Sistec ppt
-
Upload
hemant-choubey -
Category
Technology
-
view
283 -
download
3
Transcript of Sistec ppt
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
PRESENTED BY :-HEMANT CHOUBEYSISTEC-E RATIBAD
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
www.sistec.ac.in
EFFICIENT PAPR REDUCTION IN OFDM SYSTEM BASED ON A COMPANDING
TECHNIQUE WITH GAUSSIAN DISTRIBUTION
Literature survey
1 .S. H. Han and J. H. Lee, “An overview of peak-to-average power ratio reduction techniques for multicarrier transmission,” IEEE Wireless Commun., vol. 12, pp. 56–65, Apr. 2005.
2. T. Jiang and Y.Wu, “An overview: Peak-to-average power ratio reduction techniques for OFDM signals,” IEEE Trans. Broadcast., vol. 54, no. 2, pp. 257–268, Jun. 2008.
3. C. P. Li, S. H. Wang, and C. L. Wang, “Novel low-complexity SLM schemes for PAPR reduction in OFDM systems,” IEEE Trans. Signal Process., vol. 58, no. 5, pp. 2916–2921, May 2010.
The Basic Principles of OFDM◦ FFT-based OFDM System◦ Serial and Parallel Concepts◦ Modulation/Mapping
M-ary Phase Shift Keying M-ary Quadrature Amplitude Modulation
◦ IFFT and FFT Signal Representation of OFDM using IDFT/DFT
◦ Orthogonality◦ Guard Interval and Cyclic Extension◦ Advantages and Disadvantages◦ Background theory◦ Selective mapping◦ Partial transmit sequence◦ Companding◦ Companding with gaussian distribution◦ Central limit theorem◦ Reference
Outlines Of Presentation
OFDM is the most popular one. The first OFDM scheme was proposed by Chang in 1966. Even though the concept of OFDM has been around for several years, but it has not been recognized as a great method for high speed bi-directional wireless data communication until recent years. The first applications of OFDM were in the military HF radio links. Today, the OFDM technique is in many wirelesses and wired applications, such as broadband radio access networks (BRAN), Digital Audio Broadcasting (DAB), Digital Video Broadcasting-Terrestrial (DVB-T) and Asymmetric Digital Subscriber Line (ADSL)
Basic Principles of OFDM
FFT-based OFDM System
Serial-to-Parallel
Converter
SignalMapper
IFFTParallel-to-Serial
Converter
GuardIntervalInsertion
Serial Data Input
x bits0d
1d
1nd
0s
1s
1ns
D/A &Low pass
Filter
Up-Converter
Down-Converter
A/D Guard
IntervalRemoval
Serial-to-Parallel
ConverterFFT
One-tapEqualizer
SignalDemapper
Parallel-to-Serial
Converter
Serial Data
Output
0dx bits
1d
1ˆ
nd
0s1s
1ˆ ns
Channel
)(ts
Time
Frequency
Subchannels
Fast Fourier Transform
Guard Intervals
Symbols
FFT-based OFDM System OFDM Transmitter
Signal Mapper(QPSK)
IFFTParallel-to-Serial Converter
Guard IntervalInsertion
Serial-to-Parallel
Converter
2d
1nd
Serial
Data
Input
1s
2s
1ns
x bits
D/A&
LowpassFilter
1x 1d
2x
1nx
x=[0,0,0,1,1,0,1,1,….]
x1=[0,0]
x2=[0,1]
x3=[1,0]
x4=[1,1]
Q
.I
.
.
. 00
01
11
10
.I
.
.
. 00
01
11
10
Q
.
.
.
. 00
01
11
10
I.
.
.
. 00
01
11
10
d1=1
d2=i
d3=-1
d4=-i
…..
FFT-based OFDM System OFDM Transmitter
DATA CP
CP
CP
CP
CP
1
1
1
i
i
d
é ùê úê úê úê ú= ê úê úê úê ú-ê úë û
M
0 10 20 30 40 50 60 70-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
[ ]-0.09, -0.003-0.096i, , 0.01+ 0.247i, -0.035-0.0472is = L
0 10 20 30 40 50 60 70 80-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
Signal Mapper(QPSK)
IFFTParallel-to-Serial Converter
Guard IntervalInsertion
Serial-to-Parallel
Converter
2d
1nd
Serial
Data
Input
1s
2s
1ns
x bits
D/A&
LowpassFilter
1x 1d
2x
1nx
0 10 20 30 40 50 60 70 80-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
In OFDM system design, the series and parallel converter is considered to realize the concept of parallel data transmission.
Series and Parallel Concepts
Serial-to-Parallel
Converter
Serial data
Parallel data
s bT NTbT 2 bT 00 t t
Series ◦In a conventional serial data system, the
symbols are transmitted sequentially, with the frequency spectrum of each data symbol allowed to occupy the entire available bandwidth.
◦When the data rate is sufficient high, several adjacent symbols may be completely distorted over frequency selective fading or multipath delay spread channel.
Parallel
◦The spectrum of an individual data element normally occupies only a small part of available bandwidth.
◦Because of dividing an entire channel bandwidth into many narrow subbands, the frequency response over each individual subchannel is relatively flat.
◦A parallel data transmission system offers possibilities for alleviating this problem encountered with serial systems. Resistance to frequency selective
fading
The process of mapping the information bits onto the signal constellation plays a fundamental role in determining the properties of the modulation.
An OFDM signal consists of a sum of sub-
carriers, each of which contains 1. M-ary Phase Shift Keying (PSK) or 2. Quadrature Amplitude Modulated (QAM)
signals.
Modulation/Mapping
M-ary phase shift keying ◦Consider M-ary phase-shift keying (M-PSK) for
which the signal set is
where is the signal energy per symbol, is the symbol duration, and is the carrier frequency.
◦This phase of the carrier takes on one of the M possible values, namely , where
Mapping - Phase Shift Keying
2 12cos 2 0 , 1, 2,...,s
i c ss
iEs t f t t T i M
T M
2 1i i M
1,2,...,i M
sEsT
cf
An example of signal-space diagram for 8-PSK .
Mapping - Phase Shift Keying
sE
2m
3m
4m
5m
6m
7m
8m
Decisionboundary
2
messagepoint
sE
sE
d
d
MM 1m
Decisionregion
1sE
An example of signal-space diagram for 16-square QAM.
Mapping – QAM
Time domain Frequency domain
Orthogonality
Example of four subcarriers within one OFDM symbol
Spectra of individual subcarriers
Two different sources of interference can be identified in the OFDM system.
◦ Inter Symbol Interference (ISI) - crosstalk between signals within the same sub-channel of consecutive FFT frames, which are separated in time by the signaling interval T.
◦ Inter Carrier Interference (ICI) - crosstalk between adjacent sub channels or frequency bands of the same FFT frame.
Guard Interval and Cyclic Extension
Delay spread
Guard Interval and Cyclic Extension
Environment Delay Spread
Home < 50 ns
Office ~ 100 ns
Manufactures 200 ~ 300 ns
Suburban < 10 us
Guard Interval and Cyclic ExtensionIf T g < T dely-spread
Tg Symbol 1 Tg Symbol 2 Tg Symbol 3 Tg Symbol 4
Tdely-spread
If Tg > T dely-spread
Tg Symbol 1 Tg Symbol 2 Tg Symbol 3
Tg Symbol 1 Tg Symbol 2 Tg Symbol 3 Tg Symbol 4
Tg Symbol 1 Tg Symbol 2 Tg Symbol 3
Tdely-spread
﹒﹒﹒﹒
﹒﹒﹒﹒
﹒﹒﹒﹒
﹒﹒﹒﹒
o To eliminate ICI, the OFDM symbol is cyclically extended in the guard interval.
o This ensures that delayed replicas of the OFDM symbol always have an integer number of cycles within the FFT interval, as long as the delay is smaller than the guard interval.
Guard Interval and Cyclic Extension
Guard Interval(Cyclic Extension)
Effect of multipath with zero signals in the guard interval, the delayed subcarrier 2 causes ICI on subcarrier 1 and vice versa.
Guard Interval and Cyclic Extension
Part of subcarrier #2 causing ICI on subcarrier #1
Guard time FFT integration time=1/carrier spacing Guard time FFT integration time=1/carrier spacing
OFDM symbol time OFDM symbol time
Subcarrier #1
Delayed subcarrier #2
Guard Interval and Cyclic Extension
Time and frequency representation of OFDM with guard intervals.
Time
Frequency
T
Tg
1/T Subchannels
Fast Fourier Transform
Guard Intervals
Symbols
◦Immunity to delay spread
◦Resistance to frequency selective fading
◦Simple equalization
◦Efficient bandwidth usage
Advantages
◦The problem of synchronization Symbol synchronization Frequency synchronization
◦Need FFT units at transmitter, receiver
Disadvantages
◦Sensitive to carrier frequency offset ◦Problem of high peak to average power ratio
(PAPR)Problem 1. Increased complexity of ADC and DAC.Problem 2. Reduced efficiency of the RF power amplifier.
Solutions Signal distortion techniques Special forward-error-correction code Scrambling
Various reduction techniques of peak to average power reduction (PAPR) of ofdm.
o Selective mappingo Partial transmit sequenceo Companding
Background Theory
Selective Mapping
Partial Transmit Sequence
Basics Of Companding
Research Methodology
o Companding is another popular PAPR reduction scheme. Companding is a composite word formed by combining compressing and expanding. In this scheme, at the transmitter a signal with high dynamic range is applied to a compander and at the receiver a decompanding function (the inverse of companding function) is used to recover the original signal
o It increases the average power while peak remains the same therefore PAPR reduced .
Companding
function [y] = compressor(x,mu,sigma) y = (1/(sigma*sqrt(2*pi)))*exp(-((x-mu).^2)./(2*sigma^2));end function [y] = decompressor(x,mu,sigma) y = sqrt(-1*(2*sigma^2)*(log(sigma*sqrt(2*pi).*x))) + mu; end
Compression and decompression
PAPR =
Gaussian probability distribution is perhaps the most used distribution in all of science. It is also called “bell shaped curve” or normal distribution. Unlike the binomial and Poisson distribution, the Gaussian is a continuous distribution.
Companding with Gaussian distribution
The important thing to note about a normal distribution is the curve is concentrated in the center and decreases on either side
A bell curve graph depends on two factors, the mean and the standard deviation
Central Limit Theorem
C.L.T. tells us that under a wide range of circumstances the probability distribution that describes the sum of random variables tends towards a Gaussian distribution as the number of terms in the sum tends to infinite.
Sum of 12 uniform random numbers minus 6 is distributed as if it came from a Gaussian pdf with m = 0 and s = 1
NOrthogonal
carrierSNR(dB) Sigma (σ) Mu(µ) PAPR
Average
power
1000 4 0-10 1 0 2.09 0.4955
10000 4 0-10 1 0 2.05 0.50246
100000 4 0-10 1 0 2.1095 0.49941
1000 8 0-10 1 0 2.02 0.49425
Performance AnalysisTable1:Comparison of various parameter used in OFDM
1 20
0.5
1
1.5
2
2.5
Simple OFDM,OFDM compander
PA
PR
Simulated PAPR for OFDM with and without Compander
RESULTS
PAPR with and without companding
0 1 2 3 4 5 6 7 8 9 1010
-5
10-4
10-3
10-2
10-1
Eb/No, dB
Bit E
rror
Rate
Simulated BER for OFDM with different Codes under AWGN Channel
Simple OFDM
OFDM compander
BER with and without companding
[1] Richard van Nee, Ramjee Prasad, OFDM wireless multimedia communication, Artech House Boston London, 2012.
[2] Ahmad R. S. Bahai and Burton R. Saltzberg, Multi-carrier digital communications - Theory and applications of OFDM, Kluwer Academic / Plenum Publishers New York, Boston, Dordrecht, London, Moscow, 2011.
[3] Ramjee Prasad, “OFDM based wireless broadband multimedia communication,” Letter Notes on ISCOM’99, Kaohsiung, Taiwan, Nov. 7-10, 2010.
[4] L. Hanzo, W. Webb and T. Keller, Single- and multi-carrier quadrature amplitude modulation – Principles and applications for personal communications, WLANs and broadcasting, John Wiley & Sons, Ltd, 2013.
[5] Mark Engels, Wireless Ofdm Systems: How to Make Them Work? Kluwer Academic Publishers.
[6] Lajos Hanzo, William Webb, Thomas Keller, Single and Multicarrier Modulation: Principles and Applications, 2nd edition, IEEE Computer Society.
[7] Zou, W.Y.; Yiyan Wu, “ COFDM: An overview ” Broadcasting, IEEE Transactions on, Vol. 41, Issue 1, pp. 1 –8, Mar. 2011.
[8] Emmanuel C. Ifeachor & Barrie W. Jervis, Digital signal processing – A practical approach, Addision-Wesley, 2012.
[9] Blahut, R. E., Fast Algorithms for digital processing. Reading, Ma: Addison-Wesley, 2011.
[10] Simon Haykin, Communication Systems, John Wiley & Sons, Inc., 3rd edition, 2012.
[11] Roger L. Peterson, Rodger E. Ziemer, David E. Borth, Introduction to spread spectrum communications, Prentice Hall International Editions, 2010
References
THANKS