Karol Kowalik

Dublin Institute of Technology, Dublin, L, Ireland

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Publications (13)0 Total impact

  • Source
    Yin Chen, K. Kowalik, M. Davis
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    ABSTRACT: A core problem of fast handoff is when handoff should perform and which Mesh Node (MN) should associated with. We have developed a fast handoff management scheme called MeshScan to provide a novel use of channel scanning latency, by employing open system authentication in both Passive Handoff and Active Handoff. This scheme comprises three steps: firstly a client device takes advantage of the Wireless Mesh Network (WMN) architecture to maintain a list of active MNs. Secondly MeshScan Handoff Sensor performs handoff when it receives a disassociation management frame from the serving MN or when the measured signal strength from the serving MN exceeds a given threshold. Thirdly when handoff is required, a client transmits Authentication Request frames to all MNs from the list instead of broadcasting Probe Request frames, as in an active scan to discover the available MNs. The handoff delay is used as criteria for system performance. Numerical results are presented to demonstrate the feasibility of MeshScan with Active Handoff algorithm. This fast handoff scheme is feasible by upgrading the software only on the client side. This paper compares the theoretical handoff latency of MeshScan with other approaches and we demonstrate the effectiveness of our scheme through experiment.
    Wireless Communications & Signal Processing, 2009. WCSP 2009. International Conference on; 12/2009
  • Source
    Chenzhe Zhang, K. Kowalik, M. Davis
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    ABSTRACT: Next-generation wireless mobile communications will be driven by converged networks that integrate disparate technologies and services. Wireless Mesh Networks (WMNs) are expected to be one of the next generation of wireless interconnection technologies, providing flexible high bandwidth wireless backhaul over large geographical areas. While single radio mesh nodes operating on a single channel suffer from capacity constraints, equipping mesh routers with multiple radios using multiple non-overlapping channels can significantly alleviate the capacity problem and increase the aggregate bandwidth available to the network. However, it is well known that multi-radio Mesh platforms face many limitations such as interference, radiation leakage, crosstalk and limited computing resource etc. A misperception among researchers is that the so called "crosstalk" is one of the limiting factors to the performance decrease in multi-radio Mesh networks, but through a series of experiments the results shows otherwise. In this paper, we present a unique experimental approach that utilizes antenna cables, splitters, couplers and attenuators etc. to create a controlled wireless environment, and results indicates, despite negligible effect, crosstalk is not a limiting factor, but rather the finite computing resource constrains the aggregated performance of multi-radio Mesh networks, and several other factors have been investigated as well.
    Wireless Communications, Networking and Mobile Computing, 2009. WiCom '09. 5th International Conference on; 10/2009
  • Yin Chen, Karol Kowalik, Mark Davis
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    ABSTRACT: Handoff delay is one of the major problems in Wireless Mesh Network (WMN) that needs to be solved in order to allow time-critical and real-time applications run continuously during handoff. We have developed a fast handoff scheme called MeshScan to provide a novel use of channel scanning latency by employing open system authentication. This scheme comprises two steps: firstly a client device takes advantage of the WMN architecture to maintain a list of active mesh nodes. Secondly when handoff is required, a client transmits Authentication Request frames to all mesh nodes (MNs) from the list instead of broadcasting Probe Request frames as in an active scan to discover the available MNs. This fast handoff scheme is feasible by upgrading the software only on the client side. This paper compares the theoretical handoff latency of MeshScan with other approaches and we demonstrate the effectiveness of our scheme through experiment.
    Proceedings of the Seventh ACM International Workshop on Mobility Management & Wireless Access, MOBIWAC 2009, Tenerife, Canary Islands, Spain, October 26-27, 2009; 01/2009
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    ABSTRACT: Power control techniques for IEEE 802.11 wireless networks have already gained considerable attention. Such techniques are particularly attractive because they can improve various aspects of wireless network operation such as interference mitigation, spatial reuse in dense wireless deployments, topology control, and link quality enhancement. In this paper we propose a novel delivery ratio based Conservative Transmit Power Control (ConTPC) mechanism. Our implementation is conservative when it comes to deciding if the transmit power should be reduced for a given link. This is because we do not want poor quality wireless links to further reduce their quality and be overwhelmed by other links transmitting at maximum power. We have experimentally evaluated the benefit of the proposed power control scheme when compared with fixed power level systems. We show that our ConTPC mechanism can increase the throughput, however the magnitude of this enhancement largely depends on the topology of the wireless network.
    12/2008: pages 399-411;
  • Source
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    ABSTRACT: Power control techniques for IEEE 802.11 wireless networks have already gained much attention. Such techniques are particularly attractive because they can improve various aspects of wireless network operation such as interference mitigation, spatial reuse in dense wireless deployments, topology control, and link quality enhancement. However, until recently implementing such advanced power control using off-the-shelf wireless devices was not considered possible. For example, Abdesslem et al. [1] stated that ldquomany novel power control solutions cannot be efficiently implemented over existing IEEE 802.11 cardsrdquo. However, in this paper we demonstrate that power control is now feasible and can be implemented in current IEEE 802.11 cards with per-packet granularity and low power switching latency.
    Telecommunications, 2008. ICT 2008. International Conference on; 07/2008
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: Power control techniques for IEEE 802.11 wireless networks have already gained considerable attention. Such techniques are particularly attractive because they can improve various aspects of wireless network operation such as interference mitigation, spatial reuse in dense wireless deployme nts, topology control, and link quality enhancement. In this paper we propose a novel delivery ratio based Conservative Transmit Power Control (ConTPC) mechanism. Our implementation is conservative when it comes to deciding if the transmit power should be reduced for a given link. This is because we do not want poor quality wireless links to further reduce their quality and be overwhelmed by other links transmitting at maximum power. We have experi- mentally evaluated the benefit of the proposed power control scheme wh en compared with fixed power level systems. We show that our ConTPC mechanism can increase the throughput, however the magnitude of this enhancement largely depends on the topology of the wireless network.
    WINSYS 2008 - Proceedings of the International Conference on Wireless Information Networks and Systems, Porto, Portugal, July 26-29, 2008, WINSYS is part of ICETE - The International Joint Conference on e-Business and Telecommunications; 01/2008
  • Source
    B. Keegan, K. Kowalik, M. Davis
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    ABSTRACT: Wireless Mesh Networks (WMNs) represent the next generation wireless networks. The increased capacity of WMNs means that they are now capable of providing backhaul services traditionally maintained by wired networks. The attraction of WMNs is their ease of deployment and ability to self organise, self configure, and self heal. In order to successfully achieve this objective careful consideration must be applied when constructing a WMN. In order to optimise the operation of the network, data should traverse the network by means of the most efficient route. Characterisation and path selection will be determined by the routing algorithm coupled with the link cost metrics. In this paper we experimentally investigate the overhead associated with the estimation of the link quality using the Estimated Transmission Time (ETT) metric.
    Signal Processing and Communications, 2007. ICSPC 2007. IEEE International Conference on; 12/2007
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    Conference Proceeding: Making OLSR Aware of Resources
    K. Kowalik, B. Keegan, M. Davis
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    ABSTRACT: An important element of any routing protocol used for Wireless Mesh Networks (WMNs) is the link cost function used to represent the radio link characteristic. The majority of the routing protocols for WMNs attempt to accurately characterise the radio link quality by constructing the link cost function from the measurements obtained using active probing techniques which introduces overhead. In this paper we present a modified version of the Optimized Link State Routing (OLSR) protocol which uses the link cost function values provided the Resource Aware Routing for mEsh (RARE) module which employs passive monitoring to gather radio link information. This results in a smaller overhead than the other methods that require active network probing and furthermore is load independent since it does not require an access to the medium. We demonstrate the necessary modifications to OLSR required to make it work with RARE. The results of our ns-2 simulations show that such a combination (OLSR + RARE) performs well over various wireless topologies.
    Wireless Communications, Networking and Mobile Computing, 2007. WiCom 2007. International Conference on; 10/2007
  • Source
    K. Kowalik, B. Keegan, M. Davis
    [show abstract] [hide abstract]
    ABSTRACT: An important element of any routing protocol used for wireless mesh networks (WMNs) is the link cost function used to represent the radio link characteristic. The majority of the routing protocols for WMNs attempt to accurately characterise the radio link quality by constructing the link cost function from the measurements obtained using active probing techniques, which introduces overhead. In this paper we propose a new approach called resource aware routing for mesh (RARE) which instead employs passive monitoring to gather radio link information. This results in a smaller overhead than the other methods that require active network probing, and is load independent since it does not require an access to the medium. Moreover, we show that our RARE approach performs well in a real radio environment through a number of experiments performed on a static 17 node WLAN mesh testbed.
    Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
  • Source
    Karol Kowalik, Mark Davis
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    ABSTRACT: Wireless Mesh Networks (WMNs) are a type of radio-based net-work systems which require minimal configuration and infrastructure. They can be build using relatively low cost radios and inexpensive computing platforms, and consequently appear to be a compelling option for rolling out networks with a low deployment cost. One of the factors which influences the performance of WMNs is the routing protocol used. There are many routing protocols for WMNs, we estimate that there are more than a hundred of them. In this paper we attempt to answer the question why there are so many and if there is a need for such an abundance. Moreover, we elaborate on the possible development of a single routing protocol for WMNs.
    Irish Signal and Systems Conference. 07/2002;
  • Brian Keegan, Karol Kowalik, Mark Davis
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    ABSTRACT: In recent years Wireless Mesh Networks have been deployed and grown in popularity in many metropolitan areas. The deployment of such networks has allowed clients to gain access to publicly available broadband networks. The implementation of wireless mesh networks requires that backhaul services (traditionally carried by wired networks) be maintained via wireless mesh points. Because of their structure, wireless mesh networks provide an excellent means for targeting a large group of end users or simply to relay data. This may be achieved by means of broadcasting or more specifically multicasting. The lack of standards and support for multicasting over wireless mesh networks makes this area very challenging as well as providing much scope for improvement.
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    ABSTRACT: IEEE 802.11 allows for fragmentation tuning and rate selection. Their combined usage is referred sometimes to link adaptation. However, the algorithms of link adaptation are beyond the 802.11 standards. In this paper we investigate the benefits arising from proper use of link adaptation. Particularly, we develop a mathematical model describing the fragmented transmission in 802.11b. We examine potential benefits of it over AWGN and fading channels. More significantly we combine fragmentation tuning with bit-rate selection to yield the highest achievable throughput performance for any given channel conditions. Finally, we propose an algorithm that performs the optimal link adaptation.
  • Brian Keegan, Karol Kowalik, Mark Davis
    [show abstract] [hide abstract]
    ABSTRACT: Wireless Mesh Networks (WMNs) are a type of radio-based network which require minimal configuration and infrastructure. They can be built using relatively low cost radio and computing platforms. In this paper we attempt to analyze the performance of a simple WNM using various packet sizes as well as a multi-hop WMN.