The power amplifier's performance in a selective level mapping (SLM) STBC-OFDM is drastically degraded due to the presence of nonlinearities. Further the back off to be applied to the system is a function of the peak to average power of the system.A high merit factor phase sequence set achieves improved PAPR reduction compared to conventional Hadamard sequence set. In this paper, we determine the PAPR reduction capability of Golay-Hadamard phase sequence set for Independent and Concurrent SLM .Computer simulations of the STBC-OFDM system in presence of nonlinearities are analysed forOFDM signal quality metrics such as Error Vector Magnitude (EVM). It is observed that a PAPR of more than 4 dB is achieved for twelve candidate signals with EVM metric satisfying the WLAN requirements.