Mhd Zaher Mahfouz

Over-the-air (OTA) testing and electromagnetic compatibility (EMC) measurements are widely performed in classical reverberation chambers. A less-known reverberation chamber, yet a considerably efficient environment for generating multipath conditions, is the vibrating intrinsic reverberation chamber (VIRC). This article thoroughly investigates the radio propagation channel inside the VIRC. The specific channels studied are narrowband single-input single-output (SISO) systems operating in the frequency range from 670-2740 MHz. A relevant application is OTA testing wireless baseband algorithms or modems for wireless sensor networks, specifically low-power wide-area networks such as Narrowband-IoT (NB-IoT), Long Range (LoRa) and Ultra-Narrowband (UNB). The focus is on the first- and second-order temporal and spectral channel characteristics: coherence time, Doppler spectrum, Doppler spread, frequency autocovariance function, coherence bandwidth, rejection rate of chi-squared goodness-of-fit test for Rician distribution, Rician K -factor, and channel gain. Besides the impact of the frequency of operation, the investigation considers the effect of the rotational speed of the VIRC motors, two loading conditions, on the channel characteristics. An analysis of the measurement results shows that the stirring efficiency degrades while the coherence time increases at slow rotational speeds, with loading, and/or at low frequencies. Moreover, empirical models closely fitting the behavior of various investigated characteristics are proposed, for which we provide foundational physical interpretations. A further investigation is carried out to demonstrate the generality and briefly illustrate the potential usability of these models for both EMC and OTA testing.

In recent years, promising results have been reported with the vibrating intrinsic reverberation chamber (VIRC) combining performance and cost-efficiency for electromagnetic compatibility (EMC) measurements. This also makes it a potentially attractive solution for over-the-air (OTA) testing, which is yet to be investigated. Therefore, this article proposes the first systematic and thorough methodology to characterize the VIRC for use in EMC and OTA testing of wireless baseband algorithms of narrow-band single-input single-output channels. This methodology has been developed to measure and estimate the channel first- and second-order temporal and spectral characteristics taking into consideration the effect of different carrier frequencies, rotational speeds of VIRC motors, and loading conditions. It is then applied to a channel setup inside a VIRC for a preliminary investigation before the VIRC itself is fully characterized. It is shown that mounting an absorber in a specific location on the hatch significantly improves the rejection rate of the chi-squared goodness-of-fit test for Rician distribution without increasing the $K$ -factor above $-$ 10 dB over the frequency range 755–2740 MHz in the VIRC under investigation. However, the proposed methodology has been devised to be universal to any reverberation chamber, and the obtained results can be used to improve EMC testing due to the better understanding of the unique VIRC environment.

Electromagnetic compatibility (EMC) measurements and over-the-air (OTA) testing are widely performed in classical reverberation chambers. A less-known reverberation chamber, yet a rather efficient environment for generating multipath conditions, is the Vibrating Intrinsic Reverberation Chamber (VIRC), which is yet to be fully characterized. Therefore, this article thoroughly investigates a propagation channel inside a VIRC in terms of its first- and second-order temporal and spectral characteristics for EMC measurements and OTA testing of wireless baseband algorithms in narrowband single-input single-output systems. The investigated characteristics are coherence time, Doppler spectrum, Doppler spread, frequency autocovariance function, coherence bandwidth, rejection rate of Chi-squared goodness-of-fit test for Rician distribution, Rician 𝐾-factor, and channel gain. The investigation considers the effect of different rotational speeds of the VIRC motors, two loading conditions, and the frequency range 670 – 2740 MHz. An analysis of the measurement results shows that the stirring effectiveness degrades at frequencies below 820 MHz in general. For the loaded VIRC in particular, rotational speeds below 28.3 rpm are another degradation contributor. Moreover, the analysis reveals many interesting behavioral trends. This in turn is used to introduce a number of mathematical models closely fitting the behavior of various of the investigated characteristics. Such models are useful, for instance, at shortening similar measurement campaigns of comparable VIRCs.

We develop a systematic methodology to experimentally investigate the impact of interference from a non-listen-before-talk ultra-narrowband (UNB) signaling technique on Wi-Fi links. The methodology is based on a worst-case interference scenario, and consists of three investigating steps. This methodology is then applied to a measurement setup to practically study the case of 100 bps UNB signals interfering with an IEEE 802.11n transmission in the 2.4GHz band. Five different Wi-Fi devices are tested. The UNB signal is generated in two modulation schemes, the on-off-keying (OOK) and the Gaussian minimum-shift-keying. Both single and multiple simultaneous UNB interferers are considered. An analysis of the measurement results shows that three of the tested Wi-Fi devices cannot coexist with the considered non-listen-before-talk UNB communication system. The throughput performance analysis of the other tested devices shows that the OOK-modulated UNB signal has the least interfering impact, and the Wi-Fi pilot subcarriers are the most vulnerable to UNB interference. However, if a single UNB interferer avoids these subcarriers and employs the OOK-modulation scheme, then wireless coexistence is possible as long as the signal-to-interference ratio of Wi-Fi to UNB is greater than 30dB, given that a drop to 75% of the maximum Wi-Fi throughput is acceptable.