Showing papers on "Modulation published in 1999"

On the performance of adaptive modulation in cellular systems

Abstract: Adaptive modulation techniques have the potential to substantially increase the spectrum efficiency and to provide different levels of service to users, both of which are considered important for third-generation cellular systems. In this work, we propose a general framework to quantify the potential gains of such techniques. Specifically, we study the throughput performance gain that may be achieved by combining adaptive modulation and power control. Our results show that: (1) using adaptive modulation even without any power control provides a significant throughput advantage over using signal-to-interference-plus-noise ratio (SINR) balancing power control and (2) combining adaptive modulation and a suitable power control scheme leads to a significantly higher throughput as compared to no power control or using SINR-balancing power control. The first observation is especially important from an implementation point of view. Adjusting the modulation level without changing the transmission power requires far fewer measurements and feedback as compared to the SINR-balancing power control or the optimal power control. Hence, it is significantly easier to implement. Although presented in the context of adaptive modulation, the results also apply to other variable rate transmission techniques, e.g., rate adaptive coding schemes, coded modulation schemes, etc. This work provides valuable insight into the performance of variable rate transmission techniques in multi-user environments.

Differential space-time modulation

Abstract: We consider the design of space-time modulation techniques that do not require channel estimates at the transmitter or receiver. We propose a general approach to differential modulation for multiple transmit antennas based on group codes. This approach can be applied to any number of transmit antennas and any signal constellation. We also derive low-complexity differential receivers, error bounds, and modulator design criteria, which we use to design optimal modulators for two transmit antennas.

Intra-channel cross-phase modulation and four-wave mixing in high-speed TDM systems

Abstract: A comprehensive numerical and experimental study of 40 Gbit/s RZ transmission is presented which reveals two new forms of nonlinear interactions that limit the speed of high-speed systems. Both limitations originate from nonlinear interactions among neighbouring bits. The first interaction involves cross-phase modulation and leads to timing fluctuations while the second interaction originates from four-wave mixing and leads to the creation of shadow pulses.

Modulation of receptive field properties of thalamic somatosensory neurons by the depth of anesthesia.

Abstract: Modulation of receptive field properties of thalamic somatosensory neurons by the depth of anesthesia. The dominant frequency of electrocorticographic (ECoG) recordings was used to determine the de...

Trellis-coded modulation with bit interleaving and iterative decoding

Abstract: This paper considers bit-interleaved coded modulation (BICM) for bandwidth-efficient transmission using software radios. A simple iterative decoding (ID) method with hard-decision feedback is suggested to achieve better performance. The paper shows that convolutional codes with good Hamming-distance property can provide both high diversity order and large free Euclidean distance for BICM-ID. The method offers a common framework for coded modulation over channels with a variety of fading statistics. In addition, BICM-ID allows an efficient combination of punctured convolutional codes and multiphase/level modulation, and therefore provides a simple mechanism for variable-rate transmission.

Coherent zone-folded longitudinal acoustic phonons in semiconductor superlattices : excitation and detection

Abstract: Coherent zone-folded acoustic phonons are excited in GaAsyAlAs superlattices by femtosecond laser pulses via resonant impulsive stimulated Raman scattering in both forward and backward scattering directions. The relative amplitudes of three distinct modes of first and second backfolded order match well with scattering intensities calculated within an elastic continuum model. The detection of the coherent acoustic modes is based on the modulation of the interband transitions via the acoustic deformation potential and exhibits a strong enhancement at interband transitions. [S0031-9007(98)08288-X]

Characterization of spectral regrowth in microwave amplifiers based on the nonlinear transformation of a complex Gaussian process

Abstract: A statistical technique is presented for the characterization of spectral regrowth at the output of a nonlinear amplifier driven by a digitally modulated carrier in a digital radio system. The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the quadrature input signal transformed by a behavioral model of the amplifier. The amplifier model, a baseband equivalent representation, is derived from a complex radio-frequency envelope model, which itself is developed from readily available measured or simulated amplitude modulation-amplitude modulation and amplitude modulation-phase modulation data. The technique is used in evaluating the spectral regrowth for a CDMA signal.

Characterization of Spectral Regrowth in Microwave Amplifiers Based on the Nonlinear Transformation of a

Abstract: A statistical technique is presented for the character- ization of spectral regrowth at the output of a nonlinear amplifier driven by a digitally modulated carrier in a digital radio system. The technique yields an analytical expression for the autocorrela- tion function of the output signal as a function of the statistics of the quadrature input signal transformed by a behavioral model of the amplifier. The amplifier model, a baseband equivalent rep- resentation, is derived from a complex radio-frequency envelope model, which itself is developed from readily available measured or simulated amplitude modulation-amplitude modulation and amplitude modulation-phase modulation data. The technique is used in evaluating the spectral regrowth for a CDMA signal.

Tissue modulation process for quantitative noninvasive in vivo spectroscopic analysis of tissues

Abstract: Methods are provided for noninvasively measuring blood volume and analyte concentration and for obtaining spectroscopic information relating to immobile tissues, such as skin. One method is for determining concentration of an analyte, such as glucose, in blood of a subject. The method comprises irradiating a region of tissue, such as a fingertip, of the subject with a light source; collecting fluorescence spectra emitted by the region of tissue, the quantity of fluorescence spectra being indicative of blood volume; and collecting Raman spectra emitted by the region of tissue at a wavelength range that corresponds to the analyte. The method further comprises dividing the collected Raman spectra by the collected fluorescence spectra to obtain a number proportional to the concentration of analyte per unit blood volume. The method can further comprise determining the integral of net collected spectra, net collected spectra being a difference between spectra collected while the region of tissue is in a blood-replete state and spectra collected while the region of tissue is in a blood-depleted state. The method can further comprise enhancing the spectra collected by performing adjacent averaging smoothing operations. Blood volume in a region of tissue for spectroscopic measurement can be modulated by applying an ultrasonic transducer to the region of tissue, and also by applying a tourniquet.

An adaptive modulation scheme for simultaneous voice and data transmission over fading channels

Abstract: We propose a new adaptive modulation technique for simultaneous voice and data transmission over fading channels and study its performance. The proposed scheme takes advantage of the time-varying nature of fading to dynamically allocate the transmitted power between the inphase (I) and quadrature (Q) channels. It uses fixed-rate binary phase shift keying (BPSK) modulation on the Q channel for voice, and variable-rate M-ary amplitude modulation (M-AM) on the I channel for data. For favorable channel conditions, most of the power is allocated to high rate data transmission on the I channel. The remaining power is used to support the variable-power voice transmission on the Q channel. As the channel degrades, the modulation gradually reduces its data throughput and reallocates most of its available power to ensure a continuous and satisfactory voice transmission. The scheme is intended to provide a high average spectral efficiency for data communications while meeting the stringent delay requirements imposed by voice. We present closed-form expressions as well as numerical and simulation results for the outage probability, average allocated power, achievable spectral efficiency, and average bit error rate (BER) for both voice and data transmission over Nakagami-m fading channels. We also discuss the features and advantages of the proposed scheme. For example, in Rayleigh fading with an average signal-to-noise ratio (SNR) of 20 dB, our scheme is able to transmit about 2 bits/s/Hz of data at an average BER of 10/sup -5/ while sending about 1 bit/s/Hz of voice at an average BER of 10/sup -2/.

Drain current compression in GaN MODFETs under large-signal modulation at microwave frequencies

Abstract: It is shown that the discrepancy between the measured microwave power performance of GaN MODFETs and the prediction based on the DC characteristics is caused by the trapping of mobile electrons in the channel under large-signal modulation. This phenomenon manifests itself in the compression of the drain current. The strong dependence of the level of current compression on the gate bias voltage indicates that carrier trapping takes place in the AlGaN barrier or at the surface of the device.

Reduction of peak factor in orthogonal multicarrier modulation by amplitude limiting and coding

Abstract: A main disadvantage of orthogonal multicarrier modulation is that it exhibits a high peak-to-average-power ratio (PAPR). Because of this, all circuits between the output of the modulator and the input of the demodulator must be linear within a large dynamic range to avoid distortions and spectral spreading. It is therefore desirable to limit the PAPR of the multicarrier signal. A method based on amplitude limiting and forward error correcting (AL-FEC) coding is proposed for reduction of the PAPR. The performance of the AL-FEC is compared to two methods, based on block coding, specially constructed to reduce the PAPR. The AL-FEC is superior as compared to the existing methods. Moreover, its practical realization is very simple for any number of carriers.

Direct digital synthesis of precise, stable angle modulated RF signal

Abstract: An RF modulator that allows precise, stable phase shifts to be obtained. The modulator uses a PLL structure including an auxiliary feedforward path including an adaptive gain amplifier (411) used to inject a modulation signal into the PLL at a point past a loop filter (403). A phase demodulator (419) recovers from the output of the PLL phase information which is compared in a comparator (417) to the phase information of the modulation signal. A resulting error signal is used to control the gain of the adaptive gain amplifier (411). The modulator compensates for variability of the VCO (405) and other components of the PLL.

System and method for interoperable multiple-standard modulation and code selectable Feher's GMSK, enhanced GSM, CSMA, TDMA, OFDM, and third-generation CDMA, W-CDMA and B-CDMA

Abstract: Combined Digital-Analog Signal Processors, Waveforms with Time Constrained Signal (TCS) response and Long Response (LR) filtered Bit Rate Agile (BRA) Modulation-Demodulation (Modem) Format Selectable (MFS) and Code Selectable (CS) system implementations for Interoperable Multiple Standard Enhanced GSM, CSMA, TDMA, OFDM, and third-generation CDMA, W-CDMA and B-CDMA systems and associated methods Systems include Feher's Gaussian Minimum Shift Keying (GMSK or FGMSK) and Feher's Quadrature Phase Shift Keying (FQPSK) systems combined with Adaptive Antenna Arrays (AAA), Pseudo-Error (PE) based Non-Redundant Error Detection (NRED) controlled IF adaptive equalizers, smart antenna and smart diversity systems which have spectral/RF power efficiency and enhanced end-to-end performance

Ultrahigh-speed traveling-wave electroabsorption modulator-design and analysis

Abstract: Theoretical analysis and numerical calculations are presented for ultrahigh-speed (>50 GHz) traveling-wave electroabsorption modulators (TW-EAM's), including effects of velocity mismatch, impedance mismatch, and microwave attenuation. A quasi-static equivalent circuit model is used to examine the TW-EAM microwave properties, including the effect of photocurrent. Due to the optical propagation loss of the waveguide, the TW-EAM waveguide length for maximum RF link gain is currently limited to 200-300 /spl mu/m. The discussion indicates that the carrier transit time in the intrinsic layer may not severely limit the TW-EAM bandwidth. Three TW-EAM design approaches are discussed: low-impedance matching; reducing the waveguide capacitance; and distributing the modulation region.

Optical Transmission apparatuses, methods, and systems

Abstract: Apparatuses, methods, and systems are disclosed for controlling optical signal wavelength spacing by providing for simultaneous upconversion of a plurality of electrical signal on subcarrier frequencies of an optical carrier frequency with or without modulation of an electrical data signal onto the optical carrier frequency. The optical carrier lightwave is split into a plurality of split lightwaves upon which one or more electrical frequencies carrying information can be upconverted onto optical subcarriers of the lightwave carrier frequency. The relative spacings of the optical subcarrier lightwaves will thus be unaffected by variation in the carrier frequency. The optical subcarrier lightwaves can then be recombined to form the optical data signal carrying the plurality of information carried by the electrical frequencies.

Signal masking for chaotic optical communication using external-cavity diode lasers

Abstract: Amplitude modulation is used to encode a message into the output of a chaotic laser-diode optical transmitter, and decoding of the message by use of a synchronized chaotic laser-diode receiver is demonstrated experimentally. The chaotic carrier is shown to effectively mask the transmitted message.

Space vector PWM technique for two-phase inverter-fed single-phase induction motors

Abstract: In this paper, the space-vector pulsewidth modulation (SVPWM) technique for two-phase inverters is proposed. The proposed SVPWM technique is applicable to the two-phase induction motor drives. The two-phase inverters using the proposed SVPWM technique can generate only four space voltage vectors, but cannot generate zero vectors. A reference voltage vector located in the square locus is realized by adjusting the four space vectors. The switching sequence for the proposed SVPWM technique is proposed in order to minimize the ripple content of the output current. Practical verification of theoretical predictions is presented to confirm the capabilities of the new technique.

Method and apparatus for spectrum analysis and encoder

Abstract: A disc serving as a spatial radiation modulator has dispersed radiation filters thereon. Each filter has a transmittance or reflectance modulation function of the form sin2(mυ + pπ/4), where m is a positive integer and p has one of the four values 0, 1, 2, 3. A radiation beam including selected wavelength components is diffracted into an elongated image dispersed according to wavelength. Different wavelength components are focused onto different filters on the modulator and are encoded by corresponding filters. Since the modulation functions of the filters are orthogonal to one another, it is possible to extract the amplitude of each wavelength component after it has been encoded or modulated by corresponding filter from the total detected signal during one measurement.

Peak power reduction in OFDM and DMT via active channel modification

Abstract: Orthogonal frequency division multiplexing (OFDM) and discrete multitone (DMT) modulation offer many advantages for digital data transmission and have been adopted for several important standards. Their primary drawback is a high peak-to-average power ratio (PAR). Methods which introduce compensation signals in unused channels, first developed by Gatherer and Polley (see Proceedings of the 31st Asilomar Conference on Signals, Systems, and Computers, p.578-84, 1997), are among the more promising methods for reducing the PAR. However these methods apply only to systems with unused channels or require the sacrifice of data rate for PAR reduction. We present a new method for PAR reduction using active (data-carrying) channels which dynamically moves outer constellation points, within margin-preserving constraints, to minimize the peak magnitude. This scheme simultaneously decreases the bit error rate slightly while substantially reducing the peak magnitude; simulations show peak reductions of slightly more than 6 dB.

Dual mode QAM/VSB receiver

Abstract: A television receiver system capable of receiving and demodulating television signal information content that has been modulated and transmitted in accordance with a variety of modulation formats is disclosed. In particular, the system is able to accommodate receipt and demodulation of at least 8 and 16-VSB modulated signals in order to support US HDTV applications, as well as 64 and 256-QAM modulated signals, for European and potential US CATV implementations. The system includes carrier and timing recovery loops adapted to operate on an enhanced pilot signal as well as decision directed carrier phase recovery loops. Phase detectors operate on I and Q rail signals, or generate a Q rail from a Hilbert transform of the I rail. Decision directed loops incorporate a trellis decoder in order to operate on sequence estimated decisions for improved reliability in poor SNR environments.

RF transmitter architectures and circuits

Abstract: This paper describes the design of RF transmitters for wireless applications. Following a review of constant- and variable-envelope modulation, general issues regarding the baseband/RF interface and the power amplifier/antenna interface are introduced. Various transmitter architectures are then presented and the design of upconversion mixers and power amplifiers is studied. Examples of state of the art are also described.

Adaptive trellis coded MQAM and power optimization for OFDM transmission

Abstract: We propose an adaptive trellis coded modulation orthogonal frequency division multiplexing (ATCM-OFDM) scheme to provide high rate transmission with high spectral efficiency for an indoor environment Our objective is to minimize the overall transmit power in each OFDM transmission by optimizing the power distribution, the code rate and modulation scheme in each OFDM subchannel so as to maintain a constant data transmission rate and a fixed bit error rate (BER) In the simulation, the ATCM-OFDM scheme can achieve more than 7 dB power reduction compared with the OFDM scheme using fixed TCM

Filtered multitone modulation for VDSL

Abstract: We present a filter-bank modulation technique called filtered multitone (FMT) and describe its application to data transmission for very-high-speed digital subscriber line (VDSL) technology. The proposed scheme leads to significantly lower spectral overlapping between adjacent subchannels than for known multicarrier techniques such as discrete multitone (DMT) or discrete wavelet multitone. This allows mitigating interference due to echo and near-end crosstalk signals, increasing system throughput and reach, and simplifying system operations for VDSL transmission. In the receiver of an FMT system, signal equalization is accomplished in the form of per-subchannel symbol-spaced or fractionally-spaced linear or decision-feedback equalization. We study by simulation the performance that can be achieved by FMT modulation for VDSL systems where upstream and downstream signals are separated by frequency-division duplexing. We also provide comparisons with DMT modulation for a typical transmission scenario.

Theoretical study of frequency chirping and extinction ratio of wavelength-converted optical signals by XGM and XPM using SOA's

Abstract: We develop a complete large-signal dynamic model of semiconductor optical amplifier (SOA)-based wavelength converters using cross-gain modulation (XGM) and cross-phase modulation (XPM). The large-signal dynamic model has been implemented using the modified transfer matrix method (TMM). This model takes into account longitudinal variations of carrier-induced refractive index, n-parameter, internal reflection, photon density, and amplified spontaneous emission noise at each small section. Therefore, we can accurately estimate frequency chirping, optical pulse patterns, and the extinction ratio as well as the dynamic characteristics of SOA's. Frequency chirping and the extinction ratio have been calculated for various parameters such as signal power and wavelength, CW power and wavelength, and facet reflectivity. Modulation bandwidth, defined by the 3-dB drop as the eye opening ratio (EOR) is investigated with current density, confinement factor, and cavity length.

Multi-modulation radio communications

Abstract: A radio, and related methods of radio communication, consisting of a multi-modulation modem, wherein the multi-modulation modem that modulates and demodulates signals using a plurality of modulations. The radio also comprises a frequency converter coupled to the multi-modulation modem for converting the signals to a radio frequency and a transceiver unit including an antenna coupled to the frequency converter for transmitting the signals over a radio communications link. The multi-modulation modem includes a modulator that includes a modulation selector unit that selects respective ones of the plurality of modulations to modulate the signals. The multi-modulation modem also includes a demodulator for demodulating the signals having been modulated using the plurality of modulations.

Adaptive modulation method

Abstract: In the present invention, a modulation level estimation unit calculates the square error of the minimum value of distances between each signal point received at a modulation level ML and the signal point of a received signal at each modulation level ML A received power measurement unit measures the received power level of the received signal A modulation level estimation unit calculates the value obtained by multiplying the square error calculated at each modulation level ML, by a weighted calculation from both a threshold power level for switching the modulation level ML and the received power level as a likelihood value at each modulation level ML Then, the modulation level estimation unit estimates a modulation level ML corresponding to the maximum likelihood value of all the likelihood values at the modulation level ML as a modulation level ML of the received signal, without transmitting any codewords on the used modulation level

Differential Modulation by Copper and Zinc of P2X2and P2X4 Receptor Function

Abstract: Differential Modulation by Copper and Zinc of P2X2 and P2X4 Receptor Function. The modulation by Cu2+ and Zn2+ of P2X2 and P2X4 receptors expressed in Xenopus oocytes was studied with the two-elect...

Method and apparatus for accoustically coupling implantable medical device telemetry data to a telephonic connection

Abstract: An apparatus and method for communicating acoustic telemetry data produced by an implantable medical device over a communication channel includes a signal generator, a modulator, and an acoustic transmitter each provided in the implantable medical device. The modulator modulates a carrier signal with an information signal representative of information acquired or produced by the implantable medical device so as to produce a modulated information signal. The modulated information signal may have a frequency content that is readily accommodated by a public exchange communication channel. The transmitter transmits the modulated information signal as an acoustic information signal in a form communicable over the communication channel. The acoustic information signal may constitute telephonic tones which are directly communicable over a conventional telephone connection. The acoustic information signal may constitute digital telephonic tones each having a frequency and format that conforms to one or more telephony standards. In an embodiment in which the communication channel constitutes a public exchange communication channel, the acoustic information signal preferably has a frequency content that is band limited by an audio bandwidth of the public exchange communication channel. A number of different modulation techniques may be employed, including phase modulation, amplitude modulation or frequency modulation. Implantable medical devices which may incorporate telemetry circuitry of the present invention include a pacemaker, a pacemaker/cardioverter/defibrillator (PCD), an oxygen sensing device, an implantable hemodynamic monitor, a muscle stimulator device or a nerve stimulator device.

Direct conversion receiver

Abstract: A homodyne receiver according to the present invention includes a signal input and first and second mixers coupled to the signal input. A local oscillator provides a reference signal at the frequency of modulation of the input signal. The reference signal output by the local oscillator is passed through a switchable phase change element, the output of which is coupled directly to the first mixer and indirectly to the second mixer through a second phase change element. The switchable phase change element changes the phase of an input signal by a predetermined phase based on the state of a control input, such that the output of the phase change element in one state is π radians out of phase with the output of the phase change element in the other state. The second phase change element changes the phase of an input signal by π/2 radians. The outputs of the mixers are coupled to a pair of switchable inverters and low pass filters. Switching of the switchable phase change element and the switchable inverters is controlled by a switching oscillator.