Abstract-The Hybrid Coordination Function (HCF) was proposed in IEEE 802.11e, including the competition-based Enhanced Distributed Channel Access (EDCA) and polling-based HCF Controlled Channel Access (HCCA). This paper mainly carries on the research in the HCCA mechanism. In the HCCA mechanism, the Sample Scheduler offers a way to determine the time duration of the Transmission Opportunity (TXOP). The determination of TXOP is calculated by the equation according to two parameters of transmission, including the Mean Data Rate and Packet Size. Next, Sample Scheduler distributes the result of the TXOP to the QSTA. However, QSTAs are not able to completely utilize the allocated TXOP, which causes the waste of remaining TXOPs. The remaining TXOPs of each QSTA are wasted. Therefore, this paper focuses on allocating the remaining TXOP to QSTAs that can transmits more data packets and reduces the packet dropped rate. The simulation results show that the proposed scheme increases the system throughput and decreases the packet loss rate by utilizing the remaining TXOP.Index Terms-IEEE 802.11e, QoS, HCCA, TXOP.
I. INTRODUCTIONWith the development of information technology, the technologies of wireless network gradually mature. It can be seen everywhere in the products correlated with wireless network, at home network or public places. However, according to the development of multimedia in recent years, the quality of traditional IEEE 802.11 [1] mechanism cannot support the QoS service. In order to enable the Wireless Local Area Network (WLAN) to offer steady service quality as Ethernet, the standard of IEEE 802.11e was qualified in 2005 [2]. In IEEE 802.11e, the HCF was proposed to support QoS service. There are two types of channel access in the HCF, including the EDCA and HCCA. In addition, the mechanism of TXOP in HCF transmission protocol has been defined to enable the QSTA to transmit a lot of data frames within the period of TXOP. The TXOP solves the problem that only one data frame can be transmitted at one time in the traditional IEEE 802.11 standard. In the IEEE 802.11e standard, the polling will be carried out after performing the Sample Schedule. The Sample Schedule initiates the Controlled Access Phase (CAP) in one regular cycle by its length. (QSTA) can transmit a lot of data frames within this period of TXOP time. The remaining TXOP will become a waste of system resource [3]- [9]. Accordingly, G. Cecchetti proposed the W-CBS [3] to arrange the Maximum Service Interval (MSI) to each QSTA based on the weighted TXOP. However, if the calculated TXOP value is relatively small, the QSTA cannot transmit packet. If the calculated TXOP value is relatively high, there will be a lot of remaining TXOP. Therefore, this paper basically improves the computing technology of the TXOP and enables the QSTA to increase throughput. The structure of this paper is as follows. In section two, we introduce the calculation of IEEE 802.11e HCCA Sample Scheduler and the related works. In section three, we propose an Extra-TXOP (X-TXOP)...