Performance Comparison of Turbo Coded Mc-cdma and Ds-cdma with Higher Level Modulation

Multi-carrier code division multiple access (MC-CDMA), direct sequence code division multiple access (DS-CDMA) and orthogonal frequency division multiplexing (OFDM) are the major contenders for wireless signaling technique. For higher data rates, the use of higher level data modulation is desirable. In MC-CDMA [1], the data-modulated symbol to be transmitted is spread over a number of subcarriers using an orthogonal spreading sequence defined in the frequency-domain. OFDM can be taken as a special case of MC-CDMA with a spreading factor SF of 1. On the other hand, in DS-CDMA, time-domain spreading is used; DS-CDMA with minimum mean square frequency-domain equalization (MMSE-FDE) [2] gives a performance comparable to that of MC-CDMA with MMSEFDE in a frequency-selective fading channel. In all types of data transmission systems, some form of error control is needed to improve the transmission performance. Turbo coding has been found to provide strong error correction capabilities. In this paper, we evaluate by computer simulations, the bit error rate (BER) performance of the three systems when turbo coding is used for error control and higher level modulation like 16QAM and 64QAM are employed.