Abstract
Complex-valued periodic sequences, u, constructed by Göran Björck, are analyzed with regard to the behavior of their discrete periodic narrow-band ambiguity functions A p (u). The Björck sequences, which are defined on ℤ/pℤ for p>2 prime, are unimodular and have zero autocorrelation on (ℤ/pℤ)∖{0}. These two properties give rise to the acronym, CAZAC, to refer to constant amplitude zero autocorrelation sequences. The bound proven is \(|A_{p}(u)| \leq2/\sqrt{p} + 4/p\) outside of (0,0), and this is of optimal magnitude given the constraint that u is a CAZAC sequence. The proof requires the full power of Weil’s exponential sum bound, which, in turn, is a consequence of his proof of the Riemann hypothesis for finite fields. Such bounds are not only of mathematical interest, but they have direct applications as sequences in communications and radar, as well as when the sequences are used as coefficients of phase-coded waveforms.
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Acknowledgements
The authors gratefully acknowledge the support of various grants. For the first-named author, the grants are ONR Grant N00014-09-1-0144 and MURI-ARO Grant W911NF-09-1-0383. For the second named author, the grant is NSF Grant DMS-0901494. The third-named author was supported by the Norbert Wiener Center as recipient of the Daniel Sweet Undergraduate Research Fellowship. Further, at the time of the first-named author’s presentation of their results at SampTA2011 in Singapore, Professor Bruno Torresani kindly pointed out two references on which we comment in Sect. 1.2. Finally, and although not represented explicitly in this paper, we have benefitted from expert advice on hardware implementation by Drs. Michael Dellomo, Joseph Lawrence, and George Linde.
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Communicated by Thomas Strohmer.
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Benedetto, J.J., Benedetto, R.L. & Woodworth, J.T. Optimal Ambiguity Functions and Weil’s Exponential Sum Bound. J Fourier Anal Appl 18, 471–487 (2012). https://doi.org/10.1007/s00041-011-9204-3
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DOI: https://doi.org/10.1007/s00041-011-9204-3
Keywords
- Discrete narrow-band ambiguity function
- Weil’s Riemann hypothesis
- Kloosterman sums
- Constant amplitude zero autocorrelation sequences