8QAM - Modulation now available (April 2008)
Datum Systems releases firmware version 0.72 firmware code that supports both modem and FEC feature upgrades. The main addition is the ability to operate in 8QAM modulation mode, which studies have shown offers from 0.1 to 0.8 dB of improvement over 8PSK modulation. The 8QAM offers improved performance plus advantages in small stations with limited transmit power. To use this mode you must currently have 8PSK capability (M511 or M523 Feature Set) and any version of TPC FEC. See the M500-Downloads page for download of the new firmware version 0.72 with companion version 30 FEC firmware. NASA studies from several years ago showed improved performance possible for 8QAM vs. 8PSK on the order of several tenths of a dB. Our testing has shown the improvement to be approximately 0.3 dB for most cases and up to 0.7 dB for certain modes and Eb/No cases, making it highly worthwhile to implement this modulation mode. In addition, 8QAM offers improved susceptibility to problems that can be caused by non-linearities when operating a stations power amplifier with very low back-off. 8QAM is somewhat different than 8PSK in that it does not operate with Trellis Code Modulation or Viterbi FEC, and will therefore initially require that the modem have either a 4k or 16k TPC FEC card installed. The new firmware will be available for download on our web site at no charge.