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Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2011, Article ID 412036, 14 pages doi:10.1155/2011/412036 Research Article Performance of Post-Demodulator Adaptive Filters for FSK Signals in a Multipath Environment Shu-Ting Lee,1 Sally L. Wood,1 Michael J. Ready,2 and John R. Treichler2 1 Department 2 Corporate Of Electrical Engineering, Santa Clara University, Santa Clara, CA 95053, USA Division, Applied Signal Technology, Sunnyvale, CA 94086, USA Correspondence should be addressed to Shu-Ting Lee, slee1@scu.edu Received 2 July 2010; Revised 17 October 2010; Accepted 11 December 2010 Academic Editor: Antonio Napolitano Copyright © 2011 Shu-Ting Lee et al. This is an open access article distributed. | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2011 Article ID 412036 14 pages doi 10.1155 2011 412036 Research Article Performance of Post-Demodulator Adaptive Filters for FSK Signals in a Multipath Environment Shu-Ting Lee 1 Sally L. Wood 1 Michael J. Ready 2 and John R. Treichler2 1 Department Of Electrical Engineering Santa Clara University Santa Clara CA 95053 USA 2 Corporate Division Applied Signal Technology Sunnyvale CA 94086 USA Correspondence should be addressed to Shu-Ting Lee slee1@scu.edu Received 2 July 2010 Revised 17 October 2010 Accepted 11 December 2010 Academic Editor Antonio Napolitano Copyright 2011 Shu-Ting Lee et al. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited. FSK continues to be an important component of modern communication systems and discoveries of lower impact methods for mitigating performance degradation due to multipath propagation are needed in many application areas. Previous work suggested the benefit of a simple post-demodulator LMS filter but the focus was narrow and analysis was hindered by the nonlinearity of the demodulation process and the nonstationary signal environment. This paper significantly extends understanding of the post-demodulator filter and demonstrates that the statistical assumptions that align BER performance with MSE performance do not apply in this context and that simply decreasing the MSE might increase the BER rather than decrease it. An alternative post-demodulator adaptive filter with similar complexity to the LMS filter is proposed which shows improved BER performance. Analysis provides a simplified interpretation of the interaction of system and channel model parameters which may form the basis for more general use of a post-demodulator adaptive filter. 1. Introduction Frequency shift keying FSK .
