PPT on Basics of OFDM System

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Presentation onICI analysis of FrFT-OFDM system

PRESENTED BY Sandeep Kumar EnR.No.112015SANDEEP KUMAR 1

CONTENTS History of wireless communication system OFDM Evolution and Its Current Status Motivation Single carrier Transmission Scheme Multicarrier Modulation (MCM) Concept of OFDM Cyclic Prefix in OFDM Trans- Receiver Schematic of OFDM system OFDM Applications Distortion in OFDM System i)- Carrier Frequency Offset ii)- PAPR in OFDM System Methods of Cancellation of Inter Carrier Interference Time Frame2

SANDEEP KUMAR

History of wireless communication [9]

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In Dec. 1966, Robert W. Chang presented synthesis of Multi Channel Data Transmission with Real data. In Dec. 1967, B.R. Saltzberg demonstrated the performance of Efficient Parallel Data Transmission with Complex data. In Oct. 1971, S.Weinstein and P.Ebert performed Multi Carrier Transmission by using DFT. In Apr. 1980, A.Peled and A.Ruiz solved the orthogonality by introducing Cyclic Extension. In Jan. 1981, B.Hirosaki introduced an equalization algorithm to mitigate ISI and ICI. In July 1985, L.J.Cimini introduced a Pilot based method to reduce interference. In Feb. 1989, I.Kalet suggested a Sub-Carrier-Selective allocating scheme. In Mar. 2000, L.J Cimini and N.R. Sollenberger presented first PAPR Reduction Technique named as Partial Transmit Sequence (PTS). In Dec. 2011, M. Sabbaghian and Y. Kwak presented the latest PAPR Reduction technique named as Dual BCH Codes technique.SANDEEP KUMAR 4

OFDM Evolution and Its Current Status [11]

Motivation

Orthogonal frequency division multiplexing (OFDM) is a promising technology for broadband transmission. Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier

modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2.OFDM is a method of encoding digital data on multiple carrier frequencies. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. A well-known problem of OFDM is its sensitivity to frequency offset between the

transmitted and received carrier frequencies.This frequency offset introduces inter-carrier interference (ICI) in the OFDM symbol. This work studies an efficient ICI cancellation method .SANDEEP KUMAR 5

Need of OFDM [7] Flat Fading

Ts >> Bs Bc

Single Carrier Transmission : Problem of Frequency Selective FadingProblem of ISI as data rate increases

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Multicarrier Transmission Scheme [9]System with two sided B.W. ith Center frequency Fi Fi = iB/N where -(n/2-1) i (n/2); Data transmitted on ith subcarrier = Xi Modulated signal at ith subcarrier si(t) = Xi si(t)= XiBandwidth B divided in to N sub- carriers

[9]

Multi-carrier modulation system1 1

2

2

N-1

[3]

N-1

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Multicarrier Transmission SchemeN subcarriers, hence N-data stream.[9] Assume no noise s(t) = r(t)y(t)= B/N=B/N = B/N( + )

Composite transmitted signals(t) =

where -(n/2-1) i (n/2); s(t) = s(t) = Multicarrier data detection:

To decode lth data stream To decode data stream

y(t) =

0 (information symbol transmitted

by

sub carrier)

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Single Carrier Vs Multi Carrier CommunicationSingle carrier communication Multi-carrier communication

FIG[8]

FIG[8]

Available bandwidth = B Symbol Time T = 1/B sec. Symbol Rate = 1/T = B symbol /sec s(t) = X(k) where kT t (k+1)TOne symbol

Available bandwidth = B Fundamental time period T = N/B Transmission Rate = N/(N/B)MCM symbol

| 1/B |

N/B

R = B symbol per sec B Bc (Bc=200-300Khz)

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R = B symbol per sec B Bc (Bc=200-300Khz)

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Concept of OFDM [1]S.Weinstein and P. Ebert.(1971) :Data Transmission by frequency division multiplexing using the DFT.[1][9] MCM transmit signal Subcarriers Spacing =1/Ts MCM Tx.Signal Bandwidth = B Nyquist sampling rate Rs = B Sampling Time Ts = 1/Rs= 1/B s(t) = The sample t = u Ts = u/B s(u Ts) = s(u Ts) = IDFT of information symbol X(0),X(1), X(2).X(N-1)SANDEEP KUMAR 10

Cyclic prefix [9]Previous OFDM symbol Current OFDM symbol Multipath Channel

RECEIVED SYMBOLS [9]ISI Part

Cyclic prefixCopy L-1 symbols

Free From ISISANDEEP KUMAR 11

Cyclic prefixCircular ConvolutionWhere 0 k N-1

[10]

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Cyclic prefixEFFECTS OF CYCLIC PREFIX 1)Loss in system efficiency = (L-1)/(N+L-1) as N 2)Loss in system through put. N ,through put

0

Frequency selective fading channel Length of cyclic Prefix = L-1

N parallel frequency flat fading channels Delay spread

INTUITIVE FRAME WORK TO UNDERSTAND CYCLIC PREFIX

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Trans- receiver schematic of OFDM system [7]

Concept of OFDM signal

[7]216

[11]SANDEEP KUMAR 14

Distortions in OFDM system [9]1) FREQUENCY OFFSET Normalized frequency offset =B/N

Baseband received samples

=Carrier frequency offset Sampling point

FFT coefficient

Case 1st

=0

= [7]158 Interference from Adjacent sub carriersSANDEEP KUMAR

Case 2st =

R

+ ICI +15

Distortions in OFDM system2) PAPR :Peak to Average Power Ratio i) BPSK modulated Single carrier system= a= 1/N

Peak Power = PAPR = Eii)

=1 or 0 dB

Peak Power = Average Power = E PAPR = NOutput voltage

=

/N

In OFDM system

Saturation Region

[9]SANDEEP KUMAR

Dynamic Range

Input voltage Characteristic curve[9]16

Applications of OFDM Wireless LAN (Wi-Fi) standards using OFDM are: IEEE 802.11a, IEEE 802 .11g, IEEE 802.11n, IEEE 802.11ac Wireless MAN (Wi-Max) standards using OFDM are: IEEE 802.16a, IEEE 802.16e Digital Audio Broadcasting Digital Video Broadcasting Long Term Evolution (LTE) Future Applications: Ultra Wide Band (UWB)

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Methods for Cancellation of Intercarrier Interference [2]1) Optimum choice of the carrier spacing and OFDM symbol length 2) Self-interference-cancellation techniques 3) Temporal equalizers 4) Techniques that depend on the presence of unused subcarriers (null carriers) 5) Forward-error correction

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TIME FRAMEP1 P2 P3

SEMESTER-III

Basics of OFDM system, major problems associated with OFDM system. Inter-Carrier Interference(ICI) Cancellation Methods for OFDM system. Simulation of Inter-Carrier Interference(ICI) Cancellation Methods of OFDM system, FrFT based OFDM system SEMESTER-IV Mathematical analysis of Inter-Carrier Interference (ICI) for FrFT OFDM system .

P1 P2 P3

Simulation of Inter-Carrier Interference (ICI) for FrFT OFDM system . Comparison of the proposed technique with existing ICI Cancellation Methods.SANDEEP KUMAR 19

REFERENCES[1] S. Weinstein and P. Ebert, Data transmission by frequency-division multiplexing using the discrete Fourier transform, IEEE Trans. CommUC., vol. -19, no. 5, pp. 628634, Oct. 1971. [2] Andreas F. Molisch, Martin Toeltsch, and Sameer Vermani, Iterative Methods for Cancellation of Intercarrier Interference in OFDM Systems, August 2008. [3] W.Shieh, H.Bao, and Y. Tang Coherent, Coherent optical OFDM: Theory and Design Vol.16,N0.2/Optics Express 842,21 January 2008. [4] S.Driz, M.Bouziani and J.M.Rouvaen, Inter-carrier Interference cancellation For OFDM system. [5]Stephen B.Weinstein, The History of Orthogonal Frequency-Division Multiplexing IEEE communication Magazine, November 2009. [6] J.Samuel, A.Emmanuel,I.Frank,N.Charles,A.Bayonle, Modeling of Orthogonal Frequency Division Multiplexing(OFDM) for Transmission in Broadband Wireless Communications,2009-2012 CIS Journal,Vol3,No.4,April 2012. [7] Yong soo cho, Jaekwon Km,Won Young Yang, Chung- Gu Kang, MIMO-OFDM Wireless communications with MATLAB. [8] Richard Wan Nee and Ramjee Prasad, OFDM for wireless multimedia communication. [9]Prof. Aditya K. Jagannatham ,Dept. of Electrical Engineering, IIT KanpurLect-01 introduction to 3G-4G Standards NP-TEL. [10] Ramjee Prasad, OFDM for wireless communication system. [11]Nick LaSorte, W.Justin Barnes, Hazem H. Refai, The History of orthogonal Frequency Division Multiplexing.

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