Military Communications and Information Technology: A Trusted ...

506 Military Communications and Information Technology...
variants – correction to LT min level and LT min + 3 dB level. In the case of watermark
signal power correction to LT min + 3 dB level, the bit error rate is approximately
2.5%, regardless of the signal analysis time. This value can be corrected with the use
of detection and correction codes.
Figure 9. Extraction efficiency in the function of signal analysis time
As previously mentioned, the present algorithm allows for creating a hidden
transmission channel with the bitrate of 43 bps (with the division of the 1024-sample
frame into two subframes of 512 samples). Algorithm modification in the form
of dividing the frame into subframes allows for increasing the transmission rate.
Fig. 10 presents the results for signature extraction efficiency after increasing
the bitrate to 86 bps and 172 bps. The watermark power was corrected to the level
of LT min + 3 dB. In both cases the bit error rate is below 10%.
Figure 10. Comparison of extraction efficiency for different transmission rates