<s>
In	O
digital	O
communications	O
,	O
chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
(	O
CSS	O
)	O
is	O
a	O
spread	B-Architecture
spectrum	I-Architecture
technique	O
that	O
uses	O
wideband	O
linear	O
frequency	O
modulated	B-Application
chirp	B-Application
pulses	O
to	O
encode	O
information	O
.	O
</s>
<s>
A	O
chirp	B-Application
is	O
a	O
sinusoidal	O
signal	O
whose	O
frequency	O
increases	O
or	O
decreases	O
over	O
time	O
(	O
often	O
with	O
a	O
polynomial	O
expression	O
for	O
the	O
relationship	O
between	O
time	O
and	O
frequency	O
)	O
.	O
</s>
<s>
As	O
with	O
other	O
spread	B-Architecture
spectrum	I-Architecture
methods	O
,	O
chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
uses	O
its	O
entire	O
allocated	O
bandwidth	O
to	O
broadcast	O
a	O
signal	O
,	O
making	O
it	O
robust	O
to	O
channel	O
noise	O
.	O
</s>
<s>
Further	O
,	O
because	O
the	O
chirps	B-Application
utilize	O
a	O
broad	O
band	O
of	O
the	O
spectrum	O
,	O
chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
is	O
also	O
resistant	O
to	O
multi-path	O
fading	O
even	O
when	O
operating	O
at	O
very	O
low	O
power	O
.	O
</s>
<s>
However	O
,	O
it	O
is	O
unlike	O
direct-sequence	B-Device
spread	I-Device
spectrum	I-Device
(	O
DSSS	B-Device
)	O
or	O
frequency-hopping	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
(	O
FHSS	B-Protocol
)	O
in	O
that	O
it	O
does	O
not	O
add	O
any	O
pseudo-random	O
elements	O
to	O
the	O
signal	O
to	O
help	O
distinguish	O
it	O
from	O
noise	O
on	O
the	O
channel	O
,	O
instead	O
relying	O
on	O
the	O
linear	O
nature	O
of	O
the	O
chirp	B-Application
pulse	O
.	O
</s>
<s>
Additionally	O
,	O
chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
is	O
resistant	O
to	O
the	O
Doppler	O
effect	O
,	O
which	O
is	O
typical	O
in	O
mobile	O
radio	O
applications	O
.	O
</s>
<s>
Chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
was	O
originally	O
designed	O
to	O
compete	O
with	O
ultra-wideband	O
for	O
precision	O
ranging	O
and	O
low-rate	O
wireless	O
networks	O
in	O
the	O
2.45GHz	O
band	O
.	O
</s>
<s>
Chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
is	O
ideal	O
for	O
applications	O
requiring	O
low	O
power	O
usage	O
and	O
needing	O
relatively	O
low	O
data	O
rates	O
(	O
1	O
Mbit/s	O
or	O
less	O
)	O
.	O
</s>
<s>
In	O
particular	O
,	O
IEEE	O
802.15.4a	O
specifies	O
CSS	O
as	O
a	O
technique	O
for	O
use	O
in	O
low-rate	O
wireless	B-General_Concept
personal	I-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LR-WPAN	O
)	O
.	O
</s>
<s>
However	O
,	O
whereas	O
IEEE	O
802.15.4-2006	O
standard	O
specifies	O
that	O
WPANs	B-General_Concept
encompass	O
an	O
area	O
of	O
10	O
m	O
or	O
less	O
,	O
IEEE	O
802.15.4a-2007	O
,	O
specifies	O
CSS	O
as	O
a	O
physical	O
layer	O
to	O
be	O
used	O
when	O
longer	O
ranges	O
and	O
devices	O
moving	O
at	O
high	O
speeds	O
are	O
part	O
of	O
your	O
network	O
.	O
</s>
<s>
Finally	O
,	O
the	O
IEEE	O
802.15.4a	O
PHY	O
standard	O
actually	O
mixes	O
CSS	O
encoding	O
techniques	O
with	O
differential	B-General_Concept
phase	I-General_Concept
shift	I-General_Concept
keying	I-General_Concept
modulation	B-Application
(	O
DPSK	B-General_Concept
)	O
to	O
achieve	O
better	O
data	O
rates	O
.	O
</s>
<s>
Chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
may	O
also	O
be	O
used	O
in	O
the	O
future	O
for	O
military	O
applications	O
as	O
it	O
is	O
very	O
difficult	O
to	O
detect	O
and	O
intercept	O
when	O
operating	O
at	O
low	O
power	O
.	O
</s>
<s>
Very	O
similar	O
frequency	O
swept	O
waveforms	O
are	O
used	O
in	O
frequency	O
modulated	B-Application
continuous	O
wave	O
radars	O
to	O
measure	O
range	O
(	O
distance	O
)	O
;	O
an	O
unmodulated	O
continuous	O
wave	O
Doppler	O
radar	O
can	O
only	O
measure	O
range-rate	O
(	O
relative	O
velocity	O
along	O
the	O
line	O
of	O
sight	O
)	O
.	O
</s>
<s>
One	O
application	O
of	O
chirp	B-Protocol
spread	I-Protocol
spectrum	I-Protocol
is	O
LoRa	B-General_Concept
.	O
</s>
