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Selfish multi-channel random access in heterogeneous channels
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.ORCID iD: 0000-0003-4986-6123
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We analyze the behavior of selfish users in a multichannel random access system in which the propagation characteristics of the available channels in the system exhibit different statistics. We formulate the behavior of the selfish users as a Bayesian game and identify the transmission strategies at the Nash equilibria. Following this, we propose a simple iterative algorithm to obtain the transmission probabilities of the selfish uses at the Nash equilibria and investigate the convergence properties of this algorithm. Using the transmission probabilities of the selfish users at the Nash equilibria, we analyze the performance of the MRA system with selfish users in terms of sum and per-user utilities and compare this system with its cooperative and scheduling system counterparts. We find that selfish behavior results in significant performance loss compared to scheduling and cooperative systems, which increases as the system load increases.

National Category
Telecommunications Communication Systems
Identifiers
URN: urn:nbn:se:kth:diva-51071OAI: oai:DiVA.org:kth-51071DiVA: diva2:463340
Note

QC 20120328

Available from: 2011-12-09 Created: 2011-12-09 Last updated: 2016-06-20Bibliographically approved
In thesis
1. Selfish Dynamic Spectrum Access in Multichannel Wireless Networks: Complete and incomplete information analysis
Open this publication in new window or tab >>Selfish Dynamic Spectrum Access in Multichannel Wireless Networks: Complete and incomplete information analysis
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The increasing popularity and widespread deployment of wireless data systems fuel the increasing demand for more spectrum. On the other hand, various studies measuring spectrum utilization show that there is a huge variation in spectrum utilization at different times and locations. In view of this, various dynamic spectrum access (DSA) methods have been proposed in order to achieve more efficient utilization of spectrum resources by virtue of exploiting the variations in spectrum demand over time and space. Implementing DSA systems in a centralized way can lead to complexity and scalability problems due to the extensive control signaling involved. Therefore distributed implementations of DSA systems in which the users can access the system resources at their own discretion have been proposed. These distributed mechanisms typically incorporate cognitive radio systems which act as agents on behalf of users to measure the radio environment and make decisions based on these measurements. On the other hand, the freedom of the users in distributed systems to form their actions can lead each user to try to maximize its benefit from the system without regard the overall performance of the DSA system. Therefore, selfish behavior can prevail in distributed systems, which is likely to degrade the system performance.In this thesis we investigate the implications of selfish decision making in dynamic spectrum access systems. To address this broad problem, we focus our analysis on a particular system which can represent the essential properties of DSA systems and thus can shed light on the performance of the broad class of DSA systems with selfish users. Specifically, we model a DSA system as a multichannel random access system which uses ALOHA for medium access, and we analyze the behavior of the selfish users by modeling the system as a non-cooperative game. In this analysis we incorporate the effect of channel state information on the decision making of the users; we consider both cases when the users act on global (complete) and on local (incomplete) information. We determine the behavior of the selfish users at the Nash equilibria of the non-cooperative game and measure the performance of the system in terms of sum and individual utilities for various user loads and amount of available resources. We try to identify how the performance of the DSA system with selfish users compares with its cooperative counterpart. By performing these analyses we provide insights into the broader question of whether selfish users can utilize spectrum resources in a DSA system as well as cooperative users.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xi, 109 p.
Series
Trita-ICT-COS, ISSN 1653-6347 ; 1108
Keyword
Game theory, Multichannel random access, Bayesian game, Nash equilibrium Heterogeneous channels
National Category
Telecommunications Communication Systems
Research subject
SRA - ICT
Identifiers
urn:nbn:se:kth:diva-50738 (URN)
Presentation
2011-12-14, Sal C1, Electrum 1, Isafjordsgatan 26, Kista, Stockholm, 14:00 (English)
Opponent
Supervisors
Projects
MultiOperator Dynamic Spectrum access (MODyS)
Funder
Wireless@kth
Note

QC 20111208

Available from: 2011-12-08 Created: 2011-12-07 Last updated: 2013-11-08Bibliographically approved
2. Capacity analysis of densely deployed wireless LANs
Open this publication in new window or tab >>Capacity analysis of densely deployed wireless LANs
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wireless LANs (WLANs) based on the IEEE 802.11 standard have become an integral part of today’s indoor wireless communication infrastructure. As WLAN deployments become more prevalent and densely deployed, the nodes in these WLANs start to create congestion and interference with each other. This congestion and interference fundamentally limits the performance of these coexisting WLANs. We analyze the capacity limits of such densely deployed WLANs.

We begin our analysis by investigating the suitability of the attributes of WLANs, namely their cooperative operation based on locally available information, for indoor high-capacity wireless access provisioning. We compare the cooperative class of wireless systems with another class of systems whose users behave selfishly. Following this qualitative assessment, we perform a detailed, qualitative analysis of the capacity of densely deployed WLANs in terms of a number of key environmental and operational parameters. The indoor propagation environment has a significant influence on the congestion and interference that these coexisting WLANs exert on each other. Therefore we investigate the impact of propagation environment on the aggregate throughput of densely deployed WLANs. As WLANs are deployed in close proximity of each other, the transmissions in one WLAN start to influence the outcome of transmissions in other WLANs. The manner in which the access points are deployed, and the manner in which stations associate themselves with the available access points around themselves is shown to be an influential factor in the performance of these coexisting WLANs. Therefore, we investigate the impact of random versus planned access point deployment on performance of densely deployed WLANs. Similarly, we investigate the impact of stations associating with the access point with the strongest signal or with another sufficiently strong access point in their vicinity. Furthermore, we investigate the throughput of densely deployed WLANs when operating with bounded delay. More specifically we examine the case when the input traffic arriving at the transmitters are expected to reach their destination within a certain time period, thus the transmit queues cannot grow without bounded and the system should operate at a stable point.

The indoor propagation environment, creates complex interference relationships between nodes in coexisting WLANs.These complex interference relationships are compounded by the node interactions dictated by the nonlinear algorithms in the IEEE 802.11 MAC protocol, thus the problem of estimating the performance of these coexisting WLANs by means of simple analytical models becomes difficult. In contrast, detailed packet level simulations provide accurate performance estimates, although such analyses are computationally expensive. Therefore we seek to provide a model to estimate the throughput of densely deployed WLANs based on empirical throughput results of detailed simulations of such densely deployed WLANs. In addition, in our effort to develop an empirical throughput model for densely deployed WLANs, we develop a measure which we call “cell congestion” to be able to order and compare different propagation environments, and an “effective density” concept which accounts for the influence of the propagation environment on the congestion and interference experienced by a WLAN deployment of a given density. We expect these concepts to be useful in improving the operation of WLANs to be able to meet the predicted increase in demand for capacity.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. x, 91 p.
Series
TRITA-ICT-COS, ISSN 1653-6347 ; 1410
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-154343 (URN)
Public defence
2014-10-24, Sal A, Electrum 1, KTH, Isafjordsgatan 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Wireless@kth
Note

QC 20141020

Available from: 2014-10-20 Created: 2014-10-17 Last updated: 2014-10-23Bibliographically approved

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