Ali Hamidian

An enhancement to the IEEE 802.11e EDCA providing QoS guarantees

One of the challenges that must be overcome to realize the practical benefits of ad hoc networks is quality of service (QoS). However, the IEEE 802.11 standard, which undeniably is the most widespread wireless technology of choice for WLANs and ad hoc networks, does not address this issue. In order to support applications with QoS requirements, the upcoming IEEE 802.11e standard enhances the original IEEE 802.11 MAC protocol by introducing a new coordination function which has both contention-based and contention-free medium access methods. In this paper, we consider the contention-based medium access method, the EDCA, and propose an extension to it such that it can be used to provide QoS guarantees in WLANs operating in ad hoc mode. Our solution is fully distributed, uses admission control to regulate the usage of resources and gives stations with high-priority traffic streams an opportunity to reserve time for collision-free access to the medium.

Performance of internet access solutions in mobile ad hoc networks

Although an autonomous mobile ad hoc network (MANET) is useful in many scenarios, a MANET connected to the Internet is more desirable. This interconnection is achieved by using gateways, which act as bridges between a MANET and the Internet. Before a mobile node can communicate with an Internet host it needs to find a route to a gateway. Thus, a gateway discovery mechanism is required. In this paper the MANET routing protocol Ad hoc On-Demand Distance Vector (AODV) is extended to achieve the interconnection between a MANET and the Internet. Moreover, the paper investigates and compares three approaches for gateway discovery. The question of whether the configuration phase with the gateway should be initiated by the gateway, by the mobile node or by mixing these two approaches is being discussed. We have implemented and simulated these three methods and we discuss the advantages and disadvantages of the three alternatives.

Providing QoS in ad hoc networks with distributed resource reservation

As the use of WLANs based on IEEE 802.11 increases, the need for QoS becomes more obvious. The new IEEE 802.11e standard aims at providing QoS, but its contention-based medium access mechanism, EDCA, provides only service differentiation, i.e. soft QoS. In order to provide hard QoS, earlier we have proposed an extension called EDCA with resource reservation (EDCA/RR), which enhances EDCA by offering also hard QoS through resource reservation. In this paper, we extend EDCA/RR to cope with the hidden terminal problem, outline a solution for multi-hop scenarios, and compare the proposed scheme with EDCA.

A distributed MAC scheme to achieve QoS in ad hoc networks

Real-time applications introduce new requirements on wireless networks and impose quality thresholds on parameters like delay, jitter, throughput, and packet loss in order to run smoothly. This paper addresses this issue by presenting a MAC scheme that offers real-time applications the opportunity to reserve transmission time based on their QoS requirements for contention-free medium access. Our scheme, which is called EDCA with Resource Reservation (EDCA/RR), operates in a fully distributed manner, is compatible with IEEE 802.11, and provides both prioritized and parameterized QoS. In this study, we have extended EDCA/RR to handle reservation collisions and, through extensive simulations, we show that our proposal can handle multiple reservations as well as uninformed stations that lie outside the transmission range of both the transmitter and the receiver while providing QoS guarantees. We compare EDCA/RR with EDCA and our results show that, as the traffic in the network increases, EDCA/RR succeeds providing the required service to QoS-demanding applications whereas EDCA fails in this task. In addition, when the medium is lossy we show that, not only does EDCA/RR give better service to real-time traffic, but also to contending non-real-time traffic.

Performance of Internet Access Solutions in Mobile Ad Hoc Networks

Network and Capacity Planning.- Performance of Hierarchical Cellular Networks with Overlapping Cells.- A Hybrid Model of the UMTS Downlink Capacity with WWW Traffic on Dedicated Channels.- Performance of Different Proxy Concepts in UMTS Networks.- Algorithms for WLAN Coverage Planning.- Optimization Models for Designing Aggregation Networks to Support Fast Moving Users.- Medium Access and Admission Control.- Some Game-Theoretic Problems in Wireless Ad-Hoc Networks.- Admission Region of Multimedia Services for EDCA in IEEE 802.11e Access Networks.- Admission Control Policies in Multiservice Cellular Networks: Optimum Configuration and Sensitivity.- Admission Control in the Downlink of WCDMA/UMTS.- QoS in Wireless Networks.- Effects of WLAN QoS Degradation on Streamed MPEG4 Video Quality.- Integrating MPLS and Policy Based Management Technologies in Mobile Environment.- A Reservation Scheme Satisfying Bandwidth QoS Constraints for Ad-Hoc Networks.- Network (Inter)connection and Resource Access.- Performance of Internet Access Solutions in Mobile Ad Hoc Networks.- On the Fractional Movement-Distance Based Scheme for PCS Location Management with Selective Paging.- Enabling Mobile Peer-to-Peer Networking.- A Family of Encounter-Based Broadcast Protocols for Mobile Ad-Hoc Networks.