Ici self cancellation report

U11EC033, U11EC051, U11EC121, U11EC144, U10EC133 PROJECT 2014-15 Page i
A PROJECT REPORT
ON
“ICI SELF CANCELLATION TECHNIQUES IN
OFDM”
B.TECH- IV (ELECTRONICS & COMMUNICATION)
SUBMITTED BY:
SUNNY GANGISETTI (U11EC033)
BARANWAL SWEETY BINDUKUMAR (U11EC051)
IPPALA P BHAVANI SHANKAR REDDY (U11EC121)
BHASKARANI SAI KRISHNA PRADEEP (U10EC133)
ARIYARATNAM ARCHCHUNAH (U11EC144)
GUIDED BY:
PROF. SHILPI GUPTA
ECED, SVNIT
DEPARTMENT OF ELECTRONICS ENGINEERING
Year: 2014-15
SARDAR VALLABHBHAI NATIONAL INSTITUTE OF
TECHNOLOGY (SVNIT)
SURAT-395007

U11EC033, U11EC051, U11EC121, U11EC144, U10EC133 PROJECT 2014-15 Page ii
Acknowledgements
It gives us immense pleasure to present our project report on “ICI Self Cancellation
Techniques in OFDM”. No work, big or small, has ever been done without contributions of
others.
We would like to express deep gratitude towards Prof. Shilpi Gupta (Assistant professor at
Electronics Engineering Department, SVNIT) who gave us valuable suggestions,
motivation and the direction to proceed at every stage. She extended towards a kind and
valuable guidance, indispensible help and inspiration at times. In appreciation we offer her our
sincere gratitude.
In addition, we would like to thank Dr. Upena. D. Dalal (Head of Electronics Engineering
Department, SVNIT) and the entire Department for providing all the required resources for
our project. Finally, yet importantly, we would like to express our heartfelt thanks to our
beloved families for their blessings and my friends/classmates for their help and wishes for the
successful completion of this project.
SUNNY GANGISETTI (U11EC033)
BARANWAL SWEETY BINDUKUMAR (U11EC051)
IPPALA P BHAVANI SHANKAR REDDY (U11EC121)
BHASKARANI SAI KRISHNA PRADEEP (U10EC133)
ARIYARATNAM ARCHCHUNAH (U11EC144)

U11EC033, U11EC051, U11EC121, U11EC144, U10EC133 PROJECT 2014-15 Page iii
Abstract
OFDM is a promising Technique for achieving high data rates in mobile environment because
of its multicarrier modulation technique and ability to convert a frequency selective fading
channel into several nearly flat fading channels. As the sub carriers are orthogonal, the
spectrum of each carrier has a null at the center frequency of each of the other carriers in the
system. Rapid varying channel between mobile User Equipment (UE) and base station in high
vehicular speed environment have led to significant degradation in Signal to Noise ratio due to
destruction of orthogonality.
A well known problem of orthogonal frequency division multiplexing (OFDM), however, is
its sensitivity to frequency offset between the transmitted and received signals, which may be
caused by Doppler shift in the channel, or by the difference between the transmitter and receiver
local oscillator frequencies. This carrier frequency offset causes loss of orthogonality between
sub-carriers and the signals, transmitted on each carrier are not independent of each other. The
orthogonality between subcarriers in orthogonal frequency division Multiplexing (OFDM)
which leads to inter-carrier interference (ICI). In the literature, various studies have been
proposed to cancel the effects of ICI in high speed scenario like mobile, railway and
aeronautical communication. Two different approaches like estimation and compensation of
the frequency offset/phase noise at the receiver and another approach is to use signal processing
techniques in the transmitter for reducing carrier/phase offsets by using frequency domain
coding called as ICI self-cancellation at transmitter have been studied.
In ICI self cancellation various techniques are used to map one data symbol on two sub carrier
with careful selection of weighting coefficient. There are Data conversion scheme, Data
conjugate scheme, Real constant weighted scheme, Plural weighted scheme and Symmetric
data conversion scheme. These schemes improve the system performance or mitigate the effect
of ICI and also simulate their BER and CIR performances.

U11EC033, U11EC051, U11EC121, U11EC144, U10EC133 PROJECT 2014-15 Page iv
Sardar Vallabhbhai National Institute of Technology, Surat-07
Electronics Engineering Department
CERTIFICATE
This is to certify that candidates Mr..Bhaskarani.Sai.Krishna.Pradeep (U10EC133),
Mr..Sunny.Gangisetti (U11EC033), Ms..Baranwal.Sweety.Bindukumar (U11EC051),
Mr..Ippala.P.Bhavani.Shankar.Reddy (U11EC121), Mr..Ariyaratnam..Archchunah
(U11EC144) of B.TECH IV, 8TH Semester have successfully and satisfactorily presented
Project Report on the topic entitled “ICI Self Cancellation Techniques in OFDM” for the
partial fulfillment of the degree of Bachelor of Technology (B.Tech) in May. 2015.
Guide: Name: Prof. Shilpi Gupta Sign: ______________
Examiner 1 Name: ______________ Sign: ______________
Head,
ECED, SVNIT.
(Seal of the Department)

U11EC033, U11EC051, U11EC121, U11EC144, U10EC133 PROJECT 2014-15 Page v
CONTENTS
TOPICS Page No.
LIST OF FIGURES vii
CHAPTERS
1. Introduction 1
1.1 Objective of Thesis 3
1.2 Planning of the Thesis 3
1.3 Outline of the Thesis 3
1.4 Literature Survey 4
2. Basics Of OFDM 6
2.1 Orthogonality 6
2.2 OFDM Generation and Reception 7
2.2.1 Signal Mapping 8
2.2.2 Serial to Parallel & Parallel to Serial Conversion 9
2.2.3 Frequency to Time Domain Conversion 9
2.3 Inter-symbol and Inter-carrier interference 9
2.4 Guard Period 10
2.5 Cyclic Prefix 11
2.6 Different channels which are employed in the project 12
2.6.1 AWGN Channel 12
2.6.2 Rayleigh Channel 13
2.7 OFDM Advantages 14
2.8 Limitations of OFDM 14
2.9 Methods of ICI Reduction 15
2.9.1 Frequency Domain Equalization 15
2.9.2 Time Domain Windowing 16
2.9.3 Pulse Shaping 17
2.9.4 ICI Self Cancellation 17
2.10 OFDM variants and applications 18
2.10.1 OFDM variants 18

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2.10.2 Applications of OFDM 19
3. ICI Self Cancellation Techniques 20
3.1 ICI Self Cancellation 20
3.2 System Model 20
3.3 Analysis Of Inter Carrier Interference 21
3.4 ICI Self Cancellation Scheme 23
3.4.1 ICI Cancelling Modulation 24
3.4.2 ICI Cancelling Demodulation 25
3.5 Various ICI Self Cancellation Techniques 26
3.5.1 Data Conversion ICI Self Cancellation Technique 26
3.5.2 Data Conjugate ICI Self Cancellation Technique 27
3.5.3 Symmetric Data Conversion ICI Self Cancellation Technique 27
3.5.4 Real Constant Weighted Conversion ICI Self Cancellation Technique 28
3.5.5 Plural Weighted Conversion ICI Self Cancellation Technique 28
3.5.6 Plural Conjugate Data Conversion ICI Self Cancellation Technique 28
4. Simulation Results 29
4.1 OFDM Model Used For Simulation 29
4.2 Graphs 29
5. Conclusion 35
5.1 Scope of Future Work 36
REFERENCES 37
ACRONYMS 39

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LIST OF FIGURES
Figure 1: Orthogonally placed OFDM sub-carriers 7
Figure 2: Block diagram of a typical OFDM Transceiver 7
Figure 3: Guard period insertion in OFDM 11
Figure 4: Pilot sub carrier arrangement 16
Figure 5: Spectrum of a 64 sub carrier OFDM 16
Figure 6: N-sub carrier OFDM system model 21
Figure7: Frequency offset model 21
Figure 8: ICI Coefficients for N=16 Carriers 23
Figure 9: Comparison of ICI coefficients 24
Figure 10: CIR versus epsilon for standard and self-cancellation applied OFDM 26
Figure 11: OFDM Signal at transmitter end 29
Figure 12: OFDM Signal after passing through channel 30
Figure 13: SNR Vs BER Graph 30
Figure 14: SNR Vs BER Curve for Rayleigh and AWGN Channels 31
Figure 15: Bit error probability curve for different offsets 31
Figure 16: OFFSET Vs CIR 32
Figure 17: CIR curve for symmetric data conversion self cancellation scheme 32
Figure 18: CIR curve for conjugate data self cancellation scheme 33
Figure 19: CIR curve for plural weighted self cancellation scheme 33
Figure 20: CIR curve for different self cancellation schemes together 34

U11EC033, U11EC051, U11EC121, U11EC144, U10EC133 PROJECT 2014-15 Page 1
Chapter 1: Introduction
The ever increasing demand for very high rate wireless data transmission calls for technologies
which make use of the available electromagnetic resource in the most intelligent way. Key
objectives are spectrum efficiency, robustness against multipath propagation, power
consumption and implementation complexity. These objectives are often conflicting, so
techniques and implementations are sought which offer the best possible trade off between
them. The Internet revolution has created the need for wireless technologies that can deliver
data at high speeds in a spectrally efficient manner. However, supporting such high data rates
with sufficient robustness to radio channel impairments requires careful selection of
modulation techniques.
Currently, the most suitable choice appears to be OFDM (Orthogonal Frequency Division
Multiplexing).Orthogonal frequency division multiplexing (OFDM) is becoming the chosen
modulation technique for wireless communications. OFDM can provide large data rates with
sufficient robustness to radio channel impairments.
Orthogonal Frequency Division Multiplexing (OFDM) is a special form of multi carrier
modulation technique which is used to generate waveforms that are mutually orthogonal. In an
OFDM scheme, a large number of orthogonal, overlapping, narrow band sub-carriers are
transmitted in parallel. These carriers divide the available transmission bandwidth. The
separation of the sub-carriers is such that there is a very compact spectral utilization. With
OFDM, it is possible to have overlapping sub channels in the frequency domain, thus
increasing the transmission rate.[1]
OFDM has been accepted as standard in several wire line and wireless applications. Due to the
recent advancements in digital signal processing (DSP) and very large-scale integrated circuits
(VLSI) technologies, the initial obstacles of OFDM implementations do not exist anymore. In
a basic communication system, the data are modulated onto a single carrier frequency. The
available bandwidth is then totally occupied by each symbol. This kind of system can lead to
inter-symbol-interference (ISI) in case of frequency selective channel.

The attraction of OFDM is mainly because of its way of handling the multipath interference at
the receiver. Multipath phenomenon generates two effects (a) Frequency selective fading and
(b) Inter symbol interference (ISI). The "flatness" perceived by a narrowband channel
overcomes the frequency selective fading. On the other hand, modulating symbols at a very
low rate makes the symbols much longer than channel impulse response and hence reduces the
ISI.
The focus of future fourth-generation (4G) mobile systems is on supporting high data rate
services such as deployment of multi-media applications which involve voice, data, pictures,
and video over the wireless networks. At this moment, the data rate envisioned for 4G networks
is 1 GB/s for indoor and 100Mb/s for outdoor environments. Orthogonal frequency division
multiplexing (OFDM) is a promising candidate for 4G systems because of its robustness to the
multipath environment.
The main disadvantages of OFDM are the inter carrier interference (ICI) and high peak to
average power ratio (PAPR), which is caused by the sensitivity of the OFDM system due to
carrier frequency offset and Doppler shift and a large variation in envelope of OFDM signal
The undesired ICI degrades the performance of the system. To reduce the ISI, a guard interval
larger than that of the estimated delay spread is added. If the guard interval is left empty, the
orthogonality of the sub carriers no longer holds, i.e., ICI (inter carrier interference) still exists.
To prevent both the ISI as well as the ICI, OFDM symbol is cyclically extended into the guard
interval. Thus, an accurate and efficient Intercarrier Interference (ICI) reduction procedure is
necessary to demodulate the received data.
To mitigate the effect of ICI in OFDM system, ICI cancellation techniques such as frequency
domain equalization, time domain windowing method, pulse shaping and ICI self cancellation
are used. These different ICI cancellation techniques are used for different applications and
different causes of ICI. ICI self cancellation techniques is very simple and easy way to
minimize the effect of ICI in OFDM system. So, we have focused on ICI self cancellation
technique which eliminates the inter carrier interference in sub-carriers of OFDM symbols in
a OFDM signal. The various ICI self cancellation techniques are data conversion schemes, data
conjugate scheme, plural weighted scheme, real constant weighted scheme and symmetric data
conversion scheme. But the cost of the ICI self cancellation techniques are reduction in the
bandwidth efficiency.

1.1 Objective of Thesis
The main objective of this thesis is to reduce the effect of ICI in OFDM system using ICI self
cancellation techniques to improve the performance of OFDM system in terms of inter carrier
interference (ICI), bit error rate (BER), carrier to interference ratio (CIR).
Proper ICI self cancellation techniques makes a system possible to transmit data with minimum
interference. Several scheme of ICI self cancellations have been presented to reduce ICI
including Data conversion scheme, Data conjugate scheme, Plural weighted scheme, real
constant weighted scheme. Different modulation techniques (BPSK, QPSK, QAM) are
considered for ICI self cancellation and compared their BER performances over AWGN
(Additive White Gaussian Channel) and Rayleigh channel.
1.2 Planning of the Thesis
In this particular thesis following steps have been followed:
 First the concept of OFDM system was studied and understood their features to
implement in MATLAB.
 The concept of ICI self cancellation was studied in detail to mitigate the effect of ICI
in OFDM system.
 A number of ICI self cancellation schemes are studied, these ICI self cancellation
schemes are simulated and compared in terms of BER and CIR performance.
1.3 Outline of the Thesis
The organization of this thesis follows in this mannerism
 Chapter 1: Introduction to the OFDM system and ICI schemes is done. Literature
survey related to Orthogonal Frequency Division Multiplexing (OFDM) system,
various ICI self cancellation schemes has been discussed.
 Chapter 2: Introduces the brief description of basic Orthogonal Frequency Division
Multiplexing system. The concept of orthogonality is discussed in detail. OFDM
system including its transmission and reception, advantages, applications and its major
limitations such as peak-to-average power ratio (PAPR) and inter-carrier interference
(ICI) are also briefly discussed in this chapter.
 Chapter 3: This chapter introduces the mechanism of ICI in OFDM system and
analyzes the effect of ICI on the received signal with different normalized frequency

offset values. The concept of ICI self cancellation such as ICI self cancellation
modulation and ICI self cancellation demodulation are also discussed. A comparison
has been made for different Self Cancellation techniques CIR (carrier to interference
ratio) of conventional OFDM system with the CIR of ICI self cancellation OFDM
system.
 Chapter 4: Simulation results using MATLAB software have been shown. This
chapter contain all results such as, carrier to interference ratio, bit error rate
performance comparison of OFDM system. These CIR performance comparisons have
been made by taking into account the combination of various ICI self cancellation
schemes.
 Chapter 5: Conclusion drawn from the simulation and future scope has been
incorporated in this thesis.
1.4 Literature Survey
It is well known that Chang proposed the original OFDM principles in 1966, and successfully
achieved a patent in January of 1970. OFDM is a technique for transmitting data in parallel by
using a large number of modulated sub-carriers. These sub-carriers divide the available
bandwidth and are sufficiently separated in frequency so that they are orthogonal. The
orthogonality of the carriers means that each carrier has an integer number of cycles over a
symbol period.
In 1971, Weinstein and Ebert proposed a modified OFDM system [7] in which the discrete
Fourier Transform (DFT) was applied to generate the orthogonal subcarriers waveforms
instead of the banks of sinusoidal generators. Their scheme reduced the implementation
complexity significantly, by making use of the inverse DFT (IDFT) modules and the digital-
to-analog converters. In their proposed model, baseband signals were modulated by the IDFT
in the transmitter and then demodulated by DFT in the receiver. Therefore, all the subcarriers
were overlapped with others in the frequency domain, while the DFT modulation still assures
their orthogonality.
Cyclic prefix (CP) or cyclic extension was first introduced by Peled and Ruiz in 1980 [8] for
OFDM systems. In their scheme, conventional null guard interval is substituted by cyclic
extension for fully-loaded OFDM modulation. As a result, the orthogonality among the

subcarriers was guaranteed. With the trade-off of the transmitting energy efficiency, this new
scheme can result in a phenomenal ISI (Inter Symbol Interference) reduction. Hence it has been
adopted by the current IEEE standards. In 1980,Hirosaki introduced an equalization algorithm
to suppress both inter symbol interference (ISI) and ICI [9], which may have resulted from a
channel distortion, synchronization error, or phase error. In the meantime, Hirosaki also applied
QAM modulation, pilot tone, and trellis coding techniques in his high-speed OFDM system,
which operated in voice-band spectrum.
In 1985, Cimini introduced a pilot-based method to reduce the interference emanating from the
multipath and co-channels [10]. In the 1990s, OFDM systems have been exploited for high
data rate communications. In the IEEE 802.11 standard, the carrier frequency can go up as high
as 2.4 GHz or 5 GHz. Researchers tend to pursue OFDM operating at even much higher
frequencies nowadays. For example, the IEEE 802.16 standard proposes yet higher carrier
frequencies ranging from 10 GHz to 60 GHz. However, one of the main disadvantages of
OFDM is its sensitivity against carrier frequency offset which causes inter carrier interference
(ICI). The undesired ICI degrades the performance of the system. Number of authors has
suggested different methods for ICI reduction. These methods are investigated in this thesis
and their performances are evaluated

Chapter 2: Basics of OFDM
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission
technique, which divides the bandwidth into many carriers, each one is modulated by a low
rate data stream In term of multiple access technique, OFDM is similar to FDMA in that the
multiple user access is achieved by subdividing the available bandwidth into multiple channels
that are then allocated to users. However, OFDM uses the spectrum much more efficiently by
spacing the channels much closer together. This is achieved by making all the carriers
orthogonal to one another, preventing interference between the closely spaced carriers.
2.1 Orthogonality
Two signals are orthogonal if their dot product is zero. That is, if you take two signals multiply
them together and if their integral over an interval is zero, then two signals are orthogonal in
that interval.The reason why the information transmitted over the carriers in OFDM can still
be separated is the so called orthogonality relation giving the method its name. By using an
IFFT for modulation we implicitly chose the spacing of the subcarriers in such a way that at
the frequency where we evaluate the received signal (indicated as peaks) all other signals are
zero. In order for this orthogonality to be preserved the following must be true: [2]
1. The receiver and the transmitter must be perfectly synchronized. This means they both
must assume exactly the same modulation frequency and the same time-scale for
transmission (which usually is not the case).
2. The analog components, part of transmitter and receiver, must be of very high quality.
3. There should be no multipath channel.
In particular the last point is quite a pity, since we have chosen this approach to combat
the multipath channel. Fortunately there's an easy solution for this problem: The
OFDM symbols are artificially prolonged by periodically repeating the 'tail' of the
symbol and precede the symbol with it. At the receiver this so called guard interval is
removed again. As long as the length of this interval 𝚫 is longer than the maximum
channel delay 𝑻 𝒎𝒂𝒙 all reflections of previous symbols are removed and the
Orthogonality is preserved.

Figure.1: Orthogonally placed OFDM Subcarriers [13]
2.2 OFDM Generation And Reception
Figure.2: Block diagram of a typical OFDM Transceiver
The high data rate serial input bit stream is fed into serial to parallel converter to get low data
rate output parallel bit stream. Input bit stream is taken as binary data. The low data rate parallel
bit stream is modulated in Signal Mapper.
Modulation can be BPSK, QPSK, QAM etc. The modulated data are served as input to inverse
fast Fourier transform so that each subcarrier is assigned with a specific frequency. The
frequencies selected are orthogonal frequencies. In this block, orthogonality in subcarriers is

introduced. In IFFT, the frequency domain OFDM symbols are converted into time domain
OFDM symbols. Guard interval is introduced in each OFDM symbol to eliminate inter symbol
interference (ISI).
All the OFDM symbols are taken as input to parallel to serial data. These OFDM symbols
constitute a frame. A number of frames can be regarded as one OFDM signal. This OFDM
signal is allowed to pass through digital to analog converter (DAC). In DAC the OFDM signal
is fed to RF power amplifier for transmission. Then the signal is allowed to pass through
additive white Gaussian noise channel (AWGN channel).
At the receiver part, the received OFDM signal is fed to analog to digital converter (ADC) and
is taken as input to serial to parallel converter. In these parallel OFDM symbols, Guard interval
is removed and it is allowed to pass through Fast Fourier transform. Here the time domain
OFDM symbols are converted into frequency domain. After this it is fed into Signal Demapper
for demodulation purpose. And finally the low data rate parallel bit stream is converted into
high data rate serial bit stream which is in form of binary.
2.2.1 Signal Mapping
A large number of modulation schemes are available allowing the number of bits transmitted
per carrier per symbol to be varied. Digital data is transferred in an OFDM link by using a
modulation scheme on each subcarrier. A modulation scheme is a mapping of data words to a
real (In phase) and imaginary (Quadrature) constellation, also known as an IQ constellation.
For example 256-QAM (Quadrature Amplitude Modulation) has 256 IQ points in the
constellation constructed in a square with 16 evenly spaced columns in the real axis and 16
rows in the imaginary axis.
The number of bits that can be transferred using a single symbol corresponds to log2 𝑀, where
M is the number of points in the constellation, thus 256-QAM transfers 8 bits per symbol.
Increasing the number of points in the constellation does not change the bandwidth of the
transmission, thus using a modulation scheme with a large number of constellation points,
allows for improved spectral efficiency. However, the greater the number of points in the
modulation constellation, the harder they are to resolve at the receiver.

2.2.2 Serial to Parallel and Parallel to Serial Conversion
Data to be transmitted is typically in the form of a serial data stream. In OFDM, each symbol
transmits a number of bits and so a serial to parallel conversion stage is needed to convert the
input serial bit stream to the data to be transmitted in each OFDM symbol. The data allocated
to each symbol depends on the modulation scheme used and the number of subcarriers. At the
receiver the reverse process takes place, with the data from the subcarriers being converted
back to the original serial data stream. [3]
2.2.3 Frequency to Time Domain Conversion
The OFDM message is generated in the complex baseband. The frequency spacing between
adjacent subcarriers is Nπ/2, where N is the number of subcarriers. This can be achieved by
using the inverse discrete Fourier transform (IDFT), easily implemented as the inverse fast
Fourier transform (IFFT) operation. As a result, the OFDM symbol generated for an N-
subcarrier system translates into N samples, with the ith
sample being, [3, 4]
𝑥 𝑘=∑ 𝑐 𝑛
𝑁−1
𝑛=0 𝑒−𝑗2𝜋𝑘𝑛/𝑁
, 0 ≤ k ≤ N-1. (2.1)
At the receiver, the OFDM message goes through the exact opposite operation in the Fast
Fourier transform (FFT) to take the corrupted symbols from a time domain form into the
frequency domain. In practice, the baseband OFDM receiver performs the Fast Fourier
transform (FFT) of the receive message to recover the information that was originally sent.
2.3 Inter-Symbol and Inter-Carrier Interference
In a multipath environment, a transmitted symbol takes different times to reach the receiver
through different propagation paths. From the receiver‘s point of view, the channel introduces
time dispersion in which the duration of the received symbol is stretched. Extending the symbol
duration causes the current received symbol to overlap previous received symbols and results
in inter symbol interference (ISI).
In OFDM, ISI usually refers to interference of an OFDM symbol by previous OFDM symbols.
For a given system bandwidth the symbol rate for an OFDM signal is much lower than a single
carrier transmission scheme. However for OFDM the system bandwidth is broken up into N
subcarriers, resulting in a symbol rate that is N times lower than the single carrier transmission.

This low symbol rate makes OFDM naturally resistant to effects of Inter-Symbol Interference
(ISI) caused by multipath propagation. Multipath propagation is caused by the radio
transmission signal reflecting off objects in the propagation environment, such as walls,
buildings, mountains, etc. These multiple signals arrive at the receiver at different times due to
the transmission distances being different. This spreads the symbol boundaries causing energy
leakage between them.
In OFDM, the spectra of subcarriers overlap but remain orthogonal to each other. This means
that at the maximum of each sub-carrier spectrum, all the spectra of other subcarriers are zero.
The receiver samples data symbols on individual sub-carriers at the maximum points and
demodulates them free from any interference from the other subcarriers. Interference caused
by data symbols on adjacent sub-carriers is referred to Inter-carrier interference (ICI).
ICI occurs when the multipath channel varies over one OFDM symbol time. When this
happens, the Doppler shift on each multipath component causes a frequency offset on the
subcarriers, resulting in the loss of orthogonality among them. This situation can be viewed
from the time domain perspective, in which the integer number of cycles for each subcarrier
within the FFT interval of the current symbol is no longer maintained due to the phase transition
introduced by the previous symbol. Finally, any offset between the subcarrier frequencies of
the transmitter and receiver also introduces ICI to an OFDM symbol.
2.4 Guard Period
The effect of ISI on an OFDM signal can be further reduced by the addition of a guard period
to the start of each symbol. This guard period is a cyclic copy that extends the length of the
symbol waveform. Each subcarrier, in the data section of the symbol, (i.e. the OFDM symbol
with no guard period added, which is equal to the length of the IFFT size used to generate the
signal) has an integer number of cycles. Because of this placing copies of the symbol end-to-
end results in a continuous signal, with no discontinuities at the joins. In addition to
protecting the OFDM from ISI, the guard period also provides protection against time-offset
errors in the receiver.

Figure.3: Guard Period Insertion in OFDM [14]
2.5 Cyclic Prefix
The term cyclic prefix refers to the prefixing of a symbol with a repetition of the end. Although
the receiver is typically configured to discard the cyclic prefix samples, the cyclic prefix serves
two purposes.
 As a guard interval, it eliminates the inter-symbol interference from the previous
symbol.
 As a repetition of the end of the symbol, it allows the linear convolution of a frequency-
selective multipath channel to be modeled as circular convolution, which in turn may
be transformed to the frequency domain using a discrete Fourier transform. This
approach allows for simple frequency-domain processing, such as channel estimation
and equalization.
In order for the cyclic prefix to be effective, the length of the cyclic prefix must be at least
equal to the length of the multipath channel. Although the concept of cyclic prefix has been
traditionally associated with OFDM systems, the cyclic prefix is now also used in single carrier
systems to improve the robustness to multipath propagation.

2.6 Channels Employed in The Project
2.6.1 Additive White Gaussian Noise (AWGN) Channel
Noise exists in all communications systems operating over an analog physical channel, such as
radio. The main sources are thermal background noise, and electrical noise in the receiver
amplifiers, and inter-cellular interference. In addition to this noise can also be generated
internally to the communications system as a result of Inter-Symbol Interference (ISI), Inter-
Carrier Interference (ICI), and Inter- Modulation Distortion (IMD).
These sources of noise decrease the Signal to Noise Ratio (SNR), ultimately limiting the
spectral efficiency of the system. Noise, in all its forms, is the main detrimental effect in most
radio communication systems. It is therefore important to study the effects of noise on the
communications error rate and some of the trade-offs that exists between the level of noise and
system spectral Efficiency. [4]
Most types of noise present in radio communication systems can be modelled accurately using
Additive White Gaussian Noise (AWGN). This noise has a uniform spectral density (making
it white), and a Gaussian distribution in amplitude (this is also referred to as a normal
distribution). OFDM signals have a flat spectral density and a Gaussian amplitude distribution
provided that the number of carriers is large (greater than about 20 subcarriers), because of this
the inter-cellular interference from other OFDM systems have AWGN properties.
For the same reason ICI, ISI, and IMD also have AWGN properties for OFDM signals. In the
study of communication systems, the classical (ideal) additive white Gaussian noise (AWGN)
channel, with statistically independent Gaussian noise samples corrupting data samples free of
Inter symbol interference (ISI), is the usual starting point for understanding basic performance
relationships. An AWGN channel adds white Gaussian noise to the signal that passes through
it.
In the receiver side, the entire process at the transmitter side is reversed like the analog signal
received is converted to digital form using DAC and then the after removing the cyclic prefix,
the serial data is converted to parallel form after which the time domain signal is converted to
frequency domain by FFT algorithm. After passing this frequency domain signal through the
detector, it is converted to serial from which is our required output.

2.6.2 Rayleigh Channel
Rayleigh fading is a statistical model for the effect of a propagation environment on
a radio signal, such as that used by wireless devices. Rayleigh fading models assume that the
magnitude of a signal that has passed through such a transmission medium (also called
a communications channel) will vary randomly, or fade, according to a Rayleigh distribution —
the radial component of the sum of two uncorrelated Gaussian random variables.
Rayleigh fading is viewed as a reasonable model for tropospheric and ionospheric signal
propagation as well as the effect of heavily built-up urban environments on radio
signals. Rayleigh fading is most applicable when there is no dominant propagation along a line
of sight between the transmitter and receiver. If there is a dominant line of sight, Rician
fading may be more applicable.[5]
Rayleigh fading is a reasonable model when there are many objects in the environment
that scatter the radio signal before it arrives at the receiver. The central limit theoremholds that,
if there is sufficiently much scatter, the channel impulse response will be well-modelled as
a Gaussian process irrespective of the distribution of the individual components. If there is no
dominant component to the scatter, then such a process will have zero mean and phase evenly
distributed between 0 and 2π radians. The envelope of the channel response will therefore
be Rayleigh distributed.
The requirement that there be many scatterers present means that Rayleigh fading can be a
useful model in heavily built-up city centres where there is no line of sight between the
transmitter and receiver and many buildings and other objects attenuate, reflect, refract, and
diffract the signal. Experimental work in Manhattan has found near-Rayleigh fading
there. Intropospheric and ionospheric signal propagation the many particles in the atmospheric
layers act as scatterers and this kind of environment may also approximate Rayleigh fading. If
the environment is such that, in addition to the scattering, there is a strongly dominant signal
seen at the receiver, usually caused by a line of sight, then the mean of the random process will
no longer be zero, varying instead around the power-level of the dominant path. Such a
situation may be better modelled as Rician fading. [6]
Note that Rayleigh fading is a small-scale effect. There will be bulk properties of the
environment such as path loss and shadowing upon which the fading is superimposed. How
rapidly the channel fades will be affected by how fast the receiver and/or transmitter are
moving. Motion causes Doppler shift in the received signal components.

2.7 OFDM Advantages
OFDM has been used in many high data rate wireless systems because of the many advantages
it provides.
 Immunity to selective fading: One of the main advantages of OFDM is that is more
resistant to frequency selective fading than single carrier systems because it divides the
overall channel into multiple narrowband signals that are affected individually as flat
fading sub-channels.
 Resilience to interference: Interference appearing on a channel may be bandwidth
limited and in this way will not affect all the sub-channels. This means that not all the
data is lost.
 Spectrum efficiency: Using close-spaced overlapping sub-carriers, a significant
OFDM advantage is that it makes efficient use of the available spectrum.
 Resilient to ISI: Another advantage of OFDM is that it is very resilient to inter-symbol
and inter-frame interference. This results from the low data rate on each of the sub-
channels.
 Resilient to narrow-band effects: Using adequate channel coding and interleaving it
is possible to recover symbols lost due to the frequency selectivity of the channel and
narrow band interference. Not all the data is lost.
 Simpler channel equalization: One of the issues with CDMA systems was the
complexity of the channel equalization which had to be applied across the whole
channel. An advantage of OFDM is that using multiple sub-channels, the channel
equalization becomes much simpler.[7]
2.8Limitations of OFDM
(a) High Peak to Average Power Ratio (PAPR)
Time domain OFDM signal is a summation of several orthogonal sub-carriers, so OFDM
signal has high variation in its envelope. High power transmitter amplifiers need linearization.
OFDM signal has a noise like amplitude with a very large dynamic range when passes through
RF power amplifiers produces high PAPR. It causes signal distortion. So to reduce PAPR we

need linear amplifiers at the transmitter. But linear amplifiers are less efficient and costly
compared to non-linear amplifiers.
(b) Sensitive To Carrier Offset And Drift (ICI)
Because of the orthogonality of the sub-carriers, we are able to extract the symbols at the
receiver as they do not interfere with each other. Orthogonality is preserved as long as sub
carriers are harmonics to each other. But at the receiver end, if there is a change of frequency
of the sub-carriers due to any reason then the orthogonality among them is lost & ICI occurs.
As a result the signal degrades heavily. This change in frequency is called frequency offset.
There are two main reasons for frequency offset. (a) Frequency mismatch between transmitter
& receiver (b) Doppler effect. So ICI has to be reduced for effective performance of the
system and some methods are discussed. [7]
2.9 Methods of ICI Reduction
1) Frequency Domain Equalization
2) Time Domain Windowing
3) Pulse Shaping
4) ICI Self Cancellation
From the above four methods the first two methods are the initial approach, whereas the last
two methods are very effective.
2.9.1 Frequency Domain Equalization
The fading distortion in the channel causes ICI in the OFDM demodulator. The pattern of ICI
varies from frame to frame for the demodulated data but remains invariant for all symbols
within a demodulated data frame. The equalizer co-efficient for eliminating ICI in the
frequency domain can be derived from the pattern of the pilot symbol & hence a suitable
equalizer can be constructed [8,9]
Drawbacks:
It can only reduce the ICI caused by fading distortion which is not the major source of ICI.

The major source of ICI is due to the frequency mismatch between the transmitter and
Figure.4: Pilot subcarrier arrangement
receiver, and the Doppler shift. The above method cannot address to it.Again it is only suitable
for flat fading channels, but in mobile communication the channels are frequency selective
fading in nature because of multipath components. Here also the channel needs to be estimated
for every frame. Estimation of channel is complex, expensive & time consuming. Hence the
method is not effective one.
2.9.2 Time Domain Windowing
We know that OFDM signal has widely spread power spectrum. So if this signal is transmitted
in a band limited channel, certain portion of the signal spectrum will be cut off, which will lead
to inter carrier interference.
Figure.5: Spectrum of a 64 subcarrier OFDM [15]
To diminish the interference the spectrum of the signal wave form need to be more
concentrated. This is achieved by windowing the signal. Basically windowing is the process of
multiplying a suitable function to the transmitted signal wave form. The same window is used
in the receiver side to get back the original signal. The IC1 will be eliminated if the product of
the window functions satisfies the Nyquist’s vestigial symmetry criterion.

Drawbacks:
It can only reduce the ICI caused by band limited channel which is not the major source of ICI.
The major source of ICI is due to the frequency mismatch between the transmitter and receiver,
and the Doppler shift. The above method cannot address to it. Windowing is done frame by
frame & hence it reduces the spectral efficiency to a large extent. Hence the method is not
effective one.
2.9.3 Pulse Shaping
As we have seen in the OFDM spectrum that each carrier consist of a main lobe followed by a
number of side lobes with reducing amplitude. As long as orthogonality is maintained there is
no interference among the carriers because at the peak of the every carrier, there exist a spectral
null. That is at that point the component of all other carriers is zero. Hence the individual carrier
is easily separated.[8]
When there is a frequency offset the orthogonality is lost because now the spectral null does
not coincide to the peak of the individual carriers. So some power of the side lobes exists at
the centre of the individual carriers which is called ICI power. The ICI power will go on
increasing as the frequency offset increases. The purpose of pulse shaping is to reduce the side
lobes. If we can reduce the side lobe significantly then the ICI power will also be reduced
significantly.
Drawback:
Complex in implementation
2.9.4 ICI Self Cancellation
It is seen that the difference between the ICI co-efficient of two consecutive sub-carriers are
very small. Here one data symbol is not modulated in to one sub-carrier, rather at least in to
two consecutive sub-carriers. If the data symbol ‘a’ is modulated in to the 1st sub-carrier then
‘-a’ is modulated in to the 2nd sub-carrier. Hence the ICI generated between the two sub-
carriers almost mutually cancels each other. [8]
Drawbacks:
The major drawback of this method is the reduction in band width efficiency as same symbol
occupies two sub-carriers.

2.10 OFDM Variants and Applications
2.10.1 OFDM Variants
There are several other variants of OFDM for which the initials are seen in the technical
literature. These follow the basic format for OFDM, but have additional attributes or variations:
 COFDM: Coded orthogonal frequency division multiplexing. A form of OFDM
where error correction coding is incorporated into the signal.
 Flash OFDM: This is a variant of OFDM that was developed by Flarion and it is a
fast hopped form of OFDM. It uses multiple tones and fast hopping to spread signals
over a given spectrum band.
 OFDMA: Orthogonal frequency division multiple access. A scheme used to provide
a multiple access capability for applications such as cellular telecommunications when
using OFDM technologies.
 VOFDM: Vector OFDM. This form of OFDM uses the concept of MIMO technology.
It is being developed by CISCO Systems. MIMO stands for Multiple Input Multiple
output and it uses multiple antennas to transmit and receive the signals so that multi-
path effects can be utilised to enhance the signal reception and improve the transmission
speeds that can be supported.
 WOFDM: Wideband OFDM. The concept of this form of OFDM is that it uses a
degree of spacing between the channels that is large enough that any frequency errors
between transmitter and receiver do not affect the performance. It is particularly
applicable to Wi-Fi systems.
Each of these forms of OFDM utilize the same basic concept of using close spaced orthogonal
carriers each carrying low data rate signals. During the demodulation phase the data is then
combined to provide the complete signal. [7]

2.10.2 Applications of OFDM
Cable
 ADSL and VDSL broadband access via POTS copper wiring,
 DVB-C2, an enhanced version of the DVB-C digital cable TV standard,
 Power line communication (PLC),
 ITU-T G.hn, a standard which provides high-speed local area networking of existing home
wiring (power lines, phone lines and coaxial cables).
 TrailBlazer telephone line modems,
 Multimedia over Coax Alliance (MoCA) home networking.
Wireless
The wireless LAN (WLAN) radio interfaces IEEE 802.11a, g, n, ac and HIPERLAN/2.
 The digital radio systems DAB/EUREKA 147, DAB+, Digital Radio Mondiale, HD
Radio, T-DMB and ISDB-TSB.
 The terrestrial digital TV systems DVB-T and ISDB-T.
 The terrestrial mobile TV systems DVB-H, T-DMB, ISDB-T and Media FLO forward link.
 The.wireless personal.area.network (PAN) ultra-wideband (UWB) IEEE
802.15.3a implementation suggested by Wi-Media Alliance.
The OFDM based multiple access technology OFDMA is also used in several 4G and pre-
4G cellular networks and mobile broadband standards:
 The mobility mode of the wireless MAN/broadband wireless access (BWA) standard IEEE
802.16e (or Mobile-WiMAX).
 The mobile broadband wireless access (MBWA) standard IEEE 802.20.
 The downlink of the 3GPP Long Term Evolution (LTE) fourth generation mobile
broadband standard. The radio interface was formerly named High Speed OFDM Packet
Access (HSOPA), now named Evolved UMTS Terrestrial Radio Access (E-UTRA) [7]
OFDM, orthogonal frequency division multiplexing has gained a significant presence in the
wireless market place. The combination of high data capacity, high spectral efficiency, and its
resilience to interference as a result of multi-path effects means that it is ideal for the high data
applications that have become a major factor in today's communications scene.

Chapter 3: ICI Self Cancellation Techniques
3.1 ICI Self Cancellation
It is seen that the difference between the ICI co-efficient of two consecutive sub-carriers are
very small. This makes the basis of ICI self cancellation. Here one data symbol is not
modulated in to one sub-carrier, rather at least in to two consecutive sub-carriers. If the data
symbol ‘a’ is modulated in to the 1st sub-carrier then ‘-a’ is modulated in to the 2nd sub-carrier.
Hence the ICI generated between the two sub-carriers almost mutually cancels each other. This
method is suitable for multipath fading channels as here no channel estimation is required
.Because in multipath case channel estimation fails as the channel changes randomly. Thus, the
ICI signals become smaller when applying ICI cancelling modulation. On the other hand, the
ICI cancelling demodulation can further reduce the residual ICI in the received signals. The
combined ICI cancelling modulation and demodulation method is called the ICI self-
cancellation scheme.
Merits of self cancellation technique
 It is suitable for multipath fading channels
 It is also suitable for flat channels
 Channel estimation is not required
 Channel equalization is not required
 It is simple in implementation
 It is less complex and effective
3.2 System Model
The modulated data are served as input to ICI cancelling modulation. ICI coefficients can
be found in this. If there is frequency mismatch between transmitter and receiver local
oscillators frequency offset occurs. Doppler shift also introduces frequency offset. This
frequency offset (ε) occurs in OFDM signal due to these reasons.
ICI canceling demodulation is performed on the received OFDM symbols. ICI cancelling
modulation and ICI cancelling demodulation together known as ICI Self Cancellation. After
this it is fed into Signal De-Mapper for demodulation purpose. And finally the low data rate

parallel bit stream is converted into high data rate serial bit stream.
Figure. 6: N–subcarrier OFDM system model [16]
3.3 Analysis of Inter-Carrier Interference
The main disadvantage of OFDM, however, is its susceptibility to small differences in
frequency at the transmitter and receiver, normally referred to as frequency offset. This
frequency offset can be caused by Doppler shift due to relative motion between the transmitter
and receiver, or by differences between the frequencies of the local oscillators at the transmitter
and receiver. In this project, the frequency offset is modeled as a multiplicative factor
introduced in the channel, as shown in Figure.
Figure.7: Frequency offset model

The received signal is given by,
𝑦(𝑛) = 𝑥(𝑛)𝑒
𝑗2𝜋𝑛𝜀
𝑁 + 𝑤(𝑛) (3.1)
Where ε is the normalized frequency offset, and is given by ΔfNTs. Δf is the frequency
difference between the transmitted and received carrier frequencies and Ts is the subcarrier
symbol period. w(n) is the AWGN introduced in the channel. The effect of this frequency offset
on the received symbol stream can be understood by considering the received symbol Y(k) on
the k
th
sub-carrier.
𝑌(𝑘) = 𝑋(𝑘)𝑆(0) + ∑ 𝑋(𝑙)𝑆(𝑙 − 𝑘)𝑁−1
𝑙=0,𝑙≠𝑘 + 𝑛 𝑘 (3.2)
𝑘 = 0,1,2, … … … … … , 𝑁 − 1
Where N is the total number of subcarriers, X(k) is the transmitted symbol (M-ary phase-shift
keying (M-PSK), for example) for the k
th
subcarrier, nk is the FFT of w(n), and S(l-k) are the
complex coefficients for the ICI components in the received signal. The ICI components are
the interfering signals transmitted on sub-carriers other than the k
th
sub-carrier. The complex
coefficients are given by
𝑆(𝑙 − 𝑘) =
sin⁡( 𝜋(𝑙+𝜀−𝑘))
𝑁𝑠𝑖𝑛(𝜋(𝑙+𝜀−𝑘)/𝑁)
× 𝑒
(𝑗𝜋(1−
1
𝑁
)(𝑙+𝜀−𝑘))
(3.3)
To analyze the effect of ICI on the received signal, we consider a system with N=16 carriers.
The frequency offset values used are 0.2 and 0.4, and l is taken as 0, that is, we are analyzing
the signal received at the sub-carrier with index 0. The complex ICI coefficients S(l-k) are
plotted for all sub-carrier indices in Figure 3.2.

Figure 8: ICI Coefficients for N=16 Carriers
This figure shows that for a larger ε, the weight of the desired signal component, S(0),
decreases, while the weights of the ICI components increases. The authors also notice that the
adjacent carrier has the maximum contribution to the ICI. This fact is used in the ICI self-
cancellation technique described in Section 4.
The carrier-to-interference ratio (CIR) is the ratio of the signal power to the power in the
interference components. It serves as a good indication of signal quality. It has been derived
from (3.2) in [10] and is given below. The derivation assumes that the standard transmitted
data has zero mean and the symbols transmitted on the different sub-carriers are statistically
independent.
⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡𝐶𝐼𝑅 =⁡
|𝑆(𝑘)|2
∑ |𝑆(𝑙−𝑘)|2𝑁−1
𝑙=0,𝑙≠𝑘
=
|𝑆(0)|2
∑ |𝑆(𝑙)|2𝑁−1
𝑙=0
(3.4)
3.4 ICI Self-Cancellation Scheme
ICI self-cancellation is a scheme that was introduced by Yuping Zhao and Sven-Gustav
Häggman in 2001 in [10] to combat and suppress ICI in OFDM. Succinctly, the main idea is
to modulate the input data symbol onto a group of subcarriers with predefined coefficients such
that the generated ICI signals within that group cancel each other, hence the name self-
cancellation.

3.4.1 ICI Cancellation Modulation
The ICI self-cancellation scheme requires that the transmitted signals be constrained such that,
X(1)= -X(0), X(3)= -X(2), ……………, X(N-1)= -X(N-2). Using (3.3), this assignment of
transmitted symbols allows the received signal on subcarriers k and k + 1 to be written as
𝑌′(𝑘) = ∑ 𝑋(𝑙)[𝑆(𝑙 − 𝑘) − 𝑆(𝑙 + 1 − 𝑘)] + 𝑛 𝑘
𝑁−2
𝑙=0,𝑙=𝑒𝑣𝑒𝑛
⁡⁡⁡𝑌′(𝑘 + 1) = ∑ 𝑋(𝑙)[𝑆(𝑙 − 𝑘 − 1) − 𝑆(𝑙 − 𝑘)] + 𝑛 𝑘+1
𝑁−2
𝑙=0,𝑙=𝑒𝑣𝑒𝑛 (3.5)
and the ICI coefficient S’(l-k) is denoted as
⁡⁡⁡⁡⁡𝑆′(𝑙 − 𝑘) = 𝑆(𝑙 − 𝑘) − 𝑆(𝑙 + 1 − 𝑘)⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡ (3.6)
Figure 4.1 shows a comparison between |S’(l-k)| and |S(l-k)| on a logarithmic scale. It is seen
that |S’(l-k)| << |S(l-k)| for most of the l-k values. Hence, the ICI components are much smaller
in (3.6) than they are in (3.3). Also, the total number of interference signals is halved in (3.6)
as opposed to (3.3) since only the even subcarriers are involved in the summation.
Figure.9: Comparison of ICI coefficients

3.4.2 ICI Cancellation Demodulation
ICI modulation introduces redundancy in the received signal since each pair of subcarriers
transmit only one data symbol. This redundancy can be exploited to improve the system power
performance, while it surely decreases the bandwidth efficiency. To take advantage of this
redundancy, the received signal at the (k + 1)
th
subcarrier, where k is even, is subtracted from
the k
th
subcarrier. This is expressed mathematically as
𝑌′(𝑘) = 𝑌′(𝑘) − 𝑌′(𝑘 + 1)
= ∑ 𝑋(𝑙)[−𝑆(𝑙 − 𝑘 − 1) + 2𝑆(𝑙 − 𝑘) − 𝑆(𝑙 − 𝑘 + 1)] + 𝑛 𝑘 − 𝑛 𝑘+1
𝑁−2
𝑙=0 (3.7)
Subsequently, the ICI coefficients for this received signal becomes
𝑆′′(𝑙 − 𝑘) = −𝑆(𝑙 − 𝑘 − 1) + 2𝑆(𝑙 − 𝑘) − 𝑆(𝑙 − 𝑘 + 1) (3.8)
When compared to the two previous ICI coefficients |S(l-k)| for the standard OFDM system
and |S’(l-k)| for the ICI canceling modulation, |S’’(l-k)| has the smallest ICI coefficients, for
the majority of l-k values, followed by |S’(l-k)| and |S(l-k)|. This is shown in Figure.8 for N =
64 and ε = 0.4. The combined modulation and demodulation method is called the ICI self-
cancellation scheme.
The reduction of the ICI signal levels in the ICI self-cancellation scheme leads to a higher
CIR. From (4.4), the theoretical CIR can be derived as
𝐶𝐼𝑅 =
|−𝑆(−1)+2𝑆(0)−𝑆(1)|2
∑ |−𝑆(𝑙−1)+2𝑆(𝑙)−𝑆(𝑙+1)|2𝑁−1
𝑙=2,4,6…
(3.9)
Figure (9) below shows the comparison of the theoretical CIR curve of the ICI self-cancellation
scheme, calculated by (3.9), and the CIR of a standard OFDM system calculated by (3.4). As
expected, the CIR is greatly improved using the ICI self-cancellation scheme. The
improvement can be greater than 15 dB for 0 < ε < 0.5.
As mentioned above, the redundancy in this scheme reduces the bandwidth efficiency by half.
This could be compensated by transmitting signals of larger alphabet size. Using the theoretical
results for the improvement of the CIR should increase the power efficiency in the system and

gives better results for the BER. Hence, there is a tradeoff between bandwidth and power
tradeoff in the ICI self-cancellation scheme.
Figure.10: CIR versus epsilon for standard and self-cancellation applied OFDM
3.5 Various ICI Self Cancellation Techniques
It is seen that the difference of ICI coefficient between two consecutive subcarrier S(l-k) and
S(l+1-k) is very small. Hence the idea of self-cancellation is generated. The main idea is to
modulate one data symbol onto a group of subcarriers with predefined weighting coefficients.
By doing so, the ICI signals generated within a group can be self-cancelled each other . Thus
it is called self-cancellation method. There are various self cancellation methods which have
been employed in present. Let’s have an overview of them.
3.5.1 Data Conversion ICI Self Cancellation Technique
The data-conversion self-cancellation scheme for ICI mitigation based on a data symbol
allocation of X’ (k) = X (k), X’(k +1) = -X (k), for k = 0,2,…. N - 2 in consecutive subcarriers to
deal with the ICI. The received signal on subcarrier k will be
𝑌′(𝑘) = ∑ 𝑋(𝑙)[𝑆(𝑙 − 𝑘) − 𝑆(𝑙 + 1 − 𝑘)] + 𝑛 𝑘
𝑁−2
𝑙=0
𝑙=𝑒𝑣𝑒𝑛
(3.10)

And on the subcarrier k+1 the received signal will be. To further reduce ICI, demodulation is
done. The resultant signal Y (k) is determined by the difference between the adjacent subcarrier.
𝑌′′(𝑘) =
1
2
(𝑌′(𝑘) − 𝑌′(𝑘 + 1)) (3.11)
CIR of data conversion method is given as
𝐶𝐼𝑅 =
|−𝑆(−1)+2𝑆(0)−𝑆(1)|2
∑ |−𝑆(𝑙−1)+2𝑆(𝑙)−𝑆(𝑙+1)|2𝑁−2
𝑙=2,4,6,..
(3.12)
3.5.2 Data Conjugate ICI Self Cancellation Technique
In the data-conjugate scheme, subcarrier signals are remapped in the form of
X’ (k) = X (k), X’(k +1) = - X*(k), for k= 0,2 ….. N-2
The final recovered signal is as follows
𝑌′′(𝑘) =
1
2
(𝑌′(𝑘) − 𝑌′∗(𝑘 + 1)) (3.13)
CIR of data conjugate scheme is given by
𝐶𝐼𝑅 =
|𝑆(0)+𝑆∗(0)|2+|𝑆(1)+𝑆∗(−1)|2
∑ |𝑆(𝑙)+𝑆∗(𝑙)|2𝑁−2
𝑙=2,4,6,.. +|𝑆(𝑙+1)+𝑆∗(𝑙−1)|2
(3.14)
3.5.3 Symmetric Data Conversion ICI Self Cancellation Technique
In the symmetric data-conversion scheme, subcarrier signals are remapped in the form of X’
(k) = X (k), X’(N-k -1) = - X(k) for k= 0,2 ….. N-2
𝑌′′(𝑘) =
1
2
(𝑌′(𝑘) − 𝑌′∗(𝑁 − 𝑘 − 1)) (3.15)
𝐶𝐼𝑅 =
|2𝑆(0)−𝑆(𝑁−1)−𝑆(1−𝑁)|2
∑ |𝑆(𝑙)+𝑆(−𝑙)−𝑆(𝑁−𝑙−1)−𝑆(𝑙−𝑁+1)|2𝑁−2
𝑙=2,4,6,..
(3.16)

3.5.4 Real Constant Weighted Conversion ICI Self Cancellation Technique
In the constant weighted data-conversion scheme, subcarrier signals are remapped in the form
of X’ (k) = X (k), X’(k +1) = - μX(k) for k= 0,2 ….. N-2, where μ is a real constant.
𝑌′′(𝑘) =
1
1+𝜇
(𝑌′(𝑘) − 𝑌′(𝑘 + 1)) (3.17)
𝐶𝐼𝑅 =
|(1+𝜇)𝑆(0)−𝜇𝑆(1)−𝑆(−1)|2
∑ |(1+𝜇)𝑆(𝑙)−𝜇𝑆(𝑙+1)−𝑆(𝑙−1)|2𝑁−2
𝑙=2,4,6,..
(3.18)
3.5.5 Plural Weighted Data Conversion ICI Self Cancellation Technique
In the plural weighted data-conversion scheme, subcarrier signals are remapped in the form of
X’ (k) = X (k), X’(k+1) = 𝑒−𝑗𝜋/2 X(k), for k= 0,2 ….. N-2
𝑌′′(𝑘) =
1
2
(𝑌′(𝑘) − 𝑌′(𝑘 + 1)𝑒−𝑗𝜋/2
) (3.19)
⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡⁡𝐶𝐼𝑅 =
|(2𝑆(0)−𝑒
−
𝑗𝜋
2 [𝑆(1)−𝑆(−1)]|
2
∑ |2𝑆(𝑙)−𝑒
−
𝑗𝜋
2 [⁡𝑆(𝑙+1)−𝑆(𝑙−1)]|
2
𝑁−2
𝑙=2,4,6,..
(3.20)
3.5.6 Plural Conjugate Data Conversion ICI Self Cancellation Technique
In this scheme, subcarrier signals are remapped in the form of X’ (k) = X (k), X’(k +1) = 𝑒𝑗𝜋/2
X*(k) for k= 0,2 ….. N-2
𝑌′′(𝑘) =
1
2
(𝑌′(𝑘) − 𝑌′∗(𝑘 + 1)𝑒−𝑗𝜋/2
) (3.21)
𝐶𝐼𝑅 =
|𝑆(0)+𝑆∗(0)|2+|𝑒 𝑗𝜋/2 𝑆(1)+𝑒−𝑗𝜋/2 𝑆∗(−1)|
2
∑ |𝑆(𝑙)+𝑆∗(𝑙)|2𝑁−2
𝑙=2,4,6,.. +|𝑒 𝑗𝜋/2 𝑆(𝑙+1)+𝑒−𝑗𝜋/2 𝑆∗(𝑙−1)|
2 (3.22)

Chapter 4: Simulation Results
4.1 OFDM Model Used For Simulation
Figure.6 shows the Fast Fourier transform (FFT) based N-subcarrier OFDM system model
used for simulation. The simulation parameters used for the above model is as given below.
Simulation Parameters:
Parameter Specifications
IFFT Size 1024
Number of Sub Carriers 64
Channel AWGN, Rayleigh
Modulation BPSK
4.2 Graphs
Figure.11: OFDM signal at transmitter end

Figure.12: OFDM Signal after passing through channel
Figure.13: SNR vs BER Graph

Figure.14: SNR vs BER curve for Rayleigh and AWGN channels
Figure.15: Bit error probability curve for different offsets

Figure.16: Offset Vs CIR
Figure.17: CIR curve for symmetric data conversion self cancellation scheme

Figure.18 : CIR curve for conjugate data self cancellation scheme
Figure.19: CIR curve for plural weighted self cancellation scheme

Figure.20: CIR curve for different self cancellation schemes together.

Chapter 5: Conclusions
OFDM is a present day Modulation Technique with wide range of applications. orthogonality
of the sub-carriers in OFDM helps to extract the symbols at the receiver without interference
with each other. Orthogonality is preserved as long as sub carriers are harmonics to each other.
But if there are frequency offsets in the sub-carriers due to any reason then the orthogonality
among them is lost & ICI occurs.
One of the main limitations of OFDM is its sensitivity against carrier frequency offset which
causes attenuation and rotation of subcarriers, and inter carrier interference (ICI). The
frequency offset is due to frequency mismatch between the transmitter and receiver local
oscillators, and Doppler shift. The undesired ICI degrades the signal heavily and hence
degrades the performance of the system.
So, ICI mitigation techniques are essential in improving the performance of an OFDM system
in an environment which induces frequency offset error in the transmitted signal. This project
investigates an ICI self-cancellation schemes for combating the impact of ICI on OFDM
systems for different frequency offset values. It is also suitable for multipath fading channels.
We have worked on several ICI mitigation techniques that have been introduced in the chapters
above to achieve an optimum result. With the help of suitable MATLAB codes these have been
verified and from the results given above we can conclude that among all the ICI self
cancellation schemes that consider “grouping of two method”, Symmetric Data Conversion
gives the best result for the communication.

5.1 Scope Of Future Work
Following are the areas of future study which can be considered for further research work.
1. In this work the BER performance of the OFDM system is evaluated considering BPSK and
QPSK Modulation system. It can be tested with other modulation systems such as QAM and
GMSK. ICI reduction using self cancellation technique can be used for COFDM (Coded
OFDM) Systems.
2. In this work, the group size in ICI techniques is considered as 2 thereby making it less
complicated to perform. In future the group size can be increased to three or four.
3. The sequential Monte Carlo (SMC) method called sequential importance sampling (SIS) can
be implemented which requires very lower computational complexity and estimates accurately
high value frequency offsets. However, the SIS performs slightly better, which is expected due
to the nonlinearity of the state–space and it is bandwidth efficiency scheme.
4. In this dissertation the polarization effects have not been taken into account. Simulation
studies can be done for same architectures while taking into account the polarization effects.
5. We have used channel spacing of 100 GHz in this dissertation. This can be further reduced
for more bandwidth utilization and some other techniques can be introduced for further
network sharing

REFERENCES
[1] V.N. Richard and R. Prasad, “OFDM for Wireless Multimedia
Communication”, Artech house Publisher, London, 2000.
[2] T. S. Rappport, “Wireless Communications, principles and practice”,
2nd Edition, prentice- Hall publications, 2002.
[3] S .Weinstein and P. Ebert, “Data Transmission by Frequency Division
Multiplexing Using the Discrete Fourier Transform”, IEEE Trans. On
Commun., vol.19, Issue: 5, pp. 628–634, Oct.1971
[4] L. J. Cimini, “Analysis and simulation of a digital mobile channel using
orthogonal Frequency division multiplexing”, IEEE Trans. Communications.,
vol. COM-33, pp. 665-675. July 1985 .
[5] John G. Proakis (1995). Digital Communications (3rd ed.). Singapore:
McGraw–Hill Book Co. pp. 767–768.ISBN 0-07-113814-5.
[6] Dmitry Chizhik, Jonathan Ling, Peter W. Wolniansky, Reinaldo A.
Valenzuela, Nelson Costa, and Kris Huber (April 2003). "Multiple-Input–
Multiple-Output Measurements and Modeling in Manhattan". IEEE Journal on
Selected Areas in Communications 21 (3): 321–331.
doi:10.1109/JSAC.2003.809457
[7] Radio Electronics,”OFDM Tutorial” http://www.radio-
electronics.com/info/rf-technology-design/ofdm/ofdm-
[8] A Survey of ICI Reduction Techniques in OFDM System
SonikaChouhan, Deepak Sharma (IJCTT) – volume 4 Issue 8–August 2013
[9] N.A. Dhahi., “Optimum finite-length equalization for multicarrier
transceivers,” IEEE Trans. Commun., vol. 44, pp. 56–64, Jan. 1996.
[10] J. Armstrong, “Analysis of new and existing methods of reducing
intercarrier interference due to carrier frequency offset in OFDM,”IEEE Trans.
Commun., vol. 47, no. 3, pp. 365–369, Mar. 1999.
[11] P. H. Moose, “A technique for orthogonal frequency division
multiplexing ……frequency offset correction”, IEEE Trans. Commun., vol. 42,
no.10, pp. ……2908–2914, 1994

[12] Rfmw.em.keysight.com, ”Concepts of OFDM”
.http://rfmw.em.keysight.com/wireless/helpfiles/89600B/WebHelp/subsystems
./wlan-ofdm/Content/ofdm_basicprinciplesoverview.htm
[13] http://ecee.colorado.edu/~ecen4242/WiMax/WiMAX_802_16e.htm
[14] www.dsplog.com,”OFDM basics
http://www.dsplog.com/category/ofdm/
[15] ni.com,” OFDM and Multi-Channel Communication Systems
http://www.ni.com/white-paper/3740/en/

ACRONYMS
ADC Analog to Digital Converter
ADSL Asymmetric Digital Subscriber Line
AWGN Additive White Gaussian Noise
ADSL Asymmetric Digital Subscriber Lines
BER Bit Error Rate
BPSK Binary Phase Shift Keying
BWA Broadband Wireless Access
CIR Carrier to Interference Ratio
COFDM Coded Orthogonal Frequency Division Multiplexing
DAB Digital Audio Broadcasting
DFT Discrete Fourier Transform
DSL Digital Subscriber Line
DSP Digital Signal Processing
DVB Digital Video Broadcasting
DVB-C Digital Video Broadcasting - Cable
DVB-T Digital Video Broadcasting - Terrestrial
FFT Fast Fourier Transform
FOFDM Flash Orthogonal Frequency Division Multiplexing
GMSK Gaussian Minimum Shift Keying
HIPERLAN High Performance Radio LAN
HSPOA High Speed OFDM Packet Access
ICI Inter Carrier Interference
IDFT Inverse Discrete Fourier Transform
IEEE Institute of Electrical and Electronics Engineers
IFFT Inverse Fourier Transform
ISDB Integrated Service Digital Broadcasting
ISI Inter symbol Interference
IMD Inter Modulation Distortion
LAN Local Area Network
LTE Long Term Evolution

MAN Metropolitan Area Network
MBWA Mobile Broadband Wireless Access
MIMO Multiple Input – Multiple Output
OFDM Orthogonal Frequency Division Multiplexing
OFDMA Orthogonal Frequency Division Multiplexing Access
PAN Personal Area Network
PAPR Peak to Average Power Ratio
PLC Power Line Communication
PSK Phase Shift Keying
QAM Quadrature Amplitude Moduation
QPSK Quadrature Phase Shift Keying
SNR Signal to Noise Ratio
UMTS Universal Mobile Telecommunication System
UWB Ultra Wide Band
VDSL Very High Bit Rate Digital Subscriber Line
VLSI Very Large Scale Integration
VOFDM Vector Orthogonal Frequency Division Multiplexing
WiMAX Worldwide Interoperability for Microwave Access
WOFDM Wideband Orthogonal Frequency Division Multiplexing

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