An Analysis of the Timed-Channel

Fig. 13. A British WWII Supermarine Spitfire fighter plane featuring a dangerous fiducial. A set of C concentric circles with r1 = 1+1=2C 2 and 1r = 1+1=2C is expected to be a very good (although suboptimal) location shape. Experimental tests in [13] and further theoretical developments recently published in [14], led to the conclusion that the " bull's-eye " fiducial is indeed a very good, robust and practical location mark. Hence the Royal Air Force chose, rather poorly, a deadly targeting shape to be painted on its planes during World War II (see Fig. 13). Measuring photolithographic overlay accuracy and critical dimensions by correlating binarized Laplacian of Gaussian convolutions, " IEEE Trans. registration using a concentric ring fiducial, " in Proc. 10th ICPR Conf. Abstract—Golomb analyzed the Z-channel, a memoryless channel with two input symbols and two output symbols, where one of the input symbols is transmitted with noise while the other is transmitted without noise, and the output symbol transmission times are equal. We generalize to the timed Z-channel, where the output symbol transmission times are not equal. The timed Z-channel appears as the basis for a large class of covert (communication) channels appearing in multilevel secure computer systems. We give a detailed mathematical analysis of the timed Z-channel and report a result expressing the capacity of the timed Z-channel as the log of the root of a characteristic equation. This generalizes Shannon's work on noiseless channels for this special case. We also report a new result bounding the timed Z-channel's capacity from below. We show how an interesting observation that Golomb reported for the Z-channel also holds for the timed Z-channel.