Implementation of OFDM System Using Various Channel Modulation Schemes

Implementation of OFDM System Using Various Channel
Modulation Schemes
Muhammad Zunnurain Hussain Muhammad Zulkifl Hasan
Sr. Lecturer CS & IT Bahria University Lahore Campus Sr. Lecturer CS & IT Lahore Garrison University, Lahore
zunnurain.bulc@bahria.edu.pk zulkifl.hasan@lgu.edu.pk
Abstract
This report discusses the planning Associate in
nursing the implementation of an OFDM system
in several information module schemes like M-
QPSK, M-QAM. First, a short introduction is
provided by explaining the background and the
specification of the project. Then the report deals
with the system model, every block of the OFDM
system is represented (IFFT, FFT, Cyclic prefix,
modulation / reception, Channel estimation, bit
error rate). System design is analyzed. The
transmission techniques, further because the
system parameters for transmission and reception
are explained well. Finally, the results are
provided.
1 Introduction
In orthogonal frequency division multiplexing
(OFDM) the essential principle is to separate a
high rate stream into type of lower-rate streams
that area unit transmitted at an equivalent time
over type of subcarriers (SCs). Each of that's
modulated on a separate subcarriers (FDM).So,
the knowledge live of the subcarriers becomes
smaller the knowledge live of the channel
therefore, all subcarriers area unit entirely filled
with flat weakening, that produces the trouble
technique easier and straightforward. That the
image quantity of the individual subcarrier
streams is made long compared to the delay
unfold of the time-dispersive radio channel. The
dispersion area unit about to be reduced
attributable to the image amount that's inflated for
lower rate parallel subcarriers this will be caused
by multipath delay unfold. Lay image interface
are eliminated by the introduction of the guard
interval inside the sub carrier stream. By selecting
a special set of (orthogonal) carrier frequencies,
high spectral efficiency is obtained due to the
spectra of the subcarriers overlap, whereas
mutual influence among the subcarriers are
avoided. The system model shows that by
introducing a cyclic prefix (the GI), the
orthogonality are maintained over a dispersive
channel. OFDM are enforced victimization
utterly completely different parameters however;
we have used DVB-T standards 2k, 4k, 4k modes.
We have jointly used utterly completely different
modulation schemes for comparison in our
coding/ implementation section[1].
2 Previous work
People square measure performing on
OFDM because it is currently a awfully
helpful technique to send knowledge at
high rate with less ISI and delay spreads.
Previous work embrace following paper
and researches listed below:
• A MATLAB program was
written to analyze Orthogonal Frequency
Division Multiplexing (OFDM)
communication systems. This program is
effective for future researchers
simulating systems that square measure
in theory complicated to research. Single
carrier QAM and multicarrier OFDM
were compared.
• To demonstrate the strength of
OFDM in multipath channels. 2
graphical interface demonstrations show
a number of the fundamental ideas of
OFDM. [2]
• Orthogonal frequency division
multiplexing (OFDM) could be a
promising technique for the high rate
wireless communications as a result of it
International Journal of Computer Science and Information Security (IJCSIS),
Vol. 16, No. 3, March 2018
209 https://sites.google.com/site/ijcsis/
ISSN 1947-5500

may be combat inter-symbol interference
(ISI) caused by the dispersive attenuation
of wireless channels. The planned
analysis focuses on techniques that
improve the performance of OFDM
based mostly wireless communications
and its business and military
applications. In particulars the paper
addresses the subsequent aspects of
OFDM: inter-carrier interference (ICI)
suppression, co-channel interference
suppression for clustered OFDM,
clustered OFDM based mostly anti-
jamming modulation, channel estimation
for MIMO-OFDM, and precoding for
MIMI-OFDM with channel
feedback.[1], [3]
• This paper proposes a MIMO
OFDM baseband transceiver style for
future generation high output wireless
LAN mistreatment 2 transmission
antennas and 2 receiver antennas. A
MIMO OFDM receiver with algorithmic
rule for temporal arrangement and
frequency synchronization, tracking,
channel estimation, and MIMO detection
is intended and enforced in software
system. Simulation results shows that the
planned receiver is capable of
transmission with a knowledge rate that's
doubly that of the present IEEE 802.1a
wireless LAN customary.[4]
• One of the proposals for the
physical layer of this technique was
entitled innovative modulation for the
Brazilian Digital TV System (MI-
SBTVD). The MI-SBTVD Project
includes high performance error
correcting codes; transmit spacial
diversity and multi carrier modulation.
The focus of this paper is twofold. First,
we glance at the transmit diversity theme,
which mixes Alamouti committal to
writing and OFDM modulation. We tend
to then discuss the channel estimation
algorithmic rule that has been enforced
within the planned system. Pilot
subcarriers square measure inserted
among knowledge subcarriers, and each
uni-dimensional and Bi dimensional
linear interpolation at the receiver square
measure thought of. Theoretical account
results, mistreatment typical digital TV
channels, show that the planned theme is
in a position to perform on the brink of
the case of a superbly acknowledged
channel at the receiver.[2]
Figure: Basic OFDM Transmitter
Figure: Basic OFDM Receiver
3 System Design Explanation
3.1 Serial to Parallel
The data input to an OFDM transmitter is
in the form of binary bit stream, consisting of [0 ,
1]. For constellation mapping, using any useful
Serial to Parallel Data Mapper IFFT D/A Up
Conversion
Channel
Addition
Data Converter A/D FFT Sampling/
Slicing
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data scheme, we first need to convert this serial
data into parallel data. So this block provides us
with parallel data ready for constellation
mapping.
3.2 Constellation Mapper
At this stage we mapped our bit stream
data, in useful manner as per requirement of
OFDM, Orthogonal to each other, using
modulation schemes i.e. PSK and QAM. Each bit
from random binary stream is picked up and
placed according to the modulation scheme at
orthogonal frequency to avoid ISI and a graph is
being made between real and complex values in
XY-plane to see the constellation map.
QPSK, QAM: these are the two
techniques for data mapping which we have
tested in lab. Moreover, their efficiency changes
have also been recorded.
3.3 IFFT
On the transmitter aspect the IFFT of a
symptom X(k), wherever k denotes the frequency
parts, and x(l) is that the ensuing sampled signal,
that is made by the total of the modulated
frequency parts X(k) (at their corresponding
digital frequency k=K). To retrieve once more the
digital frequency parts, the inverse equation
should be used.
3.4 Parallel to Serial
In this stage for adding the cyclic prefix
and zero padding, we have to convert it to serial
data from parallel.
3.5 Digital to Analog Conversion
In this block, we have converted digital
subcarriers into analog baseband signal. For this
process, we used stream of pulses and convolved
it over our subcarriers, getting digitized pulse.
Further, by the help of pulse shaping filter, of
high order, we converted it into continuous time
baseband signal.
3.6 Up converter
We multiply the signal with high
frequency to increase the power of signal. [5]
3.7 Channel Addition
In this stage, we have a tendency to check
the behavior of our system by introducing some
channels like Rician, Lord Rayleigh and
additional AWGN noise.
In Lord Rayleigh channel, there is no
main path. Instead, the received signal is mirrored
into many tiny power signals. Therefore, it is
tough to synchronize. The Rician issue K is that
the magnitude relation of the ability of the direct
path to mirrored ways.
Fix Reception Rician:
Y(t)= ( ) + ∑ ( − )

Portable Reception Rayleigh:
Y(t)=
∑
∑ ( )
Where N is the number of echoes and
equals to 20; θi is the phase shift from scattering
of the ith path; ρ^i is the attenuation of the ith path
and t^i is the relative delay of the ith path. The
Rician channel contains a sturdy main path,
therefore it is easier to try to on synchronization
and channel estimation. Therefore, the system has
higher BER performance than the Rician channel.
as a result of the trail delays area unit continual,
we have a tendency to translate those into
separate sample index, therefore we have a
tendency to solely select one path of those with a
similar separate sample index.[4]
3.8 Down Conversion
In this stage, we multiply the signal with
same frequency to get the same signal back.[6]
3.9 Serial to Parallel
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To remove cyclic prefix (if used in
transmission) we have to convert our data from
serial to parallel. An OFDM receiver includes a
demodulator unit being tried to a receiver signal
for demodulating both an in-phase (I) component
and a quadrature-phase (Q) component of the
receiver signal, a serial to parallel unit for
converting the output of the demodulator to a
plurality of parallel paths. [7]
3.10 Analog to Digital Conversion
In this block, we have converted analog
sub band signals into digital subcarriers. For this
process, we used low order pulse shaping filter
(Butterworth).[8]
3.10 FFT
At the receiver, ignoring channel affects,
time wave form is digitized so born-again back to
a Symbol victimization AN FFT. The FFT may
be a important a part of the receiver as a result of
before reception it converts continuous sign into
carriers. once over one carrier is gift, it's the sole
sensible technique for sick the info from
overlapping carriers. it's uphill, for instance, to
use a single-carrier sixty four QAM receiver to
pull up a sixty four QAM carrier in AN OFDM
system. [9]
3.11 De mapping and sampling
In this block, we have a tendency to take
away the zeros from our knowledge to induce the
first one. The equalization (symbol Diamond
State mapping) needed for police work the
information constellation is a component wise
multiplication of the DFT output by the inverse of
the calculable channel TF (Channel Estimation).
For PM schemes, multiplication by the advanced
conjugate of the channel estimate will do the
equalization. After all, that we have a tendency to
square measure with our knowledge streams
back.[10]
3.12 Parallel to Serial
To get the output we have to convert our
data back to original form. [11]
4 Results showing effects of noise and modulation on data
4.1 4-PSK Modulated Data & AWGN Noise
Added Data
4.2 M-QAM Modulated Data & AWGN Noise
Added Data
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4.3 Rayleigh Channel Addition to 4-PSK
Modulated Data
4.4 Rayleigh Channel Addition to 4-QAM
Modulated Data
4.5 Rician Channel Addition to 4-PSK
Modulated Data
4.6 Rician Channel Addition to 4-QAM
Modulated Data
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4.7 BER Comparison Graph
These graph show comparison between bit
error rates of M- QAM & M-PSK modulated
data.
4.7.1 BER Curve Comparison for 4-PSK & 4-
QAM
4.7.2 BER Curve Comparison for 16-PSK & 16-
QAM
Conclusion & Future Work
The above research is about giving common
users, an opportunity, to observe data
transmission & reception in a step manner, with
OFDM being implemented automatically. The
user can do this by “Easy to use software”. This
GUI or software allows the user to give the
wanted DVB-T Parameters and the user has a
choice to choose a modulation type, between
QAM & PSK. The software has also a modulation
scheme order changing option. Then a channel
effect can also added along with AWGN noise at
any SNR, the user wants then all the graphs are
displayed, stepwise, on the side panel, showing
the user all the step results in graphical form, like
scatterplot of simple modulated and channel
effected data. After seeing, the complete
transmission and reception one can compare its
bit error rate of any other data, which is
transmitted using different configuration of
parameters or modulation schemes, as the
software has the ability to save two results of
different configurations and compare them, by
making a comparison BER graph with respect to
increase SNR. From these comparison graphs, it
is clear that higher order modulation scheme
have a better efficiency in even low SNR
conditions. But energy per bit increases
significantly and the modulation scheme like 4-
PSK or 4-QAM which are more vulnerable in low
SNR condition have a low energy per bit so it is a
tradeoff between accuracy and energy also we
can never say that QAM is better technique than
PSK or vice versa. Because there is, efficiency
varies with changing SNR or Eb/ No
Due to shortage of time, we could not show the
transmission and reception of a video file.
Instead, we used random bits to observe
transmission and reception. In future, we would
like to transmit and receive different video
formats and other types of data like audio and
text. In addition, we are planning to enhance the
functionality of our GUI by adding video and
image blocks.
References
[1] R. Prasad, OFDM for Wireless
Communications Systems. Artech House, 2004.
[2] G. C. Lima et al, "Design, simulation and
hardware implementation of a digital television
Vol. 16, No. 3, March 2018
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system: STC-OFDM and channel estimation," in
Spread Spectrum Techniques and Applications,
2006 IEEE Ninth International Symposium On,
2006, pp. 198-202.
[3] J. R. Oliva, "Underwater Wireless Video
Transmission using Acoustic OFDM: An
experimental approach to the transmission and
reception of OFDM signals for real-time video
communication," 2011.
[4] C. Yu, Z. Ding and T. Chiueh, "Design and
simulation of a MIMO OFDM baseband
transceiver for high throughput wireless LAN," in
Circuits and Systems, 2004. Proceedings. the
2004 IEEE Asia-Pacific Conference On, 2004, pp.
205-208.
[5] J. Yazdani et al, "Modelling of an OFDM
transmission technique for power line using
UNIX BasedCOSSAP'and power line channel
simulator," in International Symposium on
Power-Line Communications and its
Applications. T. Coffey and S. McGrath (Editors).
University of Limerick. Limerick, Ireland. 5th-7th
April, 2000, pp. 1-874653.
[6] H. Zhang, Orthogonal Frequency Division
Multiplexing for Wireless Communications, 2004.
[7] H. Zou, B. McNair and B. Daneshrad, "An
integrated OFDM receiver for high-speed mobile
data communications," in Global
Telecommunications Conference, 2001.
GLOBECOM'01. IEEE, 2001, pp. 3090-3094.
[8] T. Shahana et al, "RRNS-convolutional
concatenated code for OFDM based wireless
communication with direct analog-to-residue
converter," World Academy of Science,
Engineering and Technology, vol. 2, (2), pp. 86-
93, 2008.
[9] M. Al-Akaidi, O. Daoud and S. Linfoot, "A new
turbo coding approach to reduce the Peak-to-
Average Power Ratio of a multi-antenna-OFDM
system," International Journal of Mobile
Communications, vol. 5, (3), pp. 357-369, 2007.
[10] A. C. Brooks et al, "Design and Simulation
of Orthogonal Frequency Division Multiplexing
(OFDM) Signaling," Electronic Publication:
Digital Object Identifiers (DOIs), pp. 1-4, 2001.
[11] J. Liu, System Design and Signal Processing
for OFDM-Based Wireless Communication
Systems, 2004.
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