Propagation Delay Estimation of Fading DS-CDMA Signals
Stefan Parkvall, Erik G. Ström · 1995
In this paper we consider the problem of estimating the propagation delays of the transmitted signals in an asynchronous direct-sequence code division multiple access (DSCDMA) system operating over a fading channel. Two estimators based on subspace techniques are compared and the Cram'er-Rao Bound, a lower bound on the variance of any unbiased estimator, is derived. Special attention is paid to the near-far problem. 1 Introduction Due to the nature of the code waveforms typically used in DS-CDMA systems, accurate propagation delay estimation is important. See, for instance, [7], in which we evaluated the effect of imperfect propagation delay estimation on the popular decorrelating receiver. The classical method for achieving synchronization, the so-called sliding correlator, is described in [4]. Other methods are: rapid acquisition by sequential estimation (RASE) proposed in [9], and the multiple user extension of RASE developed in [3]. These methods assume that the user, whose propag...