Sean Murphy

• ZHAW Zurich University of Applied Sciences

Information Technology is a dominant player of our modern societies; Data Centres, lying at the heart of the IT landscape, have attracted attention, with their increasing energy consumption being a constant topic of concern, especially when it comes to the negative impact on the quality of their surrounding environment. Nevertheless, recent technol...

In this paper we outline a vision for the Connected Car which is centred around the user's mobile device. We describe the different components of the Connected Car ecosystem and highlight why it will remain very heterogeneous for some time. We describe particular technologies in this space which have real potential to be key technologies in the Con...

This paper presents the high level specification of a Self Configuration Framework for 802.11 multi-radio Wireless Mesh Networks based on a centralised topology discovery and channel assignment mechanism. The framework was designed to support the introduction of a new Mesh Node into the network at any time of the network's operational phase. Furthe...

Low cost and high bandwidth Wireless Mesh Networks (WMNs) can be seen as an attractive technology to provide Infotainment services in metropolitan areas. Many network operators and city authorities deploy mesh networks to enable Internet access for visitors and local citizens, but they do not offer any dedicated services. One of the main problems i...

The availability of reasonably priced, increasingly powerful, mobile devices is driving the growth of new video content services. One likely solution for video content delivery is based on the Peer-to-Peer (P2P) architecture. Network congestion can have a significantly negative impact on the performance of P2P distribution. This paper focuses on en...

This paper examines two specific aspects of resource management in Wireless Local Area Networks (WLANs)-Call Admission Control (CAC) and handling of Link Adaptation (LA) events. A self-consistent system to manage these for Voice over Internet Protocol (VoIP) over an IEEE 802.11 WLAN is presented. The proposed CAC scheme is based on the Endpoint Adm...

The existence of hidden and exposed nodes can have a significant negative impact on the performance of IEEE802.11 networks. Such nodes can increase the probability of collisions and limit the spatial reuse on the channel. The value of the Physical Carrier Sensing Threshold (PCST) is instrumental in the presence of such nodes in a system. This paper...

In this paper, two formulations for planning base station (BS) and Relay Station (RS) locations are proposed: a rather complex 0-1 integer programming model which can be used to determine which set of locations should be selected from a given set of BS and RS locations and a simpler decomposition approach which focuses first on the BS location prob...

Traffic routing is central to the utility and scalability of wireless mesh networks. Many recent routing studies have examined this issue, but generally they have assumed that the demand is constant and given in advance. On the contrary, wireless traffic ...

In this paper, the system capacity of a multi-cell IEEE 802.16j system operating in transparent mode is investigated. A previous published analytical model is used and incorporates interference from neighbouring cells. The model can be used to determine downlink performance under max-min fairness constraints for both sectored and omnidirectional sy...

To successfully develop IEEE 802.11a based wireless mesh network solutions that can achieve the reliability and capacities required to offer high quality triple play services the use of multiple radios in each mesh node is essential. Unfortunately, the co-location of multiple antennas in a single device leads to a number of interference problems. I...

In this paper, an interference aware algorithm for multi-cell Relay Station (RS) location planning problem is proposed in order to investigate the capacity gains possible using trans-parent mode 802.16j. The study focuses on the problem of determining the best choice of locations for RS from a given set of candidate sites -Base Station (BS) and Sub...

The existence of hidden and exposed nodes can have a significantly negative impact on the performance of IEEE802.11 networks. Such nodes can increase the probability of collisions and limit the spatial reuse on the channel. The value of the Physical Carrier Sensing Threshold (PCST) is instrumental to the trade-off between the number of hidden and e...

Wireless mesh networking is a promising, cost effective and efficient technology for realizing backhaul networks supporting high quality services. In such networks, multicast data are transmitted blindly without any mechanism protecting data from loss, ensuring data reception, and optimizing channel allocation. The multicast services may undergo, t...

Network centric handover solutions for all IP wireless networks usually require modifications to network infrastructure which can stifle any potential rollout. This has led researchers to begin looking at alternative approaches. Endpoint centric handover solutions do not require network infrastructure modification, thereby alleviating a large barri...

In this paper, the system capacity of IEEE 802.16j systems operating in transparent mode is investigated under varying numbers of relays and associated transmit power. The study is based on an extended variant of an analytical model defined in previous work and used to determine the throughput gain that can be achieved under a max-min fairness cons...

In this paper, an interference-aware analytical model of IEEE 802.16j systems operating in transparent mode is described. The model can be used to determine the throughput gain that can be achieved by 802.16J relay- based systems under a max-min fairness constraint in which the difference between the data rate delivered to all subscribers is minimi...

VOD services distribution is gaining unprecedented interest from the consumer communication industry due to its growing success in both the Internet and residential broadband market. In this article we present a scalable VOD distribution architecture for broadband operators. The solution is based on a P2P streaming concept in which a VOD streaming...

Multihop wireless systems have the potential to offer improved coverage and capacity over single-hop radio access systems. Standards development organizations are considering how to incorporate such techniques into new standards. One such initiative is the IEEE 802.16j standardization activity, adding relay capabilities to IEEE 802.16 systems. This...

In this paper, a clustering approach to solve a network planning problem for 802.16j relay networks is considered. Our clustering approach consists of three basic steps: (1) divide the nodes into k distinct clusters, (2) solve the planning problem separately for each cluster, and (3) perform a final optimization to reduce issues arising at cluster...

Existing terminal oriented handover mechanisms capable of meeting the strict delay bounds of real time applications such as VoIP do not consider the QoS of candidate handover networks. In this paper ECHO - a QoS based handover solution for VoIP- is proposed. ECHO is endpoint centric and does not require any network support; it leverages the SCTP tr...

A simulation study of the performance of transparent mode relay-based 802.16j systems is described. The study focuses on the gain in throughput that is possible in omnidirectional relay systems and increases in signalling requirements that arise due to the multihop network architecture. The study finds that the introduction of transparent mode rela...

In this article we conduct an experimental study of the Enhanced Distributed Channel Access (EDCA) mechanism of the IEEE 802.11e standard with a testbed consisting of 1 Access Point and 15 WLAN stations. The focus of our study is the proposal of guidelines for the configuration of the open parameters in the EDCA mechanism. Specifically, we aim at s...

In this paper, a problem formulation for determining optimal node location for base stations (BSs) and relay stations (RSs) in relay-based 802.16 networks is developed. The formulation results in an Integer Programming problem. A small modification to the original model is also considered in which the state space is reduced by limiting which nodes...

This paper focuses on analysing the variation in IEEE802.11k channel load measurements for neighbouring WLAN systems. The channel load functionality was implemented in the QualNet simulation tool, and several scenarios were configured for testing. The effects of different numbers of active systems with different traffic patterns were examined. The...

In this paper we present a solution for delivering streaming video-on-demand to subscribers via an 802.16 broadband wireless access network. The solution leverages the forthcoming H.264/AVC Scalable Video Coding (SVC) scheme and a mechanism to perform rate adaptation based on monitoring changes to the amount of flow traffic in the network at any ti...

In this paper, three approaches to allocating resources between interfering IEEE 802.16 systems operating in license exempt mode are described. The schemes differ in terms of how they implement the fairness/utilisation trade-off. The three schemes are Throughput Maximisation (ThM), Maximum Fairness (MaF), and a Neighbour Based Resource Allocation (...

In parallel with the growth of VoIP services, a large number of manufacturers have begun to develop multimode devices capable of connecting to multiple wireless access networks simultaneously. These multimode terminals have, in principle, the capability to support seamless handover between different radio access networks. One handover solution that...

An approach to mitigating interference between 802.16 license-exempt systems is proposed in this paper. More specifically, the approach focuses on solving problems which arise when two or more 802.16 systems operate on the same channel in close proximity to each other. The essence of the approach is a distributed mechanism which can apportion the a...

In this paper, options for providing seamless service delivery to mobile terminals via heterogeneous radio access networks are considered. Despite its current popularity, the Mobile IP solution for mobility management of mobile hosts is discounted due to problems associated with introducing the required network infrastructure and poor handover perf...

In this paper a scheme is proposed to deal with congestion problems that can arise due to Link Adaptation (LA) in Wireless Local Area Networks (WLANs) in the presence of VoIP traffic. The proposed scheme operates by first determining if LA has resulted in the system becoming congested. If not, no further action is taken. However, if, LA has resulte...

In this paper an endpoint-based admission control mechanism for VoIP over WLAN is proposed. The mechanism operates by first measuring the utilisation of the channel and comparing this to a pre-determined threshold, if the channel utilisation exceeds this threshold, the call is rejected. One important aspect of the mechanism is that it can operate i...

In this paper a transport layer handover mechanism for Voice over Internet Protocol (VoIP) in 802.11b using the Stream Control Transmission Protocol (SCTP) is proposed. The multi-homing feature of SCTP is used to allow connections to several 802.11b Access Points (AP's). Probing packets that model VoIP encoded data at various transmission rates are...

This paper presents how SCTP can stall in multi- homed scenarios during failover and under certain circum- stances. A stall is where an SCTP end-point ceases to commu- nicate for an extended period of time, but does not report any error to the upper layer. This paper presents two different sets of circumstances where a stall can occur: firstly when...

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A simulation study of delivery of streaming video on-demand via IEEE 802.16 based technologies is described. A number of scenarios are simulated which are representative of rural area deployments of such technologies. The study finds that IEEE 802.16 can support up to 9/10 simultaneous users streaming typical cinematic video content in CIF resoluti...

In this paper a scheme is proposed to deal with the problem of Link Adaptation (LA) of an ongoing call in a Voice over Wireless Local Area Network (VoWLAN) environment. The scheme operates by dropping the call from the system if the LA affects the call quality of the other ongoing calls. The proposed scheme was evaluated on an experimental test-bed...

In this paper, three approaches to modelling a distributed approach to interference mitigation in 802.16 license-exempt (LE) systems are described. An interference-free (IF) approach in which no interference is permitted at any node of the system; a controlled-interference (CI-T) and a controlled-interference with fairness (CI-F) approaches where i...

This paper examines, via simulation, the performance of an 802.11e MAC over an 802.11g PHY operating in DSSS-OFDM mode. The DSSS-OFDM scheme provides data rates of up to 54Mb/s as well as interoperability with 802.11b nodes. Due to the widespread use of 802.11b nodes, such interoperability is an important consideration. This paper involves a study...

A rudimentary approach to mitigate interference issues in license-exempt 802.16 systems is presented. This approach operates by permitting each Base Station (BS), and associated Subscriber Stations (SSs) to remain inactive for a specifled fraction of the time. Other systems can then transmit with a reduced likelihood of interference. A simulator wa...

A study of the performance of a number of different multiplexing schemes was conducted in the context of streaming of MPEG-4 object-based content, with particular emphasis on streaming content to mobile devices. The comparison involved six different schemes. The schemes differed in terms of how they packed the data for each arbitrarily shaped video...

The seamless handover of streamed video in a WLAN with UDP as the transport layer is considered. The use of handover for stationary nodes in the case of network congestion is motivated. Next, the relationship between delay and loss in WLANs is studied, with the conclusion that delay can be used as an indicator of when loss is likely to occur. Delay...

This work describes a detailed simulation-based study of the performance of an IEEE 802.11e Medium Access Control (MAC) layer over an IEEE 802.11g Physical (PHY) layer. The study focuses on the number of simultaneous bidirectional G.711 Voice over IP (VoIP) calls that can be supported by a Wireless Local Area Network (WLAN) using the Extended Rate...

The mobile wireless environment can be challenging for multimedia applications, with poor performance and handover issues causing service degradation. In this paper, a modified version of the new IETF transport protocol, SCTP, is shown to improve the performance of a voice-like application in an environment where two wireless LAN's overlap. It does...

The performance of an IEEE 802.11b ad-hoc network that uses the AODV (Ad hoc On-demand Distance Vector) routing protocol is evaluated. One significant issue relating to the behavior of WLAN cards that has considerable impact on AODV performance was observed during the initial testing of the system and it is discussed and a solution proposed. Some a...

One of the major problems in building large-scale enterprise applications is predicting the performance of the eventual solution before the application has been built. Middleware offered by component technologies such as Sun's Enterprise JavaBeans, Microsoft's .NET, or OMG's CORBA Component Model does not guarantee the fulfillment of performance re...

This document describes a distributed approach to interference mitigation for 802.16 LE systems. The scheme applies to 802.16 systems operating on a single channel; each BS in the system remains silent for some period of time to facilitate access to the medium by other BSs in the area. The performance of this distributed approach is compared with t...

In this paper a Call Admission Control (CAC) scheme for Voice over Internet Protocol (VoIP) over a Wireless Local Area Network (WLAN) is proposed. The CAC scheme is based on the Endpoint Admission Control (EAC) paradigm where the endpoints, i.e. the WLAN terminals, probe the network to ascertain if the call can be supported with acceptable Quality...

The performance of different approaches to streaming MPEG-4 video over RTP was investigated. Three specific approaches were compared: first, no multiplexing is used and only a single video data unit i.e. a coded video frame or a coded video frame segment, is transmitted per packet; in the second many video data units are multiplexed into a single R...

This paper describes an empirical study that examines the relationship between network performance and video streaming quality for different types of video content. Three classes of video content - newsclips, music and movie trailers - are studied in order to generate appropriate maps from network performance to a quality score with correlates with...

This paper provides a detailed discussion of the problem of Seamless Handover in Heterogeneous Radio Access Networks. Brief descriptions of several wireless access technologies are included to provide some background information and to illustrate the importance of solving the seamless handover problem for network subscribers. Several approaches to...

The increasing popularity of VoIP and the growing number of independent heteroge-neous wireless access networks has created a demand for the use of VoIP over wire-less networks. The availability of multimode mobile devices capable of connecting to different wireless technologies provides the user with the possibility of seamlessly ac-cessing VoIP s...