1、STD.CEPT ERC REPORT 28-ENGL L4 I 2326434 0035357 LLil ERC REPORT 28 w European Radiocommunications Committee (ERC) i _. .- -, 1, I Af I IBr/2 (4) In our case, this gives qi - qo = 10log(zBr) = 101og(0.6ps40kHz) = -16 dB. ERC REPORT 28 Page 4 Elevation I 10“ I 11.9“ I 18.8“ I 21.4“ I 34.2“ I 70“ I 90
2、“ Em (BW) I 57 I 57 I 57 I 54 I 45 I 35 I 27 I The FDR can be devided into two tem, the on-tune rejection (OTR) and the off-frequency rejection (OFR), the additional rejection which results from off-tuning interferer and receiver. Elevation G,. (Bi) Lh (a) G,.-Lh (dB) The value of FDR is taken from
3、the measured power spectrum. The OTR is 20 dB and the OFR can be found in Table 6.1. 1 O“ 11.9“ 18.8“ 21.4“ 34.2“ 22.3 22.0 19.8 17.5 12.8 163.8 163.3 161.5 160.9 158.4 -141.5 -141.3 -141.7 -143.4 -145.6 Af (MHZ) Il (2 15 I 10 om (a) I 3.5 I 11 I 17 I 22 I Af is the frequency separation from 1614 MH
4、z. Elevation 10“ 11.9“ 18.8“ 1 (BW) -120.5 -120.3 -120.7 Margin (a) -47.5 -47.7 -47.3 Table 6.1. OFR 21.4“ 34.2“ -125.4 -136.6 -42.6 -31.4 Note: Report 972 includes reference to CCIR report 654. According to that report, OTR should be calculated by 2010g(BtBr) for radar pulses. However, in formula 1
5、, this has been taken into account by the calculations of qi - qo- Consequently, in formula 1, OTR should be calculated by 101og(Bt/B,). Table 6.2. Radar EIRP The probability that more than one pulse hits the receiver at the same time has not been included in the calculations. The satellite receivin
6、g antenna gain (Gr) depends on the elevation angle and can be found in the IRIDIUM system overview (see Table 6.3). This antenna gain is valid for beams directed at Sweden. Table 6.4 Margin The antenna rotation rate is 36“/s, but for low elevation angles the radar will cause interference in all dire
7、ctions, since the backlobe will only give an attenuation of approximately 40 dB. It should be noted that this backlobe attenuation is only obtained for low elevation angles. For elevation angles approaching 90“, the margin in the main lobe will be higher, but the advantage of scanning is lost. The m
8、argin can be improved by using frequencies separated from 1614 MHz and the interference may then be intermittent due to the scanning effect. The margin would also be improved for spot beams directed at areas outside Sweden, due to possible satellite antenna discrimination. If the interference is acc
9、eptable or not, depends on how the system can co-exist with this kind of interference. Automatic repeat request is used to request retransmission of missing datapackets. If this will occur very often due to radar pulses, the traffic capacity could be reduced to an unacceptable level. STDmCEPT ERC RE
10、PORT 2B-ENGL 1794 b 2326434 00253b3 445 I 2.3 2.3.1 2.3.2 ERC REPORT 28 Page 5 The calculations have only taken into account one radar station but there are approximately 30 radar stations in operation. Some of them have a lower EIRP than used in these calculations. Assessment of BER To assess the B
11、ER, we first have to see what the interfering pulses look like in the satellite receiver. A pulse is 0.6 ps wide. This pulse will be widened in the receiver filter to approximately 2/(40 kHz) = 50 ,us. A pulse train of four pulses within 10 ps will thus be transformed into a single interfering pulse
12、 with a width of approximately 60 ps. The pulse trains are repeated every 2.5 ms. Case 1 : the radar is causing interference in all directions Two different cases can be distinguished. One case is when the margin is so low that the radar is causing interference in all directions. The binomial distri
13、bution can be used to assess the probability of one or more radars causing interference. p = Pa radar is interfering = 6012500 = 0.024; q = 1-p = 0.976; Assuming that 20 radars are operating simultaneously pn = Pn radars interfering = (20-n)20!/(,!(20-n)!). PO = 0.615; p1 = 0.303; p2 = 0.071. The pr
14、obability of interference is thus 1 - po = 0.385. A more detailed investigation is needed to assess the BER accurately. An estimated worst case value could be 0.385*0.5 = 0.19. This is assuming that the interfering signal is not causing blocking of the satellite receiver. Case 2 : improvement of the
15、 margin, antenna discrimination The second case occurs if the margin can be improved. For low elevation angles, the radar antenna discrimination would then be sufficient to keep the interfering signal below the threshold outside of a certain beamwidth. The antenna pattern for 25“ elevation is used i
16、n the following calculations. This pattern is representative for elevation angles up to 25“. The discrimination for higher angles is gradually reduced up to 90“ elevation where, of course, there is no discrimination. The improvement necessary to apply the calculations below can be derived by compari
17、ng with the results of section 2.2. It should be noted that no means to achieve this improvement have so far been identified, apart from using frequencies separated from 1614 MHz. If the margin can be improved to -30 dB, the interference would be restricted to a 10“ beamwidth. The binomial distribut
18、ion is now used to calculate the probability of one or more radars being within interference range. p = Pa radar within int. range = 10/360 = 0.028; q = 1-p = 0.972. pn = Pn radars within int. range = pn4(2o-n)20!/(n!(20-n!). = 0.567; p1 = 0.326; p2 = 0.089; p3 = P4 = .Oo2; p5+ = 0.001. Since a rada
19、r is interfering for 2.4% of the time it is within interference range, the total percentage of time that interference occurs is, assuming that interfering pulses from different radars do not overlap, T% = Zpn5i*2.4 = 1.4%. Similarly to abve, the worst case BER is estimated to 0.007. ERC REPORT 28 Pa
20、ge 6 Globalstar Based on the calculations in section 2.2, it seems uniikely that the margin can be kept above -30 dB for IRIDIUM. However, for elevation angles around 29, -40 dB seems to be a fairly realistic figure. The radar antenna discrimination would then keep the interfering signal below the t
21、hreshold outside of a 120“ beamwidth. Repeating the same calculations as above for this value gives T% = 16%, and a BER of 0.08. Odyssey 3. CDMA Globalstar and Odyssey have been chosen as two examples of CDMA systems. 3.1 Technical parameters for the MSS systems Inclination 52“ 55“ Altitude 1407 km
22、10354 km Baseband bitrate, R 4.8 kBPS 4.8 kBPS Processing gain, Gp 24.2 dB 30.4 dB 2, Minimum 4.8 dB 4.5 dB ,Mobile EIRP -2.2 dBw -0.5 dBW Mi 1, 4.4 dB 10.9 dB Allocated bandwidth per carrier BW, 1.25 MHz 5.3 m i) Mi is the acceptable ratio between the interfering and the wanted signal. where - L SY
23、S - N includes noise and intra-system interference, - I is the inter-system interference. is the system implementation losses in the receiver, a typical value is 3 dB, If 6.3 % of the interference allowance is allocated to inter-system interference, then Mi = I/C = (N+I)/C - 12 dB 2, The processing
24、gain can be estimated by the equation Gp = lOlOg(BWRp/R). in the case of Odyssey, this would give Gp=30.4 dB. An FCC report gives the value 35.4 dB. In the report, it is also stated that a change of RF bandwidth is contemplated for Odyssey from 5.5 to 16.5 MHz. It seems likely that the processing ga
25、in 35.4 dB should be associated with this new bandwidth. For this reason, the value 30.4 dF3 is assumed for these calculations. Table 6.5. Technical parameters for MSS systems STD-CEPT ERC REPORT 28-ENGL 1994 iaa 232b4L4 00L53b5 218 I Globalstar Odyssey ERC REPORT 28 Page 7 c-I(dB) Margin (dB) -53.5
26、 -49.1 -57.5 -46.6 3.2 The peak interference power The probability that more than one pulse hits the receiver is not included in the calculations. The peak interference power is according to formula 1: IGlob&tar = 57+Gr-Lb-1010g(3.M/1.25M)+101g(0.6.1.25M) = 51.3 dBW + Gr - Lb Iodyssey = 57+Gr-Lb+lo1
27、0g(ZPRF)-1010g(Z.PRp) = 57 dBw + Gr - Lb 3.3 Interference levels No information about the satellite antenna gain has been available, so in the calculations (Gr-Lb) has been assumed to be the same for the radar and the mobile. This gives the results in Table 6.6. Table 6.6. Margin for CDMA systems Si
28、nce the attenuation in the backlobe of the radar antenna is approximately 40 dJ3, the radar may cause interference in all directions. If we assume a shadow margin of approximately 10 dB, power control becomes acial. Whether sharing is possible is dependent on how the system concerned can co-exist wi
29、th intermittent interference. To be able to draw any conclusion about that, it is necessary to know for example how many chips will be perturbed by the pulses and if that is acceptable, if the decoding will improve the BER to an acceptable level and if the false alarm rate caused by the radars is ac
30、ceptable. The calculations have taken into account only one radar station, but there are approximately 30 radar stations in operation. Some of them have a lower EIRP that used in these calculations. 3.4 Assessment of BER Similar calculations to those in 2.3 can be made for OMA systems. Only the exam
31、ple of Odyssey is treated here. With a receiving bandwidth of 5.3 MHz, the pulses are virtually unaffected. Thus, p = Pa radar is interfering = 4*0.6ps/2.5ms = 0.00096, q = 1 - p = 0.99904, PO = 0.981. The probability of interference is, with twenty radars operating, 1 - po = 0.019, and the estimate
32、d worst case BER is 0.0095. 4. CONCLUSION The radar system will exceed the maximum allowable interference level. Whether sharing is possible or not is dependent on how different systems can cc-exist with intermittent interference and the limit for how much the satellite transponder can be degraded. This depends for example on the signalling, decoder and acceptable false alarm rate.
