Research Of Bandwidth Scheduling Strategy In WiMax MAC Protocol

How to provide QoS guarantees for various traffic with different QoS requirements in fixed BWA system is a very important problem. With bandwidth scheduling in MAC layer being the key parts to guarantee QoS, it is very important to use an high efficiency MAC bandwidth scheduling algorithm. Although IEEE 802.16 MAC protocols have been proposed to support QoS guarantees for various kinds of applications, they do not suggest how to schedule traffic to fulfill QoS requirements. So the QoS performance of different vendors' equipment will be disparate owing to different QoS mechanism.Technology standard and protocol stack of 802.16 is analyzed first in this paper, and then the MAC protocol is deeply studied, following that five service classes of QoS are also introduced in detail. After analyzing several traditional scheduling types, a bandwidth scheduling algorithm between different type of services is analyzed in detail. In order to meet the delay requirements of rtPS services, delay and throughput of nrtPS are sacrificed in this algorithm. Inspired by this algorithm, a scheme is proposed in this paper:the high-priority business requirements of delay performance can be improved at the expense of the QoS performance of other service whose priority is low, which can be used in some occasions that have high requirements of a certain type of service. To improve the delay performance of the ertPS service, delay and throughput of nrtPS and BE service will be sacrificed. Threshold is set to ensure the minimum QoS requirements of nrtPS and BE being guaranteed.In the scheme of 802.16e, when bandwidth is not sufficient to allow each SS using unicast polling to get bandwidth, BS will form a group of stations that utilize multicast polling and broadcast polling to contend the slots of transmitting bandwidth request. In order to decrease the delay caused by collisions, a scheme was proposed that could utilize contention free period (CFP) to get slots for bandwidth request of ertPS. The original contention period was devided into two sections:one is CFP, transmiting bandwidth requests for ertPS, the other is the same as the original contention period but shortened which was utilized to transmit other bandwidth requests. The aim of decreasing average delay and increasing average throughput is eventually attained. The simulation results in OPNET show that our method achieves lower delay time and better performance of ertPS flows due to the increasing number of BE stations.