1、 Report ITU-R RS.2187(10/2010)Determining radiosonde maximum interference levels from link analysisand flight studiesRS SeriesRemote sensing systemsii Rep. ITU-R RS.2187 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio
2、-frequency 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 Rad
3、iocommunication 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 o
4、f patent 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 Reports (
5、Also available online at http:/www.itu.int/publ/R-REP/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 related
6、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 Note: This ITU-R Report was approved
7、in English by the Study Group under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2011 ITU 2011 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R RS.2187 1 REPORT ITU-R RS.2187 Det
8、ermining radiosonde maximum interference levels from link analysis and flight studies (2010) TABLE OF CONTENTS Page 1 Purpose . 2 2 Radiosonde link availability and data availability 3 3 Procedure 3 3.1 400.15-406 MHz band 3 3.2 1 668.4-1 700 MHz band 3 4 Flight data results . 4 4.1 Flight data resu
9、lts for 400.15-406 MHz . 4 4.2 Flight data results for 1 675-1 700 MHz 6 4.2.1 Flight data for link path loss 6 4.2.2 Link availability and link margin . 6 5 Interference measurements based upon actual GPS radiosonde flight data . 7 5.1 Background . 7 5.2 Data acquisition data reproduction and inter
10、ference level measurement hardware . 8 5.3 Radiosonde RF signal acquisition 8 5.4 Radiosonde RF signal reproduction 9 5.5 Data acquisition, analysis and the determination of interference levels . 10 5.5.1 Data acquisition 10 5.5.2 Data reconstruction 11 5.5.3 Interference calibration 12 5.5.4 Theore
11、tical maximum allowable interference level . 13 5.5.5 Interference power measurement methodology . 13 6 Measurement results . 16 2 Rep. ITU-R RS.2187 Page 7 Conclusions 18 7.1 Conclusions specific to 400.15-406 MHz 18 7.2 Conclusions specific to the band 1 675-1 700 MHz . 19 Annex 1 Flight signal le
12、vel and S/N plots for 400.15-406 MHz with omnidirectional antenna 20 Annex 2 Flight signal level and S/N plots for 400.15-406 MHz with directional antennas 27 Annex 3 Flight signal level plots for 400.15-406 MHz, comparison of directional and omnidirectional antennas 31 Annex 4 Flight path loss plot
13、s for 1 675-1 700 MHz . 34 Annex 5 Flight signal strength plots for 1 675-1 700 MHz 37 1 Purpose The objectives of this study are, through field testing and analytical analysis, to: 1. validate the use of the free-space path model in link budget calculations; 2. determine the actual link margin valu
14、es that should be used in the link budget calculations; 3. determine the fading levels which must be accounted for in link budget calculations; 4. determine the maximum GPS radiosonde interference level that can be tolerated by a GPS radiosonde. Once identified, these values can be used in future co
15、mpatibility and interference studies. Calculation of interference criteria is based on both the Metaids system link margin, and the link availability values of the system. There is a need to clearly define the term availability for Metaids systems, and to determine the appropriate link budget to be
16、used with defining Metaids interference criteria. In the ITU-R, Metaids system interference criteria are typically based on the system link margin. A percentage of the link margin is given up to interference. The noise floor is raised slightly by the presence of the interference, resulting in a redu
17、ction in the link margin. The link availability objectives of the system must also be considered in order to determine the percentages of time that are applicable to the calculated interference criteria. This is the method used for the current values specified in Recommendation ITU-R RS.1263. In pas
18、t years, other radio services have noted that the Metaids performance objectives are set very high (link availability on the order of 99%) while the specified link margins are quite low (on the order of several dB or less). Such low link margins are not common radio link design practice and raised c
19、oncern for the other radio services. However, for technical and safety reasons discussed in Recommendation ITU-R RS.1165, Metaids systems are designed to make the most efficient use of transmitter power and minimize the weight and density of the Metaids transmitter package. Rep. ITU-R RS.2187 3 2 Ra
20、diosonde link availability and data availability For radiosonde systems, the value used for the availability performance objective should be link availability; the percentage of time that the receive signal strength is above the minimum receive threshold. When the receive level is above the minimum
21、receive threshold, reliable reception of data should occur. Data availability is closely related to the percentage of time the link is available. Data availability is also affected by other factors as well. In addition to the path losses resulting in the receive signal level dropping below the minim
22、um required level, radiosondes generate a small percentage of erroneous data due to sensor and processing errors. In the case of erroneous data, the link is sufficient to transmit the data to the receive station, but the receive station performs quality control and discards the bad data points durin
23、g the data processing. Radiosonde users define their data availability performance objectives with consideration for loss of data due to sensor and processing errors as well as receive levels below the minimum receive threshold. Since radiosondes often use signals that are either partially or fully
24、analogue, bit error rate values are also not applicable and data availability values are difficult to quantify. It is for these reasons that link availability should be used as the radiosonde performance objective. Link availability will be defined as the percentage of time that the received signal
25、level is sufficient to produce at least the required signal-to-noise ratio (S/N). The required S/N is defined as the minimum value where no data loss occurs due to failure of the transmission link. 3 Procedure Testing was conducted for both bands allocated to Metaids by conducting flights that appro
26、ach or reach the maximum operational link range of the system. Both receiver systems used in the testing were capable of reporting the receive signal level detected at the output of the receive antenna so the receive level could be recorded by a computer. 3.1 400.15-406 MHz band In order to assess t
27、he performance of the state-of-art radiosonde system in the 400.15-406 MHz band, and to justify the performance objectives, a small number of soundings were done using both low gain (omnidirectional antenna) and high gain (directional antenna). The system components used in this test are defined in
28、Recommendation ITU-R RS.1165. Those components were System 2 for the Receiver, Type B radiosondes, Antenna B for the directional antenna, and Antenna C for the omnidirectional antenna. With Reed Solomon error correction and use of GMSK the receive sensitivity for the system was 120 dBm. The sounding
29、s were done at Jokioinen observatory in Southern Finland in expected high wind conditions to achieve maximum distance. All together three soundings were done using the omnidirectional antenna only, and three with both omnidirectional and directional antennas. The S/N, and received signal power were
30、calculated from the software radio after the FFT conversion of the received signal. The use of advanced signal processing methods like Reed-Solomon provide processing gain of about 5 dB, suggesting that a minimum S/N ratio of 7.3 dB is the threshold for reliable reception of data. For existing analo
31、gue systems 12 dB is therefore a reasonable requirement. On the other hand the deviation in the received signal power suggests that even higher than 12 dB S/N as an average minimum would be needed. 3.2 1 668.4-1 700 MHz band Testing was conducted using a new radiosonde system being deployed in the U
32、nited States of America (System E in Recommendation ITU-R RS.1165). A series of flights were conducted, where the radiosonde signal strength at the output of the receive antenna connector was recorded at a one-second interval. The receive noise floor and the minimum receive signal threshold is known
33、 for the system, the percentage of time that the signal strength falls below the minimum receive 4 Rep. ITU-R RS.2187 signal threshold can be determined, revealing the flight link availability. In addition, the signal strength data can also be used to determine at what receive level above the minimu
34、m receive level the link availability equals the link availability performance requirement. The difference between the higher threshold and the minimum receive signal threshold can be assumed to be the link margin. The data availability design requirement for the system used for this testing is 98%
35、over the entire flight. As discussed in 3, data loss occurs in radiosonde systems for reasons other than those related to the telemetry link. Therefore, one-half of the 2% allowable data loss will attributed to the signal strength falling below the minimum receive level while the remaining one-half
36、will be attributed to other data loss factors not related to the radio link. The test results will show whether the system is meeting its design objective of 1% link unavailability. The link unavailability is determined by measuring the percentage of the time that the receive signal strength falls b
37、elow the system minimum receive threshold relative to the time of the entire flight. The minimum receive threshold for the system under test is a level of 106.8 dBm, which provides for a 12 dB signal to noise ratio above the 118.6 dBm noise floor. The system link margin for each flight is determined
38、 by determining the signal level that would correspond to a 1% data loss. This is the level that 1% of the data points fall below. The difference between this level and the minimum receive level is the link margin. In the case of this testing, the reported signal levels were at a 1 dB resolution, so
39、 it is not possible, in most cases, to determine the receive level exactly at where 1% data loss occurs. For this reason, the signal level closest to the 1% data loss point is used in calculating the margin. 4 Flight data results The flight data is presented in two ways in this contribution. Annex 4
40、 provides plots of the radiosonde to receive station link path loss over the entire time of the flight. Annex 5 provides plots of the radiosonde signal strength at the input of the receiver for the entire period of the flight. It should be noted that not all flights reached the maximum 250 km slant
41、range limit. 4.1 Flight data results for 400.15-406 MHz Table 1 provides the transmit power of the radiosonde and the distance at the end of each sounding. TABLE 1 Soundings performed Sounding Frequency (MHz) Transmit power (mW) Transmit power (dBm) Range (km) 1 402 20.3 13.07 194.42 402 22.2 13.46
42、143.4 3 402 21.4 13.30 108.44 402 20.9 13.20 131.5 5 402 22.6 13.54 365.8 (directional) 298.3 (omnidirectional) 6 405.5 19.4 12.88 272.5 Rep. ITU-R RS.2187 5 As can be seen, sounding No. 5 was exceptionally long, over 360 km. At this distance, the radiosonde was received only with the directional an
43、tenna. With the omnidirectional antenna the signal started to be too weak at about 270 km, though some errors occurred earlier. The maximum range for good quality data transmission of each sounding is presented in Table 2. TABLE 2 Maximum range for good data transmission Sounding Range of good data
44、transmission (Omnidirectional) and rejected data frames (km) Range of good data transmission (Directional) rejected data frames (km) 1 194.4 (N/A) 2 95.8 (1.67%) 3 108.4 (0.41%) 4 131.5 (0.71%) 131.5 (0.1%) 5 159 (1.05%) 354 (0.48%) 6 270 (0.48%) 272.5 (0.2%) In all figures it should be noted, that
45、the full transmission power is set on automatically only about 300 s after the beginning of the sounding. In Annex 1 the received radiosonde signal power with the omnidirectional antenna is presented. It is also compared with the theoretical receive level based on free-space attenuation (red curve).
46、 Annex 2 presents the received signal power with the directional antenna with same comparison to the theoretical receive level based on free-space path loss. In Annex 3 the signal level from the two antennas are compared. The data analysis for this band did not include the actual calculation of path
47、 loss as was done in the next section for the band 1 675-1 700 MHz. Multipath fading can cause over 20 dB additional loss, which is seen as fading in the link. It is difficult to identify the exact reasons for signal level variations, but the multipath fading is the most important. The maximum negat
48、ive and positive variations of the received signal strength from the free-space attenuation are listed in Table 3. The minimum fatal-error-free S/N value is also listed. TABLE 3 Sounding statistics Sounding Maximum negative variation (dBm) Maximum positive variation (dBm) Minimum fatal-error-free S/
49、N(dB) Omnidirectional Directional Omnidirectional Directional Omnidirectional Directional 1 28.1 6.1 7.3 2 27.5 2.0 7.3 3 26.3 4.0 7.7 4 19.5 7.5 1.3 2.2 6.9 11.8 (no errors) 5 15.9 12.4 6 1.6 7.3 7.3 6 10.8 7.7 1.8 0.8 7.5 7.3Average 21.4 9.2 3.6 1.5 7.3 7.3 6 Rep. ITU-R RS.2187 4.2 Flight data results for 1 675-1 700 MHz 4.2.1 Flight data for link path loss The data for the plots in Annex 4 were derived from the receive signal strength reported by the radiosonde receiver. Using the reported signal strength, combined with transmitter
