Performance of Multi –user MIMO system in the presence of Polarization diversity

Mohammed.et.al. Int. Journal of Engineering Research and Application www.ijera.com
ISSN : 2248-9622, Vol.7, Issue 4, ( Part -6) April 2017, pp.51-53
www.ijera.com DOI: 10.9790/9622-0704065153 51 | P a g e
Performance of Multi –user MIMO system in the presence of
Polarization diversity
Abdul Hai Muzammil Mohammed *, Muhammad Moinuddin**, and
Ubaid M. Al-Saggaf ***
*, * *, and * * * ( Centre of Excellence in Intelligent Engineering Systems (CEIES), King Abdulaziz
University, P.O. Box 80200, Jeddah 21589, KSA)
*, * *, and * * * (Department of Electrical and Computer Engineering, King Abdulaziz University)
ABSTRACT
Employing Dual Polarized antenna plays a vital role for the future generation MIMO systems due to its
advantages such as space effectiveness and robustness. In this paper, we provide Outage probability of Multi-
user Dual Polarized antenna in an uplink environment. Specifically, we provide the simulation results of Outage
Probability for different varying parameters such as an increase in a number of the user, noise variance, and
Cross Polarization Discrimination. This parameter is investigated through Monte Carlo simulation.
Keywords – Multiple-Input Multiple-Output, Cross Polar Discrimination.
I. INTRODUCTION
MIMO system has the potential of increasing
the spectral efficiency of a system through a method
known as spatial multiplexing [1], and the ability to
improve the link reliability through a method known
as transmit diversity [2]. These multiplexing and
diversity gains achieved by a MIMO system are a
strong function of the channel characteristics, which
in turn depend on the scattering environment and on
the array configuration deployed at the transmitter
and the receiver [3]. In MIMO systems correlation
takes place between the channels because of lack of
antenna spacing and the scattering properties of the
transmission environment. Because of this, the
system performance degrades. In order to have an
uncorrelated channel between the transmitter and
receiver large antenna spacing’s are required both at
the base-station and the mobile unit. Employing of
multiple antennas may not be the best solution due
to the space limitation. Employing of polarization
diversity is the best solution.
Polarization diversity refers to the signaling strategy
whereby, information signals are transmitted and
received simultaneously on orthogonally polarized
waves. In this two spatially separated unipolarized
antennas are replaced by Dual Polarized antennas.
The employment of polarization diversity results in
cost and space effective of the system. There are two
effects on the polarization difference in MIMO
systems on the channel. The first one is Cross Polar
Discrimination (XPD). The power loss in a
communication system is due to the polarization
difference between the transmitting antenna and
receiving antennas and also a communication system
with a transmitting antenna and receiving antennas
having horizontal and vertical polarization or
vertical and horizontal polarization experience a
power loss because of orthogonally polarized
antennas. This phenomenon is known as XPD [4].
The second is cross-correlation coefficient. It is a
measure of correlation between signals appearing at
the two antennas with same or distinct polarizations.
Hence, XPD and correlation coefficient plays an
important role in MIMO systems using antennas
with polarization difference. By employing
polarization diversity, the performance of a system
can be increased with transmitting and receiving
several uncorrelated signals. Though there is a vast
work on modeling and analyzing of Dual Polarized
antennas in the recent years. But, the work related to
utilization of polarization diversity with multi-user
uplink scenario is limited [5],[6]. So, there is a need
for modern communication system designs to use
the benefits of polarization diversity in Multi-user
uplink systems. It can be applied to the MIMO
communication system with lack of space such as
GSM, WIFI, LTE, WIMAX etc [7].
In this paper, we present the simulation
results of Outage probability for Multi-user Dual
polarized MIMO systemin an uplink scenario.
Notations: Throughout the paper, we took bold
lower case letters as vectors and bold upper case
letters as a matrix. (.)H
and 𝐄[.] denotes conjugate
transpose and expectation, respectively.
II. SYSTEM MODEL
A Multi-user MIMO system with Dual
polarized antennas is considered for an uplink
scenario which is characterized by a Rayleigh
fading, in which M Dual Polarized receive antennas
at mobile unit transmits the messages to one Dual
RESEARCH ARTICLE OPEN ACCESS

Polarized antenna at Base station as presented in
Figure 1. The data received from the 𝑚𝑡ℎ
mobile
unit is multiplied by a combining vector 𝐲m which
can be expressed as
wm = 𝐲m 𝛏m
= 𝐲m
H 𝐙m 𝐬m + 𝐲m
H 𝐙d 𝐬d
M
d=1 ,d≠m +
+𝐲m
H
𝐧m
(1)
where
1. 𝐬 = [s0 s1]T
is the transmit signal vector.
2. 𝛏 = [ξ0 ξ1 ]
T
is the received signal vector.
3. n is the 2x1 temporally i.i.d. zero-mean complex
Gaussian noise vector satisfying 𝐄 𝐧𝐧 𝐇
=
Σ 𝐦
𝟐
𝐈 𝟐.
4. 𝐙 is the 2x2 channel matrix.
5. 𝒚 = [ 𝑦0 𝑦1 ] 𝑇
is the combining vector.
Figure 1 General Block Diagram of multi-user Dual
Polarized uplink system
III. OUTAGE PROBABILITY FOR DUAL
POLARIZED ANTENNAS
From equation (1) the Signal-to-Interference- Plus-
Noise Ratio
𝑃
𝐼𝑁 𝑚
for a certain threshold Ƞ for
𝑚𝑡ℎ
user can be expressed as
𝑃
𝐼𝑁 𝑚
(Ƞ) =
𝐲m
H
𝐙m 𝐬m
2
𝐲m
H 𝐙d 𝐬d
M
d=1 ,d≠m
2
+ 𝐲m
2Ʃm
2
For Dual Polarized antenna system the channel
matrix can be expressed as
𝐙 =
𝑍0,0 𝑍0,1
𝑍1,0 𝑍1,1
The components 𝑍1,1 and 𝑍0,0 of the
channel matrix Z, are co-polarized components and
the components 𝑍0,1 and 𝑍1,0 are cross-polarized
components. In case of Rayleigh fading, the
components of channel matrix 𝐙 are circular
complex Gaussian with zero mean and
variance Ʃ 𝑚
2
. We consider the model provided by
Bolcskei et al. [8] for modeling and Analyzing the
Dual Polarized channel. Aforementioned above XPD
and Cross correlation coefficients are the important
factors. For DP system XPD is given as [8] XPD =
1
α
Where α lie in between 0 and 1 which
represents antenna ability to separate orthogonally
polarized waves. Based on experimental results in
[9], the transmit correlation coefficient β and
receive correlation coefficient γ for DP antennas
are expressed as
β =
𝐄 z0,0 z0,1
∗
α
=
𝐄 z1,0z1,1
∗
α
γ =
𝐄 z0,0 z1,0
∗
α
=
𝐄 z0,1z1,1
∗
α
The outage probability is found based on the
simulation setup made based on SINR equation in
(2).
IV. RESULTS
In this section, we did Monte Carlo
simulations for an uplink scenario with Dual
Polarized antennas in a multi-user environment by
averaging the channel over 10000 trials.
Figure 2 Comparison of Outage probability for a
number of users (M).
In Figure 2, we studied the effect of
increase in the number of user on Outage Probability
with Dual Polarized antennas by setting the
parameters Σm
2
= 10 β=0.6, α=0.5,and γ=0.2. It is
observed that the Outage probability gets
deteriorates with a rise in the number of users.

Figure 3 Comparison of Outage probability with
different noise variances.
In Figure 3, Performance of Dual Polarized
antenna is compared based on noise variance in
terms of Outage Probability. It is realized that
Outage Probability deteriorates with a rise in noise
variance.
Figure 4 Comparison of Outage probability with
different XPD coefficient( α).
In Figure 4, we show the effect of XPD on Dual
Polarized antennas. We found that the Outage
Probability is better at high α value.
V. CONCLUSION
In this paper, the performance metric of
Dual Polarized antenna is examined in terms of
Outage probability in multi-user MIMO systemin an
uplink system for Rayleigh fading. We consider the
presence of multiple co-channel inference and
additive white Gaussian noise with multiple Dual
Polarized antennas at the receiver. Our Simulation
results show that Outage probability degrades with
an increase in a number of users and noise variance.
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Performance of Multi –user MIMO system in the presence of Polarization diversity

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Performance of Multi –user MIMO system in the presence of Polarization diversity