User's Manual

Link Budget Analysis
InterReach Fusion Wideband Installation, Operation, and Reference Manual Page 91
D-620616-0-20 Rev K • TECP-77-044 Issue 9 • March 2015 © 2015 TE Connectivity
Table 81. Link Budget Considerations for Narrowband Systems
Consideration Description
BTS Transmit Power The Power Per Carrier transmitted from the Base Station
output.
Attenuation between
BTS and Fusion
Wideband
This includes all losses: cable, a
ttenuator, splitter/combiner, and so forth.
On the downlink, attenuation must be chosen so that the maximum Power Per Carrier going into the Main
Hub does not exceed the levels given in “Maximum Output Power Per Carrier” on page 65.
On the uplink, attenuation is chosen to keep the maximum uplink signal and
noise level low enough to
prevent Base Station alarms but small enough not to cause degradation in the system sensitivity.
If the Fusion Wideband noise figure minus the attenu
ation is at least 10 dB higher than the BTS noise
figure, the system noise figure is approximately that of Fusion Wideband alone. Refer to “Connecting a
Main Hub to a Base Station” on page 101 for ways to independently set the uplink and downlink
attenuations between the Base Station and Fusion
Wideband.
Antenna Gain The radiated output power includes antenna gain. For example, if you use a 3 dBi antenna at the RAU that
is tra
nsmitting 0 dBm per carrier, the effective radiated power (relative to an isotropic radiator) is 3 dBm
per carrier.
BTS Noise Figure This is the effective noise floor of
the Base Station input (usually Base Station sensitivity is this effective
noise floor plus a certain C/I ratio).
Fusion Wideband Noise
Figure
This is Fusion Wideband’s uplink noise figure, which varies depending on the number of Expansion Hubs
and RAUs, and
the frequen
cy band. Fusion Wideband’s uplink noise figure is specified for a 1-1-8
configuration. Thus, the noise figure for a Fusion Wideband system (or multiple systems whose uplink
ports are power combined) is NF(1-1-8) + 10*log(# of Expansion Hubs). This represents an upper-bound
because the noise figure is lower if any of the Expansion Hub’s RAU ports are not used.
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 t
r
ansmitted at highest power level setting).
Multipath Fade
Margin
This margin allows for a certain level of
fading due to multipath interference. On the inside of buildings
there is often one or more fairly strong signals and many weaker signals arriving from reflections and
diffraction. Signals arriving from multiple paths add constructively or destructively. This margin
accounts for the possibility of destructive multipath interference. In RF site surveys the effects of
multipath fading are typically not accounted for because such fading is 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, the effects of shadowing are partially accounted for
since it is characterized by relatively slow changes in power level.
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 ach
ieve adequate coverage
if the signal level is, on average, above this level over 95% of the area covered, for example.
Protocol Signal
Bandwidth
Thermal Noise
TDMA 30 kHz –129 dBm
GSM 200 kHz –121 dBm
iDEN 25 kHz –130 dBm