Method and apparatus for AM digital audio broadcasting with amplitude scaled tertiary subcarriers

摘要

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.