Mocomtech CDM-QX - Manual (Page 173)

CDM-Qx/QxL Multi-Channel Satellite Modem with DoubleTalk™ Carrier-in-Carrier® Revision 7
Forward Error Correction Options MN/CDMQX.IOM
7–7
* The occupied bandwidth is defined at the width of the transmitted spectrum taken at the -10 dB
points on the plot of power spectral density. This equates to 1.19 x symbol rate for the modem
transmit filtering.
** Included for comparative purposes.
It can be seen that the 8-PSK Rate 3/4 Turbo performance closely approaches that of the Rate 2/3
TCM/Reed-Solomon case – the BER performance is within approximately 0.4 dB. However, it should
be noted that the Rate 3/4 Turbo mode is 20% more bandwidth efficient than the TCM case. The
additional advantages of Turbo (lower delay, performance during fades etc) should also be considered.
Table 6-6. Turbo Product Coding Summary
FOR AGAINST
Exceptionally good BER performance - significant improvement
compared with every other FEC method in use today
Nothing!
No pronounced threshold effect - fails gracefully
Exceptional bandwidth efficiency
Coding gain independent of data rate (in this implementation)
Low decoding delay
Easy field upgrade in Modem