Georg Sebald

Cross-polarization interference cancellation in the presence of delay effects

It is shown how a fractionally spaced transversal canceler with five taps is capable of providing large improvement factors in channel situations of practical significance, including large delay differences. How the capability of counteracting the depolarization depends on the performance of the adaptive equalizer in the system is shown using a realistic channel model with bidirectional crosstalk. For an optimum system configuration, a matching between the equalizer and canceler capability is necessary. This has been verified experimentally for a 140 Mb/s system employing 16 QAM and operating with plesiochronous data streams.<<ETX>>

Jitter-reduced digital timing recovery for multilevel PAM and QAM systems

In multilevel pulse amplitude modulation/quadrature amplitude modulation (PAM/QAM) systems, e.g., digital radio, there is a strong demand for a reliable and precise timing phase provided by the timing recovery circuit. A phase detector that is theoretically jitter free, even in the case of noncoherent demodulation, is presented. In practical applications, with reduced complexity, a jitter reduction on the order of >15 dB is achieved. Solutions to improve the behavior of the timing recovery in case of linear channel distortions are given.<<ETX>>

Advanced Time- and Frequency-Domain Adaptive Equalization in Multilevel QAM Digital Radio Systems

Digital radio systems employing multilevel QAM are at least optionally equipped with adaptive time- and/or frequency-domain equalizers. Their purpose is to reduce the vulnerability of these systems to linear distortion caused by multipath propagation. Linear transversal filters are prominent candidates for the realization of time-domain equalizers, especially for high-capacity applications. They are well known for their good performance and their relatively easy implementation at a high data rate. On the other hand, decision feedback equalizers are known to be very capable of eliminating linear distortion, especially of the so-called minimum-phase type. But realization problems are likely to occur in a high-speed application. A solution is proposed which merges the relative advantages of both the linear transversal and the decision feedback approaches. The goal of a frequency-domain equalizer, which is the restoration of the shape of the power density spectrum of the received signal without any recovered carrier and timing signals, can also be achieved with the aid of a transversal filter. The performance obtained with the joint utilization of the novel timeand frequency-domain equalizers is described.

Fully digital ATDE's and XPIC's for a STM-1 cochannel radio system family

The new STM-1 signal format can be carried advantageously by high-capacity digital radio systems by making use of cochannel operation. This can be implemented in an economical way by fully exploiting the capabilities of silicon VLSI technology. A fully digital adaptive transversal filter IC was developed which can be used not only in the time-domain equalizer, but also in a crosspolarization interference canceler. This offers a very economical solution for a cochannel system providing twice the channel capacity. Due to synchronization of carriers and the timing of both orthogonal polarized signals the baudspaced transversal filter structure of the VLSI circuit enables superior performance both for the equalizer and for the canceler operation. The theoretical concepts behind the system are presented and experimental results are discussed.<<ETX>>

Fully digital adaptive slope equalizer for advanced digital radio systems

A robust fully digital equalization concept consisting of a slope equalizer and a baudspaced adaptive time domain equalizer was investigated. Applying a decimating control section utilizing a discrete Fourier transform (DFT) algorithm for the slope equalizer results in a very simple and attractive solution which is well suited for implementation in a VLSI technique. The whole circuit of the adaptive slope equalizer consists of only four multipliers and eight adders. The performance evaluations prove that the high requirements for equalizers, even for a 128 QAM (quadrature amplitude modulation) system, can be met with the proposed solution.<<ETX>>

Data-aided symbol timing estimation for linear modulation

Summary Timing phase estimation (TPE) plays the key role in feedforward (FF) symbol timing.For reasons of performance often data-aided (DA) methods are preferred. But frequently, they turn out to be critical with respect to theimplementation and the spectrum efficiency (due to the required overhead).This paper presents three DA TPE methods for quadrature pulse amplitude modulation (PAM). In spite of their very low complexity, these methods closelyapproach the theoretical limit for timing estimation with respect to the estimation variance, even at low SNR. This enables power efficient transmission.Further, they employ a CAZAC (constant amplitude, zero auto-correlation)sequence as training-sequence (TS), or a sequence with similar correlationproperties. Since such sequences are suited for almost all DA receiver tasks, a high spectrum efficiency can be obtained by the use of a single TS. A generalization of the proposed methods for DA TPE withrespect to the choice of the TS is also shown. The presented methods can be applied to noncoherent receivers. They are suited for high data-rate applications, since they can work with an oversampling factor of 2.