A new criterion for determining the efficiency of CDMA codes

In Code Division Multiple Access (CDMA) systems, the traditional method for selecting spreading codes in order to reduce multiple-access interference (MAI) is to compare the maximum absolute value of the periodic (even) Cross-Correlation Function (CCF) for different code-sets. In many cases this method fails to introduce the best code-set. In this paper we propose a new criterion which is based on the Bit Error Rate (BER) performance of one set of CDMA codes. Through the development of this method, we can also compare and select the best code-set for our application. Also, our method gives us this possibility to consider the channel noise together with the inter-user interference. Using the proposed method, we analyzed the performance of some well-known Direct Sequence (DS) CDMA spreading codes. While the traditional method to calculate the BER is based on the approximation of the MAI using central-limit theorem, our approach is applicable even when the number of codes is too small to use this theorem. Finally we have analyzed the performance of a family of ternary codes.