HD Radio Technology

With HD Radio (also referred to as in-band on-channel [IBOC]), analog broadcasting will gradually be replaced by digital broadcasting in VHF band II (87.5 MHz and 108.0 MHz). It enables transmitter operators to broadcast digital content during the initial phase while maintaining the existing analog broadcasting signal without any noticeable interference. The transition from analog to digital broadcasting consists of three distinct stages which basically differ in how the available frequency range is used:

  • Hybrid mode with analog and digital transmission
  • Extended hybrid mode with analog and expanded digital transmission
  • All-digital mode fully digital

HD Radio offers not only better audio quality (CD quality) and data related to the application (e.g. information about title, artist, etc.), but also the capability to transmit additional audio channels and program-independent service data (e.g. weather, traffic updates, etc.).

The new digital information in the sidebands is transmitted by means of orthogonal frequency division multiplex (OFDM). The OFDM subcarriers in the sidebands are merged to create frequency groups known as frequency partitions. Each of these consists of 18 data subcarriers and one reference subcarrier. Furthermore, additional reference subcarriers are distributed across the sidebands. Each sideband covers 69.4 kHz and 10 frequency groups. In the extended mode, three extra bands are added to the analog signal. The total power in the two sidebands is 20 dB below that of the analog carrier.

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