normal data symbol blocks t g will accept this minimum which is not to be exceeded however in this case t go must be at least as great as t g the useful symbol duration in the zero symbol t o yields t o t o t go u2266 t o t g thus t o u2266 t s t o t s in case t o u2267 t s applies there is no problem because then t go can be determined such that t o t s and thus the useful symbol durations of the zero symbol and the normal data symbol block correspond one special problem is posed if as in the configurations presently provided for the digital radio t o lt t s applies since then t o lt t s necessarily follows and thus only a shorter useful symbol duration than in the normal data symbol block is available in the zero symbol it has already been demonstrated in the description of the cofdm method that the subchannel spacing is precisely the reciprocal value of the useful symbol duration this determination is absolutely necessary for the orthogonality of the subchannels given the case in which t o lt t s the subchannels yield greater frequency spacing than in the normal data.