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The Scientific World Journal
Volume 2014 (2014), Article ID 146186, 15 pages
http://dx.doi.org/10.1155/2014/146186
Research Article

Code-Time Diversity for Direct Sequence Spread Spectrum Systems

1Benha Faculty of Engineering, Egypt
2Faculty of Engineering, Northern Border University, Saudi Arabia

Received 23 January 2014; Accepted 2 March 2014; Published 10 April 2014

Academic Editors: Y. Mao and Z. Zhou

Copyright © 2014 A. Y. Hassan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Time diversity is achieved in direct sequence spread spectrum by receiving different faded delayed copies of the transmitted symbols from different uncorrelated channel paths when the transmission signal bandwidth is greater than the coherence bandwidth of the channel. In this paper, a new time diversity scheme is proposed for spread spectrum systems. It is called code-time diversity. In this new scheme, spreading codes are used to transmit one data symbol over successive symbols interval. The diversity order in the proposed scheme equals to the number of the used spreading codes multiplied by the number of the uncorrelated paths of the channel . The paper represents the transmitted signal model. Two demodulators structures will be proposed based on the received signal models from Rayleigh flat and frequency selective fading channels. Probability of error in the proposed diversity scheme is also calculated for the same two fading channels. Finally, simulation results are represented and compared with that of maximal ration combiner (MRC) and multiple-input and multiple-output (MIMO) systems.