This study assesses a Vehicle-to-Pedestrian (V2P) collision warning system compared to conventional vehicle-issued auditory alerts in a real-world scenario simulating a vehicle on a fixed track, characterized by limited maneuverability and the need for timely pedestrian response. The results from analyzing speed variations show that V2P warnings are particularly effective for pedestrians distracted by phone use (gaming or listening to music), highlighting the limitations of auditory alerts in noisy environments. The findings suggest that V2P technology offers a promising approach to improving pedestrian safety in urban areas

The majority of research on safety in autonomous vehicles has been conducted in structured and controlled environments. However, there is a scarcity of research on safety in unregulated pedestrian areas, especially when interacting with public transport vehicles like trams. This study investigates pedestrian responses to an alert system in this context by replicating this real-world scenario in an environment using an autonomous vehicle. The results show that safety measures from other contexts can be adapted to shared spaces with trams, where fixed tracks heighten risks in unregulated crossings.

With the race towards higher levels of automation in vehicles, it is imperative to guarantee the safety of all involved traffic participants. Yet, while high-risk traffic situations between two vehicles are well understood, traffic situations involving more vehicles lack the tools to be properly analyzed. This paper proposes a method to compare Surrogate Safety Measures values in highway multi-vehicle traffic situations such as lane-changes that involve three vehicles. This method allows for a comprehensive statistical analysis and highlights how the safety distance between vehicles is shifted in favor of the traffic conflict between the leading vehicle and the lane-changing vehicle.

In this paper the feasibility of an Alert Messaging System which is based on the use of CubeSat nano satellites, Software Defined Receivers and Web Service Technologies is studied. The system resorts to the Multiple Alert Message Encapsulation protocol over Satellite (MAMES) for the delivery of alerts to population in the case of a disaster and is composed by an Alert Issuer, a MAMES Alert Provider, a Satellite Mission Control Center and a Portable SDR User Terminal. The building blocks of the whole system are described, highlighting the interactions between them. The feasibility has been discussed and the proof of the concept of the system is reported.

Cellular network energy optimization is driven by different factors, namely transmission power and activity of the base stations. Quality of Service (QoS) of users is determined by received power, interference and bandwidth allocation and cannot be neglected. In existing studies, such drivers are treated separately, i.e., bandwidth allocation is fixed while power consumption is a variable to be optimized. This paper proposes a novel optimization framework which is aimed at minimizing the power consumption in cellular networks while affording a minimum bit rate for each mobile terminal by jointly considering energy consumption and QoS drivers. Mixed Integer Quadratic Programming (MIQP) based optimization framework solves the problems of the determination of the user association, the bandwidth allocation, the identification of the active base stations and their transmission power, guaranteeing also a requested service rate for each user. The proposed solution is shown to allow power savings of up to 60%, very close to the optimum lower bound, when the traffic is below the 35% of the maximum load.

In the last years, Activity Recognition (AR) has drawn the attention of many researchers in several fields such as user mobility identification and monitoring of patients and of daily activities. In the context of Dead Reckoning (DR) navigation systems, AR has been used so far to get landmarks on the map of the buldings and permit the calibration of the considered routines. The present work aims at providing a contribution to the definition of a more effective recognition of movement in the DR applications. To this aim we describe the implementation of a Movement Segmentation procedure which permits to distinguish between posture change movements, such as lying down and standing up, and cyclic movements such as walking, walking downstairs and upstair. As it is known, these movements which are very similar and prone to critical recognition analysis, can often be misleaded; therefore, they are considered as inputs of a supervised learning technique which allows their classification. Particularly, the acceleration data are acquired from a Motion Node sensor that is worn on front right-hip and four supervised learning classification families, namely the Decision Tree (DT), the Support Vector Machine (SVM), the K-Nearest Neighbor (KNN) and the Ensamble Learner (EL), are tested. The accuracy of the considered classification models is evaluated; particularly, the confusion matrices are presented which shed light on the collection of the movements that are more likely to be mixed up.

Orthogonal Frequency Division Multiplexing (OFDM) transmission technique has been considered for the 4G LTE-Advanced system because of its high performance and low complexity. In the new 5G scenario this type of modulation is not properly suited because of the additional requirements for very high spectral efficiency, low latency and low out-of-band (OOB) emissions. Thus, new waveforms have been chosen to replace it and effectively deal with these problems. Particularly, recently proposed multicarrier techniques as the Generalized Frequency Division Multiplexing (GFDM) and the Filter Bank Multicarrier (FBMC) modulations are two of the main candidates techniques for the new 5G standard. As for classical OFDM technique, the channel estimation is a crucial functionality for the all multicarrier approaches. In this paper we generalize a recently proposed method for the computation of the MSE on the time-frequency domain for pilot based channel estimation techniques in multicarrier system. This method permits to determine the most suitable channel estimation algorithm for a given wireless channel as well as to define the suitable pilot density in order to afford a target MSE value for a given SNR level. Hence, in this paper a general design tool for multicarrier systems is proposed.

This paper describes an innovative monitoring technology that is used to detect ground-level ozone pollution and is based on the deployment of a network of wireless devices which are connected to a collection of plants and are used as biosensors. Such devices retrieve and transmit the electrical activity signals, which are generated within the plants, and use them to monitor environmental conditions. The distributed plants act as wireless sensors which communicate with a weather station, that equipped with meteorological sensors as well as data logging and both wireless and wired communication capabilities. A back end server collects and analyzes the real-time data from the station and delivers environmental and ozone pollution information to the users through a web portal. In order classify the level of ozone exposure, a correlation-based approach has been used. A pilot system has been implemented with a sensing infrastructure that is composed of four plants and started operating in November 2014. As the data collection volume increases, more accurate classification techniques can be adopted.

The objective of increasing the Energy Efficiency of communication systems must cope with a sustained growth of the market, a greater penetration of broadband services in everyday life, higher data rate services and a large increase of the number of mobile subscriptions. In this scenario, a particular attention has to be devoted to energy saving strategies that may also contribute to the reduction of greenhouse gas emissions. The goal of an effective energy saving strategy is to reduce the power consumption without introducing any significant decrease in the network and system performance. In this paper we present the complete performance evaluation of a previously proposed strategy: particularly, the considered joint Radio Resource Management (RRM) strategy is based on the use of the cell sleep mode and the reduction of the maximum transmission power at the base station; the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. A detailed evaluation of system performance is done with reference to the no energy saving case. Results show the effectiveness of the propose strategy in heterogeneous networks (Het-Nets) where cells of different sizes effectively coexist.

This paper aims at providing a thorough analysis of the energy efficiency of the TeTRA (TErrestrial Trunked RAdio) private cellular system. In particular some effective dynamic radio resource management solutions are presented, highlighting the impact on daily energy consumption. Moreover, the potential benefits of the transition which can be envisaged to the recently proposed TeTRA over LTE system are evaluated in terms of capacity and energy saving.

The definition of LTE and LTE-Advanced standards aims at improving the performance of cellular networks with the final goal of a fair competition between wired and wireless communication systems. In order to guarantee excellent performance, one of the crucial challenge to cope with is the introduction of advanced channel estimation techniques for Multiple Inputs Multiple Outputs (MIMO) systems. In this paper, we will review and compare several Pilot-Based Channel Estimation algorithms for MIMO LTE downlink communications. Channel estimation algorithms will be analysed for different multi-antenna schemes, namely 2×2 and 4×4 with Alamouti space-frequency coding. The performance of all of these schemes will be considered both for uncoded and coded systems. The simulation results will be obtained for a multipath fading channel, assuming high speed mobility for the mobile terminals.

Due to the enormous spreading of applied wireless networks, security is actually one of the most important issues for telecommunications. One of the main issue in the field of securing wireless information exchanging is the initial common knowledge between source and destination. A shared secret is normally mandatory in order to decide the encryption (algorithm or code or key) of the information stream. It is usual to exchange this common a priori knowledge by using a “secure” channel. A new modulation technique, able to encrypt the radio signal without any a priori common secret between the two nodes, was previously proposed by the authors [1]-[3]. The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. This contribution improves the previous works by exploring the real robustness of the proposed technique against the presence of DOS warriors and impairment of the radio channel, considering also implementation details, such as the bit integration time. Both the case of passive and active attacks have also been implemented and simulated by using the Matlab Simulink.

Nowadays, the pursuit of energy efficiency is one of the main challenges of present and future mobile communications. The growth of the mobile communication market which has been increased by the proliferation of smartphones and laptops and the rising of data traffic subscriptions claims for an improvement of network capacity and, consequently, of the infrastructure. In this scenario, in order to contain operative expenditures, the network operators must pay attention to energy saving strategies that may eventually also contribute to reduction of greenhouse emissions. In this paper, the exponential smoothing technique is applied to achieve a traffic forecast for all the coverage area, considering daily and weekly data communication trends: in particular, the base station transmission power can be adapted in order to save energy and guarantee the requested network capacity. Results show the effectiveness of traffic forecast technique for the prediction of the requested capacity and for the maximization of the energy efficiency, allowing performance very close to the optimum case.

This paper aims at investigating the integrated satellite/terrestrial interactive e-health system, which has been developed within the framework of the European Space Agency (ESA) project TElemedicine Services for HEALTH (TESHEALTH) in collaboration among industry, academia, and hospitals. The implementation of a secure, scalable and flexible heterogeneous network capable of providing the appropriate infrastructure, is analysed, focusing on the end to end QoS solution, that satisfies the quality level required by the telemedicine applications. Moreover the developed interactive Service Platform, which aims at sharing health information among the different applications and services (Self-Care and Assisted Services) and includes realtime audio and video interactions among patients, specialists and health service providers, is described.

In this paper we study simple and feasible cooperative relaying strategies which rely on the introduction of the Delay Diversity technique in a DVB-SH compliant hybrid satellite/terrestrial network. These strategies are investigated in a public emergency scenario where the adoption of a hybrid network combined with the cooperative diversity techniques guarantees the connection between the incident area and the external areas: particularly, the drawbacks of the Non-Line-Of-Sight (NLOS) propagation are mitigated. The proposed schemes are analysed and compared, highlighting the assumptions required and the simulation results with respect to the satellite-only and the terrestrial-only cases.

Due to the enormous spreading of applied wireless networks, security is actually one of the most important issues for telecommunications. One of the main issue in the field of securing wireless information exchanging is the initial common knowledge between source and destination. A shared secret is normally mandatory in order to decide the encryption (algorithm or code or key) of the information stream. It is usual to exchange this common a priori knowledge by using a "secure" channel. Nowadays a secure wireless channel is not possible. In fact normally the common a priori knowledge is already established (but this is not secure) or by using a non-radio channel (that implies a waste of time and resource). This contribution deals with the proposal of a new modulation technique ensuring secure communication in a full wireless environment. The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. The probability of error/detection is analytically derived for the legal users and for the third unwanted listener. The proposed scheme has also been implemented in a Xilinx Virtex II FPGA. All the results show that the performance of the proposed scheme yields the advantage of intrinsic security, i.e., the mutual information cannot be physically demodulated (passive attack) or denied (active attack) by a third terminal, leading us to conclude that the proposed technique is really useful for private key distribution in every wireless network.

Cognitive Radio provides a paradigm to enable an efficient and performing use of spectrum resources. Several challenging issues are still to be solved in order to fully exploit the CR potentials. One of these is the development of efficient distributed power allocation methods to be performed by the independent decisional entities of the network. Game Theory, and in particular S-Modular Games, are attracting since they provide useful tools for the definition of multi objective distributed decisional algorithms in the context of radio communications.

Cooperative relaying systems represent a promising solution for future wireless communications. In this paper simple cooperative relaying strategies are proposed in order to improve the performance of a WiMAX network, overcoming the drawbacks of a non-line-of-sight (NLOS) propagation. The cooperative schemes proposed combine the amplify and forward (AAF) and the decode and forward (DAF) algorithm with delay diversity (DD) and cyclic delay diversity (CDD) techniques, in order to exploit the features of the wireless communication channel. We investigated the pros and cons of each scheme, comparing the assumptions which are required and the simulation results with respect to two cooperative implementations of the Alamouti scheme.

A DVB-RCS based, hierarchical satellite network model is presented. The network is constituted by two levels for the allocation of the resources, i.e. beam level and terminal level. For each level will be studied two different approaches, in particular the second level resource allocation has been developed according two different game theoretical approaches, based on both non-cooperative and cooperative game theory.

In this paper an original detection strategy for satellite digital broadcasting communications is defined; particularly, we consider the DVB-S2 system, which is proposed as a development of the DVB systems and exploits iterative decoding and higher order modulation. The proposed approach relies on the use of the information which can be obtained by proper soft demapping schemes. Moreover, we introduce an original receiver which is based on iterative demapping and decoding. The adoption of these strategies permits a remarkable performance gain and an improvement of the system throughput.

The problem addressed in this work is the direct reception of DVB-S(2) satellite signals from mobile terminals equipped with low gain (non directive) antennas. DVB-S2 is broadcasted with GEO satellites and mobile receivers usually need great antenna gains in order to compensate the large pathloss encountered in the downlink. Cooperation strategies can help in this context. In the paper we show analytical and simulated performances of a physical level link cooperation conducted by a cluster of mobile users in the vicinity of the current active user.

This paper deals with a turbo multiuser detector suitable for applications in overloaded coded DS-CDMA systems. The turbo-MUD receiver is based on the use of a linear MMSE detector in the first iteration and a parallel interference cancellation scheme in the successive ones. The inputs of the interference cancellator are both the detector outputs and the soft information from a bank of turbo decoders. The performance of the proposed receiver has been derived by means of computer simulations and applications of the density evolution theory: in particular, this technique permits to properly evaluate the number of MMSE iterations, simplifying the overall receiver design.

This paper deals with a variable rate discrete multi-tone modulation (DMT) system for broadband power-line communications (PLCs), based on the bit-loading algorithm proposed by Leke and Cioffi. In the proposed system a suitable LMS channel estimator is considered, which is based on the insertion of a training sequence (TS). The proposed approach will be compared with the ideal channel estimates, showing its effectiveness. Moreover, different TS lengths will be compared. The performance of the system, expressed in terms of bit-rate and bit error rate (BER), with and without an estimation error is derived by simulation under the assumption of frequency-selective multipath fading channel and additive colored Gaussian noise, according to the in-building networks model.

An original turbo multiuser detector for overloaded coded DS-CDMA systems is presented and studied; the performance of the proposed system is tested by Monte Carlo simulations and by means of the density evolution theory. The turbo-MUD receiver is based on the use a combination of a linear MMSE detector in the first stage and an interference cancellation scheme in the successive ones. The inputs of both receivers are the soft information from a bank of turbo decoders. The performance of the proposed receiver can be effectively predicted in overloaded communication systems by means of the density evolution technique; the use of this technique also permits the proper number of MMSE iterations to be evaluated, making the design of the receiver easier.

In this paper, we investigate the performance of a generic filterbank transceiver in the presence of a carrier frequency offset. We propose a theoretical model to compute the error probability in the case of a generic frequency-selective channel. Moreover, the proposed method is also extended to deal with nonuniform, i.e., wavelet, transceivers. The accuracy of the model is evaluated by means of computer simulations, using several types of filterbank transceivers. Systems based on cyclic prefix (CP) and zero padding (ZP) are considered to avoid interblock interference (IBI) in frequency-selective channels. The analytical results obtained with the proposed method allow us to quickly compare different systems, characterized by a different filterbank selectivity, as well as by different methods to combat IBI (ZP or CP).

Abstract This paper investigates the use of bi‐orthogonal modulations in multiuser communication systems based on ultra wide band impulse radio (UWB‐IR) technology: the communication systems considered herein use Gaussian waveforms in AWGN channel and rely on the utilization of a time‐hopping spreading technique. A hybrid pulse modulation is defined, which is obtained by combining pulse amplitude modulation (PAM) and pulse position modulation (PPM) techniques. Particularly, we have compared the bi‐orthogonal system performance to the classical orthogonal one, also in the condition of lack of a general synchronism, possibly caused by the presence of interfering users that belong to a separate network. Moreover, we have taken into account the use of an M‐ary alphabet, in the case of orthogonal and bi‐orthogonal modulation schemes. Copyright © 2005 John Wiley & Sons, Ltd.

This work presents a turbo multiuser detector for turbo-coded DS-CDMA systems, which is based on the utilization of parallel interference cancellation scheme and antenna diversity in the receiver. Since a wireless rich-scattering block fading channel is considered, multiple access interference effects are naturally reduced by antenna diversity, and are successively and completely eliminated by a single turbo cancellation iteration, for a half-loaded system. We also show that the proposed turbo-PIC detector is characterized by the remarkable performance in terms of BER even for overloaded systems: particularly, we stress the low complexity required to suppress MAI and achieve excellent results in the block fading environment where the high correlation value strongly limits the single user bound.

This paper deals with a modified version of a blind adaptive multiuser detector for direct sequence code-division multiple-access (DS-CDMA) wireless communication systems which is named precombining blind adaptive multiuser detector (PBA-MUD). The main properties of this receiver are low complexity, multiple-access interference mitigation and remarkable near-far resistance in time-varying multipath fading scenarios. In particular, the PBA-MUD is based on a blind adaptive algorithm that allows the detector to avoid deep fading impairments and the cancellation of the desired signal due to signature sequence mismatch. Nevertheless, such a receiver experiences a performance degradation in fast fading channels. In order to overcome this problem, a window reprocessing technique (Del Re et al., 2001) was introduced which yielded a new blind detection algorithm. It will be shown that this receiver, together with this new algorithm [precombining reprocessing window blind adaptive multiuser detector (PWBA-MUD)] allows a high performance without requiring training sequences or the knowledge of the interfering signature waveforms in multipath fast fading channels.

Recent research addresses towards multitransmit, multireceive antenna scheme to improve the performance in high data rate wireless communications. In this paper, we examine the combination of Bell-Labs layered space time (BLAST) wireless architecture and the iterative demapping and decoding, the turbo decoding principle. This structure, known as T-BLAST, was evaluated according to the IEEE 802.11b standard requirements for wireless LAN. The paper considers the design of the modified 'soft' Complementary Code Keying (CCK) modulation/demodulation scheme more suitable for the iterative interference cancellation receiver and shows the performance evaluation of this T-BLAST and SOFT CCK MODEM in the specific environment of the IEEE 802.11b standard. The paper also presents the throughput versus distance to receiver varying the number of transmit antennas in the indoor environment.

This paper deals with the implementation and the assessment of a wideband directional channel model (WDCM) based on the COST 259 recommendations. Cluster of replicas are introduced by means of tapped delay line (TDL). A good compromise between accuracy of the model and complexity required by the simulator is guaranteed by a suitable statistical approach based on deterministic considerations. In the paper a WDCM implementation for a micro cell case is presented, with particular attention to the cluster position and the mobility model concept. Finally, channel model assessment is performed by comparing simulation results in the general street los radio environment with a recent measurement campaign. Proposed channel model can be used in a link level simulator (LLS).

This paper deals with the comparison among two schemes of space-time MMSE reception implemented for the forward link of a WCDMA multisatellite UMTS environment The so called space-time transmit diversity technique (STTD) has been coupled with the minimum mean square error (MMSE) interference suppression technique. The idea has come from the realization that the diversity gain is limited by a medium-high level of multiple access interference (L. Mucchi et al., 2002). The proposed schemes can be distinguished by the order in which the space-time processing and the MMSE interference suppression are performed. We named ST-MMSE Pre STTD Combining if the MMSE filtering is performed before the space-time combining and ST-MMSE Post STTD Combining if the interference suppression and the space-time combining are jointly processed. A realistic multisatellite UMTS environment has been simulated in order to compare the proposed detectors. Bit error rates have been calculated by mean of Monte Carlo simulations assuming a time-varying satellite channel model. Simulations show that the Post-combining scheme gives the best results, but it implies more complexity to the mobile terminal. Anyway, both the proposed ST-MMSE schemes yield significantly better performance than the standard STTD receiver or the conventional RAKE receiver.

This paper presents a turbo multiuser detector for turbo-coded DS-CDMA systems, based on the utilization of a PIC and a bank of turbo decoders, in which the PIC performs interference cancellation after each constituent decoder of the turbo decoding scheme. Moreover, we propose a new enhanced estimator of the signal-to-noise-plus-interference-ratio used in the decision device and in the MAP decoding algorithm. By means of computer simulations, we show that the proposed receiver outperforms other similar schemes for medium to very high system loads, in AWGN and multipath fading channel.

In the third generation communication system, due to the average increase of the radio link bandwidth requirements and the power constraints at the mobile S-UMTS terminal, the system capacity will meet its physical limitations even in a moderated deployment scenario. In the 3GPP standard, due to the complexity constraints at the user equipment, the DTX implementation on the uplink channel is heavily limited. The transmission scheme presented in this paper is an extension of the traditional informative symbol set with a zero energy symbol. The silence symbols are integrated with the informative ones and delivered to the radio link layer for transmission. The paper presents a theoretical formulation of the optimum two-state receiver. Comparisons with the traditional single-states receiver are obtained with a theoretical approach and through computer simulations. In the latter case a real Globalstar-like S-UMTS environment show the better performances of the proposed scheme for fast varying sources.

Satellite communications exhibit a tremendous growth due to three main elements: interactivity, coverage and bandwidth asymmetry. The paper explores some of the current trends in the development of next generation satellite systems by analyzing several aspects: from orbital tracks to technology, from services to business opportunities. Both positive and negative experiences are considered in order to understand fully the most probable future scenarios in the satellite area.

This paper deals with a multiuser cancellation detection scheme combined with antenna arrays, for wideband code division multiple access (WCDMA) communication systems where different traffic load and different data rate are considered. The proposed receiver, defined as space time-selective parallel interference cancellation detector, is designed to be used at the base station of a WCDMA communication system. Asynchronous users and multipath fading phenomena are considered in our analysis. The proposed receiver basic assumption is to divide signals into two different groups according to the received power level. The reliable ones are directly detected and cancelled from the whole received signal, by each sensor, before making the decision on not reliable signals, without any further processing delay. Performance evaluation has been carried out in terms of P/sub e/ (bit error probability) by means of computer simulations. In particular, it is shown here that the proposed receiver exhibits a good behaviour and lowers the computational complexity in comparison with previously proposed alternatives.

Next generation wireless communication systems are characterized by high bit-rate services. UMTS systems, already subject to standardization process, require a strict synchronization also for the uplink (mobile-to-base) channel. The operation is not trivial due to the fact that during the acquisition process, non-synchronous users can impact on the ongoing transmissions reducing the overall systems efficiency. The following proposal describes a different approach to the synchronization problem which is based on a dedicated channel, shared by more users with a OFDM-CDMA transmission technique. The paper focuses on the adaptive algorithm used by the base station to track the users into the synchronization dedicated channel. The results obtained by computer simulations explore the dependence of the performances from the many parameters involved.

In this study we propose a new method to design pseudo-QMF prototype filters to implement near perfect reconstruction (NPR) cosine-modulated filter banks. The method is based on the eigenfilter approach, that is simple to implement, but, nevertheless, is very efficient in designing high attenuation prototype filters. The method also allows to design complex coefficient prototypes that can be used to build nonuniform filter banks. The effectiveness of the method is demonstrated by means of some examples of design of both uniform and nonuniform filter banks.

This paper addresses the problem of blind equalization for digital communications using an array of sensors at the receiver to copy constant modulus signals in the presence of heavy-tailed additive channel noise. First, we demonstrate the negative effects of channel noise to the original constant modulus algorithm (CMA) cost function in terms of convergence. Then, we introduce a new CMA criterion based on the fractional lower-order statistics (FLOS) of the received data. The proposed criterion is able to mitigate impulsive noise at the receiver and at the same time restores the constant modulus character of the transmitted communication signal. We perform an analytical study of the properties of the new cost function and we illustrate its convergence behavior through computer simulations.

This paper deals with the performance evaluation of various resource management strategies that are suitable for low Earth orbit mobile satellite systems (LEO-MSSs). A user mobility model has been proposed and its statistical parameters have been derived. Both fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques have been considered. Moreover, in order to reduce the handover failure probability, we have assumed that interbeam handover requests which do not immediately obtain service can be queued. In particular, two different queuing disciplines have been compared: (a) the first input first output (FIFO) scheme and (b) a new technique called last useful instant (LUI) which is based on the knowledge of the maximum time within which the handover procedure must be accomplished. Implementation aspects for the LUI technique in a LEO-MSS have been discussed also in comparison with the measurement-based priority scheme (MBPS), previously proposed in the literature on this subject. The efficiency of the LUI queuing scheme as regards the FIFO technique has been investigated by simulations for both DCA and FCA techniques. An analytical approach has been also presented in order to allow the performance evaluation of the FCA scheme with different handover queuing disciplines.

The eigenfilter approach is applied to designing Infinite Impulse Response (IIR) filters having an arbitrary magnitude frequency response. A causal rational transfer function having an arbitrary number of poles and zeros is achieved. The procedure works in the frequency domain. Some numerical examples showing the application of the presented method to the design of multiband filters with different gains and different magnitude shape in each band are presented.

The availability of broadband networks and the advent of standards and technologies for real time multi-point communications allow a new educational system. The paper describes a live remote educational service in satellite/terrestrial environments and an educational tele-medicine service in the Ku/Ka band.

This paper deals with a multiuser detector based on a new decorrelating approach for asynchronous up-link DS/CDMA communications in which the QPSK modulation scheme is used in transmission. It is shown that the receiver proposed is near-far resistant and exhibits a low complexity which allows real-time operation. The performance is expressed in terms of the bit error rate (BER) which has been derived by simulations under the assumption of a slow frequency-selective Rayleigh fading channel.

The paper presents a Euclidean distance maximum likelihood sequence estimation (MLSE) receiver, based on the Viterbi algorithm (VA), suitable for fading and noisy communications channels, as that specified by the Group Special Mobiles (GSM). In a mobile cellular system, the fast varying channel characteristics, due to the fading and Doppler effects, require adaptive methods to update the channel coefficients to the MLSE receiver. The proposed technique continuously estimates the channel characteristics directly within the metric calculation of the VA. At each step of the VA, the sequence associated to the path with the best metric value (minimum-survivor method) among the survivor paths is used to update the channel estimate (employing conventional adaptive algorithms) throughout the entire informative sequence. However, the detection of the transmitted data sequence is performed by the VA only at the end of each burst. The proposed technique allows simpler receiver implementation and the simulation results show a good performance of this adaptive MLSE receiver in typical GSM environments.

A method of designing non-uniform FIR filter banks is presented. It is based on the cosine modulation of more than one prototype, having different passbands. The method aims at the cancellation of the main component of aliasing: this imposes constraints on the prototypes, which become dependent of each other. The method is simple and requires numerical optimization only for the narrowest prototype, being the others derived in a straightforward way from this one. For this reason, the method seems particularly suitable when banks with a large number of coefficients must be designed.

Efficient dynamic channel allocation techniques with handover queuing suitable for applications in mobile satellite cellular networks, are discussed. The channel assignment on demand is performed on the basis of the evaluation of a suitable cost function. Geostationary and low Earth orbit (LEO) satellites have been considered. In order to highlight the better performance of the dynamic techniques proposed, a performance comparison with a classical fixed channel allocation (FCA) has been carried out, as regards the probability that a newly arriving call is not completely served. It has also been shown that a higher traffic density, with respect to GEO systems, is manageable by means of LEO satellites.>

In an integrated cellular/satellite system for mobile communications a satellite subsystem cooperates with a terrestrial cellular network for providing user services. The paper addresses the problems related of the reuse of the procedures of the GSM cellular standard in an integrated system. Allowing at most changes only at the mobile terminal and/or in the satellite network. The results of the study show that most of the GSM procedures can be reused in an integrated system (in a few cases with limited protocol variations) but some others would require modifications to the cellular network. The results of this study shall also be useful for the suitable definition of the protocols of an integrated satellite/terrestrial system for the next generation of mobile and personal communication services.>

Neural networks have been successfully applied in many fields thanks to their learning and generalization capabilities and to the parallel processing and fault tolerance properties. Typical applications concern images processing, pattern recognition and digital signal processing, such as adaptive filtering and channel equalization. The authors propose the use of neural networks as digital receivers for continuous phase modulation (CPM). Simulation results refer to the European GSM digital cellular radio system. The neural receiver performance has been evaluated for coherent detection, considering an additive white Gaussian noise (AWGN) channel and compared with a maximum likelihood sequences estimator (MLSE) receiver based on the Viterbi algorithm. The paper also presents a hardware implementation of the proposed network based on a digital signal processor (DSP) and on a programmable gate array (PGA).>

Modeling alternatives for a fast packet switching system are analyzed. A nonblocking switch fabric that runs at the same speed as the input/output links is considered. The performance of the considered approaches are derived by theoretical analysis and computer simulations. Performance comparison between input queueing approaches with different selection policies are presented. Novel input and output queueing techniques are also proposed. In particular it is shown that, depending on the implementation, the input queueing approach studied in this paper achieves the same performance as the optimum (output) queueing alternative, without resorting to a faster packet switch fabric.>

A simplified structure concerning the implementation of an adaptive digital receiver suitable for the pan-European cellular system Group Special Mobile (GSM) is described. In the GSM system, the performance of the received information is strongly affected by the multipath typical of the mobile communications channel. The proposed maximum-likelihood sequence estimation (MLSE) receiver based on the Viterbi algorithm compensates for selective distortion due to the multipath propagation and Doppler shift also in the case of fast channel variations using an adaptive tracking mode method.>

Frequency-division multiple access (FDMA) and single channel per carrier (SCPC) in the uplink and time-division multiplexing (TDM) in the downlink are employed in the system described. To interface FDMA in the uplink and TDM in the downlink, multicarrier demodulation (MCD) is required onboard the satellite. The operation of the onboard MCD is the separation of each individual channel and subsequent demodulation. The results, which concern onboard frequency demultiplexing and demodulation for low-bit-rate carriers, are constrained by the requirement that new-generation payloads could serve the stations already active in the INTELSAT Business System. A digital hardware design that implements an MCD that can process three channels at 4.4 Mb/s or 12 channels at 1.1. Mb/s is described. The test results confirm the MCD feasibility, and further improvements are expected from a semicustom implementation.>

A multibeam fast packet switching satellite communication network serving multiple zones is studied. The synchronous time division multiple access protocol (TDMA) is used in transmitting messages in the uplink channels while the asynchronous time division multiple access protocol (ATDMA) is used in the downlink channels. Moreover, fast packet switching capabilities are assumed on-board the satellite. Alternatives for the architecture of the on-board fast packet switching fabric are considered. The performance of the considered approaches has been derived by theoretical analysis and computer simulations. A novel input queuing technique is also proposed and analyzed to show that it achieves better performance with respect to the classical input queuing approach. Therefore, by means of the novel input queuing approach it is possible to lower the end-to-end delay without increasing the complexity of the on-board equipment.>

A two-dimensional signal-scrambling method implemented by digital signal-processing techniques that eliminate the need for frame synchronization without impairing security is presented. Such techniques include short time Fourier analysis and the filter bank concept. The use of special digital finite-impulse-response filters, which make it possible to implement the system algorithm completely via commercial processor software, is discussed. As a result, the system can be configured with very little hardware. Methods for determining available keyspace and selecting keys are also presented.>

In this paper a complete communication system simulation package is described, which includes digital as well as analog operations to be performed on the signal to be transmitted. The package simulates the transmitter, the communication channel, and the receiver. The digital transmission simulation considers data communication systems with digital filtering, source and channel coding performing the operations of transmitter coding and receiver decoding. The two coding operations can be realized both separately and independently and in a strictly connected or "integrated" form. The analog transmission simulation includes the modulator, the transmitter pulse shaping filter, the communication channel, the receiving filter, and the demodulator. This section is very general, so that it allows the simulation of both analog and digital transmissions. Simulation results are presented regarding some combinations of the following techniques: predictive source coding, block codes able to correct random and burst errors, and modulation techniques such as AM,M-level PSK, FSK, and MSK. In particular, the paper presents the results of the analyses of an integrated source-channel coding applied to digital transmissions and of a system transmitting both voice and data for a VHF communication link between ground and aircraft for air traffic control applications.

An improved structure for an envelope detection multifrequency receiver based on digital nonrecursive quadrature filters is proposed. The receiver utilizes a property of digital nonrecursive quadrature filters to reduce the required computational complexity by a nominal factor of 2 with a negligible hardware increase. The application to the tone detector implementation for two CCITT standard signaling systems is considered, showing the low computational and structural complexity required by the proposed technique. The required multiplication rate is reduced by more than twice with respect to other conventional approaches.

A digital per-channel transmultiplexer system, based on the generation of a baseband analytic signal and on its successive interpolation and filtering, is considered. The method employs complex filters. To meet the CCITT specifications on the conversion system group delay, minimum-phase FIR complex filters are required. Their design is described in this paper. The system design also includes the evaluation of the wordlengths of the filter coefficients and the arithmetic operations. Computer simulations show that a 16 bit arithmetics is suitable throughout the whole conversion system. These characteristics suggest convenient hard-ware implementations with low-cost arithmetic circuits.

A new non-FFT approach to transmultiplexer implementation is presented, based on the theory of the baseband analytic signal and on its successive allocation in the FDM format by appropriate digital interpolation and filtering. The method allows wide transition bandwidths to the filters, avoids the use of any product modulator, and leads to a channel-by-channel structure. As a design example, the applicatiion to the 12-channel FDM primary group is Considered in detail, using FIR digital filters realized by 16 bit arithmetic standard digital Circuits. The analysis and the computer simulation of the system performance are finally reported, showing the actual feasibility of the method for the transmultiplexer implementation.