Pierre A. Humblet

Information capacity and power control in single-cell multiuser communications

We consider a power control scheme for maximizing the information capacity of the uplink in single-cell multiuser communications with frequency-flat fading, under the assumption that the users attenuations are measured perfectly. Its main characteristics are that only one user transmits over the entire bandwidth at any particular time instant and that the users are allocated more power when their channels are good, and less when they are bad. Moreover, these features are independent of the statistics of the fading. Numerical results are presented for the case of single-path Rayleigh fading. We show that an increase in capacity over a perfectly-power controlled (Gaussian) channel can be achieved, especially if the number of users is large. By examining the bit error-rate with antipodal signalling, we show the inherent diversity in multiuser communications over fading channels.

A Distributed Algorithm for Minimum-Weight Spanning Trees

Abstract : A distributed algorithm is presented that constructs the minimum weight spanning tree in a connected undirected graph with distinct edge weights. A processor exists at each node of the graph, knowing initially only the weights of the adjacent edges. The processors obey the same algorithm and exchange messages with neighbors until the tree is constructed. The total number of messages required for a graph of N nodes and E edges is at most 5N log of N to the base 2 + 2E and a message contains at most one edge weight plus log of 8N to the base 2 bits. The algorithm can be initiated spontaneously at any node or at any subset of nodes.

Models of blocking probability in all-optical networks with and without wavelength changers

We introduce a traffic model for circuit switched all-optical networks (AONs) which we then use to calculate the blocking probability along a path for networks with and without wavelength changers. We investigate the effects of path length, switch size, and interference length (the expected number of hops shared by two sessions which share at least one hop) on blocking probability and the ability of wavelength changers to improve performance. Our model correctly predicts unobvious qualitative behavior demonstrated in simulations by other authors.

On the bit error rate of lightwave systems with optical amplifiers

The problem of evaluating the performances of communication systems with optical amplifiers and a wideband optical filter is addressed. Exact probability of error expressions for optical signals in presence of amplifier spontaneous noise and photodetector shot noise are given and compared with those predicted by Gaussian approximations for amplitude shift keying (ASK), frequency shift keying (FSK), or differential phase shift keying (DPSK) modulations, both for ideal photodetectors and for the case where shot noise is significant. >

On coding for block fading channels

This work considers the achievable performance for coded systems adapted to a multipath block-fading channel model. This is a particularly useful model for analyzing mobile-radio systems which employ techniques such as slow frequency-hopping under stringent time-delay or bandwidth constraints for slowly time-varying channels. In such systems, coded information is transmitted over a small number of fading channels in order to achieve diversity. Bounds on the achievable performance due to coding are derived using information-theoretic techniques. It is shown that high diversity can be achieved using relatively simple codes as long as very high spectral efficiency is not required. Examples of simple block codes and carefully chosen trellis codes are given which yield, in some cases, performances approaching the information-theoretic bounds.

A precompetitive consortium on wide-band all-optical networks

The technical core of a precompetitive consortium formed by AT&T, DEC, and MIT to study the technology, architecture and applications of wideband all-optical networks of local to national (or international) extent is described. A general introduction to all-optical networks is given, and some proposed applications are discussed. The architecture, technology and testbed portions of this effort are described. >

Routing subject to quality of service constraints in integrated communication networks

With increasingly diverse QOS requirements, it is impractical to continue to rely on conventional routing paradigms that emphasize the search for an optimal path based on a predetermined metric, or a particular function of multiple metrics. Modern routing strategies must not only be adaptive to network changes but also offer considerable economy of scope. We consider the problem of routing in networks subject to QOS constraints. After providing an overview of prior routing work, we define various QOS constraints. We present a call architecture that may be used for QOS matching and a connection management mechanism for network resource allocation. We discuss fallback routing, and review some existing routing frameworks. We also present a new rule-based, call-by-call source routing strategy for integrated communication networks. >

Another adaptive distributed shortest path algorithm

The authors give a distributed algorithm to compute shortest paths in a network with changing topology. The authors analyze its behavior. The proof of correctness is discussed. It does not suffer from the routing table looping behavior associated with the Ford-Bellman distributed shortest path algorithm although it uses truly distributed processing. Its time and message complexities are evaluated. Comparisons with other methods are given. >

The Bulk Service Queue with a General Control Strategy: Theoretical Analysis and a New Computational Procedure

This paper develops a general framework for analyzing a wide class of vehicle dispatching strategies for bulk arrival, bulk service queues. We provide a simple derivation of the queue length transform for the embedded Markov chain, and present a new computational procedure for finding the moments of the queue length distribution. Extensive computational tests demonstrate that the new procedure is significantly faster and more stable than the standard method, from the literature, that requires solving a set of simultaneous linear equations. We give formulas for the mean and variance of the length of the queue for the general case of compound Poisson arrivals, random batch capacities, general service times and a general control strategy.

The capacity region of the totally asynchronous multiple-access channel

It is shown that the capacity region of the asynchronous multiple-access channel differs from that of the synchronous channel only by the lack of a convex hull operation.