Showing papers on "Continuous phase modulation published in 1980"

Frequency shift offset quadrature modulation and demodulation

Abstract: A Frequency Shift Offset Quadrature (FSOQ) signal which is a constant envelope frequency-shift keyed version of an offset quaternary phase shift keyed (O-QPSK) transmission is provided. A technique for generating an FSOQ signal in a manner similar to O-QPSK by modulating offset quadrature channels with selectable pulse shapes which yields the desired 3-tone continuous phase FSK approximation of O-QPSK is disclosed. Receiver synchronization circuits are also provided which enable FSOQ to be detected as a special case of O-QPSK, whereby the detection performance of synchronous coherent QPSK, rather than the relatively inferior performance of FSK detection, is obtained. FSOQ provides a constant envelope and requires less bandwidth than minimum shift keying (MSK).

Carrier recovery network for QPSK modems employing synchronized oscillators

Abstract: A carrier recovery network for QPSK modems employs a synchronous oscillator which may be used as a frequency multiplier, divider and tracking bandpass filter A preferred embodiment of the carrier recovery network includes a multiply-by-four circuit to remove QPSK data modulation, and a synchronous oscillator tuned to one-fourth the input frequency to thereby act as a frequency divider and tracking bandpass filter to provide a recovered carrier signal

System for multi-level data transmission by means of an angle-modulated carrier having a constant amplitude

Abstract: A system for transmitting n-level data signals by means of an angle-modulated carrier having a constant amplitude and a continuous phase. The constant amplitude enables amplification in non-linear transmitter output stages. Associated with the n-levels are k(k>n) phase variations in accordance with such a rule, depending on preceding phase variations, that the spectrum of the angle-modulated signal becomes narrower. In a symbol interval the phase of the carrier changes by an amount from the sequence extending from -(k-1)π/n to (k+1)π/n in increments of 2π/n. The receiver is formed by a differential n-phase receiver. The system is used inter alia for radio transmission of digital information.

Quadriphase differential demodulator

Abstract: A method and apparatus for synchronizing a digital data demodulator to a received phase modulation carrier signal in which the carrier signal is phase shifted during each modulation period of the carrier to represent one of four pairs of binary bits or dibits. A dibit clock is adjusted to the phase of a reference dibit clock whose output is used to synchronize the demodulator in establishing the location of the modulation period of the incoming carrier. In order to overcome errors found in the decoding of the carrier signal, the adjustment of the dibit clock is suppressed when the dibits 00 and 10 are being decoded.

On efficient spectrum utilization from the standpoint of communication theory

Abstract: This paper reviews the concepts of spectrum efficiency, the parameters for assessing system performance, and the techniques for improving spectrum utilization. The rationale of possible bandwidth reduction and power savings by combined modulation techniques is discussed and special attention is given to combined amplitude and phase modulation (APSK) systems. It is believed, based on the available results of several analyses over additive Gaussian noise channels, that certain combined modulation systems can have significant power savings over single-parameter modulation systems when the number of bits per symbol of the signal is large and can achieve more efficient use of the spectrum for signal-to-noise ratios greater than certain levels.

Generalized minimum shift keying (Corresp.)

Abstract: A generalized minimum shift keying (GMSK) signal is defined, and its equivalence to a modified offset quadrature shift keying signal is shown. A simple formula for the spectrum of a GMSK signal is presented and the spectrum and out-of-band power are computed for two examples.

Full wave amplitude modulation detector circuit

Abstract: A current comparator is supplied with differential currents based upon an amplitude modulated radio frequency carrier. The comparator outputs are summed in a combining stage the output of which will contain a direct current proportional to the average carrier level and a current variation which represents the carrier modulation. The circuit provides very efficient detection of the modulated carrier.

A Fast-Switching Low-Loss 12-GHz Microstrip 4-PSK Path Length Modulator

Abstract: A 4-PSK microstrip modulator operating at data rates of up to 800 Mbits/s at 12 GHz is described. The circuit is made of two cells in series. Each cell consists of a 3-dB branch-line hybrid coupler and two BTL p-i-n diodes. One cell provides 0° or 90° phase shifts, and the Other 0° or 180° phase shifts, so that four carrier phase values are obtained by appropriately exciting the two cells. The switching time of each cell is 200 ps. Simultaneous switching of both cells increases the switching time to a maximum value of 400 ps. The phase waveforms are nearly rectangular at the above-mentioned data rates. RF insertion loss is 1 dB ± 0.1dB for the four phase values over the 11.7-12.2 GHz frequency band.

Method and apparatus for receiving and tracking phase modulated signals

Abstract: A receiver for tracking and demodulating several types of phase modulated communications, either analog or digital data, for either residual carrier or suppressed carrier signal and for phase modulation or keying of two, four or higher phase angles, from 0° through 360°. A carrier component signal and a converted series sideband component signal are obtained from the incoming signal and summed to produce a carrier tracking signal, permitting more accurate tracking of the above types of phase modulated data.

Transmitting device for a navigation system

Abstract: not available for EP0045381Abstract of corresponding document: US4387375In navigation transmitters it is important that the phase difference between the carrier waves of a carrier signal and the carrier waves of sideband signals be held at a constant value. To accomplish this, the carrier waves are maintained constant relative to a reference signal in a known manner. A phase meter measures the phase difference between the carrier waves of the sideband signals and the reference signal and between the carrier waves of the carrier signal and the reference signal. The measure values are used to determine the phase difference between the carrier signal and sideband signals which are compared with a desired value. Depending on the deviation from the desired value, a controllable phase shifter controls the phase of the carrier waves of the sideband signals. Since the measurements are made on a time-division multiplex basis, little circuitry is required. Any measuring errors do not affect the formation of the desired phase difference.

Phase continuous fsk modulation system

Abstract: PURPOSE:To decrease the occupied band width as well as to improve the error rate property by securing the continuous phase at the exchange point of the modulation element with the correlation ensured and then giving the redundancy to the signal between the adjacent elements. CONSTITUTION:The transmission data is supplied through input terminal 100 in the form of ''1'' and ''0''. For the supplied data, the continuous three bits (ak, ak-1 and ak-2) are stored in shift register 1 to be stored to deliver the modulation exponents (2ak-ak-1-ak-2) to output 102 via the code converter of 2. The product of output 102 and 103 is obtained through multiplier M, and thus the shift component is obtained at output 104 from the carrier frequency which varies for 1/fs(fs=clock frequency) seconds. The sum of output 104 and 105 is secured by adder A, and the cumulative addition is given by accumulator 3 with every 1/fs seconds. The output of accumulator 3 is converted to the amplitude value of the cosine wave through the phase value and via conversion table 4 and then turned to a continuous waveform through D/A converter 5.

Phase shift circuit

Abstract: PURPOSE:To control the hue easily, by using the variable resistor to the hue control circuit in the color receiver, through continuous phase shift for the subcarrier signal according to the DC voltage obtained at the rotor of the variable resistor and the signal delayed in phase by 90 deg. from the subcarrier signal. CONSTITUTION:The subcarrier oscillator 1 oscillates the subcarrier signal S0, the phase detector 2 controls the oscillator 1 with the phase difference between the burst signal of the video signal fed to the input terminal 2a and the output signal S0 of the oscillator 1, the signal S0 is fed to the 90 deg. phase shift circuit 3 and the subcarrier signal S1 delayed in phase by 90 deg. can be obtained. Further, at the junction point a of each collector of transistors Tr 7a, 24b, and at the junction point b of each collector of Tr 7b, 23b, the signal in phase shift for the signals S0 and S1 according to the DC voltage obtained at the rotor 11a of the variable resistor 11 is obtained. Thus, in the hue control circuit of a color TV receiver, the hue can easily be controlled by using the variable resistor.

Automatic phase control system

Abstract: PURPOSE:To decrease the time required for suppressing phase distortion by detecting the phase distortion of a pulse waveform generated on a transmission line and connecting/disconnecting a fixed phase device to a phase control circuit to suppress the residual phase distortion by means of automatic continuous phase control. CONSTITUTION:The pulse waveform subjected to phase distortion on a transmission line is demodulated (DEM) and the phase distortion is detected by a 90 deg. phase shift detecting circuit SWDET from the waveform distortion of the demodulated signal. Contacts 2, 4 of a phase switching circuit SW are connected normally, but when the amplitude of the waveform distortion of the demodulation signal is larger than a prescribed value, the circuit SWDET has a large phase and it is discriminated that the phase is retarded, then contacts 1, 4 are connected to remove the fixed 90 deg. phase shifter 90 deg. PS and when it is discriminated that the phase is advanced, contacts 3, 4 are connected to connect the fixed 90 deg. phase shifter 90 deg. PS. A large phase shift is corrected in this way and the residual phase distortion is corrected by controlling the phase of the carrier of the demodulator DEM by means of the automatic continuous phase control comprising an A/D converter, a shift register SR, a phase distortion detecting section DET, a PLL circuit and voltage controlled variable phase shifter CAPC.

High‐speed continuous‐phase FSK modulation and demodulation system

Abstract: The continuous-phase FSK system is a remarkably beneficial digital modulation and demodulation system due to its good transmission performance over satellite communication circuits and others which has some band restriction elements and nonlinear components. However, no report has been made yet on its practical circuit construction or design method. Here, studies are made on practical circuit structure based on the principle of modulation and demodulation in connection with the binary continuous phase FSK, sometimes called MSK, FFSK, etc., with 0.5 modulation index. Presentation is made for the circuit structures for a modulation system by using the off-set-bipolar-modulation-and-synthesis, and for a demodulation system by using the synchronous-detective-wave-coherent-detection and 2-steps-up carrier synchronous system. These are applied appropriately to high-speed modulation and demodulation over several hundred M bit/s in the radio frequency range in or beyond the microwave frequency. As for the coherent detection, quantitative study is made on impairment figures due to the optimum reception band restriction over the Gaussian transmission system, phase errors of regenerated carriers, and timing discrimination errors. It is concluded that its error characteristics are almost equal to those of the optimum detection system at the BT product of reception, 0.5-0.6, and its phase error takes a deterioration figure of the two-phase PSK system. Furthermore, experiments were conducted on modulation and demodulation at the carrier frequency of 1.7 GHz and the data transferring speed of 100 M bit/s to confirm the basic characteristics and theoretical results. The result showed that it could have satisfactory features for practical applications.