A transmission method for transmitting digital data, comprising: encoding a block of data of a predetermined length with an error correction code; generating a real-valued symbol sequence including N S real-valued symbols by mapping the encoded block of data onto real-valued symbols a predetermined number of bits at a time; converting D-dimensional vectors into D-dimensional rotated vectors by multiplying each of the D-dimensional vectors by a D×D orthogonal matrix, each of the D-dimensional vectors having D of the real-valued symbols in the real-valued symbol sequence as elements, each of the D-dimensional rotated vectors having D of Ns real symbols as elements; and generating a complex symbol sequence from the N S real symbols resulting from the conversion, the complex symbol sequence including Nc = Ns/2 complex symbols, characterised in that the complex symbol sequence is generated by: mapping each pair of D dimensional rotated vectors respectively onto the real and imaginary components of D contiguous complex symbols, and thereby generating a first complex symbol sequence including the Nc complex symbols from the N S real symbols resulting from the conversion; and performing processing equivalent to writing the Nc complex symbols in the first complex symbol sequence column by column into an interleaver matrix having D rows, and to reading the Nc complex symbols row by row from the interleaver matrix and transmitting the read sequence of Nc complex symbols. encoding a block of data of a predetermined length with an error correction code; generating a real-valued symbol sequence including N S real-valued symbols by mapping the encoded block of data onto real-valued symbols a predetermined number of bits at a time; converting D-dimensional vectors into D-dimensional rotated vectors by multiplying each of the D-dimensional vectors by a D×D orthogonal matrix, each of the D-dimensional vectors having D of the real-valued symbols in the real-valued symbol sequence as elements, each of the D-dimensional rotated vectors having D of Ns real symbols as elements; and generating a complex symbol sequence from the N S real symbols resulting from the conversion, the complex symbol sequence including Nc = Ns/2 complex symbols, characterised in that the complex symbol sequence is generated by: mapping each pair of D dimensional rotated vectors respectively onto the real and imaginary components of D contiguous complex symbols, and thereby generating a first complex symbol sequence including the Nc complex symbols from the N S real symbols resulting from the conversion; and performing processing equivalent to writing the Nc complex symbols in the first complex symbol sequence column by column into an interleaver matrix having D rows, and to reading the Nc complex mapping each pair of D dimensional rotated vectors respectively onto the real and imaginary components of D contiguous complex symbols, and thereby generating a first complex symbol sequence including the Nc complex symbols from the N S real symbols resulting from the conversion; and performing processing equivalent to writing the Nc complex symbols in the first complex symbol sequence column by column into an interleaver matrix having D rows, and to reading the Nc complex symbols row by row from the interleaver matrix and transmitting the read sequence of Nc complex symbols.