WO2013168170A1

WO2013168170A1 - Communication device with ultrasonic capabilities and method of operating thereof

Info

Publication number: WO2013168170A1
Application number: PCT/IL2013/050408
Authority: WO
Inventors: Simon Litsyn; Igal KOTZER
Original assignee: Ramot At Tel-Aviv University Ltd.
Priority date: 2012-05-10
Filing date: 2013-05-09
Publication date: 2013-11-14

Abstract

There is provided a communication device with ultrasonic capabilities and method of operating thereof. The method comprises: detecting parameters characterizing a communication channel in the communication device; determining parameters characterizing an ultrasonic channel available in the communication device; reducing a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to the determined parameters characterizing the available ultrasonic channel, thus giving rise to an ultrasonic bit- stream; coding said ultrasonic bit-stream against errors with an error correcting code appropriate to said determined parameters characterizing the available ultrasonic channel; modulating the coded ultrasonic bit-stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and generating an over-the-air ultrasonic communication signal corresponding to the modulated ultrasonic bit-stream.

Description

COMMUNICATION DEVICE WITH ULTRASONIC CAPABILITIES AND METHOD OF OPERATING THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patent application number 61/645,334 filed May 10, 2012 and incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to wireless communication, and more particularly to devices for ultrasonic wireless communication and methods of operating thereof. BACKGROUND

Problems of utilizing ultrasonic bandwidth in wireless communication have been recognized in the contemporary art and various systems have been developed to provide a solution, for example:

US Patent Application No. 2003/0003866 (Overy) entitled "Wireless communication device and method" discloses a method of wirelessly communicating between a first and second device, as well as devices for carrying out the method. The method has the steps of: transmitting a first set of data from the first device to the second device using a radio signal; and transmitting a second set of encoded data from the first device to the second device using an acoustic signal. The first set of data comprises information related to the encoding of the second set of data.

US Patent No. 6,363,139 (Zurek et al.) entitled "Omnidirectional ultrasonic communication system" discloses an ultrasonic communication system with an omnidirectional ultrasonic transducer including a housing having a closed side and an open side defining an aperture in the housing. A diaphragm is mounted into the housing to form a sealed cavity between the diaphragm and the closed side of the housing. A second side of the diaphragm is free to transmit ultrasonic signals through the aperture. The diaphragm and aperture both have a largest dimension that is less than or equal to one-quarter wavelength of an ultrasonic signal to be transmitted by the transducer, such that the transducer behaves as a monopole and radiates substantially omnidirectionally.

US Patent No. 6,950,681 (Hoffman) entitled "Transmission of data by ultrasound" discloses a method for transmitting voice data between a head part and a base part of a hands-free telephone, which comprises: compressing information, being the voice data, to be transmitted using compression coding; digitizing the compressed information; spreading the digitized information over a wider frequency band using a CDMA technique; performing a digital to analog conversion on the spread digitized information; converting the digital to analog converted spread information into an ultrasound signal; transmitting the ultrasound signal via an air interface; at a receiver component, receiving the transmitted ultrasound signal and converting the received ultrasonic signal into an analog electrical signal; performing an analog to digital conversion on the analog electrical signal; despreading the analog to digital converted signal using a CDMA technique; and decoding the despread analog to digital converted signal.

US Patent No. 7,269, 452 (Cheung , et al.) entitled "Method and apparatus for localized delivery of audio sound for enhanced privacy" discloses a wireless communication system based on a directional speaker. The system can include an interface unit and a base unit. The audio signals from the speaker can be generated by transforming ultrasonic signals in air. This allows the production of directional audio signals even when the aperture of the speaker has dimensions in the order of a few centimeters. The audio signals from the speaker can be heard hands-free. Further, privacy protection is enhanced. In one embodiment, the interface unit can be attached or integrated to a piece of clothing at the shoulder of the user, with the audio signals from the speaker directed towards one of the user's ears. The wireless communication system can be applied to a number of different areas, including a communication device, such as a cell phone; a hearing aid; an entertainment system; and a computation system, such as a personal digital assistant or a computer. The wireless communication system can be personalized to the hearing characteristics of the user, or to the ambient noise level of the environment. DE Patent Application No. 10115784 (Lehnertz ) entitled "Ultrasound transmission module and station, e.g. for mobile phone, includes demodulator for detecting signal which is superimposed as amplitude modulated signal on carrier signal with fixed carrier frequency" and discloses a system for speech transmission and related components which have no adverse effects on the users' health e.g. mobile phones, and has an amplitude modulator for generating an audible sound effect, especially a speech signal, which is converted into an amplitude modulated signal for a carrier signal, the carrier signal of this signal being specifically above 15KHz, preferably above 20KHz for improved sound quality. US Patent Application No. 2007/0178943 discloses a mobile communication terminal board having an ultrasonic speaker system which can be used without any separate additional device during a viewing of a sky-wave broadcast or during a video calling and which can be free from an echo phenomenon. The mobile communication terminal board includes a baseband chip for processing audio data, an ultrasonic drive chip for receiving and modulating a signal output from the baseband chip to an ultrasonic band signal, and an ultrasonic speaker for outputting the ultrasonic signal output from the ultrasonic drive chip to the outside.

SUMMARY

In accordance with certain aspects of the presently disclosed subject matter, there is provided a communication device comprising: means for detecting parameters

(e.g. channel frequency response and the highest frequency available for transmission in the channel, etc.) characterizing a communication channel in the communication device; means for determining parameters (e.g. parameters indicative of a transmission band available for the ultrasonic channel in the communication device and channel frequency response characterizing said transmission band, etc.) characterizing an ultrasonic channel available in the communication device; means for reducing a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to the determined parameters characterizing the ultrasonic channel available in the communication device, thus giving rise to an ultrasonic bit-stream; means for coding said ultrasonic bit-stream against errors with an error correcting code appropriate to said determined parameters characterizing the ultrasonic channel available in the communication device; means for modulating the coded ultrasonic bit- stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and means for generating an ultrasonic communication signal (e.g. an over-the-air ultrasonic communication signal) corresponding to the modulated ultrasonic bit-stream.

The communication device can further comprise means for adjusting and transmitting the ultrasonic bit-stream in accordance with said determined parameters characterizing the ultrasonic channel available in the communication device.

The communication device can be further associated with an external earphone configured to receive the generated over-the-air ultrasonic communication signal. The earphone can comprise means for demodulating the received signal; means for expanding said demodulated signal to a full rate audio bit-stream; and means for outputting the expanded signal from the earphone. The external earphone can be located on an extension attached to the communication device, manufactured from a non- conductive material, and not comprising any conductive parts.

In accordance with other aspects of the currently presented subject matter, there is provided a method of operating a communication device, the method comprising: a) detecting parameters (e.g. channel frequency response and the highest frequency available for transmission in the channel, etc.) characterizing a communication channel in the communication device; b) determining parameters (e.g. parameters indicative of a transmission band available for the ultrasonic channel in the communication device and channel frequency response characterizing said transmission band, etc.) characterizing an ultrasonic channel available in the communication device; c) reducing a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to the determined parameters characterizing the ultrasonic channel available in the communication device, thus giving rise to an ultrasonic bit-stream; d) coding said ultrasonic bit-stream against errors with an error correcting code appropriate to said determined parameters characterizing the ultrasonic channel available in the communication device; e) modulating the coded ultrasonic bit-stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and f) generating an ultrasonic communication signal (e.g. an over-the-air ultrasonic communication signal) corresponding to the modulated ultrasonic bit-stream.

The operations a) and b) can be periodically repeated and the operations c) - f) can be respectively modified in accordance with newly determined parameters characterizing the ultrasonic channel available in the communication device.

The method can further comprise adjusting and transmitting the ultrasonic bit- stream in accordance with said determined parameters characterizing the ultrasonic channel available in the communication device.

The method can further comprise: transferring the over-the-air ultrasonic communication signal to an external earphone associated with the communication device; demodulating the received signal by a receiver in the earphone; expanding said demodulated signal to a full rate audio bit-stream; and outputting the expanded signal from the earphone.

By way of non-limiting example, modulating the coded ultrasonic bit-stream can be provided with the help of orthogonal frequency division multiplexing (OFDM) whilst using, merely, the bins corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device. By way of alternative non-limiting example, modulating the coded ultrasonic bit-stream can be provided with the help of modulating a single carrier characterized by the center frequency and the signal's bandwidth positioning said carrier in the ultrasonic frequency range within a transmission band characterizing the ultrasonic channel available in the communication device.

In accordance with other aspects of the currently presented subject matter, there is provided a transmitter for a communication device, the transmitter comprising: means for reducing a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to parameters characterizing an ultrasonic channel available in the communication device, thus giving rise to an ultrasonic bit-stream; means for coding said ultrasonic bit-stream against errors with an error correcting code appropriate to said parameters characterizing the ultrasonic channel available in the communication device; means for modulating the coded ultrasonic bit-stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and means for generating an ultrasonic communication signal corresponding to the modulated ultrasonic bit-stream.

In accordance with other aspects of the currently presented subject matter, there is provided an extension capable of being attached to a communication device comprising means for generating an over-the-air ultrasonic communication signal corresponding to a communication signal received by the communication device. The extension comprises an integral earphone configured to receive the generated over-the- air ultrasonic communication signal and a mechanical extender holding said earphone to the communication device, the integral earphone comprising: means for demodulating the received signal; means for expanding said demodulated signal to a full rate audio bit-stream; and means for outputting the expanded signal from the earphone. The extension can be manufactured from a non-conductive material and not comprise any conductive parts. In accordance with further aspects and, in combination with other aspects of the presently disclosed subject matter

Among advantages of certain embodiments of the presently disclosed subject matter is enabling a given communication device, with no need in amending the device's hardware, to support over-the-air transmission via an ultrasonic channel corresponding to at least part of the audio signal received by the given communication device.

By way of non-limiting example, such an ultrasonic channel can be used for reduction of radiation emanating to a user's brain during wireless communication. By way of another non-limiting example, the ultrasonic channel can be generated in addition to the audio channel, and can be used for remote control, m-commerce and/or other applications requiring authorization and/or authentication. Yet, by way of another non-limiting example, such an additional ultrasonic channel can be used for a variety of short-range applications requiring a privacy mode of operation with no limitation of line of sight (e.g. interrogation, guiding, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 illustrates a generalized flow chart of operating a communication device in accordance with certain embodiments of the presently disclosed subject matter;

Fig. 2 illustrates a generalized functional block diagram of a transmitter operable in a communication device in accordance with certain embodiments of the currently presented subject matter; Fig. 3 illustrates a generalized functional block diagram of a receiver operable in a communication device in accordance with certain embodiments of the currently presented subject matter; and

Figs. 4 - 5 illustrate an exemplified cell phone operable in accordance with certain embodiments of the currently presented subject matter. DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention. Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing", "computing", "calculating", "determining", "generating", |"configuring" or the like, refer to the action and/or processes of a computer that manipulate and/or transform data into other data, said data represented as physical, such as electronic, quantities and/or said data representing the physical objects. The term "computer" should be expansively construed to cover any kind of electronic device with data processing capabilities including, by way of non-limiting example, storage system and parts thereof disclosed in the present applications. The operations in accordance with the teachings herein may be performed by a computer specially constructed for the desired purposes or by a general-purpose computer specially configured for the desired purpose by a computer program stored in a computer readable storage medium.

Embodiments of the presently disclosed subject matter are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the presently disclosed subject matter as described herein.

It is to be understood that the term "non- transitory" is used herein to exclude transitory, propagating signals, but to include, otherwise, any volatile or non-volatile computer memory technology suitable to the presently disclosed subject matter.

The references cited in the background teach many principles of ultrasonic communication that are applicable to the presently disclosed subject matter. Therefore the full contents of these publications are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.

Bearing this in mind, attention is drawn to Fig. 1 illustrating a generalized flow chart of operating a communication device in accordance with certain embodiments of the currently presented subject matter. Typically, modern communication devices are characterized by a communication channel and parts thereof (e.g. speakers, analog front ends, etc.) supporting bandwidth of 20KHz or even up to 24KHz, which is beyond the upper limit of the human hearing range (about 18 KHz). Information on the cutoff frequency (i.e. the highest frequency supported by the communication device) is usually available from documentation provided by a manufacturer. Due to engineering considerations and physical phenomena, the frequency response of the entire bandwidth is not flat (e.g. decays near the cutoff frequency).

In accordance with certain embodiments of the currently presented subject matter, upon receiving an audio signal, a given communication device detects (101) parameters of a communication channel in the device and determines (102) parameters of an available ultrasonic channel. As further detailed with reference to Fig. 1, the parameters of the available ultrasonic channel are determined in a periodical manner during the period of receiving the audio signal. A communication channel of a given communication device is defined as a pathway between respective transmitter and receiver, and typically includes a digital-to-analog converter and the analog front end at the transmitter, the speaker, the acoustic path, the microphone and the analog front end and analog-to-digital converter at the receiver.

By way of non-limiting example, the parameters of the communication channel of the given communication device can be measured with the help of a test signal generated with a flat frequency response over all frequencies up to the cutoff frequency of the communication device. The generated orthogonal frequency division multiplexed (OFDM) signal shall be relatively short (the duration of this signal shall be much less than the time when the channel's characteristics are substantially invariable), so as to minimize time that is devoted to channel estimation, rather than to actual data transmission. By way of non-limiting example, duration of this OFDM signal can be between lOC^sec and 10 msec.

Upon receiving the test OFDM signal, the receiver recognizes it as a training signal. By way of non-limiting examples, the receiver can recognize that the received OFDM signal is the training signal in accordance with 'dummy' data derived by demodulation, by the fact that it is the first OFDM symbols transmitted, etc. The receiver further analyzes the received OFDM signal by comparing to a training sequence predefined for demodulation, and detects the channel frequency response (i.e. gain and phase shift at each of the frequencies) and the highest frequency available for transmission in the channel. The highest frequency available in the channel can be less than the cutoff frequency. For example, the highest frequency of an analog front end of the communication device can be 24 KHz, but due to blocking of the microphone by a user's cheek (or any other reasons), frequencies higher than 21KHz can be attenuated to an extent that they are not usable with an amplifier available in the device. Thus, the highest frequency available for transmission will be 21 KHz even though the cutoff frequency is 24 KHz.

The receiver sends to the transmitter data indicative of the channel frequency response and the highest frequency available for transmission in the communication channel (referred to hereinafter as the "highest available frequency").

The transmitter uses this data for determining (102) parameters of the available ultrasonic channel. A transmission band available for the ultrasonic channel in the given communication device is a band between (and including) the highest available frequency and the frequency corresponding to the upper limit of the human hearing range (this frequency can be pre-configured, manually configured by a user, etc.). The other parameters of the available ultrasonic channel correspond to the detected channel frequency response in the respective band.

Upon detecting parameters of the ultrasonic channel available in the given communication device, the transmitter reduces (103) the bit-rate of at least part of a communication signal received by the communication device to a bit -rate corresponding to the parameters determined in the available ultrasonic channel. For example, if the detected available band for transmission the ultrasonic channel is between 18KHz and 24 KHz, the bit-rate is reduced so that the transmitted data (including overhead as, for example, FEC, protocol overhead etc.) fits into the 24KHz -18KHz = 6KHz band, starting at 18KHz. The bit-rate of the ultrasonic bit-stream is adjusted to the highest rate possible under the determined parameters of the available ultrasonic channel. The highest achievable rate is determined as a function of both the available band and the attenuation of the signal therein. The transmitter further codes (104) the ultrasonic bit-stream against errors with an error correcting code appropriate to the determined parameters of the available ultrasonic channel. Error correction is configured in accordance with the determined ultrasonic channel parameters in order to provide the highest transmission rate with an acceptable bit error rate (acceptable bit error rate is a predefined system design parameter).

Transmission of the resulted ultrasonic bit-stream is further adjusted (105) in accordance with determined ultrasonic channel parameters in order to provide as flat and strong transmission as possible. For example, if the channel gain decreases with frequency as 1/f (f denotes the frequency), the transmitter introduces an artificial gain of f (that is the signal is linearly amplified as the frequency increases), so that when the channel attenuates the transmitted signal, the attenuation is compensated as f*(l/f) = 1.

The process of determining the parameters of the available ultrasonic channel and adjusting the transmission parameters (bit-rate, type of error correcting code, error correcting code rate, equalizing parameters, etc.) of the ultrasonic bit-stream accordingly is periodically repeated (106). The periodicity can be either set as constant (e.g. every few milliseconds) or chosen adaptively in accordance with the rate of changes in the communication channel. The coded ultrasonic bit-stream is further modulated (107) using digital modulation of one or more carriers corresponding to ultrasonic frequencies in a transmission band characterizing the ultrasonic channel available in the communication device (i.e. the frequencies between (and including) the highest available frequency and the frequency corresponding to the upper limit of the human hearing range). The transmitter generates (108) an over-the-air ultrasonic communication signal corresponding to the modulated ultrasonic bit-stream.

The generated over-the-air ultrasonic communication signal is further obtained by a receiver, demodulated, expanded to a full rate audio bit-stream; and outputted. Referring to Fig. 2, there is illustrated a schematic functional diagram of a transmitter operable in a communication device in accordance with certain embodiments of the currently presented subject matter. The transmitter 200 comprises a transformation module 202 operable to provide digital transformation of the received voice signal 201 or part thereof into an ultrasonic signal. The transformation module can be implemented in any appropriate combination of software, firmware and hardware. Optionally, the desired functionality can be achieved by running a computer program stored in a computer readable storage medium of the communication device, with no need in any hardware changes. The transformation module includes operatively coupled vocoding unit 205, error correction unit 206, equalizing unit 207 and OFDM modulating unit 208. The transformation module further comprises a testing unit 203 operatively coupled with the vocoding unit 205, the error correction unit 206, the equalizing unit 207 and OFDM modulating unit 208. The testing unit 203 is configured to generate and transmit the test signal 204

(which, by way of non-limiting example, can be transmitted to the receiver using an audio driver unit 209) and to determine parameters of the available ultrasonic channel as detailed with reference to Fig. 1. The testing unit is further configured to provide the determined parameters and/or derivatives thereof to the other units in the transmitting module 202.

The vocoding unit 205 is operable to reduce the audio data stream bit-rate from a bit-rate used in the communication device (e.g. standard enhanced full rate (EFR), half rate (HR), etc.) to the bit-rate appropriate for the acoustic ultrasonic channel in accordance with channel parameters received from the testing unit. The error correction unit 206 is operable to provide forward error correction of the resulted ultrasonic bit-stream with an error correcting code corresponding to the available ultrasonic channel parameters received from the testing unit.

The equalizing unit 207 is configured to provide a necessary equalization in accordance with parameters determined by the testing unit 203. The OFDM modulating unit 208 is operable to map the bits on the OFDM symbols and transform these symbols into a time domain signal, whilst using, merely, the bins corresponding to the frequencies characterizing the available ultrasonic channel and received from the testing unit. The resulting digital ultrasonic signal can be fed to the audio driver unit 209 of the communication device and further transmitted in the same manner as a regular audio signal.

In certain embodiments of the presently disclosed subject matter, the transformation module can transform the entire signal received by the communication device thereby replacing the received signal by a respective ultrasonic signal (e.g. as further illustrated by way of non-limiting example with reference to Figs. 4-5). Alternatively, the transformation module can transform only a part of the signal received by the communication device, thereby generating the ultrasonic digital signal in addition to the audio signal. Optionally, the transformed ultrasonic signal can further include derivatives of data obtained from the received signal (e.g. related to authentication, security, personalization, etc.).

Referring to Fig. 3, there is illustrated a schematic functional diagram of a receiver operable in a communication device in accordance with certain embodiments of the currently presented subject matter. The over-the-air ultrasonic communication signal is picked up by a microphone 301, and is digitized using an analog-to-digital converter 302 operable in the signal's bandwidth. The digitized signal is received by a receiving module 300 comprising operatively coupled OFDM equalization, demodulation and testing unit 303, decoding unit 304 and vocoding unit 305.

The OFDM demodulation, equalization, and testing unit 303 comprises blocks necessary for demodulation of the digitalized modulated signal and equalizing thereof (e.g. a symbol bound searcher, a channel estimator, a channel equalizer, slicer, etc.). If the received signal is the test signal 204, the unit 303 is further configured to analyze the test signal 204 and to provide test results and/or derivatives thereof to the testing unit 203 as detailed with reference to Fig. 1. The decoding unit 304 is configured to provide FEC decoding of the bit-stream received from the unit 303, thereby fixing errors inflicted during the transmission. The corrected bit-stream is expanded by the vocoding unit 305 to full rate audio bit-stream.

The digital full rate bit-stream is converted into an analog signal using a digital to analog converter 306 and transmitted to a speaker 307.

The receiving module can be implemented in any appropriate combination of software, firmware and hardware. Optionally, the desired functionality can be achieved by running a computer program stored in a computer readable storage medium.

The presented subject matter is not bound by the specific architecture illustrated with reference to Figs. 2-3, equivalent and/or modified functionality can be consolidated or divided in another manner and can be implemented in any appropriate combination of software, firmware and hardware.

Referring to Figs. 4 - 5, there is illustrated a non-limiting example of a cell phone 400 operable in accordance with certain embodiments of the currently presented subject matter. The cell phone is configured to use the generated ultrasonic channel for reducing cellular radiation during wireless communication.

It is well known that cell phones emit radiation. It is also less and less controversial that the RF radiation emitted by the cell phones can be potentially a source of various illnesses such as cancer (brain, salivary glands etc.). Cell phones emit strong radiation when connecting to the cellular network. Hence, holding a cell phone near the body and, especially near the brain during a conversation can be harmful.

The amount of radiation absorbed by the brain tissue can be reduced by extending the distance between the cell phone and the brain. In the cell phone illustrated in Figs. 4 - 5, the distance between the cell phone and the brain is increased with the help of extension 400 attached to the cell phone, having an integral earphone 402 and a mechanical extender 401 that holds this earphone to the cell phone case. The mechanical extension is made of plastic or other non-conducting material with no conducting elements (wires or other) inside. Thereby, the amount of radiation absorbed by the brain is reduced since the extension 400 does not serve as an antenna directing the radiation to the ear/brain. As the radiation field strength law is roughly , where r is the distance from the radiating source (the cellphone, in this case), it is enough to extend the distance between the cellphone and the brain by a few centimeters to achieve a substantial reduction in radiation on the brain.

The length of extension 400 shall be short enough to enable location of the microphone of the cell phone (not shown) close to a mouth of a user during communication.

In accordance with certain embodiments of the currently presented subject matter, the cell phone comprises a transmission module detailed with reference to Fig. 2. The transmission module transforms the received audio-bit-stream into the ultrasonic signal inaudible to a human ear and over-the-air transfers this signal from the cell phone's speaker 405 to the earphone's microphone 404 on the top of the extension 400.

The earphone 402 comprises a receiving module detailed with reference to Fig. 3. The receiving module can operate on a battery-powered processor comprised in the earphone 402. Upon receiving the over-the-air ultrasonic communication signal, the receiving module demodulates the received signal, expands the demodulated signal to a full rate audio bit-stream, and outputs the expanded signal to the earphone speaker 403.

Optionally, initial determining parameters of the available ultrasonic channel and periodical updates thereof can be provided via a separate path (not shown) from the earphone's speaker to the cell phone's microphone.

It is to be understood that the subject matter is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based can readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention.

It will also be understood that the system according to the invention can be a suitably programmed computer. Likewise, the invention contemplates a computer program being readable by a computer for executing the method of the invention. The invention further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the method of the invention.

Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope, defined in and by the claims associated with the present invention.

Claims

A communication device comprising: means for detecting parameters characterizing a communication channel in the communication device; means for determining parameters characterizing an ultrasonic channel available in the communication device; means for reducing a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to the determined parameters characterizing the ultrasonic channel available in the communication device, thus giving rise to an ultrasonic bit-stream; means for coding said ultrasonic bit-stream against errors with an error correcting code appropriate to said determined parameters characterizing the ultrasonic channel available in the communication device; means for modulating the coded ultrasonic bit-stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and means for generating an ultrasonic communication signal corresponding to the modulated ultrasonic bit-stream.

The communication device of Claim 1 further comprising means for adjusting and transmitting the ultrasonic bit-stream in accordance with said determined parameters characterizing the ultrasonic channel available in the communication device.

The communication device of Claims 1 or 2 wherein the means for generating the ultrasonic communication signal are capable of generating an over-the-air ultrasonic communication signal.

The communication device of any one of Claims 1 - 3 associated with an external earphone configured to receive the generated over-the-air ultrasonic communication signal, the earphone further comprising means for demodulating the received signal; means for expanding said demodulated signal to a full rate audio bit-stream; and means for outputting the expanded signal from the earphone.

The communication device of Claim 4 wherein the external earphone is located on an extension attached to the communication device, manufactured from a non- conductive material, and not comprising any conductive parts.

The communication device of any one of claims 1 - 5, wherein the parameters characterizing the communication channel comprise channel frequency response and the highest frequency available for transmission in the channel.

The communication device of any one of claims 1 - 6, wherein the parameters characterizing the ultrasonic channel available in the communication device comprise parameters indicative of a transmission band available for the ultrasonic channel in the communication device and channel frequency response characterizing said transmission band.

A method of operating a communication device, the method comprising: a) detecting parameters characterizing a communication channel in the communication device; b) determining parameters characterizing an ultrasonic channel available in the communication device; c) reducing a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to the determined parameters characterizing the ultrasonic channel available in the communication device, thus giving rise to an ultrasonic bit-stream; d) coding said ultrasonic bit-stream against errors with an error correcting code appropriate to said determined parameters characterizing the ultrasonic channel available in the communication device; e) modulating the coded ultrasonic bit- stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and f) generating an ultrasonic communication signal corresponding to the modulated ultrasonic bit-stream.

9. The method of Claim 8 wherein the generated ultrasonic communication signal is over-the-air ultrasonic communication signal.

10. The method of Claims 8 or 9 further comprising adjusting and transmitting the ultrasonic bit-stream in accordance with said determined parameters characterizing the ultrasonic channel available in the communication device.

11. The method of any one of Claims 8 - 10 further comprising: transferring the over-the-air ultrasonic communication signal to an external earphone associated with the communication device; demodulating the received signal by a receiver in the earphone; expanding said demodulated signal to a full rate audio bit-stream; and outputting the expanded signal from the earphone.

12. The method of any one of Claims 8 - 11, wherein modulating the coded ultrasonic bit-stream is provided with the help of orthogonal frequency division multiplexing (OFDM) whilst using, merely, the bins corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device.

13. The method of any one of Claims 8 -11, wherein modulating the coded ultrasonic bit-stream is provided with the help of modulating a single carrier characterized by the center frequency and the signal's bandwidth positioning said carrier in the ultrasonic frequency range within a transmission band characterizing the ultrasonic channel available in the communication device.

14. The method of any one of claims 8 -13 further comprising periodically repeating the operations a) and b) and modifying the operations c) - f) in accordance with newly determined parameters characterizing the ultrasonic channel available in the communication device.

15. The method of any one of claims 8 - 14, wherein the parameters characterizing the communication channel comprise channel frequency response and the highest frequency available for transmission in the channel.

16. The method of any one of claims 8 -15, wherein the parameters characterizing the ultrasonic channel available in the communication device comprise parameters indicative of a transmission band available for the ultrasonic channel in the communication device and channel frequency response characterizing said transmission band.

17. An extension capable of being attached to a communication device comprising means for generating an over-the-air ultrasonic communication signal corresponding to a communication signal received by the communication device, the extension comprising an integral earphone configured to receive the generated over-the-air ultrasonic communication signal and a mechanical extender holding said earphone to the communication device, the integral earphone comprising: means for demodulating the received signal; means for expanding said demodulated signal to a full rate audio bit-stream; and means for outputting the expanded signal from the earphone.

18. The extension of Claim 17 manufactured from a non-conductive material and not comprising any conductive parts.

19. A transmitter for a communication device, the transmitter comprising: means for reducing a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to parameters characterizing an ultrasonic channel available in the communication device, thus giving rise to an ultrasonic bit-stream; means for coding said ultrasonic bit-stream against errors with an error correcting code appropriate to said parameters characterizing the ultrasonic channel available in the communication device; means for modulating the coded ultrasonic bit-stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and means for generating an ultrasonic communication signal corresponding to the modulated ultrasonic bit-stream.

20. The transmitter of Claim 19 further comprising means for adjusting and transmitting the ultrasonic bit-stream in accordance with said parameters characterizing the ultrasonic channel available in the communication device.

21. The transmitter of Claims 19 or 20, wherein the parameters characterizing the communication channel comprise channel frequency response and the highest frequency available for transmission in the channel.

22. The transmitter of any one of claims 19-21, wherein the parameters characterizing the ultrasonic channel available in the communication device comprise parameters indicative of a transmission band available for the ultrasonic channel and channel frequency response characterizing said transmission band.

23. A non-transitory program storage device, readable by a processor and comprising instructions stored thereon to cause the processor to: a) detect parameters characterizing a communication channel in the communication device; b) determine parameters characterizing an ultrasonic channel available in the communication device; reduce a bit-rate of at least part of a communication signal received by the communication device to a bit-rate corresponding to the determined parameters characterizing the ultrasonic channel available in the communication device, thus giving rise to an ultrasonic bit-stream; code said ultrasonic bit-stream against errors with an error correcting code appropriate to said determined parameters characterizing the ultrasonic channel available in the communication device; modulate the coded ultrasonic bit-stream using digital modulation of one or more carriers corresponding to ultrasonic frequencies within a transmission band characterizing the ultrasonic channel available in the communication device; and f) generate an ultrasonic communication signal corresponding to the modulated ultrasonic bit-stream.