Riccardo Zambon

QoS Enhancement with Dynamic TXOP Allocation in IEEE 802.11e

The transmission opportunity (TXOP) mechanism defined in the IEEE 802.11 e Hybrid Coordination Function (HCF) is not optimized to meet the QoS requirements of heterogeneous applications, since it is usually allocated by default according to the different Access Categories (AC). In this paper we propose a new algorithm, named DTXOP, for the dynamic assignment of the TXOP maximum duration at the Access Point (AP) of an IEEE 802.lie WLAN. DTXOP is periodically updated according to the current traffic conditions of each specific AC. Simulation experiments show that DTXOP allows to enhance delay and throughput performance and to maintain fairness between upstream and downstream channel access times.

An admission control algorithm for QoS provisioning in IEEE 802.11e EDCA

The IEEE 802.11e standard introduces QoS features for delivering multimedia applications in a WLAN environment. However, under heavy traffic loads, network saturation is easily achieved and consequently QoS performance are inevitably degraded. In this paper an admission control algorithm for resource sharing in a wireless LAN environment is proposed, with the aim at enhancing QoS support for real-time applications (e.g., VoIP and video) that are particularly sensitive to delay and jitter. The algorithm avoids saturation and protects the admitted traffics from being degraded, through a continuous monitoring of the available resources. A further optimization of the algorithm is finally implemented through the adoption of dynamic bursty transmissions times (i.e., TXOP). Performance evaluation is carried out through computer simulations, showing the benefits gained by the 802.11e EDCA scheme in terms of goodput and delay.

Qos enhancement for multimedia traffics with dynamic txoplimit in ieee 802.11e

The transmission opportunity (TXOP) mechanism defined in the IEEE 802.11e Hybrid Coordination Function (HCF) allows a wireless station to transmit a burst of frames back-to-back without re-entering the channel contention phase. Unfortunately, the adoption of a unique value for its maximum duration (named TXOPlimit) for all stations, included the AP, results in an unfair behavior, that provokes an unbalance between uplink and downlink throughputs and consequent QoS degradation. To solve this problem we propose an algorithm capable of tuning the TXOPlimit value at the AP, in order to dynamically change its channel resources according to the current traffic conditions. Extensive simulations show that the proposed algorithm allows to enhance significantly QoS performance of multimedia traffics and to increase the global WLAN throughput.

Improving QoS Performance in IEEE 802.11e Under Heavy Traffic Loads

IEEE 802.11e standard is a concrete attempt to QoS challenge, but when the volume of traffic flows increases, this approach is not sufficient. Several techniques have been developed to improve WLAN QoS performance, mainly introducing a trade-off between performance and standard compatibility. This work describes the techniques used to enhance EDCA efficiency by suitably regulating standard’s parameters and it introduces an innovative algorithm, named Dynamic TXOP (DTXOP), capable of enhancing fairness between upstream and downstream resource allocation in Wi-Fi networks. Finally, after a brief review of admission control algorithms for QoS support under heavy traffic loads, a suitable admission control scheme is integrated with DTXOP as a possible solution for facing QoS degradation of active sources due to an excessive network load. The benefits obtained by integrating DTXOP and the proposed admission control policy are shown in terms of QoS enhancement and efficiency in resource allocation.

Evaluation of QoS Support for Multimedia Traffics in IEEE 802.11e

The efficient delivery of multimedia over wireless LANs is strongly dependent on the requirements imposed by different traffics contending the channel resources. Mechanisms for supporting QoS are needed, especially when voice and video applications come into play with stringent constraints in terms of delay and throughput. In this paper we evaluate, through simulations, the benefits derived from the adoption of the IEEE 802.11e standard in delivering multimedia over WLANs. The adoption of fine-tuned parameters regulating the EDCA MAC scheme permits to achieve high performance in terms of goodput and delay, allowing multimedia traffics to fully satisfy their QoS requirements. Realistic assumptions have been made in our simulations, by taking into account the shadowing effects, typical of closed environments, and by adopting suitable parameters to simulate 802.11e channels as exactly as possible

A WiMAX simulation module for investigating QoS during horizontal handovers

Abstract WiMAX is one of the most interesting solutions for broadband wireless access, supporting multimedia traffic and applications through an appropriate QoS management for fixed and mobile devices. Simulation tools play a central role to study network performance and to test new functionalities. In this paper we propose a new simulation module, compliant to IEEE 802.16e, which implements the five WiMAX QoS classes and handover procedures as well, so as to support investigations on QoS management during mobility in WiMAX scenarios. The developed tool has been validated and tested through exhaustive simulations, showing its conformance with the defined specifications.

Techniques for Preserving QoS Performance in Contention-Based IEEE 802.11e Networks

The new information and communication technologies should allow users to enjoy current as well as future applications and services in an efficient and effective way, in order to achieve a certain level of user perceived satisfaction. Such applications are mainly based on heterogeneous multimedia flows with different characteristics and requirements. Audio, text, video and voice are the basic components of multimedia flows and they have different needs for efficient delivery.

Performance comparison of JTCP over QoS-aware WiMAX networks

TCP is the main transport-layer communication protocol in traditional wired networks. This is also due to its efficient behavior in presence of congestion events. However, networks with wireless links and mobile hosts provide significant non-congestive losses due to bit error rate, host motion and handover mechanisms. TCP incorrectly interprets these events as a sign of network congestion, throttling its transmission rate and causing degradation of end-to-end performance. In order to enhance TCP performance on wireless networks, several algorithms have been introduced to correctly deduce whether a loss occurs for a real congestion event. This paper carries out a performance evaluation of an innovative algorithm, called Jitter-based TCP (JTCP), over WiMAX networks. Realistic IEEE 802.16e MAC and PHY layers are adopted for performing simulations, showing that JTCP outperforms other TCP versions over WiMAX networks.

An innovative uplink scheduler for enhancing multi-rate fairness in WiMAX

WiMAX is one of the most interesting solutions for broadband wireless access, offering QoS features for multimedia traffics and applications. However, without the definition of a mandatory scheduling algorithm for the assignment of channel resources, WiMAX standard is open to enhancements by QoS research groups and developers. In this paper, BS uplink scheduling algorithms are considered and an innovative solution is proposed in order to improve multi-rate fairness and QoS management. The proposed scheduler, named E-DRR, has been compared with the existing solutions through exhaustive simulations, showing its enhancements in terms of QoS performance and multi-rate fairness in resource allocation.

Ambient assisted living and digital inclusion: overview of projects, services and interfaces

The last decades have been characterized by great advances in the field of information and communication technologies and innovative applications and services have been developed in all sectors. People who are more familiar with Internet technologies can take full advantage of the benefits brought by the new systems to everyday life, but, at the same time, if services are not carefully designed, they contribute to augment the digital gap between “info-skilled” users and people who are not acquainted with the new technologies. This paper provides an overview of interesting projects developed with the aim to favor social inclusion and to tear down barriers posed by digital technology, by supporting people with special needs (e.g., elderly and people with different impairments) in the fruition of e-services through easy forms of interactions. The study is restricted to solutions that envisage the TV device as the main user interface for supporting Ambient Assisted Living. From the survey, a basic set of services and interfaces, here described, appear to be fundamental for improving digital and social inclusion, but the design methodology for developing TV-based interfaces and services must be carefully chosen to reduce social marginalization.