Uplink OFDMA schemes for loose multi-user synchronization

We investigate two kinds of uplink OFDMA schemes for relaxing the tight multi-user synchronization; 1) Sparse block Single Carrier Frequency Division Multiple Access (SC-FDMA), 2) ZCZ (zero correlation zone) code time-spread OFDMA. In order to reoBect PAPR as well as multiple access interference (MAI) on the overall performance, we simulate symbol error rates according to various values of two parameters, i.e., the linear power amplification limit of mobile terminals and the timing offset range among the users. Interestingly, it is shown that even with outstanding PAPR performance, the sparse block SC-FDMA cannot beat the ZCZ code time-spread OFDMA in quasi-synchronous environments because of significantly increasing MAI with increasing timing offset. Meanwhile, the latter has almost no MAI even with timing offsets up to one OFDM symbol duration while the degradation due to larger PAPR compared to the former is acceptable in the practical limit of linear power amplification region.