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.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
SLM-PTS BASED PAPR REDUCTION TECHNIQUES IN OFDM SYSTEMHariniChaganti1
Signals, which were initially sent in the analog domain, are being sent more and more in the digital domain these days. For better transmission, even single–carrier waves are being replaced by multi–carriers. Multi-carrier
systems like OFDM are now – a – days being implemented commonly. In the OFDM system,
orthogonally placed subcarriers are used to carry the data from the transmitter end to the receiver end. The presence of a guard band in this system deals with the problem of ISI and noise is minimized by a larger number of sub–carriers. But the large Peak– to –Average Power Ratio of these signal have some undesirable effects on the system. The Peak-to-Average Power Ratio is the ratio between the maximum power and average power of a complex passband signal. It causes many disadvantages like band-in and band-out variation, low signal to quantization noise ratio, low efficiency of power amplifier, etc. Hence, it is necessary to reduce PAPR in OFDM for its efficient use.
In this project, the main objective is to study the basics of an OFDM System and analyze and
simulate various methods such as clipping and filtering, selected mapping, Partial transmit sequence
to reduce the PAPR in the system and compare these techniques with and without PAPR reduction to
obtain an efficient technique so that this system can be used more commonly and effectively.
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.
AN OVERVIEW OF PEAK-TO-AVERAGE POWER RATIO REDUCTION TECHNIQUES FOR OFDM SIGNALSijmnct
OFDM (Orthogonal Frequency Division Multiplexing) has been widely adopted for high data rate wireless
communication systems due to its advantages such as extraordinary spectral efficiency, robustness to
channel fading and better QoS (Quality of Service) performance for multiple users. However, some
challenging issues are still unresolved in OFDM systems. One of the issues is the high PAPR (peak-toaverage
power ratio), which results in nonlinearity in power amplifiers, and causes out of band radiation
and in band distortion. This paper reviews some conventional PAPR reduction techniques and their
modifications to achieve better PAPR performance. Advantages and disadvantages of each technique are
discussed in detail. And comparisons between different techniques are also presented. Finally, this paper
makes a prospect forecast about the direction for further researches in the area of PAPR reduction for
OFDM signals
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
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.
Performance improvement for papr reduction in lte downlink system with ellipt...IJCNCJournal
This paper is concerned with the performance improvement of PAPR reduction of orthogonal frequency division multiplexing (OFDM) signal using amplitude clipping & filtering based design. Note that OFDM is one of the well adept multi-carrier multiplexing transmission scheme which has been implemented in long term evolution (LTE) downlink. Nonetheless peak to average power ratio (PAPR) is the more rattling problem with OFDM, consequently in this paper a reduction procedure of the PAPR by using amplitude clipping and filtering is proposed. Here we used IIR bandpass elliptic filter after amplitude clipping to
reduce the PAPR. The performance of the system in terms of bit error rate (BER) is also canvased as a new
filter based clipping method. Our results show that the proposed methodology of clipping method with the
IIR elliptic band pass filter significantly reduces the PAPR value.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
SLM-PTS BASED PAPR REDUCTION TECHNIQUES IN OFDM SYSTEMHariniChaganti1
Signals, which were initially sent in the analog domain, are being sent more and more in the digital domain these days. For better transmission, even single–carrier waves are being replaced by multi–carriers. Multi-carrier
systems like OFDM are now – a – days being implemented commonly. In the OFDM system,
orthogonally placed subcarriers are used to carry the data from the transmitter end to the receiver end. The presence of a guard band in this system deals with the problem of ISI and noise is minimized by a larger number of sub–carriers. But the large Peak– to –Average Power Ratio of these signal have some undesirable effects on the system. The Peak-to-Average Power Ratio is the ratio between the maximum power and average power of a complex passband signal. It causes many disadvantages like band-in and band-out variation, low signal to quantization noise ratio, low efficiency of power amplifier, etc. Hence, it is necessary to reduce PAPR in OFDM for its efficient use.
In this project, the main objective is to study the basics of an OFDM System and analyze and
simulate various methods such as clipping and filtering, selected mapping, Partial transmit sequence
to reduce the PAPR in the system and compare these techniques with and without PAPR reduction to
obtain an efficient technique so that this system can be used more commonly and effectively.
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.
AN OVERVIEW OF PEAK-TO-AVERAGE POWER RATIO REDUCTION TECHNIQUES FOR OFDM SIGNALSijmnct
OFDM (Orthogonal Frequency Division Multiplexing) has been widely adopted for high data rate wireless
communication systems due to its advantages such as extraordinary spectral efficiency, robustness to
channel fading and better QoS (Quality of Service) performance for multiple users. However, some
challenging issues are still unresolved in OFDM systems. One of the issues is the high PAPR (peak-toaverage
power ratio), which results in nonlinearity in power amplifiers, and causes out of band radiation
and in band distortion. This paper reviews some conventional PAPR reduction techniques and their
modifications to achieve better PAPR performance. Advantages and disadvantages of each technique are
discussed in detail. And comparisons between different techniques are also presented. Finally, this paper
makes a prospect forecast about the direction for further researches in the area of PAPR reduction for
OFDM signals
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
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.
Performance improvement for papr reduction in lte downlink system with ellipt...IJCNCJournal
This paper is concerned with the performance improvement of PAPR reduction of orthogonal frequency division multiplexing (OFDM) signal using amplitude clipping & filtering based design. Note that OFDM is one of the well adept multi-carrier multiplexing transmission scheme which has been implemented in long term evolution (LTE) downlink. Nonetheless peak to average power ratio (PAPR) is the more rattling problem with OFDM, consequently in this paper a reduction procedure of the PAPR by using amplitude clipping and filtering is proposed. Here we used IIR bandpass elliptic filter after amplitude clipping to
reduce the PAPR. The performance of the system in terms of bit error rate (BER) is also canvased as a new
filter based clipping method. Our results show that the proposed methodology of clipping method with the
IIR elliptic band pass filter significantly reduces the PAPR value.
Comparative Analysis of PAPR Reduction Techniques in OFDM Using Precoding Tec...IJSRD
In this modern era, Orthogonal Frequency Division Multiplexing (OFDM) has been proved to be an explicit promising technique for wired and wireless systems because of its several advantages like high spectral efficiency, robustness against frequency selective fading, relatively simple receiver implementation etc. Besides having a number of advantages OFDM suffers from few disadvantages like high Peak to Average Power Ratio (PAPR), Intercarrier Interference (ICI), Intersymbol Interference (ISI) etc. These detrimental effects, if not compensated properly and timely, can result in system performance degradation. This paper mainly concentrates on reduction of PAPR.A comparisons have been made between various precoding techniques against conventional OFDM.
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.
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.
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.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
A low complexity partial transmit sequence scheme for better papr reduction i...eSAT Journals
Abstract The main drawback of OFDM system is the high Peak to Average Power Ratio (PAPR) of the transmitted signals. Partial transmit sequence scheme is a promising algorithm to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM). The Partial Transmit Sequence (PTS) consist of several inverse fast Fourier transform (IFFT) operations and complicated calculations to obtain optimum phase sequence which results in increasing the computational complexity of PTS. A phase sequence applied to the PTS Scheme reduces its complexity but at the expense of slight degradation in PAPR reduction. In this paper, for further reduction of PAPR the peak clipping of the OFDM signal is introduced along with the PTS with new phase sequence scheme. Since clipping is one of the simplest techniques of PAPR reduction, it does not increase the complexity of the system much and a better PAPR reduction is obtained with the combined effect of clipping and PTS with New Phase Sequence. But the clipping technique introduce some distortion in the signal, however peak clipping of signal below a particular threshold can maintain the BER in the tolerable range. The clipping threshold selected will be different for different OFDM systems. Index Terms: OFDM, Peak to Average Power Ratio (PAPR), Partial Transmit Sequence (PTS), Clipping.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
An Adaptive Approach to Switching Coded Modulation in OFDM System Under AWGN ...ijsrd.com
In this paper we have studied the OFDM for different Quadrature amplitude modulation technique (QAM) The scatter plot and their output signal to noise ratio, dependent bit error rate variation is analyzed for every type of modulation in OFDM. After observing the BER for each SNR in the system, switching threshold range has been prepared and now system is ready to face the Adaptive coded modulation (ACM).The results shows the switching of modulation technique.
Performance evaluation on the basis of bit error rate for different order of ...ijmnct
Today, we have required to accommodate a large number of users under a single base station. This can be
possible only if we have some flexibility over the spectrum. Previously we have lots of multiplexing methods
to accommodate large number of signals in time and frequency domain. But now we have required to
accommodate a large number of users in the same bandwidth, without any fading over the received signal.
So, orthogonality can be maintained over the frequency response. This technology is now more popular in
the mobile communication domain, called Orthogonal Frequency Division Multiplexing (OFDM). Actually
user data can be converted into the parallel form and then they are modulated using digital modulation
techniques. Finally, they have followed by OFDM Modulator and cyclic prefix can be inserted into the
OFDM symbols. Here, I have worked on the measurement of Bit error rate for different modulation
techniques in OFDM technology. It has been considered that subchannel size is not constant. According to
that I have concluded the overall idea regarding the performance under OFDM technology.
A modified design of acf operation for reducing papr of ofdm signalijngnjournal
Next generation wireless communication technology long term evolution (LTE) has implemented
orthogonal frequency division multiplexing (OFDM) technique as a strong candidate for radio access
systems. It has several attributes such as providing robustness to multipath fading & impulse noise,
eliminating intersymbol interference (ISI), inter carrier interference (ICI) & the need for equalizers. The
major challenging issue of OFDM technique is the high peak to average power ratio (PAPR) which is
defined as the ratio of the peak power to the average power of the OFDM signal. A trade-off is
necessary for reducing PAPR with increasing bit error rate (BER), computational complexity or data rate
loss etc. In this paper, a moderately modified design of amplitude clipping & filtering operation (ACF) is
proposed and implemented which shows the significant improvement in case of PAPR reduction for both
quadrature phase shift keying (QPSK) & quadrature amplitude modulation (QAM) while increasing slight
BER match up to to an existing method.
Performance and Analysis of OFDM Signal Using Matlab SimulinkIJMER
Multi-carrier modulation is an attractive technique for fourth generation .OFDM is based on
multicarrier modulation technique. In OFDM system the bit stream is divided into many different sub
channels. An efficient and distortionless scheme for peak power reduction in OFDM is proposed. In this
paper, a set of mapping where the actual transmit signal is selected. From this set of signal reduced
PAPR. Simulation results are shown. The lowest PAPR is compared with conventional work. It is also
compared BER to SNR and best result is achieved.
Comparative Analysis of PAPR Reduction Techniques in OFDM Using Precoding Tec...IJSRD
In this modern era, Orthogonal Frequency Division Multiplexing (OFDM) has been proved to be an explicit promising technique for wired and wireless systems because of its several advantages like high spectral efficiency, robustness against frequency selective fading, relatively simple receiver implementation etc. Besides having a number of advantages OFDM suffers from few disadvantages like high Peak to Average Power Ratio (PAPR), Intercarrier Interference (ICI), Intersymbol Interference (ISI) etc. These detrimental effects, if not compensated properly and timely, can result in system performance degradation. This paper mainly concentrates on reduction of PAPR.A comparisons have been made between various precoding techniques against conventional OFDM.
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.
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.
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.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
A low complexity partial transmit sequence scheme for better papr reduction i...eSAT Journals
Abstract The main drawback of OFDM system is the high Peak to Average Power Ratio (PAPR) of the transmitted signals. Partial transmit sequence scheme is a promising algorithm to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM). The Partial Transmit Sequence (PTS) consist of several inverse fast Fourier transform (IFFT) operations and complicated calculations to obtain optimum phase sequence which results in increasing the computational complexity of PTS. A phase sequence applied to the PTS Scheme reduces its complexity but at the expense of slight degradation in PAPR reduction. In this paper, for further reduction of PAPR the peak clipping of the OFDM signal is introduced along with the PTS with new phase sequence scheme. Since clipping is one of the simplest techniques of PAPR reduction, it does not increase the complexity of the system much and a better PAPR reduction is obtained with the combined effect of clipping and PTS with New Phase Sequence. But the clipping technique introduce some distortion in the signal, however peak clipping of signal below a particular threshold can maintain the BER in the tolerable range. The clipping threshold selected will be different for different OFDM systems. Index Terms: OFDM, Peak to Average Power Ratio (PAPR), Partial Transmit Sequence (PTS), Clipping.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
An Adaptive Approach to Switching Coded Modulation in OFDM System Under AWGN ...ijsrd.com
In this paper we have studied the OFDM for different Quadrature amplitude modulation technique (QAM) The scatter plot and their output signal to noise ratio, dependent bit error rate variation is analyzed for every type of modulation in OFDM. After observing the BER for each SNR in the system, switching threshold range has been prepared and now system is ready to face the Adaptive coded modulation (ACM).The results shows the switching of modulation technique.
Performance evaluation on the basis of bit error rate for different order of ...ijmnct
Today, we have required to accommodate a large number of users under a single base station. This can be
possible only if we have some flexibility over the spectrum. Previously we have lots of multiplexing methods
to accommodate large number of signals in time and frequency domain. But now we have required to
accommodate a large number of users in the same bandwidth, without any fading over the received signal.
So, orthogonality can be maintained over the frequency response. This technology is now more popular in
the mobile communication domain, called Orthogonal Frequency Division Multiplexing (OFDM). Actually
user data can be converted into the parallel form and then they are modulated using digital modulation
techniques. Finally, they have followed by OFDM Modulator and cyclic prefix can be inserted into the
OFDM symbols. Here, I have worked on the measurement of Bit error rate for different modulation
techniques in OFDM technology. It has been considered that subchannel size is not constant. According to
that I have concluded the overall idea regarding the performance under OFDM technology.
A modified design of acf operation for reducing papr of ofdm signalijngnjournal
Next generation wireless communication technology long term evolution (LTE) has implemented
orthogonal frequency division multiplexing (OFDM) technique as a strong candidate for radio access
systems. It has several attributes such as providing robustness to multipath fading & impulse noise,
eliminating intersymbol interference (ISI), inter carrier interference (ICI) & the need for equalizers. The
major challenging issue of OFDM technique is the high peak to average power ratio (PAPR) which is
defined as the ratio of the peak power to the average power of the OFDM signal. A trade-off is
necessary for reducing PAPR with increasing bit error rate (BER), computational complexity or data rate
loss etc. In this paper, a moderately modified design of amplitude clipping & filtering operation (ACF) is
proposed and implemented which shows the significant improvement in case of PAPR reduction for both
quadrature phase shift keying (QPSK) & quadrature amplitude modulation (QAM) while increasing slight
BER match up to to an existing method.
Performance and Analysis of OFDM Signal Using Matlab SimulinkIJMER
Multi-carrier modulation is an attractive technique for fourth generation .OFDM is based on
multicarrier modulation technique. In OFDM system the bit stream is divided into many different sub
channels. An efficient and distortionless scheme for peak power reduction in OFDM is proposed. In this
paper, a set of mapping where the actual transmit signal is selected. From this set of signal reduced
PAPR. Simulation results are shown. The lowest PAPR is compared with conventional work. It is also
compared BER to SNR and best result is achieved.
„PR 2.0. W 80 minut o nowych narzędziach komunikacji” opowiada o specyfice współczesnej komunikacji, technologii w służbie PR-u i nowych zjawiskach z pogranicza PR-u i marketingu, takich jak brand journalism, content marketing czy PR behawioralny. „PR 2.0. W 80 minut o nowych narzędziach komunikacji” opisuje przykłady kampanii z wykorzystaniem social media, takich jak #HMBALMAINATION, #IAMPORTER czy Social Catwalk.
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 Modified Design Of Acf Operation For Reducing Papr Of Ofdm Signaljosephjonse
Next generation wireless communication technology long term evolution (LTE) has implemented orthogonal frequency division multiplexing (OFDM) technique as a strong candidate for radio access systems. It has several attributes such as providing robustness to multipath fading & impulse noise, eliminating intersymbol interference (ISI), inter carrier interference (ICI) & the need for equalizers. The major challenging issue of OFDM technique is the high peak to average power ratio (PAPR) which is defined as the ratio of the peak power to the average power of the OFDM signal. A trade-off is necessary for reducing PAPR with increasing bit error rate (BER), computational complexity or data rate loss etc. In this paper, a moderately modified design of amplitude clipping & filtering operation (ACF) is proposed and implemented which shows the significant improvement in case of PAPR reduction for both quadrature phase shift keying (QPSK) & quadrature amplitude modulation (QAM) while increasing slight BER match up to to an existing method.
Comparative Analysis of PAPR Reduction Techniques in OFDM Using Precoding Tec...IJSRD
In this modern era, Orthogonal Frequency Division Multiplexing (OFDM) has been proved to be an explicit promising technique for wired and wireless systems because of its several advantages like high spectral efficiency, robustness against frequency selective fading, relatively simple receiver implementation etc. Besides having a number of advantages OFDM suffers from few disadvantages like high Peak to Average Power Ratio (PAPR), Intercarrier Interference (ICI), Intersymbol Interference (ISI) etc. These detrimental effects, if not compensated properly and timely, can result in system performance degradation. This paper mainly concentrates on reduction of PAPR.A comparisons have been made between various precoding techniques against conventional OFDM.
PAPR Reduction in OFDM using Active and Non-Active ChannelsIOSR Journals
Abstract : According to the request of advance communication field there should be high data rate in addition to both power efficiency and lower bit error rate. This request of high data rate can be achieved by the multi carrier modulation scheme using the OFDM technique. But the great drawback of the OFDM technique is its high peak to average power ratio (PAPR). High PAPR reduces OFDM signals by driving the analog amplifier to work in the nonlinear region, changing this way the signal and making the amplifier to consume more power. To reduce the PAPR methods exist which adjust or present new signals to battle large signal peaks. The methods which use data carrying channels are called active channel methods and which use redundant channel are called non active channel methods. This work deals with reduction of the PAPR of OFDM signal using both Active and Non Active Channels. Clipping technique has been applied to active channels and Tone reservation has been applied to Non Active Channels. By using both channels we can get considerable reduction in PAPR. Keywords:Orthogonal Frequency Division Multiplexing (OFDM), Peak to Average Power Ratio (PAPR), Power Amplifier (PA).
Performance comparison of two clipping based filtering methods for papr reduc...ijmnct
The growth of wireless communication technologies has been producing the intense demand for high-speed,
efficient, reliable voice & data communication. As a result, third generation partnership project (3GPP)
has implemented next generation wireless communication technology long term evolution (LTE) which is
designed to increase the capacity and speed of existing mobile telephone & data networks. LTE has
adopted a multicarrier transmission technique known as orthogonal frequency division multiplexing
(OFDM). OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for
very wide carriers. One major generic problem of OFDM technique is high peak to average power ratio
(PAPR) which is defined as the ratio of the peak power to the average power of the OFDM signal. A
trade-off is necessary for reducing PAPR with increasing bit error rate (BER), computational complexity or
data rate loss etc. In this paper, two clipping based filtering methods have been implemented & also
analyzed their modulation effects on reducing PAPR.
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).
A Hybrid VLM Preceded SLM Technique Using Clipping and Filtering Method for P...IJERA Editor
MIMO-OFDM is an attractive interface for the next generation WLANs, WMAN, 4G and 5G mobile cellular
systems. However the performance of the MIMO-OFDM systems is affected by Peak to Average Power Ratio
(PAPR). PAPR is the main disadvantage associated with the MIMO-OFDM systems. So far, many techniques
have been proposed to reduce the value of PAPR but high PAPR for MIMO-OFDM systems is still a demanding
area and a different issue.In this paper, a hybrid VLM precoded SLM scheme using Clipping & Filtering has
been proposed to reduce PAPR in MIMO-OFDM systems. And it has been observed that the proposed scheme
has achieved a significant gain in PAPR reduction without increasing the system complexity and affecting the
error performance of the system.
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
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).
Ofdm-cpm Ber Performance and FOBP Under IEEE802.16 ScenarioCSCJournals
The application of Orthogonal frequency domain modulation-Continuous Phase Modulation (OFDM-CPM) in multipath Stanford University Interim (SUI) channels is presented in this paper. OFDM-CPM is proposed for IEEE 802.16 standards as an alternative technique of orthogonal frequency division multiplexing (OFDM) in physical layer. It is shown that, in addition to 0dB Peak to Average Power Ratio (PAPR) and power efficiency, un-coded OFDM-CPM exploits the frequency diversity of multipath channel. Taking into account the Input Power Back off (IBO), OFDM-CPM is shown to outperform OFDM at high bit energy-to-noise density ratios (Eb/N0). However, at low Signal to Noise Ratio (SNR), the OFDM-CPM phase demodulator receiver suffers from a threshold effect. In addition, this paper compares the spectral fractional out of band power of OFDM-CPM for different modulation indices.
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.
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.
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A Hybrid PAPR Reduction Scheme for OFDM System
1. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2, April 2015
DOI : 10.5121/ijmnct.2015.5201
1
A Hybrid PAPR Reduction Scheme for OFDM
System
Shelly Sethi1
and Tanvi Sood2
1,2
ECE Department, CEC Landran, Mohali, Punjab,India
ABSTRACT
Orthogonal frequency division multiplexing (OFDM) is considered as most efficient technique for future
wireless communication systems due to its higher spectral bandwidth efficiency, robustness to frequency
selective fading channels, etc. However, the successful implementation of the OFDM system necessitates
several difficulties. The biggest disadvantage to work with OFDM system is its high peak-to-average power
ratio PAPR leadsto severe inter carrier interference, out-of-band radiation, and poor bit error rate
performance due to the nonlinearity of the high power amplifier. In this paper, a novel hybrid technique 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.
KEYWORDS
Orthogonal frequency division multiplexing (OFDM), peak-to-average power ratio (PAPR), selected
mapping (SLM), partial transmit sequences (PTS), Convolutional encoding, Hamming Codes, RS coding.
1. INTRODUCTION
From past few years, research community has started considering orthogonal frequency division
multiplexing (OFDM) as one of the core technologies for various communication systems and
therefore it has been adopted as a standard for various wireless communication systems such as
wireless LAN, wireless MAN and digital audio/videobroadcasting [1]. It is an efficient technique
for achieving high data rate in wireless communication systems and performs better with
frequency selective fading channels [2]. Despite its advantages, an OFDM signal experience high
peak-to-average power ratio (PAPR) at the transmitter, which causes signal distortion due to the
nonlinearity of the high power amplifier (HPA) and causes higher bit error rate (BER) [3]. The
large PAPR also increase the complexity of analog-to-digital converter (ADC) and digital-to-
analog converter (DAC). Thus, PAPR reduction for OFDM systems has become a topic of
research to the academicians and researchers these days.
Many schemes have been proposed by researchers for reducing the PAPR of OFDM signals,
which can be broadly put into two categories[4]–[11]. First, the PAPR schemes can be classified
as multiplicative or additive schemes, where PAPR reduction is carried out in the OFDM
modulator. Selected mapping (SLM) and partial transmit sequence (PTS) are multiplicative
schemes because the phase sequences are multiplied with input symbol sequences or OFDM
signal sequences [4-6], [8]. whereas, tone reservation (TR) and clipping are additive schemes
because the reference signals are added [7], [9], [10]. In a second category, the PAPR schemes
can be classified as deterministic and probabilistic scheme. Deterministic schemes includes
clipping [11], limit the PAPR of the OFDM signals below a given threshold level. Probabilistic
schemes modify the thecharacteristics of the PAPR distribution statistically for OFDM signals
2. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2,April 2015
2
without signal deformation[12]. SLM and PTS are probabilistic in naturein which multiple signals
are generated and the one withthe minimum PAPR is chosen for transmission. The computational
complexity of SLM is larger than that of PTS still it outperforms over PTS if the amount of side
information is limited.
In this paper, a novel hybrid scheme has been proposed to reduce PAPR value significantly by
combining block coding scheme with selected mapping scheme. The simulated results are
presented to strengthen the idea of proposed scheme over other conventional scheme of
PAPRreduction.
2. OFDM SYSTEM MODEL
Fig. 1 shows the block diagram of typical OFDM system. A block of input bits (called symbols)
are modulated using M-arymodulation scheme and then passed to the serial to parallel converter.
Depending upon the system requirements different types of data modulator can be used e.g. M-
QAM, M-PSK etc.) [45]. The complex parallel data symbols (X୩) obtained by using modulation
techniques are given to N point IFFT block as shown in fig. 1.
The baseband transmitted OFDM signal envelope can be written as
yሺtሻ =
1
√N
Y
ିଵ
ୀ
e୧ଶπై୲
; 0 ≤ t ≤
≤ NT ሺ1ሻ
where, N is the total number of subcarriers, Y, L= 0,1,2,…., N-1 block of N input bits (symbols),
f=L f, where ∆f=1/ (Nτ), ߬=original symbol period.
Fig.1: Typical OFDMSystem
EሾX୩X୪ሿ = ቄ
1 ∀ k = l
0 ∀ k ≠ l
ቅ ሺ2ሻ
The discrete form of OFDM signal x(n ) is given by
ݔሺ݊ሻ =
ଵ
√ே
∑ ܺ݁
ೕమഏೖ
ಿேିଵ
ୀ ݂݊ݎ = 0,1,2, … . . , ܰ − 1 ሺ3ሻ
3. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2,April 2015
3
(3)shows that a signal ݔሺ݊ሻcan be extracted by performing inverse discrete Fourier transform
(IDFT) operation on the modulated input bits. Generally, IDFT operation can be performed by
using inverse fast Fourier transform (IFFT).
To remove ISI introduced due to delay spread,guard interval is used which is generally
interleaved between consecutive OFDM symbols. To remove ISI completely a guard band
interval with no signal transmission can be used. However, it may produce ICI due to high
frequency components. The guard interval can be introduced in the form of zero padding (ZP)
and cyclic extension. Cyclic extension can be extended in two ways-cyclic prefix or cyclic suffix.
On contrary to the transmitter, at receiver side, the guard interval of OFDM symbol is removed
and then unguarded OFDM symbol undergoes serial to parallel conversion. After this, FFT
operation is performed to converts parallel OFDM data streams into frequency domain.
Therefore, the output of FFT block can be expressed as-
Xሺnሻ = Fሺnሻ. xሺnሻ + wሺnሻ∀ 0 ≤ n ≤ N − 1 ሺ4ሻ
Where, W (n) is the additive white Gaussian noise (AWGN) component in frequency domain and
(.) denotes frequency response of the multipath fading channel at the sub channel
ܨሺ݉ሻ =
1
√ܰ
ℎ
ିଵ
ୀ
݁
షమഏ
ಿ ∀ m = 0,1, … … . . , ܰ − 1 ሺ5ሻ
3. PAPR
The biggest hurdle to implement OFDM system successfully is its high PAPR value of
transmitted signal thatseverely degrades the system performance. The PAPR of the continuous
time OFDM transmitted signal x (t) may be defined as the ratio of the maximum instantaneous
power and the average power of OFDM signal.
PAPR =
maxሾYሺtሻሿଶ
Eሼ|Yሺtሻ|ଶሽ
∀ 0 ≤ t ≤ NT ሺ6ሻ
Where, E denotes expectation operator and Eሼ|Yሺtሻ|ଶሽ is average power of Y(t) as well as
T is an original symbol period. PAPR mainly occurs due to large dynamic range of OFDM
symbol waveforms. High PAPR in OFDM fundamentallytake place because of IFFT pre-
processing (i.e. OFDM signal consists of a multiple independently modulated sub-carriers which
can give a large peak when added up with same phases). The discrete time baseband OFDM
signals are transformed to continuous time baseband OFDM signals by a low-pass filter called
DAC, where the peak power can be increased while maintaining a constant average power.
Generally, the PAPR of the continuous time baseband OFDM signals is larger than that of the
discrete time baseband OFDM signals by 0.5-1.0 dB [13-14].
4. PAPR REDUCTION SCHEME
The numbers of schemes have been developed to reduce the PAPR of OFDM signals. In this
section, we overview the conventional PAPR reduction schemes their advantages and
disadvantages.
4. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2,April 2015
4
4.1 Clipping
Signal clipping is one of the most commonly used technique to reduce the peak signal to
a desired signal level [12], [13]. The output signal of a Hard/soft limiter can be written as
x୬തതത = ൜
x୬|x୬| < X୲୦
X୲୦e୨∅ሺ୶ሻ
|x୬| ≥ X୲୦
ൠ ሺ7ሻ
WhereXth is the clipping level and φ (xn) represents the phase. Thoughthe scheme
guarantees peak reduction but has fewdisadvantages. For example, clipping distort the signal
shape that is treated as an interference and results increases in BER. Moreover, spectral efficiency
of OFDM system also reduced due to high frequency components regrowth. Various techniques
have been proposed by researchers time to time to overcome these shortcomings of the clipping
method. For example filtering method is most commonly employed to reduce out-of-band
emission but, at same time it cause peak regrowth. [14]–[16]. Peak windowing is another
important technique in whichsignal peak value is reduced by multiplying it with a correcting
function like Gaussian, Kaiser, and cosinewith original OFDM signal [11], [17].
4.2 Nonlinear Processing
Nonlinear processing of OFDM signal includes companding and decompanding the input
signal with an aid of digital to analog converter (DAC) in which signal amplitudes are nonlinearly
scaled by suppressing signals with large amplitudes and amplifying signals with smaller
amplitudes. At the receiver, the original signal is recovered from the companded signal by a
reverse process known as decompanding[18].
4.3 Coding
Recently, coding has evolved as one of the popular scheme to reduce PAPR. The most
widely used Golay complementary sequence is an example which ensures that the OFDM signals
may not exceed PAPR value equals to 3 dB [19-20]. The advantage of using Golay
complementary sequences is not only their small PAPR value but also theirexcellent error
correction properties. The main drawback of using these sequences is their significantrate loss
during transmission.
4.4 Partial Transmit Sequence (PTS)
As the name suggest, in PTS scheme, signal’s high PAPR issue is resolved by dividing
the input data block into independent sub blocks which are further processed by converting them
into time-domain partial transmit sequences [16]. These partial sequences are thereafter rotated
with different phase factorsto combine optimally to obtain OFDM signals with lowest PAPR
value. To find optimal phase factors is a cumbersome process and requires high computational
complexity to the system. Moreover, it requires side information to be transmitted at receiver side
for appropriate decoding and demodulation of the transmitted bit sequence[17].
4.5 Selected Mapping (SLM)
Similar to the PTS scheme, in SLM scheme the input data sequences are multiplied by
each of the phase sequences to generate alternative input symbol sequences [18]. IFFT operation
is performed on each of these alternative input data sequences and then the sequence with the
5. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2,April 2015
5
lowest PAPR is transmitted. For the successful implementation of SLM OFDM systems, the SLM
technique multiple IFFT operations and side information for each data block[19].
4.6 Tone Rejection (TR)& Tone Injection (TI)
Both, tone rejection (TR) and tone injection (TI) schemes work on the same principle of
keeping a subset of tones reserve at the transmitter and receiver side to
generating PAPR reduction signals. In TR, the time domain
signal is identified to add to the original time domain signal to reduce the PAPR. Similarly, in TI
scheme the constellation size is extended by replacing same data point with multiple possible
constellation points by duplicating the original constellation into various alternative ones [21- 22].
Fig.2: Flow Diagram of Proposed Scheme
Start
End
Initialization of parameters, branch number etc. for SLM
scheme
Generate all possible combinations for given weight factors
for SLM approach.
Apply SLM technique along with different encoding
schemes separately with 1000 generated symbols
Generate OFDM symbols for QPSK modulation scheme for
each sub carriers and set weights for SLM technique
Calculation corresponding PAPR and empirical cumulative
distribution function.
Calculation and plotting of complementary distribution
function for different PAPR values
6. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2,April 2015
6
The TI technique is more challenging than the TR technique since the injected signal occupies the
frequency band as the information bearing signals. Moreover, the alternative constellation points
in TI technique possess increased energy which results increase in the implementation complexity
for the computation the optimal translation vector [23].
5. PROPOSED SCHEME
Many techniques have been proposed by the researchers time to time to overcome PAPR problem
associated with OFDM systems. For examples, novel coding schemes, SLM, PTS schemes etc. In
this thesis, a hybrid scheme has been proposed by combining SLM technique and different
encoding schemes together to reduce PAPR value. The idea is to find the best encoding scheme
that helps in reducing PAPR significantly when combined with SLM approach. To so, the
encoding schemes taken into consideration are Convolution Encoding, Hamming Encoding and
Reed Solomon Encoding. Fig. 2 is shows the flow diagram of proposed Technique.
6.RESULTS & DISCUSSIONS
In this paper, a novel hybrid technique is proposed to overcome the PAPR of OFDM system. The
performance evaluation of the proposed schemes has been done through MATLAB simulations
for parameters enlisted in table 1. The PAPR reduction performance of the proposed technique is
evaluated in terms of Complementary Cumulative Distribution Function (CCDF) which may be
defined as the probability that the PAPR of a block is larger than a certain level.
Table 1: Parameters for the Proposed Scheme
S. No. PARAMETER NOTATION VALUE
1 Number of sub carriers N 16
2 Over sampling factors Ζ 8
3 Modulation Scheme - QPSK, QAM
4 No. of sub blocks Ψ 4 to 6
5 Total no. of IFFT combinations Χ 16,256
6 Total no. of OFDM signal generated Ξ 1000
7 SNR 16 dB QAM Ρ 15 Db
8 SNR 16 dB QPSK Λ 20 dB
9 Clipping Ratio Θ 4 dB
7. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2,April 2015
7
Figure 2: Impact of Convolution Encoding on PAPR
The comparison of CCDFs with respect to the PAPR distribution for original OFDM scheme
without any PAPR reduction scheme is done with SLM technique and proposed hybrid
(EncodedSLM) scheme. The modulation type considered here is QPSK for N=16. It has been
observed that original PAPR for OFDM is very high. For example with CCDF equals to 10-2
, the
PAPR values standard OFDM is 10.2 dB. The value of PAPR reduces significantly i.e. to 6.9 dB
with proposed scheme when compared for the same value of CCDF by employing SLM
technique. As expected, for the proposed hybrid scheme, the PAPR reduces further to 5.2 dB for
CCDF equals to 5.2 dB.
Figure 3: Impact of Reed Solomon Encoding on PAPR
Figure 4: Impact of Hamming Encoding on PAPR
123456789101112
10
-2
10
-1
10
0
PAPR (dB)
CCDF
Orignal
SLM
Conv+SLM
123456789101112
10
-2
10
-1
10
0
PAPR (dB)
CCDF
Orignal
SLM
RSC+SLM
123456789101112
10
-2
10
-1
10
0
papr
1-cdf2
orignal papr
slm papr
hamming-slm
8. International Journal of Mobile Network Communications & Telematics (IJMNCT) Vol. 5, No.2,April 2015
8
For parameters given in table 1 for OFDM system, the impact of Reed Solomon codes along with
SLM technique is observed in fig. 3. The CCDF graph shows that SLM technique helps in
reducing PAPR significantly. In proposed hybrid technique, Reed Solomon code is applied along
with SLM technique, PAPR can be reduced further up to 2 dB and therefore improve the OFDM
system performance further.
Fig. 5: Comparison of different encoding schemes for SLM based OFDM with N= 16
Fig. 6: Comparison of different encoding schemes for SLM based OFDM with N= 64
Figure 4shows the result PAPR analysis of Hamming Encoded OFDM. The results are compared
for standard PAPR with SLM based PAPR reduction and with Hamming Encoded OFDM. The
modulation type is QPSK and it is taken for N=16. It can be observed that at CCDF equals to 10-2
,
PAPR values of standard OFDM filter is approximately 9.3 dB and for SLMbased PAPR, it is
about 6.4. For Hamming encoded SLM OFDM it can be reduced further to 4.6.
The comparison of all three encoding schemes for encoded SLM based OFDM system is given in
fig. 5. The modulation scheme is QPSK and N=16. It could be observed that with proposed
hybrid scheme hamming encoding perform well in comparison with rest schemes. For example, at
CCDF equals to 10-2
for Reed Solomon codes PAPR equals to 5.4 dB, for Convolutional encoding
it is equals to 4.9 dB and for Hamming encoding it reduces to 4.4 dB. The impact of number of
sub carriers could also be observed for the proposed scheme and is given in fig. 6. The curve
becomes bit smoother in comparison with fig. 5 because more number of sub carriers and
therefore symbols that have been generated.
5. CONCLUSION
In this paper, PAPR problem of OFDM system is addressed. Many PAPR reduction techniques
have been overviewed and a hybrid scheme for reducing PAPR further is proposed by combining
SLM approach with different encoding schemes. The different encoding schemes considered in
this work are Convolutional Encoding, Reed Solomon Encoding and Hamming Encoding for
QPSK modulation scheme. The simulated results are showing that proposed idea of combining
encoding schemes along with SLM technique performs well and helps in reducing PAPR value
significantly. The comparative analysis amongst three encoding schemes is done and it has been
observed that hamming encoding scheme performs extremely well when combined with SLM
approach to reduce PAPR significantly. Approximately 2dB improvement has been observed for
proposed scheme for individual encoding scheme and a comparative analysis has also been given
amongst encoding schemes.
1.5 2 2.5 3 3.5 4 4.5 5
10
-2
10
-1
10
0
PAPR (dB)
CCDF
Hamming+SLM
RSC+SLM
Conv+SLM
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