Table of Contents
Advertisement
DMD50 Universal Satellite Modem
3.14 DoubleTalk Carrier-in-Carrier Option
B E F OR E AT T E MP T ING T O C OMMIS S ION A S AT E L L IT E L INK US ING C AR R IE R -
IN-C AR R IE R , T HE US E R
F OR NOR MAL OP E R AT ION. ONL Y WHE N T HIS HAS B E E N DONE – AND AL L
S YS T E M IS S UE S (E .G ., ANT E NNA-P OINT ING , C AB L ING , T E R R E S T R IAL
INT E R FE R E NC E , S AT E L L IT E INT E R FE R E NC E , E T C .) HAV E B E E N R E S OL VE D –
S HOUL D T HE US E R AT T E MP T T HE US E OF C AR R IE R -IN-C AR R IE R .
Space segment costs are typically the most significant operating expense for any satellite-based
service, having a direct impact on the viability and profitability of the service. For a satellite
transponder that has finite resources in terms of bandwidth and power, the leasing costs are
determined by bandwidth and power used. Therefore, a satellite circuit should be designed for
optimal utilization to use a similar share of transponder bandwidth and power.
The traditional approach to balancing a satellite circuit – once the satellite and earth station
parameters are fixed – involves trade-off between modulation and coding. A lower order
modulation requires less transponder power while using more bandwidth; conversely, higher order
modulation reduces required bandwidth, albeit at a significant increase in power.
Comtech EF Data has added a new dimension to satellite communication optimization: DoubleTalk
Carrier-in-Carrier.
3.14.1
What is DoubleTalk Carrier-in-Carrier?
The Radyne DMD50 DoubleTalk Carrier-in-Carrier option utilizes a patented (US 6,859,641)
signal processing algorithm developed by Applied Signal Technology, Inc. that allows both the
forward and reverse carriers of a full duplex link to share the same segment of transponder
bandwidth, using patented "Adaptive Cancellation." Applied Signal uses the term DoubleTalk™,
and Comtech EF Data refers to it as DoubleTalk Carrier-in-Carrier (CnC).
CnC was first introduced in Comtech EF Data products in the CDM-Qx Satellite Modem and,
more recently, in the CLO-10 Link Optimizer.
The implementation of DoubleTalk Carrier-in-Carrier in the Radyne DMD50 has been further
refined, and some of the limitations that existed in the CDM-Qx implementation have been
overcome.
This innovative technology provides a significant improvement in bandwidth and power
utilization, beyond what is possible with FEC and modulation alone, allowing users to achieve
unprecedented savings. When combined with advanced modulation and FEC, it allows for multi-
dimensional optimization:
•
Reduced operating expense (OPEX) – e.g., Occupied Bandwidth & Transponder Power;
•
Reduced capital expenditure (CAPEX) – e.g., Block Up Converter/High-Power Amplifier
(BUC/HPA) size and/or antenna size;
•
Increased throughput without using additional transponder resources;
•
Increased link availability (margin) without using additional transponder resources;
•
A combination of any of the above to meet different objectives.
Summary: When carriers share common bandwidth, up to 50% savings in transponder
utilization is possible.
MN-DMD50 Revision 4
MUST
E NS UR E T HAT T HE L INK IS R OB US T E NOUG H
Theory of Operation
3–20
Advertisement
Table of Contents
