March 21, 2006

This glossary contains terms and abbreviations relating to radio broadcasting. Many of them apply specifically to digital radio. To suggest terms to be added or to suggest corrections or updates, please contact

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AAC: Advanced Audio Coding, the lossy codec best known for its use in the Apple Ipod and Itunes. May be labeled with filename extension M4A. Operates with or without Fairplay DRM.

AAS: Advanced Application Services. A class of data services being developed for HD Radio's ancillary data capabilities. Some of the services that have already been demonstrated include traffic reports with mapping features, both commercial and non-commercial expanded messaging services, as well as timely weather and other public safety bulletins.

ACR-MOS: absolute category rating-mean opinion score. A methodology for subjectively testing audio quality where participants are presented with sound samples, one at a time, and are asked to grade them on a five-point scale. For the NRSC FM IBOC tests, the MOS scale used was 5 = excellent, 4 = good, 3 = fair, 2 = poor, 1 = bad.

absolute layer 1 frame number (ALFN): A sequential number assigned to every Layer 1 frame. The start time of ALFN 0 was 00:00:00 Universal Coordinated Time (UTC) on January 6, 1980. Each subsequent ALFN is incremented by one from the previous ALFN. The present time can be calculated by multiplying the next frame's ALFN times the frame duration, T, and adding the total to the start time of ALFN 0.

advanced authoring format (AAF): An interchange file format developed by the AAF Association, Pro-MPEG Forum and SMPTE primarily for postproduction interchange of media and metadata.

Advanced Data Services: Advanced data services are any data services consisting of either text, audio, video or other data carried on the IBOC transport other than SIS, MPSD or SPSD.

AES/EBU: abbreviation for Audio Engineering Society/European Broadcast Union. Used to refer to a digital audio encoding standard that is officially designated as AES3.

after-market: A radio designed for purchase and installation some time after purchasing an automobile.

AIFF: Audio Interchange File Format, an uncompressed file format codeveloped by Apple.

all-digital IBOC: The third of three modes in the Ibiquity FM IBOC system that increases data capacity by adding additional digital carriers. All-digital FM IBOC uses four frequency partitions and no analog carrier. In this mode, the digital audio data rate can range from 64kb/s to 96kb/s, and the corresponding ancillary data rate can range from 213kb/s for 64kb/s audio to 181kb/s for 96kb/s audio.

all-digital operation: Refers to FM IBOC operation that does not include the traditional analog composite baseband signals. More robust and with more capacity than the hybrid system, this mode is currently envisioned as a migration point for broadcasters as analog FM broadcasting is eventually phased out.

all-digital waveform: A transmitted waveform for modes composed entirely of digitally modulated subcarriers without an analog signal.

allotment (of a broadcast frequency): The creation of an availability for the placement of a certain class broadcast signal on a certain frequency in a certain area indicated (in the U.S.A.) by a city of license. (See also, assignment)

amplitude modulation (AM): Modulation in which the amplitude of a carrier wave is varied in accordance with the amplitude of the modulating signal.

amplitude scale factor: A factor that multiplies the baseband components of a particular sideband of the transmitted spectrum to constrain the radiated power to a prescribed level.

analog audio bandwidth control (AAB): A parameter that indicates whether the 5kHz of the 8kHz audio bandwidth has been selected when an AM IBOC station is in hybrid mode.

analog signal (or waveform): The frequency-modulated or amplitude-modulated signal, consisting of a modulated RF carrier and accompanying sidebands, that is incumbent in the FM and AM broadcast bands and is receivable by both IBOC and non-IBOC receivers. (See digital signal.)

anti-aliasing filter: A low-pass filter used to limit input frequencies to an A/D converter to one-half the sampling rate to satisfy Nyquist criteria and prevent sample contamination.

API: Application Programming Interface

artifacts: the undesired noise effects from digitizing an audio signal. Artifacts can be caused by poor encoding methods or by multiple endcoding/decoding processes.

assignment (of broadcast frequency): The licensing of a certain allotment to a specific entity with a specific set of parameters (power, height, location, directionality, gain and so forth.)

ATTC: The Advance Television Technology Center. The prime lab test contractor for the FM IBOC tests.

audio encoder: The process on the transmission side of the IBOC system that ingests an uncompressed digital audio stream and reduces the bit rate using a perceptual coding algorithm. It is the coder side of the two-step process called a codec. Decoding occurs at teh receiver.

audio frame: The audio information processed as a unit by the audio encoder, consisting of 2,048 audio samples at a sampling rate of 44.1kHz.

AWGN: Additive white Gaussian noise, also known as white noise, contains equal energy per frequency across the spectrum of the noise employed. In the context of the FM IBOC system tests, AWGN at radio frequencies was used in the laboratory tests to simulate the background noise present in the FM spectrum, which affects the quality of radio reception.


baseband: Communication in which only a single signal occupies a transmit or receive path at a time.

binary phase shift keying (BPSK): A form of digital phase modulation that assigns one of two discrete phases, differing by 180 degrees, to the OFDM subcarrier. Each BPSK symbol conveys one bit of information.

bit error-rate (BER): an indication of the integrity of a digital signal. Excessive bit-error rates will prevent a signal from being decoded.

bit mapping: The assignment of certain bits of information to specific positions within a vector or matrix. At higher layers bit mapping creates a structure for conveying such information as headers, payload, data fields, error checking and the like. At layer 1, bit mapping assigns bits to the various OFDM subcarriers.

bit-rate: See data rate

blend to analog: The point at which the BLER of an FM IBOC receiver falls below some predefined threshold and the digital audio is faded out while simultaneously the analog audio is faded in. This prevents the received audio from simply muting when the digital signal is lost. The receiver audio will also "blend to digital" upon re-acquisition of the digital signal.

blend to mono: The process of progressively attenuating the L–R component of a stereo decoded signal as the received RF signal decreases. The net result is a lowering of audible noise.

BLER (block error rate): A ratio of the number of data blocks received with at least one un-correctable bit to the total number of blocks received.

block encoding: The process of generating a forward error correction codeword for a block of data and appending it to that block. The encoded block consists of N symbols, containing K information symbols (K BPSK: binary phase shift keying. The modulation technique used to carry digital information within HD Radio's reference carrier. Data is impressed on the carrier by alternating its relative phase between two states that differ by 180 degrees. Each BPSK symbol conveys one bit of information. AM HD Radio transmitters must have extremely low levels of IPM if they are to pass an IBOC digital signal satisfactorily.

bus link: A communications link where every node shares a single communication medium.


carrier sense multiple access with collision detection (CSMA/CD): contention-based network control mechanism used by Ethernet networks.

CDA: Compact Disc Audio. Shortcut that a computer operating system used to identify an uncompressed audio track on a CD. Not actually a file format. May refer to WAV or AIFF files.

channel encoding: The process used to add error protection to each of the logical channels to improve the reliability of the transmitted information.

characterization parameters: The unique set of defining parameters for each logical channel for a given service mode. The channel encoding, interleaving, spectral mapping, and diversity delay of the logical channel determine its characterization parameters.

circulator: an RF device used to direct a signal in one way but not the other.

code rate: Defines the increase in overhead on a coded channel resulting from channel encoding. It is the ratio of information bits to the total number of bits after coding.

codec: Traditionally, any device employing hardware and/or software to convert analog audio to a digital data stream and vice versa. Sometimes used interchangeably in referring to the audio compression or audio bit rate reduction process of representing an audio signal with lower data throughput, while still preserving audio quality. The coding schemes are based on the perceptual characteristics of the human ear. PAC, AAC, MPEG-2, and AC-3 are just a few examples of these coding schemes.

common amplification: Applies to IBOC transmission systems that use a common RF power amplifier feeding a common antenna for both the analog and digital signal. Also referred to as "low-level combining."

compatibility: When one system has little to no negative impact on another system, it can generally be considered compatible. In the case of FM IBOC tests, compatibility testing was performed to determine the extent to which the addition of an FM IBOC signal would impact analog system performance.

complex conjugate: The mathematical operation where the sign of the imaginary component of a complex number is inverted: conj(a+jb)=a-jb. This operation is implicit in the generation of a radio signal with symmetrical sidebands above and below center frequency.

compression: Shrinking of audio file sizes using a codec, or encode/decode process. May be lossy, discarding some audible data, or lossless, precisely reconstructing the original signal with no loss in sound quality. Not to be confused with compression of analog audio signals or systems.

configuration administrator: the configuration administration is an IBOC system function that configures each of the layers using SCCH information or parameters which do not change often.

convolutional encoding: A form of forward-error-correction channel encoding that inserts coding bits into a continuous stream of information bits to form a predictable structure. Unlike a block encoder, a convolutional encoder has memory; its output is a function of current and previous inputs.

crest factor: The ration of the peak voltage to the RMS voltage of a signal. The crest factor of a sinusoidal waveform is 1.41 (the square root of 2).


D/U: Ratio of desired to undesired signals (usually expressed in dB).

data rate: The number of bits per second at which a codec operates. Affects quality of sound. Also known as bit-rate.

demand priority protocol (DPP): Network access mechanism used by 100BaseVG.

differential encoding: Encoding process in which signal states are represented as changes to succeeding values rather than absolute values.

digital signal: With respect to IBOC, the digitally modulated OFDM waveform. In the hybrid mode, the term digital signal is exclusive of the host analog signal.

disk mirroring: Data written to two (or more) identical disk drives for redundancy.

diversity delay: Imposition of a fixed time delay in one of two channels carrying the same information to defeat non-stationary channel impairments such as fading and impulsive noise.

DRM: Digital Rights Management. A software feature that prevents unauthorized copying of copyrighted material. May also prevent DRM-protected files from playing on unauthorized devices. DRM is sometimes piggybacked onto AAC, WMA and other proprietary codecs and file formats.

DRM: Digital Radio Mondiale. DRM was first conceived as a digital replacement for AM broadcasting below 30MHz in 1998 by a consortium of world broadcast organizations, which has since expanded to include 81 members, including American broadcast manufacturers Harris, Broadcast Electronics and Continental Electronics. Unlike the HD Radio AM IBOC digital system developed and licensed by Ibiquity, DRM encompasses a non-proprietary system architecture available to broadcasters and manufacturers alike. Because channel bandwidth, emission mask requirements, and propagation vary with different regions and bands, four modes of operation are specified for DRM, offering greater levels of signal robustness in exchange for lower audio data rates. Like HD Radio AM, DRM can be transmitted in a hybrid (digital/analog simulcast) mode but with a significantly lower data rate than in its purely digital implementation.


embedded Exporter: The HD Radio Exporter encodes main program service (MPS) audio, accepts program-associated data (PAD) or program service data (PSD) for the main-channel audio and coded secondary program service (SPS) audio and Advanced Application Service (AAS) data from an Importer. First versions of the Exporter were rack-mount PCs. The embedded Exporter provides the same function in a smaller package with dedicated DSP and solid-state memory to improve reliability and reduce manufacturing costs.

emissions mask: A specification for the maximum permissible power spectral density of radio frequency emissions, including those within the necessary bandwidth, out-of-band domain and spurious domain.

EOC: Ensemble Operations Center

EPG: electronic program guide

EWG: Evaluation Working Group of the NRSC DAB Subcommittee.

Exgine: a component of the HD Radio transmission system that is part of the exciter. The Exgine accepts coded audio and data from the Exporter through a LAN. Part of the generation 3 HD Radio system.

Exporter: the device that encodes main program service (MPS) audio. The Exporter also accepts program-associated data (PAD) for the main-channel audio and coded secondary program service (SPS) audio and Advanced Application Service (AAS) data from an Importer. Part of the generation 3 HD Radio system.

extended hybrid waveform: A transmitted waveform for modes composed of the analog FM signal plus digitally modulated primary main subcarriers and some or all primary extended subcarriers. This waveform will normally be used during an initial transitional phase preceding conversion to the all-digital waveform.

extended-hybrid IBOC: The second of three modes in the Ibiquity FM IBOC system that increases data capacity by adding additional carriers closer to the analog host signal. The extended-hybrid IBOC mode adds two frequency partitions around the analog carrier. In this mode, digital audio data rate can range from 64kb/s to 96kb/s, and the corresponding ancillary data rate will range from 83kb/s for 64kb/s audio to 51kb/s for 96kb/s audio.


fading: The variation (with time) of the amplitude or relative phase (or both) of one or more frequency components of a received signal.

FLAC: Free Lossless Audio Codec. A codec that is lossless, therefore discarding no audible data; and open-source, therefore available for use by any software developer. Less efficient than a lossy format, more efficient than an uncompressed format.

frequency modulation (FM): Modulation in which the instantaneous frequency of a continuous wave carrier is caused to depart from the channel center frequency by an amount proportional to the instantaneous amplitude of the modulating signal.

frequency partition: a group of 19 OFDM subcarriers containing 18 data subcarriers and one reference subcarrier.



HD generator: part of the generation 2 HD Radio system. The function of the HD generator has been split into the Exporter and the Exgine in the generation 3 system.

hermitian symmetry: A characteristic of radio frequency sidebands in which the frequency responses of the In-phase (real) components above and below center frequency are symmetrical, while the frequency responses of the Quadrature (imaginary) components above and below center frequency would be symmetrical but for the fact that the sign of one Quadrature sideband's response is inverted with respect to the other. Mathematically, this is also called conjugate symmetry, in which the sign of the imaginary component is negated on one sideband with respect to the other: conj(a+jb)=a-jb. In terms of phase and amplitude response, the amplitude response is symmetrical while the phase rotates in opposite directions above and below center frequency. (Named for Charles Hermite.)

high-level combining: An FM IBOC transmission system that combines the outputs of discrete analog and digital transmitters through the use of large scale isolators and combiner.

host signal: The analog signal that is part of the hybrid waveform, acting as a "host" to the digital portion of the hybrid waveform.

hybrid IBOC: The first of three modes in the Ibiquity FM IBOC system that increases data capacity by adding additional carriers closer to the analog host signal. The hybrid IBOC mode adds one frequency partition around the analog carrier and is characterized by the highest possible digital and analog audio quality with a limited amount of ancillary data available to the broadcaster. Digital audio data rates can range from 64kbs/s to 96kbs/s, and the corresponding ancillary data rate can range from 33kb/s for 64kb/s audio to 1kb/s for 96kb/s audio.

hybrid operation: Refers to the operation of FM IBOC that combines a standard FM analog composite baseband modulation scheme operating in tandem with the HD Radio digital signal modulation subcarriers. Hybrid operation allows for compatibility between broadcasters and new digital receivers as well as existing analog receivers.

hybrid waveform: A transmitted waveform for modes composed of the analog-modulated signal, plus digitally modulated primary main subcarriers. This waveform will normally be used during an initial transitional phase preceding conversion to the all-digital waveform.


In-Band Adjacent-Channel: Technology never fully developed that employed digital transmission in the AM and FM broadcast bands in which the digital signals are asymmetrical to the analog host and consequently may not be compatible with the existing analog emissions and frequency assignments and may fail to provide a digital channel for every analog host.

IBOC: In-band/on-channel system of digital radio where the digital signals are placed within the current AM and FM bands and within the FCC-assigned channel of a radio station.

identify an MP3 (ID3): A metadata standard for MP3 files developed in 1996 by Eric Kemp; current version 2 is known as ID3v2.

Importer: a device that accepts multiple program feeds (SPS) and the program-associated data (PAD) for those audio streams to be transmitted with the main program service (MPS). The Importer feeds the Exporter. Part of the generation 3 HD Radio system.

injector: used in a high-level combining system to add the signal from the digital transmitter to the signal from the analog transmitter.

interleaved antenna: An FM antenna configuration that allows two identical antenna configurations to be mounted in the same axis, with alternating antenna bays spaced at half-wave intervals with opposite polarization to reduce mutual coupling. This arrangement allows an FM IBOC digital transmitter and a conventional analog transmitter to combine their signals for hybrid operation without the need for large, inefficient multiport combiners, although a ferrite circulator is generally required to provide sufficient isolation between antenna and the digital transmitter output stage.

interleaver partition: A logical subdivision of the overall interleaver matrix.

interleaving process: A reordering of the message bits to distribute them in time (over different OFDM symbols) and frequency (over different OFDM subcarriers) to mitigate the effects of signal fading and interference.

interleaving process: A series of manipulations performed on one or more coded transfer frames (vectors) to reorder their bits into one or more interleaver matrices whose contents are destined for a particular portion of the transmitted spectrum.

IP: Interleaving processes

IPM: incidental phase modulation. An undesirable phenomenon occurring in some AM transmitters, where the relative phase of the carrier unintentionally varies with modulation. This characteristic is of little concern when transmitting a monaural AM analog signal, but becomes a critical parameter where analog AM stereo or any type of AM digital transmission is involved.

isolator: a circulator with a matched load port




L1 block count: An index that indicates one of 16 equal subdivisions of an L1 frame.

L1 block: A unit of time of duration Tb. Each L1 frame is comprised of 16 L1 blocks.

L1 block pair: Two contiguous L1 blocks. A unit of time duration Tp.

L1 block pair rate: The rate, equal to the reciprocal of the L1 block pair duration, at which selected transfer frames are conducted through Layer 1.

L1 block rate: The rate, equal to the reciprocal of the L1 block duration, at which selected transfer frames are conducted through Layer 1.

L1 frame: A specific time slot of duration Tf identified by an ALFN. The transmitted signal may be considered to consist of a series of L1 frames.

L1 frame rate: The rate, equal to the reciprocal of the L1 frame duration, at which selected transfer frames are conducted through Layer 1.

L2 PDU (Protocol Data Unit): Units of upper-layer content and protocol control information transferred from Layer 2 to Layer 1.

latency: 1. The time required for an IBOC receiver to acquire, buffer and decode the digital program signal. Typically, this period may be up to 6 seconds in length. For this reason, the analog audio is usually deliberately delayed so as to match the digital signal in time. 2. The time delay that a logical channel imposes on a transfer frame as it traverses Layer 1 of the OSI model. One of the three characterization parameters. (see robustness and transfer).

logical channel: A signal path that conducts transfer frames from Layer 2 through Layer 1 with a specified grade of service.

Layer 1 (L1): The lowest protocol layer in the OSI Reference Model (also known as the Physical layer). Primarily concerned with physical connections and the transmission of data over a communication channel.

Layer 2 (L2): The Data Link layer in the OSI Reference Model. Primarily concerned with specific requirements for frames (such as blocks and packets), synchronization, and error control.

link aggregation: The process of combining individual network connections (links) into a single logical link that offers higher bandwidth and/or link redundancy.

Longley-Rice: A model used to predict the long-term median transmission loss over irregular terrain that is applied to predicting signal strength at one or more locations. Longley-Rice computations are employed by the FCC allocations rules for FM stations to predict signal strength contours and by propagation modeling software to predict signal strengths in a two-dimensional grid on a map. The FCC implementation of Longley-Rice computations employs average terrain computations and an assumed 30-ft receive antenna height.

lossless: Refers to audio codecs that reduce data, cutting file size, but without discarding any data essential to sound quality. Examples: FLAC, Apple Lossless.

lossy: Refers to audio codecs that reduce data, cutting file size, using psychoacoustic principles that identify data less essential to the ear. Examples include MP3, AAC, and WMA.

lower sideband: The group of OFDM subcarriers (subcarriers number -1 through -546) below the carrier frequency.

low-level combining: An FM IBOC transmission system that combines the analog and digital signal at the exciter level, and amplifies the combined signal via a wide-band, high linearity intermediate and final power amplifier.


main program audio (MPA): Part of the MPS, the main program audio is the primary audio portion of the IBOC signal.

Main Program Service (MPS): The audio programming and program service data that a radio station broadcasts over its main channel for reception by the general public.

Main Program Service Data (MPSD): One of two general classes of information sent through the main program service (the other being main program service audio). Main program service data is program service data that is associated with the main program service. Also referred to as program-associated data (PAD).

mask: the boundaries set for RF spectrum emission

matrix: A two-dimensional block of data indicated by a double underscore. If accompanied by a subscript, the subscript elements represent matrix row and column numbers, respectively.

mesh topology: A network where each node has a point-to-point connection with every other node.

MP3: A lossy audio codec originally developed as the audio soundtrack for the MPEG-1 video codec. The most popular audio file format, used in many applications, including paid downloads, file sharing, and personal ripping of CDs for playback on a computer or music player.

MP3 pro: An improved form of MP3 that offers better sound quality in smaller file sizes. Has yet to achieve the universality of original MP3.

MP3 VBR: MP3 Variable Bit Rate. An improved version of MP3 that adjusts compression from moment to moment, depending on the demands of the source material. Supported in newer hardware and software.

MPEG-2 AAC: Advanced Audio Coder; a high-quality, low bit-rate perceptual audio coding system developed jointly by AT&T, Dolby Laboratories, Fraunhofer IIG and Sony.

MPS: Main Program Service

MPS PDU: The output of the audio transport consisting of protocol information followed by a sequence of encoded audio packets and MPSD.

multicasting: the ability of HD Radio to transmit more than one audio stream. The Main Program Service (MPS) is a simulcast of the main-channel analog stream. The Supplemental Program Service (SPS) provides additional audio streams.

multipath: an RF reception condition in which a radio signal reaching a receiving antenna arrives by multiple paths due to reflections of the signal off of various surfaces in the environment. By traveling different distances to the receiver, the reflections arrive with different time delays and signal strengths. When multipath conditions are great enough, analog reception of FM radio broadcasts is affected in a variety of ways, including stop-light fades, picket fencing and distortion of the received audio.

multistream: An encoded audio stream split into two components in which one consists of a moderate fidelity core stream that is independently decodable and another that consists of an enhanced audio stream that supplements the core, but cannot be decoded independently. The core stream is more robust by being transmitted with a higher quality of service than the enhanced, and faster to acquire by being transmitted at the block rate rather than the frame rate. Different from multicast.


necessary bandwidth: The bandwidth sufficient to ensure transmission and reception of a signal with a specified minimum quality or performance under defined conditions.

NRSC: National Radio Systems Committee, a technical standards setting body of the radio broadcasting industry, co-sponsored by the Consumer Electronics Association (CEA) and the National Association of Broadcasters (NAB).


objective testing: Using test equipment to directly measure the performance of a system under test. For example, the power output of a transmitter can be objectively measured using a wattmeter.

OEM: original equipment manufacturer. Refers to what is commonly known as the factory audio system installed in a car by the automaker before purchase.

OFDM: orthogonal frequency division multiplexing. Tthe modulation scheme used in the transmission of digital information in Ibiquity's FM HD Radio architecture. OFDM is a parallel modulation scheme in which the data stream simultaneously modulates a large number of orthogonal subcarriers. Instead of a single, wideband carrier at a high signaling rate, OFDM uses a large number of narrowband subcarriers that are simultaneously transmitted at a much lower composite symbol rate. The long symbol times of OFDM provide superior robustness in the presence of multipath fading and interference. OFDM is also inherently flexible, allowing the mapping of specific logical channels to different groups of subcarriers. The peak power in OFDM subcarriers and their sidebands vary over frequency, meaning that Hybrid FM IBOC DAB signals must be amplified using broadband, linear amplifiers, as opposed to the non-linear class C amplifiers traditionally employed in the output stages of high power analog FM transmitters. The complex and dynamic characteristics of ODFM signals also mean that conventional directional couplers are unsuitable for power measurement in IBOC DAB systems.

OFDM subcarrier: A narrowband PSK or QAM-modulated carrier within the allocated channel, which, taken together with all OFDM subcarriers, constitute the frequency domain representation of one OFDM symbol.

OFDM subcarrier mapping: The function that assigns the interleaved logical channels (interleaver partitions) to the OFDM subcarriers (frequency partitions).

OFDM symbol: Time domain pulse of duration Ts, representing all the active subcarriers and containing all the data in one row from the interleaver and system control data sequence matrices.

OGG: Open-source file format that supports open-source codecs that may be lossy or lossless.

open-source: Refers to codecs and file formats that are not proprietary and not restricted by patents or licensing.

open media framework interchange (OMFI): An open interchange standard pioneered in 1992 by Avid Technology along with industry partners to provide a platform-independent method of exchanging media and metadata.

Open Systems Interconnection (OSI) Layered Model: A multi-tiered model of network architecture and a suite of protocols (a protocol stack) to implement it. Developed by the International Standards Organization (ISO) in 1978 as a framework for international standards in heterogeneous computer network architecture. The OSI architecture is logically divided into seven protocol layers, from lowest to highest. This model is also applied to HD Radio. The HD Radio applications are noted as well.

  • Layer 1: Physical layer
    modem, interleaving, FEC, scrambling
  • Layer 2: Data Link layer
    routing Layer 1 frames to/from Layer 4; minimal frame integrity checking.
  • Layer 3: Network layer
    Not used in HD Radio
  • Layer 4: Transport layer
    builds services, reliable data delivery in format required for specific applications. Includes digital audio, control data and text, file and packet delivery
  • Layer 5: Session layer
    not used in HD Radio
  • Layer 6: Presentation layer
    services such as encoding/decoding; used for images, text, audio, PAC, HDC
  • Layer 7: Application layer
    provides means of exchanging information to the user via human machine interface. Audio: blending, audio processing etc.; Text: Processing for display; Video: Video image presentation; Specialized applications: java applets. etc.

    Each layer uses the layer immediately below it and provides a service to the layer above.

    out-of-band emissions (or domain): Emissions on frequencies immediately outside the necessary bandwidth which results from the modulation process, but excluding spurious emissions. The out-of-band domain is the region within which such emissions occur for a given waveform.


    P3 interleaver select (P3 IS): In FM IBOC service modes MP2-MP5, the P3 logical channel may utilize either a short or long interleaver depth (time span) depending on the state of the P3 interleaver select. This control bit is received from L2 via the SCCH. When the state of the P3 IS changes (as detected on an L I frame boundary) while transmitting in service mode MP2-MP5, there will be a discontinuity in the transmission of the P3 logical channel.

    PAC: A flexible high-quality perceptual audio coding system originally developed by Lucent Technologies and later refined by Ibiquity. The system can operate over a wide range of bit rates and is capable of supporting multichannel audio.

    PAD: program associated data.

    parity: In binary-coded data, a condition maintained so that in any permissible coded expression, the total number of 1s or 0s is always odd or always even.

    PCM: Pulse Code Modulation. Generic description of uncompressed digital audio. The CD is a 16-bit/44.1kHz PCM format. That means it samples a string of 16 zeroes and ones 44,100 times a second.

    peak-to-average power ratio (PAPR): The square of the crest factor, representing the ratio of the peak power to the average power of a waveform. The PAPR of a sinusoidal waveform is 2.

    perceptual audio coding: Also known as audio compression or audio bit rate reduction, this is the process of representing an audio signal with fewer bits while still preserving audio quality. The coding schemes are based on the perceptual characteristics of the human ear. Some examples of these coders are PAC, AAC, MPEG-2, and AC-3.

    power level control (PL): In the AM IBOC hybrid waveform, the nominal level of the secondary, PIDS, and tertiary sidebands (relative to the analog carrier) as indicated by one of two settings, where PL=0 selects the low level amplitude scale factors and PL=1 selects the high level amplitude scale factors.

    primary extended (PX) sidebands: The portion of the primary sideband that holds the additional frequency partitions (1, 2, or 4) inside the main partitions in the FM extended hybrid and all-digital waveforms. It consists, at most, of subcarriers 280 through 355 and -280 through -355.

    primary sidebands: The AM HD digital modulation components that exist between frequencies approx. 10kHz and 15kHz distant from the AM carrier frequency. These sidebands partially occupy a given AM station's first adjacent channel.

    primary logical channels: There are four primary logical channels that are used with the hybrid and all-digital modes of HD Radio. They are denoted as P1, P2, P3 and PIDS.

    primary main (PM) sidebands: The ten partitions in the primary sideband consisting of subcarriers 356 through 545 and -356 through -545.

    program service data (PSD): Data that is transmitted along with the program audio and that is intended to describe or complement the audio program heard by the listener (e.g. song title, artist, etc.). Unlike PAD (program associated data), PSD defines the total data payload of the HD Radio signal including all main and multicast data. In a broad sense, all PAD is PSD, but not all PSD is PAD.

    program-associated data (PAD): An HD Radio and RBDS ancillary data service provisioned to provide information such as song titles, artist names, and other related information to consumer's radios for simultaneous display or later recall. PAD can be divided into subsets, such as near-PAD (information about the current playing artist that is not song and title info, such as concert dates) and non-PAD (traffic and weather).

    proprietary codecs: Codecs bound by patent. For example, WMA is a proprietary codec owned by Microsoft. AAC was developed by AT&T, Dolby Labs and other parties and licensed to Apple and other users.

    protected contour: A representation of the theoretical signal strength of a radio station that appears on a map as a closed polygon surrounding the station's transmitter site. The FCC defines a particular signal strength contour, such as 60dBuV/m for certain classes of station, as the protected contour. In allocating the facilities of other radio stations, the protected contour of an existing station may not be overlapped by certain interfering contours of the other stations. The protected contour coarsely represents the primary coverage area of a station, within which there is little likelihood that the signals of another station will cause interference with its reception.

    protocol control information (PCI): Information about the payload data, including: stream ID, length of payload and cyclic redundancy check (CRC) for the PCI.

    protocol data unit (PDU): A protocol data unit is the generic name for any assembled data element in the IBOC protocol stack that is produced by a specific layer (or process within a layer). The PDUs of a given layer may encapsulate one or more PDUs from the next higher layer of the stack and/or include content data and protocol-control information originating in the layer itself. The sequence of assembling PDUs within PDUs as they propagate down the transmission protocol stack is reversed, recovering PDUs from within PDUs as they propagate up the protocol stack at the receiver.

    protocol stack: The organization of the various protocols for services and transports into a hierarchical structure such that the sequence of information flow is downward through the stack for transmission and upward upon reception.

    PSD: program service data

    psychoacoustics: The study of human hearing and how it is influenced by the brain. In lossy audio codecs, psychoacoustic principles are applied to determine which audio data are less critical to the ear and therefore may be discarded to reduce file size.

    pulse-shaping function: A time-domain pulse superimposed on the OFDM symbol to improve its spectral characteristics.


    QAM: quadrature amplitude modulation. A modulation technique used to transmit the secondary data stream in AM HD Radio IBOC transmission. QAM varies both the carrier amplitude and phase during modulation.

    QOS: quality of service. Sometimes abbreviated QoS.

    QPSK: quadrature phased shift keying. A form of digital phase modulation that assigns one of four discrete phases, differing by 90 degrees, to the carrier. Each QPSK symbol conveys two bits of information. Used in AM IBOC transmission for transmission of the tertiary data stream.


    RBDS: Radio Broadcast Data System. The RBDS signal is a low bit rate data stream transmitted on the 57kHz subcarrier of an FM radio signal. Radio listeners know RBDS mostly through its ability to permit RBDS-capable radios to display call letters and search for stations based on their programming format. Special traffic announcements can be transmitted to RBDS radios, as well as emergency alerts.

    Reed-Solomon encoding (RS): A type of block encoding that encodes a block of information symbol by symbol. It is especially robust against burst errors because it does not matter how many bits in a given symbol are erroneous. There are k symbols encoded with n-k parity symbols, resulting in an encoder output of n symbols. The degree of redundancy of the RS encoder determines how many erroneous symbols can be fixed in a block of data: up to (n-k)/2 erroneous symbols can be corrected. (Named for Irving S. Reed and Gustave Solomon.)

    reference subcarrier: Dedicated OFDM subcarrier modulated with the SCCH data. There are as many as 61 reference subcarriers depending on the mode (for FM) and as many as four for AM.

    resolution bandwidth (RBW): the indication of a spectrum analyzer's ability to show sufficient detail of a given spectrum. For AM, 300kHz is recommended. For FM, 1kHz is recommended.

    ripping: The encoding of an audio file, usually in a smaller file size than the original, using an audio codec.

    robustness: The ability of a logical channel to withstand channel impairments such as noise, interference, and fading. There are eleven distinct levels of robustness designed into Layer 1 of the FM air interface. One of the three characterization parameters. (see latency and transfer).

    RRS: (Radio Reading Services) an auditory reading service for the visually or physically impaired, traditionally offered in many US broadcast markets via the use of analog SCA transmissions carried by some FM broadcasters. Research is currently underway to utilize FM IBOC DAB data capacity to carry these programs via low-bit rate audio codecs.


    SAC: supplemental audio channel, see SPS

    scrambling: The process of summing the input data bits with a pseudo-random bit stream to randomize the time domain bit stream.

    SDARS: Satellite Digital Audio Radio Service, describes satellite-delivered digital audio systems such as those from XM Radio and Sirius. The digital audio data rate in these systems is specified as being 64kbs/s.

    secondary logical channels: There are six secondary logical channels that are used only with the all-digital mode of HD Radio. They are denoted as S1, S2, S3, S4, S5 and SIDS.

    secondary sidebands: The sidebands to be added in the spectrum vacated by the analog signal. The secondary sidebands are divided into the secondary main (SM) sidebands containing 10 frequency partitions, secondary extended (SX) sidebands containing four frequency partitions and the secondary protected (SP) sidebands containing two groups of twelve protected subcarriers. The secondary sidebands consist of subcarriers -279 through +279.

    separate amplification: Applies to IBOC transmission systems that use separate RF power amplifiers operating into a high-power combiner or separate antennas for the transmission of analog and digital signals.

    Serial storage architecture (SSA): A serial transport protocol developed by IBM to provide redundant data paths to up to 192 disk drives in direct attached storage configurations; utilized SCSI command set and was adopted as an ANSI X3T10.1 standard; promoted by the SSA Industry Association as an open standard but lost favor to the more widely adopted Fibre Channel protocol.

    service access point (SAP): The interface between Layer 1 and Layer 2 at which the data from Layer 2 is formatted for delivery to Layer 1.

    service control units (SCU): Units of system control data transferred between Layer 2 and Layer 1.

    service data units (SDU): Units of user content transferred from Layer 2 to Layer 1.

    service mode: A specific configuration of operating parameters specifying throughput, performance level and selected logical channels.

    signal: Detectable transmitted energy that can be used to carry information. In the radio frequency spectrum a signal has a characteristic waveform.

    SIS: Station Information Service

    SMIL: Synchronized Media Integration Language

    software-defined radio (SDR): A radio whose channel modulation waveforms are defined in software, rather than in fixed circuitry. On the transmitter side, waveforms are generated as sampled digital signals, then converted to analog via wideband DAC before being upconverted to the appropriate transmission frequency for amplification and transmission. Conversely, receivers employ a wideband ADC that captures all of the channels available to the software radio "node." The receiver then extracts, downconverts and demodulates the desired channel waveform via software running on a general-purpose processor. The advantage of SDR architecture is that radio hardware platforms themselves don't need to be modified or replaced to accommodate changes in channelization, coding or modulation schemes.

    space combining: An FM IBOC transmission system that uses co-located but separate antenna elements to transmit the outputs of discrete analog and digital transmitters.

    spectral mapping: The association of specific logical channels with specific subcarriers or groups of subcarriers.

    spectral noise and emissions limit: A specification limiting the maximum level of out-of-band components of the transmitted signal.

    split-level combining: A recently developed technique in which the digital hybrid signal is low level combined with the FM analog signal, then amplified through a low/medium power broadband transmitter, before being high level combined in-phase with the main FM analog signal. This system allows using a common antenna with greater efficiency than high-level combining, but without the requirement for a full-powered broadband analog transmitter.

    SPS: Supplemental Program Service. Sometimes called SAC. In initial tests, NPR called this Tomorrow Radio.

    spurious emissions (domain): Emissions on frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products, but exclude out-of-band emissions. The spurious domain is the region within which such emissions occur for a given waveform.

    Station Information Service (SIS): Station information services provides the necessary radio station control and identification information, such as time, station call sign identification and location reference information.

    subjective testing: Using human subjects to judge the performance of a system. Subjective testing is especially useful when testing systems that include components such as perceptual audio coders. Traditional audio measurement techniques, such as signal-to-noise and distortion measurements, are often not compatible with way perceptual audio coders work and therefore cannot characterize their performance in a manner that can be compared with other coders, or with traditional analog systems.

    supplemental program service (SPS): The Supplemental Program Service provides for the option of multiplexing additional programs with the MPS. The SPS includes Supplemental Program Service Audio (SPSA) and may also include Supplemental Program Service Data (SPSD).

    supplemental program service data (SPSD): One of two general classes of information sent through the SPS (the other being Supplemental Program Service Audio). Supplemental Program Service Data is Program Service Data that is associated with the Supplemental Program Service.

    symbol: A modulated waveform having a duration of one symbol period that conveys one vector of binary data. For instance, the QPSK-modulated OFDM subcarrier conveys two bits per symbol, while an IBOC logical channel consisting of, say, 50 QPSK subcarriers, would convey 50 x 2 = 100 bits per symbol.

    system control channel (SCCH): A channel consisting of control information from the configuration administrator and status information from Layer 1.

    system control: Data from Layer 2 specifying service mode and analog diversity delay.

    system control data sequence: A sequence of bits destined for each reference subcarrier representing the various system control components relayed between Layer 1 and Layer 2.

    system control processing: The function that generates the system control data sequence.

    system protocol stack: The protocols associated with operation of the layers of the OSI Reference Model. Also, the ordered protocols associated with data processing in the transmitter and receiver.


    telematics: emerging technologies in automotive communications, combining wireless voice and data capability for management information, safety applications, onboard communications, navigation and entertainment.

    tertiary sidebands: The AM HD Radio digital modulation components that exist between frequencies approximately 5kHz distant from the AM carrier frequency and the carrier itself.

    Tomorrow Radio: the project name given to the multicast tests conducted by NPR, Harris and Kenwood.

    training bits: A pre-determined pattern or sequence of bits, the training pattern or training sequence, that is intermingled in the transmitted information at predetermined positions to allow the receiver to detect and correct for the effects of nonuniform channel effects over the transmission path and receiver front end.

    transfer: A measure of the data throughput through a logical channel. One of the three characterization parameters. (see latency and robustness).

    transfer frame: An ordered, one-dimensional collection of data bits of specified length originating in Layer 2, grouped for processing through a logical channel.

    transfer frame modulus: The number of transfer frames in an L1 frame.

    transfer frame multiplexer: A device that combines two or more transfer frames into a single vector.

    transfer frame rate: The number of transfer frames per second entering the SAP and traversing Layer 1.

    transfer frame size: The number of bytes in a transfer frame.

    transmission subsystem: The functional component used to format and up-convert the baseband IBOC waveform for transmission through the very-high frequency (VHF) channel.


    uncompressed: Refers to an audio file that has not been subject to data reduction, either lossy or lossless. See compressed.

    upper sideband: The group of OFDM subcarriers (subcarriers number 0 through +546) above the carrier frequency.

    UDP: User Datagram Protocol. UDP is a connectionless protocol that does not require the sender and receiver to establish a connection before data is transmitted.


    vector: A one-dimensional string of data (typically presented as a binary number). In the text they are represented by a letter with a single underscore.


    WAV: Windows Waveform. An audio file format that can be used to store uncompressed digital audio signals including, but not limited to, CD.

    waveform: The amplitude-versus-time representation of a signal. The term waveform is often employed in the context of a set of time and frequency characteristics that describe a specific type of signal.

    WMA: Windows Media Audio. Family of audio codecs owned by Microsoft. Includes lossy, lossless and other formats.

    WMA lossless: Windows Media Audio Lossless. The lossless version of WMA.

    WQP: Weighted quasi peak refers to a fast attack, slow-decay detector circuit that approximately responds to signal peaks, and that has varying attenuation as a function of frequency so as to produce a measurement that approximates the human hearing system.




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