Comtech EF Data CDM-625 Advanced Satellite Modem

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 efficiency, DoubleTalk Carrier-in-Carrier utilizing advanced signal processing techniques provides a new dimension in bandwidth and power efficiency.

DoubleTalk Carrier-in-Carrier allows satellite users to achieve spectral efficiencies (i.e. bps/Hz) that cannot be achieved with traditional links. E.g., DoubleTalk Carrier-in-Carrier when used with 16-QAM approaches the bandwidth efficiency of 256-QAM (8bps/Hz).

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.

DoubleTalk Carrier-in-Carrier can be used to save transponder bandwidth and/or transponder power thereby allowing successful deployment in bandwidth-limited as well as power-limited scenarios. The following example illustrates the typical process for implementing DoubleTalk Carrier-in-Carrier in a power-limited scenario:

The conventional link is using 8-PSK, TPC 3/4:

Switching to LDPC and using a lower code rate – say 8-QAM, LDPC 2/3 increases the total transponder bandwidth, while reducing the total transponder power:

Now using DoubleTalk Carrier-in-Carrier, the second carrier can be placed over the first carrier – thereby significantly reducing the total transponder bandwidth and total transponder power when compared to the original side-by-side 8PSK, TPC 3/4 carriers:

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

CDM-625 offers an integrated LDPC and 2nd Generation TPC codec. LDPC is an advanced Forward Error Correction technique capable of providing performance much closer to Shannon limit compared to any other FEC technique. The current implementation is generally 0.7 to 1.2 dB better than an equivalent TPC code.

When combined with DoubleTalk Carrier-in-Carrier, LDPC/TPC provide unprecedented savings in transponder bandwidth and power utilization as well as Earth Station BUC/HPA size.

In order to take full advantage of the increased coding gain provided by LDPC, Comtech EF Data has developed an 8-QAM modulation that allows for acquisition and tracking at much lower Eb/No compared to 8-PSK.

70/140 MHz AND L-BAND CAPABILITY

CDM-625 supports 70/140 MHz and L-Band 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.

CDM-600/CDM-600L EMULATION MODE

CDM-625 can be placed in CDM-600 or CDM-600L emulation mode. This allows for easy integration into an existing CDM- 600/L setup without changes to M&C platform or redundancy switches.

QUAD E1 INTERFACE (QDI) WITH ENHANCED D&I++

The CDM-625 supports a Quad E1 interface that can aggregate up to 4 full or fractional E1s into a single carrier, with very low overhead. This provides significant CAPEX savings by reducing the number of modems and the simultaneous reduction in BUC/HPA size due to the elimination of multi-carrier backoff. A proprietary, closed network Drop & Insert (D&I++) allows for Dropping or Inserting any combination of 1 to 31 Time Slots on each E1. D&I++ is supported for E1-CCS only.

4-PORT ETHERNET SWITCH

CDM-625 supports a 4-port 10/100BaseT managed Ethernet switch.

EDMAC & AUPC

The CDM-625 support EDMAC, EDMAC-2, and AUPC. EDMAC/EDMAC-2 can be used to monitor and control the distant end of a satellite link using a proprietary overhead channel. AUPC enables automatic uplink power control for a duplex link.

MANAGEMENT

The CDM-625 provides a range of options for local and remote management. The modem can be managed via the front panel, the remote M&C port (EIA-232/EIA-485), or the 10/100BaseT Ethernet port. With support for SNMP, http and telnet, the modem can be easily integrated into an IP based management system.

FEATURE ENHANCEMENTS

Enhancing the capability of CDM-625 in the field is easy. Features that do not require additional hardware can be added on site, using FAST access codes purchased from Comtech EF Data.