Abstract:
A wireless telecommunication device, such as a cell phone, is coupled to a source of digital data which may comprise a GPS receiver. In one embodiment, a GPS receiver and inband signaling modem are integrated into the cell phone battery pack. A pushbutton on the battery pack is actuated by a user to trigger selected events such as formulating location data in the GPS receiver, encoding the location data in the IBS modem and inserting the resulting audio frequency tones into the voice channel of the cell phone for transmission over the voice channel of a digital, wireless telecommunications network.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/531,367 filed Mar. 21, 2000, which is a CIP of U.S. application Ser. No. 09/230,079, filed May 13, 1999 now U.S. Pat. No. 6,144,336, which is the U.S. national phase application corresponding to International Application No. PCT/US98/10317, filed May 19, 1998. 
    
    
     TECHNICAL FIELD 
     This invention is related to wireless telecommunications and more specifically to a system that transmits digital data over the audio channel of a digital wireless network “in-band.” 
     BACKGROUND OF THE INVENTION 
     A cellular telephone allows a user to talk to another user without being tethered to a “land line.” The cell phone includes circuitry that samples the audio signals from the user&#39;s voice. These voice signals are converted into a digital form using an A-D converter. The digitized voice signals are encoded by a voice coder (vocoder) and then modulated onto a carrier frequency that transmits the voice signals over a cell network. The voice signals are sent over the wireless cellular network either to another phone in the wireless cell network or to another phone in a land-line phone network. 
     Different coders/decoders (coders), modulators, vocoders, Automatic Gain Controllers (AGC), Analog to Digital converters (A/D), noise reduction circuits, and Digital to Analog converters (D/A) are used in the cellular and landline phone networks. These telephone components can implement different coding schemes for encoding and decoding the voice signals. 
     These telecommunication components are designed to efficiently transmit voice signals over wireless and landline voice communication channels. For example, a digital vocoder uses predictive coding techniques to represent the voice signals. These predictive coders filter out noise (non-voice signals) while compressing and estimating the frequency components of the voice signals before being transmitted over the voice channel. 
     A problem arises when voice communication equipment, such as the vocoder, are used for transmitting digital data. The vocoders may interpret signals representing digital data as a non-voice signal. The vocoder might completely filter out or corrupt those digital data signals. Therefore, digital data can not be reliably transmitted over the same digital audio channel used for transmitting voice signals. 
     It is sometimes necessary for a user to transmit both audio signals and digital data to another location at the same time. For example, when a cellular telephone user calls “911” for emergency assistance, the user may need to send digital location data to a call center while at the same time verbally explaining the emergency conditions to a human operator. It would be desirable to transmit this digital data through a cell phone without having to use a separate analog wireless modem. 
     Accordingly a need exists for transmitting digital data over a voice channel of a digital wireless communications network. 
     SUMMARY OF THE INVENTION 
     An inband signaling modem communicates digital data over a voice channel in a digital wireless telecommunications network. An input receives digital data. An encoder converts the digital data into audio tones that synthesize frequency characteristics of human speech. The digital data is also encoded to prevent voice encoding circuitry in the telecommunications network from corrupting the synthesized audio tones representing the digital data. An output then outputs the synthesized audio tones to a voice channel of a digital wireless telecommunications network. 
     The foregoing and other features and advantages of the invention will become more readily apparent from the following detailed description of preferred embodiments of the invention, which proceeds with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a wireless communications network that provides in-band signaling (IBS) according to the invention. 
     FIG. 2 a detailed diagram of a cellular telephone coupled to an IBS modem according to one embodiment of the invention. 
     FIG. 3 is another embodiment of the IBS modem according to the invention. 
     FIG. 4 is a detailed diagram of an IBS modem encoder. 
     FIG. 5 is a schematic diagram of a IBS packet. 
     FIG. 6 is a schematic diagram of digital data tones output from a IBS modulator. 
     FIG. 7 is a diagram showing how digital data is corrupted by an Automatic Gain Controller. 
     FIG. 8 is a diagram showing how a digital wireless network can filter out digital data tones. 
     FIG. 9 is a detailed diagram of receiving circuitry coupled to an IBS modem decoder. 
     FIG. 10 is a state diagram for the IBS decoder shown in FIG.  9 . 
     FIG. 11 is a block diagram showing a search state in the IBS decoder. 
     FIG. 12 is a block diagram showing an active state in the IBS decoder. 
     FIG. 13 is a block diagram showing a clock recovery state in the IBS decoder. 
     FIG. 14 is a schematic diagram of a cellular phone with the IBS modem located in a detachable battery pack. 
     FIG. 15 are schematic diagram showing different data sources coupled to a cellular telephone through a IBS modem. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a wireless communications network  12  includes a cell phone  14  that receives voice signals  22  from a user  23 . A voice coder (vocoder)  18  in the cell phone  14  encodes the voice signals  22  into encoded digital voice signals  31  that are then transmitted over a wireless digital audio channel  34  (cell call). The cell phone  14  transmits the encoded voice signals  31  to a cellular communications site (cell site)  36  that relays the cell call to a Cellular Telecommunications Switching System (CTSS)  38 . 
     The CTSS  38  either connects the cell call to another cell phone either in the wireless cellular network  12 , to a landline phone on a PSTN network  42  as a circuit switched call or routes the cell call over a packet switched Internet Protocol (IP) network  46  as a Voice Over IP (VoIP) call. The cell call can also be routed from the PSTN network  42  back to the cellular network  12  or from the PSTN network  42  to the IP network  46 , or visa versa. The cell call eventually reaches a telephone  44  that corresponds with a destination phone number originally entered at the cell phone  14 . 
     The invention comprises an In-Band Signaling (IBS) modem  28  that enables cell phone  14  to transmit digital data  29  from a data source  30  over the digital audio channel  34  of the cellular network  12 . The IBS modem  28  modulates the digital data  29  into synthesized digital data tones  26 . The digital data tones  26  prevent the encoding components in the cellular network  12  and landline network  42 , such as vocoder  18 , from corrupting the digital data. The encoding and modulation scheme used in the IBS modem  28  allows digital data  29  to be transmitted through the same voice coder  18  used in the cell phone  14  for encoding voice signals  22 . The IBS modem  28  enables voice signals  22  and digital data  29  to be transmitted over the same digital audio channel using the same cell phone circuitry. This prevents a user from having to transmit digital data using a separate wireless modem and enables a cell phone user to talk and send data during the same digital wireless call. The invention modulates the digital data  29  into synthesized voice tones. This prevents the cell phone vocoder  18  from filtering or corrupting the binary values associated with the digital data  29 . The same cell phone transceiver and encoding circuitry is used for transmitting and receiving both voice signals and digital data. This enables the IBS modem  28  to be much smaller, less complex and more energy efficient than a standalone wireless modem. In some embodiments, the ISB modem  28  is implemented entirely in software using only the existing hardware components in the cell phone  14 . 
     One or more servers  40  are located at any of various locations in the wireless network  12 , PSTN network  42 , or IP network  46 . Each server  40  includes one or more IBS modems  28  that encode, detect and decode the digital data  29  transmitted and received over the digital audio channel  34 . Decoded digital audio tones  26  are either processed at the server  40  or routed to another computer, such as computer  50 . 
     Referring to FIG. 2, a first transmitting portion of the IBS modem  28  includes an ISB encoder  52  and a Digital to Analog converter (D/A)  54 . The ISB encoder  52  is typically implemented using a Digital Signal Processor (DSP). The data source  30  represents any device that requires wireless transmission or reception of digital data. For example, the data source  30  can be a laptop computer, a palm computer or a Global Positioning System (GPS) (see FIG.  15 ). 
     The data source  30  outputs a digital bit stream  29  to the IBS encoder  52 . The IBS encoder  52  converts the digital data  29  into IBS packets specially formatted for transmission over a digital wireless voice channel. The IBS encoder  52  then converts the bits from the IBS packets into digital data tones that are then fed into the D/A converter  54 . 
     The IBS modem  28  outputs binary values that each represent an amplitude and phase component of an audio tone. The D/A converter  54  converts these digital values into analog audio tones  26  that are then output to an auxiliary audio port  15  on the cell phone  14 . The analog audio tones  26  are then processed by the cell phone  14  in the same manner as the voice signals  22  (FIG. 1) received through a microphone  17 . An Analog to Digital (A/D) converter  16  in the cell phone  14  encodes the synthesized analog audio tones  26  into digital values. The vocoder  18  encodes the digital representations of the synthesized tones  26  into encoded digital data  32  and outputs the encoded data to a transceiver  19  that transmits the encoded digital data  32  over the digital audio channel  34 . 
     The preferred voltage of the synthesized audio tones  26  output from the D/A converter  26  is around 25 millivolts peak to peak. This voltage level was discovered to prevent the audio tones  26  from saturating the voice channel circuitry in cell phone  14 . 
     Because the digital data  29  is fed through the existing auxiliary hands free audio port  15  in cell phone  14 , the IBS modem  28  can be installed as an after market device that can connect any data source  30  to the cell phone  14 . The data source  30  can transmit digital data  29  in any digital format. For example, the digital data  29  can be sent over an RS-232 interface, Universal Serial Bus (USB) interface, or any other serial or parallel interface. 
     FIG. 3 shows an alternative embodiment of the IBS modem  28 . The IBS modem  28  in FIG. 3 is located inside the cell phone  14  and is implemented in software using the existing cell phone processor or using some combination of its own components and the existing cell phone components. In this embodiment, the cell phone  14  may include a data port  56  that receives the digital data  29  from the external data source  30 . In an alternative embodiment, the digital data source  30  is internal to the cell phone  14 . For example, the data source  30  may be a Global Positioning System (GPS) chip that includes a GPS receiver (not shown) for receiving global positioning data from GPS satellites (FIG.  14 ). 
     The IBS encoder  52  in FIG. 3 as mentioned above typically implemented in software using a DSP and may use the same DSP used for implementing the vocoder  16 . The D/A converter  54  outputs the synthesized audio tones representing digital data  29  to the internal A/D converter  18  of the cell phone  14 . The IBS encoder  52  in an alternative embodiment, not only synthesizes the digital data  29  into audio tones but also quantizes the digital frequency values in the same manner as the A/D converter  18 . The IBS encoder  52  then outputs the quantized data  55  directly into the vocoder  16 . In still another embodiment of the invention, the IBS encoder  52  and D/A converter  54  and implemented entirely in software in the same DSP that implements the vocoder  16 . 
     The vocoder  18  uses a specific encoding scheme associated with the wireless communications network  12  (FIG.  1 ). For example, the vocoder  18  could be a VCELP encoder that converts voice signals into digital CDMA signals. The A/D converter  18 , D/A converter  54  and transceiver  19  are existing cell phone components known to those skilled in the art. 
     It is important to note that the ISB encoder  52  enables the digital data  29  to be transmitted using the same cell phone circuitry that transmits voice signals. The IBS encoder  52  prevents any signal approximation, quantization, encoding, modulation, etc. performed by the, A/D converter  18 , vocoder  16 , or transceiver  19  from corrupting or filtering any bits from the digital data  29 . 
     FIG. 4 is a detailed diagram of the IBS encoder  52  shown in FIG.  2  and FIG. 3. A data buffer  58  stores the binary bit stream  29  from the data source  30 . A packetizer  60  segments the bits in buffer  58  into bytes that comprise a IBS packet payload. A packet formatter  62  adds a packet preamble and postamble that helps prevent corruption of the IBS packet payload. An IBS modulator  64  then modulates the bits in the IBS packet with two or more different frequencies  66  and  68  to generate digital data tones  69 . 
     Preventing Corruption of Digital Data in Voice Channels 
     Cell phone voice coders increase bandwidth in voice channels by using predictive coding techniques that attempt to describe voice signals without having to send all the frequency information associated with human speech. If any unnatural frequencies or tones are generated in the voice channel (i.e., frequencies representing digital data), those frequencies might be thrown out by the voice coder  18  (FIG.  2 ). For example, if the amplitude of the digital data tones are greater than that of normal voice signals or the same digital data tone is generated for too long a time period, the voice coder  18  will filter out that high amplitude or extended frequency signal. Depending on how the digital data tones are encoded, the digital bits represented by those unnatural audio tones may be partially or entirely removed from the voice channel. 
     The IBS encoder  52  encodes the digital data  29  to synthesize voice signals in a manner where voice coders will not filter or corrupt the tones representing digital data. The IBS encoder  52  does this by controlling the amplitudes, time periods and patterns of the synthesized frequencies used to represent the binary bit values. 
     Referring to FIG. 5, the packet formatter  62  (FIG. 4) adds a packet preamble  73  that includes a header  72  and a sync pattern  74  to the front of a IBS packet  70 . A checksum  78  and a packet postamble  79  are attached to the backend of the IBS packet  70 . 
     Before the digital data is transmitted, a zero payload IBS packet  70  is sent to the destination. The destination sends back an acknowledge to the IBS modem  28  in the form of a zero packet payload IBS packet. This acknowledge packet informs the IBS modem  28  in the cell phone  14  to begin transmitting IBS packets  70 . 
     FIG. 6 shows the synthesized digital data tones  69  output from the IBS modulator  64  (FIG.  4 ). The IBS modulator  64  (FIG. 4) converts the digital bits in the IBS packet  70  into one of two different tones. A first tone is generated at an f 1  frequency and represents a binary “1” value and a second tone is generated at a f 2  frequency and represents a binary “0” value. In one embodiment the f 1  frequency is 600 Hertz and the f 2  frequency is 500 Hertz (Hz). 
     It has been determined that the most effective frequency range for generating the tones that represent the binary bit values are somewhere between 400 Hertz and 1000 Hertz. The IBS modulator  64  includes Sine and Cosine tables that are used to generate the digital values that represent the different amplitude and phase values for the f 1  and f 2  frequencies. 
     In one embodiment of the invention, the digital data is output on the audio channel  34  at a baud rate of 100 bits/second. This baud rate has been found to be effective in preventing corruption of the digital audio data by a wide variety of different cellular telephone voice coders. The sine waves for each f 1  and f 2  tone begin and end at a zero amplitude point and continue for a duration of 10 milliseconds. Eighty samples are generated for each digital data tone. 
     Referring to FIG. 7, an Automatic Gain Controller (AGC)  80  is one encoding function used in the cell phone  14 . The AGC  80  may be software that is located in the same DSP that implements the voice coder  16 . The AGC  80  scales instantaneous energy changes in voice signals. There are situations when no voice signals have been fed into the AGC  80  for a period of time followed by a series of audio tones  82 . that comprise the beginning of a IBS packet  70 . The AGC  80  scales the first group of tones  82  at the beginning of the IBS packet  70 . The AGC  80  also looks ahead at the zero signal levels  84  after the end of the IBS packet  70 , and will scale the tones  83  at the end of the IBS packet  70  as part of its prediction scaling scheme. This scaling prevents the over amplification of signal or noise when instantaneous energy changes occur in the voice channel. 
     As previously shown in FIG. 6, the “1” and “0” bits of the IBS packet  70  are represented by tones f 1  and f 2 , respectively. If these tones are scaled by the AGC  80 , the digital bits represented by those frequencies might be dropped during encoding. For example, the vocoder  16  may see the scaled tones as noise and filter them from the audio channel. To prevent the unintentional filtering of tones that represent digital data, the IBS packet  70  in FIG. 5 includes preamble bits  73  and postamble bits  79 . The preamble bits  73  and  79  do not contain any of the digital data bits  29  from the data source include a certain number of sacrificial bit that are not needed for detecting or encoding the IBS packet  70 . Thus, the tones that are generated for these sacrificial bits in the preamble and postamble can be scaled or filtered by the AGC  80  without effecting any of the digital data contained in the IBS packet payload  76 . 
     The bit pattern in the header  72  and sync pattern  74  are specifically formatted to further prevent corruption of the packet payload  76 . A random sequence and/or an alternating “1”-“0” sequence of bits is used in either the header  72  and/or sync pattern  74 . These alternating or random bit patterns prevent adaptive filters in the cell phone vocoder  18  (FIG.2) from filtering tones representing the remaining bits in the IBS packet  70 . 
     Referring to FIG. 8, adaptive filters adapt around the frequencies that are currently being transmitted over the wireless network. For example, If a long period of the same f 1  tone is currently being transmitted, an adaptive filter used in the cell phone may adapt around that f 1  frequency spectrum as shown by filter  86 . 
     Another short tone at another frequency f 2  may immediately follow the long period of f 1  tones. If the filter  86  is too slow to adapt, the first few f 2  tones may be filtered from the voice channel. If the filtered f 2  tone represent bits in the IBS bit stream, those bits are lost. 
     To prevent adaptive filters in the cell phone from dropping bits, some portion of the preamble  73  includes a random or alternating “1”-“0” bit pattern. This preconditions the adaptive filter as shown by filter  88 . The preamble  73  tries to include a portion of the same bit sequence that is likely or does occur in the packet payload  76 . For example, the IBS encoder  52  can look ahead at the bit pattern in the payload  76 . The encoder  52  can then place a subset of bits in a portion of the preamble to represent the sequence of bits in the packet payload. 
     This preconditions the adaptive filter for the same f 1  and f 2  frequencies, in the same duration and in a similar sequence that is likely to follow in the IBS packet payload  76 . Thus, the adaptive filter adapts is less likely to filter out the tones that actually represent the digital data that is being transmitted. 
     FIG. 9 is a block diagram of receive circuitry  91  that receives the voice and data signals in the audio channel  34 . The IBS modem  28  also includes an IBS decoder  98  the detects and decodes the digital data tones transmitted in the audio channel  34 . The receive circuitry  91  is located at the CTSS  38  (FIG. 1) that receives wireless transmissions from the cell sites  36  (FIG.  1 ). The same receive circuitry  91  is also be located in the cell phone  14 . 
     As described above in FIGS. 2 and 3, the decoder part of the IBS modem  28  can be external to the cell phone  14  or can be inside the cell phone  14 . Dashed line  104  shows an IBS modem  28  external to a cell phone and dashed line  106  shows an internal IBS modem  28  internal to a cell phone. IBS modems  14  can also be located at any telephone location in the PSTN network  42  or IP network  46  (FIG.  1 ). The receiving circuitry  91  may be different when the IBS modem  28  is coupled to a landline. However, the IBS modem  28  operates under the same principle by transmitting and receiving synthesized tones over the voice channel of the phone line. 
     The signals in audio channel  34  are received by a transceiver  90 . A vocoder  92  decodes the received signals. For example, the vocoder  92  may decode signals transmitted in TDMA, CDMA, AMPS, etc. A D/A converter  94  then converts the digital voice signals into analog signals. The analog voice signals are then output from an audio speaker  17 . 
     If the IBS modem  28  is external to the receiving circuitry  91 , then a A/D converter  96  converts the analog signals back into digital signals. The IBS decoder  98  demodulates any tones representing digital data back into a digital IBS packets. A packet disassembler  100  disassembles the packet payload from the IBS packets  70  and stores the original digital data pattern in a data buffer  102 . 
     FIG. 10 is a state diagram explaining how the IBS decoder  98  in FIG. 9 operates. The IBS decoder  98  repeatedly samples and decodes the audio signals received from the audio channel  34 . State  110  searches for tones in the audio signal that represent digital data. If the Signal to Noise Ratio (SNR), for tones within the frequency range of the digital data tones, are greater than a preselected value, the IBS decoder  98  goes into an active state  112 . The active state  112  collects tone samples. If at any time during the active state  112 , the SNR falls below an active threshold value, or a timeout is reached before enough tone samples are collected, the IBS decoder  98  returns to the search state  110  and begins again to search for digital data tones. 
     After a number of samples are collected, the IBS decoder  98  looks for bits that identify the preamble  73  in the IBS packet  70  (FIG.  5 ). If the preamble  73  is detected, the IBS decoder  98  moves to clock recovery state  114 . The clock recovery state  114  synchronizes with the synchronization pattern  74  in the IBS packet  70  (FIG.  5 ). The IBS decoder  98  then demodulates the packet payload  76  in state  116 . If the preamble  73  is not found, IBS decoder  98  goes back to the search state  110  and starts searching again for the beginning of an IBS packet  70 . 
     The IBS decoder  98  demodulates all of the packet payload  76  and then performs a checksum  78  as a final verification that a valid IBS packet  70  has been successfully demodulated. Control then returns back to the search state  110  and begins searching for the next IBS packet  70 . 
     FIG. 11 is a detailed diagram for the search state  110  of the IBS decoder  98 . The search state  110  uses in band and out of band filtering. “In band” is used in the following discussion to refer to tones within the frequency range of the two tones that represent the digital data binary “1” value (500 Hz) and the digital data binary “0” value (600 Hz). 
     A first band pass filter  118  (in band) measures energy for signals in the audio channel within the frequency range of about 400 Hz to around 700 Hz. A second band pass filter  120  (out of band) measures the energy in the audio channel for signals outside of the 400 Hz-700 Hz range. A Signal to Noise Ratio (SNR) is calculated in block  122  between the in band energy and the out of band energy. If tones representing the digital data exist in the audio channel, the energy measured by the in band filter  118  will be much greater then the energy measured by the out of band filter  120 . 
     If the SNR is below a selected threshold in comparator box  124 , signals in the audio channel are determined to be actual voice signals or noise. If the SNR is above the threshold, the IBS decoder  98  determines the tones represent in band digital data. When digital data is detected, the IBS decoder  98  moves into the active state  112  to begin searching for the beginning of an IBS packet  70 . 
     FIG. 12 shows the active state  112  for the IBS decoder  98 . Block  130  is notified by the search state  110  when an in band tone is detected in the audio channel. Samples of the audio tones are windowed in block  132  with a number of samples associated with a single binary bit. In one embodiment, 80 samples of the digital data tone are taken, padded with zeros, and then correlated with Discrete Fourier Transforms (DFTs). 
     A first DFT has coefficients representing a 500 Hz tone and is applied to the windowed data in block  134 . The first DFT generates a high correlation value if the samples contain a 500 Hz tone (“0” binary bit value). A second DFT represents a 600 Hz tone and is applied to the windowed samples in block  136 . The second DFT generates a high correlation value if the windowed samples contain a 600 Hz tone (“1” binary bit value). Block  138  selects either a binary “0” or binary “1” bit value for the windowed data depending on which of the 500 Hz DCT or 600 Hz DCT yields the largest correlation value. 
     The IBS decoder  98  in decision block  140  continues to demodulate the tones until the preamble of the IBS packet  70  has been detected. The IBS decoder  98  then moves to clock recovery state  114  (FIG. 13) to synchronize with the sync pattern  74  in the IBS packet  70  (FIG.  5 ). If more bits need to be demodulated before the preamble  73  can be verified, decision block  140  returns to block  132  and the next 80 samples of the digital data tones are windowed and demodulated. 
     FIG. 13 describes the clock recovery state  114  for the IBS decoder  98 . After the preamble  73  in the IBS packet  70  is detected in the active state  112 , the clock recovery state  114  demodulates the next string of bits associated with the sync pattern  74  (FIG.  5 ). The clock recovery state  114  aligns the tone samples with the center of the correlation filters described in the active state  112 . This improves decoder accuracy when demodulating the IBS packet payload  76 . 
     Decision block  142  looks for the sync pattern  74  in the IBS packet  70 . If after demodulating the next tone, the sync pattern  74  is not found, decision block  142  offsets the window used for sampling the sync pattern  74  by one sample in block  148 . Decision block  150  then rechecks for the sync pattern  74 . If the sync pattern  74  is found, decision block  144  determines the power ratio for the detected sync pattern. This power ratio represents a confidence factor of how well the demodulator is synchronized with the sync pattern. The power ratio is compared with the power ratios derived for different window shifted sampling positions. If the power ratio is greater then a previous sampling position, then that power ratio is saved as the new maximum power ratio in block  146 . 
     If the power ratio for the sync pattern  74  is less then the previously measured power ratio, the decoder in block  148  offsets the sampling window by one sample position. The power ratio is then determined for the shifted window and then compared to the current maximum power ratio in decision block  144 . The window is shifted until the maximum power ratio is found for the sync pattern  74 . The window offset value at the maximum power ratio is used to align the demodulator correlation filters with the center sample of the first bit  77  (FIG. 5) in the IBS packet payload  76 . 
     The IBS decoder  89  then jumps to demodulate state  116  (FIG. 10) where the identified window offset is used to demodulate the remaining 500 and 600 Hz tones that represent the packet payload bits  76  and check sum bits  78 . The demodulation state  116  correlates the f 1  and f 2  tones with DFTs in the same manner as in the active state (FIG.  12 ). The check sum bits  78  are then used as a final check to verify that a valid IBS packet has been received and accurately decoded. 
     FIG. 14 is a diagram of the IBS modem  28  located in a battery pack connected to the cellular telephone  14 . A hands free audio channel pin  200  couples the IBS modem  28  to the voice channel  202  in the cell phone  14 . A switch  204  couples either voice signals from the microphone  17  or digital data tones from the IBS modem  28  to the voice channel  202 . 
     The switch  204  is controlled either through a menu on a screen (not shown) in the cell phone  14  or by a button  206  that extends out of the back end of the battery pack  208 . The switch  204  can also be controlled by one of the keys on the keyboard of the cell phone  14 . 
     The button  206  can also be used to initiate other functions provided through the IBS modem  28 . For example, a Global Positioning System (GPS) includes a GPS receiver  210  located in the battery pack  208 . The GPS receiver  210  receives GPS data from a GPS satellite  212 . A cell phone operator simply pushes button  206  during an emergency situation. Pressing the button  206  automatically enables the GPS receiver  210  to collect GPS data from GPS satellite  212 . At the same time, the switch  204  connects IBS modem  28  on the voice channel  202  of the cell phone  14 . The IBS modem  28  is then activated. As soon as the GPS data is collected in the IBS modem  28 , the data is formatted, encoded and output by IBS modem  28  to the voice channel  202  of the cell phone  14 . 
     The user  23  can push the button  206  anytime after manually calling up a phone number. After the audio channel is established with another endpoint, the user  23  pushes button  206 . Switch  204  is connected to the IBS modem  28  and the IBS modem  28  is activated. The GPS data (or other digital source) is then sent as digital data tones through the IBS modem  28  to an endpoint over the established audio channel. After the data has been successfully transmitted, the user presses button  206  again reconnect switch  204  to the audio receiver  17 . 
     FIG. 15 shows the different types of data sources that can be connected to the IBS modem  28 . Any one of a palm computer  212 , GPS receiver  214  or a laptop computer  216 , etc. can are coupled to the IBS modem  28 . The IBS modem  28  converts the bits output from the device into digital data tones that are then output over the audio channel  34  in the wireless network. Because data can transmitted to another endpoint through the cell phone  14 , none of the devices  212 ,  214  or  216  need a separate wireless modem. 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. The scope of the present invention should, therefore, be determined only by the following claims.