On some properties of Walsh-Hadamard transformed OFDM

We present our study on the signal properties of a Walsh Hadamard transformed (WHT) OFDM system, i.e., an OFDM system with a WHT implemented before the OFDM modulation. Starting from a linear algebraic model, we first derive the probability density function of the transmitted signal. Then we show that the WHT-OFDM has a lower clipping probability than the conventional OFDM, especially for medium FFT sizes. We further illustrate that the analog domain spectral regrowth is also lower. Finally we present our analysis on the power spectral density of the WHT-OFDM signal and show that it has a frequency spreading property. This results in the lower block error rate performance of WHT-OFDM compared to conventional OFDM, at only marginally higher complexity.