719 research outputs found
Algebraic Network Coding Approach to Deterministic Wireless Relay Networks
The deterministic wireless relay network model, introduced by Avestimehr et
al., has been proposed for approximating Gaussian relay networks. This model,
known as the ADT network model, takes into account the broadcast nature of
wireless medium and interference. Avestimehr et al. showed that the Min-cut
Max-flow theorem holds in the ADT network.
In this paper, we show that the ADT network model can be described within the
algebraic network coding framework introduced by Koetter and Medard. We prove
that the ADT network problem can be captured by a single matrix, called the
"system matrix". We show that the min-cut of an ADT network is the rank of the
system matrix; thus, eliminating the need to optimize over exponential number
of cuts between two nodes to compute the min-cut of an ADT network.
We extend the capacity characterization for ADT networks to a more general
set of connections. Our algebraic approach not only provides the Min-cut
Max-flow theorem for a single unicast/multicast connection, but also extends to
non-multicast connections such as multiple multicast, disjoint multicast, and
two-level multicast. We also provide sufficiency conditions for achievability
in ADT networks for any general connection set. In addition, we show that the
random linear network coding, a randomized distributed algorithm for network
code construction, achieves capacity for the connections listed above.
Finally, we extend the ADT networks to those with random erasures and cycles
(thus, allowing bi-directional links). Note that ADT network was proposed for
approximating the wireless networks; however, ADT network is acyclic.
Furthermore, ADT network does not model the stochastic nature of the wireless
links. With our algebraic framework, we incorporate both cycles as well as
random failures into ADT network model.Comment: 9 pages, 12 figures, submitted to Allerton Conferenc
Algebraic Watchdog: Mitigating Misbehavior in Wireless Network Coding
We propose a secure scheme for wireless network coding, called the algebraic
watchdog. By enabling nodes to detect malicious behaviors probabilistically and
use overheard messages to police their downstream neighbors locally, the
algebraic watchdog delivers a secure global self-checking network. Unlike
traditional Byzantine detection protocols which are receiver-based, this
protocol gives the senders an active role in checking the node downstream. The
key idea is inspired by Marti et al.'s watchdog-pathrater, which attempts to
detect and mitigate the effects of routing misbehavior.
As an initial building block of a such system, we first focus on a two-hop
network. We present a graphical model to understand the inference process nodes
execute to police their downstream neighbors; as well as to compute, analyze,
and approximate the probabilities of misdetection and false detection. In
addition, we present an algebraic analysis of the performance using an
hypothesis testing framework that provides exact formulae for probabilities of
false detection and misdetection.
We then extend the algebraic watchdog to a more general network setting, and
propose a protocol in which we can establish trust in coded systems in a
distributed manner. We develop a graphical model to detect the presence of an
adversarial node downstream within a general multi-hop network. The structure
of the graphical model (a trellis) lends itself to well-known algorithms, such
as the Viterbi algorithm, which can compute the probabilities of misdetection
and false detection. We show analytically that as long as the min-cut is not
dominated by the Byzantine adversaries, upstream nodes can monitor downstream
neighbors and allow reliable communication with certain probability. Finally,
we present simulation results that support our analysis.Comment: 10 pages, 10 figures, Submitted to IEEE Journal on Selected Areas in
Communications (JSAC) "Advances in Military Networking and Communications
A Multi-hop Multi-source Algebraic Watchdog
In our previous work "An Algebraic Watchdog for Wireless Network Coding", we
proposed a new scheme in which nodes can detect malicious behaviors
probabilistically, police their downstream neighbors locally using overheard
messages; thus, provide a secure global "self-checking network". As the first
building block of such a system, we focused on a two-hop network, and presented
a graphical model to understand the inference process by which nodes police
their downstream neighbors and to compute the probabilities of misdetection and
false detection.
In this paper, we extend the Algebraic Watchdog to a more general network
setting, and propose a protocol in which we can establish "trust" in coded
systems in a distributed manner. We develop a graphical model to detect the
presence of an adversarial node downstream within a general two-hop network.
The structure of the graphical model (a trellis) lends itself to well-known
algorithms, such as Viterbi algorithm, that can compute the probabilities of
misdetection and false detection. Using this as a building block, we generalize
our scheme to multi-hop networks. We show analytically that as long as the
min-cut is not dominated by the Byzantine adversaries, upstream nodes can
monitor downstream neighbors and allow reliable communication with certain
probability. Finally, we present preliminary simulation results that support
our analysis.Comment: 5 pages, 2 figures, to appear in IEEE ITW Dublin 201
Modeling Network Coded TCP Throughput: A Simple Model and its Validation
We analyze the performance of TCP and TCP with network coding (TCP/NC) in
lossy wireless networks. We build upon the simple framework introduced by
Padhye et al. and characterize the throughput behavior of classical TCP as well
as TCP/NC as a function of erasure rate, round-trip time, maximum window size,
and duration of the connection. Our analytical results show that network coding
masks erasures and losses from TCP, thus preventing TCP's performance
degradation in lossy networks, such as wireless networks. It is further seen
that TCP/NC has significant throughput gains over TCP. In addition, we simulate
TCP and TCP/NC to verify our analysis of the average throughput and the window
evolution. Our analysis and simulation results show very close concordance and
support that TCP/NC is robust against erasures. TCP/NC is not only able to
increase its window size faster but also to maintain a large window size
despite losses within the network, whereas TCP experiences window closing
essentially because losses are mistakenly attributed to congestion.Comment: 9 pages, 12 figures, 1 table, submitted to IEEE INFOCOM 201
When Similarity Strikes Back: The Positive and Negative Role of Character-Audience Similarity in Anti-Smoking Campaigns
As media technology evolves quickly, tailored and targeted communication has emerged as an important strategy in persuasion. One of the most widely used and easiest tactics of tailoring is using an exemplar or persuader character similar to the target audience. However, the effect of character-audience similarity may significantly differ depending on other message features such as how the similar character is shown to behave within the message. This dissertation examines the positive and negative effects of the similarity between the audience and the exemplar character in anti-smoking public service announcements (PSAs), based on demographics and smoking status. Would character-audience similarity still exert positive effect on persuasion even when the target of similarity assessment is shown to behave in socially unacceptable ways?
Two secondary data analyses on video anti-smoking PSAs were conducted first. Study 1 examined the main effect of character-audience similarity, finding a significant positive effect of demographic similarity between the smoker character and the audience. Study 2 focused on the secondhand smoking (SHS)-themed PSAs, where the smoker characterโs behavior may be seen as irresponsible and immoral by causing serious harm to others. The impact of character-audience similarity depended on the severity of consequences caused by SHS, so that the usually positive effects of character-audience similarity disappeared in PSAs depicting highly severe consequences of SHS. However, the effect was only marginally significant.
Informed by these two studies, an experiment (Study 3) was conducted to systematically manipulate and examine the effect of character-audience similarity (Similar vs. Dissimilar), theme of the message (self-harm vs. harm of SHS), and severity of consequences (high vs. low severity). A consistently negative and significant two-way interaction effect between character-audience similarity and theme emerged, suggesting that seeing a similar smoker character harming their own health (self-harm condition) increased engagement with the message and identification with the character, which in turn was associated with greater perceived effectiveness (PE). However, seeing a similar smoker endangering others via secondhand smoking (SHS condition) decreased engagement and identification, causing a boomerang effect on message effectiveness.
The results provide valuable guidelines for message design regarding the use of character-audience similarity: When the exemplar character acts in socially undesirable ways, such as endangering others via secondhand smoking, character-audience similarity might backfire, and message designers should avoid tailoring via character-audience similarity. While the studies in this dissertation were limited in the topics of smoking tobacco cigarettes, other behaviors (e.g. drunk driving) may also be subject to similar effects given that driving under the influence may lead to serious negative consequences on innocent others
Placemaking and the Loss of Place: Perceptions of Tourism-Induced Neighborhood Change in South Koreaโs Disadvantaged Neighborhoods
This dissertation research uncovers how seemingly beneficial urban projects associated with tourism reinforce inequitable urban environments and loss of place by examining different perceptions and experiences of tourism-induced neighborhood change in disadvantaged neighborhoods in South Korea. I investigate how public art projects implemented by the government to regenerate daldongnesโinformal hillside settlementsโhave brought economic and social disruption to residents and generated a series of contest outcomes. In this research, I examine how touristsโ perceptions and representation of the neighborhood in social media contribute to the (re)construction of the neighborhood, how the growth of tourism has influenced place attachment, and how residents and small-business owners experience indirect displacement induced by tourist gentrification. I use ethnographic fieldwork and qualitative methods to explore how, by whom, and with what effects the neighborhoods are reimagined and reconstructed as contradictory sites to visit and explore. I have demonstrated in my research that the coexistence of tourism and everyday life in the space of residential neighborhoods has led us to rethink a series of controversial outcomes accompanied by the process of neighborhood transformation. This includes the full understanding of perceptions and experiences of different stakeholders, a fluid and relational understanding of place attachment in touristifying neighborhoods, and an expanded understanding of displacement that includes both direct and indirect displacement. By doing so, my research contributes to a wide range of scholarship within urban and tourism geography, critical tourism studies, and Asian studies by engaging with interdisciplinary theories and concepts. My key findings are as follows. First, I contend that so-called โneighborhood improvement projectsโ are, in fact, micro-scale projects of entrepreneurial place-making. The reproduction of daldongnes as tourism destinations primarily serves a โnostalgic fantasyโ for a romanticized, fading past for outsiders, instead of properly addressing the real needs of marginalized residents. This disparity has served as the seed of a complex neighborhood conflict. Second, I claim that a fluid and relational understanding of place attachment is critical in understanding the complexity in daldongnes changing through touristification. I claim that place still matters in being an object of strong attachment, and people continuously construct, adapt, and reshape their place attachment during the process of tourism-induced neighborhood change. Thus, I contend that urban policy must recognize these dynamics of place attachment in order to address community conflicts likely to emerge with tourism development. Place attachment could not only positively bring the community together but also rupture relationships. Finally, focusing only on numbers of displaced people by excessive rent increases in a touristified daldongne presents a partial understanding of neighborhood change. This is because people can experience displacement without actual physical displacement. Thus, it is critical to engage with indirect displacementโemotional, psychosocial, and material impacts of displacementโto understand the phenomenon in a daldongne fully. While daldongnes are essential and exciting in their own right, the study of these neighborhoods enriches several bodies of literature and areas of geographic investigation. As I have demonstrated in this research, uncovering tourism-induced neighborhood change is an essential and inherently geographic phenomenon that reflects a complex people-place relationship that calls for more geographers\u27 engagement. A critical analysis of such a tourism phenomenon serves not only as a way to unpack the broader issue of urban inequality and marginalization but also as a way to discover what sustainable, just, and inclusive urban-dwelling means and to envision ideal neighborhood change
An approach to Handling Irregular Oversaturation in Urban Subway Stations
Train timetable, Passenger waiting time, Oversaturated condition, Genetic algorithmThis Theses presents a data-based approach for a train scheduling that aims to minimize passenger waiting time by controlling train departure time and the number of skipped trains. In contrast to existing approaches that rely on a statistical model of passenger arrival, we develop a model based on real-world automated fare collection (AFC) data from a metro line in Daegu, a Korean city. The model consists of decomposing the travel time for each passenger into waiting, riding, and walking times, clustering of passengers by trains they ride and calculating the number of passengers in each train for any given time. Based on this, for a given train schedule, the passenger waiting time of each passenger for the entire AFC data period can be calculated. The problem is formulated using the model under realistic constraints such as headway, the number of available trains, and train capacity. To find the optimal solution, we employed a genetic algorithm (GA). The results demonstrate that the average waiting time is reduced up to 56% in the highly congested situation. Moreover, letting the trains directly go to the congested station by skipping previous stations further reduces the maximum waiting time by up to 19%. The effect of the optimization varies depending on the passenger arrival pattern of highly congested stations. This approach will improve the quality of the subway services by reducing passenger waiting time.openโ
. INTRODUCTION 1
II. RELATED WORK 4
2.1. Passenger Volume Estimation 4
2.2. Train Scheduling Optimization 5
III. PROPOSED APPROACH 6
3.1. Overview 6
3.2. Dataset 8
3.3. Scenario Analysis 9
3.3.1 Peak Hours Scenario 10
3.3.2 Congested Off-Peak Hours Scenario 10
IV. PROBLEM FORMULATION 13
4.1. Assumptions 13
4.2. Train Capacity 15
4.3. Passenger Volume Estimation 15
4.3.1. Passenger Volume on the Train 16
4.3.2. Passenger Volume on the Platform 20
4.4. Timetable Optimization Model 20
4.4.1. Train Departure Time Control 21
4.4.1.1. Passenger Waiting Time Minimization Problem 21
4.4.1.2. Oversaturation Time Minimization Problem 24
4.4.2. Train Skip Plan Control 24
4.5. Genetic Algorithm 27
V. EVALUATION 29
5.1. Peak Hours Scenario 30
5.2. Congested Off-peak Hours Scenario 32
5.2.1 Single Peak Oversaturation 32
5.2.2 Double Peak Oversaturation 36
5.2.3 Box-shaped Peak Oversaturation 40
5.3. Discussion 43
VI. CONCLUSION AND FUTURE WORK 44
REFERENCES 46
APPENDIX A. Optimization Results 48
์์ฝ๋ฌธ 81๋์ ์งํ์ฒ ์ ๋๋ก๊ตํต ์ํฉ์ ์ํฅ์ ํฌ๊ฒ ๋ฐ์ง ์์ผ๋ฉฐ ๋์ฉ๋์ ๊ตํต ์์๋ฅผ ์ฒ๋ฆฌํ ์ ์์ด ๋ง์ ์น๊ฐ๋ค์๊ฒ ์ด์ฉ๋๋ค. ํผ์กํ ์งํ์ฒ ์ ์น๊ฐ๋ค์๊ฒ ๋ถํธ์ ์ผ๊ธฐํ๋ฉฐ, ์น๊ฐ๋ค์ ์น๊ฐ์ฅ์์์ ๋๊ธฐ์๊ฐ์ ์ฆ๊ฐ์ํจ๋ค. ๋ณธ ๋
ผ๋ฌธ์ ์ด์ฐจ ์ถ๋ฐ ์๊ฐ๊ณผ ์ญ๋ค์ ๊ฑด๋ ๋ด ์ด์ฐจ ์๋ฅผ ์กฐ์ ํ์ฌ ์น๊ฐ ๋๊ธฐ ์๊ฐ์ ์ต์ํํ๋ ๊ฒ์ ๋ชฉํ๋ก ํ ์ด์ฐจ ์๊ฐํ ์ต์ ํ ๋ฐฉ์์ ์ ์ํ๋ค. ์น๊ฐ ๋์ฐฉ ํต๊ณ ๋ชจ๋ธ์ ์์กดํ๋ ๊ธฐ์กด์ ์ ๊ทผ ๋ฐฉ์๊ณผ ๋ฌ๋ฆฌ, ์ด ์ฐ๊ตฌ๋ ๋๊ตฌ์ ์งํ์ฒ ์์ ์์ง๋ ๊ตํต์นด๋ ๋ฐ์ดํฐ๋ค์ ๊ธฐ๋ฐ์ผ๋ก ํ๋ ์ต์ ํ ๋ชจ๋ธ์ ๋ง๋ ๋ค. ๋ชจ๋ธ์ ๊ฐ ์น๊ฐ์ ์ฌํ ์๊ฐ์ ์ฐจ๋ ๋๊ธฐ ์๊ฐ, ์ฐจ๋ ํ์น ์๊ฐ ๋ฐ ๋ณดํ ์๊ฐ์ผ๋ก ๊ตฌ๋ถํ๊ณ , ํ์นํ ๊ธฐ์ฐจ์ ๋ฐ๋ผ ์น๊ฐ๋ค์ ๊ตฐ์งํ ์ํจ ํ ๊ฐ ์ฐจ๋๋ง๋ค ์น๊ฐ ์๋ฅผ ์ถ์ ํ๋ ๊ฒ์ผ๋ก ๊ตฌ์ฑ๋๋ค. ์ด๋ฅผ ๋ฐํ์ผ๋ก ์ฃผ์ด์ง ์ด์ฐจ ์ค์ผ์ค์ ๋ํด ๋ชจ๋ ์น๊ฐ ๊ฐ๊ฐ์ ๋๊ธฐ ์๊ฐ๋ค์ ๊ณ์ฐํ ์ ์๋ค. ์ต์ ํ ๋ฌธ์ ๋ ์ด์ฉ ๊ฐ๋ฅํ ์ด์ฐจ ์, ์ด์ฐจ๊ฐ ์์ฉ ๊ฐ๋ฅํ ์ต๋ ์น๊ฐ ์, ํ์๊ตฌ๊ฐ๊ณผ ๊ฐ์ ํ์ค์ ์ธ ์ ์ฝ ์กฐ๊ฑด ํ์์ ๊ตฌ์ฑ๋๋ค. ์ต์ ์ ์๊ฐํ๋ฅผ ์ฐพ๊ธฐ ์ํ ๋ฐฉ๋ฒ์ผ๋ก ์ ์ ์ ์๊ณ ๋ฆฌ์ฆ์ด ์ฌ์ฉ๋์๋ค. ๊ทธ ๊ฒฐ๊ณผ ์น๊ฐ ํ๊ท ๋๊ธฐ ์๊ฐ์ ์ต๋ 56%๊น์ง ๋จ์ถ๋์์ผ๋ฉฐ, ์ด์ฐจ ์ถ๋ฐ์๊ฐ ๋ฟ๋ง ์๋๋ผ ์ผ๋ถ ์ญ์ ๊ฑด๋๋ฐ๋ ์ด์ฐจ์ ์๊น์ง ์ต์ ํํ๋ฉด ๋งค์ฐ ํผ์กํ ์ํฉ์์ ์น๊ฐ์ ์ฐจ๋ ๋๊ธฐ ์๊ฐ์ ๋์ฑ ์ค์ผ ์ ์์๋ค. ํผ์กํ ์ํฉ์์ ๊ธฐ์ฐจ๊ฐ ์ผ๋ถ ์ญ์ ๊ฑด๋๋ฐ์์ ๋, ๊ทธ๋ ์ง ์์ ๋๋ณด๋ค ์น๊ฐ ์ต๋ ๋๊ธฐ ์๊ฐ์ 19%, ์น๊ฐ ํ๊ท ๋๊ธฐ ์๊ฐ์ 15% ์ ๋ ๋์ฑ ๋จ์ถ๋์๋ค. ๋ํ ํผ์กํ ์ํฉ์์ ์น๊ฐ ๋์ฐฉ ํจํด์ ๋ฐ๋ผ ์ต์ ํ์ ํจ์จ์ด ๋ฌ๋ผ์ง๋ค๋ ๊ฒ์ ํ์ธํ์๋ค. ๋ณธ ๋ฐฉ์์ ์น๊ฐ ํ๊ท ๋๊ธฐ์๊ฐ์ ๊ฐ์์ํด์ผ๋ก์จ ์งํ์ฒ ์๋น์ค๋ฅผ ํฅ์์ํฌ ๊ฒ์ด๋ค.MasterdCollectio
Network Coding for Speedup in Switches
We present a graph theoretic upper bound on speedup needed to achieve 100%
throughput in a multicast switch using network coding. By bounding speedup, we
show the equivalence between network coding and speedup in multicast switches -
i.e. network coding, which is usually implemented using software, can in many
cases substitute speedup, which is often achieved by adding extra switch
fabrics. This bound is based on an approach to network coding problems called
the "enhanced conflict graph". We show that the "imperfection ratio" of the
enhanced conflict graph gives an upper bound on speedup. In particular, we
apply this result to K-by-N switches with traffic patterns consisting of
unicasts and broadcasts only to obtain an upper bound of min{(2K-1)/K,
2N/(N+1)}.Comment: 5 pages, 4 figures, IEEE ISIT 200
Lost & Found
Lost and Found focuses on olfactory art and stimulates the sense of smell throughvarious means and materials. In this exhibition, diverse associations of the sense of smell are evoked through visual art. Through these fragrant works of art, personal, psychological, social, and cultural dimensions are conveyed and explored. The exhibition\u27s title, Lost & Found, refers to the restoration of the sense of smell, which many people have temporarily lost due to the physiological and social effects of COVID-19
- โฆ