Enhanced contention-based bandwidth request mechanism for ertPS in IEEE 802.16 network

Abstract

IEEE 802.16 Network is promising metropolitan wireless network technology for providing a variety of applications. The MAC of IEEE 802.16 Network supports five QoS (Quality of Service) classes to provide various types of services. In the IEEE 802.16 standard, each QoS class is allowed to adopt one or more bandwidth request mechanism and how to utilize them depending on the network environment is vendor dependent. Especially among these, the contention-based bandwidth request, which several SSs contend in the contention period, is allowed to ertPS, nrtPS, and BE services. However, if these services are contended equally, the ertPS servicing VoIP service, which is sensitive to the delay or jitter, causes the more bandwidth grant delay when terminating the silent period. Even with the multicast polling, it can not satisfy the bandwidth grant delay compared with the unicast polling. Therefore, in this thesis, we propose enhanced contention-based bandwidth request (ECBR) mechanism to differentiate the contention manner of each QoS class for enhancing the bandwidth grant delay performance. Particularly, the mechanism is focused on the performance enhancement of the ertPS. The proposed mechanism allows the ertPS to adopt multicast polling basically and both multicast and broadcast polling when collision occurs. In addition, we argued about adjustment of internal backoff value of SSs when the multicast and broadcast polling exist in a frame. Simulation results show that the ertPS resolves the contention faster than the standard mechanism due to the highest successful bandwidth request probability and maintains acceptable level of the bandwidth grant delay with smaller variance than the standard mechanism. Moreover, the SS’s internal backoff value adjustment in the ECBR mechanism show better performance when the collided bandwidth request messages uses the adjusted internal backoff value during the broadcast polling period imme-diately.