NFC METHOD AND DEVICE FOR COMMUNICATION WITH IMPROVED POWER HARVESTING

Abstract

Method and devices for enabling Power Save Mode (PSM) in near field communication (NFC) between a first active NFC device and a second NFC device, when the first active NFC device and the second NFC device are in NFC connected mode.

Claims

1. Method for near field communication (NFC) with improved power harvesting, the method enabling Power Save Mode (PSM) in NFC between a first active NFC device and a second NFC device, when the first active NFC device and the second NFC device are in NFC connected mode, characterized by: the first active NFC device and the second NFC device entering PSM comprising: a first initialization step and thereafter the first active NFC device and the second NFC device concurrently alternating between the following steps: during a first time slot, called active data mode, data is exchanged between the first active NFC device and the second NFC device, the field strength optionally being controlled; and during a second time slot, called standby mode, the first active NFC device transmitting a standby sequence of NFC waves having lower average power than in the data sequence in said first slot, the NFC waves comprising at least one of: lower average field strength than in said first slot comprising substantially zero field strength; and non-continuous duration, while the first active NFC device and the second NFC device remain in NFC connected mode and the second NFC device harvesting sufficient power to remain in NFC connected mode.

2. Method according to claim 1, the first or the second NFC device comprising generating bursts of keep alive carrier (KAC) transmitted from the first active NFC device, the KAC controlled by one or more of the following parameters: field strength of the KAC; duration of a KAC burst; and resting period before a KAC burst.

3. Method according to claim 1, required parameters for power harvesting are calculated in high level SW and afterwards transferred to a chipset for real time NFC operation.

4. Method according to claim 1, where the second NFC device is an accessory NFC device.

5. Method according to claim 1, where PSM is controlled by e.g. an application program in a first active NFC device that recognizes that both the first active NFC device and the second NFC device accept transition from conventional connected mode to sub mode PSM.

6. Method according to claim 1, where PSM is controlled by e.g. a program in a chipset in the first active NFC device that recognizes that both the first active NFC device and the second NFC device accept transition from conventional connected mode to sub mode PSM.

7. Method according to claim 1, where PSM is controlled by a program in the first active NFC device and initiating PSM by transmitting a request to the second NFC device if it accepts a transition from connected mode to sub mode PSM.

8. Method according to claim 1, where PSM is controlled by the second NFC device and the second NFC device initiates PSM by transmitting, in normal NFC connected mode, a request to the first active NFC device if it accepts a transition to sub mode PSM.

9. Method according to claim 1, where controlling the NFC field strength at least partly is based on requirements for at least one of: i) data rate; ii) response time of the second NFC device; iii) reduced power consumption in the active NFC device; and iv) power harvesting in the second NFC device.

10. Method according to claim 1, where the first initialization step comprises actively changing an impedance of the antenna of the second NFC device, in order to emulate changing a distance between the first active NFC device and the second NFC device e.g. enabling more power for power harvesting in the second NFC device.

11. NFC device, adapted to implement the method according to claim 1.

12. Active NFC device according to claim 11, adapted, in connected mode, to control NFC field strength at least partly based on requirements for at least one of: i) data rate; ii) response time of the second NFC device; iii) reduced power consumption in the active NFC device; and iv) power harvesting in the second NFC device.

13. Active NFC device according to claim 11, adapted, in connected mode, to control bursts of keep alive carrier (KAC) at least partly based on requirements for at least one of: i) reduced power consumption in the active NFC device; and ii) power harvesting in the second NFC device.

14. Accessory NFC device according to claim 11, adapted, in connected mode, to control NFC field strength at least partly based on requirements for at least one of: i) data rate; ii) response time of the accessory NFC device; and iii) reduced power consumption in the active NFC device; and iv) power harvesting in the accessory NFC device.

15. NFC device according to claim 11, adapted, in connected mode, to control bursts of keep alive carrier (KAC) at least partly based on requirements for at least one of: i) reduced power consumption in the active NFC device; and ii) power harvesting in the second NFC device.

Description

DESCRIPTION OF THE DIAGRAMS

[0031] Embodiments of the invention will be described, by way of example only, with reference to the following diagrams wherein:

[0032] FIG. 1 is an illustration of communication between an active NFC device and a second NFC device.

[0033] FIG. 2 is an illustration of a time sequence of an example with conventional NFC communication between a first active NFC device and a second NFC device.

[0034] FIG. 3 is an illustration of a time sequence of an example with NFC communication between an active NFC device and a second NFC device with Power Save Mode (PSM) according to the present invention.

[0035] FIG. 4 is a simplified state diagram illustrating an algorithm how PSM can be entered, initiated from an application program in an active NFC device.

[0036] FIG. 5 is a simplified state diagram illustrating an algorithm for how Power Save Mode (PSM) can be controlled by an application program in an active NFC device.

[0037] FIG. 6 is a simplified state diagram illustrating how Standby Mode (SM) can be controlled by an application program in an active NFC device.

[0038] FIG. 7 is an illustration of an example of a second NFC device informing a controlling application program about adjusting the NFC field strength in active data mode.

REFERENCE SIGNS

[0039]

TABLE-US-00001 10 Active NFC device 11 NFC interface 12 Antenna of active NFC device 20 Second NFC device 22 Antenna of second NFC device 100 NFC polling pulse 110 NFC data exchange 200 Power Save Mode (PSM) 210 Active data mode 220 Standby mode 300 NFC not connected mode 310 NFC connected mode

DETAILED DESCRIPTION OF THE INVENTION

[0040] Embodiments of the invention will now be described, with reference to the drawings. FIG. 1 illustrates NFC communication with an active NFC device 10 with a related antenna 12 and a second NFC device 20 with a related antenna 22. The arrow indicates a magnetic field connecting the two antennas 12, 22. The antennas 12, 22 are normally integrated in the respective NFC devices 10, 20, but are presented as external elements in FIG. 1 for clarity.

[0041] Initially during normal NFC communication, an active NFC device 10 will transmit an NFC polling pulse 100 which is a short burst of carrier frequency signals with a pause before a new polling pulse 100 is transmitted. This continues until a second NFC device 10, 20 is moved from a position e.g. 50 centimeters away to a closer position within a distance of less than 10 centimeters from an active NFC device 10. Normal NFC operation is that the active NFC device 10 then detects an alteration of the impedance of its antenna 12 and initiates a sequence to wake up both NFC devices. There will often be a latency period resulting in data exchange 110 not starting immediately after the second NFC device 10, 20 is in the proximity of the active NFC device 10. A normal NFC communication will then be to transfer a chunk of data between the two NFC devices and afterwards to terminate exchanging of data. It would be possible to maintain the phase of data exchange 110 but then some dummy signals have to be exchanged to ensure the data channel not to terminate. This results in the power consumption being higher than necessary.

[0042] Turning now to FIG. 3, the present invention introduces a Power Save Mode (PSM) 200 which is a mode that is a sub mode of the normal NFC connected mode 310. An initialization step of the present invention of enabling PSM 200 may comprise actively changing the impedance of the antenna of the second NFC device 10, 20.

[0043] By doing this in a way that emulates the first active NFC device 10 and the second NFC device 10, 20 approaching each other, the first active NFC device 10 can be tempted to power up for NFC communication, regardless of physically letting said NFC devices 10, 20 approaching each other, but staying close enough to enable NFC communication. The speed in powering up can be increased, particularly if the second NFC device 10, 20 can operate more efficiently with added power from power harvesting.

[0044] Such an approach can be utilized not only for initiating normal NFC communication. This could again be used for different uses like charging batteries or for powering different kinds of equipment or systems. Special purpose NFC communication can also be emulated for the same purpose.

[0045] When the active NFC device 10 and the second NFC device 10, 20 enters data exchange mode 110, according to the present invention, the two NFC devices 10, 20 may negotiate if both accept PSM 200 and then enter PSM 200. If one of the two NFC devices 10, 20 does not recognize or accept PSM 200, the communication remains in the mode of normal NFC data exchange 110. On the other hand, if both NFC devices 10, 20 accept PSM 200, PSM 200 is entered as a subset of the mode of normal NFC data exchange 110.

[0046] PSM 200 introduces two sub modes which is a form of time division between two time slots, 210, 220.

[0047] The first sub slot of PSM 200 is an active data mode 210. When in this mode, data is transferred between the two NFC devices 10, 20.

[0048] The second sub slot of PSM 200 is a standby mode 220. When in this mode, no actual data is transferred, but different options are foreseen for the operation in standby mode in order to control required use of power in the active NFC device 10, data rate and power harvesting in the second NFC device 10, 20.

[0049] Power, data rate and power harvesting can be controlled from the active NFC device 10, from the second NFC device 10, 20 when in connected mode 310 or from an application program in the active NFC device 10. Control can be performed by hardware, firmware, software or a combination of these.

[0050] The control can be done comprising identification of the need for power, data rate, power harvesting and other factors such as stability of received signals.

[0051] During the process of controlling, a first active NFC device 10 and a second NFC device 10, 20 may communicate information between each other that may be desirable for optimizing control such as the second NFC device 10, 20 requesting more power.

[0052] One option for operating the standby mode 220 is to use NFC field pulses not necessary containing data for communication but comprise power to maintain PSM 200 between sequences of active data mode 210. The amplitude of the NFC field and the duration of the pulses or waves as well as the duration and time of pause between the pulses or waves are available elements for the controlling of these pulses. The pulses or waves in standby mode 220 may have lower average field strength than in active data mode 210 or may consist of bursts of NFC carrier waves in a fraction of the time of one standby mode slot. If the second NFC device does not require power harvesting, the standby mode 220 may consist of

[0053] Optionally, the duration of the active data mode 210 and the duration of the standby mode 220 may be a fixed multiplexing scheme set up in an initial phase based upon the requirements of an application.

[0054] Optionally, the construction of the standby mode may be fixed at an initial phase based upon the application.

[0055] Returning now to the active data mode 210, the NFC field can be controlled similar to the ways that has been described for standby mode. E.g. if the power of the NFC field is higher than necessary, it can be reduced in magnitude or duration in order to save power.

[0056] When, as described previously, a second NFC device 10, 20 is moved closer to and within a distance of less than 10 centimeters from an active NFC device 10, the NFC connected mode 310 is defined as starting when one of the active NFC device 10 and the second NFC device 10, 20 start detecting the other one. According to the present invention, the impedance of the accessory device can then be changed actively in order to invite the active NFC device 10 to increase its NFC power, by increasing the magnitude of the field or the duration of the pulses, in order to prepare for the second NFC device 10, 20 to harvest more power in this startup phase of the connected mode.

[0057] Entering PSM 200 can be done from different initiators, from the active NFC device 10 or from the second NFC device 10, 20. If entered from the active NFC device 10, it can be initiated from an NFC chip driver or from an application of the active NFC device 10. If initiated by the second NFC device 10, 20, the second NFC device 10, 20 must transmit control information to the active NFC device 10 because the active NFC device 10 directly controls the NFC field. If initiated from the active NFC device 10, control information from the second NFC device 10, 20 can be transmitted from the second NFC device 10, 20 or offline information about the second NFC device 10, 20 can be used instead if control information is not transmitted from the second NFC device 10, 20.

[0058] FIG. 4 illustrates an embodiment where active data mode 210 is entered from a telephone.

[0059] An NFC chip 11 and/or software (SW) is integrated in an active NFC device 10, e.g. a mobile phone. This SW can be a SW driver in the phone or firmware related to a chip that operates NFC for the active NFC device 10. A person in the art will understand that such a chip may be separate integrated circuit or integrated otherwise with the active NFC device 10.

[0060] In FIG. 4 is indicated that the NFC chip detects a presence of an accessory antenna, initiates NFC connected mode 310 and reports this to a phone application. The phone application then requests if PSM 200 is available for this NFC communication session. This request is accepted by the second NFC device 10, 20 by enabling PSM 200.

[0061] PSM 200 is initiated when in NFC connected mode 310 and both the active NFC device 10 and the second NFC device 10, 20 may be compatible with other devices that are not adapted to go into PSM 200.

[0062] FIG. 5 illustrates an embodiment where an application in the active NFC device 10, e.g. a mobile phone application, controls the PSM 200. This application initiates active data mode 210, e.g. turns an NFC field on when a request for data is to be transmitted from the mobile phone 10, and the second NFC device 10, 20 responds by sending the requested data. This is repeated as long as there are data be transmitted, indicated in FIG. 5 by the curved arrows. After all the requested data is received by the phone app in phone 10, the NFC field is returned to standby mode 220, e.g. turned off. In standby mode 220, the NFC system is waiting for data to be transferred.

[0063] Depending on the application, the time period in active data mode 210 and the time in standby mode 220 can be based on a time division multiplex scheme. The time division can be defined time slots controlled by an application, the active NFC device 10 or the second NFC device 10, 20. These time slots can be fixed initially or be dynamically adjusted. If the second NFC device 10, 20 controls the time slots, control information must be transmitted from the second NFC device 10, 20 to the active NFC device 10.

[0064] During active mode 210 and standby mode 220, both the strength of the NFC field and the duration of NFC field contributes to a tradeoff between need for power harvesting in the second NFC device 10, 20, response time and power consumption in the active NFC device 10.

[0065] FIG. 6 illustrates a similar scenario as FIG. 5 where control of PSM 200 is done in the active NFC device 10. In FIG. 6, the curved arrows indicate that after some number of requests, standby mode 220 is entered. For this option, the standby mode can last as long as there are no data to be transferred, either from the second NFC device 10, 20 to the active NFC device 10 or the other way. The second NFC device 10, 20 is kept alive by power harvesting as previously described.

[0066] FIG. 7 illustrates an example of how feedback from the second NFC device 10, 20 can be used to adjust the NFC field strength in order to arrive at a desirable tradeoff between power harvesting in the second NFC device 10, 20, response time for responding to a new request for data and power consumption in the active NFC device 10. The second NFC device 10, 20 informs an application program in the active NFC device 10 to adjust the NFC field strength.

[0067] Optionally, as indicated previously, the NFC field can be turned off for a controlled period of time to arrive at a desirable tradeoff between power harvesting in the second NFC device 10, 20, response time for responding to a new request for data and power consumption in the active NFC device 10.

[0068] An important property of the present invention is to maintain power in the second NFC device 10, 20 when in connected mode 310 with the first active NFC device 10. This is quite important because the second NFC device 10, 20 is prepared to be powered just via e.g. a capacitor without any primary or secondary battery. This means that harvesting of power from the first active NFC device is the primary or only source of power in the second NFC device 10, 20.

[0069] In order to ensure sufficient power, bursts of carrier waves, ‘keep alive carrier’ (KAC), can optionally be initiated. KAC is not depicted in the drawings. The parameters that define the KAC are: [0070] the field strength of the KAC; [0071] duration of a KAC burst; and [0072] resting period before a KAC burst.

[0073] The KAC can optionally be controlled by the first or the second NFC device 10, 20 in order to be able to adapt the KAC to current requirements. Controlling can be adapted to variations of parameters in electronic components and operating environment. Electronic component parameters comprise capacitance and power consumption.

[0074] When a sequence of data is transmitted over an NFC link, power harvesting is done with the normal carrier wave. If a carrier wave is not present long enough to ensure power harvesting in the second NFC device 10, 20 is able to supply the second NFC device 10, 20 with sufficient power to stay alive, a KAC burst may be introduced to enable more power. In this way the system of power harvesting can ensure continued operation of the second NFC device 10, 20.

[0075] Operations that are done in SW, particularly in high level SW, normally have a relatively long, variable and not controlled duration. When two devices communicate, such as two NFC devices 10, 20, latency has to be included to have reliable communication. The timing operation of KAC can get much improved and made more or less independent on timing of high level SW and is prepared to be performed in a chipset in a device such as a mobile telephone. Because HW in a chipset can be expected to result in much improved timing, latency can be reduced and enough power in the second NFC device is easier to maintain with less redundant power. Controlling the power harvesting to the second NFC device 10, 20 with high level SW will consequently result with less precise, higher latency timing and consequently higher power consumption than necessary.

[0076] One particularly relevant way to control the behavior of said chipset regarding KAC is to evaluate the need for power in the second NFC device by high level SW and transfer related parameters to the chipset. This optionally can be updated when in operation. In this way, power harvesting in the second NFC is more reliable, with less redundant power consumption and less dependent on timing in high level SW.

[0077] This way of administration of the chipset not only relates to KAC but also to controlling power levels of normal NFC signals.