1、 Recommendation ITU-R SM.2080-0 (08/2015) Precision of time information in output data of monitoring receivers SM Series Spectrum management ii Rec. ITU-R SM.2080-0 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-freq
2、uency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocom
3、munication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of pat
4、ent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendation
5、s (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and relat
6、ed satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Ti
7、me signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2015 ITU 2015 All rights reserved. No part of this publication may be reproduced,
8、by any means whatsoever, without written permission of ITU. Rec. ITU-R SM.2080-0 1 RECOMMENDATION ITU-R SM.2080-0 Precision of time information in output data of monitoring receivers (2015) Scope This Recommendation provides examples of possible measurement methods for the accuracy of the time infor
9、mation in I/Q data of a monitoring receiver. Keywords I/Q data, time stamp accuracy The ITU Radiocommunication Assembly, considering a) that precise time information in I/Q data is of great relevance in the field of radio monitoring; b) that ambiguities of the time stamp specification between users
10、and different manufacturers may lead to misunderstanding of time information in the I/Q data; c) that the internal clock of a monitoring receiver will drift if no measures are taken to maintain timing accuracy; d) that, depending on the settings of a monitoring receiver, there are different time del
11、ays between the arrival of the signal at the RF input connector and the moment of the insertion of the precise time information in the I/Q data; e) that a well-defined specification for precise time information in I/Q data, if adopted by manufacturers of radio monitoring receivers, will benefit user
12、s by providing an easier and more objective comparison of similar products from different manufacturers, recommends 1 that the accuracy of the time information in the I/Q data stream is constant for every sample pair (I/Q) in order to be able to mark even short-duration, intermittent or pulsed signa
13、ls with the same accuracy; 2 that the precise time information in the I/Q-data is referenced to the RF input connector of the monitoring receiver to prevent the signal propagation delay in the receiver from influencing the time stamp; 3 that the internal clock of a monitoring receiver is synchronize
14、d with a high precision clock; 4 that the accuracy of the time information in I/Q data of a monitoring receiver is defined by the deviation between the reference time and the time stamp provided by the receiver, expressed by mean value and standard deviation; 5 that the accuracy of the time informat
15、ion in I/Q data of a monitoring receiver and the measurement method is specified by the manufacturer in their datasheet. Examples of possible methods are shown in the annexes. 2 Rec. ITU-R SM.2080-0 Annex 1 Definition of the time stamp accuracy of radio monitoring receivers 1 Scope For a number of a
16、pplications in the field of radio monitoring, highly precise time information in monitoring receivers is necessary. This Annex provides a definition of time stamp accuracy in the I/Q data of a monitoring receiver. This definition should be adopted as a common understanding of the terms and used in p
17、roduct technical data by all manufactures of radio monitoring receivers. 2 Clarification The time stamp accuracy consists of two parts. One is how well the receiver is synchronized with the reference time; the other is how well the signal transmission time within the receiver is compensated. FIGURE
18、A1-1 Timing error with respect to the reference time during capturing I/Q data S M . 20 80 -A 1-0 1Referen ce t i meRecei v er t i meRecei v er RFi n p u t co n n ect o rPro p ag at i o n d el ayi n s i d e recei v erCap t u red I/ Q d at aT i me s t ampad d ed i n I/ Q d at at 1 : T i me s y n ch r
19、o n i zat i o n erro rt 2 : Pro p ag at i o n d el ay i n s i d e recei v erst 4 : T i me s t amp erro r i n s i d e recei v erst 5 : T o t al t i me s t amp erro rt5T2t4t3 t 3 : I/ Q d at a s amp l i n g erro r i n s i d e recei v erst2T1T0t1In Figure A1-1, the receiver RF input connector gets the
20、RF signal at T0 reference time, however the internal clock of a monitoring receiver has time synchronization error (t1) between its time and the reference time. Propagation delay inside the receiver is described as t2 which represents the transmission time of the signal from RF input connector to I/
21、Q data digitizers inputs. The digitizing clock of I/Q data has sampling error (t3). Finally the error of time stamping due to the internal processing may be exist (t4). The total time stamp error of the I/Q data is t5 = t1 + t2 + t3 + t4. 3 Specification of time stamp accuracy to be listed in a data
22、 sheet There are two parts of time stamp accuracy as stated above. The time synchronization accuracy (t1) and the runtime delay in the receiver (t2 + t3 + t4) should be distinguished in a data sheet Rec. ITU-R SM.2080-0 3 separately. In some cases, however, it might be difficult to distinguish one f
23、rom the other. If there are difficulties to list them separately, the time stamp accuracy can be listed as the total time stamp error (t5) as mean value and standard deviation. Annex 2 Test procedure examples for measuring the time stamp accuracy of a radio monitoring receiver 1 Scope This Annex des
24、cribes the means and procedures required to verify that a time stamp in I/Q data of a monitoring receiver accurately reflects the reference time of a high-precision clock and gives examples of measurement procedures to establish better uniformity of specification across receivers from different manu
25、facturers in terms of time stamp accuracy. 2 General aspects The measurement is performed for the entire frequency range of the receiver focusing on the compensation of the internal time delay. 3 Measurement setup FIGURE A2-1 Typical measurement setup for measuring the time stamp accuracy of a radio
26、 monitoring receiver, which has an external frequency reference input S M . 2 0 8 0 - A 2 - 0 1Freq u en cyrefer en ceARef o u tT i merefer en ceMo n i t o ri n grecei v erV ect o r s i g n alg en erat o rRef i nPPS o u tT ri g g erinRef i nRef o u tBPPS i nRef i n4 Rec. ITU-R SM.2080-0 FIGURE A2-2
27、Typical measurement setup for measuring the time stamp accuracy of a radio monitoring receiver, which has no external frequency reference input S M . 2 0 8 0 - A 2 - 0 1P P S i n(i f a p p l i c a b l e )M o n i t o ri n gre c e i v e rV e c t o r s i g n a lg e n e ra t o rR e f i nM o d u l a t i
28、o n i nR e f o u tC h . 1 i nT i m e re fe re n c eP P S s i g n a ls y n c h ro n i z e d t o re fe re n c et i m eH i g h s p e e do s c i l l o s c o p eT ri g g e r i nC h . 2 i nB a s e b a n d s i g n a lg e n e ra t o r4 Description of measurement setups Figure A2-1 A reference frequency from
29、 a common frequency reference is used to synchronize the signal generator and the monitoring receiver, whose time stamp accuracy is to be measured. A common time reference (PPS = pulse per second) serves for two purposes: With the switch in position “B” it sets the time of the internal clock of the
30、monitoring receiver correctly. The time is set only once at the beginning of the measurement. For the actual measurement the accuracy of the internal clock in the monitoring receiver is kept by the external reference frequency. Then the switch is turned over in position A, where the PPS signal from
31、the time reference triggers an output signal at the vector signal generator. The exact time of arrival of the signal at the RF input connector of the monitoring receiver is known. The time stamp accuracy is calculated from the difference between the known arrival time at the RF input connector and t
32、he time stamp in the I/Q data. Figure A2-2 Time reference must be synchronized to reference time and generate a PPS signal. Time reference triggers the baseband generator to alternate the modulation type of baseband signal by a PPS signal and is connected in parallel to a high-speed oscilloscope wit
33、h sufficient bandwidth and sampling rate to display time variation of the RF signal. The baseband signal is connected to a vector signal generator which generates RF signal. The RF signal output is connected to both receiver and oscilloscope to verify the exact time of the transformation of the modu
34、lation type at the receivers RF input connector. Thus transmission time from a PPS generator to the RF input connector must be measured by comparing the two inputs to the oscilloscope. The time stamp accuracy is calculated from the time difference between exact arrival time at receivers RF input con
35、nector and modulation transformation time based on the time information of captured I/Q data, however this accuracy includes both time synchronization accuracy (t1) and runtime delay inside the receiver (t2 + t3 + t4). Rec. ITU-R SM.2080-0 5 Time stamp accuracy will manifest as a deviation of the time stamp produced by the monitoring receiver from the reference time to be specified by mean value and standard deviation. This requires multiple measurements of the same conditions over time. _
