Abstract

In this paper, a transform domain processing (TDP) based channel estimation method for orthogonal frequency-division multiplexing (OFDM) Radio-over-Fiber (RoF) systems is proposed. Theoretically investigation shows that TDP can greatly reduce the number of required training symbols. An 8 x 4.65 Gb/s multi-user OFDM RoF system over 40 km fiber link and 60 GHz wireless link is experimentally demonstrated utilizing TDP scheme. Compared with conventional time domain averaging (TDA) scheme, the overhead can be reduced from several tens of training symbols to merely one symbol and the receiver sensitivity has been improved by 1.8 dB at BER of 3.8 x 10−3. The calculated BER performance for 8 wireless users clearly validates the feasibility of this TDP-based channel estimation method.

©2013 Optical Society of America

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References

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2012 (4)

2010 (3)

2009 (1)

2008 (2)

2006 (1)

2003 (1)

Bao, H.

Buchali, F.

Cao, Z.

Chang, G. K.

Chao, M.

C. Wei, C. Lin, M. Chao, and W. Jiang, “Adaptively modulated OFDM RoF signals at 60 GHz over-long-reach 100-km transmission systems employing phase noise suppression,” IEEE Photon. Technol. Lett. 24(1), 49–51 (2012).

Chen, L.

Chen, S.

Chi, N.

Chien, H. C.

Chowdhury, A.

Dong, Z.

Fang, Y.

Gao, Y.

He, Z.

Hsueh, Y. T.

Huang, A.

Y. Zhao and A. Huang, “A novel channel estimation method for OFDM mobile communication systems based on pilot signals and transform-domain processing,” IEEE Vehicular Technology Conference, 3, 2089–2093 (1997).

Huang, M. F.

Jia, Z.

Jian, W.

Jiang, W.

C. Wei, C. Lin, M. Chao, and W. Jiang, “Adaptively modulated OFDM RoF signals at 60 GHz over-long-reach 100-km transmission systems employing phase noise suppression,” IEEE Photon. Technol. Lett. 24(1), 49–51 (2012).

Kitayama, K.

Krongold, B. S.

Y. Tang, W. Shieh, and B. S. Krongold, “DFT-Spread OFDM for fiber nonlinearity mitigation,” IEEE Photon. Technol. Lett. 22(16), 1250–1252 (2010).
[Crossref]

Kuri, T.

Lin, C.

C. Wei, C. Lin, M. Chao, and W. Jiang, “Adaptively modulated OFDM RoF signals at 60 GHz over-long-reach 100-km transmission systems employing phase noise suppression,” IEEE Photon. Technol. Lett. 24(1), 49–51 (2012).

Liu, C.

Liu, X.

Luo, M.

Ma, Y.

Nakasyotani, T.

Shao, Y.

Shieh, W.

Tang, Q.

Tang, Y.

Y. Tang, W. Shieh, and B. S. Krongold, “DFT-Spread OFDM for fiber nonlinearity mitigation,” IEEE Photon. Technol. Lett. 22(16), 1250–1252 (2010).
[Crossref]

W. Shieh, H. Bao, and Y. Tang, “Coherent optical OFDM: theory and design,” Opt. Express 16(2), 841–859 (2008).
[Crossref] [PubMed]

Tao, L.

Toda, H.

Wang, W.

Wei, C.

C. Wei, C. Lin, M. Chao, and W. Jiang, “Adaptively modulated OFDM RoF signals at 60 GHz over-long-reach 100-km transmission systems employing phase noise suppression,” IEEE Photon. Technol. Lett. 24(1), 49–51 (2012).

Xia, M.

Yamashita, T.

Yang, Q.

Yang, Z.

Yi, X.

Yu, J.

Yu, S.

Zhang, J.

Zhao, Y.

Y. Zhao and A. Huang, “A novel channel estimation method for OFDM mobile communication systems based on pilot signals and transform-domain processing,” IEEE Vehicular Technology Conference, 3, 2089–2093 (1997).

IEEE Photon. Technol. Lett. (2)

C. Wei, C. Lin, M. Chao, and W. Jiang, “Adaptively modulated OFDM RoF signals at 60 GHz over-long-reach 100-km transmission systems employing phase noise suppression,” IEEE Photon. Technol. Lett. 24(1), 49–51 (2012).

Y. Tang, W. Shieh, and B. S. Krongold, “DFT-Spread OFDM for fiber nonlinearity mitigation,” IEEE Photon. Technol. Lett. 22(16), 1250–1252 (2010).
[Crossref]

J. Lightwave Technol. (5)

Opt. Express (5)

Other (5)

J. Lee, F. Breyer, S. Randel, J. Zeng, F. Huijskens, H. P. van den Boom, A. M. Koonen, and N. Hanik, “24-Gb/s transmission over 730 m of multimode fiber by direct modulation of an 850-nm VCSEL using discrete multitone modulation,” Opt. Fiber Conf. (OFC 2007), Anaheim, USA, PDP 6, Mar. 2011.

Y. Zhao and A. Huang, “A novel channel estimation method for OFDM mobile communication systems based on pilot signals and transform-domain processing,” IEEE Vehicular Technology Conference, 3, 2089–2093 (1997).

Q. Yang, N. Kaneda, X. Liu, S. Chandrasekhar, W. Shieh, and Y. Chen, “Real-Time coherent optical OFDM receiver at 2.5-GS/s for receiving a 54-Gb/s multi-band signal,” Opt. Fiber Conf. (OFC 2009), San Diego, USA, PDPC, Mar. 2009.

G. K. Chang, Z. Jia, J. Yu, A. Chowdhury, T. Wang, and G. Ellinas, “Super-broadband optical wireless access technologies,” Opt. Fiber Conf. (OFC 2008), San Diego, USA, OThD1, Feb. 2008.

B. Liu, X. Xin, L. Zhang, K. Zhao, and C. Yu, “Broad convergence of 32QAM-OFDM ROF and WDM-OFDM-PON system using an integrated modulator for bidirectional access networks,” Opt. Fiber Conf. (OFC 2010), San Diego, USA, JThA26, Mar. 2010.

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Figures (9)

Fig. 1
Fig. 1 The schematic diagram of OFDM RoF system. ECL: external cavity laser, TOF: tunable optical filter.

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Fig. 2
Fig. 2 The schematic diagram of the proposed OFDM signal process at the receiver.

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Fig. 3
Fig. 3 (a) (b) the transfer function H( k ) in frequency domain, (c) (d) the “spectral sequence” H T ( m ) in transform domain, (e) (f) the improved transfer function H ~ ( k ) in frequency domain in coherent OFDM systems with different chromatic dispersion.

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Fig. 4
Fig. 4 The relationship between required cutoff coefficient m c and channel parameters for systems with symbol rate of (a) 10 Gbaud, (b) 40 Gbaud, BR: the ratio between the bandwidth of band-pass filter and OFDM signal.

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Fig. 5
Fig. 5 (a) interleaved carrier distribution scheme [11], (b) localized carrier distribution scheme with 15 GHz carrier frequency spacing.

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Fig. 6
Fig. 6 Experimental setup of the DFT-S OFDM multiple-user RoF system, ECL: external cavity laser, PM: phase modulator, EA: electronic amplifier, IM: intensity modulator, AWG: arbitrary waveform generator, WSS: waveshaper.

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Fig. 7
Fig. 7 Optical spectrum (a) after phase modulator, (b) after wss1, (c) after 2:1 coupler, (d) after wss2.

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Fig. 8
Fig. 8 BER vs received optical power of one chosen channel after 40 km fiber link and 60 GHz wireless link.

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Fig. 9
Fig. 9 BER of DFT-S OFDM signal for all 8 wireless users after 40 km fiber link and 60 GHz wireless link.

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Tables (1)

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Table 1 Comparison of the three channel estimation methods

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Equations (9)

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e( t )= e j ω c t ⋅( 1+γs( t ) )
e out ( t )=( e( t )+ e j( ω c + ω r )t )⊗ h f ( t )
I PD ( t )=R⋅ e out ( t )⋅ e out * ( t ) =R | ( 1+γs( t ) )⊗ h f ( t )+ e j ω r t | 2 =R[ 1+ ( ( 1+γs( t ) )⊗ h f ( t ) ) 2 +2( ( 1+γs( t ) )⊗ h f ( t ) )cos( ω r t ) ]
I T ( t )=2R( ( ( 1+γs( t ) )⊗ h f ( t ) )⋅cos( ω r t ) )⊗ h w ( t )
I R ( t )=RA+RAγs( t )⊗ h f ( t )⊗ h w ( t )
H( k )= H f ( k )⋅ H w ( k )
H T ( m )= ∑ k=0 N−1 ( H( k ) )⋅exp( −j2πmk/N )
H ~ ( k )= 1 N ∑ m=0 N−1 H T ( m )⋅F( m )⋅exp( j2πmk/N ) , F( m )={ 1 , N 2 − m c <m< N 2 + m c 0 , others
R T = ∑ m=N/2− m c N/2+ m c | H T ( m ) | 2 / ∑ m=0 N−1 | H T ( m ) | 2

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