Multiuser CDMA systems employing parity bit selected double spreading

A double spreaded CDMA system employing Parity bit selected spreading sequences is proposed in this paper for improving the Bit error rate (BER) performance of Multiuser CDMA systems. In a CDMA system with parity bit selected spreading sequences (CDMA/PB), the transmitted data bits is used to select the spreading code from a set of mutually orthogonal spreading waveforms allocated to each user. After this the spreaded data is again undergone a second spreading using a unique PN sequence. Multiple Access Interference (MAI) caused in Multiuser CDMA/PB systems can be mitigated by this double spreading method. A new detection algorithm is also used at the receiver for the betterment of the BER performance. The complexity of this proposed method is less compared to Parallel Interference Cancellation (PIC) method in Multiuser CDMA systems. Hadamard codes are used for spreading in the proposed system in order to maintain the orthogonality between the spreading codes.