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

94 MC-CDMA and MC-DS-CDMABER10 0MF boundcombined-equalization, SD + IC (3 iter.)combined-equalization, G-pre-eq (p=1) + IC (3 iter.)10 −1G-MRC bound for p=1SD combined-equalization bound10 −21.2 dB 2.8 dB10 −310 −410 −50 1 2 3 4 5 6 7 8 9 10SNR in dBFigure 2-24 FEC coded BER versus SNR for MC-CDMA with combined equalization: fullyloaded system; channel code rate R = 1/2; QPSK; L = 8; Rayleigh fadingAt the transmitter, generalized pre-equalization (G-pre-eq) is applied with p = 1. Thecorresponding selection diversity (SD) and generalized equalization single-user boundsare given as references. As further reference, the matched filter performance is shown.Although the system is fully loaded, the performance gap towards the correspondingselection diversity combined equalization bounds is only around 1 dB at a BER of 10 −3 .Compared to the conventional matched filter bound, a gain of nearly 3 dB is obtainedat a BER of 10 −3 . Additionally, the performance of a fully loaded coded uplink MC-CDMA system that applies selection diversity together with soft interference cancellationis shown.2.2 MC-DS-CDMA2.2.1 Signal StructureThe MC-DS-CDMA signal is generated by serial-to-parallel converting data symbols intoN c sub-streams and applying DS-CDMA on each individual sub-stream. With MC-DS-CDMA, each data symbol is spread in bandwidth within its sub-channel, but in contrastto MC-CDMA or DS-CDMA not over the whole transmission bandwidth for N c > 1. AnMC-DS-CDMA system with one sub-carrier is identical to a single-carrier DS-CDMAsystem. MC-DS-CDMA systems can be distinguished in systems where the sub-channelsare narrowband and the fading per sub-channel appears flat and in systems with broadbandsub-channels where the fading is frequency-selective per sub-channel. The fading over thewhole transmission bandwidth can be frequency-selective in both cases. The complexity