1. PERFORMANCE ANALYSIS OF TRANSMISSION
SCHEMES FOR
UNDERWATER COMMUNICATION
BY:-
VINIT KUMAR (1204033)
ELECTRONICS & COMM. ENGINEERING
NIT PATNA
DEPARTMENT OF ELECTRICAL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY, PATNA

2. CERTIFICATE
This is to certify that the project entitled “performance analysis
of transmission schemes for underwater communication”
submitted by VINIT KUMAR is an authentic work carried by him
under my supervision and guidance for partial fulfillment of the
requirements for summer internship at Department of Electrical
Engineering, IIT PATNA.
DR. PREETAM KUMAR
Assistant professor
Dept. Of Electrical engineering
IIT‐PATNA, 800013
Place: Patna
Date:

3. ACKNOWLEDGEMENT
It was indeed a great privilege for me to have Dr. Preetam Kumar,
Department of Electrical Engineering, IIT Patna as my mentor for this
project. His awe‐inspiring personality, enthusiasm, superb knowledge
and constant encouragement were the motive forces behind successful
completion of this project. I express my utmost gratitude and sincere
regards to him for providing me this opportunity and his valuable time.
I would like to thank Mr. Vinay Kumar Trivedi for his persistent help,
guidance and new ideas without which this project had no meaning. I
would also like to thank all the research scholars of communication lab
for their support.
Last but not the least I would like to express my gratitude towards my
family and friends for their kind co‐operation and encouragement which
helped me in completing this project. I also place on record, my sense of
gratitude to one and all, who directly or indirectly helped me in
completing this project.

4. ABSTRACT
Two third of Earth is covered by water so data transmission through underwater is
very important for both commercial as well as military purpose. It also finds
application in UUV(Unmanned Underwater Vehicle), Ocean surface monitoring,
Disaster forecasting, locating valuable sea resources as well as in search and rescue.
All these developments have made Underwater‐communication an area of
exploration leading to intense research. Underwater channel as compared to other
channels is a harsh channel, therefore performance of various transmission
schemes degrade as compared to other wireless communication channel. It
undergoes severe attenuation, multipath, frequency selective fading, constrained
bandwidth and reduced power makes analysis of underwater channel very complex
as compared to other channels.
Acoustic communication has been widely used for underwater communication
which is the best possible alternative among other existing techniques like optical,
RF etc. In this paper we have analyzed the performance of various transmission
schemes in underwater channel and compare it with other channels like
Pedestrian, Vechular and AWGN channel. Various transmission schemes, their
working principle, advantages and disadvantages over other schemes has been
discussed in detail. Single user as well as multiple access schemes for underwater
channel is also discussed. Major portion of this project deals with SCFDMA (Single
carrier Frequency division Multiple Access), the performance of SCFDMA is
analyzed in detail for uplink as well as downlink and relatively compared on the
basis of BER, PAPR performance. A thorough analysis of various subcarrier mapping
schemes like IFDMA, LFDMA, BIFDMA is also provided.
The analysis shows that for uplink SCFDMA using LFDMA mapping is the best
alternative but for downlink though SCFDMA outperforms OFDMA in terms of both
BER as well as PAPR but easier carrier allocation and simpler receiver design of
OFDMA gives it edge over SCFDMA. So, like LTE‐3GPP SCFDMA for uplink and
OFDMA for downlink should be used for underwater channel as well.

5. TABLE OF CONTENTS
ACKNOWLEDGEMENTS I
ABSTRACT II
LIST OF TABLES III
LIST OF FIGURES IV
ABBREVIATIONS v
1. Underwater Channel 1
2. OFDM 4‐19
A. Introduction 4
B. Basic Principle 5
C. Advantages, Disadvantages 8
D. OFDM transmitter, receiver 9
E. Simulation 10
3. SCFDE 20‐23
A. Introduction 20
B. Working Principle 21
4. OFDMA 24‐27
A. Introduction 24
B. Working Principle 25
C. Advantages, Disadvantages 26
5. SCFDMA 28‐44
A. Introduction 28
B. Why SCFDMA? 28
C. Working Principle 30

6. D. Sub‐Carrier mapping 32‐41
a. LFDMA 33
b. IFDMA 35
c. B‐IFDMA 37
E. BER, PAPR 42
6. Simulation and Results 43‐61
7. Conclusion and Future Works 62
8. References 63

7. LIST OF TABLES
1. Simulation Parameters for OFDM(Data type‐Sound) 10
2. Simulation Parameters for OFDM(Data type ‐Image) 17
3. Simulation Results for Uplink 44
4. Simulation Results for Downlink 48

8. LIST OF FIGURES
2.1. FDM VS OFDM 5
2.2. OFDM SIGNAL FREQUENCY SPECTRA 6
2.3. IFFT OPERATION 7
2.4. CYCLIC PREFIX 7
2.5. OFDM TRANSMITTER 9
2.6. OFDM RECEIVER 10
2.7. TRANSMITTED SIGNAL 11
2.8. QPSK SYMBOL CONSTELLATION 11
2.9. PHASE DIFFERENCE 11
2.10. SPECTRUM OF CARRIER 12
2.11. SPECTRUM OF TRANSMITTED SIGNAL 12
2.12. TRANSMITTED SIGNAL 13
2.13. SPECTRUM OF RECEIVED SIGNAL 14
2.14. RECEIVED SIGNAL 15
2.15. PHASE DIFFERENCE 0DB 16
2.16. PHASE DIFFERENCE 5DB 16
2.17. PHASE DIFFERENCE 15DB 16
2.18. PHASE DIFFERENCE 20DB 16
2.19. BER VS SNR PLOT FOR AUDIO SIGNAL 17
2.20. ORIGINAL IMAGE 18
2.21. IMAGE RECEIVED AT 0DB 18
2.22. IMAGE RECEIVED AT 5DB 18
2.23. IMAGE RECEIVED AT 10DB 18
2.24. IMAGE RECEIVED AT 15DB 18
2.25. IMAGE RECEIVED AT 20DB 18

9. 2.26. BER VS SNR PLOT FOR IMAGE DATA 19
2.27. BER VS SNR PLOT FOR RANDOM DATA 19
3.1. SCFDE TRANSMITTER AND RECEIVER 21
3.2. BER VS SNR PLOT FOR SCFDE USING MMSE AND ZF EQUALIZATION 22
3.3. BER VS SNR PLOT FOR SCFDE AND OFDM USING MMSE EQUALIZATION 22
4.1. OFDM VS OFDMA 25
4.2. OFDMA TRANSMITTER AND RECEIVER BLOCK DIAGRAM 25
5.1. OFDMA VS SCFDMA 29
5.2. SCFDMA TRANSMITTER AND RECEIVER BLOCK DIAGRAM 30
5.3. LFDMA DATA BLOCK 34
5.4. SUBCARRIER ALLOCATION IN LFDMA 34
5.5. IFDMA DATA BLOCK 36
5.6. SUBCARRIER ALLOCATION IN IFDMA 36
5.7. BIFDMA DATA BLOCK 38
5.7.A. DATA BLOCK IN DIFFERENT TYPES OF SUBCARRIER MAPPING 40
5.8. PAPR FOR LFDMA, IFDMA, DFDMA, B-IFDMA WITH BLOCK SIZE=2 41
5.9. PAPR PLOT FOR DIFFERENT ROLL-OFF FACTORS IN IFDMA 41
5.10. PAPR PLOT FOR DIFFERENT NUMBER OF SUBCARRIERS IN IFDMA 42
6.1. BER PLOT FOR IFDMA USING MMSE EQUALIZERS. 45
6.2. BER PLOT FOR LFDMA USING MMSE EQUALIZERS. 45
6.3. BER PLOT FOR SCFDE USING MMSE EQUALIZERS. 46
6.4. BER PLOT FOR OFDM USING MMSE EQUALIZERS 46
6.5. PAPR COMPARISON AT ROLL-OFF 0.5 USING RAISED COSINE PULSE SHAPING. 47
6.6. BER COMPARISON OF OFDM AND SCFDE IN UNDERWATER CHANNEL. 47
6.7. BER PLOT FOR OFDMA-IFDMA USING MMSE EQUALIZER FOR 4 USERS. 48
6.8. BER PLOT FOR OFDMA-LFDMA USING MMSE EQUALIZER FOR 4 USERS. 49
6.9. BER OF SCFDMA-IFDMA USING MMSE EQUALIZER FOR 4 USERS. 49

10. 6.10. BER OF SCFDMA-LFDMA USING MMSE EQUALIZER FOR 4 USERS. 50
6.11. PAPR PLOT FOR QPSK DOWNLINK. 50
6.12. PAPR PLOT FOR QPSK FOR OFDMA AND SCFDMA. 51
ABBREVIATIONS
AWGN: ADDITIVE WHITE GAUSSIAN NOISE
OFDM: ORTHOGONAL FREQUENCY DIVISION MULTIPLEXNG
OFDMA: ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS
ISI: INTER SYMBOL INTERFERENCE
SC-FDMA: SINGLE CARRIER FREQUENCY DIVISION MULTIPLE ACCESS
PAPR: PEAK TO AVERAGE POWER RATIO
BER: BIT ERROR RATE
IFDMA: INTERLEAVED FREQUENCY DIVISION MULTIPLE ACCESS
LFDMA: LOCALIZED FREQUENCY DIVISION MULTIPLE ACCESS
DFDMA: DISTRIBUTED FREQUENCY DIVISION MULTIPLE ACCESS
B-IFDMA: BLOCK INTERLEAVED FREQUENCY DIVISION MULTIPLE ACCESS
IBI: INTER BLOCK INTERFERENCE
MMSE: MINIMUM MEAN SQUARE ROOT ERROR
ZF: ZERO FORCING
FFT: FAST FOURIER TRANSFORM
IFFT: INVERSE FAST FOURIER TRANSFORM
DFT: DISCRETE FOURIER TRANSFORM

11. CHAPTER-1
UNDERWATER CHANNEL
The Underwater communication channel is one of the most challenging medium
for wireless communication. There are a few means for wireless underwater
communication. Radio waves of extra low frequency (30 HZ‐300HZ) are the only
means through which waves can propagate very long distances, but the main issue
is for transmission at such a low frequency we need very antennas and high
transmission power which makes radio waves uneconomical for wireless
communication underwater. The other alternative is use of optical sources but that
too needs highly focused beam of light as spreading is prominent in underwater
channel, lasers with high intensity could be a possible alternative. Acoustics seems
to be the best alternative.
Some of the major challenges in underwater
communication are: the attenuation is frequency‐dependent, the communication
bandwidth is dependent on the distance, and the Doppler Effect is more
accentuated than in radio channels and is non‐uniform along the signal bandwidth.
In addition, the background noise is not negligible due to its frequency dependence
and noise dependence.
Acoustic Propagation:
Some of the major challenges faced by acoustic propagation in underwater
channel are described as under:
Attenuation: The attenuation in an underwater channel for distance l and
frequency f is given by
( , ) = l a(f)
Where k is spreading factor which describes geometry of propagation and a(f) is
the absorption coefficient expressed in db as
10 ( , ) = · 10log( ) + · 10log( ( ))
The absorption coefficient for frequencies above a few hundred Hz can be expressed
empirically, using the Thorp's formula which gives a(f) in dB/km for f in kHz as:

12. 10 log ( ) = 0.11 + 44 + 2.75.10 +0.003
For lower frequencies a(f) is given as
10 log ( ) = 0.002 + 0.11
1 +
+ 0.11
As it is clear from the above equations that a(f) or absorption coefficient is
directly proportional to frequency and thus it limits the maximum usable
frequency for underwater communication.
Noise: The major sources of noise in underwater channel can are turbulence,
shipping, waves and thermal noise. Most of them are described using Gaussian
statics and they do have a continuous power spectral density (PSD). The following
empirical formulae give the p.s.d. of the four noise components in dB re micro Pa per Hz
as a function of frequency in kHz:
Turbulence noise operates in low frequency range of below 10 HZ, Noise caused by
distant shipping is dominant in the frequency region 10 Hz ‐ 100 Hz, and it is modeled
through the shipping activity factor s, whose value ranges between 0 and 1 for low and
high activity, respectively. Surface motion, caused by wind‐driven waves (w is the wind
speed in m/s) is the major factor contributing to the noise in the frequency region 100 Hz
‐ 100 kHz (which is the operating region used by the majority of acoustic systems). Finally,
thermal noise becomes dominant for f > 100 kHz.
The overall p.s.d. of the ambient noise, N(f) = Nt(f) + Ns(f) + Nw(f) + Nth(f).
Propagation delay: Delays experienced in case of underwater communication
using acoustics is much higher as compared to that in case of air. Speed of sound
in water is 1500m/s which is much smaller as compared to speed of sound in air
3*10^8m/s. Thus propagation delay is very high comparatively which is one of the
major challenges for communication is underwater.

13. Multipath: Multipath arises mainly due to two reasons: sound reflection at bottom,
surface or due to other objects and the other is due to refraction in water. Speed
of sound changes with depth, salinity, temperature and pressure besides being
space variant. Temperature and pressure both are constant near the surface so is
speed of sound. Temperature decreases as depth increases before becoming
constant to 4®C while pressure increases with depth. Different sound waves reach
receiver following different paths thus varying in phase and undergo either
constructive or destructive interference at the receiver leading to reception of
different signal.
Where, h(t) is channel impulse response, the channel taps, hp, arriving at τp, can be
described by an amplitude component ρp and a phase shift φp. The distortion
introduced by multipath must be equalized at the received to avoid
misinterpretation of signal.
Doppler Effect: Doppler Effect is caused by the relative motion of the transmitter‐
receiver pair, and it causes a shift in the frequency components of the transmitted
signal. The frequency shift is mainly described by the factor v/c, where v is the relative
velocity between transmitter and receiver, and c is the signal propagation speed (the
speed of sound underwater in this case). In underwater environments c is much lower
than in open‐air, and so the Doppler effect is not ignorable. The errors introduced due
to Doppler effect should be properly dealt with otherwise it would lead to ISI and
frequency offset introduced may lead to loss of orthogonality of subcarriers.

14. CHAPTER-2
OFDM
Introduction:
Modulation: Modulation is defined as process by which some characteristics of
carrier signal usually amplitude, phase or frequency is varied with respect to
message signal.
Multiplexing: It is the process by which a bandwidth is shared among independent
data channels.
Orthogonal Frequency Division multiplexing or OFDM is a combination of
modulation and multiplexing. OFDM is a multicarrier modulation technique which
employs several carriers within the allocated bandwidth to share data among users.
Its primary objective is to transmit the data on multiple carriers to reduce inter‐
symbol interference (ISI) and design a bandwidth efficient digital communication
system. This modulation technique is being used in many latest wireless
communication techniques like Wi‐Fi, Wimax, LTE etc..
FDM VS OFDM:
OFDM is a special case of FDM (Frequency Division Multiplexing). In FDM the
bandwidth is shared among carriers in such a way that there is no relation between
carrier frequencies and different streams of information are mapped onto separate
parallel frequency channel. FDM is being used in radio and satellite communication
In OFDM null of one carrier coincides with the peak of other carrier.
OFDM differs from FDM in many aspects some of them are:‐
 IN OFDM carriers frequencies are orthogonal to each other but no such
restriction in FDM.
 IN FDM carriers are far apart but in OFDM carriers are densely packed so is
more bandwidth efficient.
 OFDM provides high data rate compared to FDM.

15. Fig2.1. FDM vs OFDM
Basic OFDM principle:
OFDM is a frequency Division Multiplexing scheme used as multi carrier modulation
schemes for digital data transmission. In OFDM orthogonal carrier frequencies are
closely spaced over entire bandwidth. The data is divided into several parallel data
streams one for each subcarrier. Each subcarrier is modulated using any of the
modulating schemes (BPSK, QPSK, DQPSK, QAM) and mapped input signal is
generated.
 Orthogonality: Two periodic signals are said to be orthogonal if the integral of
product of the two signals over a period is zero. Let us consider two sinusoidal
signals with frequencies f1 and f2, then the two signals are said to be orthogonal
if
∫ ( 2 1. ) ∗ ( 2 2. ) = 0
The "orthogonal" part of the OFDM name indicates that there is a precise
mathematical relationship between the frequencies of the carriers in the system.
It is possible to arrange the carriers in an OFDM Signal so that the sidebands of the
individual carriers overlap and the signals can still be received without adjacent
carrier’s interference. In order to do this the carriers must be mathematically
orthogonal. The Carriers are linearly independent (i.e. orthogonal) if the carrier
spacing is a multiple of 1/Ts. Where, Ts is the symbol duration. The orthogonality
among the carriers can be maintained if the OFDM signal is defined by using Fourier
transform procedures. The OFDM system transmits a large number of narrowband
carriers, which are closely spaced. Note that at the central frequency of each sub
channel there is no crosstalk from other sub channels. Orthogonality of subcarriers

16. allows high spectral efficiency as entire bandwidth can be used but at the same
time it requires high frequency synchronization at the transmitter and receiver.
Loss of synchronization may lead to loss of orthogonality causing inter‐carrier
interference.
Fig 2.2. OFDM signal frequency Spectra
 Modulation using FFT (Fast Fourier Transform):
FFT is Fast Fourier Transform operator used for computing discrete Fourier
transform in Matlab. FFT takes a random signal as input multiplies it with
complex exponential and takes it sum over entire frequency. Mathematically it
is represented as follows
( ) = x(l)e /
k=0, 1, 2, 3
…… K‐1
Where x(l) is the input signal, and f(k) represents K point FFT. FFT transforms an
input signal from time domain to frequency domain. IFFT does the reverse
operation of FFT, it transforms back signal from frequency domain to time domain.
It is used to find inverse discrete Fourier transform of any signal. Mathematically it
is represented as follows:
( ) = ∗ X(k)e /
l=0, 1, 2 ,
3…….K‐1
Where K denotes number of frequency components.

17. Fig 2.3. IFFT operation
 Guard Time:
One of the main reason of using OFDM is, it efficiently deals with multipath
delay spread of the channel. OFDM divides input data among N subcarriers thus
reducing symbol duration by N times and effectively reduces relative delay
spread with respect to symbol duration. Intersymbol interference can be
overcome by introducing guard interval in the OFDM symbols. Guard interval is
generally chosen larger than maximum delay spread of the OFDM symbol so
that one symbols can’t overcome with the adjacent symbol. Guard interval
eliminates pulse shaping requirements and reduces sensitivity to time
synchronization.
Cyclic prefix is also a type of guard interval which adds copy of
OFDM symbol from end to the beginning of the symbol thus it converts linear
convolution of frequency selective multipath channel to circular convolution.
But at the same time it increase the bandwidth.
Fig.2. 4 Cyclic Prefix
 Equalization:
It is the process of adjusting balance between frequency components within an
electronic signal. The need for highly complex time domain equalizers is avoided
in OFDM system implementations. The effects of the channel conditions, for

18. example fading caused by multipath propagation, can be considered as constant
(flat) over an OFDM sub‐channel if the sub‐channel is sufficiently narrow‐band.
This makes equalization far simpler at the receiver in OFDM in comparison to
conventional single‐carrier modulation. The equalizer only has to multiply each
detected sub‐carrier (each Fourier coefficient) by a constant complex number.
If a differential detection and differential modulation (such as DPSK or DQPSK)
is applied to the subcarriers, equalization can be completely eliminated, since
these non‐coherent schemes are insensitive to slowly changing amplitude and
phase distortion.
ADVANTAGES:
OFDM is being widely used in wireless communication due to many advantages it
provides, some of them are as under:
 Immunity to selective fading: OFDM is more resistant to frequency selective
fading as it divides incoming symbol among all subcarriers thus signals are
affected individually.
 High spectral efficiency: Orthogonality of subcarriers and reduced spacing
leads to high spectral efficiency.
 Simple and effective channel equalization in frequency domain
 Resilient to ISI (Inter Symbol Interference) and Inter carrier Interference.
 Efficient implementation using IFFT thus avoiding need for complex sub
channel filters.
 Low sensitivity to time synchronization errors.
DISADVANTAGES:
 High frequency synchronization of transmitter and receiver to avoid
frequency offsets leading to loss of orthogonality
 High PAPR (Peak to average Power Ratio) due to superposition of all
subcarriers.
 Guard interval used leads to lowering of overall spectral efficiency.

19. OFDM TRANSMITTER:
Fig 2.5. OFDM transmitter
The figure above illustrates block diagram of transmitter. Input signal is first
converted to binary form i.e in the form of 0 and 1. This stream of data is modulated
using appropriate modulation scheme namely BPSK, QPSK, DQPSK or QAM. This
modulated signal is fed as input Data to the above block. Depending on the number
of subcarriers this data is converted from serial form to parallel form whose
number of rows is determined by the number of subcarriers. Parallel data is then
sent to Constellation mapper which maps the data individually to appropriate
digital modulation format (BPSK, QPSK).An IFFT is computed on each set of symbols
giving complex time domain samples. These complex time domain samples are
converted from parallel form to serial form and cyclic prefix is added to the serial
data. The real and imaginary components are converted to analog form using DAC
block. The analog signals are then used to modulate cosine and sine waves at the
carrier frequency, fc, respectively. These signals are then summed to give the
transmitted signal.
OFDM RECEIVER:
Fig. 2.6 OFDM receiver

20. The receiver picks up the signal which is quadrature‐mixed down to baseband using
cosine and sine waves at the carrier frequency. The baseband signals are then
sampled and digitalized using ADC. Cyclic prefix is removed by separating lcp data
from the digital serial data, where lcp denotes the length of cyclic prefix. Serial data
is then converted to parallel form such that number of columns depend on number
of subcarriers. This parallel data is then fed into FFT block which converts time
domain signals back to frequency domain. Equalization is performed on the
frequency domain signal to overcome frequency distortions introduced in the
channel. This signal is de‐mapped to binary form using appropriate scheme. Data is
converted finally to serial form and the final received signal is obtained.
SIMULATION:
Parameters Values
Type of data Sound
Bandwidth 2560
Number of subcarriers 256
Symbol length 200e‐3
Carrier frequency 38e3
Sampling frequency 192e3
Guard interval 400e‐3
Number of symbols 20

21. Fig.2.7 Figure shows wave file to be transmitted and corresponding QPSK
modulated signal
Fig.2.8 QPSK symbol constellation Fig. 2.9 Phase difference

22. Fig. 2.10 Spectrum of carrier

23. Fig. 2.11 Spectrum of received signal
Fig.2.12. Transmitted signal

24. Fig. 2.13 spectrum of received signal

25. Fig. 2.14. Received signal

26. Fig 2.15. Phase difference 0db Fig 2.16. Phase difference at 5db
Fig 2.17.Phase diff. 15 db fig. 2.18 phase diff. 20 db

27. Fig 2.19 BER vs SNR plot for audio signal
For image
Parameters Values
Type of data Image
Bandwidth 3168
Number of subcarriers 396
Symbol length 200e‐3
Carrier frequency 38e3
Sampling frequency 192e3
Guard interval 400e‐3
Number of symbols 29

28. Fig 2.20.Original image
Fig.2.21 SNR=0DB Fig 2.22.SNR=5DB Fig 2.23.SNR=10
Fig 2.24.SNR=15DB Fig2.25.SNR=20DB

29. Fig 2.26. BER vs SNR plot for image data
Fig 2.27. BER vs SNR for Random data

30. CHAPTER-3
SCFDE
Introduction:
Orthogonal Frequency division multiplexing has been widely adopted for wireless
commnication purpose from audio/video broadcasting to power line
communication. The main reasons for its global acceptance are robustness to
multipath fading, intersymbol interference and high spectral efficiency. Although it
has emerged as technology for choice but still it suffers from several drawbacks
namely high PAPR, high sensitivity to CFO(channel frequency offset) and
intolerance to amplifier non linearities.
Single carrier scheme implemented with frequency
domain equalization seem to be a better alternative as its complexity and
performance is comparable to OFDM avoiding the above drawbacks associated
with multicarrier scheme. While SCFDE outperforms OFDM at relatively low SNR
and low modulation orders, OFDM performance enhances at larger SNR value.
Working Principle:
Equalization techniques are used to combat frequency selectivity of wireless
chanel.Equalizers are used to compensate for distortions introduced by the
multipah propagation channel.Equalization can be done in both time as well as
frequency domain but as time domain equalization is not feasible due to long
channel impulse response so we prefer frequency domain equalization.In time
domain when length of delay spread is greater than symbol length then it leads to
ISI and thus distorts the received signal.Whereas in frequency domain
communication bandwidth is larger than the coherence bandwidth of the channel
so distinct components of transmitted signal will undergo different distortion.
Channel equalization is the inverse filtering process to undo
linear distortions introduced in the channel by multipath propagation. Linear
filtering is convolution operation in time domain. As convolution in time domain is
analogous to multiplication in frequency domain so linear filtering is equal to point

31. wise multiplication in frequency domain.DFT is being used for conversion of signal
from time domain to frequency domain.
Fig.3.1 Block diagram for SCFDE transmitter and receiver
The block diagram above represents single carrier wireless communication with
Frequency domain equalization. Input data is first of all mapped into complex
symbols using modulation schemes like BPSK,QPSK,QAM etc.. The mapped serial
data is converted to parallel form in S/P block.Cyclic prefix is added to the data to
extend its length and prevent it from ISI at the cost of expanded bandwidth.Parallel
data after addition of CP is converted to serial form.Digital data is converted to
analog form ,after frequency upconversion and filtering the final data is ready for
transmission.
The transmitted signal after passing through wireless channel is
received by the receiver,where first of all it is down converted and converted to
digital form for furthur signal processing.Cyclic prefix is removed from serial data
and is converted to parallel form.DFT transforms the time domain parallel data to
frequency domain.The resulting signal is fed into FDE for frequency domain
equalization to compensate for channel distortions.IDFT brings back frequency
domain data to time domain, finally data decision is made and the signal is
demodulated to get the final received signal.
Apart from having lots of similarity OFDM and SCFDE differ in many
aspects,SCFDE employs both DFT and IDFT in the receiver block whereas OFDM

32. imploys IDFT in the transmitter and DFT in the receiver block.OFDM performs data
detection in frequency domain whereas SCFDE performs data detection in time
domain.
Fig. 3.2 BER for underwater channel using SCFDE
Fig. 3.3 BER plot for OFDM and SCFDE for underwater channel using MMSE equalizer

33. OFDM vs SCFDE
 OFDM is multicarrier scheme whereas SCFDE is single carrier.
 OFDM transmits parallel stream of data with low individual rate whereas
SCFDE transmits serial data with high individual symbol rate.
 OFDM suffers from high PAPR ,due to single carrier SCFDE has lower PAPR.
 OFDM is sensitive to frequency offset of carriers whereas SCFDE is relatively
less sensitive.
 OFDM is sensitive to spectral null , SCFDE provides robustness against
spectral null.
 Lower complexity at transmitter useful in cellular uplink communication

34. CHAPTER-4
OFDMA
Introduction:
Orthogonal Frequency Division Multiple Access or OFDMA has emerged as a
trending technology in many communication standards be it IEEE802.16 for
wireless broadband access or LTE technology of 3GPP for next generation high
speed data transfer. OFDMA is nothing but multiple access version of OFDM. The
major difference comes in the two schemes at subcarrier mapping and de‐mapping,
which are the extra blocks in OFDMA system. In OFDMA information is shared
among multiple users through different subcarriers assigned to each user. OFDMA
reduces selective fading as data is distributed across entire bandwidth, it also
removes multipath fading as subcarriers have orthogonal frequency so they don’t
interfere with adjacent subcarriers, and it is also bandwidth efficient due to
orthogonality of subcarriers allowing compact arrangement of subcarriers. OFDMA
combines scalability, multipath robustness and is also MIMO compatible. Due to all
these advantages OFDMA is being widely used in LTE downlink.
OFDM vs. OFDMA:
 OFDM supports multiple users via TDMA only while OFDMA supports multi‐
user via either TDMA or FDMA or both at the same time.
 OFDMA supports per channel or subcarrier power while OFDM maintains
constant power for all the subcarriers.

35. Fig. 4.1 OFDM vs OFDMA
Working Principle:

36. Fig 4.2 OFDMA transceiver
The above diagram represents transmitter and receiver modules of OFDMA. In
OFDMA system first of all input signal is converted to binary form and is modulated
using appropriate modulation technique(BPSK,QPSK,QAM,etc). The modulated
signal is fed to Subcarrier mapper where modulated data streams are mapped to
orthogonal subcarriers by dividing the available spectrum into number of
orthogonal frequency subcarriers. This makes the time domain data stream from
user a frequency domain data. IFFT block converts frequency domain data back to
time domain and these parallel stream of data is converted to serial form in P/S
block. Cyclic prefix is added to the serial data which is a copy of tail of the serial
data in order to cancel ISI(Inter Symbol Interference).The duration of this cyclic
prefix should be greater than delay spread of the channel. Finally the digital data is
converted to analog form for transmission over the channel and after conversion
to analog form final data is being transmitted.
Data transmitted from the transmitter passes through
channel which adds imperfections in the transmitted signal. Analog data received
at the receiver is converted to digital form for further signal processing. Cyclic prefix
is removed by removing lcp data from the serial data, where lcp denotes length of
cyclic prefix. Serial data after removing cyclic prefix is converted to parallel form
and fed into FFT block for converting time domain signal to frequency domain.
Frequency domain data is converted to serial form and is demapped. The
demapped signal is demodulated to get the final received signal.
Advantages:
 High spectral efficiency: Due to orthogonal subcarrier mapping it is possible
to pack them closely.
 Little interference between subcarriers.
 Robustness in multipath environment.
 Easy implementation of MIMO.
 Simpler receiver design to support high data rate communication.

37. Disadvantages:
 High PAPR(Peak to average power ratio): In OFDMA symbols are transmitted
in parallel so that each one contains a part of the transmission.The power at
a certain point is is sum of powers of all the transmitted symbols leading to
high PAPR.

38. CHAPTER-5
SCFDMA
Introduction:
Single Carrier Frequency Division Multiple access or SCFDMA uses single carrier for
transmission of data and uses frequency domain equalization at the receiver is
more or less similar to OFDMA (Orthogonal Frequency Division Multiple Access) in
performance and structure. But the major advantage of SCFDMA over OFDMA is in
terms of PAPR, PAPR of SCFDMA is far better than OFDMA which makes it a useful
technology in LTE uplink. SCFDMA has subcarrier bandwidth common to all sub‐
carriers, so there is no superposition of subcarriers like in OFDMA so the peak of
the transmitted signal is not so high thus reducing the PAPR in case of SCFDMA.
SCFDMA is also considered as DFT spread OFDM is a promising technique for high
data rate communication. Out of two types of subcarrier mapping is possible
IFDMA (Interleaved FDMA) and LFDMA (localized FDMA) BER performance of
LFDMA is better than LFDMA while in case of PAPR the situation is just inverse.
Other hybrid mapping schemes like DFDMA and BFDMA also exist whose
performance a compromise between these two is existing schemes.
WHY SCFDMA??
OFDMA is being widely used in cellular applications because it provides robustness
to multipath distortion in case of multipath propagation. In OFDM data is
transmitted on L orthogonal subcarriers at 1/L times the bit rate of the message
signal. As the data is spread across entire bandwidth so frequency selective fading
is reduced. But the major drawback of using OFDMA scheme is the high PAPR value
associated with it, in OFDMA system symbols are transmitted in parallel and power
at any instant is the sum of power contributed by each symbol so PAPR value
increases drastically. Signals with high PAPR value require high linear power
amplifier to avoid excessive inter‐modulation distortion. To achieve this linearity
the amplifier has to operate with large back off from their peak power thus
reducing power efficiency which places burden on portable wireless terminals.
OFDMA is also sensitive to frequency offset introduced in the channel so
transmitter and receiver should always be synchronized with each other. Loss of

39. synchronization may lead to loss of orthogonality thus causing multiple access
interference.
SCFDMA is perhaps answer to all the problems/challenges faced
by OFDMA.SCFDMA is just mere improvement of OFDMA, it is sometimes also
called DFT spread OFDMA. SCFDMA also uses orthogonal subcarriers for data
transmission but unlike OFDMA these symbols are in serial form, this considerably
reduces PAPR. So SCFDMA is the technology in demand for LTE uplink.
FIG. 5.1 OFDMA vs SCFDMA

40. Working principle:
Fig 5.2. SCFDMA transceiver
The above diagram represents block wise implementation of SC‐FDMA and
differences between implementation of OFDMA and SCFDMA. The transmitter
converts binary input signal to a sequence of modulated subcarriers. Binary data
which is being fed into the transmitter is first modulated using suitable modulation
scheme (BPSK, QPSK, QAM, etc..).The data block size of N complex modulated
symbols is generated at a rate Rs symbols/sec. This data is sent to DFT block which
converts time domain signal to frequency domain. N frequency domain symbols
are generated which modulate N out of M symbols. It then maps these N symbols
on M orthogonal subcarrier using any of the mapping scheme (IFDMA, LFDMA, and
BFDMA). The mapped signal is transformed to time domain using IDFT operation,
this time domain signal is converted to serial form using P/S block. After conversion
to serial form data is sent to CP block where cyclic prefix is added which acts as a
guard interval. Cyclic prefix mainly performs two operations:

41.  If the length of cyclic prefix is longer than maximum delay spread then it
avoids inter block interference introduced in the channel due to multipath
propagation.
 As cyclic prefix adds a copy of tail the original signal it converts discrete time
linear convolution into discrete time circular convolution.
Thus the transmitted data propagating through channel can be interpreted as
circular convolution of channel impulse response and data block being transmitted.
As convolution in time domain is analogous to multiplication in frequency domain
which is equivalent to point wise multiplication of DFT frequency samples.
The transmitter block also performs pulse shaping operation to suppress out of
band signal energy. In band limited systems with increase in data rate Inter Symbol
Interference also increases. There are two criteria’s under which pulse shaping is
applied to insure noninterference system, they are:
o The pulse shape exhibits zero crossing at the sampling point of all pulse
interval except its own
o The shape of pulse is in such a way that amplitude of signal decays rapidly
outside the pulse interval.
Rectangular pulses though satisfy first condition but they can’t be used in the
transmitter section as they don’t second criteria. So generally for pulse shaping in
SCFDMA Raised cosine filters/pulse shaper is being used.
Raised Cosine Pulse: A raised cosine pulse shaper is a low pass filter being widely
used in digital communication for pulse shaping operations. The frequency
response |H(f)| of a perfect raised cosine filter is symmetrical about 0 Hz, and is
divided into three parts, it is flat in the pass‐band; it sinks in a graceful cosine curve
to zero through the transition region; and it is zero outside the pass‐band. The
response of a real filter is an approximation to this behavior. In time domain Raise
cosine filter takes the shape of a Sinc pulse. The time domain and frequency domain
expressions for Raised cosine filter is as under:
( ) = . .

42. Here α is called roll‐off factor and its value varies between 0 and 1. This value of α
controls bandwidth occupied by the pulse and broadening of tail of the pulses. For
α=0 the filter acts as an ideal band pass filter but at the same time offers slowest
rate of decay in time domain while at α=1 though the bandwidth increases but the
side lobes decay rapidly. So for optimum value of out of band radiation as well as
PAPR we need to compromise the value of α. For simplicity we have considered
value of α=0.5.
The pulse shaped data which is in digital form is converted to analog form and then
transmitted. The transmitted data travels through channel leading to alteration in
the transmitted signal, errors and channel distortion also gets introduced. Receiver
block receives the signal, converts it to digital form and cyclic prefix added to the
original signal is removed. The serial data after cyclic prefix removal is converted to
parallel form and M point DFT is performed to convert back data to frequency
domain and perform frequency domain equalization. Equalizers remove distortions
introduced in the signal while propagating through the channel. IDFT operation is
performed to revert back frequency domain signal to time domain, this parallel
data is converted to serial form and after demodulating the serial data it is finally
sent to the user on the receiver side.
Sub-Carrier Mapping Schemes: Various types of Sub‐Carrier Mapping Schemes are
being used for mapping transmission symbols. There are many ways of categorizing
these mapping schemes but two of them are of prime importance.
 Distributed : In this scheme data fed into the subcarrier mapping block gets
distributed over entire bandwidth in such a way that unoccupied positions is
replaced by zeros. IFDMA (interleaved FDMA) is a special case of Distributed
FDMA.
 Localized: In this type of mapping data from DFT block is concentrated to only
some part of the bandwidth and thus forms a continuous spectrum of data, rest
part of the bandwidth is filled with zeros.

43. Subcarrier mapping schemes may be further divided into static and channel
dependent scheduling. Static scheduling is independent of channel response
whereas in CDS or channel dependent scheduling scheme subcarriers are
assigned to the users depending upon the frequency response of each user. In
both the mapping schemes DFDMA provides better frequency diversity as
transmitted signal is spread over entire bandwidth.
( ) = ( ) /
Let X(k) be the data after DFT on the transmitter side.
LFDMA: LFDMA stands for localized frequency division multiple access, in this
mapping scheme each user uses only a part of the total bandwidth and adjacent
subcarriers are being used for transmission of data. The major characteristics of
this type of mapping are:
 Block wise structure provides robustness to carrier frequency offsets as
well as high multi user diversity in case of adaptive resource allocation.
 LFDMA shows lesser frequency diversity as subcarriers allotted to each
user is localized within a part of the bandwidth.
 Better BER performance but poorer PAPR performance compared to
IFDMA.

44. Fig. 5.3 LFDMA data block
The diagram above represents LFDMA symbol mapping operation being performed
on output of DFT block. Input block size or symbols per block of 4 is spread to
number of subcarriers which is 12 here. Number of Users or terminals is 3.

45. Fig. 5.4 Allocation of subcarriers in LFDMA
Algorithm:
Algo_LFDMA(a,M,Q,N)
Here a is the DFT output, M= block size of array a, N is total number of subcarriers.
( , ) =
; = . +
n=0, 1, 2…..N‐1; q=0, 1, 2…..M‐1;
ML
k
represents the mapping matrix and final data after mapping is given by ML
k
.X(k).
IFDMA: IFDMA stands for Interleaved Frequency Division Multiple Access, in this
type of subcarrier mapping data from DFT block is mapped on subcarriers which
are equaly spaced and are spread over entire bandwidth. Unoccupied places are
initialized with zero. The major characteristics of IFDMA are:
 IFDMA provides larger frequency diversity as compared to LFDMA as
subcarriers are distributed over entire bandwidth.
 PAPR performance gets improved but BER suffers as compared to LFDMA.
 IFDMA provides flexiblity in subcarrier allocation.
Algo_LFDMA (a, M, N)
{
1. Initialize a linear array b of size N with zeros
2. i =1;
3. While( i <=M)
a. b[i] <‐ a[i];
b. i <‐ i+1;
4. Return b;
}

46. Fig 5.5. IFDMA data block
The diagram above represents IFDMA subcarrier mapping schemes. Number
of users=3,input block size=4,Number of subcarriers=12.

47. Fig.5.6 Subcarrier allocation representation for three users.
Algorithm:
Here a represents data from DFT block, M is the block size of a, N=total number of
subcarriers Q=N/M.
( , ) =
; = . +
n=0, 1, 2…..N‐1; q=0, 1, 2…..M‐1;
MI
k
represents the mapping matrix and final data after mapping is given by MI
k
.X(k).
B-IFDMA: B‐IFDMA stands for Block Interleaved Frequency Division Multiple
Access. B‐IFDMA is considered as hybrid symbol mapping technique which
possesses both the qualities of IFDMA and LFDMA. In B‐IFDMA unlike IFDMA we
take a block of data and is mapped on adjacent group of subcarriers. Rest of the
unoccupied positions is initialized to 0. The main characteristics of B‐IFDMA are:
 It has better robustness to carrier frequency offset as compared to IFDMA
as symbols are mapped in group which provides advantages of LFDMA.
 As the symbols are spread over entire bandwidth so it provides better
frequency diversity as compared to LFDMA.
Algo_IFDMA (a, M, Q, N)
{
1. Initialize a linear array b of size N with zeros.
2. V=1, i=1;
3. While( i<= M)
a. b[V] <‐ a[i];
b. i <‐ i+1;
c. V <‐ V+Q;
4. Return b;
}

48. Fig.5.7 B‐IFDMA data block
The above diagram represents block interleaved FDMA with block size=2, number
of users=3, Number of sub‐carriers=12.
Algorithm:
Algo_BIFDMA (a, M, Q, N, block_size)
{
1. Initialize linear array b of size N with zeros.
2. V=0, i=1,j=1, sp=N*block_size/M;
3. While( i<=M )
a. While(j<=block_size)
i. b[V+i]  a[i];
ii. ii+1;
b. VV + sp;
4. Return b;
}

49. Here a represents data block after DFT, M represents length of a, N=total number
of subcarriers, Q=N/M, block_size represents number of blocks which are mapped
together.
( , = . + ) =
; = . + + . _
n=0, 1, 2…..N‐1; r=0, 1, 2….block_size ; t=0, 1, 2, 3…….T‐1 where T is number of
block per user.MB
k
represents the mapping matrix and final data after mapping is
given by MB
k
.X(k).

50. Fig 5.7.a. Data blocks in different subcarrier mapping schemes

51. FIG.5.8: PAPR plot for IFDMA, LFDMA, DFDMA, BIFDMA with block size=2
Fig 5.9. PAPR plot for different roll‐off factors in IFDMA

52. Fig 5.10. PAPR plot for diff. number of subcarriers in IFDMA
BER: BER is an important parameter for analyzing systems that transmit digital
data. BER or Bit Error Rate as its name suggests is the rate at which errors occur in
digital transmission. It is the ratio of number of error bits divided by total number
of bits transmitted.
=
BER gives an idea about nature of the medium/channel through which transmitted
data travels. For good medium with high SNR(Signal to Noise Ratio) BER is very
small.
Factors affecting Bit Error Rate are:
 Interference: The level of interference present in a system severely affects
the BER as it hampers the original transmitted signal. This interference level
is set by external factors and can’t by changed by system design.

53.  Reducing Bandwidth: BER can be minimized by reducing the bandwidth,
lower levels of noise will be received thus signal to noise ratio improves
which results in improved data throughput.
 Increased transmitter power: By increasing the transmitted power the power
per bit will be improved thus data loss incurred due to noise will be
minimized leading to improved BER performance.
PAPR: PAPR or Peak to Average Power ratio as its name suggests is the ratio of
peak power to average power of a signal. Peak and Average Power of a signal is
given by:
Peak Power of transmitted signal = Maximum (x(t)* conjugate of x(t));
Average Power of transmitted signal= Mean (x(t) * conjugate of x(t));
Where x(t) represents the transmitted signal.
CCDF (Complementary cumulative Distribution Function) was used for plotting
PAPR values. CCDF of PAPR is the probability that PAPR value is higher than a
certain value PAPR0. The CDF of a given data block is given as
F (z)=1‐exp(z)
The CCDF of the PAPR of the data block is given by
Pr (P AP R > z) = 1‐Pr (PAPR<=z)
= 1‐F (z) N
= 1‐(1‐exp (‐z)) N

54. CHAPTER-6
SIMULATION RESULTS
UPLINK:
Simulation results using QPSK modulation and MMSE equalization at BER 10e-5
CHANNEL SCFDMA‐IFDMA
(SNR IN DB)
SCFDMA‐LFDMA
(SNR IN DB)
OFDM
(SNR IN DB)
SCFDE
(SNR IN DB)
AWGN 12.8 13 13 13(APPROX)
PEDESTRIAN 14.2(5 tap)
13.8(3 tap)
8.2(5 tap)
10.3(3 tap)
16 14.5
VECHULAR 17.6 7.4 20
UNDERWATER 23 10.4 28 22.5
PAPR(10^-4)
(roll off factor 0.5)
4.5 7.4 10.5

55. Fig 6.1. BER plot for IFDMA using MMSE equalizers
Fig 6.2. BER plot for LFDMA using MMSE equalizers

56. FIG6.3: SCFDE BER plot using MMSE equalizer
FIG.6.4: OFDM BER plot using MMSE equalizer

57. FIG.6.5: PAPR comparison at roll‐off 0.5 using Raised cosine Pulse shaping
Fig6.6: BER comparision for OFDM and SC‐FDE IN underwater channel

58. DOWNLINK:
Simulation results using QPSK modulation and MMSE equalization at BER 10e-5
CHANNEL SCFDMA‐IFDMA
(SNR IN DB)
SCFDMA‐LFDMA
(SNR IN DB)
OFDMA‐IFDMA
(SNR IN DB)
OFDMA‐LFDMA
(SNR IN DB)
AWGN 13 13 25 24.8
PEDESTRIAN 15 10.5 28 22
VECHULAR 17.6 15 35 26.5
UNDERWATER 23 14 >40 25.5
PAPR(10^-4)
QPSK(roll off factor 0.5)
9 10.1
PAPR(10^-4)
16QAM(roll off factor 0.5)
9.5 12.1
Fig6.7: BER plot for OFDMA‐IFDMA using MMSE equalizer for 4 users

59. Fig 6.8: BER plot fro OFDMA‐LFDMA using MMSE equalizer for 4 users
FIG 6.9: BER OF SCFDMA‐IFDMA using MMSE equalizer for 4 users

60. FIG 6.10: BER OF SCFDMA‐LFDMA using MMSE equalizer for 4 users
Fig 6.11: PAPR plot for QPSK downlink

61. Fig 6.12: PAPR plot for QPSK for OFDMA and SCFDMA respectively

62. CHAPTER-7
CONCLUSION AND FUTURE WORK
OFDM makes efficient use of available spectrum by allowing overlapping among the
carriers. It basically converts the high data rate stream in to several parallel lower data
rate streams and thereby eliminating the frequency selective fading. It has been seen that
the OFDM is a powerful modulation technique that is capable of high data rate and is able
to eliminate ISI but high PAPR makes it uneconomical for use at various places, SCFDE
provides better alternative by reducing the PAPR of OFDM besides having other
advantages. The simulation results above validate the analogy as BER of SCFDE is better
compared to OFDM.
SCFDMA is a promising technique for uplink communication providing high data rates.
Single carrier reduces the high PAPR in OFDM making it efficient for use in uplink, though
SCFDMA performs better than OFDMA in terms of BER and PAPR but receiver simplicity
and easier carrier allocation of OFDMA makes it useful in downlink. Various subcarrier
mapping perform differently and can be used cleverly to give the optimum result. Though
BER of LFDMA is better than IFDMA but in case of PAPR the situation gets exactly
reversed. BIFDMA seem to be a better alternative which provides advantages of both
IFDMA and LFDMA. The simulation results validate the fact that underwater channel is
harsher as compared to other channels used above and thus gives poorer performance.
Underwater communication has lots of scope for future developments and there is lot yet
to be explored in this field of communication. Further improvements in subcarrier
mapping schemes like making the allocation scheme adaptive can improve the
performance of transmission schemes, Better equalization and carrier frequency offset
may yield better results.

63. References
1. H. G. Myung, J. Lim, and D. Goodman, “Single carrier fdma for uplink wireless
transmission,” Vehicular Technology Magazine, IEEE, vol. 1, no. 3, pp. 30–38,
2006.
2. Myung Hyung G. Single carrier FDMA. Presentation Slides; 2008.
(hgmyung.googlepages.com/scfdma.pdf)
3. Rameez Ahmed, ”An Experimental study of OFDM in software defined
acoustic testbed”,IRIS,2010.
4. J. G. Proakis, Digital Communications. McGraw‐Hill, NY, 2001.
5. Harsha S. Eshwaraiah , A.chockalingam,” SC‐FDMA for multiuser
communication on the downlink”, IEEE 2013
6. Hyung G. Myung, Single Carrier FDMA: A new air interface for long term
evolution
7. www.mathworks.com
8. www.wikipedia.org