223 research outputs found
Novel High Isolation Antennas for Simultaneous Transmit and Receive (STAR) Applications
Radio frequency (RF) spectrum congestion is a major challenge for the growing need of wireless bandwidth. Notably, in 2015, the Federal Communications Commission (FCC) auctioned just 65 MHz (a bandwidth smaller than that used for WiFi) for more than $40 billion, indicating the high value of the microwave spectrum. Current radios use one-half of their bandwidth resource for transmission, and the other half for reception. Therefore, by enabling radios to transmit and receive across their entire bandwidth allocation, spectral efficiency is doubled. Concurrently, data rates for wireless links also double. This technology leads to a new class of radios and RF frontends. Current full-duplex techniques resort to either time- or frequency-division duplexing (TDD and FDD respectively) to partition the transmit and receive functions across time and frequency, respectively, to avoid self-interference. But these approaches do not translate to spectral efficiency.
Simultaneous transmit and receive (STAR) radios must isolate the transmitter from the receiver to avoid self-interference (SI). This SI prevents reception and must therefore be cancelled. Self-interference may be cancelled with one or more stages involving the antenna, RF or analog circuits, or digital filters. With this in mind, the antenna stage is the most critical to reduce the SI level and avoid circuit saturation and total system failure.
This dissertation presents techniques for achieving STAR radios. The initial sections of the dissertation provide the general approach of stage to stage cancellation to achieve as much as 100 dB isolation between the receiver and transmitter. The subsequent chapters focus on different antennas to achieve strong transmit/receive isolation. As much as 35 dB isolation is shown using a new spiral antenna array with operation across a 2:1 bandwidth. Also, a new antenna feed is presented showing 42 dB isolation across a 250 MHz bandwidth. Reflections in the presence of a dynamic environment are also considered
Interference charecterisation, location and bandwidth estimation in emerging WiFi networks
Wireless LAN technology based on the IEEE 802.11 standard, commonly referred
to as WiFi, has been hugely successful not only for the last hop access to the Internet
in home, office and hotspot scenarios but also for realising wireless backhaul in mesh
networks and for point -to -point long- distance wireless communication. This success
can be mainly attributed to two reasons: low cost of 802.11 hardware from reaching
economies of scale, and operation in the unlicensed bands of wireless spectrum.The popularity of WiFi, in particular for indoor wireless access at homes and offices,
has led to significant amount of research effort looking at the performance issues
arising from various factors, including interference, CSMA/CA based MAC protocol
used by 802.11 devices, the impact of link and physical layer overheads on application
performance, and spatio-temporal channel variations. These factors affect the performance
of applications and services that run over WiFi networks. In this thesis, we
experimentally investigate the effects of some of the above mentioned factors in the
context of emerging WiFi network scenarios such as multi- interface indoor mesh networks,
802.11n -based WiFi networks and WiFi networks with virtual access points
(VAPs). More specifically, this thesis comprises of four experimental characterisation
studies: (i) measure prevalence and severity of co- channel interference in urban WiFi
deployments; (ii) characterise interference in multi- interface indoor mesh networks;
(iii) study the effect of spatio-temporal channel variations, VAPs and multi -band operation
on WiFi fingerprinting based location estimation; and (iv) study the effects of
newly introduced features in 802.11n like frame aggregation (FA) on available bandwidth
estimation.With growing density of WiFi deployments especially in urban areas, co- channel
interference becomes a major factor that adversely affects network performance. To
characterise the nature of this phenomena at a city scale, we propose using a new measurement
methodology called mobile crowdsensing. The idea is to leverage commodity
smartphones and the natural mobility of people to characterise urban WiFi co- channel
interference. Specifically, we report measurement results obtained for Edinburgh, a
representative European city, on detecting the presence of deployed WiFi APs via the
mobile crowdsensing approach. These show that few channels in 2.4GHz are heavily
used and there is hardly any activity in the 5GHz band even though relatively it
has a greater number of available channels. Spatial analysis of spectrum usage reveals
that co- channel interference among nearby APs operating in the same channel
can be a serious problem with around 10 APs contending with each other in many locations. We find that the characteristics of WiFi deployments at city -scale are similar
to those of WiFi deployments in public spaces of different indoor environments. We
validate our approach in comparison with wardriving, and also show that our findings
generally match with previous studies based on other measurement approaches. As
an application of the mobile crowdsensing based urban WiFi monitoring, we outline a
cloud based WiFi router configuration service for better interference management with
global awareness in urban areas.For mesh networks, the use of multiple radio interfaces is widely seen as a practical
way to achieve high end -to -end network performance and better utilisation of
available spectrum. However this gives rise to another type of interference (referred to
as coexistence interference) due to co- location of multiple radio interfaces. We show
that such interference can be so severe that it prevents concurrent successful operation
of collocated interfaces even when they use channels from widely different frequency
bands. We propose the use of antenna polarisation to mitigate such interference and
experimentally study its benefits in both multi -band and single -band configurations. In
particular, we show that using differently polarised antennas on a multi -radio platform
can be a helpful counteracting mechanism for alleviating receiver blocking and adjacent
channel interference phenomena that underlie multi -radio coexistence interference.
We also validate observations about adjacent channel interference from previous
studies via direct and microscopic observation of MAC behaviour.Location is an indispensable information for navigation and sensing applications.
The rapidly growing adoption of smartphones has resulted in a plethora of mobile
applications that rely on position information (e.g., shopping apps that use user position
information to recommend products to users and help them to find what they want
in the store). WiFi fingerprinting is a popular and well studied approach for indoor
location estimation that leverages the existing WiFi infrastructure and works based on
the difference in strengths of the received AP signals at different locations. However,
understanding the impact of WiFi network deployment aspects such as multi -band
APs and VAPs has not received much attention in the literature. We first examine the
impact of various aspects underlying a WiFi fingerprinting system. Specifically, we
investigate different definitions for fingerprinting and location estimation algorithms
across different indoor environments ranging from a multi- storey office building to
shopping centres of different sizes. Our results show that the fingerprint definition
is as important as the choice of location estimation algorithm and there is no single
combination of these two that works across all environments or even all floors of a given environment. We then consider the effect of WiFi frequency bands (e.g., 2.4GHz
and 5GHz) and the presence of virtual access points (VAPs) on location accuracy with
WiFi fingerprinting. Our results demonstrate that lower co- channel interference in the
5GHz band yields more accurate location estimation. We show that the inclusion of
VAPs has a significant impact on the location accuracy of WiFi fingerprinting systems;
we analyse the potential reasons to explain the findings.End -to -end available bandwidth estimation (ABE) has a wide range of uses, from
adaptive application content delivery, transport-level transmission rate adaptation and
admission control to traffic engineering and peer node selection in peer -to- peer /overlay
networks [ 1, 2]. Given its importance, it has been received much research attention in
both wired data networks and legacy WiFi networks (based on 802.11 a/b /g standards),
resulting in different ABE techniques and tools proposed to optimise different criteria
and suit different scenarios. However, effects of new MAC/PHY layer enhancements
in new and next generation WiFi networks (based on 802.11n and 802.11ac
standards) have not been studied yet. We experimentally find that among different
new features like frame aggregation, channel bonding and MIMO modes (spacial division
multiplexing), frame aggregation has the most harmful effect as it has direct
effect on ABE by distorting the measurement probing traffic pattern commonly used
to estimate available bandwidth. Frame aggregation is also specified in both 802.11n
and 802.1 lac standards as a mandatory feature to be supported. We study the effect of
enabling frame aggregation, for the first time, on the performance of the ABE using an
indoor 802.11n wireless testbed. The analysis of results obtained using three tools -
representing two main Probe Rate Model (PRM) and Probe Gap Model (PGM) based
approaches for ABE - led us to come up with the two key principles of jumbo probes
and having longer measurement probe train sizes to counter the effects of aggregating
frames on the performance of ABE tools. Then, we develop a new tool, WBest+ that
is aware of the underlying frame aggregation by incorporating these principles. The
experimental evaluation of WBest+ shows more accurate ABE in the presence of frame
aggregation.Overall, the contributions of this thesis fall in three categories - experimental
characterisation, measurement techniques and mitigation/solution approaches for performance
problems in emerging WiFi network scenarios. The influence of various factors
mentioned above are all studied via experimental evaluation in a testbed or real - world setting. Specifically, co- existence interference characterisation and evaluation
of available bandwidth techniques are done using indoor testbeds, whereas characterisation of urban WiFi networks and WiFi fingerprinting based location estimation are
carried out in real environments. New measurement approaches are also introduced
to aid better experimental evaluation or proposed as new measurement tools. These
include mobile crowdsensing based WiFi monitoring; MAC/PHY layer monitoring of
co- existence interference; and WBest+ tool for available bandwidth estimation. Finally,
new mitigation approaches are proposed to address challenges and problems
identified throughout the characterisation studies. These include: a proposal for crowd - based interference management in large scale uncoordinated WiFi networks; exploiting
antenna polarisation diversity to remedy the effects of co- existence interference
in multi -interface platforms; taking advantage of VAPs and multi -band operation for
better location estimation; and introducing the jumbo frame concept and longer probe
train sizes to improve performance of ABE tools in next generation WiFi networks
User Experience Enhancement on Smartphones using Wireless Communication Technologies
학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 박세웅.Recently, various sensors as well as wireless communication technologies such as
Wi-Fi and Bluetooth Low Energy (BLE) have been equipped with smartphones. In
addition, in many cases, users use a smartphone while on the move, so if a wireless
communication technologies and various sensors are used for a mobile user, a better
user experience can be provided. For example, when a user moves while using Wi-Fi,
the user experience can be improved by providing a seamless Wi-Fi service. In addition,
it is possible to provide a special service such as indoor positioning or navigation
by estimating the users mobility in an indoor environment, and additional services
such as location-based advertising and payment systems can also be provided. Therefore,
improving the user experience by using wireless communication technology and
smartphones sensors is considered to be an important research field in the future.
In this dissertation, we propose three systems that can improve the user experience
or convenience by usingWi-Fi, BLE, and smartphones sensors: (i) BLEND: BLE
beacon-aided fast Wi-Fi handoff for smartphones, (ii) PYLON: Smartphone based Indoor
Path Estimation and Localization without Human Intervention, (iii) FINISH:
Fully-automated Indoor Navigation using Smartphones with Zero Human Assistance.
First, we propose fast handoff scheme called BLEND exploiting BLE as secondary
radio. We conduct detailed analysis of the sticky client problem on commercial smartphones
with experiment and close examination of Android source code. We propose
BLEND, which exploits BLE modules to provide smartphones with prior knowledge
of the presence and information of APs operating at 2.4 and 5 GHz Wi-Fi channels.
BLEND operating with only application requires no hardware and Android source code
modification of smartphones.We prototype BLEND with commercial smartphones and
evaluate the performance in real environment. Our measurement results demonstrate
that BLEND significantly improves throughput and video bitrate by up to 61% and
111%, compared to a commercial Android application, respectively, with negligible
energy overhead.
Second, we design a path estimation and localization system, termed PYLON,
which is plug-and-play on Android smartphones. PYLON includes a novel landmark
correction scheme that leverages real doors of indoor environments consisting of floor
plan mapping, door passing time detection and correction. It operates without any user
intervention. PYLON relaxes some requirements for localization systems. It does not
require any modifications to hardware or software of smartphones, and the initial location
of WiFi APs, BLE beacons, and users. We implement PYLON on five Android
smartphones and evaluate it on two office buildings with the help of three participants
to prove applicability and scalability. PYLON achieves very high floor plan mapping
accuracy with a low localization error.
Finally, We design a fully-automated navigation system, termed FINISH, which
addresses the problems of existing previous indoor navigation systems. FINISH generates
the radio map of an indoor building based on the localization system to determine
the initial location of the user. FINISH relaxes some requirements for current
indoor navigation systems. It does not require any human assistance to provide navigation
instructions. In addition, it is plug-and-play on Android smartphones. We implement
FINISH on five Android smartphones and evaluate it on five floors of an office
building with the help of multiple users to prove applicability and scalability. FINISH
determines the location of the user with extremely high accuracy with in one step.
In summary, we propose systems that enhance the users convenience and experience
by utilizing wireless infrastructures such as Wi-Fi and BLE and various smartphones
sensors such as accelerometer, gyroscope, and barometer equipped in smartphones.
Systems are implemented on commercial smartphones to verify the performance
through experiments. As a result, systems show the excellent performance that
can enhance the users experience.1 Introduction 1
1.1 Motivation 1
1.2 Overview of Existing Approaches 3
1.2.1 Wi-Fi handoff for smartphones 3
1.2.2 Indoor path estimation and localization 4
1.2.3 Indoor navigation 5
1.3 Main Contributions 7
1.3.1 BLEND: BLE Beacon-aided Fast Handoff for Smartphones 7
1.3.2 PYLON: Smartphone Based Indoor Path Estimation and Localization with Human Intervention 8
1.3.3 FINISH: Fully-automated Indoor Navigation using Smartphones with Zero Human Assistance 9
1.4 Organization of Dissertation 10
2 BLEND: BLE Beacon-Aided FastWi-Fi Handoff for Smartphones 11
2.1 Introduction 11
2.2 Related Work 14
2.2.1 Wi-Fi-based Handoff 14
2.2.2 WPAN-aided AP Discovery 15
2.3 Background 16
2.3.1 Handoff Procedure in IEEE 802.11 16
2.3.2 BSS Load Element in IEEE 802.11 16
2.3.3 Bluetooth Low Energy 17
2.4 Sticky Client Problem 17
2.4.1 Sticky Client Problem of Commercial Smartphone 17
2.4.2 Cause of Sticky Client Problem 20
2.5 BLEND: Proposed Scheme 21
2.5.1 Advantages and Necessities of BLE as Secondary Low-Power Radio 21
2.5.2 Overall Architecture 22
2.5.3 AP Operation 23
2.5.4 Smartphone Operation 24
2.5.5 Verification of aTH estimation 28
2.6 Performance Evaluation 30
2.6.1 Implementation and Measurement Setup 30
2.6.2 Saturated Traffic Scenario 31
2.6.3 Video Streaming Scenario 35
2.7 Summary 38
3 PYLON: Smartphone based Indoor Path Estimation and Localization without Human Intervention 41
3.1 Introduction 41
3.2 Background and Related Work 44
3.2.1 Infrastructure-Based Localization 44
3.2.2 Fingerprint-Based Localization 45
3.2.3 Model-Based Localization 45
3.2.4 Dead Reckoning 46
3.2.5 Landmark-Based Localization 47
3.2.6 Simultaneous Localization and Mapping (SLAM) 47
3.3 System Overview 48
3.3.1 Notable RSSI Signature 49
3.3.2 Smartphone Operation 50
3.3.3 Server Operation 51
3.4 Path Estimation 52
3.4.1 Step Detection 52
3.4.2 Step Length Estimation 54
3.4.3 Walking Direction 54
3.4.4 Location Update 55
3.5 Landmark Correction Part 1: Virtual Room Generation 56
3.5.1 RSSI Stacking Difference 56
3.5.2 Virtual Room Generation 57
3.5.3 Virtual Graph Generation 59
3.5.4 Physical Graph Generation 60
3.6 Landmark Correction Part 2: From Floor Plan Mapping to Path Correction 60
3.6.1 Candidate Graph Generation 60
3.6.2 Backbone Node Mapping 62
3.6.3 Dead-end Node Mapping 65
3.6.4 Final Candidate Graph Selection 66
3.6.5 Door Passing Time Detection 68
3.6.6 Path Correction 70
3.7 Particle Filter 71
3.8 Performance Evaluation 73
3.8.1 Implementation and Measurement Setup 73
3.8.2 Step Detection Accuracy 77
3.8.3 Floor Plan Mapping Accuracy 77
3.8.4 Door Passing Time 78
3.8.5 Walking Direction and Localization Performance 81
3.8.6 Impact of WiFi AP and BLE Beacon Number 84
3.8.7 Impact of Walking Distance and Speed 84
3.8.8 Performance on Different Areas 87
3.9 Summary 87
4 FINISH: Fully-automated Indoor Navigation using Smartphones with Zero Human Assistance 91
4.1 Introduction 91
4.2 Related Work 92
4.2.1 Localization-based Navigation System 92
4.2.2 Peer-to-peer Navigation System 93
4.3 System Overview 93
4.3.1 System Architecture 93
4.3.2 An Example for Navigation 95
4.4 Level Change Detection and Floor Decision 96
4.4.1 Level Change Detection 96
4.5 Real-time navigation 97
4.5.1 Initial Floor and Location Decision 97
4.5.2 Orientation Adjustment 98
4.5.3 Shortest Path Estimation 99
4.6 Performance Evaluation 99
4.6.1 Initial Location Accuracy 99
4.6.2 Real-Time Navigation Accuracy 100
4.7 Summary 101
5 Conclusion 102
5.1 Research Contributions 102
5.2 Future Work 103
Abstract (In Korean) 118
감사의 글Docto
Ultra-Wideband Phased Arrays for Small Mobile Platforms
This dissertation presents the development of a new class of Ultra-Wideband (UWB) apertures for aerial applications by introducing designs with over 50:1 bandwidth and novel differential feeding approaches. Designs that enable vertical integration for flip-chip millimeter-wave (UWB) transceivers are presented for small aerial platforms. Specifically, a new scalable tightly coupled array is introduced with differential feeding for chip integration. This new class of beam-forming arrays are fabricated and experimentally tested for validation with operation from as low as 130 MHz up to 18 GHz. A major achievement is the study of millimeter wave beamforming designs that operate from 22-80 GHz, fabricated using low-cost printed circuit board (PCB) methods. This low-cost fabrication approach and associated testing of the beamforming arrays are unique and game-changing
Customer premise service study for 30/20 GHz satellite system
Satellite systems in which the space segment operates in the 30/20 GHz frequency band are defined and compared as to their potential for providing various types of communications services to customer premises and the economic and technical feasibility of doing so. Technical tasks performed include: market postulation, definition of the ground segment, definition of the space segment, definition of the integrated satellite system, service costs for satellite systems, sensitivity analysis, and critical technology. Based on an analysis of market data, a sufficiently large market for services is projected so as to make the system economically viable. A large market, and hence a high capacity satellite system, is found to be necessary to minimize service costs, i.e., economy of scale is found to hold. The wide bandwidth expected to be available in the 30/20 GHz band, along with frequency reuse which further increases the effective system bandwidth, makes possible the high capacity system. Extensive ground networking is required in most systems to both connect users into the system and to interconnect Earth stations to provide spatial diversity. Earth station spatial diversity is found to be a cost effective means of compensating the large fading encountered in the 30/20 GHz operating band
Space Shuttle/TDRSS communication and tracking systems analysis
In order to evaluate the technical and operational problem areas and provide a recommendation, the enhancements to the Tracking and Data Delay Satellite System (TDRSS) and Shuttle must be evaluated through simulation and analysis. These enhancement techniques must first be characterized, then modeled mathematically, and finally updated into LinCsim (analytical simulation package). The LinCsim package can then be used as an evaluation tool. Three areas of potential enhancements were identified: shuttle payload accommodations, TDRSS SSA and KSA services, and shuttle tracking system and navigation sensors. Recommendations for each area were discussed
Aeronautical engineering: A special bibliography with indexes, supplement 82, April 1977
This bibliography lists 311 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1977
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