Orthogonal Frequency Division Multiplexing (OFDM) is an ideal candidate for next generation wireless communication systems. In OFDM the frequency offset distort the orthogonality between the subcarriers resulting Inter-Carrier Interference (ICI). SC-OFDM suffers significant performance degradation resulting from Inter-Carrier Interference (ICI) in high mobility environments. In this paper, the effect of ICI on an SC-OFDM system is analyzed and proposes a novel modulation scheme. The proposed Magnitude-Keyed Modulation (MKM) modulation provides SC-OFDM system immunity to ICI and with an easy implementation it significantly outperforms OFDM, SC-OFDM and MC-CDMA systems with Phase Shift Keying (PSK) modulation and Quadrature Amplitude Modulation (QAM) in severe ICI environment.