Showing papers on "Bandwidth (signal processing) published in 2002"

Spectral efficiency in the wideband regime

Abstract: The tradeoff of spectral efficiency (b/s/Hz) versus energy-per-information bit is the key measure of channel capacity in the wideband power-limited regime. This paper finds the fundamental bandwidth-power tradeoff of a general class of channels in the wideband regime characterized by low, but nonzero, spectral efficiency and energy per bit close to the minimum value required for reliable communication. A new criterion for optimality of signaling in the wideband regime is proposed, which, in contrast to the traditional criterion, is meaningful for finite-bandwidth communication.

Characterization of ultra-wide bandwidth wireless indoor channels: a communication-theoretic view

Abstract: An ultra-wide bandwidth (UWB) signal propagation experiment is performed in a typical modern laboratory/office building. The bandwidth of the signal used in this experiment is in excess of 1 GHz, which results in a differential path delay resolution of less than a nanosecond, without special processing. Based on the experimental results, a characterization of the propagation channel from a communications theoretic view point is described, and its implications for the design of a UWB radio receiver are presented. Robustness of the UWB signal to multipath fading is quantified through histograms and cumulative distributions. The all RAKE (ARAKE) receiver and maximum-energy-capture selective RAKE (SRAKE) receiver are introduced. The ARAKE receiver serves as the best case (bench mark) for RAKE receiver design and lower bounds the performance degradation caused by multipath. Multipath components of measured waveforms are detected using a maximum-likelihood detector. Energy capture as a function of the number of single-path signal correlators used in UWB SRAKE receiver provides a complexity versus performance tradeoff. Bit-error-probability performance of a UWB SRAKE receiver, based on measured channels, is given as a function of the signal-to-noise ratio and the number of correlators implemented in the receiver.

Broadband Modulation of Light by Using an Electro-Optic Polymer

Abstract: A major challenge to increasing bandwidth in optical telecommunications is to encode electronic signals onto a lightwave carrier by modulating the light up to very fast rates Polymer electro-optic materials have the necessary properties to function in photonic devices beyond the 40-GHz bandwidth currently available An appropriate choice of polymers is shown to effectively eliminate the factors contributing to an optical modulator's decay in the high-frequency response The resulting device modulates light with a bandwidth of 150 to 200 GHz and produces detectable modulation signal at 16 THz These rates are faster than anticipated bandwidth requirements for the foreseeable future

Resonator-based analysis of the combination of mobile handset antenna and chassis

Abstract: The performance of the mobile phone handset antenna-chassis combination is analyzed based on an approximate decomposition of the waves on the structure into two resonant wavemodes: the antenna-element wavemode and the chassis wavemode. A double resonator equivalent circuit model is presented and used to estimate the impedance bandwidth and the respective distributions of radiation losses with typical parameter values at 900 and 1800 MHz. It is noticed that at 900 MHz, the radiation losses of the antenna element wavemode represent typically less than 10% of the total power. Thus, the antenna element works mainly as a matching element, which couples to the low-Q resonant wavemode of the chassis. At 1800 MHz, the contribution of the antenna element wavemode is larger. By enhancing the coupling and by tuning the chassis resonance, it is possible to obtain an impedance bandwidth of over 50% (6 dB return loss) at both at 900 and 1800 MHz. The results given by the equivalent circuit study are fully supported by those of three-dimensional phone-model simulations, including calculation of the SAR and efficiency values. In prototyping, the 6 dB bandwidth of 5.5% was obtained at 980 MHz with a nonradiating coupling element with a volume of 1.6 cm/sup 3/ on a 120 mm long chassis.

Synthesis of direct-coupled-resonators bandpass filters for WDM systems

Abstract: A simple technique for the exact synthesis of selective bandpass filters for wavelength division multiplexing (WDM) systems is presented. The filters consist of direct-coupled ring resonators or cascaded Bragg gratings. The proposed technique permits the calculation of the physical dimensions of the optical structures given the desired frequency response of the filter in terms of bandwidth, free spectral range, out-of-band rejection, and frequency characteristic. The technique, explained in detail for Butterworth and Chebyshev frequency responses, is exact, uses closed-form formulae, and is physically well based. The resulting devices are very compact, have a high out-of-band attenuation, and are suitable for high-density integrated optics. Several filters for applications such as channel add-drop, channel selection, demultiplexing, multichannel filtering, and interleavers are designed, analyzed, and discussed in the paper.

Monocycle shapes for ultra wideband system

Abstract: Ultra wideband (UWB) is a promising technique for wireless communications. It is a carrier-free (base-band) technique, which can greatly reduce the complexity and cost of the transceiver. In contrast with conventional communication systems using the "sine wave", UWB information is carried in a very short pulse, which covers an extremely wide spectrum bandwidth. Several candidate monocycle (narrow pulse) shapes are investigated, their spectrum characteristics and BER performance in AWGN using pulse position modulation (PPM) are simulated, and the results are compared. Their performances in the fading multipath channel are also investigated.

Bandwidth scaling for fading multipath channels

Abstract: We show that very large bandwidths on fading multipath channels cannot be effectively utilized by spread-spectrum systems that (in a particular sense) spread the available power uniformly over both time and frequency. The approach is to express the input process as an expansion in an orthonormal set of functions each localized in time and frequency. The fourth moment of each coefficient in this expansion is then uniformly constrained. We show that such a constraint forces the mutual information to 0 inversely with increasing bandwidth. Simply constraining the second moment of these coefficients does not achieve this effect. The results suggest strongly that conventional direct-sequence code-division multiple-access (CDMA) systems do not scale well to extremely large bandwidths. To illustrate how the interplay between channel estimation and symbol detection affects capacity, we present results for a specific channel and CDMA signaling scheme.

Ultra wide bandwidth spread-spectrum communications system

Abstract: An ultra wide bandwidth, high speed, spread spectrum communications system uses short wavelets of electromagnetic energy to transmit information through objects such as walls or earth. The communication system uses baseband codes formed from time shifted and inverted wavelets to encode data on a RF signal. Typical wavelet pulse durations are on the order of 100 to 1000 picoseconds with a bandwidth of approximately 8 GHz to 1 GHz, respectively. The combination of short duration wavelets and encoding techniques are used to spread the signal energy over an ultra wide frequency band such that the energy is not concentrated in any particular narrow band (e.g. VHF: 30-300 MHz or UHF: 300-1000 MHz) and is not detected by conventional narrow band receivers so it does not interfere with those communication systems. The use of pulse codes composed of time shifted and inverted wavelets gives the system according to the present invention has a spatial resolution on the order of 1 foot which is sufficient to minimize the negative effects of multipath interference and permit time domain rake processing.

Layered space-time receivers for frequency-selective wireless channels

Abstract: Results in information theory have demonstrated the enormous potential of wireless communication systems with antenna arrays at both the transmitter and receiver. To exploit this potential, a number of layered space-time architectures have been proposed. These layered space-time systems transmit parallel data streams, simultaneously and on the same frequency, in a multiple-input multiple-output fashion. With rich multipath propagation, these different streams can be separated at the receiver because of their distinct spatial signatures. However, the analysis of these techniques presented thus far had mostly been strictly narrowband. In order to enable high-data-rate applications, it might be necessary to utilize signals whose bandwidth exceeds the coherence bandwidth of the channel, which brings in the issue of frequency selectivity. In this paper, we present a class of layered space-time receivers devised for frequency-selective channels. These new receivers, which offer various performance and complexity tradeoffs, are compared and evaluated in the context of a typical urban channel with excellent results.

Chip-interleaved block-spread code division multiple access

Abstract: A novel multiuser-interference (MUI)-free code division multiple access (CDMA) transceiver for frequency-selective multipath channels is developed. Relying on chip-interleaving and zero padded transmissions, orthogonality among different users' spreading codes is maintained at the receiver even after frequency-selective propagation. As a result, deterministic multiuser separation with low-complexity code-matched filtering becomes possible without loss of maximum likelihood optimality. In addition to MUI-free reception, the proposed system guarantees channel-irrespective symbol detection and achieves high bandwidth efficiency by increasing the symbol block size. Filling the zero-gaps with known symbols allows for perfectly constant modulus transmissions. Important variants of the proposed transceivers are derived to include cyclic prefixed transmissions and various redundant or nonredundant precoding alternatives. (Semi-) blind channel estimation algorithms are also discussed. Simulation results demonstrate improved performance of the proposed system relative to competing alternatives.

Radio frequency characterization of cable plant and corresponding calibration of communication equipment communicating via the cable plant

Abstract: A switch router and one or more gateways incorporating a diagnostic and calibration system that performs RF characterization of an underlying cable plant The switch router is connected at a point of insertion or point of distribution and each gateway is located downstream, such as at corresponding subscriber locations The switch router and each gateway sends a test signal with known characteristics and power level, and the receiving device determines noise level and power loss for the corresponding downstream and upstream channel pair The power loss information is used to calibrate the power level of the transmitters The noise levels are used to determine if the selected modulation schemes employed for normal communications is realizable A frequency analysis, such as FFT or the like, is performed on the upstream test signal spectrum to derive valuable frequency information for the upstream channel or the entire upstream bandwidth

Ultra wide bandwidth communications method and system

Abstract: An ultra wide bandwidth, high speed, spread spectrum communications system uses short wavelets of electromagnetic energy to transmit information through objects such as walls or earth. The communication system uses baseband codes formed from time shifted and inverted wavelets to encode data on a RF signal. Typical wavelet pulse durations are on the order of 100 to 1000 picoseconds with a bandwidth of approximately 8 GHz to 1 GHz, respectively. The combination of short duration wavelets and encoding techniques are used to spread the signal energy over a an ultra wide frequency band such that the energy is not concentrated in any particular narrow band (e.g. VHF: 30-300 MHz or UHF: 300-1000 MHz) and is not detected by conventional narrow band receivers so it does not interfere with those communication systems. The use of pulse codes composed of time shifted and inverted wavelets gives the system according to the present invention has a spatial resolution on the order of 1 foot which is sufficient to minimize the negative effects of multipath interference and permit time domain rake processing.

Frequency characteristics of wavelets

Abstract: Wavelets detect and locate time of disturbances successfully, but for measurement of power/energy they also have to estimate and classify them accurately. This paper investigates the factors on choice of a certain wavelet function and qualitatively shows how the number of coefficients of the wavelets is an important number that affects output decomposition and energy distribution leakage. Wavelets provide an output in terms of the time-frequency scale. The frequency bandwidth characteristics of these individual wavelet levels provide better understanding of the wavelets. The sampling frequency and the number of data points are important parameters and must be carefully selected to avoid the frequency of interest falling into the end regions.

An injection-locking scheme for precision quadrature generation

Abstract: We describe a novel quadrature splitter based on injection locking a cascade of ring oscillators to a low-phase-noise (external) single-phase reference clock. The output signals are in accurate quadrature with low phase noise over a wide bandwidth. This scheme inherently operates at high signal frequencies and is insensitive to the shape of the reference clock waveform. Experimental results at 2.7 GHz are reported for a prototype implementation in 0.25-/spl mu/m BiCMOS technology. To prove the viability of this scheme, a single-sideband upconverter was implemented along with the splitter. Over several chips, an average sideband suppression better than 45 dB over a large signal bandwidth of 100 MHz was achieved.

Bandwidth extension of audio signals by spectral band replication

Abstract: Spectral Band Replication (SBR) is a new audio coding tool that significantly improves the coding gain of perceptual coders and speech coders. Currently, there are three different audio coders that have shown a vast improvement by the combination with SBR: MPEG-AAC, MPEG-Layer II and MPEG-Layer III (mp3), all three being parts of the open ISO-MPEG standard. The combination of AAC and SBR will be used in the standardized Digital Radio Mondiale (DRM) system, and SBR is currently also being standardized within MPEG-4. SBR is a so-called bandwidth extension technique, where a major part of a signal’s bandwidth is reconstructed from the lowband on the receiving side. It is developed and marketed by Coding Technologies, an international company in the audio coding field. This paper will focus on the technical details of SBR and in particular on the filter bank, which is the basis of the SBR process.

Principles of space-time array processing for ultrawide-band impulse radar and radio communications

Abstract: The emerging ultrawide-band (UWB) impulse technology has found numerous applications in the commercial as well as the military sector. The rapid technological advances have made it possible to implement (cost-effective, short-range) impulse radar and impulse-radio communication and localization systems. Array beamforming and space-time processing techniques promise further advancement in the operational capabilities of impulse radar and impulse-radio communications to achieve long-range coverage, high capacity and interference-free quality of reception. We introduce a realistic signal model for UWB impulse waveforms and develop the principles of space-time array processing based on the signal model. A space-time resolution function (STRF), a space-frequency distribution function (SFDF) and a monopulse-tracking signal are derived for impulse waveforms received by a self-steering array beamforming system. The directivity peak-power pattern and energy pattern of the beamformer are also derived. Computer plots of the STRF, SFDF and the beam patterns are obtained. The directivity beam patterns of impulse waveforms are sidelobe-free and, therefore, there is no need for sidelobe suppression via amplitude weighting of the array elements. Also, the resolution angle for the beam patterns is derived as a decreasing function of array size and frequency bandwidth. Electronic beamsteering based on slope processing of monopulse waveforms is described.

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

Abstract: A 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.

System and method for signal classiciation of signals in a frequency band

Abstract: A system and method for classifying signals occurring in a frequency band. One or more characteristics of one or more signals in the frequency band are detected using any suitable technology, such as a device that can generate characteristics of signal pulses detected in the frequency band. Data pertaining to the signal pulses is accumulated over time. The accumulated signal data is compared against reference data associated with known signals to classify the one or more signals in the frequency band based on the comparison. The accumulated data may include one or more characteristics selected from the group consisting of: pulse center frequency, pulse bandwidth, pulse duration, time between pulses and number of different active pulses, and wherein the reference data associated with each of a plurality of known signals comprises one or more characteristics selected from the group consisting of: pulse center frequency, pulse bandwidth, pulse duration and time between pulses. The accumulated signal data is compared against the reference data, and depending on the degree of match with reference data, a signal can be classified. Additional levels of signal classification processing may be performed.

Compact Nd:YVO/sub 4/ lasers with pulse repetition rates up to 160 GHz

Abstract: We present a comprehensive study on multigigahertz repetition rate Nd:YVO/sub 4/ lasers, passively mode-locked with semiconductor saturable absorber mirrors. A brief review of Q-switching instabilities with special emphasis on high repetition rate is given. We then present basic design guidelines, and experimentally show that one can push the pulse repetition rate of a Nd: YVO/sub 4/ laser up to 157 GHz, reaching the fundamental limit to the repetition rate which is given by the pulse duration and thus by the amplification bandwidth. We also demonstrate an air-cooled diode-pumped 10-GHz Nd: YVO/sub 4/ laser with 2.1-W average output power and 13% electrical-to-optical efficiency, showing the potential of solid-state lasers generating multiwatt, multigigahertz pulse trains with high efficiency.

A method of bandwidth extension for narrow-band speech

Abstract: A system and method are disclosed for extending the bandwidth of a narrowband signal such as a speech signal. The method applies a parametric approach to bandwidth extension but does not require training. The parametric representation relates to a discrete acoustic tube model (DATM). The method comprises computing narrowband linear predictive coefficients (LPCs) from a received narrowband speech signal, computing narrowband partial correlation coefficients (parcors) using recursion, computing Mnb area coefficients from the partial correlation coefficient, and extracting Mwb area coefficients using interpolation. Wideband parcors are computed from the Mwb area coefficients and wideband LPCs are computed from the wideband parcors. The method further comprises synthesizing a wideband signal using the wideband LPCs and a wideband excitation signal, highpass filtering the synthesized wideband signal to produce a highband signal, and combining the highband signal with the original narrowband signal to generate a wideband signal. In a preferred variation of the invention, the Mnb area coefficients are converted to log-area coefficients for the purpose of extracting, through shifted-interpolation, Mwb log-area coefficients. The Mwb log-area coefficients are then converted to Mwb area coefficients before generating the wideband parcors.

Continuously tunable, precise, single frequency optical signal generator

Abstract: To realize a genuine CW optical frequency synthesizer, a continuously tunable single-frequency CWlaser has been employed to track precisely any arbitrary component of a wide bandwidth phase-stabilized optical comb. We demonstrate experimentally two fundamental aspects of optical frequency synthesis, namely, precise setting of the laser frequency at an arbitrary pre-determined value, and continuous tuning of the laser frequency with the digital precision known in radio frequency synthesis. A typical computer-automated search-and-lock procedure finishes on oneminute time scale.

A CMOS highly linear channel-select filter for 3G multistandard integrated wireless receivers

Abstract: A new approach for designing digitally programmable CMOS integrated baseband filters is presented. The proposed technique provides a systematic method for designing filters exhibiting high linearity and low power. A sixth-order Butterworth low-pass filter with 14-bit bandwidth tuning range is designed for implementing the baseband channel-select filter in an integrated multistandard wireless receiver. The filter consumes a current of 2.25 mA from a 2.7-V supply and occupies an area of 1.25 mm/sup 2/ in a 0.5-/spl mu/m chip. The proposed filter design achieves high spurious free dynamic ranges (SFDRs) of 92 dB for PDC (IS-54), 89 dB for GSM, 84 dB for IS-95, and 80 dB for WCDMA.

A method and system for broadband predistortion linearizaion

Abstract: The invention relates to a method and system for broadband digital predistortion linearizaion, which used to overcome the influence of memory effect in the radio frequency power amplifier, to expand the digital predistortion linearizaion bandwidth, and to improve the digital predistortion linearizaion performance. The method and system, according to characteristic parameter of amplifier, can get the in band and out of band predistortion signal, and then the combined signals be inputted to power amplifier as input signal; A part of the output signal from the power amplifier can be the feedback signal, compare it to the original input signal, and according to the comparative result, characteristic parameter of amplifier of in band and out of band pedistortion signal be generated by adaptive adjustment, so that the waveforms or frequency spectrum of feedback signal and input original signal could be nearest.

Design challenges for very high data rate UWB systems

Abstract: Ultrawideband (UWB) is a promising radio technology for networks delivering extremely high data rates at short ranges. In this paper, different approaches to the physical layer system design for such networks are studied, and some of the challenges and opportunities inherent in their design and implementation are compared. For example, the use of extremely short duration pulses offers great possibilities for position location, but makes the timing synchronization task more complex. The ultra-wide bandwidth offers excellent frequency diversity and multipath resolution, but the channel estimation and multipath combining tasks are correspondingly more challenging. A pulse based UWB system (or impulse radio, IR-UWB) and a novel pulsed multicarrier UWB system are compared, emphasizing timing acquisition and performance in multipath. Some other differences, including interference avoidance, equalization, etc. are briefly dealt with.

An on-chip 100 GHz-sampling rate 8-channel sampling oscilloscope with embedded sampling clock generator

Abstract: An on-chip 8-channel sampling oscilloscope macro for signal integrity checking uses a 0.13 /spl mu/m CMOS process. It contains a phase-interpolated sampling clock generator for 100GHz sampling, charge-sharing sampling heads, and ESD-tolerant decoupling capacitors for noise-immune measurement.

The ALTRO chip: a 16-channel A/D converter and digital processor for gas detectors

Abstract: The ALTRO (ALICE TPC Read Out) chip is a mixed-signal integrated circuit designed to be one of the building blocks of the readout electronics for gas detectors. Originally conceived and optimised for the Time Projection Chamber (TPC) of the ALICE experiment at the CERN LHC, its architecture and programmability makes it suitable for the readout of a wider class of gas detectors. In one single chip, the analogue signals from 16 channels are digitised, processed. compressed and stored in a multi-acquisition memory. The Analogue-to-Digital converters embedded in the chip have a 10-bit dynamic range and a maximum sampling rate in the range of 20 to 40 MHz. After digitisation, a pipelined hardwired processor is able to remove from the input signal a wide range of systematic and non- systematic perturbations, related to the non-ideal behaviour of lite detector, temperature variation of the electronics, environmental noise, etc. Moreover. the processor is able to suppress the signal tail within 1 /spl mu/s after the pulse peak with 0.1% accuracy thus narrowing the pulses to improve their identification. The signal is then compressed by removing all data below a programmable threshold, except for a specified number of pre- and post-samples around each peak. This produces non-zero data packets. Eventually, each data packet is marked with its time stamp and size - so that the original data can be reconstructed afterwards and stored in lite multi-acquisition memory that has a readout bandwidth of 300 Mbyte/sec. This paper addresses the algorithms of lite implemented digital functions and the performance of the ALTRO chip on measured data.

Subnanosecond UWB channel sounding in frequency and temporal domain

Abstract: The performance prediction and simulation of new communication and positioning systems based on UWB technology require an important effort to reach a deep knowledge of the physical channel The multipath nature of the indoor channel is the limiting factor for positioning accuracy and communication capabilities of UWB systems in real environments, in particular ISI for high data rate applications Most of the measurement performed to characterise the UWB channel have been performed in the time-domain by using a sampling oscilloscope with resolution greater than 1 ns This paper describes a frequency approach based on a vector network analyser with a subnanosecond resolution in accordance with usually UWB pulse width After an introduction the measurement technique is described and the performances of the sounding chain evaluated Then an experimental methodology is proposed in order to assess the channel characteristics at different scale levels (small, medium, large) Finally the statistical post-processing for the future measurements is described

Narrowband interference suppression in time-hopping impulse-radio systems

Abstract: Ultra-wideband (UWB) radio systems have drawn a lot of attention during the last few years. These systems use very low transmission power, spread over a bandwidth of several gigahertz. The very low transmission power and the large bandwidth used enable UWB radio systems to coexist with other narrowband systems over the same frequency band without interfering with the narrowband systems. Nevertheless, these narrowband systems may cause interference which jams the UWB receiver completely. Since standard narrowband interference suppression techniques are not applicable, techniques for interference suppression have to be developed. This paper presents novel narrowband interference suppression algorithms for UWB radio systems. Theoretical analysis of these algorithms reveal that they can eliminate the narrowband interference almost completely.

Millimeter-wave remote self-heterodyne system for extremely stable and low-cost broad-band signal transmission

Abstract: We have developed a millimeter-wave remote self-heterodyne transmission system that enables extremely stable and low-cost broad-band transmission in the millimeter-wave band. The system was applied to a 60-GHz-band transmission system for the first time. The transmitter of the developed system transmits RF modulated signals and a local oscillation signal simultaneously, and the receiver detects these signals by using a square-law-type detection technique, thus creating a very stable and low phase-noise millimeter-wave transmission link without the use of an expensive and more advanced frequency-stabilization technology. Since the receiver no longer requires a millimeter-wave oscillator for frequency conversion, the devices used in this system can be miniaturized and the cost of the system can be reduced. This paper discusses the performance of the developed system in terms of its phase-noise degradation and carrier-to-noise power ratio (CNR). We also discuss the optimal transmitter design to obtain the maximum CNR. Using our miniaturized monolithic millimeter-wave integrated-circuit-based 60-GHz-band experimental system, we demonstrate that our millimeter-wave transmission link is completely free of phase-noise and frequency-offset degradation due to the use of a millimeterwave local oscillator. We show that equal transmission-power distribution between the RF signal and local carrier gives the maximum CNR under the transmission-power-limited conditions. Also, we demonstrate that QPSK-modulated satellite broadcast multichannel video signals with a 300-MHz bandwidth, in total, can be successfully transferred over a distance of 8 m.