New Reduced-Complexity Receiver Designs for DS-CDMA Downlink Systems
Date Issued
2007
Date
2007
Author(s)
Bai, Cheng-Zong
DOI
en-US
Abstract
In recent years, DS-CDMA systems have gained its popularity and become the most widely used mobile communication systems. However, as the transmission bandwidth increases, one of the primary challenges in wireless communication is to overcome the effect of multipath channel.
The G-RAKE receiver is capable to mitigate the interference that is introduced by the multipath channel. The main defect of a G-RAKE is that one needs to evaluate a large matrix inversion. In this thesis, we propose a new MRC-MMSE-RAKE receiver which is a compromise between conventional RAKE and G-RAKE receivers. The signal fingers are placed to collect signal energy and combined with MRC. Additional noise fingers are introduced in order to suppress the interference of the MRC output by the MMSE interference estimation. We also propose an efficient finger selection algorithm (EFSA) to select valuable noise fingers. In addition, we extend the RAKE receivers to the receive diversity scheme and the MIMO transmission. From the simulation results, the MRC-MMSE-RAKE may outperform the G-RAKE with lower complexity, and the proposed EFSA can be utilized to select noise fingers effectively.
On the other hand, we also design two types of MMSE equalizers for DS-CDMA downlink systems. We propose using the Neumann series perturbation (NSP) method and the Rayleigh-Schrödinger perturbation (RSP) method to correct the FFT-based approximation in matrix inversion. Besides, an algorithm for finding the RSP correction is also derived. By analyzing the distribution of SINR, it is found that the RSP is able to reduce the probability of the occurrence of deep fading events, whereas the NSP can not be. Several strategies were proposed to enhance the statistical characteristic of SINR in RSP. From the simulation results, the RSP is able to correct the inaccuracy of the FFT-based approximation and it may achieve the performance of the optimal MMSE equalizer.
Subjects
直序分碼多工
耙狀接收機
廣義耙狀接收機
耙指選擇
最小方均誤差等化器
帶狀常對角反矩陣
微擾理論
DS-CDMA
RAKE
G-RAKE
MRC-MMSE-RAKE
finger selection
MMSE equalizer
banded Toeplitz matrix inversion
perturbation theory
Type
thesis
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