Showing papers on "Wideband published in 1998"

Wideband DS-CDMA for next-generation mobile communications systems

Abstract: Wideband wireless access based on direct sequence code division multiple access aimed at third-generation mobile communications systems is reviewed. W-CDMA is designed to flexibly offer wideband services which cannot be provided by present cellular systems, with various data rates as high as 2 Mb/s. The important concept of W-CDMA is the introduction of intercell asynchronous operation and the pilot channel associated with individual data channels. Intercell asynchronous operation facilitates continuous system deployment from outdoors to indoors. Other technical features of W-CDMA include fast cell search under intercell asynchronous operation, fast transmit power control, coherent spreading code tracking, a coherent RAKE receiver, orthogonal multispreading factor forward link, and variable-rate transmission with blind rate detection. The introduction of the data-channel-associated pilot channel allows W-CDMA to support interference cancellation and adaptive antenna array techniques that can significantly increase the link capacity and coverage. This article presents the radio link performance evaluated by computer simulation. Field experiment radio link performance results are also presented.

Space-time coded OFDM for high data-rate wireless communication over wideband channels

Abstract: There has been an increasing interest in providing high data-rate services such as video-conferencing, multimedia Internet access and wide area network over wideband wireless channels. Wideband wireless channels available in the PCS band (2 GHz) have been envisioned to be used by mobile (high Doppler) and stationary (low Doppler) units in a variety of delay spread profiles. This is a challenging task, given the limited link budget and severity of wireless environment, and calls for the development of novel robust bandwidth efficient techniques which work reliably at low SNRs. To this end, we design a space-time coded orthogonal frequency division multiplexing (OFDM) modulated physical layer. This combines coding and modulation. Space-time codes were previously proposed for narrowband wireless channels. These codes have high spectral efficiency and operate at very low SNR (within 2-3 dB of the capacity). On the other hand, OFDM has matured as a modulation scheme for wideband channels. We combine these two in a natural manner and propose a system achieving data rates of 1.5-3 Mbps over a 1 MHz bandwidth channel. This system requires 18-23 dB (resp. 9-14 dB) receive SNR at a frame error probability of 10/sup -2/ with two transmit and one receive antennas (resp. two transmit and two receive antennas). As space-time coding does not require any form of interleaving, the proposed system is attractive for delay-sensitive applications.

Capacity and mutual information of broadband multipath fading channels

Abstract: We investigate the capacity and mutual information of a broadband fading channel consisting of a finite number of time-varying paths. We show that the capacity of the channel in the wideband limit is the same as that of a wideband Gaussian channel with the same average received power. However, the input signals needed to achieve the capacity must be "peaky" in time or frequency. In particular, we show that if white-like signals are used instead (as is common in spread-spectrum systems), the mutual information is inversely proportional to the number of resolvable paths L/spl tilde/ with energy spread out, and in fact approaches 0 as the number of paths gets large. This is true even when the paths are assumed to be tracked perfectly at the receiver. A critical parameter L/spl tilde//sub crit/ is defined in terms of system parameters to delineate the threshold on L over which such overspreading phenomenon occurs.

Wideband radio propagation modeling for indoor geolocation applications

Abstract: A framework for statistical modeling of the wideband characteristics of the frequency-selective fading multipath indoor radio channel for geolocation applications is presented. Multipath characteristics of the channel are divided into three classes according to availability and the strength of the direct line of sight (DLOS) path with respect to the other paths. Statistics of the error in estimating the time of arrival of the DLOS path in a building is related to the receiver's sensitivity and dynamic range. The effects of external walls on estimating the location of the DLOS path are analyzed.

Time-domain envelope measurement technique with application to wideband power amplifier modeling

Abstract: This paper presents a new time-domain measurement technique for repetitive microwave signals that is applied to modeling wideband power amplifiers. The measurement technique concept consists of recording the microwave signal after conversion to baseband using a calibrated downconverter, which improves measurement accuracy compared to measurements at the carrier frequency. The modeling section describes how such time-domain measurements can be used to model wideband signal effects in nonlinear power amplifiers. The commonly used memory-less envelope model is limited to use on narrowband signals. A new model is developed which includes a filter before the memory-less nonlinearity to capture the memory effects associated with wideband signals. It is demonstrated that the accuracy of wideband signal simulations can be improved by optimizing the model parameters based on time-domain measurements of wideband signals.

Characterization of UHF radio propagation channels in tunnel environments for microcellular and personal communications

Abstract: Narrowband and wideband propagation measurements have been conducted in five tunnels. The effects of pedestrians, vehicles, and curvature on propagation are included in the characterization. The narrowband propagation is characterized in terms of power distance law, slow fading, and fast fading statistics: wideband propagation, rms delay spread, and its statistics. The results show that the power distance law is insensitive to the location of the transmit antenna in the cross section of a tunnel, but not to the antenna insertion loss. The lognormal distribution basically fits the slow variation of the received signals, whereas the Rician distribution, the fast fading in the straight empty sections of the tunnels. In the curved tunnel sections, the Rayleigh distribution does not fit the fast fading variation as is expected. Tunnel radio propagation channels are dependent strongly upon frequency. Higher frequency signals exhibit more severe fluctuations and larger rms delay spread. The rms delay spreads are found to be generally less than 25 and 103 ns for the emptied and occupied tunnel conditions, respectively. One can conclude that the tunnel channels have a broad coherent bandwidth and can support the data rate up to 1 Mb per second without equalization.

Method and apparatus for wideband predistortion linearization

Abstract: A predistortion signal is generated which compensates for third order and higher order intermodulation distortion over a wideband. The predistortion signal is applied to an input radio frequency signal, for example a multi-tone radio frequency signal. The predistortion signal is a low order polynomial having adjustable coefficients. The predistortion signal can compensate for intermodulation products produced a nonlinear amplifier, and the polynomial coefficients can be adjusted based on the difference between the amplifier output and the input radio frequency signal.

Communication device having a wideband receiver and operating method therefor

Abstract: To accommodate for a release of uncleared spectrum in a wideband communication system ( 10 ) while improving isolation in a receiver (FIG. 4 ) between wideband carriers, a common intermediate frequency converter down-converts differing but relatively high frequency carriers, incident to the receiver, to corresponding differing but relatively low frequency carriers. Receiver chains ( 174-176 ) response to the plurality of relatively low frequency carriers each have a filter ( 140-144 ) arranged to isolate selected ones of the relatively low frequency carriers. In a radio frequency communication system having three or more frequency sequential carriers, the receiver chains ( 174-176 ) may include branches that have filters that further isolate carriers within the receiver by applying non-sequential carriers to the branches in each receiver chain.

Apparatus for expanding narrowband speech to wideband speech by codebook correspondence of linear mapping functions

Abstract: Apparatus for expanding the bandwidth of speech signals such that a narrowband speech signal is input and digitized, the spectral envelope information and residual information are extracted from the digitized signal by linear predictive coding analysis, the spectral envelope information is expanded into wideband information by a spectral envelope converter, the residual information is expanded into wideband information by a residual converter, the converted spectral envelope information and residual information are combined to produce a wideband speech signal, frequency information not contained in the input signal is extracted from the obtained wideband speech signal by a filter, and the resulting signal is added to the original digitized input signal, and the obtained signal is converted into an analog signal as the output signal of the apparatus. The apparatus comprises a linear mapping function codebook used for converting spectral parameters, and a weights calculator and an adder for weighing and summing function outputs.

A bitrate and bandwidth scalable CELP coder

Abstract: This paper proposes a flexible CELP speech coder with bitrate and bandwidth scalabilities for multimedia applications. The coder is based on multi-pulse-based CELP coding and consists of a bitrate scalable base-band coder and a bandwidth extension tool. The bitrate scalable base-band CELP coder employs multi-stage excitation coding based on an embedded-coding approach. The multi-pulse excitation codebook at each stage is adaptively produced depending on the selected excitation signal at the previous stage. The bandwidth scalability is realized by bandwidth conversion from base-band CELP parameters to those for wideband without a widely used subband structure. The bandwidth conversion improves base-band coding quality and expands bandwidth, simultaneously. The comparison test results show that the bitrate scalable coder is equivalent in speech quality to the fixed-bitrate CELP coder at the same bitrate for the narrowband speech. In the mean opinion score (MOS) tests, the proposed 16 kbit/s coder with the bandwidth scalability achieves equivalent coding quality to ITU-T G.722 at 56 kbit/s. The proposed coder is currently evaluated as the MPEG-4 CELP speech standard.

A 3.3-V CMOS wideband exponential control variable-gain-amplifier

Abstract: A CMOS cascadable variable gain amplifier (VGA) with exponential gain control characteristic is presented. The pseudo-exponential gain control function is realized by a source-coupled pair with diode-connected loads. It is suitable for low supply and high speed applications. Using 0.5 /spl mu/m CMOS technology, experimental results show the bandwidth of the proposed amplifier is larger than 150 MHz with a gain control range of 15 dB. The power consumption is 12.5 mW from a 3.3-V power supply.

Design of a diffractive optical element for wide spectral bandwidth.

Abstract: A new method for eliminating the chromatic aberration of a diffractive optical element (DOE) for wideband wavelengths is presented. The wideband-wavelength diffractive optical element (WBDOE) consists of two aligned DOE's. The use of different dispersive materials for the two DOE's eliminates chromatic aberration. The design and simulation of a WBDOE for the visible spectrum are presented.

Wideband CDMA For Third Generation Mobile Communications: Universal Personal Communications

Abstract: From the Publisher: Here's an in-depth, comprehensive study of the developmental trends and practical design, planning, and deployment issues associated with wideband CDMA technology. Prepared by two leading authorities in the field, this book evaluates wideband CDMA as an effective third generation technology option, and gives you a clear picture of the various wideband CDMA standardization activities currently underway worldwide. Wireless system engineers responsible for designing wideband CDMA systems will appreciate the book's depth of coverage as it compares a wide array of CDMA design techniques and examines how each affects system performance. The book also describes how third generation system applications will impact radio access system design and... ? Compares and contrasts major wideband CDMA standardization proposals, including FRAMES, WCDMA in 3GPP, CDMA2000, and IS-95B ? Identifies and describes various air interface access schemes for third and fourth generation mobile communications systems ? Analyzes wideband CDMA performance in varying radio environments, and presents simulation results ? Discusses the integration of the GSM core network with wideband CDMA 1 Examines the basic principles of CDMA, including IS-95B air interference, and includes details on EDGE/136HS

Advanced receivers for wideband CDMA systems

Abstract: Advanced receiver structures capable of suppressing multiple-access interference in code-division multiple-access (CDMA) systems operating in frequency-selective fading channels are considered in this thesis. The aim of the thesis is to develop and validate novel receiver concepts suitable for future wideband cellular CDMA systems. Data detection and synchronization both for downlink and uplink receivers are studied. The linear minimum mean squared error (LMMSE) receivers are derived and analyzed in frequency-selective fading channels. Different versions of the LMMSE receivers are shown to be suitable for different data rates. The precombining LMMSE receiver, whichis also suitable for relatively fast fading channels, is shown to improve the performance of the conventional RAKE receivers signicantly in the FRAMES wideband CDMA concept. It is observed that the performance of the conventional RAKE receivers is degraded signicantly with highest data rates due to multipleaccess interference (MAI) as well as due to inter-path interference. Based on a general convergence analysis, it is observed that the postcombining LMMSE receivers are mainly suited to the high data rate indoor systems. The blind adaptive LMMSE-RAKE receiverdeveloped for relatively fast fading frequency-selective channels gives superior rate of convergence and bit error rate (BER) performance in comparison to other blind adaptive receivers based on least mean squares algorithms. The minimum variance method based delay estimation in blind adaptive receivers is shown to result in improved delay acquisition performance in comparison to the conventional matched filter and subspace based acquisition schemes. A novel delay tracking algorithm suitable to blind least squares receivers is also proposed. The analysis shows improved tracking performance in comparison to the standard delay-locked loops. Parallel interference cancellation (PIC) receivers are developed for the uplink. Data detection, channel estimation, delay acquisition, delay tracking, inter-cell interference suppression, and array processing in PIC receivers are considered. A multistage data detector with the tentative data decision and the channel estimate feedback from the last stage is developed. Adaptive channel estimation filters are used to improve the channel estimation accuracy. The PIC method is also applied to the timing synchronization of the receiver. It is shown that the PIC based delay acquisition and tracking methods can be used to improve the performance of the conventional synchronization schemes. Although the overall performance of the PIC receiver is relatively good in the single-cell case, its performance is signicantly degraded in a multi-cell environment due to unknown signal components which degrade the MAI estimates and subsequently the cancellation efficiency. The blind receiver concepts developed for the downlink are integrated into the PIC receivers for inter-cell interference suppression. The resulting LMMSE-PIC receiver is capable of suppressing residual interference and results in good BER performance in the presence of unknown signal components.

Novel active differential phase splitters in RFIC for wireless applications

Abstract: Two novel active differential phase splitters have been designed and fabricated in a GaAs MESFET process. The new circuits employ a concept of feedback to adjust gain and phase unbalance separately and accurately. The active phase splitters feature simplicity, low power supply, and wide-band performance. The circuits can provide /spl plusmn/1 dB and 180/spl plusmn/1/spl deg/ differential signals within 4 GHz bandwidth, well covering the frequency range currently used for dual-band commercial wireless communications. In narrow-band application, more accurate balanced differential signals can be achieved by external tuning.

Frames FMA2 wideband-CDMA for UMTS

Abstract: The basic principles of the physical layer of the FRAMES (Future Radio Wideband Multiple Access System) FMA2 (FRAMES Multiple Access) wideband CDMA system are described in this paper. The FMA2 is part of the FRAMES dual mode platform designed as UMTS air interface, where the harmonisation with GSM is also taken into account. The main characteristics features in the FMA2 are the asynchronous network operation and flexible layer 1 support for the variable rate transmission needs. This paper presents also performance results, which allow to conclude that the FMA2 meets UMTS air interface requirements. The FMA2 concept was a major part of the ETSI (European Telecommunications Standards Institute) wideband CDMA concept group, selected by ETSI as a basis for UMTS air interface for the paired frequency band.

Design of a wideband microstrip bowtie patch antenna

Abstract: A novel methodology is presented for the design of a wideband microstrip bowtie patch antenna of finite length placed on a dielectric substrate. The method presented is fast, computationally undemanding and reasonably accurate. This methodology is motivated by the observed array effect of the two trapezoidal halves on a single bowtie antenna. A single trapezoidal side is first designed and two such identical sides are then joined together at the apex and matched to a coaxial feed via sections of microstrip lines at the second-order resonance frequency. Experimental measurements for a bowtie designed in the X-band are shown to agree well with the simulated predictions. The bandwidth obtained was a significant 10.6%.

Wideband planar leaky-wave microstrip antenna

Abstract: A wideband leaky-wave microstrip antenna having two elongated rectangular nductive patches separated by a gap on a first dielectric material and an elongated rectangular conductive coupling patch on a second dielectric material placed over the gap. The selective placement of the conductive patches and the gap formed thereby permits impedance matching resulting in a leaky-wave propagation mode. Non-radiating modes of propagation are not excited, thereby enhancing the leaky-wave mode of propagation causing radiation. This results in a relatively wide bandwidth of operation that has a main beam that is scannable as a function of frequency. The bandwidth increases substantially as the dielectric constant approaches one. The planar construction contributes to design flexibility and ease of manufacture and has many applications military and commercial communication systems.

System and method for CDMA channel estimation

Abstract: A wideband CDMA receiver system to accept messages from asynchronously transmitting base stations is provided. The base station transmission to each receiver includes a perch channel and at least one traffic channel. Although all the channels typically include pilot symbols for the purpose of demodulating the information symbols of the channel, the pilot channel includes a higher proportion of pilot symbols to information symbols. Therefore, a perch channel based timing and estimation system is inherently more accurate. In addition, the perch channel is generally transmitted at higher power levels than a traffic channel, and the resulting, higher, signal to noise ratio signal also improves the accuracy of the timing and channel estimation. Based on the timing derived from the perch channel of a first base station, the receiver can set the timing of the traffic channel transmissions from a second base station, to more closely match the timing of traffic channel transmissions from the first base station. In this manner, the signal to noise ratio of the demodulated traffic channel information symbols is enhanced through the diversity of using the transmissions of two base stations. A method for receiving wideband CDMA transmissions from asynchronously transmitting base stations is also provided.

Low-profile, integrated radiator tiles for wideband, dual-linear and circular-polarized phased array applications

Abstract: A planar, low-profile, very wide frequency bandwidth, wide-scan, dual-linear or circular-polarized phased array antenna using integrated stacked-disc radiator tiles. The stacked-disc radiator configuration comprises a lower active radiator fed by a pair of probes for each polarization state, and a parasitic radiator separated from the active radiator by dielectric material. The stacked-disc radiator is integrated with its multi-layer feed circuits in a very compact package. The feed circuits include 90° hybrid coupler circuits and 180° hybrid coupler circuits that couple dual linear or dual circular polarized energy to and from the disk radiators.

Multiresolution sinusoidal modeling for wideband audio with modifications

Abstract: We describe a computationally efficient method of generating more accurate sinusoidal parameters {amplitude, frequency, phase} from a wideband polyphonic audio source in a multiresolution, non-aliased fashion. This significantly improves upon previous work of sinusoidal modeling that assumes a single-pitched monophonic source, such as speech or an individual musical instrument, while using approximately the same number of sinusoids. In addition to a more general analysis, we can now perform high-quality modifications such as time-stretching and pitch-shifting on polyphonic audio with ease.

An ultrahigh-speed AlGaAs-GaAs polarization converter using slow-wave coplanar electrodes

Abstract: A wide-band electrooptic polarization converter has been fabricated using slow-wave coplanar-strip electrodes on an AlGaAs-GaAs substrate. Microwave characteristics of the electrode have been measured up to 40 GHz. The microwave loss and the microwave index at 40 GHz are 0.4 Np/cm and 3.4, respectively. The optical measurements were done up to 20 GHz; a flat frequency response was observed.

Noise figure in optical amplifiers with a split-band architecture

Abstract: A wideband optical amplifier employs split-band architecture in which an optical signal passes through a common amplification stage and is then split to pass through parallel gain stages, each of which may be optimized for a particular band being traversed. A broadband grating reflector is used after the input gain section to reflect the signals of one of the bands so that they again will pass through the common input gain section before passing through gain section of the split structure dedicated to their particular wavelength. Meanwhile, the other signals pass through the reflector and move on through the gain section pertinent to their wavelength.

V-band single chip, direct carrier BPSK modulation transmitter with integrated patch antenna

Abstract: A single chip V-band pHEMT technology transmitter with wideband direct BPSK modulation and on-chip dual band patch antenna is reported. The transmitter features, 10% bandwidth electronic tuning range, substantial power output, injection locking capability, low power consumption and good patch antenna radiation characteristics. As such it is well suited to wireless digital communications systems as well in radar and phased array applications.

Wideband CMOS current conveyor

Abstract: A CMOS second generation current conveyor consisting of two matched differential pairs and based on the first generation current conveyor is presented. PSPICE simulations have shown that its performance is quite satisfactory for wideband current-mode signal processing.

Tapered transducers-design and applications

Abstract: The tapered transducer was first demonstrated over 25 years ago but until recently has seen little commercial use. This paper reviews the theory that describes how the wideband response of a tapered transducer is achieved by the summation of narrow-band channels. In addition, it discusses weighting techniques appropriate to tapered transducers including block weighting, and how the use of SPUDT electrode structures allows the same reduction in IL and triple-transit over a wide bandwidth normally achieved only with relatively narrow-band filters. Experimental results are presented along with a discussion of applications that benefit from the unique properties of tapered transducers such as a single-bounce dispersive delay line, a multi-tap delay line with low spurious reflections, a channelizer or filter bank, an AO Bragg cell, and a radar pulse compression system without range/velocity ambiguity in the presence of Doppler.

Wideband, planar, log-periodic balun

Abstract: This paper presents the design and performance characteristics of a new planar balun structure. The design is based on the log-periodic antenna theory. The design guidelines, as well as simulated and measured results are presented. It is shown that the new balun has greater than one octave bandwidth. The log-periodic balun will find applications in wireless communication circuits such as mixers, amplifiers and antennas.

Gaussian frequency-shift keying transciever for ISM wideband communication

Abstract: A GFSK (Gaussian Frequency Shift Keying) radio transceiver is provided for ISM (Industrial Scientific and Medical) wideband communication. The GFSK radio transceiver includes a transmitter for modulating transmitted signal into RF signal, and a receiver for demodulating received signal into digital form. The transmitter includes a VCO for generating an oscillating signal serving as a carrier signal in the transmitter and a first local oscillating signal in the transmitter; and a variable-gain power amplifier, capable of being adjustable between two gain values, for amplifying the RF signal. The receiver includes a mixer for downconverting the received signal into a first IF signal by using the first local oscillating signal from the transmitter; and an IF demodulator for downconverting the first IF signal into a second IF signal by using a locally generated second local oscillating signal. The GFSK radio transceiver can operate either in half-duplex mode or full-duplex mode in a time-division duplex (TDD) system through micro-processor controls. Further, it utilizes a variable-gain power amplifier that can improve the drawbacks of interference and high power consumption with the prior art, and further utilizes a single wideband VCO to generate an oscillating signal that can be used both as the carrier signal in the transmitter and the first local oscillating signal for the receiver. This allows the GFSK radio transceiver to be implemented with a fewer number of VCOs as compared to the prior art, thus reducing the manufacturing cost.

A wideband architecture for adaptive feedforward linearization

Abstract: Feedforward linearization has the potential for large operating bandwidths. However, no published work has addressed the two largest hurdles to truly wideband performance: delay mismatch and unwanted frequency dependence of the circuit elements. This paper presents two structural innovations that solve these problems. A prototype has demonstrated up to 40 dB reduction of intermodulation products over a 40 MHz range and 25 dB or more over an 80 MHz range.