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transmit diversity technology scheme in MIMO technologies. Then
the main
characteristic of this technology in MIMO. Finally we offer
simulation of the
antenna placement to get better diversity in multipath
propagation and provide our
mean conclusions and results.
Problems Identification:
Multiple received replicas of the transmitted signal sometimes
combinedestructively and signal overlay resulting in local deep
dips called Rayleigh-
Fading.
The 2nd problem faced by the world developing standard is
providing highthroughput at the cell edge without increasing
average transmit power or
frequency bandwidth.
Background Knowledge :
In this research we work on the first problem so we evaluate the
benefits of
transmit diversity in MIMO system .
Up to date WE find out three effects that enhance MIMO
technology performance
1. Increase of the Signal-to-Interference-and-Noise Ratio,2.
Spatial multiplexing,3. diversity gain
Diversity performance is measured by diversity gain, which is
the difference insignal-to-noise ratio (SNR) between the output of
a diversity combiner and the
signal on a single branch, measured at a given probability
level.
The transmit diversity technology can be applied to all the
physical channel in
downlink of LTE [1] and WiMAX, in uplink now four antenna used
for the
selection of good diversity.
Diversity is achieved by creating several independent paths
between the
transmitter and receiver. In multipath signal fading is one of
the most fundamental
features of wireless channels. Because multiple received
replicas of the transmitted
signal sometimes combine destructively and signal overlay
resulting in local deep
dips called Rayleigh-Fading [3]. Multiple antennas diversity
overcome this
problem. The receiver of independent copy of same signal by each
element in the
receive array is the basis of receive diversity . The
probability decrease that all
signals are in deep fade simultaneously.
Transmit diversity is base on multiple transmitter and receiver
antennas. MIMO
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technologies is based on both transmit and receive diversity.
MIMO and transmit
diversity increase the performance of present and future
wireless communication
systems, in MIMO transmit diversity is based on space-Frequency
Block coding
(SFBC), combine with Frequency Shift Transmit Diversity (FSTD)
in case of four
transmit antenna [4]. Transmit diversity is intended for common
downlinkchannels to provide extended diversity for transmission for
channel-dependent
scheduling is not possible. Transmit diversity can also be
applied Voice-over-IP
(VoIP) where high data rate only justify the user.
ANTENNAPLACEMENTSTUDY
In this antenna placement study spatial diversity and pattern
diversity technique
used to achieve high diversity gain. Spatial diversity uses
multiple antennas with
the same characteristics but separated in space for reception or
transmission. Base-
station spatial diversity requires wide antenna spacings for
proper operation
because the multipath arrival angle spread is narrow . Pattern
or Angle diversity
uses directional antennas discriminate over angle or space,
consists of two or more
co-located antennas with different radiation patterns. This type
of diversity makes
use of directive antennas that are usually physically separated
by some (often
short) distance [5]. Collectively they are capable of
discriminating a large portion
of angle space and can provide a higher gain versus a single
omnidirectional
radiator.
simulations are necessary to test and optimize procedures. So we
have
performed simulation to identify the best antenna placement in
MIMO
technologies to get high diversity in multipath propagation.
Ansoft designer we
used as a simulator tool with S-parameter for best pattern and
spatial diversity
antennas placement.
simulation performed on three mutual coupling pair of pattern
and spatial
diversity antennas placement. The mutual coupling pair of
antennas are set as
follows: mutual coupling (2-1), mutual coupling (2-2) and mutual
coupling (2-3).
In figure 3 all three pair are illustrated.
The essential measuring stick to quantify the performance of
MIMO antennas is
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the coupling placement of antennas in different direction and
spaces and then
using S-parameters to measure their performance graph.
S-parameters are one of
the most useful method for presenting a system as a black box
[6] and the external
behavior of this black box can be predicted without any regard
for the contents of
black box. S-parameters are measure by sending frequency signals
into the systemor network (black box) and detecting what was exit
from each port. S-parameters
have magnitude and phase thats why the input Signal magnitude
and phase both
are changed by the network, but in myr point of view how much
gain is more
important than how much the signal has phase shifted.
REFERENCES:
[1] Juho Lee, Jin-Kyu Han and Jianzhong (2009) MIMO Technologies
in 3GPP
LTE and LTE Advanced:, EURASIP Journal on Wirless Communication
and
Networking, Volume 2009,10 pages
[2] Liang Dong, Hosung Choo,(2005) Simulation of MIMO Channel
Capacity
With Antenna Polarization Diversity IEEE TRANSACTIONS ON
WIRELESS
COMMUNICATIONS, VOL. 4, NO. 4, JULY 2005
[3] Angel Lozano and Nihar Jindal(2009) Transmit Diversity v.
Spatial
Multiplexing in ModernMIMO Systems
[4] Stefan Parkvall and David Astely (2009) Journal of
Communications,volume
. 4. 3 ,pp. 146-154
[5] Carl B. Dietrich, Jr., Member, IEEE, Kai Dietze, J. Randall
Nealy, and Warren
L. Stutzman (2001) Spatial, Polarization, and Pattern Diversity
for Wireless
Handheld Terminals. IEEE TRANSACTIONS ON ANTENNAS AND
PROPAGATION, VOL. 49, NO. 9.pp 1271-1281.
[6] Jean BurnikellNa.tional Instruments paper :
http://zone.ni.com/devzone/nidzgloss.nsf/webmain/D2C4FA88321195FE8625686
B00542EDB?OpenDocument .Accessed 11 January 2011
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Enhancing MIMO technologies Performance
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Mushtaq Ahmad
Shoib Gul
Date: 27/04/2011
Subject: Wireless Communication
BAHRIA UNIVERSITY ISLAMABAD CAMPUS
