Abstract: In this paper, an overview of the radio over fiber (RoF) technology is provided. Obstacles for reducing the capital and operational expenses in the existing systems are discussed in various perspectives. Some possible RoF deployment scenarios for WiMAX
data transmission are proposed as a means for capital and operational
expenses reduction. IEEE 802.16a standard based end-to-end physical layer model is simulated including intensity modulated direct detection RoF technology. Finally the feasibility of RoF
technology to carry WiMAX signals between the base station and the
remote antenna units is demonstrated using the simulation results.
Abstract: This paper investigates the impact of the hand-hold
positions on both antenna performance and the specific absorption
rate (SAR) induced in the user-s head. A cellular handset with
external antenna operating at GSM-900 frequency is modeled and
simulated using a finite difference time-domain (FDTD)-based
platform SEMCAD-X. A specific anthropomorphic mannequin
(SAM) is adopted to simulate the user-s head, whereas a semirealistic
CAD-model of three-tissues is designed to simulate the
user-s hand. The results show that in case of the handset in hand close
to head at different positions; the antenna total efficiency gets
reduced to (14.5% - 5.9%) at cheek-position and to (27.5% to 11.8%)
at tilt-position. The peak averaged SAR1g values in head close to
handset without hand, are 4.67 W/Kg and 2.66 W/Kg at cheek and
tilt-position, respectively. Due to the presence of hand, the SAR1g in
head gets reduced to (3.67-3.31 W/Kg) at cheek-position and to
(1.84-1.64 W/Kg) at tilt-position, depending on the hand-hold
position.
Abstract: This paper predicts the effect of the user-s hand-hold
position on the Total Isotropic Sensitivity (TIS) of GSM900/1800
mobile phone antennas of realistic in-use conditions, where different
semi-realistic mobile phone models, i.e., candy bar and clamshell, as
well as different antenna types, i.e., external and internal, are
simulated using a FDTD-based platform. A semi-realistic hand model
consisting of three tissues and the SAM head are used in simulations.
The results show a considerable impact on TIS of the adopted mobile
phone models owing to the user-s hand presence at different
positions, where a maximum level of TIS is obtained while grasping
the upper part of the mobile phone against head. Maximum TIS
levels are recorded in talk position for mobile phones with external
antenna and maximum differences in TIS levels due to the hand-hold
alteration are recorded for clamshell-type phones.
Abstract: In this paper, a new design technique for enhancing
bandwidth that improves the performance of a conventional
microstrip patch antenna is proposed. This paper presents a novel
wideband probe fed inverted slotted microstrip patch antenna. The
design adopts contemporary techniques; coaxial probe feeding,
inverted patch structure and slotted patch. The composite effect of
integrating these techniques and by introducing the proposed patch,
offer a low profile, broadband, high gain, and low cross-polarization
level. The results for the VSWR, gain and co-and cross-polarization
patterns are presented. The antenna operating the band of 1.80-2.36
GHz shows an impedance bandwidth (2:1 VSWR) of 27% and a gain
of 10.18 dBi with a gain variation of 1.12 dBi. Good radiation
characteristics, including a cross-polarization level in xz-plane less
than -42 dB, have been obtained.
Abstract: Here we have considered non uniform microstrip
leaky-wave antenna implemented on a dielectric waveguide by a
sinusoidal profile of periodic metallic grating. The non distribution of
the attenuation constant α along propagation axis, optimize the
radiating characteristics and performances of such antennas. The
method developped here is based on an integral method where the
formalism of the admittance operator is combined to a BKW
approximation. First, the effect of the modeling in the modal analysis
of complex waves is studied in detail. Then, the BKW model is used
for the dispersion analysis of the antenna of interest. According to
antenna theory, a forced continuity of the leaky-wave magnitude at
discontinuities of the non uniform structure is established. To test the
validity of our dispersion analysis, computed radiation patterns are
presented and compared in the millimeter band.
Abstract: This paper describes the development of a fully
automated measurement software for antenna radiation pattern
measurements in a Compact Antenna Test Range (CATR). The
CATR has a frequency range from 2-40 GHz and the measurement
hardware includes a Network Analyzer for transmitting and
Receiving the microwave signal and a Positioner controller to control
the motion of the Styrofoam column. The measurement process
includes Calibration of CATR with a Standard Gain Horn (SGH)
antenna followed by Gain versus angle measurement of the Antenna
under test (AUT). The software is designed to control a variety of
microwave transmitter / receiver and two axis Positioner controllers
through the standard General Purpose interface bus (GPIB) interface.
Addition of new Network Analyzers is supported through a slight
modification of hardware control module. Time-domain gating is
implemented to remove the unwanted signals and get the isolated
response of AUT. The gated response of the AUT is compared with
the calibration data in the frequency domain to obtain the desired
results. The data acquisition and processing is implemented in
Agilent VEE and Matlab. A variety of experimental measurements
with SGH antennas were performed to validate the accuracy of
software. A comparison of results with existing commercial
softwares is presented and the measured results are found to be
within .2 dBm.
Abstract: Multiple-input multiple-output (MIMO) systems are
widely in use to improve quality, reliability of wireless transmission
and increase the spectral efficiency. However in MIMO systems,
multiple copies of data are received after experiencing various
channel effects. The limitations on account of complexity due to
number of antennas in case of conventional decoding techniques have
been looked into. Accordingly we propose a modified sphere decoder
(MSD-1) algorithm with lower complexity and give rise to system
with high spectral efficiency. With the aim to increase signal
diversity we apply rotated quadrature amplitude modulation (QAM)
constellation in multi dimensional space. Finally, we propose a new
architecture involving space time trellis code (STTC) concatenated
with space time block code (STBC) using MSD-1 at the receiver for
improving system performance. The system gains have been verified
with channel state information (CSI) errors.
Abstract: In this work, we study the problem of determining
the minimum scheduling length that can satisfy end-to-end (ETE)
traffic demand in scheduling-based multihop WSNs with cooperative
multiple-input multiple-output (MIMO) transmission scheme. Specifically,
we present a cross-layer formulation for the joint routing,
scheduling and stream control problem by incorporating various
power and rate adaptation schemes, and taking into account an
antenna beam pattern model and the signal-to-interference-and-noise
(SINR) constraint at the receiver. In the context, we also propose
column generation (CG) solutions to get rid of the complexity
requiring the enumeration of all possible sets of scheduling links.
Abstract: It is well known that the channel capacity of Multiple-
Input-Multiple-Output (MIMO) system increases as the number of
antenna pairs between transmitter and receiver increases but it suffers
from multiple expensive RF chains. To reduce the cost of RF chains,
Antenna Selection (AS) method can offer a good tradeoff between
expense and performance. In a transmitting AS system, Channel
State Information (CSI) feedback is necessarily required to choose
the best subset of antennas in which the effects of delays and errors
occurred in feedback channels are the most dominant factors
degrading the performance of the AS method. This paper presents the
concept of AS method using CSI from channel reciprocity instead of
feedback method. Reciprocity technique can easily archive CSI by
utilizing a reverse channel where the forward and reverse channels
are symmetrically considered in time, frequency and location. In this
work, the capacity performance of MIMO system when using AS
method at transmitter with reciprocity channels is investigated by
own developing Testbed. The obtained results show that reciprocity
technique offers capacity close to a system with a perfect CSI and
gains a higher capacity than a system without AS method from 0.9 to
2.2 bps/Hz at SNR 10 dB.
Abstract: In this paper, the effect of receive and/or transmit
antenna spacing on the performance (BER vs. SNR) of multipleantenna
systems is determined by using an RCS (Radar Cross
Section) channel model. In this physical model, the scatterers
existing in the propagation environment are modeled by their RCS so
that the correlation of the receive signal complex amplitudes, i.e.,
both magnitude and phase, can be estimated. The proposed RCS
channel model is then compared with classical models.
Abstract: Cooperative diversity (CD) has been adopted in many communication systems because it helps in improving performance of the wireless communication systems with the help of the relays that emulate the multiple antenna terminals. This work aims to provide the derivation of the performance analysis expressions of the multiuser diversity (MUD) in the two-hop cooperative multi-relay wireless networks (TCMRNs). Considering the work analysis, we provide analytically the derivation of a closed form expression of the two most commonly used performance metrics namely, the outage probability and the symbol error probability (SEP) for the fixed decode-and-forward (FDF) protocol with MUD.
Abstract: In this research paper, a slotted coaxial line fed cross
dipole excitation structure for short backfire antenna is proposed and
developed to achieve reconfigurable circular polarization. The cross
dipole, which is fed by the slotted coaxial line, consists of two
orthogonal dipoles. The dipoles are mounted on the outer conductor
of the coaxial line. A unique technique is developed to generate
reconfigurable circular polarization using cross dipole configuration.
The sub-reflector is supported by the feed line, thus requiring no
extra support. The antenna is developed on elliptical ground plane
with dielectric rim making antenna compact. It is demonstrated that
cross dipole excited short backfire antenna can achieve voltage
standing wave ratio (VSWR) bandwidth of 14.28% for 2:1 VSWR,
axial ratio of 0.2 dB with axial ratio (≤ 3dB) bandwidth of 2.14% and
a gain of more than 12 dBi. The experimental results for the designed
antenna structure are in close agreement with computer simulations.
Abstract: One of the biggest drawbacks of the wireless
environment is the limited bandwidth. However, the users sharing
this limited bandwidth have been increasing considerably. SDMA
technique which entails using directional antennas allows to increase
the capacity of a wireless network by separating users in the medium.
In this paper, it has been presented how the capacity can be enhanced
while the mean delay is reduced by using directional antennas in
wireless networks employing TDMA/FDD MAC. Computer
modeling and simulation of the wireless system studied are realized
using OPNET Modeler. Preliminary simulation results are presented
and the performance of the model using directional antennas is
evaluated and compared consistently with the one using
omnidirectional antennas.
Abstract: This paper represents an investigation on how exploiting multiple transmit antennas by OFDM based wireless LAN subscribers can mitigate physical layer error rate. Then by comparing the Wireless LANs that utilize spatial diversity techniques with the conventional ones it will reveal how PHY and TCP throughputs behaviors are ameliorated. In the next step it will assess the same issues based on a cellular context operation which is mainly introduced as an innovated solution that beside a multi cell operation scenario benefits spatio-temporal signaling schemes as well. Presented simulations will shed light on the improved performance of the wide range and high quality wireless LAN services provided by the proposed approach.
Abstract: In this paper, we consider the analysis of the
acquisition process for a hybrid double-dwell system with antenna
diversity for DS-CDMA (direct sequence-code division multiple
access) using an adaptive threshold. Acquisition systems with a fixed
threshold value are unable to adapt to fast varying mobile
communications environments and may result in a high false alarm
rate, and/or low detection probability. Therefore, we propose an
adaptively varying threshold scheme through the use of a cellaveraging
constant false alarm rate (CA-CFAR) algorithm, which is
well known in the field of radar detection. We derive exact
expressions for the probabilities of detection and false alarm in
Rayleigh fading channels. The mean acquisition time of the system
under consideration is also derived. The performance of the system is
analyzed and compared to that of a hybrid single dwell system.
Abstract: In this paper, a planar antenna for UWB applications
has been proposed. The antenna consists of a square patch, a partial
ground plane and a slot on the ground plane. The proposed antenna is
easy to be integrated with microwave circuitry for low manufacturing
cost. The flat type antenna has a compact structure and the total size
is 14.5×14.5mm2. The result shows that the impedance bandwidth
(VSWR≤ 2) of the proposed antenna is 12.49 GHz (2.95 to 15.44
GHz), which is equivalent to 135.8%. Details of the proposed
compact planar UWB antenna design is presented and discussed.
Abstract: This paper explores the implementation of adaptive
coding and modulation schemes for Multiple-Input Multiple-Output
Orthogonal Frequency Division Multiplexing (MIMO-OFDM) feedback
systems. Adaptive coding and modulation enables robust and
spectrally-efficient transmission over time-varying channels. The basic
premise is to estimate the channel at the receiver and feed this estimate
back to the transmitter, so that the transmission scheme can be
adapted relative to the channel characteristics. Two types of codebook
based channel feedback techniques are used in this work. The longterm
and short-term CSI at the transmitter is used for efficient channel
utilization. OFDM is a powerful technique employed in communication
systems suffering from frequency selectivity. Combined with
multiple antennas at the transmitter and receiver, OFDM proves to be
robust against delay spread. Moreover, it leads to significant data rates
with improved bit error performance over links having only a single
antenna at both the transmitter and receiver. The coded modulation
increases the effective transmit power relative to uncoded variablerate
variable-power MQAM performance for MIMO-OFDM feedback
system. Hence proposed arrangement becomes an attractive approach
to achieve enhanced spectral efficiency and improved error rate
performance for next generation high speed wireless communication
systems.
Abstract: This paper presented a theoretical and numerical investigation of the Compact Antenna Test Range (CATR) equipped with Super Hybrid Modulated Segmented Exponential Serrations (SHMSES). The investigation was based on diffraction theory and, more specifically, the Fresnel diffraction formulation. The CATR provides uniform illumination within the Fresnel region to test antenna. Application of serrated edges has been shown to be a good method to control diffraction at the edges of the reflectors. However, in order to get some insight into the positive effect of serrated edges a less rigorous analysis technique known as Physical Optics (PO) may be used. Ripple free and enhanced quiet zone width are observed for specific values of width and height modulation factors per serrations. The performance of SHMSE serrated reflector is evaluated in order to observe the effects of edge diffraction on the test zone fields.
Abstract: In this work the characteristics of spatial signal detec¬tion from an antenna array in various sample cases are investigated. Cases for a various number of available prior information about the received signal and the background noise are considered. The spatial difference between a signal and noise is only used. The performance characteristics and detecting curves are presented. All test-statistics are obtained on the basis of the generalized likelihood ratio (GLR). The received results are correct for a short and long sample.
Abstract: With the exponentially increasing demand for
wireless communications the capacity of current cellular systems will
soon become incapable of handling the growing traffic. Since radio
frequencies are diminishing natural resources, there seems to be a
fundamental barrier to further capacity increase. The solution can be
found in smart antenna systems.
Smart or adaptive antenna arrays consist of an array of antenna
elements with signal processing capability, that optimize the
radiation and reception of a desired signal, dynamically. Smart
antennas can place nulls in the direction of interferers via adaptive
updating of weights linked to each antenna element. They thus cancel
out most of the co-channel interference resulting in better quality of
reception and lower dropped calls. Smart antennas can also track the
user within a cell via direction of arrival algorithms. This implies that
they are more advantageous than other antenna systems. This paper
focuses on few issues about the smart antennas in mobile radio
networks.