Improving code division multiple access security by applying encryption methods over the spreading codes

Served as one of the most widely used wireless air link interfaces, code division multiple access (CDMA) has been identified as a major technique for 3G wireless communications. Here, a new method based on applying encryption algorithm over spreading codes is proposed to improve the security of CDMA. The security produced in this way is primarily associated with the complexity of the employed encryption algorithm. Because the encryption algorithm's security is highly reliable, it is suitable for any kind of data communications. Since the multi-user detection is the inherent characteristic of the CDMA, the multi-user interference must be studied carefully. For this reason, the cross-correlation between outputs of encryption algorithm, causing the multi-user interference, is studied thoroughly. Then, the combination of encrypted and unencrypted M-sequence is used as a spreading code to mitigate the system performance, and the advantage of this combination is considered from the interference level and the security point of view. A compatible algorithm for the key exchange is produced