1、Rec. ITU-R F.1190 1RECOMMENDATION ITU-R F.1190*PROTECTION CRITERIA FOR DIGITAL RADIO-RELAY SYSTEMSTO ENSURE COMPATIBILITY WITH RADAR SYSTEMSIN THE RADIODETERMINATION SERVICE(Question ITU-R 159/9)(1995)Rec. ITU-R F.1190The ITU Radiocommunication Assembly,consideringa) that radar systems can produce i
2、nterference to digital radio-relay systems (DRRS), which gives rise to regularbursts of errors related to the operational characteristics of the radar e.g. the radar antenna rotation rate;b) that the importance of radar systems is recognized worldwide, but that nevertheless efforts should be made to
3、reduce the levels of spurious emissions from such systems;c) the importance of DRRS in telecommunication networks;d) that it is necessary to establish the criteria for ensuring compatibility between radar systems and DRRS;e) that the effects of interference from radar systems are different depending
4、 on the type of radar systems;f) that although the effect of radar interference on DRRS is different depending on the modulation methodsemployed in the interfered-with systems, provisionally it seems appropriate to define the protection threshold in terms ofinterference-to-thermal noise ratio in ord
5、er to make the criteria applicable to any modulation method,recommends1 that the interference power should be evaluated in terms of peak envelope power over the entire necessarybandwidth of a radio channel of the interfered-with system;2 that in the case of interference from fixed and transportable
6、land based radar systems;2.1 the interference-to-thermal noise ratio (referred to in recommends 1) should be no greater than 0 dB (seeNOTES 1 and 2);2.2 the interference should be evaluated in an actual or planned operational situation;2.3 for the case of the main beam radio-relay antenna intercept
7、of the interference, the power flux-density at areceiving station of radio-relay systems due to unwanted emissions should be no greater than 127 dB(W/m2) in any40 MHz band in the 3 400-4 200 MHz and 4 400-5 000 MHz ranges or 130 dB(W/m2) in any 20 MHz band in the5 925-6 425 MHz range (see Annex 2);3
8、 that in the case of interference from maritime and land mobile radar systems (see NOTE 3);3.1 the interference-to-thermal noise ratio (I/N) (referred to in 1) should be no greater than 10 dB (NOTES 1, 2and 5);3.2 the interference should be evaluated in an actual or planned operational situation. Ho
9、wever, the condition of20 km distance direct exposure in line-of-sight and free space propagation, should be considered representative of themaritime mobile radars for many cases;_*This Recommendation should be brought to the attention of Radiocommunication Study Group 8 (WP 8C), the InternationalMa
10、ritime Organization (IMO) and the International Maritime Radio Association (CIRM).2 Rec. ITU-R F.11903.3 the power flux-density at a receiving station of radio-relay systems due to unwanted emissions should be nogreater than 117 dB(W/m2) in any 40 MHz band in the 3 400-4 200 MHz and 4 400-5 000 MHz
11、rangesor 120 dB(W/m2) in any 20 MHz band in the 5 925-6 425 MHz range (see NOTE 4);4 that the guidance contained in Annex 1 should be taken into consideration for evaluation of interference powerinto digital radio-relay systems due to unwanted emissions from radar systems.NOTE 1 This value was deriv
12、ed from the assumption that the interference from radar systems has an intermittentnature and occurs only with low probability. This requires further studies and tests to validate these assumptions.NOTE 2 For the time being, this criteria should apply only to radar interference in the frequency band
13、s below about7 GHz. Further studies are required.NOTE 3 Maritime mobile does not include high power naval radiolocation.NOTE 4 The power flux-density values in 3.3 above are equivalent to the unwanted emission e.i.r.p. of a radarsystem of 20 dBW in a 40 MHz band and 23 dBW in a 20 MHz band, respecti
14、vely, assuming a 20 km separationdistance (see Annex 2).NOTE 5 The I/N value was derived from the assumption that the interference from mobile radar systems is temporaryin nature.ANNEX 1Evaluation of interference power into digitalradio-relay systems due to unwantedemissions from radar systemsThe in
15、terference power due to unwanted emissions from radar systems into DRRS should be evaluated in terms of peakenvelope power over the necessary bandwidth of a radio channel of the interfered-with system (see recommends 1 of thisRecommendation). In evaluating the total power over the necessary bandwidt
16、h, the following factors should be takeninto account: it is not always possible to evaluate the peak envelope power of the interference in time domain; when measured in frequency domain, interfering components appear with a frequency spacing equal to an inverseof the pulse width of a radar system; t
17、here is more or less coherence among such interfering components and, therefore, the peak envelope power of theaggregate interference depends on the degree of coherence among interfering components; in general, it is appropriate in the evaluation of the second or third harmonic spurious emission to
18、assume a perfectcoherence among interfering components (i.e. voltage sum); in general, it is appropriate in the evaluation of non-harmonic unwanted emissions to assume a partial coherenceamong interfering components (i.e. 1.5th power sum).Based on the above considerations, the following methods shou
19、ld be employed for evaluation of interference power: Preferably the peak envelope power of radar interference over the entire bandwidth of a radio channel of theinterfered-with system should be evaluated in time domain. If the data is available only in frequency domain, consisting of n interference
20、components wi(i = 1, 2, , n)expressed in power unit, the overall peak envelope power W should be evaluated as follows:W = ( wi1/k)kwhere k should be assumed as 2.0 for the evaluation of the second or third harmonic spurious emission and 1.5 for theevaluation of non-harmonic unwanted emission. Furthe
21、r study of the validity of these values is required.Rec. ITU-R F.1190 3ANNEX 2Derivation of the maximum allowable levels1 IntroductionIn order to facilitate the understanding of the subsequent calculation examples, a brief description of an interferencescenario is given. In addition some of the conc
22、epts and the parameter values commonly used in high capacity radio-relaylinks are explained.The radio-relay links are line-of-sight (LOS) systems requiring an unobstructed path between transmitter and receiverantennas. The path length is usually 40-60 km, and in some cases even longer.Antennas are h
23、igh gain narrow beam types, normally parabolic, or in some cases similar designs (horn reflector etc.).Theemphasis is on low side-lobe levels. Usually the main beam 3 dB width is of the order of 1.5-2, and the gain at beamcentre is about 40-43 dBi.If a radar transmitter designed for operation with f
24、0near 3 GHz is in use near a radio-relay path, and if it emitsunintentionally generated spurious energy from the radar antenna, some portion of this may be intercepted by theradio-relay antenna. In many cases the spurious emission may enter the radio-relay receiving antenna through the sidelobes, bu
25、t in unfortunate situations main beam intercept may happen. A radio-relay hop with three possible locations ofan interfering radar is shown in Fig. 1. Location a will result in radio-relay side-lobe entry. Location b is near the LOSbetween radio-relay transmitter and receiver, resulting in main beam
26、 intercept. Location c is near the extension ofthe LOS behind the transmitter, also resulting in main beam intercept.bacRadarTransmitter ReceiverFIGURE 1Plan view, radio-relay path and possible radar positionsD01FIGURE 1.D01 = 3 CMThe radio-relay link is used to transport a high speed bit stream kno
27、wn as the payload. It may consist of manymultiplexed telephone channels or digitized TV video signals. Typically the capacity is 155.52 Mbit/s (STM-1), or311 Mbit/s (2 STM-1). The Telecommunication Standardization Sector (ITU-T) has issued strict transmission qualityrequirements. These are expressed
28、 in terms of maximum permitted number of errored seconds (ES) and maximumpermitted number of severely errored seconds (SES) (see ITU-T Recommendation G.826).During ES the telephone or video transmission quality is noticeably degraded and during SES the radio channel isunusable.4 Rec. ITU-R F.1190Any
29、 spurious emission from a radar which is intercepted by a radio-relay antenna and which ingresses into a radio-relayreceiver will result in a certain interference power level, I. This must be compared to the receiver background noiselevel, N. The radio-relay system design assumes that a receiver wil
30、l operate correctly with a certain minimum desiredsignal level, C and thus with a minimum C/N value. Any interference is perceived as additional noise degrading C/N andthus resulting in transmission errors. If intermittent interference (pulsed spurious emission) is received, it may beparticularly tr
31、oublesome if certain parts of the formatted bit stream are affected. This may result in loss of synchronismand thus in wholesale loss of transmission capability.In the following examples several assumptions are made concerning the scenario and the I/N required.The situation depicted in Fig. 2 is ass
32、umed where the radio-relay main beam intercept occurs. The distance from theinterfering radar is assumed to be 20 km and the path from the radar antenna to the radio-relay antenna is assumed to beunobstructed. Thus the propagation path loss for spurious emissions in the 4 GHz band is about 130 dB.Th
33、e I/N requirements are derived for a high capacity radio-relay link using an advanced high level modulation scheme.The receiver needs a certain RF signal-to-noise ratio C/N. This is achieved in the system design by providing adequatetransmitter power and antennas with suitable gain.150 m45 m40 kmTra
34、nsmitter ReceiverFIGURE 2Side view, radio-relay path; ship crossing near LOSD02FIGURE 2.D02 = 3 CM2 Non-harmonic unwanted emissionThe assumed parameters of the interfered-with system are:Operating frequency band: 3 400-4 200 MHzReceiver bandwidth: 40 MHz (see Note 1)Receiver antenna gain: 36 dB (aft
35、er subtracting feeder loss)Receiver noise figure: 4 dBFree space loss: 130 dB (20 km)Thermal noise: 140 dB(W/MHz)Thus the maximum allowable level of interference corresponding to the interference-to-thermal noise ratio of 10 dBis 114 dB(W/40 MHz) at the receiver input of the interfered-with system.
36、For a 36 dB receiver antenna gain, thisequates to a power flux-density of 117 dB(W/m2). For a free space loss of 130 dB and a 36 dB antenna gain, this alsoequates to an unwanted emission e.i.r.p. of a radar system of 20 dBW.Rec. ITU-R F.1190 5It should be noted that many mobile radar systems may not
37、 meet this requirement and further efforts are needed toimprove such radar systems. It should also be noted that in the case of a radar system employing a magnetron, the levelsof unwanted emissions are different depending on the elapse of operational time, and in general the levels ofnon-harmonic un
38、wanted emissions become higher as it approaches its life end.For the 4 400-5 000 MHz range, the assumed parameters (in particular, antenna gain and free space loss) of theinterfered-with system may be slightly different. However, calculations result in the same limit of the unwantedemission, because
39、 the increased antenna gain is just offset by the increased free space loss.NOTE 1 The receiver bandwidth is different depending on systems. If coherence among the interfering components istaken into account (see Annex 1), a system with wider receiver bandwidth is more susceptible to non-harmonicemi
40、ssions from a radar system, which generally have bandwidth broader than that of the interfered-with receiver. Thus,40 MHz is chosen as representing a system with wide receiver bandwidth.3 Second harmonic spurious emissionAssumed parameters of the interfered-with system are:Operating frequency band:
41、5 925-6 425 MHzReceiver bandwidth: 20 MHz (see Note 2)Receiver antenna gain 40 dB (after subtracting feeder loss)Receiver noise figure: 4 dBFree space loss: 134 dB (20 km)Thermal noise: 140 dB(W/MHz)Thus the maximum allowable level of interference corresponding to the interference-to-thermal noise r
42、atio of 10 dBis 117 dB(W/20 MHz) at the receiver input of the interfered-with system. This equates to a power flux-density of120 dB(W/m2) and an unwanted e.i.r.p. of a radar system of 23 dBW.It should be noted that many mobile radar systems may not meet this requirement and further efforts are neede
43、d toimprove such radar systems in this case as well.NOTE 2 Generally the bandwidth of second harmonic spurious emission is narrower than that of the interfered-withreceiver. Therefore, the interference-to-thermal noise ratio is higher at a receiver of narrower bandwidth. Thus, 20 MHzis chosen as representing a system with narrow receiver bandwidth._
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