Showing papers on "Bandwidth (signal processing) published in 2003"

Scaling and bandwidth-parameterization based controller tuning

Abstract: A new set of tools, including controller scaling, controller parameterization and practical optimization, is presented to standardize controller tuning. Controller scaling is used to frequency-scale an existing controller for a large class of plants, eliminating the repetitive controller tuning process for plants that differ mainly in gain and bandwidth. Controller parameterization makes the controller parameters a function of a single variable, the loop-gain bandwidth, and greatly simplifies the tuning process. Practical optimization is defined by maximizing the bandwidth subject to the physical constraints, which determine the limiting factors in performance. Collectively, these new tools move controller tuning in the direction of science.

On the spectral and power requirements for ultra-wideband transmission

Abstract: UWB systems based on impulse radio have the potential to provide very high data rates over short distances. In this paper, a new pulse shape is presented that satisfies the FCC spectral mask. Using this pulse, the link budget is calculated to quantify the relationship between data rate and distance. It is shown that UWB can be a good candidate for reliably transmitting 100 Mbps over distances at about 10 meters.

PACT XPP—A Self-Reconfigurable Data Processing Architecture

Abstract: The eXtreme Processing Platform (XPPTM) is a new runtime-reconfigurable data processing architecture. It is based on a hierarchical array of coarsegrain, adaptive computing elements, and a packet-oriented communication network. The strength of the XPPTM technology originates from the combination of array processing with unique, powerful run-time reconfiguration mechanisms. Parts of the array can be configured rapidly in parallel while neighboring computing elements are processing data. Reconfiguration is triggered externally or even by special event signals originating within the array, enabling self-reconfiguring designs. The XPPTM architecture is designed to support different types of parallelism: pipelining, instruction level, data flow, and task level parallelism. Therefore this technology is well suited for applications in multimedia, telecommunications, simulation, signal processing (DSP), graphics, and similar stream-based application domains. The anticipated peak performance of the first commercial device running at 150 MHz is estimated to be 57.6 GigaOps/sec, with a peak I/O bandwidth of several GByte/sec. Simulated applications achieve up to 43.5 GigaOps/sec (32-bit fixed point).

An algorithm for data-driven bandwidth selection

Abstract: The analysis of a feature space that exhibits multiscale patterns often requires kernel estimation techniques with locally adaptive bandwidths, such as the variable-bandwidth mean shift. Proper selection of the kernel bandwidth is, however, a critical step for superior space analysis and partitioning. This paper presents a mean shift-based approach for local bandwidth selection in the multimodal, multivariate case. The method is based on a fundamental property of normal distributions regarding the bias of the normalized density gradient. This paper demonstrates that, within the large sample approximation, the local covariance is estimated by the matrix that maximizes the magnitude of the normalized mean shift vector. Using this property, the paper develops a reliable algorithm which takes into account the stability of local bandwidth estimates across scales. The validity of the theoretical results is proven in various space partitioning experiments involving the variable-bandwidth mean shift.

Chaos-based digital communication systems

Abstract: Publisher Summary This chapter reviews the common chaos-based digital modulation schemes. It also explains the corresponding coherent and noncoherent demodulation schemes. The two multiple-access schemes, based on the differential chaos-shift-keying (DCSK) or the frequency-modulated DCSK modulation (FM-DCSK), and the one multiple-access scheme based on the chaotic frequency modulation are also discussed. In the chaos-based communication systems, the detection schemes are broadly classified into the coherent and noncoherent types. The coherent systems require an exact replica of the chaotic carrier used to carry the information to be reproduced at the receiver, while the noncoherent systems have no such requirement. The chaos-based digital modulation schemes occupy a much wider bandwidth than is required to transmit a stream of binary symbols. Allowing multiple users to share the same bandwidth ensures an efficient use of the spectrum. When the chaos-shift-keying (CSK) signals are decoded based on the estimation of the bit energy, the threshold of the detector is expected to shift with the noise level. This leads to a large number of errors. The DCSK modulation scheme can be useful in overcoming such a problem.

Multiple-antenna capacity in the low-power regime

Abstract: This paper provides analytical characterizations of the impact on the multiple-antenna capacity of several important features that fall outside the standard multiple-antenna model, namely: (i) antenna correlation, (ii) Ricean factors, (iii) polarization diversity, and (iv) out-of-cell interference; all in the regime of low signal-to-noise ratio. The interplay of rate, bandwidth, and power is analyzed in the region of energy per bit close to its minimum value. The analysis yields practical design lessons for arbitrary number of antennas in the transmit and receive arrays.

Control and filter design of three-phase inverters for high power quality grid connection

Abstract: The trend toward using inverters in distributed generation systems and micro-grids has raised the importance of achieving low-distortion, high-quality power export from inverters. Both switching frequency effects and pre-existing grid voltage distortion can contribute to poor power quality. A well designed filter can attenuate switching frequency components but has an impact on the control bandwidth and the impedance presented to grid distortion. This paper describes a filter designed to incorporate an isolating transformer and the design of a complementary controller that rejects grid disturbance, maintains good waveform quality and achieves real and reactive power control. A realistic discrete time implementation is discussed and validated with experimental results.

Plug-in bandwidth matrices for bivariate kernel density estimation

Abstract: We consider bandwidth matrix selection for bivariate kernel density estimators. The majority of work in this area has been directed towards selection of diagonal bandwidth matrices, but full bandwidth matrices can give markedly better performance for some types of target density. Our methodological contribution has been to develop a new version of the plug-in selector for full bandwidth matrices. Our approach has the advantage, in comparison to existing full bandwidth matrix plug-in techniques, that it will always produce a finite bandwidth matrix. Furthermore, it requires computation of significantly fewer pilot bandwidths. Numerical studies indicate that the performance of our bandwidth selector is best when implemented with two pilot estimation stages and applied to sphered data. In this case our methodology performs at least as well as any competing method considered, while being simpler to implement than its competitors.

Impedance, bandwidth, and Q of antennas

Abstract: The purpose of this paper is twofold: (1) to derive an approximate expression for the bandwidth of a tuned antenna in terms of its input impedance that holds at every frequency, i.e., throughout its entire antiresonant and resonant frequency ranges; (2) to relate this expression for bandwidth to the antenna quality factor Q. The approximate expression for the bandwidth and its relationship to Q are both more generally applicable and more accurate than previous formulas. The validity and accuracy of the expressions are confirmed by the numerical solutions to straight-wire and wire-loop, lossy and lossless tuned antennas over a wide enough range of frequencies covering several resonant and antiresonant frequency bands. We show that the matched VSWR bandwidth is a more fundamental measure of bandwidth than conductance bandwidth because it exists in general for all frequencies at which an antenna is tuned. We also find that the Foster reactance theorem does not hold at all frequencies (whether or not the antenna is lossless). Although the general formula we derive for the bandwidth of an antenna involves the frequency derivative of resistance as well as the frequency derivative of reactance, quite remarkably, the half-power matched VSWR bandwidth of a general tuned lossy or lossless antenna is proven to approximately equal to 2/Q for all frequencies if Q/spl gsim/4.

Digital receivers and transmitters using polyphase filter banks for wireless communications

Abstract: Provides a tutorial overview of multichannel wireless digital receivers and the relationships between channel bandwidth, channel separation, and channel sample rate. The overview makes liberal use of figures to support the underlying mathematics. A multichannel digital receiver simultaneously down-converts a set of frequency-division-multiplexed (FDM) channels residing in a single sampled data signal stream. In a similar way, a multichannel digital transmitter simultaneously up-converts a number of baseband signals to assemble a set of FDM channels in a single sampled data signal stream. The polyphase filter bank has become the architecture of choice to efficiently accomplish these tasks. This architecture uses three interacting processes to assemble or to disassemble the channelized signal set. In a receiver, these processes are an input commutator to effect spectral folding or aliasing due to a reduction in sample rate, a polyphase M-path filter to time align the partitioned and resampled time series in each path, and a discrete Fourier transform to phase align and separate the multiple baseband aliases. In a transmitter, these same processes operate in a related manner to alias baseband signals to high order Nyquist zones while increasing the sample rate with the output commutator.

Exploiting faster-than-Nyquist signaling

Abstract: Faster-than-Nyquist signaling introduces intersymbol interference, but increases the bit rate while preserving the signaling bandwidth. For sinc pulses, it has been established that with a small increase in the signaling rate beyond the Nyquist rate, there is no reduction in the minimum Euclidean distance for binary signaling. We generalize these observations to the family of raised-cosine pulses. The structure of the error events that reduce the minimum distance is examined, and constrained coding ideas are suggested that theoretically allow even faster signaling. Then we propose ways of achieving these gains practically by designing appropriate constrained codes and through equalization and iterative joint equalization and decoding (turbo equalization).

Bandwidth of reflectarrays

Abstract: It is shown that the dominant factor controlling reflectarray bandwidth is the bandwidth of the radiating element, and that the effect of non-constant path delays over the surface of the flat reflector has little significance unless the aperture is electrically very large and the f/D ratio is small. An example of a polarisation-twist reflectarray using aperture coupled elements with time delay lines is used to demonstrate this conclusion.

A novel power plane with integrated simultaneous switching noise mitigation capability using high impedance surface

Abstract: A novel technique for suppressing power plane resonance at microwave and radio frequencies is presented. The new concept consists of replacing one of the plates of a parallel power plane pair with a high impedance surface or electromagnetic band gap structure. The combination of this technique with a wall of RC pairs extends the lower edge of the effective bandwidth to dc, and allows resonant mode suppression up to the upper edge of the band-gap. The frequency range for noise mitigation is controlled by the geometry of the HIGP structure.

Narrow bandpass filters using dual-behavior resonators

Abstract: This paper reports on a new concept of narrow bandpass filters leading to perfectly controlled electrical responses within both the required operating bandwidth and adjacent undesired bands. A specific topology is considered for such a "global synthesis": in comparison with conventional filter performances, it provides significant improvements in terms of rejection control. The attenuated frequencies are each located apart from the bandpass frequencies and controlled by means of n transmission zeros introduced through original dual-behavior resonators (DBRs). These resonators are based on the association of different parallel open-ended stubs and allow the designer to independently control the in-band and out-of-band responses of the filter. A global synthesis approach is also discussed on a simplified architecture based on stepped impedance stubs, and the experimental results shown clearly validate the proposed concept. This simplification reduces the number of degrees of freedom when designing a DBR, and consequently the two transmission zeros become dependent.

Higher-order cyclic cumulants for high order modulation classification

Abstract: In this paper we investigate automatic modulation classification (AMC) using homogeneous feature-vectors based on cyclic cumulants (CCs) of fourth-, sixth- and eight-orders, respectively, for QAM, PSK and ASK signals within a pattern recognition framework. Analysis of CCs of the baseband signal at the receiver is performed and used for feature selection. The cycle spectrum of the baseband signal at the receiver is derived as a function of excess bandwidth for a raised cosine pulse shape and a necessary and sufficient condition on the oversampling factor is obtained. Theoretical arguments regarding the discrimination capability of the examined feature-vectors are verified through extensive simulations.

A fast recursive algorithm for optimum sequential signal detection in a BLAST system

Abstract: Bell Laboratories layered space-time (BLAST) wireless systems are multiple-antenna communication schemes that can achieve very high spectral efficiencies in scattering environments with no increase in bandwidth or transmitted power. The most popular and, by far, the most practical architecture is the so-called vertical BLAST (V-BLAST). The signal detection algorithm of a V-BLAST system is computationally very intensive. If the number of transmitters is M and is equal to the number of receivers, this complexity is proportional to M/sup 4/ at each sample time. We propose a very simple and efficient algorithm that reduces the complexity by a factor of M.

A channelized digital ultrawideband receiver

Abstract: A channelized digital ultrawideband (UWB) receiver that efficiently samples the UWB signal at a fraction of the chip frequency is proposed. The received signal is channelized in the frequency domain by employing a bank of mixers and low-pass filters. After sampling at a much reduced frequency, digital synthesis filters optimally estimate the transmitted signals. The signal-to-noise ratio (SNR) of the proposed receiver has been solved and compared against an ideal conventional receiver, which is defined as a receiver that samples at the signal Nyquist rate. When finite resolution analog-to-digital converters (ADC) are employed in the presence of a large narrowband interferer, the proposed receiver significantly outperforms the ideal conventional receiver. For example, the SNR of the proposed receiver is as much as 20 dB higher than the ideal conventional receiver when a 4-bit ADC is used in the presence of a 50 dB (relative to the noise floor) brickwall narrowband interferer with a bandwidth of 15% of the chip frequency.

Time-division superconducting quantum interference device multiplexer for transition-edge sensors

Abstract: We report on the design and performance of our second-generation 32-channel time-division multiplexer developed for the readout of large-format arrays of superconducting transition-edge sensors. We present design issues and measurement results on its gain, bandwidth, noise, and cross talk. In particular, we discuss noise performance at low frequency, important for long uninterrupted submillimeter/far-infrared observations, and present a scheme for mitigation of low-frequency noise. Also, results are presented on the decoupling of the input circuit from the first-stage feedback signal by means of a balanced superconducting quantum interference device pair. Finally, the first results of multiplexing several input channels in a switched, digital flux-lock loop are shown.

Acoustic (Underwater) Communications

Abstract: The need for underwater wireless communications exists in off-shore oil industry, environmental monitoring, speech transmission between divers, control of autonomous underwater vehicles, and mapping of the ocean floor for detection of objects and discovery of new resources. Wireless underwater communications can be established by transmission of acoustic waves. However, the communication channels have limited bandwidth, and often cause severe multipath dispersion and time-variability. Despite these limitations, research efforts of the 90's have culminated in the development of underwater acoustic modems that are capable of transmitting information at rates on the order of several kilobits per second systems over varying distances. The emerging scenario is that of an underwater communication network consisting of both stationary and mobile nodes. Current research is focusing on the design of efficient modulation and coding schemes, adaptive signal processing algorithms for equalization and diversity combining, multiple-access communication methods and network protocols suited for low bandwidth, long propagation delays and strict power requirements encountered in the underwater environment. Keywords: underwater communications; acoustic communications; bandwidt-efficient modulation; adaptive equalization; diversity combining; reduced-complexity receivers; phase-coherent detection; channel estimation; multipath propagation; multiuser detection; underwater networks

Topology design optimization of dielectric substrates for bandwidth improvement of a patch antenna

Abstract: Most literature studies dealing with design optimization for RF applications focused to a large extend on size and shape optimization So far, material and topology optimization has not been pursued primarily due to the challenges associated with the fabrication of inhomogeneous materials and the limited access to analysis tools In this paper, we focus on optimum topology/material design of dielectric substrates for bandwidth enhancement of a simple patch antenna First, the possibility of designing arbitrary dielectric constant materials using off-the-shelf dielectrics is presented as is necessary for the practical fabrication of inhomogeneous substrates Then, a formal design optimization procedure is conducted using the solid isotropic material with penalization (SIMP) method by relying on a fast full wave finite element-boundary integral (FE-BI) simulator The SIMP method is a mathematically well-posed topology optimization algorithm because a continuous density function is used to relate the cell variable to the actual material properties This also allows for a formulation in a versatile optimization framework Sequential linear programming (SLP) is used to solve the nonlinear optimization procedure with the sensitivity analysis based on the adjoint variable method An important advantage of the proposed design optimization approach is its generality to handle multiple objectives and multidisciplinary problems Using the proposed automated design procedure, inhomogeneous substrates are designed which allow for 250% bandwidth enhancement of the square patch antenna Typically, only a few iterations are needed to reach convergence Finally, the designed substrate is post-processed with image processing and fabricated using thermoplastic green machining

Reconfigurable antennas for wireless devices

Abstract: New technologies in communications electronics, such as software-defined radio (SDR) and RF switches implemented using micro-electromechanical systems (MEMS), present new challenges and opportunities for antenna design. In sharp contrast to digital technology where Moore's law reigns, a fundamental law of physics constrains the ability to realize electrically small antennas that are both efficient and broadband. As a result, covering several frequency bands concurrently with a single antenna having enough efficiency and bandwidth is a major challenge. One possible solution to this problem is to use reconfigurable antennas that tune to different frequency bands. Such an antenna would not cover all bands simultaneously, but provides narrower instantaneous bandwidths that are dynamically selectable at higher efficiency than conventional antennas. Such tunable-antenna technology is an enabler for software-definable radios, the RF front ends of which must be reprogrammable on the fly. This paper discusses the practical implementation issues, limitations, and measured results of small, narrowband, tunable antennas within portable handsets. Many of the concepts discussed in this paper will likely become practical and cost effective in the near future because of recent advances in RF MEMS switches.

Method of creating and utilizing diversity in a multiple carrier communication system

Abstract: In many cellular systems, reusing spectrum bandwidth, creates problems in boundary regions between the cells and sectors where the signal strength received from adjacent base stations or adjacent sector transmissions of a single base station may be nearly equivalent. The invention creates a new type of diversity, referred to as multiple carrier diversity by utilizing multiple carriers, assigning different power levels to each carrier frequency at each base station, and/or offsetting sector antennas. The cell and/or sector coverage areas can be set so as to minimize or eliminate overlap between cell and/or sector boundary regions of different carrier frequencies. Mobile nodes traveling throughout the system can exploit multiple carrier diversity by detecting carriers and selecting to use a non-boundary carrier based on other system criteria in order to improve performance. Boundary carriers may, but need not be, identified and excluded from consideration for use by a wireless terminal.

A fast recursive algorithm for optimum sequential signal detection in a BLAST system

Abstract: BLAST (Bell Laboratories layered Space-Time) wireless systems are multiple-antenna communication schemes which can achieve very high spectral efficiencies in scattering environments, with no increase in bandwidth or transmitted power. The most popular and, by far, the most practical architecture is the so-called vertical BLAST (V-BLAST). The signal detection algorithm of a V-BLAST system is computationally very intensive. If the number of transmitters is M and is equal to the number of receivers, this complexity is proportional to M/sup 4/ at each sample time. In this paper, we propose a simple and very efficient algorithm that reduces the complexity by a factor of M.

Investigations into nonuniform photonic-bandgap microstripline low-pass filters

Abstract: With the advent of planar photonic bandgap (PBG) materials, different PBG topologies have been proposed to improve bandgap performances of microwave signals. Conventional circular-patterned PBGs have constraints in the wide stopband performance due to high passband ripples. In this paper, we suggest two novel configurations with nonuniform dimensions of circular-patterned PBGs to improve the stop bandwidth and passband ripples. The dimensions of PBG units are varied proportionally to the coefficients of binomial and Chebyshev polynomials. The simulated and measured responses of the proposed PBG units are presented. It is seen that Chebyshev distribution produces excellent performance by suppressing passband ripples and producing distinct stopband. These performances of passband ripples and stop bandwidth are further improved with Chebyshev distributed annular-ring PBG units with their unique feature of aspect ratio control.

On the capacity of multiuser wireless channels with multiple antennas

Abstract: The advantages of multiuser communication, where many users are allowed to simultaneously transmit or receive in a common bandwidth, are considered for multiple-antenna systems in a high signal-to-noise ratio (SNR) regime. Assuming channel state information at receiver (CSIR) to be available, the ergodic capacity is characterized for both unbiased and biased channels, and the quantitative capacity gain of a multiple-antenna multiuser system is analyzed for multiple-access channels. For highly biased (correlated) channels, a multiuser system is shown to be inherently superior to a single-user system (a time- or frequency-division multiple-access (TDMA or FDMA) based system) due to the underlying multiuser diversity, and the sum capacity is shown to scale linearly with the number of antennas. For unbiased channels, the characteristics of ergodic capacity are shown to transfer to outage capacity when a large degree of space diversity exists, and to deterministic capacity when the number of receive antennas is large. Also, a brief discussion on the multiuser multiple-antenna communication in broadcast channel is provided.

System and method for real-time spectrum analysis in a radio device

Abstract: A real-time spectrum analysis engine (SAGE) that comprises a spectrum analyzer component, a signal detector component, a universal signal synchronizer component and a snapshot buffer component. The spectrum analyzer component generates data representing a real-time spectrogram of a bandwidth of radio frequency (RF) spectrum. The signal detector detects signal pulses in the frequency band and outputs pulse event information entries output, which include the start time, duration, power, center frequency and bandwidth of each detected pulse. The signal detector also provides pulse trigger outputs which may be used to enable/disable the collection of information by the spectrum analyzer and the snapshot buffer components. The snapshot buffer collects a set of raw digital signal samples useful for signal classification and other purposes. The universal signal synchronizer synchronizes to periodic signal sources, useful for instituting schemes to avoid interference with those signals.

Bi-level and full-color video combination for video communication

Abstract: Systems and methods for video communication are described. In one aspect, network bandwidth conditions are estimated. Bi-level or full-color video is then transmitted over the network at transmission bit rates that are controlled as a function of the estimated bandwidth conditions. To this end, network bandwidth capability is periodically probed to identify similar, additional, or decreased bandwidth capabilities as compared to the estimated bandwidth conditions. Decisions to hold, decrease, or increase the video transmission bit rate are made based on the estimated bandwidth conditions in view of the probing operations. When the transmission bit rate is increased or decreased, the transmission bit rate is calculated to target an upper or lower bit rate, both of which are indicated by the estimated bandwidth conditions. Bi-level video communication is switched to full-color video transmission, or vice versa, when the video transmission bit rate respectively reaches the upper bit rate or the lower bit rate.

Performance Analysis and Architectures for INS-Aided GPS Tracking Loops

Abstract: GPS and inertial sensors have complementary characteristics, which have been exploited in the design of integrated GPS-inertial navigation and guidance systems. Traditionally, most hybrid GPS-inertial systems have been mechanized by combining the information from GPS and an Inertial Navigation System using either loose integration (i.e., integration at the position, velocity and/or attitude level) or tight integration (integration at the pseudorange, Doppler, or carrier phase level). Such integration schemes provide users with limited immunity against momentary GPS outages and also allow detection of certain classes of GPS signal failures. A third scheme of integration can be used, in which the inertial sensors are used to aid the GPS phase frequency and code tracking loops directly. In this paper, this level of coupling is referred to as ultra-tight integration, and it offers potential improvements to GPS performance, such as higher phase-tracking bandwidth, and more resistance to radio frequency interference or multipath noise. In this paper we propose a simple architecture for GPS-inertial systems with ultra-tight integration and present the results of some trade studies and simulations quantifying the performance of such systems. Performances of the ultra-tight GPS-inertial system are evaluated using a simulation tool developed specifically for this study. The metrics used for the evaluation are allowable reduction in the carrier tracking loop-filter bandwidth for improved signal-to-noise ratio, and robustness against carrier-phase cycle-slips. The sensitivity of these metrics to inertial sensor quality and GPS receiver clock noise is discussed and quantified. These studies show that an ultra-tightly coupled system using low cost/performance inertial sensors and a typical temperature-compensated crystal oscillator can function with a carrier tracking loop-filter bandwidth as low as 3Hz. This structure shows a 14dB improvement in phasenoise suppression when compared to a traditional 15Hz loop filter, and comparable carrier-phase tracking bandwidth to that of the inertial sensors (>30Hz).

A comparative investigation on channel estimation algorithms for OFDM in mobile communications

Abstract: A comparative investigation on various channel estimation algorithms for OFDM system in the mobile communication environment is presented and analyzed in terms of computational complexity, mean square error, and bit error rate in this paper. As a result, Wiener filter estimation shows the best error performance. Concerning the computational complexity as well as the performance, however, the piecewise linear estimator is considered as a proper choice when the reference signal spacing is relatively narrow. And the cubic-spline estimator is a good alternative to the Wiener filter estimation if the reference signal spacing is wider than the coherent bandwidth of transmission channel.

An adaptive air interface waveform

Abstract: In one embodiment, a method for generating an adaptive air interface waveform includes generating a waveform that includes a variable carrier frequency and variable bandwidth signal. The variable bandwidth signal includes one or more subcarriers that are dynamically placeable over a range of frequencies, and each subcarrier is separately modulated according to a direct sequence (DS) spread spectrum (SS) technique. The waveform has an embedded pilot usable to optimize one or more spectrum efficiencies of the waveform. A modulation constellation, a code rate, and a code length of the generated waveform are adapted according to an available spectrum and one or more sub-carrier conditions.