Comtech EF Data CDM-625 Manual de usuario descargar pdf (Pagina 2)

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.

Figure 1

Figure 2

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

As DoubleTalk Carrier-in-Carrier allows equivalent spectral efficiency using a lower order modulation and/or code rate, it can reduce the

power required to close the link thereby reducing CAPEX by allowing a smaller BUC/Amplifier 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-ARY

modulation approaches the bandwidth efficiency of 256-ARY (8 bps/Hz).

When combined with VersaFEC-2 or VersaFEC and optimized transmit filter rolloff, 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 Registered Trademark of Raytheon Applied Signal Technology

VersaFEC



is a Registered Trademark of Comtech EF Data

Carrier-in-Carrier Automatic Power Control (CnC-APC)

The patent-pending Carrier-in-Carrier Automatic Power Control (CnC-APC) mechanism enables modems on both sides of a CnC link to

automatically measure and compensate for rain fade while maintaining the Total Composite Power. In addition to automatically

compensating for rain fade, CnC-APC also enables the modems to share link margin, i.e. a modem in clear sky conditions can

effectively transfer excess link margin to a distant end modem experiencing fade, thereby further enhancing overall availability.

VersaFEC-2 High Performance LDPC Forward Error Correction

CDM-625A offers a new high performance LDPC FEC specifically design to optimize performance at low and mid-tier sysmbol rates.

VersaFEC-2 long-block provides 38 ModCods (BPSK to 32-ARY) with performance generally better than DVB-S2 at significantly lower

latency and short-block provides 36 ModCods (BPSK to 32-ARY) with higher coding gain than first generation VersaFEC and similar

latency. All higher order constellations are quasi-circular for optimal peak-to-average performance. Both CCM and ACM operation is

support for long block and short block.

VersaFEC Forward Error Correction

CDM-625A offers VersaFEC, a patent-pending system of high-performance LDPC codes designed to provide maximum coding gain

while minimizing latency. VersaFEC is designed to support ACM and CCM mode of operation

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

Adaptive Coding & Modulation (ACM)

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

can provide significant increase in throughput as well as availability. ACM converts the fade margin into increased capacity making it

possible to more than double the throughput for Ku-band operation. Even under deep fade, ACM may be able to maintain the link at the

lower MODCOD thereby increasing availability. It is tightly integrated with packet processor QoS which allows higher priority, mission

critical traffic to be maintained even during fade.

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

CDM-625A 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 8PSK.

Dual Band Capability

CDM-625A supports 70/140 MHz and extended L-Band (950 – 2250 MHz) capability in the same unit with independently selectable

transmit and receive IF. This simplifies sparing and stocking in networks requiring 70/140 MHz and L-Band units.

4-Port Managed Ethernet Switch with VLAN & QoS

CDM-625A incorporates a 4-port 10/100Base-T managed Ethernet switch with VLAN capability and priority-based Quality of Service.

Access (Native) Mode and Trunk Mode are supported. Traffic can be prioritized using port-based priority or VLAN priority. The modem

supports jumbo frames with maximum Ethernet frame size of 2048 bytes.

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