A method of in-band on-channel (IBOC) digital audio broadcasting (DAB) comprises
the steps of providing an analog modulated carrier signal in a central frequency
band of an AM radio channel, providing a first plurality of subcarriers in an upper
sideband of the AM radio channel, providing a second plurality of subcarriers in
a lower sideband of the AM radio channel, providing a third plurality of subcarriers
in the central frequency band of the AM radio channel, modulating the first, second
and third plurality of subcarriers with one or more digitally encoded signals,
and transmitting the analog modulated signal and the first, second and third plurality
of subcarriers, wherein the subcarriers in the third plurality of subcarriers that
are positioned closest to the center of the channel are transmitted at higher power
spectral densities than the subcarriers in the third plurality of subcarriers that
are positioned farther from the center of the channel. The power spectral densities
of a first group of the subcarriers in the third plurality of subcarriers can decrease
linearly with frequency separation from the center of the channel. Transmitters
and receivers that utilize the composite IBOC DAB signal are also included.
