Daniele Migliorini

Performance evaluation of H.264/SVC video streaming over mobile WiMAX

Mobile broadband wireless networks, such as mobile WiMAX, have been designed to support several features like, e.g., Quality of Service (QoS) or enhanced data protection mechanisms, in order to provide true access to real-time multimedia applications like Voice over IP or Video on Demand. On the other hand, recently defined video coding schemes, like H.264 scalable video coding (H.264/SVC), are evolving in order to better adapt to such mobile environments with heterogeneous clients and time-varying available capacity. In this work we assess the performance of H.264/SVC video streaming over mobile WiMAX under realistic network conditions. To this aim, we make use of specific metrics, like PSNR (Peak Signal to Noise Ratio) or MOS (Mean Opinion Score), which are related to the quality of experience as perceived by the end user. Simulation results show that the performance is sensitive to the different available H.264/SVC encoding options, which respond differently to the loss of data in the network. On the other hand, if aggressive error recovery based on WiMAX data protection mechanisms is used, this might lead to unacceptable latencies in the video play out, especially for those mobiles with poor wireless channel characteristics.

QoE-Oriented performance evaluation of video streaming over WiMAX

Mobile broadband wireless networks, such as WiMAX, have been developed over the last years in order to support wireless access to real-time multimedia applications like Voice over IP or Video on Demand. To this aim, these networks are designed to provide guarantees in terms of network-related QoS parameters, like loss, delay, or jitter. However, the assessment of the performance of multimedia applications requires to take into account also the Quality of Experience (QoE), which is related to the quality of the service as it is perceived by the user, and is better measured by different metrics, like MOS or PSNR. In this paper, we first describe the simulation framework we developed to assess the QoE of video streaming over WiMAX. The framework integrates a WiMAX simulator based on ns-2 with tools for analyzing H.264/SVC compressed video, and allows to estimate the PSNR of actual videos whose streaming is simulated over WiMAX by means of ns-2. Based on this framework, we carry out a performance evaluation by considering videos encoded with different H.264/SVC scalability options and under realistic network conditions.

Ns2Voip++, an enhanced module for VoIP simulations

In the last ten years, many circuit-switched networks for voice have been replaced with packet-switched ones. Hence, simulating Voice over IP has become of paramount importance in assessing the performance of a network. However, a sound performance analysis should be carried out in conditions which are as close as possible to a real deployment. In this paper we present enhancements to ns2voip [1], a module for simulating realistic VoIP traffic with the ns2 simulator. In detail, we add new features, i.e. a correlated model for packet generation in a two-way conversation and implementing a set of realistic playout buffers to simulate the behavior of the receiver. Our code is available at http://cng1.iet.unipi.it/wiki/index.php/Ns2voip.

Power-Aware Allocation of MBSFN Subframes Using Discontinuous Cell Transmission in LTE Systems

In LTE and its evolutions, energy efficiency is a critical aspect, also in view of the dramatic traffic growth foreseen for the next years. Cell Discontinuous Transmission (DTX) techniques can be important tools to achieve the needed efficiency in the networks, and one possibility is to implement the DTX by switching off the eNB at some subframes (MBSFN subframes) and not in others (where reference signals are also transmitted). Switching schedules in LTE are made for larger periods (e.g., 40/80ms or even more). We present an algorithm that i) estimates how many resources will be needed in a period, and ii) decides how many resource blocks to activate in each subframe so as to maximize the power efficiency. We show that the power saving is significant, close to the theoretical minimum at low loads. This comes with no reduction in cell throughput and without impacting the QoS (a tolerable extra delay is added only at low loads).

Throughput-optimal resource allocation in LTE-Advanced with distributed antennas

Distributed antennas are envisaged for LTE-Advanced deployments in order to improve the coverage and increase the cell throughput. The latter in turn depends on how resources are allocated to the User Equipments (UEs) at the MAC layer. In this paper we discuss how to allocate resources to UEs so as to maximize the cell throughput, given that UEs may receive from several antennas simultaneously. We first show that the problem is both NP-hard and APX-hard, i.e. no polynomial-time algorithm exists that approximates the optimum within a constant factor. Hence, we propose and evaluate two polynomial-time heuristics whose complexity is feasible for practical purposes. Our simulative analysis shows that, in practical scenarios, the two heuristics are highly accurate.

Efficient downlink scheduling with power boosting in mobile IEEE 802.16 networks

In current mobile broadband wireless access (BWA) technologies, which are based on orthogonal frequency division multiple access (OFDMA), terminals close to cell edge experience poor channel quality, due to severe path-loss and high interference from concurrent transmissions in nearby cells. To mitigate this problem we propose: (a) to partition the set of sub-channels into chunks, which are assigned different power levels; (b) the design of a data scheduling and allocation algorithm positioned in the medium access control (MAC) layer of the base station (BS), exploiting such a partitioning. The framework is analyzed in a multi-cell IEEE 802.16 network by means of system-level packet-based simulations, with detailed MAC and physical layer abstractions in combination with realistic models of the wireless channel and interference.

Design and performance evaluation of an energy-aware scheduling framework for mobile WiMAX

Power saving is an important feature of mobile Broadband Wire-less Access (BWA) systems, since it allows user terminals to switch off the radio transceiver when there is no network activity, thus increasing the battery lifetime. In this paper, it is shown that even greater energy savings can be obtained if user terminals are put to sleep while there is network activity, by trading off performance for battery duration in a controllable way. To this aim, a framework is proposed, in which existing wireless scheduling algorithms can be fit to pursue their original goals, e.g., maximizing throughput or fairness, while improving the energy efficiency of user terminals. The framework is specifically tailored to the IEEE 802.16/WiMAX technology. Its effectiveness is assessed in this context through an extensive packet-level simulation campaign with realistic FTP data traffic.