1. An apparatus comprising: at least one processor, and at least one memory including program code, the at least one memory and the program code configured to with the at least one processor, cause the apparatus at least: to insert an anti-whitened data block, which is obtainable from a specific data block by anti-whitening, into a data block that is to be whitened by a whitening to yield a whitened data block, wherein said anti-whitening compensates said whitening so that said whitened data block will comprise said specific data block in non-whitened form, and wherein said specific data block is designed to be used by a receiver of said whitened data block to estimate a direction towards a transmitter of said whitened data block based on a received representation of said specific data block.