This paper presents a code synchronization scheme-the time-window control l
oop (TWCL)-for postdetection RAKE receiver systems that offers the path-div
ersity effect. Laboratory test results from a postdetection RAKE receiver s
ystem with TWCL under a frequency-selective fading environment are introduc
ed. RAKE combining methods, a simple integral demodulation method within a
time window and a recursive least squares (RLS) demodulation method within
the time window that uses the RLS algorithm to realize maximal ratio combin
ing, are investigated. It is found that TWCL performance,vith delay paths (
double-spike frequency-selective Rayleigh-fading model) surpasses the perfo
rmance of both acquisition and tracking without delay paths (nonfrequency-s
elective Rayleigh-fading model) because of the path-diversity effect. The l
aboratory results show that TWCL provides good acquisition and tracking per
formance under the fading conditions experienced with maximum Doppler frequ
encies of 5 or 80 Hz, It is also shown that the signal energy per bit to no
ise-power spectral-density ratio (E-b/N-0) required to achieve the bit erro
r rate (BER) of 10(-3) under the double-spike frequency-selective Rayleigh-
fading model is reduced by 10 dB compared to the nonfrequency-selective Ray
leigh-fading model. The difference in path-diversity effect between the two
RAKE combining methods is only 1 dB, From a structural viewpoint, the simp
le integral demodulation method supports miniaturization and high-speed dat
a-transmission.