Performance of a new multi-carrier DS-CDMA system with multi-code over Nakagami fading channel

A new multi-carrier, direct sequence code division multiple access (MC-DS-CDMA) system with multi-code is proposed. Transmitted data are first serial-to-parallel converted to D parallel data streams and a pre-coding with a rate of D/M is followed. Next, these pre-coded parallel streams are multiplexed by an inverse Walsh-Hadamard transform (IWHT) (M×M) and M super-bit streams are formed. Due to using the pre-coding, the super-bit streams will be two-level symbol streams. Then, the super-bits are once more serial-to-parallel converted to form M parallel super-bit sub-streams. Finally, all the M parallel super-bit streams are direct sequence spread spectrum (DS-SS) modulated and transmitted using M orthogonal carriers. In the receiver, after demodulation and WHT operation, the strategy of minimum mean square error (MMSE) is used for detection. Based on a correlator receiver for each carrier, its upper bound of bit error rate (BER) performance over Nakagami fading channel is analyzed. Numerical results are compared with those of a single carrier DS-CDMA system (SC-DS-CDMA). It is shown that the proposed MC-DS-CDMA scheme has much better BER performance compared to the SC-DS-CDMA system.