Showing papers on "Bandwidth (signal processing) published in 1999"

Cognitive radio for flexible mobile multimedia communications

Abstract: Wireless multimedia applications require significant bandwidth, some of which will be provided by third-generation (3G) services. Even with substantial investment in 3G infrastructure, the radio spectrum allocated to 3G will be limited. Cognitive radio offers a mechanism for the flexible pooling of radio spectrum using a new class of protocols called formal radio etiquettes. This approach could expand the bandwidth available for conventional uses (e.g. police, fire and rescue) and extend the spatial coverage of 3G in a novel way. Cognitive radio is a particular extension of software radio that employs model-based reasoning about users, multimedia content, and communications context. This paper characterizes the potential contributions of cognitive radio to spectrum pooling and outlines an initial framework for formal radio-etiquette protocols.

Speckle in Optical Coherence Tomography

Abstract: Speckle arises as a natural consequence of the limited spatial-frequency bandwidth of the interference signals measured in optical coherence tomography (OCT). In images of highly scattering biological tissues, speckle has a dual role as a source of noise and as a carrier of information about tissue microstructure. The first half of this paper provides an overview of the origin, statistical properties, and classification of speckle in OCT. The concepts of signal-carrying and signal-degrading speckle are defined in terms of the phase and amplitude disturbances of the sample beam. In the remaining half of the paper, four speckle-reduction methods-polarization diversity, spatial compounding, frequency compounding, and digital signal processing-are discussed and the potential effectiveness of each method is analyzed briefly with the aid of examples. Finally, remaining problems that merit further research are suggested. © 1999 Society of Photo-Optical Instrumentation Engineers.

Design and performance of multicarrier CDMA system in frequency-selective Rayleigh fading channels

Abstract: This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/receiver structure and, the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MC-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.

Area spectral efficiency of cellular mobile radio systems

Abstract: A general analytical framework quantifying the spectral efficiency of cellular systems with variable-rate transmission is introduced. This efficiency, the area spectral efficiency, defines the sum of the maximum average data rates per unit bandwidth per unit area supported by a cell's base station. Expressions for this efficiency as a function of the reuse distance for the worst and best case interference configurations are derived. Moreover, Monte Carlo simulations are developed to estimate the value of this efficiency for average interference conditions. Both fully loaded and partially loaded cellular systems are investigated. The effect of random user location is taken into account, and the impact of lognormal shadowing and Nakagami (1960) multipath fading is also studied.

Bark and ERB bilinear transforms

Abstract: Use of a bilinear conformal map to achieve a frequency warping nearly identical to that of the Bark frequency scale is described Because the map takes the unit circle to itself, its form is that of the transfer function of a first-order allpass filter Since it is a first-order map, it preserves the model order of rational systems, making it a valuable frequency warping technique for use in audio filter design A closed-form weighted-equation-error method is derived that computes the optimal mapping coefficient as a function of sampling rate, and the solution is shown to be generally indistinguishable from the optimal least-squares solution The optimal Chebyshev mapping is also found to be essentially identical to the optimal least-squares solution The expression 08517[arctan(006583fs)]/sup 1/2/-0916 is shown to accurately approximate the optimal allpass coefficient as a function of sampling rate f/sub s/ in kHz for sampling rates greater than 1 kHz A filter design example is included that illustrates improvements due to carrying out the design over a Bark scale Corresponding results are also given and compared for approximating the related "equivalent rectangular bandwidth (ERB) scale" of Moore and Glasberg (ACTA Acustica, vo82, p335-45, 1996) using a first-order allpass transformation Due to the higher frequency resolution called for by the ERB scale, particularly at low frequencies, the first-order conformal map is less able to follow the desired mapping, and the error is two to three times greater than the Bark-scale case, depending on the sampling rate

Direct bandpass sampling of multiple distinct RF signals

Abstract: A goal in the software radio design philosophy is to place the analog-to-digital converter as near the antenna as possible. This objective has been demonstrated for the case of a single input signal. Bandpass sampling has been applied to downconvert, or intentionally alias, the information bandwidth of a radio frequency (RF) signal to a desired intermediate frequency. The design of the software radio becomes more interesting when two or more distinct signals are received. The traditional approach for multiple signals would be to bandpass sample a continuous span of spectrum containing all the desired signals. The disadvantage with this approach is that the sampling rate and associated discrete processing rate are based on the span of spectrum as opposed to the information bandwidths of the signals of interest. Proposed here is a technique to determine the absolute minimum sampling frequency for direct digitization of multiple, nonadjacent, frequency bands. The entire process is based on the calculation of a single parameter-the sampling frequency. The result is a simple, yet elegant, front-end design for the reception and bandpass sampling of multiple RF signals. Experimental results using RF transmissions from the US Global Positioning System-Standard Position Service (GPS-SPS) and the Russian Global Navigation Satellite System (GLONASS) are used to illustrate and verify the theory.

Frequency-selective MEMS for miniaturized low-power communication devices

Abstract: With Q's in the tens to hundreds of thousands, micromachined vibrating resonators are proposed as integrated circuit-compatible tanks for use in the low phase-noise oscillators and highly selective filters of communications subsystems. To date, LF oscillators have been fully integrated using merged CMOS/microstructure technologies, and bandpass filters consisting of spring-coupled micromechanical resonators have been demonstrated in a frequency range from HF to VHF. In particular, two-resonator micromechanical bandpass filters have been demonstrated with frequencies up to 35 MHz, percent bandwidths on the order of 0.2%, and insertion losses less than 2 dB. Higher order three-resonator filters with frequencies near 455 kHz have also been achieved, with equally impressive insertion losses for 0.09% bandwidths, and with more than 64 dB of passband rejection. Additionally, free-beam single-pole resonators have recently been realized with frequencies up to 92 MHz and Q's around 8000. Evidence suggests that the ultimate frequency range of this high-Q tank technology depends upon material limitations, as well as design constraints, in particular, to the degree of electromechanical coupling achievable in microscale resonators.

Characteristics and applications of fast-wave gyrodevices

Abstract: Gyrodevice oscillators and amplifiers (or gyro-oscillators and gyro-amplifiers) are being utilized in a variety of applications where high power levels are required at millimeter-wave frequencies. Gyro-oscillators, developed primarily for magnetic fusion research applications, have achieved power levels near 1 MW for pulse durations in excess of 1 s at frequencies above 100 GHz. Continued work on these devices should enable them to achieve continuous-wave operation at multimegawatt power levels at frequencies in the 100-GHz to 200-GHz range, thereby meeting the requirements of planned magnetic fusion experiments. The development of gyro-oscillators for fusion experiments has led to the utilization of the devices in several industrial applications, such as ceramic sintering and metal joining. Activities in this area involve adapting the oscillators to the industrial environment where reliability, efficiency, and ease of operation are paramount. Gyro-amplifiers are being developed for applications requiring phase coherence and instantaneous bandwidth, such as in linear accelerators and millimeter-wave radar. Impressive results from X-band to W-band already suggest the promise of these devices. Potential new applications and novel gyrodevice design approaches continue to attract the attention of researchers around the world.

On the capacity formula for multiple input-multiple output wireless channels: a geometric interpretation

Abstract: The capacity of multiple input, multiple output wireless channels is computed for Ricean channels The novelty is a geometrical (ray-tracing) interpretation of the MIMO channel capacity formula to find array geometries which greatly enhance channel capacity compared to SISO systems

The digital front-end of software radio terminals

Abstract: When expanding digital signal processing of mobile communications terminals toward the antenna while making the terminal more wideband in order to be able to cope with different mobile communications standards in a software radio based terminal, the designer is faced with strong requirements such as bandwidth and dynamic range. Many publications claim that only reconfigurable hardware such as FPGAs can simultaneously cope with such diversity and requirements. Starting with considerations of the receiver architecture, we describe key functionalities of the digital front-end and highlight how the signal characteristics of mobile communications signals and commonalities among different signal processing operations can be exploited to great advantage, eventually enabling implementations on an ASIC that, although not reconfigurable, would empower the software radio concept.

High-order medium frequency micromechanical electronic filters

Abstract: Third order, high-Q, micromechanical bandpass filters comprised of three ratioed folded-beam resonators coupled by flexural mode springs are demonstrated using an integrated circuit compatible, doped polycrystalline silicon surface-micromachining technology. A complete design procedure for multiresonator micromechanical filters is presented and solidified via an example design. The use of quarter-wavelength coupling beams attached to resonators at velocity-controllable locations is shown to suppress passband distortion due to finite-mass and process mismatch nonidealities, which become increasingly important on this microscale. In addition, low-velocity coupling methods are shown to greatly alleviate the lithographic resolution required to achieve a given percent bandwidth. Ratioed folded-beam micromechanical resonators are introduced as the key impedance transforming components that enable the needed low-velocity coupling. Using these design techniques, balanced three-resonator microscale mechanical filters with passband frequencies centered around 340 kHz are demonstrated with percent bandwidths of 0.1%, associated insertion losses as small as 0.1 dB, 20-dB shape factors as low as 1.5, and stopband rejections greater than 64 dB. Measurement and theory are rigorously compared and important limitations, such as thermal susceptibility, the need for passband tuning, and inadequate electromechanical coupling, are addressed.

New planar dual-mode filter using cross-slotted patch resonator for simultaneous size and loss reduction

Abstract: A class of new planar dual-mode filters are proposed and developed for hybrid and monolithic microwave and millimeter-wave integrated-circuit design. The novelty of the proposed structure is to use a pair of unequal crossed slots that are formed on a square patch resonator such that its radiation loss and structure size can be significantly reduced simultaneously. The physical background of the crossed slots on the patch resonator is explained. Our simulation results show that the proposed filter presents a number of attractive features for practical applications. It is found that the resonant frequency of a filter is reduced, e.g., by 36%, while its unloaded Q/sub 0/ is improved from 180 to 310 as the crossed slot length increases. The coupling characteristics of two degenerate modes backed by a resonator are studied with respect to unequal length of the crossed slots. A dual-mode filter is designed and fabricated with 1.6% bandwidth operating at 1.6 GHz to showcase our proposal. Measured results validate the design predictions well.

Digital controller design for switchmode power converters

Abstract: A thorough and systematic evaluation of different digital control design approaches is presented. The performance of the approaches is compared in terms of both the bandwidth and the phase margin of the control loop, as well as the output transient response subject to line and load step change. Furthermore, the difference of these design approaches under a lower sampling rate is studied. Best digital design approach for power converter applications is identified based on the comparison results.

Optical single sideband transmission at 10 Gb/s using only electrical dispersion compensation

Abstract: A system is presented which uses optical single sideband transmission at 10 Gb/s together with electrical dispersion compensation at the receiver. Transmission with a bit error rate better than 10/sup -10/ on nondispersion shifted fiber is experimentally demonstrated over 320 km and the dispersion from 1000 km of fiber was effectively equalized in simulation. In the transmitter, driving one or two modulators with a combination of a baseband digital signal and the Hilbert transform of that signal creates an optical single sideband signal. In terms of reducing the effects of chromatic dispersion, transmitting the signal in a single sideband format has two advantages over a double sideband format. First, the optical bandwidth of the transmitted single sideband signal is approximately one half of a conventional double sideband signal. Second, an optical single sideband signal with transmitted carrier can be "self-homodyne" detected and the majority of the phase information preserved since no spectrum back folding occurs upon detection. This allows the received signal to be partially equalized in the electrical domain.

A 2-GHz wide-band direct conversion receiver for WCDMA applications

Abstract: A 2-GHz direct conversion receiver for third-generation mobile communications using wide-band code division multiple access achieves -114-dBm sensitivity for 128-kb/s data at 4.096-Mcps spreading rate. The receiver is distributed on four dies. The active RC channel selection filter can be programmed to three different bandwidths from 5 to 20-MHz radio-frequency (RF) spacing; and the gain control is merged with filtering. RF and baseband chips use a 25-GHz, 0.3-/spl mu/m BiCMOS technology while the two analog-to-digital converters are implemented with a 0.5-/spl mu/m CMOS. The double-sideband noise figure is 5.1 dB at the 94-dB maximum voltage gain, and the IIP3 and ITP2 are -9.5 and +38 dBm, respectively, The receiver draws 128 mA from a 2.7-V supply.

Reconstruction of band‐limited signals, irregularly sampled along one spatial direction

Abstract: Seismic signals are often irregularly sampled along spatial coordinates, leading to suboptimal processing and imaging results. Least squares estimation of Fourier components is used for the reconstruction of band-limited seismic signals that are irregularly sampled along one spatial coordinate. A simple and efficient diagonal weighting scheme, based on the distance between the samples, takes the properties of the noise (signal outside the bandwidth) into account in an approximate sense. Diagonal stabilization based on the energies of the signal and the noise ensures robust estimation. Reconstruction for each temporal frequency component allows the specification of a varying spatial bandwidth dependent on the minimum apparent velocity. This parameterization improves the reconstruction capability for the lower temporal frequencies. In practical circumstances, the maximum size of the gaps in which the signal can be reconstructed is three times the (temporal frequency dependent) Nyquist interval. Reconstruction in the wavenumber domain allows a very efficient implementation of the algorithm, and takes a total number of operations a few times that of a 2-D fast Fourier transform corresponding to the size of the output data set. Quality control indicators of the reconstruction procedure can be computed which may also serve as decision criteria on in-fill shooting during acquisition. The method can be applied to any subset of seismic data with one varying spatial coordinate. Applied along the cross-line direction, it can be used to compute a 3-D stack with improved anti-alias protection and less distortion of the signal within the bandwidth.

Piezoelectric microactuator for dual stage control

Abstract: This paper presents a piezoelectric-based microactuator concept that could provide an economical and easily integrated option for dual stage actuation used in rigid disk drives (RDDs). The design and operation of a prototype version is described. Manufacturability of the actuator and its integration in the RDD assembly is assessed. Approaches to providing the voltages required to drive the microactuator to achieve displacement specifications are shown. A model for the dynamic performance is shown, and experimental results are presented. Issues involving dual-input single-output control loop integration are discussed.

A new method for varying adaptive bandwidth selection

Abstract: A novel approach is developed to solve a problem of varying bandwidth selection for filtering a signal given with an additive noise. The approach is based on the intersection of confidence intervals (ICI) rule and gives the algorithm, which is simple to implement and adaptive to unknown smoothness of the signal.

Near ground wideband channel measurement in 800-1000 MHz

Abstract: Frequency domain channel propagation measurements in the 800-1000 MHz band have been performed with ground-lying antennas. The range of path-loss exponent and shadowing variance for indoor and outdoor environment were determined. The range of these values roughly agree with those measured for higher elevation antennas. The frequency selectivity of the RF channel was also characterized by means of determining the average coherence bandwidth (CBW). It was observed that there is a relationship between CBW and distance between transmitting and receiving antennas.

SFDR-bandwidth limitations for high speed high resolution current steering CMOS D/A converters

Abstract: Although very high update rates are achieved in recent publications on high resolution D/A converters, the bottleneck in the design is to achieve a high spurious free output signal bandwidth. The influence of the dynamic output impedance on the chip performance has been analyzed and has been identified as an important limitation for the spurious free dynamic range (SFDR) of high resolution DAC's. Based on the presented analysis an optimized topology is proposed.

Method for transferring and displaying compressed images

Abstract: An image of certain resolution higher than possible in a single transmission over a finite bandwidth channel is obtained by transferring a progressively-rendered, compressed image. Initially, a low quality image is compressed and transmitted over a finite bandwidth channel. Then, a successively higher resolution image information is compressed at a source and is transmitted. The successively higher resolution image information received at the destination end is used to display a higher resolution image at the destination end.

A single-chip narrow-band frequency-domain excisor for a Global Positioning System (GPS) receiver

Abstract: In recent gears, we have witnessed the rapid adoption of the Department of Defense's Global Positioning System (GPS) for navigation in a number of military and civilian applications. Unfortunately, the low-power GPS signal is susceptible to interference. This paper presents a novel VLSI architecture that removes narrow-band signals from the wide-bandwidth GPS spectrum. The interference suppression technique employed is frequency-domain excision. The single-chip frequency-domain excisor transforms the received signal (GPS signal+noise+interference) to the frequency domain, computes signal statistics to determine an excision threshold, removes all spectral energy exceeding that threshold, and restores the remaining signal (GPS signal+noise) to the temporal domain. The heart of this VLSI implementation is an on-chip 256-point fast Fourier transform processor that operates at 40 million complex samples per second. It processes 12-bit (for each I and Q) sampled complex data. The 1.57 million-transistor chip was fabricated in 0.5-/spl mu/m CMOS triple metal technology and is fully functional.

A simple low-bandwidth broadcasting protocol for video-on-demand

Abstract: Broadcasting protocols can reduce the cost of video-on-demand services by using much less bandwidth to transmit videos that are simultaneously watched by many viewers. Unfortunately, the most efficient broadcasting protocols are also the most difficult to implement because they allocate a multitude of very low bandwidth streams to each video. We present a protocol that uses between three and seven high-bandwidth streams per video and never requires more than five percent more bandwidth than any other protocol to guarantee a given average waiting time.

Tailoring unconventional actuators using compliant transmissions: design methods and applications

Abstract: Matching a drive system to the force-displacement characteristics of the load is the cardinal principle in electromechanical systems design. Unconventional actuation schemes; such as piezoelectric, electrostatic, and shape-memory alloys (SMAs), seem to exhibit certain limitations in terms of power density, stroke length, bandwidth, etc., when one attempts to employ them directly to an application. Integrating them with mechanical transmission elements so that the integrated actuator-transmission system matches the load characteristics of the application can enhance the utility of such unconventional actuators. Conventional mechanical devices are sometimes difficult to integrate with unconventional actuating schemes. For instance, the two-dimensional nature of microelectromechanical systems (MEMS) and no-assembly constraints arising from their batch fabrication make it difficult to fabricate, assemble, and integrate a conventional micromechanism with an electrostatic actuator. However, a monolithic "solid-state" mechanical transmission device enables easy integration. The paper presents a systematic method of designing such unconventional mechanisms. The paper presents a generalized methodology for designing compliant mechanisms. Our systematic synthesis formulations provide a mathematical basis for designing compliant mechanisms for: (1) topology generation and (2) size and shape optimization. Design examples illustrate integration with electrostatic, piezoelectric, and SMA actuators for MEMS and smart-structures applications.

Broad-band linearization of a Mach-Zehnder electrooptic modulator

Abstract: Analog optical-link dynamic range in excess of 75 dB in a 1-MHz band has been achieved using specially designed electrooptic modulators that minimize one or more orders of harmonic and intermodulation distortion. To date, however, such "linearized" modulators have only enabled improved link dynamic ranges at frequencies below 1 GHz. Additionally, linearization across more than an octave bandwidth has required precise balancing of the signal voltage levels on multiple electrodes in a custom modulator, which represents a significant implementation challenge. In this paper, a link linearization technique that uses a standard Mach-Zehnder lithium-niobate modulator with only one RF and one dc-bias electrode to achieve broad-band linearization is discussed, resulting in a dynamic range of 74 dB in 1 MHz across greater than an octave bandwidth (800-2500 MHz). Instead of balancing the voltages on two RF electrodes, the modulator in this new link architecture simultaneously modulates optical carriers at two wavelengths, and it is the ratio of these optical carrier powers that is adjusted for optimum distortion canceling. The paper concludes by describing a second analogous link architecture in which it is the ratio of optical power at two modulated polarizations that is adjusted in order to achieve broad-band linearization.

Multiuser OFDM

Abstract: This paper outlines some of the potential advantages of multiuser OFDM. An overview of several new techniques that improve system reliability and spectral efficiency are presented. These include adaptive modulation, adaptive frequency hopping, and multiple transmitter cells. A low bandwidth hardware implementation is also presented.

Ultra wideband data transmission system and method

Abstract: A data-modulated ultra wideband transmitter that modulates the phase, frequency, bandwidth, amplitude and/or attenuation of ultra-wideband (UWB) pulses. The transmitter confines or band-limits UWB signals within spectral limits for use in communication, positioning, and/or radar applications. One embodiment comprises a low-level UWB source (e.g., an impulse generator or time-gated oscillator (fixed or voltage-controlled)), a waveform adapter (e.g., digital or analog filter, pulse shaper, and/or voltage variable attenuator), a power amplifier, and an antenna to radiate a band-limited and/or modulated UWB or wideband signals. In a special case where the oscillator has zero frequency and outputs a DC bias, a low-level impulse generator impulse-excites a bandpass filter to produce an UWB signal having an adjustable center frequency and desired bandwidth based on a characteristic of the filter. In another embodiment, a low-level impulse signal is approximated by a time-gated continuous-wave oscillator to produce an extremely wide bandwidth pulse with deterministic center frequency and bandwidth characteristics. The UWB signal may be modulated to carry multi-megabit per second digital data, or may be used in object detection or for ranging applications. Activation of the power amplifier may be time-gated in cadence with the UWB source thereby to reduce inter-pulse power consumption. The UWB transmitter is capable of extremely high pulse repetition frequencies (PRFs) and data rates in the hundreds of megabits per second or more, frequency agility on a pulse-to-pulse basis allowing frequency hopping if desired, and extensibility from below HF to millimeter wave frequencies.

100 nm bandwidth flat gain Raman amplifiers pumped and gain-equalized by 12-wavelength-channel WDM high power laser diodes

Abstract: We demonstrate 100 nm bandwidth Raman amplifiers using 12-wavelength-channel WDM pump laser diode unit. The gain flatness is less than /spl plusmn/0.5 dB, which is achieved through an asymmetric channel allocation of pump and without any gain equalization filters.

A micromachined vibrating rate gyroscope with independent beams for the drive and detection modes

Abstract: We investigated the mechanical coupling between the drive and detection modes of micromachined vibrating rate gyroscopes, and designed and fabricated a gyroscope with a new structure to reduce the coupling. The coupling of the oscillator was measured using a new measurement system with a two-dimensional laser displacement meter. The oscillations were found to have an elliptical motion due to the coupling. When the frequency mismatch was reduced by means of electrostatic frequency tuning with a DC bias voltage, the coupling increased. The new structure, which has independent beams for the drive and detection modes, exhibited weaker coupling; and the resolution was 0.07 deg/sec at a bandwidth of 10 Hz.

Wideband radio channel measurement system at 2 GHz

Abstract: This paper describes the wideband radio channel sounding techniques for mobile radio channel measurements. Implementation of the cross-correlation method using both a sliding correlator and a matched filter detector is presented. Limitations and accuracy of radio channel measurements are discussed. Typically, delay resolution of about 20 ns is achieved with 100 MHz bandwidth. With a sliding correlator, a dynamic range of 25 dB was obtained with maximum Doppler bandwidth of 25 Hz and maximum excess delay of 19 /spl mu/s. Digital matched filtering with a maximum sampling rate of 125 MHz can be used in real-time measurements with Doppler shifts of several kilohertz and 30 dB dynamic range. Using matched filter deconvolution as a resolution enhancement technique is discussed. Examples of the time-variant complex impulse response measurements are given.