Abstract

A major performance-limiting factor in terrestrial optical wireless (OW) systems is turbulence-induced fading. Exploiting the additional degrees of freedom in the spatial dimension, multiple laser transmitters combined with multiple receive apertures provide an effective solution for fading mitigation. Although multiple-input multiple-output (MIMO) OW systems have been extensively studied in recent years, most of these works are mainly limited to symbol-by-symbol decoding. MLSD exploits the temporal correlation of turbulence-induced fading and promises further performance gains. In this paper, we investigate MLSD for intensity-modulation/direct-detection MIMO OW systems over log-normal atmospheric turbulence channels. Even with a low-order modulation scheme such as OOK, which is typically used in OW systems, the complexity of MLSD might be prohibitive. We therefore present an iterative sequence detector based on the expectation–maximization (EM) algorithm. The complexity of the proposed algorithm is considerably less than a direct evaluation of the log-likelihood function, and it is independent of the channel's fading statistics. The Monte Carlo simulation results demonstrate that the EM-based algorithm outperforms the symbol-by-symbol decoder and achieves a performance, which lies within 0.3 dB of that of the optimal MLSD.

© 2010 IEEE

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  1. L. Andrews, R. L. Philips, C. Y. Hopen, Laser Beam Scintillation With Applications (SPIE Press, 2001).
  2. D. Kedar, S. Arnon, "Urban optical wireless communications networks: The main challenges and possible solutions," IEEE Commun. Mag. 42, 2-7 (2003).
  3. X. Zhu, J. M. Kahn, "Performance bounds for coded free-space optical communications through atmospheric turbulence channels," IEEE Trans. Commun. 51, 1233-1239 (2003).
  4. M. Uysal, S. M. Navidpour, J. Li, "Error rate performance of coded free-space optical links over strong turbulence channels," IEEE Commun. Lett. 8, 635-637 (2004).
  5. E. Lee, V. Chan, "Part 1: Optical communication over the clear turbulent atmospheric channel using diversity," IEEE J. Sel. Areas Commun. 22, 1896-1906 (2004).
  6. S. G. Wilson, M. Brandt-Pearce, C. Qianling, M. Baedke, "Optical repetition MIMO transmission with multipulse PPM," IEEE J. Sel. Areas Commun. 23, 1901-1910 (2005).
  7. T. A. Tsiftsis, H. G. Sandalidis, G. K. Karagiannidis, M. Uysal, "Optical wireless links with spatial diversity over strong atmospheric turbulence channels," IEEE Trans. Wireless Commun. 8, 951-957 (2009).
  8. S. M. Navidpour, M. Uysal, "BER performance of free-space optical transmission with spatial diversity," IEEE Trans. Wireless Commun. 6, 2813-2819 (2007).
  9. X. Zhu, J. M. Kahn, "Free-space optical communication through atmospheric turbulence channels," IEEE Trans. Commun. 50, 1293-1300 (2002).
  10. X. Zhu, J. M. Kahn, "Markov chain model in maximum-likelihood sequence detection for free-space optical communication through atmospheric turbulence channels," IEEE Trans. Commun. 51, 509-516 (2003).
  11. X. Zhu, J. M. Kahn, "Pilot-symbol assisted modulation for correlated turbulent free-space optical channels," SPIE Int. Symp. Opt. Sci. Technol. San DiegoCA (2001).
  12. M. L. B. Riediger, R. Schober, L. Lampe, "Fast multiple-symbol detection for free-space optical communications," IEEE Trans. Commun. 57, 1119-1128 (2009).
  13. M. L. B. Riediger, R. Schober, L. Lampe, "Fast multiple-symbol detection for photon-counting MIMO free-space optical communications," IEEE Trans. Wireless Commun. 7, 5369-5379 (2008).
  14. M. L. B. Riediger, R. Schober, L. Lampe, "Blind detection of on-off keying for free-space optical communications," Proc. CCECE/CCGEI (2008) pp. 1361-1364.
  15. A. Dempster, N. M. Laird, D. B. Rubin, "Maximum-likelihood from incomplete data via the EM algorithm," J. R. Statist. Soc. 39, 1-17 (1977).
  16. C. N. Georghiades, J. C. Han, "Sequence estimation in the presence of random parameters via the EM algorithm," IEEE Trans. Commun. 45, 300-308 (1997).
  17. C. Cozzo, B. L. Hughes, "Joint channel estimation and data detection in space-time communications," IEEE Trans. Commun. 51, 1266-1270 (2003).
  18. Y. Li, C. N. Georghiades, G. Huang, "Iterative maximum-likelihood sequence estimation for space-time coded systems," IEEE Trans. Commun. 49, 948-951 (2001).
  19. M. Safari, M. Uysal, "Do we really need OSTBCs for free-space optical communication with direct detection?," IEEE Trans. Wireless Commun. 7, 4445-4448 (2008).
  20. S. Karp, R. Gagliardi, S. E. Moran, L. B. Stotts, Optical Channels (Plenum, 1988).
  21. D. J. T. Heatley, D. R. Wisely, I. Neild, P. Cochrane, "Optical wireless: The story so far," IEEE Commun. Mag. 36, 72-74 (1998).
  22. J. G. Proakis, Digital Communications (McGraw-Hill, 2000).

2009 (2)

T. A. Tsiftsis, H. G. Sandalidis, G. K. Karagiannidis, M. Uysal, "Optical wireless links with spatial diversity over strong atmospheric turbulence channels," IEEE Trans. Wireless Commun. 8, 951-957 (2009).

M. L. B. Riediger, R. Schober, L. Lampe, "Fast multiple-symbol detection for free-space optical communications," IEEE Trans. Commun. 57, 1119-1128 (2009).

2008 (2)

M. L. B. Riediger, R. Schober, L. Lampe, "Fast multiple-symbol detection for photon-counting MIMO free-space optical communications," IEEE Trans. Wireless Commun. 7, 5369-5379 (2008).

M. Safari, M. Uysal, "Do we really need OSTBCs for free-space optical communication with direct detection?," IEEE Trans. Wireless Commun. 7, 4445-4448 (2008).

2007 (1)

S. M. Navidpour, M. Uysal, "BER performance of free-space optical transmission with spatial diversity," IEEE Trans. Wireless Commun. 6, 2813-2819 (2007).

2005 (1)

S. G. Wilson, M. Brandt-Pearce, C. Qianling, M. Baedke, "Optical repetition MIMO transmission with multipulse PPM," IEEE J. Sel. Areas Commun. 23, 1901-1910 (2005).

2004 (2)

M. Uysal, S. M. Navidpour, J. Li, "Error rate performance of coded free-space optical links over strong turbulence channels," IEEE Commun. Lett. 8, 635-637 (2004).

E. Lee, V. Chan, "Part 1: Optical communication over the clear turbulent atmospheric channel using diversity," IEEE J. Sel. Areas Commun. 22, 1896-1906 (2004).

2003 (4)

D. Kedar, S. Arnon, "Urban optical wireless communications networks: The main challenges and possible solutions," IEEE Commun. Mag. 42, 2-7 (2003).

X. Zhu, J. M. Kahn, "Performance bounds for coded free-space optical communications through atmospheric turbulence channels," IEEE Trans. Commun. 51, 1233-1239 (2003).

X. Zhu, J. M. Kahn, "Markov chain model in maximum-likelihood sequence detection for free-space optical communication through atmospheric turbulence channels," IEEE Trans. Commun. 51, 509-516 (2003).

C. Cozzo, B. L. Hughes, "Joint channel estimation and data detection in space-time communications," IEEE Trans. Commun. 51, 1266-1270 (2003).

2002 (1)

X. Zhu, J. M. Kahn, "Free-space optical communication through atmospheric turbulence channels," IEEE Trans. Commun. 50, 1293-1300 (2002).

2001 (1)

Y. Li, C. N. Georghiades, G. Huang, "Iterative maximum-likelihood sequence estimation for space-time coded systems," IEEE Trans. Commun. 49, 948-951 (2001).

1998 (1)

D. J. T. Heatley, D. R. Wisely, I. Neild, P. Cochrane, "Optical wireless: The story so far," IEEE Commun. Mag. 36, 72-74 (1998).

1997 (1)

C. N. Georghiades, J. C. Han, "Sequence estimation in the presence of random parameters via the EM algorithm," IEEE Trans. Commun. 45, 300-308 (1997).

1977 (1)

A. Dempster, N. M. Laird, D. B. Rubin, "Maximum-likelihood from incomplete data via the EM algorithm," J. R. Statist. Soc. 39, 1-17 (1977).

IEEE Commun. Lett. (1)

M. Uysal, S. M. Navidpour, J. Li, "Error rate performance of coded free-space optical links over strong turbulence channels," IEEE Commun. Lett. 8, 635-637 (2004).

IEEE Commun. Mag. (2)

D. Kedar, S. Arnon, "Urban optical wireless communications networks: The main challenges and possible solutions," IEEE Commun. Mag. 42, 2-7 (2003).

D. J. T. Heatley, D. R. Wisely, I. Neild, P. Cochrane, "Optical wireless: The story so far," IEEE Commun. Mag. 36, 72-74 (1998).

IEEE J. Sel. Areas Commun. (2)

E. Lee, V. Chan, "Part 1: Optical communication over the clear turbulent atmospheric channel using diversity," IEEE J. Sel. Areas Commun. 22, 1896-1906 (2004).

S. G. Wilson, M. Brandt-Pearce, C. Qianling, M. Baedke, "Optical repetition MIMO transmission with multipulse PPM," IEEE J. Sel. Areas Commun. 23, 1901-1910 (2005).

IEEE Trans. Commun. (7)

X. Zhu, J. M. Kahn, "Performance bounds for coded free-space optical communications through atmospheric turbulence channels," IEEE Trans. Commun. 51, 1233-1239 (2003).

X. Zhu, J. M. Kahn, "Free-space optical communication through atmospheric turbulence channels," IEEE Trans. Commun. 50, 1293-1300 (2002).

X. Zhu, J. M. Kahn, "Markov chain model in maximum-likelihood sequence detection for free-space optical communication through atmospheric turbulence channels," IEEE Trans. Commun. 51, 509-516 (2003).

M. L. B. Riediger, R. Schober, L. Lampe, "Fast multiple-symbol detection for free-space optical communications," IEEE Trans. Commun. 57, 1119-1128 (2009).

C. N. Georghiades, J. C. Han, "Sequence estimation in the presence of random parameters via the EM algorithm," IEEE Trans. Commun. 45, 300-308 (1997).

C. Cozzo, B. L. Hughes, "Joint channel estimation and data detection in space-time communications," IEEE Trans. Commun. 51, 1266-1270 (2003).

Y. Li, C. N. Georghiades, G. Huang, "Iterative maximum-likelihood sequence estimation for space-time coded systems," IEEE Trans. Commun. 49, 948-951 (2001).

IEEE Trans. Wireless Commun. (4)

M. Safari, M. Uysal, "Do we really need OSTBCs for free-space optical communication with direct detection?," IEEE Trans. Wireless Commun. 7, 4445-4448 (2008).

M. L. B. Riediger, R. Schober, L. Lampe, "Fast multiple-symbol detection for photon-counting MIMO free-space optical communications," IEEE Trans. Wireless Commun. 7, 5369-5379 (2008).

T. A. Tsiftsis, H. G. Sandalidis, G. K. Karagiannidis, M. Uysal, "Optical wireless links with spatial diversity over strong atmospheric turbulence channels," IEEE Trans. Wireless Commun. 8, 951-957 (2009).

S. M. Navidpour, M. Uysal, "BER performance of free-space optical transmission with spatial diversity," IEEE Trans. Wireless Commun. 6, 2813-2819 (2007).

J. R. Statist. Soc. (1)

A. Dempster, N. M. Laird, D. B. Rubin, "Maximum-likelihood from incomplete data via the EM algorithm," J. R. Statist. Soc. 39, 1-17 (1977).

Other (5)

L. Andrews, R. L. Philips, C. Y. Hopen, Laser Beam Scintillation With Applications (SPIE Press, 2001).

M. L. B. Riediger, R. Schober, L. Lampe, "Blind detection of on-off keying for free-space optical communications," Proc. CCECE/CCGEI (2008) pp. 1361-1364.

S. Karp, R. Gagliardi, S. E. Moran, L. B. Stotts, Optical Channels (Plenum, 1988).

X. Zhu, J. M. Kahn, "Pilot-symbol assisted modulation for correlated turbulent free-space optical channels," SPIE Int. Symp. Opt. Sci. Technol. San DiegoCA (2001).

J. G. Proakis, Digital Communications (McGraw-Hill, 2000).

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