Francesco Guidolin

A study on the coexistence of fixed satellite service and cellular networks in a mmWave scenario

The use of a larger bandwith in the millimeter wave (mmWave) spectrum is one of the key components of next generation cellular networks. Currently, part of this band is allocated on a co-primary basis to a number of other applications, such as the fixed satellite services (FSSs). In this paper, we investigate the coexistence between a cellular network and FSSs in a mmWave scenario. In light of the parameters recommended by the standard and the recent results presented in the literature on the mmWave channel model, we analyze different BSs deployments and different antenna configurations at the transmitters. Finally, we show how, exploiting the features of a mmWave scenario, the coexistence between cellular and satellite services is feasible and the interference at the FSS antenna can be kept below recommended levels.

A Markov-based framework for handover optimization in HetNets

The deployment of small cells in Heterogeneous Networks (HetNets) raises new challenges in relation to the Handover process and the mobility management. In fact, the performance of a mobile user within a HetNet scenario highly depends on the setting of the handover parameters in relation to other context parameters, such as the channel conditions and the user position and speed. In this paper, we derive a general theoretical analysis to characterize the user performance as a function of the mobility model, the power profile received from the neighboring cells, and the handover parameters. More in detail, we propose a Markov-based framework to model the user state during the handover process and, based on such model, we derive an optimal context-dependent handover criterion. The mathematical model is validated by means of simulations, showing that our strategy outperforms conventional handover optimization techniques by exploiting the context information.

Investigating Spectrum Sharing between 5G Millimeter Wave Networks and Fixed Satellite Systems

In this paper we study coexistence of 5G small cells with fixed satellite systems (FSSs) in a scenario where both systems operate co-channel in the large spectrum bandwidth available around 28 GHz. Such studies are of great importance to inform the research community,industry and regulators which are currently investigating spectrum requirements and technology options for 5G systems. Focusing on the FSS uplink scenario, we use realistic FSS parameters and radiation pattern, combined with very recent channel from the literature, we analyzed the impact of interference resulting from FSS radiation on the achievable capacity and throughput of 5G small cells considering various multiple antenna configurations at the base stations (BSs) and different deployments of the mobile transmitters when no cooperation is allowed between the BSs. Starting from the lower bound, represented by an omnidirectional configuration of the transmitters, we extend our work to the analysis of large antenna arrays that will be used in the new generation of mobile cellular systems. Our results indicate that by exploiting a large number of antennas at the BSs and properly setting the protection distance between FSS and cellular BS, co-channel deployment of 5G small cells with FSS earth stations is possible, in the sense that adequate user data rates could be provided to the majority of mobile users.

Context-Aware Handover Policies in HetNets

Next generation cellular systems are expected to entail a wide variety of wireless coverage zones, with cells of different sizes and capacities that can overlap in space and share the transmission resources. In this scenario, which is referred to as Heterogeneous Networks (HetNets), a fundamental challenge is the management of the handover process between macro, femto and pico cells. To limit the number of handovers and the signaling between the cells, it will hence be crucial to manage the users mobility considering the context parameters, such as cells size, traffic loads, and user velocity. In this paper, we propose a theoretical model to characterize the performance of a mobile user in a HetNet scenario as a function of the users mobility, the power profile of the neighboring cells, the handover parameters, and the traffic load of the different cells. We propose a Markov-based framework to model the handover process for the mobile user, and derive an optimal context-dependent handover criterion. The mathematical model is validated by means of simulations, comparing the performance of our strategy with conventional handover optimization techniques in different scenarios. Finally, we show the impact of the handover regulation on the users performance and how it is possible to improve the users capacity exploiting context information.

A cooperative scheduling algorithm for the coexistence of fixed satellite services and 5G cellular network

The increasing demand for higher data rates has accelerated research on the next generation of mobile cellular networks (5G). One of the key factors of 5G is the use of a larger bandwidth allocated in the millimeter wave (mmWave) frequency spectrum. In particular, one of the candidate bands is the portion of spectrum between 17 and 30 GHz that is currently used by other technologies such as fixed satellite services (FSS) and the cellular network backhaul. In this paper, we analyze the coexistence between mobile services and FSS considering the main characteristics of the mmWave spectrum recently investigated in the literature. Moreover, we present a novel cooperative scheduling algorithm based on a game theoretic framework that exploits the use of analog beamforming at the base stations (BS). Finally, we show that adopting this algorithm ensure that the system meets the regulatory recommendation concerning the interference level at the FSS and at the same time provides a good user spectral efficiency.

A Distributed Clustering Algorithm for Coordinated Multipoint in LTE Networks

Coordination and cooperation among transmitters are fundamental paradigms to improve the performance of next-generation mobile networks. By grouping multiple transmitters into clusters, interference can be managed to improve the performance at the end users side. In this letter, we present a novel distributed clustering algorithm that adapts the cluster configuration according to the users distribution and the average cluster size. We compare the performance obtained with other clustering solutions in an LTE scenario using the open-source network simulator ns3. Our proposed algorithm is shown to significantly outperform the other approaches, particularly for the users with low signal-to-noise ratio (SNR), with a 26% improvement of throughput for the worst 10% of the low-SNR users compared with greedy clustering.

Statistical analysis of non orthogonal spectrum sharing and scheduling strategies in next generation mobile networks

Spectrum sharing has been recently proposed as a promising paradigm to improve the efficiency of resource usage in next generation mobile networks. In particular, non orthogonal spectrum sharing allows the operators to re-use the available frequencies at the cost of higher interference at the receivers. In this paper, we mathematically analyze the performance of this technique and how it is statistically related to the channel coefficients. Moreover, we compare different kinds of schedulers that exploit various aspects of non orthogonal spectrum sharing. Finally, the resulting system performance is assessed, first through an exact statistical framework and then by simulating the schedulers in an LTE scenario with the open-source network simulator ns3.

Context-aware handover in HetNets

In this paper, we focus on the average performance experienced by a mobile user while crossing a pico/femtocell as a function of context parameters, such as user speed, pico/femto cell radius, transmit power of main and subsidiary base stations. The analysis is based on a mathematical model that provides an approximate expression of the average Shannon capacity experienced by a mobile user when crossing the femtocell. The optimal handover policy obtained from such a model is then validated through simulations against other policies, showing that a context-aware handover policy may achieve better performance than handover policies based on a more limited set of context parameters.

A tunable framework for performance evaluation of spectrum sharing in LTE networks

Current spectrum allocation policies, imposing exclusive usage of a licensed operator, may lead to inefficient management and waste of resources. Spectrum sharing, i.e., usage by the same frequency band by multiple operators, can improve the efficiency of the allocation. We analyze a scenario where two mobile operators managing neighboring cells also share a fraction of their available spectrum and quantify the performance gain. To this end, we propose a framework based on the definition of the Interference Suppression Ratio, which models effects such as beamforming or directional antennas. Depending on its value, mutual interference among the operators is reduced and sharing gains can be achieved. We implemented this framework in the well known open-source simulator ns-3 and we ran a parametric analysis of the impacting factors, including noise and cell radius. Simulation results confirm that significant gains can be achieved in terms of network capacity and throughput, provided that the Interference Suppression Ratio is above a given value.

Fairness evaluation of practical spectrum sharing techniques in LTE networks

In the context of dynamic spectrum access, spectrum sharing among multiple operators has recently emerged as a promising paradigm to improve the efficiency of resource usage. Several theoretical evaluations have proven the benefits offered by pooling the available frequencies so as to tune the capacity offered by the operators according to their different needs, especially the service demands from their users. However, practical aspects concerning the application of sharing techniques are rarely studied, and deserve more detailed investigations. This paper aims at tackling this problem, in particular investigating the impact of asymmetries and dynamics of the user demands on the implementation of spectrum sharing techniques and the resulting performance, especially in terms of fairness among the users, which seems to be often neglected by many studies. We show that in variable traffic conditions, a constantly monitored and updated sharing of frequency bands performs much better than a static allocation simply based on average traffic loads. However, it is possible to choose the update rate of the spectrum allocation so that it does not represent a heavy computational and signaling burden, while retaining most of the improvements brought by the spectrum sharing paradigm.