Low PAPR full-diversity space-frequency codes for MIMO-OFDM systems

Use of preceding transforms such as Hadamard transforms and phase alteration for peak to average power ratio (PAPR) reduction in OFDM systems are well known. In this paper we propose use of inverse discrete Fourier transform (IDFT) and Hadamard transform as preceding transforms in MIMO-OFDM systems to achieve low peak to average power ratio (PAPR). We show that while our approach using IDFT does not disturb the diversity gains of the MIMO-OFDM systems (spatial, temporal and frequency diversity gains), it offers a better trade-off between PAPR reduction and ML decoding complexity compared to that of the Hadamard transform precoding. We study in detail the amount of PAPR reduction achieved for the following two recently proposed full-diversity space-frequency coded MIMO-OFDM systems using both the IDFT and the Hadamard transform: (i) W. Su, Z. Safar, M. Olfat, K. J. R. Liu (IEEE Trans. on Signal Processing, Nov. 2003), and (ii) W. Su, Z. Safar, K. J. R. Liu (IEEE Trans. on Information Theory, Jan. 2005).