ABSTRACT
In-Band, On-Channel (IBOC) digital radio is a new radio technology that is currently being deployed in the United States, whereby a digital signal is combined with the signal from an analog station. The name IBOC indicates that the digital service shares the same band and channel as the analog service. The AM and FM band IBOC systems being deployed in the United States, called HD Radio, were developed by iBiquity Digital Corporation. Following a rigorous evaluation by the National Radio Systems Committee (NRSC), completed in early 2002, the FCC in October 2002 approved HD Radio technology for use under an interim authorization. This allows FM broadcasters to transmit IBOC 24/7 but restricts AM transmissions to daytime-only use. At the time of this action, very little technical information was available about how AM IBOC would perform at night in the more difficult skywave propagation environment (see Chapter 17 for more on propagation).
