WHY DVB-S2/ACM? - Satellite Evolution Group

WHY DVB­S2/ACM
A C-COM White Paper
www.c-comsat.com
By Jonathan Lee,
Bilal Awada,
Leslie Klein
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Compared with terrestrial wireless, such as microwave and fibre, satellite transmission capacity is
largely limited by two factors, frequency spectrum and power. For example a full Ku‐band
frequency spectrum for a satellite is only about 500MHz whereas fibre transmission has almost
unlimited useable frequency spectrum; satellites cannot compete in terms of capacity. Another
major limitation of the satellite technology is that its power is fully dependent on on‐board fuel or
solar power.
To increase satellite transmission capacity, improvements related to more efficient use of frequency
spectrum and power are needed; however, there is a dilemma. We all know that the use of higher
modulation can greatly improve the efficiency of utilization of frequency spectrum. For example a
54 MHz Ku‐band transponder using 32APSK modulation can produce over 200 Mbps bandwidth,
compared with 48 Mbps using QPSK modulation. However, with higher modulation, more power is
required. This is why high modulation rates are possible only with earth stations using large
amplifiers capable of delivering the required power.
Figure 1: Required C/N versus spectrum efficiency on the AWGN channel (ideal demodulation), where C/N refers
to the average power 1
1 EBU TECHNICAL REVIEW – October 2004, A. Morello and V. Mignone: DVB‐S2— ready for lift off
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In reality, there are two other factors that affect modulation and power used in satellite
transmission: weather conditions and EIRP of location. When the link budget is calculated, it is
based on the worst case scenario, which means that under heavy rain conditions (as specified by
ITU’s classification of rain fade zone), the satellite link must continue to function normally. To make
sure the link is always on, the lowest possible modulation and highest possible power will be used.
However, in reality, this kind of situation only takes place on very rare occasions. For example,
according to Environment Canada’s statistics, heavy rain in Ottawa will take place on average only 5
days a year. If the link budget is calculated based on this heavy rain situation, this will translate to a
tremendous waste of energy and bandwidth for 360 days a year. On those 360 days, higher
modulation and much less power could be used to generate more bandwidth.
Rainfall
Days
>= 0.2 mm 118.5
>= 5 mm 45
>= 10 mm 23.9
>= 25 mm 5
Table 1: Annual Average Rainfall Days in Ottawa 1971‐2000 2
Another factor is satellite power distribution or EIRP by location,
which is different from one place to another. For example, the area
that is covered by the 44 dB contour should be able to use lower
level modulation in order to make sure it can continuously receive
good signal levels. This is based on the assumption that the rest of
the conditions remain the same as those covered by the 48 dB
contour, such as the size of antenna and weather. However, if lower
modulation is implemented in all areas, then those in the 48 dB
contour will be short changed, as they are supposed to be able take
advantage of higher modulation to save frequency spectrum or
power.
Figure 2: Sample of Satellite Footprint
The indication here is that if modulation and power levels can be adjusted accordingly, this will
greatly improve the efficiency of utilization of satellite power and frequency spectrum. This was
2 Source: Environment Canada Website
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not possible in the past. For example, under the DVB regime, the carrier comes from the hub, which
is called the Forward link. Forward link is a large carrier with one fixed modulation and coding
setup, no matter what the receiver’s EIRP and receiver’s weather conditions may be at its location.
This was the case for most satellite links in the past, where modulation and coding changes were
accomplished through a manual operation.
Recent improvements in the DVB‐S2
technology have enabled this
important change to be
accomplished automatically and ondemand;
this process is called
Adaptive Coding and Modulation
(ACM).
Figure 3 to the right is an illustration
of how ACM enables the use of
various modulations and coding
combinations over different EIRP
areas and weather conditions.
Compared with the lower EIRP area,
the high EIRP area has been
implemented at higher level
modulation and more powerful
coding combination to achieve
high throughput.
Figure 3: ACM enables each remote to achieve maximum data
throughput by utilizing the most efficient coding and modulation scheme
dependent upon the location within the satellite contour, antenna size,
and clear sky conditions versus rain fade.
3 www.satellite-evolution.com | November/December 2007, Jonathan Barter, Planning for DVB-S2/ACM
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Figure 4: Capacity Comparison of DVB‐S2 ACM over DVB‐S2 CCM and DVB‐S
/Source: www.hughes.com
Such advancements made possible through the new ACM technology are very significant. They
represent over 50%‐80% bandwidth improvement over the traditional DVB standard.
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C‐COM’s next generation iNetVu ® 7000 Controllers already support the latest DVB‐S2/ACM
modulation technique. This capability will allow C‐COM’s auto deploying antenna systems to work
with the most advanced satellite modems and two‐way services which are being deployed
worldwide using the DVB‐S2/ACM technology.
The major benefit of supporting DVB‐S2/ACM is its international acceptance and compliance by
DVB‐S2/ACM satellite remote equipment vendors. Having this feature available in the 7000
controller makes the iNetVu ® Comm‐On‐The‐Pause auto deploying technology one of the fastest at
acquiring satellite today. Controllers that do not have such capability but are required to work on
DVB‐S2/ACM satellites not having any DVB‐S1 carriers available on them, would have to rely on
modem integration, or a combination of either modem and beacon, or modem and reference
satellite with DVB‐S1 carrier, in order to complete the acquisition. This is a longer process, which
can usually add an additional 5 to 10 minutes to the typical DVB‐S1 based acquisition process. In
addition, this can be an expensive affair if additional hardware has to be purchased to make this
possible (like beacon receiver).
Figure 5: iNetVu ® 7000 Auto‐pointing Controller
By directly zooming
onto the S2/ACM carrier
on the same service satellite, the iNetVu ® systems can find DVB‐S2/ACM satellites in less than 2
minutes.
With this new capability the iNetVu ® 7000 controller leads the way for a new generation of DVB‐
S2/ACM capable controllers. Its early adaptation has positioned C‐COM far ahead of its competition
and in sync with the new generation of modems and satellites supporting this latest advancement
in satellite technology.
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