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2 Journal of Telecommunications and Information Technology

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On a method to authenticate and verify digital streams

Wysocki B.J., Wang Y., Safavi-Naini R.

Journal of Telecommunications and Information Technology

2002

nr 2

45-52

Recently, digital streams have become widely used to make audio, video, and other media available in real-time over the Internet. As with other transmission methods, the recipient needs to have a possibilty to verify the source and authenticity of the received information. Several techniques have been proposed to deal with this issue. Most of them are vulnerable to packet losses or they introduce unacceptable computational and/or communication overheads. Some of the graph-based techniques provide immunity to burst losses of certain length. However, these techniques are not immune to the loss of packets containing signatures or occasional burst of lengths greater than the assumed one. In the paper, we propose a modification to one of the graph-based techniques that introduces immunity to the loss of packets containing signatures, without introducing any additional overheads.

Error statistics for concatenated systems on non-renewal time-varying channels

Pimentel C.

Journal of Telecommunications and Information Technology

2001

nr 3

55-60

The statistics of the error process generated by a discrete super channel formed by the concatenation of a constrained encoder, a non-renewal finite state channel (FSC), and a constrained decoder is studied in this paper. First, recursions are developed for the error weight distribution. This statistics is relevant to the design of coding schemes and interleaving in concatenated. systems. We also study the renewal nature of the residual error process as modified by the constrained decoder. Ferreira et al. conjectured that if the channel model is a renewal FSC, the super channel can be modeled as a similar renewal model. We use a statistics called the multigap distribution to analytically disprove this hypothesis. Furthermore, the effect of interleaving is investigated from a new perspective using the variance of the multigap distribution.