WO2014098673A1

WO2014098673A1 - Power usage mode selection

Info

Publication number: WO2014098673A1
Application number: PCT/SE2012/051447
Authority: WO
Inventors: Joachim Sachs; Jari Arkko; Anders E Eriksson
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2012-12-20
Filing date: 2012-12-20
Publication date: 2014-06-26

Abstract

It is presented a method for selecting a power usage mode for a wireless communication device. The method is performed in a power mode determiner and comprises the steps of: determining a device requirement for the wireless communication device, the device requirement comprising at least one of a response latency requirement and a battery lifetime requirement; selecting, from a plurality of power usage modes, a power usage mode for the wireless communication device based on the device requirement. A corresponding power mode determiner, network node, computer program, computer program product are also presented.

Description

Power usage mode selection

TECHNICAL FIELD

The invention relates to power management of wireless devices in cellular networks.

BACKGROUND

With the rise of machine-to-machine (M2M) communication in a networked society, increasingly simply devices like sensors/meters communicate with other devices and servers over cellular networks. Communication is typically infrequent with small data volumes. However, there is a general need to enable more power efficient communication of such devices, since many devices need to operate for a long time using only a battery as a power source.

One way to increase power efficiency is increased paging cycles and DRX (Discontinuous Reception) configurations, which mean that devices can remain connected to the network for transmitting or receiving data, while at the same time less activity of the device is required, such as reading paging channels, network system information, or perform connectivity

measurements. However, this optimization exists only for some radio access technologies and only for some network nodes which comply with a particular version of the communication standard.

It would be of great benefit if power efficiency for wireless devices could be improved even more.

SUMMARY

It is an object of embodiments presented herein to provide a new way to select power mode for wireless devices.

According to a first aspect, it is presented a method for selecting a power usage mode for a wireless communication device. The method is performed in a power mode determiner and comprises the steps of: determining a device requirement for the wireless communication device, the device requirement comprising at least one of a response latency requirement and a battery lifetime requirement; and selecting, from a plurality of power usage modes, a power usage mode for the wireless communication device based on the device requirement. By having the ability to switch modes depending on a device requirement, the best mode for the particular situation can be selected. This improves battery lifetime and/or latency compared to only using one power usage mode.

Each power usage mode of the plurality of power usage modes may differ from other power usage modes in a scheme of when the wireless device is in a communicable state and when it is in an incommunicable state.

The step of selecting may comprise: when the device requirement only comprises a response latency requirement, selecting a power usage mode which is predicted to maximise battery lifetime while satisfying the response latency requirement. In this way, the response latency requirement is satisfies while the battery lifetime is maximised.

The step of selecting may comprise: when the device requirement only comprises a battery lifetime requirement, selecting a power usage mode which is predicted to minimise response latency while satisfying the battery lifetime requirement. In this way, the battery lifetime requirement is satisfies while the response latency is maximised.

The step of selecting may comprise: when the device requirement only comprises a battery lifetime requirement and the device requirement is satisfied by an active usage mode, selecting the active usage mode. The active usage mode typically provides the best response latency.

In the step of selecting, the plurality of power usage modes may comprise a device polling mode in which the wireless device is arranged to poll for inbound data at configurable intervals, and a discontinuous reception mode in which the wireless device is arranged to only receive data at configurable intervals. In between intervals, the wireless device may be incommunicable, which reduces power usage.

In the step of selecting, the plurality of power usage modes may comprise a device polling mode in which the wireless device is arranged to poll for inbound data at configurable intervals, a discontinuous reception mode in which the wireless device is arranged to only receive data at configurable intervals and an active usage mode.

In the step of selecting, the plurality of power usage modes may comprise a constrained application protocol server mode. In the step of selecting, the plurality of power usage modes may comprise a constrained application protocol client mode.

The wireless device may be a machine to machine device, configured to mainly communicate with machines.

The method may further comprise the step of: adjusting the device requirement based on a current state of the wireless device.

According to a second aspect, it is presented a power mode determiner arranged to select a power usage mode for a wireless communication device. The power mode determiner comprises: a processor; and a computer program product storing instructions that, when executed by the processor, causes the power determiner to: determine a device requirement for the wireless communication device, the device requirement comprising at least one of a response latency requirement and a battery lifetime requirement; and select, from a plurality of power usage modes, a power usage mode for the wireless communication device based on the device requirement. Each power usage mode of the plurality of power usage modes may differ from other power usage modes in a scheme of when the wireless device is in a communicable state and when it is in an incommunicable state. The instructions to selecting may comprise instructions to: when the device requirement only comprises a response latency requirement, select a power usage mode which is predicted to maximise battery lifetime while satisfying the response latency requirement. The instructions to select may comprise instructions to: when the device requirement only comprises a battery lifetime requirement, select a power usage mode which is predicted to minimise response latency while satisfying the battery lifetime requirement.

The instructions to select may comprise instructions to: when the device requirement only comprises a battery lifetime requirement and the device requirement is satisfied by an active usage mode, select the active usage mode.

The plurality of power usage modes may comprise a device polling mode in which the wireless device is arranged to poll for inbound data at configurable intervals, and a discontinuous reception mode in which the wireless device is arranged to only receive data at configurable intervals.

The plurality of power usage modes may comprise a device polling mode in which the wireless device is arranged to poll for inbound data at configurable intervals, a discontinuous reception mode in which the wireless device is arranged to only receive data at configurable intervals and an active usage mode.

The plurality of power usage modes may comprise a constrained application protocol server mode.

The plurality of power usage modes may comprise a constrained application protocol client mode.

The instructions may comprise instructions to: adjust the device requirement based on a current state of the wireless device. The power determiner maybe arranged to the power usage mode for the wireless device comprising the power mode determiner.

The wireless device may be a machine to machine device, configured to mainly communicate with machines. According to a third aspect, it is presented a network node comprising the power mode determiner according to the second aspect.

According to a fourth aspect, it is presented a computer program for selecting a power usage mode for a wireless communication device. The computer program comprising computer program code which, when run on a power mode determiner, causes the power mode determiner to: determine a device requirement for the wireless communication device, the device requirement comprising at least one of a response latency requirement and a battery lifetime requirement; and select, from a plurality of power usage modes, a power usage mode for the wireless communication device based on the device requirement.

According to a fifth aspect, it is presented a computer program product comprising a computer program according to the fourth 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 and fourth aspects may, where appropriate, be applied to any other of these aspects.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Fig l is a schematic diagram illustrating a cellular network where

embodiments presented herein may be applied,

Fig 2 is a state diagram illustrating various power states for a wireless device of Fig l;

Figs 3A-B are schematic block diagrams illustrating the operation of a mirror proxy device and a proxy device, respectively, Fig 4 is a schematic graph illustrating example relationships between response latency and battery lifetime for various power usage modes;

Figs 5A-C are flow charts illustrating methods for selecting a power usage mode for a wireless communication device;

Fig 6 is a schematic diagram illustrating some components of the power mode determiner used to perform one or more of the methods of Figs 5A-C;

Figs 7A-D are schematic diagrams illustrating various locations where the power mode determiner of Fig 6 can be implemented; and

Fig 8 shows one example of a computer program product comprising computer readable means. DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig l is a schematic diagram illustrating a cellular network 8 where

embodiments presented herein maybe applied. The cellular network 8 comprises a core network 3 and one or more radio base stations 1, here in the form of evolved Node Bs, also known as eNode Bs or eNBs. The radio base stations 1 could also be in the form of Node Bs, BTSs (Base Transceiver Stations) and/ or BSSs (Base Station Subsystems), etc. The radio base stations 1 provide radio connectivity to a plurality of wireless devices 2. The term wireless device is also known as mobile communication terminal, user equipment, mobile terminal, user terminal, user agent, machine-to-machine devices etc., and can be, for example, what today are commonly known as a mobile phone or a tablet/laptop with wireless connectivity or fixed mounted terminal. If the wireless device 2 is a machine to machine (M2M) device, it is configured to mainly communicate with machines. The M2M device does not need to have a user interface, but can optionally be provided with a simple user interface for maintenance functions. The M2M device can e.g. be configured as a sensor and/ or actuator being able to communicate with a network server 6 (see below).

In one embodiment, the protocol used for communication to and from the wireless device is COAP (Constrained Application Protocol), which

resembles HTTP (Hypertext Transfer Protocol) but is targeted at simple communication exchanges among machine devices. COAP supports several communication models.

In a first communication model, the wireless device 2 is both a COAP client and a COAP server. This allows the wireless device 2 to receive data from the network server 6 (the wireless device 2 acts as a COAP server) and the wireless device 2 can also initiate communication (the wireless device 2 acts as a COAP client) with the network server 6. It is to be noted that the term network server 6 denotes the device. The device called network server 6 can assume both a server role and a client role, depending on the circumstances.

In a second communication model, the wireless device is only a COAP client. By comprising only a COAP client, all communication needs to be initiated from the wireless device 2. While this model still allows the wireless device 2 to receive data, this needs to be triggered by the device first contacting some network peer, e.g. a mirror proxy in the network (see 5 of Fig 3A), i.e. by polling. This mode of operation enables the wireless device 2 to control its power consumption, since the device is in control with regard to when and how often it communicates with the network and can e.g. enter an idle mode (also known as an incommunicable state) between to save power.

The cellular network 8 may e.g. comply with any one or a combination of LTE-SAE (Long Term Evolution - System Architecture Evolution), W-CDMA (Wideband Code Division Multiplex), EDGE (Enhanced Data Rates for GSM (Global System for Mobile communication) Evolution), GPRS (General

Packet Radio Service), CDMA2000 (Code Division Multiple Access 2000), or any other current or future wireless network, such as LTE-Advanced, as long as the principles described hereinafter are applicable.

Uplink communication (from the wireless device) and downlink

communication (to the wireless device) between each wireless device 2 and the radio base station 1 occur over a wireless radio interface 4. The quality of the wireless radio interface 4 to each wireless device 2 can vary over time and depending on the position of the wireless device 2, due to effects such as fading, multipath propagation, etc. The radio base stations 1 are also connected to the core network 3 for connectivity to central functions and a wide area network 7, such as the Internet. One or more network servers 6 are also connected to the wide area network 7. In this way, the wireless device 2 can communicate with the one or more network servers 6, initiated by the wireless device 2 and/ or by the server 6. In one embodiment, one or more of the network servers 6 is an M2M server, and the wireless device is an M2M device. The M2M server then collects data from the M2M device and/or controls the actuator of the M2M device.

Fig 2 is a state diagram illustrating various power states for a wireless device of Fig 1 in an example power usage mode of a discontinuous reception mode. Each state uses an average power and involves an average latency for communication. In the diagram of Fig 2, states further to the left involve a greater latency and states further up involve greater average power usage for the wireless device in question. The states are used for Discontinuous Reception (DRX), which is a feature provided in LTE/E-UTRAN (Evolved UMTS Terrestrial Radio Access

Network) for power saving in the wireless device, and thus reduces battery consumption. A DRX cycle consists of an ON period of an ON duration and an OFF period of an OFF duration. No data can be received during the energy saving OFF duration, whereby the device is in an incommunicable state. If data is received in downlink during the ON duration, or if data is sent via uplink, the wireless device will stay awake and start an inactivity timer. When in the ON state, the wireless device is in a communicable state.

There are other examples of discontinuous reception modes, where for determining when going into an OFF state. For example, there is network assisted power saving, which is a solution for UE power optimisation which is being discussed in 3GPP at the time of filing this application.

There are two main states shown in Fig 2, an RRC_IDLE state 116 and an RRC_CONNECTED state 112. In DRX, the RRC_CONNECTED state 112 comprises three individual states: a long DRX state 115, a short DRX state 114 and an active state 113, being the only communicable state for DRX. The active state 113 is above the other states 114, 115, 116 in the diagram of Fig 2, thereby using more power. Hence, the short DRX state 114, the long DRX state and the RRC_IDLE state 116 are known as power saving states, or incommunicable states. In other words, the power saving states 114, 115, 116 all use less power on average than the active state 113.

When in one of the long and short DRX states 114-115, the wireless device does not constantly monitor the PDCCH (Physical Downlink Control

Channel) every TTI (Transmission Time Interval), but only during specific time intervals. During these non-active states 114-115, the wireless device can go into power saving OFF period for part of the time, which decreases power consumption.

Hence, two DRX cycles can be set for each wireless device: a short DRX cycle and a long DRX cycle for the short DRX state 114 and the long DRX state 115, respectively. When the wireless device is in the active state 113, an inactivity timer is started after a downlink packet is received. When the inactivity timer expires, the wireless device switches to the short DRX state 114. In the short DRX state 114, the wireless device can only receive packets during the ON duration.

If a packet is received while in the short DRX state 114, the wireless device returns to the active state 113. Otherwise, a short DRX cycle timer is started. When the short DRX cycle timer expires, the wireless device switches to the long DRX state 115. In the long DRX state, the wireless device can switch to the RRC_IDLE state 116 when an inactivity timer expires. If a data packet is received during the ON Duration of the long DRX state 115, the wireless device returns to the active state 113 directly, without passing via the short DRX state 114. Uplink data packets always trigger the wireless device switching to the active state 113, if not already there. From the RRC_IDLE state 116, a random access procedure is required to get the wireless device back to the RRC_CONNECTED state 112 in general, and the active state 113 in particular.

There are a number of power state parameters that can be configured in the DRX state, such as On Duration, the inactivity timer, the short DRX cycle timer, the long DRX cycle timer, the duration of the short DRX cycle, the duration of the long DRX cycle, retransmission timer, start offset, etc. These power state parameters can be configured for each wireless device separately and thus at least partly define when the wireless device is to be in an active state or one of the power saving states 114, 115, 116. The retransmission timer parameter specifies the maximum number of consecutive PDCCH (Physical Downlink Control Channel) subframes the wireless device should remain active to be ready to receive an incoming retransmission after the first available retransmission time. The start offset parameter is an offset for each wireless device so that, in the time domain, not all wireless device s start receiving at the same time.

Figs 3A-B are schematic block diagrams illustrating the operation of a mirror proxy device and a proxy device, respectively.

In Fig 3A, a mirror proxy 5 is illustrated. The mirror proxy 5 allows two devices, such as the wireless device 2 and the server 6 to both act as clients. If the server 6 is to send a message to the wireless device 2, the server 6 sends the message to the mirror proxy 5. The wireless device 2 then can receive the message from the mirror proxy 5 using either pull or push technology. For example, the wireless device 2 can regularly poll the mirror proxy 5 for messages, implementing a pull technology since it is the wireless device 2 that initiates the communication. Alternatively, the mirror proxy 5 initiates the communication with the wireless device 2, e.g. by contacting a server process (e.g. a COAP server or an HTTP server) of the wireless device 2.

Optionally, the mirror proxy 5 is configured in a bi-directional manner, whereby the wireless device 2 can also initiate communication with the server in a client process, using the mirror proxy 5.

In Fig 3B, a traditional proxy 9 is illustrated. The proxy 9 allows the network server 6 and the wireless device 2 to communicate with each other, even when the recipient of the communication is unavailable (e.g. due to being in idle mode, being an incommunicable state). In this configuration, the network server can assume a client and/or a server role. Analogously, the wireless device can also assume a client and/or server role. For example, if the network server 6 is to send a message to the wireless device 2, the network server 6 sends the message to the proxy 9. As with the mirror proxy 5 illustrated in Fig 3A, the wireless device 2 can then receive the message from the proxy 9 using either pull or push technology. For example, the wireless device 2 can regularly poll the proxy 9 for messages, implementing a pull technology since it is the wireless device 2 that initiates the

communication. Alternatively, the proxy 9 initiates the communication with the wireless device 2, e.g. by contacting a server process of the wireless device 2. Optionally, the proxy 9 is configured in a bi-directional manner, allowing the wireless device 2 to initiate communication with the network server 6 also through the proxy 9.

Fig 4 is a schematic graph illustrating example relationships between response latency and battery lifetime for various power usage modes for the wireless device of Fig 1. In all these graphs, response latency is represented on the vertical axis and battery lifetime is represented on the horizontal axis. Response latency is a measurement of how long it takes for an external entity to get a response from the wireless device. The response latency can be measured as a maximum (worst case) response latency or an average response latency. The battery lifetime is any suitable indicator (real or estimated) of battery lifetime. It is also to be noted that all relationships here are schematic and may or may not be linear relationships as indicated here. Moreover the relationships can be predictions and may, but do not need to, correspond to every possible real situation. In this model, the wireless device in question is always at an operating point which in the diagram is on one of the lines for the three power usage modes.

There are three lines representing three power usage modes: an active usage mode 13, a device polling mode 11, and a discontinuous reception mode 12. Each power usage mode differs from other power usage modes in a scheme of when the wireless device is in an active state and when it is in an

incommunicable state. Within each power usage mode, various parameters could be configured, which defines where on the line of Fig 4 the wireless device is located in terms of response latency and battery lifetime. For example, the discontinuous reception mode 12 could be implemented using DRX, whereby the position on the line for the discontinuous reception mode 12 could be configured using the parameters described with reference to Fig 2 above. The device polling mode 11 works such that the wireless device is configured to, on occasion, poll for any inbound communication. Between the polling, the wireless device is set in an incommunicable state being a low power state (e.g. idle state). In one embodiment, the polling is performed at configurable regular intervals. By increasing the intervals, the battery life is increased, but this also results in greater response latency. The device polling mode 11 is typically not as efficient as the discontinuous reception mode 12. This can be seen in the graph in that for a given response latency, the battery lifetime is smaller for the device polling mode 11 than for the discontinuous reception mode 12. The reason for this can be that the wireless device may have to detach and reattach to the cellular network between each occasion of polling, which requires significant signalling. However, the device polling mode 11 it is a more simple power usage mode and, since it has no end point, can accommodate any given battery lifetime requirements (at the expense of longer response latency). This is particularly useful for e.g. wireless devices being M2M devices with sensors, where long periods of time can pass between reporting measurements. In one embodiment, the device polling mode 11 is implemented by setting the wireless device to implement COAP client only.

The active usage mode 13 represents a mode where the wireless device is not in any particular power saving mode. In other modes, the wireless device is, in the active usage mode, always in an communicable state and never in an incommunicable state. In one embodiment, the active usage mode 13 is implemented by setting the wireless device to implement both a COAP client and a COAP server. In this mode, the wireless device can receive

configuration requests from a proxy (or directly from a network server) in its role as a server. If the proxy or network server decides that the wireless device should go into a device polling mode, e.g. in line with a COAP mirror- proxy configuration, then the proxy or network server sends such a

configuration request to the wireless device. In one embodiment, such a decision is based on the absence of energy saving features in the cellular network nodes in communication with the wireless device. It is to be noted though that it may also be the wireless device itself which determines the network capabilities and can trigger a mirror-proxy configuration in the network.

As explained in more detail below, depending on the device requirements for the wireless device in question, an appropriate power usage mode is selected. There are a few points in the graph of Fig 4 which of are of particular interest. In this example, due to DRX parameters such as a maximum listening interval, there is an end point 15 to the discontinuous reception mode 12. This end point 15 corresponds to a battery lifetime of BL2 and a response latency of RLi. For the same response latency RLi, the device polling mode 11 is at an operating point 16 which gives a lower battery lifetime BLi. Moreover, for the same battery lifetime BL2 of the end point 15, the device polling mode 11 results in higher response latency RL2.

The active usage mode 13 also has an end point 18, which defines a maximum battery lifetime which can be achieved using the active usage mode 13. As shown in the example of Fig 4, it is generally better to have a power usage mode which is more towards the right, since that results in greater battery lifetime for a given response latency. However, there are exceptions. Consider a device requirement with a high battery lifetime BL3 requirement. In this example, the only power usage mode which can meet such a requirement is the device polling mode 11, represented by an operating point 17. While this gives a rather large response latency, this is the only option here to meet the device requirement of the battery lifetime BL3.

Figs 5A-C are flow charts illustrating methods performed in a power mode determiner (see Figs 6 and 7A-D below). The method selects a power usage mode for a wireless communication device and is performed in a power mode determiner.

In a determine device requirement step 50, a device requirement for the wireless communication device is determined. The device requirement comprises at least one of a response latency requirement and a battery lifetime requirement. The device requirement can be received in a message from another network node, such as the network server (6 of Fig 1).

In a select power usage mode step 52, a power usage mode is selected from a plurality of power usage modes for the wireless communication device based on the device requirement. The plurality of usage modes can comprise any two or more of the device polling mode (see 11 of Fig 4) in which the wireless device is arranged to poll for inbound data at configurable intervals, the discontinuous reception mode (see 12 of Fig 4) in which the wireless device is arranged to only receive data at configurable intervals and the active usage mode (see 13 of Fig 4). In one embodiment, the selection of power usage mode is based on relationships between battery lifetime and response latency for various power usage mode, as illustrated in Fig 4 above. In one

embodiment, a power usage mode is selected which is determined to best match the device requirements. In one embodiment, supported power usage modes are first determined, and a power usage mode is selected which is one of the supported power usage modes. In this way, it is ensured that a power usage mode is selected which is supported by the wireless device and attached network.

In some strictly policed networks, the number of attachments / re- connections of a wireless device to a network may be restricted by a network policy. In this case, the wireless device can detect a presence of this policy, either from information provided by the network or by storing the

occurrences of failed re-attachment attempts. If a re-attachment restriction is detected, it is determined if the device polling mode can be used (depending on length of sleeping times) and if not, the device polling mode is categorized as a non-viable alternative. l6

The method illustrated in Fig 5B is similar to the method to the method illustrated in Fig 5A and the steps of Fig 5A will not be described again.

In this embodiment, after the determine device requirements step 50, there is an adjust device requirements step 51. In the adjust device requirements step 51, the device requirement are adjusted based on a current state of the wireless device. For example, an application in the wireless device can request a specific device requirement, and this can be calculated dynamically depending on the needs of the application. Another example is that response latency could be sacrificed for additional battery lifetime when the battery power is lower than a threshold level, indicating that the battery is about to run out.

In Fig 5C, a flow chart is presented which shows details of the select power usage mode step 52 according to one embodiment.

In a conditional only response latency requirement step 53, it is determined whether the device requirement only has a response latency requirement. If this is true, the method continues to a maximise battery lifetime step 54. Otherwise, the method continues to a conditional only battery lifetime requirement step 55.

In the maximise battery lifetime step 54, a power usage mode is selected which is predicted to maximise battery lifetime while satisfying the response latency requirement. After this step, the entire select power usage mode step 52 ends.

In the conditional only battery lifetime requirement step 55, it is determined whether the device requirement only has a battery lifetime requirement. If this is true, the method continues to conditional satisfied by active usage mode step 56. Otherwise, the method continues to a select based on all requirements step 59.

In the conditional satisfied by active usage mode step 56, it is determined whether the device requirement (here being only a battery lifetime requirement) is satisfied by the active usage mode. If this is true, the method continues to a select active usage mode step 58. Otherwise, the method continues to a minimise response latency step 57.

In the minimise response latency step 57, a power usage mode is selected which is predicted to minimise response latency while satisfying the battery lifetime requirement. After this step, the entire select power usage mode step 52 ends.

In the select active usage mode step 58, the active usage mode is selected. After this step, the entire select power usage mode step 52 ends. In the select based on all requirements step 59, a more complex selection is performed, based on both the response latency requirement and the battery lifetime requirement. Optionally, the selection can also be based on the type of traffic the wireless device in question receives and or transmits. After this step, the entire select power usage mode step 52 ends. Fig 6 is a schematic diagram showing some components of the power mode determiner 10 arranged to execute any one or more of the methods of Figs 5A-C. The components shown here can be components used from a host device containing the power mode determiner 10, or components for the power mode determiner 10, separate from the host device. A processor 50 is 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 etc., capable of executing software instructions contained in a computer program 58 stored in a computer program product 54, e.g. in the form of a memory, but not in the form of a signal or any form of electromagnetic wave. The processor 50 can be configured to execute the method described with reference to Figs 5A- C above.

The computer program product 54 is here a memory being any combination of read-and-write memory (RAM) and read-only memory (ROM). The memory also comprises persistent storage, which, for example, can be any l8 single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The processor 50 controls the general operation of the power mode determiner 10.

The power mode determiner 10 further comprises a data memory 59, which is a read-and-write memory. The data memory 59 may 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. Optionally, the computer program product 54 and the data memory 59 can form part of the same memory device. The power mode determiner 10 further comprises an 1/ O interface 57 for communicating with external entities, e.g. to be able receive device requirements and to configure a power usage mode of the wireless device. Other components of the power mode determiner 10 are omitted in order not to obscure the concepts presented herein. Figs 7A-D are schematic diagrams illustrating various locations where the power mode determiner of Fig 6 can be implemented. The power mode determiner 10 selects a power usage mode for a wireless communication device. The power mode determiner 10 can be located in, or in conjunction to, any suitable host device anywhere in the cellular network (see 8 of Fig 1). In Fig 7A, an embodiment is shown where the power mode determiner 10 is located in the radio base station 1.

In Fig 7B, an embodiment is shown where the power mode determiner 10 is located in the core network, 3, such as in or by an SGSN (Serving GPRS (General Packet Radio Service) Support Node), a GGSN (Gateway GPRS Support Node), a Serving Gateway, or a Packet Data Network Gateway.

In Fig 7C, an embodiment is shown where the power mode determiner 10 is located in the wireless device 2. In Fig 7D, an embodiment is shown where the power mode determiner 10 is located distinct from, but in direct communication with, the radio base station 1. Optionally, different power mode determiners 10 or different parts of the power mode determiner 10 can be housed in multiple devices.

Fig 8 shows one example of a computer program product 70 comprising computer readable means. On this computer readable means a computer program 71 can be stored, which computer program can cause a controller to execute a method according to embodiments described herein. In this example, the computer program product is an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. As explained above, the computer program product could also be embodied as a memory of a device, such as the computer program product 54 of Fig 6. While the computer program 71 is here schematically shown as a track on the depicted optical disk, the computer program can be stored in any way which is suitable for the computer program product.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A method for selecting a power usage mode for a wireless

communication device (2), the method being performed in a power mode determiner (10) and comprising the steps of:

determining (50) a device requirement for the wireless communication device, the device requirement comprising at least one of a response latency requirement and a battery lifetime requirement; and

selecting (52), from a plurality of power usage modes, a power usage mode for the wireless communication device (2) based on the device requirement.

2. The method according to claim 1, wherein each power usage mode of the plurality of power usage modes differs from other power usage modes in a scheme of when the wireless device is in a communicable state and when it is in an incommunicable state.

3. The method according to claim 1 or 2, wherein the step of selecting (52) comprises: when the device requirement only comprises a response latency requirement, selecting a power usage mode which is predicted to maximise battery lifetime while satisfying the response latency requirement.

4. The method according to any one of the preceding claims, wherein the step of selecting (52) comprises: when the device requirement only comprises a battery lifetime requirement, selecting a power usage mode which is predicted to minimise response latency while satisfying the battery lifetime requirement.

5. The method according to any one of the preceding claims, wherein the step of selecting (52) comprises: when the device requirement only comprises a battery lifetime requirement and the device requirement is satisfied by an active usage mode (13), selecting the active usage mode (13).

6. The method according to any one of the preceding claims, wherein in the step of selecting (52), the plurality of power usage modes comprises a device polling mode (11) in which the wireless device is arranged to poll for inbound data at configurable intervals, and a discontinuous reception mode (12) in which the wireless device (2) is arranged to only receive data at configurable intervals.

7. The method according to any one of the preceding claims, wherein in the step of selecting (52), the plurality of power usage modes comprises a device polling mode (11) in which the wireless device is arranged to poll for inbound data at configurable intervals, a discontinuous reception mode (12) in which the wireless device (2) is arranged to only receive data at configurable intervals and an active usage mode (13).

8. The method according to any one of the preceding claims, wherein in the step of selecting (52), the plurality of power usage modes comprises a constrained application protocol server mode.

9. The method according to any one of the preceding claims, wherein in the step of selecting (52), the plurality of power usage modes comprises a constrained application protocol client mode.

10. The method according to any one of the preceding claims, wherein the wireless device (2) is a machine to machine device, configured to mainly communicate with machines.

11. The method according to any one of the preceding claims, further comprising the step of:

adjusting (51) the device requirement based on a current state of the wireless device (2).

12. A power mode determiner (10) arranged to select a power usage mode for a wireless communication device (2), the power mode determiner (10) comprising:

a processor (50); and

a computer program product (54) storing instructions that, when executed by the processor, causes the power determiner (10) to: determine a device requirement for the wireless communication device, the device requirement comprising at least one of a response latency requirement and a battery lifetime requirement; and

select, from a plurality of power usage modes, a power usage mode for the wireless communication device based on the device requirement.

13, The power mode determiner (10) according to claim 12, wherein each power usage mode of the plurality of power usage modes differs from other power usage modes in a scheme of when the wireless device is in a

communicable state and when it is in an incommunicable state.

14. The power mode determiner (10) according to claim 12 or 13, wherein the instructions to selecting comprise instructions to: when the device requirement only comprises a response latency requirement, select a power usage mode which is predicted to maximise battery lifetime while satisfying the response latency requirement.

15. The power mode determiner (10) according to any one of claims 12 to

14, wherein the instructions to select comprise instructions to: when the device requirement only comprises a battery lifetime requirement, select a power usage mode which is predicted to minimise response latency while satisfying the battery lifetime requirement.

16. The power mode determiner (10) according to any one of claims 12 to

15, wherein the instructions to select comprise instructions to: when the device requirement only comprises a battery lifetime requirement and the device requirement is satisfied by an active usage mode (13), select the active usage mode (13).

17. The power mode determiner (10) according to any one of claims 12 to

16, wherein the plurality of power usage modes comprises a device polling mode (11) in which the wireless device is arranged to poll for inbound data at configurable intervals, and a discontinuous reception mode (12) in which the wireless device (2) is arranged to only receive data at configurable intervals.

18. The power mode determiner (10) according to any one of claims 12 to 16, wherein the plurality of power usage modes comprises a device polling mode (11) in which the wireless device is arranged to poll for inbound data at configurable intervals, a discontinuous reception mode (12) in which the wireless device (2) is arranged to only receive data at configurable intervals and an active usage mode (13).

19. The power mode determiner (10) according to any one of claims 12 to

18, wherein the plurality of power usage modes comprises a constrained application protocol server mode.

20. The power mode determiner (10) according to any one of claims 12 to

19, wherein the plurality of power usage modes comprises a constrained application protocol client mode.

21. The power mode determiner (10) according to any one of claims 10 to

20, wherein the instructions comprise instructions to: adjust the device requirement based on a current state of the wireless device (2).

22. A wireless device (2) comprising the power mode determiner (10) according to any one of claims 12 to 21, wherein the power determiner is arranged to the power usage mode for the wireless device comprising the power mode determiner.

23. The wireless device (2) according to claim 22, wherein the wireless device (2) is a machine to machine device, configured to mainly communicate with machines.

24. A network node (1) comprising the power mode determiner (10) according to any one of claims 12 to 21.

25. A computer program (71, 58) for selecting a power usage mode for a wireless communication device (2), the computer program comprising computer program code which, when run on a power mode determiner (10), causes the power mode determiner (10) to:

determine a device requirement for the wireless communication device, the device requirement comprising at least one of a response latency requirement and a battery lifetime requirement; and

26. A computer program product (54, 70) comprising a computer program (71, 58) according to claim 25 and a computer readable means on which the computer program (71, 58) is stored.