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Telecommunications and Radio Engineering

ISSN Print: 0040-2508
ISSN Online: 1943-6009

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Telecommunications and Radio Engineering

DOI: 10.1615/TelecomRadEng.v69.i7.60
pages 639-652


Saniay Kumar Sharma
Dept. of Electronics and Communication Engg, Krishna Institute of Engg. and Technology, 13 KM stone, Ghaziabad-Meerut Road, Ghaziabad-201206
S. Naseem Ahmad
Department of Mathematics, Jamia Millia Islamia, New Delhi - 110025


In recent times, there has been a lot of interest in integration of voice, data and video traffic in wireless mobile communication networks. With these growing interests, wideband code division multiple access (WCDMA) has immerged as an attractive and efficient access technique. The performance of WCDMA system is deteriorated in presence of multipath fading environment. In WCDMA, the frequency selective fading destroys the orthogonility and produces multiple access interference (MAI). A Rake receiver is a usual solution in the WCDMA downlink channel. In essence, because of path diversity, a rake receiver yields reasonable system performance. However, it does not restore the orthogonality. For this, we can adopt an equalizer to restore orthogonality without significantly increasing the system complexity. The linear adaptive equalizers have proven to be the most promising method to enhance the performance of WCDMA downlink receivers. They provide an acceptable balance between system performance and system complexity and yield simple adaptive implementations and exhibit reasonable robustness with respect to the underlying assumptions. However, the adaptive equalizers do not perform well on channels having spectral nulls in the pass band. As a more attractive and efficient receiver structure, we prefer a decision feedback equalizer (DFE). A DFE exhibits better immunity against the spectral channel characteristics. The paper presents an interference cancellation based minimum mean square error (MMSE) Decision Feedback Equalizer (DFE) for wideband code division multiple access (WCDMA) in a frequency selective channel. The filter coefficients in MMSE DFE are optimized to suppress noise, intersymbol interference (ISI), and multiple access interference (MAI) with reasonable system complexity. The work includes the design of the DFE when the transmit diversity in the form of Alamouti approach is employed at the transmitter. For the above structure, we have presented the estimation of Bit Error Rate (BER) for a MMSE DFE using computer simulation experiments. The simulation process takes into consideration the effects of interference which includes additive white Gaussian noise, multipath fading, intersymbol interference (ISI) and multiple access interference (MAI). Furthermore, the performance is compared with standard adaptive linear equalizer (LE) and RAKE receiver. Numerical and simulation results show that the MMSE DFE exhibits significant performance improvement over the standard adaptive linear equalizer (LE) and RAKE receiver