WO2013190410A1

WO2013190410A1 - Hybrid rf – optical link for mobile communication devices

Info

Publication number: WO2013190410A1
Application number: PCT/IB2013/054442
Authority: WO
Inventors: Julian Charles Nolan; Alexander Henricus Waltherus Van Eeuwijk; Cornelis Jojakim Jalink; Ag AA
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-06-21
Filing date: 2013-05-29
Publication date: 2013-12-27

Abstract

Proposed is a mobile communication device (100), comprising a first means for communication (110) -such as an RF transceiver -with another communication device, a second means for communication (120) -such as a light source -with the other communication device, and a controller (130) for switching between the first and second means for communication. The controller is arranged to switch by applying a figure of merit indicator based on a biologicalparameter. This is especially advantageous for avoiding health risks due to exposure to electromagnetic radiation detrimental to the human body.

Description

Hybrid RF - Optical link for mobile communication devices

FIELD OF THE INVENTION

The invention relates to a communication device enabled to establish a hybrid wireless radio frequency (RF) and optical communication link between (mobile)

communication devices, such as used in a terrestrial communication system. Such a hybrid link is used in particular to safeguard a maximum data transmission rate irrespective of atmospheric circumstances and operating conditions.

BACKGROUND OF THE INVENTION

A hybrid wireless RF and optical communication link is known from

US2004/0208591. That document discloses a communication system and link utilizing free- space optical and RF paths for transmitting data and control and status information. The optical link provides the primary path for the data, as it provides a higher capacity path when favourable free-space atmospheric conditions prevail. Free-space optical links transmit a light or laser beam through the atmosphere between an optical transmitter and an optical receiver. Communication systems based on free-space optical links require a clear line-of- sight between the transmitter and receiver. The optical beam, while allowing high data rates, however, is subject to degradation by smoke, dust, fog, rain, snow, and any other particles in the atmosphere between the communication points. In contrast, wireless RF communication links involve broadcasting an RF signal carrying the data. Typically particles and substances in air do not cause substantial RF signal degradation, allowing a greater assurance of accurate and effective data transmission although at a lower data transfer rate. Thus, when free-space atmospheric conditions have degraded the effectiveness of the optical path to such a point that a quality-of-service parameter falls below a predetermined level, it is more effective to transmit the data over the secondary RF path. Control and status information is preferably transmitted over the more reliable RF path in either circumstance.

While the prior art provides guidance on switching over from the optical path to the RF communication path, there is a need for an indicator for switching from the RF path back to the optical path, especially under circumstances and for devices designed to have the RF link as the primary communication path. SUMMARY OF THE INVENTION

The invention has as an objective providing a communication device of the kind set forth, which provides reliable and safe operation conditions for its users. This object is achieved according to the invention with a communication device comprising a first transceiver for communication with another communication device in a first part of the electromagnetic spectrum, and a second transmitter for communication with the other communication device in a second part of the electromagnetic spectrum, wherein the communication device further comprises a controller arranged to switch between the first transceiver and the second transmitter by applying a figure-of-merit indicator based on a biological parameter.

The invention provides a communication device that minimises the exposure of users to high frequency electromagnetic fields. The invention is based on the insight that mobile communication devices, such as mobile phones, smart phones, tablet computers, wireless microphones, and the like, have a RF link as their primary communication channel with other mobile devices or with a base station. Moreover, RF radiation (100 kHz - 300 GHz) is known to provide a health hazard at sufficiently large power levels, and international studies towards possible cancer risks due to the relative high local exposure of the user's head when using mobile phones are on-going. Thus switching over to an optical free-space data link under circumstances where the exposure to an RF field approaches biological effective levels minimizes the health risks to users. Such circumstances may occur when use of mobile communication devices is made inside constructions - such as buildings, elevators, tunnels, etc. - which may severally reduce the transmission of the RF data signals. The inventors have recognised that in such circumstances, the lighting infrastructure available inside the constructions allows for an excellent alternative communication network wherein data is transmitted in the optical part of the electromagnetic spectrum by modulation of the light emitted by light sources such that these modulations are invisible to the human eye.

An embodiment of the invention according to claim 2 provides a communication device wherein the biological parameter is related to a Specific Absorption Rate (SAR) indicator of the mobile communication device as defined by international standards, like IEC 62209-1 :2005 and IEC 62209-2:2010. Advantageously this defines a biological parameter relevant for health risks

According to an embodiment of the invention the controller of the communication device is further arranged to switch between the first transceiver and the second transmitter based on an estimation of the SAR indicator from an instantaneous power level of radiation emitted via the first means for communication.

In an embodiment of the communication device according to the invention the controller is further arranged to switch between the first transceiver and the second transmitter based on an estimation of the SAR indicator from a predicted future power level of radiation to be emitted via the first transceiver.

In an embodiment of the invention the controller is further arranged to switch between the first transceiver and the second transmitter based on an estimation of the SAR indicator from a cumulative power level of radiation emitted over a predetermined usage time of the communication device via the first transceiver.

In an embodiment the first transceiver comprises an RF transceiver and the first part of the electromagnetic spectrum comprises radio frequencies in the range 20 MHz - 10 GHz.

In an embodiment the second transmitter comprises a light source and the second part of the electromagnetic spectrum comprises visible light.

According to an embodiment the light source comprises a light emitting diode. In yet another embodiment, the communication device further comprises a photosensor for receiving data embedded into light emitted by the other communication device (such as a luminaire comprised in a lighting infrastructure of a construction).

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Appreciate, however, that these embodiments may not be construed as limiting the scope of protection for the invention. They may be employed individually as well as in combination. BRIEF DESCRIPTION OF THE DRAWINGS

Further details, features and advantages of the invention are disclosed in the following description of exemplary and preferred embodiments in connection with the drawings.

Fig. 1 schematically shows an illustration of a communication device according to the present invention.

Fig. 2 shows diagrammatically shows a communication device according to an embodiment of the invention. Fig. 3 shows the use of CDMA OnOff-Keying modulation with pulse width modulation (PWM) and pulse amplitude modulation (PAM), according to another embodiment of the invention.

Fig. 4 shows the use of CDMA BiPhase (DC-BP) modulation with Duty Cycle modulation and amplitude modulation, according to a further embodiment of the invention.

Fig. 5 shows a flow chart showing the steps of an embodiment of the method for controlling the data communication path chosen when using a hybrid communication link, according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows a communication device 100 comprising a hybrid communication link for transmitting and receiving data. The hybrid communication link comprises a first means 110, such as a transceiver, for communication with another communication device in a first part of the electromagnetic spectrum via a first path 111. It furthermore comprises a second means 120, such as a transmitter, for communication in a second part of the electromagnetic spectrum via a second path 121. Moreover, the hybrid communication link comprises a controller 130, such as a microprocessor, enabled to switch transmission and reception of data from the first transceiver 110 to the second transmitter 120 and back.

Preferably the first part of the electromagnetic spectrum comprises radio frequencies (RF) in the range 20 MHz - 10 GHz, more preferably in the range 100 MHz - 6 GHz, such as the 900 Mhz, 1800 MHz, and 1900 MHz transmission bands. The RF communication signal is broadcast in the first path, i.e. RF path 111. Preferably the second part of the electromagnetic spectrum comprises light emitted by a light source of the communication device 100 as part of the second transmitter 120, such as a light emitting diode or laser diode. In an embodiment, the light comprises visible light or infrared light.

Both the RF signal and the light signal are transmitted wirelessly through free- space from the communication device 100 to the other communication device (not shown), enabling data to be transmitted between the communication devices. The other

communication device could be a base station for receiving and forwarding the data to and from the communication device 100. Alternatively, it could be a second communication device, similar to the communication device 100, if a device-to-device network is utilized, for example. Alternatively still, the other communication device could be a luminaire comprised in an illumination system of a construction, such as a building, tunnel, elevator, etc. An input/output (I/O) interface 140 allows connection between the

communication device 100 and other communication stations (not shown) or devices (such as memory devices) via an I/O path 141, enabling the communication device 100 to connect with a larger communication network. Such a connection may be realised by e.g. an optical fibre or an electrical wire channel. Alternatively, the I/O interface 140 may be a

microphone/speaker user interface for enabling a user to interact with the communication device 100 via an audio path 141. Thus, the data transmitted via the first 111 and/or second 121 paths is received from and/or delivered to the I/O signal path 141.

The first path, i.e. RF path 111, serves as the main or preferred communication path for the data to be transmitted. The second path, i.e. optical path 121 serves as the safety communication path in case the power level of the RF radiation in the first path 111 causes a biological parameter to reach or surpass a predetermined safety level or threshold value. Above this safety level a user of the communication device 100 may be increasingly concerned about health risks due to the interaction of the RF radiation with the user's body.

Considering the interaction between electromagnetic fields and biological tissue, such as the human body, several frequency ranges have been identified, as exposure to time-varying electromagnetic fields result in internal body currents and energy absorption in tissues that depend on the coupling mechanism and the frequency involved. Exposure to low- frequency electric and magnetic fields (<100 kHz) normally results in negligible energy absorption and no measurable temperature rise in the body. However, exposure to

electromagnetic fields with frequencies above 100 kHz can lead to significant absorption of energy and temperature increases. In general, exposure to a uniform (plane wave)

electromagnetic field results in a highly non-uniform deposition and distribution of energy within the body. With respect to the absorption of energy in the human body, electromagnetic fields can be divided into four ranges:

Frequencies from about 100 kHz to less than about 20 MHz, at which absorption in the trunk decreases rapidly with decreasing frequency, and significant absorption may occur in the neck and legs;

Frequencies in the range from about 20 MHz to 300 MHz, at which relatively high absorption can occur in the whole body, and to even higher values if partial body (e.g. head) resonances are considered;

Frequencies in the range from about 300 MHz to several GHz, at which significant local, non-uniform absorption occurs; and Frequencies above 10 GHz, at which energy absorption occurs primarily at the body surface.

The International Commission on Non-Ionizing Radiation Protection

(ICNIRP) Guidelines for limiting exposure to time varying electromagnetic fields (published in Heath Physics 74(4):494-522, 1998) take into account the following dosimetric quantities within the body in the different frequency ranges:

Current density, J [A/m²], in the frequency range up to 10 MHz; Current, I [A], in the frequency range up to 110 MHz;

Specific energy absorption rate, SAR [W/kg], in the frequency range 100 kHz - 10 GHz;

Specific energy absorption, SA [J/kg], for pulsed fields in the frequency range 300 MHz - 10 GHz; and

Power density, S [W/m²], in the frequency range 10 GHz - 300 GHz.

For mobile communication devices especially the Specific energy Absorption Rate (SAR) is of interest, given the operational frequencies of their RF links. Moreover, for these devices and frequencies human exposure can occur under near- field conditions, as the phone may be used close to the head. The frequency-dependence of energy absorption under these conditions is very different from that described for far- field conditions. Near-field exposure can result in high local SAR (e.g. in the head, wrist, ankles). Furthermore, whole- body and local SAR values are strongly dependent on the separation distance between the RF source and the body. ICNIRP advises the following restrictions for time varying

electromagnetic fields in the frequency range 100 kHz - 10 GHz (with f the frequency in Hz):

The SAR indicator, as defined by e.g. the standards IEC 62209-1 :2005 and IEC 62209-2:2010, is related to the local electric field E(r) in the body according to

Here p is the density of the body, and σ its electrical conductivity. SAR values are averaged over a 6 minute period and use a 10 gram average mass of biological material (tissue, bones, etc.)

Thus in order to calculate or estimate the SAR indicator under operational conditions the RF power transmitted by communication device 100 and its distance r to the body of the operator are determining factors.

The power transmitted by the communication device 100 is preferably controlled by a fast closed loop power control. By measuring the signal-to-interference ratio (SIR) on a regular basis - typically every millisecond or less - and comparing this to a target SIR level, a controller, e.g. located in a base station or other communication device, calculates a power control command that is send to the communication device 100 via a downlink data control channel. This downlink data control channel may be established via the first 111 and/or second 121 path. If the measured SIR level is below target, the controller instructs the communication device to increase its transmit power. Similarly, if the measured SIR is above target, an instruction to decrease the transmit power is provided. Increase and decrease of the transmit power typically is done in 1 dB steps. As a consequence, the communication device 100 regularly adjusts its transmit power up and down to hold the received SIR at the base station close to the target value. Alternatively, the controller may be located in communication device 100 itself and SIR is measured applying a communication link with another communication device.

The target SIR value itself is adjusted over longer timescales through measuring the block-error-rate (BLER) in the received signal by the base station. By comparing the measured BLER with a target value associated with the data stream, the base station decides to adjust the SIR target value. If the measured BLER is greater than its target value, the target SIR value is adjusted upwards. Similarly, a downward adjustment of the target SIR value follows a measured BLER below its target value. An upward adjustment of the target SIR value will cause the communication device 100 to increase its transmit power, thus reducing the error rate.

In an embodiment the SAR value may be calculated based on the power level of the RF radiation emitted by communication device 100 and a predetermined value of the distance between the communication device 100 and the user's body. In order to establish the distance between communication device 100 and a user's body more accurately, the communication device may comprise a proximity sensor 150 - see Fig. 2. The proximity sensor 150 may be a capacitance sensor comprising a first or ground electrode and a second electrode. The proximity sensor may be coupled to the processor 130 for enabling it to calculate the SAR value using a determined distance between the communication device 100 and the user's body. As an alternative to the capacitance sensor, the proximity sensor 150 may comprise an infrared detector, a temperature detector, a pressure sensitive pad, an ultrasound range finder, or a mechanical switch that is depressed when in contact with the user's body.

When the proximity sensor 150 determines contact or close proximity with the user's body (typically at distances between sensor and body of up to 1 cm), the processor 130 may establish a high SAR value, as the electrical field typically is proportionate to the reciprocal of the distance to the source. The SAR indicator established by processor 130 may be based on an instantaneous power level of radiation emitted via the first transceiver 1 lOr. Furthermore, it may be based on the distance established by the proximity sensor 150. If the SAR indicator established in this way surpasses a predetermined threshold level, controller 130 may switch between the first transceiver 110 of communication and the second transmitter 120 of communication. The predetermined threshold level or value may be stored in a memory of the communication device 100. Alternatively, the communication device 100 may comprise a user interface, such as a graphical user interface via a display of the communication device, or a mechanical user interface such as a slider or rotary knob, allowing a user to adjustably control the threshold level.

As an alternative to establishing the SAR indicator based on an instantaneous power level emitted by communication device 100, the SAR indicator may be established based on an estimation of the SAR indicator from a predicted future power level of radiation to be emitted via the first transceiver 110. As an example, controller 130 may use the power level control commands received via the downlink from a base station in the communication system to predict a future emitted power level.

In another embodiment, controller 130 may be arranged to switch between the first transceiver 110 and the second transmitter 120 based on an estimation of the SAR indicator using a cumulative power level of radiation emitted over a predetermined usage time of the mobile communication device 100 via the first transceiver. Advantageously, this allows protection of a user to health risks based on the user's cumulative usage of the communication device 100.

The communication link established through the second path 121 may employ data embedded in the light emitted by the light source comprised in the second transmitter 120. To embed the data in the light emitted, the light source may be connected to a modulator for modulation of the driving signal to (one or more of the light elements in) the light source. The communication device 100 may further comprise a sensor, such as a photodetector, and a demodulator for demodulation of the received signal over the second path 121. The signal received may originate from a transmitter 120 of another communication device 100.

Alternatively, the second communication path 121 is established between a communication device 100 and a lighting infrastructure of a construction, e.g. a building, in which the user of the communication device dwells. Alternatively, the lighting infrastructure with which the communication link is established is fore instance part of a road or street lighting

infrastructure within an urban or rural area. The lighting infrastructure, comprising luminaires or fixtures to provide illumination of the environment in which it is installed as a primary function, may further be connected or comprise a first means 110 to establish a communication link over a first path 111 with a base station of the communication system. Advantageously, the distance between the user of the communication device 100 and the transceiver 110 of the lighting infrastructure can be made so large that the biological effect on the user's body of the RF fields generated are negligible.

In the embodiments described above, the communication link of communication device 100 comprises an up-link to the other communication device and a down-link from the other communication device. Under circumstances without any health related risks, both the up and down link may be established via the first or RF path 111. In case, communication device 100 determines that the biological parameter, such as the SAR indicator reaches or surpasses the threshold level, a switch is made enabling the

communication link to be established via the second or optical path 121. Here both the uplink and the down- link may be established via the optical path 121. As by far the largest contribution to the SAR indicator originates from communication device 100 itself when transmitting RF radiation, in an embodiment of the invention the up-link may be established via optical path 121 while the down- link from the base station of the communication system may still be established via RF path 111. Thus, communication device 100 may operate in this embodiment in a hybrid RF (receiving data) - optical (transmitting data) mode.

The modulation and demodulation of the light transmitted and received over the second path 121 may be based on similar modulation schemes as used in encoding data over the first path 111, such as FDMA, TDMA, and CDMA. As an example, the data modulation may be embedded in the signal transmitted over the second path 121 by On-Off Keying modulating. On-Off Keying (OOK) modulation is a type of modulation where digital data is represented as the presence or absence of a carrier wave. In its simplest form the presence of a carrier for a specific duration represents a binary "one" and its absence for the same duration represents a binary "zero", although in principle any digital encoding scheme may be used.

Figure 3 shows two examples on the driving signal to the light source, such as an LED, in order to guarantee the embedded data does not perceivably influence the required illumination of the lighting infrastructure: (1) applying pulse width modulation (PWM) to the second part of a pulse, and (2) applying pulse amplitude modulation (PAM) to the pulse. In Fig. 3 "chip 0" and "chip 1" will have different widths. In principle this would lead to a variation in the light output of the light sources. Nevertheless, this can be repaired by using balanced codes, which means that there is provided the same number of chips 0 and 1.

Therefore the width of pulses, averaged over a code word in the data transmitted, will be exactly the average value between "chip 0" and "chip 1" widths, resulting in the modulation being invisible to the human eye.

In yet another embodiment of the invention, as illustrated in Fig. 4, the modulation method is a generalization of BiPhase (BP) modulation, to allow an arbitrary duty cycle. When the duty cycle equals 50%, Duty Cycle BiPhase (DC-BP) degenerates to BP modulation. In this case, the data is carried in the signal by transmitting "chip 0" and "chip 1" accordingly. To guarantee the required illumination, i.e. light output level of the light sources in the lighting infrastructure, there are two options: (1) modify the duty-cycle of the pulses, and (2) modify the amplitude of the pulses.

Referring to the flow chart of Fig. 5, an embodiment of a method for controlling the data communication path 111, 121 chosen when using a hybrid

communication link comprising a first transceiver 110 and a second transmitter 120 according to this invention comprises the following steps:

Determine a power level of radiation via the first transceiver 110 when using the first communication path 111 for data transmission, box 501;

Determine a distance between the first transceiver 110 and the body of a user of the communication device 100, box 502;

- Establish a figure-of-merit indicator based on a biological parameter representing the biological effective influence of the radiation emitted by the first transceiver 110, box 503;

Determine if the figure-of-merit indicator is larger than a predetermined threshold value, box 504; If the indicator is lower than the predetermined threshold value return to box 501 for repeating the procedure;

Switch over to the second communication path 121 for data transmission via the second transmitter 120 if the indicator is larger than the predetermined threshold value, box 505.

Although the invention has been elucidated with reference to the embodiments described above, it will be evident that alternative embodiments may be used to achieve the same objective. The scope of the invention is therefore not limited to the embodiments described above. Accordingly, the spirit and scope of the invention is to be limited only by the claims and their equivalents.

Claims

CLAIMS:

1 A communication device comprising

(i) a first transceiver for communication with another communication device in a first part of the electromagnetic spectrum, and

(ii) a second transmitter for communication with the other communication device in a second part of the electromagnetic spectrum,

(iii) wherein the communication device further comprises a controller arranged to switch between the first transceiver for communication and the second transmitter for communication by applying a figure-of-merit indicator based on a biological parameter. 2 The communication device according to claim 1, wherein the biological parameter is related to a Specific Absorption Rate (SAR) indicator of the mobile

communication device as defined by an international standard.

3 The communication device according to claim 2, wherein the controller is further arranged to switch between the first transceiver and the second transmitter based on an estimation of the SAR indicator from an instantaneous power level of radiation emitted via the first transceiver.

4 The communication device according to claim 2, wherein, the controller is further arranged to switch between the first transceiver and the second transmitter based on an estimation of the SAR indicator from a predicted future power level of radiation to be emitted via the first transceiver.

5 The communication device according to claim 2, wherein the controller is further arranged to switch between the first transceiver and the second transmitter based on an estimation of the SAR indicator from a cumulative power level of radiation emitted over a predetermined usage time of the communication device via the first transceiver. 6 The communication device according to any of the claims 1 to 5, wherein the first transceiver comprises an RF transceiver and the first part of the electromagnetic spectrum comprises radio frequencies in the range 20 MHz - 10 GHz. 7 The communication device according to any of the claims 1 to 6, wherein the second transmitter comprises a light source and the second part of the electromagnetic spectrum comprises visible light.

8 The communication device according to claim 7, wherein the light source comprises a light emitting diode.

9 The communication device according to claim 7, wherein the communication device further comprises a photosensor for receiving data embedded into light emitted by the other communication device.

10 A method for controlling a data communication path of a hybrid

communication link of a communication device comprising a first transceiver and a second transmitter, comprising the following steps:

Determine a power level of radiation emitted via the first transceiver;

Establish a figure-of-merit indicator based on a biological parameter representing the biological effective influence of radiation emitted by the first transceiver;

Determine whether the figure-of-merit indicator is larger than a predetermined threshold value;

Switch over to a second communication path for data transmission by the second transmitter if the indicator is larger than the threshold value.

11 A method according to claim 10, the method further comprising the step: Determine a distance between the first transceiver and a body of a user of the communication device for establishing the figure-of-merit indicator.