Connecting a Main Hub to a Base Station
6-40
InterReach Unison Installation, Operation, and Reference Manual
CONFIDENTIAL
D-620003-0-20 Rev J
6.6.2.1
Uplink Attenuation Exception: CDMA
In CDMA systems, the power transmitted by the mobile is determined by the charac-
teristics of both the uplink and downlink paths. The power transmitted by the mobile
should be similar in open-loop control (as determined by the downlink path) as dur-
ing closed-loop control (as determined by the uplink and downlink paths). In addi-
tion, the mobile’s transmit power when it communicates with a base station through
Unison should be similar to the power transmitted when it communicates with a base
station in the outdoor network (during soft hand-off). Because of these consider-
ations, you should not allow the downlink and uplink gains to vary widely.
Open-loop power control:
P
TX
= –76 dBm (for PCS) – P
RX
where P
TX
is the power transmitted and P
RX
is the power received by the mobile. If
PL is the path loss (in dB) between the RAU and the mobile, and P
DL
is the downlink
power radiated by the RAU, then
P
TX
= –76 dBm (for PCS) – P
DL
+ PL
Closed-loop power control:
P
TX
= noise floor + uplink NF – process gain + Eb/No + PL
= –113 dBm/1.25 Mhz + NF – 19 dB + 7 dB + PL
where Eb/No = 7 dB is a rough estimate, and NF is the cascaded noise figure of the
Unison uplink, the uplink attenuation, and the base station noise figure. Equating P
TX
for the open-loop and closed-loop we see that
NF = 49 – P
DL
where P
DL
is determined by the downlink attenuation. Since P
DL
for Unison is about
10 dBm, the cascaded noise figure is about 39 dB, which is considerably higher than
that of Unison itself. This implies that we should use a fairly large attenuation on the
uplink. This case suggests using as much attenuation on the downlink as on the
uplink. The drawback is that the uplink coverage sensitivity is reduced. A link budget
analysis clarifies these issues. Typically, the uplink attenuation between the Main
Hub and the base station will be the same as, or maybe 10 dB less than, the downlink
attenuation.
