<s>
The	O
angle	B-Algorithm
of	I-Algorithm
arrival	I-Algorithm
(	O
AoA	O
)	O
of	O
a	O
signal	O
is	O
the	O
direction	O
from	O
which	O
the	O
signal	O
(	O
e.g.	O
</s>
<s>
Measurement	O
of	O
AoA	O
can	O
be	O
done	O
by	O
determining	O
the	O
direction	O
of	O
propagation	O
of	O
a	O
radio-frequency	O
wave	O
incident	O
on	O
an	O
antenna	B-Algorithm
array	I-Algorithm
or	O
determined	O
from	O
maximum	O
signal	O
strength	O
during	O
antenna	O
rotation	O
.	O
</s>
<s>
Generally	O
this	O
TDOA	O
measurement	O
is	O
made	O
by	O
measuring	O
the	O
difference	O
in	O
received	O
phase	O
at	O
each	O
element	O
in	O
the	O
antenna	B-Algorithm
array	I-Algorithm
.	O
</s>
<s>
This	O
can	O
be	O
thought	O
of	O
as	O
beamforming	B-Algorithm
in	O
reverse	O
.	O
</s>
<s>
In	O
beamforming	B-Algorithm
,	O
the	O
signal	O
from	O
each	O
element	O
is	O
weighed	O
to	O
"	O
steer	O
"	O
the	O
gain	O
of	O
the	O
antenna	B-Algorithm
array	I-Algorithm
.	O
</s>
<s>
In	O
optics	B-Algorithm
,	O
AoA	O
can	O
be	O
calculated	O
using	O
interferometry	O
.	O
</s>
<s>
AoA	O
is	O
generally	O
used	O
to	O
discover	O
the	O
location	O
of	O
pirate	B-Application
radio	I-Application
stations	I-Application
or	O
of	O
any	O
military	O
radio	O
transmitter	O
.	O
</s>
<s>
Limitations	O
on	O
the	O
accuracy	O
of	O
estimation	O
of	O
angle	B-Algorithm
of	I-Algorithm
arrival	I-Algorithm
signals	O
in	O
digital	B-Algorithm
antenna	I-Algorithm
arrays	I-Algorithm
are	O
associated	O
with	O
jitter	O
ADC	O
and	O
DAC	O
.	O
</s>
