The error performance of a digital FM system is studied in the presence of additive Gaussian noise. This system is a conventional one employing a voltage-controlled oscillator as the modulator and a limiter-discriminator followed by a low-pass filter as the demodulator. The notion of "clicks" introduced by Rice, and used by Mazo and Salz, is adopted and the performance of the above system is theoretically studied when the intersymbol interference caused by band limitation cannot be neglected. Special consideration has been given to binary frequency-shift keying (FSK) systems. For such systems, the probability of error is given in a closed form.

An overshoot suppression scheme to improve the performance of the digital Song adaptive delta modulator (DM) for picture transmission is described. This scheme allows for a faster increase in the step sizes than permitted by overshoot and settling time considerations, thus improving rise-time performance. The overshoot suppression (OSS) algorithm used has been verified using computer simulation on a PDP-8. Furthermore, experimental results using computer generated test pictures as well as pictures from a flying-spot scanner show the improvements due to the overshoot suppression scheme. It is also shown that the additional hardware required for the actual implementation of the algorithm is simpler than those encountered in the literature, and gives better signal-tracking accuracy. Upper bounds for the settling time, with and without OSS, are derived showing an improvement with the suppression scheme. Stability conditions are also derived permitting the proper selection of DM parameters.

This paper describes a procedure for a suboptimal routing of simultaneous multiterminal multicommodity flows in circuit switched communication networks. The procedure is based on a concept of topological importance of a branch in a capacitated net with a given structure and relative to a given pattern of communication requirements. Once these importance weights have been attached to the branches of the net, the problem reduces to finding in a weighted network the shortest path between two nodes. The chosen objective here is to optimize the grade of service (GS) by satisfying (on a long-range traffic policy basis) the changing "call" demands presented to the network, as fully as possible.

A Monte Carlo simulation program that enables the evaluation of different routing policies in a communication network is described. This simulation is intended to deal with nonoriented (telephone) networks and the grade of service (G/S) is taken as the performance measure. However, it can easily be adapted to deal with oriented or mixed networks. The program assigns to each branch of the analyzed network a price function. For each call, the route of minimal cost, among all available under the present load conditions in the network, is then chosen. The program was used for comparing routing policies, as initiated by different price functions. The comparisons were made on several test networks and for different traffic loads. The results obtained showed a significant improvement in the G/S for the policy that aimed at distributing the flow through the network in the most homogenous way possible. This homogenous flow distribution was obtained by using the above minimal-cost policy and a price function, assigned to each channel, that monotonically increases with the traffic load of the branch to which the particular channel belongs. The influence of the topological configuration of the network on the G/S, under equal external demands, was also investigated and the results are given. The way in which the results are printed out enables the simulation program to serve also as a practical and useful tool in the design (or the redesign) of a communication net.