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15、T OF THE USE OF THE CONTENTS HEREOF, AND THESE CONTENTS WOULD NOT BE PUBLISHED BY TIA WITHOUT SUCH LIMITATIONS. TIA-102.BABG Foreword This document has been submitted to PROJECT 25 by the Telecommunications Industry Association (TIA), as provided for in a Memorandum of Understanding (MOU) dated Dece
16、mber 1993. That MOU provides that PROJECT 25 will devise a Common System Standard for digital public safety communications (the Standard), and that TIA shall provide technical assistance in the development of documentation for the Standard. This document has been developed with inputs from the TIA P
17、roject 25, Interface Committee (APIC), the APIC Vocoder Task Group, and TIA industry members. This document is being published because it is felt that there is an urgent need for Project 25 to set a standard for spectrum efficiency equivalent to 6.25 kHz as stated by the FCC. Technology choices for
18、the TDMA Two Slot Air Interface are based on Project 25 Steering Committee decisions regarding the vocoder, modulations and over all bit rate made at their meeting of 27-April-2007. iTIA-102.BABG TABLE OF CONTENTS 1. Introduction 1 1.1 Scope 1 1.2 Objectives 1 1.3 Standard Definitions 2 1.3.1 Standa
19、rd Average Speech Level . 2 1.3.2 Standard Vocoder Sample Rate 3 1.3.3 Standard Audio Sample Rate 3 1.3.4 Standard Reference Encoder. 3 1.3.5 Standard Reference Decoder. 3 1.3.6 Standard Test Tone . 4 1.3.7 Standard Decibel Level Units . 4 1.4 Standard Test Conditions. 5 1.4.1 Digital Channel Test I
20、nterface 5 1.4.2 Digital Audio Test Interface . 5 1.4.3 Standard Test Sentence Pairs 6 1.4.4 Standard Test Noises. 6 1.5 Characteristics of Test Equipment and Software. 8 1.5.1 WAV Files 8 1.5.2 PCM Files . 8 1.5.3 DAT Files 9 1.5.4 PESQ and MOS LQO Calculation 9 1.5.5 Software Floating Point Precis
21、ion 10 1.5.6 Active Speech Level . 10 1.5.7 Standard Hex Interpolation. 10 1.5.8 Standard Hex Decimation. 11 2. Methods of Measurement 13 2.1 Encoder 13 2.1.1 Audio Sensitivity 13 2.1.2 Noise Reduction 14 2.2 Decoder 15 2.2.1 Audio Output Level 15 2.2.2 Residual Noise 16 3. Performance Specification
22、s . 18 3.1 Encoder 18 3.1.1 Audio Sensitivity 18 3.1.2 Noise Reduction 18 3.2 Decoder 18 3.2.1 Audio Output Level 18 3.2.2 Residual Noise 19 4. References, Abbreviations and History . 20 4.1 Normative References 20 4.2 Informative References. 20 4.3 Abbreviations and Acronyms 20 4.4 Revision History
23、 21 iiTIA-102.BABG 1. Introduction Clause 1 introduces the scope of this standard and its objectives. Clause 1 also introduces standard definitions, standard test conditions, and the characteristics of test equipment (hardware and software) required by this standard. The subsequent two clauses provi
24、de the methods of measurement (clause 2) and performance specifications (clause 3) defined by this standard. The final clause 4 identifies the references and abbreviations used in this standard. 1.1 Scope This document defines the methods of measurement to test performance of the Project 25 (P25) en
25、hanced vocoder. The measurements can then be compared to performance specifications to meet the voice and audio quality objectives defined by this standard for the P25 enhanced vocoder. The P25 enhanced vocoder is a dual-rate vocoder with a full-rate mode for interoperability with P25 Phase 1 equipm
26、ent and a half-rate mode for interoperability with P25 Phase 2 equipment. The test methods and performance specifications are defined for both modes of operation. The test methods and performance specifications are defined for both the encoder and the decoder components of the P25 enhanced vocoder.
27、The P25 enhanced vocoder to be tested shall be applicable to both a radio, and a fixed infrastructure device such as a console. 1.2 Objectives The objectives of the Project 25 standard that were expressed in the APCO Project 25 System and Standards Definition bulletin, TSB-102-A 4.2.2, are as follow
28、s. Obtain maximum radio spectrum efficiency, Ensure competition in system life cycle procurement, Allow effective, efficient and reliable intra-agency and inter-agency communications, Provide user friendly equipment. The APCO Project 25 Statement of Requirements 4.2.1 defines a key goal to achieve s
29、pectrum efficiency in Phase 2 equivalent to four-to-one spectrum utilization in a 25 kHz channel. The Two-Slot TDMA standard for Phase 2 doubles the spectrum efficiency of the Phase 1 standard for 12.5 kHz operation to contribute to the first objective of the Project 25 standard suite and a key goal
30、 of the Statement of Requirements. The Two-Slot TDMA standard also maintains interoperability and compatibility with the Phase 1 standard and is based on the Phase 2, 12.5 kHz TDMA (i.e., two-slot TDMA) requirements defined in the P25 Statement of Requirements to preserve the achievement of the othe
31、r three objectives. In order to meet these objectives, the P25 standards use a vocoder that is defined in the Project 25 Vocoder Description and its associated annexes 4.1.1. A baseline vocoder defined in prior versions of 4.1.1 for Phase 1 is outside the scope of the tests defined in this document.
32、 In general, the baseline vocoder cannot pass the tests defined here, except as may be explicitly indicated in the test description. 1TIA-102.BABG This standard defines performance levels that shall be achieved by P25 enhanced vocoders to achieve voice and audio quality that is equivalent to or bett
33、er than that achievable using vocoders implementing the P25 Enhanced Full-Rate Vocoder (Phase 1 operation) or the P25 Enhanced Half-Rate Vocoders (Phase 2 operation) that have passed the tests defined in 4.2.3 and 4.2.4.12This standard uses the same PC executable vocoder from the MOS tests as a refe
34、rence for interoperation with a candidate vocoder under test. The tests in this standard use the reference vocoder as either the encoder or decoder in a test configuration with the candidate vocoder under test in the complimentary position. Some performance parameters are then measured in the test c
35、onfiguration. For the Encoder tests, the candidate vocoder encoder performance is tested with the reference vocoder decoder. For the Decoder tests, the candidate vocoder decoder performance is tested with the reference vocoder encoder. In this way, the test directly verifies interoperation with the
36、vocoder from the MOS tests. The tests with noise include the sentences from the MOS test as representative signals for the measurement of active speech level and PESQ since these measurements are designed for such speech signals. The noises from the MOS tests are also included in the noise measureme
37、nts. Although the list of noise types used in this testing is wide ranging, it is not an inclusive list of every existing version of that noise type. The performance specification limits are set from measurements with the reference vocoder from the MOS test in both the encoder and decoder positions.
38、 In this way, the test measures the performance of the candidate vocoder as both an encoder and a decoder, independently, to obtain performance equivalent to that of the reference vocoder as tested in the MOS tests. This standard includes standard parameter titles, definitions, test conditions, test
39、 equipment, and test reference software for the purpose of measuring vocoder performance. The tests use WAV files with test sentences and test noises as described in clauses 1.4.3 and 1.4.4, and these files are provided with this standard for use in the measurements. 1.3 Standard Definitions The fol
40、lowing standard definitions are used in the methods of measurement. 1.3.1 Standard Average Speech Level The standard average speech level shall be -22 dBm0. This equates to -28.02 dBov. This is the level used for the MOS tests. 1The relevant performance levels for the P25 Enhanced Full-Rate Vocoder
41、are those established by TIA Engineering Committee TR8.4 (Experiments 1 and 2) and ITS (Experiment 3) in 2003-2005 using Mean Opinion Score testing and documented respectively in 4.2.3 (TSB-102.BABE, Project 25 Vocoder Evaluation, Mean Opinion Score Test, Telecommunication Industry Association, May
42、2007). The relevant performance levels for the P25 Enhanced Half-Rate Vocoder are those defined in 4.2.4 (TSB-102.BABF, Experiment 3 MOS Test Plan for Vocoder Technology for Project 25 Phase 2, Telecommunications Industry Association, 2008). 2This requirement is focused on the enhanced performance l
43、evel and differentiation of non-enhanced from enhanced performance and does not supersede the requirement for audio quality as stated in the P25 Statement of Requirements. 2TIA-102.BABG 1.3.2 Standard Vocoder Sample Rate The standard vocoder sample rate is 8 kHz. This is the sample rate used by the
44、audio input to the standard reference vocoder encoder, and also the sample rate used by the audio output of the standard reference vocoder decoder. This sample rate is also used by the PESQ algorithm. 1.3.3 Standard Audio Sample Rate The standard audio sample rate is 48 kHz. This is the sample rate
45、used by the audio WAV files used as input to the standard reference encoder, and also the sample rate of WAV files used by the audio output of the standard reference decoder. 1.3.4 Standard Reference Encoder The standard reference encoder is test reference software that emulates the operation of an
46、instantiated encoder with the enhanced MBE vocoder. The standard reference encoder consists of two parts. The first part decimates the audio sample rate from 48 kHz to 8 kHz, which is called hex decimation. The second part is the part of the vocoder that operates within the encoder. In many cases, t
47、he audio may already be sampled at 8 kHz, and so the hex decimation part of the encoder may not be necessary. 1.3.4.1 Standard Hex Decimation The first part of the standard reference encoder decimates an input audio WAV file at a 48 kHz sample rate to 8 kHz. A WAV file at a 48 kHz sample rate is cap
48、able of recording noise with spectrum components above the 4 kHz frequency limit that would apply to an 8 kHz sample rate. The input to the vocoder encoder is a PCM file sampled at 8 kHz with 16-bit linear samples. Standard hex decimation algorithms are described in clause 1.5.8. 1.3.4.2 Standard Re
49、ference Vocoder Encoder The second part is the standard reference vocoder encoder. The standard reference vocoder encoder is software that takes a digital representation of the input signal sampled at the standard vocoder sample rate of 8 kHz with 16 bits of precision. The output of the PC executable software is a DAT file representing the encoded audio. The standard reference vocoder encoder is software that shall obtain the performance demonstrated by the MOS tests in 4.2.3 and 4.2.4. The standard reference vocoder encoder also represents the standard fo
