Low-power Wireless Systems Research Articles

Lure: A simulator for networks of batteryless intermittent nodes

The emerging paradigm of batteryless intermittent sensor networks (BISNs) presents new challenges for researchers of low-power wireless systems and protocols. The nature of these challenges exacerbates the difficulty of evaluating networks of physical sensor nodes, making simulation an even more important component in evaluating performance metrics, such as communication throughput and delay, for BISN designs. To our knowledge, existing simulators and analytical models do not meet the unique needs of BISN research; therefore, we have created a new open-source BISN simulator named Lure. Lure is designed from the ground-up for simulation of batteryless intermittent systems and networks. Written in Python, Lure is powerful, flexible, highly configurable, and supports rapid prototyping of new protocols, systems, and applications, with a low learning curve. In this paper, we present Lure and validate it with experimental data to show that Lure can accurately reflect the reality of BISNs. We then demonstrate the process of applying Lure to research questions in select case studies.

RF Energy Harvesting and Wireless Power Transfer for Energy Autonomous Wireless Devices and RFIDs

Radio frequency (RF) energy harvesting and wireless power transmission (WPT) technologies —both near-field and far-field—have attracted significant interest for wireless applications and RFID systems. We already utilize near-field WPT products in our life and it is expected that RF EH and far-field WPT systems can drive the future low-power wireless systems. In this article, we initially present a brief historical overview of these technologies. The main technical challenges of rectennas and WPT transmitters are discussed. Furthermore, this paper presents the recent advances on the development of these technologies, including the possibility of powering RFID systems through the millimeter wave power from 5G networks, the trends in flexible rectennas design and the technological developments on the simultaneous wireless information and power transfer (SWIPT).

BER Performance of Co-operative Relay NOMA-assisted PS Protocol with Imperfect SIC and CSI

Objective: Wireless networks and devices are consuming a significant amount of energy as wireless communication is rapidly expanding, radio frequency (RF) energy harvesting has been envisioned as a feasible technology for powering low-power wireless systems. Aims: This paper investigates a bit error rate (BER) of the non-orthogonal multiple access with cooperative relay-assisted power splitting (CR-NOMA-PS) based energy harvesting (EH). Methods: We consider that the relay works in the decode and forward (DF) mode. For more practical scenarios, we consider the imperfect successive interference cancellation (SIC) and channel state information (CSI) are available. Results: We obtain the end-to-end (e2e) BER expressions for the CR-NOMA-PS with imperfect CSI. Under different scenarios of PS, we evaluate and discuss the BER performance of the users with imperfect SIC and CSI. We validate the derivation of the BER expressions by simulation results. Conclusion: The results indicated that the high values of the PS factor reduce the users' performance. Furthermore, in the high signal-to-noise ratio (SNR), the CSI error degrade BER performance and produced an error floor.

Remote Monitoring and Control System of a Water Distribution Network using LoRaWAN Technology

The problems related to the proper management and control in the distribution of potable water affect environmental sustainability generated by leaks and breaks in the infrastructure, causing leaks and loss of water. According to reports from the National Superintendence of Sanitation Services of Peru, more than 50% of complaints about the water service are related to billing problems and water leaks. It is for this reason that technologies such as the Internet of Things technology contribute to generating solutions for the automatic acquisition of data in residences and houses. That is why this paper aims to use long-range and low-power wireless communication systems to improve the service-oriented to the control of the water distribution network, monitoring of vandalism, and detection of anomalous events, reducing response time and economic losses. The paper's development methodology considers the implementation of a water controller node with flow control sensors and solenoid valves and a gateway with Lora communication. In addition, a solenoid valve control circuit and a remote visualization and control system are implemented. The results indicate that the implemented nodes allow adequate monitoring and control in real-time of the water flow, contributing to the adequate management of its consumption and supporting the detection of anomalous events using a Web application.

Design and implementation of miniaturized tri-band microwave bandpass filter

PurposeThis paper is aimed to study the design of a miniaturized filter with tri-band characteristics. In this paper, perturbation is used to realize circuit miniaturization and multi-band by exploiting the inductive property. During this process, vias are added for twofold benefit, namely, circuit miniaturization and enhanced frequency selectivity at high frequency. Thus, with the introduction of the shorting via, the single-band dual-mode bandpass filter is converted into a tri-band filter with a smaller electrical size.Design/methodology/approachThis paper presents the design and characterization of a miniaturized two-port filter with tri-band operating characteristics. The proposed filter is constructed using a square patch resonator operating at 5.2 GHz with a capacitively coupled feed configuration. A square perturbation is added to the corner of the square patch to achieve diagonal symmetry and to excite dual mode. The perturbation offers a sharp transmission zero defining bandwidth of the proposed filter. In addition, a shorting post is introduced to achieve an 88% size reduction by lowering the operating frequency to 1.8 GHz.FindingsThe prototype filter has insertion less than 1.2 dB and return loss better than 12 dB throughout all the realized frequency bands. The prototype filter is fabricated and the simulation results are validated using experimental measurements. The realized fractional bandwidths of the proposed bandpass filter are 11/5.6/1 at 1.8/4.6/5.85 GHz, respectively. The quality factor of the proposed antenna is greater than 80 and a peak Q-factor of 387 is realized at 5.85 GHz. The high Q-factor indicates low loss and improved selectivity. The rejection levels in the stopband are greater than 20 dB.Originality/valueThe results indicate that the proposed filter is a suitable choice for low-power small-scale wireless systems operating in the microwave bands. The realized filter has the smallest footprint of 0.36λeff × 0.19λeff where λeff is the effective wavelength calculated at the lowest frequency of operation.

Band gap and gate metal engineering of novel hetero-material InAs/GaAs-based JLTFET for improved wireless applications

This paper investigates the reliability of a dual metal gate-hetero-material junctionless tunnel FET (DMG-HJLTFET), by using a novel combination of III–V compound semiconducting materials, $$\mathrm{InAs}$$ (lower bandgap) in the source region and $$\mathrm{GaAs}$$ (higher bandgap) in the channel and drain regions. We applied bandgap engineering and dual material gate engineering to improve the linearity metrics and distortion parameters by optimizing an appropriate lower work function tunnel gate toward the source and higher work function supplementary gate toward the drain and compared all the results with SMG (single metal gate)-HJLTFET and Si-JLTFET. The DMG-HJLTFET showed marked improvements in terms of ION, ION/IOFF, SS, $${g}_{\mathrm{m}}$$ , $${g}_{\mathrm{m}3}$$ , VIP2, VIP3, and 1-dB compression point. The input power, IIP3 of DMG-HJLTFET, is 158% greater than SMG-HJLTFET and is 154.7% greater than Si-JLTFET. The distortion power, IMD3 of DMG-HJLTFET, is 171.8% and 20.5% lower than SMG-HJLTFET and Si-JLTFET, respectively, thereby making it suitable for low-power distortion-free wireless communication systems.

Maximum Likelihood Time Synchronization for Zero-Padded OFDM

Existing Orthogonal Frequency-Division Multiplexing (OFDM) variants based on cyclic prefix (CP) allow for efficient time synchronization, but suffer from lower power efficiency compared to zero-padded (ZP)-OFDM. Because of its power efficiency, ZP-OFDM is considered as an appealing solution for the emerging low-power wireless systems. However, in the absence of CP, time synchronization in ZP-OFDM is a very challenging task. In this paper, the non-data-aided (NDA) maximum-likelihood (ML) time synchronization for ZP-OFDM is analytically derived. We show that the optimal NDA-ML synchronization algorithm offers a high lock-in probability and can be efficiently implemented using Monte Carlo sampling (MCS) technique in combination with golden-section search. To obtain the optimal NDA-ML time synchronization algorithm, we first derive a closed-form expression for the joint probability density function (PDF) of the received ZP-OFDM samples in frequency-selective fading channels. The derived expression is valid for doubly-selective fading channels with mobile users as well. The performance of the proposed synchronization algorithm is evaluated under various practical settings through simulation experiments. It is shown that the proposed optimal NDA-ML synchronization algorithm and its MCS implementation substantially outperforms existing algorithms in terms of lock-in probability.

Characterization of sparse WLAN data traffic in opportunistic indoor environments as a prior for coexistence scenarios of modern wireless technologies

CR enabled radio environment provides the seamless operating framework to cope with the requirements of next generation wireless systems like higher data rates, massive machine time communication and interference free coexistence scenarios of wireless technologies. Traffic characterization studies assist to optimize coexistence framework by providing necessary information about the usage patterns of wireless services in observed radio bands. Prior knowledge about the observed sparse wireless local area network (WLAN) data traffic is a key for opportunistic radio resource allocation and utilization in the given coexistence scenarios of WLAN either with cellular systems (including 5G-NR/4G Long Term Evolution (LTE)) or with low power wireless systems (including Bluetooth and ZigBee). Parametric methodology is adapted to model the sparse WLAN data traffic observed in 2.4 GHz Industrial, Scientific and Medical (ISM) band as spectral and temporal activity. The multivariate Gaussian mixture model (MGMM) is proposed in both scenarios where either dependency is considered between the observed WLAN data traffic or assuming that the observed traffic is independent and identically distributed (i.i.d). It is to be validated that in order to have an efficient characterization of sparse WLAN data traffic, the dependency (correlation) between neighbored frequency subbands must be considered. By considering the dependency either between neighbored frequency subbands or neighbored time domain signals actually help to characterize the sparse WLAN data traffic in more realistic way which could not be possible by assuming them i.i.d. Such statistics to characterize sparse data traffic really help as user activity for efficient allocation and utilization of radio resources in CR enabled coexistence scenarios of wireless technologies where WLAN acitivity is considered nominal either as secondary user or classify it grey spectrum as primary user.

Dynamic modulation scaling enabled multi-hop topology control for time critical wireless sensor networks

The previous work on connection driven topology control has shown that it has significant potential to reduce energy consumption of Wireless Sensor Networks (WSNs). Dynamic Modulation Scaling (DMS) which is a technique that manages transmission power levels in order to change the number of bits encoded per symbol has a direct impact on connection driven topology control. In this paper we investigate the transmission scheduling of multi-hop real-time WSNs equipped with DMS enabled radio chips while taking the effect of DMS on topology control into account. To our best knowledge, this is the first paper that addresses this issue. The current work on DMS enabled WSN tend to rely on theoretical DMS models to predict network performance metrics. However, there is little, if any, work that is based upon empirically verified network performance outcomes using DMS especially on its effect on connection driven topology control. This paper fills this gap by using GNU Radio and Software Defined Radio hardware to show how to emulate DMS in low power wireless systems and measure the impact of varying Signal-to-Noise levels, distance and elevation on throughput and delivery rates for different DMS control strategies. Next, we present the Mixed Integer Nonlinear Optimization Problem of minimizing energy consumption of DMS enabled connection driven topology control on real-time WSNs. Lastly, we present two polynomial time heuristics and compare their performance against the optimal solution.

A 2.2 to 2.9 GHz Complementary Class-C VCO With PMOS Tail-Current Source Feedback Achieving – 120 dBc/Hz Phase Noise at 1 MHz Offset

The performance of low-powered transceivers is required to meet stringent specifications for an advanced wireless radio application. It is critical for a voltage-controlled oscillator (VCO) to meet multi-standard and multiple frequency operation with low-power consumption and amplitude enhanced complementary mode of operation. This paper proposes a novel technique for wide tuning range in a complementary class-C VCO employing a capacitive-source degeneration (CSD) to meet multi-standard operation for low-power transceivers. The technique that employs two sets of symmetrical split PMOS biased current source operating in the subthreshold region achieves the desired low phase noise (PN) performance at a tuning range of 2.2-2.9 GHz with a supply headroom of 1.2 V. The control of the dc bias point reduces the conduction angle, which improves the current efficiency, power consumption, and PN. Concurrently, an auxiliary -g m NMOS only class-B oscillator is incorporated to mitigate the start-up issue of the class-C VCO. At the center frequency of 2.45 GHz, the proposed VCO achieves a power consumption of 1.73 mW, phase noise of -120 dBc/Hz at the 1-MHz offset, and a figure-of-merit (FoM) of 185.41 dBc/Hz at 1 MHz. The total active chip area is only 0.3-mm 2 excluding bond pads. The proposed VCO serves as a promising solution for low-power wireless communication systems.

An Impulse Radio PWM-Based Wireless Data Acquisition Sensor Interface.

A sensor interface circuit based on impulse radio pulse width modulation (IR-PWM) is presented for low power and high throughput wireless data acquisition systems (wDAQ) with extreme size and power constraints. Two triple-slope analog-to-time converters (ATC) convert two analog signals, each up to 5 MHz in bandwidth, into PWM signals, and an impulse radio (IR) transmitted (Tx) with an all-digital power amplifier (PA) combines them while preserving the timing information by transmitting impulses at the PWM rising and falling edges. On the receiver (Rx) side, an RF-LNA followed by an envelope detector recovers the incoming impulses, and a T-flipflop reverts the impulse sequence back to PWM to be digitized by a time-to-digital converter (TDC). Detailed analysis and design guideline on ATC was introduced, and a proof-of-concept prototype was fabricated for a capacitive micromachined ultrasound transducer (CMUT) imaging system in a 0.18-μm HV CMOS process, occupying 0.18 mm2 active area and consuming 3.94 mW from a 1.8 V supply. The proposed TDC in this prototype yielded 7-bit resolution, while the entire wDAQ achieved 5.8 effective number of bits (ENOB) at 2 × 10 MS/s.

Wireless Information and Power Transfer: Probability-Based Power Allocation and Splitting With Low Complexity

Despite energy harvesting (EH) using radio frequency (RF) signals and the concept of simultaneous wireless information and power transfer (SWIPT) being attractive technologies to adapt in various low-power wireless systems, the research in these fields was mostly built upon less-practical configurations. While a resource allocation strategy was proposed to identify the optimal performance bounds for SWIPT systems, a huge computational complexity makes it impractical to apply to real-world systems. In this work, we figure out that the strategy for achieving the optimal performance bounds follows a water-filling algorithm similarly. We use this observation to propose a heuristic algorithm for finding a water level for power allocation and effective power splitting ratio with minimal complexity. Using analysis and simulations, we show that the proposed scheme achieves near-optimal performance with a significant lower complexity compared to previously proposed optimal-bound identifying schemes.

A Novel Complex-Coefficient In-Band Interference Suppression Algorithm for Cognitive Ultra-Wide Band Wireless Sensors Networks.

With the rapid development of wireless communication systems and electronic techniques, the limited frequency spectrum resources are shared with various wireless devices, leading to a crowded and challenging coexistence circumstance. Cognitive radio (CR) and ultra-wide band (UWB), as sophisticated wireless techniques, have been considered as significant solutions to solve the harmonious coexistence issues. UWB wireless sensors can share the spectrum with primary user (PU) systems without harmful interference. The in-band interference of UWB systems should be considered because such interference can severely affect the transmissions of UWB wireless systems. In order to solve the in-band interference issues for UWB wireless sensor networks (WSN), a novel in-band narrow band interferences (NBIs) elimination scheme is proposed in this paper. The proposed narrow band interferences suppression scheme is based on a novel complex-coefficient adaptive notch filter unit with a single constrained zero-pole pair. Moreover, in order to reduce the computation complexity of the proposed scheme, an adaptive complex-coefficient iterative method based on two-order Taylor series is designed. To cope with multiple narrow band interferences, a linear cascaded high order adaptive filter and a cyclic cascaded high order matrix adaptive filter (CCHOMAF) interference suppression algorithm based on the basic adaptive notch filter unit are also presented. The theoretical analysis and numerical simulation results indicate that the proposed CCHOMAF algorithm can achieve better performance in terms of average bit error rate for UWB WSNs. The proposed in-band NBIs elimination scheme can significantly improve the reception performance of low-cost and low-power UWB wireless systems.

Low-Power Wireless Systems for Hospital Patient Monitoring: The Challenges and Solutions for Emerging Application Areas

Although the medical device industry is slow to replace wired by wireless connectivity, the convenience and other benefits that wireless can bring means that new applications for wireless patient monitoring are starting to emerge. Since the development of lowpower standards is mainly driven by consumer and other large markets, it is inevitable that such standards do not currently prioritize the high reliability and security requirements needed by medical devices. However, as the market keeps developing, we anticipate that the needs currently addressed by custom or niche wireless protocols and SoCs may begin to be met by widely available offtheshelf devices.

Physical Layer Security in MIMO Backscatter Wireless Systems

Backscatter wireless communication is an emerging technique widely used in low-cost and low-power wireless systems, especially in passive radio frequency identification (RFID) systems. Recently, the requirement of high data rates, data reliability, and security drives the development of RFID systems, which motivates our investigation on the physical layer security of a multiple-input multiple-output (MIMO) RFID system. In this paper, we propose a noise-injection precoding strategy to safeguard the system security with the resource-constrained nature of the backscatter system taken into consideration. We first consider a multi-antenna RFID tag case and investigate the secrecy rate maximization (SRM) problem by jointly optimizing the energy supply power and the precoding matrix of the injected artificial noise at the RFID reader. We exploit the alternating optimization method and the sequential parametric convex approximation method, respectively, to tackle the non-convex SRM problem and show an interesting fact that the two methods are actually equivalent for our SRM problem with the convergence of a Karush-Kuhn-Tucker (KKT) point. To facilitate the practical implementation for resource-constrained RFID devices, we propose a fast algorithm based on projected gradient. We also consider a single-antenna RFID tag case and develop a low-complexity algorithm which yields the global optimal solution. Simulation results show the superiority of our proposed algorithms in terms of the secrecy rate and computational complexity.

Compressive Sensing Based Sampling and Reconstruction for Wireless Sensor Array Network

For low-power wireless systems, transmission data volume is a key property, which influences the energy cost and time delay of transmission. In this paper, we introduce compressive sensing to propose a compressed sampling and collaborative reconstruction framework, which enables real-time direction of arrival estimation for wireless sensor array network. In sampling part, random compressed sampling and 1-bit sampling are utilized to reduce sample data volume while making little extra requirement for hardware. In reconstruction part, collaborative reconstruction method is proposed by exploiting similar sparsity structure of acoustic signal from nodes in the same array. Simulation results show that proposed framework can reach similar performances as conventional DoA methods while requiring less than 15% of transmission bandwidth. Also the proposed framework is compared with some data compression algorithms. While simulation results show framework’s superior performance, field experiment data from a prototype system is presented to validate the results.

Adaptive Kalman filter for indoor localization using Bluetooth Low Energy and inertial measurement unit.

This paper proposes a novel indoor localization method using the Bluetooth Low Energy (BLE) and an inertial measurement unit (IMU). The multipath and non-line-of-sight errors from low-power wireless localization systems commonly result in outliers, affecting the positioning accuracy. We address this problem by adaptively weighting the estimates from the IMU and BLE in our proposed cascaded Kalman filter (KF). The positioning accuracy is further improved with the Rauch-Tung-Striebel smoother. The performance of the proposed algorithm is compared against that of the standard KF experimentally. The results show that the proposed algorithm can maintain high accuracy for position tracking the sensor in the presence of the outliers.

On Location Estimation Technique Based of the Time of Flight in Low-power Wireless Systems

Abstract This study deals with the distance estimation issue in low-power wireless systems being usually used for sensor networking and interconnecting the Internet of Things. There is an effort to locate or track these sensor entities for different needs the radio signal time of flight principle from the theoretical and practical side of application research is evaluated. Since these sensor devices are mainly targeted for low power consumption appliances, there is always need for optimization of any aspects needed for regular sensor operation. For the distance estimation we benefit from IEEE 802.15.4a technology, which offers the precise ranging capabilities. There is no need for additional hardware to be used for the ranging task and all fundamental measurements are acquired within the 15.4a standard compliant hardware in the real environment. The proposed work examines the problems and the solutions for implementation of distance estimation algorithms for WSN devices. The main contribution of the article is seen in this real testbed evaluation of the ranging technology.

A Low-Power Miniaturized Microelectronic System for Continuous Glucose Monitoring

The design and fabrication of miniaturized, implantable, low-power wireless systems for continuous glucose monitoring hold great promise for diabetes mellitus inflicted patients. This involves addressing a variety of issues including extreme circuit miniaturization, robust electrochemical sensors as well as counteracting negative tissue response and biofouling following sensor implantation. In this contribution, we present a highly miniaturized microelectronic sensor platform that fits through a hypodermic needle and holistically addresses all aforementioned tribulations. For this, a custom designed complementary metal-oxide-semiconductor electronic device employing the 0.35 µm design rule has been integrated with a high performance amperometric electrochemical glucose sensor. The fabricated electrochemical sensor utilizes the stratification of five functional layers resulting in linear amperometric response within the physiological glucose range (2 – 22mM). The sensor is encased with a thick polyvinyl alcohol (PVA) hydrogel containing poly (lactic-co-glycolic acid) (PLGA) microspheres which provides continuous, localized delivery of dexamethasone utilized to combat inflammation and fibrosis subsequent to implantation. In vivo evaluation in a rat has shown that this system accurately tracks glycemic events. Such miniature size and low power operation (0.665 mm2 and 140 µW, respectively) of the electronic system render it an ideal platform for continuous glucose monitoring and other metabolic sensing applications.

An objective measurement of brace usage for the treatment of adolescent idiopathic scoliosis

Effectiveness of orthotic treatment for scoliosis depends on how much time and how well the orthosis is worn. Questionnaires and clinical judgment are subjective methods to wear compliance. Even though using a temperature sensor can objectively record how long the orthosis has been used, it may not be able to answer the orthosis effectiveness without knowing the wear tightness. Custom made thoracolumbosacral orthoses (TLSO) were instrumented with low power wireless data acquisition systems to measure the time and loads imposed by the pressure pad during daily activities. Force measurements were recorded at 1 sample/min and the system was able to record data up to 4 months without patient-involvement. Ten subjects (9F, 1M), age between 9 and 13.5 years, average 11.6 ± 1.3 years, who prescribed a new TLSO and full-time brace wear were took part in this study over 4.4 ± 1.0 months. Long-term logging of loads within a spinal orthosis is a reliable method to measure compliance objectively. The monthly quantity of brace wear ranged from 33% to 82%, average 60.0 ± 4.3%. The monthly average loads imposed by the pressure pads varied from 39% to 78% relative to the reference level, average 64.3 ± 4.6%. There was a statistically significant decrease in force, but increase in wear time over the period after the brace fitting session. This information may help to better understand the effectiveness of bracing and to predict the brace treatment outcomes.