Showing papers on "Modulation published in 2004"

Design of low-density parity-check codes for modulation and detection

Abstract: A coding and modulation technique is studied where the coded bits of an irregular low-density parity-check (LDPC) code are passed directly to a modulator. At the receiver, the variable nodes of the LDPC decoder graph are connected to detector nodes, and iterative decoding is accomplished by viewing the variable and detector nodes as one decoder. The code is optimized by performing a curve fitting on extrinsic information transfer charts. Design examples are given for additive white Gaussian noise channels, as well as multiple-input, multiple-output (MIMO) fading channels where the receiver, but not the transmitter, knows the channel. For the MIMO channels, the technique operates within 1.25 dB of capacity for various antenna configurations, and thereby outperforms a scheme employing a parallel concatenated (turbo) code by wide margins when there are more transmit than receive antennas.

UWB theory and applications

Abstract: Introduction. UWB Channel Models. Modulation Schemes. Receiver Structures. Integrated Circuit Topologies. UWB Antennas. Medium Access Control. Positioning.

Simple direct power control of three-phase PWM rectifier using space-vector modulation (DPC-SVM)

Abstract: This paper proposes a novel and simple direct power control of three-phase pulsewidth-modulated (PWM) rectifiers with constant switching frequency using space-vector modulation (DPC-SVM). The active and reactive powers are used as the pulse width modulated (PWM) control variables instead of the three-phase line currents being used. Moreover, line voltage sensors are replaced by a virtual flux estimator. The theoretical principle of this method is discussed. The steady-state and dynamic results of DPC-SVM that illustrate the operation and performance of the proposed system are presented. It is shown that DPC-SVM exhibits several features, such as a simple algorithm, good dynamic response, constant switching frequency, and particularly it provides sinusoidal line current when supply voltage is not ideal. Results have proven excellent performance and verify the validity of the proposed system.

The nearest three virtual space vector PWM - a modulation for the comprehensive neutral-point balancing in the three-level NPC inverter

Abstract: This letter presents a new modulation approach for the complete control of the neutral-point voltage in the three-level three-phase neutral-point-clamped voltage source inverter. The new modulation approach, based on the virtual space vector concept, guarantees the balancing of the neutral-point voltage for any load (linear or nonlinear) over the full range of converter output voltage and for all load power factors, the only requirement being that the addition of the output three-phase currents equals zero. The implementation of the proposed modulation is simple according to the phase duty-ratio expressions presented. These expressions are only dependent on the modulation index and reference vector angle. The performance of this modulation approach and its benefits over other previously proposed solutions are verified experimentally.

Power line channel characteristics and their effect on communication system design

Abstract: The development of power line communication systems requires detailed knowledge of the channel properties, such as transfer function, interference scenario, and channel capacity in order to choose suitable transmission methods. This article presents appropriate power line channel models, which form the basis for the design of a channel emulator. Such a device turns out to be extremely helpful for various tests and the comparison of performance of different communication systems. A basic estimation of the power line channel capacity clearly demonstrates their enormous potential for high-speed communication purposes. Eventually, an evaluation of different modulation schemes is carried to optimize PLC system design.

An active-set approach for OFDM PAR reduction via tone reservation

Abstract: Common to all orthogonal frequency division multiplexing (OFDM) systems is a large peak-to-average-power ratio (PAR), which can lead to low power efficiency and nonlinear distortion at the transmit power amplifier. Tone reservation uses other unused or reserved tones to design a peak-cancelling signal that lowers the PAR of a transmit OFDM block. In contrast to previous methods, the new active-set method proposed here converges very quickly toward a minimum-PAR solution at a lower computational cost. An efficient real-baseband algorithm is well suited for discrete multitone (DMT) modulation over twisted-pair copper wiring, where some subchannels may have an insufficient SNR to reliably send data. The real PAR problem occurs in the analog signal before the power amplifier, and results focus on this figure of merit. The performance of oversampling before applying PAR reduction is analyzed, and results show that this is necessary to sufficiently handle the analog PAR problem. An extension of the real-baseband technique can be applied to complex-baseband signals to help reduce PAR in wireless and broadcast systems. By sacrificing 11 out of 256 OFDM tones (4.3%) for tone reservation, over 3 dB of analog PAR reduction can be obtained for a wireless system.

A wideband frequency-shift keying wireless link for inductively powered biomedical implants

Abstract: A high data-rate frequency-shift keying (FSK) modulation protocol, a wideband inductive link, and three demodulator circuits have been developed with a data-rate-to-carrier-frequency ratio of up to 67%. The primary application of this novel FSK modulation/demodulation technique is to send data to inductively powered wireless biomedical implants at data rates in excess of 1 Mbps, using comparable carrier frequencies. This method can also be used in other applications such as radio-frequency identification tags and contactless smartcards by adding a back telemetry link. The inductive link utilizes a series-parallel inductive-capacitance tank combination on the transmitter side to provide more than 5 MHz of bandwidth. The demodulator circuits detect data bits by directly measuring the duration of each received FSK carrier cycle, as well as derive a constant frequency clock, which is used to sample the data bits. One of the demodulator circuits, digital FSK, occupies 0.29 mm/sup 2/ in the AMI 1.5-/spl mu/m, 2M/2P, standard CMOS process, and consumes 0.38 mW at 5 V. This circuit is simulated up to 4 Mbps, and experimentally tested up to 2.5 Mbps with a bit error rate of 10/sup -5/, while receiving a 5/10-MHz FSK carrier signal. It is also used in a wireless implantable neural microstimulation system.

How accurate channel prediction needs to be for transmit-beamforming with adaptive modulation over Rayleigh MIMO channels?

Abstract: Adaptive modulation improves the system throughput considerably by matching transmitter parameters to time-varying wireless fading channels. Crucial to adaptive modulation is the quality of channel state information at the transmitter. In this paper, we first present a channel predictor based on pilot symbol assisted modulation for multiple-input multiple-output Rayleigh fading channels. We then analyze the impact of the channel prediction error on the bit error rate performance of a transmit-beamformer with adaptive modulation that treats the predicted channels as perfect. Our numerical results reveal the critical value of the normalized prediction error, below which the predicted channels can be treated as perfect by the adaptive modulator; otherwise, explicit consideration of the channel imperfection must be accounted for at the transmitter.

Measurement of the linewidth enhancement factor of semiconductor lasers based on the optical feedback self-mixing effect

Abstract: A new method for the measurement of the linewidth enhancement factor of semiconductor lasers is presented, based on the interferometric self-mixing effect. It is a fast and easy to perform method that does not require radio frequency nor optical spectrum measurements. A small fraction of the emitted light is backreflected into the laser cavity by a remote target driven by a sine waveform. The mixing of the returned and the lasing fields generates a modulation of the optical output power in the form of an interferometric waveform, with a shape that depends on the optical feedback strength and the linewidth enhancement factor /spl alpha/, according to the well-known Lang-Kobayashi theory. We show that the value of /spl alpha/ can be retrieved from a simple measurement of two characteristic time intervals of the interferometric waveform. Experimental results obtained on different laser diodes show an accuracy of /spl plusmn/6.5%.

Adaptive modulation systems for predicted wireless channels

Abstract: When adaptive modulation is used to counter short-term fading in mobile radio channels, signaling delays create problems with outdated channel state information. The use of channel power prediction will improve the performance of the link adaptation. It is then of interest to take the quality of these predictions into account explicitly when designing an adaptive modulation scheme. We study the optimum design of an adaptive modulation scheme based on uncoded M-quadrature amplitude modulation, assisted by channel prediction for the flat Rayleigh fading channel. The data rate, and in some variants the transmit power, are adapted to maximize the spectral efficiency, subject to average power and bit-error rate constraints. The key issues studied here are how a known prediction error variance will affect the optimized transmission properties, such as the signal-to-noise ratio (SNR) boundaries that determine when to apply different modulation rates, and to what extent it affects the spectral efficiency. This investigation is performed by analytical optimization of the link adaptation, using the statistical properties of a particular, but efficient, channel power predictor. Optimum solutions for the rate and transmit power are derived, based on the predicted SNR and the prediction error variance.

The generalized discontinuous PWM scheme for three-phase voltage source inverters

Abstract: This paper presents analytical techniques for the determination of the expressions for the modulation signals used in the carrier-based sinusoidal and generalized discontinuous pulse-width modulation schemes for two-level, three-phase voltage source inverters. The proposed modulation schemes are applicable to inverters generating balanced or unbalanced phase voltages. Some results presented in this paper analytically generalize the several expressions for the modulation signals already reported in the literature and new ones are set forth for generating unbalanced three-phase voltages. Confirmatory experimental and simulation results are provided to illustrate the analyses.

Adaptive Modulation for multiantenna transmissions with channel mean feedback

Abstract: Adaptive modulation has the potential to increase the system throughput significantly by matching transmitter parameters to time-varying channel conditions. However, adaptive modulation schemes that rely on perfect channel state information (CSI) are sensitive to CSI imperfections induced by estimation errors and feedback delays. In this paper, we design adaptive modulation schemes for multiantenna transmissions based on partial CSI, that models the spatial fading channels as Gaussian random variables with nonzero mean and white covariance, conditioned on feedback information. Based on a two-dimensional beamformer, our proposed transmitter optimally adapts the basis beams, the power allocation between two beams, and the signal constellation, to maximize the transmission rate, while maintaining a target bit-error rate. Adaptive trellis-coded multiantenna modulation is also investigated. Numerical results demonstrate the rate improvement, and illustrate an interesting tradeoff that emerges between feedback quality and hardware complexity.

Evaluation of modulation schemes for three-phase to three-phase matrix converters

Abstract: This paper presents a method for evaluating different modulation schemes employed with three-phase to three-phase matrix converters. The evaluation method addresses three important modulator characteristics: the output waveform quality, the input waveform quality and the switching losses associated with the modulation schemes. The method is used to evaluate four different modulation strategies, all based on the direct space-vector modulation approach. Further, regarding the switching losses, the paper proposes a new space-vector approach by which the switching losses can be reduced by 15%-35%, depending on the output load angle. This new modulation approach is applicable whenever the output voltage reference is below half the input voltage and the output voltage quality is then superior to that of the conventional space vector modulation scheme. The functionality of the new modulation scheme is validated by both simulations and experimental results and compared to waveforms obtained by using exiting space vector modulation schemes. The output voltage of the proposed scheme turns out to be comparable to the best of the conventional schemes while the input current is more distorted.

Pulse frequency modulation for induction charge device

Abstract: The present invention is related to a pulse frequency modulation for induction charge device, which comprises a pulse frequency modulation for induction charge device being provided to charge a portable electronic device, wherein, the portable electronic device comprises a induction coil, which comprises: an electric magnetic field generate and the secondary coil react circuit; a detection and modulation generate circuit; and a control switch circuit; whereby, the detection and modulation generate circuit could generate pulse singles with various frequencies according to the load varying generated due to distance varying between the portable electronic device and the charged device, and charge to the portable electronic device according the pulse singles so as to reach the goal of effective management the power.

An inductive power system with integrated bi-directional data-transmission

Abstract: An inductive powering system is presented, capable of remotely powering implantable monitoring and stimulating devices. The system is capable of delivering at least 50 mW, with an efficiency of 36% over a distance of 3 cm. The power transfer frequency is 700 kHz. Optimisation of the power transfer efficiency and the misalignment tolerance was obtained using a self-developed design tool. Bi-directional data-transmission is integrated in the system: amplitude modulation is applied for the downlink transmission, absorption modulation for the uplink transmission. Our new system is capable of transmitting data at a maximal bit rate of 60,000 bits/s.

Optimal pilot waveform assisted modulation for ultrawideband communications

Abstract: Ultrawideband (UWB) transmissions induce pronounced frequency-selective fading effects in their multipath propagation. Multipath diversity gains can be collected to enhance performance, provided that the underlying channel can be estimated at the receiver. To this end, we develop a novel pilot waveform assisted modulation (PWAM) scheme that is tailored for UWB communications. We select our PWAM parameters by jointly optimizing channel estimation performance and information rate. The resulting transmitter design maximizes the average capacity, which is shown to be equivalent to minimizing the mean-square channel estimation error, and thereby achieves the Crame/spl acute/r-Rao lower bound. Application of PWAM to practical UWB systems is promising because it entails simple integrate-and-dump operations at the frame rate. Equally important, it offers a flexible UWB channel estimator, capable of striking desirable rate-performance tradeoffs depending on the channel coherence time.

Wavelength modulation absorption spectroscopy with 2 f detection using multiplexed diode lasers for rapid temperature measurements in gaseous flows

Abstract: Multiplexed fiber-coupled diode lasers are used to probe second-harmonic line shapes of two near-infrared water absorption features, at 1343 nm and 1392 nm, in order to infer temperatures in gases containing water vapor, such as combustion flows. Wavelength modulation is performed at 170 kHz, and is superimposed on 1-kHz wavelength scans in order to recover full second-harmonic line shapes. Digital waveform generation and lock-in detection are performed using a data-acquisition card installed in a PC. An optimal selection of the modulation indices is shown to greatly simplify data interpretation over extended temperature ranges and to minimize the need for calibration when performing 2 f ratio thermometry. A theoretical discussion of this optimized strategy for 2 f ratio thermometry, as well as results from experimental validations in a heated cell, at pressures up to atmospheric, are presented in order to illustrate the utility of this technique for rapid temperature measurements in gaseous flow fields.

Ultrasonic diagnostic apparatus

Abstract: Encoded transmission and reception which reduces time side lobe are realized while suppressing increase of circuit scale. Transmission signals corresponding to a composite modulation code sequence composed from two or more modulation code sequences are outputted as transmission signals. A reception means demodulates reception signals stepwise by two or more demodulators. The demodulator can be thereby divided into two or more stages, and therefore with a circuit scale corresponding to the sum of the operation circuit numbers of two or more demodulators, time side lobe reduction effect can be obtained at a level equivalent to that obtainable with a circuit scale corresponding to the product of the operation circuit numbers of two or more demodulators.

Multi-mode wireless devices having reduced-mode receivers

Abstract: Multi-mode wireless devices having single-mode or reduced-mode receivers. In one embodiment, a wireless device is provided with a transmitter and a receiver. The transmitter transmits with any one of multiple selectable modulation techniques, the selected modulation technique being selected to correspond to a modulation technique supported by a target wireless device. The receiver receives signals modulated in accordance any one of a subset of the selectable modulation techniques. The subset might include only one modulation technique. Also disclosed is a wireless communications method in a wireless device having a transmitter configurable to transmit in at least one modulation mode other than that receivable by the wireless device.

An impulse radio asynchronous transceiver for high data rates

Abstract: The purpose of this paper is to provide an operative way of achieving high data rates for impulse radio (IR) transmission based systems. Since applications targeted for ultra wide band (UWB) are liable to be low-cost, we especially focus on simple transceiver design. To that effect, we present an original demodulation scheme adapted to a multi-band ON-OFF keying modulation. From the receiver point of view, we impose relaxed channel estimation constraints and derive suitable signal processing schemes and simple hardware architectures. Indeed, we only consider the benefit from a limited a priori channel knowledge: approximative delay spread and energy level. The associated optimum demodulation turns out to be a non-trivial energetic threshold comparison whose precise theoretical computation admits an analytical solution proving its feasibility. Numerical results are eventually performed for IEEE 802.15.3a channel models and FCC requirements; they obviously demonstrate the potential of these techniques.

Rate selection for a multi-carrier mimo system

Abstract: To select a rate for data transmission in a multi-carrier MIMO system with a multipath MIMO channel, a post-detection SNR for each subband k of each spatial channel is initially determined and used to derive a constrained spectral efficiency based on a constrained spectral efficiency function of SNR and modulation scheme M. An average constrained spectral efficiency for all subbands of all spatial channels used for data transmission is next determined based on the constrained spectral efficiencies for the individual subbands/spatial channels. An equivalent SNR needed by an equivalent system with an AWGN channel to support a data rate of is determined based on an inverse constrained spectral efficiency function . A rate is selected for the multi-carrier MIMO system based on the equivalent SNR. The selected rate is the highest rate among all supported rates with a required SNR less than or equal to the equivalent SNR.

Constellation shaping for pragmatic turbo-coded modulation with high spectral efficiency

Abstract: We propose a new turbo-encoding scheme for high spectral efficiency with performance close to the Gaussian channel capacity. The scheme combines nonuniform signaling on a Gaussian channel with pragmatic turbo-coded modulation (TCM) for simple and flexible implementation. A variable-rate turbo code is followed by a Huffmann code mapping onto nonequiprobable points in a quadrature amplitude modulation constellation. The rate of the turbo code is matched to the Huffmann code by variable puncturing, such that both the input bit rate and the output symbol rate are constant. It is shown that the new scheme provides shaping gains of 0.6 and 0.9 dB, at rates 2 and 3 b/dimension, respectively, compared with the equiprobable pragmatic TCM, and reach about 1 dB from the continuous input Gaussian channel capacity.

Doubly resonant single-layer bandpass optical filters

Abstract: A bandpass filter based on guided-mode resonance effects in a single-layer periodic waveguide is presented. Strong refractive-index modulation is used to support the excitation of a resonance pair in which leaky waveguide mode TE0 is excited by the second diffraction order and TE2 by the first diffraction order. It is shown that one resonance provides a broad low-transmission band, whereas the other supplies the transmission peak through its asymmetrical line shape. A bandpass filter with central wavelength at 1.55 µm is presented to demonstrate this concept.

Switching control circuit having off-time modulation to improve efficiency of primary-side controlled power supply

Abstract: A voltage-waveform detector produces a voltage-feedback signal and a discharge-time signal by multi-sampling a voltage signal of a transformer. The discharge-time signal represents a discharge time of a secondary-side switching current. A voltage-loop error amplifier amplifies the voltage-feedback signal and generates a control signal. An off-time modulator correspondingly generates a discharge-current signal and a standby signal in response to the control signal and an under-voltage signal. The under-voltage signal indicates a low supply voltage of the controller. An oscillator produces a pulse signal in response to the discharge-current signal. The pulse signal determines the off-time of the switching signal. A PWM circuit generates the switching signal in response to the pulse signal and the standby signal. The standby signal further controls the off-time of the switching signal and maintains a minimum switching frequency. The switching signal is used for regulating the output of the power supply.

Constant envelope OFDM phase modulation: spectral containment, signal space properties and performance

Abstract: A class of constant envelope OFDM phase modulated (OFDM-PM) signals is studied. The motivation behind OFDM-PM is to alleviate the high peak-to-average power ratio of conventional OFDM systems. Power density spectrum plots and fractional out-of-band power curves are given. For small modulation indices, the OFDM-PM signals are shown to be more spectrally contained than conventional OFDM. The signal space is studied by considering the correlation properties of the OFDM-PM signals. A performance bound on the optimum OFDM-PM receiver is compared to simulation results. Also, a sub-optimum phase demodulator receiver is analyzed and an AWGN performance approximation is compared to simulation results. It is shown that for a small modulation index and high signal-to-noise ratio, the sub-optimum receiver performs close to the optimum receiver.

All-optical logic based on ultrafast gain and index dynamics in a semiconductor optical amplifier

Abstract: We investigate nonlinear carrier dynamics in a multiquantum-well semiconductor optical amplifier (SOA) in the context of ultrafast all-optical logic. A rate-equation model is presented that accounts for two-photon absorption, free-carrier absorption, self- and cross phase modulation, carrier heating, spectral, spatial hole burning, and self- and cross polarization modulation. The nonlinear refractive index dynamics is investigated theoretically and experimentally. We find nonlinear phase changes larger than /spl pi/ radians, which recovers on a timescale in the order of 1 ps. We also investigate a nonlinear AND gate that consists of an SOA that is placed in an asymmetric Mach-Zehnder interferometer. We show that the gate can be operated using 800-fJ optical pulses with duration of 200 fs while having a contrast ratio larger than 11 dB.

Photon lifetime dependence of modulation efficiency and K factor in 1.3μm self-assembled InAs∕GaAs quantum-dot lasers: Impact of capture time and maximum modal gain on modulation bandwidth

Abstract: We studied small-signal modulation characteristics of 1.3μm InAs∕GaAs self-assembled quantum-dot lasers in terms of the modulation efficiency and the K factor as a function of the photon lifetime. We could explain the measured photon-lifetime dependence based on the rate equation model considering explicitly the carrier-capture process and Pauli blocking in quantum dots. Our model shows how the modulation bandwidth of quantum-dot lasers is limited by the carrier-capture time and by the maximum modal gain via the K factor. We present prerequisite designs of quantum-dot active regions for over 10GHz modulation.

Totally blind channel estimation for OFDM on fast varying mobile radio channels

Abstract: A new blind channel estimation scheme for orthogonal frequency division multiplexing systems is proposed based on the maximum likelihood principle. By avoiding the use of second- and higher-order statistics, a very fast convergence rate is achieved. A novel approach is also proposed for resolving the phase ambiguity of the blind channel estimate without the need for any reference symbols. The approach combines different modulation schemes on adjacent subcarriers, such as 3-phase shift keying (PSK) and quarternary PSK (QPSK), to resolve phase ambiguity. Simulations were performed for mobile radio environments with high Doppler frequencies and short-to-medium delay spreads. The achieved performance is comparable to that of pilot-based channel estimation for the case of QPSK-modulation.

Adaptive receivers for bit rate agile (BRA) and modulation demodulation (modem) format selectable (MFS) signals

Abstract: Systems, apparatus, and methods for new generations of wireless systems, including multiple standard, interoperable Third-Generation (3G) and Second-Generation (2G), Spread Spectrum CDMA, WCDMA, GSM, Enhanced GSM systems and CSMA, TDMA and OFDM. Bit Rate Agile (BRA), Modulation and Code Selectable processing techniques of Gaussian Minimum Shift Keying (GMSK), Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (QAM), and of Mis-Matched demodulator filters in which the demodulator filter set is mismatched to the filter set of the signal modulator.

Concise modulation strategies for four-leg voltage source inverters

Abstract: The continuous, discontinuous pulse-width modulation (PWM) schemes and a novel space vector modulation methodology are proposed in this paper for four-leg dc-ac inverters. Using a space vector definition that includes the zero sequence voltage component and partitioning the feasible sixteen modes into two separate sets - one set having zero sequence voltages with positive magnitudes and the other set with negative magnitudes - the novel space vector implementation technique is determined as also the discontinuous carrier based PWM scheme. For the continuous carrier based PWM scheme, the indeterminate defining output voltage equations expressed in terms of the existence functions of the switching devices are solved using an optimization technique. The modulation schemes determined are shown by experimental results to synthesis any desirable balanced or unbalanced three-phase voltage sets when operating in the linear modulation region.