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In-band on-channel (IBOC) is a hybrid method of transmitting
digital radio Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. Types In digital broadcasting s ...
and analog radio
broadcast Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a one-to-many model. Broadcasting began wi ...
signals simultaneously on the same frequency. The name refers to the new digital signals being broadcast in the same AM or FM band (in-band), and associated with an existing radio channel (on-channel). By utilizing additional digital
subcarrier A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio bro ...
s or
sideband In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands com ...
s,
digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...
information is "
multiplexed In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
" on existing signals, thus avoiding re-allocation of the broadcast bands. IBOC relies on unused areas of the existing spectrum to send its signals. This is particularly useful in North America style FM, where channels are widely spaced at 200 kHz but use only about 50 kHz of that
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
for the audio signal. In most countries, FM channel spacing may be as close as 100 kHz, and on AM it is only 10 kHz. While these all offer some room for additional digital broadcasts, most attention on IBOC is in the FM band in North American systems; in Europe and many other countries, entirely new bands were allocated for all-digital systems. Digital radio standards generally allow multiple program channels to be multiplexed into a single digital stream. In North American FM, this normally allows two or three high-fidelity signals in one channel, or one high-fidelity signal and several additional channels at medium-fidelity levels that are much higher quality than AM. For even greater capacity, some existing subcarriers can be taken off the air to make additional bandwidth available in the modulation
baseband In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into a ...
. On FM for instance, this might mean removing stereo from the analog signal, relying on the digital version of that signal to provide stereo where available, and making room for another digital channel. Due to the lack of available bandwidth in AM, IBOC is incompatible with analog stereo, although this is rarely used today, and additional channels are limited to highly compressed voice such as traffic and
weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the t ...
. Eventually, stations can go from digital/analog-hybrid mode to all-digital, by eliminating the baseband monophonic audio.


FM methods

On FM there are currently three methods of IBOC broadcasting in use, mainly in the United States.


HD Radio Broadcasting

The first, and currently only, digital technology approved for use on AM and FM broadcast frequencies by the Federal Communications Commission in the United States, is the proprietary HD Radio system developed by
iBiquity iBiquity Digital Corporation is a company formed by the merger of USA Digital Radio and Lucent Digital Radio. Based in Columbia, Maryland, with additional offices in Basking Ridge, New Jersey, and Auburn Hills, Michigan, iBiquity is a privately ...
Digital Corporation, which transmits energy beyond the allotted ±100 kHz FM channel. This creates potential interference issues with adjacent channels. This is the most widespread system in use, with approximately 1,556 stations transmitting HD radio in the US, plus over 800 new multicast channels (as of Jan 2010). There is a one-time license fee to iBiquity Digital, for the use of its intellectual property, as well as costs for new equipment which range from $50,000 to $100,000 US (2010) per station.


FMeXtra

The other system is
FMeXtra FMeXtra is a deprecated in-band on-channel digital radio broadcasting technology created by Digital Radio Express. It is intended to allow a second all-digital signal to be broadcast in simulcast fashion with an existing analog FM radio station, o ...
by Digital Radio Express, which instead uses subcarriers within the existing signal. This system was introduced more recently. The system is compatible with HD Radio in hybrid mode, but not in all-digital mode, and with
RBDS Radio Data System (RDS) is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardizes several types of information transmitted, including time, station identificati ...
. The stereo subcarrier can be removed to make more space available for FMeXtra in the modulation baseband. However, the system is not compatible with other existing 67–92 kHz subcarriers which have mostly fallen into disuse. The system is far less expensive and less complicated to implement, needing only to be plugged into the existing exciter, and requiring no licensing fees. FMeXtra has generally all the user features of HD Radio, including multicast capability; the ability to broadcast several different audio programs simultaneously. It uses the aacPlus (HE-AAC) codec. FMeXtra can control listening with
conditional access Conditional access (CA) is a term commonly used in relation to software and to digital television systems. Conditional access is that ‘just-in-time’ evaluation to ensure the person who is seeking access to content is authorized to access the c ...
and encryption.


DRM

Digital Radio Mondiale Digital Radio Mondiale (DRM; ''mondiale'' being Italian and French for "worldwide") is a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting—p ...
allows for simultaneous transmission of multiple data streams alongside an audio signal. The DRM mode for VHF provides bandwidths from between 35 kbit/s to 185 kbit/s and up to four simultaneous data streams, allowing 5.1 surround vdv quality audio to be broadcast alongside other multimedia content - images, video or HTML content are typical examples. While it is not backwardly compatible with existing FM receiver equipment, with broadcasts digitally encoded using HE-AAC or
xHE-AAC Unified Speech and Audio Coding (USAC) is an audio compression format and codec for both music and speech or any mix of speech and audio using very low bit rates between 12 and 64 kbit/s. It was developed by Moving Picture Experts Group (MPEG ...
, this ability to operate within the internationally agreed FM spectrum of 88-108 MHz makes DRM a viable candidate for future adoption when countries begin to switch off their analogue broadcasts.


AM methods


HD Radio Broadcasting

iBiquity also created a
mediumwave Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band. During the dayt ...
HD Radio system for AM, which is the only system approved by the Federal Communications Commission for digital AM broadcasting in the United States. The HD Radio system employs use of injected digital sidebands above and below the audible portion of the analog audio on the primary carrier. This system also phase modulates the carrier in quadrature and injects more digital information on this phase-modulated portion of the carrier. It is based on the principle of AM stereo where it puts a digital signal where the
C-QUAM C-QUAM (Compatible QUadrature Amplitude Modulation) is the method of AM stereo broadcasting used in Canada, the United States and most other countries. It was invented in 1977 by Norman Parker, Francis Hilbert, and Yoshio Sakaie, and published ...
system would put the analog stereo decoding information.


DRM

Digital Radio Mondiale has had much more success in creating an AM system, and one that could be much less expensive to implement than any
proprietary {{Short pages monitor