1. IEEE Sponsored 2nd International Conference on Innovations in Information Embedded and Communication Systems
ICIIECS’15
Improvement in Channel Capacity Using MIMO
OFDM System for Radio Propagation in Ocean
Vessels
Mrs.Janci Rani1
, Dr.TRV.Anandharajan2
, S.Pavithra3
, M.B.Subhashree4
, A.Thilagavathy5
Department of Electronics and Communication Engineering
Velammal Institute of Technology, Panchetti 601204
1
janci_ranii@yahoo.in, 2
trvanandharajan@gmaill.com, 3
pavisubbiah@gmail.com,
4
subhashreekrishnanmb@gmail.com,5
thismijjarumugam@gmail.com.
Abstract: Immensely robust Spatial Frequency Block Coding
(SFBC), Multi Input Multi Output antennas–Orthogonal
Frequency Division Multiplexing (MIMO–OFDM) Schemes in a
Rayleigh fading channel have been proposed, along with the
Selective Mapping (SLM) which is utilized to obliterate the Peak
to Average Power Ratio (PAPR) in OFDM, which increases the
channel capacity and signal reliability in spite of reflections
caused due to metals. A metallic environment acts as defiance for
wireless networks as it leads to great attenuation of signals
predominantly, in below-deck compartments in the ship. The
metallic partitions of the ship cause multiple reflections. The
paper measures four different OFDM based schemes in below-
deck spaces of ship and compares various techniques and their
efficiency have been estimated.
Index terms- channel capacity MIMO OFDM Rayleigh fading
channel Signal reliability
I. INTRODUCTION
Metal structures of ocean vessels constitute diversified
environments which results in noticeable challenges in
establishing wireless networks. The objective of this paper is
replacing wired network by wireless network in below deck
spaces of ship in Rayleigh fading channel and there by
manifesting improvement in capacity, signal integrity and
reliability, that can be accomplished through the use of OFDM
(Orthogonal Frequency Division Multiplexing) and multi
antenna techniques with higher modulation technique
Quadrature Amplitude Modulation (QAM). OFDM is the best
multi-carrier modulation technique for transmitting signals in
an unguided medium. A huge number of tightly spaced
orthogonal subcarriers are used to consign several sequences
of parallel data and the guard intervals are lodged between the
symbols to get rid of the intersymbol interference (ISI). The
spectrum of all the subcarriers in a symbol has a void
spectrum at the mid frequency of all the other subcarriers
within the symbol. Hence intercarrier interference (ICI) is
quashed. Multi Input Multi Output (MIMO) signaling
techniques enhances wireless transmissions which exploits the
spatially correlated fading of wireless channels common in
diversified environments. Multi-antenna signaling techniques,
including ( 2 × 2) Alamouti Space Frequency Block
Coding(SFBC) and ( 2 × 2 )Multiple-Input-Multiple-Output
Spatial Multiplexing (MIMO-SM), were estimated with the
capabilities of (1 × 2)Maximal Ratio Combining (MRC) and a
traditional Single-Input-Single-output (SISO) technique
respectively. Shannon channel capacity and Estimation of the
Post-Processing Signal-to-Noise-Ratio (PP-SNR) are derived.
Since we are analyzing MIMO-OFDM techniques in ocean
vessel, it is essential to discuss its exhaustive literature survey.
II. RELATED WORKS
The Study of OFDM-MIMO technology in flat fading channel
was developed in [1]
to improve the channel capacity in below
deck environments. They presented a feasibility study of a
Wireless Network by comparing Ultra wideband channel
measurements within the hull of a ship. These measurements
were used to designate the propagation within single chamber
as well as through a locked abutment door[4]
.The main
application of the study was to investigate the
telecommunication systems on board, for both commercial
and security purpose, which was demonstrated in the aboard
trains with the help of propagation channels[3]
.The design and
optimization of mobile radio networks operating at Very High
Frequency(VHF)& Ultra High Frequency (UHF) bands with
brief look at microwave links, sometimes used for
backhaul[10]
.The characterization of Line of sight(LOS) and
Non Line of sight (NLOS) link were performed over military.
Ultra High Frequency band (225-450 MHz) which was
introduced in merchant ship[5]
.
To intensify the channel capacity, we need high data rate and
signal reliability which is achieved by the following proposed
system
III. PROPOSED SYSTEM
Fig. 1 Rise in channel capacity using QAM, Alamouti SFBC techniques in
Rayleigh fading channel
International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.20 (2015)
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2. IEEE Sponsored 2nd International Conference on Innovations in Information Embedded and Communication Systems
ICIIECS’15
As in Fig.2, The digital input in bits is converted in to blocks
in encoding process. The modulation scheme used here is
OFDM in turn the subcarrier modulation employed is QAM.
The original data source is converted in to parallel streams of
data by serial to parallel converter and IFFT (Inverse Fast
Fourier Transform) is performed to convert frequency domain
to time domain for easy implementation purpose. It is carried
via Rayleigh fading channel by MIMO techniques and
antithetical operations are performed in receiver to obtain the
original data.
There are four proposed techniques to increase the channel
capacity which is given below.
Fig. 2 Functional diagram that portrays OFDM-MIMO systems in Rayleigh
fading channel
G/R- GENERATED
ENCODE-ENCODING
RX-RECEIVED
DECODE-DECODING
DEMOD- DEMODULATION
A) Extensive Modulation technique:
16-QAM Technique has been done to transmit two digital
messages by varying the amplitude of two carriers .The
carriers used are sine and cosine waves which are 90 degree
phase shifted with each other. Consequently, the name
Quadrature carriers. The sum of modulated waves results in
both Amplitude Shift Keying (ASK) and Phase Shift Keying
(PSK).Inflated Spectral efficiency can be achieved for
constellation size and intensification in bit rate.
B) Diversity Coding Technique: Alamouti Spatial Frequency
Block Coding: In SFBC-OFDM, a single data sequence
a = [a0,a1,a2,…,aN-1] which is obtained from previous
modulation scheme , given to standard Alamouti SFBC
encoder where the output is mapped as follows
Each row is buffered to form N symbols,
Where
b1
=[a0,-a1
*
,a2,-a3
*
.......aN-2,-aN-1
*
]
b2
=[a1,a0
*
,a3,a2
*
……,aN-1,aN-2
*
]
.
b1
is carried via through antenna 1 and b2
is carried via
antenna 2.[8]
SFBC performs better than STBC at high movability.
The performance degradation of Space Time Block Coding
(STBC) is primarily from the ISI, due to time selectivity of the
channel in an Alamouti code block at high mobility. The
performance of STBC and SFBC is evaluated using Minimum
Mean Square Error (MMSE) decoder. This decoder can
reduce ISI in Alamouti Block. But, still the performance of
SFBC is better than STBC by 0.5dB [6]
and thus increases
signal reliability.
C) To assess the potential of OFDM physical layers, Rayleigh
fading channel is used.
When the passage between the transmitter and receiver is a
deviating track, then the multipath elements of the fading
channel can be expressed using Rayleigh distribution in fading
channels. The acquired signal is explained by:
r(t) = s(t)*h(t) + n(t)
Where s (t) is transmitted signal, h(t) is the channel matrix
following Rayleigh distribution and n(t) is the additive white
Gaussian noise.
Rayleigh fading has the variance of 2б2
and envelope x. The
variance is same as the sum of two Gaussian processes whose
standard deviation is б. The probability density function
(PDF) of Rayleigh Distribution is:
Where the time-mean power of is received.
The derivation of channel capacity from the signal power and
noise power is as follows.
D) Selective Mapping (SLM) is used in OFDM to expunge
PAPR
The SLM with IFFT is proposed over SLM with Inverse
Discrete Fourier Transform (IDFT) because of the
disadvantages associated with the IDFT such as the poor
energy compaction and intricacy. As a result of it, the PAPR is
extirpated.
IV.MATHEMATICAL MODEL
The amount of noise present is represented in terms of its
mean noise power (as shown in 1)
DATA
G/R
ENCODE QAM S/P IFFT MIMO
DATA
RX
DECODE DEMOD P/S FFT
RAYLEIGH FADING
CHANNEL
International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.20 (2015)
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3. IEEE Sponsored 2nd International Conference on Innovations in Information Embedded and Communication Systems
ICIIECS’15
………. (1)
R = characteristic impedance of the channel or system
VN =Root Mean Square (RMS) noise voltage.
S = V2
S/R, average signal power
VS = signal’s RMS voltage.
The transmitted power is given in (2)
…(2)
Typical combined RMS voltage is given in (3)
.. (3)
Therefore, combined signal and noise will generally be
confined to a voltage range ± ŋVT .
Now dividing this range into 2b
bands of equal size.
Hence each of these bands will cover as shown in (4)
..(4)
Noise will randomize the actual voltage as in (4), which tend
to make additional bits absurd.
Thus maximum number of bits of information obtained is (5)
…(5)

 

This can be rearranged as shown in equation (6)
…..(6)
As shown in equation (7), where M is obtained from
b= bit measurements of the level in a time (T)
then the total amount of information(H) collected in bits is
…(7)
The information transmission rate, I, bits per unit time, will be
given in (8)
….(8)
From the Sampling Theorem, a channel of bandwidth B has
the highest practical sampling rate. Hence M/T is given as
shown below in (9)
M/T = 2B … (9)
Combining the equation (8) and equation (9), we obtain
equation (10).

This expression represents Shannon channel capacity. It is
interpreted as the maximum rate at which the data can be
reliably carried via channel.
For a flat fading channel, the capacity is defined as in (11)
…(11)
PTX is transmit power, |h| is the complex channel gain, and
N0 is the noise power in the channel.
For an OFDM link with k subcarriers, there are K narrowband
Rayleigh fading channels as shown in (12)
… (12)
For MIMO the above expression is expanded as given below
in (13)
.(13)
Where PTX is transmit power,
|h| is the complex channel gain,
N0 is the noise power in the channel.
The channel capacity becomes the addition of the capacities of
each subcarrier. This increased channel capacity in ocean
vessel is visualized as given below.
V. SIMULATION SCENARIO
The Engine room and Coupled Compartments are selected for
the experiment.
A) Engine Room
International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.20 (2015)
© Research India Publications; http://www.ripublication.com/ijaer.htm
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4. IEEE Sponsored 2nd International Conference on Innovations in Information Embedded and Communication Systems
ICIIECS’15
The reason for selecting engine room for the experiment is that
it is a congested place which is a complete metallic
environment. Since the scattering of signal is more, the
anticipated probability of debacle of a signal is extreme.
Additionally, the key reason for selecting engine room is that
it is necessary to collect the status of the vital machinery
spaces in the engine room.
B) Coupled Compartment
The reason to consider the coupling compartments is to
demonstrate the effect of opening doors and closing doors in
signal integrity.
After simulating the process, results obtained are discussed
below.
VI .RESULTS AND DISCUSSION
As far as result been concerned, MIMO over SISO techniques
and Alamouti over MRC, in Engine room have been
implemented.
A. Engine Room
The average capacity of each technique can be shown in the
graph in terms of Signal to noise ratio. Out of these techniques
Independent Identically Distributed (I.I.D) has highest
theoretical gain and it is used for reference. Decorrelation in
channel makes MIMO to improve performance than SISO.
PP-SNR of Alamouti (SFBC) coding is increased than MRC
due to the addition of diversity gain. BER (Bit Error Rate)
performance of (2 × 2) Alamouti and (2 × 1) MRC in Rayleigh
Fading channel is also implemented.
Fig.3 Analysis of performance in capacity for MIMO SM and SISO
techniques
In Fig.3, for SNR of 14dB, the capacity for SISO is 0.3
bps/Hz and our proposed method MIMO-SM has the capacity
of 0.5bps/Hz.The IID,maximum theoratical gain is around 1
and hence there is a efficiency of 60% and for Received SNR
18dB, the capacity for SISO is 1.2bps/Hz and for MIMO-SM
is 1.3bps/Hz and the maximum theoratical gain is
2bps/Hz(IID). Hence the obtained efficiency is 92%.
Fig.4 Analysis of performance in capacity for ALAMOUTI (SFBC) and MRC
techniques
In Fig.4, for SNR of 14dB, the capacity for MRC is 0.8bps/Hz
and for our proposed system is 1.0bps/Hz. Hence, the obtained
efficiency is 80%.For, the Received SNR 18dB, the Channel
Capacity for MRC is 1.4bps/Hz and for Alamouti is
1.6bps/Hz. Hence, the obtained efficiency is 87%.
It has been observed that Alamouti at low SNR has
double data rate when compared to the above four techniques
Fig.5 Analysis of BER performance of SISO, MRC, Alamouti (SFBC)
techniques in Rayleigh Fading Channel.
In Fig.5, there is a linear decrease in BER for SISO, whereas
for the MIMO, there is a exponential decrease of BER which
proves that MIMO performs better than SISO.
VI. CONCLUSION
It has been observed that the channel capacity and signal
reliability has been improved through OFDM-MIMO
techniques albeit strenuous situation. Estimation of Shannon
International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.20 (2015)
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5. IEEE Sponsored 2nd International Conference on Innovations in Information Embedded and Communication Systems
ICIIECS’15
channel capacity demonstrates that multipath scattering can be
exploited by MIMO spatial multiplexing and data rate gets
doubled through Alamouti (SFBC) techniques, thereby
increasing channel capacity .OFDM with SISO technique in
Rician fading channel can be implemented in future.
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International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.20 (2015)
© Research India Publications; http://www.ripublication.com/ijaer.htm
17806