1、 Rec. ITU-R BT.1832 1 RECOMMENDATION ITU-R BT.1832 Digital video broadcast-return channel terrestrial (DVB-RCT) deployment scenarios and planning considerations (Question ITU-R 16/6) (2007) Scope This Recommendation sets forth some deployment scenarios and considerations to assist regulators whose t
2、ask it will be to allocate spectrum for interactive return paths employing the digital video broadcast-return channel terrestrial (DVB-RCT) system. The ITU Radiocommunication Assembly, considering a) that the DVB-RCT is a telecommunication system, designed to operate in conjunction with the digital
3、terrestrial television broadcasting system, DVB-T, to provide it with a return path and interactive application capabilities; b) that Recommendations ITU-R BT.1306-1 and ITU-R BT.1667, together with the cross-reference ETSI EN 301 958 V.1.1.1 (2002/03), have already identified potential system chara
4、cteristics for the return path; c) that the return path can optionally be deployed as described in Annex 1 to provide a high-spectrum efficiency and spectrum reuse; d) that the orthogonal frequency division multiplex access (OFDMA) technology for the return path of DVB-RCT has an inherent flexibilit
5、y and scalability, as it enables to trade-off the throughput (per user), capacity (number of users supported), available links and cell size. These features are implemented with adaptive modulation and coding together with power concentration in sub-path assignments, bringing about system gain from
6、user sites; e) that DVB-RCT performance has been successfully tested in the field with several pilot systems in several countries. These systems involved different interactive applications, deployed to validate sharing of the return path among large numbers of users; f) that DVB-RCT is capable of hi
7、gh efficiency and large system capacity. It can be an optimum solution for deployment in large cells in underserved and rural areas, thus helping to bridge the digital divide, recommends 1 that the planning for deployment of DVB-RCT should take into account the planning considerations as described i
8、n Annex 1; 2 that the DVB-RCT system performance data and possible deployment scenarios can be used as a basis for future co-existence studies without interference to primary services; 3 that pertinent measurement results, obtained from the field, should be used to update cell capacity and efficienc
9、y analysis defined in Annex 1. 2 Rec. ITU-R BT.1832 Annex 1 DVB-RCT deployment scenarios and planning considerations 1 DVB_RCT system data 1.1 System parameters The main parameters of the DVB-RCT system, as described in Recommendation ITU-R BT.1667, Annex 1, are: Forward broadcasting path frequency
10、VHF: 170 MHz to 230 MHz (174-230 MHz) UHF: 470 MHz to 860 MHz (470-862 MHz) Return transmission power: 20 dBm (typ.) to 30 dBm (max.) Return antenna gain: 13 dBi (directional) User antenna gain: 3 dBi (omnidirectional) Base station receiver sensitivity Rural fixed, 1 kHz spacing, 4-QAM 1/2: 135 dBm
11、Urban/portable 4 kHz spacing, 64-QAM 3/4: 109 dBm Base station operational C/N Rural fixed, 1 kHz spacing, 4-QAM 1/2: 5 dB Urban/portable 4 kHz spacing, 64-QAM 3/4: 22 dB. The return path transmission power spectrum mask is shown in Fig. 1. FIGURE 1 Return path RCT spectrum mask Rec. ITU-R BT.1832 3
12、 In Fig. 1, f0indicates the central frequency, f1= 0.375/Ts and f2= 1.2515/Ts, where f = f f0; and Du is the duplex spacing and it depends on the chosen non-interference criteria and filtering technology. In future analysis we suggest that for higher frequency duplex spacing the power can be reduced
13、 according to Table 1 (based on data measurements on commercialized user unit): TABLE 1 Reduction of spectral density power as a function of frequency separation f 16 MHz 24 MHz 32 MHz 40 MHz 48 MHz 56 MHz Attenuation 17 dB 27 dB 37 dB 47 dB 57 dB 62 dB Thus the overall RCT relative interference spe
14、ctral density, as a function of frequency separation, is given in Table 2. TABLE 2 RCT relative interference spectral density, Af(dBc/kHz) f 29 dB 24-29 22-24 18-22 30.7% 51% 12% 6% 37.7% 46.6% 13.6% 2% 6 29 dB 24-29 22-24 18-22 72.3% 26.3% 1.3% 0% 48.53% 43.9% 6.8% 0.68% 2.2.1 Capacity calculation
15、The average capacity, supported by a single carrier (SC) system using adaptive modulation, can be calculated according to the area ratios indicated in Table 3, assuming a uniform distribution of users within the area. For OFDMA, the calculation is more elaborate, thanks to the path splitting and pow
16、er concentration capabilities. The OFDMA may be operational even in the presence of large interference or low-field strength of received signal. Table 4 summarizes the average capacity and RF efficiency in terms of the overall capacity per cell sector, the spectral efficiency in bit/s/Hz and the sys
17、tem efficiency in terms of bit/s/Hz/cell. A typical/theoretical SC system has been used as a reference. For a single frequency path case, it cannot operate, as it requires a minimal C/I level not available in this scenario. In contrast, the OFDMA splits the bandwidth so that interference is avoided.
18、 In this case, although full capacity cannot be supported, some traffic can still be transmitted. Rec. ITU-R BT.1832 7 TABLE 4 Capacity per sector and efficiency of SC and OFDMA systems Cell size Number of forward frequency paths 2 km 6 km SC 0 0 Mbit/s/sector OFDMA 2.35 2.35 SC 0 0 Bit/s/Hz OFDMA 0
19、39 0.39 SC 0 0 1 Bit/s/Hz/cell OFDMA 2.35 2.35 SC 7.4 7.3 Mbit/s/sector OFDMA 8.96 8.92 SC 0.62 0.61 Bit/s/Hz OFDMA 0.75 0.74 SC 3.70 3.65 2 Bit/s/Hz/cell OFDMA 4.48 4.46 SC 11.2 11.8 Mbit/s/sector OFDMA 13.3 13.44 SC 0.62 0.66 Bit/s/Hz OFDMA 0.74 0.75 SC 3.73 3.93 3 Bit/s/Hz/cell OFDMA 4.43 4.48 S
20、C 13.6 12.4 Mbit/s/sector OFDMA 15 15 SC 0.38 0.34 Bit/s/Hz OFDMA 0.42 0.42 SC 2.27 2.07 6 Bit/s/Hz/cell OFDMA 2.50 2.50 Table 4 shows a consistent advantage of OFDMA between 5% and 25% of higher efficiency. 2.3 Antenna deployment The RCT standard envisages two antenna deployment scenarios, indoor a
21、nd outdoor. The RCT antenna can share the downstream DVB-T antenna (which can also be an outdoor or an indoor antenna) using either a switch or a duplexer. Alternatively the two antennas can be separated. Those possibilities are given in the standard and shown here in Fig. 3. Note that BIM is an abb
22、reviation of broadcast interface module (DVB-T), while IIM stands for the interactive interface module (RCT). Dx means duplexer. It is to be noted that the switch options do not enable simultaneous operation of TV reception and DVB-RCT transmissions, therefore it is expected that most deployments would not use them. 8 Rec. ITU-R BT.1832 FIGURE 3 Antenna deployment
