Efficient Variants of Square Contour Algorithm for Blind Equalization of QAM Signals

Authors: Ahmad Tariq Sheikh, Shahzad Amin Sheikh

Abstract:

A new distance-adjusted approach is proposed in which static square contours are defined around an estimated symbol in a QAM constellation, which create regions that correspond to fixed step sizes and weighting factors. As a result, the equalizer tap adjustment consists of a linearly weighted sum of adaptation criteria that is scaled by a variable step size. This approach is the basis of two new algorithms: the Variable step size Square Contour Algorithm (VSCA) and the Variable step size Square Contour Decision-Directed Algorithm (VSDA). The proposed schemes are compared with existing blind equalization algorithms in the SCA family in terms of convergence speed, constellation eye opening and residual ISI suppression. Simulation results for 64-QAM signaling over empirically derived microwave radio channels confirm the efficacy of the proposed algorithms. An RTL implementation of the blind adaptive equalizer based on the proposed schemes is presented and the system is configured to operate in VSCA error signal mode, for square QAM signals up to 64-QAM.

Keywords: Adaptive filtering, Blind Equalization, Square Contour Algorithm.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1060731

References:

[1] D. Godard, Self recovering equalization and carrier tracking in twodimensional data communication systems, IEEE Trans. Commun. COM-28(1980) 1867-1875.
[2] J. R. Treichler, B. G. Agee, A new approach to multipath correction of constant modulus signals, IEEE Trans. on Acoust., Speech, Signal Processing ASSP-31 (2) (1983) 459-472
[3] S. U. H. Qureshi, Adaptive equalization, Proceedings of the IEEE 73 (9) (1985)1349-1387.
[4] J. Liu, X. Lin, Equalization in high-speed communication systems, IEEE Circuits and Systems Magazine (2004) 4-17.
[5] J. J. Shynk, R. P. Gooch, G. Krishnamurthy, C. K. Chan, A comparative performance study of several blind equalization algorithms, SPIE 1565 (1991)102-117.
[6] J.-J. Werner, J. Yang, D. Harman, G. A. Dumont, Blind equalization for broadband access, IEEE Communications Magazine (1999) 87-93.
[7] J. Yang, J.-J. Werner, G. A. Dumont, The multimodulus blind equalization and its generalized algorithms, IEEE Journal on selected areas in communication 20 (5) (2002) 997-1015.
[8] J. Yang, J.-J. Werner, G. A. Dumont, The multimodulus blind equalization algorithm, in: Proc. Int. Conf. on Digital Signal Processing, 1997, pp. 127-130.
[9] Y. Sato, A method of self-recovering equalization for multilevel amplitude-modulation systems, IEEE Trans. Commun. COM-23 (1975)679-682.
[10] T. Thaiupatump, S.A. Kassam, Square contour algorithm: A new algorithm for blind equalization and carrier phase recovery, in: Proc. 37th Asilomar Conference on Signals, Systems and Computers, 2003, pp. 647-651.
[11] T. Thaiupatump, L. He, S.A. Kassam, Square contour algorithm for blind equalization of QAM signals, Signal Process. 86 (11) (2006) 3357-3370.
[12] K. Banovic, E. Abdel-Raheem, M. A. S. Khalid, A novel radiusadjusted approach for blind adaptive equalization, IEEE Signal Processing Letters 13 (1) (2006) 37-40.
[13] F. C. C. De Castro, M. C. F. De Castro, and D. S. Arantes, "Concurrent blind deconvolution for channel equalization," in Proc. ICC, Helsinki, Finland, Jun. 2001, pp. 366-371.
[14] A configurable fractionally-spaced blind adaptive equalizer for QAM demodulators Digital Signal Processing, Volume 17, Issue 6, November 2007, Pages 1071-1088. Kevin Banović, Mohammed A.S. Khalid, Esam Abdel-Raheem.