1、ITU-T RECMN*O.333 93 4862573 057Lb88 528 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 0.1 33 (03/93) SPECIFICATIONS FOR MEASURING EQUIPMENT EQUIPMENT FOR THE MEASUREMENT OF DIGITAL AND ANALOGUE/DIGITAL PARAMETERS EQUIPMENT FOR MEASURING THE PERFORMANCE
2、OF PCM ENCODERS AND DECODERS ITU-T Recommendation 0.1 33 (Previously “CCITT Recommendation”) ITU-T RECMN*OmL33 93 m 4b259L 059Lb 4b4 FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for stu
3、dying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study G
4、roups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation 0.133 was revised by the ITU-T Study Group IV (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union
5、 (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publica
6、tion of this Recommendation, no change has been made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU stru
7、cture. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, elect
8、ronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. 1 2 3 4 ITU-T RECMN*O=L33 93 = Y862591 0591b90 L8b CONTENTS Introduction General . 2.1 2.2 Measuring functions and physical configuration Measuring accuracy and compatibility objectives 2.3 Measure
9、ment capabilities . Instrument specifications 3.1 Interfaces 3.2 Analogue signal generator 3.4 Digital signal generator . Measuring accuracy . 4.1 4.2 3.3 Analogue signal analyzer 3.5 Digital signal analyzer Definition of the error limits of the measuring instrumentation . Summary of total measuring
10、 errors 5 Operating environment . Annex A - Intrinsic errors in the PCM encoding processwhich may affect the interpretation of measured results A.l Introduction A.2 A.3 Quantizing distortion measurements . A.4 General notes to tables and graphs . References . Measurement of gain and variation of gai
11、n with input level Page 1 1 1 1 2 3 3 4 5 5 7 9 9 10 14 14 14 15 22 26 26 Recommendation 0.133 (03/93) i Abstract Defines the requirements for an equipment to measure the performance of PCM equipments in analogue-to-digital (A-D), digital-to-analogue (D-A), analogue-to-analogue (A-A) and digital-to-
12、digital (D-D) modes. Key words Measurement, tester, PCM tester, gain, variation of gain/loss with time, return loss, longitudinal balance, attenuatiodfrequency distortion, weighted noise, discrimination against out-of-band input signals, spurious out-of-band output signals, single frequency noise, t
13、otal distortion, variation of gain with input level, crosstalk, interference from signalling, frequency of repetitive signal, load capacity. Il Recommendation 0.133 (OY93) ITU-T RECMN*O.L33 73 4862571 0591b92 T57 W Recommendation 0.133 EQUIPMENT FOR MEASURING THE PERFORMANCE OF PCM ENCODERS AND DECO
14、DERS (Published 1984; revised 1988, 1993) 1 Introduction 1.1 Encoders and decoders conforming to Recommendation G.711 11 for converting voice-frequency signals to digital (PCM) signals and vice versa are contained in various equipment described by relevant CCITT Recommendations. Examples of these eq
15、uipment are: - - - PCM multiplexers (see Recommendations G.732 2 and G.733 3); transmultiplexers (see Recommendations G.793 4 and G.794 5); subsystems of digital exchanges (e.g. Recommendations Q.552 6 and Q.553 i i). To ensure that the overall performance limits specified in the CCITT Recommendatio
16、ns are always met where the PCM equipments are interconnected, it is necessary to separately specify and measure the analogue-digital (A-D) and digital-analogue (D-A) performance of the equipment. In addition, analogue-analogue (A-A) and digital-digital (D-D) measurements have to be carried out. 1.2
17、 The measuring instrumentation described below allows these measurements to be made on PCM equipment operating at 2048 kbit/s and/or 1544 kbit/s as specified in Recommendations G.732 2, G.733 31, G.793 41, G.794 151 and relevant Series Q Recommendations. 2 General 2.1 Measuring functions and physica
18、l configuration The instrumentation described in this Recommendation consists of the following functional units. 2.1.1 under test. An analogue signal generator to apply voice-frequency signals to the analogue input ports of the equipment 2.1.2 equipment under test. An analogue signal analyzer to pro
19、cess voice-frequency signals received from the analogue output ports of the 2.1.3 A digital signal generator to apply test signals to the digital input ports of the equipment under test. 2.1.4 A digital signal analyzer to process signals received from the digital output ports of the equipment under
20、test. 2.1.5 determined by the supplier. The four units mentioned in 2.1.1 to 2.1.4 may be provided in any convenient physical arrangement as 2.1.6 digital-to-analogue conversion techniques, or by direct digital processing techniques. The functions described in 2.1.3 and 2.1.4 may be realized using e
21、ither conventional analogue-to-digital and 2.2 Measuring accuracy and compatibility objectives 2.2.1 As a general objective, the accuracy of the measuring instrumentation should be an order of magnitude better than the relevant performance limits of the equipment under test. Due to technical and cos
22、t limitations, however, it may not always be possible to meet this objective. 2.2.2 parts of the equipment under test are not accessible at the same location (end-to-end measurements). In addition errors may increase if instrumentation of different design is interworking or if the input and output R
23、ecommendation 0.133 (03/93) 1 2.2.3 Where the test methods of Recommendations such as O. 13 1 121 or O. 132 131 are referenced below, it should be noted that some of the design requirements of such Recommendations may be insufficient to guarantee the accuracy called for in this Recommendation. Even
24、when observing the specifications of this and other relevant Recommendations (e.g. 0.131, 0.132), compatibility problems may arise especially when pseudorandom noise signals are used as stimuli leading to reduced measuring accuracy and/or fluctuating results indications. 2.2.4 In order to facilitate
25、 interworking of instrumentation of different design, it is recommended to provide pseudorandom noise signals having a specified periodicity (see 3.2.3.1 and 3.4.2.1). A-D D-A 2.3 Measurement capabilities Table 1 contains a list of parameters which can be measured on the various equipment. In additi
26、on, the required measuring configuration is indicated. It should be noted, however, that not all the listed parameters can be measured with the instrumentation specified in this Recommendation. Where applicable, reference is made to other pertinent Recommendations. facility A-A D-D TABLE U0.133 Meas
27、urement capabilities I I Gain (relationship between encoding law and audio level) Load capacity Parameter + + + + a) E O - - - + Variation of gain (loss) with time Return loss (at voice-frequency ports) + + + + E O + + + - Longitudinal balance Attenuatiodfrequency distortion O + + + + + + + E - Weig
28、hted noise Discrimination against out-of-band input signals + + + + E A A A A O Spurious out-of-band output signals Single frequency noise A A A A O A A A A O Total distortion (including quantizing distortion) Variation of gain with input level a) b, E Essential O Optional + Yes - Not applicable A C
29、apability not provided NOTES 1 assessing the Longitudinal Interference Threshold (LIT). 2 Measurement to be performed while injecting an auxiliary signal in the disturbed channel. Stimulus for signalling channel is not specified. The receive sections of the equipment specified in this Recommendation
30、 may be used for level measurements when Where no symbol is shown, the need for the measurement is under study. + + + + E + + + + E 2 Recommendation 0.133 (03/93) Crosstalk (measured with sinewave signals)a) Crosstalk (measured with conventional telephone signal) + + + + E A A + A O interference fro
31、m signallingb) Frequency of repetitive signal O + + + + O , 3 Instrument specifications In this clause the minimum requirements to be met by the four functional units of the instrumentation are described. The measuring accuracy is covered in clause 4 below. Measurement functions described in this Re
32、commendation which require pseudo-random noise stimuli are optional. 3.1 Interfaces 3.1.1 Analogue interfaces 3.1.1.1 3.1.1.2 Output and input impedances, balanced earth free: 600 and/or 900 ohms. Return loss from 200 Hz to 4 kHz: 136 dB. 3.1.1.3 Longitudinal conversion loss (frequency range 200 Hz
33、to 4 kHz): 2 46 dB. 3.1.1.4 Complex impedances For measurements at interfaces with complex impedances, the instrument shall be equipped with corresponding input impedances. Examples of such impedances are given in Table VQ.552 6. For this application, the instrument shall be calibrated in accordance
34、 with A.3/G.100 181, namely: At the reference frequency of 1020 Hz, O dBmO represents an absolute power level of 1 milliwatt measured at the transmission reference point (O dBr point). The voltage V of a O dBmO tone at any voiceband frequency is given by the expression: v = ,/i w . 10-3 . I z,I wher
35、e lZ10201 is the modulus of the nominal impedance, Z, at the reference frequency 1020 Hz. Z may be resistive or complex. 3.1.2 Digital interfaces 3.1.2.1 The instrumentation is required to operate satisfactorily with interface levels in accordance with Recommenda- tion G.703 7. One or both of the fo
36、llowing conditions of interface and frame formats, including extended frame formats and cyclic redundancy check (CRC) procedures, shall be provided: At 1544 kbivs, clause 2/G.703 7 and Recornmendations G.733 3 and G.704 lo. At 2048 kbi/s, clause 6lG.703 7 and Recommenda6ons G.732 2 and G.704 lo. Add
37、itionally the digital analyzer is required to operate satisfactorily when connected via a length of cable which has an insertion loss of 6 dB at the half bit rate of the signal. The insertion IQSS of the cable at other frequencies will be proportional to fi. In addition to providing for terminated m
38、easurements the instrumentation may also be required to monitor at protected test points on digital equipment. Therefore a high impedance and/or additional gain should be provided to compensate for the loss at monitoring points already provided on some equipment. Level conditions and frame format 3.
39、1.2.2 Impedances of digitalinterfaces The impedances at the digital outputs and inputs shall conform to clause 2/G.703 and clause 6/G.703 7. The return loss measured against the nominal impedance shall be: - 1544 kbit/s (with pre-emphasis) frequency range 20 kHz to 1.6 MHz at the input: 2 20 dB freq
40、uency range 20 kHz to 500 kHz at the output: 2 14 dB frequency range 500 kHz to 1.6 MHz at the output: 1 16 dB Recommendation 0.133 (03/93) 3 ITU-T RECMN*O-L33 93 = Y862591 059Lb95 7b8 - 1544 kbitk (without emphasis) frequency range 20 kHz to 1.6 MHz at both input and output: 2 20 dB - 2048 kbit/s f
41、requency range 40 kHz to 2.5 MHz at both input and output: 2 20 dB 3.1.2.3 Longitudinal conversion loss (Under study.) 3.2 Analogue signal generator The following minimum functions shall be provided. 3.2.1 Relative levels See Recommendation G.232 SI. 3.2.1.1 Relative levels (minimum range): -16 dBr
42、to O dBr. 3.2.2 Sinusoidal test signals 3.2.2.1 At levels of O and -10 dBmO, the generator shall produce test signals in the frequency range 200 to 3600 Hz. The frequencies of 3.2.2.2 below, comprising the reference and break points of the relevant masks, shall be provided as a minimum. See 4.1.4 fo
43、r a note on the choice of test frequencies. 3.2.2.2 3600 Hz. Test signal frequencies (approximately): 200, 300, 420, 500, 600, 820, 1020, 2400, 2800, 3000, 3400 and 3.2.2.3 Deviation of transmitted frequency from indicated valuef: f 2 Hz f 0.1% off. 3.2.2.4 For at least one frequency (preferably app
44、roximately 1020 Hz), it shall be possible to adjust the level of the signal between +3 dBmO and -55 dBmO. The levels of 3.2.2.5 comprising the reference and break points of the relevant masks shall be provided as a minimum. See 4.1.4 for a note on the choice of test frequencies. 3.2.2.5 Test signal
45、levels: -55, -50, -45, -40, -30, -20, -10, O, +3 dBmO. 3.2.2.6 shall nevertheless be provided to make relative measurements as defined in 4.2 within the specified tolerances. must be considered when reading the measuring accuracies quoted in this Recommendation. 3.2.2.7 given in the diagram of Figur
46、e A.YG.712 9. Deviation of transmitted level from indicated level over the operating range of the instrument: f 0.2 dB. Means NOTE - This tolerance is specified to facilitate interworking. Deviations in measurement results due to errors in test levels Total distortion referred to a measurement bandw
47、idth of 20 kHz is to be at least 20 dB better than the limits 3.2.3 Pseudorandom test signal 3.2.3.1 A pseudorandom test signal in accordance with Recommendation 0.131 shall be provided. To facilitate interworking, the sequence repetition rate (period) shall be fixed at 256 ms (2048 samples) derived
48、, where possible, from the sampling rate of the encoder under test. Otherwise, the tolerance shall be f 1 ms. NOTE - This requirement is also met by a period of 128 f 0.5 ms (1024 samples). The level of the pseudorandom test signal shall be adjustable between -3 dBmO and -55 dBmO. The levels 3.2.3.2
49、 of 3.2.3.3 below, comprising the reference and break points of the relevant masks, shall be provided as a minimum. 3.2.3.3 Test signal levels: -55, -50, -40, -34, -27, -10, -6, -3 dBmO. 3.2.4 Auxiliary signal 3.2.4.1 injection into the disturbed channel shall be provided. In order to increase the accuracy when performing crosstalk measurements, an auxiliary (activating) signal for 4 Recommendation 0.133 (03/93) ITU-T RECMN*O.L33 93 = 4862593 0593696 bT4 3.2.4.2 Band-limited noise located between 350 and 550 Hz similar to that specified
