Showing papers on "Modulation published in 1997"

Demonstration of 110 GHz electro-optic polymer modulators

Abstract: Electro-optic modulation up to 113 GHz has been demonstrated using traveling wave polymer modulators. The modulation signal was directly detected at 1.3 μm using a laser heterodyne system with an external-cavity tunable semiconductor laser. The device optical response variation, as a function of frequency over the whole W band, was within 3 dB. A well-matched coplanar probe was used to launch W band millimeter wave driving power into the microstrip line electrode on the device. Based upon these measurements, high speed electrodes with integrated millimeter wave transitions had been fabricated and tested.

Ultrawide-band communication system and method

Abstract: An impulse radio communications system using one or more subcarriers to communicate information from an impulse radio transmitter to an impulse radio receiver. The impulse radio communication system is an ultrawide-band time domain system. The use of subcarriers provides impulse radio transmissions added channelization, smoothing and fidelity. Subcarriers of different frequencies or waveforms can be used to add channelization of impulse radio signals. Thus, an impulse radio link can communicate many independent channels simultaneously by employing different subcarriers for each channel. The impulse radio uses modulated subcarrier(s) for time positioning a periodic timing signal or a coded timing signal. Alternatively, the coded timing signal can be summed or mixed with the modulated subcarrier(s) and the resultant signal is used to time modulate the periodic timing signal. Direct digital modulation of data is another form of subcarrier modulation for impulse radio signals. Direct digital modulation can be used alone to time modulate the periodic timing signal or the direct digitally modulated the periodic timing signal can be further modulated with one or more modulated subcarrier signals. Linearization of a time modulator permits the impulse radio transmitter and receiver to generate time delays having the necessary accuracy for impulse radio communications.

A 27-mW CMOS fractional-N synthesizer using digital compensation for 2.5-Mb/s GFSK modulation

Abstract: A digital compensation method and key circuits are presented that allow fractional-N synthesizers to be modulated at data rates greatly exceeding their bandwidth. Using this technique, a 1.8-GHz transmitter capable of digital frequency modulation at 2.5 Mb/s can be achieved with only two components: a frequency synthesizer and a digital transmit filter. A prototype transmitter was constructed to provide proof of concept of the method; its primary component is a custom fractional-N synthesizer fabricated in a 0.6-/spl mu/m CMOS process that consumes 27 mW. Key circuits on the custom IC are an on-chip loop filter that requires no tuning or external components, a digital MASH /spl Sigma/-/spl Delta/ modulator that achieves low power operation through pipelining, and an asynchronous, 64-modulus divider (prescaler). Measurements from the prototype indicate that it meets performance requirements of the digital enhanced cordless telecommunications (DECT) standard.

Adaptive coded modulation for fading channels

Abstract: We propose a variable-power and variable-rate coded MQAM modulation technique for high-speed data transmission on fading channels. Coding gain is obtained by superimposing trellis codes designed for AWGN channels on the adaptive modulation, and we obtain the same coding gains as these codes exhibit in AWGN. We present analytical and simulation results which show a 3dB coding gain relative to uncoded adaptive modulation for a simple 4-state trellis code, and a 4 dB coding gain for an 8-state trellis code. More complex trellis codes achieve higher gains.

A comparison of peak power reduction schemes for OFDM

Abstract: Two powerful and distortionless peak power reduction schemes for orthogonal frequency division multiplexing (OFDM) are compared. One investigated technique is selected mapping (SLM) where the actual transmit signal is selected from a set of signals and the second scheme utilizes phase rotated partial transmit sequences (PTS) to construct the transmit signal. Both approaches are very flexible as they do not impose any restriction on the modulation applied in the subcarriers or on their number. They both introduce some additional system complexity but nearly vanishing redundancy to achieve markedly improved statistics of the multicarrier transmit signal. The schemes are compared by simulation results with respect to the required system complexity and transmit signal redundancy.

A novel peak power reduction scheme for OFDM

Abstract: An efficient and distortionless scheme for peak power reduction in orthogonal frequency division multiplexing (OFDM) is proposed, which introduces some additional complexity but nearly vanishing redundancy. The approach is very flexible and works with arbitrary numbers of subcarriers and without restriction on the type of modulation applied in them. The core of the approach is the coordination of appropriately phase rotated signal parts to minimize the peak power of the multiplex signal. The improved statistics of peak power in the optimized transmit signal are demonstrated by simulation results. Finally, it is shown that this scheme is close to the theoretical limit curve of redundancy versus minimum peak-to-average power ratio (PAR).

Comparison between adaptive OFDM and single carrier modulation with frequency domain equalization

Abstract: The aim of the paper is to compare multicarrier and single carrier modulation schemes for radio communication systems. In both cases the fast Fourier transform (FFT) and its inverse are utilized. In the case of OFDM (orthogonal frequency division multiplexing), the inverse FFT transforms the complex amplitudes of the individual subcarriers at the transmitter into the time domain. At the receiver the inverse operation is carried out. In the case of single carrier modulation, the FFT and its inverse are used at the input and output of the frequency domain equalizer in the receiver. Different single carrier and multicarrier transmission systems are simulated with time-variant transfer functions measured with a wideband channel sounder. In the case of OFDM, the individual subcarriers are modulated with fixed and adaptive signal alphabets. Furthermore, a frequency-independent as well as the optimum power distribution are used.

Method and apparatus for the production of a structure by focused laser radiation on a photosensitively coated substrate

Abstract: A system for writing geometric structures on a photosensitive substrate including a modulated laser beam source, a focusing lens, a deflector for producing a scanning action between the light source and the lens, and a device for mechanically moving the surface relative to the laser beam. Compressed data for use in writing the geometric structures is read out of a memory into a data delivery circuit such that the data is formatted to have both beam power and position information. A modulator logic circuit operates to call up the data from the data delivery circuit, form a modulation drive signal based on the power information, and delay the modulation drive signal based the position data. The modulator logic circuit thus operates to vary the modulation drive signal to begin or end exposure along the scan lines with greater resolution or pixel density by at least a factor of four more than the resolution or spacing density between adjacent scan lines. The scan lines are arranged within stripes, and adjacent stripes preferably are made to overlap such that the stripes are blended in the overlap according to a predetermined stepwise changing function.

Ultrasensitive laser measurements without tears

Abstract: Several easily implemented devices for doing ultrasensitive optical measurements with noisy lasers are presented. They are all-electronic noise cancellation circuits that largely eliminate excess laser intensity noise as a source of measurement error and are widely applicable. Shot-noise-limited optical measurements can now easily be made at baseband with noisy lasers. These circuits are especially useful in situations where strong intermodulation effects exist, such as current-tuned diode laser spectroscopy. These inexpensive devices ~parts cost ’$10! can be optimized for particular applications such as wideband or differential measurements. Although they cannot eliminate phase noise effects, they can reduce amplitude noise by 55‐70 dB or more, even in unattended operation, and usually achieve the shot-noise limit. With 1-Hz signal-to-noise ratios of 150‐160 dB, they allow performance equal or superior to a complex heterodyne system in many cases, while using much simpler dual-beam or homodyne approaches. Although these devices are related to earlier differential and ratiometric techniques, their noise cancellation performance is much better. They work well at modulation frequencies from dc to several megahertz and should be extensible to ’100 MHz. The circuits work by subtracting photocurrents directly, with feedback applied outside the signal path to continuously adjust the subtraction for perfect balance; thus the excess noise and spurious modulation ideally cancel at all frequencies, leaving only the shot noise. The noise cancellation bandwidth is independent of the feedback bandwidth; it depends only on the speeds of the photodiodes and of the bipolar junction transistors used. Two noise-canceled outputs are available; one is a high-pass filtered voltage proportional to the signal photocurrent and the other is a low-pass filtered voltage related to the log ratio of the signal and comparison photocurrents. For reasonable current densities, the noise floors of the outputs depend only on the shot noise of the signal beam. Four variations on the basic circuit are presented: low noise floor, high cancellation, differential high power, and ratio-only. Emphasis is placed on the detailed operation and design considerations, especially performance extension by compensation of the nonideal character of system components. Experience has shown that some applications advice is required by most users, so that is provided as well. © 1997 Optical Society of America

The relationship between space-vector modulation and regular-sampled PWM

Abstract: The relationship between regular-sampled pulse-width modulation (PWM) and space-vector modulation for inverter drives is defined, and it is shown that, under certain circumstances, the two approaches are equivalent. The various possibilities of adding a zero-sequence component to the regular-sampled sinusoidal modulating wave are explored, and these effects are quantified. It is shown that this leads to "equal-null" pulse times, which extend the linear modulation range and simplify the microprocessor implementation.

Acousto-optic tomography with multiply scattered light

Abstract: We have investigated the modulation of the optical field transmitted through a colloid of polystyrene spheres by a narrow quasi-cw ultrasound beam. Measurements of the scale dependence of the heterodyne modulation signal at the acoustic frequency are obtained for samples that are up to 140 scattering lengths thick. A calculation of the modulation signal predicts the possibility of tomographic imaging, which is confirmed experimentally.

Modeling auditory processing of amplitude modulation

Abstract: A popular model of the processing of amplitude modulation (AM) [Viemeister, J. Acoust. Soc. Am. 66, 1364–1380 (1979)] consists of a bandpass filter, a rectifying nonlinearity, a low‐pass filter, and a decision device. The low‐pass filtering (or integration) stage was intended to simulate the temporal resolution limit by attenuating rapid changes in the envelope of the signal. Fleischer [Acustica 47, 155–163 (1981)] developed a model describing the influence of the inherent fluctuations within a noise carrier on the detectability of added modulation. The modulation spectrum was weighted by a certain factor which also essentially represented a low‐pass characteristic. In a recent modeling approach [Dau et al., submitted to J. Acoust. Soc. Am. (1997)], a modulation filterbank replaced the low‐pass filter, to analyze the envelope fluctuations of the stimuli in each peripheral auditory filter. The inclusion of a modulation filterbank was motivated by results from several studies on modulation masking which provided evidence for frequency selectivity in the modulation‐frequency domain. In addition, the role of peripheral filtering for the processing of amplitude modulation, the envelope statistics, and the spectral distribution of modulation power in the modulation spectrum are discussed.

Stacked-carrier discrete multiple tone communication technology and combinations with code nulling, interference cancellation, retrodirective communication and adaptive antenna arrays

Abstract: A "stacked-carrier" spread spectrum communication system based on frequency domain spreading that multiplies a time-domain representation of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In a preferred embodiment, the spreading energizes the bins of a large fast Fourier transform (FFT). This provides a considerable savings in computational complexity for moderate output FFT sizes. Point-to-multipoint and multipoint-to-multipoint (nodeless) network topologies are possible. A code-nulling method is included for interference cancellation and enhanced signal separation by exploiting the spectral diversity of the various sources. The basic system may be extended to include multi-element antenna array nulling methods also for interference cancellation and enhanced signal separation using spatial separation. Such methods permit directive and retrodirective transmission systems that adapt or can be adapted to the radio environment. Such systems are compatible with bandwidth-on-demand and higher-order modulation formats and use advanced (maximum-SINR) despreader adaptation algorithms.

Analog-to-digital conversion via duty-cycle modulation

Abstract: An exchange of the amplitude axis for the time axis offers a possibility of overcoming resolution problems in analog-to-digital conversion in low-voltage CMOS circuits and/or of circumventing special resistor options in silicided processes. This exchange can be effected via some form of duty-cycle modulation. For its implementation a circuit configuration is described, consisting of an asynchronous sigma-delta modulator, followed by a phase-synchronized tapped ring oscillator which produces a poly-phase signal for sampling the asynchronous signal at a relatively low frequency. A detailed analysis is presented which accurately predicts the properties of the conversion scheme with respect to aliasing, quantization noise and nonlinear distortion. The results are illustrated with simulations of a design example.

Non-contact system for sensing and signalling by externally induced intra-body currents

Abstract: A wireless system includes one or more transmitters and one or more remote receivers that are respectively coupled through one or more users and room ground. The transmitters each produce low-frequency, low power signals that, through capacitive coupling, pass as displacement currents into and from the body of the user, which acts as a conductive node. A receiver that couples capacitively to the user responds to the displacement currents and reproduces the signals. The transmitter includes a signal generator and a pair of electrodes. The signal generator produces modulated signals that vary the voltage between the electrodes, a first one of which is closely coupled capacitively to the user's body such that the "quasi-electrostatic" field resulting from the electrode potential causes a displacement current to pass to the user's body. The second electrode is oriented so that its coupling to the room ground is stronger than that of the first electrode, such that room ground acts as a return path for the current from the receiver. The signal generator may modulate the information to be transmitted using, for example, a pseudorandom code, to produce spread spectrum signals. This increases noise immunity and allows multiple transmitters, each using a different modulation code, to operate at the same time. The receivers each include a detector/demodulator that acquires and tracks the signals from the one or more transmitters.

A new optimized space-vector modulation strategy for a component-minimized voltage source inverter

Abstract: This paper presents a new space-vector modulation strategy suitable for a low-cost pulse-width-modulation (PWM) voltage-source (VS) inverter employing only four switches, four diodes, and a split-capacitor bank in the DC link. The work is motivated by the need for an efficient and flexible modulation method, which is optimized with respect to minimum machine-torque ripple. The modulation strategy is named space-vector modulation for four-switch inverter (SVMFSI), and it is realized by planning the switching patterns between four active voltage vectors on the basis of a desired flux trajectory for the stator-flux vector in the AC machine. The strategy is implemented in a single 8-bit microcontroller as a double-sided modulation strategy. Simulations of the machine-torque ripple are performed at a switching frequency of 4 kHz and indicate a torque ripple of 14% at nominal load. Finally, selected results are verified experimentally on a 1.5-kVA prototype B4 inverter. The test results indicate high-quality output-voltage spectra with no low-order voltage harmonics and a harmonic-loss factor (HLF) of 1.12% at unity modulation index.

Elimination of the fibre chromatic dispersion penalty on 1550 nm millimetre-wave optical transmission

Abstract: Dispersion causes a power penalty at certain fibre distances and frequencies in conventional millimetre-wave intensity modulation. Single sideband optical modulation at millimetre-wave frequencies using a fibre Bragg grating eliminates the dispersion-induced penalty over modulation frequency and fibre length.

Modulation coding for pixel-matched holographic data storage.

Abstract: We describe a digital holographic storage system for the study of noise sources and the evaluation of modulation and error-correction codes. A precision zoom lens and Fourier transform optics provide pixel-to-pixel matching between any input spatial light modulator and output CCD array over magnifications from 0.8 to 3. Holograms are angle multiplexed in LiNbO3:Fe by use of the 90° geometry, and reconstructions are detected with a 60-frame/s CCD camera. Modulation codes developed on this platform permit image transmission down to signal levels of ∼2000 photons per on camera pixel, at raw bit-error rates (BER’s) of better than 10-5. Using an 8–12–pixel modulation code, we have stored and retrieved 1200 holograms (each with 45,600 user bits) without error, for a raw BER of <2×10-8.

Wavelength conversion using semiconductor optical amplifiers

Abstract: This paper reports a detailed theoretical study of the dynamics of wavelength conversion using cross-gain and cross-phase modulation in semiconductor optical amplifiers (SOA's) involving a large signal, multisection rate equation model. Using this model, recently reported experimental results have been correctly predicted and the effects of electrical and optical pumping on the conversion speed, modulation index, and phase variation of the converted signal have been considered. The model predicts, in agreement with experimental data, that recovery rates as low as 12 ps are possible if signal and pump powers in excess of 14 dBm are used. It also indicates that conversion speeds up to 40 Gb/s may be achieved with less than 3 dB dynamic penalty. The employment of cross-phase modulation increases the speed allowing, for example, an improvement to 60 Gb/s with an excess loss penalty less than 1 dB.

Optical communication system

Abstract: PROBLEM TO BE SOLVED: To stabilize reception intensity on a reception side even if frequency characteristics of an optical external modulator change by controlling the carrier frequency of the modulating signal of the optical external modulator according to the output of a temperature detector provided to the optical external modulator. SOLUTION: Of the optical communication system which modulates the plane of polarization of light propagated in an optical transmission line 1 with the modulating signal of the optical external modulator 2 from outside the optical transmission line 1, the optical external modulator 2 is provided with the temperature detector 3 and the carrier frequency of the modulating signal of the optical external modulator 2 is controlled according to the output of this temperature detector 3. Thus, the carrier frequency of the modulating signal of the optical external modulator 2 is controlled according to the output of the temperature detector 3 provided for the optical external modulator 2 and then the degree of modulation of the optical external modulator 2 vary with temperature to stabilize the reception intensity of the light signal, thereby enabling an optical communication of high reliability.

Controlling clipping probability in DMT transmission

Abstract: A discrete multitone signal has a much higher peak to average ratio than a comparable single tone modulation signal. Therefore a DMT transmitter has to either have a significantly more expensive analog front end (both in terms of the DAC, the analog filter and line driver) or it has to control the amount of clipping. We describe two general techniques for clipping control and present performance comparisons to previous techniques.

Dual-mode digital FM communication system

Abstract: A dual-mode digital communication system for communicating an information signal during operation in frequency-modulated (FM) and multiple-access modes is disclosed herein. The digital communication system includes a dual-mode transmitter for transmitting the information signal using an FM communication signal during FM mode operation, and for transmitting the information signal using a multiple-access communication signal during multiple-access mode operation. The communication system further includes a dual-mode receiver for receiving the FM communication signal during FM mode operation, and for receiving the multiple-access communication signal during multiple-access mode operation. Incorporated within the dual-mode receiver is a digital demodulator for recovering the information signal from the received FM signal during operation in the FM mode, and for recovering the information signal from the received multiple-access signal during multiple-access mode operation. In a preferred implementation the dual-mode transmitter is disposed to convert a first sequence of binary data within the information signal into a sampled modulation waveform, and to provide the FM communication signal by modulating a carrier signal based at least in part on the sampled modulation waveform. The dual-mode transmitter may also be configured to multiplex a second sequence of wideband message data with the sampled modulation waveform so as to form a composite FM modulation waveform.

Apparatus and method for detecting signal points using signal point-mapping

Abstract: An apparatus and method for detecting signal points transmitted over a transmission line. A data transmitter encodes input data and maps this data in accordance with a Trellis Code Modulation technique. The mapped data is then modulated onto a particular carrier wave, and transmitted to a data receiver. The data receiver compensates for any detected phase shift in the carrier wave, and decodes the phase-corrected data to quickly detect parallel path information of the received data.

High-performance hysteresis modulation technique for active filters

Abstract: A new, substantial improvement of the hysteresis current control method for voltage source inverters is presented. A simple and fast prediction of the hysteresis band is added to a linearized version of the phase-locked loop control, thus ensuring constant switching frequency and tight control of the position of modulation pulses. This allows high accuracy in tracking highly distorted current waveforms and minimizes the ripple in multiphase systems. The implementation of this technique is very simple and robust, employing only a small number of conventional inexpensive analog and logic components. It does not require trimmings or tunings, giving the control the capability to adjust itself to the different operating conditions. The proposed method is compared with the most diffused modulation techniques, demonstrating its superior performance in responding to the most demanding conditions met in active filters. The behavior of the method has been fully verified by simulation and by experimental tests.

Propagation of light waves in thue-morse dielectric multilayers

Abstract: We investigate the propagation of light waves in an aperiodic multilayer which is composed of dielectric slabs arranged following the Thue-Morse sequence. Both refractive index modulation and optical thickness modulation are considered. The recursion relations of the transfer matrix elements are derived to calculate the transmission. By introducing a localization index we explore the localization properties of light in the aperiodic system. Around a particular center frequency (the midgap frequency of a periodic quarter-wavelength multilayer), the transmission is more sensitive to the optical thickness modulation.

All-optical wavelength conversion at bit rates above 10 Gb/s using semiconductor optical amplifiers

Abstract: This work assesses the prospects for high-speed all-optical wavelength conversion using the simple optical interaction with the gain in semiconductor optical amplifiers (SOAs) via the interband carrier recombination. Operation and design guidelines for conversion speeds above 10 Gb/s are described and the various tradeoffs are discussed. Experiments at bit rates up to 40 Gb/s are presented for both cross-gain modulation (XGM) and cross-phase modulation (XPM) in SOAs demonstrating the high-speed capability of these techniques.

Additive noise effect in digital phase detection

Abstract: The characteristic polynomials associated with the algorithms used in digital phase detection are used to investigate the effects of additive noise on phase measurements. First, it is shown that a loss factor η can be associated with any algorithm. This parameter describes the influence of the algorithm on the global signal-to-noise ratio (SNR). Second, the variance of the phase error is shown to depend mainly on the global SNR. The amplitude of a modulation of this variance at twice the signal frequency depends on a single parameter β. The material presented here extends previously published results, and as many as 19 algorithms are analyzed.

Fading-resistant modulation using several transmitter antennas

Abstract: This paper proposes a bandwidth-efficient fading-resistant transmission scheme which implements transmitter diversity using L antennas at the base station. When the antennas are spaced sufficiently far apart, the transmission from each antenna undergoes a different degree of fading. These transmissions are coordinated to mitigate the effects of Rayleigh fading, and the mobile receiver can recover the entire L-dimensional transmitted vector signal as long as the signal energy of at least one coordinate is large enough. L-dimensional fading-resistant signal constellations are generated by maximizing a figure of merit for the Rayleigh fading channel. This scheme offers a significant performance improvement over a conventional single-antenna binary phase-shift keying (BPSK) scheme when coding is ineffective due to slow fading.

Wavelength conversion for WDM communication systems using four-wave mixing in semiconductor optical amplifiers

Abstract: Four-wave mixing (FWM) in semiconductor optical amplifiers is an attractive mechanism for wavelength conversion in wavelength-division multiplexed (WDM) systems since it provides modulation format and bit rate transparency over wide tuning ranges. A series of systems experiments evaluating several aspects of the performance of these devices at bit rates of 2.5 and 10 Gb/s are presented. Included are single-channel conversion over 18 nm of shift at 10 Gb/s, multichannel conversion, and cascaded conversions. In addition time resolved spectral analysis of wavelength conversion is presented.

A dual-mode radio architecture

Abstract: This invention relates to a multi-mode radio transceiver. The transceiver is operable, in one embodiment, to communicate with digital and analogue modulation format cellular radio systems. The handset utilises a novel frequency plan and architecture to enable a minimum level of complexity for dual-mode operation. The frequency plan preferably uses two local oscillators 1LO, 2LO to generate all the required frequencies for both the digital and analogue modulation format transceivers, derived from a single reference crystal oscillator. A radio architecture is used to enable switchable dual-mode operation with maximum commonality of functional blocks to facilitate silicon integration.