| 摘要 |
The invention combines pulse position modulation, PPM, with the signal being given a high degree of optical noise, shot noise. This entails, on the one hand, that a minimum amount of light must be taken out of the connection and, on the other hand, that a selected code according to PPM must be known for the tapped information to be interpretable. The fact that a large part of the energy must be tapped out means that the probability of useful information being tapped out of the system is very low. If sufficient energy is taken out of the system for ensuring correct detection, detection elements in the receiver detect that energy has disappeared during the transmission. If the receiver lacks such equipment, the probability of incorrectly received information is increased, as a result of which the interception is exposed. <IMAGE> |
