User Manual

MDR2400/5800-SR, Orion2410/5810-SRi and Orion 5825-SR
862-01881 Issue 12c Page 28
3.5 Microcell Backhaul Applications of MDR / Orion 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 minimise 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
correct operation.
3.5.1 Setting the Transmitted Power Levels
To minimise 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. Power levels are easily adjusted via point and click selection utilizing
the provided NMS / GUI, installed on your laptop or via SNMP network architecture.
3.5.2 Frequency Multiplexing
The MDR2400 and Orion2410i offers three frequency channel plans, the MDR5800
and Orion5810i four and the Orion 5850 also four. Refer to paragraph 2.2.1 for more
detail on the 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 RF Unit’ of a system transmits on the higher of
the two sub-bands. The ‘Low-band RF 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 RF
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 RF Units at the
central site, rather than group high and low-band RF 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.