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Showing papers on "Modulation published in 1981"


Journal ArticleDOI
TL;DR: In this article, a digital modulation for future mobile radio telephone services is proposed, and its fundamental properties are clarified with the aid of machine computation, and the constitution of modulator and demodulator is discussed from the viewpoints of mobile radio applications.
Abstract: This paper is concerned with digital modulation for future mobile radio telephone services. First, the specific requirements on the digital modulation for mobile radio use are described. Then, premodulation Gaussian filtered minimum shift keying (GMSK) with coherent detection is proposed as an effective digital modulation for the present purpose, and its fundamental properties are clarified with the aid of machine computation. The constitution of modulator and demodulator is then discussed from the viewpoints of mobile radio applications. The superiority of this modulation is supported by some experimental test results.

720 citations


Journal ArticleDOI
TL;DR: It is concluded that partial response CPM systems have spectrum compaction properties and at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained.
Abstract: An analysis of constant envelope digital partial response continuous Phase modulation (CPM) systems is reported. Coherent detection is assumed and the channel is Gaussian. The receiver observes the received signal over more than one symbol interval to make use of the correlative properties of the transmitted signal. The Systems are M -ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases with M . Receiver and transmitter configurations are presented.

341 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that when Pierce's pulse-position modulation scheme with 2L positions is used on a self-noise-limited direct-detection optical communication channel, there results a 2L-ary erasure channel that is equivalent to the parallel combination of L "completely correlated" binary erasure channels.
Abstract: It is shown that When Pierce's pulse-position modulation scheme with 2Lpositions is used on a self-noise-limited directdetection optical communication channel, there results a 2L-ary erasure channel that is equivalent to the parallel combination of L "completely correlated" binary erasure channels. The capacity of the full channel is the sum of the capacities of the component channels, but the cutoff rate of the full channel is shown to be much smaller than the sum of the cutoff rates. An interpretation of the cutoff rate is given that suggests a complexity advantage in coding separately on the component channels. It is shown that if short-constraint length convolutional codes with Viterbi decoders are used on the component channels, then the performance and complexity compare favorably with the Reed-Solomon coding system proposed by McEliece for the full channel. The reasons for this unexpectedly fine performance by the convolutional code system are explored in detail, as are various facets of the channel structure.

157 citations


Journal ArticleDOI
TL;DR: Computer simulation results show that sidelobe regeneration caused by the channel nonlinearity is much less for SQORC than it is for the other modulation formats considered, and the power spectral density of QORC is shown to take on the form of the product of thePower spectral densities of MSK and QPSK.
Abstract: A variation of an old but neglected pulse shaping technique, raised-cosine, is investigated. By overlapping raised-cosine pulses in each of two data streams and then by quadrature combining them, a simple QPSK/MSK type modulation results. This quadrature overlapped raised-cosine (QORC) modulation exhibits a hybrid structure of QPSK and MSK modulations. The power spectral density of QORC is shown to take on the form of the product of the power spectral densities of MSK and QPSK. The obvious consequences are that the power spectral density main lobe retains the width of the spectral density main lobe of QPSK, but the sidelobes drop off much faster (1/f^{6}) . A simple QORC modulator can be implemented similar to an MSK modulator. Several correlation type receivers are investigated and their performances calculated. Computer simulation results are used to compare end-to-end system performance of QORC and staggered QORC (SQORC) with MSK, QPSK, and staggered QPSK (SQPSK) for both linear and nonlinear satellite channels. The performance of QORC and SQORC compares very favorably with QPSK, SQPSK, and MSK. QORC performs particularly well in the presence of a nonlinear channel. The effect of phase equalization of the channel filter was investigated with outstanding performance improvement. The simulation results show that sidelobe regeneration caused by the channel nonlinearity is much less for SQORC than it is for the other modulation formats considered.

88 citations


Journal ArticleDOI
01 Dec 1981

88 citations


Journal ArticleDOI
TL;DR: Oversampling and digital filtering have been used to design a per-channel voiceband codec with resolution that exceeds the typical transmission system requirement by more than 15 dB and the response of the codec is described mathematically and the results are confirmed by measurements of experimental breadboard models.
Abstract: Oversampling and digital filtering have been used to design a per-channel voiceband codec with resolution that exceeds the typical transmission system requirement by more than 15 dB. This extended dynamic range will allow for the use of digital processing in the management of signal levels and system characteristics in many telecommunication applications. Digital filtering contained in the codec provides rejection of out-of-band inputs and smoothing of the analog output that is sufficient to eliminate the need for analog filtering in most telephone applications. Some analog filtering may be required only to maintain the expanded dynamic range in cases where there is a danger of large amounts of out-of-band energy on the analog input impairing the dynamic range of the modulator. The encoder portion of the oversampled codec comprises an interpolating modulator that samples at 256 kHz followed by digital filtering that produces a 16-bit PCM code at a sample rate of 8 kHz. In the decoder, digital processing is used to raise the sampling rate to 1 MHz prior to demodulation in a 17-level interpolating demodulator. The circuits in the codec are designed to be suitable for large-scale integration. Component matching tolerances required in the analog circuits are of the order of only ± 1 percent, While the digital circuits can be implemented with fewer than 5000 gates with delays on the order of 0.1 μs. In this paper the response of the codec is described mathematically and the results are confirmed by measurements of experimental breadboard models.

79 citations



Journal ArticleDOI
TL;DR: The role of secondary electron emission in the operation of the MSLM is discussed, and design modifications that would yield a spatial resolution of ~10 cycles/mm at the 50% point on an MTF curve are proposed.
Abstract: The microchannel spatial light modulator (MSLM) is a versatile, highly sensitive, and optically addressed modulator that is well suited for low-light level real-time optical information processing. The image processing operations that can be achieved with the MSLM include contrast reversal, contrast enhancement, edge enhancement, image addition and subtraction, analog and digital intensity level thresholding, and binary level logic operations such as AND, OR, EXCLUSIVE OR, and NOR. Several of these operations are demonstrated herein. Recent prototype MSLMs have exhibited a halfwave exposure of 2.2 nJ/cm(2), an optical information storage time of more than two months, and a framing rate of 40 Hz with full modulation depth (200 Hz with 20% modulation depth). The role of secondary electron emission in the operation of the MSLM is discussed, and design modifications that would yield a spatial resolution of ~10 cycles/mm at the 50% point on an MTF curve are proposed.

68 citations


Journal ArticleDOI
TL;DR: In this article, a longwavelength back-illuminated PIN photodiodes capable of detecting optical signals at multigigabit modulation rates have been fabricated and tested in a stripline circuit.
Abstract: Long-wavelength back-illuminated PIN photodiodes capable of detecting optical signals at multigigabit modulation rates have been fabricated and tested in a stripline circuit. A transit-time-limited response time of about 30 ps has been realised in a 25 μm-diameter diode.

68 citations


Journal ArticleDOI
TL;DR: It is experimentally confirmed that the proposed modulation method is effective in reducing speckle noise, and the results of the transmission tests have confirmed the feasibility of analog video transmission using semiconductor laser diodes.
Abstract: This paper investigates the effects of speckle noise on analog video transmission systems using semiconductor laser diodes. The system linearity degradation due to speckle noise is examined using different fiber types. Then this paper proposes a new modulation technique employing a superimposed pulse scheme to reduce speckle noise. It is experimentally confirmed that the proposed modulation method is effective in reducing speckle noise. Based on the above investigations, analog video transmission experiments are performed using single-mode fibers, step-index multimode fibers, and graded-index multimode fibers in the 0.8 and 1.3 μm wavelength regions. The results of the transmission tests have confirmed the feasibility of analog video transmission using semiconductor laser diodes.

64 citations


Journal ArticleDOI
TL;DR: Parakeets were tested for the ability to detect sinusoidal amplitude modulation of broad band noise and results are somewhat different from amplitude modulation functions in humans suggesting different degrees of temporal resolving power in birds and humans.
Abstract: Parakeets were tested for the ability to detect sinusoidal amplitude modulation of broad band noise. Instrumental avoidance conditioning and a psychophysical modified method of limits procedure were used to measure the threshold for detecting amplitude modulation at 10 modulation frequencies between 2 and 2,048 Hz. Below about 40 Hz, modulation threshold is independent of modulation rate and noise level. Above 40 Hz, modulation threshold decreases with modulation frequency at the rate of 3 dB/ octave. These results are somewhat different from amplitude modulation functions in humans suggesting different degrees of temporal resolving power in birds and humans. Thresholds for changes in modulation rate are 1–2 orders of magnitude higher than pure tone frequency difference limens.

01 Jan 1981
TL;DR: In this paper, an analysis of constant envelope digital partial response continuous phase modulation (CPM) systems is reported and an optimum receiver based on the Viterbi algorithm is presented.
Abstract: An analysis of constant envelope digital partial response continuous phase modulation (CPM) systems is reported. Coherent detection is assumed and .the channel is Gaussian. TPe receiver observes the, received signal over more than one symbol interval to make use of the correlative, properties of the transmitted signal. The systems are M-ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. .It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases with M. Receiver and transmitter configurations are presented.

Patent
04 Nov 1981
TL;DR: In this article, a microprocessor-based circuit controls the inverter using pulse width modulation techniques, where both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin θ, where θ is the angular displacement of the pulse center at the stator frequency from a fixed reference point on the carrier waveform.
Abstract: An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin θ, where θ is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120° at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Journal ArticleDOI
TL;DR: In this article, the transmission of multi-h phase coded signals over a Gaussian noise channel with Viterbi decoder is simulated and the power gain compared to MSK modulation varies from 1.5 dB at bit error rate 0.05 to 4 dB at 0.0001.
Abstract: Multi- h phase coded signals are constant-envelope sinusoids whose phase varies in a piecewise linear manner driven by cyclically chosen slopes. The transmission of these over a Gaussian noise channel with Viterbi decoder is simulated. Decoded error events are of two types normal and long, but in either case only a few bit errors are caused; events are empirically independent, they do not propagate, and their frequency is that predicted by signal space theory. Power gain compared to MSK modulation varies from 1.5 dB at bit error rate 0.05 to 4 dB at 0.0001 .

Journal ArticleDOI
TL;DR: A procedure is presented for calculating the power spectrum of the class of digital continuous-phase signals known as multi- h phase codes, which have been shown to have attractive power advantages over other uncoded digital schemes, and represent a bandwidth-efficient alternative to other coding.
Abstract: A procedure is presented for calculating the power spectrum of the class of digital continuous-phase signals known as multi- h phase codes. These signals have been shown to have attractive power advantages over other uncoded digital schemes such as QPSK, and represent a bandwidth-efficient alternative to other coding. techniques. The method is general, handling M -ary signaling, various frequency pulse shapes, and arbitrary sets of modulation indices. Numerical results are shown for several specific codes. In addition, the issue of spectral lines is resolved, and simple spectral approximations are developed.


Patent
13 Nov 1981
TL;DR: In this paper, the low voltage operation of an electro-optic modulator is realized by a unique system configuration in which the input light beam is first separated into two linearly polarized components of equal intensity, the beams are then focused into two crystals where the beams propagate as pure E waves, the crystals are electrically modulated and the output beams from each crystal are then recombined and recollimated.
Abstract: The low voltage operation of this electro-optic modulator is realized by a unique system configuration in which the input light beam is first separated into two linearly polarized components of equal intensity, the beams are then focused into two crystals where the beams propagate as pure E waves, the crystals are electrically modulated and the output beams from each crystal are then recombined and recollimated. The low voltage operation is rendered possible by the fact that there is no cancellation between the E and O components as in conventional modulation systems of this type since both beams are transmitted as pure E waves during the modulation process.

Journal ArticleDOI
TL;DR: In this paper, the optical frequency spectra of a directly frequency modulated AlGaAs semiconductor laser in the 0?5.2 GHz range were measured by using a Fabry-Perot interferometer and a birefringent optical filter.
Abstract: Optical frequency spectra of directly frequency modulated AlGaAs semiconductor laser in the 0?5.2 GHz range were measured by using a Fabry-Perot interferometer and a birefringent optical filter. The frequency deviation is linearly proportional to the RF modulation current. The measured modulation frequency characteristics for the frequency deviation show that the thermal effect is predominant in the frequency below 10 MHz. It has a resonance peak which behaves just like the peak observed in the modulation. Experimental results agreed well with theoretical values calculated by considering thermal effect and carrier-dependent refractive index variation.

Journal ArticleDOI
TL;DR: This paper examines the demodulation of the multi- h signals, and in particular examines the behavior of a decision-directed carrier loop which utilizes the Viterbi algorithm decoder in the calculation of the loop error signal.
Abstract: Multi- h phase coding is a bandwidth-efficient modulation which offers substantial performance improvement over conventional digital modulations with little or no bandwidth expansion. This paper examines the demodulation of the multi- h signals, and in particular examines the behavior of a decision-directed carrier loop which utilizes the Viterbi algorithm decoder in the calculation of the loop error signal. Both analytic and simulation results are presented and the agreement between the two is shown to be very close.

Journal ArticleDOI
On-Ching Yue1
TL;DR: It is shown that using linear combining in the MFSK system causes the performance to degrade considerably, and the system can accommodate many more users than the ones with differential-phaseshift-keying.
Abstract: In comparing two proposed frequency-hopping mobile radio systems for digitized speech, Goodman et al. have observed that the system employing multiple-frequency-shift-keying (MFSK) can accommodate many more users than the ones with differential-phaseshift-keying (DPSK). Besides the difference in modulation methods, the MFSK system uses hard-limited combining while the DPSK one uses linear combining. In this paper, we show that using linear combining in the MFSK system causes the performance to degrade considerably.

Patent
29 May 1981
TL;DR: In this article, a motion sensing system which can be oriented in any position and which provides an output signal when it is moved or tilted is presented, where the amplitude of the oscillator signal is modulated responsive to motion.
Abstract: A motion sensing system which can be oriented in any position and which provides an output signal when it is moved or tilted. The system includes an oscillator which provides an output signal; the amplitude of the oscillator signal is modulated responsive to motion. A signal level detector provides an output signal when the modulation amplitude exceeds a predetermined level. The output signal from the level detector indicates excessive motion and can be used to provide an alarm or to control associated equipment.

Journal ArticleDOI
TL;DR: In this article, a new contactless optical modulation technique for the determination of photogenerated carrier lifetimes in semiconductors is presented, which consists of measuring the modulation in the transmitted intensity of a dc probe beam due to a modulated pump beam (h/ω≳Eg).
Abstract: A new contactless optical modulation technique for the determination of photogenerated carrier lifetimes in semiconductors is presented. The technique consists of measuring the modulation in the transmitted intensity of a dc probe beam (h/ω

PatentDOI
TL;DR: In this paper, a novel signal synthesizer provides high frequency synthesized waveforms for the user by converting phase information into digital outputs in parallel and selectively coupling these digital outputs, an ordered digital output is formed to provide the high frequency waveforms.
Abstract: A novel signal synthesizer provides high frequency synthesized waveforms for the user. By converting phase information into digital outputs in parallel and by selectively coupling these digital outputs, an ordered digital output is formed to provide the high frequency waveforms. This ordered digital output, which represents points on a sine function, is converted to an analog signal for the synthesizer output. Furthermore, frequency and phase modulations of the synthesized waveforms are easily implemented with this novel signal synthesizer; the modulation information is simply added to the digital outputs prior to selectively coupling. Thus when the ordered digital output is converted to an analog signal, the analog signal contains the modulation information.

Journal ArticleDOI
TL;DR: The sensitivity of Observers to interaural delay in either the envelope or the carrier of an amplitude-modulated sinusoid was measured in a two-interval forced-choice task as a function of the frequency of the modulation and the frequencyof the carrier.

Journal ArticleDOI
TL;DR: In this article, a system providing strong, stable acousto-optic loss modulation for active mode-locking of cw lasers is described, and the effect of pump noise on a synchronously pumped dye laser is demonstrated.

Patent
10 Aug 1981
TL;DR: In this article, a magnetic recorder including a playback circuit for decoding a ternary waveform digital data signal is disclosed, wherein positive and negative threshold levels, used to distinguish between signal levels representative of data ones from signal levels representing data zeros, are automatically adjusted to compensate for occasional reductions in overall signal level that can occur due to dropouts and modulation noise on the magnetic medium.
Abstract: A magnetic recorder including a playback circuit for decoding a ternary waveform digital data signal is disclosed, wherein positive and negative threshold levels, used to distinguish between signal levels representative of data ones from signal levels representative of data zeros, are automatically adjusted to compensate for occasional reductions in overall signal level that can occur due to dropouts and modulation noise on the magnetic medium Two sample and hold units are used to generate an output signal whose amplitude reflects only those signal levels that are greater than some minimum absolute value This output signal is filtered and then used to generate the compensated positive and negative threshold levels

Journal ArticleDOI
TL;DR: In this paper, a twin-guide laser with distributed Bragg reflector was directly modulated with microwave modulation current superimposed on a DC bias which was fixed at 1.1 times the threshold current, and single-wavelength operation was experimentally confirmed with a modulation frequency up to 1 GHz and a modulation depth of 100%.
Abstract: 1.53 μm GaInAsP/InP buried-heterostructure integrated twin-guide laser with distributed Bragg reflector (BH-DBR-ITG laser) was directly modulated with microwave modulation current superimposed on a DC bias which was fixed at 1.1 times the threshold current, and single-wavelength operation was experimentally confirmed with a modulation frequency up to 1 GHz and a modulation depth of 100%.

Journal ArticleDOI
TL;DR: Borders are determined on the error rate improvement made possible by multiple bit observation for optimum and suboptimum noncoherent detection of binary CPC signals in additive white Gaussian noise (AWGN).
Abstract: Chirp (linear FM) signals provide an attractive wideband digital modulation scheme in applications where interference rejection is important. This paper evaluates the error rate (performance) of coherent binary continuous phase chirp (CPC) receivers operating on the additive white Gaussian noise (AWGN) channel and determines the improvement in performance made possible by multiple bit observation. In particular, it is shown that a receiver with two bit observation, giving up to 1.75 dB signal-to-noise ratio (SNR) improvement over the optimum single bit chirp receiver, provides a good compromise between SNR gain and system complexity. Furthermore, a simple, suboptimum, average matched filter (AMF) receiver is analyzed, and it is shown that a two-bit observation is optimum, giving a performance equivalent to that of antipodal phaseshift keying (PSK). An implementation of this receiver in the form of in-phase and quadrature demodulators is also derived.

Journal ArticleDOI
TL;DR: In this paper, a GaInAsP/InP material system with an intracavity electroabsorption modulator has been fabricated and the additional absorption loss produced by operating the modulator near maximum reverse bias has been shown to increase the laser threshold by a factor of as much as 2.9 relative to the threshold with open circuited.
Abstract: Diode lasers with an intracavity electroabsorption modulator have been fabricated in the GaInAsP/InP material system. The additional absorption loss produced by operating the modulator near maximum reverse bias increased the laser threshold by a factor of as much as 2.9 relative to the threshold with the modulator open circuited. Large depth of modulation of the laser output at frequencies up to 2.5 GHz, the measurement system limit, has been achieved by application of a microwave signal to the modulator.

Journal ArticleDOI
TL;DR: In this paper, the effect of lateral carrier diffusion on the modulation characteristics of the semiconductor laser was investigated and a self-consistent analysis of the spatially dependent rate equations was performed using a finite element model.
Abstract: The effect of lateral carrier diffusion upon the modulation characteristics of the semiconductor laser is investigated. A self‐consistent analysis of the spatially dependent rate equations is performed using a finite element model. The transverse junction stripe laser is treated as an example and a comparison is made between lateral carrier diffusion and spontaneous emission as damping mechanisms for the resonance peak. Experimental results bear out the conclusion that the relaxation resonance in this device is damped mainly by lateral carrier diffusion. In addition, a simple analytic result is presented which illustrates qualitatively the effect of lateral carrier diffusion upon such devices. The conclusion from this result is that lateral carrier diffusion serves to damp the relaxation resonance in the semiconductor laser quite well, but probably will not serve to improve the upper limit on modulation frequency as might have been suspected.