User's Manual

Designing a Unison Solution PRELIMINARY
8-48 InterReach Unison User Guide and Reference Manual
PN 8700-10
620003-0
8.6.1 Attenuation
Figure 8-3 shows a typical setup wherein a duplex base station is connected to a Main
Hub. For a simplex base station, eliminate the circulator and connect the simplex
ports of the base station to the simplex ports of the Main Hub. Add attenuators to reg-
ulate the power appropriately.
Figure 8-3 Main Hub to Duplex Base Station or Repeater Connections
Duplex
Base Station
Main Hub
Forward
Reverse
A3
A1
A2
• A typical circulator has an IP3 of +70dBm. If you drive the circulator too hard it will produce
intermods that are bigger than the intermods produced by Unison. The IP3 at the Forward
port input of the Main Hub is approximately +38 dBm. The IP3 of the circulator at that same
point (i.e., following attenuator A1) is +70dBm – A1. Thus, to keep the system IP3 from
being adversely affected by the circulator, attenuator A1 should be no more than approxi-
mately +30 dB.
• A filter diplexer can be used in place of the circulator. The IP3 of the diplexer can be
assumed to be greater than +100 dBm. If a diplexer is used, A3 can be omitted.
• A1+A3 should be chosen so that the output power per carrier at the RAU’s output is correct
for the number of carriers being transmitted. Suppose the base station transmits 36 dBm
per carrier and it is desired that the RAU output be 6 dBm per carrier and the forward port
gain is 0 dB. Then A1+A3=30 dB.
• A2+A3 should, ideally, be at least 10 dB less than the noise figure plus the gain of the Uni-
son system. For example, if the reverse port has a 0 dB gain and if there are 32 RAUs, the
noise figure is approximately 22 dB. So A2+A3 should be about 10 dB. If A2+A3 is too
large, the uplink coverage can be severely reduced.
• Given these three equations:
A1 < 30 dB
A1+A3 = 30 dB (in this example)
A2+A3 < 10 dB (in this example)
we could choose A1=20 dB, A2=0 dB, A3=10 dB
or
Repeater