Showing papers on "Bandwidth (signal processing) published in 2001"

The future of wires

Abstract: Concern about the performance of wires wires in scaled technologies has led to research exploring other communication methods. This paper examines wire and gate delays as technologies migrate from 0.18-/spl mu/m to 0.035-/spl mu/m feature sizes to better understand the magnitude of the the wiring problem. Wires that shorten in length as technologies scale have delays that either track gate delays or grow slowly relative to gate delays. This result is good news since these "local" wires dominate chip wiring. Despite this scaling of local wire performance, computer-aided design (CAD) tools must still become move sophisticated in dealing with these wires. Under scaling, the total number of wires grows exponentially, so CAD tools will need to handle an ever-growing percentage of all the wires in order to keep designer workloads constant. Global wires present a more serious problem to designers. These are wires that do not scale in length since they communicate signals across the chip. The delay of these wives will remain constant if repeaters are used meaning that relative to gate delays, their delays scale upwards. These increased delays for global communication will drive architectures toward modular designs with explicit global latency mechanisms.

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.

A 1.75 GHz highly-integrated narrow-band CMOS transmitter with harmonic-rejection mixers

Abstract: A highly integrated 175-GHz 035-/spl mu/m CMOS transmitter is described The I/Q modulator-based transmitter facilitates integration through the use of a unique mixer, termed a harmonic-rejection mixer, and a wide loop bandwidth phase-locked loop (PLL) for the RF synthesizer The harmonic-rejection mixers are used to eliminate the need for a discrete IF filter and the use of a wide loop bandwidth PLL allowed for the complete integration of the synthesizers using low-Q components while achieving low phase noise The entire transmit signal path from the digital-to-analog converters to the power amplifier, including two fully integrated frequency synthesizers, is integrated into a single-chip solution The transmitter was tested with a testing buffer before the power amplifier (PA) and achieved less than 13/spl deg/ rms phase error when modulating a DCS-1800 GMSK signal The prototype consumed 151 mA from a 3-V supply A class-C PA, capable of driving 25 dBm off-chip, was included and the output was compared to the testing buffer with little change in the transmitter performance

Blind estimation of symbol timing and carrier frequency offset in wireless OFDM systems

Abstract: Orthogonal frequency-division multiplexing (OFDM) systems are highly sensitive to synchronization errors. We introduce an algorithm for the blind estimation of symbol timing and carrier frequency offset in wireless OFDM systems. The proposed estimator is an extension of the Gini-Giannakis (see IEEE Trans. Commun., vol.46, p.400-411, 1998) estimator for single-carrier systems. It exploits the cyclostationarity of OFDM signals and relies on second-order statistics only. Our method can be applied to pulse shaping OFDM systems with arbitrary time-frequency guard regions, OFDM based on offset quadrature amplitude modulation, and biorthogonal frequency-division multiplexing systems. We furthermore propose the use of different subcarrier transmit powers (subcarrier weighting) and periodic transmitter precoding to achieve a carrier frequency acquisition range of the entire bandwidth of the OFDM signal, and a symbol timing acquisition range of arbitrary length. Finally, we provide simulation results demonstrating the performance of the new estimator.

Ultra-Wideband Technology for Short- or Medium-Range Wireless Communications

Abstract: Ultra-Wideband (UWB) technology is loosely defined as any wireless transmission scheme that occupies a bandwidth of more than 25% of a center frequency, or more than 1.5GHz. The Federal Communications Commission (FCC) is currently working on setting emissions limits that would allow UWB communication systems to be deployed on an unlicensed basis following the Part 15.209 rules for radiated emissions of intentional radiators, the same rules governing the radiated emissions from home computers, for example. This rule change would allow UWB-enabled devices to overlay existing narrowband systems, which is currently not allowed, and result in a much more efficient use of the available spectrum. Devices could, in essence, fill in the unused portions of the frequency spectrum in any particular location. These recent developments by the FCC give Intel a unique opportunity to develop equipment that could potentially take advantage of the vast amount of usable spectrum that exists in the wireless space, and that could provide an engine to drive the future high-rate applications that are being conceived throughout this industry. Intel Architecture Labs (IAL) is currently researching UWB technology in order to better understand its benefits, limitations, and technical challenges when used for high-rate communications. This paper introduces the reader to this technology, from potential applications to regulatory hurdles, to possible implementations and future challenges.

Nettimer: a tool for measuring bottleneck link, bandwidth

Abstract: Measuring the bottleneck link bandwidth along a path is important for understanding the performance of many Internet applications Existing tools to measure bottleneck bandwidth are relatively slow, can only measure bandwidth in one direction, and/or actively send probe packets We present the nettimer bottleneck link bandwidth measurement tool, the libdpcap distributed packet capture library, and experiments quantifying their utility We test nettimer across a variety of bottleneck network technologies ranging from 192Kb/s to 100Mb/s, wired and wireless, symmetric and asymmetric bandwidth, across local area and cross-country paths, while using both one and two packet capture hosts In most cases, nettimer has an error of less than 10%, but at worst has an error of 40%, even on cross-country paths of 17 or more hops It converges within 10KB of the first large packet arrival while consuming less than 7% of the network traffic being measured

A phenomenological model for the responses of auditory-nerve fibers: I. Nonlinear tuning with compression and suppression.

Abstract: A phenomenological model was developed to describe responses of high-spontaneous-rate auditory-nerve (AN) fibers, including several nonlinear response properties. Level-dependent gain (compression), bandwidth, and phase properties were implemented with a control path that varied the gain and bandwidth of tuning in the signal-path filter. By making the bandwidth of the control path broad with respect to the signal path, the wide frequency range of two-tone suppression was included. By making the control-path filter level dependent and tuned to a frequency slightly higher than the signal-path filter, other properties of two-tone suppression were also included. These properties included the asymmetrical growth of suppression above and below the characteristic frequency and the frequency offset of the suppression tuning curve with respect to the excitatory tuning curve. The implementation of this model represents a relatively simple phenomenological description of a single mechanism that underlies several important nonlinear response properties of AN fibers. The model provides a tool for studying the roles of these nonlinearities in the encoding of simple and complex sounds in the responses of populations of AN fibers.

New microstrip "Wiggly-Line" filters with spurious passband suppression

Abstract: In this paper, we present a new parallel-coupled-line microstrip bandpass filter with suppressed spurious passband. Using a continuous perturbation of the width of the coupled lines following a sinusoidal law, the wave impedance is modulated so that the harmonic passband of the filter is rejected while the desired passband response is maintained virtually unaltered. This strip-width perturbation does not require the filter parameters to be recalculated and, this way, the classical design methodology for coupled-line microstrip filters can still be used. At the same time, the fabrication of the resulting filter layout does not involve more difficulties than those for typical coupled-line microstrip filters. To test this novel technique, 3rd-order Butterworth bandpass filters have been designed at 2.5 GHz, with a 10% fractional bandwidth and different values of the perturbation amplitude. It is shown that for a 47.5 % sinusoidal variation of the nominal strip width, a harmonic rejection of more than 40 dB is achieved in measurement while the passband at 2.5 GHz is almost unaltered.

Synchronous-frame harmonic control for high-performance AC power supplies

Abstract: In order to achieve the reduction of voltage distortion in AC power supplies (ACPSs), this paper describes an implementation of synchronous-frame control for selected frequencies in the output voltage. The regulation of the fundamental output voltage, as well as that of some low-order harmonics, is achieved using a synchronous-frame controller for each selected frequency in addition to a conventional control. The conventional part conserves good dynamic performance under load changes, while rotating-frame controllers allow a slow, but very precise compensation of the residual errors within the assumption that the harmonics produced by distorting load are slowly varying. Moreover, motivated by a fixed-point implementation, a set of refinements and modifications of the original scheme is proposed, allowing a reduction of signal processing requirements and a new control algorithm structure less sensitive to quantization and rounding errors. This solution is particularly effective for high-power fully digitally controlled ACPSs, where the voltage loop bandwidth is usually not large enough to provide regulation at harmonic frequencies. The proposed control scheme has been implemented using a fixed-point single-chip digital signal processor (ADMC401 by Analog Devices). Experimental results on a 3-kVA three-phase converter prototype show the effectiveness of the proposed approach.

On the performance of ultra-wide-band signals in Gaussian noise and dense multipath

Abstract: An ultra-wide-band (UWB) signal is characterized by a radiated spectrum with a very wide bandwidth around a relatively low center frequency. In this paper, we study the reduced fading margin property of UWB signals. To evaluate the fading margin, we compare the performance of UWB signals in an environment with only additive white Gaussian noise (AWGN) versus the performance of UWB signals in a dense multipath environment with AWGN. The assumption here is that the presence of multipath causes a small increase in the signal-to-noise ratio required to achieve reasonable levels of bit error rate. A numerical example confirms this assumption, more specifically, the example shows that to achieve a bit error rate equal to 10/sup -5/, we require about 13.5 dB in the AWGN case and about 15 dB in the multipath case, resulting in a fading margin of just 1.5 dB. This small fading margin can be understood by the ability of the UWB signal to resolve the dense multipath.

Excess power statistic for detection of burst sources of gravitational radiation

Abstract: We examine the properties of an excess power method to detect gravitational waves in interferometric detector data. This method is designed to detect short-duration $(\ensuremath{\lesssim}0.5$ s) burst signals of unknown waveform, such as those from supernovae or black hole mergers. If only the bursts' duration and frequency band are known, the method is an optimal detection strategy in both Bayesian and frequentist senses. It consists of summing the data power over the known time interval and frequency band of the burst. If the detector noise is stationary and Gaussian, this sum is distributed as a ${\ensuremath{\chi}}^{2}$ (non-central ${\ensuremath{\chi}}^{2})$ deviate in the absence (presence) of a signal. One can use these distributions to compute frequentist detection thresholds for the measured power. We derive the method from Bayesian analyses and show how to compute Bayesian thresholds. More generically, when only upper and/or lower bounds on the bursts duration and frequency band are known, one must search for excess power in all concordant durations and bands. Two search schemes are presented and their computational efficiencies are compared. We find that given reasonable constraints on the effective duration and bandwidth of signals, the excess power search can be performed on a single workstation. Furthermore, the method can be almost as efficient as matched filtering when a large template bank is required: for Gaussian noise the excess power method can detect a source to a distance at least half of the distance detectable by matched filtering if the product of duration and bandwidth of the signals is $\ensuremath{\lesssim}100,$ and to a much greater fraction of the distance when the size of the matched filter bank is large. Finally, we derive generalizations of the method to a network of several interferometers under the assumption of Gaussian noise. However, further work is required to determine the efficiency of the method in the realistic context of a detector network with non-Gaussian noise.

A Memory-Based Approach to Anti-Spam Filtering

Abstract: This paper presents an extensive empirical evaluation of memory-based learning in the context of anti-spam filtering, a novel cost-sensitive application of text categorization. Unsolicited commercial e-mail, also known as “spam”, floods the mailboxes of users, causing frustration, wasting bandwidth and money, and exposing minors to unsuitable content. Using a recently introduced publicly available corpus, a thorough investigation of the effectiveness of a memory-based anti-spam filter is performed, including different attribute and distance weighting schemes, and studies on the effect of the neighborhood size, the size of the attribute set, and the size of the training corpus. Three different cost scenarios are identified, and suitable cost-sensitive evaluation functions are employed. We conclude that memory-based anti-spam filtering is practically feasible, especially when combined with additional safety nets. Compared to a previously tested Naive Bays filter, the memory-based filter performs on average better, particularly when the misclassification cost for non-spam messages is high.

Progress in the methodologies for the electrical modeling of interconnects and electronic packages

Abstract: The rapid growth of the electrical modeling and analysis of the interconnect structure, both at the electronic chip and package level, can be attributed to the increasing importance of the electromagnetic properties of the interconnect circuit on the overall electrical performance of state-of-the-art very large scale integration (VLSI) systems. With switching speeds well below 1 ns in today's gigahertz processors, and VLSI circuit complexity exceeding the 100 million transistors per chip mark, power and signal distribution is characterized by multigigahertz bandwidth pulses propagating through a tightly coupled three-dimensional wiring structure that exhibits resonant behavior at the upper part of the spectrum. Consequently, in addition to the inductive and capacitive coupling, present between adjacent wires across the entire frequency bandwidth, distributed electromagnetic effects, manifested as interconnect-induced delay, reflection, radiation, and long-range nonlocal coupling, become prominent at high frequencies, with a decisive impact of overall system performance. The electromagnetic nature of such high-frequency effects, combined with the geometric complexity of the interconnect structure, make the electrical design of today's performance-driven systems extremely challenging. Its success is heavily dependent on the availability of sophisticated electromagnetic modeling methodologies and computer-aided design tools. This paper presents an overview of the different approaches employed today for the development of an electromagnetic modeling and simulation framework that can effectively tackle the complexity of the interconnect circuit and facilitate its design. In addition to identifying the current state of the art, an assessment is given of the challenges that lie ahead in the signal integrity-driven electrical design of tomorrow's performance- and/or portability-driven, multifunctional ULSI systems.

A "better than" Nyquist pulse

Abstract: A novel ISI-free pulse is presented that has smaller maximum distortion, a more open receiver eye, and a smaller probability of error in the presence of symbol timing error than the Nyquist pulse for the same excess bandwidth.

System for bandwidth extension of narrow-band speech

Abstract: A system, computer-readable medium and generated signal are disclosed for extending the bandwidth of a first signal (i.e., a narrowband signal) such as a speech signal. The system produces a second signal from a first signal by computing first area coefficients from a first signal, generating second area coefficients from the first area coefficients and generating a second signal using the second area coefficients. The first signal may be a narrowband signal and second signal may be a wideband signal. The first area coefficients may be narrowband coefficients and the second area coefficients may be wideband area coefficients.

Control of the impedance bandwidth of wideband planar monopole antennas using a beveling technique

Abstract: Wideband planar monopole antennas have recently been proposed for use on digital mobile terminals. The square planar monopole is the simplest to analyze, and suffers little degradation of radiation pattern within the impedance bandwidth. The addition of a bevel on one or both sides of the feed probe is shown to increase the bandwidth with good control of the upper edge frequency. The impedance bandwidth ratio for this antenna is shown to vary from 2:1 to 6:1, which can be controlled by beveling the planar geometry. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 229–232, 2001.

Fabrication and characterization of narrow-band Bragg-reflection filters in silicon-on-insulator ridge waveguides

Abstract: We describe the design, fabrication and measurement of an integrated-optical Bragg grating filter, operating at a freespace wavelength of 1543 nm, based upon a silicon-on-insulator (SOI) ridge waveguide. The measured spectral response for a 4-mm long grating has a bandwidth of 15 GHz (0.12 nm), and shows good agreement with theoretical predictions.

On the upper cutoff frequency of the auditory critical-band envelope detectors in the context of speech perception

Abstract: Studies in neurophysiology and in psychophysics provide evidence for the existence of temporal integration mechanisms in the auditory system. These auditory mechanisms may be viewed as “detectors,” parametrized by their cutoff frequencies. There is an interest in quantifying those cutoff frequencies by direct psychophysical measurement, in particular for tasks that are related to speech perception. In this study, the inherent difficulties in synthesizing speech signals with prescribed temporal envelope bandwidth at the output of the listener’s cochlea have been identified. In order to circumvent these difficulties, a dichotic synthesis technique is suggested with interleaving critical-band envelopes. This technique is capable of producing signals which generate cochlear temporal envelopes with prescribed bandwidth. Moreover, for unsmoothed envelopes, the synthetic signal is perceptually indistinguishable from the original. With this technique established, psychophysical experiments have been conducted to quantify the upper cutoff frequency of the auditory critical-band envelope detectors at threshold, using high-quality, wideband speech signals (bandwidth of 7 kHz) as test stimuli. These experiments show that in order to preserve speech quality (i.e., for inaudible distortions), the minimum bandwidth of the envelope information for a given auditory channel is considerably smaller than a critical-band bandwidth (roughly one-half of one critical band). Difficulties encountered in using the dichotic synthesis technique to measure the cutoff frequencies relevant to intelligibility of speech signals with fair quality levels (e.g., above MOS level 3) are also discussed.

High-efficiency power modulators

Abstract: The present invention, generally speaking, incorporates the power amplifier as a fundamental constituent of a modulator, using polar modulation techniques. Thus, it is possible to achieve the combination of precision signal generation (including envelope variations) along with high energy efficiency in combinations not possible heretofore. In accordance with one embodiment of the invention, a modulated radio (passband) signal generator produces high quality signals of general type, which specifically includes signals with varying envelopes. Signals are generated with high energy efficiency in the conversion of applied DC power to output RF signal power. The result is longer battery life for products such as mobile phone handsets. Dramatically improved efficiency also allows for a dramatic reduction (10 to 1 or greater) in the size of any required heatsink for the radio transmitter, which significantly lowers both cost and size. Furthermore, continuous operation of these radio transmitters is made possible with small temperature rises using small heatsinks, or even without any heatsink components. This provides for high operating reliability, as well as for greater throughput due to the longer operating time allowed. Another aspect of the invention allows the generation of high quality signals with wide bandwidth, without the need for continuous feedback during operation. This further reduces costs by greatly simplifying the design, manufacturing, and complexity of the transmitter circuitry.

Low complexity high-speed communications transceiver

Abstract: A communication system is disclosed that allows high data-rate transmission of data between components. N-bit parallel data is transmitted in K-frequency separated channels on the transmission medium so as to fully take advantage of the overall bandwidth of the transmission medium. As a result, a very high data-rate transmission can be accomplished with low data-bit transmission on individual channels. A transmitter system and a receiver system are described for the communication system.

LOTTERYBUS: a new high-performance communication architecture for system-on-chip designs

Abstract: This paper presents Lotterybus, a novel high-performance communication architecture for system-on-chip (SoC) designs. The Lotterybus architecture was designed to address the following limitations of current communication architectures: (i) lack of control over the allocation of communication bandwidth to different system components or data flows (e.g., in static priority based shared buses), leading to starvation of lower priority components in some situations, and (ii) significant latencies resulting from variations in the time-profile of the communication requests (e.g., in time division multiplexed access (TDMA) based architectures), sometimes leading to larger latencies for high-priority communications.We present two variations of Lotterybus: the first is a low overhead architecture with statically configured parameters, while the second variant is a more sophisticated architecture, in which values of the architectural parameters are allowed to vary dynamically.Our experiments investigate the performance of the Lotterybus architecture across a wide range of communication traffic characteristics. In addition, we also analyze its performance in a 4x4 ATM switch sub-system design. The results demonstrate that the Lotterybus architecture is (i) capable of providing the designer with fine grained control over the bandwidth allocated to each SoC component or data flow, and (ii) well suited to provide high priority communication traffic with low latencies (we observed upto 85.4\% reduction in communication latencies over conventional on-chip communication architectures).

Provision of digital data via multiple broadcasts

Abstract: Internet access is provided through bandwidth available in broadcasted digital television signals, such as the digital television signals produced by terrestrial broadcast towers. Bandwidth is dynamically allocated or provisioned among clients, and is managed in part by the clients, thus providing dynamic, distributed management of spectrum allocation. Automatic provisioning may be applied among different terrestrial transmission towers, or different satellites, among transponders or channels on a given tower, or a given satellite, or among other forms of multiple broadcast origination points. The provisioning dynamically and automatically equalizes load among those multiple broadcast points. Principles of the present invention may also be applied to automatic provisioning of digital content among non-television broadcast sources, such as cellular telephone towers having available bandwidth, analog or digital radio broadcasts having available bandwidth, or satellite broadcast facilities, and/or dedicated broadcast towers or satellites operating in an allocated spectrum and limited to broadcasting requested digital content. In a satellite embodiment, provisioning may occur among multiple satellites as well as between transponders or time- or frequency-multiplexed channels provided by a single satellite.

A system and method for distributing information via a communication network

Abstract: A communication system (100) for distributing information via an HFC network to subscriber destinations (109) including a multi-port switch (119), one or more radio frequency (RF) modems (121) coupled to restrictive ports of the switch, a combiner (125) and a transmitter (127). The switch forwards source information to the RF modems based on address information. Each RF modem modulates and up converts information from the switch to an RF signal within a respective subscriber channel of the television broadcast spectrum. Each channel is assigned to one or more subscribers, and is subscriber is allocated unshared bandwidth. The HFC network includes a distribution point (103), one or more optical nodes (105) and corresponding coaxial cables (137). Each subscriber destination includes a gateway device (139) that is tuned to a corresponding channel to retrieve source information from that channel, and to deliver the information to one or more local subscriber devices.

Pulse compression over a 170-THz bandwidth in the visible by use of only chirped mirrors

Abstract: We report on double-chirped mirrors with custom-tailored dispersion characteristics over a bandwidth of 170 THz in the visible. The mirrors are used in a prismless compressor for a noncollinear optical parametric amplifier in the visible. The compressed pulses, characterized for the what is believed to be first time by use of the spectral phase interferometry for direct electric field reconstruction technique, display a nearly flat phase from 510 to 710 nm and have a duration of 5.7 fs.

High performance stacked crystal filters for GPS and wide bandwidth applications

Abstract: Stacked Crystal Filters, (SCF), are composed of multi-layers of piezoelectric and metal layers. Normally these filters have a complex frequency spectrum containing near-in spurious responses. However, by having the SCF formed in a Solidly Mounted Resonator (SMR) format, the performance of the device is greatly improved by the finite bandwidth of the SMR reflector. The conventional SCF also has a bandwidth that is too small for some wireless applications. This paper will describe the design and performance issues associated with stacked crystal filters using bulk wave thin films with aluminum nitride as the piezoelectric. Filters without spurious responses, filters having wide bandwidths, and filters operating at frequencies up to 8.5 GHz will be described in addition to GPS filters.

Speech enhancement via frequency bandwidth extension using line spectral frequencies

Abstract: This paper contributes to narrowband speech enhancement by means of frequency bandwidth extension A new algorithm is proposed for generating synthetic frequency components in the high-band (ie, 4-8 kHz) given the low-band ones (ie, 0-4 kHz) for wide-band speech synthesis It is based on linear prediction (LPC) analysis-synthesis It consists of a spectral envelope extension using efficiently line spectral frequencies (LSF) and a bandwidth extension of the LPC analysis residual using a spectral folding The low-band LSF of the synthesis signal are obtained from the input speech signal and the high-band LSF are estimated from the low-band ones using statistical models This estimation is achieved by means of four models that are distinguished by means of the first two reflection coefficients obtained from the input signal linear prediction analysis

Real-time location of multiple time-varying strain disturbances, acting over a 40-km fiber section, using a novel dual-Sagnac interferometer

Abstract: Updated results using a novel sensing architecture based on a Sagnac interferometer are presented and, for the first time, real-time separation and positioning of multiple disturbances has been realized. A 40-km long dual-Sagnac sensor was formed by spectral slicing of light from a single, broad-band erbium-doped-fiber super-luminescent source and wavelength division multiplexed (WDM) routing around the loop to form an inherently low loss system. Independent active phase biasing of each Sagnac was employed, allowing the use of a single optical detector. The effects of residual optical cross talk between the two Sagnacs has been accurately modeled, allowing resulting errors to be corrected. The new system has capability for narrow-band fast Fourier transform (FFT) analysis of detected disturbance signals, and hence their separation in the frequency domain. For audio-frequency excitation, an average positional resolution of 100 m over a 40-km length was achieved with a postdetection signal processing bandwidth of 8 Hz.

System and method for adapting rf transmissions to mitigate the effects of certain interferences

Abstract: An unlicensed RF data delivery system uses interference characterization to adapt the RF transmission to accommodate the interferences It uses at least one detection system to determine the type of interference present in an RF band A channel per channel measurement of interference is made, usually in conjunction with a sweep of the total operating spectrum, generating a picture of the interference over the entire frequency spectrum The system characterizes not only interference levels, but bandwidth of the interference A profile is generated, the response to that interference profile is one of several methods, such as frequency change; changing modulation to higher or lower levels; changing the channel width; changing the code rate; changing antenna polarity; and using hub diversity By first characterizing the type of interference, the system response is tailored to maximize the available interference free spectrum

Power spectral strain estimators in elastography

Abstract: Elastography can produce quality strain images in vitro and in vivo. Standard elastography uses a coherent cross-correlation technique to estimate tissue displacement and tissue strain using a subsequent gradient operator. While coherent estimation methods generally have the advantage of being highly accurate and precise, even relatively small undesired motions are likely to cause enough signal decorrelation to produce significant degradation of the elastogram. For elastography to become more universally practical in such applications as hand-held, intravascular and abdominal imaging, the limitations associated with coherent strain estimation methods that require tissue and system stability, must be overcome. In this paper, we propose the use of a spectral shift method that uses a centroid shift estimate (Fig. 5) to measure local strain directly. Furthermore, we also show theoretically that a spectral bandwidth method can also provide a direct strain estimation. We demonstrate that strain estimation using the spectral shift technique is moderately less precise but far more robust than the cross-correlation method. A theoretical analysis as well as simulations and experimental results are used to illustrate the properties associated with this method.