IRJET- PAPR Reduction in UF-OFDM and F-OFDM 5G Systems using ZCT Precoding Technique

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 04 | Apr 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 2848
PAPR Reduction in UF-OFDM and F-OFDM 5G Systems using ZCT
Precoding Technique
Naziya Begum1, Dr. Muhieddin Amer2
1 Graduate Student, Dept. of Electrical Engineering, Rochester Institute of Technology, Dubai, UAE
2Professor, Department Chair, Dept. of Electrical Engineering, Rochester Institute of Technology, Dubai, UAE
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract – 5G networks employ multicarrier modulations
(MCM)s such as filtered-orthogonal frequency division
multiplexing (F-OFDM) and universal filtered orthogonal
frequency division multiplexing (UF-OFDM) as a solution to
overcome the challenges of high data rates and spectral
efficiency [1]. However, MCMs have high peak to average
power ratio (PAPR) which drives the power amplifier (PA)
in the linear region resulting in the reduced efficiency. To
overcome this problem PAPR should be reduced [1-4]. In this
paper, precoding based PAPR reduction techniques such as
Discrete Fourier Transform (DFT), Discrete Cosine
Transform DCT) and Zadoff-Chu Transform (ZCT) are
implemented using MATLAB for F-OFDM and UF-OFDM
systems. Comparison analysis shows that Zadoff-chu
Transform precoding technique for PAPR reduction gives
better results. Hence, ZCT precoding is proposed for both F-
OFDM and UF-OFDM systems. Simulation results show that
proposed technique lowers down the power spectral density
(PSD) tails at the PA output, reduces PAPR and
instantaneous to average power ratio (IAPR) and conserves
the bit error rate (BER) in the AWGN channel.
Key Words: 5G, UF-OFDM, F-OFDM, peak to average
power ratio (PAPR), IAPR, precoding, Zadoff-Chu
Transform (ZCT), Power Spectral Density (PSD), BER.
1. INTRODUCTION
For 5G systems, mm-wave communication is
envisioned to be the key component to meet the demands
of high data rates, high spectral efficiency and low latency
[5]. For 5G mm-wave communication, selection of
waveform is an important criterion. 4G systems employ
OFDM (orthogonal frequency division multiplexing) for
downlink and DFTS-OFDM (Discrete Fourier Transform-
spread-OFDM) for transmission in uplink. Apart from
several important features such as low complex
transceiver design, easy integration with MIMO,
robustness to frequency selective channel, OFDM comes
with the major drawbacks of high PAPR and high OOB
(out-of-bound) emissions [5]. To improve OOB emissions,
several MCMs have been proposed for 5G systems such as
F-OFDM and UF-OFDM [2], [6-7]. Compared to OFDM,
these filtered MCMs provide lower OOB emission, lowers
power spectral density (PSD) side lobes and preserves the
OFDM based transceiver design [2],[6]. However, these
modulation schemes have high PAPR [2]. The high PAPR
results in the high design complexity of Analog to Digital
(A/D) and Digital to Analog (D/A) converters and drives
the operation of PA in the linear region which increases
the cost and complexity of PA and reduces the efficiency
RF high power amplifier (HPA) [1], [3], [8]. Thus, PAPR
reduction techniques are conventionally used which solve
the design complexity of A/D and D/A converters and
increases the transmit power, improves received SNR for
the same range, resulting in the increased efficiency [1],
[8].
Several PAPR reduction techniques have been
suggested in the literature as presented in papers [1-4],
[8-12]. However, the precoding based PAPR reduction
techniques seem to be promising as they are linear and
simple to implement without requiring the side lobe
information [2]. Earlier, several precoding techniques
have been proposed as a solution for PAPR reduction in
multicarrier modulation systems OFDM, F-OFDM, and UF-
OFDM, as supported in papers [2-3],[8], [10-12].
Comparison analysis of some precoding techniques for
OFDM is shown in paper [3], ZCT Precoding is
implemented earlier on OFDM systems as shown in [8-10],
DFT precoding technique is implemented in paper [11-12]
for OFDM systems. DCT Precoding Techniques is
implemented for OFDM system as shown in paper [13].
This has motivated us to implement ZCT precoding
technique for PAPR reduction in F-OFDM and UF-OFDM
multicarrier modulations that are the main candidates of
5G cellular communication system.
This paper presents the MATLAB based implementation
and comparison analysis of the precoding techniques DFT,
DCT and ZCT to minimize the PAPR in both F-OFDM and
UF-OFDM 5G systems. Comparison analysis is based on
parameters, PAPR, IAPR, PSD and BER. MATLAB
simulation results show that PAPR and IAPR of F-OFDM
and UF-OFDM are reduced, PSD at the PA output is
improved and BER of considered AWGN channel is
unaffected.
This paper is presented as follows:
In section 2, some of the precoding techniques are
discussed. In section 3, adopted precoding technique
(ZCT) for F-OFDM and UF-OFDM systems is detailed. In

section 4, MATLAB simulation results show the
comparison analysis of ZCT with other precoding
techniques like DFT and DCT, based on PAPR, IAPR, PSD
and BER. Finally, paper conclusion is given in section 5,
which shows that Zadoff-chu precoding proves to be the
more efficient technique for PAPR reduction in F-OFDM
and UF-OFDM systems compared to other precoding
techniques.
2. PRECODING TECHNIQUES
Main objective of using precoding techniques is to
obtain a signal with low PAPR. The precoding-based PAPR
reduction techniques are very promising since they are
linear and simple to implement without requiring the side
lobe information. Precoding-based techniques reduces
PAPR without increasing the complexity of the system [3].
There are three different precoding techniques used in
this paper: Discrete Cosine Transform DCT), Zadoff-Chu
Transform (ZCT) and Discrete Fourier Transform (DFT).
2.1 Zadoff-Chu Transform (ZCT)
The Zadoff-Chu Transform is a matrix formed by the
general polyphase sequences having properties of
correlation, which is optimum. Important property of
Zadoff-Chu code is that, they have ideal auto correlation
periodically and magnitude of cross correlation is constant
for a sequence length of L [3].
They are defined by the following equation:
(2.1)
Where , is any integer, is the
code index, is the length of sequence and prime
number √ .
In case of a prime number N, the set of Zadoff-chu codes
consist of L-1 number of sequences.
2.2 Discrete Cosine Transform (DCT)
Mathematical expression for the Discrete Cosine
Transform of an input data sequence x (n) of length N is
given by [3]:
(2.2)
Where k is an integer.
2.3 Discrete Fourier Transform (DFT)
The DFT of a sequence x (n) of length N and IDFT of X
(K) can be expressed as [11-12]:
(2.3)
Where k and n are integers.
3. PAPR REDUCTION IN F-OFDM and UF-
OFDM USING ZCT PRECODING
In this proposed system a precoding-based PAPR
reduction is implemented by using the Zadoff-chu
transform precoding method for F-OFDM and UF-OFDM
systems as well. In this method, F-OFDM signal is
transformed to single carrier signal and UF-OFDM signal is
converted to a lower order summation of signals having
single carrier. The flow diagram of the proposed system for
UF-OFDM as illustrated in Fig -1 and Fig -2 shows the flow
diagram for F-OFDM.
In this system, first the input data sequence is
generated randomly and then the generated data symbols
are subjected to the modulation process. For that in our
proposed system, we use the QAM modulation. After the
modulation process, the data is converted from the serial to
parallel format for further process. After that, the
converted parallel data is subjected to the Fourier
transform process and corresponding filters filter the
signal. Here Chebyshev filter is used for UF-OFDM
precoding, spectrum-shaping filter is used for F-OFDM
precoding, and the signal is precoded by the ZCT method
after that the signal is passed through the channel then the
reversal operations are performed at the receiver as shown
in the flow diagrams of Fig-1 and Fig-2. In addition, the
performance of the proposed system is evaluated by
analyzing the parameters such as BER, PAPR, IAPR,
normalized (PSD) responses obtained using MATLAB
simulations.
3.1 Description for ZCT Precoded system
At the transmitter, the digital data to be transmitted is
modulated first. Here the modulation technique used in
this work is QAM. After the modulation, the modulated
data is converted into parallel data stream for efficient and
faster utilization of bandwidth. Then the data stream is
precoded using a Zadoff-chu transform precoding method.
The Zadoff-chu codes are discussed in section 2.1 and
represented by equation (2.1).

In the ZCT precoding based MCMs systems, the
baseband modulated data is passed through serial to
parallel converter which generates a complex vector of
size N that can be written as X= [X0, X 1, X 2,…X N-1]. Then
ZCT precoding is applied to this complex vector, which
transforms this complex vector into new vector of same
length. After that the precoded data can be represented as
time domain signal with the help of an Inverse Fast
Fourier Transform (IFFT). Then the time domain data is
extended by adding cyclic prefix to each symbol to solve
the Inter Symbol Interference (ISI) as well as Inter carrier
interference (ICI) problems. These signals are then filtered
using Chebyshev filtering for UF-OFDM systems and by
spectrum shaping filtering for F-OFDM systems [2].
The ZCT technique for UF-OFDM block consist of
precoding matrix before the subset assignment IFFT block.
The precoding matrix is of the same size as subcarrier
vector that are allocated [2]. The dimension of the ZCT
precoding matrix A is N x N which can be obtained by,
[ ] (3.1)
Where, amn is obtained by substituting k = mN + n in
equation (2.1) with m rows and n columns.
The precoded constellation symbols can be given as follows
∑ (3.2)
Therefore, the output signal of UF-OFDM can be expressed
as follows [2],
∑ ∑ ̃ (3.3)
Where, ̃ is the OFDM signal after applying the precoding
scheme and it is given by,
̃ ∑ ∑ (3.4)
The resultant frequency domain of the precoding signal can
be converted into time domain signal using IFFT and this
can be expressed as
Denoting by , and ̃ can be expressed as
̃ ∑ (3.5)
̃ ( ) (3.6)
Therefore, by replacing ̃ by in (3.3)
∑ ∑ (3.7)
By setting ∑ , the UF-OFDM output
signal can be obtained as,
∑ (3.8)
Where, is the single carrier signal (SC) at the output of
the pulse-shaping filter. Consequently, the precoded UF-
OFDM signal is the summation of B SC signals. Even though
UF-OFDM signal is still a multicarrier signal, the number of
the subcarriers is reduced from the IFFT size M to the
number of the sub-sets B. The UF-OFDM PAPR is reduced,
as it is a function of a smaller number of subcarriers [2].
Now the precoding scheme for F-OFDM can be given as,
∑ ∑ [ ] (3.9)
Where,
∑ (3.10)
The resultant frequency domain of the precoding signal can
be converted into time domain signal using IFFT and this
can be expressed as follows:
By setting ̃ , we have (̃ )
Hence,
∑ [ ] ∑ (̃ )
∑ [ ] ( (̃ )) (3.11)
So that ∑ ̃ [ ] (3.12)
Therefore, is the SC signal at the output of the pulse
shaping filter and hence the F-OFDM system becomes
equivalent to a SC system [2].
After this for analysis purpose, AWGN channel is
considered for transmission of signal. At the receiver
section, the reverse processes of transmitter section are
employed. i.e., the received serial data is converted to
parallel form to apply FFT to convert the time domain
signal into a frequency domain signal. Then the frequency
domain signal is processed with reverse precoding and
demodulated using QAM demodulator. Finally, the
demodulated signal is converted back into serial data.
3.2 DCT and DFT based precoded systems
For the sake of comparing performance of ZCT,
precoding method with other precoding techniques, DCT

and DFT based precoding is implemented on F-OFDM and
F-OFDM systems. The principle of operation is same as
explained in previous section for ZCT preceded system
except for the precoding matrix used.
Fig -1: Flow Diagram of UF-OFDM system employing ZCT precoding
Fig -2: Flow Diagram of F-OFDM system employing ZCT precoding
Fig -3: Magnitude response of the spectrum-shaping filter

The flow diagram of the proposed system for UF- OFDM
as illustrated in Fig -1 and Fig -2 shows the flow diagram
for F-OFDM. Here, precoding matrix is implemented based
on equations for DCT and DFT as presented in section 2.2
and 2.3 respectively. All other blocks and processes
remains as ZCT precoded system.
In this system, first the input data sequence is
generated randomly and then the generated data symbols
are subjected to the modulation process. For that in our
proposed system, we use the QAM modulation. After the
modulation process, the data is converted from the serial
to parallel format for further process. After that, the
converted parallel data is subjected to the Fourier
transform process and the signal is filtered by
corresponding filters. Here Chebyshev filter is used for UF-
OFDM precoding and spectrum-shaping filter is used for F-
OFDM precoding and the signal is precoded by the DCT
and DFT method respectively, after that the signal is
passed through the channel then the reversal operations
are performed as shown in the flow diagrams of Fig-1 and
Fig-2. And the performance of the proposed ZCT system is
evaluated by analyzing and comparing the parameters
such as BER, PAPR, IAPR, normalized (PSD) values
obtained using MATLAB simulations for DFT, DCT and ZCT
precoding techniques for F- OFDM and UF-OFDM systems.
4. SIMULATION RESULTS
In section, analysis of the MATLAB simulation results is
presented for F-OFDM and UF-OFDM modulations using
precoding techniques ZCT, DFT and DCT. First, simulation
analysis of PAPR and IAPR is carried out for both the F-
OFDM and UF-OFDM and results will be compared for
different precoding techniques. Then, Power spectral
density function (PSD) of the signal at the input and output
of power amplifier (PA) is analyzed for both F-OFDM and
UF-OFDM employing the different precoding techniques:
ZCT, DCT and DFT with 16 and 64- QAM.
Table -1: Signal Parameters
DFT size: M 1024
Allocated subcarriers: N 480
Constellations 16-QAM, 64-QAM
UF-OFDM: Filter Chebyshev
UF-OFDM: Filter length: L 72
UF-OFDM: Side lobe attenuation 40 dB
UF-OFDM: Sub-set size: NB 12
UF-OFDM: Sub-set number: B 40
F-OFDM: Filter Truncated raised root cosine
[2]
Table -1 shows the signal parameters considered for
MATLAB simulations. And Fig- 3 shows the output of
truncated raised root cosine spectrum shaping filter.
4.1 Analysis of PAPR and IAPR
In the MATLAB based simulation results, perform
analysis of PAPR and IAPR is expressed in terms of
Complementary Cumulative Distribution Function (CCDF)
[3]. Fig- 4 and Fig -5 shows PAPR and IAPR performance
for different precoding techniques applied to both F-OFDM
and UF-OFDM systems.
Fig -4: CCDF PAPR based comparison of ZCT precoding with
other precoding techniques for F-OFDM and UF-OFDM.
Table -2: CCDF PAPR based comparison of ZCT precoding with
other precoding techniques for F-OFDM and UF-OFDM
Table- 2 presents the comparison results at a level of 10-3
on the graph of PAPR of Fig -4. It shows that, when ZCT
precoding technique is applied PAPR is reduced to 6 dB
and 6.6 dB for F-OFDM and UF-OFDM systems respectively.
Which is up to 1 dB less than the DFT precoding and about
3 dB less than DCT precoding technique. Hence, it can be
concluded that ZCT precoding has proven to be as
predicted better precoding technique than other
techniques considered in his paper.
Table- 3 presents the comparison results at a level of 10-2
on the graph of IAPR of Fig -5. It shows that, when ZCT
precoding technique is applied IAPR is reduced to 4.5 dB
for F-OFDM and 5.1 dB for UF-OFDM systems. Here IAPR
ZCT-F-
OFDM
ZCT-
UF-
OFDM
DFT-F-
OFDM
DFT-
UF-
OFDM
DCT-F-
OFDM
DCT-F-
OFDM
6 dB 6.6 dB 7.2 dB 8.5 dB 9.2 dB 10 dB

using ZCT is about 1.5 dB less than that of DFT precoding
and about 2.3 dB less than DCT precoding technique.
Hence, it is noted that ZCT precoding is a better precoding
technique.
Fig- 5: CCDF IAPR based comparison of ZCT precoding with
Table -3: CCDF IAPR based comparison of ZCT precoding with
other precoding techniques for F-OFDM and UF-OFDM
ZCT-F-
OFDM
ZCT-UF-
OFDM
DFT-F-
OFDM
DFT-
UF-
OFDM
DCT-F-
OFDM
DCT-F-
OFDM
4.5 dB 5.1 dB 5.95 dB 6.7 dB 6.8 dB 7.5 dB
4.2 Analysis of PSD and BER
PSD of power amplifier output and Bit error rate of
AWGN channel are analyzed here. In the case of 16-QAM
and 64-QAM and AWGN channel, the BER is analyzed here.
Fig -6: Normalized PSD-based comparison of ZCT precoding with
Table -4: PSD based comparison of ZCT precoding with other
precoding techniques for F-OFDM and UF-OFDM at frequency =
15.36 MHz
Fig- 6 and Fig -7 show PSD and BER performance for
different precoding techniques applied to both F-OFDM
and UF-OFDM systems. Table- 4 presents the comparison
results at the frequency of 15.36 MHz on the graph of PSD
of Fig -6. It shows that, when ZCT precoding technique is
applied PSD performance is improved to -32 dB and -44
dB for F-OFDM and UF-OFDM systems respectively. Which
is better than the DFT precoding and DCT precoding
techniques. Hence, it can be concluded that ZCT precoding
has provided better results than other precoding
techniques.
Fig -7: Comparison of BER performance for ZCT-UF-OFDM with
other precoding techniques for 16-QAM and 64-QAM
constellations.
Fig -7 shows BER performance of ZCT precoding
technique as applied to UF-OFDM of 16-QAM and 64-QAM
constellations in comparison to DFT and DCT precoding
techniques. It is observed that the PAPR CCDF
performance of the system has been improved and bit
error rate of the AWGN channel is conserved.
5. CONCLUSIONS
In this paper, a PAPR reduction technique using the
Zadoff Chu transform precoding for the UF-OFDM and the
ZCT-F-
OFDM
ZCT-
UF-
OFDM
DFT-F-
OFDM
DFT-
UF-
OFDM
DCT-F-
OFDM
DCT-F-
OFDM
-32 dB -44 dB -24 dB -26 dB -29 dB -26 dB

F-OFDM modulation scheme was proposed. The proposed
system shows better performance for ZCT precoding
applied to F-OFDM and UF-OFDM than the system with
DCT and DFT as evident in the simulation results. The
performance of the proposed system is evaluated by
comparing the BER, PAPR, IAPR and normalized PSD
values with the DCT and DFT precoded systems. i.e., when
ZCT precoding technique is applied PAPR is reduced to 4.5
dB for F-OFDM and 5.1 dB for UF-OFDM systems.
In this system, BER in an AWGN channel is conserved.
For further studies, the system could be modeled for
Rayleigh fading or multipath fading channel. Further
research could be extended to focus on the Discrete
Wavelet Transform (DWT) precoding based PAPR
reduction for MCM schemes.
In future the problems due to uplink transmission
should be considered and need to be solved. In addition, a
new technique of Partial transmit sequence will be
implemented for reducing the PAPR in 5G systems.
REFERENCES
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BIOGRAPHIES
Naziya Begum received her B.E.
degree in Electronics and
Communication Engineering from
VTU-Visveswaraya Technology
University (2003), India and is
currently pursuing her master’s
degree M.S. in Electrical
Engineering, Communications
System specialization, at Rochester
Institute of Technology (RIT),
Dubai, United Arab Emirates.
Dr. Muhieddin Amer is a professor
of Electrical Engineering at RIT
Dubai. He received his PhD degree
in Electrical Engineering from the
University of Texas at Arlington in
1999. His research interest
includes MIMO systems and
interference control in 4G and 5G
wireless systems.

IRJET- PAPR Reduction in UF-OFDM and F-OFDM 5G Systems using ZCT Precoding Technique

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IRJET- PAPR Reduction in UF-OFDM and F-OFDM 5G Systems using ZCT Precoding Technique