Maria Luisa MERANI - personale UniMoRe

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Maria Luisa MERANI

Professore Associato
Dipartimento di Ingegneria "Enzo Ferrari"

Pubblicazioni

2023 - A comparative analysis of the semi-persistent and dynamic scheduling schemes in NR-V2X mode 2 [Articolo su rivista]
Lusvarghi, Luca; Molina-Galan, Alejandro; Coll-Perales, Baldomero; Gozalvez, Javier; Merani, Maria Luisa
abstract

Over the last years, the evolution of Vehicle-to-Everything (V2X) services from basic safety-related to enhanced V2X (eV2X) applications prompted the development of the 5G New Radio (NR)-V2X technology. Standardized by the Third Generation Partnership Project (3GPP) in Release 16, NR-V2X features a distributed resource allocation mode, known as Mode 2, that allows vehicles to autonomously select their transmission resources employing a Semi-Persistent Scheduling (SPS) or a Dynamic Scheduling (DS) scheme. The SPS approach relies on the periodic reservation of resources, whereas the DS scheme is a reservation-less solution that forces the selection of new transmission resources for every generated message. 3GPP standards do not indicate under which conditions each scheduling scheme should be used. In this context, this study analyzes and compares the performance of SPS and DS under different traffic types and Packet Delay Budget (PDB) requirements. Simulation results demonstrate that the SPS scheme represents the best solution for serving fixed size periodic traffic, whereas DS is more adequate for aperiodic traffic (of fixed or variable size). The study shows that the superiority of DS over SPS becomes more evident when tighter PDB requirements are considered, and that the performance of the DS scheme is independent of the PDB. It is also demonstrated that an adaptive scheduling strategy, which allows vehicles to select the scheduling scheme that best suits the type of generated traffic, is the best solution in mixed traffic scenarios where fixed size periodic traffic and variable size aperiodic traffic sources coexist.

2023 - Awareness Messages by Vulnerable Road Users and Vehicles: Field Tests via LTE-V2X [Articolo su rivista]
Lusvarghi, Luca; Grazia, CARLO AUGUSTO; Klapez, Martin; Casoni, Maurizio; Merani, Maria Luisa
abstract

2022 - Fundamental Limits on the Uplink Performance of the Dynamic-Ordered SIC Receiver [Articolo su rivista]
Lusvarghi, Luca; Merani, Maria Luisa
abstract

Due to the rapid and widespread growth of the Internet-of-Things (IoT) paradigm, present days witness an exponential increase in the number of connected devices. In this regard, the orthogonal transmission techniques featured by conventional 4G and 5G systems can only support a limited number of simultaneously active users, due to their low spectral efficiency and poorly flexible resource allocation. To overcome such limitations, the 6G framework will include novel Next Generation Multiple Access (NGMA) solutions that will efficiently and flexibly connect a significantly larger number of devices over the same portion of spectrum. Under the NGMA umbrella, the Power-Domain Non-Orthogonal Multiple Access (PD-NOMA) technology is able to accommodate multiple users on the same frequencies by carefully assigning different power levels to the active users and employing Successive Interference Cancellation (SIC) receivers. In this work, we put forth a novel analytical approach to evaluate the performance that PD-NOMA achieves on the uplink of a single cell when a dynamic-ordered SIC receiver is considered. With respect to other existing works, the fundamental limits on the system performance are assessed analytically for an arbitrary number = of simultaneously transmitting users, and both the case of Rayleigh and lognormal-shadowed Rayleigh fading are examined. The closed-form expressions presented in this work, whose correctness and excellent accuracy are validated through Monte Carlo simulations, disclose the impact of lognormal shadowing and an increasingly larger number of active users on the PD-NOMA performance.

2022 - How Does 5G NR V2X Mode 2 Handle Aperiodic Packets and Variable Packet Sizes? [Relazione in Atti di Convegno]
Molina-Galan, Alejandro; Coll-Perales, Baldomero; Lusvarghi, Luca; Gozalvez, Javier; Merani, Maria Luisa
abstract

—5G NR V2X complements LTE V2X to support advanced V2X services for connected and automated driving. 5G NR V2X introduces novel features at the MAC layer that are designed to cope with potential packet collisions, and that could help address the LTE V2X MAC inefficiencies observed under aperiodic traffic of variable size. This is the case of the reevaluation mechanism that is a mandatory MAC feature of 5G NR V2X, and that seeks avoiding possible packet collisions detected before a vehicle transmits in selected resources. Evaluations conducted to date of 5G NR V2X do not consider the re-evaluation mechanism, and have focused on traffic patterns that do not fully account for the traffic variability of advanced V2X services. This paper extends the current state of the art with the first evaluation of a fully standard compliant 5G NR V2X implementation under the traffic patterns recommended by 3GPP for advanced V2X services. Our study shows that 5G NR V2X Mode 2 still faces MAC challenges when using semi-persistent scheduling (SPS) to efficiently support aperiodic traffic of variable size.

2022 - Machine Learning for Disseminating Cooperative Awareness Messages in Cellular V2V Communications [Articolo su rivista]
Merani, Maria Luisa; Lusvarghi, Luca
abstract

This paper develops a novel Machine Learning (ML)-based strategy to distribute aperiodic Cooperative Awareness Messages (CAMs) through cellular Vehicle-to-Vehicle (V2V) communications. According to it, an ML algorithm is employed by each vehicle to forecast its future CAM generation times; then, the vehicle autonomously selects the radio resources for message broadcasting on the basis of the forecast provided by the algorithm. This action is combined with a wise analysis of the radio resources available for transmission, that identifies subchannels where collisions might occur, to avoid selecting them. Extensive simulations show that the accuracy in the prediction of the CAMs’ temporal pattern is excellent. Exploiting this knowledge in the strategy for radio resource assignment, and carefully identifying idle resources, allows to outperform the legacy LTE-V2X Mode 4 in all respects.

2021 - MoReV2X - A New Radio Vehicular Communication Module for ns-3 [Relazione in Atti di Convegno]
Lusvarghi, L.; Merani, M. L.
abstract

The Third Generation Partnership Project (3GPP) recently released the 5G New Radio (NR) Vehicle-to-Everything (V2X) standard. NR-V2X is expected to support a large set of enhanced V2X applications, characterized by stringent requirements in terms of latency, reliability and data rate. The use of simulations plays a crucial role in the preliminary assessment of NR-V2X achievable performance, providing valuable insights on the strengths and limits of the new solution. This work introduces MoReV2X, an open-source ns-3 module for the simulation of NR-V2X communications. The development of MoReV2X adheres to 3GPP specifications, includes various traffic models, features an accurate implementation of the NR propagation channel between vehicles and allows to determine a thorough set of Key Performance Indicators (KPIs). A first set of exemplary results is reported to testify the proper functioning of the module. Moreover, the results reveal the impact that different subcarrier spacings have on system performance, when periodic and aperiodic traffic sources are considered.

2021 - Rings for Privacy: an Architecture for Large Scale Privacy-Preserving Data Mining [Articolo su rivista]
Merani, M. L.; Croce, D.; Tinnirello, I.
abstract

This paper proposes a new architecture for privacy-preserving data mining based on Multi Party Computation (MPC) and secure sums. While traditional MPC approaches rely on a small number of aggregation peers replacing a centralized trusted entity, the current study puts forth a distributed solution that involves all data sources in the aggregation process, with the help of a single server for storing intermediate results. A large-scale scenario is examined and the possibility that data become inaccessible during the aggregation process is considered, a possibility that traditional schemes often neglect. Here, it is explicitly examined, as it might be provoked by intermittent network connectivity or sudden user departures. For increasing system reliability, data sources are organized in multiple sets, called rings, which independently work on the aggregation process. Two different protocol schemes are proposed and their failure probability, i.e., the probability that the data mining output cannot guarantee the desired level of accuracy, is analytically modeled. The privacy degree, the communication cost and the computational complexity that the schemes exhibit are also characterized. Finally, the new protocols are applied to some specific use cases, demonstrating their feasibility and attractiveness.

2020 - An Effective Machine Learning (ML) Approach to Quality Assessment of Voice over IP (VoIP) Calls [Articolo su rivista]
Cipressi, Elena; Merani, Maria Luisa
abstract

This letter puts forward a supervised ML tech2 nique to determine the Quality of Experience (QoE) of VoIP calls. It takes its beginning from an investigation on VQmon, an enhanced E-model version that estimates the quality of IP-based voice calls adopting an objective approach. The current study demonstrates VQmon shortcomings via a comparison between the Mean Opinion Score (MOS) values this technique predicts and the actual average ratings collected from a subjective listening quality campaign. It proposes to deploy Ordinal Logistic Regression (OLR) for speech quality assessment, and results disclose that OLR outperforms popular ML algorithms, in accuracy and confusion matrices.

2020 - Estimation of Traffic Matrices via Super-resolution and Federated Learning [Poster]
Amoroso, Roberto; Esposito, Flavio; Merani, Maria Luisa
abstract

Network measurement and telemetry techniques are central to the management of today’s computer networks. One popular technique with several applications is the estimation of traffic matrices. Existing traffic matrix inference approaches that use statistical methods, often make assumptions on the structure of the matrix that may be invalid. Data-driven methods, instead, often use detailed information about the network topology that may be unavailable or impractical to collect. Inspired by the field of image processing, we propose a superresolution technique for traffic matrix inference that does not require any knowledge on the structural properties of the matrix elements to infer, nor a large data collection. Our experiments with anonymized Internet traces demonstrate that the proposed approach can infer fine-grained network traffic with high precision outperforming existing data interpolation techniques, such as bicubic interpolation.

2020 - On the Coexistence of Aperiodic and Periodic Traffic in Cellular Vehicle-to-Everything [Articolo su rivista]
Lusvarghi, Luca; Merani, Maria Luisa
abstract

Cellular Vehicle-to-Everything (C-V2X) communications are the key to connected and autonomous driving, and pave the way for future Intelligent Transport Systems (ITS). To support non-safety and safety critical applications in the demanding out-of-coverage scenario, the 3rd Generation Partnership Project (3GPP) has standardized the distributed C-V2X Mode 4 solution, whose behavior has been thoroughly analyzed for periodic traffic. In the current work, the problem of allocating aperiodic traffic in Mode 4 is tackled, a matter that has not been addressed before and that raises several challenging questions. A solution for serving such traffic type is put forth, and an analytical insight on the attainable performance is offered. Further, it is numerically proved that guaranteeing aperiodic flows good service levels is hard when their packets are not small sized. This holds true even for sophisticated physical layer choices and at relatively modest traffic densities, revealing that novel approaches to radio resource assignment are a necessity in Fifth Generation (5G) vehicular communications.

2019 - A Comparative Study on the Quality of Narrow-Band and Wide-Band AMR VoLTE Calls [Relazione in Atti di Convegno]
Merani, Maria Luisa; Cipressi, Elena
abstract

This work performs a comparative analysis of the end-to-end quality guaranteed by Voice over LTE (VoLTE), examining several millions of VoLTE calls that employ two popular speech audio codecs, namely, Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wide Band (AMR-WB). To assess call quality, VQmon, an enhanced version of the standardized E-Model, is utilized. The study reveals to what extent AMRWB based calls are more robust against network impairments than their narrowband counterparts; it further shows that the dependence of call quality on the packet loss rate is approximately exponential for both types of codec.

2019 - A Novel Weighted-Counter Method for Simulating Coherent TWDP Fading Channels [Articolo su rivista]
Merani, Maria Luisa; Beaulieu, Norman C.
abstract

New channel simulation models are needed for the study of future wireless networks, 5G and beyond. A novel simulation technique dubbed weighted-counting is proposed. It is used to generate random variates having the two-wave with diffuse power (TWDP) fading amplitude distribution. The TWDP channel model describes high-speed train, femtocell, sea surface, heterogeneous and other channels having two different dominant line-of-sight waves as well as scatter power components.

2019 - Effects of Packet Loss and Jitter on VoLTE Call Quality [Relazione in Atti di Convegno]
Cipressi, Elena; Merani, Maria Luisa
abstract

This work performs a preliminary, comparative analysis of the end-to-end quality guaranteed by Voice over LTE (VoLTE), examining several millions of VoLTE calls that employ two popular speech audio codecs, namely, Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate WideBand (AMR-WB). To assess call quality, VQmon, an enhanced version of the standardized E-Model, is utilized. The study reveals to what extent AMR-WB based calls are more robust against network impairments than their narrowband counterparts; it further shows that the dependence of call quality on the packet loss rate is approximately exponential when the AMR codec is used, whereas it is nearly linear for the AMR-WB codec.

2018 - Out-of-Coverage Multi-Hop Road Safety Message Distribution via LTE-A Cellular V2V (C-V2V) [Relazione in Atti di Convegno]
Gibellini, Lorenzo; Merani, Maria Luisa
abstract

This work investigates the performance of a multi-hop scheme for the dissemination of road safety messages on highway segments, employing the recently standardized LTE-A Cellular Vehicle-to-Everything (C-V2X) technology. In order to guarantee a seamless service in areas where cellular coverage is unavailable, vehicles directly communicate over the unlicensed ITS 5.9 GHz frequency band, operating in accordance to Mode 4 of the C-V2X standard. The behavior of the proposed scheme reveals that the delivery of safety messages can successfully take place on a dedicated radio channel, as well as on a shared channel where periodic messages are broadcast at the maximum frequency foreseen by ETSI.

2018 - Recovery Failure Probability of Power-based NOMA on the Uplink of a 5G Cell for an Arbitrary Number of Superimposed Signals [Relazione in Atti di Convegno]
Merani, Maria Luisa
abstract

This work puts forth an analytical approach to evaluate the recovery failure probability of power-based NOMA on the uplink of a 5G cell, the recovery failure being defined as the unfortunate event where the receiver is unable to decode even one out of the n simultaneously received signals. In the examined scenario, Successive Interference Cancellation (SIC) is considered and an arbitrary number of superimposed signals is present. For the Rayleigh fading case, the recovery failure probability is provided in closed-form, clearly outlining its dependency on the signal-to-noise ratio of the users that are simultaneously transmitting, as well as on their distance from the receiver.

2017 - Successfully Mapping DASH over a P2P Live Streaming Architecture [Articolo su rivista]
Merani, Maria Luisa; Natali, Laura
abstract

This work proposes to combine Peer-to-Peer (P2P) and Dynamic Adaptive Streaming over HTTP (DASH), leveraging the scalability and self-organization properties of the former and the capability of the latter to adapt the rate of the delivered video to varying operating conditions. The devised P2P-DASH architecture is a multi-overlay P2P platform, where every peer implements a decentralized rate control strategy that steers its transitions from one overlay to another, so as to achieve a good viewing quality and also preserve the good functioning of the entire system. At peer’s site, the new architecture displays the following salient features: (i) an augmented pool of neighbors, to provide every node with the knowledge of the streaming process within adjacent overlays; (ii) a priority mechanism to speed up the delivery of video chunks to peers that newly enter the system or switch from the current to a new overlay, in order to quickly turn them into active peers; (iii) some alternative rate control algorithms to guarantee, with different degrees, more resources to overlays that deliver higher streaming rates, therefore reducing the misalignment among streaming processes which occur in different overlays, and ultimately improve the viewing quality of the single user. System behavior is extensively investigated through simulation and some clear design guidelines are provided.

2016 - Adaptive Streaming in P2P Live Video Systems: a Distributed Rate Control Approach [Articolo su rivista]
Merani, Maria Luisa; Natali, Laura
abstract

Dynamic Adaptive Streaming over HTTP (DASH) is a recently proposed standard that offers different versions of the same media content to adapt the delivery process over the Internet to dynamic bandwidth fluctuations and different user device capabilities. The peer-to-peer (P2P) paradigm for video streaming allows to leverage the cooperation among peers, guaranteeing to serve video requests with increased scalability and reduced cost. We propose to combine these two approaches in a P2P-DASH architecture, exploiting the potentiality of both. The new platform is made of several swarms and a different DASH representation is streamed within each of them; unlike client-server DASH architectures, where each client autonomously selects which version to download according to current network conditions and to its device resources, we put forth a new rate control strategy implemented at peer site to maintain a good viewing quality to the local user and to simultaneously guarantee the successful operation of the P2P swarms. The effectiveness of the solution is demonstrated through simulation and it indicates that the P2P-DASH platform is able to warrant its users a very good performance, much more satisfying than in a conventional P2P environment where DASH is not employed. Through a comparison with a reference DASH system modeled via the Integer Linear Programming (ILP) approach, the new system is shown to outperform such reference architecture. To further validate the proposal, both in terms of robustness and scalability, system behavior is investigated in the critical condition of a flash crowd, showing that the strong upsurge of new users can be successfully revealed and gradually accommodated.

2016 - An IP-TV P2P streaming system that improves the viewing quality and confines the startup delay of regular audience [Articolo su rivista]
Merani, Maria Luisa; Natali, Laura; Barcellona, Cettina
abstract

This paper investigates how a p2p television platform can take advantage of the presence of frequent channel viewers to grant them a more satisfying service than to less regular spectators, and how such privileged users can also be protected when unfavorable operating conditions manifest within the overlay. The explored idea is to learn beforehand about the users’ interests, monitoring their behavior in the recent past, in order to cluster them in groups that display different habits; then, the video chunk scheduling algorithm of the overlay is altered, with the aim of serving frequent spectators in a privileged manner, providing them with a better viewing experience and a faster access to the selected channel without overly penalizing less habitual customers. An analytical model is developed, to capture the difference in average startup delay that the proposed modifications introduce; several additional performance metrics are numerically determined, in order to thoroughly size up the performance of both groups of viewers. The obtained results show that a clear service differentiation is attained and demonstrate that, if bandwidth resources become scarce, frequent viewers are protected and still enjoy a broadcasting service of superior quality.

2015 - A Novel Rate Control Strategy for Adaptive Video Streaming in P2P Overlays [Relazione in Atti di Convegno]
Natali, Laura; Merani, Maria Luisa
abstract

This work proposes a novel P2P-DASH architecture that jointly leverages the intrinsic cooperation property of P2P and the adaptivity of Dynamic Adaptive Streaming over HTTP (DASH) to deliver videos to a large population of users with heterogeneous streaming requests. The system is made of several overlays, each distributing a different DASH representation; every peer within the system autonomously enforces a newly devised rate control strategy that steers its movements from one overlay to another, in order to maintain a good viewing experience and to simultaneously guarantee the successful operation of the P2P overlays. The effectiveness of the solution is demonstrated through simulation and it indicates that the P2P-DASH platform is able to guarantee its users a very good performance, much more satisfying than in a conventional P2P environment where DASH is not employed. Moreover, through the comparison with a reference system modeled via the Integer Linear Programming (ILP) approach,it is shown that our system outperforms such reference architecture in terms of viewing quality; at the same time, the number of users streaming the video at the desired bit rate is extremely close to the optimum of the ILP setting in the most favorable scenarios, and only moderately suboptimal in the worst.

2015 - Experimental evaluation of privacy-preserving profiling schemes on PlanetLab [Relazione in Atti di Convegno]
Randazzo, Francesco; Croce, Daniele; Tinnirello, Ilenia; Barcellona, Cettina; Merani, Maria Luisa
abstract

New pervasive technologies often reveal many sensitive information about users' habits, seriously compromising the privacy and sometimes even the personal security of people. To cope with this problem, researchers have developed the idea of privacy-preserving data mining which refers to the possibility of releasing aggregate information about the data provided by multiple users, without any information leakage about individual data. These techniques have different privacy levels and communication costs, but all of them can suffer when some users' data becomes inaccessible during the operation of the privacy preserving protocols. It is thus interesting to validate the applicability of such architectures in real-world scenarios. In this paper we experimentally evaluate two promising privac-preserving techniques on PlanetLab, analyzing the execution time and the failure rate that each scheme exhibits.

2015 - Multi-cloud Privacy Preserving Schemes for Linear Data Mining [Relazione in Atti di Convegno]
Merani, Maria Luisa; Barcellona, Cettina; Tinnirello, Ilenia
abstract

This paper presents an approach to privacy-preserving data mining that relies upon a relatively simple secret sharing scheme. Its main feature is that users, sensitive data owners, are engaged in the secret sharing operations that protect their privacy. They are grouped in independent clouds connected to a central unit, the data miner, that only manages the aggregated data of each cloud, therefore avoiding the disclosure of information belonging to single nodes. We propose two privacy preserving schemes, with different privacy levels and communication costs. When designing them, we assume that some users' data might become inaccessible during the operation of the privacy preserving protocols, due to intermittent network connectivity or sudden user departures, and therefore introduce a new performance metric, the failure probability, defined as the probability that the mining output cannot guarantee the desired level of accuracy. We then discuss the attractive tradeoffs between privacy, accuracy and communication overhead that each scheme exhibits.

2014 - An interest-aware video streaming platform: Shaping its architecture to better suit users' demands [Relazione in Atti di Convegno]
Natali, Laura; Barcellona, Cettina; Merani, Maria Luisa
abstract

This paper investigates how a p2p television platform can take advantage of the presence of frequent channel viewers to grant them a more satisfying service than to less regular spectators. The idea we explore is to learn beforehand about the users' interests, in order to cluster them in groups that display different behaviors; then, the video chunk scheduling algorithm of the p2p overlay is altered, with the aim of serving frequent spectators in a privileged manner, providing them with a faster access to the selected channel. An analytical model is developed, to capture the difference in startup delay that the proposed changes introduce; several additional performance metrics are numerically determined, in order to thoroughly size up the performance of different groups of viewers. The obtained results show that a clear service differentiation is achieved and also quantify the effects that the setting of different system parameters have on the amount of such gap.

2014 - Leveraging users' likes in a video streaming P2P platform [Relazione in Atti di Convegno]
Natali, Laura; Barcellona, C.; Merani, Maria Luisa
abstract

This paper investigates how a p2p television platform can take advantage of the presence of frequent channel viewers to grant them a more satisfying service than to less regular spectators. The idea we explore is to learn beforehand about the users' interests, in order to cluster them in groups that display different behaviors; then, the neighborhood creation strategy and video chunk scheduling algorithm of the overlay is altered, with the aim of serving frequent spectators in a privileged manner, providing them with a faster access to the selected channel without overly penalizing less habitual customers. An analytical model is developed, to capture the difference in startup delay that the proposed modifications introduce; several additional performance metrics are numerically determined, in order to thoroughly size up the performance of both groups of viewers. The obtained results show that a clear service differentiation is achieved and also quantify the effects that alternative neighborhood creation algorithms have on the amount of such gap.

2014 - Performance Analysis of Randomized Distributed Space-Time Codes over Composite Gamma/Lognormal Fading Channels [Relazione in Atti di Convegno]
Soffritti, Jacopo; Duong, T. Q.; Merani, Maria Luisa; Zepernick, H. J.
abstract

This work investigates the end-to-end performance of randomized distributed space-time codes with complex Gaussian distribution, when employed in a wireless relay network. The relaying nodes are assumed to adopt a decode-and-forward strategy and transmissions are affected by small and large scale fading phenomena. Extremely tight, analytical approximations of the end-to-end symbol error probability and of the end-to-end outage probability are derived and successfully validated through Monte-Carlo simulation. For the high signal-to-noise ratio regime, a simple, closed-form expression for the symbol error probability is further provided.

2014 - Rings for privacy: An architecture for privacy-preserving user profiling [Relazione in Atti di Convegno]
Barcellona, Cettina; Tinnirello, Ilenia; Merani, Maria Luisa
abstract

In present days, where anyone stays online nearly everywhere and everytime, it is crucial from the viewpoint of service providers to collect consumers data, so that questions such as “what kind of advertisement do they click on?”, “what do they buy online?”, “what IP-TV channels do they watch?” and “what do they like to do on social networks?” are answered and some relevant information about the users' habits and likes are extracted, resold for business, or employed to provide services that are better tailored to the customers' interests. Several privacy issues have however to be taken into account, when sensitive data are managed. We believe that approaches which guarantee the users' privacy have to be pursued: accordingly, we put forth a solution that performs users' profiling and keeps sensitive information private; additionally, it lends itself to a decentralized, cost-effective implementation.

2013 - Cooperation Among Members of Online Communities: Profitable Mechanisms to Better Distribute Near-Real-Time Services [Capitolo/Saggio]
Merani, Maria Luisa; Capetta, M.; Saladino, Daniela
abstract

In recent years, classical Internet applications have been accompanied by the surging of a greatvariety of new services and exciting possibilities. Among such broad range, two particular phenomenaare highly successful: Online Social Networks (OSNs) and Peer-to-Peer (P2P) services.This paper merges these distinct worlds, via the proposal of a P2P streaming system that takesadvantage of the friendship relationships of an underlying OSN, to better distribute videos among theoverlay peers that are also friends within the OSN. A category of privileged users is therefore created,that is guaranteed a satisfying viewing experience when the P2P overlay operates in critical conditions,i.e, when bandwidth availability is scarce. We show that the help of direct friends, two-hops awayfriends and, in the limit, of the entire OSN community brings in considerable advantages to the peersthat are OSN members. In particular:- the number of those among them that are able to download the entire video significantly increases;- the number of video portions they can obtain consistently raises;- as desired, when the P2P system is operating in underloaded conditions, a proper functioning isguaranteed to all of its nodes, regardless of their being members of the OSN or plain P2P users.

2013 - Performance Analysis of Randomized Distributed Space-Time Codes in Nakagami-m Fading [Relazione in Atti di Convegno]
J., Soffritti; H. J., Zepernick; Merani, Maria Luisa
abstract

This paper presents a performance analysis of randomized distributed space-time codes (RDSTCs) in Nakagami- fading channels over a multiple Decode-and-Forward (DF) relay network. The performance is assessed in terms of symbol error probability (SEP) and outage probability (OP). The results of this research provide exact analytical expressions for these two performance metrics. In addition, the diversity gain of the considered system is derived from these expressions and compared with some results already presented in literature to verify its soundness. Finally, numerical results for some example scenarios are provided to illustrate applications of the derived expressions for performance analysis.

2011 - A Model to Seize the Instantaneous Performance of P2P Streaming Platforms: Simulative and Experimental Validation [Relazione in Atti di Convegno]
Merani, Maria Luisa; Saladino, Daniela; Leonardi, Gian Paolo
abstract

In recent years P2P technology has gained great popularity not only in file sharing applications but also in the field of video distribution. This work proposes a simple model to assess the performance a P2P system designed for video streaming can achieve, measured in terms of average video delivery rate. The model allows to compute system efficiency in a simple but accurate way through the partition of peers in two distinct populations: bad peers, that are not collaborative, and good peers, that contribute to share their video contents with others. As a meaningful example, it is employed to investigate the behavior of a real P2P prototype subject to high peer dynamics: its effectiveness is proved via experimental results, and sheds a new light on the way a streaming service overlay can be centrally and timely monitored.

2011 - How Helpful Can Social Network Friends Be in Peer-to-Peer Video Distribution [Relazione in Atti di Convegno]
Merani, Maria Luisa
abstract

Today two keywords more and more frequently recur over the Internet: Peer-to-Peer (P2P) and social networks. P2P, in all of its different declinations, represents a widely-adopted approach for content distribution, particularly for video diffusion. In parallel, the proliferation of social networks is an analogously stunning phenomenon, of unprecedented popularity and scope. In the present work we examine a mesh-based P2P overlay, specifically designed for video streaming, and put forth some modifications to the neighborhood creation and chunk scheduling algorithm the platform adopts, with the goal of favoring peers belonging to a social network and granting them better performance. The improvements that such modifications attain are measured in terms of delivery ratio (throughput) and playback delay. We find that it is possible to guarantee a clear service differentiation, so that social network peers experience an improved viewing experience at the expense of ordinary overlay members, and that the scheduling mechanism modifications warrant the more consistent gains; we also show the role that different percentages of peers belonging to the social network have on the considered metrics. We finally suggest that the attained differentiated service level can be leveraged as an incentive to convince peers of the video overlay to join the social network.

2011 - Preface to the International Workshop on Data Mining in Networks [Relazione in Atti di Convegno]
Di Fatta, G.; Liotta, A.; Agoulmine, N.; Agrawal, G.; Berthold, M. R.; Bordini, R. H.; Borgelt, C.; Boutaba, R.; Calzarossa, M. C.; Cannataro, M.; Choudhary, A.; Cortes, U.; Dagiuklas, T.; De Turck, F.; De Vleeschauwer, B.; Demestichas, P.; Dhoedt, B.; Festor, O.; Fortino, G.; Friderikos, V.; Giunchiglia, F.; Gravier, C.; Guo, Y.; Hunter, D.; Karypis, G.; Krishnaswamy, S.; Limam, N.; Medhi, D.; Merani, M. L.; Nurnberger, A.; Pardede, E.; Parthasarathy, S.; Gaspary, L. P.; Ranc, D.; Sivakumar, K.; Stadler, R.; Stiller, B.; Strassner, J.; Syed, A.; Talia, D.; Urso, M. A.; Van Der Meer, S.; Wolff, R.; Granville, L. Z.
abstract

2011 - Taking Advantage of Social Network Relationships in P2P Streaming Overlays [Relazione in Atti di Convegno]
Merani, Maria Luisa; Capetta, M.; Saladino, Daniela
abstract

In recent years, classical Internet applications have been accompanied by the surging of a great variety of new services and exciting possibilities. Among such broad range, two particular phenomena are highly successful: Online Social Networks (OSNs) and Peer-to-Peer (P2P) services. This paper merges these distinct worlds, via the proposal of a P2P streaming system that takes advantage of the friendship relationships of an underlying OSN, to better distribute videos among the overlay peers that are also friends within the OSN. A category of privileged users is therefore created, that is guaranteed a satisfying viewing experience when the P2P overlay operates in critical conditions, i.e, when bandwidth availability is scarce. We show that the help of direct friends, two-hops away friends and, in the limit, of the entire OSN community brings in considerable advantages to the peers that are OSN members. In particular: the number of those among them that are able to download the entire video significantly increases; the number of video portions they can obtain consistently raises; as desired, when the P2P system is operating in underloaded conditions, a proper functioning is guaranteed to all of its nodes, regardless of their being members of the OSN or plain P2P users.

2010 - Peer-to-peer systems for video delivery [Articolo su rivista]
Merani, Maria Luisa
abstract

In the very recent years, peer-to-peer for streaming videoapplications has gained considerable attention: commercialsystems have appeared, raising interest among a communityof potential users that have quickly increased and reachedan impressive size. The pioneering experience of theCoolstreaming prototype has been soon paired by popularsystems such as PPlive, Sopcast and PPStream, platformscapable of attracting thousands of users to watch videoprograms over the Internet.Among academia too, peer-to-peer streaming architectureshave spurred curiosity: a significant body of papershas been produced, bringing forth studies on heterogeneousaspects related to these systems.Nevertheless, much work remains to be done. The fieldof modeling is only partly explored; the understanding ofthe basilar laws that shape the behaviour of these systems isfar from being satisfying; the mutual relation betweensystem performance and the different algorithms that can beemployed for scheduling and peer selection still awaits for asound answer. How to provide differentiated service levelsto different users is a further open question, and so appearsthe validation of peer-to-peer approaches for video applicationswith tight reliability constraints.In this special issue we make an attempt to focus on afew specific issues of this realm: the contributionspresented below shed some light on the examined problems,and let the reader appreciate the strength and noveltyof their reach.

2009 - Hands-On Networking From Theory to Practice [Monografia/Trattato scientifico]
Merani, Maria Luisa; Casoni, Maurizio; Cerroni, Walter
abstract

Learn the core theory and explore real-world networking issues with this richly illustrated example-based textbook. It provides an accurate view of modern networks through detailed coverage of the most relevant networking technologies, with no unnecessary extras. Carefully designed, affordable laboratory exercises based on open-source software networking tools are included for hands-on practice with real networking devices. Numerous case studies and examples further link theory to practice, whilst the topologies, tools and configurations needed to carry out practical exercises are provided to guide students through each task. Its bottom-up approach is easy for students to follow and perfect for lab-oriented courses.

2009 - Live Video and IP-TV [Capitolo/Saggio]
Merani, Maria Luisa; Saladino, Daniela
abstract

P2P architectures designed for video broadcasting have in the very last years gained a prominent role. This Chapter aims at providing a comprehensive insight of the most recent advances in the field, focusing on live video streaming. The first part of the Chapter puts forth a classification of P2P video solutions, adoptingalternative sorting criteria that hide different design approaches. It then concentrates on the conceptually attractive issue of data diffusion process within the P2P overlay.An overview of the most interesting P2P IP-TV systems currently available over the Internet is also provided, and the most salient features they exhibit highlighted.Next, the definition of the quality of experience (QoE) for a system user, as well as the recording of the whole system performance via local and centralized measurementapproaches, is commented upon. The second part of the Chapter completes the view, bringing up the modeling efforts that capture the main characteristics and limits of a P2P streaming system, both analytically and numerically. The Chapteris closed by a pristine look at some challenging, open questions: the issue of peers that lie behind NAT and firewalls is discussed; the benefits and the limits of crosslayer design are commented, with a specific emphasis onto the adoption of advancedcoding techniques.

2009 - Scalability and Peer Churning in IP-TV: an Analytical Insight [Relazione in Atti di Convegno]
Merani, Maria Luisa; Leonardi, Gian Paolo; Saladino, Daniela
abstract

Abstract-Peer-to-peer (P2P) technology for TV broadcasting over the Internet is becoming more and more popular in the very last years. This paper introduces a network-wide metric to assess the efficiency of P2P streaming systems and develops a mathematical model to explain: (i) the scalability of such architectures with the number of peers, as evidenced by recent measurements; (ii) the initial decrement of efficiency (hence, quality) when a sharp increase in the number of peers in system occurs, as reported by experimental data. As for the second point, the proposed model builds upon the fundamental remark that when a peer first joins the system, it has no video content to share with others: its upload contribution is null for an initial time interval and the new peer behaves as a free rider. Three situations concerning the system reaction to the requests of the new entering peers are examined: full compensation; partial compensation; no reaction at all. Depending on the system answer and on its extent, system efficiency is shown to exhibit different time trends.

2008 - Effectiveness and issues of congestion control in 802.11g wireless LANs [Articolo su rivista]
Borri, M; Casoni, Maurizio; Merani, Maria Luisa
abstract

The current paper presents a collection of experimentaldata portraying the performance achieved in the wirelesssetting by several TCP-friendly congestion controls recentlyproposed in literature. Thiswork is partly motivated bythe consideration that the majority of the analytical results inthis area are validated by simulation, rather than by field tests.Examining these algorithms in real environments can helpverify their actual effectiveness over the wireless Internet.To reach such goal, two representative controls among theso-called window-based TCP-friendly schemes have beenimplemented, namely, the General Additive Increase MultiplicativeDecrease (GAIMD) strategy, and the SQuare RooT(SQRT) binomial control; the most representative algorithmamong rate-based controls, the TCP Friendly Rate Control(TFRC), has also been considered. Their TCP-fairnessand smoothness have been comprehensively evaluated in anIEEE 802.11g Wireless Local Area Network (WLAN). Theobtained results show that the GAIMD and SQRT strategiesreveal non-negligible scalability and smoothness problems,that markedly limit their performance. It is empiricallydemonstrated that their “optimal” increase/decrease rules,based on TCP-Reno analytical model, cannot guarantee anadequate performance when GAIMD and SQRT competewith TCP-Sack, a de facto standard for current TCP implementations.TFRC is demonstrated to occasionally behave bewildering: properly tuning one of its congestion controlparameters and enhancing the algorithm with a flow-controlmechanism result in a definitely fairer share of bandwidthwith concurrent TCP flows.

2007 - RTP-Primal: A New Congestion Control Scheme Suitable for Smooth Multimedia Delivery [Relazione in Atti di Convegno]
M., Borri; A., Ferrarini; Merani, Maria Luisa
abstract

This paper mathematically frames the relation between window-based and rate-based source congestion control algorithms when the assumption of variable round-trip time conditions is introduced, and then it proposes a new, rate-based control designed to be suitable for use by multimedia streams. The behavior of the new strategy is assessed by simulation, demonstrating that it exhibits good responsiveness and satisfying smoothness, guaranteeing consistent and intra-fair throughput allocation. Moreover, a simple version of the control can be readily implemented resorting to RTP basic functionalities.

2007 - Window-Based and Rate-Based Congestion Controls: a Local Stability Analysis under Variable RTT Conditions and the Proposal of an RTP-Based Algorithm [Relazione in Atti di Convegno]
M., Borri; A., Ferrarini; Merani, Maria Luisa
abstract

The paper mathematically frames the relation between window-based and rate-based congestion control algorithms, when the assumption of variable round-trip time conditions is introduced. Under this hypothesis, the local stability analysis of a specific class of source, window-based controls is first developed; then a new, rate-based control suitable for use by multimedia streams is proposed. The novel strategy is demonstrated to guarantee consistent and intra-fair throughput allocation, good responsiveness and satisfying smoothness, even in a first, easy-to-implement version.

2006 - Adaptive GAIMD with Binary Decision: A Novel Congestion Control Approach for the Internet [Relazione in Atti di Convegno]
M., Borri; C., Finelli; M., Gerla; Merani, Maria Luisa
abstract

The current paper proposes a novel end-to-end congestion control suitable for multimedia flows, with the primary aim of guaranteeing a good level of smoothness to the connections that employ it. The suggested strategy, termed Adaptive GAIMD, has as its starting point a blind, window-based scheme named General Additive Increase Multiplicative Decrease (GAIMD); it however enhances it through a measurement-based prediction of network conditions, based on the observation of the interarrival times of the most recently received triple duplicate acknowledgments. Such forecast allows the control to selectively switch to the AIMD policy, i.e., to a TCP-like behavior, when the network drifts towards overload conditions. On the other hand, if the network is sensed lightly loaded, the control behaves as GAIMD. In all cases, Adaptive GAIMD guarantees a smoother packet delivery than native GAIMD and TCP would. The validity of the proposed approach is experimentally proved, performing numerous tests and comparisons between Adaptive GAIMD, GAIMD and TCP-Sack, that took place on a geographical link spanning from Modena, Italy, to Los Angeles, United States.

2006 - Allocation policies of quasi-orthogonal codes on the forward link of a multicarrier DS-CDMA system [Articolo su rivista]
U., Manzoli; Merani, Maria Luisa
abstract

Alternative code assignment policies for the forward link of a multicarrier DS-CDMA system employing the recently proposed quasi-orthogonal sequences are put forth in this letter. It is demonstrated how different allocation strategies of quasi-orthogonal codes alter the interference level suffered by active units; it is also shown how to shape the rate of interference growth as a function of the number of active users within the reference cell, implementing some specific code allocation patterns. The performance achieved by various schemes is assessed in a frequency selective fading environment, in terms of average bit error probability.

2006 - Goodput and delay analysis of a radio link control protocol operating over a multicarrier DS-CDMA architecture [Articolo su rivista]
Manzoli, U; Merani, Maria Luisa
abstract

This work proposes an analytical model to investigate the behavior of a Radio Link Control (RLC) protocol on the forward link of a mobile radio system and to relate its performance to transmission design. As a reference case, a multicarrier DS-CDMA architecture employing Walsh and Quasi-Orthogonal channelization codes, similar to the current cdma2000 system, is considered. Jointly modelling the features of the data link layer and of the underlying physical channels, it is possible to identify the interaction between transmission parameters and the RLC protocol behavior. The latter is assessed by analysis, determining the RLC protocol goodput and the average delivery time suffered by a data unit transferred over the radio channel, when two different coding approaches are. adopted: namely, rate compatible punctured convolutional codes and code combining.

2006 - How to Veritably Determine the Accomplishments of Static and Dynamic OVSF Code Assignment Algorithms [Relazione in Atti di Convegno]
Merani, Maria Luisa; M., Pettenati
abstract

In this paper reference is made to some allocation techniquessuitable for the assignment of OVSF (Orthogonal VariableSpreading Factor) codes on the downlink of a WCDMA system.Yet, in contrast to what has been previously assumed inliterature, this work proposes a criterion for the admission of anew user that explicitly takes into account transmission requirements.In detail, two distinct conditions are to be fulfilled to leta new call enter the system: given a code allocation strategyis selected, the corresponding rules are first applied with thegoal of finding a free code to assign the user, fitting the user’sdata rate needs; additionally, it is required that the signal-tonoiseratio – computed accounting for the presence of the newuser – takes on values higher than a proper threshold with aprobability sufficiently high (higher than a predefined admissionvalue) for all ongoing connections. Equivalently, systemload can be increased, but only up to the point where the assignmentof a new code within the tree does not degrade transmissionquality below an acceptable level. An accurate descriptionof the underlying physical layer is employed, and it is demonstratedhow markedly the requisite of adequate transmissionconditions affects the number of admitted users. As it is the interferencelevel to ultimately drive the OVSF code assignment,realistic limits on the performance that some popular code allocationtechniques can achieve in a Wideband CDMA systemare clearly evidenced.

2006 - M_OBS_SIM: A powerful modular optical burst switched (OBS) network SIMulator [Articolo su rivista]
Casoni, Maurizio; Luppi, E; Manzoli, U; Merani, Maria Luisa
abstract

This paper introduces M_OBS_SIM, a network simulator conceived to evaluate the performance of networks where the Optical Burst Switching (OBS) paradigm is implemented. Its accurate design allows to investigate the behavior of optical edge and core routers, as well as to assess the performance of the whole optical network; its modular construction guarantees a high degree of flexibility and a facilitated introduction of further developments. Its functional blocks, properly configured, allow to explore the effects that the most salient features of an OBS network - input traffic statistics, assembly algorithms, resource reservation policies, routing strategies - have on user performance. New and valuable results for different classes of applications with diverse service requirements are provided and discussed. (C) 2006 Elsevier B.V. All rights reserved.

2006 - Performance Evaluation of Channel Scheduling Algorithms With Different QoS Classes [Relazione in Atti di Convegno]
Casoni, Maurizio; Luppi, E; Merani, Maria Luisa
abstract

This paper compares the performance of different schedulingalgorithms, with and without void filling, considering a completeOptical Burst Switched (OBS) network scenario, given by edge andcore routers, under real traffic conditions.Performance is investigated taking into account both burst lossprobability and the complexity of the algorithms, evaluated interms of scheduling time. For an effective comparison both aspectshave to be considered in order to understand if an algorithm whichprovides low burst blocking probabilities is actually feasible ornot.In this paper the authors propose a scheduling algorithm whichrepresents a good trade-off between burst blocking performance andscheduling time.

2005 - An Experimental Study on Congestion Control in Wireless and Wired Networks [Relazione in Atti di Convegno]
M., Borri; Casoni, Maurizio; Merani, Maria Luisa
abstract

This paper presents an extensive experimental analysis of two TCP-friendly congestion controls recently proposed in the literature, placing a special emphasis on the wireless setting. This work is motivated in part by the consideration that, to our knowledge, the majority of the results in this area are validated by simulation analysis rather than by experimentation. Testing these algorithms in real environments can help to verify their actual effectiveness for possible employment over the Internet. To reach our goal, we have implemented one representative algorithm among the so-called window-based TCP-friendly congestion controls, namely, the general additive increase multiplicative decrease (GAIMD) strategy, and used the publicly available code for the most popular control of the rate-based family, i.e., the TCP-friendly rate control (TFRC). We have then evaluated their TCP-fairness and smoothness in a test-bed featuring Cisco WAN equipment, as well as in an IEEE 802.11g wireless local area network (WLAN). Based on our results, we first propose and justify the tuning of TFRC to avoid a weird behavior that in the wireless environment this control occasionally exhibited. We next show that the GAIMD strategy reveals non-negligible scalability and smoothness problems that limit its performance, mainly in the radio setting. We empirically demonstrate that its increase/decrease rules, based on a TCP-Reno analytical model, do not guarantee an adequate performance when GAIMD competes with TCP-Sack, a de facto standard for current TCP implementations.

2005 - Guaranteeing seamless end-to-end QOS in OBS networks [Capitolo/Saggio]
Casoni, M.; Merani, M. L.; Giorgetti, A.; Valcarenghi, L.; Castoldi, P.
abstract

In this paper the authors propose a method to guarantee end-to-end QoS to multiple traffic classes in optical burst switched (OBS) scenario, even in case of network congestion. The OBS network utilizes a core node architecture with no fiber delay lines and a limited set of wavelength converters. Traffic class performance differentiation is achieved by allowing high class traffic to utilize more node fianctionalities than low class traffic. To improve the likelihood of finding a route, even upon network congestion, bursts are allowed either to be deflected from their default route or to choose from a set of preplanned end-toend paths. Network performance evaluation is focused on burst blocking probability and end-to-end TCP throughput. Performance is determined under the assumption of exponentially distributed burst interarrival times and arbitrarily distributed burst durations. Numerical results show that the proposed approach is able to guarantee different end-to-end TCP throughput performance to each traffic class. Moreover the proposed burst routing policies allows to decrease, with respect to a shortest path routing policy, the burst blocking probability. Thus the end-to-end TCP throughput is seamlessly guaranteed even in case of network congestion. © 2005 by International Federation for Information Processing.

2005 - Message from the ISWCS 2005 Technical Program Chairs [Relazione in Atti di Convegno]
Gerla, M.; Merani, M. L.
abstract

2005 - On the performance of TCP over optical burst switched networks with different QoS classes [Relazione in Atti di Convegno]
Casoni, Maurizio; Merani, Maria Luisa
abstract

In this paper we investigate the end-to-end performance of an optical burst switched (OBS) network that adopts a core router architecture with no fiber delay lines and limited set of wavelength converters. In particular, by evaluating both the node and a reference network performance in terms of burst blocking probability we want to determine the end-to-end performance when a transport protocol like TCP is employed. Core node analysis is employed to identify the blocking experienced by incoming bursts, under the assumption of exponentially distributed burst interarrival times and arbitrarily distributed burst durations.

2004 - A Tree Partitioning Dynamic Policies for OVSF Codes Assignment in Wideband CDMA. [Articolo su rivista]
Dell'Amico, Mauro; F., Maffioli; Merani, Maria Luisa
abstract

This paper proposes some novel techniques to accommodate users with different rate requirements in a Wideband CDMA system employing orthogonal variable spreading factor codes. Several static and dynamic code assignment strategies areput forth and their behavior investigated, in terms of call blocking probability and number of required reassignments. The efficiency they exhibit under various traffic profiles is demonstrated, quantitatively comparing their performance to some codeassignment schemes recently presented in literature.

2004 - An analytical Model to Evaluate Throughput and TCP-Fairness of the SQRT Congestion Control Protocol over Wireless Lossy Links [Relazione in Atti di Convegno]
M., Borri; Merani, Maria Luisa
abstract

We develop an accurate analytic model to predict the send rate of the SQRT binomial congestion control protocol, under the assumption that the protocol operates in an environment where the packet loss rate is relatively high. Based on this model, a study of its TCP-friendliness is performed, remarking on the non-negligible effects on fairness that different queue managements have.

2004 - Comparison between the performance of conventional and selective RAKE receiver schemes [Articolo su rivista]
U., Manzoli; Merani, Maria Luisa
abstract

In this paper, we determine the effects of different diversity schemes on the behavior of a direct-sequence spread-spectrum RAKE receiver that operates with random sequences in a multipath fading channel with an arbitrary power-delay profile. Two different receiver architectures, the former employing the L instantaneously strongest paths out of the N-r resolved ones and the latter simply the L strongest on average paths out of the received N-r, are confronted in terms of symbol-error probability, when an M-level phase-shift keying system is assumed. The analytical approach devised for assessing such a comparison gives the symbol-error probability in terms of simple elementary integrals and immediately evidences the influence on system behavior of the number of resolved paths, bandwidth occupancy of the signal- and power-delay profiles with a remarkably moderate computational effort.

2004 - Congestion Control in Wireless Environments: Experimental Assessments and Simulation [Relazione in Atti di Convegno]
Casoni, Maurizio; Merani, Maria Luisa
abstract

This work investigates the TCP-friendliness of a particular congestion control mechanism, the TCP friendly rate control protocol (TFRC), when it is employed to regulate the transmission rate of nonTCP sources competing for bandwidth with different TCP flows (Reno, Sack and Westwood) in an IEEE 802.11b wireless LAN. Throughput of simultaneously active TFRC and TCP flows have been both experimentally measured and investigated through simulation, revealing that the wireless indoor radio channel plays a significant role on such parameter. Moreover, some useful insights have been derived on the behavior of TFRC and its degree of friendliness in an environment featuring a low degree of statistical multiplexing, such as the wireless context examined.

2004 - Generation of Multiple Rayleigh Fading Sequences with Specified Cross-Correlations [Articolo su rivista]
N. C., Beaulieu; Merani, Maria Luisa
abstract

A recent technique for generating two spatially correlated Rayleigh fading envelope sequences is generalized to give an efficient method for the generation of multiple correlated Rayleigh fading sequences. By coloring the quadrature components of the Rayleigh sequences, any desired envelope correlations can be realized for an arbitrary number of diversity branches. The computational complexity of the new method is compared to the computational complexity of a direct method. It is shown that properly utilizing the underlying block Toeplitz structure of the correlation matrix gives computational savings over the direct method.

2004 - Impact of assembly algorithms on end-to-end performance in Optical Burst Switched networks with different QoS classes [Relazione in Atti di Convegno]
Casoni, M.; Luppi, E.; Merani, M. L.
abstract

This paper investigates the performance of a complete OBS (Optical Burst Switched) network that implements the JET (Just Enough Time) reservation mechanism. The network under examination adopts a core node architecture with no fiber delay lines and a limited set of wavelength converters, while featuring an edge node architecture with a mix of input, output and shared buffers. We investigate the overall network performance and design, specifically focusing on burst delay and end-to-end TCP throughput. In order to study the OBS network behavior, we develop a modular and flexible simulation tool, that we call MOBSSIM (Modular OBS Simulator). MOBSSIM is the means to accurately build an arbitrary topology OBS network via its main functional blocks, edge and core routers: its sound degree of development enables us to accurately evaluate several figures of merit, e.g., burst blocking probability and delay, and also allows for a critical comparison of alternative design solutions in terms of assembly algorithms, reservation strategies and QoS oriented routing.

2004 - Performance and TCP-fairness of TFRC in an 802.11g WLAN: Experiments and tuning [Relazione in Atti di Convegno]
M., Borri; Casoni, Maurizio; Merani, Maria Luisa
abstract

In this paper we discuss some experimental results obtained from a laboratory testing of TCP-friendly rate control (TFRC), when such control is employed in an IEEE 802.11g wireless local area network (WLAN). We show that, despite TFRC exhibiting a good responsive behavior and a considerable TCP-friendliness in a wired environment, occasionally it does not behave in the same manner in the wireless test-bed. We discuss the possible reasons of such unexpected behavior, and propose a tuning of some of its congestion indicators, as well as a simple enhancement of the control, in order to get rid of the undesirable effects we observed. In detail, our proposal consists of an additional mechanism for flow control, similar to the one TCP employs, of a more tightly computed no feedback timer, and of a parameter that rules the way TFRC backs-off when it detects a loss event. We pleasantly notice that our modifications and tuning result quite effective for two reasons: first, they completely succeed at eliminating the aggressive behavior sometimes exhibited by TFRC; second, they do not affect the good performance, nor the TCP-friendly behavior of TFRC in those circumstances where the native control already performs satisfyingly.

2004 - Performance and TCP-friendliness of the SQRT congestion control protocol in lossy environments [Articolo su rivista]
M., Borri; Merani, Maria Luisa
abstract

In this letter, an accurate analytic model to predict the send rate of the SQRT binomial congestion control protocol is derived, under the assumption that the protocol operates in an environment where the packet loss rate is relatively high. Based on this model, a study of its TCP-friendliness is performed, remarking the nonnegligible effects on fairness that different queue managements have.

2004 - Rake reception with unequal power path signals [Articolo su rivista]
R., Maffei; U., Manzoli; Merani, Maria Luisa
abstract

This letter analytically determines the effects of selective diversity on the performance of a Rake receiver in dense multi-path channels featuring an arbitrary power delay profile. The approach devised permits assessing the symbol-error probability of the Rake receiver with simple computations, and determining the influence on system behavior of different power delay profiles and number of resolved paths, as well as signal bandwidth.

2003 - Alternative DS-CDMA Architectures for Voice/Data Applications with Best Base Station Assignment [Articolo su rivista]
M., Malavasi; Merani, Maria Luisa
abstract

This paper analyzes the uplink behavior of the multicode and variable spreading factor DS-CDMA systems that accommodate users with different transmission rate requirements in a multicell mobile radio system. It takes into account the possibility of a portable to choose the least interfered among N c nearest base stations, imperfect power control on slow signal fluctuations resulting from shadowing and random location of the users. System capacity is determined analytically, employing two distinct approximations featuring low computational costs, and by simulation. It is shown that having the portable controlled by the least interfered base produces a remarkable improvement on the performance of both classes of users and that either architecture (multicode or variable spreading factor) can favor voice or data applications through a suitable tuning of system parameters. Moreover, the simulation approach allows to assess the accuracy of the analytical approximations for an interesting range of system parameters.

2003 - Performance of a 3rd Generation Radio Link Control Protocol on a Multicarrier DS-CDMA System [Relazione in Atti di Convegno]
Manzoli, U.; Merani, M. L.
abstract

This work investigates the behavior of a 3 rd Generation Radio Link Control Protocol on the forward link of a Multicarrier DS-CDMA architecture that employs Walsh and Quasi-Orthogonal channelization codes. Protocol performance is analytically assessed, determining the average delay suffered by a data unit transferred over the radio channel. For alternative allocation policies of Walsh and Quasi-Orthogonal codes, the effects on throughput of different transmission qualities and size of protocol data units are evaluated. system design.

2003 - Service Differentiation in Optical Burst Switching: Performance Evaluation under LRD Traffic [Relazione in Atti di Convegno]
Casoni, Maurizio; Merani, Maria Luisa
abstract

This work proposes a method for service differentiation in optical burst switching (OBS) nodes adopting theJust Enough Time, JET, reservation mechanism. It consists of optimizing the number of wavelength convertersemployed in the node and proper setting of the extra-offset time intervals to satisfy different levels of qualityof service (QoS). The ON/OFF model with exponentially distributed OFF periods, both exponentially andheavy-tailed distributed ON periods is adopted to assess the node performance under different traffic patterns.The OBS node investigated in this paper is equipped with M £M optical interfaces with N wavelengths eachat 2:5 Gbits/s. We suppose that wavelength converters are available and that the system is bufferless, i.e., nofiber delay lines are available. One way to reduce the blocking of higher priority users is to grant them a longerextra-offset time. Another way to provide higher priority users with better performance is to allow them onlyto employ wavelength converters. Low priority incoming bursts can be retransmitted on the output link on thesame wavelength only.

2002 - Admission control in T/CDMA systems supporting voice and data applications [Articolo su rivista]
Casoni, Maurizio; Immovilli, Gianni; Merani, Maria Luisa
abstract

This paper analyses the behavior of two hybrid time-code division multiple-access (T/CDMA) architectures on the up-link of a macrocellular mobile radio system. For the examined schemes two categories of users-voice and data-share the domain of available resources, made up of time slots and codewords, through two. alternative assignment strategies. Both solutions attribute voice users one single resource pair, i.e., one time slot and a single code to employ on that time slot, but differ in the way data users requests. are accommodated: they are either simultaneously granted several codes over the same time slot or are assigned a single code over several distinct time slots. Call admission control is performed by a channel assignment algorithm which dynamically attributes resources only if specified levels of transmission quality are met on the radio channels. The blocking and the outage probability of the two classes of users are determined and compared, showing that one of the proposed schemes exhibits better performance and allows to satisfyingly serve a significant percentage of data users.

2002 - Efficient algorithms for the assignment of OVSF codes in wideband CDMA [Relazione in Atti di Convegno]
Dell’Amico, M.; Merani, M. L.; Maffioli, F.
abstract

This paper proposes some novel techniques to accommodate users with different transmission rate requirements in a CDMA system which employs orthogonal variable spreading factor codes. Several static and dynamic code assignment strategies are put forth and their behavior investigated, in terms of call blocking probability and number of required call reassignments. Their efficiency in dealing with various traffic loads is demonstrated, quantitatively showing the superior performance of our dynamic scheme with respect to a so-called "optimal" code assignment strategy recently presented in the literature.

2002 - Impact of fast fading compensations on mobile radio system performance [Articolo su rivista]
C., Caini; Merani, Maria Luisa
abstract

This paper explores what benefits can result from the compensation of both log-normal shadowing and Rayleigh/Rice-fading fluctuations in a mobile radio environment. The focus is on those power-control policies that exclusively make use of local power-level measurements in order to improve the performance, measured in terms of signal-to-cochannel interference ratio, of time-division multiple-access cellular radio systems; the aim is in fact to demonstrate under what circumstances the power compensation can be advantageously exploited. The corresponding analysis accounts for the errors due to the delay constraints that time-division and transmission techniques such as interleaving inevitably force onto the control loops. The numerical results quantitatively outline the maximum benefits on system performance that derive from the introduction of fast fading compensation for the class of power-control policies investigated in this paper. The remarkable influence of delay errors on the effectiveness of the fast fading control procedures are clearly revealed.

2002 - MPlS vs LOBS in an Optical Burst Switching Node: Impact ofLong-Range Dependent Traffic on Multiclass Services [Relazione in Atti di Convegno]
A., Brandani; Casoni, Maurizio; Merani, Maria Luisa
abstract

This work investigates the behavior of a reservation mechanismknown as JET, Just Enough Time, highly promisingin WDM networks adopting the optical burst switching(OBS) paradigm. In this article we assess the performance,in terms of burst blocking probability, that an optical crossconnectachieves when employing JET in conjunction withthe MultiProtocol Lambda Switching in the control planeon top of the optical layer, and compare it with the LabeledOptical Burst Switching, LOBS, solution. The burstblocking probabilities of three service classes with differentQoS requirements are determined, demonstrating thatthe LOBS alternative guarantees a remarkable improvementwith respect to the MultiProtocol Lambda Switching- OBS combination.

2002 - Multicarrier DS-CDMA performance with different assignment strategies of quasi-orthogonal codes [Relazione in Atti di Convegno]
Manzoli, U.; Merani, M. L.
abstract

Alternative code assignment policies for the forward link of a multicarrier DS-CDMA system employing the recently proposed quasi-orthogonal sequences are put forth in this paper. It is demonstrated how different allocation strategies of quasi-orthogonal codes alter the interference level suffered by active units; it is also shown how to shape the rate of interference growth as a function of the number of active users within the reference cell, by implementing some specific code allocation patterns. The performance, in terms of average bit error probability, achieved by various schemes is assessed in a frequency selective fading environment, and the advantages of different solutions highlighted. ©2002 IEEE.

2002 - On the assignment of Walsh and quasi-orthogonal codes in a multicarrier DS-CDMA system with multiple classes of users [Relazione in Atti di Convegno]
Amadei, M.; Manzoli, U.; Merani, M. L.
abstract

Several code allocation policies, suitable for the forward link of a Multicarrier DS-CDMA mobile radio system that employs Walsh and quasi-orthogonal sequences, were presented. Their effect on system performance was evaluated in the presence of a single class of users. The performance achieved by two classes of subscribers was assessed in a frequency selective fading environment.

2002 - Performance trade-offs of different rake receivers [Relazione in Atti di Convegno]
Maffei, R.; Manzoli, U.; Merani, M. L.
abstract

In this paper we determine the effects of different diversity schemes on the behavior of a direct-sequence spread spectrum Rake receiver which operates with random spreading sequences, in a multipath channel with arbitrary power delay profile. Two different receiver architectures, the former employing the L instantaneously strongest paths out of the Nr resolved ones, and the latter simply the L first paths out of the received Nr, are confronted in terms of symbol error probability, when an M-level PSK system is assumed. The analytical approach devised for assessing such comparison gives the symbol error probability in terms of simple elementary integrals, and immediately evidences the influence on system behavior of the number of resolved paths, bandwidth occupancy of the signal and power delay profile, with a remarkably moderate computational effort.

2002 - Supporting Multirate Services in a TDD-TD/CDMA Architecture [Relazione in Atti di Convegno]
Casoni, Maurizio; Merani, Maria Luisa
abstract

In this study we determine the Erlang capacityof a TDD-TD/CDMA architecture providing multirateservices to different classes of subscribers. The qualityof service perceived by speech and data users is assessedand some design criteria are evidenced, with referenceto both traffic and transmission parameters.

2001 - DCA Schemes For Differentiated Qos In Microcells [Relazione in Atti di Convegno]
Casoni, Maurizio; Merani, Maria Luisa
abstract

This paper investigates in a microcellularset-up the behavior of a new class of dynamic channelallocation policies, tailored to provide different QoS degreesto distinct user classes of a wireless system. Theperformance achieved by a network employing theseschemes is evaluated in terms of call blocking, taking intoaccount the requirements raised by multi-rate applications.Some design criteria effective to optimize the managementof the scarce radio resources are furnished andthe goal of providing radio users with both low and highspeed connections, suitable for a basic set of audio andvideo applications, is achieved.

2001 - Erlang Capacity of a TDD-TD/CDMA Architecture Supporting Heterogeneous Traffic [Relazione in Atti di Convegno]
Casoni, Maurizio; Merani, Maria Luisa
abstract

In this paper we study the performance ofa TDD-TD/CDMA architecture with two classes of subscribers,voice and data, when an interference-driven admissioncontrol policy is adopted. The blocking and theoutage probability of the system users are evaluated undervarious traffic conditions for several uplink/downlinkconfigurations of the time slots, demonstrating that thetime division full duplex approach needs a careful tuningin order to maximize system capacity.

2001 - Erlang capacity of a TDD-TD/CDMA architecture supporting heterogeneous traffic [Articolo su rivista]
Casoni, Maurizio; Merani, Maria Luisa
abstract

This letter determines the capacity of a TDD-TD/CDMA architecture which supports different classes of subscribers and adopts an interference-driven admission control policy. The blocking probability of the system users are evaluated under various traffic conditions for several uplink/downlink configurations of the time slots, demonstrating that the time division full duplex approach needs a careful tuning in order to maximize system capacity.

2001 - Integrating voice and data applications in T/CDMA architectures [Articolo su rivista]
Casoni, Maurizio; Immovilli, Gianni; Merani, Maria Luisa
abstract

This letter analyzes the behavior of two time-code division architectures serving voice and data applications on the uplink of a cellular system. Both solutions attribute speech users one code over a timeslot, whereas data users are granted several codes over the same timeslot or a single code over several time slots. Call admission control dynamically attributes resources if specified levels of transmission quality are met. The blocking probability of the two classes of users is determined, demonstrating that the multicode T/CDMA approach performs better than the multislot solution and than a pure CDMA system.

2001 - On the Performance of TDD-TD/CDMA Architectures with Heterogeneous Traffic [Relazione in Atti di Convegno]
Casoni, Maurizio; Merani, Maria Luisa
abstract

This paper determines the capacity of a TDD- TD/CDMA architecture which supportsdifferent classes of subscribers and adopts an interference-drivenadmission control policy.The blocking and the outage probability of the system users areevaluated under various traffic conditionsfor several uplink/downlink configurations of the timeslots, demonstrating that the time division full duplex approach needs a careful tuningin order to maximize system capacity.Our work further shows that even when data traffic plays the predominant role,the TDD system can satisfyingly cope with remarkable traffic loads and support severalErlangs of traffic per cell.

2001 - Performance Evaluation of an Interference based admission control schemein T/CDMA systems with voice and dat users [Relazione in Atti di Convegno]
Casoni, Maurizio; Immovilli, Gianni; Merani, Maria Luisa
abstract

This paper analizes the behaviour of two-time code division architectures serving voice and data users on the uplink of a cellular system.

2001 - Performance evaluation of an interference based admission control scheme in T/CDMA systems with voice and data users [Relazione in Atti di Convegno]
Casoni, M.; Immovilli, G.; Merani, M. L.
abstract

This paper analyzes the behavior of two time-code division architectures serving voice and data applications on the uplink of a cellular system. Both solutions attribute speech users one code over a time slot, whereas data users are granted several codes over the same time slot or a single code over several time slots. Call admission control is performed by a channel assignment algorithm which dynamically attributes resources if specified levels of transmission quality are met. The blocking probability of the two classes of users is determined, and it is demonstrated that the multicode T/CDMA approach performs better than the multislot solution and than a pure CDMA system.

2001 - Voice and data services in multicode and variable spreading factor DS-CDMA systems [Relazione in Atti di Convegno]
Malavasi, S.; Merani, M. L.
abstract

This paper analyzes the uplink capacity of multicode and variable spreading factor DS-CDMA cellular systems which accommodate users with different transmission rate requirements. It takes into account imperfect power control on slow signal fluctuations due to shadowing, the presence of Rayleigh fading and a random location of the users. The circumstance where the portable transmits to the nearest base station is examined; when shadowing only is present, the possibility that the user chooses the least interfered among Nc nearest base stations is also considered. System capacity is determined analytically, employing two distinct approximations featuring low computational costs, as well as by simulation. The latter approach allows to compare the accuracy of the analytical approximations for a wide range of system parameters.

2000 - Channel Allocation Schemes Providing QoS in Wireless Networks [Relazione in Atti di Convegno]
Casoni, Maurizio; Immovilli, Gianni; Merani, Maria Luisa
abstract

In this paper we propose a new class of interference adaptive dynamic channel allocation policies, tailored to provide different QoS degrees in a cellular mobile radio system. The performance achieved by a wireless network employing these schemes is evaluated in terms of call blocking probability, in a multirate application scenario featuring heterogeneous traffic. Some useful design criteria to optimize the management of the scarse radio resources are also furnished: the ultimate goal is to provide radio users with high speed connections, suitable for a basic set of audio and video applications.

2000 - Efficient simulation of correlated diversity channels [Relazione in Atti di Convegno]
Beaulieu, N. C.; Merani, M. L.
abstract

A recent technique for generating two spatially correlated Rayleigh fading envelope sequences is generalized to give an efficient method for generating multiple cross-correlated Rayleigh fading sequences. Any desired cross-correlations can be realized for an arbitrary number of diversity branches. The computational complexity of the new method is compared to the computational complexity of a direct method. It is shown that properly utilizing the underlying block Toeplitz structure of the correlation matrix can give computational savings of several orders of magnitude.

1999 - Performance Analysis of Channel Allocation Schemes for Wireless Communications [Relazione in Atti di Convegno]
Casoni, Maurizio; M., Garuti; Immovilli, Gianni; Merani, Maria Luisa
abstract

This paper evaluates the performance of different networkinfrastructures for the support of multimedia services in a cellularmobile radio system. The performance of twodifferent channel allocation policies in terms of call blocking,outage probability and throughput are investigated for differentclasses of service that system users may require.A specific type of interference adaptive dynamic channel allocationscheme is here proposed and evaluated as possible solution foroptimizing the management of the scarce radio resources. The goal isto provide users with high speed connections, suitable for a basic setof audio and video applications.

1998 - A Wireless ATM LAN with an 802.11-like Data Link Layer [Relazione in Atti di Convegno]
F., Callegati; Casoni, Maurizio; Merani, Maria Luisa; C., Raffaelli
abstract

In this paper a semi-analytical procedure isemployed to evaluate the performance of a wireless ATMlocal area network based on the IEEE 802.11 MAC protocol,taking into account the effects of propagation over a real radiochannel. Numerical results are presented as a function of theMAC frame length and of the signal-to-noise ratio in order toevaluate network performance and to provide guidelines forthe overall system design.

1998 - Performance evaluation of a DS Spread Spectrum system over a 60 GHz multipath channel [Relazione in Atti di Convegno]
Caini, C.; Merani, M. L.; Coralli A., Vanelli
abstract

This work aims at evaluating the performance of a Direct Sequence Spread-Spectrum (DS-SS) system over a 60 GHz real indoor channel characterized by the presence of severe multipath. The channel has been described by 1680 impulse response data calculated by means of a 3-D ray-tracing program. Both multipath components with delays shorter and longer than the chip time have been examined, and a special emphasis has been placed onto the study of the multipath effects on the DLL tracking circuit. The obtained results show the spatial distribution of the effective received energy per bit at the data demodulator input and provide some useful indications about the design criteria for an indoor wireless wideband local area network at EHF.

1997 - A Simplified Approach to the Performance Evaluation of FDMA/CDMA Systems [Articolo su rivista]
Merani, Maria Luisa; Shahin, M. K.; Immovilli, Gianni
abstract

This work shows it is possible to apply for the performance evaluation of FDMA-CDMA cellular mobile systems a simple analytical approximated method, previously successfully proposed by two of the authors with reference to FDMA-TDMA systems. The distinctive feature of the methodology we describe is that it allows for an immediate determination of both the indexes traditionally employed to define system performance, i.e., average bit error probability and outage probability at a very low computational cost. The hypothesis required to apply the proposed approximation is that the examined spread spectrum system be characterized by a bandwidth occupancy lower than the coherence bandwidth of the transmission channel. This could be the case of a wireless DS-CDMA system envisioned to provide voice service and exploiting a processing gain of the order of a hundred. We apply our methodology to determine the performance improvements introduced increasing the protection of the transmitted information through error correcting codes and interleaving, in different operating conditions as regards the functioning of the power control loops. A comparison is also satisfyingly carried out with some other approximated analytical methods found in literature. We strongly point out that the corresponding results are achieved at a much more modest computational cost than in traditional approaches.

1996 - Design Trade-Offs in a DS-CDMA Wireless LAN with Different Priority Traffic Streams [Relazione in Atti di Convegno]
Immovilli, Gianni; Merani, Maria Luisa; M. K., Shahin
abstract

In this paper we haved faced the issue of tying the transmission design of a wireless CDMA LAN, envisioned to serve two classes of users with different priority requirements, to traffic constraints. The performance indexes we have considered to define the transmission quality experienced by network users are the average bit error probability and the outage probability.The behavior of both merit figures as a function of the coefficient of utilization of the queueing scheme modeling the system strongly evidences the trade-off between good transmission performance/high utilization of the available network resources.

1996 - PRIORITY TRAFFIC IN WIRELESS PCS SYSTEMS: TRANSMISSION AND TRAFFIC PARAMETERS TRADE-OFF, [Relazione in Atti di Convegno]
Immovilli, Gianni; Merani, Maria Luisa
abstract

We have investigated a possible technique for efficiently handling the reverse link (mobile-to-base) traffic inside a cell of a wireless PCS system, assigning different priority classes to new calls and hand-offs. For the corresponding queueing scheme we have determined those traffic quantities which more directly interact with the design of the transmission system. Further, we have targeted the issue of tying the engineering of both CDMA and TDMA systems to traffic constraints. To this regard we have quantitatively demonstrated how deeply and differently the traffic parameters of the examined queueing scheme influence the capacity determination for these two systems

1995 - NETWORK AND SINGLE USER PERFORMANCE EVALUATION OF A MOBILE DATA SYSTEM OVER FLAT FADING TRANSMISSION CHANNELS [Articolo su rivista]
Castoldi, P.; Immovilli, Gianni; Merani, Maria Luisa
abstract

In this paper the constrasting effects of transmission impairments and capture on both the network and single user performance of a slotted Aloha system are investigated in a mobile radio environment, accounting for frequency non-selective random propagation phenomena, and employing the packet error probability in order to define packet losses and capture. With this study we demonstrate that it is possible to generalize in a real propagation context a method previously proposed in literature for evaluating the network behavior in terms of steady-state throughput, backlog and stability in conventional transmission conditions, i.e., when all the transmission channels were error free and the collisions caused the loss of all the packets involved.

1994 - OUTAGE PROBABILITY IN FDMA/TDMA MOBILE COMMUNICATION NETWORKS [Articolo su rivista]
C., Caini; Immovilli, Gianni; Merani, Maria Luisa
abstract

One of the most crucial problems to solve in the field of mobile communication networks is the evaluation for a generic link of the network of the outage probability due to the random characteristic of the transmission system, essentially determined by anomalous propagation conditions, cochannel interference and user mobility. The exact analytical solution to this problem is very burdensome, regardless to the system implementation technique considered. In this paper the effects of cochannel interference, nonselective fading and user mobility in FDMA/TDMA mobile radio networks are investigated, and an extremely simple approximated methodology is presented for the analytical evaluation of the outage probability and of the frequency reuse distance. It is worth noting that the proposed method allows to consider a general statistical description for the nonselective propagation media of the radio network. Here we successfully apply it the path loss, fading and shadowing scenario which are typical of cellular and microcellular structures.

1992 - A New Methodology for the Evaluation of Outage Probability in Cellular Systems [Relazione in Atti di Convegno]
Immovilli, Gianni; Merani, Maria Luisa
abstract

The effects od cochannel interference in cellular mobile radio networks are investigated, in order to highlight how to develop the analytical evaluation of the corresponding outage ptobability – and consequently of the frequency reuse distance – in extremely simplified manner. The methodology presented is in particolar applied when Rayleigh fading, lognormal shadowing and path losses larger than in free space are considered.It is however worth noting that this metodology can also be applied to other fading and shadowing scenarios, like microcells or satellite mobile communications, because it allows the consideration of general statistical conditions for the propagation media.

1992 - A comparison between outage probability evaluations in microcellular systems [Relazione in Atti di Convegno]
Merani, M. L.
abstract

The effects of cochannel interference in a UHF microcellular system operating in a Ricean/Rayleigh fading environment are investigated: the aim is to prove in the microcell domain the validity of a simplified analytical methodology, already successfully applied in traditional cellular structures, which allows to evaluate almost effortlessly the outage probability, i.e., the probability of failing to achieve a satisfying signalto-interference ratio. The results obtained confirm the validity of this new approach also in the microcell environment, for a wide range of the parameters involved in the system, fading and propagation model description.

1992 - OUTAGE PROBABILITY FOR CELLULAR MOBILE RADIO SYSTEMS: SIMPLIFIED ANALYTICAL EVALUATION AND SIMULATION RESULTS [Articolo su rivista]
C., Caini; Immovilli, Gianni; Merani, Maria Luisa
abstract

A simulation program has been carried out to further check the simplified method proposed by Immovilli and Merani for the analytical evaluation of outage probability in cellular mobile radio systems, due to cochannel interference and random propagation phenomena, nonselective in type. The results of the two different procedures show an excellent agreement.

1991 - Effect of the Transmission Impairments on the Peformance of Packet Radio Network [Articolo su rivista]
Immovilli, Gianni; Merani, Maria Luisa
abstract

Packet radio has recently gained great interest in the wider context of mobile communications. In this scenario, the signal worsening due to real transmission conditions (linear and non linear distorsion, fading, interferences, noise) deeply affect the network performance. It is then necessary to verfy whether it is feasible, and if so, how to dimension the transmission system supporting the network itself, in order to respect a fixed quality condition.In this work we suggest the introduction of a quality criterion which seems particularly suitable to set up a relationship between transmission and network parameters, and therefore to solve the problem previously submitted. We determine this relationship with reference to a star topology network, where the slotted Aloha protocolo is employed in cojunction with a narrow band modulation scheme; independent, non-selective and slowly varying fading conditions on every link of the network are also assumed. The treatment developed is then applied to a significant example of packet radio network, and many numerical results are reported.

1991 - Outage probability in packet radio networks due to cochannel interferences and Rayleigh fading [Relazione in Atti di Convegno]
Immovilli, Gianni; Merani, Maria Luisa
abstract

The behavior of a packet radio network which makes use of the slotted Aloha protocol is investigated, focusing on the effects of the transmission impairments on its performance. A narrowband modulation scheme has been considered. Independent Rayleigh fading conditions and cochannel interferences on every link of the network have been accounted for. The methodology highlights the simplifications that can be introduced in evaluating the interference effects. The numerical results reported show that a good single user performance is by far a more critical target than a good network performance

1991 - Simplified Evaluation of Outage Probability for Cellular Mobile Radio Systems [Articolo su rivista]
Immovilli, Gianni; Merani, Maria Luisa
abstract

The effects of cochannel interference in a mobile radio network are investigated, to highlight a method with which to analytically evaluate the corresponding outage probability in an extremely simplified manner. The general methodology presented can in particolar be applied when Rayleigh fading, log-normal shadowing and path losses larger than those in free space are considered.

1989 - Combined Effects of Transmitter Nonlinearity and Multipath Fading on the Availability of CPFSK Systems [Articolo su rivista]
G., Corazza; Immovilli, Gianni; Merani, Maria Luisa
abstract

A study is presented whose aim is to evaluate the behaviour of CPFSK systems with modulation pulse shaping and limiter-discriminator detection in the presence of multipath fading and nonlinearity in the transmitter. This work, which completes a previous one where nonlinearities are absent, confirms the possibility to effectively control the lower bound of the system outage probability Pout (i.e. the asymptotic value of Pout when the transmitted power tends to infinity) by varying the maximum frequency deviation of the signal

Università degli studi di Modena e Reggio Emilia

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