Marco Passafiume

A scalable distributed positioning system augmenting WiFi technology

This paper presents a distributed localization system for indoor environment based on a network of compact anchor nodes. The system is based on available low-cost commercial components and it is capable of standard WiFi connectivity at 2.45 GHz. The basic node is equipped with a switch-beam antenna, which is the enabling technology for a Direction of Arrival (DoA) estimation based on Maximum-Likelihood criteria. The adopted DoA estimation procedure is tolerant to noisy power measurements, making it suitable for low-cost effective solutions based on RSSI measurements. The node is designed to be placed in an unobtrusive area for the movement of a mobile target node and is capable to operating as an independent anchor, but it is optimized to cooperate with other identical nodes to form a coordinated network of anchors, capable to monitor an extended indoor area. An experimental characterization demonstrates the DoA performance of the single node.

Realtime Gas Emission Monitoring at Hazardous Sites Using a Distributed Point-Source Sensing Infrastructure

This paper describes a distributed point-source monitoring platform for gas level and leakage detection in hazardous environments. The platform, based on a wireless sensor network (WSN) architecture, is organised into sub-networks to be positioned in the plant’s critical areas; each sub-net includes a gateway unit wirelessly connected to the WSN nodes, hence providing an easily deployable, stand-alone infrastructure featuring a high degree of scalability and reconfigurability. Furthermore, the system provides automated calibration routines which can be accomplished by non-specialized maintenance operators without system reliability reduction issues. Internet connectivity is provided via TCP/IP over GPRS (Internet standard protocols over mobile networks) gateways at a one-minute sampling rate. Environmental and process data are forwarded to a remote server and made available to authenticated users through a user interface that provides data rendering in various formats and multi-sensor data fusion. The platform is able to provide real-time plant management with an effective; accurate tool for immediate warning in case of critical events.

A Distributed Positioning System Based on a Predictive Fingerprinting Method Enabling Sub-Metric Precision in IEEE 802.11 Networks

In this paper, we present a distributed positioning system for indoor environment based on a mesh of compact independent anchor nodes. Each node is built of low-cost off-the-shelf components and operates as specialized access points capable of standard connectivity at 2.45 GHz. The key technology for the localization strategy is the switched beam antenna (SBA), which enables a space division multiple access (SDMA) paradigm. The coordinated operation of SBA-equipped anchor nodes constitutes a legacy unmodified IEEE 802.11 network which can exploit the multiplexing mechanism. The latter is the driving force of the estimation strategy, with the positional information obtained as the result of a maximum likelihood algorithm driven by the comparison of a real-time received signal strength indicator (RSSI) with the predicted signal level distribution, which can be estimated and stored without the need of lengthy offline measurement. The signal level prediction is based on a simple propagation model which is effective because benefits of both the elementary antenna radiation beams directivity and the circular polarization operation, two strong aids for the mitigation of the multipath impairment. In turn, these feature make the estimation procedure tolerant to noisy power measurements, hence particularly suitable for cost-effective solutions based on RSSI. Experimental validations demonstrate the performance of a network composed of four anchors arranged in a 2.6 × 3.8 m 2 mesh in a 6 × 7 m 2 office room, and dealing with a single target node. The mean error inside the mesh area is 63 cm while the mean error in the entire room is 1.1 m. Focusing on the cumulative distribution of the error, the 90th percentile value is 1 m considering only the mesh and 1.9 m for the entire room.

An Improved Approach for RSSI-Based only Calibration-Free Real-Time Indoor Localization on IEEE 802.11 and 802.15.4 Wireless Networks

Assuming a reliable and responsive spatial contextualization service is a must-have in IEEE 802.11 and 802.15.4 wireless networks, a suitable approach consists of the implementation of localization capabilities, as an additional application layer to the communication protocol stack. Considering the applicative scenario where satellite-based positioning applications are denied, such as indoor environments, and excluding data packet arrivals time measurements due to lack of time resolution, received signal strength indicator (RSSI) measurements, obtained according to IEEE 802.11 and 802.15.4 data access technologies, are the unique data sources suitable for indoor geo-referencing using COTS devices. In the existing literature, many RSSI based localization systems are introduced and experimentally validated, nevertheless they require periodic calibrations and significant information fusion from different sensors that dramatically decrease overall systems reliability and their effective availability. This motivates the work presented in this paper, which introduces an approach for an RSSI-based calibration-free and real-time indoor localization. While switched-beam array-based hardware (compliant with IEEE 802.15.4 router functionality) has already been presented by the author, the focus of this paper is the creation of an algorithmic layer for use with the pre-existing hardware capable to enable full localization and data contextualization over a standard 802.15.4 wireless sensor network using only RSSI information without the need of lengthy offline calibration phase. System validation reports the localization results in a typical indoor site, where the system has shown high accuracy, leading to a sub-metrical overall mean error and an almost 100% site coverage within 1 m localization error.

Improving phaseless DoA estimation in multipath-impaired scenarios by exploiting dual-band operations

This paper presents an approach improving phaseless Direction-of-Arrival (DoA) estimation accuracy for indoor environments. The positioning systems anchor is equipped with a dual-band transceiver and a switched beam antenna, operating in circular polarization at both 2.45GHz and 5.7 GHz, hence compatible with legacy IEEE 802.11abg connectivity. The estimation of DoA of a nomadic node equipped with a monopole antenna, is the result of a likelihood criteria driven by the expected signal partition. Considering the weak correlation of the multi-path at incommensurate frequencies, the data fusion collected at both 2.45 GHz and 5.7 GHz for the likelihood algorithm is expected to mitigate noise and in turn it allows for better estimation performance. The experimental validations demonstrate the performance of the proposed approach positioning the node at the distance of 3.5m inside a 5×4×3 m3 setup, being the latter perturbed with a large and invasive conductive ground aimed at the multi-path generation. Despite a very critical localization result at each single frequency, with a worst case of 90% of the observed domain affected by an error up to 50°, the data fusion approach boosts the performance getting the error below 12° in the same conditions. Similar improvements are observed for both the horizontal and vertical polarization of the nomadic node and for multiple configuration of the reflecting plane, demonstrating the effectiveness of the proposed approach.

A distributed positioning system based on real-time RSSI enabling decimetric precision in unmodified IEEE 802.11 networks

In this paper we present a distributed positioning system for indoor environments based on a network of compact independent anchor nodes operating as specialized WiFi access points. Each node is built with component-off-the-shelves and it is capable of standard IEEE 802.11 connectivity at 2.45 GHz. The enabling technology for the localization is the Switched Beam Antenna (SBA) equipped in each node, which permits a space division multiple access at network-level. The positional information is the result of a maximum likelihood estimation driven by the expected signal space partition of the constellation, and it is tolerant to noisy power measurements, such as Received Signal Strength Indicator, thanks to angular filtering capability of the SBA, which in addition operates in circular polarization. Experimental validations demonstrate the performance of a 3-anchors network, operating within the IEEE 802.11 protocol, monitoring a single nomadic node inside a 7 m2 indoor square area. It results that 68% of the square area is covered with a localization error below 50 cm, with a mean error of 47 cm. Inside the triangular mesh defined by the three anchors, the mean error drops to 39cm, with 88% of the area being below 50 cm. In addition, the maximum error is always below 77 cm.

Interference cancellation for the coexistence of 5.8 GHz DSRC and 5.9 GHz ETSI ITS

In this paper we analyze the cancellation of the interference caused by a Intelligent Transportation Systems (ITS) on devices operating in the Dedicated Short Range Communications (DSRC) framework. The cancellation is operated by an interference canceller based on the active feed-forward architecture. The canceller is designed to operate over the frequency band 5.2 GHz - 6.4 GHz, hence it is suitable for the mitigation of mutual interference on signal pertinent to DSRC at 5.8GHz due to ITS signals at 5.9 GHz. When applied to a Road Side Unit (RSU) for electronic toll collection (ETC) operating at 5.8 GHz, the proposed technique is capable to improve the performance of the front-end by cancelling the interfering signal in the 5.9 GHz bandwidth such as IEEE 802.11p signals involved in the ITS protocols; signal-to-interference improvement of 25 dB operating on 10MHz bandwidth signal is herein reported. The paper introduces the architecture of the canceller as well as the experimental results which describe the capability of the technical approach.

Car Talk: Technologies for Vehicle-to-Roadside Communications

The vision for intelligent transportation systems (ITS) in the near term foresees establishing radio communications between vehicles and the road infrastructure using the 5.9-GHz frequency band to propagate useful information aimed at passenger safety and efficient traffic management [1]-[3]. To date, three classes of applications have been distinguished at the communication application layer: road safety, traffic efficiency, and a catch-all category of other applications. All rely on roadside equipment (RSE) capable of broadcasting either regulatory or contextual information to vehicles, along with onboard units (OBUs) capable of communicating with the RSE and, in some cases, of forwarding the information to other vehicles.

Multipath Robust Azimuthal Direction of Arrival Estimation in Dual-Band 2.45–5.2 GHz Networks

This paper presents a technique capable to ameliorating the impairment caused by radio channel multipath, in the estimation of the wireless communications direction of arrival (DoA). This feature is enabled by a space division multiple access approach supported by a DoA technique based on the combination of the estimates achieved at both 2.45 and 5.2 GHz. The DoA estimation relies on a comparison between the real-time received signal strength indicator and the predicted signal level distribution, which can be estimated and stored without the need of lengthy offline measurement. The experimental setup adopted for the technique validation involves an active interferer, by which arbitrary multipath levels can be implemented. An equivalent reflection coefficient signal-to-interference ratio is defined as the ratio of the unperturbed signal and the induced coherent isofrequency interferer signal, compatible with the two-ray model of the multipath impairment. The proposed technique exploits a dual-band frequency planning, and because of the combined use of the data at the two frequencies, a mean error of 2.6° is observed within a domain ranging from 0.5 to 4 m, for the entire 360° angle in the reference anechoic scenario. The 90th percentile of the cumulative error distribution is 5.4°. In the presence of a strong coherent interferer, compatible with a total reflection from the walls, the mean error is 4.9°, while the 90th percentile of the cumulative error distribution is 10.5°. In the presence of the strongest coherent interferer signal available, which is more severe than the worst case of total reflection, the mean error is 7.1°, while the 90th percentile of the cumulative error distribution is 15.1°.