Jens C. Arnbak

Capacity of Slotted ALOHA in Rayleigh-Fading Channels

Fading channels may improve the capacity of slottedALOHA networks. Rayleigh fading and spatially distributed packet transmitters diminish mutual packet interference and thus reduce the average blocking probability of a shared receiver. A transmission model, combining Poisson statistics of the offered data traffic with Rayleigh statistics for the fading channel, is developed. Analytical and numerical results are presented, indicating significant improvements to signaling in cellular mobile networks and in packet radio systems with fading radio channels.

Graphical correspondence in electronic-mail networks using personal computers

A telegraphic technique for electronic-mail correspondence between industry-standard PC facilities equipped with a writing tablet is described. Algorithms for encoding graphical information into the fixed-word format used in the common message-handling architectures are discussed. It is proposed to adopt differential chain encoding which allows an efficient representation of graphics as strings of ASCII-compatible bytes. telematic service that is feasible with this PC networking approach is compared to standard facsimile transmission of compound documents with text and graphics. >

Relative vector probabilities in differential chain-coded line-drawings

A derivation is given of the probabilities of the relative vectors which represent the approximating segments in a square coding ring for differential chain coding (DCC) of line drawings. These probabilities are required to calculate rate (coding efficiency) and distortion-versus-rate characteristics. The performances of the differential and nondifferential chain codes are compared. It is established that DCC has higher efficiency.<<ETX>>

Regulation for next-generation technologies and markets

Intense technological dynamics is perturbing the classical liberalisation course of fixed telephony markets followed in most national policies. Major shifts in the distribution of production costs of regulated firms are induced by modern microelectronics, photonics, and fixed and mobile internet platforms, creating new networked service markets adjacent to the regulated telephone activities. The confluence of regulated and unregulated markets poses dilemmas in deciding on issues of open access to the new opportunities for competitive providers and/or consumers. This contribution briefly discusses the general regulatory issues and two specific cases, namely, fixed-mobile service integration and licensing of third-generation mobile networks.

Effects of Rayleigh fading on packet radio channels with shadowing

The combined effect of Rayleigh fading and log-normal shadowing on slotted-Aloha data communications in the mobile radio channel is studied. The joint presence of these two propagation effects is shown to yield higher channel throughput than with either effect alone. The results are useful for packet radio systems with contention-limited performance.<<ETX>>

Improved Performance of Mobile Data Networks Using Stack Algorithms and Receiver Capture

We consider a slotted multi-user channel with a common packet receiver which may be captured by one user packet in the presence of other packet transmissions. The unsuccessful user terminals repeat their transmissions using a stack-algorithm protocol for conflict resolution. Three alternative algorithms are considered; these differ by the feed-back information available to the contending users. The capture probability is modelled by various analytical expressions, corresponding to advanced receivers in typical fading packet radio channels. The average packet delay and the channel throughput are calculated for different combinations of algorithms and capture models: considerably enhanced performance appears possible for certain of these combinations.

Compound document transfer between electronic-mail network and facsimile terminals

The authors present a system for combining the two related yet separated modes of electronic document transfer, namely, electronic-mail (E-mail) and facsimile. Messages prepared at desk-top terminals, supporting compound document creation and editing, and submitted to the E-mail network can thus be received by both interconnected terminals in the common E-mail architecture and by facsimile terminals connected to the public switched telephone networks (PSTN). The latter transmission is achieved by facsimile gateways which connect the two different architectures and perform the necessary protocol conversions.<<ETX>>

Trans-border communications networks: Technology-driven or social innovation?

In this article, Jens Arnbak argues that the racing tide of development of information technology, and of telecommunications networks and services in particular, is not matched by its social and user acceptance and application. Two case studies are cited, both in the field of telecommunications: Nordic mobile telephony networks, and a comparison between facsimile transmission based on paper and electronic mail in inter-office communication. Both illustrate that, despite clear technical and even cost advantages, social resistance is preventing the speedy adoption of high-tech telecommunications networks across national borders. The authors prescription-innovation in novel telecommunications must take careful account of social and cultural adaptation rates in national and international institutions and markets.

Many voices, one structure: The challenge of telematics

Abstract The confluence of computers and telecommunications, in the telematics sector, is being enforced by common hardware and software developments. Despite this joint use of modern information technology, there is still a gulf separating the two professional cultures of data processing and public telecommunications. The former is more flexible and capability‐oriented; the latter is oriented at higher reliability, equal access, and standardized performance. The author examines the critical professional issues behind these differences and argues that broader education and systems engineering have roles to play in our preparation for the information society.

A method for intermodulation noise calculations in a cable television network with HD-MAC, PAL and FM radio signals

A statistical method for calculating intermodulation noise in CATV systems whose traffic can be characterized as a sum of a large number of independent signals is presented. The method is demonstrated by calculating the signal-to-intermodulation-noise ratio in the various channels of a prototype cable network supporting HD-MAC, PAL, and FM radio signals. The spectra of these individual signals are simplified in order to perform part of the calculation analytically. It is shown that the signal-to-intermodulation-noise ratio decreases when the total signal power is increased. This method can be used to calculate the necessary back-off of a cable network for a given frequency plan and to determine suitable plans for loading and controlling CATV networks. >