Rep. Itu-r bt. 2025 report itu-r b
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2.4.1.4.2.2.1 Frequency allocationConcerning the frequency allocations f2 and f3, measurements and calculations not given here for a BER limit of 10–4 indicate that a margin loss of 7 dB appears between allocation 1 and 2, and 4 dB between allocation 1 and 3, proving the interfering effect of the tested sub-carriers and the required RF power increase to overcome this effect. However, additional tests need to be performed with the upgraded demonstrator, as the Viterbi decoder will certainly alleviate part of the interfering effect of the analogue sub-carriers. 2.4.1.4.2.2.2 Data correlationA data correlation analysis performed on the received television signal strength levels in the survey vehicle and the received return link signal at the broadcasting site indicated a strong correlation (> 0.92) between the signals at both ends. This confirmed that the received TV signals could be used as an indicator of the return link feasibility. 2.4.1.4.2.2.3 Max RF Power (outdoor conditions)The RF power needed to take into account various distances and propagation conditions can be derived from Table 2.5 by selecting the Tx level needed for a 10–4 BER. The large variations in Tx level observed (up to 36 dB for the same distance) are due to various propagation conditions; § 2.4.1.4.4.2 gives further explanations of the geographical situation of each point which may be clear ( line of sight), or obstructed. By analysing the data in Table 2.5, it is possible to derive as a first conclusion that a 30 dBm transmission power offers enough margin to enable a return link service to work even at the points where TV service is absent; however, further analysis is needed. The TV reception signal level thresholds commonly used are : – analogue TV reception : 55 dBV i.e., –54 dBm 75 – digital DVB-T reception in 8K 64-QAM 1/32 guard interval in Gaussian channel (C/N 22 dB): 35 dBV i.e., ‑74 dBm 75 . By taking into consideration outdoor points where both analogue and digital reception levels are both above their thresholds (points 16/25), Pmax 11 dBm (point 4); taking only digital reception (which is more realistic; points 22/25), leads to Pmax 26 dBm at point 5 located approximately at mid-range of the TV service area radius (50 km). Figure 2.7 compares a prediction based on the actual transmission parameters (installed antenna, preamplifiers, receiver sensitivity at BER 10–4, etc.) and propagation model Recommendation ITU-R P.370 (50,50) with the experimental Tx levels. As already mentioned, this limited set of data does not permit definitive conclusions to be derived; nevertheless, it should be mentioned that prediction is quite pessimistic, as 70% of the points are under the Recommendation ITU‑R P.370 based curve. A fitting function was also applied on the experimental data in order to derive its logarithmic tendency, and it shows a good 10 dB difference with the ITU-R based curve at the edge of the TV analogue or digital service area ( 40 km). To be mentioned also is the need for the determination of the Tx power margin needed to cope with the field strength variability due to various location configurations (test points 22, 23, 24, almost co-located, clearly show the variability effect). A standard deviation figure is generally derived from a large set of experimental data (in order to determine TV planning parameters) and applied as an additional margin on a 50% location prediction model in order to give a certain degree of service availability (for example, 90% in fixed DVB-T reception). This standard deviation was provisionally assessed to be the same as that used in an analogue channel as narrow bandwidth channels were being considered ( 10 dB in analogue UHF and 1.3 for 90% location coverage probability); this figure also needs to be validated with further tests. A provisional assessment of the maximum RF power needed to cover a 50 km distance using the actual experimental set-up can be made. The following calculation based on Fig. 2.7, gives the maximum required Tx power: – Tx power for 50 km (log fitting curve for 50% of location) : 15 dBm – Margin for increasing 50% 90% locations 13 dB – Coding gain for CR 3/4 : –5 dB Max Tx power : 15 13 – 5 23 dBm. This figure is compatible with the theoretical one given in § 2.4.1.4.4.5 (20 dBm for 50 km range in mode 1) although the reception configurations are slightly different (improved installation, reception in a non-interfered channel). 
FIGURE 2.7 [2025-027] Directory: dms pub -> itu-r -> opb -> rep rep -> Report itu-r m. 2243 (11/2011) rep -> Report itu-r bt. 2053-2 (11/2009) L rep -> Report itu-r m. 2038 Technology trends rep -> Report itu-r sa. 2312-0 (09/2014) rep -> Report itu-r rep -> Report itu-r sm. 2179 (09/2010) Short-range radiocommunication devices measurements rep -> Report itu-r rep -> Report itu-r rs. 2194 (10/2010) rep -> Report itu-r rs. 2165 (09/2009) Download 2.21 Mb. Share with your friends:
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