Jhoanna Rhodette I. Pedrasa

MOBIX: System for managing mobility using information exchange

It is evident that mobile devices of the future will have multiple wireless interfaces. For small, energy-constrained devices, determining network availability by keeping all radio interfaces turned on at all times will negatively impact battery lifetime even when these interfaces are idle. Predicting future network availability from user history requires a period of training and learning user habits. This method will fail when users deviate from their routines constantly or move to locations not visited before. We propose a different approach to determining network availability of mobile nodes which leverages on the fact that nodes on the move will meet other nodes who will be able to share conditions of networks they have recently encountered. This paper presents MOBIX, a system where nodes exchange information about network conditions using short-range communication such as Bluetooth. Our simulation results show that the required number of nodes needed for 100% success is not unrealistic of densely populated metropolitan areas. Even with relatively low population densities, we can expect a data store hit more than 50% of the time. Although our evaluation used WiFi, our scheme can easily be extended for other technologies such as GSM and WiMax.

A proposed architecture for context-aware mobility management

Mobility management is one area where context-awareness can be of great use. However, most context-management systems have been developed for smart spaces and are not designed for highly mobile devices. We propose an architecture for context-aware mobility management that is both distributed and hierarchical. The architecture consists of a global context server, a number of local proxy and adaptation servers, and the mobile nodes. Our architecture is unique in that both the local servers and the mobile nodes make mobility decisions, instead of having all the intelligence reside on network side components or central servers only, as is the case in most context management systems.

Evaluation of hierarchical DHTs to mitigate churn effects in mobile networks

This research reviews recent works on flat DHTs under high churn.This research evaluates a flat DHT and a hierarchical DHT with or without churn.This research assesses the performance of two HDHTs with or without churn. Existing flat peer-to-peer (P2P) systems based on distributed hash tables (DHTs) perform unsatisfactorily under churn due to their non-hierarchical topology. These flat DHTs (FDHTs) experience low lookup success ratio, high lookup latency and high bandwidth usage as a consequence of the presence of churn. With this, we explore the use of hierarchical DHT (HDHT), specifically the superpeer design, in mitigating the effects of churn. To the best of our knowledge, we are the first to intensively examine HDHTs with and without high churn through simulations.Using the OMNeT++ simulator and the OverSim framework, we analyze flat and hierarchical DHTs with and without churn. Results show that the implemented HDHTs perform more satisfactorily than a flat DHT because of better fault isolation and smaller cluster sizes at the cost of higher superpeer traffic. HDHTs are more stable as they have better lookup success ratios. They are more efficient as evidenced by lower lookup latencies and lower average node bandwidth usage. They are more scalable since their performance do not degrade significantly even at high population. With this, the implemented HDHTs can be utilized to alleviate the effects of churn in mobile networks.

Information Exchange for Enhanced Network Selection

Current devices use a network selection policy that is mostly driven by the physical layer, choosing the point of attachment with the highest Received Signal Strength Indicator (RSSI). Unfortunately for 802.11 networks, RSSI is not a good indicator of actual network performance as it is normally the bandwidth to the Internet and not the wireless signal conditions which dictates the quality of service a user might experience. Worse, the AP may belong to a pay service which renders it inaccessible to the user. MOBIX is a system which leverages on the fact that nodes on the move will meet other nodes who will be able to share conditions of networks they have recently used. MOBIX exchanges reports with other nodes it encounters using a short-range communication channel such as Bluetooth. Our simulation results show that exchanging throughput information resulted in 70% success rate over relying on RSSI measurements alone. Using our power measurements, we show that we can achieve energy savings of more than 80%.

Network availability prediction: Can it be done?

With the availability of more powerful mobile devices and a variety of access networks, users are expecting more and more services whilst on the move. There have been many attempts develop methods of providing these types of services form a user as well as a service provider perspective. All of these methods are based on the ability to predict the future. In this paper, will first present an overview of the research on one aspect of this, namely network availability prediction. We first, summarise the work that has been done in network availability prediction and categorize them. Using the categorisation, we show that one of the existing mechanisms provide the necessary accuracy and robustness. Then we present a hybrid design which overcome the limitations of the current systems. We show the viability of the the proposed hybrid system by summarising a dynamic baysean network and report exchange based predication mechanisms. We conclude the paper with a brief discussion on the open issues of developing such a hybrid scheme.

Determining network availability on the move

Users today have come to expect constant connectivity through their mobile devices even when they are on the move, as most urban areas are heavily blanketed with Access Points and GSM Base Stations. Network selection poses a problem however as it is driven primarily by physical layer information, such as Received Signal Strength, which is a poor indicator of actual network performance. Thus there is a need for a more sophisticated method of discovering network resources that goes beyond radio interface characteristics. A way to address this is to use information not only from within the node, but also externally, for instance by enabling nodes to exchange information in a peer to peer manner. One of the biggest challenges of adopting this approach stems from the fact that nodes participating in such systems are not equally trustworthy. Therefore it is necessary to develop mechanisms that make the decision making process robust against dishonest information. In this work we evaluate data fusion techniques in the context of reconciling conflicting information due to the presence of dishonest or malfunctioning nodes. We show that it is possible to adapt classical data fusion techniques to develop a more robust decision-making mechanism, and moreover that Dempster-Shafer Theory is the optimal choice.

Factor Effects for Routing in a Delay-Tolerant Wireless Sensor Network for Lake Environment Monitoring

Delay-tolerant wireless sensor networks (DTWSN) is a promising tool to facilitate communication in disruptive and challenged sensor network environments not usually catered by traditional systems. In this paper, DTWSN application to a real-life lake scenario is considered with the description of the routing problem and proposed solution. Opportunistic Network Environment (ONE) simulator was utilized to determine the performance of First Contact, Epidemic and Spray and Wait routing protocols on the map-based mobility model of the lake. Factors considered are the number of nodes, bit rate and ferry speed. Analyses of delivery probability, latency and overhead ratio as well as buffer time and hop count as metrics of performance evaluation against the protocols are done using JMP software. Results revealed that Spray and wait outperforms the other protocols for the given scenario.

Comparison of contention-based MAC protocols for Underwater Sensor Networks

Typically Underwater Sensor Networks (UWSNs) consist of sensor nodes that use acoustic signal for data transmission. Due to the nature of the environment where these networks are deployed, there is a need to implement a reliable, energy efficient, and propagation-delay aware MAC protocol. In this paper, the common factors affecting the performance of three contention-based MAC protocols for underwater environment, RMAC, UWALOHA and UWANMAC, such as average end-to-end delay, throughput, and over-all energy consumption, are compared and evaluated. These protocols are implemented in an NS-2 based simulator, Aqua-Sim. In the simulation, the metrics namely bit rate, number of nodes and topology are varied in order to evaluate the overall MAC protocol performance. For optimum performance, UWANMAC provides maximum desirability. When there is a need for more data to be sent but energy consumption is of lesser importance, UWALOHA can be used and if end-to-end delay is of relevance, UWANMAC and UWALOHA are the better fit.

Development of a doorway occupancy counter based on thermal array sensing technology

This papers discusses current methodologies of determining occupancy count as well as current development progress of an embedded thermal array sensor capable of tracking motion within a sensing area. The proposed algorithm counts the net occupancy count by logging each entry and exit through a doorway of a room. Results show that net occupancy count has been found to be accurate for a one person case in each pass. The findings are promising which is why further development is needed to extend the scenario to multiple person case and perform actual experiment in a real world scenario to assess the systems accuracy in determining occupancy count for longer period of time.

Space comfort maximization - a review

Minimization of energy consumption through the automation of HVAC is widely implemented. These implementations assume that as long as the temperature set-point is confined to a temperature range, users are comfortable. These are not the case for actual settings. A consequence is that users tend to feel uncomfortable, therefore decreases productivity. There have been emerging technologies in which user participation are used in order to accurately gauge user comfort. This work aims to discuss the two approaches in maximizing temperature comfort, namely local and shared space control.