Comtech EF Data has introduced 1:1 and 1:N redundancy support for the CDM-710G High-Speed Satellite Modem. 1:1 redundancy is provided by the CRS-170A (L-Band) and CRS-180 (70/140 MHz) switches and 1:N redundancy uses the CRS-300 switch. This new satmodem supports DVB-S2 QPSK, 8-PSK, 16-APSK and 32APSK modulation up to 45 Msps and offers data rates exceeding 124 Mbps, depending on the modulation type and code rate. The modem operates in the constant coding and modulation (CCM) mode and has selections for pilots ON/OFF and spectral roll off at 20, 30 or 45 percent. Software based options are added to the unit using FAST (Fully Accessible System Topology) upgrade. Unit management is available from the front panel keypad / display, web browser, SNMP or Telnet.
VersaFEC provides maximum coding gain with the lowest possible latency to support cellular backhaul and other latency-sensitive voice, video and data applications. VersaFEC is a system of short-block, low latency Low Density Parity Check (LDPC) codes designed to support latency-sensitive applications, such as cellular backhaul over satellite. Designed to provide maximum coding gain while minimizing the end-to-end latency, VersaFEC provides an excellent alternative to existing LDPC and DVB-S2 codes. VersaFEC is specifically designed for low latency applications. As a comparison, Comtech EF Data’s current LDPC Rate 2/3 8-QAM and VersaFEC Rate 0.642 8-QAM provide essentially identical spectral efficiency and Eb/No performance. However, at 64 kbps, the latency has been reduced from 350 milliseconds to 89 milliseconds — a reduction by a factor of 4. Compared to DVB-S2 short block, the VersaFEC provides a latency reduction of anywhere from a factor of 4 to as much as a factor of 10. E.g. DVB-S2 QPSK Rate 2/3 and VersaFEC QPSK 0.631 have near identical spectral efficiency and Eb/No performance. However, at 64 kbps, the VersaFEC latency is 59 ms compared to more than 500 ms for DVB-S2 – a reduction by a factor of over 8. In addition to using smaller block sizes, to further reduce latency, VersaFEC uses non-interleaved systematic LDPC codes. Compared to DVB-S2’s interleaved codes, this achieves a significant reduction in latency. The total end-to-end latency for a high code rate systematic code (such as VersaFEC) asymptotically approaches half the latency of an interleaved code (such as DVB-S2). Compared to the DVB-S2 short block ACM, VersaFEC ACM could reduce the system latency by as much as one order of magnitude.
