A New Pilot Architecture for Sub-Band Uplink OFDMA Systems

In sub-band uplink orthogonal frequency division multiple access (OFDMA) systems, the data signals of the different users are transmitted on non-overlapping frequency sub-bands. Moreover, the pilots used to estimate the carrier frequency offset (CFO) and channel state are generally placed at the edge of each sub-band. However, the accuracies of the CFO and channel estimates are seriously degraded by multiple-user interference (MUI) between neighboring subscribers. Conventionally, the effects of MUI are mitigated by inserting a guard sub-carrier between adjacent users and adding a single pilot to either edge of the data sub-carrier. However, in the present study, the guard sub-carrier is more fully exploited by adding three pilots to each side of the data subcarrier. Notably, in the proposed approach, the pilots of neighboring users are overlapped. As a result, the proposed architecture has the same bandwidth efficiency as that of the conventional guard subcarrier insertion scheme. It is shown that the proposed pilot design yields a lower MUI than the conventional guard subcarrier insertion method and achieves an improved bit error rate (BER) performance as a result.