<s>
Incremental	B-Device
frequency	I-Device
keying	I-Device
,	O
also	O
known	O
as	O
IFK	O
or	O
IFK+	B-Device
,	O
is	O
a	O
modified	O
type	O
of	O
MFSK	B-Device
modulation	O
where	O
the	O
data	O
to	O
be	O
transmitted	O
is	O
represented	O
by	O
the	O
difference	O
in	O
frequency	O
between	O
the	O
previously	O
received	O
tone	O
and	O
the	O
currently	O
received	O
tone	O
.	O
</s>
<s>
This	O
modulation	O
produces	O
a	O
signal	O
which	O
is	O
much	O
more	O
tolerant	O
of	O
receiver	O
mis-tunings	O
and	O
frequency	O
drift	O
than	O
MFSK	B-Device
modulation	O
.	O
</s>
<s>
Additionally	O
,	O
IFK	O
modulation	O
is	O
more	O
resistant	O
to	O
multipath	O
interference	O
and	O
intersymbol	O
interference	O
caused	O
by	O
multipath	O
propagation	O
than	O
traditional	O
MFSK	B-Device
.	O
</s>
<s>
This	O
combination	O
of	O
features	O
makes	O
IFK	O
modulation	O
well	O
suited	O
for	O
high	B-Algorithm
frequency	I-Algorithm
communications	O
.	O
</s>
