Soft-Chip Combining MIMO Multicarrier CDMA Antijam System

Multicarrier code division multiple access (MC-CDMA) systems using complex quadratic spreading sequences facilitate frequency- or time-domain chip combining to mitigate different types of jamming. In this paper, anti-jamming receivers estimating the jammer state information (JSI) and using them for chip combining in frequency- and time-domains to suppress partial band noise jamming (PBNJ) and pulse jamming (PJ), respectively, are studied for a turbo coded constant envelope multicarrier code division multiple access (MC-CDMA) system with cyclic delay diversity (CDD). A soft JSI (S-JSI) based chip combining technique is proposed that outperforms the conventional hard JSI (H-JSI) based chip combining by at least 1.75 dB at BER of 10^-4 under both types of jamming. It is also shown that without pilot assisted a priori JSI, iterative despreading (includes JSI estimation and chip combining), demapping and decoding (IDDD) has almost similar performance as one-shot despreading followed by iterative demapping and decoding (IDD)