<s>
DVB-RCT	B-Device
(	O
Digital	O
Video	O
Broadcasting	O
-	O
Return	O
Channel	O
Terrestrial	O
)	O
,	O
provides	O
a	O
method	O
by	O
which	O
the	O
DVB-T	O
(	O
and	O
in	O
theory	O
DVB-T2	B-Protocol
but	O
DVB-T2	B-Protocol
probably	O
trialled	O
first	O
about	O
5	O
years	O
after	O
last	O
DVB-RCT	B-Device
field	O
trial	O
)	O
platform	O
can	O
become	O
a	O
bi-directional	O
,	O
asymmetric	O
,	O
data	O
path	O
using	O
wireless	O
between	O
broadcasters	O
and	O
customers	O
.	O
</s>
<s>
DVB-T	O
when	O
completed	O
with	O
DVB-RCT	B-Device
can	O
be	O
used	O
not	O
only	O
for	O
Interactive	O
TV	O
(	O
voting	O
,	O
quiz	O
,	O
etc	O
.	O
</s>
<s>
Various	O
degrees	O
of	O
interactivity	O
could	O
be	O
offered	O
,	O
without	O
implying	O
any	O
return	O
channel	O
back	O
from	O
the	O
user	O
to	O
the	O
service	O
provider	O
:	O
data	O
carrousel	O
or	O
Electronic	O
Programs	O
Guides	O
(	O
EPG	B-Device
)	O
are	O
examples	O
of	O
such	O
enhanced	O
TV	O
services	O
which	O
make	O
use	O
of	O
“	O
Local	O
Interactivity	O
”	O
,	O
without	O
any	O
return	O
path	O
from	O
customer	O
to	O
provider	O
.	O
</s>
<s>
To	O
implement	O
new	O
interactive	O
services	O
having	O
a	O
closely	O
coupled	O
and	O
real-time	O
relationship	O
with	O
the	O
TV	O
programs	O
(	O
e.g.	O
,	O
interactive	O
advertising	O
,	O
tele-voting	O
,	O
tele-quiz	O
)	O
,	O
a	O
low	O
latency	O
return	O
channel	O
technology	O
is	O
mandatory	O
,	O
and	O
this	O
is	O
the	O
goal	O
of	O
the	O
DVB-RCT	B-Device
.	O
</s>
<s>
By	O
2006	O
the	O
main	O
developer	O
of	O
DVB-RCT	B-Device
Runcom	B-Device
had	O
abandoned	O
it	O
(	O
no	O
deployments	O
due	O
to	O
Mobile	O
Phone	O
Penetration	O
)	O
and	O
switched	O
the	O
expertise	O
to	O
portable	O
WiMax	O
Modems	O
and	O
Infrastructure	O
,	O
later	O
adding	O
LTE	O
.	O
</s>
<s>
Many	O
people	O
mistakenly	O
think	O
DVB-RCT	B-Device
would	O
have	O
allowed	O
Viewers	O
to	O
browse	O
the	O
Internet	O
.	O
</s>
<s>
Partially	O
the	O
mistaken	O
Internet	O
belief	O
was	O
due	O
to	O
the	O
"	O
It	O
's	O
TV	O
"	O
Proposal	O
in	O
Ireland	O
in	O
2000/2001	O
and	O
RTE-NL	O
(	O
now	O
2RN	O
)	O
1999	O
field	O
trials	O
assisted	O
by	O
Runcom	B-Device
.	O
</s>
<s>
The	O
Cable	O
version	O
DVB-RCC	O
never	O
succeeded	O
in	O
competing	O
against	O
Cablelabs	O
DOCSIS	B-Protocol
though	O
Internet	O
by	O
Satellite	O
did	O
use	O
DVB-RCS	O
,	O
but	O
Ka-Sat	O
and	O
others	O
since	O
2005	O
are	O
deploying	O
Satellite	O
versions	O
of	O
DOCSIS	B-Protocol
.	O
</s>
<s>
T-commerce	B-Application
clearly	O
requires	O
a	O
Return	O
Path	O
from	O
the	O
home	O
back	O
to	O
the	O
Digital	B-Application
TV	I-Application
Service	O
Provider	O
.	O
</s>
<s>
DVB-RCT	B-Device
is	O
the	O
response	O
that	O
offers	O
a	O
wireless	O
interaction	O
channel	O
for	O
Interactive	O
Digital	B-Application
Terrestrial	I-Application
Television	I-Application
,	O
usable	O
in	O
the	O
congested	O
UHF/VHF	O
bands	O
:	O
</s>
<s>
DVB-RCT	B-Device
is	O
a	O
spectrum	O
efficient	O
,	O
low	O
cost	O
,	O
powerful	O
and	O
flexible	O
Multiple	O
Access	O
OFDM	B-Protocol
system	O
.	O
</s>
<s>
DVB-RCT	B-Device
can	O
serve	O
large	O
cells	O
,	O
up	O
to	O
65km	O
radius	O
,	O
providing	O
a	O
typical	O
bitrate	O
capacity	O
of	O
several	O
kilobits	O
per	O
second	O
,	O
for	O
each	O
TV	O
viewer	O
,	O
even	O
at	O
the	O
edge	O
of	O
the	O
coverage	O
area	O
.	O
</s>
<s>
Typically	O
,	O
these	O
large	O
cells	O
closely	O
match	O
the	O
downstream	O
coverage	O
area	O
of	O
the	O
Digital	B-Application
Television	I-Application
broadcast	O
signal	O
.	O
</s>
<s>
DVB-RCT	B-Device
can	O
handle	O
very	O
large	O
peaks	O
in	O
traffic	O
,	O
as	O
it	O
has	O
been	O
specifically	O
designed	O
to	O
process	O
up	O
to	O
20,000	O
short	O
interactions	O
per	O
second	O
in	O
Tele-polling	O
Mode	O
,	O
this	O
in	O
each	O
sector	O
of	O
each	O
cell	O
.	O
</s>
<s>
DVB-RCT	B-Device
can	O
be	O
employed	O
with	O
smaller	O
cells	O
,	O
to	O
constitute	O
denser	O
networks	O
of	O
up	O
to	O
3.5km	O
radius	O
cells	O
,	O
providing	O
to	O
the	O
user	O
a	O
bitrate	O
capacity	O
of	O
up	O
to	O
several	O
Megabits	O
per	O
second	O
.	O
</s>
<s>
DVB-RCT	B-Device
does	O
not	O
require	O
access	O
to	O
spectrum	O
on	O
a	O
primary	O
basis	O
;	O
the	O
system	O
has	O
been	O
designed	O
to	O
use	O
any	O
gaps	O
or	O
under-utilised	O
spectrum	O
anywhere	O
in	O
Bands	O
III	O
,	O
IV	O
and	O
V	O
without	O
interfering	O
with	O
the	O
primary	O
analogue	O
and	O
digital	O
broadcasting	O
services	O
.	O
</s>
<s>
DVB-RCT	B-Device
is	O
able	O
to	O
serve	O
portable	O
DVB-T	O
devices	O
.	O
</s>
<s>
DVB-RCT	B-Device
can	O
be	O
used	O
with	O
DVB-T	O
systems	O
using	O
6	O
,	O
7	O
or	O
8MHz	O
channels	O
.	O
</s>
<s>
DVB-RCT	B-Device
does	O
not	O
require	O
more	O
than	O
0.5W	O
rms	B-General_Concept
power	O
transmission	O
from	O
the	O
User	O
Terminal	O
or	O
Set	O
Top	O
Box	O
to	O
the	O
base	O
station	O
.	O
</s>
<s>
From	O
a	O
pure	O
technical	O
point	O
of	O
view	O
,	O
DVB-RCT	B-Device
is	O
built	O
around	O
technologies	O
for	O
digital	O
transmission	O
and	O
information	O
theory	O
;	O
in	O
addition	O
to	O
the	O
benefits	O
of	O
first	O
generation	O
OFDM	B-Protocol
technology	O
for	O
broadband	O
portable	O
and	O
mobile	O
services	O
,	O
Multiple	O
Access	O
OFDM	B-Protocol
included	O
in	O
the	O
DVB-RCT	B-Device
specification	O
provides	O
the	O
following	O
characteristics	O
:	O
</s>
<s>
As	O
a	O
result	O
,	O
some	O
Modulation	O
Modes	O
of	O
DVB-RCT	B-Device
require	O
a	O
C/N	O
of	O
only	O
4dB	O
.	O
</s>
<s>
This	O
ensures	O
that	O
the	O
coverage	O
area	O
of	O
the	O
Multiple	O
Access	O
OFDM	B-Protocol
signals	O
can	O
be	O
designed	O
to	O
closely	O
match	O
the	O
service	O
area	O
of	O
Digital	B-Application
Terrestrial	I-Application
Television	I-Application
broadcast	O
,	O
thus	O
reducing	O
the	O
need	O
for	O
new	O
installations	O
.	O
</s>
<s>
DVB-RCT	B-Device
can	O
use	O
Channel	O
50	O
in	O
the	O
adjacent	O
Coverage	O
Area	O
B	O
at	O
2MHz	O
above	O
the	O
Vision	O
Carrier	O
,	O
where	O
the	O
interfering	O
energy	O
is	O
30dB+	O
down	O
relative	O
to	O
the	O
vision	O
carrier	O
.	O
</s>
<s>
Dynamically	O
Assignable	O
Adaptive	O
Modulation	O
(	O
DAAM	O
)	O
:	O
DVB-RCT	B-Device
supports	O
within	O
the	O
same	O
cell	O
the	O
simultaneous	O
use	O
of	O
different	O
types	O
of	O
modulation	O
from	O
4QAM	B-Device
(	O
1/2	O
rate	O
)	O
to	O
64QAM	B-Device
(	O
3/4	O
rate	O
)	O
.	O
</s>
<s>
Power	O
Ranging	O
:	O
DVB-RCT	B-Device
uses	O
a	O
power	O
ranging	O
system	O
,	O
similar	O
to	O
that	O
used	O
in	O
Cellular	O
phones	O
,	O
to	O
ensure	O
that	O
the	O
lowest	O
power	O
is	O
used	O
by	O
the	O
Interactive	O
Terminals	O
at	O
all	O
times	O
.	O
</s>
<s>
Downstream	O
Channel	O
(	O
DS	O
)	O
OFDM	B-Protocol
,	O
ETS	O
300	O
744	O
(	O
DVB-T	O
)	O
compliant	O
Return	O
Interaction	O
Channel	O
Multiple	O
Access	O
OFDM	B-Protocol
(	O
MA-OFDM	O
)	O
Forward	O
Interaction	O
Channel	O
(	O
US	O
)	O
Embedded	O
in	O
DS	O
,	O
compliant	O
with	O
ETS	O
300	O
744	O
(	O
DVB-T	O
)	O
OFDM	B-Protocol
Carrier	O
set	O
1024	O
(	O
1K	O
)	O
,	O
2048	O
(	O
2K	O
)	O
OFDM	B-Protocol
Carrier	O
spacing	O
(	O
CS	O
)	O
~	O
1K	O
,	O
~	O
2K	O
,	O
~	O
4K	O
Transmission	O
modes	O
6	O
modes	O
(	O
as	O
combination	O
of	O
3	O
CS	O
and	O
2	O
Carrier	O
set	O
)	O
Carrier	O
shaping	O
Nyquist	O
,	O
Rectangular	O
Guard	O
Interval	O
1/8	O
,	O
1/16	O
,	O
1/32	O
(	O
for	O
Rectangular	O
shaping	O
only	O
)	O
Transmission	O
Frames	O
TF1	O
,	O
TF2	O
Data	O
randomization	O
PRBS	O
with	O
polynomial	O
:	O
1+X14+x15	O
Modulation	O
QPSK	O
,	O
16QAM	B-Device
,	O
64QAM	B-Device
Useful	O
data	O
payload	O
per	O
burst	O
18	O
,	O
27	O
,	O
36	O
,	O
54	O
,	O
81	O
bytes	O
(	O
1	O
burst	O
=	O
144	O
modul	O
.	O
</s>
