Aniello Napolitano

An Eigenvalue Decomposition-Based Method for In-Service Testing of Wireless Communications Systems

Reliably measuring the relevant parameters (like channel power, occupied bandwidth, and carrier frequency) characterizing the signals involved in wireless communications systems turns out to be the key for their in-service testing at a physical layer. This task, however, would not succeed whenever other signals, generated by different wireless systems, interfere with the useful one both in the time and frequency domains. To overcome this limitation, the authors have recently assessed the suitability of eigenvalue decomposition-based algorithms in accurately estimating the power spectrum of a given number of signals that overlap in the time domain and occupy, fully or partially, the same frequency band. Starting from the promising outcomes of the cited algorithms and taking advantage of some nice features of information theoretical criteria, a new measurement method is designed and implemented hereinafter. Designed directly for the in-service physical layer testing of wireless communications systems, the method allows a blind separation of the power spectrum of the useful signal from those of the interfering ones. The evaluation of the desired parameters of the useful signal as well as the frequency-domain characterization of the interfering ones is thus possible, whatever the number of involved signals. The results obtained in a number of laboratory experiments under different in-channel interference conditions show the reliability and efficacy of the method also in the presence of severe in-channel interference.

Modeling and Measuring Link Capacity in Communication Networks

The capacity of a link is a fundamental parameter in communication networks. Its knowledge is needed for both network planning and management. This is why capacity estimation was one of the first measurement challenges in wired communication networks. In the recent past, some experimental tests permitted imputing the poor performance of capacity measurement techniques in wireless networks to some pitfalls of the capacity model that they are based on. This paper is the natural evolution of those experimental findings. It presents a new multilayer capacity model that is consistent with the classical capacity definition but does not suffer from such pitfalls, along with an improved measurement method based on the deployment of proper software probes. The results of experiments that are conducted on IEEE 802.11x wireless links are also given.

Modulation Quality Measurement in WiMAX Systems Through a Fully Digital Signal Processing Approach

The performance assessment of worldwide interoperability for microwave access (WiMAX) systems is dealt with. A fully digital signal processing approach for modulation quality measurement is proposed, which is particularly addressed to transmitters based on orthogonal frequency-division multiplexing (OFDM) modulation. WiMAX technology deployment is rapidly increasing. To aid researchers, manufactures, and technicians in designing, realizing, and installing devices and apparatuses, some measurement solutions are already available, and new ones are being released on the market. All of them are arranged to complement an ad hoc digital signal processing software with an existing specialized measurement instrument such as a real-time spectrum analyzer or a vector signal analyzer. Furthermore, they strictly rely on a preliminary analog downconversion of the radio-frequency input signal, which is a basic front-end function provided by the cited instruments, to suitably digitize and digitally process the acquired samples. In the same way as the aforementioned solutions, the proposed approach takes advantage of existing instruments, but different from them, it provides for a direct digitization of the radio-frequency input signal. No downconversion is needed, and the use of general-purpose measurement hardware such as digital scopes or data acquisition systems is thus possible. A proper digital signal processing algorithm, which was designed and implemented by the authors, then demodulates the digitized signal, extracts the desired measurement information from its baseband components, and assesses its modulation quality. The results of several experiments conducted on laboratory WiMAX signals show the effectiveness and reliability of the approach with respect to the major competitive solutions; its superior performance in special physical-layer conditions is also highlighted.

Cross-Layer measurement on an IEEE 802.11g wireless network supporting MPEG-2 video streaming applications in the presence of interference

The performance of wireless local area networks supporting video streaming applications, based on MPEG-2 video codec, in the presence of interference is here dealt with. IEEE 802.11g standard wireless networks, that do not support QoS in according with IEEE 802.11e standard, are, in particular, accounted for and Bluetooth signals, additive white Gaussian noise, and competitive data traffic are considered as sources of interference. The goal is twofold: from one side, experimentally assessing and correlating the values that some performance metrics assume at the same time at different layers of an IEEE 802.11g WLAN delivering video streaming in the presence of in-channel interference; from the other side, deducing helpful and practical hints for designers and technicians, in order to efficiently assess and enhance the performance of an IEEE 802.11g WLAN supporting video streaming in some suitable setup conditions and in the presence of interference. To this purpose, an experimental analysis is planned following a cross-layer measurement approach, and a proper testbed within a semianechoic chamber is used. Valuable results are obtained in terms of signal-to-interference ratio, packet loss ratio, jitter, video quality, and interference data rate; helpful hints for designers and technicians are finally gained.

Measuring

This paper presents a new method for measuring the I /Q impairments affecting the worldwide interoperability for microwave access (WiMax) transmitters through the analysis of the signal acquired through a general-purpose I /Q receiver. Based on a model of the effects of the I /Q impairments on the output signal that is suitable for orthogonal frequency-division multiplexing (OFDM) systems like WiMax, the method is designed to correctly take into account the peculiarities of systems compliant with the IEEE 802.16-2004 standard, such as the potentially noxious effects of the impairments on signal normalization and threshold decisions. The results of the experiments carried out on the standard-compliant signals are given.

I/Q

A new digital signal processing method capable of measuring signals typical parameters, such as channel power, channel bandwidth, and carrier frequency, is presented hereinafter. In particular, thanks to some attractive features of the exploited MUSIC algorithm, the method allows the measurement of typical parameters of wideband signals even though they occupy, fully or partially, the same frequency range of other signals, such as interference or noise. This property is relevant for modern telecommunication systems that do not use an own licensed band, but rather share an unlicensed band with other systems, such in the case of those based on the standard IEEE 802.11x. The performance of the method is assessed by means of a number of experiments involving different kinds of desired and disturbing signal as well as different Signal-Interference to Noise Ratio (SINR) conditions. Obtained results show the satisfying reliability and efficacy of the proposed method, thus suggesting its use in the presence of in-channel interference.

Impairments in WiMAX Transmitters

The performance of video streaming applications over wireless local area network (WLANs), in presence of interference, are here dealt with. In particular, the IEEE 802.11g standard is considered and Bluetooth and WLAN competitive data traffic are analyzed as interferer. The analysis is conducted experimentally following a cross-layer approach and through the use of properly developed testbed within a semi-anechoic chamber. The goal is to investigate the performance of video streaming applications over WLAN in the presence of both network/transport and physical layer interference, and to deduce from the experiments valuable hints for improving the setup of a WLAN.

Measuring true signal parameters in digital wireless systems in the presence of in-channel interference

Wireless networks such as WiFi suffer communication performance issues in addition to those seen on wired networks due to the characteristics of the radio communication channel used by their Physical Layers (PHY). Understanding these issues is a complex but necessary task given the importance of wireless networks for the transfer of wide ranging packet steams including video as well as traditional data. Simulators are not accurate enough to allow all the intricacies of such communication to be accurately understood, especially when complex interactions between the protocols of different layers occurs. The paper suggests cross layer measurement as a solution to the problem of understanding and analysis of such complex communication issues and proposes a framework in which appropriate performance measurements can be made from a WiFi network supporting a video streaming application. The framework has been used to collect these measurements at the PHY, MAC, Transport and Application layers. Analysis of the collected measurements has allowed the effects of noise interference at the PHY to be related to the perceived performance at the Application Layer for a video streaming application. This has allowed the effect of the SNR on the download time of a video sequence to be studied.

Are IEEE 802.11 Wireless Networks Appropriate for Video Streaming in the Presence of Interference? An Experimental Answer

Several wireless systems and networks share the same or contiguous frequency bands to provide wideband connectivity. Due to the different channel access techniques, the related communication signals are often transmitted, at the same time, over frequency intervals partially or fully overlapping to one another. In such cases, classical approaches either in the frequency or joint time-frequency domain fail in evaluating the power spectrum of each signal, thus preventing relevant measurement information, like channel power, occupied bandwidth and carrier frequency, to be accurately gained.

An experimental analysis of the effects of noise on Wi-Fi video streaming

The paper presents a new method for measuring the most common I/Q impairments affecting WiMAX transmitters, that are gain imbalance and quadrature error. The method operates on the signal at the output of the transmitter, acquired through a general purpose I/Q receiver. It is designed to correctly take into account the peculiarities of systems compliant to the standard IEEE 802.16-2004, such as the potentially noxious effects of impairments on signal normalization. The results of experiments carried out on standard-compliant signals are also given.