(Ofdm)

Introduction to OFDM Fire Tom Wada Professor, Information Engineering, Univ. of the Ryukyus Chief Scientist at Magna Design Net, Inc [email_address] http://www.ie.u-ryukyu.ac.jp/~wada/ 06/07/09 System Arch 2007 (Fire Tom Wada)

What is OFDM? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Outline ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Why OFDM is getting popular ？ ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Japan Terrestrial Video Broadcasting service ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Brief history of OFDM ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Digital modulation basics ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) OFDM uses combination of ASK and PSK such as QAM, PSK

Symbol Waveform 06/07/09 System Arch 2007 (Fire Tom Wada) 1 0 1 0 0 Digital Information carrier ASK PSK FSK Symbol length

Multi bit modulation 06/07/09 System Arch 2007 (Fire Tom Wada) 1 0 1 0 0 carrier BPSK 1bit per symbol QPSK 2bit per symbol 10 11 01 00 01 Symbol length

Mathematical expression of digital modulation ,[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Indicates carrier sinusoidal Digital modulation Digital modulation can be expressed by the complex number

Constellation map ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) QPSK I Q data a k b k 00 π/4 01 3π /4 11 5π /4 10 7π /4

Quadrature Amplitude Modulation (QAM) 06/07/09 System Arch 2007 (Fire Tom Wada) I Q I Q 16QAM 64QAM

Summary of digital modulation ,[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) I Q

Frequency Division Multiple Access (FDMA) ,[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Radio frequency f ｃ１ f ｃ 2 f ｃ 3 f ｃ N Carrier frequency Occupied BW Channel separation Guard band

Japan VHF channel assignment ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Channel number Frequency (MHz) 1 90-96 2 96-102 3 102-108 4 170-176 5 176-182 6 182-188 7 188-194 8 192-198 9 198-204 10 204-210 11 210-216 12 216-222

Multi-carrier modulation ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) data LPF LPF LPF data DEMULTIPLEX MULTIPLEX

Spectrum comparison for same data rate transmission 06/07/09 System Arch 2007 (Fire Tom Wada) frequency Single carrier frequency OFDM frequency Multi carrier

OFDM vs. Multi carrier ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Thousands of PSK/QAM symbol can be simultaneously transmitted in one OFDM symbol

OFDM carriers ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Symbol period T

Sinusoidal Orthogonality ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Orthogonal Orthogonal Orthogonal

A sub-carrier of f=nf 0 ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) n cycles t=0 t=T Time

Base-band OFDM signal 06/07/09 System Arch 2007 (Fire Tom Wada) Ｔ n=0 n=1 n=2 n=3 n=4 n=5 n=6 s B (t)

How a n ,b n are calculated from s B (t) - Demodulation Procedure - ,[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Pass-band OFDM signal ,[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Actual OFDM spectrum 06/07/09 System Arch 2007 (Fire Tom Wada) f ｃ＋ｋｆ０ f ｃ＋ ( ｋ -1) ｆ０ f ｃ＋ ( ｋ +1) ｆ０

OFDM power spectrum ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

OFDM signal generation ,[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

OFDM signal generation in digital domain ,[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) u(k) = IFFT (d n ) = IFFT(a n + jb n )

OFDM modulator 06/07/09 System Arch 2007 (Fire Tom Wada) M A P S / P I-DFT P / S Real ＢＰＦ generated 0 ~d Ｎ－１ AIR Bit stream Imag

OFDM demodulation 06/07/09 System Arch 2007 (Fire Tom Wada) d n = FFT(u(k))

OFDM demodulator (Too simple) 06/07/09 System Arch 2007 (Fire Tom Wada) T u n e r S / P DFT P / S A / D LPF Channel π/2 LPF D E M A P Bit Stream

Summary of OFDM signal ,[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Time Symbol period T=1/f ０

Multi-path ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Multi-pass effect ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) T=1/f ０ Symbol k Symbol k-1 Symbol k+1 Sampling Period No multi-path Sampling Period Multi-path Direct Delayed

Guard Interval T g ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) OFDM symbol(1/f 0 ) Copy signal T g T g Direct Delayed OFDM symbol (1/f 0 ) T g Sampling Period

Multi-path ,[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

Multiple Frequency Network ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Area 1 Area 2 Area 3 Area 4 f １ f2 f3 f1

Single Frequency Network ,[object Object],06/07/09 System Arch 2007 (Fire Tom Wada) Area 1 Area 2 Area 3 Area 4 f １ f １ f １ f1

That ’ s all for introduction ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],06/07/09 System Arch 2007 (Fire Tom Wada)

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