Showing papers on "Demodulation published in 1983"

Frequency-hopped single sideband mobile radio system

Abstract: The present invention relates to a frequency-hopped single sideband (SSB) mobile radio system implemented by hopping the carrier frequency of an input signal (s(t)) every τ seconds. The hopping is controlled by a carrier-frequency-hopped sequence (f i (t)) generated by a carrier-frequency-hopping generator (16,24). When employed in a frequency-hopped SSB transmitter (10), the carrier sequence functions to modulate the input signal, "hopping" it to a different carrier frequency every τ seconds. The carrier-frequency-hopped SSB receiver (20) employs the identical carrier sequence as used by the transmitter to demodulate the transmitted carrier-frequency-hopped SSB signal, thereby recovering the original single sideband signal (s(t)). By frequency hopping the carrier signal of an SSB signal, the present invention mitigates the effects of co-channel interference and frequency selective fading inherent in prior art SSB cellular mobile radio systems.

XPSK: A New Cross-Correlated Phase-Shift Keying Modulation Technique

Abstract: A new modulation technique, cross-correlated phase-shift keying ( XPSK ), is introduced. XPSK is a band-limited offset QPSK modulation technique which has an almost constant envelope. In XPSK modulators, a controlled amount of cross correlation between the in-phase ( I ) and quadrature ( Q ) channels is introduced. I and Q cross correlation reduce the envelope fluctuation Of the intersymbol-interference and jitter-free OQPSK (IJF-OQPSK) modulation scheme, introduced by Feher et al. [1], [2], from 3 dB to approximately 0 dB, thus further improving the performance of IJF-OQPSK systems in nonlinear radio systems [7], [14]. It is shown that the baseband signal of the modulator, the P_{e} = f(E_{b}/N_{0}) performance, and the spectral characteristics of nonlinearly amplified (hard-limited or saturated) radio systems of XPSK and tamed frequency modems (TFM) are practically the same. The XPSK demodulator is a conventional OQPSK demodulator, the TFM demodulator requires a somewhat more complex signal processor. For this reason, the XPSK approach may lead to significant demodulator hardware cost savings, particularly in point-to-multipoint distribution systems such as broadcast systems. Simulation results for linear and nonlinear (saturated amplifier) systems operated in an adjacent-channel interference environment (in addition to thermal noise) are presented. Measurement results performed on a 128 kbit/s rate hardware-prototype modem are also reported. Experimental eye diagram and power spectrum density measurement results are in close agreement with the computer simulation results.

Spread spectrum correlator for recovering CCSK data from a PN spread MSK waveform

Abstract: In a spread spectrum communications system employing cyclic code shift keying as its primary modulation, the transmission waveform is spread for transmission security by modulo-2 adding a pseudo-noise sequence to the CCSK data symbols prior to phase modulating onto a carrier signal for transmission. If the transmission modulation is minimum shift keying (MSK) the two components of the data stream are applied to the carrier with a differential encoding step implicit in the modulation scheme. This differential encoding characteristic makes stripping of the PN spread function prior to CCSK demodulation difficult at the receiving end. In order to demodulate this waveform in an optimum manner, an array correlator, the adjacent correlator stages of which have one chip relative time displacements of their CCSK reference waveform, is employed. In effect the array correlator becomes a parallel array of matched filters matched to each cyclic shift of the incoming waveform. By modulo-2 addition of the PN spreading waveform with the time displaced CCSK reference waveform in each stage of the correlator, the correlator can be made to match all versions of the spread symbol being received.

Optical Fibre Sensing and Signal Processing

Abstract: This book reviews the potential of this powerful technology and demonstrates where the electronics and the mechanical engineering can play their part in the design of a real practical system.

Signal distribution system

Abstract: A head-end for a signal distribution system with selection facility, includes a matrix (8) and a multiplexer (12) connected thereto for forming a multiplex signal. The head-end further comprises A/D converters (4-1 to Δ-N) for converting the wide-band input signals into digital signals prior to supply to the matrix. The multiplexer comprises two amplitude modulators (13, 14) for the mutual quadrature amplitude modulation of a carrier (17) by two digital signals, and a summing means (18) for adding a digital signal in the base band to the modulated signal. A signal receiver for one of the modulated signals comprises a synchronous amplitude demodulator (21) connected to a synchronized carrier source (20) and also comprises means for digital-to-analog conversion (24).

Adaptive A/D Converter to Suppress CW Interference in DSPN Spread-Spectrum Communications

Abstract: The non-Gaussian nature of CW interference is exploited to suppress the CW via the A/D converter following chip demodulation in a direct sequence pseudonoise (DSPN) communication link. The modulation is coherent BPSK. The A/D converter quantizes to 2 bits, sign and magnitude. A scheme of threshold adaptation and postquantization weighting gains great advantage from making very reliable decisions on a relatively small percentage of the demodulated chips. The bit error rate performance in CW interference generally surpasses that of an ideal analog DSPN correlator. The performance in Gaussian noise is within 0.6 dB of ideal analog.

Performances of the Delay-Line Multiplier Circuit for Clock and Carrier Synchronization in Digital Satellite Communications

Abstract: This paper is concerned with clock and carrier synchronization in digital satellite transmissions, using the delay-line multiplier circuit. For clock recovery from baseband signal, with random data, a closed form formula is derived which gives the spectrum after multiplication, for any arbitrary pulse shape. This spectrum contains spectral lines at the clock frequency and its harmonics, and a continuous part which is the pattern noise. This pattern noise may be decomposed in noise in phase with the recovered clock, and noise in quadrature whose power spectral density is always zero at zero frequency. The effect of Gaussian noise on the channel is taken into account to calculate signal-to-noise ratio at the clock frequency as a function of the classical parameter E/N_{o} . With a modulated input carrier, the signal at the output of the delay-line multiplier may be separated into two parts: a low frequency signal that contains clock information and a bandpass spectrum signal around twice the carrier frequency that contains carrier information, when possible. Spectrum and signal-to-noise ratio in carrier recovery are studied for BPSK and offset quadrature modulation.

Reception of PSK Signals Over Fading Channels Via Quadrature Amplitude Estimation

Abstract: We consider here a new approach to PSK signal detection over a slow nonselective Rayleigh fading channel which does not require a carrier recovery loop. The receiver achieves coherent demodulation by making use of estimates of the quadrature amplitudes of the received PSK signals in its likelihood ratio test. The receiver is assumed to have a memory containing information on the past received signals which enables it to generate the estimates. The error rate of the receiver can be evaluated analytically and computer simulation results are presented to verify the predicted performance.

Zero IF receiver AM/FM/PM demodulator using sampling techniques

Abstract: Apparatus is depicted which enables the sampling of the phase angle of a modulated signal and manipulates the sample signals to demodulate the same. The apparatus is particularly adaptable for use in demodulating the I and Q channel signals of a zero IF receiver. The system contains an angle sensing circuit which combines the I and Q channel signals in differential form to produce a series of output signals of an angular range indicative of the present value of the instanteous phase. The signals from the angle detector are coupled to an octant decoder which operates to determine the particular octant that the angle is to be included in. In the present system eight octants are used, each comprising 45°. The octant decoder determines which octant the angle belongs in and assigns a predetermined angle value to that angle. In one embodiment, the assigned angle values are 0°, 45°, 90°, 135°, 180°, 225°, 270° or 315°. The value of the assigned angles are then sampled by means of a clock at a high frequency rate whereby the resultant pulses indicative of the angles are then processed as differentiated to produce an output signal indicative of the information content on the original signal.

Demodulation of Amplitude Modulated Noise: A Mathematical Evaluation of a Demodulator for Pathological Tremor EMG's

Abstract: A mathematical description is given of amplitude modulated noise, simulating EMG signals of pathological tremors, and its demodulation into a tremor signal by means of a fuli wave rectifier. In this description these signals are considered in the frequency domain in the form of power spectra. The mathematically derived formulas are compared with the results of an experimental setup using a demodulator designed for use in clinical practice. The purpose of the experiments was to determine the signal-to-noise ratio of the tremor signal with respect to the demodulation noise, the latter being an inevitable consequence of demodulating the amplitude modulated carrying noise. The theoretically derived data are in acceptable agreement with the experimental results obtained in this way. As a result of the theoretical approach to the amplitude modulated noise, the signal-to-noise ratio of the demodulated signal is proportional to the bandwidth of the carrying noise of the amplitude modulation, and, for small modulation depths, is proportional to the square of the modulation depth.

Demodulation scheme fibre interferometric sensors employing laser frequency switching

Abstract: A demodulation technique suitable for use with fibre interferometric sensors is described The scheme employs a frequency switched diode laser and an unbalanced Mach-Zehnder interferometer Minimum phase sensitivity ≈ 2× 10-5 rad is obtainable, and can be shown to be limited by the laser phase noise

Signal processing for high resolution electronic still camera

Abstract: In an effort to provide exceptionally high resolution playback of video information recorded in the environment of an electronic still camera, the invention calls for: (a) Use of double side band FM recording, which in the prior art would have been productive of playback interference between the side bands of harmonics and the side bands of corresponding fundamentals unless the relative head-to-media speed was high enough to accommodate high carrier frequencies. (b) Bias recording such FM video information, thereby to prevent the inherent production of harmonic information within the media. (c) Up-converting the harmonic-free playback signal, before the harmonic-causing procedure of amplitude-limiting such playback signal, thereby to cause such signal to have a spectrum-wise wide disparity between the modulated fundamental in question and its harmonics, as caused by such amplitude limiting. (d) Removing the generated harmonics (and their side bands) prior to or during demodulation of the modulated fundamental.

Low Complexity Decoders for Constant Envelope Digital Modulations

Abstract: Digital angle modulations having input symbol memory can be demodulated using maximum likelihood sequence estimation (MLSE or Viterbi decoding). The demodulation of the more bandwidth efficient of these can require a large number of computations. In this paper, lower complexity decoding approaches are presented. These decoders use a predetermined processing order and a reduced number of survivor signals, S , at every-time NT . Processing is performed on the signal sequences using metrics (likelihoods) obtained by a matched filter bank similar to that needed for MLSE. The decoders can achieve asymptotic optimality of error rate while being computationally faster and simpler than MLSE for many modulations. In addition, error rate performance can be traded for complexity reduction. Expected performance has been verified for representative modulations.

Costas Loop Experiments for a 10.6 µm Communications Receiver

Abstract: We have transferred the principle of the Costas-type nonlinear phase-locked loop to the \lambda = 10.6 \mu m wavelength of CO 2 lasers. The ability of the optical Costas loop to regenerate the carrier of a binary phase-shift-keyed input signal and to perform coherent demodulation was demonstrated at a data rate of 20 Mbits/s.

SSB System with pilot coded squelch

Abstract: A single sideband communications system conveying a message through a transmitter to one or more predetermined receivers which are enabled by a coded squelch signal unique to the predetermined receivers is disclosed. The transmitter comprises means to angle modulate both the pilot signal and the information bearing single sideband signal with the coded signal at a predetermined deviation and to transmit the resulting signal. Each receiver frequency control means tracks the frequency excursions of a selected portion of the transmitted signal up to predetermined limits so that the message can be demodulated without frequency distortion being introduced. Each receiver demodulates the coded squelch without interfering with the message demodulation or tracking functions and activates the receiver squelch of those preselected receivers.

Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator

Abstract: The passive quadrature demodulator (PQD) eliminates the phase stretcher and feedback electronics frequently used in fiber interferometric sensors by passively extracting the desired signal using two distinct interferometers which differ in phase by \pi/2 . A fusion technique is described to fabricate a fiber PQD which is sufficiently stable with respect to temperature, polarization, and wavelength to maintain the sensitivity of interferometric sensors constant to 0.25 dB.

Modem with improved escape sequence mechanism to prevent escape in response to random occurrence of escape character in transmitted data

Abstract: An FSK modem for coupling a standard data port (50) to a telephone line (45) in which the signal path between the phone line and the data port passes through a processor (55). When the modem is in a transparent mode of operation, for transmitting data, a timer (190) detects the passage of a predetermined period of time after the most recent data input signal input to a data port (50). If the next sequence of data signals corresponds to an escape character, the program (112) controlling the modem waits to see if a second occurrence of the predetermined period of time follows provision of the escape character. If this occurs, the modem switches to a command mode of operation in which it ceases to modulate and transmit signals and waits for commands to be entered at the data port. The same frequency detection apparatus (83, 192, 180) is used to both demodulate FSK encoded signals and detect the presence of a telephone ringing signal on the line. A pair of impedances (161, 162) provide alternate paths either through an input filtering network (167) or bypassing the network (135, 69) in a manner which allows the ring signals to pass directly to the input (69) of the frequency detector while assuring that only filtered FSK signals reach the input. Also shown is the use of the same frequency synthesizing apparatus (86, 253, 259) for generating FSK output signals and high group DTMF signals with appropriate switchable attenuation (88) provided in this signal path.

Differential PSK System with Nonredundant Error Correction

Abstract: Theoretical analysis and experimental results for a DPSK system with nonredundant error correction are described. The error correction capability of the proposed demodulation method is achieved without utilizing additional bandwidth. The demodulator utilizes outputs of differentially coherent detectors that employ the received signal delayed by two or more time slots as references. These outputs are shown to be the parity check sums of two or more conSecutive outputs of the conventional detector under noise-free conditions. The error rate performance of the proposed demodulation method is theoretically and experimentally studied for quaternary DPSK. Experimental results agree with the theory, which indicates that performance is superior to conventional DPSK by 1.2 dB, but poorer than coherent detection by 1.3 dB. This method can be applied effectively to TDMA communications and to on-board regenerative repeaters.

Signaling system for FM transmission systems

Abstract: A signaling system for FM transmission systems is disclosed that utilizes one or more so-called quadrature subcarriers for transmitting at least one data signal, including signaling tones, digital data, program material, or the like. The signal is modulated on outer edges of the quadrature channel so as to minimize crosstalk interference with the conventional FM stereo difference channel subcarrier and to place the signals in regions of low hearing acuity. Use of a quadrature subchannel also enables a signal to be modulated onto the quadrature subcarrier to provide the capability of modulating a noise compressed difference signal in a manner so as to minimize degrading crosstalk with the adjacent difference channel subcarrier. A receiving apparatus is disclosed for decoding the quadrature subcarrier data independently of standard FM stereo demodulation.

Data compression of ECG data using delta modulation

Abstract: A data recording arrangement for recording ECG data within the body of a patient, for transmitting the ECG data to a point external to the body of a patient, and for recovering the transmitted ECG data is disclosed. The recording arrangement employs delta modulation circuitry for delta modulating the ECG data to obtain a delta modulated digital pulse train. The digital pulse train may be stored within the body of a patient for subsequent transmission external to the body of a patient. Transmission of the data external to the body of a patient may be by a piezoelectric transducer which transmits the digital data audibly for external detection and delta demodulation. Alternatively, delta demodulation may occur within the patient's body, and the demodulated analog signal may then be transmitted by FM, using the piezoelectric transducer to provide the FM audible signal detectable by an FM demodulator external to the body.

Space diversity receiving system for multi-direction time division multiplex communication

Abstract: A space diversity receiving system for the central station of a multi-direction time division multiplex communication network having a plurality of satellite stations, and one central station. Each satellite station transmits signals to the central station during an assigned time slot. The central station receives burst signals from the satellite stations. A first receiver has a main antenna. A second receiver has a supplementary antenna. Both receivers include a demodulator coupled to the corresponding antenna and a detector for detecting bit errors in the resulting demodulated signals, and for providing error pulses when appropriate. Each satellite station, needing space diversity, has a counter for competitively counting the error pulses from the receivers. A signal switcher responds to the demodulated signals and the counter for selecting a demodulated signal having a lower bit error rate.

Receiver for multicarrier signals protected from unwanted signals

Abstract: The invention relates to a multicarrier signal receiver protected against unwanted signals. Between the high frequency circuit and the intermediate frequency circuit, it has a frequency-selective attenuation and preselection circuit, while a circuit for detecting the disturbed channels is coupled to the demodulation circuit and supplies control signals characteristic of the appearance and disappearance of the unwanted signals. The receiver also comprises a control circuit eliminating the disturbed channel for processing demodulated signals and for the automatic control of the intermediate frequency amplifier circuit, and controlling the attenuation of the disturbed channel in the selective attenuation circuit.

Minimum-shift keyed modem implementations for high data rates

Abstract: IGITAL communications links capable of conveying data at hundreds of megabits per second (Mb/s) are becoming increasingly important in various applications. An example is the use of time division multiple access (TDMA) transmission through a satellite relay wherein several data channels are routed through single uplink and downlink paths (antenna beams). Separation of the channels from each other is accomplished through interleaving and deinterleaving in time, with possible rerouting taking place in the satellite. When carrying traffic from large metropolitan areas, the required data rates can exceed 100 Mb/s. One such implementation, currently under study by NASA,' involves data transmission at rates of up to 550 Mb/s. Such applications require the use of modulation schemes that use the available bandwidth efficiently. Furthermore, because power is at a premium on board a satellite, the utmost in power efficiency is desired of the chosen modulation scheme. This implies the use of a constant-envelope modulation scheme since amplifiers, such as traveling wavetube amplifiers, are most efficient when operated near saturation. Three popular constant-envelope modulation schemes for efficient transmission of digital data are quadriphase-shift keying (QPSK), offset (or staggered) quadriphase-shift keying (OQPSK), and minimum-shift keying (MSK). Two excellent recent articles [1,2] in IEEE Communications Magazine have discussed their general properties and attributes as well as those of other modulation schemes with constant (or nearly constant) envelopes. Other recent papers [3-61 have presented analytical results and computer

Duplex communication transceiver with modulation cancellation

Abstract: A duplex FM communication transceiver 10 is disclosed in which a modulated transmit carrier signal is utilized as the receiver first mixer (32) injection signal. The receiver portion of the transceiver comprises dual conversion circuitry, and the transmit information signal used for modulating the transmit carrier signal is phase and amplitude adjusted and then utilized to modulate the receiver second injection local oscillator 41 which provides the input injection signal to the receiver second mixer 36. The second mixer substantially cancels all of the transmit information signal and provides just received information signals to a demodulator 43 which provides audio signals to a speaker 46.

Descrambler for sync-suppressed TV signals

Abstract: Suppressed sync TV signals are descrambled by restoring their sync intervals with restoring pulses generated in predetermined time relationship with timing pulses which are transmitted with the TV signals, amplitude modulated on the audio carrier (the center of the sound or audio frequency portion of the TV signal). The timing pulses are derived by intercarrier demodulation of the television signals which are transmitted on a RF (radio frequency) channel so as to avoid loss of the timing pulses in the event of deviation of the RF TV signals in frequency, either on transmission or due to frequency errors in an up/down converter which is tuned to select the RF TV channel. Baseband signals containing the audio portion of the TV signals are envelope detected in a manner to discriminate against changes in the average level of the sound carrier envelope due, for example, to variations between the sound and picture carrier components of the transmitted TV signal, as by a comparator which responds to the difference between the average value of the envelope and the pulses superimposed upon the envelope attenuated 6 dB such that the timing pulses are detected when they reach fifty percent of peak amplitude.

Multi-phase PSK demodulator

Abstract: A multi-phase PSK (phase shift key) demodulator is applied to recover a binary encoded serial data from a continuous multi-phase modulated signal source. This demodulator mainly comprises a carrier detect, a hard limiter, a harmonic phase-locked clock regenerator, a digital multi-phase demodulator, a data clock divider and a reference phase synchronizer. The digital multi-phase demodulator applies the output of the harmonic phase-locked clock regenerator and N-th phase rectangular wave PSK signal to produce a demodulated binary encoded parallel data. Then the demodulated parallel data is converted into a serial data via a parallel to serial converter. The reference phase synchronizer can obtain a reference signal through the information of the leader preamble or continuous distributed sync words. Thus a retransmission is not required for phase resynchronization. The regeneration of carrier related clock signal and data demodulation are independent of data pattern if the input signal is preemphasized or conditioned.

Coherent spread spectrum pseudonoise tracking loop

Abstract: A detector (20) is provided for use in a communication receiver where a received spread spectrum data signal is detected using a locally generated reference signal to decode the data signal. The detector (20) includes first (22) and second channels (24) and circuitry (90) for applying the received encoded data signal to the first (22) and second channels (24). A local generator (50) is provided for generating the reference signal wherein the reference signal has polarity transitions. A demodulator (40) is included in the first channel (22) for generating a detected recovered data signal from the received data signal in response to the reference signal. Circuitry (52) is provided for detecting the polarity transitions in the reference signal and for generating a differential PN signal. Circuitry (42) is further provided in the second channel (24) for correlating the received data signal and the differential PN signal to thereby generate a recovered error signal. The recovered data signal and the recovered error signal are correlated by circuitry (58) to generate a control signal for application to the local generator (50) for locking the reference signal to a component of the received data signal.

Complex demodulation: Some theory and applications

Abstract: Publisher Summary Complex demodulation may be viewed in part as a narrow-band filtering technique that provides a look at the components of a time series, within a small frequency band of interest, as a function of time. The theory of modulation or demodulation is, therefore, a well-established and often-used technique in communications. Because the method of complex demodulation shifts each frequency of interest to zero and then applies a low-pass filter, the author observed that it made sense to look at the resulting low-frequency images of the more or less gross-frequency components of the time series as they would be more evident to the eyes. There is a vast amount of time-series literature written on the subject of filters. The usual considerations that are taken into account to make a choice in this matter will also apply when using complex demodulation. For a stationary series, the estimated amplitude, or equivalently power, should be constant within sampling fluctuations.

Television receiver for demodulating a two-language stereo broadcast signal

Abstract: Apparatus for demodulating a multiplexed sound signal comprised of a first sound signal formed by the sum of a left channel signal and a right channel signal in a first language, a second sound signal formed by the difference of the left channel signal and the right channel signal, and a third sound signal in a second language, comprising a single demodulation circuit for producing either the second sound signal or third sound signal in response to the multiplexed sound signal; a selector switch for selectively changing the center frequency of the demodulation circuit to control the latter to produce either the second sound signal or third sound signal in response to the multiplexed sound signal; a matrix circuit for producing a stereo sound signal in response to the first and second sound signals; a pair of output terminals; and a switch device for supplying the third sound signal as a second language monaural sound signal from the demodulation circuit to one output terminal when the selector switch controls the demodulation circuit to produce the third sound signal and for supplying the stereo sound signal to both output terminals from the matrix circuit as a first-language stereo signal when the selector switch controls the demodulation circuit to produce the second sound signal.

Adaptable demodulator for arbitrary amplitude and phase keyed modulation signals

Abstract: A demodulator for demodulating a received signal which has been modulated in accordance with a modulation scheme which falls within the class of APK modulation The demodulator uses a phase locked loop (PLL) to recover the carrier A ROM in the demodulator provides information in both the sweep and locked modes of operation of the PLL to control the PLL The ROM also provides at its output the digital data which has been encoded at the modulator in accordance with the selected APK scheme The information stored in the ROM is uniquely determined by the signal points associated with the selected scheme A modulator for generating the modulated signal received by the demodulator is also disclosed