(19)
(11)EP 3 289 661 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
05.09.2018 Bulletin 2018/36

(21)Application number: 16717587.6

(22)Date of filing:  08.04.2016
(51)Int. Cl.: 
H04W 72/00  (2009.01)
H02J 50/10  (2016.01)
H02J 7/02  (2016.01)
H04B 7/26  (2006.01)
H02J 50/40  (2016.01)
H04B 5/00  (2006.01)
(86)International application number:
PCT/EP2016/057677
(87)International publication number:
WO 2016/173822 (03.11.2016 Gazette  2016/44)

(54)

INDUCTIVE WIRELESS POWER TRANSFER WITH TIME SLOTTED COMMUNICATION

INDUKTIVE DRAHTLOSE LEISTUNGSÜBERTRAGUNG MIT ZEITSCHLITZKOMMUNICATION

TRANSMISSION DE PUISSANCE INDUCTIVE SANS FIL AVEC COMMUNICATION À CRÉNEAUX TEMPORELS


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 29.04.2015 EP 15165700

(43)Date of publication of application:
07.03.2018 Bulletin 2018/10

(73)Proprietor: Koninklijke Philips N.V.
5656 AE Eindhoven (NL)

(72)Inventors:
  • VAN WAGENINGEN, Andries
    5656 AE Eindhoven (NL)
  • STARING, Antonius Adriaan Maria
    5656 AE Eindhoven (NL)

(74)Representative: Coops, Peter 
Philips Intellectual Property & Standards High Tech Campus 5
5656 AE Eindhoven
5656 AE Eindhoven (NL)


(56)References cited: : 
WO-A1-2012/058724
US-A1- 2009 284 082
US-A1- 2013 234 661
US-A1- 2009 271 048
US-A1- 2010 181 961
US-A1- 2015 098 353
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    FIELD OF THE INVENTION



    [0001] The present invention relates to a method of allocating communication time slots contained in repeating frames for communication between an inductive wireless power transmitter and at least two inductive wireless power receivers. The invention further relates to an inductive wireless power transmitter, and to an inductive wireless power receiver.

    BACKGROUND OF THE INVENTION



    [0002] Inductive wireless power transfer is becoming increasingly popular. In this technology a power transmitter device generates a magnetic field using a primary coil. A power receiver device taps energy from this magnetic field using a secondary coil, inductively coupled to the primary coil by proximity. Thus power is transferred without making electrical contact. One such technology is standardized in the Wireless Power Consortium, and is known under the name of Qi.

    [0003] In an application example of this technology, a mobile phone acts as the power receiver and has a secondary coil built in. For charging of the phone's batteries, it is placed on the surface of a wireless charging pad that has a primary coil built in. The two coils are coupled by proper placement and alignment, and power is transferred from the charger to the phone wirelessly by induction. Thus the phone can be charged by simply placing it on a dedicated charger surface, without the need for attaching connectors and wires to the phone. The charging of a mobile phone or other portable device is a low-power application, with typically about 1 to 5 watt of power transferred from transmitter to receiver. High-power applications of inductive wireless power transfer may be used for cooking food or even charging an electrical car wirelessly.

    [0004] The Qi standard for inductive wireless power transfer specifies a communication interface for communication between a wireless power transmitter and a wireless power receiver. Such communication is needed a.o. to properly match the power transmission to the characteristics of the receiving device. So far, this communication has been specified only for a single transmitter working with a single receiver. Only receiver to transmitter communication is supported, achieved by load modulation on the receiver side. The load modulation leads to modulation of the transmitted power, which can be detected on the transmitter side as modulation of the voltage or current in the primary coil. The single receiver communicates its power needs, and the transmitter obliges. This is described e.g. in WO 2014020464.

    [0005] The patent application US 2009/0271048 describes a power transmitting apparatus for communicating via induction coupling with several power receiving apparatus. The transmitting apparatus uses a power transmission frame in which a synchronization signal indicates the start of the frame. Slot synchronization signals indicate the start of each power transmission slot. The frame also includes an allocation information signal from which the power receiving apparatus can recognize in which power transmission slot in the next frame power is being transmitted. Each power receiving apparatus can transmit a request for power transmission in response to a power transmission request accepting information.

    [0006] A solution is needed for the situation where a single primary coil (or multiple primary coils operated in series or parallel) in a power transmitter is coupled to multiple secondary coils in multiple power receiver devices. This may arise for example in case of a larger charging pad that can accommodate several portable devices simultaneously.

    SUMMARY OF THE INVENTION



    [0007] It is an object of the invention to provide a wireless powering technology enabling communication between a single inductive wireless power transmitter and multiple inductive wireless power receivers. The inventors have realized that multiple receivers can each communicate with a single transmitter using load modulation, but a receiver will be unable to detect communication from another receiver because the coupling between the secondary coils of two receivers is far too weak. This means a receiver is unable to back off when another receiver is communicating simultaneously, because the receiver simply cannot tell that this is the case. Therefore an approach is needed in which communication from the multiple receivers is separated to avoid collisions by multiple receivers communicating simultaneously, and organised without the need for communication, or even detection of communication, between receivers.

    [0008] This is achieved, according to a first aspect of the invention, by a method of allocating communication time slots contained in repeating frames for communication between an inductive wireless power transmitter and at least two inductive wireless power receivers, wherein the power transmitter and the power receivers are arranged to communicate by means of modulation and demodulation of an inductive power signal, the method comprising the steps of:
    • sending, by the transmitter, synchronization messages marking the start of the communication time slots and the frames,
    • sending, by the transmitter, before the start of an unallocated communication time slot, a message indicating that the unallocated communication time slot is unallocated,
    • sending, by a first receiver, during the unallocated communication time slot, an allocation request message to the transmitter to request allocation of the unallocated communication time slot to the first receiver,
    • sending, by the transmitter, after the end of the unallocated communication time slot, a reception status message indicating reception success of a message during the unallocated communication time slot,
    • further sending, by the transmitter, in case of successful reception of the allocation request message, a grant message indicating that the requested allocation is granted.


    [0009] This has the advantage that time slots can be allocated to individual inductive wireless power receivers, even though the receivers cannot detect each other's communication. The allocation is granted by the single power transmitter which is able to communicate with each of the power receivers, and is therefore also able to detect collisions caused by two receivers communicating simultaneously.

    [0010] In an embodiment, the message indicating that the unallocated communication time slot is unallocated is part of the synchronization message immediately preceding the unallocated communication time slot. In another embodiment the reception status message and the grant message are part of the synchronization message immediately following the unallocated communication time slot. This has the advantage that the communication remains compact and efficient, which is necessary, given the low bit rates that can be achieved in practice by modulation of the power signal.

    [0011] In a further embodiment, the duration of the synchronization messages marking the start of the communication time slots and the frames is in a range of 30 to 60 milliseconds. In yet another embodiment the duration of the communication time slots is in a range of 30 to 60 milliseconds. These have the advantage to make the communication approach compatible with the existing Qi wireless power specification in which a 'digital ping window' duration of 65 msec is specified. Staying within that duration ensures that a power transmitter running the above protocol can also detect and correctly operate with a power receiver that is only compatible with the already existing specification.

    [0012] According to a second aspect of the invention the object is achieved by an inductive wireless power transmitter comprising
    • a primary coil for transferring an inductive power signal to at least two inductive wireless power receivers,
    • a power converter for providing power to the primary coil,
    • a power modulation and demodulation unit for modulating and demodulating the inductive wireless power signal, and
    • a communication and control unit,
    the communication and control unit being arranged to control the power modulation and demodulation unit to communicate with the inductive wireless power receivers in communication time slots contained in repeating frames, and the communication and control unit being further arranged to execute the following communication protocol:
    • send to the receivers synchronization messages marking the start of the communication time slots and the frames;
    • send to the receivers, before the start of an unallocated communication time slot, a message indicating that the unallocated communication time slot is unallocated;
    • if a first inductive wireless power receiver, during the unallocated communication time slot, sends an allocation request message requesting allocation of the unallocated communication time slot to the first receiver, then receive the allocation request message;
    • send to the receivers, after the end of the unallocated communication time slot, a reception status message indicating reception success of a message during the unallocated communication time slot;
    • if an allocation request message was successfully received during the unallocated communication time slot, then further send to the receivers, after the end of the unallocated communication time slot, a grant message indicating that the requested allocation is granted.


    [0013] This inductive wireless power transmitter has the advantage that it can allocate time slots to individual inductive wireless power receivers, even though the receivers cannot detect each other's communication. The allocation is granted by the power transmitter which is able to communicate with each of the power receivers, and is therefore also able to detect collisions caused by two receivers communicating simultaneously.

    [0014] According to a third aspect of the invention, the object is achieved by an inductive wireless power receiver comprising
    • a secondary coil for receiving an inductive wireless power signal from an inductive wireless power transmitter,
    • a power converter for converting the power signal to an output power,
    • a power modulation and demodulation unit for modulating and demodulating the inductive wireless power signal,
    • and a communication and control unit
    the communication and control unit being arranged to control the power modulation and demodulation unit to communicate with an inductive wireless power transmitter, in communication time slots contained in repeating frames, and further arranged to execute the following communication protocol:
    • receive from the transmitter synchronization messages marking the start of the communication time slots and the frames,
    • receive from the transmitter, before the start of an unallocated communication time slot, a message indicating that the unallocated communication time slot is unallocated,
    • if the receiver needs to communicate with the transmitter, send to the transmitter, during the unallocated communication time slot, an allocation request message to request allocation of the unallocated communication time slot to the receiver,
    • receive from the transmitter, after the end of the unallocated communication time slot, a reception status message indicating reception success of a message during the unallocated communication time slot,
    • receive from the transmitter, in case of successful reception of the allocation request message, a grant message indicating that the requested allocation is granted.


    [0015] This inductive wireless power receiver has the advantage that it can request and receive allocation of time slots from an inductive wireless power transmitter, and thus communicate without collision with other receivers communicating simultaneously even though the receivers cannot detect each other's communication. The allocation is granted by the power transmitter which is able to communicate with each of the power receivers, and is therefore also able to detect collisions caused by two receivers communicating simultaneously.

    [0016] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0017] These and other aspects of the method and apparatus according to the invention will be apparent from and elucidated with reference to the implementations and embodiments described hereinafter, and with reference to the accompanying drawings, which serve merely as non-limiting specific illustrations exemplifying the more general concept.

    Fig. 1 illustrates a charge pad with two chargeable mobile devices;

    Fig. 2 illustrates a wireless power transmitter and two receivers;

    Fig. 3 illustrates a wireless power transmitter;

    Fig. 4 illustrates a wireless power receiver;

    Fig. 5 illustrates a frame comprising time slots;

    Fig. 6 illustrates a communication frame comprising synchronization slots;

    Fig. 7 illustrates a method for allocating time slots.


    DETAILED DESCRIPTION OF EMBODIMENTS



    [0018] The following description focuses mainly on embodiments of the invention applied in for example wirelessly charging the batteries of mobile phones. However, it must be appreciated that the invention is not limited to that application only, but may be applied in many other devices such as smart watches, tablets, laptops, shavers, electrical toothbrushes, cooking or kitchen appliances, ranging in power transfer need from 1-5 watt for the smaller devices to much higher values.

    [0019] Throughout the document, inductive wireless power transmitters and inductive wireless power receivers are also simply referred to as power transmitter and power receiver, or even just transmitter and receiver.

    [0020] Figure 1 illustrates an example of a wireless power application. Two mobile devices 12 and 12a are placed on a wireless charging pad 10. This charging pad is just an example and may come in many forms, it may be a separate device or e.g. be part of a car dashboard, or built in to a work top surface or integrated in a piece of furniture. The charging pad is equipped with a single primary coil 11, and acts as an inductive wireless power transmitter. The mobile devices are each equipped with a secondary coil 13 and 13a, and act as inductive wireless power receivers. The charging pad sends an alternating current through the primary coil, which causes an alternating magnetic field. This magnetic field in turn induces an alternating voltage and current in the two secondary coils, which can be rectified and used to charge the batteries of the mobile devices. Thus power is transferred from charger to mobile device wirelessly, as an inductive wireless power signal. The principle is similar to a traditional transformer, but with much weaker coupling, and the two coils now reside in separate devices.

    [0021] Typically the amount of power to be transferred is around 1 to 5 watt or more, depending on the application and on the requirements of the receiver. A secondary coil in a wireless power receiver in these applications will typically be in a size range fitting a portable device, say 1 to 15 cm in diameter for devices ranging from smart watches to kitchen appliances. The primary coil may be about the same size, or may be larger in order to accommodate multiple receivers, as illustrated in Figure 1. Instead of a single large primary coil, a number of primary coils in series or in parallel may also be used and operated almost the same as a single coil.

    [0022] In the example of Figure 1, two mobile devices are being charged at the same time. It may well be that one device has other power requirements than the other, for example because one device is already fully charged while the other is not, or because one of the devices cannot handle a power level as high as the other device can. Both devices must be able to communicate their power needs to the charging pad. This can be achieved by modulation of the power transferred through load modulation on the receiver side: if a receiver varies the current through the secondary coil, for example by switching an additional load such as a resistor in series or parallel, this will lead to a modulation of the current through the primary coil as well, due to the mutual induction between primary and secondary coil. Thus the receiver can modulate the inductive wireless power signal. These modulations can readily be detected in the power transmitter, and in this way bit or byte coded messages can be transferred from power receiver to power transmitter. The mutual induction between the two secondary coils 13 and 13aof the two mobile devices, however, is very low due to their poor alignment, and therefore the two mobile devices cannot communicate with each other in the same way, in fact can they cannot detect if another receiver device is communicating. It may therefore occur that the two devices attempt to communicate with the charging pad simultaneously, which leads to errors in reception of the communication and to both messages being lost. Simply trying again later is not an acceptable solution, as some of the data may be time critical. For example, a message that the power must immediately be switched off should not be delayed too much as that could potentially lead to damage.

    [0023] The inventors have realized that a solution is needed that enables timely communication between multiple inductive wireless power receivers and a single inductive wireless power transmitter. Since the receivers cannot detect each other, it is not possible for a receiver to notice that another receiver is communicating simultaneously. The inventors have realized this, and concluded that the communication must be coordinated by the power transmitter, which is able to communicate with each of the coupled receivers.

    [0024] Figure 2 schematically illustrated a single inductive wireless power transmitter 22 (PTx) coupled to two inductive wireless power receivers 23 and 23a (PRx). The power transmitter comprises a primary coil 25, and obtains power from a power source 21, which may for example be the mains electricity. The two power receivers each comprise a secondary coil, 26 and 26a, and send the power they receive to a load, 24 and 24a. This load may for example be a battery that is to be charged, but many other options are possible, for example an electromotor may be powered, or a resistive element may be powered for heating purposes.

    [0025] Figure 3 schematically shows more detail of an inductive wireless power transmitter. The transmitter comprises a primary coil 25 for transferring an inductive wireless power signal to coupled inductive wireless power receivers, and an input for power coming from the power source 21. Additionally it comprises a power converter 31, a power modulation and demodulation unit 32, and a communication and control unit 33.

    [0026] The power converter 31 converts the input power received from the power source 21 into a power signal suitable for driving the primary coil. For example, it may convert an AC or DC input power to an AC power of a frequency suitable for inductive wireless power transfer.

    [0027] The power modulation/demodulation unit 32 enables communication with coupled receivers by modulating and demodulating the inductive wireless power signal. When a receiver sends a communication message by modulating the current through its secondary coil as described above, the current through the primary coil in the transmitter will be modulated as well. In this way, the inductive wireless power signal is modulated by the receiver. This can be detected by monitoring the current through the primary coil or the voltage across the primary coil in the modulation/demodulation unit 32. The voltage or current variations are demodulated and translated into bits and bytes and interpreted by the communication and control unit 33.

    [0028] To send a communication message in the form of a pattern of bits or bytes to a receiver, the modulation/demodulation unit 32 modulates the current through the primary coil, thereby modulating the inductive wireless power signal being transferred, which leads to a modulation in the current through the secondary coils as well due to the mutual induction. The modulation may be amplitude modulation, which may be achieved for example by switching a resistor in series or parallel to the primary coil. Alternatively frequency or phase modulation may be applied, where the frequency or phase of the AC current through the primary coil is modulated, which again can be detected in the receiver.

    [0029] The communication and control unit 33 controls the power converter and handles the communication in conjunction with the modulation and demodulation unit 32. It sends and receives messages by controlling the modulation/demodulation unit and it controls the operation of the power transmitter. For example it may send a short inductive power pulse, a 'ping', to check if any receivers are present. If a receiver is present, it may respond with a message indicating its power needs. The communication and control unit, upon receiving this message may switch on power transmission continuously, controlling the power converter 31 to maintain the required power level. When the receiver no longer needs power, for example because a battery is fully charged, this again will be communicated by sending a message from receiver to transmitter, and the communication and control unit 33 will, upon reception of this message, switch off the power transmission by controlling the power converter 31, at least if no other device still needs powering.

    [0030] Figure 4 schematically shows more detail of an inductive wireless power receiver. The receiver comprises a secondary coil 26, and an output for the power to a load 24. Additionally it comprises a power converter 41, a power modulation and demodulation unit 42, and a communication and control unit 43.

    [0031] The power converter 41 converts the AC inductive power signal received by the secondary coil into an output power suitable for driving the load. For example, it may convert the received power signal to an AC or DC power suitable for the load.

    [0032] The power modulation/demodulation unit 42 enables communication with a coupled power transmitter. It can modulate the inductive wireless power signal by load modulation as described above. When a transmitter sends a communication message by modulating the amplitude of the inductive wireless power signal as described above, the current through the secondary 26 coil in the receiver will be modulated in amplitude as well. This can be detected by monitoring the current through the secondary coil or the voltage across the secondary coil in the modulation/demodulation unit 42. The voltage or current variations are translated into bits and bytes and interpreted by the communication and control unit 33. In case the power transmitter uses frequency modulation of the power signal for communication, then the current through the secondary coil in the receiver will be frequency modulated as well. This can be detected by monitoring the frequency, for example by detecting zero-transitions of the current in the secondary coil, or of the voltage across the secondary coil, and measuring the duration of one or more cycles.

    [0033] The communication and control unit 43 controls the power converter and handles the communication in conjunction with the modulation/demodulation unit. It sends and receives messages by controlling the modulation/demodulation unit, and it controls the operation of the power receiver. For example it may detect a short inductive power pulse, a 'ping', sent by a power transmitter to check if any receivers are present. It may then respond with a message indicating its power needs. When subsequently the power transmitter switches on power transmission continuously, the communication and control unit 43 engages the power converter 41 to properly feed the wirelessly received power to the load 24. When the load no longer needs power, for example because a battery is fully charged, the communication and control unit in the power receiver may send a message to the transmitter to indicate no more power is needed, and disengage the power converter.

    [0034] The communication and control units 33 and 43 may be implemented in many ways, including dedicated electronic circuits, field-programmable gate arrays, or with general purpose microprocessors and memory, configured or programmed to run the required methods and protocols for communication and control according to the invention.

    [0035] The inventors have realized that the communication between a power transmitter and one or more power receivers must be coordinated by the transmitter, because the receivers are not able to communicate with each other, or even detect any communication by another power receiver. Therefore a power receiver is not able to determine by itself if the communication channel is free to use, or already occupied by another receiver. The inventors have adopted a solution in which the communication is handled in time slots, and in which multiple time slots are contained in communication frames, which repeat in time. The general principle is illustrated in Figure 5. In this example a frame 51 starts with a frame header 52, and comprises N time slots 53, labelled S1 - SN. Here N may be a fixed integer number, chosen to be at least equal to the maximum number of power receivers that a power transmitter is designed to communicate with. For example, if a maximum of 4 mobile phones fit on a charging pad such as illustrated in Figure 1, then N must be chosen at least equal to 4. The value of N may also be determined for example by a standard.

    [0036] In the frame header the power transmitter will communicate, while the slots S1 - SN are reserved for communication by the power receivers. To avoid simultaneous communication by receivers, the time slots need to be allocated to individual receivers. To enable quick allocation, the communication frames according to the invention comprise additional synchronization time slots, as illustrated in Figure 6. A communication frame 61 starts with a frame header 62 and comprises n time slots 64, labelled S1 - SN. Each time slot 64 is preceded by a synchronization time slot 63, labelled Sync1 - SyncN. In this approach the frame header 62 and the synchronization time slots 63 are used for communication by the power transmitter, and the time slots 64 are used for communication by the power receivers. It is possible to omit a separate frame header, and instead have the first synchronization time slot provide frame header functionality.

    [0037] During the synchronization time slots the power transmitter sends a synchronization message, a bit pattern or a sequence of bits. These messages serve multiple purposes. Firstly, they mark the beginning of the next communication time slot for the receivers, and thus maintain the time base for communication. Secondly, the synchronization message comprises information on the allocation status of the next communication time slot. If the next time slot is not yet allocated to a receiver, the message will indicate that it is unallocated or free. If on the other hand the next time slot is allocated to a particular receiver, the synchronization message will indicate that it is allocated, and which receiver it is allocated to. Thirdly, the synchronization message can indicate success or failure of reception by the power transmitter of a communication message in the preceding communication time slot. Fourthly, the synchronization message can comprise a response to a message successfully received in the preceding communication time slot.

    [0038] Note that in Figure 6 no synchronization slot follows the last communication time slot SN. Instead, the first synchronization time slot in the following frame may serve to indicate successful reception in that slot.

    [0039] Once a power receiver has a time slot allocated to it, it may use that time slot for sending messages to the power receiver. Other receivers will not use that same time slot, as it is flagged as being allocated.

    [0040] If a particular power receiver, hereinafter referred to as the first receiver, needs to communicate but does not have a time slot allocated to it, it needs to request allocation of a free time slot. This is illustrated in Figure 7, focussing on an unallocated time slot 72, labelled Sn. In the preceding synchronization time slot 71, labelled Syncn, the power transmitter will indicate the allocation status of time slot Sn, which in this example is unallocated. During the unallocated time slot Sn the first power receiver will send to the power transmitter an allocation request message, requesting that the slot Sn be allocated to it.

    [0041] In the following synchronization time slot 73, labelled Sn+1, the power transmitter will send a message indicating if a message was successfully received during the time slot Sn. If the allocation request was successfully received and the slot is free, the power transmitter can grant the allocation and send a message indicating the grant of allocation of slot Sn to the first receiver.

    [0042] If however a second receiver attempted to communicate as well during the time slot Sn, for example because it too requested allocation of the same time slot, then the two communication attempts interfere in the primary coil of the power transmitter and no message will be correctly received by the power transmitter. The transmitter will therefore send a message during the following synchronization time slot that there was no successful reception of a message during time slot Sn, and no allocation will consequently be granted. This indicates to the first and second receivers that their allocation requests have failed, and they need to try again to achieve a time slot allocation. In order to avoid the same collision between the two power receivers competing for allocation of the next time slot, the receivers will not immediately try again, but wait for a number of slots. Of course the two receivers must wait for periods of different duration, or else the collision will repeat itself. For example a (semi)random waiting period can be applied, which strongly reduces the likelihood that a collision will repeat itself multiple times.

    [0043] If a receiver does not use the time slot allocated to it, the communication and control unit 31 may decide de de-allocate the time slot. It may do so, for example, after the allocated time slot has not been used for communication by the receiver in several consecutive frames. The time slot will then be flagged as unallocated again, and is available for allocation to receivers that request it.

    [0044] The inventors have realized that the duration of the communication of time slots described above must be chosen wisely. Due to the nature of the modulation methods and the nature of the devices, the bitrate achieved in the communication will be low, and the time slots cannot be chosen too short. In the Qi standard for a single power transmitter working with a single power receiver, it is required that a receiver responds within 65 msec to a transmitter 'ping' as described above. When a wireless power receiver detects a power transmitter, it must be possible to establish well within those 65 msec whether the transmitter supports the time slotted communication, or is of an older type that does not. Therefore the duration of a sync message time slot 71 is preferably chosen in a range of 30 to 60 msec. Preferably also the time slot for receiver communication 72 is chosen in the same range. The inventors have found that a period of 50 msec works well for both the synchronization time slot and the communication time slot. With these limitations, a receiver can always detect at least a part of a synchronization message within the 65 msec, and thus determine the communication capabilities of the transmitter.

    [0045] In general, the bit rates achievable by modulation in inductive wireless power transfer as described are low, and only a limited number of bits may be sent in a synchronization time slot. This requires efficient coding of the information to be conveyed, which includes successful reception of a message in the preceding communication time slot, grant or reject of an allocation request received in the preceding communication time slot, and allocation status of the next communication time slot. This may, for example, be achieved by an efficient 3-bit coding as illustrated in Table 1, where pp indicates a 2-bit response to the preceding communication time slot, and n indicates a 1-bit allocation status of the next communication time slot (and x is used to indicate 'any' bit value). Here the message is efficiently formed of a short part indicating an understanding of the communications status, combined with a short part indicating the availability of the successive time slot.
    Table 1: example of synchronization message coding
    pp nMeaning
    00 x No communication received in preceding slot
    01 x Collision detected in preceding slot
    10 x Data correctly received in preceding slot, allocation of slot rejected
    11 x Data correctly received in preceding slot, allocation of slot accepted
    xx 0 Succeeding slot is free
    xx 1 Succeeding slot is occupied


    [0046] To achieve a duration of the synchronization time slot close to, but not exceeding, a chosen maximum duration, for example 50 msec, a small number of preamble bits may be used. The number of preamble bits may be adjusted to the operating conditions of the wireless power transfer system, so as to achieve a synchronization time slot as close as possible to the chosen duration.

    [0047] A typical method of allocating communication time slots to wireless power receivers following a protocol as described above is illustrated in Figure 8. In a first step 81, an inductive wireless power transmitter sends synchronization messages to mark the start of the communication time slots. This enables the inductive wireless power receivers to detect the timing of the communication frames and slots, and to synchronize to their timing. In a next step 82, the wireless power transmitter sends a message indicating the allocation status of a subsequent time slot. For an unallocated time slot, this message will indicate that the slot is unallocated. This message needs to be sent before the start of that unallocated time slot.

    [0048] In a next step 83, a wireless power receiver in need of a time slot for communication, requests allocation of that time slot, so it can use it for communication in subsequent communication frames. This happens during the unallocated time slot.

    [0049] In a next step 84, the power transmitter sends a message indicating if any communication was successfully received during the unallocated time slot. This happens after the end of the unallocated time slot in question. If the allocation request message was indeed successfully received, in a next step 85 the power transmitter sends a further message indicating that the time slot is now allocated to the receiver that requested it.

    [0050] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. In fact many features may be combined which a skilled person will recognize as mutually compatible, such as the durations of various time slots and messages, the nature of the messages sent, or the inductive power levels transferred.

    [0051] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

    [0052] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. Any reference signs in the claims should not be construed as limiting the scope.


    Claims

    1. A method of allocating communication time slots contained in repeating frames for communication between an inductive wireless power transmitter (22) and at least two inductive wireless power receivers (23), wherein the power transmitter and the power receivers are arranged to communicate by means of modulation and demodulation of an inductive power signal,
    the method being characterized by comprising the steps of:

    - sending, by the transmitter, synchronization messages marking the start of the communication time slots and the frames,

    - sending, by the transmitter, before the start of an unallocated communication time slot, a message indicating that the unallocated communication time slot is unallocated,

    - sending, by a first receiver, during the unallocated communication time slot, an allocation request message to the transmitter to request allocation of the unallocated communication time slot to the first receiver,

    - sending, by the transmitter, after the end of the unallocated communication time slot, a reception status message indicating reception success of an allocation request message during the unallocated communication time slot,

    - further sending, by the transmitter, in case of successful reception of the allocation request message, a grant message indicating that the requested allocation is granted.


     
    2. A method according to claim 1, wherein the message indicating that the unallocated communication time slot is unallocated is part of the synchronization message immediately preceding the unallocated communication time slot.
     
    3. A method according to claim 1 or 2, wherein the reception status message and the grant message are part of the synchronization message immediately following the unallocated communication time slot.
     
    4. A method according to claim 1, wherein the first receiver, in case no grant message is sent by the transmitter in response to the allocation request message, waits for a period of more than one frame before again requesting allocation of a communication timeslot to the first receiver.
     
    5. A method according to any of claims 1 to 4, wherein the duration of the synchronization messages marking the start of the communication time slots and the frames is in a range of 30 to 60 milliseconds.
     
    6. A method according to any of claims 1 to 5, wherein the duration of the communication time slots is in a range of 30 to 60 milliseconds.
     
    7. An inductive wireless power transmitter (22) comprising

    - a primary coil (25) for transferring an inductive power signal to at least two inductive wireless power receivers (23),

    - a power converter (31) for providing power to the primary coil,

    - a power modulation and demodulation unit (32) for modulating and demodulating the inductive wireless power signal, and

    - a communication and control unit (33),

    the communication and control unit being arranged to control the power modulation and demodulation unit to communicate with the inductive wireless power receivers in communication time slots contained in repeating frames, and characterized by the communication and control unit being further arranged to execute the following communication protocol:

    - send to the receivers synchronization messages marking the start of the communication time slots and the frames;

    - send to the receivers, before the start of an unallocated communication time slot, a message indicating that the unallocated communication time slot is unallocated;

    - if a first inductive wireless power receiver, during the unallocated communication time slot, sends an allocation request message requesting allocation of the unallocated communication time slot to the first receiver, then receive the allocation request message;

    - send to the receivers, after the end of the unallocated communication time slot, a reception status message indicating reception success of an allocation request message during the unallocated communication time slot;

    - if an allocation request message was successfully received during the unallocated communication time slot, then further send to the receivers, after the end of the unallocated communication time slot, a grant message indicating that the requested allocation is granted.


     
    8. An inductive wireless power transmitter according to claim 7, wherein the communication and control unit is further arranged to send the message indicating that the unallocated communication time slot is unallocated as part of the synchronization message immediately preceding the unallocated communication time slot.
     
    9. An inductive wireless power transmitter according to claim 7, wherein the communication and control unit is further arranged to send the message indicating that the unallocated communication time slot is unallocated as part of the synchronization message marking the start of the frame comprising the unallocated communication time slot.
     
    10. An inductive wireless power transmitter according to claim 7 or 8, wherein the communication and control unit is further arranged to send the reception status message and the grant message as part of the synchronization message immediately following the unallocated time slot.
     
    11. An inductive wireless power transmitter according to any of the claims 7 to 10, wherein the duration of the synchronization messages marking the start of the communication time slots and the frames is in a range of 30 to 60 milliseconds.
     
    12. An inductive wireless power transmitter according to any of the claims 7 to 11, wherein the duration of the communication time slots is in a range of 30 to 60 milliseconds.
     
    13. An inductive wireless power receiver (23) comprising

    - a secondary coil (26) for receiving an inductive wireless power signal from an inductive wireless power transmitter,

    - a power converter (41) for converting the power signal to an output power,

    - a power modulation and demodulation unit (42) for modulating and demodulating the inductive wireless power signal,

    - and a communication and control unit (43)

    the communication and control unit being arranged to control the power modulation and demodulation unit to communicate with an inductive wireless power transmitter (22), in communication time slots contained in repeating frames, and further characterized by the communication and control unit being arranged to execute the following communication protocol:

    - receive from the transmitter synchronization messages marking the start of the communication time slots and the frames,

    - receive from the transmitter, before the start of an unallocated communication time slot, a message indicating that the unallocated communication time slot is unallocated,

    - if the receiver needs to communicate with the transmitter, send to the transmitter, during the unallocated communication time slot, an allocation request message to request allocation of the unallocated communication time slot to the receiver,

    - receive from the transmitter, after the end of the unallocated communication time slot, a reception status message indicating reception success of an allocation request message during the unallocated communication time slot,

    - receive from the transmitter, in case of successful reception of the allocation request message, a grant message indicating that the requested allocation is granted.


     
    14. An inductive wireless power receiver according to claim 13, further arranged to wait for a period of more than one frame before again requesting allocation of a communication timeslot to the first receiver, in case no grant message is sent by the transmitter in response to the allocation request message.
     


    Ansprüche

    1. Verfahren zur Zuordnung von Kommunikationszeitfenstern, welche in sich wiederholenden Datenrahmen enthalten sind, zur Kommunikation zwischen einem induktiven drahtlosen Leistungssender (22) und zumindest zwei induktiven drahtlosen Leistungsempfängern (23), wobei der Leistungssender und die Leistungsempfänger eingerichtet sind, mithilfe von Modulation und Demodulation eines induktiven Leistungssignals zu kommunizieren,
    wobei das Verfahren dadurch gekennzeichnet ist, dass es die folgenden Schritte umfasst:

    - Senden, durch den Sender, von Synchronisierungsnachrichten, welche den Start der Kommunikationszeitfenster und der Datenrahmen markieren,

    - Senden, durch den Sender, vor dem Start eines nicht zugeordneten Kommunikationszeitfensters, einer Nachricht, welche darauf hinweist, dass das nicht zugeordnete Kommunikationszeitfenster nicht zugeordnet ist,

    - Senden, durch einen ersten Empfänger, während des nicht zugeordneten Kommunikationszeitfensters, einer Zuordnungsanforderungsnachricht an den Sender, um Zuordnung des nicht zugeordneten Kommunikationszeitfensters zu dem ersten Empfänger anzufordern,

    - Senden, durch den Sender, nach dem Ende des nicht zugeordneten Kommunikationszeitfensters, einer Empfangsstatusnachricht, welche auf den erfolgreichen Empfang einer Zuordnungsanforderungsnachricht hinweist, während des nicht zugeordneten Kommunikationszeitfensters,

    - weiter Senden, durch den Sender, im Fall eines erfolgreichen Empfangs der Zuordnungsanforderungsnachricht, einer Erteilungsnachricht, welche darauf hinweist, dass die angeforderte Zuordnung erteilt wurde.


     
    2. Verfahren nach Anspruch 1, wobei die Nachricht, welche darauf hinweist, dass das nicht zugeordnete Kommunikationszeitfenster nicht zugeordnet ist, Teil der Synchronisierungsnachricht ist, welche dem nicht zugeordneten Kommunikationszeitfenster unmittelbar vorangeht.
     
    3. Verfahren nach Anspruch 1 oder 2, wobei die Empfangsstatusnachricht und die Erteilungsnachricht Teil der Synchronisierungsnachricht sind, welche dem nicht zugeordneten Kommunikationszeitfenster unmittelbar folgt.
     
    4. Verfahren nach Anspruch 1, wobei der erste Empfänger, im Fall, dass keine Erteilungsnachricht von dem Sender als Reaktion auf die Zuordnungsanforderungsnachricht gesendet wird, für eine Zeitspanne von mehr als einem Datenrahmen wartet, bevor erneut Zuordnung eines Kommunikationszeitfensters zu dem ersten Empfänger angefordert wird.
     
    5. Verfahren nach einem der Ansprüche 1 bis 4, wobei die Dauer der Synchronisierungsnachricht, welche den Start der Kommunikationszeitfenster und der Datenrahmen markiert, in einem Bereich von 30 bis 60 Millisekunden liegt.
     
    6. Verfahren nach einem der Ansprüche 1 bis 5, wobei die Dauer der Kommunikationszeitfenster in einem Bereich von 30 bis 60 Millisekunden liegt.
     
    7. Induktiver drahtloser Leistungssender (22), umfassend

    - eine Primärwicklung (25) zum Transferieren eines induktiven Leistungssignals an zumindest zwei induktive drahtlose Leistungsempfänger (23),

    - einen Leistungswandler (31) zum Bereitstellen von Leistung für die Primärwicklung,

    - eine Leistungsmodulations- und -demodulationseinheit (32) zum Modulieren und Demodulieren des induktiven drahtlosen Leistungssignal, und

    - eine Kommunikations- und Steuerungseinheit (33),

    wobei die Kommunikations- und Steuerungseinheit eingerichtet ist, die Leistungsmodulations- und -demodulationseinheit zu steuern, um mit den induktiven drahtlosen Leistungsempfängern in Kommunikationszeitfenstern, welche in sich wiederholenden Datenrahmen enthalten sind, zu kommunizieren, und dadurch gekennzeichnet ist, dass die Kommunikations- und Steuerungseinheit weiter eingerichtet ist, das folgende Kommunikationsprotokoll auszuführen:

    - Synchronisierungsnachrichten, welche den Start der Kommunikationszeitfenster und der Datenrahmen markieren, an die Empfänger senden;

    - vor dem Start eines nicht zugeordneten Kommunikationszeitfensters eine Nachricht an die Empfänger senden, welche darauf hinweist, dass das nicht zugeordnete Kommunikationszeitfenster nicht zugeordnet ist;

    - wenn ein erster induktiver drahtloser Leistungsempfänger während des nicht zugeordneten Kommunikationszeitfensters eine Zuordnungsanforderungsnachricht sendet, welche Zuordnung des nicht zugeordneten Kommunikationszeitfenster, an den ersten Empfänger anfordert, dann die Zuordnungsanforderungsnachricht empfangen;

    - nach dem Ende des nicht zugeordneten Kommunikationszeitfensters eine Empfangsstatusnachricht an die Empfänger senden, welche auf den erfolgreichen Empfang einer Zuordnungsanforderungsnachricht während des nicht zugeordneten Kommunikationszeitfensters hinweist;

    - wenn eine Zuordnungsanforderungsnachricht während des nicht zugeordneten Kommunikationszeitfensters erfolgreich empfangen wurde, dann nach dem Ende des nicht zugeordneten Kommunikationszeitfensters weiter eine Erteilungsnachricht, welche darauf hinweist, dass die angeforderte Zuordnung erteilt wurde, an die Empfänger senden.


     
    8. Induktiver drahtloser Leistungssender nach Anspruch 7, wobei die Kommunikations- und Steuerungseinheit weiter eingerichtet ist, die Nachricht, welche darauf hinweist, dass das nicht zugeordnete Kommunikationszeitfenster nicht zugeordnet ist, als Teil der Synchronisierungsnachricht, welche dem nicht zugeordneten Kommunikationszeitfenster unmittelbar vorangeht, zu senden.
     
    9. Induktiver drahtloser Leistungssender nach Anspruch 7, wobei die Kommunikations- und Steuerungseinheit weiter eingerichtet ist, die Nachricht, welche darauf hinweist, dass das nicht zugeordnete Kommunikationszeitfenster nicht zugeordnet ist, als Teil der Synchronisierungsnachricht, welche den Start des Datenrahmens markiert, welcher das nicht zugeordnete Kommunikationszeitfenster umfasst, zu senden.
     
    10. Induktiver drahtloser Leistungssender nach Anspruch 7 oder 8, wobei die Kommunikations- und Steuerungseinheit weiter eingerichtet ist, die Empfangsstatusnachricht und die Erteilungsnachricht als Teil der Synchronisierungsnachricht, welche dem nicht zugeordneten Kommunikationszeitfenster unmittelbar folgt, zu senden.
     
    11. Induktiver drahtloser Leistungssender nach einem der Ansprüche 7 bis 10, wobei die Dauer der Synchronisierungsnachricht, welche den Start der Kommunikationszeitfenster und der Datenrahmen markiert, in einem Bereich von 30 bis 60 Millisekunden liegt.
     
    12. Induktiver drahtloser Leistungssender nach einem der Ansprüche 7 bis 11, wobei die Dauer der Kommunikationszeitfenster in einem Bereich von 30 bis 60 Millisekunden liegt.
     
    13. Induktiver drahtloser Leistungsempfänger (23), umfassend

    - eine Sekundärwicklung (26) zum Empfangen eines induktiven drahtlosen Leistungssignals von einem induktiven drahtlosen Leistungssender,

    - einen Leistungswandler (41) zum Umwandeln des Leistungssignal in eine Ausgangsleistung,

    - eine Leistungsmodulations- und -demodulationseinheit (42) zum Modulieren und Demodulieren des induktiven drahtlosen Leistungssignals,

    - und eine Kommunikations- und Steuerungseinheit (43)

    wobei die Kommunikations- und Steuerungseinheit eingerichtet ist, die Leistungsmodulations- und -demodulationseinheit zu steuern, um mit einem induktiven drahtlosen Leistungssender (22) in Kommunikationszeitfenstern, welche in sich wiederholenden Datenrahmen enthalten sind, zu kommunizieren, und weiter dadurch gekennzeichnet ist, dass die Kommunikations- und Steuerungseinheit eingerichtet ist, das folgende Kommunikationsprotokoll auszuführen:

    - Synchronisierungsnachrichten, welche den Start der Kommunikationszeitfenster und der Datenrahmen markieren, von dem Sender empfangen,

    - vor dem Start eines nicht zugeordneten Kommunikationszeitfensters eine Nachricht, welche darauf hinweist, dass das nicht zugeordnete Kommunikationszeitfenster nicht zugeordnet ist, von dem Sender empfangen,

    - wenn der Empfänger mit dem Sender kommunizieren muss, während des nicht zugeordneten Kommunikationszeitfensters eine Zuordnungsanforderungsnachricht zum Zuordnen des nicht zugeordneten Kommunikationszeitfenster zu dem Empfänger an den Sender senden,

    - nach dem Ende des nicht zugeordneten Kommunikationszeitfensters, eine Empfangsstatusnachricht, welche auf den erfolgreichen Empfang einer Zuordnungsanforderungsnachricht während des nicht zugeordneten Kommunikationszeitfensters hinweist, von dem Sender empfangen,

    - im Fall eines erfolgreichen Empfangs der Zuordnungsanforderungsnachricht, eine Erteilungsnachricht, welche darauf hinweist, dass die angeforderte Zuordnung erteilt wurde, von dem Sender empfangen.


     
    14. Induktiver drahtloser Leistungsempfänger nach Anspruch 13, welcher weiter eingerichtet ist, für eine Zeitspanne von mehr als einem Datenrahmen zu warten, bevor Zuordnung eines Kommunikationszeitfensters zu dem ersten Empfänger erneut angefordert wird, für den Fall, dass keine Erteilungsnachricht von dem Sender als Reaktion auf die Zuordnungsanforderungsnachricht gesendet wird.
     


    Revendications

    1. Procédé d'attribution de créneaux temporels de communication contenus dans des trames répétitives pour la communication entre un émetteur de puissance inductive sans fil (22) et au moins deux récepteurs de puissance inductive sans fil (23), dans lequel l'émetteur de puissance et les récepteurs de puissance sont agencés pour communiquer au moyen d'une modulation et démodulation d'un signal de puissance inductive,
    le procédé étant caractérisé par le fait qu'il comprend les étapes de :

    - envoi, par l'émetteur, de messages de synchronisation marquant le début des créneaux temporels de communication et des trames,

    - envoi, par l'émetteur, avant le début d'un créneau temporel de communication non attribué, d'un message indiquant que le créneau temporel de communication non attribué est non attribué,

    - envoi, par un premier récepteur, durant le créneau temporel de communication non attribué, d'un message de demande d'attribution à l'émetteur pour demander l'attribution du créneau temporel de communication non attribué au premier récepteur,

    - envoi, par l'émetteur, après la fin du créneau temporel de communication non attribué, d'un message de statut de réception indiquant le succès de la réception d'un message de demande d'attribution durant le créneau temporel de communication non attribué,

    - envoi supplémentaire, par l'émetteur, en cas de réception réussie du message de demande d'attribution, d'un message d'accord indiquant que l'attribution demandée est accordée.


     
    2. Procédé selon la revendication 1, dans lequel le message indiquant que le créneau temporel de communication non attribué est non attribué fait partie du message de synchronisation précédant immédiatement le créneau temporel de communication non attribué.
     
    3. Procédé selon la revendication 1 ou 2, dans lequel le message de statut de réception et le message d'accord font partie du message de synchronisation suivant immédiatement le créneau temporel de communication non attribué.
     
    4. Procédé selon la revendication 1, dans lequel le premier récepteur, dans le cas où aucun message d'accord n'est envoyé par l'émetteur en réponse au message de demande d'attribution, attend pendant une période de plus d'une trame avant de demander à nouveau l'attribution d'un créneau temporel de communication au premier récepteur.
     
    5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel la durée des messages de synchronisation marquant le début des créneaux temporels de communication et des trames est dans une plage de 30 à 60 millisecondes.
     
    6. Procédé selon l'une quelconque des revendications 1 à 5, dans lequel la durée des créneaux temporels de communication est dans une plage de 30 à 60 millisecondes.
     
    7. Émetteur de puissance inductive sans fil (22) comprenant

    - une bobine primaire (25) pour transférer un signal de puissance inductive à au moins deux récepteurs de puissance inductive sans fil (23),

    - un convertisseur de puissance (31) pour fournir de la puissance à la bobine primaire,

    - une unité de modulation et démodulation de puissance (32) pour la modulation et démodulation du signal de puissance inductive sans fil, et

    - une unité de communication et de commande (33),

    l'unité de communication et de commande étant agencée pour commander l'unité de modulation et démodulation de puissance pour communiquer avec les récepteurs de puissance inductive sans fil dans des créneaux temporels de communication contenus dans des trames répétitives, et caractérisée par l'unité de communication et de commande étant en outre agencée pour exécuter le protocole de communication suivant :

    - envoyer aux récepteurs des messages de synchronisation marquant le début des créneaux temporels de communication et des trames ;

    - envoyer aux récepteurs, avant le début d'un créneau temporel de communication non attribué, un message indiquant que le créneau temporel de communication non attribué est non attribué ;

    - si un premier récepteur de puissance inductive sans fil, durant le créneau temporel de communication non attribué, envoie un message de demande d'attribution demandant l'attribution du créneau temporel de communication non attribué au premier récepteur, alors recevoir le message de demande d'attribution ;

    - envoyer aux récepteurs, après la fin du créneau temporel de communication non attribué, un message de statut de réception indiquant le succès de la réception d'un message de demande d'attribution durant le créneau temporel de communication non attribué ;

    - si un message de demande d'attribution a été reçu avec succès durant le créneau temporel de communication non attribué, alors en outre envoyer aux récepteurs, après la fin du créneau temporel de communication non attribué, un message d'accord indiquant que l'attribution demandée est accordée.


     
    8. Émetteur de puissance inductive sans fil selon la revendication 7, dans lequel l'unité de communication et de commande est en outre agencée pour envoyer le message indiquant que le créneau temporel de communication non attribué est non attribué en tant que partie du message de synchronisation précédant immédiatement le créneau temporel de communication non attribué.
     
    9. Émetteur de puissance inductive sans fil selon la revendication 7, dans lequel l'unité de communication et de commande est en outre agencée pour envoyer le message indiquant que le créneau temporel de communication non attribué est non attribué en tant que partie du message de synchronisation marquant le début de la trame comprenant le créneau temporel de communication non attribué.
     
    10. Émetteur de puissance inductive sans fil selon la revendication 7 ou 8, dans lequel l'unité de communication et de commande est en outre agencée pour envoyer le message de statut de réception et le message d'accord en tant que partie du message de synchronisation suivant immédiatement le créneau temporel non attribué.
     
    11. Émetteur de puissance inductive sans fil selon l'une quelconque des revendications 7 à 10, dans lequel la durée des messages de synchronisation marquant le début des créneaux temporels de communication et des trames est dans une plage de 30 à 60 millisecondes.
     
    12. Émetteur de puissance inductive sans fil selon l'une quelconque des revendications 7 à 11, dans lequel la durée des créneaux temporels de communication est dans une plage de 30 à 60 millisecondes.
     
    13. Récepteur de puissance inductive sans fil (23) comprenant

    - une bobine secondaire (26) pour recevoir un signal de puissance inductive sans fil provenant d'un émetteur de puissance inductive sans fil,

    - un convertisseur de puissance (41) pour convertir le signal de puissance en une puissance de sortie,

    - une unité de modulation et démodulation de puissance (42) pour la modulation et démodulation du signal de puissance inductive sans fil,

    - et une unité de communication et de commande (43)

    l'unité de communication et de commande étant agencée pour commander l'unité de modulation et démodulation de puissance pour communiquer avec un émetteur de puissance inductive sans fil (22), dans des créneaux temporels de communication contenus dans des trames répétitives, et en outre caractérisée par l'unité de communication et de commande étant agencée pour exécuter le protocole de communication suivant :

    - recevoir en provenance de l'émetteur des messages de synchronisation marquant le début des créneaux temporels de communication et des trames,

    - recevoir en provenance de l'émetteur, avant le début d'un créneau temporel de communication non attribué, un message indiquant que le créneau temporel de communication non attribué est non attribué,

    - si le récepteur a besoin de communiquer avec l'émetteur, envoyer à l'émetteur, durant le créneau temporel de communication non attribué, un message de demande d'attribution pour demander l'attribution du créneau temporel de communication non attribué au récepteur,

    - recevoir en provenance de l'émetteur, après la fin du créneau temporel de communication non attribué, un message de statut de réception indiquant le succès de la réception d'un message de demande d'attribution durant le créneau temporel de communication non attribué,

    - recevoir en provenance de l'émetteur, en cas de réception réussie du message de demande d'attribution, un message d'accord indiquant que l'attribution demandée est accordée.


     
    14. Récepteur de puissance inductive sans fil selon la revendication 13, en outre agencé pour attendre une période de plus d'une trame avant de demander à nouveau l'attribution d'un créneau temporel de communication au premier récepteur, dans le cas où aucun message d'accord n'est envoyé par l'émetteur en réponse au message de demande d'attribution.
     




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    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description