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Massive MIMO in 5G Communication
Usman Arshad
Department of Electrical Engineering
Institute of Space Technology
Islamabad, Pakistan.
Email: ee usman@live.co.uk
Telephone: (0092) 321-9534-375
Fawad Khattak
Department of Electrical Engineering
Institute of Space Technology
Islamabad, Pakistan.
Email: fawadkttk@gmail.com
Telephone: (0092) 312-7070-070
Abstract—MIMO is a very new hot and exciting research work
these days for the upcoming cellular generation. This research
will play a significant role and will be the most exciting research
work. This research work promises a very high data rate and
will be more reliable as compared to other. It will consume less
power comparison to other technologies. A problem known as
pilot contamination has been introduced and the techniques to
remove are also being proposed i.e. SCN. It is proposed that
while reducing the cell size, pilot contamination factor can be
minimized equivalent to negligible. This wireless research with
gain more popularity then other it will accommodate more users
and more traffic also its connectivity will make a cloud i.e. every
device will be connected to each other. 5G will cover a high
potential of signals with better coverage and a heterogeneous
deployment of cells and massive antennas array. This Research
topic provides high data rate and high bandwidth that would be
compulsory to use it in coming MIMO cellular networks.
I. INTRODUCTION
As we see devices are becoming larger in numbers as the
population get increases with this, each and every individual
needs data rate and that should be high to drive their apps
streaming and many more. Todays devices are hungry of more
and more data rates [1]. This communication system will use
array of antenna installed in single largely antenna or simply
group of antenna. This wireless communication will give you
more data rate with best amount of data bandwidth for the flow
of data rate and also more power transmission. This network
or wireless communication will be more reliable comparison
to others more coverage also it is to be noted that more
energy efficiency will be there and it will take less time to
round trip of data between user equipment and base station
antenna i.e. zero latency. Link will be more reliable using
more than 64 antennas. It decreases radiated power and just
focus the energy on the targeted mobile user or equipment
by using one of the most popular technique i.e. precoding
technique. While directing the specific energy to the specific
user at the same time the radiated power will be reduced
and also interference between two users whom using mobile
phones will decreases. In massive MIMO terminals of the
transmitter are less in number as compared to BS antennes,
massive MIMO can be furthermore developed by using ZT
Zero forcing or MRT(maximum ratio transmission).
Simply if see in emerging technologies and compared it with
current and upcoming technologies. There is also introduction
to problem occurend when MIMO systems are used, i.e. Pilot
contamination. How it occurs and how to mitigate it, there are
several techniques proposed. We will focus on SCN technique
to eliminate the factor of pilot contamination from massive
MIMO systems.Then 5G and with the massive MIMO antenna
is the best choice for the future generation, it will open the
door for the new world and bring revolution [3].
II. MASSIVE MIMO AND 5G CELLULAR
A. Massive MIMO
Massive MIMO is very hot topic of now a days, having the
large number of antennas installed at base station. From the
literature review from [4] and [5], we can conclude that the
use of massive MIMO in 5G is a constrained as we have no
other way. As because we are using very high frequencies in
5G system, so antenna size gets small, means aperture will
also be small.
Fig. 1. Massive MIMO BS syncronising UE’s
Then how to overcome this issue, it is proposed that use
of large number of transmission antennas can resolve the
problem. This is the main reason, why we had adopted the
massive MIMO technique. This formula explains the reason
for using massive MIMO systems [3].
Pr =
Pt
4πR2
λ2
4π
GrGt (1)
As it can be seen clearly, higher the frequency, lesser will
be the wavelength, so lesser wil be th size of antennas which
results in decreased received power. Hence massive MIMO
gives the solution. Then, a question can be raised, how many
antennas can be needed to form a massive MIMO system?
Answer is, there can be 300 to 3000,totally depending on
the efficiency of algorithm used at receiver side, known as
equalizer design. In 4G LTE, the MIMO system is beinged

used, having the maximum number of antennas is 8 x 2 or
4 x 4. Following diagram shows the different systems along
massive antenna based multi user MIMO system.
Fig. 2. Different Input-Output Systems
B. Milimeter Wave Frequencies
Currently frequency of the range in between 600Mhz to
1600mhz is already in use in todays cellular system. In Future
we can utilize high frequency to propagate and we can use it
for communication. According to [8], high spectrum like in
gigahertz and terahertz could be in use by one the technique
called cognitive radio, after this. Highly potential field is
exploited by wavelength in millimeter range and hence the
term millimeter wave is in practice. Today every cellular and
wireless firms want increase in the capacity and it can be
use in upcoming years by different wireless standards like
4G LTE. It is also expected that the increase of traffic will
be increased by 2020 due to more usage of internet accessing
more users more population more equipments devices and they
all are hungry of data rates and cellular network will face a
high speech and traffic means more requirement of data rate so
more bandwidth is also required for more data rate so wireless
5G will come and it will remove the thirst of every individual
by increased data rate in gigabit per second which can only be
processes by only high bandwidth which is millimeter wave
spectrum, millimeter wave frequency scarily used by other
other technologies and do not pass in other objects and do
not produce any interference.
Fig. 3. Range of Milimeter Wave Frequencies
These are one of the unique waves which will be highly use
in 5G and its massive MIMO system. Since Massive MIMO
is spatial processing technique which would have orthogonal
polarization and beam forming adaption. Cost of base station
would be reduced because of innovative architecture of co-
operative MIMO. Mobile operators are also working hard to
fulfill their dream and requirement of people by combining
of share spectrum for this solution which would be beneficial
beyond 2020 [1].
C. Beam Forming
As mm-Wave frequencies are to be used in 5G proposed
celluler network. Described earlier, use of greater frequencies
results in smaller elements of antennas. For example, for
15GHz, the antenna with 200 elements would be only 20cm
tall and 5cm wide. So if greater the number of antennas , it
is possible to steer the transmitted signals towards the specific
reciver. This resuts also in the improvement of system capacity.
Fig. 4. BS communicating UE’s transmitting beams
When there are large number of antennas , the beam formed
will be narrower. It becomes easy to transmit the signal in
appropriate and specific direction easily while having the max-
imized received signal enegergy at user quipment. This type
of phenomena and scheme is called beam forming [5][6][14].
It is possible to steer the transmitted beam in horizontal and
verticle dimensions for every individual user equipment. The
direction of beam may be changed many times in miliseconds
depending upon the location on users, as there will be a large
number of users in the cell.
III. ARCHITECTURE AND SYSTEM MODELLING
As MIMO system is being used in 5G communication
system, so it will have large no. of BTS at user side with
large number of antennas. The system can be represented as:
Fig. 5. 5G Network Road Map Architecture

It will allocate large no. of antennas installed at BTS to
communicate with multiple of user equipments at a time
simultaneously [4].
A. Co-Pilot cells
In 5g communication using massive MIMO systems, the
concept of co-pilot cells is introduced [9]. Co-pilot cells uses
same array of pilot sequences for channel estimation. So
we can take the co-pilot distance as the minimum distance
between the centers of two co-pilot cells. It is a different
concept then frequency reuse. Similarly it can be concluded
that co-pilot distance is also a different concept with respect to
frequency reuse. Although it is not necessary that the distance
between them is not equal to each other.
B. Modelling
Now from [9], considering a cellular network having hexag-
onal shape of cells having radius R. Every cell is also having
a BTS with very large number of antennas(M), which is
serving K users that have single antenna. Here, we are going
to suppose the number of users per unit area are same that is:
Fig. 6. Cell Network With Cell Radius R and Co-Pilot Distance D
k
4πR2
= Constant (2)
Now, the coefficient βjkl is telling us shadowing effect and
path loss. The value of βjkl will be equal for every antenna
on BS. βjkl can be described as following:
βjkl =
zjkl
rα
jkl
(3)
Where, rjkl is defined as the distance between the BS and
user. i.e Kth
user present in the lth
cell connected with jth
BS. Also, α is the exponent of path loss. Whereas zjkl is
expressing the shadowing effect. As we know, when channel
estimation has to be done, each and every user present in cell
transmits the pilot sequence that is being assigned. To get
the better understanding and behaviour of system, we should
consider worst case that will deeply describe the problem
occurred when pilot sequences get interrupted by co-pilot
cells pilot sequences, known as called pilot contamination.
It gives network a finite Signal to Interference Ratio (SIR)
which bounds the capacity of system [3]-[6] . So assuming
the reception and transmission in every cell is synchronized.
Now when pilot sequences are generated, 7 cells which are
surrounding the cell, are co-pilot. we can write the equation
of estimated channel of cell 1 [9] as follows, describing nj is
noise matrix, where transmission SNR can be represented as
ρρ :
Y =
√
ρρ
7
0
Gj + nj (4)
It can be seen clearly, that channel estimatation has factor
of pilot contamination due to souurnding co-pilot cells. So it
gives us another equation showing us Signal to Interfernce
Ratio:
SIR(user)
=
β2
(user)
β2(BS → user)
(5)
So capacity can be expressed as, involving bandwidth with
variable B:
Capacity = Blog2(1 + SIR) (6)
IV. TECHNIQUES TO REMOVE PILOT CONTAMINATION
Many techniques have been proposed for mitigating the
pilot contamination factor from massive MIMO systems. So
proposed techniques were non-linear decoding and channel
estimation methods which are knows to be very complex as
compare to linear channel estimation techniques [6][9]. As the
factor pilot contamination is the result of linear pre-coding
and detection schemes in Massive MIMO systems. So how
to get that factor removed easily? As described in [3] , this
problem can be eliminated while using the concept of small
cell networks. In SCN, the size of each cell is kept very
small, so it results cheap in cost, power and management as
they are considered to be self organised network. When cell
size reduces , the effect of pilot contamination get vanish.
For SCN the capacity of the system [9] can be described as
following, it can be seen that the capacity of the system is
not depending on the SIR factor as SCN eliminated this factor
from the network using massive MIMO. Very low SIR, almost
negligible because cell size ratio is very small and capacity
of the network is depending on the radius R of the cell and
distance D of the co-pilot cells.
Capacity = Blog2(1 +
1
6
(
D
R
− 1)α
) (7)

V. CONCLUSION
In this paper, we have introduced the idea of future 5th
generation of wireless network, and its features, delivering
promises and technologies used in it like massive MIMO. It
would be supporting 10 Gbps data rate to user equipments,
having maximum perception of coverage, availability and min-
imum latency rate. The reason for using massive MIMO has
been efficiently explained in the paper. As there use of mm-
Wave frequencies, so greater the carier frequency, smaller will
be the antenna size, resulting very high decrease in received
power. Hence the received power can be efficiently increased
by increasing the number of transmitters and recievers on a
single device and base station. So they require a large number
of antennas on BS to communicate with users simultaneously
using the procedure of beam forming. Similarly the problem
occurred while using massive MIMO having the concept of
pilot reuse, known as pilot contamination has been discussed.
Pilot contamination factor is introduced to system by the
interfence of same pilot sequence which are used by different
users and cells resulting decrease in the capacity of system.
As due to beam forming procedure used in the massive MIMO
systems,it eliminates the effects of noise and small scale
fading. Massive MIMO is efficient way to increase the capacity
of the system upto 100 times due to improved raidiated energy
efficiency [11]-[15]. As massive MIMO also holds the property
to efficiently work against intentional jamming and unintended
man made interference as it had increased robustness. It is
concluded that the idea of SCN can efficiently eliminate the
factor of pilot contamination from the network. Hence we
can conclude that small cell networks, if used with massive
MIMO can provide a system with high capacity and efficeient
in energy. In around 2020, 5G communication will start to
work in some countries of world and it will be like a door to
new world wide wireless web (wwww) , like world is in our
hands.
VI. FUTURE SCOPE
The deployment of 5G cellular network was started in 2014.
5G is a proposed idea and it is hoped that 5G will be a practical
system near about 2020, called world of internet. Massive
MIMO, technique proposed for 5G cellular network, is now a
days, very hot research topic. As in the paper, massive MIMO
is best technique supporting 5G cellular idea. It has been
concluded that only limiting factor in massive MIMO systems
was pilot contamination, where SCN promises to eliminate
this factor. This work can be led to investigate interesting
estimation of the effect of SCN, although it is known to be
interesting that when cell size reduces, the distance between
co-pilot cells also decreases.
ACKNOWLEDGEMENT
The authors would like to thank Dr. Farukh Bhatti for their
constant support and motivation, about the massive MIMO
technique proposed for upcoming 5G cellular networks.
REFERENCES
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[11] T. L. Marzetta, “Noncooperative cellular wireless with unlimited num-
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