A method for performing, by a station, STA, apparatus, multi-user, MU, transmission in a wireless communication system, the method comprising: generating a physical protocol data unit, PPDU, including a data field and plural signal fields; and transmitting the PPDU to another STA, wherein the PPDU further comprises one or more long training field, LTF, symbols for at least one of synchronization or channel estimation, wherein the LTF symbols are generated based on a LTF sequence that is generated in a frequency domain according to an MU transmission bandwidth by multiplying a predefined sequence by one row of a predefined matrix, each row corresponding to each space-time stream, wherein the predefined sequence has a plurality of equal length first parts and a remaining part that is shorter than any of the first parts of the predefined sequence, wherein the LTF sequence comprises a first part concatenated with a second part, wherein the second part of the LTF sequence is shorter than the first part of the LTF sequence, wherein the first part of the LTF sequence is generated by multiplying the plurality of equal length first parts of the predefined sequence by all elements of the one row of the predefined matrix in order to generate a plurality of concatenated elements, wherein the predefined matrix is a matrix of M rows and M columns, M being natural number greater than 0, having orthogonality between each of rows and, wherein the second part of the LTF sequence is generated by multiplying the second part of the predefined sequence by only a subset of the one row, the subset of the one row consisting of a number of cyclically consecutive elements corresponding to a number of elements in the second part of the predefined sequence. generating a physical protocol data unit, PPDU, including a data field and plural signal fields; and transmitting the PPDU to another STA, wherein the PPDU further comprises one or more long training field, LTF, symbols for at least one of synchronization or channel estimation, wherein the LTF symbols are generated based on a LTF sequence that is generated in a frequency domain according to an MU transmission bandwidth by multiplying a predefined sequence by one row of a predefined matrix, each row corresponding to each space-time stream, wherein the predefined sequence has a plurality of equal length first parts and a remaining part that is shorter than any of the first parts of the predefined sequence, wherein the LTF sequence comprises a first part concatenated with a second part, wherein the second part of the LTF sequence is shorter than the first part of the LTF sequence, wherein the first part of the LTF sequence is generated by multiplying the plurality of equal length first parts of the predefined sequence by all elements of the one row of the predefined matrix in order to generate a plurality of concatenated elements, wherein the predefined matrix is a matrix of M rows and M columns, M being natural number greater than 0, having orthogonality between each of rows and, wherein the second part of the LTF sequence is generated by multiplying the second part of the predefined sequence by only a subset of the one row, the subset of the one row consisting of a number of cyclically consecutive elements corresponding to a number of elements in the second part of the predefined sequence.