<s>
Diversity	B-Protocol
combining	I-Protocol
is	O
the	O
technique	O
applied	O
to	O
combine	O
the	O
multiple	O
received	O
signals	O
of	O
a	O
diversity	B-Protocol
reception	I-Protocol
device	O
into	O
a	O
single	O
improved	O
signal	O
.	O
</s>
<s>
Various	O
diversity	B-Protocol
combining	I-Protocol
techniques	O
can	O
be	O
distinguished	O
:	O
</s>
<s>
Selection	B-Protocol
combining	I-Protocol
:	O
Of	O
the	O
N	O
received	O
signals	O
,	O
the	O
strongest	O
signal	O
is	O
selected	O
.	O
</s>
<s>
When	O
the	O
N	O
signals	O
are	O
independent	O
and	O
Rayleigh	O
distributed	O
,	O
the	O
expected	O
diversity	B-Protocol
gain	I-Protocol
has	O
been	O
shown	O
to	O
be	O
,	O
expressed	O
as	O
a	O
power	O
ratio	O
.	O
</s>
<s>
Sometimes	O
more	O
than	O
one	O
combining	O
technique	O
is	O
used	O
–	O
for	O
example	O
,	O
lucky	O
imaging	O
uses	O
selection	B-Protocol
combining	I-Protocol
to	O
choose	O
(	O
typically	O
)	O
the	O
best	O
10%	O
images	O
,	O
followed	O
by	O
equal-gain	O
combining	O
of	O
the	O
selected	O
images	O
.	O
</s>
<s>
When	O
the	O
focus	O
is	O
on	O
the	O
wireless	O
transmission	O
of	O
longer	O
signal	O
sequences	O
,	O
such	O
as	O
for	O
example	O
Ethernet	O
packets	O
,	O
specific	O
performance	O
characteristics	O
regarding	O
diversity	B-Protocol
gain	I-Protocol
on	O
a	O
parallel	O
redundant	O
wireless	O
transmission	O
system	O
can	O
be	O
observed	O
.	O
</s>
<s>
Diversity	B-Protocol
combining	I-Protocol
,	O
or	O
voting	O
,	O
in	O
two-way	O
radio	O
systems	O
is	O
a	O
method	O
for	O
improving	O
talk-back	O
range	O
from	O
walkie-talkie	B-Application
and	O
vehicular	O
mobile	O
radios	O
.	O
</s>
<s>
Voting	O
comparators	O
in	O
analog	B-Application
FM	I-Application
systems	O
can	O
switch	O
between	O
receivers	O
in	O
tenths	O
-	O
or	O
hundredths-of-a-second	O
,	O
(	O
faster	O
than	O
one	O
syllable	O
)	O
.	O
</s>
<s>
In	O
this	O
arrangement	O
,	O
receivers	O
at	O
remote	O
sites	O
are	O
connected	O
to	O
the	O
voting	O
comparator	O
by	O
private	O
telephone	O
lines	O
,	O
a	O
channel	O
in	O
a	O
D4	O
channel	O
bank	O
on	O
a	O
DS1	B-Protocol
,	O
or	O
an	O
analog	O
microwave	O
baseband	O
channel	O
.	O
</s>
<s>
The	O
pitch	O
of	O
the	O
tone	O
changed	O
to	O
represent	O
the	O
received	O
signal	O
level	O
,	O
or	O
FM	B-Application
receiver	O
limiter	O
voltage	O
,	O
at	O
the	O
remote	O
receiver	O
.	O
</s>
<s>
Newer	O
voting	O
comparators	O
compare	O
signal-to-noise	O
ratio	O
at	O
the	O
voting	O
comparator	O
,	O
accounting	O
for	O
end-to-end	O
noise	O
,	O
bad	O
phone	O
lines	O
,	O
poor	O
level	O
discipline	O
,	O
as	O
well	O
as	O
the	O
best	O
diversity	B-Protocol
reception	I-Protocol
path	O
.	O
</s>
<s>
When	O
communicating	O
with	O
hand-held	O
radios	O
(	O
walkie-talkies	B-Application
)	O
,	O
base	O
stations	O
generally	O
talk	O
out	O
further	O
than	O
they	O
can	O
receive	O
.	O
</s>
<s>
Diversity	B-Protocol
combining	I-Protocol
reduces	O
one	O
possible	O
single-point	O
failure	O
:	O
any	O
single	O
receiver	O
failure	O
,	O
or	O
local	O
interference	O
to	O
a	O
single	O
receiver	O
,	O
will	O
not	O
block	O
reception	O
on	O
the	O
entire	O
system	O
.	O
</s>
<s>
These	O
unwanted	O
,	O
distant	O
signals	O
can	O
be	O
stronger	O
than	O
desired	O
signals	O
from	O
local	O
walkie-talkies	B-Application
.	O
</s>
<s>
The	O
majority	O
of	O
installations	O
using	O
diversity	B-Protocol
combining	I-Protocol
equipment	O
continually	O
evaluate	O
the	O
best	O
received	O
signal	O
against	O
all	O
other	O
signals	O
.	O
</s>
<s>
As	O
a	O
walkie-talkie	B-Application
user	O
causes	O
a	O
signal	O
fade	O
by	O
turning	O
their	O
head	O
,	O
or	O
a	O
passing	O
tractor-trailer	O
rig	O
blocks	O
their	O
signal	O
at	O
the	O
voted	O
receive	O
site	O
,	O
the	O
combining	O
unit	O
rapidly	O
changes	O
to	O
a	O
different	O
receiver	O
.	O
</s>
<s>
In	O
some	O
installations	O
,	O
diversity	B-Protocol
combining	I-Protocol
equipment	O
is	O
configured	O
to	O
lock	O
on	O
a	O
receiver	O
.	O
</s>
<s>
If	O
the	O
diversity	B-Protocol
combining	I-Protocol
equipment	O
votes	O
"	O
north	O
,	O
"	O
the	O
next	O
time	O
the	O
dispatcher	O
presses	O
the	O
transmit	O
button	O
,	O
the	O
north	O
transmitter	O
will	O
key	O
.	O
</s>
<s>
The	O
diversity	B-Protocol
combining	I-Protocol
equipment	O
switches	O
fast	O
enough	O
that	O
syllables	O
are	O
not	O
lost	O
but	O
not	O
fast	O
enough	O
that	O
bits	O
are	O
not	O
lost	O
.	O
</s>
