Study regarding compatibility between networks for mobile communication in the 800 MHz-band and digital terrestrial television below 790 MHz
11/02/2009
Progira Radio Communication AB has on behalf of PTS made a study to analyse the risk of interference on digital terrestrial television below 790 MHz from a new network for mobile communication in the 800 MHz-band.
The opportunities for introducing new communication networks in the 800 MHz-band (790-862 MHz) are currently being investigated in CEPT working groups. Results from the study may be used within this work.
For any questions please contact Jan Boström (jan.bostrom@pts.se).
This report presents the results of a study of potential interference from a future mobile service in the frequency range 790 – 862 MHz into digital TV broadcasting below 790 MHz in Sweden. The focus of the study is to assess potential interference from the mobile downlink into DVB-T channel 60 assuming fixed rooftop antennas.
Calculations of the existing DVB-T networks coverage on channels 58-60 have been used as a basis, while the mobile network is based upon an existing GSM 900 network in Sweden.
With the assumptions made, the result of the calculations shows that the potentially interfered population in the channel 60 areas is between 2.5% and 17%. The results are very sensitive to the assumed protection ratio between the mobile network service and the DVB-T service. The results presented above are valid for protection ratios -30 dB and -15 dB, respectively. The area where interference may occur is relatively small compared to the population affected. This is due to the large number of mobile base stations present in densely populated areas where there is need for high capacity in the mobile networks.
In order to minimize the interference from the mobile network it seems necessary to insert a frequency separation (guard band) of 2 MHz above 790 MHz. This will reduce the impact of interference to less than 8% of the population where DVB-T channel 60 is received.
Interference into DVB-T channels 58 and 59 from the mobile downlink seems to be
significantly less compared to the case of DVB-T channels 60, due to the increase of the protection ratios at larger frequency separations.
Interference into portable DVB-T reception seems to affect a larger relative area compared to the rooftop reception cases, when receiving antenna discrimination is applicable. However the relative population affected remains in the same order in the two cases.
Further to the insertion of a 2 MHz frequency separation between the broadcast and the mobile downlink (guard band), other mitigations techniques may be needed to reduce the impact of the interference. These techniques could involve:
- Use of vertical polarisation at the mobile base stations, will reduce the impact of interference significantly
- Power limitations for the mobile base stations in areas where channel 60 is used
- Use of a more stringent spectrum mask at the mobile base stations (BS)
- Insertion of a passive filter before the RF front end in the DVB-T receiver
Further studies are recommended to access the impact of these measures and the possible impact of DVB-T receiver overload. Further analysis when protection ratios between LTE and DVB-T become available is also suggested.