Indoor Radio Planning: A Practical Guide for GSM, DCS, UMTS, HSPA and LTE, Second Edition

7.4 Noise Power from Parallel Systems

Often there will be more than one noise signal (noise power sources) present at the input of a system. This could be two parts of an active DAS, using two repeaters, that needs to be combined to a base station receiver, like the GSM (200 kHz) example in Figure 7.13.

Figure 7.13 Two parallel noise sources combined into one output

7.4.1 Calculating Noise Power from Parallel Sources

Random Power Signals

Noise is random (white noise), and two noise signals will be noncorrelated. Thus the noise powers (in Watts) of two sources can be added in order to calculate the total noise power from the system.

First we need calculate the noise floor for each of the two amplifiers (GSM):

Watts

We need to sum up the noise, by adding the power contribution from each source.

Now we convert the noise powers from dBm to mW:

Then we can sum up the two powers:

Convert to dBm

We convert the noise power back to dBm:

The Combiner

The noise power is combined in a splitter ...