Computation sharing is one of the most promising services in fog computing allowing the Fog Nodes (FNs) to share among themselves data and tasks to be computed. In case of battery powered-FNs, energy consumption becomes an issue. Simultaneous Wireless Information and Power Transfer (SWIPT) is a recently introduced technology enabling data and power transfer through microwave links among different nodes. In this work, we have considered the presence of a battery powered FN able to simultaneously share data and harvest energy from a Fog Access Point (F-AP), supposed to be plugged to the electrical network. The aim of this work is to define two suitable bounds able to drive the offloading decision to be taken by the battery powered FN, based on the estimated packet generation time, with the aim of having a stable energy system. We have further studied the impact of bandwidth and packet size on the two bounds. Simulation results demonstrate the impact of SWIPT-based offloading decision algorithm on network in terms of latency and network lifetime.

Edge Computing refers to a recently introduced approach aiming to bring the storage and computational capabilities of the cloud to the proximity of the edge devices. Edge Computing is one of the main techniques enabling Fog Computing and Networking. Among several application scenarios, the urban scenario seems one of the most attractive for exploiting edge computing approaches. However, in an urban scenario, mobility becomes a challenge to be addressed, affecting the edge computing. By gaining from the the presence of two types of devices, Fog Nodes (FNs) and Fog-Access Points (F-APs), the idea in this paper is that of exploiting Device to Device (D2D) communications between FNs for assisting computation offloading requests between FNs and F-APs by exchanging status information related to the F-APs. With this knowledge, this paper proposes a partial offloading approach where the optimal tasks amount to be offloaded is estimated for minimizing the outage probability due to the mobility of the devices. In order to reduce the outage probability we have further considered a relaying approach among F-APs. Moreover, the impact of the number of tasks that each F-AP can manage is shown in terms of task processing delay. Numerical results show that the proposed approaches allow to achieve performance closer to the lower bound, by reducing the outage probability and the task processing delay.

Fog Computing offers storage and computational capabilities to the edge devices by reducing the traffic at the fronthaul. A fog environment can be seen as composed by two main classes of devices, Fog Nodes (FNs) and Fog-Access Points (F-APs). At the same time, one of the major advances in 5G systems is decoupling the control and the data planes. With this in mind we are here proposing an optimization technique for a mobile environment where the Device to Device (D2D) communications between FNs act as a control plane for aiding the computational offloading traffic operating on the data plane composed by the FN - F-AP links. Interactions in the FNs layer are used for exchanging the information about the status of the F-AP to be exploited for offloading the computation. With this knowledge, we have considered the mobility of FNs and the F-APs' coverage areas to propose a partial offloading approach where the amount of tasks to be offloaded is estimated while the FNs are still within the coverage of their F-APs. Numerical results show that the proposed approaches allow to achieve performance closer to the ideal case, by reducing the data loss and the delay.

This paper is motivated by the concept that the successful, effective, and sustainable implementation of the smart city paradigm requires a close cooperation among researchers with different, complementary interests and, in most cases, a multidisciplinary approach. It first briefly discusses how such a multidisciplinary methodology, transversal to various disciplines such as architecture, computer science, civil engineering, electrical, electronic and telecommunication engineering, social science and behavioral science, etc., can be successfully employed for the development of suitable modeling tools and real solutions of such sociotechnical systems. Then, the paper presents some pilot projects accomplished by the authors within the framework of some major European Union (EU) and national research programs, also involving the Bologna municipality and some of the key players of the smart city industry. Each project, characterized by different and complementary approaches/modeling tools, is illustrated along with the relevant contextualization and the advancements with respect to the state of the art.

Fog computing is a fascinating paradigm which has drawn attention recently by bringing the cloud capabilities closer to the users. A fog computing infrastructure can be seen as composed by two layers: one including Fog Nodes (FNs) and another the Fog Access Points (F-APs). While FNs are usually battery operated, the F-APs are instead connected to the electrical networks having unlimited energy. Moreover, F-APs facilitate the computation of tasks due to their higher storage and computational capabilities compared to the FNs. Considering FN energy consumption and task processing delay, we propose a suboptimal partial offloading technique aiming at exploiting jointly both FNs and F-APs. The simulation results demonstrate how partial offloading has a profound impact on the network lifetime and reduces energy consumption and task processing delay by comparing the single and two layer architectures.

Interference detection and mitigation are important issues to guarantee the availability and service continuity of Global Navigation Satellite Systems. In this paper, a new method based on a joint spectral and time-frequency (TF) analysis is proposed for jamming excision. It localizes the time-varying energy spectral density of the interfering signal by using the S-transform, then employs a binary mask to filter out the interference power. This approach is not model-driven and is computationally efficient. These features make it a practical add-on for GNSS receivers. We evaluate the effectiveness of the method presented by testing the acquisition of a Galileo signal under jamming attack. Simulation results prove that the performance in terms of code acquisition are significantly enhanced, even under challenging reception conditions.

The evolutionary trends of the Information Society have lead to the definition of the so-called Smart City, an environment characterized by the interaction of several heterogeneous technologies aiming at providing unprecedented services and efficiency. The Smart City is one of the most challenging scenarios for the Internet of Things (IoT) applicability. Among several things composing a Smart City, the computing infrastructures are responsible for giving a distributed elaboration intelligence to the environment. This paper takes into consideration the presence of the Mobile Cloud Computing (MCC), where different types of Cloud Computing Infrastructures (CCIs) are available through different wireless connections. MCC can be exploited by Smart Mobile Devices (SMDs) for offloading applications towards powerful remote servers and other SMDs pooled together, shortening execution time and extending battery life. Aim of this paper is to propose a cluster based computation offloading technique able to work in a distributed environment, in order to better satisfy the Quality of Service (QoS) requirements of the SMD users, by minimizing a cost function taking into account a tradeoff between SMD's energy consumption and execution time.

The Smart cities applications are gaining an increasing interest among administrations, citizens and technologists for their suitability in managing the everyday life. One of the major challenges is regarding the possibility of managing in an efficient way the presence of multiple applications in a Wireless Heterogeneous Network (HetNet) environment, alongside the presence of a Mobile Cloud Computing (MCC) infrastructure. In this context we propose a utility function model derived from the economic world aiming to measure the Quality of Service (QoS), in order to choose the best access point in a HetNet to offload part of an application on the MCC, aiming to save energy for the Smart Mobile Devices (SMDs) and to reduce computational time. We distinguish three different types of application, considering different offloading percentage of computation and analyzing how the cell association algorithm allows energy saving and shortens computation time. The results show that when the network is overloaded, the proposed utility function allows to respect the target values by achieving higher throughput values, and reducing the energy consumption and the computational time.

The modern approach in wireless multimedia communications is toward the adaptation of transmission parameters subject to internal and external requirements and constraints, represented by, e.g., the user QoS, the propagation environment, the traffic behavior, the external interferences. One of the most challenging issues that arises during the parameters adaptation is the temporal behavior due to the continuous change of the external context; in that sense it is important to focus the attention on the timing constraints that impact on the system capability of adapting the transmission parameters in a reliable way. The satellite communications (SatCom) are especially affected by the delay problems, due to the high propagation Round Trip Time (RTT). Herein we analyze the temporal behavior of the Land Mobile Satellite (LMS) environment, aiming to define a reliability index for different operational speeds and scenarios.

This paper deals with the co-existence of terrestrial digital television (DTT) networks and White Space Devices (WSD) on the same frequency band, assisted by a geolocation database. The database evaluates and provides to the WSD the local emission power. The common approach adopted in Europe to estimate such limits is expanded to the case of Single-Frequency-Network (SFN) planning of DTT networks. Also, the criterion for setting the allowable DTT quality degradation is discussed and a novel approach is proposed, based on local DTT quality. The complete procedure to evaluate WSD emission limits is applied to a real Italian DTT scenario. We compare different DTT planning strategies over the same set of transmitters and the same area, from the point of view of potential WSD presence. This comparison highlights the advantage of SFN planning both in terms of DTT coverage and allowed WSD emissions.

In the last years we are seeing the increasing presence of multimedia applications together with a wide variety of terminals, from the PCs to the notebooks, from the smartphones to the tablets. In order to exploit such advanced services, ubiquitous and broadband connections are required. While urban or suburban areas can be covered by using terrestrial wireless broadband networks, there are several rural or low populated areas with narrowband access. To this aim, satellite community has developed in the last years two communications standards specifically suited for mobile communications, i.e., DVB-SH and DVB-RCS NG. Among others they consider adaptive waveforms techniques for increasing the system reliability and throughput aiming to exploit the variable channel behavior. Adaptive coding and modulation (ACM) belongs to this family of algorithms, by adapting the modulation and coding scheme based on the channel behavior. In this paper we focus on a state adaptive algorithm suited for mobile applications.

This paper presents a new phase-alignment algorithm for distributed beamforming [1].1This scheme is more energy-efficient than existing solutions, since it requires each node to transmit only once, but it converges at least as fast as all other previously proposed algorithms. In contrast with all other studies of distributed beamforming, where noise had been neglected, here it is explicitly included in the signal model and shown to have a considerable impact on synchronization that cannot be ignored. With and without noise, analytical expressions that characterize the performance of the new algorithm are provided, with emphasis on various limiting regimes of interest.

This paper presents a new approach, named Rotation Invariant Subcarrier Mapping (RISM), to Peak-to-Average-Power-Ratio (PAPR) reduction in OFDM systems. This technique enables data transmission over those subcarrier which are dedicated to the PAPR reduction if a state-of-the-art method, Tone Reservation, is employed. We apply RISM to DVB-T2 systems, showing that the reserved tones foreseen by the standard only for PAPR reduction purposes can effectively carry additional useful information to the receiver, and, at the same time, RISM achieves a PAPR reduction very close to the Tone Reservation. Thus, the proposed technique offers improved spectral efficiency while keeping the robustness against nonlinear distortion effects.

In the last years the increasing presence of multimedia applications and devices is even requiring higher throughput links with a higher availability. In order to exploit such advanced services, ubiquitous and broadband connections are required. Even if much of populated areas are nowadays covered by terrestrial wireless broadband networks, there is an increasing request of satellite communications able to cover low density populated areas and to fill the coverage gaps. In the last years two novel communication standards specifically suited for mobile satellite communications, i.e., DVB-SH and DVB-RCS NG, have been introduced. Among others, they consider adaptive waveforms techniques for increasing the system reliability and throughput aiming to exploit the variable channel behavior. Adaptive coding and modulation (ACM) belongs to this family of algorithms, by adapting the modulation and coding scheme based on the channel behavior. In this paper we focus on a state adaptive algorithm suited for mobile applications by considering the effect of the mobile speed.

In this paper, we introduce a new framework to compute the Outage Probability (Pout) and the Average Symbol Error Probability (ASEP) of dual-hop Amplify-and-Forward (AF) relaying in the presence of noise, fading, and network interference. The interfering nodes are randomly distributed in the 2D Euclidean plane according to a homogeneous Poisson point process. Our framework provides closed-form expressions of Poutand ASEP over Rayleigh fading channels, additive noise at the relay and at the destination, and network interference at the destination. The accuracy of our analytical derivation is substantiated through extensive Monte Carlo simulations.

In this paper, we introduce an analytical framework to compute the average rate of downlink heterogeneous cellular networks. The framework leverages recent application of stochastic geometry to other-cell interference modeling and analysis. The heterogeneous cellular network is modeled as the superposition of many tiers of Base Stations (BSs) having different transmit power, density, path-loss exponent, fading parameters and distribution, and unequal biasing for flexible tier association. A long-term averaged maximum biased-received-power tier association is considered. The positions of the BSs in each tier are modeled as points of an independent Poisson Point Process (PPP). Under these assumptions, we introduce a new analytical methodology to evaluate the average rate, which avoids the computation of the Coverage Probability (Pcov) and needs only the Moment Generating Function (MGF) of the aggregate interference at the probe mobile terminal. The distinguishable characteristic of our analytical methodology consists in providing a tractable and numerically efficient framework that is applicable to general fading distributions, including composite fading channels with small- and mid-scale fluctuations. In addition, our method can efficiently handle correlated Log-Normal shadowing with little increase of the computational complexity. The proposed MGF-based approach needs the computation of either a single or a two-fold numerical integral, thus reducing the complexity of Pcov-based frameworks, which require, for general fading distributions, the computation of a four-fold integral.

In this paper, we introduce an analytical framework for performance analysis and design of Single-Input-Multiple-Output (SIMO) wireless systems in the presence of noise, fading, and radio frequency interference produced by randomly distributed active interferers surrounding an intended probe receiver. The framework leverages recent application of stochastic geometry and Poisson Point Processes (PPPs) theory to network interference modeling. To assess the impact of spatial dependence across multiple receive-antennas, three models of network interference are studied: i) the isotropic model, where all receive-antennas see interferers belonging to the same PPP; ii) the independent model, where each receive—antenna sees interferers belonging to an independent PPP; and iii) the mixture model, which is a superposition of isotropic and independent interferences. Depending on the fading distribution of the interferers, the Nakagami-m fading parameter of the probe link, and the number of receive-antennas, either exact or upper-bound formulas of the error probability averaged over noise, fading, and spatial interference are given. Our analysis shows that, depending on the interference model, performance can either improve or get worse with multiple antennas at the receiver. The proposed analytical methodology is applicable to single- and multi-PPPs interference environments.

This paper presents a new deterministic closed-loop phase-alignment algorithm based on quantized feedback from the receiver for distributed beamforming. In contrast with previously proposed methods, which entailed repeated transmissions from all the nodes in the network, this new algorithm requires each node to transmit only once during the synchronization cycle. This drastically reduces the amount of power consumed to achieve phase alignment, yet the new algorithm converges at least as fast as all other existing schemes. In contrast with previous analyses of distributed beamforming based on random phase updates, where noise had been disregarded, here it is explicitly included in the models and shown to have a considerable effect that cannot be ignored. With and without noise, analytical expressions that characterize the performance of the new algorithm are provided, with emphasis on various limiting regimes of interest.

This paper presents an assessment of several interference cancellation and gateway cooperation strategies for the return link of a multi-gateway multi-beam broadband satellite system. The aim of the work is to provide theoretical upper bounds to the achievable average per user spectral efficiency and maximum system throughput under different coverage schemes and frequency reuse patterns, considering actual system parameters and antenna design. The trade-off between spectral efficiency and system complexity is also addressed focusing on the amount of information that has to be exchanged amongst different gateways during the iterations of the interference cancellation algorithm.

This papers addresses the design of new energy-efficient Continuous Phase Modulation (CPM) waveforms suitable for being adopted in satellite mesh networks that are characterized by the absence of the Hub, and by small antennas and power amplifiers with moderate to low output saturated power at the user terminal. In particular, a CPM modulation format concatenated with a proper convolutional code for low spectral efficiency values has been selected to implement an efficient waveform for power-limited scenarios. Performance results show the gain obtained with respect to the DVB-RCS2 CPM waveforms at higher spectral efficiency also when transmission techniques, such as Burst Repetition, are considered, and confirm the suitability of the new designed CPM waveforms for satellite hub-less scenarios.

This paper addresses detailed waveform trade-offs for mesh satellite networks. The waveform analysis is carried out considering spectral efficiency, resilience against non linear distortion, channel impairments and interference for both linear and continuous phase modulation schemes defined in the DVB-RCS2 standard.

Accurate modeling of network interference, deep understanding of its impact on the achievable performance, and development of efficient techniques to mitigate or exploit it are three important and fundamental research assets in current and next-generation cellular networks. In this context, Andrews, Baccelli, and Ganti [1] have recently introduced a new analytical approach to estimate coverage and rate of cellular networks subject to other-cell interference. In this paper, we move from the approach developed in [1], and propose an alternative analytical derivation to compute the rate of cellular networks. More specifically, by using stochastic geometry and Poisson point processes theory, we derive a simple and easy-to-compute expression of the rate, which can be used for arbitrary network and channel parameters, e.g., path-loss exponent, receiver noise, density of Base Stations (BSs), etc. Compared to [1], our framework has two main distinguishable features: i) the rate can be computed via a single numerical integral, rather than via a three-fold numerical integral; and ii) the formula is applicable to arbitrary fading distributions on the intended link, rather than being useful for Rayleigh fading only. Our analytical derivation is substantiated through extensive Monte Carlo simulations.

In this paper, we introduce a new framework to compute the Average Symbol Error Probability (ASEP) of an intended wireless communication system subject to network interference and noise. The interfering nodes are assumed to be randomly distributed in the 2D Euclidean plane according to a homogeneous Poisson point process. Our framework is applicable to performance prediction and optimization of, e.g., emerging heterogeneous cellular and cognitive radio networks. More specifically, we move from and generalize the semi-analytical framework recently introduced by Pinto and Win [1], and develop a new mathematical model which offers a simple single-integral expression of the ASEP under very general channel and interference conditions. The framework is exact, avoids Monte Carlo methods for its computation, and is applicable to asynchronous and synchronous scenarios. Our numerical examples show that both setups have almost the same performance, and that the ASEP in the presence of synchronous interference is a very tight upper-bound of the ASEP in the presence of asynchronous interference. This is a relevant result, as we show in this paper that in the former case all parameters of interest can be computed in closed-form. Our analytical derivation is substantiated through extensive Monte Carlo simulations.

Coarse beamforming is a space processing scheme which allows for efficient use of the available spectral resources on the feeder link of a multi-beam broadband satellite system. In this framework, spectral occupancy of the multiplexed antenna signals that must be exchanged between the satellite and the gateway is a critical issue, up to the point that a costly multiple gateway infrastructure could be required to restrain bandwidth usage. Alternatively, a hybrid on board/on ground processing architecture is desirable, where the effect of space processing allows to project feed signals on a subspace, thus reducing the required feeder link bandwidth. This foresees a fixed processing scheme on board the satellite, which we refer to as Coarse Beamforming, yielding an overall system which relies on reasonable payload complexity, together with on ground processing flexibility. We explore two Coarse Beamforming techniques for the return link of a multi beam satellite system, and we evaluate the effect of compression in terms of reconstructed signal degradation. We show how, without significant distortion, bandwidth occupancy can be considerably reduced.

In the “Internet of Things” (IoT) vision the physical world blends with virtual one, while machine-to-machine interaction improve our daily life. Clearly, how these virtual objects are exposed to us is critical, so that their user interface must be designed to support the easiness of usage that is driven by the users' needs, which is different from what machines requires. These two requirements must be solved, and an integrated solution should emerge, if we want to bring the IoT to the 50 billions network that is predicted to became in the next years. We believe that these requirements cannot be met by the same communication protocol, and so we propose a new kind of broker, named QEST that can bridge the two worlds, represented by their state-of-the-art protocols: MQTT and REST. In this paper, we demonstrate that our approach allows rapid development of user-facing IoT systems, while grating machines all the performance they need.

In this paper, OFDM data-aided channel estimation based on the decimation of the Channel Impulse Response (CIR) through the selection of the Most Significant Samples (MSS) is addressed. Our aim is to approach the Minimum Mean Square Error (MMSE) channel estimation performance, while avoiding the need for a-priori knowledge of channel statistics (KCS). The optimal set of samples is defined in the instantaneous and average senses. We derive lower bounds on the estimation mean-square error (MSE) performance for any MSS selection strategy. We show how MSS-based channel estimation can approach these MSE lower bounds. We introduce novel MSS strategies oriented towards instantaneous decimation (Instantaneous Energy Selection - IES), and windowed decimation (Average Energy Selection - AES). We also consider decimation via Threshold Crossing Selection (TCS), which we characterize analytically, to derive the optimum threshold in the minimum MSE sense. We also propose a sub-optimal method for threshold setting that does not require KCS. Finally, we provide numerical results in terms of both MSE estimation performance and Bit Error Rate (BER) of a coded OFDM system using the proposed channel estimators, to show that they indeed approach MMSE performance.

We consider a windowed decoding scheme for LDPC convolutional codes that is based on the belief-propagation (BP) algorithm. We discuss the advantages of this decoding scheme and identify certain characteristics of LDPC convolutional code ensembles that exhibit good performance with the windowed decoder. We will consider the performance of these ensembles and codes over erasure channels with and without memory. We show that the structure of LDPC convolutional code ensembles is suitable to obtain performance close to the theoretical limits over the memoryless erasure channel, both for the BP decoder and windowed decoding. However, the same structure imposes limitations on the performance over erasure channels with memory.

Signal processing in satellite applications is usually performed either on-ground or on-board, i.e. at the gateway station or in the payload. Within the framework of the European Space Agency (ESA) SatNEx III study, a hybrid approach has been considered by splitting the processing between the satellite and the gateway, aiming to strike a better balance between performance and payload complexity. The design of a high-capacity multi-beam system has been carried out, to assess the potential applicability of a hybrid space-ground processing architecture (Digisat) for satellite broadband systems; this is achieved via hybrid space-ground beamforming, MIMO and MIMO-MUD, Precoding, as well as Digital Feeder link techniques.

In the satellite communications component of the future Internet, peer-to-peer mesh connectivity of satellite terminals is an impellent necessity. In particular, delay sensitive applications such as real-time multimedia, collaborative conferencing and cellular backhauling are appealing use-cases for adopting mesh network topologies. Moreover, the use of a single satellite hop for directly connecting remote terminals (as opposed to a double-hop connection required in star topologies) reduces the satellite traffic load and leads to savings in operational costs of the satellite network. In this paper, we propose a multi-beam satellite mesh network based on a semi-transparent or fully regenerative satellite with different on board switching capabilities. In particular, four network solutions have been assessed in terms of flexibility, complexity and capacity, trading-off between network performance and implementation cost.

In a wireless sensor network, distributed beamforming is a cooperative technique that enables a group of nodes to emulate a virtual array and to steer a beam in a particular direction in space. This allows for shared message delivery to a distant receiver in a condition where typically communication range is limited due to power consumption constraints. Potential gains in terms of received power are compelling, but one of the main challenges is to achieve coherence of the transmitted signals at the destination in such a distributed scenario. This work presents innovative phase synchronization algorithms for a wireless sensor network that not only prove to be very efficient in terms of energy consumption, but also present good channel tracking capabilities in a time varying scenario.

This paper takes a broad view on the history and the present status of satellite communications and broadcasting. The necessary starting point of this overview is the visionary papers produced by Sir Arthur C. Clarke and John Pierce. This was the real dawn of the satellite communication era. This paper attempts to explain the “fil rouge” of the evolution of satellite technologies across six decades, analyzing successes and failures of past satellite missions, and concluding with a picture of future satellite communications.

The mobile satellite broadcasting arena is witnessing a constant increase in demand for improved transmission quality and higher number of services in order to remain on par with the corresponding terrestrial counterparts. A promising way forward in this regard is the migration from the conventional single polarization per beam to an advanced dual polarization per beam architecture for effective spectrum exploitation; this also enables the application of advanced multiple antenna (MIMO) techniques. The present paper moves from DVB-SH the current state-of-the-art for mobile satellite services towards a more advanced system architecture doubling the overall system capacity with a minimum power increase. It turns out that a multiplexing gain equal to two comes at a cost of about 6 dB for the conventional single polarization system, whereas for the advanced system the corresponding cost is about 3.5 dB.

In this paper we propose the usage of Single Carrier Frequency Division Multiple Access (SC-FDMA) in the Broadband Satellite Return Channel. Notably, SC-FDMA is able to improve the physical layer spectral efficiency with respect to single carrier systems, which has been used so far in the Return Channel Satellite (RCS) standards. However, it requires a strict synchronization and it is also sensitive to phase noise of local radio frequency oscillators. For this reason, we propose an effective pilot tone arrangement within the SC-FDMA frame, and a novel Joint Multi-User (JMU) estimation method for the SC-FDMA. As shown by numerical results, the proposed scheme manages to satisfy strict synchronization requirements and to guarantee a proper demodulation of the received signal.

In this paper we present the concept of cognitive satellite terrestrial radios (CSTR) for hybrid satellite-terrestrial systems (HSTS). The cognitive radio (CR) technology is being motivated by the radio regulatory bodies for efficient utilization of the radio spectrum. The future satellite ground terminals therefore need to integrate and co-exist with the spectrally crowded terrestrial wireless systems and hence we propose the idea of CSTR. The key issues are addressed and the concepts of developing CR based satellite ground terminals in HSTS for dynamic spectrum access on the ground are presented. Furthermore, the concept of 3D-Spatial reuse of the spectrum is also presented using the CSTR considering low elevated satellite ground stations. Two particular HSTS applications to illustrate the CSTR concept, a) the hybrid satellite-UWB (ultra wideband) communication system for personal area networks (PAN) with short range on ground communications, and b) the hybrid satellite-WRAN (wireless regional area networks) for long range on ground communications are presented. In both the applications the satellite uplink and the terrestrial radios adopt the CR functionalities. The key enabling technologies and their integrated architecture for the CSTR are also presented.

We consider terminated LDPC convolutional codes (LDPC-CC) constructed from photographs and explore the performance of these codes on correlated erasure channels including a single-burst channel (SBC) and Gilbert-Elliott channel (GEC). We consider code performance with a latency-constrained message passing decoder and the belief propagation decoder. We give theoretical bounds on the code efficiency over the SBC and describe a construction that achieves this bound.We show that the designed codes with belief propagation (BP) decoding perform as well as the regular LDPC-CCs presented in the literature on the binary erasure channel (BEC) and the GEC, while achieving significant gains on the SBC. In the case of windowed decoding, our codes perform much better than the best known regular LDPC-CCs over the BEC and the GEC, with very low decoding latencies.

This paper addresses the problem of robust frame synchronization for TDM/TDMA systems in the presence of frequency errors, accomplished through data-aided recognition of the Unique Word (UW) preamble in the transmission flow. Robust detection design is performed applying, through approximations, the Maximum Likelihood (ML) criterion coupled to Post Detection Integration (PDI), to obtain a novel detector identified as Balanced-GPDI (B-GPDI). This new approach considerably outperforms other schemes available in the literature, at the cost of a moderate complexity increase. This is possible thanks to an optimized use of coherent accumulation, which enhances the correlation term in the decision variable, along with highly accurate modeling of the energy correction factor. To limit complexity increase and memory requirements, several approximations of the exact B-GPDI are proposed and discussed in the paper, to provide the designer with practical solutions that are still able to outperform other approaches in specific application scenarios. In particular, approximations for low and high Signal-to-Noise Ratio (SNR) are presented. Different application scenarios are considered in the paper for numerical analysis. In particular, the cases of forward link Continuous Transmission (CTX) and return link Burst Transmission (BTX) are addressed.

This paper investigates the concept of single frequency satellite networks (SFSNs), whereby multiple satellite beams that have no form of mutual phase coherence are unified through baseband signal processing to achieve uniform coverage across wide areas. We present a realistic application scenario and its link budget analysis, which allows to highlight the advantages with respect to a classic single beam approach. Our technique is based on the use of orthogonal frequency division multiplexing and on the creation of synthetic multipath at the gateway, realizing a form of delay diversity. The synthetic power delay profile is beam specific, and it is the key instrument that allows to avoid destructive interference amongst the signals transmitted from the multiple beams. The main benefit is that homogeneous coverage is guaranteed with a generic multi-beam antenna, that can be easily reconfigured according to traffic and service needs.

Providing low-latency high-quality data services to mobile terminals has become a mandatory requirement for all mobile broadband standards. Therefore, effective countermeasures against mobile channel impairments, like small- and largescale fading, are of the utmost importance whenever traditional physical layer channel codes do not provide sufficient resilience or request too much hardware resources. Among the possible countermeasures, the paper investigates the application of packet layer coding, which basically consists in applying forward error control techniques at upper layer (UL-FEC). In the paper the UL-FEC decoder performance analytical model already developed by authors is generalized and extended to include nonperiodic shadowing and small-scale fading. Analytical results are then validated through numerical simulation considering a real application scenario.

Some recently proposed robust methods for time domain timing and frequency synchronization in OFDM systems incorporate the use of cross-correlation based threshold detection in their timing adjustment and joint time-frequency algorithms. In this paper, we analyze the threshold criterion used and derive its theoretical performance. This translates into a better characterization of these OFDM synchronization algorithms, leading to a closer match between design expectations and practical performance. Computer simulations show a strong agreement between theoretical predictions and numerical results.

In this paper, we address the problem of OFDM data-aided channel estimation based on the selection of the most significant samples (MSS) of the channel impulse response (CIR), i.e. those samples which contain most of the useful energy. We provide a novel and complete analytical characterization for MSS selection based on threshold crossing, which yields a closed form for the estimate mean-square error (MSE), that we use to derive analytically the optimum threshold in the minimum MSE sense. The optimum threshold value is matched to the specific channel power profile, but this information is hardly available to the receiver. For these reason, we also propose a suboptimal method for threshold setting that does not require any knowledge of channel statistics. We show that the performance of this sub-optimal method is very close to the optimum case, as well as to Wiener channel estimation in the case of sparse multipath channels. Our proposed method outperforms previous approaches based on heuristically set thresholds.

A novel approach is introduced for the design of a unique word (UW) for frame synchronization in time division multiplexing/time division multiple access (TDM/TDMA) systems. In particular, the UW symbols are distributed in each frame in a specific pattern in order to optimize the UW autocorrelation properties. The distribution patterns are scalable, since they preserve their autocorrelation properties under truncation. The resulting frame structure enables the use of several types of UWs, including the silent-UW (SUW) and the unit-UW (UUW), that are novel approaches for which the optimal Bayes detector is derived. An analytical performance characterization is presented along with comparisons with state-of-the-art alternatives. We show that SUW can significantly outperform the classic UW in the presence of frequency offsets or whenever data interference is the main impairment to cope with, i.e. at moderate to high signal to noise ratios. Interestingly, this performance improvement comes with the further advantage of a considerable complexity reduction. Hence UUW is shown to provide both performance improvement and complexity reduction.

This paper tackles the problem of time synchronization for the mobile extension of DVB-S2/RCS air interfaces. To increase robustness against other system interference, Direct Sequence Spread Spectrum (DS-SS) is selected, which calls for efficient code acquisition. Designed to operate jointly with frame synchronization, a novel high level control logic is proposed for code acquisition, along with robust detectors to cope with the large frequency uncertainty experienced at terminal start-up. The results show that the mean acquisition time is always limited to a few milliseconds, allowing fast acquisition even in the most challenging railway scenario.

The paper investigates coding and encapsulation techniques for the possible extension of the digital video broadcasting-return channel satellite (DVB-RCS) to ensure a global coverage for mobile terminals. specifically, link layer- forward error correction (LL-FEC) appears to be a reliable solution, allowing to improve the C/N performance and to counteract the Doppler effect typical of mobile channels, avoiding scalability and latency issues of Automatic Repeat reQuest (ARQ) approaches. In the paper we evaluate LL-FEC performance when applied to the railway environment. It is shown how this scenario deeply affects the LL-FEC code performance both in the multi protocol encapsulation (MPE), and the generic stream encapsulation (GSE) cases. In order to counteract this performance reduction two different approaches are considered. In the first case, we increase the number of rows of the LL-FEC Reed Solomon (RS) matrix. In the second case we exploit the sliding encoding mechanism. We also introduce a modified version of GSE that shows reduced overhead and improved performance. Results show that DVB-RCS can greatly benefit from LL-FEC RS coding in reducing residual errors that cannot be counteracted at the physical layer for efficiency reasons.

This paper tackles the problem of unified frame and symbol timing synchronization for the return link of a DVB satellite system with Continuous Phase Modulation. Robust schemes are introduced to cope with the carrier frequency uncertainty affecting the received signal. The novel approach employs the same detector to recover the frame alignment and the symbol synchronism, based on Post Detection Integration strategy. It is shown that this unified approach is able to provide quasi-optimal performance limiting complexity at the same time.

The problem of code acquisition for the Galileo system is investigated in this paper. The effect of non-ideal sampling on the binary offset carrier (BOC) modulated signal is evaluated and a novel detection scheme, identified as Quadribranch, is proposed. Detection performance is investigated by analysis and simulations taking into account frequency errors and non ideal sampling with actual Galileo signals. The notable result is that Quadribranch is able to improve performance in terms of detection probability and mean acquisition time, and, differently from the conventional approach, allows to achieve robust code acquisition without oversampling.

In any conditions where DC and RF power are at a prime, such as in satellite systems, transmit amplifiers are operated close to the saturation region to maximize both output power and DC-to-RF efficiency, at the price of introducing non-negligible spectral regrowth and in-band distortion. In order to mitigate these effects, predistortion techniques can be applied at the transmitter; however, mass-produced terminal equipment have operating characteristics that exhibit large dispersion, and for cost reasons calibration procedures are ruled out. Therefore, feedback from the power amplifier output is required to apply predistortion, but the presence of phase noise over the feedback signal impairs the correct recovery of the amplifier phase characteristics, and attention must be focused on amplitude only. This paper proposes two adaptive predistortion schemes which are able to track and compensate the amplitude distortion in the power amplifier, based on neural networks and on look-up-tables, respectively. The two techniques are compared both in terms of performance and complexity, giving insights on the available design trade-offs. Thanks to the reduced spectral regrowth, the techniques are shown to enable the adoption of high order modulations also in those cases where it would have been prevented by out-of-band spectral masks.

In this paper the symbol timing estimation problem is addressed for bursty transmission in mobile satellite communications. In particular, a classical approach and iterative techniques are compared in terms of estimation performance. The iterative techniques are based on the expectation-maximization approach and they exploit the soft a-posteriori data information delivered by the iterative decoder in order to aid the synchronization process. A new iterative approach is here proposed with the aim to overcome the biased results observed on exiting algorithms for large timing offset values.

This paper investigates the possible robust technique of frame synchronization for DVB-S2 system. Basically, we focus on the improvement of correlation characteristic, instead of establishing the strategy of frame synchronization with optimal scenario due to variable transmission frame lengths of DVB-S2 standard. To cope with a large frequency offset as a maximum 20% value normalized to symbol rate, the differential generalized post detection integration scheme is newly proposed in the paper. The fruitful results of the paper are described by the suitable analytical approach through parameter optimization. The proposed scheme is shown to provide a good trade-off relation between complexity and performance and is verified in detail their improved performance.

The authors deal with the sum–product algorithm (SPA) based on the hyperbolic tangent (tanh) rule when it is applied for decoding low-density parity-check (LDPC) codes. Motivated by the finding that, because of the large number of multiplications required by the algorithm, an overflow in the decoder may occur, two novel modifications of the tanh function (and its inverse) are proposed. By means of computer simulations, both methods are evaluated using random-based LDPC codes with binary phase shift keying (BPSK) signals transmitted over the additive white Gaussian noise (AWGN) channel. It is shown that the proposed modifications improve the bit error rate (BER) performance up to 1 dB with respect to the conventional SPA. These results have also shown that the error floor is removed at BER lower than 10−6. Furthermore, two novel approximations are presented to reduce the computational complexity of the tanh function (and its inverse), based on either a piecewise linear function or a quantisation table. It is shown that the proposed approximations can slightly improve the BER performance (up to 0.13 dB) in the former case, whereas small BER performance degradation is observed (<0.25 dB) in the latter case. In both cases, however, the decoding complexity is reduced significantly.

In the context of spread spectrum communications, this paper investigates the use of likelihood ratio testing techniques for the design of post detection integration (PDI) methods for code acquisition in the presence of phase and frequency uncertainty. The proposed methods are derived as theoretical and pragmatic alternatives to the conventional approach based on noncoherent integration, which would be optimal in the absence of frequency uncertainty. Two competing alternatives are introduced to handle the unknown frequency error, respectively based on the generalized and average likelihood ratio tests, and identified as generalized PDI (GPDI) and average PDI (APDI). The GPDI versus APDI tradeoff is far from trivial and leads to numerous interesting insights, particularly with respect to the impact on performance of the frequency offset entity. Performance is also contrasted to that of conventional PDI techniques, i.e., noncoherent and differential PDI, to reveal significant gains in favor of the proposed methods.

In this paper, the problem of code acquisition for spread-spectrum systems is investigated in the presence of frequency errors. The classic approach of noncoherent post detection integration (NCPDI) is contrasted with differential post detection integration (DPDI), presented in two different versions, namely DPDI-Real and DPDI-Abs, respectively, suited for fine and large frequency offsets. The differential schemes are characterized thoroughly introducing a novel analytical treatment that is validated by simulations. In order to fairly quantify the potential gains introduced by the differential solutions, specific detector parameter optimization is performed for each scheme. The interesting result is that the DPDI significantly outperforms the classic NCPDI approach for large frequency errors, and behaves close to it for small offsets. DPDI can, thus, be considered as a very robust PDI solution with moderate complexity.

High data rate (HDR) CDMA systems are designed for cellular data distribution networks with maximized overall throughput and quality of service (QoS). Both figures of merit rely critically on the adoption of highly performant medium access control (MAC) algorithms, which are the focus of this paper. In particular, the closed loop resource allocation (CLRA) MAC algorithm for the reverse link of an HDR system is described. CLRA entails different properties and advantages that make it attractive for application in HDR or similar mobile Internet networks. First of all, CLRA is a macro control loop with distributed intelligence stimulated by busy tones issued by the base stations to inform terminals about their current load. Rate allocation is performed at terminals, whereby fairness is ensured by a stochastic rate assignment algorithm based on data queue states, rate history, and minimum rate guarantee. Network stability is guaranteed by controlled ramping driven by base stations busy tones. Further, a specific feature is introduced to account also for possible effects on base stations which are not in the rake active set; this feature is identified as candidate set protection. Finally, power headroom margins are used to minimize the occurrence of outage events. The analytical characterization of this MAC algorithm is derived using Markov chain modeling, and the results confirm the CLRA robustness, fairness and efficiency. The proposed algorithm is applicable to the 1xEV-DO system standardized by 3GPP2 within the cdma2000 family.

In all short-medium term business/market forecasts, the efficient provision of digital multimedia broadcasting (DMB) services in mobile systems appears to be of key importance for mobile operators and broadcasters. Several DMB systems are being developed around the world, with several proposed competing standards. In this framework, the DVB (digital video broadcasting) forum is working to define a new air interface, identified as DVB-SSP, to deliver satellite services to portable devices, and several possibilities are being considered as viable options, including the use of DVB-H (handheld). A critical factor to be considered is the resilience to non linear distortion effects. In fact, DVB-H signals are obtained through an OFDM modulation, which traditionally was considered unfit for satellite communications. Recently (S. Cioni et al., 2005), it has been proved that the adoption of strong channel coding techniques in conjunction with the use of non-linear distortion compensation techniques can lead to good OFDM performance even when operating close to amplifier saturation. Following this avenue, this paper investigates the adaptation of the DVB-H physical layer to the satellite environment, and validates the improved robustness of the proposed scheme to non linear distortion

Frame synchronization is conventionally intended as "epoch recovery" of a symbols synchronous stream. But, what happens when symbol timing is unknown? A typical approach to this problem involves oversampling, which is computational intensive. This paper introduces a novel alternative approach whereby the detector is made aware of the emerging ISI due to imperfect symbol timing recovery in order to achieve the wanted performance with low computational complexity. The resulting sequence, identified as ISI-UW, is obtained as the combination of several conventional UW appropriately shifted in time. The adoption of this particular sequence structure allows to enhance performance in the worst case scenario, at the cost of a slight performance loss in the ideal case, and reveals to be an interesting low-complexity alternative to conventional oversampling techniques to cope with symbol timing fractional misalignments

A novel approach is introduced here for the design of the unique word (UW) to be inserted into TDM/TDMA systems for frame synchronization purposes. In particular, the UW is a very simple sequence of ones that are distributed along the frame in order to improve autocorrelation properties. The resulting UW is identified as unit-UW (U-UW). We show in this paper that U-UW leads to an optimum detector with very limited complexity, which does not require any multiplication. A fully analytical performance characterization is also presented and validated through numerical simulations

Frame synchronization and frequency estimation have historically been completely separate problems in digital receiver design. Here, a common avenue is discovered and transformed into practical algorithms. The proposed approach is based on the adoption of a differential post detection integration (DPDI) scheme for the acquisition of the unique word marking the beginning of the frame. The DPDI decision variable can indeed be used also for frequency estimation purposes, with very limited complexity. The adoption of a modular preamble structure with a two stage detector is also proposed to improve performance and optimize the detector structure. Performance is studied through simulations and analysis, providing closed form expressions for the estimation error variance. Both simulations and analysis show that the proposed joint approach is able to provide estimation performance close to the Cramer-Rao bound, as well as practically error-free frame synchronization, with very limited complexity

In a recent paper, the modified Gardner detector has been proposed for advanced symbol-timing recovery of M-ary phase-shift keying signals. Compared with the original algorithm, the self-noise jitter can be considerably reduced for highly bandlimited systems and smaller values of M. In this letter, a completely different approach is investigated, which improves the self-noise performance for larger values of M, as well

The paper considers the comparison of orthogonal frequency division multiplexing (OFDM) and high speed downlink packet access (HSDPA) techniques in the physical layer of a satellite system devoted to the provision of digital multimedia broadcasting (DMB) services. In particular, the paper demonstrates that the inherently high spectrum efficiency of OFDM can be retained even in unfavorable propagation channels affected by heavy non-linear and linear distortion, respectively introduced by the on-board high power amplifier and by frequency selective propagation. This encouraging performance, achieved through the proper design and application of coding and pre-distortion techniques, is compared with the standardized HSDPA radio interface for 3G terrestrial mobile networks, and is shown to be in line on non-selective channels. Advantages for OFDM are demonstrated in frequency selective channels, using low complexity equalization in the frequency domain

This paper proposes a novel frame acquisition method for continuous transmissions in TDM/TDMA systems. The approach is based on a multi-dwell procedure, with approximate maximum likelihood criterion (MAX) applied in search mode, followed by a parallel threshold crossing (TC) verification stage. The particular case of single TC verification and the conventional all-TC procedures, which perform TC also in search mode, are considered for comparison. A thorough performance analysis is presented exploiting the flow-graph approach, along with numerical results. The proposed method allows achieving a gain in terms of mean frame acquisition time with respect to other solutions, with no significant complexity increase.

A novel approach is introduced for the design of the unique word (UW) to be inserted into TDM/TDMA systems for frame synchronization purposes. In particular, the UW is composed by all zero symbols that are distributed along the frame in order to improve the autocorrelation properties. The resulting UW is identified as silent-UW (S-UW). We show in this paper that S-UW leads to an optimum detector with very limited complexity, and with performance that can be significantly better than the classic UW in the presence of frequency offsets or at moderate to high signal-to-noise ratios. A fully analytical performance characterization is presented reporting also comparisons with state-of-the-art alternatives.

This paper applies the theoretical framework for the evaluation of code acquisition in the presence of fading developed in the companion Part I paper. Code synchronization for code-division multiple-access (CDMA) cellular networks, such as IS-95 and cdma2000, is considered. A multidwell testing procedure is adopted. Notably, a procedure for the optimization of the multidwell parameters (number of dwells, dwell lengths, thresholds) to achieve minimum acquisition time is introduced and enforced. The effects of fading, interchip interference (ICI), frequency offset, multiple-access interference, and noise are taken into account in the determination of false alarm and detection probabilities. In particular, anomalous ICI despreading and internal interference-cancellation effects are described. Numerical and simulation results, in terms of time for correct acquisition, confirm the accuracy of the proposed approach and show how it can be effectively used in the design and evaluation of a code-acquisition subsystem.

This paper deals with the analysis of the code-acquisition process performed by a mobile terminal in a code-division multiple-access cellular system. The fundamental contribution is the setting of a theoretical framework for code-acquisition analysis, accounting for the presence of fading and shadowing with specified coherence time. A multidwell architecture is considered, accounting for different verification strategies. The MAX/TC detection criterion is used, and the acquisition performance is analyzed, following both the direct and flow-graph approaches. Expressions for the acquisition time probability density function under different assumptions are given, as well as closed-form expressions for the mean and variance of the acquisition time. Practical applications and numerical results are reported in the Part II companion paper.

In this paper we address the study of systems implementing unequal error protection (UEP) by means of the multi level coding (MLC) technique, taking into account the impact of asymmetric constellations and the effect of puncturing. UEP can lead to significant improvements when applied to multimedia broadcast and multicast services (MBMSs), which should represent an important share of the consumer market in the next years. Theoretical considerations and performance assessment of an MLC system implemented by means of turbo codes are undertaken, considering several modulation options.

In recent years large scientific interest has been devoted to joint data decoding and parameter estimation techniques. In this paper, iterative turbo decoding joint to channel frequency and phase estimation is proposed. The phase and frequency estimator is embedded into the structure of the turbo decoder itself, taking into consideration both turbo interleaving and puncturing. Results show that the proposed technique outperforms conventional approaches both in terms of detection capabilities and implementation complexity.

In the context of spread spectrum systems, this paper illustrates a novel and improved method to implement post detection integration in a code acquisition scheme in the presence of an unknown frequency error. The method is developed in the AWGN channel but is applicable to fading channels, too. The novel method is obtained through the application of the maximum likelihood criterion. The result is compared with the classic noncoherent and differential post detection integration schemes, showing significant improvements. Possible applications are in cellular CDMA networks and in satellite navigation and positioning systems.

W-CDMA and SW-CDMA (satellite W-CDMA) air interfaces require that a user equipment in a given cell acquires slot and frame synchronization, and identifies the primary scrambling code used by the target cell before starting communications. This synchronization procedure is identified as cell search procedure in W-CDMA and beam search procedure in SW-CDMA. Notwithstanding the extensive commonalities between the two air interfaces, the two procedures are actually different. The paper aims at the evaluation of the false acquisition probability achievable by the two procedures in a scenario in which the receiver may experience both satellite and terrestrial radio propagation conditions. This is a sensible evaluation scenario since, in the delivery of multicast-broadcast multimedia services, the satellite UMTS network represents an efficient complement to terrestrial UMTS, since its coverage is extended to indoor and urban areas through, for example, the use of terrestrial intermediate repeaters. Rayleigh fading, Rice fading, and vehicular multipath propagation channels are used for the performance assessment.

In the paper, the preamble structure of IMT-2000 SW-CDMA air radio interface is considered in the evaluation of the performance of different post detection integration techniques for code acquisition in the return link of a satellite W-CDMA system. In particular, non-coherent post detection integration (NCPDI) and two different options of differential post detection integration (DPDI) techniques, namely DPDI-abs and DPDI-real, are investigated in terms of missed detection and false alarm probabilities. AWGN and Rician channels are considered in the presence of a frequency error. Both analytical and simulation results are provided.

New bounds are proposed for the Marcum Q-function, which is defined by an integral expression where the 0th-order modified Bessel function appears. The proposed bounds are derived by suitable approximations of the 0th-order modified Bessel function in the integration region of the Marcum Q-function. They prove to be very tight and outperform bounds previously proposed in the literature. In particular, the proposed bounds are noticeably good for large values of the parameters of the Marcum Q-function, where previously introduced bounds fail and where exact computation of the function becomes critical due to numerical problems.

The paper addresses the exploitation of satellite diversity in a satellite mobile network. In particular, we focus on the impact of diversity on service availability and on system capacity, considering the forward link of a CDMA system with a multisatellite and multibeam architecture. The analysis includes the effects of path blockage, intrabeam and interbeam interference, imperfect power control, and fading correlation in the time-domain due to nonideal interleaving. A closed-form solution is given for the estimation of system capacity. We show that satellite diversity is essential in providing service availability in urban and suburban areas, while the impact of satellite diversity on system capacity may be positive or negative, mainly depending on the fading channel characteristics. In particular, diversity becomes more and more beneficial for increasing fading time-domain correlation (i.e., for low mobile speed and/or limited interleaving depth). The analytical results have been validated by means of Monte Carlo simulation.

In unknown channels, nonadaptive maximum likelihood sequence detection (NA-MLSD) is far from optimum in the presence of channel-induced uncertainty. To counteract this uncertainty, conventional solutions augment MLSD with external channel estimators. However, for very low SNR values this estimation procedure becomes marginal and the conventional adaptive MLSD (CA-MLSD) approaches perform poorly. We consider joint data decoding and parameter estimation techniques, and in particular per survivor processing (PSP) techniques, as a potentially effective solutions to this problem, at the expense of increased complexity. The performance/complexity tradeoff is addressed for a convolutionally encoded Q-PSK return link of an SHF/EHF satellite system for multimedia services impaired by phase noise and frequency offsets. By contrasting NA-MLSD, CA-MLSD, and PSP, ranges are provided for channel conditions where the tradeoff favors a particular technique. Further, CA-MLSD and PSP are also contrasted in terms of scalar/ vector estimation performance.

The application of per-suvivor processing (PSP) to digital satellite communications at Ka-band and beyond is considered. The PSP approach is used in a convolutionally encoded M-PSK transmission scheme to effectively counteract the degradations caused by phase noise and frequency offsets. Second order tracking loops are considered for per-survivor parameter estimation. A comparison is carried out between conventional adaptive maximum likelihood sequence detection (CA-MLSD) and PSP schemes both in terms of detection and estimation performance. Emphasis is placed on the analysis of the estimation quality one of the most unexplored research areas in the field of PSP-based systems. To this aim, novel definitions for a decision-related tracker and virtual tracker are introduced and their performance analyzed. Monte-Carlo simulations are provided to show the improvement in both estimation and detection quality brought about by PSP with respect to CA-MLSD.

The paper addresses the exploitation of satellite diversity in a satellite mobile network. In particular, we focus on the impact of diversity on service availability and on system capacity, considering the forward link of a CDMA system with a multi-satellite and multi-beam architecture. The analysis includes the effects of path blockage, imperfect power control, and fading correlation. We show that satellite diversity is essential in providing service availability in urban and suburban areas. Also, we show that the impact of satellite diversity on system capacity may be positive or negative, mainly depending on the transmission channel characteristics. In particular, diversity becomes very beneficial whenever fading correlation is considered. The analytical results have been validated by means of Monte Carlo simulation.

Many future mobile communication networks will include some form of code division multiple access in their radio interface. All such systems must guarantee efficient initial code acquisition at the mobile terminal, both for call start-up and for soft-handoff handling. To this end, a spread pilot tone is generally adopted. In this paper we compare two approaches for pilot design, namely the conventional continuous pilot (CP) and a burst pilot (BP) with fractional duty cycle. We trade-off the two solutions based on acquisition error probability P/sub e/, signal-to-noise ratio (SNR), dwell time T/sub d/, and impact at system level. The main result is that for equal P/sub e/ and T/sub d/ the BP solution yields a considerable gain in requested SNR. However, CP can be forced to achieve the same P/sub e/ objective with the same SNR by allowing a longer T/sub d/, and its impact at system level is considerably milder.

A pilot-aided coherent uplink transmission scheme is proposed for mobile satellite communications at L-band. The scheme is designed to enhance link performance as compared to coded noncoherent M-ary orthogonal modulation, while maintaining small envelope fluctuations and low complexity. A rigorous analysis is performed for the proposed technique, when used in conjunction with a direct-sequence code-division multiple-access convolutionally encoded binary phase shift keying link, in a Rice-fading channel with satellite diversity. The pilot-aided scheme has been extensively simulated, accounting for finite interleaving in slow fading and nonideal carrier frequency recovery. The results show a significant performance gain with respect to noncoherent schemes designed for similar links, which goes up to 1.8 dB for 9.6 kb/s services with slow moving users exploiting dual-satellite diversity.

The paper analyzes possible transmission schemes for satellite personal communication systems adopting low/medium-Earth orbit (LEO/MEO) constellations and direct-sequence code division multiple access (DS-CDMA) in the presence of fading and shadowing, the statistics of which are functions of the satellite elevation angle. In particular, the performance of M-ary Walsh-Hadamard orthogonal (MWHO) convolutionally coded DS-CDMA over a Rice-log-normal fading channel is analyzed in depth, and compared to the simpler coded differential BPSK (DBPSK) scheme. Optimization of the performance/complexity tradeoff in the metric computation for soft inputs to the Viterbi (1979) decoder is addressed. Upper bounds on the error probability without or with satellite diversity and equal gain combining are evaluated considering different coding rates. The effect of correlated fading is also taken into account via simulation. Among the various results, it is shown that the optimal coding rate is a function of the satellite elevation angle and of the diversity order, that the loss for using DBPSK instead of MWHO is in the range 1-1.4 dB, and that interleaving depth is a critical parameter.

In this paper we propose a method for symbol erasure decision in a dispersive propagation environment, based on Bayesian decision theory. The decision rule is used with Reed-Solomon coding and error-and-erasures decoding. The proposed method is based on a decision feedback approach to eliminate statistical dependence among envelope detector's outputs of an M-FSK non-coherent demodulator. The performance is analyzed for channels with different levels of selectivity and synchronous multiple access interference. It is shown that the use of memoryless decision approaches result in poor performance, whereas the proposed technique provides large coding gains even for severe selectivity. Sensitivity results on error propagation due to decision feedback are also given.

The paper addresses the analysis of multidimensional trellis-coded M-ary phase shift keying (MPSK) modulation over a Rice-lognormal fading channel model, applicable to a variety of environments and to both terrestrial and satellite mobile communications. Bounds to the bit error probability are derived and applied to the analysis of a few selected trellis-coded modulation (TCM) schemes. The results, confirmed by simulation, show that on the Rice channel there exists a threshold in bit energy-to-noise density ratio above which the effective code length is the dominant parameter, while the free distance is dominating below. However, the influence of both parameters is mitigated when shadowing is present.

The performance of space and frequency diversity techniques at 1800 MHz in an indoor environment are investigated. Three linear signal combining techniques are considered: signal selection (SEL), maximal ratio combining (MRC), and equal gain combining (EGC). The computations of received fading envelopes are performed by means of an analytical model, based on a three-dimensional ray-tracing (RT)/uniform theory of diffraction (UTD) technique; the reliability of the adopted approach is confirmed by comparison with some test measurements. The electromagnetic field components are adequately processed to obtain the single branch and combined signal envelope. The results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage for both diversity techniques. Antenna spacings of about 0.75-1/spl lambda/ are nearly sufficient for achieving optimum performance, whereas frequency separation on the order of 10 MHz is needed for sufficiently decorrelated transmission on the two carriers.

We analyze in depth the MAX/TC criterion for code acquisition in spread-spectrum transmissions. The uncertainty region is divided into sectors: inside each sector, the cell with associated maximum test variable is selected (MAX criterion), and sectors are serially tested according to the threshold crossing (TC) criterion. The most commonly used analysis tools for code acquisition, namely the direct and the flow-graph approaches, are extended to the MAX/TC criterion. An accurate but simple approximation to the acquisition time probability density function is found in terms of a gamma distribution, which is shown to yield much better accuracy than the Gaussian distribution. The general formulation is applied to the particular case of direct-sequence spread-spectrum multiple-access (DS-SSMA) systems, showing that sector size is a fundamental parameter to be optimized in the minimization of acquisition time, and that in some cases MAX/TC with parallel architecture performs marginally better than MAX/TC with serial architecture.

This letter addresses performance evaluation in a nonselective fading channel modeled by a combination of Rice and lognormal (RLN) statistics. The RLN model is valid under widely different environmental conditions, both for terrestrial cellular and for satellite personal communication systems. The letter provides semianalytical expressions for the average error probability in the RLN channel for coherent M-ary phase shift keying (PSK) and noncoherent M-ary orthogonal transmissions, then it highlights the relationship between outage probability and cell coverage for macro and microcellular systems, and finally it provides some error probability results for nongeostationary (non-GEO) satellite systems.

Future wireless personal communications will find important applications in indoor environments; hence, an accurate analysis of the propagation characteristics within buildings and their impact on system design parameters is highly desirable. The performance of space diversity techniques in an indoor environment is investigated. Three linear signal combining techniques are considered: signal selection, maximal ratio combining and equal gain combining. The calculation of received fading envelope in the environment has been performed by using a 3D ray-tracing/UTD technique. The obtained results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage, as well as the good agreement with the general achievements of previous experimental works.

Several multisatellite and multispot systems have been recently proposed for provision of mobile and personal services with global coverage, adopting GEO or non-GEO (i.e., MEO, LEO) satellite constellations. The paper addresses an in-depth analysis of these constellations, evaluating both geometrical performance measures and cochannel interference levels caused by extensive frequency reuse. The geometrical analysis yields the statistics for coverage, frequency of satellite hand-overs, and link absence periods. The interference analysis is based on a general model valid for all access techniques, which is here applied to the case of FDMA. The outage probability as a function of the specification on carrier-to-interference power ratio is evaluated for four selected constellations. Several techniques are introduced for interference reduction in non-GEO systems, in which the satellites coverage areas may intersect: spot turnoff, intraorbital plane frequency division, and interorbital plane frequency division. The effects of Rice fading have also been analyzed by means of an analytic approximated method. The overall analysis allows a fair comparison between LEO, MEO, and GEO constellations.>

The event of handing over a call from one base station to another in a cellular mobile radio network requests the cooperation of many system elements, with a consequent load of signalling traffic. Therefore, accurate design of handover procedures must be ensured, to avoid the occurrence of forced terminations and unnecessary handovers. This can be pursued by averaging the received power samples with a window of suitable shape and length, N, and by introducing a hysteresis cycle with margin H (dB). In the paper, a software simulator is described that allows the design of N and H considering the handover occurrence rate and the probability of unnecessary handover. Rectangular and exponential averaging window shapes have been considered.>

In next generation mobile satellite systems very high spectrum efficiency will be a primary objective. High spectrum efficiency is often related to a significant amount of co-channel and/or adjacent channel interference. Therefore, system design should in general include consideration of both interference and noise effects. Interference evaluation in a mobile satellite cellular system is different from the case of a terrestrial system due to the presence of the on-board antenna which acts as a spatial filter. The paper addresses the modeling of interference in single and multi-satellite cellular system and provides some results of the analysis.>

An EHF satellite system for land-mobile applications to be integrated with a terrestrial cellular system is described. An approach to evaluate the carrier-to-cochannel interference occurring in multispot satellite coverage adopting frequency reuse is introduced, and results from the analysis are shown. Criteria for spectrum efficiency evaluation are also outlined along with traffic and link budget estimates. Possible options for payload implementation and mobile terminal design are presented.>