Principles of Modern Radar - Volume 2 1891121537

17.6 Multichannel Processing for Detection Performance Improvement 805TABLE 17-9Cancellation Performance against Real DataExploited Frequency CA Theo CA CA LossAntennas [MHz] [dB] [dB] [dB]Ref-V/Surv-V 92.1 (SFC2) 45.4 22.2 23.294.3 (SFC4) 45.8 8.5 37.3Ref-H/Surv-V 92.1 (SFC2) 45.1 22.1 2394.3 (SFC4) 45.6 7.9 37.7Ref-V/Surv-H 92.1 (SFC2) 47.5 28.3 19.294.3 (SFC4) 48.1 23.6 24.5Ref-H/Surv-H 92.1 (SFC2) 47.1 27.8 19.394.3 (SFC4) 47.8 23.4 24.4in the surveillance signal after the cancellation stage. This clearly demonstrates that thedisturbance contributions in the surveillance signal have been effectively reduced by thecancellation filter. However, its performance is actually limited by the interfering signalslevel rather than by thermal noise only (as assumed in the evaluation of the theoreticalCA). Specifically, the actual CA is limited by the direct signal-to-interference plus noiseratio at the surveillance channel (CA ≈ DINR surv ). In addition, the quality of the listenedprogram after cancellation is better at those channels for which a higher CA loss wasmeasured. In fact, assuming that the interference level is well above the noise floor (INR≫ 1), we have CA = CA Theo | dB − CA Loss | dB ≈ DNR| dB − INR| dB, and we conclude thatthe CA loss is a measure of the interference power level. Obviously, different interferingsignals may affect the desired surveillance signal. A detailed analysis of the transmitterslocated in the area surrounding the receiver site allowed some broadcasted radio channelsto be identified that are probably responsible for interchannel interferences at the exploitedFM radio channels. The identified transmissions are listed in Table 17-10 in decreasingorder of expected power level at the receiver site (evaluated on the basis of the availableinformation). They are broadcasted by FM emitters located in the surveillance area atdistances largely comparable with the PBR baseline (see Figure 17-31).TABLE 17-10 Potential Interfering FM Radio Channels for the Exploited FM RadioChannels (SFC2 and SFC4)Frequency FM Radio[MHz] Broadcast Transmitter Distance [km] Polarization92.2 RTL 102.5 TX1 (Terminillo) 105 N/A92.0 Radio Domani TX2 (Vignanello) 50 N/A92.2 RTL 102.5 TX5 (Monte Gennaro) 80 V92.0 R. 101 TX5 (Monte Gennaro) 80 V92.0 R. Suby TX6 (Soriano) 49 N/A92.2 RTL 102.5 TX4 (Monte Cavo) 83 V92.2 R. Immagine TX7 (Velletri) 84 N/A94.2 Subasio TX3 (Albano) 82 V94.5 Subasio TX4 (Monte Cavo) 83 V94.1 Subasio TX1 (Terminillo) 105 H94.4 RAI R.2 TX1 (Terminillo) 105 H