Showing papers on "Modulation published in 2001"

Intercarrier interference self-cancellation scheme for OFDM mobile communication systems

Abstract: For orthogonal frequency-division multiplexing (OFDM) communication systems, the frequency offsets in mobile radio channels distort the orthogonality between subcarriers resulting in intercarrier interference (ICI). This paper studies an efficient ICI cancellation method termed ICI self-cancellation scheme. The scheme works in two very simple steps. At the transmitter side, one data symbol is modulated onto a group of adjacent subcarriers with a group of weighting coefficients. The weighting coefficients are designed so that the ICI caused by the channel frequency errors can be minimized. At the receiver side, by linearly combining the received signals on these subcarriers with proposed coefficients, the residual ICI contained in the received signals can then be further reduced. The carrier-to-interference power ratio (CIR) can be increased by 15 and 30 dB when the group size is two or three, respectively, for a channel with a constant frequency offset. Although the redundant modulation causes a reduction in bandwidth efficiency, it can be compensated, for example, by using larger signal alphabet sizes. Simulations show that OFDM systems using the proposed ICI self-cancellation scheme perform much better than standard systems while having the same bandwidth efficiency in multipath mobile radio channels with large Doppler frequencies.

Turbo-coded modulation for systems with transmit and receive antenna diversity over block fading channels: system model, decoding approaches, and practical considerations

Abstract: We study the use of turbo-coded modulation for wireless communication systems with multiple transmit and receive antennas over block Rayleigh fading channels. We describe an effective way of applying turbo-coded modulation as an alternative to the current space-time codes with appropriate interleaving. We study the performance with the standard iterative turbo decoding algorithm, as well as the iterative demodulation-decoding algorithm. In addition to the introduction of the turbo-coded modulation scheme, we consider a variety of practical issues including the case of large number of antennas, the effects of estimated channel state information, and correlation among subchannels between different transmit-receive antenna pairs. We present examples to illustrate the performance of the turbo-coded modulation scheme and observe significant performance gains over the appropriately interleaved space-time trellis codes.

A multicarrier CDMA architecture based on orthogonal complementary codes for new generations of wideband wireless communications

Abstract: This article is a review of our ongoing research effort to construct a new multicarrier CDMA architecture based on orthogonal complete complementary codes, characterized by its innovative spreading modulation scheme, uplink and downlink signaling design, and digital receiver implementation for multipath signal detection. There are several advantages of the proposed CDMA architecture compared to conventional CDMA systems pertinent to current 2G and 3G standards. First of all, it can achieve a spreading efficiency (SE) very close to one (the SE is defined as the amount of information bit(s) conveyed by each chip); whereas SEs of conventional CDMA systems equal 1/N, where N denotes the length of spreading codes. Second, it offers MAI-free operation in both upand downlink transmissions in an MAI-AWGN channel, which can significantly reduce the co-channel interference responsible for capacity decline of a CDMA system. Third, the proposed CDMA architecture is able to offer a high bandwidth efficiency due to the use of its unique spreading modulation scheme and orthogonal carriers. Lastly, the proposed CDMA architecture is particularly suited to multirate signal transmission due to the use of an offset stacked spreading modulation scheme, which simplifies the rate-matching algorithm relevant to multimedia services and facilitates asymmetric traffic in up- and downlink transmissions for IP-based applications. Based on the above characteristics and the obtained results, it is concluded that the proposed CDMA architecture has a great potential for applications in future wideband mobile communications beyond 3G, which is expected to offer a very high data rate in hostile mobile channels.

Single side-band modulation performance of a LiNbO 3 integrated modulator consisting of four-phase modulator waveguides

Abstract: Single side-band (SSB) technologies are especially useful in optical fiber communication systems, such as higher density wavelength multiplexing and long-haul fiber transmission due to less nonlinear optical effects, because of the reduced optical power. This letter reports on the SSB modulation performance of a LiNbO/sub 3/ integrated modulator consisting of four phase modulator waveguides. Optical SSB modulation with suppressions of main carrier (-22.6 dB) and J/sub 3/ subcarrier (-18.4 dB) of a 10-GHz single-tone signal with a driving voltage of 6.3 V/sub p-p/ was demonstrated. The total insertion loss was 10.6 dB.

High efficiency high performance communications system employing multi-carrier modulation

Abstract: Transmitter and receiver units for use in a communications system and configurable to provide antenna, frequency, or temporal diversity, or a combination thereof, for transmitted signals. The transmitter unit includes a system data processor, one or more modulators, and one or more antennas. The system data processor receives and partitions an input data stream into a number of channel data streams and further processes the channel data streams to generate one or more modulation symbol vector streams. Each modulation symbol vector stream includes a sequence of modulation symbol vectors representative of data in one or more channel data streams. Each modulator receives and modulates a respective modulation symbol vector stream to provide an RF modulated signal, and each antenna receives and transmits a respective RF modulated signal. Each modulator may include an inverse (fast) Fourier transform (IFFT) and a cyclic prefix generator. The IFFT generates time-domain representations of the modulation symbol vectors, and the cyclic prefix generator repeats a portion of the time-domain representation of each modulation symbol vector. The channel data streams are modulated using multi-carrier modulation, e.g., OFDM modulation. Time division multiplexing (TDM) may also be used to increase flexibility.

Switching voltage regulator with dual modulation control scheme

Abstract: A switching voltage regulator employs a “dual modulation” scheme to control the regulator's switching components. A control circuit indirectly monitors load current. When the load decreases, the control circuit reduces both the duty ratio and the frequency of the control signals which operate the switching transistors, thereby maintaining a high efficiency level over a wider output current range than can be achieved with fixed-frequency control signals. In a preferred embodiment, the regulator employs three operating modes. For heavy loads, the switching components are operated at a constant frequency. For moderate-to-light loads, the dual modulation control scheme is used. For light loads, the regulator enters a “pulse-skipping” mode which can achieve very low operating frequencies to further improve efficiency. The invention may be used with switching regulators using peak current mode, average current mode, or voltage mode control, as well as buck, buck-boost, and boost power stages.

Cardiac gap junction channels: modulation of expression and channel properties.

Abstract: In the heart, intercellular gap junction channels constructed from connexin molecules are crucial for conduction of the electric impulse. Cardiomyocytes can be interconnected by channels composed of three types of connexin proteins: Cx40, Cx43 or Cx45. In mammalian hearts, these three isoforms are regionally differently expressed and even between the species differences exist. Each of these channel-types possesses specific properties and are susceptible to modulation by various mechanisms. In this paper we compare the differences in properties of these channels as deduced from studies on transfected cells and isolated cardiomyocytes and discuss the factors involved in modulation of channel properties. Next, we evaluate the consequences of alterations in expression and modulation of channel properties for cardiac function. Therefore, we have compared reports on genetically engineered animals and discuss this information in relation to various pathophysiological disorders.

Space modulation on wireless fading channels

Abstract: To increase the data rate for future wireless systems, a novel scheme using multiple transmit antennas for space digital modulation is proposed. In the scheme of space modulation, more than two antennas are employed to transmit and signal the information bits. The novel space modulation scheme is termed space shift keying (SSK). Numerical results are presented to examine the reception performance.

Performance of ultrawideband SSMA using time hopping and M-ary PPM

Abstract: Wireless spread spectrum multiple access (SSMA) using time hopping and block waveform encoded (M-ary) pulse position modulated (PPM) signals is analyzed. For different M-ary PPM signal designs, the multiple-access performance in free-space propagation renditions is analyzed in terms of the number of users supported by the system for a given bit error rate, signal-to-noise ratio, bit transmission rate, and number of signals in the M-ary set. The processing gain and number of simultaneous users are described in terms of system parameters. Tradeoffs between performance and receiver complexity are discussed. Upper bounds on both the maximum number of users and the total combined bit transmission rate are investigated. This analysis is applied to ultrawideband impulse radio modulation. In this modulation, the communications waveforms are practically realized using subnanosecond impulse technology. A numerical example is given that shows that impulse radio modulation is theoretically able to provide multiple-access communications with a combined transmission capacity of hundreds of megabits per second at bit error rates in the range 10/sup -4/ to 10/sup -7/ using receivers of moderate complexity.

Mechanisms of ultrasonic modulation of multiply scattered coherent light: an analytic model.

Abstract: An analytic model of the ultrasonic modulation of multiply scattered coherent light in scattering media is developed based on two mechanisms: the ultrasonic modulation of the index of refraction and the ultrasonic modulation of the displacements of Rayleigh scatterers. In water solutions, for example, the first mechanism is slightly less important than the second mechanism when the scattering mean free path is less than a critical fraction (0.0890) of the acoustic wavelength, and it becomes increasingly more important beyond this point. This model agrees well with an independent Monte Carlo model.

Digital scalar pulse-width modulation: a simple approach to introduce nonsinusoidal modulating waveforms

Abstract: The digital scalar pulse-width modulation (DSPWM) gathers the characteristics of simplicity of implementation found in the regular sampling with the flexibility of manipulation of the switching patterns in the space vector modulation (SVPWM). This paper establishes a correlation between the SVPWM and DSPWM techniques. It also shows how to make the DSPWM strategy equivalent to the SVPWM technique without losing its simplicity of implementation. By using such an equivalence concept a microprocessor-based scheme, which uses standard timer circuits and a simple software algorithm, is proposed to implement the DSPWM technique. The introduction of the "distribution ratio" in this technique, allows the development of a systematic approach for implementing either conventional or any modified vector strategies without changing the modulator scheme. This corresponds to generating any attractive nonsinusoidal modulating signals (NSMS) in the carrier-based modulation techniques. Furthermore, the simple digital blocks can be easily implemented as a specialized integrated circuit. Simulated and experimental results demonstrate the validity of the proposed methods.

Soft-switching PWM three-level converters

Abstract: This paper proposes a family of modulation strategies for PWM three-level (TL) converters. The modulation strategies can be classified into two kinds according to the turn-off sequence of the two switches of the pair of switches. The concept of the leading switches and the lagging switches is introduced to realize soft-switching for PWM TL converters. The realization of soft-switching for both the leading switches and the lagging switches is proposed, based on which, soft-switching PWM TL converters can be classified into two kinds: zero-voltage-switching (ZVS) and zero-voltage and zero-current-switching (ZVZCS), for which the suitable modulation strategies are pointed out respectively from the family of modulation strategies. A novel ZVZCS TL converter is proposed, its operation principle and parameter design are analyzed, and the experimental results are also included.

Systems for CMOS-compatible three-dimensional image sensing using quantum efficiency modulation

Abstract: A preferably CMOS-implementable system measures distance and/or brightness by illuminating a target with emitted optical energy having a modulated periodic waveform whose high frequency component may be idealized as S 1 =cos(ω·t). A fraction of the emitted optical energy is reflected by a target and detected with at least one in a plurality of semiconductor photodetectors. Photodetector quantum efficiency is modulated to process detected signals to yield data proportional to the distance z separating the target and photodetector. Detection includes measuring phase change between the emitted optical energy and the reflected fraction thereof. Quantum efficiency can be modulated with fixed or variable phase methods and may be enhanced using enhanced photocharge collection, differential modulation, and spatial and temporal multiplexing. System power requirements may be reduced with inductors that resonate with photodetector capacitance at the operating frequency. The system includes on-chip photodetectors, associated electronics, and processing.

Differential modulation using space-time block codes

Abstract: We consider a space-time differential modulation scheme where neither the transmitter nor the receiver has to know the channel. Our scheme is based on the theory of unitary space-time block codes. Compared to the existing differential modulation schemes for multiple antennas our scheme has a much smaller computational complexity. Moreover, our codes have a higher coding gain and lower bit error rate than the codes proposed by other researchers.

Parametric audio system

Abstract: A parametric audio system having increased bandwidth for generating airborne audio signals with reduced distortion. The parametric audio system includes a modulator (112) for modulating an ultrasonic carrier signal with a processed audio signal, a driver amplifier (118) for amplifying the modulated carrier signal, and an array of acoustic transducers (122) for projecting the modulated and amplified carrier signal through the air along a selected projection path to regenerate the audio signal. Each of the acoustic transducers in the array (122) is a membrane-type transducer (Fig. 2a and 2b). Further, the acoustic transducer array (122) is a phased array capable of electronically steering, focusing, or shaping one or more audio beams.

High-frequency generator for performing high-frequency surgery having adjustable power limitation, and method for controlling the power limitation

Abstract: The invention relates to an HF generator and to a method for limiting the output effective power of the HF generator, especially for performing HF surgical cutting and coagulation of human or animal tissue. According to the invention, the output voltage and the HF output current of the HF generator (1) are detected by at least two detector devices (2, 3), the peak values and the effective values of the HF output voltage and of the output current as well as the mean value of the output effective power of the HF generator are determined by an evaluation device (4), and the calculated mean value is compared to a defined maximum mean value of the output effective power of the HF generator by a comparison device (5). Afterwards, a modulation device (7) modulates the HF output voltage using a pulse-shaped modulation signal. A control device (6) controls the modulation device (7) in such a manner that the pulse duration of the pulse-shaped modulation signal and/or the pulse duration between the pulse-shaped modulation signals is modified in order to keep the peak value of the output voltage constant when the calculated mean value of the output effective power is greater than the maximum mean value of the output effective power. Alternatively, the HF generator (1) is equipped with a sensor for evaluating the intensity of electric arcs between an electrode connected to the HF generator and the tissue.

Continuous-Time Sigma-Delta Modulation for IF A/D Conversion in Radio Receivers

Abstract: List of abbreviations. List of symbols. Preface. 1. Introduction. 2. A/D conversion in radio receivers. 3. Continuous-time sigma-delta modulation. 4. Realization of an IF-to-baseband sigma-delta modulator. 5. Realization of a quadrature sigma-delta modulator. 6. Benchmark. Index.

Methods and devices for vascular plethysmography via modulation of source intensity

Abstract: A time-varying modulating signal is used as a plethysmography signal, rather than a time-varying detected optical power. The time-varying detected optical power is used (e.g., in a feedback loop) to adjust the source intensity. Light is transmitted from a light source, wherein an intensity of the transmitted light is based on a light control signal. A portion of the light transmitted from the light source is received at a light detector, the portion having an associated detected light intensity. A feedback signal is produced based the portion of light received at the light detector, the feedback signal indicative of the detected light intensity. The feedback signal is compared to a reference signal to produce a comparison signal. The light control signal is then adjusted based on the comparison signal, wherein at least one of the comparison signal and the light control signal is representative of volume changes in blood vessels.

Direct electrical-to-optical conversion and light modulation in micro whispering-gallery-mode resonators

Abstract: Techniques (100) for directly converting an electrical signal into an optical signal (114) by using a whispering gallery mode optical resonator (101, 116, 110) formed of a dielectric material that allows for direct modulation of optical absorption by the electrical signal

Phase-map measurements by interferometry with sinusoidal phase modulation and four integrating buckets

Abstract: Phase-shifting interferometry based on the integrating-bucket technique with sinusoidal phase modulation is studied theoretically and demonstrated experimentally to obtain phase maps from double-beam interferometers. The method uses four frames obtained by integration of the time-varying intensity in an interference pattern during the four quarters of the modulation period. An optimum sinusoidal phase modulation is found to minimize the effect of the additive noise. The absolute accuracy of the phase measurements is discussed. Possible applications of the method are demonstrated with two interference microscopes with which the phase modulation is achieved by sinusoidal oscillation of a mirror attached to a piezoelectric transducer and by sinusoidal birefringence modulation with a photoelastic modulator. In both experimental arrangements, phase images can be produced in real time at a rate of several hertz. Noise measurements are reported and compared with theory.

Analysis of signal degree of polarization degradation used as control signal for optical polarization mode dispersion compensation

Abstract: The basic property of degree of polarization (DOP) degradation of optical signal induced by polarization mode dispersion (PMD) in high-speed optical fiber transmission is investigated in detail. The DOP of the optical signal reflects the degree of waveform degradation caused by PMD, therefore, it is proposed to be used as the control signal judging the best compensation point for the optical adaptive PMD compensation techniques. However, the signal DOP is not only affected by PMD, but also by various factors, such as the modulation format, modulator chirp, fiber nonlinearity, amplified spontaneous emission (ASE), and so on. We use numerical simulations and experiments to explore the basic DOP property to detect PMD with these factors. We also show that using the signal DOP as control signal is especially useful for the optical duo-binary modulation because of its high sensitivity and wide PMD detection range.

General expressions for IM/DD dispersive analog optical links with external modulation or optical up-conversion in a Mach-Zehnder electrooptical modulator

Abstract: A general derivation of the optical modulation process in a dual-drive Mach-Zehnder modulator (DD-MZM) is introduced. The expressions include all harmonics and are entirely general in terms of bias point. Chromatic dispersion is also included allowing the prediction of a number of important phenomena in photonic signal transmission. Examples of special cases of these general equations are then presented. Similar expressions are introduced for harmonic optical up-conversion through a photonic mixer based on a DD-MZM covering any bias point or phase shift between DD-MZM drives.

Digital generation of RF signals for wireless communications with band-pass delta-sigma modulation

Abstract: This paper demonstrates a high speed digital technique to produce binary (digital) signals that encode representative RF signals (with time varying envelope) as needed for wireless communications. Specifically, it shows that IS-95 format CDMA signals can be generated with a single bit digital data stream at 3.6 Gb/S. The technique uses band-pass delta-sigma modulation so that the quantization noise is shaped out of the frequency band of interest. This approach points the way to single-chip, DSP-based transmitters, used in conjunction with switching mode power amplifiers and simple analog filters, to implement all the functions of a wireless transmitter.

Orthogonal frequency division multiplex system and transmitter-receiver

Abstract: PROBLEM TO BE SOLVED: To reduce the processing quantity of control over a modulation system by reducing the amount of control information. SOLUTION: A received electric power measurement part 22 measures the received electric power of each subcarrier of an OFDM signal to put together continuous subcarriers having received electric power which do not exceed a threshold ΔE preliminarily set in a control part 26 in a block. Modulation information consisting of modulation system specification information specifying a modulation system corresponding to the received electric power of each block and the head subcarrier numbers of the respective blocks is generated by the control part 26 and reported from a mobile station 2 to a base station 1. The base station 1 stores the modulation information in a modulation information management table 15a in a control part 15 and controls modulation systems of the respective subcarriers of the OFDM signal to be sent to the mobile station 2, block by block, according to the modulation information. COPYRIGHT: (C)2003,JPO

Single-transverse-mode vertical-cavity lasers under continuous and pulsed operation

Abstract: Using a hybrid ion implanted/selectively oxidized device structure, we report high-power single-mode operation of an 850-nm vertical-cavity laser. Under continuous-wave operation, >4 mW of single-mode power with 45 dB of side-mode suppression is achieved. The spectral behavior under pulsed modulation is determined to be influenced by thermal lensing. When biased to threshold, single-mode operation with >35-dB side-mode suppression is obtained for large signal modulation.

A blockwise loading algorithm for the adaptive modulation technique in OFDM systems

Abstract: The OFDM transmission technique has the inherent flexibility to adapt the modulation scheme on each subcarrier according to the reception quality, i.e. the signal-to-noise ratio (SNR) on a subcarrier. The allocation of bits to subcarriers is performed by so-called loading algorithms. In this paper, a new and rather simple loading algorithm is introduced which shows comparable performance and lower computational complexity compared to the well-known algorithm of Chow et al. (1995). In the proposed algorithm, subcarriers are clustered in blocks, which are allocated the same modulation scheme. This way, the signalling overhead can be reduced in comparison with standard subcarrier bit loading algorithms.

Joint MAP equalization and channel estimation for frequency-selective and frequency-flat fast-fading channels

Abstract: This paper presents a new fractionally-spaced maximum a posteriori (MAP) equalizer for data transmission over frequency-selective fading channels. The technique is applicable to any standard modulation technique. The MAP equalizer uses an expanded hypothesis trellis for the purpose of joint channel estimation and equalization. The fading channel is estimated by coupling minimum mean square error techniques with the (fixed size) expanded trellis. The new MAP equalizer is also presented in an iterative (turbo) receiver structure. Both uncoded and conventionally coded systems (including iterative processing) are studied. Even on frequency-flat fading channels, the proposed receiver outperforms conventional techniques. Simulations demonstrate the performance of the proposed equalizer.

Multi-carrier cdma communication device, multi-carrier cdma transmitting device, and multi-carrier cdma receiving device

Abstract: The transmitter comprises a data/modulation control section (4) which sets predetermined parameters necessary for demodulation processing, sub-carrier group modulation processing sections (6a to 8c) which perform frequency spreading for each sub-carrier signal in the sub-carrier group, and time spreading sections (10a to 10c) which multiplex all signals after the modulation processing and the frequency spreading for each sub-carrier signal, and perform time spreading with respect to the multiplexed signals. The receiver comprises time despreading sections (35a to 35c) which perform time despreading for each sub-carrier signal, and sub-carrier group demodulation processing sections (36a to 38c) which perform frequency despreading for each sub-carrier signal after the time despreading.

Method and device for optoelectronic distance measurement

Abstract: The invention is directed to a method for optoelectronic distance measurement and a measurement device based on this method, in which two light emitters, particularly laser emitters and two photodiode receivers are used for calibration Part of the modulated output of the main emitter reaches the measurement object and then arrives at the main photoreceiver in the form of scattered light and another part of the output of the main emitter travels directly to a reference photoreceiver, while a part of the modulated output of the reference light emitter is guided directly to the main photoreceiver and another part is guided directly to the reference photoreceiver According to the invention, the light intensities of the main emitter and the reference emitter are simultaneously modulated with different modulation frequencies (f 1 , f 2 ), and a signal mixture is formed in the main receiver as well as in the reference receiver, which signal mixture contains a signal with the intensity modulation frequency (f 1 ) of the main emitter and a signal with the intensity modulation frequency (f 2 ) of the reference emitter The phases of the two signals of the signal mixture are measured simultaneously and the separation of the two phases is carried out by the different frequencies in a subordinate intermediate frequency range and by the different intensity modulation frequencies At least two sequential measurement processes are preferably carried out, wherein the intensity modulation frequencies of the reference emitter and main emitter are exchanged in the second measurement process Phase errors depending upon temperature, aging and reception power can be entirely eliminated by the invention in electro-optic distance measuring devices

Performance analysis of synchronous MC-CDMA in mobile Rayleigh channel with both delay and Doppler spreads

Abstract: Rapid time variations of the mobile communication channel have a dramatic effect on the performance of multicarrier modulation. This paper models the Doppler spread and computes its effect on the bit error rate (BER) for multicarrier code division multiple access (MC-CDMA) transmission and compares it to orthogonal frequency division multiplexing (OFDM). Also, we evaluate the transmission capacity per subcarrier to quantify the potential of MC-CDMA and (coded-) OFDM. We focus on linear receivers, in particular those using the minimum mean-square error (MMSE) criterion. Our channel and system models allow the computation of analytical performance results. Simulations verify some commonly used, yet critical assumptions.