The underwater acoustic channel is considered as one of the most challenging channels for reliable communications. Long delay spread and Doppler effect bring a great challenge to directly apply the algorithms in radio communications to underwater communications, which calls for modification and enhancement. In this study, a pilot-assisted linear turbo equalisation algorithm termed P-TE is proposed. Unlike the existing pilot methods that insert pilot into the modulated symbols to facilitate the channel estimation, the authors insert the known bits into the uncoded binary sequence to assist equalisation as well as decoding with the careful design of the bit positions. A second-order least mean square adaptive algorithm as well as adaptive step size method is introduced for weights update. Furthermore, a modified low-density parity-check decoding algorithm is presented to describe the pilot-assisted decoding algorithm, which does not increase the complexity. Moreover, pilot extraction from error-free blocks is proposed for enhanced performance. Experimental results have indicated that P-TE can significantly improve the performance and reduce the required number of the iterations, leading to lower complexity. Furthermore, experiments show that the effective throughput of P-TE can be higher than the method without pilot at a signal-to-noise ratio of 10 dB.

References

1. 1)
  - 7. Johnson, M., Freitag, L., Stojanovic, M.: ‘Improved Doppler tracking and correction for underwater acoustic communications’. Proc. Int. Conf. Acoustics, Speech, and Signal Processing, Munich, Germany, April 1997, pp. 575–578.
2. 2)
  - 7. Tüchler, M., Singer, A.C.: ‘Turbo equalization: an overview’, Trans. Inf. Theory, 2011, 57, (2), pp. 920–952 (doi: 10.1109/TIT.2010.2096033).
3. 3)
  - M. Stojanovic , J. Preisig . Underwater acoustic communication channels: propagation models and statistical characterization. IEEE Commun. Mag. , 1 , 84 - 89
4. 4)
  - D.J.C. MacKay . Good error-correcting codes based on very sparse matrices. IEEE Trans. Inf. Theory , 2 , 399 - 431
5. 5)
  - 18. Choi, J.W., Drost, R.J., Singer, A.C., et al: ‘Iterative multi-channel equalization and decoding for high frequency underwater acoustic communications’. Proc. Int. Conf. Sensor Array and Multichannel Signal Processing Workshop, Darmstadt, Germany, July 2008, pp. 127–130..
6. 6)
  - 16. Li, Q., Teh, K.C., Li, K.H.: ‘Low-complexity channel estimation and turbo equalisation for high frequency channels’, IET Commun., 2013, 7, (10), pp. 980–987 (doi: 10.1049/iet-com.2012.0811).
7. 7)
  - S. Gazor . Prediction in LMS-type algorithm for smoothly time varying environments. IEEE Trans. Signal Process. , 6 , 1735 - 1739
8. 8)
  - 24. Flanagan, M.F., Fagan, A.D.: ‘Iterative channel estimation, equalization, and decoding for pilot-symbol assisted modulation over frequency selective fast fading channels’, IEEE Trans. Veh. Technol., 2007, 56, (4), pp. 1661–1670 (doi: 10.1109/TVT.2007.897215).
9. 9)
  - M.C. Domingo . Overview of channel models for underwater wireless communication networks. Elsevier Phys. Commun. , 163 - 182
10. 10)
  - B. Li , S. Zhou , M. Stojanovic , L. Freitag , P. Willett . Multicarrier communication over underwater acoustic channels with nonuniform Doppler shifts. IEEE J. Ocean. Eng. , 2 , 198 - 209
11. 11)
  - C. Laot , A. Glavieux , J. Labat . Turbo equalization: adaptive equalization and channel decoding jointly optimized. IEEE J. Select. Areas Commun. , 9 , 1744 - 1752
12. 12)
  - B.S. Sharif , J. Neasham , O.R. Hinton , A.E. Adams . A computationally efficient doppler compensation system for underwater acoustic communications. IEEE J. Ocean. Eng. , 1 , 52 - 61
13. 13)
  - M. Tüchler , R. Koetter , A.C. Singer . Turbo equalization: principles and new results. IEEE Trans. Commun. , 5 , 754 - 766
14. 14)
  - D. Kilfoyle , A. Baggeroer . The state of the art in underwater acoustic telemetry. IEEE J. Ocean. Eng. , 1 , 4 - 27
15. 15)
  - 20. Sifferlen, J.F., Song, H., Hodgkiss, W.S., et al: ‘An iterative equalization and decoding approach for underwater acoustic communication’, IEEE J. Ocean Eng., 2008, 33, (2), pp. 182–197 (doi: 10.1109/JOE.2008.923552).
16. 16)
  - G. Caire , G. Taricco , E. Biglieri . Bit-interleaved coded modulation. IEEE Trans. Inf. Theory , 5 , 927 - 946
17. 17)
  - R.R. Lopes , J.R. Barry . The soft-feedback equalizer for turbo equalization of highly dispersive channels. IEEE Trans. Commun. , 5 , 783 - 788
18. 18)
  - T. Aboulnasr , K. Mayyas . A robust variable step-size LMS-type algorithm: analysis and simulations. IEEE Trans. Signal Process. , 3 , 631 - 639
19. 19)
  - 32. Yapici, Y., Yilmaz, A.: ‘Low-complexity iterative channel estimation and tracking for time-varying multi-antenna systems’. Proc. Int. Conf. Personal, Indoor and Mobile Radio Communications, Tokyo, Japan, September 2009, pp. 1317–1321.
20. 20)
  - 17. Oberg, T., Nilsson, B., Olofsson, N., et al: ‘Underwater communication link with iterative equalization’. Proc. Int. Conf. Oceans, Boston, MA, September 2006, pp. 1–6.
21. 21)
  - 9. Labat, J.: ‘Real time underwater communications’. Proc. Int. Conf. Oceans Engineering for Today's Technology and Tomorrow's Preservation, Brest, France, September 1994, pp. III–501.
22. 22)
  - R. Koetter , A.C. Singer , M. Tuchler . Turbo equalization. IEEE Signal Process. Mag. , 67 - 80
23. 23)
  - 23. Valenti, M.C., Woerner, B.D.: ‘Iterative channel estimation and decoding of pilot symbol assisted turbo codes over flat-fading channels’, IEEE J. Sel. Areas Commun., 2001, 19, (9), pp. 1697–1705 (doi: 10.1109/49.947034).
24. 24)
  - 5. Liu, C., Zakharov, Y.V., Chen, T.: ‘Doubly selective underwater acoustic channel model for a moving transmitter/receiver’, IEEE Trans. Veh. Technol., 2012, 61, (3), pp. 938–950 (doi: 10.1109/TVT.2012.2185258).
25. 25)
  - C. Douillard , M. Jézéquel , C. Berrou , A. Picart , P. Didier , A. Glavieux . Iterative correction of intersymbol interference: turbo-equalization. Eur. Trans. Telecomm. , 5 , 507 - 511
26. 26)
  - 21. Choi, J.W., Riedl, T.J., Kim, K., et al: ‘Adaptive linear turbo equalization over doubly selective channels’, IEEE J. Ocean Eng., 2011, 36, (4), pp. 473–489 (doi: 10.1109/JOE.2011.2158013).
27. 27)
  - 22. Otnes, R., Eggen, T.H.: ‘Underwater acoustic communications: long-term test of turbo equalization in shallow water’, IEEE J. Ocean Eng., 2008, 33, (3), pp. 321–334 (doi: 10.1109/JOE.2008.925893).
28. 28)
  - 28. Mason, S.F., Berger, C.R., Zhou, S., et al: ‘Detection, synchronization, and Doppler scale estimation with multicarrier waveforms in underwater Aoustic communication’, IEEE J. Sel. Areas Commun., 2008, 26, (9), pp. 1638–1649 (doi: 10.1109/JSAC.2008.081204).
29. 29)
  - R. Gallager . Low-density parity-check codes. IRE Trans. Inf. Theory , 21 - 28
30. 30)
  - M. Stojanovic , J. Catipovic , J.G. Proakis . Phase-coherent digital communications for underwater acoustic channels. IEEE J. Oceanic Eng. , 1 , 100 - 111
31. 31)
  - 6. Haykin, S.: ‘Adaptive filter theory’ (Prentice-Hall, 1996, 2001, 4th edn.).
32. 32)
  - M. Stojanovic . Recent advances in high-speed underwater acoustic communication. IEEE J. Ocean. Eng. , 125 - 136
33. 33)
  - 19. Sozer, E., Proakis, J., Blackmon, F.: ‘Iterative equalization and decoding techniques for shallow water acoustic channels’. Proc. Int. Conf. Ocean, Honolulu, America, 2001, pp. 2201–2208.

Pilot-assisted linear turbo equaliser over doubly selective channels

References

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