. For example, Wideband Code Division Multiple Access (WCDMΛ), which is the over-the-air protocol implemented in the 3GPP proposals, specifies IDLE and ACTIVE states for a mobile device (in fact there are three ACTIVE states; paging state (URA PCH or CeIl PCH), CeIl FACH state, or Cell_DCH state). In Idle, the mobile does only a very few operations, and the network has limited information of the UE placement. In the IDLE state, it can take some time, e.g. 1 to 3 seconds, for an IDLE UE to obtain a communication link. In the paging state, the UE listens periodically to the paging channel. The paging cycle can be varied with a shorter paging cycle giving, on average, faster access to the mobile. In the Cell_FACH state, the UE listens continuously to a common channel, while in Cell_DCH state the UE has continuous access to a channel, both uplink and downlink. For farther details reference should be made to 3GPP TS 25.331. Switching between operating states is controlled by a Radio Resource Management (RRM) entity located in the Radio Network Controller (RNC) of the RAN.

It will be understood that other wireless communication protocols define similar multi- state operating procedures. For example, GSM define IDLE and TRANSFER MODE states.

A device operating in an ACTIVE state consumes significantly more battery power than when in the IDLE state. Furthermore, the ACTIVE states consume differing amounts of battery power, increasing in the order in which they are listed above. In order to take advantage of the low power consumed in the IDLE state to conserve battery power, the RRM will switch a mobile device from an ACTIVE state to the IDLE state when the device has been inactive for some predefined period of time.

Various systems are known in the prior art for signalling power levels from an electrical device to a network, e.g. US6,072,784, US6,408,172, and US2001031626.

Summary of the Invention

The power saving mechanism implemented by the RRM is effective in conserving battery power. However, it is necessary to consider the disadvantages suffered by a mobile device, or rather its user, when the device is switched from an ACTIVE to the IDLE state. Connection set-up times will be considerably longer in the latter than in the former, resulting in a user perceiving sluggish device performance when the device is switched to the IDLE state. This situation may be unavoidable when the load on the network is high, and a device is switched to the IDLE state after being idle for some period of time. It may also be acceptable when network load is low, and a user device is battery power limited. However, when a device is not battery power limited and network usage is low, there is little or no reason to switch a mobile device to the IDLE state. A similar argument applies to switching between different ACTIVE states.

In order to address this issue, it is proposed here to enable mobile devices to signal their electrical power capabilities to the radio access network, in order to allow the network to make a more informed decision regarding the switching of the mobile devices between operating states.

According to a first aspect of the present invention there is provided a method of controlling the operating state of a wireless user device attached to a radio access network of a cellular communications system, the method comprising: signalling an indication of electrical power availability at the device, from the device to the radio access network; and at the radio access network, controlling the operating state of the wireless device in dependence upon the signalled indication of power availability.

The signalled indication of power availability is one of a number of factors used by the radio access network to determine the state in which a mobile device should be operated. Other factors may include; the period during which a device has remained idle, and network load due to all users.

The radio access network may be a UMTS Radio Access Network (UTRAN), in which case the operating state of the device is one of an IDLE state or an ACTIVE state, where a number of ACTIVE states are available. When the signalled indication indicates that the device is power limited, the network switches the device to the IDLE state, network resources permitting when the device is inactive. When the signalled indication indicates that the device is not power limited, the network maintains the device in an ACTIVE state, network resources permitting, even when the device is inactive. The network may also switch between different ACTIVE states depending upon the signalled indication.

Preferably, said signalling is transported using the Radio Resource Control (RRC) protocol, contained within Information Elements, between the device and a Radio Network Controller (RNC) of the UTRAN. The method may comprise sending this signalling in response to a request sent from the Radio Network Controller, also using the RRC protocol. More preferably, the request specifies the power indications to be sent by the device and, optionally, the frequency with which the indications should be sent or the events which trigger the sending of the indications. At the RNC, state control is performed by a Radio Resource Management entity.

The invention is applicable to other communication standards including, but not limited to, GSM/GPRS/EDGE and CDMA2000.

The method may comprise the step of determining at the wireless device one or more of: the type of power source(s) available, e.g. mains or battery; the current battery power level (fill level) of a battery power source; whether or not the power in a battery is low; the device type, e.g. cell phone or laptop.

The determined information may be signalled to the network directly, or the device may make a further determination of power availability based upon an analysis of the determined factors, and signal the result to the network.

A user may have the option to override any determination made by the device so as to cause the network to disregard device power availability when determining device operating state.

According to a second aspect of the present invention there is provided a method of operating a wireless user device attached to a radio access network of a cellular communications system, the method comprising: determining at the device the electrical power availability at the device; and signalling the determined power availability or an indication thereof to a Radio

Resource Management entity of the radio access network.

In one embodiment of the invention, the radio access network is a UMTS Terrestrial

Radio Access Network (UTRAN), and the wireless device is a WCDMA enabled device. According to a third aspect of the present invention there is provided a method of operating a radio network controller of a radio access network of a cellular communications system, the method comprising: receiving from a wireless user device an indication of the electrical power availability at the device; and controlling the operating state of the wireless device in dependence upon the signalled indication of power availability.

Brief Description of the Drawings

Figure 1 illustrates schematically functional elements of a mobile wireless terminal;

Figure 2 illustrates schematically functional elements of a Radio Network Controller within a UMTS Radio Access Network; and

Figure 3 illustrates signalling associated with a status control mechanism implemented in the Radio Network Controller of Figure 2.

Detailed Description of Certain Embodiments

There is shown in Figure 1 a 3GPP mobile wireless terminal or UE (User Equipment) 1. The UE comprises a detachable battery 2 and a dc power socket 3 which is connected internally to the battery 2 for charging the battery. When a power line 4 is plugged into the dc power socket 3, power from that line may be used directly to power the UE 1. A main processor 5 of the UE 1 performs power management functions including monitoring the level of power stored in the battery 2, and detecting when the power line 3 is connected and charging the battery. Results of these measurements are typically displayed on a screen 6 of the UE to provide a visual indication of battery life/status to a user (e.g. in the form of a battery with a variable fill level). The functionality so far described is present in conventional 3G terminals. The invention here proposes the signalling of terminal power status to the UMTS Radio Access Network (UTRAN) in order to allow the UTRAN to make intelligent decisions regarding the operating status of the terminal based upon the power availability at the terminal.

Figure 2 illustrates schematically a Radio Network Controller (RNC) of the UTRAN. Within the UTRAN a number of functional entities are implemented. These include a Radio Resource Management (RRM) entity responsible for the setup and release of bearers, and for handling state changes as have been discussed above, e.g. a change from an IDLE state to an ACTIVE state. The Radio Resource Control protocol, specified in 3GPP TS.25.331, is the protocol used by the RRM entity to signal relevant information to the UE.

3GPP TS.25.331 specifies a number of different procedures for requesting information from a UE. For example, the UTRAN can request a UE to report the uplink buffer status, so that the UTRΛN (RRM) can decide what transmission resources are needed. It is possible for the UTRAN to specify that the UE must report on the RLC buffer status if it exceeds or is less than some set threshold. TS.25.331 specifies certain Information Element in the RRC protocol for this purpose.

It is proposed here to standardise in the RRC specification 3GPP TS.25.331 Information Elements and associated reporting criteria which allows the UTRAN to specify to the

UE the (event driven) criteria which should trigger the sending of a power status report to the UTRAN. A basic reporting criterion might be: Is the UE connected to a charger

(e.g. mains or car charger)? The Information Elements and reporting criteria may specify that the UE send a response following each change of event, i.e. each time the charger is plugged or unplugged, or only once in response to receipt of a power status request.

The Information Elements and reporting criteria may additionally or alternatively specify that the UE should report the power level remaining in the battery. This could be a percentage fill value, a remaining "talk" time, or an indication that the battery fill level is low (specified by the UE as some predefined percentage fill value).

By way of example, consider a UE attached to a UTRΛN and which has reported to the RRM within the serving RNC that it is attached to a battery charger, indicating that the UE is not battery power limited. In this case, so long as capacity is available on the UTRAN, the RRM will maintain the temporarily inactive UE in an ACTIVE state, and will not attempt to downgrade the UE to the IDLE state. This will ensure that the service provided to the UE, e.g. in terms of access speed, is maintained at a high level. Only if the network is congested, and the UE is not engaged in an ongoing session, will the RRM downgrade the UE to an IDLE state. Of the various ACTIVE states, the RRM may maintain the UE in the Cell_DCH state, i.e. the most responsive and therefore power hungry state, providing that network resources are available. The UE may be switched down successively to the CeIl FACH state, paging state, and IDLE state as network traffic volume increases.

On the other hand, if the UE has reported to the RRM entity that it is battery power limited, e.g. the charger is unplugged and/or the battery fill level is low, the RRM will switch the UE to the IDLE state when the UE is not involved in an ongoing session, regardless of the level of traffic in the UTRAN. This will ensure that the battery power consumption at the UE is minimised.

Figure 3 illustrates the basic signalling associated with this procedure, where a status change is signalled to the UE following a status change decision made by the RRM in the RNC. "ACTIVE ID" indicates that there are a number of possible ACTIVE states which must be identified in the status change signalling.

As well as mobile wireless devices such as cellular phones, the principles outlined here may be applied to other devices which make use of the UTRAN to provided communication links. An example is a laptop computer provided with a 3G wireless "card", e.g. a PCMCIA card. The power available to such a device from its battery may be significant relative to the power consumed in the ACTIVE states. Even when such a device is not connected to a battery charger, it may be appropriate to maintain the device in an ACTIVE state, network resources permitting. The RRC (IEs and reporting criteria) may therefore allow (or request) that the user device signal to it a device type indication. The RRM uses this indication to control the state of the device.

The merits of having an indication of UE electrical power resources can be particularly great for best-effort type shared channels of High Speed Downlink Packet Access (HSDPA) type, where a user can stay on HSDPA for a very long time (assuming that the cell is unloaded). This would give the user a "LAN-quality" access, as there would be no inertia associated with a sudden transmission need. Without the present invention, the user must be switched away from HSDPA during inactive periods, in order to save presumed battery resources. An example of such a use-case could for example be a traveller checking his mailbox in his hotel room using WCDMA as the access technology.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing ftom the scope of the present invention. In one modification, a user may have the option to override the automatic power status reporting of the terminal by selecting one of a "performance mode" and "power-saving mode". A UE set to power-saving would never report high power availability, while a UE set to performance would report high power status irrespectively of the actual status. In another modification, the RRM may vary the paging (DRX) cycle for a UE depending upon the signalled resources of that UE. For example, shorter "listening" periods may be specified for UEs with high power resources, resulting in faster access for these UEs.

Whilst the invention has been described above with reference to WCDMA in 3G, it is equally applicable to other communication standards including GSM/GPRS/EDGE and CDMA2000 and other, as yet undefined, radio access technologies.

Claims

1. A method of controlling the operating state of a wireless user device attached to a radio access network of a cellular communications system, the method comprising: signalling an indication of electrical power availability at the device, from the device to the radio access network; and at the radio access network, controlling the operating state of the wireless device in dependence upon the signalled indication of electrical power availability.

2. A method according to claim 1, wherein the radio access network is a UMTS Radio Access Network (UTRAN), and the operating state of the device is one of an IDLE state or an ACTIVE state.

3. A method according to claim 2, said step of controlling the operating state of the wireless device comprising maintaining the device to the IDLE state, network resources permitting, when the device is inactive and the signalled indication indicates that the device is power limited.

4. A method according to claim 2 or 3, said step of controlling the operating state of the wireless device comprising maintaining the device in an ACTIVE state, network resources permitting, even when the device is inactive, when the signalled indication indicates that the device is not power limited.

5. A method according to any one of claims 2 to 4, there being a plurality of ACTIVE operating states for the wireless device, said step of controlling the operating state of the wireless device comprising switching between different ACTIVE states and the IDLE state in dependence upon the signalled power availability.

6. A method according to any one of claims 2 to 5, wherein said signalling is transported using the Radio Resource Control (RRC) protocol, contained within

Information Elements, between the device and a Radio Network Controller (RNC) of the UTRAN.

7. A method according to any one of claims 2 to 6, state control being performed by a Radio Resource Management entity.

8. A method according to any one of the preceding claims and comprising sending a request for an indication of power availability from the network to the wireless device.

9. A method according to claim 8, wherein said request is sent from the Radio Network Controller using the RRC protocol.

10. A method according to claim 9, said the request specifying the power indications to be sent by the device and, optionally, the frequency with which the indications should be sent or the events which trigger the sending of the indications.

11. A method according to claim 1, the radio access network being one of a GSM/GPRS/EDGE and CDMA2000 network.

12. A method according to any one of the preceding claims wherein said indication of power availability comprises one or more of: the type of power source(s) available, e.g. mains or battery; the current battery power level (fill level) of a battery power source; whether or not the power in a battery is low; the device type, e.g. cell phone or laptop.

13. A method according to claim 1, wherein said indication of power availability corresponds to a user input at the wireless device.

14. A method of operating a wireless user device attached to a radio access network of a cellular communications system, the method comprising: determining at the device the electrical power availability at the device; and signalling the determined power availability or an indication thereof to a Radio

Resource Management entity of the radio access network.

15. A method according to claim 14, the radio access network being a UMTS Terrestrial Radio Access Network (UTRAN), and the wireless device being a WCDMA enabled device.

16. A method of operating a radio network controller of a radio access network of a cellular communications system, the method comprising: receiving from a wireless user device an indication of the electrical power availability at the device; and controlling the operating state of the wireless device in dependence upon the signalled indication of power availability.