Vladimir Vukadinovic

Video streaming performance under proportional fair scheduling

In this paper, we study the performance of the proportional fair scheduler, which has been proposed for some of the emerging radio access systems. It maximizes the spectral efficiency of the systems, which is a strong incentive for network providers to use it. Our goal is to investigate how the proportional fair scheduling affects the performance of streaming users. Focus is on the throughput-delay trade-offs associated with proportional fair scheduling in CDMA/HDR systems. Special attention is devoted to defining appropriate performance measures and creating a realistic simulation environment. Our results indicate that the opportunistic scheduling may face difficulties in providing the user-level performance in cases where streaming flows constitute a significant share of the traffic load.

Spectral efficiency of mobility-assisted podcasting in cellular networks

We consider a wireless podcasting service for mobile users. That can be provided by mobile operators in their coverage areas. Our focus is on dense urban environments. The latency and throughput requirements of the podcasting service are flexible and, therefore, podcast contents do not need to be delivered to all users via the operators network: they can be relayed from one user to another in a store-carry-and-forward fashion. Hence, mobility of users can be used as a supplementary transport mechanism to off-load the operators network and relieve strain on scarce spectrum resources. In this paper, we evaluate the achievable throughputs and spectrum savings of the mobility-assisted wireless podcasting for various mobility patterns and user densities in an area.

Video Streaming in 3.5G: On Throughput-Delay Performance of Proportional Fair Scheduling

In this paper, we study the performance of the proportional fair scheduler, which has been proposed for the emerging 3.5G radio access systems. It maximizes the spectral efficiency of the systems, which is a strong incentive for network providers to use it. Our goal is to investigate whether the proportional fair scheduler also provides benefits to the streaming users. Focus is on the throughput-delay trade-offs associated with video streaming over HSDPA. Special attention is devoted to defining appropriate performance measures and creating a realistic simulation environment. Our results indicate that the opportunistic scheduling faces major difficulties in providing the user-level performance in cases where streaming flows constitute a significant share of the traffic load.

Characterization of a simple communication network using Legendre transform

We describe an application of the Legendre transform to communication networks. The Legendre transform applied to max-plus algebra linear systems corresponds to the Fourier transform applied to conventional linear systems. Hence, it is a powerful tool that can be applied to max-plus linear systems and their identification. Linear max-plus algebra has been already used to describe simple data communication networks. We first extend the Legendre transform as the slope transform to non-concave/non-convex functions. We then use it to analyze a simple communication network. We also propose an identification method for its transfer characteristic, and we confirm the results using the ns-2 network simulator.

Opportunistic wireless communication in theme parks: a study of visitors mobility

Ad hoc networks of wireless devices carried by theme park visitors can be used to support variety of services. In such networks, links between the devices sporadically appear and disappear with the mobility of visitors. The network performance strongly depends on how often they encounter each other and for how long the contact opportunities last. In this paper, we study the mobility of visitors based on GPS traces collected in an entertainment theme park. We demonstrate and discuss the implications of the observed mobility on the efficiency of opportunistic message forwarding. On an example, we show how arrivals, departures, and spatial distribution of the park visitors affect the delay of a broadcast application.

Enhanced power saving mode for low-latency communication in multi-hop 802.11 networks

The Future Internet of Things (IoT) will connect billions of battery-powered radio-enabled devices. Some of them may need to communicate with each other and with Internet gateways (border routers) over multi-hop links. While most IoT scenarios assume that for this purpose devices use energy-efficient IEEE 802.15.4 radios, there are use cases where IEEE 802.11 is preferred despite its potentially higher energy consumption. We extend the IEEE 802.11 power saving mode (PSM), which allows WLAN devices to enter a low-power doze state to save energy, with a traffic announcement scheme that facilitates multi-hop communication. The scheme propagates traffic announcements along multi-hop paths to ensure that all intermediate nodes remain awake to receive and forward the pending data frames with minimum latency. Our simulation results show that the proposed Multi-Hop PSM (MH-PSM) improves both end-to-end delay and doze time compared to the standard PSM; therefore, it may optimize WLAN to meet the networking requirements of IoT devices. MH-PSM is practical and software-implementable since it does not require changes to the parts of the IEEE 802.11 medium access control that are typically implemented on-chip. We implemented MH-PSM as a part of a WLAN driver for Contiki OS, which is an operating system for resource-constrained IoT devices, and we demonstrated its efficiency experimentally.

RED with Dynamic Thresholds for improved fairness

We investigate the fair bandwidth sharing among responsive and unresponsive traffic flows. When these flows compete for the same output link in a router, unresponsive flows tend to occupy more than their fair share of the link capacity. We propose a new active queue management algorithm named Random Early Detection with Dynamic Thresholds (RED-DT) that dynamically adapts queue parameters to achieve a more fair distribution of the link capacity.

Enhanced IEEE 802.11 Power Saving for Multi-hop Toy-to-Toy Communication

In the future Internet of Things (IoT), battery-powered devices equipped with short range radios may need to communicate with each other over multi-hop links. This may significantly increase their energy consumption. Whereas most research on IoT assumes that the devices use energy-efficient IEEE 802.15.4 wireless transceivers, we focus on IEEE 802.11 because of its wide penetration in consumer electronics such as toys. We extend the IEEE 802.11 power saving mode (PSM), which allows the devices to enter the low-power doze state, with a traffic announcement scheme that facilitates multi-hop communication. The scheme propagates traffic announcements along multi-hop paths to ensure that all intermediate nodes remain awake to forward the pending data frames with minimum latency. Simulation results show that the proposed Multi-Hop PSM (MH-PSM) improves both end-to-end delay and doze time compared to the standard PSM. MH-PSM is practical and software-implement able since it does not require changes to the parts of the IEEE 802.11 medium access control that are typically implemented in hardware.

Statistical multiplexing gains of H.264/AVC video in E-MBMS

With the increasing acceptance of H.264/AVC as a video coding standard for mobile multimedia, it becomes very important to control the extreme burstiness of the traffic generated by the H.264/AVC encoder. Statistical multiplexing of video streams can be used to reduce the bit rate variations. In practice, the number of video streams that can be multiplexed together is quite limited and therefore, additional mechanisms are needed to eliminate the residual burstiness and to adapt the bit rate of the bundle to the bit rate of the transport channel. Here we evaluate the potential statistical multiplexing gains with and without the coordination in the encoders. The gains are measured relative to the case where rate-controlled (capped) streams are delivered on individual transport channels.

Impact of human mobility on wireless ad hoc networking in entertainment parks

Ad hoc networks of wireless devices carried by entertainment park visitors can support a variety of services. In such networks, communication links between the devices sporadically appear and disappear with the mobility of visitors. The network performance strongly depends on how often they encounter each other and for how long the contact opportunities last. In this paper, we study the mobility of visitors based on GPS traces collected in two entertainment parks. We demonstrate and discuss the implications of the observed mobility on the efficiency of opportunistic data forwarding. We show how hourly changes in the number and spatial distribution of the park visitors affect the delay of a broadcast application. Our results suggest that generic mobility models commonly used in wireless research are not appropriate to study this and similar scenarios: Targeted mobility models are needed in order to realistically capture non-stationarity of the number and spatial distribution of nodes. Therefore, we developed a mobility simulator for entertainment parks that can be used to scale up the evaluation scenarios to a large number of devices. The simulator implements an activity-based mobility model, where the mobility of park visitors is driven by the activities they wish to perform in the park. The simulator is calibrated based on the GPS traces and validated on several metrics that are relevant for the performance of wireless ad hoc networks.