TAILIEUCHUNG - Adaptive WCDMA (P4)

Code tracking CODE-TRACKING LOOPS Theoretically switching from code acquisition to code tracking in this chapter means switching from open loop maximization of likelihood function (equation ) to the closed-loop tracker defined by equation () of Chapter 3. A variety of practical implementation options are shown in the sequel. The baseband implementation of equation () of Chapter 3 is shown in Figure . The input signal is correlated with two locally generated, mutually delayed, replicas of the pseudonoise (PN) code. After filtering, the useful component of the control signal e(t) will be proportional to DD (δ) = Rc (δ − /2) −. | Adaptive WCDMA Theory And Practice. Savo G. Glisic Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-84825-1 4 Code tracking CODE-TRACKING LOOPS Theoretically switching from code acquisition to code tracking in this chapter means switching from open loop maximization of likelihood function equation to the closed-loop tracker defined by equation of Chapter 3. A variety of practical implementation options are shown in the sequel. The baseband implementation of equation of Chapter 3 is shown in Figure . The input signal is correlated with two locally generated mutually delayed replicas of the pseudonoise PN code. After filtering the useful component of the control signal e t will be proportional to Dd 8 Rc 8 - 2 - Rc 8 A 2 where Rc 8 is the auto correlation of the sequence. For the analysis of the tracking error variance results from the standard phase lock loop theory can be used directly 1 . In Code Division Multiple Access CDMA system the input signal in Delay lock loop DLL will be a complete Direct Sequence Spread Spectrum DSSS signal. In order to get rid of information a noncoherent structure shown in Figure a may be used with the simplest form of the input signal r t s t n t and s t Ab t c t cos w0t It can be shown that the direct current DC component of e t 8 is A2Da 8 2 where Da 8 R A y 8 2 R 8 T Tc 4-4 The tracking error variance can be expressed as 1 T 2 1 8 2pl 2 1 pif 4-5 80 CODE TRACKING DA d A R d - AjrJ - R2 d 2 Tc Delay-lock discriminator Figure Conceptual block diagram baseband delay-lock tracking loop. a Figure a Full-time early-late noncoherent code-tracking loop b Noncoherent tracking loop with interference cancellation IC DLL IC 2 . Reproduced from Sheen W. and Tai C. 1998 A noncoherent tracking loop with diversity and multipath interference cancellation for direct-sequence spread-spectrum systems. IEEE Trans. Commun. 46 11 1516-1524 by permission of IEEE. c Comparisons of DLL and DLL IC tracking loops 2 . .

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