A low-complexity precoding scheme for PAPR reduction in SC-FDMA systems

Single carrier frequency division multiple access (SC-FDMA) has been receiving much attention as the uplink multiple access technology in the next generation communication systems due to its lower peak-to-average power ratio (PAPR) compared to OFDMA. However, it was shown that PAPR is still an issue for SCFDMA, especially with the localized subcarrier allocation (SC-LFDMA) scheme. The precoding method has been shown to be effective in reducing the peak power. However, the construction of the codewords is a nondeterministic polynomial-time hard (NP-hard) problem. In this paper, we first formulate the problem of PAPR reduction by precoding as a combinatorial problem, and then propose the semidefinite relaxation approach with which the problem can then be solved in polynomial time. It will be shown that the proposed scheme can efficiently reduce the peak power with much lower complexity. By taking the transmit power limit into consideration, we further demonstrate the existence of a tradeoff between the transmit power increase and the peak power reduction. Specifically, less stringent power constraint will lead to more significant PAPR reduction.