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  • 1. Cho, Jeong-woo
    et al.
    Chang, Yong
    Kim, Yuchul
    Chon, JaeHong
    WLC10-2: Analytic Optimization of HARQ Performance in Wireless Packet Data Systems2006Conference paper (Refereed)
    Abstract [en]

    We propose an analytical framework that optimizes the performance of various Hybrid Automatic Repeat reQuest (HARQ) schemes in wireless packet data systems. The optimization framework lends itself to maximizing the user throughput without assuming a specific HARQ scheme, a target packet error rate, and a mapping of signal-to-interference-noise ratios (SINR) into modulation and coding scheme (MCS) sets. Thus, a user selects an optimal amount of redundancy bits used for retransmissions, an optimal packet error rate, and an optimal SINR-MCS mapping such that the user throughput would be maximized. We show that there exists an optimal redundancy block size of incremental redundancy (IR) scheme when the number of retransmissions is limited, while as small as possible redundancy size is optimal when the number of retransmissions is unlimited. Our analytical results are verified through extensive simulations of the IEEE 802.16e system.

  • 2.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Cho, Dong-ho
    KAIST (Korea Advanced Institute of Science and Technology).
    A Dynamic Buffer Management Scheme Based on Rate Estimation in Packet-Switched Networks2001In: IEEE Global Telecommunications Conference, 2001. GLOBECOM '01, IEEE Press, 2001, p. 2304-2310Conference paper (Refereed)
    Abstract [en]

    While traffic volume of real-time applications is rapidly increasing, current routers do not guarantee minimum QoS values of fairness and they drop packets in a random fashion. If routers provide a minimum QoS, resulting a less delay, reduced delay-jitter, more fairness, and smooth sending rates, TCP-friendly rate control (TFRC) can be adopted for real-time applications. We propose a dynamic buffer management scheme that meets the requirements described above, and can be applied to TCP flow and to data flow for transfer of real-time applications. The proposed scheme consists of a virtual threshold function, an accurate and stable per-flow rate estimation, and a per-flow exponential drop probability. We discuss how this scheme motivates real-time applications to adopt TCP-friendly rate control.

  • 3. Cho, Jeong-woo
    et al.
    Cho, Dong-ho
    KAIST (Korea Advanced Institute of Science and Technology).
    Dynamic Buffer Management Scheme Based on Rate Estimation in Packet-Switched Networks2002In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 39, no 6, p. 769-787Article in journal (Refereed)
    Abstract [en]

     While traffic volume of real-time applications is rapidly increasing, current routers do not guarantee minimum QoS values of fairness and drop packets in random fashion. If routers provide a minimum QoS, resulting less delays, more fairness, and smoother sending rates, TCP-friendly rate control (TFRC) can be adopted for real-time applications. We propose a dynamic buffer management scheme that meets the requirements described above, and can be applied to TCP flow and to data flow for transfer of real-time applications. The proposed scheme consists of a virtual threshold function, an accurate and stable per-flow rate estimation, a per-flow exponential drop probability, and a dropping strategy that guarantees fairness when there are many flows. Moreover, we introduce a practical definition of active flows to reduce the overhead coming from maintaining per-flow states. We discuss how proposed scheme motivates real-time applications to adopt TFRC.

  • 4.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Telecommunication Systems Laboratory, TSLab (closed 2012-01-01).
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Stabilized Max-Min Flow Control Using PID and PII2 Controllers2005In: IEICE transactions on communications, ISSN 0916-8516, E-ISSN 1745-1345, Vol. E88-B, no 8, p. 3353-3364Article in journal (Refereed)
    Abstract [en]

     This paper describes an 'analytical framework for the weighted max-min flow control of elastic flows in packet networks using PID and PII2 controller when flows experience heterogeneous round-trip delays. Our algorithms are scalable in that routers do not need to store any per-flow information of each flow and they use simple first come first serve (FCFS) discipline, stable in that the stability is proven rigorously when there are flows with heterogeneous round-trip delays. We first suggest two closed-loop system models that approximate our flow control algorithms in continuous-time domain where the purpose of the first algorithm is to achieve the target queue length and that of the second is to achieve the target utilization. The slow convergence [1] of many rate-based flow control algorithms, which use queue lengths as input signals, can be resolved by the second algorithm. Based on these models, we find the conditions for controller gains that stabilize closed-loop systems when round-trip delays are equal and extend this result to the case of heterogeneous round-trip delays with the help of Zero exclusion theorem. We simulate our algorithms with optimal gain sets for various configurations including a multiple bottleneck network to verify the usefulness and extensibility of our algorithms.

  • 5. Cho, Jeong-woo
    et al.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Stabilized Max-Min Flow Control Using PID and PII2 Controllers2004In: GLOBECOM '04: IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, VOLS 1-6, IEEE Press, 2004, p. 1411-1417Conference paper (Refereed)
    Abstract [en]

    This paper describes an analytical framework for the weighted max-min flow control of elastic flows in packet networks using PID and PII2 controller when flows experience heterogeneous round-trip delays. Our algorithms are scalable in that routers do not need to store any per-flow information of each flow and they use simple first come first serve (FCFS) discipline, stable in that the stability is proven rigorously when there are flows with heterogeneous round-trip delays. We first suggest two closed-loop system models that approximate our flow control algorithms in continuous-time domain where the purpose of the first algorithm is to achieve the target queue length and that of the second is to achieve the target utilization. The slow convergence of source rates traversing routers with empty buffers which is inherent in many flow control algorithms can be resolved by the second algorithm. Based on these models, we find the conditions for controller gains that stabilize closed-loop systems when round-trip delays are equal and extend this result to the case of heterogeneous round-trip delays with the help of Zero exclusion theorem. We simulate our algorithms with optimal gain sets for various configurations including a multiple bottleneck network to verify the usefulness and extensibility of our algorithms.

  • 6.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Utility Max-Min Flow Control Using Slope-Restricted Utility Functions2005In: GLOBECOM '05: IEEE Global Telecommunications Conference, Vols 1-6: DISCOVERY PAST AND FUTURE, IEEE Press, 2005, p. 819-824Conference paper (Refereed)
    Abstract [en]

    We present a network architecture for the distributed utility max-min flow control of elastic and non-elastic flows where utility values of users (rather than data rates of users) are enforced to achieve max-min fairness. We provide a distributed link algorithm that does not use the information of users' utility functions. To show that the proposed algorithm can be stabilized not locally but globally, we found that the use of nonlinear control theory is inevitable. Even though we use a distributed How control algorithm, it is shown that any kind of utility function can be used as long as the minimum slopes of the functions are greater than a certain positive value. We believe that the proposed algorithm is the first to achieve utility max-min fairness with guaranteed stability in a distributed manner.

  • 7.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Utility Max-Min Flow Control Using Slope-Restricted Utility Functions2007In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 55, no 5, p. 963-972Article in journal (Refereed)
    Abstract [en]

    We present a network architecture for the distributed utility max-min flow control of elastic and nonelastic flows where utility values of users (rather than data rates of users) are enforced to achieve max-min fairness. The proposed link algorithm converges to utility max-min fair bandwidth allocation in the presence of round-trip delays without using the information of users' utility functions. To show that the proposed algorithm can be stabilized not locally but globally, we found that the use of nonlinear control theory is inevitable. Even though we use a distributed flow-control algorithm, it is shown that any kind of utility function can be used as long as the minimum slopes of the functions are greater than a certain positive value. Though our analysis is limited to the single-bottleneck and homogeneous-delay case, we believe that the proposed algorithm is the first to achieve utility max-min fairness with guaranteed stability in a distributed manner

  • 8.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Jiang, Yuming
    NTNU (Norwegian University of Science and Technology).
    Basic Theorems on the Backoff Process in 802.112009In: Performance Evaluation Review, ISSN 0163-5999, E-ISSN 1557-9484, Vol. 37, no 2, p. 18-20Article in journal (Refereed)
  • 9.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Jiang, Yuming
    NTNU (Norwegian University of Science and Technology).
    Fundamentals of the Backoff Process in 802.11: Dichotomy of the Aggregation2015In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 61, no 4, p. 1687-1701Article in journal (Refereed)
    Abstract [en]

    This paper discovers fundamental principles of the backoff process that governs the performance of IEEE 802.11. A simplistic principle founded upon regular variation theory is that the backoff time has a truncated Pareto-type tail distribution with an exponent of $ { (log gamma !)/log m}$ ( $boldsymbol {m}$ is the multiplicative factor and $ {gamma }$ is the collision probability). This reveals that the per-node backoff process is heavy-tailed in the strict sense for $ { gamma > 1/m^{2}}$ , and paves the way for the following unifying result. The state-of-the-art theory on the superposition of the heavy-tailed processes is applied to establish a dichotomy exhibited by the aggregate backoff process, putting emphasis on the importance of time-scales on which we view the backoff processes. While the aggregation on normal time-scales leads to a Poisson process, it is approximated by a new limiting process possessing long-range dependence (LRD) on coarse time-scales. This dichotomy turns out to be instrumental in formulating short-term fairness, extending existing formulas to arbitrary population, and to elucidate the absence of LRD in practical situations. A refined wavelet analysis is conducted to strengthen this argument.

  • 10.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Kim, Seong-Lyun
    Yonsei University.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Capacity of Interference-Limited Ad Hoc Networks with Infrastructure Support2006In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 10, no 1, p. 16-18Article in journal (Refereed)
    Abstract [en]

    In this letter, we consider the capacity of ad hoc networks with infrastructure support. Although Grossglauser-Tse mobile network model enables Θ(1) per-node throughput scaling, the mobility assumption may be too unrealistic to be accepted in some practical situations. One of the key observations we acquired is that the infrastructure support plays the same role played by the mobility in the Grossglauser-Tse model. We show that nodes can utilize the randomly located infrastructure support instead of mobility when nodes are nearly static. In this case, we show that the per-node throughput of Θ(1) is still achievable when the number of access points grows linearly with respect to the number of nodes.

  • 11.
    Cho, Jeong-woo
    et al.
    Dept. of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.
    Kim, Seong-Lyun
    Yonsei University.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Infrastructure Support Increases the Capacity of Ad Hoc Wireless Networks2005In: VTC2005-FALL: 2005 IEEE 62ND VEHICULAR TECHNOLOGY CONFERENCE, 1-4, PROCEEDINGS, IEEE Press, 2005, p. 2663-2668Conference paper (Refereed)
    Abstract [en]

     In ad hoc wireless networks, one of the hottest research directions has been to increase the throughput capacity scaling with respect to the number of nodes n. Gupta and Kumar (2000) introduced a fixed random network model and showed that the throughput per source-destination pair is Theta(1/root nlogn) when the network is coordinated by a centralized entity. Grossglauser and Tse (2001) introduced a mobile random network model and showed that a source-destination pair acquires a constant throughput of Theta(1) assuming that delays incurred by mobile nodes with low mobility are tolerable.In this paper, we consider the capacity of ad hoc wireless networks with infrastructure support. Although Grossglauser-Tse mobile network model enables Theta(1) per-node throughput scaling, the mobility assumption may be too unrealistic to be accepted in some practical situations. One of the key observations we acquired is that the infrastructure support plays the same role played by the mobility in the Grossglauser-Tse model. We show that nodes can utilize the randomly located infrastructure support instead of mobility when nodes are nearly static. In this case, we show that the per-node throughput of Theta(1) is still achievable when the number of access points grows linearly with respect to the number of nodes. Furthermore., we show that there is additional per-node throughput improvement of Theta(1) when nodes are mobile.

  • 12. Cho, Jeong-woo
    et al.
    Kwon, Taesoo
    Koo, Changhoi
    Park, DS
    Kim, Daegyun
    Cho, Dong-ho
    KAIST (Korea Advanced Institute of Science and Technology).
    Multiple Quality Control: A New Framework for QoS Control in Forward Link of 1xEV-DV Systems2002In: IEEE 55TH VEHICULAR TECHNOLOGY CONFERENCE, VTC SPRING 2002, VOLS 1-4, PROCEEDINGS, IEEE , 2002, p. 1165-1169Conference paper (Refereed)
    Abstract [en]

    One of main issues in 1xEV-DV systems is how to support and satisfy various QoS requirements of data services and voice service simultaneously. Another main issue in 1xEV-DV systems is how to increase throughput of data services without sacrificing voice service's QoS requirements. The main motivation for our proposed architecture, MQC (Multiple Quality Control), is to use per-stream buffers in physical layer and to fully utilize air resource. The problem of existing architecture is that PDUs from only one stream can be transmitted and those PDUs may not fill out the allocated time slots. In contrast to existing architecture, MQC can multiplex several streams into one PLP(Physical Layer Packet) because MQC utilizes per-service buffers in physical layer. We also introduce a multiplexing scheme that minimizes queueing delays of realtime traffic and maximizes cell throughputs.

  • 13.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Le Boudec, Jean-Yves
    EPFL (École Polytechnique Fédérale de Lausanne).
    Jiang, Yuming
    NTNU (Norwegian University of Science and Technology).
    On the Asymptotic Validity of the Decoupling Assumption for Analyzing 802.11 MAC Protocol2012In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 58, no 11, p. 6879-6893Article in journal (Refereed)
    Abstract [en]

    Performance evaluation of the 802.11 MAC protocol is classically based on the decoupling assumption, which hypothesizes that the backoff processes at different nodes are independent. This decoupling assumption results from mean field convergence and is generally true in transient regime in the asymptotic sense (when the number of wireless nodes tends to infinity), but, contrary to widespread belief, may not necessarily hold in stationary regime. The issue is often related with the existence and uniqueness of a solution to a fixed point equation; however, it was also recently shown that this condition is not sufficient; in contrast, a sufficient condition is a global stability property of the associated ordinary differential equation. In this paper, we give a simple condition that establishes the asymptotic validity of the decoupling assumption for the homogeneous case (all nodes have the same parameters). We also discuss the heterogeneous and the differentiated service cases and formulate a new ordinary differential equation. We show that the uniqueness of a solution to the associated fixed point equation is not sufficient; we exhibit one case where the fixed point equation has a unique solution but the decoupling assumption is not valid in the asymptotic sense in stationary regime.

  • 14.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Le Boudec, Jean-Yves
    EPFL (École Polytechnique Fédérale de Lausanne).
    Jiang, Yuming
    NTNU (Norwegian University of Science and Technology).
    On the Validity of the Fixed Point Equation and Decoupling Assumption for Analyzing the 802.11 MAC Protocol2010In: Performance Evaluation Review, ISSN 0163-5999, E-ISSN 1557-9484, Vol. 38, no 2, p. 36-38Article in journal (Refereed)
    Abstract [en]

    Performance evaluation of the 802.11 MAC protocol is classically based on the decoupling assumption, which hypothesizes that the backoff processes at different nodes are independent. A necessary condition for the validity of this approach is the existence and uniqueness of a solution to a fixed point equation. However, it was also recently pointed out that this condition is not sufficient; in contrast, a necessary and sufficient condition is a global stability property of the associated ordinary differential equation. Such a property was established only for a specific case, namely for a homogeneous system (all nodes have the same parameters) and when the number of backoff stages is either 1 or infinite and with other restrictive conditions. In this paper, we give a simple condition that establishes the validity of the decoupling assumption for the homogeneous case. We also discuss the heterogeneous and the differentiated service cases and show that the uniqueness condition is not sufficient; we exhibit one case where the fixed point equation has a unique solution but the decoupling assumption is not valid

  • 15.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Mo, Jeonghoon
    Yonsei University.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Joint Network-wide Opportunistic Scheduling and Power Control in Multi-cell Networks2007In: 2007 IEEE INTERNATIONAL SYMPOSIUM ON A WORLD OF WIRELESS, MOBILE AND MULTIMEDIA NETWORKS, VOL 1, IEEE Press, 2007, p. 1-12Conference paper (Refereed)
    Abstract [en]

    We present a unified analytical framework that maximizes generalized utilities of a wireless network by network-wide opportunistic scheduling and power control. That is, base stations in the network jointly decide mobile stations to be served at the same time as the transmission powers of base stations are coordinated to mitigate the mutually interfering effect. Although the maximization at the first glance appears to be a mixed, twofold and nonlinear optimization requiring excessive computational complexity, we show that the maximization can be transformed into a pure binary optimization with much lower complexity. To be exact, it is proven that binary power control of base stations is necessary and sufficient for maximizing the network-wide utilities under a physical layer regime where the channel capacity is linear in the signal-to-interference-noise ratio. To further reduce the complexity of the problem, a distributed heuristic algorithm is proposed that performs much better than existing opportunistic algorithms. Through extensive simulations, it becomes clear that network-wide opportunistic scheduling and power control is most suitable for fairness-oriented networks and underloaded networks.

  • 16. Cho, Jeong-woo
    et al.
    Mo, Jeonghoon
    Yonsei University.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Joint Network-wide Opportunistic Scheduling and Power Control in Multi-cell Networks2009In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 8, no 3, p. 1520-1531Article in journal (Refereed)
    Abstract [en]

    We present a unified analytical framework that maximizes generalized utilities of a wireless network by network-wide opportunistic scheduling and power control. That is, base stations in the network jointly decide mobile stations to be served at the same time as the transmission powers of base stations are coordinated to mitigate the mutually interfering effect. Although the maximization at the first glance appears to be a mixed, twofold and nonlinear optimization requiring excessive computational complexity, we show that the maximization can be transformed into a pure binary optimization with much lower complexity. To be exact, it is proven that binary power control of base stations is necessary and sufficient for maximizing the network-wide utilities under a physical layer regime where the channel capacity is linear in the signal-to-interference-noise ratio. To further reduce the complexity of the problem, a distributed heuristic algorithm is proposed that performs much better than existing opportunistic algorithms. Through extensive simulations, it becomes clear that network-wide opportunistic scheduling and power control is most suitable for fairness-oriented networks and under loaded networks. We believe that our work will serve as a cornerstone for network-wide scheduling approaches from theoretical and practical standpoints.

  • 17.
    Cho, Jeong-woo
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Yi, Yung
    KAIST (Korea Advanced Institute of Science and Technology).
    On the Payoff Mechanisms in Peer-Assisted Services With Multiple Content Providers: Rationality and Fairness2014In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 22, no 3, p. 731-744Article in journal (Refereed)
    Abstract [en]

    This paper studies an incentive structure for cooperation and its stability in peer-assisted services when there exist multiple content providers, using a coalition game-theoretic approach. We first consider a generalized coalition structure consisting of multiple providers with many assisting peers, where peers assist providers to reduce the operational cost in content distribution. To distribute the profit from cost reduction to players (i.e, providers and peers), we then establish a generalized formula for individual payoffs when a "Shapley-like" payoff mechanism is adopted. We show that the grand coalition is unstable, even when the operational cost functions are concave, which is in sharp contrast to the recently studied case of a single provider where the grand coalition is stable. We also show that irrespective of stability of the grand coalition, there always exist coalition structures that are not convergent to the grand coalition under a dynamic among coalition structures. Our results give us an incontestable fact that a provider does not tend to cooperate with other providers in peer-assisted services and is separated from them. Three facets of the noncooperative (selfish) providers are illustrated: 1) underpaid peers; 2) service monopoly; and 3) oscillatory coalition structure. Lastly, we propose a stable payoff mechanism that improves fairness of profit sharing by regulating the selfishness of the players as well as grants the content providers a limited right of realistic bargaining. Our study opens many new questions such as realistic and efficient incentive structures and the tradeoffs between fairness and individual providers' competition in peer-assisted services.

  • 18.
    Cho, Jeong-woo
    et al.
    KAIST (Korea Advanced Institute of Science and Technology).
    Yi, Yung
    KAIST (Korea Advanced Institute of Science and Technology).
    On the Shapley-like Payoff Mechanisms in Peer-Assisted Services with Multiple Content Providers2012In: Game Theory for Networks: 2nd International ICST Conference, GameNets 2011, Shanghai, China, April 11-18, 2011, Revised Selected Papers / [ed] Rahul Jain, Kannan, Rajgopal, Springer Science+Business Media B.V., 2012, Vol. 75Conference paper (Refereed)
    Abstract [en]

    This paper studies an incentive structure for cooperation and its stability in peer-assisted services when there exist multiple content providers, using a coalition game theoretic approach. We first consider a generalized coalition structure consisting of multiple providers with many assisting peers, where peers assist providers to reduce the operational cost in content distribution. To distribute the profit from cost reduction to players (i.e., providers and peers), we then establish a generalized formula for individual payoffs when a “Shapley-like” payoff mechanism is adopted. We show that the grand coalition is unstable, even when the operational cost functions are concave, which is in sharp contrast to the recently studied case of a single provider where the grand coalition is stable. We also show that irrespective of stability of the grand coalition, there always exist coalition structures which are not convergent to the grand coalition. Our results give us an important insight that a provider does not tend to cooperate with other providers in peer-assisted services, and be separated from them. To further study the case of the separated providers, three examples are presented; (i) underpaid peers, (ii) service monopoly, and (iii) oscillatory coalition structure. Our study opens many new questions such as realistic and efficient incentive structures and the tradeoffs between fairness and individual providers’ compQC 2012etition in peerassisted services.

  • 19. Gao, Yuehong
    et al.
    Zhang, Xin
    Jiang, Yuming
    NTNU (Norwegian University of Science and Technology).
    Cho, Jeong-woo
    Centre for Quantifiable Quality of Service in Communication Systems (Q2S).
    System Spectral Efficiency and Stability of 3G Networks: A Comparative Study2009In: 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-8: IEEE International Conference on Communications, IEEE Press, 2009, p. 5398-5403Conference paper (Refereed)
    Abstract [en]

    CDMA2000, WCDMA and WiMAX are three widely used 3G technologies. Since they share the same goal, which is to provide broader coverage and higher throughput in 3G networks, an impartial comparison of their performance is indispensable. However, they are based on different design principles and methodologies, which make the comparison challenging. This paper presents a comparative study of these technologies, with focus on system spectral efficiency and stability in 3G networks. Specifically, the paper presents a framework for the comparison based on the common set of configurations adopted by these technologies, which include channel models, system parameters and key algorithms. Through extensive simulations, the system spectral efficiency and stability of CDMA2000 1x EV-DO Rev.A, WCDMA HSDPA/HSUPA and Mobile WiMAX are compared. It is found that while WiMAX can provide highest throughput, the two CDMA-based technologies achieve higher system spectral efficiency, especially on the downlink. Regarding system stability, it is observed that CDMA2000 1x EV-DO Rev.A can operate under higher interference levels than WCDMA HSDPA/HSUPA and Mobile WiMAX. In addition, the comparison on system spectral efficiency between CDMA2000, WCDMA and WiMAX is also conducted when relevant enhanced technologies, i.e., MIMO and interference cancelation, are adopted. We believe that our work will serve as a cornerstone for a fair comparison between the various technologies for prospective 3G networks.

  • 20. Jeong, J.
    et al.
    Yi, Y.
    Cho, Jeong Woo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Eun, D. Y.
    Chong, S.
    Wi-Fi Sensing: Should Mobiles Sleep Longer As They Age?2013In: 2013 Proceedings IEEE INFOCOM, 2013, p. 2328-2336Conference paper (Refereed)
    Abstract [en]

    An essential condition precedent to the success of mobile applications based on Wi-Fi (e.g., iCloud) is an energy-efficient Wi-Fi sensing. From a user's perspective, a good Wi-Fi sensing policy should depend on both inter-AP arrival and contact duration time distributions. Prior work focuses on limited cases of those two distributions (e.g., exponential) or introduces heuristic approaches such as AI (Additive Increase). In this paper, we formulate a functional optimization problem on Wi-Fi sensing under general inter-AP and contact duration distributions, and propose how each user should sense Wi-Fi APs to strike a balance between energy efficiency and performance, depending on the users' mobility pattern. To that end, we derive an optimal condition which sheds insights into the aging property, the key feature required by efficient Wi-Fi sensing polices. Guided by the analytical studies and the implications, we develop a new sensing algorithm, called WiSAG (Wi-Fi Sensing with AGing), which is demonstrated to outperform the existing sensing algorithms up to 34% through extensive trace-driven simulations using the real mobility traces gathered from smartphones.

  • 21.
    Jeong, Jaeseong
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Yi, Yung
    Cho, Jeong-Woo
    KTH, School of Information and Communication Technology (ICT).
    Eun, Do Young
    Chong, Song
    Energy-Efficient Wi-Fi Sensing Policy Under Generalized Mobility Patterns With Aging2016In: IEEE/ACM Transactions on Networking, ISSN 1063-6692, E-ISSN 1558-2566, Vol. 24, no 4, p. 2416-2428Article in journal (Refereed)
    Abstract [en]

    An essential condition precedent to the success of mobile applications based on Wi-Fi (e. g., iCloud) is an energy-efficient Wi-Fi sensing. Clearly, a good Wi-Fi sensing policy should factor in both inter-access point (AP) arrival time (IAT) and contact duration time (CDT) distributions of each individual. However, prior work focuses on limited cases of those two distributions (e. g., exponential) or proposes heuristic approaches such as Additive Increase (AI). In this paper, we first formulate a generalized functional optimization problem on Wi-Fi sensing under general inter-AP and contact duration distributions and investigate how each individual should sense Wi-Fi APs to strike a good balance between energy efficiency and performance, which is in turn intricately linked with users mobility patterns. We then derive a generic optimal condition that sheds insights into the aging property, underpinning energy-aware Wi-Fi sensing polices. In harnessing our analytical findings and the implications thereof, we develop a new sensing algorithm, called Wi-Fi Sensing with AGing (WiSAG), and demonstrate that WiSAG outperforms the existing sensing algorithms up to 37% through extensive trace-driven simulations for which real mobility traces gathered from hundreds of smartphones is used.

  • 22. Lee, H.
    et al.
    Jang, H.
    Yi, Y.
    Cho, Jeong-woo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    On the interaction between content-oriented traffic scheduling and revenue sharing among providers2013In: Proceedings - IEEE INFOCOM, 2013, p. 3201-3206Conference paper (Refereed)
    Abstract [en]

    The Internet consists of economically selfish players in terms of access/transit connection, content distribution, and users. Such selfish behaviors often lead to techno-economic inefficiencies such as unstable peering and revenue imbalance. Recent research results suggest that cooperation in revenue sharing (thus multi-level ISP settlements) can be a candidate solution for the problem of unfair revenue share. However, it is unclear whether providers are willing to behave cooperatively. In this paper, we study the interaction between how content-oriented traffic scheduling at the edge is and how stable the intended cooperation is. We consider three traffic scheduling policies having various degrees of content-value preference, compare them in terms of implementation complexity, network neutrality, and stability of cooperation, and present interesting trade-offs among them.

  • 23. Lee, H.
    et al.
    Jang, H.
    Yi, Y.
    Cho, Jeong-Woo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    On the interaction between content-oriented traffic scheduling and revenue sharing among providers2013In: 2013 IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS 2013), IEEE Communications Society, 2013, p. 333-338Conference paper (Refereed)
    Abstract [en]

    The Internet consists of economically selfish players in terms of access/transit connection, content distribution, and users. Such selfish behaviors often lead to techno-economic inefficiencies such as unstable peering and revenue imbalance. Recent research results suggest that cooperation in revenue sharing (thus multi-level ISP settlements) can be a candidate solution for the problem of unfair revenue share. However, it is unclear whether providers are willing to behave cooperatively. In this paper, we study the interaction between how content-oriented traffic scheduling at the edge is and how stable the intended cooperation is. We consider three traffic scheduling policies having various degrees of content-value preference, compare them in terms of implementation complexity, network neutrality, and stability of cooperation, and present interesting trade-offs among them.

  • 24.
    Lee, Hyang-Won
    et al.
    KAIST (Korea Advanced Institute of Science and Technology).
    Cho, Jeong-woo
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    A Distributed Max-Min Flow Control Algorithm for Multi-rate Multicast Flows2004In: GLOBECOM '04: IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, VOLS 1-6, IEEE Press, 2004, p. 1140-1146Conference paper (Refereed)
    Abstract [en]

    We present a distributed algorithm to compute bandwidth max-min fair rates in a multi-rate multicast network. The significance of the algorithm, compared to previous algorithms [1], [21, [3], is that it is more scalable in that it does not require each link to maintain the saturation status of all sessions and virtual sessions travelling through it, more stable in that it converges asymptotically to the desired equilibrium satisfying the minimum plus max-min fairness even in presence of heterogeneous round-trip delays, and has explicit link buffer control in that the buffer occupancy of every bottlenecked link in the network asymptotically converges to the pre-defined value. In addition, we propose an efficient feedback consolidation algorithm which is computationally simpler than its hard-synchronization based counterpart and eliminates unnecessary consolidation delay by preventing it from awaiting backward control packets(BCPs) that do not directly contribute to the session rate. Through simulations we verity the performance of the proposed multi-rate multicast flow control scheme based on these two algorithms.

  • 25.
    Lee, Hyang-Won
    et al.
    KAIST (Korea Advanced Institute of Science and Technology).
    Cho, Jeong-woo
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Distributed Max-Min Flow Control for Multi-rate Overlay Multicast2010In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 54, no 11, p. 1727-1738Article in journal (Refereed)
    Abstract [en]

    We present a distributed algorithm to compute bandwidth max-min fair rates in an overlay multicast network supporting multi-rate data delivery. The proposed algorithm is scalable in that it does not require each logical link to maintain the saturation status of all sessions and virtual sessions traveling through it, stable in that it converges asymptotically to the desired equilibrium satisfying the minimum plus max-min fairness even in the presence of heterogeneous round-trip delays, and has explicit link buffer control in that the buffer occupancy of every bottlenecked link in the network asymptotically converges to the pre-defined value. The algorithm is based on PI (proportional integral) control in the feedback control theory and by appealing to the Nyquist stability criterion, a usable stability condition is derived in the presence of sources with heterogeneous round-trip delays. In addition, we propose an efficient feedback consolidation algorithm which is computationally simpler than its hard-synchronization based counterpart and eliminates unnecessary consolidation delay by preventing it from awaiting backward control packets that do not directly contribute to the session rate. Through simulations we further verify the analytical results and the performance of the proposed multi-rate multicast flow control scheme based on these two algorithms.

  • 26.
    Lee, Hyojung
    et al.
    KAIST (Korea Advanced Institute of Science and Technology).
    Jang, Hyeryung
    KAIST (Korea Advanced Institute of Science and Technology).
    Cho, Jeong-woo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Yi, Yung
    KAIST (Korea Advanced Institute of Science and Technology).
    On the stability of ISPs' coalition structure: Shapley value based revenue sharing2012Conference paper (Refereed)
    Abstract [en]

    The Internet is a complex system, consisting of different economic players in terms of access/transit connection and content distribution, which are typically selfish and try to maximize their own profits. Due to this different perspective of economic interest as well as dynamic changes of the Internet market, a certain degree of techno-economic inefficiency has naturally been observed, e.g., unstable peering and revenue imbalance among content, eyeball, and transit ISPs (Internet Service Providers). At the center of this issue is “good” revenue sharing among them. Recently, revenue sharing based on the notion of Shapley Value (SV) from cooperative game theory has been applied to address the afore-mentioned issue, shedding light upon many nice properties which have been used not only to understand the current Internet eco-system but also to predict its future. However, the positive features from the SV based revenue sharing can be practically feasible only when the providers agree to form a grand coalition, which may not hold in practice. In this paper, we first investigate the conditions under which the grand coalition is stable under SV by classifying the network into two cases: under-demanded and over-demanded. We then study the gap between the conditions of the grand coalition's stability and optimal coalition structures (i.e., coalition structures that maximize the aggregate revenue of ISPs).

  • 27. Lee, Hyojung
    et al.
    Jang, Hyeryung
    Cho, Jeong-woo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Yi, Yung
    Traffic Scheduling and Revenue Distribution Among Providers in the Internet: Tradeoffs and Impacts2017In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, no 2, p. 421-431Article in journal (Refereed)
    Abstract [en]

    The Internet consists of economically selfish players in terms of access/transit connection and content distribution. Such selfish behaviors often lead to techno-economic inefficiencies, such as unstable peering and revenue imbalance. Recent research results suggest that cooperation-based fair revenue sharing, i.e., multi-level Internet service provider (ISP) settlements, can be a candidate solution to avoid unfair revenue share. However, it has been under-explored whether selfish ISPs actually cooperate or not (often referred to as the stability of coalition), because they may partially cooperate or even do not cooperate, depending on how much revenue is distributed to each individual ISP. In this paper, we study this stability of coalition in the Internet, where our aim is to investigate the conditions under which ISPs cooperate under different regimes on the traffic demand and network bandwidth. We first consider the under-demanded regime, i.e., network bandwidth exceeds traffic demand, where revenue sharing based on Shapley value leads ISPs to entirely cooperate, i.e., stability of the grand coalition. Next, we consider the over-demanded regime, i.e., traffic demand exceeds network bandwidth, where there may exist some ISPs who deviate from the grand coalition. In particular, this deviation depends on how users' traffic is handled inside the network, for which we consider three traffic scheduling policies having various degrees of content-value preference. We analytically compare those three scheduling policies in terms of network neutrality, and stability of cooperation that provides useful implications on when and how multi-level ISP settlements help and how the Internet should be operated for stable peering and revenue balance among ISPs.

  • 28.
    Ryu, Hyung-Keun
    et al.
    Korea Telecom.
    Cho, Jeong-woo
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Chong, Song
    KAIST (Korea Advanced Institute of Science and Technology).
    Stabilized Edge-to-Edge Aggregate Flow Control2004In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 3042, p. 573-587Article in journal (Refereed)
    Abstract [en]

     In this paper, we present a distributed flow control scheme which achieves weighted max-min fair bandwidth allocation among all source-destination pairs on a per-aggregate basis within its network. The motivation behind the scheme is the absence of per-aggregate flow control in the current Internet, resulting in inability to enforce a certain fairness on source-destination flows. In our scheme, the distributed algorithm to compute weighted max-min fair rates is based on PI control in feedback control theory. We mathematically prove the asymptotic stability of the algorithm in presence of aggregate flows with heterogeneous round-trip delays. Through simulations we demonstrate the effectiveness of the proposed scheme in controlling per-aggregate flows.

  • 29. Sankararaman, Abishek
    et al.
    Cho, Jeong-woo
    KTH, School of Information and Communication Technology (ICT).
    Baccelli, Francois
    Performance-Oriented Association in Large Cellular Networks with Technology Diversity2017In: 2016 28TH INTERNATIONAL TELETRAFFIC CONGRESS (ITC 28), VOL 1, IEEE Press, 2017, p. 94-102Conference paper (Refereed)
    Abstract [en]

    The development of mobile virtual network operators, where multiple wireless technologies (e.g. 3G and 4G) or operators with non-overlapping bandwidths are pooled and shared is expected to provide enhanced service with broader coverage, without incurring additional infrastructure cost. However, their emergence poses an unsolved question on how to harness such a technology and bandwidth diversity. This paper addresses one of the simplest questions in this class, namely, the issue of associating each mobile to one of those bandwidths. Intriguingly, this association issue is intrinsically distinct from those in traditional networks. We first propose a generic stochastic geometry model lending itself to analyzing a wide class of association policies exploiting various information on the network topology, e.g. received pilot powers and fading values. This model firstly paves the way for tailoring and designing an optimal association scheme to maximize any performance metric of interest (such as the probability of coverage) subject to the information known about the network. In this class of optimal association, we prove a result that the performance improves as the information known about the network increases. Secondly, this model is used to quantify the performance of any arbitrary association policy and not just the optimal association policy. We propose a simple policy called the Max-Ratio which is not-parametric, i.e. it dispenses with the statistical knowledge of base station deployments commonly used in stochastic geometry models. We also prove that this simple policy is optimal in a certain limiting regime of the wireless environment. Our analytical results are combined with simulations to compare these policies with basic schemes, which provide insights into (i) a practical compromise between performance gain and cost of estimating information and; (ii) the selection of association schemes under environments with different propagation models, i.e. path-loss exponents.

  • 30.
    Tanyingyong, Voravit
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Olsson, Robert
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Cho, Jeong Woo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Hidell, Markus
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Sjödin, Peter
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    IoT-grid: IoT Communication for Smart DC Grids2016In: 2016 IEEE Global Communications Conference, GLOBECOM 2016 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 7841917Conference paper (Refereed)
    Abstract [en]

    IoT technology is considered an essential imperative for Smart Grids (SGs). However, IoT devices have inherently limited responsiveness that may not be sufficient for a time critical SG with stringent demands on communication delay. In practice, it remains an outstanding problem to combine IoT technology with existing grids. To facilitate deployment of IoT-based grids in domestic environments, we propose IoT-grid, a programmable, small-scale, direct current (DC) grid, that can be easily implemented with low-power hardware with limited processing capacity. The proposed grid adopts relatively cheap DC-DC converters which not only provide high conversion efficiency but also accommodate existing small-scale DC power systems (e.g. solar panels). We then explore the communication aspects of IoT-grid, namely, control and monitoring functions. We observe that processing delays of IoT devices have large impact on IoT-grid, which cause a chain of control commands to take considerable longer time as the number of commands increases. To mitigate this problem, we propose a mechanism based on sending burst commands with scheduled responses. Our experimental results show that, in the presence of processing delays, this method can significantly reduce the overall response time.

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