Prefix design for TDS-OFDM supporting frequency domain multiple access

Different to orthogonal frequency division multiplexing using cyclic prefix (CP-OFDM), time division synchronous OFDM (TDS-OFDM) employs pseudo noise (PN) sequence as the prefix. TDS-OFDM provides better power efficiency than CP-OFDM since the PN prefix can be used for channel estimation while CP-OFDM needs dedicated pilot symbols. However, when TDS-OFDM is considered with frequency domain multiple access (FDMA) where multiple users share the sub-carriers, serious interference is generated between the prefixes of different users since the PN prefix occupies the whole bandwidth. To facilitate the application of TDS-OFDM with FDMA, two prefix design methods are proposed. The prefix should employ time domain repeated PN sequence when discrete grouped sub-carriers are allocated to different mobile stations (MS), while time domain expanded PN sequence should be used when continuous sub-carriers are allocated to different MSs.