Synchronous Data Transmission Research Articles

Adaptive Equalization of Highly Dispersive Channels for Data Transmission

This paper analyzes an adaptive training algorithm for adjusting the tap weights of a tapped delay line filter to minimize mean-square intersymbol interference for synchronous data transmission. The significant feature of the adjustment procedure is that convergence is guaranteed for all channel response pulses, even for very severe amplitude and phase distortion. The author examines convergence, rate of convergence, and the effect of noisy observations of the received pulses, and he shows that the noisy observations result in a random sequence of tap weight settings whose mean value converges to a suboptimal setting. The mean-square deviation of the tap weights from the suboptimal values is asymptotically bounded with a bound that can be made as small as desired by sufficiently reducing the speed of convergence. The suboptimality arising here results from the use of isolated test pulses for the training signal. However, a training scheme using pseudorandom sequences or the actual data signal does not suffer from the suboptimality effect. Hence, although of possible utility in other pulse shaping applications, the technique presented here appears to be primarily of value in providing a conceptual framework for the closely related but more practical techniques to be examined in the sequel to this paper to be published shortly.

A Unified View of Synchronous Data Transmission System Design

This paper illustrates the basic equivalence of many of the linear data transmission design techniques. It shows the unifying feature of these techniques to be a generalization of Nyquist's original ideas relating time samples and frequency domain constraints. It examines pulse amplitude (with and without constraints on the input data) and pulse shape modulation systems, and shows their relationships. It uses a number of previously-described systems to illustrate the range of possibilities of the very general design approach. This paper presents some new results on noise and channel parameter monitoring and on spectrum shifting by constraining the input data.

Timing Recovery for Synchronous Binary Data Transmission

This paper analyzes different methods of adjusting the sampling time for detecting synchronous binary data, based on properties of the random data signal itself. The static error and the variance of the jitter of the resultant sampling instant are calculated where the effects of frequency offset, additive noise, signal overlap, and jitter of the reference source are included. The threshold crossing timing recovery system adjusts the sampling time in response to the times at which the data signal crosses the amplitude threshold. The sampled-derivative system uses the time derivative of the signal at the sampling time to adjust sampling phase. It is shown that both systems lead to approximately the same amount of jitter in the presence of noise and signal overlap for a given bandwidth of the control loop. An improved timing recovery system is presented which is constructed by adding correction signals to the sampled-derivative system. This system accounts for intersymbol interference in a manner that tends to set the sampling time at the point of maximum eye opening, where the error probability is minimum for the most adverse message sequence.