Mauro Biagi

Location Assisted Routing Techniques for Power Line Communication in Smart Grids

Smart Grid collectively refers to various visions of how energy generation, distribution, and consumption should be managed to overcome many of the shortcomings of todays electricity grids and to sustain our ever more electricity dependent societies. One important enabling component of Smart Grid will be a fine-grained and reliable communications infrastructure that links together the many elements of the grid. Since by definition all these elements are connected to power lines, power line communications (PLC) technology is a natural candidate to build parts of such an infrastructure. In this paper, we consider the use of PLC in low- and medium-voltage distribution grids to connect network nodes (e.g., meters, actuators, sensors) through multihop transmission. In particular, we address the problem of routing of unicast messages making use of the stationarity of nodes. To this end, we motivate and investigate the application of geographic routing protocols and gauge their performance with respect to energy consumption and transmission delay.

Adaptive Receiver for Indoor Visible Light Communications

Visible light communications seeks to leverage an unused medium for indoor wireless communications. A major goal is to deliver very high data-rates through LED luminaires to all places where we use lighting. However, the characteristics of LEDs and the nature of indoor lighting conspire to distort the signals. Illumination powers LEDs have low signaling bandwidth and exhibit severe frequency distortion. Their wide dispersion patterns, required for light and signal coverage, also add multipath distortion. Intermittent shadowing results in a wide range of channel characteristics. In this paper we address these challenges with an adaptive receiver. Namely, training is used to identify channel impairments, and our proposed receiver applies specific countermeasures including threshold detection, RAKE reception and adaptive channel equalization. Analysis and simulation demonstrate that our design mitigates distortion problems yielding a performance improvement of 40% to 100% with respect to the current literature in achievable bit-rate depending on the propagation scenario.

Optimal discrete bit loading for DMT based constrained multicarrier systems

We present the solution for the optimal discrete bit loading in multicarrier systems employing discrete multitone (DMT) modulation, when additional constraints on either the maximum allowable energy for each subchannel or the maximal cardinality of the QAM constellations to be used are given. Conditions for the optimality of greedy algorithms in this context are also provided. The solution is based on some results in matroid theory about combinatorial optimization.

Optimal integer bit-loading for multicarrier ADSL systems subject to spectral-compatibility limits

In this paper, we develop and test new algorithms for the optimal discrete bit-loading of digital subscriber loop (DSL) multicarrier (MC) systems when constraints on both the total available energy and the maximum energies per carrier are active. Although pressing spectral-compatibility issues limit performance of emerging G.DMT-based wide-band ADSL services, nevertheless, up to now none of the several published discrete-loading algorithms claiming optimality accounts for peak-energy limitations. Therefore, after proving the matroid structure of the underlying combinatorial optimization problem, we develop fast-implementable iterative greedy-type algorithms that converge to the desired optimal discrete loading. Several numerical results and comparisons carried out on standardized ADSL loops are presented that allow us to evaluate the systems losses induced by the imposed spectral-compatibility constraints.

LAST: A Framework to Localize, Access, Schedule, and Transmit in Indoor VLC Systems

The need allowing indoor access to the Internet services requires to reduce the electromagnetic pollution. Recently, the scientific community is looking for alternatives to the use of radio frequency communication, leading to propose and study the new paradigm of visible light communications. In order to present a system implementing transmission and access procedures, we propose a logical stream starting from user localization, so as to decide which LEDs can provide access, thus basically performing a space-division multiple access by scheduling data on the basis of the bits to be transmitted. For this aim, a two-bands access scheme is proposed, and implemented through the use of a separated channel where signaling specifies where, in the wavelength domain, the reception must be operated by the different users. A multiple-input multiple-output scheme is considered for data transmission, in order to increase rate with a reliable error rate performance. Performance is evaluated for what concerns localization and access tasks, so as to show the effectiveness of the proposed scheme. Performance comparison with the recent literature has been also reported.

Optimal MIMO UWB-IR Transceiver for Nakagami-fading and Poisson-Arrivals

In this contribution, we develop a (novel) fam- ily of Multiple-Input Multiple-Output (MIMO) UWB Impulse-Radio (UWB-IR) transceivers for Orthogonal PPM- modulated (OPPM) coded transmissions over (baseband) multipath-faded MIMO channels. To by-pass expensive channel-estimation procedures, the MIMO channel path- gains are assumed to be fully unknown at the receiver. Thus, according to the UWB-IR statistical channel-models currently reported in the literature for both indoor/outdoor application scenarios, we develop and analyze three versions of the resulting noncoherent transceiver, that are optimal for Nakagami, Gaussian, and Log-normal distributed channel- gains, respectively. As dictated by the Saleh-Valenzuela (SV) UWB model, the resulting noncoherent Maximum- Likelihood (ML) Decoder explicitly accounts for the Poisson- distribution of the path-arrivals. Hence, after analytically evaluating the performance of the proposed noncoherent transceiver via suitable versions of the Union-Chernoff bound, we prove that the family of Space-Time OPPM (STOPPM) recently presented in the Literature is able to at- tain full-diversity in the considered multipath-affected appli- cation scenario. To corroborate the carried out performance analysis, we report several numerical results supporting both the medium/long coverage ranges attained by the proposed STOPPM-coded noncoherent transceiver, and its perfor- mance robustness against the degrading effects induced by Inter-Pulse-Interference (IPI), spatially-correlated multipath fading and mistiming.

Optimized Power Allocation and Signal Shaping for Interference-Limited Multi-antenna “Ad Hoc” Networks

This paper deals with optimized Multiple-Input Multiple Output (MIMO) channel estimation and ensuing information throughput conveyed by pilot-based multi-antenna systems affected by both spatially colored Multiple Access Interference (MUI) and errors in the available channel estimates. The architecture of the Minimum Mean Square Error (MMSE) MIMO channel estimator is derived and the related analytical conditions for the optimal design of space-time training sequences are provided. Afterwards, closed form expressions for the maximum information throughput sustained by the considered systems for Gaussian distributed input signals are given and, then, a novel powers’ allocation algorithm for the asymptotical achievement of the system capacity is developed. Considerations about optimized space-division MAC strategies are also provided.

On the information throughput and optimized power allocation for MIMO wireless systems with imperfect channel estimation

In this paper, we focus on the throughput analysis, outage evaluation and optimized power allocation for Multiple-Input Multiple-Output (MIMO) pilot-based wireless systems subject to short-term constraints on the radiated power and equipped with a feedback-path for communicating back to the transmitter the imperfect MIMO channel estimates available at the receiver. The case of the ergodic throughput for Gaussian distributed input signals is analyzed, and the conditions for the (asymptotical) achievement of the Shannon capacity are pointed out. The main contributions of this work may be so summarized. First, we develop closed-form analytical expressions for the computation of the ergodic information throughput conveyed by the considered MIMO system for the case of ideal feedback link. Second, we present an iterative algorithm for the optimized power allocation over the transmit antennas that explicitly accounts for the imperfect MIMO channel estimates available at the receiver. Third, after relaxing the assumption of ideal feedback link, we test the sensitivity of the proposed power allocation algorithm on errors possibly introduced by the feedback channel, and then, we numerically evaluate the resulting throughput loss. Finally, we develop closed-form upper and lower bounds on the outage probability that are asymptotically tight.

Smart Vehicles, Technologies and Main Applications in Vehicular Ad hoc Networks

Vehicular Ad hoc NETworks (VANETs) belong to a subcategory of traditional Mobile Ad hoc NETworks (MANETs). The main feature of VANETs is that mobile nodes are vehicles endowed with sophisticated “on-board” equipments, traveling on constrained paths (i.e., roads and lanes), and communicating each other for message exchange via Vehicle-to-Vehicle (V2V) communication protocols, as well as between vehicles and fixed road-side Access Points (i.e., wireless and cellular network infrastructure), in case of Vehicle-to-Infrastructure (V2I) communications [1].

Trace-Orthogonal PPM-Space Time Block Coding Under Rate Constraints for Visible Light Communication

Visible light communications (VLC) represents a new frontier of communications allowing high data-rate Internet access, specially in indoor environments, where the use of light emitting diodes (LEDs) is growing as a viable alternative to traditional illumination. As a result, LED output intensity can be varied faster than human eye can perceive, thus guaranteeing simultaneous wireless communications and illumination. One of the key challenges is the limited modulation bandwidth of sources that is typically around several MHz. The use of multiple input and multiple output (MIMO) techniques in optical wireless system helps to increase the capacity of the system and thus improve the system performance. In this paper, we investigate the use of an optical MIMO technique jointly with pulse position modulation (PPM) in order to improve the data rates without reducing the reliability of the link. PPM is known to be signal-to-noise ratio efficient modulation format, while it is bandwidth inefficient so the use of MIMO can compensate that drawback with reasonable complexity. Furthermore, an offline tool for VLC system planning, including error probability and transmission rate, has been proposed in order to solve the tradeoff between transmission rate and error rate. Finally, several numerical results and performance comparisons are reported.