Digital Audio Broadcasting Supplementary Analog SCA Compatibility Tests Test Plan and Procedures Document No. 02-15 April 2002 Advanced Television Technology Center 1330 Braddock, Suite 200 Alexandria, VA 22314-1650 (703) 739-3850 (703) 739-3230 (Fax) www.attc.org ©2002 ATTC, Inc. Advanced Television Technology Center Table of Contents 1 INTRODUCTION 1 1.1 BACKGROUND 1 1.2 DOCUMENT SCOPE 1 1.3 DOCUMENT STRUCTURE 1 1.4 RELATED DOCUMENTS 1 2 TEST OVERVIEW 3 2.1 OBJECTIVES 3 2.2 METHODOLOGIES 3 2.3 TEST CONDITIONS 3 2.4 EVALUATION METHODS 3 3 SIGNAL DESCRIPTIONS 4 3.1 RF SIGNALS 4 3.1.1 DESIRED ANALOG – TYPE I 4 3.1.2 DESIRED ANALOG – TYPE II 4 3.1.3 DESIRED ANALOG – TYPE III 5 3.1.4 DESIRED HYBRID – TYPE I 5 3.1.5 DESIRED HYBRID – TYPE II 5 3.1.6 DESIRED HYBRID – TYPE III 6 3.1.7 UNDESIRED ANALOG 6 3.1.8 UNDESIRED HYBRID 6 3.1.9 ADDITIVE WHITE GAUSSIAN NOISE 7 3.2 STEREO CLIPPED USASI NOISE 7 3.2.1 INTRODUCTION 7 3.2.2 USASI NOISE SOURCE CHARACTERIZATION 7 3.2.3 RECORDING PROCESS AND CHARACTERIZATION 10 3.2.4 SURVEY OF “REAL-WORLD” BROADCAST STATIONS 11 3.2.5 MODULATED SPECTRUM CHARACTERIZATION 14 4 STANDARD METHODOLOGIES 17 4.1 FM B AND AND RF M EASUREMENTS 17 4.1.1 FM ANALOG POWER 17 4.1.2 IBOC HYBRID MODE POWER 18 4.1.3 POWER IN THE PRESENCE OF MULTIPATH 19 4.1.4 RATIO OF ANALOG TO DIGITAL POWER (IBOC HYBRID MODE) 20 4.1.5 ADDITIVE WHITE GAUSSIAN NOISE POWER 21 4.1.6 DEVIATION AND CHANNEL CONFIGURATION 24 4.2 BASEBAND AUDIO MEASUREMENTS 26 4.2.1 SIGNAL-TO-NOISE RATIO (SNR) 26 ©2002 ATTC, Inc. i Advanced Television Technology Center 5 TEST PROCEDURES 28 5.1 SCA RECEIVER PERFORMANCE IN THE PRESENCE OF ANALOG AND IBOC ADJACENT CHANNELS 28 5.2 SCA RECEIVER PERFORMANCE IN THE PRESENCE OF AN ANALOG OR IBOC HOST 30 5.3 SCA RECEIVER PERFORMANCE IN THE PRESENCE OF AN ANALOG OR IBOC HOST IN MULTIPATH CONDITIONS 32 6 - APPENDIX A - LIST OF RECEIVERS UNDER TEST 34 7 - APPENDIX B - MULTIPATH PROFILES 35 7.1 CHARACTERIZATION OF STATIC MULTIPATH PROFILES 35 7.2 MULTIPATH PROFILES - STATICMP1 40 7.3 MULTIPATH PROFILES – STATICMP2 43 7.4 MULTIPATH PROFILES – STATICMP3 45 ©2002 ATTC, Inc. ii Advanced Television Technology Center 1 Introduction 1.1 Background The Advanced Television Technology Center (ATTC) has conducted an extensive DAB test program over the course of the past two years. This program has primarily focused on fulfilling the laboratory test requirements of the National Radio System Committee’s (NRSC) DAB Subcommittee in evaluating iBiquity Digital’s IBOC system. As such, many of the test program objectives, methodologies, and test conditions have been well defined by the various NRSC Working Groups. However, other parties have recently expressed an interest in conducting IBOC DAB tests that are outside the scope of the NRSC process, in order to examine certain aspects of IBOC compatibility in more detail than originally required by the NRSC. In particular, National Public Radio (NPR) and the International Association of Audio Information Services (IAAIS) are interested in further evaluating the compatibility of FM IBOC with existing analog SCA services (e.g. “Reading For The Blind” SCA services). This test plan is a result of a collaborative effort between iBiquity, NPR, IAAIS, and ATTC to develop test procedures that are appropriate for examining IBOC compatibility with 67kHz and 92kHz analog audio SCA services. In addition to greatly expanding the test conditions of the original NRSC tests, the field of SCA receivers under test has been expanded to encompass a wider variety of models and manufacturers. Multipath test conditions have also been added to the program to gauge the effect of multipath on IBOC compatibility with host SCA services. 1.2 Document Scope This document contains the laboratory plan and procedures to be utilized for the Supplementary Analog SCA Compatibility Tests of the iBiquity Digital In-Band On- Channel (IBOC) Digital Audio Broadcasting (DAB) System. 1.3 Document Structure This document is written in such a way that signal types and measurement methodologies used repeatedly throughout testing are defined once. Prior to defining the test procedures there are sections dedicated to the defining signals and measurement methodologies (Sections 3 and 4 respectively). When the test procedures call for a specific signal or measurement, the reader should refer to the appropriate section for the complete definition. 1.4 Related Documents For a detailed description of the physical test platform that will be used during supplementary analog SCA compatibility testing refer to the following ATTC documents: ATTC Document No. 01-20, Digital Audio Broadcasting, Test Bed Proof of Performance Plan, Revision 2.0, November 2001 ATTC Document No. 01-01, Digital Audio Broadcasting, Test Bed Proof of Performance Record, Revision 2.0, November 2001 ©2002 ATTC, Inc. 1 Advanced Television Technology Center ATTC Document No. 01-16, Digital Audio Broadcasting, Test Bed Daily Calibration Procedure, Revision 4.0, October 2001 Digital Audio Broadcasting, Test Bed Daily Calibration Record of Test Results”(open ATTC Document) The previous (NRSC specified) analog SCA compatibility test procedures and results are detailed in the following ATTC documents: ATTC Document No. 01-03, Digital Audio Broadcasting, IBOC Laboratory Test Procedures – FM Band, Revision 4.2, August 2001 ATTC Document No. 01-16B, Digital Audio Broadcasting, SCA Compatibility of the IBOC System in the FM Band, Summary of Test Results, October 2001 ©2002 ATTC, Inc. 2 Advanced Television Technology Center 2 Test Overview 2.1 Objectives The test procedures described in this document have one main objective, to quantify the impact of IBOC on existing SCA services. This is known as Compatibility testing. In compatibility testing various adjacent channel and multipath conditions are simulated in the laboratory. For each channel condition, tests will be conducted to determine the impact of IBOC, if any, on SCA services. 2.2 Methodologies To meet the objective described in the previous section, a series of controlled laboratory tests will be conducted. Each of these tests will include some channel impairment that is commonly observed in the FM broadcast band. These interference scenarios will be created in the laboratory, and the performance of certain commercially available SCA receivers 1 will be evaluated. The receivers will be tested under these conditions in the presence and absence of an IBOC signal on either the “host” or adjacent channel station. 2.3 Test Conditions Below is a list of the test conditions to be utilized during the testing process: 1. First adjacent channel interference 2. Second adjacent channel interference 3. “Host” channel interference 4. “Host” channel interference in the presence of multipath NPR, the IAAIS, iBiquity Digital, and the ATTC developed the test scenarios outlined in this document. 2.4 Evaluation Methods The performance of the SCA receivers will be determined objectively. Objective evaluation of an SCA receiver requires the use of standard audio test equipment to measure and objectively quantify audio quality in an accurate and repeatable manner. Audio quality will be measured in terms of the audio signal-to-noise ratio (SNR). 1 NPR and the IAAIS have chosen the SCA receivers to be tested. For a list of these receivers refer to section 6 of this document. ©2002 ATTC, Inc. 3 Advanced Television Technology Center 3 Signal Descriptions The purpose of this section is to define all of the signals (RF and audio) to be used throughout testing. Later sections of this test plan may refer to a “Desired Hybrid Type I”, for example, the definition of which can be found in this section. 3.1 RF Signals 3.1.1 Desired Analog – Type I A desired analog Type I signal is designed for use in tests of analog host compatibility with multipath. This type of signal shall be used in the tests of both 67kHz and 92kHz subcarriers. The injection of both subcarriers for this type of signal is 10% regardless of which SCA is being tested. However, the audio only modulates the SCA being evaluated. When the 67kHz SCA is being tested, for example, there will be no audio present on the 92kHz SCA (resulting in 0kHz Deviation). This signal type will yield a total channel modulation of 110% when configured as shown in Table 3-1. Table 3-1 - Desired Analog – Type I Signal Characteristics Main Channel Main Channel Power 67kHz Subcarrier 92kHz Subcarrier Audio 1) 97.9MHz Clipped USASI Moderate 1) 10% injection 1) 10% injection with peaks equal (-62dBm) 2) Stereo Transmission 80% modulation 2) 150ms pre- 2) 150ms pre- (60kHz Peak emphasis emphasis 3) 10% Pilot Injection Deviation) 3) 6kHz Peak 3) 7kHz Peak 4) 75ms Pre-emphasis Deviation with a Deviation with a 400Hz Tone – 0kHz 400Hz Tone – 5) Total Modulation = with Silence 0kHz with Silence 110% 4) Test Dependent 4) Test Dependent Audio – 400Hz Audio – 400Hz Tone or Silence Tone or Silence 3.1.2 Desired Analog – Type II A desired analog Type II signal is designed for use in first adjacent interference tests, second adjacent interference tests, and analog host compatibility with no multipath. When using this type of signal, keep in mind that the injection of the SCA being evaluated is to be 10% while the other SCA should be turned off (0% injection). This configuration will yield a total channel modulation of 105% when configured as shown in Table 3-2. Table 3-2 - Desired Analog – Type II Signal Characteristics Main Channel Main Channel Power 67kHz Subcarrier 92kHz Subcarrier Audio 1) 97.9MHz Clipped USASI Moderate 1) 10% injection or Off 1) 10% injection or Off with peaks equal (-62dBm) 2) Stereo Transmission 85% modulation 2) 150ms pre- 2) 150ms pre- (63.75kHz Peak emphasis emphasis 3) 10% Pilot Injection Deviation) ©2002 ATTC, Inc.