Multistage detector for adaptive separation of QAM-modulated multiuser CDMA signals

Document Type

Conference Proceeding

Publication Date

1-1-1998

Abstract

Code Division Multiple Access (CDMA) proves to be an attractive method for multiuser communication due to its potential capacity increase and anti-multipath fading capability. However, its performance is limited by the existence of multiple access interference energy (MAI), which results in the so called near-far problem. To reduce the MAI effect, different structures for multiuser separators have been proposed. Among these are different decorrelating detectors, adaptive and non-adaptive. One of these adaptive decorrelators is the so called `bootstrap' decorrelator. To further improve performance, multi-stage receivers has also been proposed using as a second stage a fixed canceler that depends on knowing the signals amplitude or adaptive that needs no such knowledge. All these different detection methods assumed BPSK modulation. For high bit/cycle modulation such as QAM, one can extend the BPSK based detectors by modifying them to PAM and handle the I and Q rails separately. However, considering the QAM as complex modulation signals, we propose in this paper the generalized complex bootstrap, and implement it in a multi-stage receiver, which can handle multiuser M-QAM data. Simulation results showed the adequacy of the scheme in improving the performance of the detection by reducing MAI.

Identifier

0031641956 (Scopus)

Publication Title

IEEE International Symposium on Spread Spectrum Techniques Applications

First Page

927

Last Page

931

Volume

3

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