A novel cooperative least mean square adaptation rule is proposed with application to fractionally spaced blind channel equalization schemes used in quadrature amplitude modulation data links. A novel cost function based on second-order statistics only of the received signal is defined and jointly used with another chosen among classical blind cost functions such as decision directed and other Bussgang-type ones. Numerical results show that severe misconvergence observed in classical blind equalization algorithms is drastically mitigated using the here described technique.

The development of wireless personal area networks is one of the key challenges in the new frontier of communications. The standardization activities of the IEEE802.15.6 and IEEE802.15.4f workgroups along with the proposed 368-369 ECMA specifications open new roads to optimize performance in ultrawideband (UWB) communication links and services. In this perspective, new communications require high reliability, high throughput for multimedia content delivery, very low latency, and bit error rates are required. In this regard, this contribution deals with a turbo-like mechanism that, starting from an interference acquisition phase, proceeds with data-aided channel estimation and synchronization to data detection of ultrawideband impulse-radio (UWB-IR) terminals operating over broadband channels affected by multipath fading and in the presence of imperfect orthogonal access. The performance of the proposed transceiver has been evaluated in terms of both required number of pilot symbols for the channel estimation/data synchronization and bit error rate resulting from the channel estimation and interference analysis. Moreover, the performance related to system efficiency (i.e., data transmitted with respect to the whole information needed for estimation purposes) is evaluated by showing the balance between achieved transmission rate and bit error rate. Numerical comparisons have been performed as well as tests on real data and partial implementation of the proposed scheme.

This paper addresses the problem of texture images recovery from compressively sampled measurements. Texture images hardly present a sparse, or even compressible, representation in transformed domains (e.g. wavelet) and are therefore difficult to deal with in the Compressive Sampling (CS) framework. Herein, we resort to the recently defined Graph-based transform (GBT), formerly introduced for depth map coding, as a sparsifying transform for classes of textures sharing the similar spatial patterns. Since GBT proves to be a good candidate for compact representation of some classes of texture, we leverage it for CS texture recovery. To this aim, we resort to a modified version of a state-of-the-art recovery algorithm to reconstruct the texture representation in the GBT domain. Numerical simulation results show that this approach outperforms state-of-the-art CS recovery algorithms on texture images.

In compressive sensing, the Restricted Isometry Property is an analytical condition on the measurement matrix that assures reconstruction of a signal which is sparse either in the spatial or in a transformed domain given an undersampled measurements' set. In this paper, we demonstrate the RIP for a sparse, structured measurements matrix, referred to as Radon-like CS matrix. The sparse Radon-Like CS matrix favorably applies to real sensing problems, since it significantly reduces the energy/bandwidth cost of actually collecting each and every sensed values contributing to the CS measurements. Simulation results confirm the feasibility of field reconstruction from undersampled CS measurements set obtained using the Radon-Like CS matrix.

Vertical handover (VHO) procedure facilitate service continuity in an heterogeneous wireless scenario under varying network as well as channel conditions. Decision criteria for VHO are, mainly, designed to maximize a combination of network parameters in order to guarantee an acceptable service level and maximize network operators and/our users expectation. The objective of this paper is to formalize the VHO decision criteria as a QoS constrain bound problem and propose two strategies that permits to achieve QoS constrains without wasting resources. The former that minimize the power consumption and the latter that minimize the number of VHO. Numerical results are provided in order to compare the two strategies.

Convergence of one-way broadcast and bidirectional unicast networks can be leveraged for efficient delivery of on-demand broadband contents in future telecommunication systems. In this work we are modelling an integrated broadcast and unicast bidirectional network with transcoding capabilities and addressing optimization of on demand content delivery under alternative approaches. Two alternatives are considered which maximize the efficiency of the integrated network providing a compromise between the efficiency and QoS respectively. The approaches are validated through simulations and assessed again a broadcast network without transcoding facilities.

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.

A novel model-based steganographic technique for JPEG images is proposed where themodel, derived from heuristic assumptions about the shape of the DCT frequency histograms, is dependent on a stegokey. The secret message is embedded in DCT domain through an accurate selection of the potentially modifiable coefficients, taking into account their visual and statistical relevancy. A novel block measure, named discrepancy, is introduced in order to select suitable areas for embedding. The visual impact of the steganographic technique is evaluated through PSNR measures. State-of-the-art steganalytical test is also performed to offer a comparison with the original model-based techniques.

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.

One of the hot topics in the communication world is to realize a network able to offer a combination of services complying with different requirements in every place of the world, thus achieving the concept of "entertainment everywhere". In such a context a key role is played by aeronautical world that seems to be one of the last remaining islands in which broadband communications are not available. The present paper aims at studying resource management for a CDMA-based return link via satellite to provide passengers with new generation services. We focus on the connection admission control problem for QoS guarantees, analyzing in particular, the effective bandwidth concept over CDMA discussing its applicability to a multi-service packet switched network. Two admission control algorithms are then derived, based on the effective bandwidth concept for the circuit switched-like services and on a moving average window and linear predictor model for packet switched services. Finally, the performance over aeronautical broadband communication system is evaluated

The choose to perform a C-OFDM modulation directly by satellite makes the design of cost-effective new communication scenarios possible, in periods in which satellite communications call for a higher penetration in everyday services provision, avoiding the high costs of terrestrial-segment infrastructures to make the satellite signal exploitable by mobile users in urban environments. This paper focuses on the analysis of the performances of a C-OFDM-based communication scheme for the provision of a high quality and scalable bit rate radio signal over satellite links and exploitable in urban environments. Due to these preambles, the almost unemployed specifically satellite-oriented Mode-III of the DAB standard is considered, in conjunction with the design of an high-effective receiver based on soft-decision schemes, in cohabitation with almost very spread terrestrial DAB services. The degradations due to propagation and signal distortions introduced by the payload are also taken into account in the analysis of the transmission system

This contribution considers the power control and signal-shaping problem for ad-hoc networks composed by multi-antenna non-cooperative terminals affected by spatially colored multiple-access interference (MAI). The multi-antenna interference channel is modeled as a non cooperative and strategic game. Furthermore iterative power control and signal shaping algorithms are presented to efficiently achieve the Nash equilibrium under best effort and "contracted QoS" policies.

A novel radio modem architecture is proposed for a single-hop ad hoc networks (WLAN) providing wireless access to Internet. The system works at 17 GHz, employs OFDM modulation and provides very high bit rate (up to 160 Mbit/s at physical layer) using TDMA access scheme. Network control is centralized and handled by a device (master), which is run-time selected among all the active devices (slaves). The main focus of the paper is to address the power consumption issue, which is a crucial requirement for portable devices. In particular, the paper described the developed MAC procedures and algorithms concerning the interface with physical layer. Simulation trials show that a considerable power saving can be attained without decreasing system performance.

A novel receiver is proposed for CDMA links with recursive turbo coding, based on a soft-input soft-output multistage interference canceler (IC) and an iterative turbo decoder (TD). After performing IC and TD a first time, the coder state estimates available from the two soft-output Viterbi algorithms in the last TD iteration are exploited to calculate the data bits and the redundancy bits. These are employed for preliminary hard cancellation in the first iteration of a supplementary IC run, and then the TD is run again. An alternative solution with soft feedback is obtained by approximating the reliabilities of the redundancy bits with those of the coder state estimates, and using them for preliminary soft cancellation. Simulation results show the effectiveness of the proposed solutions.

A new maximum a posteriori (MAP) equalizer is proposed for digital radio links affected by large multipath delays. The "sparse" nature of the channel, where a few nonzero powerful taps are spaced by many negligible taps, is exploited to achieve a complexity proportional to the number of nonzero taps. When the channel is time-varying, an efficient nonlinear Kalman like channel estimator is employed to track only the nonzero taps.

We present a new blind equalizer that achieves identification of a channel by exploiting only second-order statistics of the observations. The novelty of the proposed approach is that the receiver accomplishes channel identification by using soft statistics; roughly speaking, it consists of an Abend-Fritchman (1970) type maximum a posteriori (MAP) equalizer that feeds a nonlinear Kalman-like channel-estimator with the soft statistics constituted by the a posteriori probabilities (APPs) of the channel-state sequence. So, since the receiver employs second-order statistics only, it achieves channel identification with fewer symbols than most techniques based on higher-order statistics.

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 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.

GMSK is an efficient modulation technique for digital mobile communications. In this paper a simple solution to the modeling and simulation of GMSK systems impaired by fading channels and additive white Gaussian noise is given, and its effects on the channel characteristics are also considered. The modeling is based on the well-known linearized representation of phase-modulated signals. The analysis is not only useful for modeling and simulation purposes, but also gives a tool for the design of simple receivers.

A new tight analytical upper bound is presented for the performance of finite-delay symbol-by-symbol (SBS) Abend-Fritchman-like decoding of trellis-encoded data crossing arbitrary (eventually time-varying) discrete memoryless channels (DMCs). On the basis of this bound, a related criterion for the optimal design of trellis codes with SBS decoding is then proposed. It gives rise to an effective procedure for the construction of good trellis codes (generally time varying and nonlinear) with assigned decoding complexity.

New analytical upper bounds are derived for the performance of symbol-by-symbol maximum-likelihood (ML) Abend-Fritchman-type detectors for multi-amplitude/phase-modulated digital sequences transmitted over time-dispersive (generally) time-variant linear channels introducing finite intersymbol interference (ISI) and additive white Gaussian noise (AWGN). The proposed bounds are obtained starting from a novel form of the standard Bhattacharyya bound and take explicitly into account the allowed decoding delay. Both deterministic and random multipath slow-fading Rayleigh transmission ISI channels are considered. Simulation results obtained for some test channels of practical interest show the tightness of the derived analytical bounds.

The convergence behaviour of the constant modulus algorithm (CMA) is analytically evaluated in terms of the mean and the variance of the equalized sequence conditioned on the transmitted symbol, thus characterizing the dispersion pattern of the equalized samples around the QAM constellation points. This extends to the CMA and improves the approach of Weerackody et al. (see ibid., vol.40, no.6, p.1383, 1992) , where the MSE trajectory of the generalized Sato algorithm (GSA) was analysed.>

The optimal analog discrete-time feedback communication system is designed for the transmission of a Markov process, such as that generated by a combined source/channel encoder. The forward channel is affected by an additive white Gaussian noise, while the feedback channel is causal and noiseless; no repetition of the transmitted sample is assumed. On the basis of the minimum mean square error (MMSE) criterion, the optimal transmitter and receiver are derived under the constraint of a maximum power level for the transmission over the forward channel. The resulting optimized system is adaptive and fully exploits the available power, thus maximizing the information rate transferred by the system itself. For comparison purposes, the optimal MMSE communication system without feedback link is also designed. The MSE performance of both systems, with and without feedback link, is evaluated by means of closed-form expressions and their convergence rate to the steady state is also computed. Using the feedback link gives significant performance improvements when the input-encoded process is moderately or highly correlated; in this case, the advantages offered by the combined source-channel coding techniques are fully exploited by the proposed optimized feedback communication systems.

The least square estimation problem for pinned-to-zero discrete-index reciprocal Gaussian processes in additive white noise is solved, thus completing and extending some previous results available in the literature. In particular, following the innovations approach a (finite) set of recursive equations is obtained for the filter and for the three standard classes of smoothers (fixed-point, fixed-interval, fixed-lag). Recursive expressions for the mean square performance of the proposed estimators are also given.>

A recursive multistage structure for multicast asynchronous transfer mode (ATM) switching is proposed, based on a connection network with a copying facility and external links connecting the outlets to the inlets. While the network generates only a few copies of an output multicast cell, the remaining are obtained by recycling the output copied cells to the corresponding inputs as many times as necessary. The basic features of a prototype binary multicast switch following the strategy are described. Its performance is also evaluated in terms of throughput and delay, via computer simulation. It is shown that due to the recursive mechanism, the copy generation is spatially distributed in the whole structure and is spread in time. This favorably affects the network's performance.>

The complementary aspects of spectrum estimation based on higher-order order statistics are considered. Higher-order analysis of stochastic array data is formalized in a general fashion through the introduction of the class of hybrid nonlinear (HNL) moments. HNL moments comprise, as a special case, slice cumulants and their mixtures. In this framework, the case of joint use of covariance and fourth-order slice cumulant is handled in a simple and direct way. Simulation results confirm the theoretical analysis.>

The problem of recognizing and locating isolated objects from their images is addressed, and a complete procedure is described. The technique is based on a template matching in the log-polar amplitude spectrum domain and in the space domain. This makes it possible to take properly into account both spectral features and spatial details and to measure with accuracy the scale factor, the orientation, and the absolute position of the object. To reduce the computational burden, pairs of tomographic projections are used in both domains. As an example, the double tomographic method is applied to the classical problem of the automatic reading of printed characters, with the additional specification of unknown size and orientation, and shows good results.>

The technique of template matching in the log-polar visibility (magnitude of Fourier transform in the logarithmic radius and azimuth plane) is proposed as a promising tool for many problems of isolated object recognition irrespective of its position, scale, and rotation. The properties of the log-polar visibility suggests the use of partial information to implement some forms of "reduced template matching". These techniques imply substantial reduction in the computational cost.

The problem of frequency and frequency rate estimation from interrupted observations is addressed. The intuitive fact that the accuracy can be greatly improved by using separate observation intervals is quantitatively discussed. Cramer-Rao bounds and ambiguity functions are given and structures of maximum likelihood receivers are considered.