Plessey MDR2400-SR, User Manual, Page: 29 / 131

MDR2400-SR, MDR5800-SR and Orion 5825-SR
Issue 10
Page 29
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 offers three frequency channel plans, the MDR5800 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 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.