IEEE 802.11e standard is proposed to support Quality of Service (QoS) in wireless local area networks (WLANs). The distributed access method of 802.11e, Enhanced Distributed Channel Access (EDCA), prioritizes traffic generated by delay-sensitive applications by increasing probability to access medium for this type of traffic. EDCA resets the Contention Window (CW) of mobile stations to a minimum value after each successful transmission. This static behavior is not adapted to dynamic conditions of wireless network as it degrades network performance when channel access requests increases. Several mechanisms focusing on network adaptation have been proposed to improve the performance of IEEE 802.11e standard. The main limitation for these approaches is slow adaptation to the network state when the channel experiences bursty traffic.In this paper, we propose a new dynamic approach for contention window adjustement for each Access Category (AC) according to the traffic and network conditions. We compare our proposal with the IEEE 802.11e EDCA standard as well as some other mechanisms in the literature.Simulation results show that our proposed approach outperforms EDCA of 802.11e as well as some other enhancement to the standard present in the literature.

IEEE 802. 11e is standardized to enhance real-time multimedia applications’ Quality of Service. This standard introduces four access categories for different types of applications. Each access category has four adjustable parameters: Arbitrary Inter-Frame Space Number, minimum Size of Contention Window, maximum size of Contention Window, and a Transmission Opportunity limit. A Transmission Opportunity limit is the time interval, in which a wireless station can transmit a number of frames consecutively, without releasing the channel and any further contention with other wireless stations. Transmission Opportunity improves network throughput as well as service differentiation. Proper Transmission Opportunity adjustment can lead to better bandwidth utilization and Quality of Service provisioning. This paper studies the dynamic adjustment of Transmission Opportunity in IEEE 802. 11e using a game-theory based approach called Game Theory Based Dynamic Transmission Opportunity. Based on the proposed method, each wireless node chooses its appropriate Transmission Opportunity according to its queue length and media access delay. Simulation results indicate that the proposed approach improves channel utilization, while preserving efficiency in WLANs and minimizing selfishness behaviors of stations in a distributed environment.

The type of the applications for which Internet is being used has changed over the years. Multimedia applications, Real-time applications and Game playing require Quality of service. IEEE has proposed IEEE 802.11e, a quality of service extension to the wireless LAN standard IEEE 802.11. In this paper service differentiation ability of 802.11e is evaluated. Identical traffic is considered for all Access categories to quantitatively differentiate different Access categories. The results indicate, 802.11e achieves service differentiation with some limitations. NS-2.26 is used for simulation.

To date, many vehicular ad hoc network unicast routing protocols have been proposed to support efficient packet transmission between vehicles in urban environments. However, when there is insufficient vehicle density during non-rush hour times, the vehicular ad hoc network is often intermittently connected. These unicast routing protocols, therefore, perform poorly when forwarding packets over this vehicular disruption tolerant network. This paper adopts the controlled replication approach, in a proposed IG-Ferry routing protocol, to spray a limited number of packet copies, denoted by packet token values, to relay vehicles in a vehicular disruption tolerant network. We then identify three kinds of relay vehicle, i.e. direct buses, non-direct buses and private cars according to their travel itineraries. Based on the proposed delay evaluation function for the three types of intermediate vehicle, the IG-Ferry packet spraying mechanism, instead of that of traditional binary spraying, can efficiently spray appropriate packet tokens to vehicles. Finally, intensive NS2 simulations are conducted using the realistic Shanghai city vehicle traffic trace, IEEE 802.11p protocol, with EDCA and the Nakagami radio propagation model, to show that IG-Ferry outperforms three well-known VDTN routing protocols, in terms of average packet delivery ratios, end-to-end transmission delays and packet replication overheads, with respect to various combinations of five communication parameters.