Showing papers on "Modulation published in 1993"

Chaos shift keying: modulation and demodulation of a chaotic carrier using self-synchronizing Chua's circuits

Abstract: Describes a technique for transmitting digital information using a chaotic carrier. Each symbol to be transmitted is coded as an attractor in Chua's circuit. The symbols are detected at the receiver by cascaded self-synchronizing Chua's circuit subsystems. A proof of the synchronization effect is demonstrated using weak assumptions on the statistical behavior of the chaotic carrier to be transmitted. Furthermore a bound for the average time of synchronization is given. Results of both practical experimentation and simulations are presented which verify the approach. >

A new bandwidth efficient transmit antenna modulation diversity scheme for linear digital modulation

Abstract: A system is proposed and analyzed, which uses several transmit antennas to achieve diversity in a flat fading mobile radio environment. The signals at different antennas carry the same digital information, but have different modulation parameters (modulation diversity). In contrast to other proposals, no bandwidth expansion is required. Modulation diversity for quadrature amplitude modulation (QAM) type modulation is achieved by using different partial response type base pulses. Simulation results confirm the expected gain. >

Digital micro-mirror based image simulation system

Abstract: An image simulation system 20 for testing sensor systems 26 and for training image sensor personnel wherein synthetic image data is generated by a scene generator 21 and projected by an image projector 23. The image projector 23 uses a digital micromirror device array 27 to modulate the incident energy and create an image. Four modulation schemes are discussed including digital pulse-width modulation, phase contrast modulation, full complex modulation, and analog modulation. The digital pulse width modulation technique will typically require synchronizing the image sensor and the image projector. Phase contrast modulation, full complex modulation, and analog modulation do not require synchronizing the image projector 23 and the sensor system 26. Phase contrast modulation and full complex modulation have the capability to produce phase information within the image. The image simulation system 20 can produce high contrast images and is more flexible than prior art system.

Multiresolution broadcast for digital HDTV using joint source/channel coding

Abstract: The use of multiresolution (MR) joint source-channel coding in the context of digital terrestrial broadcasting of high-definition television (HDTV) is shown to be an efficient alternative to single-resolution techniques, which suffer from a sharp threshold effect in the fringes of the broadcast area. It is shown how matched multiresolution source and channel coding can provide a stepwise graceful degradation and improve the behavior, in terms of coverage and robustness of the transmission scheme, over systems not specifically designed for broadcast situations. The alternative available for multiresolution transmission through embedded modulation and error correction codes are examined. It is also shown how multiresolution trellis-coded modulation (TCM) can be used to increase coverage range. Coding results and simulations of noisy transmission are presented, and tradeoffs are discussed. >

Equalizer training algorithms for multicarrier modulation systems

Abstract: In a multicarrier data transmission system the length of a symbol is often limited by the maximum permissible delay of data from input to output. If the length of the impulse response of the channel is not negligible compared to the permitted symbol length, the impulse response can be shortened by passing the received signal through a time-domain equalizer before modulation. The best performance for a given computational complexity can then be achieved by appending to each block of samples of the transmit signal a cyclic prefix that has the same length as the shortened impulse response. Several algorithms for designing the time-domain equalizer, which use adaptation in the frequency domain and windowing in the time domain in order to minimize the mean squared error of the equalized response, are described. >

Analysis and synthesis of randomized modulation schemes for power converters

Abstract: After establishing that the proper objects of study for randomized modulation of converters are the power spectra of signals, we classify such modulation schemes and present associated spectral formulas, several of which are new. We also discuss numerical (Monte Carlo) verification issues for power spectral formulas. A general spectral formula for stationary randomized modulation schemes is presented, and specialized to several modulation schemes of practical interest for DC/DC converters. Analytical results are then given for block-stationary randomized modulation schemes that are suitable for inverter operation. In the process, we present results for several modulation schemes that have been reported in the literature without analytical explanations. Experimental verifications of some of our analytical results are presented. We formulate narrow-band and wide-band synthesis problems in randomized modulation, and solve them numerically. Our results suggest that randomized modulation is very effective in satisfying narrow-band power constraints, but has limited effectiveness in meeting wide-band constraints. >

All-Optical Switch with Switch-Off Time Unrestricted by Carrier Lifetime

Abstract: We propose a symmetric Mach-Zehnder-type all-optical switch which is based on the nonlinear refractive index change induced in semiconductors. Unlike most all-optical switches, the switch-off time, as well as the switch-on time, of this novel device is not limited by the usually slow carrier lifetime, allowing a very fast switching speed. Its switching characteristics are theoretically examined under various conditions. It is shown that the device offers a nearly square modulation characteristic that is suitable for most switching applications.

Navigation receiver with coupled signal-tracking channels

Abstract: The navigation receiver with coupled-tracking channels is intended for use in radio navigation systems based on trilateration wherein the times of arrival of radio signals transmitted by a plurality of ground- or space-based terminals are measured by a user terminal and utilized by the user terminal in calculating its position and orientation. The coupled-tracking navigation receiver periodically measures carrier phase, carrier frequency, modulation phase, and carrier amplitude for all of the signals arriving at the receiving ports of the receiver and periodically estimates the present values of carrier phase, carrier frequency, and modulation phase for all of the received signals, the estimating process utilizing for each parameter estimate the parameter measurements for a plurality of the received signals properly combined in a statistically appropriate manner by taking into account the relative geometry of the line-of-sight paths, receiver clock time dynamics, and dynamics and motion constraints of the receiver platform, thereby obtaining better performance under poor signal reception conditions and more accurate estimates of carrier phase, carrier frequency, and modulation phase for each of the received signals than independent measurements alone could provide. It follows that these more accurate estimates of the basic signal parameters lead to more accurate estimates of platform position and attitude and the rates of change of these quantities.

Multi purpose digital signal regenerative processing apparatus

Abstract: A multi purpose digital signal regenerative processing apparatus (1) has three modulation sub-systems (2, 3 and 4) in parallel. Each sub-system is selectively selectable to enable a plurality of users to access, independently of one another, a sub-band of a frequency band in individually selectable access modes and modulation formats. The first sub-system (1) is operable in TDM format, the second (3) is operable in FDM or OFDM format and the third sub-system (4) is operable in CDM format.

Method and apparatus for digital signal transmission using orthogonal frequency division multiplexing

Abstract: A digital signal transmission using OFDM modulation scheme in which the valid transmission data can be reproduced without requiring a recovery of the carriers at a receiver side. On a transmitter side, the transmission data sequence in which predetermined reference data for each carrier are placed among valid transmission data is modulated according to an orthogonal frequency division multiplexing (OFDM) modulation scheme using a plurality of carriers and obtained OFDM transmission signals are transmitted. On a receiver side, the received OFDM transmission signals are demodulated to obtain received data sequence containing valid received data and received reference data, and the valid transmission data are estimated from the received data sequence according to the valid received data, the received reference data, and the predetermined reference data for each carrier.

Utilizing HVDC to damp power oscillations

Abstract: Damping of slow oscillations with active and reactive power modulation of high-voltage direct current (HVDC)-links is analyzed with the aim of gaining a physical insight into the problem. The analysis shows that active power modulation is efficient when applied a short mass-scaled electrical distance from one of the swinging machines, and reactive power modulation is most efficient when a well-defined power flow direction exists and the modulation is made at a point close to the electrical midpoint between the swinging machines. It is shown that the intuitively appealing feedback signal frequency and derivative of the voltage are appropriate for active and reactive power modulation. The impact of the constraints imposed by the HVDC equations is analyzed, and it is determined when the implicit reactive power modulation resulting from constant gamma control may be detrimental for the damping. >

Optical frequency comb generator using phase modulation in amplified circulating loop

Abstract: A method to generate a comb of precisely spaced optical frequencies over a terahertz span is presented. This scheme uses a sinusoidally driven phase modulator and an optical amplifier placed within an optical fiber loop, so that the modulation is enhanced by multiple passes through the loop. By maintaining the loop round-trip gain slightly below unity, a comb of tens to hundreds of frequencies can be generated. If the loop input is derived from a laser locked to an absolute frequency reference, then each of the output frequencies has an absolute accuracy approaching that of the input. >

Method and apparatus for transmission and reception of a digital television signal using multicarrier modulation

Abstract: A method and apparatus for modulating and demodulating an MCM television signal is described which is particularly useful in proposed "simulcast" HDTV terrestrial broadcasting. The MCM spectrum of the television signal is shaped using weighting coefficients which are derived from either an idealized NTSC signal or an actual NTSC co-channel signal. These coefficients are used to shape the respective MCM carriers to provide an energy distribution in the MCM signal which provides greater degree of robustness with a minimum degree of co-channel interference to and from an NTSC co-channel signal. The instant invention further takes advantage of the interference characteristics of composite television signals described above, to position the placement of the MCM carriers in frequency, to minimize interference with an NTSC co-channel signal. Several methods of deriving the weighting coefficients are described including an adaptive approach whereby the characteristics of the interfering NTSC transmission are received and the instantaneous NTSC spectrum calculated therefrom and weighting coefficients assigned accordingly. These coefficients can be transmitted to a receiver to update its coefficient table.

System for transmission of digital data using orthogonal frequency division multiplexing

Abstract: A system is disclosed which provides a significantly enhanced transmission rate for digital data transmitted over a channel, while also providing immunity to signal interference caused by multipath reception. One embodiment of the system transmits a signal containing digital data in the vertical blanking interval of a television signal. Before being transmitted, the digital data is modulated by a process called orthogonal frequency division multiplexing, or OFDM. A guard interval is optionally prefixed to the front end of the data signal to provide additional immunity to multipath interference. A further feature of the present system is the optional inclusion in the transmitted signal of an error correcting code which allows detection and correction of multiple sequential data transmission errors.

Large nonlinear phase modulation in quasi-phase-matched KTP waveguides as a result of cascaded second-order processes

Abstract: Nonlinear spectral modulation and broadening have been observed in quasi-phase-matched KTP waveguides near 850 nm, indicative of self-phase modulation that is due to cascaded second-order processes. Numerical beam-propagation simulations indicate nonlinear peak phase shifts larger than π for 600 W of peak power in a 2.8-mm-long guide.

Differential detection of pi /4-shifted-DQPSK for digital cellular radio

Abstract: The detection of pi /4-shifted-DQPSK modulation using a tangent-type differential detector with an integrated symbol timing and carrier frequency offset correction algorithm is discussed. pi /4-shifted-DQPSK modulation has been proposed for use in a high-capacity, TDMA-based digital cellular system being developed in the US; differential detection could potentially allow the production of low-complexity mobile units. Results obtained using the proposed IS-54 TDMA frame structure for base to mobile transmissions are presented. Theoretical and simulation bit-error-rate (BER) results are presented for static and Rayleigh fading channels. BER results are provided as a function of E/sub b//N/sub 0 /and C/I, where the interferer is a second pi /4-shifted-DQPSK signal. Additional results are provided which show the BER sensitivity to Doppler frequency shifts, time delay spread, and carrier frequency offsets. >

A fully digital feedforward MSK demodulator with joint frequency offset and symbol timing estimation for burst mode mobile radio

Abstract: A strictly feedforward demodulator structure for minimum shift keying (MSK) modulation with joint nondata-aided symbol clock and frequency offset estimation is presented. Due to its feedforward operation, clock synchronization and frequency offset compensation are hang-up free, and the demodulator is well suited for a digital implementation. The sampled baseband signal is passed through a nonlinearity and smoothed by a digital filter. The magnitude of the filter output directly drives the clock recovery process. The phase of the smoothed signal is an estimate of the carrier frequency offset and is used for offset compensation. Following synchronization, the signal is demodulated by differentially coherent detection. The performance of the demodulator is assessed for the AWGN and the Rayleigh flat and frequency-selective fading channel by computer simulations. >

Threshold modulation in error diffusion

Abstract: A theoretical analysis of threshold modulation in error diffusion is given. It is shown that spatial modulation of the threshold is mathematically identical to processing an equivalent input image with the standard error diffusion algorithm. The equivalent input is the sum of the original image with a high-pass-filtered version of the threshold spatial modulation. The filter is a function only of the weights used to distribute the errors. This result can be used to explain the several published observed effects of threshold modulation, such as edge enhancement and the effects of adding noise to the threshold.

Maximum dynamic range operation of a microwave external modulation fiber-optic link

Abstract: We fully analyze the analog performance of an external modulation fiber-optic link. We express relevant figures of merit-including gain, noise figure, third-order intermodulation distortion, AM compression, and dynamic range-in terms of the microwave scattering matrices of the modulator and detector circuits, and we predict the modulator bias condition promoting optimum link performance. Our predictions match the measured gain, noise figure, and dynamic range of an experimental 870-930 MHz external modulation fiber-optic link. Maximum spurious-free dynamic range-77 dB.MHz/sup 2/3/ (117 db.Hz/sup 2/3/)-occurs when the modulator is biased at its halfwave voltage, where the optical throughput is nearly pinched off. >

Cascaded optical modulation system with high linearity

Abstract: An optical modulation system having cascade-coupled electro-optic modulator stages in either dual tandem (figs. 9 and 15) or split tandem (figs. 12 and 13) configurations. An electrical splitter (80) derives multiple electrical drives (79, 99) for the multiple stages (61, 63) from a single modulating input signal (129). The multiple drive signals are linearly related in magnitude and preferably induce simultaneous antiphase (180° out-of-phase) optical modulation in the tandem stages. While a double Mach-Zehnder cascade configuration could be used, at least one modulator stage might instead be a balanced-bridge interferometer-type (BBI) modulator having at least one directional coupler (95, 115). At least one directional coupler in such a configuration may be a Δ β coupler. Application of bias voltages to the interferometer sections (77, 97) and to coupler sections (95, 115) by means of a parametric feedback loop (121-137) is done in order to simultaneously enhance the linear modulation coefficient, minimize odd order distortions and null the even order distortions that are associated with biased Δ β couplers.

Receiver adaptively operable for multiple signal transmission systems

Abstract: A receiver for selectively receiving high frequency signals from analog modulated signals and digital modulated signals. The receiver has an intermediate frequency signal circuit for selecting a desired channel of the high frequency signals and for frequency-converting the high frequency signal of the selected channel into an intermediate frequency signal, a demodulator for demodulating the intermediate frequency signal, which is adapted to be capable of demodulating modulated signals in a variety of modulation systems, the demodulator including at least a digital section, and a controller for controlling the demodulator to be able to discriminate between the analog modulated signals and the digital modulated signals, based on a demodulated signal output from the digital section of the demodulator and to be switched into a demodulation mode suited for modulation system of the selected channel of the high frequency signals.

Coherent detection with reference-symbol based channel estimation for direct sequence CDMA uplink communications

Abstract: A new coding/modulation arrangement for up-link direct-sequence code division multiple access (DS-CDMA) communication, which employs coherent detection with reference-symbol based channel estimation, is presented. It is shown that the required E/sub b//N/sub O/ for this scheme is about 2 dB to 2.5 dB lower than non-coherent detection of Walsh coding with bit interleaving and about 1 dB to 1.3 dB lower than noncoherent detection with Walsh symbol interleaving over the entire range of practical vehicle speeds. A frequency domain analysis of this scheme is given.

Method and apparatus for multiplexed oversampled analog to digital modulation

Abstract: Apparatus for time multiplexed oversampled analog to digital modulation (700) is provided. Embodiments generally include a plurality of energy collection elements (702a and 702m) coupled to individual pixel processors (704a and 704m) preferably mounted proximate to each energy collection element. Each pixel processor shares a commons block of conversion logic (720, 722, 724) to form a plurality of integration loops to process the signal generated by each energy collection element. Specific embodiments are shown using CCD, CID, FET and charge well technologies.

Optically readable record carrier for recording information, method and apparatus for manufacturing such, apparatus for recording and reading information on a such a record carrier

Abstract: A record carrier on which information may be optically recorded and/or read, having a disc-shaped substrate with a spiral or concentric pattern of preformed tracks thereon and a radiation-sensitive layer extending over such track pattern. The tracks are in the form of ridges of substantially constant width and having a periodic radial wobble of a substantially constant mean frequency, which frequency is modulated by a position-information signal identifying the relative positions of the tracks in the track pattern. Apparatus for forming such a track pattern includes means for modulating the radial track wobble in accordance with the position-information signal. Apparatus for reading an information signal recorded on such a record carrier includes an FM demodulator for recovering the position-information signal from variations in the reflected scanning beam produced by the track modulation, and which also recovers from such variations a clock signal corresponding to the mean frequency of such modulation and which is used to control the scanning velocity. Apparatus for recording an information signal on such a record carrier includes an FM demodulator for recovering the position-information signal from variations in the radiation reflected from the tracks during recording.

Soliton transmission control in time and frequency domains

Abstract: Soliton transmission control techniques in both the time and frequency domains designed to enable ultra-long-distance soliton transmission are described in detail. Soliton transmission control in the time domain, which can be realized by synchronous modulation, is a retiming technique which removes jitter and nonlinear interaction between adjacent solitons. In addition, a transfer function reduces noise and the noise power eventually converges to a low level for any transmission distance. Soliton transmission control in the frequency domain, which can be realized with a bandpass optical filter, stabilizes the soliton pulse. A million-kilometer transmission experiment confirms the usefulness of these techniques. >

Impulse noise mitigation strategies for multicarrier modulation

Abstract: Short time-duration and high magnitude noise, taking on the form of time-domain impulse noise over copper twisted-pairs or multipath fading in wireless communication, can potentially be the limiting impairment on performance in many high-speed data transmission applications. Coding techniques are presented, designed specifically for multicarrier modulated systems to mitigate the effects of such impairment. Several coding combinations, involving soft error protection, in addition to hard forward error correction, are considered. The techniques can be applied with minor variation to a number of possible applications employing multicarrier modulation, including wireless digital audio broadcasting (DAB) systems and high-speed data/video transmission over coaxial cables. >

Multicarrier modem for digital HDTV terrestrial broadcasting

Abstract: A digital modulation system using orthogonal frequency division and multiplexing (OFDM) is addressed in this paper. Such a system presents the advantage of coping with echoes more easily than classical single-carrier modems, thanks to the insertion of a guard interval between two symbols. The signal equalization is then achieved in the frequency domain. This OFDM modem is improved by using dual polarizations. In this configuration, it can convey a 70 Mbits/s (HDTV) bit stream in an 8 MHz UHF channel. Some experimental results relate field trials carried out in several countries with such equipment.

About The Effects Of Different Modulation Index On The Iron Losses In Soft Magnetic Materials Supplied By Pwm Inverter

Abstract: The increase in iron-loss in soft magnetic materials due to the modulation depth in pulse width modulation (PWM) inverters is analyzed. In particular, the specific loss variations with different modulation indexes are measured, both in wound cores realized with high quality grain oriented magnetic material, and in induction motors. >

Joint source and channel coding using a non-linear receiver

Abstract: The joint optimization of the source and channel coders in a system consisting of a vector quantizer (VQ) whose output indices are mapped directly into points in the modulation signal space is considered. A decoder based on a nonlinear estimator is used to reconstruct the source signal. An iterative algorithm is introduced which jointly optimizes the VQ and the modulation signal set using as optimality criterion the minimum mean-square error (MSE) between the original and the reconstructed signals. It is shown that a jointly optimized system based on average channel characteristics significantly outperforms (by up to 5 dB) a reference system based on a VQ designed for the given source and a standard quadrature amplitude modulation (QAM) modulation signal set. >