Comtech CDM-625A Advanced Satellite Modem

The Comtech EF Data CDM-625A Advanced Satellite Modem builds on a legacy of providing the most efficient satellite modems. With support for VersaFEC® Forward Error Correction (FEC), the revolutionary DoubleTalk® Carrier-in-Carrier® bandwidth compression, additional rolloffs and advanced packet processing, the CDM-625A provides significant savings under all conditions.

This combination of advanced technologies enables multi-dimensional optimization, allowing satellite communications users to:

  • Minimize operating expenses (OPEX)
  • Maximize throughput without using additional transponder resources
  • Maximize availability (margin) without using additional transponder resources
  • Minimize capital expenses (CAPEX) by allowing a smaller BUC/HPA and/or antenna
  • Or, a combination to meet specific business needs

CDM-625A Typical Users

  • Mobile Network Operators
  • Telecom Operators
  • Satellite Service Providers
  • Government & Military
  • Enterprise
  • Offshore

Common Applications

  • Mobile Backhaul
  • G.703 Trunking
  • IP Trunking
  • Offshore & Maritime Communications
  • Enterprise
  • Communications on-the-Move
  • Satellite News Gathering

CDM-625A Features

  • DoubleTalk Carrier-in-Carrier bandwidth compression
  • Carrier-in-Carrier Automatic Power Control
  • VersaFEC FEC with Adaptive Coding and Modulation (ACM)
  • 5%, 10%, 15%, 20%, 25% and 35% Filter Rolloff
  • Packet Processor with header compression, payload compression, advanced Quality of Service (QoS) and Managed Switch Mode with VLAN support
  • Integrated 4-port managed Ethernet switch with VLAN and QoS
  • Jumbo frame support
  • Dual Band Capability: 70/140 MHz and extended L-Band (950 – 2250 MHz) in same unit
  • Data Rate: 18 kbps to 25 Mbps
  • Symbol Rate: 18 ksps to 12.5 Msps
  • Modulation: BPSK, QPSK/OQPSK, 8PSK/8-QAM, 16-QAM
  • FEC: Viterbi, Sequential, Concatenated Reed Solomon, TCM, Turbo Product Code (TPC) (IESS-315 Compliant), LDPC Code and VersaFEC (low-latency LDPC)
  • Widest Range of data interfaces: EIA-422/530, V.35, G.703 T1, G.703 E1, G.703 T2, G.703 E2, Quad G.703 E1, ASI, LVDS, HSSI, 4-port 10/100Base-T Ethernet
  • IEEE 1588v2 Precision Time Protocol
  • Sub Mux to multiplex IP/Ethernet traffic with serial or G.703 traffic
  • Drop & insert for T1/E1
  • Enhanced D&I++ for single T1/E1 & quad E1
  • Management: 10/100Base-T Ethernet with SNMP, Distant End SNMP Proxy, HTTP, Telnet and EIA-232/EIA-485
  • Carrier ID using MetaCarrier® Technology
  • Embedded Distant-end Monitor and Control (EDMAC)
  • Automatic Uplink Power Control (AUPC)
  • Engineering Service Channel (ESC/ESC++)
  • Standard high-stability internal reference (± 6 x 10-8)
  • 5-tap Adaptive Equalizer
  • L-Band TX: 10 MHz reference for BUC, FSK communications and optional BUC power supply
  • L-Band RX: 10 MHz reference and LNB power supply
  • L-Band: Advanced FSK for LPOD M&C
  • 1:1 and 1:10 redundancy switches available
  • Backwards compatible with CDM-625

Doubletalk Carrier-in-Carrier

DoubleTalk Carrier-in-Carrier, based on patented “Adaptive Cancellation” technology, allows transmit and receive carriers of a duplex link to share the same
transponder bandwidth. 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.

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.
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/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 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 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 2nd 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.

…for more Satellite Modems

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