4,527 research outputs found
Optimal design of linear phase FIR digital filters with very flat passbands and equiripple stopbands
A new technique is presented for the design of digital FIR filters, with a prescribed degree of flatness in the passband, and a prescribed (equiripple) attenuation in the stopband. The design is based entirely on an appropriate use of the well-known Reméz-exchange algorithm for the design of weighted Chebyshev FIR filters. The extreme versatility of this algorithm is combined with certain "maximally flat" FIR filter building blocks, in order to generate a wide family of filters. The design technique directly leads to structures that have low passband sensitivity properties
Results on optimal biorthogonal filter banks
Optimization of filter banks for specific input statistics has been of interest in the theory and practice of subband coding. For the case of orthonormal filter banks with infinite order and uniform decimation, the problem has been completely solved in recent years. For the case of biorthogonal filter banks, significant progress has been made recently, although a number of issues still remain to be addressed. In this paper we briefly review the orthonormal case, and then present several new results for the biorthogonal case. All discussions pertain to the infinite order (ideal filter) case. The current status of research as well as some of the unsolved problems are described
Design of Compact BPF and Planar Diplexer for UMTS using Embedded-scheme Resonator
A compact planar diplexer utilizing embedded-scheme resonator (ESR) is designed for universal mobile telecommunications system (UMTS). The ESR is formed by embedding interdigital resonators into an open loop resonator. Based on the proposed ESR, a narrowband bandpass filter suitable for diplexer design is proposed, fabricated and measured. The measured results demonstrate that the filter exhibits good transmission properties within band and high frequency selectivity. The rectangular area occupied by the filter has overall dimensions only 0.086λg by 0.105λg, promises good potential in wireless communication systems that require compact size and high encapsulation quality. Then, a compact planar diplexer operating at the TX-band of 1920-1980MHz and the RX-band of 2110-2170MHz, which is composed of a meander T-junction and two filters initially separately designed, is synthesized, simulated and measured. Both the simulated and measured results indicate that satisfied impedance matching and good isolation between two paths have been achieved
Frequency-Selective PAPR Reduction for OFDM
We study the peak-to-average power ratio (PAPR) problem in orthogonal
frequency-division multiplexing (OFDM) systems. In conventional clipping and
filtering based PAPR reduction techniques, clipping noise is allowed to spread
over the whole active passband, thus degrading the transmit signal quality
similarly at all active subcarriers. However, since modern radio networks
support frequency-multiplexing of users and services with highly different
quality-of-service expectations, clipping noise from PAPR reduction should be
distributed unequally over the corresponding physical resource blocks (PRBs).
To facilitate this, we present an efficient PAPR reduction technique, where
clipping noise can be flexibly controlled and filtered inside the transmitter
passband, allowing to control the transmitted signal quality per PRB. Numerical
results are provided in 5G New Radio (NR) mobile network context, demonstrating
the flexibility and efficiency of the proposed method.Comment: Accepted for publication as a Correspondence in the IEEE Transactions
on Vehicular Technology in March 2019. This is the revised version of
original manuscript, and it is in press at the momen
EUV Spectra of the Full Solar Disk: Analysis and Results of the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
We analyze EUV spectra of the full solar disk from the Cosmic Hot
Interstellar Plasma Spectrometer (CHIPS) spanning a period of two years. The
observations were obtained via a fortuitous off-axis light path in the 140 --
270 Angstrom passband. The general appearance of the spectra remained
relatively stable over the two-year time period, but did show significant
variations of up to 25% between two sets of Fe lines that show peak emission at
1 MK and 2 MK. The variations occur at a measured period of 27.2 days and are
caused by regions of hotter and cooler plasma rotating into, and out of, the
field of view. The CHIANTI spectral code is employed to determine plasma
temperatures, densities, and emission measures. A set of five isothermal
plasmas fit the full disk spectra well. A 1 -- 2 MK plasma of Fe contributes
85% of the total emission in the CHIPS passband. The standard Differential
Emission Measures (DEMs) supplied with the CHIANTI package do not fit the CHIPS
spectra well as they over-predict emission at temperatures below log(T) = 6.0
and above log(T) = 6.3. The results are important for cross-calibrating TIMED,
SORCE, SOHO/EIT, and CDS/GIS, as well as the recently launched Solar Dynamics
Observatory.Comment: 27 Pages, 13 Figure
A new approach to the realization of low-sensitivity IIR digital filters
A new implementation of an IIR digital filter transfer function is presented that is structurally passive and, hence, has extremely low pass-band sensitivity. The structure is based on a simple parallel interconnection of two all-pass sections, with each section implemented in a structurally lossless manner. The structure shares a number of properties in common with wave lattice digital filters. Computer simulation results verifying the low-sensitivity feature are included, along with results on roundoff noise/dynamic range interaction. A large number of alternatives is available for the implementation of the all-pass sections, giving rise to the well-known wave lattice digital filters as a specific instance of the implementation
Color Gradients and Surface Brightness Profiles of Galaxies in the Hubble Deep Field-North
We fit elliptical isophotes to the Hubble Deep Field-North WFPC-2 and NICMOS
data to study the rest-frame UV_{218}-U_{300} color profiles and rest-frame B
surface brightness profiles of 33 intermediate redshift galaxies (0.5 <= z <=
1.2) with I_{814} < 25 and 50 high redshift galaxies (2.0 <= z <= 3.5) with
H_{160}< 27. From the weighted least-squares fit to the color profiles we find
that, at intermediate redshifts, the galaxies possess negative color gradients
indicating a reddening towards the center of the profile similar to local
samples whereas, at high redshifts, the galaxies possess positive color
gradients. This indicates that star formation is more centrally concentrated in
the distant galaxy sample which differs from the prevalent mode of extended
disk star formation that we observe in the local universe. Additionally, we
find that it is critical to correct for PSF effects when evaluating the surface
brightness profiles since at small scale lengths and faint magnitudes, an
r^{1/4} profile can be smoothed out substantially to become consistent with an
exponential profile. After correcting for PSF effects, we find that at higher
look-back time, the fraction of galaxies possessing exponential profiles have
slightly decreased while the fraction of galaxies possessing r^{1/4} profiles
have slightly increased. Our results also suggest a statistically insignificant
increase in the fraction of peculiar/irregular type galaxies. We compare our
results with recent semi-analytical models which treat galaxy formation and
evolution following the cold dark matter hierarchical framework.Comment: 31 pages, 10 JPEG figures. To be published in AJ Vol. 124, October
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