arXiv subjects

Yaowen Zhang

Publications and source records attributed to Yaowen Zhang.

23 records · Page 2Linked to original sources

arXiv2024

Broadband microwave waveform generation with programmable chirp shapes via recirculating phase-modulated optical fiber loop controlled by low-speed electronics

Broadband microwave waveforms with programmable chirp shapes are captivating in numerous practical applications. Compared with electronic technology, photonic-assisted solutions exhibit excellent performance in bandwidth and flexibility, but still suffer from complex architecture and requirement of high-speed electronics. Besides, rapid manipulation of chirp shape is still a challenge in the scientific community. In this paper, we propose and demonstrate a novel concept for generating broadband microwave waveforms with programmable chirp shapes. This concept is realized on a simple fiber-optic platform involving a continuous-wave laser source, a recirculating phase-modulated optical fiber loop, and low-speed electronics with a sampling rate at the level of MS/s. Based on this method, chirped microwave waveforms with a bandwidth up to tens of GHz can be generated, where the chirp shape is identical to the low-frequency driving waveform of the recirculating phase-modulated optical fiber loop. In addition, all the parameters of the generated chirped microwave waveforms can be easily reconfigured in real time, including the bandwidth, the central frequency, and the temporal duration. In the experiment, broadband microwave waveforms with customized chirp shapes are generated, where the center frequency and bandwidth tuning ranges exceed 21 GHz, the temporal duration is tuned in the range of 9 ns to 180 ns, and the coherent time of the generated microwave waveform is larger than 100 μs. This simple fiber-optic platform paves a way to generate broadband microwave waveforms with user-definable chirp shapes, which can find applications in broadband radar systems, electronic warfare and wireless communications.

physics.optics↗

arXiv2022

Configuring Intelligent Reflecting Surface with Performance Guarantees: Blind Beamforming

This work gives a blind beamforming strategy for intelligent reflecting surface (IRS), aiming to boost the received signal-to-noise ratio (SNR) by coordinating phase shifts across reflective elements in the absence of channel information. While the existing methods of IRS beamforming typically first estimate channels and then optimize phase shifts, we propose a conditional sample mean based statistical approach that explores the wireless environment via random sampling without performing any channel estimation. Remarkably, the new method just requires a polynomial number of random samples to yield an SNR boost that is quadratic in the number of reflective elements, whereas the standard random-max sampling algorithm can only achieve a linear boost under the same condition. Moreover, we gain additional insight into blind beamforming by interpreting it as a least squares problem. Field tests demonstrate the significant advantages of the proposed blind beamforming algorithm over the benchmark algorithms in enhancing wireless transmission.

cs.IT↗

arXiv2021

Configuring Intelligent Reflecting Surface with Performance Guarantees: Optimal Beamforming

This work proposes linear time strategies to optimally configure the phase shifts for the reflective elements of an intelligent reflecting surface (IRS). Specifically, we show that the binary phase beamforming can be optimally solved in linear time to maximize the received signal-to-noise ratio (SNR). For the general K-ary phase beamforming, we develop a linear time approximation algorithm that guarantees performance within a constant fraction (1+\cos(π/K))/2 of the global optimum, e.g., it can attain over 85% of the optimal performance for the quadrature beamforming with K=4. According to the numerical results, the proposed approximation algorithm for discrete IRS beamforming outperforms the existing algorithms significantly in boosting the received SNR.

cs.IT↗

arXiv2021

On the Foundation of Sparse Sensing (Part I): Necessary and Sufficient Sampling Theory and Robust Remaindering Problem

In the first part of the series papers, we set out to answer the following question: given specific restrictions on a set of samplers, what kind of signal can be uniquely represented by the corresponding samples attained, as the foundation of sparse sensing. It is different from compressed sensing, which exploits the sparse representation of a signal to reduce sample complexity (compressed sampling or acquisition). We use sparse sensing to denote a board concept of methods whose main focus is to improve the efficiency and cost of sampling implementation itself. The "sparse" here is referred to sampling at a low temporal or spatial rate (sparsity constrained sampling or acquisition), which in practice models cheaper hardware such as lower power, less memory and throughput. We take frequency and direction of arrival (DoA) estimation as concrete examples and give the necessary and sufficient requirements of the sampling strategy. Interestingly, we prove that these problems can be reduced to some (multiple) remainder model. As a straightforward corollary, we supplement and complete the theory of co-prime sampling, which receives considerable attention over last decade. On the other hand, we advance the understanding of the robust multiple remainder problem, which models the case when sampling with noise. A sharpened tradeoff between the parameter dynamic range and the error bound is derived. We prove that, for N-frequency estimation in either complex or real waveforms, once the least common multiple (lcm) of the sampling rates selected is sufficiently large, one may approach an error tolerance bound independent of N.

cs.IT↗

arXiv2021

Evaluation of blood coagulation by optical vortex tracking

We investigated a new optical approach for the detection of the coagulation dynamic process by means of the information on the optical vortex. In our study, laser speckle was captured using a high-speed CMOS camera, and the statistical information of the optical vortex characterized the change in coagulation properties with time. Similar to the scattering particles, the motion of the optical vortex is restricted during coagulation, as a result, the whole process of coagulation can be detected by calculating the mean square displacement(MSD) of the optical vortex. The results demonstrate a close correlation between coagulation parameters measured using the optical vortex method and thrombelastography(TEG), creating a powerful opportunity for self-testing and real-time detection of coagulation.

physics.med-ph↗