Abstract
This paper presents an adaptive multiuser transceiver scheme for DS-CDMA systems in which pilot symbols are added to users’ data to estimate complex channel fading coefficients. The performance of receiver antenna diversity with maximal ratio combining (MRC) technique is analyzed for imperfect channel estimation in flat fading environments. The complex fading coefficients are estimated using least mean square (LMS) algorithm and these coefficients are utilized by the maximal ratio combiner for generating the decision variable. Probability of error in closed form is derived. Further, the effect of pilot signal power on bit error rate (BER) and BER performance of multiplexed pilot and data signal transmission scenario are investigated. We have compared the performance of added and multiplexed pilot-data systems and concluded the advantages of both systems. The proposed CDMA technique uses the chaotic sequence as spreading sequence. Assuming proper synchronization, the computer simulation results demonstrate the better bit error rate performance in the presence of channel estimator in the chaotic based CDMA system and the receiver antenna diversity technique further improves the performance of the proposed system. Also, no channel estimator is required if there is no phase distortion to the transmitted signal.
Highlights
The fundamental phenomenon which makes reliable wireless transmission difficult is time varying multipath fading
No channel estimator is required for real fading coefficients
We propose the pilot-added transceiver for CDMA system in flat fading channel in which chaotic sequences are used for spreading the data symbols of various users
Summary
The fundamental phenomenon which makes reliable wireless transmission difficult is time varying multipath fading. It is this phenomenon which makes wireless transmission a challenge when compared to fiber, coaxial cable, line-ofsight microwave, or even satellite transmission. Severe rapid fluctuation in received signal due to multipath environment makes it extremely difficult for the receiver to determine the transmitted signal [1]. BER improvement of order 10−2 to 10−3 using typical modulation and coding schemes may require SNR improvement up to 10 dB. Channel estimation algorithms, and diversity techniques [3] are widely used methods for mitigating the effect of fading without increasing the transmission power
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