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  • 1.
    Blomgren, Mats
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Traffic estimation and traffic sensitive scheduling in mobile ad hoc networks2005Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Different CSMA variants (Carrier Sense Multiple Access), such as the widely spread WLAN-standards IEEE 802.11, are often suggested as MAC-protocols in ad hoc networks. Many of the problems that a CSMA-system suffers in a one-hop network are aggravated in a multi-hop network. This makes CSMAschemes less attractive to use in ad hoc networks. Several methods of scheduling transmissions in TDMA and in its more evolved form STDMA (Spatial reuse TDMA) have proved to give a higher maximum throughput than CSMA. TSST (Traffic Sensitive Scheduled TDMA) is proposed in this work, it is a novel algorithm for scheduling transmissions.

    TSST makes schedules based on the estimated queue length in every node.

    It is assumed that reports of queue lengths cannot instantaneously propagate from node to node. The updates will be received with a fixed delay (lag). Using this lagged information with support of traffic estimates and the knowledge of previous send schedules, TSST is capable of estimate the current queue lengths.

    The results show that TSST can achieve higher throughput than CSMA. The results also show that TSST can achieve lower end to end delay than idealised forms of prior TDMA-schemes, even if it has to estimate the queue lengths with quite old information and inaccurate traffic estimates.

    It is concluded that TSST is an efficient way of scheduling for TDMA and that the accuracy of the traffic estimator is of great importance.

  • 2.
    Blomgren, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Chacholski, Wojciech
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Farjoun, E. D.
    Segev, Y.
    Idempotent transformations of finite groups2013In: Advances in Mathematics, ISSN 0001-8708, E-ISSN 1090-2082, Vol. 233, no 1, p. 56-86Article in journal (Refereed)
    Abstract [en]

    We describe the action of idempotent transformations on finite groups. We show that finiteness is preserved by such transformations and enumerate all possible values such transformations can assign to a fixed finite simple group. This is done in terms of the first two homology groups. We prove for example that except special linear groups, such an orbit can have at most 7 elements. We also study the action of monomials of idempotent transformations on finite groups and show for example that orbits of this action are always finite.

  • 3.
    Blomgren, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Decentralized market-based radio resource management in multi-network environments2007In: IEEE VTS VEH TECHNOL CONF, 2007, p. 2884-2889Conference paper (Refereed)
    Abstract [en]

    For voice, an efficient radio resource management (RRM) essentially boils down to providing a predefined signal to interference ratio (SIR) at lowest cost possible and centralized schemes has, evidently, been an effective approach to address these problems. Delay-elastic data services, however, introduce both heterogeneous user requirements and possibilities for opportunistic RRM. One way, among others,to handle this would be to let autonomous trade-agents, acting on behalf of users, manage the radio resources, and this is our point of departure. We propose a market-based framework for decentralized RRM in environments populated by multiple, possibly heterogeneous, "access points" (APs), and the provided service for the users consists of file transfers. Resources (transmission time) are partitioned between users through a proportionally fair divisible auction. The problem at hand for the user (trade-agent), is then to determine how much resources it should purchase from the different APs in order to maximize its utility ("value for money"). Our results indicate that decentralized selfish bidding strategies are able to capitalize on temporary beneficial conditions and offer comparable performance with a centralized scheme (based on the 'mu C-rule') that requires knowledge about peak data-rates, queue lengths, and preferences for all users in the system.

  • 4.
    Blomgren, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Demand-responsive pricing in open wireless access markets2007In: IEEE VTS VEH TECHNOL CONF, 2007, p. 2990-2995Conference paper (Refereed)
    Abstract [en]

    Radio resource management (RRM) across operator boundaries is emerging as a salient feature for wireless systems beyond 3G. Until recently, research has been confined to solutions where cooperating networks enter explicit sharing agreements that define how responsibilities and revenues should be divided. An alternative would be to share the infrastructure implicitly by establishing an open wireless access market wherein networks not only compete for users on a long-term time-scale, but also on a much shorter time-base. This could be realized with an architecture where autonomous trade-agents, that reside in terminals and access points (APs), manage the resources through negotiations. In this paper we develop a framework for studying demand-responsive pricing in contexts where APs with overlapping coverage compete for users. Resources are partitioned through a proportional fair divisible auction and our aim is to establish if, and when, an open market for wireless access can be se sustained. Compared to a scenario where APs cooperate, our results show that, an open access market results in better services at lower price which in the prolonging also yields more satisfied customers. As an effect demand will increase and, from the perspective of the APs, act as a counterbalance to the reduced prices. Thus, the revenue earned by the AN will be comparable to the one in which obtained through AP cooperation and monopoly (cartel) pricing. Generally speaking, the difference between the cooperative and noncooperative RRM is small when the demand is concave and increases with the convexity of demand.

  • 5.
    Blomgren, Mats
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Hultell, Johan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cai, Rui
    Cai, Tao
    Distributed demand-aware access selection in wireless multi-cell data networks2007In: 2007 IEEE 18th International Symposium On Personal, Indoor And Mobile Radio Communications: Vols 1-9, 2007, p. 2888-2892Conference paper (Refereed)
    Abstract [en]

    Regardless of advances in transmission technology, wireless broadband access will result in that fewer active users can be supported in a given cell. This may, due to lower levels of statistical multiplexing, yield in an unbalanced network. For such contexts load aware access point (AP) selection (load balancing) has been proposed as a means to increase network performance. This paper evaluates the downlink capacity (maximum number of users that can be admitted given a throughput requirement) of distributed load aware AP selection criteria for a well planned network, where the expected number of users per cell coincide. We propose a market based algorithm in which AP selection is aided by market mechanisms. In contrast to most of the existing research, we account for that interference levels generated in different cells depend on user assignment, and therefore varies as terminals perform handoff. Compared to single-frequency systems where users base their selection on the received signal strength our results show that the downlink capacity can be increased with around 25 percent by introducing a channel plan in combination with demand, or load, aware AP selection criteria. This gain is fairly insensitive to the throughput requirement and does not come at the expense of uplink performance. To benefit from demand metrics it is, however, of paramount importance that the entire system bandwidth is not reused in all cells.

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