<s>
Software-defined	B-Architecture
radio	I-Architecture
(	O
SDR	O
)	O
is	O
a	O
radio	O
communication	O
system	O
where	O
components	O
that	O
have	O
been	O
traditionally	O
implemented	O
in	O
analog	O
hardware	O
(	O
e.g.	O
</s>
<s>
mixers	O
,	O
filters	O
,	O
amplifiers	O
,	O
modulators/demodulators	O
,	O
detectors	B-Algorithm
,	O
etc	O
.	O
)	O
</s>
<s>
are	O
instead	O
implemented	O
by	O
means	O
of	O
software	O
on	O
a	O
personal	B-Device
computer	I-Device
or	O
embedded	B-Architecture
system	I-Architecture
.	O
</s>
<s>
A	O
basic	O
SDR	O
system	O
may	O
consist	O
of	O
a	O
personal	B-Device
computer	I-Device
equipped	O
with	O
a	O
sound	B-Device
card	I-Device
,	O
or	O
other	O
analog-to-digital	O
converter	O
,	O
preceded	O
by	O
some	O
form	O
of	O
RF	O
front	O
end	O
.	O
</s>
<s>
Software	B-Architecture
radios	I-Architecture
have	O
significant	O
utility	O
for	O
the	O
military	O
and	O
cell	O
phone	O
services	O
,	O
both	O
of	O
which	O
must	O
serve	O
a	O
wide	O
variety	O
of	O
changing	O
radio	O
protocols	O
in	O
real	O
time	O
.	O
</s>
<s>
In	O
the	O
long	O
term	O
,	O
software-defined	B-Architecture
radios	I-Architecture
are	O
expected	O
by	O
proponents	O
like	O
the	O
Wireless	O
Innovation	O
Forum	O
to	O
become	O
the	O
dominant	O
technology	O
in	O
radio	O
communications	O
.	O
</s>
<s>
SDRs	O
,	O
along	O
with	O
software	O
defined	O
antennas	O
are	O
the	O
enablers	O
of	O
the	O
cognitive	B-Protocol
radio	I-Protocol
.	O
</s>
<s>
Superheterodyne	O
receivers	O
use	O
a	O
VFO	O
(	O
variable-frequency	O
oscillator	O
)	O
,	O
mixer	O
,	O
and	O
filter	O
to	O
tune	O
the	O
desired	O
signal	O
to	O
a	O
common	O
IF	O
(	O
intermediate	O
frequency	O
)	O
or	O
baseband	B-Algorithm
.	O
</s>
<s>
Real	O
software	B-Architecture
radios	I-Architecture
often	O
have	O
two	O
or	O
three	O
analog	O
channel	O
filters	O
with	O
different	O
bandwidths	O
that	O
are	O
switched	O
in	O
and	O
out	O
.	O
</s>
<s>
A	O
laboratory	O
called	O
the	O
Gold	O
Room	O
at	O
TRW	O
in	O
California	O
created	O
a	O
software	O
baseband	B-Algorithm
analysis	O
tool	O
called	O
Midas	O
,	O
which	O
had	O
its	O
operation	O
defined	O
in	O
software	O
.	O
</s>
<s>
In	O
1982	O
,	O
while	O
working	O
under	O
a	O
US	O
Department	O
of	O
Defense	O
contract	O
at	O
RCA	O
,	O
Ulrich	O
L	O
.	O
Rohde	O
’s	O
department	O
developed	O
the	O
first	O
SDR	O
,	O
which	O
used	O
the	O
COSMAC	B-General_Concept
(	O
Complementary	O
Symmetry	O
Monolithic	O
Array	O
Computer	O
)	O
chip	O
.	O
</s>
<s>
Rohde	O
was	O
the	O
first	O
to	O
present	O
on	O
this	O
topic	O
with	O
his	O
February	O
1984	O
talk	O
,	O
“	O
Digital	O
HF	B-Algorithm
Radio	I-Algorithm
:	O
A	O
Sampling	O
of	O
Techniques	O
”	O
at	O
the	O
Third	O
International	O
Conference	O
on	O
HF	B-Algorithm
Communication	O
Systems	O
and	O
Techniques	O
in	O
London	O
.	O
</s>
<s>
In	O
1984	O
,	O
a	O
team	O
at	O
the	O
Garland	O
,	O
Texas	O
,	O
Division	O
of	O
E-Systems	O
Inc	O
.	O
(	O
now	O
Raytheon	O
)	O
coined	O
the	O
term	O
"	O
software	B-Architecture
radio	I-Architecture
"	O
to	O
refer	O
to	O
a	O
digital	O
baseband	B-Algorithm
receiver	O
,	O
as	O
published	O
in	O
their	O
E-Team	O
company	O
newsletter	O
.	O
</s>
<s>
A	O
'	O
Software	B-Architecture
Radio	I-Architecture
Proof-of-Concept	O
'	O
laboratory	O
was	O
developed	O
by	O
the	O
E-Systems	O
team	O
that	O
popularized	O
Software	B-Architecture
Radio	I-Architecture
within	O
various	O
government	O
agencies	O
.	O
</s>
<s>
This	O
1984	O
Software	B-Architecture
Radio	I-Architecture
was	O
a	O
digital	O
baseband	B-Algorithm
receiver	O
that	O
provided	O
programmable	O
interference	O
cancellation	O
and	O
demodulation	B-Device
for	O
broadband	O
signals	O
,	O
typically	O
with	O
thousands	O
of	O
adaptive	O
filter	O
taps	O
,	O
using	O
multiple	O
array	B-Operating_System
processors	I-Operating_System
accessing	O
shared	O
memory	O
.	O
</s>
<s>
In	O
1991	O
,	O
Joe	O
Mitola	O
independently	O
reinvented	O
the	O
term	O
software	B-Architecture
radio	I-Architecture
for	O
a	O
plan	O
to	O
build	O
a	O
GSM	O
base	O
station	O
that	O
would	O
combine	O
Ferdensi	O
's	O
digital	O
receiver	O
with	O
E-Systems	O
Melpar	O
's	O
digitally	O
controlled	O
communications	O
jammers	O
for	O
a	O
true	O
software-based	O
transceiver	O
.	O
</s>
<s>
E-Systems	O
Melpar	O
sold	O
the	O
software	B-Architecture
radio	I-Architecture
idea	O
to	O
the	O
US	O
Air	O
Force	O
.	O
</s>
<s>
Melpar	O
built	O
a	O
prototype	O
commanders	O
 '	O
tactical	O
terminal	O
in	O
1990	O
–	O
1991	O
that	O
employed	O
Texas	B-Architecture
Instruments	I-Architecture
TMS320C30	I-Architecture
processors	O
and	O
Harris	O
digital	O
receiver	O
chip	O
sets	O
with	O
digitally	O
synthesized	O
transmission	O
.	O
</s>
<s>
The	O
Melpar	O
prototype	O
did	O
n't	O
last	O
long	O
because	O
when	O
E-Systems	O
ECI	O
Division	O
manufactured	O
the	O
first	O
limited	O
production	O
units	O
,	O
they	O
decided	O
to	O
"	O
throw	O
out	O
those	O
useless	O
C30	O
boards	O
"	O
,	O
replacing	O
them	O
with	O
conventional	O
RF	O
filtering	O
on	O
transmit	O
and	O
receive	O
,	O
reverting	O
to	O
a	O
digital	O
baseband	B-Algorithm
radio	O
instead	O
of	O
the	O
SpeakEasy	B-General_Concept
like	O
IF	O
ADC/DACs	O
of	O
Mitola	O
's	O
prototype	O
.	O
</s>
<s>
So	O
instead	O
,	O
with	O
USAF	O
permission	O
,	O
in	O
1991	O
,	O
Mitola	O
described	O
the	O
architecture	O
principles	O
without	O
implementation	O
details	O
in	O
a	O
paper	O
,	O
"	O
Software	B-Architecture
Radio	I-Architecture
:	O
Survey	O
,	O
Critical	O
Analysis	O
and	O
Future	O
Directions	O
"	O
which	O
became	O
the	O
first	O
IEEE	O
publication	O
to	O
employ	O
the	O
term	O
in	O
1992	O
.	O
</s>
<s>
When	O
Mitola	O
presented	O
the	O
paper	O
at	O
the	O
conference	O
,	O
Bob	O
Prill	O
of	O
GEC	O
Marconi	O
began	O
his	O
presentation	O
following	O
Mitola	O
with	O
:	O
"	O
Joe	O
is	O
absolutely	O
right	O
about	O
the	O
theory	O
of	O
a	O
software	B-Architecture
radio	I-Architecture
and	O
we	O
are	O
building	O
one.	O
"	O
</s>
<s>
Prill	O
gave	O
a	O
GEC	O
Marconi	O
paper	O
on	O
PAVE	O
PILLAR	O
,	O
a	O
SpeakEasy	B-General_Concept
precursor	O
.	O
</s>
<s>
SpeakEasy	B-General_Concept
,	O
the	O
military	O
software	B-Architecture
radio	I-Architecture
was	O
formulated	O
by	O
Wayne	O
Bonser	O
,	O
then	O
of	O
Rome	O
Air	O
Development	O
Center	O
(	O
RADC	O
)	O
,	O
now	O
Rome	O
Labs	O
;	O
by	O
Alan	O
Margulies	O
of	O
MITRE	O
Rome	O
,	O
NY	O
;	O
and	O
then	O
Lt	O
Beth	O
Kaspar	O
,	O
the	O
original	O
DARPA	O
SpeakEasy	B-General_Concept
project	O
manager	O
and	O
by	O
others	O
at	O
Rome	O
including	O
Don	O
Upmal	O
.	O
</s>
<s>
Although	O
Mitola	O
's	O
IEEE	O
publications	O
resulted	O
in	O
the	O
largest	O
global	O
footprint	O
for	O
software	B-Architecture
radio	I-Architecture
,	O
Mitola	O
privately	O
credits	O
that	O
DoD	O
lab	O
of	O
the	O
1970s	O
with	O
its	O
leaders	O
Carl	O
,	O
Dave	O
,	O
and	O
John	O
with	O
inventing	O
the	O
digital	O
receiver	O
technology	O
on	O
which	O
he	O
based	O
software	B-Architecture
radio	I-Architecture
once	O
it	O
was	O
possible	O
to	O
transmit	O
via	O
software	O
.	O
</s>
<s>
A	O
few	O
months	O
after	O
the	O
National	O
Telesystems	O
Conference	O
1992	O
,	O
in	O
an	O
E-Systems	O
corporate	O
program	O
review	O
,	O
a	O
vice-president	O
of	O
E-Systems	O
Garland	O
Division	O
objected	O
to	O
Melpar	O
's	O
(	O
Mitola	O
's	O
)	O
use	O
of	O
the	O
term	O
"	O
software	B-Architecture
radio	I-Architecture
"	O
without	O
credit	O
to	O
Garland	O
.	O
</s>
<s>
The	O
Garland	O
VP	O
said	O
:	O
"	O
No	O
,	O
of	O
course	O
not	O
—	O
ours	O
is	O
a	O
software	B-Architecture
radio	I-Architecture
receiver.	O
"	O
</s>
<s>
Many	O
amateur	O
radio	O
operators	O
and	O
HF	B-Algorithm
radio	I-Algorithm
engineers	O
had	O
realized	O
the	O
value	O
of	O
digitizing	O
HF	B-Algorithm
at	O
RF	O
and	O
of	O
processing	O
it	O
with	O
Texas	O
Instruments	O
TI	O
C30	O
digital	B-Architecture
signal	I-Architecture
processors	I-Architecture
(	O
DSPs	O
)	O
and	O
their	O
precursors	O
during	O
the	O
1980s	O
and	O
early	O
1990s	O
.	O
</s>
<s>
Mitola	O
's	O
publication	O
of	O
software	B-Architecture
radio	I-Architecture
in	O
the	O
IEEE	O
opened	O
the	O
concept	O
to	O
the	O
broad	O
community	O
of	O
radio	O
engineers	O
.	O
</s>
<s>
His	O
May	O
1995	O
special	O
issue	O
of	O
the	O
IEEE	O
Communications	O
Magazine	O
with	O
the	O
cover	O
"	O
Software	B-Architecture
Radio	I-Architecture
"	O
was	O
regarded	O
as	O
a	O
watershed	O
event	O
with	O
thousands	O
of	O
academic	O
citations	O
.	O
</s>
<s>
Mitola	O
was	O
introduced	O
by	O
Joao	O
da	O
Silva	O
in	O
1997	O
at	O
the	O
First	O
International	O
Conference	O
on	O
Software	B-Architecture
Radio	I-Architecture
as	O
"	O
godfather	O
"	O
of	O
software	B-Architecture
radio	I-Architecture
in	O
no	O
small	O
part	O
for	O
his	O
willingness	O
to	O
share	O
such	O
a	O
valuable	O
technology	O
"	O
in	O
the	O
public	O
interest	O
"	O
.	O
</s>
<s>
Both	O
transmitter	O
and	O
receiver	O
of	O
an	O
adaptive	O
digital	O
satellite	O
modem	B-Application
were	O
implemented	O
according	O
to	O
the	O
principles	O
of	O
a	O
software	B-Architecture
radio	I-Architecture
,	O
and	O
a	O
flexible	O
hardware	O
periphery	O
was	O
proposed	O
.	O
</s>
<s>
In	O
1995	O
,	O
Stephen	O
Blust	O
coined	O
the	O
term	O
"	O
software	B-Architecture
defined	I-Architecture
radio	I-Architecture
"	O
,	O
publishing	O
a	O
request	O
for	O
information	O
from	O
Bell	O
South	O
Wireless	O
at	O
the	O
first	O
meeting	O
of	O
the	O
Modular	O
Multifunction	O
Information	O
Transfer	O
Systems	O
(	O
MMITS	O
)	O
forum	O
in	O
1996	O
,	O
organized	O
by	O
the	O
USAF	O
and	O
DARPA	O
around	O
the	O
commercialization	O
of	O
their	O
SpeakEasy	B-General_Concept
II	O
program	O
.	O
</s>
<s>
Mitola	O
objected	O
to	O
Blust	O
's	O
term	O
,	O
but	O
finally	O
accepted	O
it	O
as	O
a	O
pragmatic	O
pathway	O
towards	O
the	O
ideal	O
software	B-Architecture
radio	I-Architecture
.	O
</s>
<s>
Although	O
the	O
concept	O
was	O
first	O
implemented	O
with	O
an	O
IF	O
ADC	O
in	O
the	O
early	O
1990s	O
,	O
software-defined	B-Architecture
radios	I-Architecture
have	O
their	O
origins	O
in	O
the	O
U.S.	O
and	O
European	O
defense	O
sectors	O
of	O
the	O
late	O
1970s	O
(	O
for	O
example	O
,	O
Walter	O
Tuttlebee	O
described	O
a	O
VLF	B-Architecture
radio	I-Architecture
that	O
used	O
an	O
ADC	O
and	O
an	O
8085	B-General_Concept
microprocessor	I-General_Concept
)	O
,	O
about	O
a	O
year	O
after	O
the	O
First	O
International	O
Conference	O
in	O
Brussels	O
.	O
</s>
<s>
One	O
of	O
the	O
first	O
public	O
software	B-Architecture
radio	I-Architecture
initiatives	O
was	O
the	O
U.S.	O
DARPA-Air	O
Force	O
military	O
project	O
named	O
SpeakEasy	B-General_Concept
.	O
</s>
<s>
The	O
primary	O
goal	O
of	O
the	O
SpeakEasy	B-General_Concept
project	O
was	O
to	O
use	O
programmable	O
processing	O
to	O
emulate	O
more	O
than	O
10	O
existing	O
military	O
radios	O
,	O
operating	O
in	O
frequency	O
bands	O
between	O
2	O
and	O
2000	O
MHz	O
.	O
</s>
<s>
Another	O
SpeakEasy	B-General_Concept
design	O
goal	O
was	O
to	O
be	O
able	O
to	O
easily	O
incorporate	O
new	O
coding	O
and	O
modulation	B-Application
standards	O
in	O
the	O
future	O
,	O
so	O
that	O
military	O
communications	O
can	O
keep	O
pace	O
with	O
advances	O
in	O
coding	O
and	O
modulation	B-Application
techniques	O
.	O
</s>
<s>
From	O
1990	O
to	O
1995	O
,	O
the	O
goal	O
of	O
the	O
SpeakEasy	B-General_Concept
program	O
was	O
to	O
demonstrate	O
a	O
radio	O
for	O
the	O
U.S.	O
Air	O
Force	O
tactical	O
ground	O
air	O
control	O
party	O
that	O
could	O
operate	O
from	O
2	O
MHz	O
to	O
2	O
GHz	O
,	O
and	O
thus	O
could	O
interoperate	O
with	O
ground	O
force	O
radios	O
(	O
frequency-agile	O
VHF	B-Algorithm
,	O
FM	B-Application
,	O
and	O
SINCGARS	O
)	O
,	O
Air	O
Force	O
radios	O
(	O
VHF	B-Algorithm
AM	B-Device
)	O
,	O
Naval	O
Radios	O
(	O
VHF	B-Algorithm
AM	B-Device
and	O
HF	B-Algorithm
SSB	B-Device
teleprinters	O
)	O
and	O
satellites	O
(	O
microwave	O
QAM	B-Device
)	O
.	O
</s>
<s>
There	O
was	O
some	O
discontent	O
with	O
failure	O
of	O
these	O
early	O
software	B-Architecture
radios	I-Architecture
to	O
adequately	O
filter	O
out	O
of	O
band	O
emissions	O
,	O
to	O
employ	O
more	O
than	O
the	O
simplest	O
of	O
interoperable	O
modes	O
of	O
the	O
existing	O
radios	O
,	O
and	O
to	O
lose	O
connectivity	O
or	O
crash	O
unexpectedly	O
.	O
</s>
<s>
The	O
SpeakEasy	B-General_Concept
architecture	O
was	O
refined	O
at	O
the	O
MMITS	O
Forum	O
between	O
1996	O
and	O
1999	O
and	O
inspired	O
the	O
DoD	O
integrated	O
process	O
team	O
(	O
IPT	O
)	O
for	O
programmable	O
modular	O
communications	O
systems	O
(	O
PMCS	O
)	O
to	O
proceed	O
with	O
what	O
became	O
the	O
Joint	O
Tactical	O
Radio	O
System	O
(	O
JTRS	O
)	O
.	O
</s>
<s>
The	O
basic	O
arrangement	O
of	O
the	O
radio	O
receiver	O
used	O
an	O
antenna	O
feeding	O
an	O
amplifier	O
and	O
down-converter	O
(	O
see	O
Frequency	O
mixer	O
)	O
feeding	O
an	O
automatic	O
gain	O
control	O
,	O
which	O
fed	O
an	O
analog-to-digital	O
converter	O
that	O
was	O
on	O
a	O
computer	O
VMEbus	B-Architecture
with	O
a	O
lot	O
of	O
digital	B-Architecture
signal	I-Architecture
processors	I-Architecture
(	O
Texas	O
Instruments	O
C40s	O
)	O
.	O
</s>
<s>
The	O
transmitter	O
had	O
digital-to-analog	O
converters	O
on	O
the	O
PCI	B-Protocol
bus	I-Protocol
feeding	O
an	O
up	O
converter	O
(	O
mixer	O
)	O
that	O
led	O
to	O
a	O
power	O
amplifier	O
and	O
antenna	O
.	O
</s>
<s>
This	O
has	O
since	O
become	O
a	O
standard	O
design	O
scheme	O
for	O
wideband	O
software	B-Architecture
radios	I-Architecture
.	O
</s>
<s>
The	O
goal	O
was	O
to	O
get	O
a	O
more	O
quickly	O
reconfigurable	O
architecture	O
,	O
i.e.	O
,	O
several	O
conversations	O
at	O
once	O
,	O
in	O
an	O
open	B-Application
software	I-Application
architecture	O
,	O
with	O
cross-channel	O
connectivity	O
(	O
the	O
radio	O
can	O
"	O
bridge	O
"	O
different	O
radio	O
protocols	O
)	O
.	O
</s>
<s>
The	O
software	O
architecture	O
identified	O
standard	O
interfaces	O
for	O
different	O
modules	O
of	O
the	O
radio	O
:	O
"	O
radio	O
frequency	O
control	O
"	O
to	O
manage	O
the	O
analog	O
parts	O
of	O
the	O
radio	O
,	O
"	O
modem	B-Application
control	O
"	O
managed	O
resources	O
for	O
modulation	B-Application
and	O
demodulation	B-Device
schemes	O
(	O
FM	B-Application
,	O
AM	B-Device
,	O
SSB	B-Device
,	O
QAM	B-Device
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
"	O
waveform	O
processing	O
"	O
modules	O
actually	O
performed	O
the	O
modem	B-Application
functions	O
,	O
"	O
key	O
processing	O
"	O
and	O
"	O
cryptographic	O
processing	O
"	O
managed	O
the	O
cryptographic	O
functions	O
,	O
a	O
"	O
multimedia	O
"	O
module	O
did	O
voice	O
processing	O
,	O
a	O
"	O
human	O
interface	O
"	O
provided	O
local	O
or	O
remote	O
controls	O
,	O
there	O
was	O
a	O
"	O
routing	O
"	O
module	O
for	O
network	O
services	O
,	O
and	O
a	O
"	O
control	O
"	O
module	O
to	O
keep	O
it	O
all	O
straight	O
.	O
</s>
<s>
Instead	O
,	O
they	O
send	O
messages	O
over	O
the	O
PCI	B-Protocol
computer	B-General_Concept
bus	I-General_Concept
to	O
each	O
other	O
with	O
a	O
layered	O
protocol	O
.	O
</s>
<s>
The	O
project	O
was	O
the	O
first	O
known	O
to	O
use	O
FPGAs	B-Architecture
(	O
field	B-Architecture
programmable	I-Architecture
gate	I-Architecture
arrays	I-Architecture
)	O
for	O
digital	O
processing	O
of	O
radio	O
data	O
.	O
</s>
<s>
Today	O
,	O
the	O
time	O
to	O
write	O
a	O
program	O
for	O
an	O
FPGA	B-Architecture
is	O
still	O
significant	O
,	O
but	O
the	O
time	O
to	O
download	O
a	O
stored	O
FPGA	B-Architecture
program	O
is	O
around	O
20	O
milliseconds	O
.	O
</s>
<s>
The	O
SpeakEasy	B-General_Concept
SDR	O
system	O
in	O
the	O
1994	O
uses	O
a	O
Texas	B-Architecture
Instruments	I-Architecture
TMS320C30	I-Architecture
CMOS	B-Device
digital	B-Architecture
signal	I-Architecture
processor	I-Architecture
(	O
DSP	O
)	O
,	O
along	O
with	O
several	O
hundred	O
integrated	O
circuit	O
chips	O
,	O
with	O
the	O
radio	O
filling	O
the	O
back	O
of	O
a	O
truck	O
.	O
</s>
<s>
By	O
the	O
late	O
2000s	O
,	O
the	O
emergence	O
of	O
RF	O
CMOS	B-Device
technology	O
made	O
it	O
practical	O
to	O
scale	O
down	O
an	O
entire	O
SDR	O
system	O
onto	O
a	O
single	O
mixed-signal	O
system-on-a-chip	B-Architecture
,	O
which	O
Broadcom	O
demonstrated	O
with	O
the	O
BCM21551	O
processor	O
in	O
2007	O
.	O
</s>
<s>
The	O
Broadcom	O
BCM21551	O
has	O
practical	O
commercial	O
applications	O
,	O
for	O
use	O
in	O
3G	B-Architecture
mobile	I-Architecture
phones	O
.	O
</s>
<s>
This	O
goal	O
is	O
achieved	O
through	O
the	O
use	O
of	O
SDR	O
systems	O
based	O
on	O
an	O
internationally	O
endorsed	O
open	B-Application
Software	I-Application
Communications	O
Architecture	O
(	O
SCA	O
)	O
.	O
</s>
<s>
This	O
standard	O
uses	O
CORBA	B-Architecture
on	O
POSIX	O
operating	O
systems	O
to	O
coordinate	O
various	O
software	O
modules	O
.	O
</s>
<s>
Still	O
,	O
software	B-Architecture
defined	I-Architecture
radio	I-Architecture
's	O
inherent	O
flexibility	O
can	O
yield	O
substantial	O
benefits	O
in	O
the	O
longer	O
run	O
,	O
once	O
the	O
fixed	O
costs	O
of	O
implementing	O
it	O
have	O
gone	O
down	O
enough	O
to	O
overtake	O
the	O
cost	O
of	O
iterated	O
redesign	O
of	O
purpose	O
built	O
systems	O
.	O
</s>
<s>
A	O
typical	O
amateur	O
software	B-Architecture
radio	I-Architecture
uses	O
a	O
direct	O
conversion	O
receiver	O
.	O
</s>
<s>
Unlike	O
direct	O
conversion	O
receivers	O
of	O
the	O
more	O
distant	O
past	O
,	O
the	O
mixer	O
technologies	O
used	O
are	O
based	O
on	O
the	O
quadrature	O
sampling	O
detector	B-Algorithm
and	O
the	O
quadrature	O
sampling	O
exciter	O
.	O
</s>
<s>
First	O
generation	O
SDRs	O
used	O
a	O
44kHz	O
PC	O
sound	B-Device
card	I-Device
to	O
provide	O
ADC	O
functionality	O
.	O
</s>
<s>
The	O
newer	O
software	B-Architecture
defined	I-Architecture
radios	I-Architecture
use	O
embedded	O
high	O
performance	O
ADCs	O
that	O
provide	O
higher	O
dynamic	O
range	O
and	O
are	O
more	O
resistant	O
to	O
noise	O
and	O
RF	O
interference	O
.	O
</s>
<s>
A	O
fast	O
PC	O
performs	O
the	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
(	O
DSP	O
)	O
operations	O
using	O
software	O
specific	O
for	O
the	O
radio	O
hardware	O
.	O
</s>
<s>
Several	O
software	B-Architecture
radio	I-Architecture
implementations	O
use	O
the	O
open	O
source	O
SDR	O
library	O
DttSP	O
.	O
</s>
<s>
The	O
SDR	O
software	O
performs	O
all	O
of	O
the	O
demodulation	B-Device
,	O
filtering	O
(	O
both	O
radio	O
frequency	O
and	O
audio	O
frequency	O
)	O
,	O
and	O
signal	O
enhancement	O
(	O
equalization	O
and	O
binaural	O
presentation	O
)	O
.	O
</s>
<s>
Uses	O
include	O
every	O
common	O
amateur	O
modulation	B-Application
:	O
morse	O
code	O
,	O
single-sideband	B-Device
modulation	I-Device
,	O
frequency	B-Application
modulation	I-Application
,	O
amplitude	B-Device
modulation	I-Device
,	O
and	O
a	O
variety	O
of	O
digital	O
modes	O
such	O
as	O
radioteletype	O
,	O
slow-scan	O
television	O
,	O
and	O
packet	B-Application
radio	I-Application
.	O
</s>
<s>
Amateurs	O
also	O
experiment	O
with	O
new	O
modulation	B-Application
methods	O
:	O
for	O
instance	O
,	O
the	O
DREAM	O
open-source	B-Application
project	O
decodes	O
the	O
COFDM	B-Protocol
technique	O
used	O
by	O
Digital	O
Radio	O
Mondiale	O
.	O
</s>
<s>
the	O
FiFi	O
SDR	O
for	O
shortwave	O
,	O
or	O
the	O
Quadrus	O
coherent	O
multi-channel	O
SDR	O
receiver	O
for	O
short	O
wave	O
or	O
VHF/UHF	O
in	O
direct	O
digital	O
mode	O
of	O
operation	O
.	O
</s>
<s>
Eric	O
Fry	O
discovered	O
that	O
some	O
common	O
low-cost	O
DVB-T	O
USB	B-Protocol
dongles	O
with	O
the	O
Realtek	O
RTL2832U	O
controller	O
and	O
tuner	O
,	O
e.g.	O
</s>
<s>
This	O
project	O
is	O
being	O
maintained	O
at	O
Osmocom	B-Application
.	O
</s>
<s>
The	O
HPSDR	B-Device
(	O
High	O
Performance	O
Software	B-Architecture
Defined	I-Architecture
Radio	I-Architecture
)	O
project	O
uses	O
a	O
16-bit	O
analog-to-digital	O
converter	O
that	O
provides	O
performance	O
over	O
the	O
range	O
0	O
to	O
comparable	O
to	O
that	O
of	O
a	O
conventional	O
analogue	O
HF	B-Algorithm
radio	I-Algorithm
.	O
</s>
<s>
The	O
receiver	O
will	O
also	O
operate	O
in	O
the	O
VHF	B-Algorithm
and	O
UHF	O
range	O
using	O
either	O
mixer	O
image	O
or	O
alias	O
responses	O
.	O
</s>
<s>
Interface	O
to	O
a	O
PC	O
is	O
provided	O
by	O
a	O
USB	B-Protocol
2.0	O
interface	O
,	O
although	O
Ethernet	O
could	O
be	O
used	O
as	O
well	O
.	O
</s>
<s>
The	O
project	O
is	O
modular	O
and	O
comprises	O
a	O
backplane	B-Architecture
onto	O
which	O
other	O
boards	O
plug	O
in	O
.	O
</s>
<s>
An	O
exciter	O
provides	O
of	O
RF	O
over	O
the	O
same	O
range	O
or	O
into	O
the	O
VHF	B-Algorithm
and	O
UHF	O
range	O
using	O
image	O
or	O
alias	O
outputs	O
.	O
</s>
