Long codes for generalized FH-OFDMA through unknown multipath channels

A Generalized Frequency Hopping (GFH) OFDMA system is developed in this paper as a structured long code DS-CDMA system in order to bridge frequency hopped multi-carrier transmissions with long code DS-CDMA. Through judicious code design, multiuser interference is eliminated deterministically in the presence of unknown frequency-selective multipath channels. Thanks to frequency hopping, no single user suffers from consistent fading effects and constellation-irrespective channel identifiability is guaranteed regardless of channel nulls. A host of blind channel estimation algorithms are developed trading off complexity with performance. Two important variants, corresponding to slowand fast-hopping, are also addressed with the latter offering symbol recovery guarantees. Performance analysis and simulation results illustrate the merits of GFHOFDMA relative to conventional OFDMA and long code DS-CDMA with PN codes and RAKE reception. Keywords— Frequency-Hopping, Multi-Carrier CDMA, Spread Spectrum Systems, Multipath Fading Channels, Blind Channel Estimation