Multi-hop infrastructure-based communication is expected to play a vital role in supporting high data-rate multimedia access to mobile devices. The advantages are significant in highly mobile scenarios such as intra-vehicular networks. However, mobile nodes in these networks suffer from long authentication delays, which adversely affect the goodput. In this work, we propose two techniques to shorten the initial authentication delay without compromising the authentication process and overall security. One of the techniques, called fast authentication, admits data traffic temporarily through the network to the gateway and the immediate parent node of the joining node presents network-side authentication. The other technique, called prefetch-assisted authentication, allows the authenticated wireless nodes to prefetch and store the authentication vectors of the potential mobile clients. We investigate several unique features of our proposed schemes and find their performance to be suitable for infrastructure-based multi-hop wireless communications.

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.

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.

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 RPL's 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.

It is essential to consider drivers' perceptions and reactions when building Vehicular Cyber-Physical Systems (VCPS) since the effectiveness and efficiency of VCPS will largely depend on how drivers could benefit from such a system. This paper considers, for the first time, novel service scheduling problems from a Human Factors (HF) standpoint by taking into consideration the following fact: a driver may not be able to receive more than one service in a short period of time, even if multiple services can be transmitted to the driver from the conventional communications and networking standpoint. We study a family of the HF-aware Service Scheduling (HFSS) Problems, where the goal is to deliver up to n services, each having a time-dependent (and possibly decreasing) utility to a subset of intended drivers so as to minimize the system-wide total utility loss due to unsuccessful delivery of some services. We show that such problems are different from all existing problems. We formulate the basic HFSS problem (BHFSSP) using Integer Linear Programming (ILP) and prove its NP-Completeness. We then propose efficient heuristics for BHFSSP and its more general versions, and present numerical results from large-scale test cases. We also address several practical issues related to wireless transmission failures, distributed implementation in the multisender scenario, and other HF related considerations.

Simple yet cost effective hybrid Wireless Sensor Networks (WSN) with both standard nodes and transmit-only nodes are promising for their great potential as the "edge" of the "Internet of Things". However the lack of receivers at many transmit-only nodes in the hybrid network renders most existing MAC protocols invalid. Our previous efforts showed the benefits of this hybrid architecture for building single-hop efficient and reliable hybrid WSN cluster for QoS aware applications. This work explores the capability of building multi-hop communications in a hybrid WSN with multiple clusters (where each cluster consists of a sink as well as a certain number of standard nodes and transmit-only nodes) via a cross-layer protocol design. The proposed M-QoMoR protocol and HPAssist scheme are built based on the resource information from the underlying MAC layer. Through the analysis and extensive simulations, we showed that the hybrid WSN architecture can efficiently support multi-hop communications across multiple hybrid clusters. It also achieves certain performance boost that is not viable in the previous single hybrid WSN clusters.

We focus on a new class of home networking applications 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.

Low cost and low power Wireless Sensor Networks (WSN) with transmit-only nodes are attracting more attention due to their advantages in achieving a good balance of cost, fine-grained sensing and differentiated service for data collection applications. This work addresses the reliability and performance issues of a single-hop hybrid WSN with both transmit-only nodes and standard nodes and proposes the RH-QoMoR protocol, whose robust scheme is able to provide reliable data services and the EARE (Enhanced Automatic Resource Estimation) scheme can remove time synchronization overhead and provide more resources. The analysis and extensive simulation demonstrates its capability of providing the best possible performance to the high priority nodes under harsh environment as well as minimizing the energy consumption while maintaining QoS guarantee. The protocol can also efficiently handle dynamic network changes due to the packet loss and post-deployment adjustment.

Low cost and low power consumption are two major design criteria in wireless sensor networks (WSN). To meet the increasing demand for localized fine-grained sensing with densely deployed WSNs, this paper proposes the use of a hybrid WSN that consists of nodes with standard transceivers and nodes with only transmitters. A two-phase Constrained-Scheduling based MAC protocol is proposed, which employs the "Automatic Resource Estimation (ARE)" method. Through analysis and extensive simulations, the proposed protocol is shown to achieve a significant performance improvement in terms of data delivery probability, QoS differentiation and energy minimization over existing MAC protocols for such networks. To the best of our knowledge, this work is the first effort to bring scheduling to WSNs that contains asynchronous and uncoordinated transmit-only nodes.

In this work, we envision a fully collaborative network paradigm in which both the evolved Node Bs (eNBs) and the User Equipment (UE)s collaborate between themselves to achieve the full benefits of MIMO communication. One of the major building blocks in deploying fully collaborative networks is achieving efficient UE-UE collaboration. We study various UE-UE collaboration scenarios in the context of MIMO communications and evaluate them using an enterprise grade simulator. The results show significant improvements in the UE throughputs in a realistic cellular network. The studied UE-UE collaboration schemes are also applicable to similar collaborative relationships between UEs and other elements (e.g., relay stations) of a cellular network.

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.

We present a practical plant-and-play wireless sensor network system for entry-exit monitoring. Our system is easily configurable and robust, making it feasible to be deployed in a wide range of entry-exit monitoring applications. At the core of our system lies a novel MAC protocol that is self-synchronizing. Notably, our MAC protocol allows the nodes to maintain a very low duty cycle (the radios are in sleep mode 100% of the time in the absence of detections), while also enabling quick synchronization of the nodes (when needed) for a consistent classification of entry or exit events. We have deployed this system for monitoring a faculty parking lot at our university and integrated it with an SMS notification system to provide information on the availability of parking spots on demand. We present the parking lot occupancy trends obtained through this deployment and discuss some of the reliability issues encountered.

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.