Energy-Efficient Wireless Circuits and Systems for Internet of Things

As the demand of ultra-low power (ULP) systems for internet of thing (IoT) applications has been increasing, large efforts on evolving a new computing class is actively ongoing. The evolution of the new computing class, however, faced challenges due to hard constraints on the RF systems. Significant efforts on reducing power of power-hungry wireless radios have been done. The ULP radios, however, are mostly not standard compliant which poses a challenge to wide spread adoption. Being compliant with the WiFi network protocol can maximize an ULP radio’s potential of utilization, however, this standard demands excessive power consumption of over 10mW, that is hardly compatible with in ULP systems even with heavy duty-cycling. Also, lots of efforts to minimize off-chip components in ULP IoT device have been done, however, still not enough for practical usage without a clean external reference, therefore, this limits scaling on cost and form-factor of the new computer class of IoT applications. This research is motivated by those challenges on the RF systems, and each work focuses on radio designs for IoT applications in various aspects. First, the research covers several endeavors for relieving energy constraints on RF systems by utilizing existing network protocols that eventually meets both low-active power, and widespread adoption. This includes novel approaches on 802.11 communication with articulate iterations on low-power RF systems. The research presents three prototypes as power-efficient WiFi wake-up receivers, which bridges the gap between industry standard radios and ULP IoT radios. The proposed WiFi wake-up receivers operate with low power consumption and remain compatible with the WiFi protocol by using back-channel communication. Back-channel communication embeds a signal into a WiFi compliant transmission changing the firmware in the access point, or more specifically just the data in the payload of the WiFi packet. With a specific sequence of data in the packet, the transmitter can output a signal that mimics a modulation that is more conducive for ULP receivers, such as OOK and FSK. In this work, low power mixer-first receivers, and the first fully integrated ultra-low voltage receiver are presented, that are compatible with WiFi through back-channel communication. Another main contribution of this work is in relieving the integration challenge of IoT devices by removing the need for external, or off-chip crystals and antennas. This enables a small form-factor on the order of mm3-scale, useful for medical research and ubiquitous sensing applications. A crystal-less small form factor fully integrated 60GHz transceiver with on-chip 12-channel frequency reference, and good peak gain dual-mode on-chip antenna is presented.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162975/1/jaeim_1.pd

Interference-robust CMOS receivers for IoT:Highly linear RF front-ends at low power

Wireless technologies have brought Internet access to more than half of the world’s population in the last decade. Nowadays, Internet-of-Things (IoT) technology extends the internet connectivity to sensor nodes embedded in machines, animals, and plants. It will soon put us in a realm of billions of interconnected sensor nodes networking and communicating with each other. Such unprecedented growth of wireless devices puts a big challenge of sustainable and robust connectivity in front of us. Concretely, this challenge demands a wireless sensor node with low power and robust connectivity. Radios are the physical interface for sensor nodes with the external world and are one of the power-hungry components in sensor nodes. Hence it is imperative to make them energy-efficient and interference-robust. This thesis explores CMOS passive mixer-first receiver topology to enhance the interference tolerance of receivers in IoT radios. The dissertation proposes a novel N-path filter/mixer topology at the circuit level and a multipath cross-correlation technique at the system level. Two test-chips of mixer-first receiver front ends, using these techniques, are implemented in CMOS FDSOI 22nm technology as a proof-of-concept. The experimental prototypes demonstrate voltage gain in passive mixers and exhibit high-Q widely-tunable RF filtering, large out-of-band and harmonic interferer tolerance, and moderate noise figure while consuming much lower power than several state-of-the-art receivers

Clock Error Impact on NB-IoT Radio Link Performance

3GPP has recently addressed the improvements in Random Access Network (RAN) and specified some new technologies such as enhanced Machine Type Communication (eMTC) and Narrow Band – Internet of Things (NB-IoT) in its release 13 which is also known as LTE-Advanced Pro. These new technologies are addressed mainly to focus on development and deployment of cellular IoT services. NB-IoT is less complex and easily deployable through software upgradation and is compatible to legacy cellular networks such as GSM and 4G which makes it a suitable candidate for IoT. NB-IoT will greatly support LPWAN, thus, it can be deployed for Smart cities and other fields such as smart electricity, smart agriculture, smart health services and smart homes. The NB-IoT targets for low cost device, low power consumption, relaxed delay sensitivity and easy deployment which will greatly support above mentioned fields. This thesis work studies the clock error impact on the radio link performance for up-link transmission on the NB-IoT testbed based on Cloud-RAN using Software Defined Radios (SDR) on a LTE protocol stack. The external clock error is introduced to the network and performance issues are analyzed in the radio link. The analysis indicates packet drops up to 51% in the radio link through the study of received power, packet loss, retransmissions, BLER and SINR for different MCS index. The major performance issues depicted by the analysis are packet loss up to 51% and retransmission of packets up to 128 times for lower SINR and high clock errors. Also, clock errors produce CFO up to 1.25 ppm which results in bad synchronization between UE and eNodeB

Energy-Efficient Wireless Connectivity and Wireless Charging For Internet-of-Things (IoT) Applications

During the recent years, the Internet-of-Things (IoT) has been rapidly evolving. It is indeed the future of communication that has transformed Things of the real world into smarter devices. To date, the world has deployed billions of “smart” connected things. Predictions say there will be 10’s of billions of connected devices by 2025 and in our lifetime we will experience life with a trillion-node network. However, battery lifespan exhibits a critical barrier to scaling IoT devices. Replacing batteries on a trillion-sensor scale is a logistically prohibitive feat. Self-powered IoT devices seems to be the right direction to stand up to that challenge. The main objective of this thesis is to develop solutions to achieve energy-efficient wireless-connectivity and wireless-charging for IoT applications. In the first part of the thesis, I introduce ultra-low power radios that are compatible with the Bluetooth Low-Energy (BLE) standard. BLE is considered as the preeminent protocol for short-range communications that support transmission ranges up to 10’s of meters. Number of low power BLE transmitter (TX) and receiver (RX) architectures have been designed, fabricated and tested in different planar CMOS and FinFET technologies. The low power operation is achieved by combining low power techniques in both the network and physical layers, namely: backchannel communication, duty-cycling, open-loop transmission/reception, PLL-less architectures, and mixer-first architectures. Further novel techniques have been proposed to further reduce the power the consumption of the radio design, including: a fast startup time and low startup energy crystal oscillators, an antenna-chip co-design approach for quadrature generation in the RF path, an ultra-low power discrete-time differentiator-based Gaussian Frequency Shift Keying (GFSK) demodulation scheme, an oversampling GFSK modulation/demodulation scheme for open loop transmission/reception and packet synchronization, and a cell-based design approach that allows automation in the design of BLE digital architectures. The implemented BLE TXs transmit fully-compliant BLE advertising packet that can be received by commercial smartphone. In the second part of the thesis, I introduce passive nonlinear resonant circuits to achieve wide-band RF energy harvesting and robust wireless power transfer circuits. Nonlinear resonant circuits modeled by the Duffing nonlinear differential equation exhibit interesting hysteresis characteristics in their frequency and amplitude responses that are exploited in designing self-adaptive wireless charging systems. In the magnetic-resonance wireless power transfer scenario, coupled nonlinear resonators are proposed to maintain the power transfer level and efficiency over a range of coupling factors without active feedback control circuitry. Coupling factor depends on the transmission distance, lateral, and angular misalignments between the charging pad and the device. Therefore, nonlinear resonance extends the efficient charging zones of a wireless charger without the requirement for a precise alignment.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169842/1/omaratty_1.pd

Programmable DSP-enabled multi-adaptive optical transceivers based on OFDM technology for software defined networks

The dynamic behavior of the traffic demand, due to the advent of technologies such as cloud services or Internet of Things (IoT), is increasing. In fact, heterogeneous connections with different characteristics (bandwidth or bit rate) are expected that coexist in the optical networks. In this respect, an evolution towards Elastic Optical Networks (EONs) has emerged as a cost-effective, flexible and dynamic solution, to face the new claims. The main idea is the efficient utilization of the optical spectrum by combining flexible transceivers, flexi-grid and flexible optical switching. Including the principles of Software Defined Network (SDN) paradigm further flexibility and adaptability can be achieved. The Sliceable Bandwidth Variable Transceiver (S-BVT), as a key element in EONs, provides flexibility and adaptability to the optical networks. It is able to dynamically tune the optical bandwidth or bit rate changing parameters such as the modulation format, bandwidth, among others, to find a trade-off between transmission reach and spectral efficiency, serving multiples destinations. The combination of programmable Digital Signal Processing (DSP) modules with advanced transmission techniques based on Orthogonal Frequency Division Multiplexing (OFDM) technology using Direct Detection (DD) or COherent (CO) detection are proposed to be implemented at the S-BVT making it suitable for elastic optical metro/regional networks. Furthermore, the envisioned migration from fixed-grid to flexi-grid, can benefit from the use of S-BVTs since they are able to generate or receive multiple channels and slicing the aggregated flow into multiples flows with different capacities and destinations. We propose the use of S-BVTs based on multi-band OFDM systems. In particular, we focus on the theoretical model of an advanced transmission technique based on OFDM technology with DD. Then we evaluate the system for a realistic optical metro network. In the context of flexi-grid optical metro/regional networks, as well as the sliceability of the channels, the reduction of channel width for low bit rate connections can be envisioned. It involves that the signal traverses several nodes with the corresponding filtering elements, causing a substantially decrease and distortion of the signal bandwidth. This phenomenon known as filter narrowing effect has been also studied in this thesis, by simulations and experimentally for an adaptive cost-effective OFDM system using DD and for a standard OOK system. Apart from adaptive, flexible and programmable transceivers, metro optical networks have to be equipped with flexible optical switching systems at the node level. In this respect, we propose the adoption of adaptive S-BVTs based on advanced transmission techniques using DD with Discrete MultiTone (DMT) modulation and adaptive capabilities in combination with Semiconductor Optical Amplier (SOA)-based switching nodes. SOAs can be conveniently used for optical switching in metro networks because of their low cost or low power consumption, among others relevant characteristics. The system has been experimentally analyzed with and without considering filtering elements. Thanks to the combination of adaptive DMT modulation and SOA-based switching nodes, impairments due to the fiber links and the filtering elements can be compensated. Finally, to enhance the tranmission distance and data rate, we propose the combination of multidimensional constellations implemented at the DSP modules of the S-BVT with CO detection and OFDM technology. Thus, the deployed infrastructure is more efficiently exploited since the quadrature and the polarization dimensions are used to transmit the signal. In particular, we focus on CO-OFDM systems using Dual Polarization Quadrature Phase Shift Keying (DPQPSK) constellation transmitting the signal over the time and the polarization dimensions in the optical domain.El comportamiento dinámico de la demanda de tráfico, debido a la llegada de tecnologías como los servicios en la nube o el Internet of Things (IoT), está aumentando. De hecho, se espera que coexistan en las redes ópticas conexiones heterogéneas con características diferentes, tales como ancho de banda o tasa de bits. Para hacer frente a estas demandas es crucial una evolución de las redes ópticas. En este sentido, las Elastic Optical Networks (EONs) emergen como una solución rentable, flexible y dinámica. La idea principal se basa en la utilización eficiente del espectro óptico mediante la combinación de transceptores flexibles, redes flexibles y conmutación óptica flexible. Una mayor flexibilidad y adaptabilidad se puede conseguir incluyendo los principios del paradigma conocido como Software Defined Network (SDN). La adopción de la arquitectura SDN implica la separación del plano de control y de datos, permitiendo la programabilidad dinámica de la red. Un elemento clave en las EONs es el Sliceable Bandwidth Variable Transceiver (SBVT), ya que provee de flexibilidad y adaptabilidad a las redes ópticas. El S-BVT es capaz de cambiar el ancho de banda o la tasa de bits medicando parámetros como el formato de modulación, el ancho de banda o la codificación de Forward Error Correction (FEC), entre otros, para encontrar un equilibrio entre el alcance de la transmisión y la eficiencia espectral, sirviendo múltiples destinos. La combinación de módulos programables de Digital Signal Processing (DSP) con técnicas de transmisión avanzadas, basadas en la tecnología Orthogonal Frequency Division Multiplexing (OFDM) con detección directa o detección coherente, se han propuesto para ser implementadas en el S-BVT, haciéndolo adecuado para su uso en redes ópticas elásticas metropolitanas y regionales. Además, la migración prevista de las redes fijas a las redes flexibles, con el fin de explotar la granularidad de 12:5 GHz, puede beneficiarse del uso de S-BVTs ya que son capaces de generar y recibir múltiples canales y dividir el flujo agregado en múltiples flujos con diferentes capacidades y destinos. A este respecto, proponemos el uso de S-BVTs basados en señales OFDM multi banda combinadas en el dominio eléctrico con el fin de limitar los recursos optoelectrónicas y relajar los requerimientos de los convertidores digitales analógicos y analógicos digitales. En particular, nos centramos en el modelo teórico de una técnica de transmisión avanzada basada en la tecnología OFDM con detección directa. A continuación, evaluamos el sistema para una red metropolitana óptica realista. En el contexto de redes metropolitanas y regionales flexibles, además de la capacidad de división de los canales, se puede prever una posible reducción del ancho de canal para las conexiones de baja tasa de bits. Esto implica que la señal atraviese varios nodos con los correspondientes elementos filtrantes causando un substancial decremento y distorsión del ancho de banda de la señal. Este fenómeno conocido como el efecto de estrechamiento de filtrado ha sido también estudiado en esta tesis, mediante simulaciones y de manera experimental para un sistema OFDM rentable y adaptativo usando detección directa y un sistema estándar On-Off Keying (OOK). El sistema OFDM de detección directa ha resultado ser un buen candidato para aumentar la flexibilidad y la robustez frente a las deficiencias de transmisión sin necesidad de compensar la dispersión. Aparte de los transceptores adaptables, flexibles y programables, las redes ópticas metropolitanas deben estar equipadas con sistemas de conmutación óptica flexible a nivel de nodo. En este sentido, proponemos la adopción de S-BVTs adaptativos basados en técnicas de transmisión avanzadas usando detección directa con modulación Discrete MultiTone (DMT) y capacidades adaptativas, adoptando nodos de conmutación basados en Semiconductor Optical Amplifier (SOA). Los SOAs pueden ser utilizados para la conmutación óptica en redes metropolitanas debido a su bajo coste o bajo consumo de energía, entre otras características relevantes. El sistema ha sido analizado experimentalmente considerando y sin considerar la presencia de elementos filtrantes. Gracias a la combinación de la modulación DMT adaptativa y los nodos de conmutación basados en SOA, las degradaciones debidas a los enlaces de fibra y a los elementos filtrantes se pueden compensar. Finalmente, para mejorar la distancia de transmisión y la tasa de datos, proponemos la combinación de constelaciones multidimensionales implementadas en los módulos DSP del S-BVT utilizando detectaron coherente y la tecnología OFDM. De hecho, los sistemas OFDM coherentes tienen un espacio de señal 4D (dos cuadraturas y dos polarizaciones), que puede ser utilizado con constelaciones multidimensionales, pudiendo éstas ser más eficientes que las convencionales Binary Phase-Shift Keying (BPSK) o Quadrature Phase-Shift Keying (QPSK). De este modo, la infraestructura desplegada se explota de manera más eficiente, ya que tanto la dimensión de cuadratura como de polarización se utilizan para transmitir la señal. Además, los sistemas OFDM coherentes pueden recuperar la amplitud y la fase de la señal en el receptor, mitigando los efectos de la fibra aumentando, de esta forma, la distancia de transmisión. El sistema OFDM coherente que utiliza el formato de constelación Dual Polarization Quadrature Phase Shift Keying (DPQPSK) y que transmite la señal a lo largo del tiempo ha demostrado ser una solución prometedora.El comportament dinàmic de la demanda de transit, a causa de l'arribada de tecnologies, com poden ser els serveis al núvol o l'Internet of Things (IoT), està creixent. De fet, s'espera que coexisteixin a les xarxes òptiques connexions heterogènies amb característiques diferents, tal com l'ample de banda o la taxa de bits. Per a fer front a aquestes demandes és crucial una revolució de les xarxes òptiques. En aquest sentit, les Elastic Optical Networks (EONs) emergeixen com una solució rendible, flexible i dinàmica. La idea principal es basa en la utilització eficient de l'espectre òptic mitjançant la combinació de transceptors flexibles, xarxes flexibles i commutació òptica flexible. Una major flexibilitat i adaptabilitat es pot aconseguir incloent els principis del paradigma conegut com a Software Defined Networks (SDN). L’adopció de l'arquitectura SDN implica la separació del plànol de control i de dades permetent la programabilitat de la xarxa d'una forma dinàmica. Un element clau en les EONs és l'Sliceable Bandwith Variable Transceiver (S-BVT), ja que aporta flexibilitat i adaptabilitat a les xarxes òptiques. L' S-BVT és capaç de canviar l'ample de banda o la taxa de bits modificant paràmetres com el format de modulació, l'ample de banda o la codificació del Forward Error Correction (FEC), entre altres, per a trobar un equilibri entre l’assistència assolida i l’eficiència espectral, servint múltiples destinacions. La combinació de mòduls de Digital Signal Processing (DSP) amb tècniques de transmissió avançades basades en la tecnologia Orthogonal Frequency Division Multiplexing (OFDM) i detecció directa o detecció coherent s'han proposat per a ser implementades en l'S-BVT, fent-lo adient per a les xarxes òptiques elàstiques metropolitanes i regionals. A més, la migració prevista des de les xarxes fixes a les xarxes flexibles, amb el fi d'explotar la granuralitat de 12:5GHz, pot beneficiar-se de l’ús d'S-BVTs ja que són capaços de generar i rebre múltiples canals i dividir el flux agregat en múltiples fluxos amb diferents capacitats i destinacions. Per aquest motiu, proposem l’ús d'S-BVTs basats en senyals OFDM multi banda combinats en el domini elèctric amb el fi de limitar els recursos optoelectrònics i relaxar els requeriments dels convertidors digitals analògics i analògics digitals. Particularment, ens centrem en el model teòric d'una tècnica de transmissió avançada basada en la tecnologia OFDM amb detecció directa. A continuació, avaluem el sistema per a una xarxa metropolitana òptica realista. En el context de xarxes metropolitanes i regionals flexibles, a més de la propietat de divisió dels canals, es pot preveure una possible reducció de l'ample de canal per a les connexions de baixa taxa de bits. Això implica que el senyal travessi diversos nodes amb els corresponents elements filtrants causant un substancial decrement i distorsió de l'ample de banda del senyal. Aquest fenomen conegut com l'efecte d'estretament de filtrat ha sigut també estudiat en aquesta tesi, mitjançant simulacions i de manera experimental en el cas d'un sistema OFDM rendible i adaptatiu utilitzant detecció directa i un sistema estàndard On-Off Keying (OOK). El sistema OFDM de detecció directa ha resultat ser un bon candidat per augmentar la flexibilitat i la robustesa front a les deficiències de transmissió sense necessitat de compensar la dispersió. A part dels transceptors adaptables, flexibles i programables, les xarxes òptiques metropolitanes han d'estar equipades amb sistemes de commutació òptica flexible a nivell de node. En aquest sentit, proposem l’adopció d'un S-BVT adaptatiu basat en tècniques de transmissió avançades i utilitzant detecció directa amb modulació Discrete MultiTone (DMT) i capacitats adaptatives, adoptant nodes de comunicació basats en Semi-conductor Optical Amplifier (SOA). Els SOAs poden ser utilitzats per la commutació _òptica en xarxes metropolitanes degut al seu baix cost o baix consum d'energia, entre altres característiques rellevants. El sistema ha sigut analitzat experimentalment considerant i sense considerar la presència d'elements filtrants. Gràcies a la combinació de la modulació DMT adaptativa i dels nodes de commutació basats en SOA, les degradacions degudes als enllaços de fibra i als elements filtrants es poden compensar. Finalment, per a millorar la distància de transmissió i la taxa de dades, proposem la combinació de constel·lacions multidimensionals implementades als mòduls DSP de l'SBVT utilitzant detecció coherent i la tecnologia OFDM. De fet, els sistemes coherents OFDM tenen un espai de senyal 4D (dues quadratures i dues polaritzacions), que pot ser utilitzat amb constel·lacions multidimensionals, arribant a ser més eficients que les modulacions convencionals Binary Phase-Shift Keying (BPSK) o Quadrature Phase-Shift Keying (QPSK). D'aquesta manera, la infraestructura desplegada s'explota de forma més eficient, ja que tant la dimensió de quadratura com de polarització s'utilitzen per transmetre el senyal. A més, els sistemes coherents basats en OFDM poden recuperar l'amplitud i la fase del senyal en el receptor, mitigant els efectes de la fibra i d'aquesta forma augmentant la distància de transmissió. El sistema OFDM coherent que utilitza el format de constel·lació Dual Polarization Quadrature Phase Shift Keying (DPQPSK) i que transmet el senyal al llarg del temps ha demostrat ser una solució prometedora.Postprint (published version

Energy and spectral efficiency tradeoff in wireless communication

In the wireless communication world, a significant number of new user equipments is connecting to the network each and every day, and day after day this amount is increasing with no known bounds. Diverse quality of service (QoS) along with better system throughput are the crying needs at present. With the advancement in the field of massive multiple-input multiple-output (MMIMO) and Internet-of-things (IoT), the QoS is provided smoothly with the limited spectrum by the wireless operator. Hundreds of antenna elements in the digital arrays are set up at the base station in order to provide the smooth coverage and the best throughput within these spectra. However, implementing hundreds of antenna elements with associated a huge number of RF chains for digital beamforming consumes too much energy. Energy efficiency optimization has become a requirement at the present stage of wireless infrastructure. Due to the conflicting nature between the energy efficiency and the spectral efficiency, it is hard to make a balance. This thesis investigates how to achieve a good tradeoff between the energy and the spectral efficiency with maximum throughput outcomes from MMIMO, with the help of existing topologies and a futuristic perspective. Although the signal noise power is less in massive MIMO than the conventional cellular system, it still needs to be decreased and at the same time, the average channel gain per user equipment must be increased. Fixed power requirement for control signaling and load-independent power of backhaul infrastructure must be cut at least by a factor two as well as the power amplifier efficiency has to increase by 10% than LTE networks. The minimum mean square error (MMSE) estimator can be a possible solution in terms of the energy and the spectral efficiency despite having computational complexity which can be solved with the aid of Moore’s law and it is proposed by the non-profit research organization IMEC, which has developed an online web tool for observing and predicting contemporary as well as futuristic cellular base station’s power consumption. It supports various types of base stations with a wide range of operating conditions. The multicell minimum mean square error (M-MMSE) scheme can perform better than other existing schemes and showcase satisfactory tradeoff with frequency reuse factor higher than 2, where regularized zero-forcing (RZF) and maximum ratio (MR) combining fall down their capabilities for performing. With the precipitous rising of IoT, the Narrowband Internet-of-things (NB-IoT) may play an efficient supportive role if we can collaborate it with MMIMO. With its low power, wide area topologies combining with MMIMO technologies can show better tradeoffs. Due to its narrow bandwidth, the signal noise power would be less compared to the existent wideband topologies, and the average channel gain of active user equipment would be higher too. Hence it will give a great impact in terms of the tradeoff between energy and the spectral efficiency which is addressed in this thesis