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Three dimensional radiation pattern of the miniature low-VHF antenna showing omni-directional response.
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A low-power, low-frequency, ad-hoc networking paradigm is considered for robust communications among mobile agents in complex non-line-of-sight (NLOS) indoor and urban-type scenarios. Compared with higher frequency the lower portion of the Very High Frequency (VHF) band offers improved penetration and reduced multipath in such scenarios. Low-VHF is...
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Citations
... Moreover, assume a dynamics threshold m to set a power limit for communication activities of this node. This limit determines an upper bound associated with the allowable power consumed by a node due to performance and energy considerations [59]. ...
Traffic dynamics is universally crucial in analyzing and designing almost any network. This article introduces a novel theoretical approach to analyzing network traffic dynamics. This theory’s machinery is based on the notion of traffic divergence, which captures the flow (im)balance of network nodes and links. It features various analytical probes to investigate both spatial and temporal traffic dynamics. In particular, the maximal traffic distribution in a network can be characterized by spatial traffic divergence rate, which reveals the relative difference among node traffic divergence. To illustrate the usefulness, we apply the theory to two network-driven problems: throughput estimation of data center networks and power-optimized communication planning for robot networks, and show the merits of the proposed theory through simulations.
... We assume that the client and each adversary carry a single antenna; the signal st propagates in free space with no reflection or scattering; there is no mutual coupling between the agents' antennas; and the time discretization is coarse enough to ensure that inter-symbol interference is negligible. In addition to free space propagation, the assumptions may also hold at longer wavelengths even when propagating through a complex environment [20]. We express the narrowband wireless channel between the agent i∈[m] and a receiver in the direction θ∈[−π, π) by a known complex scalar gain hi(θ). ...
We study the problem of securely communicating a sequence of information bits with a client in the presence of multiple adversaries at unknown locations in the environment. We assume that the client and the adversaries are located in the far-field region, and all possible directions for each adversary can be expressed as a continuous interval of directions. In such a setting, we develop a periodic transmission strategy, i.e., a sequence of joint beamforming gain and artificial noise pairs, that prevents the adversaries from decreasing their uncertainty on the information sequence by eavesdropping on the transmission. We formulate a series of nonconvex semi-infinite optimization problems to synthesize the transmission strategy. We show that the semi-definite program (SDP) relaxations of these nonconvex problems are exact under an efficiently verifiable sufficient condition. We approximate the SDP relaxations, which are subject to infinitely many constraints, by randomly sampling a finite subset of the constraints and establish the probability with which optimal solutions to the obtained finite SDPs and the semi-infinite SDPs coincide. We demonstrate with numerical simulations that the proposed periodic strategy can ensure the security of communication in scenarios in which all stationary strategies fail to guarantee security.
... 5) The routing tree is constructed by the Routing Protocol in the network layer for Low power and Lossy networks (RPL) and once the routing tree is constructed, each parent node knows the child nodes connected with it [12] [29]. ...
... Recent research on channel characterization of the low Very High Frequency (VHF) band [7]- [8] reveals favorable propagation properties when compared to conventional microwave frequency bands (e.g., Wi-Fi band) especially in Non-Line-of-Sight (NLoS) indoor and outdoor scenarios. Communications experiments have also been carried out with ZigBee radios at 40 MHz using a full-duplex frequency conversion circuit [9]. The results demonstrate that low-VHF operation can provide more reliable and persistent communications in complex scenes, when compared to higher frequency operation, albeit at a reduced bandwidth. ...
... To understand the complexity of this specific scenario, we first carry out path-loss comparison measurements at two different frequency bands with a different combination of antennas (low-VHF vs. Wi-Fi). Unlike other complex environments in [7]- [9], the path-loss difference between the two bands is not as high as other complex environments previously tested where we observed well above 30 dB improvement at low VHF. Furthermore, a significantly higher level of received signal fluctuation at Wi-Fi band is observed. ...
This paper presents an experimental investigation of real-time digital video streaming in physically complex Non-Line-Of-Sight (NLoS) channels using a low-power, low-VHF system integrated on a compact robotic platform. Reliable video streaming in NLoS channels over infrastructure-poor ad-hoc radio networks is challenging due to multipath and shadow fading. In this effort, we focus on exploiting the near-ground low-VHF channel which has been shown to have improved penetration, reduced fading, and lower power requirements (which is critical for autonomous agents with limited power) compared to higher frequencies. Specifically, we develop a compact, low-power, low-VHF radio test-bed enabled by recent advances in efficient miniature antennas and off-the-shelf software-defined radios. Our main goal is to carry out an empirical study in realistic environments of how the improved propagation conditions at low-VHF affect the reliability of video-streaming with constraints stemming from the limited available bandwidth with electrically small low-VHF antennas. We show quantitative performance analysis of video streaming from a robotic platform navigating inside a large occupied building received by a node located outdoors: bit error rate (BER) and channel-induced Peak Signal-to-Noise Ratio (PSNR) degradation. The results show channel-effect-free-like video streaming with the low-VHF system in complex NLoS channels.
... However, it may result in distorted signal waveforms, such as non-monotonous signal damping oscillation [15]- [17], large signal overshoot [18]- [20] and frequency shift [21]. Furthermore, a wearable device should be small [22], light and flexible. However, an air-core coil usually has diffusive magnetic field line distribution, weakening signal strength. ...
This study has designed a micro-power antenna architecture in which a component-based flexible ferromagnetic core is integrated into a coaxial diameter-distributed coil with twisted loop antenna (DDC-TLA). A stereo-crossed distributed winding method is introduced to reduce the paradise capacitance in the DDC-TLA. The magnetic-core components are made of the mixture of Fe/Citrate nanoparticle composite and polydimethylsiloxane solution, they are filled in a flexible rubber substrate to achieve adjustable permeability and wearable flexibility. Based on the above architecture, an optimized algorithm is proposed to reduce power loss while determining the preferable structure of the DDC-TLA and the suitable ingredients of the magnetic core. Finally, simulations and experiments are conducted to confirm its performance in terms of higher quality factor, lower heat loss as well as better signal waveform. OAPA
Autonomous teams of unmanned ground and air vehicles rely on networking and distributed processing to collaborate as they jointly localize, explore, map, and learn in sometimes difficult and adverse conditions. Co-designed intelligent wireless networks are needed for these autonomous mobile agents for applications including disaster response, logistics and transportation, supplementing cellular networks, and agricultural and environmental monitoring. In this paper we describe recent progress on wireless networking and distributed processing for autonomous systems using a low frequency portion of the electromagnetic spectrum, here defined as roughly 25 to 100 MHz with corresponding wavelengths of 3 to 12 meters. This research is motivated by the desire to support autonomous systems operating in dense and cluttered environments by harnessing low frequency propagation, where meters long wavelengths yield significantly reduced scattering and enhanced penetration of obstacles and structures. This differs considerably from higher frequency propagation, requiring different low frequency propagation models than those widely employed for other bands. Progress in use of low frequency for autonomous systems has resulted from combined advances in low frequency propagation modeling, networking, antennas and electromagnetics, geolocation, multi-antenna array distributed beamforming, and mobile collaborative processing. This article describes the breadth and the depth of interaction between areas, leading to new tools and methods, especially in physically complex indoor/outdoor, dense urban, and other challenging scenarios. We bring together key results, models, measurements, and experiments that describe the state of the art for new uses of low frequency spectrum for multi-agent autonomy.
Anytime‐wireless‐everywhere (AWE) aspirations for Internet‐of‐things (IoT) applications to be enabled through current 5G and evolving 6G and beyond ecosystems necessitate the development of innovative electrically small antennas (ESAs). While a variety of ESA systems are reviewed, those realized from the near‐field resonant parasitic (NFRP) antenna paradigm are emphasized. Efficiency, bandwidth, and directivity issues are highlighted. Multifunctional, reconfigurable, passive and active systems that have been achieved are discussed and illustrated; their performance characteristics and advantages described. This overview finalizes by going back to the future and considers enterprising research areas of current and forward‐looking interest.
We consider a mobile multi-agent network in which the agents locate themselves in an environment through imperfect measurements and aim to transmit a message signal to a far-field base station via collaborative beamforming. The agents imperfect measurements yield localization errors that degrade the quality of service at the base station due to unknown phase offsets in the channels. Assuming that the localization errors follow Gaussian distributions, we study the design of a one-shot (non-iterative) beamforming strategy that ensures reliable communication between the agents and the base station despite the localization errors. We formulate a risk-sensitive discrete optimization problem to choose an agent subset for transmission so that the desired signal-to-interference-plus-noise ratio (SINR) at the base station is attained with minimum variance. We show that, when the localization errors have small variances characterized in terms of the carrier frequency, greedy algorithms globally minimize the variance of the received SINR. Moreover, when the localization errors have large variances, we show that the variance of the received SINR can be locally minimized by exploiting the supermodularity of the mean and variance of the received SINR. Simulations demonstrate that the proposed algorithms synthesize beamformers orders of magnitude faster than convex optimization-based approaches while achieving comparable performance with fewer agents.
