In this paper, a generalized OFDM (G-OFDM) which protects the out of band (OOB) leakage and satisfies the orthogonality between subcarriers is proposed for next generation wireless communications. This scheme maps many data symbols to many subchannels through filter matrix, unlike the conventional OFDM that maps a data symbol to a subchannel in a one-to-one fashion. In G-OFDM, the filter matrix is used in order to limit the OOB leakage of the spectrums of input data, which is generated through processes such as jump-removing, filtering, and orthogonalizing a specially chosen initial matrix. G-OFDM is compared with OFDM in view of OOB leakage, crest factor, complementary cumulative distribution function, and bit error rate (BER) performance.