Abstract:
A system and a method for the transmission and reception of digital data wirelessly using acoustic tones comprises a device having an encoder, a modulator system, a demodulator system, and a decoder. The modulator system uses a plurality of acoustical tones with a fundamental frequency and multiple harmonics that are amplitude modulated. The received signal is demodulated and detected by quadrature detectors comprising replicas of the acoustical tones. An extended Golay code based decoder is used for correcting errors occurring during transmission.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The contents of this application are related to provisional applications having Ser. Nos. 60/390,500 (filed Jun. 21, 2002) and 60/390,476 (filed Jun. 21, 2002). The contents of these related provisional applications are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to communication devices for communicating signals wirelessly.  
           [0004]    Especially, the present invention relates to a system and method for transmitting digital data between communicating devices using acoustic tones as the information carriers for the data.  
           [0005]    2. General Background  
           [0006]    One of the most difficult challenges faced by providers of low cost wireless computer peripheral devices is the need to distribute custom interface hardware so that the peripheral device can communicate with the computer. The interface hardware not only adds cost to the product, but for many products such as low cost toys, the sales and distribution channels are not prepared to support the distribution of these additional computer devices.  
           [0007]    As a result, a mechanism is required whereby devices can communicate with a personal computer, or with each other, using standard hardware (e.g., digital signal processing chips, analog to digital converters, etc.). In addition, the devices, employing this communication mechanism, should be flexibly designed to operate in conditions where line-of-sight communication between said devices is required.  
           [0008]    There are many techniques that encode data into an audio frequency signal for transmission and subsequent detection over a communications channel. These techniques as a class are fundamentally different in that they do not use the acoustic medium (air or another material) pressure waves as the communications mechanism.  
         SUMMARY OF THE INVENTION  
         [0009]    Clearly there is a need for using sound or acoustic tones as carriers of digital data in simple and low cost devices. Specifically, the present invention of using acoustic tones as carriers of digital data arose from the need to transmit low bandwidth data between a peripheral device and a computer (or another device) using existing sound recording and playback means such as loudspeakers and microphones, respectively.  
           [0010]    The system and method of the present invention allows for the transmission (and reception) of digital data wirelessly using sound. Specifically, this technique modulates digital data bits onto chords consisting of three or more pure tone musical notes. This involves a modulation scheme, such as amplitude modulation, of each of the individual tones within the chord relative to each other. Because of the nature of the modulation, humans are unable to discern a difference in the sound of the transmission for different data patterns. At the receiver, demodulation is done so that the digital data is extracted from the pure tone musical notes. The use of this technique can be extended such that the tonal “content” for a variety of applications can be developed where such tonal content is not adversely affected by the presence of external noise. From a hardware perspective, the communication between devices is enabled by means of digital signal processors (DSPs) that have embedded algorithms to perform modulation and demodulation, analog-digital converters, loudspeakers, etc.  
           [0011]    Accordingly, in one embodiment of the present invention, the digital data transmitting system using acoustic tones comprises a device having: (i) at least one generator for generating digital data; (ii) a modulator system, the modulator system modulating a plurality of pure tone notes with the digital data; and (iii) at least one loudspeaker, the loudspeaker transmitting the modulated tones. Additionally, the digital data includes a pseudo random code, a plurality of message bits, and a plurality of correction bits. The correction bits are based on error correcting codes such as an extended Golay code. The pure tone notes may either lie in the infrasonic, audio, or ultrasonic band. Furthermore, the device may include a view screen, scroll buttons (or a mouse type device) for selecting a specific object displayed on the screen. The digital data, corresponding to the object, may be used as a vehicle for transmitting the object to another device. For example, in a children&#39;s game, the object may correspond to a magic wand, and a player can transfer this wand, using the present invention, to another player having a similar device.  
           [0012]    In another embodiment of the present invention, a receiver, in the device, for receiving the acoustic tones modulated by digital data comprises: (i) a plurality of quadrature detectors, one for each of the plurality of tones, for recovering a baseband signal from a bandpass signal, the bandpass signal includes the plurality of amplitude modulated tones; (ii) a data detector for detecting data in the baseband signal following a first pseudo random code sequence and a second pseudo random code sequence; (iii) a correlator for extracting the plurality of message bits following the first pseudo random code sequence and the plurality of correction bits following the second pseudo random code sequence; and (iv) a decoder for determining the number of errors in the message bits. The decoder may be an extended Golay code decoder. Additionally, the device will include a microphone for receiving the digitally modulated data. After demodulation, the view screen on the device will depict the object corresponding to the demodulated data. For example, the object could be the magic wand transmitted from another device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    In order that the manner in which the above-recited advantages and objects of the invention are attained, as well as others which will become apparent, more particular description of the invention briefly summarized above may be had by reference to the specific embodiments thereof that are illustrated in the appended drawings. It is to be understood, however, that the appended drawings illustrate only typical embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0014]    In the drawings:  
         [0015]    [0015]FIG. 1 is a block diagram of the communication system for using acoustic tones for wireless communication;  
         [0016]    [0016]FIG. 2 shows a block diagram of the modulator depicting an exemplary embodiment of the tones having specific amplitudes and frequencies used for modulation;  
         [0017]    [0017]FIG. 3 is a block diagram depicting the receiver demodulator for the present invention;  
         [0018]    [0018]FIG. 4 displays the outputs of the six demodulators/quadrature detectors of FIG. 3;  
         [0019]    [0019]FIG. 5 is a plot of the detected tones when the sequence, corresponding to FIG. 4, was transmitted from a computer and digitized on a second computer in the presence of background noise;  
         [0020]    [0020]FIG. 6 is a close up snapshot of the message portion corresponding to the data in FIG. 5;  
         [0021]    [0021]FIG. 7 is an exemplary view of a device having at least one embedded DSP chip for performing modulation/demodulation, analog-digital converters, digital-analog converters, microphone, loudspeaker, scroll buttons, selection buttons, and a view screen;  
         [0022]    [0022]FIG. 8 shows a child obtaining the device from a shopkeeper;  
         [0023]    [0023]FIG. 9 depicts one application of the present invention where there is a bi-directional exchange of data between the devices used by children in a room environment;  
         [0024]    [0024]FIG. 10 is a display on the view screen that shows specific objects collected by the child after completing the data exchange according to FIG. 9;  
         [0025]    [0025]FIG. 11 depicts one application of the present invention where there is an unidirectional data flow between a radio/boom-box and the device in a room environment;  
         [0026]    [0026]FIG. 12 depicts one application of the present invention where there is a bi-directional exchange of data between the devices used by child and an adult in a non-confined environment (e.g., a playground);  
         [0027]    [0027]FIG. 13 depicts one application of the present invention where there is a bi-directional exchange of data between the device and a telephone;  
         [0028]    [0028]FIG. 14 shows a computer screen that includes a web link to access a page having information related to the device;  
         [0029]    [0029]FIG. 15 depicts one application of the present invention where there is a bi-directional exchange of data between the devices used by children in an open environment (e.g., a playground);  
         [0030]    [0030]FIG. 16 shows a selected object, on a view screen of the device, that is to be transmitted or received via the present invention;  
         [0031]    [0031]FIG. 17 depicts one application of the present invention where there is an unidirectional data flow between a speaker connected to a computer and the device;  
         [0032]    [0032]FIG. 18 shows a front view of the device according to one embodiment; and  
         [0033]    [0033]FIG. 19 shows the back view of the device of FIG. 18. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    Referring now in detail and by reference characters to the drawings (FIGS.  1 - 19 ), which illustrate several different embodiments of the present invention, therein shown is a system for transmitting and receiving acoustic tones for wireless communications. Such a system, as in the present invention, employs circuits that enable transmission of low bandwidth data between multiple devices (or a computer) using the device&#39;s hardware (e.g., sound card, microphone, loudspeaker, DSP chips, analog-digital converters, etc.). The communication environment could be a living room, an automobile cabin, a telephone channel, a non-confined environment (e.g., a playground), etc.  
         [0035]    The device is designed to reliably receive and decode digital data (also referred to as tokens throughout the specification) sent over an audio signal (from TV speakers, home-theater speakers, boom-box/radio, computer speakers, etc.) in the average living room, media room or den, anywhere within a reasonable distance, such as between about 2-30 ft of the speakers, and within a volume of space subtended by pi radians in front of the speakers. The device is designed so that the signal reception is independent of the loudspeaker system and room characteristics (e.g., reverberation time), and it is reliable in the presence of noise when the audio is at normal listening levels. Furthermore, the device is designed so that signal reception at the device is independent of the location of the device inside the specified distance from the sound source.  
         [0036]    As an example, the range of normal listening level for a TV speaker at a viewing distance of 10 ft is between 50 to 60 dBA, and typical interior residential noise level is 30 to 40 dBA, and 50 to 55 dBA with voices. Possible ambient noise sources include voices, music, barking dogs and other household sounds. Both impulsive and continuous noise sources can be expected. A reasonable upper limit for background noise level is 60 dBA. Thus the device is designed to transmit/receive signals at the expected signal to noise ratio ranging between +27 dBA to −3 dBA in a typical room.  
         [0037]    The source signal (as shown in FIG. 1) could be an audio based signal (frequency range of 20 Hz-20 kHz), an infrasonic signal (below the threshold of hearing), or an ultrasonic signal (above 20 kHz). For example, the sound source could be the “Dong” at the end of the sound that is played on the TV show “Who Wants to be a Millionaire”. Digital data (also called tokens) could be encoded into this “Dong” sound, via the encoding scheme of the present invention, and the received signal could be demodulated/decoded by a receiver embedded in the device. The demodulation scheme, implemented in the receiver, is done via the present invention.  
         [0038]    It is important that the communication of digital data or tokens between the devices be reliable. Specifically, in the preferred embodiment under best-case conditions, no more than 1 misread or undetected token out of 10,000 tokens broadcast are allowed. Under the worst-case conditions, no more than  1  misread or undetected token out of 1000 tokens broadcast should be permitted.  
         [0039]    Furthermore, the communication algorithms, according to the present invention, should be robust under the presence of noise in different environments. Noise can be characterized as continuous or impulsive, and broadband or fixed-frequency (narrow band). Noise can also be classified by annoyance factors: voices and music may be deemed more annoying than random noise, as are hammering (impulsive) or continuous tones (narrow band). As a reference, once a noise level exceeds 67 dBA, it begins to interfere with communication between people 3 ft. apart. Further details on noise and its effects in different environments will be presented below.  
         [0040]    It is also important to maintain a certain data rate for communication between the devices. While a minimum data rate of 24 bits/sec should be achieved, a more important measure is the duration of a token. A 16-bit token at 24 bits/sec takes two thirds of a second, but this does not take into account the bits that may be required for synchronization and/or data correction schemes. Thus, in one aspect of the present invention, a complete token is no longer than 1 second in duration.  
         [0041]    The devices can communicate with each other in a variety of environments, and at various signal to noise ratios, including:  
       Living Room  
       [0042]    The devices are able to reliably receive and decode digital data or tokens sent over a television audio signal in the average living room, media room or den, anywhere within approximately 2-30 ft of the TV screen, and within a volume of space subtended by pi radians in front of the speakers. The devices are designed so that the signal reception is substantially independent of the speaker system and room characteristics. Also, the devices are designed to communicate reliably in the presence of noise when the TV audio is at normal listening levels. Furthermore, the signal reception is independent of the location of the device inside the specified distance from the screen.  
         [0043]    Regarding noise, the typical interior residential noise level is 30 to 40 dBa, 50 to 55 dBa with voices. Possible ambient noise sources include voices, music, barking dogs and other household sounds. Both impulsive and continuous noise sources can be expected. A reasonable upper limit for background noise level is 60 dBa. Accordingly, the devices are designed to accommodate a signal to noise ratio ranging between +27 dB and −3 dB.  
       Automobile  
       [0044]    The devices are able to reliably receive and decode tokens sent over a radio signal in the average automobile. The devices are designed so that the the signal reception is substantially independent of the speaker system and automobile cabin interior characteristics, and the devices operate reliably in the presence of noise when the audio is at normal listening levels. Also, the signal reception, at the devices, is independent of the location of the device inside the vehicle.  
         [0045]    While very dependent on vehicle type, the range of the normal listening level for an audio signal, such as radio, in an automobile is typically 65 dBA (at low speeds) to 78 dBA (at high speeds). A reasonable lower limit is 60 dBA.  
         [0046]    Regarding noise, it can vary considerably with the velocity of the car. Engine and drive train noise is typically low frequency (&lt;100 Hz), while aero-acoustic and tire noise is middle frequency and increases with increasing velocity. Also, there are air conditioning and air sounds from open windows. Other than the occasional horn blast and crash, most interior vehicle noise is generally continuous.  
         [0047]    Typical interior vehicle noise levels (for test vehicles such as Honda Accord and CRV):  
         [0048]    Stopped, in traffic 53 dBA  
         [0049]    70 mph, constant 66 dBA to 70 dBA  
         [0050]    Accelerating with window partially open 86 dbA  
         [0051]    The occupants typically set the radio volume at 3 to 10 dB over the ambient noise. Accordingly, the devices are designed to accommodate a signal to noise ratio ranging between +12 dB to −10 dB.  
       Desktop Environment  
       [0052]    The devices are able to reliably receive and decode tokens, sent via personal computer multimedia speakers in the average bedroom, office or den, anywhere within an average distance, perhaps, 4 ft, of the speakers. The devices are designed so that the signal reception is substantially independent of the speaker system and room characteristics. Also, the devices operate with reliability in the presence of noise when the PC audio is at normal listening levels. Additionally, the device is designed so that the signal reception is independent of the location of the device inside the specified distance from the speakers.  
         [0053]    The range of normal listening level for PC audio at a distance of 4 ft is 55 to 65 dBA. A reasonable lower limit is 55 dBA. In the home environment, noise levels are expected to be of the order of the levels found in the living room environment. In an: office environment, typical background noise levels are about 45 to 55 dBA, including fan noise, or 55 to 65 dBA when a person is listening to music on his or her computer. Nearby activity and conversation can raise this to anywhere from 65 to 80 dBA. A reasonable worst case for background noise in an office is 75 dBA. Accordingly, the devices are designed to accommodate a signal to noise ratio ranging between +10 dB to −10 dB.  
       Telephone Channel  
       [0054]    The devices are able to reliably receive and decode tokens sent via a telephone audio signal within about 2 in. of the telephone headset or hands-free speaker.  
         [0055]    A telephone dial tone at this distance ranges from 48 dBA to 55 dBA, with 52 dBA being typical, and 48 dBA being a reasonable lower limit.  
         [0056]    Expected background noise is similar to the home and office scenarios above, and are therefore expected to be 50 to 65 dBa, with 65 dBa being a reasonable upper limit. Accordingly, the devices are designed to accommodate a signal to noise ratio ranging between +5 dB to −17 dB.  
       Open Environment (e.g., Playground)  
       [0057]    The device is able to reliably receive and decode tokens sent by another device in relatively close proximity, or within 2 to 4 in, in a variety of environments, including outdoors. Of course, this distance may be varied. A typical location is a school playground during recess.  
         [0058]    This scenario is interesting for two reasons: (i) the token can be sent from a speaker of many different designs and at volumes that we can be specified, and (ii) lower reliability is acceptable, since to a certain extent users will retry until the token transfer is accomplished.  
         [0059]    Typical noise levels in an outdoor urban environment are both impulsive and continuous and are in the range of 45 to 65 dBA, with peaks of up to 70 dBA, depending on proximity to traffic and commercial noise sources. Kids yelling in a playground can exceed 90 dBA. Accordingly, the devices are designed to accommodate a range of signal to noise ratios.  
         [0060]    An example of such a device is shown in FIG. 7. Specifically, FIG. 7 shows an exemplary view of a device  500  having at least one embedded DSP chip (not shown) for performing encoding/decoding of digital signals, analog-digital converters (not shown), digital-analog converters (not shown), microphone  510 , loudspeaker  550 , scroll buttons  530 , selection buttons  540 , and a view screen or display  520 . Thus, information received by the microphone  510  is decoded and the item corresponding to the transmitted digital data (or token) is displayed on the view screen  520 . As an example, the view screen  520  displays items such as sorcerer hats and candles, and these items may have been transmitted from another similar device. In another aspect of the invention, if a person wants to transmit an item, such as a candle, during a trade, the person may then use scroll buttons  530  and the selection button  540  to locate and select the candle on the view screen  520 . Upon selection of the item, the digital data (or token) corresponding to the candle may be loaded from a buffer or synthesized by means of a sound card. The digital data (or token) may be encoded, and the resulting signal may then be used to modulate an audio/sound signal. The modulated signal is finally transmitted by a loudspeaker to another similar device.  
         [0061]    [0061]FIG. 8 shows a child obtaining the device  500  from a shopkeeper. Alternatively, the device  500  may be given as part of a promotion to attract people/children to an event.  
         [0062]    [0062]FIG. 9 depicts one application of the present invention where there is a bi-directional exchange of data between the devices  500  used by children in a room environment. In this case, the token data (corresponding to an item to be traded between the children) may be transmitted by means of musical tones (depicted as  600 ) which are pleasing to the ear. Alternatively, the token data may be embedded in non-musical audio signals (e.g., in a Mickey Mouse character&#39;s voice).  
         [0063]    [0063]FIG. 10 is a display on the view screen that shows specific objects collected by the child after completing the data exchange according to FIG. 9. Alternatively, the device  500  may be designed to include at least one game that will allow children to be entertained.  
         [0064]    [0064]FIG. 11 depicts one application of the present invention where there is a unidirectional data flow between a radio/boom-box  610  and the device  500  in a room environment. The data/tokens may be transmitted by means of a musical or non-musical audio signal  620  via a regular radio program or through a special promotional event. The device  500  may thus capture the tokens, which may subsequently be redeemed for either a cash prize or an article.  
         [0065]    [0065]FIG. 12 depicts another application of the present invention where there is a bi-directional exchange of data (or tokens) using a musical/non-musical audio signal  630  between multiple devices  500  in a non-confined environment (e.g., a playground).  
         [0066]    [0066]FIG. 13 depicts one application of the present invention where there is a bi-directional exchange of data between the device  500  and a telephone  700 . In this situation, a person may redeem a prize by transmitting a certain number of tokens  720  from the device  500  to an end server (not shown) via the telephone link.  
         [0067]    [0067]FIG. 14 shows a computer screen, depicting a web-page  730 , that includes a link  732  to access a remote site (not shown). By clicking the relevant link on the web-page, a person may be directed to a remote site where he or she may be able to exchange tokens between a remote server and the device by means of desktop computer speakers and microphones. This aspect is shown in FIG. 17, where tokens  820  are transmitted from a remote server to the device  500 .  
         [0068]    [0068]FIG. 15 depicts another application of the present invention where there is a bi-directional exchange of data/tokens  740  between the devices  500  used by children in an open environment (e.g., a playground). Specifically, shown therein is a candle item  780  exchanged between two children and a sorcerer&#39;s hat item  760  exchanged between another two children.  
         [0069]    [0069]FIG. 16 shows selectable objects or items (i.e., 3 sorcerer hats and 4 magic wands), on a view screen of the device  500 . These items can be viewed by means of the scroll buttons  530  and selected by means of the selection button  540  before transmission using audio/sound signals.  
         [0070]    [0070]FIG. 17 depicts one application of the present invention where there is unidirectional data flow between a speaker connected to a computer and the device.  
         [0071]    [0071]FIGS. 18 and 19 show front and back view of the device  500  according to another embodiment of the present invention.  
         [0072]    Thus, the full system for transmitting and receiving digital data or tokens includes a device  500  having (i) a sound synthesis means (e.g., a sound card); (ii) a sound/data receiving means (e.g., a microphone); (iii) a sound/data transmission means (e.g., a loudspeaker); (iv) a processing means for encoding and decoding digital data (e.g., a DSP chip); and (v) analog-digital and digital-analog converters. The following description explains the encoding and decoding method of digital data/tokens with reference to FIGS.  1 - 6 .  
         [0073]    The present system, in its preferred embodiment, encodes the source signal using, for example, an extended Golay code encoding scheme  10 . The encoded sequence or digitized data, at the output of the encoder  10 , is modulated using the modulator system  12  onto chords consisting of three or more pure tone musical notes. This modulation involves amplitude modulation of each of the individual tones within the chord relative to each other. Because of the nature of the modulation, humans are unable to discern a difference in the sound of the transmission for different data patterns. The use of this system can be extended so that sound “content” for a variety of applications can be developed where the content is not adversely affected by the presence of the data. For the aforementioned scenario, the system can achieve a bit rate of about 12 bps (40 symbols per second, using redundancy and coding) so the tone would be a couple of seconds long—about the length of time that the “Dong” lasts in “Millionaire”.  
         [0074]    The encoded or message signal at the output of the encoder  10  is a digital signal. Depending on the nature of the encoder the digital signal may be of a predetermined length. In the present system the message consists of 40 bits having the following format: 00111010dddddddddddd00111010cccccccccccc, where ‘d’ is a data bit and ‘c’ is a correction bit.  
         [0075]    The fixed pattern of 00111010 is an 8-bit section of a 7-length pseudo random number code. The twelve data bits, represented as ‘d’, can be any combination of bits. The correction bits, represented by ‘c’, are based on an extended Golay code. As is well known in the art, the code in the present case can correct 1, 2, or 3 errors. Four errors are uncorrectable but recognizable. More than 4 errors may be recognized as uncorrectable or may be falsely corrected.  
         [0076]    For the modulation process in the modulator system  12 , the sound consists of N tones (in the present exemplary depiction, N=6) with a fundamental frequency off f 0  Hz (in the present exemplary depiction, F 0 =263 Hz) and M multiples of the fundamental frequency (in the present exemplary depiction, M=5). In one aspect of the invention, the non-fundamental tones (viz., the harmonics) may be at frequencies that are integer multiples of the fundamental frequency. In another aspect of the invention, the harmonics may be at non-integer multiples of the fundamental frequency. The tones are amplitude modulated. The frequencies f i  (i=0, . . . , M=5) and amplitude factors as (I=0, . . . , M=5) are:  
                                                                                 amplitude   amplitude       index   multiplier   frequency   data = 0   data = 1                                0   1   263   0.7   1.3       1   3/2   395   1.3   0.7       2   2   526   0.7   1.3       3   3   789   1.3   0.7       4   4   1952   0.7   1.3       5   6   1578   1.3   0.7                  
 
         [0077]    The details of the modulator system  12  are depicted in FIG. 2. The encoded signal at the output of the encoder  10  is supplied to a bank of correlators  210 . Each correlator  120  has two inputs, one input coming from the encoder  10  and the other input being a sinusoidal signal with appropriate frequencies and amplitude factors as tabulated above. The modulated tones are then summed in the summer  220  after the modulation.  
         [0078]    The bit length is 6 cycles of the fundamental frequency. The data rate is therefore 44 bps. The data bit transitions occur at nulls of the modulated tones. The entire message is less than 1 second long.  
         [0079]    A receiver is employed at the computer terminal or peripheral to receive the encoded and modulated signal transmitted by the peripheral or computer via the channel  14  (FIG. 1). The first step in the receiver,  16  (FIG. 1), is the recovery of the modulated tones.  
         [0080]    The details of the first stage in the receiver  16 , the demodulator and detector, are shown in FIG. 3. A quadrature detector  310  for each tone consists of a one-bit long replica of the tone that is convolved with the received signal both inphase and quadrature. The power of the output is sampled  4  times per bit length. This produces 6 time series. The sum of the odd index tones is subtracted from the sum of the even index tones to produce the signal which is used for data detection.  
         [0081]    In the next stage of the detection process, and as denoted by  320  (FIG. 3), the signal is first examined to find two occurrences of the pattern 00111010 that are displaced by 20 bits. Data is detected by computing the sum of 8 consecutive bits and thresholding one sample in each bit interval. The mean is computed separately in each 8-bit interval. If 15 of the 16 bits are correct, the first step is successful and processing proceeds to the second step.  
         [0082]    In the following step of data detection, and as denoted by  330 , a data pattern 0111010 is convolved with the signal starting at the first sample used in step  1  and at 12 quarter bit interval after that. The maximum convolution output is determined for each repetition of the pattern. If the separation of the maxima is 80≅2, then the second step is successful. The start of the data is adjusted by the position of this maximum correlation output.  
         [0083]    In the final step, and as denoted by  340 , the mean of the first 8 bits in step  1  is used to recover the 12 data bits. The mean of the second 8-bits in step  1  are used to recover the 12 correction bits. The combined 24 bits are then passed to an Extended Golay decoder. If the number of sensed errors is less than 4, then the data recovery is successful.  
         [0084]    It is observed that: (i) the use of tones that are simultaneously increased and decreased leads to a more pleasing sound than all tones modulated in phase; (ii) the recovered tones have experimentally been found to have very different amplitudes due to the characteristics of the speakers and microphone that were used; (iii) combining all tones allows the stronger tones to dominate the data recovery; (iv) amplitude thresholding allows more errors to be accepted in the synchronization patterns and can provide more robust detection; and (v) the two synchronization patterns are separated by and separately used to set the data and correction thresholds to reduce the impact of fading in the channel.  
         [0085]    In another aspect, coherent detection could be used to provide some gain over the incoherent quadrature detectors. Incoherent detection is used to avoid any issues of channel flatness or dispersion that might be more important in a coherent approach.  
         [0086]    Experiments demonstrate the workings of the present system. The experiment used 12 data bits of the form 000110101100. The 12 correction bits were 010101110011. The 40 bit message followed five notes made with unmodulated tones. The output of the 6 quadrature filters is shown in FIG. 4. Five notes can be seen to precede the message, which is at the right of the figure. The third note matches the message frequency, but is not modulated. The sound is damped without modulation following the last message bit.  
         [0087]    The above sequence was broadcast from a first computer and digitized on a second computer while a radio was used to generate background noise. The detected tones are shown in FIG. 5. A close-up of the message portion is shown in FIG. 6. In summary, the data was successfully recovered. The notes that precede the message, and the background noise, were successfully rejected using all  6  tones and with most combinations of fewer tones.  
         [0088]    While the specification describes particular embodiments of the present invention, those of ordinary skill can devise variations of the present invention without departing from the inventive concept. For example, the number of frequency components used may be more or less than six. The fundamental frequency, the multipliers, and the amplitude factors may be designed according to the application involved such as in Bluetooth based devices for vehicular, multimedia, and other environments. Also, the probability of bit error may be minimized by designing appropriate modulator (demodulator) systems such as a Quadrature Amplitude Modulator (QAM).