Yu-Ming Mao

A simple adaptive optimization scheme forIEEE 802.11 with differentiated channel access

This letter proposes an adaptive scheme to optimize the system throughput of IEEE 802.11 with differentiated channel access ability. Due to the difficulty of estimating the number of active stations and that approaches based on the estimation may not converge reported in previous research, the proposed scheme is developed to maximize the system throughput without the requirement of station number information while providing service differentiation among different traffic classes. Specially, the scheme is simple to implement and it only requires to measure the time the channel is in idle and collision states separately. Performance evaluation results show that the scheme is effective in achieving near to the theoretical maximum system throughput.

An Adaptive Transmission Control MAC Scheme for DCF to Improve Throughput and Short-Term Fairness

In this paper, we propose an adaptive optimization scheme for IEEE 802.11 DCF to enhance the network performance. The scheme is based on the channel sensing result and thus we call it CSTC (channel sensing transmission control). The key idea to approach optimal performance dynamically in our scheme is that the transmission attempt from the DCF is filtered by an adjustable probability P_T, which is dynamically regulated according to the current channel competing level among the network stations. The strongpoint of CSTC is that there is no need to perform complex on-line estimation of the number of active stations in the network when seeking the optimal operation point of the network. Detailed simulation results indicate that by adopting the CSTC scheme, near-optimal throughput is adaptively achieved and short-term fairness is also largely increased.

An Adaptive MAC Scheme to Achieve Throughput Optimization and Airtime Fairness for IEEE 802.11 Multirate Networks

In an IEEE 802.11 multirate network, the aggregate system throughput is unfavorably dominated by stations with the lowest data rate. To improve the performance, it is required to provide airtime fairness for stations regardless of their data rates. Unfortunately, the IEEE 802.11 MAC protocol DCF (Distributed Coordination Function) fails to satisfy this requirement. In this paper, we propose an adaptive MAC scheme, named Time Fairness Transmission Control (TFTC), to maximize the system throughput while maintaining airtime fairness among the competing stations. Specifically, making use of the information provided to each station by the carrier sensing mechanism, TFTC dynamically adjusts the transmission probabilities for stations transmitting at each data rate. As opposed to the previous works, our proposed scheme has strong ability to lead the network to work under near optimal state without the requirement of estimating the number of active stations in the network. Performance evaluation results show that the scheme is effective in achieving near to the theoretical maximum system throughput and providing time fair channel allocation among stations with different data rates.

Analysis of voice capacity in IEEE 802.11 Wireless LANs with/without data traffic

IEEE 802.11 based wireless local area networks (WLANs) are becoming more and more popular in home, office, enterprise and public areas primarily due to their low cost, simplicity of installation and mobility for users. On the other hand, voice over Internet protocol (VoIP) is poised to become an important Internet application. The combination of these two technologies, i.e. VoIP over WLAN, attracts more and more attentions. In this paper, models are presented to investigate the voice capacity in IEEE 802.11 WLANs with/without simultaneous data traffic. Although the channel data rate is so high, no more than a few voice sessions can be supported due to various protocol overheads, especially when there are data traffic flows in the network.