Field of the Invention

The present invention relates to a mobile communication terminal. Specifically, the present invention relates to a mobile communication terminal, comprising a processor, an elec- tronic communication circuit for mobile radio communication, and a battery.

Background of the Invention

Keyless entry systems have become widely used in applications ranging from vehicle entry systems and vehicle access control, to building, room, and location access control. Earlier magnetic stripe cards which reguire a user to swipe a card through a reader have mostly been replaced by radio-freguency identification ( RFID) transponders (or tags) which the user brings into contact (or brings very close to) a reader device. Other known solutions which do not reguire such close contact use infrared systems or radio systems to transmit an authenticating signal from the user device to a vehicle security system or to a building access control terminal. The authentication can be initiated either by the user, for instance by pressing a button on the user device, or from the access control terminal itself which periodically transmits reguest signals and waits for a response message.

An increasing number of access control systems that users use day to day reguire an in creasing number of transponders or tags to be carried, making their use cumbersome. Mobile phones equipped with NFC modules have allowed mobile phones to be used for the use of making payments and access control, however the operational distance remains small and security concerns remain. Specifically, the communication layer may be vulnera ble to relay attacks. Furthermore, reliability remains a concern for users. Summary of the Invention

It is an object of this invention to provide a mobile communication terminal which does not have at least some of the disadvantages of the prior art mobile communication terminals.

According to the present invention, these objects are achieved through the features of the independent claims. In addition, further advantageous embodiments follow from the de- pendent claims.

A mobile communication terminal comprises a processor, an electronic communication cir cuit for mobile radio communication, and a battery connected to the processor and the electronic communication circuit. The processor is configured to determine an energy state of the battery and to perform a shutdown operation of the mobile communication termi- nal, upon determining that the energy state of the battery is below a defined minimum energy threshold, such that the processor and the electronic communication circuit are no longer operating. According to the present invention, the above-mentioned objects are particularly achieved in that the mobile communication terminal further comprises an access control system which comprises an electronic control circuit and a transceiver, whereby the electronic con trol circuit and the transceiver are connected to the battery. The electronic control circuit is configured to control the transceiver to exchange access control data with an external ac cess control device unaffected by the shutdown operation, such as to continue operating when the energy state of the battery is below the minimum energy threshold.

In an embodiment, the electronic control circuit is further configured to determine that the energy state of the battery is below the defined minimum energy threshold, and to reduce a polling freguency for the transceiver, such as to detect the presence of the external access control device at extended time intervals, when the energy state of the battery is below the defined minimum energy threshold.

In an embodiment the access control system further comprises a data store connected to the electronic control circuit, the data store having stored therein an encrypted emergency access reguest. The electronic control circuit is further configured to determine that the energy state of the battery is below a defined emergency energy threshold. When the en ergy state of the battery is below the defined emergency energy threshold, electronic con trol circuit is further configured to control the transceiver to transmit to the external access control device the encrypted emergency access reguest. The encrypted emergency access reguest enables the external access control device to determine from the encrypted emer- gency access request credentials associated with the mobile communication terminal, us ing a secret cryptographic key, and to check access rights of the mobile communication terminal, using the credentials.

In an embodiment the processor is configured to receive from a user of the mobile com- munication terminal a selection of access request credentials, and to generate and store the encrypted emergency access request, using a secret cryptographic key associated with the selected access request credentials.

In an embodiment the access control system further comprises a Near Field Communica tions ( NFC) circuit. The electronic control circuit is configured to determine that the energy state of the battery is below a defined switch-over energy threshold, and to stop polling by the transceiver, when the energy state of the battery is below the defined switch-over en ergy threshold, until a presence of the external access control device is indicated by the Near Field Communications circuit.

In an embodiment the access control system further comprises a Near Field Communica- tions circuit configured to harvest energy irradiated by the external access control device.

In an embodiment the mobile communication terminal comprises an electrical connection between the access control system and the battery, which electrical connection is non-in- terruptible by the processor, such as to enable the electronic control circuit and the trans ceiver to draw electrical energy from the battery after a shutdown operation by the pro cessor.

In an embodiment the transceiver comprises an ultra-wideband transceiver configured to exchange ultra-wideband transmissions with the external access control device.

In an embodiment the electronic control circuit is configured to determine a distance of the external access control device from the mobile communication terminal, using transmis sion properties of the ultra-wideband transmissions.

In a further embodiment the electronic control circuit is configured to control the trans- ceiver to exchange the access control data with the external access control device, depend ing on a comparison of the distance to a proximity threshold.

In a further embodiment the electronic control circuit is configured to adjust a polling fre quency for the transceiver, depending on the distance.

Brief Description of the Drawings The present invention will be explained in more detail, by way of example, with reference to the drawings in which: Fig. 1 shows a block diagram illustrating schematically a mobile communication ter minal and an access control device;

Fig. 2 shows a flow diagram illustrating an exemplary seguence of steps for perform ing access control between a mobile communication terminal and an access control device in a low battery state of the mobile communication terminal.

Detailed Description of the Preferred Embodiments

In Figure 1 , reference numeral 1 refers to a mobile communication terminal, more specifi cally, mobile electronic communication devices such as mobile radio phones (cellular phones), tablet computers, laptop computers, smart watches, or other operable mobile electronic devices comprising a battery powered electronic circuit, e.g. a programmed pro cessor and /or an application specific integrated circuit (ASIC), and a radio transceiver.

The mobile communication terminal 1 comprises a processor 1 1 which controls such func tions as monitoring power connections, regulating voltage and enabling dynamic voltage scaling, monitoring battery charging and battery discharging, and controlling power to other components of the mobile communication terminal 1 , such as an electronic commu nication circuit 1 2, a display screen, and input/output hardware such as audio transducers and microphones. The processor 1 1 may comprise a system on a chip (SoC), or other pro cessing units, such as a central processing unit (CPU ), a graphics processing unit (GPU), memory, input/output ports, and further integrated circuitry or modules for specific com- puting tasks involving digital, analog, mixed-signal, and radio-freguency functions. Spe cifically, the processor 1 1 comprises a power management unit ( PM U ), a power manage ment integrated circuit ( PM IC), a system management unit (SM U), and/or a system man agement controller (SMC). The mobile communication terminal 1 comprises a battery 1 3 which is connected to the processor 1 1 . The battery 1 3, more specifically a rechargeable battery, such as a Lithium- ion battery, has an energy state which decreases as the mobile communication terminal 1 consumes electrical energy, and increases when the mobile communication terminal is connected to a charging device. As illustrated in Figure 1 , the mobile communication terminal 1 comprises an access control system 1 0, more specifically an electronic module comprising integrated circuits, discrete components and other electronic components for processing data, storing data, receiving data, and transmitting data. The access control system 1 0 is connected to the battery 1 3 by way of an electrical connection 1 00, more specifically by a cable or by a conductive trace. The access control system 1 0 comprises a data store 1 01 , more specifically a memory module of flash memory or EEPROM memory. The processor 1 1 is connected to the data store 1 01 of the access control system 1 0.

The access control system 1 0 comprises an electronic control circuit 1 02. The electronic control circuit 1 02 comprises a programmable processor, an application specific integrated circuit (ASIC), and/or other logic units configured to perform various functions and oper ations as described later in more detail.

The access control system 1 0 comprises a transceiver 1 03, more specifically an ultra-wide band transceiver. The transceiver 1 03 is connected to the electronic control circuit 1 02 and comprises an antenna (not shown). The transceiver 1 03 comprises a plurality of modes including at least an active mode and an inactive mode. When the transceiver 1 03 is in the inactive mode it consumes no energy or at least less electrical energy than when it is in the active mode. When the transceiver 1 03 is in inactive mode it does not transmit or receive transmissions. The transceiver 1 03 can be switched between active mode and inactive mode by the electronic control circuit 1 02. The active mode of the transceiver 1 03 further comprises a plurality of modes including a transmitting mode, a listening mode, and a sleep mode. If the transceiver 1 03 is not in the transmitting mode, the transceiver 1 03 periodi cally switches between a listening mode, in which the transceiver 1 03 listens for reguest messages for a listening period, and a sleep mode in which the transceiver does not listen for reguest messages. In the sleep mode the transceiver 1 03 consumes less energy than in the listening mode. Specifically, the listening period may be between 1 0 ms and 1 ms, and the sleep period may be between 1 0 s and 0.1 s. The number of times per second in which the transceiver 1 03 is in the listening mode is determined by a polling freguency. The elec tronic control circuit 1 02 is configured to reduce or increase the polling freguency by trans- mitting a signal to the transceiver 1 03. For example, if the electronic control circuit 1 02 transmits a signal to the transceiver to reduce the polling freguency, the transceiver 1 03 increases the sleep period. The access control system 1 0 further comprises a near field communication circuit ( N FC) 1 04. The near field communication circuit 1 04 is configured to transmit and receive infor mation and energy using electromagnetic induction via a loop antenna ( not shown). In an embodiment, the near field communication circuit 1 04 is connected to the battery 1 3. The mobile communication terminal 1 comprises an electronic communication circuit 1 2, which may comprise a WLAN transceiver (Wireless Local Area Network), a mobile radio transceiver, and a Bluetooth transceiver. The electronic communication circuit 1 2 is con nected to the battery 1 3 via a switch S. The state of the switch S is controlled by the pro cessor 1 1 . If the switch S is closed, the electronic communication circuit 1 2 is connected to the battery 1 3. If the switch S is open, the electronic communication circuit 1 2 is discon nected from the battery 1 3. In an embodiment, the switch S is integrated into the electronic communication circuit 1 2. In another embodiment, the processor 1 1 is configured to power up or power down the electronic communication circuit 1 2 by transmission of a signal. Reference numeral 2 refers to an external access control device, more specifically an elec tronic device which is part of an access control system, mounted on or in a wall near a doorway or access control location, or incorporated into a door or gate itself. The external access control device 2 is connected to a lock ( not shown) and configured to generate a locking and/or unlocking signal for the lock to lock or unlock the door or gate such as to block or unblock access to an access controlled area. The external access control device 2 comprises a transceiver, specifically an ultra -wideband transceiver. The external access control device 2 is configured to exchange ( receive and transmit) data with the mobile communication terminal 1 , using the transceiver, in a transmission T. In an embodiment, the external access control device 2 comprises a near field communications circuit. The ex ternal access control device 2 is configured to transmit data and energy to the mobile com- munication terminal 1 , using the near field communication circuit, in a near field commu nications transmission N. The external access control device 2 is separated from the mobile communication terminal 1 by a distance d. A proximity threshold P is a predetermined dis tance from the external access control device 2, specifically a distance of 5 meters, 2 me ters, or 1 meter. At this point it is be pointed out, that portable devices typically do not utilize all available battery energy during normal operation. Specifically, during normal operation, the battery 1 3 of the mobile communication terminal 1 is not discharged until no energy is left in the battery 1 3. The battery 1 3 is generally operated between a minimum energy threshold and a maximum energy threshold, as routinely charging the battery 1 3 above the maximum energy threshold, or routinely discharging the battery 1 3 below the minimum energy threshold would place the battery 1 3 under stress, resulting in a gradual decline in battery performance. There is, however, still energy available in the battery 1 3 belowthe minimum energy threshold. This energy is made available to the access control system 1 0 for per forming emergency access control, therefore enabling the user of the mobile communica- tion terminal 1 to gain access to the access control location even when the mobile commu nication terminal 1 is shut down, as is explained below in more detail. The minimum energy threshold may be expressed as a percentage of charge of a full charge. For example, the minimum energy threshold may be between 5% and 25% of a full charge. Alternatively, the minimum energy threshold may be expressed as a battery cell voltage. For example, if the battery 1 3 is a Lithium-ion battery, the minimum energy threshold may be between 2.9 V and 3.1 V, specifically 3 V. Other battery chemistries may have other minimum energy thresholds. Alternatively, the minimum energy threshold may be expressed as an amount of electric charge. For example, the minimum energy threshold may be between 1 00 mAh and 400 mAh. The specific value of the minimum energy threshold depends on the specific battery chemistry used in the battery 1 3, the expected operating conditions of the mobile communication terminal 1 , and other factors such as the number of charge and discharge cycles the battery 1 3 has undergone, and the number of charge and discharge cycles the battery 1 3 is expected to undergo during the opera tional lifetime of the battery 1 3. The minimum energy threshold is a value stored in the mobile communication terminal 1 during design and/or commissioning. The processor 1 1 may be configured to change the minimum energy threshold using a counter, which coun ter stores the number of charge and discharge cycles the battery 1 3 has undergone. Alter natively, the processor 1 1 may be configured to change the minimum energy threshold using a stress indicator, which stress indicator represents the total stress the battery 1 3 has been exposed to during its operational life, the total stress being an accumulation of stresses due to charging and discharging, remaining at given charge or discharge states for extended periods of time, exposure to cold temperatures, and other factors which affect battery performance. In addition to the minimum energy threshold, a plurality of further energy thresholds are also defined (stored) in the mobile communication terminal 1 , including at least a switch over energy threshold and an emergency energy threshold. As above for the minimum en ergy threshold, the energy thresholds may be expressed as percentages of a full charge of the battery 1 3, as specific values of the voltage of the battery 1 3, or as an amount of elec tric charge of the battery 1 3. Also, as above for the minimum energy threshold, the plural ity of energy thresholds are set during the design and/or commissioning of the mobile communication terminal 1 , and may be changed by the processor 1 1 during the opera tional lifetime of the battery 1 3. As is explained below in more detail, the electronic control circuit 1 02 is configured to determine the energy state of the battery 1 3 and compare it to the energy thresholds, and to perform specific functions using the comparison of the en ergy state of the battery 1 3 with the plurality of energy thresholds.

In the following paragraphs, described with reference to Figure 2 are the steps, functions, and operations performed by the processor 1 1 , the electronic control circuit 1 02 of the access control system 1 0, and the external access control device 2, for exchanging access control data between the mobile communication terminal 1 and the external access control device 2.

Departing from step S1 1 , the processor 1 1 receives a selection of access reguest creden tials from a user of the mobile communication terminal 1 . In an embodiment, the selection of access reguest credentials are received by the processor 1 1 from an access control server (not illustrated) via the electronic communication circuit 1 2, or via the access control sys tem 1 0.

In step S 1 2, the processor 1 1 generates an encrypted emergency access reguest, using a secret cryptographic key associated with the access reguest credentials selected. The pro- 5 cessor 1 1 transfers the encrypted emergency access reguest to the data store 1 01 , which stores the encrypted emergency access reguest.

In step S1 3, the energy state of the battery 1 3 is determined by the processor 1 1 . In an embodiment, the processor 1 1 determines the energy state of the battery 1 3 by measuring the voltage of the battery 1 3. 0 In step S 1 4, the processor 1 1 compares the determined energy state of the battery 1 3 to the minimum energy threshold. If, in step S1 4, the processor 1 1 determines the energy state of the battery 1 3 to be above the minimum energy threshold, the processor 1 1 re turns to step S 1 3. If, in step S 1 4, the processor 1 1 determines the energy state of the bat tery 1 3 to be belowthe minimum energy threshold, the processor 1 1 performs a shutdown5 operation in step S 1 5.

In the shutdown operation of step S1 5, the processor 1 1 disconnects the battery 1 3 from the electronic communication circuit 1 2 by opening the switch S. The shutdown operation also shuts down the processor 1 1 , or places it in a sleep mode, where it consumes little or no electrical energy, until the energy state of the battery 1 3 is above the minimum energy threshold. The shutdown operation further disconnects other components (not shown) of the mobile communication terminal 1 from the battery 1 3, such thatthe other components shut down and no longer consume electrical energy. The shutdown operation however does not disconnect the access control system 1 0 from the battery 1 3. The access control system 1 0 remains connected to the battery 1 3 by at least the electrical connection 1 00. In an embodiment, the near field communication circuit 1 04 in the access control system 1 0 is further connected to the battery 1 3 via a connection separate from the electrical con nection 1 00.

In step S21 , the electronic control circuit 1 02 of the access control system 1 0 determines the energy state of the battery 1 3. The electronic control circuit 1 02 determines the energy state of the battery 1 3 by determining the voltage on the electrical connection 1 00.

In step S22, the electronic control circuit 1 02 compares the energy state of the battery 1 3 with the switch-over energy threshold, which may be a switch-over voltage threshold be tween 2.5 V and 3.2 V, such as 2.9 V, or 2.7 V.

In step S23, if the energy state of the battery 1 3 is less than the switch-over energy thresh old, the electronic control circuit 1 02 sends a signal to the transceiver 1 03, switching it to inactive mode. The electronic control circuit 1 02 returns to step S21 after a wait period.

In step S24, if the energy state of the battery 1 3 is determined by the electronic control circuit 1 02 to be higher than the switch-over energy threshold, the energy state of the battery 1 3 is compared by the electronic control circuit 1 02 to the emergency energy threshold, which may be an emergency voltage threshold between 2.5 V and 3.2 V, such as 3 V, or 2.8 V.

In step S25, if the energy state of the battery 1 3 was determined by the electronic control circuit 1 02 to be lower than the emergency energy threshold, then the electronic control circuit 1 02 reads, from the data store 1 01 , the encrypted emergency access reguest. The electronic control circuit 1 02 transmits the encrypted emergency access reguest to the transceiver 1 03.

In step S26, if the energy state of the battery 1 3 was determined by the electronic control circuit 1 02 to be higher than the emergency energy threshold, then the electronic control circuit 1 02 checks whether the energy state of the battery 1 3 is lower than the minimum energy threshold.

In step S27, if the energy state of the battery 1 3 is lower than the minimum energy thresh old, the electronic control circuit 1 02 sends a signal to the transceiver 1 03 to reduce the polling f reguency. Reducing the polling freguency of the transceiver 1 03 reduces the elec- trical energy consumed by the transceiver 1 03. If the energy level of the battery 1 3 is de termined by the electronic control circuit 1 02 to be higher than the minimum energy threshold, the electronic control circuit 1 02 returns to step S21 after a predetermined wait period.

The loop antenna (not shown ) of the Near Field communication circuit 1 04 receives the near field transmission N from the access control device 2. In step S29, the Near Field communication circuit 1 04 of the access control system 1 0 checks whether a near field transmission N was detected.

The energy received and harvested by the Near Field communication circuit 1 04 in the near field transmission N is transmitted to the access control system 1 0, specifically the elec- tronic control circuit 1 02 and /or the transceiver 1 03, such that the transceiver 1 03 re ceives energy to operate.

In step S28, upon receiving the near field transmission N, the near field communications circuit 1 04 transmits a signal to the transceiver 1 03, such that the transceiver 1 03 switches to the active mode, insofar as the transceiver 1 03 is not already in the active mode. As detailed above, when the transceiver 1 03 is in active mode it may receive transmissions and transmit transmissions, exchanging data with the access control device 2.

In step S31 , the transceiver 1 03 detects the access control device 2. The access control device 2 periodically transmits reguest messages. The access control device 2 further listens for response messages. If the transceiver 1 03 is in active mode it may receive the reguest message in a transmission from the access control device 2 during the listening period of the transceiver 1 03. Upon receiving the reguest message, the transceiver 1 03 transmits a response message, using the reguest message, which is received by the access control de vice 2. The access control device 2 determines the distance d between the access control device 2 and the mobile communication terminal 1 , using transmission properties of the transmissions. The transmission properties comprise a time difference between transmit ting the reguest message and receiving the response message. The time difference, along with a processing time of the transceiver 1 03, is used to determine a time-of -flight of the request message and /or the response message, which time-of -flight is used to determine the distance d.

The electronic control circuit 1 02 is configured to adjust the polling frequency for the trans ceiver 1 03 depending on the distance d. For example if the distance d is very large com- pared to the proximity threshold P, the polling frequency is reduced. If the distance d is only slightly larger than the proximity threshold P, the polling frequency is increased.

In step S32, if the distance d is less than or equal to the proximity threshold P, then the mobile communication terminal 1 is within access control range, and the mobile commu nication terminal 1 and the access control device 2 exchange access control data. If the electronic control circuit 1 02 determines that the energy level of the battery 1 3 is higher than the minimum energy threshold, exchanging access control data comprises the trans ceiver 1 03 transmitting an access request message, comprising encrypted access request credentials associated with the mobile communication terminal 1 . If, however, the energy level of the battery 1 3 was determined by the electronic control circuit 1 02 to be less than the emergency energy threshold, then the access request message comprises the en crypted emergency access request determined in step S25. The encrypted emergency ac cess request of the access request message further comprises an emergency status indica tor, such that the access control device 2 can determine, using the emergency status indi cator, that the mobile communication terminal 1 is shut down, specifically, that the energy state of the battery 1 3 of the mobile communication terminal 1 is below the emergency energy threshold. The access control device 2 receives the access request message, and checks the access rights of the mobile communication terminal 1 using the encrypted ac cess request credentials. If the access control device 2 validates the access rights, then the door or gateway associated with the access control device 2 is unlocked or opened and the user of the mobile communication terminal 1 is granted access to the access control loca tion.

In an embodiment, the mobile communication terminal 1 further comprises a user activat- able operating element, enabling the user to manually activate the transceiver 1 03. The user activatable operating element, specifically a switch, button, or other hardware ele ment, is connected to the electronic control circuit 1 02 of the access control system 1 0. Upon activation of the user activatable operating element by the user, the electronic con trol circuit 1 02 activates the transceiver 1 03 for a predetermined period of time, for exam- pie between 2s and 1 0s, such that it may receive the reguest message in a transmission from the access control device 2. Upon receiving the reguest message, the transceiver 1 03 and the access control device 2 perform access control as detailed above.