Abstract: A mobile radio communication apparatus having a communication function adaptable to both an analog mode and a digital mode is controlled by a control unit, when it receives from a radio base station a message signal representing that the digital mode is provided. When the strength of the message signal in the analog mode received by a receiving unit from the radio base station is at a predetermined level or higher, a mode of communication services is shifted into the digital mode. When the strength is lower than the predetermined level, the standby status in the analog mode is maintained. Therefore, the mode of communication services is not alternated between the analog mode and the digital mode, with the result that both an outgoing call and an incoming call can be performed successfully even in an unstable service area where a transmitted signal cannot reach the radio base station.

Abstract: A random number generator includes a sample clock having a sample clock rate, a chaotic oscillator having a characteristic upper frequency, and an output section. The chaotic oscillator includes a quantized linear section and a non-linear section. The quantized linear section includes multiple quantized integrators coupled to the sample clock and intercoupled in a linear intercoupling. The non-linear section is coupled in a feedback manner with the quantized linear section. The output section generates a random binary output signal having the sample clock rate, formed by a logical combination of binary signals, of which one binary signal is generated by each of the multiple quantized integrators. Each quantized integrator includes an analog to digital converter that preferably includes a sigma delta converter that generates one of the binary signals.

Abstract: In a system for simulcasting digitally modulated and analog FM signals over the same FM frequency band, the effect of the analog FM signal on the digitally modulated signal in the simulcast is calculated and canceled from the latter signal before its transmission. As a result, the digital transmission is free from interference from the analog FM signal. Moreover, the digital transmission is achieved by adaptively inserting a time varying number of carriers modulated by digital data into the FM band. The carriers are selected frame by frame to control their interference with the analog FM signal. In accordance with the invention, the carriers are selected in a predetermined order, and in a preferred embodiment grouped contiguously with one another in the FM band. As a result, the rate of control information required to identify the inserted carriers to a receiver is advantageously low.

Abstract: A device having alternative intercommunication formats, and an automated method of selecting the appropriate format to use, in dependence upon the ability of the device to which it is interconnected to utilize this format. Many devices utilize standard analog formats, such as NTSC, PAL, SECAM, and others, to communicate with other devices; many of these devices utilize digital formats, such as MPEG and others, for internal processing or storage. By appending a supplemental signal to the analog signal, the ability of the device to use a digital format can be communicated to the device to which it is interconnected. By communicating their capabilities, devices which have the ability to utilize the same digital format can automatically switch to this digital format for intercommunication, thereby avoiding the signal degradations typically associated with conversions to and from an analog form.

Abstract: A cable modem tuner includes, in the same casing, an up-stream circuit to transmit an up-stream data signal to a CATV station, and a reception circuit for receiving a down-stream signal via a HPF that removes the up-stream data signal. The reception circuit includes a select circuit that selects a signal of a desired frequency band out of one of three frequency bands, a signal processing block including three local oscillation circuits to convert a signal of a desired frequency band into an intermediate frequency signal of a desired channel using an oscillation signal of a corresponding oscillation circuit, and a down converter with a local oscillation circuit converting an applied signal into a signal for demodulating a received signal. The down converter provides a baseband signal used to demodulate a received signal by the QAM when a digital signal modulated by the QAM is received.

Abstract: The present invention provides for a receiver addressable AM compatible digital broadcast system and method. The digital broadcast signal includes a plurality of digitally modulated signals and an analog signal. A transmitter useable within the system includes a data combiner for generating an aggregate digital data signal, and a waveform generator for forming the digital broadcast signal. A receiver useable within the system comprises a waveform detector for separating the signals and a data parser for separating the digitally modulated signals. The present invention further provides for a method of selectively transmitting data via a digital broadcast signal. The method includes forming the digital broadcast signal from an analog signal and a plurality of digitally modulated signals, transmitting and receiving the digital broadcast signal.

Abstract: An adaptive gain algorithm allows the maximization of gain of an audio signal that is transmitted with a digital data signal by allowing a trellis decoder to compensate for occasional excursions of the audio and noise signal across a signal space boundary. By measuring the short term energy present in an audio signal, the algorithm of the present invention allows the maximum power to be used to transmit an analog signal without overloading the trellis decoder.

Abstract: A phase detection circuit detects a phase of a phase detection signal output from a complex multiplication circuit. A frequency error detection circuit detects a frequency error of a phase-detected signal, with the first frequency error detection characteristic in which a first frequency domain is defined as a detection range. An average circuit converts a signal having the detected frequency error into a signal having a second frequency error detection characteristic in which a second frequency domain other than the first frequency domain is defined as a detection range. After the average circuit calculates an average of frequency error signals for each period of time, it converts an average signal into a signal having the original first frequency error detection characteristic and outputs it to an AFC loop filter.

Abstract: In a system for simulcasting digitally modulated and analog FM signals over the same FM frequency band, the effect of the analog FM signal on the digitally modulated signal in the simulcast is calculated and canceled from the latter signal before its transmission. As a result, the digital transmission is free from interference from the analog FM signal. Moreover, the digital transmission is achieved by adaptively inserting a time varying number of carriers modulated by digital data into the FM band. The carriers are selected frame by frame to control their interference with the analog FM signal. In accordance with the invention, the carriers are selected in a predetermined order, and in a preferred embodiment grouped contiguously with one another in the FM band. As a result, the rate of control information required to identify the inserted carriers to a receiver is advantageously low.

Abstract: The invention provides a FM modulation system using a quadrature modulator, wherein a circuit for exclusive use in FM modulation and a change-over means can be dispensed with. In this system, modulating signals are inputted to a baseband signal processing circuit, converted into digital signals after integration, and turned into an analog signal by reading out a sine wave signal pre-stored in a sin ROM, thereby generating a baseband signal I for an equi-phase signal and a baseband signal Q for a quadrature signal. By adding together results of multiplication of the baseband signal I for the equi-phase signal and the baseband signal Q for the quadrature signal by a local signal of cosine and a sine wave signal obtained by phase shifting the local signal through 90 degrees, respectively, a quadrature modulation signal containing a FM modulated signal and the maximum frequency deviation can be generated.

Abstract: A double mode modulator, particularly, for a portable telephone, which is adapted to realize both digital and analog modulations and have a low phase noise and a reduced locking time with a device readily integrated in an integrated circuit, including: a frequency synthesizer for synthesizing a particular frequency from an external reference clock signal; a digital modulator for performing a quadrature modulation for an output signal of the frequency synthesizer; and an analog modulator for performing a frequency modulation for the output signal of the frequency synthesizer.

Abstract: Radio receivers for receiving DTV signals, in accordance with the Advanced Television System Committee (ATSC) standard, or analog TV, in accordance with the National Television Systems Committee (NTSC) standard, each use a single first detector for both types of signal. This single is followed with an intermediate-frequency amplifier providing amplification both for digital television signal and for the amplitude-modulated NTSC video carrier of an analog television signal. Preferably, the shared intermediate-frequency amplifier is a high-band intermediate-frequency amplifier having fixed gain and having its bandwidth determined using a surface-acoustic-wave filter with flat-amplitude midband response, steep-slope skirts, and linear phase throughout its passband.

Abstract: A method and device for analog simultaneous voice and data transmission over an analog channel encodes at a voice signal sampling rate a sampled voice signal including spectral and pitch information. During encoding, the spectral and pitch information is extracted from the sampled voice signal to produce a residual signal, and the residual signal is converted into a sequence of residual vectors at a Baud rate. Then, a bitstream including non voice data and the extracted spectral and pitch information is produced. A modem unit, operating at Baud rate and producing an output carrier wave supplied to the analog channel, produces a sequence of symbol vectors in response to the sequence of residual vectors and the bitstream, and modulates the output carrier wave in response to the sequence of symbol vectors.

Abstract: In a system for simulcasting a digitally modulated signal and an analog FM signal over the same FM frequency band, the composite signal is received and applied to a conventional FM receiver, and a digital receiver in accordance with the invention. An extended Kalman filter is employed in the digital receiver to estimate the analog FM signal based on a version of the recovered FM signal from the FM receiver, and a discrete version of the composite signal whose spectrum has been translated and is at an intermediate carrier frequency. The estimated FM signal, which is in a discrete form, is subtracted from the discrete version of the composite signal. The resulting signal, which is an estimated version of the digitally modulated signal, is demodulated to recover the digital data as transmitted.

Abstract: Apparatus, and an associated method, for converting an inband signal, such as a DTMF signal, into a form to permit transmission thereof to a receive station. An inband signal, such as a DTMF signal generated by a wireline device is applied to a digital transmitter, such as a fixed cellular terminal having a digital transceiver. The inband signal is detected and encoded. The inband signal is encoded in a manner to permit its transmission according to an appropriate air interface standard.

Abstract: A system and method for transmitting digital information through a medium such as atmospheric free-space includes a transmitter which generates a signal based on a basis set of mutually orthogonal, spectrally-shaped, sequences of substantially equal length and having predetermined autocorrelation values. The sequences may resemble noise in at least some of their characteristics. The orthogonality or cross-correlation characteristics, the autocorrelation characteristics and the resemblance to noise are due to features derived from sequences of pseudo-random numbers which themselves resemble noise in at least some of their characteristics. The waveform set based on the sequences is modulated digitally. The modulated set may be summed together along with a wideband reference signal of reduced amplitude and optionally an FM analog signal to form a composite signal which is broadcast typically through free space to at least one receiver.

Abstract: An apparatus and method for generating a broadcast waveform is provided which, for generating an in-phase component, includes an in-phase digital signal generator; a first filter for filtering the in-phase digital signal; a first digital-to-analog converter for converting the filtered digital signal into a first analog signal; an AM baseband signal generator producing an AM baseband signal; a first summer for summing the first analog and AM baseband signals to produce a composite analog signal; and a first modulator for modulating the composite analog signal with a first carrier signal at a transmission frequency, thus producing a first modulated signal.

Abstract: A high speed modem for simultaneously transmitting both voice and precoded digital data signals over a single communication channel. The modem is operable to combine a voice signal with a precoded digital data signal for transmission at high speeds, high power levels and low distortion previously attainable by high speed data-only modems. The voice signal is processed using conventional data processing techniques to produce a voice signal and a control signal containing information relating to the coding of the voice signal. The control signal is multiplexed and mapped for transmission with the digital data. Selected bits of the multiplexed data are used to define the rotation of the digital data and to rotate the voice vector. The digital data is precoded to compensate for and minimize noise in the communication channel. The rotated voice vector and the precoded digital data are then combined and transmitted.

Abstract: A protocol processor functionality and a data pump functionality are included in a modem which is configurable in a number of modes of operation to effectuate both analog and digital data communications. When configured for analog data communications either over a telephone line of the wireline telephone network or using an analog capable mobile station of the cellular telephone network, data signals are routed through both the protocol processor functionality and the data pump functionality. The protocol processor is also connected to the mobile station to transmit and receive call supervision signals. When configured for digital data communications using a digital capable mobile station of the cellular telephone network, the data signals by-pass the data pump functionality and are transmitted by the protocol processor functionality along with the call supervision signals.

Abstract: A system and device for, and method of, detecting, characterizing, and mitigating deterministic distortion in a communication system. An exemplary communication system includes a digital adaptor for sending octets on to a backbone of a PSTN, which then sends, and potentially distorts the octets, received by a line interface. The line interface converts the octets to baseband signals received by an analog adaptor. Several mechanisms and methods are described in which the analog and digital adaptor cooperate to detect the presence of distortion, in particular, robbed bit signaling, on the communication system. The characterization may then be used to mitigate the effects of the distortion. Several receive constellations are provided, each constructed in view of the transmit constellation and in view of the manner in which the deterministic distortion will distort signals transmitted over the system. The receive constellations differ from the transmit constellation.

Abstract: A method for handoff of an analog connection within a cellular communication system which relies upon mobile station synchronization to a system time is disclosed herein. In order to reduce the acquisition time for a mobile station commencing operation in a digital mode, an estimate of master system time is transferred to the mobile station in analog mode before entering digital mode. The alignment operates within the protocols of existing analog systems, and hence requires only minimal changes in the mobile station. Time alignment may be initiated upon the base station sending to the mobile station a command to continually transmit a periodic signaling tone. The base station compares the phase of the signaling tone from the mobile station to a master system clock and determines an error signal. The base station notifies the mobile station to delay or advance in time the transmitted signaling tones based on the error signal.

Abstract: A system for combining AM and FM transmissions. In-band, On-channel, FM Digital Audio Broadcast (IBOC FM-DAB) allows simultaneous transmission of DAB and FM over existing FM allocations without interfering with conventional analog FM signals. The utility of existing FM spectrum allocations is therefore enhanced.

Abstract: Mobile stations include a data pump functionality for performing digital bit to waveform coding on a received digital data signal. The waveform coded output (analog data signal) is transmitted over the analog air interface using either an analog traffic channel or analog control channel. For transmission over the analog control channel, the data pump functionality multiplexes the wave form coded analog data signal with mobile station generated cellular system control signals. A data pump functionality is also provided at the other end of the air interface transmission to recover the digital data signal from the waveform coded analog data signal transmission. De-multiplexing of the received analog control channel transmission to extract the data signal is also performed, if necessary. For a data communication sent instead to the mobile station, the reverse operations are performed by the included data pump functionalities at either end of the analog air interface.

Abstract: A digital-analog shared circuit in dual mode radio equipment, which shares a local oscillator in a digital mode and analog mode. A first frequency synthesizer generates a first and a second local oscillation frequency in a digital and an analog receiving mode, respectively, in response to a control signal from a switching control. In the digital receiving mode, a quadrature demodulater including a first and a second demodulator in a demodulator section is enabled, and carries out quadrature detection of a received signal fed from an RF stage, thereby supplying the detected signal to a baseband signal processor stage. In the analog receiving mode, a buffer to which the second local oscillation frequency is supplied is enabled to deliver the second local oscillation frequency to the analog IF stage. A second frequency synthesizer generates a third local oscillation frequency in a digital transmitting mode and a fourth local oscillation frequency in an analog transmitting mode.

Abstract: When at a starting time of an apparatus with a power supply turned ON a designation operation of a communication mode is carried out or one communication operation is finished, a base station search control section (21) in a control circuit (20) conducts a search on control channels received from respective base station, selects from among those base stations whose control channels are received at an electric field strength greater than a predetermined level a base station possessing a desired communication mode and having the greatest electric field strength, and acquires and sets this base station, thus effecting a transfer to a standby state.

Abstract: A spread spectrum modulating and demodulating apparatus which is capable of providing FSK or PSK spread spectrum communications. In a transmitting device an input information signal is fed either to an oscillator or to a side of a power supply which is in turn connected to an operation device. An oscillator produces a carrier frequency signal which multiplied by a multiplier by the predetermined integer N1. A frequency divider divides the frequency of the carrier by a predetermined integer N2. A spread code generator uses an output signal of the frequency divider as a clock signal, and generates a spread code which is fed to the operation device. A switch selectively feeds an input information signal to either the oscillator for frequency shift keying the oscillator or through the side of the power supply connected to the operation device will effect a phase shift key operation.

Abstract: A digital and analog reception apparatus includes a first mixer (MIX1) which converts up a reception signal having an input frequency fa inputted into an input terminal IN and a second mixer (MIX2) which converts down a first intermediate frequency fc of a signal outputted from the first mixer (MIX1) by using a second local frequency fd and a second intermediate frequency fe. The apparatus is also provided with a phase-locked loop (PLL), an automatic frequency controller (AFC) which comprises a second local oscillator and a low frequency band pass filter unit LPF adjusts a second local frequency fd, and a microcomputer discriminates an analog/digital distinction of the reception signal having the input frequency fa. Upon receiving an analog signal, the digital and analog reception apparatus deactivates a low-pass filter unit LPF, thereby having an AFC signal control a second local oscillator.

Abstract: A mobile radio unit having all improved signal processing technique is disclosed. The unit is used in a dual-mode cellular communications system wherein analog and digital channels are used in combination. The mobile radio unit is provided with a front end whereat an incoming radio frequency signal is converted to a corresponding IF. An orthogonal detector is coupled to receive the IF signal and generates in-phase (I) and quadrature (Q) signals. These I and Q signals are respectively digitized by two analog-to-digital (A/D) converters which in turn produce I and Q digital data respectively. A digital signal processor is supplied with the I and Q digital data and demodulates the analog signal using one of the I and Q digital data when the mobile radio unit is using the analog channel while demodulating the digital channel using both the I and Q data when the unit is using the digital channel.

Abstract: A system and method are provided for reducing perceived distortion in an output audio signal derived from an amplitude modulated compatible digital broadcast signal having an analog portion and a digital portion. The digital portion of this signal is demodulated to produce a demodulated digital signal and the analog portion of the signal is demodulated to produce a demodulated analog signal. The noise in the demodulated digital signal is measured and an estimate of the signal-to-noise ratio is derived. This estimated signal-to-noise ratio is compared with a threshold level which is set at the minimum acceptable signal quality for the digital signal. Based upon the estimated signal-to-noise ratio, a switch directs either the analog derived audio output or the digitally derived audio output as the system output signal.

Abstract: The method of quickly locating non-standard control channels in private cellular systems is accomplished in an embodiment of the present invention by determining the modulation type of a particular channel. The mobile station scans a received RF channel. The received signal is used for the evaluation of the modulation type of that channel by using matched filters designed for the specific signal of interest, and/or in another embodiment of the present invention is used for producing the spectral energy distribution of the channel revealing the type of modulation.

Abstract: Components for analog or digital input signals are in each case connected by switchable means to a controllable oscillator. The switch condition of the switchable means is set automatically and/or manually as a function of the input signal.

Abstract: A circuit is provided for use in a dual mode mobile phone for selectively one of phase modulating or frequency modulating an RF signal. The circuit includes an IQ generator for generating one of first quadrature waveshapes or second quadrature waveshapes in response to a modulating signal; a quadrature mixer for mixing the first quadrature waveshapes or the second quadrature waveshapes with an RF signal to generate a phase modulated RF signal or a frequency modulated signal, respectively; and a limiter, such as at least one limiting amplifier, that has an input coupled to an output of the quadrature mixer for reducing an amplitude modulation component of only the frequency modulated signal. The at least one limiting amplifier has an input coupled to a limit control signal that has a magnitude selected for setting a dynamic range of the at least one limiting amplifier. The phase modulated signal may be a .pi./4-DQPSK signal.

Abstract: A dual-mode communications processor disposed to be incorporated within a dual-mode communications device is disclosed herein. The dual-mode communications processor comprises a dual-mode voiceband signal processor having an input port for receiving digitized data. Within the dual-mode voiceband signal processor, first and second signal processing operations are performed upon the digitized data received during operation in first and second modes, respectively. These separate signal processing operations may advantageously be performed using common circuit elements within the dual-mode voiceband signal processor. In an exemplary embodiment the first signal processing operation is performed in accordance with a predefined vocoding algorithm, while the second signal processing operation involves the filtering of the digitized data as prescribed by FM cellular telephone standards.

Abstract: In a dual mode transmitter for modulating, in a digital mode, an input digital signal and transmitting a modulated digital signal and modulating, in an analog mode, an input analog signal and transmitting a modulated analog signal, a digital modulating section modulates the input digital signal to thereby generate the modulated digital signal, and outputs the modulated digital signal. An analog modulator/carrier generator modulates the input analog signal to thereby generate the modulated analog signal, and outputs it. Also, the analog modulator/carrier generator generates a carrier signal for up-converting the modulated digital signal. The up-converter up-converts, in the digital mode, the modulated digital signal by using the carrier signal and receives, in the analog mode, the modulated analog signal and passes it therethrough.

Abstract: A dual-mode frequency and phase RF modulator (11) for use in a transmitter of a radiotelephone. A dual-mode modulation approach is employed wherein, in the analog (FM) mode of operation, a phase modulator, such as a .pi./4-shift DQPSK modulator, is bypassed and may be powered down. A frequency modulated RF carrier is coupled through a bypass circuit (52) to a modulator output node (50) for transmission from the radiotelephone. In the digital mode of operation, the bypass signal path is disabled, the .pi./4-shift DQPSK modulator is enabled, and in-phase (I) and quadrature (Q) signals are input to the .pi./4-shift DQPSK modulator which provides a phase modulated RF carrier that is coupled to the modulator output node for transmission from the radiotelephone. The teaching of this invention can be employed with radiotelephones having, by example, TDMA/analog capability or CDMA/analog capability.

Abstract: The voice over data component of a personal communications system enables the operator to simultaneously transmit voice and data communication to a remote site. This voice over data function directly encodes digitized voice samples onto the carrier using quadrature amplitude modulation to transmit multiple bits of the voice sample for every baud. The system also allocates selected bauds of the carrier to voice and to data so the voice over data may be transmitted using the same allocated bandwidth. The system may also dynamically reallocate the bandwidth over the telephone line depending on the demands of the voice grade digitized signal.

Abstract: A system and method for transmitting digital information through a medium such as atmospheric free-space includes a transmitter which generates a signal based on a basis set of mutually orthogonal, spectrally-shaped, sequences of substantially equal length and having predetermined autocorrelation values. The sequences may resemble noise in at least some of their characteristics. The orthogonality or cross-correlation characteristics, the autocorrelation characteristics and the resemblance to noise are due to features derived from sequences of pseudo-random numbers which themselves resemble noise in at least some of their characteristics. The waveform set based on the sequences is modulated digitally. The modulated set may be summed together along with a wideband reference signal of reduced amplitude and optionally an FM analog signal to form a composite signal which is broadcast typically through free space to at least one receiver.

Abstract: A digital system accommodates analog communications, thus avoiding the need for separate subsystems each dedicated to either analog or digital communications. The system includes a receive circuit for converting received signals into an intermediate frequency, a transmit circuit for modulating and transmitting signals and signal processors for processing the intermediate frequency signals and the signals to be transmitted, wherein the signals can be processed into digital or analog format using substantially the same circuitry.

Abstract: A radio communication apparatus of this invention includes a mode designation switch for selectively designating and inputting a desired mode from an analog mode and a digital mode, and a mode storage circuit for storing the desired mode designated and input by the mode designation switch and has a mode setting control function, a mode comparison function, and a mode change control function. In order to establish a radio link, control is performed to set a mode for transmitting a communication signal in accordance with the desired mode stored in the mode storage circuit. After the start of transmission of the communication signal, the mode comparison function compares the mode set by the mode setting control function with the desired mode stored in the mode storage circuit.

Abstract: A cellular communication system having all of its components operating under a single system control unit is provided so that the various components of the system can be adjusted as the parameters of the other components or the dynamic characteristics of the cellular channel change.

Abstract: In accordance with IS-136 standard, an analog wireless signal and a digitally encoded wireless signal can be received by a remote telecommunicating device. The remote device can differentiate between the analog wireless signal and the digitally encoded wireless signal by measuring the average energy of the signal in the portion of the baseband signal that is expected to contain the Supervisory Audio Tone signal, and the portion of the baseband signal that is expected to be outside of the audio band for an analog signal. The average energy of the portion outside of the audio band is subtracted from the average energy of the SAT signal. The difference is compared to a threshold, and based upon the comparison, the characteristic of the received wireless signal, i.e. analog or digital, is determined.

Abstract: Auxiliary data subband samples representing an auxiliary data signal are transported in a subband-coded compressed digital audio signal without decompressing the data. A pre-existing packetized data stream is provided to an input of a encoder. Subband audio samples are extracted from the packet stream and normalized if required. The data to be transported modulates data carrier subbands including, for example, a pseudo-noise (PN) spread spectrum signal, each subband of which has a bandwidth corresponding to those of the digital audio signal. The data carrier sequence can also include a sparse PN sequence, sample twiddle sequence, or a bit twiddle sequence. The modulated data carrier sequence is combined with the audio subband samples to form a combined signal in which the auxiliary data subband samples are carried. The combined signal is then multiplexed into the pre-existing packet stream. In a decoder, the combined signal is demodulated to recover the auxiliary data signal.

Abstract: A transmitting apparatus transmits at least one of a main and a supplementary modulated signal in response to a transmitting signal. The apparatus includes a first modulating circuit for modulating the transmitting signal in a main modulation system to produce the main modulated signal. The apparatus also includes a second modulating circuit for modulating the transmitting signal in a supplementary modulation system to produce the supplementary modulated signal. The apparatus further includes a selective supplying circuit for selectively supplying the transmitting signal to at least one of the first and second modulating systems. The apparatus also includes a control circuit connected to the first and second modulating circuits for controlling operation of the first and second modulating circuits and the selective supplying circuit.

Abstract: The dual mode amplifier network of the present invention enables a radiotelephone to operate efficiently in both the U.S. Digital Cellular mode and the FM analog cellular mode. Multiple, switched branches (110 and 120) permit one branch (110) with an isolator (103) to be used in the in the U.S. Digital Cellular mode while the other branch (120) is switched out. In the analog mode, the transmit filter branch (120) is used while the isolator branch (110) is switched out.

Abstract: In a simultaneous voice and data communications system comprising two modems, an autorate feature is implemented in one illustrative method by adding a silence detector to the receiver circuitry of at least one of the modems in such a way that noise statistics for the communications channel are only accumulated during intervals of silence. If the resulting noise statistics exceed a predetermined threshold, i.e., the communications channel is too noisy, the receiving modem negotiates a lower data rate with the transmitting modem. In another illustrative method, the transmitting modem provides a signal, which represents an interval of silence, to the receiving modem. Upon receipt of the signal, the receiving modem accumulates error statistics in order to determine if the communications channel is too noisy.

Abstract: At a transmitting end, frequencies used to a construct a digital signal are substantially removed from an analog signal by a notch filter circuit to produce an interim signal which is then combined with the digital signal as by combining to produce a composite analog signal that is transmitted to a receiving end. At the receiving end the frequencies used to construct the digital signal are substantially removed from the composite analog signal by a notch filter circuit. In this way the digital signal can be transmitted simultaneously with the analog signal without errors that could be introduced by the analog signal, and with only a slight change to the frequency spectrum of the analog signal. In a second embodiment, the system provides clear and error free continuous transmission of digital signals over an analog channel simultaneously with an analog signal by periodically analyzing the analog signal and, during any given period, transmitting the digital signals in open bands, i.e.

Abstract: An arrangement for modulating orthogonal signals with an analog signal or a digital information signal. In either event, the information signal is partitioned into component signals which respectively modulate an associated one of the orthogonal signals. The analog signal has a predetermined bandwidth and may be represented by samples generated at no less than a predetermined rate. The component signals derived from this analog signal, on the other hand, may be represented by samples generated at a rate which is less than the predetermined rate. Apparatus is incorporated which detects a predetermined event which, in turn, determines whether the orthogonal signals are modulated by the analog or digital information signal. The value of the latter signal may be known at any time, such as when the digital information signal is a training sequence, or may be unknown. The foregoing modulation arrangement can also incorporate privacy or encryption schemes.

Abstract: A dual mode cellular telephone contains modulator and demodulator circuitry that use the same I and Q signals for processing both analog and digital voice data, A power amplifier (PA) bias voltage is varied in coordination with the phone operating mode and geographical location to increase energy efficiency. The power supply for the PA is controlled in combination with a controlled ramp up and ramp down of the modulated I and Q signals to eliminate "spectral splatter" of the transmission band into adjacent frequencies. A variable gain amplifier is coupled to the front end of the phone receiver circuitry to increase the overall dynamic range for the gain of the demodulated I and Q signals. A switching power supply is used in the dual mode phone to increase energy efficiency and reduce the required size of the battery pack.

Abstract: In a DC offset circuit for a Cartesian loop, a DSP supplies step by step a slope voltage from a minimum DC output voltage, up to a maximum DC output voltage, to input sections of operational amplifiers for modulation. This arises each time transmission is started in a state where a signal Q' and a signal I', each based on only a carrier wave, are outputted from a quadrature demodulator. When comparators detect that output from operational amplifiers is 0 V, the DSP decides a value of the slope voltage then as a DC offset voltage value. Operation is started centering on this DC offset voltage value.

Abstract: A multiple-modulation communication system includes a transmitter that modulates and transmits communication signals modulated by a first modulation technique and communication signals modulated by a second modulation technique. The first modulation technique and the second modulation technique are different. The communication system also includes a receiver capable of receiving the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique and demodulating the communication signals.