Influence of long code auto-correlation on RAKE reception performance in DS-CDMA mobile communications

This paper investigates the influence of long codes on RAKE reception in DS-CDMA mobile radio communications. Conventional DS-CDMA mobile communication systems employ long codes in order to "whiten" the interference signals from other cells. The conventional long code randomizes not only the undesired signals but also the different delay components of the desired signal which, therefore, become noise and are not combined in the RAKE processing. This phenomena impairs the RAKE performance. A method is proposed in order to reduce this impairment by introducing a new long code with higher correlation between chip intervals. An analysis shows the relationship between the auto-correlation and de-spread signals, and its influence on the BER performance. Finally, computer simulations verify the effectiveness of the proposed method.