Chapter 1 - An Introduction to HD Radio Technology

Abstract

HD Radio is the trademark for iBiquity Digital Corporation's in-band on-channel (IBOC) digital radio system. While there are differences between amplitude modulation (AM) and frequency modulation (FM) band HD Radio systems, an HD Radio signal can be generally described as a digitally modulated RF signal that is transmitted around, under and along side the present-day analog AM and FM signals. It should be noted that, strictly speaking, a hybrid HD Radio signal actually has two components - an analog modulated component (the legacy AM or FM signal) and the digitally modulated component referred to here. These digital signals are composed of multiple orthogonal frequency division multiplexed (OFDM) subcarriers, which are transmitted at a level to meet the specifications of the RF masks (AM and FM) as mandated in the United States by the Federal Communications Commission (FCC), and as specified in the digital radio broadcasting standard (NRSC-5-A) of the National Radio Systems Committee (NRSC). Since the OFDM subcarriers of the HD Radio signals are contained within these masks, and are therefore considered to be contained within the allotted channel for a given station without allocating any additional spectrum, it is considered to be an “in-band on-channel” system.