On maximizing the performance of SC-FDMA systems with rotated constellation

In this paper, we consider the optimization of Single-Carrier FDMA (SC-FDMA) performance using rotated constellation. Using maximum-likelihood (ML) detection, it was previously shown that the diversity order of SC-FDMA is upper-bounded by the number of multi-paths or the number of subcarriers employed. As in OFDM, channel coding is usually required in SC-FDMA system in order to maximize the frequency diversity performance, especially when number of subcarriers is small. By using rotated constellation and the proposed angles of rotation, we show that the SC-FDMA system may attain the maximum diversity and coding performance without a reduction in bandwidth-efficiency or a significant change in the peak-to-average power ratio. Furthermore, when the number of subcarriers allocated in a SC-FDMA system is small, it becomes feasible to employ high-complexity detection methods such as ML or QR-decomposition method. In particular, to handle resource blocks of various sizes, we propose that the block of subcarriers be divided into pairs so that rotation can be separately applied in each pair over the block. As such, ML detection and flexible allocation of subcarriers can be facilitated for short or long resource block in the proposed SC-FDMA system. Simulations have shown that the proposed SC-FDMA system may outperform the ordinary SC-FDMA system and OFDM system in situations where coding rate is high.