Ambient trigger-based transmission and reception of radio signals

Abstract

There is provided techniques for ambient trigger-based reception of a radio signal. A method is performed by a communication device. The communication device comprises an environment sensor and a radio receiver. The radio receiver is associated with a sleep mode and an active mode. The method comprises detecting, using the environment sensor and whilst keeping the radio receiver in sleep mode, an ambient trigger for waking up the radio receiver. The method comprises, in response thereto, waking up the radio receiver for the radio receiver to be in active mode at a reception time relative to a point in time when the ambient trigger was detected. The method comprises receiving, using the radio receiver in the active mode, the radio signal at the reception time.

Description

[0001] AMBIENT TRIGGER-BASED TRANSMISSION AND RECEPTION

[0002] OF RADIO SIGNALS TECHNICAL FIELD

[0003] Embodiments presented herein relate to a method, a communication device, a computer program, and a computer program product for ambient trigger-based reception of a radio signal. Embodiments presented herein further relate to a method, a radio equipment, a computer program, and a computer program product for ambient trigger-based transmission of a radio signal.

[0004] BACKGROUND

[0005] One of the key challenges in deploying Internet-of-Things (loT) devices and other power-constrained devices is ensuring a ubiquitous and sustainable power supply, particularly for deployments in remote or inaccessible locations. Traditional power sources, such as batteries or wired connections, impose significant limitations in terms of maintenance, operational longevity, and deployment feasibility.

[0006] Consequently, ambient energy harvesting has emerged as a potential remedy, with specific standardization efforts being pursued by the third-generation partnership project (3 GPP) in the context of Ambient-IoT devices.

[0007] Radio frequency (RF) energy harvesting is one approach for providing a continuous and renewable power supply for loT devices. The widespread deployment of wireless communication technologies, such as cellular networks, wireless local area networks, Bluetooth, has resulted in an abundance of ambient RF signals in urban and industrial environments. Through the use of specialized antennas and rectifying circuits, ambient RF signals can be converted into usable electrical energy, potentially eliminating the need for battery replacements or wired power sources. However, challenges remain in the practical implementation of RF energy harvesting due to the inherent limitations in energy availability and conversion efficiency.

[0008] One constraint arises from the high attenuation of RF waves due to Free Space Path Loss (FSPL), coupled with the low efficiency of RF rectifiers at low input power levels, which typically operate with an efficiency of less than 10%. As a result, the power available at an RF energy -harvesting device is extremely low, typically ranging from tens of nanowatts to about one microwatt, depending on factors such as distance from the transmitting radio equipment and the Effective Isotropic Radiated Power (EIRP) of the radio equipment antenna.

[0009] Given the limited amount of available power, loT devices may operate in a duty -cycled manner, where they first accumulate energy in an energy storage component, such as a capacitor or a rechargeable battery, before activating their power-consuming receive / transmit (RX / TX) circuitry to communicate with the network. One challenge arising from this is network synchronization. Synchronization is essential for minimizing energy consumption, optimizing communication protocols, and ensuring the efficient operation of a network. An accurate oscillator with a low frequency error (e.g., below 20 ppm) would bebeneficial for reducing the synchronization duration and associated energy expenditure. However, oscillators with such accuracy typically require high power consumption at high frequencies in the gigahertz range. While low-power, accurate oscillators can be implemented at low frequencies (e.g., tens of kilohertz) using crystal-based oscillators, such alternatives are not viable for some ultra-low-cost loT devices due to the necessity of external components and the associated cost constraints. As a result, a relaxed frequency accuracy range of 104- 105ppm has been considered for such devices.

[0010] Existing approaches have explored the use of broadcast messages as synchronization references, where the time interval between multiple transmissions within a burst is utilized as a timing reference. However, for RF energy-harvesting devices, network synchronization poses additional challenges due to the extremely low power available. Poor clock accuracy in these devices necessitates more frequent synchronization with the transmitter, leading to increased energy consumption and resource utilization. Furthermore, to facilitate synchronization, the transmitter, such as any type of radio equipment, must emit high RF power at regular intervals to ensure that devices can harvest sufficient energy to perform synchronization tasks. This increased transmission power requirement introduces additional complexity in network orchestration and elevates the overall energy consumption of both the RF energy -harvesting devices and the transmitter.

[0011] Traditional synchronization methods that rely on RF communication between the transmitter and receiver do not provide significant improvements over existing mobile communication systems, which already employ broadcast synchronization signals.

[0012] Beyond RF energy -harvesting loT devices, other low-power connected devices also face similar power and synchronization constraints. Devices such as smartwatches, smart rings, healthcare wearables, and other wireless devices are designed with low-cost, battery-constrained architectures for which the energy usage should be optimized. These devices typically rely on compact power sources, such as coin cell batteries, and require efficient solutions for time referencing and synchronization to prolong battery life. Synchronization is thus an issue for not only for loT devices but also other low-power connected devices. Therefore, in both RF energy -harvesting loT devices and other constrained, battery-operated, wireless devices, achieving network synchronization with minimal energy consumption remains a challenge. SUMMARY

[0013] An object of embodiments herein is to address the above challenges and provide energy-efficient synchronization of loT devices and other low-power connected devices.

[0014] A particular object is to enable synchronization of loT devices and other low-power connected devices whilst still enabling the devices to remain in sleep mode as long as possible.According to a first aspect there is presented a method for ambient trigger-based reception of a radio signal. The method is performed by a communication device. The communication device comprises an environment sensor and a radio receiver. The radio receiver is associated with a sleep mode and an active mode. The method comprises detecting, using the environment sensor and whilst keeping the radio receiver in sleep mode, an ambient trigger for waking up the radio receiver. The method comprises, in response thereto, waking up the radio receiver for the radio receiver to be in active mode at a reception time relative to a point in time when the ambient trigger was detected. The method comprises receiving, using the radio receiver in the active mode, the radio signal at the reception time.

[0015] According to a second aspect there is presented a communication device for ambient trigger-based reception of a radio signal. The communication device comprises processing circuitry. The processing circuitry is configured to cause the communication device to detect, using the environment sensor and whilst keeping the radio receiver in sleep mode, an ambient trigger for waking up the radio receiver. The processing circuitry is configured to cause the communication device to, in response thereto, wake up the radio receiver for the radio receiver to be in active mode at a reception time relative to a point in time when the ambient trigger was detected. The processing circuitry is configured to cause the communication device to receive, using the radio receiver in the active mode, the radio signal at the reception time.

[0016] According to a third aspect there is presented a computer program for ambient trigger-based reception of a radio signal. The computer program comprises computer code which, when run on processing circuitry of a communication device, causes the communication device to perform actions. One action comprises the communication device to detect, using the environment sensor and whilst keeping the radio receiver in sleep mode, an ambient trigger for waking up the radio receiver. One action comprises the communication device to, in response thereto wake up the radio receiver for the radio receiver to be in active mode at a reception time relative to a point in time when the ambient trigger was detected. One action comprises the communication device to receive, using the radio receiver in the active mode, the radio signal at the reception time.

[0017] According to a fourth aspect there is presented a method for ambient trigger-based transmission of a radio signal. The method is performed by radio equipment. The method comprises determining that an ambient trigger associated with an event has occurred. The method comprises, in response thereto, initiating transmission of the radio signal towards a communication device at a transmission time relative to a point in time when the ambient trigger was determined to have occurred.

[0018] According to a fifth aspect there is presented a radio equipment for ambient trigger-based transmission of a radio signal. The radio equipment comprises processing circuitry. The processing circuitry is configured to cause the radio equipment to determine that an ambient trigger associated with an event has occurred. The processing circuitry is configured to cause the radio equipment to, in response thereto, initiatetransmission of the radio signal towards a communication device at a transmission time relative to a point in time when the ambient trigger was determined to have occurred.

[0019] According to a sixth aspect there is presented a computer program for ambient trigger-based transmission of a radio signal. The computer program comprises computer code which, when run on processing circuitry of a radio equipment, causes the radio equipment to perform actions. One action comprises the radio equipment to determine that an ambient trigger associated with an event has occurred. One action comprises the radio equipment to, in response thereto, initiate transmission of the radio signal towards a communication device at a transmission time relative to a point in time when the ambient trigger was determined to have occurred.

[0020] According to a seventh aspect there is presented a computer program product comprising a computer program according to at least one of the third aspect and the sixth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

[0021] Advantageously, these aspects enable energy -efficient time synchronization of loT devices and other low-power connected devices.

[0022] Advantageously, with further respect to time synchronization, in case multiple communication devices are configured to detect one and the same ambient trigger, all these communication devices can be coordinated and duty cycled by one common ambient trigger as time reference. These aspects therefore reduce the need for transmission of dedicated synchronization signals. In turn, this may reduce the total amount of generated interference.

[0023] Advantageously, these aspects enable the radio receiver in the communication device to remain in sleep mode as long as possible.

[0024] Advantageously, with further respect to energy savings, from the perspective of the radio equipment, these aspects reduce the need to transmit high-power radio signals when no energy harvesting and no communication is required. Since such radio signals may consume very large amounts of energy, the savings in the radio equipment can be significant.

[0025] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0026] 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, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. Thesteps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0029] Fig. 1 is a schematic illustration of a first communication network according to embodiments;

[0030] Fig. 2 is a schematic illustration of a second communication network according to embodiments;

[0031] Fig. 3 is a block diagram of a communication device according to embodiments;

[0032] Figs. 4 and 5 are flowcharts of methods according to embodiments;

[0033] Fig. 6 is a schematic illustration of a communication device waking up its radio receiver according to embodiments;

[0034] Fig. 7 shows circuit diagrams of environment sensors according to embodiments;

[0035] Fig. 8 is a schematic diagram showing structural units of a communication device according to an embodiment;

[0036] Fig. 9 is a schematic diagram showing structural units of a radio equipment according to an embodiment; and

[0037] Fig. 10 shows one example of a computer program product comprising computer readable means according to an embodiment.

[0038] DETAILED DESCRIPTION

[0039] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept 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 inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

[0040] As noted above achieving network synchronization with minimal energy consumption remains a challenge for both RF energy -harvesting loT devices and other constrained, battery-operated, wireless devices.As a non-limiting example, in typical wireless communication systems, the discontinuous reception (DRX) time reference is used to manage the timing of communication tasks and the related power consumption of wireless communication devices. In more detail, the DRX cycle defines the timing parameters for when the radio receiver in a wireless communication is to be active and when the radio receiver can be in sleep mode to conserve battery energy. During the active period of the DRX cycle, the radio receiver is awake and capable of receiving data from the network (e.g., network system information, paging etc.). Once the active period ends, the radio receiver enters a sleep mode to conserve battery energy. The cycle then repeats, with the radio receiver periodically waking up to check for incoming data and then returning to sleep. The duration of the active and sleep periods, as well as the frequency of the cycle, are typically determined by network configuration.

[0041] However, for both RF energy-harvesting loT devices and other constrained, battery-operated, wireless devices, waking up the radio receiver in accordance with the aforementioned DRX cycle may consume too much energy.

[0042] The herein disclosed embodiments are instead based on the communication device, such as an RF energyharvesting loT device or other constrained, battery-operated, wireless device, using an ambient trigger as DRX time reference. The ambient trigger will not occur at regular intervals, as in the case for the aforementioned DRX time reference, but it will occur when a specific event happens, which is detected by both the communication device and the radio equipment in the network.

[0043] In general terms, the ambient trigger can be regarded as a contextual stimulus detected by the communication device for the communication device to initiate an automated response without direct user input or explicit instructions from a radio equipment. In the present disclosure, this automated response involves waking up the radio receiver in the communication device. The ambient trigger may be based on environmental factors such as light, sound, movement, or even temperature, etc. Thus, some non-limiting examples of events that can be used as ambient trigger are: a certain movement being performed, a certain sound being emitted, a certain light being emitted, or the occurrence of any other event that can be detected by a sensor in the communication device. For this purpose, the communication device may comprise one or more sensors for detecting the ambient trigger, such as light sensors, microphones, motion sensors, etc. For instance, a motion sensor can be used to detect ambient triggers in the form of movement. A light sensor can be used to detect ambient triggers in the form of light signals. A microphone, or other type of sound sensor, can be used to detect ambient triggers in the form of audio signals. A temperature sensor can be used to detect ambient triggers in the form of changing temperature conditions. For example, the ambient trigger could be a light trigger (e.g., a lamp switched on). For example, the ambient trigger could be a sound trigger, e.g., within a given frequency range. For example, the ambient trigger could be a common movement and / or acceleration pattern among devices on the same vehicle (e.g., a ship rolling on waves or a train movement). For example, the ambient trigger could be some predefined movement occurring during walking or running. For example, the ambient trigger couldbe a predefined movement occurring during bicycle pedaling. For example, the ambient trigger could be defined by some other type of movements, for instance movement caused by driving over a bump in the road. Further, the ambient trigger may be generated by any external source, e.g., from human activity, from surrounding sound, light etc. Examples include, but is not limited to, a user voice command, a user sound generation (knocking etc.), an ambient light change, etc. In some cases, the ambient trigger is generated by a mobile device, e.g. a UE. For example, a network node may use events such as a mobile phone making a sound to alert the user of an incoming call or message as an ambient trigger. In some examples, and as will be disclosed in further detail below, a network node may request the UE to activate an ambient trigger, such as emitting a sound, to start synchronization with the communication device. In this way, the communication device may hence start synchronization with the network not at regular intervals, but only when an ambient trigger event occurs, and thus when an ambient trigger is detected by the communication device. To detect the ambient trigger, any of the aforementioned sensors must be implemented in the communication device.

[0044] Fig. 1 is a schematic diagram illustrating a first communication network 100 where embodiments presented herein can be applied. The first communications network 100 comprises radio equipment 110 represented by a network node. The network node could be any of a (radio) access network node, radio base station, base transceiver station, node B (NB), evolved node B (eNB), gNB, access point, access node, transmission and reception point (TRP), integrated access and backhaul (IAB) node. The radio equipment 110 provides coverage, and thus network access for communication devices 120a: 120d. These communication devices 120a: 120d could be RF energy -harvesting loT devices or other energy-constrained, battery-operated, wireless devices or even ordinary user equipment (UE), portable wireless devices, mobile stations, mobile phones, handsets, wireless local loop phones, smartphones, laptop computers, tablet computers, wireless modems, wireless sensor devices, network equipped vehicles, game controllers, etc. operating in a low-power mode or for other reasons having a need to keep the radio receiver in a sleep mode for as long as possible. In Fig. 1 is also schematically illustrated an ambient trigger 130. As before, this ambient trigger 130 may represent a certain movement occurring, a light signal, an audio signal, etc. that is detectable by the communication devices 120a: 120d. Unless the ambient trigger 130 is issued by the radio equipment 110, or at least initiated by the radio equipment 110, then also the radio equipment 110 needs to comprise the necessary sensor(s) for detecting the ambient trigger 130.

[0045] Fig. 2 is a schematic diagram illustrating a second communication network 200 where embodiments presented herein can be applied. The second communications network 200 comprises radio equipment 210, 240 represented by a network node 210 and a UE 240. The network node 210 and the UE 240 are configured for communication with each other. Further, the UE 240 is configured for communication with communication devices 220a:220d, which, again, could be RF energy -harvesting loT devices or other energy -constrained, battery-operated, wireless devices, etc. In this scenario, an ambient trigger 230 may represent a certain movement occurring, a light signal, an audio signal, etc. that is detectable by thecommunication devices 220a:220d. Unless the ambient trigger 230 is issued by any of the radio equipment 210, 240, or at least initiated by the radio equipment 210, 240, then also the radio equipment 210, 240 may need to comprise the necessary environment sensor(s) for detecting the ambient trigger 230. Further details relating thereto will be disclosed below.

[0046] In Fig. 3 is provided a block diagram of a communication device 300 according to an embodiment. At the front end, an antenna 310 is configured for transmission and reception of RF signals. These signals are then directed to an energy harvester and power management unit 320, which extracts energy from the received RF signals and regulates power distribution within the communication device 300. The harvested energy is stored in an energy storage 330 component. A clock 340 generates timing signals necessary for synchronization and operation of other components within the communication device 300. A digital processor 350 is responsible for executing communication protocols, processing data, and managing system functions. For communication purposes, a radio transmitter (TX chain) 360 is responsible for sending out signals and a radio receiver (RX chain) 370 is configured for receiving incoming signals. The radio receiver 370 is associated with a sleep mode and an active mode. The radio transmitter 360 and the radio receiver 370 interact with the digital processor 350 for enabling the transmission and reception of data and other types of signals. The communication device 300 further comprises an environment sensor 380. The environment sensor 380 is configured to, upon detecting an ambient trigger, send a signal to the digital processor 350 for waking up the radio receiver 370 from sleep mode.

[0047] Reference is now made to Fig. 4 illustrating a method for ambient trigger-based reception of a radio signal as performed by the communication device 120a: 120d, 220a:220d, 300 according to an embodiment.

[0048] S106: The communication device 120a: 120d, 220a:220d, 300 detects, using the environment sensor 380 and whilst keeping the radio receiver 370 in sleep mode, an ambient trigger 130, 230 for waking up the radio receiver 370.

[0049] S108: The communication device 120a: 120d, 220a:220d, 300, in response to having detected the ambient trigger, wakes up the radio receiver 370. The radio receiver 370 is woken up for the radio receiver 370 to be in active mode at a reception time relative to a point in time when the ambient trigger 130, 230 was detected.

[0050] SI 10: The communication device 120a: 120d, 220a:220d, 300 receives, using the radio receiver 370 in the active mode, the radio signal at the reception time.

[0051] The communication device 120a: 120d, 220a:220d, 300 thereby starts synchronization with the network upon the ambient trigger having been detected.Embodiments relating to further details of ambient trigger-based reception of a radio signal as performed by the communication device 120a: 120d, 220a:220d, 300 will now be disclosed with continued reference to Fig. 4.

[0052] In some aspects, the communication device 120a: 120d, 220a:220d, 300 informs the radio equipment about capabilities to detect and use ambient triggers 130, 230. In particular, in some embodiments, the communication device 120a: 120d, 220a:220d, 300 is configured to perform (optional) step S102.

[0053] S102: The communication device 120a: 120d, 220a:220d, 300 sends a capability report to a radio equipment 110, 210, 240 being in operative communication with the communication device 120a: 120d, 220a:220d, 300. The capability report comprises information about type of environment sensor 380 available at the communication device 120a: 120d, 220a:220d, 300 for detecting ambient triggers 130, 230 and information about capabilities and time duration for switching the radio receiver 370 between the sleep mode and the active mode.

[0054] As disclosed above, the radio signal is received at a reception time which is relative to a point in time when the ambient trigger 130, 230 was detected. In some aspects, the reception time has a default time offset to the point in time when the ambient trigger 130, 230 was detected. In other aspects, the communication device 120a: 120d, 220a:220d, 300 receives information about the time offset. Therefore, in some embodiments, the communication device 120a: 120d, 220a:220d, 300 is configured to perform (optional) step SI 04.

[0055] S104: The communication device 120a: 120d, 220a:220d, 300 receives configuration pertaining to a time offset relative to detection of the ambient trigger 130, 230.

[0056] The reception time can then be set in accordance with the time offset and the time duration for switching the radio receiver 370 between the sleep mode and the active mode.

[0057] If the communication device 120a: 120d, 220a:220d, 300 has the appropriate environment sensors and capabilities, the communication device 120a: 120d, 220a:220d, 300 can then start using the configuration. Otherwise, the communication device 120a: 120d, 220a:220d, 300 can use regular synchronization (requiring a higher energy consumption).

[0058] In some aspects, the ambient trigger is used as DRX time reference. In particular, in some embodiments, the ambient trigger 130, 230 is by the communication device 120a: 120d, 220a:220d, 300 used as a common time reference for setting a duty cycle with respect to the sleep mode and the active mode for the radio receiver 370, and the radio receiver 370 is woken up in accordance with the duty cycle. This means that the communication device 120a: 120d, 220a:220d, 300 does not need to wake up at regular intervals to listen to the network for incoming data, but it will wake up only during one or more occasions after a specific ambient trigger event has occurred.Different types of communication device 120a: 120d, 220a:220d, 300 with different hardware characteristics and different energy consumption may have different DRX patterns. For instance, communication device 120a: 120d, 220a:220d, 300 closer to the radio equipment can be synchronized more often, while communication device 120a: 120d, 220a:220d, 300 that are farther away from the radio equipment may be synchronized less often to reduce energy consumption. Therefore, in some embodiments, the duty cycle depends on at least one of: hardware characteristics of the communication device 120a: 120d, 220a:220d, 300, energy consumption characteristics of the communication device 120a: 120d, 220a:220d, 300, signal strength characteristics of the communication device 120a: 120d, 220a:220d, 300.

[0059] In some aspects, the radio signal itself is used by the communication device 120a: 120d, 220a:220d, 300 for synchronization purposes (independently of the actual content of the radio signal). Therefore, in some embodiments, the communication device 120a: 120d, 220a:220d, 300 is configured to perform (optional) step SI 12.

[0060] SI 12: The communication device 120a: 120d, 220a:220d, 300 time-synchronizes, based on the received radio signal, the communication device 120a: 120d, 220a:220d, 300 with a transmitter of the radio signal. In some aspects, the radio signal radio signal comprises explicit synchronisation information. Therefore, in some embodiments, the radio signal comprises time synchronization information, and the communication device 120a: 120d, 220a:220d, 300 uses the synchronization information for timesynchronizing the communication device 120a: 120d, 220a:220d, 300.

[0061] Further, the communication device 120a: 120d, 220a:220d, 300 may use the radio signal for energy harvesting. That is, in some embodiments, the communication device 120a: 120d, 220a:220d, 300 is configured to perform (optional) step SI 14.

[0062] SI 14: The communication device 120a: 120d, 220a:220d, 300 performs energy harvesting for the communication device 120a: 120d, 220a:220d, 300 using the received radio signal.

[0063] Reference is now made to Fig. 5 illustrating a method for ambient trigger-based transmission of a radio signal as performed by the radio equipment 110, 210, 240 according to an embodiment.

[0064] S214: The radio equipment 110, 210, 240 determines that an ambient trigger 130, 230 associated with an event has occurred.

[0065] S216: The radio equipment 110, 210, 240, in response thereto, initiates transmission of the radio signal towards a communication device 120a: 120d, 220a:220d, 300 at a transmission time relative to a point in time when the ambient trigger 130, 230 was determined to have occurred.As disclosed above, this enables the communication device 120a: 120d, 220a:220d, 300 to be time-synchronized with the radio equipment. In this respect, in case there are several communication devices 120a: 120d, 220a:220d, 300, as in Fig. 1 and in Fig. 2, in case all these communication devices 120a: 120d, 220a:220d, 300 detect the same trigger event, this enables a common time reference to be set among multiple communication devices 120a: 120d, 220a:220d, 300.

[0066] Embodiments relating to further details of ambient trigger-based transmission of a radio signal as performed by the radio equipment 110, 210, 240 will now be disclosed with continued reference to Fig. 5.

[0067] As disclosed above, there may be different types of ambient triggers. Correspondingly, the event may pertain to any of: emission of a light signal, emission of a sound signal, or occurrence of motion.

[0068] As disclosed above, the communication device 120a: 120d, 220a:220d, 300 informs the radio equipment about capabilities to detect and use ambient triggers 130, 230. Therefore, in some embodiments, the radio equipment 110, 210, 240 is configured to perform (optional) step S202.

[0069] S202: The radio equipment 110, 210, 240 receives a capability report from the communication device 120a: 120d, 220a:220d, 300. The capability report comprises information about type of environment sensor available at the communication device 120a: 120d, 220a:220d, 300 for detecting ambient triggers 130, 230 and information about capabilities and time duration for switching a radio receiver 370 at the communication device 120a: 120d, 220a:220d, 300 between a sleep mode and an active mode.

[0070] The time offset may then be set to a value that depends on the information in the capability report.

[0071] As further disclosed, the communication device 120a: 120d, 220a:220d, 300 may receive information about the time offset. Therefore, in some embodiments, the radio equipment 110, 210, 240 is configured to perform (optional) step S204.

[0072] S204: The radio equipment 110, 210, 240 sends, to the communication device 120a: 120d, 220a:220d, 300, configuration pertaining to a time offset relative to detection of the ambient trigger 130, 230.

[0073] The radio equipment 110, 210, 240 may use measurements from its sensors as well as information from a capability report obtained from the communication device 120a: 120d, 220a:220d, 300 to determine suitable configuration , e.g., what type of environment sensors to use for detection of ambient triggers, what events to use as ambient triggers, and what time-out procedure to use in case no event is detect for a relatively long time. The configuration may further be based on statistics of how often and how regularly different events have occurred. Thus, in some embodiments, the radio equipment 110, 210, 240 has access to statistics of how often and how regularly different events associated with the ambient trigger 130, 230 have occurred, and the time offset has a value that depends on the statistics. The configuration can then be communicated to the communication device 120a: 120d, 220a:220d, 300. When a new communication device 120a: 120d, 220a:220d, 300 enters the network coverage region of the radioequipment, the radio equipment and the communication device 120a: 120d, 220a:220d, 300 may initially communicate with each other using a regular synchronization scheme. However, the radio equipment may then inform the new communication device 120a: 120d, 220a:220d, 300 about the configuration so that the new communication device 120a: 120d, 220a:220d, 300 can switch to using that configuration and start saving energy.

[0074] There may be different actions performed by the radio equipment depending on what type of radio equipment the radio equipment is. For example, the type of action may depend on whether the radio equipment is a network node 110, 210 or a UE 240.

[0075] For example, if the radio equipment is a network node, then the radio equipment may provide instructions, or configuration, to a UE for the UE to detect the ambient trigger and transmit the radio signal. Therefore, in some embodiments, the radio equipment 110, 210, 240 is a first radio equipment 210 (such as a network node), and the radio equipment 110, 210, 240 is configured to perform (optional) step S206.

[0076] S206: The radio equipment 110, 210, 240 sends instructions to a second radio equipment (such as a UE) 240 for the second radio equipment 240 to determine that the ambient trigger 130, 230 has occurred and for the second radio equipment 240 to then initiate transmission of the radio signal accordingly.

[0077] Correspondingly, if the radio equipment is a UE, then the radio equipment may receive instructions, or configuration, from a network node for the UE to detect the ambient trigger and transmit the radio signal, as in below step S212.

[0078] For example, if the radio equipment is a network node, then the radio equipment may coordinate multiple radio equipment 110, 210, 240 for synchronized trigger-based transmissions. Therefore, in some embodiments, the radio equipment 110, 210, 240 is a first radio equipment 210 (such as a first network node), and the radio equipment 110, 210, 240 is configured to perform (optional) step S208.

[0079] S208: The radio equipment 110, 210, 240 coordinates with at least one second radio equipment 110, 210, 240 (such as a second network node or a UE) to synchronize transmission times of radio signal towards communication devices 120a: 120d, 220a:220d, 300 based on determined ambient triggers 130, 230. Further, there may be different ways for the radio equipment 110, 210, 240 to in step S214 determine that the ambient trigger 130, 230 associated with the event has occurred, for example depending on whether the radio equipment is a network node or a UE. Different aspects relating thereto will be disclosed next. In some aspects, the determining in step S214 is a result of the radio equipment itself having generated the event. Hence, in some embodiments, the radio equipment 110, 210, 240 is configured to perform (optional) step S210.S210: The radio equipment 110, 210, 240 generates the event. The ambient trigger 130, 230 is then determined to occur in response to the event being generated.

[0080] This applies regardless of whether the radio equipment is a network node or a UE. Thus, the event may be generated by either a network node or a UE. For example, in case the event is generated by a UE, the UE may by itself set up and coordinate communication with one or more communication devices 120a: 120d, 220a:220d, 300, as in Fig. 2.

[0081] Then, generating the event may comprise activating the ambient trigger 130, 230.

[0082] In some aspects, the determining in step S214 is a result of the radio equipment having sent instructions to another radio equipment to activate the ambient trigger. That is, in some embodiments, the radio equipment 110, 210, 240 is a first radio equipment 210 (such as a network node), and generating the event comprises sending instructions to a second radio equipment 240 (such as a UE) to activate the ambient trigger 130, 230.

[0083] Correspondingly, in case the radio equipment is such a UE, the radio equipment may receive such instructions from a network node. Hence, in some embodiments, the radio equipment 110, 210, 240 is a first radio equipment 240 (such as a UE), and generating the event comprises: (i) receiving instructions from a second radio equipment 210 (such as a network node) for the first radio equipment 240 to activate the ambient trigger 130, 230, and (ii) the first radio equipment 240 activating the ambient trigger 130, 230.

[0084] Further, as disclosed above, if the radio equipment is a UE, then the radio equipment receives provide instructions, or configuration, from a network node for the UE to detect the ambient trigger and transmit the radio signal. Hence, in some embodiments, the radio equipment 110, 210, 240 is a first radio equipment 240 (such as a UE) and the radio equipment 110, 210, 240 is configured to perform (optional) step S212.

[0085] S212: The radio equipment 110, 210, 240 receives instructions from a second radio equipment 210 (such as a network node) for the first radio equipment 240 to determine that the ambient trigger 130, 230 has occurred and for the first radio equipment 240 to then initiate transmission of the radio signal accordingly. Regardless of whether the radio equipment is a network node or a UE, the radio equipment may comprise an environment sensor. Then, the radio equipment 110, 210, 240 may be configured to perform (optional) step S214-2 as part of determining that the ambient trigger 130, 230 has occurred.

[0086] S214-2: The radio equipment 110, 210, 240 detects, using the environment sensor, the ambient trigger 130, 230.In this case, the environment sensor of the radio equipment is of the same type as the radio equipment 380 of the communication device 120a: 120d, 220a:220d, 300. This allows the event causing the ambient trigger to be generated externally to the radio equipment, whilst still enabling time-synchronization between the communication device 120a: 120d, 220a:220d, 300 and the radio equipment.

[0087] However, in embodiments where either the radio equipment itself generates the event or instructs another radio equipment to generate the event, the radio equipment does not need to comprise an environment sensor for this purpose. This is because the radio equipment already knows the timing between generation of the event and transmission of the radio signal.

[0088] Further, there may be different ways for the radio equipment 110, 210, 240 to initiate transmission of the radio signal in step S216, depending on whether the radio equipment is a network node or a UE. In some aspects, for example in case the radio equipment is a network node, the radio equipment may itself transmit the radio signal. Hence, in some embodiments, initiating transmission of the radio signal comprises transmitting the radio signal. In other aspects, for example also in case the radio equipment is a network node, the radio equipment may instruct another radio equipment (such as a UE) to transmit the radio signal. That is, in some embodiments, the radio equipment 110, 210, 240 is a first radio equipment 210 (such as a network node), and initiating transmission of the radio signal comprises sending instructions to a second radio equipment 240 (such as a UE) to transmit the radio signal.

[0089] One non-limiting example of a communication device waking up its radio receiver upon detection of an ambient trigger will be disclosed next with reference to Fig.6. In Fig. 6 is illustrated a timeline along which two ambient triggers are detected by the communication device. Upon detection of each ambient trigger, the communication device wakes up its radio receiver (loT ON duration) for reception of a radio signal (BS sync signal) for time-synchronizing the communication device with the radio equipment. Once having achieved such time synchronization, the communication device transmits a data packet (Data packet sent by loT device) towards the radio equipment. The communication device then remains idle (with the radio receiver in sleep mode) until the next ambient trigger is detected.

[0090] Reference is next made to Fig. 7 in which three example implementations of environment sensors 700a, 700b, 700c are provided. The environment sensor 700a has ultra-low cost and complexity since it is formed by only three components; a resistor R, a light emitting diode (LED), and a transistor T. Even though LEDs are typically used to generate light, LEDs can also be used as ultra-low power light detectors. When the LED is exposed to light, a voltage drop between Vd and the gate of the transistor will turn on the transistor, pulling Vout towards Vd. When the LED is not exposed to light, the transistor will be in an off-state and Vout will be pulled to ground.

[0091] The environment sensor 700a has a constant low output when there is no light, and a constant high output when there is light. This type of sensor can be used to detect, for instance, when the light in a room has been turned on or off. To detect light intensity changes, a resistor-capacitor (RC) low pass fdter (as forenvironment sensor 700b) or a high pass filter (as for environment sensors 700c) can be added to the output of the sensor, as illustrated by environment sensors 700b, 700c. Here, the output will be high only while the light intensity is changing. These types of environment sensors 700b, 700c could for instance be used in scenarios where the light intensity may be varied to signal some action.

[0092] The environment sensors 700a:700c all have a capability to detect light intensity changes, and are thus configured for detection of ambient triggers representing light. However, any of these environment sensors 700a:700c can be generalized to detect other types of ambient triggers. For example, similar environment sensors can be designed that have a capability to detect some other type of intensity changes, such as intensity changes in sound or movement. Such variation may be for detecting a level of change (e.g. that the environment sensor 700a:700c would indicate that sensed light, or other sensor stimulus, is changing faster than a certain level. In some examples, also combinations of variations or trigger levels may be used, for detecting a certain sequency of two or more individual ambient triggers, or events. In such case, the environment sensors 700a: 700c may be used for triggering the occurrence of the time reference occasion only once the sequence of events (two or more events) has been detected.

[0093] Fig. 8 schematically illustrates, in terms of a number of structural units, the components of a communication device 800 according to an embodiment. Processing circuitry 810 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1010a (as in Fig. 10), e.g. in the form of a storage medium 830. The processing circuitry 810 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0094] Particularly, the processing circuitry 810 is configured to cause the communication device 800 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 830 may store the set of operations, and the processing circuitry 810 may be configured to retrieve the set of operations from the storage medium 830 to cause the communication device 800 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 810 is thereby arranged to execute methods as herein disclosed.

[0095] The storage medium 830 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.

[0096] The communication device 800 may further comprise a communications (comm.) interface 820 for communications with other entities, functions, nodes, and devices, as in Fig. 1 and Fig. 2. As such the communications interface 820 may comprise one or more transmitters and receivers, comprising analogue and digital components.The processing circuitry 810 controls the general operation of the communication device 800 e.g. by sending data and control signals to the communications interface 820 and the storage medium 830, by receiving data and reports from the communications interface 820, and by retrieving data and instructions from the storage medium 830. Other components, as well as the related functionality, of the communication device 800 are omitted in order not to obscure the concepts presented herein.

[0097] Fig. 9 schematically illustrates, in terms of a number of structural units, the components of a radio equipment 900 according to an embodiment. Processing circuitry 910 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1010b (as in Fig. 10), e.g. in the form of a storage medium 930. The processing circuitry 910 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0098] Particularly, the processing circuitry 910 is configured to cause the radio equipment 900 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 930 may store the set of operations, and the processing circuitry 910 may be configured to retrieve the set of operations from the storage medium 930 to cause the radio equipment 900 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 910 is thereby arranged to execute methods as herein disclosed.

[0099] The storage medium 930 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.

[0100] The radio equipment 900 may further comprise a communications interface 920 for communications with other entities, functions, nodes, and devices, as in Fig. 1 and Fig. 2. As such the communications interface 920 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 910 controls the general operation of the radio equipment 900 e.g. by sending data and control signals to the communications interface 920 and the storage medium 930, by receiving data and reports from the communications interface 920, and by retrieving data and instructions from the storage medium 930. Other components, as well as the related functionality, of the radio equipment 900 are omitted in order not to obscure the concepts presented herein.

[0101] The radio equipment 900 may be provided as a standalone device or as a part of at least one further device. For example, the radio equipment 900 may be provided in a node of the radio access network or in a node of the core network. Alternatively, functionality of the radio equipment 900 may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the radio access network or the core network) or may be spread between atleast two such network parts, or even between a network node and a UE. Thus, a first portion of the instructions performed by the radio equipment 900 may be executed in a first device, and a second portion of the instructions performed by the radio equipment 900 may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the radio equipment 900 may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a radio equipment 900 residing in a cloud computational environment. Therefore, although a single processing circuitry 910 is illustrated in Fig. 9 the processing circuitry 910 may be distributed among a plurality of devices, or nodes. The same applies to the computer program 1020b of Fig. 10.

[0102] Fig. 10 shows one example of a computer program product 1010a, 1010b comprising computer readable means 1030. On this computer readable means 1030, a computer program 1020a can be stored, which computer program 1020a can cause the processing circuitry 810 and thereto operatively coupled entities and devices, such as the communications interface 820 and the storage medium 830, to execute methods according to embodiments described herein. The computer program 1020a and / or computer program product 1010a may thus provide means for performing any steps of the communication device 120a: 120d, 220a:220d, 300, 800 as herein disclosed. On this computer readable means 1030, a computer program 1020b can be stored, which computer program 1020b can cause the processing circuitry 910 and thereto operatively coupled entities and devices, such as the communications interface 920 and the storage medium 930, to execute methods according to embodiments described herein. The computer program 1020b and / or computer program product 1010b may thus provide means for performing any steps of the radio equipment 110, 210, 240, 900 as herein disclosed.

[0103] In the example of Fig. 10, the computer program product 1010a, 1010b is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 1010a, 1010b could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 1020a, 1020b is here schematically shown as a track on the depicted optical disk, the computer program 1020a, 1020b can be stored in any way which is suitable for the computer program product 1010a, 1010b.

[0104] The inventive concept 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 inventive concept, as defined by the appended patent claims.

Claims

CLAIMS1. A method for ambient trigger-based reception of a radio signal, the method being performed by a communication device (120a: 120d, 220a:220d, 300, 800), the communication device (120a: 120d, 220a:220d, 300, 800) comprising an environment sensor (380) and a radio receiver (370), the radio receiver (370) being associated with a sleep mode and an active mode, the method comprising:detecting (S106), using the environment sensor (380) and whilst keeping the radio receiver (370) in sleep mode, an ambient trigger (130, 230) for waking up the radio receiver (370); and in response thereto:waking up (S108) the radio receiver (370) for the radio receiver (370) to be in active mode at a reception time relative to a point in time when the ambient trigger (130, 230) was detected; and receiving (SI 10), using the radio receiver (370) in the active mode, the radio signal at the reception time.

2. The method according to claim 1, wherein the ambient trigger (130, 230) is by the communication device (120a: 120d, 220a:220d, 300, 800) used as a common time reference for setting a duty cycle with respect to the sleep mode and the active mode for the radio receiver (370), and wherein the radio receiver (370) is woken up in accordance with the duty cycle.

3. The method according to claim 2, wherein the duty cycle depends on at least one of: hardware characteristics of the communication device (120a: 120d, 220a:220d, 300, 800), energy consumption characteristics of the communication device (120a: 120d, 220a:220d, 300, 800), signal strength characteristics of the communication device (120a: 120d, 220a:220d, 300, 800).

4. The method according to any preceding claim, wherein the method further comprises:sending (S102) a capability report to a radio equipment (110, 210, 240, 900) being in operative communication with the communication device (120a: 120d, 220a:220d, 300, 800), wherein the capability report comprises information about type of environment sensor (380) available at the communication device (120a: 120d, 220a:220d, 300, 800) for detecting ambient triggers (130, 230) and information about capabilities and time duration for switching the radio receiver (370) between the sleep mode and the active mode.

5. The method according to claim 4, wherein the method further comprises:receiving (SI 04) configuration pertaining to a time offset relative to detection of the ambient trigger (130, 230), and wherein the reception time is set in accordance with the time offset and the time duration for switching the radio receiver (370) between the sleep mode and the active mode.

6. The method according to any preceding claim, wherein the method further comprises:time-synchronizing (SI 12), based on the received radio signal, the communication device (120a: 120d, 220a:220d, 300, 800) with a transmitter of the radio signal.

7. The method according to any preceding claim, wherein the radio signal comprises time synchronization information, and wherein the communication device (120a: 120d, 220a:220d, 300, 800) uses the synchronization information for time-synchronizing the communication device (120a: 120d, 220a:220d, 300, 800).

8. The method according to any preceding claim, wherein the method further comprises:performing (SI 14) energy harvesting for the communication device (120a: 120d, 220a:220d, 300, 800) using the received radio signal.

9. The method according to any preceding claim, wherein the environment sensor (380) is any of: a light sensor, a microphone, a motion sensor.

10. A method for ambient trigger-based transmission of a radio signal, the method being performed by radio equipment (110, 210, 240, 900), the method comprising:determining (S214) that an ambient trigger (130, 230) associated with an event has occurred; and in response thereto:initiating (S216) transmission of the radio signal towards a communication device (120a: 120d, 220a:220d, 300, 800) at a transmission time relative to a point in time when the ambient trigger (130, 230) was determined to have occurred.

11. The method according to claim 10, wherein the radio equipment (110, 210, 240, 900) comprises an environment sensor, and wherein determining that the ambient trigger (130, 230) has occurred comprises:detecting (S214-2), using the environment sensor, the ambient trigger (130, 230).

12. The method according to claim 10, wherein the method further comprises:generating (S210) the event, and wherein the ambient trigger (130, 230) is determined to occur in response to the event being generated.

13. The method according to claim 12, wherein generating the event comprises activating the ambient trigger (130, 230).

14. The method according to claim 12, wherein the radio equipment (110, 210, 240, 900) is a first radio equipment (210), and wherein generating the event comprises sending instructions to a second radio equipment (240) to activate the ambient trigger (130, 230).

15. The method according to claim 12, wherein the radio equipment (110, 210, 240, 900) is a first radio equipment (240), and wherein generating the event comprises: (i) receiving instructions from a second radio equipment (210) for the first radio equipment (240) to activate the ambient trigger (130, 230) and (ii) activating the ambient trigger (130, 230).

16. The method according to claim 10, wherein initiating transmission of the radio signal comprises transmitting the radio signal.

17. The method according to claim 10, wherein the radio equipment (110, 210, 240, 900) is a first radio equipment (210), and wherein initiating transmission of the radio signal comprises sending instructions to a second radio equipment (240) to transmit the radio signal.

18. The method according to claim 10, wherein the radio equipment (110, 210, 240, 900) is a first radio equipment (240), and wherein the method further comprises:receiving (S212) instructions from a second radio equipment (210) for the first radio equipment (240) to determine that the ambient trigger (130, 230) has occurred and for the first radio equipment (240) to initiate transmission of the radio signal accordingly.

19. The method according to claim 10, wherein the radio equipment (110, 210, 240, 900) is a first radio equipment (210), and wherein the method further comprises:sending (S206) instructions to a second radio equipment (240) for the second radio equipment (240) to determine that the ambient trigger (130, 230) has occurred and for the second radio equipment (240) to initiate transmission of the radio signal accordingly.

20. The method according to claim 10, wherein the method further comprises:sending (S204), to the communication device (120a: 120d, 220a:220d, 300, 800), configuration pertaining to a time offset relative to detection of the ambient trigger (130, 230).

21. The method according to claim 20, wherein the radio equipment (110, 210, 240, 900) has access to statistics of how often and how regularly different events associated with the ambient trigger (130, 230) have occurred, and wherein the time offset has a value that depends on the statistics.

22. The method according to claim 20, wherein the method further comprises:receiving (S202) a capability report from the communication device (120a: 120d, 220a:220d, 300, 800), wherein the capability report comprises information about type of environment sensor (380) available at the communication device (120a: 120d, 220a:220d, 300, 800) for detecting ambient triggers (130, 230) and information about capabilities and time duration for switching a radio receiver (370) at the communication device (120a: 120d, 220a:220d, 300, 800) between a sleep mode and an active mode, andwherein the time offset has a value that depends on the information in the capability report.

23. The method according to claim 10, wherein the radio equipment (110, 210, 240, 900) is a first radio equipment (110, 210, 240, 900), and wherein the method further comprises:coordinating (S208) with at least one second radio equipment (110, 210, 240, 900) to synchronize transmission times of radio signal towards communication devices (120a: 120d, 220a:220d, 300, 800) based on determined ambient triggers (130, 230).

24. The method according to any of claims 10 to 23, wherein the event pertains to any of: emission of a light signal, emission of a sound signal, or occurrence of motion.

25. A communication device (120a: 120d, 220a:220d, 300, 800) for ambient trigger-based reception of a radio signal, the communication device (120a: 120d, 220a:220d, 300, 800) comprising processing circuitry (810), the processing circuitry being configured to cause the communication device (120a: 120d, 220a:220d, 300, 800) to:detect, using an environment sensor and whilst keeping a radio receiver (370) in the communication device (120a: 120d, 220a:220d, 300, 800) in sleep mode, an ambient trigger (130, 230) for waking up the radio receiver (370); and in response thereto:wake up the radio receiver (370) for the radio receiver (370) to be in active mode at a reception time relative to a point in time when the ambient trigger (130, 230) was detected; andreceive, using the radio receiver (370) in the active mode, the radio signal at the reception time.

26. The communication device (120a: 120d, 220a:220d, 300, 800) according to claim 25, further being configured to perform the method according to any of claims 2 to 9.

27. A radio equipment (110, 210, 240, 900) for ambient trigger-based transmission of a radio signal, the radio equipment (110, 210, 240, 900) comprising processing circuitry (910), the processing circuitry being configured to cause the radio equipment (110, 210, 240, 900) to:determine that an ambient trigger (130, 230) associated with an event has occurred; and in response thereto:initiate transmission of the radio signal towards a communication device (120a: 120d, 220a:220d, 300, 800) at a transmission time relative to a point in time when the ambient trigger (130, 230) was determined to have occurred.

28. The radio equipment (110, 210, 240, 900) according to claim 27, further being configured to perform the method according to any of claims 11 to 24.

29. A computer program (1020a) for ambient trigger-based reception of a radio signal, the computer program comprising computer code which, when run on processing circuitry (810) of a communication device (120a: 120d, 220a:220d, 300, 800), causes the communication device (120a: 120d, 220a:220d, 300, 800) to:detect (S106), using an environment sensor (380) and whilst keeping a radio receiver (370) in the communication device (120a: 120d, 220a:220d, 300, 800) in sleep mode, an ambient trigger (130, 230) for waking up the radio receiver (370); and in response thereto:wake up (S108) the radio receiver (370) for the radio receiver (370) to be in active mode at a reception time relative to a point in time when the ambient trigger (130, 230) was detected; and receive (SI 10), using the radio receiver (370) in the active mode, the radio signal at the reception time.

30. A computer program (1020b) for ambient trigger-based transmission of a radio signal, the computer program comprising computer code which, when run on processing circuitry (910) of a radio equipment (110, 210, 240, 900), causes the radio equipment (110, 210, 240, 900) to:determine (S214) that an ambient trigger (130, 230) associated with an event has occurred; and in response thereto:initiate (S216) transmission of the radio signal towards a communication device (120a: 120d, 220a:220d, 300, 800) at a transmission time relative to a point in time when the ambient trigger (130, 230) was determined to have occurred.

31. A computer program product (1010a, 1010b) comprising a computer program (1020a, 1020b) according to at least one of claims 29 and 30, and a computer readable storage medium (1030) on which the computer program is stored.

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