Lookup NU author(s): Dr Amjad Aliewi,
Dr Charalampos Tsimenidis,
Professor Bayan Sharif,
Dr Martin Johnston
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Spread spectrum techniques have been used for many cellular communication systems, and arebeing adopted widely for military communication networks. The motivation for employing thistechnique is its ability to suppress fading due to multipath propagation. In this paper, receiversbased on chip level equalization are considered for a downlink code division multiple access(CDMA) system employing user-specific long or short spreading sequences to ensure goodperformance at low signal-to-noise ratios (SNRs). Adaptive turbo architectures for jointparameter estimation and multiple-access interference cancellation integrate the functions ofequalization, multi-access interference cancellation, error correction and phase-carriertracking. A direct adaptive CDMA receiver uses continuous pilots as training data and the filtercoefficients are optimized based on the minimum mean square error (MMSE) criterion tosuppress noise, ISI, and multiple access interference (MAI) with reasonable system complexity.Moreover, the proposed detectors with continuous pilots operate just in a tracking mode afterthe initial delay acquisition is accomplished. By exploiting the presence of a continuous pilotsignal in the entire transmitted frame, this approach is well suited to tracking fast fadingchannels. The receivers are compared with Rake multiuser receiver-based channel estimation(CE) techniques using data obtained from experimental trials in the North Sea. Furthermore,three simultaneous users are reliably acquired and demodulated using a few stages. Theseresults show that the direct adaptive receivers in both types of CDMA exhibit better immunityagainst the spectral channel characteristics and significant performance improvement over CEbased receivers.
Author(s): Tsimenidis CC; Aliesawi S; Sharif BS; Johnston M
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: 4th International Conference and Exhibition Underwater Acoustic Measurements: Technologies & Results
Year of Conference: 2011