Giulio Bartoli

Beamforming for small cell deployment in LTE-advanced and beyond

Integrating the standard coverage of traditional macrocells with cells of reduced dimensions (i.e., small cells) is considered one of the main enhancements for Long Term Evolution systems. Small cells will be overlapped with macrocells and possibly also with each other in areas where wider coverage capability and higher throughput are needed. Such heterogeneous network deployment presents many potential benefits but also some challenges that need to be resolved. In particular, multi-antenna techniques and processing in the spatial domain will be key enabling factors to mitigate these issues. This article presents different small cell deployment approaches: sharing the same frequency bands with the macrocell, or using separated higher frequency bands. For each approach, the benefits of beamforming are discussed.

LTE-A femto-cell interference mitigation with MuSiC DOA estimation and null steering in an actual indoor environment

This paper deals with a cognitive approach used to reduce the co-channel interference arising from the coexistence of an LTE macrocell and an LTE femtocell sharing the same frequency band. Multiple-antennas technology is considered to exploit the angle dimension as a new spectrum opportunity: femtocell acts as a secondary system and inserts nulls in the directions of the UE connected to the macrocell thus protecting the downlink transmission of the primary base station. MuSiC algorithm is used to detect the DOA of the UE signal replicas in an indoor environment assuming a variable number of multipath components characterized by a very large angle spread. The proposed scheme permits to increase the signal to interference ratio at the UE side thus reducing the achieved error rate on the downlink connection even when the number of resolvable paths is higher than the number of antennas. Finally the UE mobility is considered to take into account the effect of variable DOAs.

A novel emergency management platform for smart public safety

Summary This paper proposes an efficient architecture of a smart public safety platform that involves public professional operators as well as citizens. The proposed system is compliant with the emerging paradigm of a smart city. Its main features are that of monitoring, forecasting and managing emergency situations, arising from environmental disasters or crimes. The proposed platform performs a smart and functional integration of heterogeneous components as a smart data gathering and analysis system, a novel professional communication system, wireless sensor networks and social networks. Each element acts not only as an information collector but has autonomous capabilities to cooperate with the others in order to increase the system efficiency and to reduce the need of human interactions. Finally, the paper highlights some open research issues that represent critical aspects and require additional investigations in order to further improve the performance of the proposed platform. Copyright

AeroMACS: A new perspective for mobile airport communications and services

Broadband wireless technologies are becoming more and more pervasive in several fields of application to supply new services and to satisfy operational constraints. Among them, this article deals with the use of WiMAX technology in future air traffic management system. This technology is expected to increase the safety and to allow the exchange of large volumes of data among heterogeneous users, including aircraft. In particular, Eurocontrol and ICAO identified a WiMAX-based technology for communications on the airport surface, named Aeronautical Mobile Airport Communication System (Aero- MACS). The scope of this article is to provide an overview of AeroMACS, with a description of its main features, requirements, PHY and MAC profile choices, and related network architecture. Finally, the article highlights some open issues for AeroMACS that represent critical aspects and require, at this time, additional investigation.

The Structure and Performance of an Optimal Continuous-Time Detector for Laplace Noise

An optimal detector for a known signal in Laplace noise is determined. The analysis starts with a sampled digital receiver, leading to an asymptotic analysis when the number of samples approaches infinity. The optimum detector for Laplace noise achieves twice the signal-to-noise ratio of the matched filter for Gaussian noise. The theoretical analysis is corroborated by computer simulations.

An Optimized Resource Allocation Scheme Based on a Multidimensional Multiple-Choice Approach with Reduced Complexity

Long Term Evolution (LTE) is considered one of the main candidate to provide wireless broadband access to mobile users. Among main LTE characteristics, flexibility and efficiency can be guaranteed by resorting to suitable resource allocation schemes, in particular by adopting adaptive OFDM schemes. This paper proposes a novel solution to the sub-carrier allocation problem for the LTE downlink that takes into account the queues length, the QoS constraints and the channel conditions. Each user has different queues, one for each QoS class, and can transmit with a different data rate depending on the propagation conditions. The proposed algorithm defines a value of each possible sub-carrier assignment as a linear combination of all the inputs following a cross-layer approach. The problem is formulated as a Multidimensional Multiple-choice Knapsack Problem (MMKP) whose optimal solution is not feasible for our purposes due to the too long computing time required to find it. Hence, a novel efficient heuristic has been proposed to solve the problem. Results shows good performance of the proposed resource allocation scheme both in terms of throughput and delay while guarantees fairness among the users. Performance has been compared also with fixed allocation scheme and round robin.

Physical Resource Block clustering method for an OFDMA cognitive femtocell system

Abstract This paper deals with a heterogeneous Orthogonal Frequency Division Multiple Access (OFDMA) network where a user-deployed low power femtocell operates in the coverage area of a traditional macro-cell using the same frequency band. Femtocells represent a promising solution to increase the network capacity in next-generation wireless networks. However, the arising interference must be mitigated by means of suitable resource allocation policies. In particular, an OFDMA system allows a flexible usage of the resources that are organized in Physical Resource Blocks (PRBs). This flexibility can be fully exploited in a heterogeneous network if the femtocell base station knows how the PRBs are organized and grouped. This paper considers a cognitive femtocell base station that is able to sense the environment and identify the set of PRBs allocated to a given user by the macro-cell base station. A PRBs clustering method is proposed here. Initially, suitable inputs are derived and then provided to the K -means algorithm for a clustering refinement. The method proposed here is able to correctly gather together the PRBs of each user. Performance comparisons with a hierarchical clustering method is presented. The benefits of PRBs clustering on direction of arrival estimation are shown in order to prove the effectiveness of the proposed methods.

Subcarriers Suppression Methods for OFDM Systems with Decode-and-Forward Network Coding

This paper deals with the performance evaluation of Decode and Forward Physical Layer Network Coding schemes under multipath fading channel propagation conditions. Physical Layer Network Coding in Two Way Relay Networks ideally allows to drastically increase the network throughput. However, under the assumption of actual channel propagation conditions, the performance quickly degrades due to high decoding error probability. With the aim of counteracting this drawback, the paper proposes a suitable approach for Orthogonal Frequency Division Multiplexing systems based on a signal pre-equalization technique. Furthermore, in order to lower the decoding error probability, three subcarriers suppression methods are introduced. These methods differ from each other for the performance achieved and the required amount of signaling that nodes have to exchange. An important result obtained here is that the combined use of channel inversion and subcarriers suppression allows to enhance the system reliability with a slight decrease of the throughput.

Physical Layer Network Coding in Multipath Channel: Effective Precoding-Based Transmission Scheme

This paper analyzes the performance of the Physical Layer Network Coding (PLNC) approach based on Decode-and-Forward (DF) and operating in multipath fading channel. In actual channel affected by multipath fading the DF method has poor performance since the relay node cannot properly perform data decoding. In addition the decoding at the relay requires the knowledge of the channels involved in the communication with a consequent signaling overhead. In order to overcome these problems this paper proposes an Orthogonal Frequency Division Multiplex (OFDM) system where the pre-emphasis approach is considered jointly with an efficient method of sub-carrier suppression named Blind Subcarrier Suppression (BSS). Simulations results show that BSS achieves high throughput with a Bit Error Probability (BER) near to that of a classical OFDM system in multipath channel.

Angular interference suppression in cognitive LTE-A femtocells

We consider a heterogeneous Long Term Evolution Advanced (LTE-A) network where a cognitive femtocell operates in the coverage area of a traditional macrocell sharing the same frequency band. A new method is proposed here to avoid the interference generated by the femtocell on the macrocell downlink communications. In particular, the estimation of the direction of arrival of the primary user signals is used to place nulls in the femtocell transmission paths by means of a suitable beamforming algorithm. The novelty of the proposed approach is that it works on a physical resource basis, taking into account the specific LTE-A access scheme. In this way it is able to manage the interference towards several macrocell users characterized by a high angle dispersion of the multipath components. The obtained numerical results show that the system is able to significantly reduce the interference in different operational conditions, especially when the physical resource blocks belonging to the same macrocell user can be clustered, thus increasing the dimension of the snapshot used for the direction of arrival estimation.