Abstract: A new variable bandwidth selector for kernel estimation is proposed The application of this bandwidth selector leads to kernel estimates that achieve optimal rates of convergence over Besov classes This implies that the procedure adapts to spatially inhomogeneous smoothness In particular, the estimates share optimality properties with wavelet estimates based on thresholding of empirical wavelet coefficients

Abstract: The development of small integrated antennas plays a significant role in the progress of the rapidly expanding military and commercial communications applications. The recent advances in RF and microwave high-density circuit packaging technologies in multifunction wireless communications systems have called for the parallel development of compact and efficient antennas that can be used over a wide frequency range. This paper addresses the development and characterization of several low-profile and integrated antennas with enhanced bandwidth for wireless communications systems. The new radiators are developed by adding parasitic elements or tuning devices to a familiar integrated antenna-the planar inverted F antenna (PIFA). Simulations based upon the finite-difference time-domain (FDTD) method and method of moments (MoM) are used to model the performance of the antennas. Comparisons with measured results on fabricated antenna structures are provided for simulations validation.

Abstract: The utilization of signal processing techniques in nondestructive testing, especially in ultrasonics, is widespread. Signal averaging, matched filtering, frequency spectrum analysis, neural nets, and autoregressive analysis have all been used to analyze ultrasonic signals. The Wavelet Transform (WT) is the most recent technique for processing signals with time-varying spectra. Interest in wavelets and their potential applications has resulted in an explosion of papers; some have called the wavelets the most significant mathematical event of the past decade. In this work, the Wavelet Transform is utilized to improve ultrasonic flaw detection in noisy signals as an alternative to the Split-Spectrum Processing (SSP) technique. In SSP, the frequency spectrum of the signal is split using overlapping Gaussian passband filters with different central frequencies and fixed absolute bandwidth. A similar approach is utilized in the WT, but in this case the relative bandwidth is constant, resulting in a filter bank with a self-adjusting window structure that can display the temporal variation of the signal's spectral components with varying resolutions. This property of the WT is extremely useful for detecting flaw echoes embedded in background noise. The detection of ultrasonic pulses using the wavelet transform is described and numerical results show good detection even for signal-to-noise ratios (SNR) of -15 dB. The improvement in detection was experimentally verified using steel samples with simulated flaws.

Abstract: A foveated imaging system, which can be implemented on a general purpose computer and greatly reduces the transmission bandwidth of images has been developed. This system has demonstrated that significant reductions in bandwidth can be achieved while still maintaining access to high detail at any point in an image. The system is implemented with conventional computer, display, and camera hardware. It utilizes novel algorithms for image coding and decoding that are superior both in degree of compression and in perceived image quality and is more flexible and adaptable to different bandwidth requirements and communications applications than previous systems. The system utilizes novel methods of incorporating human perceptual properties into the coding the decoding algorithms providing superior foveation. One version of the system includes a simple, inexpensive, parallel pipeline architecture, which enhances the capability for conventional and foveated data compression. Included are novel applications of foveated imaging in the transmission of pre-recorded video (without eye tracking), and in the use of alternate pointing devices for foveation.

Abstract: A motion video signal encoder maximizes image quality without exceeding transmission bandwidth available to carry the encoded motion video signal by comparing encoded frames of the motion video signal to a desired size of frame. If the size of encoded frames differ from the desired size, encoding is adjusted to produce encoded frames closer in size to the desired size. In addition, a cumulative bandwidth error records an accumulated amount of available bandwidth. The cumulative bandwidth error is adjusted as time elapses to add to the available bandwidth and as each frame is encoded to thereby consume bandwidth. As the cumulative bandwidth error grows in magnitude above or below zero, encoding is adjusted as needed to either improve image quality to more completely consume available bandwidth or to reduce image quality to thereby consume less bandwidth and to thereby cause the cumulative bandwidth error to move toward zero. Rapid changes in the amount of change or motion in the motion video signal are detected by comparing the amount of change between two consecutive frames and filtering the amount of change with previously measured amounts of change. Encoding is pre-compensated according to the filtered measurement of rapid change.

Abstract: Operating conditions for modulation bandwidth enhancement, noise reduction, and stable locking to be simultaneously fulfilled in a semiconductor laser subject to strong optical injection are investigated. When the strength of the injection signal is fixed, the optimum detuning of the injection frequency exists as a tradeoff between bandwidth enhancement and noise reduction. When the laser is injection-locked at a given value of frequency detuning in the stable locking region, both bandwidth enhancement and noise reduction are improved as the injection parameter is increased over a wide range.

Abstract: Publisher Summary This chapter establishes the merits of digital signal processing (DSP) and identifies its abound applications. The term DSP generally refers to the use of digital computers to process signals. Normally, these signals can be handled by analog processes, but, for a variety of reasons, it may be preferred to handle them digitally. Signals stored digitally are large arrays of numbers. As such, they are immune to the physical limitations of analog signals. Once the signals have been converted to digital numbers, it is a straightforward process to program a computer to perform the filtering. DSP can allow large bandwidth signals to be sent over narrow bandwidth channels. Communications security can be greatly improved through DSP. Digitally processing a signal allows doing things with signals that would have been either difficult or impossible with analog approaches. With modern components and techniques, these advantages can often be realized economically and efficiently.

Abstract: The architecture of this 12 b ADC is based on a three-stage conversion, using cascaded folding and interpolating techniques. Compared to other multi-stage ADC architectures, folding and interpolating ADCs are based on non-linear analog pre-processing. This architecture is an attractive solution for high-resolution ADCs, as extremely linear circuit topologies are not required. To increase the resolution of folding and interpolating ADCs above the published 8 b examples, without raising the number of parallel input stages or the number of comparators in the fine-comparator, a cascaded folding and interpolating architecture is introduced. The ADC achieves 64 dB signal-to-noise ratio (SNR) and 75 dB spurious-free dynamic range (SFDR), while quantizing a 15 MHz full-scale input signal at 50 MSample/s. The 7.0 mm/sup 2/ ADC is fabricated in a 13 GHz, 1 /spl mu/m BiCMOS process and dissipates 300 mW from a single 5.0 V supply. The device is mounted in a standard 44-pin plastic package.

Abstract: A system and method is disclosed for distributing a radio frequency (RF) signal within a building structure or other structure not readily transparent to radio frequencies. The RF signal originates at a wireless local loop (WLL) base station and is intercepted by a main antenna on the building structure. The intercepted RF signal, which is contained in a RF bandwidth, is distributed throughout the building structure over a low bandwidth medium, e.g., in-building cabling, which has a transmission bandwidth below the RF bandwidth. In order to accomplish this, the system has a global reference oscillator for distributing a global reference tone of high stability to the entire system. Local oscillators controlled by this global reference tone deliver RF reference tones of high stability required for mixing the RF signal to obtain an intermediate frequency (IF) signal which is fed through the low bandwidth medium to remote sites. At the remote sites the RF signal recovered from the IF signal by mixing with the RF reference tone and re-transmitted, often to WLL communication units. When the WLL base station has a connection to the Public Switch Telephone Network (PSTN), the WLL communication units provide users with wireless telephone services.

Abstract: A number of serious consortiums develop satellite communication networks. The objective of these communication projects is to service personal communication users almost everywhere on Earth. The intersatellite links in those projects use microwave radiation as the carrier. Free-space optical communication between satellites networked together can make possible high-speed communication between different places on Earth. Some advantages of an optical communication system over a microwave communication system in free space are: (1) smaller size and weight, (2) less transmitter power, (3) larger bandwidth, and (4) higher immunity to interference. The pointing from one satellite to another is a complicated problem due to the large distance between the satellite, the narrow beam divergence angle, and vibration of the pointing system. Such vibration of the transmitted beam in the receiver plane decreases the average received signal, which increases the bit error rate. We review: (1) the present status of satellite networks, (2) developing efforts of optical satellite communication around the world, (3) performance results of vibration effects on different kinds of optical communication satellite networks, and (4) seven approaches to overcome the problems caused by transmitter pointing vibration.

Abstract: Photodetector efficiency decreases as bandwidth increases, Bandwidth-efficiency limitations of traveling-wave photodetectors (TWPDs) are substantially greater than those of lumped-element photodetectors because the velocity-mismatch bandwidth limitation is independent of device length. TWPDs can be long for high efficiency without significantly compromising bandwidth. The TWPD is modeled by a terminated section of transmission line with a position-dependent photocurrent source propagating on it at the optical group velocity. A wave model for the transmission line confirms the accuracy of an equivalent-circuit model for electrical wave propagation. The velocity-mismatch impulse and frequency response are determined by absorption coefficient and wave velocities rather than junction capacitance and load resistance. The velocity-mismatch bandwidth limitations can be written in a simple form which elucidates the factors affecting device response, A discretized periodic TWPD is described by the same equations as the fully distributed version. This more complicated device offers additional degrees of freedom in design and potentially improved performance.

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

Abstract: A system and method for transmitting a radio frequency (RF) signal in a RF bandwidth over a low bandwidth medium (60), e.g., in-building cabling, which has a transmission bandwidth below the RF bandwidth. The system (50) has a unit (52) for receiving the RF signal and global reference oscillator (66) for distributing a global reference tone of high stability to the entire system (50). Local oscillators (58 and 86) are controlled by adjustement signals derived from this global reference tone to deliver RF reference tones of high stability required for mixing the RF signal to obtain an intermediate frequency (IF) signal which is fed through the low bandwidth medium (60). The global reference tone is preferably delivered through the same low bandwidth medium (60) to desired locations, such as remote coverage sites in a network for cellular communications, cordless telephony, local RF communications, interactive multi-media video, and high bit-rate communications.

Abstract: A receiver comprising a sigma-delta analog-to-digital converter (ΣΔ ADC) can be utilized in one of four configurations, as a subsampling bandpass receiver, a subsampling baseband receiver, a Nyquist sampling bandpass receiver, or a Nyquist sampling baseband receiver. For subsampling ΣΔ receivers, the sampling frequency is less than twice the center frequency of the input signal into the ΣΔ ADC. For Nyquist sampling ΣΔ receivers, the sampling frequency is at least twice the highest frequency of the input signal into the ΣΔ ADC. For baseband ΣΔ receivers, the center frequency of the output signal from the ΣΔ ADC is approximately zero or DC. For bandpass ΣΔ receivers, the center frequency of the output signal from the ΣΔ ADC is greater than zero. The sampling frequency can be selected based on the bandwidth of the input signal to simplify the design of the digital circuits used to process the output samples from the ΣΔ ADC. Furthermore, the center frequency of the input signal can be selected based on the sampling frequency and the bandwidth of the input signal. The ΣΔ ADC within the receiver provides many benefits.

Abstract: A new architecture for a CMOS A/D converter overcomes many of the known problems in the parallel operation of multiple pipelined stages. The input signal is sampled in one channel, and after quantization to 4 b, the residue is distributed into many channels. A prototype implemented in 1-/spl mu/m CMOS achieves 60 dB signal-to-noise plus distortion ratio (SNDR) at low conversion rates, with a resolution bandwidth of greater than 20 MHz. The SNDR drops by 3 dB at a 95 MHz conversion rate, and the bandwidth remains the same.

Abstract: We obtain the Shannon capacity region of the down-link (broadcast) channel in fading and additive white Gaussian noise (AWGN) for time-division, frequency-division, and code-division. For all of these techniques, the maximum capacity is achieved when the transmitter varies the data rate sent to each user as their channels vary. This optimal scheme requires channel estimates at the transmitter; dynamic allocation of timeslots, bandwidth, or codes; and variable-rate and power transmission. For both AWGN and fading channels, nonorthogonal code-division with successive decoding has the largest capacity region, while time-division, frequency-division, and orthogonal code-division have the same smaller region. However, when all users have the same average received power, the capacity region for all these techniques is the same. In addition, the optimal nonorthogonal code is a multiresolution code which does not increase the signal bandwidth. Spread-spectrum code-division with successive interference cancellation has a similar rate region as this optimal technique, however, the region is reduced due to bandwidth expansion. We also examine the capacity region of nonorthogonal code-division without interference cancellation and of orthogonal code-division when multipath corrupts the code orthogonality. Our results can be used to bound the spectral efficiency of the downlink channel using time-division, frequency-division, and code-division, both with and without multiuser detection.

Abstract: This paper describes an I/O scheme for use in a high-speed bus which eliminates setup and hold time requirements between clock and data by using an oversampling method. The I/O circuit uses a low jitter phase-locked loop (PLL) which suppresses the effect of supply noise. Measured results show peak-to-peak jitter of 150 ps and r.m.s. jitter of 15.7 ps on the clock line. Two experimental chips with 4-pin interface have been fabricated with a 0.6 /spl mu/m CMOS technology, which exhibits the bandwidth of 960 Mb/s per pin.

Abstract: We report the fabrication of a near-infrared avalanche photodetector with a gain-bandwidth product of over 300 GHz. The detector uses a Si multiplication layer and an InGaAs absorption layer. A 3 dB bandwidth of over 9 GHz was measured for current gains as high as 35. Photocurrent measurements using 1.3 μm light indicate a quantum efficiency for the detector of 0.60, near the limit expected based on the absorber thickness.

Abstract: A time-interleaved bit addressed weighted pulse width modulation (PWM) method and apparatus reduces the bandwidth requirement necessary for providing a plurality of data entries regarding multiple points of information. As is well known, a weighted PWM scheme modulates an output by utilizing a frame time that is divided into events of varying durations; most conventional schemes have each bit in the frame being half the duration of its predecessor. The modulated signal is activated during all, some or none of the events in the frame to develop a signal representing a particular parameter. This method and apparatus can be used in a display for selecting among varying levels of gray scale or from among multiple colors on a palette. In one application for a display, a register containing the same number of data pits as pixels in a row of the display is provided. The register is loaded with one bit per frame for each pixel in the entire row. The bandwidth is reduced because the bits for each of the pixels are not all for the same weight event. This allows a bit for a long duration event to be displayed in one pixel, while more than one bit for shorter duration events to be displayed in another pixel. This obviates the need to load one bit for each pixel in the row during the shortest event duration. The organization of the sequence of the events amongst the various rows can be pseudo-random to achieve reduced bandwidth. If the organization is pseudo-random, the order can be pre-selected for an optimized bandwidth or organized into a predetermined format to achieve a pseudo-random effect.

Abstract: A novel approach of true-time delay (TTD) optical feeder for phased-array antennas is proposed and demonstrated. A compact size continuously variable TTD is achieved by employing tunable lasers and one wide bandwidth chirped-fiber grating as dispersive element. A high-resolution performance (5.3 ps) is obtained for a 26-GHz phased-array antenna employing narrow tuning bandwidth lasers with a wavelength stability of 0.005 nm and a 4 nm bandwidth chirped grating.

Abstract: The present invention employs a method and apparatus for providing improved power control when changing the rate at which data is sent in a communications system. When data arrives at the transmitter for transmission at a high rate, power control feedback is changed from a slow mode (with a low bandwidth feedback channel) to a fast mode (with a high bandwidth feedback channel). This control changes even before the data is transmitted at the high rate. Once the power level is accurately estimated for data transmission at the high rate, then data transmission begins at the high rate.

Abstract: A system for redistributing a broadband audio-visual-data signal to a multiplicity of receiver units within a multiple dwelling unit (MDU) includes a main receiving antenna that receives a broadband video/audio/data signal having a number of individual program multiplex signals therein and a transmodulator device that transmodulates the individual program multiplex signals associated with the broadband signal from a first modulation scheme to a second modulation scheme to reduce the bandwidth of the broadband signal The transmodulated signals are broadcast over a cable network, along with terrestrial signals, to individual receiver units at the MDU The receiver units demodulate the transmodulated and/or terrestrial signals and provide user-specified channels to television sets for display

Abstract: Oversampled bandpass A/D converters based on sigma-delta (/spl Sigma//spl Delta/) modulation can be used to robustly digitize the types of narrowband intermediate frequency (IF) signals that arise in radios and cellular systems. This paper proposes a two-path architecture for a fourth-order, bandpass modulator that is more tolerant of analog circuit limitations at high sampling speeds than conventional implementations based on the use of switched-capacitor biquadratic filters. An experimental prototype employing the two-path topology has been integrated in a 0.6-/spl mu/m, single-poly, triple-metal CMOS technology with capacitors synthesized from a stacked metal structure. Two interleaved paths clocked at 40 MHz digitize a 200-kHz bandwidth signal centered at 20 MHz with 75 dB of dynamic range while suppressing the undesired mirror image signal by 42 dB. At low input signal levels, the mixing of spurious tones at DC and f/sub s//2 with the input appears to degrade the performance of the modulator; out-of-band sinusoidal dither is shown to be an effective means of avoiding this degradation. The experimental modulator dissipates 72 mW from a 3.3 V supply.

Abstract: An apparatus (50) for sourcing an interrogation signal for use in an object identification system including a frequency hopping source (100) for generation of an interrogation transmission by a bi-directional antenna (12) to a tag Upon receipt, the tag provides a return signal that is backscatter modulated to include tag identification or other data which is processed by the sourcing system (50) The frequency hopping source (100) includes a voltage controller oscillator (206) which is driven by a pseudo random code generator (200) for selecting one of a plurality of hopping frequencies at which the interrogation signal is to be generated based on the available bandwidth

Abstract: A new rail-to-rail CMOS input architecture is presented that delivers behavior nearly independent of the common-mode level in terms of both transconductance and slewing characteristics. Feedforward is used to achieve high common-mode bandwidth, and operation does not rely on analytic square law characteristics, making the technique applicable to deep submicron technologies. From the basis of a transconductor design, an asynchronous comparator and a video bandwidth op amp are also developed, providing a family of general purpose analog circuit functions which may be used in high (and low) bandwidth mixed-signal systems. Benefits for the system designer are that the need for rigorous control of common-mode levels is avoided and input signal swings right across the power supply range can be easily handled. A further benefit is that having very consistent performance, the circuits can be easily described in VHDL (or other behavioral language) to allow simulation of large mixed-signal systems. The circuits presented may be easily adapted for a range of requirements. Results are presented for representative transconductor, op amp, and comparator designs fabricated in a 0.5 /spl mu/m 3.3 V digital CMOS process.

Abstract: A system and method for transmitting a radio frequency (RF) signal in a RF bandwidth over a low bandwidth medium, e.g., in-building unshielded twisted pair (UTP) cabling, which has a transmission bandwidth below the RF bandwidth. The system has a unit for receiving the RF signal and a global reference oscillator for distributing a global reference tone of high stability to the entire system. Local oscillators controlled by this global reference tone deliver RF reference tones of high stability required for mixing the RF signal to obtain an intermediate frequency (IF) signal which is fed through the low bandwidth medium to remote sites. A 10 base T cable network, often pre-existing in many building structures, provides a suitable, cost effective low bandwidth medium for such RF communication. Two of the four twisted pair cables of a UTP cable are sufficient to support bi-directional communication. The remaining twisted pair cables are used to control remote site antenna functions or support other types of communication services such as data LAN, video, wired voice, or other wireless services such as PCS or wireless LAN.

Abstract: A communications system employing the Discrete Multitone (DMT) line code divides the used frequency band W into a large number of subchannels, each with a bandwidth Δf=W/N. The signal in each subchannel is independently modulated at the symbol rate 1/Δf. Because of noise and the non-ideal characteristics of the transmission channel, the signal-to-noise ratio (SNR) varies for different subchannels across the frequency band. Each subchannel is used to transmit an integer number of bits in a two-dimensional signal constellation, the susceptibility to noise increasing with the size of the constellation assuming that the same signal energy is used. In order to use the transmission channel optimally, subchannels are assigned different numbers of bits depending on their specific SNR values, i.e., a subchannel with a high SNR value is assigned a large number of bits and vice versa. An optimal bit allocation is determined that ensures a certain bit error rate (BER) is obtained for all subchannels. In order to simplify numerical computations, thresholding is employed to make initial bit assignments. Further simplification of the bit loading procedures is obtained by ending bit allocation optimization efforts after a targeted BER is achieved.

Abstract: Design techniques for equiripple phase CMOS continuous-time filters are presented, and their integration within a partial-response maximum likelihood (PRML) disk drive read channel is discussed. A programmable seven-pole two asymmetric zero filter implementation is described based on a new transconductance (G/sub m/) cell. The impact of integrator finite output impedance, excess phase, and other implementation related nonidealities is discussed. A filter tuning circuit that requires an accurate time base but no external components is presented. The filter has a cutoff frequency (f/sub c/) range of 6-43 MHz, where f/sub c/ is the -3 dB point of the magnitude transfer function with the two zeros set to infinity. Also, with finite zeros it is able to provide up to 12 dB of boost which is defined as the maximum value of the magnitude transfer function referred to dc. The group delay ripple stays within /spl plusmn/2% for frequencies below 1.75 f/sub c/. The cutoff frequency exhibits a 650 ppm//spl deg/C temperature dependency and a variation of /spl plusmn/1%/V with the power supply. Total harmonic distortion (THD) values are below -40 dB at twice the nominal operating input voltage (V/sub nominal/=320 mV peak-to-peak differential), and the dynamic range exceeds 60 dB (for a maximum input signal of 640 mV peak-to-peak differential, maximum bandwidth setting, and no boost). Both the filter and a tuning circuit were implemented in a 0.6-/spl mu/m single-poly triple-metal n-well CMOS process. They consume 90 mW from a single 5 V power supply and occupy an area of 0.8 mm/sup 2/.

Abstract: A linear, fully balanced, voltage-tunable CMOS operational transconductance amplifier (OTA) with large dc gain and wide bandwidth is described. The approach uses a two-differential-pair transconductor with a cross-coupled input stage together with a negative resistance load for compensating the parasitic output resistance of the OTA. Since no additional internal nodes are generated, dc gain enhancement is obtained without bandwidth limitation. SPICE simulations show that total harmonic distortion at 1.42 V/sub p-p/ is less than 1% with dynamic range equal to 66 dB at a power consumption of 2.7 mW from a single 5-V supply. As an example, the OTA is used to design a third-order elliptic lowpass filter in the very-high-frequency range, simulated in a standard 2 /spl mu/m CMOS process (MOSIS). The cutoff frequency of the filter is tunable in the range of 12-50 MHz.