A method and apparatus for generating a data structure to be embedded in a ranging signal or in a synchronization preamble of a digital signal are disclosed. In a preferred embodiment, a plurality of blocks 0 through i, where i is an integer, are formed from random sequences of components A0 to Ai, each of the components being N bits, and each block including A0 through Ai components. A plurality of random sequences of components B0 through Bi, where i is an integer, of 2N bits is also formed. The components A0 through Ai in blocks 0 to i are formed into a matrix and the polarities of the components A0 through Ai are made to correspond to the polarities of a Hadamard matrix. The components A0 through Ai of each block are randomly permuted with components B0 through Bi. When the permuted components of the blocks are embedded in a ranging signal or in a synchronization preamble of a signal, the blocks will appear to an unauthorized user of the signal as being unrelated.