Giorgio Picchi

Self-Orthogonalizing Adaptive Equalization in the Discrete Frequency Domain

A self-orthogonalizing discrete adaptive equalizer for synchronous data transmission is presented, based on the overlapsave filtering technique. Self-orthogonalization in the discrete frequency domain is adaptively performed by premultiplying by a diagonal matrix the MSE gradient estimates before projecting by means of Rosens gradient projection method. The diagonal of the matrix is the inverse of the power spectrum of the received sequence taken at equally spaced frequencies, and estimates are obtained by using Bartletts procedure of periodograms averaging for spectrum estimation. Projection is accomplished by means of an off-line derived projection matrix. Confidence of gradient estimates is improved by means of a block correlated estimation technique using available DFTs of blocks of data. This equalizer is compared to time-domain self-orthogonalizing algorithms as regards speed of convergence and ease of implementation. During the short startup phase, convergence is competitive with that of Godards algorithm, which is the fastest algorithm known, and in the decision-directed mode, fast convolution performed by blocks results in a considerable reduction of the number of multiplications with respect to the time domain algorithms. A computationally simpler, unconstrained startup algorithm is also examined, obtained by removing the projection while retaining gradient block estimates in the DFD.

Synchronous and fractionally-spaced blind equalization in dually-polarized digital radio links

Two-dimensional equalization structures with symbol-rate or fractional tap-spacing are used to counteract the combined effects of selective fading and cross-polarization interference in dually polarized digital radio links. After generalizing the known optimum equalizers to the case of two-dimensional complex signals, steady-state analysis is presented based on the evaluation of a bound on the outage probability. Finite-length structures are considered and compared to the optimum linear receiver. The blind acquisition of two-dimensional T- and T/2-spaced equalizers is also shown by using a stop-and-go decision-directed algorithm in a simulation analysis.<<ETX>>

Load-aware transparent reach maximization in flexible optical networks

We propose a novel load-aware power-selection strategy for maximizing the transparent reach in dispersion-uncompensated flexible optical networks with coherent modulation formats, and we quantify the savings in opto-electronic regenerations with respect to using the standard full-load transparent reach.

Incremental adaptive equalizers using ternary +1, 0, -1 tap coefficients and/or delta modulation input encoding

In this paper a new approach to fractionally-spaced adaptive equalization is presented, which uses for the input and/’or the impulse response of the filter a delta modulation — type incremental encoding with a substantially reduced number of bits (binary + 1, − 1 or ternary + 1, 0, − 1 representation). When the oversampling factor is of the order of few tens, performance of these equalizers is comparable to that of the corresponding non-incremental equalizers with oversampling factor of few units. This approach to adaptive equalization appears promising for implementation simplicity in both filtering and control algorithms.AnalyseOn présente une approche nouvelle de l’égalisation adaptative avec suréchantillonnage, qui utilise un codage incrémental du type modulation delta pour le signal d’entrée, pour la réponse impulsionnelle du filtre ou pour les deux et qui nécessite ainsi un nombre nettement plus faible de bits grâce à une représentation binaire (+ 1 et − 1, ou ternaire (0, ± 1. Quand le facteur de suréchantillonnage est de l’ordre de quelques dizaines, ces égaliseurs ont des performances comparables à celles des égaliseurs non incrémentaux classiques utilisant un suréchantillonnage de quelques unités. C’est là une approche prometteuse de l’égalisation adaptative à cause de sa simplicité de mise en œuvre tant pour le filtrage que pour l’algorithme d’adaptation.

Advanced techniques for spectrally efficient DVB-S2X systems

We investigate different techniques to improve the spectral efficiency of systems based on the DVB-S2 standard, when the transmitted signal bandwidth cannot be increased because it has already been optimized to the maximum value allowed by transponder filters. We will investigate and compare several techniques to involve different sections of the transceiver scheme. The techniques that will be considered include the use of advanced detection algorithms, the adoption of time packing, and the optimization of the constellation and shaping pulses. The LDPC codes recently proposed for the evolution of the DVB-S2 standard will be considered, as well as the adoption of iterative detection and decoding. Information theoretical analysis will be followed by the study of practical modulation and coding schemes.

Regeneration savings in flexible optical networks with a new load-aware reach maximization

Abstract We propose and analyze a new load-aware reach maximization procedure based on the Gaussian Noise model for dispersion-uncompensated optical networks with coherent detection. We estimate the opto-electronic regeneration savings with respect to the standard full-load reach approach, and find examples where significant savings can be achieved. The load aware reach and its corresponding optimal power can be computed in real time by the routing and wavelength assignment unit to make statistical decisions about setting-up new lightpaths or regenerating existing ones.

Tunable complexity RSSE decoding of TCM signals

Maximum likelihood sequence estimation (MLSE) of trellis coded modulation (TCM) signals affected by intersymbol interference (ISI) requires an optimal path search on a trellis diagram usually of a very large size. This optimal search can be performed in principle by a Viterbi algorithm, but is impractical due to the large number of trellis states. Among the various suboptimal alternatives, we concentrate on reduced state sequence estimation (RSSE), in which the trellis diagram is reduced in size by partially representing the ISI characteristics into the trellis diagram itself. A Viterbi algorithm operates on the reduced trellis diagram, taking into account the effects of residual ISI components by means of per-survivor ISI cancellation. This technique entails the cancellation of residual ISI terms, necessary for computing the branch metrics, independently on each survivor path using the code sequence uniquely associated to the survivor path itself.<<ETX>>

Detection of linear modulations in the presence of strong phase and frequency instabilities

The previously proposed noncoherent sequence detection (NSD) algorithms have a performance which approaches that of coherent detectors and are robust to phase negligible performance loss in the presence of a frequency offset, provided this offset does not exceed an order of 1% of the signaling frequency. For higher values, the performance rapidly degrades. In this paper, two detection schemes are proposed, characterized by high robustness to frequency offsets and capable of tolerating offset values up to 10% of the signaling frequency. More generally, these detection schemes are very robust to rapidly varying phase and frequency instabilities. The general case of coded linear modulations is addressed, with explicit reference to M-ary phase shift keying (M-PSK) and quadrature amplitude modulation (M-QAM).

Architectures and Techniques for All’Optical Networks

Abstract Some recent results on all-optical packet-switching and broadcasting networks are presented. The performance evaluation problem of packet-switching transparent optical networks with deflection routing is addressed. Transmission error arguments show how, for a given optical bit rate, the size of an all-optical nonregenerative multishop network is limited by the accumulation of noise and distortion in the optical fiber channel. Time-domain multiple access techniques are exploited in novel architectures based on recently proposed all-optical sampling gates to realize the matching of the ultrahigh optical speed allowed by the large bandwidth of the fiber with the lower speed of the electronic components needed at the user ends. These architectures allow great simplification of the node structure in the considered all-optical multihop and broadcast networks.

Applications of reduced state sequence estimation to terrestrial digital radio links

Applications of reduced state sequence estimation (RSSE) to the design of receivers for terrestrial digital radio links employing trellis coded modulation (TCM) are investigated and compared to standard techniques that separately perform the specific tasks of equalization and TCM decoding. Numerical results based on computer simulation are provided, showing that a significant performance improvement is attainable by a receiver based on RSSE for typical radio-link channels affected by intersymbol interference (ISI) and thermal noise. In addition, special attention is devoted to the receiver complexity, expressed in terms of number of equalizer taps and number of states of the assumed trellis diagram. Most of the potential gain is shown to be attainable by receivers of affordable complexity.<<ETX>>