Two years ago I used a mobile phone that could show me the GSM frequency channels to find out whether all GSM network operators in Germany make use of the GSM 900 MHz band. While the original two GSM network operators obviously made good use of their beachfront property, the other two network operators that came later and at first only had 1800 MHz spectrum made little to no use of the 900 MHz spectrum. With my SDR-Sharp + DVB-T Stick Layer 1 utility I now revisited the topic to have a look at the complete band owned by the original 1800 MHz carriers in the 900 MHz band to see if I had overlooked something or if something had changed in the meantime.
The result is pretty much the same as two years ago. One of the two operators makes a bit of use, I could observe at least one or two carriers in their 5 MHz part of the spectrum in Cologne (i.e. in the city). This is very little compared to the two original GSM network operators that have many many cells on air in the same amount of spectrum.
The second original 1800 MHz operator still doesn't seem to make any use of GSM 900 in Cologne. I could only see very faint 200 kHz signals and I am not quite sure what they are. Perhaps echos of other carriers nearby shown here by my tracing hardware which has its limitations? Or perhaps cells used outside of Cologne that are still visible here?
In any case, both make so little use of it that I wonder if one day one of them might just start with either a UMTS 900 or an LTE 900 carrier in this part of the spectrum.
One thought on “Probing Layer 1 – Part 3: Further Thoughts on GSM 900 Use in Cities”
I think that the 2 E-Netz networks originally planned their network based on the exclusive use of 1800MHz frequencies. In cities this required a denser planning of BTS to increase indoor coverage – you can’t just increase power, as this’ll increase interference, and anyway, the handsets are limited to lower transmit powers at 1800MHz, so may not be heard at the BTS, even if the higher BTS power penetrates a building.
The 900MHz are used in rural areas, as this offers significant benifits, and in the case of o2, the rural coverage only really got started once 900MHz carriers became available.
I think that in some cases the use of 900MHz carriers must be limited to replacing the 1800MHz lost in exchange. This could also mean that 900MHz can not be used for capacity ebnhancements or macro cells, as they are already placed into an existing coverage lyer as 1 to 1 relplacements of lost frequencies. Using 900MHz means that you have to replan the power levels, and also the physical characteristics of the BTS antenna so that you come close to replicating the 1800MHz coverage. You don’t want to do this too often as it must be costly.
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