A method performed by an apparatus, said method comprising: combining N groups of lower-order modulation symbols into N groups of higher-order modulation symbols, N being a positive integer greater than 1; determining N to-be-sent signals based on the N groups of higher-order modulation symbols; for each integer value of k from 1 to N, sending a k th to-be-sent signal in the N to-be-sent signals using a k th channel in N channels; wherein combining the N groups of lower-order modulation symbols into the N groups of higher-order modulation symbols comprises: for each integer value of i from 1 to M, forming an i th column vector using the i th lower-order modulation symbol from each of the N groups of lower-order modulation symbols, wherein each of the N groups of lower-order modulation symbols comprises M lower-order modulation symbols, and M is a positive integer greater than 1; and for each integer value of i from 1 to M, an i th higher-order modulation symbol in each of the N groups of higher-order modulation symbols is obtained by combining an i th lower-order modulation symbol from each of the N groups of lower-order modulation symbols as follows: for each integer value of s from 1 to N, determining a product of a row vector of an s th row in a matrix Q and the i th column vector as an i th higher-order modulation symbol in an s th group of higher-order modulation symbols in the N groups of higher-order modulation symbols; wherein the value of N is 2, and the lower order modulation is a binary phase shift keying BPSK, the higher-order modulation is a quadrature phase shift key QPSK and wherein the matrix Q is the following matrix: Q = 1 2 1 j 1 − j, combining N groups of lower-order modulation symbols into N groups of higher-order modulation symbols, N being a positive integer greater than 1; determining N to-be-sent signals based on the N groups of higher-order modulation symbols; for each integer value of k from 1 to N, sending a k th to-be-sent signal in the N to-be-sent signals using a k th channel in N channels; wherein combining the N groups of lower-order modulation symbols into the N groups of higher-order modulation symbols comprises: for each integer value of i from 1 to M, forming an i th column vector using the i th lower-order modulation symbol from each of the N groups of lower-order modulation symbols, wherein each of the N groups of lower-order modulation symbols comprises M lower-order modulation symbols, and M is a positive integer greater than 1; and for each integer value of i from 1 to M, an i th higher-order modulation symbol in each of the N groups of higher-order modulation symbols is obtained by combining an i th lower-order modulation symbol from each of the N groups of lower-order modulation symbols as follows: for each integer value of s from 1 to N, determining a product of a row vector of an s th row in a matrix Q and the i th column vector as an i th higher-order modulation symbol in an s th group of higher-order modulation symbols in the N groups of higher-order modulation symbols; wherein the value of N is 2, and the lower order modulation is a binary phase shift keying BPSK, the higher-order modulation is a quadrature phase shift key QPSK and wherein the matrix Q is the following matrix: Q = 1 2 1 j 1 − j, for each integer value of i from 1 to M, forming an i th column vector using the i th lower-order modulation symbol from each of the N groups of lower-order modulation symbols, wherein each of the N groups of lower-order modulation symbols comprises M lower-order modulation symbols, and M is a positive integer greater than 1; and for each integer value of i from 1 to M, an i th higher-order modulation symbol in each of the N groups of higher-order modulation symbols is obtained by combining an i th lower-order modulation symbol from each of the N groups of lower-order modulation symbols as follows: for each integer value of s from 1 to N, determining a product of a row vector of an s th row in a matrix Q and the i th column vector as an i th higher-order modulation symbol in an s th group of higher-order modulation symbols in the N groups of higher-order modulation symbols; wherein the value of N is 2, and the lower order modulation is a binary phase shift keying BPSK, the higher-order modulation is a quadrature phase shift key QPSK and wherein the matrix Q is the following matrix: Q = 1 2 1 j 1 − j,