Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

88 MC-CDMA and MC-DS-CDMA10 010 −1soft IC, initial detectionsoft IC, 1 iterationMLSE, MLSSEMC-CDMA single-user boundOFDM (OFDMA, MC-TDMA)10 −2BER10 −310 −410 −50 1 2 3 4 5 6 7 8E b /N 0 in dBFigure 2-17 FEC coded BER versus SNR for MC-CDMA with different multi-user detectiontechniques: fully loaded system; channel code rate R = 1/2; QPSK; Rayleigh fadingThe FEC coded BER versus the SNR per bit for multiuser detection with soft IC, MLSE,MLSSE, and single-user detection with MMSE equalization is shown in Figure 2-17for code rate 1/2. Coded MC-CDMA systems with the soft IC detection technique outperformcoded OFDM (OFDMA, MC-TDMA) systems and MC-CDMA systems withMLSE/MLSSE. The performance of the initial stage with soft IC is equal to the performancewith MMSE equalization. Promising results are obtained with soft IC already afterthe first iteration.The FEC coded BER versus the SNR per bit for different symbol mapping schemesin MC-CDMA systems with soft IC and in OFDM (OFDMA, MC-TDMA) systems isshown in Figure 2-18 for code rate 2/3. Coded MC-CDMA systems with the soft ICdetection technique outperform coded OFDM (OFDMA, MC-TDMA) systems for allsymbol mapping schemes at lower BERs due to the steeper slope obtained with MC-CDMA.Finally, the spectral efficiency of MC-CDMA with soft IC and of OFDM (OFDMA,MC-TDMA) versus the SNR is shown in Figure 2-19. The results are given for the coderates 1/3, 1/2, 2/3, and 4/5 and are shown for a BER of 10 −4 . The curves in Figure 2-19show that MC-CDMA with soft IC can outperform OFDM (OFDMA, MC-TDMA).