A Practical Cross-layer QoS Mechanism for Voice over IP in IEEE 802.11e WLANs
In this paper, we study the behavior of voice over IP (VoIP) traffic over IEEE 802.11 wireless networks. Specifically, we propose a QoS provisioning mechanism for VoIP traffic, and suggest a practical solution to configuring the 802.lie enhanced distributed control access (EDCA) parameter sets for different types of traffic. With our mechanism, the EDCA parameter sets can be easily configured via software interface in off-the-shelf WiFi phone products and it is not required to modify the operations of access points or 802.11 MAC layer protocols. The performance of our mechanism is evaluated via ns-2 simulations and via laboratory experiments over Quanta's 02 dual-mode handsets. The results show our mechanism can provide effective and efficient QoS provisioning for VoIP traffic over IEEE 802.11 WLANs.
This paper addresses the problem of channel and propagation delay estimation in asynchronous DS/CDMA systems. We consider the uplink connection in DS/CDMA with long spreading codes. The MIMO stochastic gradient algorithm proposed in [6] is estimating a linear combination of the channel impulse responses and the propagation delays. This estimate suffices for the equalization purposes. The propagation delays are estimated with a simple matching scheme.