Long codes for generalized FH-OFDMA through unknown multipath channels

A generalized frequency-hopping (GFH) orthogonal frequency-division multipl e-access (OFDMA) system is developed in this paper as a structured long cod e direct-sequence code-division multiple-access (DS-CDMA) system in order t o bridge frequency-hopped multicarrier transmissions with long code DS-CDMA . Through judicious code design, multiuser interference is eliminated deter ministically in the presence of unknown frequency-selective multipath chann els. Thanks to frequency-hopping, no single user suffers from consistent fa ding effects and constellation-irrespective channel identifiability is guar anteed regardless of channel nulls, A host of blind channel estimation algo rithms are developed trading off complexity with performance. Two important variants, corresponding to slow- and fast-hopping, are also addressed with the latter offering symbol recovery guarantees. Performance analysis and s imulation results illustrate the merits of GFH-OFDMA relative to convention al OFDMA and long code DS-CDMA with pseudorandom noise codes and RAKE recep tion.