Comtech EF Data LPOD Manual do Utilizador descarregar pdf (Página 2)

Adaptive Coding & Modulation (ACM)

Satellite users have traditionally relied on worst case link margin to overcome rain fade which leads to significant inefficiencies. ACM

converts the fade margin into increased throughput – gain of 100% or more is possible. The CDM-625 with VersaFEC was specifically

architected to support ACM for IP/Ethernet traffic. ACM maximizes throughput under all conditions – rain fade, inclined orbit satellite

operation, antenna mis-pointing, noise, interference and other impairments.

VersaFEC ACM can provide almost 85% reduction in latency compared to DVB-S2 (short block).

ACM can also be used with DoubleTalk Carrier-in-Carrier.

Low Density Parity Check Codes (LDPC) & Turbo Product Codes (TPC)

CDM-625 offers an integrated LDPC and 2

Generation TPC codec. LDPC is an advanced Forward Error Correction technique capable

of providing performance much closer to Shannon limit. The current LDPC implementation can provide 0.7 to 1.2 dB additional coding

gain compared to an equivalent TPC code.

In order to take full advantage of the increased coding gain provided by LDPC, Comtech EF Data has developed a patented 8-QAM

modulation that allows for acquisition and tracking at much lower Eb/No compared to 8-PSK.

Figure 1 shows the typical full-duplex satellite link, where the two carriers are adjacent to each other.

Figure 2 shows the typical DoubleTalk Carrier-in-Carrier operation, where the two carriers are overlapping, thus sharing the same

spectrum.

When observed on a spectrum analyzer, only the Composite is visible. Carrier 1 and Carrier 2 are shown in Figure 2 for reference only.

DoubleTalk Carrier-in-Carrier is complementary to all advances in modem technology, including advanced FEC and modulation

techniques. As these technologies approach theoretical limits of power and bandwidth efficiencies, DoubleTalk Carrier-in-Carrier utilizing

advanced signal processing techniques provides a new dimension in bandwidth efficiency.

As DoubleTalk Carrier-in-Carrier allows equivalent spectral efficiency using a lower order modulation and/or FEC Code, it can

simultaneously reduce CAPEX by allowing a smaller BUC/HPA and/or antenna. Alternatively, DoubleTalk Carrier-in-Carrier can be used

to achieve very high spectral efficiencies E.g., DoubleTalk Carrier-in-Carrier when used with 16-QAM approaches the bandwidth

efficiency of 256-QAM (8 bps/Hz).

When combined with VersaFEC or LDPC/TPC, it can provide unprecedented savings in transponder bandwidth and power utilization.

This allows for its successful deployment in bandwidth-limited and power-limited scenarios, as well as reduction in earth station

BUC/HPA power requirements.

Carrier-in-Carrier

is a Registered Trademark of Comtech EF Data

DoubleTalk

is a Trademark of Applied Signal Technology, Inc.

VersaFEC



is a Registered Trademark of Comtech AHA Corp.

VersaFEC Forward Error Correction

CDM-625 is the first modem to offer VersaFEC, a patented system of high performance short-block low-latency LDPC codes designed to

support latency-sensitive applications, such as cellular backhaul over satellite. VersaFEC provides excellent coding gain with lowest

possible latency. VersaFEC’s Eb/No performance is similar to that of DVB-S2 (short block) or LDPC (16k block) with 70-90% lower

latency. Compared to TPC, VersaFEC can provide coding gain of 1.0 dB or more.

The new Ultra Low Latency (ULL) codes provide even lower latency compared to standard VersaFEC codes.

Figure 1 Figure 2

1 2 3 4 5 6

Sem comentários

Comtech EF Data LPOD Manual do Utilizador Página 2