Raghuram S. Sudhaakar

A Comprehensive Evaluation of RPL under Mobility

This paper focuses on routing for vehicles getting access to infrastructure either directly or via multiple hops through other vehicles. We study routing protocol for low-power and lossy networks (RPL), a tree-based routing protocol designed for sensor networks. Many design elements from RPL are transferable to the vehicular environment. We provide a simulation performance study of RPL and RPL tuning in VANETs. More specifically, we seek to study the impact of RPLs various parameters and external factors (e.g., various timers and speeds) on its performance and obtain insights on RPL tuning for its use in VANETs. We then fine tune RPL and obtain performance gain over existing RPL.

RPL under mobility

This paper focuses on routing for vehicles getting access to infrastructure either directly or via multiple hops though other vehicles. We study Routing Protocol for Low power and lossy networks (RPL), a tree-based routing protocol designed for sensor networks. Many design elements from RPL are transferable to the vehicular environment. We provide a simulation performance study of RPL and RPL tuning in VANETs. More specifically, we seek to study the impact of RPLs various parameters and external factors (e.g., various timers and speeds) on its performance and obtain insights on RPL tuning for its use in VANETs.

Improve Efficiency and Reliability in Single-Hop WSNs with Transmit-Only Nodes

Wireless Sensor Networks (WSNs) will play a significant role at the “edge” of the future “Internet of Things.” In particular, WSNs with transmit-only nodes are attracting more attention due to their advantages in supporting applications requiring dense and long-lasting deployment at a very low cost and energy consumption. However, the lack of receivers in transmit-only nodes renders most existing MAC protocols invalid. Based on our previous study on WSNs with pure transmit-only nodes, this work proposes a simple, yet cost effective and powerful single-hop hybrid WSN cluster architecture that contains not only transmit-only nodes but also standard nodes (with transceivers). Along with the hybrid architecture, this work also proposes a new MAC layer protocol framework called Robust Asynchronous Resource Estimation (RARE) that efficiently and reliably manages the densely deployed single-hop hybrid cluster in a self-organized fashion. Through analysis and extensive simulations, the proposed framework is shown to meet or exceed the needs of most applications in terms of the data delivery probability, QoS differentiation, system capacity, energy consumption, and reliability. To the best of our knowledge, this work is the first that brings reliable scheduling to WSNs containing both nonsynchronized transmit-only nodes and standard nodes.

A novel Qos-aware MAC scheme using optimal retransmission for wireless networks

This paper proposes a novel medium access control scheme for low cost, single-hop wireless networks where the source nodes have a transmitter module but no receiver module and hence they can only transmit data to a sink but cannot receive any control signals, like an ACK or NAK, from any other node. The goal of the proposed scheme is to provide QoS (in terms of packet delivery probability) to the nodes in such a network, where the existing schemes like polling or scheduled transmissions, CSMA and ARQ will be ineffective because of the unavailability of a receiver module at the nodes. The proposed scheme uses distributed control and allows the nodes to transmit each packet an optimal number of times at random instants in time within the packet generation interval. We define two optimization problems based on minimizing total network traffic and maximizing the delivery probability of the class of nodes requiring the highest QoS, respectively, and develop mathematical formulae and efficient algorithms to solve them. Numerical analysis and simulation results show that our scheme can provide high QoS to networks of different sizes.

QoMOR: A QoS-aware MAC protocol using Optimal Retransmission for Wireless Intra-Vehicular Sensor Networks

The paper proposes a MAC layer protocol called QoMOR (QoS-aware MAC protocol using optimal retransmission) that is designed to provide QoS in a decentralized network with multiple sensor (source) nodes that do not have the capability to receive acknowledgements from the sink node. A minimum data delivery probability between the sensor and sink nodes is achieved by allowing each source node to transmit each new packet an optimal number of times in every interval of time. The paper first discusses the single QoS class case and derives the maximum achievable frame delivery probability and then extends the concepts to the multiple QoS class case. It also addresses a few design optimization criteria. Simulation and numerical analysis results show that QoMOR can effectively provide QoS guarantees under distributed control without using conventional ARQ-based schemes.

On-road video delivery with integrated heterogeneous wireless networks

Abstract We consider on-road video delivery using heterogeneous wireless networks, e.g., usage-limited 3G (or 4G) cellular networks and coverage-limited Wi-Fi networks consisting of scattered road-side Access Points (APs), in order to improve mobile user (passenger) experience of such video services. We address the following three fundamental, non-trivial issues and associated challenges: (1) how to dynamically allocate Wi-Fi bandwidth within each AP’s coverage; (2) how to dynamically allocate cellular bandwidth subject to data usage limits; and (3) how to jointly optimize the solutions to the former two issues. In particular, we focus on a new optimization problem called On-road Video Delivery ( OVD ) with integrated heterogeneous networks . Our whole objective is to maximize the system-wide User Experience Index ( UEI ), which is a performance metric used to evaluate the user experience of such on-road video services. To the best of our knowledge, this work is the first that focuses on on-road video delivery with both cellular and Wi-Fi networks. We prove OVD to be NP-Complete and propose two efficient solutions to deal with the above issues. We also design an online version of one proposed algorithm by considering the dynamic arrival of users. The numerical results from large-scale simulations are also presented to evaluate their effectiveness.

Data fusion with flexible message composition in Driver-in-the-Loop vehicular CPS

Abstract This work addresses a unique data fusion problem in Vehicular Cyber-Physical Systems (VCPS) arising from Human Factors (HF) considerations. Typically, a VCPS message intended for human drivers is composed of many data elements (DEs), and different messages can be fused by the sender before transmission e.g., by eliminating identical (or redundant) DEs in order to save transmission bandwidth in the wireless network. Still, not all distinct DEs can be received properly due to the limited transmission resources available to the sender and/or transmission errors. Subsequently, some of the messages intended for a driver cannot be delivered. On the other hand, a partially delivered message may still be beneficial (in terms of generating some utility) to a driver. More specifically, when considering HF, the DEs can be grouped into two distinct parts: essential and auxiliary. While a partially reconstructed message missing even a single essential DE fails to produce any benefit (or utility) for a driver, each auxiliary DE can independently produce an additional utility so long as all the essential DEs of the message are also available. In this paper, we deal with a new Driver-in-the-Loop Data Fusion Problem (DDFP) with the primary issue being: given a list of out-going messages and a limit on the number of DEs that can be transmitted, how does the sender choose which DEs (each carrying a different utility) to transmit, in order to maximize the system-wide utility at the receiver. We formulate DDFP mathematically, and prove it to be NP-Complete. We study DDFP in both ideal and lossy communication networks, and propose several efficient algorithms for them. Besides the Single-Sender-Single-Receiver model, we also look into DDFP in Multiple-Sender-Single-Receiver and Single-Sender-Multiple-Receiver models with several practical considerations. Numerical results from large scale simulations are also presented.

A MAC protocol for real-time sensing applications using asymmetric transceivers

We consider a class of single hop wireless sensor networks in which the sensor nodes collect data periodically and transmit it to a sink. To reduce the complexity, cost and energy consumption of the nodes we propose the use of an asymmetric transceiver model in which the sensor nodes can transmit to the sink using standard physical layer modulation schemes that support relatively high data rates but can receive from the sink using basic modulation schemes that can only support very low data rates. The use of the transceiver module in each sensor node is thus limited to receiving simple feedback in the form of a few bytes of ACK from the sink node. In this paper we propose and study a new MAC protocol that enables effective communication between the sensor nodes and sink in such a network. We develop an analytical model to evaluate the performance of the MAC protocol and verify these results through extensive simulations. We also present results from the implementation of the protocol on a test bed consisting of XSM motes and evaluate its performance in a real world scenario.

A Holistic Approach to Service Delivery in Driver-in-the-Loop Vehicular CPS

Vehicular Cyber-Physical Systems (VCPS) provide human drivers with various services related to road safety, and on-road infotainments. Since a service (message) delivery includes service transmission, service display and driver processing, many challenges arise due to limited network resources, possible pre-emption and contention between services for the display and non-negligible driver processing delay. In this paper, we address a new Driver-centric Service Delivery Problem (DSDP) from a cross-disciplinary resource allocation standpoint. Our goal is to deliver a number of services to a set of intended drivers in a given time period so as to maximize the system-wide performance in terms of total utility income (TUI) to drivers. We show that DSDP differs from all existing problems and is NP-Complete. A number of efficient heuristics are proposed to address several issues, including wireless transmission failure as well as distributed implementation of the multi-sender systems. Utilizing real traces collected from taxis in the city of Shanghai, we also present a case study in a more realistic scenario and conduct comprehensive simulations providing numerical results.

Optimizing the WiMedia Frame Structure for Home Networking Applications

We focus on a new class of home networking appli- cations that enable wireless communication between multimedia devices using the WiMedia MAC protocol. Applications like streaming video from DVD players to HDTVs, generate high data rates and can easily saturate the bandwidth even at the rates provided by UWB transmissions. Thus we need to enhance the MAC layer to improve bandwidth utilization and efficiently handle the requirements of such applications. In this paper, we propose a new TDMA frame structure for the WiMedia MAC protocol that uses the specific characteristics of the traffic to minimize MAC and PHY overhead while providing delay bounds within the tolerable limits of the applications. Our results show that the proposed frame structure can provide up to 10% increase in bandwidth utilization over the WiMedia frame structure and achieve a throughput gain of about 48Mbps at the highest data rate of the MB-OFDM physical layer.