Installation Manual Part 5

PRELIMINARY
D-19
BWX 8415 Basestation Installation and Commissioning Guide
OL-19519-01
Appendix D RF Center Frequency and Interference Analysis Guidelines
Spectrum Analyzer Settings
Time Domain Interference Sweeps Analysis
The Time Domain sweeps capture how the interference sources behave, if the interference is constantly
there or operating in a hopping method. Time Domain sweeps are typically used for the unlicensed 2.4
GHz systems’ interference measurements.
Calculating the Theoretical Noise Floor
All analysis of interference is done from the theoretical noise floor. This is the best-case noise floor in
a perfectly clean environment. The following algorithm is used to determine the noise floor.
Theoretical noise floor (NF) = thermal NF @ 1 Hz and 20° C + sub-carrier
channel energy + Cisco BWX Mobile WiMAX system noise figure
Thermal NF @ 1 Hz and 20° C = -174
Sub-carrier channel energy = 10log(500 KHz) = +57 dB
Cisco BWX Mobile WiMAX system noise figure = +5 dB
Resulting theoretical noise floor
-174+57+5 = -112 dBm
If the setting on the spectrum analyzer was 30 KHz and not 500 KHz, there would be a 12 dB difference
in the setting, which means the thermal noise floor for 30 KHz @ 20° C would be –124 dBm. If the
setting on the spectrum analyzer is set for 1 MHz and not 500 KHz, there is a 3 dB difference in the noise
floor, meaning that the theoretical noise for 1 MHz @ 20° C is –109 dBm.
Analyze the Time Domain Sweeps
The BS is able to compensate for 320 μs per each 10 ms frame. This 320 μs timeframe only comes into
play when the signal level of the interferer is above the levels determined in the Max-hold section. The
320 μs duration is an additive duration throughout the 10 ms timeframe. If all of the interference signals
above the determined signal level add up to be longer than 320 μs, then that frame is unusable.