Patent ID: 7746939

Claim:
A method of modulating a signal to encode information, comprising: modulating the signal in the time domain using a first modulation scheme to encode first information in the signal; transforming the time-domain modulated signal into the frequency domain via a fast Fourier transform (FFT) of length N, such that the frequency-domain signal is represented by N frequency bins; mapping information bits to a corresponding code comprising a set of M frequency bins that represent the information bits, the code being defined by identities of a particular combination of frequency bins that constitute the set, such that different combinations of M frequency bins constitute different codes that represent different information bits; modulating the frequency-domain signal in the frequency domain using a second modulation scheme to encode second information in the signal by selectively nulling the M frequency bins from the signal represented by the N frequency bins, where M is greater than one and less than N to encode the information bits in the signal via the code defined by the particular combination of M frequency bins, wherein the number of information bits encoded by nulling the M frequency bins is greater than M; transforming the selectively nulled signal to the time domain via an inverse FFT; and transmitting the selectively hulled signal containing the first information and the second information.