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Presentation on

PRESENTED BYSandeep KumarEnR.No.112015

ICI analysis of FrFT-OFDM system

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CONTENTSHistory of wireless

communication systemOFDM Evolution

and Its Current Status

MotivationSingle carrier

Transmission Scheme

Multicarrier Modulation (MCM)

Concept of OFDMCyclic Prefix in

OFDM

Trans- Receiver Schematic of

OFDM systemOFDM ApplicationsDistortion in OFDM

Systemi)- Carrier Frequency Offsetii)- PAPR in OFDM System

Methods of Cancellation of Inter Carrier Interference

Time Frame

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History of wireless communication [9]

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OFDM Evolution and Its Current Status [11]• 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.

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Motivation•Orthogonal frequency division multiplexing (OFDM) is a promising technologyfor 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 .

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Need of OFDM [7]

Single Carrier Transmission : Problem of Frequency Selective Fading

Problem of ISI as data rate increases

Flat Fading Freq. Selective Fading

Ts >> στBs << Bc

Ts << στBs >> Bc

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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 subcarriersi(t) = Xi

si(t)= Xi

Bandwidth B divided in to N sub- carriers

1

2

N-1

1

2

N-1

Multi-carrier modulation system

Multicarrier Transmission Scheme [9]

[3]

[9]

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N subcarriers, hence N-data stream.[9]Composite transmitted

signal s(t) = where -(n/2-

1)≤ i ≤(n/2); s(t) = s(t) = Multicarrier data detection: To decode lth data

stream

Assume no noise s(t) = r(t)y(t)= B/N

=B/N

= B/N ( + )

0

y(t) = (information symbol transmitted

by sub carrier) To decode data stream

Multicarrier Transmission Scheme

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

| |1/B

One symbol

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

N/B

Available bandwidth = BFundamental time period Tₒ = N/BTransmission Rate = N/(N/B)

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

MCM symbol

Multi-carrier communicationSingle carrier communication

FIG[8] FIG[8]

Single Carrier Vs Multi Carrier Communication

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Subcarriers Spacing =1/TsMCM Tx.Signal Bandwidth = BNyquist sampling rate Rs = BSampling Time Ts = 1/Rs= 1/Bs(t) =

Concept of OFDM [1]

The sample t = u Ts = u/Bs(u Ts) =s(u Ts) =

IDFT of information symbol X(0),X(1),X(2)…………….X(N-1)

S.Weinstein and P. Ebert.(1971) :DataTransmission by frequency divisionmultiplexing using the DFT.[1][9]

MCM transmit signal

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Previous OFDM symbolCurrent OFDM symbol Multipath Channel RECEIVED SYMBOLS

ISI Part

Copy L-1 symbols

Free From ISI

Cyclic prefix

Cyclic prefix [9]

[9]

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Cyclic prefix

Circular ConvolutionWhere 0≤ k ≤ N-1

[10]

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Frequency selective fading channel N parallel frequency flat fading channelsLength of cyclic Prefix = L-1 ≥ Delay spread

INTUITIVE FRAME WORK TO UNDERSTAND CYCLIC PREFIX

EFFECTS OF CYCLIC PREFIX1)Loss in system efficiency = (L-1)/(N+L-1) as N2)Loss in system through put. N ,through put 0

Cyclic prefix

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Trans- receiver schematic of OFDM system [7]

Concept of OFDM signal[7]216

[11]

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Distortions in OFDM system [9]

1) FREQUENCY OFFSET

Interference fromAdjacent sub carriers

Carrier frequency offsetSamplingpoint

Normalized frequency offset = B/N

Baseband received samples

= FFT coefficient

Case 1st =0

=

Case 2st = R + ICI +[7]158

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Distortions in OFDM system2) PAPR :Peak to Average Power Ratio

PAPR =E = =1 or 0 dB

i) BPSK modulated Single carrier system = a

Peak Power

ii) In OFDM system

Peak Power = Average Power = E = /N

PAPR = NOutput voltage

Input voltageDynamic RangeCharacteristic curve[9]

Saturation Region

= 1/N

[9]

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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 techniques3) Temporal equalizers4) Techniques that depend on the presence

of unused subcarriers (null carriers)5) Forward-error correction

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P1

• Basics of OFDM system, major problems associated with OFDM system.

P2

• Inter-Carrier Interference(ICI) Cancellation Methods for OFDM system.

P3

• Simulation of Inter-Carrier Interference(ICI) Cancellation Methods of OFDM system, FrFT based OFDM system

SEMESTER-III

P1

• Mathematical analysis of Inter-Carrier Interference (ICI) for FrFT –OFDM system .

P2

• Simulation of Inter-Carrier Interference (ICI) for FrFT –OFDM system .

P3

• Comparison of the proposed technique with existing ICI Cancellation Methods.

TIME FRAME

SEMESTER-IV

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[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. 628–634, 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 cancellationFor 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-OFDMWireless 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 Kanpur”Lect-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”.

REFERENCES

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