Ambient backscatter communication enables passive sensors to convey sensing data on ambient RF signals in the air at ultralow power consumption. To extract data bits from such signals, threshold-based decoding has generally been considered, but suffers against Wi-Fi signals due to severe fluctuation of OFDM signals. In this paper, we propose a pattern-matching-based decoding algorithm for Wi-Fi backscatter communications. The key idea is the identification of unique patterns of signal samples that arise from the inevitable smoothing of Wi-Fi signals to filter out noisy fluctuation. We provide the mathematical basis of obtaining the pattern of smoothed signal samples as the slope of a line expressed in a closed-form equation. Then, the new decoding algorithm was designed to identify the pattern of received signal samples as a slope rather than classifying their amplitude levels. Thus, it is more robust against signal fluctuation and does not need tricky threshold configuration. Moreover, for even higher reliability, the pattern was identified for a pair of adjacent bits, and the algorithm decodes a bit pair at a time rather than a single bit. We demonstrate via testbed experiments that the proposed algorithm significantly outperforms conventional threshold-based decoding variants in terms of bit error rate for various distances and data rates.

To meet the increasing demands for remote sensing, a number of radar systems using Linear Frequency Modulation (LFM) waveforms have been deployed, causing the problem of depleting frequency resources. To address this problem, several researchers have proposed the Spectrum Shared Radar System (SSRS) in which multiple radars share the same frequency band to transmit and receive their own signals. To mitigate the interferences caused by the signal transmission by other radars, SSRS employs orthogonal waveforms that inherit the orthogonality of the waveforms from orthogonal codes. However, the inherited orthogonality of the codes is significantly reduced when incorporating LFM waveforms with the codes. To solve this problem, in this paper, we propose a novel but simple scheme for generating a set of optimized coded LFM waveforms via new optimization framework. In the optimization framework, we minimize the weighted sum of autocorrelation sidelobe peaks ($ASP$) and cross-correlation peaks ($CP$) of the coded LFM waveforms to maximize the orthogonality of the waveforms. Through computer simulations, we show that the waveforms generated by the proposed scheme outperform the waveforms created by previous proposals in terms of $ASP$ and $CP$.

Weather Radar Networked System (WRNS) is composed of multiple weather radars that transmit a radio signal and receive an echo signal reflected by weather targets. In the current form of WRNS, each radar exploits a different non-orthogonal frequency band, which leads to inefficiency in frequency usage. To tackle this issue, we propose a novel frequency-shared WRNS and investigate its feasibility via actual experiments. The challenges in a frequency-shared WRNS lie in mitigating 1) interference from other radars (inter-site interference) and 2) interference from nearby scatterers (intra-site interference). To mitigate inter-site interference, we modulate a waveform with an orthogonal code and conduct matched filtering. To mitigate intra-site interference, we adopt an interference-aware sidelobe suppression algorithm and integrate the algorithm with a novel algorithm having an adaptive configuration. We have implemented a prototype of the proposed WRNS using X-band radars and a MATLABbased signal processing module. An experimental study using this prototype shows that estimation errors are less than those required by a commercial weather radar (WSR-88D) when ten radars operate with in the same frequency band. To the best of our knowledge, this paper is the first to implement a prototype for frequency-shared WRNS and explore the feasibility of frequency sharing among weather radars via experimentation with real weather radars.

Reliable safety message dissemination is a fundamental primitive for constructing intersection safety systems. Normally, the dissemination is based on vehicular communications, of which the de-facto standard is Dedicated Short Range Communications (DSRC). However, due to high frequency operations, a DSRC signal is seriously attenuated when being propagated in Non Line-Of-Sight (NLOS) conditions. Previous schemes leveraged the use of centralized infrastructures or relay vehicles enabling a safety message to bypass large obstacles. However, implementing the infrastructures in all intersections would be very costly; one may not find proper relay vehicles in low density, and frequent rebroadcasts cause serious network congestion in high density. To address this challenge, we propose a novel scheme that exploits excellent propagation characteristics of a TV White Space (TVWS) band (in addition to a DSRC band) for reliable dissemination in NLOS intersections. To ensure reliable dissemination throughout a broad range of densities without infrastructures, our scheme employs two innovative mechanisms: a collaborative procedure and a Dynamic optimal Configuration (DoC). To our knowledge, this is the first that simultaneously satisfies two vital demands for intersection safety system: 1) lacking infrastructures and 2) working well in all densities. Simulation studies show that the proposed scheme outperforms previous infrastructure-based schemes.

In wireless networks, broadcasting is a fundamental communication primitive for network management and information sharing. However, in multichannel networks, broadcast efficiency is very poor as devices are distributed across various channels. Thus, a sender tries all channels to broadcast a single message, causing large overhead. In this paper, we propose a novel, drastically different scheme for efficient broadcast in multichannel networks. Our scheme leverages an overlapped band of adjacent channels, which is the frequency range that partially overlapped channels share within their channel boundaries. Specifically, a sender advertises a rendezvous channel through the overlapped band of adjacent channels; message sharing is done on the rendezvous channel. Our scheme employs signaling via overlapped band (SOB), which defines a new signal processing mechanism for communication via the overlapped band. SOB is integrated with the following Multiple Access Control (MAC) layer mechanisms: 1) Reserve idle spectrum fragment to reduce waiting time, 2) multisender agreement on rendezvous channel to support multisender broadcasts, and 3) reinforce switch notification to reduce the residing time at a wrong channel. Our scheme can also be integrated with two remarkably simple but efficient mechanisms for improving the packet delivery ratio and reducing delay in a multiple contention domain. We implemented our scheme on the SORA software radio platform. Experimental results validated communication through the overlapped band. Intensive simulation studies showed that our scheme dramatically outperformed a previous approach.

This article investigates access control in cyber-physical systems, making a decision to permit or deny a user’s request for access operations on a system. Access operations in cyber-physical system result in diverse impacts on human beings and are perceived with different importance. Say, controlling a nuclear plant and reading data from it must be given different priorities. Access requests for these operations must be authorized distinctively with different protection levels, named prioritization issue. Existing solutions, however, do not either satisfy the prioritization requirement efficiently or work well in cyber-physical system environment. To solve the prioritization problem, we propose a new access control mechanism, named multi-factor access control, that employs a multi-factoring technique. In multi-factor access control, a user is granted multiple secret keys (i.e. factors) from independent authorities. When accessing a highly prioritized object, the user must present more than two factors, each of which is issued from different authorities. This decreases the probability that it presents false evidence of qualification, increasing protection level. To demonstrate the feasibility, we implement the proposed scheme and apply it to our smart building testbed. Throughout real-world experiments, we evaluate the performance of computation cost and illustrate automated, prioritized smart building controls.