User's Manual

PN 8100-40 Help Hot Line (U.S. only): 1-800-530-9960 7-33
620004-0 Rev. B
Link Budget Analysis
Thermal Noise This is the noise level in the signal bandwidth (BW).
Thermal noise power = –174 dBm/Hz + 10Log(BW).
Required C/I ratio For each wireless standard a certain C/I (carrier to interference) ratio is needed to obtain acceptable
demodulation performance. For narrowband systems, (TDMA, GSM, EDGE, iDEN, AMPS) this
level varies from about 9 dB to 20 dB.
Mobile Transmit
Power
The maximum power the mobile can transmit (power transmitted at highest power level setting).
Multipath Fade
Margin
This margin allows for a certain level of fading due to multipath interference. Inside buildings there
is often one or more fairly strong signals and many weaker signals arriving from reflections and dif-
fraction. Signals arriving from multiple paths add constructively or destructively. This margin
accounts for the possibility of destructive multipath interference. In RF site surveys this margin will
not appear because it will be averaged out over power level samples taken over many locations.
Log-normal Fade
Margin
This margin adds an allowance for RF shadowing due to objects obstructing the direct path between
the mobile equipment and the RAU. In RF site surveys, this shadowing will not appear because it
will be averaged out over power level samples taken over many locations.
Body Loss This accounts for RF attenuation caused by the user’s head and body.
Minimum Received
Signal Level
This is also referred to as the “design goal”. The link budget says that you can achieve adequate cov-
erage if the signal level is, on average, above this level over 95% of the area covered, for example.
Table 7-28 Link Budget Considerations for Narrowband Systems (continued)
Consideration Description
Protocol
Signal
Bandwidth
Thermal
Noise
TDMA 30 kHz –129 dBm
CDMA 1.25 MHz –113 dBm
GSM 200 kHz –121 dBm
iDEN 25 kHz –130 dBm