106 research outputs found
Mobile WiMAX Performance Investigation
Although the Mobile-WiMAX technology is being deployed in the United States, Europe, Japan, Korea, Taiwan and in the Mideast, there are still ongoing discussions about the potential of this technology. What is really remarkable, in fact, with regard to the Mobile-WiMAX profile, is the high number of degrees of freedom that are left to manufacturers. The final decision on a lot of very basic and crucial aspects, such as, just to cite few of them, the bandwidth, the frame duration, the duplexing scheme and the up/downlink traffic asymmetry, are left to implementers. It follows that the performance of this technology is not clear yet, even to network operators.
This consideration motivated our work, which is focused on the derivation of an analytical framework that, starting from system parameters and implementation choices, allows to
evaluate the performance level provided by this technology, carefully taking all aspects of IEEE802.16e into account. In particular, the analysis starts from the choices to be made at the
physical layer, among those admitted by the specification, and "goes up" through the protocol pillar to finally express the application layer throughput and the number of supported
voice over IP (VoIP) users, carefully considering "along the way" all characteristics of the the medium access control (MAC) layer, the resource allocation strategies, the overhead introduced,
the inherent inefficiencies, etc
Performance Evaluation of Connection Admission Control for IEEE 802.16 Networks
Quality of Service (QoS) provisioning to the various kinds of network traffic is one of the major design criteria of IEEE 802.16 WiMAX standard. The MAC and physical layers of
802.16 standards are designed to support different types of real time application by providing QoS. Scheduling, Connection Admission Control (CAC) and traffic policing are the major issues to ensure QoS. In standard, scheduling and admission control are kept as open issues. Admission control is the ability of a network to control admission of new traffic based on the availability of resources. As per the specification the CAC
considers minimum reserved rate of a connection as an
admission criterion, in which the system can admit more
connections, but packets of admitted connection may encounter large delays. In this paper average data rate (avg-rate CAC) and maximum sustained rate (max-rate CAC) of the connections are considered as admission criteria in CAC, along with minimum reserved rate (min-rate CAC). The performance of the WiMAX network is evaluated and compared for min-rate, avg-rate and max-rate CAC by considering the performance metrics such as number of connections admitted, throughput and delay using QualNet simulation tool
Multi Radio Resource Management over WiMAX-WiFi Heterogeneous Networks: Performance Investigation
Mobile communication systems beyond the third generation will see the interconnection of heterogeneous radio access networks
(WiMax, wireless local area networks, etc.) in order to always provide the best quality of service (QoS) to users with
multimode terminals. This scenario poses a number of critical issues, which have to be faced in order to get the best from the
integrated access network. In this paper, we investigate the issue of parallel transmission over multiple radio access technologies (RATs), focusing the attention on the QoS perceived by \ufb01nal users. Both the alternative and the parallel use of two RATs is considered. In
particular, a scenario with a point of access providing both WiMAX and WiFi coverage will be investigated, and the performance level experienced by \u201cdual-mode users\u201d is assessed
Subcarrier and Power Allocation in WiMAX
Worldwide Interoperability for Microwave Access (WiMAX) is one of the latest technologies for providing Broadband Wireless Access (BWA) in a metropolitan area. The use of orthogonal frequency division multiplexing (OFDM) transmissions has been proposed in WiMAX to mitigate the complications which are associated with frequency selective channels. In addition, the multiple access is achieved by using orthogonal frequency division multiple access (OFDMA) scheme which has several advantages such as flexible resource allocation, relatively simple transceivers, and high spectrum efficient. In OFDMA the controllable resources are the subcarriers and the allocated power per subband. Moreover, adaptive subcarrier and power allocation techniques have been selected to exploit the natural multiuser diversity. This leads to an improvement of the performance by assigning the proper subcarriers to the user according to their channel quality and the power is allocated based on water-filling algorithm. One simple method is to allocate subcarriers and powers equally likely between all users. It is well known that this method reduces the spectral efficiency of the system, hence, it is not preferred unless in some applications.
In order to handle the spectral efficiency problem, in this thesis we discuss three novel resources allocation algorithms for the downlink of a multiuser OFDM system and analyze the algorithm performances based on capacity and fairness measurement. Our intensive simulations validate the algorithm performances.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format
Coexistence of WiFi and WiMAX Systems Based on PS-Request Protocolsâ€
We introduce both the coexistence zone within the WiMAX frame structure and a PS-Request protocol for the coexistence of WiFi and WiMAX systems sharing a frequency band. Because we know that the PS-Request protocol has drawbacks, we propose a revised PS-Request protocol to improve the performance. Two PS-Request protocols are based on the time division operation (TDO) of WiFi system and WiMAX system to avoid the mutual interference, and use the vestigial power management (PwrMgt) bit within the Frame Control field of the frames transmitted by a WiFi AP. The performance of the revised PS-Request protocol is evaluated by computer simulation, and compared to those of the cases without a coexistence protocol and to the original PS-Request protocol
Channel Aware Uplink Scheduler for a Mobile Subscriber Station of IEEE 802.16e
The scheduling part of the IEEE 802.16 (WiMAX) standards
is kept as an open issue to provide differentiation among
equipment manufacturers and operators. The uplink
scheduling is very significant and more complex compared
to downlink scheduling. Uplink scheduling is divided into
two parts; one is scheduling the resources among many users
from a base station (BS) and the other is sharing the
resources among its services in a single user. BS uplink
scheduling has been given more attention compared to
subscriber station (SS) uplink scheduling. SS scheduler
plays a significant role in providing the quality of service
(QoS) among its services. The channel status awareness is
vital in designing the SS scheduler as the channel conditions vary for a mobile user. This work proposes a scheduling algorithm for SS, which utilizes the channel information and queue length variation for the reallocation of received aggregated bandwidth grant to optimize the QoS parameters. The performance of the proposed algorithm is studied by conducting simulations using QualNet 5.0.2 simulation tool. Simulation results demonstrate the effectiveness of the proposed algorithm to improve the QoS
Desempenho de redes WiMAX com mobilidade
Mestrado em Engenharia Electrónica e TelecomunicaçõesCom a crescente evolução das tecnologias sem fios e a grande necessidade
de estarmos sempre on(line) em qualquer lugar veio culminar com o
desenvolvimento de uma nova norma a IEEE802.21, pelo grupo IEEE. Esta
norma visa optimizar os handovers entre as diferentes tecnologias através de
mecanismos e de eventos normalizados, com o objectivo de tornar as
diferentes tecnologias transparentes para as camadas superiores.
Esta dissertação apresenta mecanismos de mobilidade independentes entre
algumas tecnologias sem fios, em especial a tecnologia WiMAX com suporte
para mobilidade e a tecnologia WiFi. É descrita a forma como se processam os
handovers de redes heterogéneas com base na norma IEEE802.16 e
IEEE802.21 e são propostas algumas modificações.
Posteriormente Ă© analisado o simulador de redes, o qual foi utilizado para
avaliar o desempenho dos handovers em redes heterogéneas através dos
novos mecanismos definidos e propostos, e são efectuadas alterações para
suportar a sinalização e funcionalidades especificadas.
Nesta Tese são simulados vários cenários com handovers de intra-tecnologia
e de inter-tecnologia a fim de se obterem parâmetros de desempenho. Os
resultados obtidos com as alterações produzidas no simulador mostram que
esta nova norma e o mecanismo proposto de integração com as tecnologias
802.11 e 802.16, trazem melhorias significativas nos tempos de handover,
assim como no suporte de QoS.
ABSTRACT: With the growing trend of wireless technologies and the great need of being
always on (line) and anywhere culminate with the development of a new
standard the IEEE802.21, by the IEEE group. This standard is designed to
streamline the handovers between different technologies through normalized
mechanisms and events, with the purpose of making the different technologies
seamless to the upper-layers
This thesis presents mobility mechanisms independent of the wireless
technologies at this stage, particularly WiMAX technology with support for
mobility and the WiFi technology. It is described how are processed
heterogeneous handovers based on IEEE802.16 standard and the IEEE802.21
and are purposed some changes on it.
It is then analyzed the network simulator, which was used to assess the
performance of the handovers in heterogeneous networks through the new
mechanisms established and purposed, and changes are made to support the
signalling and features specified.
On this Thesis are simulated several scenarios with handovers of intratechnology
and inter-technology in order to obtain performance parameters.
The obtained results with the changes produced in the simulator show that this
new standard and the purposed mechanism of integration with the technologies
802.11 and 802.16, bring significant improvements on the time of handovers as
well as on the support of QoS
Comparison among Cognitive Radio Architectures for Spectrum Sensing
Recently, the growing success of new wireless applications and services has led to overcrowded licensed bands, inducing the governmental regulatory agencies to consider more flexible strategies to improve the utilization of the radio spectrum. To this end, cognitive radio represents a promising technology since it allows to exploit the unused radio resources. In this context, the spectrum sensing task is one of the most challenging issues faced by a cognitive radio. It consists of an analysis of the radio environment to detect unused resources which can be exploited by cognitive radios. In this paper, three different cognitive radio architectures, namely, stand-alone single antenna, cooperative and multiple antennas, are proposed for spectrum sensing purposes. These architectures implement a relatively fast and reliable signal processing algorithm, based on a feature detection technique and support vector machines, for identifying the transmissions in a given environment. Such architectures are compared in terms of detection and classification performances for two transmission standards, IEEE 802.11a and IEEE 802.16e. A set of numerical simulations have been carried out in a challenging scenario, and the advantages and disadvantages of the proposed architectures are discussed
- …