Dilip Krishnaswamy

Game theoretic formulations for network-assisted resource management in wireless networks

This paper proposes game-theoretic formulations for addressing resource management issues in GSM/GPRS/EGPRS-based and CDMA/HDR-CDMA-based wireless networks. Network-assisted resource management is used, with minimal inter-base signaling costs, to transfer the intelligence and control needed from the terminal to the network. Both non-cooperative and coalitional games are used to address resource management issues such as link adaptation with power control, channel re-allocation, channel re-assignment, and, hard and soft handoffs with power control.

Robust Routing and Scheduling in Wireless Mesh Networks under Dynamic Traffic Conditions

Joint routing-and-scheduling has been considered in wireless mesh networks for its significant performance improvement. While existing work assumes it, accurate traffic information is usually not available due to traffic dynamics, as well as inaccuracy and delay in its measurement and dissemination. In addition, the joint routing and scheduling usually requires a centralized controller to calculate the optimal routing and scheduling and distribute such policies to all the nodes. Thus, even if the accurate traffic information is always available, the central controller has to compute the routing and scheduling repeatedly because the traffic demands change continuously. This leads to prohibitive computation and distribution overhead. Therefore, in this paper, we propose a joint routing-scheduling scheme that achieves robust performance under traffic information uncertainty. In particular, it achieves worst-case optimal performance under a range of traffic conditions. This unique feature validates the use of centralized routing and scheduling in wireless mesh networks. As long as the traffic variation is within the estimation range, the routing and scheduling do not need to be recomputed and redistributed. Through extensive simulations, we show that our proposed scheme meets the objective (i.e., optimizes the worst-case performance). Moreover, although it only guarantees the worst-case performance in theory, its average performance is also good. For example, our proposed scheme can perform better than a fixed optimal routing and scheduling scheme in more than 80 percent of 500 random traffic instances. Our scheme provides insights on the desired properties of multipath routing, namely, spatial reuse and load balancing.

Adaptive modulated scalable video transmission over wireless networks with a game theoretic approach

The robust delivery of video over emerging wireless networks poses many challenges due to the heterogeneity of access networks, the variations in streaming devices, and the expected variations in network conditions caused by interference and co-existence. By combining the continuous scalability of MPEG-4 fine-granularity-scalability (FGS) video coding with the robustness of variable modulation, a powerful method of video transmission is achieved that allows a video stream to be viewed with imperceptible degradation over a continuously changing wireless channel. In addition, sigmoid functions for throughput modelling for 802.11a networks are presented, and a game theoretic approach is suggested for further adapting the modulation and channel coding strategy to improve the video transmission performance under different wireless channel conditions.

Multi-Level Weighted Combining of Retransmitted Vectors in Wireless Communications

This paper proposes weighted combining of retransmitted vectors for improved data recovery in single and multiple-antenna wireless LAN transceivers. Combining is suggested at multiple levels in the receiver design: at the post-equalizer, post-demapper and post-decoder stages. The best performance is obtained by exploiting diversity in time, equivalent to performing maximal-ratio combining of the information from repeated transmissions of the same data packet, separated in time (MRC-In-Time), over a SISO or MIMO WLAN channel. The proposed schemes can also be applied to a cooperative-diversity scenario where a receiver combines transmissions of the same message from multiple sources.

Overlays on wireless mesh networks: implementation and cross-layer searching

After years of research on ad hoc networks, practical wireless mesh networks are moving towards mainstream industry deployment. As wireless mesh networks become more ubiquitous, how to enable distributed applications and services is a challenging research topic. A new network architecture called OverMesh is recently proposed, in which computational overlays provide the facility to deploy distributed services across mobile mesh nodes. In this paper, we present the first implementation of the OverMesh architecture. The overlays are built over an IEEE 802.11s wireless mesh network pre-standard prototype. The platform enables development and deployment of concurrent distributed experiments on wireless mesh networks. Based on this platform, we further introduce a cross-layer searching algorithm, which combines traditional overlay searching with ad hoc network routing so that a physically short searching route is facilitated. Both experimentation and simulation results are presented.

Robust Routing and Scheduling in Wireless Mesh Networks

Joint routing-and-scheduling has been considered in wireless mesh networks for its significant performance improvement. While existing work assumes it, accurate traffic information is usually not available due to traffic dynamics, as well as inaccuracy and delay in its measurement and dissemination. In addition, the joint routing and scheduling usually requires a centralized controller to calculate the optimal routing and scheduling and distribute such policies to all the nodes. Thus, even if the accurate traffic information is always available, the central controller has to compute the routing and scheduling repeatedly because the traffic demands change continuously. This leads to prohibitive computation and distribution overhead. Therefore, in this paper, we propose a joint routing-scheduling scheme that achieves robust performance under traffic information uncertainty. In particular, it achieves worst-case optimal performance under a range of traffic conditions. This unique feature validates the use of centralized routing and scheduling in wireless mesh networks. As long as the traffic variation is within the estimation range, the routing and scheduling do not need to be recomputed and redistributed. Through extensive simulations, we show that our proposed scheme meets the objective (i.e., optimizes the worst-case performance). Moreover, although it only guarantees the worst-case performance in theory, its average performance is also good. For example, our proposed scheme can perform better than a fixed optimal routing and scheduling scheme in more than 80 percent of 500 random traffic instances. Our scheme provides insights on the desired properties of multipath routing, namely, spatial reuse and load balancing.

Cross-layer Video Streaming Over 802.11e-Enabled Wireless Mesh Networks

We propose an integrated cross-layer optimization algorithm for maximizing the decoded video quality of delay-constrained streaming in a quality-of-service (QoS) enabled multi-hop wireless mesh network. The key to our algorithm is the synergistic optimization of control parameters at each node of the multi-hop network, across the protocol layers - application, network, medium access control (MAC) and physical (PHY) layers, as well as end-to-end, i.e. across the various network nodes. To drive this optimization, we assume an overlay network infrastructure, which conveys information on the conditions of each link. Quantitative results are presented that demonstrate the merits and the need for cross-layer optimization in an efficient solution for real-time video transmission using existing protocols and infrastructures

PROMETHEUS: A Proactive Method for Thermal Management of Heterogeneous MPSoCs

In this paper, we propose PROMETHEUS, a framework for proactive temperature aware scheduling of embedded workloads on single instruction set architecture heterogeneous multiprocessor systems-on-chip. It systematically combines temperature aware task assignment, task migration, and dynamic voltage and frequency scaling. PROMETHEUS is based on our novel low overhead temperature prediction technique, Tempo. In contrast to previous work, Tempo allows accurate estimation of potential thermal effects of future scheduling decisions without requiring any runtime adaptation. It reduces the maximum prediction error by up to an order of magnitude. Using Tempo, PROMETHEUS framework provides two temperature aware scheduling techniques that proactively avoid power states leading to future thermal emergencies while matching the performance needs to the workload requirements. The first technique, TempoMP, integrates Tempo with an online multiparametric optimization method to guide decisions on task assignment, migration, and setting core power states in a temperature aware fashion. Our second scheduling technique, TemPrompt uses Tempo in a heuristic algorithm that provides comparable efficiency at lower overhead. On average, these two techniques reduce the lateness of the tasks by 2.5× and energy-lateness product (ELP) by 5× compared to the previous work.

Model-driven adaptive wireless sensing for environmental healthcare feedback systems

While the connectivity, sensing, and computational capabilities of todays smartphones have increased, congestion in wireless channels and energy consumption remain major issues. We present a technique for model-driven adaptive environmental sensing, designed to reduce the amount of data that is communicated over the cellular network. In simulations of an exposure monitoring system, our technique reduced the number of messages sent by 85%, obtained power savings of 80% while generating a global model of pollution with error of maximum 0.5 ppm, a negligible amount for the application of interest.

Concurrent bandwidth aggregation over wireless networks

Mobile client platforms have emerged with the ability to access and utilize multiple wireless networks concurrently. Aggregation can be performed using wireless modems on one device or cooperatively across devices within wireless proximity of each other. This paper explores various concurrent bandwidth aggregation schemes. The aggregation can be achieved on the application-layer, transport layer like MultipathTCP, or on layers below IP such as the RLC layer. These schemes are compared. In general, aggregation on the lower layer is closer to the client device and easier to adapt to the varying channel and loading conditions. However, lower layer aggregation needs more changes to wireless access stratum infrastructure. Aggregation above the IP layer is simpler to implement. A feasibility study of MultipathTCP aggregation over multiple WWANs is presented.