Showing papers on "Modulation published in 1990"

Electronic analog of the electro‐optic modulator

Abstract: We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

Multicarrier modulation for data transmission: an idea whose time has come

Abstract: The general technique of parallel transmission on many carriers, called multicarrier modulation (MCM), is explained. The performance that can be achieved on an undistorted channel and algorithms for achieving that performance are discussed. Ways of dealing with channel impairments and of improving the performance through coding are described, and implementation methods are considered. Duplex operation of MCM and the possible use of this on the general switched telephone network are examined. >

Very low rate convolution codes for maximum theoretical performance of spread-spectrum multiple-access channels

Abstract: A spread-spectrum multiple-access (SSMA) communication system is treated for which both spreading and error control is provided by binary PSK modulation with orthogonal convolution codes. Performance of spread-spectrum multiple access by a large number of users employing this type of coded modulation is determined in the presence of background Gaussian noise. With this approach and coordinated processing at a common receiver, it is shown that the aggregate data rate of all simultaneous users can approach the Shannon capacity of the Gaussian noise channel. >

Quantization noise spectra

Abstract: Several results describing the behavior of quantization noise in a unified and simplified manner are discussed. Exact formulas for quantizer noise spectra are developed. They are applied to a variety of systems and inputs, including scalar quantization (PCM), dithered PCM, sigma-delta modulation, dithered sigma-delta modulation, two-stage sigma-delta modulation, and second-order sigma-delta modulation. >

Theory and design of the liquid crystal TV as an optical spatial phase modulator

Abstract: An expression is derived for the complex amplitude transmittance of the liquid crystal TV (LCTV) and verified experimentally. It is shown that spatial phase modulation is realizable with good linearity, high transmission efficiency, and small intensity distortion. Although the commercial LCTV does not provide a sufficiently large dynamic range for continuous phase modulation, a dynamic range of 2'rr can be obtained by making appropriate changes in the design.

Frequency-hopping spread-spectrum modulation for digital communications over electrical power lines

Abstract: A solution for the precise and cost-effective generation of frequency-hopping spread-spectrum waveforms using digital frequency synthesis based on read-only-memories (ROM, PROM, EPROM) is studied. For matched filter reception of frequency-hopping spread-spectrum waveforms a new approach based on lock-in amplifiers combined with synchronous voltage controlled oscillators (SVCO) brought remarkable results in practical field tests. An application-specific digital signal processor for receiver operation in form of a CMOS gate array was also designed. Prototypes according to two different system concepts were built, and measurements of bit error probability were carried out on indoor and outdoor power-line networks. Computer simulations based on channel analysis to predict bit error probability are proposed and compared with measured results. Indoor prototypes are designed for a data rate of 300 b/s and a frequency-hop rate of 900 s/sup -1/ with a transmission voltage approximately=0.35 V/sub rms/ in a spectral range from 30 to 146 kHz. Outdoor prototypes are intended for remote meter reading featuring a data rate of 60 b/s and a frequency-hop rate of 300 s/sup -1/. Transmission voltage is variable from 0.35 to 1 V/sub rms/ in a spectral range from 30 to 146 kHz. >

Performance of coherent optical receivers

Abstract: Coherent optical communications, an area of research that shows great promise for future high-bandwidth and long-haul applications, is reviewed. Coherent optical receivers, which add light to the received signal as part of the detection process, have numerous advantages over direct-detection receivers, most notably increased sensitivity and increased selectivity, at the cost of increased complexity. The performance of coherent optical receivers under shot-noise-limited conditions is reviewed for a variety of modulation and demodulation formats. In addition, laser phase noise is discussed, and its effect on receiver performance is analyzed. >

Dual parallel modulation schemes for low-distortion analog optical transmission

Abstract: The use of two integrated-optical modulators operated in parallel to attain low-distortion analog optical transmission is examined. This static feedforward approach achieves significantly improved linearity at the expense of small increases in the required optical power and moderate increases in the required drive voltage. A novel variation that uses the unique characteristics of an integrated-optical modulator to correct the dominant quadratic distortion of a directly modulated laser is proposed. >

The performance of rate-compatible punctured convolutional codes for digital mobile radio

Abstract: The unequal error protection capabilities of convolutional codes belonging to the family of rate-compatible punctured convolutional codes (RCPC codes) are studied. The performance of these codes is analyzed and simulated for the first fading Rice and Rayleigh channels with differentially coherent four-phase modulation (4-DPSK). To mitigate the effect of fading, interleavers are designed for these unequal error protection codes, with the interleaving performed over one or two blocks of 256 channel bits. These codes are decoded by means of the Viterbi algorithm using both soft symbol decisions and channel state information. For reference, the performance of these codes on a Gaussian channel with coherent binary phase-shift keying (2-CPSK) is presented. A number of examples are provided to show that it is possible to accommodate widely different error protection levels within short information blocks. Unequal error protection codes for a subband speech coder are studied in detail. A detailed study of the effect of the code and channel parameters such as the encoder memory, the code rate, interleaver depth, fading bandwidth, and the contrasting performance of hard and soft decisions on the received symbols is provided. >

Direct-sequence spread-spectrum parallel acquisition in a fading mobile channel

Abstract: A parallel acquisition scheme for direct-sequence spread-spectrum systems is proposed, and its mean acquisition time performance is analyzed in both nonfading and Rayleigh-fading environments. An expression for the mean acquisition time is derived in terms of the probabilities of detection, missing, and false alarm. These parameters are first analyzed for a typical AWGN (additive white Gaussian noise) channel, then the Rayleigh-fading channel encountered in a typical UHF or microwave land mobile radio channel is studied. The channel is assumed frequency nonselective, and the effect of data modulation and code Doppler is not considered. The performance of the parallel system is compared to the corresponding serial system, and it is shown that a significant improvement can be achieved. >

Spread-spectrum code acquisition in the presence of Doppler shift and data modulation

Abstract: A spread-spectrum code acquisition technique for a direct-sequence (DS) system in the presence of Doppler effect and data modulation is investigated. Both the carrier-frequency offset and code-frequency offset due to severe Doppler effect are considered. The code-chip slipping during the correlation process caused by code-frequency offset can degrade the acquisition performance significantly. However, this issue can be alleviated by compensating code-frequency offset in an appropriate manner. Results are presented for the cases with and without data modulation. Coherent detection is considered when there is no data modulation. If data modulation is present, the authors partition the correlation time into subintervals and the integration results in these subintervals are square-law noncoherently combined for detection. The implementation of this code acquisition technique using the fast Fourier transform (FFT) algorithm is described. The use of theoretical results to estimate the hardware complexity of an actual system is illustrated step by step, showing that implementation is feasible with existing technology. The tradeoff between hardware complexity and acquisition performance is discussed. >

Method and apparatus for the reception and demodulation of spread spectrum radio signals

Abstract: A spread spectrum receiver with filters matched to transmitter chip codes are implemented in digital circuits along with a digital circuit for acquisition and tracking of the arrival times of the chip codes. The digital circuit implementations are used for the noncoherent demodulation of pulse position spread spectrum modulation signals where the pulse is a carrier modulator by a chip code and for the noncoherent demodulation of multiple chip code modulation signals where each information symbol is represented by one of several chip codes modulating a carrier.

Automatic modulation classification using zeroç crossing

Abstract: A modulation recogniser that automatically reports modulation types of constant-envelope modulated signals is developed using zero-crossing techniques. The zero-crossing sampler, as a signal conditioner, has the advantage of providing accurate phase transition information over a wide dynamic frequency range. Signal parameters such as zero-crossing variance, carrier-to-noise ratio (CNR) and carrier frequency are estimated. Phase difference and zero-crossing interval histograms play the role of features for modulation recognition. The classifier performance is given in the form of a confusion matrix. The simulation results obtained demonstrate that a reasonable average probability of correct classification is achievable for CNR ≥ 15 dB.

Narrow-band modulation of semiconductor lasers at millimeter wave frequencies (>100 GHz) by mode locking

Abstract: The possibility of mode locking a semiconductor laser at millimeter wave frequencies approaching and beyond 100 GHz was investigated theoretically and experimentally. It is found that there are no fundamental theoretical limitations in mode locking at frequencies below 100 GHz. At these high frequencies, only a few modes are locked and the output usually takes the form of a deep sinusoidal modulation which is synchronized in phase with the externally applied modulation at the intermodal heat frequency. This can be regarded for practical purposes as a highly efficient means of directly modulating an optical carrier over a narrow band at millimeter wave frequencies. Both active and passive mode locking are theoretically possible. >

Multiple-modulator fractional-n divider

Abstract: A fractional-N type frequency synthesizer includes a frequency divider having a selectable integer divide number which is periodically temporarily altered to provide an average rational divide number for the frequency divider. A number of modulator circuits coupled in cascade fashion provide a zero sum modulation signal which varies the value of the frequency divider divisor value such that the net change in divisor value due to the modulation signal is zero thereby reducing phase noise resulting from the temporary altering of the integer divisor value close to the frequency synthesizer carrier frequency.

Digital data and analog radio frequency transmitter

Abstract: A digital Non Return to Zero (NRZ) and Frequency Modulated (FM) radio transmitter intended but not unique to, for the transmission of Digital, Tone Only or Tone and Voice paging messages is described. This transmitter is built on the concept that the separate signals required are individually constructed, and then combined together into the actual RF output. This provides for optimized circuitry for each particular function for the highest performance. There is no reason for compromising the performance of a particular function, and the implementation of the modulation and synthesis with direct digital technology provides extremely linear and fast radio performance at no extra cost. Maintenance is also simplified since the individual blocks can be troubleshooted and repaired (or replaced) requiring a minimum of down time.

Random pulse-width modulation technique for voltage-controlled power inverters

Abstract: As an alternative to the existing deterministic pulse-width modulation methods, a random pulse-width modulation technique for voltage-controlled power inverters is proposed. Advantages of the technique include non-repetitiveness of the switching pattern, simplicity of the hardware, and uncommonly high limits of switching frequency. A prototype random pulse-width modulator is described and experimental results are presented.

Induced focusing of optical beams in self-defocusing nonlinear media.

Abstract: The novel phenomenon of induced focusing occurring in a self-defocusing nonlinear medium is discussed theoretically. Induced focusing of a weak optical beam occurs when it copropagates with an intense pump beam whose intensity peaks at a place different from that of the weak beam. The physical mechanism behind induced focusing is cross-phase modulation that couples the two beams. The conditions under which induced focusing can occur are discussed by solving numerically the coupled amplitude equations which incorporate the effects of diffraction, self-phase modulation, and cross-phase modulation.

Spread spectrum goes commercial

Abstract: The use of spread-spectrum techniques to achieve more efficient utilization of available frequency spectra is examined. The two main spread-spectrum techniques, direct sequence and frequency hopping, are explained. In frequency hopping, the transmitter repeatedly changes (hops) the carrier frequency from one frequency to another. Direct-sequence transmission spreads the spectrum not by periodically changing the frequency but by modulating the original (information) baseband signal with a very wide-baseband digital signal. The wideband modulating signal's amplitude changes continually between two states, high and low, arbitrarily called +1 and -1, respectively, with the sequence of highs and lows being pseudorandom. Applying spread spectrum to code-division multiaccess (CDMA) communication, in which each user is assigned an identification code (a distinct sequence of frequencies for frequency hopping or +1 s and -1 s for direct-sequence modulation) is discussed. The use of CDMA for cellular radio, where it promises a capacity of over 1000 users per cell, by the authors' calculations, is considered. The potential of spread spectrum for relieving spectrum congestion is addressed. >

Method and means for parallel frequency acquisition in frequency domain fluorometry

Abstract: A digital frequency domain fluorometer utilizing a computer-controlled digital data acquisition system is use for the study of fluorescence and phosphorescence phenomena in the bio-chemical, biological and bio-physics arts. The computer is used for the direct collection of data, as well as for the filtering and calculation of the phase and modulation values of the sample under study. From these values, fluorescence lifetimes and anisotropy decay times can determined. The digital data acquisition system provides for the simultaneous collection and processing of several modulation frequencies. In addition, the digital frequency domain fluorometer can utilize an array detector for detecting the modulated light from the various samples under study. The use of the array detector provides a means for independently collecting data over a large number of pixels. This configuration allows for a time resolved image to be collected at once.

Microcellular direct-sequence spread-spectrum radio system using N-path RAKE receiver

Abstract: A microcellular local area network (LAN) for indoor communications is proposed using code-division multiple access (CDMA) and differential phase-shift keying (DPSK) for data modulation. The pseudonoise (PN) codes in the transmitters of the base station are mutually synchronized. For this purpose, sets of Gold code sequences having low cross correlation have been found by an exhaustive computer search. Together with wideband measurements of the indoor radio channel at 900 MHz, a five-path RAKE receiver was designed to combat fading effects and to process the time diversity by using multipath signal reception. Each receiver path is demodulated independently. Several methods of diversity combining of these paths have been investigated. Acquisition and tracking of the spreading code in the receiver are controlled by a digital signal processor (DSP). Experimental results of the CDMA system are presented, showing the behavior in a multipath environment. >

All‐optical modulation using an n‐doped quantum‐well structure

Abstract: The modulation of interband‐resonant light by intersubband‐resonant light using an n‐doped quantum well is proposed, and results of the theoretical analysis are reported. It is shown that a large change in absorption coefficient from 100 to 3160 cm−1 for interband‐resonant light can be obtained by changing the intensity of intersubband‐resonant light from 0 to 1 MW/cm2. Very fast modulation speed (∼ps) can be expected.

Two-channel polarization modulation ellipsometer.

Abstract: A new wavelength-scanning two-channel polarization modulation ellipsometer is described, where a photo-elastic modulator is used and the analyzed light is separated into orthogonally polarized beams using a Wollaston prism. Both beams are detected using phototubes whose bias voltage is dynamically controlled for constant dc. The dc from each phototube is measured with a digital voltmeter, and the fundamental and second harmonic of the phototube current are measured using individual lock-in amplifiers. All three of the associated ellipsometric parameters (N = cos2psi, S = sin2psi sindelta, and C = sin2psi, cosDelta) can be determined simultaneously in a single scan. The versatility of the instrument is demonstrated by the determination of the optical functions of Si from 238 to 652 nm (5.3-1.9 eV).

Pseudo field modulation in EPR spectroscopy

Abstract: This paper develops methodology for computer simulation of the effect on an experimental EPR spectrum that would occur if an additional field modulation were applied followed by eventual phase sensitive detection at the modulation frequency or at one its harmonics. The algorithm, which is called pseudomodulation, transforms the digitized spectrum and also filters the noise. If a second harmonic spectrum is desired in order to make subtle changes in curvature more apparent, it is shown that it is always preferable to obtain an experimental second harmonic spectrum. The signals are identical, but because of the filtering properties of the pseudomodulation algorithm, the noise is lower. Pseudomodulation should be applied to simulated spectra prior to fitting a model to data in order more precisely to simulate the experimental signal. It is argued that such fits ought to involve not only first harmonics but also higher harmonics, since the various harmonics are sensitive in different ways to input parameters in the spin Hamiltonian. Application of pseudomodulation to the EPR spectrum of the blue copper-protein azurin is described.

Magnetostatic-forward-volume-wave-based guided-wave magneto-optic Bragg cells and applications to communications and signal processing

Abstract: Realization of magnetostatic forward volume wave (MSFVW)-based guided-wave magneto-optic (MO) Bragg cells and their applications to communications and signal processing are reported. Bragg diffraction of guided-optical waves from the MSFVW in a noncollinear coplanar geometry is analyzed. The design of microstrip line transducers that facilitate wideband MO Bragg diffraction with electronically tunable microwave carrier frequencies (2.0 to 12.0 GHz) are briefly discussed. Experimental results obtained with the resulting Bragg cells in both pure and bismuth-doped yttrium-iron-garnet (YIG) waveguides and a comparison to the theoretical predictions are presented. Applications of the Bragg cells to light beam modulation, scanning/switching, and RF spectral analysis are presented in detail. >

Binary phase shift keying modulation system

Abstract: A low cost spread spectrum modulator for BPSK, or Binary Phase Shift Keying capable of outputting the high modulation rate and suppressed carrier output needed in spread spectrum systems. The present invention provides high quality BPSK modulation without the double balance mixers as required in the prior art, thereby dispensing with the necessity of complex transistor/potonciometer or diode/transformer arrangements. The present invention provides BPSK modulation utilizing only one transformer, which can be adjusted for carrier suppression and two transistors, allowing the present system to be driven from low power CMOS logic levels, yet producing eight db of gain.

Charge-coupled device image sensor as a demodulator in a 2-D polarimeter with a piezoelastic modulator

Abstract: It is shown how demodulation of rapidly modulated light beams can be achieved within a single charge-coupled device (CCD). Two interlaced image planes are created by optically masking every second CCD row and transferring the charges back and forth between the two image planes in synchrony with the modulation. The method has been successfully tested for modulation frequencies of 50 and 100 kHz, using integration times up to 1 s. No significant accumulated charge transfer losses are seen for integration times as long as 10(5) modulation cycles (1 s). This demonstrates the feasibility of a CCD polarimeter using piezoelastic modulation of the state of polarization.

Relativistic klystron amplifiers driven by modulated intense relativistic electron beams

Abstract: An overview is provided for the novel relativistic klystron amplifiers which are under active study at the Naval Research Laboratory. These amplifiers are driven by an annular intense relativistic electron beam (500-kV, 10-kA range), which is modulated by an external RF source (1.3-GHz, 100-kW range). Experiments, theory, simulation, and simple models are presented to illustrate the unusual properties of such devices which result from the intense space charge of the beam. Chief among them are electrostatic insulation against vacuum breakdown at high power levels, efficient current modulation, short bunching length, and amplitude and phase stability of the output signal. Many of these unexpected features were revealed in two separate experiments: one with a lower current beam (5 kA, 2-cm beam radius), and the other one with a higher current beam (16 kA, 6.6-cm beam radius). Three gigawatts of RF power at 1.3 GHz were generated with the large diameter beam at an efficiency of 35% with 37-dB gain. These experiments are reviewed, along with a combination of particle simulation results and analytic models which facilitate the interpretation. Special attention is paid to the unfamiliar features of these amplifiers, and the critical problems which must be solved before such amplifiers can fulfil their potential in a wide range of applications are addressed. >

A concatenated coded modulation scheme for error control

Abstract: A concatenated coded modulation scheme is presented for error control in data communications. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary phase-shift keying (PSK) modulation. Error performance of the scheme is analyzed for an additive white Gaussian noise (AWGN) channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner-code and a relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The scheme is particularly effective for high-speed satellite communications for large file transfer where high reliability is required. A simple method is also presented for constructing block codes for M-ary PSK modulation. Soome short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft-decision Viterbi decoding algorithm. Furthermore, some of these codes are phase invariant under multiples of 45 degrees rotation. >

Light wave range finder

Abstract: PROBLEM TO BE SOLVED: To provide a light wave range finder capable of efficiently creating a signal necessary for measurement and capable of performing the measurement in a short timeSOLUTION: A light wave range finder includes: a light emission element 11 for emitting a range finding light 28; signal generators 33, 34 for generating a plurality of proximity frequencies; intermittent pulse generators 35, 36 for generating a pulsed modulation signal in a prescribed width; an emission optical system for sequentially switching and emitting an intermittent modulation range finding light for each proximity frequency; a light reception part 21 for receiving a reflected distance measuring light 28'; the other signal generators 55, 56 for generating a frequency signal having a difference of the predetermined frequency; frequency conversion parts 39, 43, 44, 57, and 58 for converting the frequencies into difference frequencies by mixing; and a calculation control part 52 The calculation control part intermittently generates respective proximity frequencies so that the pulse width of the intermittent modulation distance measuring light is made shorter than the cycle of the difference frequency A difference frequency waveform is calculated A phase is obtained from the waveform for one cycle of the difference frequency, a precise measuring distance is calculated, a mutual phase difference of the difference frequency waves is calculated, a rough measuring distance value is calculated, and the distance is measured from the rough measuring distance value and the precise measuring distance valueSELECTED DRAWING: Figure 2