Research Summary

 

 

Introduction (Click here for slides)

The rapid development of wireless digital communication technology and the corresponding network software systems have created new horizons for communication beyond the Internet realizing the connected society. Among them, the field of mobile ad hoc networking (MANET) is experiencing unprecedented growth in its scale and application diversity. Without requiring the preexistence of communication infrastructures, a temporary network can be established on demand and disappears when there is no need. Although some basic concepts have been identified and elaborated, the filed of MANET is still in its early stage of research and development. Multihop communication with dynamic topology caused by mobility poses interesting but unique challenges ranging from the network-layer connectivity problem to the link-layer capacity issue. And, it should not be considered as a natural extension of infrastructure-based networks, such as cellular networks and IEEE 802-11 networks, because it often leads to confusion and non-optimal design choices.

Click here for more details on Mobile Computing Research Lab. Current projects are as follows.

Communication parameter adaptation

The field of wireless networking has received unprecedented attention from the research community during the last decade due to its great potential to create new horizons for communication beyond the Internet. Wireless LANs (WLANs) based on the IEEE 802.11 standard, called Wi-Fi hot spots, have become prevalent in public as well as residential areas. Numerous efforts, planned or unplanned, have been made to provide Internet connectivity over a larger geographical area, which is known as wireless mesh networks (WMNs). They could be used as a backbone to support mobile social networking for exchanging information and multimedia data. vehicular ad hoc networks (VANETs) will become an important part of future ubiquitous communication infrastructure as they support the last-mile solution for drivers on the wheel. As ground transportation is considered one technological area in which change is long overdue, a break-through can be achieved through a well-designed VANET infrastructure. For example, a VANET can allow a vehicle to deliver an urgent message to the next bumper(s) so that they can avoid involving in an accident.

However, as WMNs become more popular and their scale and complexity continue to grow, they become increasingly vulnerable to problems such as end-to-end latency, bandwidth degradation, and radio interference. Among them, the issue of latency is particularly important, as the trend of Internet usage has shifted from short-lived applications such as web browsing and emails to long-lived, delay sensitive multimedia applications. Latency is also a critical issue in emergency-related VANET applications. It is important to offer sufficient bandwidth but the corresponding design schemes should not adversely impact the latency. Therefore, the goal of this proposal is to support low-latency applications in wireless multihop networks by proposing the opportunistic transmission mechanism. It operates over multiple hops to minimize the multihop transmission delay in large-scale multihop networks. The proposed mechanisms will be evaluated through simulation studies and prototypes in an integrated manner to understand the impact these proposed techniques have on overall performance of delay-sensitive applications.

Currently, we are investigating adaptive modulation methods in urban mesh networks using USRP / GNU Radio platform, which is identified as one of Key Technologies to Watch in 2008 by Bristol Systems. Click here for more information on USRP / GNU Radio. Also, see a class website.

Multiuser cooperation

A major obstacle in wireless multihop networks is signal fading (due to communication environment) and interference (due to other nodes). A node is regarded as a greedy adversary to other nodes in its proximity as they compete with each other to grab the shared medium, interfere each other’s communication, and cause collisions. At the physical layer, a node’s data transfer not only provides interference to other nodes depriving their opportunity of using the medium but also incurs energy wastage by rendering them to overhear. Cooperation among the nodes is considered critically important in addressing these problems. Therefore, the goal of the proposed research is to bring “relaying” a main driver of entire network protocols of different layers and to develop cooperative “relaying” mechanism at MAC- and PHY-layer to reduce the end-to-end latency in wireless multihop networks. Specifically, we would like to:

(i) Design MAC-layer cooperative transmission: We plan to investigate an opportunistic transmission scheme that allows opportunistic back-to-back transmission over multiple hops to eliminate the MAC-layer overhead between hops. The proposed scheme is innovative in the sense that it is a path-centric approach, targets multihop communications, and addresses both throughput and latency issues, while the conventional opportunistic communication schemes are link-centric and only address the throughput problem.

(ii) Design PHY-layer cooperative transmission: We will design a new cooperative coding mechanism among multiple radios that enhances robustness, data rate, range of communication, and battery life of a radio member. These would include new code designs for multiple partners and high-rate coded cooperative schemes.

(iii) Develop a team-formation and information sharing service: Central to this proposed research is the development of a framework for dynamically forming an environment- and situation-aware team of mobile radios, SNR monitoring and sharing, and collaboration and resource sharing. For instance, a mobile radio that experiences a poor channel condition may use another radio’s antenna based on the principle of cooperative communication. It is also possible to make a radio team on-the-fly to improve the relaying functionality in an interference-prevalent, multi-hop environment. The proposed approach allows (i) each radio device to measure the channel’s impulse response and SNR of every other radio device in the team, and (ii) the channel information to be exchanged between different radio devices in a team so as to decide which radio devices should cooperate with each other.

This work is supported by NSF Award in Network Technology and Systems (NeTS) Program in 2008, project entitled "Exploring Data Access in Internet-based Wireless Mobile Networks"

Uncertainty in wireless sensor networks

Inspired by the Smart Dust project started in 1998, researchers have shown enormous interests in wireless sensor networks (sensornets) because of their long-term potential in many interesting pervasive applications. During the last decade, we have witnessed a number of real-life deployments and quite a few evolutionary and revolutionary advances in terms of miniaturization, integration, and energy efficiency. However, one of the challenges for sensornets to become a prevailing technology in the next decade comes from the complexity of managing the raw data distributed in a sensornet and turning it into information for decision-making purposes. Two major sources of the complexity are resource constraints and uncertainties. While the former (e.g., severe energy constraints and limited bandwidth) has attracted a lot of attention from the research community, little work has been done on the complexity due to ontological and epistemic uncertainties. Ontological uncertainty can emerge from the lack of specification of what kind of entities could exist and epistemic uncertainty emerges due to inadequate representation of knowledge that is often incomplete, imprecise, fragmentary, and ambiguous. The main goal of the proposed research is to develop a conceptual framework that deals with those uncertainties based on classical rough set theory and to reconsider sensornet architectures and algorithms in a way to support as well as exploit the framework.

For example, one can imagine a surveillance network for contaminant detection in water distribution system (see 2007 Hollywood movie, Fire Down Under). A conventional detection problem asks for a tradeoff between the probability of detection and the false alarm rate because the consequence of a warning could be the stoppage of the infrastructure service which is quite a costly measure, the false alarm must be avoided as much as possible. However, a major challenge is that there are so many contaminants that a large array of (contaminant-specific) sensors might be required, while still leaving the system vulnerable to contaminants for which no effective sensor was available or not employed. This ontological uncertainty can be approached by monitoring more general water parameters to identify a signature of “normal” conditions, and flag anomalies. This would require a more significant sensornet component, and would involve a more substantive “multi-parameter filtering” problem - to estimate the state of the system and derive a conditional probability that the condition is normal or anomalous. Questions to how many sensors, where to sense, and how often to sense constitute epistemic uncertainty: the observation of coarser granularity offers less detail while the clumping of information into an aggregate form may prevent finer entities from being distinguished. While uncertainty in general affects a systems ability to perform with accuracy and precision, the impact of uncertainty in sensornets. We are also considering to apply the same idea in sensornet-based rehab applications.

This work was in part supported by CSU Undergraduate Summer Research Experience Program in 2008, project entitled "Improving Work Zone Safety using Sensor Networks"

Network science, user behavior/mobility, and surviving stressful mobile networks

Mobile networks are vulnerable to the presence of extreme conditions such as network partitions (due to high node speeds) and strong interference (in urban environments). As existing link and network layer solutions do not take these extreme conditions into consideration, it is critically important to know whether a mobile network is still a dependable subnet under such situations. The goal of this project is to investigate the performance of mobile wireless networks in highly stressed environment and to seek novel methods to survive the stress and achieve a reasonable performance. One of the non-goals of this project is capacity analysis as we are interested in sustainable rather than theoretically maximum performance. At the same time, we are not interested in non-functional requirements such as availability, reliability, maintainability, or security but functional ones such as performability. It refers to the network’s capability of undergoing graceful degradation of performance under harsh conditions.

This work is supported by NSF Award on Major Research Instrumentation (MRI) Program in 2008, project entitled "Performabiity in Mobile Wireless Networks" See here for presentation by the current director of CISE, NSF, Dr. Jeannette Wing. See Network Science of Engineering (NetSE) homepage of Computing Community Consortium.

Others

Body area networks

Handoff

VANET

MRI Project

RF MEMS

Autonomous Systems

USRP/GNU Radio

Etc.
Last updated: April 20, 2009.

Chansu Yu
E-mail: c dot yu91 at csuohio dot edu