Slot timing maximum likelihood estimation with bursty pilot signals for DS-CDMA in multipath fading channels

Caire, Giuseppe; Humblet, Pierre A; Montalbano, Giuseppe; Nordio, Alessandro
GLOBECOM 2000, IEEE Global telecommunications conference, November 27-December 1, 2000, San Francisco, USA

This paper focuses on the initial slot timing acquisition in DS-CDMA with bursty pilot signals, when the propagation channel is affected by multipath and by fading. Subject to certain simplifying working assumptions, we obtain a nice form for the likelihood function and we derive the maximum likelihood estimator by solving a constrained maximization problem via the Lagrange-Kuhn-Tucker method. Our maximum likelihood slot timing estimator has linear complexity in the observation window length (i.e., constant complexity per observation sample). The relation to other estimation methods is addressed, and
performance comparisons are provided by simulation. When our assumptions are not satisfied, the performance of the proposed estimator may deteriorate. Then, we provide an extremely simple method to cope with the model mismatch. The resulting estimator offers good results over all fading channels with delay spread not larger than a given
maximum spread. Finally, the computation of the Cramer-Rao bound for slot timing estimation based on bursty pilot signals is addressed.

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