F.M.J. Willems

The discrete memoryless multiple-access channel with cribbing encoders

The capacity regions are determined for various communication situations in which one or both encoders for a multiple access channel crib from the other encoder and learn the channel input(s) (to be) emitted by this encoder. Most of the achievability proofs in this paper hinge upon the new concept of backward decoding. Also, the notion of Shannon strategies seems to be of crucial importance. It is demonstrated that in some situations parts of the total cooperation line are achievable. Moreover, it is proved that if the encoders and the decoder are allowed to be nondeterministic, the capacity regions are not increased.

Switching between two universal source coding algorithms

This paper discusses a switching method which can be used to combine two sequential universal source coding algorithms. The switching method treats these two algorithms as black-boxes and can only use their estimates of the probability distributions for the consecutive symbols of the source sequence. Three weighting algorithms based on this switching method are presented. Empirical results show that all three weighting algorithms give a performance better than the performance of the source coding algorithms they combine.

Context weighting for general finite-context sources

Context weighting procedures are presented for sources with models (structures) in four different classes. Although the procedures are designed for universal data compression purposes, their generality allows application in the area of classification.

Estimating the Secrecy-Rate of Physical Unclonable Functions with the Context-Tree Weighting Method

We propose methods to estimate the secrecy-rate of fuzzy sources (e.g. biometrics and physical unclonable functions (PUFs)) using context-tree weighting. In this paper we focus on PUFs. In order to show that our estimates are realistic we first generalize Maurers (1993) result to the ergodic case. Then we focus on the fact that the entropy of a stationary two-dimensional structure is a limit of a series of conditional entropies, a result by Anastassiou and Sakrison (1982). We extend this result to the conditional entropy of one two-dimensional structure given another one. Finally we show that the general CTW-method approaches the source entropy also in the two-dimensional stationary case. We further extend this result to the two-dimensional conditional entropy. Based on the obtained results we do several measurements on (our) optical PUFs. These measurements allow us to conclude that a secrecy-rate of 0.3 bit/location is possible

Partial feedback for the discrete memoryless multiple access channel (Corresp.)

The region Cover and Leung found for the discrete memoryless multiple access channel with feedback to both encoders is proved achievable also with feedback to only one encoder. The novel ideas of nonrandom partitions and restricted decoding are used to avoid list coding techniques.

Live-and-die coding for binary piecewise i.i.d. sources

We propose a binary live-and-die scheme based on arithmetic coding. We also discuss Q-ary live-and-die coding methods. They have a better redundancy behavior than the binary method but also higher complexity demands.

A context-tree weighting method for text generating sources

Summary form only given. The authors discuss context tree weighting (Willems et al. 1995). This was originally introduced as a sequential universal source coding method for the class of binary tree sources. The paper discusses the application of the method to the compaction of ASCII sequences. The estimation of redundancy and model redundancy are also considered.

On the context tree maximizing algorithm

The context tree weighting algorithm was introduced at the 1993 ISIT. Here we are concerned with the context tree maximizing algorithm. We discuss several modifications of this algorithm.

Reducing model cost by weighted symbol decomposition

We discuss a symbol-decomposition method that combines the descriptions of the resulting models to save model redundancy. The proposed method is based on weighting.

Reducing the complexity of the context-tree weighting method

The storage complexity of the CTW-method is decreased by combining the estimated probability of a node in the context tree and the weighted probabilities of its children in a single ratio.