International Journal of Engineering Trends and Technology (IJETT) – Volume 21 Number 4 – March 2015
Performance analysis of hybrid SLM-PTS system
under Rayleigh Fading channel
Mr. Ashutosh D. Gabhane1, Dr. Mrs. A.J. Vyavahare2
1
P.G. Student, E&TC Department, PES’s Modern College of Engineering, Pune, India
2
Professor, E&TC Department, PES’s Modern College of Engineering, Pune, India
Abstract— One of the main drawback of OFDM is the high Peak
to Average power ratio of OFDM signal. This are multicarrier
systems have a setback that Peak to Average power ratio
increases with the increase of number of subcarrier, which
results poor effectiveness or sober performance degradation to
transmit power amplifier. In most cases, the high peak-toaverage power ratio (PAPR) of transmitted signals for OFDM
systems reduces the system efficiency and hence there is
increment the cost of the radio frequency (RF) power amplifier.
In plot, a modified hybrid algorithm is explained to obtain
superior
PAPR
reduction
performance
and reduce
computational complexity compared with the conventional
hybrid method and performance analyzed of Hybrid scheme like
CH,SH,MH system under Rayleigh Fading channel.
Peak-to-Average Power Ratio (PAPR) is defined as
the large variation or ratio between the average signal power
and the maximum or minimum signal power.
Theoretically, large peaks in OFDM system can be
expressed as Peak-to-Average Power Ratio (PAPR) and it is
usually defined as[1] :
(1)
Where;
represents peak power,
means average power.
E[.] denotes the expected value,
Keywords— OFDM,PAPR ,SLM,PTS,BER.
I.INTRODUCTION
High Bit Rate and reliable communication system
demand led to have different modulation techniques.
Technique is used Orthogonal Frequency Division
Multiplexing (OFDM) is central in Wireless Communication
system as it having High Data Rate and efficient to Multiple
delay spread. OFDM has its significance for lead contain in
Fourth Generation (4G) wireless services. OFDM system has
enormous application in wired and wireless system, DABDigital Audio Broadcasting, (DVBT) Digital Video
Broadcasting Terrestrial, Wireless PAN and LAN.OFDM
signal consist of multiple sub-carriers, the system cause high
Peak Power. One of major disadvantage of OFDM system is
High Peak power to Average Power Ratio (PAPR), high
PAPR causes waveform distortion due to nonlinear amplifier
characteristics High PAPR can causes for Inter-modulation
and Out of band radiation in transmission channel[2][3].
Review of literature, the multiple signal
demonstration is recognized as PAPR reduction technique for
OFDM systems. Numerous useful methods related to SLMbased and PTS-based methods have been developed for
improving PAPR reduction performance or reducing the
computational complexity. This schemes consisting of
conventional hybrid (CH) method and modified SLM scheme.
A new modified hybrid (MH) algorithm is developed by
combining the additional hybrid (AH) with switching hybrid
(SH) schemes to decrease the number of IFFT and gain a
important PAPR reduction performance in OFDM
systems[5][6].
II. PEAK-TO-AVERAGE POWER RATIO (PAPR)
ISSN: 2231-5381
represents the transmitted OFDM signals which are
obtained by taking IFFT operation on modulated input
symbols . Mathematical, is expressed as:
(2)
th
An OFDM system having N sub-carriers and peak
power of received signals is N times the average power when
phase values are the same.
The baseband signal PAPR of will reach its theoretical
maximum at[1]:
(3)
Another commonly used parameter is the Crest Factor (CF),
which is defined as the ratio between maximum amplitude of
OFDM signal and root-mean-square (RMS) of the waveform.
The Crest Factor is defined as[7]:
(4)
III. METHODOLOGY
1. Conventional Hybrid Scheme
SLM and PTS schemes are combined to
form Conventional Hybrid scheme (CH) is one of PAPR
reduction technique In this scheme the novel OFDM symbol
is multiplied with U phase rotation sequences, and afterward
every new OFDM symbol is partitioned into V pair wise
dislodge sub-blocks[1]. Every optimization of PTS blocks is
done to calculated values OFDM sub-blocks[8]. Normally, for
ease supposing V to be 2. Each one signal (
), where
u=1, ...,U, among least PAPR is chosen by apiece
optimization block .
It can be given as:
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International Journal of Engineering Trends and Technology (IJETT) – Volume 21 Number 4 – March 2015
Hence,
=1/2, the average power of
is equal to one half of the sum of average power of
(5)
and
(6)
Where, 1≤ u ≤ U. With the selection block, the
relative small PAPR retained from those least PAPR values of
each one PTS slab. For the CH scheme CCDF can be given as:
CCDFCH= ( Pr (PAPRPTS>PAPR0)) U
Where, w is the no. of allowable phase rotations. The
first and the second term in the equation represent the SLM
and PTS mandatory side information bits respectively.
By generating a huge number of unusual OFDM
signal sequences without raising the number of IFFT to avoid
high computational complexity as PAPR reduction is
improved in CH scheme
2. Additional hybrid scheme
By combining the modified SLM scheme with CH
scheme get additional hybrid (AH) scheme. In AH scheme
system efficiency is not compromised. Evidently, the U
signal
, where =1,…., U, are the related as the signal
in the CH design. Additionally, linear combination of the subblock signal from dissimilar PTS blocks after IFFT operation
results to form different OFDM signal sequence. Via linear
property of Fourier transform, the linear combination of this
sequence given by[5][3]:
and
(
()
+
( )
(9)
Where +1 ≤ ≤ 2, 1≤ , ≤ ,1 ≤ ≤ 2, and ( )
)
are some coefficient to be chosen later. It is stated that,
if OFDM signal sequence
and
, substitute OFDM
signal sequence is obtained exclusive of performing IFFT
process. Every component of
and
to have Unit
magnitude under the state that each component of the phase
sequence c( ) and c( ) has unit magnitude. Originally, the
component of the sequence
and
if the following conditions are satisfied:
()
=±(1 / 2 ) and
( )
(10)
)=
+
=±(1/ 2 ) and
(11)
Where; U+1≤ ≤ 2.
We have to pick and transmit the ensuing OFDM
signal sequence
, which has the lowest amount PAPR
among the whole OFDM signal sequence of on the whole
least PAPR
sequences, which are composed by
after apiece optimization operation. The
number of essential side information bits for transmitter can
be given as[1][2]:
=log2 2+ ( −1) log2
(12)
3. Switching hybrid scheme
A new switching hybrid (SH) designs by combining
the switching method with the CH method. In system
presentation is advantageous that the number of IFFT is
reduced but the PAPR reduction concert is not compromised.
By the switching block, we can use inventive U pairs
to create extreme
pairs of OFDM
sequences exclusive of increasing the number of IFFT units.
Hence, totally 2 pairs
are operation done by every
optimizing unit. Visibly, the first U signals
), where
=1,...,U, are the identical as the signals in the CH design.
Behind the optimizing blocks, another different OFDM
sequences with least PAPR
can be given as:
(13)
have unit magnitude
Every element of P( ) and P( ) takes the value in ±1.
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can obtain
extreme pair sub-block sequences thus;
there are whole 2 extreme pair sub-blocks sequence for AH
design.
Then another OFDM signal of low PAPR in AH scheme can
be written as:
(7)
Respectively to get well transmitted data information,
the knowledge of side information must have to receiver. Thus
essential side information bits given as[1]:
NCH=log2U+ (V−1) log2W
(8)
=
..From U binary phase rotation sequences, we
=
+
(14)
Where U + 1 ≤ u ≤ U2, 1 ≤ i, k ≤ U and i ≠ k.
In (14),
and
, i ≠ k come from dissimilar PTS blocks,
which are generated by different phase rotation sequences, so
that ( )and ( ) , where 1 ≤ i, k ≤ U, i≠k, can gain differently
substitute OFDM sequences with the minimum PAPR[1][3].
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International Journal of Engineering Trends and Technology (IJETT) – Volume 21 Number 4 – March 2015
xtensively, the number of necessary side information bits can
be given as:
=log2 2 + ( −1) log2
(15)
4. Modified hybrid scheme
Modified hybrid (MH) algorithm is developed by
combining AH and SH scheme to create additional alternative
OFDM sequences, to further improve the PAPR reduction
performance with no raising the number of IFFT. Individuals
pairs, where; 1 ≤ ≤ ,indicate signal inputs of
the additional hybrid block and switching hybrid block
respectively and concurrently.
By linear combination of phase rotation sequences
can receive extreme
alternative OFDM sequences with
help of linear property of Fourier transform. Overall buck
PAPR
can be given later optimization of blocks. Using
the switching technique with PTS blocks, the signal having U
phase rotation sequences can obtain excessive
alternative OFDM sequences.
In the MH design, if V = 2 and U phase rotation
sequences are supposed, the original signals
can create
log2W
AH
=log2 2+ ( −1)
log2
9 dB
SH
=log2 2+ ( −1)
log2
9.2dB
MH
=log2 (2 2− ) +
(V−1) log2
8 dB
.
Apparently, in Fig. 2 and Fig. 3, AH and SH methods
by U = 2 and U = 4 have similar performance comparing to
CH design with U = 4 and U = 16, in that order. In Fig. 4, the
MH method with U = 2 and U = 4 has almost the same
performance compared with the CH scheme with U = 8 and U
= 26 respectively.
extreme
pairs of sequences respectively and
simultaneously by either additional block or switching block.
Here whole 2 2− OFDM sequences with the low PAPR in
the MH design[3]. Number of required side information bits to
recover the transmitted data information can be given as:
=log2 (2 2− ) + (V−1) log2
(16)
V. SIMULATION AND RESULTS
Table I- SIMULATION PARAMETERS FOR DESIGN
Simulation Parameters
Specification
No. of OFDM symbols
1000
No. of Subcarriers
64
No. of Sub blocks
V=2
Modulation scheme
QPSK
Phase rotation sequence
Fig.1- Performance analysis of the system for Convention
hybrid.
Phase rotation factor
In Table I; system parameters for relative simulations
are planned. The with the For the CH design for different
values of U Phase rotations shows the PAPR reduction
performance is shown in Fig. 1. PAPR reduction performance
can be superior with the increases number of U Phase
rotations.
Fig.2- Performance analysis of the system for Additional
hybrid.
Table II- SIDE INFORMATION BITS AND OBSERVED
PAPR FOR DIFFERENT HYBRID.
Schemes
Side information bits
PAPRo(10-3)
CH
NCH=log2U+ (V−1)
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8.5dB
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International Journal of Engineering Trends and Technology (IJETT) – Volume 21 Number 4 – March 2015
Table III- BER for different hybrid schmes under a Rayleigh
Fading Channel.at Ebno=12
Hybrid schemes
Bit Error Rate (BER)
CH
10-0.3
AH
10-0.5
MH
10-0.7
Fig.3- Performance analysis of the system for Switching
hybrid.
MH scheme having best PAPR reduction
performance with small increment in computational
complexity. Table II explains system complexity of different
hybrid designed for PAPR reduction, where the number of
IFFT is set as 8, that is, U = 4, V = 2 and W = 4.Hence, MH
scheme requires number less of IFFT compared to CH scheme.
R2009 using the rayleighchan () function with sampling
period of 100μs and Doppler Frequency shift of 10. Then the
signal is passed through this channel using the filter ()
function. Fig. 5 represents the BER related with a variety of
signal sequence values for CH, SH and MH design. The plot
evidently shows that the performance of the system is better
when there is a Rayleigh Fading Channel.
VI. CONCLUSION
Observing simulation results it can be stated that,
with the number of 'U' increases CH method gives better
PAPR reduction concert at the cost of computational
complexity with the raising of the number of IFFT. The other
hybrid schemes AH, SH and MH provides improved PAPR
reduction performance related to CH with similar number of
IFFT.
To conclude, the simulation output show that MH is
the most efficient hybrid scheme for better PAPR reduction
performance, comparing with all other hybrid mehods but at
the cost of speed. As, MH scheme required less FFT unit to
retain same PAPR reduction performance excepting increase
in side information bits and hence its helpful for getting low
BER under Rayleigh Fading channel.
VII. REFERENCES
[1]
Fig.4- Performance analysis of the system for Modified hybrid.
[2]
[3]
[4]
[5]
[6]
[7]
Fig.5- Performance analysis of the system under Rayleigh
Fading channel
Now, considering the performance of CH, SH and
MH design under Rayleigh Fading channel. The Rayleigh
Fading channel is designed by Rayleigh block in MATLAB
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[8]
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