Roberto Cusani

Combined channel estimation and data detection using soft statistics for frequency-selective fast-fading digital links

A novel adaptive nonlinear equalizer for fast time-varying multipath channels that combines the channel estimation and data detection tasks is presented. The a posteriori probabilities (APPs) of the states of the intersymbol interference (ISI) channel are recursively computed from the received data by a symbol-by-symbol (SbS) detector and are then employed by a Kalman-type nonlinear channel estimator. Robust channel tracking and good data-detection performance are obtained, with a reasonable receiver complexity.

A Location-Based Vertical Handover Algorithm for Limitation of the Ping-Pong Effect

In this paper a location-based algorithm is proposed for managing soft mobile-controlled vertical handover between wireless systems. The case of a dual-mode terminal equipped with UMTS and IEEE 802.11 network interface cards is analysed in detail, and an novel approach for optimizing goodput and limit the so-called ping-pong effect is defined. The novel algorithm is based on a preliminary handover initiation phase triggered on the basis of mobile node location. Handover is then carried out by following a goodput estimation phase allowed by a transient of by casting during soft handovers. Experimental results provide an assessment on the use of location information to drive handover decisions.

Methods for estimating the autocorrelation function of complex Gaussian stationary processes

New methods for estimating the autocorrelation function (acf) of a complex Gaussian stationary process are presented. These methods are based on a general invariance property for the autocorrelation of a common class of the above processes. This property suggests estimation procedures based on magnitude hard limiting and phase quantization. The procedures are an extension of the relay estimator, currently employed for real processes. The computational cost and the general properties of the methods are discussed. In particular, some estimators especially suited for very simple implementations are considered. The performance of the complex hybrid sign estimator is evaluated and compared to that of the classical Direct estimator. The proposed methods are attractive for many applications in the field of digital signal processing.

Recursive Kalman-type optimal estimation and detection of hidden Markov chains

Abstract Efficient algorithms for computing the ‘a posteriori’ probabilities (APPs) of discrete-index finite-state hidden Markov sequences are proposed. They are obtained by reducing the APPs computation to the optimal nonlinear minimum mean square error (MMSE) estimation of the noisily observed sequences of the indicator functions associated with the chain states. Following an innovations approach, finite-dimensional and recursive Kalman-like ‘filter’ and ‘smoothers’ for the Markov chain state sequence are thus obtained, and exact expressions of their MSE performance are given. The filtered and smoothed state estimates coincide with the corresponding APP sequences. Finite-dimensional MMSE nonlinear filter and smoothers are also given for the so-called ‘number of jumps’ and for the ‘occupation time’ processes associated with the Markov state sequence.

On a fast digital method of estimating the autocorrelation of a gaussian stationary process

The zero-mean stationary Gaussian processes have the property that if they are input into an instantaneous nonlinear device, the cross correlation of input and output is proportional to the auto-correlation of the input. This suggests an estimation procedure for the autocorrelation function based mainly on additions, which is a modified type of the PCC (polarity coincidence correlator). The object of this paper is to compute the bias and the variance of such an estimator and to discuss some fundamental properties. As a reference, some examples are provided which compare the behavior of the modified PPC estimator to the classical one based on products and additions.

Smart Vehicles, Technologies and Main Applications in Vehicular Ad hoc Networks

Vehicular Ad hoc NETworks (VANETs) belong to a subcategory of traditional Mobile Ad hoc NETworks (MANETs). The main feature of VANETs is that mobile nodes are vehicles endowed with sophisticated “on-board” equipments, traveling on constrained paths (i.e., roads and lanes), and communicating each other for message exchange via Vehicle-to-Vehicle (V2V) communication protocols, as well as between vehicles and fixed road-side Access Points (i.e., wireless and cellular network infrastructure), in case of Vehicle-to-Infrastructure (V2I) communications [1].

A novel adaptive receiver with enhanced channel tracking capability for TDMA-based mobile radio communications

The paper presents a novel fast-adaptive nonlinear receiver which exploits soft statistics for tracking the random fluctuations experienced by time division multiple access (TDMA) mobile radio links impaired by frequency-selective time-variant multipath phenomena. The detection task is accomplished by an Abend-Fritchman-like symbol-by-symbol maximum likelihood (SbS-ML) detector which delivers both hard decisions and soft statistics in form of a posteriori probabilities (APPs) of the states of the intersymbol interference (ISI) channel. In the proposed adaptive receiver, these APPs are employed in place of the conventional hard-detected data to feed an ad hoc developed nonlinear recursive Kalman-type channel estimator. Extensive computer simulations show that the exploitation of soft statistics enhances the tracking capability of the channel estimator so that the proposed receiver generally outperforms the usual ones based on adaptive maximum likelihood sequence estimators (MLSEs) for signal-to-noise ratio (SNR) values over 12-13 dB. Furthermore, the experienced performance gap with respect to more complex per-survivor processing (PSP)-based multi-estimator detectors appears generally small on slowly and moderately fast time-varying channels characterized by values of the product Doppler bandwidth /spl times/ signaling period B/sub D/T/sub S/ below 5/spl times/10/sup -3/.

A Combined Vertical Handover Decision Metric for QoS Enhancement in Next Generation Networks

Vertical handover (VHO) techniques are applied when mobile users require service continuity and a seamless roaming between heterogeneous networks. A VHO decision can be taken on the basis of physical parameters, such as the received signal strength (RSS), data rate and signal-to-interference and noise ratio (SINR). In this paper, we compare three VHO decision criterions, each of them based on different physical metrics. A smart combination of several VHO criterions is the core of our proposed approach, which uses not only RSS or SINR parameters, but also a hybrid mixture from different wireless access networks. To improve quality of service for mobile users, a data rate gain parameter is introduced that lets an efficient VHO be executed. Simulation results of the proposed VHO approach are in terms of both end-users efficiency, i.e. cumulative received bits, and network performances, i.e. VHO frequency.

Text Independent Automatic Speaker Recognition System Using Mel-Frequency Cepstrum Coefficient and Gaussian Mixture Models

The aim of this paper is to show the accuracy and time results of a text independent automatic speaker recognition (ASR) system, based on Mel-Frequency Cepstrum Coefficients (MFCC) and Gaussian Mixture Models (GMM), in order to develop a security control access gate. 450 speakers were randomly extracted from the Voxforge.org audio database, their utterances have been improved using spectral subtraction, then MFCC were extracted and these coefficients were statistically analyzed by GMM in order to build each profile. For each speaker two different speech files were used: the first one to build the profile database, the second one to test the system performance. The accuracy achieved by the proposed approach is greater than 96% and the time spent for a single test run, implemented in Matlab language, is about 2 seconds on a common PC.

A novel MAC and scheduling strategy to guarantee QoS for-the new-generation WIND-FLEX wireless LAN

The novel W-LAN currently developed in the framework of the WIND-FLEX project of the European IST Program, suitable for small-office home-office environments, is described. Particular emphasis is given to the MAC layer, which provides efficient utilization of the channel capacity and includes a Scheduler as an efficient means to guarantee quality of service. WINDFLEX devices exchange data at rates ranging from 64 kb/s to 100 Mb/s over a 50 MHz channel at 7.1 GHz. The modulation is adaptive OFDM, the access scheme TDMA, the duplexing technique asymmetric TDD. The MAC controls the adaptivity of the physical layer by adjusting a set of parameters based on some link measurements. The WIND-FLEX network is full-meshed single-hop and is based on a master/slave architecture where the master acts as the coordination point (but not as a relay or base station). Computer simulations show the efficiency of the proposed strategy in terms of delay and packet loss, also checking the system capability to support high traffic loads.