Enhanced in-band signaling for data communications over digital wireless telecommunications networks

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DESCRIPTION

Enhanced intra-band signaling for data transmission over digital wireless telecommunications networks.

Technical field

This invention relates to wireless telecommunications and more specifically to a system that transmits digital data over the audio channel of an "intra-band" digital wireless network.

Background of the invention

A cell phone allows a user to talk to another user without being tied to a land line. The cell phone includes circuitry that generates an audio signal from the voice of the user. These voice signals are converted to digital form using AD converters. The digitized speech signals are encoded by a speech coder (vocoder) and then modulated on a carrier frequency that transmits the speech signals over a cellular network. Voice signals are sent over the wireless cellular network either to another phone on the wireless cellular network or to another phone on a landline telephone network.

Different encoders / decoders (codecs), modulators, vovo encoders, automatic gain controllers, analog-to-digital (AD) converters, noise reduction circuits, and digital-to-analog (DA) converters are used in cellular and terrestrial telephone networks. These telephone components can implement different coding schemes to encode and decode the voice signals.

These telecommunication components are designed to efficiently transmit d4e voice signals over wireless and terrestrial voice communication channels. For example, a digital vocoder uses predictive coding techniques to represent speech signals. These predictive coders remove noise (non-speech signals) while compressing and estimating the frequency components of speech signals before transmitting them on the voice channel.

Sometimes it is necessary for a user to transmit both audio signals and digital data to another location. For example, when a cell phone user calls 911 for emergency assistance, the user may need to send digital location data to a control center while verbally explaining the emergency conditions to a human operator. It would be desirable to transmit the digital data via a cell phone without having to use a separate analog wireless modem.

Consequently, there is a need to transmit digital data over a voice channel of a wireless digital communication network.

US 6021163 discloses a radio or exchange base station having two parts that can be separated by a certain distance, and addresses the problem of transmitting data by cable between said two parts. In particular, US6021163 notes that if the data is modulated at the intermediate frequency in the first part and processed at the intermediate frequency along the cable to the second part, signal attenuation can be a problem. US6021163 proposes to modulate the data to a frequency lower than the intermediate frequency in the first part, and then transmit the modulated data over the cable to the second part. US6021163 does not mention the frequency at which the proposed modulation takes place, other than that it is less than the intermediate frequencies of 200 MHz and 800 MHz.

Summary of the invention

An intra-band signaling modem communicates digital data over a voice channel in a digital wireless telecommunication network. One input receives digital data. An encoder converts digital data into audio tones that synthesize frequency characteristics of the human voice. Digital data is also encoded to prevent speech encoding circuits in the telecommunications network from degrading the synthesized audio tones that digital data represents. An output then outputs the synthesized audio tones to a voice channel of a digital wireless telecommunication network.

The above object of the invention can be achieved by an intra-band signaling modem according to claim 1.

Brief description of the drawings

Fig. 1 is a diagram showing a wireless telecommunication network providing intra-band signaling (IBS) according to the invention.

Fig. 2 is a detailed diagram of a cellular phone coupled to an IBS modem according to an embodiment of the invention.

Fig. 3 is another embodiment of the IBS modem according to the invention.

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Fig. 4 is a detailed diagram of an IBS modem encoder.

Fig. 5 is a schematic diagram of an IBS packet.

Fig. 6 is a schematic diagram of digital data tone output from an IBS modulator.

Fig. 7 is a diagram showing how digital data is degraded by an automatic gain controller.

Fig. 8 is a diagram showing how digital data is degraded by an automatic gain controller.

Fig. 9 is a detailed receive circuit diagram 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 is a schematic diagram showing different data sources coupled to a cellular phone through an IBS modem.

Fig. 16 is a schematic diagram showing the IBS modem implementation using a sound card.

Figs. 17 and 18 are block diagrams showing how the sound card of Fig. 16 operates.

Fig. 19 is a block diagram of a synchronization circuit for the IBS modem.

Fig. 20 is a detailed diagram of the timing circuit of Fig. 19.

Fig. 21 is a timing diagram showing how the timing circuit of Fig. 19 operates.

Fig. 22 is a graph showing how the synchronization circuit identifies the optimal synchronization start time.

Fig. 23 is an alternative embodiment of the synchronization circuit.

Fig. 24 is a coding diagram for a multi-channel IBS modem.

Fig. 25 is a decoding diagram for a multi-channel IBS modem.

Figs. 26 and 27 show different configurations for the multi-channel IBS modem shown in Figs. 24 and 25.

Detailed description of the preferred embodiment

Referring to Fig. 1, a wireless telecommunications network 12 includes a cellular phone 14 that receives voice signals 22 from a user 23. A voice coder (vocoder) 18 in the mobile phone encodes voice signals 22 into signals. encoded digital voices 31 which are then transmitted over a wireless digital radio channel 34 (cellular call). The cellular telephone 14 transmits the encoded digital voice signals 31 to a cellular communications site (cell site) 36 which relays the cellular call to a Cellular Telecommunications Switching System (CTSS) 38.

The CTSS 38 either connects the cellular call to another cellular phone either on the cellular wireless network 12, to a land line phone on a PSTN network 42 as a circuit switched call, or routes the call over an Internet Protocol (IP) network. packet switching 46 as a Voice over IP (VoIP) call. The cellular call can also be routed from PSTN network 42 back to cellular network 12 or from PSTN network 42 to IP network 46, or vice versa. The cellular call eventually arrives at a telephone 44 that corresponds to a destination telephone number originally entered in the cellular telephone 14.

Additional data can be inserted at any point in cellular network 12, such as PSTN network 42 AND IP network 46, and the signal be remodulated for transmission over cable or cellular networks. Such data could be system related such as routing information, rate information, etc.

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An intra-band signaling (IBS) modem 28 enables cellular telephone 14 to transmit digital data 29 from a data source 30 over radio channel 34 of cellular network 12. IBS modem 28 modulates digital data 29 into synthesized tones of digital data 26. Digital data tones 26 prevent encoding components in cellular network 12 and terrestrial network 42, such as vocoder 18, from degrading digital data. The coding and modulation scheme used in IBS modem 28 allows digital data 29 to be transmitted through the same coz encoder 18 used in cell phone 14 to encode voice signals 22. Any device such as a vending machine, etc. ., could be improved by this technology.

Synthesized tones are defined as signals that represent digital data that also have signaling characteristics that enable the signals to be encoded and decoded by a voice codec without losing digital data information in the signal. In one example, frequency shift keying (FKM) signals are used to create the synthesized tones at different frequencies within the audio range of human speech.

The IBS modem 28 enables the transmission of voice signals 22 and digital data 29 over the same digital audio channel using the same cellular phone circuitry. This prevents a user from having to transmit digital data using a separate wireless modem and allows a cell phone user to speak and send data during the same wireless digital call.

The invention modulates digital data 29 into synthesized audio tones. This prevents the cell phone vocoder 18 from filtering or degrading the binary values ​​associated with the digital data 29. The same cell phone transceiver and scrambling circuitry are used to transmit and receive digital data and voice signals. This enables the IBS 28 modem to be much smaller, less complicated, and more energy efficient than a stand-alone wireless modem. In some embodiments, the IBS modem 28 is fully software implemented using only the existing hardware components in the cellular phone 14.

One or more servers 40 are located at any of several locations in 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 transmitted digital data 29. and received on digital radio channel 34. Decoded digital data is either processed at server 40 or routed to another computer such as computer 50.

Referring to Fig. 2, a first portion of the IBS modem 28 includes an IBS encoder 52 and a digital-to-analog (D / A) converter 54. The IBS encoder 52 is typically implemented using a Digital Signal Processor (PSD). Data source 30 represents any device that requires wireless transmission or reception of digital data. For example, data source 30 can be a laptop, a palm computer, or a Global Positioning System (GPS) (see Fig. fifteen).

Data source 15 outputs a digital bit stream 29 to IBS encoder 52. IBS encoder 52 converts digital data 29 into specially formatted IBS packets for transmission over a digital wireless voice channel. IBS encoder 52 converts bits from IBS packets to digital data tones which are then fed into D / A converter 54.

The IBS modem 28 outputs binary values ​​each representing an amplitude and phase component of an audio tone. The D / A converter 54 converts these digital values ​​into analog audio tones 26 which are then output to an auxiliary audio port 15 on cell phone 14. Analog audio tones 26 are then processed by cell phone 14. An analog-to-digital (A / D) converter 16 in cellular telephone 14 encodes the synthesized analog audio tones 26 into digital values. The vocoder 18 encodes the digital representations of the synthesized tones 26 into digital encoded data 32 and sends the encoded data to a transceiver 19 which transmits the digital encoded data on radio channel 34.

The preferred voltage of the output of the synthesized audio tones 26 from the D / A converter is about 25 millivolts peak-to-peak. This voltage level was found to prevent audio tones 26 from saturating the voice channel circuitry in cell phone 14.

Since the digital data 26 is fed to the cell phone 14 through the existing hands-free auxiliary audio port 15, the IBS modem can be installed as a replacement device that can connect any data source 30 to the cell phone 14. The source of data 30 can transmit digital data 29 in any digital format. For example, 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 within the cell phone 14 and is implemented in software using the cell phone's existing processor or using some combination of its own components and the existing components of the cell phone. In this embodiment, cellular phone 14 may include a data port 56 that receives digital data 29 from external data source 30. In an alternative embodiment, external data source 30 is internal to cell phone 14. For example, digital 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).

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The IBS encoder 52 in Fig. 3 as mentioned above is typically implemented in software using a DSP and can use the same DSP used to implement the vocoder 18. The D / A converter 54 outputs the synthesized audio tones representing data. digital 29 to internal A / D converter 16 of cell phone 14. The IBS encoder 52 in an alternative embodiment, not only synthesizes the digital data 29 in audio tones but also quantizes the digital frequency values. The IBS encoder 52 then outputs the quantized data 55 directly to the vocoder 18. In another different embodiment of the invention, the IBS encoder 52 is fully software implemented in the same DSP that the vocoder 18 implements.

Vocoder 18 uses a specific coding scheme associated with wireless communication network 12 (Fig. 1). For example, vocoder 18 may be a VCELP encoder that converts voice signals to CDMA digital signals. A / D converter 16, D / A converter 54, and transceiver 19 are existing components of cellular telephones known to those of skill in the art.

It is important to note that the IBS encoder 52 makes it possible to transmit the digital data 29 using the same cellular phone circuitry that transmits voice signals. The IBS encoder 52 prevents any signal approximation, quantization, encoding, modulation, etc. performed by the A / D converter 16, the vocoder 18 or the transceiver 19 from being degraded or filtered of any bit 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 data source 30. A packetizer 60 segments the bits in buffer 58 in bytes comprising an IBS packet payload. A packet formatter 62 adds a preamble and an epilogue that help prevent degradation 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.

Prevention of Digital Data Degradation in Voice Channels

Cell phone voice coders increase the bandwidth in voice channels using predictive coding techniques that try to describe voice signals without having to send all the information associated with human speech. If any unnatural frequencies or tones are generated in the speech channel (eg, frequencies representing digital data), these frequencies can be removed by speech coder 18 (FIG. 2). For example, if the amplitude of digital data tones is greater than that of normal voice signals or the same digital data tones are generated over a long period, the voice coder 18 can eliminate that large amplitude or extended signal from frequency. Depending on how the digital data tones are encoded, the digital bits represented by those unnatural tones can be completely removed from the voice channel.

IBS encoder 52 encodes digital data 29 in a way that speech coders do not degrade tones representing digital data. The IBS encoder 52 does this by controlling the amplitudes, time periods, and patterns of the synthesized audio tones used to represent the binary bit values.

Referring to Fig. 5, the packet formatter 62 (Fig. 4) adds a packet preamble 73 and a header 75 in front of the IBS packet 70. The packet preamble 73 includes a preamble pattern 72 and a sync pattern 74 A control total 78, and an end of packet 79 are added to the end of IBS packet 70.

Fig. 6 shows the synthesized digital data 69 tone output from IBS modulator 64 (Fig. 4). The IBS 64 modulator (Fig. 4) converts the digital bits in the IBS 70 packet to one of two different tones. A first tone is generated at a frequency f1 and represents a binary value "1" and a second tone is generated at a frequency fs and represents a binary value "0". In one embodiment the frequency f1 is 600 Hertz and the frequency f2 is 500 Hertz (Hz).

The most effective frequency range for generating the tones representing the binary bit values ​​has been determined to be anywhere between 400 and 1600 Hertz. The IBS modulator 64 includes sine and cosine tables that are used to generate the digital values ​​representing the different amplitude and phase values ​​for the frequencies f1 and f2.

In one embodiment of the invention, digital data exits radio channel 34 at a baud rate of 100 bits / s. Baud rate has been found to be effective in preventing degradation of digital audio data for a wide variety of different cellular phone vocoders. The sine waves for each tone f1 and f2 begin and end at a point of zero amplitude and continue for 10 milliseconds. Eighty samples are generated for each digital data tone.

Referring to FIG. 7, an automatic gain controller (AGC) is a scrambling function used in cell phone 14. AGC 80 may be software that is located on the same DSP that implements voice scrambler 18. The CAG 80 instantly scales energy changes in voice signals. There are situations where no voice signals have been fed into the CAG 80 for a while followed by a series of audio tones 82, comprising the beginning of an IBS 70 packet. The CAG 80 scales the first group of tones 82 to beginning of IBS packet 70. CAG 80 also anticipates zero signal levels 84 after the end of IBS packet 70, and will scale tones 83 at the end of IBS packet 70 as part of its prediction scaling scheme. This scaling prevents over-amplification of signal or noise when instantaneous power changes occur in the voice channel.

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As previously shown in FIG. 6, bits "1" and "0" of IBS packet 70 are represented by tones f1 and f2 respectively. If these tones are scaled by the AGC 80, the digital bits represented by these frequencies could be discarded during encoding. For example, the vocoder 18 may view the scaled tones as noise and remove them from the audio channel. To avoid unintentional removal of tones representing digital data, the IBS packet 70 in Fig. 5 includes preamble 72 and epilogue 79 bits. Preamble 72 and epilogue 79 bits do not contain any of the digital data bits 29 from the data source but include a certain number of protection bit (s) that are not needed to detect or encode the IBS 70 packet. The tones that are generated for these guard bits in the preamble and epilogue can be scaled or filtered by the CAG 80 without affecting any of the digital data contained in the payload 76 of the IBS packet.

The bit pattern in the preamble 72 and the sync pattern 74 are further specifically formatted to prevent degradation of the packet payload 76. A random sequence and / or an alternating "1" - "0" bit sequence is used in the preamble 72 and / or the sync configuration 74. These alternating or random bit configurations prevent adaptive filters in the phone's vocoder 18 cellular (Fig. 2) remove tones that represent the remaining bits in the IBS 70 packet.

Referring to Fig. 8, the adaptive filters adapt around the frequencies that are normally transmitted over the wireless network. For example, if a long period of the same tone f1 is being transmitted, an adaptive filter used in the cell phone can adapt around the frequency spectrum f1 as shown by filter 86.

Another short tone at another frequency f2 can immediately follow the long period of tones f1. If filter 86 is too slow to adapt, the first few tones f2 can be filtered from the voice channel. If the filtered f2 tones represent bits in the IBS bit stream, those bits are lost.

To prevent adaptive filters in the cell phone from dropping bits, some part of preamble 73 includes an alternating or random "1" - "0" bit pattern. This preconditions the adaptive filter as shown by filter 88. Preamble 73 (Fig. 5) tries to include a part of the same bit sequence that occurs or is likely to occur in the payload 76 of the packet. For example, the IBS encoder 52 may anticipate the bit setting in payload 76. Encoder 52 may then place a subset of bits in a part of the preamble to represent the sequence of bits in the payload.

This preconditions the adaptive filter for the same frequencies f1 and f2, for the same duration and at a frequency similar to what it is likely to follow in packet payload 76. Consequently, the adaptive filter is less likely to remove the tones that actually represent the digital data being transmitted.

FIG. 9 is a block diagram of receiver circuit 91 that receives voice and data signals on radio channel 34. IBS modem 28 also includes an IBS decoder 98 that detects and decodes digital data tones transmitted on the radio channel 34. Receiver circuit 91 is located on CTSS 38 (Fig. 1) that receives wireless transmissions from cell sites 36 (Fig. 1). The same receiver circuit 91 is also located in the cellular receiver circuit 91 14.

As previously described in Figs. 2 and 3, the decoding part of the IBS modem 28 can be external to the cell phone 14 or it can be inside the cell phone 14. The dotted line 104 shows an IBS modem 28 external to a cell phone and the dotted line 106 shows a IBS 28 modem internal to a cell phone. The IBS modems 14 can be located in any location of the telephone in the PSTN network 42 or in the IP network (Fig. 1). Receiver circuit 91 may be different when IBS modem 28 is coupled to a land line. However, the IBS modem 28 operates on the same principle by transmitting and receiving synthesized tones over the voice channel of the telephone line.

Signals on radio channel 34 are received by a transceiver. A vocoder 92 decodes the received signals. For example, vocoder 92 can decode signals transmitted in TDMA, CDMA, AMPS, etc. An A / D converter 94 then converts the digital voice signals to analog signals. The analog voice signals are then output from an audio speaker 17.

If the IBS modem 28 is external to the receiver circuit 91, then the A / D converter 96 converts the analog signals to digital again. The IBS decoder 98 demodulates any tone representing digital data back to an IBS digital packet. A packet disassembler 100 disassembles the packet payload from IBS packets 70 and stores the decoded digital data in a data buffer 102.

FIG. 10 is a state diagram explaining how IBS decoder 98 operates. IBS decoder 98 repeatedly samples and decodes audio signals received from radio channel 34. State 110 searches the audio signal for tones representing digital data. If the Signal to Noise Ratio (SNR), for tones within the frequency range of digital data tones, is greater than a preset value, the IBS decoder 98 enters an active state 112. 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 restarts scanning. search for digital data tones.

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After a number of samples have been collected, the IBS decoder 98 looks for bits identifying the preamble 73 in the IBS packet 70 / Fig. 5). If the preamble 73 is detected, the IBS decoder 98 moves to the clock recovery state 114. The clock recovery state 114 synchronizes with the timing pattern 74 in the IBS packet 70 (FIG. 5). The IBS decoder 98 then demodulates the payload of packet 76 in state 116. If the preamble 73 is not found, the IBS decoder 98 returns to the search state 110 and starts searching again at the beginning of the IBS packet 70.

The IBS decoder 98 demodulates the entire payload of packet 76 and then does a totalization 78 as a final check that an IBS packet 70 has been successfully demodulated. The control then returns to 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 intra-band and out-of-band filtering. In the following discussion, “intraband” is used to refer to tones within the frequency range of the two tones that represent the binary value “1” of digital data (500 Hz) and the binary value “0” of digital data (600 Hz).

A first band-pass filter 118 (intra-band) measures the energy of the signals in the audio channel within the frequency range of about 400 Hz to about 700 Hz. A second band-pass filter 120 (out-of-band) it measures the energy of the signals in the audio channel outside the 400-700 Hz frequency range. A Signal to Noise Ratio (SNR) is calculated in block 122 between the intra-band energy and the out-of-band energy. If there are tones in the audio channel representing the digital data, the energy measured by the intra-band filter 118 will be much greater than the energy measured by the out-of-band filter 120.

If the SNR is below a threshold selected in the comparer box 124, it is determined which signals on the audio channel are actual speech or noise signals. If the SNR is above the threshold, the IBS decoder 98 determines that the tones represent intraband digital data. When digital data is detected, the IBS decoder 98 moves to an active state 112 (FIG. 10) to start searching from the beginning of the 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 intraband tone is detected on the audio channel. Samples of the audio tones are displayed at block 132 with a number of samples associated with a single binary bit. In one embodiment, 80 samples of digital data tones are taken, padded with zeros, and then correlated with Discrete Fourier Transforms (DFT).

A first DFT has coefficients representing a 500 Hz tone and is applied to the data displayed in block 134. The first DFT generates a high correlation value if the samples contain a 500 Hz tone (binary "0" bit value). A second DFT represents a 600 Hz tone and is applied to the data displayed in block 136. The second DFT generates a high correlation value if the samples contain a 600 Hz tone (binary "1" bit value). Block 138 selects either a "0" or "1" binary bit value for the data displayed in the window depending on which of the 500 Hz or 600 Hz DFTs gives the higher correlation value.

The IBS decoder 98 at 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 the clock recovery state 114 (Fig. 13) to synchronize with the model. sync 74 in the IBS 70 package (Fig. 5). If more bits need to be demodulated before preamble 73 can be verified, decision block 140 returns to block 132 and the next 80 samples of the digital data tones are displayed 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 bit string associated with the sync 74 model (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 the accuracy of the decoder when demodulating the IBS packet payload 76.

Decision block 142 searches for sync pattern 74 in IBS packet 70. If after demodulating the next tone, the sync pattern is not found, decision block 142 changes the window used to sample sync pattern 74 to a sample in block 148. Decision block 150 then rechecks sync pattern 74. If sync pattern 74 is found, decision block 144 determines the power ratio for the detected sync pattern. This power ratio represents a confidence factor for the quality of the demodulator's synchronization with the sync model. The power ratio is compared to the power ratios derived from different displayed sample positions. If the power ratio is greater than a previous sample position, the power ratio is saved as the new maximum power ratio in block 146.

If the power ratio for the sync model 74 is less than the previously measured power ratio, the decoder at block 148 changes the sampling window by a sample position. The power ratio is then determined for the moved window and then compared to the current maximum power ratio in decision block 144. The window is moved until the maximum power ratio is found for the sync 74 model. The window shifted value to 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 header of the IBS packet 75.

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The IBS decoder 89 then jumps to demodulation state 116 (Fig. 10) where the identified window moved is used to demodulate the remaining 500 and 600 Hz tones representing the packet payload bits 76 and totals the bits 78. The state Demodulation 116 correlates the tones f1 and f2 with the DFTs in the same way as in the active state (Fig, 12). The totaled bits 78 are then used to verify that a valid IBS packet has been accurately received and decoded.

Fig. 14 is a diagram of the IBS modem 28 located in a battery pack connected to the cell phone 14. A hands-free audio channel pin 200 couples the IBS modem 28 to the voice channel 202 on the cell phone 14. A switch 204 couples either voice signals from microphone 17 or digital data tones from IBS modem 28 to voice channel 202.

Switch 204 is controlled either through a menu on a screen (not shown) on cell phone 14 or by a button 206 projecting from the rear of battery pack 208. Switch 204 can also be controlled by one of cell phone keypad keys 14.

Button 206 can also be used to initiate other functions provided through IBS modem 28. For example, a Global Positioning System (GPS) includes a GPS 210 receiver located in battery pack 208. GPS receiver 210 receives GPS data from a GPS satellite 212. A cell phone operator simply presses button 206 during an emergency situation. Pressing button 206 automatically enables GPS receiver 210 to collect data from GPS satellite 212. At the same time, switch 204 connects IBS modem 28 to voice channel 202 of cell phone 14. 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 broadcast by the IBS modem 28 to the voice channel 202 of the cell phone 14.

User 23 can press button 206 at any time after manually calling a telephone number. After the audio channel is established with the other end, the user 23 presses the button 206. The switch 204 is connected to the IBS modem 28 and the IBS modem 28 is activated. The GPS (or other digital source) data is then sent as digital data tones through the IBS modem 28 to an endpoint on the established audio channel. After successfully transmitting the data, the user presses button 206 again reconnecting switch 204 to audio receiver 17.

Fig. 15 shows the different types of data sources that can be connected to the IBS 28 modem. Any of a palm computer 212, GPS receiver 214 or computer 216, etc., can be coupled to the IBS 28 modem. The IBS 28 modem converts the bit output from the device in digital data tones which are then output on radio channel 34 in the wireless network. Since data can be transmitted to another endpoint by cell phone 14, neither device 212, 214, or 216 needs a separate wireless modem.

Implementation of intra-band signaling modem on a sound card

The IBS 28 modem can be implemented on a standard computer sound card. Referring to Fig. 16, a sound card 252, such as a Sound Blaster card manufactured by Creative Labs, Inc., 1523 Cimarron Plaza, Stillwater, Ok 74075 is included in a computer 250. A speaker output 253 of the sound card 252 outputs audio tones to a hands-free port 257 on a cell phone 258. A microphone input 259 on sound card 252 connects to a speaker output of cell phone 258.

The computer includes a processor 254 that converts digital data to an audio format used by sound card 252 to output synthesized audio tones. Cell phone 258 encodes and transmits those audio tones over the voice channel of a wireless communications network. A cell site 261 receives the transmitted audio tones and sends them over a PSTN network 263. A computer 262 connects to a telephone line 260 at the destination location of the telephone call. Another sound card 264 and a processor 266 in the computer 262 demodulates the audio tones back into digital data. The digital data represented by the audio tones is presented to the computer 262. The sound cards can be used for data encoding or decoding, or both.

With reference to Figs. 16 and 17, data files, GPS data, data entered by a user keyboard, or any other digital data is packaged and formatted by computer 250 into IBS packets at block 270. Packetization and packet formatting is described in figs. 4 and 5. The binary bit values ​​in the IBS packets are converted in block 272 to a digital format used by sound card 252 (FIG. 16) to generate synthesized audio tones. For example, binary "1" bit values ​​in the IBS packet are converted to a digital format representing a first tone of frequency f1 and binary bit values ​​"0" are converted to a second tone of frequency f1. The tones f1 and f2 are generated in a similar way to that described in Fig. 8.

The sound card in block 274 outputs analog tones that represent the binary bit values ​​in a similar way to the IBS encoder 52 and to the analog converter 54. The cell phone in block 276 encodes the audio tones and transmits the encoded audio tones over the voice channel in the wireless communications network at block 278.

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Referring to Figs, 16 and 18, the cell phone call is established with a destination phone number. At block 280, either a user picks up the calling phone line or the computer 262 (FIG. 16) at the destination end of the cell phone call is programmed to detect a call signal from the phone line 260. If a ringing signal is detected, either a user of computer 262 at block 282 generates an "off-hook" signal on telephone line 260. Sound card 264 at block 284 acts as an analog-to-digital converter by converting audio tones. on telephone line 260 in digital data. The sound card 264 in conjunction with the processor 266 (Fig. 16) decodes the IBS audio tones in a similar way to the IBS decoder 98 described in Figs. 9-13. The digital representations of the detected IBS tones are then displayed on the computer screen 262 at block 290.

In one example, a user wants to find the location for cell phone 258. The user instructs computer 262 (Fig. 16) to dial the phone number for cell phone 258. Computer 262 uses sound card 264 to send IBS tones that instruct the cell phone 258 to respond with the GPS location data. Computer 250 may have a GPS receiver or cell phone 258 may have a standalone GPS receiver. If the GPS receiver and IBS modem are internal to cell phone 258 as shown in Figs. 2-9, computer 250 does not need to connect to cell phone 258.

The GPS data converted to IBS tones either by sound card 252 as described in Fig. 17 or by an internal IBS modem as described in Figs. 2-9. IBS tones representing GPS data are transmitted back over the wireless communication channel and PSTN network 263 to telephone line 260. Sound card 264 in computer 262 controls telephone line 260 for audio tones IBS. When detected, the IBS tones are converted to GPS digital data and presented by computer 266 to the user on the screen of computer 262. A correlation process in computer 262 can then convert the GPS longitude and latitude values ​​to a state , city and street address.

Synchronization

Fig. 19 shows an alternative technique to demodulate and synchronize the IBS modem in the IBS decoder

300. IBS audio tones are received over the voice channel of the wireless communications network on the interface

301. The IBS audio tones are converted from analog to digital by the A / D converter 302. The IBS signal detector 304 detects the presence of the IBS audio tones in the same manner as described in FIG. 11.

The alternative technique for synchronizing begins with decoder 300 tuning the IBS signals to complex base bands with multipliers 306 and 308. Multiplier 306 effectively moves any IBS tones on the first and second frequencies f1 and f2 to DC. This first baseband signal is referred to as S_TO'and the second baseband signal is named as S_B'. A tuned filter bank 310 applies the tuned filters to baseband signals having the expected pulse shapes for the two audio tones representing the binary values ​​"0" and "1". The signal output S_TO'from the tuned filter bank 310 represents a binary value 1 and the signal output S_B'from the tuned filter bank 310 represents a binary value 0. The tuned filter bank may also add filtering in relation to known characteristics of the wireless communication channel that may exist in the SA or SB signals.

The tuned filter is selected to tune the pulse shape applied to the modulator. The pulse shape is selected for the best compromise between signaling bandwidth, bit rate, and inter-symbol interference. The pulse shape filter is applied to the built-in phase of the modulator's numerical oscillator.

An IBS synchronizer aligns the modulator with the synchronization scheme attached to the beginning of the IBS packet. Segments 316 of S signal samples_TO and S_B are input to sync demodulator 314 along with a sample start time T_B. The demodulator 314 outputs a power value 320 to the IBS synchronizer 312 that indicates how synchronized the demodulator is with the start bit in the timing scheme. The IBS 312 synchronizer uses the power values ​​320 for each sample start time T_B to determine the optimal sync start time (* T_B) to demodulate the remaining bits in the IBS packet. The IBS packet 322 modulator then uses the optimal sync start time (* T_B) to demodulate the binary bit values ​​from the SA and SB signals.

Fig. 20 is a more detailed description of the sync demodulator 314 and IBS packet demodulator 322 of Fig. 19. A first integrator 324 integrates the first sample segment for signal S_TO. The integrator starts at the sample start time TB and integrates a number N of samples representing the duration T of an IBS bit (Baud time). A rectifier 326 feeds the magnitude of the integration value to an adder 332. Similarly, an integrator 328 integrates the sample segments for signal SB that begins at the sample start time TB. A rectifier 330 feeds the magnitude of the integrated segment of signal SB to adder 332 .. The output of the adder 332 is a power signal 320 that is fed back to the synchronizer 312. The IBS packet demodulator 322 (Fig. 19) also includes a comparator 334 that generates either a binary value 1 or a binary value 0 according to the magnitudes of the signals SA and SB.

For a more detailed explanation, Fig. 21 shows a representation of the signals SA and SB, which are output from the tuned filter bank 310. A number of samples 336 of the signal S_TO and S_B represents the bit duration T of an IBS tone. In the example shown in Fig. 21, five samples are taken for each bit duration T. Time

ES 2 332 875 T3 sample start T_B a sample is shifted for each integration. A start sample for the first integration begins at the sample start time T_b1. As seen in Fig. 21, the sample start time T_b1 not aligned with the S signal_TO which represents a binary value "1" or the signal S_B A representing a binary value "0". The sinc demodulator 314 of Fig. 20 generates a power output value of 0.0 for T_b1.

When using a sample start time T_B2, the demodulator 314 generates an output value of -2.0. The sample start time T_B3 represents the sample with the best synchronization with the beginning of tone “0” in signal S_B. At sample start time T_B3 the output power is -3. As the sample start times T_B4 and T_B5 move farther from the best timing position, the magnitude of the power output decreases. Fig. 22 shows the magnitude of the power distribution for different sample start times. The maximum power magnitude is identified at the sample start time T_B3. Consequently, the optimal sample start time T is used by the synchronizer 312 (Fig. 19)._B3.

With reference to Figs. 20 and 21, a first sample segment 338 starting at sample start time TB3 generates an output value from adder 332 in FIG. 20 of -3. Comparator 334 in FIG. 20 generates a binary value "0" for any adder value less than zero. The output of adder 332 for a second segment of sample values ​​340 generates an output value of +3. Since the output value for the second sample segment is greater than 0, the comparator 334 generates a binary value "1". The IBS packet modulator 322 (Fig. 19) continues to decode the tones in the S signals_TO and S_B for the rest of the IBS bit stream.

Fig. 23 shows a variation of the timing scheme described in Figs. 19-22. IBS tones are detected in block 341. IBS tones are baseband shifted by multipliers 342 for both the audio tone frequency fA representing a binary bit value "1" and the audio tone frequency. fB representing a binary "0" bit value. The baseband shift is made for each individual sample T (x) of the fA and fB signals.

Instead of adding an integer baud of samples, a moving sum of the last baud value is taken using the new sample T (x) in block 344. For example, with a sample rate of 20 samples per bit, the sample n 21 T (N + 1) is dropped from the moving sum and the next sample (x) is added to the moving sum. The magnitude of each of the two moving sums for tone A and tone B are taken in blocks 345 and compared by comparator 346. A binary value "1" or "0" is output from comparator 346 depending on which of the tone samples A or B has the greater magnitude value. L The binary bit value output from comparator 346 is mapped to the known sync pattern in correlation blocks 347. Sample start time * T_B selected is identified as the last sample that generates the highest correlation value with the synchronization model. The remaining bits of the IBS packet are then demodulated according to the sample start time * T_B selected.

Multichannel Intraband Signaling Modem

FIG. 24 shows the encoder portion 350 of a Multichannel Intraband Signaling (MIBS) modem. A data source 351 generates a stream of binary bits. The MIBS encoder 350 generates multiple channels of intraband signaling within the same voice channel. A data buffer 352 stores the binary bit stream from data source 351. A packet assembler 353 assembles the bits in buffer 352 into a packet payload and adds a preamble and epilogue to the packet payload to form IBS packets as described in Fig. 4.

Encoder 350 includes two modulators 356 and 362, each generating different audio tones that represent the bits in the IBS packets. Modulator 356 modulates binary "1" values ​​using a frequency f1 360 and modulates binary "0" values ​​using a frequency f2 358. Modulator 365 modulates other bits in IBS packets that have binary "1" values ​​using a frequency f3 364 and modulates binary "0" values ​​using a frequency f4 366. The f1 and f2 tone outputs of modulator 356 are referenced as a first intraband signaling channel and the f3 and f4 tone outputs of modulator 362 are referenced as a second IBS channel. The tone outputs from modulators 356 and 362 are combined by an adder 368 and then output to D / A converter 370 and other cellular telephone circuit 14 (Fig. 2). Cell phone circuit 14 encodes and transmits the tones on the two IBS channels over an audio channel of the cell phone network.

Each of the individual modulators 356 and 366 is similar in operation to the IBS modulator 64 shown in Fig. 4. Any number of IBS channels can be generated on the IBS modem 24. For example, a third IBS channel could be provided that modulates bits to a third portion of the IBS packets by adding a third IBS modulator that modulates bits for a third portion of the IBS packets in tones using frequencies f5 and f6. The output of the third IBS modulator would be fed into adder 368. For simplicity, however, only one two-channel modem with two corresponding modulators 356 and 362 is shown in Fig. 24.

An IBS channel controller 354 controls how multiple IBS channels are used by the transmitting and receiving modems. For example, a first IBS channel can only be used by a first IBS modem to transmit IBS packets and a second IBS channel can only be used by that first IBS modem to receive IBS packets. A second IBS modem at the opposite end of the transmission then uses the first IBS channel for reception. The IBS channel controller 354 adds control bits in the IBS packets that negotiate the use of the multiple IBS channels between the two communicating IBS modems. The different configurations for IBS modems are described in more detail

ES 2 332 875 T3 below in Figs. 26 and 27. Controller 354 also controls which portions of the IBS packets are modulated by modulators 356 and 362. For example, the modulators can modulate alternate IBS packets or each modulator can modulate different portions of the same IBS packets.

FIG. 25 shows decoder 375 of the MIBS modem. Audio tones from the audio channel are decoded by receiver circuit 372 and fed to an A / D converter 374. A first filter 376 removes signals outside of a frequency range of the two tones on the first IBS channel and a second Filter 378 removes signals out of frequency ranges from the two tones on the second IBS channel. The frequency range of filter 376 is from f1-Af to f2 + Af and the frequency range of filter 378 is from f3-Af to f4 + Af. Filters 376 and 378 are displayed before decoders 380 and 382. However, filters 376 and 378 can be implemented in the same DSP anywhere in the decoder process.

A first IBS channel decoder 380 detects and demodulates the two tones in the first IBS channel into binary bit values ​​and a second IBS channel decoder 382 detects and demodulates the two tones in the second IBS channel into binary bit values. Decoders 380 and 382 detect, synchronize, and demodulate IBS tones in the same way as described for decoder 98 in Fig. 9 or decoder 300 in Fig. 19. A packet assembler 386 assembles the bit output from the two decoders 380 and 382 into IBS packets which are then output to a data buffer 388.

The IBS channel controller 384 in the receiving IBS modem synchronizes the two decoders 380 and 382 and determines which decoders demodulate which portions of which IBS packets. Controller 384 also conducts a communication protocol with the transmitting IBS modem that negotiates which IBS modem is transmitting and which IBS modem is receiving IBS packets on which IBS channels.

Filter 376 and decoder 380 for the first IBS channel and filter 378 and decoder 382 for the second IBS channel can be implemented in software on the same DSP. Alternatively, a DSP can be used for each encoder and decoder in each IBS modem.

It is preferred for IBS modems that the f1 and f2 frequencies are well separated from the f3 and f4 frequencies. An advantage of the MIBS is the mitigation of interference and the ability to adapt to variations in the performance of cell phones between manufacturers through changes frequency dynamics when performance is poor. A robust low baud rate control signal can be sent to choose a new frequency when a modem detects errors.

Fig. 26 shows a possible configuration for two Multichannel Intraband Signaling (MIBS) modems 390 and 396. The two IBS channels 398 and 400 are transmitted from the MIBS 390 modem over the voice channel of a wireless communications network and then possibly via a terrestrial telephone network to the MIBS modem 396. The two MIBS modems shown in Fig. 29 they operate in a half duplex mode where one of the MIBS modems transmits IBS packets on both the first IBS channel 398 and the second IBS channel 400 simultaneously.

After the first IBS modem has completed a transmission of IBS packets on the two IBS channels, the second IBS modem 396 is enabled to start a transmission 394 back to modem 390 on the two IBS channels 398 and 400. The IBS modem 390 sends information in one of the IBS packets indicating to MIBS modem 396 that transmission 392 is complete.

Fig. 27 shows an alternative configuration where the first IBS 398 channel is dedicated to transmitting IBS packets from the MIBS 390 modem and the second IBS 400 channel is dedicated to transmitting packets from the MIBS 396 modem. Thus, both IBS 398 channels are dedicated To transmit IBS packets from MIBS modems 390 and 396 can transmit and receive packets at the same time. This full duplex configuration can provide faster communications for certain types of IBS transmissions.

The MIBS modem 390 can transmit different portions of the same IBS packets on the two IBS channels 398 and 400 or they can alternate transmission of different packets on the two IBS channels. In other configurations, one IBS channel can be used to transmit IBS packets and the second channel can be used exclusively for signaling and communication protocol between the two IBS modems. In another alternative configuration, bit portions of the same IBS packets are interleaved on the two IBS channels or the same IBS packets are transmitted on both IBS channels for redundancy. The information on the two IBS channels can be reconfigured according to the application associated with the IBS packet data.

A request to reconfigure the IBS channels can be encoded in the header of the IBS packet. For example, the IBS channel controller (FIG. 24) in the IBS modem 390 may send an IBS packet to the MIBS modem 396 that contains a reconfiguration request 73 in the preamble of the IBS packet (FIG. 5). The reconfiguration request from modem 390 can request both the first IBS 398 channel and the second IBS 400 channel and then request assignment of a third IBS 401 channel, with a lower baud rate, to the MIBS 396 modem to transmit received messages. to the 390 modem. The 396 MIBS modem then waits for an acknowledgment of the 396 modem configuration request.

ES 2 332 875 T3

The IBS channel controller 384 (FIG. 25) in the MIBS modem 396 reads the reconfiguration request in the preamble of the IBS packet. Controller 384 then issues an acknowledgment through the MIBS modem encoder 396. The encoder formats the acknowledgment in the preamble of an IBS response packet which is then modulated and transmitted back to MIBS modem 390 over one or more currently assigned IBS channels. The controller in modem 396 then reconfigures the encoder to receive IBS packets on the first and second IBS channels 398 and 400 and transmits packets on the third low baud rate channel 401.

When the acknowledgment from modem 396 is received at modem 390, the controller instructs the encoder and decoder at modem 390 to transmit on the first and second IBS channels and receive from the third low baud rate channel. The two modems 390 and 396 then transmit and receive IBS packets according to the new channel configuration.

References cited in description

This list of references cited by the applicant is solely for the convenience of the reader. It is not part of the European Patent document. Although great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims any liability in this regard.

Patent documents cited in the description • US 6021163 A