Sara Pizzi

Channel-Aware Scheduling for QoS and Fairness Provisioning in IEEE 802.16/WiMAX Broadband Wireless Access Systems

In the last few years, standardization activities within the IEEE 802.16 Working Group have resulted in the publication of specifications for an air interface of Fixed broadband wireless access systems. WiMAX is the commercial name of products compliant with the approved IEEE 802.16 standard. Although the standard suggests the main principles in designing a QoS architecture to support multimedia broadband services, implementation details are left to manufacturers. This article addresses a channel-aware scheduling algorithm conceived for a point-to-multipoint WiMAX architecture. It aims at enabling downlink traffic delivery with differentiated service treatment, even in nonideal channel conditions. A technique to compensate for channel errors is proposed to preserve QoS and fairness of a WF2Q+ based scheduling algorithm. The performance behavior of the proposed algorithm is confirmed by the outputs of a comprehensive simulation campaign.

DBA-MAC: DYNAMIC BACKBONE-ASSISTED MEDIUM ACCESS CONTROL PROTOCOL FOR EFFICIENT BROADCAST IN VANETS

Active safety systems based on dissemination of alert messages are one of the most important applications of Vehicular ad Hoc Networks (VANETs). These systems typically require to provide efficient and reliable delivery of safety information to all the vehicles travelling over a geographical area. Reducing the delivery delay is also a crucial issue due to the real-time nature of the communication. To meet these requirements, in this paper we design a cross-layered MAC and clustering solution for the fast propagation of broadcast messages in a VANET. A distributed dynamic clustering algorithm is proposed in order to create a dynamic virtual backbone inside the vehicular network. The vehicle-members of the backbone are responsible for implementing an efficient message propagation. The backbone creation and maintenance are proactively performed aiming to balance the stability of backbone connections as well as cost/efficiency trade-off and hops-reduction when forwarding the broadcast messages. A fast multi-hop MAC forwarding scheme is defined to exploit the role of backbone vehicles, under a cross-layered approach. Simulation results show that our cross-layer scheme guarantees high message delivery ratio, reduces the delivery delay and provides efficient channel utilization when compared with other dissemination schemes for VANETs.

Enhancing multi-hop communication over multi-radio multi-channel wireless mesh networks: A cross-layer approach

The multi-channel multi-radio technology represents a straightforward approach to expand the capacity of wireless mesh networks (WMNs) in broadband wireless access scenarios. However, the effective leveraging of this technology in WMNs requires (i) enhanced MAC protocols, to coordinate the access to multiple channels with a limited number of radio interfaces, and (ii) efficient channel allocation schemes, to mitigate the impact of co-channel interference. The design of channel assignment schemes and MAC protocols is strictly interrelated, so that joint design should be considered to optimize the mesh network performance. In this paper, a channel assignment and fast MAC architecture (CAFMA) is proposed, which exploits the benefits provided by the multi-channel multi-radio technology to (i) enhance the performance of multi-hop communications, (ii) maximize the resource utilization, and (iii) support differentiation of traffic classes with different quality of service (QoS) requirements. CAFMA is designed with a cross-layer approach and includes (1) a novel MAC scheme, which provides multi-channel coordination and fast data relaying over multi-hop topologies, and (2) a distributed channel allocation scheme, which works in cooperation with the routing protocol. Simulation results confirm the effectiveness of CAFMA when compared with other single-layer and cross-layer solutions for multi-radio multi-channel WMNs.

Radio-aware subgroups formation for multicast traffic delivery in WiMAX networks

This paper focuses on the design of radio resource management policies for multicast service delivery in WiMAX networks. With the purpose of finding an alternative solution to the conventional multicast scheme that is conservative towards resource utilization, we propose to use a subgroup-based link adaptation technique that dynamically chooses the modulation and coding schemes based on the perceived channel conditions in each subgroup of multicast receivers. The main idea is to split the multicast destinations into different subgroups depending on the perceived channel quality, and to apply subgroup-based adaptive modulation and coding for a more efficient spectrum exploitation. The performance of different solutions for the subgroups formation will be analyzed and their effectiveness evaluated through simulations to show how the network can take advantage from the proposed subgrouping approach.

Joint Channel Assignment and Multi-path Routing for Multi-radio Wireless Mesh Networks

Multi-radio Wireless Mesh Networks (MR-WMNs) are being increasingly deployed to provide affordable Internet access on large residential areas. MR-WMNs allow the supported mesh clients (MCs) to access the Internet gateway by multi-hop packet forwarding over the mesh routers (MRs), which can be equipped with multiple radio interfaces. In such a scenario, the routing protocol should (i) decide the address of the next-hop node and the radio-interface to be used for each transmission and (ii) exploit the presence of multiple paths between the MCs and the Internet gateways. To address these issues, we propose a cross-layer architecture that comprises a novel joint multi-path routing and channel allocation scheme for MR-WMNs. During the route setup, multiple node-disjoint paths are discovered and channel allocation is performed so that nodes on different paths, but within the same interference domain, transmit on different channels. Moreover, we propose a load-balancing scheme, which allows to distribute traffic among the available node- and channel-disjoint paths. The simulation results show that the proposed scheme reduces the end-to-end delay and enhances the system good put significantly over several network topologies and under different traffic workloads.

On the Performance of "Compensation-Based" and "Greedy" Scheduling Policies in IEEE 802.16 Networks

The provision of Quality of Service (QoS) is one of the primary requirements for IEEE 802.16/WiMAX to become a reference technology for multimedia service delivery. This paper reports on the design and analysis of some channel-aware scheduling algorithms for downlink traffic delivery in a fixed point-to-multipoint WiMAX network. In particular, compensation-based and greedy approaches are compared according to their ability to provide QoS and fairness to traffic flows when not working in ideal channel conditions. Simulations highlight that the greedy philosophy fails to provide service differentiation, especially when users perceive heterogeneous channel conditions.

A cross-layer architecture for robust video streaming over multi-radio multi-channel wireless mesh networks

Video streaming over Wireless Mesh Networks (WMNs) can take advantage of the presence of multiple paths between each source and destination pair, as well as of the availability of multiple radio interfaces on the mesh nodes. In this paper, we propose a novel Channel Assignment and Multipath Routing Architecture (CAMRA) for supporting robust video streaming over Multi-Radio Multi-Channel WMNs. During route setup, multiple node disjoint paths are discovered between a source and a destination node. Channel allocation is performed so that the mutual among different paths is greatly mitigated, for the same source-destination pair. In order to enhance the reliability of video transmission, a load balancing scheme is introduced so that video frames are redundantly forwarded on multiple paths, based on the performance on each path and on packet-level loss estimations. Simulation results show that the proposed scheme is able to mitigate the impact of packet loss on streaming quality, while maintaining low overhead cost and low implementation complexity.

A cross-layer architecture for service differentiation in multi-channel multi-radio Wireless Mesh Networks

Due to their self-configuration and auto-configuration properties, Wireless Mesh Networks (WMNs) are expected to support a plethora of applications, including traditional Internet services and novel multimedia applications. Service differentiation is needed to support applications with different Quality of Service (QoS) requirements. In this paper, we propose a novel cross-layer framework that provides efficient communication and service differentiation in multi-radio multichannel WMNs. The proposed solution includes a distributed channel allocation scheme, integrated in the routing protocol, and a multi-channel MAC protocol, inspired to the IEEE 802.11e EDCA (Enhanced Distributed Channel Access). At the MAC layer, we propose “fast-forwarding” mechanisms to reduce the contention delay of delay-sensitive applications in multi-hop topologies. At the network layer, the channel allocation scheme aims at loading channels with an equal number of per-class traffic flows. The simulation results confirm the effectiveness of the proposed scheme in providing differentiated treatment to traffic classes with different QoS requirements.

A Unified Approach for Efficient Delivery of Unicast and Multicast Wireless Video Services

Recently, mobile multimedia services have represented an increasingly large source of revenue for the telecommunication industry. Subscribers are often interested in simultaneously receiving the same data flow and, hence, they fuel the growing demand for multicast multimedia services. Therefore, the design of efficient radio resource management strategies to jointly handle multicast and more traditional unicast traffic and to increase user satisfaction is of primary importance for the successful deployment of future mobile networks. This paper proposes an efficient radio resource management framework to handle unicast and multicast multi-layer video services. The proposed virtual unified group (VUG) approach makes use of a channel-aware subgrouping principle to provide fair throughput to both unicast and multicast users. The idea is to assign unicast subscribers to a virtual group, thus allowing them to compete for network resources on an equal footing with multicast users. Simulations highlight the benefits that VUG provides in a long term evolution network scenario, under different traffic load conditions, in terms of throughput and fairness in the distribution of resources to unicast and multicast users.

A Novel Approach for Unicast and Multicast Traffic Management in Wireless Networks

The rapid demand growth for group-oriented services mandates telco operators to efficiently manage the contemporary presence of the unicast services and the emerging multicast applications. We propose a novel radio resource management approach for providing fair throughput to unicast and multicast users in a broadband wireless network. The idea is to assign unicast subscribers to a virtual group in order to compete on an equal footing with multicast users for network resource distribution. We also revisit the traditional fairness indexes in order to capture the fairness in the degree of user satisfaction for unicast and multicast users. Simulations highlight the effectiveness of the virtual group strategy in terms of achieved fairness in several scenarios and under different traffic loads.