Showing papers on "Modulation published in 1991"

Effects of HPA-Nonlinearity on a 4-DPSK/OFDM-Signal for a Digital Sound Broadcasting System.

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) in conjunction with a 4-DPSK modulation format has been proposed for the future digital audio broadcasting system (DAB), that should provide compact disk sound quality in portable, vehicular and fixed receivers. With properly chosen parameters, this system should be appropriate for both terrestrial and satellite transmission. In this paper the influence of the nonlinear distortions introduced by the high power amplifier (HPA) of the transmitter is examined. In particular, the degradation in power efficiency due to intermodulation effects and backoff operating, as well as spectral degradations are investigated.It is shown for three different kinds of limiting amplifier models, that even with an output backoff (OBO) in the region of 5-6 dB, the degradation of, e.g., a 512-carrier 4-DPSK/OFDM system relative to the linear case is below 1.7 dB, while the regenerated sidelobes of the transmitted spectrum are kept below -20 dB.

Telemetry format for implanted medical device

Abstract: A method and apparatus are disclosed for telemetering both analog and digital data from an implantable medical device to an external receiver, such as between an implanted cardiac pacer and its external programming equipment. Analog data is first converted to digital format by an analog-to-digital converter, such that the transmission is digital data. A damped carrier at 175 kilohertz is pulse position modulated by the data. The modulation scheme defines a frame of slightly less than 2 milliseconds. The frame is divided into 64 individual time periods using a crystal clock. The data, along with synchronization and identification codes, are positioned into predefined ranges within each frame as measured by the individual time periods. The data is uniquely identified by the position of a burst of the carrier within the predetermined range. This modulation scheme enables necessary data to be transmitted at sufficiently high rates with reduced power requirements thereby conserving the internal battery of the implantable device. This modulation scheme provides flexibility of use, for example, with complex medical devices where transmission of increased volumes of data is desirable, such as cardiac devices having dual-chamber or multisensor capabilities, and for controlling particular conditions, such as tachyarrhythmia.

Spread spectrum digital data transmission over TV video

Abstract: A co-channel communication system allows transmission of one or more data signals in an active or visible portion of a video raster in a manner that is imperceptible to a viewer. More particularly, the data signal is transmitted over a preselected active video lines of a video raster. In order to reduce the perceptibility of the data signal, the video lines over which the data signal is transmitted is varied according to a random sequence. In an alternate embodiment, the data is also modulated at relatively low modulation levels, for example, by converting the data signal to a spread spectrum signal.

Contactless, inductive data transmission system

Abstract: A contactless inductive data transmission system provides bidirectional signal transfer between a sending-and-receiving station and one or more batteryless transponders. A high-frequency signal from the sending-and-receiving station is pulse width modulated for data transmission to a transponder and provides a system clock, which is extracted in both the sending-and-receiving station and in the transponder for synchronization, and provides the electrical power for operation of the transponder. The pulse width modulated signal is demodulated in the transponder for triggering a response wherein a modulating signal is applied by load modulation to the pulse width modulated high-frequency signal to form an information-carrying load modulated high-frequency signal, which is demodulated in the sending-and-receiving station.

Effects of carrier transport on high‐speed quantum well lasers

Abstract: We present a model for the dynamic response of quantum well lasers which shows that the carrier transport across the separate confinement heterostructure region and the barriers can be critical in determining the modulation bandwidth. We also show that, depending on the particular quantum well laser structure, a large part of the experimentally measured reduction in modulation bandwidth is due to transport factors.

Method and apparatus for the modulation 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.

Modulation and coding for information storage

Abstract: Many of the types of modulation codes designed for use in storage devices using magnetic recording are discussed. The codes are intended to minimize the negative effects of intersymbol interference. The channel model is first presented. The peak detection systems used in most commercial disk drives are described, as are the run length-limited (d,k) codes they use. Recently introduced recording channel technology based on sampling detection-partial-response (or PRML) is then considered. Several examples are given to illustrate that the introduction of partial response equalization, sampling detection, and digital signal processing has set the stage for the invention and application of advanced modulation and coding techniques in future storage products. >

A 20-GHz electro-optic polymer Mach-Zehnder modulator

Abstract: An electro-optic (EO) polymer Mach-Zehnder modulator was built with the special feature so that each arm could be modulated independently with a separate 50 Ω microstrip electrode. The design permitted modulation by separate synthesizers at frequencies above the bandwidth of our available detectors. Using this two-tone modulation technique the device was driven at frequencies up to 20 GHz, which is the highest modulation frequency yet reported in an organic EO polymer-based device.

Effects of fiber nonlinearities and amplifier spacing on ultra-long distance transmission

Abstract: It is shown that it should be possible to send error-free signals at a 2.5-Gb rate (or higher) over distances of at least 9000 km using an amplitude shift keying (ASK) soliton modulation system. To accomplish this, the amplifiers must be kept close enough that their power gain is less than 10 dB. (It is noted that timing jitter and other noise effects measured in recent soliton transmission experiments carried out at low D and with amplifier spacing of 25 km are in close accord with predictions of this work). Frequency division multiplexing of several channels over the same fiber should also be possible, as solitons of different frequencies interact very weakly, provided the distance over which they pass through one another is large compared to the amplifier spacing. >

Portable field-programmable detection microchip

Abstract: A read/write device includes a transmitter for producing an RF signal and a modulator coupled to said transmitter for modulating the RF signal and, finally a data receiver for receiving RF data signals from a portable microchip. The microchip includes a resonant circuit tuned to the RF frequency of the read/write transmitter and a receiver that is coupled to the resonant circuit for detecting the RF signal. There is also provided a charging capacitor capable of storing the electrical energy from the RF signal so that the microchip can be powered during pulse pauses of the RF signal. The microchip includes a memory circuit for storing the identification code of the microchip, and a code generator that is coupled to the memory circuit for generating an RF signal that is modulated with the identification data. A switching element that couples the resonant circuit to the code generator de-tunes the resonant circuit when the identification data is transmitted back to the read/write device. The same resonant circuit also serves to field program the memory circuit of the microchip by receiving pulse pause modulation signals (PPM) of the RF carrier signal thus allowing the identification code of the microchip to be altered by the read/write device.

Device for the transmission of digital data with at least two levels of protection and corresponding reception device

Abstract: A device for the transmission of digital data with at least two levels of protection, of the type providing for the distribution of the data to be transmitted in the form of digital elements in the time-frequency space and the transmission of symbols each formed by a multiplex of N orthogonal carriers modulated by a set of the digital elements, and transmitted simultaneously, the device including channel .[.encoding.]. .Iadd.encodes .Iaddend.means comprising at least two types of modulation and/or at least two encoding efficiency levels. This enables to optimize the use of the transmission channel by assigning differentiated transmission techniques to portions of data of a same digital train as a function of the different levels of protection sought, against transmission errors.

Spread spectrum communications system

Abstract: A spread spectrum communication system for direct sequence transmission of digital information having a modulation format which is particularly suitable for indoor communication within residential, office and industrial structures. The modulation format combines BPSK or MSK spreading with FM carrier modulation by data bits and a carrier frequency shift whose magnitude is related to both a chip rate and a spreading sequence length. The carrier, chip clock and data clock are all synchronous and the sequence length is an integral submultiple of the bit length. The system reduces the frequency error between the transmitter chip clock and the receiver chip clock to permit the elimination of a code phase tracking loop in the receiver to reduce the receiver complexity. The receiver has an extended dynamic range which makes possible the reception of very strong signal without an automatic gain control loop (AGC) as well as reducing the time needed for code phase acquisition. The transmission system is highly resistant to CW jamming and short distance multipath effects.

OFDM for data communication over mobile radio FM channels. I. Analysis and experimental results

Abstract: The performance of OFDM/FM modulation for digital communication over Rayleigh-fading mobile radio channels is described. The use of orthogonal frequency division multiplexing (OFDM) over mobile radio channels was proposed by Cimini (1985). OFDM transmits blocks of bits in parallel and reduces the bit error rate (BER) by averaging the effects of fading over the bits in the block. OFDM/FM is a modulation technique in which the OFDM baseband signal is used to modulate an FM transmitter. OFDM/FM can be implemented simply and inexpensively by retrofitting existing FM communication systems. Expressions are derived for the BER and word error rate (WER) within a block when each subchannel is QAM-modulated. Several numerical methods are developed to evaluate the overall BER and WER. An experimental OFDM/FM system was implemented and tested using unmodified VHF FM radio equipment and a fading channel simulator. The BER and WER results obtained from the hardware measurements agree closely with the numerical results. >

Modulation of Turbulence by a Dispersed Phase

Abstract: The results of an earlier investigation that demonstrated the significance of the particle diameter/fluid length scale ratio in determining whether or not the addition of a dispersed phase would cause an increase or decrease in the carrier phase turbulent intensity are extended to radial locations other than the centerline.

Signal sets matched to groups

Abstract: Recently, linear codes over Z/sub M/ (the ring of integers mod M) have been presented that are matched to M-ary phase modulation. The general problem of matching signal sets to generalized linear algebraic codes is addressed based on these codes. A definition is given for the notion of matching. It is shown that any signal set in N-dimensional Euclidean space that is matched to an abstract group is essentially what D. Slepian (1968) called a group code for the Gaussian channel. If the group is commutative, this further implies that any such signal set is equivalent to coded phase modulation with linear codes over Z/sub M/. Some further results on such signal sets are presented, and the signal sets matched to noncommutative groups and the linear codes over such groups are discussed. >

Mode locking in solitary lasers

Abstract: We present an analysis of passively mode-locked lasers in which pulse formation is dominated by the interplay between self-phase modulation and negative dispersion in separate cavity elements. Steady-state pulse parameters and stability issues are discussed. Stability in these solitary systems relies on some passive amplitude modulation, and the ultimate system performance is found to depend sensitively on the magnitude of amplitude modulation relative to that of phase modulation.

Transmission and reception in a hostile interference environment

Abstract: A low power OFDM signal may be transmitted in an environment where it is subject to interference from other transmissions, e.g. broadcast television services. In a receiver interference is reduced by ignoring information modulating OFDM carriers at the frequencies corresponding to the carriers of the interfering transmissions; adjacent channel interference is reduced by ignoring data on OFDM carriers at the band edges and interference from third order intermodulation products is reduced by the ignoring OFDM carriers affected. Image channel interference is reduced by using an intermediate frequency for a first mixing process in the receiver such that the image channel interference affects OFDM carriers at frequencies which are already being ignored by the receiver. Preferably no data is modulated onto OFDM carriers which are to be ignored by the receiver. Preferably the modulation of the OFDM carriers is arranged so as to produce a real baseband representation of the OFDM signal.

Multi-frequency differentially encoded digital communication for high data rate transmission through unequalized channels

Abstract: A differentially encoded digital signal waveform is generated as a discrete time representation of a desired analog signal utilizing multi-frequency modulation techniques. The computational capability of present day, industry-standard microcomputers (57) equipped with a floating point array processor or digital signal processor chip is utilized to perform digital frequency encoding and compute both discrete Fourier transforms (31) and inverse discrete Fourier transforms (25) to provide a transmitter (51) and receiver (53) system utilizing suitably programmed microcomputers coupled by a communications channel.

Method and apparatus for the correlation of sample bits of spread spectrum radio signals

Abstract: A spread spectrum receiver correlator for a 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

An electrooptic intensity modulator with improved linearity

Abstract: A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths. >

High-mobility modulation-doped SiGe-channel p-MOSFETs

Abstract: A novel subsurface SiGe-channel p-MOSFET is demonstrated in which modulation doping is used to control the threshold voltage without degrading the channel mobility. A novel device design consisting of a graded SiGe channel, an n/sup +/ polysilicon gate, and p/sup +/ modulation doping is used. A boron-doped layer is located underneath the graded and undoped SiGe channel to minimize process sensitivity and maximize transconductance. Low-field hole mobilities of 220 cm/sup 2//V-s at 300 K and 980 cm/sup 2//V-s at 82 K were achieved in functional submicrometer p-MOSFETs. >

Use of leading-edge modulation to transform boost and flyback converters into minimum-phase-zero systems

Abstract: In leading edge modulation, the pulse width modulated (PWM) signal is turned off at the clock signal and turned on when the error signal crosses the ramp waveform. It is shown that the positive zero in the power stage transfer function of boost and flyback regulators can be shifted into the left-half-plane under suitable conditions. These conditions are as follows: (1) leading edge modulation must be used in the pulse width modulator; (2) the feedback compensation must not average the capacitor EST-generated output voltage switching ripple; and (3) appropriate power stage parameter values are necessary. The design procedure for shifting the positive zero into the left-half-plane is presented. Experimental verification is provided. >

Apparatus and method for the compression and transmission of multiformat data

Abstract: Video data is compressed, at a first site, by a transform scaling data compressor (12), and carrier signals are modulated with audio and digital data by a delta modulation data modulator (14) and a delta-sigma modulation data modulator (16) respectively. Their output signals are combined by a multichannel data compressor (18) and transmitted to a second site, where the procedures are essentially reversed to effectively regenerate the data as originally formatted.

Advances in constant envelope coded modulation

Abstract: An overview is given of recent advances in constant envelope combined coding and modulation. Modulation codes and trellises are discussed, and major classes of trellis modulation codes are described. Continuous phase modulation is defined, and concatenations of phase codes and convolutional codes are examined. The ultimate capability of phase modulation coding and the size of CPM trellis codes are addressed. Implementation issues are considered. >

Fast adaptive equalizers for narrow-band TDMA mobile radio

Abstract: It is pointed out that the future European cellular digital mobile radio system in the 900 MHz band adopts a narrowband time division multiple access (TDMA) scheme with Gaussian minimum-shift keying (GMSK) modulation and burst type transmission. Consequently, very fast adaptation methods are necessary to cope with the time- and frequency-selective distortions produced by Rayleigh and multipath fading. The authors examine a few theoretical aspects of the application of recursive least squares (RLS) adaptation algorithms to the narrowband TDMA mobile radio system and give the relevant performance results for the fast Kalman algorithm, which turns out to be suitable for the considered application. In particular, signature curves, bit error rate, speed of convergence, steady-state behavior, numerical stability, required accuracy, and hardware complexity are discussed. Linear transversal and nonlinear decision-feedback equalizers are considered. >

Linearization of electro-optic modulators by a cascade coupling of phase-modulating electrodes

Abstract: Theoretical predictions and experimental results on two slightly different kinds of linearized optical modulators for use in wideband analog transmission is presented. Both modulators are based on a cascade coupling of phase-modulated parallel wave guide sections. In both cases, 95 dB suppression of the 3rd harmonic of a single test tone with an optical modulation depth of 20% is theoretically obtained. Some initial experimental results are presented for both modulators.

Photoplethysmographics using component-amplitude division multiplexing

Abstract: A plurality of carrier signals, distinguishable by amplitudes of signal components (e.g., frequency components), are respectively applied to a plurality of energy emitters (e.g., infrared and red light emitters). A detector receives the sum of the energy after modulation at each emitter wavelength, e.g. by blood tissue of a patient. An output of the detector is then demultiplexed, whereby a component of modulation at each emitter wavelength may be determined. The carrier signals may comprise time-varying periodic signals with identical frequency and frequency components, such as mixtures of identical sets of pure sine waves. When the number of signal components exceeds the number of emitter wavelengths, sufficient information is provided during demultiplexing to detect and correct errors introduced by ambient light sources and other interference.

Channel equalisation in particular for fading channels

Abstract: A digital radio system is described in which data symbols are transmitted over a radio channel using multi-level modulation. A receiver receives the multi-level modulation signal and a first symbol estimator gives a first estimate of a symbol represented by the received multi-level modulation signal and a second estimator gives a second estimate of a symbol represented by said signal; the output of the first estimator is provided when the first and second ouputs are the same or have a predetermined relationship and an ouput based on the output of the second estimator is provided otherwise.

Full-duplex, sub-band spread spectrum communications system

Abstract: An improved spread spectrum communications system is provided for establishing full-duplex voice/data radio communications within a single specified FCC ISM band. Spectrum spreading is performed relative to a plurality of sub-bands respectively defined about the lower and upper band-edges of the prescribed ISM band and having spectral roll-off characteristics which satisfy FCC requirements for radio frequency radiation outside the ISM bands on the corresponding band-edges thereof. Full-duplex operation is implemented by the use of digital MSK modulation and associated filtering in order to conserve available bandwidth and accommodate the filtered, modulated signal within the sub-bands defined in the prescribed ISM frequency band, and the system is capable of being easily interfaced to related digital communications services.