Abstract

We propose a new way to structure the digital signal processing for reduced guard-interval (RGI) OFDM optical receivers. The idea is to digitally parallelize the processing over multiple parallel virtual sub-channels, occupying disjoint spectral sub-bands. This concept is well known in the optical or analog sub-carrier domains, but it turns out that it can also be performed efficiently in the digital domain. Here we apply critically sampled uniform analysis and synthesis DFT filter bank signal processing techniques in order to realize a novel hardware efficient variant of RGI OFDM, referred to as Multi-Sub-Band OFDM (MSB-OFDM), reducing by 10% receiver computational complexity, relative to a single-polarization version of the CD pre-equalizer. In addition to being more computationally efficient than a conventional RGI OFDM system, the signal flow architecture of our scheme is amenable to being more readily realized over multiple FPGAs, for experimental demonstrations or flexible prototyping.

© 2011 OSA

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References

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  1. X. Liu, S. Chandrasekhar, B. Zhu, P. J. Winzer, A. H. Gnauck, and D. W. Peckham, “448-Gb/s Reduced-Guard-Interval CO-OFDM Transmission Over 2000 km of Ultra-Large-Area Fiber and Five 80-GHz-Grid ROADMs,” J. Lightwave Technol. 29(4), 483–490 (2011).
    [CrossRef]
  2. A. Tolmachev and M. Nazarathy, “Real-time-realizable Filtered-Multi-Tone (FMT) Modulation for Layered-FFT Nyquist WDM Spectral Shaping - paper SPMB3,” in European Conference of Optical Communication (ECOC)(2011).
  3. L. B. Du and A. J. Lowery, “Mitigation of dispersion penalty for short-cyclic-prefix coherent optical OFDM systems,” in European Conference of Optical Communication (ECOC)(2011).
  4. S. L. Jansen and T. Schenk, “Optical OFDM for Long-Haul Transport Networks - Tutorial MH1,” in LEOS - IEEE Lasers and Electro-Optics Society Annual Meeting Conference Proceedings(2008).
  5. A. Tolmachev and M. Nazarathy, “Low-Complexity Multi-Band Polyphase Filter Bank for Reduced-Guard-Interval Coherent Optical OFDM - paper SPMB3,” in Signal Processing in Photonic Communications (SPPCom), Advanced Photonics OSA Conference(2011).
  6. T. M. Schmidl and D. C. Cox, “Robust frequency and timing synchronization for OFDM,” IEEE Trans. Commun. 45(12), 1613–1621 (1997).
    [CrossRef]
  7. R. I. Killey, Y. Benlachtar, R. Bouziane, P. A. Milder, R. J. Koutsoyannis, C. R. Berger, J. C. Hoe, M. Püschel, P. M. Watts, and M. Glick, “Recent Progress on Real-Time DSP for Direct Detection Optical OFDM Transceivers - paper OMS1,” in Optical Fiber Communication Conference (OFC/NFOEC)(2011).
  8. F. J. Harris, Multirate Signal Processing for Communication Systems (Prentice Hall, 2004).
  9. J. Leibrich and W. Rosenkranz, “Frequency Domain Equalization with Minimum Complexity in Coherent Optical Transmission Systems,” in Optical Fiber Communication Conference (OFC/NFOEC)(2010).
  10. W. Shieh and K. P. Ho, “Equalization-enhanced phase noise for coherent-detection systems using electronic digital signal processing,” Opt. Express 16(20), 15718–15727 (2008).
    [CrossRef] [PubMed]
  11. Q. Zhuge, B. Châtelain, C. Chen, and D. V. Plant, “Mitigation of Equalization-Enhanced Phase Noise Using Reduced-Guard-Interval CO-OFDM,” in Optical Fiber Communication Conference (OFC/NFOEC)(2011).
  12. E. Ip, N. Bai, and T. Wang, “Complexity versus Performance Tradeoff for Fiber Nonlinearity Compensation Using Frequency-Shaped, Multi-Sub band Back propagation - paper OThF4,” in Optical Fiber Communication Conference (OFC/NFOEC)(2010).

2011 (1)

2008 (1)

1997 (1)

T. M. Schmidl and D. C. Cox, “Robust frequency and timing synchronization for OFDM,” IEEE Trans. Commun. 45(12), 1613–1621 (1997).
[CrossRef]

Chandrasekhar, S.

Cox, D. C.

T. M. Schmidl and D. C. Cox, “Robust frequency and timing synchronization for OFDM,” IEEE Trans. Commun. 45(12), 1613–1621 (1997).
[CrossRef]

Gnauck, A. H.

Ho, K. P.

Liu, X.

Peckham, D. W.

Schmidl, T. M.

T. M. Schmidl and D. C. Cox, “Robust frequency and timing synchronization for OFDM,” IEEE Trans. Commun. 45(12), 1613–1621 (1997).
[CrossRef]

Shieh, W.

Winzer, P. J.

Zhu, B.

IEEE Trans. Commun. (1)

T. M. Schmidl and D. C. Cox, “Robust frequency and timing synchronization for OFDM,” IEEE Trans. Commun. 45(12), 1613–1621 (1997).
[CrossRef]

J. Lightwave Technol. (1)

Opt. Express (1)

Other (9)

Q. Zhuge, B. Châtelain, C. Chen, and D. V. Plant, “Mitigation of Equalization-Enhanced Phase Noise Using Reduced-Guard-Interval CO-OFDM,” in Optical Fiber Communication Conference (OFC/NFOEC)(2011).

E. Ip, N. Bai, and T. Wang, “Complexity versus Performance Tradeoff for Fiber Nonlinearity Compensation Using Frequency-Shaped, Multi-Sub band Back propagation - paper OThF4,” in Optical Fiber Communication Conference (OFC/NFOEC)(2010).

A. Tolmachev and M. Nazarathy, “Real-time-realizable Filtered-Multi-Tone (FMT) Modulation for Layered-FFT Nyquist WDM Spectral Shaping - paper SPMB3,” in European Conference of Optical Communication (ECOC)(2011).

L. B. Du and A. J. Lowery, “Mitigation of dispersion penalty for short-cyclic-prefix coherent optical OFDM systems,” in European Conference of Optical Communication (ECOC)(2011).

S. L. Jansen and T. Schenk, “Optical OFDM for Long-Haul Transport Networks - Tutorial MH1,” in LEOS - IEEE Lasers and Electro-Optics Society Annual Meeting Conference Proceedings(2008).

A. Tolmachev and M. Nazarathy, “Low-Complexity Multi-Band Polyphase Filter Bank for Reduced-Guard-Interval Coherent Optical OFDM - paper SPMB3,” in Signal Processing in Photonic Communications (SPPCom), Advanced Photonics OSA Conference(2011).

R. I. Killey, Y. Benlachtar, R. Bouziane, P. A. Milder, R. J. Koutsoyannis, C. R. Berger, J. C. Hoe, M. Püschel, P. M. Watts, and M. Glick, “Recent Progress on Real-Time DSP for Direct Detection Optical OFDM Transceivers - paper OMS1,” in Optical Fiber Communication Conference (OFC/NFOEC)(2011).

F. J. Harris, Multirate Signal Processing for Communication Systems (Prentice Hall, 2004).

J. Leibrich and W. Rosenkranz, “Frequency Domain Equalization with Minimum Complexity in Coherent Optical Transmission Systems,” in Optical Fiber Communication Conference (OFC/NFOEC)(2010).

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Figures (15)

Fig. 1
Fig. 1

Proposed digital Multi-Band structure: Each WDM channel (assumed here 25 GHz) is digitally frequency division de-multiplexed into M sub-bands (here M = 16). The extreme sub-band (partitioned into two wrapped-around halves) is dedicated to the filtering roll-off transition of the ADC image-rejection analog filter.

Fig. 2
Fig. 2

Standard OFDM Link, and time-frequency representations (time horizontally, frequency vertically) of the OFDM symbol at the Tx and Rx.

Fig. 3
Fig. 3

Reduced Guard Interval (RGI) OFDM link, using a frequency-domain CD pre-equalizer at the Rx.

Fig. 4
Fig. 4

Filter Bank Based OFDM.

Fig. 5
Fig. 5

Filter Bank Based OFDM Transmitter.

Fig. 6
Fig. 6

A generic frequency-division-multiplexed communication link based on a synthesis filter bank in the Tx and an analysis filter bank (notice that the usual combination of filter banks in DSP textbooks, for data compression purposes, has the opposite order of the analysis and synthesis filter banks).

Fig. 7
Fig. 7

Sub-band frequency response for a critically sampled filter bank with M paths (sub-bands).

Fig. 8
Fig. 8

Equivalent filter-bank based representation of the frequency-division-multiplexed communication link based on discrete-time up/down converters and baseband prototype filters.

Fig. 9
Fig. 9

Equivalent filter-bank based representation of the frequency-division-multiplexed communication link based on M-points (I)DFT and M polyphase filters (corresponding to the M polyphases of the prototype filter). Notice that the receive filters were selected here to be matched filters relative to the transmit filters (matched-filters, in the communication-theoretic sense, i.e. with complex conjugate frequency responses, which would be optimal for a flat frequency response).

Fig. 10
Fig. 10

Block diagram of the end-to-end MSB-OFDM system.

Fig. 11
Fig. 11

(a): A sketch of the spectral structure. (b): Simulated spectrum of a single Nyquist WDM channel containing 16 MSB-OFDM sub channels.

Fig. 12
Fig. 12

(a): Simulated received QPSK Constellation (noiseless, back-to-back). (b): Modulation Error Ratio (MER) vs. OFDM subcarrier index for each sub-channel.

Fig. 13
Fig. 13

Average BER vs. OSNR over MSB-OFDM sub-channel (and over the overall Nyquist WDM channel).

Fig. 14
Fig. 14

Complexity Comparison of conventional RGI OFDM (red-slanted curve) vs. MSB-OFDM (the constant complexity of which is due to the system experiencing negligible dispersion in each sub-band up to the maximal distance considered in the plot).

Fig. 15
Fig. 15

Top-level block diagram of SB-OFDM receiver with polarization de-multiplexing.

Equations (5)

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C M PolyphaseFilter = L PF log 2 ( L PF )+ L PF L PF N PF +1 C M FFT = 1 2 log 2 ( M ); C M FB =[ C M PolyphaseFilter +C M FFT ]
C M SB = 1 2 log 2 ( MN )+ 1 2 log 2 ( N )+1
C M MSB-OFDM [ M 1 , M 2 , N PF , L PF ]=2C M FB +C M SB
C M MSB-OFDM [ M, N , N PF , L PF ]= L PF log 2 ( L PF )+ L PF L PF N PF +1 + log 2 ( M ) 2 +[ log 2 ( N ) 2 +1 ]+ log 2 ( MN ) 2
C M FDEOFDM [ M, N , N CD , L FDE ]= L FDE log 2 ( L FDE )+ L FDE L FDE N CD +1 + log 2 ( MN )+1

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