Abstract: An apparatus and method for improved security in wire or wireless communication systems includes scrambling the audio signal, combining a masking signal with the scrambled audio signal, and then transmitting the scrambled masked signal. To recover the original audio, a receiver must by synchronized and know the characteristics of the masking signal and the scrambling technique. Such a receiver removes the masking signal, descrambles the audio and thus recovers the original audio. Any attempted interception of the communication would hear white noise, and even if the white noise mask where removed, the communication would still have the security level of the scrambling. The mask removes any remnants of the original audio that might be used to try to locate and intercept the communication.

Abstract: An apparatus and method for concealing data bursts in an analog scrambler using audio repetition. What otherwise would be periodic data bursts appearing at the audio output are replaced with samples from audio portions of the multiplexed signal. Preferably the replaced audio samples come from immediately past portions of the audio of the signal. The data bursts are therefore effectively concealed from the audio output which improves on the degradation of audio otherwise caused by the data bursts that are mixed in periodically with the audio portions of the signal.

Abstract: An apparatus and method for creating voice privacy by performing frequency spectrum inversion in electronic voice transmission systems includes the steps of digitizing an analog signal and inverting the frequency spectrum of the digitized audio signal. From the inverted spectrum, a complex signal is created from which the real component is extracted to produce a real signal suitable for transmitting. The digital signal processing is performed entirely with software. The scrambling and descrambling processes are nearly identical, therefore, the same hardware and software may be used to scramble and descramble the signal. The apparatus may uses a "rolling code" to increase the effectiveness of the scrambling.

Abstract: An apparatus and device for continuously scrambling audio while transmitting or receiving synchronization data. When transmitting, synchronization data will be substituted for scrambled audio but the audio scrambling will continue during those time periods so that once the substituted synchronization data is stopped, the scrambled audio will pick up at a point correlated to the then existing condition of a time dependent scrambling algorithm. The receiver will descramble the scrambled audio but will replay past scrambled audio to replace portions in the received signal that would be otherwise occupied by the synchronization data. In this manner, the quality of received audio is enhanced.

Abstract: A superheterodyne receiving circuit and a superheterodyne transmitting circuit are provided. A PLL forms a local oscillation signal in the receiving circuit, and a PLL forms a carrier signal in the signal transmitting circuit. A circuit converts digital data into signals suitable for transmission, and an oscillating circuit provides an oscillation signal. A frequency-dividing circuit forms a frequency-division signal of a reference frequency which is supplied to the PLLs by frequency-dividing the oscillation signal circuit, and a frequency-dividing circuit generates a clock signal required in the conversion circuit by frequency-dividing the oscillation signal. A frequency-dividing circuit forms a signal for descrambling the received voice signals which have been scrambled by frequency-dividing the oscillation signal, and a frequency-dividing circuit forms a signal for scrambling the voice signals to be transmitted by frequency-dividing the oscillation signal.

Abstract: A method for encrypting and decrypting digital data. The digital data is initially latched by an input register. Sixteen separate cipher stages cascaded in series are used to encrypt the digital data. These cipher stages are operating at a maximum frequency limited only by the process technology. The encoded digital data from the last cipher stage is stored in an output register. The input and output registers are capable of being docked at an interface frequency that is different from that of the DES core's data frequency. After an appropriate number of cycles have elapsed, the output register is sampled. A programmable counter is used to indicate when the output register contains valid encrypted data.

Abstract: A frequency inversion scrambler in a cordless telephone utilizes an integrated high-pass filter (14) between a first stage low-pass filter (12) and modulator (16) to reduce the filter order while maintaining low group delay in the audio signal. The first stage low-pass filter and high-pass filter remove high frequency components and any DC offset from the filtered audio signal. The modulator translates the spectrum of the filtered signal to sum and difference frequencies. A second stage low-pass filter (18) removes the upper portion of the spectrum such that the resulting frequency spectrum is inverted with respect to the original audio signal to prevent eavesdropping of transmissions between the handset and base unit of the cordless telephone. Another frequency inversion circuit (30, 32, 34, 36) in the base unit inverts the frequency spectrum again back to its original state for transmission along telephone lines.

Abstract: Audio signals are descrambled by double sideband modulating the scrambled audio signal with a modulation carrier having a carrier frequency slightly above the highest audio signal present in the scrambled audio. This produces a double sideband signal that is passed through a low pass filter which in turn is modulated by a second carrier frequency lower than the first carrier signal by an amount equal to the offset spectrum of the original scrambled signal. The first low pass filter nulls out any residual carrier from the first modulator that results from the of intermodulation of the two modulation frequencies that would be audible at its descrambler output. The modulators used are low noise switch type modulators that improve the signal to noise ratio in the descrambled signal over the previously used linear modulators. The use of switch type modulators provides a lower cost device with improved performance.

Abstract: The present invention provides a modulation/ demodulation circuit and a communication system utilizing the modulation/demodulation circuit. The modulation/ demodulation circuit can be operated in either of a modulation/demodulation mode wherein an input signal is frequency inverted and scrambled or descrambled and a through mode wherein the input signal is directly outputted therefrom without being subject to any processing. In a private communication system, two such modulation/ demodulation circuits are used as a scrambler in the transmission-side and as a descrambler in the reception-side. In order to prevent the low band characteristic of the reception-side output in the through mode from being different from that of the modulation/demodulation mode, the modulation/demodulation circuit may include a high pass filter. The high pass filter a low band cut-off characteristic reciprocal to a low pass filter for removing the upper side band from the output of a double balanced mixer.

Abstract: A cordless phone system includes a first cordless phone and a second cordless phone which are coupled to each other by a network, the first cordless phone being formed of a first personal station and a first base station, the second cordless phone being formed of a second personal station and a second base station.

Abstract: A transmitter and receiver for spread spectrum communications using a Fourier series coefficients module, a notch gate, a fast Fourier transform module, and memory. The Fourier series coefficient module generates magnitude and phase values of a Fourier series. The notch gate notches the Fourier series coefficients at selected bands of frequencies. The selected band of frequencies are chosen so as not to provide interference with a preexisting user such as a cellular user, microwave user, or other radio communications. The fast Fourier transform generates from the notched Fourier series coefficients a spreading signal. The spreading signal has notches in its spectrum so as not to cause interference with the preexisting users. At the transmitter, the spreading signal is used to spread-spectrum process message data to generate a spread-spectrum signal for transmitting over a communications channel. At the receiver, the spreading signal is used to despread a receive spread-spectrum signal.

Abstract: A digital speech-band spectrum inversion apparatus for use in a cordless telephone system provides transmission security of the voice signal between the handset (10) and the base station (18). The apparatus includes an A/D converter (24) for converting an input analog voice-band signal to a digital signal, a digital signal processor (30) for modifying the digital signal in accordance with a prescribed algorithm, and a D/A converter (32) for converting the modified digital signal to an output analog signal, the output analog signal being inverted in frequency spectrum from the input analog signal. A/D converter (24) samples the input analog signal at a periodic rate, and converts the sampled voltage levels to digital representations thereof. The algorithm performed by the digital signal processor (30) computes the two's complement inversion of the digital representations of alternate samples of the input analog signal.

Abstract: The wireless telephone of the present invention is comprised of a base unit, coupled to a land-line telephone system, and a remote unit that communicates with the base unit over radio frequencies. The remote unit has scrambling circuits (207 and 216) for encrypting voice signals transmitted to the base unit and decrypting voice signals received from the base unit. The base unit also has scrambling circuits (107 and 116) for encrypting voice signals transmitted to the remote unit and decrypting voice signals received from the remote unit. The wireless telephone uses a keypad (222) for initiating a demonstration mode that allows both parties to the conversation to hear the scrambled voice signal.

Abstract: Audio signals are scrambled by single side band modulating with a modulation signal carrier having a frequency lying within the audio frequency band so that the signals are frequency translated upward. The scrambled audio signals are descrambled after broadcasting or recording/reproducing using a substantially identical modulation carrier signal to restore the original audio signals. Security is enhanced by varying the frequency of the modulation carrier signal in a pseudo random manner in response to start (ACLK) and rate (A0, A1) control signals. The control signals accompany the scrambled audio signals and are used during the descrambling process to aid in the generation of the descrambling carrier modulation signal.

Abstract: Decoder for encrypted sound signals which are encrypted by modulating the sound signals on an alternating carrier signal having a frequency which is generally unknown to receiving parties. A modulator receives the encrypted sound signal as well as a second reference electrical signal. The reference signal is provided by an oscillator controlled through a phase locked loop. The phase locked loop includes a phase comparator connected through an exclusive OR logic gate and a sequential circuit to supply a control signal for the oscillator. The sequential circuit provides for a control signal polarity depending on the relative phase between the oscillator signal and input alternating carrier frequency signal. A signal divider is provided on each input of the comparator to require only comparison between phases of signals with frequencies lower than the carrier frequency signal and oscillator frequency signal.

Abstract: The wireless telephone of the present invention is comprised of a base unit, coupled to a land-line telephone system, and a remote unit that communicates with the base unit over radio frequencies. The remote unit has scrambling circuits (207 and 216) for encrypting voice signals transmitted to the base unit and decrypting voice signals received from the base unit. The base unit also has scrambling circuits (107 and 116) for encrypting voice signals transmitted to the remote unit and decrypting voice signals received from the remote unit. The wireless telephone uses a keypad (222) for initiating a demonstration mode that allows both parties to the conversation to hear the scrambled audio signal.

Abstract: Disclosed is a voice band splitting scrambler. To simplify the hardware thereof, the apparatus comprises a band splitting unit (11) for splitting an input voice signal into a plurality of band channels, and a scrambled voice signal generating unit (13) for carrying out spectrum-inverting and band-relocating operations on the respective channels to generate a scrambled voice signal. The scrambled voice signal generating unit (13) includes a modulating unit (15) for band-relocating the respective channels by noninverting carriers of inverting carriers set in different bands respectively; and an adding unit (17) for adding the signals of the noninverting channels and the signals of the inverted channels to each other.

Abstract: Audio signals are scrambled by inverting the original; frequency spectrum so that frequency portions originally lying at the lower end of the audio frequency band are shifted to the upper end while those portions originally lying near the upper end of the band are shifted to the lower end. A pilot tone of known frequency is recorded along with the frequency shifted audio signals, along with accompanying video signal portions. Upon reproduction, any variations in phase and frequency introduction by the recording or reproduction process are tracked by the pilot tone, which is used to generate the demodulation signal for restoring the original frequency content of the audio signals.

Abstract: The useful bandwidth of a bandwidth-limited input signal (s(t)) is reduced, to obtain a coded signal (q(t)) by forming a combined input and feedback signal, low-pass filtering the combined signal, and passing the low-pass filtered signal through a feedback loop which includes symmetrical frequency-voltage (f/V) conversion, substantial amplification, and voltage-frequency (V/f) reconversion, the reconverted signal being combined with the input signal in a multiplier, the coded output signal being derived from the output of the low-pass filter. Amplification of the amplifier is so high that the bandwidth of the resulting frequency-modulated feedback signal is greater than the bandwidth of the original input signal. The resulting coded signal can be decoded by derived scanning signals which are combined with bandwidth-enhanced coded signals and processed in an inversion matrix for subsequent reconstitution of the original signal.

Abstract: A speech privacy processing apparatus is disclosed including:a unit for obtaining the number of coefficients commonly included in a set of coefficients obtained by Fourier transformation and corresponding to high-frequency spectrum components of an input original speech signal and the set of coefficients corresponding to the high-frequency spectrum components after scrambling processing;scrambler for repetitively performing scrambling processing until the number of the common coefficients becomes smaller than a predetermined threshold value;a counter for counting the number of repetitions of the scrambling processing and transmitting the count to a receiver side;a unit for extracting a repetition count of scrambling processing from a reception signal;descrambler for performing descrambling processing in accordance with the extracted repetition count; anda unit for reproducing a speech signal.

Abstract: A method and apparatus for decoding of frequency inversion based scramblers is disclosed. A quadrature amplitude modulation detector determines the frequency of the tone used for inverting the scrambled signal by determining which of a plurality of quadrature detector pairs, each using a different conversion frequency, has the greatest magnitude difference between the quadraturely related signals. The frequency of the quadrature pair with the greatest difference is the frequency of the inverting tone during the inverting period of time. This frequency information is used to generate a reinversion tone to unscramble the scrambled signal.

Abstract: A fully digital phase-locked loop comprises a sampler (1), an analog-to-digital converter (2), two quadrature demodulators (3 and 4) and their associated filters (5 and 6), and a decision logic (7) effecting the correction of the sampling phase around the value of the free-running frequency (f.sub.e) by the addition or subtraction of machine cycles of a signal processor (9).

Abstract: Disclosed is a secret speech equipment for ensuring the secrecy of an analog voice signal, and used in voice communication systems such as an analog telephone and mobile radio. The equipment comprises a sub-band signal generating unit for treating input digital samples as frequency-multiplexed signals of voice spectra, to split the frequency-multiplexed signals into a plurality of frequency bands, and thus obtain sub-band signals of the frequency bands, a sub-band signal permutating unit for permuting the sequence of the sub-band signals, and a sub-band signal multiplexing unit for multiplexing the permutated sub-band signals.

Abstract: A toy helmet that permits the wearer to speak as to generate unintelligible noise so far as bystanders are concerned but which can be understood by another child wearing an identical helmet. Each helmet is equipped with internal and external microphones and an external speaker and internal earphones. Scrambler/descrambler circuitry is selectively connectable by means of a push-to-talk switch that delivers speech from the internal microphone to the external loudspeaker of the first helmet. The external microphone and the corresponding scambler/descrambler circuitry and push-to-talk switch of the second helmet delivers unscrambled speech to its internal earphone to permit the two helmet wearers to communicate intelligibly with one another. The scrambler/descrambler circuitry samples the low-pass filtered signals applied to its microphones at a sampling rate equal to the cut-off frequency of the low-pass filter.

Abstract: An intermediate scrambling device for a radiotelephone system is disclosed by which it is possible to establish and maintain scrambled communications between an originating scrambler terminal and the most distant companion scrambler on the circuit. The intermediate scrambler may establish and maintain the scrambled communications if it is the most distant scrambler, or it may become transparent to a more distant scrambler.

Abstract: Encoding is realized by means of a first low-pass input filter (21), a first modulator (20), a second low-pass filter (19), a second modulator (18) whose modulating signal has a frequency which is pseudo-random modified in the course of time, which signal is pseudo-random chosen between two signals of different frequencies (45, 46) and an output filter (17). According to the invention a first generator providing two signals is constituted by two phase-locked loop oscillators each having a frequency divider (7, 9) in the loop and both being controlled by the same reference signal generator (3, 4) while the reference signal generator itself is constituted by an oscillator of the same type (3, 4) controlled by the field synchronizing signal of the television transmitter, and this signal as well as the reference signal are applied to a first pseudo-random generator (14) for controlling the instants of change of the modulation signal. Decoding is effected similarly in the reverse order.

Abstract: The present invention is directed to an inversion scrambler and unscrambler having pseudo-randomly controlled polarity-reversing switches to invert and re-invert, respectively, an audio signal so as to restrict the intelligent dissemination of the audio signal. To improve security of the scrambled signal, the audio signal is concealed prior to scrambling. Concealment includes clamping the original audio signal to a predetermined value and optionally offsetting this clamped signal prior to scrambling. The concealed signal is scrambled by inverting contiguous portions of the signal at pseudo-random intervals, accomplished by a polarity-reversing switching network controlled by a pseudo-random code generator. Upon unscrambling, artifacts will appear at the inversion points of the unscrambling signal, due to bandwidth limitations inherent in any transmission path.

Abstract: An analog frequency inversion scrambler employing an exchange of random number seeds between an originating scrambler and an answering scrambler to create two pseudo-random frequency hopping rolling codes has been disclosed. The rolling code used in one direction of a duplex channel is different than the rolling code in the opposite direction and each code is synchronized by periodic synchronization signals.

Abstract: The respective feature parameters extracted from a speech signal is converted into the corresponding line spectrum data in a first frequency band obtained by dividing the speech signal frequency band. Each of the line spectrum data is allocated previously to each one of the feature parameters. The extracted feature parameters are further converted into the corresponding line spectrum data in the other divided frequency bands other than the first frequency band. The converted line spectrum data are multiplexed for transmission. The corresponding line spectrum data in the divided frequency bands allocated to the same feature parameter are logically added to restore the feature parameters. Thus higher confidential communication is realized.

Abstract: Method of distorting a speech signal by rearranging and/or reversing frequency bands in this signal. The speech signal is divided into a plurality of sub-bands by filtering, and the sub-bands are individually sampled at a sampling frequencing which is at least double that of the sub-band bandwidth, for providing a plurality of first spectra each with periodic repetition of the respective sub-band. Alternating samples are polarity-reversed for providing a plurality of second spectra each with periodic repetition of the respective sub-band in reversed form. From one of these two types of spectrum a desired sub-band is then filtered out, and corresponds to the original sub-band, but is reversed and/or displaced in the frequency band as desired. All the obtained sub-bands are finally added to send the distorted signal.As an addition to the method of distorting, there is also proposed a method of recomposing the distorted speech signal.

Abstract: A wireless transmitter for PM (phase modulation) signal with a spectrum scrambler for relocation of input spectrum for privacy purposes is comprised of a differential circuit coupled with an input terminal, a spectrum scrambler coupled with output of said differential circuit, and FM (frequency modulation) modulator coupled with output of the spectrum scrambler. Due to the position of the differential circuit before the spectrum scrambler, modulation index of modulated PM signal and/or the frequency band of the modulated PM signal does not increase irrespective of spectrum scrambling.

Abstract: A band scrambler which processes only time domain samples is described. The band scrambler has the effect of dividing the input signal spectrum into N sub-bands. The N sub-bands are permuted such that the r th band is mapped onto the k.r th band modulo N, where N is a constant of the scrambler and k is the key which is variable in the range 2<k<N-1. The output samples y(n) produced by the scrambler from the input speech signal samples x(n) are defined by the equation: ##EQU1## The down-sampling function s(n'+n(k-1)) determines which of N series of ganged switches is closed and the window function h(n') determines the values of the factors stored in the multipliers. The summation is carried out by the adder in order to produce the required output time samples which are reconverted to an analogue signal via a digital-to-analogue converter. The signal can be de-scrambled by sampling and passing through another identical scrambler operating with a key, k*, where kk*=1 (mod N).

Abstract: The present invention relates to speech scrambling techniques and systems and in particular to a frequency or time domain speech scrambling technique and system which does not require any frame synchronization. This invention is technique and system for scrambling speech signal in frequency or time domain by means of speech analysis-synthesis techniques. The system described above is very attractive because it has avoided the frame synchronization problem. The existing analog telephone channel can be utilized directly for transmission because bandwidth expansion is completely controllable. In addition, the "key space" is very large and a high degree of security can be achieved.

Abstract: A wireless receiver for a PM (phase modulation) signal with a spectrum scrambling for relocation of speech spectrums for the privacy of purpose is comprised of an antenna for receiving PM modulated signals, an FM demodulator coupled with the antenna, a spectrum de-scrambler connected to output of the FM demodulator, an integration circuit connected to output of said spectrum de-scrambler, and an output terminal coupled with output of the integration circuit. Due to the location of the de-scrambler between the FM demodulator and the integration circuit, a noise spectrum of a reception signal is independent from a design of spectrum scrambling, and an excellent substantial S/N is obtained irrespective of spectrum scrambling.

Abstract: System for the secret transmission of audio signals having at one end a coding arrangement comprising an input low-pass filter which selects the secret audio signals to be transmitted, two parallel signal paths at the output of this filter, each path having a modulator of the phase-inverting type and a further low-pass filter, a stage for generating two modulation signals of the frequencies F.sub.1 and F.sub.2 and a first change-over switch which alternately switches through the output of the two paths in dependence of the state of a binary quasi-random signal, the encoded audio signals to be transmitted being available at the output of the change-over switch, and in which at the other end there is a decoding arrangement comprising a stage for regenerating the modulation signals of the said frequencies F.sub.1 and F.sub.

Abstract: In order to upgrade input signals for further processing, one or more of the input signals is split up by a decimating technique into spectral component signals which are processed according to the desired purpose and recombined by means of an interpolation technique into an output signal. In this manner a digital filtering device can be selectively employed for achieving an arbitrary combination of simultaneous filtering, signal improvement, echo or feedback compensation, or signal masking of the input signals.