![](media/image1.wmf){width="4.769444444444445in" height="2.09375in"}

**IBOC AM Transmission Specification**

**November 2001**

**iBiquity Digital Corporation**

+------------------------------------+---------------------------------+
| **8865 Stanford Boulevard, Suite   | **20 Independence Boulevard**   |
| 202**                              |                                 |
|                                    | **Warren, New Jersey 07059**    |
| **Columbia, Maryland 21045**       |                                 |
|                                    | **(908) 580-7000**              |
| **(410) 872-1530**                 |                                 |
+------------------------------------+---------------------------------+

Table of Contents

Contents

[1 Scope 1](#scope)

[2 Abbreviations, Symbols, and Conventions
2](#abbreviations-symbols-and-conventions)

[2.1 Introduction 2](#introduction)

[2.2 Abbreviations and Acronyms 2](#abbreviations-and-acronyms)

[2.3 Presentation Conventions 3](#presentation-conventions)

[2.4 Mathematical Symbols 3](#mathematical-symbols)

[2.4.1 Variable Naming Conventions 3](#variable-naming-conventions)

[2.4.2 Arithmetic Operators 4](#arithmetic-operators)

[2.5 AM System Parameters 5](#am-system-parameters)

[3 IBOC Layers 6](#iboc-layers)

[3.1 Introduction 6](#introduction-1)

[3.2 Waveforms and Spectra 6](#waveforms-and-spectra)

[3.2.1 Hybrid Waveform 7](#hybrid-waveform)

[3.2.2 All Digital Waveform 7](#all-digital-waveform)

[3.3 System Control Channel 7](#system-control-channel)

[3.4 Logical Channels 7](#logical-channels)

[3.4.1 Functional Components 8](#functional-components)

[3.4.2 L1 Service Access Point 9](#l1-service-access-point)

[3.4.3 Scrambling 9](#scrambling)

[3.4.4 Channel Encoding 10](#channel-encoding)

[3.4.5 Interleaving 10](#interleaving)

[3.4.6 System Control Processing 10](#system-control-processing)

[3.4.7 OFDM Subcarrier Mapping 10](#ofdm-subcarrier-mapping)

[3.4.8 OFDM Signal Generation 10](#ofdm-signal-generation)

[3.4.9 Transmission Subsystem 10](#transmission-subsystem)

[4 Functional Description 11](#functional-description)

[4.1 Introduction 11](#introduction-2)

[4.2 Functionality 11](#functionality)

[4.3 Transmission Subsystem 13](#transmission-subsystem-1)

[4.3.1 Introduction 13](#introduction-3)

[4.4 Functional Components 14](#functional-components-1)

[4.4.1 Symbol Concatenation 14](#symbol-concatenation)

[4.4.2 Diversity Delay 14](#diversity-delay)

[4.4.3 Low Pass Filtering 15](#low-pass-filtering)

[4.4.4 Analog AM Modulator 15](#analog-am-modulator)

[4.4.5 Analog/Digital Combiner 15](#analogdigital-combiner)

[4.4.6 Up-Conversion 15](#up-conversion)

[4.5 GPS Synchronization 16](#gps-synchronization)

[5 Waveforms and Spectra 17](#waveforms-and-spectra-1)

[5.1 Introduction 17](#introduction-4)

[5.2 Spectral Conventions 17](#spectral-conventions)

[5.3 Hybrid Spectrum 17](#hybrid-spectrum)

[5.4 All Digital Spectrum 19](#all-digital-spectrum)

[6 Supplement A AM Transmission Specifications
21](#supplement-a-am-transmission-specifications)

[6.1 Introduction 21](#introduction-5)

[6.2 Service Mode Switching 21](#service-mode-switching)

[6.3 Synchronization Tolerances 21](#synchronization-tolerances)

[6.3.1 Analog Diversity Delay 21](#analog-diversity-delay)

[6.3.2 Time and Frequency Accuracy and Stability
21](#time-and-frequency-accuracy-and-stability)

[6.3.3 L1 Frame Timing Phase 22](#l1-frame-timing-phase)

[6.3.4 AM Spectral Emissions Limits 22](#am-spectral-emissions-limits)

[6.3.5 Alternative Spectral Emissions Limit for Hybrid Mode
22](#alternative-spectral-emissions-limit-for-hybrid-mode)

[6.3.6 Alternative Spectral Emissions Limit for All Digital Mode
24](#alternative-spectral-emissions-limit-for-all-digital-mode)

[6.4 Digital Sideband Levels 25](#digital-sideband-levels)

[6.5 Analog Audio Source 27](#analog-audio-source)

List of Figures

[Figure 3‑1 AM Air Interface L1 Functional Block Diagram
9](#__RefHeading___Toc532350107)

[Figure 4‑1 OFDM Signal Generation Conceptual Block Diagram
11](#__RefHeading___Toc532350108)

[Figure 4‑2 Pulse Shaping Function 12](#__RefHeading___Toc532350109)

[Figure 4‑3 Hybrid Transmission Subsystem Functional Block Diagram
13](#__RefHeading___Toc532350110)

[Figure 4‑4 All Digital Transmission Subsystem Functional Block Diagram
14](#__RefHeading___Toc532350111)

[Figure 5‑1 AM IBOC Hybrid Waveform Spectrum
18](#__RefHeading___Toc532350112)

[Figure 5‑2 AM All Digital Waveform Spectrum
19](#__RefHeading___Toc532350113)

[Figure 6‑1 Recommended Spectral Emissions Limit for Hybrid
Transmissions 24](#__RefHeading___Toc532350114)

[Figure 6‑2 Recommended Spectral Emissions Limit for All Digital
Transmissions 25](#__RefHeading___Toc532350115)

List of Tables

[Table 3‑1 Approximate Information Rate of AM Logical Channels
8](#__RefHeading___Toc532269986)

[Table 5‑1 AM Hybrid Waveform Spectral Summary
18](#__RefHeading___Toc532269987)

[Table 5‑2 AM All Digital Waveform Spectral Summary
19](#__RefHeading___Toc532269988)

[Table 6‑1 FCC AM Spectral Emissions Mask
22](#__RefHeading___Toc532269989)

[Table 6‑2 Modulation Normalization Factors
26](#__RefHeading___Toc532269990)

# Scope

The iBiquity Digital Corporation's digital audio broadcasting system is
designed to permit a smooth evolution from current analog Amplitude
Modulation (AM) and Frequency Modulation (FM) radio to a fully digital
in-band on-channel (IBOC) system. This system delivers digital audio and
data services to mobile, portable, and fixed receivers from terrestrial
transmitters in the existing Medium Frequency (MF) and Very High
Frequency (VHF) radio bands. Broadcasters may continue to transmit
analog AM and FM simultaneously with the new, higher-quality and more
robust digital signals, allowing themselves and their listeners to
convert from analog to digital radio while maintaining their current
frequency allocations

# Abbreviations, Symbols, and Conventions

## Introduction

Section presents the following items pertinent to a better understanding
of this document:

Abbreviations and Acronyms

Presentation Conventions

Mathematical Symbols

AM System Parameters

**Note:** A glossary defining the technical terms used herein is
provided at the end of this document.

## Abbreviations and Acronyms

AAB Analog Audio Bandwidth Control

AABI Analog Audio Bandwidth Indicator

AM Amplitude Modulation

BC L1 Block Count

BPSK Binary Phase Shift Keying

CC Control Channel

DD Analog Diversity Delay Control

DDI Analog Diversity Delay Indicator

DL Data Link

EAS Emergency Alert System

FCC Federal Communications Commission

FM Frequency Modulation

FT File Transfer

GCS Grounded Conductive Structures

GPS Global Positioning System

HTML Hypertext Markup Language

IBOC In-band On-channel

IDS IBOC Data Service

IP Interleaving Process

ISI Intersymbol Interference

JPG Joint Photographic Experts Group

L1 Layer 1

L2 Layer 2

MA1--MA4 AM Service Modes 1 through 4

MF Medium Frequency

MPA Main Program Audio

MPD Main Program Data

MUX Multiplexer

N/A Not Applicable

OFDM Orthogonal Frequency Division Multiplexing

OSI Open Systems Interconnection

P1--P3 Primary Logical Channels 1 through 3

PAC Perceptual Audio Code

PDF Portable Document Format

PIDS Primary IBOC Data Service Logical Channel

PL Power Level Control

PLI Power Level Indicator

PSM Service Mode Control

QPSK Quadrature Phase Shift Keying

RF Radio Frequency

RSID Reference Subcarrier Identification

SAP Service Access Point

SCCH System Control Channel

SDU Service Data Unit

SMI Service Mode Indicator

TBD To Be Determined

UTC Universal Time Coordinated

VHF Very High Frequency

WML Wireless Markup Language

XML eXtensible Markup Language

## Presentation Conventions

Unless otherwise noted, the following conventions apply to this
document:

Information enclosed in braces { } is either unavailable at the present
time or subject to change.

Glossary terms are presented in italics upon their first usage in the
text.

All vectors are indexed starting with 0.

The element of a vector with the lowest index is considered to be first.

In drawings and tables, the leftmost bit is considered to occur first in
time in time.

Bit 0 of a byte or word is considered the least significant bit.

When presenting the dimensions of a matrix, the number of rows is given
first (e.g., an n x m matrix has n rows and m columns).

In timing diagrams, earliest time is on the left.

Binary numbers are presented with the most significant bit having the
highest index.

In representations of binary numbers, the least significant bit is on
the right.

## Mathematical Symbols

### Variable Naming Conventions

The variable naming conventions defined below are used throughout this
document.

  -------------------------------------------------------------------------------------------------------------------
  Category                                Definition             Examples
  --------------------------------------- ---------------------- ----------------------------------------------------
  Lower and upper case letters            Indicates scalar       i, j, J, g~11~
                                          quantities             

  Underlined lower and upper case letters Indicates vectors      [u]{.underline}, [V]{.underline}

  Double underlined lower and upper case  Indicates              u, V
  letters                                 two-dimensional        
                                          matrices               

  \[i\]                                   Indicates the i^th^    [u]{.underline}\[0\], [V]{.underline}\[1\]
                                          element of a vector,   
                                          where i is a           
                                          non-negative integer   

  \[ \]                                   Indicates the          [v]{.underline} = \[0, 10, 6, 4\]
                                          component of a vector  

  \[i\] \[j\]                             Indicates the element  u\[i\]\[j\], V\[i\]\[j\]
                                          of a two-dimensional   
                                          matrix in the i^th^    
                                          row and j^th^ column,  
                                          where i and j are      
                                          non-negative integers  

  ![](media/image2.wmf){width="0.625in"   Indicates the          ![](media/image3.wmf){width="0.9027777777777778in"
  height="0.4305555555555556in"}          components of a matrix height="0.4305555555555556in"}

  n ...m                                  Indicates all the      3 ...6 = 3, 4, 5, 6
                                          integers from n to m,  
                                          inclusive              

  n:m                                     Indicates bit          Given a binary vector i = \[0, 1, 1, 0, 1, 1, 0,
                                          positions n through m  0\], i~2:5~ = \[1, 0, 1, 1\]
                                          of a binary sequence   
                                          or vector              
  -------------------------------------------------------------------------------------------------------------------

### Arithmetic Operators

The arithmetic operators defined below are used throughout this
document.

  ----------------------------------------------------- ----------------------------- ----------------------------------------------------
  Category                                              Definition                    Examples

  ∙                                                     Indicates a multiplication    3∙4 = 12
                                                        operation                     

  INT( )                                                Indicates the integer portion INT(5/3) = 1\
                                                        of a real number              INT(-1.8) = -1

  a MOD b                                               Indicates a modulo operation  33 MOD 16 = 1

  ![](media/image4.wmf){width="0.16666666666666666in"   Indicates modulo-2 binary     ![](media/image5.wmf){width="0.5138888888888888in"
  height="0.16666666666666666in"}                       addition                      height="0.18055555555555555in"}

  \|                                                    Indicates the concatenation   [B]{.underline} = \[[S]{.underline} \|
                                                        of two vectors                [F]{.underline}\]\
                                                                                      The resulting vector [B]{.underline} consists of the
                                                                                      elements of [S]{.underline} followed by the elements
                                                                                      of [F]{.underline}.

  J                                                     Indicates the square-root of  j =
                                                        -1                            ![](media/image6.wmf){width="0.3611111111111111in"
                                                                                      height="0.2361111111111111in"}

  Re( )                                                 Indicates the real component  If x = (3 + j4), Re(x) = 3
                                                        of a complex quantity         

  Im( )                                                 Indicates the imaginary       If x = (3 + j4), Im(x) = 4
                                                        component of a complex        
                                                        quantity                      

  log~10~                                               Indicates the base-10         log~10~(100) = 2
                                                        logarithm                     

  \*                                                    Indicates complex conjugate   If x = (3 + j4), x\* = (3 - j4)
  ----------------------------------------------------- ----------------------------- ----------------------------------------------------

## AM System Parameters

The AM system parameters defined below are used throughout this
document.

  --------------------- -------- ------- -------------------------- ---------------
  Parameter Name        Symbol   Units   Exact Value                Computed Value\
                                                                    (to 4
                                                                    significant
                                                                    figures)

  OFDM Subcarrier       ∆f       Hz      1488375/8192               181.7
  Spacing                                                           

  Cyclic Prefix Width   α        none    7/128                      5.469 x 10^-2^

  OFDM Symbol Duration  T~s~     Sec.    (1+α) /∆f =\               5.805 x 10^-3^
                                         (135/128)∙(8192/1488375)   

  OFDM Symbol Rate      R~s~     Hz      = 1/T~s~                   172.3

  L1 Frame Duration     T~f~     Sec.    65536/44100 = 256∙T~s~     1.486

  L1 Frame Rate         R~f~     Hz      = 1/T~f~                   6.729 x 10^-1^

  L1 Block Duration     T~b~     Sec.    = 32∙T~s~                  1.858 x 10^-1^

  L1 Block Rate         R~b~     Hz      = 1/T~b~                   5.383

  Digital Diversity     N~dd~    none    3                          3
  Delay Frames                                                      

  Diversity Delay Time  T~dd~    Sec.    = N~dd~∙T~f~               4.458
  --------------------- -------- ------- -------------------------- ---------------

# IBOC Layers

The IBOC detailed performance specifications are organized in terms of
the International Standards Organization Open Systems Interconnection
(ISO OSI) layered model. The definitions of this model are summarized
below for reference

-   Layer 5 (Application) -- presents content to the user (program
    source or listener).

-   Layer 4 (Encoding)-- content-specific source coding (e.g., PAC,
    HTML) as well as station identification and control capabilities.

-   Layer 3 (Transport) -- one or more application-specific protocols
    tailored to provide robust and efficient transfer of Layer 4 data.
    Also provides generic packet and/or file-based services.

-   Layer 2 (Service Mux)--limited error detection, addressing, Layer 3
    multiplexing to logical channels.

-   Layer 1 (Physical Layer) -- modulation, framing, and signal
    processing (encoding, interleaving, etc.) to the specified grade of
    service.

Each OSI layer of the broadcasting system has a corresponding layer,
termed a peer, in the receiving system. The functionality of these
layers is such that the combined result of lower layers is to effect a
virtual communication between a given layer and its peer on the other
side.

For the purposes of this document covering the IBOC Transmission System
only Layer 1 will be described.

## Introduction

Layer 1 of the AM system converts information and *system* control from
*layer 2* (L2) into an AM IBOC waveform for transmission in the existing
allocation in the MF band. The information and control is transported in
discrete *transfer frames* via multiple *logical channels* through the
layer 1 *service access point* (SAP). Information transfer frames are
referred to as layer 1 *service data units* (SDUs).

The L1 SDUs vary in size and format depending on the *service mode*. The
service mode, a major component of system control, determines the
transmission characteristics of each logical channel. After assessing
the requirements of their candidate applications, higher protocol layers
select service modes that most suitably configure the logical channels.
The plurality of logical channels reflects the inherent flexibility of
the system, which supports simultaneous delivery of various classes of
digital audio and data.

This section presents the following:

-   An overview of the waveforms and spectra

-   An overview of the system control, including the available service
    modes

-   An overview of the logical channels

-   A high-level discussion of each of the functional components
    comprising the layer 1 AM air interface

**Note**: Throughout this document, various system parameters are
globally represented as mathematical symbols. Refer to Subsection 2.5
for their values.

## Waveforms and Spectra

The design provides a flexible means of transitioning to a digital
broadcast system by providing two new waveform types: Hybrid and All
Digital. The Hybrid waveform retains the analog AM signal, while the All
Digital waveform does not. Both new waveform types conform to the
currently allocated *spectral emissions mask*.

The *digital signal* is modulated using *orthogonal frequency division*
multiplexing (OFDM). OFDM is a parallel modulation scheme in which the
data stream modulates a large number of orthogonal subcarriers that are
transmitted simultaneously. OFDM is inherently flexible, readily
allowing the mapping of logical channels to different groups of
subcarriers.

Refer to Section for a detailed description of the spectra of the two
waveform types.

### Hybrid Waveform

In the Hybrid waveform, the digital signal is transmitted in *primary*
and secondary *sidebands* on either side of the host analog signal, as
well as underneath the host analog signal in *tertiary sidebands*.

The total power of all the digital sidebands is significantly below the
total power in the analog AM signal. The level of each OFDM subcarrier
within a given primary or secondary sideband is fixed at a constant
value. Primary or secondary sidebands may be scaled relative to each
other.

In the tertiary sideband, the OFDM subcarrier power levels for the
hybrid waveform are not fixed, but may be adjusted. In addition, there
are two reference subcarriers for system control whose levels are fixed
at a value that is different from the other sidebands.

The analog host is a monophonic signal. The Hybrid system does not
support analog AM stereo transmissions.

### All Digital Waveform

The greatest system enhancements are realized with the All Digital
waveform. In this waveform the analog signal is replaced with the
primary sidebands whose power is increased relative to the Hybrid
waveform levels. In addition, the secondary and tertiary sidebands are
moved to either side of the primary sidebands and their power is also
increased relative to the Hybrid levels. The end result is a higher
power digital signal with an overall bandwidth reduction. These changes
provide a more robust digital signal that is less susceptible to
adjacent channel interference. Reference subcarriers are also provided
to convey system control information. Their levels are fixed at a value
that is different from the other sidebands.

## System Control Channel

The *system control channel* (SCCH) transports control and status
information. The *service mode control* (PSM), *analog diversity delay
control* (DD), *analog audio bandwidth control* (AAB), and *power level
control (PL)* are all sent from layer 2 to layer 1, while
synchronization information is sent from layer 1 to layer 2. In
addition, several bits of the system control data sequence designated
"reserved" are controlled from layers above L1 via the "reserved control
data" interface.

Four service modes dictate all permissible configurations of the logical
channels. They are:

1.  Hybrid service mode MA1

2.  Hybrid service mode MA2

3.  All Digital service mode MA3

4.  All Digital service mode MA4

## Logical Channels

A logical channel is a signal path that conducts L1 SDUs in transfer
frames into and out of layer 1 with a specific grade of service,
determined by service mode. Layer 1 of the AM air interface provides
four logical channels to higher layer protocols: P1, P2, P3 and PIDS.
P1, P2 and P3 are intended for general purpose audio and data transfer,
while the PIDS channel is designed to carry the IBOC data services (IDS)
information. The P1 and P2 logical channels are designed to be more
robust than the P3 logical channel. Logical channels P1 and P3 are
available for all services modes, while P2 is only available for
specific service modes. This allows a transfer of information that can
be tailored to conform to a number of diverse applications.

Modes MA2 and MA4 provide higher throughput than MA1 and MA3 by making
available an additional logical channel (i.e. P2) at the expense of P1
robustness. The approximate information rates of the four logical
channels for each of the four service modes are shown in Table 0-1.

[]{#__RefHeading___Toc532269986 .anchor}Table 0‑1 Approximate
Information Rate of AM Logical Channels

  ------------------------------------------------------------------------------
  Service Mode       Approximate                                 Waveform
                     Channel                                     
                     Information                                 
                     Rate (kbps)                                 
  ------------------ ------------- --------- --------- --------- ---------------
                     P1            P2        P3        PIDS      

  MA1                20            0         16        0.4       Hybrid

  MA2                20            20        16        0.4       Hybrid

  MA3                20            0         20        0.4       All Digital

  MA4                20            20        20        0.4       All Digital
  ------------------------------------------------------------------------------

The performance of each logical channel is completely described through
three *characterization parameters: transfer, latency*, and *robustness.
Channel encoding, spectral* mapping*, interleaver depth*, and *diversity
delay* are the components of these characterization parameters. The
service mode uniquely configures these components for each active
logical channel, thereby allowing the assignment of appropriate
characterization parameters.

In addition, the service mode specifies the framing and synchronization
of the transfer frames through each active logical channel.

### Functional Components

This subsection includes a high-level description of each layer 1
functional block and the associated signal flow. Figure 0-1 is a
functional block diagram of the layer 1 processing. Audio and data are
passed from the higher OSI layers to the physical layer, the modem,
through the Layer 1 Service Access points.

![](media/image7.wmf){width="5.9944444444444445in"
height="6.266666666666667in"}

[]{#__RefHeading___Toc532350107 .anchor}Figure 0‑1 AM Air Interface L1
Functional Block Diagram

### L1 Service Access Point

The L1 SAP defines the interface between layer 2 and layer 1 of the
system protocol stack. Each channel enters layer 1 in discrete transfer
frames, with a unique size and rate determined by service mode. Transfer
frames which carry information from layer 2 are referred to as L1 SDUs.

### Scrambling

This function randomizes the digital data carried in each logical
channel to mitigate signal periodicities. At the output of scrambling,
the logical channel vectors retain their identity.

### Channel Encoding

This function uses *convolutional encoding* to add redundancy to the
digital data in each logical channel to improve its reliability in the
presence of channel impairments. The size of the logical channel vectors
is increased in inverse proportion to the *code rate*. The encoding
techniques are configurable by service mode. Diversity delay is also
imposed on selected logical channels. At the output of the channel
encoder, the logical channel vectors retain their identity.

### Interleaving

*Interleaving* in time and frequency is employed to mitigate the effects
of burst errors. The interleaving techniques are tailored to the MF
non-uniform interference environment and are configurable by service
mode. In this process, the logical channels lose their identity

### System Control Processing

This function generates a vector of *system control data sequences* that
includes system control information received from layer 2 (such as
service mode), and status for broadcast on the reference subcarriers.

### OFDM Subcarrier Mapping

This function assigns the interleaver matrices and system control vector
to *OFDM subcarriers*. One row of each active interleaver matrix and one
bit of the system control vector is processed each OFDM *symbol* (every
T~S~ seconds) to produce one output vector [X]{.underline}, which is a
frequency domain representation of the signal. The mapping is
specifically tailored to the non-uniform interference environment
encountered in the AM band and is a function of the service mode.

### OFDM Signal Generation

This function generates the digital portion of the time-domain AM IBOC
waveform. The input vectors [X]{.underline} are transformed into a
shaped time-domain baseband pulse, y~n~(t), defining one OFDM symbol.

### Transmission Subsystem

This function formats the baseband waveform for transmission through the
MF channel. Major sub-functions include pre-compensation, symbol
concatenation, and frequency up-conversion. When transmitting the Hybrid
waveform, this function modulates the AM analog audio source and
combines it with the digital signal to form a composite Hybrid signal,
s(t), ready for transmission.

# Functional Description

## Introduction

OFDM signal generation receives complex frequency-domain OFDM symbols
from the output of OFDM subcarrier mapping and outputs time-domain
pulses representing the digital portion of the AM IBOC signal. A
conceptual block diagram of OFDM signal generation is shown in Figure
0-2 OFDM Signal Generation Conceptual Block Diagram.

![](media/image8.wmf){width="1.7493055555555554in"
height="1.9513888888888888in"}

[]{#__RefHeading___Toc532350108 .anchor}Figure 0‑2 OFDM Signal
Generation Conceptual Block Diagram

The input to OFDM signal generation is a complex vector,
[X]{.underline}~n~ of length L, representing the complex constellation
values for each OFDM subcarrier in OFDM symbol n. The output of OFDM
signal generation is a complex, baseband, time-domain pulse y~n~(t),
representing the digital portion of the AM IBOC signal for symbol n.

## Functionality

Let [X]{.underline}~n~\[k\] be the complex scaled constellation points
from OFDM subcarrier mapping for the n^th^ symbol, where k = 0, 1, ...,
L-1 indexes the OFDM subcarriers. Let y~n~(t) denote the complex
time-domain output of OFDM signal generation for the n^th^ symbol. Then
y~n~(t) can be written in terms of [X]{.underline}~n~\[k\] as follows:

![](media/image9.wmf){width="3.1666666666666665in"
height="0.5097222222222222in"}

where n = 0,1,...,∞, 0 ≤ t ≤ ∞, L = 163 is the minimum number of OFDM
subcarriers, and T~S~ and ∆f are the OFDM symbol period and OFDM
subcarrier spacing, respectively, as defined in Section .

The *pulse-shaping function* W(ξ) is defined as:

![](media/image10.wmf){width="4.198611111111111in"
height="1.6902777777777778in"}

where

![](media/image11.wmf){width="4.1in" height="1.5659722222222223in"}

α is the cyclic prefix width defined in Subsection , and T = 1/∆f is the
reciprocal of the OFDM subcarrier spacing. Figure 0-3 Pulse Shaping
Function shows a plot of the pulse shaping function W(ξ).

![](media/image12.png){width="4.001388888888889in"
height="3.0006944444444446in"}

[]{#__RefHeading___Toc532350109 .anchor}Figure 0‑3 Pulse Shaping
Function

## Transmission Subsystem

### Introduction

The transmission subsystem formats the baseband AM IBOC waveform for
transmission through the MF channel. Functions include symbol
concatenation, pre-compensation and frequency up-conversion. In
addition, when transmitting the Hybrid waveform, this function delays,
filters, and modulates the baseband analog audio signal before
coherently combining it with the digital portion of the waveform.

The input to this module is a complex, baseband, time-domain OFDM
symbol, y~n~(t), from OFDM signal generation. A baseband analog audio
signal, m(t), is also input from an analog source when transmitting the
Hybrid waveform. In addition, analog diversity delay control (DD) is
input from layer 2 via the SCCH. The output of this module is the MF AM
IBOC waveform.

Refer to Figure 0-4 Hybrid Transmission Subsystem Functional Block
Diagram and Figure 0-5 All Digital Transmission Subsystem Functional
Block Diagram for functional block diagrams of the Hybrid and All
Digital transmission subsystems, respectively.

![](media/image13.wmf){width="4.501388888888889in" height="5.1125in"}

[]{#__RefHeading___Toc532350110 .anchor}Figure 0‑4 Hybrid Transmission
Subsystem Functional Block Diagram

![](media/image14.wmf){width="2.551388888888889in"
height="3.977777777777778in"}

[]{#__RefHeading___Toc532350111 .anchor}Figure 0‑5 All Digital
Transmission Subsystem Functional Block Diagram

## Functional Components

The functional components of the transmission subsystem are specified in
Subsections through .

### Symbol Concatenation

The individual time-domain OFDM symbols output from ISI pre-compensation
are summed to produce a continuum of pulses over 0 ≤ t ≤ ∞ as follows:

![](media/image15.wmf){width="1.0416666666666667in"
height="0.4722222222222222in"}

### Diversity Delay

When broadcasting the Hybrid waveform, y(t) is combined with the analog
host AM signal a(t), as shown in Figure 0-4 Hybrid Transmission
Subsystem Functional Block Diagram. The first step in generating a(t) is
the application of diversity delay to the baseband analog audio signal
m(t).

The analog diversity delay control bit (DD), received from layer 2 via
the SCCH, to enable or disable the diversity delay. If DD is 0, the
diversity delay is disabled; if DD is 1, it is enabled. When diversity
delay is enabled, an adjustable delay τ~d~ is applied to the baseband
analog audio signal m(t). The delay is set so that, at the output of the
analog/digital combiner, a(t) lags the audio content of the
corresponding digital signal, y(t), by T~dd~. For example, if both the
analog and digital signals carry the same audio program, the analog
audio would be delayed from the corresponding digital audio by T~dd~ at
the output of the analog/digital combiner. The delay is adjustable to
account for processing delays in the analog and digital chains. When the
state of DD changes while operating in service mode MA1 or MA2, there
will be a discontinuity in the analog signal.

The absolute accuracy of the diversity delay, when enabled, is defined
in Supplement A.

### Low Pass Filtering

In hybrid mode, this process low pass filters the analog audio data
according to the state of the AAB control received from layer 2. If the
control bit is zero, the analog audio is filtered to a 5 kHz bandwidth
according to the specifications in Supplement A. If the control bit is
one, the analog audio is filtered to an 8 kHz bandwidth according to the
specifications in Supplement A.

### Analog AM Modulator

When broadcasting the hybrid waveform, this process computes the
envelope of the analog AM signal by applying a modulation index and
adding a DC offset and as follows:

![](media/image16.wmf){width="1.6333333333333333in"
height="0.2534722222222222in"}

where a(t) is the envelope, m(t-T~dd~) is the delayed analog source and
g is the modulation gain. Typically, g = 1.25, representing a +125%
modulation level. The input analog audio source, m(t), must be
preprocessed external to the AM IBOC exciter, so that a(t) does not
assume negative values. See Supplement A for a complete description of
the requirements on the input analog audio source.

### Analog/Digital Combiner

When broadcasting the Hybrid waveform, the real analog AM baseband
waveform, a(t), is coherently combined with the digital baseband
waveform, y(t), to produce the complex baseband AM IBOC Hybrid waveform
z(t), as follows:

Re \[z(t)\] = Re \[y(t)\] + a(t)

Im \[z(t)\] = Im \[y(t)\]

The levels of the digital sidebands in the output spectrum are
appropriately scaled by OFDM subcarrier mapping as shown in Supplement
A, Section 6.4.

Changing service modes form MA1 to MA2 or MA2 to MA1 shall not cause any
interruptions or discontinuities in the analog signal. Refer to
Supplement A for further details.

### Up-Conversion

The concatenated digital signal z(t) is translated from baseband to the
RF carrier frequency as follows:

![](media/image17.wmf){width="1.44375in" height="0.25in"}

where f~c~ is the RF channel frequency and Re( ) denotes the real
component of the complex quantity. For the All Digital waveform, z(t) is
replaced with y(t).

The AM IBOC DAB waveform is broadcast in the current AM radio band and
its power levels and spectral content are limited to be within the
spectral mask as defined in 47 CFR §73.44. See Supplement A.

The carrier frequency spacing and channel numbering schemes are
compatible with 47 CFR §73.14. Channels are centered at 10 kHz intervals
ranging from 540 to 1700 kHz. Both the analog and digital portion of the
hybrid waveform are centered on the same carrier frequency. The absolute
accuracy of the carrier frequency is defined in Supplement A.

## GPS Synchronization

In order to ensure precise time synchronization and rapid station
acquisition each station is GPS synchronized. This is normally
accomplished through synchronization with a signal synchronized in time
and frequency to the Global Positioning System (GPS)[^1]. Transmissions
that are not locked to GPS, will not benefit from fast tuning since they
cannot be synchronized with other stations[^2].

# Waveforms and Spectra

## Introduction

This section describes the output spectrum for Hybrid and All Digital
waveforms. Each spectrum is divided into several sidebands, which
represent various subcarrier groupings. All spectra are represented at
baseband.

## Spectral Conventions

Each spectrum described in the following subsections shows the
subcarrier number and center frequency of certain key OFDM subcarriers.
The center frequency of a subcarrier is calculated by multiplying the
subcarrier number by the OFDM subcarrier spacing ∆f. The center of
subcarrier 0 is located at 0 Hz. In this context, center frequency is
relative to the radio frequency (RF) *allocated channel*.

For example, subcarriers 57 and 81, whose center frequencies are located
at 10356.12488 Hz and 14716.59851 Hz, respectively, bound the primary
upper sideband of the Hybrid waveform. Refer to Table 0-2. Thus, the
frequency span of the primary upper sideband is 4360.47363 Hz
(14716.59851 -- 10356.12488).

## Hybrid Spectrum

The digital signal is transmitted in primary and secondary sidebands on
either side of the analog host signal, as well as in tertiary sidebands
beneath the analog host signal as shown in Figure 0-6. In addition,
status and control information is transmitted on reference subcarriers
located on either side of the main carrier. Each sideband has both an
upper and a lower component. The PIDS logical channel is transmitted in
individual subcarriers just above and below the frequency edges of the
upper and lower secondary sidebands. The power level of each OFDM
subcarrier is fixed relative to the unmodulated main analog carrier.
However, the power level of the secondary, PIDS, and tertiary
subcarriers is adjustable.

Table 0-2 summarizes the spectral characteristics of the Hybrid
waveform. Individual subcarriers are numbered from -81 to 81 with the
center subcarrier at subcarrier number 0. Table 0-2 lists the
approximate frequency ranges and bandwidths for each sideband. In Table
0-2, the subcarriers 54 to 56 and -54 to -56 are not represented. This
is because they are not transmitted to avoid interference with first
adjacent signals.

The amplitude scale factors listed in Table 0-2 and Table 0-3 refer to
the multiplication constants used to scale the individual subcarriers to
the proper levels relative to the unmodulated main carrier. These scale
factors are defined in Supplement A. Refer to Section Digital Sideband
Levels for details of the subcarrier scaling operation.

![](media/image18.wmf){width="6.38125in" height="3.1770833333333335in"}

[]{#__RefHeading___Toc532350112 .anchor}Figure 0‑6 AM IBOC Hybrid
Waveform Spectrum

[]{#__RefHeading___Toc532269987 .anchor}Table 0‑2 AM Hybrid Waveform
Spectral Summary

+-----------+---------+--------------------+-----------+--------------+
| Sideband  | Sub     | Subcarrier         | Frequency | Amplitude    |
|           | carrier | Frequencies (Hz    | Span (Hz) | Scale Factor |
|           | Range   | from channel       |           |              |
|           |         | center)            |           |              |
+===========+=========+====================+===========+==============+
| Primary   | 57 to   | 10356.1 to 14716.6 | 4360.5    | CH~P~        |
| Upper     | 81      |                    |           |              |
+-----------+---------+--------------------+-----------+--------------+
| Primary   | -57 to  | -10356.1 to        | 4360.5    | CH~P~        |
| Lower     | -81     | -14716.6           |           |              |
+-----------+---------+--------------------+-----------+--------------+
| Secondary | 28 to   | 5087.2 to 9447.7   | 4360.5    | CH~S1~ or    |
| Upper     | 52      |                    |           | CH~s2~       |
+-----------+---------+--------------------+-----------+--------------+
| Secondary | -28 to  | -5087.2 to -9447.7 | 4360.5    | CH~S1~ or    |
| Lower     | -52     |                    |           | CH~s2~       |
+-----------+---------+--------------------+-----------+--------------+
| Tertiary  | 2 to 26 | 363.4 to 4723.8    | 4360.4    | [CH~         |
| Upper     |         |                    |           | T1~]{.underl |
|           |         |                    |           | ine}\[0:24\] |
|           |         |                    |           |              |
|           |         |                    |           | [CH~         |
|           |         |                    |           | T2~]{.underl |
|           |         |                    |           | ine}\[0:24\] |
+-----------+---------+--------------------+-----------+--------------+
| Tertiary  | -2 to   | -363.4 to -4723.8  | 4360.4    | [CH~         |
| Lower     | -26     |                    |           | T1~]{.underl |
|           |         |                    |           | ine}\[0:24\] |
|           |         |                    |           |              |
|           |         |                    |           | [CH~         |
|           |         |                    |           | T2~]{.underl |
|           |         |                    |           | ine}\[0:24\] |
+-----------+---------+--------------------+-----------+--------------+
| Reference | 1       | 181.7              | 181.7     | CH~B~        |
| Upper     |         |                    |           |              |
+-----------+---------+--------------------+-----------+--------------+
| Reference | -1      | -181.7             | 181.7     | CH~B~        |
| Lower     |         |                    |           |              |
+-----------+---------+--------------------+-----------+--------------+
| IDS1      | 27      | 4905.5             | 181.7     | CH~I1~ or    |
|           |         |                    |           | CH~I2~       |
+-----------+---------+--------------------+-----------+--------------+
| IDS2      | 53      | 9629.4             | 181.7     | CH~I1~ or    |
|           |         |                    |           | CH~I2~       |
+-----------+---------+--------------------+-----------+--------------+
| IDS1\*    | -27     | -4905.5            | 181.7     | CH~I1~ or    |
|           |         |                    |           | CH~I2~       |
+-----------+---------+--------------------+-----------+--------------+
| IDS2\*    | -53     | -9629.4            | 181.7     | CH~I1~ or    |
|           |         |                    |           | CH~I2~       |
+-----------+---------+--------------------+-----------+--------------+

## All Digital Spectrum

In the All Digital waveform, the analog signal is replaced with higher
power primary sidebands. The unmodulated AM carrier is retained. In
addition, the secondary upper sideband moves to the higher frequencies
above the primary upper sideband and the tertiary lower sideband moves
to the lower frequencies below the primary lower sideband. The secondary
lower and tertiary upper sidebands are no longer used. Furthermore, the
power of both the secondary and tertiary sidebands is increased. These
changes result in the overall bandwidth being reduced, making the All
Digital waveform less susceptible to adjacent channel interference. The
reference subcarriers are located on either side of the unmodulated AM
carrier as in the hybrid waveform, but at a higher level. The spectrum
of the All Digital waveform is illustrated in Figure 0-7. The power
level of each of the OFDM subcarriers within a sideband is fixed
relative to the unmodulated main analog carrier. Table 0-3 summarizes
the spectral characteristics of the All Digital waveform.

![](media/image19.wmf){width="5.0in" height="3.0729166666666665in"}

[]{#__RefHeading___Toc532350113 .anchor}Figure 0‑7 AM All Digital
Waveform Spectrum

[]{#__RefHeading___Toc532269988 .anchor}Table 0‑3 AM All Digital
Waveform Spectral Summary

  --------------------------------------------------------------------------
  Sideband     Subcarrier   Subcarrier           Frequency     Scale Factor
               Range        Frequencies\         Span (Hz)     
                            (Hz from channel                   
                            center)                            
  ------------ ------------ -------------------- ------------- -------------
  Primary      2 to 26      363.4 to 4723.8      4360.5        CD~P~
  Upper                                                        

  Primary      -2 to -26    -363.4 to --4723.8   4360.5        CD~P~
  Lower                                                        

  Secondary    28 to 52     5087.2 to 9447.7     4360.5        CD~E~

  Tertiary     -28 to -52   -5087.2 to -9447.7   4360.5        CD~E~

  Reference    1            181.7                181.7         CD~B~
  Upper                                                        

  Reference    -1           -181.7               181.7         CD~B~
  Lower                                                        

  IDS1         27           4905.5               181.7         CD~I~

  IDS2         -27          4905.5               181.7         CD~I~
  --------------------------------------------------------------------------

# Supplement A AM Transmission Specifications

## Introduction

This supplement presents the key transmission specifications for the AM
IBOC system, as described in the body of this document.

## Service Mode Switching

When the broadcaster changes the service mode, it is desirable to
minimize any signal interruptions and make the transition as seamless as
possible. However, different service modes may employ different
diversity delays and interleaving so that truly seamless operation is
not possible. The following requirements shall apply:

When the AM service mode is changed from any hybrid service mode (MA1,
MA2) to any other hybrid service mode, the analog audio output shall not
be interrupted.

When switching from any AM service mode to any other AM service mode,
the reference broadcast system shall not interrupt digital audio and/or
data services for more than 1 minute.

When switching from any AM service mode to any other AM service mode,
the commercial broadcast system shall not interrupt digital audio and/or
data services for more than 10 seconds.

## Synchronization Tolerances

The system shall support two levels of synchronization for each
broadcaster:

Level I: Network synchronized (Assumed using Global Positioning System
(GPS) locked transmission facilities)

Level II: Non networked synchronized (Non-GPS-locked transmission
facilities)

Normally, transmission facilities will operate as Level I facilities in
order to support numerous advanced system features.

### Analog Diversity Delay

The absolute accuracy of the analog diversity delay in the transmission
signal will be within ±68 microseconds (μsec) for both synchronization
Level I and Level II transmission facilities.

The absolute accuracy of the analog diversity delay in the receive
system will be within ±68 microseconds (μsec) for both synchronization
Level I and Level II transmission facilities.

Diversity delay accuracy will be verified with a calibrated test
receiver receiving the RF channel under test. A digitally generated
4-kHz sinusoidal test tone at a level of --6 dB from full scale will be
applied to both the analog and digital transmit signal paths. The tone
will be a pulsed signal, consisting of a repeating pattern of 0.5
seconds on, followed by 4.5 seconds off.

### Time and Frequency Accuracy and Stability

The total modulation symbol-clock frequency absolute error shall be
budgeted according to the following requirements:

For the entire end-to-end system: ±101 ppm maximum

Caused by the receive system: ±100 ppm maximum

Caused by the broadcast system: ±1 ppm maximum for synchronization Level
I facilities

±.01 ppm maximum for synchronization Level II facilities

The total carrier frequency absolute error shall be budgeted according
to the following requirements:

The total (analog and digital) carrier frequency absolute error of a
synchronization Level I broadcast system as observed at the RF output
shall be [+]{.underline}.02 Hz maximum.

The total (analog and digital) carrier frequency absolute error of a
synchronization Level II broadcast system as observed at the RF output
shall be [+]{.underline}2.0 Hz maximum.

The total (analog and digital) carrier frequency absolute error as
observed at the receiver baseband demodulator input shall be:

Due to the entire end-to-end system: [+]{.underline}1272 Hz maximum

(Refer to \[1\] Subsection 8.4)

Due to the receive system only: [+]{.underline}1270 Hz

(exclusive of the broadcast system errors specified in object IDs
SY1012-39 and SY1012-40)

It is recommended that all carrier and clock oscillators be
frequency-locked to the same reference within the broadcast system and
within the receive system if possible.

### L1 Frame Timing Phase

For Level I transmission facilities, all transmissions will phase lock
their L1 frame timing (and the timing of all OFDM symbols) to absolute
GPS time within ±1 μsec.

In the above specification, if a synchronization Level I transmission
facility is violated due to a GPS outage or other occurrence, it will be
classified as a synchronization Level II transmission facility until the
above specification is again met.

### AM Spectral Emissions Limits

Hybrid and all digital transmissions shall remain within the FCC
emissions mask per 47 CFR §73.44 and summarized in Table 1-1. All
measurements assume a measurement resolution bandwidth of 300 Hz.

[]{#__RefHeading___Toc532269989 .anchor}Table 0‑4 FCC AM Spectral
Emissions Mask

  ------------------------- ---------------------------------------------
  Offset From Carrier       Level Relative To Unmodulated Carrier
  Frequency                 

  10.2 to 20 kHz            -25 dB

  20 to 30 kHz              -35 dB

  30-60 kHz                 -5 - 1 dB/kHz

  60-75 kHz                 -65 dB

  \> 75 kHz                 -80 or \[-43 -10∙log~10~ (power in watts)\]
                            dBc, whichever is less
  ------------------------- ---------------------------------------------

More stringent spectral emissions limits will most likely be required to
minimize interference to an IBOC carrier from adjacent IBOC carriers. In
order to meet system coverage specifications, the following alternative
spectral emissions limits are recommended in and .

### Alternative Spectral Emissions Limit for Hybrid Mode

The measured power spectral density of the hybrid analog and digital
signals at frequencies removed from the carrier frequency by more than 5
kHz up to and including 10 kHz must not exceed -39 dBc/300 Hz.

The measured power spectral density at frequencies greater than 10 kHz,
up to and including 15 kHz, from the carrier frequency must not exceed
-25 dBc/300 Hz.

The measured power spectral density of the hybrid signal at frequencies
removed from the carrier frequency by more than 15 kHz, up to and
including 20.5 kHz must not exceed

-78 - ( \| offset frequency in kHz \| - 15) \* 4.0 dBc/ 300 Hz

The measured power spectral density of the hybrid signal at frequencies
removed from the carrier frequency by more than 20.5 kHz, must not
exceed --100 dBc/300 Hz.

0 dBc is defined as the total power of the unmodulated analog AM
carrier. Measurements of the hybrid analog and digital signals will be
made by averaging the power spectral density of the signal in each 300
Hz bandwidth over a 30 second segment of time. Measurements to determine
compliance with this section for transmitter type acceptance are to be
made using signals sampled at the output terminals of the transmitter
when operating into an artificial antenna of substantially zero
reactance. Measurements of operating station emissions are to be made at
the transmitter's output sampling loop for non-directional stations or
at the common point of a directional station. Refer to Figure 6.1 for an
illustration of the spectral emissions limit.

![](media/image20.wmf){width="5.979861111111111in"
height="4.886805555555555in"}

[]{#__RefHeading___Toc532350114 .anchor}Figure 0‑8 Recommended Spectral
Emissions Limit for Hybrid Transmissions

### Alternative Spectral Emissions Limit for All Digital Mode

The measured power spectral density of the all digital signal at
frequencies removed from the carrier frequency by more than 300 Hz up to
and including 5 kHz must not exceed -10 dBc/300 Hz.

The measured power spectral density of the all digital signal at
frequencies removed from the carrier frequency by more than 5 kHz up to
and including 10 kHz must not exceed -25 dBc/300 Hz.

The measured power spectral density of the all digital signal at
frequencies removed from the carrier frequency by more than 10 kHz, up
to and including 20.5 kHz must not exceed

-58 - ( offset frequency in kHz - 10) \* 4.0 dBc/ 300 Hz

The measured power spectral density of the all digital signal at
frequencies removed from the carrier frequency by more than 20.5 kHz,
must not exceed --100 dBc/300 Hz. Refer to Figure 6.2 for an
illustration of the spectral emissions limit.

Measurements of the all digital signal will be made by averaging the
power spectral density in a 300 Hz bandwidth over a 30-second segment of
time. 0 dBc is defined as the allocated power of the unmodulated AM
carrier and is equal to the reference level used in subsection . Refer
to Figure 6.2 for an illustration of the spectral emissions limit.

The digital waveform will be measured to determine compliance with this
section for transmitter type. Acceptance is to be made using signals
sampled at the output terminals of the transmitter when operating into
an artificial antenna of substantially zero reactance.

Measurements of operating station emissions are to be made at the
transmitter's output sampling loop for non-directional stations or at
the common point of a directional station.

![](media/image21.wmf){width="6.495833333333334in"
height="6.004166666666666in"}

[]{#__RefHeading___Toc532350115 .anchor}Figure 0‑9 Recommended Spectral
Emissions Limit for All Digital Transmissions

#### Additional Bandwidth Requirements

The system shall provide a means of broadcasting only Class 3 digital
audio and disabling Class 4 audio in order to reduce transmission
bandwidth.

## Digital Sideband Levels

The amplitude scaling of each OFDM subcarrier within each digital
sideband is given in Table 6.3 for the Hybrid and All Digital waveforms.
The amplitude scale factors are such that the average power in the
constellation for that subcarrier meets the subcarrier levels shown in
dB. For the Hybrid waveform, the subcarrier levels are specified
relative to the total power of the unmodulated analog AM carrier
(assumed equal to 1). For the All Digital waveform, the subcarriers
levels are specified relative to the level of subcarrier zero (set to
1). The scale factors include the normalization factors shown in Table
6-2 for each modulation type.

The selection of CH~S1~, CH~T1~\[ \], CH~I1~ versus CH~S2~, CH~T2~\[ \],
CH~I2~is determined by the Power Level Control (PL) received from L2.

The amplitude scaling of each OFDM subcarrier within each digital
sideband is given in Table 6-3 for the Hybrid and All Digital waveforms.
The amplitude scale factors are such that the average power in the
constellation for that subcarrier meets the average per subcarrier power
spectral density shown in dB.

For the Hybrid waveform, the subcarrier levels are specified relative to
the total power of the unmodulated analog AM carrier (assumed equal to
1). For the All Digital waveform, the subcarriers levels are specified
relative to the level of subcarrier zero (set to 1). The scale factors
include the normalization factors shown in Table 6-3 for each modulation
type.

The selection of CH~S1~, CH~T1~\[ \], CH~I1~ versus CH~S2~, CH~T2~\[ \],
CH~I2~is determined by the Power Level Control (PL) received from L2.

[]{#__RefHeading___Toc532269990 .anchor}Table 0‑5 Modulation
Normalization Factors

  ------------------------------------ ----------------------------------
  Modulation Type                      Normalization Factor

  BPSK                                 0.500

  QPSK                                 0.707

  16-QAM                               1.581

  64-QAM                               3.240
  ------------------------------------ ----------------------------------

Table 0‑6 OFDM Subcarrier Amplitude Scaling

  ------------------------------------------------------------------------------
  Waveform   Sideband    Amplitude   Modulation     Amplitude    Power Spectral
                         Scale       Type           Scale Factor Density,
                         Factor                     per          dB/Subcarrier
                         Notation                   subcarrier   
  ---------- ----------- ----------- -------------- ------------ ---------------
  Hybrid     Primary     CH~P~       64-QAM         9.76 x       -30
                                                    10^-3^       

             Secondary   CH~S1~      16-QAM         4.48 x       -43
                                                    10^-3^       

                         CH~S2~      16-QAM         8.93 x       -37
                                                    10^-3^       

             Reference   CH~B~       BPSK           1.00 x       -26
                                                    10^-1^       

             Tertiary    CH~T1~      QPSK           8.92 x       {TBA}
                         \[0\]                      10^-3^       

                         CH~T1~      QPSK           8.42 x       {TBA}
                         \[1\]                      10^-3^       

                         CH~T1~      QPSK           7.95 x       {TBA}
                         \[2\]                      10^-3^       

                         CH~T1~      QPSK           7.51 x       {TBA}
                         \[3\]                      10^-3^       

                         CH~T1~      QPSK           7.09 x       {TBA}
                         \[4\]                      10^-3^       

                         CH~T1~      QPSK           6.69 x       {TBA}
                         \[5\]                      10^-3^       

                         CH~T1~      QPSK           6.32 x       {TBA}
                         \[6\]                      10^-3^       

                         CH~T1~      QPSK           5.96 x       {TBA}
                         \[7\]                      10^-3^       

                         CH~T1~      QPSK           5.63 x       {TBA}
                         \[8\]                      10^-3^       

                         CH~T1~      QPSK           5.32 x       {TBA}
                         \[9\]                      10^-3^       

                         CH~T1~      QPSK           5.02 x       {TBA}
                         \[10\]                     10^-3^       

                         CH~T1~      QPSK           4.74 x       {TBA}
                         \[11\]                     10^-3^       

                         CH~T1~      QPSK           4.47 x       {TBA}
                         \[12:24\]                  10^-3^       

                         CH~T2~      QPSK           8.92 x       {TBA}
                         \[0:24\]                   10^-3^       

  Hybrid     IDS         CH~I1~      16-QAM         4.48 x       -43
                                                    10^-3^       

                         CH~I2~      16-QAM         8.93 x       -37
                                                    10^-3^       

  All        Primary     CD~P~       64-QAM         5.49 x       -15
  Digital                                           10^-2^       

             Secondary   CD~E~       64-QAM         9.76 x       -30
                                                    10^-3^       

             Tertiary    CD~E~       64-QAM         9.76 x       -30
                                                    10^-3^       

             Reference   CD~B~       BPSK           3.56 x       -15
                                                    10^-1^       

             IDS         CH~D~       16-QAM         2.00 x       -30
                                                    10^-2^       
  ------------------------------------------------------------------------------

## Analog Audio Source

The requirements in this subsection must be met to ensure that the
existing analog signal does not significantly impact the performance of
the digital subcarriers.

For hybrid mode operation, the power spectral density of the modulated
AM carrier measured with the IBOC digital component disabled, at
frequencies removed from the carrier frequency by more than 5 kHz
(AAB=0) or 8 kHz (AAB=1) and up to 20 kHz must not exceed -75 dBc/300
Hz. 0 dBc is defined as the total power of the modulated AM carrier.

The analog signal may not exceed the modulation levels specified in
Title 47 CFR §73.1570: "In no case shall the amplitude modulation of the
carrier wave exceed 100% on negative peaks of frequent recurrence, or
125% on positive peaks at any time".

IBOC is not compatible with existing analog AM stereophonic broadcasts.
The input analog signal must be a monophonic signal.

[^1]: GPS Locked stations are referred to as Level I: GPS-locked
    transmission facilities

[^2]: Level II: Non-GPS locked transmission facilities