Abstract
In this paper, we analyze the timing behavior of the EDCA communication mechanism defined in the IEEE 802.11e standard, when it is used to support real-time (RT) traffic. In the context of this paper RT traffic means small sized packets generated in periodic intervals, which must be delivered before the end of the message stream period. Otherwise. the message is considered to be delayed and a deadline loss occurs. The tat-get of this paper is to understand the limitations of the highest priority level of the EDCA mechanism (voice category) when supporting RT communication. We have assessed this mechanism considering an open communication environment, where there are RT and non-RT stations operating in the same frequency band. Furthermore, a realistic error-prone model channel was used to measure the impact of interferences against an error-free channel. we show that in the most cases evaluated, both the number of packet losses and the average packet delays forecast an unacceptable number of deadline losses for the RT Message streams, even for intermediate load cases. As a conclusion of this paper, we present some potential future directions toward improved QoS in wireless networks.

Abstract
This paper proposes a real-time communication scheme for wireless local area network (WLAN) infrastructure. This strategy was called Group Sequential Communication (GSC). The GSC has the main goal to reduce the network overhead due to the Polling, Ack and QoS Null Frames of Hybrid Coordination Function Controlled Channel Access (HCCA) in IEEE 802.11e, because it uses a Virtual Token Passing procedure to priority the real-time communication over WLAN. In order to improve the confiability of the new scheme is presented a fault-tolerant mechanism based on Block-Ack strategy to avoid missing real-time messages. The GSC was implemented in NS2 and simulation results have proved the superior performance of GSC in comparison with HCCA for real-time industrial communications.

Abstract
Currently, there is a trend towards the implementation of industrial communication systems using wireless networks. However, keeping up with the timing constraints of real-time traffic in wireless environments is a hard task. The main reason is that real-time devices must share the same communication medium with timing unconstrained devices. The VTP-CSMA architecture has been proposed to deal with this problem. It considers an unified wireless system in one frequency band, where the communication bandwidth is shared by real-time and non-real-time communicating devices. The proposed architecture is based on a virtual token passing (VTP) procedure that circulates a virtual token among real-time devices. This virtual token is complemented by an underlying traffic separation mechanism that prioritizes the real-time traffic over the non-real-time traffic. This is one of the most innovative aspects of the proposed architecture, as most part of real-time communication approaches are not able to handle timing unconstrained traffic sharing the same communication medium. A ring management procedure for the VTP-CSMA architecture is also proposed, allowing real-time stations to adequately join/leave the virtual ring.

Abstract
The main objective of this thesis' is to address the following question: "How to guarantee the timing requirements of real-time (RT) control data, when the communication medium is shared with timing unconstrained traffic?". That is, to propose mechanisms that enable the support of RT communication services in CSMA-based communication infrastructures, specifically when such infrastructures are also being used to support multipurpose data transfer applications. The target is to address the timing requirements of typical industrial applications. Thus, a new RT-communication approach (VTP-CSMA) has been proposed, which is based on the use of traffic separation mechanisms. Such mechanisms are able to prioritize RT-traffic over multipurpose traffic, without directly controlling the latter. That is, instead of controlling all the traffic generated by all the stations, this approach controls only the traffic generated by the RT stations. The VTP-CSMA approach forces the collision resolution in favor of the RT stations, enabling the fulfillment of the RT communication requirements.

Abstract
In this paper we propose the use of a coordination layer to handle real-time communication in infrastructured WiFi networks. This layer combines a TDMA scheme with a traffic separation mechanism (FCR MAC), which enables the prioritization of real-time (RT) traffic over uncontrolled (external) traffic sources. The target of this paper is to assess the behavior of this coordination layer when supporting RT communication and to compare these results with those obtained with IEEE 802.11e EDCA. The simulation assessment considers an open communication environment, where a set of RT and non-RT stations share the same coverage area and frequency band. A realistic error-prone channel was used to measure the impact of interferences against an error-free channel. We show that the proposed solution offers a significant improvement when compared with EDCA, in what concerns average deadline losses and delay.

Abstract
Currently there is a trend for the implementation of industrial communication systems on top of wireless communications. However, keeping up with the timing constraints of real-time traffic in open medium environments is a hard task. The main source for complexity is that, if the set of communicating devices is not previously agreed, the timing constraints imposed by such devices cannot be predicted at the system setup time, nor can be effectively controlled at the system run-time. In this paper, we propose the VTP-CSMA architecture to deal with this problem. This architecture allows the coexistence of default IEEE 802.11e devices with real-time devices sharing the same communication medium, enabling the prioritization of real-time traffic. The proposed solution is based on the control of the medium access rights by means of a Virtual Token Passing procedure (VTP), complemented by an underlying traffic separation mechanism that prioritizes realtime traffic over the traffic from default IEEE 802.11 stations. The simulation analysis shows that the VTP-CSMA architecture guarantees values for both the throughput and the average access delay that significantly improves the results obtained for default IEEE 802.11e stations operating under EDCA mode.