Dominique Godard

Self-Recovering Equalization and Carrier Tracking in Two-Dimensional Data Communication Systems

Conventional equalization and carrier recovery algorithms for minimizing mean-square error in digital communication systems generally require an initial training period during which a known data sequence is transmitted and properly synchronized at the receiver. This paper solves the general problem of adaptive channel equalization without resorting to a known training sequence or to conditions of limited distortion. The criterion for equalizer adaptation is the minimization of a new class of nonconvex cost functions which are shown to characterize intersymbol interference independently of carrier phase and of the data symbol constellation used in the transmission system. Equalizer convergence does not require carrier recovery, so that carrier phase tracking can be carried out at the equalizer output in a decision-directed mode. The convergence properties of the self-recovering algorithms are analyzed mathematically and confirmed by computer simulation.

Passband Timing Recovery in an All-Digital Modem Receiver

The performance of conventional modem receivers, where adaptive equalization is achieved by a digital transversal filter with tap gains spaced at the symbol interval, depends critically on the choice of the sampling phase. In this paper, a digital timing recovery loop is described and analyzed in the case of passband quadrature amplitude modulated data signals. Under conditions likely to be encountered on actual voiceband communication channels, the clock phase derived is shown to prevent spectral nulls and to accurately approximate the optimum timing phase for an infinite equalizer. Computer simulations show that the proposed system is capable of fast timing acquisition.

Prospect and design choices for integrated private networks

This paper reviews some of the choices that will be available in the next few years, as the much-discussed move toward implementing voice and data integration within a single wide-area integrated private network proceeds. After the term :hp1de-area integrated private network:ehp1. has been defined, a discussion is given of requirements the network ought to satisfy for its users. Then two particularly promising approaches, fast packet switching (FPS) and hybrid switching (HS), are defined, and specimen design points for FPS and HS are postulated, so that the two can be compared. While a definitive comparison would require systematic cost and performance studies, much insight can be gained from the qualitative comparison that we present here. We assess some of the arguments that have been put forward in favor of FPS or HS and conclude that, although today both architectures have promise, and research on both should continue, FPS appears to be slightly simpler to implement and operate.