Vijay K. Konangi

Uncertainty-aware Wireless Sensor Networks

The characterisation of uncertainty and the management of Quality of Service are important issues in mobile communications. In a Wireless Sensor Network, there is a high probability of redundancy, correlation and noise in the sensor features since data is often collected from a large array of densely deployed neighbouring sensors. This article proposes a soft computing approach to manage uncertainty by reasoning over inconsistent, incomplete, and fragmentary information using classical rough set and dominance-based rough set theories. A methodological and computational basis is provided and is illustrated in a real world sensor network application of aquatic biodiversity mapping under uncertainty.

Performance of VDL mode 2 for the Aeronautical Telecommunications Network

VHF Digital Link (VDL) has been identified as a method of communication between aircraft and ground stations in the Aeronautical Telecommunications Network (ATN). VDL Mode 2, the first of three modes to be implemented, has been modeled in software for simulation. The simulations investigate the performance of a single ground station communicating with up to 150 aircraft in several scenarios. The number of aircraft that can be supported by a single ground station is determined based on the FAA specified limit of the subnetwork delay.

Comparison of IEEE 802.11 and wireless 1394 for intersatellite links in formation flying

In order to take advantage of the full potential of formation flying satellite systems, intra-formation communications is a critical element. Using simulations, performance comparisons are made between IEEE 802.11 and wireless IEEE 1394. The asynchronous version of 1394 provides the best performance for the scenarios that were investigated.

Comparison of VDL modes in the aeronautical telecommunications network

VHF digital link (VDL) has been identified as a method of communication between aircraft and ground stations in the aeronautical telecommunications network (ATN). Three different modes of VDL have been suggested for implementation. Simulations were conducted to compare the data transfer capabilities of VDL modes 2, 3, and 4. These simulations focus on up to 50 aircraft communicating with a single VDL ground station. The data traffic is generated by the standard file transfer protocol (FTP) and hyper text transfer protocol (HTTP) applications in the aircraft. Comparisons of the modes are based on the number of files and pages transferred and the response time.

Local area network for space-based instrument control

The design and development of a local area network for space-based instrument control is presented. The instrument LAN and associated hardware and software can be used to emulate a space-based system such as a spacecraft or a terrestrial-based system such as rovers for aerospace engine and vehicle inspections. In either case, the LAN is designed using controller area network technology as the bus architecture. The LAN consists of fixed sensors as well as an RF interface to a robotic vehicle. The state of the sensors on the LAN and the position of the robotic vehicle can be observed and controlled over an IP-based network using a standard Internet web browser. This research allows the evaluation of both space-based and terrestrial-based systems that utilize commercially available hardware and software as well as standard Internet technologies.

Evaluation of VDL modes in the en-route domain

In this paper we investigate the performance of VDL modes 2,3, and 4 in the en-route domain by simulating mobile aircraft that dynamically establish and disconnect links to the ground station. In simulation one, the aircraft modeled are within a single sector of airspace which is the current boundary for en-route aircraft communication. The second simulation models all aircraft within range of the VDL network, a 200 nautical miles radius. In both simulations, the aircraft trajectories simulate real traffic patterns of aircraft controlled by the Cleveland Air Route Traffic Control Center (ARTCC). The primary statistic used to evaluate the performance of the VDL modes is the subnetwork delay. Based on the simulation scenarios investigated in this research, the subnetwork delays for all three modes are substantially less than the corresponding maximums specified in the standards.

Application of wireless sensor networks in forest fire detection under uncertainty

This paper proposes a soft computing approach to manage uncertainty and rule discovery by reasoning over inconsistent, incomplete and fragmentary information using dominance-based rough set theories. A methodological and computational basis is illustrated in a sensor network application scenario of a forest fire detection system.

Characteristics and Capacity of VDL Mode 2, 3, and 4 Subnetworks

In the current National Airspace System (NAS), voice communications for Air Traffic Services (ATS) are transmitted by analog VHF radios. Aeronautical Operational Communications (AOC) use a character-oriented system operating in the VHF band known as Aircraft CommunicationsAddressing and Reporting System (ACARS). These radios are neither capable of supporting the growth in air traffic expected in the near future, nor are they capable of enabling new services under development. Three bit-oriented digital VHF radios, VDL Modes 2, 3, and 4, have been proposed as solutions to frequency congestion in the aeronautical VHF band. In this paper each mode is investigated through simulations which explore their individual characteristics under variable loads. The three modes are also tested in realistic terminal and en route domain scenarios. The capacity of each mode is estimated based on the subnetwork delays specified in the standards. The results indicate that VDL Mode 2 can support the highest traffic load, but cannot provide deterministic delays for critical applications. Mode 3 supports the least load due to large downlink delays, but provides the required mechanisms for critical information transfer. Mode 4 has a marginally higher capacity than Mode 3 with similar prioritization capabilities.

Asymmetric ATM switch modules with imbalanced traffic

This paper analyzes the performance of output channel grouped asymmetric packet switch modules in ATM networks, under geometrically bursty input traffic with input/output traffic imbalance. The switch module considered has n inputs and m outputs. A packet destined for a particular output address (out of g) needs to access only one of the r available physical output ports; m=gr. The motivation for the study of these switch modules is that they are the key building blocks in many large multistage switch architectures. A combination of exact derivation and numerical analysis yields the saturation throughput of input buffered switch modules for a wide range of traffic nonuniformity factors and burstiness. Results show a degradation in the maximum throughput, under input/output imbalance, as the average burst length increases. An interesting observation is that asymmetric switches tend to diminish the throughput advantage of the output-buffered switch module over the input buffered switch module under any traffic nonuniformity and burstiness. Our results also indicate that increasing the number of output ports per output address can significantly improve the switch performance, especially when traffic is highly nonuniform and bursty.

Comparison of VDL modes in the terminal domain

In This work we investigate the comparative performance of VDL modes 2, 3 and 4 by simulating mobile aircraft that dynamically establish and disconnect links to the ground station. The principal consideration was to model and simulate realistic data traffic and aircraft traffic patterns in the terminal domain, which in these simulations is the area within a 70 nautical mile radius from the terminal. The simulated aircraft traffic patterns are based on actual data from the Detroit Metropolitan Airport. We consider two aircraft traffic patterns, and the data traffic profile used for the simulations is defined in the relevant standard. The performance criteria used to compare the performance of the three modes is the subnetwork delay. For the simulation scenarios investigated in this research, we recommend VDL Mode 3 in the terminal domain.