Section3 4 OFDM fundamentals
Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Chapter 3: Physical-layer transmission techniques Section 3.4: Orthogonal Frequency Division Multiplexing (OFDM) Fundamentals Instructor: Nguyen Le Hung Email: nlhung@dut.udn.vn; nnguyenlehung@yahoo.com Department of Electronics & Telecommunications Engineering Danang University of Technology, University of Danang Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 1 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions 1 Introduction Development of mobile communications systems - Revisit Mobile broadband technology evolution - Revisit 2 Fundamentals of OFDM transmissions Functional blocks in OFDM transmitter and receiver Transmitted OFDM signals Time-variant multipath channels Received OFDM signals MQAM symbol detection in the frequency domain 3 Possible research problems in OFDM transmissions Carrier frequency offset (CFO) estimation Doubly selective channel estimation Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 2 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Development of mobile communications systems - Revisit Mobile broadband technology evolution - Revisit Development of mobile communications systems - Revisit time code frequency code space FDMA (1G) e.g., AMPS ~ 1980s TDMA (2G) e.g., GSM ~ 1990s OFDM, SDMA (4G) e.g., WiMAX, LTE 2010s CDMA (3G) e.g., W-CDMA ~ 2000s frequency time time ~ 1 Gbps (stationary), ~ 100 Mbps (mobile) frequency frequency ~ 14 Mbps (downlink), ~ 5.8 Mbps (uplink) ~ 50 Kbps A new signal dimension will be exploited in 5G ? Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 3 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Development of mobile communications systems - Revisit Mobile broadband technology evolution - Revisit Development of mobile communications systems - Revisit time code frequency code space FDMA (1G) e.g., AMPS ~ 1980s TDMA (2G) e.g., GSM ~ 1990s OFDM, SDMA (4G) e.g., WiMAX, LTE 2010s CDMA (3G) e.g., W-CDMA ~ 2000s frequency time time ~ 1 Gbps (stationary), ~ 100 Mbps (mobile) frequency frequency ~ 14 Mbps (downlink), ~ 5.8 Mbps (uplink) ~ 50 Kbps A new signal dimension will be exploited in 5G ? Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 3 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Development of mobile communications systems - Revisit Mobile broadband technology evolution - Revisit Mobile broadband technology evolution - Revisit LTE Advanced 802.16m R 2.0 WCDMA 3GPP HSDPA HSPA Mobile WiMAX 802.16e R 1.0 EVDO Rev A EVDO Rev B CDMA 2000 3GPP2 LTE 802.16e R 1.5 2005 2009 20102006 2007 2008 2011 2012 CDMA based OFDMA based R99 “4G” IMT-Advanced The last decade has witnessed numerous intensive studies in employing orthogonal frequency division multiplexing (OFDM) for the emerging broadband communications systems (e.g., WiFi, WiMAX, LTE) to exploit its high spectral efficiency and robustness against multipath (frequency selective) fading channels. Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 4 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Functional blocks in OFDM transmitter and receiver Transmitted OFDM signals Time-variant multipath channels Received OFDM signals MQAM symbol detection in the frequency domain Functional blocks in OFDM transmitter and receiver Burst structure S/P IFFT Insert CP DAC RF Clk Osc RF LO Pilotinsertion Conv. Encoder P/S c i MQAM mapping Pilot OFDM symbols Data OFDM symbols Information bits,u i RF LO Clk Osc MQAM Demapper RF ADC S/P decoder -1 FFT CP Information bits,u i Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 5 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Functional blocks in OFDM transmitter and receiver Transmitted OFDM signals Time-variant multipath channels Received OFDM signals MQAM symbol detection in the frequency domain Transmitted OFDM signals Consider a coded OFDM system using 𝑀-ary quadrature amplitude modulation (M-QAM). The encoded bit stream is bit-interleaved. Then, the resulting sequence of interleaved bits is organized as a sequence of 𝑄-bit tuples {d 𝑘,𝑚 } where 𝑄 = log 2 𝑀 and d 𝑘,𝑚 = [𝑑 𝑘,𝑚,0 , ., 𝑑 𝑘,𝑚,𝑄−1 ] 𝑇 . The sequence is further mapped to a complex-valued symbol 𝑋 𝑘,𝑚 ∈ 𝔸 where 𝔸 is the 𝑀-ary modulation signaling alphabet, and 𝑚 and 𝑘 denote the indices of OFDM symbol and subcarrier, respectively. m X ,0 mN X ,1 1,0 m X 1,1 mN X mk X , 1, mk X T Qmkmkmk dd ], .,[ 1,,0,,, d The m-th OFDM symbol The k-th subcarrier Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 6 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Functional blocks in OFDM transmitter and receiver Transmitted OFDM signals Time-variant multipath channels Received OFDM signals MQAM symbol detection in the frequency domain Transmitted OFDM signals Consider a coded OFDM system using 𝑀-ary quadrature amplitude modulation (M-QAM). The encoded bit stream is bit-interleaved. Then, the resulting sequence of interleaved bits is organized as a sequence of 𝑄-bit tuples {d 𝑘,𝑚 } where 𝑄 = log 2 𝑀 and d 𝑘,𝑚 = [𝑑 𝑘,𝑚,0 , ., 𝑑 𝑘,𝑚,𝑄−1 ] 𝑇 . The sequence is further mapped to a complex-valued symbol 𝑋 𝑘,𝑚 ∈ 𝔸 where 𝔸 is the 𝑀-ary modulation signaling alphabet, and 𝑚 and 𝑘 denote the indices of OFDM symbol and subcarrier, respectively. m X ,0 mN X ,1 1,0 m X 1,1 mN X mk X , 1, mk X T Qmkmkmk dd ], .,[ 1,,0,,, d The m-th OFDM symbol The k-th subcarrier Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 6 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Functional blocks in OFDM transmitter and receiver Transmitted OFDM signals Time-variant multipath channels Received OFDM signals MQAM symbol detection in the frequency domain Transmitted OFDM signals (cont.) Each OFDM symbol consists of 𝑁 information bearing subcarriers 𝑋 𝑘,𝑚 , 𝑘 = 0, ., 𝑁 − 1, where 𝑁 is the size of the fast Fourier transform (FFT) and inverse-FFT (IFFT) used in the multicarrier transmission. mn x , QAM symbols mk X , CP samples IFFT P/S DAC RF Burst structure S/P IFFT Insert CP DAC RF Clk Osc RF LO Pilotinsertion Conv. Encoder P/S c i MQAM mapping Information bits,u i Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 7 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Functional blocks in OFDM transmitter and receiver Transmitted OFDM signals Time-variant multipath channels Received OFDM signals MQAM symbol detection in the frequency domain Transmitted OFDM signals (cont.) Copy and paste the last N g samples CP portion CP portion mNN g x , …. mN x ,1 m x ,0 m x ,1 m x ,2 …. mNN g x ,1 mNN g x , …. mN x ,1 one OFDM symbol of samples After inverse FFT (IFFT) and cyclic prefix (CP) insertion, the transmitted baseband signal of the 𝑚th OFDM symbol can be written as 𝑥 𝑛,𝑚 = 1 √ 𝑁 𝑁−1 𝑘=0 𝑋 𝑘,𝑚 exp 𝑗2𝜋𝑘𝑛 𝑁 , (1) where 𝑛 ∈ {−𝑁 𝑔 , ., 0, ., 𝑁 − 1}, 𝑁 𝑔 denotes the CP length. Mobile Communications - Chapter 3: Physical-layer transmissions Section 3.4: OFDM fundamentals 8 . 3 .4: OFDM fundamentals 4 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Functional blocks in OFDM. 3 .4: OFDM fundamentals 5 Outline Introduction Fundamentals of OFDM transmissions Possible research problems in OFDM transmissions Functional blocks in OFDM