1、 Report ITU-R RS.2186(10/2010)Radio services and radio-frequency environment within the bandbelow 20 kHzRS SeriesRemote sensing systemsii Rep. ITU-R RS.2186 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency sp
2、ectrum 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 Radiocommunicati
3、on 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 patent stat
4、ements 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 (Also availabl
5、e 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 satellite ser
6、vices 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 in English by
7、 the Study Group under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R RS.2186 1 REPORT ITU-R RS.2186 Radio services a
8、nd radio-frequency environment within the band below 20 kHz (2010) TABLE OF CONTENTS Page 1 Background . 1 2 Introduction 2 3 Survey of bands below 20 kHz . 2 3.1 Allocations in RR Article 5 before WRC-12 2 3.2 Radionavigation systems 2 3.2.1 Omega 2 3.2.2 Alpha system (RSDN-20) 3 3.3 Meteorological
9、 aids systems . 4 3.4 Fixed and maritime mobile systems . 4 3.5 Standard frequency and time signal 4 4 Spectral analysis of ATD receiver locations 4 5 Summary . 7 1 Background WRC-12 Agenda item 1.16 calls for consideration of the needs of passive systems for lightning detection in the meteorologica
10、l aids service, including the possibility of an allocation in the frequency range below 20 kHz, and for WRC-12 to take appropriate action. It resolved to invite ITU-R to conduct and complete the required studies leading to technical and procedural recommendations to WRC-12 to decide an appropriate m
11、ethod for providing recognition to the long established systems of the meteorological aids service operating in the frequency range below 20 kHz. Part of the necessary work for this agenda item involved identification of current spectrum uses and services within the band below 20 kHz, with a view to
12、 initiate sharing and compatibility studies to meet the requirements of this agenda item. This Report sets out those services and associated characteristics currently in operation within the frequency band below 20 kHz. 2 Rep. ITU-R RS.2186 2 Introduction The Arrival time difference (ATD) system uti
13、lizes a network of “detector” outstations to monitor spectral emissions of cloud to ground lightning strikes centred between about 5 and 20 kHz. At these frequencies the sky waves reflected off the ionosphere propagate for very large distances with relatively little attenuation, and at shorter range
14、s may be preceded by a ground wave. Thus, it is possible to receive the emissions from the cloud to ground strokes at thousands of kilometres from the stroke location. Naturally occurring emissions from lightning strikes can be easily masked by active radio services. Manmade emissions are distinctly
15、 different than those from natural sources; such signals tend to be higher in power than natural emissions and can saturate the ATD receiver. Additionally, due to propagation effects at these low frequencies, active radio services geographically separated by very large distances can still adversely
16、affect throughput, performance and measurement capability of the ATD network system. This increases the necessity to monitor spectral emissions in a spectrum that is void of other radio transmissions as far as possible. The optimal frequency for ATD measurements is 9.766 kHz and has been in use sinc
17、e 1939. Recent monitoring since 2004 has shown that it was not practical to use this frequency at all the sensor sites, because of transmissions near 10 kHz in some locations which prevented the operation of the passive sensors. This adversely impacted the performance and accuracy of the system. Due
18、 to this, the system now operates at 13.733 kHz. Note that, before this time, the lightning detection systems have coexisted with the existing services below 20 kHz. Technical characteristics of the ATD system are specified within Recommendation ITU-R RS.1881. This contribution is intended to initia
19、te necessary work on the identification of services and stations within the band below 20 kHz. It also seeks to illustrate the complex RF environment within which the arrival time difference lightning detection system currently operates, and to identify areas of spectrum below 20 kHz where the ATD s
20、ystem can operate without placing any undue constraints on existing services or allocations. 3 Survey of bands below 20 kHz 3.1 Allocations in RR Article 5 before WRC-12 Based on Article 5 of the Radio Regulations, Edition 2008, in the frequency range 9-20.05 kHz a frequency bands are allocated to:
21、radionavigation, fixed, maritime mobile, standard frequency and time services on a worldwide primary basis. Utilization of these bands by the systems of these services is presented below. 3.2 Radionavigation systems 3.2.1 Omega Omega was originally developed by the United States of America for aviat
22、ion users. Approved for development in 1968 with only eight transmitters, each station transmitted a continuous wave (CW) which consisted of a pattern of four tones unique to the station that was repeated every ten seconds. The Omega system operated under bilateral agreements with six partner nation
23、s (Norway, Liberia, France, Argentina, Australia and Japan). The stations transmitted time-shared signals on four frequencies, in the following order: 10.2 kHz, 11.33 kHz, 13.6 kHz and 11.05 kHz. In addition to these common frequencies, each station transmitted a unique frequency to aid station iden
24、tification and to enhance receiver performance. Due to the success of the Global Positioning System the use of Omega declined during the 1990s, to a point where the cost of operating Omega could no longer Rep. ITU-R RS.2186 3 be justified. Omega was permanently terminated on 30 September 1997 and al
25、l stations ceased operation. 3.2.2 Alpha system (RSDN-20) Alpha is a Russian system for long-range radionavigation. Alpha works similarly to the former Omega navigation system but within the frequency band 10-17 kHz. The Alpha system consists of three transmitters, which stand in the proximity of No
26、vosibirsk, Krasnodar and Komsomolsk. These transmitters radiate 3.6 second long signals consisting of 400 ms long frequency combinations with 200 ms spacing. In June 2010 the following 6 frequency assignments to Alpha system are included in the Master International Frequency Register (MIFR): 11.905
27、kHz, 12.500 kHz, 12.649 kHz, 13.281 kHz, 14.881 kHz and 15.625 kHz, this system can also use other frequencies of the range 10-17 kHz. Alpha system is used for long-range radionavigation and for short-term earthquake prediction. This prediction is possible due to the fact that before earthquake ther
28、e are abnormal electromagnetic, geochemical and hydrogeological phenomena which effect electric parameters of the Earths crust, atmosphere and ionosphere in the areas of forthcoming earthquake. These changes impact on the propagation conditions of electromagnetic waves in the VLF-range and can be de
29、tected by remote sensing stations. It allows to predict earthquake before 10-20 days and to evaluate its magnitude. Currently the Alpha system allows the possibility to predict earthquakes with sources located not lower than 70 km in the Earths crust. The technical characteristics of the Alpha syste
30、m are given in Table 1. TABLE 1 Characteristics of radionavigation transmitters registered in the MIFR (June 2010) operating in the 11.905-15.625 kHz band Parameter Value Fixed or mobile Fixed Transmission frequency (kHz) 11.905 12.500 12.649 13.281 14.881 15.625 TX power (dBW) 57 Antenna gain (dBi)
31、 N/A(1)Antenna polarization Unspecified Modulation Necessary bandwidth (Hz) AXX 100 AXX 200 Operational range (km) 10.000 (1)N/A: Not applicable. 4 Rep. ITU-R RS.2186 3.3 Meteorological aids systems Meteorologists used to utilize radionavigation service signals for a variety of purposes. The use of
32、Omega navigation signals (frequencies between 10 to 13 kHz) became widespread for tracking radiosondes in the MetAids service from about 1985 onwards until its termination of operation. This was because the radiosonde systems could be used with simple base station antenna, processing was automated a
33、nd the systems were easy to maintain in remote locations. At the time of the closure of the Omega transmitters in 1997, more than 20% of the radiosonde systems in the WMO network had to be changed. Most of these ground systems were modified or replaced to use radiosondes receiving and processing GPS
34、 navigation signals. 3.4 Fixed and maritime mobile systems Several fixed station transmitters have been identified that operate in the 14-19.55 kHz band. These stations operate in the fixed service and provide information to widely dispersed ship borne receivers operating in the maritime mobile serv
35、ice. A summary of the technical characteristics of these fixed station transmitters is provided in Table 2. TABLE 2 Characteristics of fixed transmitters operating in the 14-19.55 kHz band Parameter Value Fixed or mobile Fixed (including transportable) Tuning range (kHz) 14-19.55 TX power (dBm) 90 A
36、ntenna gain (dBi) N/A Antenna polarization Vertical Modulation Necessary bandwidth (Hz) A1A 100 F1B 300 F1B 600 J3B 600 J7B 600 3.5 Standard frequency and time signal No systems under the standard frequency and time signal service operate in this frequency range and no systems are expected to be ope
37、rating in the foreseeable future. 4 Spectral analysis of ATD receiver locations The ATD lightning detection system relies on naturally occurring emissions from lightning strikes and can be badly compromised by interference from other man made sources. Interfering signals are often transient, whilst
38、others have specific repeat cycles. However because of long-range propagation of interfering signals, interference can affect many stations simultaneously and this does seriously degrade system performance. Interference reduces the number of events seen at one or more outstations and/or cause inaccu
39、racy in measuring the time differences between one or more pairs of stations. This reduces the number of fixes in an area, thus reducing the apparent severity of a storm. Rep. ITU-R RS.2186 5 A survey for each of the ATD network receiver locations was executed by the United Kingdom met office to exa
40、mine the spectral environments and types of interference received at each ATD receiver location within the frequency band 6 to 22 kHz. The results of this analysis are shown in Figs 1 and 2. FIGURE 1 Spectral plots of RFI between 6 and 20 kHz at Helsinki, Payerne, Camborne, Azores, Keflavik and Reun
41、ion ATD receiver locations 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequen
42、cy (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)Spectral plot from Helsinki ATD receiver Spectral plot from Payerne ATD receiverSpectral plot from Camborne ATD receiver Spectral plot from Azores ATD receiverSpectral plot from Keflavik ATD receiver Spectral plot from Reunion ATD receiv
43、er20.025.030.035.040.045.050.055.060.065.070.075.080.085.090.020.025.030.035.040.045.050.055.060.065.070.075.080.085.090.020.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0Power(dB)Power(dB)Power(dB)20.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0Power(dB)20.025.030.035.040.045
44、.050.055.060.065.070.075.080.085.090.0Power(dB)20.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0Power(dB)6 Rep. ITU-R RS.2186 FIGURE 2 Spectral plots of RFI between 6 and 20 kHz at Gibraltar, Akrotiri, Exeter, Lerwick, Nordeney and Valentia ATD receiver locations 6.0 8.0 10.0 12.0 14.0 16
45、.0 18.0 20.0 22.0Frequency (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)10.0 12.0 14.0 16.0 18.0 19.0 20.0Frequency (Hz)6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)Spectral plot from Gibraltar ATD receiver Spectral pl
46、ot from Akrotiri ATD receiverSpectral plot from Exeter ATD receiver Spectral plot from Lerwick ATD receiverSpectral plot from Nordeney ATD receiver Spectral plot from Valentia ATD receiver6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0Frequency (Hz)11.0 13.0 15.0 17.020.025.030.035.040.045.050.055.060.06
47、5.070.075.080.085.090.020.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0Power(dB)Power(dB)20.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0Power(dB)20.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0Power (dB)20.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0
48、Power(dB)20.025.030.035.040.045.050.055.060.065.070.075.080.085.090.0Power(dB)The above examples, which are typical, are useful for understanding that man-made transmitter sources vary in frequency and amplitude from ATD receiver location. In addition, the same sources of interference can affect dif
49、ferent geographically separated ATD receiver sites. To demonstrate this, the same RFI can be seen at around 12 kHz and 15 kHz at both Helsinki and Camborne receiver sites. Additionally, interference sources can be seen to be about 20 dB to 30 dB above the level of the atmospheric noise. These effectively dominate and mask any sferic1emissions, preventing measurements within the same fre
