This document proposes a method to reduce peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems using high PAPR sequence scrambling. It uses an array of scramblers to change high PAPR sequences into lower PAPR sequences. Scrambling stops once the PAPR goes below a threshold, reducing complexity compared to conventional selective mapping. Simulation results show the method reduces PAPR over 4dB and most sequences require few or no scramblers. It provides a complexity-reduction tradeoff by selecting the scrambler array size and threshold value.
There are many types of wireless channel impairments such as noise, path loss, shadowing, and fading and impairment Mitigation techniques should be adopted according to system requirements and channel environments.
There are many types of wireless channel impairments such as noise, path loss, shadowing, and fading and impairment Mitigation techniques should be adopted according to system requirements and channel environments.
Design Ofdm System And Remove Nonlinear Distortion In OFDM Signal At Transmit...Rupesh Sharma
although OFDM seems to be a solution to keep up with
the demand of increasing data rates, it has some drawbacks.
Sensitivity to high PAPR is the most significant of these
drawbacks. The main objective of this paper was to investigate
and document the effects of PAPR on the performance of OFDM
based digital communications under different channel conditions.
A step-by-step approach was adopted in order to achieve the
objective of this paper. The first step is to provide a basic
background on the principles of OFDM. The reasons for the
PAPR and a theoretical analysis of these effects on OFDM
systems are documented. The OFDM system has a high peak-toaverage
power ratio (PAPR) that can cause unwanted saturation
in the power amplifiers, leading to in-band distortion and out-ofband
radiation. To be able to observe the system behavior, the
simulation results for different channel models are presented in
graphical form. Next, the simulation results obtained in this work
are compared to the simulation results reported in related studies
orthogonal frequency division multiplexing(OFDM)
its orthogonal frequency multiplexing topic basicallly in digital signal processing , network signal and system , it also helpful in engineering course either electrical or electronics and communication engineering.
satellite communication jntuh
Satellite Link Design: Basic Transmission Theory, System Noise Temperature, and G/T Ratio,
Design of Down Links, Up Link Design, Design Of Satellite Links For Specified C/N, System Design
Examples.
Multiple Access: Frequency Division Multiple Access (FDMA), Inter modulation, Calculation of C/N,
Time Division Multiple Access (TDMA), Frame Structure, Examples, Satellite Switched TDMA
Onboard Processing, DAMA, Code Division Multiple Access (CDMA), Spread Spectrum Transmission
and Reception.
In this chapter we examine the capacity of a single-user wireless channel where transmitter and/or receiver have a single antenna. We will discuss capacity for channels that are both time invariant and time varying. We first look at the well-known formula for capacity of a time-invariant additive white Gaussian noise (AWGN) channel and then consider capacity of time-varying flat fading channels. We will first consider flat fading channel capacity where only the fading distribution is known at the transmitter and receiver. We will also treat capacity of frequency-selective fading channels. For time -invariant frequency-selective channels the capacity is known and is achieved with an optimal power allocation that water-fills over frequency instead of time. We will consider only discrete-time systems in this chapter.
An Overview : Peak to Average Power Ratio (PAPR) in OFDM system using some ne...Z AL Hashemi
An Overview : Peak to Average Power Ratio (PAPR) in OFDM system using some new PAPR techniques (with matlab code)
By
Zainab Saad Hadi AL-Hashemi
A graduate of University of Baghdad, College of Engineering Electronic & Communications Engineering Department
Design Ofdm System And Remove Nonlinear Distortion In OFDM Signal At Transmit...Rupesh Sharma
although OFDM seems to be a solution to keep up with
the demand of increasing data rates, it has some drawbacks.
Sensitivity to high PAPR is the most significant of these
drawbacks. The main objective of this paper was to investigate
and document the effects of PAPR on the performance of OFDM
based digital communications under different channel conditions.
A step-by-step approach was adopted in order to achieve the
objective of this paper. The first step is to provide a basic
background on the principles of OFDM. The reasons for the
PAPR and a theoretical analysis of these effects on OFDM
systems are documented. The OFDM system has a high peak-toaverage
power ratio (PAPR) that can cause unwanted saturation
in the power amplifiers, leading to in-band distortion and out-ofband
radiation. To be able to observe the system behavior, the
simulation results for different channel models are presented in
graphical form. Next, the simulation results obtained in this work
are compared to the simulation results reported in related studies
orthogonal frequency division multiplexing(OFDM)
its orthogonal frequency multiplexing topic basicallly in digital signal processing , network signal and system , it also helpful in engineering course either electrical or electronics and communication engineering.
satellite communication jntuh
Satellite Link Design: Basic Transmission Theory, System Noise Temperature, and G/T Ratio,
Design of Down Links, Up Link Design, Design Of Satellite Links For Specified C/N, System Design
Examples.
Multiple Access: Frequency Division Multiple Access (FDMA), Inter modulation, Calculation of C/N,
Time Division Multiple Access (TDMA), Frame Structure, Examples, Satellite Switched TDMA
Onboard Processing, DAMA, Code Division Multiple Access (CDMA), Spread Spectrum Transmission
and Reception.
In this chapter we examine the capacity of a single-user wireless channel where transmitter and/or receiver have a single antenna. We will discuss capacity for channels that are both time invariant and time varying. We first look at the well-known formula for capacity of a time-invariant additive white Gaussian noise (AWGN) channel and then consider capacity of time-varying flat fading channels. We will first consider flat fading channel capacity where only the fading distribution is known at the transmitter and receiver. We will also treat capacity of frequency-selective fading channels. For time -invariant frequency-selective channels the capacity is known and is achieved with an optimal power allocation that water-fills over frequency instead of time. We will consider only discrete-time systems in this chapter.
An Overview : Peak to Average Power Ratio (PAPR) in OFDM system using some ne...Z AL Hashemi
An Overview : Peak to Average Power Ratio (PAPR) in OFDM system using some new PAPR techniques (with matlab code)
By
Zainab Saad Hadi AL-Hashemi
A graduate of University of Baghdad, College of Engineering Electronic & Communications Engineering Department
Hybrid approach to solve the problem of papr in ofdm signal a surveyeSAT Journals
“Orthogonal frequency division multiplexing
method used to achieve the today’s need of wireless communication
3GPP Association for the use of LTE. The
higher data rate, higher bit rate, mitigated delay spread, lower multipath distortion,
OFDM system has few major issues associated with
ratio (PAPR)” associated with the signal.
interleaved OFDM, selective mapping (SLM)
windowing, clipping, filtering, tone rejection(TR), tone injection(TI), compandin
As the aviation community continues to implement Next Generation Air Transportation System (NextGen) initiatives, operators want to know what the initiatives are and how they affect individual operators. The question always comes down to value: If I upgrade my aircraft, what will I get for the often substantial investment?
Datalink services are available in most of the world’s oceanic routes and in some domestic airspace, as well. The services provide invaluable support at transfer points where aircraft enter or exit domestic airspace and enter oceanic. The enhanced communication abilities aid the ATC on both sides of tracks and particularly when a controller at one center hands off an aircraft to another ATC center because with a FANS-equipped aircraft, the handoff occurs seamlessly behind the scenes.
Along the routes that have not yet been mandated for FANS, the flight crew has to call an ATC and give verbal updates as to their whereabouts with no support from ground surveillance. This lack of accurate position data is a problem because if an ATC doesn’t know exactly where an aircraft is, the ATC has to maintain greater distance between aircraft. With FANS, an ATC can track aircraft along the entire route and safely and efficiently track and accommodate more aircraft in the airspace. The majority of these enhanced services are available to FANS 1/A-equipped aircraft. Ground facilities around the world are upgrading to FANS work stations.
Which datalink service a particular operator selects depends entirely on what equipment is available for the type of aircraft.
FLY SAFE!!!!
Bessel Companding Transform for reducing PAPR, OBI and BER in OFDM SystemsIOSR Journals
Abstract : Orthogonal Frequency division multiplexing (OFDM) is a very popular technique in wireless communications which provides excellent robustness to channel fading and immune to interference. OFDM is one of a popular modulation technique for transmitting large amounts of digital data over radio carriers. One of the major problems that had been observed in this is the Peak-To Average power Ratio (PAPR). PAPR is a distortion that had occurred due to large number of sub carriers that are used in OFDM for modulating the digital data. Many techniques were available to reduce the PAPR in OFDM systems, among them the companding technique can be used to enhance the OFDM transmission performance by decreasing the PAPR effectively and hence BER. Here we proposed “Bessel Companding Algorithm” to reduce this significant drawback in OFDM Systems. Keywords : Orthogonal Frequency Division Multiplexing (OFDM), peak to average power ratio (PAPR), bit error rate (BER), Out Band Interference (OBI), Additive White Gaussian Noise (AWGN), Bessel Companding Algorithm, Quadrature Amplitude Modulation (QAM) and Multi Carrier Modulation (MCM).
Low Peak to Average Power Ratio and High Spectral Efficiency Using Selective ...theijes
A low complexity peak to average power ratio (PAPR) reduction scheme for orthogonal frequency division multiplexing (OFDM) systems is proposed. All pass filters technique used PAPR is reduction but small amount of reduction, So use Selective Mapping (SLM) technique reduce PAPR and SNR increases.
Impact of Clipping and Filtering on Peak to Average Power Ratio of OFDM Systemijsrd.com
Orthogonal Frequency Division Multiplexing (OFDM) is an emerging field of research in the field of 4G broadband wireless communications due to its robustness against multipath fading and relatively simple implementation. Peak to Average Power Ratio (PAPR) is the limiting factor for an OFDM system as it consists of large number of independent subcarriers as a result of which the amplitude of such a signal can have high peak values which degrades the system performance. Such a signal when amplified by a Power Amplifier without processing results spectral regrowth and intermodulation among subcarrier. Hence this non linearity destroys the orthogonally of the OFDM signal and introduces out-of-band radiation and in band distortions causing significant performance degradation. The clipping and filtering method is analysed which is an efficient and simple method to reduce the PAPR. We have shown the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate.
A Hybrid PAPR Reduction Scheme for OFDM System ijmnct
Orthogonal frequency division multiplexing (OFDM) i
s considered as most efficient technique for future
wireless communication systems due to its higher sp
ectral bandwidth efficiency, robustness to frequenc
y
selective fading channels, etc. However, the succes
sful implementation of the OFDM system necessitates
several difficulties. The biggest disadvantage to w
ork with OFDM system is its high peak-to-average po
wer
ratio PAPR leadsto severe inter carrier interferenc
e, out-of-band radiation, and poor bit error rate
performance due to the nonlinearity of the high pow
er amplifier. In this paper, a novel hybrid techniq
ue is
proposed to reduce PAPR further and comparison has
been done with conventional techniques as well.
Simulated results are presentedconfirm theoretical
results.MATLAB 7.5 is used to simulate the results
for system parametersconsidered.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
Analysis of Reduction of PAPR by Linear Predictive Coding in OFDM AnuragSingh1049
The major challenge in orthogonal frequency division multiplexing (OFDM) is to reduce high peak to average power ratio (PAPR) that leads to non linear distortion for the application of high power amplifier. PAPR is defined as the ratio between the maximum instantaneous power and its average power. In this paper, we have presented new PAPR reduction technique to reduce peak to average power ratio using Linear predicting coding (LPC) in OFDM system. In this paper, proposed technique show the significant reduction in PAPR without any harmful degradation in power spectral density (PSD), computational complexity (CC) and performance error of the system. This proposed method can be applied for any number of subcarrier and independent of modulation scheme under Additive White Gaussian Noise (AWGN) channel.
Performance of Multiple symbol representation with clipping scheme for PAPR r...ijsrd.com
OFDM is one of the multicarrier modulation technique used in various communication systems. The major problem one faces while implementing this system is the high peak to average power .For an efficient OFDM system this PAPR should be low. In this paper a hybrid PAPR (peak to average power ratio) reduction technique for the OFDM (orthogonal frequency division multiplexing) signal which combines a multiple symbol representations method with a signal clipping method is proposed. In multiple symbol representations alternative signaling points are used to represent one symbol and PAPR is further reduced with the clipping scheme. The performance of the hybrid scheme is compared with the partial transmit sequence which is one of the other PAPR reduction scheme. In partial transmit sequence the input data is divided in to disjoint blocks transformed in to time domain sequence and rotated by phase factors. Theoretical analysis and simulation results validate that the proposed scheme has the ability to provide large PAPR reduction, low bit error rate. Performance analysis is also done with the partial transmit sequence scheme.
Computationally Efficient Algorithm for Reducing PAPR in OFDM using Null Subc...idescitation
A new algorithm is proposed which is used with
existing null-data subcarrier switching method of Peak to
Average Power Ratio (PAPR) reduction in OFDM to lower the
computational complexity. This proposed algorithm is very
simple and achieves significant reduction in computational
overhead without sacrificing PAPR reduction capability of
null-data subcarrier switching method. The proposed
algorithm is compatible with the current commercial systems
and it can be used with other existing algorithms to reduce
the computational overhead further. The proposed algorithm
is very useful in delay sensitive services. The effectiveness of
the proposed algorithm is demonstrated by presenting
simulation results of PAPR and computational time
requirement.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Analysis of Peak to Average Power Ratio Reduction Techniques in Sfbc Ofdm SystemIOSR Journals
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) has become the most popular modulation echnique for high speed data transmission. But the great disadvantage of the OFDM technique is its high Peak to Average Power Ratio (PAPR). In this paper, the Selected Mapping (SLM) technique and Clipping and Differential Scaling is applied to Space Frequency Block Coded (SFBC) OFDM systems to reduce the PAPR with Alamouti coding scheme. In SLM technique, different representations of OFDM symbols are generated by rotation of the original OFDM frame by different phase sequences, and the signal with minimum PAPR is selected and transmitted. To compensate for the effect of the phase rotation at the receiver, it is necessary to transmit the index of the selected phase sequence as side information (SI). Additionally, a suboptimum detection method that does not need SI is introduced at the receiver side. In Clipping and Differential Scaling technique, the amplitude of complex OFDM signal is clipped and then scaled in such a way so that the PAPR is reduced without causing much degradation in bit error rate (BER). The threshold values for clipping and scaling is determined using Monte Carlo Simulations. Simulation results show that the SLM method and Clipping and Scaling method effectively reduce the PAPR. Keywords: Orthogonal frequency division multiplexing (OFDM), peak to average power ratio (PAPR), selected mapping (SLM), space frequency block coded (SFBC), Side information (SI), high power amplifiers (HPA), complementary cumulative density function (CCDF), inter-symbol interference (ISI).
PAPR REDUCTION OF OFDM SIGNAL BY USING COMBINED HADAMARD AND MODIFIED MEU-LAW...IJCNCJournal
Orthogonal frequency division multiplexing (OFDM) is a technique which gives high quality of service (QOS) to the users by mitigating the fading signals as well as high data rates in multimedia services. However, the peak-to-average power ratio (PAPR) is a technical challenge that reduces the efficiency of RF power amplifiers. In this paper, we propose the combined Hadamard transform and modified meu-law companding transform method in order to lessen the effects of the peak-to-average power ratio of the
OFDM signal. Simulation results show that the proposed scheme reduces PAPR compared to other companding techniques as well as the Hadamard transform technique when used on its own.
Hardware Implementation of OFDM system to reduce PAPR using Selective Level M...IOSR Journals
Abstract : OFDM is a modulation as well as multiplexing technique which is widely used in various high speed mobile and wireless communication systems because of its capacity of ensuring high level robustness against interference. In this paper the design and implementation of OFDM system along with SLM implementation to reduce PAPR[6]is illustrated and a detailed simulation of the OFDM system with 16-QAM. OFDM transceiver is implemented using FPGA Spartan6 kit. The hardware results show a detailed study of RTL schematics and Test Bench. In this paper, the software simulation results show 2dB reduction in the peaks. Keywords - Field Programmable Gate Array, Matlab Simulink, Orthogonal Frequency Division Multiplexing , Peak-to-Average Power Ratio, Selective level Mapping and Xilinx
Performance Evaluation of CE-OFDM in PLC ChannelCSCJournals
One major drawback associated with an OFDM system is that the transmitter’s output signal may have a high peak-to-average ratio (PAPR). High levels of PAR may be a limiting factor for power line communication (PLC) where regulatory bodies have fixed the maximum amount of transmit power. To overcome this problem, many approaches have been presented in the literature. One potential solution for reducing the peak-to-average power ratio (PAPR) in an OFDM system is to utilize a constant envelope OFDM (CE-OFDM) system. This paper describes a CE-OFDM based modem for Power Line Communications (PLC) over the low voltage distribution network. The impact of the electrical appliances on the signal transmission is investigated. The good performances of the BER have been checked by the simulation platform of real PLC channel using Matlab. Finally, CE-OFDM-CPM is compared with conventional OFDM under HomePlug AV.
Comparative performance analysis of different modulation techniques for papr ...IJCNCJournal
One of the most important multi-carrier tran
smission techniques used in the latest wireless com
munication
arena is known as Orthogonal Frequency Division Mul
tiplexing (OFDM). It has several characteristics
such as providing greater immunity to multipath fad
ing & impulse noise, eliminating Inter Symbol
Interference (ISI) & Inter Carrier Interference (IC
I) using a guard interval known as Cyclic Prefix (C
P). A
regular difficulty of OFDM signal is high peak to a
verage power ratio (PAPR) which is defined as the r
atio
of the peak power to the average power of OFDM Sign
al. An improved design of amplitude clipping &
filtering technique of us previously reduced signif
icant amount of PAPR with slightly increase bit err
or rate
(BER) compare to an existing method in case of Quad
rature Phase Shift Keying (QPSK) & Quadrature
Amplitude Modulation (QAM). This paper investigates
a comparative performance analysis of the differen
t
higher order modulation techniques on that design.
Comparative performance analysis of different modulation techniques for papr ...
papr-presentation
1. 1
High PAPR Sequence Scrambling for Reducing OFDM
Peak-to-Average Power Ratio
Heshani Gamage, Nandana Rajatheva, Matti Latva-aho
University of Oulu
c
3. 3
OFDM Introduction
A digital multi-carrier modulation method where large number of closely
spaced orthogonal sub-carrier signals are used to carry data on several
parallel data streams or channels.
x(t) =
1
N
N−1
k=0
Xkej2πfkt
; 0 ≤ t < NT (1)
Resilient to multipath fading, inter-symbol interference (ISI), co-channel
interference and impulsive parasitic noise, due to multiple narrow band
sub channels with a lower data rate on each sub channel.
Lower implementation complexity compared with the single carrier
solution with usage of Fast Fourier transform (FFT)/Inverse FFT (IFFT)
blocks.
Has a high spectral efficiency due to usage of closely spaced overlapping
subcarriers.
c
5. 5
Drawbacks of OF OFDM
High Peak-to-Average Power Ratio(PAPR).
Sensitive to carrier offset and drift.
c
6. 6
Peak-to-Average Power Ratio of OFDM
For better approximation of the PAPR of continuous-time OFDM signals,
OFDM signal samples are obtained by L times oversampling.
L-times oversampled IFFT output can be expressed as 1
,
x [n] =
1
√
N
N−1
k=0
Xkej 2πnk
LN ; 0 ≤ n < LN − 1 (2)
PAPR of OFDM signal,
PAPR{x [n]} =
max0≤n≤NL |x [n] |2
E [|x [n] |2]
(3)
1T. Jiang and Y. Wu, ”An Overview: Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals” in IEEE Transactions on
Broadcasting , vol. 54,no. 2,pp. 257–268 , 2008.
c
7. 7
PAPR Problem
Figure: Sum power and average power of a composite signal of 4 subcarriers
N base stations (BSs) and K users.
c
8. 8
PAPR Problem ctd.
Figure: Signal Power and Average Power
of an OFDM Signal with 1024 subcarriers
Figure: CCDF of the PAPR of OFDM
signal with 1024 subcarriers
c
9. 9
Effect of subcarriers on PAPR
Figure: CCDF of OFDM PAPR for different number of subcarriers
c
10. 10
Drawbacks of high PAPR
Distortion of the signal if the transmitter has nonlinear components such
as power amplifiers (PAs).
Nonlinear devices will cause spectral spreading, inter modulation and
constellation distortion.
To avoid this, usage of expensive high power amplifiers in a very large
linear range, approximately equal to the dynamic range of the OFDM
signal is required.
High PAPR signals prevent PA from operating in near saturation region
reducing the PA efficiency.
c
11. 11
PAPR Reduction Schemes
Clipping and Filtering.
Selective Mapping (SLM).
Coding / Complement block coding.
Partial Transmit Sequence (PTS).
Tone reservation and tone injection.
Nonlinear companding (µ-law / exponential companding ).
Almost all the methods have one or more above drawbacks of
High computational complexity.
Degradation in BER Performance.
High average power and requirement of additional transmit power.
Bandwidth expansion or spectral spillage.
c
12. 12
Selective Mapping
U different OFDM signals are generated as candidates for a specific
signal and then one with the lowest PAPR is selected for the actual
transmission.
At the receiver, it is necessary to know which one of U candidates is
transmitted. Hence transmission of side information is needed in
conventional methods resulting a data rate loss.
There are several techniques to generate different OFDM signals
including, phase rotation and turbo coding.
Usually the complexity is very high due to its requirement of calculating
U × N IFFTs whenever SLM is applied for an OFDM system with N
subcarriers.
c
13. 13
For a small number of N, the probability that the PAPR of the OFDM
signal exceeds a certain threshold λ is given by2
,
Pr{PAPR > λ} = 1 − (1 − e−λ
)N
(4)
In SLM it is assumed that, U statistically independent alternative
sequences, which represent the same information are generated by some
suitable means. The sequence with the lowest PAPR is selected for
transmission. The probability that the lowest PAPR λl exceeds a certain
threshold λ is given by3
,
Pr{λl > λ} = (Pr{PAPR > λ})U
(5)
2S. Shepherd, J. Orriss, and S. Barton, Asymptotic limits in peak envelope power reduction by redundant coding in orthogonal frequency division
multiplex modulation, in IEEE Transactions in Communications, vol. 46, no. 1, pp. 5-10, Jan. 1998.
3R. W. Bauml, R. F. H. Fisher,J. B. Huber, Reducing the Peak-to-Average Power Ratio of Multicarrier Modulation by Selected Mapping in IEE
Electronics Letters, vol. 32, no. 22, pp. 2056-2057, Oct.1996
c
14. 14
Proposed Method
Since all the signals do not exceed the threshold (About 85% of
sequences will exceed a 7dB threshold and about 42% sequences will
exceed an 8dB), we apply the PAPR reduction scheme only for those
signals which exceed the PAPR threshold.
We keep an array of U scramblers to change a high PAPR sequence into
a lower PAPR sequence.
Once the PAPR of the scrambled sequence goes below the threshold, the
scrambling will be terminated and the scrambled sequence will be
transmitted, reducing the computational Complexity.
c
17. 17
Scrambler and Descrambler
Figure: Scrambler for an N length sequence Figure: Descrambler for an N length sequence
These scramblers can be defined by the scrambler polynomial P where,
P = [ 1 P1 P2 ... PS] ; PS ∈ {1, 0} for s = 1..S
c
18. 18
Simulation Parameters
In order to verify the performance of the high PAPR sequence scrambling
in reduction of PAPR, we considered a base band OFDM system with the
number of subcarriers N = 128 throughout the computer simulations.
The oversampling factor is L is set to 4.
Randomly generated input data is modulated by 16-quadrature amplitude
modulation (16QAM).
We used an array of U = 15 scramblers for PAPR reduction throughout
the simulations so that only one subcarrier is needed for side information.
c
19. 19
Simulation Results with 8dB as the threshold
Figure: PAPR comparison of OFDM and
proposed technique 128 subcarriers with 8dB
threshold and 15 scramblers
Figure: Percentage of sequences which has
used each scrambler for Th = 8dB. Zero
means no scrambler is used
c
20. 20
Simulation Results with 8dB as the threshold
Although 15 scramblers are used in this case, it can be seen from the
histogram that
More than 58% of the sequences do not need any scrambler.
About another 25% of signals go below threshold after the 1st scrambler.
About 10% more of signals get below threshold after 2 scramblers.
Another 4.3% of signals go below threshold after 3 scramblers.
Only 0.4% sequences need more than 5 scramblers.
Less than 0.007% sequences have to use more than 10 scramblers to
achieve PAPR below threshold.
Hence this technique reduces the computational complexity of the
original SLM technique as it does not need to compute all U candidate
sequences and choose the optimum.
c
21. 21
Simulation Results with 7dB as the threshold
Figure: PAPR comparison of OFDM and
proposed technique 128 subcarriers with 7dB
threshold and 15 scramblers
Figure: Percentage of sequences which has
used each scrambler for Th = 7dB. Zero
means no scrambler is used
c
22. 22
Figure: CCDF of OFDM PAPR for different
numbers of subcarriers N
Figure: Performance of the system with
increasing number of subcarriers N, for
threshold Th
c
23. 23
Comparison with existing PAPR reduction methods4 5
4T. Jiang and Y. Wu, ”An Overview: Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals” in IEEE Transactions on
Broadcasting , vol. 54,no. 2,pp. 257–268 , 2008.
5D.J.G. Mestdagh, ”Reduction Peak-to-Average Power Ratio of OFDM Systems: A Tutorial Overview”,2014
c
24. 24
Conclusion
Search for a low PAPR sequence will be terminated when a sequence is
generated with PAPR lower than the preset threshold. Hence
computational complexity of this method is significantly decreased from
the conventional SLM method.
Proposed technique is effective in reducing PAPR more than 4 dB of the
original signal for an arbitrary number of subcarriers.
We can find a compromise between PAPR reduction and computational
complexity by selecting an appropriate threshold value and the overhead
of scrambler index side information can be used for trade off in PAPR
reduction capability by choosing a suitable value as the size of the
scrambler array.
c