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

Simple wideband extended aperture antenna-inspired circular patch for V-band communication systems

This article presents the design and realization of compact, geometrically simple, wideband and high gain antenna for V-band communication systems. The antenna is designed by using a conventional circular patch, which is further modified by using another fractal circular patch. Furthermore, the addition of three elliptical shaped patches significantly increases the bandwidth of the antenna. Afterwards, a circular slot is etched from the radiator to improve the radiation pattern of the antenna. The proposed structure comprises of an overall substrate size of 13 × 12 × 0.508 mm3 and designed using Duroid 5880 having very low loss tangent of 0.0009. To verify the presented results, the antenna prototype is fabricated and tested. The comparison among simulated and measured results shows a strong performance. Moreover, the comparison with state of the artwork shows that the antenna offers compact size, wide bandwidth, high gain, and good radiation efficiency. Thus, it makes the proposed antenna a potential candidate for the V-band communication systems.The authors sincerely appreciate the funding from Universidad Carlos III de Madrid and the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant 801538. Also, this work is partially supported by Antenna and Wireless Propagation Group (AWPG); https://sites.google.com/view/awpgrp, and from the Researchers Supporting Project number (RSP-2021/58), King Saud University, Riyadh, Saudi Arabia

Novel Multi-User Chirp Signaling Schemes for Future Aviation Communication Applications

Many wireless communication systems will need to accommodate a larger number of users in the future. One application in particular in which this is critical is low data rate, long range communication links with very large numbers of nodes, such as the internet of things (IoT), possibly the internet of flying things (IoFT), etc. These systems demand advanced multi-access techniques with minimal multiple access interference (MAI). They should also be robust to multiple impairments, including multipath channel distortions, Doppler spreading, and interference. Chirp waveforms are one type of waveform set that can satisfy future system demands in the presence of these impairments. When the constant amplitude variety of chirp is used, this exhibits a desirable very low peak to average power ratio (PAPR). The ridge-shaped ambiguity function of chirp signals can also be useful for radar and channel modeling (sounding) applications. Hence chirps are promising candidates for many such applications. Chirps are specified in the IEEE 802.15.4a standard as chirp spread spectrum (CSS). Another growing application area requiring advanced communications is aviation. In particular, unmanned aircraft systems (UAS), also known as unmanned aerial vehicles (UAVs), and “drones,” will in the future operate within airspace along with commercial, cargo, and other piloted aircraft. The command and control (C2), or control and non-payload communications (CNPC) link must provide highly reliable safety critical information for the control of the UAV both in terrestrial-based line of sight conditions and in satellite communication links. Chirp signaling features make chirp signal sets good candidates to meet CNPC link requirements. In this dissertation, we investigate multi-user chirp signaling for future aviation communication and channel sensing systems. We describe the basics of chirp signaling, chirp sounding, and investigate via mathematical analysis, computer simulations, and some experiments, the effects of aviation channel-induced non-idealities such as Doppler and asynchronism on the chirp signaling schemes. We also describe a hybrid design where the system is not only a communication entity but also does channel estimation (sounding). We describe methods to increase spectral efficiency and how to avoid multiple access interference among users (and intersymbol interference for a given user). We also conducted experiments on chirp channel sounding using a small drone and software defined radios, and provide some channel characterization results. The majority of this work, and our major contributions, pertain to detailed evaluation of performance of multi-user chirp spread spectrum systems under a variety of conditions. We find, analytically, new expressions for bit error rate performance of binary coherent and noncoherent chirp spread spectrum signals, and we compare and validate numerical and analytical results with simulations. These error probability expressions are general, and can be used for any multi-user chirp signaling set. We also design more practical sets of chirp signals that out-perform existing chirp signal sets when synchronization is imperfect, a condition we term quasi-synchronous. These new practical chirp designs employ nonlinear trajectories in the time-frequency plane. Our new chirp designs also outperform existing schemes in the presence of Doppler shifts. We provide examples of air to ground link performance with empirical channel models to illustrate the superior performance of our proposed designs

High-resolution multipath channel parameter estimation using wavelet analysis

This thesis explores the novel use of wavelet analysis as a high-resolution digital signal processing algorithm for multipath channel parameter estimation. The results obtained from this research indicate that this wavelet-based digital signal processing algorithm overcomes the resolution limitation in conventional high-resolution algorithm. This may provide a more cost-effective means of implementing channel sounding equipments for very high-resolution measurements