Carrier Emitter Research Articles

Direct Link Interference Suppression for Bistatic Backscatter Communication in Distributed MIMO

Backscatter communication (BC) is a promising technique for future Internet-of-Things (IoT) owing to its low complexity, low cost, and potential for energy-efficient operation in sensor networks. There are several network infrastructure setups that can be used for BC with IoT nodes. One of them is the bistatic setup where typically there is a need for high dynamic range and high-resolution analog-to-digital converters at the reader. In this paper, we investigate a bistatic BC setup with multiple antennas. We propose a novel transmission scheme, which includes a protocol for channel estimation at the carrier emitter (CE) as well as a transmit beamformer construction that suppresses the direct link interference between the two ends of a bistatic link (namely CE and reader), and increases the detection performance of the backscatter device (BD) symbol. Further, we derive a generalized log-likelihood ratio test (GLRT) to detect the symbol/presence of the BD. We also provide an iterative algorithm to estimate the unknown parameters in the GLRT. Finally, simulation results show that the required dynamic range of the system is significantly decreased, and the detection performance of the BD symbol is increased, by the proposed algorithm compared to a system not using beamforming at the CE.

Energy-Efficient Backscatter Aided Uplink NOMA Roadside Sensor Communications Under Channel Estimation Errors

This work presents non-orthogonal multiple access (NOMA) enabled energy-efficient alternating optimization framework for backscatter aided wireless powered uplink sensors communications for beyond 5G intelligent transportation system (ITS). Specifically, the transmit power of carrier emitter (CE) and reflection coefficients of backscatter aided roadside sensors are optimized with channel uncertainties for the maximization of the energy efficiency (EE) of the network. The formulated problem is tackled by the proposed two-stage alternating optimization algorithm named AOBWS (alternating optimization for backscatter aided wireless powered sensors). In the first stage, AOBWS employs an iterative algorithm to obtain optimal CE transmit power through simplified closed-form computed through Cardano’s formulae. In the second stage, AOBWS uses a non-iterative algorithm that provides a closed-form expression for the computation of optimal reflection coefficient for roadside sensors under their quality of service (QoS) and a circuit power constraint. The global optimal exhaustive search (ES) algorithm is used as a benchmark. Simulation results demonstrate that the AOBWS algorithm can achieve near-optimal performance with very low complexity, which makes it suitable for practical implementations.

Intelligent Reflecting Surface-Assisted Bistatic Backscatter Networks: Joint Beamforming and Reflection Design

Bistatic backscatter communication (BackCom) allows passive tags to transmit over extended ranges, but at the cost of having carrier emitters either transmitting at high powers or being deployed very close to tags. In this paper, we examine how the presence of an intelligent reflecting surface (IRS) could benefit the bistatic BackCom system. We study the transmit power minimization problem at the carrier emitter, where its transmit beamforming vector is jointly optimized with the IRS phase shifts, whilst guaranteeing a required BackCom performance. A unique feature in this system setup is the multiple IRS reflections experienced by signals traveling from the carrier emitter to the reader, which renders the optimization problem highly nonconvex. Therefore, we propose algorithms based on the minorization-maximization and alternating optimization techniques to obtain approximate solutions for the joint design. We also propose low-complexity algorithms based on successive optimization of individual phase shifts. Our results reveal considerable transmit power savings in both single-tag and multi-tag systems, even with moderate IRS sizes, which may be translated to significant range improvements using the original transmit power or a reduction of the reliance of tags on carrier emitters located at close range.

Capacity Analysis for Tunnel Diode Amplifier Assisted Ambient Backscatter Communications

The ambient backscatter communication (AmBC) technology addresses connectivity, cost, and congestion bottlenecks for the Internet of Things (IoT) deployment. AmBC, by avoiding a dedicated power infrastructure and carrier emitter, allows tags to communicate by simply reflecting ambient radio frequency (RF) signals to the reader. Thus, the tag can operate in the low-maintenance, battery-free mode and be powered with energy harvesting. However, a fundamental bottleneck is the limited communication range. A novel solution is integrating tunnel diode amplifiers into tags to enhance their backscattered signal power and thus extend the communication range. This paper studies that solution and investigates the resulting capacity performance. Specifically, we first develop the system’s mathematical model, elaborate on the tunnel diode’s amplification mechanism, and derive its reflection gain. Subsequently, we derive the closed-form channel capacity and propose a reader-tag distance adjustment scheme to improve the system performance. Finally, simulation results corroborate our theoretical results. They show that the tunnel diode amplifier can significantly increase the system capacity by an order of magnitude when the tag receives less than -30 dBm of incident RF signal power. They also demonstrate a significant increase in the communication range.

BER Analysis of a Backscatter Communication System With Non-Orthogonal Multiple Access

Backscatter communication (BackCom) has been emerging as a prospective candidate in tackling lifetime management problems for massively deployed Internet-of-things (IoT) devices, which suffer from battery related issues, i.e., replacements, charging, and recycling. This passive sensing approach allows a backscatter sensor node (BSN) to transmit information by reflecting the incident signal from a carrier emitter without initiating its transmission. To multiplex multiple BSNs, power-domain non-orthogonal multiple access (NOMA) is fully exploited in this work. In this paper, we present the design and analysis of a NOMA enhanced bistatic BackCom system for a battery-less smart communication paradigm. Specifically, we derive the closed-form bit error rate (BER) expressions for a cluster of two devices in a bistatic BackCom system employing NOMA with imperfect successive interference cancellation under Nakagami- m fading channel. The obtained expressions are utilized to evaluate the reflection coefficients of devices needed for the most favorable system performance along with the performance comparison with orthogonal multiple access-time domain multiple access scheme (OMA-TDMA).

Energy-Efficient Covert Communications for Bistatic Backscatter Systems

In this paper, we consider covert communications for bistatic backscatter systems, where a tag transmits information passively to a reader by reflecting incident carrier signals with artificial noise (AN) generated from a dedicated carrier emitter (CE) under the supervision of a warden. By exploiting the channel uncertainty introduced by CE, we analytically derive the warden's minimum sum of error probabilities to evaluate communication covertness. We find that communication covertness can be improved by reducing the tag's reflection coefficient, but is not affected by the CE's transmit power. Therefore, in order to achieve energy-efficient design, we optimize the tag's reflection coefficient to minimize the CE's transmit power under the constraints of communication covertness and reliability. Our analysis shows that the minimum CE's transmit power can be further reduced with a minor loss of the achievable covert rate.

An Overview on Backscatter Communications

As a key low-power communication technique, backscatter communications exploits the reflected or backscattered signals to transmit data, where the backscattered signals can be the reflection of ambient radio frequency (RF) signals, the RF signals from the dedicated carrier emitter or the signal photons in the non-classical quantum entangled pairs, etc. In the past 70 years, various kinds of backscatter communication systems have been developed, which will enable the low-power communications as required in the Internet of things (IoTs) and green communications. This article provides a historical view on the development and the research achievements on backscatter communications, including the fundamental principles, the applications, the challenges, and the potential research topics. This article will benefit the researchers and engineers concerning the area of backscatter communications, especially for applications in IoTs.

Ambient Backscatter Assisted Wireless Powered Communications

Ambient backscatter communication technology has been introduced recently, and is quickly becoming a promising choice for self-sustainable communication systems, as an external power supply or a dedicated carrier emitter is not required. By leveraging existing RF signal resources, ambient backscatter technology can support sustainable and independent communications and consequently open up a whole new set of applications that facilitate Internet of things (IoT). In this article, we study an integration of ambient backscatter with wireless powered communication networks (WPCNs). We first present an overview of backscatter communication systems with an emphasis on the emerging ambient backscatter technology. Then we propose a novel hybrid transmitter design by combining the advantages of both ambient backscatter and wireless powered communications. Furthermore, in the cognitive radio environment, we introduce a multiple access scheme to coordinate hybrid data transmissions. The performance evaluation shows that the hybrid transmitter outperforms traditional designs. In addition, we discuss open issues related to ambient backscatter networking.

Mitigation of Phase Cancellation for Efficient Decoding and RF Energy Harvesting in Tag-to-Tag Communications

In this paper, we investigate a phase cancellation problem that occurs in tag-to-tag communication systems. These are the systems wherein several tags communicate with each other by backscattering an external constant wave signal. A transmitting tag modulates baseband information into the reflected signal using backscatter modulation. At the receiving tag, the received signal is the superposition of the transmitted signals by the carrier emitter and the transmitting tag. The resulting signal is demodulated using the envelope detector that causes the phase cancellation problem. This problem exists in all tag-to-tag communication systems and largely impacts on the reliability and communication range. We theoretically analyze and experimentally demonstrate this problem for the tags that use amplitude-shift keying-based backscattering. We propose an algorithm for the mitigation of the phase cancellation based on the phase rotation control. We examine the performance of the proposed algorithm through theoretical analysis and computer simulations. We confirm that the proposed algorithm can significantly mitigate the phase cancellation.

The Influence of the Base Material Parameters on Quantum and Photoconversion Efficiency of the Si Solar Cells

Abstract The influence of a p-type Si with different resistivity, charge carrier lifetime and emitter dopant impurities concentration on the crystalline silicon solar cells parameters were analyzed and experimentally checked. The findings were determined by quasi-steady-state photoconductance, current-voltage and spectral response methods. The study was accompanied by solar device simulation using a numerical PC1D program. The highest photoconversion efficiency of 15.13 % was obtained for the moncrystalline (Cz-Si) solar cell with a base resistivity of 1.8 Ωcm and an effective charge carrier lifetime of 22.9 μs. The results clearly confirmed the importance concerning the dopant level in a Si base material in relation to open circuit voltage and short circuit current possible to obtain from the solar cell. Reduction of a base material resistivtiy leads to a lower value of an effective charge carrier lifetime and photoconversion efficiency both for Cz-Si and multicrystalline (mc-Si) solar cells. The experimental results and calculation showed, that in the case of a solar cell produced on the basis of crystalline silicon, the most important spectral range for an efficiency of a cell is covering a wavelength range of 587 ÷ 838 nm.

Organic Spin-Valves and Beyond: Spin Injection and Transport in Organic Semiconductors and the Effect of Interfacial Engineering.

Since the first observation of the spin-valve effect through organic semiconductors, efforts to realize novel spintronic technologies based on organic semiconductors have been rapidly growing. However, a complete understanding of spin-polarized carrier injection and transport in organic semiconductors is still lacking and under debate. For example, there is still no clear understanding of major spin-flip mechanisms in organic semiconductors and the role of hybrid metal-organic interfaces in spin injection. Recent findings suggest that organic single crystals can provide spin-transport media with much less structural disorder relative to organic thin films, thus reducing momentum scattering. Additionally, modification of the band energetics, morphology, and even spin magnetic moment at the metal-organic interface by interface engineering can greatly impact the efficiency of spin-polarized carrier injection. Here, progress on efficient spin-polarized carrier injection into organic semiconductors from ferromagnetic metals by using various interface engineering techniques is presented, such as inserting a metallic interlayer, a molecular self-assembled monolayer (SAM), and a ballistic carrier emitter. In addition, efforts to realize long spin transport in single-crystalline organic semiconductors are discussed. The focus here is on understanding and maximizing spin-polarized carrier injection and transport in organic semiconductors and insight is provided for the realization of emerging organic spintronics technologies.

무선전력 통신네트워크를 위한 Backscatter 통신

본 논문에서는 무선 센서 네트워크 환경에서 전력의 제약이 있는 센서들의 장거리통신을 가능케 하는 backscatter 통신에 대해 소개하고, 이를 접목해 무선전력 통신네트워크(wireless-powered communication networks, WPCN)의 doubly near-far 문제를 해결하는 방안을 논의한다. Backscatter에 기반한 WPCN에서 유저들은 하이브리드 엑세스 지점으로부터 전송되는 신호와 반송파 송신기로부터 전송되는 반송파 신호로부터 에너지를 수집한 후, 주파수 편이 변조를 이용한 반송파 신호의 반사를 통해 정보를 전송하게 된다. 위의 통신환경에서 energy-free 조건과 신호대 잡음비 outage 영역을 정의한다. 또한 본 논문에서는 에너지 수집과 정보 전송을 위한 최적의 시간 할당 방법을 제안하고, 이를 통해 시스템 전체의 정보전송 효율을 최대화할 수 있는 backscatter 기반의 수집 후 전송 프로토콜을 설계한다. 실험결과를 통해 제안한 backscatter 기법이 종래의 WPCN에 비해 광범위한 서비스 영역과 축소된 신호대 잡음비 outage 영역을 갖는 것을 보였고, 정보전송 효율을 최대화할 수 있음을 보였다. In this paper, we introduce backscatter communication for power-limited sensors to enable long-range transmission in wireless sensor networks, and envision a way to avoid doubly near-far problem in wireless-powered communication network (WPCN) with this technology. In backscatter based WPCN, users harvest energy from both the signal broadcasted by the hybrid access point and the carrier signal transmitted by the carrier emitter in the downlink, and then transmit their own information in a passive way via the reflection of the carrier signal using frequency-shift keying modulation in the uplink. We characterize the energy-free condition and the signal-to-noise ratio (SNR) outage zone in backscatter based WPCN. Further, we propose backscatter based harvest-then-transmit protocol to maximize the sum-throughput of the backscatter based WPCN by optimally allocating time for energy harvesting and information transmission. Numerical results demonstrate that the backscatter based WPCN increases significantly the transmission range and diminishes greatly the SNR outage zone.

Coherent Detection and Channel Coding for Bistatic Scatter Radio Sensor Networking

With rapid advances of scatter radio systems, the principle of reflection rather than active transmission employed by backscatter sensor networks, has emerged as a potential key enabler for low-cost, large-scale and dense ubiquitous sensor networks. Despite the presence of three different unknown channel links due to the bistatic setup (i.e., carrier emitter and receiver are dislocated), as well as multiple unknown scatter radio-related parameters, this work offers a novel coherent receiver of frequency-shift keying (FSK) modulation for the bistatic scatter radio channel. Furthermore, with the objective of range maximization, specific short block-length cyclic channel codes are utilized. The proposed approach requires minimum encoding complexity, ideal for resource-constrained, ultra-low power (e.g. microcontroller unit-based), low-bit rate scatter radio tags, adheres to simple low-complexity decoding at the receiver and achieves high-order signal diversity. Analysis is followed by experimental validation with a commodity software-defined radio (SDR) reader and a custom scatter radio tag; tag-to-reader ranges up to 150 meters are demonstrated with as little as 20 milliWatt transmission power, increasing sensing ranges by approximately 10 additional meters, compared to state-of-the-art bistatic scatter radio receivers. With the imminent emergence of backscatter sensor networks, this work serves as a small step forward towards the realization of low-cost, low-power, increased-range, wireless sensing applications.

Wireless Environmental Sensor Networking With Analog Scatter Radio and Timer Principles

Environmental variables monitoring with wireless sensor networks (WSNs) is invaluable for precision agriculture applications. However, the effectiveness of existing low-power, conventional (e.g., ZigBee-type) radios in large-scale deployments is limited by power consumption, cost, and complexity constraints, while the existing WSN solutions employing nonconventional, scatter-radio principles have been restricted to communication ranges of up to a few meters. In this paper, the development of a novel analog scatter-radio WSN is presented, that employs semipassive sensor/tags in bistatic topology (i.e., carrier emitter placed in a different location from the reader), consuming <;1 mW of power, with communication range exceeding 100 m. The experimental results indicate that the multipoint surface fitting calibration, in conjunction with the employed two-phase filtering process, both provide a mean absolute error of 1.9% environmental relative humidity for a temperature range of 10 °C-50 °C. In addition, the energy consumption per measurement of the proposed environmental monitoring approach can be lower than that of conventional radio WSNs. Finally, the proposed approach operational characteristics are presented through a real-world network deployment in a tomato greenhouse.

Increased Range Bistatic Scatter Radio

Scatter radio achieves communication by reflection and requires low-cost and low-power RF front-ends. However, its use in wireless sensor networks (WSNs) is limited, since commercial scatter radio (e.g. RFID) offers short ranges of a few tens of meters. This work redesigns scatter radio systems and maximizes range through non-classic bistatic architectures: the carrier emitter is detached from the reader. It is shown that conventional radio receivers may show a potential 3dB performance loss, since they do not exploit the correct signal model for scatter radio links. Receivers for on-off-keying (OOK) and frequency-shift keying (FSK) that overcome the frequency offset between the carrier emitter and the reader are presented. Additionally, non-coherent designs are also offered. This work emphasizes that sensor tag design should accompany receiver design. Impact of important parameters such as the antenna structural mode are presented through bit error rate (BER) results. Experimental measurements corroborate the long-range ability of bistatic radio; ranges of up to 130 meters with 20 milliwatts of carrier power are experimentally demonstrated, with commodity software radio and no directional antennas. Therefore, bistatic scatter radio may be viewed as a key enabling technology for large-scale, low-cost and low-power WSNs.

Growth of Submicron AlGaN/GaN/AlGaN Heterostructures by Hydride Vapor Phase Epitaxy (HVPE)

Multilayer AlGaN/GaN epitaxial structures were grown on SiC by HVPE method. Characterization of the grown structures was performed using SEM, SIMS, mercury probe, electroluminescence and photoluminescence techniques. Thicknesses of nitride layers in nanometer range were achieved. Stimulated emission from double confined heterostructure grown by HVPE was detected at room temperature under optical pumping. Short wave UV electroluminescence (λ max 340-350 nm) was measured for p-AlGaN/n-AlGaN structures having up to 38 mol% and 9 mol% of AIN in p-AlGaN carrier emitter layers and n-AlGaN light emitting layers, respectively.

Growth of Submicron AlGaN/GaN/AlGaN Heterostructures by Hydride Vapor Phase Epitaxy (HVPE)

Multilayer AlGaN/GaN epitaxial structures were grown on SiC by HVPE method. Characterization of the grown structures was performed using SEM, SIMS, mercury probe, electroluminescence and photoluminescence techniques. Thicknesses of nitride layers in nanometer range were achieved. Stimulated emission from double confined heterostructure grown by HVPE was detected at room temperature under optical pumping. Short wave UV electroluminescence (λ max 340-350 nm) was measured for p-AlGaN/n-AlGaN structures having up to 38 mol% and 9 mol% of AIN in p-AlGaN carrier emitter layers and n-AlGaN light emitting layers, respectively.

An H-L junction room temperature long-wavelength IR detector using the avalanche effect

A room temperature long-wavelength 10.6 mu m avalanche-type detector using laser-induced hot carriers is proposed for improvement of the minimum detectable power. The detectors are made by constructing high-low (H-L) junctions on p-type Ge. The L region is a substrate layer and the H region is a layer which absorbs 10.6 mu m radiation, and its also acts as a hot carrier emitter. This junction is referred to as the L-H junction. A responsivity of 41 V W-1 was obtained at wavelength 10.6 mu m under avalanche voltage conditions. This is comparable with the responsivity of CMT detectors operated at room temperature.

Reduction of the latch effect in SOI MOSFETS by the silicidation of the source

A simple physical model is developed to assess the effect on single transistor latch voltage of carrier lifetime reduction and emitter efficiency degradation. The model predicts the efficacy of the latter mechanism and this is achieved experimentally by silicidation of the source. This has the effect of effectively placing the source ohmic contact close to the source/body metallurgical junction thus enhacing the hole component of the total current across the junction thereby reducing the emitter efficiency. In comparison to a non-silicided source, a 20% increase in breakdown voltage is achieved. Silicidation of both the source and drain regions is performed simultaneoulsy thus maintaining device symmetry and simplicity of processing. No significant degradation of drain leakage current was observed.