RF Nodes Research Articles

Radio Tomography Imaging using Adjacent Criterion Method to determine the Localization Error

Observed that most setups have limitations in the number of RF nodes due to a limited number of measurements. However, it is well known that the main difficulty in radio tomographic imaging attributes to the uncertainties in the receive signal strength (RSS) measurements of transceivers due to multipath effects, especially, when the environment of interest is much cluttered, and requirements on the larger number of nodes for the performance improvements. However, no study has been conducted to solve the inverse problem and improve the quality of the reconstructed image using a reduced sensor model for Radio tomography system localization. This work focuses on the design and development of a Radio tomography system for human localization that will employ a transceiver sensor arrangement to increase the number of measurements, without making any changes to the hardware design as well as the number of pixels in the sensing domain. An image reconstruction technique namely, Adjacent Criterion Method (ACM) was proposed to enhance the image spatial resolution. A number of experiments were used to evaluate the performance of the system. The results showed that the proposed technique improves the spatial resolution and exhibits more accurate tomograms

Precise micromotion compensation of a tilted ion chain

Excess micromotion can be a substantial source of errors in trapped-ion based quantum processors and clocks due to the sensitivity of the internal states of the ion to external fields and motion. This problem can be fixed by compensating background electric fields in order to position ions at the RF node and minimize their driven micromotion. Here we describe techniques for compensating ion chains in scalable surface ion traps. These traps are capable of cancelling stray electric fields with fine spatial resolution in order to compensate multiple closely spaced ions due to their large number of relatively small control electrodes. We demonstrate a technique that compensates an ion chain to better than 5 V/m and within 0.1 degrees of chain rotation.

Enhancing indoor radio tomographic imaging based on minimum RF nodes

Enhancing indoor radio tomographic imaging based on minimum RF nodes

A compact TM03 mode penta‐polarization agile MSA for interference mitigation in 5G ultra‐dense point to point environment

Signal interference in the recent 5G ultra-dense environment is becoming severe due to the co-existence of large RF nodes operating in the constrained spectrum. In this article, a polarization agile approach for the designing of an RF system is studied to mitigate interference issues besides the communication and signal processing approach. A compact single-fed single layer penta-polarization agile higher-order microstrip patch is analyzed probably for the first time in the literature. The proposed antenna possesses a very low profile of less than 0.01 λ (λ free-space wavelength). Reconfigurable orthogonal feeding with switches is connected with the horizontal and vertical patch edges. Subsequently, these are excited separately and simultaneously using switchable PIN diodes and appropriate bias networks to realize horizontal, vertical, and 45° slant polarization states. Successively, diagonal patch corners are truncated to initiate right and left-hand circular polarizations. Slots are etched on specific orientation of currents on the patch surface to improve side-lobe levels. A prototype is analyzed, simulated, and fabricated at TM03 mode and operating at 5.8 GHz band with penta-polarization agility. A consistent 11 dBi realized broadside gain is measured covering the 10 dB reflection loss and 3 dB axial ratio bandwidth in both the principal planes.

Never Use Labels: Signal Strength-Based Bayesian Device-Free Localization in Changing Environments

Device-free localization (DFL) methods use measured changes in the received signal strength (RSS) between many pairs of RF nodes to provide location estimates of a person inside the wireless network. Fundamental challenges for RSS DFL methods include having a model of RSS measurements as a function of a person's location, and maintaining an accurate model as the environment changes over time. Current methods rely on either labeled empty-area calibration or labeled fingerprints with a person at each location. Both need to be frequently recalibrated or retrained to stay current with changing environments. Other DFL methods only localize people in motion. In this paper, we address these challenges by, first, introducing a new mixture model for link RSS as a function of a person's location, and second, providing the framework to update model parameters without ever being provided labeled data from either empty-area or known-location classes. We develop two new Bayesian localization methods based on our mixture model and experimentally validate our system at three test sites with seven days of measurements. We demonstrate that our methods localize a person with non-degrading performance in changing environments, and, in addition, reduce localization error by $\mathbf {11-51}$ 11 - 51 percent compared to other DFL methods.

Game-Theoretic Spectrum Trading in RF Relay-Assisted Free-Space Optical Communications

This work proposes a novel hybrid RF/FSO system based on a game theoretic spectrum trading process. It is assumed that no RF spectrum is preallocated to the FSO link and only when the link availability is severely impaired by the infrequent adverse weather conditions, i.e. fog, etc., the source can borrow a portion of licensed RF spectrum from one of the surrounding RF nodes. Using the leased spectrum, the source establishes a dual-hop RF/FSO hybrid link to maintain its throughout to the destination. The proposed system is considered to be both spectrum- and power-efficient. A market-equilibrium-based pricing process is proposed for the spectrum trading between the source and RF nodes. Through extensive performance analysis, it is demonstrated that the proposed scheme can significantly improve the average capacity of the system, especially when the surrounding RF nodes are with low traffic loads. In addition, the system benefits from involving more RF nodes into the spectrum trading process by means of diversity, particularly when the surrounding RF nodes have high probability of being in heavy traffic loads. Furthermore, the application of the proposed system in a realistic scenario is presented based on the weather statistics in the city of Edinburgh, UK. It is demonstrated that the proposed system can substantially enhance the link availability towards the carrier-class requirement.

Performance analysis of mixed RF/FSO cooperative systems with wireless power transfer

This paper investigates the performance of mixed radio frequency-free space optical (RF/FSO) systems where the battery-limited RF nodes can harvest the required energy for information transmission. The analysis takes into account the Rayleigh fading caused by signal propagation in the RF link and Gamma–Gamma atmospheric turbulence with the effect of pointing errors in the FSO link. Two different scenarios have been considered; in the first scenario, the source uses an RF random power provided by a relay for information transmission in a dual-hop cooperative configuration; whereas in the second scenario there is also a direct RF link between the source and destination. We provide closed-form expressions for the outage probability, bit error probability and ergodic capacity for the dual-hop amplify-and-forward relaying system that performs energy harvesting. Asymptotic expressions are also provided for the high SNR regime where the diversity order of the system is calculated. The accuracy of the proposed analytical formulations is proved by means of a set of numerical results. For instance, for the second scenario, fixing the average electrical SNR of the FSO link, we show that the link diversity order is equal to one. However, when fixing the average SNR of the RF links, the link diversity order equals zero, resulting in an error floor due to the dominant effect of the RF link.

A Miller N-Path Bandpass Filter with Improved Second Harmonic Rejection

While a Miller N-path filter is capable of channel selection at RF, it cannot sufficiently reject harmonic responses before going through the baseband circuitry. To suppress the second harmonic at the LNA output, this paper adds a feedback path to the conventional Miller N-path filter. The added feedback path distinguishes between the first and the second harmonic and exhibits a relatively large loop gain for the latter. As a result, the design suppresses the second harmonic at RF nodes. This is achieved without losing the desired characteristics of a conventional Miller N-path at the fundamental harmonic. The design example is a 500-MHz four-path filter simulated with the 90 nm CMOS. It achieves 13 dB gain, 2.6 dB noise figure, and $$+$$ 9.6 dBm out-of-band IIP3 at 50 MHz offset from the center frequency and burns 16 mW of power.

Analysis of an Enhanced-Q N-Path Filter with Improved Even-Order Harmonic Rejection

Based on a feedback system, an N-path bandpass filter robust to even-order harmonic mixing (BPF-REHM) is presented. BPF-REHM consists of a conventional differential N-path filter around a gain stage. Despite assuming a single-ended antenna, this work aims at partial rejection of even-order harmonics before the signal travels through the baseband circuitry. Linear periodically time-varying analysis of the new filter is presented. Mathematical derivations verify an enhanced-Q filtering behavior in addition to even-order harmonic rejection at RF nodes. Drawback of BPF-REHM, i.e., input impedance mismatch, is addressed by proposing a two-stage LNA. The second stage of the new LNA, which is the BPF-REHM, suppresses even-order harmonic blockers while the first stage matches the input to the source and provides enough gain to accomplish an acceptable overall noise performance. The design example is a 500?MHz four-path filter simulated with the 90?nm CMOS. It achieves >22?dB even harmonic rejection with an enhanced-Q filtering characteristic thanks to the new technique. Besides, this design achieves 21?dB gain, 2?dB NF, and $$+$$+2.5?dBm out-of-band IIP3 at 50?MHz offset while consuming 8.3?mW of power.

The BLIXER, Integrated Balun-LNA-Mixer for ZigBee Application

Objectives: The main objective of this paper is to design a Blixer using noise-cancelling technique and balun –LNA-Mixer for better performance. Methods: As studied in literature of mixers, it shows they have less bandwidth disadvantage. This paper is concentrated to realize a wide bandwidth mixer by keeping the real part of the impedance of all RF nodes low, and using this mixer there is no capacitive loading problem. Findings: By avoiding use of inductors, the on chip size of circuit will be reduced and also the bandwidth extension requirement is fulfilled. This gives less DC-voltage drop after IF filtering. The design is implemented and simulated using Advanced Design System tool in CMOS 0.18um technology. The noise figure of the final BLIXER is obtained as 0.6dB and that of LNA is less than 2dB. This results are one of the best seen for a BLIXER. Applications: This design is well suited for wideband ZigBee receiver in wireless communication systems.

Channel-aware routing and priority-aware multi-channel scheduling for WSN-based smart grid applications

Wireless Sensor Networks (WSNs) are one of the most promising solutions for smart grid applications due to advantages, such as their low-cost, different functionalities, and successful adoption to smart grid environments. However, providing quality of service (QoS) requirements of smart grid applications with WSNs is difficult because of the power constraints of sensor nodes and harsh smart grid channel conditions, such as RF interference, noise, multi-path fading and node contentions. To address these communication challenges, in this paper link-quality-aware routing algorithm (LQ-CMST) as well as the priority and channel-aware multi-channel (PCA-MC) scheduling algorithm have been proposed for smart grid applications. Furthermore, the effect of different modulation and encoding schemes on the performance of the proposed algorithms has been evaluated under harsh smart grid channel conditions. Comparative performance evaluations through extensive simulations show that the proposed algorithms significantly reduce communication delay and the choice of encoding and modulation schemes is critical to meet the requirements of envisioned smart grid applications.

3D‐printed spherical dipole antenna integrated on small RF node

New three-dimensional (3D) printing techniques enable the integration of an antenna directly onto the package of a small wireless sensor node. This volume-filling approach ensures near-optimal bandwidth performance of the small antenna, increasing a system's battery life, data rate or range. Simulated results show that the fabricated spherical antenna's bandwidth-efficiency product is more than half of the fundamental limit and radiation pattern measurements exhibit a dipole pattern with −0.7 dBi gain.

A Programmable 0.7–2.7 GHz Direct $\Delta \Sigma$ Receiver in 40 nm CMOS

This paper presents a wideband direct ΔΣ receiver for the 0.7-2.7 GHz frequency range. The architecture embeds a wideband direct-conversion RF front-end into a continuous-time feedback ΔΣ modulator, which initiates the analog-to-digital conversion of the selected channel already at the RF nodes. A feedback-type architecture enables simultaneous filtering of nearby interfering signals. The inductorless 40 nm CMOS receiver supports programmable ΔΣ modulator coefficients and RF channel bandwidths up to 20 MHz. The receiver consumes 90 mW from a 1.1 V supply, and it provides a peak SNDR of 46 dB, NF of 5.9-8.8 dB, and an IIP3 of -2 dBm.

Formula omitted]-WiNoC: Exploring scalable wireless on-chip micronetworks for heterogeneous embedded many-core SoCs

Modern embedded SoC design uses a rapidly increasing number of processing units for ubiquitous computing, forming the so-called embedded many-core SoCs (McSoC). Such McSoC devices allow superior performance gains while side-stepping the power and heat dissipation limitations of clock frequency scaling. The main advantage lies in the exploitation of parallelism, distributively and massively. Consequently, the on-chip communication fabric becomes the performance determinant. To bridge the widening gap between computation requirements and communication efficiency faced by gigascale McSoCs in the upcoming billion-transistor era, a new on-chip communication system, dubbed Wireless Network-on-Chip (WiNoC), has been proposed by using the recently developed RF interconnect technology. With the high data-rate, low power and ultra-short range interconnection provided by UWB technology, the WiNoC design paradigm calls for effective solutions to overhaul the on-chip communication infrastructure of gigascale McSoCs.In this work, an irregular and reconfigurable WiNoC platform is proposed to tackle ever increasing complexity, density and heterogeneity challenges. A flexible RF infrastructure is established where RF nodes are properly distributed and IP cores are clustered. Consequently, a performance-cost effective topology is formed. A region-aided routing scheme is further deigned and implemented to realize loop-free, minimum path cost and high scalability for irregular WiNoC infrastructure. To implement the data transmission protocol, the RF microarchitecture of WiNoC is developed where the RF nodes are designed to fulfill the functions of distributed table routing, multi-channel arbitration, virtual output queuing, and distributed flow control. Our simulation studies based on synthetic traffics demonstrate the network efficiency and scalability of WiNoC.

Design of a high gain and highly linear common-gate UWB mixer in K-band

In this paper, in order to design a K-band common-gate Gilbert-cell mixer via a 0.18 μm CMOS technology, the ?-Network and post-distortion cancellation (PDC) techniques are implemented simultaneously, resulting in the improvement of gain, bandwidth, noise figure and linearity. Also, a new method for implementing the ?-Network, using the parasitic capacitances between RF and LO stage nodes, is proposed which improves the mixer performance and makes the mixer design possible at high frequencies. It is shown that the ?-Network enhances the gain and bandwidth by generating complex poles in system frequency response without the need for extra power consumption. The suitable location of these poles, which gives rise to high gain and high bandwidth, is discussed and determined by MATLAB simulation. Results of simulation illustrate 3.36 dB improvement in power conversion gain and 2 dB reduction in noise figure at the same power consumption with LO power of ?1 dBm in comparison with the case when PDC technique is used only. Compared to conventional mixer, it improves the IIP3 by 6 dB. Also, the power consumption of the mixer together with the designed bias circuit is 9.68 mW at 1.8 V.

The Blixer, a Wideband Balun-LNA-I/Q-Mixer Topology

This paper proposes to merge an I/Q current-commutating mixer with a noise-canceling balun-LNA. To realize a high bandwidth, the real part of the impedance of all RF nodes is kept low, and the voltage gain is not created at RF but in baseband where capacitive loading is no problem. Thus a high RF bandwidth is achieved without using inductors for bandwidth extension. By using an I/Q mixer with 25% duty-cycle LO waveform the output IF currents have also 25% duty-cycle, causing 2 times smaller DC-voltage drop after IF filtering. This allows for a 2 times increase in the impedance level of the IF filter, rendering more voltage gain for the same supply headroom. The implemented balun-LNA-I/Q-mixer topology achieves > 18 dB conversion gain, a flat noise figure < 5.5 dB from 500 MHz to 7 GHz, IIP2 = +20 dBm and IIP3 = -3 dBm. The core circuit consumes only 16 mW from a 1.2 V supply voltage and occupies less than 0.01 mm2 in 65 nm CMOS.

SD-MAC: Design and Synthesis of a Hardware-Efficient Collision-Free QoS-Aware MAC Protocol for Wireless Network-on-Chip

To bridge the widening gap between computation requirements and communication efficiency faced by gigascale heterogeneous SoCs in the upcoming ubiquitous era, a new on-chip communication system, dubbed Wireless Network-on-Chip (WNoC), is introduced by using the recently developed CMOS UWB wireless interconnection technology. In this paper, a synchronous and distributed medium access control (SD-MAC) protocol is designed and implemented. Tailored for WNoC, SD-MAC employs a binary countdown approach to resolve channel contention between RF nodes. The receiver_select_sender mechanism and hidden terminal elimination scheme are proposed to increase the throughput and channel utilization of the system. Our simulation study shows the promising performance of SD-MAC in terms of throughput, latency, and network utilization. We further propose a QoS-aware SD-MAC to ensure the serviceability of the entire system and to improve the bandwidth utilization. As a major component of simple and compact RF node design, a MAC unit implements the proposed SD-MAC that guarantees correct operation of synchronized frames while keeping overhead low. The synthesis results demonstrate several attractive features such as high speed, low power consumption, nice scalability and low area cost.

Troubleshooting wireless mesh networks

Effective network troubleshooting is critical for maintaining efficient and reliable network operation. Troubleshooting is especially challenging in multi-hop wireless networks because the behavior of such networks depends on complicated interactions between many factors such as RF noise, signal propagation, node interference, and traffic flows. In this paper we propose a new direction for research on fault diagnosis in wireless mesh networks. Specifically, we present a diagnostic system that employs trace-driven simulations to detect faults and perform root cause analysis. We apply this approach to diagnose performance problems caused by packet dropping, link congestion, external noise, and MAC misbehavior. In a 25 node mesh network, we are able to diagnose over 10 simultaneous faults of multiple types with more than 80% coverage.

Troubleshooting multihop wireless networks

Effective network troubleshooting is critical for maintaining efficient and reliable network operation. Troubleshooting is especially challenging in multihop wireless networks because the behavior of such networks depends on complicated interactions between many unpredictable factors such as RF noise, signal propagation, node interference, and traffic flows. In this paper we propose a new direction for research on fault diagnosis in wireless networks. Specifically, we present a diagnostic system that employs trace-driven simulations to detect faults and perform root cause analysis. We apply this approach to diagnose performance problems caused by packet dropping, link congestion, external noise, and MAC misbehavior. In a 25 node multihop wireless network, we are able to diagnose over 10 simultaneous faults of multiple types with more than 80% coverage. Our framework is general enough for a wide variety of wireless and wired networks.

An analysis of flicker noise rejection in low-power and low-voltage CMOS mixers

The sensitivity of RF CMOS receivers using a direct conversion or a low-IF architecture is strongly affected by flicker noise. This paper gives theoretical guidelines to predict the flicker noise in Gilbert-cell mixers. The conversion gain, the equivalent input and output noise, and the effect of the pole at the single internal RF node are discussed. For the first time, results which are valid in all modes of operation are given. Such complete results are required for some ultra low-power and low-voltage applications, since the transistors might be operated in moderate or even weak inversion region. The theoretical gains are found to remain within a 2-dB margin with respect to the measurements of a UHF downconverter built in a 0.5 /spl mu/m process, for a large range of bias conditions and local oscillator swing.