Youngtae Noh

VAPR: Void-Aware Pressure Routing for Underwater Sensor Networks

Underwater mobile sensor networks have recently been proposed as a way to explore and observe the ocean, providing 4D (space and time) monitoring of underwater environments. We consider a specialized geographic routing problem called pressure routing that directs a packet to any sonobuoy on the surface based on depth information available from on-board pressure gauges. The main challenge of pressure routing in sparse underwater networks has been the efficient handling of 3D voids. In this respect, it was recently proven that the greedy stateless perimeter routing method, very popular in 2D networks, cannot be extended to void recovery in 3D networks. Available heuristics for 3D void recovery require expensive flooding. In this paper, we propose a Void-Aware Pressure Routing (VAPR) protocol that uses sequence number, hop count and depth information embedded in periodic beacons to set up next-hop direction and to build a directional trail to the closest sonobuoy. Using this trail, opportunistic directional forwarding can be efficiently performed even in the presence of voids. The contribution of this paper is twofold: a robust soft-state routing protocol that supports opportunistic directional forwarding; and a new framework to attain loop freedom in static and mobile underwater networks to guarantee packet delivery. Extensive simulation results show that VAPR outperforms existing solutions.

HydroCast: Pressure Routing for Underwater Sensor Networks

A Sensor Equipped Aquatic (SEA) swarm is a sensor cloud that drifts with water currents and enables 4-D (space and time) monitoring of local underwater events such as contaminants, marine life, and intruders. The swarm is escorted on the surface by drifting sonobuoys that collect data from the underwater sensors via acoustic modems and report it in real time via radio to a monitoring center. The goal of this study is to design an efficient anycast routing algorithm for reliable underwater sensor event reporting to any surface sonobuoy. Major challenges are the ocean current and limited resources (bandwidth and energy). In this paper, these challenges are addressed, and HydroCast, which is a hydraulic-pressure-based anycast routing protocol that exploits the measured pressure levels to route data to the surface sonobuoys, is proposed. This paper makes the following contributions: a novel opportunistic routing mechanism to select the subset of forwarders that maximizes the greedy progress yet limits cochannel interference and an efficient underwater dead end recovery method that outperforms the recently proposed approaches. The proposed routing protocols are validated through extensive simulations.

CLIPS: Infrastructure-free collaborative indoor positioning scheme for time-critical team operations

Indoor localization has attracted much attention recently due to its potential for realizing indoor location-aware application services. This paper considers a time-critical scenario with a team of soldiers or first responders conducting emergency mission operations in a large building in which infrastructure-based localization is not feasible (e.g., due to management/installation costs, power outage, terrorist attacks). To this end, we design and implement a collaborative indoor positioning scheme (CLIPS) that requires no preexisting indoor infrastructure. We assume that each user has a received signal strength map for the area in reference. This is used by the application to compare and select a set of feasible positions, when the device receives actual signal strength values at run time. Then, dead reckoning is performed to remove invalid candidate coordinates eventually leaving only the correct one which can be shared amongst the team. Our evaluation results from an Android-based testbed show that CLIPS converges to an accurate set of coordinates much faster than existing noncollaborative schemes (more than 50% improvement under the considered scenarios).

Software-defined underwater acoustic networking platform and its applications

As underwater communications adopt acoustics as the primary modality, we are confronting several unique challenges such as highly limited bandwidth, severe fading, and long propagation delay. To cope with these, many MAC protocols and PHY layer techniques have been proposed. In this paper, we present a research platform that allows developers to easily implement and compare their protocols in an underwater network and configure them at runtime. We have built our platform using widely supported software that has been successfully used in terrestrial radio and network development. The flexibility of development tools such as software defined radio, TinyOS, and Linux have provided the ability for rapid growth in the community. Our platform adapts some of these tools to work well with the underwater environment while maintaining flexibility, ultimately providing an end-to-end networking approach for underwater acoustic development. To show its applicability, we further implement and evaluate channel allocation and time synchronization protocols on our platform.

Evaluation of underwater optical-acoustic hybrid network

The deployment of underwater networks allows researchers to collect explorative and monitoring data on underwater ecosystems. The acoustic medium has been widely adopted in current research and commercial uses, while the optical medium remains experimental only. According to our survey on the properties of acoustic and optical communications and preliminary simulation results have shown significant trade-offs between bandwidth, propagation delay, power consumption, and effective communication range. We propose a hybrid solution that combines the use of acoustic and optical communication in order to overcome the bandwidth limitation of the acoustic channel by enabling optical communication with the help of acoustic-assisted alignment between optical transmitters and receivers.

Key Schemes for Security Enhanced TEEN Routing Protocol in Wireless Sensor Networks

In wireless sensor networks (WSNs), hierarchical routing protocol is commonly used for energy efficiency. In particular, the TEEN (Threshold sensitive Energy Efficient sensor Network) protocol is used widely as a basic clustered multihop routing protocol. However, energy efficient routing protocols without proper security suffer from many security vulnerabilities. Hence, in this paper, we propose a hybrid key scheme specially for the TEEN protocol: a symmetric key scheme for the intracluster and a public key scheme for the intercluster. The simulation results show that network lifetime of the proposed hybrid key scheme decreases about 8% than the TEEN protocol and about 4% compared with the TEEN protocol with symmetric key scheme. On the other hand, a hybrid key scheme provides better probability of successful transmission than that of the symmetric key scheme.

Basestation-Aided Coverage-Aware Energy-Efficient Routing Protocol for Wireless Sensor Networks

In wireless sensor networks, an energy-efficient routing protocol is a key design factor to prolong network lifetime. Recently, Optimal Coverage-Preserving Scheme (OCoPS) is proposed in [11] as an extension of the Low Energy Adaptive Clustering Hierarchy (LEACH) routing protocol with the coverage-preserving scheme which saves energy consumption through excluding redundant nodes of which sensing ranges are fully overlapped by their on-duty neighbors. In this paper, we propose a basestation-aided clustering-based routing protocol, namely, the Basestation-aided clustering routing protocol with the Coverage-Preserving Scheme (BCoPS). In BCoPS, the base station substitutes energy intensive tasks for deployed sensor nodes to prolong network lifetime. The performance of BCoPS is compared with the LEACH and OCoPS. The extensive simulation results show that BCoPS outperforms OCoPS by more than 20% on network lifetime and by more than 30% network lifetime until the coverage rate is higher than 80%.

Infrastructure-Free Collaborative Indoor Positioning Scheme for Time-Critical Team Operations

Indoor localization is the key infrastructure for indoor location-aware applications. In this paper, we consider an emergency scenario, where a team of soldiers or first responders perform time-critical missions in a large and complex building. In particular, we consider the case where infrastructure-based localization is not feasible for various reasons such as installation/management costs, a power outage, and terrorist attacks. We design a novel algorithm called the collaborative indoor positioning scheme (CLIPS), which does not require any pre-existing indoor infrastructure. Given that users are equipped with a signal strength map for the intended area for reference, CLIPS uses this map to compare and extract a set of feasible positions from all positions on the map when the device measures signal strength values at run time. Dead reckoning is then performed to remove invalid candidate coordinates, eventually leading to only correct positions. The main departure from existing peer-assisted localization algorithms is that our approach does not require any infrastructure or manual configuration. We perform testbed experiments and extensive simulations, and our results verify that our proposed scheme converges to an accurate set of positions much faster than existing noncollaborative solutions.

WaterCom: A Multilevel, Multipurpose Underwater Communications Test Platform

Underwater Communications is very much an experimental science because of the complex medium - the water - and its unpredictable propagation properties, thus mandating experiments to validate theory. The medium is particularly challenging for the transmission of acoustic and optical signals. Thus, the true performance of a transmitter/receiver system can be evaluated only in the water. It would then appear that UW research be inevitably associated with a testbed. However, this is not always the case because UW testbeds are difficult to set up, calibrate and instrument. The purpose of the recent NSF CRI Ocean-TUNE project is precisely that of deploying inexpensive UW testbeds accessible by the Community. UCLA, as a participant in the Ocean-TUNE project, has recognized that one UW testbed cannot fit all applications and therefore has been developing WaterCom, a multilevel testing platform consisting of three testbeds - small, medium and large scale. The small testbed is deployed in a tank, with two modems; it is used for point-to-point communications at close range. It is instrumented for remote access and allows the testing of variable TX power values with different obstacles, reflected rays absorption and water purity values (for optical experiments). The medium scale testbed, deployed at the Marina del Rey UCLA boathouse, will enable remotely monitored experiments of MAC and network protocols with three nodes, one of them mobile. The large scale open water testbed is deployed in the Catalina channel. It will employ OFDM Modems as well as small submersible, mobile platforms. WaterCom will enable two types of experiments: environment measurements, like subsurface currents, presence of deposits in the water, etc, and; network protocol and application measurements in the open water. The paper describes the testbeds in detail and introduces preliminary small scale testbed measurements.

SER Analysis of Scheduled TAS With MRC in the Presence of Non-Identical Channel Estimation Errors

In this letter, we present a performance analysis of scheduled transmit antenna selection with maximal ratio combining (TAS-MRC) in the presence of non-identical channel estimation errors. This letter derives the probability density function (PDF) of the instantaneous effective signal-to-noise ratio for the scheduled TAS-MRC over Rayleigh fading channels with non-identical channel estimation errors. Using this PDF, we derive exact closed-form expressions for the scheduled TAS-MRC symbol error rate in the presence of non-identical channel estimation errors. The analysis results show that the order of diversity of scheduled TAS-MRC is improved in terms of transmit spatial diversity and multiuser diversity, whereas the received diversity is diminished by non-identical channel estimation errors, regardless of the modulation type.