An analytical model for performance evaluation of multimedia applications over EDCA in an IEEE 802.11e WLAN

We extend the modeling heuristic of (Harsha et al. 2006. In IEEE IWQoS '06, pp 178-187) to evaluate the performance of an IEEE 802.11e infrastructure network carrying packet telephone calls, streaming video sessions and TCP controlled file downloads, using Enhanced Distributed Channel Access (EDCA). We identify the time boundaries of activities on the channel (called channel slot boundaries) and derive a Markov Renewal Process of the contending nodes on these epochs. This is achieved by the use of attempt probabilities of the contending nodes as those obtained from the saturation fixed point analysis of (Ramaiyan et al. 2005. In Proceedings ACM Sigmetrics, '05. Journal version accepted for publication in IEEE TON). Regenerative analysis on this MRP yields the desired steady state performance measures. We then use the MRP model to develop an effective bandwidth approach for obtaining a bound on the size of the buffer required at the video queue of the AP, such that the streaming video packet loss probability is kept to less than 1%. The results obtained match well with simulations using the network simulator, ns-2. We find that, with the default IEEE 802.11e EDCA parameters for access categories AC 1, AC 2 and AC 3, the voice call capacity decreases if even one streaming video session and one TCP file download are initiated by some wireless station. Subsequently, reducing the voice calls increases the video downlink stream throughput by 0.38 Mbps and file download capacity by 0.14 Mbps, for every voice call (for the 11 Mbps PHY). We find that a buffer size of 75KB is sufficient to ensure that the video packet loss probability at the QAP is within 1%

A prioritized MAC protocol for multihop, event-driven wireless sensor network

Master'sMASTER OF ENGINEERIN

Co-projecto em FPGA da MAC IEEE 802.11p para comunicações veiculares

Mestrado em Engenharia Electrónica e TelecomunicaçõesThe advancements and dissemination of telecommunication technologies has caused them to be employed more and more in our day-to-day life. Recently, these technologies have been applied to vehicles, as a way of not only improving driving safety but also the drivers' and passengers' comfort. If vehicular communications are to become a reality, communication standards must be created in order to allow the development of compatible communication platforms, while also serving as a basys for application development. The standards IEEE WAVE, alongside the IEEE 802.11p amendment, were proposed in order to meet these demands and address some of the speci c issues with vehicular networks, such as short connectivity times and the highly dynamic nature of the propagation environment. This thesis ts within the HEADWAY project, the goal of which is the creation of a device that will perform communication between vehicles. In order to incorporate every layer of the WAVE (Wireless Access in Vehicular Environments) protocol stack, a development platform was conceived that will enable the creation of a standardized communications system for vehicles. The development platform created features an antenna, RF modules, DAC and ADC circuits, an FPGA, a general purpose microprocessor and a GPS module. This work is focused in the development and implementation in FPGA of a MAC layer in accordance with the WAVE standards. The MAC layer's di erent functionalities were divided according to their complexity and execution time, causing our MAC's division in Upper MAC (UMAC) and Lower MAC (LMAC). The UMAC will be implemented in software (C) running in an FPGA embedded microprocessor and will contain the MAC's functions that are more complex, algorithmically speaking, but are not required to be excuted in a very short time interval, such as frame processing and decoding. The LMAC will be implemented by VHDL modeled hardware logic and will perform time critical functions, such as the timestamping of received frames, and complex calculations that bene t from the paralelism o ered by hardware logic, such as CRC computation and error checking. This MAC layer was implemented in an FPGA and its mechanisms were validated

Cooperative communication in wireless local area networks

The concept of cooperative communication has been proposed to improve link capacity, transmission reliability and network coverage in multiuser wireless communication networks. Different from conventional point-to-point and point-to-multipoint communications, cooperative communication allows multiple users or stations in a wireless network to coordinate their packet transmissions and share each other’s resources, thus achieving high performance gain and better service coverage. According to the IEEE 802.11 standards, Wireless Local Area Networks (WLANs) can support multiple transmission data rates, depending on the instantaneous channel condition between a source station and an Access Point (AP). In such a multi-rate WLAN, those low data-rate stations will occupy the shared communication channel for a longer period for transmitting a fixed-size packet to the AP, thus reducing the channel efficiency and overall system performance. This thesis addresses this challenging problem in multi-rate WLANs by proposing two cooperative Medium Access Control (MAC) protocols, namely Busy Tone based Cooperative MAC (BTAC) protocol and Cooperative Access with Relay’s Data (CARD) protocol. Under BTAC, a low data-rate sending station tries to identify and use a close-by intermediate station as its relay to forward its data packets at higher data-rate to the AP through a two-hop path. In this way, BTAC can achieve cooperative diversity gain in multi-rate WLANs. Furthermore, the proposed CARD protocol enables a relay station to transmit its own data packets to the AP immediately after forwarding its neighbour’s packets, thus minimising the handshake procedure and overheads for sensing and reserving the common channel. In doing so, CARD can achieve both cooperative diversity gain and cooperative multiplexing gain. Both BTAC and CARD protocols are backward compatible with the existing IEEE 802.11 standards. New cross-layer mathematical models have been developed in this thesis to study the performance of BTAC and CARD under different channel conditions and for saturated and unsaturated traffic loads. Detailed simulation platforms were developed and are discussed in this thesis. Extensive simulation results validate the mathematical models developed and show that BTAC and CARD protocols can significantly improve system throughput, service delay, and energy efficiency for WLANs operating under realistic communication scenarios