On the Use of Reciprocal Filter against WiFi Packets for Passive Radar

This paper aims at a critical review of the signal processing scheme used in WiFi-based passive radar in order to limit its complexity and enhance its suitability for short range civilian applications. To this purpose the exploitation of a reciprocal filtering strategy is investigated as an alternative to conventional matched filtering at the range compression stage. Along with the well-known advantage of a remarkable sidelobes control capability for the resulting range-Doppler response, the use of a reciprocal filter is shown to provide additional benefits for the specific sensor subject of this study. Specifically, it allows to streamline the disturbance cancellation stage and to implement a unified signal processing architecture which is capable to handle the different modulation schemes typically adopted in WiFi transmissions. Appropriate adjustments are also proposed to the theoretical reciprocal filter in order to cope with the inherent loss in term of signal-to-noise power ratio. The effectiveness of the revised signal processing scheme encompassing the reciprocal filtering strategy is proved against both simulated and experimental datasets

Reducing the Computational Complexity of WiFi-Based Passive Radar Processing

WiFi-based passive radar is considered in this paper as an effective technology for short range monitoring applications. Aiming at limiting its complexity and enhancing its suitability for civilian applications, appropriate modifications are proposed to the signal processing scheme originally designed for such sensor. Specifically, we show that a simple inversion in the order of the main processing stages, namely clutter cancellation and range compression, allows to both reduce the number of floating-point operations and relax the requirements on the data management. Moreover, the use of a reciprocal filter in lieu of a matched filter to implement the range compression stage is proved to yield a further simplification in the resulting processing scheme along with additional benefits in terms of achievable performance in the considered application. The alternative processing schemes are compared in terms of computational burden and the effectiveness of the proposed cost-effective solutions is proved against experimental datasets

OFDM based WiFi Passive Sensing: a reference-free non-coherent approach

WiFi based passive sensing is attracting considerable interest in the scientific community for both research and commercial purposes. In this work, we aim at taking a step forward in an endeavor to achieve good sensing capabilities employing compact, low-cost, and stand-alone WiFi sensors. To this end, we resort to a reference-free non-coherent signal processing scheme, where the presence of a moving target echo is sought by detecting the amplitude modulation that it produces on the direct signal transmitted from the WiFi access point. We first validate the proposed strategy against simulated data, identifying advantages and limitations. Then, we apply the conceived solution on experimental data collected in a small outdoor area with the purpose of detecting a small cooperative drone

DVB-T based forward scatter radar for small target surveillance

This paper investigates the target detection capability of a Passive Forward Scatter Radar (PFSR) exploiting a DVB-T transmitter as illuminator of opportunity. Specifically, it is shown that conventional processing schemes adopted in PFSR might suffer from significant performance degradation when dealing with OFDM waveforms of opportunity compared to the case of FM radio broadcast. In fact, a non-negligible increase of the disturbance background is observed in the final spectrogram, which yields an undesired masking effect on weak target echoes. Therefore, we propose a signal-based processing technique to mitigate the observed effect and improve the target detection capability. The proposed approach exploits the possibility to recover a good copy of the transmitted signal based on its digital nature; this is then used to cancel the fluctuating component of the output arising from the adopted modulation of the waveform of opportunity. The effectiveness of the proposed approach is proved against simulated data

On the Use of Reciprocal Filter against WiFi packets for passive radar

Questo articolo descrive un innovativo schema unificato di elaborazione del segnale per radar passivi basati su WiFi al fine di limitarne la complessità e migliorarne l'idoneità per applicazioni civili a corto raggio. A tal fine, si studia l'utilizzo di una strategia di filtraggio reciproco come alternativa al filtraggio adattato convenzionale nello stadio di compressione in range. Insieme al noto vantaggio di una notevole capacità di controllo dei lobi laterali per la risultante risposta range-Doppler, viene dimostrato che l'uso di un filtro reciproco fornisce ulteriori vantaggi per lo specifico sensore oggetto di questo studio. In particolare, consente di semplificare la fase di cancellazione del disturbo e di implementare un'architettura di elaborazione del segnale unificata in grado di gestire i diversi schemi di modulazione tipicamente adottati nelle trasmissioni WiFi. Vengono inoltre proposti opportuni aggiustamenti al filtro reciproco teorico al fine di far fronte alla perdita intrinseca in termini di rapporto potenza segnale-a-rumore. L'efficacia dello schema di elaborazione del segnale proposto che comprende la strategia di filtraggio reciproco è dimostrata rispetto a set di dati simulati e sperimentali.This paper derives a novel unified signal processing scheme for WiFi-based passive radar in order to limit its complexity and enhance its suitability for short range civilian applications. To this purpose, the exploitation of a reciprocal filtering strategy is investigated as an alternative to conventional matched filtering at the range compression stage. Along with the well-known advantage of a remarkable sidelobes control capability for the resulting range-Doppler response, the use of a reciprocal filter is shown to provide additional benefits for the specific sensor subject of this study. Specifically, it allows to streamline the disturbance cancellation stage and to implement a unified signal processing architecture which is capable to handle the different modulation schemes typically adopted in WiFi transmissions. Appropriate adjustments are also proposed to the theoretical reciprocal filter in order to cope with the inherent loss in terms of signal-to-noise power ratio. The effectiveness of the proposed signal processing scheme encompassing the reciprocal filtering strategy is proved against both simulated and experimental datasets

The treatment of stable and unstable proximal femoral fractures with a new trochanteric nail: results of a multicentre study with the Veronail

The incidence of hip fractures continues to rise. This study is the first evaluation of a new intramedullary implant, the Veronail, that provides double axis fixation into the femoral head and allows the surgeon to choose whether to use sliding or fixed locked proximal screw fixation for trochanteric femoral fractures. The fractures were classified according to the AO classification, and function was assessed with the Modified Harris Hip Score. 111 patients with trochanteric fractures were evaluated in eight Italian hospitals. The stable 31.A1 fractures were treated with sliding proximal screws, the subtrochanteric 31.A3 fractures with converging proximal screws, and the unstable 31.A2 fractures were treated with both types of proximal fixation. The unstable fractures treated with locked converging screws had the same function at one year as those treated with sliding screws. This study suggests a possible new method of treating unstable trochanteric femoral fractures. This may be the solution to prevent excessive collapse of the fracture with the resultant poor function and persisting pain noted in the literature. Two converging locked proximal screws seem to provide stable fixation in 31.A2 femoral fractures and produce as good a result as the use of traditional sliding screws. The role of converging locked proximal screws in unstable trochanteric fractures requires further evaluation