METHOD AND APPARATUS FOR AM COMPATIBLE DIGITAL BROADCASTING WITH A PERIODIC TRAINING SEQUENCE

摘要

A broadcasting method for simultaneously broadcasting analog and digital signals in a standard AM broadcasting channel is provided by: broadcasting an amplitude modulated radio frequency signal having a first frequency spectrum, wherein the amplitude modulated radio frequency signal includes a first carrier at a frequency of fo modulated by an analog program signal representative of program material; and simultaneously broadcasting a plurality of digitally modulated orthogonal frequency division multiplexed carrier signals within a frequency range of about fo +/- 15 kHz, which encompasses the first frequency spectrum, each of the digitally modulated carrier signals being modulated by a portion of a digital program signal, wherein the digital signal includes a digital representation of the program material, additional data, or a combination of the program material and the additional data. A first group of the digitally modulated carrier signals lying within the first frequency spectrum are modulated in-quadrature with the first carrier signal, and second and third groups of the digitally modulated carrier signals lie outside of the first frequency spectrum and are modulated both in-phase and in-quadrature with the first carrier signal. A training sequence of known data is periodically transmitted using selected ones of the digitally modulated carrier signals. Transmitters and receivers which operate in accordance with the above method are also provided.