Wireless power transfer

Abstract

Examples of the disclosure relate to wireless power transfer wireless power transfer in communication networks. A device is arranged to receive a signal for wireless power transfer from a network node and determine information relating to an energy harvesting rate for the device. The device can then transmit a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device. The device can receive further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device.

Description

[0001] TITLE

[0002] Wireless Power Transfer

[0003] TECHNOLOGICAL FIELD

[0004] Examples of the disclosure relate to wireless power transfer. Some relate to wireless power transfer in communication networks.

[0005] BACKGROUND

[0006] Wireless power transfer can be used to transfer power to energy harvesting devices. The energy harvesting devices can comprise Internet of Things (loT) devices, User Equipments (UEs) or any suitable type of devices. The use of wireless power transferring can help to provide the expected services from the energy harvesting devices by avoiding interruptions due to a shortage of power. Providing a reliable power supply to such devices is therefore beneficial.

[0007] BRIEF SUMMARY

[0008] According to various, but not necessarily all, examples of the disclosure there is provided a device comprising means for: receiving, from a network node, a signal for wireless power transfer; determining information relating to an energy harvesting rate for the device using the received signal for wireless power transfer; transmitting a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device. The information relating to the energy harvesting rate may comprise at least one of: an indication of amount of energy harvested by the device from the received signal for wireless power transfer; an indexed value representing an energy harvesting rate with respect to the transmit data requirements of the device.

[0009] The energy harvesting rates corresponding to respective indices can be received from the network node during configuration.

[0010] The energy harvesting rates corresponding to respective indices can be determined by a communications protocol.

[0011] The information relating to transmit data requirements of the device may comprise information based on buffered data.

[0012] The means may be for determining the energy harvesting rate using information indicating power used for transmitting the signal for wireless power transfer and time for which the signal for wireless power transfer is transmitted.

[0013] The means may be for receiving, from the network node, at least one of: information indicating power used for transmitting the signal for wireless power transfer; and time for which the signal for wireless power transfer is transmitted.

[0014] At least one of the information indicating power used for transmitting the signal for wireless power transfer and the time for which the signal for wireless power transfer is transmitted can be received in the signal for wireless power transfer.

[0015] The at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, can be received in accordance with a decision made by the network node based at least in part on at least one of the information relating to the energy harvesting rate or transmit data requirements of the device. The means may be for, following receipt of a signal indicating that wireless power transfer is suspended, determining at least one alternative node for wireless power transfer.

[0016] The means may be for harvesting energy from the received signal for wireless power transfer.

[0017] The means may be for determining that the device is energy deficient and transmitting an indication to the network node that the device is energy deficient.

[0018] According to various, but not necessarily all, examples of the disclosure there is provided a method comprising: receiving, from a network node, a signal for wireless power transfer; determining information relating to an energy harvesting rate for the device using the received signal for wireless power transfer; transmitting a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device.

[0019] According to various, but not necessarily all, examples of the disclosure there is provided a computer program comprising instructions which, when executed by a device, cause the device to perform at least: receiving, from a network node, a signal for wireless power transfer; determining information relating to an energy harvesting rate for the device using the received signal for wireless power transfer; transmitting a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device. According to various, but not necessarily all, examples of the disclosure there is provided a network node comprising means for: transmitting a signal for wireless power transfer; monitoring response signals from one or more devices wherein the response signals comprise information relating to an energy harvesting rate for the respective devices using the signal for wireless power transfer; determining whether to support transmitting a signal for wireless power transfer based on the response signals; and transmitting at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the determination.

[0020] Determining whether to support transmitting signals for wireless power transfer comprises using information received in one or more response signals to compute one or more parameters of a signal for wireless power transfer that meet energy requirements of the device and comparing the one or more parameters to respective thresholds.

[0021] The one or more parameters of the signal for wireless power transfer may comprise at least one of: time for which signal is transmitted; bandwidth of the signal; transmission power of the signal.

[0022] The thresholds for the one or more parameters may be adjusted based on the number or devices from which the network node has received a response signal.

[0023] The thresholds for the one or more parameters may be adjusted based on availability of one or more alternative power sources for the one or more devices.

[0024] The signal for wireless power transfer may comprise information indicating at least one of: power used for transmitting the signal for wireless power transfer; time for which the signal for wireless power transfer is transmitted.

[0025] The means may be for, if the network node determines to support transmitting the signal for wireless power transfer, determining a set of parameters to use for the signal for wireless power transfer.

[0026] The means may be for, if no response signals are received within a response time period, determining to suspend transmitting signals for wireless power transfer.

[0027] The means may be for, if the network node determines to suspend transmitting the signal for wireless power transfer determining at least one alternative node for providing a wireless power transfer signal.

[0028] The means may be for transmitting an energy threshold to a device, wherein the energy threshold is for determining if the device is energy deficient.

[0029] The means may be for receiving, from a device, an indication that the device is energy deficient and transmitting the signal for wireless power transfer in response to the received indication.

[0030] According to various, but not necessarily all, examples of the disclosure there is provided a method comprising: transmitting a signal for wireless power transfer; monitoring response signals from one or more devices wherein the response signals comprise information relating to an energy harvesting rate for the respective devices using the signal for wireless power transfer; determining whether to support transmitting a signal for wireless power transfer based on the response signals; and transmitting at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the determination. According to various, but not necessarily all, examples of the disclosure there is provided a computer program comprising instructions which, when executed by a network node, cause the network node to perform at least: transmitting a signal for wireless power transfer; monitoring response signals from one or more devices wherein the response signals comprise information relating to an energy harvesting rate for the respective devices using the signal for wireless power transfer; determining whether to support transmitting a signal for wireless power transfer based on the response signals; and transmitting at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the determination.

[0031] While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all of the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all of the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate.

[0032] BRIEF DESCRIPTION

[0033] Some examples will now be described with reference to the accompanying drawings in which:

[0034] FIG. 1 shows an example network;

[0035] FIG. 2 shows an example cell;

[0036] FIG. 3A and 3B show example methods;

[0037] FIG. 4 shows an example method;

[0038] FIG. 5 shows an example method;

[0039] FIG. 6 shows an example method;

[0040] FIG. 7 shows an example controller. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Corresponding reference numerals are used in the figures to designate corresponding features. For clarity, all reference numerals are not necessarily displayed in all figures.

[0041] DEFINITIONS gNB Base Station loT Internet of Things

[0042] O-RAN Open Radio Access Network

[0043] RAN Radio Access Network

[0044] RF Radio Frequency

[0045] SIM Subscriber Identity Module

[0046] UE User Equipment

[0047] DETAILED DESCRIPTION

[0048] Fig. 1 illustrates an example of a network 100 such as a 5G NR network. The network 100 comprises a plurality of different types of nodes 110, 120, 130. The different types of nodes can comprise terminal nodes 110, network nodes 120 and core network nodes 130 and / or any other suitable type of nodes.

[0049] The network nodes 120 can be configured to communicate with the terminal nodes 110. The one or more core network nodes 130 communicate with the network nodes 120. In some examples the one or more core network nodes 130 communicate with the terminal nodes 110.

[0050] The one or more core network nodes 130 can, in some examples, communicate with each other. The one or more network nodes 120 can, in some examples, communicate with each other. The network 100 can be a cellular network comprising a plurality of cells 122. Each of the cells is served by a network node 120. The network node 120 can provide an access node. In this example, the interface between the terminal nodes 110 and a network node 120 defining a cell 122 is a wireless interface 124.

[0051] The network node 120 comprises one or more cellular radio transceivers. The terminal node 110 comprises one or more cellular radio transceivers.

[0052] In the example illustrated the cellular network 100 is a third generation Partnership Project (3GPP) network in which the terminal nodes 110 are user equipment (UE) and the network nodes 120 can be access nodes such as base stations (gNB).

[0053] The term ‘user equipment’ is used to designate mobile equipment comprising a smart card for authentication / encryption etc. such as a Subscriber Identity Module (SIM). In some examples the term ‘user equipment’ is used to designate mobile equipment comprising circuitry embedded as part of the user equipment for authentication / encryption such as software SIM.

[0054] The network node 120 can be a base station. The network node 120 can be any suitable type of base station. A base station is an access node. The network node 120 can be a network entity responsible for radio transmission and reception in one or more cells to or from the UE 110. The network node 120 can be a network element in a Radio Access Network (RAN), an Open-Radio Access Network (O-RAN), a E-UTRA (Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access) network, or any other suitable type of network.

[0055] The core network nodes 130 can be part of a core network. The core network nodes 130 can be configured to manage functions relating to connectivity for the UEs 110. For example, the core network nodes 130 can be configured to manage functions such as connectivity, mobility, authentication, authorization and / or other suitable functions.

[0056] In the example of Fig. 1 the core network node 130 is shown as a single entity. In some examples the core network node 130 could be distributed across a plurality of entities. For example, the core network node 130 could be cloud based or distributed in any other suitable manner.

[0057] The network 100 can be a 4G or 5G network, for example. It can for example be a New Radio (NR) network that uses gNB or eNB as access nodes 120. New Radio is the 3GPP name for 5G technology. In such cases the network nodes 120 can comprise gNodeBs (gNBs) 120 configured to provide user plane and control plane protocol terminations towards the UE 110 and / or to perform any other suitable functions. The gNBs 120 are interconnected with each other by means of an X2 / Xn interface 126. The gNBs 120 are also connected by means of the N2 interface 128 to the core network node 130. Other types of networks and interfaces could be used in other examples. Other types of networks could comprise next generation mobile and communication network, for example, a 6G network.

[0058] Fig. 2 shows an example cell 122 that could be part of the network 100 of Fig. 1 or any other suitable network. The example cell 122 comprises a network node 120, multiple UEs 110 and multiple energy harvesting devices 200.

[0059] The UEs 110 can comprise terminal nodes with a battery or other power source that do not rely on energy harvesting. The UEs 110 can comprise Radio Frequency (RF) components for RF signal generation. The UEs 110 can be configured for RF communication with the network node 120. The UEs 110 can comprise smart phones or any other suitable type of terminal nodes.

[0060] The energy harvesting devices 200 can comprise devices that use wireless power transfer for a power supply. The energy harvesting devices 200 can be configured to use RF signals as a source of energy. The RF signals can be provided by the network node 120 and / or by any other suitable source. The energy harvesting devices 200 could comprise Internet of things (loT) devices or any other suitable type of devices.

[0061] At least some of the energy harvesting devices 200 comprise RF components for RF signal generation. The energy harvesting devices 200 can use RF signals to communicate with the network node 120 and / or one or more UEs 110. The energy harvesting devices 200 can use the same or similar access protocols to the UEs 110 for RF communication.

[0062] In examples of the disclosure the energy harvesting devices 200 comprise energy storage. If the energy stored in the energy storage falls below a threshold then the energy harvesting device 200 can be determined to be energy deficient. The threshold at which an energy harvesting device 200 is determined to be energy deficient can be based on transmission requirements of the energy harvesting device and / or any other suitable factor such as link budget considerations for the device.

[0063] If the energy harvesting device 200 is determined to be deficient then the energy harvesting device 200 can request wireless power transfer from the network node 120 or other suitable network operated power source. For instance, an energy harvesting device 200 that comprises RF components can transmit one or more RF signals to the network node 120.

[0064] In examples of the disclosure the network node 120 can be the main candidate to provide wireless power transfer for the energy harvesting devices 200. However, in some use cases it might not be efficient to use the network node due to the higher link budget between the network node 120 and the respective energy harvesting devices 200 because the amount of RF energy harvested degrades quickly with increasing distance between the network node 120 and the energy harvesting devices 200. In the example of Fig. 2 some of the energy harvesting devices 200 are close to the network node 120 but some of the energy harvesting devices 200 are at the edge of the cell 122. The energy harvesting devices 200 that are close to the network node 120 could be well served for wireless power transfer by the network node 120. However, the energy harvesting devices 200 that are at the edge of the cell 122 might not be well served due to the distance between the network node 120 and the energy harvesting devices 200.

[0065] Increasing power used by the network node 120 to provide wireless power transfer to the energy harvesting devices 200 can increase the energy harvested but would also create interference for the UEs 110 within the cell 122 and / or interference to UEs in other cells which can negatively affect the transmissions and may not be feasible for the network node 120.

[0066] Examples of the disclosure address the problem of identifying and deciding if energy harvesting devices 200 can be served for wireless power transfer by the network node 120.

[0067] Fig. 3A and 3B show example methods that can be used in examples of the disclosure. Fig.3A shows an example method that can be implemented using a device such as an energy harvesting device 200. Fig. 3B shows an example method that can be implemented by a network node 120 or any other suitable entity. The network node 120 can be configured for wireless power transfer.

[0068] In the example of Fig. 3A the method comprises, at block 300, receiving, from a network node 120, a signal or message for wireless power transfer. The energy harvesting device 200 can harvest energy from the received signal for wireless power transfer.

[0069] The signal for wireless power transfer can be received in response to a request for wireless power transfer made by the energy harvesting device 200 and / or following any other suitable trigger event.

[0070] In some examples the energy harvesting device 200 can determine that the energy harvesting device 200 is energy deficient. The energy harvesting device 200 can transmit an indication to the network node 120 that the energy harvesting device 200 is energy deficient. The signal for wireless power transfer can be received in response to the indication that the energy harvesting device 200 is energy deficient.

[0071] At block 302 the method comprises determining information relating to an energy harvesting rate for the energy harvesting device 200 using the received signal for wireless power transfer. The information relating to an energy harvesting rate can be an estimate of the energy harvesting rate or any parameter reflecting an effect of energy harvesting rate. In some examples the information relating to an energy harvesting rate can comprise information that enables a different entity to determine the estimate of the energy harvesting rate and / or any other suitable information.

[0072] In some examples the information relating to the energy harvesting rate comprises an indication of amount of energy harvested by the energy harvesting device 200 from the received signal for wireless power transfer. In some examples the information relating to the energy harvesting rate can comprise an indexed value representing an energy harvesting rate with respect to the transmit data requirements of the device. The respective energy harvesting rates and transmit data requirements corresponding to the respective indices can be determined by a communications protocol or received from the network node 120 during configuration or determined in any other suitable manner.

[0073] Any suitable means or processes can be used to determine the energy harvesting rate. For example, the energy harvesting rate can be determined using information indicating power used for transmitting the signal for wireless power transfer and time for which the signal for wireless power transfer is transmitted for a fixed bandwidth. In some examples the energy harvesting device 200 can receive, from the network node 120, information indicating power used for transmitting the signal for wireless power transfer and time for which the signal for wireless power transfer is transmitted, and / or any other suitable information that can be used to determine an energy harvesting rate. In some examples this information can be received in the signal for wireless power transfer. In some examples this information can be received in a different signal or message.

[0074] At block 304 the method comprises transmitting a response signal or message comprising at least one of, the information relating to the energy harvesting rate, or transmit data requirements of the energy harvesting device 200, or any other suitable information. The transmit data requirements, or other suitable information, can provide an indication of the energy that the energy harvesting device 200 will need to collect from the wireless power transfer signal. The information relating to transmit data requirements of the energy harvesting device 200 can comprise information based on buffered data and / or any other suitable information.

[0075] At block 306 the method comprises one of receiving further signals for wireless power transfer or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device and / or any other suitable information. The further signals for wireless power transfer or the signal indicating that wireless power transfer is suspended can be received in accordance with a decision made by the network node 120 based at least in part on at least one of the information relating to the energy harvesting rate or transmit data requirements of the device.

[0076] If a decision is made by the network node 120 to support the wireless power transfer then the energy harvesting device 200 can receive further wireless power transfer signals from the network node 120 and can use these to harvest energy. In some examples one or more parameters of the wireless power transfer signals can be determined to optimize, or substantially optimize, wireless power transfer for the energy harvesting device 200.

[0077] If a decision is made by the network node 120 not to support the wireless power transfer then the energy harvesting device 200 does not receive further wireless power transfer signals from the network node 120 and does not harvest any more energy from the network node 120. In such examples the energy harvesting device 200 can receive one or more signals that indicate that wireless power transfer is suspended. Following receipt of a signal indicating that wireless power transfer is suspended, energy harvesting device 200 can determine at least one alternative node for wireless power transfer. The alternative nodes for wireless power transfer could be one or more UEs 110 and / or any other suitable nodes.

[0078] The method of Fig. 3B can be performed by a network node 120 that is configured to provide wireless power transfer. The network node 120 can be configured to provide wireless power transfer for the energy harvesting device 200 that performs the method of Fig. 3A. In the example of Fig. 3B the method comprises, at block 310, transmitting a signal for wireless power transfer.

[0079] If an energy harvesting device 200 determines that it is energy deficient then it can transmit a signal indicating this to the network node 120. Therefore, the network node can receive an indication that the energy harvesting device 200 is energy deficient. The network node 120 can transmit the signal for wireless power transfer in response to the received indication. Other trigger events can be used to cause the transmission of the signal for wireless power transfer.

[0080] In some examples the signal for wireless power transfer can comprise information indicating at least one of: power used for transmitting the signal for wireless power transfer, time for which the signal for wireless power transfer is transmitted, and / or any other suitable information. In other examples this information could be provided in a different signal.

[0081] At block 312 the method comprises monitoring response signals from one or more devices such as energy harvesting devices 200. The response signals comprise information relating to an energy harvesting rate for the respective devices using the signal for wireless power transfer. In some examples the response signals can comprise information relating to transmit data requirements of the energy harvesting devices 200.

[0082] At block 314 the method comprises determining whether to support transmitting a signal for wireless power transfer based on the response signals. Determining whether to support transmitting a signal for wireless power transfer can comprise deciding if the energy harvesting devices 200 can be efficiently served for the wireless power transfer by the network node 120 or if wireless power transfer between the network node 120 and the energy harvesting device 200 should be suspended. In some examples it can be determined if the wireless power transfer between the network node 120 and the energy harvesting device 200 would use an excess of power which could cause interference for UEs 110 and / or other devices in the area around the network node 120. In some examples, it can be determined if the wireless power transfer between the network node 120 and the energy harvesting device 200 would use an excess of radio frequency resources which would increase the network overhead and also cause interference for UEs 110.

[0083] In some examples determining whether to support transmitting signals for wireless power transfer can comprise using information received in one or more response signals to compute one or more parameters of a signal for wireless power transfer that meet energy requirements of the energy harvesting device 200 and comparing the one or more parameters to respective thresholds. For instance, if the response signals indicate the transmission requirements of the energy harvesting device 200 and / or the energy harvesting rate of the energy harvesting device 200 then this can be used to determine the power needed for a wireless power transfer signal and / or the time for which such a signal would need to be transmitted. These parameters can then be compared to thresholds or other information to determine if signals using these parameters would cause interference, or be otherwise problematic, for the network node 120 and / or for UEs 110 within the cell 122 of the network node 120.

[0084] The parameters that are used to determine whether to support transmitting signals for wireless power transfer can comprise at least one of: time for which the signal for wireless power transfer is transmitted, bandwidth of the signal for wireless power transfer, transmission power of the signal for wireless power transfer, and / or any other suitable parameters.

[0085] The thresholds for the one or more parameters can be adjusted based on the number of energy harvesting devices 200 from which the network node 120 has received a response signal. For instance, if there is only a single energy harvesting device 200 that requires wireless power transfer the threshold could be set lower so as to reduce interference for the UEs 110 in neighboring cells. If there are multiple energy harvesting devices 200 that require wireless power transfer then the threshold could be set higher so as to reduce the number of energy harvesting devices 200 that are energy deficient.

[0086] In some examples the thresholds for the one or more parameters can be adjusted based on availability of one or more alternative power sources for the one or more energy harvesting devices 200. For instance, in some cases nearby UEs 110 could be used to provide signals for the wireless power transfer to the energy harvesting devices 200. A network node 120 could be aware of the locations of suitable UEs 110 with the cell 122. If such alternative power sources are available then the thresholds for the signals for wireless power transfer signals for the network node 120 could be reduced because it might be more efficient to use the alternative power sources for wireless power transfer.

[0087] At block 316 the network node either transmits further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the determination made at block 314.

[0088] If it is determined that the network node 120 is to support transmitting the signal for wireless power transfer, then a set of parameters to use for the signal for wireless power transfer can be determined. These parameters can be optimized, or substantially optimized, for power transfer with reduced disruption to the nearby UEs 110.

[0089] If it is determined that the network node 120 is to suspend transmitting the signal for wireless power transfer then, the network node 120 can transmit one or more signals indicating that wireless power transfer is suspended. In some examples, the network node 120 can determine at least one alternative node for providing a wireless power transfer signal. The alternative nodes can comprise one or more UEs 110 that might be located close to the energy harvesting device 200, or any other suitable nodes.

[0090] In some examples the network node 120 might not receive any response signals within a response time period. This could be the case if the link is so poor that the response signals from the energy harvesting devices 120 do not reach the network node 120. In such cases the network node 120 can determine to suspend transmitting signals for wireless power transfer.

[0091] In some examples the network node 120 can be configured to transmit an energy threshold to the energy harvesting devices 200. The energy threshold is for determining if the device is energy deficient. This information can be transmitted before the signal for wireless power transfer is transmitted and can be used by the energy harvesting device to determine if it is energy deficient. This information can be transmitted to an energy harvesting device 200 during configuration or at any other suitable time.

[0092] Fig. 4 shows an example method that can be used in examples of the disclosure.

[0093] The method comprises at block 400 the energy harvesting device 200 registering with the network node 120. In the example of Fig. 4 one energy harvesting device 200 is shown. In examples of the disclosure there could be multiple energy harvesting devices 200 that register with the network node 120.

[0094] The network node can also find information about any UEs 110 within the vicinity of the energy harvesting device 200. The network node 120 is the default power source for the energy harvesting device 200 however, one or more of the UEs 110 could potentially provide an alternative power source. The presence of the one or more UEs 110 can be taken into account by the network node 120 when deciding whether to support wireless power transfer. The network node 120 need not start any communication with the one or more other UEs 110.

[0095] In some examples the network node 120 can determine an energy threshold that is to be used by the energy harvesting device 200. The energy threshold provides an indication of an amount of energy that is to be stored in an energy harvesting device 200. If the stored energy falls below the defined threshold then the energy harvesting device 200 can be determined to be energy deficient. The energy thresholds can be set by the network node 120 or any other suitable entity. The energy thresholds can be determined by the transmission requirements of the energy harvesting device 200, availability of alternative power sources, expected energy harvesting rates and / or any other suitable factors.

[0096] In some examples the energy threshold could be set by the energy harvesting device 200 rather than the network node 120. This can enable energy harvesting devices 200 that have a higher energy consumption or a higher energy storage capacity to use a different energy threshold to energy harvesting devices 200 that have a lower energy consumption or a lower energy storage capacity.

[0097] At block 402 the energy harvesting device 200 performs an energy evaluation. The energy harvesting device 200 performs the energy evaluation to determine if the energy harvesting device 200 is energy deficient.

[0098] Any suitable information can be used to determine if the energy harvesting device 200 is energy deficient. This information can comprise link budget considerations, transmission requirements, the energy threshold set by the network node 120, and / or any other suitable information.

[0099] In some examples the energy harvesting device 200 can compare the energy stored within storage means, such as a battery, of the energy harvesting device 200 with the energy threshold. If the stored energy is above the energy threshold then the energy harvesting device 200 is determined not to be energy deficient. If the stored energy is below the energy threshold then the energy harvesting device 200 is determined to be energy deficient.

[0100] If the energy harvesting device 200 is not energy deficient then the energy harvesting device 200 does not need to request wireless power transfer. However, if the energy harvesting device 200 is energy deficient then, at block 404, the energy harvesting device 200 transmits a request for wireless power transfer to the network node 120. The request can indicate that the energy harvesting device 200 is energy deficient.

[0101] In response to the request for wireless power transfer the network node 120 transmits, at block 406, a signal for wireless power transfer. The signal for wireless power transfer can be used to enable the network node to evaluate whether to support wireless power transfer. The signal for wireless power transfer can be used to determine parameters of signals for wireless power transfer that would be needed to provide adequate charging for the energy harvesting device 200. The parameters that are assessed can comprise power and duration of transmission of the signal for wireless power transfer. These parameters can be affected by the link budget between the network nodes 120 and the energy harvesting device 200. The signal for wireless power transfer can be sent with a fixed power and for a defined duration and a fixed bandwidth. Information indicative of the power and duration used can be transmitted to the energy harvesting device 200. This information can be comprised in the signal for wireless power transfer or could be transmitted in one or more different signals.

[0102] At block 408 the energy harvesting device 200 performs energy harvesting using the signal for wireless power transfer that is received from the network node 120. The energy harvesting lasts for a time period T which is equal to the duration of the transmission of the signal for wireless power transfer.

[0103] The energy harvesting device 200 can also determine information relating to an energy harvesting rate for the energy harvesting device 200 using the received signal for wireless power transfer. The energy harvesting rate indicates how much energy was harvested from the received signal for wireless power transfer over the time period T (not considering bandwidth for simplicity). The energy harvesting rate can be estimated using equation (1)

[0104] Where P is the power used for transmission of the signal for wireless power transfer and T is the time period for which the signal for wireless power transfer was transmitted.

[0105] In some cases the link budget, which may comprise a coupling loss or a path loss between the network node 120 and the energy harvesting device 200, might not be known. In such cases a mapping between the transmitted power and the energy harvested could be used to approximate an energy harvesting rate.

[0106] The energy harvesting rate can be different for different energy harvesting devices 200. For instance, in the example of Fig. 2 different energy harvesting devices 200 could have different energy harvesting rates even though they all receive the signal for wireless power transfer from the same network node 120. The energy harvesting rate can be affected by energy harvesting circuitry and / or other types of circuitry within the energy harvesting device 200, the link budget between the network node and the energy harvesting device 200 and / or any other suitable factors.

[0107] The energy harvesting device 200 can generate an energy report based on the information relating to an energy harvesting rate. In some examples the energy harvesting device 200 can calculate the energy harvesting rate information and include this in the energy report. In other examples the energy harvesting device 200 can determine values that can be used to calculate an energy harvesting rate and can then include these in the energy report. These values could then be used by the network node, or other suitable entity, to calculate an energy harvesting rate. In this case the values could be a measurement of energy harvested within the time period T, or any other suitable values.

[0108] The energy report can also comprise any other information that can be used by the network node 120 to determine whether to support wireless power transfer. In some examples the energy report can comprise information indicating transmit data requirements of the energy harvesting device 200. The transmit data requirements can give an indication of the energy requirements of the energy harvesting device 200.

[0109] At block 410 the energy harvesting device 200 transmits the energy harvesting report to the network node 120. This signal provides a response signal that comprises information relating to the energy harvesting rate of the energy harvesting device 200 and / or the transmit data requirements of the energy harvesting device 200.

[0110] The network node 120 monitors for response signals from the energy harvesting device 200.

[0111] In some examples the response signals transmitted by the energy harvesting devices 200 might not be received by the network node 120. This is shown at block 412 in Fig. 4. This scenario could arise if the link condition between the energy harvesting device 200 and the network node 120 is poor. In such cases the network node 120 would perform the monitoring for a given time period. The time period can be configured based on a time required to receive a backscattering response from a tag after sending an illuminator signal. An additional delay could be added to the time period for monitoring. If no response is received then this can be an indication that the energy harvesting device 200 is not able to harvest sufficient energy and report back to the network node 120. Therefore, if no response is received the network node 120 can determine to suspend transmission of the signal for wireless power transfer. This decision can be made without estimating or calculating the actual energy harvesting rate.

[0112] If a response signal is received by the network node 120 (as shown at block 410) then at block 414 the network node makes a decision whether to continue to support wireless power transfer. The information that is received in the response signals can be used to make this decision. For example, the network node can use the energy harvesting rate to determine parameters of a signal for wireless power transfer that would be needed for the energy harvesting device 200. These parameters could comprise transmission power, transmission duration and / or any other suitable parameters. These parameters could be compared to thresholds to determine if the signal for wireless power transfer would be too disruptive for UEs 110 or other devices in the cell 122. If it is determined that the signal for wireless power transfer would not be too disruptive then the network node 120 can transmit further signals for wireless power transfer.

[0113] If it is determined that the signal for wireless power transfer would be too disruptive then the network node 120 suspend transmission of signals for wireless power transfer. In some examples the network node 120 can, at block 416, identify one or more alternative power nodes that can provide wireless power transfer for the energy harvesting device 200. These alternative power sources could comprise UEs 110 that are in the vicinity of the energy harvesting device 200.

[0114] If it is determined that the network node 120 is to suspend wireless power transfer then, at block 418, the network node 120 transmits a signal indicating that wireless power transfer is suspended. In some examples the network node 120 could transmit a NACK (Negative Acknowledgement) signal. This could be transmitted if the network node 120 does not receive the energy harvesting report for example. In some examples the signal indicating that wireless power transfer is suspended or the NACK signal may be transmitted at a predetermined time and in a predetermined frequency resource that the energy harvesting device 200 is monitoring. In these examples, if the energy harvesting device 200 does not receive the signal indicating that wireless power transfer is suspended or the NACK signal then it may determine that wireless power transfer is not suspended.

[0115] When the energy harvesting device 200 receives the signal indicating that wireless power transfer is suspended the energy harvesting device 200 can, at block 420, search for alternative nodes to provide wireless power transfer.

[0116] Fig. 5 shows another example method that can be used in examples of the disclosure. The method can be the same as that shown in Fig. 1 for blocks 400 to 408 and corresponding reference numerals are used for these blocks.

[0117] The example method of Fig. 5 comprises an additional block (block 500) after the energy harvesting at block 408. At block 500 the energy harvesting device 200 evaluates the energy that has been harvested. The energy harvesting device 200 can evaluate whether the energy harvested is sufficient to meet the requirements, such as the transmission requirements, of the energy harvesting device 200. The energy harvesting report that is transmitted at block 410 can then be based on this evaluation.

[0118] In some examples the energy harvesting report could comprise an indexed value. This can be a compact way of transmitting information to the network node 120. The respective indices could represent energy harvesting rates with respect to transmit data requirements.

[0119] Example indices could comprise:

[0120] Index (0) -> harvested energy is too low at power P for time T, network node 120 may need very high-power P to support direct wireless power transfer.

[0121] Index (1) -> harvested energy is low but network node 120 needs to increase power P by delta 1 or / and time T by delta 2 to meet requirements, where delta 1 and delta 2 are fixed and known by network node 120.

[0122] Index (2)-> harvested energy is good, network node 120 can use power P and time T. Other indices could be used in other examples.

[0123] The energy harvesting rates that are represented by the indices need to be known by both the network node 120 and the energy harvesting device 200. In some cases these could be determined by a communications protocol. In some cases the energy harvesting rates that are represented by the indices could be sent from the network node 120 to the energy harvesting device 200 during configuration or at any other suitable time.

[0124] At block 410 the energy harvesting device 200 transmits the energy harvesting report comprising the indexed information to the network node 120. This signal provides a response signal that comprises information relating to the energy harvesting rate of the energy harvesting device 200 and / or the transmit data requirements of the energy harvesting device 200.

[0125] When the network node 120 receives the response signal the network node 120 uses the indexed information to make a decision whether to continue to support wireless power transfer.

[0126] Using the example indices given above, if the index 2 is used then the network node 120 can decide to support wireless power transfer. If the index 0 is used then the network node 120 can decide not to support wireless power transfer. If index 1 is used then the network node can compare the increases in power and / or time to a threshold parameter to decide whether to continue to support wireless power transfer.

[0127] Blocks 412 to 420 can be as shown in Fig. 4.

[0128] Fig. 6 shows an example method that can be used by a network node 120 when determining whether to support wireless power transfer.

[0129] At block 600 the network node 120 receives an energy harvesting report from one or more energy harvesting devices 200. The energy harvesting report can comprise information relating to the energy harvesting rate and / or transmit data requirements of the energy harvesting devices 200. The energy harvesting report can comprise an energy harvesting rate or information that can be used to calculate and energy harvesting rate as shown in Fig. 4. In some examples the energy harvesting report can comprise indexed values as shown in Fig. 5. Other types of energy report could be used in other examples.

[0130] At block 602 the network node 120 starts the decision making process.

[0131] At block 604 the network node 120 computes the parameters that are needed to satisfy the transmission data requirements or other energy requirements of the one or more energy harvesting devices 200.

[0132] The parameters that are determined can comprise time for which the signal for wireless power transfer is transmitted, bandwidth of the signal for wireless power transfer, transmission power of the signal for wireless power transfer. These parameters could be determined using equation (1) given above or using any other suitable method.

[0133] In some examples the parameters could be determined from the energy harvesting report. For instance, if the energy harvesting report comprises indexed information that represents an increase in power and / or time, then this can be used to calculate the parameters needed for the signal for wireless power transfer.

[0134] In some examples parameters that are optimized, or substantially optimized for wireless power transfer can be computed.

[0135] At block 606 the network node 120 determines if the computed parameters satisfy criteria. For example, the network node 120 can determine if the computed parameters satisfy a given threshold.

[0136] As an example, at block 604 a time T can be computed. At block 606 this computed time T can be compared to a threshold time. If the time T is equal to or below the threshold then it is determined that the computed parameters satisfy the threshold. If the time T is above the threshold then it is determined that the computed parameters do not satisfy the threshold. Similarly if a power P or bandwidth BW is computed this can be compared to other relevant thresholds. The thresholds that are used can be determined by environmental factors of the energy harvesting device 200 and / or any other suitable factors. For instance, if the network nodes that there are alternative power sources available to the energy harvesting device 200 then this can be taken into account by adjusting the thresholds. In such cases the thresholds for determining not to support wireless power transfer could be lower than for cases where there is no alternative power source.

[0137] In some cases the number of energy harvesting devices 200 that are requesting wireless power transfer can also be taken into account by adjusting the thresholds. If there is only one energy harvesting device 200 or only a small number of energy harvesting devices 200 then the thresholds could be set lower so as to reduce disruption to UEs 110 or other nearby device. Conversely if there are multiple energy harvesting devices 200 then the thresholds could be set higher so as to reduce the number of energy deficient devices.

[0138] If, at block 606, it is determined that the computed parameters satisfy the thresholds then the method proceeds to block 608 and the network node 120 can start wireless power transfer. The network node 120 can use the parameters computed at block 604 for the signal for wireless power transfer.

[0139] If, at block 606, it is determined that the computed parameters do not satisfy the thresholds then the method proceeds to block 610 and the network node 120 can suspend wireless power transfer. In this case no signal for wireless power transfer would be transmitted by the network node 120.

[0140] In some cases the network node can find one or more alternative power sources for the energy harvesting device 200 and wireless power transfer with these alternative sources could be initiated. In some cases the network node 120 can transmit a NACK signal to the energy harvesting device 200 or any other suitable signal that can indicate the wireless power transfer is suspended.

[0141] At block 612 the process is completed. Examples of the disclosure therefore enable a network node to make a decision as to whether to support wireless power transfer. This can ensure that devices that require wireless power transfer are adequately supported while reducing the disruption to other devices or UEs 110 in the cell 122.

[0142] Fig. 7 illustrates an example controller 700. The controller 700 could be provided within an entity such as a network node for providing wireless power transfer signals or a device such as an energy harvesting device. Implementation of the controller 700 may be as controller circuitry. The controller 700 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

[0143] As illustrated in Fig. 7 the controller 700 can be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 706 in a general-purpose or special-purpose processor 702 that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor 702.

[0144] The processor 702 is configured to read from and write to the memory 704. The processor 702 may also comprise an output interface via which data and / or commands are output by the processor 702 and an input interface via which data and / or commands are input to the processor 702.

[0145] The memory 704 stores a computer program 706 comprising computer program instructions (computer program code) that controls the operation of the device or network node when loaded into the processor 702. The computer program instructions, of the computer program 706, provide the logic and routines that enables the device or the network node to perform the methods illustrated in the Figs. The processor 702 by reading the memory 704 is able to load and execute the computer program 706.

[0146] In some examples where the controller 700 is provided within a device 200 such as an energy harvesting device the controller 700 therefore comprises: at least one processor 702; and at least one memory 704 storing instructions that, when executed by the at least one processor 702, cause the device to perform at least: receiving 300, from a network node 120, a signal for wireless power transfer; determining 302 information relating to an energy harvesting rate for the device 200 using the received signal for wireless power transfer; transmitting 304 a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving 306 at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device 200.

[0147] In some examples where the controller 700 is provided within a network node 120 such as a gNB the controller 700 therefore comprises: at least one processor 702; and at least one memory 704 storing instructions that, when executed by the at least one processor 702, cause the network node 120 to perform at least: transmitting 310 a signal for wireless power transfer; monitoring 312 response signals from one or more devices wherein the response signals comprise information relating to an energy harvesting rate for the respective devices using the signal for wireless power transfer; determining 314 whether to support transmitting a signal for wireless power transfer based on the response signals; and transmitting 316 at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the determination.

[0148] The computer program 706 may arrive at the device or network node 120 via any suitable delivery mechanism 708. The delivery mechanism 708 may be, for example, a machine-readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 706. The delivery mechanism may be a signal configured to reliably transfer the computer program 706. The device or network node 120 may propagate or transmit the computer program 706 as a computer data signal. The computer program 706 can comprise computer program instructions for causing a device to perform at least the following or for performing at least the following: receiving 300, from a network node 120, a signal for wireless power transfer; determining 302 information relating to an energy harvesting rate for the device 200 using the received signal for wireless power transfer; transmitting 304 a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving 306 at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device 200.

[0149] The computer program 706 can comprise computer program instructions for causing a network node 120 to perform at least the following or for performing at least the following: transmitting 310 a signal for wireless power transfer; monitoring 312 response signals from one or more devices wherein the response signals comprise information relating to an energy harvesting rate for the respective devices using the signal for wireless power transfer; determining 314 whether to support transmitting a signal for wireless power transfer based on the response signals; and transmitting 316 at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the determination.

[0150] The computer program instructions may be comprised in a computer program, a non- transitory computer readable medium, a computer program product, a machine- readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program.

[0151] Although the memory 704 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage.

[0152] Although the processor 702 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 702 may be a single core or multi-core processor.

[0153] The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one...” or by using “consisting”.

[0154] In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., so as to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components.

[0155] As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, " determine / determining" can include resolving, selecting, choosing, establishing, and the like.

[0156] In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

[0157] Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

[0158] Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

[0159] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0160] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0161] The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

[0162] The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

[0163] In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

[0164] The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

[0165] Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. l / we claim:

Claims

CLAIMS1 . A device comprising means for: receiving, from a network node, a signal for wireless power transfer; determining information relating to an energy harvesting rate for the device using the received signal for wireless power transfer; transmitting a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device.

2. A device as claimed in claim 1 wherein the information relating to the energy harvesting rate comprises at least one of: an indication of amount of energy harvested by the device from the received signal for wireless power transfer; an indexed value representing an energy harvesting rate with respect to the transmit data requirements of the device.

3. A device as claimed in claim 2 wherein the energy harvesting rates corresponding to respective indices are received from the network node during configuration.

4. A device as claimed in claim 2 wherein the energy harvesting rates corresponding to respective indices are determined by a communications protocol.

5. A device as claimed in any preceding claim wherein the information relating to transmit data requirements of the device comprises information based on buffered data.

6. A device as claimed in any preceding claim wherein the means are for determining the energy harvesting rate using information indicating power used fortransmitting the signal for wireless power transfer and time for which the signal for wireless power transfer is transmitted.

7. A device as claimed in claim 6 wherein the means are for receiving, from the network node, at least one of: information indicating power used for transmitting the signal for wireless power transfer; and time for which the signal for wireless power transfer is transmitted.

8. A device as claimed in claim 7 wherein at least one of the information indicating power used for transmitting the signal for wireless power transfer and the time for which the signal for wireless power transfer is transmitted are received in the signal for wireless power transfer.

9. A device as claimed in any preceding claim wherein the at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, are received in accordance with a decision made by the network node based at least in part on at least one of the information relating to the energy harvesting rate or transmit data requirements of the device.

10. A device as claimed in any preceding claim wherein the means are for, following receipt of a signal indicating that wireless power transfer is suspended, determining at least one alternative node for wireless power transfer.

11. A device as claimed in any preceding claim wherein the means are for harvesting energy from the received signal for wireless power transfer.

12. A device as claimed in any preceding claim wherein the means are for determining that the device is energy deficient and transmitting an indication to the network node that the device is energy deficient.

13. A method comprising: receiving, from a network node, a signal for wireless power transfer;determining information relating to an energy harvesting rate for the device using the received signal for wireless power transfer; transmitting a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device.

14. A computer program comprising instructions which, when executed by a device, cause the device to perform at least: receiving, from a network node, a signal for wireless power transfer; determining information relating to an energy harvesting rate for the device using the received signal for wireless power transfer; transmitting a response signal comprising at least one of the information relating to the energy harvesting rate or transmit data requirements of the device; and receiving at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the at least one of the information relating to the energy harvesting rate or transmit data requirements of the device.

15. A network node comprising means for: transmitting a signal for wireless power transfer; monitoring response signals from one or more devices wherein the response signals comprise information relating to an energy harvesting rate for the respective devices using the signal for wireless power transfer; determining whether to support transmitting a signal for wireless power transfer based on the response signals; and transmitting at least one of: further signals for wireless power transfer, or a signal indicating that wireless power transfer is suspended, in accordance with the determination.

16. A network node as claimed in claim 15 wherein determining whether to support transmitting signals for wireless power transfer comprises using information receivedin one or more response signals to compute one or more parameters of a signal for wireless power transfer that meet energy requirements of the device and comparing the one or more parameters to respective thresholds.

17. A network node as claimed in claim 16 wherein the one or more parameters of the signal for wireless power transfer comprise at least one of: time for which signal is transmitted; bandwidth of the signal; transmission power of the signal.

18. A network node as claimed in any of claims 16 to 17 wherein the thresholds for the one or more parameters are adjusted based on the number or devices from which the network node has received a response signal.

19. A network node as claimed in any of claims 16 to 18 wherein the thresholds for the one or more parameters are adjusted based on availability of one or more alternative power sources for the one or more devices.

20. A network node as claimed in any of claims 15 to 19 wherein the signal for wireless power transfer comprises information indicating at least one of: power used for transmitting the signal for wireless power transfer; time for which the signal for wireless power transfer is transmitted.

21. A network node as claimed in any of claims 15 to 20 wherein the means are for, if the network node determines to support transmitting the signal for wireless power transfer, determining a set of parameters to use for the signal for wireless power transfer.

22. A network node as claimed in any of claims 15 to 21 wherein the means are for, if no response signals are received within a response time period, determining to suspend transmitting signals for wireless power transfer.

23. A network node as claimed in any of claims 15 to 22 wherein the means are for, if the network node determines to suspend transmitting the signal for wirelesspower transfer determining at least one alternative node for providing a wireless power transfer signal.

24. A network node as claimed in any of claims 15 to 23 wherein the means are for transmitting an energy threshold to a device, wherein the energy threshold is for determining if the device is energy deficient.

25. A network node as claimed in any of claims 15 to 24 wherein the means are for receiving, from a device, an indication that the device is energy deficient and transmitting the signal for wireless power transfer in response to the received indication.

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