249 research outputs found
Limiting Performance of Conventional and Widely Linear DFT-precoded-OFDM Receivers in Wideband Frequency Selective Channels
This paper describes the limiting behavior of linear and decision feedback
equalizers (DFEs) in single/multiple antenna systems employing
real/complex-valued modulation alphabets. The wideband frequency selective
channel is modeled using a Rayleigh fading channel model with infinite number
of time domain channel taps. Using this model, we show that the considered
equalizers offer a fixed post signal-to-noise-ratio (post-SNR) at the equalizer
output that is close to the matched filter bound (MFB). General expressions for
the post-SNR are obtained for zero-forcing (ZF) based conventional receivers as
well as for the case of receivers employing widely linear (WL) processing.
Simulation is used to study the bit error rate (BER) performance of both MMSE
and ZF based receivers. Results show that the considered receivers
advantageously exploit the rich frequency selective channel to mitigate both
fading and inter-symbol-interference (ISI) while offering a performance
comparable to the MFB
Exploiting Spatial Interference Alignment and Opportunistic Scheduling in the Downlink of Interference Limited Systems
In this paper we analyze the performance of single stream and multi-stream
spatial multiplexing (SM) systems employing opportunistic scheduling in the
presence of interference. In the proposed downlink framework, every active user
reports the post-processing signal-to-interference-plus-noise-power-ratio
(post-SINR) or the receiver specific mutual information (MI) to its own
transmitter using a feedback channel. The combination of scheduling and
multi-antenna receiver processing leads to substantial interference suppression
gain. Specifically, we show that opportunistic scheduling exploits spatial
interference alignment (SIA) property inherent to a multi-user system for
effective interference mitigation. We obtain bounds for the outage probability
and the sum outage capacity for single stream and multi stream SM employing
real or complex encoding for a symmetric interference channel model.
The techniques considered in this paper are optimal in different operating
regimes. We show that the sum outage capacity can be maximized by reducing the
SM rate to a value less than the maximum allowed value. The optimum SM rate
depends on the number of interferers and the number of available active users.
In particular, we show that the generalized multi-user SM (MU SM) method
employing real-valued encoding provides a performance that is either
comparable, or significantly higher than that of MU SM employing complex
encoding. A combination of analysis and simulation is used to describe the
trade-off between the multiplexing rate and sum outage capacity for different
antenna configurations
Numerical modeling of high temperature shell and tube heat exchanger and chemical decomposer for hydrogen production
This thesis deals with the development of a three-dimensional numerical model of high temperature shell and tube heat exchanger and chemical decomposer to examine the percentage decomposition of a sulfur trioxide gaseous mixture for the production of hydrogen by the sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. A counter flow type straight tube shell and heat exchanger concept is chosen for the analysis. The reacting fluid is a mixture of sulfur trioxide gas and water vapor inside the tubes of the heat exchanger and high temperature helium is the gas which flows through the shell. Proceeding with the simple, basic two-dimensional tube model, the percentage decomposition of sulfur trioxide gaseous mixture was investigated. A steady-state, laminar, two-dimensional axisymmetric shell and tube model with counter flow and parallel flow arrangements and simple uniform cubical packing was developed using a porous medium approach to investigate the fluid flow, heat transfer and chemical reactions in the decomposer. The effects of inlet velocity, temperature and the porous medium properties on the pressure drop across the porous medium were studied. The influence of geometric parameters mainly the diameter of the tube, diameter of the shell and the length of the porous zone on percentage decomposition of sulfur trioxide in the tube was investigated as well. From the performed calculations, it was found that the Reynolds number played a significant role in affecting the sulfur trioxide decomposition. The percentage decomposition decreases with an increase in Reynolds number; Flow rate uniformity in the heat exchanger tubes was also investigated. Simulations of the three dimensional straight tube configuration, tube configuration with baffle plate arrangement and with pebble bed region inside the tubes were performed to examine the flow distribution on tube side. It was found the flow maldistribution along the tube direction is very serious with the simple tube configuration. An improvement of the header configuration has been done by introducing a baffle plate into the header section. With the introduction of the baffle plate, there was a noticeable decrease in the flow maldistribution in the tubes. Uniformity of flow was also investigated with catalytic bed inside the tubes. A significant decrease in flow maldistribution was observed with this arrangement. Simulations were performed on three dimensional numerical model of the shell and tube heat exchanger with and without baffles to evaluate the percentage decomposition of sulfur trioxide where it was found that the baffles play an important role in increasing the percentage decomposition of sulfur trioxide
Method and apparatus for a cluster specific CSI feedback
Embodiment herein provide a method and system of reporting cluster specific CSI feedback by user equipment (UE) to a cloud system. The UE associates with the cloud using a biased association or an unbiased association. In a biased association, a ratio between the highest received power from a Macro BS and a Pico base station is determined by the UE and compared with a threshold (bias). If the ratio is greater than the bias, the UE associates with the Pico BS. The UE reports CSI for a set of dominant Macro BSs and Pico BSs within a cluster. The UE can report the IDs of the BSs which contribute to dominant interference caused by the BSs of neighboring clusters
Detection of Sand Boils from Images using Machine Learning Approaches
Levees provide protection for vast amounts of commercial and residential properties. However, these structures degrade over time, due to the impact of severe weather, sand boils, subsidence of land, seepage, etc. In this research, we focus on detecting sand boils. Sand boils occur when water under pressure wells up to the surface through a bed of sand. These make levees especially vulnerable. Object detection is a good approach to confirm the presence of sand boils from satellite or drone imagery, which can be utilized to assist in the automated levee monitoring methodology. Since sand boils have distinct features, applying object detection algorithms to it can result in accurate detection. To the best of our knowledge, this research work is the first approach to detect sand boils from images. In this research, we compare some of the latest deep learning methods, Viola Jones algorithm, and other non-deep learning methods to determine the best performing one. We also train a Stacking-based machine learning method for the accurate prediction of sand boils. The accuracy of our robust model is 95.4%
A Novel Beamformed Control Channel Design for LTE with Full Dimension-MIMO
The Full Dimension-MIMO (FD-MIMO) technology is capable of achieving huge
improvements in network throughput with simultaneous connectivity of a large
number of mobile wireless devices, unmanned aerial vehicles, and the Internet
of Things (IoT). In FD-MIMO, with a large number of antennae at the base
station and the ability to perform beamforming, the capacity of the physical
downlink shared channel (PDSCH) has increased a lot. However, the current
specifications of the 3rd Generation Partnership Project (3GPP) does not allow
the base station to perform beamforming techniques for the physical downlink
control channel (PDCCH), and hence, PDCCH has neither the capacity nor the
coverage of PDSCH. Therefore, PDCCH capacity will still limit the performance
of a network as it dictates the number of users that can be scheduled at a
given time instant. In Release 11, 3GPP introduced enhanced PDCCH (EPDCCH) to
increase the PDCCH capacity at the cost of sacrificing the PDSCH resources. The
problem of enhancing the PDCCH capacity within the available control channel
resources has not been addressed yet in the literature. Hence, in this paper,
we propose a novel beamformed PDCCH (BF-PDCCH) design which is aligned to the
3GPP specifications and requires simple software changes at the base station.
We rely on the sounding reference signals transmitted in the uplink to decide
the best beam for a user and ingeniously schedule the users in PDCCH. We
perform system level simulations to evaluate the performance of the proposed
design and show that the proposed BF-PDCCH achieves larger network throughput
when compared with the current state of art algorithms, PDCCH and EPDCCH
schemes
Optimize Power Allocation Scheme to Maximize Sum Rate in CoMP with Limited Channel State Information
Extensive use of mobile applications throws many challenges in cellular systems like cell edge
throughput, inter cell interference and spectral e�ciency. Many of these challenges have been
resolved using Coordinated Multi-Point (CoMP), developed in the Third Generation Partnership
Project for LTE-Advanced) to a great extent. CoMP cooperatively process signals from base sta-
tions that are connected to various multiple terminals (user equipment (UEs)) at transmission and
reception. This CoMP improves throughput, reduces or even removes inter-cell interference and
increases spectral e�ciency in the downlink of multi-antenna coordinated multipoint systems.
Many researchers addressed these issues assuming that BSs have the knowledge of the common
control channels dedicated to all UEs and also about the full or partial channel state information
(CSI) of all the links. From the CSI available at the BSs, multiuser interference can be managed
at the BSs. To make this feasible, UEs are responsible for collecting downlink CSI. But, CSI
measurement (instantaneous and/or statistical) is imperfect in nature because of the randomly
varying nature of the channels at random times. These incorrect CSI values available at the BSs
may, in turn, create multi-user interference. There are many techniques to suppress the multi-user
interference, among which the feedback scheme is the one which is gaining a lot of attention. In
feedback schemes, CSI information needs to be fed back to the base station from UEs in the uplink.
It is obvious, the question arises on the type and amount of feedback need to be used. Research
has been progressing in this front and some feedback techniques have been proposed. Three basic
CoMP Feedback schemes are available. Explicit or statistical channel information feedback scheme
in which channel information like channels's covariance matrix of the channel are shared between the
transmitter and receiver. Next, implicit or statistical channel information feedback which contains
information such as Channel quality indication or Precoding matrix indicator or Rank indicator. 1st
applied to TDD LTE type structure and 2nd of feedback scheme can be applied in the FDD system.
Finally, we have UE which tranmit the sounding reference signal (CSI). This type of feedback scheme
is applied to exploit channel reciprocity and to reduce channel intercell interference and this can be
applied in the TDD system. We have analyzed the scenario of LTE TDD based system. After this,
optimization of power is also required because users at the cell edge required more attention than
the user locating at the center of the cell. In my work, it shows estimated power gives exponential
divercity for high SNR as low SNR too.
In this method, a compression feedback method is analyzed to provide multi-cell spatial channel
information. It improves the feedback e�ciency and throughput. The rows and columns of the
channel matrix are compressed using Eigenmode of the user and codebook based scheme speci�ed
in LTE speci�cation. The main drawback of this scheme is that spectral e�ciency is achieved with
the cost of increased overheads for feedback and evolved NodeB (eNB). Other factor is complexity
of eNodeB which is to be addressed in future work
System-Level Modelling and Beamforming Design for RIS-assisted Cellular Systems
Reconfigurable intelligent surface (RIS) is considered as key technology for
improving the coverage and network capacity of the next-generation cellular
systems. By changing the phase shifters at RIS, the effective channel between
the base station and user can be reconfigured to enhance the network capacity
and coverage. However, the selection of phase shifters at RIS has a significant
impact on the achievable gains. In this letter, we propose a beamforming design
for the RIS-assisted cellular systems. We then present in detail the
system-level modelling and formulate a 3-dimension channel model between the
base station, RIS, and user, to carry out system-level evaluations. We evaluate
the proposed beamforming design in the presence of ideal and discrete phase
shifters at RIS and show that the proposed design achieves significant
improvements as compared to the state-of-the-art algorithms
- …