부산대학교 도서관

This paper develops a new method for peak-to- average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems using an expanded constellation of points in quadrature amplitude modulation (QAM). On each OFDM subcarrier, the scheme uses a specialized representation of QAM symbols that allows mapping of a group of symbols from the conventional constellation onto an alternative symbol from the external square of signalling points. The design of the expanded constellation maintains the minimum distance between signalling points with a minimal increase in the average power. Its advantage stems from the location of the alternative signalling point being "radially symmetric" to the group of original signalling points in QAM. In systems using coding, the alternative signalling points represent recoverable erasures introduced at the transmitter for the purpose of reducing PAPR. The proposed PAPR reduction method is especially applicable to QAM schemes with high number of constellation points such as M = 64 and M = 256. Significant PAPR reduction is achieved by careful mapping and selection of alternative signalling points for transmission that result in lower PAPRs. Specifically, the complementary cumulative distribution function (CCDF) of the modified OFDM signal shows (5) dB improvement in PAPR at a clipping probability of 10 -4 over the original OFDM signal.