361 research outputs found
GSM mobility management using an intelligent network platform
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Modeling and analyzing the evolution of cellular networks using stochastic geometry
The increasing complexity of cellular network due to its continuous evolution has made the conventional system level simulations time consuming and cost prohibitive. By modeling base station (BS) and user locations as spatial point processes, stochastic geometry has recently been recognized as a tractable and efficient analytical tool to quantify key performance metrics. The goal of this dissertation is to leverage stochastic geometry to develop an accurate spatial point process model for the conventional homogeneous macro cellular network, and to address the design and analysis challenges for the emerging cellular networks that will explore new spectrum for cellular communications. First, this dissertation proposes to use the repulsive determinantal point processes (DPPs) as an accurate model for macro BS locations in a cellular network. Based on three unique computational properties of the DPPs, the exact expressions of several fundamental performance metrics for cellular networks with DPP configured BSs are analytically derived and numerically evaluated. Using hypothesis testing for various performance metrics of interest, the DPPs are validated to be more accurate than the Poisson point process (PPP) or the deterministic grid model. Then the focus of this dissertation shifts to emerging networks that exploit new spectrum for cellular communications. One promising option is to allow the centrally scheduled cellular system to also access the unlicensed spectrum, wherein a carrier sensing multiple access with collision avoidance (CSMA/CA) protocol is usually used, as in Wi-Fi. A stochastic geometry-based analytical framework is developed to characterize the performance metrics for neighboring Wi-Fi and cellular networks under various coexistence mechanisms. In order to guarantee fair coexistence with Wi-Fi, it is shown that the cellular network needs to adopt either a discontinuous transmission pattern or its own CSMA/CA like mechanisms. Next, this dissertation considers cellular networks operating in the millimeter wave (mmWave) band, where directional beamforming is required to establish viable connections. Therefore, a major design challenge is to learn the necessary beamforming directions through the procedures that establish the initial connection between the mobile user and the network. These procedures are referred to as initial access, wherein cell search on the downlink and random access on the uplink are the two major steps. Stochastic geometry is again utilized to develop a unified analytical framework for three directional initial access protocols under a high mobility scenario where users and random blockers are moving with high speed. The expected delay for a user to succeed in initial access, and the average user-perceived downlink throughput that accounts for the initial access overhead, are derived for all three protocols. In particular, the protocol that has low beam-sweeping overhead during cell search is found to achieve a good trade-off between the initial access delay and user-perceived throughput performance. Finally, in contrast to the high mobility scenario for initial access, the directional cell search delay in a slow mobile network is analyzed. Specifically, the BS and user locations are fixed for long period of time, and therefore a strong temporal correlation for SINR is experienced. A closed-form expression for the expected cell search delay is derived, indicating that the expected cell search delay is infinite for noise-limited networks (e.g., mmWave) whenever the non-line-of-sight path loss exponent is larger than 2. By contrast, the expected cell search delay for interference-limited networks is proved to be infinite when the number of beams to search at the BS is smaller than a certain threshold, and finite otherwise.Electrical and Computer Engineerin
Measurement and Optimization of LTE Performance
4G Long Term Evolution (LTE) mobile system is the fourth generation communication system adopted worldwide to provide high-speed data connections and high-quality voice calls. Given the recent deployment by mobile service providers, unlike GSM and UMTS, LTE can be still considered to be in its early stages and therefore many topics still raise great interest among the international scientific research community: network performance assessment, network optimization, selective scheduling, interference management and coexistence with other communication systems in the unlicensed band, methods to evaluate human exposure to electromagnetic radiation are, as a matter of fact, still open issues.
In this work techniques adopted to increase LTE radio performances are investigated. One of the most wide-spread solutions proposed by the standard is to implement MIMO techniques and within a few years, to overcome the scarcity of spectrum, LTE network operators will offload data traffic by accessing the unlicensed 5 GHz frequency. Our Research deals with an evaluation of 3GPP standard in a real test best scenario to evaluate network behavior and performance
Investigating the possibility of electronic intermodality and interoperability of innovative urban public transport systems in the City of Tshwane
Abstract: Urban areas have the purpose of satisfying citizenโs needs to interact and conduct different activities such as work, study or leisure. Public transport systems are designed to allow the efficiently and reliable movement of people within the city (Amaya et al. 2017). Globally, developed countries always work on different methods in order to have the best formal urban public transportation system. This involves integration of various modes of public transport including technological innovations such as integrated e-smart cards and information dissemination. In South Africa, there has been the development of innovative urban public transport to enhance the public transport network and eliminate negative impacts on the road. Within Gauteng province in the past 10 years, the City of Tshwane has introduced innovative Formal Urban Public Transport (FUPT) systems that will convey commuters efficiently to desired locations with no delays and at more frequent intervals through an effective public transport network. However, the innovative FUPT network is fragmented and departments do not work with one other in any form...M.Tech. (Operations Management
User Rofde Identification in Future Mobile Telecommunications Systems
Nevertheless, researchers are working for the specification of the Universal Mobile Telecommunications System (UMTS), which will be a third-generation system for mobile telecommunications. The UMTS [3] will provide a wide range of telecommunication services to a very large number of Mobile Users (MUS). Services highly comparable to those offered by fixed networks will be available via various Mobile Terminals (MTs). The UMTS will be a multi-operator system and will consist of a range of sub-networks, providing userswith access to different environments, according to the entitlement of the subscriptionswith which they are associated. As a user moves between sub-networks during a call, handover functions from one environment to another may take place [4]. Each of these environments has different technical and economic constraints and will require different solutions. In addition, the UMTS radio access point must be able to connect to or cooperate with fixed networks and be capable of operating as a stand-alone network for operation in non-B-ISDN environments, although itsintegrationwithB-ISDNisanobjectivefor UMTS. Other critical aspects of UMTS are the techniques used to store and manipulate the large amount of information involved, and the intelligence needed in order to control calls and cope with user and terminal mobility. In order to make use of a service, a UMTS user will be able to register on an MT for this particular service [5]. Since user registrations will be performed on a per service basis, a user may be registered on more than one MT for different services. Moreover, some types of UMTS terminals will support multiple user registrations,' but only one of the registered users will be allowed to make use of the terminal at a time. The UMTS will also support Universal Personal Telecommunications (UPT), which means that UPT users will be able to register onto (one or more) UMTS terminals in order to make and accept calls. The ability of a user to roam into the various UMTS environments and make use of the resources and services via different terminals will be checked every time this user enters an environment and/or uses resources and services. This means that an information entity must exist for every user so as to be retrieved every time such achecking is required. This user-related information entity is called the UMTS User Profile (UUP). The UUP is stored in the UMTS Distributed Data Base (UMTS DDB) and can be accessed from every point in the network.2 Management operations on a particular user profile can b e performed only by authorized UMTS operators and possibly by the subscriber concemedorbyauser authorizedbythissubscriber. A U U P includes user authentication information, service access information, access domain information, user charging and accounting information, etc. This article discusses the UMTS user profile identification issues. The authors introduce first the concept of user profile and the UMTS entities related to it. Then, the user profile is described and its management requirements are discussed followed by the description of two scenarios proposed for the user profile identification. Finally, the authors give a comparison of the two scenarios and their concluding remarks. The study of the impact of the proposed scenarios upon UMTS operators, subscribers, users, and mobile terminals is beyond the authors' intent for the scope of this article. Entities Related to the UMTS User Profile efore introducing the UMTS User Profile, we B attempt to identify a number of UMTS entities related to this concept
๋น๋ฉดํ๋์ญ ์ ๋ฃฐ๋ผ ํต์ ์ ์ฑ๋ฅ ๋ถ์ ๋ฐ ์ฑ๋ฅ ํฅ์ ๊ธฐ๋ฒ ์ฐ๊ตฌ
ํ์๋
ผ๋ฌธ (๋ฐ์ฌ) -- ์์ธ๋ํ๊ต ๋ํ์ : ๊ณต๊ณผ๋ํ ์ ๊ธฐยท์ ๋ณด๊ณตํ๋ถ, 2021. 2. ๋ฐ์ธ์
.3GPP๋ LAA (licensed-assisted access)๋ผ๊ณ ํ๋ 5GHz ๋น๋ฉดํ ๋์ญ
LTE๋ฅผ ๊ฐ๋ฐํ์ต๋๋ค. LAA๋ ์ถฉ๋ ๋ฐฉ์ง ๊ธฐ๋ฅ์ ์ฌ์ฉํ๊ธฐ ์ํด Wi-Fi์ CSMA /
CA (Carrier Sense Multiple Access with Collision avoidance)์ ์ ์ฌํ LBT (Listen
Before Talk) ์์
์ ์ฑํํ์ฌ ๊ฐ LAA ๋ค์ด ๋งํฌ ๋ฒ์คํธ์ ํ๋ ์ ๊ตฌ์กฐ ์ค๋ฒ ํค๋๋
๊ฐ๊ฐ์ ์ข
๋ฃ ์๊ฐ์ ๋ฐ๋ผ ๋ฌ๋ผ์ง๋๋ค. ์ด์ LBT ์์
. ์ด ๋
ผ๋ฌธ์์๋ ๋น๋ฉดํ ๋์ญ
์
๋ฃฐ๋ฌ ํต์ ์ ๋ถ์ํ๊ธฐ์ํ ์์น ๋ชจ๋ธ์ ์ ์ํ๋ค. ๋ค์์ผ๋ก, ๋น๋ฉดํ ๋์ญ ์
๋ฃฐ๋ฌ
ํต์ ์ ๋ค์ ๋ ๊ฐ์ง ํฅ์๋ ๊ธฐ๋ฅ์ ๊ณ ๋ คํฉ๋๋ค. ๋์ญ ๋
๋ฆฝํ ์
๋ฃฐ๋ฌ ํต์ . ๊ธฐ์กด WiFi ๋ถ์ ๋ชจ๋ธ๋ก๋ LAA์ ์ฑ๋ฅ์ ํ๊ฐํ ์ ์๋ค๋ ์ ์ ๊ฐ์ํ์ฌ ๋ณธ ์์ ์์๋
์ฌ๋ฌ ๊ฒฝํฉ ์งํ ๋ NodeB๋ก ๊ตฌ์ฑ๋ LAA ๋คํธ์ํฌ์ ์ฑ๋ฅ์ ๋ถ์ํ๊ธฐ์ํ ์๋ก์ด
Markov ์ฒด์ธ ๊ธฐ๋ฐ ๋ถ์ ๋ชจ๋ธ์ ์ ์ํฉ๋๋ค. LAA ํ๋ ์ ๊ตฌ์กฐ ์ค๋ฒ ํค๋์ ๋ณํ.
LTE-LAA๋ LTE์์ ์์ ๋ ์๋ ์ ์ ์๊ณ ๋ฆฌ์ฆ์ ์ํด ์ ์ ๋ณ์กฐ ๋ฐ ์ฝ๋ฉ (AMC)
์ ์ฑํํฉ๋๋ค. AMC๋ ์งํ ๋ nodeB (eNB)๊ฐ ํ์ฌ ์ ์ก์ ์ฑ๋ ํ์ง ํ์๊ธฐ ํผ๋
๋ฐฑ์ ์ฌ์ฉํ์ฌ ๋ค์ ์ ์ก์์ํ ๋ณ์กฐ ๋ฐ ์ฝ๋ฉ ๋ฐฉ์ (MCS)์ ์ ํํ๋๋ก ๋์ต๋๋ค.
๋ผ์ด์ ์ค ๋์ญ์์ ๋์ํ๋ ๊ธฐ์กด LTE์ ๊ฒฝ์ฐ ๋
ธ๋ ๊ฒฝํฉ ๋ฌธ์ ๊ฐ ์์ผ๋ฉฐ AMC ์ฑ๋ฅ
์ ๋ํ ์ฐ๊ตฌ๊ฐ ์ ์งํ๋๊ณ ์์ต๋๋ค. ๊ทธ๋ฌ๋ ๋น๋ฉดํ ๋์ญ์์ ๋์ํ๋ LTE-LAA
์ ๊ฒฝ์ฐ ์ถฉ๋ ๋ฌธ์ ๋ก ์ธํด AMC ์ฑ๋ฅ์ด ์ ๋๋ก ์ฒ๋ฆฌ๋์ง ์์์ต๋๋ค. ์ด ํธ์ง์์๋
AMC ์ด์์ ๊ณ ๋ คํ ํ์ค์ ์ธ ์ฑ๋ ๋ชจ๋ธ์์ LTELAA ์ฑ๋ฅ์ ๋ถ์ํ๊ธฐ์ํ ์๋ก
์ด Markov ์ฒด์ธ ๊ธฐ๋ฐ ๋ถ์ ๋ชจ๋ธ์ ์ ์ํฉ๋๋ค. ๋ฌด์ ๋คํธ์ํฌ ๋ถ์์ ๋๋ฆฌ ์ฌ์ฉ๋๋
Rayleigh ํ์ด๋ฉ ์ฑ๋ ๋ชจ๋ธ์ ์ฑํํ๊ณ ๋ถ์ ๊ฒฐ๊ณผ๋ฅผ ns-3 ์๋ฎฌ๋ ์ดํฐ์์ ์ป์ ๊ฒฐ๊ณผ
์ ๋น๊ตํฉ๋๋ค. ๋น๊ต ๊ฒฐ๊ณผ๋ ํ๊ท ์ ํ๋๊ฐ 99.5%๋ก ๋ถ์ ๋ชจ๋ธ์ ์ ํ๋๋ฅผ ๋ณด์ฌ์ค๋๋ค. ๋์ ๋ฐ์ดํฐ ์๋์ ๋ํ ์๊ตฌ ์ฌํญ์ผ๋ก ์ธํด 3GPP๋ LTE-LAA๋ฅผ์ํ ๋ค์ค
๋ฐ์กํ ์ด์์ ์ ๊ณตํ์ต๋๋ค. ๊ทธ๋ฌ๋ ๋ค์ค ๋ฐ์กํ ๋์์ OOBE์ ์ทจ์ฝํ๊ณ ์ ํ๋
์ ์ก ์ ๋ ฅ์ ์ฌ์ฉํ์ฌ ๋นํจ์จ์ ์ธ ์ฑ๋ ์ฌ์ฉ์ ์ด๋ํฉ๋๋ค. ๋ณธ ๋
ผ๋ฌธ์ ์ฑ๋ ํจ์จ์
๋์ด๊ธฐ์ํ ์๋ก์ด ๋ค์ค ๋ฐ์กํ ์ ๊ทผ ๋ฐฉ์์ ์ ์ํ๋ค. ์ฐ๋ฆฌ๊ฐ ์ ์ํ ๋ฐฉ์์ ์ ์ก
๋ฒ์คํธ๋ฅผ ์ฌ๋ฌ ๊ฐ๋ก ๋ถํ ํ๊ณ ์ ์ก ์ ๋ ฅ ์ ํ์ ์ถฉ์กฑํ๋ฉด์ ์งง์ ์๋ธ ํ๋ ์ ์ ์ก
์ ์ฌ์ฉํฉ๋๋ค. ๋ํ ์ฑ๋ ์ํ๋ฅผ ์ ํํ๊ฒ ํ๋จํ์ฌ OOBE ๋ฌธ์ ๋ฅผ ๊ทน๋ณต ํ ์์๋
์๋์ง ๊ฐ์ง ์๊ณ ๋ฆฌ์ฆ์ ์ ์ํฉ๋๋ค. ์ํํธ์จ์ด ์ ์ ๋ผ๋์ค๋ฅผ ์ฌ์ฉํ๋ ํ๋กํ
ํ์
์ 99% ์ด์์ ์ ํ๋๋ก ์ฑ๋ ์ํ๋ฅผ ๊ฒฐ์ ํ๋ ์๋์ง ๊ฐ์ง ์๊ณ ๋ฆฌ์ฆ์ ์คํ
๊ฐ๋ฅ์ฑ๊ณผ ์ฑ๋ฅ์ ๋ณด์ฌ์ค๋๋ค. ns-3 ์๋ฎฌ๋ ์ด์
์ ํตํด ์ ์ ๋ ๋ค์ค ๋ฐ์กํ ์ก์ธ์ค
๋ฐฉ์์ด ๊ธฐ์กด LBT ์ ํ A ๋ฐ ์ ํ B์ ๋นํด ์ฌ์ฉ์์ธ์ง ์ฒ๋ฆฌ๋์์ ๊ฐ๊ฐ ์ต๋ 59%
๋ฐ 21.5%์ ์ฑ๋ฅ ํฅ์์ ๋ฌ์ฑ ํจ์ ํ์ธํ์ต๋๋ค. ๋ ๊ฑฐ์ LAA์๋ ๋ฐฐํฌ ๋ฌธ์ ๊ฐ
์๊ธฐ ๋๋ฌธ์ 3GPP์ MulteFire ์ผ๋ผ์ด์ธ์ค๋ ๋น๋ฉดํ ๋์ญ ๋
๋ฆฝํ ์
๋ฃฐ๋ฌ ํต์ ์์ค
ํ
์ ์ ์ํ์ต๋๋ค. ๊ทธ๋ฌ๋, ์ข
๋์ ๋น๋ฉดํ ๋์ญ ๋
๋ฆฝํ ์
๋ฃฐ๋ฌ ํต์ ์์คํ
์ ์ํฅ
๋งํฌ ์ ์ด ๋ฉ์์ง์ ์ ์ก ํ๋ฅ ์ด ๋ฎ๋ค. ์ด ๋
ผ๋ฌธ์ Wi-Fi ๋ธ๋ก ACK ํ๋ ์์ ์
๋งํฌ
์ ์ด ๋ฉ์์ง๋ฅผ ๋ฃ๋ W ARQ : Wi-Fi ์ง์ HARQ๋ฅผ ์ ์ํฉ๋๋ค. ๋ํ W-ARQ์ ์ฒ
๋ฆฌ ์ฑ๋ฅ์ ํฅ์์ํค๊ธฐ ์ํด ๋ณ๋ ฌ HARQ ๋ฐ ํด๋ฌ์คํฐ๋ง ๋ Minstrel์ ์ ์ํฉ๋๋ค.
์ฐ๋ฆฌ๊ฐ ์ ์ํ ์๊ณ ๋ฆฌ์ฆ์ ๊ธฐ์กด MulteFire๊ฐ ๊ฑฐ์ ์ ๋ก ์ฒ๋ฆฌ๋ ์ฑ๋ฅ์ ๋ณด์ด๋ ๊ฒฝ์ฐ
๋์ ์ฒ๋ฆฌ๋ ์ฑ๋ฅ์ ๋ณด์ฌ์ค๋๋ค. ์์ฝํ๋ฉด ๋น๋ฉดํ ๋์ญ ์
๋ฃฐ๋ฌ ํต์ ์ ์ฑ๋ฅ์ ๋ถ์
ํฉ๋๋ค. ์ ์ ๋ ๋ชจ๋ธ์ ์ฌ์ฉํจ์ผ๋ก์จ ์ฐ๋ฆฌ๋ ๋ ๊ฑฐ์ ๋ค์ค ๋ฐ์กํ ๋์์ ์ฃผ์ฅํ๋ฉฐ
๋น๋ฉดํ ์
๋ฃฐ๋ฌ ํต์ ์ HARQ๋ ํจ์จ์ ์ด์ง ์๋ค. ์ด๋ฌํ ์ด์ ๋ก, ์ฐ๋ฆฌ๋ ์ต์ฒจ๋จ ๊ธฐ
์ ์ ๋นํด UPT ๋ฐ ์ฒ๋ฆฌ๋๊ณผ ๊ฐ์ ๋คํธ์ํฌ ์ฑ๋ฅ ํฅ์์ ๋ฌ์ฑํ๋ OOBE ์ธ์ ์ถ๊ฐ
์ก์ธ์ค ๋ฐ W-ARQ๋ฅผ ์ ์ํฉ๋๋ค.3GPP has developed 5 GHz unlicensed band LTE, referred to as licensed-assisted
access (LAA). LAA adopts listen before talk (LBT) operation, resembling Wi-Fis
carrier sense multiple access with collision avoidance (CSMA/CA), to enable collision
avoidance capability, while the frame structure overhead of each LAA downlink burst
varies with the ending time of each preceding LBT operation.
In this dissertation, we propose numerical model to analyze unlicensed band cellular communication. Next, we consider the following two enhancements of unlicensed band cellular communication: (i) out-of-band emission (OOBE) aware additional carrier access, and (ii) Wi-Fi assisted hybrid automatic repeat request (H-ARQ)
for unlicensed-band stand-alone cellular communication.
Given that, existing analytic models of Wi-Fi cannot be used to evaluate the performance of LAA, in this letter, we propose a novel Markov chain-based analytic model
to analyze the performance of LAA network composed of multiple contending evolved
NodeBs by considering the variation of the LAA frame structure overhead. LTE-LAA
adopts adaptive modulation and coding (AMC) for the rate adaptation algorithm inherited from LTE. AMC helps the evolved nodeB (eNB) to select a modulation and
coding scheme (MCS) for the next transmission using the channel quality indicator
feedback of the current transmission. For the conventional LTE operating in the licensed band, there is no node contention problem and AMC performance has been
well studied. However, in the case of LTE-LAA operating in the unlicensed band,
AMC performance has not been properly addressed due to the collision problem. In
this letter, we propose a novel Markov chain-based analysis model for analyzing LTELAA performance under a realistic channel model considering AMC operation. We
adopt Rayleigh fading channel model widely used in wireless network analysis, and
compare our analysis results with the results obtained from ns-3 simulator. Comparison results show an average accuracy of 99.5%, which demonstrates the accuracy of
our analysis model.
Due to the requirement for a high data rate, the 3GPP has provided multi-carrier
operation for LTE-LAA. However, multi-carrier operation is susceptible to OOBE and
uses limited transmission power, resulting in inefficient channel usage. This paper proposes a novel multi-carrier access scheme to enhance channel efficiency. Our proposed
scheme divides a transmission burst into multiple ones and uses short subframe transmission while meeting the transmission power limitation. In addition, we propose an
energy detection algorithm to overcome the OOBE problem by deciding the channel status accurately. Our prototype using software-defined radio shows the feasibility
and performance of the energy detection algorithm that determines the channel status with over 99% accuracy. Through ns-3 simulation, we confirm that the proposed
multi-carrier access scheme achieves up to 59% and 21.5% performance gain in userperceived throughput compared with the conventional LBT type A and type B, respectively.
Since the legacy LAA has deployment problem, 3GPP and MulteFire alliance proposed unlicensed band stand-alone cellular communication system. However, conventional unlicensed band stand-alone cellular communication system has low transmission probability of uplink control messages. This disertation proposes W-ARQ: Wi-Fi
assisted HARQ which put uplink control messages into Wi-Fi block ACK frame. In
addition we propose parallel HARQ and clustered Minstrel to enhance throughput
performance of W-ARQ. Our proposed algorithm shows high throughput performance
where conventional MulteFire shows almost zero throughput performance.
In summary, we analyze the performance of unlicensed-band cellular communication. By using the proposed model, we insist the legacy multi-carrier operation and HARQ of unlicensed cellular communication is not efficient. By this reason, we propose
OOBE aware additional access and W-ARQ which achievee enhancements of network performance such as UPT and throughput compared with state-of-the-art techniques.Abstract i
Contents iv
List of Tables vii
List of Figures viii
1 Introduction 1
1.1 Unlicensed Band Communication System . . . . . . . . . . . . . . . 1
1.2 Overview of Existing Approaches . . . . . . . . . . . . . . . . . . . 2
1.2.1 License-assisted access . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 Further LAA . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.3 Non-3GPP Unlicensed Band Cellular Communication . . . . 6
1.3 Main Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1 Performance Analysis of LTE-LAA . . . . . . . . . . . . . . 6
1.3.2 Out-of-Band Emission Aware Additional Carrier Access for
LTE-LAA Network . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.3 W-ARQ: Wi-Fi Assisted HARQ for Unlicensed Band StandAlone Cellular Communication System . . . . . . . . . . . . 8
1.4 Organization of the Dissertation . . . . . . . . . . . . . . . . . . . . 8
2 Performance Analysis of LTE-LAA network 10
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Proposed Markov-Chain Model . . . . . . . . . . . . . . . . . . . . . 14
2.3.1 Markov Property . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.2 Markov Chain Model for EPS Type Variation . . . . . . . . . 16
2.3.3 LAA Network Throughput Estimation . . . . . . . . . . . . . 18
2.4 Model Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Out-of-Band Emission Aware Additional Carrier Access for LTE-LAA
Network 35
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Related work and Background . . . . . . . . . . . . . . . . . . . . . 37
3.2.1 Related work . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.2 Listen Before Talk . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.3 Out-of-Band Emission . . . . . . . . . . . . . . . . . . . . . 39
3.3 Multi-carrier Operation of LTE-LAA . . . . . . . . . . . . . . . . . . 39
3.4 Carrier Sensing considering Out-of-Band Emission . . . . . . . . . . 47
3.4.1 Energy Detection Algorithm . . . . . . . . . . . . . . . . . . 49
3.4.2 Nominal Band Energy Detection . . . . . . . . . . . . . . . . 50
3.4.3 OOBE-Free Region Energy Detection . . . . . . . . . . . . . 51
3.5 Additional Carrier Access Scheme . . . . . . . . . . . . . . . . . . . 52
3.5.1 Basic Operation . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.5.2 Transmission Power Limitation . . . . . . . . . . . . . . . . 53
3.5.3 Dividing Transmission Burst . . . . . . . . . . . . . . . . . . 54
3.5.4 Short Subframe Decision . . . . . . . . . . . . . . . . . . . . 54
3.6 Performance Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.6.1 Performance of Energy Detection considering OOBE . . . . . 57
3.6.2 Simulation Environments . . . . . . . . . . . . . . . . . . . . 57
3.6.3 Performance of Proposed Carrier Access Scheme . . . . . . . 58
3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4 W-ARQ: Wi-Fi Assisted HARQ for Unlicensed Band Stand-Alone Cellular Communication System 66
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.3 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.4 W-ARQ: Wi-Fi assisted HARQ for Unlicensed Band Stand-Alone Cellular Communication System . . . . . . . . . . . . . . . . . . . . . . 69
4.4.1 Parallel HARQ . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.4.2 Clustered Minstrel . . . . . . . . . . . . . . . . . . . . . . . 72
4.5 Performance Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5 Concluding Remarks 80
5.1 Research Contributions . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Abstract (In Korean) 90
๊ฐ์ฌ์ ๊ธ 93Docto
A Trust-Based Relay Selection Approach to the Multi-Hop Network Formation Problem in Cognitive Radio Networks
One of the major challenges for todayโs wireless communications is to meet the growing demand for supporting an increasing diversity of wireless applications with limited spectrum resource. In cooperative communications and networking, users share resources and collaborate in a distributed approach, similar to entities of active social groups in self organizational communities. Usersโ information may be shared by the user and also by the cooperative users, in distributed transmission. Cooperative communications and networking is a fairly new communication paradigm that promises significant capacity and multiplexing gain increase in wireless networks. This research will provide a cooperative relay selection framework that exploits the similarity of cognitive radio networks to social networks. It offers a multi-hop, reputation-based power control game for routing. In this dissertation, a social network model provides a humanistic approach to predicting relay selection and network analysis in cognitive radio networks
Factors Impacting Key Management Effectiveness in Secured Wireless Networks
The use of a Public Key Infrastructure (PKI) offers a cryptographic solution that can overcome many, but not all, of the MANET security problems. One of the most critical aspects of a PKI system is how well it implements Key Management. Key Management deals with key generation, key storage, key distribution, key updating, key revocation, and certificate service in accordance with security policies over the lifecycle of the cryptography. The approach supported by traditional PKI works well in fixed wired networks, but it may not appropriate for MANET due to the lack of fixed infrastructure to support the PKI. This research seeks to identify best practices in securing networks which may be applied to new network architectures
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