Saturday, July 30, 2011

How GPS Works with Presentation

Global Positioning System satellites transmit signals to equipment on the ground. GPS receivers passively receive satellite signals; they do not transmit. GPS receivers require an unobstructed view of the sky, so they are used only outdoors and they often do not perform well within forested areas or near tall buildings. GPS operations depend on a very accurate time reference, which is provided by atomic clocks at the U.S. Naval Observatory. Each GPS satellite has atomic clocks on board.
Each GPS satellite transmits data that indicates its location and the current time. All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant. The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times because some satellites are farther away than others. The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver. When the receiver estimates the distance to at least four GPS satellites, it can calculate its position in three dimensions.
There are at least 24 operational GPS satellites at all times. The satellites, operated by the U.S. Air Force, orbit with a period of 12 hours. Ground stations are used to precisely track each satellite's orbit.
Determining Position
A GPS receiver "knows" the location of the satellites, because that information is included in satellite transmissions. By estimating how far away a satellite is, the receiver also "knows" it is located somewhere on the surface of an imaginary sphere centered at the satellite. It then determines the sizes of several spheres, one for each satellite. The receiver is located where these spheres intersect. 

Distributed Optical Fiber Sensors and Their Applications

This presentation contains the theory behind optical fiber sensing measurement and the latest trends in optical fiber sensing measurement and its applications.Smart structures and materials in which an optical fiber acts as a sensor to measure distributed strain and/or temperature along the fiber have applications in health monitoring functions, such as preventive maintenance, product efficiency improvement, and maintenance cost reduction. Furthermore, optical fiber has the advantage that it is essentially explosion-proof, needs no electric power supply, and is not affected by outside noise, such as lightening or high-voltage electrical power lines. This makes optical fiber suitable for plant and civil applications.




Friday, July 29, 2011

Future Cooperative Wireless Networks



cellularMIMO.jpg
The density of nodes in mobile communication networks as well as the requirement for data throughput has increased steadily in the last decades. Since the available frequency spectrum is limited and bandwidth is a scarce resource, future communication systems are expected to utilize it as efficient as possible. In future systems, increased spectral efficiency (more bits per second per Hertz of bandwidth) as well as improved link reliability become even more important. In order to meet the continuously growing demands, extensive efforts are made to develop new standards for the evolution of existing third generation (3G) technologies. The next steps in the development of future cellular networks are the implementation of 3GPP long term evolution (LTE) technology and its upcoming fourth generation (4G) successor LTE-Advanced. The aim of next generation technologies is to provide mobile users with high data rates that meet the requirements for future cellular networks. LTE-Advanced offers higher bandwidths as compared to 3G technologies, but the carrier frequency is expected to be increased (possibly to 2.6 GHz). Since transmission at higher frequencies may reduce coverage range due to increased attenuation, concepts to mitigate this effect are required to fulfill the demands on 4G systems also at the cell edges. Recent research results show that cooperative schemes can solve many of the issues faced by future wireless networks. Such cooperative schemes can include cooperation among several base stations or between mobile user equipment in order to form distributed multiple-input multiple-output (MIMO) arrays to achieve higher spectral efficiency and/or data rates. Other schemes make use of one or several (cooperating) relay stations that increase data rates over larger distances.
cellularMIMO.jpg
The aim of this project is to develop cooperative methods for implementation in LTE-Advanced based cellular networks. The schemes are required to fulfill the demands of 4G systems as defined by the International Telecommunication Union (ITU), while the costs such as the required infrastructure (e.g. number of base stations), backhaul traffic, delay, or financial costs should be minimized. Such costs might be reduced by sophisticated cooperative schemes. Recent academic results suggest a huge potential for performance increase in cooperative communication networks. Relay based concepts and multinode cooperation are expected to be key enablers for high spectral efficiency, large coverage, and low latency. The expected gains should be investigated under realistic conditions. The concepts developed in this project should be applicable specifically for LTE and LTE-Advanced networks. In particular, we focus on three different scenarios:
  • A: Cooperation between base stations and possibly also between mobile user stations in micro- and femtocells,
  • B: Multinode cooperation with the use of additional nodes acting as relays in macrocells as well as in micro- and femtocells, and
  • C: Relaying concepts in wireless home networks.
pixel