TAILIEUCHUNG - Adaptive WCDMA (P7)

Interference suppression and CDMA overlay NARROWBAND INTERFERENCE SUPPRESSION To get an initial insight into the problem, we assume that the received signal after frequency down conversion has the form x(i) = b · c(i) + J (i) + n(i) () where at sampling instant iTc , b is data, c(i) is the code, J (i) is the narrowband interference, Tc is the chip interval and n(i) is the Gaussian noise. The receiver structure is shown in Figure . For the two types of filters, from Figures and we define vectors of input samples and filter taps as follows: Xi1 =. | Adaptive WCDMA Theory And Practice. Savo G. Glisic Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-84825-1 7 Interference suppression and CDMA overlay NARROWBAND INTERFERENCE SUPPRESSION To get an initial insight into the problem we assume that the received signal after frequency down conversion has the form x i b c i J i n i where at sampling instant iTc b is data c i is the code J i is the narrowband interference Tc is the chip interval and n i is the Gaussian noise. The receiver structure is shown in Figure . For the two types of filters from Figures and we define vectors of input samples and filter taps as follows Xi-1 Xi Xi-i Xi-2 . Xi-L T Xi2 xi M Xi M-1 . . . xi 1 xi-1 . . . Xi-M T W1 1 a2 . l T W2 a-M a-M 1 . a-1 a1 . aM T where T stands for transpose. With this notation the filter output signal can be represented as ylf xlf - Wf Xlf where f 1 for one-sided filter 1SF and f 2 for two-sided filter 2SF . In the sequel index f can be dropped for simplicity whenever this does not cause any ambiguity. If the interfering signal is stronger than the sum of Gaussian noise and useful signal then the whole process can be interpreted as the estimation of J i in the presence of an equivalent noise. In this case equation can be interpreted as the estimation error. 192 INTERFERENCE SUPPRESSION AND CDMA OVERLAY Chip rate Synchronized PN sequence c i Figure Receiver block diagram. Figure Single-sided transversal filter. Linear prediction filter. Figure Two-sided transversal filter. NARROWBAND INTERFERENCE SUPPRESSION 193 The filter coefficients will be evaluated from the condition that the Mean-Square Error mse of the estimation is minimized. So we first evaluate y2 x2 - 2xiXTW WTXiXTW The mean value can be represented as I E y2 E x 2 - 2E xfX T W WTE X X2 W E x2 - 2PTW WTRW where PT E x Xi1 R E X X px k - m k m 1 . . . M where px k - m is the signal covariance function. To minimize the estimation error the filter tap .

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