User's Manual
PN 8100-40 Help Hot Line (U.S. only): 1-800-530-9960 7-47
620004-0 Rev. B
Connecting a Main Hub to a Base Station
7.5.2.1 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
the LGCell 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
DN
is the downlink
power radiated by the RAU, then
P
TX
= –76 dBm (for PCS) – P
DN
+ 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
LGCell 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
DN
where P
DN
is determined by the downlink attenuation. Since P
DN
for the LGCell is
about 10 dBm, we see that the cascaded noise figure is about 39 dB, which is consid-
erably higher than that of the LGCell 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 of doing this is that the uplink coverage
sensitivity is reduced. A link budget analysis will clarify these issues. Typically, the
uplink attenuation between the LGCell and the base station will be the same as, or
maybe 10dB less than, the downlink attenuation.