Reducing peak power for coded OFDM systems by multiple symbol mapping

Abstract

In this paper, we propose a method for reducing the peak power of the signal for orthogonal frequency division multiplex (OFDM) system in which convolutional code is used for an error-correcting code. In the system, the bit sequence encoded using a convolutional code is mapped onto the multiple symbols which may constrain the peak power of the signal. In the conventional scheme, encoded bits are mapped onto a symbol sequentially. In such a method, the symbols assigned to each subcarrier are mutually uncorrelated and it is therefore difficult to let the symbols have a correlation with other symbols to constrain the peak power of the OFDM signal. In the proposed scheme, the encoded bit sequence is mapped onto the multiple symbols in which each symbol is correlated such as to reduce the peak power of the signal. In this way we are able to keep the peak power of the OFDM signal lower than that of the conventional scheme. For further performance improvement, set partitioning is performed to a set of multiple symbols to increase the Euclidean distance. This approach is made possible by multiple trellis-coded modulation (MTCM) that applies set partitioning to multiple symbols. We evaluate the performance of the proposed scheme in the presence of the effects of nonlinear amplification and show that the proposed scheme is effective for nonlinear amplification. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(3): 67–76, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.10168