26 research outputs found
Handover management in mobile WiMAX using adaptive cross-layer technique
The protocol type and the base station (BS) technology are the main communication media between the Vehicle to Infrastructure (V2I) communication in vehicular networks. During high speed vehicle movement, the best communication would be with a seamless handover (HO) delay in terms of lower packet loss and throughput. Many studies have focused on how to reduce the HO delay during lower speeds of the vehicle with data link (L2) and network (L3) layers protocol. However, this research studied the Transport Layer (L4) protocol mobile Stream Control Transmission Protocol (mSCTP) used as an optimal protocol in collaboration with the Location Manager (LM) and Domain Name Server (DNS). In addition, the BS technology that performs smooth HO employing an adaptive algorithm in L2 to perform the HO according to current vehicle speed was also included in the research. The methods derived from the combination of L4 and the BS technology methods produced an Adaptive Cross-Layer (ACL) design which is a mobility oriented handover management scheme that adapts the HO procedure among the protocol layers. The optimization has a better performance during HO as it is reduces scanning delay and diversity level as well as support transparent mobility among layers in terms of low packet loss and higher throughput. All of these metrics are capable of offering maximum flexibility and efficiency while allowing applications to refine the behaviour of the HO procedure. Besides that, evaluations were performed in various scenarios including different vehicle speeds and background traffic. The performance evaluation of the proposed ACL had approximately 30% improvement making it better than the other handover solutions
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Performance evaluation of fixed WiMax physical layer under high fading channels
This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.A radio channel characteristic modelling is essential in every network planning. This project deals with the performance of WiMax networks in an outdoor environment while using fading channel models. The radio channels characteristics are analyzed by simulations have been done using Matlab programming. Stanford University Interim(SUI) Channels set was proposed to simulate the fixed broadband wireless access channel environments where IEEE 802.16d is to be deployed. It has six channel models that are grouped into three categories according to three typical different outdoor Terrains, in order to give a comprehensive study of fading channels on the overall performance of the system, WiMax system has been tested under SUI channels that modified into account for 30o directional antennas, with 90% cell coverage and with 99.9% reliability in its geographical covered area. Furthermore, in order to combat the fading which occurs in urban areas and improve the capacity and the throughput of the system, multiples antennas at both ends of communication link are used, the transmission gain obtained when using multiple antennas instead of only a single antenna. Space-time coding and maximum ratio combining for more than one transmit and receive antenna is implemented to allow performance investigations in various MIMO scenarios. It has been concluded that uses multiple antennas at the receiver offers a significant improvement of 3 dB of gain in the channel SNR. This thesis also contain implementation of all compulsory features of the WiMax OFDM physical layer specified in IEEE 802.16-2004 using Matlab coding. In order to combat the temporal variations in quality on a multipath fading channel, an adaptive modulation technique is used. This technique employs multiple modulation schemes to instantaneously adapt to the variations in the channel SNR, thus maximizing the system throughput and improving BER performance. WiMax transceiver has been tested with and without encoding and studied the effect of encoding on multipath channel. Testing the system with flexible channel bandwidth has been part of this thesis. Finally it has been explained in this thesis the affect of increasing the size of cyclic prefix on overall performance of WiMax system
Co-evolution of an emerging mobile technology and mobile services : a study of the distributed governance of technological innovation through the case of WiBro in South Korea
This thesis is a study of the development and uptake of an emerging infrastructural
technology: the mobile Wireless Broadband technology and service known as WiBro
in South Korea, and Mobile WiMAX internationally. WiBro has emerged through a
national development effort since the early 2000s. The commercial service was
launched in 2006. However, uptake fell far below initial expectations, only
succeeding in niche markets. This study was motivated by concerns about the
perceived gulf between development and diffusion and the ‘failure’ of WiBro.
However, this study seeks to go beyond the technology-driven perspective that
informs conceptions of diffusion gap: it aims to explicate the sociotechnical factors
leading to such a gap.
This study draws on Science and Technology Studies (STS) and in particular the
Social Shaping of Technology (SST) perspective, which provides tools to scrutinize
the interactions among the various interests and factors involved in the process of
technological innovation. The SST perspective goes beyond approaches that treat
technology as a static object to be developed and diffused. It provides tools to
examine the complex and dynamic forces that develop technical capacity towards
particular forms and uses. The ‘social learning’ perspective extends SST and
provides concepts to explore the changing dynamics over multiple cycles of
innovation. Here, Jørgensen’s concept of ‘development arena’ helps examine the
interlinked, yet dispersed and multiple spaces in which differing goals, motivations
and strategies of innovation players together shape technological innovation.
Through comprehensive analyses of a longitudinal study of WiBro, a broader view
of the process and the outcomes of technological innovation have been achieved.
Rather than viewing the technology as a stable object that would progress in a linear
manner through the stages of design, development, and diffusion, it has focused on
the process of shaping of WiBro through multiple cycles of innovation. Several
arenas of innovation were identified as diverse players sought to align their interests
towards exploiting the resources, capacities, and tools for innovation that seemed to
be available. In these spaces, conflicting and yet coevolving dynamics were
observed: one involving coordination through alignments of multiple interests, and
the other incorporating tensions and misalignments among the differing concerns,
aims and commitments towards the innovation. The complex dynamics involved a
multi-level game where the collective actions among the innovation players and their
individual strategies diverged to a degree. Furthermore, changing contingencies,
linked to shifting choices of innovation players, resulted in the deviation of the
innovation from the initial visions and aims.
The study thus illustrates the outcomes of highly divergent interactions at play in
innovation process and the mutual enrollment efforts of players that constituted the
distributed governance of innovation. Here the complex interplays among the
innovation players involved in multi-level games produced a gap between the
generic vision and the actual uptake of WiBro. Changing contingencies, especially
linked to broader and evolving structures and relations - brought about the reshaping
of the generic vision of WiBro. This research therefore suggests the concept
of the ‘distributed governance of innovation’ as a new mode for governance: that
accommodates not only differing knowledges and interests but also the shifting
choices and visions through the various cycles of technological innovation. The
boundary of social learning is thus extended to incorporate diverging choices over
time and across the multiple spaces of innovation. Its implications for policy include
achieving reflexivity by incorporating into the policy framework the learning process
that takes place as the innovation players go through the varying stages and cycles of
technological innovation
Comparison of vertical handover decision-based techniques in heterogeneous networks
Industry leaders are currently setting out standards for 5G Networks projected for 2020 or even sooner. Future generation networks will be heterogeneous in nature because no single network type is capable of optimally meeting all the rapid changes in customer demands. Heterogeneous networks are typically characterized by some network architecture, base stations of varying transmission power, transmission solutions and the deployment of a mix of technologies (multiple radio access technologies). In heterogeneous networks, the processes involved when a mobile node successfully switches from one radio access technology to the other for the purpose of quality of service continuity is termed vertical handover or vertical handoff. Active calls that get dropped, or cases where there is discontinuity of service experienced by mobile users can be attributed to the phenomenon of delayed handover or an outright case of an unsuccessful handover procedure. This dissertation analyses the performance of a fuzzy-based VHO algorithm scheme in a Wi-Fi, WiMAX, UMTS and LTE integrated network using the OMNeT++ discrete event simulator. The loose coupling type network architecture is adopted and results of the simulation are analysed and compared for the two major categories of handover basis; multiple and single criteria based handover methods. The key performance indices from the simulations showed better overall throughput, better call dropped rate and shorter handover time duration for the multiple criteria based decision method compared to the single criteria based technique. This work also touches on current trends, challenges in area of seamless handover and initiatives for future Networks (Next Generation Heterogeneous Networks)