Modified HCCA Mechanism for Improving QoS Support in IEEE 802.11e Networks

• Main Authors: Yuan Wei Lee, 李元瑋
• Other Authors: Yeong Sheng Chen
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/81303669622487444884

碩士 === 國立臺北教育大學 === 資訊科學系碩士班 === 95 === Recently, QoS has become an active research topic in WLAN technologies. IEEE 802.11e Medium Access Control (MAC) standard proposes Hybrid Coordination Function (HCF), which is composed of HCCA (HCF Controlled Channel Access) and EDCA (Enhanced Distributed Channel Access) mechanism for QoS support. HCCA is a contention-free mechanism, and EDCA is a contention-based method. The former usually applies to the network that is managed by a coordinator. Given that most of the wireless environments belong to infrastructure networks with a coordinator, our study is focused on the discussion of HCF mechanism. In HCF mechanism, an AP can use the information of the association or reassociation frames transmitted by mobile stations to build a polling list. However, a station may not always have pending data to transmit, and therefore polling all the stations may waste time and will deteriorate the transmission performance. In this thesis, we propose a modified HCCA mechanism which uses the beacon frame broadcasted by the AP to notify the STA that has pending data to transmit so as to improve the transmission performance. The simulation results show that the performance improvement of our proposed mechanism is significant for QoS support.