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ABSTRACT: This paper presents a coherent demodulation scheme that reduces the multiple-access interference (MAI) considerably in a band-limited direct-sequence code-division multiple-access system. The despreading signal is obtained from a combination of the conventional despreading signal and its weighted early and late versions that are used in the delay-locked loop (DLL). It is shown that with appropriate choice of the weighting parameter of the early-late signals of the DLL, the signal-to-interference-plus-noise ratio of the decision variable is increased, which leads to improvement in the bit-error performance and hence the potential increase in the system capacity by about 25%. The analyses are performed in the frequency domain. The effect of imperfect synchronization on the system performance is also analyzed
IEEE Transactions on Vehicular Technology 06/2006; · 1.92 Impact Factor
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ABSTRACT: The performance of a coherent delay-locked tracking scheme for
direct-sequence/spread-spectrum systems using half-sine or triangular
chip waveforms for early and late despreading sequences is analyzed. The
effect of band-limiting on the received signals is considered. Mean time
to lose lock (MTLL) and root mean square (rms) tracking error of the
delay-locked loop (DLL) are compared with that of a conventional DLL
which uses rectangular chip despreading waveforms. Linear and nonlinear
(based on the renewal process approach) analyses are employed to
evaluate the performance of the DLL. Results show that the use of either
the half-sine or triangular chip waveform reduces the rms tracking error
and increases the MTLL considerably when the early-late spacing is
approximately between 0.7-1.3 chip times. The results apply in
particular to the commonly used DLL using one chip early-late spacing.
Computer simulation for band-limited signals confirms the analytical
results. The use of these despreading chip waveforms also reduces
tracking offset in multipath environments
IEEE Transactions on Communications 09/2000; · 1.68 Impact Factor
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ABSTRACT: This paper presents the code tracking performance on the use of
weighted chip despreading PN sequence in a coherent delay locked
tracking scheme for direct-sequence spread-spectrum (DS/SS) systems. In
the delay locked loop (DLL), the conventional rectangular chip waveform
for early and late despreading PN sequences is replaced by a weighted
exponential chip waveform. The chip weight (γ) is tuned to
optimise the DLL performance. The early-late spacing is considered as
one chip time. This scheme is analysed for both ideal and band limited
received signals in the presence of additive white Gaussian noise
Spread Spectrum Techniques and Applications, 1998. Proceedings., 1998 IEEE 5th International Symposium on; 10/1998
