Chirp Spread Spectrum Signaling for Future Air-Ground Communications

In this paper, we investigate the use of chirp spread spectrum signaling over air-ground channels. This includes evaluation of not only the traditional linear chirp, but also of a new chirp signal format we have devised for multiple access applications. This new format is more practical than prior multi-user chirp systems in the literature, because we allow for imperfect synchronism. Specifically we evaluate multi-user chirp signaling over air-ground channels in a quasi-synchronous condition. The air-ground channels we employ are models based upon an extensive NASA measurement campaign. We show that our new signaling scheme outperforms the classic linear chirp in these air-ground settings.Comment: This paper published in IEEE Milcom conference November 2019. arXiv admin note: text overlap with arXiv:1909.0988

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

HIGH RESOLUTION TIME-OF-ARRIVAL RANGING OF WIRELESS SENSOR NODES IN NON-HOMOGENOUS ENVIRONMENTS

Wireless Sensor Networks (WSN) have emerging applications in homogeneous environments such as free space. In addition, WSNs are finding new applications in non-homogeneous (NH) media. All referred applications entail location information of measured data or observed event. Localization in WSNs is considered as the leading remedy, which refers to the procedure of obtaining the sensor nodes relative location utilizing range measurements. Localization via Time-of-Arrival (ToA) estimation has received considerable attention because of high precision and low complexity implementation, however, the traditional techniques are not feasible in NH media due to frequency dispersion of transmitted ranging waveform. In this work, a novel and effective ToA-based ranging technique for localization in NH media consisting of frequency dispersive sub-media is proposed. First challenges of ToA estimation in NH media regarding frequency dispersion is investigated. Here, a novel technique which improves ToA estimation resolution at fixed bandwidth via maximum rising level detector (MRLD) technique is discussed. The MRLD receiver utilizes oversampling and multiple correlation paths to evaluate with high resolution the path corresponding to the maximum rising level of matched filters output. In order to achieve higher resolution, a novel and effective ToA estimation is introduced that incorporates orthogonal frequency division multiple access (OFDMA) subcarriers. In the proposed technique, pre-allocated orthogonal subcarriers are utilized to construct a ranging waveform which enables high performance ToA estimation in dispersive NH media in frequency domain. Here, we show that each frequency component of propagated waveform is received with different time delay and phase which dramatically increases the number of unknowns in the received signal system model. Then, we propose a novel idea based on frequency domain analysis of the transmitted OFDMA subcarriers to reduce the number of unknowns exploiting feasible approximations. Finally, the proposed ToA technique is applied multiple times at different carrier frequencies to create a system of linear equations which can be solved to compute the available sub-mediums thickness and range. Simulation results prove that the proposed technique offers high resolution range measurements given simulated ToA estimation error at different signal to noise ratio regimes in NH media

Measurement, Modeling, and OFDM Synchronization for the Wideband Mobile-to-Mobile Channel

Wideband measurements of the mobile-to-mobile channel, especially of the harshest channels, are necessary for proper design and certification testing of mobile-to-mobile communications systems. A complete measurement implies that the Doppler and delay characteristics are measured jointly. However, such measurements have not previously been published. The main objective of the proposed research is to develop channel models for specific scenarios from data obtained in a wideband mobile-to-mobile measurement campaign in the 5.9 GHz frequency band. For this purpose we developed a channel sounding system including a novel combined waveform. In order to quantify and qualify either the recorded channel or the proposed generated channel, we developed a simulation test-bed that includes all the characteristics of the proposed digital short range communications (DSRC) standard. The resulting channel models needed to comply with the specifications required by hardware channel emulators or software channel simulators. From the obtained models, we selected one to be included in the IEEE 802.11p standard certification test. To further aid in the development of software radio based receivers, we also developed an orthogonal frequency division multiplexing (OFDM) synchronization algorithm to analyze and compensate synchronization errors produced by inaccessible system clocks.Ph.D.Committee Chair: Ingram, Mary Ann; Committee Member: Lanterman, Aaron; Committee Member: Li, Ye; Committee Member: Pratt, Thomas G.; Committee Member: Rogers, Peter H

Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic Channels

The objective of this study is to evaluate Grassmannian constellations combined with a spread spectrum multiple access scheme for underwater acoustic mobile multiple access communication systems. These communication systems enable the coordination of a fleet of Autonomous Underwater Vehicles (AUVs) from a surface or bottom control unit, e.g., a boat. Due to its robustness against phase rotation, the demodulator of Grassmannian constellations uses non-coherent detection, and the main advantage of such modulation lies in the spectrum efficiency gain with respect to conventional differential modulation. The communication system under study in this paper consists of (i), at the transmitter side, a Grassmannian modulation used in an orthogonal spread spectrum multiple access scheme called Multiuser Hyperbolic Frequency Modulation (MU-HFM) and (ii), at the receiver side, a non-coherent array decoder. The modulation and demodulation are presented as well as the considered spreading sequences. Finally, performances of the proposed transmission scheme are evaluated over replayed underwater acoustic channel responses collected at sea by a multi-sensor acoustic acquisition system.Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic ChannelspublishedVersio