User Manual

SPEEDCOM SC5800 User Manual
22
3.5 Micro-cell Backhaul Applications of SC5800 Digital
Radios
In applications where more than one independent and separate links, need to radiate from a
central site, a number of parameters can be taken advantage of, to provide isolation and minimize
interference between these links:
• Frequency multiplexing
• Antenna polarization
• Choice of High Antenna Gain
It is important to note that these methods only provide isolation between two radio systems, and
that power levels in the separate systems should be balanced to ensure correc t operation.
3.5.1 Setting the Transmitted Power Levels
To minimize interference, received power levels should be balanced between separate radio links.
This means that transmit power levels should be set to provide similar levels of received power, as
indicated by the RSSI values of the adjacent receivers at the central site.
3.5.2 Frequency Multiplexing
The SC5800 offers four frequency channel plans. A radio link requires two channels (one for
transmit and one to receive) to provide full-duplex operation. Each radio has a high and a low sub-
band, one that it uses for transmission and another for reception. Terminology definition: the
‘High-band Outdoor Unit’ of a system transmits on the higher of the two sub-bands. The ‘Low-
band Outdoor Unit’ of a system transmits on the lower of the two sub-bands. A system (link)
always has one High Band and one Low Band Outdoor Unit. It is important to note that unwanted
transmitted signals in adjacent frequency bands can affect other receivers operating in an
adjacent band if insufficient antenna isolation is provided. A solution is to group high-band or low-
band Outdoor Units at the central site, rather than group high and low-band Outdoor Units
together.
3.5.3 Antenna Isolation
Separate links at a central site will have sufficient isolation when radio systems operate outside
the radiation beamwidth or side lobes of the system antenna. The achievable isolation can be
established by examining the measured radiation patterns of the system antennas. Directional
isolation can be used if the antenna radiation is 15 dB or lower relative to the adjacent main
beam. Antennas with high directionality will allow reduced angular separation of adjacent
systems. Antenna cross-polarization isolation can be used for adjacent radio links, radiating in
the same direction. Typical isolation of 30 dB can be achieved using high quality antennas.