The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
M Limon - One of the best experts on this subject based on the ideXlab platform.
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first year wilkinson microwave anisotropy probe wmap observations galactic signal contamination from sidelobe pickup
Astrophysical Journal Supplement Series, 2003Co-Authors: Cris W Barnes, R S Hill, G Hinshaw, Lyman A Page, C L Bennett, M Halpern, N Jarosik, A Kogut, M LimonAbstract:Since the Galactic center is ~1000 times brighter than fluctuations in the cosmic microwave background (CMB), CMB experiments must carefully account for stray Galactic pickup. We present the level of contamination due to Sidelobes for the first-year CMB maps produced by the Wilkinson Microwave Anisotropy Probe (WMAP) observatory. For each radiometer, full 4π sr antenna gain patterns are determined from a combination of numerical prediction and ground-based and space-based measurements. These patterns are convolved with the WMAP first-year sky maps and observatory scan pattern to generate the expected sidelobe signal contamination, for both intensity and polarized microwave sky maps. When the main beams are outside of the Galactic plane, we find rms values for the expected sidelobe pickup of 15, 2.1, 2.0, 0.3, and 0.5 μK for the K, Ka, Q, V, and W bands, respectively. Except for at the K band, the rms polarized contamination is 1 μK. Angular power spectra of the Galactic pickup are presented.
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first year wilkinson microwave anisotropy probe wmap observations galactic signal contamination from sidelobe pickup
arXiv: Astrophysics, 2003Co-Authors: Cris W Barnes, R S Hill, G Hinshaw, Lyman A Page, C L Bennett, M Halpern, N Jarosik, A Kogut, M Limon, S S MeyerAbstract:Since the Galactic center is ~1000 times brighter than fluctuations in the Cosmic Microwave Background (CMB), CMB experiments must carefully account for stray Galactic pickup. We present the level of contamination due to Sidelobes for the year one CMB maps produced by the WMAP observatory. For each radiometer, full 4 pi sr antenna gain patterns are determined from a combination of numerical prediction, ground-based and space-based measurements. These patterns are convolved with the WMAP year one sky maps and observatory scan pattern to generate expected sidelobe signal contamination, for both intensity and polarized microwave sky maps. Outside of the Galactic plane, we find rms values for the expected sidelobe pickup of 15, 2.1, 2.0, 0.3, 0.5 uK for K, Ka, Q, V, and W bands respectively. Except at K band, the rms polarized contamination is <<1 uK. Angular power spectra of the Galactic pickup are presented.
Chardir Chung - One of the best experts on this subject based on the ideXlab platform.
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Spectrally Precoded OFDM and OFDMA with Cyclic Prefix and Unconstrained Guard Ratios
IEEE Transactions on Wireless Communications, 2011Co-Authors: Hao-ming Chen, Wei-chang Chen, Chardir ChungAbstract:Spectrally precoded orthogonal frequency-division multiplexing with cyclic prefix (SP-CP-OFDM) and SP-CP-OFDM multiple access (SP-CP-OFDMA) are investigated in this paper. A general constraint on spectral precoding is developed for both SP-CP-OFDM and SP-CP-OFDMA signal formats with unconstrained guard ratios and arbitrary input data statistics to ensure very small power spectral Sidelobes decaying asymptotically as f-2J-2, with J a predesigned integer-valued parameter. In the SP-CP-OFDM signaling format, new spectral precoders are devised to meet the constraint. It is shown that the proposed SP-CP-OFDM signals can provide much smaller spectral Sidelobes than the previously designed SP-CP-OFDM signals with block partitioning and constrained guard ratios. In the SP-CP-OFDMA signaling format, a general procedure is proposed to facilitate the precoder design for SP-CP-OFDMA signals with arbitrary subcarrier allocation for each user and some spectral precoders are accordingly devised. It is shown that the proposed SP-CP-OFDMA signals can suppress sidelobe powers effectively and thus achieve higher spectral compactness than nonprecoded rectangularly-pulsed CP-OFDMA.
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spectral precoding for constant envelope ofdm
IEEE Transactions on Communications, 2010Co-Authors: Chardir ChungAbstract:Spectrally precoded orthogonal frequency-division multiplexing (OFDM) and constant-envelope OFDM (CE-OFDM) are two modified OFDM formats that enhance the signaling features of OFDM, while allowing for the efficient implementation by discrete Fourier transform and the insertion of guard intervals to counteract channel dispersion. The spectrally precoded OFDM signal provides very small power spectral Sidelobes decaying asymptotically as f-2J-2 with J integer-valued design parameter, thereby suppressing sidelobe powers effectively and achieving higher spectral efficiency than nonprecoded rectangularly-pulsed OFDM which has power spectral Sidelobes decaying asymptotically as f-2. The CE-OFDM signal exhibits a unity peak-to-average power ratio, and thus enables the efficient use of transmitter's power amplifier. In this paper, a specific CE-OFDM block signaling format is proposed to incorporate spectral precoding with an aim to suppressing sidelobe powers more effectively than conventional nonprecoded CE-OFDM. The general constraint on spectral precoding is developed to ensure that the power spectral Sidelobes of the spectrally precoded CE-OFDM block signal with arbitrary data statistics decay asymptotically as f-2J-2. Some spectral codes previously found for spectrally precoded OFDM are shown to meet the constraint and thus suited for spectrally precoded CE-OFDM. Specifically, spectral performance is analyzed for the spectrally precoded CE-OFDM block signal with independent and identically distributed data to illustrate the prevailing spectral advantage. The corresponding receiver is also developed to demodulate the spectrally precoded CE-OFDM block signal over dispersive channels.
Petre Stoica - One of the best experts on this subject based on the ideXlab platform.
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unimodular sequence design for good autocorrelation properties
International Conference on Acoustics Speech and Signal Processing, 2009Co-Authors: Hao He, Petre Stoica, Jian LiAbstract:Unimodular (i.e., constant modulus) sequences with good autocorrelation properties are useful in several areas, including communications, radar and sonar. The integrated sidelobe level (ISL) is often used to express the goodness of the autocorrelation properties of a given sequence. In this paper, we present several cyclic algorithms for the local minimization of ISL-related metrics. To illustrate the performance of the proposed algorithms, we present a number of examples including the design of sequences that have virtually zero autocorrelation Sidelobes in a specified lag interval, and of long sequences that could hardly be handled by means of other algorithms previously suggested in the literature.
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new algorithms for designing unimodular sequences with good correlation properties
IEEE Transactions on Signal Processing, 2009Co-Authors: Petre StoicaAbstract:Unimodular (i.e., constant modulus) sequences with good autocorrelation properties are useful in several areas, including communications and radar. The integrated sidelobe level (ISL) of the correlation function is often used to express the goodness of the correlation properties of a given sequence. In this paper, we present several cyclic algorithms for the local minimization of ISL-related metrics. These cyclic algorithms can be initialized with a good existing sequence such as a Golomb sequence, a Frank sequence, or even a (pseudo)random sequence. To illustrate the performance of the proposed algorithms, we present a number of examples, including the design of sequences that have virtually zero autocorrelation Sidelobes in a specified lag interval and of long sequences that could hardly be handled by means of other algorithms previously suggested in the literature.
Cris W Barnes - One of the best experts on this subject based on the ideXlab platform.
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first year wilkinson microwave anisotropy probe wmap observations galactic signal contamination from sidelobe pickup
Astrophysical Journal Supplement Series, 2003Co-Authors: Cris W Barnes, R S Hill, G Hinshaw, Lyman A Page, C L Bennett, M Halpern, N Jarosik, A Kogut, M LimonAbstract:Since the Galactic center is ~1000 times brighter than fluctuations in the cosmic microwave background (CMB), CMB experiments must carefully account for stray Galactic pickup. We present the level of contamination due to Sidelobes for the first-year CMB maps produced by the Wilkinson Microwave Anisotropy Probe (WMAP) observatory. For each radiometer, full 4π sr antenna gain patterns are determined from a combination of numerical prediction and ground-based and space-based measurements. These patterns are convolved with the WMAP first-year sky maps and observatory scan pattern to generate the expected sidelobe signal contamination, for both intensity and polarized microwave sky maps. When the main beams are outside of the Galactic plane, we find rms values for the expected sidelobe pickup of 15, 2.1, 2.0, 0.3, and 0.5 μK for the K, Ka, Q, V, and W bands, respectively. Except for at the K band, the rms polarized contamination is 1 μK. Angular power spectra of the Galactic pickup are presented.
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first year wilkinson microwave anisotropy probe wmap observations galactic signal contamination from sidelobe pickup
arXiv: Astrophysics, 2003Co-Authors: Cris W Barnes, R S Hill, G Hinshaw, Lyman A Page, C L Bennett, M Halpern, N Jarosik, A Kogut, M Limon, S S MeyerAbstract:Since the Galactic center is ~1000 times brighter than fluctuations in the Cosmic Microwave Background (CMB), CMB experiments must carefully account for stray Galactic pickup. We present the level of contamination due to Sidelobes for the year one CMB maps produced by the WMAP observatory. For each radiometer, full 4 pi sr antenna gain patterns are determined from a combination of numerical prediction, ground-based and space-based measurements. These patterns are convolved with the WMAP year one sky maps and observatory scan pattern to generate expected sidelobe signal contamination, for both intensity and polarized microwave sky maps. Outside of the Galactic plane, we find rms values for the expected sidelobe pickup of 15, 2.1, 2.0, 0.3, 0.5 uK for K, Ka, Q, V, and W bands respectively. Except at K band, the rms polarized contamination is <<1 uK. Angular power spectra of the Galactic pickup are presented.
P K Tan - One of the best experts on this subject based on the ideXlab platform.
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design of a uniform amplitude time modulated linear array with optimized time sequences
IEEE Transactions on Antennas and Propagation, 2005Co-Authors: Shiwen Yang, Y B Gan, Anyong Qing, P K TanAbstract:A novel approach to realize uniform amplitude time modulated linear arrays with both suppressed Sidelobes and sidebands is proposed. The approach utilizes the direct optimization of the "switch-on" time sequence of each array element via the simple genetic algorithm (SGA). As compared to previous time modulated linear arrays, the new array has the advantages of having low sidelobe level (SLL), low sideband level (SBL) and uniform excitations simultaneously. Experimental results on an experimental prototype of a 16-element printed dipole linear array with the SGA optimized time sequences verified the approach.
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linear antenna arrays with bidirectional phase center motion
IEEE Transactions on Antennas and Propagation, 2005Co-Authors: Shiwen Yang, Y B Gan, P K TanAbstract:The theoretical and experimental studies of linear antenna arrays with bidirectional phase center motion (BPCM) is presented. BPCM is achieved by exciting only part of the linear array elements and sweeping the excited part from one end to the other and back. The Sidelobes of the linear arrays with BPCM experience both upper and lower Doppler frequency shift effect in turn, as compared to linear arrays with unidirectional phase center motion (UPCM). Numerical results show that linear arrays with BPCM are also capable of synthesizing low/ultralow Sidelobes, but with a much lower excitation dynamic range ratio as compared to that in conventional arrays. In addition, some characteristics, such as passband bandwidth or sideband levels, are better than those of arrays with UPCM or time modulated variable aperture size arrays. An L-band 16-element printed dipole linear array with BPCM was designed. Experimental results show that a -35 dB relative sidelobe level (SLL) can be achieved.
