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Signal Processing for Wireless Power and Information Transfer
The rapid development of the Internet of Things (IoT) and wireless sensor network (WSN) technologies enable easy access and control of a variety forms of information and data from numerous number of smart devices, and give rise to many novel applications and research areas such as smart home, machine type communications, etc. However due to the small sizes, sophisticated environment, and large number of devices in network, it is hard to directly power the devices from grid. Hence the power connectivity remains one of the major issues that needs to be addressed for related IoT applications. Wireless power transfer (WPT) and backscatter communications are provisioned to be prominent solutions to overcome the power connectivity challenge, but they suer strong efficiency limitation which becomes the barrier to universally popularize such technologies. On the other hand, network optimization is also a research focus of such applications which significantly affects the performance of the system due to the high volume of connected devices and different features. In this thesis we propose advanced techniques to overcome the challenges on the low efficiency and network design of the wireless information and power transfer systems. The thesis consists of two parts. In the first part we focus on the power transmitter design which addresses the low efficiency issue associated with backscatter communication and WPT. In Chapter 2, we consider a backscatter RFID system with the multi-antenna reader and propose a blind transmit and receive adaptive beamforming algorithm. The interrogation range and data transmission performance are both investigated under such configuration. In Chapter 3 we study wireless power transfer by the beamspace large-scale MIMO system with lens antenna arrays. We first present the WPT model for the beamspace MIMO which is derived from the spatial MIMO model. By constraining on the number of RF chains in the transmitter, we formulate two WPT optimization problems: the sum power transfer problem and the max-min power transfer problem. For both problems we consider two different transmission schemes, the multi-stream and uni-stream transmissions, and we propose different algorithms to solve both problems in both schemes respectively. In the second part we study the network optimization problems in the WPT and backscatter systems. In Chapter 4, we study the resource allocation problem for a RF-powered network, where the objective is to maximize the total data throughput of all sensors. We break the problem into two subproblems: the sensor battery energy utilization problem and the charging power allocation problem of the central node, which is an RF power transmitter that transmits RF power to the sensors. We analyze and show several key properties of both problems, and then propose computationally efficient algorithms to solve both problems optimally. In Chapter 5, we study the time scheduling problem in RF-powered backscatter communication networks, where all transmitters can operates in either backscattering mode or harvest-then-transmit (HTT) mode. The objective is to decide the operating mode of each transmitter and minimize the total transmission time of the network. We also consider both ideal and realistic transmitters based on different internal power consumption models for HTT transmitters. Under both transmitter models we show several key properties, and propose bisection based algorithms which has low computational complexity that solves the problem optimally. The results are then extended to the massive MIMO regime
A RISC-V SOC for Terahertz IoT Devices: Implementation and design challenges
Terahertz (THz) communication is considered a viable approach to augmenting
the communication capacity of prospective Internet-of-Things (IoT) resulting in
enhanced spectral efficiency. This study first provides an outline of the
design challenges encountered in developing THz transceivers. This paper
introduces advanced approaches and a unique methodology known as Modified
Pulse-width Modulation (MPWM) to address the issues in the THz domain. In this
situation involving a transceiver that handles complex modulation schemes, the
presence of a mixed signal through a high-resolution digital-to-analog
converter (DAC) in the transmitter greatly contributes to the limitation in
maintaining linearity at high frequencies. The utilization of Pulse-width
Modulation-based Digital-to-Analog Converters (PWM-DACs) has garnered
significant attention among scholars due to its efficiency and affordability.
However, the converters' performance is restricted by insufficient conversion
speed and precision, especially in the context of high-resolution, high-order
modulation schemes for THz wireless communications. The MPWM framework offers a
multitude of adjustable options, rendering the final MPWM-DAC highly adaptable
for a diverse array of application scenarios. Comparative performance
assessments indicate that MPWM-DACs have enhanced conversion speed compared to
standard PWM-DACs, and they also provide greater accuracy in comparison to
Pulse-count Modulation DACs (PCM-DACs). The study presents a comprehensive
examination of the core principles, spectrum characteristics, and evaluation
metrics, as well as the development and experimental validation of the MPWM
method. Furthermore, we present a RISC-V System-on-Chip (SoC) that incorporates
an MPWM-DAC, offering a highly favorable resolution for THz IoT communications.Comment: 18 pages, 17 figures, journa
A survey on hybrid beamforming techniques in 5G : architecture and system model perspectives
The increasing wireless data traffic demands have driven the need to explore suitable spectrum regions for meeting the projected requirements. In the light of this, millimeter wave (mmWave) communication has received considerable attention from the research community. Typically, in fifth generation (5G) wireless networks, mmWave massive multiple-input multiple-output (MIMO) communications is realized by the hybrid transceivers which combine high dimensional analog phase shifters and power amplifiers with lower-dimensional digital signal processing units. This hybrid beamforming design reduces the cost and power consumption which is aligned with an energy-efficient design vision of 5G. In this paper, we track the progress in hybrid beamforming for massive MIMO communications in the context of system models of the hybrid transceivers' structures, the digital and analog beamforming matrices with the possible antenna configuration scenarios and the hybrid beamforming in heterogeneous wireless networks. We extend the scope of the discussion by including resource management issues in hybrid beamforming. We explore the suitability of hybrid beamforming methods, both, existing and proposed till first quarter of 2017, and identify the exciting future challenges in this domain
Non-Orthogonal Multiple Access For Near-Field Communications
The novel concept of near-field non-orthogonal multiple access (NF-NOMA)
communications is proposed. The near-filed beamfocusing enables NOMA to be
carried out in both angular and distance domains. Two novel frameworks are
proposed, namely, single-location-beamfocusing NF-NOMA (SLB-NF-NOMA) and
multiple-location-beamfocusing NF-NOMA (MLB-NF-NOMA). 1) For SLB-NF-NOMA, two
NOMA users in the same angular direction with distinct quality of service (QoS)
requirements can be grouped into one cluster. The hybrid beamformer design and
power allocation problem is formulated to maximize the sum rate of the users
with higher QoS (H-QoS) requirements. To solve this problem, the analog
beamformer is first designed to focus the energy on the H-QoS users and the
zero-forcing (ZF) digital beamformer is employed. Then, the optimal power
allocation is obtained. 2) For MLB-NF-NOMA, the two NOMA users in the same
cluster can have different angular directions. The analog beamformer is first
designed to focus the energy on both two NOMA users. Then, a singular value
decomposition (SVD) based ZF (SVD-ZF) digital beamformer is designed.
Furthermore, a novel antenna allocation algorithm is proposed. Finally, a
suboptimal power allocation algorithm is proposed. Numerical results
demonstrate that the NF-NOMA can achieve a higher spectral efficiency and
provide a higher flexibility than conventional far-field NOMA
Intelligent Reflecting Surface Aided Wireless Power Transfer With a DC-Combining Based Energy Receiver and Practical Waveforms
This paper studies intelligent reflecting surface (IRS) aided wireless power transfer (WPT) to batteryless Internet of Everything (IoE) devices. A practical energy receiver (ER) with multiple antennas is investigated. Multiple RF energy flows gleaned by all the receive antennas are input multiple energy harvesters, which are further rectified to direct-current (DC) energy. The resultant multiple DC energy flows are then combined in the DC domain for energy storage. Three classic waveforms, namely deterministic waveform, M-QAM waveform, and Gaussian waveform, are considered for WPT. We maximize the output DC power by jointly designing the active transmit beamformer of the transmitter and the passive reflecting beamformer of the IRS with the above-mentioned waveforms, respectively, subject to the transmit power constraint at the transmitter and to the limited resolution constraints on the phase-shifters of the IRS. A low complexity alternating optimization (AO) algorithm is proposed, which converges to a Karush-Kuhn-Tucker (KKT) point and thus results in a locally optimal solution. The numerical results demonstrate that the Gaussian waveform has the best energy performance with a low input RF power to the energy harvesters. By contrast, the deterministic waveform becomes superior with a high input RF power to the energy harvesters
Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View
The next-generation wireless technologies, commonly referred to as the sixth
generation (6G), are envisioned to support extreme communications capacity and
in particular disruption in the network sensing capabilities. The terahertz
(THz) band is one potential enabler for those due to the enormous unused
frequency bands and the high spatial resolution enabled by both short
wavelengths and bandwidths. Different from earlier surveys, this paper presents
a comprehensive treatment and technology survey on THz communications and
sensing in terms of the advantages, applications, propagation characterization,
channel modeling, measurement campaigns, antennas, transceiver devices,
beamforming, networking, the integration of communications and sensing, and
experimental testbeds. Starting from the motivation and use cases, we survey
the development and historical perspective of THz communications and sensing
with the anticipated 6G requirements. We explore the radio propagation, channel
modeling, and measurements for THz band. The transceiver requirements,
architectures, technological challenges, and approaches together with means to
compensate for the high propagation losses by appropriate antenna and
beamforming solutions. We survey also several system technologies required by
or beneficial for THz systems. The synergistic design of sensing and
communications is explored with depth. Practical trials, demonstrations, and
experiments are also summarized. The paper gives a holistic view of the current
state of the art and highlights the issues and challenges that are open for
further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications
Surveys & Tutorial
The Road to Next-Generation Multiple Access: A 50-Year Tutorial Review
The evolution of wireless communications has been significantly influenced by
remarkable advancements in multiple access (MA) technologies over the past five
decades, shaping the landscape of modern connectivity. Within this context, a
comprehensive tutorial review is presented, focusing on representative MA
techniques developed over the past 50 years. The following areas are explored:
i) The foundational principles and information-theoretic capacity limits of
power-domain non-orthogonal multiple access (NOMA) are characterized, along
with its extension to multiple-input multiple-output (MIMO)-NOMA. ii) Several
MA transmission schemes exploiting the spatial domain are investigated,
encompassing both conventional space-division multiple access (SDMA)/MIMO-NOMA
systems and near-field MA systems utilizing spherical-wave propagation models.
iii) The application of NOMA to integrated sensing and communications (ISAC)
systems is studied. This includes an introduction to typical NOMA-based
downlink/uplink ISAC frameworks, followed by an evaluation of their performance
limits using a mutual information (MI)-based analytical framework. iv) Major
issues and research opportunities associated with the integration of MA with
other emerging technologies are identified to facilitate MA in next-generation
networks, i.e., next-generation multiple access (NGMA). Throughout the paper,
promising directions are highlighted to inspire future research endeavors in
the realm of MA and NGMA.Comment: 43 pages, 38 figures; Submitted to Proceedings of the IEE
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