This document discusses MIMO (multiple-input multiple-output) communication systems which use multiple antennas at the transmitter and receiver. It describes the mathematical model of MIMO and compares it to previous technologies like SISO and MIMO. The key benefits of MIMO are that it can increase data rates using spatial multiplexing and improve reliability using diversity techniques. MIMO systems are used in wireless technologies like 3G, WiMAX, and LTE.

1. MIMO COMMUNICATAION
SYSTEM
VINOD RAJ PRAJAPAT
ECE 3RD
YEAR
14116075
VNDPRAJAPAT8@GMAIL.COM
ABSTRACT
The use of multiple antennas at both ends of a
wireless link (MIMO technology) holds the
potential to drastically improve the spectral
efficiency and link reliability in future wireless
communications systems. This report gives a basic
idea of model of MIMO and how efficiency and
data rate can b increased with the help of this
technology.
INTRODUCTION
MIMO is a an antenna wireless technology in which
multiple antenna are used in both transmitter and
receiver side . The antennas are designed and
combined in such a way to reduce error in signal
and maximize the data speed.
There were several techniques which were used
before mimo such as SISO(Single input, Single
output), SIMO(Single input, Multiple output),
MISO(Multiple input , Single output), all the
technologies are differentiated by the number of
antenna used in transmitter and receiver side.
In SISO one antenna at transmitter and receiver
side, In SIMO one at transmitter and multiple at
receiver while in MISO, one at transmitter multi at
receiver.
MATHMATICAL MODEL OF MIMO
Let the transmitter have M antenna then it will be
represented by a M*1 matrix X(x1,x2….,xM),
while receiver has N antenna it will be represented
by N*1 matrix Y(y1,y2….,yN), as then the MIMO
channel matrix will be represented by a matrix of
order N*M having element H(h11,h12…..hMN).
And the mathematical equation is:-
y = hx+n;
Where n is the noise added to the signal.
PROBLEM WITH SINGLE ANTENNA
If a single antenna is used in both transmitter and
receiver side, There are high chances that signal met
with obstruction such as hills, building etc and get
phenomenons such as reflection diffraction can
occur and signal reaches at receiver via different

2. path. Travelling of signal via different path is called
Multipath. It can cause reduction in data speed and
increase number of errors in digital wireless
communication. This problem can be solved using
multiple antennas at both side.
PROBLEM IN WIRELESS
COMMUNICATION
1. We cannot transfer signal at higher rate there is a
maximum channel capacity C,given by the
Shannon-HartleyTheorem
C=B*log(1+SNR)
C=channel capacity in bits per second
B= Bandwidth of channel in hertz.
SNR= Signal to Noise Ratio
2. Quality: Due to noise , multipath etc the signal is
always faded and the quality of signal is reduced.
MAJOR MIMO TECHNOLOGIES
Other than configuration of antenna, there are two
major ways by which data is transmitted across the
channel. Both these technique help us to resolve
major issues in wireless communication.
1 MIMO diversity technique
2 MIMO spatial technique
MIMO Diversity Technique
In diversity technique, same information is being
sent via different independent fading channel , when
same signal will be sent through different channel
the amount of fade suffered by each signal will also
be different. And then there will be one copy which
will be less faded as compared to other and receiver
will look after that copy.
Increasing fading channel increase reliability of
system and improvement in reliability led to
improvement in performance and being measured as
diversity gain.
Diversity gain= NT*NR
NT=number of antenna in transmitter side
NR=number of antenna in receiver side.
MIMO Spatial technique
In spatial technique each bit of the data stream is
multiplexed in different channel to increase the data
speed, each spatial carries independent information.
This technique can be compared to
OFDM(Orthogonal Frequency Division
Multiplexing) in which different frequency sub
channel carries different part of the signal.
In this technique if scattering by environment is rich
enough several independent channel can be created
in same bandwidth. Thereby reducing additional
cost of bandwidth or power loss.
The multiplexing gain here is being referred as
degree of freedom:-
Degree of freedom=Min(NT,NR)
NT and NR are the no of antenna in transmitter and
receiver side.
This figure shows the way how channel capacity is
being increased using mimo spatial technique.
COMBINATION OF DIVERSITY AND
SPATIAL TECHNIQUE
Lets take a 6*4 antenna it can be used as a
combination of both technique as

3. case1: For higher reliable mode, In this case we will
use 2 antenna for multiplexing signal and such 3
combination to increase diversity so
Multiplexing Rate = 2 && diversity gain =3*2=6
Case2: For higher data mode we will use 3 antenna
for multiplexing signal each side so,
Multiplexing Rate =3 && diversity gain =
2*1=2
ADVANTAGES
MIMO Technology implemented using diversity
multiplexing technique helps to provide diversity
gain and aims on improving the reliability
MIMO Technology implemented using spatial
multiplexing techniques helps to provide
multiplexing gain or degree of freedom which
helps to improve the data rate of the system
APPLICATION
1).3G
2).WIMAX(IEEE)
3).LTE(4G)
References
1) Communication System,fourth edition
2001 :-Simon Haykin
2) Channel Estimation for Wired MIMO
Communication Systems Multidimensional
DSP Project, Daifeng Wang, Spring 2005