Gianni Cerro

Proposal and analysis of new algorithms for wideband spectrum sensing in cognitive radio

The growing demand for available frequency bands in contrast to the scarcity of allocated spectrum slots, is promoting the development of smart wireless transmission terminals generally called cognitive radios. These devices are able to select the most suitable operating frequency and modulation scheme in order to minimize the probability of interference with other users operating in the same area. A key operation to reach this goal, is an accurate and reliable spectrum sensing, especially in environment characterized by the contemporaneous presence of many users, which could even transmit with a very low power. In order to implement this operation in cost-effective hardware, efforts for containing the computational burden should be also pursued. Several techniques for spectrum sensing are today present in literature, many of them require some knowledge about the context in which the system works, while further ones do not require any hypothesis on the signal to be detected. In this framework the authors propose and compare three algorithms based on a wideband analysis, possibly suited for the purpose. They all are thought for working in blind scenarios.

A dual step energy detection based spectrum sensing algorithm for cognitive vehicular ad hoc networks

Intelligent Transportation Systems (ITS) are fundamental in order to improve safety and road efficiency. In this framework inter-vehicle communications play a primary role. To this aim several vehicle-to-vehicle (V2V) communication standards have been developed. The most important is IEEE 802.11p that operates in ISM band (5.85-5.92) GHz. Unfortunately at these frequencies communication ranges are limited and Doppler effect could not be neglected, especially when the carrier spacing of the adopted modulation techniques is close to 1 kHz, as it happens in modern standard for digital mobile communications. In order to overcome these issues, a possible solution could be the adoption of a dynamic spectrum access model able to identify frequency holes in UHF band. In this framework, this paper presents a novel approach to spectrum sensing based on the application of a dual step energy detection algorithm. It has been designed and tailored to be effective in identifying DVB-T signals. A test campaign carried out in simulation environment has confirmed the goodness of the proposal.

Analysis and implementation of a wavelet based spectrum sensing method for low SNR scenarios

In Cognitive Radio applications, spectrum sensing plays a fundamental role in order to learn the behavior of primary users (PUs) and access to the spectral resource opportunistically. Among the available methods, a surely promising approach is the wavelet based one. It allows to subdivide the wide-band spectrum under analysis in a proper number of sub-bands, based on Power Spectral Density (PSD) irregularities, remarked by the extrema of the Continuous Wavelet Transform (CWT) first derivative. Generally, such kind of methods works well as long as good Signal-to-Noise Ratio (SNR) can be experienced over the span of interest. In this context, starting from an approach present in literature, the present work proposes, customizes and implements a wavelet based spectrum sensing method, thought to operate also in challenging SNR scenarios.

The effectiveness of Savitzky-Golay smoothing method for spectrum sensing in cognitive radios

The paper proposes a new smoothing method to reduce noise contribution in frequency spectra, whose analysis is accomplished in order to perform spectrum sensing task for Cognitive Radio applications. The smoothing phase is a fundamental step in frequency analysis, since noise often corrupts user signals, by preventing them to be detected and, consequently, either protection or demodulation become impracticable. Such a need is usually satisfied through the use of moving average filters. These kinds of filters are affected by some problems which make the sensing stage not accurate and scarcely reliable. The authors propose the employment of Savitzky-Golay filters, which are already widely used in biomedical image analysis, but they are almost absent in Cognitive Radio field, to our knowledge. The goodness of such an approach is proved by two different figures of merit, testing the filtering abilities and the sensing performance improvement, thanks to the previous smoothing stage. A comparison is finally proposed with the standard linear moving average method.

Analysis of different wavelet segmentation methods for frequency-domain energy detection based spectrum sensing

Usually energy-detection based spectrum sensing techniques for Cognitive Radios need, as preliminary operation, the spectrum segmentation in smaller sub-bands, in order to apply test statistic over each sub-band rather than over the entire span, resulting in a sensitivity and selectivity improvement of the output. Despite uniform subdivision is the easiest way, the problem resides on the optimal sub-band width to achieve sensing purposes. In this paper, three different approaches based on wavelet transform are proposed as preliminary stage of a frequency domain energy detection scheme. The advantage in using a wavelet based segmentation is: (i) spectrum is segmented according to its irregularities, (ii) segmentation is not uniform but adaptive to the scenario, (iii) the number of sub-bands is usually less than in the uniform case, (iv) it employs a mathematical tool with fewer DoFs than usual optimization procedures and (v) it can be made completely automatic. As confirmed by obtained results, the considered approaches guarantee different levels of accuracy, even if all of them provide good results for the analyzed figures of merit.

Preliminary realization of a monitoring system of activated carbon filter RLI based on the SENSIPLUS® microsensor platform

This paper proposes the realization and preliminary characterization of a smart sensor platform for the online monitoring of the residual life of activated carbon air based filters. The platform performs the measurement to give reliable information about the filter maintenance or early warning for the presence of dangerous gases both in industrial and military scenarios. A preliminary feasibility study has been carried out to evaluate the activated carbon filter electrical impedance sensitivity to chemicals adsorption. After a detailed presentation of the employed hardware and software solutions, a description of the experimental setup is given and a preliminary proof of the assumed relationship is provided.

How to perform fully compliant spectrum sensing in IEEE 802.22 framework

The paper proposes a customized frequency domain energy detection spectrum sensing scheme. It is needed to fulfill requirements provided by the IEEE 802.22 standard, aimed at extending Internet services to Television White Space frequencies. It provides a detection scheme allowing to achieve strict sensitivity required by the protocol either in sensing time or in detection capabilities. In particular, considered constraints in time and computational burden are tailored to make the method effective in low cost Software Defined Radios, that are envisioned to be typical devices working into IEEE 802.22 framework. Such method should guarantee stability and repeatability in its performance. Therefore, the authors propose to combine standard ROC curve analysis to measurement accuracy evaluation, to return the optimal work-point.

Experimental analysis of software network emulators in packet delay emulation

Network emulators are powerful tools that allow to test and characterize network equipment and protocols. The market offers several measurement solutions. The most widely adopted are software network emulators and among them surely free or open-source emulators are the most used especially in research contexts. Unfortunately, software network emulators are not distributed with technical support and certified performance information. Certified information, about the ability of these software to accurately reproduce the wanted network conditions, is very important to validate the results obtained during design activity and test campaigns that involve them. In this paper, an experimental analysis of the ability of two widely used network emulators to emulate several imposed network conditions in different test set-ups is carried out. In particular, we have focused the attention on analyzing the fidelity in the generation of both static and random packet delays under different operating conditions. Obtained results confirm that imposed conditions are not equally reproduced and particular attention has to be paid in specific situations, as very low static delay imposed conditions.

Employment of software defined radios for dual-use in distributed spectrum monitoring system

The paper proposes a distributed architecture to monitor spectrum occupancy status through the use of Software Defined Radios (SDRs). Such a monitoring process is useful in order to fulfill a geolocation database, whose consultation is a mandatory task for license-exempt devices operating under the IEEE 802.22 standard rules. Moreover, the system is thought for a dual use scenarios: it can be enforced with higher security levels and different sensing approaches when an emergency situation occurs and a military control of the architecture has to be taken; conversely, it can be used by civil authorities for new generation networks, in normal conditions. The system has been tested in laboratory conditions with real SDR devices and Ethernet connection to the central node. First performance results in terms of sensing capabilities are shown in the paper.