<s>
Delay	B-Algorithm
Doppler	I-Algorithm
coordinates	O
are	O
coordinates	O
typically	O
used	O
in	O
a	O
radar	B-Application
technology-inspired	O
approach	O
to	O
measurement	O
.	O
</s>
<s>
When	O
used	O
in	O
wireless	O
communication	O
,	O
the	O
Delay	B-Algorithm
Doppler	I-Algorithm
domain	O
mirrors	O
the	O
geometry	O
of	O
the	O
reflectors	O
comprising	O
the	O
wireless	O
channel	O
,	O
which	O
changes	O
far	O
more	O
slowly	O
than	O
the	O
phase	O
changes	O
experienced	O
in	O
the	O
rapidly	O
varying	O
time-frequency	O
domain	O
.	O
</s>
<s>
In	O
radar	B-Application
theory	O
,	O
the	O
Delay	B-Algorithm
Doppler	I-Algorithm
variables	O
are	O
used	O
to	O
represent	O
and	O
separate	O
moving	O
targets	O
through	O
their	O
delay	O
(	O
range	O
)	O
and	O
Doppler	O
(	O
velocity	O
)	O
characteristics	O
.	O
</s>
<s>
Delay	B-Algorithm
Doppler	I-Algorithm
variables	O
can	O
also	O
represent	O
information-carrying	O
signals	O
.	O
</s>
<s>
The	O
Delay	B-Algorithm
Doppler	I-Algorithm
signal	O
representation	O
,	O
sometimes	O
referred	O
to	O
as	O
the	O
lattice	O
representation	O
of	O
the	O
Heisenberg	O
group	O
,	O
is	O
in	O
a	O
sense	O
a	O
hybrid	O
of	O
the	O
traditional	O
time	O
and	O
frequency	O
representations	O
.	O
</s>
<s>
In	O
contrast	O
,	O
in	O
the	O
Delay	B-Algorithm
Doppler	I-Algorithm
representation	O
,	O
one	O
can	O
construct	O
localized	O
pulses	O
which	O
behave	O
as	O
if	O
they	O
are	O
simultaneously	O
localized	O
both	O
in	O
time	O
and	O
in	O
frequency	O
.	O
</s>
<s>
Such	O
delay-Doppler	O
pulses	O
can	O
be	O
used	O
effectively	O
for	O
Delay	B-Algorithm
Doppler	I-Algorithm
Radar	B-Application
multi-target	O
detection	O
and	O
wireless	O
communication	O
.	O
</s>
<s>
This	O
immunity	O
amounts	O
to	O
slowing	O
down	O
the	O
channel	O
aging	O
process	O
,	O
which	O
has	O
implications	O
for	O
various	O
network	O
functions	O
that	O
require	O
extended	O
latency	O
,	O
such	O
as	O
MU-MIMO[4][9]	O
and	O
CRAN	O
.	O
</s>
<s>
When	O
the	O
delay-Doppler	O
channel	O
representation	O
is	O
appropriately	O
incorporated	O
in	O
MU-MIMO	B-Architecture
architecture	O
,	O
it	O
enables	O
non-trivial	O
network	O
functionality	O
,	O
such	O
as	O
intelligent	O
user	O
pairings	O
and	O
SNR	O
predictions	O
.	O
</s>
<s>
These	O
functionalities	O
result	O
in	O
improved	O
spectral	O
utilization	O
and	O
performance	O
for	O
any	O
waveform	O
,	O
thus	O
constituting	O
a	O
universal	O
technology	O
of	O
spectrum	O
multiplying	O
for	O
mobile	O
networks	O
that	O
can	O
operate	O
in	O
both	O
FDD	B-Protocol
and	O
TDD	O
and	O
with	O
any	O
generation	O
network	O
.	O
</s>
<s>
Delay	B-Algorithm
Doppler	I-Algorithm
channel	O
representation	O
utilizes	O
existing	O
uplink	O
reference	O
signals	O
such	O
as	O
SRS	O
&	O
DMRS	O
,	O
along	O
with	O
periodic	O
DL	O
CQI	O
reports	O
to	O
extract	O
robust	O
geometric	O
information	O
and	O
to	O
compute	O
downlink	O
SINR	O
and	O
predict	O
downlink	O
CSI	O
—	O
even	O
on	O
paired	O
FDD	B-Protocol
spectrum	O
separated	O
by	O
as	O
much	O
as	O
400MHz	O
.	O
</s>
<s>
Delay	B-Algorithm
Doppler	I-Algorithm
processing	O
techniques	O
are	O
used	O
to	O
extract	O
robust	O
geometric	O
information	O
about	O
the	O
link	O
to	O
every	O
user	O
,	O
yielding	O
accurate	O
DL	O
SINR	O
estimation	O
as	O
well	O
as	O
precise	O
DL	O
CSI	O
(	O
extrapolated	O
in	O
frequency	O
and	O
predicted	O
in	O
time	O
)	O
.	O
</s>
<s>
Due	O
to	O
its	O
geometric	O
nature	O
,	O
the	O
slow	O
changing	O
Delay	B-Algorithm
Doppler	I-Algorithm
channel	O
representation	O
opens	O
up	O
the	O
door	O
for	O
functionality	O
disaggregation	O
.	O
</s>
<s>
When	O
wireless	O
channels	O
are	O
represented	O
and	O
processed	O
in	O
the	O
delay-Doppler	O
domain	O
,	O
4G	B-Architecture
and	O
5G	O
networks	O
can	O
effectively	O
utilize	O
MU-MIMO	B-Architecture
in	O
both	O
TDD	O
and	O
FDD	B-Protocol
,	O
and	O
the	O
channel	O
measurements	O
become	O
more	O
robust	O
to	O
latency	O
(	O
cloud	O
)	O
,	O
channel	O
impairments	O
and	O
high	O
mobility	O
.	O
</s>
