In the context of 5G, 3GPP introduced New Radio vehicle to everything (NR-V2X) for direct vehicle-to-vehicle communication. However, starting from Release 18 the focus of the standard has been expanded from vehicles to any device and use case that can benefit from direct communication. In 3GPP terminology, the standard is now referred to simply as Sidelink communication. This standard allows direct communication between devices based on synchronous resource scheduling. Users can rely on controlled scheduling when in network coverage or, in the absence of coverage, autonomously select resources for transmission via a distributed resource allocation mechanism. Focusing on the autonomous resource allocation, this paper in-vestigates the possibility of applying Release 18 Sidelink communication to Air-to-Air (A2A) links between airborne entities. The paper outlines the main challenges and required modifications to adapt the current standard for longer links in the order of kilometres. The analysis identifies the propagation delay as a critical limitation. Communications at distances over 42.4 km require a restriction of the user's transmitting opportunities. However, sidelink communication remains feasible for distances below this threshold without modifications to the standard.

The deployment of cooperative-intelligent transport systems (C-ITS) has started, and standardization and research activities are moving forward to improve road safety and vehicular efficiency. An aspect that is still felt as a limitation by the research groups active in the field, is the difficulty to validate the solutions with real hardware and software, because of the huge investments that are needed when multiple equipped vehicles need to be considered. In this work, we present a platform with low-cost hardware based on a Raspberry Pi and a Wi-Fi module transmitting at 5.9 GHz, and on the open-source software Open Stack for Car (OScar), which is compliant with the ETSI C-ITS standards. With a limited cost in the order of 200 €, the platform realizes a device which is standard compliant and can be used as either on-board unit (OBU) or road side unit (RSU). The limited cost makes the testbed scalable to several units with limited budget and the limited size makes it also deployable on mini-cars to test advanced connected and autonomous vehicle (CAV) networks and applications. Our tests demonstrate its interoperability with other devices, compliance in terms of power spectrum, and a range of a few hundred meters in line-of-sight (LOS) conditions using the standard settings of ITS-G5.

Infrastructure-assisted automated driving will highly rely on real-time updates received from the network about the surroundings, which demand for ultra-low latency, high-throughput and highly reliable wireless connectivity. In the future, the quality of connectivity will directly impact the driving capability of these autonomous vehicles: lower downlink quality will in fact reduce the situational awareness, forcing the vehicle to, for example, reduce speed and increase safety distance. In this context, we propose a solution which allows a vehicle to choose the route that ensures the best connectivity conditions to reach its destination. Specifically, we consider that different connected and automated driving (CAD) Modes are possible depending on the estimated downlink radio quality, and the route is selected accordingly. Experiments have been conducted through simulations in an urban environment, utilizing the SUMO mobility simulator and the Sionna RT channel modelling tool. The obtained results demonstrate that the network quality can indeed significantly influence route selection, paving the way for future research towards sixth generation (6G) where services and mobility predictions can drive network optimizations.

In the context of fully distributed systems, we consider a scenario densely populated with wireless nodes which are equipped with simultaneous wireless information and power transfer (SWIPT) capabilities and can act as relays between a source and a destination. In this scenario, the probability of finding a node able to provide a useful contribution to the quality of the link tends to be high and can be exploited adopting a suitable relay selection scheme. Assuming nodes distributed following a Poisson point process and communicating only with source and destination to ensure the scalability of the system, we consider two well-known relay selection schemes, which are typically used as performance benchmarks, and derive an analytical framework to investigate the performance of the source-destination link in terms of outage probability. In our analysis we include, through the use of a simple but effective model, the non-linear effects of the energy harvesting circuitry of the devices and introduce a simple signaling mechanism between source, SWIPT nodes and destination to identify the most suitable relay among the various SWIPT devices. The impact of multiple access during the phase of relay selection is also modeled and investigated.

In the fifth generation (5G) Vehicle-to-Everything (V2X) autonomous mode, vehicles may select radio resources for their packet transmissions without the support of the base station (BS). For periodic traffic, the same resources can be accessed at consecutive reservation intervals to improve the selection procedure. However, potential collisions occurring during this period may remain undetected and persist over time. Previous studies introduced algorithms leveraging in-band full-duplex (FD) transceivers to detect and react to collisions by performing resource reselection. However, as demonstrated in this paper, in more realistic scenarios where part of the data traffic is not periodic, performing reselections after collisions, regardless of the traffic type, may not be effective and could even be counterproductive. To address this issue, this work introduces two novel alternative schemes, each with its own advantages and drawbacks, both based on FD transceivers. Simulation results demonstrate that both solutions effectively handle scenarios with mixed traffic. Without penalising the aperiodic traffic, the range of periodic traffic is improved by up to 38% over the legacy Mode 2 under heavy traffic conditions.

The Third Generation Partnership Project (3GPP) recently introduced the fifth-generation (5G) new radio (NR) sidelink to enable vehicle-to-everything (V2X) communications supporting advanced safety services. Nevertheless, improvements over the previous generation still pose challenges to meet the reliability and latency requirements of V2X communications, particularly in the allocation of distributed resources, i.e., Mode 2. In Mode 2, vehicles autonomously select radio resources for their message transmissions and can maintain the selected resources for a given reservation period to efficiently handle periodic data traffic. However, potential collisions during this period may remain undetected due to half-duplex communications and unacknowledged broadcast transmissions, resulting in persistent message losses and posing a threat to road safety. This paper aims to improve the 5G NR-V2X sidelink for systems beyond 5G-Advanced by exploiting full-duplex transceivers. We propose a novel medium access control (MAC) scheme where vehicles can detect collisions while transmitting, dynamically adapt the collision detection threshold according to the measured channel load, and react to detected collisions through appropriate resource reselection and retransmission procedures. Extensive simulations conducted under various settings show that this MAC scheme brings substantial performance gains in terms of reliability and latency, compared to the current legacy Mode 2 procedure and a benchmark full-duplex scheme from the literature.

Applications envisioned to enable connected and autonomous vehicles entail the exchange of data through reliable and low-latency direct communications between vehicles. The current specifications for the cellular-vehicle-to-everything (C-V2X) technology can still barely match such requirements. To tackle this issue, we investigate here the joint application to the C-V2X sidelink with autonomous resource allocation of two techniques that are being considered for the evolution of cellular systems, i.e., in-band full-duplex (FD) and non-orthogonal multiple access (NOMA). In particular, we consider FD capabilities to detect ongoing collisions while transmitting and thus resolve persistent resource allocations, which are causing repeated errors at the neighboring receivers. Regarding NOMA, we consider the use of successive-interference cancellation (SIC) for the decoding of multiple signals when different vehicles are transmitting simultaneously using the same resources, thus converting packet losses into improved spectral efficiency. The investigation is based on the latest fifth generation (5G) New Radio (NR)-V2X specifications and focuses on broadcast transmissions, which are expected to cover the majority of the exchanged traffic in V2X contexts. As shown through simulations in large-scale scenarios, the two techniques, both relying on signal processing at the receiver to cancel the (self or successive) interference, provide complementary advantages under different conditions. FD is in fact very effective to improve the delivery performance at short distances when periodic data traffic is assumed, while SIC-based NOMA improves the reception probability at medium distances both under periodic and aperiodic data traffic conditions.

Efforts are underway to finalize the fifth generation (5G) vehicle-to-everything (V2X) communication technology. Direct communication among vehicles over the sidelink interface through the autonomous selection of radio resources is among the main and more challenging capabilities of such a connectivity solution. Nonetheless the crucial enhancements conceived by the Third Generation Partnership Project (3GPP) in Release 16, the autonomous resource allocation (a.k. a. Mode 2) still suffers from collisions due to the wrong estimation of the resource occupancy status enforced by half-duplex (HD) transceivers. In this paper, we argue in favour of the usage in vehicles of in-band full-duplex (FD) transceivers, gaining momentum in the research towards sixth generation (6G) systems thanks to their simultaneous transmission and reception capability. Exploiting FD, we propose to enhance the autonomous mode by detecting collisions and triggering resource reselection procedures in a more conscious manner. Simulation results show that the conceived proposal allows sidelink V2X to achieve significant improvements in terms of reliability and timeliness when compared against the legacy Mode 2.

On the path towards fully connected and automated vehicles, two sets of technologies are under consideration for enabling short-range vehicle-to-everything (V2X) communications within the intelligent transport system (ITS) band around 5.9 GHz. The first group of technologies includes IEEE 802.11p plus its upcoming evolution IEEE 802.11bd. The second group includes the 3rd generation partnership project (3GPP)-defined sidelink cellular-V2X (C-V2X) standards. However, the coexistence of these technologies and the resulting interference pose new challenges for guaranteeing reliable operation in emerging vehicular networks. In this work, we investigate the impact of the interference resulting from C-V2X transmission on the sensing procedure of IEEE 802.11p/bd. To this end, we develop a detection framework based on clear channel assessment (CCA) mechanism in the IEEE 802.//p/bd network under the assumption of Rayleigh distribution channel fading; where we employed stochastic geometry and the characteristic function approach. It is shown through analytical evaluations that a lower threshold than the one defined in the specifications could better cope with the received interference without sensibly increasing the impact of false alarms.

Connectivity and automation are increasingly getting importance in the automotive industry, which is observing a radical change from vehicles driven by humans to fully automated and remotely controlled ones. The test and validation of all the related devices and applications is thus becoming a crucial aspect; this is raising the interest on hardware-in-the-loop (HiL) platforms which reduce the need for complicated field trials, thus limiting the costs and delay added to the process. With reference to the test and validation of vehicle-to-everything (V2X) communications aspects, and assuming either sidelink LTE/5G-V2X or IEEE 802.11p/bd technologies, in this work we focus on the real-time HiL simulation of the information exchanged by one vehicle under test and the surrounding, simulated, objects. Such exchange must be reproduced in a time-efficient manner, with elaborations done fast enough to allow testing the applications in real-time. More precisely, we discuss the simulation of non-ideal positioning and channel propagation taking into account current impairments. We also provide details on optimization solutions that allowed us to trade-off minor loss in accuracy with a significant reduction of the computation time burden, reaching up to more than one order of magnitude speed increase in our experiments.

Vehicle-to-everything (V2X) connectivity is deemed crucial to enable upcoming cooperative automated driving applications. The Cellular-V2X (C-V2X) technology supports direct interactions among vehicles over the sidelink interface. According to the autonomous mode, vehicles select sidelink radio resources for their message transmissions in a completely distributed manner, without the support of the base station. The majority of works focused so far on periodic message transmissions, for which sidelink resources can be semi-persistently reserved after a channel sensing procedure. In this paper, we take a step forward by considering both periodic and high-priority aperiodic messages, such as sporadic decentralized environmental notification messages (DENMs), competing for the same resources. The impact of some new sidelink features devised in 5G-V2X (Release 16) for the autonomous mode, such as the new radio (NR) flexible numerology, the short-term sensing, the pre-emption mechanism, are preliminarily investigated in this paper. They are coupled with a newly proposed resource reservation scheme for the repetitions of DENMs. Results showcase the improvements of our proposal in terms of higher DENM reliability achieved with little-to-none additional signaling, with a negligible impact on periodically transmitted messages.

Current vehicular communication technologies were designed for a so-called phase 1, where cars needed to advise of their presence. Several projects, research activities and field tests have proved their effectiveness to this scope. But entering the phase 2, where awareness needs to be improved with non-connected objects and vulnerable road users, and even more with phases 3 and 4, where also coordination is foreseen, the spectrum scarcity becomes a critical issue. In this work, we provide an overview of various 5G and beyond solutions currently under investigation that will be needed to tackle the challenge. We first recall the undergoing activities at the access layer aimed to satisfy capacity and bandwidth demands. We then discuss the role that emerging networking paradigms can play to improve vehicular data dissemination, while preventing congestion and better exploiting resources. Finally, we give a look into edge computing and machine learning techniques that will be determinant to efficiently process and mine the massive amounts of sensor data.

Most of the applications envisaged for the forthcoming connected vehicles are based on the broadcasting by each vehicle of periodic messages describing its characteristics, state, and actions. Such messages are denoted as cooperative awareness messages (CAMs) in the ETSI standardization. From a communication perspective, the success of CAM delivery is thus a particularly important aspect to evaluate and the obvious method to address large scale scenarios consists in performing simulations. Normally, given that the relevance of the information is related to the distance between communicating vehicles, output metrics are restricted to a given range. However, no attention is typically posed on the relative positions and movements of the vehicles, which could be, for example, on parallel roads. In this work, we propose a novel method to identify and neglect those transmissions that are not really meaningful, based only on the position and direction of the vehicles. Particular emphasis is laid on the efficiency of the methodology for possible large-scale simulations. The described approach is evaluated in a complex urban scenario, where hundreds of vehicles are equipped with either LTE-V2V or IEEE 802.11p. Results show that, in the considered cases, even less than half of the transmissions could be meaningful and that neglecting those that are not relevant significantly impacts on the quality of the investigated application.

We investigate a dual-user scenario where sources transmit their messages to the destinations by means of relays in an amplify-and-forward two-hop mechanism. In this scenario, the presence of co- channel interference requires the design of a suitable relay selection algorithm to minimize outage events. To this aim, we present a relay selection algorithm specifically tailored for amplify-and-forward relaying. The performance of the relay selection mechanism is evaluated analytically, in terms of outage probability, under the assumption that relay nodes are distributed according to a homogeneous Poisson point process. Numerical results show that the proposed algorithm outperforms a conventional one, based only on the measurement of the power received from the desired transmitters.

On the path to zero fatalities on the roadways, all vehicles have to periodically broadcast cooperative awareness messages (CAMs) in a timely and reliable manner, even in areas of high traffic density. The carrier senses multiple access with collision avoidance (CSMA/CA) scheme of IEEE 802.11, the de-facto standard for vehicular communications, is known to offer no reliability to broadcast packets that cannot be acknowledged, and to poorly perform at high network load due to collisions and interference. In this paper, an enhanced CSMA/CA protocol is analyzed for vehicular networks, which improves the CAM timeliness and reliability by leveraging full-duplex (FD) transceivers on board. FD devices can listen to the channel while transmitting, thus making collision detection viable. A FD vehicle can detect a CAM collision while sending, promptly abort the packet and retransmit it later. Results achieved through an analytical model under mathematically tractable assumptions, and through extensive system-level simulations in a complex urban environment, show the effectiveness of the protocol to cope with direct collisions, especially in high traffic areas, paving the way towards the realization of cooperative automated driving.

Vehicle-to-everything (V2X) communications may radically change the transportation system allowing a real-time and highly reliable exchange of information, which can be processed by vehicles in the neighborhood or by the road-side infrastructure to enable safety, mobility and environmental applications. In this context, 3GPP-based cellular networks, and especially long term evolution (LTE), are offering progressively higher performance and enabling a wider set of operations. To this aim, vehicle-to-vehicle (V2V) has been recently added as a new feature to LTE, but the usage of radio resources still needs to be optimized and is subject of extensive research activities. In this work, we focus on autonomous V2V resource reselection schemes, which allow communications also in out-of-coverage areas, we propose MAP-RP, a reselection procedure based on the embedding of a map of resources, as detected by each receiving vehicle, in the broadcasted packet, and we compare it to two sensing-based benchmark algorithms found in the literature. Results are achieved through simulations performed on a realistic highway scenario and demonstrate that the proposed solution guarantees a lower update delay and allows to achieve up to 20% of improvement in terms of packet reception ratio, with respect to the best-performing benchmark algorithm.

Current wireless access technologies cannot satisfy all the requirements of future vehicular networks, and 5G could provide a solution to the actual limitations enabling super-fast, reliable, and low latency connections. The road to 5G vehicular networks can be considered opened by the Release 14 of Long Term Evolution (LTE), which enables vehicle-to-vehicle (V2V) communications also out of coverage of the eNodeB. This work firstly focuses on radio access of actual and next generation vehicular networks, by highlighting the main limitations and potentialities. Then, it focuses on beaconing for cooperative awareness and compares the performance of LTE when adopted in different fashions, from the actual legacy solution in vehicle-to-infrastructure (V2I) mode to future potential alternatives, such as LTE-V2V, LTE-V2V with short subframe and LTE-V2V with full duplex (FD) radios. Performance results are provided in terms of medium access efficiency and success probability of resource allocation, and show the potential advantages of future solutions, especially those provided by LTE-V2V with FD radios.

Resource allocation is a challenging issue in multiuser wireless systems. Since users are not all in the same conditions and do not achieve the same performance given the same amount of resources, resource allocation must typically deal with the following two conflicting objectives: on the one hand, the overall performance should be maximized, tending to prioritize few users in better conditions, and on the other hand, fairness among users should be maximized, consequently reducing the overall performance. Identifying the compromise that is somehow optimum is all but simple and this aspect is normally worsened by the absence of a curve describing how the maximum performance varies changing the accepted level of fairness. To cover this gap, in this paper, we propose a unified and general mathematical formulation of the optimal performance versus fairness tradeoff in multiuser wireless communication systems. Differently from the existing literature, our approach is based on the generalized Lagrange method and adopts general definitions for both performance and fairness. Besides the exact solving equations describing how the maximum performance varies with fairness, we also derive a simpler lower bound with reduced computational cost. Example results are provided for two case studies, respectively, concerning linear and logarithmic dependence of performance on resources.

In this paper, we consider a multi-user scenario where an arbitrary number of sources transmit their messages to the intended destinations by means of relays in a decode-and-forward two-hop mechanism. To minimize the interference generated in the scenario, two opportunistic relay selection mechanisms are proposed and investigated. The performance of the two selection mechanisms is analytically evaluated, in terms of outage probability and average achievable rate, under the assumption that relay nodes are distributed according to a Poisson point process. Asymptotical analysis is also presented for infinite node density. Numerical results show that the selection of the relays has a significant impact on the amount of interference generated and a suitable choice can improve the overall performance.

In a near future, vehicles will be equipped with wireless communications technologies to periodically broadcast information to their neighbors on their position and speed. The messages carrying such information, normally denoted as beacons, will reduce the probability of accidents and improve the safety of drivers and passengers. The main candidate technologies for this scope today are IEEE 802.11p and LTE-Advanced with device-to-device communications (LTE-D2D), which is now evolving into vehicle-to-vehicle communications features (LTE-V2V). The aim of this paper is thus to compare the performance in terms of scalability of these two technologies when used for beacon transmission. The comparison is made analytically, through the definition of common scenario and metrics.

We consider a multi-user scenario where sources transmit their messages to the destinations by means of a two-hop mechanism. To minimize the interference generated in the scenario, a simple opportunistic relay selection mechanism is investigated. The performance of the scenario is evaluated using some results of the stochastic geometry under the assumption that relay nodes are distributed according to a Poisson point process. Results show that, when the relay density is sufficiently high, a suitable choice of the relay leads to a limited amount of interference generated during source-relay and relay-destination transmissions.

Vehicular ad hoc networks (VANETs) drive new challenging research issues at different layers of the protocol pillar, from physical to application. Focusing on the medium access layer, one of the most promising and not yet fully explored option is the adoption of orthogonal frequency division multiple access (OFDMA). Besides guaranteeing high spectral efficiency and effective resource allocation, it relies at the physical layer on orthogonal frequency division multiplexing, which allows repetitions of the same signals to be opportunistically combined at the receiver even if they are not perfectly synchronized. Exploiting this property, here we suggest and discuss the use of OFDMA for alert message flooding in VANETs to increase reliability and resource usage efficiency. The achievable benefit and the potential drawback (in terms of high delivery delay) are here assessed through a simple yet realistic model that allows to compare, in highway scenarios, OFDMA with carrier sensing multiple access/collision avoidance, currently adopted by IEEE 802.11p for distributed communications in high mobility scenarios.

Optimal resource allocation is an outstanding issue in wireless communication systems. In this work we focus on the ever challenging optimization of the tradeoff between throughput and fairness. Specifically, we propose a novel framework to analytically derive the maximum average throughput versus fairness under the assumptions that the throughput of each user i) increases if more resources are allocated to him and ii) depends on how many resources and not which resources are allocated. We achieve a general formulation of the tradeoff optimization problem and we also derive and validate a closed form solution in those scenarios where throughput linearly depends on resources, which cover several realistic cases. Besides these valuable results, the framework also lays solid basis toward a more general solution.

Vehicular ad hoc networks (VANETs) based on IEEE 802.11p are moving new safety and traffic applications beyond the present limitations given by infrastructures. However, due to the high variability in time and position of nodes, the medium access control layer of IEEE 802.11p, which is based on carrier sensing multiple access with collision avoidance (CSMA/CA), could lead to severe performance degradation in terms of delivery delay and delivery ratio as the node density increases. Because of its higher efficiency, we propose the use of orthogonal frequency division multiple access (OFDMA) as access technique in VANETs, discussing and evaluating i) its feasibility, ii) the challenges posed by the distributed allocation of resources, and iii) its performance in terms of resource allocation efficiency (specifically, delivery rate and delivery delay) when compared to CSMA/CA. Results, obtained by means of simulations that jointly take into account realistic road maps, vehicular traffic, and the whole network architecture from the application down to the physical layer, show that OFDMA allows up to four times higher delivery rate and that it also guarantees lower delivery delay in heavy loaded network conditions.

When energy is harnessed by wireless nodes from renewable sources, its availability becomes uncertain and its use for communications must be carefully designed. While the optimal power allocation has been derived in previous works when energy availability is fully (a priori) known, practical algorithms are needed when only causal and statistical information is available. In this paper, we study the optimal transmission policy when only the statistical distribution of the energy arrival intervals is known and no information is available on the amount of energy that will be harnessed. We firstly obtain an exact solution for the case of a step-wise transmission power profile. This result is then extended to the time-continuous case. Within energy arrival intervals, the obtained power profile is shown to be non increasing as a function of time and non decreasing as a function of the residual energy. Numerical results are finally provided focusing on an exponentially distributed energy arrival process as a case study.

Routing strategies deeply affect the performance of wireless ad hoc networks, in terms of coverage, interference, and delay. In this work, we investigate the impact of different routing strategies on the overall amount of interference generated in a distributed ad hoc network with power control. To this end, we derive an analytical model for the evaluation of the performance in terms of mean value and variance of the interference when signal level power control is adopted and different routing strategies, based on long-hop and short-hop relay selections schemes, are considered. This model allows us to quantify the performance of the overall network in terms of interference, average number of hops and path efficiency. Numerical results have been also verified by simulations.

Considering vehicles as sensors for traffic and pollution information is a new paradigm to monitor the environment and to open the way to an efficient smart navigation. In this work we focus on the uplink acquisition of traffic information from vehicles toward a remote control center. With the increase in the number of vehicles equipped with on board units (OBUs) enabling cellular transmissions, this service is leading to higher loads for the cellular network itself and, consequently, to higher costs. In this paper we discuss the opportunity to take advantage of vehicle-to-vehicle (V2V) and vehicle-to-roadside communications in addition to vehicle-to-infrastructure cellular transmissions. The objective is twofold: to investigate the potential reduction of data transmitted over the cellular networks and to verify the potential transmission delay reduction, by sharing and aggregating information through V2V communications. Results are obtained through an integrated simulation platform jointly taking into account both realistic vehicular environments and wireless network communication aspects.

Real time information to vehicular users is proposing new challenging questions to which wireless systems designers are called to answer. Nowadays many vehicles are already equipped with devices able to connect to cellular networks, and to transmit and receive in real time traffic information through vehicle-to-infrastructure (V2I) communication. Focusing on the uplink transmission of real time measurements, this is leading to high costs in terms of network load and billing. In this work we discuss the opportunity to take advantage of vehicle-to-vehicle (V2V) in addition to V2I communications to reduce the amount of data to be transmitted from vehicles to a remote control center, and thus also to reduce the resulting costs for transmissions over the cellular networks. Having in mind to allow a first understanding of the achievable advantages, we propose a simple mathematical model through which we discuss how many vehicles are necessary to guarantee an useful V2V communication and which are the advantages in terms of network load and, consequently, costs reductions for the V2I network.

Nowadays, wireless systems allow us to have connectivity almost everywhere. Different radio access technologies are integrated in the same device and they can be used following the specific service requirements, the actual received signal levels, and the costs related to their use. Presently, technologies are always seen as alternatives, but it is envisioned that different wireless connections may be used cooperatively in order to enhance the throughput perceived by the end user. In this paper we discuss this opportunity trying to understand what would be the impact of a multi technology combining in a multi user scenario with no coordination among access networks.

Real time traffic information systems represent a growing sector of the wireless communication industries. To provide traffic information to drivers in a short term, cellular systems represent the answer: on the one hand many vehicles are equipped with global positioning system (GPS) navigators integrating cellular devices; on the other a large percentage of people has smart phones integrating advanced positioning systems. In this paper we aim at evaluating the feasibility of real time traffic information transmission to drivers by exploiting the universal mobile telecommunication system (UMTS) as the enabling technology. In particular, we compare the performance in the downlink of a urban scenario of the UMTS adopted in unicast and multicast mode, in terms of service feasibility and impact on the capacity left for other services. Results, performed through a simulation platform integrating a vehicular simulator tool together with a UMTS network simulator, will show which between unicast and multicast has to be preferred as a function of the considered environment.

In this paper we provide the outcomes of a measurement campaign aimed at characterizing the UMTS femtocell propagation in an indoor scenario. The accuracy of a commonly adopted estimator of the signal-to-noise ratio is discussed, then the minimum measurement interval needed to derive an accurate characterization of the average received power is discussed. Finally we compare the measurement outcomes with those predicted using ray tracing tools and analytical models, showing the achievable accuracy levels.

Future wireless access will involve a variety of integrated and interworking technologies. Depending on the conditions (e.g., the specific application, the quality of service requirements, the user mobility) each session will be served through the most suited access network; following some event, there will be a variation of the access technology, which is called vertical handover. Although the use of one technology at a time is mostly envisioned, the use of multiple wireless links at the same time, hereafter called parallel transmission, is also envisioned for higher throughput. On the basis of parallel transmission, in this paper the original definition of softer vertical handover is given and an algorithm for softer vertical handover in heterogeneous wireless access networks is proposed; the achievable improvement is shown in two reference scenarios.

The seamless integration of heterogeneous wireless access networks is currently one of the issues of major interest in the field of telecommunication systems. In an early future technologies like UMTS, WLAN and WiMAX will give broadband access to users that perform their voice/video calls or data sessions without knowledge of the specific technology their terminals are using, following the paradigm of always best connected. In this scenario, UMTS and WLAN integration has a primary role, due to the coverage of cellular systems and the low cost of the latter technology. This work, in particular, focuses on the gain in terms of capacity that the deployment of WLAN access points allows in an area fully covered by an UMTS network, assuming that the radio resources are not managed by complex multi radio resource management algorithms. For this scope a real scenario is accurately simulated and the end users perception is evaluated taking care of all aspects related to each level of the protocol stack, with particular attention to radio propagation.

Intelligent transportation systems (ITS) make use of wireless communication technologies to provide traffic efficiency and road safety without altering the existing road infrastructure. To really impact on traffic management, ITS should act in real-time, requiring updated traffic information; hence, the collection of small amounts of information frequently transmitted from a high number of vehicles is needed. Cellular systems represent the most suitable technological solution to achieve this service, since they do not require any further installation of network infrastructures. However, they were designed for different applications: voice, web browsing or e-mailing. In this paper we aim at discussing the feasibility of frequent acquisition of small amount of data from vehicles through the universal mobile telecommunication system (UMTS), and at investigating its impact on the services already provided by the network. Numerical results are obtained by means of simulations, paying particular attention to realistic scenarios, both in terms of wireless systems and users mobility.

Efficient mobility management is an issue of vast economic importance for its consequences on urban and suburban mobility. In this context, telecommunications are gaining a key role, allowing to increase people safety, traffic efficiency, and travel comfort. To investigate the telecommunication systems behavior in new infomobility scenarios, advanced simulations tools are needed jointly taking into account realistic road traffic mobility and telecommunication networks protocols in all their aspects. In this paper we discuss the architecture of a complex and complete simulation platform we are developing on the behalf of the Italian project PEGASUS: the choice of traffic simulators, the network simulation and their interface will be presented and described.

Communication networks beyond 3G will see the interconnection of heterogeneous radio access networks in order to always provide the best quality of service in the most efficient way to users with multi-mode terminals. This scenario poses a number of critical issues, which have to be faced in order to get the best from the integrated network. In this paper we investigate the issue of parallel transmission over multiple radio access networks: in particular we propose simple but effective radio resource management algorithms, whose performance is investigated by means of a simulative approach in UMTS-IEEE802.11a and IEEE802.16e-IEEE802.11a heterogeneous networks (adopted as case studies). An insight on TCP level critical aspects, strictly related to the parallel transmission over multiple access networks, is also provided.

IEEE 802.16 standard family enables the convergence of fixed and mobile broadband networks through a common wide area broadband access technology. With reference to the recent IEEE802.16e-2005 amendment, aimed at supporting user mobility, in this paper we propose a scheduling strategy aimed at providing a fair service to best effort users as well as a simple link adaptation strategy to dynamically adapt the physical level behavior to the channel reliability. Numerical results, obtained via simulation, showed the effectiveness of our proposals.

This paper addresses the performance evaluation of multi-carrier code division multiple access systems both at physical and TCP levels. A partial equalization technique improving the performance at physical layer in the presence of interference is investigated and its impact on the performance at upper layer is studied. The results are obtained through an integrated simulation platform carefully reproducing all main aspects affecting the quality of service perceived by the final user. Works of this nature enable a deep investigation of the real gain perceived by the user provided by proper signal processing techniques at the physical level.

IEEE802.16e wireless MAN-OFDMA is expected to be a significant step in the evolution of communication technologies for the provision of broadband services to mobile users. Nonetheless, its potential, in terms for instance of transport level throughput, is not clear yet, since it depends on a large number of system parameters and implementation choices. This large amount of degrees of freedom makes also an hard task the choice of the set of system parameters to be adopted in order to get the best from this technology. In order to overcome these limitations, in this paper we provide an analytical framework that can be used to get an insight on IEEE802.16e wireless MAN-OFDMA performance, and, above all, to drive the choices of network operators in terms of system configuration.

This work reports some results of a joint activity research pursued within the Project C of NEWCom (European network of excellence in communications). The aim of the activity is to investigate adaptive cross-layer techniques for heterogeneous wireless networks and try to obtain some general rules. In particular the singular or joint adaptation of scheduling and link adaptation algorithms is studied by means of simulation platforms for which proper scenarios and metrics have been defined.

Heterogeneous networks integration and interwork- ing, with particular reference to third generation (3G) cellular networks and wireless local area networks (WLANs), is a challenging issue for the early future wireless communications world. In our researches we consider the opportunity to convert those circuit switched voice flows that would be blocked by UMTS for resource saturation into voice over IP streams to be served through the WLAN connection. In order to increase voice users satisfaction when WLAN available resources are critically falling off, in this paper we investigate, by means of a simulation approach, different WLAN call admission control strategies within the context of 3G-WLAN integrated networks. I. INTRODUCTION Heterogeneous networks integration and interworking, with particular reference to third generation (3G) cellular networks and wireless local area networks (WLANs), is a challenging issue for the early future wireless communications world. Provided that the WLAN hot spot is within the 3G network coverage and that the final user is equipped with a dual mode terminal, integrating the two technologies, thus increasing the pool of available resources, would considerably increase both users satisfaction and networks utilization efficiency. In the last few years several projects were dedicated to the issue of 3G/WLAN interworking networks (e.g., (1)) and many papers appeared, investigating specific aspects mainly related to architectural/signalling issues (e.g., (2)) and vertical handover (e.g., (3)). Besides the data users exchange between UMTS and WLAN, in this paper we focused our attention on the possi- bility to serve by means of the WLAN technology those voice calls that within the hot spot region cannot be served by the 3G network (and would therefore be blocked) in case of saturation of its radio resources. Obviously a format conversion from circuit-switched (CS) voice flows into packet-switched (PS) Voice over IP (VoIP) flows (and vice versa) is needed in order to allow the radio network switching (see (4) for details on the network architecture). The benefits of 3G/WLAN interworking are here inves- tigated with reference to the Chinese TD-SCDMA UMTS This work was carried out in the framework of VICOM Project funded by MIUR. technology (5) and to the upcoming IEEE802.11e (6) WLAN technology. In this paper, in particular, the users satisfaction level provided in a realistic scenario by the integrated network is assessed by means of a dedicated simulation platform. Three simple but effective call admission control (CAC) strategies for the WLAN are implemented in our simulation platform in order to prevent WLAN overloads. Their performance have been derived and compared. The paper is outlined as follows. In section II the WLAN CAC strategies are described, in section III the scenario under investigation is introduced; in section IV and in section V the simulations settings and the related numerical results are reported and finally, in section VI the final conclusions are drawn.

The interworking of different radio access technologies aimed at providing always the best service to mobile users is the future of wireless communications. Many researchers are already investigating appropriate architectural solutions, coexistence problems, common radio resource management algorithms and other topics concerning this issue. In this paper we illustrate a simulation platform developed in our research group to investigate the performance and to test new management strategies of such interworking networks. Our purpose, however, is not to show the details of our tool, that would be useless for the reader; we aim, on the contrary, at providing those researchers who are facing the realization of a similar simulation tool with the main general criteria to develop a flexible and efficient simulation platform.

In this paper several strategies are presented aimed at reducing the burden of physical level simulations within the context of network simulations, and their characteristics are discussed, both in terms of time efficiency and accuracy. The simulation of an IEEE802.11a network is also presented as a case study in order to highlight the peculiarities of each strategy and the impact on accuracy of correlation in both the time and frequency domains

In this paper the issue of link adaptation (LA) for IEEE 802.11 WLANs is investigated with emphasis on realistic environments. Different from most of the papers that appeared on this topic, here the impact of collisions on the performance provided by several LA solutions is assessed through accurate simulations. Two original LA solutions are also suggested, which outperform previously proposed strategies

In this paper the issue of networks interworking is faced with reference to UMTS cellular networks and IEEE 802.11 wireless local area networks. A feasible architectural solution of the integrated network is given and the possibility to serve by means of the WLAN technology also those voice calls that would be blocked by UMTS, in case of resource saturation, is investigated. The performance level provided by the integrated network in a realistic scenario is here assessed considering both IEEE 802.11a and the forthcoming IEEE 802.11e WLAN technologies for possible integration with UMTS

In this paper two simple but efficient call admission control (CAC) strategies for IEEE 802.11 WLANs are investigated, which are both based on a simple centralized evaluation of the current network congestion level. A realistic scenario has been considered for the evaluation of the proper choice of the CAC parameters as well as for the assessment of the performance level they provide for different traffic mixes. Simulation results show that the investigated CAC strategies could significantly improve users satisfaction and network fairness