User's Manual

MDS 05-3627A01, Rev. D LEDR Series I/O Guide 111
12.0 SPACE DIVERSITY OPERATION
12.1 Introduction
Space diversity operation is an effective mechanism of increasing a
radio link’s resilience to transmission impairments such as multipath
fading or frequency selective fading. In difficult transmission environ-
ments such as over highly reflective and moving water paths, or in arid
environments where atmospheric ducting occurs, space diversity is the
most effective way of maintaining a continuous radio link.
In a space diversity link, two radio receivers are operated in parallel,
from two separate antennas mounted several wavelengths apart verti-
cally on the antenna tower. The separation of antennas is such that when
one antenna experiences fading due to multi-path interference, the other
antenna, being several wavelengths away, is not likely to experience the
same fade. Thus, one receive path may experience uncorrectable errors,
while the other path will be error free. Similar to the protected operation,
the receive modem switch will determine which buffered data path is
operating with the highest integrity, and select that path without
inducing any additional bit errors into the link.
Space diversity is especially effective in changeable multi-path environ-
ments such as over tidal water paths. Since water is highly reflective,
there will be continual “constructive” and “destructive” interference at
each single antenna over the course of the day as the water rises and falls
and the reflected water path interferes with the line-of-sight path. By
correct vertical positioning of the antennas, these effects can be negated,
allowing one antenna to see a good signal while the other is experi-
encing fading, and the modem switching accordingly to allow the link
to operate error- free.
The space diversity LEDR radio is available only in a hot standby con-
figuration.
12.2 User Interface & Control
Protected operation is configured using the Redundant screen (Page 41)
on either radio front panel, or with the
rdnt command from a NMS ter-
minal (see Page 74).
12.3 Transmit Clock Selection
There is no difference between a space diversity system and redundant
radio arrangements with respect to transmit clock selection. Fullrate
radios require no user intervention for clocking. Users of subrate sys-
tems should set the radio clocks as described for subrate systems. See
“Transmit Clock Selection” on Page 111 for further information.