In-Band On-Channel (IBOC), also known as HD Radio, is a proprietary digital radio broadcasting system developed by iBiquity. This technology enables the simultaneous transmission of digital radio signals alongside conventional AM or FM signals on the same frequency and at the same time. As digital receivers become more widespread, the analog signal can gradually be replaced with additional digital channels, allowing for a seamless transition from analog to digital radio broadcasting without the need for additional frequency bands.

Key features and characteristics of IBOC include:

1. Support for Program-Associated Data: IBOC enables the transmission of program-associated data, including information such as the radio station’s name, playlist, and enhanced data services. Additionally, the digital radio channel can be utilized for data transfer.
2. Both AM and FM Solutions: iBiquity has developed solutions for both AM and FM broadcasting. In the case of FM IBOC, it utilizes Orthogonal Frequency Division Multiplexing (OFDM) to create sidebands on either side of the analog FM signal. These combined analog and digital signals fit within the same spectral mask as traditional FM broadcasting. This is made possible by transmitting the digital sidebands at a much lower power level and allocating part of the analog FM signal for datacasting, with datacasting transmission eventually ceasing.
3. AM IBOC: Similar to FM IBOC, AM IBOC operates by transmitting digital sidebands alongside the conventional analog AM signal. The digital sidebands are transmitted at a lower power level to fit within the spectrum mask of the analog AM signal. This approach results in a minor performance penalty for the analog side to accommodate the IBOC digital signal. The digital sidebands have a bandwidth of 10 kHz each, with the combined signal having a total bandwidth of 30 kHz. It’s worth noting that not all analog AM receivers may filter out the digital sidebands, which can lead to them being audible.

In summary, IBOC, or HD Radio, is a digital radio broadcasting system developed by iBiquity. It allows digital and analog signals to coexist on the same frequency, making it possible to transition from analog to digital radio broadcasting smoothly. IBOC supports program-associated data and offers solutions for both FM and AM broadcasting, with the goal of enhancing the quality and capabilities of radio transmission.