<s>
Space-time	B-Algorithm
adaptive	I-Algorithm
processing	I-Algorithm
(	O
STAP	O
)	O
is	O
a	O
signal	B-General_Concept
processing	I-General_Concept
technique	O
most	O
commonly	O
used	O
in	O
radar	B-Application
systems	I-Application
.	O
</s>
<s>
It	O
involves	O
adaptive	O
array	B-Algorithm
processing	I-Algorithm
algorithms	O
to	O
aid	O
in	O
target	O
detection	O
.	O
</s>
<s>
Radar	B-Application
signal	B-General_Concept
processing	I-General_Concept
benefits	O
from	O
STAP	O
in	O
areas	O
where	O
interference	O
is	O
a	O
problem	O
(	O
i.e.	O
</s>
<s>
Coupling	O
multiple	O
spatial	O
channels	O
with	O
pulse-Doppler	B-Algorithm
waveforms	O
lends	O
to	O
the	O
name	O
"	O
space-time.	O
"	O
</s>
<s>
This	O
weight	O
vector	O
is	O
applied	O
to	O
the	O
coherent	O
samples	O
received	O
by	O
the	O
radar	B-Application
.	O
</s>
<s>
For	O
ground-based	O
radar	B-Application
,	O
cluttered	O
returns	O
tend	O
to	O
be	O
at	O
DC	O
,	O
making	O
them	O
easily	O
discriminated	O
by	O
Moving	O
Target	O
Indication	O
(	O
MTI	O
)	O
.	O
</s>
<s>
While	O
primarily	O
developed	O
for	O
radar	B-Application
,	O
STAP	O
techniques	O
have	O
applications	O
for	O
communications	O
systems	O
.	O
</s>
<s>
This	O
means	O
that	O
we	O
are	O
filtering	O
over	O
multiple	O
dimensions	O
,	O
and	O
multi-dimensional	O
signal	B-General_Concept
processing	I-General_Concept
techniques	O
must	O
be	O
employed	O
.	O
</s>
<s>
Thus	O
,	O
the	O
goal	O
is	O
to	O
suppress	O
noise	O
,	O
clutter	O
,	O
jammers	O
,	O
etc.	O
,	O
while	O
keeping	O
the	O
desired	O
radar	B-Application
return	O
.	O
</s>
<s>
The	O
goal	O
is	O
to	O
perform	O
beamforming	B-Algorithm
such	O
that	O
the	O
beam	O
appears	O
stationary	O
as	O
the	O
airborne	O
radar	B-Application
is	O
in	O
motion	O
over	O
discrete	O
time	O
periods	O
so	O
the	O
clutter	O
appears	O
without	O
Doppler	O
.	O
</s>
<s>
The	O
goal	O
is	O
to	O
compactly	O
model	O
the	O
interference	O
,	O
at	O
which	O
point	O
it	O
can	O
then	O
be	O
processed	O
using	O
principal	B-Application
component	I-Application
techniques	O
or	O
diagonal-loading	O
SMI	O
(	O
where	O
a	O
small	O
magnitude	O
,	O
random	O
diagonal	O
matrix	O
is	O
added	O
to	O
attempt	O
to	O
stabilize	O
the	O
matrix	O
prior	O
to	O
inverting	O
)	O
.	O
</s>
<s>
The	O
principal	B-Application
component	I-Application
method	O
firsts	O
applies	O
principal	B-Application
component	I-Application
analysis	I-Application
to	O
estimate	O
the	O
dominant	O
eigenvalues	O
and	O
eigenvectors	O
,	O
and	O
then	O
applies	O
a	O
covariance	O
taper	O
and	O
adds	O
an	O
estimated	O
noise	O
floor	O
:	O
</s>
<s>
Frequency-selective	O
channel	O
compensation	O
can	O
be	O
used	O
to	O
extend	O
traditional	O
equalization	B-Algorithm
techniques	O
for	O
SISO	O
systems	O
using	O
STAP	O
.	O
</s>
<s>
to	O
minimize	O
the	O
mean	B-Algorithm
squared	I-Algorithm
error	I-Algorithm
(	O
MSE	O
)	O
.	O
</s>
<s>
STAP	O
has	O
been	O
extended	O
for	O
MIMO	B-Algorithm
radar	I-Algorithm
to	O
improve	O
spatial	O
resolution	O
for	O
clutter	O
,	O
using	O
modified	O
SIMO	O
radar	B-Application
STAP	O
techniques	O
.	O
</s>
<s>
New	O
algorithms	O
and	O
formulations	O
are	O
required	O
that	O
depart	O
from	O
the	O
standard	O
technique	O
due	O
to	O
the	O
large	O
rank	O
of	O
the	O
jammer-clutter	O
subspace	O
created	O
by	O
MIMO	B-Algorithm
radar	I-Algorithm
virtual	O
arrays	O
,	O
which	O
typically	O
involves	O
exploiting	O
the	O
block	O
diagonal	O
structure	O
of	O
the	O
MIMO	O
interference	O
covariance	O
matrix	O
to	O
break	O
the	O
large	O
matrix	O
inversion	O
problem	O
into	O
smaller	O
ones	O
.	O
</s>
<s>
In	O
comparison	O
with	O
SIMO	O
radar	B-Application
systems	I-Application
,	O
which	O
will	O
have	O
transmit	O
degrees	O
of	O
freedom	O
,	O
and	O
receive	O
degrees	O
of	O
freedom	O
,	O
for	O
a	O
total	O
of	O
,	O
MIMO	B-Algorithm
radar	B-Application
systems	I-Application
have	O
degrees	O
of	O
freedom	O
,	O
allowing	O
for	O
much	O
greater	O
adaptive	O
spatial	O
resolution	O
for	O
clutter	O
mitigation	O
.	O
</s>
