Performance of MC DS-CDMA over Nakagami-M Fading Channel Using Diversity Techniques

A class of generalized Multi-Carrier Direct Sequence CDMA (MC DS-CDMA) Schemes is defined and its performance over Nakagami-m fading channels for the Maximal ratio combining (MRC) and Equal gain combining (EGC) diversity combining techniques are considered. The expression for the Probability of bit error rate (BER) using MRC combiner is derived, considering a Multipath Intensity Profile (MIP). The BER expression, the approximation is valid only when the numbers of sub carriers are high. The sub-carrier spacing required for the optimal BER performance is investigated using the numerical results. From the observations it is noticed that the optimal carrier spacing depends on the fading Parameter m and the number of sub-carriers used. The optimal sub-carrier spacing also depends on the receiver complexity i.e. the number of RAKE fingers available at the receiver. The BER expression for the MC DS-CDMA scheme with a RAKE receiver using EGC technique is also derived. In order to make the analysis tractable MIP was assumed. It is observed that the EGC scheme leads to 2 to 10 dB loss compared to a MRC scheme with perfect channel estimates.