132 research outputs found
Wireless broadband access: WiMAX and beyond - Investigation of bandwidth request mechanisms under point-to-multipoint mode of WiMAX networks
The WiMAX standard specifies a metropolitan area broadband wireless access air interface. In order to support QoS for multimedia applications, various bandwidth request and scheduling mechanisms are suggested in WiMAX, in which a subscriber station can send request messages to a base station, and the base station can grant or reject the request according to the available radio resources. This article first compares two fundamental bandwidth request mechanisms specified in the standard, random access vs. polling under the point-to-multipoint mode, a mandatory transmission mode. Our results demonstrate that random access outperforms polling when the request rate is low. However, its performance degrades significantly when the channel is congested. Adaptive switching between random access and polling according to load can improve system performance. We also investigate the impact of channel noise on the random access request mechanism
Performance Analysis of ARQ Mechanism in WiMAX Networks
WiMAX (Worldwide Interoperability for MicrowaveAccess) is the IEEE 802.16 standards-based wireless technology, provides Broadband Wireless Access (BWA) for Metropolitan Area Networks (MAN). The Automatic Repeat reQuest (ARQ) mechanism in WiMAX uses a feedback channel for the confirmation of error-free packet delivery or for packet
retransmission request. This method can increase
network throughput when radio channel condition is
worse. In this paper attempt has been made to study
the effect of implementation of ARQ on the performance of WiMAX network through simulation. Simulation study has been carried out for WiMAX network with and without enabling ARQ. The performance is been compared by considering the
performance metrics like throughput, delay and jitter
New contention resolution schemes for WiMAX
AbstractâThe use of Broadband Wireless Access (BWA) technology is increasing due to the use of Internet and multimedia applications with strict requirements of endâtoâend delay and jitter, through wireless devices. The IEEE 802.16 standard, which defines the physical (PHY) and the medium access control (MAC) layers, is one of the BWA standards. Its MAC layer is centralized basis, where the Base Station (BS) is responsible for assigning the needed bandwidth for each Subscriber Station (SS), which requests bandwidth competing between all of them. The standard defines a contention resolution process to resolve the potential occurrence of collisions during the requesting process. In this paper, we propose to modify the contention resolution process to improve the network performance, including endâtoâend delay and throughput
A Fair and Efficient Packet Scheduling Scheme for IEEE 802.16 Broadband Wireless Access Systems
This paper proposes a fair and efficient QoS scheduling scheme for IEEE
802.16 BWA systems that satisfies both throughput and delay guarantee to
various real and non-real time applications. The proposed QoS scheduling scheme
is compared with an existing QoS scheduling scheme proposed in literature in
recent past. Simulation results show that the proposed scheduling scheme can
provide a tight QoS guarantee in terms of delay, delay violation rate and
throughput for all types of traffic as defined in the WiMAX standard, thereby
maintaining the fairness and helps to eliminate starvation of lower priority
class services. Bandwidth utilization of the system and fairness index of the
resources are also encountered to validate the QoS provided by our proposed
scheduling scheme
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
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=OpinnÀytetyö kokotekstinÀ PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=LÀrdomsprov tillgÀngligt som fulltext i PDF-format
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