User's Manual

Designing a Fusion Wideband Solution
Page 64 InterReach Fusion Wideband Installation, Operation, and Reference Manual
© 2015 TE Connectivity D-620616-0-20 Rev K • TECP-77-044 Issue 9 • March 2015
DOWNLINK RSSI DESIGN GOAL
Wireless service providers typically provide a minimum downlink signal level and an associated
confidence factor when specifying coverage requirements. These two figures of merit are a
function of wireless handset sensitivity and margins for fading and body loss. Wireless handset
sensitivity is the weakest signal that the handset can process reliably and is a combination of the
thermal noise in the channel, noise figure of the handset receiver front end and minimum
required SNR. Fade margins for multipath fading (fast or small-scale) and log-normal shadow
fading (slow or large-scale) are determined by the desired confidence factor, and other factors.
Downlink Received Signal Strength Indicator (RSSI) design goal calculations for the GSM protocol
are shown below for a 95% area coverage confidence factor.
Downlink design goals on the order of –85 dBm are typ
ical for protocols such as GSM. Wireless
service providers may choose a higher level to ensure that in-building signal dominates any
macro signal that may be leaking into the building.
Noise Power
10 Log (KT)+10 Log (200 kHz); K=1.38X10
-23
, T=300 degrees Kelvin
-121 dBm
Wireless Handset Noise Figure 8 dB
Required SNR 9 dB
Multipath Fade Margin
95% Reliability for Rician K=6 dB
6 dB
Log-normal Fade Margin
95% Area/87% Edge Reliability for 35 dB PLS and 9 dB Sigma
10 dB
Body Attenuation + 3 dB
Downlink RSSI Design Goal (P
DesignGoal
)
Signal level received by wireless handset at edge of coverage area
-85 dBm