Mahmud Harun - Academia.edu (original) (raw)
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Papers by Mahmud Harun
IEEE Transactions on Antennas and Propagation, 2008
We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multi... more We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multiple-output (MIMO) system in which both ends of the wireless link are located in a hallway. This scenario is of interest due to the increasing mobility of wireless devices, and because hallways have previously been reported to create difficulties for MIMO propagation. In this paper we focus on the variation in capacity as a function of position as one side of the wireless link is moved laterally (i.e., vertically and horizontally) in the hallway. We find not only significant degradation in MIMO capacity due to rank collapse, but also identify considerable variability due to changes in the signal strength. The capacity along a vertical cut is found to be relatively constant about 7.5 1 bps/Hz for a reference signal-to-noise ratio (SNR) of 10 dB at a range of 12 m, which is significantly less than the ideal maximum of 11.5 bps/Hz. The capacity along a horizontal cut is found to be about 6.7 3 bps/Hz under the same conditions, dominated by a large-scale signal strength variation which can be attributed to identifiable propagation mechanisms. We also consider the performance relative to simpler rank-1 (diversity/beamforming) schemes, with and without channel state information.
Radio Science, 2011
A new feed system is designed for operation below 100 MHz. The only existing system on the EVLA o... more A new feed system is designed for operation below 100 MHz. The only existing system on the EVLA operating below 100 MHz is the "4 m" (74 MHz) system which uses crossed half-wave dipoles located in front of the Cassegrain subreflector as the feed. However, the dipole feeds of this system introduce blockage, and a reduction in system sensitivity (estimated to be ∼6% at 1.4 GHz) is observed at higher frequency bands; hence the dipoles are removed most of the time. An alternative feed concept is therefore proposed in this paper. The proposed system appears to reduce sensitivity degradation at 1.4 GHz by 3% and thus might be permanently mounted. Moreover, the new system has sensitivity comparable to the existing system at frequencies below 100 MHz. The feed for this system consists of dipoles mounted between the adjacent struts of the reflector and is thus referred to as a strut-straddling feed array. This design and the analysis methodology used in this paper should be applicable in meeting the contiguous frequency coverage requirement (50-470 MHz) of the new low frequency system proposed for the EVLA. Also, it may be applied in the modification of other existing large reflector antennas for low frequency operation.
... Keywords: Low Frequency, Radio Astronomy, Reflector Antennas, Feeds, Sensitivity CopyrightMah... more ... Keywords: Low Frequency, Radio Astronomy, Reflector Antennas, Feeds, Sensitivity CopyrightMahmud Harun Page 2. Abstract ... 7 1.4 A GMRT reflector antenna. Courtesy: Suman Majumdar, IIT Kharagpur, India (used with permission, see Appendix E). . . . 9 ...
IEEE Transactions on Antennas and Propagation, 2008
We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multi... more We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multiple-output (MIMO) system in which both ends of the wireless link are located in a hallway. This scenario is of interest due to the increasing mobility of wireless devices, and because hallways have previously been reported to create difficulties for MIMO propagation. In this paper we focus on the variation in capacity as a function of position as one side of the wireless link is moved laterally (i.e., vertically and horizontally) in the hallway. We find not only significant degradation in MIMO capacity due to rank collapse, but also identify considerable variability due to changes in the signal strength. The capacity along a vertical cut is found to be relatively constant about 7.5 1 bps/Hz for a reference signal-to-noise ratio (SNR) of 10 dB at a range of 12 m, which is significantly less than the ideal maximum of 11.5 bps/Hz. The capacity along a horizontal cut is found to be about 6.7 3 bps/Hz under the same conditions, dominated by a large-scale signal strength variation which can be attributed to identifiable propagation mechanisms. We also consider the performance relative to simpler rank-1 (diversity/beamforming) schemes, with and without channel state information.
filebox.vt.edu
Consider the case of a time interleaved ADCs (round robin sampling with multiple ADCs) where timi... more Consider the case of a time interleaved ADCs (round robin sampling with multiple ADCs) where timing jitter can create harmonics in the sampled signal. One potential way to deal with this is to intentionally jitter the sampling instances using a pseudo-random sequence to jitter the ...
IEEE Transactions on Antennas and Propagation, 2008
We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multi... more We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multiple-output (MIMO) system in which both ends of the wireless link are located in a hallway. This scenario is of interest due to the increasing mobility of wireless devices, and because hallways have previously been reported to create difficulties for MIMO propagation. In this paper we focus on the variation in capacity as a function of position as one side of the wireless link is moved laterally (i.e., vertically and horizontally) in the hallway. We find not only significant degradation in MIMO capacity due to rank collapse, but also identify considerable variability due to changes in the signal strength. The capacity along a vertical cut is found to be relatively constant about 7.5 1 bps/Hz for a reference signal-to-noise ratio (SNR) of 10 dB at a range of 12 m, which is significantly less than the ideal maximum of 11.5 bps/Hz. The capacity along a horizontal cut is found to be about 6.7 3 bps/Hz under the same conditions, dominated by a large-scale signal strength variation which can be attributed to identifiable propagation mechanisms. We also consider the performance relative to simpler rank-1 (diversity/beamforming) schemes, with and without channel state information.
Radio Science, 2011
A new feed system is designed for operation below 100 MHz. The only existing system on the EVLA o... more A new feed system is designed for operation below 100 MHz. The only existing system on the EVLA operating below 100 MHz is the "4 m" (74 MHz) system which uses crossed half-wave dipoles located in front of the Cassegrain subreflector as the feed. However, the dipole feeds of this system introduce blockage, and a reduction in system sensitivity (estimated to be ∼6% at 1.4 GHz) is observed at higher frequency bands; hence the dipoles are removed most of the time. An alternative feed concept is therefore proposed in this paper. The proposed system appears to reduce sensitivity degradation at 1.4 GHz by 3% and thus might be permanently mounted. Moreover, the new system has sensitivity comparable to the existing system at frequencies below 100 MHz. The feed for this system consists of dipoles mounted between the adjacent struts of the reflector and is thus referred to as a strut-straddling feed array. This design and the analysis methodology used in this paper should be applicable in meeting the contiguous frequency coverage requirement (50-470 MHz) of the new low frequency system proposed for the EVLA. Also, it may be applied in the modification of other existing large reflector antennas for low frequency operation.
... Keywords: Low Frequency, Radio Astronomy, Reflector Antennas, Feeds, Sensitivity CopyrightMah... more ... Keywords: Low Frequency, Radio Astronomy, Reflector Antennas, Feeds, Sensitivity CopyrightMahmud Harun Page 2. Abstract ... 7 1.4 A GMRT reflector antenna. Courtesy: Suman Majumdar, IIT Kharagpur, India (used with permission, see Appendix E). . . . 9 ...
IEEE Transactions on Antennas and Propagation, 2008
We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multi... more We report measurements of the capacity of a 2.4 GHz vertically-polarized 3 4 multiple-input multiple-output (MIMO) system in which both ends of the wireless link are located in a hallway. This scenario is of interest due to the increasing mobility of wireless devices, and because hallways have previously been reported to create difficulties for MIMO propagation. In this paper we focus on the variation in capacity as a function of position as one side of the wireless link is moved laterally (i.e., vertically and horizontally) in the hallway. We find not only significant degradation in MIMO capacity due to rank collapse, but also identify considerable variability due to changes in the signal strength. The capacity along a vertical cut is found to be relatively constant about 7.5 1 bps/Hz for a reference signal-to-noise ratio (SNR) of 10 dB at a range of 12 m, which is significantly less than the ideal maximum of 11.5 bps/Hz. The capacity along a horizontal cut is found to be about 6.7 3 bps/Hz under the same conditions, dominated by a large-scale signal strength variation which can be attributed to identifiable propagation mechanisms. We also consider the performance relative to simpler rank-1 (diversity/beamforming) schemes, with and without channel state information.
filebox.vt.edu
Consider the case of a time interleaved ADCs (round robin sampling with multiple ADCs) where timi... more Consider the case of a time interleaved ADCs (round robin sampling with multiple ADCs) where timing jitter can create harmonics in the sampled signal. One potential way to deal with this is to intentionally jitter the sampling instances using a pseudo-random sequence to jitter the ...