| Summary: | 碩士 === 中原大學 === 電子工程研究所 === 86 === Multipath fading is one of the important factors that affect the performance of wireless communication systems. In conventional communication systems such as the TDMA system, equalizer is widely adopted to deal with the multipath fading. The concept of diversity is the other way to overcome the multipath fading. The CDMA systems or more generally the Direct Sequence Spread Spectrum (DSSS) systems, which exploit the characteristic of pseudo-random (PN) sequence, make use of the time diversity scheme to manipulate multipath-fading problems. This kind of time diversity scheme is usually known as RAKE receiver.Channel estimation is the essential issue for RAKE receiver design, and its main goal is to accurately estimate the impulse response of transmission channel. Several methods have been studied for channel estimation in DSSS systems, and the pre-known probe sequence method is one of them. This thesis will investigate some practical design issues for pre-known probe sequence method. The practical issues include the selection of probe sequence length, and the influence of Doppler bandwidth.This thesis will also review a multipath fading channel model. Along with the pre-known probe sequence method, a Recursive Least Square (RLS) adaptive channel estimator based on the least mean square method is developed to estimate the amplitude characteristics of multipath fading channel. Simulation results show fast convergent rate and excellent tracking property of our channel estimator. It is superior to the conventional cross-correlation and serial probe methods. Bit error rate (BER) is utilized as the criterion to evaluate the system performance.
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