Research activities

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The CNG group is active in the following research fields.


QoS Provisioning

When traffic flows pertaining to multiple traffic classes, each with different QoS requirements, coexist in a network, resource management needs to be flexible enough to efficiently provide each flow with a different type of service according to its class, at a feasible computational complexity. The research of the CNG group in this area includes design and performance evaluation of scheduling and routing algorithms, for both wired and wireless networks. Some research achievements in this area are:

  • MAC-layer resource allocation algorithms for LTE and LTE-Advanced (including distributed antennas, relays, CoMP, device-to-device communications, DRX).
  • Resource allocation algorithms for virtual BBUs in 5G virtualized-RAN cellular networks.
  • QoS-oriented link-scheduling and channel-assignment algorithms for TDMA and 802.11-based Wireless Mesh Networks.
  • MAC-layer scheduling algorithms aimed at providing IEEE 802.16 users with strict QoS guarantees.
  • Optimal joint routing and resource provisioning algorithms with explicit delay guarantees for wired networks
  • Definition and implementation of a Traffic Engineering module, that manages inter-domain routing configuration and resource provisioning in a pure IP Autonomous System.
  • Design of scheduling algorithms for wired networks at O(1) complexity, suitable for Internet routers.

Performance evaluation Techniques and Methodologies

Current and future networks are required to support the provision of reliable services on a wide scale, including real-time ones. Suitable Methods and tools are needed to assess and evaluate the solutions being proposed. Our research on these topics encompasses contributions to the advancement of analytical methdos (e.g., Network Calculus) and the development of simulation tools. Some research achievements in this area are:

  • Formal methods to compute upper bounds on the delay of single flows in multi-hop networks.
  • Development of credible simulation tools for broadband technologies, such as LTE-Advanced, Wi-MAX, 802.11

Performance Evaluation of MAC Protocols for Wireless LANs

Some recent achievement in this area have been:

  • The evaluation of Long Term Evolution (LTE) and LTE-Advanced access networks.
  • The evaluation of the High Speed Packet Access (HSPA) for the UMTS network.
  • The evaluation of the performance of IEEE 802.16 in Point-to-Multipoint (PMP) mode, with the OFDMA physical layer. The analysis is carried out by means of simulation with realistic traffic models, so as to assess the effectiveness of the IEEE 802.16 to support multimedia applications that have stringent QoS requirements. We are currently devising cross-layer MAC/physical scheduling algorithms to optimize the system performance in terms, e.g., of bandwidth utilization and admission control. Furthermore, we will investigate advanced features of the IEEE 802.16, such as automatic repeat request (ARQ) and adaptive modulation and coding (AMC).
  • The evaluation of downlink frame allocation strategies in the IEEE 802.16 with the OFDMA physical layer. This study is carried out by means of numerical analysis so as to devise algorithms and guidelines to maximize the transmission efficiency from the base station to the subscriber stations, in both fixed and mobile environments.
  • Participation (on behalf of Telecom Italia) in the standardization committee of ETSI BRAN (Broadband Radio Access Network).
  • Evaluation of the ETSI standard HIPERLAN Type 2 for broadband WLAN access.
  • The evaluation of the ETSI WLAN standard HIPERLAN Type 1. The analysis was carried out using realistic traffic models (such as those mirroring the behavior of WWW applications. In order to carry out a stability analysis of the protocol, its statistical properties (related to the contention resolution algorithm) were analytically derived. This also proved the optimality of the parameter selection done in the standard.

Energy Management in Mobile Computing Systems

Energy management is a key ingredient in mobile computing systems since portable computers are typically battery powered. We have proposed several proxy-based energy-saving schemes suitable for infra-structured wireless networks (e.g., the mobile Internet). In particular, we have considered both application-dependent and application-independent strategies operating at the middleware layer. We evaluated the performance of our strategies in a real test-bed and we have found that our solution allows a considerable saving in energy (up to 80%) without a significant impact on the QoS perceived by the user. Currently, we are also investigating schemes for ad hoc networks.

Reliable Multicast in Distributed Mobile Systems

We have designed a reliable multicast protocol for distributed mobile systems that supports dynamic membership and neatly accommodates three increasingly strong delivery ordering guarantees: FIFO, Causal and Total. The system model assumed by the protocol is quite general and includes incomplete spatial coverage of the wireless network while no limitations are posed on the mobility pattern of group members. The protocol is not based on hand-off and was designed bearing in mind that MHs may have scarce resources. Simulation results have shown that it has good scalability properties. Furthermore, simulation revealed that the absence of hand-off does not introduce significant costs in terms of memory requirements and/or power consumption.

Transport Protocols for Ad Hoc Networks

Recent simulation and experimental studies have highlighted that the behaviour of the TCP protocol in multi-hop ad hoc networks is far from ideal. In mobile ad hoc networks the performance of the TCP protocol may be very much influenced by route failures caused by the mobility of nodes. Even in static networks TCP performance may be affected by the interactions between the TCP mechanisms and the MAC protocol mechanisms. Currently, we are defining an innovative transport protocol to be used as an alternative to the TCP protocol in ad hoc networks.

Performance Measurements of Ad Hoc Networks

There is extensive literature on the performance of the TCP protocol in ad hoc networks. However, almost all these studies are based on simulation. We have set up an experimental test-bed based on laptops running the Linux Mandrake 8.2 operating system and equipped with D-LinkAir DWL 650 IEEE 802.11b cards operating at the nominal bit rate of 1, 2, 5.5 and 11 Mbps. The experimental analysis revealed several aspects that are usually neglected in simulation analysis. The transmission ranges are in practice much shorter than usually assumed in simulation analysis, and are not constant but highly variable (even in the same session). Furthermore, the througput achieved by a TCP/UDP application is much lower than the nominal bandwidth (i.e., 11 Mbps) even in the case of a single source-destination session. Currently we are performing additional measurements on our testbed.

Wireless Sensor Networks

The activity in this field includes:

  • Sleep/Wakeup Scheduling in Sensor Networks
  • Sensor Networks with Mobile Elements (Data Mules)
  • Performance Measurements of Sensor Networks
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