Research
An Enhanced QoS Provisioning Approach for Video Streams using Cross Layer Design in IEEE 802.16
Wimax networks are increasingly deployed for commercial use because of its high bandwidth. This has necessitated application level changes in QoS provisioning techniques. In this paper, we propose an efficient method at the application layer of the wimax architecture. The video stream is partitioned at the application layer into I, P and B frames. Frames corrupted at receiver are detected using negative acknowledgements received from the physical layer. Probability of Byte Loss (BL) is calculated at physical layer which is used to calculate the redundant data. Redundant data is communicated from PHY layer to application layer via link layer using cross-layer signalling mechanism. Redundant data is piggybacked into the subsequent frame and sent only if BL is less than 0.2. This technique has improved the throughput of the network considerably which is evident from the performance analysis.
An Enhanced scheduling algorithm for QoS optimization in 802.11e based Networks
Quality of Service (QoS) is the ability to guarantee a certain level of performance to a data flow ie., guaranteeing required bit rate, delay, etc. IEEE 802.11 a/b/g networks do not provide QoS differentiation among multimedia traffic. QoS provisioning is one of the essential features in IEEE 802.11e. It uses Enhanced Distributed Channel Access (EDCA) which is a contention-based channel access mode to provide QoS differentiation. EDCA works with four Access Categories (AC). Differentiation of Access Categories are achieved by differentiating the Arbitration Inter-Frame Space (AIFS), the initial contention window size (CWmin), the maximum contention window size (CWmax) and the transmission opportunity (TXOP). However AIFS, CWmin, CWmax are considered to be fixed for a given AC, while TXOP may be varied. A TXOP is a time period when a station has the right to initiate transmissions onto the wireless medium. By varying the TXOP value among the ACs the QoS optimization- throughput stability and minimum delay is achieved. EDCA has many advantages such as it fully utilizes the channel bandwidth, and does not require centralized admission control and scheduling algorithms over the contention-free access mode.
